FLAT SECURITY ELEMENT WITH OPTICAL SECURITY FEATURES

Abstract

A flat security element with optical security features includes at least one first surface region with a first sub-wavelength structure. The structure elements that define the first sub-wavelength structure periodically repeat in the plane of the security element. In order to be able to convey a motif with increased forgery protection using at least two different color impressions, which motif is easy to produce, the first sub-wavelength structure of at least one partial region of the first surface region is additionally provided with an interference coating for producing a color-shifting effect.

Claims

1. A flat security element with optical security features, comprising at least one first surface region with a first sub-wavelength structure, wherein the structure elements that define the first sub-wavelength structure periodically repeat in the plane of the security element, wherein the first sub-wavelength structure of at least one partial region of the first surface region is additionally provided with an interference coating for producing a color-shifting effect, wherein an unstructured surface region lies adjacent to a first surface region, which unstructured surface region does not have a sub-wavelength structure, but has, at least in one partial region, the same interference coating as at least one partial region of the first surface region, and wherein a motif is conveyed by the first surface region and the unstructured surface region using at least two different color impressions.

2. (canceled)

3. The flat security element according to claim 1, wherein the security element comprises, in addition to a first surface region with a first sub-wavelength structure, at least one second surface region with a second sub-wavelength structure, with the first surface region being arranged beside the second surface region, wherein the structure elements which define the first and second sub-wavelength structures and that periodically repeat in the plane of the security element are different for both surface regions.

4. The flat security element according to claim 1, wherein the security element comprises, in addition to a first surface region with a first sub-wavelength structure, at least one second surface region with a second sub-wavelength structure, with the first surface region being arranged beside the second surface region, wherein the structure elements which define the first and second sub-wavelength structures and that periodically repeat in the plane of the security element are the same for both surface regions, but are oriented towards a first surface of the security element in the first surface region and are oriented towards a second surface of the security element in the second surface region, which second surface is opposite from the first surface.

5. The flat security element according to claim 3, wherein the second sub-wavelength structure of at least one portion of the second surface region is additionally provided with an interference coating for producing a color-shifting effect.

6. The flat security element according to claim 1, wherein the first sub-wavelength structure of a first surface region and/or possibly the second sub-wavelength structure of a second surface region comprise two or more different interference coatings for producing a color-shifting effect beside one another.

7. The flat security element according to claim 1, wherein at least one first surface region is arranged adjacently to a second surface region.

8. The flat security element according to claim 3, wherein the first surface region is arranged spaced apart from the second surface region, wherein an unstructured surface region that does not have a sub-wavelength structure lies between the first and second surface regions.

9. The flat security element according to claim 3, wherein the structure elements that define the first and second sub-wavelength structures comprise columns or holes and the plane of the top surfaces of the columns in the first surface region corresponds to the plane of the surrounding surfaces of the columns in the second surface region, or that the plane of the bottoms of the holes in the first surface region corresponds to the plane of the surrounding surfaces of the holes in the second surface region.

10. The flat security element according to claim 1, wherein the interference coating is applied directly to the sub-wavelength structure at least in one surface region

11. The flat security element according to claim 1, wherein the effective depth of the sub-wavelength structure is smaller than the thickness of the interference coating.

12. A data storage device or value document comprising a security element according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The invention will now be explained in greater detail with the aid of schematic drawings which depict the exemplary embodiments of device according to the invention. The following are thereby shown:

[0047] FIG. 1 a top view of a flat security element according to the invention, still without interference coating;

[0048] FIG. 2 a top view of the security element from FIG. 1, with interference coating;

[0049] FIG. 3 a longitudinal section through the security element from FIG. 2 according to the sectional line A-A;

[0050] FIG. 4 a longitudinal section through a security element according to the invention with two sub-wavelength structures and an interference coating;

[0051] FIG. 5 a longitudinal section through a security element according to the invention with two sub-wavelength structures inverted from one another and an interference coating.

WAYS OF EMBODYING THE INVENTION

[0052] FIG. 1 shows the top view of a flat security element 4, which is rectangular in this case. In a first surface region 1, it comprises a first sub-wavelength structure. In the adjacent surface region, no sub-wavelength structure is provided; this is an unstructured surface region 3. The boundary between the two surface regions 1, 3 is formed by the diagonal of the rectangle.

[0053] In order to provide the security element 4 with the feature of the interference coating 5 according to the invention, an interference coating 5 is then applied in a rectangular partial region of the security element 4, but not in the remaining portion of the security element 4; see FIG. 2, where an interference coating 5 covers slightly more than the right half of the security element 4. In this case, the interference coating 5 has the same properties everywhere, that is, is an identically designed interference coating shared by both surface regions 1, 3. The interference coating 5 thus has the same thickness and the same construction everywhere. In this manner, it is still possible to achieve four different color effects.

[0054] Of course, one or more differently shaped first surface regions I with a first sub-wavelength structure can be present on a security element 4, and many separate first surface regions 1 with a first sub-wavelength structure can be present, wherein one contiguous or many separate unstructured surface regions 3 can be located between and/or around these first surface regions

[0055] In this case, all surface regions 1, 3 can thereby be provided with the same continuous interference coating 5, or only some surface regions 1, 3 can be completely or partially covered with a contiguous, full-area interference coating 5. Or, multiple separate regions can be provided with an interference coating 5 which only cover the first surface regions 1 congruently. Or, the region(s) of the interference coating 5 do not completely overlap with first surface regions 1 and from a pattern independent thereof.

[0056] The security element 4 illustrated can be part of a value document, for example can cover a partial area of a value document.

[0057] FIG. 3 shows a longitudinal section through the security element 4 in order to display the construction of the sub-wavelength structure and of the interference coating 5. The plane of the security element 4 thus runs horizontally here. The first sub-wavelength structure is provided in the first surface region 1. This structure is composed of columns 8 that periodically repeat in two directions with one period P each. In this case, only the period P in the direction from left to right in the drawing plane is visible. The period in the direction perpendicular to the drawing plane can be the same as or different from that in the drawing plane. The height of the columns 8 corresponds to the effective depth T of the sub-wavelength structure. The columns 8 can have any desired cross section, for example, circular, oval, rectangular, or square. The cross section should, to the extent possible under production conditions, ideally be constant over the height of the column 8.

[0058] On the sub-wavelength structure of the first surface region 1 and on the unstructured surface region 3, the interference coating 5 is then applied, which in this case is composed of three layers: The reflective layer 13 is applied directly to the top surface 9 of the column 8, to the surrounding surface 10 of the column 9, and to the surface of the unstructured surface region 3. The dielectric layer 6 is then applied to this reflective layer 13. The absorber layer 7 is applied to the dielectric layer 6. The reflective layer 13 could optionally be omitted. A coating or lamination can then be applied to the absorber layer 7.

[0059] With the, normally metallic, reflective layer 13 of the interference coating 5, plasmonic effects can also be excited.

[0060] Light would, in this case, fall on the security element from above; the color effect that is caused by the sub-wavelength structure together with the interference coating would accordingly be visible in the reflected light, that is, from above. Light could also fall on the security element from below (if the carrier substrate 12 is translucent); the color effect that is caused by the sub-wavelength structure would likewise accordingly be visible in the reflected light, that is, from below. A color effect in transmission (if the carrier substrate 12 is translucent) is not precluded, however.

[0061] FIG. 4 shows a longitudinal section through a security element 4 that comprises two different sub-wavelength structures. The first sub-wavelength structure is provided in the first surface region 1. In the second surface region 2, a second sub-wavelength structure is provided Which differs from the first in that the columns thereof 11 are less high and wide. These columns 11 also periodically repeat in two directions with one period each, which in the drawing plane can be the same as or different from that Which is perpendicular to the drawing plane. The period of the sub-wavelength structure of the first surface region I can be different from that of the second surface region 2. The two surface regions 1, 2 with sub-wavelength structures are separated by an unstructured surface region 3 without sub-wavelength structures. All three surface regions 1-3 are provided with the same interference coating 5.

[0062] In this manner, it is possible to convey, at different viewing angles, up to six different color impressions, two different color impressions each per surface region 1-3. If the first surface region 1 and/or the second surface region 2 are not completely covered with an interference coating 5, that is, in FIG. 4 for example the regions lying further to the left or right no longer bear an interference coating 5, two different color impressions per structured surface region 1, 2 can also be achieved at the same viewing angle.

[0063] However, the unstructured surface region 3 could also be omitted, so that the first surface region 1 and second surface region 2 are directly adjacent to one another. Additional surface regions, also with other sub-wavelength structures, can also be provided.

[0064] FIG. 5 shows a longitudinal section through a security element 4 that comprises two different sub-wavelength structures. Both sub-wavelength structures are constructed using the same structure elements, namely columns 11, but in this ease the columns 11, which periodically repeat in two directions in the plane of the security element 4, are oriented towards a first surface of the security element 4 in the first surface region 1 and are oriented towards a second surface of the security element 4 in the second surface region 2, which second surface is opposite from the first surface. Both surface regions 1, 2 are provided with the same interference coating 5. The two surface regions 1, 2 with sub-wavelength structures could also be separated by an unstructured surface region 3 without sub-wavelength structures.

[0065] In this embodiment, the sub-wavelength structure of the second surface region 2 corresponds to that of FIG. 4. Here, the sub-wavelength structure of the first surface region 1 is mirrored from that of the second surface region 2, namely over a plane that is horizontal in this case. The columns 11 of the first surface region 1 are in this case directed downward and form when the depressions in the carrier substrate 12 are filled.

[0066] Here, the plane of the top surfaces 9 of the columns 11 in the first surface region 1 lie in the plane of the surrounding surfaces 10 of the columns 11 in the second surface region 1.

LIST OF REFERENCE SIGNS

[0067] First surface region

[0068] 2 Second surface region

[0069] 3 Unstructured surface region

[0070] 4 Security element

[0071] 5 Interference coating

[0072] 6 Dielectric layer

[0073] 7 Absorber layer

[0074] 8 Column

[0075] 9 Top surface of the column

[0076] 10 Surrounding surface of the column

[0077] 11 Column

[0078] 12 Carrier substrate

[0079] 13 Reflective layer

[0080] P Period

[0081] T Effective depth