EP1631719B1 - Value document provided with a safety element and method for producing said value document - Google Patents

Abstract

The invention relates to a value document (1) provided with at least one safety element (6) comprising a marking layer (8) which is arranged in a marking area (4) and is applied to a substrate (2) containing electroluminescent pigments (10). The aim of said invention is to produce a value document complying with particularly high safety standards even when automatic evaluation methods are used. For this purpose, each electroluminescent pigment (19) comprises a pigment core (20) made of an electroluminescent material enclosed by an active optical layer (24).

Description

The invention relates to a value document having at least one security element,
which comprises in a marking region a marking layer applied to a carrier body, comprising electroluminescent pigments. It further relates to an electroluminescent pigment suitable for use in such a value document, to a method for producing such a value document and to a method for producing such electroluminescent pigments.

Luminescent compounds of general type are in DE 101 34 977 A1 disclosed.

To protect against counterfeiting or counterfeiting value or security documents, such as banknotes, identity cards or smart cards, provided with so-called security features or security elements that should exclude for example in paper-shaped documents of value, inter alia, an imitation by making color copies safely. The security elements can be configured in particular as optically variable elements, such as holograms or interference layer elements, which convey different color impressions when viewing depending on the viewing angle, but are not transmitted to the copy during the copying process. However, such security elements are difficult or impossible to machine-read or evaluate, so that an automated security check of the respective value documents is possible only conditionally and with great technical effort.

From the DE 197 08 543 However, a value document is known, which is particularly suitable for automated evaluation of its security elements. For this purpose, the value document as a security element in a marking area has a marking layer applied to a carrier body, for example the banknote paper, which is mixed with electroluminescent pigments. When checking or authenticating this security element, the marking layer containing the electroluminescent pigments is exposed to an alternating electric field contactlessly via a suitably designed test device.

The alternating electric field in turn excites the electroluminescent pigments contained in the marking layer to emit electromagnetic radiation, which can be registered directly or indirectly in a suitable receiver. In particular, in combination with the corresponding test apparatus, the valuable document thus equipped is therefore particularly suitable for an automated and thus particularly reliable evaluation with only limited technical effort.

The invention has for its object to provide a value document of the above type, which has a particularly high safety standard. In addition, an electroluminescent pigment suitable for use in such a value document, a method for producing such a value document and a method for producing such pigments are to be specified.

With regard to the value document, this object is achieved according to the invention in that the electroluminescent pigments each comprise a pigment core formed from electroluminescent material, which is surrounded by an optically active coating.

The invention is based on the consideration that the value document for a particularly high safety standard should be equipped with electroluminescent pigments.

In the evaluation of radiation emitted by electroluminescent pigments radiation is usually provided a vote of the receiver portion of the tester used on the emission spectrum of the electroluminescent pigments. In the targeted use of electroluminescent pigments with mutually distinguishable spectra, it is thus possible to make the characteristic signature of the security feature particularly concise and thus improve the quality of authentication, in terms of authentication can also be provided to determine a degree of agreement to compare the spectrum received during the test with an expected spectrum. In this case, the higher the accuracy in the evaluation and thus the higher the fuse function of the the more specific the spectrum emitted by the electroluminescent pigments can be adjusted, with a rather sharply defined spectrum allowing a higher selectivity and detection accuracy than a rather broadband spectrum. In contrast, however, the emission spectra of known electroluminescent pigments are comparatively broad-band and dopants which are more suitable via the setting can be expanded only to a limited number of clearly distinguishable spectra.

The value document should be equipped with a particularly high safety standard with electroluminescent pigments, which are designed especially for the emission of a characteristic, selectively identifiable spectrum. Such a selectively identifiable spectrum should in particular have a comparatively narrow bandwidth, so that a wavelength-sensitive evaluation of particularly reliable assignment of emitted signals to individual pigment groups or types is possible. Namely, authenticity detection can be made dependent in particular on the presence of specific pigment groups or types. For a comparatively small bandwidth of the emitted spectrum, a coating of the electroluminescent pigment core is provided such that, depending on the wavelength, partial "filtering" of the spectrum actually emitted by the electroluminescent material takes place. The coating is designed for this purpose as an optically active coating. In the case of a single-layer coating, for example, a wavelength-selective transmission takes place through the use of a non-linearly absorbing coating. In such a non-linearly absorbing coating, suitable energetic levels can be generated in the crystal lattice of the coating, for example by selective doping of the coating, eg with metal ions (Fe ³⁺ , Co ³⁺ , Ni ³⁺ ), which can be excited with sufficient light intensity and thus the nonlinearity cause. The coating can be designed such that parts of the emission spectrum are defined suppressed.

Particularly advantageous optical properties are expediently achievable by a targeted use of interference effects, by means of which the emitted spectrum can be selectively suppressed or attenuated in individual wavelengths or wavelength ranges. A use of such interference effects is realized by a coating of the electroluminescent pigment cores, which preferably has at least two layers which differ from each other in their refractive index.

Basically, the coating of pigments with consequences of thin layers with varying refractive index is known from US Pat EP 1 138 743 A1 or from the EP 0 852 977 A1 , The concepts disclosed therein, however, are directed to the coating of magnetic pigment cores, wherein the coatings should ensure an increased refractive index and thus a high reflectivity and a light color of the pigments. The methods described in these publications for applying the coatings to the pigment cores can also be present now
Concept to apply.

Advantageously, the value document is suitable for application of the security element by means of a printing process, preferably by means of screen printing, intaglio printing, offset printing, letterpress printing or a transfer process to the carrier body. For this purpose, the pigments expediently have an average pigment size of about 1 μm to 50 μm, preferably from about 3 μm to 8 μm, so that they are particularly suitable for use in a security printing process.

Particularly fine-grained pigments, which are therefore particularly suitable for use in a printing process, are obtainable in that the electroluminescent material forming the respective pigment core advantageously has a preferably cubic crystal structure.

The electroluminescent material forming the respective pigment core expediently consists of a II-VI compound, namely according to the invention of (co) doped ZnS, ZnSe, SrS, CaS or CdS, the doping as activator being Cu and / or Au and / or Mn and as co-activator comprises halide ions or 3-valent cations. Alternative or additional advantageous dopants may include Ag, Fe, Co, Ni and / or rare earths, in particular Tm, Tb, Dy, Gd, Yb, Sm, Eu.

The coating surrounding the pigment core in the manner of a microencapsulation has at least one layer of inorganic material. The inorganic material comprises a metal of Fe and / or Co and / or Ni and / or Cr and / or Mo and / or W and / or V and / or Nb, preferably of oxides, nitrides, oxysulphides, Sulfides of metals or semi-metals, which may be (co-) doped with metals or semimetals, on. In this case, SiO ₂ , SiO ₂ , TiO ₂ , NiO, Ni ₂ O ₃ , CoO, Co ₂ O ₃ , Y ₂ O ₃ or ZrO _{2 is} provided in a further advantageous embodiment as an inorganic material.

Depending on the electrical conductivity of the coating, the encapsulation of the pigment cores by the Faraday cage type coating could result in the pigment core being completely shielded from externally applied electric fields. This would make the excitation of the pigment core by the electric field, in particular the alternating electric field, difficult or completely impossible in the authentication of the value document. Therefore, in a further advantageous embodiment, the coating only partially covers the surface of the respective pigment core.

Advantageously, the coating is designed to profile the emission spectrum of the respective pigment core to a particular extent and to modify it for a particularly characteristic signature. In order to provide an emission spectrum of the pigment with comparatively low bandwidth in this sense, the coating is selected in a particularly advantageous embodiment with respect to the refractive indices of their layers and / or dimensioned in their coating thickness such that the spectral transmission of the coating at a given wavelength, preferably one Wavelength at which the natural emission spectrum of the electroluminescent material is particularly pronounced has a maximum. In this case, the material parameters refractive index and / or layer thickness are deliberately predetermined such that the desired focusing of the emission spectrum of the pigments occurs due to the use of the interference effects in the coating. By appropriate specifications, the coating can act, for example, in the manner of a bandpass filter or in the manner of an upper or lower edge filter, and maxima can be shifted or additional maxima can be generated in the emission spectrum.

With regard to the electroluminescent pigment, the stated object is achieved in that a pigment core formed from electroluminescent material is surrounded by a coating with nonlinear transmission and / or absorption behavior. Particularly advantageous developments of the electroluminescent pigment and the coating correspond to the designs provided for the document of value.

Such an electroluminescent pigment can preferably also be used in a luminescent device as a light-emitting component of light-emitting diodes, displays or backlighting. As a result of the coating, the electroluminescent pigment is expediently protected from environmental influences, in particular from water vapor migration.

To solve the object directed to the method for producing the document of value, two variants are proposed which can be used individually or else in combination with one another. In a first variant, a resin is applied and softened to produce the marking layer, wherein in the softened state of the resin Pigmentkeme be applied such that the Pigmentkeme at least partially sink into the resin, so that only a part of the surface of the Pigmentkeme from Resin out, whereupon the coating is applied by means of physical vapor deposition (PVD) and / or chemical vapor deposition (CVD). This ensures that only a part of their surface is provided with the coating in the coating of the pigment core, so that a shielding of the Pigmentkeme against the exciting electric field due to a consistently enclosing surface coating is safely excluded.

In this case, an acrylate-based resin is advantageously used, wherein in alternative or additional advantageous development, the pigment particles are scattered on a sieve on the resin. The use of the sieve makes it possible to special easy way a high homogeneity and equal distribution of the pigment cores over the surface.

In a second variant, the marking layer is applied to the carrier body by means of a printing process, preferably by screen printing, intaglio printing, offset printing, letterpress printing or a transfer printing process. Such a method is particularly suitable for the production of large quantities with relatively simple means.

In this case, an ink is advantageously used in the application of the marking layer, in addition to the electroluminescent pigments, a solvent and / or a binder are included. Appropriately, the ink is designed in terms of their composition and in terms of their components for a particularly favorable usability in a printing process. For this purpose, the printing ink advantageously contains a pigment content of less than 30%, advantageously less than 25%.

With regard to the method for producing electroluminescent pigments which are particularly suitable for use in the value document, the stated object is achieved in a second variant by using pigment veins by means of physical vapor deposition (PVD), chemical vapor deposition (CVD) and / or plasma methods and / or sol Gel process and / or Aufpolymerisierens and / or electrochemical / galvanic coating and / or fluidized bed process and / or by means of self-assembly (self-assembling) and / or hybridization with the coating. In order to ensure a shielding of the pigment core from the impressed electric field that the coating only partially encloses the pigment core, the pigment cores are subjected according to the invention after their coating a grinding process such that a portion of the coating is broken away, so that subsequently at most a part the surface of the respective pigment core is covered with the coating.

The grinding process is expediently carried out in a ball mill, wherein a grinding aid is supplied before the beginning or during the grinding. When Milling aid is particularly suitable acetylcholine and / or oil and / or an aqueous suspension.

For a particularly low production cost, the grinding process can be advantageously integrated into the paint production. For this purpose, the grinding process is advantageously carried out in a color production in a Dreiwalzenfarbstuhl, the coated pigments are part of the color. As further constituents of the paint, color binders and color pigments are advantageously provided. In order to ensure the desired comparatively fine-grained structure of the pigments, the spacing of the surfaces of the rolls of the three-roll color wheel is advantageously set to a value of at most the average diameter of the pigments.

The grinding process is carried out in an advantageous embodiment for a maximum of two hours, so that it is ensured that the coating is not completely removed from the pigment cores again.

The advantages achieved by the invention are, in particular, that a wavelength-selective transmission takes place through an optically active coating of the pigment nuclei. This is achieved, for example, in the case of a single-layer coating by means of a non-linearly absorbing coating by targeted doping, for example with metal ions (Fe ³⁺ , Co ³⁺ , Ni ³⁺ ). Furthermore, due to interference effects, a targeted modification of the spectrum emitted by the electroluminescent pigment spheres can be made possible by a multilayer coating of the pigment nuclei, in which two, three or even more coating layers with completely or partially different refractive indices can be provided. In particular, this spectrum can be made comparatively narrow-band, so that a particularly characteristic signature of the emission spectrum can be achieved. It is thus possible, by a suitable choice of material for the electroluminescent Pigmentkem in combination with the specification of suitably selected coating parameters, ie in particular suitably selected refractive indices and layer thicknesses for the coating layers, from each other on the basis of their emission spectrum distinguishable pigment groups or varieties, so that in terms of their characteristic emission wavelength distinguishable security features are available.

As a result of the high level of flexibility with regard to the emission properties in the security features that can be achieved, a particularly high security standard can be achieved in the respective security document. The possibility of targeted use of the properties of the coating of pigments is thus now being developed for a pigment class important for the mechanical verification of value and security documents.

In addition, a local reinforcement of the exciting electric field can be achieved in a particularly favorable manner if the coating has a certain electrical conductivity at least in one of the layers. The respective coating layer then acts in the manner of a local "floating" electrode in the immediate vicinity of the electroluminescent material which effects compression and focusing of the contactless externally applied electric field in the immediate surrounding region of the electroluminescent material. As a result, the excitation field of the electroluminescent material can locally be exceeded even with a comparatively low externally impressed field strength, so that a reliable excitation of the luminescence is made possible with comparatively small externally pronounced field strengths. Due to the particularly advantageous combination of these effects, it is thus possible to produce both a particularly concise, narrow-band spectrum and the use of comparatively small test field strengths in the evaluation.

Fig. 1

ein Wertdokument in Draufsicht,

Fig. 2

den Markierungsbereich des Wertdokuments nach Fig. 1 im Schnitt,

Fig. 3

Schnitte durch ein Sicherheitselement des Wertdokuments nach Fig. 1 (schematisch),

Fig. 4, 5

jeweils ein elektrolumineszierendes Pigment im Schnitt,

Fig. 6

schematisch je ein Emissionsspektrum eines elektrolumineszierenden Pigments mit unbeschichteten (Fig. 6a) und beschichteten (Fig. 6b-6g) Pigmenten,

Fig. 7

Beispiele für elektrolumineszierende Pigmente im Schnitt, und

Fig. 8

einen Schnitt durch einen Teil eines Sicherheitselements während dessen Herstellung (schematisch).

An embodiment of the invention will be explained in more detail with reference to a drawing. Show:

Fig. 1

a value document in plan view,

Fig. 2

the marking area of the value document Fig. 1 on average,

Fig. 3

Cuts through a security element of the value document Fig. 1 (Schematically)

Fig. 4, 5

each an electroluminescent pigment in section,

Fig. 6

schematically each an emission spectrum of an electroluminescent pigment with uncoated ( Fig. 6a ) and coated ( Fig. 6b-6g ) Pigments,

Fig. 7

Examples of electroluminescent pigments in section, and

Fig. 8

a section through a part of a security element during its production (schematically).

Identical parts are provided with the same reference numerals in all figures.

The value document 1 according to FIG. 1 which may be, for example, a banknote, an identification card, a chip card or any other security document or product secured against counterfeiting or copying, comprises as a basic element a carrier body 2, depending on the intended use of the document of value 1 made of paper Plastic, can be constructed of laminated plastic layers or other suitably chosen material. On the carrier body 2, a security element 6 is applied in a marking area 4. The security element 6 and the marking area 4 covered by the latter can be dimensioned and designed according to any criteria tailored to the intended use and, in particular, can be configured for optical reproduction of a printed image, for example a numerical value.

The security element 6 serves in the manner of a security feature for detecting whether the value document 1 is genuine. For this purpose, verification or authentication methods are used that check certain chemical or physical properties of the security feature and thus detect whether the security feature meets the expected specifications.

The security element 6 is designed to a particular extent for automated readability of its security function. For this purpose, the security element 6, as in the embodiment according to FIG. 2 is shown in section, in the marking area 4 a marking layer 8 applied to the carrier body 2. The marking layer 8 is constructed to ensure automated evaluability on the basis of electroluminescent pigments 10. In this case, for the authentication or evaluation of the security element 6, the contactless irradiation of electromagnetic radiation in the marking layer 8 of a suitably selected test device, as for example in the DE 197 08 543 is disclosed provided. The electromagnetic radiation radiated into the marking layer 8 triggers electroluminescence phenomena in the pigments 10, wherein the electromagnetic response radiation generated thereby can be detected by a suitable sensor and evaluated automatically.

As in FIG. 3a 1, the marking layer 8 can be applied to the carrier body 2 by a printing process, in particular by screen printing, intaglio printing, offset printing or letter set printing. In this case, the marking layer 8 comprises, on the one hand, the electroluminescent pigments 10 and, on the other hand, further constituents of the printing ink, such as, for example, color pigments and / or color binders 12. As an alternative to the printing process, it is also possible to use a different coating technique, such as, for example, painting. In the embodiment according to FIG. 3b In contrast, the security element consists of a substrate 14 and a coating 16. The substrate 14 may be a paper, a plastic or a composite material. As a coating 16 could in this case, the electroluminescent pigments 10 comprehensive powder or a mixture of in FIG. 3a shown used type. The security element 6 with the in FIG. 3b shown construction can be connected to the document of value 1, for example by gluing or laminating.

In a further exemplary embodiment for the production of the security element 6 or the value document 1, a powder comprising the electroluminescent pigments 10 can be mixed with plastic particles or plastic precursor particles and processed into a film by calendering, extruding or film casting. The film may in this case already represent the value document 1 or the security element 6 or be connected to a carrier by means of one or more lamination or adhesive steps.

The security element 6 is designed to comply with particularly high security standards. For this purpose, it is ensured that the electroluminescent pigments 10 of the security element 6 have a particularly narrow-band emission spectrum in response to the radiated alternating electric field, so that an individualized recognition and assignment of a specified group or type of electroluminescent pigments 10 is made possible with appropriate tuning of the tester. To ensure this, the electroluminescent pigments 10 each comprise an in FIG. 4 exemplified Pigmentkem 20, which is bounded by its surface 22. The Pigmentkem 20 consists of an electroluminescent material, that is, of a material that emits electromagnetic radiation upon application of an alternating electric field. Typical electroluminescent materials consist of a host lattice, a II-VI compound, for example zinc sulfide (ZnS), zinc selenide (ZnSe), strontium sulfide (SrS), calcium sulfide (CaS) or cadmium sulfide (CdS). Such materials have an activator, this activator being provided as doping in the host lattice. Such dopants may consist of copper (Cu), gold (Au) or manganese (Mn).

Furthermore, electroluminescent materials have coactivators, which are also dopants of the host lattice. These dopants can be used as halide ions (chlorine ions (Cl ^- ), bromine ions (Br ^- ) or iodine ions (I ^- )) or as 3-valent cations (aluminum ions (Al ³⁺ ), gallium ions (Ga ³⁺ ), indium ions (In ³⁺ ), europium ions (Eu ³⁺ ), prometium ions (Pm ³⁺ ), praseodymium ions (Pr ³⁺ )). For example, a widely used electroluminescent material consists of a zinc sulfide host lattice with a manganese and chlorine dopant (ZnS: Mn, Cl) and preferably has a cubic crystal lattice. Alternatively or additionally, the doping can be silver (Ag), iron (Fe), cobalt (Co), nickel (Ni) and / or selected rare earths such as thulium (Tm), terbium (Tb), dysprosium (Dy), gadolinium (Gd ), Ytterbium (Yb), samarium (Sm), europium (Eu).

The electromagnetic radiation emitted by the electroluminescent pigment cores 20 when excited by an alternating electric field lies in a wavelength range between 200 nm and 3 μm. The mean diameter (the so-called D-index 50 value) of such pigment core 20 in the exemplary embodiment is at most 30 μm, preferably less than 25 μm, particularly advantageously approximately 1 μm to 15 μm.

In order to ensure the desired optical properties, the respective pigment core 20 is surrounded by an at least single-layer optically active coating 24 in order to form the actual pigments 10. In the case of a single-layer coating, for example, a wavelength-selective transmission by means of a non-linearly absorbing coating is effected by targeted doping, for example with metal ions (Fe ³⁺ , Co ³⁺ , Ni ³⁺ ). In the embodiment according to FIG. 5 In this case, to additionally utilize interference effects, an optically active coating 24 of three layers 26, 28, 30 is shown. However, it is also possible to provide another suitably selected number of coating layers, for example two or even more than three.

The layers 26, 28, 30 forming this coating 24 are made of inorganic material in the exemplary embodiment. However, they may also be organic polymer-based materials such as PET and / or PMMA. Suitable inorganic materials are metals, in particular iron (Fe), cobalt (Co), nickel (Ni), chromium (Cr), molybdenum (Mo), tungsten (W), vanadium (V) or niobium (Nb). Metal oxide layers are preferably composed of silicon dioxide (SiO ₂ ) silicon monoxide (SiO), titanium dioxide (TiO ₂ ) yttrium oxide (Y ₂ O ₃ ) or zirconium dioxide (ZrO ₂ ). The thickness of such a layer 26, 28, 30 should be at most 1 μm, but preferably 50 to 200 nm.

The optically active coating 24 is applied to the respective pigment core with the aim of suitably modifying the emission spectrum of the electroluminescent material of the pigment core 20 by targeted utilization of interferences and, in particular, making it comparatively narrow-band. For this, the layers 26, 28, 30 of the coating 24 of the exemplary embodiment are chosen such that the refractive index between adjacent layers 26, 28, 30 differs considerably. In this case, it is ensured that the electroluminescent material forming the pigment core 20 emits electromagnetic radiation when excited by an alternating electric field, which then exposes the coating 24 to interference effects.

oder $$\mathrm{n}\mathrm{\cdot }\mathrm{d}\mathrm{=}\mathrm{m}\mathrm{\cdot }\frac{\lambda }{4},$$

je nachdem, ob in dem betreffenden Wellenbereich eine Verstärkung oder eine Auslöschung erreicht werden soll, wobei m eine ganze Zahl und λ die Wellenlänge der elektromagnetischen Strahlung ist, die verstärkt oder ausgelöscht werden soll. Die Lagen 26, 28, 30 werden dann als sogenannten $\frac{\lambda }{2}$

- bzw. $\frac{\lambda }{4}$

-Schichten bezeichnet.The layers 26, 28, 30 are designed with regard to the layer thickness and their respective refractive index such that the electromagnetic radiation emitted by the electroluminescent material of the pigment core 20 passes through the layers only in certain predetermined regions of the wavelength spectrum. The following known law is used: $$\mathrm{n}\mathrm{\cdot }\mathrm{d}\mathrm{=}\mathrm{m}\mathrm{\cdot }\frac{\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}{\mathrm{2}}$$

or $$\mathrm{n}\mathrm{\cdot }\mathrm{d}\mathrm{=}\mathrm{m}\mathrm{\cdot }\frac{\mathrm{<figure-callout\; id="4"\; label="\lambda "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}{4}.$$

depending on whether a gain or an extinction is to be achieved in the relevant waveband, where m is an integer and λ is the wavelength of the electromagnetic radiation which is to be amplified or extinguished. The layers 26, 28, 30 are then called so-called $\frac{\lambda }{2}$

- respectively. $\frac{\mathrm{<figure-callout\; id="4"\; label="\lambda "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}{4}$

Layers.

By using such a coating 24 for the pigment cores 20, the emission spectrum of the pigment nuclei 20 can be significantly modified, as exemplified by the spectra in FIGS FIGS. 6a to 6g is explained. While, as in FIG. 6a shown qualitatively in the form of an intensity (I) wavelength (λ) spectrum for a non-coated Pigmentkem 20, the electroluminescent material has a comparatively broad-band emission spectrum with a maximum at a wavelength λ ₀ , the width of this spectrum can be through the coating 24th reduce significantly. An example of this is in FIG. 6b represented by a further intensity (I) wavelength (λ) spectrum. This characteristic spectrum for electroluminescent pigments 10 formed of pigment coats 20 provided with a coating 24 has a significantly lower bandwidth Δλ in comparison to FIG FIG. 6a shown spectrum. In the in the Figures 6b and 6c In this case, the coating 24 is selected such that both for wavelengths below the wavelength λ ₀ (or λ ₀ and λ ₁ and for wavelengths above the wavelength λ ₀ (or λ ₀ and λ ₁ ) filtering or attenuation of emitted radiation is made, so that in this case the coating 24 acts in the manner of a bandpass filter and a maximum is achieved ( FIG. 6b ) or several maxima, eg two maxima ( FIG. 6c ), be achieved. Depending on the desired specification of the spectrum of the electroluminescent pigments 10, the coating 24 may also be in the manner of an upper edge filter (FIG. FIG. 6d ), which in particular attenuates the emitted radiation having a wavelength of more than the wavelength λ ₀ , or in the manner of a lower edge filter (US Pat. FIG. 6e ) Which attenuates in particular radiation of a wavelength less than the wavelength λ _0, be designed. Furthermore, an additional maximum ( FIG. 6f ) or shift a maximum in the emission spectrum, as in FIG. 6g indicated by the double arrow.

In order to avoid the complete shielding of the pigment cores 20 from the impressed alternating electric field due to the Farraday effect in the selected materials, in particular with regard to the metallic components in the coating 24, is in the embodiments according to FIG. 7 the coating 24 is applied to the respective pigment core 20 in such a way that it only partially covers its surface 22. To ensure this, in the production of the value document 1, a method can be used, for which an intermediate in FIG. 8 is shown. In this embodiment for the production of the security element 6, a substrate 14 is provided for the security element 6. On the substrate 14, a resin 32 is applied, wherein the resin 32 is softened after application or before or during the application by heat input. Subsequently, pigment cores 20 of an electroluminescent material are scattered on the surface of the resin 32. This is preferably done through a sieve, so that a particularly uniform distribution of the pigment core 20 is ensured. The softening of the resin 32 is thereby made in a thickness such that the pigment grains 20 do not completely sink into the resin 32, but that almost all the cores protrude with a part of their surface from the resin 32. Subsequently, a coating is then carried out, for example by means of PVD or CVD method, so that the pigment cores 20 are only partially coated.

Alternatively, however, it may also be envisaged to apply the pigments 10 in a first working step with a complete coating 24, as in FIG FIG. 5 shown to produce. The coating of the pigment core 20 with the coating 24 can be effected in particular by means of physical vapor deposition (PVD), chemical vapor deposition (CVD) or a sol-gel process. In order to ensure starting from such prepared pigments 10 a only partially coated surface 22 of the pigments 20, the milling step is followed by a grinding process. By grinding, part of the coating is broken away from the initially completely coated pigment core 20. The grinding process is carried out, for example, in a ball mill, wherein the powder is added before or during grinding, a grinding aid. As a grinding aid may be provided acetylcholine ([N (CH ₃ ) ₃ (C ₂ H ₅ O)] ⁺ COO ^- ), oil or an aqueous suspension.

Alternatively, however, the grinding process can also take place in the context of the production of a printing ink, so that the total manufacturing effort required is kept particularly low. For this purpose, the electroluminescent pigments 10 are added to an ink, with which then the document of value 1 for producing the security element 6 and its marking layer 8 can be printed. The color, which is generally composed of binder and color pigments, in this case additionally contains the electroluminescent pigments 10 with the complete optically active coating 24. If the color is then placed in a three-color roller, which is generally customary in color production, and the distance the roll surface of the rollers of the three-roll color set such that the distance is slightly smaller or at most equal to the average diameter of the powder particles, then here the Pulververteilchen-Keme subjected to the complete coating a grinding process, so that subsequently a mixture of color and electroluminescent Pigments 10 is present, whose Pigmentkeme 20 are only partially coated on its surface 22.

The meal in the ball mill or the grinding process in the three-roll paint chair are preferably 30 minutes to 2 hours. After this period, a sufficient homogenization is achieved, with destruction of the pigment core 20 is reliably avoided by grinding.

LIST OF REFERENCE NUMBERS

1

value document

2

support body

4

marking region

6

security element

8th

marking layer

10

electroluminescent pigments

12

arrow

14

electrodes

16

coating

20

Pigmentkem

22

surface

24

optically active coating

26,28,30

documents

32

resin

I

intensity

λ, λ ₀ λ ₁

wavelength

Δλ

bandwidth

Claims (26)

1. Value document (1) comprising at least one security element (6) which comprises in a marking region (4) a marking layer (8), which is applied to a substrate (2) and comprises electroluminescent pigments (10), the electroluminescent pigments (10) each comprising a pigment core (20) which is formed from electroluminescent material having an emission spectrum (Fig. 6a), characterised in that the pigment core (20) is surrounded by a coating (24) which optically filters the emission spectrum (Fig. 6a) in a wavelength-selective manner, the electroluminescent material which forms the respective pigment core (20) consisting of doped or co-doped ZnS, ZnSe, SrS, CaS or CdS, and the doping comprising Cu and/or Au and/or Mn as activators and halide ions or trivalent cations as coactivators, and at least one layer (26, 28, 30) of the coating (24) being formed from inorganic material in the form of a metal selected from Fe and/or Co and/or Ni and/or Cr and/or Mo and/or W and/or V and/or Nb.
2. Value document (1) according to claim 1, in which the coating (24) forms an interference coating and comprises at least two layers (26, 28, 30) of a different refractive index, and one layer has a thickness of at most 1 µm, preferably of approximately 50 to 200 nm.
3. Value document (1) according to either claim 1 or claim 2, in which the pigments (10) exhibit an average pigment size of approximately 1 µm to 50 µm, preferably of approximately 3 µm to 8 µm.
4. Value document (1) according to any one of claims 1 to 3, comprising a pigment core (20) formed from electroluminescent material, in which the coating (24) exhibits non-linear transmission and/or absorption characteristics due to the coating (24) being doped with metal ions.
5. Value document (1) according to any one of claims 1 to 4, in which the electroluminescent material forming the pigment core (20) exhibits a cubic crystal structure.
6. Value document (1) according to any one of claims 1 to 5, in which at least one further layer (26, 28, 30) of the coating (24) is formed from inorganic material selected from oxides, nitrides, oxysulphides, sulphides of metals or semi-metals or the like, which is in a form doped or co-doped with metals or semi-metals.
7. Value document (1) according to claim 6, in which the inorganic material is formed from SiO₂ SiO, TiO₂, NiO, Ni₂O₃, CoO, Co₂O₃, Y₂O₃ or ZrO₂.
8. Value document (1) according to any one of claims 1 to 7, in which the coating (24) only covers the surface of the respective pigment core (20) in part.
9. Value document (1) according to any one of claims 1 to 8, in which the coating (24) exhibits a spectral transmission which exhibits a maximum at a predetermined wavelength.
10. Value document (1) according to claim 9, in which the coating (24) comprises means for creating an additional maximum in the emission spectrum.
11. Value document (1) according to claim 9, in which the coating (24) comprises means for shifting a maximum in the emission spectrum.
12. Value document (1) according to any one of claims 1 to 11, in which the coating (24) comprises a further layer which causes compression and focussing of an externally applied electric field in the direct vicinity of the electroluminescent material.
13. Method for manufacturing a value document (1) according to any one of claims 1 to 12, in which a resin (32) is applied to the substrate (2) and softened to produce the marking layer (8), characterised in that once the resin (32) has softened, pigment cores (20) are applied in such a way that the pigment cores (20) sink into the resin (32) at least in part, in such a way that merely part of the surface of the pigment cores (20) projects out from the resin (32), and in that the coating (24) is subsequently applied by physical vapour deposition (PVD) and/or chemical vapour deposition (CVD).
14. Method according to claim 13, in which an acrylate-based resin (32) is used.
15. Method according to either claim 13 or claim 14, in which the pigment cores (20) are scattered onto the resin (32) via a sieve.
16. Method according to any one of claims 13 to 15, in which the marking layer (8) is applied to the substrate (2) by a transfer method.
17. Method for manufacturing a value document (1) according to any one of claims 1 to 12, in which for manufacturing electroluminescent pigments (10), the pigment cores (20) are provided with the coating (24) by physical vapour deposition (PVD) and/or chemical vapour deposition (CVD) and/or plasma-enhanced deposition and/or a sol-gel process and/or grafting and/or electroplating/electrochemical plating and/or fluidised bed processes and/or by self-assembling and/or hybridisation, characterised in that after being coated (24), the pigment cores (20) are subjected to a grinding process, in such a way that part of the coating (24) is broken away in each case, in such a way that subsequently at most part of the surface of the respective pigment core (20) is covered by the coating (24).
18. Method according to claim 17, in which the grinding process is carried out in a ball mill, a grinding agent being introduced before the start of or during the grinding.
19. Method according to either claim 17 or claim 18, in which acetylcholine and/or oil and/or an aqueous suspension is used as a grinding agent.
20. Method according to any one of claims 17 to 19, in which the grinding process is carried out during dye manufacture in a three-roller dye mill, the coated pigments (10) being a constituent of the dye.
21. Method according to claim 20, in which dye binders and dyeing pigments are provided as further constituents of the dye.
22. Method according to either claim 20 or claim 21, in which the distance of the surfaces of the rollers of the three-roller dye mill is set to a value of at most the average diameter of the pigments (10).
23. Method according to any one of claims 17 to 22, in which the grinding process is carried out for at most 2 hours.
24. Method according to any one of claims 17 to 23, in which the marking layer (8) is applied to the substrate by printing, preferably by screen printing, recess printing, offset printing or letterset printing.
25. Method according to any one of claims 17 to 24, in which when applying the marking layer (8), a printing dye is used which comprises a solvent and/or binder in addition to the electroluminescent pigments (10).
26. Method according to any one of claims 17 to 25, in which the printing dye comprises a pigment content of less than 30 %, preferably less than 25 %, in total.

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