CN111757812A - Optically variable security element with reflective surface area - Google Patents

Abstract

The invention relates to an optically variable security element (12) for protecting valuable items, having a carrier (22) with a reflective surface area (20), the extent of which defines an x-y plane and a z-axis perpendicular to the x-y plane, wherein the reflective surface area (20) comprises a plurality of reflective sub-areas (30) and each sub-area (30) has a plurality of identically oriented reflective edge faces (32), and the orientation of each edge face (32) relative to the x-y plane is determined by data of a normalized normal vector (n) thereof, the projection of which normal vector into the x-y plane defines an inclination direction (r) of the edge face, the length (L) of the edge face is the dimension of the edge face in the inclination direction, the width (B) of the edge face is the dimension of the edge face perpendicular to the inclination direction in the x-y plane, the height (H) of a facet is the dimension of the facet in the z-direction. According to the invention, in the reflective partial regions (30), the identically oriented facets (32) are arranged with a reduced length (L) and a reduced height (H) in the common inclination direction (r) thereof.

Description

Optically variable security element with reflective surface area

The invention relates to an optically variable security element for protecting valuable items, comprising a carrier with a reflective surface area, which comprises a plurality of reflective subregions, wherein each subregion has a plurality of identically oriented reflective facets.

Data carriers, such as value or certificate documents, or other valuable items, such as branded goods, are often provided with security elements in order to achieve protection, which enable verification of the authenticity of the data carrier and at the same time serve as protection against impermissible imitation.

Security elements with a viewing-angle-dependent or three-dimensional appearance have a special effect on the protection of authenticity, since they cannot be reproduced even with the most modern copy machines. For this purpose, the security element is equipped with optically variable elements which give the viewer different image impressions at different viewing angles and, for example, display different color or brightness impressions and/or different graphic patterns depending on the viewing angle. In the prior art, for example, motion effects, pump effects, depth effects, relief effects or flip effects are referred to as optically variable effects, which are realized by means of holograms, microlenses or micromirrors.

Hologram-based optically variable elements are widely used, but their attractiveness and identifiability is impaired due to their relatively low gloss and diffractive color separation of the reflected light. Furthermore, it is less forgery-proof due to its relative ease of manufacture compared to security elements based on microlens or micromirror structures.

The above-described optically variable effect achieved by means of microlenses allows good visibility without being affected by illumination. However, the microlens structure mostly results in a large layer thickness of the security element. The manufacture of microlens-based authenticity features also presents some technical challenges: in the pattern layer under the lens layer, a pattern as large as only a few micrometers must be displayed with high quality, and not only the lens layer but also the pattern layer must be manufactured with high grid accuracy. In practice, at present, only periodic patterns, the size of which is limited to a few millimeters, can be generated in most cases. Here, the representation of the symbols is usually slightly distorted and blurred, which reduces the identification value of the security element.

An attractive variant design is therefore to achieve optically variable effects by means of micromirrors, which are technically less complex and which make it possible to achieve large-area and sharp patterns in flat security elements. The brightness and the gloss of the micromirror structure are particularly important here for good perceptibility and appealing visual impression.

At present, micromirror devices are produced in security elements, for example, in that the desired effect surface is divided into identical pixels of dimensions of, for example, 20 μm by 20 μm, each pixel corresponding to a mirror slope (german: Spiegelsteigung), i.e. it is determined in which way the micromirror of a pixel is tilted with respect to the plane of the substrate layer, and the pixel is then filled with a wedge-shaped micromirror of the corresponding mirror slope. The micromirror has a fixed base surface, usually 10 μm x 10 μm. An example of a similar design is described in document EP 2390106B 1. A disadvantage in this design, however, is that the periodic arrangement of the micromirrors often results in undesirable diffraction effects and colored light reflections, which interfere with the truly desired achromatic appearance of the micromirror device.

Aperiodic arrangements of micromirrors are also known and described, for example, in document WO 2012/055505 a 1. In a non-periodic arrangement, diffraction effects are avoided as much as possible, for which a greater number of micromirrors is generally required in order to fill a given surface area, which results in a lower area ratio of smooth mirror surfaces to (practically) rounded edge regions and thus in a reduced gloss.

On this basis, the object of the invention is to provide an optically variable security element of the type mentioned above, which avoids the disadvantages of the prior art and in which, in particular, high security against forgery is combined with high brightness and gloss.

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

In such a security element the extent of the reflective face region defines an x-y plane and a z-axis perpendicular to that plane. The orientation of each facet with respect to the x-y plane is determined by data from its normalized normal vector, wherein the projection of the normal vector into the x-y plane defines the direction of inclination of the facet. The dimension of the facets in the oblique direction is referred to as the length of the facet, the dimension of the facet in the x-y plane perpendicular to the oblique direction is referred to as the width of the facet, and the dimension of the facet in the z direction is referred to as the height of the facet. According to the invention, it is now provided in such a security element that in the reflected partial regions, the identically oriented facets are arranged with a reduced length and a reduced height in their common inclination direction.

This produces a faceted device that can produce the desired appearance of a panel with high brightness and gloss, but without periodicity at all. Due to the lack of periodicity, such facet devices are difficult to imitate and therefore have a strong resistance to forgery. At the same time, disruptive diffraction effects and the resulting colored light reflections are avoided, as a result of which a greater quantity of light is available for the desired reflection. The device proposed at present has the advantage over conventional non-periodic designs that only a small number of facets are required for filling the sub-regions. The larger associated surface with high brightness is produced mainly in flat facet inclinations. Additionally, the mutual shadowing effect is minimized by the reduced facet size in the oblique direction.

In a preferred embodiment, the identically oriented facets are arranged in their common inclination direction at least in a subset of the partial regions and decrease in length and height by the same constant factor. Specifically, the subsequent (k +1) th ridge surface in the oblique direction is obtained from the height and length of the k-th ridge surface in the oblique direction, and the formula is

H_k+1＝f*H_kAnd L is_k+1＝f*L_k

Wherein the factor f is smaller than 1, which is accordingly invariant for the entire sub-region. The invariant factors may also be the same for all sub-regions of the subset.

Advantageously, the invariant factor is between 0.6 and 0.95, preferably between 0.75 and 0.85. In an advantageous design, the equally oriented facets are arranged even in all sub-regions in the manner described above.

In a further, likewise advantageous embodiment, the identically oriented facets are arranged in their common inclination direction in each case at least in a subset of the partial regions and their height decreases from facet to facet by a constant height difference. Specifically, the subsequent (k +1) th ridge surface in the oblique direction is obtained from the height and length of the k-th ridge surface in the oblique direction, and the formula is H_k+1＝H_kThe length of each facet is derived from its height by the angle of inclination α, L_k＝H_kTan (α) the height difference Δ is constant for the whole sub-area, respectively, however it may even be the same for all sub-areas of the subset.

Advantageously, the constant height difference is between 50nm and 400nm, preferably between 80nm and 150 nm. In an advantageous embodiment, the equally oriented facets are arranged in all subregions in the manner described above.

In the variant with the constant factor or constant height difference, the height of the facets can additionally be varied with a small, respectively substantially randomly selected height variation, wherein the additional substantially random height variation is advantageously less than 5%, in particular less than 2%, of the initial height before the height variation. The length of the land is then adjusted accordingly to maintain the rake angle constant.

The expression chosen here, i.e. the height of the facets, changes with a substantially randomly chosen height variation, taking into account the fact that the random variation can also be implemented, for example, by means of computer-generated "random numbers" which are strictly deterministic.

The height of the facets of the reflective surface area preferably does not exceed the maximum height H_maxThe maximum height is less than 20 μm, preferably 10 μm or less, particularly preferably 5 μm or less. This can be achieved, for example, by configuring the first edge surface of the last of the sub-regions in the oblique direction to have a height which is less than or equal to the maximum height.

Advantageously, the identically oriented facets meet directly in a common direction of inclination. Alternatively, the facets may also be arranged at a smaller pitch in the x-y plane in the oblique direction. The distance between the edge faces is advantageously less than 10%, in particular less than 5%, of the average length of two adjoining edge faces.

The reflective partial regions expediently have a length in the common direction of inclination of the prism faces of less than 300 μm, preferably less than 100 μm, particularly preferably between 20 μm and 100 μm. The reflective subregions may have a square, rectangular contour, but may also have an arbitrary contour. In particular, at least a part of the reflected partial area can be formed with a contour in the form of a pattern, in particular a character or symbol. In the case of a general profile, it is expedient if the maximum dimension of the neutron region in the plane is less than 300 μm, preferably less than 100 μm, particularly preferably between 20 μm and 100 μm.

The width of the facets preferably occupies the maximum available width of the sub-regions, respectively. The edge surface shape advantageously follows the course of the edge of the partial region, which may also run obliquely or in a curved manner.

In the sub-regions of the reflection, eight or fewer, preferably five or fewer, in particular two, three or four, facets are advantageously arranged in a common oblique direction.

The reflective facets are advantageously oriented such that the reflective surface regions can be perceived by the observer as curved, in particular continuously curved, surfaces, preferably as curved, in particular continuously curved, surfaces in both spatial directions. Furthermore, it is advantageous if the reflective facets are oriented such that, when the security element is tilted or rotated, the reflective facets produce a displacement effect, a pump effect, a depth effect, a relief effect and/or a flip effect.

Advantageously, the reflecting facets have a metallic or semiconductive coating, a highly refractive coating or a coating with a layer which is discolored or tilted in color (German). The color-changing layer can be designed in particular as a thin-film system or as a thin-film interference coating. In this case, for example, a layer sequence of metal layer to dielectric layer to metal layer or a layer sequence of at least three dielectric layers can be realized, wherein the refractive index of the intermediate layer is lower than the refractive indices of the other two layers. As the dielectric material, for example, ZnS, SiO₂、TiO₂、MgF₂。

The discolored layer may also be configured as an interference filter, a semi-transparent thin metal layer with selective transmission by plasmon resonance effects, nanoparticles, or the like. The color-changing layer can likewise be realized as a diffractive relief structure or as a subwavelength grating.

Alternatively or additionally, the reflective surface area can be provided with a liquid crystal coating, preferably with a full-surface cholesteric liquid crystal coating.

The reflecting facets appear as substantially flat surface elements inclined with respect to the x-y plane, wherein the expression "substantially" takes into account that in practice it is not possible to produce perfectly flat surface elements in connection with manufacture. The facets of the sub-regions are all oriented in the same way, wherein small variations of a few percent of the inclination angle are possible. Preferably, the difference in inclination of the subregions is less than 3%, preferably less than 2%, in particular less than 1%.

The invention also comprises a data carrier with a security element of the type described. The data carrier is in particular a value document, for example a banknote, in particular a banknote, a polymer banknote or a film composite banknote, which may be a stock certificate, a bond, a certificate, a voucher, a check, a high-quality ticket, or a certificate card, for example a credit card, bank card, cash card, certificate, identity card or passport personal information page.

The invention also comprises a method for manufacturing a security element of the above-mentioned type, wherein,

providing a carrier and providing a reflective face region, the extent of the face region defining an x-y plane and a z-axis perpendicular to the x-y plane,

the reflective surface area is formed with a plurality of reflective sub-areas and each sub-area is formed with a plurality of identically oriented reflective facets,

-wherein the orientation of each facet with respect to the x-y plane is determined by data of its normalized normal vector, the projection of which into the x-y plane defines the direction of inclination of the facet, the length of the facet is the dimension of the facet in the direction of inclination, the width of the facet is the dimension of the facet in the x-y plane perpendicular to the direction of inclination, the height of the facet is the dimension of the facet in the z-direction, and

in the reflected subregions, the identically oriented facets are arranged with a reduced length and a reduced height in their common direction of inclination.

Further embodiments and advantages of the invention are explained below with reference to the drawings, which are not to scale and are shown to scale in order to improve readability.

In the drawings:

figure 1 shows a schematic representation of a banknote with an optically variable security element in the form of a transfer element affixed according to the invention,

figure 2 shows a diagram for realizing the three-dimensional appearance of the security element of figure 1,

fig. 3 shows a perspective view of a reflective partial region, which is filled with five successive facets,

fig. 4 shows in detail one of the facets of fig. 3, in order to visualize the dimensional definition describing the orientation and dimensions of the facet,

figure 5 shows in perspective view the sub-area inside the reflective surface area to be filled with facets,

figure 6 shows a vertical elevation of the panel and sub-regions of figure 5,

fig. 7 shows the height profile of the relief structure given by the facets of the sub-regions in a side view from the direction VII of fig. 6.

The invention will now be explained on the basis of an example of a security element for banknotes. To this end, fig. 1 shows a schematic representation of a banknote 10 having an optically variable security element 12 in the form of a transfer element affixed thereto according to the invention. Of course, however, 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 for protecting documents, identity cards, passports, credit cards, health cards, etc. In the case of banknotes and similar documents, for example, security elements in the form of security threads or security strips are considered in addition to transfer elements.

The security element 12 shown in fig. 1 is itself designed to be very flat and has a maximum height difference of about 10 μm, but also gives the observer a clear three-dimensional impression of the image presented, i.e. a high brightness and gloss figure 14 which appears to be raised from the plane of the banknote 10. The security element 12 for this purpose comprises a reflective surface area 20, the extent of which defines an x-y plane, which coincides here with the surface of the banknote 10. The z-axis is perpendicular to the x-y plane so that the coordinate system formed by these three axes constitutes the right hand system.

The specific structure of the optically variable security element according to the invention will now be explained in more detail with reference to fig. 2 to 4. First, fig. 2 shows an implementation of the three-dimensional appearance of the security element 12, wherein reference numeral 40 denotes a surface that is curved in two spatial directions, such as the numeral 14 of fig. 1, as perceived by an observer when observing the security element 12.

In this case, the curved surface 40 itself, which is perceived by the observer, is not formed in the carrier 22 of the security element 12, but rather the relief structure 24 has a plurality of small, reflective subregions 30, of which four subregions 30-1 to 30-4 are shown in the detail view of fig. 2. The partial regions 30 each have a plurality of reflective facets 32, which are each formed in the partial regions 30 so as to all have the same orientation.

For a more detailed illustration, fig. 3 shows a perspective view of a reflective partial region 30, which is filled with five successive edge surfaces 32-1 to 32-5. The facets 32-1 to 32-5 present substantially flat surface elements inclined with respect to the x-y plane. One of the facets 32 of fig. 3 is shown in more detail in fig. 4 to visually represent the dimensional definition describing the orientation and dimensions of the facet.

Referring first to fig. 4, the orientation of each facet 32 is determined by its data normalized normal vector n ═ (nx, ny, nz), where | n | ═ 1 and the z component is positive. The projection of the normal vector n into the x-y plane of the face region 20 defines the tilt direction r in the x-y plane. The tilt direction r is a vector lying in the x-y plane, the direction of which indicates the direction in which normally incident light is reflected by the facets 32. If the normal vector n should be perpendicular to the x-y plane in a subregion, the tilt direction of this subregion can be chosen arbitrarily in the x-y plane for the structure described below.

As shown in fig. 4, the dimensions of the facets 32 are now defined in terms of their respective directions of inclination r. The dimension of the facet in the oblique direction is referred to as the length L of the facet 32, the dimension of the facet in the x-y plane perpendicular to the oblique direction is referred to as the width B of the facet, and the dimension of the facet in the z direction is referred to as the height of the facet. As can be seen directly in FIG. 4, the angle of inclination α of the facets 32 with respect to the x-y plane is related to the length and height of the facets: tan (α) ═ H/L.

Referring to the illustration of fig. 2, in order to imitate the reflection properties of the cambered surface 40, the prism surfaces 32 of the surface regions 20 are exactly oriented in each subregion 30 such that their normal vector N corresponds there to the local normal vector N of the cambered surface 40 averaged over the extent of the subregion 30.

In the embodiment shown, the sub-regions 30 are designed with a square profile, but they may in general have any other profile shape, as shown in the embodiments of fig. 5 to 7 below. The edge length K or the maximum dimension of the partial region 30 in the x-y plane is less than 300 μm and in particular in the range from 20 μm to 100 μm.

The length L and width B of the facets 32 are greater than 3 μm, preferably greater than 5 μm, and the height of the facets is between 0 and 10 μm, preferably between 0 and 5 μm, so that the entire reflective surface area has a height difference of at most 10 μm, imperceptible to the naked eye.

Since the geometrical reflection condition "angle of incidence equal to reflection angle" for the reflection of the directed light 42 (fig. 2) depends only on the local orientation of the normal vectors of the reflective faces 40, 24 and, furthermore, the subregions 30 are small and therefore do not appear themselves, the reflective face region 20 with the relief structure 24 shows substantially the same reflection properties as the three-dimensional face 40 to be simulated and thus, despite its small height difference, produces a noticeable three-dimensional impression of the simulated face 40 for the observer.

The invention is now distinguished by the fact that the edge faces 32 are arranged particularly neatly in the partial regions 30, which leads to a high brightness and gloss of the surface region 20.

Since the facets 32 in the sub-regions 30 are each oriented identically, i.e. have the same inclination angle α and the same normalized normal vector, the inclination direction r projected into the x-y plane is the same for all facets 32 of the sub-regions 30, so that in each sub-region there is a common inclination direction of the facets as it were.

As fig. 2 and 3 show, the identically oriented facets 32 or 32-1 to 32-5 are arranged in the reflecting sub-region 30 in their common oblique direction r with a reduced height H and a reduced length L. For this purpose, it can be provided, for example, that the first (last) edge surface 32-1 of the partial region 30 in the oblique direction r has a desired maximum height H_maxAnd the following facets 32 in the direction of inclination r have respectively 80% of the height and 80% of the length of the preceding facets, since the height and the length of the facets 32 here always vary by the same factor, the inclination angle obtained by tan (α) ═ H/L remains unchanged.

To illustrate a specific numerical example, the first land 32-1 has an H for the desired inclination angle α of the face region of 30 °₁A height of 10 μm is taken as the maximum desired height. Its length L₁The relationship L is used from an inclination angle α of 30 °₁＝H₁Tan (α) gives L₁17.32 μm. The second land 32-2 directly abuts the first land 32-1 in the oblique direction, but has only H₂＝0.8*H₁Height of 8 μm, length L determined by inclination α₂＝H₂Tan (α) ═ 13.86 μm, where L also applies automatically according to the structure₂＝0.8*L₁. The third land 32-3 is directly adjacent to the second land 32-2 in the oblique direction, but has only H₃＝0.8*H₂Height of 6.4 μm and L from inclination α₃＝H₃A length of 11.08 μm/tan (α), where L also applies here₃＝0.8*L₂. Similarly, the other facets 32-4 and 32-5 haveH₄＝5.12μm，H₅Height of 4.1 μm and corresponding length L₄Or L₅. Length L₁To L₅The sum of which coincides with the edge length K of the sub-region 30. The width of the facets 32-1 to 32-5 is constant in the embodiment and coincides with the edge width K of the square sub-area 30.

This arrangement is completely without periodicity and therefore has a high anti-counterfeiting security and also a high gloss due to the absence of disturbing diffraction effects and colored light reflection. The gloss of the facet device is significantly improved compared to conventional non-periodic designs, since a larger associated facet can be achieved, in particular at smaller angles of inclination α. The mutual shadowing effect is also minimized by the reduced facet size in the oblique direction.

The arrangement of the facets 32 and the selection of the facet data for a generic, designed subregion 30 with an arbitrary contour are now explained in more detail with reference to fig. 5 to 7. First, fig. 5 shows a perspective view of the partial region 30 in the reflective surface region 20, which is filled with the prism surfaces 32. Starting from the local normal vector N of the curved surface 40 to be represented, a desired normalized normal vector N for the partial region 30 is obtained by averaging. The common inclination direction r for all facets of the sub-region 30 is derived from this normal vector n by projection into the x-y plane. The angle between the vectors n and r is here the complement of the angle of inclination α with respect to the edge surface, i.e. 90 ° in addition to the angle of inclination α. The inclination angle α is, for example, 30 ° in the partial region 30.

The facets 32 should now be arranged with a decreasing height and a decreasing length from back to front along a line 50 to the direction of inclination r. The terms "rear" and "front" are herein based on the direction of the vector r and are therefore always well defined. Referring to fig. 6, which shows the surface area 20 with the partial area 30 in a vertical plan view, first of all two tangents 52 are provided on the contour 34 of the partial area 30, which are perpendicular to the straight line 50 and whose spacing indicates the length L of the partial area 30 in the direction of inclination r_ges. In an embodiment, the spacing is, for example, L_ges＝55μm。

The desired maximum height for the edge surface is now specified, for example H _max10 μm and a scaling factor specifying the facet size for reduction, e.g., f 0.8. Then choose to have H₁＝H_maxAnd a corresponding length L is determined₁＝H₁And/tan (30 °) to 17.32 μm. Addition of a compound having H₂＝f*H₁And L₂＝f*L₁Has the same inclination angle α as the first facet, tan (α) ═ H, due to the choice of values for height and length₂/L₂＝H₁/L₁. In the examples, substantially H₂8 μm and L₂＝13.86μm。

Then adding facets that are respectively reduced by a scaling factor f until the sum of the facet lengths reaches or exceeds the sub-region L_gesLength of (d). In the embodiment after the addition of the fifth facets, since the sum of the facet lengths is

L_sum＝17.32μm+13.86μm+11.08μm+8.87μm+7.09μm＝58.22μm

Thereby exceeding the length L_ges＝55μm。

In order to arrange such a facet arrangement in the sub-region 30, the length and height are scaled to a desired overall length L_gesAnd all lengths and heights are multiplied to this end by an adjustment factor P-L_ges/L_sumWhere P is 55/58.22. This ensures

a) The facet arrangement fits exactly into the sub-region in the oblique direction r, since the scaled sum of the facet lengths is exactly L_ges。

b) Not exceeding the maximum height H_maxSince, according to design, the adjustment factor is always less than or equal to 1,

c) the inclination angle α does not change due to scaling, since the length L and the height H are multiplied by the same adjustment factor, so that the inclination angle resulting from the quotient (P × H)/(P × L) ═ H/L remains unchanged.

For example, in the illustrated embodiment, the height of first land 32-1 is H 'after scaling'₁＝P*H₁Length L'₁＝P*L₁16.36 μm. The dimensions of the other facets 32-2 to 32-5 are correspondingly respectively 0.8 times smaller than the preceding facet,namely H'₂7.56 μm and L'₂13.09 μm, etc. all facets have an inclination of α ═ 30 °, the sum of the facet lengths resulting from the scaling being exactly L_ges＝55μm。

With reference to fig. 6, a rectangle is filled with the facets 32-1 to 32-5 scaled in this way, which rectangle is defined by the two already mentioned tangents 52 and the two tangents 54 on the sub-region 30 parallel to the straight line 50. These facets are then confined to the interior of the sub-regions 30, so that only the sub-regions 30 are filled, but they are completely filled with said facets. In fig. 6, for the sake of illustration, the facets 32-1 to 32-5 are alternately shaded differently from the rear (upper left in fig. 6) to the front (lower right in fig. 6).

Fig. 7 shows the height variation of the relief structure 24 composed of facets 32-1 to 32-5, which shows a side view of the subregion 30 from the direction VII of fig. 6, i.e. in the oblique direction r and along the line 50 of fig. 6. The normalized normal vector n of the sub-region 30 is also drawn, which represents the initial point of the structure of the facets 32-1 through 32-5.

In varying the height of the relief structure 24, the absolute height of the relief structure 24 relative to the x-y plane changes, in addition to the corresponding dimension of the facets 32-1 through 32-5 in the z-direction. The facets are formed in the surface of the carrier such that the lowest point or the smallest height value of all the facets lies in one plane (parallel to the x-y plane) (the facets 32-1 to 32-5 are essentially flat surface elements inclined to the x-y plane).

If the respective peak or maximum (absolute) height values of all the facets 32-1 to 32-5 of the sub-region 30 are on the other hand at the same height or in a plane parallel to the x-y plane with respect to the x-y plane, which corresponds to the relief structure 24 shown in fig. 7 (or the reflecting boundary surface formed by the facets 32-1 to 32-5) viewed from the rear side, the facets 32-1 to 32-5 are arranged with increasing length and increasing height in their common direction of inclination. The mutual shadowing effect is also minimized in this arrangement.

List of reference numerals:

10 banknote

12 Security element

14 numbers with curved convex

20 reflective surface area

22 Carrier

24 relief structure

30 sub-region

30-1 to 30-4 sub-regions

32 facets

32-1 to 32-5 facets

34 profile

40 arched noodle

42 incident light

50 straight line

52 tangent line

54 tangent line

Claims (17)

1. An optically variable security element for protecting valuable articles, having a carrier with a reflective surface area, the extent of which defines an x-y plane and a z-axis perpendicular to the x-y plane, wherein

The reflective surface area comprises a plurality of reflective sub-areas and each sub-area has a plurality of identically oriented reflective facets, and

the orientation of each facet with respect to the x-y plane is determined by data of its normalized normal vector, the projection of which into the x-y plane defines the direction of inclination of the facet, the length of the facet being the dimension of the facet in the direction of inclination, the width of the facet being the dimension of the facet in the x-y plane perpendicular to the direction of inclination, the height of the facet being the dimension of the facet in the z-direction,

it is characterized in that the preparation method is characterized in that,

in the reflected subregions, the identically oriented facets are arranged with a reduced length and a reduced height in their common direction of inclination.

2. A security element according to claim 1, characterized in that the identically oriented facets are arranged in their common inclination direction at least in a subset of the sub-regions, respectively, and that the length and height of the identically oriented facets decrease by the same constant factor.

3. A security element according to claim 2, characterized in that said constant factor is between 0.6 and 0.95, preferably between 0.75 and 0.85.

4. Safety element according to at least one of claims 1 to 3, characterized in that the identically oriented facets are arranged in their common inclination direction at least in a subset of the sub-regions and the height of the identically oriented facets decreases from facet to facet with a constant height difference.

5. Security element according to claim 4, characterized in that said constant height difference is between 50nm and 400nm, preferably between 80nm and 150 nm.

6. Security element according to at least one of claims 1 to 5, characterised in that the height of the facets of the reflective surface area does not exceed the maximum height H_maxThe maximum height is less than 20 μm, preferably 10 μm or less, particularly preferably 5 μm or less.

7. Security element according to at least one of claims 1 to 6, characterized in that the identically oriented facets directly adjoin one another in a common oblique direction.

8. Security element according to at least one of claims 1 to 7, characterized in that the reflective partial regions have a length in the common direction of inclination of the prism faces of less than 300 μm, preferably less than 100 μm, particularly preferably between 20 μm and 100 μm.

9. Safety element according to at least one of claims 1 to 8, characterized in that the width of the identically oriented facets each occupies the maximum available width of a subregion, wherein the facet shape advantageously follows the edge course of the subregion.

10. Security element according to at least one of claims 1 to 9, characterized in that eight or less, preferably five or less, in particular two, three or four facets are arranged in the common oblique direction in the reflected sub-regions.

11. Security element according to at least one of claims 1 to 10, characterized in that at least a part of the reflective partial areas can be configured with a contour in the form of a pattern, in particular a character or symbol.

12. Security element according to at least one of claims 1 to 11, characterized in that the reflective edge surfaces are oriented such that the reflective surface areas can be perceived to the observer as curved, in particular continuously curved, surfaces, preferably as curved, in particular continuously curved, surfaces in both spatial directions.

13. Security element according to at least one of claims 1 to 12, characterized in that the reflective facets are oriented such that upon tilting or rotation of the security element the reflective facets produce a displacement effect, a pump effect, a depth effect, a relief effect and/or a flip effect.

14. Security element according to at least one of claims 1 to 13, characterized in that the reflective facets have a metallic or semiconducting coating, a highly refractive coating or a coating with a color-gradient layer.

15. Security element according to at least one of claims 1 to 14, characterized in that the reflective surface area is provided with a liquid crystal coating, preferably with a full-surface cholesteric liquid crystal coating.

16. A data carrier having a security element as claimed in at least one of claims 1 to 15.

17. Method for producing an optically variable security element according to one of claims 1 to 15, wherein

Providing a carrier and providing a reflective face region, the extent of the face region defining an x-y plane and a z-axis perpendicular to the x-y plane,

wherein the reflective surface area is formed with a plurality of reflective sub-areas and each sub-area is formed with a plurality of identically oriented reflective facets,

-wherein the orientation of each facet with respect to the x-y plane is determined by data of its normalized normal vector, the projection of which into the x-y plane defines the direction of inclination of the facet, the length of the facet is the dimension of the facet in the direction of inclination, the width of the facet is the dimension of the facet in the x-y plane perpendicular to the direction of inclination, the height of the facet is the dimension of the facet in the z-direction,

in the reflected subregions, the identically oriented facets are arranged with a reduced length and a reduced height in their common direction of inclination.

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