HK1106934B - A security element and the method for manufacturing the same, a transfer element, a security paper and a valuable article - Google Patents

Abstract

The invention relates to a safety element for protecting valuable objects comprising an optically-variable layer (20) producing different colour effects when viewed at different angles. According to said invention, a semi-transparent colour layer (34) is disposed in a covering area (32) over the optically variable layer (20), wherein the colour effect produced by said optically variable layer (20) when viewed under predetermined viewing conditions is adapted to the colour effect produced by the semi-transparent colour layer (34) in the covering area.

Description

Security element, transfer element, security paper and valuable article

Technical Field

The invention relates to a security element for protecting valuable articles, which security element has an optically variable layer which gives the impression of different colours at different viewing angles. The invention also relates to a method for producing such a security element, a transfer element, a security paper and a valuable article having such a security element.

Background

For protection, valuable items, such as branded items and value documents, are often provided with security elements which allow the authenticity of the valuable item to be verified, while at the same time serving as protection against unauthorized copying. The meaning of the valuable items according to the invention includes in particular banknotes, stocks, bonds, certificates, tickets, cheques, valuable entrance tickets and other paper items which are at risk of counterfeiting, such as passports and other identity documents, and also product-protecting elements, such as labels, seals, packaging or the like. In the following, the term "valuable item" encompasses all such items, documents and product protection components. The term "security paper" should be understood to mean a non-flowable precursor (non-flowable precursor) of a value document.

The security elements can be formed, for example, in the form of embedded security threads, applied to banknotes, for example security strips applied in patches or labels or self-supporting transfer elements (transfer elements), which are used on the value documents after their production.

In order to prevent the reproduction of security elements with even high-quality color copiers, the security elements have a plurality of optically variable elements which give the viewer different image impressions from different viewing angles and which, for example, give different color impressions or different motif themes.

In this connection it is known to use security elements having a multi-layer thin film element in which the colour impression for the viewer varies with the viewing angle, the colour changing as the security feature is tilted, for example moving from green to blue, from blue to magenta or from magenta to green. Such a color change when the security element is tilted is referred to hereinafter as color shift effects.

Publication US3,858,977 describes such an optical interference coating with a color shift effect in combination with a security element. Depending on the type and number of layers in the layer structure, different color effects may occur with two or more viewing angles.

A security element embedded in or applied to a security document is known from publication WO03/068525a 1. The security element has a substrate with a reflective layer, on each side of which there are interference elements with a colour shift effect. In addition, the security element may have a diffractive pattern and/or areas with reversed text.

Documents of value with optically variable materials in security elements are also described in the publication WO00/50249A 1. Here, the optically variable material is present in the form of an interference layer material or a liquid crystal material, likewise producing different color impressions at different viewing angles. There is described an embodiment in which two liquid crystal materials having thermochromic properties are used in the border region, having the same appearance under normal ambient conditions, but each exhibiting a different colour shift when heated.

If the regions of the security element have only a simple color shift effect, this effect is often only less pronounced and can easily be ignored as a reliable feature. Indeed, the color shift effect with different color variations is more pronounced for each of the two adjacent regions, but is often perceived as confusing by the viewer.

Disclosure of Invention

Based on this, it was an object of the present invention to provide a generic security element with high security against forgery, in order to overcome the drawbacks of the background art.

This object is achieved by a security element having the features of the main claim. A method for the manufacture of a security element, a transfer element, a security paper and a valuable article having such a security element is provided in the subclaims. Improvements of the invention are the subject of the dependent claims.

According to the invention, in the cover area, a translucent ink layer is arranged on the optically variable layer, the color impression of the optically variable layer being coordinated with the color impression of the translucent ink layer in the cover area when viewed under predetermined viewing conditions. The invention is here based on the idea of using a combination of two color regions which look very similar from a certain viewing direction and in which the color impression of one of the regions changes when tilted, but the other region remains color-constant. Such a combination seems optically attractive and clear to the user himself, and therefore further has a high security against forgery.

The direct proximal ends of the color-variable and color-constant regions enhance the optical significance and thus direct the attention of the observer to the security element. Here, the color constant region simultaneously forms a visual balance influence (stabilization influence) in the plausibility check and forms a comparison point with the color variable region. The combination of the two color effects in the immediate proximal end prevents the reproduction of the security element, since the freely available ink or foil with the color-shifting effect can no longer be used directly.

The use of a translucent ink layer enables a better adaptation of the color impression of the optically variable layer and the covered area under predetermined viewing conditions than the use of an opaque ink layer. In particular, as explained in detail below, unavoidable color variations in the optically variable layer can be detected in the production flow and the brilliance and gloss in the cover layer are adjusted to high values typical for optically variable layers.

In a preferred embodiment, the translucent ink layer has a transmission of 60% to 100%, preferably between 80% and 100%, in a spectral range in which the color impression of the optically variable layer is coordinated with the color impression of the translucent ink layer.

The translucent ink layer, which is advantageously printed on the optically variable layer, can be applied in different ways, for example by screen printing (screen printing), intaglio printing (intaglio printing), flexo printing (flexo printing) or other suitable printing methods.

In order to introduce additional features into the security element, in a preferred embodiment the translucent ink layer is present in the form of characters, patterns or codes. The translucent ink layer itself may also have gaps in the form of patterns, characters or codes.

A particularly attractive effect can be achieved if the optically variable layer and the translucent ink layer are coordinated with one another in such a way that, when the security element is viewed perpendicularly, the color impression of the optically variable layer outside the covering region substantially corresponds to the color impression of the translucent ink layer in the covering region. Thus, when viewed vertically, which often occurs when a security element applied to a valuable article is first felt, the color-changeable and color-constant zones first produce substantially the same color impression. When the security element is tilted, the color impression varies in the color variable region and remains the same in the color constant coverage region.

Instead of a translucent ink layer, the security element according to the invention may also be provided with a screen ink layer (screen ink layer). In this way, an adjustment of the color impression of the optically variable layer and the covering area under predetermined viewing conditions can likewise be achieved in comparison with the use of an adjoining opaque ink layer. Thus, with the aid of the added screen, a translucent ink layer is created so that in the area of constant coverage of the color, an opaque ink layer can also be used. In a preferred embodiment, the screen ink layer is present as a negative (negative) screen, a positive (positive) screen or a line grating.

The optically variable layer may consist of a single layer, but in order to achieve a more attractive optically variable effect it is typically formed of a plurality of sub-layers.

In a preferred variant of the invention, the optically variable layer is formed by a thin film element having a color shifting effect and preferably comprising a reflective layer, an absorbing layer and a dielectric spacing layer (dielectric spacing layer) arranged between the reflective layer and the absorbing layer. In such thin film elements, the color-shift effect is based on a viewing-angle-dependent (viewing-angle-dependent) interference effect due to multiple reflections in 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 absorbing layer and the reflecting layer and on the other hand it varies with each viewing angle.

Since the path difference is the size of the wavelength of visible light, and the destruction and amplification of the interference of certain wavelengths, the observer produces an angle-dependent color impression. By suitable choice of the material and thickness of the dielectric spacer layer, a number of different color-shifting effects can be devised, such as a tilting effect, in which the color impression varies 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 the reflective layer, comprises a dielectric spacer layer which is partly formed to be absorbent. In this case, the additional absorption layer may be omitted.

The reflective layer of the thin-film element is preferably formed by an opaque or by a semi-transparent metal layer. As a reflective layer, it is magnetic at least in some regions, so that no additional layers in the layer structure are required, and the authenticity feature can be further integrated.

The reflective layer may also have gaps in the form of patterns, characters or codes, which gaps form transparent or translucent areas in the thin-film element. In the transparent or translucent gap region, a viewer can see a color shift effect that makes a significant contrast with the surroundings. In particular, when the thin-film element is applied to a transparent substrate, a pattern, character or code can be brightly lit in transmitted light.

The thin-film element can also be formed by stacking absorber layers (stacked absorbers) and dielectric gap spacers, alternatively also a plurality of absorber layers and spacer layers can be stacked. Instead of alternating absorbing layers and dielectric spacers, it is also possible to exclusively provide dielectric spacers, with adjacent layers having significantly different refractive indices, so that a color-shifting effect results. Here, the refractive indices of the adjoining dielectric spacer layers expediently differ by at least 0.03.

The dielectric spacer layer is preferably formed by a printed layer or by an ultra thin foil, especially a stretched polyester foil.

Alternatively or in addition to the gaps in the reflective layer, the absorbing layer and/or the spacer layer may also have gaps in the form of patterns, characters or codes. No color shift effect occurs in the gap region of the absorber layer or spacer layer.

The film elements formed by the sub-layers can also be present in the form of pigments or particles which have a suitable particle size, distribution and form factor and can be added to other materials, in particular printing inks.

In a further, likewise preferred variant of the invention, the optically variable layer comprises one or more layers consisting of liquid crystal material, in particular of cholesteric liquid crystal material. The liquid-crystalline material is here suitably present as a liquid-crystalline polymer material or in the form of a pigment embedded in a binder matrix.

In a further similar preferred variant of the invention, the optically variable layer is formed by a diffraction pattern. In this variant, the diffractive pattern and the translucent ink layer are preferably coordinated with one another in such a way that they produce substantially the same color impression when viewed at a predetermined, non-perpendicular viewing angle. The security element according to the invention thus first displays two different color impressions to the observer when viewed vertically, which when tilted are adjusted to one another until the color impressions of the color-variable and color-constant regions match in the predetermined viewing direction.

In a preferred embodiment, the diffraction pattern forms a grating image for depicting a true color image having a plurality of true color regions that emit light in a predetermined true color when the grating image is illuminated.

A grating pattern with a given grating constant diffracts light of only certain wavelengths in the viewing direction, such that the grating area covered with the uniform grating pattern always emits light in one of the spectral colors. In order to be able to generate naturally occurring colors, so-called true colors, which are generated as mixed colors of certain main colors, with the raster image. Since the human eye has three different cone systems (con systems) with overlapping sensitivity ranges in the red, green and blue parts of the visible spectrum, the usual approach is to select the red, green and blue colors as the dominant colors. The small sub-regions in the real color area of the grating image are then defined, for example, as three different gratings that are introduced to diffract red, green and blue light in the desired viewing direction. Here, the percentage of the surface covered with the grating pattern is selected according to the percentage of red, green and blue of each real color.

In a refinement of the invention, the security element comprises at least one further layer having a security feature. The at least one further layer may preferably comprise an optically active microstructure (effective microstructure) arranged below the layer structure consisting of the optically variable layer and the translucent ink layer. In particular, the optically active microstructures may be formed as diffractive patterns. In this way it is possible to realize color-shift holograms (color-shift holograms), for example in which the color-shifting effect of the optically variable layer is combined with the holographic effect. Alternatively, the optically active microstructures may also be matte patterns (matte patterns) which do not show diffractive effects when viewed but only have scattering effects. In a further advantageous embodiment, the optically active microstructures can be provided by micromirrors, microlenses, etc.

In order to facilitate automatic authenticity checking and, if applicable, further sensor-based detection and processing of the valuable item provided with the security element, the at least one further layer may also comprise a machine-readable feature substance, in particular a magnetic, electrically conductive, phosphorescent, fluorescent or other luminescent substance.

In an advantageous embodiment, the security element has a substrate on which the optically variable layer and the translucent ink layer are arranged. The substrate may in particular be formed by a plastic foil. Preferably, the security element is a security thread, a security strip, a patch or a label applied to security paper, value documents or similar items.

The invention also comprises a method of manufacturing a security element of the above-mentioned type, wherein in the covered area a semi-transparent ink layer is arranged on top of an optically variable layer which creates different color impressions at different viewing angles. Here, the color impression of the optically variable layer is coordinated with the color impression of the translucent ink layer in the covered area when viewed under predetermined viewing conditions.

Advantageously, in the method according to the invention, a semi-transparent ink layer is printed on the optically variable layer. It is suitable to apply the optically variable layer itself, in particular by printing, onto a substrate. If a transparent substrate is used, it is also possible to print a translucent ink layer first thereon and then to apply, in particular print, an optically variable layer on the translucent ink layer.

In an advantageous development, the optically variable layer and/or the translucent ink layer are provided with gaps in the form of patterns, characters or codes.

The invention further comprises a transfer element for application to security paper, value documents and the like, which is provided with a security element of the type described above. The transfer element preferably has a substrate foil on which the security element is produced in the reverse order of how it is later placed on the security paper or valuable item and is subsequently transferred to the security paper or valuable item in the desired contour by means of an adhesive layer, for example an adhesive or a lacquer layer, in a hot embossing process. It is therefore suitable to first apply, in particular print, a translucent ink layer onto the substrate foil. The optically variable layer is then advantageously printed onto the translucent ink layer. Alternatively, the optically variable layer can also be evaporated (vaporized) or applied in another suitable manner. After the transfer, the separate substrate foil can then be removed from the layer structure of the security element. Alternatively, as a fixed part of the security element, the substrate foil may remain on the layer structure as a protective layer. Alternatively, a separate or separate layer, for example wax, may be provided between the security element and the substrate foil.

Security paper for the manufacture of security documents, such as banknotes, identity cards and the like, is preferably provided with a security element of the type described above. In particular, the security paper may comprise a carrier substrate (carrier substrate) consisting of paper or plastic.

The invention also comprises valuable items, such as branded goods, value documents, etc., with a security element of the type described above. The valuable item can be in particular security paper, a value document or a product packaging.

Drawings

Exemplary embodiments and advantages of the present invention are explained below with reference to the drawings, wherein the depiction in scale and proportion is omitted for the purpose of improving their clarity. In the figure:

FIG. 1 is a schematic illustration of a banknote with an embedded security thread and an attached transfer element according to an exemplary embodiment of the present invention;

FIG. 2 is a top view of a subregion of the security thread in FIG. 1;

fig. 3 is a cross-section of the security thread taken along the line III-III in fig. 2;

FIG. 4 is a graph showing the reflection spectrum of a thin-film element, alone and after printing of a semi-transparent ink layer, for a wavelength range λ from 300nm to 2,000 nm;

FIG. 5 is a cross-section through a transfer material according to the present invention;

FIG. 6 is a more accurate view of the transfer member of FIG. 1 from above;

FIG. 7 is a cross-section of a holographic security thread according to another exemplary embodiment of the present invention;

fig. 8 is a layer structure of a security element according to the invention with a liquid crystal structure as an optically variable layer; and

fig. 9 is a layer structure of a security element according to the invention, having a diffraction pattern as an optically variable layer;

fig. 10 is a graph showing the transmission spectrum of a transparent plastic foil printed with a translucent ink layer, with a wavelength range λ from 300nm to 750 nm.

Detailed Description

The invention will now be explained in more detail using banknotes as an example. To this end, fig. 1 shows a schematic view of a banknote 10 having security elements 12 and 16, each formed according to an exemplary embodiment of the present invention. The first security element constitutes the security thread 12 of certain window regions 14 present on the surface of the banknote 10, while it is embedded inside the banknote 10 in the region between them. The second security element is formed by an attached transfer element 16 of arbitrary shape.

The structure of the security thread 12 will now be explained in more detail with reference to fig. 2 and 3. Here, fig. 2 shows a top view of a sub-region of the safety line 12, and fig. 3 depicts a cross section through the safety line along the line III-III in fig. 2.

The security thread 12 comprises a thin film element 20 which has a colour shift effect and which is applied to a transparent substrate foil 22. The optically variable thin-film element 20 comprises a reflective layer 24 formed from an opaque aluminium layer, an ultra-thin spacer layer 26 applied to the reflective layer, and a semi-transparent absorbing layer 28, for example consisting of chromium. As described above, the color shift effect of the thin film element 20 is based on interference effects caused by multiple reflections in the different sub-layers 24, 26, 28 of the element.

Half of the security thread 12 is formed with a covered region 32 in which a layer 34 of translucent ink is printed on the thin film element 20. In the directly adjacent, uncovered areas 36, there is an optically variable layer 20 without a layer of printing ink. Here, the film element 20 and the ink layer 34 are coordinated with one another in such a way that they produce a substantially identical color impression at a vertical viewing angle. The color impression of the thin-film element 20 at a vertical viewing angle is also referred to below as vertical tilt color (vertical tilt color).

When the security thread 12 is tilted, the color impression of the film element 20 changes in the uncovered regions 36, while the color impression in the covered regions 32 remains almost unchanged. By this combination of color variable and color constant regions in the immediate vicinity, the visual significance of the color shift effect is more significantly enhanced, since the human eye reacts more strongly to color differences than to the color change itself. The attention of the observer is thus more strongly attracted to the security feature. Furthermore, the mode of action of the security element is clear (self-exhibition), so that it can be easily checked for authenticity by anyone without difficulty.

It is generally perceived that the combination of static coloring elements and color gradient elements is very optically attractive. For possible counterfeiting, the combination of the two color effects in the immediate proximal end means a significant copy resistance, since freely available inks or foils with color-shifting effects can no longer be used directly.

The inventive use of the translucent ink layer 34 has a number of advantages, which will be explained in more detail below.

The use of the translucent ink layer 34 leads to an additional adjustment of the color impression of the thin-film element 20 in the uncovered area 36 and of the translucent ink layer 34 in the covered area 32. Although the color locus of the printed translucent ink layer 34 can be set very precisely and reproducibly, the vertical tilting color of the film element at vertical viewing angles generally varies slightly from security element to security element due to product fluctuations. Although these color variations from the very high sensitivity of the ink visible at normal angles to the layer thickness of the dielectric spacer layer are very small, they are fully perceptible to the naked eye.

If the ink layer 34 formed according to the invention is translucent, the vertically inclined colour of the thin-film element 20 is partially transmitted through the ink layer 34 and contributes to gathering the colour impression of the security element in the cover area 32 when viewed vertically. If the vertically inclined color in the uncovered area 36 of the film element 20 varies slightly between the security element and the security element, the color impression in the covered area 32 also varies accordingly due to the part that is seen through. In this way, the overall color impression in the covered area 32 is adjusted to the color impression in the uncovered area 36.

The contribution of the vertically tilted colors to the aggregate color impression is illustrated in the graph of fig. 4, which fig. 4 shows the reflection spectrum 40 of the thin-film element 20 in the uncovered area 36 at vertical viewing angles. The combination of the thin-film element 20 and the translucent ink layer 34 in the cover area 32 is similarly depicted. It will be apparent that the colour impression of the thin-film element 20 remains visible through the translucent ink layer 34 and contributes to the overall colour impression. In this way, it is possible to achieve an excellent agreement of the color impression in the two regions for perpendicular viewing, despite small thickness variations in the spacing layer which are unavoidable.

However, the translucent ink layer 34 is very transparent only when the viewing angle is almost vertical. At oblique viewing angles, it reflects significantly more light than at normal viewing, which causes a fraction of the light below the thin-film element 20 to be incident on the background.

In summary, the color contribution of the film element 20 of the see-through covering region 32 contributes to the adjustment of the color impression of the two adjoining regions when viewed perpendicularly. At oblique viewing angles, the color contribution of the perspective recedes into the background, so that the color of the translucent ink layer 34 is constantly contributing, and then dominates the overall impression of the coverage area 32. The color composition of the translucent ink layer will now be explained in detail with reference to the transmission spectrum 46 of the color printed transparent plastic foil shown in fig. 10. In the red spectral range, the translucent ink layer, in this embodiment a red printing ink, has a very good transparency (about 90%), whereas it has only a transparency of about 15%, for example in the green spectral range at a wavelength of about 550 nm. The effect according to the invention becomes accurate and effective due to the different spectral transmission. In particular, the color impression of the translucent ink layer in the covered area is well adapted to the underlying oblique color, e.g. magenta appears at vertical viewing angles, since the translucent ink layer is almost transparent in the relevant spectral range. In contrast, if the security element is viewed at another oblique angle, the color impression of the oblique color changes from magenta to green, for example. In this wavelength range, the translucent ink layer has a substantially lower transparency, which causes the oblique color contribution of the perspective to fade into the background, and the color-constant contribution of the covering ink layer dominates.

Another advantage of using a semi-transparent ink layer is the adjustment of the luminance of the two sub-areas 32 and 36. The reflective layer 24 of the thin film element 20 is typically designed such that it reflects about 90% of the incident light, so that the color shift effect appears very bright and glaring in the uncovered areas 36. The luminance value or L-value in the CIELab color space, which substantially represents a contribution of the reflected light, is thus very high in the uncovered area 36. Such high luminance and such high L value cannot be achieved by ordinary printing inks. Thus, when opaque printing ink is used for the overlay, the color impression of the vertically tilted colors and the printing ink will be different even if the chromaticity coordinates (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 translucent ink layer, in the covered area 32, an additional light contribution of the thin-film element 20 is obtained, such that its luminance increases, thus further approaching the color impression of the uncovered area 36.

Furthermore, the interference layer structure of the thin-film element 20 is very generally smooth, so that the uncoated layer 36 also has a high gloss and acts almost as a chromatic mirror. In contrast, the gloss of the printing ink is substantially lower. In opaque printing inks, this gloss difference appears clearly to the observer, even if the chromaticity coordinates (again expressed by a and b in the CIELab system) are almost identical. By using a translucent ink layer 34, the gloss in the covered area 32 is increased by the see-through high-gloss film element 20, so that the visual impression of the viewer is adjusted to that of the uncovered area 36.

In the exemplary embodiment of fig. 2 and 3, a gap 30, which may form, for example, a reverse letter, is also introduced into the reflective layer 24 of the thin-film element 20. The film element 20 is transparent in the region of these gaps 30, which makes a significant contrast effect with the transmitted light possible in addition to the described effects.

If the security element, for example the transfer element 16 in fig. 1, is applied to the valuable item to be protected in the form of a patch or strip, it is first prepared, suitably in the form of a label material or transfer material, issued in the desired shape and then transferred to the item to be protected. An example of such a transfer material is shown in cross-section in fig. 5, and a issued transfer element 16 secured to a valuable article, viewed from above, is depicted in fig. 6.

The transfer material 50 comprises a substrate layer 52, in particular a plastic foil, to which a layer structure 54 consisting of an optically variable layer and a translucent ink layer is applied. Here, it is advantageous to provide a separating layer 56 between the layer structure 54 and the substrate layer 52. An adhesive layer 58, for example a hot-melt adhesive layer, is provided on the layer structure 54 of the transfer material, with which adhesive layer the security element can be fixed to the article to be protected.

For transfer, the transfer material 50 is placed on the article and the adhesive layer 58 is activated, such as by heat. Subsequently, the backing layer 52 is removed from the article such that only the securing layer structure 54 remains on the article to be protected. The layer sequence of the layer structure 54 is reversed by fixing to the item to be protected compared to the position in the transfer material 50, so that after the transfer material has been manufactured, a translucent ink layer on top of the item must be applied to the backing layer 52 before the optically variable layer.

Fig. 6 shows the issued and fixed transfer element 16 viewed from above. Similar to the security thread in fig. 2 and 3, the transfer element comprises an optically variable thin film element 60 having a colour shift effect and a translucent ink layer 62 arranged on some areas of the thin film element 60.

In an exemplary embodiment, the thin-film element 60 and the ink layer 62 are formed by concentric discs (concentric discs), with the translucent ink layer 62 covering only a central, interior region of the thin-film element 60. In the outer, uncovered area 64, in which there is a thin-film element 60 that is not covered by an ink layer, a gap 66 is introduced into the reflective layer of the thin-film element 60, which gap is brightly displayed in transmitted light in the form of the text "PL 2004".

Also in this exemplary embodiment, the film element 60 and the translucent ink layer 62 are coordinated with one another in such a way that, at a vertical viewing angle, they give rise to a substantially identical color impression. The entire disk of the membrane element 60 thus appears to have a consistent color impression when viewed vertically. When the transfer member 16 is tilted, the color impression of the outer, uncovered ring 64 changes due to the color shifting effect of the thin film member 60, while the inner disc with the translucent ink layer 62 printed thereon remains color constant.

The security element of the exemplary embodiment shown in fig. 7 comprises a holographic security thread 70, wherein the optically variable layer with a colour shift effect additionally has a regional optical microstructure. The microstructure may be, for example, a diffraction pattern 74(diffraction pattern). For this purpose, an embossing lacquer layer 78 is applied to the backing foil 76, wherein the desired diffraction pattern 74 is embossed. A layer structure of the film element 72, which can be formed, for example, as in fig. 3, is applied to the embossing lacquer layer 78.

A semi-transparent ink layer 80 is applied to a sub-region of the holographic security thread 70, and the semi-transparent ink layer 80 and the thin-film element 72 are coordinated with one another in such a way that, at a vertical viewing angle, they give rise to a substantially identical colour impression. In addition to the effects described in connection with fig. 2 and 3, the holographic security thread 70 shows a holographic effect combined with a color shift effect.

In the exemplary embodiments described so far, the optically variable layer is generally formed by thin film elements having a color shift effect. However, the combination of the optically variable layer and the translucent ink layer according to the present invention is not limited to such an embodiment, but may be additionally used for all other types of optically variable layers, as shown in the following examples using a liquid crystal structure (fig. 8) and a diffraction pattern (fig. 9).

To this end, fig. 8 shows the main layer structure of a security element 90 according to the invention, in which the optically variable layer comprises one or more layers consisting of liquid crystal material. For this purpose, a smoothing foil 92, for example a PET foil of good surface quality, is provided with an absorbing, black background layer 94. One or more layers 96-1, 96-2, … 96-n of cholesteric liquid crystal material are applied to the background layer 94. Between the liquid crystal layers, an alignment layer and/or an adhesive layer 98 for aligning the liquid crystals in the liquid crystal layer or connecting individual liquid crystal layers and compensating for surface irregularities in the background may be provided.

Sub-regions of the security element 90 are provided with a translucent ink layer 100. Here, the translucent ink layer and the liquid crystal structure are coordinated with one another in such a way that, at a vertical viewing angle, they give rise to a substantially identical color impression. When the security element 90 is tilted, the liquid crystal structure gives the viewer a varying color impression, while the color impression of the area provided with the ink layer 100 remains substantially constant.

In the security element 110 of figure 9, the optically variable layer is formed from a diffractive pattern which, when viewed under predetermined viewing conditions, exhibits a colour impression with which the translucent ink layer is coordinated.

The security element 110 comprises a base foil 112 and a printed, embossed and bent UV lacquer layer 114. In a subsequent evaporation step, the relief pattern (relief pattern) of the lacquer layer 114 is provided with a thin reflective metal layer 116 or dielectric layer, so that a diffraction pattern having the desired properties is produced on embossing. For example, in diffuse illumination, the diffraction pattern may diffract red light along the predetermined look direction 120. For illustration purposes, the direction 120 of oblique viewing is shown at a viewing angle of 60 ° from vertical.

In the sub-areas the diffraction pattern is provided with a translucent ink layer 118, the translucent ink layer 118 and the diffraction pattern being coordinated with each other in such a way that they give rise to a substantially identical color impression when viewed from the predetermined viewing direction 120. In a typical embodiment, the translucent ink layer 118 is selected such that in diffuse illumination it similarly reflects red light along the viewing direction 120.

When viewed vertically, the security element 110 in fig. 9 first shows the viewer with an impression of two different colors. When the security element is tilted, the color impressions of the areas covered with the ink layer and the uncovered areas are adjusted to each other until they actually match from the predetermined viewing direction 120. By suitable design of the diffraction pattern, a very narrow angular range can be provided for matching the color impression, so that characteristic color effects which are difficult to imitate are produced.

Of course, in addition to the layers in the above exemplary embodiments, further layers may be present, however, are omitted here for the sake of clarity. For example, the above layer structure may have a protective layer formed of, for example, a plastic layer or foil. Furthermore, the individual layers of the security element, in particular the optically variable layer and the translucent ink layer, may be separated by further transparent layers or be present on different sides of the transparent substrate foil.

Claims (44)

1. A security element for protecting valuable articles, having an optically variable layer which gives different color impressions at different viewing angles, characterized in that in a covered region a translucent ink layer is arranged on top of the optically variable layer, the color impression of the optically variable layer, viewed under predetermined viewing conditions, being coordinated with the color impression of the translucent ink layer in the covered region; wherein the translucent ink layers have different spectral transmittances and exhibit a transmittance of 60% to 100% in a spectral range in which the color impression of the optically variable layer is coordinated with the color impression of the translucent layer.

2. A security element as claimed in claim 1 in which the translucent ink layer has a transmission of 80% to 100%.

3. A security element according to claim 1, wherein the semi-transparent ink layer is printed on the optically variable layer.

4. A security element as claimed in claim 1 in which the translucent ink layer is in the form of a character, pattern or code.

5. A security element as claimed in claim 1 in which the translucent ink layer has gaps in the form of characters, patterns or codes.

6. A security element according to claim 1, characterized in that the color impression of the optically variable layer outside the covered area substantially corresponds to the color impression of the translucent ink layer in the covered area when the security element is viewed perpendicularly.

7. A security element according to claim 1, wherein the optically variable layer is composed of a plurality of sub-layers.

8. A security element according to claim 1, wherein the optically variable layer is formed from a thin film element having a colour shift effect.

9. A security element according to claim 8, wherein the thin film element comprises a reflective layer, an absorbing layer and a dielectric spacer layer arranged between the reflective layer and the absorbing layer.

10. A security element as claimed in claim 8 in which the thin film element comprises a reflective layer and a dielectric spacer layer formed to be partially absorbing.

11. A security element as claimed in claim 9 or 10 in which the reflective layer is formed from an opaque or semi-transparent metal layer.

12. Security element according to claim 9 or 10, characterized in that the reflective layer is present as a magnetic layer at least in some areas.

13. Security element according to claim 8, characterized in that said thin-film element comprises at least one absorbing layer and at least one dielectric spacer layer, the absorbing layer and the dielectric spacer layer being stacked alternately.

14. A security element as claimed in claim 8 in which the thin film element comprises a plurality of dielectric spacer layers, adjacent layers of which have substantially different refractive indices.

15. A security element as claimed in claim 14 in which the refractive indices of the adjoining dielectric spacer layers differ by at least 0.03.

16. A security element as claimed in claim 9 or 10 in which the dielectric spacer layer is formed from a printed layer.

17. A security element as claimed in claim 9 or 10 in which the dielectric spacer layer is formed from an ultra-thin foil.

18. The security element according to claim 17, wherein the ultrathin foil is a stretched polyester foil.

19. A security element as claimed in claim 9 or 10 in which the reflective layer has gaps in the form of patterns, characters or codes which form transparent or translucent regions in the thin film element.

20. A security element according to claim 9 or 10, wherein the absorbing layer and/or spacer layer has gaps in the form of patterns, characters or codes, in which no colour shift effect is perceived.

21. Security element according to claim 9 or 10, characterized in that the thin-film element is present in the form of pigments or particles of suitable size and form factor.

22. A security element according to claim 1, wherein the optically variable layer comprises one or more layers composed of liquid crystal material.

23. A security element according to claim 22, wherein the liquid crystal material is cholesteric liquid crystal material.

24. Security element according to claim 22, characterized in that the liquid crystal material is present as a liquid crystal polymer material or in the form of a pigment embedded in a binding compound.

25. A security element as claimed in claim 1 in which the optically variable layer is formed from a diffractive pattern.

26. A security element as claimed in claim 25 in which the diffraction pattern forms a grating image for depicting a true colour image having a plurality of true colour regions which glow with a predetermined true colour when the grating image is illuminated.

27. The security element according to claim 1, characterized in that the security element comprises at least one further layer having a security feature.

28. The security element according to claim 27, characterized in that the at least one further layer comprises optically active microstructures arranged below the layer structure consisting of the optically variable layer and the translucent ink layer.

29. A security element according to claim 28, wherein the optically active microstructures are diffractive patterns, matte patterns or optically active microstructures produced by micromirrors or microlenses.

30. A security element according to claim 27, wherein the at least one further layer comprises a machine-readable feature substance.

31. A security element as claimed in claim 30 in which the machine-readable feature substance is a magnetic, conductive, phosphorescent, fluorescent or other light-emitting substance.

32. A security element according to claim 1, wherein the security element has a substrate on which the optically variable layer and the translucent ink layer are arranged.

33. A security element as claimed in claim 32 in which the substrate is formed from a plastics foil.

34. The security element according to claim 1, characterized in that the security element forms a security thread, a security strip, a patch or a label applied to a security paper, a value document.

35. A method of manufacturing a security element as claimed in at least one of claims 1 to 34, wherein in the covered region a translucent ink layer is arranged on top of an optically variable layer which gives different color impressions at different viewing angles, the color impression of the optically variable layer being coordinated with the color impression of the translucent ink layer in the covered region when viewed under predetermined viewing conditions.

36. The method of claim 35, wherein the semi-transparent ink layer is printed on the optically variable layer.

37. A method according to claim 35 or 36, wherein the optically variable layer is applied to a substrate.

38. A method according to claim 35, wherein the optically variable layer and/or the translucent ink layer is provided with gaps in the form of patterns, characters or codes.

39. A transfer element for application to security paper, value documents, having a security element as claimed in at least one of claims 1 to 38.

40. The transfer element of claim 39, wherein the transfer element comprises a substrate foil.

41. A security paper for producing security or value documents, which is provided with a security element as claimed in at least one of claims 1 to 38 or a transfer element as claimed in claim 39 or 40.

42. A security paper as claimed in claim 41, characterized in that the security paper comprises a carrier substrate consisting of paper or plastic.

43. A valuable article having a security element as claimed in at least one of claims 1 to 38 or a transfer element as claimed in claim 39 or 40.

44. The value article according to claim 43, wherein the value article is a security paper, a value document or a product packaging.