Method for manufacturing a security element with relief structure and security element with relief structure

Abstract

The invention relates to a method for manufacturing a security element (4) comprising the following steps: providing a UV embossing varnish layer (8) and embossing a relief structure (9) and curing the UV embossing varnish layer (8), printing a varnish as a primer onto the relief structure (9) and drying the varnish, wherein the dried primer has a layer thickness of a maximum of 2 µm, and PVD deposition of a ZnS layer (12) of a maximum thickness of 1 µm to cover the dried primer layer (10).

Description

[0001] The invention relates to a method for producing a security element comprising providing a UV embossing lacquer layer and embossing a relief structure and hardening the UV embossing lacquer layer and PVD deposition of a maximum 1 µm thick zinc sulfide (ZnS) layer for covering the relief structure.

[0002] The invention further relates to a security element comprising a UV embossing lacquer layer into which a relief structure is embossed, and a maximum 1 µm thick, PVD-deposited ZnS layer for covering the relief structure.

[0003] Such a security element is known, for example, from DE 102020000732 A1. It provides an optically variable security element for protecting valuables, etc., which has a ZnS layer on a relief structure. Similar structures are known from the following publications: EP 2953798 B1, DE 10201805447 A1, DE 102018005454 A1, and DE 10201005474 A1.

[0004] Security elements with micromirrors or relief structures are also disclosed in the following publications: EP 1966769 B2, EP 1879154 B1, EP 2507068 B1, EP 2632739 B1, EP 2633344 B1, EP 2655080 A2, EP 2909660 A2, EP 3294566 B1, EP 3302998 B1, EP 3339048 B1, EP 3621819 A1, EP 2539158 B1, EP 3427968 B1, EP 3372420 B1, EP 3194178 B1, EP 3415964 B1, EP 3634770 B1 and EP 3752371 A2. WO 2022 / 096833 A1 describes such a security element with a multilayer structure on the relief structure forming the micromirrors. WO 2019 / 158625 A2 discloses a list for two superimposed, flat layers, which includes, among other things, an unspecified adhesion promoter layer and a high-index layer. A layer thickness range of a few nanometers to a few micrometers is specified.

[0005] Thin ZnS layers, i.e., layers with a maximum layer thickness of 1 µm, applied to UV embossing lacquer using PVD, exhibit adhesion problems. To improve adhesion, it is known to use plasma treatment with various gases, such as nitrogen, oxygen, or argon, during the PVD process and to apply excitation, for example, with direct current or medium-frequency voltage. While this improves adhesion, it does not improve adhesion to the extent that the ZnS layer cannot be removed using adhesive tape. Accordingly, the durability of such a security element is insufficient. Counterfeiting is also possible, particularly if, as is usually the case, the ZnS layer is covered with a leveling protective layer. In this case, a counterfeiter can remove the leveling protective layer using adhesive tape, as the ZnS layer detaches from the embossing lacquer layer along with the leveling protective layer.In this way, the embossed structure can be molded and used for a counterfeit.

[0006] The invention is therefore based on the object of further developing the manufacturing method or the security element mentioned at the outset in such a way that the resistance is increased and the susceptibility to counterfeiting attacks is reduced.

[0007] The invention is defined in the independent claims. The dependent claims relate to preferred developments.

[0008] The process for producing a security element involves, in a first step, providing a UV embossing lacquer layer, and embossing and curing a relief structure thereon. Before applying the ZnS layer, a primer in the form of a lacquer is printed onto the relief structure as a layer, which acts as an adhesion promoter. The primer layer is dried. The dried primer layer has a maximum layer thickness of 2 µm. Subsequently, a maximum 1 µm thick ZnS layer is deposited using PVD to cover the primer layer.

[0009] The thickness of the primer layer ensures that the embossed structures of the relief structure are not undesirably rounded. For a relief structure formed as a micromirror structure, the dried primer layer is preferably formed with a layer thickness of 100 nm to 300 nm, preferably 150 nm to 250 nm. If the relief structure has a hologram structure, thinner layer thicknesses are preferred, namely a range of 30 nm to 200 nm, preferably 50 nm to 100 nm.

[0010] The primer is a varnish. It preferably contains at least one volatile solvent and a film-forming agent as a non-volatile component. The solvent evaporates during the physical drying process, and the non-volatile components adhere to the relief structure as a smooth film.

[0011] The varnish can be a clear varnish, i.e. pigment-free. Alternatively, a comparatively small proportion of pigments can be present. They serve as spacers to improve the winding behavior of a web with the security elements and the leveling. The pigments do not significantly influence the chemical composition or drying behavior of the varnish. Particle materials, e.g. carbon black or TiO2, are therefore generally suitable as solid materials for the pigments. They have a minimum dimension that does not exceed the achievable dry film thickness of the primer, and are therefore usually nanoscale particles. Since, as will be explained, the pigments are present in a very small proportion at most, they do not noticeably interfere with the visual impression of the security element. Their visual effect is therefore irrelevant.

[0012] To achieve the desired thin, homogeneous layer thickness with the printing process, the varnish is adjusted to a comparatively high viscosity using a film former and, if present, contains only a small amount of solids in the form of pigments, which does not adversely increase the viscosity. This can be determined, if necessary, through a simple series of experiments. Commercially available primers are designed in an inverted manner for this purpose and contain a high solids content in the comparatively low-viscosity film former (also known as the binder).

[0013] In order to achieve the thin layer thickness of a maximum of 2 µm for the dried primer layer and at the same time use a technically advantageous printing process to produce the primer layer, it is preferable to set a specific viscosity for the film former (also referred to as binder). The viscosity is preferably in the range of 10 mPa s to 400 mPa s, more preferably 80 mPa s. The varnish is a clear varnish or contains, as a pigment, only a low solids content of a maximum of 8 wt.%, preferably a maximum of 5 wt.%. This lack of or low solids content makes it easier to achieve the desired thin layer thickness during printing. Commercially available primers, on the other hand, are formulated to have the highest possible solids content.

[0014] A varnish made of nitrocellulose dissolved in esters and / or ketones, which has a viscosity in the above range without the pigment components, makes it possible to work without or with the above-mentioned very small addition of pigments, ie solid materials, and still provide a viscosity suitable for printing.

[0015] For the further manufacturing process, it is preferable if the primer is tack-free after drying. "Tack-free" in the technical sense means that the surface is not sticky. A surface is tack-free when coated film pieces of approximately 100 cm 2 which were stacked, loaded with a weight of 10 kg and stored at 40 °C for 72 hours, can then be easily separated from each other without damaging the coatings.

[0016] Tests have shown that a solvent-based 2K PU primer is particularly preferred. Such primers typically contain, and here, also preferably, esters and / or ketones as solvents. This polyurethane coating consists of a polyol component and an isocyanate component as a crosslinker. These can be aliphatic or aromatic. The polyol component is preferably a polyester polyol. Examples of solvents that can be used include ethyl acetate, butyl acetate, propyl acetate, MEK, acetone, and dimethyl carbonate.

[0017] Optionally, the ZnS layer is covered with a leveling top layer, usually transparent in the visible spectral range. This allows the resistance of the security element to be easily improved without the top layer being removed and used to replicate the relief layer in a counterfeit attack.

[0018] The following commonly used UV-curing embossing lacquers are suitable for the UV embossing lacquer layer. Possible materials include: prepolymers, e.g., high-molecular-weight acrylic acid esters, urethane acrylates, epoxy acrylates, polyester acrylates, amine-modified polyester acrylates, reactive diluents, low-molecular-weight compounds for adjusting viscosity, e.g., TPGDA, TMPTA, DPGDA, HDDA, and stabilizers that prevent premature reaction or gelling. Possible photoinitiators include phosphine oxide derivatives, benzophenone derivatives, thioxanthones, and alpha-hydroxy ketones. The primers mentioned achieve the desired adhesion for all of these ingredients of the UV embossing lacquer layer, which can be used individually or in any combination.

[0019] Analogous to the manufacturing process, a security element is also provided, featuring a UV embossing lacquer layer with a relief structure embossed into it. A primer layer with a maximum thickness of 2 µm is printed directly onto the UV embossing lacquer layer. A maximum 1 µm thick ZnS layer is deposited by PVD onto this primer layer, which acts as an adhesion promoter. The primer layer is thus located directly between the UV embossing lacquer layer and the ZnS layer.

[0020] The properties of the security element achieved above in connection with the manufacturing process naturally also apply to the security element itself.

[0021] The invention is explained in more detail below using exemplary embodiments with reference to the accompanying drawings, which also disclose features essential to the invention. These exemplary embodiments are for illustrative purposes only and are not to be interpreted as restrictive. For example, a description of an exemplary embodiment with a large number of elements or components should not be interpreted as meaning that all of these elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of different exemplary embodiments may be combined with one another unless otherwise stated. Modifications and variations described for one of the exemplary embodiments may also be applicable to other exemplary embodiments.To avoid repetition, identical or corresponding elements in different figures are designated by the same reference numerals and are not explained more than once. The figures show: Fig. 1 in plan view a valuable document with a security element, Fig. 2 a schematic sectional view through the security element, Fig. 3 a block diagram of a method for producing the security element of the Fig. 2.

[0022] Fig. Figure 1 shows a top view of a value document 2 with a security element 4. This is preferably an optically variable security element. A sectional view through the security element 4 along the line AA is shown in Fig. 2 shown.

[0023] With regard to the optically variable properties, the security element 4 can, in particular, have all possible configurations described in DE 102020000732 A1, which is explicitly cited and incorporated herein. Where a simplified structure is explained below, this is equally possible and clarifies the crucial configurations, including those with regard to the security element(s), described in the aforementioned DE 102020000732 A1.

[0024] The security element 4 has a substrate 6 on which a UV embossing lacquer layer 8 is arranged. The materials mentioned above are suitable for the UV embossing lacquer 8. A relief structure 9 is formed in the UV embossing lacquer 8, which is designed, for example, as a micromirror structure and / or a hologram structure. A primer layer 10 made of the materials mentioned above, in particular a solvent-based 2K PU primer, is located on the UV embossing lacquer 8. The solvents are, for example, esters or ketones.

[0025] The primer layer 10 has a layer thickness of preferably less than 2 µm; for a relief structure with micromirrors, a layer thickness in the range of 200 nm is preferred; for a hologram structure, the primer layer 10 is preferably thinner, namely with a layer thickness preferably between 50 nm and 100 nm, particularly preferably 75 nm. As will be apparent from the Fig. As explained in Figure 3, the primer layer 10 is applied to the embossed embossing lacquer layer 8 by means of a printing process. The carrier substrate 6 comprises, for example, a PET film.

[0026] After the primer layer 10 has been physically dried, a thin ZnS layer 12 is applied using PVD. The primer layer 10 now achieves a level of adhesion that prevents the ZnS layer 12 from being removed using adhesive tape.

[0027] A leveling cover layer 14 covers the relief structure 9 coated in this way. Due to the adhesion provided by the primer layer 10, it is not possible to peel off the cover layer 14 with the ZnS layer 12 in order to remove the shape of the relief structure 9 in a counterfeiting attack.

[0028] Fig. Figure 3 shows the multi-step manufacturing process in a block diagram.

[0029] In a step S1, a UV embossing varnish 8 is applied, for example, printed, to the substrate 6, which is in the form of a PET film. Particularly preferred is the material based on a mixture of urethane acrylate and amine-modified polyester acrylate with TPGDA as a reactive diluent. Subsequently, the relief structure 9 is embossed into the UV embossing varnish 8 (step S2). The UV embossing varnish 8 is then cured using UV radiation (step S3), so that the embossed relief structure 9 is stabilized for the subsequent process steps. Subsequently, in a step S4, the primer, preferably a 2K PU primer, is printed on using a printing process. Particularly preferred is the film former containing nitrocellulose and no pigments, thus being a clear varnish. Alternatively, a nanoscale particle material, e.g. carbon black or TiO2, is added as pigment in a proportion of max. 8 wt.% or less, e.g. 1, 2, 3, 4, 5, 6 or 7 wt.%.The viscosity of the film former, ie the nitrocellulose in the solvent, is in a range of 10 mPa s to 400 mPa s and particularly preferably has a value of 80 mPa s.

[0030] Subsequently, in step S5, a ZnS layer 12 is applied using a PVD process. Standard manufacturing processes can be used for this purpose.

[0031] Subsequently, in step S6, the security element 4 is covered with an equalizing cover layer 14. List of reference symbols 2 Value document 4 Security element 6 (Carrier) substrate 8 UV embossing varnish 9 Relief structure 10 Primer layer 12 ZnS layer 14 leveling top layer S1-S6 step QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 102020000732 A1 [0003, 0023] EP 2953798 B1

[0003] DE 10201805447 A1

[0003] DE 102018005454 A1

[0003] DE 10201005474 A1

[0003] EP 1966769 B2

[0004] EP 1879154 B1

[0004] EP 2507068 B1

[0004] EP 2632739 B1

[0004] EP 2633344 B1

[0004] EP 2655080 A2

[0004] EP 2909660 A2

[0004] EP 3294566 B1

[0004] EP 3302998 B1

[0004] EP 3339048 B1

[0004] EP 3621819 A1

[0004] EP 2539158 B1

[0004] EP 3427968 B1

[0004] EP 3372420 B1

[0004] EP 3194178 B1

[0004] EP 3415964 B1

[0004] EP 3634770 B1

[0004] EP 3752371 A2

[0004] WO 2022 / 096833 A1

[0004] WO 2019 / 158625 A2

[0004]

Claims

[1] Method for producing a security element (4) comprising the following steps: - Providing a UV embossing lacquer layer (8) and embossing a relief structure (9) and hardening the UV embossing lacquer layer (8), - printing a varnish as a primer onto the relief structure (9) and drying the varnish, the dried primer having a layer thickness of maximum 2 µm, and - PVD deposition of a maximum 1 µm thick ZnS layer (12) to cover the dried primer layer (10). [2] The method of claim 1, wherein the primer comprises a physically drying film former. [3] The process according to claim 2, wherein the film former has a viscosity of 10 mPa s to 400 mPa s. [4] Method according to one of claims 1 to 3, wherein the lacquer is a clear lacquer or has as pigment a solid material content of max. 8 wt.% of a particulate material. [5] A method according to any one of claims 1 to 4, wherein the lacquer is tack-free after drying. [6] Method according to one of claims 1 to 5, wherein the primer is a solvent-based 2K PU varnish. [7] A process according to any one of claims 1 to 6, wherein the film former comprises nitrocellulose dissolved in ester. [8] Method according to one of claims 1 to 7, wherein the UV embossing lacquer layer (8) comprising a micromirror structure is provided as a relief structure (9) and the dried primer layer (10) has a layer thickness of 100 nm to 300 nm, preferably 150 nm to 250 nm. [9] Method according to one of claims 1 to 8, wherein the UV embossing lacquer layer (8) comprising a hologram structure is provided as a relief structure (9) and the dried primer layer (10) has a layer thickness of 30 nm to 200 nm, preferably 50 nm to 100 nm. [10] Method according to one of claims 1 to 9, wherein the ZnS layer (12) is covered with a cover layer (14) leveling the relief structure (9). [11] Security element comprising: - a UV embossing lacquer layer (8) into which a relief structure (9) is embossed, - a primer layer (10) printed onto the UV embossing lacquer layer (8) with a maximum layer thickness of 2 µm, and - a maximum 1 µm thick, PVD-deposited ZnS layer (12) on the primer layer (10), - wherein the primer layer (10) lies directly between the UV embossing lacquer layer (8) and the ZnS layer (12). [12] Security element according to claim 11, wherein the primer layer (10) is a nitrocellulose lacquer layer. [13] Security element according to one of claims 11 to 12, wherein the UV embossing lacquer layer (8) has a micromirror structure provided as a relief structure (9) and the primer layer (10) has a layer thickness of 100 nm to 300 nm, preferably 150 nm to 250 nm. [14] Security element according to one of claims 11 to 13, wherein the UV embossing lacquer layer (8) has a hologram structure as a relief structure (9) and the primer layer (10) has a layer thickness of 30 nm to 200 nm, preferably 50 nm to 100 nm. [15] Security element according to one of claims 11 to 14, wherein the ZnS layer (12) is covered with a cover layer (14) leveling the relief structure (9). [16] A value document or a precursor of a value document not yet fit for circulation, comprising a security element (4) according to one of claims 11 to 15.

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