Security element, value document, and method for producing same

Abstract

The invention relates to a security element for protecting a value document, comprising a support substrate, a coating which is provided with an optical surface marking, and a heat-sealable adhesive layer which is suitable for adhering the security element to a value document substrate. The invention is characterized in that the surface of the adhesive layer is provided with a coating which can be washed off upon being contacted by a cleaning liquid.

Description

[0001] Security element, value document and method for producing the same

[0002] The invention relates to a security element for protecting a value document, comprising a carrier substrate, a coating provided with an optical surface marking, and a heat-sealable adhesive layer suitable for bonding the security element to a value document substrate. The invention further relates to a value document, in particular a banknote, provided with the security element according to the invention, and to a method for producing the value document.

[0003] Valuable documents, especially banknotes, are often provided with security features for security purposes. These allow for verification of the authenticity of the valuable document and also serve as protection against unauthorized reproduction. Security features with viewing-angle-dependent effects play a special role in authenticity protection, as these cannot be reproduced even with the most modern copiers. These security features are equipped with optically variable elements that convey a different image impression to the viewer at different viewing angles, for example, displaying a different color or brightness impression and / or a different graphic motif depending on the viewing angle.

[0004] It is known to incorporate security elements in the form of security threads or to apply them in the form of security strips, security patches, or security labels to valuable documents such as banknotes. Security elements typically have a heat-sealable adhesive layer that anchors the security element to the paper. When exposed to heat, the heat-sealable adhesive layer melts and acts as an adhesive. EP 1 776 240 B1 describes a security element for securing a valuable document, comprising a heat-sealable adhesive layer suitable for bonding the security element to a valuable document substrate, which is essentially non-sticky at room temperature, and which is additionally UV-curing. During UV curing, the adhesion of the security element to the valuable document substrate improves.

[0005] The security elements provided during the production of a security document are usually in the form of a continuous film. The heat-sealable adhesive layer applied to the security elements can, under certain circumstances, lead to mutual adhesion of the security elements stacked on top of each other in the wound continuous film. The risk of mutual adhesion exists particularly in the case of a UV-curing, heat-sealable adhesive layer.

[0006] The present invention is therefore based on the object of providing a security element of the type mentioned at the outset which avoids the disadvantages of the prior art.

[0007] This problem is solved on the basis of the feature combinations defined in the independent claims.

[0008] Further developments of the invention are the subject of the subclaims.

[0009] Summary of the invention 1. (First aspect of the invention) Security element for securing a value document, comprising a carrier substrate, a coating provided with an optical surface marking and a heat-sealable adhesive layer suitable for bonding the security element to a value document substrate, in particular substantially non-sticky at room temperature, characterized in that the surface of the adhesive layer is provided with a coating which can be washed off upon contact with washing liquid.

[0010] 2. (Preferred embodiment) Security element according to clause 1, wherein the heat-sealable adhesive layer suitable for bonding the security element to a value document substrate, in particular substantially non-sticky at room temperature, is additionally UV-curing.

[0011] 3. (Preferred embodiment) Security element according to clause 1 or 2, wherein the coating provided with an optical surface marking has an optically variable effect, in particular a diffraction pattern, a hologram, a micromirror arrangement, a color shift effect or a color change that varies when viewed in reflected light and when viewed in transmitted light.

[0012] 4. (Preferred embodiment) Security element according to one of clauses 1 to 3, wherein the coating provided with an optical surface marking comprises an embossed lacquer provided with an embossed relief and a metallization, wherein the metallization is in particular a multilayer thin-film element such as a reflector / dielectric / absorber multilayer arrangement or a multilayer arrangement comprising two semitransparent metallizations with a dielectric layer embedded therebetween. 5. (Preferred embodiment) Security element according to one of clauses 1 to 4, wherein the security element is a security thread, a security strip, or a security patch.

[0013] 6. (Second aspect of the invention) A value document comprising a security element provided therewith according to any one of clauses 1 to 5.

[0014] 7. (Preferred arrangement) A security document as defined in Clause 6, wherein the security document is a banknote.

[0015] 8. (Third aspect of the invention) A method for producing the value document according to clause 6 or 7, comprising:

[0016] - the provision of a value document substrate;

[0017] - providing a security element comprising a carrier substrate, a coating provided with an optical surface marking and a heat-sealable adhesive layer suitable for bonding the security element to the value document substrate, in particular substantially non-sticky at room temperature, wherein the surface of the adhesive layer is provided with a coating which can be washed off upon contact with washing liquid;

[0018] - washing the washable coating using a washing liquid in order to release the adhesive layer;

[0019] - providing the value document substrate with the security element by means of the released adhesive layer at increased pressure and elevated temperature.

[0020] 9. (Preferred embodiment) Method according to clause 8, wherein the adhesive layer is additionally UV-curing and, in the course of providing the valuable document substrate with the security element, the adhesive layer is additionally cured by means of UV radiation.

[0021] 10. (Preferred embodiment) A method according to clause 8 or 9, wherein the security element is a security thread and the step of washing off the washable coating by means of a washing liquid to thereby release the adhesive layer takes place before embedding the security thread in the value document substrate.

[0022] Detailed description of the preferred embodiments

[0023] The present invention is based on the idea of ​​providing a security element for securing a value document with a heat-sealable adhesive layer suitable for bonding the security element to a value document substrate, which is essentially non-sticky at room temperature, wherein the surface of the adhesive layer is provided with a coating that can be washed off upon contact with a washing liquid. The coating that can be washed off upon contact with a washing liquid is preferably produced by printing using a printing ink. The coating that can be washed off upon contact with a washing liquid is therefore referred to as a "wash-off ink" for the sake of simplicity.

[0024] Suitable coatings that can be washed off upon contact with a washing liquid are known in the prior art. EP 1 972462 B1 describes a wash ink for producing a security element with sharply contoured negative writing. As soon as the wash ink comes into contact with a washing liquid, a gas is generated. Even tiny amounts of gas lead to a significant increase in pressure and thus to the exertion of a strong mechanical force, so that a metallization present above the wash ink is torn open. The resulting recesses in the metallization, which are particularly formed in the form of characters, patterns, or codes, are perceived by the observer as sharply contoured negative writing.

[0025] The idea underlying the present invention is based on the use of the wash ink known from the prior art as a cover for a heat-sealable adhesive layer. The security element to be produced, in particular a security thread, security strip, or security patch, is additionally provided with wash ink at the location where a heat-sealable adhesive layer is present. The wash ink is preferably applied by printing. The wash ink is preferably washed off using water as a suitable washing liquid. After the wash ink has dissolved, the heat-sealable adhesive layer is present in free form and can bond unhindered to a value document substrate to be secured with the security element, e.g., a paper substrate.

[0026] Suitable coatings that can be washed off upon contact with washing liquid are described, for example, in EP 1 972462 B1. The wash-off ink is based in particular on a water-soluble binder, e.g. hydroxypropyl cellulose, polyethylene glycol, casein and / or polyvinylpyrrolidone, with one or more types of fillers optionally being added, e.g. titanium dioxide, silicate and / or polymethyl ureas. Large amounts of fillers serve to impart porosity to the wash-off ink, which enables rapid access of the washing medium. The security elements according to the invention are usually in the form of a continuous film. The heat-sealable adhesive layer with which the security elements are provided is additionally coated with wash-off ink in order to prevent the security elements stacked on top of one another in the wound continuous film from sticking to one another.The risk of mutual sticking exists particularly in the case of a UV-curing, heat-sealable adhesive layer.

[0027] The security element according to the invention for protecting a value document comprises a carrier substrate, preferably a polyethylene terephthalate (PET) film, and a coating provided with an optical surface marking. The coating provided with an optical surface marking ensures reproducibility that is difficult for a counterfeiter and thus increases the counterfeit security of the value document to be equipped with the security element according to the invention. The coating provided with an optical surface marking preferably has an optically variable effect, in particular a diffraction pattern, a hologram, a micromirror arrangement, a color-shift effect, or a color change that varies when viewed in reflected light and when viewed in transmitted light.

[0028] The coating provided with an optical surface marking preferably comprises an embossing lacquer provided with an embossed relief and a metallization, wherein the metallization is in particular a multilayer thin-film element such as a reflector / dielectric / absorber multilayer arrangement or a multilayer arrangement comprising two semi-transparent metallizations with a dielectric layer embedded between them. In particular, an embossing lacquer that can be crosslinked by means of UV radiation can be used as the embossing lacquer. A color-shifting reflector / dielectric / absorber multilayer arrangement would be, for example, an Al / SiCb / Cr multilayer arrangement, which is particularly obtainable by vapor deposition. A multilayer arrangement that exhibits a varying color change when viewed in reflected light and when viewed in transmitted light is, for example,from WO 2011 / 082761 Al and WO 2019 / 068362 Al and is in particular a multilayer arrangement comprising two semi-transparent metallizations with a dielectric layer embedded therebetween, e.g. a.

[0029] Al / SiO? / Al multilayer arrangement or an Ag / SiO? / Ag multilayer arrangement.

[0030] According to a preferred embodiment, the security element according to the invention is designed such that both the heat-sealable adhesive layer suitable for bonding the security element to a value document substrate, in particular substantially non-tacky at room temperature, and the coating present above the adhesive layer which can be washed off upon contact with washing liquid are each structured in the form of a pattern, in the form of characters or in the form of a code. According to a special variant, the heat-sealable adhesive layer and the wash ink present above the adhesive layer are arranged outside the region of the coating provided with an optical surface marking. A structured heat-sealable adhesive layer is known in the prior art, see e.g. EP 1 880 864 A1.According to the present invention, the structured arrangement of the heat-sealable adhesive layer and the wash ink can preferably take place in edge regions of the security element, in particular in register with the region of the coating provided with an optical surface marking. Such a structured arrangement would be particularly advantageous if the security element according to the invention is present as a security thread. Especially if the security element according to the invention is present as a so-called window security thread, the heat-sealable adhesive layer and the wash ink are preferably arranged in a structured manner in the regions to be provided with paper webs (when the security thread is embedded in a paper substrate), in particular in register with the regions of the coating provided with an optical surface marking (see, for example, Figure 4a of EP 1 880864 B1).

[0031] The heat-sealable adhesive layer, which is suitable for bonding the security element to a value document substrate and is essentially non-tacky at room temperature, is preferably also UV-curable. During the application of the security element to a value document substrate to be secured with it, e.g., a paper substrate, the adhesion of the security element to the value document substrate improves during UV crosslinking, and the internal strength of the cured adhesive layer increases advantageously. The temperature of the adhesive layer immediately before, during, and after UV crosslinking is an important parameter determining the achievable degree of crosslinking. At higher temperatures, a higher degree of crosslinking can be achieved because the mobility of the reactive groups is greater.Suitable heat-sealable adhesive layers which are essentially non-tacky at room temperature and which are additionally UV-curing are known in the art, see for example EP 1 776 240 Bl.

[0032] The invention further relates to a value document comprising a security element according to the invention provided therewith, wherein the value document is in particular a banknote. The invention further relates to a method for producing a value document, comprising:

[0033] - the provision of a value document substrate;

[0034] - providing a security element comprising a carrier substrate, a coating provided with an optical surface marking and a heat-sealable adhesive layer suitable for bonding the security element to the value document substrate, in particular substantially non-sticky at room temperature, wherein the surface of the adhesive layer is provided with a coating which can be washed off upon contact with washing liquid;

[0035] - washing the washable coating using a washing liquid in order to release the adhesive layer;

[0036] - providing the value document substrate with the security element by means of the released adhesive layer at increased pressure and elevated temperature.

[0037] According to a preferred embodiment, the adhesive layer is additionally UV-curable, whereby during the process of providing the value document substrate with the security element, the adhesive layer is additionally cured by UV radiation. The security element is, in particular, a security thread, and the step of washing off the washable coating using a washing liquid to release the adhesive layer takes place before the security thread is embedded in the value document substrate. For optimized washing off, spray nozzles can be used if necessary. The washing liquid is preferably water.

[0038] A suitable hot stamping press for carrying out the inventive

[0039] This method is known in the prior art. For example, EP 3 173232 B1 describes a suitable hot stamping press with a foil application unit designed for transferring or laminating foil material by hot stamping onto a substrate fed in the form of successive sheets, wherein the hot stamping press additionally comprises a UV curing unit.

[0040] Further advantages of the invention are explained below using exemplary embodiments in conjunction with schematically highly simplified figures, in which a true-to-scale and proportional representation has been omitted in order to increase clarity.

[0041] They show:

[0042] Figure 1 shows a security element according to the invention according to a first embodiment;

[0043] Figure 2 shows a valuable document provided with the security element according to the invention in accordance with the first embodiment;

[0044] Figures 3 and 4 show a security element according to the invention according to a second embodiment; and

[0045] Figure 5 shows a security element according to the invention according to a third embodiment.

[0046] Figure 1 shows a cross-sectional view of a security element 1 according to the invention, in this example a security patch, according to a first exemplary embodiment. A polyethylene terephthalate (PET) film serves as the substrate 2. The substrate 2 is provided with a UV embossing lacquer 3, which has an embossed relief on the main surface opposite the substrate 2. For the sake of simplicity, the embossed relief is not shown in Figure 1. The embossed relief can, for example, have micro- and / or nanostructures, so that in combination with a reflective layer 4, e.g., a high-index layer or a metallization, diffractive optical effects, hologram effects, or micro-mirror effects are generated. In the case of metallization, it can optionally be a thin-film element, e.g., a reflector / dielectric / absorber multilayer arrangement exhibiting a color-shift effect. Examples of high-index materials are CaS, CrO2, ZnS, TiCb, SiO xThe reflective layer 4 can also be applied in the form of patterns or characters, in particular positive or negative patterns. A UV dispersion is applied over the reflective layer 4 and thermally dried, e.g., at 80°C, creating a heat-sealable adhesive layer 5 suitable for bonding the security element to a value document substrate, which is essentially non-sticky at room temperature and additionally UV-curable. The surface of the adhesive layer 5 is then provided by printing with a coating 6 that can be washed off upon contact with washing liquid.

[0047] Optionally, a release layer, e.g., a wax layer, can be arranged between the substrate 2 and the UV embossing varnish 3, so that the substrate 2 can be removed after the security element 1 has been applied to a valuable document to be secured therewith. Furthermore, a primer layer or adhesion promoter layer can be arranged between the reflective layer 4 and the adhesive layer 5, if required. Since the heat-sealable adhesive layer 5, with which the security element 1 shown in Figure 1 is provided, is additionally equipped with a wash ink 6, mutual sticking of the security elements 1 stacked on top of one another in a wound-up continuous film is prevented. The risk of mutual sticking exists particularly in the case of a UV-curing, heat-sealable adhesive layer 4.

[0048] The washing off of the wash ink 6 is preferably carried out using water as a suitable washing liquid. After the dissolution of the wash ink 6, the heat-sealable adhesive layer 5 is present in a free form and can bond unhindered to a value document substrate 6 to be protected with the security element, e.g., a paper substrate (see Figure 2).

[0049] Figure 2 shows a value document 7, in the example a banknote, secured with the security element 1 according to the invention according to the first embodiment.

[0050] Figure 3 shows a cross-sectional view of a security element 8 according to the invention according to a second exemplary embodiment, in the example a security thread. The cross-section shown in Figure 3 was taken perpendicular to the longitudinal direction of the security thread 8. The security thread 8 is based on a substrate 2, in the example a polyethylene terephthalate (PET) film, with a top side 9 and a bottom side 10. The substrate 2 is provided on its top side 9 in the central region with a UV embossing lacquer 3, which has an embossed relief on the main surface opposite the substrate 2. For the sake of simplicity, the embossed relief can have, for example, micro- and / or nanostructures, so that in combination with a reflective layer 4, e.g. a high-refractive index layer or a metallization, diffractive optical effects, hologram effects or micromirror effects are produced.A UV dispersion is applied to the upper side 9 of the substrate 2, in each of the two edge regions, and thermally dried, e.g., at 80°C. This creates a heat-sealable adhesive layer 5 that is essentially non-sticky at room temperature and suitable for bonding to paper strips when embedding the security thread 8 in a banknote. The adhesive layer 5 is, in particular, additionally UV-curable. The surface of the adhesive layer 5 is subsequently provided with a coating 6 that can be washed off upon contact with washing liquid.

[0051] A UV dispersion is applied over the entire underside 10 of the substrate 2 and thermally dried, e.g., at 80°C. This creates a heat-sealable adhesive layer 5 that is essentially non-sticky at room temperature and is suitable for reliably anchoring the security thread 8 in the paper when embedding it in a banknote. The adhesive layer 5 is additionally UV-curable. The surface of the adhesive layer 5 is subsequently provided with a coating 6 that can be washed off upon contact with washing liquid.

[0052] Figure 4 shows a plan view of the top side of the security thread 8 shown in Figure 3.

[0053] Figure 5 shows a security element 9 according to the invention according to a third embodiment, in a plan view of the top side of the security element. The third embodiment is based on the second embodiment according to Figures 3 and 4. Just as in Figure 3, layers 5 and 6 are arranged over the entire surface of the underside 10 of the substrate 2. On the top side 9 of the substrate 2, layers 3 and 4, on the one hand, and layers 5 and 6, on the other hand, are spatially arranged differently in the case of the window security thread 9 than in the case of the security thread 8.In the case of the window security thread 9 shown in Figure 5, the heat-sealable adhesive layer 5 and the wash ink 6 are arranged in a structured manner in the areas to be provided with paper webs when the security thread 9 is embedded in a paper substrate, namely in register with the areas of the coating provided with an optical surface marking (see reference numbers 3 and 4).

Claims

Patent claims 1. A security element for securing a value document, comprising a carrier substrate, a coating provided with an optical surface marking and a heat-sealable adhesive layer suitable for bonding the security element to a value document substrate, characterized in that the surface of the adhesive layer is provided with a coating that can be washed off upon contact with washing liquid.

2. Security element according to claim 1, wherein the heat-sealable adhesive layer suitable for bonding the security element to a value document substrate is additionally UV-curing.

3. Security element according to claim 1 or 2, wherein the coating provided with an optical surface marking has an optically variable effect, in particular a diffraction pattern, a hologram, a micromirror arrangement, a color shift effect or a color change that varies when viewed in reflected light and when viewed in transmitted light.

4. Security element according to one of claims 1 to 3, wherein the coating provided with an optical surface marking comprises an embossed lacquer provided with an embossed relief and a metallization, wherein the metallization is in particular a multilayer thin-film element such as a reflector / dielectric / absorber multilayer arrangement or a multilayer arrangement comprising two semi-transparent metallizations with a dielectric layer embedded therebetween.

5. Security element according to one of claims 1 to 4, wherein the security element is a security thread, a security strip or a security patch.

6. A value document comprising a security element provided therewith according to one of claims 1 to 5.

7. A value document according to claim 6, wherein the value document is a banknote.

8. A method for producing the value document according to claim 6 or 7, comprising: - the provision of a value document substrate; - providing a security element comprising a carrier substrate, a coating provided with an optical surface marking and a heat-sealable adhesive layer suitable for bonding the security element to the value document substrate, wherein the surface of the adhesive layer is provided with a coating that can be washed off upon contact with washing liquid; - washing the washable coating using a washing liquid in order to release the adhesive layer; - providing the value document substrate with the security element by means of the released adhesive layer at increased pressure and elevated temperature.

9. The method according to claim 8, wherein the adhesive layer is additionally UV-curing and, in the course of providing the value document substrate with the security element, the adhesive layer is additionally cured by means of UV radiation.

10. The method according to claim 8 or 9, wherein the security element is a security thread and the step of washing off the washable coating by means of a washing liquid in order to release the adhesive layer is carried out before embedding the security thread in the value document substrate.

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