EP3000614A1 - Optically variable security element having reflective surface area - Google Patents

Abstract

The invention relates to an optically variable security element (12) for protecting valuables, comprising a support having a reflective area (20) whose extent defines an x-y plane and a z-axis perpendicular thereto. According to the invention, it is provided that the reflective surface region (20) includes a plurality of reflective pixels (30), each having one or more similarly oriented reflective facets (32), wherein an orientation of each facet (32) relative to the xy plane is indicated by its normalized Normal vector is determined - The reflective facets (32) are oriented so that the reflective surface area (20) for a viewer as compared to its actual spatial form projecting and / or receding surface (40) is perceptible, and - At least a part of the facets (32) is provided with a diffractive grating pattern (34) of a plurality of grid lines (36) whose grid vector is parallel to the cross product of the unit vector in the z direction with the normal vector of the respective facet (32).

Description

The invention relates to an optically variable security element for safeguarding valuables, having a carrier with a reflective surface area whose extent defines an x-y plane and a z axis perpendicular thereto. The invention also relates to a method for producing such a security element as well as a correspondingly equipped data carrier.

Data carriers, such as valuables or identity documents, or other valuables, such as branded articles, are often provided with security elements for the purpose of security, which permit verification of the authenticity of the data carriers and at the same time serve as protection against unauthorized reproduction.

Security elements with viewing-angle-dependent effects play a special role in the authentication of authenticity since they can not be reproduced even with the most modern copiers. The security elements are thereby equipped with optically variable elements that give the viewer a different image impression under different viewing angles and, for example, show a different color or brightness impression and / or another graphic motif depending on the viewing angle.

A technique widely used in the field of security elements, which gives a practically flat film a three-dimensional appearance, are various forms of holography. However, these techniques have some disadvantages for use with security features, in particular banknotes. On the one hand, the quality of the three-dimensional representation of a hologram depends strongly on the lighting conditions. Especially with diffuse lighting, the representations of holograms are often difficult to recognize. In addition, have holograms the disadvantage that they are now present in everyday life in many places and therefore their special position disappears as a mark of authenticity.

Based on this, the present invention seeks to provide an optically variable security element of the type mentioned above, which avoids the disadvantages of the prior art, and in particular to provide a security element, despite flat design, a visually attractive three-dimensional appearance with high attention and Recognition value has.

This object is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

• der reflektive Flächenbereich eine Vielzahl von reflektiven Pixeln enthält, die jeweils eine oder mehrere, gleich orientierte reflektive Facetten aufweisen, wobei eine Orientierung jeder Facette relativ zur x-y-Ebene durch die Angabe ihres normalisierten Normalenvektors bestimmt ist,
• die reflektiven Facetten so orientiert sind, dass der reflektive Flächenbereich für einen Betrachter als gegenüber seiner tatsächlichen Raumform vor- und/ oder zurückspringende Fläche wahrnehmbar ist, und
• zumindest ein Teil der Facetten mit einem diffraktiven Gittermuster aus einer Vielzahl von Gitterlinien versehen ist, dessen Gittervektor parallel zum Kreuzprodukt des Einheitsvektors in z-Richtung mit dem Normalenvektor der jeweiligen Facette liegt.

According to the invention, it is provided in a generic security element that

• the reflective area includes a plurality of reflective pixels each having one or more equally oriented reflective facets, wherein an orientation of each facet relative to the xy plane is determined by the indication of its normalized normal vector;
• the reflective facets are oriented in such a way that the reflective surface area is perceptible to a viewer as an area that protrudes and / or recesses relative to its actual spatial form, and
• at least a part of the facets is provided with a diffractive grating pattern of a plurality of grating lines whose grating vector is parallel to the cross product of the unit vector in the z-direction with the normal vector of the respective facet.

By these measures, the security element despite extremely flat design with a maximum height difference of, for example, only 10 microns produce a clear three-dimensional impression of the subjects shown. In addition, the special coordination of the orientation of the facets and the diffractive grating pattern formed on the facets allows the dispersion of the light in ground transparent materials, such as glass or diamond, to be reproduced convincingly, as explained in detail below.

As usual, the grating vector of a grating pattern is a vector which is perpendicular to the grating lines and whose magnitude indicates the grating period.

The reflective pixels preferably each contain two or more equally oriented facets, but it is also possible that a portion of the pixels or all pixels each contain only one facet. At least a part of the pixels and / or the facets is advantageously formed with an outline in the form of a motif, in particular in the form of characters or symbols. The particular outlines may be used as an additional authentication feature that will only be visible under magnification. Furthermore, a microtext may additionally be inscribed in a part of the pixels or facets. The microtext can be written both on the facets or instead of some of the facets on the carrier.

In an expedient development of the invention, of the facets lying parallel to the xy plane at least one part with a diffractive grid pattern of a plurality of grid lines whose grid vector is substantially parallel to the grid vectors of the grid patterns of adjacent facets. This requirement takes account of the fact that the above-mentioned condition on the lattice vector can not be applied to facets lying parallel to the xy plane since the cross product of the unit vector in the z direction then disappears with the normal vector. In order to obtain a uniform dispersion impression, the facets lying parallel to the xy plane are therefore advantageously provided with a grid pattern whose grid vector lies substantially parallel to the grid vectors of the grid patterns of adjacent facets. For example, the grating vector of such a facet may be chosen as the average of the grating vectors of the adjacent facets with a valid grating vector.

The reflective facets are advantageously oriented so that the reflective area can be perceived by a viewer as a curved, in particular continuously curved, surface. With particular advantage, the reflective area can be perceived as an arched in two spatial directions, in particular continuously curved surface.

The grating patterns of the reflective facets advantageously produce colored reflections in the first and possibly higher diffraction orders, which are perceptible to a viewer as a dispersion of a transparent material, such as glass or diamond.

The inclination of the reflective facets against the xy plane preferably has no dominant preferred direction, so that there is no plane perpendicular to the xy plane in which more than 80% of the normal vectors of the reflective facet lie.

In a preferred embodiment, the grid lines of all of the facets provided with a diffractive grid pattern have a grid vector parallel to the cross product of the unit vector in the z direction with the normal vector of the respective facet. The diffractive grating patterns advantageously have a grating period between 0.3 μm and 4 μm, preferably between 0.6 μm and 3 μm.

In an advantageous variant of the invention, all grid patterns of the area area have the same grid period. Alternatively, the grating period of individual facets can be chosen differently, whereby the strength of the imitated dispersion can be varied.

mit Konstanten c_x, c_y, und c₀ und einem zusammenhängenden Bereich B der x-y-Ebene aufweist.The facets are preferably formed essentially as planar surface elements. The wording "substantially" takes into account the fact that in practice production-related can not produce perfectly flat surface elements. Alternatively, the facets can also be formed as curved, in particular concave, convex or corrugated surface elements. In general, a facet can be described by specifying the facet surface h (x, y), where a planar facet is a facet surface of the shape $${\mathrm{H}}_{\mathrm{1}}\left(\mathrm{x},\mathrm{y}\right)={\mathrm{c}}_{\mathrm{x}}*\mathrm{x}+{\mathrm{c}}_{\mathrm{y}}*\mathrm{y}+{\mathrm{c}}_{\mathrm{0}}.\mathrm{For}\left(\mathrm{x},\mathrm{y}\right)\in \mathrm{B}$$

with constants c _x , c _y , and c ₀ and a contiguous area B of the xy plane.

In an expedient embodiment, the reflective facets are arranged in a periodic grid and in particular form a sawtooth grid. Alternatively, the reflective facets are arranged aperiodically, with a Aperiodic arrangement of the facets is currently preferred, as this unwanted diffraction effects, resulting from a regular arrangements of the facets, can be avoided.

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.

The facets advantageously have a dimension of 10 μm or more, preferably 20 μm or more, particularly preferably 30 μm or more, in the direction of the grating vector of the grating pattern. In the direction perpendicular to the grating vector, the facets advantageously have a dimension between 5 μm and 30 μm, preferably between 7.5 μm and 15 μm, and the height of the facets is advantageously between 0 and 10 μm, preferably between 0 and 5 μm.

In advantageous embodiments, the reflective facets have a metallic coating, a high-index coating, or a coating with a color-shifting layer.

In an advantageous embodiment of the invention, a part of the facets is formed without a diffractive grid pattern. Due to the proportion of lattice-free facets, the degree of the imitated dispersion can be adjusted.

The described reflective surface area can be combined with other security features, for example with holograms, in particular true color holograms, with subwavelength gratings or other subwavelength structures, with micromirror arrangements without diffractive gratings, or also with security features based on specific material properties, such as electrical conductivity, magnetic properties, luminescence, fluorescence or the like. The other security features may for example be provided in gaps of the reflective surface area and be nested therewith.

Finally, it should be noted that the specified condition that the grid vector is parallel to the cross product of the unit vector in the z direction with the normal vector of the respective facet, for real structures, of course, must not be mathematically exactly met or can, but that it understands the expert in that small, for example production-related, unavoidable deviations from the mathematically exact conditions do not impair the described effects and the functioning of the security elements.

The invention also includes a data carrier with a security element of the type described. 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, a share, a bond, a certificate, a coupon , a check, a high-quality entrance ticket, but also an ID card, such as a credit card, a bank card, a cash card, an authorization card, an identity card or a pass personalization page.

• ein Träger bereitgestellt und mit einem reflektiven Flächenbereich versehen wird, dessen Ausdehnung eine x-y-Ebene und eine darauf senkrecht stehende z-Achse definiert,
• wobei der reflektive Flächenbereich mit einer Vielzahl von reflektiven Pixeln ausgebildet wird, die jeweils eine oder mehrere, gleich orientierte reflektive Facetten aufweisen, wobei eine Orientierung jeder Facette relativ zur x-y-Ebene durch die Angabe ihres normalisierten Normalenvektors bestimmt ist,
• die reflektiven Facetten so orientiert werden, dass der reflektive Flächenbereich für einen Betrachter als gegenüber seiner tatsächlichen Raumform vor- und/oder zurückspringende Fläche wahrnehmbar ist, und
• zumindest ein Teil der Facetten mit einem diffraktiven Gittermuster aus einer Vielzahl von Gitterlinien versehen wird, dessen Gittervektor parallel zum Kreuzprodukt des Einheitsvektors in z-Richtung mit dem Normalenvektor der jeweiligen Facette liegt.

The invention further includes a method for producing an optically variable security element of the type described above, in which

• a support is provided and provided with a reflective surface area, the extent of which defines an xy plane and a z axis perpendicular thereto,
• wherein the reflective area is formed with a plurality of reflective pixels, each having one or more similarly oriented reflective facets, an orientation of each facet relative to the xy plane being determined by the indication of its normalized normal vector,
• the reflective facets are oriented such that the reflective surface area is perceptible to an observer as an area that protrudes and / or recesses relative to its actual spatial form, and
• at least a part of the facets is provided with a diffractive grid pattern of a plurality of grid lines whose grid vector is parallel to the cross product of the unit vector in the z direction with the normal vector of the respective facet.

To produce a security element according to the invention, the reflective facets can be written into a photoresist together with the diffractive grating patterns, for example by means of gray scale lithography, subsequently developed, galvanically formed, embossed and mirrored in a UV varnish. The mirror coating can be realized for example by an applied, for example vapor-deposited metal layer. Typically, an aluminum layer with a thickness of, for example, 50 nm is applied. Of course, other metals such as silver, copper, chromium, iron, nickel or alloys thereof may also be used. Also, as an alternative to metals, semiconductors such as silicon, high-index coatings, for example made of ZnS, Al ₂ O ₃ or TiO ₂ , or also color-shifting layers can be applied. The application, in particular vapor deposition can be carried out over the entire surface, but it is also possible to perform a coating only in regions or grid-shaped, so that the security element is partially transparent or translucent.

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 Sicherheitselement in Form eines aufgeklebten Transferelements,

Fig. 2

illustriert das Zustandekommen des dreidimensionalen Erscheinungsbilds des Sicherheitselements der Fig. 1,

Fig. 3

einen Detailausschnitt des reflektiven Flächenbereichs mit drei Pixeln entlang einer Höhenlinie der in Fig. 2 gezeigten gewölbten Fläche,

Fig. 4

eine perspektivische Ansicht einer einzelnen Facette mit ihrem Gittermuster,

Fig. 5

einen Ausschnitt eines reflektiven Flächenbereichs eines erfindungsgemäßen Sicherheitselements, bei dem jedes Pixel aus nur einer Facette besteht und bei dem die Pixel bzw. Facetten aperiodisch in der x-y-Ebene angeordnet sind,

Fig. 6

den reflektiven Flächenbereich eines Sicherheitselements nach einem weiteren Ausführungsbeispiel der Erfindung im Querschnitt, und

Fig. 7

in (a) bis (c) die Spiegelreflexe und die beim Kippen auftretende Dispersionswirkung anhand der Darstellung der Wertzahl "50" der Fig. 1, wobei (a) eine Aufsicht ohne Darstellung der Dispersionswirkung, und (b) und (c) einerseits die Bewegung der farblosen und lichtstarken Reflexionen in 0-ter Beugungsordnung und andererseits das Auftreten farbiger Reflexionen beim Kippen des Sicherheitselements zeigen.

Show it:

Fig. 1

a schematic representation of a banknote with an optically variable security element according to the invention in the form of a glued transfer element,

Fig. 2

illustrates the realization of the three-dimensional appearance of the security element of Fig. 1 .

Fig. 3

a detail of the reflective area with three pixels along a contour line of Fig. 2 shown curved surface,

Fig. 4

a perspective view of a single facet with its grid pattern,

Fig. 5

a section of a reflective surface area of a security element according to the invention, in which each pixel consists of only one facet and in which the pixels or facets are arranged aperiodically in the xy plane,

Fig. 6

the reflective surface area of a security element according to a further embodiment of the invention in cross section, and

Fig. 7

in (a) to (c) the mirror reflections and the dispersion effect occurring during tilting on the basis of the representation of the value "50" of Fig. 1 in which (a) shows a plan view without representation of the dispersion effect, and (b) and (c) on the one hand the movement of the colorless and bright reflections in the 0th diffraction order and on the other hand the appearance of colored reflections on tilting of the security element.

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 security element 12 according to the invention in the form of a glued transfer element. It is understood, however, that the invention is not limited to transfer elements and banknotes but can be used in all types of security elements, such as labels on goods and packaging or in the security of documents, ID cards, passports, credit cards, health cards and the like. For banknotes and similar documents, in addition to transfer elements, for example, security threads or security strips may also be considered.

This in Fig. 1 shown security element 12 is itself extremely flat with maximum height differences of about 10 microns formed, but conveys the viewer a clear three-dimensional impression of the subjects shown, for example, the brilliant 14 and from the plane of the banknote 10 seemingly arched outstanding value 16. In addition, the show both motifs 14,16 when going back and forth the security element 12 colored reflections, as they occur in the dispersion of light in ground transparent materials such as glass or diamond. The security element 12 therefore has a high value and also a high attention and recognition value.

The optically variable security element 12 contains a reflective surface area 20 whose extent defines an x-y plane, which here coincides with the surface of the banknote 10. The z-axis is perpendicular to the x-y plane, so that the coordinate system formed by the three axes forms a legal system.

The construction of security elements according to the invention and the realization of the three-dimensional representation with imitated dispersion will now be described with reference to FIGS FIGS. 2 to 4 explained in more detail. First illustrated Fig. 2 the realization of the three-dimensional appearance of the security element 12, wherein the reference numeral 40 of the viewer at represents the viewing of the security element 12 perceived, curved in two spatial directions area. FIG. 3 shows a detail of the reflective surface area 20 with three pixels 30 along a contour line 44 of the curved surface 40 and Fig. 4 shows a perspective view of a single facet 32 with its grid pattern 34.

Coming back to the presentation of the first Fig. 2 For example, in the carrier 38 of the security element 12, not the curved surface 40 perceived by the viewer is formed, but a plurality of reflective pixels 30, each containing three reflective facets 32 with the same orientation, and the orientation of the facets 32 the reflective behavior of the curved surface 40 imitated.

Here, the orientation of each facet 32 by the inclination of the facet against the xy plane and an azimuthal angle or by the indication of their normalized normal vector n = (n _x, n _y, n _z) | n | = 1 and positive z-component determined. The azimuth angle of a facet is the angle between the projection of the normal vector n into the xy plane and a predetermined reference direction R (FIG. Fig. 3 ). In order to simulate the reflection behavior of the curved surface 40, the facets 32 are each oriented such that their normal vector n corresponds to the local normal vector N of the curved surface 40 averaged over the extent of a pixel 30.

In the exemplary embodiment, the pixels 30 are formed with a square outline, but they can generally also have other outline shapes, in particular a motif shape, such as characters or symbols. The edge length of the pixels 30 is below 300 μm and is in particular in the range from 20 μm to 100 μm. Length and width of the facets 32 are above 5 microns to avoid color splits by the facet assembly itself. The height of the facets is only between 0 and 10 .mu.m, preferably between 0 and 5 .mu.m, so that the entire reflective area 20 has height differences of at most 10 .mu.m, which are imperceptible to the naked eye.

Since the geometric reflection condition "angle of incidence equals angle of reflection" for the reflection of directed light 42 depends only on the local orientation of the normal vector of the reflective surface 40, 20 and the pixels 30 are also very small and thus do not appear themselves, the reflective surface area shows 20 essentially the same reflection properties as the three-dimensional surface 40 to be imitated, and therefore produces the pronounced three-dimensional impression of the imitated surface 40 in the viewer despite its small height differences.

The reflective facets 32 are overall oriented in such a way that the reflective area 20 can be perceived by a viewer as an area 40 that protrudes and / or recesses relative to its actual spatial form. The actual spatial form of the reflective surface area 20 is given by the sequence of the inclined facets, in the exemplary embodiment approximately by the regular sawtooth arrangement of the facets 32. Because of the generality of the construction described, the reflective area 20 can be used to generate virtually any three-dimensionally perceptible motifs, such as portraits, representations of objects, animals or plants, or spatial representations of alphanumeric characters, for example the "50" value Fig. 1 ,

In addition to the imitation of the three-dimensionality of the surface 40 also occurring in polished transparent materials dispersion of the To be able to imitate light, the reflective facets 32 of the surface region 20 are additionally provided with diffractive grating patterns 34, each consisting of a plurality of parallel grid lines 36. In the context of the invention, the orientation of the grating lines 36 is chosen so that the grating vector g of the grating pattern 34, which by definition is perpendicular to the grating lines 36 and whose magnitude indicates the grating period, parallel to the cross product of the unit vector e _z in the z direction the normal vector n of the respective facet lies.

With e _z = (0,0,1) and n = ( n _x , n _y , n _z ) we have g ∥ ( e _z × n ) and the grating vector of each facet can be expressed as g = ( g _x , g _y , 0) with the grating period | g | to be written. In Fig. 4 the relationship between the normal vector n, the unit vector e _z and the grating vector g of the grating pattern 34 for a facet 32 is graphically illustrated. Also plotted is the inclination γ of the facet against the xy plane.

The detail of the Fig. 3 shows in plan view three pixels 30 each having three facets 32, which along a contour line 44 of the curved surface 40 of Fig. 2 Therefore, they essentially do not differ in the inclination γ of the facets against the xy plane, but only in the azimuth angle A of the facets. In Fig. 3 For this purpose, the projection of the normal vector n into the xy plane, the reference direction R and the azimuth angle A are shown in each case for the pixels 30. FIG. 3 also shows the resulting grating vector g and the associated grating lines 36 of the grating pattern 34. For the sake of clarity, the grating lines 36 are drawn only in one of the three facets 32 of each of the pixels 30. Since the facets 32 of a pixel 30 are all the same orientation, the other facets of the pixel 30 have the same normal vector n, and thus also the same grating vector g and thus also the same grating pattern 34. As in Fig. 3 represented, lie the boundary lines The outline of the facets 32 with advantage as far as possible perpendicular to the grid lines 36. This can be achieved that with each orientation of the facets as large a number of grid lines 36 is available for the diffraction and thus for a brilliant appearance. In addition, larger facet heights can be largely avoided, especially in the case of micromirrors with the same mirror slope.

If only a reflective facet 32 without a diffractive grating pattern 34 is initially considered for a more detailed explanation, the lattice-free facet 32 acts as an achromatically reflecting micromirror which reflects incident light without color splitting according to the laws of geometrical optics. If, from a viewing direction lying in the plane spanned by the normal vector and the z-axis, the facet 32 meets the reflection condition "angle of incidence equal to the angle of reflection", the facet appears colorless bright, otherwise dark. Since the reflection condition is exactly fulfilled only for one tilt angle, an abrupt, discrete change in brightness results when tilting the reflective facet perpendicular to the plane mentioned.

If one then adds the diffractive grating pattern 34, so that additionally the diffraction of the incident light on the grating pattern has to be taken into account, the direction of the 0th diffraction order of the grating pattern occurs instead of the direction of the geometrically directionally reflected light beam. In the direction of the 0th order of diffraction, the reflection condition "angle of incidence equal to the angle of reflection" is satisfied, the facet appears bright and colorless, though typically with somewhat less brightness than in the lattice-free case described above, because a portion of the light is diffracted in other spatial directions.

angegeben, in der m die Beugungsordnung, |g| den Betrag des Gittervektors und damit die Gitterperiode, und λ die Wellenlänge bedeuten. Die Winkel α bzw. β sind die Winkel des einfallenden bzw. reflektierenden Lichts, projiziert in die von dem Gittervektor g und dem Normalenvektor n aufgespannte Ebene. Der Winkel α wird dabei stets positiv genommen, der Winkel β positiv, wenn er, wie bei den erfindungsgemäßen Gestaltungen üblich, bezüglich der Gitternormalen auf derselben Seite wie α liegt, ansonsten negativ.In the lattice patterns 34, the propagation direction of the diffracted light is in a plane subtended by the lattice vector g and the direction of the 0th order of diffraction. Within this plane, the direction of the diffracted light is determined by the grid equation $$\mathrm{sin\; .alpha}+\mathrm{sin\beta }=m\mathrm{\lambda }/\left|G\right|$$

given in m the diffraction order, | g | the amount of the grating vector and thus the grating period, and λ denote the wavelength. The angles α and β, respectively, are the angles of the incident or reflected light projected into the plane spanned by the grating vector g and the normal vector n . The angle α is always taken positive, the angle β positive if it, as usual in the embodiments according to the invention, with respect to the lattice normal on the same side as α, otherwise negative.

For the above-mentioned viewing direction in the plane of the normal vector and the z-axis, the angles α and β of the grating equation do not change when tilting the reflective facet μm an axis perpendicular to said plane. On the other hand, with a tilt about another axis, tilting also gradually changes the angles α and β in the grid equation. In the case of such tilting, therefore, a gradual change in color and / or intensity occurs, as a result of which, in particular, the color impression of the facet 32 changes continuously.

Returning now to a reflective area 20 consisting of a plurality of facets 32 with different angles of inclination γ and azimuth angles A, the totality of the facets does not have an excellent tilting axis. Rather, every tilt is at an arbitrary A part of the facets 32 show a discrete intensity change, while another part shows a gradual change in color and / or intensity. The colorless and high-intensity reflections in the 0th diffraction order contribute in particular to the impression of a three-dimensional curved surface 40, since they adjust the reflection by the curved surface 40.

The colored reflections of the first and higher orders of diffraction additionally suggest to the viewer the occurrence of dispersion familiar to him from ground transparent objects. Of particular importance is that the colored reflections of adjacent pixels 30 are not independent of each other, since the orientations of the facets 32 adjacent pixels are not independent of each other, but are just chosen so that the pixels 30 in their entirety just the reflection behavior of reproduce three-dimensional surface 40. With the spatial orientation, therefore, the colored reflections of adjacent pixels 30 are correlated and lead to macroscopically recognizable colored reflections, which, as the inventors have surprisingly found, mimic the occurrence of dispersion in transparent materials.

The above-mentioned condition according to which the grating vector g of the grating pattern should lie parallel to the cross product of the unit vector in the z direction e _z with the normal vector n of the respective facet can not be applied to facets lying parallel to the xy plane since the cross product is there is equal to zero. As described above, the facets lying parallel to the xy plane are therefore advantageously provided with a grid pattern whose grid vector lies substantially parallel to the grid vectors of the grid patterns of adjacent facets.

Further, the above condition applies to the grating vector g only its direction, but not its magnitude. Rather, can be adjusted by the choice of the grating period, regardless of the previous considerations, the degree of the imitated dispersion. Smaller grating periods lead to a more pronounced spatial fanning of the light into spectral colors and thus to colored reflections of lesser intensity. Thus, after determining the direction of the grating vector, the grating period is selected according to the magnitude of the desired dispersive appearance of the curved surface 40.

Another way to adjust the degree of mimic dispersion is to form a certain part of the facets without lattice patterns and to reduce the degree of mimic dispersion by the proportion of lattice-free facets.

The reflective pixels 30 and the reflective facets 32 can, as in Fig. 3 shown, arranged in a regular grid and form, for example, a regular Blazegitter. However, the surface areas according to the invention are not limited to regular pixel or facet arrangements, but rather even aperiodic pixel or facet arrangements are used, as this unwanted diffraction effects, such as may occur through regular arrangements are avoided.

FIG. 5 shows an embodiment in which, for ease of illustration, each pixel 30 consists of only one facet 32 and in which the pixels or facets are arranged aperiodically in the xy plane. In order to obtain a surface area with clear diffraction colors despite the height differences of adjacent facets and the associated phase shift, the dimension of the facets in the direction of the grating vector g of the grating pattern 34 is at least 10 μm, preferably at least 20 μm, particularly preferably at least 30 μm. In the direction perpendicular to the grating vector g , the dimension of the facets is in each case between 5 μm and 30 μm, preferably between 7.5 μm and 15 μm. The height of the facets is between 0 and 10 microns, preferably between 0 and 5 microns. As in Fig. 3 The boundary lines of the outline of the facets 32 and the pixels 30 are advantageously perpendicular to the grid lines 36 as far as possible. As a result, regardless of the orientation of the facets or pixels, a maximum number of grid lines 36 is available for the diffraction and thus for a brilliant appearance available. Also, larger facet heights can be largely avoided.

Another possibility to suppress unwanted diffraction effects by the division of the surface area in facets is to aperiodically offset the facets in their height above the surface area. For example, shows Fig. 6 the reflective surface area 50 of a security element 12 in cross section, in which the facets shown in the cutout 52 all have the same inclination, but are offset in aperiodischer, in particular in an irregular manner by a height offset between zero and at least half a wavelength from its regular starting position. As a result, the path differences between different facets 52-j, 52-k are changed in an irregular manner by a value between zero and at least one entire wavelength. The light beams 54-j and 54-k reflected by the different facets 52-j, 52-k are then in a random phase relationship so that the array of facets 52 does not act as a diffractive structure, despite a periodic arrangement of equally aligned facets 52 and therefore no disturbing secondary diffraction effects occur.

FIG. 7 schematically illustrates the mirror reflexes and the dispersion effect occurring during tilting on the basis of the representation of the value 16 of FIG Fig. 1 , Regarding Fig. 7 (a) the numerical value 16 appears with vaulted numerals 60 clearly protruding from the xy plane of the surface region 20. The inner numerical regions appearing white in the figure represent bright mirror reflections 62, which convey to the observer the illusion of a surface curving towards him. This illusion is reinforced by the apparent movement of the mirror reflexes 62 when tilting about one of the tilting axes 70, 72. As in Fig. 7 (b) represented, the mirror reflections 62 when tilting about the horizontal tilt axis 70 in the figure move upwards or when tilting in the opposite direction down and behave so as well as the mirror reflections on the imitated three-dimensional surface. In the same way, when tilted, the mirror reflexes 62 travel to the right about the tilting axis 72 perpendicular in the figure or to the left when tilting in the opposite direction, as in FIG Fig. 7 (c) shown and behave like the mirror reflexes on the imitated three-dimensional surface.

In addition to this movement of the SLRs 62, which is caused by the colorless and bright reflections in the 0th diffraction order, the grating patterns 34 of the facets 32 in the first and the higher diffraction orders produce colored reflections 64 FIGS. 7 (b) and 7 (c) illustrated, the colored reflections 64 are more pronounced due to the particular orientation of the grid pattern 34 when tilted about the horizontal tilt axis 70 in the vertical areas 66 of the mirror reflexes 62 and are more pronounced when tilted about the vertical tilt axis 72 in the horizontal areas 68 of the mirror reflections 62. Such colored reflections 64 usually occur with polished transparent objects and therefore suggest to the viewer the presence of corresponding objects. By the appealing and impressive visual impact increases the attention and recognition value and thus also the forgery security of the security element 12.

LIST OF REFERENCE NUMBERS

10

bill

12

security element

14

brilliant motive

16

value number

20

reflective surface area

30

pixel

32

reflective facets

34

diffractive grid pattern

36

gridlines

38

carrier

40

arched area

42

Reflection of directional light

44

contour

50

reflective surface area

52, 52-j, 52-k

facets

54-y, 54-k

reflected light rays

50

reflective surface area

52, 54

subregions

60

digits

62

mirror reflections

64

colored reflections

66

vertical areas

68

horizontal areas

70, 72

tilting axes

Claims (18)

An optically variable security element for securing valuables, comprising a support having a reflective surface area whose extent defines an xy plane and a z axis perpendicular thereto,
characterized in that the reflective surface area contains a plurality of reflective pixels, each having one or more equally oriented reflective facets, an orientation of each facet relative to the xy plane being determined by the indication of its normalized normal vector, - The reflective facets are oriented so that the reflective surface area is perceptible to an observer as compared to its actual spatial form and / or receding surface, and - At least a part of the facets is provided with a diffractive grating pattern of a plurality of grid lines whose grating vector is parallel to the cross product of the unit vector in the z-direction with the normal vector of the respective facet. A security element according to claim 1, characterized in that of the facets lying parallel to the xy plane at least one part is provided with a diffractive grating pattern of a plurality of grating lines whose grating vector is substantially parallel to the grating vectors of the grating patterns of adjacent facets. Security element according to claim 1 or 2, characterized in that the reflective facets are oriented such that the reflective surface area is perceptible to a viewer as a curved, in particular continuously curved surface, preferably as a curved in two spatial directions, in particular continuously curved surface is perceptible. A security element according to at least one of claims 1 to 3, characterized in that the lattice patterns of the reflective facets in the first and possibly higher orders of diffraction produce colored reflections perceptible to a viewer as a dispersion of a transparent material such as glass or diamond. A security element according to at least one of claims 1 to 4, characterized in that the inclination of the reflective facets against the xy plane has no dominant preferential direction, in particular that there is no plane perpendicular to the xy plane, in which more than 80% of the Normal vectors of the reflective facet lie. A security element according to at least one of claims 1 to 5, characterized in that the diffractive grating patterns have a grating period between 0.3 μm and 4 μm, preferably between 0.6 μm and 3 μm. A security element according to at least one of claims 1 to 6, characterized in that all the grating patterns of the surface area have the same grating period. Security element according to at least one of claims 1 to 7, characterized in that the facets are formed substantially as planar surface elements. Security element according to at least one of claims 1 to 8, characterized in that the reflective facets are arranged in a periodic grid and in particular form a sawtooth grid. Security element according to at least one of claims 1 to 8, characterized in that the reflective facets are arranged aperiodically. A security element according to at least one of claims 1 to 10, characterized in that the facets are aperiodically offset in height from each other over the surface area. A security element according to at least one of claims 1 to 11, characterized in that the lattice-patterned facets in the direction of the lattice vector of the lattice pattern have a dimension of 10 μm or more, preferably 20 μm or more, particularly preferably 30 μm or more, and / or that the facets in the direction perpendicular to the grating vector have a dimension between 5 μm and 30 μm, preferably between 7.5 μm and 15 μm, and / or that the height of the facets is between 0 and 10 μm, preferably between 0 and 5 microns. Security element according to at least one of claims 1 to 12, characterized in that the reflective facets a metallic or semiconducting coating, a high-refractive coating or a coating with a color-shifting layer. Security element according to at least one of claims 1 to 13, characterized in that a part of the facets is formed without a diffractive grid pattern. A security element according to at least one of claims 1 to 14, characterized in that at least a part of the reflective facets is formed with an outline having in the direction of the grating vector of the grating pattern at least one boundary line which is perpendicular to the grating lines of the grating pattern. Security element according to at least one of claims 1 to 15, characterized in that at least a part of the pixels is formed with an outline in the form of a motif, in particular in the form of characters or symbols. Data carrier with a security element according to at least one of claims 1 to 16. A method of manufacturing an optically variable security element according to any one of claims 1 to 16, wherein a support is provided and provided with a reflective surface area, the extent of which defines an xy plane and a z axis perpendicular thereto, wherein the reflective area is formed with a plurality of reflective pixels, each having one or more similarly oriented reflective facets, wherein an orientation of each facet relative to the xy plane is determined by the indication of its normalized normal vector, - The reflective facets are oriented so that the reflective surface area is perceptible to an observer as compared to its actual space shape and / or receding surface, and - At least a portion of the facets is provided with a diffractive grating pattern of a plurality of grid lines whose grating vector is parallel to the cross product of the unit vector in the z-direction with the normal vector of the respective facet.

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