EP2979893B2 - Optically variable security element - Google Patents

Description

The invention relates to an optically variable security element for protecting security papers, value documents and other data carriers, with a motif area that shows different image information from different viewing directions.

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

Examples of conventional security elements are in WO 2014/086531 A1 and DE 10 2006 029850 A1 revealed.

Security elements with viewing-angle-dependent effects play a special role in authenticity assurance, as these cannot be reproduced even with the most modern copying machines. These security elements are equipped with optically variable elements that convey a different image impression to the viewer at different viewing angles, for example, displaying a different color or brightness impression and/or a different graphic motif depending on the viewing angle.

To ensure that an optically variable security element displays different image information from different viewing directions, the motif area of the security element is usually divided into a plurality of square or circular pixels or a plurality of rectangular stripes. The pixels or stripes are divided into several groups, with each group of pixels or stripes generating the image information for a specific viewing direction. Based on this, the invention is based on the object of specifying an optically variable security element of the type mentioned above with particularly high levels of forgery protection.

This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the subclaims.

• der Motivbereich des Sicherheitselements aus zwei oder mehr Gruppen jeweils kongruenter Pixelelemente besteht, von denen zumindest zwei Gruppen eine Bildinformation in unterschiedlichen Betrachtungsrichtungen erzeugen,
• die Pixelelemente die Kacheln einer Parkettierung der Ebene bilden und den Motivbereich lückenlos und überlappungsfrei überdecken,
• die Pixelelemente eine komplexe Umrissform aufweisen, die weder dreieckig, quadratisch, hexagonal noch kreisförmig ist, und dass
• die Pixelelemente eine maximale Abmessung von 500 µm oder weniger aufweisen.

The invention contains four aspects of the invention, claim 1 to claim 4. In all four aspects of the invention, it is provided in a generic optically variable security element that

• the motif area of the security element consists of two or more groups of congruent pixel elements, of which at least two groups generate image information in different viewing directions,
• the pixel elements form the tiles of a tiling of the layer and cover the motif area without gaps and overlaps,
• the pixel elements have a complex outline shape that is neither triangular, square, hexagonal nor circular, and that
• the pixel elements have a maximum dimension of 500 µm or less.

Ticking is understood to mean a seamless and overlap-free covering of the plane by uniform partial areas (hereinafter referred to as tiles). While the actual ticking of the plane as such extends to infinity by definition, for the invention only a finite sub-area of the plane, namely the sub-area formed by the motif area, is of interest. In this sub-area, the pixel elements of the motif area correspond to the tiles of the ticking. Just as the tiles cover the plane seamlessly and without overlap, the pixel elements also cover the motif area seamlessly and without overlap. Since the pixel elements within the motif area represent the tiles of the ticking, the terms pixel element and tile are often used synonymously in this description.

As explained in more detail below, all tiles in the tiling can have the same shape, or there is a finite set of different tile templates (hereafter called prototiles) that determine the shape of the tiles appearing in the tiling.

Each pixel element (tile) has a maximum dimension below 500 µm and preferably between 5 µm and 500 µm.

Advantageously, each tile of the tiling is congruent to an element of a set of distinct prototiles, with the cardinality of the prototile set being advantageously less than or equal to 6 and, in particular, 1, 2, 3, or 4. In particularly advantageous designs, the cardinality of the prototile set is 1, so that each tile of the tiling is congruent to exactly one prototile. Such a tiling is called a monohedral tiling.

Except for the second aspect of the invention (claim 2), in an advantageous variant of the invention, the tiling is periodic, i.e., the symmetry group of the tiling contains two linearly independent shifts. As is customary, a mapping that maps the tiling onto itself is referred to as the symmetry of the tiling. The set of all such symmetries forms a group, which is referred to as the symmetry group of the tiling.

In the first aspect of the invention (claim 1), the symmetry group of the tiling contains at least one rotational symmetry of order 3 or 6. In the other aspects of the invention, in advantageous embodiments, the symmetry group of the tiling contains at least one rotational symmetry of order 2, 3, 4 or 6.

In the second aspect of the invention (claim 2), the tiling is aperiodic and in particular represents a Penrose tiling. Aperiodic tilings can be constructed from one or more prototiles.

Those edge points of the tiles where at least three tiles touch are referred to as nodes, as in graph theory, and the edge areas between the nodes are referred to as edges. The tiles of the tiling, particularly the tiles of a monohedral tiling, advantageously have no straight edges. This means that none of the edges of the single prototile (monohedral tiling) or of all prototiles is straight. In this way, complete coverage of the plane can be combined with a complex outline shape of the individual tiles, thus providing the designer with considerable design freedom. In the third aspect of the invention (claim 3), the edges are each composed of two or more straight line segments, each forming an angle. In the other aspects of the invention, the edges can also be curved and described, for example, by second-degree Bezier curves, B-splines, or NURBS (Non-Uniform Rational B-splines).

In the fourth aspect of the invention (claim 4), the edge of at least one prototile represents a natural motif, namely a plant, an animal, a human, or a mythical creature. In the other aspects of the invention, the edge of at least one prototile advantageously represents a natural motif, in particular a plant, an animal, a human, or a mythical creature. Such designs have the advantage that they can usually be recognized and identified at first glance. In the field of art, such tiling with recognizable tile motifs has been used in numerous works, particularly by the Dutch artist and graphic designer M.C. Escher.

In the fourth aspect of the invention (claim 4), the motif area contains a naked-eye image motif whose outline corresponds to the outline of a prototile. The naked-eye image motif expediently has dimensions of more than 5 mm, in particular more than 10 mm. The size ratio of the image motif to the corresponding prototile is preferably 10 or more, in particular 20 or more, or even 50 or more.

The pixel elements of the groups generating image information are suitably covered with diffractive structures, holographic structures, subwavelength gratings, printed structures, color-shifting thin-film elements, color-producing nanoparticles, polarizing elements, refractive structures such as micromirrors, microlenses or microfresnel lenses, or other functional layers.

The structures can, for example, have Gaussian or sinusoidal profiles or be formed by rectangular gratings, cones, triangular gratings or subwavelength gratings.

At least some of the pixel elements can additionally be covered with further functional layers, in particular with electrical or magnetic functional layers, which can generate an additional, machine-verifiable coding in the security element.

The pixel elements can also be covered with multiple structures simultaneously, for example, to create mixed colors. It is also not necessary for all pixel elements to be covered with the same type of structure. For example, a first group of pixel elements can be covered with holographic structures, while another group is covered with micromirrors or printed structures.

It can also be provided that a group of pixel elements does not generate any image information, so that these pixel elements act like cutouts in the subject area.

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

Fig. 1

eine schematische Darstellung einer Banknote mit einem erfindungsgemäßen Sicherheitselement,

Fig. 2

schematisch eine Aufsicht auf den Motivbereich des Sicherheitselements der Fig. 1,

Fig. 3

zur Erläuterung der Kacheleigenschaften eine Kachel des Motivbereichs der Fig. 2 und gestrichelt zusätzlich die angrenzenden Kacheln,

Fig. 4

schematisch eine Aufsicht auf den Motivbereich eines Sicherheitselements nach einem anderen Ausführungsbeispiel der Erfindung,

Fig. 5

schematisch eine Aufsicht auf den Motivbereich eines Sicherheitselements nach einem weiteren Ausführungsbeispiel der Erfindung, und

Fig. 6

in (a) zwei Protokacheln einer Penrose-Parkettierung und in (b) schematisch eine Aufsicht auf den Motivbereich eines erfindungsgemäß Sicherheitselements mit einer Penrose-Parkettierung unter Verwendung der in Protokacheln von (a).

They show:

Fig. 1

a schematic representation of a banknote with a security element according to the invention,

Fig. 2

schematic view of the motif area of the security element of the Fig. 1 ,

Fig. 3

To explain the tile properties, a tile of the motif area of the Fig. 2 and dashed additionally the adjacent tiles,

Fig. 4

schematically shows a plan view of the motif area of a security element according to another embodiment of the invention,

Fig. 5

schematically a plan view of the motif area of a security element according to a further embodiment the invention, and

Fig. 6

in (a) two prototiles of a Penrose tiling and in (b) schematically a plan view of the motif area of a security element according to the invention with a Penrose tiling using the prototiles of (a).

The invention will now be explained using the example of security elements for banknotes and other valuable documents. Fig. 1 shows a schematic representation of a banknote 10 provided with a security element according to the invention in the form of an adhesively bonded transfer element 12. In the exemplary embodiment, the transfer element 12 represents an alternating image that presents the viewer with different image information 14A, 14B, and 14C from three different viewing directions.

In the illustrated embodiment, the image information for illustration is formed by holographic letters "A", "B", and "C", respectively. The viewer perceives the letter "A" when viewed diagonally from the left, the letter "B" when viewed vertically from above, and the letter "C" when viewed diagonally from the right. By tilting the banknote, the appearance of the security element alternates between the three image information items 14A, 14B, and 14C. It is understood that in practice, more complex motifs, such as geometric patterns, portraits, architectural, technical, or natural motifs, are generally used instead of the letters shown here for illustration. A changing image can also contain only two or more than three pieces of image information, or the security element can have a moving image, a pump image, a morphed image, or a stereo image instead of a changing image.

In such images with different image information for different viewing directions, the subject area typically consists of several groups of pixel elements, each of which generates the image information for one of the different viewing directions. The pixel elements are conventionally designed in the form of squares, circles, or parallel stripes, as explained in more detail above.

The special feature of the present invention consists in a special design and arrangement of the pixel elements, the realization of which places the highest technological demands and therefore significantly increases the forgery security of the security element.

As an example, Fig. 2 A schematic view of the motif area 20 of the security element 12. The motif area consists of three groups of congruent pixel elements 22-A, 22-B, and 22-C, which are indicated in the figure by different hatching. The pixel elements 22-A, 22-B, and 22-C form the tiles of a tiling and, despite their complex shape and congruence, cover the motif area 20 seamlessly and without overlap.

As from Fig. 2 As can be seen further, the pixel elements (or tiles) all have the same shape, namely the shape of a lizard, which is shown as prototile 24 next to the section of the motif area 20. The tiles 22 of the tiling are all congruent with the prototile 24 and result from it by translation and rotation.

The size of the tiles in the example is 100 µm (maximum dimension of the lizard shape, here from the left front to the right rear foot), but can generally range between 5 µm and 500 µm. In the lower part of the specified range, the lizard shape of the tiles is not resolvable to the human eye without aids, while at the upper end of the range, it is visually perceptible as an irregular lizard shape.

In the exemplary embodiment, the pixel elements or tiles 22 are each covered with holographic structures, namely the pixel elements or tiles 22-A with first holographic structures (wide hatching), which, when illuminated vertically, reconstruct the letter "A" diagonally to the left in the first viewing direction, the pixel elements or tiles 22-B with second holographic structures (medium hatching), which, when illuminated vertically, reconstruct the letter "B" vertically upwards in the second viewing direction, and the pixel elements or tiles 22-C with third holographic structures (narrow hatching), which, when illuminated vertically, reconstruct the letter "C" diagonally to the right in the third viewing direction.

When viewing banknote 10 with the naked eye, the special tiling of motif area 20 is not visible. Rather, the elements of the group of pixel elements 22-A, 22-B, and 22-C interact to reconstruct the holographic image of the letters "A," "B," or "C" in the respective viewing direction. Only when viewed with a magnifying glass or microscope does the lizard-like tiling of motif area 20 become visible, thus serving as a higher-level authenticity feature that can only be detected with aids.

At the Fig. 2 The tiling shown is a periodic tiling, i.e. a tiling whose symmetry group contains two linearly independent displacements. The displacement vectors 26 of the two linearly independent displacements are in Fig. 2 for illustration purposes. In addition, the symmetry group of the tiling contains rotational symmetries of order 3, as can be seen particularly in the representation of the Fig. 3 which shows an arbitrarily selected tile 22-A and, in dashed lines, the adjacent tiles 22-B, 22-C.

The edge points of tile 22-A (and any other tile) where at least three tiles touch, represent the nodes 60, 62 of the tile outline, the border areas 64 between the nodes 60, 62 represent the edges of the tile outline. Every second node 60 (full dots in Fig. 3 ) is the intersection point of the rotation axis of a rotational symmetry of order 3. As in Fig. 3 As shown, the nodes 60, 62 of the lizard tiles lie on the vertices of a regular hexagon 66. However, to create the lizard shape, the edges of the hexagon 66 were replaced by non-straight edges 64 composed of several straight segments. Due to the symmetry of the tiling, three of these non-straight edges result from the other three edges by rotating them around one of the nodes 60. The use of tiles 22 with exclusively non-straight edges leads to complex outline shapes of the tiles, which are difficult to recreate and offer the designer a high degree of design freedom.

Another characteristic of the tilings according to the invention is that the symmetry group of the tilings does not contain any mirror symmetry.

Instead of holographic structures, the pixel elements can also be covered with other structures that generate image information, as described above. As in Fig. 4 As shown, a group of pixel elements 32-A in a subject area 30 can also be unoccupied and generate no image information. While the pixel elements 32-B and 32-C each generate image information, for example, an alternating image, the unoccupied areas 32-A within the subject area 30 act like recesses with a complex outline shape.

With reference to Fig. 5 The shape of the tiles 22 can also accommodate a macroscopically existing outline of a view 44 of the motif area 42. For example, the motif area 42 of a security element 40 can show a holographic view 44 of a lizard, which is designed, for example, as a three-dimensional true color hologram. The individual color pixels of the true color hologram are formed by the tiles 46-A, 46-B and 46-C of the tiling of the motif area. In the exemplary embodiment, the tiling already described in Fig. 2 described tiling with three groups of pixel elements 46-A, 46-B, 46-C is used, all of which are formed in lizard shape congruent with the prototile 24 and the outline of the holographic view 44.

The maximum dimension of the view 44 is, for example, 5 mm, while the corresponding maximum dimension of the tiles 46 is only 100 µm, so that the size ratio of the view 44 and the corresponding prototile 24 in the exemplary embodiment is 50. The correspondence of the microscopic information formed by the outline shape of the tiles 46 and the macroscopic information formed by the outline shape of the view 44 can be used as an additional authenticity feature.

While in the embodiments described so far there is exactly one prototile to which each tile of the tiling is congruent, there may also be several different prototiles. An embodiment with two different prototiles 50-A, 50-B is described with reference to Fig. 6 illustrated. The Fig. 6(a) The prototile 50-A shown is a rhombus with interior angles of 72° and 108°, and the prototile 50-B is a rhombus with interior angles of 36° and 144°. These prototiles can be used to create a so-called Penrose tiling 54 of a motif area 52, which, as shown in Fig. 6(b) shown, consists of pixel elements or tiles 56-A and 56-B. The tiles 56-A are all congruent to the prototile 50-A, and the tiles 56-B are all congruent to the prototile 50-B. The special feature of these Penrose tilings is that they allow a gapless and overlap-free, yet aperiodic covering of the plane.

In the exemplary embodiment, the pixel elements or tiles 56-A, 56-B are each covered with holographic structures for different viewing directions, resulting in an overall tilted image with two views. Aperiodic tiling and Penrose tiling can also be formed from more than two prototiles, which can be used accordingly for alternating images with more than two views.

Since the prototiles of a Penrose tiling, such as prototiles 50-A and 50-B, allow the generation of an infinite number of different Penrose tilings, the Penrose tiling implemented in a security element can be used as an additional authenticity mark. For example, using a suitable algorithm, a uniquely defined Penrose tiling can be generated from the serial number of a banknote or security document and used to create the motif area of the associated security element. During the authentication process, the serial number can be read, the corresponding Penrose tiling can be generated, and checked for congruence with the tiling implemented on the security element.

Although the invention has been explained primarily with reference to interchangeable images, it is not in any way limited to interchangeable images or the aforementioned variants. Rather, the invention can be applied to all optically variable security elements in which a motif area displays different image information from different viewing directions. The invention is also not limited to the transfer elements used for illustration on banknotes; it can also be used, for example, with security threads, wide security strips, or cover foils arranged over a window area or a continuous opening in a document.

List of reference symbols

10

Banknote

12

Transfer element

14-A, 14-B, 14-C

Image information

20

Motif area

22, 22-A, 22-B, 22-C

Pixel elements, tiles

24

Protocol tile

26

Displacement vectors

30

Motif area

32-A, 32-B, 32-C

Pixel elements, tiles

40

Security element

42

Motif area

44

holographic view of a lizard

46, 46-A, 46-B, 46-C

Pixel elements, tiles

50-A, 50-B

Prototiles

52

Motif area

54

Penrose tiling

56-A, 56-B

Pixel elements, tiles

60.62

node

64

Edge

66

regular hexagon

Claims (10)

1. An optically variable security element (12) for securing security papers, value documents and other data carriers, having a motif region (20) that, from different viewing directions, shows different pieces of image information (14-A, 14-B, 14-C):

   - the motif region (20) consisting of two or more groups of, in each case, congruent pixel elements (22-A, 22-B, 22-C), of which at least two groups (22-A, 22-B, 22-C) produce a piece of image information (14-A, 14-B, 14-C) in different viewing directions,

   - the pixel elements (22-A, 22-B, 22-C) forming the tiles of a tiling of the plane and covering the motif region (20) with no gaps or overlaps,

   - the pixel elements (22-A, 22-B, 22-C) comprising a complex contour shape that is neither triangular, quadratic, hexagonal nor circular,

   - the pixel elements (22-A, 22-B, 22-C) having a maximum dimension of 500 µm or less, and

   - the symmetry group of the tiling includes at least one rotational symmetry of the order 3 or 6.
2. An optically variable security element (12) for securing security papers, value documents and other data carriers, having a motif region (20) that, from different viewing directions, shows different pieces of image information (14-A, 14-B, 14-C):

   - the motif region (20) consisting of two or more groups of, in each case, congruent pixel elements (22-A, 22-B, 22-C), of which at least two groups (22-A, 22-B, 22-C) produce a piece of image information (14-A, 14-B, 14-C) in different viewing directions,

   - the pixel elements (22-A, 22-B, 22-C) forming the tiles of a tiling of the plane and covering the motif region (20) with no gaps or overlaps,

   - the pixel elements (22-A, 22-B, 22-C) comprising a complex contour shape that is neither triangular, quadratic, hexagonal nor circular,

   - the pixel elements (22-A, 22-B, 22-C) having a maximum dimension of 500 µm or less, and

   - the tiling is aperiodic, especially constitutes a Penrose tiling.
3. An optically variable security element (12) for securing security papers, value documents and other data carriers, having a motif region (20) that, from different viewing directions, shows different pieces of image information (14-A, 14-B, 14-C):

   - the motif region (20) consisting of two or more groups of, in each case, congruent pixel elements (22-A, 22-B, 22-C), of which at least two groups (22-A, 22-B, 22-C) produce a piece of image information (14-A, 14-B, 14-C) in different viewing directions,

   - the pixel elements (22-A, 22-B, 22-C) forming the tiles of a tiling of the plane and covering the motif region (20) with no gaps or overlaps,

   - the pixel elements (22-A, 22-B, 22-C) comprising a complex contour shape that is neither triangular, quadratic, hexagonal nor circular,

   - the pixel elements (22-A, 22-B, 22-C) having a maximum dimension of 500 µm or less, and

   - the tiles (22-A, 22-B, 22-C) of the tiling comprise no straight edges, but rather the edges are each composed of two or more straight-line pieces that each form an angle, wherein those boundary points of the tiles where at least three tiles touch are called nodes, and the boundary areas between the nodes are called edges.
4. An optically variable security element (12) for securing security papers, value documents and other data carriers, having a motif region (20) that, from different viewing directions, shows different pieces of image information (14-A, 14-B, 14-C):

   - the motif region (20) consisting of two or more groups of, in each case, congruent pixel elements (22-A, 22-B, 22-C), of which at least two groups (22-A, 22-B, 22-C) produce a piece of image information (14-A, 14-B, 14-C) in different viewing directions,

   - the pixel elements (22-A, 22-B, 22-C) forming the tiles of a tiling of the plane and covering the motif region (20) with no gaps or overlaps,

   - the pixel elements (22-A, 22-B, 22-C) comprising a complex contour shape that is neither triangular, quadratic, hexagonal nor circular,

   - the pixel elements (22-A, 22-B, 22-C) having a maximum dimension of 500 µm or less,

   - each tile (56-A, 56-B) in the tiling is congruent to an element of a set of different prototiles (50-A, 50-B), and

   - the motif region (20) includes an image motif that is visible with the naked eye and whose contour shape corresponds to the contour shape of a prototile, the size ratio of the image motif and the corresponding prototile preferably being 10 or more, especially 20 or more or even 50 or more, and wherein the border of at least one prototile constitutes a natural motif, namely a plant, an animal, a person or a mythical creature.
5. The security element according to at least one of claims 1, 3 or 4, characterized in that the tiling is periodic, such that the symmetry group of the tiling includes two linearly independent displacements.
6. The security element according to at least one of claims 1, 3, 4 or 5, characterized in that the symmetry group of the tiling includes no mirror symmetry.
7. The security element according to at least one of claims 1 to 3, 5 or 6, characterized in that the border of at least one prototile constitutes a natural motif, especially a plant, an animal, a person or a mythical creature.
8. The security element according to at least one of claims 1 to 7, characterized in that the pixel elements (22-A, 22-B, 22-C) of the groups that produce a piece of image information are covered with diffractive patterns, holographic patterns, subwavelength gratings, refractive patterns such as mi-cromirrors, microlenses or micro-Fresnel lenses, printed patterns, color-shifting thin-film elements, chromophoric nanoparticles or polarizing elements.
9. The security element according to at least one of claims 1 to 8, characterized in that a group of pixel elements produces no piece of image information.
10. A data carrier having a security element according to at least one of claims 1 to 9.

Images