Flat security element with optical security features

Abstract

The invention relates to a planar security element with optical security features, comprising at least one area with: - a color-shifting layer (6) - and a thermochromic layer (4) arranged below the color-shifting layer (6) in a first viewing direction (7), - and an absorbing pattern (3) arranged either between the color-shifting layer (6) and the thermochromic layer (4) or below the thermochromic layer (4) in the first viewing direction (7). To ensure a reduced thickness and lower visibility of the absorbing pattern (3) in reflected light on the side of the security element facing away from the color-shifting layer (6), the absorbing pattern (3) is designed as a black aluminum oxide layer, and a reflective layer (2) is provided below the absorbing pattern (3) in the first viewing direction (7).

Description

AREA OF INVENTION

[0001] The invention relates to a planar security element with optical security features, comprising at least one planar area with The invention comprises a color-shifting layer, a thermochromic layer arranged below the color-shifting layer in a first viewing direction, and an absorbing pattern arranged either between the color-shifting and thermochromic layers or below the thermochromic layer in the first viewing direction. The invention also relates to a method for manufacturing such a safety element. STATE OF THE ART

[0002] From EP 2234816 A2, an optically variable security element is known, wherein a substrate is provided with a print, in particular an offset print in the form of patterns, lines, characters, or a code. A thermochromic base layer is applied to the print by screen printing, flexographic printing, or intaglio printing, and an optically variable ink layer is applied to the thermochromic layer. The thermochromic layer is designed such that the color-shifting effect of the ink layer disappears for the observer when the thermochromic layer is activated. Upon cooling, the color of the thermochromic layer changes back to black or to its original dark appearance; the color-shifting effect of the ink layer then becomes clearly visible again, and the dark layer once more obscures the print beneath it.

[0003] EP 1226308 B2 discloses a security element with a layered structure in which a substrate is first printed with a dark, preferably black, inscription. A full-surface layer of thermochromic material is applied over this inscription, followed by an optically variable translucent layer. If the thermochromic layer uses a material that is dark and opaque at ambient temperature, the optically variable layer appears as a brilliant layer with a color-changing effect. Above the transition temperature of the thermochromic material, the layer becomes transparent, and the optically variable layer can only be clearly seen in the area of ​​the underlying marking. In this way, it is possible to create information that is only visible above the transition temperature of the thermochromic material.

[0004] From US 2010231846 A1, the combination of a liquid crystal layer with a thermochromic layer and a printed absorbing pattern is known, wherein the thermochromic layer can be arranged above the liquid crystal layer or below the liquid crystal layer and the absorbing pattern. PRESENTATION OF THE INVENTION

[0005] At a first temperature, the thermochromic layer obscures the absorbing pattern or exhibits a similar light absorption to the absorbing pattern, so that it is not perceptible in reflected light as seen from the color-shifting layer, whereas at a second temperature, the thermochromic layer is more transparent than at the first temperature or exhibits a different light absorption than the absorbing pattern, so that the absorbing pattern or the color-shifting effect of the color-shifting layer above the absorbing pattern is visible in reflected light as seen from the color-shifting layer.

[0006] One object of the invention is to provide a security element with optical security features, comprising a color-shifting layer, a thermochromic layer and an absorbing pattern, which results in a smaller thickness of the absorbing pattern and a lower visibility of the absorbing pattern in reflected light on the side of the security element facing away from the color-shifting layer.

[0007] This task is for a planar security element with optical security features, comprising at least one area with a color-shifting layer and a thermochromic layer arranged below the color-shifting layer in a first viewing direction, and an absorbing pattern arranged either between the color-shifting and the thermochromic layer or below the thermochromic layer in the first viewing direction, is solved by the fact that the absorbing pattern is designed as a black aluminum oxide layer and a reflective layer is provided below the absorbing pattern when viewed in the first viewing direction.

[0008] A so-called black aluminum oxide layer is known to those skilled in the art. It contains substoichiometric aluminum oxide as a significant proportion and is produced by evaporating aluminum in an oxygen-containing environment. One possible method for producing a black aluminum oxide layer is disclosed in EP 1522606 A1. This patent also refers to US 5766827 A, which specifies that the degree of blackening is determined by an oxygen content of the aluminum oxide of 19 to 58 atm% and an optical density, measured in transmission, of at least 0.3 at wavelengths from 200 nm to 1100 nm. The mole fraction of oxygen is thus between 19 and 58%. With the specified oxygen content, more precisely the mole fraction, and the optical density, the thickness and the degree of oxidation, and therefore also the degree of blackening, are sufficiently defined.

[0009] According to EP 1522606 A1, a black aluminum oxide layer with an aluminum mass coverage exceeding a certain threshold is deposited by evaporating aluminum and adding oxygen to the aluminum vapor. The degree of blackness is described by the visual color impression in reflection. Above the threshold for aluminum mass coverage, this impression is surprisingly little affected by the layer thickness. This offers several advantages. In particular, it eliminates the need to control the aluminum evaporation rate, as achieving the minimum amount of aluminum evaporated must be guaranteed. To measure the visual impression of the black layer, it is advantageous to define value ranges for the parameters a*, b*, and L* in the L*a*b* color space of CIE 1976 [DIN 5033] and to monitor compliance with these ranges. A layer would be absolutely black if L* = 0, i.e., no light is reflected.However, this is rarely achievable in practice. To characterize the reflection properties, the value L* in the CIELAB L*a*b* color space 1976, or a value closely correlated with L*, can be advantageously used. The reflection properties are thus kept within a target range defined by the product requirements. This is particularly advantageous when an opaque substrate, such as white PET film, is used as the ribbon-like substrate.

[0010] According to EP 1522606 A1, below the minimum value of the aluminum mass coverage, no operating point can be found across the entire range of oxygen addition at which the layer exhibits a sufficiently black color. This can be partly explained by the fact that below a minimum layer thickness, the optical density of the aluminum oxide is too low, so that light passing through the substrate or reflected from the substrate becomes visible. Above the minimum layer thickness, however, the influence of the substrate disappears, so that the process becomes almost independent of layer thickness variations, provided the minimum layer thickness is maintained. Another possible explanation for this effect is that, in addition to the oxidation state of the aluminum, structural effects also play a role in the blackening process, influencing light absorption.For this reason, the minimum value for aluminum mass coverage according to EP 1522606 A1 is not a value independent of technological parameters, but must be determined anew for each set of process parameters. Furthermore, it depends on the quality requirements placed on the coated product. Above a certain aluminum mass coverage, a structure forms that leads to broadband, strong light absorption. This is already partially the case above 15 µg / cm², frequently above 20 µg / cm², and certainly above 35 µg / cm². Maintaining a minimum aluminum mass coverage also simplifies process control, as it only needs to be ensured that the minimum aluminum mass coverage is not undershot; the blackening can then be controlled by adjusting just one parameter.This parameter can be the amount of oxygen supplied to the evaporation chamber when the aluminum mass coverage of the aluminum oxide layer is essentially constant, or the aluminum evaporation rate when the amount of oxygen supplied to the evaporation chamber is essentially constant.

[0011] The reflective layer reduces the visibility of the absorbing pattern in reflected light on the side of the security element facing away from the color-shifting layer. This is advantageous because the pattern only plays a role in reflected light on the other side of the security element, the side with the color-shifting layer. The reflective layer can be, for example, a metal layer, preferably an aluminum layer.

[0012] The black aluminum oxide layer is thinner than printed layers, resulting in a correspondingly flat absorbing pattern. Similarly, the reflective layer is typically so thin that the combined thickness of the black aluminum oxide layer and the reflective layer is less than the thickness of printed layers.

[0013] The reflective layer is typically positioned directly beneath the absorbing pattern, without any intermediate layer. In particular, the reflective layer can be applied directly to the black aluminum oxide layer, or vice versa.

[0014] Due to the reflective layer, the absorbing pattern appears less absorbent when viewed from the reflective layer than when viewed from the first viewing direction, i.e., when viewing the absorbing pattern through the color-shifting layer. Therefore, the absorbing pattern is less pronounced on the underside of the security element than on the top side, where it interacts with the color-shifting layer and is intended to be visible.

[0015] In the case of an aluminum layer, the reflective layer can be produced in a single operation, i.e., without removing the already partially coated material from the coating system or introducing a new coating material, along with the black aluminum oxide layer. The reflective layer can then transition seamlessly into the black aluminum oxide layer in the direction of thickness. This can be achieved either by starting with the production of the aluminum layer and then continuously increasing the oxygen content during the coating process, for example, during vacuum coating, so that a black aluminum oxide layer forms with increasing layer thickness, or by starting with the production of the black aluminum oxide layer and continuously decreasing the oxygen content during the coating process, for example, during vacuum coating, so that an aluminum layer is deposited at the end.

[0016] A thermochromic layer contains substances that change their light absorption when exposed to temperature changes, i.e., when excited. This alters the light absorption of the thermochromic layer itself. These changes in light absorption are usually due to alterations in the molecular or crystal structure. The change in light absorption results in either the thermochromic layer appearing transparent in the unexcited state and opaque in the excited state (less transparent than in the unexcited state), or the thermochromic layer appearing opaque in the unexcited state and transparent in the excited state (less opaque than in the unexcited state). The change in light absorption can be reversible; for example, after heating, the thermochromic layer will return to its original light absorption, particularly its original color, upon cooling.However, there are also thermochromic layers that irreversibly change their light absorption, particularly their color, after a temperature change. This means, for example, that after heating, the thermochromic layer retains the altered light absorption, especially the altered color, and does not return to its original light absorption, especially the original color, even after cooling. Both reversible and irreversible thermochromic substances or thermochromic layers are known from the prior art.

[0017] For the safety element according to the invention, thermochromic layers are particularly suitable which obscure the absorbing pattern at a first temperature or have a similar light absorption to the absorbing pattern, and which are more transparent at a second temperature than at the first temperature or have a different, namely lower, light absorption than the absorbing pattern.

[0018] A color-shifting layer creates a color-shifting effect, meaning that the perceived color of the layer changes depending on the viewing angle. This means that at a steep viewing angle, i.e., at an angle of approximately 75°–90° to the surface of the security element, the layer produces a different perceived color than at a shallow viewing angle, i.e., an angle of less than 75°, and especially less than 45°. The viewing angle is 90° when the security element is viewed perpendicular to its plane, and 0° when viewed parallel to the plane of the security element.

[0019] Known color-shifting layers that can be advantageously used in the present invention are, for example, liquid crystal layers (LC layers), layers with liquid crystal pigments (LC pigment layers) and layers with interference pigments.

[0020] An LC layer is typically first arranged on a separate substrate, as the liquid crystals contained in the LC layer must first be electrically and / or magnetically aligned and / or along a structure or embossing of the substrate, e.g., on a film surface, in order to be suitable for generating a color-shifting effect. Preferably, the alignment is achieved by the preferred direction of the substrate, which can be, in particular, a plastic film. Only then is the LC layer applied to one of the layers of the security element, e.g., by means of an adhesive layer. The substrate of the LC layer can either be removed from the LC layer or left in place.

[0021] Liquid crystal pigment layers (LC pigment layers) comprise both liquid crystal pigments and a carrier substance, namely a binder, which can hold the liquid crystal pigments without impairing their function. It is essential that this carrier substance be transparent.

[0022] In order to produce clearly recognizable color impressions, an LC layer or an LC pigment layer requires an underlying dark to black absorber layer.

[0023] Layers containing interference pigments, that is, pigments whose effect is based primarily or entirely on the interference of light at thin, high-refractive-index layers, comprise both the interference pigments themselves and a carrier substance, namely a binder, which can hold the interference pigments without impairing their function. It is essential that this carrier substance be transparent. A dark to black absorber layer placed beneath the interference pigment layer intensifies the color effect, shifting from pastel shades to more intense hues.

[0024] When an LC layer, an LC pigment layer, or a layer with interference pigments is used, no additional absorber layer is required. The function of the absorber layer is fulfilled by the thermochromic layer when it is in a state of high light absorption, as well as by the absorbing pattern. The color of the color-shifting layer and the color-shifting effect when the security element is tilted are then clearly visible.

[0025] Between the color-shifting layer, the thermochromic layer, and the absorbing pattern, one or more further layers, such as adhesive layers or primer layers, can be arranged. These further layers must be sufficiently transparent that the inventive effect, i.e., the change in the light-absorbing background of the color-shifting layer, is still perceptible when viewed from the first direction.

[0026] In one embodiment of the invention, the reflective layer is designed to be congruent with the absorbing pattern. While the invention would in principle also be possible with a continuous reflective layer, thus covering the spaces between the absorbing pattern, in this embodiment a reflective layer is only provided where there is also an absorbing pattern.

[0027] If the absorbing pattern is arranged between the color-shifting and the thermochromic layer, it can be provided that the thermochromic layer has such a similar light absorption to the absorbing pattern at a first temperature that, when viewed in the first direction, a uniform color impression prevails over the surface of the color-shifting layer, while at a second temperature the thermochromic layer has a lower light absorption than the absorbing pattern, so that, when viewed in the first direction, the color intensity of the color-shifting layer is greater in the area of ​​the absorbing pattern than in an area outside the absorbing pattern.

[0028] Because the thermochromic layer, in its opaque state, exhibits the same or very similar light absorption as the absorbing pattern, they appear together, from the first viewing angle, as a continuous, dark, absorbing surface, which makes the color effect of the color-shifting layer clearly visible. The absorbing pattern does not produce a corresponding pattern in the color-shifting layer; the latter essentially displays the same color with the same intensity wherever it overlaps with the thermochromic layer, at a given viewing angle. However, when the thermochromic layer is transparent, it no longer acts as an absorber for the color-shifting layer, or at least less so than the absorbing pattern, whose light absorption does not change with temperature.Consequently, only the absorbing pattern acts as an absorber, or at least the absorbing pattern acts more strongly as an absorber than the thermochromic layer. Therefore, the color effect of the color-shifting layer is only visible, or at least more intensely visible, as a vibrant color where the absorbing pattern lies beneath it. Outside of the absorbing pattern, no color from the color-shifting layer is visible, or only a color with a lower intensity than that visible above the absorbing pattern.

[0029] If the absorbing pattern is positioned between the color-shifting and thermochromic layers, and the individual layers are arranged on a common substrate, the substrate can be located in front of the color-shifting layer, between the color-shifting layer and the absorbing pattern, between the absorbing pattern and the thermochromic layer, or after the thermochromic layer when viewed from the first direction.

[0030] If the absorbing pattern is located below the thermochromic layer in the first viewing direction, it can be provided that the thermochromic layer has such high light absorption at a first temperature that, when viewed in the first direction, the absorbing pattern is obscured and a uniform color impression prevails over the surface of the color-shifting layer, while at a second temperature the thermochromic layer has lower light absorption than the absorbing pattern, so that, when viewed in the first direction, the color intensity of the color-shifting layer is greater in the area of ​​the absorbing pattern than in an area outside the absorbing pattern.

[0031] Since the thermochromic layer exhibits high light absorption in its opaque state, the underlying absorbing pattern is obscured when viewed from the first angle. The thermochromic layer forms a continuous, dark, absorbing surface, which is essential for the color effect of the color-shifting layer to be clearly visible. The absorbing pattern does not produce a corresponding pattern in the color-shifting layer; the latter essentially displays the same color and intensity wherever it overlaps with the thermochromic layer, regardless of the viewing angle. However, when the thermochromic layer is transparent, it no longer acts as an absorber for the color-shifting layer, or at least less so than the absorbing pattern, whose light absorption does not change with temperature.Consequently, only the absorbing pattern acts as an absorber, or at least the absorbing pattern acts more strongly as an absorber than the thermochromic layer. Therefore, the color effect of the color-shifting layer is only visible, or at least more intensely visible, as a vibrant color where the absorbing pattern lies beneath it. Outside of the absorbing pattern, no color from the color-shifting layer is visible, or only a color with a lower intensity than that visible above the absorbing pattern.

[0032] If the absorbing pattern is located below the thermochromic layer in the first viewing direction, and the individual layers are arranged on a common support layer, the support layer can be located in front of or above the color-shifting layer, between the color-shifting layer and the thermochromic layer, between the thermochromic layer and the absorbing pattern, or after or below the absorbing pattern.

[0033] In a preferred embodiment of the invention, the color-shifting layer is a liquid crystal layer. This layer appears colored and produces a color-shifting effect only when a dark absorbing layer is present behind it in the viewing direction. According to the invention, this is either the thermochromic layer in its opaque state, resulting in a continuous colored area without a pattern, with a change in color occurring at different viewing angles; or it is the absorbing pattern, resulting in the pattern appearing colored in contrast to the area surrounding the pattern, which appears less colored or, ideally, not colored at all due to the color-shifting layer. At most, colors from layers located below the thermochromic layer and the absorbing pattern may show through in the area surrounding the pattern.

[0034] The liquid crystal layer is usually attached to one of the other layers of the flat security element using an adhesive layer.

[0035] According to one embodiment of the invention, the thermochromic layer is a thermochromic layer with reversible light absorption. This means that by heating and subsequent cooling, the security element can be returned to its initial state, from which it can be reheated to the excited state, and so on. The thermochromic layer can therefore be repeatedly switched from an opaque state to a transparent state and vice versa. This embodiment is suitable for security elements that are frequently used for authenticity verification, such as identity cards or banknotes.

[0036] According to an alternative embodiment of the invention, the thermochromic layer is a thermochromic layer with an irreversible change in light absorption. This means that a single heating process results in a single change in light absorption, and subsequent cooling does not alter this change. Therefore, the security element cannot be returned to its original state. The thermochromic layer can thus only be changed once from an opaque state to a transparent state, or vice versa. This embodiment is suitable for security elements that serve only a single authentication purpose, such as seals for packaging of valuable goods, vouchers, or scratch-off lottery tickets.

[0037] According to one embodiment of the invention, the thickness of the absorbing pattern is less than 1 µm. Such a small thickness combined with good light absorption can be achieved by vapor-depositing a black aluminum oxide layer.

[0038] According to one embodiment of the invention, the planar safety element comprises a carrier layer, and the absorbing pattern is arranged in one or more recesses of the carrier layer. In particular, the absorbing pattern is flush with the surface of the carrier layer. In this way, the thickness of the absorbing pattern does not affect the height of the safety element, which generally must include a carrier layer anyway. Any congruent reflective layer would be arranged at the bottom of the recess, below the absorbing pattern. It is also conceivable that the absorbing pattern is arranged at the bottom of the recess and the reflective layer, in particular a congruent one, is arranged above the absorbing pattern and is flush with the surface of the carrier layer.

[0039] According to one embodiment of the invention, the thermochromic layer can be manually activated by friction. Thus, no technical devices are necessary to bring about the change in light absorption.

[0040] The invention also includes data carriers or valuable documents that have a planar security element according to the invention.

[0041] The safety element according to the invention generally comprises a carrier substrate in the form of a carrier layer, onto which the individual layers are applied. Suitable carrier substrates include, for example, transparent carrier films, preferably flexible plastic films. For example, the support substrate can be made from or comprise one of the following materials: polyimide (PI), polypropylene (PP), monoaxially oriented polypropylene (MOPP), biaxially oriented polypropylene (BOPP), polyethylene (PE), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherketone (PEK), polyethyleneimide (PEI), polysulfone (PSU), polyaryletherketone (PAEK), polyethylene naphthalate (PEN), liquid crystal polymers (LCP), polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyamide (PA), polycarbonate (PC), cycloolefin copolymers (COC), polyoxymethylene (POM), acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC).Ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene hexafluoropropylene fluoroterpolymer (EFEP), cellulose- or lignin-based plastics, polyhydroxyalkanoates (PHA), thermoplastic starch (TPS), polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT) and / or at least one recycled and / or biodegradable and / or marine-degradable plastic and / or mixtures and / or copolymers of these materials. The carrier films can be transparent, translucent, semi-opaque, or opaque.

[0042] The support layer formed from the support substrate preferably has a thickness of 5-700 µm, preferably 5-200 µm, and particularly preferably 5-50 µm.

[0043] The security element can also be surface-treated, coated, or laminated on one or both surfaces, for example, coated or laminated with plastics, or lacquered to protect the security features on the security element against mechanical, physical, and / or chemical influences. A protective lacquer layer can be based, for example, on nitrocellulose, acrylates and their copolymers, polyamides and their copolymers, polyvinyl chlorides and their copolymers, or consist of a cross-linking lacquer. Furthermore, the security element can be provided with an adhesive layer on one or both sides to enable it to be affixed to or embedded in a data carrier or valuable document. This adhesive layer can be applied as a heat-seal, cold-seal, or self-adhesive coating.

[0044] The layers according to the invention can be applied to the substrate to form the security element. This security element can then be assembled, before or after surface treatment, and at least partially embedded in or applied to a data carrier or a valuable document as a strip, thread, or patch. In this respect, the invention also encompasses a data carrier or a valuable document, e.g., a banknote, which incorporates a security element according to the invention.

[0045] In a method for producing a planar safety element according to the invention, it is provided that either an aluminum layer is first deposited as a reflective layer and immediately afterwards a black aluminum oxide layer is deposited as an absorbing pattern by increasing the oxygen content, or that a black aluminum oxide layer is first deposited as an absorbing pattern and immediately afterwards an aluminum layer is deposited as a reflective layer by reducing the oxygen content.

[0046] "Immediately following" here means that one step follows the other in time. This also means that the two layers – the black aluminum oxide layer and the reflective layer – are spatially connected directly, without any further intermediate layer.

[0047] The aluminum layer (as a reflective layer) and the black aluminum oxide layer can be produced in a single operation, without removing the partially coated material from the coating system. The reflective layer can then transition seamlessly into the black aluminum oxide layer in the thickness direction. This results in a particularly strong and simple bond between the reflective layer and the black aluminum oxide layer.

[0048] The process either begins with the production of an aluminum layer and then the oxygen content is continuously increased during the coating process, for example during vacuum coating, so that a black aluminum oxide layer forms with increasing layer thickness. Or, the process begins with the production of a black aluminum oxide layer and the oxygen content is continuously reduced during the coating process, for example during vacuum coating, so that an aluminum layer is deposited at the end. BRIEF DESCRIPTION OF THE FIGURES

[0049] The invention will now be explained in more detail with reference to schematic figures that illustrate exemplary embodiments of a device according to the invention. These figures show Fig. 1 a cross-section of a first safety element according to the invention, Fig. 2 a cross-section of a second safety element according to the invention, Fig. 3 a cross-section of a third safety element according to the invention, Fig. 4 a cross-section of a fourth safety element according to the invention, Fig. 5 a top view of a safety element according to the invention according to one of the Fig. 1-4 . WAYS TO IMPLEMENT THE INVENTION

[0050] Fig. 1 This shows a cross-section of the safety element to illustrate its layered structure. The plane of the safety element is horizontal here. For a top view of the safety element, see... Fig. 5 , the absorbing pattern 3 can be, for example, the capital letter E, of which the three crossbars of the E are visible in cross-section.

[0051] On a substrate layer 1, here a PET film, a reflective layer 2, here an aluminum layer, is first applied, and congruently on top of this, an absorbing pattern 3. The substrate layer 1 is first coated with aluminum for the reflective layer 2 and then with substoichiometric aluminum oxide, which forms the absorbing pattern 3.

[0052] A thermochromic layer 4 is applied to the substrate layer 1 with the absorbing pattern 3, and a color-shifting layer 6, in this case an LC layer, is applied over this. The LC layer is produced on a substrate and, while still on the substrate, is bonded to the thermochromic layer 4 by means of an adhesive layer 5. The substrate of the LC layer, which is in Fig. 1 The layer above the color-shifting layer 6 can either remain on it or be peeled off.

[0053] In the first state of the thermochromic layer 4, when it is opaque and appears black, it acts as an absorber for the overlying LC layer, which acts as a color-shifting layer 6. From the first viewing direction 7, the observer sees the effect of the color-shifting layer 6 in reflected light: a coloration of a specific hue across the entire surface of the color-shifting layer 6, which coincides with the thermochromic layer 4. The absorbing pattern 3, for example, the capital letter E, is not visible because it lies beneath the now black thermochromic layer 4. From the second viewing direction 8, the observer sees a bright pattern in reflected light through the now transparent support layer 1. This pattern is formed by the reflective layer 2 on the underside of the absorbing pattern 3, surrounded by a black background formed by the black thermochromic layer 4. The observer would therefore see, for example...A bright E can be seen against a dark background. In transmitted light, depending on the transparency of the thermochromic layer 4, either – if the thermochromic layer 4 is opaque – only a black area is visible, or – if the thermochromic layer 4 is somewhat transparent – ​​the absorbing pattern 3 can be seen as slightly darker than the surrounding area.

[0054] In the second state of the thermochromic layer 4, when it is translucent and appears transparent, it no longer acts as an absorber for the overlying LC layer 6, which acts as a color-shifting layer. Only the absorbing pattern 3 still serves as an absorber for the color-shifting layer 6, and in the first viewing direction 7, an intense color is visible in the area of ​​the absorbing pattern 3 in reflected light, thus revealing the letter E (see Fig. 5 ), but not in between. The area outside the absorbing pattern 3 appears less intensely colored or colorless if the substrate 1 is transparent. Thus, in reflected light, in the first viewing direction 7, one sees, for example, a large colored E that changes color at least once depending on the viewing angle, surrounded by a colorless or at least less intensely colored background. In the second viewing direction 8, the absorbing pattern 3 appears white or at least light and does not stand out from the background, which also appears light. In transmitted light, the absorbing pattern 3 is dark and therefore clearly recognizable. In transmitted light, one would see, for example, a dark E.

[0055] In principle, it would also be conceivable that the carrier layer 1 is arranged between the absorbing pattern 3 and the thermochromic layer 4, or between the thermochromic layer 4 and the color-shifting layer 6, or above the color-shifting layer 6. In these cases, it would also be conceivable that the absorbing pattern 3 is produced first, followed by the reflective layer 2: in the first case, the absorbing pattern 3 would be applied to the carrier layer 1, and in the second and third cases, to the thermochromic layer 4.

[0056] In Fig. 2 The thermochromic layer 4 is not as described in Fig. 1 The thermochromic layer 4 is not located between the color-shifting layer 6 and the absorbing pattern 3, but rather below the absorbing pattern 3. For example, the thermochromic layer 4 is located on the underside of the support layer 1, which contains the absorbing pattern 3 and the reflective layer 2 on its upper side. However, the support layer 1 could also be located below the thermochromic layer 4, or between the absorbing pattern 3 and the color-shifting layer 6, or above the color-shifting layer 6.

[0057] In the first state of the thermochromic layer 4, when it is opaque and appears black, it forms, together with the absorbing pattern 3, the absorber for the overlying LC layer as the color-shifting layer 6. From the first viewing direction 7, the observer sees the effect of the color-shifting layer 6 in reflected light, i.e., the entire color-shifting layer 6 is tinted a specific color. The absorbing pattern 3, e.g., the capital letter E, is not visible against the now black thermochromic layer 4. From the second viewing direction 8, the observer sees only the black thermochromic layer 4 in reflected light. In transmitted light, depending on the transparency of the thermochromic layer 4, either—if the thermochromic layer 4 is opaque—only a black area is visible, or—if the thermochromic layer 4 is somewhat transparent—the absorbing pattern 3 is recognizable as slightly darker than the surrounding area.

[0058] In the second state of the thermochromic layer 4, when it is translucent and appears transparent, it no longer acts as an absorber for the overlying LC layer 6, which acts as the color-shifting layer. Only the absorbing pattern 3 still serves as an absorber for the color-shifting layer 6, and in the first viewing direction 7, the color-shifting effect is visible in the area of ​​the absorbing pattern 3 under reflected light, but not in the area in between. The area outside the absorbing pattern 3 appears transparent or light to white. Thus, in reflected light, in the first viewing direction 7, one sees, for example, a large colored E that changes color at least once, depending on the viewing angle, against a colorless or at least less intensely colored background. In the second viewing direction 8, the absorbing pattern 3 appears white or at least light and does not stand out against the background, which also appears light. In transmitted light, the absorbing pattern 3 is dark and therefore clearly visible.In transmitted light, one would therefore be able to see, for example, a dark E.

[0059] In principle, it would also be conceivable that the carrier layer 1 is located in front of the color-shifting layer 6, between the color-shifting layer 6 and the absorbing pattern 3, or after the thermochromic layer 4. In the second case, it would also be conceivable that during production, the absorbing pattern 3 is first produced on the carrier layer 1 and then the reflective layer 2 is applied to the absorbing pattern 3.

[0060] In the Fig. 1 und 2 In the described embodiments, the thermochromic layer 4 could be changed from the first, opaque state to the second, transparent state, or vice versa, by heating, for example by rubbing with the hand. The change of state can be irreversible, meaning that cooling has no effect, or reversible, so that cooling restores the initial state and rubbing causes another change of state.

[0061] Fig. 3 shows a cross-section of a safety element with the same layer sequence as in Fig. 1 Unlike Fig. 1 In the recesses 9 of the substrate layer 1, a reflective layer 2, again an aluminum layer, is first deposited, and on this, within the recesses 9, an absorbing pattern 3 is applied. The recesses 9 of the substrate layer 1 thus form a pattern that corresponds to the absorbing pattern 3. The recesses 9 of the substrate layer 1 are first coated with aluminum for the reflective layer 2 and then with substoichiometric aluminum oxide, which forms the absorbing pattern 3. The absorbing pattern 3 is flush with the surface of the substrate layer 1. Otherwise, the manufacturing process and layer structure are identical to those of [reference to be added]. Fig. 1 , whereby in the manufacture of the safety element according to Fig. 3 First, the reflective layer 2 is applied, and then the absorbing pattern 3 is applied, for example by vapor deposition.

[0062] Fig. 4 shows a cross-section of a safety element with the same layer sequence as in Fig. 2 Unlike Fig. 2 Here, in recesses 9 of the substrate layer 1, a reflective layer 2, again an aluminum layer, is first deposited, and on this, within the recesses 9, an absorbing pattern 3 is applied. The recesses 9 of the substrate layer 1 thus form a pattern that corresponds to the absorbing pattern 3. The recesses 9 of the substrate layer 1 are first coated with aluminum for the reflective layer 2 and then with substoichiometric aluminum oxide, which forms the absorbing pattern 3. The absorbing pattern 3 is flush with the surface of the substrate layer 1. Otherwise, the manufacturing process and layer structure are identical to those of Fig. 2 , whereby in the manufacture of the safety element according to Fig. 4 first the reflective

[0063] Layer 2 and the absorbing pattern 3 is applied to it, for example by vapor deposition. REFERENCE MARK LIST

[0064] 1 Carrier layer 2 Reflective layer 3 Absorbing pattern 4 Thermochromic layer 5 Adhesive layer 6 Color-shifting layer 7 First viewing direction 8 Second viewing direction 9 Recess

Claims

1. Planar security element with optical security features, comprising at least one area with - a color-shifting layer (6) - and a thermochromic layer (4) arranged in a first viewing direction (7) below the color-shifting layer (6), - and an absorbing pattern (3) arranged either between the color-shifting (6) and the thermochromic layer (4) or in the first viewing direction (7) below the thermochromic layer (4), characterized by the fact that the absorbing pattern (3) is formed as a black aluminium oxide layer and, as seen in the first viewing direction (7), a reflective layer (2) is provided under the absorbing pattern (3).

2. Planar safety element according to claim 1, characterized by the fact that the reflective layer (2) is a metal layer.

3. Flat safety element according to claim 2, characterized by the fact that the reflective layer (2) is an aluminum layer.

4. Flat safety element according to one of the preceding claims, characterized by the fact that the reflective layer (2) is identical to the absorbing pattern (3).

5. Flat safety element according to one of the preceding claims, characterized by the fact thatthe absorbing pattern (3) is arranged between the color-shifting (6) and the thermochromic layer (4) and the thermochromic layer (4) has a light absorption similar to that of the absorbing pattern (3) at a first temperature, such that when viewed in the first direction (7) a uniform color impression prevails over the surface of the color-shifting layer (6), while at a second temperature the thermochromic layer (4) has a lower light absorption than the absorbing pattern (3), so that when viewed in the first direction (7) the color intensity of the color-shifting layer (6) is greater in the area of ​​the absorbing pattern (3) than in an area outside the absorbing pattern (3).

6. Planar safety element according to one of claims 1 to 4, characterized by the fact thatThe absorbing pattern (3) is arranged under the thermochromic layer (4) in the first viewing direction (7), and the thermochromic layer (4) has such high light absorption at a first temperature that, when viewed in the first viewing direction (7), the absorbing pattern (3) is obscured and a uniform color impression prevails over the surface of the color-tilting layer (6), while at a second temperature the thermochromic layer (4) has lower light absorption than the absorbing pattern (3), so that, when viewed in the first viewing direction (7), the color intensity of the color-tilting layer (6) is greater in the area of ​​the absorbing pattern (3) than in an area outside the absorbing pattern (3).

7. Planar safety element according to one of the preceding claims, characterized by the fact that the color-shifting layer (6) is a liquid crystal layer.

8. Flat safety element according to one of the preceding claims, characterized by the fact that the thermochromic layer (4) is a thermochromic layer with reversible change in light absorption.

9. Planar safety element according to one of claims 1 to 7, characterized by the fact that the thermochromic layer (4) is a thermochromic layer with irreversible change in light absorption.

10. Flat safety element according to one of the preceding claims, characterized by the fact that the thickness of the absorbing pattern (3) is less than 1 µm.

11. Planar safety element according to one of the preceding claims, characterized by the fact that this comprises a carrier layer (1) and the absorbing pattern (3) is arranged in one or more recesses (9) of the carrier layer (1).

12. Planar safety element according to one of the preceding claims, characterized by the fact that the thermochromic layer (4) can be manually activated by friction.

13. Data carrier or security document comprising a planar security element according to one of claims 1 to 12.

14. Method for producing a planar safety element according to one of claims 3 to 12, wherein either an aluminum layer is first deposited as a reflective layer (2) and immediately afterwards a black aluminum oxide layer is deposited as an absorbing pattern (3) by increasing the oxygen content, or wherein a black aluminum oxide layer is first deposited as an absorbing pattern (3) and immediately afterwards an aluminum layer is deposited as a reflective layer (2) by reducing the oxygen content.

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