EP2318181B1 - Security element - Google Patents

Description

The invention relates to a security element for securing data carriers, a method for producing such a security element, a correspondingly equipped data carrier and a method for producing the same.

Data carriers, such as valuables or identity documents, but also other valuables, such as branded goods, are often provided with security features for security, which allow a verification of the authenticity of the data carrier and at the same time serve as protection against unauthorized reproduction.

Security features, which can not be reproduced even with state-of-the-art copiers, play a special role in ensuring authenticity. For this purpose, special printing inks, which contain luster pigments or other optical effect pigments, are often printed, since the characteristic luster and color play of such pigments can not be copied.

In addition to the safety area, gloss or effect pigments are also used in other areas of technology, such as car paints, decorative coatings or cosmetic formulations. Black luster pigments often have a particular appeal here because the contrast of black color and luster is visually attractive on the one hand and the dark appearance on the other can provide a suitable background for a variety of optical effects, such as the color shift effects of interference layer systems or liquid crystal layers. An example of an optically variable element that appears black is in the document EP 0 395 410 A2 given. The element comprises a three-layer coating having first and second partially transmissive absorber layers and a dielectric layer disposed between the first and second absorber layers.

Based on this, the present invention seeks to provide a security element of the type mentioned above with attractive visual appearance and high security against counterfeiting.

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

According to the invention, a security element of the aforementioned type comprises a three-layered thin-film element comprising a reflection layer, an absorber layer and a dielectric spacer layer arranged between the reflection layer and the absorber layer, in which the reflection layer, the absorber layer and the dielectric spacer layer are matched to one another such that the Thin-film element for viewing from the absorber layer side has a very low reflection at all viewing angles and in the entire visible spectral range and appears black.

The reflection of the thin-film element for viewing from the absorber layer side is below 20%, preferably below 15%, particularly preferably below 10%, at all viewing angles and in the entire visible spectral range. Advantageously, the thin-film element for viewing from the absorber layer side in the entire visible spectral range and at all viewing angles on no reflection maximum.

In some embodiments, the thin-film element for viewing from the absorber layer side has a reflection maximum in the ultraviolet spectral range, which can be used as a characteristic authenticity mark and detected with suitable spectroscopic instruments. The exact position of the reflection maximum in the ultraviolet spectral range depends on the viewing angle, so that the variation of the reflection maximum in the ultraviolet can also be used as an authenticity feature.

The layer thickness of the dielectric spacer layer is preferably between about 20 nm and about 90 nm. In an advantageous variant, the spacer layer is essentially formed of a low-refractive dielectric with refractive index n <1.8, in particular SiO ₂ or MgF ₂ , and has a layer thickness between 50 nm and 90 nm, in particular of about 70 nm. In an alternative, likewise advantageous variant, the spacer layer is essentially formed from a high-index dielectric with a refractive index n ≥ 1.8, in particular from TiO ₂ or ZnS, and has a layer thickness between 20 nm and 50 nm, in particular approximately 40 nm.

Due to the matching of the thickness and the materials of the reflection layer, the absorber layer and the dielectric spacer layer in the entire visible spectral range and for all viewing angles, the thin-film element according to the invention has a very low reflection and therefore appears black to the viewer. Of course, by deliberately changing the thicknesses of the absorber layer, dielectric spacer layer and reflection layer, in particular by changing the thickness of the dielectric spacer layer, it is also possible to obtain a thin-film element in some areas, which is not the case for the viewer at all Viewing angles and / or not in the entire visible spectral range appears black. For example, by varying the layer thickness of the dielectric spacer layer, a thin-film element can be obtained which has a very low reflection in a first region due to the inventive tuning of reflection layer, absorber layer and dielectric spacer layer and appears black to the viewer in the entire visible spectral range, whereas in a second Area of the thin-film element, the thickness of the dielectric spacer layer is selected so that this second area of the thin-film element for the viewer in incident light does not appear black as the first area, but blue. When tilting the second area, the viewer then perceives, for example, a color change from blue (top view) to black (oblique viewing angle). In other words, the first region of the thin-film element appears black to the viewer in the entire visible spectral range and at all viewing angles, while the second region does not appear black to the observer, at least at one viewing angle and / or in a part of the visible spectral range.

Furthermore, with a sufficiently thick dielectric layer it is possible to produce a thin-film element with a reflection maximum in the infrared, just beyond the visible spectral range. Since in this case in the visible spectrum always sufficiently intense reflection maxima are, the thin-film element for the viewer appears in a different color of black. However, if the thin-film element is provided with a suitable, filtering color, in particular a film which, for example, absorbs blue light and transmits red light, then the thin-film element appears black to the observer in incident light. When tilting this thin-film element with filtering color becomes the reflection maximum shifted from the infrared into the visible spectral range (red), so that the tilted thin-film element for the viewer appears red. Such a thin-film element with filtering color thus shows a color shift effect from black (top view) to red (oblique viewing angle) for the viewer. It is understood that by a suitable choice of the materials and thicknesses of the reflective layer, absorber layer and dielectric spacer layer, a thin-film element may also be indicated which exhibits a color shift effect of eg red (top view) or blue (top view) to black (oblique viewing angle) As described above, additional filtering colors can be combined with the respective thin-film element.

In advantageous developments of the invention, the dielectric material of the spacer layer can be mixed with an absorbent material, for example with absorbing metal ions. The dielectric spacer layer may be vapor-deposited or printed. In the latter case, for example, carbon black may be incorporated as the absorbent.

If special embodiments of the invention are to be produced which, in addition to the areas appearing black to the viewer in all viewing angles in the entire visible spectral range, also have colored areas, the dielectric spacer layers of changed thickness required for the colored and / or non-colored areas (see above) can be produced. be printed with advantage. In principle, it is of course also conceivable to obtain the areas of the thin-film element that appear black to the observer by vapor-depositing the layers of the thin-film element and to form only the areas that do not appear black to the observer as a colored motif, which is in one at all Viewing angles and in the entire visible spectral range for the viewer black appearing environment is arranged.

It should be mentioned at this point that the security element according to the invention for securing data carriers can be formed not only by a flat, three-layer thin-film element of a reflective layer, absorber layer and interposed dielectric spacer layer, but also by a flat application of thin-film pigments with the three-layered invention Construction. Depending on the size of the individual thin-layer pigments (thin-layer flakes), the visual impression of a security element with thin-film pigments that is visually discernible to a viewer can hardly be distinguished from the visual impression of a security element having a flat, three-layer thin-film element. At present, however, black-appearing thin-film pigments and the security elements formed therefrom are not preferred for the observer at all viewing angles in the entire visible spectral range.

When viewed from the reflection layer side, the thin-film element according to the invention appears high-gloss metallic at all viewing angles and in the entire visible spectral range. This metallic reflection can be used in particular in security elements that are also visible from the underside. On the one hand, it enables the visual differentiation of the thin-film element from conventional black print layers, and on the other hand, it can also function as part of another authenticity feature, as explained below on the basis of a polarization feature in which the metallic reflection layer interacts with a phase-shifting layer.

In one development of the invention, the thin-film element has recesses in the form of patterns, characters or codes which form transparent or translucent regions in the thin-film element. The recesses may extend through the entire thin-film element or may also be formed only in the reflection layer.

According to a particularly advantageous development of the invention, the security element has a color-shifting layer of a cholesteric liquid-crystalline material, which faces the absorber layer side of the thin-film element, so that the black-appearing thin-film element forms a dark background for the color-shifting layer. The color-shifting layer can of course also be combined with the recesses in the thin-film element. If the security element has a carrier foil, then the thin-layer element and the color-shifting layer can be arranged on the same side or on opposite sides of the carrier foil.

The security element can furthermore have at least one further, machine-readable security feature, in particular a security feature with magnetic, electrically conductive, phosphorescent, fluorescent or other luminescent substances. If the security element has a carrier foil, the thin-layer element and the further security feature can be arranged on the same side or on opposite sides of the carrier foil. It is understood that the further security features can be combined with color-shifting layers and / or with recesses in the thin-film element. Of course, it is also conceivable in principle that the thin-film element according to the invention is arranged on a carrier foil which, as a further security feature, has a diffraction structure or matt structure, wherein the thin-film element in addition to the diffraction structure or matt structure or else above / below the diffraction structure or matt structure is arranged. In a further specific embodiment, a security feature which can be excited in the ultraviolet spectral range is combined with the security element according to the invention. For example, the UV-stimulable layer can be arranged above the black thin-film element according to the invention (ie facing the absorber layer side) or else on the side of the thin-film element facing the reflection layer side.

In suitable embodiments, the security element is present on a carrier film, in particular a PET film with a layer thickness between 6 .mu.m and 23 .mu.m. After the security element has been transferred to a data carrier, the carrier film can be pulled off the remaining layer structure of the security element or it can remain as an integral part of the security element in the layer structure.

According to an advantageous development of the invention, the security element has a phase retardation layer of a nematic liquid-crystalline material which faces the reflection layer side of the thin-film element, so that the phase retardation layer together with the reflection layer forms a polarization feature that can be tested with a polarization filter. The phase delay layer can be present in particular in the form of patterns, characters or codes, so that the formed motif emerges when viewed through a suitable polarization filter. If the security element has a carrier foil, the thin-film element and the phase delay layer can be arranged on the same side or on opposite sides of the carrier foil. In the latter case, a carrier film is expediently used which itself has no or only slight polarizing properties.

According to a further embodiment, the security element has a phase delay layer made of a suitable liquid-crystalline material, the phase-delay layer facing the absorber layer side of the thin-film element. For example, the phase retardation layer of nematic liquid crystalline material may be disposed over a layer of cholesteric liquid crystalline material, wherein the layer of cholesteric liquid crystalline material exhibits a color shift effect together with the thin film element according to the invention. In such an embodiment, the observer can perceive from the absorber layer side the color-shift effect of the cholesteric liquid-crystalline material in combination with the thin-film element and, with suitable aids, check the polarization effect of the polarization feature of nematic liquid-crystalline material.

In a further preferred embodiment, the security element has a three-layer thin-film element according to the invention, which has a very low reflection for viewing from the absorber layer side at all viewing angles in the entire visible spectral range and therefore appears black to the observer. In a second region, in particular directly adjacent to the first region, the security element furthermore has a thin-film element, which is e.g. by changing the thickness of the dielectric spacer layer does not appear black to the viewer at all viewing angles and / or throughout the entire visible spectral range.

If now such a security element with first areas appearing black for the viewer and second areas not appearing black to the viewer at all viewing angles and / or not in the entire visible spectral range, as described above, provided with a color-shifting layer of a suitable cholesteric liquid-crystalline material, wherein the color-tilting layer faces the absorber layer side of the thin-film element, the black-appearing thin-film element in the first regions forms a dark background for the color-shifting layer, whereas in the second regions for the viewer due to the different background of black, gives a color that differs to the color of the first area. In other words, the security element according to the invention has a first area, which shows a first color-shift effect for the viewer, and a second area, which shows a second, different color-shift effect from the first one.

Of course, this special security element with first and second color-shifting areas can basically be designed as described for the security element with only one color-shifting layer. In particular, the thin-film element with first and second regions and the color-shifting layer can be arranged on the same side or on opposite sides of a carrier film. And the combination with a further, in particular machine-readable security feature, as well as the combination with a phase delay layer of a nematic liquid-crystalline material is conceivable. The security element described above is characterized by an extraordinarily large security against counterfeiting.

It is understood that the security element according to the invention can have a region which has essentially the same color, which is different from black, at all viewing angles and in the entire visible spectral range. For example, a security element according to the invention, as described above, with a color-shifting layer from a cholesteric liquid-crystalline material, which faces the absorber layer side of the thin-film element, so that the black-appearing thin-film element forms a dark background for the color-shifting layer, to be arranged on a suitable carrier film such that the color-shifting thin-film structure directly adjoins a region likewise arranged on the carrier film adjacent, which has substantially the same color different from black at all viewing angles and in the entire visible spectral range. Such security elements, in which a color-shifting thin-film structure according to the invention is arranged directly adjacent to a region which has substantially the same color at all viewing angles and in the entire visible spectral range, are very attractive to the viewer and are characterized by particularly high counterfeit security.

Of course, the security feature having areas that exhibit a color shift effect and areas that exhibit substantially a particular, non-variable color may also be combined with other security features, such as a phase retardation layer of a suitable liquid crystal material, as described above.

The security element is advantageously 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 encompasses a method for producing a security element of the type described, in which a reflective layer, a dielectric spacer layer and an absorber layer are superimposed to form a three-layered thin-film element, and in which the reflection layer, the absorber layer and the dielectric spacer layer are matched to one another such that the thin-film element has a very low reflection for viewing from the absorber layer side at all viewing angles and in the entire visible spectral range and appears black.

The invention further comprises a data carrier, in particular a value document, such as a banknote, an identity card or the like, with a security element of the type described. For producing such a data carrier, a security element of the type described is applied to a data carrier substrate, for example a printed or unprinted paper or paper Plastic substrate, applied or fully or partially embedded in such a data carrier substrate. The security element can in particular also be arranged over a window area or a continuous opening of the data carrier and thus be visible from both sides.

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

Fig. 1

eine schematische Darstellung einer Banknote mit einem eingebetteten Sicherheitsfaden,

Fig. 2

schematisch den Schichtaufbau eines erfindungsgemäßen Sicherheitselements im Querschnitt,

Fig. 3

schematisch das Reflexionsspektrum des in Fig. 2 dargestellten Dünnschichtelements für senkrechte Betrachtungsrichtung von oben,

Fig. 4

schematisch das Reflexionsspektrum einer dicken, gedruckten, schwarzen Schicht auf einer Folie,

Fig. 5

eine Sicherheitsfolie wie sie für die Herstellung eines in Fig. 1 dargestellten Sicherheitsfadens eingesetzt werden kann,

Fig. 6

schematisch das Reflexionsspektrum der Sicherheitsfolie der Fig. 5 in nicht ausgesparten Bereichen bei senkrechter Betrachtung von oben,

Fig. 7, 8

weitere Ausführungsbeispiele erfindungsgemäßer Sicherheitsfolien,

Fig. 9, 10

weitere Sicherheitsfolien nach Ausführungsbeispielen der Erfindung, die zusätzliche maschinenlesbare Sicherheitsmerkmale enthalten, und

Fig. 11 bis 13

Sicherheitselemente nach weiteren Ausführungsbeispielen der Erfindung, bei denen das Dünnschichtelement mit einer Phasenverzögerungsschicht aus doppelbrechendem Material kombiniert ist.

Show it:

Fig. 1

a schematic representation of a banknote with an embedded security thread,

Fig. 2

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

Fig. 3

schematically the reflection spectrum of in Fig. 2 shown thin-film element for vertical viewing direction from above,

Fig. 4

schematically the reflection spectrum of a thick, printed, black layer on a film,

Fig. 5

a security foil as used in making an in Fig. 1 shown security thread can be used

Fig. 6

schematically the reflection spectrum of the security film of Fig. 5 in non-recessed areas when viewed vertically from above,

Fig. 7, 8

further embodiments of security films according to the invention,

Fig. 9, 10th

Further security films according to embodiments of the invention, which contain additional machine-readable security features, and

Fig. 11 to 13

Safety elements according to further embodiments of the invention, in which the thin-film element is combined with a phase retardation layer of birefringent material.

The invention will now be explained using the example of security elements for banknotes. Fig. 1 shows a schematic representation of a banknote 10, which is provided with a security element 12 according to the invention.

The security element shown represents a security thread 12 that protrudes at certain window areas 14 on the surface of the banknote 10 while it is embedded in the intervening areas inside the banknote 10.

When viewed, the security thread 12 exhibits a color shift effect with brilliant colors whose color changes in the embodiment from green when viewed perpendicularly to blue when viewed at an acute angle. In addition, the security thread has 12 negative characters 16, which are formed in the embodiment in the form of the alternating letter sequences "PL" and "10". In incident light, the negative characters 16 can be recognized by the absence of a colored impression or of the color shift effect. Negative characters 16 appear particularly strong when viewing the banknote 10 in transmitted light, where they shine bright against the otherwise opaque background of the embedded security thread 12.

In order to achieve such a visual impression, the security thread 12 contains a specially designed thin-film element which forms with its upper side a generally black background for a color-tilting liquid-crystal layer, as explained in more detail below.
Regarding Fig. 2 In the simplest case, a security element according to the invention comprises a three-layered thin-film element 20 with a reflection layer 22, an absorber layer 26 and a dielectric spacing layer 24 arranged between the reflection layer 22 and the absorber layer 26.

The reflection layer 22 is formed in the embodiment of a 30 nm thick aluminum layer. Basically come as reflector materials However, other metals, such as silver, nickel, copper, iron, chromium, gold or other highly reflective metals into consideration. The layer thickness of the reflection layer is typically between 10 nm and 200 nm, usually between about 30 nm and about 100 nm.

On the one hand, low-index dielectrics with a refractive index below 1.8 are suitable for the dielectric spacer layer 24, such as, for example, SiO ₂ , MgF, SiO _x with 1 ≦ _x ≦ 2, or Al ₂ O ₃ . On the other hand, it is also possible to use high-index dielectrics with a refractive index of 1.8 or more, such as ZrO ₂ , ZnS, TiO ₂ or indium tin oxide (ITO). The layer thickness of the spacer layer 24 is preferably between about 50 nm and about 90 nm for low-index dielectrics, preferably between about 20 nm and about 50 nm for high-index dielectrics Fig. 2 For example, the dielectric spacer layer 24 is formed by an 80 nm-thick SiO ₂ layer.

The absorber layer 26 is formed in the embodiment by a 6 nm thick chromium layer. In principle, however, other materials, such as iron, gold, aluminum or titanium, which are applied in a thickness between 2 nm and about 10 nm, are suitable as absorber layers. Further details on the construction of thin-film elements and in particular on the materials which can be used for the reflection layer, the dielectric spacer layer and the absorber layer, as well as the layer thicknesses which may be considered for the reflection layer and the absorber layer, can be found in the document WO 01/03945 A1 are removed, the disclosure of which is included in the present application in this respect.

The reflection layer 22, the absorber layer 26 and the dielectric spacer layer 24 are coordinated according to the invention such that the Thin-film element 20 for viewing 28 from the side of the absorber layer 26 at all viewing angles 28, 28 'and in the entire visible spectral range between λ = 400 nm and λ = 800 nm has a very low reflection and appears black to a viewer.

The perceptible color impression of a thin-film element with the described structure is based on viewing angle-dependent interference effects due to multiple reflections in the different sub-layers of the element and depends in particular on the optical thickness of the dielectric spacer layer. In conventional thin-film elements, the path difference of the beams reflected at different partial layers is of the order of the wavelengths of visible light, so that an angle-dependent color impression in the visible spectral range results due to the extinction and amplification of specific wavelengths.

In the case of the thin-film elements 20 according to the invention, the layer thickness of the dielectric spacer layer 24 is now selected to be so small that all constructive interference maxima are in the ultraviolet spectral range and the thin-film elements in the visible spectral range have no reflection maximum at all viewing angles. By suitable matching, in particular of refractive index and layer thickness of the spacer layer 24, it can surprisingly be achieved that the reflectivity of the thin-film element in the entire visible spectral range, ie from λ = 400 nm to λ = 800 nm, is very low and largely uniform, so that such a Thin-film element appears black when viewed from the side of the absorber layer ago.

Fig. 3 schematically shows the reflection spectrum 30 of in Fig. 2 shown thin-film element 20 for vertical viewing 28. With increasing Wavelength decreases the reflection to a maximum reflection 32 in the ultraviolet spectral range, which is in the exemplary embodiment at about 250 nm, strong and is then in the entire visible spectral range of 400 nm to 800 nm well below 10%.

When the thin-film element 20 is viewed at an acute angle 28 ', the reflection maximum 32 shifts to even shorter wavelengths due to the physical conditions, ie it remains in the non-visible, ultraviolet spectral range. As seen from the flat slope 34 of the reflection of the thin-film element between 800 nm and 1000 nm ( Fig. 3 ), a blue shift of the reflection spectrum does not lead to a significant increase in the reflection in the visible spectral range, especially since the human eye is only slightly sensitive at the red end of the spectral range. The thin-film element 20 therefore also appears with an oblique view 28 'for the viewer with a deep black hue.

In Fig. 4 For reference, reference is made to the reflection spectrum 40 of a thick printed black layer on a foil. As can be seen from a comparison of the reflection curves 30, 40, the thin-film element 20 according to the invention produces a black impression in the visible spectral range from 400 nm to 800 nm, which is very similar to that of a black print layer.

As already mentioned, it is also possible, in particular by a suitable choice of the thickness of the dielectric spacer layer of the thin-film element, to create a region of the security element according to the invention which does not appear black to the viewer for all viewing angles and / or in the entire visible spectral range.

When viewing 29 of the thin-film element 20 from the underside, that is to say the side of the reflection layer 22, the thin-film element 20 appears high-gloss metallic at all viewing angles 29, 29 'and in the entire visible spectral range. The thin-film structure of the element 20 can therefore easily be distinguished from a conventional black printing layer even without auxiliary means. In addition, the position of the reflection maximum 32 in the ultraviolet spectral range and its displacement during tilting of the thin-film element 20 can be used as characteristic authenticity characteristics and detected with the aid of suitable spectroscopic instruments.

The metallic reflection from the reflection layer side can be used for security elements that are at least partially visible from the underside, for example for security elements, which are arranged above a see-through or window area of a banknote or a value document. In conjunction with a phase-shifting layer, the metallic reflection can also be used to generate a polarization feature, as explained in more detail below. In addition, the opacity of the metallic reflective layer 22 in cooperation with demetallisierten areas can be used to produce negative patterns, as already on the negative characters "PL" and "10" of the security thread 12 of Fig. 1 illustrated.

In some embodiments, it may be advantageous to provide the dielectric material of the spacer layer with an absorbent. For example, SiO ₂ can be provided with absorbing metal ions, or glass breakage can be evaporated in a particularly simple variant for applying the spacer layer 24. Instead of the vapor deposition layer, the dielectric spacer layer 24 can also be designed as a pressure layer In this case, an absorbing material such as carbon black can easily be incorporated.

The embodiment of Fig. 5 shows a security film 50, as used for making a in Fig. 1 shown security thread 12 can be used.

The security film 50 contains a carrier film 52 in the form of a transparent plastic film, on which an aluminum reflection layer 54, a 70 nm thick spacer layer 56 made of SiO ₂ and a 4 nm thick absorber layer 58 made of chromium are applied in a layer sequence from bottom to top three-layered thin-film element 60, which appears black from all viewing directions when viewed from the absorber layer 58 side.

Further, recesses 62 in the form of patterns, characters or codes are formed in the thin-film element 60 and form transparent or translucent areas in the thin-film element 60. To produce the recesses 62, the carrier film 52 was printed in the region of the desired recesses with an activatable ink in the embodiment and then the layers 54, 56, 58 of the thin-film element 60 vapor-deposited over the entire surface of the printed carrier film. Subsequently, the ink was activated and the three overlying layers 54, 56, 58 removed in regions.

For example, printing inks having foamable additives which split off gas under the action of heat are able to reduce the adhesion to the carrier film as a result of the resulting increase in volume, and thus treatment methods acting mechanically below provide a good point of attack for working out the negative patterns. Further details of such a washing process can the document EP 0 516 790 B1 are removed, the disclosure of which is included in the present application in this respect. It goes without saying that other methods known to those skilled in the art for producing recesses can also be used to produce negative patterns, such as that in the document WO 99/13157 described, based on the printing of a soluble ink with a porous structure based washing process, or even etching of all kinds.

On the structured thin-film element 60, a color-shifting, cholesteric liquid-crystal layer 66 is further applied over an entire surface over an adhesive or primer layer 64. In the non-recessed areas 68, the black-appearing thin-film element 60 forms a dark background for the liquid crystal layer 66 and makes its color-shift effect appear with brilliant colors.

Fig. 6 schematically shows the reflection spectrum 70 of FIG Fig. 5 illustrated security film 50 in the non-recessed areas 68 when viewed vertically from above, so when viewed from the side of the color-tilting liquid crystal layer 66 ago. The reflection spectrum 70 shows a clearly pronounced reflection maximum 72 in the green spectral range at a wavelength of about 550 nm. The security film 50 therefore appears when viewed vertically in a brilliant, bright green. For acute viewing angles, the reflection maximum 72 shifts to shorter wavelengths, in the present case into the blue spectral range, due to the physical conditions. The security film 50 therefore appears deep blue when viewed at an acute angle, so that when the film 50 is tilted, a pronounced color shift effect from green to blue can be observed.

In the region of the recesses 62, the liquid crystal layer 66 is typically present against a light background, such as a paper background with partially embedded or glued security elements. Against such a light background, the color-shift effect of the liquid crystals is not or only slightly visible, so that the recesses 62 appear in supervision as color-free areas without color-shift effect. Particularly noteworthy are the recessed areas 62 when viewed in transmitted light, where they emerge bright against the background of the otherwise opaque thin-film element 60.

Another embodiment of a security film 80 according to the invention is shown in FIG Fig. 7 shown. The structure of the security film 80 corresponds largely to the structure of the security film 50 of Fig. 5 , but with the difference that only the reflection layer 54 of the thin-film element 60 is provided with recesses, while the spacer layer 56 and the absorber layer 58 are formed over the entire surface. The visual appearance of the security film 80 is similar to the appearance of the security film 50, however, in the recessed areas 62, the absorber layer 58 still present there darkens the negative pattern area somewhat.

According to the in Fig. 8 As shown in the further embodiment 90, the thin-film element 60 and the liquid crystal layer 66 can also be arranged on different sides of the carrier film 52. It is only essential for the effect according to the invention that the liquid-crystal layer 66 faces the absorber layer side 58 of the thin-film element 60. The recesses of the thin-film element 60 may again extend through the entire element or, as in the embodiment of FIGS Fig. 8 shown to be formed only in the reflection layer 54.

The layer structure of the security elements according to the invention can also receive further, in particular machine-readable security features, as in the exemplary embodiments 100 and 110 of FIG Figures 9 and 10 illustrated by the example of a magnetic security feature. The magnetic regions 102 can be printed as printed areas directly or else via a primer onto the black absorber layer side of the thin-film element 60. The magnetic regions 102 are usually black and therefore do not or only slightly fall in front of the black background of the thin-film element 60.

The magnetic regions 102 may also be printed on the opposite side of the carrier film 52. This in Fig. 10 shown variant has the advantage that the magnetic areas then from the visible side (the absorber layer side of the thin-film element) can not notice in principle. For this, the black magnetic regions must be effectively optically covered in some applications, in order not to attract attention to the highly reflective environment. Such a cover can be effected, for example, by a coating with metallic effect pigments and / or opaque white printing layers.

As in the Figures 11 and 12 As shown, the thin-film element, which is black on one side and shiny on the other side, can also be combined with a phase-delay layer of birefringent material in further embodiments of the invention.

With respect to the security element 120 of Fig. 11 For example, a thin-film element 60 is applied to the upper side of a carrier foil 52, and a color-tilting liquid-crystal layer 66 is applied via an adhesive layer, as already basically associated with FIG Fig. 5 described. Additionally is on the bottom the support film 52 is provided in the form of a motif applied phase delay layer 122, which consists of a birefringent material, for example of nematic liquid crystalline material. The phase delay of the visible light phase retardation layer 122 is typically between about λ / 4 and about λ / 2 and in the exemplary embodiment described is λ / 4.

When the security element 120 is viewed from below with ordinary unpolarized light and without auxiliary means, the subareas with and without phase retardation layer 122 are virtually indistinguishable since the phase delay acts equally on all polarization directions of the incident light and the light absorption of the phase retardation layer 122 is negligibly small.

On the other hand, when the security element 120 is viewed through a circular polarizer 124, the interaction of the phase retardation layer 122 and the metallically reflecting reflection layer 54 causes large differences in contrast between the portions with and without the phase retardation layer 122, so that the pattern formed by the retardation layer 122 clearly appears ,

Briefly speaking, the contrast differences that occur are based on the different influencing of the polarization of the incident light and the light reflected by the reflection layer 54 in the regions with or without the phase retardation layer 122, which results in the reflected light being able to pass through the circular polarizer 124 in one case and is locked in the other case. For a more detailed description of the operation and for advantageous embodiments of the phase delay layer is based on the German patent application DE 10 2006 021 429 A1 referred to, the disclosure of which is included in the present application.

As the incident light in the design of the Fig. 11 Before and after the reflection on the reflection layer 54 has to pass through the carrier film 52, a carrier film 52 is advantageously used, which itself has no or only low polarizing properties.

Alternatively, the phase retardation layer 122 may be disposed directly on the reflective layer 54 as in the security element 130 of FIG Fig. 12 shown. In this case, the polarizing properties of the carrier film for the polarization feature is irrelevant.

In the embodiments of the Figures 11 and 12 For example, the polarization feature of the phase retardation layer 122 is combined with a color-shifting layer 66 and recesses 62 in the thin film element 60. The polarization feature can of course also be provided with security elements without recesses and / or with security elements without color-shifting layers. In the latter case, the polarization feature is present on the metallically reflecting side of a thin-film element, while the opposite side appears black glossy to the viewer. For example, the shiny black surface can be used as a design element or as a black background for another security or design element.

For example, a banknote may be provided with the black glossy thin-film element in a first region and may contain a liquid-crystal layer in a see-through window of another region. If the liquid crystal layer by folding the banknote on the black surface of the Laying thin-film element, so the previously not visible or barely visible color shift effect of the liquid crystal layer clearly shows.

Furthermore, it is with reference to Fig. 13 It is also possible to arrange a phase delay layer on the side facing the absorber layer side of the thin-film element, for example over a layer of cholesteric liquid-crystalline material 66, which is arranged above a thin-film element 60. While at the in Fig. 13 shown security element 140, the layer sequence of carrier film 52, thin-film element 60 and cholesteric liquid-crystalline material 66 the structure of in Fig. 11 Corresponding to the shown security element 120, the phase retardation layer 142 of the security element 140 is arranged on the color-tilting liquid crystal layer 66. For example, the phase retardation layer 142 may be comprised of nematic liquid crystalline material and may have a thickness suitable for achieving phase retardation resulting in a phase delay between about λ / 4 or about λ / 2. With a circular polarizer 144, the polarization effect, as in Fig. 11 described, be examined by the viewer. In this case, the cholesteric liquid-crystalline material 66 acts together with the thin-film element 60 as a reflector for the phase retardation layer of nematic liquid-crystalline material 142. In the security element 140, the observer can thus see both the color-shift effect of the layer of cholesteric liquid-crystalline material 66 above the thin-film element from the side facing the absorber layer side 60 as well as the polarization effect of the nematic liquid crystalline material 142 with a suitable polarization filter 144.

The polarization effect of the security element 140 is not, as may be the case with the security element 120 of FIG Fig. 12 , affected by polarizing properties of the film 52.

It is understood that all with respect to the Fig. 1 to Fig. 13 described embodiments may in principle have a range in which the thin-film element due to the chosen thickness, in particular the dielectric spacer layer for the viewer not in the entire visible spectral range and / or not appear for all viewing angles black and therefore result in Farbkippeffekte, from the with reference to the Fig. 1 to Fig. 13 differentiate color shift effects described. It is of course also conceivable to combine a security element according to the invention with regions which have essentially the same color for the viewer in the visible spectral range and at all viewing angles.

It should also be noted that the carrier foil of the security element according to the invention can optionally also have a particular embossed diffraction structure and / or matt structure, which is arranged next to or above / below the thin-film element and produces interesting synergistic effects, in particular incident light / transmitted light effects. which further increase the counterfeit protection of the security element.

Claims (24)

1. A security element for securing data carriers, having a three-layer thin-film element (20) composed of a reflection layer (22), an absorber layer (26) and a dielectric spacing layer (24) arranged between the reflection layer and the absorber layer, in which the thickness and materials of the reflection layer (22), the absorber layer (26) and the dielectric spacing layer (24) are coordinated with each other in such a way that the thin-film element exhibits at least in a region, for viewing from the absorber layer side (26) at all viewing angles (28, 28') and in the entire visible spectral range, a very low reflection and appears black, characterized in that for viewing from the absorber layer side (26) at all viewing angles and in the entire visible spectral range, the reflection of the thin-film element (20) is at least in said region below 20%, and that the thin-film element (20) appears highly metallically glossy when viewed from the reflection layer side (22) at all viewing angles (29, 29') and in the entire visible spectral range.
2. The security element according to claim 1, characterized in that for viewing from the absorber layer side (26) at all viewing angles and in the entire visible spectral range, the reflection of the thin-film element (20) is at least in said region below 15%, particularly preferably below 10%.
3. The security element according to claim 1 or 2, characterized in that the thin-film element (20) exhibits at least in said region, for viewing from the absorber layer side (26) in the entire visible spectral range and at all viewing angles (28, 28'), no reflection maximum.
4. The security element according to at least one of claims 1 to 3, characterized in that the thin-film element (20) exhibits at least in said region, for viewing from the absorber layer side (26), a reflection maximum in the ultraviolet spectral range.
5. The security element according to at least one of claims 1 to 4, characterized in that the layer thickness of the dielectric spacing layer (24) is between 20 nm and 90 nm.
6. The security element according to claim 5, characterized in that the spacing layer (24) is formed substantially from a low-index dielectric having a refractive index n < 1.8, especially composed of SiO₂ or MgF₂, and exhibits a layer thickness between 50 nm and 90 nm, especially of about 70 nm.
7. The security element according to claim 5, characterized in that the spacing layer (24) is formed substantially from a high-index dielectric having a refractive index n ≥ 1.8, especially composed of TiO₂ or ZnS, and exhibits a layer thickness between 20 nm and 50 nm, especially of about 40 nm.
8. The security element according to at least one of claims 1 to 7, characterized in that the dielectric material of the spacing layer (24) is supplemented with an absorbent substance, especially with absorbent metal ions.
9. The security element according to at least one of claims 1 to 8, characterized in that the thin-film element (20) exhibits gaps in the form of patterns, characters or codes that form transparent or translucent regions in the thin-film element (20).
10. The security element according to claim 9, characterized in that the gaps are present only in the reflection layer of the thin-film element (20).
11. The security element according to at least one of claims 1 to 10, characterized in that the security element exhibits a color-shifting layer composed of a cholesteric liquid crystal material that faces the absorber layer side (26) of the thin-film element (20), such that the black-appearing thin-film element (20) forms a dark background for the color-shifting layer.
12. The security element according to at least one of claims 1 to 11, characterized in that the security element exhibits at least one further, machine-readable security feature, especially having magnetic, electrically conductive, phosphorescent, fluorescent or other luminescent substances.
13. The security element according to at least one of claims 1 to 12, characterized in that the security element is present on a carrier foil, especially a PET foil, having a layer thickness between 6 µm and 23 µm.
14. The security element according to at least one of claims 1 to 13, characterized in that the security element exhibits a phase-delay layer composed of a nematic liquid crystal material that faces the reflection layer side (22) of the thin-film element (20), such that the phase-delay layer forms, together with the reflection layer (22), a polarization feature that is verifiable with a polarization filter.
15. The security element according to claim 14, characterized in that the phase-delay layer is present in the form of patterns, characters or codes.
16. The security element according to at least one of claims 1 to 15, characterized in that the security element has in addition to said region, in which the thin film element (20) exhibits, for viewing from the absorber layer side (26) at all viewing angles (28, 28') and in the entire visible spectral range, a very low reflection and appears black, a second region having a thin film element, which does not appear black at all viewing angles and/or not in the entire visible spectral range.
17. A method for manufacturing a security element according to at least one of claims 1 to 16, in which a reflection layer (22), a dielectric spacing layer (24) and an absorber layer (26) are stacked to form a three-layer thin-film element (20), and in which the thickness and materials of the reflection layer (22), the absorber layer (26) and the dielectric spacing layer (24) are coordinated with each other in such a way that the thin-film element (20) exhibits at least in a region, for viewing from the absorber layer side (26) at all viewing angles (28, 28') and in the entire visible spectral range, a very low reflection and appears black, characterized in that, for viewing from the absorber layer side (26) at all viewing angles and in the entire visible spectral range, the reflection of the thin-film element (20) is below 20% in at least said region, and that the thin-film element (20) appears highly metallically glossy when viewed from the reflection layer side (22) at all viewing angles (29, 29') and in the entire visible spectral range.
18. The method according to claim 17, characterized in that, as a dielectric spacing layer (24), substantially a low-index dielectric having a refractive index n < 1.8, especially SiO₂ or MgF₂, is applied in a layer thickness between 50 nm and 90 nm.
19. The method according to claim 17, characterized in that, as a dielectric spacing layer (24), substantially a high-index dielectric having a refractive index n ≥ 1.8, especially TiO₂ or ZnS, is applied in a layer thickness between 20 nm and 50 nm.
20. The method according to at least one of claims 17 to 19, characterized in that the dielectric spacing layer (24) is vapor deposited or imprinted.
21. The method according to at least one of claims 17 to 20, characterized in that the thin-film element (20) is provided with gaps in the form of patterns, characters or codes.
22. The method according to at least one of claims 17 to 21, characterized in that the security element is provided, on the side facing the absorber layer side (26) of the thin-film element (20), with a color-shifting layer composed of a cholesteric liquid crystal material, such that the black-appearing thin-film element forms a dark background for the color-shifting layer.
23. A data carrier, especially a value document, such as a banknote, identification card or the like, having a security element according to one of claims 1 to 16.
24. A method for manufacturing a data carrier, in which a security element according to one of claims 1 to 16 is applied to a data carrier substrate or completely or partially embedded in a data carrier substrate.

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