Anti-counterfeiting elements with tilting effect

Abstract

The anti-counterfeiting element presents alternating images with at least two different views. The first view shows a first pattern, and the second view shows a second pattern, both appearing in the same or at least overlapping areas. They each consist of a bright foreground area and a dark background area surrounding that foreground area. When the anti-counterfeiting element is tilted about a first axis, the first pattern appears only within a first viewing angle, and the second pattern appears only within a second viewing angle; the two viewing angles are different and do not overlap. Within the first and second viewing angles, the sheet-like pattern can be tilted about the second axis by an angle range of at least 5°, preferably at least 10°, and more preferably at least 20°, without the first and second views disappearing or undergoing substantial changes. The bright foreground areas of the two patterns are embossed structures formed by the optical effects of light; the dark background areas are embossed structures that absorb incident light and / or reflect incident light in directions intended for use outside the viewing angle ranges of the two views.

Description

Technical Field

[0001] The present invention relates to an anti-counterfeiting element for anti-counterfeiting paper, valuable documents, etc., which presents to an observer an alternating image having at least two different views, wherein the first view shows a first pattern and the second view shows a second pattern, and the first and second patterns appear in the same or at least overlapping areas. Background Technology

[0002] Various anti-counterfeiting elements are disclosed in the prior art, which display image switching between two or more different patterns to an observer when tilted. More specifically, tilted images based on microlens arrays are disclosed, as well as tilted images achieved by diffraction gratings (commonly referred to as "holograms") or micromirrors.

[0003] For particularly effective anti-counterfeiting elements that can be clearly, quickly, and very simply verified even under difficult lighting conditions, the key characteristics include the following:

[0004] 1) The high brightness and high contrast of the image are depicted.

[0005] 2) Rapid image switching and clear separation of two or more images when tilted around the axis used for verification.

[0006] 3) Regarding the extremely low sensitivity of tilting around other axes, the observer does not need to try multiple tilt angles around other tilt axes to "find" the target image.

[0007] Considering the characteristics in point 1, micromirror-based anti-counterfeiting elements are particularly recommended: compared to lens-based or holographic-based anti-counterfeiting elements, they have highly directional reflections, providing higher brightness and better contrast.

[0008] A relatively simple micromirror-based tilted image is known from EP 0868313 A1. In this case, the micromirrors belonging to a single depiction each have a fixed orientation, and the background area is, for example, flat (without relief) or occupied by diffractive or matte structures. The fixed or uniform orientation of a single depicted micromirror provides very high brightness, which is especially observable under directional illumination, but only over a small range of tilt angles. Furthermore, the background area without relief or occupied by matte structures often appears very bright, thus reducing the optimal contrast between the tilted image depiction and the background. Additionally, if the background is illuminated (e.g., in the case of a flat background, bright illumination from specular reflection, or in the case of a diffractive structure, iridescent illumination over a relatively large range of angles), this can cause interference, especially between the illuminations of the two tilted views.

[0009] As is known from DE 10 2012 020 257 A1, a wider field of view and less background interference can be achieved through a tilting effect, which displays an arched depiction. However, in general, this depiction does not appear with such high brightness, does not exhibit abrupt appearance and disappearance when tilted, and typically has only a small contrast with the background. Summary of the Invention

[0010] Therefore, the object of the present invention is particularly to provide an anti-counterfeiting element that is more effective than solutions known in the prior art and simultaneously satisfies the above-mentioned characteristics of points 1 to 3.

[0011] To illustrate the various tilt axes, a distinction will be made here and below between north-south tilt and east-west tilt; see [link to relevant documentation]. Figure 1 North-south tilt (left image) is understood to mean that the viewer is tilted around the horizontal axis Q, while east-west tilt (right image) refers to tilting around the vertical axis H, such as... Figure 1 As shown. In each case, it is envisioned that the viewer sees the image switching when tilted north-south, and that when tilted east-west, the tilted image remains substantially unchanged within a sufficiently large angular range. The latter aims to make the depiction easily visible even under highly directional lighting, without having to precisely find a narrow range of envisioned angles in the east-west direction.

[0012] The subject matter of this invention can, of course, also be designed in principle for other tilt axes, i.e., for example, for tilts on east-west tilts, where there is a large viewing range in north-south, or for tilts around different axes (e.g., northwest / southeast or other axes).

[0013] The object of the present invention is achieved by an anti-counterfeiting element having the features of claim 1. In this case, the anti-counterfeiting element in the form of an optically variable sheet pattern provides the observer with a tilted image having at least two different views, which respectively show a bright foreground and a dark background. Here, the foreground area is generated by means of reflective microstructures, especially by means of micromirror devices. The micromirrors here are oriented such that micromirrors belonging to the same view respectively reflect light within different spatial angle ranges relative to a first tilt axis (north-south tilt in an exemplary embodiment). Here, the tilt angle ranges do not overlap, are preferably spaced apart from each other, and / or each covers only a relatively small tilt angle range, in which the corresponding depiction is very brightly illuminated. However, regarding the second tilt direction (east-west tilt in an exemplary embodiment), according to the invention, the covered angle range should be at least large enough so that the viewer can tilt relatively widely around the axis without the view changing or even disappearing. Thus, in the case of light incident in a highly directional manner, the view is intended not to change or disappear within a tilt angle range of at least 5°, preferably at least 10°, more preferably at least 20°. If a micromirror with a basically planar surface is used, the tilt angle range in that direction can be expanded by randomly varying the orientation component of the corresponding mirror surface; or, a micromirror that is curved at least in that direction can be used to make the reflected light fan out in that direction, thereby achieving the same effect.

[0014] The anti-counterfeiting element of this invention is passive because it does not emit or generate light itself, but only reflects incident ambient light in different directions in different areas. Therefore, in a completely dark environment, it will be completely dark. Thus, the terms "bright" and "dark" should be understood here as, under typical viewing conditions (e.g., in a room with ceiling lighting or light entering through a window), the microstructures in the "bright" area reflect a large amount of light from the environment toward the viewer's eye, while less ambient light is reflected from the "dark" area to the viewer's eye. "Bright" and "dark" are specifically related to each other. The actual brightness or darkness of the anti-counterfeiting element depends on the ambient light conditions. The contrast achieved by the subject matter of this invention, i.e., the difference between "bright" and "dark," also depends on the ambient light conditions, as is the case with other reflective anti-counterfeiting elements in the prior art. Therefore, the contrast between "bright" and "dark" areas is generally higher under highly directional lighting than under diffused light. With respect to the subject matter of this invention, the term "emitting light" should also be understood in this sense as a particularly large amount of incident light being reflected to the observer relative to prior art anti-counterfeiting elements.

[0015] The bright areas of the first and second views are intended to overlap, thereby allowing a tilted image with image switching to be realized at the same location. For this purpose, the micromirrors of the two views can be arranged alternately within a single imprinting plane, or alternatively, in different overlapping planes. A particularly advantageous configuration with two imprinting planes is known in particular from DE 102020 000 732 A1. In certain embodiments, it can also be specified that the micromirrors belonging to different views reflect incident light in different colors; thus, the two views present different patterns in different colors, which further enhances the tilting effect. This color switching can be achieved by a structure with two imprinting planes, for example known from DE 10 2020 000 732 A1, or by altering the color of the light reflected at the micromirrors through nanostructures superimposed on the mirrors (more specifically, regular or irregular subwave structures with structural spacing or periodicity, e.g., 50 nm to 600 nm, preferably 200 nm to 400 nm). Here, the nanostructure can produce color, for example, in combination with simple metallization (e.g., aluminum coating), more specifically through plasma effects, or in combination with interference coatings (color-shifting coatings with reflector / dielectric / absorber structures—e.g., Al / SiO2 / Cr structures) to alter the color of the interference coating.

[0016] The backgrounds of the first and second views (which have a dark or muted appearance) are respectively occupied by embossed structures, which are dark in many and preferably all oblique directions, advantageously especially in the entire viewing angle range between and within the first and second views. The following can be advantageously used for this purpose:

[0017] • Micromirrors, which have a greater tilt angle about the first and / or second tilt direction than micromirrors providing a bright foreground, deflect the incident light more strongly than mirrors providing a bright foreground, or at least deflect the incident light in significantly different directions.

[0018] • Light-trapping structures, particularly those with dimensions in the subwavelength range (below the wavelength of visible light), such as subwavelength structures called "moth-eye structures" or "diffraction blacks," are preferably metallized and composed of periodic gratings or aperiodic arrangements, and more particularly have a high aspect ratio, i.e., a high ratio of structure height to depth, or

[0019] • Other light-trapping structures, which have dimensions above the “subwavelength range”, and more particularly have structural dimensions of about 0.5 μm to preferably no more than 20 μm, are examples of light-trapping “microcavities”.

[0020] This combination ensures that, relative to an undesirable tilt about the east-west axis (more generally: the second tilt axis), the tilt effect always displays a high-contrast tilt effect when tilted north-south (more generally: the first tilt axis). Furthermore, the preferred embodiment of the background ensures that the tilt from the first tilt view to the second tilt view is not accompanied by any disruptive effects, such as a sudden brightening of the background.

[0021] According to another advantageous configuration of the anti-counterfeiting element, the light optical effect relief structures of the bright areas belonging to the first pattern and the second pattern are arranged alternately, and the alternate arrangement is preferably achieved on such a small length scale that the human eye cannot distinguish them without auxiliary means; more specifically, the alternate arrangement is achieved by dividing them into pixels or stripes with a size of less than 100 μm and advantageously less than 50 μm.

[0022] According to another advantageous configuration of the anti-counterfeiting element, the light-optical embossed structure of the bright areas belonging to the first pattern and the second pattern respectively is a micromirror with a substantially straight surface, wherein each individual micromirror reflects incident light substantially only in one direction under directional illumination, and the visibility of the first pattern and the second pattern is maintained by individual micromirrors having multiple different orientations, respectively, when tilted about the second axis at 5°, preferably 10° or more preferably 20°, within the expected viewing angle range relative to the first tilt axis. These orientations are particularly different in the component belonging to the second tilt axis, such that the light reflected at the entire micromirror is fanned out to a correspondingly larger angular range.

[0023] According to another advantageous configuration of the anti-counterfeiting element, the component of the micromirror orientation belonging to the second tilt axis is randomly or pseudo-randomly selected from a specified range.

[0024] According to another advantageous configuration of the anti-counterfeiting element, the light optical effect relief structure of the bright areas belonging to the first pattern and the second pattern respectively is a micromirror with a curved surface, which causes the incident light to fan out under directional illumination, so that it covers an angle range of at least 5°, preferably at least 10°, and more preferably at least 20° relative to the second tilt axis.

[0025] According to another advantageous design scheme of anti-counterfeiting elements, light-trapping micron or nanostructures, especially periodic or non-periodic moth-eye structures, are set in the dark background area.

[0026] According to another advantageous design of the anti-counterfeiting element, a reflective micromirror with a curved or straight surface is provided in the dark background area, the reflective micromirror having a slope of at least 10%, preferably at least 50%, higher than the micromirror belonging to the foreground area.

[0027] According to another advantageous design of the anti-counterfeiting element, the foreground areas of the two patterns, or the foreground and background areas of at least one pattern, have different hues. In this case, preferably, the different hues are produced by nanostructures superimposed on the light-optical embossed structure.

[0028] According to another advantageous design of the anti-counterfeiting element, the micromirror is equipped with a color-changing coating.

[0029] According to another advantageous configuration of the anti-counterfeiting element, the light optical reflection embossed structures belonging to the foreground of the first and second patterns respectively exist in two different imprinted planes spaced apart from each other, wherein the light reflected by the embossed structures in the first and second imprinted planes respectively preferably has different hues.

[0030] According to another advantageous design of the anti-counterfeiting element, the areas of the first and second views are surrounded by a frame with an arched appearance, and the arched effect of the frame is achieved by a reflective, essentially light-optical, embossed structure that mimics the reflective properties of an arched metal surface. Preferably, in this case, the frame accommodates two intersecting arched effects visible at different tilt angles when tilted about a first axis, and the two arched effects show the same or different frames with an arched appearance, wherein the tilt angle range of the first arched effect covers a first tilt angle range where the first pattern is visible, and the tilt angle range of the second arched effect covers a second tilt angle range where the second pattern is visible, such that a viewer can see either the first or second pattern in each case using a frame with an arched appearance that is visible or illuminated within the same viewing angle range.

[0031] Valuable documents for which the anti-counterfeiting elements of the present invention can be used include banknotes, stocks, bonds, certificates, vouchers, checks, high-value admission tickets, and other papers at risk of counterfeiting, such as passports and other identity documents, as well as cards, such as credit or debit cards, the card body of which includes at least one layer of security paper, and product protection elements, such as labels, seals, packaging, folding boxes, packaging inserts, etc. The simplified term "valuable documents" includes all the above-mentioned materials, documents, and product protection devices.

[0032] It should be understood that the features described above and those not yet set forth below may be used not only in the combinations shown, but also in other combinations, without departing from the scope of the invention, provided that such use is within the scope of the claims. Attached Figure Description

[0033] The advantages of the invention are illustrated below with reference to the exemplary embodiments and accompanying drawings. The exemplary embodiments constitute preferred embodiments, but are not intended to limit the invention to them. Furthermore, for ease of understanding, the representations in the drawings are highly schematic and do not reflect actual conditions. In particular, the scale shown in the drawings does not match real-world conditions and is used only to improve clarity. Moreover, for ease of understanding, the embodiments described in the following exemplary embodiments are simplified to the essential core information. In actual implementation, substantially more complex drawings or images may be used.

[0034] In detail and illustratively,

[0035] Figure 1 To illustrate, two different tilt directions are shown.

[0036] Figure 2 The anti-counterfeiting element of the present invention is shown in plan view from a first tilt angle range (100) and from a second tilt angle range (200) relative to a first tilt axis.

[0037] Figure 3 The anti-counterfeiting element of the present invention is shown in a plan view, wherein Figure 2 The tilting effect is combined with different tilting effects, and more specifically with the arched tilting effect.

[0038] Figure 4 The anti-counterfeiting element of the present invention is shown in a plan view, wherein the tilt effect is achieved with more than one color. Detailed Implementation

[0039] Figure 2 The anti-counterfeiting element of the present invention is shown as viewed from a first tilt angle range (100) and from a second tilt angle range (200) relative to a first tilt axis. The image switching between 100 and 200 can occur, for example, at a north-south tilt angle of, for example, 20°: for today's anti-counterfeiting elements (security threads, security strips, patches), the typical size of such depictions is a few millimeters or several millimeters. Here, the observer sees the letters "PL" brightly illuminated in the first tilt angle range, and the number "25" brightly illuminated in the second tilt position. These depictions consist of a bright foreground (101, 201) and a dark background (102, 202), respectively.

[0040] One possible implementation of the bright area is the use of micromirrors. These can have dimensions, for example, from 3 μm to 100 μm, preferably from 5 μm to about 20 μm. For the tilting effect around the north-south axis, for example, the mirror of foreground 101 can be tilted "north" (i.e., upwards), while the mirror of foreground 201 is tilted "south," such that, depending on the tilt position, only one mirror emits bright light, while the other mirrors are correspondingly dark and almost or completely unrecognizable against the dark background. The north-south tilt angle can be exactly the same for all micromirrors of foreground 101 or for all micromirrors of foreground 201 in each case, or it can vary within a specified range. For example, all mirrors depicting 101 can be tilted 10° north, and all mirrors of 201 can be tilted 10° south. Thus, with north-south tilting, very bright but also very short (only within a narrow range of tilt angles) visible emission will be achieved. In other embodiments, these values ​​can also vary around corresponding intermediate values, and are thus selected, for example, from a range of 5° to 15° or -15° to -5°. Generally, those skilled in the art can adjust the degree of tilt that must be performed to observe the image transition by selecting an intermediate orientation, and the size of the corresponding range then affects the brightness and "display time" of the depiction when tilted. For maximum sharpness of the separation of views 100 and 200 (as opposed to a slow "cross gradient"), the angular ranges of the north and south components of the mirrors of foreground 101 and 201 should be as non-overlapping as possible; preferably, in fact, they are separated from each other by at least a few degrees (at least 3°, more preferably at least 5°).

[0041] To maintain visibility even with small or advantageously relatively large tilts in the east-west direction, mirrors can, for example, have an east-west tilt component. Specifically, this component can be chosen randomly or pseudo-randomly such that a portion of the mirror always emits bright light within a certain tilt range relative to that axis. The smaller the micromirror, the more effectively a largely uniform brightness can be achieved across multiple angles. As mirrors become larger, the more likely different luminous properties are to be visible to the naked eye—however, this is not necessarily negative and can also be perceived, for example, as a "flare effect."

[0042] Due to the overlap of foreground patterns 101 and 201, the associated micromirrors are arranged in an alternating pattern. This alternating arrangement is preferably achieved on a length scale below the resolution of the human eye; for example, the regions for the micromirrors 101 and 201, respectively, can exist in a checkerboard or striped pattern, wherein the fields or stripes can have dimensions between 10 μm and about 100 μm.

[0043] Micromirrors can also be present in background regions 202 and 102. These micromirrors can preferably have a much larger tilt angle than the micromirrors in foreground regions 101 and 201 in the north-south and / or east-west directions. In the example above, with a north-south tilt component of + / -10°, the background mirrors can, for example, have twice the tilt component (i.e., + / -20°). Similarly, in the east-west direction of mirrors 101 and 201, a range of variation from -10° to +10° can be provided, while the corresponding tilt components in regions 202 and 102 can, for example, be +20° and / or 20°. Mirrors in the background regions can all have the same or different orientations. For example, in practice, an arrangement with four different orientations is advantageous, where the mirrors are largely aligned in the northeast, northwest, southeast, and southwest directions (provided technical limitations allow). Therefore, the background will only glow brightly when the observer tilts the anti-counterfeiting element to its maximum extent around the two tilt directions from the center position, and even then, only some mirrors (in this case, a quarter) will glow.

[0044] Figure 3 The anti-counterfeiting element of the present invention is shown, wherein Figure 2 The tilting effect is combined with different tilting effects, more specifically with arched tilting effects, as known from DE 10 2012 020 257 A1. In this case, such arched tilting effect can also well provide a frame with an arched appearance having a tilting effect around the invention. At the corresponding tilt angle relative to the first tilt axis, the frame with an arched appearance can become visible when tilted. For the first view and the second view, the frame can have different shapes, or in particular the same shape. The latter is actually an "arched tilting effect" itself, and has the advantage over the standard arched effect that in each case, the frame is only brightly visible when the relevant tilt of the invention is also visible. When tilted around the first axis, the viewer then sees the following image sequence, where 103 and 203 represent the arched frame visible in each case, which here shows the same appearance ("arched tilt itself"), while in the middle position, the middle tilt and the frame are dark. In addition to the frame, different or additional arched tilting elements can also be provided.

[0045] Figure 4The anti-counterfeiting element of the present invention is shown, wherein the tilting effect is achieved using more than one color. As mentioned above, multiple colors can be achieved, in particular, through nanostructures on the micromirrors. Alternatively, it can also be achieved using two imprinted planes, as is known in particular from DE 10 2020 000 732 A1. In this case, the mirrors 101 and 201 are located in different imprinted planes and do not necessarily have to be staggered in the plane. In embodiments with nanostructures, for example, the micromirror of 101 can have a blue-looking nanostructure, while the micromirror of 201 can have a yellow-looking nanostructure. Additionally or alternatively, the frame regions 103, 203 can also have nanostructures of different or the same color superimposed thereon (here: red in each case).

[0046] In other embodiments, foreground regions 101 and 201 may also have the same color, but at least one of background regions 102 and 202 or frames 103 and 203 may have a different color than that of regions 101 and 102.

Claims

1. An anti-counterfeiting element for anti-counterfeiting paper, valuable documents, etc., the anti-counterfeiting element presents to an observer alternating images having at least two different views, wherein a first view displays a first pattern, a second view displays a second pattern, and the first and second patterns appear in the same or at least overlapping areas, wherein, • The first and second patterns are each composed of a bright foreground area and a dark background area surrounding the foreground area. • Under directional lighting, when the anti-counterfeiting element is tilted around the first axis, the first pattern appears only within a first viewing angle, and the second pattern appears only within a second viewing angle. The two viewing angles are different and do not overlap. • Within the first and second viewing angles, the sheet-like pattern can be tilted around a second axis by an angle range of at least 5°, preferably at least 10°, and more preferably at least 20°, without the first and second views disappearing or undergoing substantial changes. • The bright foreground areas of both patterns are relief structures created by the optical effects of light, and more specifically, micromirror structures. • The dark background area is an embossed structure that absorbs incident light and / or reflects incident light in directions intended for use in both views.

2. The anti-counterfeiting element according to claim 1, wherein, The embossed structures of the light optical effects belonging to the bright areas of the first pattern and the second pattern are arranged in an alternating manner, and the alternating arrangement is preferably achieved on such a small length scale that the human eye cannot distinguish the alternating arrangement without auxiliary means; more specifically, the alternating arrangement is achieved by dividing the area into pixels or stripes with a size of less than 100 μm and advantageously less than 50 μm.

3. The anti-counterfeiting element according to claim 1 or 2, wherein, The relief structure of the light optical effect of the bright areas belonging to the first pattern and the second pattern respectively is a micromirror with a substantially flat surface, wherein each individual micromirror reflects incident light substantially only in one direction under directional illumination, and the visibility of the first pattern and the second pattern is maintained by the individual micromirrors having a plurality of different orientations, which are particularly different in the component belonging to the second tilt axis, such that the light reflected at the entire micromirror is fanned out over a correspondingly larger angular range.

4. The anti-counterfeiting element according to at least one of the preceding claims, wherein, The components of the micromirror orientation belonging to the second tilt axis are randomly or pseudo-randomly selected from the specified range.

5. The anti-counterfeiting element according to at least one of the preceding claims, wherein, The light-optical relief structure belonging to the bright areas of the first pattern and the second pattern respectively is a micromirror with a curved surface. The micromirror emits incident light in a fan shape under directional illumination, such that it covers an angular range of at least 5°, preferably at least 10°, and more preferably at least 20° relative to the second tilt axis.

6. The anti-counterfeiting element according to at least one of the preceding claims, wherein, The dark background region contains light-trapping micron or nanostructures, more particularly periodic or non-periodic moth-eye structures.

7. The anti-counterfeiting element according to at least one of the preceding claims, wherein, A reflective micromirror with a curved or flat surface is disposed in the dark background area, the reflective micromirror having a slope of at least 10%, preferably at least 50%, higher than that of the micromirror belonging to the foreground area.

8. The anti-counterfeiting element according to at least one of the preceding claims, wherein, The foreground areas of two patterns, or the foreground and background areas of at least one pattern, have different hues.

9. The anti-counterfeiting element according to claim 8, wherein, The different hues are produced by nanostructures superimposed on the relief structure of the light's optical effect.

10. The anti-counterfeiting element according to at least one of the preceding claims, wherein, The micromirror is equipped with a color-changing coating.

11. The anti-counterfeiting element according to at least one of the preceding claims, wherein, The light optical reflection relief structures belonging to the foreground of the first pattern and the second pattern respectively exist in two different embossed planes spaced apart from each other, wherein the light reflected by the relief structures in the first embossed plane and the second embossed plane respectively preferably have different hues.

12. The anti-counterfeiting element according to at least one of the preceding claims, wherein, The areas of the first and second views are surrounded by a frame with an arched appearance, and the arched effect of the frame is achieved by a reflective, essentially light-optical relief structure that mimics the reflective properties of an arched metal surface.

13. The anti-counterfeiting element according to claim 12, wherein, The frame accommodates two staggered arched effects, which are visible at different tilt angles when tilted around the first axis, and the two arched effects show the same or different frames with an arched appearance, wherein the tilt angle range of the first arched effect covers the first tilt angle range visible to the first pattern, and the tilt angle range of the second arched effect covers the second tilt angle range of the second pattern, such that an observer can see either the first or second pattern using the frame in each case, the frame being visible or illuminated within the same viewing angle and having an arched appearance.

Images