CN111032364B

CN111032364B - Optically variable transmission security element and data carrier

Info

Publication number: CN111032364B
Application number: CN201880050733.2A
Authority: CN
Inventors: B.图费尔; K.H.谢勒; W.霍夫米勒
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient GmbH
Priority date: 2017-10-04
Filing date: 2018-09-27
Publication date: 2021-02-02
Anticipated expiration: 2038-09-27
Also published as: EP3691911A1; WO2019068362A1; CN111032364A; DE102017009226A1; EP3691911B1

Abstract

The invention relates to an optically variable security element for providing security to valuable articles, having a flat, optically variable flat pattern which displays a different color in transmitted light than in reflected light and has virtually no color gradient effect in transmitted light, wherein the optically variable flat pattern comprises a plurality of prism faces which substantially produce an illuminating optical effect, the orientation of which is characterized in each case by an angle of inclination a in the range from 0 DEG to 30 DEG relative to the plane of the flat pattern, wherein the prism faces are provided with a translucent functional layer which displays a different color in transmitted light than in reflected light and has virtually no color gradient effect in transmitted light, and the optically variable flat pattern comprises at least two partial regions which each have a plurality of similarly oriented prism faces, in this case, the facets of one sub-region have a smaller inclination angle α and the facets of the other sub-region have a larger inclination angle α, so that the optically variable surface pattern appears in transmitted light with a higher saturation or chromaticity in the sub-region in which the facets have a smaller inclination angle α and with a lower saturation or chromaticity in the sub-region in which the facets have a larger inclination angle α.

Description

Optically variable transmission security element and data carrier

Technical Field

The invention relates to an optically variable security element for providing security to valuable articles, comprising a flat, optically variable surface pattern which displays a different color in transmitted light than in reflected light.

Background

Data carriers, such as value documents or certificates, but also other value articles, such as name-card goods, are often provided with security elements to ensure security, which enable the authenticity of the data carrier to be verified and at the same time serve as protection against unauthorized copying. In this context, see-through security element features, such as see-through windows in banknotes, are becoming increasingly attractive.

WO 2016/096094 a1 describes an optically variable security element for providing security to a valuable article, the colored appearance of the optically variable surface pattern displayed in perspective having a multicolored color transformation dependent on the viewing angle.

Disclosure of Invention

Starting from this, the object of the invention is to provide a see-through security element which combines an attractive visual appearance with improved security against forgery and which can be produced ideally on a large technical scale required in the field of forgery protection.

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

Summary of the invention

(first aspect of the invention) an optically variable security element for safeguarding valuable articles, having a flat, optically variable planar pattern which exhibits a different color in transmitted light (in Durchichht) than in reflected light (in Aufsicht) and which has virtually no color gradient effect in transmitted light,

it is characterized in that the preparation method is characterized in that,

the optically variable surface-like pattern comprises (a) a plurality of facets (Facetten) which substantially produce the illumination optical effect, the orientation of said facets being characterized in each case by an angle of inclination a in the range from 0 ° to 30 ° relative to the plane of the surface-like pattern,

the prism faces are provided with a translucent functional layer which exhibits a different color in transmitted light than in reflected light and which has little color gradient effect in transmitted light, and

the optically variable flat pattern comprises at least two partial regions each having a plurality of similarly oriented facets, wherein the facets of one partial region have a smaller inclination angle α and the facets of the other partial region have a larger inclination angle α, so that the optically variable flat pattern appears in transmitted light with a higher chroma or chromaticity in the partial regions in which the facets have a smaller inclination angle α and with a lower chroma or chromaticity in the partial regions in which the facets have a larger inclination angle α.

Chroma or chroma describes the relative color effect compared to a reference white, i.e. compared to the determined brightest point of the color space. Chroma is suitable as a measure for example for a cone-shaped color space, in which it can be measured from the top. These systems have practical significance in the printing industry, where the white color of paper represents zero color and as much color ink as for saturated red color needs to be applied for saturated black color. The chroma of white is 0, the hue (tone) and dark black are not more than 100%, and the middle gray is 50%.

The optically variable surface pattern is based in particular on a relief structure, i.e. a reflective microstructure, which is embossed into an embossing lacquer layer and is in the form of a mosaic made up of a plurality of reflective mosaic elements or edges, which can be characterized by the parameters size, contour shape, relief shape, reflectivity and spatial orientation and form a predetermined motif (Motiv) in such a way that various different groups of mosaic elements having different characteristic parameters reflect incident light into different spatial regions, wherein the mosaic elements have a transverse dimension l below the eye resolution limit. The lateral dimension l of the mosaic element is graphically represented visually in fig. 2 of EP 1966769B 1. In this case, a translucent functional layer which exhibits a different color in transmitted light than in reflected light and has virtually no color gradient effect in transmitted light is used as the reflective layer.

(preferred embodiments) for example, in the case of the see-through security element according to the invention, the area occupied by each partial area on the optically variable areal pattern is at least 50 times, preferably at least 100 times, particularly preferably at least 1000 times greater than the area occupied on average by the individual facets of this surface area.

(preferred embodiments) for example, in the case of the see-through security element according to the invention, the edge faces of the at least two partial regions differ by 5 ° or more, preferably by 10 ° or more, in the angle of inclination formed with respect to the plane.

(preferred embodiment) for example, with the see-through security element according to the invention, the facets of the one partial region having the smaller inclination angle α have an inclination angle α in the range from 0 ° to 15 °, preferably in the range from 0 ° to 10 °, and the facets of the other partial region having the larger inclination angle α have an inclination angle α in the range from 15 ° to 30 °, preferably in the range from 20 ° to 30 °.

(preferred embodiment) for example, in the case of the see-through security element according to the invention, the edge faces are each provided with a translucent functional layer which, in transmitted light, exhibits a different color than in reflected light, the layer thickness of the functional layer varying with the angle of inclination α of the edge face, preferably decreasing with increasing angle of inclination α.

(preferred embodiments) for example, in the case of the see-through security element according to the invention, the at least two partial regions are arranged in the form of a pattern and the pattern appears in transmitted light with two or more different saturation values that can be visually distinguished with the naked eye.

(preferred embodiment) for example, with the see-through security element according to the invention, the optically variable area pattern additionally has, in partial regions, a black mask adapted to the oblique edge surfaces, which black mask is used to adjust the see-through brightness of the edge surfaces in the respective partial regions.

(preferred embodiment) for example, in the case of the see-through security element according to the invention, the prism surface is embossed in an embossing lacquer layer having a first refractive index, and a lacquer layer having a second refractive index is applied to the translucent functional layer, which differs from the first refractive index by less than 0.3, in particular by less than 0.1.

(preferred embodiment) for example, with the see-through security element according to the invention, the translucent functional layer has a multi-layer structure with two translucent metal layers and a dielectric layer arranged between the two translucent metal layers.

(preferred design) for example, for the see-through security element according to the invention, the two translucent metal layers are formed independently of one another from a metal and the metal is selected from the group consisting of Al, Ag, Ni, Cr, Cu, Au and alloys of one or more of the aforementioned elements, and the dielectric layer is SiO₂Layer, ZnO layer, Al₂O₃Layer, TiO₂Layer, layer consisting of a nitride or oxynitride of one of the elements Si, Zn, Al or Ti, or MgF₂A layer or a layer of nitrocellulose, for example, which can be obtained by printing techniques.

(preferred embodiment) for example, in the case of the see-through security element according to the invention, the two translucent metal layers are selected independently of one another from Al or Ag and the dielectric layer is SiO₂And (3) a layer.

(preferred embodiments) for example, for the see-through security element according to the invention, the translucent functional layer is based on an effect pigment composition.

(preferred embodiment) for example, with the see-through security element according to the invention, the optically variable area pattern displays a blue color when viewed in transmitted light and a gold color when viewed in reflected light.

(preferred embodiment) for example, in the case of the see-through security element according to the invention, the edge faces are designed as substantially flat surface elements.

(preferred embodiments) for example, with the see-through security element according to the invention, the facets are arranged as a periodic grid and in particular form a sawtooth grid, or the facets are arranged non-periodically.

(preferred embodiments) for example, for the see-through security element according to the invention, the facets have a minimum dimension (or transverse dimension l) of more than 2 μm, preferably more than 5 μm, in particular more than 10 μm, and/or the facets have a height of less than 100 μm, preferably less than 50 μm, in particular less than 10 μm.

(second aspect of the invention) a data carrier with a see-through security element according to the invention, wherein the see-through security element is preferably arranged in or on a window area or through opening of the data carrier.

(preferred embodiments) for example, the data carrier according to the invention, wherein the data carrier is a document of value, in particular a banknote.

Detailed description of the preferred embodiments

According to the invention, it is provided in an optically variable security element of the type according to the invention that,

the see-through security element comprises a flat, optically variable planar pattern which, in transmitted light (i.e. in transmission or when viewed in transmitted light), exhibits a different color than in reflected light (i.e. when viewed in reflected light) and has little color-tilting effect in transmitted light,

the optically variable flat pattern comprises a plurality of facets which substantially produce the illumination optical effect, the orientation of the facets being characterized in each case by an inclination angle α formed relative to the plane of the flat pattern in the range from 0 ° to 30 °,

Chroma or chroma describes the relative color effect compared to a reference white, i.e. compared to the determined brightest point of the color space. Chroma is suitable as a measure for example for a cone-shaped color space, in which it can be measured from the top. These systems have practical significance in the printing industry, where the white color of paper represents zero color and requires as much application of color ink (or ink, ink) for saturated black as for saturated red. The chroma of white is 0, the hue (tone) and dark black are not more than 100%, and the middle gray is 50%.

The see-through security element according to the invention is optically variable, i.e. forms different views at different viewing angles.

The optically variable security element known from WO 2016/096094 a1 exhibits in transmitted light a color appearance with a multicolored color transformation dependent on the viewing angle; in contrast to the aforementioned see-through security elements, the optically variable see-through security element according to the invention, which has little color gradient effect in transmitted light, is characterized in that it has a color change when viewed in reflected light/transmitted light, which is achieved by its attractive color effect in reflected light and in transmitted light, wherein, by means of the adjustment of the angle of inclination of the facets and the saturation of the see-through color (see-through color) achieved thereby, it is possible to increase the contrast and thus highlight specific elements of the motif in transmitted light. By adjusting the transmission properties of the translucent functional layer, a wider color palette, in particular from gray to saturated blue, can be provided in transmitted light. The increase in contrast results in an additional level of verification in the case of authenticity verification and thus provides improved protection against forgery.

The invention is based on the recognition that the chroma or chromaticity is largely dependent on the embossed structure or the relief evaporated with the translucent functional layer when viewed in transmitted light. If the optically variable surface pattern contains partial regions in which the facets have a smaller inclination angle α (so-called "smooth" partial regions) or if there are smooth or unembossed partial regions without any facets or micromirrors, the transmitted color appears to the observer with a higher chroma or chromaticity. The reason for the higher chroma is that the embossing lacquer is relatively smooth or flat on its surface, i.e. the light is not refracted or scattered during transmission through the film structure and enters the eye of the observer straight. Furthermore, in the case of flat or smooth substrates, the thickness of the translucent functional layer corresponds to the target thickness and is therefore particularly effective optically. If the optically variable surface pattern contains partial regions in which the facets have a greater inclination angle α (so-called "coarse" partial regions), the transmission color appears to the observer with less saturation or shade, i.e. the transmission color appears dull or pale. The reason for the low chroma is that the embossing lacquer has very pronounced relief comprising recesses, projections and/or edges on its surface, i.e. light is diffusely refracted or scattered in all spatial directions during transmission through the film structure. The optical path through the translucent functional layer and thus the transmission spectrum likewise differ as a function of the angle of refraction. The different chromatograms generally form grey tones. In addition, in the case of rough substrates, the thickness of the translucent functional layer differs from the target thickness and therefore acts less optically, i.e. deviates from the actual optical transmission effect.

Suitable translucent functional layers which exhibit a different color in transmitted light than in reflected light and have little color tilt effect in transmitted light are known, for example, from WO 2011/082761 a 1. WO 2011/082761 a1 describes a translucent lamellar element which, viewed in reflected light, exhibits a gold colour and, viewed in transmitted light, exhibits a blue colour with little colour gradient effect.

Suitable translucent functional layers are based, for example, on a multilayer structure having two translucent metal layers and a dielectric layer arranged between the two translucent metal layers. Such functional layers are obtained, for example, by means of a vacuum evaporation method. A suitable multilayer structure having two translucent metal layers and a dielectric layer arranged between the two translucent metal layers preferably has the following specific properties:

the two translucent metal layers are preferably selected from Al or Ag; dielectric layer, especially SiO₂Layer or MgF₂Layer, preferably SiO₂A layer;

in the case of two translucent metal layers each based on Al, the respective preferred layer thickness is in the range from 5nm to 20nm, particularly preferably in the range from 10nm to 14 nm; dielectric SiO₂The layer preferably has a layer thickness in the range from 50nm to 450nm, further preferably in the range from 80nm to 260nm and particularly preferably in the range from 210nm to 260nm, wherein the ranges from 80nm to 100nm and from 210nm to 240nm are particularly preferred, in particular for providing a gold/blue conversion;

in the case of two translucent metal layers each based on Ag, the respective preferred layer thickness is in the range from 15nm to 30nm, particularly preferably from 15nm to 25 nm; dielectric SiO₂The layer preferably has a layer thickness in the range from 50nm to 450nm, further preferably in the range from 80nm to 260nm and particularly preferably in the range from 210nm to 260nm, wherein the ranges from 80nm to 100nm and from 210nm to 240nm are particularly preferred, in particular for providing a gold/blue conversion.

The above-described multilayer structure having two translucent metal layers and a dielectric layer disposed between the two translucent metal layers may have a symmetrical three-layer structure in which the material and layer thickness of the two translucent metal layers are the same. However, an asymmetrical three-layer structure may alternatively be present, in which the material and/or layer thickness of the two translucent metal layers are different, for example

-a silver/dielectric/aluminium layer system, wherein the layer thicknesses of the silver layer and the aluminium layer are the same or different;

-a silver/dielectric/silver layer system; wherein the layer thicknesses of the two silver layers are different;

an aluminum/dielectric/aluminum layer system, in which the layer thicknesses of the two aluminum layers are different.

The multilayer layer structure described above not only enables the production of translucent functional layers which appear golden when viewed with reflected light and blue when viewed with transmitted light, but also, depending on the choice of the layer thickness, in particular of the dielectric layer, can produce other color changes, for example

Magenta in reflected light and cyan in transmitted light;

-a turquoise colour in reflected light and an orange colour in transmitted light;

-gold in reflected light and blue-violet in transmitted light;

silver in reflected light and purple in transmitted light.

According to a further preferred embodiment, the translucent functional layer can be obtained by means of an effect pigment composition by means of printing techniques. The printed layers based on the effect pigment compositions exhibit a different colour when viewed with reflected light than when viewed with transmitted light, in particular a gold/blue colour shift, a gold/violet colour shift, a green-gold/magenta colour shift, a violet/green colour shift or a silver/opaque colour shift, these printed colours being described, for example, in WO 2011/064162A 2. The longest dimension of the pigment from end to end ("change dimension of edge length") is preferably in the range from 15nm to 1000nm and is based on a transition metal selected from Cu, Ag, Au, Zn, Cd, Ti, Cr, Mn, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt. The transition metal is preferably Ag. The aspect ratio (i.e. the ratio of the longest dimension to the thickness from end to end) is preferably at least 1.5, in particular in the range of 1.5 to 300. The ratio of binder to metallic pigment is preferably less than 10:1, especially less than 5: 1. Depending on the choice of the aspect ratio of the pigment, its longest dimension from end to end and the adjustment of the pigment/binder ratio, the color when the printed layer is viewed in transmission and the color when viewed in reflection can be adjusted (for example blue in transmission and silver, gold, bronze, copper or violet in reflection; furthermore violet, magenta, pink, green or brown in transmission and a different color in reflection in relation to the choice of the pigment/binder ratio). Colors with a gold/blue color shift between reflection and transmission (in other words between reflected light viewing and transmitted light viewing) are mentioned for example in examples 1, 2 and 3 in table 1 of WO 2011/064162 a 2. Further, example 4 shows a color with a gold/purple color transform, example 5 shows a color with a green-gold/magenta color transform, example 7 shows a color with a purple/green color transform, and example 8 shows a color with a silver/opaque color transform.

The mosaic elements form a predetermined pattern in such a way that various different groups of mosaic elements having different characteristic parameters reflect incident light rays into different spatial regions. Furthermore, the mosaic elements have a lateral dimension below the eye resolution limit.

The mosaic elements preferably have a lateral dimension of less than 100 μm, particularly preferably less than 30 μm. Such smaller mosaic elements can be produced on the one hand with established thin-film technology due to the smaller profile depth associated with the smaller dimensions, and on the other hand the smaller element dimensions enable a large number of possible arrangements for the mosaic elements, as will be explained in more detail below together with the respectively associated advantages.

The mosaic elements advantageously have a lateral dimension greater than 3 μm, preferably greater than 5 μm. This dimensioning ensures that the wavelength-dependent light diffraction effects can be ignored and that the incident light is reflected achromatic by the mosaic element without disturbing color effects.

Suitably, the mosaic elements have a square, rectangular, circular, oval, honeycomb or polygonal outline shape. The lateral dimension of the mosaic elements is advantageously no greater than five times the dimension in any direction than in one of the other directions.

In an advantageous variant of the invention, the mosaic element has a simple relief shape with exactly one reflection surface inclined with respect to the surface of the security element. The angle of inclination of the reflective surfaces of the mosaic elements is expediently less than 90 °, preferably less than about 45 °. The reflective surface of the mosaic element may be flat or may be convexly or concavely curved.

In a further, likewise advantageous variant of the invention, the mosaic element has a relief shape with two or more reflection surfaces which are inclined in different directions relative to the surface of the security element. The mosaic element may in particular have a top structure or a multi-sided pyramidal structure. In this variant, the angle of inclination of the reflective surfaces of the mosaic elements is also expediently less than 90 °, preferably less than about 45 °, and the reflective surfaces of the mosaic elements can be both flat and concave or convexly curved.

In a further advantageous variant of the invention, the mosaic element has, in regions, a simple relief shape with an average reflection surface inclined with respect to the surface of the security element (so-called average orientation). The inclination angles of the reflective surfaces of the mosaic elements vary substantially randomly around different average orientations which are locally preset. In this way a sparkling effect is formed which in practice corresponds to the appearance of the magnetically oriented pigments of the optically variable security ink. To this end, the average orientation of the reflective surfaces (or facets) of the different mosaic elements (or pixels) is chosen to be similar to the average orientation of the pigments. The glitter effect of these color inks is based on the fact that the individual pigments are not reflected exactly in a predetermined direction, but rather have a somewhat random variation in the direction of reflection. Optically variable security elements with such microstructures are known from WO 2011/066991 a 2. Preferably, the change in the reflection direction predetermined by the change in the orientation of the facets of the different pixels is at least approximately 1 °, preferably at least approximately 3 °, particularly preferably at least approximately 10 °.

According to a further advantageous variant of the invention, the mosaic element forms a cat-eye reflector, i.e. a multi-reflecting structure which reflects light rays incident from a certain angular range back in the direction of incidence. The mosaic element has in particular a cube-corner structure having a relief shape composed of three reflecting surfaces which are substantially perpendicular to one another and face one another. The three reflection surfaces define an optical axis which, for a cube-corner structure, is given by the spatial diagonal of the corresponding cube. The optical axis thus defined is preferably directed in a preselected direction for each mosaic element, so as to be able to present one or more image patterns, as described in more detail below.

The mosaic itself preferably presents a grid image consisting of a plurality of image points, wherein each image point is formed by one or more achromatic reflecting mosaic elements. The brightness of the pixels of the grid image can be determined by one or more of the parameters of the size, contour shape, relief shape, reflectivity and spatial orientation (or orientation) of the mosaic elements of the respective pixel, or by the number of mosaic elements having specific characteristic parameters in the respective pixel.

In an embodiment of the security element according to the invention, further information is encoded in the array of mosaic elements within a pixel.

According to the invention, the mosaic of the security element can also reflect two or more different image patterns into different spatial regions, so that an oblique image or a moving image is formed for the observer upon a corresponding movement of the security element. In a further embodiment, the mosaic can also reflect increasing or decreasing contours of the image pattern into different spatial regions, so that a pump image (Pumpbild) is formed for the observer with a corresponding movement of the security element. If the mosaic reflects at least two views of the image pattern into different spatial regions, a stereoscopic image of the image pattern is formed for the viewer at a preselected viewing distance.

In all of the described embodiments, the parameters of size, contour shape, relief shape, reflectivity and spatial orientation of the mosaic element can be selected such that one or all of the motif images are visible to the observer in the flat orientation of the security element. Alternatively or additionally, these parameters can also be selected such that one or all of the motif images are only visible to the observer when the security element is deformed in a preselected manner.

In addition to the embodiment of the security element itself, which is viewed by the observer, these embodiments can also be considered, in which the parameters of the size, contour shape, relief shape, reflection capacity and spatial orientation of the mosaic element are selected such that, in a preselected illumination, the security element projects one or all of the motif images onto a receiving surface having a preselected geometry.

The security element according to the invention can be combined with other security features. For example, the security element can additionally have information in the form of patterns, symbols or codes, which are formed by non-reflective regions inside the mosaic. The reflective microstructures may also be combined with holographic patterned or hologram-like diffractive structures, or provided with: an embedded magnetic substance; embedded phosphorescent, fluorescent or other luminescent substances; the resulting conductivity is specifically set, in particular by specifically setting the resulting thickness of the metal reflective layer; color-tilting effects or dyed embossing lacquers and the like.

The invention also relates to a method for producing a security element of the aforementioned type, in which method a surface contour of an optically variable areal pattern, in particular a microstructure, is embossed into a lacquer layer, and the embossed lacquer layer is coated with a translucent functional layer, for example by means of PVD (physical vapor deposition). In this case, the surface contour is preferably embossed into a lacquer layer that can be cured by UV (ultraviolet) and the lacquer layer is cured after embossing.

The surface contours, in particular the microstructures, of the optically variable areal pattern can in principle be introduced into all known materials which can be used in an embossing process. In addition to the lacquers already mentioned and preferably curable by UV, it is therefore also possible to use, for example, thermoplastic embossing lacquers. The thermoplastic embossing lacquer is, for example, a thermoplastic plastic material into which the surface profile according to the invention is embossed by means of a suitable embossing tool under the action of heat. Very widely used are, for example, thermoplastic plastics which are provided with the microstructure according to the invention by means of a nickel stamp as embossing tool at a temperature of approximately 130 °.

The optically variable security element according to the invention can be present in particular as a patch or a label, as a security thread or as a security strip.

The invention also encompasses data carriers, in particular value documents, such as banknotes, identification cards or the like, which are equipped with a security element of the type mentioned.

Drawings

Further embodiments and advantages of the invention are explained below with reference to the drawings, which are not drawn to scale and are drawn to scale in order to improve the intuitiveness. In the drawings:

figure 1 shows a schematic representation of a banknote with an optically variable see-through security element according to the invention,

figure 2 shows a security element according to a first embodiment viewed in reflected light,

figure 3 shows a security element according to a first embodiment viewed in transmitted light,

figure 4 schematically shows the structure of a security element according to a first embodiment in cross-section,

figure 5 shows in cross-section the relief structure of a security element according to a second embodiment,

figure 6 shows in cross-section the relief structure of a security element according to a third embodiment,

FIG. 7 shows a detail of the individual micromirror regions in the smooth partial regions of the optically variable areal pattern, and

fig. 8 shows a detail of the individual micromirror regions in the rough partial region of the optically variable area pattern.

Detailed Description

The invention will now be illustrated by way of example of a security element for banknotes. To this end, fig. 1 shows a schematic representation of a banknote 1 having an optically variable see-through security element 2 according to the invention, which is arranged in the form of a patch on a through-opening of the banknote 1. The security element 2 exhibits a different colour appearance in reflected light than in transmitted light.

According to a first exemplary embodiment, the security element 2 displays a gold color when viewed in reflected light, wherein the pattern 3 of the arched cross protrudes three-dimensionally in the foreground region (see fig. 2) which is in front of the overlapping, evanescent background region 4.

When viewed in transmitted light, the security element 2 displays a blue color, the motif 3 protruding in sharp contrast from the light blue to gray background region 4 in a saturated dark blue (see fig. 3).

Fig. 4 schematically shows the structure of a security element 2 according to a first exemplary embodiment in cross section (along the dashed lines in fig. 2 and 3).

The security element is based on a carrier film 5, for example a polyethylene terephthalate (PET) film, which is provided with a transparent embossing lacquer 6. Embossed into the embossing lacquer 6 is a relief structure which is produced in such a way that a flat, optically variable, flat pattern (or two-dimensional pattern) is formed which has a plurality of facets 7 which substantially produce the optical effect of the illumination. The facets 7 are formed by planar surface elements and are each characterized by their shape, size and orientation. The orientation of the edge surface 7 is illustrated by the inclination α with respect to the plane 8 of the surface area. The facets 7 have a square profile with a dimension of 20 μm x 20 μm in this embodiment.

As shown in fig. 4, the edge surface 7 has the same inclination angle α in the partial regions 9 and 11, for example α is 30 °. The edge surface 7 is present in the subregion 10 at an angle α of 0 °. The partial regions 9 and 11 form so-called rough regions and the partial region 10 forms so-called smooth regions, respectively.

The translucent functional layer 12 can be formed, for example, from a three-layer film structure Al/SiO produced by evaporation or PVD₂Al or Ag/SiO₂Ag, the three-layer film structure being golden when viewed in reflected light and showing blue when viewed in transmitted light and having little color-tilting effect in transmitted light.

A further lacquer layer 13 is applied on top of the translucent functional layer 12, said further lacquer layer having substantially the same refractive index as the lacquer layer 6, which ensures that incident light traverses the layer sequence of the security element substantially without directional deflection irrespective of the local inclination angle α of the edge face 7 and thus produces a uniform brightness distribution in the plane of the flat pattern.

The partial regions 10 appear to the observer as a saturated dark blue when viewed in transmitted light, while the partial regions 9 and 11 respectively appear light blue to gray, so that the colored partial regions 10 stand out in sharp contrast in the form of foreground regions from the diffuse, colorless background regions 9 and 11.

In the first exemplary embodiment shown in fig. 4, the edge surface 7 is formed in the surface of the embossing lacquer 7 in such a way that the smooth partial region 10 is in the form of an edge surface having an inclination angle α of 0 °. However, it is also possible for the smooth partial regions to be formed by lands having a smaller inclination angle. Fig. 5 shows a security element according to a second embodiment, wherein only the relief structure of the embossing lacquer is shown in the drawing for the sake of clarity. The facets in the

partial regions

15 and 17 have the same inclination angle α, for example α equal to 30 °. In the

partial regions

14 and 16, the edge faces are each present at an angle α of 5 °. The

partial regions

15 and 17 form rough regions, respectively, and the

partial regions

14 and 16 form smooth regions, respectively.

In a first embodiment, shown in fig. 6, the facets 18 are oriented in the surface of the embossing lacquer in such a way that the observer perceives the surface area as a convex and/or concave surface relative to its true spatial shape. These relief structures are known from WO 2011/066990 a 2.

The transmission of a light beam through the layer structure according to the invention is explained with reference to fig. 7 and 8.

Fig. 7 shows a part of a smooth partial region of the optically variable area pattern. The layer structure comprises a carrier film 19, an embossing lacquer 20 and a translucent functional layer consisting of aluminum layers 21, 23 and SiO arranged therebetween₂Layer 22. The light beam 24 is not refracted or scattered as it is transmitted through the layer structure and enters the eye of the observer straight.

Fig. 8 shows a detail of the individual micromirror regions in the rough partial region of the optically variable area pattern. At the interface between the translucent functional layer and the embossing lacquer, the light beam is scattered or refracted, which forms a grey tone.

Claims

1. An optically variable security element for providing security to valuable articles, having a flat, optically variable planar pattern which exhibits a different color in transmitted light than in reflected light and has virtually no color gradient effect in transmitted light,

it is characterized in that the preparation method is characterized in that,

2. A see-through security element according to claim 1, wherein the area occupied by each partial area on the optically variable area-like pattern is at least 50 times larger than the area occupied on average by the individual facets of this surface area.

3. A see-through security element according to claim 1 or 2, wherein the facets of the at least two partial areas differ by 5 ° or more in the angle of inclination formed with respect to the plane.

4. A see-through security element according to claim 1 or 2, wherein the facets of the one partial region having the smaller inclination angle α have an inclination angle α in the range from 0 ° to 15 °, and the facets of the other partial region having the larger inclination angle α have an inclination angle α in the range from 15 ° to 30 °.

5. A see-through security element according to claim 1 or 2, wherein the edge surfaces are each provided with a translucent functional layer which, in transmitted light, exhibits a different color than in reflected light, the layer thickness of the functional layer varying with the angle of inclination α of the edge surfaces.

6. The see-through security element according to claim 5, wherein the layer thickness of the functional layer decreases with increasing tilt angle α.

7. The see-through security element according to claim 1 or 2, wherein the at least two partial regions are arranged in the form of a pattern and the pattern appears in transmitted light in two or more different, visually distinguishable chroma values with the naked eye.

8. A see-through security element according to claim 1 or 2, characterized in that the optically variable area pattern additionally has a black mask adapted to the oblique edge surface in partial areas, said black mask being used to adjust the see-through brightness of the edge surface in the respective partial area.

9. A see-through security element according to claim 1 or 2, wherein the prism surface is embossed in an embossing lacquer layer having a first refractive index, and a lacquer layer having a second refractive index is applied to the translucent functional layer, the second refractive index differing from the first refractive index by less than 0.3.

10. The see-through security element according to claim 1 or 2, wherein the translucent functional layer has a multi-layer structure with two translucent metal layers and a dielectric layer arranged between the two translucent metal layers.

11. The see-through security element according to claim 10, wherein the two translucent metal layers are formed independently of each other from a metal and the metals are each selected from the group consisting of Al, Ag, Ni, Cr, Cu, Au and alloys of one or more of the foregoing elements, and the dielectric layer is SiO₂Layer, ZnO layer, Al₂O₃Layer, TiO₂Layer, layer consisting of a nitride or oxynitride of one of the elements Si, Zn, Al or Ti, or MgF₂A layer or a nitrocellulose layer.

12. The see-through security element according to claim 11, characterized in that the nitrocellulose layer is obtainable by printing techniques.

13. The see-through security element according to claim 10, wherein the two semi-transparent metal layers are selected independently of each other from Al or Ag and the dielectric layer is SiO₂And (3) a layer.

14. The see-through security element according to claim 1 or 2, characterized in that the translucent functional layer is based on an effect pigment composition.

15. A see-through security element according to claim 1 or 2, wherein the optically variable area pattern appears blue when viewed in transmitted light and gold when viewed in reflected light.

16. The see-through security element according to claim 1 or 2, characterized in that the edge surfaces are designed as substantially flat surface elements.

17. A see-through security element according to claim 1 or 2, wherein the facets are arranged as a periodic grid and form a sawtooth grid, or the facets are arranged non-periodically.

18. A see-through security element according to claim 1 or 2, wherein the facets have a smallest or transverse dimension/greater than 2 μm and/or the facets have a height below 100 μm.

19. A data carrier with a see-through security element according to one of claims 1 to 18, characterized in that the see-through security element is arranged in or on a window region or through-opening of the data carrier.

20. A data carrier as claimed in claim 19, characterized in that the data carrier is a value document.

21. A data carrier as claimed in claim 20, characterized in that the data carrier is a banknote.