Security element with color shift film structure

Abstract

The invention relates to a security element (20) for protecting documents of value, comprising a color-shifting film structure comprising an absorber layer (22), a reflective layer (24) and a dielectric spacer layer (28) arranged between the absorber layer and the reflective layer, Here, according to the invention, an ultra-thin tackifier layer (28) having a thickness between 1 nm and 10 nm is arranged between the dielectric spacer layer (26) and the reflective layer (24).

Description

Technical Field

[0001] The invention relates to a security element for protecting valuable documents, which has a color-shifting thin-film structure comprising an absorber layer, a reflector layer and a dielectric spacer layer arranged between the absorber layer and the reflector layer. Background Art

[0002] For security purposes, data carriers (such as value or identification documents) and other valuable objects (e.g., trademarked items) are often equipped with a security element. This element allows verification of the authenticity of the data carrier and simultaneously protects against unauthorized copying. Security elements can take the form of, for example, a security thread embedded in a banknote, a cover foil for a banknote with a hole, an applied security strip, a self-supporting transfer element, or even a characteristic area directly embossed on the value document.

[0003] Security elements with a perspective-dependent appearance play a special role in guaranteeing authenticity, as they cannot be reproduced even with the most modern duplicators. To this end, security elements are equipped with optically variable elements that convey different image impressions to the observer from different viewing angles and, for example, display different colors or brightness impressions and / or different graphic patterns depending on the viewing angle.

[0004] To this end, security elements are often used that feature multilayer thin-film elements whose color impression to the observer changes with viewing angle (hereinafter referred to as a color shift effect). In such thin-film elements, the color shift effect is based on a viewing angle-dependent interference effect caused by multiple reflections in the element's different sublayers. The path difference of light reflected at the different layers depends on the optical thickness of the dielectric spacer layer, which determines the distance between the semitransparent absorber layer and the reflective layer, and also varies with the respective viewing angle. Because the path difference is on the order of the wavelength of visible light, the angle-dependent color impression is produced for the viewer due to destructive interference and amplification of certain wavelengths. A variety of different color shift effects can be produced by appropriately selecting the materials and thicknesses of the layers involved in the interference effect.

[0005] However, known thin-film elements having a layer sequence consisting of an absorber layer, a dielectric spacer layer, and a reflector layer tend to have a high tendency to split, which depends on the thickness of the dielectric spacer layer and also on any embossing lacquer that may be used and arranged below the layer sequence of the thin-film element. Problems can arise in particular in the production of security elements having a thin-film structure, particularly in terms of cycling stability, due to the poor adhesion of the reflector layer material to the dielectric spacer layer. Summary of the Invention

[0006] Starting from this perspective, the object of the present invention is to specify a security element of the aforementioned type which has improved splitting protection and high cyclic stability.

[0007] This object is achieved by the features of the independent claim. Further developments of the invention are the subject matter of the dependent claims.

[0008] According to the present invention, in a general security element, an ultra-thin tackifier layer with a thickness between 1 nm and 10 nm is provided and is arranged between the dielectric spacer layer and the reflective layer. The inventors have surprisingly found that the adhesion between the dielectric spacer layer and the reflective layer has been significantly improved by this additional ultra-thin tackifier layer, particularly a chromium layer or a titanium layer, and can overcome the problems associated with the splitting tendency of traditional three-layer structures. At the same time, the ultra-thin tackifier layer within the thickness range mentioned has only a slight influence on the color effect and the color shift effect of the film structure. If necessary, this slight influence can be compensated by adjusting the layer thickness of the dielectric spacer layer.

[0009] In a preferred embodiment, the absorber layer is formed by a chromium layer, which advantageously comprises a layer thickness between 2 nm and 10 nm, for example approximately 6 nm.

[0010] The reflective layer is advantageously formed from an aluminum layer, in particular an opaque aluminum layer. The aluminum layer may have a layer thickness between 5 nm and 200 nm, in particular between 30 nm and 100 nm.

[0011] The dielectric spacer layer is advantageously formed by a SiO 2 layer. Here, the layer thickness of the dielectric spacer layer is selected so that the desired color shift effect is achieved, ie a first color impression when viewed vertically and a second color impression different from the first color impression when viewed obliquely.

[0012] The ultra-thin adhesion promoter layer is advantageously formed by a chromium layer or a titanium layer, preferably by a chromium layer or a titanium layer having a thickness between 1 nm and 4 nm. Currently, the use of chromium as an adhesion promoter layer is particularly preferred.

[0013] An ultrathin chromium or titanium layer thickness of 3 nm has proven to be particularly advantageous.

[0014] In a preferred design, the color shifting thin film structure constitutes a four-layer structure, which sequentially includes an absorber layer composed of chromium, a dielectric spacer layer composed of SiO2, the ultra-thin chromium layer, and a reflective layer composed of aluminum.

[0015] In an advantageous development of the invention, the color-shifting film structure is applied to an embossed lacquer layer provided with a relief structure.

[0016] Here, the relief structure is advantageously a diffraction structure, in particular a hologram, a holographic grating image or a hologram-like diffraction structure, an achromatic structure, in particular a matte structure, or a micromirror device with a sawtooth groove profile or a blazed grating or a Fresnel lens device, or is formed by a combination of two or more of said structures.

[0017] The security element is preferably a security thread, a security strip, a patch or a label.

[0018] The present invention also includes a data carrier, in particular a valuable document, having a security element of the described type. The data carrier can be, in particular, a valuable document, such as a banknote, in particular a paper banknote, a polymer banknote, or a foil composite banknote, a stock certificate, a bond, a certificate, a voucher, a check, a valuable ticket, and an identification card, such as a credit card, a bank card, a cash card, an authorization card, a personal identification card, or a personalized page of a passport. The security element can be arranged, in particular, in the window area of ​​the data carrier.

[0019] The invention also includes a method for producing a security element of the described type, wherein an absorber layer, a dielectric spacer layer and a reflector layer are applied to a substrate, and wherein an ultrathin adhesion promoter layer with a thickness of between 1 nm and 10 nm is applied (in particular sputtered) between the dielectric spacer layer and the reflector layer.

[0020] The substrate can be formed in particular by a carrier foil or by an already coated carrier foil, for example provided with an embossed embossing lacquer layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Further exemplary embodiments and advantages of the present invention are explained below with reference to the accompanying drawings, in which the depiction to scale and proportion is omitted in order to improve the clarity thereof.

[0022] Shown are:

[0023] Figure 1 Schematic diagram of a banknote with two security elements according to the invention,

[0024] Figure 2 A cross section of a security element according to an exemplary embodiment of the present invention, and

[0025] Figure 3 According to a further exemplary embodiment of the invention, a security element is provided in which the color-shifting thin-film structure is combined with a relief structure. DETAILED DESCRIPTION

[0026] The invention will now be explained using the example of a security element for a banknote. Figure 1A schematic diagram of a banknote 10 is shown, which is equipped with two security elements 12 and 14 according to the invention. The first security element constitutes a security thread 12 applied to the surface of the banknote. Of course, this security thread can also be formed by a window security thread, which appears at certain window areas on the surface of the banknote and is embedded in the banknote interior in the areas located therebetween.

[0027] The second security element is formed by an attached transfer element 14 of any shape, which is arranged in a window region 16 of the banknote 10 and covers there, for example, a through-opening in the banknote. However, the transfer element can also be arranged on an opaque or translucent material region of the banknote.

[0028] Now refer to Figure 2 Explaining in more detail the special structure of the security element according to the invention, for example the security thread 12 or the transfer element 14 , Figure 2 A cross section through a security element 20 according to the invention is shown schematically.

[0029] The security element 20 comprises a four-layer, color-shifting thin-film structure having an absorber layer 22 composed of chromium, a reflective layer 24 composed of aluminum, and a dielectric spacer layer 26 composed of SiO 2 arranged between the absorber layer 22 and the reflective layer 24. As a distinguishing feature, to improve adhesion, an ultrathin chromium layer 28 with a thickness of between 1 nm and 10 nm, in particular between 1 nm and 4 nm, is arranged between the dielectric spacer layer 26 and the reflective layer 24, resulting in a total of a four-layer structure.

[0030] Surprisingly, it has been shown that by means of such an additional ultra-thin chromium layer 28 the adhesion between the spacer layer 26 and the reflector layer 24 can be significantly improved and the problems associated with the tendency towards splitting of conventional three-layer structures can be reduced or even completely overcome.

[0031] In this case, a layer thickness of approximately 3 nm for the ultra-thin chromium layer 28 has proven to be particularly effective.

[0032] Due to the presence of the additional (somewhat light-absorbing) chromium layer 28, the color effect of the original layer sequence consisting of absorber 24, dielectric 26 and reflector 28 is indeed slightly shifted, but this shift can easily be compensated if necessary by adjusting the layer thickness of the dielectric spacer layer 26. As a result, a thin-film structure according to the invention can be provided with the same color effect as a conventional thin-film structure, but with significantly improved splitting protection.

[0033] It should be understood that, depending on the application, Figure 2 The basic layer structure in can be supplemented by further layers known per se, such as protective layers, adhesive layers or embossed lacquer layers. Instead of an ultra-thin chromium layer, an ultra-thin titanium layer can also be used to improve adhesion.

[0034] Figure 3 A security element 30 according to a further exemplary embodiment of the invention is shown, in which a colour-shifting thin film structure is combined with a relief structure, such as a micromirror arrangement.

[0035] The security element 30 comprises a carrier foil 32, for example a transparent, colorless PET foil, to which an embossing lacquer layer 34 is applied and provided with a relief embossing 36. The relief embossing 36 can constitute, for example, a micromirror arrangement in order to produce a desired optical effect.

[0036] Then, as already in principle Figure 2 In this example, an absorber layer 22 composed of chromium, a dielectric spacer layer 26 composed of SiO2, an ultrathin chromium layer 28 having a thickness between 1 nm and 10 nm, in particular between 1 nm and 4 nm, and a reflective layer 24 composed of aluminum are applied to an embossed embossing lacquer layer 34. Furthermore, a leveling lacquer layer 38 and further layers 40, such as a primer layer and an adhesive layer, are provided for applying the security element to a target substrate. After the security element has been applied to the target substrate, the carrier foil 32 can be removed, or alternatively, it can remain in the layer structure. In the former case, a release layer can also be provided between the carrier foil 32 and the embossing lacquer layer 34 to facilitate its release.

[0037] Figure 3 The security element 30 in FIG. 3 is designed for viewing from one side of the carrier foil 32 because, from this viewing direction, the reflective layer 24 constitutes the thin-film structure layer farthest from the viewer. If viewing were to occur from the opposite side of the security element, the layers of the thin-film structure could also be applied to the embossing lacquer layer 34 in the reverse order, i.e., in the order of reflective layer 24, adhesion-improving ultra-thin chromium layer 28, dielectric spacer layer 26, and absorber layer 22. A leveling lacquer layer 38 and a further layer 40 are then applied to the absorber layer 22.

[0038] In this embodiment, an ultra-thin titanium layer may be used instead of the ultra-thin chromium layer to improve adhesion.

[0039] Reference numerals

[0040] 10 banknotes

[0041] 12 Safety Line

[0042] 14 Transfer elements

[0043] 16 Window Area

[0044] 20 Security Element

[0045] 22 Absorber layer

[0046] 24 Reflection layer

[0047] 26 Dielectric spacer

[0048] 28 Ultra-thin chrome layer

[0049] 30 Security Elements

[0050] 32 Carrier Foil

[0051] 34 Embossed paint layer

[0052] 36 Embossed

[0053] 38 Leveling paint layer

[0054] 40 additional layers

Claims

1. A security element for protecting valuable documents, comprising a color-shifting thin-film structure comprising an absorber layer, a reflector layer and a dielectric spacer layer arranged between the absorber layer and the reflector layer, It is characterized in that An ultra-thin adhesion promoter layer having a thickness between 1 nm and 10 nm is disposed between the dielectric spacer layer and the reflective layer.

2. The security element according to claim 1, characterized in that The absorber layer is formed of a chromium layer.

3. The security element according to claim 1 or 2, characterized in that The reflective layer is formed of an aluminum layer.

4. The security element according to any one of claims 1 to 3, characterized in that The dielectric spacer layer is formed of a SiO2 layer.

5. The security element according to any one of claims 1 to 4, characterized in that The ultra-thin adhesion promoter layer is formed of a chromium layer or a titanium layer, preferably a chromium layer or a titanium layer with a thickness between 1 nm and 4 nm.

6. The security element according to claim 5, characterized in that The ultra-thin chromium or titanium layer comprises a thickness of 3 nm.

7. The security element according to any one of claims 1 to 6, characterized in that The color-shifting film structure is applied to an embossed lacquer layer provided with a relief structure.

8. The security element according to claim 7, characterized in that The relief structure forms a diffractive structure, in particular a hologram, a holographic grating image or a hologram-like diffractive structure, an achromatic structure, in particular a matte structure, a micromirror arrangement, a blazed grating with a sawtooth groove profile or a Fresnel lens arrangement, or a combination of two or more of these structures.

9. The security element according to any one of claims 1 to 8, characterized in that The security element is a security thread, a security strip, a patch or a label. 10 . A data carrier, in particular a value document, having a security element according to claim 1 .

11. Method for producing a security element according to any one of claims 1 to 9, wherein an absorber layer, a dielectric spacer layer and a reflective layer are applied to a substrate, and wherein an ultrathin adhesion promoter layer with a thickness of between 1 nm and 10 nm is applied, in particular sputtered, between the dielectric spacer layer and the reflective layer.

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