EP3098086A1 - Piezochrome security element - Google Patents

Abstract

The invention relates to a piezochromic security element (30) for securing valuables, comprising at least one feature region (32) comprising an elastomer (34) and a plurality of magnetically alignable particles (36), preferably formed of magnetite and / or superparamagnetic particles wherein the magnetically alignable particles (36) in the elastomer (34) have been magnetically arranged in the form of a regular grid to form a photonic crystal, and wherein the feature region (32) exhibits a first visual appearance without external force, and upon application of tensile or compressive forces (42; 44), due to a change in the lattice spacing of the regular grating of the photonic crystal, exhibits a second visual appearance which has a discernible hue change from the first visual appearance.

Description

The invention relates to a security element for securing valuables, a method for producing such a security element and a data carrier equipped with such a security element.

Data carriers, such as valuables or identity documents, or other valuables, such as branded articles, are often provided with security elements for the purpose of security, which permit verification of the authenticity of the data carriers and at the same time serve as protection against unauthorized reproduction.

The authentication of security elements utilizes various human senses, such as the visual perception of seeing optically variable colors, the auditory perception of hearing the distinctive sound of a banknote substrate, or the tactile perception of feeling elevated stitch patterns on a bill.

Interactive security features are particularly interesting as counterfeit protection, because they attract special attention through the involvement of the user and are also particularly easy to memorize through the involvement of several senses.

Banknotes and other value documents currently use only a few interactive authentication features. One known example is a thermochromic security feature for banknotes in which the heat of a fingertip is sufficient to change the color of the banknote at a particular location. However, such thermochromic security features usually only work satisfactorily when the ambient temperature well below the body temperature of the user. If the ambient temperature is too high, the feature is often already triggered or there is no noticeable effect.

Proceeding from this, the object of the invention is to provide a security element of the type mentioned at the beginning, which permits an interactive authenticity check independently of the ambient conditions.

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

According to the invention, a generic security element is provided with at least one feature area comprising an elastomer and a plurality of particles, preferably formed of magnetite and / or superparamagnetic particles, the particles being magnetically magnetizable in position in the elastomer Form of a regular grid have been arranged to form a photonic crystal. The feature area exhibits a first visual appearance without external force, and upon application of tensile and / or compressive force due to a change in lattice spacing of the regular grating of the photonic crystal, exhibits a second visual appearance having a discernible hue change from the first visual appearance.

Preferably, the external force is a mechanical force. Alternatively or additionally, the external force is a magnetic force.

As will be explained in more detail below, the feature region generates characteristic reflection colors, which are essentially given by the spacing of the lattice planes of the photonic crystal formed by the particles. By subjecting the feature area with tensile and / or compressive forces, the security element is elastically deformed and thereby also changes the color-determining distance of the lattice planes. Because of the elasticity of the elastomer, the security element returns after removing the external forces back to the starting position with the original lattice spacing and thus the original color. The tensile and / or compressive stress can be applied by the user, for example, by folding, buckling or bending of the security element or by local application of pressure, such as with a thumb or index finger. This corresponds in particular to a mechanical force.

The particles are magnetically positionable particles which have been magnetically placed in the elastomer in the form of the regular lattice at the time of curing (/ crosslinking) of the elastomer. The relative arrangement of the particles to the elastomer is irreversible. The particles can be arranged with the elastomer by a force - which can also be magnetic - in a different grid spacing. This elastic deformation is naturally reversible.

Furthermore, it can be provided that the user also uses a tool instead of a finger. An aid may be, for example, an electromagnet or a permanent magnet in addition to a pin in order to achieve a deformation (by means of tensile and compressive forces) of the security element and thus a change in the original hue. Preferably, in the case of a magnet as an aid, the elastomer allows the magnetizable particles to be moved by a magnetic force of the magnet Magnetic field of their original arrangement, ie without external force, take a different, new arrangement, whereby a color changes is caused.

The user can thus interactively trigger a reversible color change of the security element.

Preferably, aids, in particular magnets may have a dark color. Particularly preferably, the aids can have one or more dark or black coating (s), so that a coloring of the elastomer or the security element is not required, as will be explained later.

The state without external force is hereinafter also referred to as unloaded state, the state with the application of tensile or compressive forces as a loaded state of the feature area or the security element.

In an advantageous embodiment, the magnetically orientable particles are nanoparticles having a size below 100 nm. However, the magnetically orientable particles may also be agglomerates of nanoparticles. The nanoparticles have a size below 100 nm, while the agglomerate size is in particular between 50 and 300 nm. The nanoparticles preferably have a size of less than 20 nm, for example from 6 to 12 nm. The magnetically orientable particles are preferably formed from magnetite, paramagnetic particles or superparamagnetic particles. The particles with superparamagnetic properties or with a very low remanence preferably consist of non-magnetically oriented aggregated nano-magnetite particles and / or superparamagnetic particles (eg carbonyl iron). The term magnetically oriented particles in their position covers both individual nanoparticles and agglomerates of nanoparticles.

Paramagnets exhibit non-zero magnetization only as long as they are in an external magnetic field. The magnetically alignable particles are thus magnetically magnetizable temporarily.

Advantageously, the magnetically-alignable particles forming the photonic crystal are all substantially the same size and are in the range of ± 20%, preferably in the range of ± 10%, around a central size value.

Preferably, the feature area is machine-readable or machine-readable. In particular, it may be provided that the color change is detected by means of a sensor in a tester and the reversible deformation of the elastomer via a magnet (electromagnet, permanent magnet), a pressurization via a mechanical plunger, a roller and a Zugbeaufschlagung over a wrap angle or a differential speed in one Transport system takes place.

In an advantageous embodiment, the feature area remains substantially color constant when tilting the security element. The color change caused by the external forces is then easy to recognize and particularly impressive, since it is not superimposed by an optical variability of the security element.

The security element may have a homogeneous feature area with a uniform photonic crystal. In advantageous designs However, the feature area will have several subregions with different arrangements of the magnetically alignable particles, the subregions advantageously showing different first visual appearances and / or different second visual appearances.

The first and second appearances may each have a hue in the visible spectral range, for example, the reversible hue change between green and blue or between red and green may take place. However, it is also possible that the reflection color of the photonic crystal is either outside the visible spectral range in the loaded or unloaded state. The feature region then appears colorless, transparent or in a color produced by other colorants in this state, depending on the color of the elastomer.

The at least one feature region may preferably have a plurality of partial regions with different deformation properties. In particular, a plurality of independent / separate / spaced feature areas may have mutually different deformation characteristics.

For example, different deformation properties can be achieved by influencing the Shore hardness or elongation properties of the elastomer by controlling the degree of crosslinking or vulcanization.

For example, two partial regions with different Shore hardness or elongation properties can be produced by using two elastomers with different Shore hardnesses or elasticities. Here, a first elastomer having a higher elasticity than the second Elastomer has to be applied in both partial areas. The second elastomer is then applied only in the second portion. Consequently, then the first portion has a higher elasticity than the second portion.

For rubbers, for example, this can be achieved by using 0-5% vulcanization accelerator 0-5%, vulcanization retarder and 0-2% plasticizer in Katuschuk.

In the case of UV-crosslinking polymers, the degree of crosslinking can be influenced by a modulated exposure mask. For this one would apply a (not yet cross-linked) elastomer to a carrier substrate. Thus, first a first partial area can be networked with a first radiation source and a diaphragm, and then the second partial area can be networked with a second radiation source. By selecting two different photoinitiators in an elastomer starting material having different spectral absorption properties (e.g., other wavelengths), one can thus determine the number of free radical initiators in the regions, thereby affecting the chain length, thereby adjusting the elasticity.

For example, two portions having different hue changes in the case of an external force can be generated by using an elastomer. In this case, the elastomer is applied in both partial areas in a first step. In a second step, the elastomer is applied again, but only in the second subregion. Consequently, the first subregion then has a smaller layer thickness than the second subregion, as a result of which the elongation occurs when external force is applied the sub-areas and thus different color changes are achieved.

For example, a carrier substrate may have a varying layer thickness, so that a higher extensibility is present in one area with a layer thickness that is smaller than in another area (with a higher layer thickness). In the area with the lower layer thickness, the color change sets earlier, so that according to the layer thickness variation, a pattern / motif is recognizable. Furthermore, alternatively or additionally, a stabilizing foil can be provided. In the area where the stabilizing film is provided, then higher tensile and / or compressive forces must be applied to achieve a color change.

In an advantageous development of the invention, the photonic crystal of the feature region reflects light in the infrared spectral range in at least one subregion without external force and reflects light in the visible spectral range, in particular in the case of tensile or compressive forces due to a change in the lattice spacings of the regular lattice of the photonic crystal Redden.

In a further advantageous development, the photonic crystal of the feature region reflects light in the visible spectral range, in particular in the blue, in at least one subarea and reflects light in the ultraviolet upon application of tensile or compressive forces due to a change in the lattice spacings of the regular lattice of the photonic crystal spectral range.

Although in the invention the color change perceptible by a human user is in the foreground, the hue change also be detected by machine, for example by means of a sensor. This is especially true when the reflection color of the photonic crystal in a state of the feature region is outside the visible spectral range. Thus, a sensor can directly detect the IR or UV radiation reflected from the photonic crystal, while a human observer can only indirectly perceive the change in reflection color toward the infrared or ultraviolet, such as by changing the feature area from a colored state to a transparent state.

The elastomer is advantageously selected from the group consisting of elastic silicones, acrylates, polyester acrylates, rubbers, polyisobutene, polyurethanes and polyvinyl butoxylates.

Preferably, the offset with the magnetically orientable particles elastomer forms a film whose thickness is below 1000 microns, preferably below 600 microns and more preferably below 300 microns. The minimum thickness of the film is advantageously at least 10 microns. Preferably, for applications in banknotes and / or cards, such as identity cards, the film has a thickness in the range of 20 μm to 100 μm, more preferably in the range of 20 μm to 50 μm.

Preferably, the thickness of the film or the elastomer corresponds to the thickness of the document of value, so that the film / the elastomer has neither a significantly higher nor a significantly smaller thickness than the value document.

The elastomer is advantageously substantially transparent and colorless, such that the perceived color of the feature region is determined by the reflection color of the photonic crystal. However, it is basically also possible to use a colored elastomer, so that the perceived color of the feature region from a color mixture of the intrinsic color of the elastomer and the reflection color of the photonic crystal. Alternatively or additionally, the elastomer comprises one or more layers or one or more coatings. Preferably, such layers or coatings are arranged on / on the elastomer. In particular, the elastomer may have a dark layer / coating, preferably a black layer / coating. Such a dark or black layer / coating preferably serves to provide a good contrast between the color of the photonic crystal and the dark or black layer / coating, so that a viewer can perceive the color or color change of the photonic crystal well. In other words, to visualize the hue of the photonic crystal, the elastomer may be provided with a dark coating.

Preferably, the elastomer has a first major surface and a second major surface facing each other. Preferably, a dark layer / coating is disposed on / on the first major surface while a viewer views the elastomer from the side of the second major surface.

If an adjuvant has one or more dark color (s) or black coating (s), it is not necessary to color the elastomer or a multiple dark or black coating (s) on the elastomer. In other words, in a case where the elastomer-which forms the photonic crystal-is not deposited on an opaque layer / coating, an absorbent / black tool (eg, a pen) may be used to change the hue or color change of the feature area to make visible.

Alternatively, preferably, such a dark layer / coating is an elastic layer. Preferably, the elastic layer has similar or equal deformation properties as the elastomer. In particular, the elastic layer may consist of the same (basic) material as the elastomer, with the difference that the elastic layer has no photonic crystals but color pigments or dyes for coloring the layer. For the coloration, for example, carbon black or a mixture of fringe pigments, such as yellow, red and blue, are available to produce a black color impression.

Further preferably, the elastomer comprises a translucent interference coating. Preferably, such a translucent interference coating is disposed on the second major surface of the elastomer. Preferably, a translucent interference coating is a liquid crystal coating. Preferably, a translucent interference coating is a coating based on interference pigments. In the case of interference pigments, these are incorporated in a binder, wherein the interference pigments do not completely cover the second major surface of the elastomer. In particular, the translucent interference coating can be based on so-called STEP pigments.

When external forces are applied to the elastomer or feature area, an observer can perceive a mixed color of the color of the photonic crystal of the elastomer and the color of the translucent interference coating.

Further preferably, two or more feature areas may be arranged side by side. In this case, the elastomers or distinguish the photonic crystals of the feature areas. Alternatively or additionally, the elastomers may have one or more mutually different layers / coatings.

In particular, it can be provided that the layer (s) / coating (s) are arranged on different main surfaces of the elastomers. For example, a layer / coating may be disposed on the first major surface of the elastomer of a first feature region while a layer / coating is disposed on the second major surface of the elastomer of the second feature region adjacent to the first feature region.

Furthermore, one or more layers may also comprise elastomers that form photonic crystals, wherein this further elastomer in its visual appearance differs from the (first) elastomer that distinguishes the photonic crystal having the first and second visual appearance.

Further preferably, a layer / coating may be provided which reduces the extensibility of the feature area or a portion of the feature area. For example, a stabilizing film may be provided as the layer / coating. In the area where the stabilizing film is provided, then higher tensile and / or compressive forces must be applied to achieve a color change.

Preferably, a layer / coating may be a dark / colored elastomer or elastic film applied to / on a major surface of the elastomer.

For example, layers / coatings can be laminated to the elastomer. For example, layers / coatings can be applied to the elastomer by means of a cast coating. For example, layers / coatings can be printed on the elastomer or applied by printing technology.

Further preferably, the elastomer may have one or more transparent layers / coatings. Further preferably, the elastomer may have one or more translucent layers / coatings. Further preferably, the elastomer may have one or more colored layers / coatings.

For example, the security element may be designed such that a color change due to the described piezochromic effect is visible when viewing the security element from one side or main surface, while a translucent and / or colored coating is visible when viewing the security element from another side or main surface ,

In one development, the elastomer has, in addition to the magnetically alignable particles, further feature substances, in particular luminescent substances or IR-absorbing substances. The further feature substances preferably do not or hardly influence the hue without visible excitation or the scattering of the elastomer. By suitable feature substances, the elastomer can in particular be made machine readable.

The elastomer may be formed both as a self-supporting film and as a coating on a carrier substrate. Such a carrier substrate can optionally deducted after a transfer of the security element to a target volume.

For example, a carrier substrate may have a varying layer thickness. That that with the same force input, the elongation in one area with a smaller layer thickness is higher than in another area with a higher layer thickness. In the area with the lower layer thickness, the color change sets earlier, so that according to the layer thickness variation, a pattern / motif is recognizable.

According to an advantageous development of the invention, the magnetically orientable particles are provided with a feature coating which lends the particles luminescence or IR-absorbing properties.

Alternatively or additionally, the magnetically orientable particles may be provided with a hydrophobic coating, which may be an inorganic coating, an organic coating or a hybrid coating. The inorganic hydrophobic coating may in particular be a silane coating, the organic hydrophobic coating in particular a layer of halogenated polymers, such as PTFE, PVC, or halogenated acrylates.

Furthermore, the magnetically orientable particles can advantageously be equipped with transparent, mechanically acting spacers. The spacers can be based on both an inorganic and an organic coating.

The feature area as a whole and / or the above-mentioned subregions with different arrangements of the magnetically alignable particles are preferably in the form of characters, patterns or coding.

In a further development of the invention, a functional layer is arranged from the viewing direction below the feature area, which can be influenced by the change in hue of the feature area. Such a functional layer can be formed, for example, by a UV- or IR-absorbing layer which absorbs UV or IR radiation as long as the photonic crystal does not reflect this radiation but transmits it. In this way, a change in the lattice spacings of the photonic crystal of the feature region can also be detected with the aid of the underlying functional layer.

Also, a dark or black coating may be provided below the feature area to increase the visibility of the hue change. The dark or black coating may be over the entire surface or in the form of patterns, characters or a code.

In a development of the invention, the security element in the feature area comprises a further magnetic partial area. The additional magnetic subregion can be provided for an improved magnetic force on the security element, in particular so as to achieve a sufficient force with a smaller external magnetic field. The other magnetic portion has a higher magnetization or magnetizability than the elastomer with the photonic crystal, for example, another material is used and / or a higher concentration of (the) magnetic particles. Preferably, the further magnetic portion should have a lower elasticity than the elastomer, preferably inelastic. Is the other magnetic part fixed / inelastic, a local additional effect can be observed. In particular, the elastomer is deformed more directly next to the fixed, magnetic portion, so locally show a different color effect. The further magnetic portion may be arranged in the same layer as the elastomer or in another layer. The magnetic portion may be provided in the form of a separate motif. Preferably, the elastomer and the magnetic portion are arranged on a common layer, in particular on a carrier layer or on a laminated layer. More preferably, the magnetic portion is disposed within a region of the elastomer (surrounded by elastomer). Alternatively, the magnetic portion may be disposed laterally on at least one side of the elastomer, preferably on two sides and more preferably around the elastomer. If the further magnetic subregion is arranged in a further (own) layer, it can be arranged under a continuous layer with the photonic crystal. If the further magnetic subarea arranged under the elastomer is made opaque, a color effect - viewed from below - can only be seen next to the magnetic subarea. Viewed from above, on the other hand, the entire feature area and its color effect would be visible. If the additional magnetic subregion is configured as an alternative or in addition, a color effect (for both viewing directions) can only be observed laterally of the magnetic subregion.

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

The invention also includes a data carrier with a security element of the type described above. The data carrier may in particular be a value document, such as a banknote, in particular a paper banknote, a polymer banknote or a film composite banknote, a share, a bond, a document, a Voucher, a check, a high-quality ticket, but also to act as an identification card, such as a credit card, a bank card, a cash card, an authorization card, an identity card or pass personalization page.

In an advantageous embodiment, the feature area of the piezochromic security element is arranged in a recess of the data carrier, in which the feature area of the security element can be pressurized. In this case, the security element is preferably arranged in the recess such that the feature area can be pressurized from one data carrier side and the resulting color change is visually perceptible on the opposite data carrier side. The color change is triggered by pressurization by the user, for example by the user presses with thumb or forefinger in the recess and thereby extends the feature area arranged there at least locally.

For example, the security element can be provided as a window film or in a window of a value document. In this case, the elastomer preferably has a thickness which corresponds to the thickness of the document of value.

In another, likewise advantageous embodiment, the feature area of the piezochromic security element is arranged in a stretchable or bendable area of the data carrier. The color change is in in this case, simply by stretching or bending the volume by the user.

In a further, likewise advantageous embodiment, the data carrier has tactile relief structures in a partial area and the feature area of the piezochromic security element can be brought into pressure contact with the tactile relief structures by bending, folding, folding or folding the data carrier. In pressure contact, the feature area is locally stretched by the tactile relief structures, thereby triggering a local hue change. The feature area is advantageously arranged in the region of a recess or a transparent window, so that the color change can be easily visually perceived.

Advantageously, the data carrier additionally has at least one reference color element / solid color element whose color tone corresponds to the color tone of the first or second visual appearance of the feature area. The hue of a reference color element represents a fixed reference point, which makes the hue change of the feature area more easily recognizable, since the human eye is more sensitive to the color differences that occur than to the color change per se. The reference color elements may be formed, for example, by colored print layers or other colored structures.

In particular, it can be provided that the color of the elastomer or the security element is visible by placing it on a dark background or a black coating on the back of the elastomer.

The feature region preferably has partial regions in which the elastomer has different layer thicknesses from one another. Preferably, different forces are required for a deformation in these subregions, so that there are subregions with different discoloration in the case of (equal) tensile loading / force exertion.

Preferably, the elastomer can be coated on an elastic carrier. In particular, the carrier substrate may be an elastic carrier.

Preferably, the elastic support is provided with a dark coating. Alternatively, the elastic carrier is dyed dark.

Preferably, the elastomer is coated in partial areas with mutually different elastic films. Preferably, a layer / coating may be an elastic film.

The elastomer is preferably applied to a carrier substrate or value document substrate by means of casting methods and doctoring and / or application by means of nozzles, and / or by printing technology. Preferably, the magnetically orientable particles in the elastomer are fixed in their orientation.

• in ein noch nicht gehärtetes Elastomer eine Vielzahl magnetisch ausrichtbarer Partikel eingebracht werden,
• die magnetisch in Ihrer Position ausrichtbaren Partikel durch zumindest ein äußeres Magnetfeld in Form eines regelmäßigen Gitters ausgerichtet werden um einen photonischen Kristall zu bilden, vorzugsweise wird das Magnetfeld durch eine Magnetplatte mit Oberflächenrelief und/ oder einer Vielzahl von Einzelmagneten erzeugt, und
• das Elastomer bei angelegtem Magnetfeld mit den ausgerichteten Partikeln getrocknet und/oder gehärtet oder /und chemisch vernetzt wird.

The invention also includes a method for producing a piezochromic security element of the type described above, in which

• a plurality of magnetically orientable particles are introduced into an uncured elastomer,
• the magnetically orientable particles in their position by at least one external magnetic field in the form of a regular grid aligned In order to form a photonic crystal, preferably the magnetic field is generated by a magnetic plate with surface relief and / or a plurality of individual magnets, and
• the elastomer is dried and / or cured or / and chemically crosslinked with applied magnetic field with the aligned particles.

Preferably, the magnetic disk and / or the plurality of individual magnets may consist of permanent magnets or of electromagnets.

Preferably, the elastomer is processed in a roll-to-roll process.

A method for machine testing of a security element can in the present case be configured advantageously. In particular, a piezochromic security element with an elastic feature region, for example as described above, can be tested.

• ein Einbringen einer Zug- und/oder Druckkraft auf einen elastischen Merkmalsbereich eines Sicherheitselements, insbesondere durch mechanische oder magnetische Krafteinwirkung; und
• ein Erfassen einer Dicke im Merkmalsbereich des Sicherheitselements in Antwort auf die Krafteinwirkung auf den Merkmalsbereich des Sicherheitselements.

In a first variant, checking the security element comprises the following substeps:

• introducing a tensile and / or compressive force on an elastic feature area of a security element, in particular by mechanical or magnetic force; and
• detecting a thickness in the feature area of the security element in response to the force applied to the feature area of the security element.

• ein Einbringen einer Zug- und/ oder Druckkraft auf einen Merkmalsbereich eines Sicherheitselements durch magnetische Krafteinwirkung;
• ein Erfassen einer vorgegebenen Eigenschaft des Sicherheitselements in Antwort auf die Krafteinwirkung auf den Merkmalsbereich des Sicherheitselements.

In a second variant, checking the security element comprises the following substeps:

• applying a tensile and / or compressive force to a feature area of a security element by magnetic force;
• detecting a predetermined property of the security element in response to the force applied to the feature area of the security element.

• eine Krafteinbringungseinheit, welche eingerichtet ist eine vorgegebene Zug- und/oder Druckkraft auf einen elastischen Merkmalsbereich eines Sicherheitselements einzubringen; und
• eine Erfassungseinheit, welche eingerichtet ist eine Eigenschaft des Merkmalsbereichs des Sicherheitselements in Antwort auf die Krafteinwirkung auf den Merkmalsbereich des Sicherheitselements zu erfassen.

A corresponding test unit for machine testing a security element comprises:

• a force introduction unit which is set up to apply a predetermined tensile and / or pressure force to an elastic feature area of a security element; and
• a detection unit configured to detect a property of the feature area of the security element in response to the force applied to the feature area of the security element.

The detection unit measures the property, such as e.g. a thickness or a length of the feature area in the security element or the security element or the data carrier with security element or a color of the feature area in reflection. In particular, a change of the property (thickness, length, color ...) is detected. Optionally, the test unit also contains an evaluation unit for the measurement signals / values of the detection unit, the evaluation unit evaluates in particular whether a predetermined property (or a predetermined change of a property) is present.

The test can be prepared or accompanied by heating the security element. Preferably, the security element is characterized by a magnetic Alternating field, which acts on the magnetically oriented particles, heated. Warming changes the rheological properties of the elastomer. This leads, for example, that the desired effects can already be achieved with lower mechanical or magnetic forces, such as thickness change, change in length, color change. Likewise, with the same mechanical or magnetic forces, the lattice spacing change is stronger.

• Farbtonänderung in Reflexion (UV/ VIS/ IR), wobei eine Prüfung insbesondere mittels Spektralphotometer, CCD-Kamera, Scanner erfolgt,
• Dickenänderung des Elastomeres in dem beaufschlagten Bereich, wobei die Prüfung insbesondere mittels Ultraschallsensor, kapazitiver Prüfung oder Piezoelement erfolgt oder
• Längenänderung des Elastomeres in dem beaufschlagten Bereich, wobei die Größe eines definierten Bereiches (z.B. Skala, Kantenlänge eines Quadrats, Durchmesser eines Kreiselementes), beispielsweise mittels CCD-Kamera, Scanner erfasst und geprüft wird.

Examples of the machine-detectable properties are:

• Color change in reflection (UV / VIS / IR), whereby a test is carried out in particular by means of spectrophotometer, CCD camera, scanner,
• Thickness change of the elastomer in the applied area, the test is carried out in particular by means of ultrasonic sensor, capacitive test or piezo element or
• Length change of the elastomer in the applied area, wherein the size of a defined area (eg scale, edge length of a square, diameter of a circle element), for example by means of CCD camera, scanner is detected and tested.

The force can also be frequency-dependent, so that the speed of the restoring forces of the elastomer (relaxation time) is taken into account during the test. Thus, the material-specific properties of the elastomer or the test element can be tested depending on the temperature with.

Preferably, the step of detecting the security element may be at least twice. In particular, the detection can take place for a given, first force action and a predetermined, second force action.

• mit und ohne die äußere Zug- oder/Druckkraft Kraft, und/ oder
• bei vorhandener Krafteinwirkung mit und ohne Erwärmung erfassen, und/oder
• bei vorgegebener erster und zweiter Krafteinwirkung.

For example, the test unit may record the property in at least two steps of detection:

• with and without the external tensile or / compressive force, and / or
• detect with existing force with and without heating, and / or
• for a given first and second force.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a representation true to scale and proportion has been dispensed with in order to increase the clarity.

Fig.1

eine schematische Darstellung einer Banknote mit einem erfindungsgemäßen piezochromen Sicherheitselement in Form eines Fenstersicherheitsfadens,

Fig. 2

einen Querschnitt durch die Banknote der Fig.1 entlang des Fenstersicherheitsfadens im Ausschnitt, wobei (a) die Banknote in ungefaltetem Zustand und (b) die Banknote in gefaltetem Zustand zeigt,

Fig. 3

schematisch im Querschnitt ein piezochromes Folienelement nach einem Ausführungsbeispiel der Erfindung,

Fig. 4

das piezochrome Folienelement der Fig. 3 bei Beaufschlagung mit Zugkräften,

Fig. 5

ein Ausführungsbeispiel der Erfindung in Form eines Passbuchs, wobei (a) das Passbuch im aufgeklappten Zustand und (b) das Passbuch im zugeklappten Zustand zeigt,

Fig. 6

ein Passbuch mit einem auf Druckbeaufschlagung ansprechenden piezochromen Folienelement nach einem weiteren Ausführungsbeispiel der Erfindung, wobei (a) das Passbuch im aufgeklappten Zustand und (b) das Passbuch im zugeklappten Zustand zeigt,

Fig. 7

eine Identifikationskarte nach einem weiteren Ausführungsbeispiel der Erfindung, in (a) in Aufsicht und in (b) im Querschnitt,

Fig. 8

eine schematische Schnittansicht eines Sicherheitselements mit einem Merkmalsbereich, und

Fig. 9

eine schematische Schnittansicht eines Sicherheitselements mit zwei Merkmalsbereichen.

Show it:

Fig.1

a schematic representation of a banknote with a piezochromic security element according to the invention in the form of a window security thread,

Fig. 2

a cross section through the banknote of Fig.1 along the windowed security thread in the cutout, where (a) shows the banknote unfolded and (b) the folded banknote,

Fig. 3

schematically in cross-section a piezochromic film element according to an embodiment of the invention,

Fig. 4

the piezochrome film element of Fig. 3 when subjected to tensile forces,

Fig. 5

an embodiment of the invention in the form of a passport booklet, wherein (a) shows the passport in the unfolded state and (b) the passport in the closed state,

Fig. 6

a passport with a responsive to pressurization piezochromic film element according to another embodiment of the invention, wherein (a) shows the passbook in the unfolded state and (b) the passbook in the closed state,

Fig. 7

an identification card according to a further embodiment of the invention, in (a) in plan view and in (b) in cross-section,

Fig. 8

a schematic sectional view of a security element with a feature area, and

Fig. 9

a schematic sectional view of a security element with two feature areas.

The invention will now be explained using the example of security elements for banknotes and other data carriers.

FIG. 1 1 shows a schematic representation of a banknote 10 having a piezochromic security element 12 according to the invention in the form of a windowed security thread which protrudes at certain window areas 14 on the surface of the banknote 10 while it is embedded in the interior of the banknote 10 in the areas located therebetween.

FIG. 2 shows a cross section through the banknote along the window security thread 12 in the neckline, wherein Fig. 2 (a) the banknote in unfolded condition and Fig. 2 (b) the banknote shows in folded state.

In the unfolded state, the security element 12 in the window areas 14 of the banknote has a first visual appearance, for example appears evenly with the hue green. If the banknote 10 and thus the security element 12 are folded back around a longitudinal axis 16, then the color tone of the security element 12 in the area of the fold 20 changes markedly, the security element appears there blue, for example. In the folded state ( Fig. 2 (b) ) contains the security element 12 thus two areas with different appearance, namely first areas 22 away from the fold 20, in which a green appearance is unchanged in the window areas 14, and second areas 24 in the fold 20, in which in the window areas 14 a blue Appearance is visible.

If the banknote 10 unfolds again, then the original, uniformly green hue sets in again, the hue change is thus completely reversible. This reversible color change occurs at each position of the security element 12 during folding and represents because of their interactivity and easy recognizability and simple and easy-to-memorize authenticity mark.

The structure of inventive security elements and the conclusion of the color change will now be with reference to the FIGS. 3 and 4 explained in more detail. This in Fig. 3 schematically shown in cross-section piezochrome film element 30 is formed in a feature area 32 substantially by a colorless elastomer 34, which in the finished security element is physically and / or chemically dried and forms a stable, self-supporting film of a thickness of about 250 microns. As an elastomer, for example, an elastic silicone can be used.

In order to produce the piezochromic color effect, a multiplicity of magnetically alignable particles 36, specifically magnetite, paramagnetic and / or superparamagnetic particles, were incorporated into the not yet cured elastomer 34 during the production of the film element 30. In the exemplary embodiment, nanoscale magnetites with a diameter of about 50 nm in a concentration of about 5% were incorporated into the silicone for this purpose.

Due to their magnetic alignability, the particles 36 arrange themselves in the weak magnetic field of an external magnet 40 (dashed in FIG Fig. 3 ) in the form of a regular grating and form a photonic crystal in the surrounding elastomer 34. The elastomer 34 is dried with the magnetic field applied and the spatial arrangement of the particles 36 and the photonic crystal fixed so that the photonic crystal is retained even after removal of the external magnet 40.

When viewed, the feature region 32 generates reflection colors characteristic of the photonic crystal, which are substantially given by the distance d of the lattice planes 38 of the particle assembly. In the embodiment, the feature area appears in supervision about green. By appropriate selection of the magnetic field applied when the elastomer 34 is dried, the visual impression of the feature region 32 can be adjusted as desired within wide limits.

The feature region 32 can also have several subregions with different arrangements of the magnetically alignable particles. For example, local different strong magnetic fields lead to locally different spacings of the lattice planes 38 and thus to different reflection colors of the feature region 32 during drying. These different partial regions, like the entire feature region 32, can be in the form of patterns, characters or a coding.

If the piezochromic film element 30 is now subjected to tensile or compressive forces, as in Fig. 4 As shown by the example of tensile forces 42, the elastic properties of the elastomer 34 allow for a strong elastic deformation of the security element 30. Since the volume of the elastomer 34 is substantially retained during deformation, an extension in one spatial direction is made by corresponding shortenings in the other spatial directions balanced. If the film element 30, for example, as in Fig. 4 stretched in a direction 42 in the plane of the security element, so the height of the elastomer and thus the distance d of the lattice planes 38 decreases accordingly. Since the reflection color is determined essentially by the spacing of the lattice planes 38, the film element 30 which is subjected to tensioning acts Fig. 4 a reflection color of shorter wavelength and appears blue, for example. After completion of the Zugkraftbeaufschlagung the film member 30 returns due to the elastic properties of the elastomer 34 in the starting position of Fig. 3 back and then shows the original green appearance again.

This process also explains the color change in the Figs. 2 (a) and 2 (b) shown embodiment, since there the window security thread 12 is stretched when folding the banknote in the region of the fold 20 and thus stretched, so that there is a hue change from green to blue takes place. Outside the fold 20, no forces act on the window security thread during folding, so that no color change is produced there.

In the Fig. 4 shown deformation of the piezoelectric film element 30 can be generated not only by a tensile load 42 in the plane of the security element, but also by a compressive load 44 perpendicular to the plane of the security element. In this way, pressure forces can lead to color shifts to shorter wavelengths, as explained below with reference to a further embodiment.

The lattice spacings of the particles 36 in the elastomer 34 may in particular be selected such that the reflection condition is satisfied either only in the unloaded state or loaded state only for light outside the visible spectral range. For example, the photonic crystal of the film element 30 shown above without external force ( Fig. 3 ) Reflect light in the infrared spectral range and in the tensile load state ( Fig. 4 ) reflect light in the visible spectral range due to the smaller spacing of the lattice planes 38. Since the elastomer 34 itself is colorless and the photonic crystal formed by the particles 36 in the unloaded state reflects infrared light, the feature region 32 initially appears colorless. Under tensile stress, the reflection shifts to shorter wavelengths towards the red, so that the loaded areas of the feature area 32 now appear colored. In the case of a feature area 32 embodied in the form of a motif, an initially invisible motif appears to be created afresh by the tensile stress of the viewer. Due to the reversibility of the effect, the color or the colored motif disappears after completion of the tensile stress. Appearance and disappearance of the motif can thus be triggered interactively by the user.

Similarly, the film element 30 may be formed so that the photonic crystal without external force ( Fig. 3 ) Reflected light in the visible spectral range and in the tensile load state ( Fig. 4 ) reflects 38 light in the ultraviolet spectral range due to the smaller spacing of the lattice planes. In this case, the feature area in the unloaded state initially appears in color, for example blue. Upon tensile stress, the reflection shifts to the ultraviolet and the loaded areas of the feature area 32 appear colorless to the viewer. In the case of a feature area 32 designed in the form of a motif, the subject initially visible appears to disappear under tensile stress and to reappear when the tensile load ceases. Also in this embodiment, the disappearance and reappearance of the motif can be triggered interactively.

When using the piezochromic security element on a document of value or other data carrier reference color elements may additionally be provided, which reproduce the unloaded starting color tone or hue when subjected to tensile or pressure. By the reference hue of the reference color elements, the hue change of the piezochromic security element can be made even more noticeable. In addition, by the juxtaposition of the fixed hue of the reference color element and the variable hue of the security element, the viewer's attention is directed even more to the security element and a lack of color change made conspicuous.

FIG. 5 shows an embodiment in the form of a passport book 50, in the fold 52 a piezochromes film element 30 of the type described above is arranged. In the unfolded state of the passport ( Fig. 5 (a) ) no external forces act on the feature area 32 of the foil element 30, so that this appears green with its first visual appearance, in the exemplary embodiment. This green color is picked up by a first reference color element 54 arranged in the immediate vicinity of the fold 52 on the inside 56 of the passport book 50. The reference color element 54 may be, for example, an imprinted green pattern element.

In the folded state of passport 50 ( Fig. 5 (b) ) the security element 30 is stretched and the feature area 32 therefore appears with its second visual appearance, in the exemplary embodiment approximately blue. This blue color is picked up by a second reference color element 58 arranged in the immediate vicinity of the fold 52 on the outside 55 of the passport book. The reference color element 58 may be, for example, an imprinted blue pattern element.

Therefore, for a successful authentication, the user need not know that the sheet member 30 shows a hue change from green to blue, it is sufficient to detect the color match or mismatch of the feature portion 32 with the reference color members 54, 58.

The embodiment of Fig. 6 is a passbook 60 with a responsive to pressurization piezochromic film element. As in best in the unfolded representation of the Fig. 6 (a) To recognize this is the upper cover 62 of the passport passport provided with a recess 64 which is closed on the inside 66 of the book cover with a piezochromic film element 30 of the type described above. The opposite inner side 68 of the passport is provided with tactile structures 70 by embossing or printing, which are thus arranged on the inner side 68 are that the recess 64 comes to lie with the film element 30 when folding the passbook 60 on the tactile structures 70. For example, the tactile structures 70 may appear red and are in the form of a motif, such as a graphic pattern or lettering. The film element 30 appears green as described above in the unloaded state and blue in the loaded state.

If the passbook 60 is closed, as in Fig. 6 (b) As shown, the piezochromic film element 30 is pressed onto the tactile structures 70 and thereby pressurized and locally stretched in the region of the relief-like elevations of the tactile structures. In these stretched areas 72, the color tone of the film element therefore changes from green to blue, while the green color is retained outside the elevations of the tactile structures. The motif formed by the tactile structures 70, which appears red in the unfolded passbook, is visible even after the passbook 60 has been folded open by the recess 64, but then appears blue against a green background.

The invention can also be used advantageously in maps, as with reference to the embodiment of Fig. 7 illustrated. FIG. 7 (a) shows an identification card 80, such as an identification card, bank card, credit card or driver's license in cross-section, Fig. 7 (b) shows the same map 80 in supervision. In the case of the three-layer identification card 80, the two outer layers 82 are recessed in a partial region, for example in the form of a circular recess 86 with a diameter of approximately 15 mm. In the region of the recess 86, a piezochromic film element 30 of the type described above is arranged in the middle layer 84 and clamped with its edge between the two outer layers 82.

In unloaded condition, the film element 30 appears green. If a user presses, for example, with the index finger or thumb from below against the film element 30 (pressure load 88), then the film element 30 is pressurized and locally stretched because of the clamping of the edges. When viewing the recess 86 from above, so the pressure load 88 opposite card page, the viewer 90 then a color change from green to blue visible.

The cross-sectional representation of Fig. 7 (a) shows the appearance of the card 80 in the unloaded state, the supervision of Fig. 7 (b) in the pressurized state with triggered safety element. In practice, a uniform blue color impression will generally not be established in the recess since the amount of compressive stress increases from the edge of the recess 86 toward the center. Typically, the film element 30 therefore appears green at the edge of the recess 64 and blue in the center of the recess.

FIG. 8 11 shows a schematic sectional view of a security element 800 having a feature area 810 with elastomer 802 and photonic crystals embedded therein (not shown) according to an embodiment.

The elastomer 802 is formed as a coating on a carrier substrate 806 in this embodiment. Such a carrier substrate 806 may optionally be withdrawn after a transfer of the security element to a target medium. The carrier substrate 806 has first and second major surfaces HF1T, HF2T. The illustration of adhesive layers and / or release layers has been omitted and are not shown. In particular, the security element 800 may include further layers disposed on / on the elastomer 802 and the carrier substrate 806, respectively are. For example, the elastomer 802 may have further color layers on the first major surface HF1T, for example, the dark layer 804 may be disposed between the elastomer 802 and such other color layers.

Preferably, the elastomer 802 has a first major surface HF1E and a second major surface HF2E facing each other. Preferably, a dark layer / coating 804 is disposed on / on the first major surface HF1E of the elastomer. An observer may look at the elastomer 802 from the side of the second major surface HF2E, i. from the direction BR, to perceive a change in color with external forces.

Preferably, the dark layer / coating 804 is an elastic layer. Preferably, the elastic layer 804 has similar or equal deformation properties as the elastomer 802. In particular, the elastic layer 804 may be made of the same (basic) material as the elastomer 802, with the difference that the elastic layer 804 has no photonic crystals but color pigments or dyes for coloring the layer. For the coloration, for example, carbon black or a mixture of fringe pigments, such as yellow, red and blue, are available to produce a black color impression.

Further preferably, a translucent interference coating 808 may be applied to the second major surface HF2E of the elastomer 802. When external forces act on the feature area 810, a viewer may perceive a blend color of the color of the photonic crystal of the elastomer 802 and the color of the translucent interference coating 808.

Further preferably, a layer / coating (not shown) may be provided which reduces the extensibility of the feature area or a portion of the feature area. For example, a stabilizing film can be used as the layer / coating. In the area where the stabilizing film is used, then higher tensile and / or compressive forces must be applied to achieve a color change. By way of example, such a stabilization foil could be applied to one of the main surfaces HF1T, HF2T of the carrier substrate 806. Alternatively, such a stabilizing foil could be applied on the main surface HF1E of the elastomer 802 or on the layer 804.

Furthermore, a layer may be provided with a further elastomer which forms a photonic crystal. This layer may be disposed on / on the opaque layer 804 so that the opaque layer 804 is between the elastomer 802 and the layer with the further elastomer (not shown). Preferably, the visual appearance differs from the elastomer 802 and the other elastomer.

FIG. 9 shows a schematic sectional view of a security element 900 with two feature areas 910a, 910b.

Feature regions 910a, 910b include elastomers 902a, 902b and photonic crystals (not shown) embedded therein, according to one embodiment.

The elastomers 902a, 902b is formed as a coating on a carrier substrate 906 in this embodiment. Such a carrier substrate 906 may optionally after a transfer of the security element on to deduct a target volume. The carrier substrate 906 has a first and a second main surface HF1T, HF2T.

The elastomers 902a, 902b have a first major surface HF1Ea and HF1Eb and a second major surface HF2Ea and HF2Eb, respectively, which face each other. In the first feature area 910a, a dark layer / coating 904a is disposed on / on the second major surface HF2Ea of the elastomer 902a. An observer can not look at the elastomer 902a from the side of the second major surface HF2Ea, i. from the perspective BR1. However, a viewer may look at the elastomer 902a from the side of the first major surface HF1Ea, i. from the viewing direction BR2, in order to perceive a color change with external forces.

The second feature area 910b is analogous to FIG. 8 explained.

The feature areas 910a, 910b may directly adjoin one another, as in FIG FIG. 9 shown or at a distance from each other.

According to one embodiment, the carrier substrate 906 may have a varying layer thickness, as in FIG Fig. 9 shown by way of example.

LIST OF REFERENCE NUMBERS

10

bill

12

piezochromic security element

14

panes

16

longitudinal axis

20

fold

22

first areas

24

second areas

30

piezochromic film element

32

feature region

34

elastomer

36

magnetically orientable particles

38

lattice planes

40

external magnet

42

tensile load

44

pressure load

50

pass book

52

fold

54

Reference color element

56

inside

58

Reference color element

55

outside

60

pass book

62

book cover

64

recess

66

inside

68

opposite inside

70

tactile structures

72

stretched areas

80

identification card

82

outer layers

84

middle location

86

recess

88

pressure load

90

observer

Claims (19)

Piezochrome security element for safeguarding valuables,
at least one feature region comprising an elastomer and a plurality of particles, wherein
the particles in the elastomer are arranged in the form of a regular grating to form a photonic crystal, the particles being magnetically positionable particles magnetically placed in the elastomer in the form of the regular grating, and wherein
the non-exertional feature region shows a first visual appearance, and upon application of tensile and / or compressive forces due to a change in lattice spacings of the regular grating of the photonic crystal, exhibits a second visual appearance having a discernible hue change from the first visual appearance. A security element according to claim 1, characterized in that the magnetically orientable particles are nanoparticles having a size below 100 nm, or that the magnetically alignable particles are agglomerates of nanoparticles with a size below 100 nm and with an agglomerate size between 50 and 300 nm. A security element according to claim 1 or 2, characterized in that the magnetically orientable particles are magnetite, paramagnetic particles or superparamagnetic particles; and / or the elastomer is selected from the group consisting of elastic silicones, Acrylates, polyester acrylates, rubbers, polyisobutene, polyurethanes and polyvinyl butoxylates. A security element according to at least one of claims 1 to 3, characterized in that the feature area comprises a plurality of partial areas with different arrangements of the magnetically alignable particles, wherein the partial areas advantageously show different first visual appearances and / or different second visual appearances; and or
the feature area has a plurality of partial areas with different deformation properties. A security element according to at least one of claims 1 to 4, characterized in that the photonic crystal of the feature region reflects light in the infrared spectral range in at least one sub-area without external force and upon application of tensile and / or compressive forces due to a change in the grid spacing of the regular grid of photonic crystal reflects light in the visible spectral range, or that the photonic crystal of the feature region reflects light in the visible spectral range in at least a portion without external force and upon application of tensile and / or compressive forces due to a change in the lattice spacings of the regular grating of the photonic crystal light in reflected ultraviolet spectral range. Security element according to at least one of claims 1 to 5, characterized in that the tensile and / or compressive forces are introduced by magnetic force. A security element according to at least one of claims 1 to 6, characterized in that the elastomer with the magnetically alignable particles forms a film whose thickness is below 1000 microns, preferably below 600 microns and more preferably below 300 microns, and more preferably above 10 microns is. A security element according to at least one of claims 1 to 7, characterized in that the elastomer is substantially transparent and colorless; and or
the elastomer in addition to the magnetically alignable particles further feature substances, in particular luminescent substances or IR-absorbing substances; and or
the magnetically alignable particles are provided with a feature coating which imparts luminescent or IR-absorbing properties to the particles. Security element according to at least one of claims 1 to 8, characterized in that the magnetically alignable particles are provided with a hydrophobic coating; and / or the magnetically alignable particles are equipped with transparent, mechanically acting spacers. Security element according to at least one of Claims 1 to 9, characterized in that the feature area as a whole and / or subregions of the feature area are formed with different arrangements of the magnetically alignable particles in the form of characters, patterns or an encoding. Security element according to at least one of claims 1 to 10, characterized in that below the feature region, a functional layer is arranged, which can be influenced by the hue change of the feature region, in particular that the functional layer is formed by a UV or IR-absorbing layer. Data carrier, in particular banknote, with a security element according to one of claims 1 to 11. A data carrier according to claim 12, characterized in that the feature area of the piezochromic security element is arranged in a recess of the data carrier in which the feature area is pressurizable, preferably that the feature area from a volume side is druckbeaufschlagbar and the resulting color change on the opposite volume side visually perceptible is; or
the feature region of the piezochromic security element is arranged in a stretchable or bendable region of the data carrier; or
the data carrier has tactile relief structures in a partial region and the feature region of the piezochromic security element can be brought into pressure contact with the tactile relief structures by bending, folding, folding or folding the data carrier. A data carrier according to claim 13, characterized in that the data carrier has at least one reference color element whose hue corresponds to the hue of the first or second visual appearance of the feature region. A method of manufacturing a piezochromic security element according to any one of claims 1 to 11, wherein a plurality of magnetically orientable particles are introduced into an uncured elastomer, - The magnetically alignable particles are aligned by at least one external magnetic field in the form of a regular grid to form a photonic crystal, preferably the magnetic field is generated by a magnetic plate with surface relief and / or a plurality of individual magnets, and - The elastomer is dried with applied magnetic field with the aligned particles and / or cured or / and chemically crosslinked. A method for machine testing a security element, in particular a piezochromic security element according to one of claims 1 to 11, wherein the checking of the security element comprises the following substeps: Introducing a tensile and / or compressive force on a feature area of a security element, in particular by mechanical or magnetic force; and Detecting a thickness in the feature area of the security element in response to the force applied to the feature area of the security element. A method for machine testing a security element, in particular a piezochromic security element according to one of the claims 1 to 11, wherein the checking of the security element comprises the following substeps: Applying a tensile and / or compressive force to a feature area of a security element by magnetic force; Detecting a predetermined property of the security element in response to the force applied to the feature area of the security element. The method of claim 16 or 17, wherein
a heating, preferably by an alternating magnetic field, of the security element takes place; and or
the step of detecting for the security element takes place at least twice, in particular for a predetermined, first force and a predetermined, second force. Test unit for machine testing a security element, in particular according to one of the methods of claim 16 to 18, comprising a force input unit which is adapted to introduce a predetermined tensile and / or compressive force on a feature area of a security element; and
a detection unit configured to detect a property of the feature area of the security element in response to the force applied to the feature area of the security element.

Images