EP3606765B1 - Security element with relief structure and method for the production thereof - Google Patents

Description

The invention relates to a security element for the production of documents of value, such as banknotes, checks or the like, which shows a motif against a background, the security element having a relief structure that covers a motif area of the security element and provides the motif there and a background area of the security element covered and provides the background there.

The invention further relates to a document of value with a security element.

Finally, the invention also relates to a production method for a security element for the production of documents of value, such as banknotes, checks or the like, which shows a motif against a background, with a relief structure being produced that covers a motif area of the security element and provides the motif there and covers a background area of the security element and provides the background there.

Security features for banknotes contain motifs, such as symbols, images or real-color images, which are intended to be particularly easy to identify and counterfeit-proof. Such motifs are known, for example, from the following publications: H. Lochbihler, "Colored images generated by metallic sub-wavelength gratings", Opt. Express, Vol. 17, pp. 12189-12196, 2009 ; WO 2012/156049 A1 ; EP 1434695 B1 ; EP 2453269 A1 ; WO 2013/091858 A9 ; US9188716B2 , DE 102014011425 A1 , DE 10 2008 046 128 A1 , WO 2011/029602 A1 and WO 97/19820 .

However, motifs with such security elements are in need of improvement in terms of recognizability in poor lighting conditions.

The invention is therefore based on the object of improving a security element, a document of value and a production method of the type mentioned at the outset in such a way that the detectability is increased. At the same time, simple production should be possible.

The invention is defined in claims 1 and 14.

The security element for the production of documents of value, such as banknotes, checks or the like, which shows a motif against a background, has a relief structure that covers a motif area of the security element and provides the motif there and covers a background area of the security element and provides the background there; In addition, an outline is provided which delimits the motif area from the background area and which is also formed by the relief structure, with the relief structure of the outline differing from the relief structure of the motif area and that of the background area, so that there is a brightness and/or color contrast between the outline on the one hand and subject area and background area on the other hand.

In the production process for a security element for the production of documents of value, such as banknotes, checks or the like, which shows a motif against a background, a relief structure is produced which covers a motif area of the security element and provides the motif there and covers a background area of the security element and there the Background provides, and provided an outline that delimits the subject area against the background area and also through the Relief structure is formed, the relief structure of the outline differing from the relief structure of the motif area and that of the background area, so that there is a brightness and/or color contrast between the outline on the one hand and the motif area and background area on the other.

The invention is based on the finding that the motif is easier to recognize when it is delimited from the background by a high-contrast outline. In order to achieve a particularly good contrast and to facilitate manufacturability, the outline is also defined by the relief structure, which, however, differs in the outline area from the motif area and the background area, so that there is a brightness and/or color contrast between the outline area on the one hand and the motif area and the background area on the other hand. This procedure circumvents registration requirements that would arise, for example, when conventionally printing an outline with a high-contrast color. At the same time, the outline can be designed in such a way that the maximum contrast to the subject and the background is achieved, i.e. a light outline is also easily possible. The invention thus significantly increases the perceptibility of the motif for a viewer.

The contrast between the outline area and the motif area as well as the background area can be achieved, for example, by appropriate selection of the profile geometry of the relief structure. The relief structures are usually coated, for example metallically, with a high refractive index or with a layered composite that produces a color effect, such as is shown, for example, in WO 2008/080499 A1 is known. Various relief structures are known from the prior art for generating motifs, ie it is possible to use these relief structures a contrast between the subject area on the one hand and the background area on the other hand can be achieved. For example, relief structures with micromirrors are known from the prior art (cf. DE 102010049617 A1 ). These micromirrors can be arranged in pixels, each of which has the same oriented micromirrors. Furthermore, Fresnel structures (cf. EP 1562758 B1 ) can be used or combined with micromirrors. Relief heights of 1 μm to a maximum of 100 μm and lateral dimensions of less than 10 μm to less than 100 μm are known for micromirrors. Another known relief structure for creating a motif are hologram gratings in the form of relief holograms. They consist of metalized relief structures with grating periods of 500 nm to 2 µm and are arranged in such a way that a viewer perceives a motif or a true-color image in the first diffraction order. the US9188716B1 uses relief structures in the form of retroreflective structures to create colored motifs. One or two-dimensional sub-wavelength gratings are also known for generating a motif or the background, for example from the publication H. Lochbihler, "Colored images generated by metallic sub-wavelength gratings", Opt. Express, Vol. 17, pp. 12189-12196, 2009 , or the WO 2012/156049 . By arranging relief structures pixel by pixel with different profile parameters, true color images can be generated in the zeroth diffraction order, which can also be used to generate a motif in front of a background. It is also possible to create movement effects in an image by arranging certain relief structures, for example microstructures, in a row (cf. DE 102010047250 A1 ). All of these different relief structures can be used and combined within the scope of the present invention to produce the motif and the background, ie in the motif area and the background area and to produce the outline. Of course, one each can be used for the background area and subject area and outline other relief structure can be used. It is crucial that there is a contrast between the outline area and the motif area and between the outline area and the background area that can be perceived visually with the naked eye. Another example of sub-wavelength structures are so-called moth-eye structures (cf. WO 2006/026975 A2 and EP 2453269 A1 ). Colored motifs can be produced by coloring a relief structure.

In a further development, the outline area can be provided with a structure by designing the relief structure accordingly. Texturing may involve a break in the outline area and/or may include microtext or information not visible to the naked eye.

The outline can also be a contour line within a complex motif. A complex motif consists of several motif components, whereby one of the motif components is to be understood as the background compared to the other in optical perception, so that the outline delimits the background area, i.e. a motif area of the complex motif, from another motif area of the complex motif. In special embodiments, the outline can also be unstructured.

Fig. 1

eine Draufsicht auf ein Sicherheitselement mit mehreren Motiven vor einem Hintergrund, wobei Umrisslinien die Motive gegen den Hintergrund abgrenzen,

Fig. 2

eine schematische Schnittdarstellung durch das Sicherheitselement S mit drei Bereichen I bis III entsprechend dem Motivbereich, dem Umrisslinienbereich und dem Hintergrundbereich des Sicherheitselementes der Fig. 1,

Fig. 3

eine Darstellung ähnlich der Fig. 2, wobei andere Reliefstrukturen für Motivbereich, Hintergrundbereich und Umrisslinienbereich verwendet werden, und

Fig. 4

eine Darstellung ähnlich der Fig. 2 und 3, wobei wiederum andere Reliefstrukturen für Motivbereich, Hintergrundbereich und Umrisslinienbereich zum Einsatz kommen.

The invention is explained in more detail below by way of example with reference to the figures, which can also show features that are essential to the invention. In the drawings shows:

1

a top view of a security element with multiple motifs against a background, with outlines delimiting the motifs against the background,

2

a schematic sectional view through the security element S with three areas I to III corresponding to the motif area, the outline area and the background area of the security element 1 ,

3

a representation similar to that 2 , using different relief structures for subject area, background area and outline area, and

4

a representation similar to that 2 and 3 , whereby other relief structures are used for the motif area, background area and outline area.

1 shows a security element S, the motif of which is a hummingbird with a year in front of a structured background. A motif area 1 and a background area 2 are formed by different relief structures, which form an optical contrast in reflection, so that the motif can be perceived with the naked eye. The motif is separated from the background by a narrow outline. The year is also set off from the background by an outline. The outlines in outline areas 3 are also produced by relief structures, which are designed in such a way that they form a contrast both to motif area 1 , 4 and to background area 2 . This significantly increases the perceptibility of the motifs for a viewer. The motif area 1, 4 and the background area 2 are characterized by relief structures formed, which are metallized, for example, and embedded in a dielectric. The same applies to the outline 3. The contrast between the different areas is created by an appropriate selection of the profile geometry of the relief structure.

2 shows schematically a sectional view for examples of such relief structures. The area I corresponds to the motif area 1 or 4, the area II to the background area 2 and the area III to the outline area 3. The security element S is formed on a substrate film 5, on which an embossing lacquer layer 6 was applied, in which the relief structure was introduced, which was then metallized. A topcoat layer 8 and a cover film 9 complete the security element S, which can span a window area of a bank note, for example.

Both the area I and the area II are formed in the embodiment of the hologram grating 7, 10 with a sinusoidal profile. The hologram gratings 7 and 10 differ in their configuration with regard to the image they generate. The contrasting outline area 3 is realized by a sub-wavelength grating 12 in area III. The sub-wavelength grating 12 can be periodic in one or two dimensions. It creates a contrast both in relation to the hologram grating 7 and in relation to the hologram grating 10 and thus emphasizes the motif, which is formed by the motif area 1, 4, against the background, which is formed by the background area 2, as an outline.

3 shows another embodiment to illustrate that the relief structures in areas I, II and III can be freely selected in large areas as long as there is a contrast between areas I and II and a contrast between area III and areas I and II given is. In the embodiment of 3 the background area 2 is designed differently. On the one hand, ie in some sections, it is formed by the hologram grating 7 and on the other hand, ie in other sections, by a smooth surface 15. The motif area is realized by a micromirror arrangement 13. The outline areas are filled with light absorbing moth eye structures 14 in areas III.

4 shows an embodiment in which the outline area implements a light border. The areas I and II are designed here with transmissive hologram gratings, such as those from DE 102014011425 A1 are known. In addition to the zeroth diffraction order 0.0. and the first diffraction order 1.0., they also have an additional effect in transmission, ie incident radiation E is not only reflected as reflected radiation R, as is the case in the embodiments of FIG 2 and 3 was the case, but also partially transmitted as transmitted radiation T. In this way, a transmitted light motif is also possible. In area III, this is combined with a conventional hologram grating, which is opaque after metallization. In this way, a demarcation of the motif area 1, 4 from the background area 2 is achieved in a plan view, which results in a bright outline. The structure of 4 also shows a motif in transmission. In this way of looking at it, the outline, ie area III, appears dark and makes this motif more recognizable. These contrast changes in transmission can generally be realized by opaque outlines. Suitable for this purpose are relief structures which are metallized and have a profile which has an aspect ratio, ie a ratio of depth to period, of less than 0.4. Particular examples are smooth metalized surfaces, micromirror arrangements, matt structures or conventional holographic structures etc. Transmissive structures can in particular be those as described in the publication mentioned at the outset from Lochbihler, Opt. Express, or from the WO 2012/156049 are known. Such transmissive structures generally appear darker in reflection than opaque metallic structures with a low aspect ratio, since the transmitted light component reduces the reflection. Therefore, these flat structures, as bright outlines, significantly improve the perception of the subject in reflection.

The embodiments of Figures 2 to 4 naturally show only examples of the lateral arrangement of different relief structures in areas I to III. Other combinations of micromirror arrangements, Fresnel-like structures, μ-lenses, hologram gratings, retroreflection structures, one- or two-dimensional sub-wavelength gratings or moth-eye structures and microcavities are also possible, which provide a brightness and/or color contrast between the respective areas for a viewer.

It is also possible to provide dark structures in the outline areas. Such appear dark from different, preferably all viewing directions. The in 3 used moth eye structures 14. From the literature, various ways are known to produce such moth eye structures 14. As an example, reference is made to the one already mentioned WO 2006/026975 A2 or the EP 1434695 B1 referred. These publications describe metallically vapour-deposited random surfaces which form a layer with a gradient in refractive index and have a good absorption effect. In this case, the structure depth is preferably more than 50 nm and the mean distance between adjacent elevations is less than 500 nm, hence the name sub-wavelength structures. Such random surfaces can be produced from plastic substrates, eg PMMA, using a plasma etching process. Alternatively, periodically arranged moth eye structures are used. It is also known that moth-eye structures that are coated with a multilayer, e.g. a so-called color-shift coating, produce high-contrast dark colors (cf. EP 2453269 A1 ). Structures that have an average distance of more than 500 nm can also show a high absorption effect after metallization. Such so-called microcavities preferably have a hemispherical indentation with a ratio of depth to aperture width of more than 0.5 and are arranged next to one another, for example, hexagonally or orthogonally. From the EP 1434695 B1 a moth's eye structure is known, which is formed by a metallized cross grating with a period of less than 420 nm. A two-dimensional periodic sub-wavelength grating can also be used for light absorption, as is the case, for example, in WO 2012/156049 A1 is described. This grid is also suitable for color filtering. The geometry parameters of the grating can be selected in such a way that maximum light absorption occurs and the average reflection is below 20%, preferably below 10%.

The demarcation between background area, motif area and outline area can be achieved by such structures acting as color filters. These do not necessarily have to be black, but can also appear in another color, eg red or blue. However, dark colors are advantageous for recognizing the motif. These metallic sub-wavelength structures mentioned show increased light absorption in the visible spectral range, partly due to resonant light absorption, which leads to a colored reflection. A high contrast between the outline area and the motif area or background area is guaranteed, since the average absorption in the visible wavelength range is always higher than that of mirror-smooth surfaces, such as micromirrors. Alternatively, these structures can also consist of some directions will not be dark. For example, the outline area can also be filled with micromirrors, which are all oriented in the same way and then only light up brightly at one angle at the same time. Although this has the disadvantage that the areas III then (undesirably) light up brightly at a certain angle, i.e. at this angle the outline area under certain circumstances does not bring about the demarcation between motif and background, but this disadvantage is technically particularly easy to implement , since no other structures have to be produced in addition to micromirrors, in particular no nanostructures. It is then possible to implement the relief structures for the background area, outline area and motif area exclusively by micromirrors, with only the orientation of the micromirrors changing between the individual areas. Advantageously, the angle of the undesired lighting up of these areas is selected so that it is as unobtrusive as possible, for example all mirrors in this area can be oriented downwards as far as possible, so that the lighting up effect only occurs when the view is very oblique. Alternatively, tilting in the east/west direction can be selected with the micromirrors oriented extremely far, for example to the east.

Relief structures with a low aspect ratio are suitable for forming bright outlines. After metallization, such structures are largely opaque in transmission and appear bright to an observer in reflection. Micromirrors, hologram gratings, retroreflection structures and flat surfaces are particularly suitable for this.

When using color-shift coating, the bump texture can change the color-shift color in the outline area to effect the delineation.

For good visibility, the average brightness of the outline area is less than 50% of the average brightness of the motif area and the background area in reflection and optionally also in transmission. Alternatively, the average brightness of the outline area is more than 20% higher than that of the subject area and the background area in reflection and optionally also in transmission.

Micromirrors, hologram gratings and/or sawtooth gratings are preferably used in the motif area and background area, and sub-wavelength structures (especially color-filtering or moth-eyes), hologram gratings and/or matt structures are used in the outline area.

The relief structure is preferably produced using lithographic methods, for example an e-beam system or a laser writing system which works, for example, with a two-photon absorption process. Alternatively, it can be created in a two-step lithographic process. In a first step, nanostructuring is carried out. This is done, for example, by an electron beam lithographic process. Alternatively, laser beam interference methods can also be considered. Aperiodic moth-eye structures can also be produced by plasma etching or by structuring with ultra-short laser pulses. In a subsequent step, such an original or a copy of it is leveled with photoresist. Spin coating or dip coating processes are particularly suitable for this. Then the relief structure is written in the photoresist in a photolithographic step and the desired areas of the structures are exposed. This process can be done with the help of a laser writer in the direct exposure process. The resulting original can then be copied galvanically or using photopolymers (e.g. Ormocere). The surface structure of one made in this way Stamps can now be duplicated next to each other over a larger area using a step-and-repeat process. An embossing cylinder can be produced from this original, which has been replicated on the surface, by galvanic molding. Finally, the structure can be embossed on foil in a continuous roll-to-roll process. Nanoimprint processes such as hot embossing or embossing in UV-curable materials can be used here. Finally, the embossed foil is metallically vapour-deposited. The common evaporation processes are electron beam evaporation, thermal evaporation or sputtering. Metals such as aluminum, silver, copper, palladium, gold, chromium, nickel, iron, cobalt and/or tungsten and their alloys can be used as the metallic material. After the vapor deposition, the structure is optionally laminated and protected with the cover film 9. Instead of a simple metal coating, the relief structure can also be coated with a multiple layer. So-called color-shift coatings, which consist of a semi-transparent metal layer, a dielectric spacer layer and a metallic mirror layer located underneath, are particularly suitable for this purpose. SiO ₂ , MgF ₂ , Ta ₂ O ₅ , ZnS and polymers are particularly suitable as dielectrics. Another alternative is a dielectric coating with a high-index material. If additional demetallized areas are required on the film element, wash ink is printed on the desired areas before vapor deposition and then removed after vapor deposition. Alternatively, these areas can also be created with laser demetallization or wet-chemical etching processes.

In a further embodiment, a motif (eg in the form of a cord) is provided with a movement effect. The motif area 1, 4 is generated by a series of micromirrors and has a "rolling Bar" effect on how they look eg DE 102010047250 A1 are known in which bright bars move up and down when tilted. The movements of several bars can be the same or opposite. Such motifs are much easier to recognize with outlines, since otherwise a viewer might only see a "mess" of bright light reflections. The outline area makes the actual shape easily visible to a viewer. He can e.g. B. by color-filtering sub-wavelength structures or - be realized by moth eye structures - if a dark contour is desired. In particularly advantageous variants, the micromirrors can be provided with a colour-shifting coating (eg triple-layer structure with the sequence absorber, dielectric, reflector). The relief structures in the contour line area particularly advantageously change the color impression of this coating, e.g. B. by suitable sub-wavelength structures. In this way, not only light or dark outlines can be generated, but also outlines with a different color than the color within the motion effects.

Another effect that can be produced in particular with sub-wavelength structures in the outline area is higher transmission. Metallic sub-wavelength gratings, which have a pronounced transmission, show a clear contrast to flat surfaces, hologram gratings or micro-mirror structures. In particular when using moth-eye structures in the outline area, this appears dark when viewed from above and light when viewed through (e.g. when used in a banknote window). If color-filtering sub-wavelength structures are used in the outline area, the color of the outline area can differ from the color of the motif area with a movement effect when viewed from above or seen through. The outline area itself can also show different colors in reflected and transmitted light.

Reference sign

1.4

subject area

2

background area

3

outline area

5

substrate film

6

embossing layer

7

hologram structure

8th

top layer

9

cover sheet

10

hologram structure

12

sub-wavelength grating

13

micromirror structure

14

moth eye texture

15

smooth area

16

transmissive hologram grating

17

opaque hologram grid

S

security element

E

incident radiation

R

reflected radiation

T

transmitted radiation

0.O.

zero order

1. O

first order

I-III

area

Claims (15)

1. A security element for producing security documents, such as bank notes, checks or the like, which displays a motif on a background, wherein the security element (S) has a relief structure (7, 10, 12, 13, 14, 16, 17), which covers a motif region (1, 4) of the security element (S) and provides the motif there and covers a background region (2) of the security element (S) and provides the background there, wherein an outline is provided, which delimits the motif region (1, 4) from the background region (2) and which is also formed by the relief structure, wherein the relief structure (12,14,17) of the outline differs from the relief structure (12,13,16a) of the motif region (1, 4) and the relief structure (7,16) of the background region (2), so that a brightness and/ or color contrast exists between the outline, on the one hand, and the motif region (1, 4) and the background region (2), on the other hand.
2. The security element as claimed in claim 1, characterized in that the relief structure (12,14) of the outline has a sub-wavelength grating.
3. The security element as claimed in claim 2, characterized in that the motif region (1, 4) and background region (2) are otherwise free of sub-wave gratings.
4. The security element as claimed in claim 2 or 3, characterized in that the relief structure of the outline has a moth-eye structure (14).
5. The security element according to claim 4, characterized in that the motif region (1, 4) and background region (2) are otherwise free from moth-eye structures.
6. The security element as claimed in any one of claims 1 to 5, characterized in that the relief structure (12,14) of the outline has micro-cavities.
7. The security element as claimed in any one of claims 1 to 6, characterized in that the relief structure of the outline has a micromirror structure.
8. The security element as claimed in any one of claims 1 to 7, characterized in that the relief structure of the outline has a hologram structure.
9. The security element as claimed in any one of claims 1 to 8, characterized in that the relief structure of the outline has retro-reflection structures.
10. The security element as claimed in any one of claims 1 to 9, characterized in that the relief structure of the outline is metallic, highly refractive or coated with a color effect-producing layer composite.
11. The security element as claimed in any one of claims 1 to 10, characterized in that the outline comprises a contour line for a motif component.
12. The security element as claimed in claim 11, characterized in that the structuring of the outline comprises interruptions in the outline and/or microtext or information items not detectable or resolvable with the naked eye.
13. A security document having a security element as claimed in any one of claims 1 to 12.
14. A production method for a security element (S) for producing security documents, such as banknotes, checks or the like, which displays a motif on a background, wherein a relief structure (7, 10, 12, 13, 14, 16, 17) is generated, which covers a motif region (1, 4) of the security element (S) and provides the motif there and covers a background region (2) of the security element (S) and provides the background there, wherein an outline is provided, which delimits the motif region (1, 4) from the background region (2) and which is also formed by the relief structure, wherein the relief structure (12,14,17) of the outline differs from the relief structure (10,13,16a) of the motif region (1, 4) and the relief structure (7,16b) of the background region (2), so that a brightness and/or color contrast exists between the outline, on the one hand, and the motif region and the background region (2), on the other hand.
15. The production method as claimed in claim 14, characterized in that the security element is produced according to any one of claims 1 to 12.

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