Optically variable security element comprising a colour-shifting interference layer element, item of value, and manufacturing method

Abstract

The invention relates to an optically variable security element (12) for securing security papers, value documents, and other items of value, said security element comprising at least one colour-shifting, multilayer interference layer element (22) having a reflector layer (28), at least one absorber layer (24), and at least one dielectric spacer layer (26) that is positioned between the reflector layer (28) and the at least one absorber layer (24), wherein the multilayer interference layer element (22), owing to its layered structure, produces an intrinsic colour-shifting effect with a first colour when viewed from a first viewing direction and a different second colour when viewed from a second viewing direction. According to the invention, a blue-light absorber (32) having an absorption edge within the wavelength range of 380 nm to 460 nm is arranged above and / or below the at least one multilayer interference layer element (22), said absorber selectively absorbing the blue light component and thereby modifying the intrinsic colour-shifting effect of the at least one multilayer interference layer element (22) such that the security element (12) exhibits a modified colour-shifting effect between a third colour when viewed from the first viewing direction (40) and a different fourth colour when viewed from the second viewing direction (42), wherein the third colour differs from the first colour in hue and / or colour purity and / or the fourth colour differs from the second colour in hue and / or colour purity.

Description

[0001] Optically variable security element with color-shifting

[0002] Interference layer element, valuable object and manufacturing process

[0003] The invention relates to an optically variable security element for protecting security papers, valuable documents, and other valuables, comprising at least one color-shifting, multilayer interference layer element. The invention also relates to a method for producing such a security element and a correspondingly equipped valuable object.

[0004] Valuable items, such as security paper, valuables, or identification documents, are often provided with security elements for protection. These allow the authenticity of the valuable item to be verified and also serve as protection against unauthorized reproduction. Security elements with viewing-angle-dependent effects play a special role in authenticity assurance, as these cannot be reproduced even with the most modern copying machines. These security elements are equipped with optically variable elements that convey a different image impression to the viewer at different viewing angles, for example, displaying a different color or brightness impression and / or a different graphic motif depending on the viewing angle.

[0005] Security elements with multilayer thin-film elements are often used, whose color impression changes for the viewer with the viewing angle (hereinafter referred to as the color shift effect). The layer primarily responsible for the color effect is a thin dielectric layer, typically arranged between an absorber layer and a reflective layer. These thin-film elements represent interference layer elements, in which the colors generated in reflection are produced by interference of the light rays reflected from various sublayers of the element. Therefore, such interference layer elements can only produce specific color changes compatible with the physical interference conditions.In some cases, the colors produced are also created by mixing spectral colors, for example red and blue, and then often have a dark and unattractive appearance due to the lack of color purity.

[0006] Based on this, the invention is based on the object of specifying a generic security element which avoids the disadvantages of the prior art and which in particular enables the generation of color shift effects with novel color changes or with color changes between colors of high color purity.

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

[0008] The invention contains an optically variable security element for protecting security papers, valuable documents and other valuables.

[0009] The security element contains at least one color-shifting, multilayer interference layer element with a reflector layer, at least one absorber layer, and at least one dielectric spacer layer arranged between the reflector layer and the at least one absorber layer. The multilayer interference layer element, with its layer structure, generates an intrinsic color-shift effect with a first color in a first viewing direction and a different second color in a second viewing direction.

[0010] A blue light absorber with an absorption edge in the wavelength range between 380 nm and 460 nm is arranged above and / or below the at least one multilayer interference layer element. This absorber modifies the intrinsic color-shift effect of the at least one multilayer interference layer element by selectively absorbing the blue light component. The security element therefore exhibits a modified color-shift effect between a third color in the first viewing direction and a different fourth color in the second viewing direction, wherein the third color differs from the first color in hue and / or color purity and / or the fourth color differs from the second color in hue and / or color purity.

[0011] The color-shift effect of the security element as a whole is also referred to as the extrinsic color-shift effect in this description to distinguish it from the intrinsic color-shift effect of the interference layer element. The extrinsic color-shift effect arises as a combination effect through the influencing and modification of the intrinsic color-shift effect by the blue light absorber of the selective absorption layer. This allows, in particular, a targeted change of the first and / or second color to colors of greater color purity or to colors that cannot be produced by interference effects alone.

[0012] The absorption edge of the blue light absorber is particularly advantageously located in a narrower wavelength range between 400 nm and 440 nm. The exact position of the absorption edge of the blue light absorber is advantageously matched to the reflection spectrum of the multilayer interference layer element, in particular to the position of a short-wavelength peak in the first and second viewing directions.

[0013] According to a particularly preferred embodiment, the multilayer interference layer element has a reflection spectrum with a short-wavelength peak in the blue spectral range, the maximum of which lies at a first wavelength in the first viewing direction and at a second, different wavelength in the second viewing direction, wherein the absorption edge of the blue light absorber lies between the first and second wavelength.

[0014] The blue light absorber advantageously exhibits a sharp transition at its absorption edge from high absorption at shorter wavelengths to high transmission at longer wavelengths. The width of the absorption edge of the blue light absorber, defined as the wavelength difference between 10% and 90% of the maximum transmission in the wavelength range between 350 nm and 500 nm, is preferably less than 40 nm, advantageously less than 30 nm, and in particular less than 20 nm. A sharp absorption edge allows for a targeted and particularly effective modification of the intrinsic color shift effect of the multilayer interference layer element.

[0015] Preferably, the blue light absorber is highly transparent in the visible range at wavelengths above the absorption edge and preferably has a transmission of at least 80%, advantageously at least 90%, or even at least 95%, in order to minimize the impact on the long-wave red component of the reflected light. Below the absorption edge, the blue light absorber is advantageously highly absorbent and preferably has a transmission of less than 20%, less than 10%, or even less than 5%, in order to significantly suppress the short-wave blue component of the reflected light.

[0016] In an advantageous embodiment, the blue light absorber exhibits high light stability. The light stability of a blue light absorber can be defined and quantified, for example, by the change in shortwave absorption at the base of the absorption edge after irradiation of the absorber with a xenon arc lamp for 100 hours. For an absorber with little or no light stability, the shortwave absorption changes significantly; for example, the transmission increases from approximately 0% - 10% before irradiation to 50% - 70% after 100 hours of irradiation. In contrast, for a blue light absorber with high light stability, the shortwave absorption hardly decreases even after 100 hours of irradiation with a xenon arc lamp, and thus the shortwave transmission hardly increases.Advantageously, the transmission of the blue light absorber at the base of the absorption edge is still less than 20%, especially less than 10% or even less than 5%, after 100 hours of irradiation with a xenon arc lamp. The region at the base of the absorption edge, for example, covers a wavelength range of 30–40 nm below the base of the absorption edge in the transmission curve.

[0017] According to a further development of the invention, the blue light absorber has a high decomposition temperature of 270°C or more, in particular of 280°C or more. Blue light absorbers with a high decomposition temperature exhibit good long-term stability against environmental influences and in particular against solar radiation, thus allowing the production of security elements with a color-shift effect that remains constant over their lifetime. The at least one dielectric spacer layer is advantageously formed from SiCh, TiCl, ZnS, MgF, or Al2O3 and has a layer thickness between 100 nm and 500 nm. If two dielectric spacer layers are provided in the multilayer interference layer element, they are advantageously formed from the same material and with the same layer thickness.

[0018] The reflector layer is preferably made of aluminum, an aluminum-iron alloy, an iron alloy, or silver. The at least one absorber layer is advantageously made of chromium, an iron alloy, a chromium-iron alloy, or titanium. If two absorber layers are provided in the multilayer interference layer element, they are advantageously made of the same material. The security element can also contain more than one reflection layer, as explained in more detail below.

[0019] In an advantageous embodiment, with the intrinsic color-shift effect of the multilayer interference layer element, the first color is blue and the second color is a dark red of low color purity. With the extrinsic color-shift effect of the security element, the third color is a lighter blue compared to the first color, and the fourth color is a lighter and more color-pure red compared to the second color. In the context of this description, the term "lighter blue" does not refer to a blue of higher radiation intensity, but rather to a brighter, lighter, or more pastel blue appearance of the color.

[0020] A blue-to-red color shift effect is desirable in numerous applications. However, conventional designs based on the intrinsic color shift effect of the interference layer elements suffer, particularly from a dark red with low color purity when viewed at an angle, which is often difficult to detect and visually unattractive.

[0021] By selecting a suitable blue light absorber, particularly the position and width of the absorption edge, other color-shift effects can also be modified. For example, in another, equally advantageous embodiment, the first color for the intrinsic color-shift effect of the multilayer interference layer element is gold and the second color is green, while the third color for the extrinsic color-shift effect of the security element is orange and the fourth color is green or yellow. A color-shift effect with such a color change cannot be easily realized with conventional designs.

[0022] In a further, equally advantageous embodiment, the first color of the intrinsic color-shift effect of the multilayer interference layer element is magenta and the second color is green, while the third color of the extrinsic color-shift effect of the security element is red and the fourth color is green or yellow. A color-shift effect with such a color change is not easily realized with conventional designs.

[0023] The first viewing direction is preferably a vertical viewing direction and the second viewing direction is an oblique viewing direction of 45°.

[0024] In an advantageous variant of the invention, the security element comprises a carrier foil and a thin-film element applied over a large area to the carrier foil, which is formed by a single one of the aforementioned interference layer elements. The security element can then, in particular, be a foil security element, such as a security thread, a security band, or a security patch.

[0025] The thin-film element is advantageously formed by a three-layer interference layer element with a reflector layer, an absorber layer and a dielectric spacer layer arranged between the reflector layer and the absorber layer.

[0026] The blue light absorber is preferably arranged in a lacquer layer applied to the carrier film or the thin-film element, an embossing lacquer layer, a primer layer, a heat-sealing lacquer layer, or in the carrier film itself.

[0027] In an advantageous further development, the security element contains a translucent color layer with a red body color, which is preferably applied to the carrier film, the large-area thin-film element or a layer containing the blue light absorber.

[0028] In another, equally advantageous variant of the invention, the security element contains a printed layer containing, in a binder, a plurality of color-shifting, platelet-shaped pigments, each having a so-called interference layer element. In this variant, the security element can, in particular, be a printed element applied to a valuable object, but also a foil security element, such as a security thread, a security band, or a security patch. The platelet-shaped pigments advantageously each have an interference layer element with at least five layers, comprising an outer first absorber layer, a first dielectric spacer layer, a central reflector layer, a second dielectric spacer layer, and an outer second absorber layer.The platelet-shaped pigments are advantageously constructed symmetrically, so that the two absorber layers and the two dielectric spacer layers are each made of the same material and have the same layer thicknesses.

[0029] For magnetic alignment and / or the mechanical detection of their magnetic properties, the platelet-shaped pigments can in particular also contain at least one magnetic layer. Thus, an additional magnetic layer can be incorporated into the structure and / or the absorber and / or reflector layer can be formed from magnetic metal or a magnetic alloy. The magnetic layer can also form a middle layer in the layer structure of the platelet-shaped pigments, which, if the magnetic layer is not itself highly reflective, is expediently sandwiched between two reflective layers. The sandwich of reflective layer, magnetic layer, and second reflective layer can then be provided on each side with a dielectric spacer layer and an absorber layer, as described above, to form a preferably symmetrical interference layer element.

[0030] The blue light absorber is advantageously incorporated into the binder of the printing layer, or it is present in an overprint or overcoat of the printing layer. According to another variant, the blue light absorber is arranged in a coating of the platelet-shaped pigments themselves. The coating must be located outside the absorber layers in order to influence the intrinsic color-shift effect of the pigments. In particular, the coating with the blue light absorber can represent the outermost layer of the pigments.

[0031] In an advantageous further development, the security element contains a translucent ink layer with a red body colour, which is preferably applied to the printing layer with the colour-shifting, platelet-shaped pigments or a layer containing the blue light absorber.

[0032] The invention also includes a valuable object, in particular a security paper, a value document or an identity document with a security element of the type described.

[0033] Finally, the invention also includes a method for producing a security element of the type described, in which at least one color-shifting, multi-layer interference layer element is provided, which has a reflector layer, at least one absorber layer and at least one dielectric spacer layer arranged between the reflector layer and the at least one absorber layer, wherein the multi-layer interference layer element with its layer structure produces an intrinsic color-shift effect with a first color in a first viewing direction and a different second color in a second viewing direction, a blue light absorber with an absorption edge in the wavelength range between 380 nm and 460 nm is arranged above and / or below the at least one multi-layer interference layer element,which modifies the intrinsic color-shift effect of the at least one multilayer interference layer element by selective absorption of the blue light component, so that the security element exhibits a modified color-shift effect between a third color in the first viewing direction and a different fourth color in the second viewing direction, wherein the third color differs from the first color in hue and / or color purity and / or the fourth color differs from the second color in hue and / or color purity.

[0034] In an advantageous variant of the invention, a carrier foil is provided, and a thin-film element formed by a single one of the aforementioned interference layer elements is applied to the carrier foil over a large area. The partial layers of the thin-film element can be vapor-deposited, for example, using a PVD process.

[0035] The blue light absorber can be printed on the opposite side of the carrier film or on the thin-film element. The blue light absorber can also be incorporated into an embossing lacquer layer, a primer layer, a heat-seal lacquer layer, or into the carrier film itself.

[0036] In another advantageous variant of the invention, a security printing ink containing a binder containing a plurality of color-shifting, platelet-shaped pigments, each of which has a so-called interference layer element, is used to produce the security element. With such a security printing ink, a printing layer is applied directly to a target valuable item or to an intermediate carrier. The blue light absorber can be arranged in a binder of the printing layer, in an overprint or overcoat of the printing layer, or in a coating of the platelet-shaped pigments themselves.

[0037] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0038] They show:

[0039] Fig. 1 schematically shows a banknote with two optically variable security elements according to embodiments of the invention,

[0040] Fig. 2 schematically shows the layer structure of the first security element of Fig. 1 in cross section,

[0041] Fig. 3 is a diagram illustrating the origin of the intrinsic color shift effect of the interference layer element,

[0042] Fig. 4 shows the transmission of some blue light absorbers suitable for the invention in the wavelength range from 360 to 520 nm,

[0043] Fig. 5 the simulated reflection spectrum of the entire security element of Fig. 2,

[0044] Fig. 6 schematically shows the layer structure of a modification of the security element of Fig. 2, Fig. 7 schematically shows the layer structure of the second security element of Fig. 1 in cross section,

[0045] Fig. 8 one of the platelet-shaped pigments of Fig. 7 separately,

[0046] Fig. 9 schematically shows the layer structure of a modification of the security element of Fig. 7, and

[0047] Fig. 10 schematically shows the layer structure of a further development of the security element of Fig. 2.

[0048] The invention will now be explained using banknotes as an example. Figure 1 shows a schematic representation of a banknote 10 provided with two optically variable security elements 12 and 14 according to embodiments of the invention.

[0049] The first security element represents an adhesively bonded transfer element 12, the layer structure of which is shown schematically in the cross-section of Fig. 2. The second security element is formed by a printing element 14 printed on the paper substrate 16 of the banknote 10, which is described in more detail below in connection with Fig. 6.

[0050] Referring first to Fig. 2, the optically variable security element 12 exhibits a blue-to-red color shift effect, in which the color impression for a viewer changes between a strong blue when viewed vertically 40 and a strong red of high color purity when viewed obliquely 42.

[0051] The security element 12 contains a transparent carrier film 20, on whose

[0052] A color-shifting three-layer interference layer element 22 is arranged on the underside, which, starting from the carrier film 20, has an absorber layer 24 made of chromium, a dielectric spacer layer 26 made of SiO, and an opaque reflector layer 28 made of aluminum. To generate a blue-to-red color-shift effect, the layer thickness of the absorber layer can be, for example, between 2 nm and 8 nm, the thickness of the dielectric spacer layer between 220 nm and 330 nm, and the thickness of the aluminum layer between 20 nm and 50 nm.

[0053] The color shift effect generated by the interference layer element 22 alone is referred to in this description as the intrinsic color shift effect of the interference layer element 22. It is essentially determined by the material and layer thickness of the dielectric spacer layer 26.

[0054] With the specified layer structure, the interference layer element 22 in the exemplary embodiment produces a relatively unattractive intrinsic color shift effect, which alternates between a strong blue in the vertical viewing direction 40 and a dark red of low color purity in the oblique viewing direction 42.

[0055] To generate the visually attractive color-shift effect exhibited overall by the security element 12, a selective absorber layer 30 is applied to the upper side of the carrier film opposite the interference layer element 22. The selective absorber layer 30 contains a blue light absorber 32 with a sharp absorption edge at a wavelength of 430 nm (curve 68 in Fig. 4). As explained in detail below, the blue light absorber 32 of the selective absorption layer 30 significantly modifies the intrinsic color-shift effect of the interference layer element 22, so that the security element 12 overall exhibits a visually appealing color-shift effect between a lighter blue and a pure red. On the underside of the reflector layer 28, the security element 12 is also provided with an adhesive layer 36, with which it is adhered to the paper substrate 16 of the banknote 10.

[0056] Figure 3 first illustrates the occurrence of the intrinsic color shift effect of the interference layer element 22. The diagram 50 shows the reflection R of the interference layer element 22 as a function of the wavelength X at an almost vertical viewing angle of 8° (reflection curve 52) and at an oblique viewing angle of 45° (reflection curve 54).

[0057] As can be seen from the figure, the reflection spectrum of the interference layer element 22 has two peaks in the visible and near infrared range, a narrow short-wavelength peak 52-B or 54-B in the wavelength range of 400 - 500 nm and a broad, long-wavelength peak 52-R or 54-R in the wavelength range of 700 - 900 nm.

[0058] When viewed essentially perpendicularly (reflection curve 52), the maximum of the long-wavelength peak 52-R lies in the near infrared, while the maximum of the short-wavelength peak 52-B lies in the blue region at approximately 465 nm. When viewed perpendicularly, the color impression of the interference layer element 22 is therefore determined by the short-wavelength peak 52-B in the blue region. The increase in reflection at approximately 800 nm hardly affects the color purity of the blue color impression, since the spectral sensitivity of the human eye is already very low above 700 nm.

[0059] When viewed at an angle (reflection curve 54), the maximum of the long-wavelength peak 54-R has migrated into the visible red range, while the short-wavelength peak 54-B has not completely disappeared into the UV range, which is invisible to the human eye, but still exhibits a high intensity in the visible blue spectral range. Therefore, when viewed at an angle, the color impression of the interference layer element 22 is determined by an overlay of the two peaks 54-B and 54-R, which creates a mixed color perceived as dark red. Due to the low color purity, the dark red of the shift color, in particular, appears visually unattractive.

[0060] However, a visually attractive blue-red color shift effect is created by combining the interference layer element 22 with the blue light absorber 32 of the selective absorption layer 30.

[0061] Figure 4 shows, in diagram 60, the transmission of several blue light absorbers suitable for the present invention, such as those commercially available from Toyocolor, BASF or SEMA. In contrast to UV absorbers, which are typically used to suppress wavelengths below 380 nm, such blue absorbers can be used to specifically block wavelengths in the blue spectral range, in particular in the wavelength range between 380 nm and 450 nm. Figure 4 shows transmission curves 62, 64, 66, 68 of four blue light absorbers, each of which has an absorption edge at approximately 400 nm (curve 62), at approximately 415 nm (curve 64), at approximately 420 nm (curve 66) and at approximately 430 nm (curve 68). As usual, the position of the absorption edge is given as the wavelength at which the transmission of the absorber is Tiow + (Thigh - Tiow) / 2, where Ti owThigh denotes the transmission just below the absorption edge, and Thigh denotes the transmission just above the absorption edge. As can be seen from Fig. 4, the blue light absorbers combine high absorption in the blue spectral range on the short-wavelength side of the absorption edge with high transmission on the long-wavelength side of the absorption edge. The transition from high absorption to high transmission occurs in a very narrow wavelength range: The width of the absorption edges, defined here as the difference between the wavelength with 90% of the maximum transmission and the wavelength with 10% of the maximum transmission, each in the wavelength range between 350 nm and 500 nm, is only about 25 nm.

[0062] By selecting a blue light absorber with a suitable position and width of the absorption edge, an advantageous modification of the intrinsic blue-red color shift effect can be achieved. Specifically, in the exemplary embodiment shown in Fig. 2, for example, the blue light absorber 32 of the transmission curve 68 with an absorption edge at approximately 430 nm is selected. The absorption edge of the blue light absorber 32 is thus approximately midway between the short-wavelength peak 52-B for perpendicular viewing (at approximately 465 nm) and the short-wavelength peak 54-B for oblique viewing (at approximately 415 nm).

[0063] The modification of the color shift effect is illustrated in Fig. 5, which shows the measured reflection spectrum of the entire security element 12 in diagram 90.

[0064] Due to the high transmission of the blue light absorber 32 above the absorption edge, the reflection of the interference layer element 22 is only insignificantly affected when viewed vertically. When viewed vertically, the security element 12 therefore exhibits a reflection curve 92 that hardly differs from the reflection curve 52 of Fig. 3 and is particularly dominated by the short-wavelength peak 92-B in the blue range, while the long-wavelength peak 92-R barely influences the appearance due to the low spectral sensitivity of the human eye above 700 nm. The security element 12 therefore appears a strong blue when viewed vertically.

[0065] When viewed at an angle, the maximum of the short-wave reflection of the interference layer element 22 has migrated below the absorption edge of the blue light absorber 32, so that its high absorption in the blue range becomes apparent and greatly reduces the intensity of the short-wave peak 54-R of the reflection curve 54. When viewed at an angle, the security element 12 displays a reflection curve 94 that hardly differs from the reflection curve 54 of Fig. 3 in the red range due to the high transmission of the blue light absorber 32 there, but in which the short-wave peak 94-B in the blue range is significantly suppressed. Therefore, when viewed at an angle, the security element 12 appears to have a red color impression of high color purity.

[0066] Returning to the design of Fig. 2, the security element 12 thus displays an attractive color shift effect between a strong blue in plan view 40 to a red of high color purity in oblique view 42 through the combination of the interference layer element 22 with the selective absorption layer 30. The extent of modification of the intrinsic color shift effect of the interference layer element 22 can be adjusted as desired by the concentration or amount of the blue light absorber 32 as well as the length and width of the absorption edge of the blue light absorber 32.

[0067] In the embodiment of Fig. 2, the selective absorption layer 30 and the interference layer element 22 are arranged on opposite sides of the carrier film 20, but other relative arrangements of the two elements are also possible. The only essential factor is that a sufficient amount of blue light absorber 32 is located between the

[0068] viewer 44 and the interference layer element 22.

[0069] Figure 10 shows a further development of the embodiment of Figure 2, in which the security element 12 is additionally provided with a translucent color layer 38 with a red body color. The translucent red body color layer 38 can, as shown in the figure, be arranged between the interference layer element 22 and the carrier film 20, but it can also be provided on the side of the carrier film 20 facing the viewer, below or above the selective absorption layer 30. It has been found that such a translucent red body color layer 38 further improves the color effect of the blue-to-red color shift effect.

[0070] With reference to the embodiment of Fig. 6, the blue light absorber 32 can, for example, be provided in the carrier film 20 itself instead of in a separate layer. In embodiments in which the interference layer element 22 is arranged on an embossed structure, the blue light absorber 32 can, for example, be incorporated into the embossed lacquer layer of the embossed structure. It is also possible to arrange the blue light absorber 32 in a primer layer, a hot-seal lacquer coating, or another lacquer coating. Even in such an embodiment, a translucent red body color layer can additionally be provided above or below the carrier film 20 to further enhance the color effect of the blue-to-red color shift effect.

[0071] Returning to the illustration in Fig. 1, the banknote 10 contains, as a second security element, an optically variable printing element 14, which is shown schematically in cross-section in Fig. 7. The printing element 14, like the transfer element 12, exhibits a blue-to-red color shift effect, in which the color impression for a viewer alternates between a strong blue when viewed vertically 40 and a red of high color purity when viewed obliquely 42.

[0072] The printing element 14 is formed by a security printing ink 70 printed onto the paper substrate 16 of the banknote 10, which contains a transparent binder 72 with a plurality of color-shifting platelet-shaped pigments 74 and a blue light absorber 32.

[0073] One of the platelet-shaped pigments 74 is shown separately in more detail in Fig. 8. Each of the platelet-shaped pigments 74 represents a color-shifting five-layer interference layer element with a symmetrical structure and consists of an outer first chromium absorber layer 80, a first SiO spacer layer 82, a middle, opaque aluminum reflector layer 84, a second SiCh spacer layer 86, and an outer second chromium absorber layer 88. The layer thicknesses of the dielectric spacer layers, the reflector layer, and the absorber layers are advantageously within the ranges mentioned above. For a symmetrical structure, the two SiCh spacer layers 82, 86 and the two absorber layers 80, 88 are each essentially the same thickness.

[0074] The platelet-shaped pigments 74 distributed in the binder 72 of the security printing ink 70 are aligned essentially parallel to the surface of the paper substrate 16 during printing by the forces acting during printing. Due to the symmetrical structure of the pigments 74, it is irrelevant for the observable color effect which of the two chromium absorber layers 80 or 88 faces the paper substrate or the viewer. Due to the analogous layer structure, the intrinsic color-shift effect of the platelet-shaped pigments 74 corresponds to the color-shift effect of the interference layer element 22 in Fig. 2, thus showing a relatively unattractive alternation between a strong blue in the vertical viewing direction 40 and a dark red of low color purity in the oblique viewing direction 42.

[0075] To create the visually attractive color-shift effect exhibited overall by the printing element 14, the intrinsic color-shift effect of the platelet-shaped pigments 74 is modified by the blue light absorber 32 contained in the binder 72 in such a way that the viewer sees a visually significantly more appealing color-shift effect between a somewhat lighter blue and a pure red. The mode of action is analogous to the explanation given in connection with Figures 2 to 5: The absorption edge of the blue light absorber 32 lies between the blue peak when viewed vertically and the blue peak, which is shifted slightly to shorter wavelengths, when viewed obliquely.When viewed at an angle, the high absorption of the blue light absorber 32 comes into play and the blue component of the reflected radiation is greatly reduced compared to the red component, while the blue component of the reflected radiation is hardly affected when viewed vertically due to the high transmission of the blue light absorber 32 above the absorption edge.

[0076] The printing element 14 therefore displays an overall attractive color-shift effect between a strong blue in plan view 40 to a red of high color purity in oblique view 42. The extent of the modification of the intrinsic color-shift effect of the interference layer element 22 can be adjusted as desired by the concentration or amount of the blue light absorber 32 and the position of the absorption edge of the blue light absorber 32. Figure 9 shows, as a further exemplary embodiment, a modification of the printing element of Figure 7, in which the blue light absorber 32 is not mixed into the binder of the security printing ink, but is present in a separate overcoat 90, which is applied to a printing layer 92 with a plurality of color-shifting, platelet-shaped pigments 74.

[0077] Here too, the combined effect of the color-shifting pigments 74 and the blue absorber 32 results in the desired blue-red color-shift effect with a pure red when viewed at an angle.

[0078] In the embodiments of Figures 7 and 9, the color effect of the blue-to-red color shift effect can also be further enhanced by a translucent red body color layer. Such a translucent red body color layer can be applied, in particular printed, to the security printing ink 70 of Figure 7, to the printing layer 92 of Figure 9, or to the overcoat 90 of Figure 9.

Claims

P a t e n t a n s p r ü c h e 1. An optically variable security element for protecting security papers, valuable documents, and other valuables, comprising at least one color-shifting, multilayer interference layer element with a reflector layer, at least one absorber layer, and at least one dielectric spacer layer arranged between the reflector layer and the at least one absorber layer, wherein the multilayer interference layer element, with its layer structure, produces an intrinsic color-shift effect with a first color in a first viewing direction and a different second color in a second viewing direction, characterized in that a blue light absorber with an absorption edge in the wavelength range between 380 nm and 460 nm is arranged above and / or below the at least one multilayer interference layer element,which modifies the intrinsic colour shift effect of the at least one multi-layer interference layer element by selective absorption of the blue light component, so that the security element displays a modified colour shift effect between a third colour in the first viewing direction and a different fourth colour in the second viewing direction, wherein the third colour differs from the first colour in, hue and / or color purity and / or the fourth color differs from the second color in hue and / or color purity.

2. Security element according to claim 1, characterized in that the multilayer interference layer element has a reflection spectrum with a short-wavelength peak in the blue spectral range, the maximum of which lies at a first wavelength in the first viewing direction and at a second, different wavelength in the second viewing direction, the absorption edge of the blue light absorber lying between the first and second wavelength.

3. Security element according to claim 1 or 2, characterized in that the width of the absorption edge of the blue light absorber (10% or 90% of the maximum transmission in the wavelength range between 350 nm and 500 nm) is less than 40 nm, advantageously less than 30 nm, in particular less than 20 nm.

4. Security element according to at least one of claims 1 to 3, characterized in that the blue light absorber is highly transparent in the visible range at wavelengths above the absorption edge and preferably has a transmission of at least 80%, at least 90% or even at least 95%.

5. Security element according to at least one of claims 1 to 4, characterized in that the blue light absorber has a high light resistance.

6. Security element according to at least one of claims 1 to 5, characterized in that the at least one dielectric spacer layer is formed from SiCh, TiCh, ZnS, MgF or Al2O3 and has a layer thickness between 100 nm and 500 nm, and / or that the reflector layer is formed from aluminum, an aluminum-iron alloy, or silver, and / or that the at least one absorber layer is formed from chromium, an iron alloy, a chromium-iron alloy or titanium.

7. Security element according to at least one of claims 1 to 6, characterized in that the first color is blue and the second color is a dark red of low color purity and the third color is a lighter blue compared to the first color and the fourth color is a lighter and more color-pure red compared to the second color, or that the first color is gold and the second color is green, and the third color is orange and the fourth color is green or yellow, or that the first color is magenta and the second color is green, and the third color is red and the fourth color is green or yellow.

8. Security element according to at least one of claims 1 to 7, characterized in that the first viewing direction is a vertical viewing direction and the second viewing direction is an oblique viewing direction of 45°.

9. Security element according to at least one of claims 1 to 8, characterized in that the security element contains a carrier film and a thin-film element applied over a large area to the carrier film, which is formed by a single one of the said interference layer elements.

10. Security element according to claim 9, characterized in that the thin-film element is formed by a three-layer interference layer element with a reflector layer, an absorber layer and a dielectric spacer layer arranged between the reflector layer and the absorber layer.

11. Security element according to claim 9 or 10, characterized in that the blue light absorber is arranged in a lacquer layer applied to the carrier film or the thin-film element, an embossing lacquer layer, a primer layer, a heat-sealing lacquer layer, or in the carrier film itself.

12. Security element according to at least one of claims 9 to 11, characterized in that the security element contains a translucent color layer with a red body color, which is preferably applied to the carrier film, the large-area thin-film element or a layer containing the blue light absorber.

13. Security element according to at least one of claims 1 to 8, characterized in that the security element contains a printing layer which contains, in a binder, a plurality of color-shifting, platelet-shaped pigments, each having a said interference layer element.

14. Security element according to claim 13, characterized in that the platelet-shaped pigments each form a five-layer interference layer element with an outer first absorber layer, a first dielectric spacer layer, a central reflector layer, a second dielectric spacer layer and an outer second absorber layer, and are preferably constructed symmetrically.

15. Security element according to claim 13 or 14, characterized in that the platelet-shaped pigments each contain at least one magnetic layer and can thus be aligned by means of external magnetic fields.

16. Security element according to one of claims 13 to 15, characterized in that the blue light absorber is arranged in the binder of the printing layer, in an overprint or an overcoat of the printing layer, or in a coating of the platelet-shaped pigments themselves.

17. Security element according to at least one of claims 13 to 16, characterized in that the security element contains a translucent ink layer with a red body color, which is preferably applied to the printing layer with the color-shifting, platelet-shaped pigments or a layer containing the blue light absorber.

18. Valuable object, in particular security paper, value document or identity document with a security element according to one of claims 1 to 17.

19. A method for producing a security element according to one of claims 1 to 17, in which at least one color-shifting, multi-layer interference layer element is provided, which comprises a reflector layer, at least one absorber layer and at least one dielectric spacer layer, which is arranged between the reflector layer and the at least one absorber layer, wherein the multilayer interference layer element with its layer structure produces an intrinsic color-shift effect with a first color in a first viewing direction and a different second color in a second viewing direction, characterized in that a blue light absorber with an absorption edge in the wavelength range between 380 nm and 460 nm is arranged above and / or below the at least one multilayer interference layer element, which modifies the intrinsic color-shift effect of the at least one multilayer interference layer element by selectively absorbing the blue light component, so that the security element displays a modified color-shift effect between a third color in the first viewing direction and a different fourth color in the second viewing direction,where the third color differs from the first color in hue and / or color purity and / or the fourth color differs from the second color in hue and / or color purity.

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