EP1827864B1 - Safety element provided with an optically-variable layer and method for the production thereof - Google Patents

Abstract

The present invention relates to a security element for securing valuable articles, having an optically variable layer (20) that imparts different color impressions at different viewing angles. According to the present invention, in a covering area (32), a semi-transparent ink layer (34) is disposed on top of the optically variable layer (20), the color impression of the optically variable layer (20) being coordinated with the color impression of the semi-transparent ink layer (34) in the covering area (32) when viewed under predefined viewing conditions.

Description

The invention relates to a security element for securing valuables with an optically variable layer, which conveys different color impressions at different viewing angles. The invention further relates to a method for producing such a security element, a transfer element, a security paper and a valuable article with such a security element.

Valuables, such as branded goods or documents of value, are often provided with security elements for the purpose of protection, which allow verification of the authenticity of the object of value and at the same time serve as protection against unauthorized reproduction. Valuables within the meaning of the present invention are in particular banknotes, stocks, bonds, certificates, vouchers, checks, high-quality admission tickets, but also other counterfeit-endangered papers, such as passports and other identification documents, as well as product security elements, such as labels, seals, packaging and the like. The term "object of value" in the following includes all such objects, documents and product protection means. The term "security paper" is understood to mean the precursor that can not yet be processed to a value document.

The security elements can be designed, for example, in the form of a security thread embedded in a banknote, an applied security strip or a self-supporting transfer element, such as a patch or a label, which is applied to a value document after its manufacture.

To prevent the adjustment of the security elements even with high-quality color copiers, the security elements often optical variable elements that give the viewer a different image impression under different viewing angles and show, for example, a different color impression or different graphic motifs.

In this context, it is known to use security elements with multi-layered thin-film elements, in which the color impression for the viewer changes with the viewing angle, and for example changes from green to blue, blue to magenta or magenta to green when the security feature is tilted. Such color changes when tilting a security element are referred to below as a color shift effect or color shift effect.

The publication US 3,858,977 describes such optical interference coatings with color shift effect in connection with security elements. Depending on the type and number of layers in the layer structure, two or more different color effects depending on the viewing angle may occur.

The publication WO 99/04983 A1 discloses certain properties of Schichter.

From the publication WO 03/068525 A1 A security element is known for storage in or application to a security document. The security element has a substrate with a reflection layer and an interference element with a color shift effect on each side of the reflection layer. In addition, the security element may have diffractive structures and / or areas with negative writing.

A value document with an optically variable material in the security element is also in the document WO 00/50249 A1 described. Here lies the optically variable material in the form of interference layer material or of liquid crystalline material that also provides different color impressions at different viewing angles. An embodiment is described in which two liquid-crystalline materials with thermochromic properties are used in adjoining areas, which have the same appearance under normal ambient conditions, but show a color change to different colors when heated.

If an area of a security element merely has a simple color-shift effect, then this is often only slightly noticeable and is easily overlooked as an authenticity feature. Two adjacent areas, each showing a color shift effect with different color changes, are more conspicuous, but are often perceived as confusing by viewers.

On this basis, the invention has for its object to provide a generic security element with high security against counterfeiting, which avoids the disadvantages of the prior art.

This object is achieved by the security element having the features of the main claim. A manufacturing method for the security element, a transfer element, a security paper and a valuable article 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 semitransparent ink layer is arranged over the optically variable layer in a covering region, wherein the color impression of the optically variable layer when observed under predetermined Viewing conditions adapted to the color impression of the semitransparent ink layer in the coverage area. The invention is based on the idea to use a combination of two color areas, which seem very similar from a certain viewing direction, and in which the color impression of one of the areas changes when tilted, the other area remains constant in color. Such a combination looks visually attractive, is self-explanatory for the user and also has a high security against counterfeiting.

The immediate vicinity of color variable and color constant area enhances the visual conspicuousness and thus draws the attention of the observer to the security element. The color-constant region simultaneously forms a visually stationary pole and a comparison point for the color-variable region in the authenticity test. The combination of the two color effects in the immediate vicinity makes an adjustment of the security element more difficult since freely available colors or foils with color-shift effects can no longer be used directly.

The use of a semitransparent ink layer causes, compared to the use of opaque color layers, a much greater approximation of the color impressions of the optically variable layer and the coverage area under the predetermined viewing conditions. In particular, as explained in detail below, unavoidable color variations of the optically variable layer within a production run can be accommodated and the brilliance and gloss in the coverage area can be adjusted to the high values typical of optically variable layers.

In a preferred embodiment, the semitransparent ink layer in a spectral range in which the color impression of the optically variable Layer is adapted to the color impression of the semitransparent ink layer, a light transmission between 60% and 100%, more preferably between 80% and 100%.

The semi-transparent ink layer can be applied in various ways, advantageously it is printed on the optically variable layer, for example in screen printing, gravure printing, flexographic printing, or any other suitable printing process.

In order to introduce additional features into the security element, the semitransparent color layer is present in preferred embodiments in the form of characters, patterns or codes. The semitransparent ink layer can also have recesses in the form of characters, patterns or codes.

A particularly appealing effect can be achieved if the optically variable layer and the semitransparent ink layer are matched to one another such that, when the security element is viewed vertically, the color impression of the optically variable layer outside the coverage area essentially corresponds to the color impression of the semitransparent ink layer in the coverage area. When viewed vertically, which often results from the first perception of a security element applied to a valuable item, the color-variable and the color-constant range initially impart essentially the same color impression. When tilting the security element, the color impression changes in the color-variable range, while it remains unchanged in the color-constant coverage area.

Instead of having a semi-transparent ink layer, the security element according to the invention can also be equipped with a screened ink layer. As a result, in comparison to the use of full-surface opaque color layers, an alignment of the color impressions of the optically variable layer and the coverage area under the predetermined viewing conditions is also effected. The screening thus creates a kind of semitransparency of the color layer, so that opaque color layers in the color-constant coverage area can also be used. In preferred embodiments, the screened ink layer is present as a negative screen, a positive screen or a bar screen.

The optically variable layer can consist of a single layer, but as a rule it is formed to achieve particularly attractive, optically variable effects of several partial layers.

In a preferred variant of the invention, the optically variable layer is formed by a thin-film element with color-shift effect, which preferably contains a reflection layer, an absorber layer and a dielectric spacer layer arranged between the reflection layer and the absorber layer. The color shift effect in such thin-film elements is based on viewing angle-dependent interference effects due to multiple reflections in the different sub-layers of the element. The path difference of the light reflected at the different layers depends on the one hand on the optical thickness of the dielectric spacer layer, which determines the distance between the absorber layer and the reflection layer, and on the other hand varies with the respective viewing angle.

Since the path difference is on the order of the wavelength of visible light, there are some due to cancellation and amplification Wavelengths an angle-dependent color impression for the viewer. By a suitable choice of material and thickness of the dielectric spacer layer, a multiplicity of different color-shift effects can be designed, for example tilting effects in which the color impression changes with the viewing angle from green to blue, from blue to magenta or from magenta to green.

Alternatively, the thin-film element may have a layer structure which, in addition to a reflective layer, comprises a dielectric spacer layer that is partially absorbent. An additional absorber layer can be omitted in this case.

The reflection layer of the thin-film element is preferably formed by an opaque or by a semitransparent metal layer. As a reflection layer, an at least partially magnetic layer can be used, so that a further authenticity feature can be integrated without requiring an additional layer in the layer structure.

The reflective layer may also have recesses in the form of patterns, characters or codes that form transparent or semi-transparent regions in the thin-film element. In the transparent or semi-transparent recess areas, the viewer is presented with a striking contrast to the surrounding color shift effect. In particular, the patterns, characters or codes in transmitted light can light up brightly when the thin-film element is applied to a transparent carrier.

The thin-film element can also be formed by absorber layers and dielectric spacer layers lying one on top of another, with several absorber and spacer layers also being arranged alternately one above the other could be. Instead of alternating absorber layers and dielectric spacer layers, it is also possible to provide exclusively dielectric spacer layers, wherein adjoining layers have very different refractive indices in order to produce a color-shift effect. The refractive indices of the adjoining dielectric spacer layers advantageously differ by at least 0.03.

The dielectric spacer layer is preferably formed by a print layer or by an ultrathin film, in particular a stretched polyester film.

As an alternative or in addition to recesses in the reflection layer, the absorber layer and / or the spacer layer may also have recesses in the form of patterns, characters or codes. There is no color shift effect in the recessed areas of the absorber layer or the spacer layer.

The thin-layer element formed from partial layers can also be present in the form of pigments or particles having a suitable particle size, distribution and form factor, which can be admixed to other materials, in particular a printing ink.

In another, likewise preferred variant of the invention, the optically variable layer contains one or more layers of liquid-crystalline material, in particular of cholesteric liquid-crystalline material. The liquid-crystalline material is expediently present as a liquid-crystalline polymer material or in the form of pigments embedded in a binder matrix.

In a further equally advantageous variant of the invention, the optically variable layer is formed by a diffractive diffraction structure. In this variant, the diffractive diffraction structure and the semitransparent color layer are advantageously matched to one another in such a way that they produce essentially the same color impression when viewed at a predetermined, non-perpendicular viewing angle. The security element according to the invention then shows the observer, when viewed vertically, first two different color impressions which equalize during tilting until the color impressions of the color-variable and the color-constant region coincide in the predetermined viewing direction.

In an advantageous embodiment, the diffractive diffraction pattern forms a grating image for displaying a true color image, which has a plurality of true color areas which illuminate in a desired true color when the grating image is illuminated.

Lattice patterns with a given lattice constant only diffract light of a certain wavelength into the viewing direction, so that the lattice fields occupied with a uniform lattice pattern always shine in one of the spectral colors. In order to represent the naturally occurring colors, the so-called "true colors", with lattice images, these true colors are displayed as a mixture of certain basic colors. Since the human eye has three distinct pin systems with overlapping sensitivity ranges in the red, green and blue portions of the visible spectrum, it is a common practice to select the colors red, green and blue as the primary colors. In the true color areas of a grid image, small subregions are then defined in which, for example, three different gratings are introduced, which bend red, green and blue light in the desired viewing direction. The with the grid patterns occupied area proportions are chosen according to the red, green and blue proportions of the respective true colors.

In one development of the invention, the security element contains at least one further layer provided with a security feature. The at least one further layer may advantageously comprise an optically effective microstructure which is arranged below the layer structure of optically variable layer and semitransparent color layer. In particular, the optically effective microstructure can be designed as a diffractive diffraction structure. Thus, for example, color-shift holograms can be realized in which the color-shift effect of the optically variable layer is combined with a holographic effect. Alternatively, the optically effective microstructure may also be a matt structure, which does not show any diffractive effects when viewed, but only has a scattering effect. In a further advantageous embodiment, the optically effective microstructure may be formed by an arrangement of micromirrors, microlenses or the like.

In order to enable an automatic authenticity check and possibly further sensory detection and processing of the valuables equipped with the security element, the at least one further layer may also contain machine-readable feature substances, in particular magnetic, electrically conductive, phosphorescent, fluorescent or other luminescent substances.

In an advantageous embodiment, the security element has a substrate on which the optically variable layer and the semitransparent color layer are arranged. This substrate may in particular be formed by a plastic film.

Preferably, the security element is a security thread, a security tape, a security strip, a patch or a label for application to a security paper, document of value or the like.

The invention also includes a method for producing a security element of the type described above, in which a semitransparent color layer is arranged in a covering region via an optically variable layer, which imparts different color impressions at different viewing angles. The color impression of the optically variable layer when viewed under predetermined viewing conditions is adapted to the color impression of the semitransparent ink layer in the coverage area.

The semitransparent ink layer is advantageously printed on the optically variable layer in the method according to the invention. It is advisable to apply the optically variable layer itself on a substrate, in particular imprint. When using a transparent substrate, it is also possible to first print this with the semitransparent ink layer, on which then in turn applied the optically variable layer, in particular can be printed.

In advantageous developments, the optically variable layer and / or the semitransparent ink layer are provided with recesses in the form of patterns, characters or codes.

The invention further comprises a transfer element for application to a security paper, value document or the like, which is equipped with a security element of the type described above. The transfer element preferably has a carrier foil on which the security element in the reverse order, as it later comes to rest on the security paper or the object of value, and then prepared by means of an adhesive layer, for. B. adhesive or lacquer layer is transferred in a hot embossing process in the desired contour contours on the security paper or the object of value. It is therefore appropriate first of all to apply the semitransparent ink layer to the carrier film, in particular to print it on. The optically variable layer is then advantageously printed on the semi-transparent ink layer. Alternatively, the optically variable layer can also be vapor-deposited or applied in another suitable manner. The separate carrier film can then be removed after the transfer of the layer structure of the security element. Alternatively, the carrier film can remain as a protective layer as an integral part of the security element on the layer structure. Optionally, between the security element and the carrier film, a release or release layer, for. As a wax may be provided.

A security paper for the production of security documents, such as banknotes, identity cards or the like, is preferably provided with a security element of the type described above. In particular, the security paper may comprise a carrier substrate made of paper or plastic.

The invention also includes a valuable article such as a brand name article, a value document or the like provided with a security element as described above. The valuable item may be, in particular, a security paper, a value document or a product packaging.

Further embodiments and advantages of the invention will be explained below with reference to the figures, in the representation thereof to a scale and proportioned reproduction has been omitted in order to increase the clarity.

Fig.1

eine schematische Darstellung einer Banknote mit einem eingebetteten Sicherheitsfaden und einem aufgeklebten Transferelement, jeweils nach einem Ausführungsbeispiel der Erfindung,

Fig. 2

eine Aufsicht auf einen Teilbereich des Sicherheitsfadens von Fig. 1,

Fig. 3

einen Querschnitt durch den Sicherheitsfaden von Fig. 2 entlang der Linie III-III,

Fig. 4

ein Diagramm, das die Reflexionsspektren eines Dünnschichtelements alleine und nach Aufdruck einer semitransparenten Farbschicht im Wellenlängenbereich λ von 300 nm bis 2000 nm zeigt,

Fig. 5

einen Querschnitt durch ein erfindungsgemäßes Transfermaterial,

Fig. 6

eine genauere Darstellung des Transferelements von Fig.1 in Aufsicht,

Fig. 7

einen Hologrammsicherheitsfaden nach einem weiteren Ausführungsbeispiel der Erfindung im Querschnitt,

Fig. 8

den Schichtaufbau eines erfindungsgemäßen Sicherheitselements mit einer Flüssigkristallstruktur als optisch variabler Schicht, und

Fig. 9

den Schichtaufbau eines erfindungsgemäßen Sicherheitselements mit einer diffraktiven Beugungsstruktur als optisch variable Schicht,

Fig. 10

ein Diagramm, das das Transmissionsspektrum einer mit einer semitransparenten Farbschicht bedruckten transparenten Kunststofffolie im Wellenlängenbereich λ von 300 nm bis 750 nm zeigt.

Show it:

Fig.1

1 is a schematic representation of a banknote with an embedded security thread and a glued transfer element, each according to an embodiment of the invention,

Fig. 2

a view of a portion of the security thread of Fig. 1 .

Fig. 3

a cross section through the security thread of Fig. 2 along the line III-III,

Fig. 4

a diagram showing the reflection spectra of a thin-film element alone and after printing a semitransparent ink layer in the wavelength range λ from 300 nm to 2000 nm,

Fig. 5

a cross section through a transfer material according to the invention,

Fig. 6

a more detailed representation of the transfer element of Fig.1 in supervision,

Fig. 7

a hologram security thread according to another embodiment of the invention in cross-section,

Fig. 8

the layer structure of a security element according to the invention having a liquid crystal structure as an optically variable layer, and

Fig. 9

the layer structure of a security element according to the invention with a diffractive diffraction structure as optically variable layer,

Fig. 10

a diagram showing the transmission spectrum of a printed with a semi-transparent ink layer transparent plastic film in the wavelength range λ from 300 nm to 750 nm.

The invention will now be explained in more detail using the example of a banknote. Fig.1 shows a schematic representation of a banknote 10 with two security elements 12 and 16, which are each formed according to an embodiment of the invention. The first security element represents a security thread 12 that emerges at certain window areas 14 on the surface of the banknote 10, while it is embedded in the intervening areas inside the banknote 10. The second security element is formed by a glued transfer element 16 of any shape.

The structure of the security thread 12 will now be described with reference to FIGS FIGS. 2 and 3 explained in more detail. Fig. 2 shows a plan view of a portion of the security thread 12, Fig. 3 represents a cross section through the security thread along the line III-III of Fig. 2 represents.

The security thread 12 includes a thin-film element 20 with a color-shift effect, which is applied to a transparent carrier foil 22. The optical Variable thin-film element 20 comprises a reflective layer 24 formed by an opaque aluminum layer, an ultrathin spacer layer 26 applied to the reflective layer, and a partially transparent absorber layer 28, eg of chromium. As explained above, the color shift effect of the thin film element 20 is due to interference effects due to multiple reflections in the different sublayers 24, 26, 28 of the element.

One half of the security thread 12 forms a covering area 32, in which a semi-transparent ink layer 34 is printed on the thin-film element 20. In the immediately adjacent, uncovered region 36, the optically variable layer 20 is present without printed ink layer. The thin-film element 20 and the color layer 34 are matched to one another in such a way that they produce substantially the same color impression at a perpendicular viewing angle. The color impression of the thin-film element 20 at a normal viewing angle is also referred to below as a vertical tilting color.

When the security thread 12 is tilted, the color impression of the thin-film element 20 changes in the uncovered region 36, while the color impression in the covering region 32 remains virtually unchanged. By such a combination of a color-variable range with a color-constant range in the immediate vicinity, the visual conspicuousness of the color-shift effect is significantly enhanced because the human eye reacts more strongly to the color differences that occur than to the color change per se. The viewer's attention is therefore drawn even more to the security feature. The operation of the security element is also self-explanatory, so that it can easily be checked for authenticity by anyone.

The combination of a color-calm element with a color-tilting element is generally perceived as visually very appealing. For potential counterfeiters, the combination of the two color effects in the immediate vicinity is a significant complication of the adjustment, since freely available colors or slides with color shift effects can not be used directly.

The use according to the invention of a semi-transparent ink layer 34 has several advantages which will be explained in detail below.

The use of a semi-transparent ink layer 34 leads to an additional alignment of the color impression of the thin-film element 20 in the uncovered region 36 and the color impression of the semitransparent ink layer 34 in the overlap region 32. While the color location of the printed semitransparent ink layer 34 can be set very accurately and reproducibly, this varies vertical tilting color, in which the thin-film element appears at a normal viewing angle, by manufacturing fluctuations usually something of security element to security element. These color variations, which are due to the extremely high sensitivity of the color visible at a normal angle to the layer thickness of the dielectric spacer layer, are small, but quite perceptible to the naked eye.

If the color layer 34 is semitransparent according to the invention, the vertical tilt color of the thin-film element 20 partially shines through the color layer 34 and contributes to the overall color impression of the security element in the overlap area 32 when viewed perpendicularly. Now varies the vertical tilt color of the thin-film element 20 in the uncovered region 36 of security element to security element something, then the color impression in the covering area 32 changes accordingly by the translucent component. The overall color impression in the overlapping region 32 thus adapts to the color impression in the uncovered region 36.

The contribution of the vertical tilt color to the overall color impression is in the diagram of Fig. 4 illustrating the reflection spectrum 40 of the thin-film element 20 in the uncovered region 36 at a perpendicular viewing angle. Also shown is the reflection spectrum 42 of the combination of thin-film element 20 and semitransparent ink layer 34 in the covering region 32. It can be clearly seen that the color impression of the thin-film element 20 remains visible through the semitransparent ink layer 34 and amounts to the overall color impression. For vertical viewing, in spite of the unavoidable small thickness variations of the spacer layer, it is possible to achieve an excellent match of the color impressions in the two areas.

However, the semitransparent ink layer 34 is highly translucent only at near vertical viewing angles. At an oblique viewing angle, it reflects significantly more light compared to perpendicular viewing so that the light portion of the underlying thin film element 20 is forced into the background.

Overall, when viewed vertically, the translucent color contribution of the thin-film element 20 in the overlapping region 32 contributes to the equalization of the color impressions of the two adjacent regions. At an oblique viewing angle, the translucent color contribution occurs in the background, so that then the color-constant contribution of the semitransparent color layer 34 dominates the overall impression of the covering region 32.

The color contribution of the semitransparent color layer is now based on an in Fig. 10 illustrated transmission spectrum 46 of a color printed, transparent plastic film explained in more detail. The semi-transparent ink layer, in the example a red ink, has a very good transparency in the red spectral range (about 90%), while z. B. in the green spectral range at a wavelength of about 550 nm only has a light transmittance of about 15%. The effect according to the invention becomes effective precisely due to this different spectral transmission. In particular, the color impression of the semitransparent ink layer in the overlapping region of an underlying tilting color, which appears magenta, for example, at a perpendicular viewing angle, fits well, since the semitransparent ink layer in the relevant spectral region is almost transparent. If, however, the security element is viewed at a different tilt angle, the color impression of the tilt color changes, for example, from magenta to green. The semitransparent color layer has a much lower transparency in this wavelength range, so that the translucent color contribution of the tilting color passes into the background and instead the color-constant contribution of the overlying color layer dominates.

A further advantage of using semitransparent color layers is the alignment of the brilliance of the two partial areas 32 and 36. The reflection layer 24 of the thin-film element 20 is usually designed to reflect about 90% of the incident light, the color-shift effect therefore occurring in the uncovered area 36 very bright and with high brilliance in appearance. The luminance value or the L value in the CIELab color space, which essentially indicates the proportion of the reflected light, is therefore very high in the uncovered area 36. Common inks achieve such high brilliance and high L-values.

Therefore, when an opaque ink for covering is used, the color impression of the vertical tilt color and the ink will be different even if the color loci (expressed by the red-green color information a and the blue-yellow color information b in the CIELab system) are almost the same , When using a semi-transparent ink layer, an additional light contribution of the thin-film element 20 is obtained in the overlapping area 32, so that its brilliance is increased and thus further approximated to the color impression of the uncovered area 36.

Moreover, the interference layer structure of the thin film element 20 is extremely flat, so that the uncovered region 36 also has a high gloss and acts almost like a colored mirror. The gloss of printing inks is much lower in comparison. For opaque inks, this difference in glossiness is evident to a viewer, even if the color loci (again expressed by a and b in the CIELab system) are nearly identical. The use of a semi-transparent ink layer 34 increases the gloss in the coverage area 32 thanks to the translucent high-gloss thin-film element 20, so that the visual impression for the viewer is matched to the impression of the uncovered area 36.

In the reflection layer 24 of the thin-film element 20 are in the embodiment of the FIGS. 2 and 3 recesses 30 are introduced, which can form a negative writing, for example. In the area of these recesses 30, the thin-film element 20 is transparent, so that in addition to the described effects, a striking contrast effect in the transmitted light results.

If a security element, such as the transfer element 16 of Fig.1 applied in the form of a patch or strip on the valuable item to be protected, so it is useful initially prepared in the form of label material or transfer material, triggered in the desired shape and then transferred to the object to be protected. An example of such a transfer material is in Fig. 5 shown in cross-section, the triggered, adhered to a valuable item transfer element 16 is in Fig. 6 shown in supervision.

The transfer material 50 contains a carrier layer 52, in particular a plastic film, onto which the layer structure 54 of optically variable layer and semitransparent color layer is applied. It may be advantageous to provide a separating layer 56 between the layer structure 54 and the carrier layer 52. On the layer structure 54 of the transfer material, an adhesive layer 58, for example a hot melt adhesive layer, is provided, with which the security element can be fastened on the object to be protected.

For transfer, the transfer material 50 is placed on the article and the adhesive layer 58 activated, for example by heat. Subsequently, the carrier layer 52 is removed from the article, so that only the adhered layer structure 54 remains on the object to be protected. The layer sequence of the layer structure 54 is reversed by adhering to the object to be protected with respect to the layer in the transfer material 50, so that the semitransparent ink layer on top of the article must be applied to the carrier layer 52 before the optically variable layer in the production of the transfer material.

Fig. 6 shows the triggered and glued transfer element 16 in supervision. The transfer element contains like the security thread of FIGS. 2 and 3 an optically variable thin-film element 60 with a color shift effect and a partially arranged above the thin-film element 60, semitransparent ink layer 62.

In the exemplary embodiment, the thin-film element 60 and the color layer 62 are formed by concentric circular disks, the semitransparent ink layer 62 covering only the central, inner region of the thin-film element 60. In the outer, uncovered region 64, in which the thin-film element 60 is present without covering by a colored layer, recesses 66 in the form of the lettering "PL 2004" are introduced into the reflection layer of the thin-film element 60, which appear bright in transmitted light.

The thin-film element 60 and the semi-transparent ink layer 62 are coordinated with one another in this exemplary embodiment such that they produce substantially the same color impression at a perpendicular viewing angle. The entire circular disk of the thin-film element 60 thus appears with a uniform color impression when viewed vertically. When tilting the transfer element 16 changes due to the color shift effect of the thin-film element 60, the color impression of the outer, uncovered ring 64, while the inner, overprinted with the semitransparent ink layer 62 disc remains constant in color.

The security element of in Fig. 7 1 shows a hologram security thread 70 in which an optically variable layer with a color shift effect is additionally provided with a planar optical microstructure. This microstructure may be, for example, a diffraction structure 74. For this purpose, an embossing lacquer layer 78 is applied to a carrier film 76, into which the desired diffraction structure 74 is embossed.

The thin-film element 72, the layer structure of which, for example, as in Fig. 3 can be formed, is applied to the embossing lacquer layer 78.

A semitransparent ink layer 80 is applied to a portion of the hologram security thread 70, and the semitransparent ink layer 80 and the thin film element 72 are matched to each other to produce substantially the same color appearance at a perpendicular viewing angle. In addition to those associated with the FIGS. 2 and 3 the hologram security thread 70 exhibits a holographic effect combined with the color-shift effect.

In the embodiments described so far, the optically variable layer is always formed by a thin-film element with a color-shift effect. However, the combination of optically variable layer and semitransparent color layer according to the invention is not limited to such embodiments, but can likewise be used for all other types of optically variable layers, as described below using the example of a liquid crystal structure ( Fig. 8 ) and a diffractive diffraction structure ( Fig. 9 ).

Fig. 8 shows the basic layer structure of a security element 90 according to the invention, in which the optically variable layer contains one or more layers of liquid-crystalline material. For this purpose, a smooth film 92, for example a PET film of good surface quality, is provided with an absorbing, dark background layer 94. Onto this background layer 94 is applied one or more layers 96-1, 96-2, ... 96-n of a cholesteric liquid crystalline material. Alignment layers and / or adhesive layers 98 may be provided between the liquid crystal layers, which serve to align the liquid crystals in the liquid crystal layers or the connection of the individual liquid crystal layers and to compensate for unevenness in the background.

A portion of the security element 90 is provided with a semi-transparent ink layer 100. The semitransparent ink layer and the liquid crystal structure are matched to one another in such a way that they produce substantially the same color impression at a perpendicular viewing angle. When tilting the security element 90, the liquid crystal structure offers the viewer a changing color impression, while the color impression of the area provided with the color layer 100 remains substantially constant.

In the security element 110 of Fig. 9 For example, the optically variable layer is formed by a diffractive diffraction structure which, when observed under predetermined viewing conditions, provides a certain color impression to which the semitransparent color layer is tuned.

The security element 110 contains a base film 112 and a printed, embossed and cured UV lacquer layer 114. The relief structure of the lacquer layer 114 is provided with a thin reflective metal layer 116 or a dielectric layer in a subsequent vapor deposition step, so that depending on the embossing a diffractive diffraction structure with the desired properties arises. For example, in diffuse illumination, the diffractive structure may diffract red light into a predetermined viewing direction 120. For illustration, an oblique viewing direction 120 is shown in the figure with a viewing angle of 60 ° to the vertical.

In a partial region, the diffractive diffraction structure is provided with a semitransparent color layer 118, wherein the semitransparent color layer 118 and the diffraction structure are matched to one another substantially when viewed from the predetermined viewing direction 120 produce the same color impression. In the exemplary embodiment, the semitransparent color layer 118 is selected so that it also reflects red light in the viewing direction 120 under diffuse illumination.

The security element 110 of Fig. 9 shows the viewer when viewed vertically two different color impressions. When the security element is tilted, the color impressions of the area covered with the color layer and the area uncovered equalize until they practically coincide from the predetermined viewing direction 120. By means of a suitable design of the diffractive diffraction structure, it is possible to set a very narrow angular range for the match of the color impressions, so that a characteristic color effect which is difficult to imitate arises.

Of course, in addition to the layers described in the preceding embodiments, further layers may be present, which have been omitted here for reasons of clarity. Thus, the above layered structures may have protective layers formed, for example, by a plastic layer or film. In addition, the individual layers of the security elements, in particular the optically variable layer and the semitransparent ink layer, can be spaced apart by further transparent layers or be present on different sides of a transparent carrier film.

Claims (43)

1. A security element (12) for securing valuable articles (10), having an optically variable layer (20) that imparts different color impressions at different viewing angles, characterized in that, in a covering area (32), a semi-transparent ink layer (34) is disposed on top of the optically variable layer (20) and that, when viewed under predefined viewing conditions, the color impression of the optically variable layer (20) is coordinated with the color impression of the semi-transparent ink layer (34) in the covering area (32).
2. The security element (12) according to claim 1, characterized in that, in a spectral range in which the color impression of the optically variable layer (20) is coordinated with the color impression of the semi-transparent layer (34), the semi-transparent ink layer (34) exhibits a transmittance between 60% and 100%, preferably between 80% and 100%.
3. The security element (12) according to claim 1 or 2, characterized in that the semi-transparent ink layer (34) is imprinted on the optically variable layer (20).
4. The security element (12) according to at least one of claims 1 to 3, characterized in that the semi-transparent ink layer (34) is present in the form of characters, patterns or codes.
5. The security element (12) according to at least one of claims 1 to 4, characterized in that the semi-transparent ink layer (34) exhibits gaps in the form of characters, patterns or codes.
6. The security element (12) according to at least one of claims 1 to 5, characterized in that, when the security element (12) is viewed vertically, the color impression of the optically variable layer (20) outside the covering area (32) corresponds substantially to the color impression of the semi-transparent ink layer (34) in the covering area (32).
7. The security element (12) for securing valuable articles, having an optically variable layer (20) that imparts different color impressions at different viewing angles, characterized in that, in a covering area (32), a screened ink layer is disposed on top of the optically variable layer (20) and that, when viewed under predefined viewing conditions, the color impression of the optically variable layer (20) is coordinated with the color impression of the screened ink layer in the covering area (32).
8. The security element (12) according to claim 7, characterized in that the screened ink layer exhibits a negative screen, a positive screen or a line grating.
9. The security element (12) according to at least one of claims 1 to 8, characterized in that the optically variable layer (20) is formed from multiple sub-layers.
10. The security element (12) according to at least one of claims 1 to 9, characterized in that the optically variable layer (20) is formed by a thin-film element (20) having a color-shift effect.
11. The security element (12) according to claim 10, characterized in that the thin-film element (20) includes a reflection layer (24), an absorber layer (28) and a dielectric spacing layer (26) disposed between the reflection layer (24) and the absorber layer (28).
12. The security element (12) according to claim 10, characterized in that the thin-film element (20) includes a reflection layer (24) and a dielectric spacing layer (26), the dielectric spacing layer (26) being formed to be partially absorptive.
13. The security element (12) according to claim 11 or 12, characterized in that the reflection layer (24) is formed by an opaque or a semi-transparent metal layer.
14. The security element (12) according to at least one of claims 11 to 13, characterized in that the reflection layer (24) is present at least in some areas as a magnetic layer.
15. The security element (12) according to claim 10, characterized in that the thin-film element (20) includes at least one absorber layer (28) and at least one dielectric spacing layer (26), the absorber layers (28) and the dielectric spacing layers (26) being stacked alternatingly.
16. The security element (12) according to claim 10, characterized in that the thin-film element (20) includes multiple dielectric spacing layers (26), adjoining layers of the dielectric spacing layers (26) having highly different refractive indices.
17. The security element (12) according to claim 16, characterized in that the refractive indices of the adjoining dielectric spacing layers (26) differ by at least 0.03.
18. The security element (12) according to at least one of claims 11 to 17, characterized in that the dielectric spacing layer (26) is formed by a printing layer.
19. The security element (12) according to at least one of claims 11 to 18, characterized in that the dielectric spacing layer (26) is formed by an ultrathin foil, especially a stretched polyester foil.
20. The security element (12) according to at least one of claims 11 to 14, characterized in that the reflection layer (24) exhibits gaps (30) in the form of patterns, characters or codes that form transparent or semi-transparent areas in the thin-film element (20).
21. The security element (12) according to at least one of claims 11 to 20, characterized in that the absorber layer (28) and/or the spacing layer (26) exhibits gaps (30) in the form of patterns, characters or codes in which no color-shift effect is perceptible.
22. The security element (12) according to at least one of claims 11 to 19, characterized in that the thin-film element (20) is present in the form of pigments or particles having a suitable size and form factor.
23. The security element (12) according to at least one of claims 1 to 9, characterized in that the optically variable layer (20) includes one or more layers composed of liquid crystal material, especially composed of cholesteric liquid crystal material.
24. The security element (12) according to claim 23, characterized in that the liquid crystal material is present as a liquid crystal polymer material or in the form of pigments embedded in a binder matrix.
25. The security element (12) according to at least one of claims 1 to 9, characterized in that the optically variable layer (20) is formed by a diffraction pattern.
26. The security element (12) according to claim 25, characterized in that the diffraction pattern forms a grating image for depicting a true color image that exhibits a plurality of true color regions that shine in a desired true color when the grating image is illuminated.
27. The security element (12) according to at least one of claims 1 to 26, characterized in that the security element (12) includes at least one further layer provided with a security feature.
28. The security element (12) according to claim 27, characterized in that the at least one further layer comprises an optically effective microstructure that is disposed below the layer structure composed of the optically variable layer and the semi-transparent ink layer.
29. The security element (12) according to claim 28, characterized in that the optically effective microstructure is a diffraction pattern, a matte pattern or an optically effective microstructure produced by micromirrors or microlenses.
30. The security element (12) according to at least one of claims 27 to 29, characterized in that the at least one further layer includes machine-readable feature substances, especially magnetic, electrically conductive, phosphorescent, fluorescent or other luminescent substances.
31. The security element (12) according to at least one of claims 1 to 30, characterized in that the security element (12) exhibits a substrate on which the optically variable layer (20) and the semi-transparent ink layer (34) are disposed.
32. The security element (12) according to claim 31, characterized in that the substrate is formed by a plastic foil.
33. The security element (12) according to at least one of claims 1 to 32, characterized in that the security element (12) forms a security thread (12), a security band, a security strip, a patch or a label for application to a security paper, value document or the like.
34. A method for manufacturing a security element (12) according to at least one of claims 1 to 33, in which, in a covering area (32), a semi-transparent ink layer (34) is disposed on top of an optically variable layer (20) that imparts different color impressions at different viewing angles, the color impression of the optically variable layer (20) being coordinated with the color impression of the semi-transparent ink layer (34) in the covering area (32) when viewed under predefined viewing conditions.
35. The method according to claim 34, characterized in that the semi-transparent ink layer (34) is imprinted on the optically variable layer (20).
36. The method according to claim 34 or 35, characterized in that the optically variable layer (20) is applied to, especially imprinted on, a substrate.
37. The method according to at least one of claims 34 to 36, characterized in that the optically variable layer (20) and/ or the semi-transparent ink layer (34) is provided with gaps (30) in the form of patterns, characters or codes.
38. A transfer element for application to a security paper, value document or the like, having a security element (12) according to at least one of claims 1 to 37.
39. The transfer element according to claim 38, characterized in that the transfer element comprises a substrate foil.
40. A security paper for manufacturing security or value documents, such as banknotes, checks, identification cards or the like, that is furnished with a security element (12) according to at least one of claims 1 to 37 or a transfer element according to claim 38 or 39.
41. The security paper according to claim 40, characterized in that the security paper comprises a carrier substrate composed of paper or plastic.
42. A valuable article, such as a branded article, value document or the like, having a security element (12) according to at least one of claims 1 to 37 or a transfer element according to claim 38 or 39.
43. The valuable article according to claim 42, characterized in that the valuable article is a security paper, a value document or a product packaging.

Images