Security element with patterned liquid crystal layer

Abstract

The invention relates to a security element (20) for protecting articles of value (10), having a pattern layer based on a liquid crystal material designed and determined to form a recessive pattern. According to the invention, it is provided that the security element (20) comprises a first embossing paint layer (26) arranged on the carrier foil (22), a nematic liquid crystal material-based pattern layer (30) partially present on the first embossing paint layer (26), and a single-layer or multi-layer second embossing paint layer (34) present over the entire surface. The surface of the first imprint paint layer (26) facing the nematic liquid crystal material is provided with an imprint having at least two regions (28A, 28B) of a different orientation structure in order to form a second recessive pattern. At least one of the oriented structures of the patterned regions (28A, 28B) forms a grid pattern with wire grid lines, the pitch of which varies on the face of the patterned regions such that the oriented structures form an aperiodic grid.

Description

Technical Field

[0001] This invention relates to a security element for protecting valuable articles, the security element having a patterned layer based on a liquid crystal material designed and determined to form an invisible pattern. The invention also relates to a corresponding manufacturing method and a data carrier having such a security element. Background Technology

[0002] Data carriers, such as valuable documents or certificates, and other valuable items, such as branded goods, are typically protected with security elements that enable verification of the data carrier's authenticity while preventing unauthorized copying. Security elements that rely on viewing angle or three-dimensional appearance play a special role in authenticity protection because they cannot be copied even using the most modern copying equipment.

[0003] The special properties of liquid crystal materials, especially the angle-dependent color impression and / or light polarization effect of liquid crystals, are also frequently utilized.

[0004] This material is practically invisible once applied to a substrate; however, against a suitable background, such as a reflective printed substrate, and with the aid of a linear or circular polarizer, it will exhibit a noticeable visual optical effect. The coated area will only be more or less optically visible when viewed through a linear or circular polarizer. Furthermore, these impressions may also be highly dependent on the (angular) position of the polarizer.

[0005] The method used here is based, for example, on the provision of a nematic liquid crystal layer on a reflective metal layer to enable good identification of polarization effects. Document WO 2005 / 105475 A1 describes a method in which a nematic liquid crystal material, such as a solvent-based UV-crosslinkable liquid crystal paint, is patterned onto a carrier foil.

[0006] The plastic carrier foil used in these methods has a preferred orientation (along the direction of operation) due to its internal structure, which is sufficient to orient the liquid crystal material in the desired form. Plastic foils with surface structures formed during manufacturing, such as PET foil, are particularly suitable.

[0007] Then, in another working step, a UV-curable embossing layer is printed over the entire surface of the carrier foil and nematic layer. A desired embossed structure, such as a diffraction structure, is embossed into the embossing layer, and a reflective layer, for example in the form of a metal layer, is applied by vapor deposition, in which voids can be introduced by partial demetallization. Finally, for transfer to a target substrate (e.g., paper), a tackifying or primer layer is applied to the layer composite, and an adhesive layer is applied on top of this primer layer.

[0008] Viewed from above, this results in the following layer sequence: nematic liquid crystal, UV varnish (with an imprinted structure), and metallization. The optical effects to be observed associated with the nematic liquid crystal are based on layers with optical anisotropy or layers that influence light polarization. Therefore, without auxiliary tools, the layer complex only displays optically variable diffraction structures, such as holograms, provided by the imprinted structure. However, when observed through a circular polarizing filter, additional structures are revealed. Regions with metallization but no nematic liquid crystal layer appear black or at least dark, while regions with nematic liquid crystal exhibit a bright appearance. Horizontal rotation of the circular polarizing filter does not cause a change in contrast here.

[0009] The working principle of a circular polarizer is explained below using a metal layer as an example. Figure 4 A schematic diagram of a circular polarizer is shown here. This polarizer consists of a first layer in the form of a linear polarizing filter and a second layer in the form of a λ / 4 layer, or "λ / 4 plate," rotated 45° relative to the linear polarizing filter. When isotropic light shines on the circular polarizer, the first layer, acting as a linear polarizing filter, only allows linearly polarized light to pass through. The transmitted linearly polarized light then shines on the λ / 4 layer, rotated 45° relative to the linear polarizing filter, which converts the linearly polarized light into circularly polarized light. The circularly polarized light is then reflected by the metal surface and converted by the second layer into linearly polarized light with its polarization plane rotated by 90°. Because the first layer does not allow light with its polarization plane rotated to pass through, the metal layer appears dark when viewed with a circular polarizer.

[0010] As an alternative to observation using a circular polarizing filter, these structures can also be visualized using a linear polarizing filter (or by viewing from the back, i.e., a "flipped" circular polarizing filter). In this case, the metallized areas without the liquid crystal coating are always bright. In areas where nematic liquid crystal material is additionally provided, a contrasting impression of darkness relative to areas without a nematic layer can be produced by appropriately rotating the linear polarizing filter horizontally, or these areas may appear bright with no perceptible contrast relative to the surrounding metallized areas.

[0011] To contrast with areas without nematic layers, the following description uses a λ / 4 sheet made of nematic liquid crystal material as an example.

[0012] Isotropic light incident on a linear polarizing filter exits as linearly polarized light. When this light strikes a λ / 4 plate made of nematic liquid crystal material at a 45° angle, the linearly polarized light is converted into circularly polarized light. This light then strikes a reflector, for example, in the form of a metal layer, reflecting circularly polarized light, which then strikes the λ / 4 plate again. After passing through the λ / 4 plate, the light is converted back into linearly polarized light, where the polarization plane has rotated by 90°. This light then strikes a linear polarizing filter, which blocks the light whose polarization plane has rotated by 90°. As a result, the area thus formed appears dark under the polarizing filter.

[0013] Therefore, on the one hand, when a circular polarizer ( Figure 4 When placed on a reflective layer, especially a metallic one, a dark appearance is produced; on the other hand, a dark appearance is also produced when a λ / 4 layer made of nematic liquid crystal material performs the function of a λ / 4 plate in a circular polarizer.

[0014] Liquid crystal layers made from solvent-based formulations are often difficult to apply at high resolution because a fairly large wet film thickness needs to be printed. Due to the low viscosity of the formulation, these wet films exhibit significant leveling or “flowing” after printing.

[0015] To achieve optimal contrast, the nematic liquid crystal layer is formed as a λ / 4 layer targeting light within a predetermined wavelength range. Due to the birefringence of liquid crystal molecules, a specific layer thickness (on the order of 1 g / m²) is required, thus preventing arbitrary thin printing. Adding thickeners typically leads to a loss of optical performance in the liquid crystal layer.

[0016] Optically anisotropic foils in the optical path can also reduce the achievable contrast, thus peelability from the carrier foil is advantageous. However, very thin UV-crosslinked (liquid crystal) layers typically have poor peelability.

[0017] Typically, solvent-based liquid crystal paints require conditions that promote orientation to function. In other methods, special alignment layers or oriented layers are used for this purpose. In particular, alignment layers composed of linear photopolymers are used, which are exposed to appropriate radiation to achieve orientation. Furthermore, liquid crystal materials can also be oriented using alignment layers, which are provided by finely structured layers or layers oriented by applying shear forces.

[0018] For example, if a nematic liquid crystal material is coated with an embossed structure having two different orientations, the resulting regionally different orientations of the liquid crystal make the embossed pattern visible with positive or negative contrast using a linear polarizing filter (or a rotating polarizing filter). Conversely, the pattern cannot be recognized using a circular polarizing filter.

[0019] Security elements with hidden images, such as those described in document WO 2019 / 068655 A1, are also used, where the liquid crystal layer is based on a liquid crystal mixture containing a dichroic dye. The liquid crystal mixture is printed onto an imprinting varnish layer with imprinting portions and is also imprinted during the imprinting process. Here, the liquid crystal is oriented independently at the two interfaces. Combined with the dichroic dye, this produces security features that display different, independent patterns from both sides, which can be revealed by irradiation with linearly polarized light. A similar method is described in document EP 4 129 709 A1, according to which the liquid crystal layer contains a dichroic dye whose absorption of polarized light depends on its orientation (relative to the polarization direction of the incident polarized light). Transparent security features can be produced when irradiated with polarized light. Double-sided imprinting may cause uncured material to be flattened, thus producing undefined patterns. Summary of the Invention

[0020] Based on this, the technical problem to be solved by the present invention is to provide a security element of the type described at the beginning, which avoids the disadvantages of the prior art, can be manufactured simply and at low cost, and has higher anti-counterfeiting protection in addition to having an attractive appearance.

[0021] The technical problem described herein is solved by the features of the independent claim. The improvements of this invention are the subject of the dependent claim.

[0022] According to the present invention, a safety element of the type described herein is defined as comprising a first embossed enamel layer disposed on a carrier foil, a patterned layer based on a nematic liquid crystal material partially present on the first embossed enamel layer, and a second embossed enamel layer present in one or more layers over the entire surface.

[0023] Here, an imprinting portion is provided on the surface of the first imprinted coating layer facing the nematic liquid crystal material. The imprinting portion has at least two regions with different orientation structures for forming a second latent pattern. At least one of the orientation structures in the pattern-forming region forms a grid pattern with wires, the spacing of which varies across the surface of the pattern-forming region, such that the orientation structure forms a non-periodic grid.

[0024] The patterned layer is arranged regionally directly on the first imprinted paint layer in the form of a first latent pattern and overlaps with the area forming the second latent pattern. The nematic liquid crystal material is uniformly oriented with different orientations in the areas forming the pattern in the form of the second latent pattern, so that the patterns formed by the different orientation structures are identifiable when observed through a polarizer.

[0025] The second embossed coating layer has an embossed portion for creating a micro-optical relief structure and an enhanced reflective coating.

[0026] Layers composed of nematic liquid crystal materials exhibit polarization-dependent optical effects that are not perceptible to the naked eye but can be detected by auxiliary tools, such as linear or circular polarization filters, and in particular, these auxiliary tools can reveal these optical effects to the observer's eye.

[0027] By varying the spacing of the grid lines according to the invention, it is possible to ensure that the view of the safety element is free from superimposed diffraction patterns in the nematic liquid crystal material region, even though the grid line size is small.

[0028] Unlike periodic arrangements, in aperiodic arrangements of wire grid lines, the distances between adjacent wire grid lines do not have a simple, regular relationship. This reliably prevents constructive interference of light reflected at adjacent wire grid lines, and thus prevents the formation of superimposed diffraction patterns, especially in the region of nematic liquid crystal materials.

[0029] Furthermore, it has been shown that the orientation characteristics of oriented structures are not affected by non-periodic arrangements that exist in the form of varying spacing.

[0030] Preferably, the spacing of the grid lines varies according to a random number distribution or a pseudo-random number distribution. Pseudo-random numbers are sequences that appear random but are calculated by a deterministic algorithm, and therefore are not truly random in the strict sense. Nevertheless, pseudo-random numbers are widely used because the statistical properties of the pseudo-random number distribution, such as the equal probability of individual numbers or the statistical independence of consecutive numbers, are usually sufficient for practical purposes, and unlike true random numbers, pseudo-random numbers are easy to generate by computers. The pseudo-random number distribution is always aperiodic in the sense of this application because there is no fixed, constant distance (“period”) between consecutive values ​​in the pseudo-random number distribution.

[0031] However, the non-periodic variation of the spacing between the grid lines is not limited to a pseudo-random number distribution, but can also be achieved through other irregular distributions of the spacing.

[0032] In a favorable design, all the directional structures in the patterned area form a grid pattern with grid lines, the spacing of which varies on the surface of the patterned area, thus forming a non-periodic grid.

[0033] Advantageously, the orientation structure exists in the form of fine grooves or channels, through which the molecules of the nematic liquid crystal material are oriented.

[0034] To achieve optimal contrast, the patterned layer is advantageously formed as a λ / 4 layer for light within a predetermined wavelength range. Due to the birefringence of the liquid crystal molecules, a specific layer thickness (on the order of 1 g / m²) is required for this.

[0035] In advantageous designs, the aperiodic grid has an average period length of 0.2 µm to 2.0 µm, preferably 350 nm to 800 nm, and a profile depth of 50 nm to 600 nm, preferably 200 nm to 400 nm.

[0036] Advantageously, the embossing portion of the first embossed lacquer layer used to form the second hidden pattern has two regions, the two regions having oriented structures with different orientation directions, wherein the angles at which the orientation directions present relative to each other are selected from the group consisting of 45° and 135°.

[0037] The first imprinted coating layer is preferably present across the entire surface. At least in the regions of the patterned layer, this first imprinted coating layer advantageously does not have areas lacking structures that promote the orientation of the liquid crystal material.

[0038] Advantageously, the refractive index of the first and / or second embossed enamel layer in the visible spectrum is between that of the patterned layer, which depends on the orientation. It is also advantageous that the refractive indices of the first and second embossed enamel layers in the visible spectrum differ by no more than 0.1, and especially no more than 0.05.

[0039] The orientation structure can also be set only in the area of ​​the pattern layer, and in particular, it can be set to be precisely registered with that area.

[0040] In an advantageous design, the first implicit pattern comprises one or more first image elements, and the second implicit pattern comprises multiple second image elements, wherein the first and second image elements include alphanumeric symbols, patterns, or codes. Advantageously, the second image elements are arranged in a grid pattern.

[0041] Micro-optical relief structures are advantageously formed by diffractive structures, especially one-dimensional or two-dimensional periodic diffractive structures, by sub-optical structures, by subwavelength structures, especially subwavelength gratings or moth-eye structures, and / or by arrangements of non-diffractive microstructures, especially (directionally reflective) micromirrors or microlenses.

[0042] The invention also includes a data carrier having a security element of the type described above. This data carrier can be, in particular, valuable documents such as banknotes, especially paper banknotes, polymer banknotes, or foil composite banknotes, stocks, bonds, certificates, coupons, checks, seals, tax stamps, luxury tickets, or identification cards such as credit cards, bank cards, cash payment cards, authorization cards, identity cards, or passport personal information pages.

[0043] Finally, the present invention also provides a method for manufacturing the aforementioned type of safety element, wherein...

[0044] - A first imprinted coating layer is applied to a carrier foil to form an alignment layer for uniformly aligning the liquid crystal material.

[0045] - An embossing section is provided for the first embossing paint layer to create at least two regions with different oriented structures in order to form a second hidden pattern, and the embossing paint is cured.

[0046] - A patterned layer based on a nematic liquid crystal material is applied regionally and directly onto a first imprinted coating layer in the form of a first latent pattern, overlapping with a region forming a second latent pattern. The nematic liquid crystal material is oriented with different, uniform orientations through the orientation structures of the patterned regions, such that patterns formed by different orientation structures are identifiable when observed through a polarizer. At least one orientation structure of the patterned regions forms a grid pattern with wires, the spacing of which varies across the surface of the patterned regions, resulting in a non-periodic grid.

[0047] - By applying radiation to cure liquid crystal materials, and

[0048] - A single or multiple layers of a second embossed paint layer are applied to the entire surface of a carrier foil with a patterned layer, an embossed portion is provided for the second embossed paint layer to produce a micro-optical relief structure, and then an enhanced reflective coating is provided.

[0049] According to an advantageous design of the method, the first imprinted coating layer is imprinted without pre-curing. Preferably, other coating layers are applied to the carrier foil and at least partially cured before the first imprinted coating layer is applied.

[0050] Advantageously, the liquid crystal material is physically dried before radiation is applied. The liquid crystal material is preferably cured by applying UV radiation.

[0051] Like the second embossing layer, the first embossing layer is preferably applied to the entire surface. It is particularly advantageous to print the first and / or second embossing layers and / or pattern layers.

[0052] In addition, it is particularly suitable to metallize the second embossed enamel layer and, if necessary, regionally demetallize it.

[0053] In other advantageous designs, one or more other layers are applied, particularly a primer layer, a heat-sealing varnish layer, a printing receiving layer, and / or a protective layer, on the second embossed varnish layer.

[0054] Between the first imprinted enamel layer (“liquid crystal layer structure”) with an orientation structure and a patterned layer made of nematic liquid crystal material, and the second imprinted enamel layer (“reflector structure”) with an enhanced reflective coating—and thus in the optical path—any isotropic transparent layer can be used. For example, in cases where the safety element consists of separately manufactured sub-elements (liquid crystal layer structure or reflector structure), an isotropic transparent bonding adhesive can be provided. If, for example, the intermediate adhesion is insufficient, a single-layer or double-layer primer structure can also be used. However, the use of birefringent foils or foils whose birefringence is not precisely specified or whose birefringence is strongly dependent on wavelength should be avoided between the observer and the reflector. Attached Figure Description

[0055] The invention will now be described in more detail with reference to the accompanying drawings, which also reveal the essential features of the invention and are not drawn to scale. These embodiments are for illustrative purposes only and should not be construed as restrictive. For better understanding, the views in the figures are highly schematic and do not reflect actual conditions. To avoid repetition, the same or corresponding elements in different figures are indicated by the same reference numerals and will not be explained repeatedly. In the figures:

[0056] Figure 1 A schematic diagram of a banknote with an embedded security thread and an adhesive transfer element is shown.

[0057] Figure 2 A cross-sectional view of the structure of a safety element according to an embodiment of the present invention is shown;

[0058] Figure 3 (a) shows a top view of an embodiment of a safety element having a structured alignment layer and a liquid crystal layer applied in a patterned manner, and (b) shows an enlarged view of the alignment structure.

[0059] Figure 4 A schematic diagram of a circular polarizer is shown;

[0060] Figure 5a This shows the observation without auxiliary tools. Figure 3 A top view of the safety components;

[0061] Figure 5b This shows the effect when viewed through a circular polarizer. Figure 3 A top view of the safety components;

[0062] Figure 5c This shows the observation at the first position via a linear polarizer. Figure 3 A top view of the safety components; and

[0063] Figure 5dThis illustrates the observation from a second position rotated relative to the first position using a linear polarizer. Figure 3 A top view of the safety components. Detailed Implementation

[0064] The invention will now be described using a security element for banknotes as an example. Figure 1 A schematic diagram of a banknote 10 is shown here, which is equipped with two security elements 12 and 16 according to an embodiment of the invention. The first security element is a security thread 12, which protrudes at a specific window area 14 on the surface of the banknote 10 and is embedded inside the banknote 10 in the area therebetween. The second security element is formed by an adhesive transfer element 16 of arbitrary shape. The transfer element may in particular exist as a patch or strip, which may or may not have its own carrier layer. The security element 16 may also be designed as a cover foil, which is arranged above the window area or through opening of the banknote.

[0065] Now according to Figure 2 The cross-section details the structure and manufacture of the safety element 20 according to the first embodiment.

[0066] The safety element 20 is based on a high-quality stretched PET carrier foil 22, on which, in this embodiment, a thin layer 24 of UV-curable varnish is applied across the entire surface. On the (partially or fully cured) varnish layer 24, a UV-curable embossing varnish 26 is applied across the entire surface, which is embossed in a process known as "casting" with minimal or no pre-curing.

[0067] Sub-regions 28A and 28B are each provided with an orientation structure 32 covering their entire surface. The orientation structure 32 is regionally composed of multiple parallel grooves arranged side-by-side, with varying spacing, achieving the orientation of the liquid crystal molecules. These grooves, for example, form aperiodic gratings in sub-regions 28A and 28B, with an average period length of 0.2 µm to 2.0 µm, preferably 350 nm to 800 nm, and a profile depth of 200 nm to 600 nm. Smaller profile depths, such as in the range of 50 nm, are also possible. The longitudinal direction of these grooves is here the orientation direction of the orientation structure in sub-regions 28A and 28B.

[0068] from Figure 2 and Figure 3 As can be seen from the diagram, the orientation directions of the oriented structures 32 in sub-regions 28A and 28B are different. For example, sub-region 28A has multiple parallel grooves arranged vertically, while sub-region 28B has multiple parallel grooves rotated 45° relative to the vertical direction. These parallel grooves are provided with varying spacing (in... Figure 3(Schematic representation by shaded lines in the b-section). The non-periodic arrangement of the grooves reliably prevents constructive interference of light reflected at adjacent grid lines, thereby reliably preventing the formation of superimposed diffraction patterns, especially in the liquid crystal material region.

[0069] When the orientation structure is constructed as a periodic grid, this effect can occur, for example, when the safety element is strongly tilted. In a periodic arrangement, the grid lines are arranged at the grid points of a regular grid. Possible diffraction effects are essentially eliminated in regions where the UV-curable enamel 26 is directly coated in a single-layer or multi-layer enamel structure 34, the refractive index of which in the visible spectrum is no different from that of the UV-curable enamel 26, or only slightly different, especially not exceeding 0.1. However, in regions where the safety element contains nematic liquid crystal material, especially when the safety element is strongly tilted, a more or less noticeable diffraction effect can indeed be observed. This behavior is undesirable for implicit safety features.

[0070] Without being constrained by this explanation, this could be due to the different refractive indices of the liquid crystal material resulting from its orientation. Therefore, the liquid crystal has a different refractive index longitudinally relative to the initial molecules than laterally relative to them (e.g., n = 1.57, Δn = 0.14). This causes the refractive index of the liquid crystal material to differ significantly from, at least at specific angles, from that of the adjacent UV-curable embossing varnish 26 when the liquid crystal material is intentionally oriented. Thus, even if the refractive indices are matched (e.g., by selecting the refractive index of the UV embossing varnish 26 to be between the two orientation-dependent refractive indices of the liquid crystal layer 30), a refractive index jump can still occur. In this case, the liquid crystal material acts similarly to an HRI coating.

[0071] Unlike periodic arrangements, in the non-periodic arrangement of the wire grid lines according to the invention, the distances between adjacent wire grid lines do not have a simple, regular relationship. This reliably prevents constructive interference of light reflected at adjacent wire grid lines, thereby preventing the formation of superimposed diffraction patterns.

[0072] Furthermore, it has been shown that the orientation characteristics of the orientation structure are not affected by the non-periodic arrangement of the wire grid lines constructed as grooves in the embodiments.

[0073] In the embodiment, sub-region 28A is arranged in a grid pattern in front of a background composed of sub-region 28B in the form of multiple repeating image elements (small “25”), which has a different orientation (“wallpaper pattern”) (rotated 45° here).

[0074] On the orientation structure 32, a thin layer 30 composed of nematic liquid crystal material is applied, in particular printed, in the form of a motif (large "25"). To improve edge sharpness, it is advantageous to apply the motif at the edges or boundaries with reduced basis weight.

[0075] The patterns applied by means of liquid crystal material can advantageously have high line strength. The size of the image elements generated by liquid crystal material 30 can be selected to be significantly, preferably several times, larger than the size of the image elements formed by the sub-region 28A of the orientation structure 32.

[0076] After the liquid crystal layer 30 is applied, the nematic liquid crystal is uniformly oriented in sub-regions 28A and 28B according to the orientation structure 32. Therefore, the liquid crystal pattern layer 30 has regions corresponding to sub-regions 28A and 28B, in which the liquid crystal orientation differs. The orientation thus obtained is then fixed by crosslinking the liquid crystal layer 30 with UV radiation after physical drying to remove any solvent.

[0077] A single or multiple layers of embossed varnish structure 34 are applied to the obtained layer sequence. An embossed structure 38, such as a holographic structure, micromirror structure, and / or subwavelength grating, is embossed into this embossed varnish structure, followed by an enhanced reflective coating, such as a metallization layer 36. In the preferably vapor-deposited metal layer 36 (e.g., made of aluminum), voids (not shown), for example in the form of intaglio characters, can be introduced by partial demetallization.

[0078] Voids can be created using either etching or washing processes. In a washing process, a soluble wash ink is printed before applying the metal layer; after vapor deposition, this ink, along with the deposited PVD layer, is washed away. In an etching process, the PVD coating is performed first, followed by the printing and structuring of a resist varnish. In unprotected areas, the PVD layer is subsequently removed with an etchant. Residual resist varnish can be left on the PVD layer or removed using a suitable solvent.

[0079] As an alternative to a metallic layer, the relief structure 38 can also be equipped with a high refractive index layer. Examples of suitable high refractive index materials are CaS, CrO2, ZnS, TiO2, or SiOx. Similarly, thin-film elements with color tilting effects can also be applied to the relief structure 38 via a PVD coating process, with gaps provided where necessary. Such thin-film elements are particularly based on the angle-dependent interference effect generated by multiple reflections through different sublayers of the element.

[0080] The resulting product can be directly prepared as heat-sealable through a primer layer and heat-sealable varnish (not shown) and applied, for example, to a substrate 52, such as paper. The carrier foil 22 can be removed after application to the substrate 52 or retained in the structure as a cover foil. The last mentioned design is particularly used for applying security elements that should cover through openings in the article to be protected. For example, unlike L-LEAD strips, for T-LEAD (Longlasting Economical Anti-copy Device) strips (where T stands for "transfer"), the carrier foil, which may be present, is typically removed after application to security paper or valuable documents. L-LEAD designs are particularly used for applying security elements that should cover through openings in the article to be protected.

[0081] Prior to applying the heat-sealing varnish, other machine-readable and / or decorative layers may be applied on the partially demetallized embossed varnish layer 34, if necessary, especially overlapping the metallization layer 36. Furthermore, the heat-sealing varnish may contain machine-readable characteristic materials, such as magnetic, conductive, phosphorescent, or fluorescent materials.

[0082] Between the embossed paint 26 (“liquid crystal layer structure”) equipped with the orientation structure 32 and the liquid crystal layer 30, and the second embossed paint structure 34 (“reflector structure”) equipped with the metallization layer 36 as an enhanced reflective coating—and thus in the optical path—an arbitrary isotropic transparent layer can also be used. For example, in the case where the safety element 20 consists of separately manufactured sub-elements (liquid crystal layer structure and reflector structure), an isotropic transparent bonding adhesive can be provided. If, for example, the intermediate adhesion is insufficient, a single-layer or double-layer primer structure can also be used.

[0083] This layer structure can also be alternatively further processed into, for example, so-called patches or individual safety elements. For this purpose, other foils, such as PET foil with a smaller thickness (e.g., 6 µm), can be laminated or attached to the layer structure. A support foil can then be laminated to one side of the carrier foil 22 for cutting or stamping processes if necessary, and the surface of the thin PET foil can be coated with a primer and a heat-sealing varnish. After pre-cutting or stamping the contour shape and removing waste, the pre-manufactured individual safety elements (patches) can be applied to the substrate. Methods for manufacturing such safety element transfer material and methods for transferring safety elements from safety element transfer material to valuable articles are described, for example, in document WO 2010 / 031543A1, the disclosure of which is incorporated herein by reference.

[0084] Figure 5 shows a top view of each individual safety element 40, illustrating the appearance of the safety element when viewed without the aid of an auxiliary tool. When viewed without an auxiliary tool, the safety element 40 displays an optically variable microstructure with a metallic sheen, which in this embodiment is a shield-shaped relief image 44 produced by a micromirror. Figure 5a ).

[0085] When this safety element 40 is viewed through a circular polarizing filter 42, the image pattern 46 generated by the liquid crystal layer 30 becomes visible and appears brightly on the dark background 50 in the form of the symbol "25" in that area. Figure 5b Rotating the polarizing filter 42 will not cause any change in appearance.

[0086] Another pattern can become visible when observing the security element using a linear polarizing filter (not shown) (or a circular polarizing filter viewed from the back, i.e., "flipped over"). In this case, the metal-coated area without a liquid crystal layer—regardless of the position of the linear polarizing filter—always appears bright, while the observer 48, under the first orientation of the linear polarizing filter, perceives sub-region 28B as a dark, large image element (large "25") in the liquid crystal layer area, and perceives region 28A as a bright pattern of small image elements (small "25") arranged in a grid-like manner. Figure 5c ).

[0087] When the linear polarizing filter is rotated, the relative brightness changes, and at a rotation of 45°, the brightness is reversed in the region of liquid crystal layer 30, making the small image elements now formed in region 28A visible as dark patterns. Their outlines, indicated by dashed lines, are preset by the region of liquid crystal layer 30. The background corresponding to sub-region 28B appears as image pattern 46, having little or no contrast compared to the background 50 of the equally bright security element 40 without liquid crystal layer 30. Figure 5d Here, the smaller character (small "25") is used to define the outline of the larger character (large "25").

[0088] A particular advantage of these designs is that they incorporate various latent patterns that can be revealed depending on the choice of polarizing filters used as auxiliary tools. In particular, in addition to easily identifiable "macroscopic" patterns, very clearly defined "microscopic" patterns can also be produced, because the resolution of the polarized patterns is no longer determined solely by printing precision, but also by the precision of the embossed enamel layer structure.

[0089] Furthermore, the aperiodic arrangement of the orientation structure or the variation in the spacing of the wire grids forming the orientation structure effectively prevents potentially interfering diffraction effects that could otherwise lead to the undesirable visibility of latent patterns generated by the nematic liquid crystal material under certain observation conditions. Moreover, it was surprisingly found that the orientation characteristics of the orientation structure are unaffected by the aperiodic arrangement present in the form of varying spacing.

[0090] Furthermore, compared to known liquid crystal-based latent pattern security features, this invention provides visually more interesting images. If a security element is interesting to an observer, he or she is more likely to pay attention to that element and the valuable item in which it is located, thus achieving a greater security effect.

[0091] Since different patterns can be confusing depending on the side of the (circular) polarizing filter used to observe the security element, the desired pattern can be stylized and reproduced on the polarizing filter used as the verification medium, on each of its upward-facing sides. For one side of the circular polarizing filter corresponding to the linear polarizing filter in operation (the "flipped" circular polarizing filter) or for the linear polarizing filter, two patterns that can be achieved by rotation can also be stylized and reproduced.

[0092] For verification, in principle, both the incident and emitted light must be polarized / been polarized, which can be achieved by placing a polarizing filter. However, other variations can also be considered. For example, the light source illuminating the observation area can emit polarized light. In this case, the observer can place a polarizing filter, for example, in the form of polarized glasses, at any point between themselves and the object being verified.

[0093] The optically important steps in manufacturing a safety element begin with the first imprint. A pattern made of nematic liquid crystal material 30 is applied, in particular, printed, onto the resulting alignment structure 32. The alignment structure 32 (with an outline depth of, for example, 200 nm and a nematic liquid crystal layer thickness of, for example, 1 µm) is filled with nematic liquid crystal in this area. With appropriate selection of the refractive index of the UV imprinting varnish 26, the imprinted structure disappears optically.

[0094] Ideally, the refractive indices of adjacent materials match, preventing strong refractive index jumps that would make the oriented pattern permanently visible even without tools. Since the liquid crystal layer has an orientation-dependent refractive index, the UV embossing varnish 26 is preferably chosen to have a refractive index between the two orientation-dependent refractive indices of the liquid crystal layer 30.

[0095] If the recognizability of the nematic liquid crystal layer is not expected when observing the safety element without auxiliary tools, the orientation quality of the orientation structure 32 in all regions 28A and 28B should be comparable.

[0096] During the process following the coating of the liquid crystal material, a UV embossing varnish 34 is applied to the entire surface of the actual embossed portion, such as a hologram or micromirror pattern 44 (performed in two steps in the embodiment). Thus, the nematic liquid crystal layer 30 is embedded between the UV varnish layers. Except for the nematic liquid crystal pattern, the embossing varnish layer 34 is applied directly onto the existing embossing 32 or embossing varnish 26. If the refractive indices are similar, i.e., differing by no more than 0.1 in the visible spectrum, especially no more than 0.05, then the “orientation” embossed portion or orientation structure 32 here also disappears optically.

[0097] The liquid crystal layer 30 and the second imprinted paint structure 34 can have different refractive indices. Ideally, the refractive indices are also matched to each other to prevent strong refractive index jumps.

[0098] The first imprinting section can be confined to the area where nematic liquid crystal material should or may be printed (registration fluctuation). However, when printing liquid crystal material, this confinement needs to be embedded in the working steps, which may be associated with a higher scrap rate.

[0099] In addition, embedding steps may also be necessary to prevent weld seams (embossing tools with oriented patterns and embossing patterns) from entering the pattern and causing problems for each other due to the construction.

[0100] List of reference numerals

[0101] 10 banknotes

[0102] 12 safety lines

[0103] 14 Window Area

[0104] 16 Transfer elements

[0105] 20 Safety Components

[0106] 22 Carrier foil

[0107] 24, 26 Embossing Paint

[0108] Subregions 28A and 28B

[0109] 30 liquid crystal layers

[0110] 32 Oriented Structure

[0111] 34 Embossing Paint

[0112] 36 Metallization

[0113] 38. Relief Structure

[0114] 40 Safety Components

[0115] 42 Polarizer

[0116] 44 Relief Images

[0117] 46 Image Patterns

[0118] 48 Observers

[0119] 50 Background

[0120] 52 Substrate

Claims

1. A security element for protecting valuable articles, the security element having a patterned layer based on a liquid crystal material, the liquid crystal material being designed and determined to form a hidden pattern, characterized in that, - The safety element includes: a first embossed paint layer disposed on a carrier foil, a patterned layer based on a nematic liquid crystal material partially present on the first embossed paint layer, and a single or multiple second embossed paint layer present over the entire surface. - Wherein, the surface of the first embossed paint layer facing the nematic liquid crystal material is provided with an embossed portion, the embossed portion having at least two regions with different orientation structures to form a second hidden pattern. - Wherein, at least one of the oriented structures in the patterned area forms a grid pattern with grid lines, the spacing of which varies on the surface of the patterned area, such that the oriented structure forms a non-periodic grid. - Wherein, the patterned layer is regionally arranged directly on the first imprinted paint layer in the form of a first latent pattern and overlaps with the region forming the second latent pattern. The nematic liquid crystal material is uniformly oriented with different orientations in the regions forming the second latent pattern, so that the patterns formed by different orientation structures can be identified when observed through a polarizer. - Furthermore, the second embossed paint layer is provided with an embossed portion for creating a micro-optical relief structure and an enhanced reflective coating.

2. The safety element according to claim 1, characterized in that, All oriented structures in the patterned area form a grid pattern with grid lines, the spacing of which varies on the surface of the patterned area, so that the oriented structures form a non-periodic grid.

3. The safety element according to claim 1 or 2, characterized in that, The orientation structure exists in the form of fine grooves or channels, through which the molecules of the nematic liquid crystal material are oriented.

4. The safety element according to any one of claims 1 to 3, characterized in that, The aperiodic grid has an average period length of 0.2 µm to 2.0 µm, preferably 350 nm to 800 nm, and a profile depth of 50 nm to 600 nm, preferably 200 nm to 400 nm.

5. The safety element according to any one of claims 1 to 4, characterized in that, The spacing between the grid lines varies according to a random number distribution or a pseudo-random number distribution.

6. The safety element according to any one of the preceding claims, characterized in that, The embossing portion of the first embossed lacquer layer used to form the second hidden pattern has two regions, the two regions having oriented structures with different orientation directions, wherein the angle of the orientation directions relative to each other is selected from the group consisting of 45° and 135°.

7. The safety element according to any one of the preceding claims, characterized in that, The first embossed paint layer is present on the entire surface.

8. The safety element according to any one of the preceding claims, characterized in that, The refractive index of the first and / or second embossed paint layer in the visible spectrum is between that of the pattern layer, which depends on the orientation.

9. The safety element according to any one of the preceding claims, characterized in that, The difference in refractive index between the first and second embossed paint layers in the visible spectrum does not exceed 0.1, and especially does not exceed 0.

05.

10. The safety element according to any one of the preceding claims, characterized in that, The first latent pattern includes one or more first image elements, and the second latent pattern includes multiple second image elements, wherein the first and second image elements include alphanumeric symbols, patterns, or codes, and wherein the second image elements are preferably arranged in a grid pattern.

11. The safety element according to any one of the preceding claims, characterized in that, The micro-optical relief structure is composed of diffraction structures, especially one-dimensional or two-dimensional periodic diffraction structures, sub-optical structures, subwavelength structures, especially subwavelength gratings or moth-eye structures, and / or arrangements of non-diffraction microstructures, especially micromirrors or microlenses.

12. A data carrier having a security element according to any one of claims 1 to 11, wherein, The data carrier is especially a valuable document or identification card.

13. A method for manufacturing a security element for protecting valuable articles, the security element having a patterned layer made of a liquid crystal material, the liquid crystal material being designed and determined to produce a latent pattern, wherein, In the method, - A first imprinted paint layer is applied to the carrier foil to form an orientation layer for uniformly aligning the liquid crystal material. - An embossing portion is provided for the first embossing paint layer to create at least two regions with oriented structures having different orientations in order to form a second hidden pattern, and the embossing paint is cured. - A patterned layer based on a nematic liquid crystal material is applied regionally and directly onto a first imprinted coating layer in the form of a first latent pattern, overlapping with a region forming a second latent pattern. The nematic liquid crystal material is oriented with different uniform orientations through the orientation structures of the patterned regions, making the patterns formed by different orientation structures recognizable when observed through a polarizer. At least one orientation structure of the patterned regions forms a grid pattern with wires, the spacing of which varies across the surface of the patterned regions, such that the orientation structure forms a non-periodic grid. - By applying radiation to cure nematic liquid crystal materials, and - A single or multiple layers of a second embossed paint layer are applied to the entire surface of a carrier foil with a patterned layer, an embossing portion is provided for the second embossed paint layer to produce a micro-optical relief structure, and then an enhanced reflective coating is provided.

14. The method according to claim 13, characterized in that, The first embossing paint layer is embossed without pre-curing, wherein, preferably, other paint layers are applied to the carrier foil and at least partially cured before the first embossing paint layer is applied.

15. The method according to claim 13 or 14, characterized in that, The liquid crystal material is physically dried before radiation is applied.

16. The method according to at least one of claims 13 to 15, characterized in that, The first embossed paint layer is applied to the entire surface.

Images