Optical security element with effect region

Abstract

The invention relates to an optical security element (12) for protecting articles of value, comprising at least two effect regions (14, 16) for producing different optical effects, said effect regions adjoining one another along a boundary line (18). According to the invention, the effect regions (14, 16) are each formed by a plurality of pixels (34; according to the invention, the first effect region (14) and the second effect region (16) consist of pixels (34, 36), and a dithered transition region (20) is formed along a boundary line between the first effect region (14) and the second effect region (16), in which transition region the area fraction of the pixels (34) of the first effect region (14) gradually decreases from 100% to 0% and the area fraction of the pixels (36) of the second effect region (16) gradually increases from 0% to 100%, the transition region is arranged so that the optical effect of the first effect region is smoothly transitioned into the optical effect of the second effect region in the transition region during observation. At least one of the two effect regions may be formed by a micromirror region having a directional reflective micromirror.

Description

[0001] The invention relates to an optical security element for protecting valuable articles, which has at least two effect areas for producing different optical effects. The invention also relates to a data carrier having such a security element and a method for producing such a security element.

[0002] Data carriers such as securities or identity documents and other valuable objects such as branded goods are often equipped with security elements which allow the authenticity of the data carrier to be verified and at the same time prevent unauthorized duplication.

[0003] Typically, a combination of several different optical effects is used to increase the counterfeit resistance of optical security elements. If effect areas with different optical effects are adjacent, a boundary line is defined between them. This boundary line can be used as a reference for the observer to detect register fluctuations that occur in other process steps. Such deviations can be disturbing to the observer. In addition to the reduced visual appeal, the counterfeit resistance of the security element is also reduced, because counterfeits often have alignment errors, and therefore it is difficult to reliably distinguish between originals and counterfeits when register fluctuations occur in the original.

[0004] Based on this, the technical problem to be solved by the present invention is to provide an optical security element of the aforementioned type with high anti-counterfeiting properties and an attractive visual appearance.

[0005] The technical problem is solved by the features of the independent claim. Improvements of the invention are the technical solutions of the dependent claims.

[0006] The present invention provides an optical security element for protecting valuable articles, which has at least two effect areas for producing different optical effects, wherein these effect areas are adjacent to each other along a boundary line. At least one of the two effect areas can be formed by a micromirror area with directional reflective micromirrors.

[0007] Here, the effect areas are respectively composed of a large number of pixels. A dithering transition area is formed along the boundary line between the first effect area and the second effect area, in which the area share of the pixels of the first effect area gradually decreases from 100% to 0%, and the area share of the pixels of the second effect area gradually increases from 0% to 100%, so that when observed, the optical effect of the first effect area smoothly transitions to the optical effect of the second effect area in the transition area.

[0008] In an advantageous embodiment, at least two effect regions are formed by micromirror regions with directional reflective micromirrors and different micromirror effects. One of these micromirror regions can be metallized in particular, and the other micromirror region is not metallized, in particular demetallized after metallization.

[0009] In another likewise advantageous embodiment, one of the effect regions is formed by a micromirror region having directional reflecting micromirrors and the other effect region is formed by a diffractive speckle structure, in particular by a hologram, a holographic grating image or a holographic-like diffractive structure.

[0010] In all embodiments, it can be advantageously provided that one or more micromirror regions each contain a non-diffractive mirror, preferably a plane mirror, a concave mirror and / or a Fresnel mirror.

[0011] Preferably, the effect area is composed of a large number of pixels of the same shape, in particular square or rectangular pixels. Preferably, the maximum size of the pixel is between 1µm and 100µm. Since the pixels themselves cannot be distinguished by the naked eye, the observer can still perceive a soft transition despite the discrete division of the transition area into pixels.

[0012] Advantageously, these pixels seamlessly fill the effect area and the transition area, respectively, thus forming a planar tessellation.

[0013] In an advantageous embodiment, one of the effect regions forms an outer effect region, which surrounds another effect region forming an inner effect region, and the boundary line is formed by the contour of the inner effect region. In particular, two effect regions can be provided, wherein one effect region surrounds the other effect region.

[0014] The width of the transition region is expediently between 50 μm and 50 mm, preferably between 50 μm and 10 mm, particularly preferably above the resolution limit of the human eye, in particular between 0.5 mm and 5 mm.

[0015] The invention also relates to a data carrier having the above-mentioned optical security element. The data carrier can be a valuable security such as a banknote, in particular a paper banknote, a polymer banknote or a composite film banknote, a stock, a bond, a certificate, a coupon, a check, a stamp, a tax stamp, a high-value ticket, or an identity document such as a credit card, a bank card, a cash card, an authorization card, an identity card or a personalized page of a passport.

[0016] The security element may be present as a separate security element which is arranged on the data carrier to be protected, or the security element may be a part of the data carrier to be protected itself.

[0017] The invention also relates to a method for producing an optical security element of the aforementioned type, wherein

[0018] - at least two effect areas for producing different optical effects are formed on the carrier, the effect areas adjoining each other along a boundary line, and

[0019] - The effect areas are respectively composed of a large number of pixels, and a dithering transition area is formed along the boundary line between the first effect area and the second effect area, in which the area share of the pixels of the first effect area gradually decreases from 100% to 0%, and the area share of the pixels of the second effect area gradually increases from 0% to 100%, so that when observed, the optical effect of the first effect area smoothly transitions to the optical effect of the second effect area in the transition area.

[0020] Preferably, at least one of the two effect regions is formed by a micromirror region having directional reflection micromirrors.

[0021] In an advantageous embodiment of the method, the dithering transition region is calculated using a dithering algorithm, in particular a threshold value algorithm, a random dithering algorithm, a pattern dithering algorithm, a sequential dithering algorithm or an error diffusion algorithm.

[0022] Advantageous examples of ordered dithering algorithms are halftone dithering, Bayer matrix and gap and clustering algorithms. Advantageous examples of error diffusion algorithms are Floyd-Steinberg algorithm, minimum mean error, Stucki, Burkes, Sierra, two-line Sierra, Filter Lite, Atkinson or gradient-based error diffusion algorithms.

[0023] Preferably, in order to generate a dithered transition region,

[0024] - generating a continuous change in the size of the transition region, said change starting and ending with a discrete value, which is assigned to one of the different effect regions,

[0025] - reduce the continuous variation to the required number of discrete values ​​by using a dithering algorithm, where each discrete value is assigned to one of the different effect areas, and

[0026] - Filling each pixel position in the transition area with pixels of the corresponding effect area according to the discrete value determined for each pixel position in the dithering algorithm.

[0027] Advantageously, the continuous variation is monotonic, in particular strictly monotonic. The continuous variation can be, for example, linear, but also non-linear, for example quadratic or following a hyperbolic tangent function.

[0028] Further embodiments and advantages of the invention are explained below with reference to the accompanying drawings, which are not drawn to scale for the sake of increased clarity.

[0029] In the attached picture:

[0030] Figure 1Schematic representation of a banknote having a security element according to the invention, which has two effect areas adjacent to each other along a boundary line,

[0031] Figure 2 (a) shows a detail view of a security element according to the invention, with two effect regions perfectly aligned and with a transition region, and (b) shows a security element not according to the invention without a transition region,

[0032] Figure 3 (a) shows a detailed view of a security element according to the invention, with a typical positional deviation of the two effective regions, and (b) shows a security element not according to the invention without a transition region,

[0033] Figure 4 showing a detail of a transition area between two effect areas with pixels, and a further enlarged view of the first effect area, the transition area and the second effect area with pixels,

[0034] Figure 5 A security element is shown, wherein a first effect area is formed by a metallized micromirror area and a second effect area is formed by a demetallized micromirror area, wherein Figure (a) shows the design specifications, Figure (b) shows a security element not according to the present invention without a transition area as a comparative example, and Figure (c) shows a security element according to the present invention with a transition area.

[0035] The invention is described here by way of example using a security element for banknotes. Figure 1 A banknote 10 having a security element 12 according to the invention is shown in schematic form.

[0036] The security element 12 comprises two effect regions 14, 16 for producing different optical effects, which are adjacent along a border line 18. In the present embodiment, the effect regions 14, 16 are formed by micromirror regions with directional reflective micromirrors, which display different micromirror effects. For example, the effect region 14 displays a 3D effect, while the effect region 16 displays a motion effect.

[0037] In particular, a transition region 20 is formed along the boundary line 18 in the two effect regions 14 , 16 , in which transition region, when viewed, the optical effect of the first effect region 14 transitions smoothly into the optical effect of the second effect region 16 .

[0038] The two different effect areas 14, 16 will usually have certain registration fluctuations with the (structural) features generated in other process steps, but these registration fluctuations will be masked by the transition area. As mentioned above, conventional designs often face the problem that registration fluctuations reveal weaknesses in the production process and visible position deviations of the effect areas will cause confusion to the observer.

[0039] These difficulties can be overcome by providing a smooth, soft transition between the two effect areas 14, 16, such as Figures 2 to 4 Shown in more detail.

[0040] first, Figure 2 (a) shows a detail view of a security element 12 with effect regions 14, 16 and a transition region 20 formed along a boundary line 18, the ideal assumption being a perfect alignment of the two effect regions 14, 16, in which case, for example, the boundary line 18 between the effect regions lies exactly at the height of the structural feature 22 in accordance with the design specifications. For comparison, Figure 2 (b) shows a security element 12 ′ not according to the invention without a transition region having this idealized perfect alignment of the boundary line 18 ′ and the structural feature 22 .

[0041] Then, Figure 3 (a) shows Figure 2 The security element 12 in (a) has a typical position deviation Δ of the effect regions 14, 16 relative to the structural features 22, which is caused by unavoidable register fluctuations in the individual process steps for generating the structural features 22. For comparison, Figure 3 (b) shows a security element 12 ′ not according to the invention without a transition region, which has the same position deviation Δ.

[0042] Due to the design of the transition region 20, which will be described in more detail below, the optical effect of the first effect region 14 transitions smoothly there into the optical effect of the second effect region 16. Figure 2 (a) and Figure 3 The design form in (a) has no clear boundary between the two optical effects, so that there is no fixed reference point to indicate the correct position of the structural feature 22. Figure 2 (a) The idealized perfectly aligned position and the Figure 3 The differences between the locations where (a) typically appear in reality are small and do not cause interference when observing.

[0043] In contrast, since the boundary line 18' is relative to Figure 2 (b) The clearly identifiable position of the perfect alignment position, Figure 3In the comparative security element 12' of (b), the misalignment of the clear boundary line 18' relative to the structural feature 22 is clearly noticeable and leads to the above-mentioned adverse effects.

[0044] Figure 4 The generation of a transition region 20 between two effect regions 14, 16 is shown in more detail in this transition region, in which a detail 30 of the security element according to the invention near the boundary line is shown in more detail (see Figure 2 (a) and Figure 3 (a)).

[0045] The two effect areas 14, 16 are respectively composed of a plurality of square pixels 34 and 36, wherein the pixels 34 of the effect area 14 produce a 3D effect as a first optical effect, and the pixels 36 of the effect area 16 produce a motion effect as a second optical effect. In the present embodiment, each pixel 34, 36 is formed by only one single micromirror, but in other embodiments, each pixel can also be composed of a group of multiple micromirrors, in particular micromirrors aligned in the same manner. The size of the pixel is below the resolution limit of the human eye, for example 10µm x 10µm.

[0046] exist Figure 4 In the overview sketch in the right half of , for simplicity, pixels 34 of the first effect area 14 are shown in white, pixels 36 of the first effect area 16 are shown in black, while pixels in the larger magnified portion corresponding to the generation of the first and second optical effects are shown as wide shading (pixel 34, first optical effect) or narrow shading (pixel 36, second optical effect), respectively.

[0047] Along the boundary line 18, a transition area 20 with a width B is formed between the effect areas 14 and 16. In the transition area, the area share of the pixels 34 of the first effect area 14 is gradually reduced from 100% to 0% in the direction 32 perpendicular to the boundary line 18 by a dithering algorithm, while the area share of the pixels 36 of the second effect area 16 is gradually increased from 0% to 100%. Due to the small size of the pixels 34 and 36, they cannot be distinguished individually when observed. For the observer, the optical effect of the first effect area 14 smoothly transitions to the optical effect of the second effect area 16 along the direction 32. The width B of the transition area 20 can be a few tenths of a millimeter or a few millimeters.

[0048] In order to reduce or increase the area share of the pixels in the transition area as described, a dithering algorithm originally derived from image processing is used, which controls the occupation of each pixel position in the area of ​​the security element by one of the pixels of the first and second effect areas. The process is explained in detail below using the example of the Floyd-Steinberg algorithm, but it should be understood that other dithering algorithms can also be used accordingly.

[0049] Specifically, if the size of the security element is, for example, 10 mm x 10 mm, the size of the pixels 34, 36 should be 10 µm x 10 µm, so that the security element consists of 1000 x 1000 pixels. A horizontal borderline at y=5 mm separates the first effect area 14 extending from y=0 to the borderline from the second effect area 16 extending from the borderline to y=10 mm. In order to mask register fluctuations, a transition area with a width of B=2 mm is generated around the borderline, in which a soft transition between the optical effects of the effect areas 14, 16 can be seen.

[0050] The security element 12 then has 1000 pixels in each case in the x and y direction, wherein the transition region in the y direction extends in pixels from ymin=400 to ymax=600.

[0051] For simplicity, a linear transition is generated in this case. Specifically, the default fields V(x,y) are initialized in pseudo code as follows:

[0052] for y = 1 to 1000

[0053] for x = 1 to 1000

[0054] if y ≤ 400 thenV(x,y) = 0;

[0055] else if y ≥ 600 thenV(x,y) = 1;

[0056] elseV(x, y) = (y-400) / 200;

[0057] Thus, for all 1000 x 1000 pixels, the default field is initialized so that it is equal to 0 in a first effect range of y ≤ 400, equal to 1 in a second effect range of y ≥ 600, and increases linearly from 0 to 1 in a transition range with 200 pixel width in the y direction (corresponding to 2 mm). For example, V(x,450) = (450-400) / 200 = 0.25, V(x,500) = (500-400) / 200 = 0.5, V(x,550) = (550-400) / 200 = 0.75, for all values ​​of x = 1…1000.

[0058] In order to also obtain only discrete values ​​0 and 1 in the transition region between 400 and 600, a dithering algorithm, namely the Floyd-Steinberg algorithm, is applied to the default field V(x,y). In pseudo code:

[0059] for y = 1 to 1000

[0060] for x = 1 to 1000

[0061] initialValue = V(x,y);

[0062] newValue = findClosestValue (initialValue);

[0063] V(x,y) = newValue;

[0064] quantizationError = initialValue – newValue;

[0065] V(x+1,y) = V(x+1,y) + quantizationError × 7 / 16;

[0066] V(x-1,y+1) = V(x-1,y+1) + quantizationError × 3 / 16;

[0067] V(x,y+1) = V(x,y+1) + quantizationError × 5 / 16;

[0068] V(x+1,y+1) = V(x+1,y+1) + quantizationError × 1 / 16;

[0069] in

[0070] findClosestValue (val) = 1 when val > 0.5

[0071] = 0, otherwise.

[0072] As can be seen from the pseudocode, in the Floyd-Steinberg algorithm, all 1000 x1000 pixels in the security element are traversed and by applying the function findClosestValue(), each pixel is set to 0 or 1 depending on the value of initialValue.

[0073] The quantization error ("quantizationError") resulting from this discretization is distributed proportionally over the four neighboring pixels that have not yet been processed. Therefore, the average value of the pixel remains essentially unchanged. After running the Floyd-Steinberg algorithm, the default field V(x,y) contains only the values ​​0 and 1, where in the transition region, the surface density of pixels with V(x,y)=0 decreases linearly from 100% to 0%, while the surface density of pixels with V(x,y)=1 increases linearly from 0% to 100%. The quantization error ("quantizationError") resulting from this discretization is distributed proportionally over the four neighboring pixels that have not yet been processed. Therefore, the average value of the pixel remains essentially unchanged. After running the Floyd-Steinberg algorithm, the default field V(x,y) contains only the values ​​0 and 1, where in the transition region, the surface density of pixels with V(x,y)=0 decreases linearly from 100% to 0%, while the surface density of pixels with V(x,y)=1 increases linearly from 0% to 100%.

[0074] Then, in a further step, all 1000 x 1000 pixel positions of the security element 12 are traversed and at pixel position (x,y), when V(x,y)=0, a pixel 34 with a first optical effect is generated, and when V(x,y)=1, a pixel 36 with a second optical effect is generated.

[0075] The dithering algorithm ensures that after applying the dithering algorithm, V(x,y) for each pair of values ​​(x,y) is either 0 or 1. 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 pixels with V(x,y)=0 decreases from 100% to 0%, while the density of pixels with V(x,y)=1 increases from 0% to 100% accordingly.

[0076] Accordingly, in the finished security element, the area share of the pixels 34 of the first effect area in the transition region decreases from 100% to 0%, while the area share of the pixels of the second effect area increases from 0% to 100%, as shown in FIG. Figure 4 shown.

[0077] Unlike image processing where the grayscale is simulated as a true intermediate tone between white and black by a dithering algorithm, in this embodiment, there is no intermediate level between the first and second optical effects whose appearance can be simulated. The two visual effects may even be completely different or even incompatible with each other. Instead, in this embodiment, a soft transition is produced between two different discrete optical effects by a dithering algorithm.

[0078] Figure 5Another exemplary embodiment is shown, 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, Figure 5 (a) shows the design specifications of an idealized star-shaped demetallization 46 in the surrounding metallization area 44 .

[0079] As a comparative example, Figure 5 (b) shows a security element 52' not according to the invention without transition regions, ie with a sharp edge 58' and with a certain register fluctuation of a demetallized portion 56' within a metallized region 54'. Figure 5 As shown in (b), the occurrence of registration fluctuations is clearly noticeable to the observer due to the irregular star shape and the clearly defined boundary 58'.

[0080] at last, Figure 5 (c) shows a security element 52 according to the present invention, in which a dithered transition region 60 is formed at a boundary line between a demetallized micromirror region 56 and a metallized micromirror region 54 .

[0081] The dither transition region may have a width of, for example, 1 mm and may be calculated from a linear transition using the Floyd-Steinberg algorithm as described above. In this case, the pixels of the first and second effect regions are formed by metallized micromirror elements or demetallized micromirror elements, respectively.

[0082] In this way, a soft, smooth transition is created between the metallized area 54 and the demetallized area 56, which masks the presence of register fluctuations, such as Figure 5 (c) as shown.

[0083] Reference numerals list

[0084] 10 Banknotes

[0085] 12 Security Elements

[0086] 12' Comparison Example

[0087] 14, 16 Effect Area

[0088] 18 Boundary Line

[0089] 18' Boundary line in comparison example

[0090] 20 Transition Zone

[0091] 22 Structural features

[0092] 30 Details

[0093] 32 Direction perpendicular to the boundary line

[0094] 34, 36 pixels

[0095] 44 Metallization Areas in Design Specifications

[0096] 46 Demetallized Areas in Design Specifications

[0097] 52 Security Element

[0098] 52' Comparison example

[0099] 54 Metallized micromirror area

[0100] 54' Metallized area in comparison example

[0101] 56 Demetallized micromirror area

[0102] 56' Demetallized area in comparison example

[0103] 58' Clearly defined boundary line in the comparison example

[0104] 60 Transition Zone

Claims

1. An optical security element for protecting valuables, comprising at least two effect areas for producing different optical effects, wherein: These effect areas are adjacent to each other along a boundary line, and are characterized in that the effect areas are respectively composed of a large number of pixels, and a dithering transition area is formed along the boundary line between the first effect area and the second effect area, in which the area share of the pixels of the first effect area gradually decreases from 100% to 0%, and the area share of the pixels of the second effect area gradually increases from 0% to 100%, so that when observed, the optical effect of the first effect area smoothly transitions to the optical effect of the second effect area in the transition area.

2. The optical security element according to claim 1, characterized in that At least one of the two effect regions is formed by a micromirror region having directional reflective micromirrors.

3. The optical security element according to claim 2, characterized in that At least two effect regions are formed by micromirror regions having directional reflection micromirrors and different micromirror effects.

4. The optical security element according to claim 3, characterized in that One of the micromirror regions is metallized and the other micromirror region is not metallized, in particular is demetallized.

5. The optical security element according to claim 2, characterized in that One of these effect regions is formed by a micromirror region having directional reflective micromirrors and the other effect region is formed by a diffractive speckle structure, in particular by a hologram, a holographic grating image or a holographic-like diffractive structure.

6. The optical security element according to claim 2, characterized in that One or more micromirror regions each contain a non-diffractive mirror, preferably a plane mirror, a concave mirror and / or a Fresnel mirror.

7. The optical security element according to claim 1, characterized in that The effect areas each consist of a plurality of pixels of the same shape, in particular square or rectangular pixels.

8. The optical security element according to claim 1, characterized in that These pixels seamlessly fill the effect area and transition area, respectively.

9. The optical security element according to claim 1, characterized in that The maximum dimension of the pixel is between 1µm and 100µm.

10. The optical security element according to claim 2, characterized in that Each pixel in at least one effect area formed by a micromirror area having directional reflective micromirrors is composed of a single micromirror or a group of a plurality of micromirrors.

11. The optical security element according to claim 1, characterized in that One of these effect areas forms an outer effect area, which surrounds another effect area forming an inner effect area, and the border line is formed by the contour of the inner effect area.

12. The optical security element according to claim 1, characterized in that The width of the transition region is between 50 μm and 50 mm, preferably between 50 μm and 10 mm, particularly preferably above the resolution limit of the human eye, in particular between 0.5 mm and 5 mm.

13. A data carrier having an optical security element according to any one of claims 1 to 12.

14. A method for producing an optical security element according to any one of claims 1 to 12, wherein - at least two effect areas for producing different optical effects are formed on the carrier, the effect areas adjoining each other along a boundary line, and - The effect areas are respectively composed of a large number of pixels, and a dithering transition area is formed along the boundary line between the first effect area and the second effect area, in which the area share of the pixels of the first effect area gradually decreases from 100% to 0%, and the area share of the pixels of the second effect area gradually increases from 0% to 100%, so that when observed, the optical effect of the first effect area smoothly transitions to the optical effect of the second effect area in the transition area.

15. The method according to claim 14, characterized in that At least one of the two effect regions is formed by a micromirror region having directional reflective micromirrors.

16. The method according to claim 14 or 15, characterized in that The dithering transition area is calculated using a dithering algorithm, in particular a threshold value algorithm, a random dithering algorithm, a pattern dithering algorithm, a sequential dithering algorithm or an error diffusion algorithm.

17. The method according to at least one of claims 14 to 16, characterized in that To create the dithering transition area, - generating a continuous change in the size of the transition region, said change starting and ending with a discrete value, which is assigned to one of the different effect regions, - reduce the continuous variation to the required number of discrete values ​​by using a dithering algorithm, where each discrete value is assigned to one of the different effect areas, and - Filling each pixel position in the transition area with pixels of the corresponding effect area according to the discrete value determined for each pixel position in the dithering algorithm.

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