Optically variable security element, value document and production method

Abstract

The invention relates to an optically variable security element for securing security papers, value documents and other valuable objects, comprising a substrate body (2) which has a front side (4) and a rear side (6), and a printing layer (8) which is applied to the front side (4) of the substrate body (2) and contains first pigments (10). The first pigments (10) each have a multilayer structure comprising a reflector layer, an absorber layer and a dielectric spacer layer which is arranged between the reflector layer and the absorber layer, the multilayer structure being designed such that it produces a first colour shift effect with a first colour in a first viewing angle range and another second colour in a second viewing angle range. The printing layer (8) contains a plurality of second, different pigments (12) which produce a second colour shift effect by virtue of the fact that they are transparent in the first viewing angle range and have a colour in the second viewing angle range.

Description

[0001] O p t i s c h v a r i a b l e s S i c h e r h e i t s e l e m e n t , W e r t d o k u m e n t u n d H e r s t e l l u n g s v e r f a h r e n

[0002] The invention relates to an optically variable security element for securing security documents, valuables, and other valuables, comprising a substrate body having a front and a back, and a printing layer applied to the front of the substrate body, which includes first pigments. The first pigments comprise a multilayer structure with a reflector layer, an absorber layer, and a dielectric spacer layer arranged between the reflector layer and the absorber layer. This multilayer structure produces a color-shifting effect with a first color in a first viewing angle range and a second color in a second viewing angle range. The invention also relates to a method for manufacturing such a security element and a correspondingly designed valuables document.

[0003] For added security, valuable documents are often enhanced with security features containing effect pigments, such as color-shifting pigments with a viewing angle-dependent effect. These allow for verification of the document's authenticity and simultaneously increase counterfeit protection, as they cannot be reproduced even with the most advanced copying equipment. Effect pigments can be integrated into the document's substrate or applied to it, for example, in the form of an ink. In this case, the effect pigments are contained within a binder and can therefore be easily printed.

[0004] The color-shifting pigments with viewing-angle-dependent effects are optically variable pigments that present the viewer with a different image under different viewing angles.

[0005] PAT 4143 / 256-PCT January 15, 2026 convey an impression and, for example, show a different color or brightness impression depending on the viewing angle.

[0006] The reflection spectra of these color-shifting pigments usually exhibit several bands. Therefore, in many color changes, the reflection spectrum, both in top view and in inversion, is a superposition of several bands. For example, blue-red pigments have a reflective band in both the blue and red regions of the visible spectrum. However, since the human eye is not as sensitive in the red spectral range, the red appears unattractive to the viewer.

[0007] When the described color-shifting pigments are used in a security thread or in optically variable (magnetic or non-magnetic) inks, the color change, which depends on the viewing angle, appears relatively dark and is therefore difficult to detect. This results from the fact that, for example, with blue-red pigments, the red shift color is usually very dark because it is clearly overlaid by the blue color visible from above – there is a lack of color purity.

[0008] The invention is based on the objective of providing a generic safety element that avoids the disadvantages of the prior art and, in particular, enables the generation of color-shifting effects with color changes between colors of high color purity, thus making the optical effect more attractive.

[0009] This problem is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims. An optically variable security element is provided for securing security documents, valuables, and other valuables. The security element has a substrate body with a front and a back. Polymer substrates, such as PET substrates, paper substrates, or combined paper and polymer substrates can be used as substrate bodies.

[0010] A printed layer containing a variety of first pigments is applied to the front surface of the substrate. These first pigments comprise a multilayer structure consisting of a reflector layer, an absorber layer, and a dielectric spacer layer positioned between the reflector and absorber layers. This multilayer structure creates a first color-shifting effect, with one color appearing in a first viewing angle range and a different, second color appearing in a second viewing angle range. The first pigments are color-shifting pigments, and the dielectric spacer layer, located between the absorber and reflector layers, is the primary component responsible for the color effect.The multilayer structure described above represents an interference layer element, in which the colors produced by reflection are generated by interference of light rays reflected from different sublayers of the interference layer element. This results in a color effect that depends on the viewing angle.

[0011] The printed layer on the front of the substrate also contains a second set of pigments. These create a second color-shifting effect by being transparent at the first viewing angle and colored at the second, thus improving both the optical effect and increasing counterfeit protection. The second pigments preferably exhibit the second color at the second viewing angle. This second color-shifting effect then particularly intensifies the first by producing colors with higher purity at both viewing angles – the colors appear brighter or lighter, but this is not accompanied by increased radiation intensity.Due to the increase in color purity in at least one viewing angle range, especially preferably in both viewing angle ranges, the optical effect becomes more attractive and at the same time the counterfeit protection is increased.

[0012] Preferably, the second pigments are liquid crystal pigments exhibiting a chiral, i.e., twisted, molecular structure. They display direction-dependent (anisotropic) physical properties, like a crystal – they are referred to as cholesteric liquid crystal platelets. A maximum light transmission of 720–730 nm is particularly preferred for the second pigments. For this purpose, 38.5 g of nematic liquid crystals and 1.46 g of twisting agent are mixed, resulting in a twisting agent concentration of approximately 3.7% of the solid after drying.

[0013] The second pigments can also have a layer stack in which two alternating layers with different refractive indices are repeated. The alternating layers can be metal oxide and / or plastic layers.

[0014] It goes without saying that different types of secondary pigments can also be used in combination. For example, in a printed layer, pigments with the described layer stack of two alternating layers can be used as secondary pigments, and in a further printed layer above this, liquid crystal pigments can be used as secondary pigments.

[0015] The second pigments exhibit a significantly lower intensity of reflected wavelength compared to the first pigments. Consequently, security features constructed solely from these second pigments typically appear less brilliant and visually appealing. However, the security element according to the invention utilizes the advantage of these second pigments, namely that they exhibit only a relatively narrow band of circularly polarized light. For this reason, the first color-shifting pigments are combined with the second pigments to complement their optical properties with their own color-shifting effect, thereby intensifying their color impression and improving the overall visual appearance of the printed layer.

[0016] Preferably, the first viewing angle range comprises a perpendicular viewing direction, and the second viewing angle range a viewing angle of 45°. Then, particularly preferably, the first pigments produce a color-shifting effect from a first blue color (when viewed perpendicularly) to a second red color (when viewed at a 45° angle). Thus, the first pigments exhibit a viewing-angle-dependent color change from blue to red, typically displaying a blue peak in the 400-500 nm range in their reflection spectrum, regardless of the viewing angle. This blue peak has the same intensity / height as a red peak in the 700-900 nm range. The shifting red color appears very dark or undefined at a 45° viewing angle because the blue peak does not completely disappear into the UV range, which is invisible to the human eye, at this angle, while simultaneously maintaining a high intensity.The "mixed color" of the red tipping color, which is composed of the red peak and the blue peak, appears dark and unattractive because it is not a pure red.

[0017] The second pigments used are preferably those that are transparent when viewed perpendicularly, thus not affecting the first blue color, and that appear red when viewed at a 45° angle, thereby intensifying the second red color of the first pigment – ​​thus increasing the color purity when viewed obliquely. This compensates for the low sensitivity of the human eye and improves the attractiveness of the optical effect. The advantage of this approach over adding a simple red pigment is that the red color is specifically enhanced, while the blue color remains unchanged, since the second pigments are transparent to the human eye in the visible spectral range when viewed from above. Simple red pigments would indeed enhance the red color, but would also alter the blue color, as they would be visible from above as well.

[0018] In principle, it is possible to specifically improve the optical effect of the first pigments by adding the second pigments in two further variations.

[0019] In a second variant, the blue residual color can be attenuated when viewed obliquely using a second pigment. For this purpose, second pigments can be used that shift a reflection maximum of the printed layer into the UV range at the second viewing angle. Then, at a viewing angle of, for example, 45°, the blue component of the reflection spectrum would no longer be visible to the human eye, thus improving the purity of the red tint, which in turn enhances the optical impression. Ideally, the second pigments should have a chiral component – ​​their direction of rotation can then be left-handed or right-handed. The second pigments reflect only the portion of white, unpolarized light whose polarization corresponds to the handedness of the respective second pigment. Conversely polarized light can pass through the second pigments unimpeded.This portion of the light, which passes through the second pigments unimpeded, therefore does not contribute to an improvement in the optical effect of the first and second variants. This can be prevented in a third variant by adding second pigments of both rotation directions in a 1:1 ratio. The third variant thus combines the first variant with the second, thereby intensifying the red tint in two ways – creating a particularly attractive optical effect.

[0020] It follows, therefore, that the first two variants can of course be combined with each other (as in variant 3, for example) by using different types of second pigments. Different ratios of pigments with different directions of rotation are also possible. Likewise, it is possible to use liquid crystal pigments on the one hand and pigments with the described layer stack of two alternating layers with different refractive indices as second pigments on the other.

[0021] Preferably, the printed layer is printed with a single ink in which both the primary and secondary pigments are contained in a binder. This allows the optical effect of the primary pigments to be enhanced with the help of the secondary pigments with minimal manufacturing effort, as only a single printed layer needs to be applied, resulting in only a single printed text.

[0022] It is particularly preferred that the printing layer comprises a first partial printing layer and a second partial printing layer above it, wherein the first partial printing layer includes the first pigments and the second partial printing layer includes the second pigments. This embodiment further enhances the optical effect, since the second partial printing layer lies entirely above the first partial printing layer, and thus all the second pigments also lie above the first pigments – the second pigments, which enhance the effect, are therefore not covered by the first pigments.

[0023] It is understood that it is also possible to combine the two aforementioned embodiments of the printing layer. It is particularly preferred to print a further layer containing only second pigments onto a layer containing both first and second pigments, thereby further enhancing the optical effect of the underlying layer and thus improving the overall visual impression. If multiple printing layers are used, it is equally possible for all layers to have the same binder, but different binders can also be used.

[0024] To enable a targeted spatial arrangement of the first pigments over the second pigments, or vice versa, it is also possible to pretreat the first or second pigments in such a way that they function as leafing pigments. With this type of pretreatment, the interfacial tension of the pigments is increased, preventing them from being completely wetted by the binder. The first or second pigments, configured as leafing pigments, therefore float on the binder and thus automatically align themselves over the other pigments. It is particularly advantageous for the second pigments to be configured as leafing pigments so that, once applied, they are not covered by the first pigments, thereby maximizing the optical effect of the second pigments. However, it is also possible to create a see-through feature with the printed layer, which is viewed from below.In this case, it is advantageous to form the first pigments as leafing pigments so that they do not cover the second pigments when viewed from below.

[0025] The combination of color-shifting (first) pigments and secondary pigments in the printing layer offers further advantages beyond enhancing the optical effect of the first pigments: The color-shifting first pigments typically contain aluminum as a reflective layer, which has the disadvantage of being susceptible to corrosion. By adding the secondary pigments to the first color-shifting pigments, the aluminum content in the printing layer's ink is reduced, making the printing layer less prone to corrosion. Furthermore, due to the secondary pigments, the printing layer reflects circularly polarized light, making it well-suited for use with polarizing filters – the printing layer then appears light in one window of a Step-Watcher and dark in another.

[0026] Preferably, the dielectric spacer layer is made of SiCh, TiCh, ZNS, MgFz or Al2O3 and has a layer thickness between 100 nm and 500 nm. The reflector layer is preferably made of aluminum, an aluminum-iron alloy, or silver, and the absorber layer is preferably made of chromium, an iron alloy, a chromium-iron alloy, or titanium.

[0027] Preferably, either the substrate body is light-absorbing on its front side, e.g., black, or a background layer is arranged between the substrate body and the printing layer, the side of which facing the printing layer is light-absorbing, e.g., black. This improves the optical effect.

[0028] A particularly preferred optically variable security element is a foil security element, such as a security thread, security tape, or security patch. It can then be easily applied as a transfer element to a valuable document.

[0029] It is also a security document, such as a banknote, check, credit or other payment card, identification card, or the like, provided with the described optically variable security element. It is understood that the security document can be modified in the same ways as the optically variable security element, as already described.

[0030] It is equally possible to apply the described printing layer directly to the valuable document.

[0031] Also provided is a method for manufacturing an optically variable security element for securing security papers, valuable documents, and other valuables. This method involves providing a substrate body with a front and a back, and applying a printing layer containing first pigments to the front of the substrate body. The first pigments have a multi-layer structure consisting of a reflector layer, an absorber layer, and a dielectric spacer layer positioned between the reflector and absorber layers. This creates a first color-shifting effect, with a first color in a first viewing angle range and a second color in a second viewing angle range.The printing layer also contains second, different pigments, which create a second color-shifting effect by being transparent in the first viewing angle range and exhibiting color in the second viewing angle range.

[0032] It is understood that the method for manufacturing the optically variable security element can be modified in the same ways as the optically variable security element and the security document already described.

[0033] The printing layer is applied to the entire surface or to specific areas of the front surface of the substrate. The first and second pigments are both contained within the same printing layer. They are either mixed together in a binder or are located in two superimposed partial printing layers of the printing layer, which preferably overlap, and more preferably overlap exactly. "Exactly overlap" here means that the two partial printing layers completely overlap within the limits of register accuracy, with a maximum area deviation of 2%. Thus, both the first and second pigments are present on the security element across the entire area where the printing layer is applied. Together, they create the optically variable effect of the printing layer.An optically variable security element for securing security papers, valuable documents, and other valuables is disclosed, comprising a substrate body (2) having a front (4) and a back (6), and a printing layer (8) applied to the front (4) of the substrate body (2) and containing first pigments (10). The first pigments (10) each have a multilayer structure comprising a reflector layer, an absorber layer, and a dielectric spacer layer arranged between the reflector layer and the absorber layer, configured to produce a first color-shifting effect with a first color in a first viewing angle range and a second color in a second viewing angle range.The printing layer (8) contains a variety of second, different pigments (12) that create a second color-shifting effect by being transparent in the first viewing angle range and exhibiting color in the second viewing angle range.

[0034] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings, which also disclose essential features of the invention. These exemplary embodiments serve only for illustration and are not to be interpreted as limiting. For example, a description of an exemplary embodiment with a plurality of elements or components is not to be interpreted as meaning that all of these elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components from different exemplary embodiments may be combined with one another unless otherwise specified. Modifications and variations described for one of the exemplary embodiments may also be applicable to other exemplary embodiments.To avoid repetition, identical or corresponding elements in different figures are designated with the same reference symbols and are not explained multiple times. The figures show:

[0035] Fig. 1 shows a first embodiment of an optically variable safety element in sectional view.

[0036] Fig. 2 shows a second embodiment of an optically variable safety element in sectional view.

[0037] Fig. 3 shows a reflection spectrum of the first pigments and

[0038] Fig. 4 shows a reflection spectrum of second pigments.

[0039] Structures that are structurally or functionally equivalent are each marked with the same reference symbol in the figures.

[0040] Fig. 1 shows a first embodiment of a safety element 1 in sectional view. A printed layer 8 is applied to a substrate body 2, which has a front side 4 and a back side 6.

[0041] The substrate body 2 can be, for example, a polymer substrate such as a PET substrate, but paper substrates or combined paper-polymer substrates are also possible.

[0042] The printing layer 8 comprises a plurality of first pigments 10 and second pigments 12 in a binder 14. The first pigments 10 have a three-layer structure, with a dielectric spacer layer arranged between a reflector layer and an absorber layer. They produce a first color-shifting effect with a first color in a first viewing angle range and a different, second color in a second viewing angle range.

[0043] Figure 1 shows a first viewing direction 16 and a second viewing direction 18. The first viewing direction 16 represents a perpendicular viewing direction (0°) and is located in the first viewing angle range. The second viewing direction 18 represents an oblique viewing direction of 45° to the surface of the substrate body 2 and is located in the second viewing angle range. In this embodiment, the first pigments 10 exhibit the color blue in the first viewing direction 16 and the color red in the second viewing direction 18. They thus produce a viewing angle-dependent color shift effect. This viewing angle-dependent color effect is explained below using a color shift from blue to red as an example; however, other color changes, for example from green to magenta, from magenta to green, etc., are of course equally conceivable.

[0044] Also contained in the printing layer 8 are the second pigments 12. The second pigments are preferably liquid crystal pigments that have a chiral molecular structure and thus exhibit direction-dependent physical properties, like a crystal. The second pigments 12 create a second color-shifting effect because they are transparent in the first viewing angle range and exhibit a color in the second viewing angle range. In this example, the second pigments 12 are transparent in the first viewing direction 16 and red in the second viewing direction 18, so that they do not affect the blue color of the first pigments in the first viewing direction 16, but intensify the red color of the first pigments 10 in the second viewing direction 18.

[0045] Figure 2 shows a second embodiment of the safety element 1 in sectional view. The printing layer 8 is again applied to the front surface 4 of the substrate body 2, this time comprising a first partial printing layer 20 and a second partial printing layer 22. The first partial printing layer 20 is applied directly to the front surface 4 of the substrate body 2 and contains the first pigments 10 in a first binder 24. The second partial printing layer 22, which contains the second pigments 12 in a second binder 26, is applied to the surface of the first partial printing layer 20. The first binder 24 and the second binder 26 can be the same, but different binders can also be used.

[0046] The first pigments 10 and the second pigments 12 of the embodiment shown in Fig. 2 produce the same optical effect as the pigments 10, 12 of the embodiment shown in Fig. 1 – a color shift from blue to red. However, the optical effect in the embodiment shown in Fig. 2 is more attractive because the second partial printing layer 22 is located entirely above the first partial printing layer 20, meaning that all second pigments 12 are always positioned above the first pigments 10. This intensifies the color shift effect because it specifically prevents the second pigments 12, which enhance the color effect of the first pigments 10, from being covered by the first pigments 10. This improves the optical impression – the optical effect itself remains the same.

[0047] The optical effect of the two arrangements is illustrated in Fig.

[0048] Figures 1 and 2 in Figures 3 and 4 show the measurement results for the reflection as a function of the wavelength for first pigments 10 and second pigments 12.

[0049] Fig. 3 shows the reflection spectrum as a function of wavelength of first pigments 10, in this case with a three-layer structure consisting of a chromium layer as the absorber layer, a SiCh layer as the dielectric spacer layer, and an aluminum layer as the reflector layer on a PET substrate. A first curve 28 shows the behavior in the first viewing angle range (measured at 8°) and a second curve 30 the behavior in the second viewing angle range (measured at 45°). It can be seen in Fig. 3 that the first pigments 10 produce a viewing angle-dependent color change from blue to red, as they have a blue peak in the range of 400–500 nm, independent of the viewing angle, and a red peak in the range of 700–900 nm, which appears very dark at a viewing angle of 45°.This results from the fact that the blue peak does not completely disappear into the UV range, which is invisible to the human eye, at this viewing angle, and at the same time has a high intensity - one perceives a mixed color of blue and red, which appears dark and unattractive.

[0050] Fig. 4 shows the reflection spectrum as a function of wavelength of the second pigments 12. A third curve 32 shows the progression in the first viewing angle range (measured at 8°) and a fourth curve 34 the progression in the second viewing angle range (measured at 45°). It can be seen that the second pigments 12 exhibit a color change from transparent when viewed from above to red when viewed obliquely. This results from the fact that the peak in the first viewing angle range is in the infrared range and therefore not perceptible to the human eye; the red peak in the second viewing angle range, however, is visible. When the two pigments 10 and 12 are combined, the described intensification effect of the color shift from blue when viewed from above to red when viewed obliquely occurs—the optical effect (color shift) is improved or made more attractive.

[0051] Due to the twisted molecular structure of the second pigments 12, both variants can be combined by using both left-handed and right-handed second pigments 12 in a 1:1 ratio, making it possible to intensify the red tint on the one hand and to weaken the blue residual tint in the second viewing angle range on the other. Reference symbol list

[0052] 1 safety element

[0053] 2 substrate bodies

[0054] 4 Front

[0055] 6 Back

[0056] 8 printing layers

[0057] 10 first pigment

[0058] 12 second pigment

[0059] 14 binders

[0060] 16 first perspective

[0061] 18 second perspective

[0062] 20 first partial printing layer

[0063] 22 second partial printing layer

[0064] 24 first binder

[0065] 26 second binder

[0066] 28 first curve

[0067] 30 second curve

[0068] 32 third curve

[0069] 34 fourth turn

Claims

Patent claims 1. Optically variable security element for securing security papers, valuable documents and other valuables, comprising a substrate body (2) having a front (4) and a back (6), and a printing layer (8) applied to the front side (4) of the substrate body (2) and containing first pigments (10), wherein the first pigments (10) each have a multilayer structure comprising a reflector layer, an absorber layer and a dielectric spacer layer arranged between the reflector layer and the absorber layer, which is designed to produce a first color-shifting effect with a first color in a first viewing angle range and another, second color in a second viewing angle range, characterized by the fact that the printing layer (8) second, different contains pigments (12) that produce a second color-shifting effect by being transparent in the first viewing angle range and exhibiting color in the second viewing angle range.

2. Safety element according to claim 1, characterized in that the second pigments (12) have the second color in the second viewing angle area.

3. Safety element according to one of the above claims, characterized in that the second color-shifting effect intensifies the first color-shifting effect.

4. Safety element according to one of the above claims, characterized in that the second pigments (12) are liquid crystal pigments.

5. Safety element according to one of claims 1 to 3, characterized in that the second pigments (12) have a layer stack in which two alternating layers with different refractive indices are repeated.

6. Safety element according to claim 5, characterized in that the alternating layers are metal oxide layers and / or plastic layers.

7. Safety element according to one of the above claims, characterized in that the printing layer (8) contains the first pigments (10) and the second pigments (12) in a binder (14).

8. Safety element according to one of the above claims, characterized in that the printing layer (8) has a first partial printing layer (20) and a second partial printing layer (22) above it, wherein the first partial printing layer (20) comprises the first pigments (10) and the second partial printing layer (22) comprises the second pigments (12).

9. Safety element according to claim 8, characterized in that the first partial printing layer (20) comprises a first binder (24) and the second partial printing layer (22) comprises another, second binder (26).

10. Safety element according to one of claims 8 or 9, characterized in that the first partial printing layer (20) and the second partial printing layer (22) overlap.

11. Safety element according to one of the above claims, characterized in that the first pigments (10) or the second pigments (12) are pretreated such that they are formed as leafing pigments.

12. Safety element according to one of the above claims, characterized in that the second pigments (12) shift a reflection maximum of the printing layer (8) in the second viewing angle range into the UV range.

13. Safety element according to one of the above claims, characterized in that two different types of second pigments (12) are contained in the printing layer (8) in a ratio of 1:1, wherein one type is right-handed and the second type is left-handed.

14. Safety element according to one of the above claims, characterized in that the first viewing angle range comprises a perpendicular viewing direction (16) and the second viewing angle range comprises an oblique viewing direction (18) of 45° to the surface of the substrate body (2), wherein the first color is blue and the second color is red.

15. Safety element according to one of the above claims, characterized in that the dielectric spacer layer is formed from SiOz, TiOz, ZNS, MgFz or Al2O3 and has a layer thickness between 100 nm and 500 nm.-22- 16. Safety element according to one of the above claims, characterized in that the reflector layer is made of aluminium, an aluminium-iron alloy or silver.

17. Safety element according to one of the above claims, characterized in that the absorber layer is formed of chromium, an iron alloy, a chromium-iron alloy or titanium.

18. Safety element according to one of the above claims, characterized in that the substrate body (2) has a light-absorbing front side (4), or a background layer is arranged between the substrate body (2) and the printing layer (8), the side of which facing the printing layer (8) is light-absorbing.

19. Security element according to one of the above claims, characterized in that the printing layer is applied to the front surface of the substrate body over the entire area or in certain areas, and the first pigments and the second pigments are both present on the security element over the entire area in which the printing layer is applied to the substrate body.

20. A security document, such as a banknote, a check, a credit or other payment card, an identification card or the like, with an optically variable security element (1) according to any one of claims 1 to 19.

21. Method for manufacturing an optically variable security element (1) according to any one of claims 1 to 19, wherein a substrate body (2) having a front (4) and a back (6) is provided, and a printing layer (8) containing first pigments (10) is applied to the front (4) of the substrate body (2), wherein the first pigments (10) each have a multilayer structure comprising a reflector layer, an absorber layer and a dielectric spacer layer arranged between the reflector layer and the absorber layer, which is designed to produce a first color-shifting effect with a first color in a first viewing angle range and another, second color in a second viewing angle range, characterized by the fact that the printing layer (8) second, different contains pigments (12) which produce a second color-shifting effect by being transparent in the first viewing angle range and having a color in the second viewing angle range.

Images