EP1836057B1 - Security element and method for producing the same - 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. The invention further relates to a method for producing such a security element and a valuable article, which is equipped with such a security element.

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.

There is a constant interest in protecting securities against falsification and unauthorized reproduction. Especially with regard to today's copying and printing techniques, it is becoming increasingly difficult to find effective security features that at least clearly identify an unauthorized reproduction or falsification, if not prevent it.

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 checked purely visually, for example by tilting the security element, and are thus readily observable even by laymen. Although the wavelength-selective reflectivity and the polarization effects of the material also allow a mechanical verification of such security elements. However, optically relatively complex test and detector arrangements are required.

From the WO 98/52077 A security element is known in which a linearly polarizing layer, a layer of a light-optical-oriented polymer network (PPN) and an anisotropic layer of a crosslinkable liquid-crystalline monomer are arranged on a transparent substrate. When irradiated with light of a suitable wavelength, the layer of liquid-crystalline monomer is crosslinked to give a liquid-crystalline polymer (LCP) with specification of the molecular orientation of this layer through the PPN layer. The LCP layer may be arranged as a phase-shifting layer on a cholesteric layer. In transmitted light, a pattern stored in the LCP layer becomes visible by means of an external polarizer.

In the EP 1120 737 A1 an optical security element is described in which at least one phase-shifting LCP layer is arranged on a substrate, which has areas of different and predetermined orientation. A reflective layer of cholesteric material is disposed between a substrate which may be light absorbing and the patterned phase-shifting LCP layer. The LCP layer has three levels of examination, each with the naked eye, by means of an optical inspection instrument and by means of an optical test instrument for decryption an encrypted object are recognizable.

From the US 2002/0022093 A1 For example, a multilayer reflective film is known that selectively reflects light, with reflective properties depending on the viewing angle. The film comprises a reflective layer, a circularly polarizing layer and optionally an optically phase-shifting layer.

It has long been known to provide security documents with security threads made of plastic, which have a magnetic coating and thus serve as a machine-readable security feature. For example, describes the EP 0 407 550 A1 a security document with a stored security thread provided with a binary code of magnetic material.

However, because such security elements do not provide a quick visual verification capability, as is necessary in many daily life situations, it has also been proposed to combine machine-readable security features with visual features. From the EP 0 516 790 A1 A security document with such a security element is already known. The security thread described here consists of a transparent plastic carrier layer with a metallic coating, in which recesses in the form of characters or patterns, the so-called "negative writing" are provided. These recesses and the metallic environment, if the thread is present in the pulp, hardly visible when viewed in incident light. When viewed in transmitted light, however, the translucent recesses contrast strongly from their opaque environment and are thus easily recognizable. At the same time, the security element has a magnetic coating which, for example, is provided below the metal layer in the edge regions of the thread and symmetrically to the recesses along the running direction of the element in the document.

Proceeding from this, the present invention seeks to propose a security element of the type mentioned above, which offers increased protection against counterfeiting and at the same time 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 production and a valuable article 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, the security element has, at least in regions, a first layer of cholesteric liquid-crystalline material and, at least in regions, a second layer of liquid-crystalline material. The security element also contains an at least partially present further layer with a machine-readable feature, which is at least partially covered by the first and second layer of liquid-crystalline material.

This security element has, in addition to novel, visually verifiable effects that exploit the properties of the combined liquid crystal layers, the advantage of machine testability. About the special mutual assignment on the security element while a relation to the individual security features increased counterfeit protection is guaranteed.

The security element has an opaque layer, which is provided at least in regions. In this transmission visible first recesses may be provided in the form of patterns and / or characters as a first information. In the context of the present Description means the term "opaque" non-translucent in the sense of a certain opacity, so that for example in the opaque layer present (translucent) recesses in contrast contrast in transmitted light, but also the effects of arranged on such a layer liquid crystal layers are well perceived.

In order to increase the visibility of the color and polarization effects of the layers of liquid-crystalline material described below, the opaque layer can furthermore be present as a dark, preferably black layer. For this purpose, this can be formed for example of black ink or a black-colored paint.

Advantageously, the opaque layer may itself be magnetically and / or electrically conductive and / or luminescent and thus provide the further layer with the machine-readable feature. Alternatively, the opaque layer may also be present as a separate layer.

In a preferred embodiment, a second information in the form of second recesses may be provided in the opaque layer, which differ in size from the first recesses. The recesses can, for example, together with the first and / or second layer of liquid-crystalline material provide additional information, in particular in the form of a new geometric shape.

In an advantageous variant of the invention, the circular polarization direction of the light, which reflects the second layer of liquid-crystalline material itself or in cooperation with the first layer of liquid-crystalline material, is opposite to the circular polarization direction of the light reflected by the first layer. This can be in one or more the liquid crystal layers encode information that can be read only by using circular or linear polarizers. If the second layer of cholesteric liquid-crystalline material is also formed, the intensity of the total reflected light can also be increased by using the two opposite circular polarization directions.

The second layer of liquid-crystalline material forms a phase-shifting layer according to a preferred embodiment. Preferably, the second layer for light forms substantially a λ / 2-layer from the wavelength range reflected from the first layer. In this case, the second 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.

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.

According to a further preferred variant of the invention, the wavelength range in which the second layer selectively reflects light differs from the wavelength range in which the first layer selectively reflects light. Here, the second layer is expediently formed from cholesteric liquid-crystalline material. For example, it can be provided that at least a layer of the first and second layers in a viewing direction reflects only light from the invisible portion of the spectrum. As discussed in detail below, the additive color mixing of the reflectance spectra of the two layers of cholesteric liquid crystalline material permits the generation of broader and more unusual color-shift effects. The light from the non-visible part of the spectrum can be, for example, infrared radiation or ultraviolet radiation.

In other embodiments, at least one further layer of cholesteric liquid-crystalline material may also be provided. Preferably, at least one of the layers of liquid crystal material is in the form of pigments 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. The pigment-based printing inks also need no alignment promoting measures. In addition, at least one of the layers of liquid crystalline material may advantageously be in the form of characters and / or patterns.

In all embodiments described, a separate first magnetic layer can furthermore be provided at least in regions. This is preferably covered by the opaque layer. For example, the first magnetic layer may be in the form of spaced-apart magnetic regions that form an encoding. The first and / or second recesses of the opaque layer are expediently arranged in the magnetic layer-free intermediate regions. The coding can furthermore extend only over a partial area of the security element. However, the first magnetic layer can also be present in the form of longitudinal strips running parallel to the thread direction.

According to a further preferred variant of the invention, a second magnetic layer is provided. This can also be arranged so that the visible in transmission recesses remain free. The second magnetic layer can, for example, connect the magnetic regions of the coding to one another.

In all embodiments described, a separate electrically conductive layer may also be provided at least in regions. Preferably, this is in the form of a layer which is formed from extending parallel to the thread direction, electrically conductive strip, or which is substantially transparent.

According to a preferred variant of the invention, additionally or alternatively, a separate metallic layer may be provided at least in regions. This can also have recesses. However, the separate metallic layer can also be present over the entire surface, in particular as a rastered metal layer or as a thin, full-surface semitransparent metal layer. In the context of the present description, the term "semitransparent" or "translucent" means translucent in the sense of a certain translucency, but, unlike transparent materials, objects located behind translucent materials are only diffuse or not recognizable at all. The semitransparent metal layer preferably has an opacity of 40% to 90%. The rastered metal layer can be in the form of a negative grid, in particular in the form of transparent, ie demetallized dots, as a positive grid, in particular in the form of metallic dots, or as a bar screen, in particular in the form of metallic diagonal stripes.

In all embodiments, the separate metallic layer of the opaque layer, in particular of the black-colored paint, at least partially covered. In addition to the black-colored lacquer, areas of a layer of a transparent lacquer can also be applied to the separate metallic layer. In addition, the separate metallic layer may additionally have magnetic properties.

Furthermore, in the embodiments described, at least one of the layers of the security element can contain at least one additional authenticity feature, for example in the form of luminescent substances, color pigments and effect pigments, which are incorporated into the corresponding layer. Alternatively or additionally, separate layers with a luminescent substance may also be provided.

In all described embodiments, it can be provided that the layers of the security element are arranged on an at least translucent plastic layer.

In an advantageous embodiment, the security element takes the form of a thread or strip at least partially embedded in a document material, such as e.g. Banknote paper, embedded or can be arranged on the surface. In a further advantageous embodiment, the security element forms 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 layer of cholesteric liquid-crystalline material and a second layer of liquid-crystalline material are applied to a carrier film, so that they can be deposited in an overlap region are arranged one above the other. The two liquid crystal layers can each be applied to a separate carrier film, in particular printed, and then laminated on top of each other. This makes it possible to check the liquid crystal layers after application to the carrier film separately for suitability for further processing and optionally discard. Alternatively, the two liquid crystal layers can also be applied successively on the same carrier film.

After the application of the first and second layers of liquid-crystalline material, these layers are applied to an at least partially present further layer with a machine-readable feature such that the further layer is at least partially covered by the first and second layers of liquid-crystalline material. The further layer with the machine-readable feature can, for example, be printed with an opaque layer before the first and second layers of liquid-crystalline material are applied.

The invention further comprises a valuable article, such as a branded article, a value document or the like, with a security element of the type described. The valuable article may, in particular, be a security paper, a value document or a product packaging.

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 safety devices. By contrast, "security paper" is understood to mean that the preliminary stage, which is not yet executable, is a value document. Security paper is usually in quasi-endless form and will be further processed at a later date.

Further embodiments and advantages of the invention will be explained below with reference to the figures, the representation has been dispensed to scale and proportionate reproduction 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 nach einem Ausführungsbeispiel der Erfindung im Querschnitt,

Fig. 4

in (a) den Querschnitt eines Sicherheitselements nach einem anderen Ausführungsbeispiel der Erfindung mit einem Zirku- larpolarisator zum Lesen der codierten Information, in (b) und (c) jeweils eine Ansicht dieses Sicherheitselements bei senkrech- ter Betrachtung mit einem Zirkularpolarisator, der nur rechts- bzw. linkszirkular polarisiertes Licht transmittiert,

Fig. 5

in (a) den Querschnitt eines Sicherheitselements nach einem anderen Ausführungsbeispiel der Erfindung mit einem Linear- polarisator zum Lesen der codierten Information, in (b) eine schematische Darstellung dieses Sicherheitselements bei senk- rechter Betrachtung, in (c) bis (f) jeweils Ansichten dieses Si- cherheitselements bei senkrechter Betrachtung mit einem je- weils um 90° gedrehten Linearpolarisator,

Fig. 6

in (a) eine schematische Darstellung der relativen Anordnung der Negativschrift und der Codierung eines Sicherheitsele- ments nach einem weiteren Ausführungsbeispiel der Erfindung in Aufsicht, in (b) den Querschnitt dieses Sicherheitselements, in (c), (d) jeweils eine Ansicht dieses Sicherheitselements bei senkrechter Betrachtung mit einem Zirkularpolarisator, der nur rechts- bzw. linkszirkular polarisiertes Licht transmittiert,

Fig. 7

ein Sicherheitselement nach einem noch weiteren Ausfüh- rungsbeispiel der Erfindung im Querschnitt,

Fig. 8

ein Sicherheitselement nach einem noch weiteren Ausfüh- rungsbeispiel in Aufsicht, bei dem sowohl die Farbeffekte als auch die Polarisationseffekte der Flüssigkristallschichten aus- genutzt werden, wobei das Sicherheitselement (a) auf einem hellen Untergrund bzw. in Durchsicht, (b) auf einem schwarzen Untergrund, (c) auf einem schwarzen Untergrund bei Betrach- tung mit einem Zirkularpolarisator und (d) auf einem hellen Untergrund bei Betrachtung mit einem Zirkularpolarisator ge- zeigt ist,

Fig. 9

ein Sicherheitselement nach noch einem weiteren Ausfüh- rungsbeispiel der Erfindung mit einem Zirkularpolarisator zum Lesen der codierten Information,

Fig. 10

ein Sicherheitselement nach noch einem weiteren Ausfüh- rungsbeispiel der Erfindung im Querschnitt,

Fig.11

in (a) den Querschnitt eines Sicherheitselements nach einem anderen Ausführungsbeispiel der Erfindung, in (b) eine Ansicht dieses Sicherheitselements bei senkrechter Betrachtung und in (c) eine Ansicht bei spitzwinkliger Betrachtung,

Fig. 12

eine Darstellung wie in Fig. 11 eines Sicherheitselements nach einem weiteren Ausführungsbeispiel der Erfindung,

Fig. 13

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

Fig. 14

ein Sicherheitselement nach dem Prinzip der Fig. 13 bei Be- leuchtung mit rechtszirkular polarisiertem Licht,

Fig. 15

ein weiteres Sicherheitselement nach dem Prinzip der Fig. 13 mit einer in zwei λ/4-Schichten unterteilten λ/2-Schicht,

Fig. 16

ein Sicherheitselement nach einem weiteren Ausführungsbei- spiel der Erfindung, 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.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 according to an embodiment of the invention in cross-section,

Fig. 4

in (a) the cross-section of a security element according to another embodiment of the invention with a circular polarizer for reading the coded information, in (b) and (c) respectively a view of this security element when viewed vertically with a circular polarizer, the right only - or left circularly transmitted polarized light,

Fig. 5

in (a) the cross section of a security element according to another embodiment of the invention with a linear polarizer for reading the encoded information, in (b) a schematic representation of this security element when viewed perpendicularly, in (c) to (f) respectively views this safety element when viewed vertically with a linear polariser rotated in each case by 90 °,

Fig. 6

in (a) a schematic representation of the relative arrangement of the negative writing and the coding of a security element according to a further embodiment of the invention in plan view, in (b) the cross section of this security element, in (c), (d) respectively a view of this security element when viewed perpendicularly with a circular polarizer which transmits only right- or left-circularly polarized light,

Fig. 7

a security element according to yet a further exemplary embodiment of the invention in cross-section,

Fig. 8

a security element according to yet another embodiment in plan view, in which both the color effects and the polarization effects of the liquid crystal layers are exploited, the security element (a) on a light background or in review, (b) on a black background (c) is shown on a black background when viewed with a circular polarizer and (d) on a light background when viewed with a circular polarizer,

Fig. 9

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

Fig. 10

a security element according to yet another embodiment of the invention in cross-section,

Figure 11

in (a) the cross-section of a security element according to another embodiment of the invention, in (b) a view of this security element when viewed vertically and in (c) a view at acute angle,

Fig. 12

a representation like in Fig. 11 a security element according to a further embodiment of the invention,

Fig. 13

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. 14

a security element according to the principle of Fig. 13 when illuminated with right circular polarized light,

Fig. 15

another security element according to the principle of Fig. 13 with a λ / 2 layer divided into two λ / 4 layers,

Fig. 16

a security element according to another embodiment of the invention, 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) show the situation when viewed through various circular polarizers.

The invention will now be explained in more detail using the example of a banknote. Fig. 1 shows a schematic representation of a banknote 1, the two security elements 2 and 6, respectively, which are each formed according to an embodiment of the invention. The first security element represents a security thread 2 which emerges in certain window areas 4 on the surface of the banknote 1 while it is embedded in the intervening areas inside the banknote 1. The second security element is formed by a glued-on transfer element 6 of any shape that has been prepared on a separate layer, for example a plastic film, in the reverse order as it comes to rest on the banknote 1.

The following examples are described with reference to a security element in the form of a thread. However, it is within the scope of the invention also possible to give the security element any other outline shape, and to form this as a transfer element.

Fig. 2 shows the basic layer structure of a security element 10 according to the invention in cross section. On a background layer 22 provided with a machine-readable feature, two layers 13, 14 of liquid-crystalline material are applied. As described in detail below, the liquid crystal layers 13, 14 may each have different but also partially the same light-polarizing or refractive properties.

According to the invention, at least the first liquid crystal layer 13 consists of a cholesteric liquid-crystalline material and selectively reflects light in a first wavelength range with a first circular polarization direction. The second liquid crystal layer 14, which is 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. The second liquid-crystal layer can likewise be formed from cholesteric liquid-crystalline material or else from nematic liquid-crystalline material and is present here only in regions in the form of a motif, for example a lettering, or a pattern.

The layer 22 provided with a machine-readable feature may be formed as an opaque layer which contains or is formed from electrically conductive, magnetic, luminescent substances or substances with other properties which can be checked by machine. In order to increase the recognizability of the color and polarization effects of the liquid crystal layers 13, 14 described below, the opaque layer can furthermore be present as a dark, preferably black layer.

In addition to the layers described above, further layers may be present, which have been omitted here for the sake of clarity. Thus, the above layer structure can be present on a film, for example a PET film of good surface quality. In addition, alignment or alignment layers and / or adhesive layers may be provided between the liquid crystal layers, the alignment of the liquid crystals in the liquid crystal layers or the connection of the individual liquid crystal layers and the compensation of unevenness serve the underground. Other layers, such as protective layers, release layers or other auxiliary layers may also be provided.

Fig. 3 shows a security element 20 according to an embodiment of the invention, in which on an opaque, preferably black layer 25, a first cholesteric liquid crystal layer 23 and on this a second liquid crystal layer 24 are arranged. The second liquid crystal layer 24 is only partially in the form of a motif, such as a lettering, or a pattern before. The opaque layer 25 is arranged in the exemplary embodiment on a fully machine-readable layer 26. This can be provided for example by a magnetic layer, an electrically conductive layer, in particular a metal layer.

To produce the security element 20, the first and second liquid crystal layers 23 and 24 can each be printed on a smooth PET film of good surface quality. Suitable printing methods are all printing processes suitable for liquid-crystalline layers, such as intaglio, flexographic printing, knifecoating, curtain or blade techniques.

After drying the liquid crystal layers 23, 24, the quality and the color spectrum of the individual layers can already be tested in this production stage and, if appropriate, rejected rejects. The liquid crystal layers 23 and 24 are then laminated to the opaque layer 25 and the first liquid crystal layer 23, respectively, using commercially available laminating adhesives. The smoothness of the surface influences the degree of gloss of the security element. The laminating adhesive may cause unevenness of the Underground, as they may occur in the construction of a typical security thread 2, are balanced, so that even for such security elements, a good gloss can be achieved.

After the adhesion of the liquid crystal layers 23 and 24, 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 full surface.

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 laminating the first liquid crystal layer 23 on the opaque layer 25, the second liquid crystal layer 24 is applied in an analogous manner to the laminated in the composite now above the first liquid crystal layer 23.

In the Fig. 3 As well as the embodiments described below, the liquid crystal layers can each be laminated on top of each other, printed on top of each other or applied in a different way, wherein optionally not shown alignment layers or adhesive layers between the layers can be provided.

The FIGS. 4 . 5 . 6 . 8th . 9 and FIGS. 13 to 16 show further exemplary embodiments of the invention in which, in addition to the color-shift effect, the particular light-polarizing properties of the liquid crystal layers are utilized above all. The polarization direction of the light is indicated in part 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 embodiment of Fig. 4 1 shows a security element 80 having a first cholesteric liquid crystal layer 82 and a λ / 2 layer 84 applied in regions on the liquid crystal layer 82 and containing nematic liquid-crystalline material ( Fig. 4 (a) ). 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 having a preselected circular polarization direction, for example, left circularly polarized light (L). In the overlapping area 88 of the two layers, the security element 80 reflects light with the opposite polarization direction, in the exemplary embodiment, right-circularly polarized light (R), since the incident unpolarized light is not affected by the λ / 2 layer 84, the polarization direction of the first liquid crystal layer 82 is reflected, however, by the path difference between the ordinary and the extraordinary beam in its polarization orientation just reversed, left circularly polarized light from the λ / 2 layer 84.

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 89 which transmits only right-circularly polarized light, then the motif formed in the λ / 2 layer 84 emerges with a clear contrast. As in Fig. 4 (b) 1, the image parts 88 covered by the λ / 2 layer 84 appear bright or colored, the uncovered image parts 86 dark or black. Any thickness differences in the λ / 2 layer are perceived only conditionally by the viewer. A reverse (negative) image impression results when using a circular polarizer, which transmits only left circularly polarized light ( Fig. 4 (c) ). The circular polarizer 89, for example, by a linear polarizer with downstream λ / 4-plate be formed. It is understood that both liquid crystal layers 82, 84 may also be present in the form of motifs.

The above effects can be observed when the nematic liquid crystalline material is achromatically dispersive, i. if the dispersion or the wavelength dependence of the refractive index over the selected wavelength range is negligible. In this case, the direction of rotation of the circular polarization in the nematic liquid crystal layer is reversed, the phase shift corresponding to λ / 2. If the nematic liquid-crystalline material is chromatically dispersive, then the phase shift in the nematic liquid-crystal layer is no longer exactly λ / 2 for each wavelength and elliptical polarization occurs. The nematic layer then appears dark gray rather than black.

To produce the security element 80, first of all a nematic liquid crystal layer 84 in the form of a motif can be printed on a smooth PET film of good surface quality in a layer thickness which is chosen such that a wavelength range in which the first liquid crystal layer 82 selectively reflects λ / 2 layer is obtained. For example, the liquid crystal layer is applied at a coating weight of about 2 g / m ² . After physical drying to remove the solvent, the liquid crystal layer is crosslinked by means of ultraviolet radiation. Subsequently, a layer 82 of cholesteric liquid-crystalline material is printed over the entire surface of the PET film partially coated with nematic liquid-crystalline material, for example likewise in a coating weight of approximately 2 g / m ² . It is understood that the required coating quantities depend in particular on the paints used. This layer is also crosslinked after physical drying by means of ultraviolet radiation.

The two-layered liquid-crystal structure produced in this way is then laminated by means of commercially available laminating adhesives via the cholesteric liquid-crystal layer 82 now lying on top to an opaque, preferably black layer 22, which is additionally electrically conductive in this exemplary embodiment. Such an electrically conductive black background can be provided, for example, by a lacquer layer colored with carbon black pigments. Alternatively, the opaque layer 22 may also be formed by a black ink provided with magnetic pigments. 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, the cholesteric liquid crystal layer 82 imprinted 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 peeled off, which can occur, in particular, when non-full-surface layers are transferred.

Another embodiment of the invention is in Fig. 5 shown schematically. In the security element 90, a first liquid crystal layer 92 of cholesteric liquid-crystalline material is applied to an opaque, preferably black layer 22, and a second liquid crystal layer 94 of nematic liquid-crystalline material in the form of a motif is applied thereon. The layer thickness of the second nematic liquid crystal layer 94 is chosen such that it forms approximately a λ / 2 layer. The opaque layer 22 in this embodiment contains a material made of a magnetic material, for example in the form of magnetic pigments or magnetic iron. A section along A - A through this security element is in Fig. 5 (b) shown.

This in Fig. 5 (a) shown, formed by the λ / 2 layer 94 motif, which is composed of the λ / 2-layer covered image portions 98 and uncovered image portions 96 is barely recognizable without aids, since the security element 90 in the covered as the uncovered areas reflects substantially the same amount of light and the unaided eye can not distinguish the circular polarization direction of the light.

If one now considers the security element 90 through a linear polarizer 91, further effects can be observed, the effect of which is caused by the main optical axis 95 of the nematic liquid-crystalline material. The exact layer thickness of the nematic liquid crystal layer 94 plays a rather minor role in this additional effect. When the linear polarizer 91 is rotated to a position where the major optical axis 93 of the linear polarizer 91 is collinear with the main optical axis 95 of the nematic liquid crystalline material ( Fig. 5 (c), (e) ), the image part 98 covered by the nematic liquid crystal layer or the motif formed therewith is barely perceptible. On the other hand, the main axes 93 and 95 are rotated by 90 ° ( Fig. 5 (d), (f) ), the image part 98 covered by the nematic liquid crystal layer 94 appears black.

The circularly polarized light reflected by the cholesteric liquid crystal layer 92 constitutes a linear combination of linearly polarized light. With the aid of the linear polarizer 91, it is therefore possible to incorporate into the in Fig. 5 (c), (e) situations that recognize a portion of the circularly polarized light, in the in Fig. 5 (d), (f) ) situations illustrated the other. The background formed by the uncovered image parts 96 therefore appears gray to the viewer essentially independently of the position of the linear polarizer.

Fig. 6 shows in principle the external appearance of a security element 160 shown in the form of a thread according to a further embodiment of the invention. For better clarity, in Fig. 6 (a) only the (hidden) coding 165 and the recesses 163, 164 shown in their relative position to each other on the security element 160.

The coding 165 extends over the entire width of the thread. It is composed of regions 161 provided with magnetic material and magnetic layer-free regions 162. In a particular embodiment, the encoding 165 consists of equal-sized bit cells, either filled with magnetic material (e.g., binary "1") or not (e.g., binary "0"). According to the invention, the magnetic-layer-free regions 162 of the coding 165 are used in order to arrange the transmittable recesses 163, 164 here. In this way, the negative writing formed by the recesses 163, 164 and the coding 165 can be jointly provided on a thread without interfering with each other. The recesses 163 can therefore be arranged in the middle of the thread and produced in the usual size, as is the case with threads which have only one negative writing. In addition, apart from the color-tilting or polarization effects produced by liquid-crystal layers 172, 174, explained below in detail, the thread has the same external appearance as a conventional negative-writing security thread. Nothing indicates from the outside that a magnetic coding is arranged on the thread at the same time.

An increased protection against counterfeiting is achieved when the recesses 164 are executed as micro-characters, ie have a much smaller size than the recesses 163, since the micro-characters can not be imitated or only with great effort. For example, you can the recesses 163 have a size of more than 1 mm and the recesses 164 have a size of less than 1 mm.

If the security element 160 is viewed through a circular polarizer (not shown here) which transmits only right-circularly polarized light, then the motif formed in the nematic liquid-crystal layer 174 formed as a λ / 2 layer emerges with a clear contrast. As in Fig. 6 (c) 1, the image parts 168 covered by the λ / 2 layer 174 appear light or colored, whereas the uncovered image parts 166 appear dark or black. When using a circular polarizer, which transmits only left circularly polarized light, there is a reverse (negative) image impression ( Fig. 6 (d) ). Without tools, the motif formed by the λ / 2 layer 174 is hardly recognizable.

A section along B - B through this thread is in Fig. 6 (b) shown schematically. The magnetic coding 165, which is formed by the regions 161 provided with magnetic material and the magnetic layer-free regions 162 and is completely covered by an opaque, preferably black layer 175, is present in the exemplary embodiment on a rastered metal layer 176, which in turn is arranged on an at least translucent plastic layer 170, for example a PET film. The rasterized metal layer 176 incorporated in the Fig. 6 (a), (c), (d) is indicated in the recesses 163, 164, in the exemplary embodiment, a dashed line 167 on. This creates a certain semitransparency of the metal layer 176, whereby the recesses 163,164 are also visible in transmitted light. An analogous effect can be achieved by using a very thin, continuous metal layer.

For the production of in Fig. 6 The plastic material 170 is provided in a first step with a metal layer 176, which is produced by rastered application of an opaque metal layer in the form of a grid. Alternatively, a very thin, continuous metal layer can also be vapor-deposited. The magnetic layer 165 is applied to the metal layer 176 in the regions 161, which is subsequently covered with an opaque, preferably black ink, at the same time producing the negative characters formed by the recesses 163, 164. Finally, in a final step, the liquid crystal layers 172, 174 are provided above this layer structure. Due to the semitransparency of the metal layer, recesses 163, 164 remain transparent in transmitted light.

It is understood that the security element according to other embodiments may have additional magnetic layers. In particular, the security element according to the invention can also be combined with magnetic encodings in a particularly advantageous manner, as is known from US Pat WO 98/25236 A1 are known.

The embodiment of Fig. 7 shows a security element according to the invention 180 with a first cholesteric liquid crystal layer 182 and a second liquid crystal layer 184, which, as described in detail below, also from cholesteric material or from nematic liquid-crystalline material is formed. The security element 180 further comprises a metal layer 185 which is applied to an at least translucent plastic layer 181 and which is printed with an opaque, preferably black layer 186. In the exemplary embodiment, the opaque layer 186 is formed by a protective lacquer containing black pigments. The black pigments may also be provided by carbon black pigments. A such protective lacquer then additionally has a certain electrical conductivity and is accordingly machine-readable. In order to obtain a magnetizable opaque layer 186, the resist may also be provided with magnetic pigments. On the metal layer 185, a layer 188 of a transparent protective lacquer is further provided.

To produce the recesses 183, which are in the form of patterns and / or characters, in particular in the form of negative writing, the metal layer 185 printed with the black and the transparent protective lacquer layer 186 or 188 is partially demetallised by means of one of the known methods, for example using an etchant. The areas not provided with the protective lacquer layers 186, 188 are thereby removed. The liquid-crystal layers are then applied to this layer structure as described above, wherein optionally not shown alignment layers or adhesive layers can be provided between the layers.

If the security element 180 is viewed from the side of the liquid crystal layers 182, 184, the metal layer 185 is only perceptible in the areas provided with the transparent protective lacquer layer 188. In contrast, in the areas in which the black-colored protective lacquer layer 186 is present, the security element has the color-shift effects described here, which clearly appear due to the dark background. When viewed from the side of the translucent plastic layer 181, the opaque metal layer 185 can be seen both in the areas with the transparent protective lacquer layer 188 and in the areas with the blackened protective lacquer layer 186.

In a further exemplary embodiment of the invention, the security element is configured in such a way that the recesses in the opaque layer together with the liquid crystal layers form additional information, for example a new geometric shape, whereby both the color effects and the polarization effects of the liquid crystal layers are utilized. The principle of this embodiment will now be described with reference to FIGS FIGS. 8 (a) to (d) which illustrate a security element 190 according to the invention in various situations.

The security element 190 has a layer structure whose layer sequence is substantially the same as in FIG Fig. 3 corresponds to the layer sequence shown. In the exemplary embodiment, however, the metal layer 191 is designed as a thin, semitransparent or rastered metal layer which is present over the whole area. On the metal layer 191 is an in Fig. 8 not shown opaque, preferably black layer disposed on which a cholesteric liquid crystal layer 192 is present in overlap. The liquid crystal layer 192 clearly appears in the shape of a triangle 194 only in the areas where it overlaps with the opaque layer. The image parts 196 covered by the λ / 2 layer of nematic liquid crystal material are indicated by a dotted line in FIG Fig. 8 (a) merely indicated and can hardly be recognized without aids, since the security element in the covered as well as the uncovered areas reflects substantially the same amount of light.

If the security element 190 is arranged on a black base 198 ( Fig. 8 (b) ), the star pattern formed by the cholesteric liquid crystal layer 192 appears substantially completely. Considering now the security element 190 by a circular polarizer 199, the only light of a circular polarization, for example left circular polarized light, transmitted, so the formed in the formed as a λ / 2-layer nematic liquid crystal layer motif emerges clearly in the form of a hexagon. As in Fig. 8 (c) In this case, the image parts 196 covered by the λ / 2 layer appear dark or black, whereas the uncovered image parts appear light or colored. A reverse (negative) image impression results when using a circular polarizer, which transmits only right circularly polarized light. In the Fig. 8 (d) illustrated situation corresponds to in Fig. 8 (c) shown except for the fact that the security element 190 is present here on a light surface. The liquid crystal layer 192 therefore clearly appears only in the areas overlapping with the opaque layer.

The FIGS. 9 to 16 schematically show further embodiments of the invention, in which specifically the special properties of the liquid crystal layers are used.

The security element 60 of Fig. 9 contains two cholesteric liquid crystal layers 62 and 64, which are applied in the embodiment on an opaque, preferably black layer 22 provided with a machine-readable feature. Of course, other layers can be provided in the layer structure. 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 embodiment reflects left circularly polarized light, the second liquid crystal layer 64 reflects right circularly polarized light. In contrast, left circularly polarized light is transmitted by the second liquid crystal layer 64 without substantial absorption. It is understood that the polarization directions given serve only for illustration and, of course, can be chosen differently within the scope of the invention.

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 above-described embodiments, 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 embodiment of the Fig. 9 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.

If the security element 60 is now viewed through a circular polarizer 72, which transmits only left circularly polarized light, then the motif formed by the first liquid crystal layer 62 occurs with strong brightness contrast because the circular polarizer 72 completely fades out the right circularly polarized light reflected by the second liquid crystal layer 64. As described above, such a circular polarizer 72 may 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.

Fig. 10 shows a security element 30 according to an embodiment of the invention, in which on an provided with a machine-readable feature opaque, preferably black 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-changing game in which the color impression of the security element when tilting from short-wave to longer-wave light is due to the fact that the first liquid crystal layer 32 reflects blue light (arrow 321) in the vertical viewing direction and shorter-wave UV radiation (arrow 322) in the acute-angled viewing direction. 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 reflection components 321 and 342 lying outside the visible spectral range 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.

Another embodiment of the invention is in Fig. 11 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 opaque, preferably black layer 22 provided with a machine-readable feature. As in Fig. 11 (b) 1, the first liquid crystal layer 42 is only applied in regions to the opaque layer 22 and forms a motif by the shape or 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 FIG applied to the exposed areas on the opaque layer 22.

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. 11 (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. 11 (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 mixing 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 overlapping area only the 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. 12 shown. For this purpose, a partially applied cholesteric liquid crystal layer 52 is so formed so that it shows a color shift effect of infrared (arrow 521) to red (arrow 522) when tilting. A second cholesteric liquid crystal layer 54 again exhibits 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.

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. 13 explained.

The security element 100 has a layer sequence applied to an opaque, preferably black layer 22 provided with a machine-readable feature, which comprises a first cholesteric liquid crystal layer 102, a λ / 2 layer 104 of nematic liquid-crystalline material 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, so that the two layers taken by themselves have light in the same preselected wavelength range and with reflect the same preselected circular polarization direction. All layers can be applied over the entire surface 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 Fig. 13 illustrated. It is assumed that the two cholesteric liquid crystal layers 102 and 106 reflect left-circularly polarized light and the illumination of the security element takes place 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. 4 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. 13 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 circular polarized Light is also transmitted by the lower liquid crystal layer 102 and absorbed in the black 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. 14 includes, as the above-described security element 100 of Fig. 13 a layer sequence comprising a first cholesteric liquid crystal layer 102, a λ / 2 layer 104 of nematic liquid crystal material and a second cholesteric liquid crystal layer 106 applied to an opaque, preferably black layer 22 provided with a machine-readable feature. In this embodiment, only the λ / 2-layer 104 formed 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 is in the areas 126 in which all three Layers overlap, is reflected, while in areas 128 without λ / 2-layer 104 from the upper and lower liquid crystal layers 106 and 102, respectively, and absorbed in the black layer 22.

Fig. 15 shows a security element 130 according to a further embodiment of the invention, with respect to its layer sequence substantially as the security element 120 of Fig. 14 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. 14 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. 14 - Transmitted from the layer sequence and finally absorbed by the black 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 reflect from the layer sequence becomes. The size of the reflected portion decreases with increasing rotation angle continuously off. By a different angle of rotation θ in different surface areas of the intermediate layer 132, for example, halftone motifs can be encoded in the security element, which barely appear when illuminated with unpolarized light, but appear in the case of illumination with circularly polarized light as greyscale images for the viewer without further aids ,

It is understood that in an analogous manner, even in layer sequences which do not have a second cholesteric liquid crystal layer, as for example in the exemplary embodiment of FIG Fig. 4 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.

Fig. 16 shows an embodiment in which both the color effects and the polarization effects of the liquid crystal layers are utilized. Fig. 16 (a) FIG. 5 shows the construction of a security element 150 having an opaque, preferably black, layer 22, a first cholesteric liquid crystal layer 152 and a second cholesteric liquid crystal layer 154 applied thereto, provided with a machine-readable feature.

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 illuminated with unpolarized Considered light and without auxiliary means, 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. 16 (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. 16 (c) shown. It is understood that each of the liquid crystal layers 152, 154 may also be replaced by a combination of a λ / 2 layer with a cholesteric layer mirroring the original layer.

Of course, in the embodiments in which the color-shift effects and the particular light-polarizing properties of the liquid crystal layers are utilized, instead of an opaque, preferably black layer 22 provided with a machine-readable feature, one of them can also be used Figures 3 . 6 or 7 described layer sequences are provided.

Claims (43)

1. A security element (10, 160) for securing valuable articles, comprising

   - a first layer (13, 172), composed of cholesteric liquid crystal material, that is present at least in some areas,

   - a second layer (14, 174), composed of liquid crystal material, that is present at least in some areas and forming a phase-shifting layer, and

   - a further layer (22, 161), having a machine-readable feature, that is present at least in some areas and that is covered at least in some areas by the first (13, 172) and second (14, 174) layer composed of liquid crystal material, and

   - an opaque layer (22, 175) that is provided at least in some areas, forming a dark background for the first (13, 172) and/or second layer (14, 174) composed of liquid crystal material.
2. The security element according to claim 1, characterized in that, in the opaque layer (175), first gaps (163) in the form of patterns and/or characters that are perceptible in transmission are provided as a first piece of information.
3. The security element according claim 1 or 2, characterized in that the opaque layer (22, 175) is formed from black printing ink or a black-colored lacquer.
4. The security element according to at least one of claims 1 to 3, characterized in that the opaque layer (22,175) is magnetically and/or electrically conductive and/or luminescent.
5. The security element according to at least one of claims 1 to 4, characterized in that the opaque layer (22) forms the further layer having the machine-readable feature.
6. The security element according to at least one of claims 1 to 4, characterized in that the opaque layer (175) is present as a separate layer.
7. The security element according to at least one of claims 2 to 6, characterized in that a second piece of information is provided in the form of second gaps (164) in the opaque layer (175) that differ in size from the first gaps (163).
8. The security element according to at least one of claims 2 to 7, characterized in that the first (163) and/or second (164) gaps in the opaque layer (175) constitute, together with the first (172) and/or second (174) layer composed of liquid crystal material, an additional piece of information.
9. The security element according to at least one of claims 1 to 8, characterized in that the circular polarization direction of the light that the second layer (84) composed of liquid crystal material reflects, in coaction with the first layer (82) composed of liquid crystal material, is opposite to the circular polarization direction of the light reflected by the first layer (82).
10. The security element according to at least one of claims 1 to 9, characterized in that the second layer (84) for light from the wavelength range reflected by the first layer (82) substantially forms a λ/2-layer.
11. The security element according to at least one of claims 1 to 10, characterized in that the second layer (84) is formed from nematic liquid crystal material.
12. The security element according to at least one of claims 1 to 11, characterized in that the security element exhibits at least one further layer composed of cholesteric liquid crystal material (82).
13. The security element according to at least one of claims 1 to 12, characterized in that at least one (84) of the layers (82, 84) composed of liquid crystal material is present in the form of characters and/or patterns.
14. The security element according to at least one of claims 1 to 13, characterized in that at least one of the layers (13, 14) composed of liquid crystal material is present in the form of pigments that are embedded in a binder matrix.
15. The security element according to at least one of claims 1 to 14, characterized in that a separate first magnetic layer (26, 161) is provided at least in some areas.
16. The security element according to claim 15, characterized in that the separate first magnetic layer (26, 161) is covered by the opaque layer (25, 175).
17. The security element according to claim 15 or 16, characterized in that the separate first magnetic layer (161) is present in the form of spaced apart magnetic areas that form a code.
18. The security element according to at least one of claims 15 to 17, characterized in that the first (163) and/or second (164) gaps are disposed in the magnetic-layer-free in-between areas.
19. The security element according to at least one of claims 15 to 18, characterized in that the code extends only across a sub-area of the security element.
20. The security element according to at least one of claims 15 to 19, characterized in that the separate first magnetic layer (161) is present in the form of horizontal stripes that run parallel to the thread direction.
21. The security element according to at least one of claims 1 to 20, characterized in that a second magnetic layer (175) is provided.
22. The security element according to claim 21, characterized in that the second magnetic layer (175) joins the magnetic areas of the code formed by the separate first magnetic layer (161).
23. The security element according to at least one of claims 1 to 22, characterized in that a separate electrically conductive layer (26, 176, 185) is provided at least in some areas.
24. The security element according to claim 23, characterized in that the separate electrically conductive layer (26, 176, 185) is present in the form of a layer that is formed from electrically conductive stripes that run parallel to the thread direction, or that is substantially transparent.
25. The security element according to at least one of claims 1 to 24, characterized in that a separate metallic layer (26, 176, 185) is provided at least in some areas.
26. The security element according to claim 25, characterized in that the separate metallic layer (185) exhibits gaps (183).
27. The security element according to claim 25 or 26, characterized in that the separate metallic layer (176, 185) is a screened metal layer or a thin, contiguous semitransparent metal layer.
28. The security element according to claim 27, characterized in that the screened metal layer (185) exhibits a negative screen, especially in the form of transparent dots, a positive screen, especially in the form of metallic dots, or a line grating, especially in the form of metallic diagonal stripes.
29. The security element according to claim 27, characterized in that the semitransparent metallic layer (176) exhibits an opacity of 40% to 90%.
30. The security element according to at least one of claims 25 to 29, characterized in that the separate metallic layer (26, 176, 185) is covered at least in some areas by the opaque layer (25, 161, 186).
31. The security element according to at least one of claims 25 to 30, characterized in that the separate metallic layer (185) is covered at least in some areas by the black-colored lacquer (186).
32. The security element according to claim 31, characterized in that, in addition to the black-colored lacquer (186), also areas (188) of a layer composed of a transparent lacquer are applied on the separate metallic layer (185).
33. The security element according to at least one of claims 25 to 32, characterized in that the separate metallic layer (26, 176, 185) exhibits magnetic properties.
34. The security element according to at least one of claims 1 to 33, characterized in that at least one of the layers (13, 23, 14, 24, 22, 25, 26) of the security element includes at least one additional authenticating feature.
35. The security element according to claim 34, characterized in that the additional authenticating feature is selected from the group consisting of luminescent substances, color pigments and effect pigments.
36. The security element according to at least one of claims 1 to 35, characterized in that a separate layer having a luminescent substance is provided that is present in some areas.
37. The security element according to claim 35 or 36, characterized in that the luminescent substance emits in the visible wavelength range after excitation with an excitation radiation that lies outside of the visible spectral range.
38. The security element according to at least one of claims 1 to 37, characterized in that the layers of the security element are disposed on a translucent plastic layer (170) or plastic foil.
39. The security element according to at least one of claims 1 to 38, characterized in that the security element exhibits the form of a stripe.
40. A method for manufacturing a security element according to at least one of claims 1 to 39, in which, on a substrate foil, a first layer (13, 172) composed of cholesteric liquid crystal material and a second layer (14, 174) composed of liquid crystal material and forming a phase-shifting layer are applied such that they are stacked in an overlap area, the first (13, 172) and second (14, 174) layer composed of liquid crystal material being applied in such a way to a further layer (22, 161) that is present at least in some areas and having a machine-readable feature, that the further layer (22, 161) is covered at least in some areas by the first (13, 172) and second (14, 174) layer composed of liquid crystal material, wherein an opaque layer (22, 175) that is provided at least in some areas is provided, which forms a dark background for the first (13,172) and/or second (14, 174) layer composed of liquid crystal material.
41. The method according to claim 40, characterized in that, on the further layer (161) having the machine-readable feature, an opaque layer (175) is applied before application of the first (172) and second (174) layer composed of liquid crystal material.
42. A valuable article, such as a branded article, value document or the like, having a security element according to at least one of claims 1 to 39.
43. The valuable article according to claim 42, characterized in that the valuable article is a security paper, a value document or a product packaging.

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