EP2303594A1

EP2303594A1 - Security element

Info

Publication number: EP2303594A1
Application number: EP09768928A
Authority: EP
Inventors: Winfried HOFFMÜLLER; Marius Dichtl; Manfred Heim; Mario Keller
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient GmbH
Priority date: 2008-06-23
Filing date: 2009-06-16
Publication date: 2011-04-06
Anticipated expiration: 2029-06-16
Also published as: WO2009156079A1; EP2303594B1; US9399366B2; ATE539898T1; US20110109078A1; DE102008029638A1

Abstract

The present invention relates to a security element for security papers, value documents and the like, having a micro-optical moiré magnification arrangement having a first motif image that consists of a planar periodic or at least locally periodic arrangement of a plurality of first micromotif elements (38) that produce a hidden piece of image information, and a planar periodic or at least locally periodic arrangement of a plurality of microfocusing elements (34) for the moiré-magnified viewing of the first micromotif elements of the motif image, the first micromotif elements (38) being formed from nematic liquid crystal material and forming a phase-shifting layer for light from a specified wavelength range, and the magnified moiré image being perceptible substantially only upon viewing the security element through a polarizer.

Description

security element

The invention relates to a security element for security papers, security documents and the like, and more particularly relates to such a security element with a micro-optical moire magnification arrangement. The invention further relates to a method for producing such a security element, a security paper and a data carrier with such a security element.

Data carriers, such as valuables or identity documents, but also other valuables, such as branded goods, are often provided with security elements for the purpose of security, which permit verification of the authenticity of the data carrier and at the same time serve as protection against unauthorized reproduction. The security elements can be embodied, for example, in the form of a security thread embedded in a banknote, a covering film for a banknote with a hole, an applied security strip or a self-supporting transfer element which is applied to a value document after its manufacture.

Security elements with optically variable elements, which give the viewer a different image impression under different viewing angles, play a special role, since they can not be reproduced even with high-quality color copying machines. For this purpose, the security elements can be equipped with security features in the form of diffraction-optically active microstructures or nanostructures, such as with conventional embossed holograms or other hologram-like diffraction structures, as described, for example, in the publications EP 0330 733 A1 or EP 0 064 067 A1.

BESTATIGUNGSKOPIE It is also known to use lens systems as security features. Thus, for example, EP 0 238 043 A2 describes a security thread made of a transparent material, on the surface of which a grid of several parallel cylindrical lenses is embossed. The thickness of the security thread is chosen so that it corresponds approximately to the focal length of the cylindrical lenses. On the opposite surface of a printed image is applied register accurate, the print image is designed taking into account the optical properties of the cylindrical lenses. Due to the focusing effect of the cylindrical lenses and the position of the printed image in the focal plane different subregions of the printed image are visible depending on the viewing angle. By appropriate design of the printed image so that information can be introduced, which are visible only at certain angles. Although a certain embodiment of the printed image also makes it possible to produce "moving" images, the motif moves only approximately continuously from one location on the security thread to another location when the document is rotated about an axis parallel to the cylindrical lenses.

For some time, micro-optical structures, such as blazed lattice structures, microlens structures, fresnel lens-like structures or so-called Moire magnification arrangements are used as security features. The principal operation of such moiré magnification arrangements is described in the article "The Moire Magnifier", MC Hutley, R. Hunt, RF Stevens and P. Savander, Pure Appl. Opt. 3 (1994), pp. 133-142 After that, moiré magnification refers to a phenomenon that occurs when viewing a raster of identical image objects through a lenticular of approximately the same pitch In this case appears as an enlarged and possibly rotated image of the repeated elements of the image grid.

The production of the Bildobjektraster takes place in the known Moire- larger-scale arrangements with classical printing techniques or by means of embossing techniques with various processing steps. Both printing and suitable embossing techniques, however, are now generally available on the market, so that moire magnification arrangements of counterfeiters can be mimicked relatively easily.

Based on this, the object of the invention is to avoid the disadvantages of the prior art and, in particular, to specify a security element with a micro-optical moire magnification arrangement of high counterfeit security.

This object is achieved by the security element having the features of the main claim. A method for producing such a security element, a security paper and a data carrier with such a security element are specified in the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, a generic security element includes a micro-optical moiré magnification arrangement

a first motif image consisting of a planar periodic or at least locally periodic arrangement of a plurality of first micromotif elements generating hidden image information, and a planar periodic or at least locally periodic arrangement of a plurality of microfocusing elements for moire-magnified viewing of the first micromotif elements of the first motif image,

wherein the first micromotif elements are formed of nematic liquid-crystalline material and form a phase-shifting layer for light of a predetermined wavelength range, and the magnified moiré image is substantially detectable only by viewing the security element through a polarizer.

The chosen formulation, according to which the magnified moiré image can be recognized essentially only when the security element is viewed through a polarizer, takes account of the fact that the motif image emerges only when using a polarizer with a clear contrast, but barely up to the unaided eye not recognizable at all. The typical visual appearance of the Moire magnification arrangement can therefore only be observed with the aid of additional aids and thus forms a hidden security feature integrated in the security element.

In an advantageous variant of the invention, the first micromotif elements are formed by a partially different layer thickness of the nematic liquid-crystalline material. For example, the degree of phase rotation can be proportional to the layer thickness, so that the influence of the polarized light on the layer thickness can be adjusted in a targeted manner. The nematic liquid-crystalline material may also be present only in regions and in the form of the first micromotif elements. This configuration presents itself as an extreme case of the embodiment just mentioned, if the recessed areas of the nematic liquid-crystalline material are regarded as a layer with a layer thickness of zero.

In a preferred embodiment of the invention, the first micromotif elements for light from the predetermined wavelength range form a λ / 4 layer at least in partial regions. Advantageously, the security element contains a metallic reflector, in particular in this embodiment. The metallic reflector can be formed for example by a layer of aluminum, copper, silver, chromium or a metal pigment layer.

In another, likewise preferred embodiment of the invention, the first micromotif elements for light from the predetermined wavelength range form a λ / 2 layer at least in partial regions. The security element contains, in particular in this embodiment, advantageously a linear polarizer. Alternatively or additionally, one or more layers of cholesteric liquid crystalline material may be provided.

In all embodiments, the nematic liquid-crystalline material may be added with another nematic liquid-crystalline material which additionally has a fluorescence functionality. Alternatively, the nematic liquid crystalline material may itself be provided with these properties. Such a liquid-crystalline material exhibits a defined fluorescence upon irradiation with light of suitable wavelength and polarization, which is also polarized. To further increase the security against counterfeiting, the first micromotif elements generating the hidden image information can be combined with at least one further motif image which consists of a planar periodic or at least locally periodic arrangement of a plurality of second micromotif elements which generate visible image information. The enlarged Moire image of these second micromotif elements can already be seen without the use of auxiliary means when viewed with the naked eye. Accordingly, the security element shows a different appearance when viewed with white light / without aids and when viewed through a polarizer. As explained in detail below, such a configuration can also be used to generate further, completely novel optical effects. In particular, the first and second micromotif elements can also form moire images that are meaningful.

In a preferred embodiment of the invention, the arrangement of first micromotif elements, the arrangement of microfocusing elements and optionally the arrangement of second micromotif elements at least locally each form a two-dimensional Bravais lattice, the arrangement of first micromotif elements and / or the arrangement of microfocusing elements and / or the arrangement of second micromotif elements preferably form a Bravais grating with the symmetry of a parallelogram grating.

In an advantageous variant of the invention, the arrangement of the first

Micromotiv elements and the arrangement of second micromotif elements in their grating periods and lattice orientations identical, each lattice site of the arrangement of first micromotif elements with a first micromotif element and / or a second micromotif element is occupied.

Preferably, the first and the second micromotif elements are arranged alternately. Each lattice site is therefore occupied by a first micromotif element or a second micromotif element. According to an alternative embodiment, each lattice site may also be occupied by a first micromotif element and a second micromotif element, wherein the first and second micromotif elements are at least partially adjacent to one another.

In a likewise advantageous variant of the invention, the arrangement of first micromotif elements and the arrangement of second micromotif elements differ in their grating periods and / or grating orientations.

According to a preferred development of the invention, the arrangement of first micromotif elements and the arrangement of second micromotif elements are arranged in different layers and can be present, for example, separated from one another by additional layers. In addition to the arrangement in multilayer configurations, however, the first and second micromotif elements can also be arranged in the same layer.

The lateral dimensions of the first and optionally the second micromotif elements and the microfocusing elements are preferably below about 100 μm, preferably between about 5 μm and about 50 μm, particularly preferably between about 10 μm and about 35 μm. The first and / or the second micromotif elements are preferably used with a line thickness between about 1 μm and about 10 μm, preferably between about 1 μm and about 5 μm and / or with a structure thickness between about between about 1 μm and about 10 μm, preferably between formed about 1 micron and about 5 microns. Of course, the micromotif elements can also contain areal areas and can have both positive elements and negative elements.

In all embodiments, the first and / or optionally the second micromotif elements are advantageously present in the form of micro-characters or micro-patterns. It will be understood that the micromotif elements must be substantially identical to produce the moiré magnification effect. However, a slow, in particular periodically modulated change in the appearance of the micromotif elements and thus also of the enlarged images is likewise within the scope of the invention. Also, individual or a part of the micromotif elements can be equipped with additional information that does not appear in the enlarged moiré image, but which can be used as an additional authenticity indicator.

In order to protect them from counterfeiting attacks, or to facilitate the further processing, for example the generation of negative writing in applied metallic or ink-tipping layers, the first and / or the second micromotif elements can be provided with an optically substantially isotropic overcoat.

The motif images and the arrangement of microfocusing elements are expedient on opposite surfaces of an optical distance sensor. layer arranged. The spacer layer may comprise, for example, a plastic film and / or a lacquer layer.

The microfocusing elements of the moire magnification arrangement can be present as transmissive, refractive or diffractive lenses or as a mixed form. Preferably, they are formed by non-cylindrical microlenses, in particular by microlenses with a circular or polygonal limited base surface. Advantageously, the microlenses of the arrangement of microfocusing elements are formed by spherical or aspherical lenses.

One or more optically substantially isotropic adhesive layers and / or one or more optically substantially isotropic adhesion promoter layers are advantageously provided in the security element.

The security element can moreover be equipped with one or more functional layers, in particular with layers with visually and / or machine-detectable security features. In this case, for example, all-surface or partial reflective, high-refractive or color-shifting layers in question, or even polarizing or phase-shifting layers, opaque or transparent conductive layers, soft or hard magnetic layers or fluorescent or phosphorescent layers.

The invention also includes a method for producing a security element with a microoptical moire magnification arrangement, in which a first motif image which consists of a planar periodic or at least locally periodic arrangement of a plurality of first micromotif elements forming hidden image information, and a plastically Nare periodic or at least locally periodic arrangement of a plurality of Mikrofokussierelementen be arranged so that the first micromotif elements are magnified when viewed through the Mikrofokussierelemente recognizable. The first micromotif elements are formed from nematic liquid-crystalline material such that they form a phase-shifting layer for light from a predetermined wavelength range.

In an advantageous variant of the invention, the first micromotiv elements are formed by a layer thickness of the nematic liquid-crystalline material that is different in certain areas. The first micromotif elements are expediently embossed into a layer of nematic liquid-crystalline material which is applied to a carrier foil.

The nematic liquid-crystalline material can also be formed only area wise and in the form of the first micromotif elements.

In a preferred development of the invention, the first micromotif elements of nematic liquid-crystalline material are printed on a carrier foil.

The nematic liquid-crystalline material is advantageously applied to a carrier film designed for aligning liquid crystals. Alternatively, the carrier foil may also be provided with an alignment layer for aligning liquid crystals. For example, a smooth PET film of good surface quality can advantageously be used as the carrier film. The carrier film may also comprise a plurality of partial layers, for example an above-mentioned alignment layer. As an alignment layer, for example, a layer of a linear Photopolymer, a finely structured layer or aligned by exerting shear forces layer questioned. A suitable finely structured layer can be produced for example by embossing, etching or scoring.

In a preferred embodiment of the invention, a carrier film is provided, the surface of which has an arrangement of elevations and depressions in the form of the desired motif image. To form the first micromotif elements, the wells of the carrier foil are filled with nematic liquid-crystalline material. Without being bound to these explanations, it is believed that the geometry of the structures is responsible for aligning the nematic liquid crystalline material in the wells without additional alignment structures. For alignment of the nematic liquid-crystalline material in the recesses of the carrier film, therefore, preferably no alignment structures are provided in the form of a film provided with an alignment layer or a film designed for aligning liquid crystals.

The thickness of the carrier film is expediently between about 5 μm and about 50 μm, preferably between about 5 μm and about 25 μm.

In some designs, it is useful to use a carrier foil that is optically substantially isotropic to light from the predetermined wavelength range. For example, such a carrier film may consist of cycloolefin copolymers or be formed by a combination of two or more differently oriented plastic films.

Alternatively, the carrier foil has a defined optical anisotropy for light from the predetermined wavelength range with a light intensity exceeding the extension of the security element constant retardation. In particular, carrier films with a path difference of n * λ, with n from the natural numbers, and above all with a path difference of l * λ are preferred, since the light polarization when passing through such a film as in an optically isotropic film, remains essentially unchanged.

The nematic liquid-crystalline material is advantageously formed in a layer thickness such that the micromotif elements for light from the predetermined wavelength range form a λ / 4 layer or a λ / 2 layer at least in some areas.

According to a preferred embodiment of the invention, the first micromotif elements generating the hidden image information are combined with at least one further motif image which consists of a planar periodic or at least locally periodic arrangement of a plurality of second micromotif elements which generate visible image information.

A security paper according to the invention for the production of security or value documents, such as banknotes, checks, identity cards, documents or the like, is equipped with a security element of the type described above. The security paper may in particular comprise a carrier substrate made of paper or plastic.

The invention also includes a data carrier, in particular a brand article, a value document, decorative article, such as a packaging, postcards or the like, with a security element of the type described above. area, ie a transparent or recessed area of the data carrier, be arranged.

Further exemplary embodiments and advantages of the invention will be explained below with reference to the figures. For better clarity, a scale and proportioned representation is omitted in the figures.

Show it:

1 is a schematic representation of a banknote with an embedded security thread and a glued transfer element,

2 schematically the layer structure of a security element according to the invention in cross-section,

3 shows a security element according to the invention with a hidden motif image, wherein (a) shows a schematic plan view and (b) shows a cross section through the security element and a circular polarizer for viewing the security element,

4 shows a security element with a hidden motif image according to a further exemplary embodiment of the invention in cross-section,

5 is a security element with a hidden motif image according to yet another embodiment of the invention in cross section, Fig. 6 shows a security element according to the invention with a hidden and a visible motif image, wherein (a) shows a schematic plan view of the motif images and (b) shows a cross section through the security element, and

7 shows a security element according to the invention with a hidden and a visible motif image, which form moire images in a meaningful relationship, wherein (a) shows a schematic plan view of the motif images and (b) shows a cross section through the security element.

The invention will now be explained using the example of a security element for a banknote. 1 shows a schematic representation of a banknote 10 which is provided with two security elements 12 and 16 according to exemplary embodiments of the invention. In this case, the first security element represents a security thread 12 which emerges in certain window areas 14 on the surface of the banknote 10, while it is embedded in the intervening areas in the interior of the banknote 10. The second security element is formed by a glued transfer element 16 of any shape. The security element 16 can also be designed in the form of a security strip, a label or a cover film, which is arranged over a window area or a through opening of the banknote.

Both the security thread 12 and the transfer element 16 may include a moire magnification arrangement with hidden image information according to an embodiment of the invention. First, the basic mode of operation of inventive micro-optical moiré magnification arrangements will be briefly explained with reference to FIG. Fig. 2 shows schematically the layer structure of a security element according to the invention 20 in cross section, wherein only the parts of the layer structure required for the explanation of the functional principle are shown. The security element 20 includes an optical spacer layer 22, the upper side of which is provided with a regular array of microlenses 24. The arrangement of the microlenses 24 in each case partially forms a grid with preselected screen parameters, such as screen ruling, grid orientation and grid symmetry. The lattice symmetry can be described by a two-dimensional Bravais lattice, the hexagonal symmetry being assumed for the following explanation for the sake of simplicity, even if the Bravais lattice according to the invention can have a lower symmetry and thus a more general shape.

On the underside of the spacer layer 22, a motif layer 26 is arranged, which contains a likewise grid-shaped arrangement of similar micro-motive elements 28. The arrangement of the micromotif elements 28 can also be described by a two-dimensional Bravais lattice with a preselected symmetry, again assuming a hexagonal lattice symmetry for illustration. As indicated in FIG. 2 by the offset of the micromotif elements 28 relative to the microlenses 24, the Bravais grid of the micromotif elements 28 differs slightly in its symmetry and / or in the size of the grid parameters from the Bravais grid of the microlenses 24 to the desired one Moire magnification effect.

The distance of adjacent microlenses 24 is preferably chosen as small as possible in order to ensure the highest possible area coverage and thus a high-contrast representation. The spherically or aspherically configured microlenses 24 have a diameter between 5 μm and 50 microns, preferably only between 10 microns and 35 microns and are therefore not visible to the naked eye. The grating period and the diameter of the micromotif elements 28 are of the same order of magnitude as those of the microlenses 24, that is to say in the range from 5 μm to 50 μm, preferably from 10 μm to 35 μm, so that the micromotif elements 28 themselves can not be recognized by the naked eye are.

The optical thickness of the spacer layer 22 and the focal length of the microlenses 24 are matched to one another such that the micromotif elements 28 are approximately at a distance of the lens focal length. Due to the slightly differing lattice parameters, when the security element 20 is viewed from above through the microlenses 24, the observer sees a slightly different subarea of the micromotif elements 28, so that the multiplicity of microlenses overall produces an enlarged image of the micromotif elements 28. The resulting moire magnification depends on the relative difference of the lattice parameters of the Bravais lattice used. If, for example, the grating periods of two hexagonal grids differ by 1%, the result is a 100-fold moire magnification. For a more detailed description of the mode of operation and for advantageous arrangements of the micromotif elements and the microlenses, reference is made to the publications DE 102005 062132 A1 and WO 2007/076952 A2, the disclosure content of which is incorporated in the present application in this respect.

In such moiré magnification arrangements, the micromotif elements according to the invention are now formed from nematic liquid-crystalline material and form a phase-shifting layer for light from a predetermined wavelength range, so that the enlarged moiré image in the present case sentlichen only by looking at the security element by a polarizer is recognizable.

FIG. 3 shows a security element according to the invention with a hidden motif image which can be designed in the form of a security thread 30 for a banknote. 3 (a) shows a schematic plan view of the motif image, FIG. 3 (b) shows a cross section through the security element and a circular polarizer for viewing the security element.

The security thread 30 has as a carrier a transparent PET film 32 having a thickness of about 25 μm. On a first surface of the PET film 32, a periodic arrangement of microlenses 34 is applied by embossing a UV-curing lacquer. On the opposite surface of the film 32, a UV-curable lacquer 48 was first applied, in which microstructures 36 were generated by means of an embossing tool, not shown, consisting of an array of elevations and depressions in the form of the desired motif image. The depressions are filled with nematic liquid-crystalline material to form the hidden micro-motive elements 38. Even without additional alignment structures, the nematic liquid-crystalline material aligns in the embossed depressions. Without being bound to these explanations, the geometry of the embossed structures is probably responsible for this. In FIG. 3 (a), the micromotif elements 38 forming the motif image are shown for illustration only as simple letters "A".

With nematic liquid crystals, phase-shifting layers can be produced along the main crystal axes due to the different refractive indices of the rod-shaped liquid crystals. With appropriately selected layer thickness d, one obtains for a given wavelength rich, for example, a λ / 4 layer. The layer thickness d of the layer of nematic liquid-crystalline material is specified in the exemplary embodiment by the appropriately selected depth of the microstructures 36.

The arrangement of the micromotif elements 38 is provided with a transparent overcoat 42 and thus protected against counterfeiting attacks. On the recoating 42, a metallic reflector layer 44 is applied, for example, aluminum, chromium, silver or copper, which contains negative image elements in the form of uncoated portions 46. As a result of the overcoating 42, such coatings with recesses can be produced well by a washing process, as is known, for example, from the document WO 99/13157 A1, since the overcoat 42 can compensate for the increased roughness of the micro-motive elements 38 present in the depressions.

Without aids, the motif formed by the micromotif elements 38 present as a λ / 4 layer is hardly recognizable, since the security element in the areas of the micromotif elements essentially reflects the same amount of light as in the other areas and the unarmed eye reflects the linear polarization of the light in the Regions of micromotif elements reflected light can not detect.

On the other hand, if the security element is viewed through a circular polarizer 40, the motif image formed in the λ / 4 layer of the micromotif elements 38 emerges with a clear contrast, so that a moiré magnification effect can be observed. The micromotif elements 38 appear bright, the areas of the metallic reflector layer 44 not covered by the micromotif elements 38 dark. A suitable circular polarizer 40 may be formed for example by a linear polarizer and a downstream λ / 4 plate.

When viewing the security element with a linear polarizer, the motif image formed in the λ / 4 layer of the micromotif elements 38 can be made visible by a light / dark effect when rotating the linear polarizer. While the brightness of the metallic reflector layer 44 remains substantially unchanged upon rotation of the linear polarizer, the micromotif elements 38 appear bright in a first position of the polarizer, but become darker as the polarizer rotates to a second position.

In an alternative embodiment not shown here, instead of the metallic reflector layer 44, the security element may contain a layer of cholesteric liquid-crystalline material. In this case, the layer thickness of the micromotif elements 38 made of nematic liquid-crystalline material is selected such that a λ / 2 layer is obtained for the wavelength range in which the semiconductor liquid crystal layer selectively reflects. The security element further contains, at least in some areas, a dark background layer which forms an absorbent background. The dark background layer can be present even in the form of characters and / or patterns. In particular, it may be printed by coloring a substrate or by applying a laser beam to a substrate.

In the areas uncovered by the micromotif elements 38, the cholesteric liquid crystal layer reflects light with a preselected circular polarization direction, for example left circularly polarized light. In the areas of the micromotif elements 38, in which the two fluids overlap sigkristallschichten, the security element reflects light with the opposite polarization direction, in the embodiment so right circularly polarized light, since the incident unpolarized light from the λ / 2 layer of the micromotif elements 38 is not affected, the Poisa- risationsrichtung of the cholesteric liquid crystal layer reflected, left circular polarized light from the λ / 2-layer, however, is just reversed by the path difference between the ordinary and the extraordinary ray in its polarization orientation.

Without aids, the motif formed by the micro-motive elements 38 present as a λ / 2 layer is barely discernible, since the security element in the covered and uncovered areas reflects substantially the same amount of light and the unaided eye does not distinguish the circular polarization direction of the light can.

On the other hand, if the security element is viewed through a circular polarizer 40 which transmits only right-circularly polarized light, then the motif image formed in the λ / 2 layer of the micromotif elements 38 emerges with clear contrast, so that a moire magnification effect can be observed. The micromotif elements 38 appear bright, the uncovered areas of the cholesteric liquid crystal layer 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 40 can be formed, for example, by a linear polarizer with a λ / 4 plate connected downstream.

In a further development of this embodiment, a color change can be achieved when viewing the circular polarizer. In this case, the micromotif elements 38 of the security element formed as a λ / 2 layer lie between two layers of cholesteric liquid crystalline material which selectively reflect light from different wavelength ranges but the same circular polarization direction. For example, a first cholesteric liquid crystal layer in viewing direction may reflect blue light in the perpendicular viewing direction and shorter wavelength UV radiation in the acute viewing direction, while a second cholesteric liquid crystal layer disposed below the λ / 2 layer in the viewing direction may be formed such that It reflects red light in the vertical viewing direction and shorter wavelength green light in the acute viewing direction. When viewed with a circular polarizer, depending on the transmission properties of the circular polarizer, which transmits either only right or left circularly polarized light, as well as the polarization properties of the cholesteric liquid crystal layers when tilting the security element, only in the λ / 2 layer of the micro polarizer. In the areas of interest, there are certain color-shift effects: from blue to ultraviolet (motif image disappears when tilted) or from red to green (motif image changes color). Viewed without tools, the security element uniformly displays a color shift effect from magenta to green. The motif image formed in the λ / 2 layer of the micromotif elements 38 is hardly recognizable here.

The dark background layer, which is essential for the recognizability of the described coloration or polarization effects, can alternatively also be provided by a separate display element and be formed, for example, by a commercial printing ink printed on one side of the banknote. Only when the banknote is folded, so that in this case expediently designed as a see-through security element Security element comes to rest on the display element, the intended color and / or polarization effects can be detected.

The security element 50 shown in FIG. 4 according to a further exemplary embodiment of the invention has a hidden motif image in which the micromotif elements are formed by a thickness of a layer of nematic liquid-crystalline material that is different in certain areas. The security element 50 can also be a security thread or a cover sheet for banknotes.

On the opposite side of a carrier 52 provided with a periodic arrangement of microlenses 54, for example a PET film, a layer 56 of nematic liquid-crystalline material was first applied, preferably printed, into which an array of elevations and depressions in the form of the desired one Motiv image was embossed. Preferably, the carrier used is a film designed for aligning liquid crystals. Alternatively, the carrier 52 may also be provided with an alignment layer for aligning liquid crystals. The printing of the layer 56 of nematic liquid-crystalline material can take place, for example, in the gravure, inkjet, flexographic, offset or multi-roll printing process. In this case, in printing processes that require a low viscosity, a suitable dilution with solvents. In printing processes which require a high viscosity, such as the offset printing process or the multi-roll printing process, the viscosity of the liquid-crystalline material can be achieved, for example, by applying the liquid-crystalline material from the melt. In the micromotif elements 58 forming regions of the layer 56, the layer thickness di is selected such that one obtains a λ / 4 or a λ / 2 layer for a predetermined wavelength range. The layer thickness d2 of the intermediate regions 59 in the exemplary embodiment is less than about 0.5 μm, preferably less than about 0.3 μm. The optical effect of these regions 59 of the nematic liquid crystal layer 56 can be neglected due to their small layer thickness d ₂ . Typically, nematic liquid crystal layers require a layer thickness on the order of about 0.5 μm to about 3 μm in order to achieve a significant phase-shifting effect.

According to an alternative embodiment, the nematic liquid crystal layer 56 may also be printed in the various subregions 58, 59 in the form of the desired motif image with different sized layer thickness d ₁ or d2, for example in several printing processes.

5 shows a security element according to the invention with a hidden motif image which may be in the form of a security thread or, as in the exemplary embodiment, in the form of a cover film 60 for a banknote with a hole.

The cover film 60 has as a carrier a transparent PET film 62 with a thickness of about 20 .mu.m, on one surface of which a periodic arrangement of microlenses 64 is applied. The opposite surface of the carrier film 62 is first pretreated for a good anchoring of the nematic liquid-crystalline material, for example by means of an adhesion-promoting corona process, in which the process atmosphere can deviate from air. A motif image of micromotif elements 68 is then applied to the pretreated surface. For applying the micromotif elements 68, a tool mold, not shown here, is used whose surface has an arrangement of elevations and depressions in the form of the desired microstructure. The recesses of the tool mold are filled with a curable nematic liquid-crystalline material, for example in the form of a liquid-crystalline melt, and the surface of the mold is then brought into contact with the surface-treated support film 62, the nematic liquid-crystalline material in contact with the support film being introduced into the mold Wells of the mold is cured.

Finally, the surface of the tool mold is removed again from the carrier film 62, so that the hardened nematic liquid-crystalline material connected to the carrier film in the form of the micromotif elements 68 can be pulled out of the depressions of the mold or embossing mold. The depth of the depressions of the tool mold is selected such that the micromotif elements 68 produced thereby form a λ / 2 layer for a predetermined wavelength range in the exemplary embodiment. Further details of such a printing method can be found in the document WO 2008/000350 A1, the disclosure of which is incorporated in the present application in this respect.

For alignment of the nematic liquid-crystalline material, the depressions of the mold or embossing mold may have an alignment-order structure. Without being bound by these explanations, alternatively or additionally, the geometry of the recesses of the tool or embossing mold may be responsible for the alignment of the nematic liquid-crystalline material. In addition, shear forces, such as occur during filling of the depressions, can have an influence on the orientation of the nematic liquid-crystalline material. It is understood that the micromotif elements 68 can be formed by both the depressions and the elevations in the tool mold. In the first case, micromotif elements hidden in transparent surroundings, hidden in the carrier foil 62 and recognizable only by means of a polarizer, are obtained, in the latter case transparent micromotif elements in an environment recognizable only by means of a polarizer. The information content of the applied micromotif elements is the same in both cases.

The arrangement of the micromotif elements 68 is embedded in a transparent overlay 66 and thus protected against counterfeiting attacks, wherein the transparent overpainting forms an optically substantially isotropic layer. In the exemplary embodiment, a linear polarizer 70 is applied to the transparent overcoat.

If further opaque functional layers are dispensed with, application of the covering film 60 in the register to the banknote paper results in a moire magnification effect observable in transmission and, for example, by means of a linear polarizer, in the finished banknote. Thus, when rotating a linear polarizer held over the cover sheet 60, the viewer perceives the motif image formed in the λ / 2 layer of the micromotif elements 68 in the form of a light / dark effect. However, such an effect is dependent on the choice of the carrier film 62 through which the viewer looks at the micromotif elements 68. In an embodiment in which both the microlenses 64 and the micromotif elements 68, including the linear polarizer 70, are arranged on the same side of the carrier foil 62, the effect can also be observed independently of the optical properties of the carrier foil. In an alternative embodiment, the micromotif elements 68 for a given wavelength range instead of a λ / 2 layer can form a phase-shifting layer with a constant path difference not equal to n * λ, with n from the natural numbers. In this embodiment too, when the viewer rotates a linear polarizer held over the covering film 60, the viewer perceives the motif image formed by the micromotif elements 68 in the form of a light / dark effect.

If the security element, instead of the linear polarizer 70, is to be provided with a metallic reflector layer which optionally has recesses, it is also advantageous to provide the arrangement of the micromotif elements with a transparent overcoat 66. As a result of the overlap 66, such coatings with recesses can be produced well by a washing process, as is known, for example, from document WO 99/13157 A1, since the overcoating compensates for the greatly increased local roughness of the applied micromotif elements 68. In addition, it is avoided in this way that when washing the wash color remains in the recesses between the micromotif elements.

The security element 80 shown in FIG. 6 according to a further exemplary embodiment of the invention has, in addition to a hidden one, a motif image which is visible to the naked eye. Also, the security element 80 may be a security thread or a cover sheet for banknotes.

Micro-motive elements with hidden and visible information can be generated in several printing processes, for example, with several filled with nematic liquid-crystalline material or colored paint Tool molds or embossing molds, as described in connection with FIG. 5. The micromotif elements need not all be present in the same layer, it is also possible to realize multi-layer designs. Thus, when arrays of micromotif elements with hidden and visible image information are generated, the various arrays do not generally need to be matched, as the relative orientation of the microlens array and the respective micromotif element array is critical to the moiré effect. Depending on the application, however, an accurate registration of the micromotif element arrangements relative to one another can also be advantageous.

The arrangement of the micromotif elements 82, shown in plan view in FIG. 6 (a), includes micromotif elements 82-1, which form hidden information and whose outline is shown in dotted lines in the figure, and hatched micromotility elements 82-2, which provide visible information form. For illustration, both the micromotif elements 82-1 and also the micromotif elements 82-2 in FIG. 6 (a) are only shown as simple letters "A." The different micromotif elements can be deposited on a carrier foil, in the exemplary embodiment of an optically isotropic carrier foil, for example using of two tools that are filled with nematic liquid-crystalline material to form the hidden micromotif elements 82-1 and with colored lacquer to form the micromotif visible elements 82-2 It is understood that the micromotif elements 82-1 and 82-2 may also be shaped different microcharacters or micro-patterns can be configured.

The arrangement of the micromotif elements 82 is embedded in a transparent overlay 84 and thus protected against counterfeiting attacks. If desired, additional layers can be applied, for example one in Fig. 6 (b) shown in dashed lines metallic reflector layer 86, which may contain negative image elements in the form of uncoated portions. Alternatively, instead of the metallic reflector layer 86, the security element 80 may also contain a layer of cholesteric liquid-crystalline material or a linear polarizer.

The enlarged moiré image of the micromotive elements 82-2 forming visible information is already clearly recognizable to a viewer without any aids. On the other hand, since the security element 80 reflects substantially the same amount of light in the areas covered with the nematic liquid crystalline material as the uncovered areas, and the unaided eye can not distinguish the polarization of the light, the motif formed by the micromotif elements 82-1 is hardly accessible without the aid detect. However, if the security element is viewed through a circular polarizer, the motif image formed by the micromotif elements 82-1, for example in a λ / 4 or λ / 2 layer, emerges with a clear contrast, so that a moiré magnification effect also applies to the Micromotif elements 82-1 can be observed.

In this case, when the hidden micromotif elements 82-1 form a λ / 4 layer, they appear bright when viewed with a circular polarizer, whereas the uncovered areas of the metallic reflector layer appear dark, as described, for example, in connection with FIG. When viewed with a circular polarizer, the observer therefore specifically perceives the previously hidden micromotif elements 82-1 Moire-magnified, while the micromotif elements 82-2 are now present against a dark background and, depending on the color of the micromotif elements, may no longer be clearly visible or even disappear completely. When using an optically anisotropic carrier film can the effects described above are reversed, ie the hidden microparticles 82-1 appear dark when viewed with a circular polarizer, while the uncovered areas of the metallic reflector layer appear bright.

FIG. 7 shows a further embodiment of a security element 90 according to the invention with a hidden and a visible motif image. In the exemplary embodiment, adjacent, differently configured micromotives 92-1, 92-2 are applied, which form moire images that are meaningful.

The micro-motif elements 92-1, which form hidden information and dot-shaped, radially surround the micromotif elements 92-2 filled with hatching, which form visible information. Considering the security element 90 with a suitable Polarisa tor recognizable without aids, formed by the micromotif elements 92-2 motif image (circular area) is supplemented by the radial arrangement of the micromotif elements 92-1 to an overall image (sun).

It will be appreciated that the hidden and visible micromotif elements may be present not only together on the same lattice sites but also separately in different areas of the security element. For example, one subarea of a security element can be provided only with hidden micromotif elements, another subarea only with visible micromotif elements. If one considers such a security element with a suitable polarizer, in addition to the already visible motif image, for example, colored fish arranged in an upper region of the security element, the hidden micromotif elements also moire-enlarged, for example in a lower region of the security element as wavy lines, in appearance. With the aid of the polarizer, a motivic image that can already be recognized without any aids can therefore be added to a (complete) overall picture.

In addition, the security element of FIG. 7 can also be provided with additional layers, such as a metallic reflector layer, a layer of cholesteric liquid-crystalline material or a linear polarizer, as already described in connection with FIG. 6. Alternatively, these layers can also be provided by an additional presentation element, for example at another location of a value document provided with the security element.

Claims

Patent claims

1. security element for security papers, documents of value and the like with a micro-optical moire magnification arrangement with

a first motif image, which consists of a planar periodic or at least locally periodic arrangement of a plurality of first micromotif elements, which generate hidden image information, and

a planar periodic or at least locally periodic arrangement of a plurality of microfocusing elements for moire-enlarged viewing of the first micromotif elements of the first motif image,

wherein the first micromotif elements are formed of nematic liquid-crystalline material and form a phase-shifting layer for light of a predetermined wavelength range, and wherein the magnified moiré image is substantially detectable only by viewing the security element through a polarizer.

2. Security element according to claim 1, characterized in that the first micromotif elements are formed by a partially different thickness of the nematic liquid-crystalline material.

3. Security element according to claim 1 or 2, characterized in that the nematic liquid-crystalline material is present only in regions and in the form of the first micromotif elements.

4. Security element according to at least one of claims 1 to 3, characterized in that the first micromotif elements for light from the predetermined wavelength range form a λ / 4-layer at least in some areas.

5. Security element according to at least one of claims 1 to 4, characterized in that a metallic reflector is provided.

6. The security element according to at least one of claims 1 to 3, characterized in that the first micromotif elements for light from the predetermined wavelength range form a λ / 2 layer at least in partial regions.

7. The security element according to at least one of claims 1 to 6, characterized in that a linear polarizer and / or one or more layers of cholesteric liquid-crystalline material are provided.

8. The security element according to claim 1, characterized in that the nematic liquid-crystalline material additionally has a fluorescence functionality, or in that a further nematic liquid-crystalline material having a fluorescence functionality is added to the nematic liquid-crystalline material.

9. Security element according to at least one of claims 1 to 8, characterized in that the hidden image information generating first micromotif elements are combined with at least one further motif image consisting of a planar periodic or at least locally periodic arrangement of a plurality of second micromotif elements that produce visible image information.

10. The security element according to claim 1, characterized in that the arrangement of first micromotif elements, the arrangement of microfocusing elements and optionally the arrangement of second micromotif elements at least locally each form a two-dimensional Bravais lattice, wherein the arrangement of first micromotif elements and or the arrangement of microfocusing elements and / or the arrangement of second micromotif elements preferably form a Bravais lattice with the symmetry of a parallelogram lattice.

11. A security element according to claim 10, characterized in that the arrangement of the first micromotiv elements and the arrangement of second micromotif elements in their grating periods and lattice orientations are identical, each lattice position of the array of first micromotif elements element with a first motif and / or occupied a second motif element is.

12. Security element according to claim 11, characterized in that

a) each lattice site is occupied by either a first micromotif element or a second micromotif element, so that the first and the second micromotif elements are arranged alternately, or

b) each lattice site is occupied by a first motif element and a second motif element and the first and second micromotif elements are present at least partially next to one another.

13. The security element according to claim 10, characterized in that the arrangement of first micromotiv elements and the arrangement of second micromotif elements differ in their grating periods and / or lattice orientations.

14. A security element according to at least one of claims 9 to 13, characterized in that the arrangement of the first micromotif elements and the arrangement of second micromotif elements are arranged in different layers.

15. A security element according to at least one of claims 9 to 13, characterized in that the arrangement of first micromotif elements and the arrangement of second micromotif elements are arranged in the same layer.

16. A security element according to at least one of claims 9 to 15, characterized in that the first and the second micromotivem elements form coherent moiré images.

17. A method for producing a security element with a micro-optical moiré magnification arrangement, in which a first motif image which consists of a planar periodic or at least locally periodic arrangement of a plurality of first micromotif elements which form a hidden image information, and a planar periodic or At least locally periodic arrangement of a plurality of Mikrofokussier- elements are arranged so that the first micromotif elements are magnified when viewed through the Mikrofokussierelemente recognizable, wherein the first micromotif elements of nematic liquid-crystalline Material are formed such that they form a phase-shifting layer for light from a predetermined wavelength range.

18. The method according to claim 17, characterized in that the first micromotif elements are formed by a partially different layer thickness of the nematic liquid-crystalline material.

19. The method according to claim 18, characterized in that the first micromotif elements are embossed into a layer of nematic liquid-crystalline material, which is applied to a carrier foil.

20. The method according to at least one of claims 17 to 19, characterized in that the nematic liquid-crystalline material is formed only partially and in the form of the first micromotif elements.

21. The method according to claim 20, characterized in that the first micromotif elements of nematic liquid-crystalline material are printed on a carrier film.

22. The method according to at least one of claims 19 to 21, characterized in that is provided as a carrier film designed for the alignment of liquid crystals film or provided with an alignment layer for the alignment of liquid crystals film.

23. The method according to at least one of claims 20 to 22, characterized in that a carrier film is provided, whose surface has an array of elevations and depressions in the form of the desired motif image, and the recesses of the carrier film for Formation of the first micromotif elements are filled with nematic liquid-crystalline material.

24. The method according to claim 23, characterized in that no alignment structures are provided for the alignment of the nematic liquid-crystalline material in the recesses of the carrier film.

25. The method according to claim 17, characterized in that the nematic liquid-crystalline material is formed in a layer thickness such that the micromotif elements for light from the predetermined wavelength range form a λ / 4-layer or a λ / 2 at least in partial regions. Forming a layer.

26. The method according to at least one of claims 17 to 25, characterized in that the hidden image information generating the first

Micromotif elements are combined with at least one further motif image, which consists of a planar periodic or at least locally periodic arrangement of a plurality of second micromotif elements that generate visible image information.

27. Security paper for the production of security or value documents, such as banknotes, checks, identity cards, certificates or the like, or data carriers, in particular branded articles, value documents, decorative articles or the like, having a security element according to at least one of claims 1 to 26.