EP3079921B1 - Security element having a uv-excitable field dependent effect, method for verification of such security element and structural colour composition - Google Patents

Description

The invention relates generally to a security element with a UV-excitable effect, a method for verifying such a security element and a structural color.

From the prior art, a large number of security and value documents with security features and security elements are known, which have a luminescent effect. Luminescence is the emission of light during or after a previous excitation. The luminescence is usually distinguished according to the type of excitation. If the excitation is triggered by one or more photons, it is called photoluminescence. In general, a photoluminescence is excited by an irradiation of UV light. The emission light emitted during luminescence generally has a greater wavelength than the excitation radiation. When excited with UV light, for example, luminescence light is emitted in the visible wavelength range.

A luminescent effect in a security feature or security element can be used to verify the object provided with the security feature or security element in terms of its authenticity and possibly also its integrity. In the simplest case, the existence of luminescence is used as a security feature. Verification then requires verification that luminescence is observed upon UV excitation.

From the WO 2008/028477 A2 a security document with a security feature is known, which has a semiconductor region, which comprises at least a first semiconductor layer and a second semiconductor layer, which are contacted with each other and form a type II semiconductor contact system. A security document designed in this way shows luminescence upon UV excitation. In this case, it is possible to record the luminescence intensity in a time-resolved manner immediately after a luminescence excitation. This gives the possibility to determine a time constant of the decay behavior. In the described security documents, a decay behavior of the luminescence can be significantly influenced by applying a voltage to the semiconductor layers, so that in addition to the presence of a Luminescence also at least one other property of the luminescence can be evaluated.

In the WO 2011/020603 A1 a security element is described, which emits a luminescence radiation upon irradiation with electromagnetic excitation radiation. With continuous excitation, however, the intensity of the luminescent radiation decreases or disappears almost completely. This effect can be used to form color envelopes.

Also the WO 2012/003854 A1 describes a security feature with a luminescent pigment which has a luminescent host lattice which is optically excitable for the emission of luminescent light. Host lattice and luminophore and the mole fraction of the luminophore are chosen such that even slight increases or decreases in the mole fraction of the luminophore cause a large change in the Lumineszenspektrums.

From the WO 2009/050448 A1 For example, a method for forming an optically variable security element is known. Here, a photonic crystal material is applied to a security document. The photonic crystal is locally deformed to form first and second regions that exhibit a different optical effect in the reflection or transmission of light.

In addition to luminescence, other optical effects in the field of security and value documents are used. Thus, for example, printing inks are known from the prior art, the color impression of which is brought about by microparticles contained in one color, which are aligned with one another and arranged in a crystal structure.

From the EP 2 463 111 are known such printing inks. There, printing inks are described which have a multiplicity of particles in a printing medium which are dispersed in the medium and have electrical or magnetic properties such that they align with one another in a crystal structure when an electric or magnetic field is used. This crystal structure ensures that light of a certain wavelength can propagate only along certain directions or not at all in the crystal structure and is reflected accordingly. This is about Color impression caused due to the wavelength selective reflected light. In contrast to a body color can be spoken of a structural color, since a geometric arrangement of the colloidal particles is responsible for the expression of the color.

From the DE 10 2009 024 447 A1 and the WO 2010/142391 A1 For example, a security element with an optical appearance that can be changed by an external magnetic field is known. It is envisaged that the security element has a multiplicity of microcapsules which contain a suspension of a carrier liquid and magnetic nanoparticles which reversibly form a photonic crystal in an external magnetic field in the microcapsules.

It is a general endeavor to develop security documents in such a way that they contain security elements and features which are harder to imitate and / or manipulate for counterfeiters.

The invention is therefore based on the technical object to provide a novel security element to provide a method with which the security element is verifiable in a simple manner and to create a substance with which the security element can be formed.

The invention is based on the idea of further developing the structure colors known from the prior art, which have an optical effect similar to that of a photonic crystal, and / or to combine them with another printing ink in order to obtain novel effects. For this purpose, luminescent pigments or a luminescent color are used.

This gives a security element which has novel optical effects which are due both to the luminescence and to a reflection or transmission property that can be influenced by excitation with an electric or magnetic field. The effort to produce such a security element is significantly increased, so that a forgery is difficult.

Thus, a novel security element is created, which can be checked for its presence and its integrity by means of a novel verification procedure.

definition

Features that can be used for verification and thus provide protection against unauthorized duplication or creation, tampering or the like are referred to as security features. Entities having at least one security feature are referred to as security elements. Thus, any physically trained object that includes at least one security feature is a security element.

Documents having at least one security feature are referred to as security documents. Security documents include, but are not limited to, ID cards, driver's licenses, identity cards, banknotes, postage stamps, visas, and counterfeit-proofed labels and packages, tickets, and the like.

Pigments which show emission of light as a result of excitation, for example irradiation of UV light, are referred to as luminescent pigment. The emission caused by the excitation is referred to as luminescence, the excitation as luminescence excitation.

A preparation that can be used to print information is also referred to as ink or ink.

A preparation whose color impression produced in the printed state is caused by pigments which absorb and / or remit / reflect certain wavelengths of light independently of environmental conditions and / or excitation are referred to as body colors.

Printing preparations or inks or inks whose color impression in the printed state is caused by the fact that a plurality of particles are arranged in a crystal-like regular structure, so that a light propagation of individual wavelengths through the crystal structure only in certain directions or not at all possible and hereby Color impression is caused, are referred to as structural colors.

From the prior art, in particular the EP 2 463 111 A2 are known pressure preparations, which are structural colors. There are described printing formulations comprising a plurality of nano- or microparticles having electrical or magnetic properties which are arranged in an electric or magnetic field relative to each other in a crystal-like regular structure. There it is described that the crystal-like structures can be photonic crystals. A photonic crystal is a regular periodic structure that promotes or suppresses light propagation for single or multiple wavelengths due to quantum mechanical effects. This creates a color impression of the corresponding photonic crystal.

Structure colors, which have a changed color impression when excited, are also in the EP 2 463 111 A2 described. These may be formed such that the printing preparation comprises microcapsules enclosing a substrate in which in turn a plurality of colloidal particles is arranged, which again a have electrical or magnetic property and arrange in an electric or magnetic field relative to each other to a crystal or a crystal-like structure. There, it is described that the colloidal particles may be, for example, charged particles comprising, for example, aluminum, copper, silver, tin, titanium, tungsten, zirconium, zinc, silicon, iron, nickel, goblin or the like. The particles may further comprise a substance containing a polymer material, for example, polystyrene (PS), polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyethylene terephthalate (PET), etc. According to other embodiments, uncharged particles may have a be charged material loaded. For example, particles may be coated with metal inorganic oxides such as silicon oxide SiO _x , titanium oxide TiO _x , etc. However, polymer material coated particles coated with ion exchange resins and many more can also be used. In the EP 2 463 111 A2 a variety of exemplary embodiments is described.

The substance in which the colloidal particles are arranged in the microcapsules may be a phase change material. This means that the material can be present in different phases, which have a different viscosity. Depending on the phase in which the substance is located, the colloidal particles dispersed therein may or may not align to a crystal structure upon external excitation. Also, it is possible that a crystal structure induced by external excitation in one phase of the substance is "frozen" by a change in the phase of the substance, so that the crystal structure is retained even after removing / removing the excitation to orient the colloidal particles remains.

In other embodiments, the viscosity of the substance in the microcapsules, in which the colloidal particles are dispersed, which arrange themselves upon application of an electric or magnetic field to a crystal structure, is always maintained.

An electrorheological fluid is a fluid whose viscosity is adjustable or controllable via an electric field strength. In a room where no electric field is applied, an electrorheological fluid has a low viscosity. Colloidal particles dispersed therein thus have high mobility. When an electric field is applied, the viscosity sharply increases, so that mobility of particles dispersed therein is greatly restricted or inhibited.

A magnetorheological fluid is a fluid whose viscosity is adjustable or controllable via a magnetic field strength. In a space where no magnetic field is applied, a magnetorheological fluid has a low viscosity. Colloidal particles dispersed therein thus have high mobility. When a magnetic field is applied, the viscosity sharply increases, so that mobility of particles dispersed therein is greatly restricted or inhibited.

Field-free is a space in which neither an electric nor a magnetic field is present. For the purposes of the objects described here, this is understood to mean the absence of an externally adjusted electrical or magnetic field. A field caused by magnetic particles or electrically charged particles intrinsically present in an article is left unattended. Similarly, the magnetic field strength caused by the earth's magnetic field is considered to be insignificant, so that a space is field-free despite the existing geomagnetic field, if no additional magnetic field is present in the room.

If the orientation of the colloidal particles is brought about only by the electric field, the space is considered to be field-free if there is no electric field even if, for example, a magnetic field is applied to influence a magenta-rheological fluid in the room in terms of its viscosity ,

The same applies to the case where a magnetic field is used to align the colloidal particles and an electric field is used to control the viscosity of an electrorheological fluid. The space is field-free if there is no "outer" magnetic field with a field strength in the space that is greater than the field strength of the Earth's magnetic field.

A field strength which causes a structure excitation is denoted by E _SA . An adjusted parenthetical expression (λ = λ _L ) or (λ = λ _UV ) expresses that the structure excitation in the structure color influences the influence of light with the wavelength λ. For example, E _SA (λ = λ _UV ) indicates that the pattern excitation causes the pattern color to affect light in the UV region. E _SA (λ = λ _I ) indicates that the pattern excitation causes the pattern color to affect light having a luminescence wavelength λ _I.

Printing inks or inks which, in the case of a luminescence excitation, in particular an irradiation of UV light, emit an emission of light, i. show a luminescence, are referred to as luminescent.

A time-resolved acquisition of a measured value or a quantity is understood to be the acquisition of this measured value or variable at different successive points in time.

Decay behavior is understood as the decrease of intensity in a time sequence.

A characteristic time constant is a determined time which, in combination with a statistical function, can describe a decay behavior of a measured variable. Assuming that a physical process responsible for the decay behavior follows a Poisson statistic, for example, a half-life, i. the period of time in which the value of the detected quantity halves, or a so-called lifetime is determined as the characteristic time instant, wherein the lifetime indicates the period in which the measured variable falls to 1: e of the measured variable. e is the Euler number.

Preferred embodiments

The security element according to the invention is defined in claim 1. It is thus created a security feature, which on the one hand shows a photoluminescent effect, but in addition via a structure excitation in Form of an electric or magnetic field in the region of the security element can be varied. This means that an observable luminescence with constant UV excitation can be influenced via the structure excitation with the electrical or / and the magnetic field and thus varies with the structure excitation. Such a security element is difficult to reproduce for counterfeiters and also not immediately apparent, since generating an electric field or a magnetic field in the area of a security element is not part of the usual Verifikationsmaßnahmen. In addition, such a structure excitation does not itself lead to an observable effect, but only in combination with the additional luminescence excitation in the form of an irradiation of UV light.

A corresponding method for verifying such a security element is defined in claim 10.

In one embodiment, it is provided that the luminescent pigments are arranged in the microcapsules themselves, in which the colloidal particles, which are preferably particles with a diameter in the nanometer range, are dispersed in a medium or a substance in which they arrange in the structure excitation to the crystal-like structure or, if they are already arranged in a field-free space in a crystal-like structure, change their structure, the optical properties of the crystal-like structure change with regard to reflection and / or transmission of light in the range of at least one wavelength of the luminescence light. At least some of the luminescent pigments are thus "incorporated" into the critical lattice. For these luminescent pigments, then, in the structure-excited state, propagation of the luminescence light, ie for at least one spectral line of the luminescent light, is possible only under certain propagation directions in the crystal lattice-like structure, which may have the properties of a photonic crystal. Thus, one obtains an angular dependence of the luminescence radiation emerging from the crystal lattice-like structure. Since the orientation of the crystal lattice is caused or at least influenced by the structure excitation, alignment of the crystal lattices in the different microcapsules takes place in the electric or magnetic field at the same time. Thus, the preferential propagation or transmission directions for the luminescent light in all microcapsules are the same with respect to a coordinate system which is virtually coupled to the structure excitation or its field, so that macroscopically the exit directions from the different crystal-like structures formed in the microcapsules are collinear with each other and so on a macroscopically observable effect occurs in such a way that the emitted luminescence radiation is direction-dependent with simultaneous luminescence excitation and structure excitation.

Thus, according to one embodiment, a verification method is carried out such that when the emission light is detected, an intensity of the emission light is used in each case as the one or more properties.

As another effect that occurs, particularly when the crystal-like structure exhibits properties of a photonic crystal in the structure-excited state, some or all of the luminescence emission directions are prohibited due to the crystal lattice-like structure of the colloidal particles. In the case of a luminescence emission, this leads to a change in the lifetime of that excited state of the luminescence pigment from which the transition emitting the luminescence radiation originates. This life extension is based on the decay behavior determine the luminescence. Clearly, this extension results from the fact that, in contrast to the usual luminescence emission, which takes place statistically isotropically in all spatial directions, such emissions are avoided, which would take place in "forbidden" spatial directions. Thus, fewer emission events occur on average over time. The lifetime of the excited state is thus longer and the decay behavior shows a longer time constant.

In a development of the security element, it is provided that the microcapsules in a field-free space are transparent for at least one wavelength of the luminescence light emitted during luminescence of the luminescent pigments and in a structure-excited state in which an electrical and / or magnetic field is formed via the structure excitation. a transmission for light of this at least one wavelength or another wavelength of the luminescence light emitted in the luminescence is at least limited. The reason for this is the arrangement of the colloidal particles in the crystal structure.

A verification thus provides that upon detection of the emission light, an intensity of the emission light is determined time-resolved immediately after termination of the luminescence excitation, and as the one or more properties of the luminescence light, a time constant is derived from the time decay behavior of the intensity of the emission light, and the time constant is used for the comparison. In principle, it would also be possible to carry out a verification by carrying out only a time-resolved measurement in the structure-excited state and comparing the time constant determined here, which could be, for example, the mean lifetime or half-life of the decay behavior, with a default value. However, a lifetime of a luminescence transition can also be influenced by other effects, so that a verification method which makes use of a change in the determined lifetime as a function of the structure excitation as a verification condition is superior. Moreover, it is not necessary to have a precise wavelength determination which would otherwise be necessary to prevent the lifetime from being produced by a skilful mixture of different luminescent pigments which have different lifetimes and would overlap in an integral measurement such that an expected decay behavior of the Luminescence would be achieved.

In one embodiment, it is provided that in the structure-excited state, the luminescence emission has a directional dependence.

In addition, it is provided in another embodiment or development that the luminescence has a changed time behavior of the luminescence intensity with pulsed UV excitation between the non-structure-excited state and the structure-excited state.

In another embodiment, it is provided that the luminescent pigments are not contained in the microcapsules. In such an embodiment, a structure color is formed in a first layer and the luminescent pigments are arranged as constituents of a luminescent color different from the structure color in a second layer over the first layer. In this embodiment, it is provided in one embodiment that the colloidal ponds are configured such that they have a reflectivity or at least an increased reflectivity in the field-free space or alternatively and preferably in the structure-excited state with respect to the respective other excited state for that wavelength with which the luminescence excitation is performed. For this purpose, an appropriate size of the colloidal particles is to be adapted such that a crystal lattice-like structure is formed which has a reflection for light, for example at a wavelength of 365 nm or at a wavelength of 254 nm, in the ultraviolet wavelength range, preferably in the structure-excited state, both are common wavelengths for UV excitation. In such a case, there is an increased reflectivity of the structure color for the UV light of the luminescence excitation arranged under the luminescence color, at least for individual directions of irradiation. The ultraviolet light of luminescence excitation which passes through the luminescent color printed layer upon excitation is thus reflected on the pattern color under excellent irradiation directions and re-irradiated into the luminescent color layer. As a result, an excitation efficiency of the luminescent pigments is increased, so that in the structure-excited state or alternatively in the field-free state, an increased luminescence intensity compared to the field-free or alternatively the structure-excited state is observed.

In addition, a directional dependence of this increased luminescence depending on the direction of irradiation directed UV light is observed. Thus, in one embodiment, the microcapsules and the colloidal particles contained therein are such that they have no or little reflectivity for UV excitation light of the luminescence excitation at least for some angles of incidence, under the structurally excited state for at least some angle of incidence the non-structure excited state have higher reflectivity for the UV excitation light of the excitation radiation.

A verification of this described effect is preferably carried out with a verification method, which is intended to irradiate directionally when carrying out the luminescence excitation UV light and to vary an irradiation of the UV light during the detection of the emission light, so that dependent on the excitation direction detection of the emission light takes place and as one or more properties of the direction of irradiation dependent luminescence is used. For example, when detecting the emission light, the luminescence intensity can be detected time-resolved in each case and assigned to the different irradiation directions. With the time-resolved detection is thus accompanied by a temporally staggered change in the direction of irradiation, so that a certain irradiation is associated with a certain detection time.

In the description so far it has been assumed that the luminescence excitation takes place from the side of the luminescent color layer, which faces away from the layer on which the structure color is located. If, for example, the structure color and above the luminescent color are printed on a substrate of a security document first, an incident light observation, in which the emission light is viewed and detected from the side from which the luminescence excitation is also carried out, and the effect just described are observed. If the substrate or a security document is transparent in the area of the security element, at least for the luminescent light, then a similar effect can also be observed in transmission. In this case, a correspondingly reduced luminescence can be observed under those irradiation directions under which there is an increased reflection in the structure-excited state at the crystal lattice-like structure in the microcapsules. It is assumed here that the microcapsules are transparent in the field-free space for the wavelength of the luminescence excitation.

In a further embodiment, it is provided that the structure color in the first layer is laterally structured and the luminescence color in the second layer is formed flat over it homogeneously. In such an embodiment, position-dependent luminescence effects are observable both in transmission and in remission. In those regions of the layer printed with the luminescent color, below which constituents of the structure color are present, an increased luminescence is observed in the reflected light observation under certain irradiation directions of the luminescence light in one of the excitation states, preferably in the structure-excited state. In transmission, correspondingly a reduced luminescence is observed. In this case, it is again assumed that the microcapsules in the field-free space are transparent to the wavelength of the UV light wavelength irradiated during luminescence excitation. Otherwise, the effect is reversed accordingly. Thus, in the UV excitation those areas are localized at which the structure color below the luminescent color are printed relative to a Auflichtbetrachtung below the luminescent color.

According to the invention thus also defined in claim 15 structure color is created new. This is understood to mean that this UV excitation can take place if the luminescent pigments are not incorporated into the microcapsules, namely, as described above, in the microcapsules, if appropriate, such that no luminescence is present in the excited state or no luminescence under certain directions of irradiation is observable, since propagation of the luminescent light through the crystal structure is prevented or excitation entirely omitted.

An embodiment of the security elements may be made by a method comprising the steps of: providing a substrate layer; imprint a first layer by means of a structural paint; Imprinting a second layer which at least partially covers the first layer with a luminescent color. In this case, a structure color is used which contains no luminescent pigments. If the structure color in the microcapsules themselves contains the luminescent pigments, then a corresponding security element can be produced by printing this structure color.

In addition to the described embodiments, those in which at least part of the luminescent pigments are incorporated into the crystal-like structure, the structural color is formed in a first layer, and other luminescent pigments other than the luminescent pigments as constituents of a luminescent color different from the structural color in one are possible second layer are arranged above the first layer, wherein a luminescence spectrum of the further luminescent pigments is different from the luminescence spectrum of the luminescent pigments. In this case, the effects already described above, which occur during the incorporation of the luminescence pigments into the crystal structure, can occur in addition to the other effects described above. These other effects now occur for the luminescence of the further luminescent pigments.

In a further development, the structure color in the first layer is laterally structured and the luminescence color is homogeneously formed with the further luminescence pigments in the second layer over it. Spatially resolved, the different effects for the different luminescent pigments can occur. Different information can be saved via this.

The verification method can in particular be developed such that it is investigated as the one or more properties whether different direction-dependent luminescence intensities and / or UV light irradiation direction depend on two different wavelengths in which luminescence of different luminescent pigments occurs upon excitation Luminescence intensities and / the different Lumineszenzintensityabklingverhalten and / or different spatially resolved luminescence intensities are found.

Fig. 1a - 1c

schematische Darstellungen einer Mikrokapsel einer Strukturfarbe zum Erläutern eines Strukturfarbeffekts, abhängig von einer Strukturanregung;

Fig. 2a - 2c

eine schematische Darstellung von Mikrokapseln zur Erläuterung eines Strukturfarbeffekts bei einer zweiten Ausführungsform;

Fig. 3a

schematische Draufsichten auf ein Sicherheitsdokument mit einem Sicherheitselement nach einer ersten Ausgestaltung, bei dem eine Strukturfarbe verwendet ist, bei der die Mikrokapseln der Strukturfarbe Lumineszenzpigmente umfassen;

Fig. 3b

eine schematische Schnittansicht eines Sicherheitsdokuments nach Fig. 3a;

Fig. 4a, 4b

schematische Darstellungen eines Sicherheitsdokuments ähnlich zu dem nach Fig. 3a und 3b während einer Lumineszenzanregung ohne eine Strukturanregung (4a) und mit einer Strukturanregung (4b);

Fig. 5a, 5b

schematische Darstellungen zur Erläuterung eines Abklingverhaltens abhängig von einer vorliegenden Strukturanregung, wobei in Fig. 5a keine Strukturanregung und in Fig. 5b eine Strukturanregung vorliegt;

Fig. 6a

eine schematische Explosionsansicht einer anderen Ausführungsform eines Sicherheitsdokuments mit einem Sicherheitselement, bei dem eine Strukturfarbe und darüber eine Lumineszenzfarbe verdruckt sind;

Fig. 6b

eine schematische Schnittansicht durch ein solches Sicherheitsdokument;

Fig. 6c

eine weitere schematische Schnittansicht durch ein alternatives Sicherheitsdokument;

Fig. 7a - 7c

schematische Ansichten eines Sicherheitsdokuments nach Fig. 6a und 6b während einer Lumineszenzanregung in Auflicht (Fig. 7a, 7b) sowie in Transmission (7b, 7c);

Fig. 8a - 8d

Erläuterungen einer winkelabhängigen Einstrahlung des UV-Lichts jeweils ohne und mit Strukturanregung für unterschiedliche Winkel (Fig. 8a - 8c) sowie eine grafische Auftragung der erfassten Lumineszenzintensität an einer Position, an der eine Lumineszenzfarbe über der Strukturfarbe verdruckt ist in Abhängigkeit von der Zeit (8d), wobei die Fig. 8a bis 8d jeweils die Situation in Auflichtanregung und -betrachtung darstellen;

Fig. 9a - 9d

Darstellung der entsprechenden Situation für eine Lumineszenzanregung in Transmission;

Fig. 10

ein schematisches Ablaufdiagramm eines Verifikationsverfahrens;

Fig. 11

eine schematische Darstellung der Kristallstruktur zur Veranschaulichung einer Richtungsabhängigkeit der Transmission/Emission von Lumineszenzlicht; und

Fig. 12

eine schematischer Darstellung zur Erläuterung der Lumineszenzerhöhung aufgrund einer im UV-Wellenlängenbereich im strukturangeregten Zustand reflektierenden Strukturfarbe.

The invention will be explained in more detail with reference to a drawing. Hereby show:

Fig. 1a - 1c

schematic representations of a microcapsule of a structure color for explaining a structural color effect, depending on a structure excitation;

Fig. 2a - 2c

a schematic representation of microcapsules for explaining a structural color effect in a second embodiment;

Fig. 3a

schematic plan views of a security document with a security element according to a first embodiment, in which a structure color is used, in which the microcapsules of the structure color luminescent pigments include;

Fig. 3b

a schematic sectional view of a security document according to Fig. 3a ;

Fig. 4a, 4b

schematic representations of a security document similar to the Fig. 3a and 3b during a luminescence excitation without a structure excitation (4a) and with a structure excitation (4b);

Fig. 5a, 5b

schematic representations for explaining a decay behavior depending on a present structure excitation, wherein in Fig. 5a no structural stimulus and in Fig. 5b a structural stimulation is present;

Fig. 6a

a schematic exploded view of another embodiment of a security document with a security element in which a structural color and on a luminescent color are printed;

Fig. 6b

a schematic sectional view of such a security document;

Fig. 6c

a further schematic sectional view through an alternative security document;

Fig. 7a - 7c

schematic views of a security document after Fig. 6a and 6b during a luminescence excitation in incident light ( Fig. 7a, 7b ) as well as in transmission (7b, 7c);

Fig. 8a - 8d

Explanation of an angle-dependent irradiation of the UV light in each case without and with structure excitation for different angles ( Fig. 8a - 8c and a plot of the detected luminescence intensity at a position where a luminescent color is printed over the pattern color as a function of time (8d) Fig. 8a to 8d each represent the situation in incident light excitation and observation;

Fig. 9a - 9d

Representation of the corresponding situation for a luminescence excitation in transmission;

Fig. 10

a schematic flow diagram of a verification method;

Fig. 11

a schematic representation of the crystal structure to illustrate a directional dependence of the transmission / emission of luminescent light; and

Fig. 12

a schematic representation for explaining the luminescence increase due to a reflected in the UV wavelength range in the structure excited state structure color.

Based on Fig. 1a to 1c and 2a to 2c is to be explained schematically by way of example the mode of action of different structural colors, which each contain microcapsules 10. The same technical features are provided in the figures with the same reference numerals. A structure color contains a multiplicity of such microcapsules, which are responsible for the color impression of the structure color. The microcapsules 10 each have a shell 11 which encloses a transparent substance 12 with colloidal particles, eg nanoparticles 13, contained therein. The sheath 11 is formed of a transparent material. The substrate 12 is also transparent and constitutes a fluid in which the nanoparticles 13 according to the embodiments Fig. 1a to 1c, 2a to 2c can move. The nanoparticles are for example clusters of iron oxide with a charged layer or plastic nanospheres with a charged coating. In other embodiments, they may also be paramagnetic or superparamagnetic particles. With regard to concrete embodiments of both the sheaths, the substances contained therein and the Nanoparticles will be particularly useful on the EP 2 463 111 A2 directed. In addition, structural paints containing such microcapsules are also available from Nanobrick, Gyeonggi-do, Korea.

In the embodiment according to Fig. 1a to 1c are the colloidal nanoparticles in the field - free space, which in Fig. 1a is shown, arranged irregularly. The microcapsules 10 of the colloidal nanoparticles have no special optical property, so that they do not significantly influence the color impression of the structure color in which they are contained. This can thus be regarded, for example, as almost transparent in the printed state. If an electric field with a field strength E1 is applied, the charged nanoparticles align themselves to form a lattice-like crystal structure 15. This is in Fig. 1b and 1c shown. Since the nanoparticles themselves carry a charge, this leads to a repulsion between them. A ratio of the electric field strength E1 or E2 to the own repulsion due to the charge determines a lattice spacing of the nanoparticles.

The crystal structure thus formed has characteristics of a photonic crystal. In this, propagation is only possible along certain spatial directions for some wavelengths. For other wavelengths, propagation may not be possible in any direction. This means that all the light of this wavelength and from all the sinks is reflected. As a result, the color of the microcapsule is conditional. In the example shown in FIG Fig. 1b At the field strength E1, for example, when illuminated with white light from a black body radiator, a red wavelength component is reflected. If the electric field strength is increased to a value E2> E1, a distance between the nanoparticles is reduced since the ratio between the force due to the external electric field and the repulsive force between the like-charged nanoparticles is given a different ratio. This changes the crystal structure so that a blue component is now reflected, for example, from the white light of a black body radiator, so that the microcapsule provides a blue color impression. This is in Fig. 1c shown.

In the Fig. 2a to 2c another embodiment of microcapsules 10 is shown schematically. These differ in that the colloidal particles already in the field-free space in the microcapsule 10 have a crystal structure 15, so that from the white light of a blackbody ray a red color component is reflected. When the field strength is increased, the distance between the particles in the crystal lattice decreases, so that now a green color component is reflected. If the field strength continues to increase ( Fig. 2c ), the grid spacing becomes even smaller, so that again a blue color component is reflected again.

In Fig. 3a schematically the top view of a security document 100 is shown, on which a security element 110 is applied in the form of a print with a here designated as Lumineszenzstrukturfarbe print preparation. A luminescent structure color is a printing preparation in which luminescent pigments are contained in the microcapsules of the structure color. In the illustrated embodiment, the security element is formed as a rectangular printing on a substrate. It is understood that any structure and graphics could be printed with the luminescent structure color.

In Fig. 3b a sectional view of the security document 100 is shown. Evident is a document body, which is formed from one or more substrate layers 160. A surface 165 of one of the substrate layers 160 is printed with a luminescent structure ink 170. This forms the security feature 110. Above this, a cover layer 180 is arranged, which is transparent both for luminescence light in the visible wavelength range and for UV light for exciting a luminescence. The substrate layers 160 may be transparent or opaque or, for example, also have a transparent window for the UV excitation and / or the luminescent light only in the area in which the surface 165 is printed with the luminescent structure ink 170.

In Fig. 4a is a schematic plan view of the security document according to Fig. 3a and 3b shown while UV excitation is taking place. When viewing Fig. 4a the security element 110 is located in the field-free space. Shown are images of the security document 100 to be observed at different angles, which are designated by reference symbols 201, 202 and 203 for viewing angles α1, α2, α3 measured against a surface normal 190 of the document 100. All three views for the different viewing angles show an identical luminescence in the area of the security element 110. A luminescence intensity is indicated by a hatching. The stronger the hatching, the higher the Luminescence intensity. This convention is followed in all figures of this application. The same technical features are provided in all figures with identical reference numerals.

In Fig. 4b the same security document is shown with identical luminescence excitation. However, an electric field E _SA (λ = λ _L ) is applied as a structure excitation whose field strength is dimensioned such that a lattice structure is formed in the luminescent structure color due to the colloidal particles contained therein, which for the wavelength of the luminescent light, ie for at least one Spectral line of the luminescent, having a restriction of the transmission at least for an excellent propagation direction relative to the electric field. It is understood that the field strength is to be selected in accordance with the wavelength of the light whose propagation is to influence the crystal-like structure, and the design of the colloidal ponds of the structure color. The electric field strength is selected in the illustrated embodiment, without limiting the generality parallel to the surface normal 190. It can be seen that the views 201-1 to 201-3 in the area of the security element 110 show different levels of luminescence. This can be explained by the fact that for some excellent directions a constructive interference of the luminescence photons diffracted or scattered on the colloidal particles occurs and for others a destructive interference occurs.

In Fig. 11 this is indicated schematically. There arise in the crystal structure 15 individual levels 17, 18, which, if a distance d _o , d _{1 of} these levels 17, 18 corresponds to half the wavelength, lead to a destructive interference. There two exemplary lattice planes are shown, which have a different spacing of the lattice planes. Further, the intensities I _{o, o} , I _{o, 1} , I _{1, o} , I _1,1 , ... for different diffraction orders with respect to the first lattice planes and the second lattice planes are shown. The first index indicates the intensity reference to the lattice plane group, the second index indicates the diffraction order relative to the lattice plane group. Thus, under excellent directions with respect to the first lattice planes 17 and excellent directions with respect to the second lattice planes 18, emission may take place. The emission of the luminescent pigments 16 has different strengths among the various directions of excellence. This is in Fig. 4 indicated by way of example. From the fact that not all emission directions are possible and no isotropic spread of the Luminescent light of luminescent takes place, which are involved in the lattice structure, the life for the state from which the radiative decay occurs in the emission of the luminescent light also changes.

In Fig. 5a and 5b this is indicated. In Fig. 5a the state is shown in which a luminescence excitation 120 without structure excitation (E = 0) is first carried out and, after switching off the luminescence excitation time-resolved decay of the luminescence intensity is detected. This is indicated in a graph in which the intensity is plotted against time. From this curve a lifetime τ1 of the excited state can be derived. For this purpose, the function is either plotted on logarithmic paper and a straight line gradient is determined, or an adaptation of an exponential decay function to the detected intensity values is carried out.

In Fig. 5b the same measuring procedure is shown for the case that in addition an electrical field E _SA (λ = λ _L ) is followed by a structure excitation, which leads to a crystal lattice structure formation in the microcapsules of the luminescent structure color, which has a wavelength λ _{L of} the luminescence 130 with respect to its propagation through the Crystal influences. It can be seen that the luminescence intensity less rapidly decreases with time and thus the determined time constant τ2 is greater than the time constant τ1, which is determined for the field-free state. This difference in the determined lifetimes, which can also be mathematically converted into a half-life of the decay curve, can be used for verification. If, for example, no different lifetimes are determined for both states, the document is not genuine.

In Fig. 6a another embodiment of a security document is shown as a schematic exploded view. Printed on a substrate 160 or a lamination body is a schematically represented letter "A" having a structure color 210 which does not comprise any fluorescent pigments and is designed to influence a light propagation of light either in the field-free state or preferably in the structure-excited state, which is used for luminescence excitation is used. The microcapsules are preferably transparent in the field-free space for a UV excitation of the wavelength of 365 nm or 254 nm and accordingly leave a transmission of light in the wavelength range of 365 in the structure-excited state nm or 254 nm only under certain spatial directions and thus show an increased reflectivity under other solid angles. A second, completely closed layer with a luminescent color 220 is printed over the first layer printed with the structure ink, which shows a luminescence upon excitation with UV light. The luminescent color is designed such that it does not show any change even when the structure is excited. For protection, a cover layer 180 is provided. Between the structure color and the luminescent color, one or more substrate layers may be arranged.

In Fig. 6b a schematic sectional view is shown, in which the luminescent color 220 is printed directly on the structure color 220.

In Fig. 6c an alternative embodiment is shown in which a substrate layer, which is designated as intermediate layer 260, is arranged between the structure color 210 and the luminescent color 220.

Based on the Fig. 7a to 7c It will be explained by way of example how the luminescence behavior varies as a function of the structure excitation, both in the case of incident light excitation and in the case of transmission excitation. If the excitation takes place from the same side as the viewing through the luminescent color layer, then in a structure excitation with a field strength which forms a crystal lattice structure so that the UV excitation light is reflected at least under individual irradiation directions, the spatial structure of the structure color above it recognizable that a luminescence at these locations where the structure color is formed below the luminescent color can be seen. This is due to the fact that the portion of the UV excitation light passing through the luminescent color layer is at least partially reflected by the structure color and thus an excitation probability of the luminescent pigments is increased. This presupposes that an intensity of the UV excitation light is chosen such that a luminescence of the luminescence color layer is not in saturation. This means that an increase in the intensity of the excitation light also leads to an increase in the observed luminescence.

In Fig. 12 this situation is again shown schematically. On a substrate layer surface 165 of a substrate layer 160, a structure color 210 is printed, which contains no luminescent pigments. On a top 265 one Intermediate layer 260, a luminescent color 220 is printed. In the area of the structure color 200, there is a structure excitation with a field strength E = E _SA (λ = λ _UV ). This means that the electric field strength is dimensioned such that the crystal-like structure of the structure color influences light in the UV wavelength range which is used for the luminescence excitation 120 with regard to transmission and reflection, preferably under some or all angles of incidence. Thus, a luminescence 130, or better said intensity, is greater when the feature color is located below the luminescent color. The intensity of the intensity is indicated by the arrow lengths of the luminescence 130.

In Fig. 7b the case is shown in which the structure excitation is not present. Both in transmission and in incident light excitation uniform homogeneous luminescence for the surface of the security element 110 is observed.

In Fig. 7c In the case where the pattern excitation predominates again, but the excitation is in transmission, that is, through the pattern color layer into the luminescent color layer and observation from the side of the luminescent color layer. Since part of the excitation light is reflected on the structure color, luminescence excitation is reduced in those areas where the structure color is below the luminescent color. Thus, a luminescence intensity in the region of the structure color is lower, so that the letter "A" can be observed virtually inversely, that is to say with less or no luminescence intensity in the security element.

In Fig. 8a to 8d is an angle dependence of the UV excitation schematically explained. In Fig. 8a to 8c the excitation and emission detection geometry is shown schematically on the left. It is excited with directed UV light, wherein in each case an angle relative to the surface normal 190 is measured. In the middle, a spatially resolved detection of the luminescence in the field-free state is shown and, on the right, a spatially resolved luminescence detection with predominant structure excitation, wherein the generated crystal structure influences the luminescence excitation radiation. The three measurements at the angles α1, α2 and α3 are carried out successively at the times corresponding to t1, t2 and t3. It can be seen that no angle dependence is observed in the field-free state. In the structure-excited state, however, when viewed in incident light excitation, ie in remission, initially a slight increase in the luminescence in the area of the printed structure color, in Fig. 8b is not increased To observe luminescence and in Fig. 8c a greatly increased luminescence in the area of the structure color. In Fig. 8d schematically is the intensity in a bit 230 or a pixel of the security element in which the structure color is printed, schematically plotted for the three times or three angles. It can be seen that an angle-dependent luminescence intensity can be recognized in the region in which the structure color is printed under the luminescence color.

In Fig. 9a to 9d the same situation is presented for the viewing geometry, in which the excitation in transmission through the document takes place and a view from the opposite side of the luminescence takes place under which the structure color is printed in part again as letter "A". The angle dependence can also be seen here, but the luminescence in the area of the structure color is attenuated.

In Fig. 10 schematically a flowchart of a verification method 500 is shown. First, a security document with a security element is provided 510. Subsequently, a field clearance in the area of the security element is brought about 520. Subsequently, a luminescence excitation 530 takes place. During or subsequent to the UV excitation, an emission light detection 540 takes place. During the luminescence excitation, for example, a spatially resolved luminescence detection 541 or an excitation angle-dependent luminescence detection 542 or following the luminescence excitation time-resolved emission intensity detection 543. Subsequently, a structure excitation is carried out, for example by generating an electric field in the region of the security element or a magnetic field, so a structure excitation of the structure color or the luminescent structure takes place. Again, a UV excitation 630 and a corresponding emission light detection 640 take place. This may comprise a spatially resolved emission light detection 641 and / or an excitation angle-dependent emission light intensity detection 642 and / or a time-resolved emission light detection 643 executed subsequently to the UV excitation 630. From the emission light intensities detected in method steps 540 and 640, properties are derived 710, for example a luminescence light intensity or a time constant of the decay behavior, and then a comparison 720 is carried out. Based on the comparison, a verification decision is derived 730, for example, a document can be considered genuine be verified if a difference in the luminescence time constant between the field-free and structure-excited state is determined. A security document is verified to be non-genuine if no change in the time constant between the nonstructured and the structurally excited state is detected. Finally, the verification decision is issued 740.

In order to be able to carry out a reliable structure excitation in a simple manner during the verification in the area of the security element, for example, electrodes can be or are formed on diametrically opposite sides of the security element. For example, transparent electrodes of zinc sulfide (ZnS) can be produced. Also lattices of conductive materials, such as metals, in a suitable embodiment, no high transparency. In order to perform excitation with a magnetic field, a coil can be formed around the security element. For example, a helical conductive structure may be applied to a substrate layer, e.g. to be printed. In either case, terminals may be routed to a document surface to apply a voltage to the electrodes or to supply a current to the coil.

It is understood that only exemplary embodiments are described here.

The features described in the different embodiments can be combined in any combination for the realization of the invention, as far as it is covered by the scope of the claims.

LIST OF REFERENCE NUMBERS

10

microcapsule

11

shell

12

substance

13

colloidal particles

15

lattice structure

16

luminescent

100

The security document

110

security element

120

luminescence

130

Luminescence

150

document body

160

substrate layers

165

surface

170

Luminescence Strukturfarbe

180

covering

190

surface normal

201, 202, 203

Viewing angle α1, α2, α3

201-1 - 201-3

views

210

Structure color (without luminescent pigments)

220

Luminescent color (without colloidal dispersed nanoparticles)

230

bit

260

interlayer

265

top

500-740

steps

R

Viewing in reflection / reflected light

T

Viewing in transmission / transmitted light

E _SA (λ = λ _L | λ _UV )

(electric) field strength of the structure excitation, which leads to a crystal structure that affects light of wavelength λ _L or λ _UV

λ _L

Wavelength of the luminescent light

λ _UV

Wavelength of the luminescence excitation light

Claims (15)

1. Security element (110) with a UV-excitable effect comprising a structure colour, which in turn comprises microcapsules (10) in which colloidal particles (13) are contained, which can be arranged and/or rearranged relative to each other in a crystalline structure by means of a structural excitation, which comprises a forming of an electrical and/or magnetic field, wherein the crystalline structure (15) has reflective and/or transmissive properties for light which can be influenced and/or adjusted via the structural excitation, wherein additionally luminescence pigments are provided, which display a luminescence in the case of a luminescence excitation which occurs by way of an irradiation of UV light, and the luminescence pigments are arranged in such a way that an observable luminescence (130) is dependent on the structural excitation by means of the electrical and/or magnetic field.
2. Security element (110) in accordance with claim 1, characterised in that at least a part of the luminescence pigments are integrated into the crystalline structure (15).
3. Security element (110) in accordance with claim 1 or 2, characterised in that the luminescence pigments are arranged in the microcapsules (10).
4. Security element (110) in accordance with claim 3, characterised in that the microcapsules (10) are, in a field-free space, transparent for at least one wavelength of the luminescence light of the luminescence pigments emitted during the luminescence (130), and, in a structurally-excited state in which, by means of the structural excitation, an electrical and/or magnetic field is formed, and a transmission for light of this at least one wavelength or another wavelength of the luminescence light emitted during the luminescence (130) is at least restricted due to the arrangement of the colloidal particles (13) in the crystalline structure (15).
5. Security element (110) in accordance with claim 4, characterised in that, in the structurally-excited state, the luminescence emission exhibits a direction dependency.
6. Security element (110) in accordance with claim 4 or 5, characterised in that the luminescence exhibits a changed temporal behaviour of the luminescence intensity under pulsed UV-excitation between the structurally-non-excited state and the structurally-excited state.
7. Security element (110) in accordance with claim 1, characterised in that the structure colour (210) is formed in a first layer, and the luminescence pigments (16), as constituent parts of a luminescence colour (220) which is different from the structure colour, are arranged in a second layer above the first layer.
8. Security element (110) in accordance with any one of claims 1 to 6, characterised in that the structure colour (210) is formed in a first layer, and further luminescence pigments different from the luminescence pigments as constituent parts of a luminescence colour which is different from the structure colour are arranged in a second layer above the first layer, wherein a luminescence spectrum of the further luminescence pigments is different from the luminescence spectrum of the luminescence pigments.
9. Security element (110) in accordance with claim 8, characterised in that the structure colour (210) in the first layer is structured laterally, and the luminescence colour with the further luminescence pigments is formed in the second layer above it, with a homogenous surface.
10. Method for verifying a security element (110) in accordance with any one of claims 1 to 9 in a security document (100),

    a) carrying out a luminescence excitation (120) by means of an irradiation of UV light onto the security element (110), while this is in a structurally-non-excited state, wherein the security element (110) is in the structurally-non-excited state, when a region in which the security element (110) is located is field-free, and

    b) detecting emission light which is emitted by the security element (110) in a wavelength range in which predetermined luminescence pigments (16) show a luminescence (130) under the UV excitation during or immediately after the luminescence excitation (120); and

    c) carrying out a structural excitation, in that an electrical field and/or magnetic field is produced in the region of the security element (110), such that the security element (110) is put into a structurally-excited state, such that colloidal particles (13) which are contained in microcapsules (10), which in turn are comprised in the security element, are arranged and/or rearranged relative to each other in a crystalline structure, and

    d) repeat or ongoing carrying out of the luminescence excitation; and

    e) detecting of emission light, analogous to the method step b);

    f) evaluating and comparing of one or more properties of the emission light detected in the structurally-non-excited state and in the structurally-excited state;

    g) deriving a verification decision on the basis of the comparison carried out of the one or more properties;

    h) issuing of the verification decision.
11. Verification method according to claim 10, characterised in that, at the evaluating and comparing of the one property or the plurality of properties of the emission light in the structurally-non-excited state and in the structurally-excited state, an evaluation is made, as the one property or as one of the plurality of properties, as to whether, for at least one spectral line of the luminescence light, only specific dissemination directions occur in the crystalline structure, as is the case if at least a part of the luminescence pigments are integrated into a crystalline structure (15) which is formed by an arrangement of colloidal particles (13) of the security element (110) at least during the structural excitation.
12. Verification method according to claim 10 or 11, characterised in that, at the detecting of the emission light, in each case an intensity of the emission light is determined, time-initiated, immediately after the ending of the luminescence excitation (120), and, as the one property or as one of the plurality of properties of the emission light, a time constant (τ₁, τ₂) is derived from a time decay behaviour of the intensity of the emission light, and this time constant is used for the comparison.
13. Verification method according to any one of the preceding claims 10 to 12, characterised in that, at the detecting of the emission light, in each case the intensity of the emission light is detected as direction-dependent, and the direction dependency of the emission light is used as the one property or as one of the plurality of properties.
14. Verification method according to any one of the preceding claims 10 to 13, characterised in that, at the carrying out of luminescence excitation, UV light is irradiated in a directed manner, and an irradiation direction of the UV light during the detection of the emission light is varied in each case, such that a detection of the emission light takes place as a dependency of the excitation direction, and a luminescence intensity dependent on the irradiation direction is used as the one property or as one of the plurality of properties.
15. Structure colour, comprising a medium, which comprises a plurality of microcapsules (10) and a binding agent, wherein the microcapsules (10) comprise a substance in which in each case a plurality of colloidal particles (13) are contained, which, in an electrical field or in a magnetic field, arrange themselves inside the microcapsule in each case to form a crystalline structure (15), wherein the crystalline structure (15) influences a transmission and/or reflection of light at least of one wavelength, characterised in that additional luminescence pigments are contained in the substance in the microcapsules (10), which can be excited, by means of a luminescence excitation in the form of a UV-light irradiation, to a luminescence.

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