WO2024056130A1 - Optical security element having effect regions - Google Patents

Abstract

The invention relates to an optical security element (12) for protecting value items, comprising at least two effect regions (14, 16) for generating different optical effects, wherein the effect regions border one another along a borderline. According to the invention, the effect regions (14, 16) each consist of a plurality of pixel elements (34; 36) and a dithered transition region (20) is formed along the borderline between a first effect region (14) and a second effect region (16), in which transition region the area percentage of the pixel elements (34) of the first effect region (14) reduces from 100% to 0% and the area percentage of the pixel elements (36) of the second effect region (16) increases from 0% to 100%, so that, in the transition region, when viewed, the optical effect of the first effect region transitions smoothly into the optical effect of the second effect region. At least one of the two effect regions can be formed by a micromirror region having directional reflective micromirrors.

Description

Optical security element with effect areas

The invention relates to an optical security element for securing valuables with at least two effect areas for producing different optical effects. The invention also relates to a data carrier with such a security element, as well as a method for producing such a security element.

Data carriers, such as valuables or identification documents, but also other valuables, such as branded items, are often provided with security elements for security purposes, which allow the authenticity of the data carrier to be checked and which at the same time serve as protection against unauthorized reproduction.

A combination of several different optical effects is often used to increase the anti-counterfeit security of an optical security element. If effect areas with different optical effects border one another, a boundary line is defined between the effect areas. This boundary line can serve the viewer as a reference for register fluctuations that arise in other work processes. Such fluctuations can have an irritating effect on a viewer. In addition to a lower visual attractiveness, the security against forgery of the optical security element is also reduced, since counterfeits in particular often have register errors and it is therefore more difficult to reliably distinguish between the original and the counterfeit when register fluctuations occur in originals.

Proceeding from this, the invention is based on the object of providing an optical security element of the type mentioned at the outset with a high level of protection against forgery and an attractive visual appearance. This task is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

The invention provides an optical security element for securing valuables, with at least two effect areas for generating different optical effects, the effect areas adjoining one another along a boundary line. In particular, at least one of the two effect areas can be formed by a micromirror area with directionally reflecting micromirrors.

The effect areas each consist of a large number of pixel elements. A dithered transition area is formed along the boundary line between a first effect area and a second effect area, in which the area share of the pixel elements of the first effect area decreases from 100% to 0% and the area share of the pixel elements of the second effect area increases from 0% to 100%, so that in the transition area when viewed, the optical effect of the first effect area smoothly transitions into the optical effect of the second effect area.

In an advantageous embodiment, the at least two effect areas are formed by micromirror areas with directionally reflecting micromirrors and different micromirror effects. In particular, one of the micromirror areas can be metallized and another of the micromirror areas cannot be metallized, for example demetalized after metallization. In another, also advantageous embodiment, one of the effect areas is formed by a micro mirror area with directed reflecting micro mirrors and another of the effect areas is formed by a diffractive relief structure, in particular a hologram, a holographic grid image or a hologram-like diffraction structure.

In all designs it can advantageously be provided that the micromirror region(s) each contain non-diffractive mirrors and preferably flat mirrors, concave mirrors and/or Fresnel-like mirrors.

The effect areas preferably each consist of a large number of pixel elements of the same shape, in particular square or rectangular pixel elements. Preferably, the pixel elements have a maximum dimension that is between 1 gm and 100 gm. The pixel elements themselves are therefore not visible to the naked eye, so that despite the discrete division of the transition area into pixel elements, a smooth transition is created for the viewer.

The pixel elements advantageously fill the effect areas and the transition area completely without gaps, thus forming a tiling of the layer.

In an advantageous development, it is provided that one of the effect areas forms an outer effect area which surrounds another of the effect areas, which forms an inner effect area, and the boundary line is formed by the outline of the inner effect area. In particular, two effect areas can be provided, with one effect area surrounding the other effect area. The width of the transition region is expediently between 50 gm and 50 mm, preferably between 50 mm and 10 mm, particularly preferably above the resolution limit of the human eye and in particular between 0.5 mm and 5 mm.

The invention also contains a data carrier with an optical security element of the type described. The data carrier can in particular be a document of value, such as a banknote, in particular a paper banknote, a polymer banknote or a film composite banknote, a share, a bond, a certificate, a Voucher, a check, a seal, a tax stamp, a high-quality admission ticket, but also an identification card, such as a credit card, a bank card, a cash payment card, an authorization card, an ID card or a passport personalization page.

The security elements described can be present as a separate security element that is applied to a data carrier to be secured, but they can also be part of the data carrier to be secured itself.

The invention further contains a method for producing an optical security element of the type described, in which at least two effect areas are generated on a carrier for generating different optical effects, which border one another along a boundary line, and the effect areas are each formed from a large number of pixel elements and A dithered transition area is formed along the boundary line between a first effect area and a second effect area, in which the area share of the pixel elements of the first effect area decreases from 100% to 0% and the area share of the pixel elements of the second effect area increases from 0% to 100%, so that in the transition area the optical effect of the first effect area merges smoothly into the optical effect of the second effect area when viewed.

Preferably, at least one of the two effect areas is formed by a micromirror area with directionally reflecting micromirrors.

In an advantageous procedure, the dithered transition region is calculated using a dither algorithm, in particular a threshold algorithm, a random dither algorithm, a pattern dither algorithm, ordered dithering or with an error diffusion algorithm.

Advantageous examples of ordered dither processes are halftone dithering, Bayer matrix and void-and-cluster. Advantageous examples of error diffusion algorithms are the Floyd-Steinberg algorithm, minimized average error, Stucki, Burkes, Sierra, two-row Sierra, Filter Lite, Atkinson or gradient-based error diffusion algorithms.

To generate the dithered transition region, a continuous course of the size of the transition region is preferably generated, which begins and ends with a discrete value that is assigned to one of the different effect regions, the continuous course is reduced to a desired number of discrete values using a dither algorithm, where each discrete value is assigned to one of the different effect areas, and Each pixel position in the transition area is assigned a pixel element of the assigned effect area in accordance with the discrete value determined for this pixel position in the dither algorithm.

The continuous course is advantageously monotonous, in particular strictly monotonous. The continuous course can be linear, for example, but also non-linear, for example quadratic or following a tanh function.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, which are not reproduced to scale and proportions in order to increase clarity.

Show it:

1 shows a schematic representation of a banknote with a security element according to the invention with two effect areas adjoining one another along a boundary line,

2 in (a) a detailed view of a security element according to the invention with a transition area with perfect alignment of the two effect areas and in (b) a security element not according to the invention without a transition area, 3 in (a) a detailed view of a security element according to the invention with a typical position deviation of the effect areas and in (b) a security element not according to the invention without a transition area,

4 shows a detailed section of the transition area between the two effect areas, as well as even more enlarged sections of the first effect area, the transition area and the second effect area with the pixel elements,

5 illustrates a security element in which the first effect area is formed by a metallized micro-mirror area and the second effect area is formed by a demetallized micro-mirror area, whereby (a) the design is given, (b) as a comparative example, a security element not according to the invention without a transition area and ( c) shows a security element according to the invention with a transition area.

The invention will now be explained using the example of security elements for banknotes. Figure 1 shows a schematic representation of a banknote 10 with a security element 12 according to the invention.

The security element 12 contains two effect areas 14, 16 for generating different optical effects, which adjoin one another along a boundary line 18. In the exemplary embodiment, the effect areas 14, 16 are formed by micromirror areas with directionally reflecting micromirrors which show different micromirror effects. For example, the effect area 14 shows a 3D effect, while the effect area 16 shows a motion effect. As a special feature, a transition area 20 is formed along the boundary line 18 in the two effect areas 14, 16, in which the optical effect of the first effect area 14 smoothly transitions into the optical effect of the second effect area 16 when viewed.

The two different effect areas 14, 16 typically have certain register fluctuations compared to (structural) features generated in other operations, which, however, are concealed by the transition area. As described above, conventional designs often have the problem that register fluctuations reveal weaknesses in production processes and that the visible positional deviations of the effect areas have an irritating effect on a viewer.

These difficulties are overcome by providing a flowing, soft transition between the two effect areas 14, 16, as explained in more detail with reference to Figures 2 to 4.

First, Fig. 2(a) shows a detailed view of the security element 12 with the effect areas 14, 16 and a transition area 20 formed along the boundary line 18 with the idealized assumption of a perfect alignment of the two effect areas 14, 16, in the present case, for example, an orientation in which the Border line 18 between the effect areas is exactly at the height of the structural feature 22 in accordance with the design specification. For comparison, Fig. 2(b) shows a security element 12' not according to the invention without a transition region with such an idealized, perfect alignment of the boundary line 18' to the structural feature 22. 3(a) then shows the security element 12 of FIG. 2(a) with a typical position deviation A of the effect areas 14, 16 relative to the structural feature 22, which occurs in a separate operation due to the inevitable register fluctuations when producing the structural feature 22. Figure 3(b) again shows, for comparison, a security element 12' not according to the invention without a transition area with the same position deviation A.

Due to the design of the transition region 20 described in more detail below, the optical effect of the first effect region 14 flows smoothly into the optical effect of the second effect region 16. The designs of FIGS. 2(a) and 3(a) therefore do not have a sharp boundary between the two optical effects, so that visually there is no fixed reference point for the correct position of the structural feature 22. The differences between the idealized, perfectly aligned position of FIG. 2(a) and a position typically occurring in reality according to FIG. 3(a) are therefore small and are not disturbing when viewed.

In contrast, the misalignment of the sharp boundary line 18' with the structural feature 22 in the comparative security element 12' of Figure 3(b) is due to the clearly visible position of the boundary line 18' compared to the perfectly aligned position of Figure 2(b). clearly noticeable and leads to the adverse effects mentioned above.

The creation of the transition area 20 between the two effect areas 14, 16 is illustrated in more detail in FIG is shown. The two effect areas 14, 16 each consist of a plurality of square pixel elements 34 and 36, respectively, with the pixel elements 34 of the effect area 14 producing a 3D effect as the first optical effect, and the pixel elements 36 of the effect area 16 producing a movement effect as the second optical effect. In the exemplary embodiment, each pixel element 34, 36 is formed by only a single micromirror, but in other designs the pixel elements can also each consist of a group of several, in particular identically aligned, micromirrors. The size of the pixel elements is below the resolution limit of the human eye, for example 10 |im x 10 m.

In the overview sketch of the right half of Fig. 4, for the sake of simplicity, the pixel elements 34 of the first effect area 14 are shown in white, the pixel elements 36 of the first effect area 16 are shown in black, while the pixel elements in the more enlarged sections correspond to the generation of the first and second optical Effect with wide hatching (pixel elements 34, first optical effect) or with narrow hatching (pixel elements 36, second optical effect) are shown.

A transition region 20 of a width B is formed along the boundary line 18 in the effect areas 14, 16, in which the surface area of the pixel elements 34 of the first effect region 14 decreases from 100% to 0% in a direction 32 perpendicular to the boundary line 18 by a dither process and the Area proportion of the pixel elements 36 of the second effect area 16 increases from 0% to 100%. Due to the small dimensions of the pixel elements 34, 36, they cannot be seen separately when viewed. Rather, the optical effect of the first effect area 14 is lost to the viewer. along the direction 32 flowing into the optical effect of the second effect area 16. The width B of the transition region 20 can be, for example, a few tenths of a millimeter or even a few millimeters.

In order to make the surface area of the pixel elements in the transition area decreasing or increasing as described, a dither method originally from image processing is used, which controls the occupancy of each pixel position in the area of the security element 12 with one of the pixel elements 34, 36 of the first or second effect area . The procedure is explained in detail below using the Floyd-Steinberg algorithm as an example, but it is understood that other dither algorithms can also be used accordingly.

Specifically, for example, the size of the finished security element should be 10 mm x 10 mm and the size of the pixel elements 34, 36 should each be 10 gm x 10 |im, so that the security element consists of 1000 x 1000 pixel elements. A horizontal boundary line at y = 5 mm is intended to separate a first effect area 14, which extends from y = 0 to the boundary line, from a second effect area 16, which extends from the boundary line to y = 10 mm. In order to conceal register fluctuations, a transition area with a width of B = 2 mm should be created around the boundary line, in which a soft transition between the optical effects of the effect areas 14, 16 can be seen.

The security element 12 then contains 1000 pixel elements in the x and y directions, whereby the transition area in the y direction, expressed in pixel elements, should extend from ymin = 400 to ymax = 600. For the sake of simplicity, a linear transition is created here. Specifically, a default field V(x,y) is initialized in pseudocode as follows: for y = 1 to 1000 for x = 1 to 1000 if y < 400 then V(x,y) = 0; else if y > 600 then V(x,y) = 1; else V (x, y) = (y-400)/200;

The default field is initialized for all 1000 x 1000 pixel elements so that it is equal to 0 in the first effect area when y < 400, equal to 1 in the second effect area when y > 600, and in a transition area that has a width of 200 in the y direction Pixels (corresponding to 2 mm), grows linearly from 0 to 1. For example, V(x, 450) = (450-400)/200 = 0.25, V(x, 500) = (500-400)/200 = 0.5 and V(x, 550) = (550- 400)/200 = 0.75, each for all values x = 1...1000.

In order to only obtain the discrete values 0 and 1 in the transition range between 400 and 600, a dither process, in this case the Floyd-Steinberg algorithm, is applied to the default field V(x,y). In pseudocode: for y = 1 to 1000 for x = 1 to 1000 initialV alue = V (x,y ) ; newValue = findClosestValue(initialValue);

V(x,y) = newValue; quantizationError = initialValue - newValue;

V(x+l,y) = V(x+l,y) + quantizationError x 7 /16;

V(x-1, y+1) = V(xl,y+l) + quantizationError * 3 /16; V(x, y+1) = V(x, y+1) + quantizationError * 5 /16;

V(x+1, y+1) = V(x+l,y+l) + quantizationError * 1 /16; where findClosestV alue (val) = 1 if val > 0.5

= 0, else.

As can be seen from the pseudocode, in the Floyd-Steinberg algorithm all 1000 x 1000 pixels in the security element are scanned and by applying the function findClosestV alue() each pixel is set to either the value 0 or the value 1 according to the value of initialValue.

The quantization error (“quantizationError”) generated by this discretization is distributed proportionately to four neighboring pixels that have not yet been treated. The average value of the pixels therefore remains essentially unchanged. After running through the Floyd-Steinberg algorithm, the default field V(x,y) only contains the values 0 and 1, whereby in the transition area the area density of the pixels with V(x,y) = 0 decreases linearly from 100% to 0% , while the area density of the pixels increases linearly from 0% to 100% with V(x,y) = 1.

Then, in a further step, all 1000 x 1000 pixel positions of the security element 12 are gone through and a pixel element 34 with the first optical effect is generated at a pixel position (x,y) when V(x,y) = 0, and a pixel element 36 with the second optical effect is generated when V(x,y) = 1. The dither algorithm ensures that V(x,y) is either 0 or 1 for each pair of values (x,y) after applying the dither algorithm. In the first effect area 14 V(x,y) is always 0, in the second effect area 16 V(x,y) is always 1, and in the transition area the density of the pixel elements with V(x,y) = 0 increases from 100% to 0%, while the density of the pixel elements with V(x,y) = 1 increases accordingly from 0% to 100%.

Correspondingly, in the finished security element, the area share of the pixel elements 34 of the first effect area 14 in the transition area decreases from 100% to 0%, while the area share of the pixel elements 36 of the second effect area increases from 0% to 100%, as illustrated in Fig. 4.

Unlike image processing, in which gray levels are simulated as real intermediate tones between white and black using a dither process, in the present designs there are no intermediate levels between the first and second optical effects whose appearance could be simulated. The two optical effects can even be completely dissimilar and even incompatible with each other. In the present case, the dither process creates a smooth transition between two different, discrete optical effects.

5 shows a further exemplary embodiment in which the first effect area is formed by a metallized micromirror area 54 and the second effect area is formed by a demetallized micromirror area 56. For illustration, Fig. 5(a) shows the design specification of an idealized, star-shaped demetallization 46 within a surrounding metallized area 44. 5(b) shows, as a comparative example, a security element 52' not according to the invention without a transition region, i.e. with a sharp boundary 58' and with a certain register fluctuation of the demetallization 56' within the metallized region 54'. As illustrated in Fig. 5(b), the occurrence of the register fluctuations is clearly noticeable to an observer due to the irregular star shape and the sharply defined boundary 58'.

5(c) finally shows a security element 52 according to the invention, in which a dithered transition region 60 is formed at the boundary line between the demetallized micro-mirror region 56 and the metallized micro-mirror region 54.

The dithered transition region can, for example, have a width of 1 mm and, as described above, can have been calculated from a linear transition using the Floyd-Steinberg algorithm. In this case, the pixel elements of the first and second effect areas are formed by metallized micromirror elements or by demetallized micromirror elements.

This results in a smooth, flowing transition between the metallized region 54 and the demetallized region 56, which conceals the presence of register fluctuations, as illustrated in FIG. 5(c).

Reference symbol list

10 banknote

12 security element

12' comparison example

14, 16 effect areas

18 boundary line

18' boundary line in the comparison example

20 transition area

22 structural feature

30 detailed section

32 Direction perpendicular to the boundary line

34, 36 pixel elements

44 metallized area in design specification

46 Demetallization in design specification

52 security element

52' comparison example

54 metallized micromirror area

54' metallized area in the comparative example

56 demetallized micromirror area

56' demetallization in the comparative example

58' sharply defined border in the comparison example

60 transition area

Claims

P atent claims 1. Optical security element for securing valuables, with at least two effect areas for generating different optical effects, the effect areas adjoining one another along a boundary line, characterized in that the effect areas each consist of a plurality of pixel elements and that along the boundary line between a first effect area and a second effect area, a dithered transition area is formed, in which the area share of the pixel elements of the first effect area decreases from 100% to 0% and the area share of the pixel elements of the second effect area increases from 0% to 100%, so that in the transition area when viewing the optical effect of the first effect area flows smoothly into the optical effect of the second effect area. 2. Optical security element according to claim 1, characterized in that at least one of the two effect areas is formed by a micromirror area with directionally reflecting micromirrors. 3. Optical security element according to claim 2, characterized in that the at least two effect areas are formed by micromirror areas with directionally reflecting micromirrors and different micromirror effects. 4. Optical security element according to claim 3, characterized in that one of the micro mirror areas is metallized and another of the micro mirror areas is not metallized, in particular demetallized. 5. Optical security element according to claim 2, characterized in that one of the effect areas is formed by a micromirror area with directed reflecting micromirrors and another of the effect areas is formed by a diffractive relief structure, in particular a hologram, a holographic grid image or a hologram-like diffraction structure. 6. Optical security element according to at least one of claims 2 to 5, characterized in that the micromirror region(s) each contain non-diffractive mirrors and preferably plane mirrors, concave mirrors and/or Fresnel-like mirrors. 7. Optical security element according to at least one of claims 1 to 6, characterized in that the effect areas each consist of a large number of pixel elements of the same shape, in particular square or rectangular pixel elements. 8. Optical security element according to at least one of claims 1 to 7, characterized in that the pixel elements fill the effect areas and the transition area completely. 9. Optical security element according to at least one of claims 1 to 8, characterized in that the pixel elements have a maximum dimension which is between 1 gm and 100 gm. 10. Optical security element according to one of claims 2 to 9, characterized in that each pixel element of the at least one The effect area formed by a micromirror area with directed reflecting micromirrors consists of a single micromirror or a group of several micromirrors. 11. Optical security element according to at least one of claims 1 to 10, characterized in that one of the effect areas forms an outer effect area which surrounds another of the effect areas, which forms an inner effect area, and the boundary line is formed by the outline of the inner effect area. 12. Optical security element according to at least one of claims 1 to 11, characterized in that the width of the transition region is between 50 μm and 50 mm, preferably between 50 gm and 10 mm, particularly preferably above the resolution limit of the human eye and in particular between 0. 5 mm and 5 mm. 13. Data carrier with an optical security element according to one of claims 1 to 12. 14. A method for producing an optical security element according to one of claims 1 to 12, in which at least two effect areas are generated on a carrier for generating different optical effects, which border one another along a boundary line, and the effect areas are each formed from a plurality of pixel elements and a dithered transition area is formed along the boundary line between a first effect area and a second effect area, in which the area share of the pixel elements of the first effect area decreases from 100% to 0% and the area share of the pixel elements of the second effect area increases from 0% to 100%, so that in the transition area the optical effect of the first effect area merges smoothly into the optical effect of the second effect area when viewed 15. The method according to claim 14, characterized in that at least one of the two effect areas is formed by a micro mirror area with directionally reflecting micro mirrors. 16. The method according to claim 14 or 15, characterized in that the dithered transition area using a dither algorithm, in particular a threshold algorithm, a random dither algorithm, a pattern dither algorithm, ordered dithering or with an error diffusion algorithm is calculated. 17. The method according to at least one of claims 14 to 16, characterized in that to generate the dithered transition area, a continuous course of the size of the transition area is generated, which begins and ends with a discrete value that is assigned to one of the different effect areas, the continuous Course is reduced to a desired number of discrete values using a dither algorithm, each discrete value being assigned to one of the different effect areas, and each pixel position in the transition area corresponding to the discrete value determined for this pixel position in the dither algorithm with a pixel element of the assigned one effect area is occupied.