EP2065214B1 - Safety element and method for its production - Google Patents

Abstract

The security element production process involves applying an effect layer (34) to a plastic support film (32), and an auxiliary transfer layer (36) to the entire surface of both. The adhesion of the auxiliary transfer layer to the support film is less than that to the effect layer. An adhesive layer (38) is then applied to the target substrate (35) to transfer the formed layer compound.

Description

The invention relates to a security element for securing valuables with a first optically active layer of cholesteric liquid-crystalline material present at least in regions. The invention further relates to a method for producing such a security element, a security arrangement which, in addition to such a security element, comprises a separate display element, as well as a security paper and a valuable article, which are equipped with such a security element or security arrangement.

Valuables, such as branded goods or documents of value, are often provided with security elements for the purpose of protection, which allow verification of the authenticity of the object of value and at the same time serve as protection against unauthorized reproduction.

In many cases, optically variable elements are used as security elements, which give the viewer a different image impression, for example a different color impression, at different viewing angles. From the publication EP 0 435 029 A2 is such a security element with a plastic-like layer of a liquid crystal polymer is known which shows at room temperature a pronounced color change game. The optically variable effects of the liquid crystal polymers can be combined by coloring any layers with conventional colors, which can produce patterns that become visible only when tilting the security elements. The dyes themselves may be incorporated in any layer or applied as a printed image.

In the described security elements, the color shift effect of the liquid crystal layers due to the physical conditions always leads to a shift of the reflected light wavelength from the longer wavelength range when viewed perpendicularly to the shorter wavelength range when viewing the layers at an acute angle. The possibilities for generating different color shift effects are therefore limited.

From the publication EP 1156 934 B1 For example, a security element having a liquid crystal layer as an optically variable material is known. An embodiment is described with a passerhaltiger arrangement of printing layers of dextrorotatory and levorotatory liquid crystal material, which show the same appearance under normal lighting, so that an information represented by the shape or the outline of the areas can not be detected. Only when the layers are viewed through a suitable polarization filter can the information be recognized by the brightness difference between the printed layers. In order to achieve this effect, however, a register-accurate application of the liquid-crystalline layers is required.

The publication WO 98/52077 A describes an optical device with an optically anisotropic layer having at least two regions with different molecular orientations. The anisotropic layer is a retarder layer formed from crosslinked liquid crystal monomers.

The publication JP 2003 145912 A discloses a tamper-proof printed matter in which a cholesteric liquid crystal layer and a thermotropic polymer liquid crystal layer are provided in the order named on at least one side of a base material. By orientation at least part of the thermotropic polymer liquid crystal layer exhibits a desired pattern when viewed through a circular polarizer.

The publication JP 2000 255200 A describes a tamper-resistant material comprising a base material 11, a first light selectively reflecting layer 12 formed on a predetermined region of the material 11 to reflect only one right and left circularly polarized incident light, a phase shifting layer 13 formed on layer 12 is formed to reflect incident left circularly polarized light as right circularly polarized light and to reflect incident right circularly polarized light as left circularly polarized light; and second light selectively reflecting layer 14 formed on a predetermined portion of layer 13 To reflect light having the same polarization as the light reflected from the layer 12.

Based on this, the present invention seeks to provide a security element of the type mentioned above with high security against counterfeiting, which avoids the disadvantages of the prior art.

This object is achieved by the security element having the features of the main claim. A method for its manufacture, a security arrangement and a valuable object with such a security element are given in the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, in a generic security element, an at least partially present second optically active layer is provided, wherein the first and the second layer are arranged one above the other in an overlapping region. The first optically active layer selectively reflects light in a first wavelength range with a first circular polarization direction, while the second optically active layer selectively reflects light in a second wavelength range with a second circular polarization direction either itself or in the overlap region in cooperation with the first optically active layer , ,

The second optically active layer forms a phase shift layer that forms a λ / 2 layer for light from the first wavelength range. In this case, the λ / 2 layer is preferably formed from nematic liquid-crystalline material which, because of the optical anisotropy of the aligned rod-shaped liquid crystals, makes it possible to produce optically active layers.

The second optically active layer is in the form of characters and / or merstein.

As a result, it is possible to achieve novel effects which exploit the light-polarizing or phase-shifting properties of the liquid crystal layers, which retain or even increase the advantageous security against forgery of known security elements. As explained in detail below, the additive color mixing of the reflection spectra of the two optically active layers allows the generation of wider and unusual color-shift effects. Also, the intensity of the total reflected light can be increased by the use of the two counter-rotating circular polarization directions. In addition, information which can only be read out using circular polarizers can be coded in one or more of the liquid crystal layers.

In an advantageous variant of the invention, the second circular polarization direction of the light, which reflects the second optically active layer itself or in cooperation with the first optically active layer, is opposite to the first circular polarization direction. In a likewise advantageous variant of the invention, the wavelength range reflected by the second optically active layer corresponds to the first wavelength range.

In order to attenuate the effect of the λ / 2 layer in regions and / or to produce new effects, the λ / 2 layer may also be formed from a plurality of partial layers arranged one above the other and partially rotated relative to one another in the layer plane. The partial layers are particularly advantageously formed by two λ / 4 layers. By partially different rotation of the two λ / 4-part layers, their influence on circularly polarized light can be selectively used to produce, for example, coded halftone images.

In the embodiments with λ / 2 layer can advantageously be provided a third optically active layer of cholesteric liquid-crystalline material which, like the first optically active layer, selectively reflects light in the first wavelength range with the first circular polarization direction. The λ / 2-layer is arranged at least partially between the first and the third optically active layer.

The wavelength range reflected by the second optically active layer differs in a likewise advantageous variant of the invention from the first wavelength range.

In all described embodiments it can be provided that the first optically active layer only reflects light from the non-visible part of the spectrum in a first viewing direction. In contrast, the first optically active layer preferably reflects visible light of a first color in a second viewing direction. Also the second optically active layer In an advantageous embodiment, in one or the second viewing direction, only light from the non-visible part of the spectrum is reflected. It also advantageously reflects visible light of a third color in one or the first viewing direction.

Overall, it can then be provided in a particularly preferred embodiment that one of the two optically active layers as light from the invisible part of the spectrum infrared radiation, and the other of the two optically active layers as light from the non-visible part of the spectrum ultraviolet radiation in the corresponding Viewing direction reflected.

If the first optically active layer only reflects light from the non-visible part of the spectrum and possibly visible light in a second viewing direction of a first color in a first viewing direction, then the second optically active layer may also be configured to be in the first viewing direction visible light of a third color and in the second viewing direction visible light of a fourth color other than the third color reflected.

In other embodiments, the first optically active layer reflects visible light of a first color in a first viewing direction and visible light of a second color different from the first color in a second viewing direction. The second optically active layer can then reflect in the second viewing direction only light from the non-visible part of the spectrum and optionally visible in the first viewing direction light of a third color. Alternatively, the second reflects optically active layer in the first viewing direction visible light of a different color from the first color third color and in the second viewing direction light of a fourth color different from the third color.

In all embodiments, in addition to the second optically active layer, the first and / or optionally the third optically active layer may be in the form of characters and / or patterns. It is also possible to provide further optically active layers of nematic and / or cholesteric liquid-crystalline material. At least one of the optically active layers of cholesteric liquid-crystalline material and / or optionally at least one layer of nematic liquid-crystalline material is expediently present in the form of pigments which are embedded in a binder matrix. Such pigments are easier to print than liquid crystals from solution and do not place such high demands on the smoothness of the substrate. In addition, pigment-based inks do not require alignment-promoting measures.

In a preferred embodiment, the optically active layers are at least partially, preferably over the entire surface, arranged on a dark, preferably black background. The dark background can be present even in the form of signs and / or patterns. In particular, it can be printed, produced by coloring a substrate or by the action of a laser beam on a substrate.

The optically active layers and, where appropriate, the dark background are in expedient embodiments on a substrate. The substrate is advantageously formed from paper or plastic.

In advantageous embodiments, the security element forms a security thread, a label or a transfer element.

The invention also encompasses a method for producing a security element of the type described, in which a first and a second optically active layer are applied to a carrier film such that they are arranged one above the other in an overlapping area, a cholesteric one being used to form the first optically active layer liquid crystalline material is applied. The two optically active layers can each be applied to a separate carrier film, in particular printed on and then laminated one above the other. This makes it possible to examine the optically active layers separately after application to the carrier film for suitability for further processing and optionally to separate them out. Alternatively, the two optically active layers can also be applied successively on the same carrier film.

The liquid crystalline material may be applied from a solvent or from the melt. Furthermore, in particular, cholesteric liquid crystalline material can be applied in pasty form as a UV-curable cholesteric mixture, wherein such a system neither includes typical solvents nor is based on a melt or pigments, but instead contains further UV-curable lacquers. Depending on the method used, the liquid crystalline material is then physically dried, aligned and cured to remove the solvent. The alignment can be done directly over the carrier film or via so-called alignment layers, by applying shear forces, by electrostatic methods, etc. For hardening the liquid-crystalline This material can be crosslinked, for example by means of ultraviolet radiation or by electron beam (ESH). However, the liquid-crystalline material can also be fixed by adding certain additives.

Advantageously, after the application of all the optically active layers, the one or, if appropriate, both carrier films are removed. This is done in particular via separating layers or by using a laminating adhesive whose adhesion to the carrier film is lower than its adhesion with respect to the associated optically active layer.

Alternatively, an all-over auxiliary layer can be applied to the optically active layer present on the carrier film whose adhesion to the carrier film is less than its adhesion with respect to the optically active layer in order to allow the separation. As a result, the laminating adhesive can be applied over the entire surface, at the same time preventing uncontrolled adhesion. The auxiliary layer is advantageously a UV lacquer layer.

The formation of the cholesteric liquid crystal layers can be done with advantage by combination of a nematic liquid crystal system with a Verdriller.

The invention further includes a security arrangement for security papers, valuables and the like having a security element of the type described or a security element producible according to the method described and a separate display element which, in cooperation with the security element, has a color shift effect and / or a polarization effect and / or a brightness effect ., an intensity gain for the viewer makes recognizable.

In a preferred embodiment, the security element is formed without a dark background layer, while the separate display element comprises a dark, preferably black background.

In another, likewise preferred embodiment, the security element can also comprise a dark background layer. The separate display element in this embodiment comprises a linear or circular polarizer with which the color and / or polarization effects of the security element can be made visible.

In a further preferred embodiment, the security element has a layer of cholesteric liquid-crystalline material and a layer of nematic liquid-crystalline material, which are arranged one above the other in an overlapping region. In this embodiment, the separate display element comprises a layer of cholesteric liquid-crystalline material which, in cooperation with the security element, makes a region-wise increase in intensity visible to the viewer.

Furthermore, the invention comprises a security arrangement for security papers, valuables and the like having a security element comprising at least one layer of liquid-crystalline material, which is arranged at least partially on a transparent carrier film, and a separate display element, which in cooperation with the security element a color shift effect for the Viewer makes recognizable and includes a dark, preferably black background.

The invention further comprises a valuable article, such as a branded article, a value document or the like, having a security element or a security arrangement of the type described. The valuable article may, in particular, be a security paper, a value document or a product packaging. The security element is advantageously arranged in a window region of the valuable article.

Particularly preferred is a flexible object of value, in which the security element and the presentation element can be laid one on top of the other by bending or folding the valuables for self-authentication.

Valuables within the meaning of the present invention are in particular banknotes, shares, identity cards, credit cards, bonds, certificates, vouchers, checks, high-quality admission tickets, but also other papers that are subject to counterfeiting, such as passports and other identity documents, as well as product security elements such as labels, seals, packaging and the like , The term "object of value" in the following includes all such objects, documents and product protection means. Under the term "security paper", the precursor, which is not yet executable, becomes a value document understood that in addition to the security element further authenticity features, such as luminescent substances provided in the volume, may have. Security paper is usually in quasi-endless form and will be further processed at a later date.

In a method for checking the authenticity of a security element, a security arrangement or a valuable article of the type described above, it is checked whether there is a predetermined color-shift effect and / or if there is a predetermined polarization effect and / or if there is a predetermined brightness effect. The authenticity of the item being tested is then assessed on the basis of the test result. Advantageously, in the test method using a linear or circular polarizer, additionally, information encoded in the security element can be read, and the authenticity of the item under test can be judged based on the reading result.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a representation true to scale and proportion has been dispensed with in order to increase the clarity.

Fig. 1

eine schematische Darstellung einer Banknote mit einem einge- betteten Sicherheitsfaden und einem aufgeklebten Transferele- ment, jeweils nach einem Ausführungsbeispiel der Erfindung,

Fig. 2

den allgemeinen Schichtaufbau eines erfindungsgemäßen Si- cherheitselements im Querschnitt,

Fig. 3

ein Sicherheitselement im Querschnitt,

Fig. 4

in (a) den Querschnitt eines Sicherheitselements , in (b) eine Ansicht dieses Sicherheitselements bei senkrechter Betrachtung und in (c) eine Ansicht bei spitzwinkliger Betrachtung,

Fig. 5

eine Darstellung wie in Fig. 4 eines Sicherheitselements ,

Fig. 6

ein Sicherheitselement nach noch einem weiteren Beispiel der Erfindung mit einem Zirkularpolarisator zum Lesen der codierten Information,

Fig. 7

eine Darstellung wie in Fig. 6 eines Sicherheitselements nach einem Ausführungsbeispiel der Erfindung,

Fig. 8

das Prinzip von Sicherheitselementen mit einem dreischichti- gen Flüssigkristallaufbau, bei dem eine λ/2-Schicht zwischen zwei cholesterischen Flüssigkristallschichten angeordnet ist,

Fig. 9

ein Sicherheitselement nach dem Prinzip der Fig. 8 bei Beleuch- tung mit rechtszirkular polarisiertem Licht,

Fig. 10

ein weiteres Sicherheitselement nach dem Prinzip der Fig. 8 mit einer in zwei λ/4-Schichten unterteilten λ/2-Schicht,

Fig. 11

ein Sicherheitselement , bei dem sowohl die Farbeffekte als auch die Polarisationseffekte der Flüssigkristallschichten ausgenutzt werden, wobei (a) den Schichtaufbau des Sicherheitselements und (b) und (c) die Situation bei Betrachtung durch verschiede- ne Zirkularpolarisatoren zeigt, und

Fig. 12

in (a) eine schematische Darstellung einer Banknote mit einer erfindungsgemäßen Sicherheitsanordnung aus einem Sicher- heitselement und einem Darstellungselement, und in (b) eine Aufsicht auf die gefaltete Banknote von (a) mit einer durch das Aufeinanderlegen der beiden Elemente sichtbar gemachten Bildinformation.

Show it:

Fig. 1

2 a schematic representation of a banknote with an embedded security thread and a glued transfer element, in each case according to an exemplary embodiment of the invention,

Fig. 2

the general layer structure of a safety element according to the invention in cross-section,

Fig. 3

a security element in cross section,

Fig. 4

in (a) the cross-section of a security element, in (b) a view of this security element when viewed vertically, and in (c) a view on an acute-angled view,

Fig. 5

a representation like in Fig. 4 a security element,

Fig. 6

a security element according to yet another example of the invention having a circular polarizer for reading the coded information,

Fig. 7

a representation like in Fig. 6 a security element according to an embodiment of the invention,

Fig. 8

the principle of security elements with a three-layer liquid crystal structure in which a λ / 2 layer is arranged between two cholesteric liquid crystal layers,

Fig. 9

a security element according to the principle of Fig. 8 when illuminated with right circular polarized light,

Fig. 10

another security element according to the principle of Fig. 8 with a λ / 2 layer divided into two λ / 4 layers,

Fig. 11

a security element in which both the color effects and the polarization effects of the liquid crystal layers are utilized, wherein (a) the layer structure of the security element and (b) and (c) shows the situation when viewed through different circular polarizers, and

Fig. 12

in (a) is a schematic representation of a banknote with a security arrangement according to the invention of a security element and a display element, and in (b) a plan view of the folded banknote of (a) with an image information made visible by the juxtaposition of the two elements.

The invention will now be explained in more detail using the example of a banknote. Fig. 1 shows a schematic representation of a banknote 10, the two security elements 12 and 16, respectively, which are each formed according to an embodiment of the invention. The first security element represents a security thread 12 that emerges at certain window areas 14 on the surface of the banknote 10, while it is embedded in the intervening areas inside the banknote 10. The second security element is formed by a glued transfer element 16 of any shape. Fig. 2 shows the basic layer structure of the security elements 12 and 16 in cross section. A smooth film 20, for example a PET film of good surface quality, is provided with an absorbent, dark background layer 22. Two or more, in the general case, n optically active layers 24-1, 24-2,... 24-n of liquid-crystalline material are applied to this background layer 22. As described in detail below, the liquid crystal layers 24-1, 24-2,... 24-n may each have different but also partially the same light-polarizing or phase-shifting properties.

Alignment layers and / or adhesive layers 26 may be provided between the liquid crystal layers, which serve to align the liquid crystals in the liquid crystal layers or the connection of the individual liquid crystal layers and to compensate for unevenness in the background.

According to the invention, at least one of the liquid-crystalline layers 24-1, 24-2, ... 24-n consists of a cholesteric liquid-crystalline material and selectively reflects light in a first wavelength range with a first circular polarization direction. A second layer, superimposed in an overlap region with the first layer, selectively reflects light in a second wavelength range with a second circular polarization direction, either by itself or in cooperation with the first layer.

In some embodiments of the invention, the dark background layer 22 is not part of the security element. The liquid crystal layers 24-1, 24-2,... 24-n and possible alignment and adhesive layers 26 are then applied directly to the film 20. Likewise, in some embodiments, it is advantageous to remove the film 20 after application of the finished security element to a valuable item, as explained in more detail below.

Fig. 3 shows a security element 30 illustrati of the invention, in which on an absorbent, preferably black background layer 22, a first cholesteric liquid crystal layer 32 and on this a second cholesteric liquid crystal layer 34 are arranged. Due to the interplay of the two liquid crystal layers 32 and 34, the security element 30 has a novel color-shift effect, which conveys to the viewer a color impression that changes with the viewing direction. When viewed vertically, the security element 30 appears to the viewer in the exemplary embodiment blue / violet (reflected radiation 301), while viewed from an acute angle, it offers a red color impression (reflected radiation 302).

This novel color interplay, in which the color impression of the security element changes from short-wave to longer-wave light when tilted, is due to the fact that the first liquid crystal layer 32 blue light (arrow 321) in the vertical viewing direction and shorter-wave UV radiation (arrow 322) in the acute Viewing direction reflected. The second liquid crystal layer 34 is formed to reflect infrared radiation (arrow 341) in the perpendicular viewing direction and shorter wavelength red light (arrow 342) in the acute viewing direction. The two lying outside the visible spectral range Reflection components 321 and 342 do not contribute to the color impression of the security element, so that a blue color impression 301 results for the viewer when viewed vertically and a long-wave red color impression 302 when viewed at an acute angle.

To produce the security element 30, the first and second liquid crystal layers 32 and 34 can each be printed on a smooth PET film of good surface quality. Suitable printing methods are all suitable printing processes for liquid-crystalline layers, such as intaglio, flexographic printing, knifecoating, curtain or blade techniques.

After drying the liquid crystal layers 32, 34, the quality and the color spectrum of the individual layers can already be tested at this stage of production and, if appropriate, rejects rejects. The liquid crystal layers 32 and 34 are then laminated to the background layer 22 and the first liquid crystal layer 32, respectively, using commercially available laminating adhesives. The smoothness of the surface influences the degree of gloss of the security element. The laminating adhesive can compensate for unevenness in the surface, as can occur during the construction of a typical security thread 12, so that good gloss can also be achieved for such security elements.

After bonding the liquid crystal layers 32 and 34, the carrier foils can be removed. This can be done for example via so-called separation or release layers. These are in particular UV coatings or waxes, which can be activated mechanically or thermally. When separating layers are used, they can be structured on the surface in order to locally promote or prevent orientation of the liquid crystals during application. By a partially different orientation of the liquid crystals so motifs such as characters or patterns can be introduced into the liquid crystal layers even when applied over the entire area.

If no release layer is provided, it is expedient to choose a laminating adhesive whose adhesion to the carrier film is less than its adhesion to the liquid-crystal layer, in order to prevent a film tear. Also, the adhesion of the liquid crystals to the support film must be less than the adhesion of the adhesive to the liquid crystals to permit separation. Furthermore, the adhesion of the adhesive to the layer to which the system is to be transferred must be better than the adhesion of the liquid crystals to the carrier film. It must also be better than the adhesion of the adhesive to the carrier film. The above requirements of the laminating adhesive are particularly important if the liquid crystal layer to be transferred is not formed over the entire surface.

After the first liquid-crystal layer 32 has been laminated to the substrate 22, the second liquid-crystal layer 34 is laminated in an analogous manner to the first liquid-crystal layer 32, which is now located above the composite.

In the Fig. 3 as well as the examples and embodiments described below, the liquid crystal layers may each be laminated one on top of the other, printed on top of each other or otherwise applied one above the other, wherein optionally not shown alignment layers or adhesive layers between the layers may be provided.

Another example is in Fig. 4 shown schematically. In the security element 40, a first cholesteric liquid crystal layer 42 and on this a second cholesteric liquid crystal layer 44 are applied to an absorbing, preferably black background layer 22. As in Fig. 4 (b) 1, the first liquid crystal layer 42 is applied only in regions to the substrate 22 and forms a motif by the shape or the outline of the applied areas, in the exemplary embodiment a blazon 46. The second liquid crystal layer 44 is over the entire area on the first liquid crystal layer 42 or in the released areas on the substrate layer 22 applied.

The two liquid crystal layers are matched to one another such that the coat of arms motif 46 when viewing the security element (FIG. Fig. 4 (b) ) is clearly visible to the viewer and disappears when tilting the security element 40, ie the transition from vertical to acute angle viewing, as in Fig. 4 (c) indicated by the dashed outline. The disappearance of the coat of arms motif 46 is achieved in that the partially applied liquid crystal layer 42 when tilting a color shift effect of blue (arrow 421) to ultraviolet (arrow 422) shows, while the second liquid crystal layer 44 has a changing between two colors of the visible spectral range color shift effect, and for example, varies between red (arrow 441) and green (arrow 442).

When the security element 40 is viewed perpendicularly, a color impression 401 results in the overlapping area 48 of the two layers, which is given by the additive color mixture of the blue light 421 of the first liquid crystal layer 42 and the red light 441 of the second liquid crystal layer 44, while outside the overlap area only the color layer 401 red color impression of the second liquid crystal layer 44 can be seen. Due to the color contrast in the reflected light 401, the crest motif 46 clearly emerges for the viewer.

If the observer now tilts the security element 40 so that he sees it at an acute angle, then the first liquid crystal layer 42 in the overlap region 48 only reflects ultraviolet light lying outside the visible spectral range to the observer. The liquid crystal layer 42 thus contributes neither to the color impression 402 of the security element 40 in the overlapping area 48 nor outside the overlapping area. Under acute viewing angle, the motif is therefore not visible, and the viewer has the impression that the crest motif 46 disappears when tilting the security element 40 from the vertical.

In an analogous manner, a security element 50 with a motif appearing on tilting can be produced, as in FIG Fig. 5 illustrated. For this purpose, the areally applied liquid crystal layer 52 is formed so that it shows a color shift effect of infrared (arrow 521) to red (arrow 522) when tilting. The second liquid crystal layer 54 again shows a color shift effect between two colors of the visible spectral range, and varies, for example, between cyan (arrow 541) and violet (arrow 542).

In this constellation, the subject 56 is not visible when viewed perpendicularly in the reflected light 501, since at most invisible infrared radiation from the first liquid crystal layer 52 is reflected in the vertical viewing direction. Only when the security element 50 is tilted does the subject become recognizable to the observer, since the first liquid crystal layer 52 then reflects red light to the viewer in the overlapping area 58, and the subject 56 in the reflected light 502 thus stands out from the violet color impression outside the overlapping area 58.

The FIGS. 6 to 11 show further examples and embodiments of the invention, in which in addition to the color shift effect, especially the special lichtpolarisierenden properties of the liquid crystal layers are exploited. The polarization direction of the light is indicated in these figures by additional arrow symbols on the propagation vectors of the light. As usual, a circular polarization in which the circular motion of the electric field strength vector is clockwise from an observer's point of view, is referred to as right circular polarization, counter polarization as left circular polarization.

The security element 60 of Fig. 6 includes two cholesteric liquid crystal layers 62 and 64 deposited on a dark background layer 22. The two liquid crystal layers 62 and 64 have the same color reflection spectrum, but differ in the orientation of the reflected circular polarization. While the first liquid crystal layer 62 in the example reflects left circularly polarized light, the second liquid crystal layer 64 reflects right circularly polarized light. Left circular polarized light is from the second liquid crystal layer 64, on the other hand, passed without significant absorption. It is understood that the polarization directions given are for illustration only and of course can be chosen differently.

Such opposing selective reflection can be achieved, for example, by creating the two cholesteric liquid crystal layers 62 and 64 from the same nematic liquid crystal system using mutually mirror-image twisters. Thus, a mirror-image helical arrangement of the rod-shaped liquid crystal molecules in the two liquid crystal layers can be achieved, so that one layer reflects right-handed, the other layer left circularly polarized light. The color of the light reflected from the liquid crystal layers depends on the viewing direction as in the examples described above, and changes from red to green, for example, in the transition from vertical to acute viewing.

The first liquid crystal layer 62 is in the example of Fig. 6 only partially in the form of a motif, such as a lettering, or a pattern ago. If the security element 60 is viewed without auxiliary means, then the color-shift effect of the second liquid-crystal layer 64 appears in the first place. In the overlapping region 68 of the two layers, the motif is recognizable with the same color impression, but with respect to its surroundings increased brightness, since in the overlap region 68 light of both circular polarization directions is reflected, while outside only rechtszirkular polarized light is reflected, as by the arrows 70 of the reflected light displayed.

Considering the security element 60 through a circular polarizer 72 that transmits only left circularly polarized light, the high brightness contrast pattern formed by the first liquid crystal layer 62 emerges because the circular polarizer 72 completely blankes out the right circularly polarized light reflected from the second liquid crystal layer 64. Such a circular polarizer 72 can be formed for example by a linear polarizer and a downstream λ / 4 plate.

It is understood that the second liquid crystal layer 64 or both liquid crystal layers 62, 64 may be present in the form of motifs in an analogous manner. A motif in the second liquid crystal layer 64 can be made clearly visible by using a circular polarizer which transmits right circularly polarized light. With a viewing device containing both types of polarizers, the motifs can be easily displayed in one or both layers.

The embodiment of Fig. 7 shows a security element 80 with a first cholesteric liquid crystal layer 82 and on the liquid crystal layer 82 partially applied λ / 2 layer 84 containing nematic liquid crystals. With nematic liquid crystals, it is possible to produce optically active layers along the main crystal axes due to the different refractive indices of the rod-shaped liquid crystals. With a correspondingly selected layer thickness, a λ / 2 layer is obtained for the wavelength range in which the first liquid crystal layer 82 selectively reflects.

In the regions 86 uncovered by the λ / 2 layer 84, the first liquid crystal layer 82 reflects light with a preselected circular polarization direction, for example, left circularly polarized light. In the overlapping area 88 of the two layers, the security element 80 reflects light with the opposite polarization direction, in the exemplary embodiment therefore right-circularly polarized light, since the incident unpolarized light is not affected by the λ / 2 layer 84, the polarization direction of the reflected from the first liquid crystal layer 82, left circularly polarized light from the λ / 2 layer 84, however, is just reversed by the path difference between the ordinary and extraordinary beams in its polarization orientation.

Without aids, the motif formed by the λ / 2 layer 84 is barely discernible since the security element in the covered and uncovered areas reflects substantially the same amount of light and the unaided eye can not distinguish the circular polarization direction of the light.

On the other hand, if the security element 80 is viewed through a circular polarizer 92 which transmits only right-circularly polarized light, the motif formed in the λ / 2 layer 84 emerges with a clear contrast. The image parts 88 covered by the λ / 2 layer 84 appear bright, while the uncovered image parts 86 appear dark. A reverse (negative) image impression results when using a circular polarizer which transmits only left circularly polarized light. As described above, the circular polarizer 92 may be formed by, for example, a linear polarizer followed by a λ / 4 plate.

To produce the security element 80, a nematic liquid crystal layer in the form of a motif may first be printed on a smooth PET film of good surface quality in a layer thickness selected such that a λ / 2-layer receives. After physical drying to remove the solvent, the liquid crystal layer is crosslinked by means of ultraviolet radiation. Subsequently, a layer of cholesteric liquid-crystalline material is printed over the entire area of the PET film partially coated with nematic liquid-crystalline material. This layer is also crosslinked after physical drying by means of ultraviolet radiation. The two-layered liquid crystal structure thus produced is then laminated to the background layer 22 by means of commercially available laminating adhesives via the cholesteric liquid crystal layer now lying on top, which forms an absorbent substrate. Such an absorbent substrate can be provided, for example, by a security thread, which may have further security elements.

After bonding, finally, the carrier film can be removed. This can be done for example via separating layers. These are in particular UV coatings or waxes, which can be activated mechanically or thermally. If no separating layer is provided, then the cholesteric liquid crystal layer printed over the entire surface can also serve as an auxiliary layer between the laminating adhesive and the PET film and thus prevent the film tear otherwise possible when the PET film is pulled off, which can occur, in particular, during the transfer of non-full-surface layers. The same auxiliary function can also be a full-surface applied auxiliary layer from a UV varnish or other suitable material that can be easily removed from the carrier film. Since uncontrolled sticking through the laminating adhesive is prevented by the full-surface application, the laminating adhesive can be printed over the entire surface.

In further embodiments of the invention, the security element has a three-layered liquid crystal structure in which a λ / 2 layer is arranged between two cholesteric liquid crystal layers having the same light-polarizing properties. The principle of these embodiments will now be described with reference to Fig. 8 explained.

The security element 100 has a layer sequence applied to a dark, preferably black background layer 22, which comprises a first cholesteric liquid crystal layer 102, a λ / 2 layer 104 and a second cholesteric liquid crystal layer 106. The light-polarizing properties of the first and second liquid crystal layers 102 and 106 are identical, such that the two layers in themselves reflect light in the same preselected wavelength range and in the same preselected circular polarization direction. All layers can be applied over the entire area or only in certain areas in order to form different or complementary motifs such as characters or patterns.

The reflection properties of the different possible layer sequences are in the Fig. 8 illustrated. It is assumed that the two cholesteric liquid crystal layers 102 and 106 are left circularly polarized Reflecting light and illuminating the security element with unpolarized light.

In a first region 110 in which only the first liquid crystal layer 102 is present, left circularly polarized light is reflected. In a second region 112, in which the first liquid crystal layer 102 is covered by the λ / 2 layer 104, the security element reflects, as already described in connection with FIG Fig. 7 explains, right circularly polarized light. In a third region 114 in which all three layers are present, the upper liquid crystal layer 106 reflects left circularly polarized light and transmits right circularly polarized light. The transmitted light is converted by the λ / 2 layer 104 into left circularly polarized light, which is then reflected by the first liquid crystal layer 102. The reflected light is converted by the λ / 2 layer 104 again into right-circularly polarized light, which is transmitted from the second liquid crystal layer 106. Thus, the layer sequence 102, 104, 106 also reflects right-circularly polarized light in addition to left circularly polarized light, as in FIG Fig. 8 shown.

In the fourth region 116 where only the two cholesteric liquid crystal layers 102 and 106 are present, the upper liquid crystal layer 106 reflects left circularly polarized light. The transmitted right circularly polarized light is also transmitted by the lower liquid crystal layer 102 and absorbed in the background layer 22. The security element thus reflects only left circularly polarized light in this area. The same applies to the fifth region 118 in which the second liquid crystal layer 106 is present alone.

The numerous possibilities of variation due to the different layer sequences allow a multitude of application possibilities for security elements, of which only some are explained in more detail by way of example.

The security element 120 of Fig. 9 includes, as the above-described security element 100 of Fig. 8 a layer sequence applied to a black background layer 22 comprising a first cholesteric liquid crystal layer 102, a λ / 2 layer 104 and a second cholesteric liquid crystal layer 106. In this embodiment, only the λ / 2 layer 104 is in the form of a motif, while the first and second liquid crystal layers 102 and 106 are applied over the entire surface.

In normal illumination with unpolarized light, the motif of the λ / 2 layer 104 appears with the same color impression as its surroundings, but is already in the regions 126 due to the reflection of both the left circular and the right circularly polarized light by the substantially double amount of reflected light recognizable without aids. Further, when the security element 120 is illuminated by a circular polarizer 122 with right circularly polarized light, the subject appears to the viewer 124 without further aids having strong contrast since the right circularly polarized light reflects in the areas 126 in which all three layers overlap while being transmitted in regions 128 without λ / 2 layer 104 from the upper and lower liquid crystal layers 106 and 102, respectively, and absorbed in the black background layer 22.

Fig. 10 shows a security element 130 according to a further embodiment of the invention, with respect to its layer sequence substantially like the security element 120 of the Fig. 9 is constructed. In contrast to the security element described there, the intermediate layer 132 of the security element 130 is constructed from two λ / 4 partial layers 134 and 136, which can be locally rotated relative to one another in their orientation in the layer plane.

If the partial layers 134 and 136 in a partial region 138 are undiluted, ie arranged one above the other at a rotational angle θ = 0 °, then together they form a λ / 2 layer which, like the λ / 2 layer 104 of the exemplary embodiment of FIG Fig. 9 ensures that in the partial area 138, right-circularly polarized light is reflected by the layer sequence. In another subarea 140, the two λ / 4 layers 134 and 136 are rotated in their orientation by a rotation angle of θ = 90 ° against each other, so that their effect on incident circularly polarized light just picks up. In the partial area 140, right-circularly polarized light is therefore - analogous to the partial area 128 of FIG Fig. 9 - Transmitted from the layer sequence and finally absorbed by the background layer 22.

If the two λ / 4 layers 134 and 136 are rotated relative to one another in a partial region 142 by an angle of rotation θ between 0 ° and 90 °, the intermediate layer 132 causes a certain proportion of right-circularly polarized light to be reflected by the layer sequence , The size of the reflected portion decreases continuously with increasing rotation angle. By a different angle of rotation θ in different surface areas of the intermediate layer 132, for example, halftone motifs can be coded in the security element, which barely appear when illuminated with unpolarized light when illuminated circularly polarized light but for the viewer without further aids as gray scale images in appearance.

It is understood that in an analogous manner in layer sequences which do not have a second cholesteric liquid crystal layer, as for example in the embodiment of the Fig. 7 is shown, the λ / 2 layer can of course also be replaced by two λ / 4-part layers. These λ / 4-part layers may also be locally rotated in their orientation in the layer plane against each other.

Figure 11 shows an example in which both the color effects and the polarization effects of the liquid crystal layers are utilized. Fig. 11 (a) FIG. 12 shows the construction of a security element 150 having an underlying absorbent layer 22, a first cholesteric liquid crystal layer 152, and a second cholesteric liquid crystal layer 154 deposited thereon.

The first liquid crystal layer 152 has a first color-shift effect, for example from green to blue, and in addition only reflects light of a preselected circular polarization direction, for example right-circularly polarized light. The second liquid crystal layer 154 has a second color shift effect, for example from magenta to green, and also reflects only light of the circular polarization direction opposite the first liquid crystal layer, in the exemplary embodiment left circularly polarized light. If the security element 150 is viewed when illuminated with unpolarized light and without auxiliary means, then the two color shift effects are superimposed by additive color mixing of the reflected light. If the security element 150 is viewed through a circular polarizer 156 which transmits only right-circularly polarized light, the color-shift effect of the first liquid-crystal layer 152 alone can be observed when tilting the security element, as in FIG Fig. 11 (b) illustrated. On the other hand, only a color-shifting effect of the second liquid crystal layer 154 is manifested by a circular polarizer 158 transmitting only left circularly polarized light, as in FIG Fig. 11 (c) shown. It is understood that each of the liquid crystal layers 152, 154 can also be replaced by a combination of a λ / 2 layer with a cholesteric layer mirroring the original layer.

The principles of the described examples and embodiments can also be used for self-authenticating security arrangements on any data carrier. Fig. 12 For illustration, a banknote 160 equipped with a two-part security arrangement comprising a security element 162 and a presentation element 164 is shown. The security element 162 and the presentation element 164 are arranged on the banknote 160 such that, when the banknote is folded along the center line 166, they come to lie on one another, as in FIG Fig. 12 (b) shown. It is understood that such an arrangement of the security element 162 and the display element 164 is not mandatory and that the elements 162,164 can of course also be arranged at other locations on the banknote 160, as long as it is ensured that they come to rest when folding the banknote ,

In one exemplary embodiment, the security element 162 consists of a layer sequence of cholesteric layers applied to a transparent film and / or nematic liquid crystal layers, as in Fig. 2 shown, but without the dark background layer 22. The layers may be applied over the entire surface or even in regions, to form different or complementary motifs. The layer sequence as such can also be present on the transparent film in the form of a motif. The security element 162 is present in a papermaking-made or punched-out window of the banknote 160 and appears in the unfolded position of the banknote in reflected light or transmitted light substantially transparent and inconspicuous.

The dark background layer, which is essential to the visibility of the described color or polarization effects, is provided by separate display element 164 in this embodiment and may be formed, for example, by a commercial ink printed on one side of the bill. Only when the banknote, as in Fig. 12 (b) , is folded so that the security element 162 comes to lie on the display element 164, the intended color and / or polarization effects can be detected. In the embodiment occurs after folding the banknote 160, a previously unrecognizable crest motif 168 in appearance. It is understood that a motif may also be present in the presentation element 164, in particular in addition to the motif in the security element 162, wherein the two motifs may complement one another and thereby form an encoding.

In other embodiments of the invention, the security element 162 is present as one of the security elements described above, including the dark background layer 22, and the presentation element 164 contains a circular polarizer, which is formed for example by a linear polarizer and a downstream λ / 4 plate. The detection mechanisms described above for the motifs introduced into the security element 162 when viewed through a circular polarizer can then be realized by folding the banknote 160, so that the user can carry out self-authentication of the security element and thus of the banknote 160 without additional aids.

In a further embodiment according to the invention, the security element 162 consists of a layer sequence applied to a dark background layer, as in FIG Fig. 7 which comprises a first cholesteric liquid crystal layer and a λ / 2 layer applied to these in regions, which contains nematic liquid crystals. The security element 162 may be formed here for example by a glued transfer element or a security thread. In the unfolded position of the banknote, the security element 162 essentially only shows a color shift effect in incident light. The motif formed by the λ / 2 layer, however, is hardly recognizable.

The display element 164 is present in a papermaking or punched-out window of the banknote 160 and consists of a cholesteric liquid crystal layer applied to a transparent film whose light-polarizing properties are identical to those of the first cholesteric liquid crystal layer of the security element 162. In particular, the two layers individually reflect light in the same preselected wavelength range and with the same preselected circular polarization direction. The presentation element 164 appears in unfolded Location of the banknote in reflected light or transmitted light substantially transparent and inconspicuous.

When the banknote is folded so that the imaging element 164 on the security element 162 comes to rest such that the cholesteric liquid crystal layer of the imaging element 164 directly adjoins the security element 162, those described in connection with FIGS FIGS. 8 and 9 observed effects are observed. In particular, the subject of the λ / 2 layer in normal illumination with unpolarized light due to the reflection of light of both circular polarization directions has a relation to its surroundings increased brightness and is thus recognizable without further aids. It is then a previously not or barely recognizable motif clearly in appearance.

In a further embodiment not shown, the security element consists of a liquid crystal layer applied to a transparent film. The security element as well as the security element lies in the Fig. 12 illustrated self-authenticating security arrangement in a papermaking or punched window, for example, a banknote ago. The partially applied in the form of a motif liquid crystal layer appears transparent and unobtrusive both in reflected light and transmitted light and is essentially indistinguishable from the surrounding transparent film. By a separate display element, which is arranged at another point of the banknote so that the security element comes to rest when folding the banknote on this, the typical liquid crystal color shift effects by providing a dark, preferably black background layer be made visible. Such a background layer can be provided, for example, by printing one side of the banknote with a commercially available printing ink.

Of course, the embodiments for self-authenticating security arrangement can also be provided on a plastic document, such as a Kunststoffbanknote. Here, the transparent window is preferably formed by a non-printed area of the document.

Claims (20)

1. A security element (80) for securing valuable articles, having a first optically active layer (82) that is present in at least some areas and comprises cholesteric liquid crystal material, and a second optically active layer (84) that is present in at least some areas, wherein the first and the second layer (82, 84) are stacked in an overlap area (88), the first optically active layer (82) selectively reflects light in a first wavelength range having a first direction of circular polarization, the second optically active layer (84), either itself or, in the overlap area (88), in coaction with the first optically active layer (82), selectively reflects light in a second wavelength range having a second direction of circular polarization, in that the second optically active layer (84) forms a phase-shifting layer that forms a λ/2 layer for light from the first wavelength range, characterized in that the second optically active layer (84) is present in the form of characters and/or patterns.
2. The security element (80) according to claim 1, characterized in that the second wavelength range in which the second optically active layer (84) reflects, itself or in coaction with the first optically active layer (82), corresponds to the first wavelength range.
3. The security element (80) according to claim 1 or 2, characterized in that the second optically active layer (84) is formed from nematic liquid crystal material.
4. The security element (80) according to at least one of claims 1 to 3, characterized in that the λ/2 layer is formed from multiple sub-layers (134, 136) that are stacked and, in some areas, twisted toward one another in the layer plane, preferably that the multiple sub-layers are formed by two λ/4 layers.
5. The security element (100) according to at least one of claims 1 to 4, characterized in that a third optically active layer (106) comprising cholesteric liquid crystal material is provided that selectively reflects light in the first wavelength range having the first direction of circular polarization, and in that the phase-shifting layer (104) is disposed, at least in some areas, between the first (102) and the third (106) optically active layer.
6. The security element (80) according to at least one of claims 1 to 5, characterized in that the first optically active layer (82) reflects only light from the non-visible part of the spectrum in a first viewing direction, preferably that the first optically active layer (82) reflects visible light of a first color in a second viewing direction.
7. The security element (80) according to at least one of claims 1 to 6, characterized in that the second optically active layer (84) reflects only light from the non-visible part of the spectrum in a or the second viewing direction, preferably that the second optically active layer (84) reflects visible light of a third color in a or the first viewing direction.
8. The security element (80) according to claim 6 or 7, characterized in that one of the two optically active layers (82, 84) reflects infrared radiation as light from the non-visible part of the spectrum and the other of the two optically active layers (82, 84) reflects ultraviolet radiation as light from the non-visible part of the spectrum in the appropriate viewing direction.
9. The security element (80) according to claim 6, characterized in that the second optically active layer (84) reflects, in the first viewing direction, visible light of a third color and, in the second viewing direction, visible light of a fourth color that differs from the third color.
10. The security element (80) according to at least one of claims 1 to 5 or 7, characterized in that the first optically active layer (82) reflects, in a first viewing direction, visible light of a first color and, in a second viewing direction, visible light of a second color that differs from the first color, preferably that the second optically active layer (84) reflects, in the first viewing direction, visible light of a third color that differs from the first color, and in the second viewing direction, light of a fourth color that differs from the third color.
11. The security element (80) according to at least one of claims 1 to 10, characterized in that the first and/or, if applicable, the third optically active layer is present in the form of characters and/ or patterns.
12. The security element (80) according to at least one of claims 1 to 11, characterized in that the second direction of circular polarization of the light that the second optically active layer (84) reflects, itself or in coaction with the first optically active layer (82), is opposite to the first direction of circular polarization.
13. The security element (80) according to at least one of claims 1 to 12, characterized in that the optically active layers (82, 84) are disposed at least in part on a dark, preferably black background (22).
14. A method for manufacturing a security element (80) according to at least one of claims 1 to 13, in which a first and a second optically active layer (82, 84) are applied to a substrate foil such that they are stacked in an overlap area (88), a cholesteric liquid crystal material being applied to form the first optically active layer (82), and wherein the second optically active layer (84) is formed as a phase-shifting layer, namely as a λ/2 layer for light from the first wavelength range and in the form of characters and/or patterns.
15. The method according to claim 14, characterized in that, following the application of all optically active layers, one or, if applicable, both substrate foils are removed, especially via separation layers or by using a laminating adhesive whose adhesion to the substrate foil is less than its adhesion to the optically active layer, or via an auxiliary layer, preferably an UV lacquer layer, that is applied contiguously to the optically active layer and whose adhesion to the substrate foil is less than its adhesion to the optically active layer.
16. A security arrangement for security papers, valuable articles and the like, having

    - a security element (162) according to at least one of claims 1 to 13, and

    - a separate display element (164) that, in coaction with the security element (162), makes a color shift effect and/or a polarization effect and/or a brightness effect perceptible for the viewer.
17. The security arrangement according to claim 16, characterized in that the security element (162) is formed according to at least one of claims 1 to 12 and the display element (164) comprises a dark, preferably black background, or that the security element (162) is formed according to at least one of claims 1 to 13 and the display element (164) comprises a linear or circular polarizer.
18. A valuable article, such as a branded article, value document or the like, having a security element (80) according to at least one of claims 1 to 13.
19. A valuable article, such as a branded article, value document or the like having a security arrangement (162) according to claims 16 or 17, wherein the valuable article is flexible such that the security element (162) and the display element (164) are layable on top of one another by bending or folding the valuable article for self-authentication.
20. A method for checking the authenticity of a security element according to one of claims 1 to 13, of a security arrangement according to one of claims 16 to 17 or of a valuable article according to one of claims 18 to 19, characterized in that it is checked whether a predefined color shift effect is present and/ or whether a predefined polarization effect and/ or a predefined brightness effect is present, and the authenticity of the checked element is assessed on the basis of the check result.

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