Security element comprising a motif-producing liquid crystal layer and method for the manufacture thereof

Abstract

The invention relates to a security element (20) for securing valuable objects (10), comprising a motif layer based on a liquid crystal material which is designed and intended to form a latent motif. According to the invention, the security element (20) comprises a first embossed lacquer layer (26) arranged on a carrier film (22), a motif layer (30) partially present on the first embossed lacquer layer (26) and based on a nematic liquid crystal material, and a single-layer or multi-layer second embossed lacquer layer (34) present over the entire surface. The nematic liquid crystal material contains at least one dichroic fluorescent dye, from which the emission of polarised light depends on its orientation. The surface of the first embossed lacquer layer (26) facing the nematic liquid crystal material is provided with an embossing which has at least two regions (28A, 28B) with alignment structures of different orientation in order to form a second latent motif, wherein the nematic liquid crystal material is homogeneously aligned by the motif-forming regions (28A, 28B) in the form of the second latent motif, each having a different orientation, such that the second latent motif formed by the different alignment structures can be recognised by the emission of polarised light. The motif layer (30) is arranged directly on the first embossed lacquer layer (26) in some regions in the form of a first latent motif (46) and overlaps with the regions (28A, 28B) forming the second latent motif. The second embossed lacquer layer (34) is provided with an embossing for producing a micro-optical relief structure (38) and a reflection-increasing coating (36).

Description

[0001] SAFETY ELEMENT WITH MOTIVATIONAL LIQUID CRYSTAL LAYER AND ITS MANUFACTURING METHOD

[0002] The invention relates to a security element for protecting valuables, comprising a motif layer based on a liquid-crystalline material designed and intended to form a latent motif. The invention further relates to an associated manufacturing process and a data carrier with such a security element.

[0003] Data carriers, such as valuables or identification documents, but also other valuables like branded goods, are often equipped with security features to ensure authenticity. These features allow verification of the carrier's authenticity and simultaneously serve as protection against unauthorized reproduction. Security features with a viewing angle-dependent or three-dimensional appearance play a particularly important role in authenticity assurance, as these cannot be reproduced even with the most modern copying equipment.

[0004] The special properties of liquid crystalline materials are often exploited, especially the viewing angle-dependent color impression and / or the light-polarizing effect of the liquid crystals.

[0005] Such materials are practically invisible after being applied to a substrate, but exhibit pronounced visual optical effects when viewed on a suitable surface, such as a reflective substrate, and with the aid of linear or circular polarizers. Only when viewed through a linear or circular polarizer do the coated areas become more or less optically visible. Furthermore, the resulting impressions can be highly dependent on the (angular) position of the polarizer.

[0006] The methods used here are based, for example, on the application of a nematic liquid crystal layer over a reflective metal layer to ensure good visibility of the polarization effects. Publication WO 2005 / 105475 Al describes a method in which the nematic liquid crystal material, for example, a solvent-based UV-curable liquid crystal lacquer, is printed in a pattern onto a carrier film. Due to their internal structure, the plastic carrier films used in these methods have a preferred orientation (in the direction of travel) that is sufficient to align the liquid crystal material in the desired shape. Plastic films with a surface structure created during manufacturing, such as PET films, are particularly suitable.

[0007] In a further step, a UV-curable embossing varnish layer is printed over the entire surface of the carrier film and the nemat layer. A desired embossing structure, e.g., a diffraction pattern, is then embossed into the varnish layer, and a reflective layer, e.g., in the form of a metal layer, is applied, particularly by vapor deposition. Partial demetallization can create recesses in this reflective layer. Finally, for transfer onto a target substrate (e.g., paper), an adhesion promoter or primer layer and an adhesive layer are applied to the composite layer.

[0008] Viewed from above, the resulting layer sequence is as follows: nematic liquid crystals, UV varnish (with embossed structure), metallization. The optical effect observed in connection with nematic liquid crystals is based on the formation of an optically anisotropic layer, i.e., a layer that influences the polarization of light. Viewed without any aids, the layered structure therefore only shows the optically variable diffraction patterns provided by the embossed structure, such as holograms. However, when viewed through a circular polarizing filter, additional structures become visible. Areas with metallization and without a nematic liquid crystal layer appear black or at least dark, while areas with nematic liquid crystals appear bright. A horizontal rotation of the circular polarizing filter does not result in any change in contrast.

[0009] The operating principle of a circular polarizer is explained below using the example of metal layers. Fig. 7 shows a schematic representation of a circular polarizer. This consists of a first layer in the form of a linear polarizing filter and a second layer in the form of an X / 4 layer, or an "X / 4 plate," rotated 45° relative to the polarizing filter. When isotropic light strikes the circular polarizer, the first layer, acting as a linear polarizing filter, transmits only linearly polarized light. The transmitted linearly polarized light strikes the X / 4 layer, which is rotated 45° relative to the linear polarizing filter and converts the linearly polarized light into circularly polarized light. The circularly polarized light is then reflected at the metallic surface and converted by the second layer into linearly polarized light with a polarization plane rotated 90°.Since the first layer does not allow light with a now rotated polarization plane to pass through, metallic layers appear dark when viewed with a circular polarizer.

[0010] As an alternative to viewing with a circular polarizing filter, the structures can also be visualized with a linear polarizing filter (or a circular polarizing filter viewed from the back, i.e., "reversed"). In this case, the metallically coated areas without the liquid crystal coating always appear bright. In the areas additionally coated with the nematic liquid crystal material, a suitable horizontal rotation of the linear polarizing filter can either produce a dark impression, contrasting with the areas without the nematic layer, or the areas will appear bright without any perceptible contrast to the surrounding metallized areas.

[0011] This creates an impression that contrasts with the areas without a nematic layer, as described below using the example of a layer of nematic liquid crystalline material formed as an X / 4 platelet.

[0012] Light striking a linear polarizing filter (isoptropic light) exits as linearly polarized light. When this light strikes the X / 4 plate made of nematic liquid-crystalline material at a 45° angle, the linearly polarized light is converted into circularly polarized light. Upon striking a reflector, such as a metallic layer, circularly polarized light is reflected and strikes the A / 4 plate again. After passing through the X / 4 plate, this light is converted back into linearly polarized light, but with its plane of polarization rotated by 90°. This light then strikes the linear polarizing filter, which blocks the light, now rotated by 90° in its plane of polarization. As a result, the area formed under the polarizing filter appears dark.

[0013] A dark appearance results on the one hand when a circular polarizer (Fig. 7) is placed on a reflective, especially metallic, layer, and on the other hand when the X / 4 layer made of nematic liquid crystalline material takes over the function of the X / 4 plate in the circular polarizer.

[0014] Liquid crystalline layers produced from solvent-based formulations are generally difficult to apply at high resolution because significant wet film thicknesses would have to be printed, which, due to the low viscosity of the formulations, exhibit significant flow or "flow" after printing.

[0015] For optimal contrast, the nematic liquid crystal layer forms an X / 4 layer for light from the intended wavelength range. Depending on the birefringent property of the liquid crystal molecules, a specific layer thickness (on the order of 1 g / m²) is required. 2This is necessary, which is why arbitrarily thin printing is not possible. The addition of thickeners generally leads to a loss of quality in the optical properties of the liquid crystal layers.

[0016] Optically anisotopic films in the optical path can also reduce the achievable contrast, making release capability from the substrate advantageous. However, very thin UV-crosslinked (liquid crystal) layers often have poor release capability.

[0017] In general, solvent-based liquid crystal coatings require alignment-promoting conditions to be effective. In other processes, special alignment layers are used for this purpose. In particular, alignment layers consisting of a linear photopolymer exposed to suitable radiation are employed. Furthermore, liquid crystal materials can also be aligned using alignment layers provided by a finely structured layer or a layer aligned by applying shear forces.

[0018] For example, if an aligning embossed structure with two different orientations is coated with nematic liquid crystalline material, the resulting regionally different orientation of the liquid crystals allows the embossed motif to be made visible in positive or negative contrast using a linear polarizing filter (by rotating the polarizing filter). With a circular polarizing filter, however, no motif can be discerned.

[0019] Security features with latent images are also used, in which the liquid crystal layer is based on a liquid crystalline mixture containing dichroic dyes, as described, for example, in publication WO 2019 / 068655 Al. The liquid crystalline mixture is printed onto an embossed varnish layer and then embossed itself. In this process, the liquid crystals are aligned independently at both interfaces. Together with the dichroic dye, this creates security features that display different, independent images from each side, which can be made visible by irradiation with linearly polarized light.A similar approach is described in publication EP 4129709 Al, according to which the liquid crystal layer contains a dichroic dye whose absorption of polarized light depends on its orientation (relative to the polarization orientation of the incident polarized light). When illuminated with polarized light, this allows for the creation of see-through security features. However, embossing on both sides can lead to the unhardened material being rolled out, resulting in undefined designs.

[0020] Based on this, the invention aims to provide a security element of the type mentioned above that avoids the disadvantages of the prior art, is easy and inexpensive to manufacture and, in addition to an attractive appearance, offers increased protection against counterfeiting.

[0021] This problem is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0022] According to the invention, a security element of this type comprises a first embossed lacquer layer arranged on a carrier film, a motif layer partially present on the first embossed lacquer layer based on a nematic liquid-crystalline material, and a second embossed lacquer layer consisting of one or more layers and covering the entire surface. The nematic liquid-crystalline material contains at least one dichroic fluorescent dye whose emission of polarized light depends on its orientation. Dichroic fluorescent dyes align themselves with the liquid crystals in a nematic liquid-crystalline matrix. Accordingly, the incorporated dichroic fluorescent dye also has a preferred orientation. The dichroic fluorescent dye can be present in the liquid-crystalline material, for example, in a proportion of up to 5 wt.%, preferably up to 2 wt.%, and particularly preferably more than 0.1 wt.%.-% and up to 1 wt%, based on the total formulation of the nematic liquid crystalline material, may be contained.

[0023] The surface of the first embossing lacquer layer facing the nematic liquid-crystalline material is embossed with a pattern that forms a second latent motif, featuring at least two areas with orientational structures of different orientations. The nematic liquid-crystalline material is homogeneously aligned by the motif-forming areas, each with a different orientation, so that the second latent motif formed by the different orientational structures is visible through the emission of polarized light.

[0024] The motif layer, in the form of a first latent motif, is arranged in areas directly on the first embossing varnish layer and overlaps with the areas forming the second latent motif. The second embossing varnish layer is embossed to create a micro-optical relief structure and coated with a reflection-enhancing finish.

[0025] The layer of nematic liquid crystalline material exhibits polarization-dependent optical effects that cannot be perceived by the eye, but can be detected by means of aids, e.g., by linear or circular polarization filters, and in particular can be made visible to the eye of the observer with such aids.

[0026] Suitable dichroic fluorescent dyes for use in polymer networks are known in the art. The dichroic fluorescent dye can, in particular, possess a functional group that enables it to be incorporated into the (liquid-crystalline) network. Dichroic fluorescent dyes exhibit fluorescence and can be excited, for example, by UV light. DDUV F375 (from Colour Synthesis Solutions Ltd.) is an example of a UV-excitable dichroic fluorescent dye. Fluorescent dyes with a 9,10-diphenylane thracene fluorophore or a coumarin fluorophore are also particularly well-suited.

[0027] In an advantageous embodiment, the at least one dichroic fluorescent dye exhibits polarization-dependent light absorption, which depends on its orientation (relative to the polarization orientation of the incident polarized light). This polarization-dependent light absorption occurs only in the UV range. Liquid crystals on their own do not show significant light absorption or reflection. Therefore, the light absorption is determined by the dichroic fluorescent dye.

[0028] Advantageously, the embossing of the first embossing varnish layer for the formation of the second latent motif features two areas with orthogonally oriented alignment structures. When illuminated with polarized light, this results in maximum contrast between the areas.

[0029] In an advantageous further development, the embossing of the first embossing lacquer layer for the formation of the second latent motif has at least three areas with alignment structures of different orientation directions, wherein the orientation directions assume angles relative to each other that are selected from the group consisting of 45°, 90°, and 135°. In addition to the contrast differences recognizable by the emission of polarized light, such designs can also make polarization-dependent optical effects visible in the form of latent motifs of the nematic liquid-crystalline material.

[0030] According to an advantageous embodiment of this development, the security element includes a partially present additional motif layer based on a nematic liquid-crystalline material, which is arranged in the form of a third latent motif directly on the first embossed lacquer layer in certain areas. The first embossed lacquer layer is provided with a further embossing, which, to form a fourth latent motif, has at least two areas with orientation structures of different orientations. The additional motif layer is arranged overlapping with the areas forming the fourth latent motif, wherein the nematic liquid-crystalline material is homogeneously aligned with the motif-forming areas of the fourth latent motif, each with a different orientation, so that the fourth motif formed by the different orientation structures is visible when viewed through a polarizer.Advantageously, the additional motif layer does not contain a dichroic dye, especially not a dichroic fluorescent dye.

[0031] In the case where a first latent motif is applied to the first embossing varnish layer using dichroic fluorescent dyes in nematic liquid-crystalline material, and a second (third) latent motif is applied using only nematic liquid-crystalline material, only a single, unified motif is visible when a circular polarizing filter is applied. Regardless of the orientation of the alignment structures and the position of the polarizing filter, all areas printed with nematic liquid-crystalline material appear bright. When viewed with a linear polarizing filter, the areas with an orientation of 0° and 90° cannot be distinguished. Instead, these areas always change simultaneously from dark to light when the linear polarizing filter is rotated. However, the areas rotated by 45° in their orientation direction each exhibit maximum contrast compared to the areas with an orientation of 0° or 90°.In general, only the liquid crystal areas above a reflective background can be detected.

[0032] When irradiated with UV light, all areas containing dichroic fluorescent dye fluoresce. Areas without dichroic fluorescent dye always remain dark. When viewed through a linear polarizing filter (preferably positioned between the observer and the substrate, not between the UV source and the substrate), the areas with an orientation of 0° to the polarizing direction of the polarizing filter appear maximally bright, those with an orientation of 90° appear maximally dark, and those with an orientation of 45° appear at medium brightness. Rotating the polarizing filter by 90° reverses the contrast between the areas with an orientation of 0° and 90°.

[0033] The thickness of the nematic liquid crystalline material layer plays only a very minor role in the polarization of the emitted light. Therefore, forming the motif layer, for example, as an X / 4 layer for light from the intended wavelength range is not necessary when using dichroic fluorescent dyes.

[0034] In configurations where the polarization-dependent optical effects of the nematic liquid crystal material are also to be made visible, the nematic liquid crystal layer advantageously forms an X / 4 layer for light from the intended wavelength range for optimal contrast.

[0035] The first embossing varnish layer preferably covers the entire surface. At least in the area of ​​the motif layer, it advantageously has no area without structures that promote the alignment of the nematic liquid crystalline material.

[0036] According to an advantageous embodiment, the alignment structures are in the form of fine grooves or channels through which the molecules of the nematic liquid crystalline material and the molecules of the at least one dichroic fluorescent dye contained in the nematic liquid crystalline material are aligned.

[0037] At least one of the alignment structures of the motif-forming areas can advantageously form a grid pattern with dashed lines spaced at a fixed period, so that the alignment structure forms a periodic grid. The periodic grid preferably has a period length of 0.2 pm to 2.0 m, particularly preferably 350 nm to 800 nm, and a profile depth of 50 nm to 600 nm, particularly preferably 200 nm to 400 nm.

[0038] Alternatively or additionally, it is also possible to vary the period of the grooves or channels within a region, so that the grooves or channels exist as aperiodic structures. Advantageously, at least one of the alignment structures of the motif-forming regions forms a grid pattern with dashed lines whose spacing varies across the area of ​​the motif-forming region, so that the alignment structure forms an aperiodic grid. The aperiodic grid has a mean period length of 0.2 pm to 2.0 pm, particularly preferably from 350 nm to 800 nm, and a profile depth of 50 nm to 600 nm, particularly preferably from 200 nm to 400 nm.

[0039] Unlike periodic spacing, aperiodic spacing of the grating lines does not have a simple, regular relationship between the distances between adjacent grating lines. This minimizes or even completely prevents constructive interference of the light reflected from adjacent grating lines and thus the formation of a superimposed diffraction pattern.

[0040] Preferably, the spacing of the grid lines varies according to a random number distribution or a pseudorandom number distribution. Pseudorandom numbers are sequences of numbers that appear random but are calculated by a deterministic algorithm and are therefore not true random numbers in the strict sense. Nevertheless, pseudorandom numbers are widely used because the statistical properties of a pseudorandom number distribution, such as the equal probability of each number or the statistical independence of consecutive numbers, are generally sufficient for practical purposes, and pseudorandom numbers are easy to generate with computers, unlike true random numbers. A pseudorandom number distribution is always aperiodic within the meaning of this application, since there is no fixed, constant interval ("period") between consecutive values ​​in a pseudorandom number distribution.

[0041] However, an aperiodic variation in the spacing of the grid lines is not limited to pseudorandom number distributions, but can also be achieved by another irregular distribution of the spacing.

[0042] Advantageously, the refractive index of the first and / or second embossing varnish layer lies between the orientation-dependent refractive indices of the motif layer in the visible spectrum. Equally advantageous is that the refractive indices of the first and second embossing varnish layers differ by no more than 0.1, and in particular by no more than 0.05, in the visible spectrum.

[0043] In an advantageous embodiment, the first latent motif contains one or more first image elements, and the second latent motif contains a plurality of second image elements, wherein the first and second image elements comprise alphanumeric characters, patterns, or codes. Advantageously, the second image elements are arranged in a grid.

[0044] The micro-optical relief structure can be formed by a diffracting structure, in particular a one- or two-dimensional periodic diffractive structure, by a matte structure, a subwavelength structure, in particular a subwavelength grating or a moth-eye structure, and / or by a non-diffractive microstructure, in particular an arrangement of (directionally reflecting) micromirrors or microlenses.

[0045] The invention also includes a data carrier with a security element of the type described. The data carrier can be, in particular, a valuable document such as a banknote, especially a paper banknote, a polymer banknote or a foil composite banknote, a share, a bond, a certificate, a voucher, a check, a seal, a tax stamp, a high-quality admission ticket, but also an identification card such as a credit card, a bank card, a cash payment card, an authorization card, an identity card or a passport personalization page.

[0046] Finally, the invention also provides a method for manufacturing a safety element of the type described, in which

[0047] A first embossing lacquer layer is applied to a carrier film to form an alignment layer for the homogeneous orientation of a liquid crystalline material.

[0048] the first embossing varnish layer is embossed to create at least two areas with alignment structures of different orientations in order to form a second latent motif, and the embossing varnish is cured,

[0049] A motif layer based on a nematic liquid crystalline material in the form of a first latent motif is applied directly onto the first embossing varnish layer in certain areas and overlapping with the areas forming the second latent motif, wherein the liquid crystalline material contains at least one dichroic fluorescent dye whose emission of polarized light depends on its orientation.

[0050] wherein the nematic liquid crystalline material is aligned by the alignment structures of the motif-forming areas with different, homogeneous orientations, so that the second latent motif formed by the different alignment structures is recognizable by emission of polarized light,

[0051] the nematic liquid crystalline material is hardened by exposure to radiation, and

[0052] A single or multi-layer second embossing varnish layer is applied over the entire surface of the carrier film with the motif layer, the second embossing varnish layer is provided with an embossing to create a micro-optical relief structure and is then provided with a reflection-enhancing coating.

[0053] According to an advantageous embodiment of the process, the first embossing lacquer layer is embossed without pre-curing. Preferably, a further lacquer layer is applied to the carrier film and at least partially cured before the first embossing lacquer layer is applied.

[0054] It is advantageous to physically dry the nematic liquid-crystalline material before exposure to radiation. The nematic liquid-crystalline material is preferably cured by exposure to UV radiation.

[0055] Like the second embossing varnish layer, the first embossing varnish layer is also preferably applied over the entire surface.

[0056] Furthermore, it is particularly advantageous if the second embossing lacquer layer is metallized and, if necessary, partially demetallized.

[0057] With particular advantage, the first and / or the second embossing varnish layer and / or the motif layer are printed on.

[0058] In further advantageous embodiments, one or more additional layers, in particular a primer layer, a heat-seal varnish layer, a pressure-receiving layer and / or a protective layer, are applied to the second embossing varnish layer, in particular printed on.

[0059] Any isotropic transparent layer can also be used between the first embossing varnish layer ("liquid crystal layer structure"), which contains the alignment structures and the motif layer made of nematic liquid crystal material, and the second embossing varnish layer ("reflector structure"), which contains the reflection-enhancing coating—and thus in the optical path. For example, in cases where the security element is composed of separately manufactured sub-elements (liquid crystal layer structure or reflector structure), an isotropic transparent laminating adhesive can be used. If, for example, the interlayer adhesion is insufficient, a one- or two-layer primer structure can also be used.

[0060] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying figures, which also disclose essential features of the invention and whose representation is not to scale or proportion. These exemplary embodiments serve only for illustration and are not to be interpreted as limiting. For the sake of clarity, the representations in the figures are highly schematic and do not reflect actual conditions. To avoid repetition, identical or corresponding elements in different figures are designated with the same reference numerals and are not explained multiple times. The figures show:

[0061] Fig. 1 shows a schematic representation of a banknote with an embedded security thread and an attached transfer element.

[0062] Fig. 2 shows a cross-sectional view of the structure of a safety element according to an embodiment of the invention.

[0063] Fig. 3 in (a) a top view of an embodiment of a security element with a structured alignment layer and a motif-shaped liquid crystal layer, and in (b) an enlarged view of the alignment structures, Fig. 4 a top view of the security element of Fig. 3 as it appears (a) when viewed without aids, (b) when viewed with a circular polarizer, (c) when viewed with a linear polarizer in a first position and (d) when viewed with a linear polarizer in a second, rotated position, (e) when irradiated with unpolarized UV light, (f) when irradiated with unpolarized UV light and viewed through a linear polarizer in a first position, (g) when irradiated with unpolarized UV light and viewed through a linear polarizer in a second position,

[0064] Fig. 5 in (a) a top view of a further embodiment of a safety element with a structured alignment layer and a liquid crystal layer applied in sub-motifs, and in (b) and (c) an enlarged view of the alignment structures of a sub-motif,

[0065] Fig. 6 shows a top view of the safety element of Fig. 5 as it appears (a) when viewed with a circular polarizer, (b) when viewed with a linear polarizer in a first position, (c) when viewed with a linear polarizer in a second, rotated position, (d) when irradiated with unpolarized UV light, (e) when irradiated with unpolarized UV light and viewed through a linear polarizer in a first position, (f) when irradiated with unpolarized UV light and viewed through a linear polarizer in a second position.

[0066] Fig. 7 shows a schematic representation of a circular polarizer,

[0067] Fig. 8 in (a) a top view of a further embodiment of a safety element with a structured alignment layer and a motif-shaped liquid crystal layer, and in (b) an enlarged view of the alignment structures,

[0068] Fig. 9 shows a top view of the safety element of Fig. 8 in the section of Fig. 8b, as it appears (a) when irradiated with unpolarized UV light, (b) when irradiated with unpolarized UV light and viewed through a linear polarizer in a first position, (c) when irradiated with unpolarized UV light and viewed through a linear polarizer in a second position, (d) when irradiated with unpolarized UV light and viewed through a linear polarizer in a third position.

[0069] The invention will now be explained using the example of security features for banknotes. Fig. 1 shows a schematic representation of a banknote 10, which is provided with two security features 12 and 16 according to embodiments of the invention. The first security feature is a security thread 12, which protrudes from the surface of the banknote 10 at certain window areas 14, while it is embedded in the interior of the banknote 10 in the intervening areas. The second security feature is formed by an affixed transfer element 16 of any shape. Transfer elements can be, in particular, patches or strips, each with or without their own backing layer. The security element 16 can also be in the form of a cover film that is arranged over a window area or a through-hole in the banknote.

[0070] The construction and manufacture of a safety element 20 according to a first embodiment will now be explained in more detail with reference to the cross-section of Figure 2.

[0071] The safety element 20 is based on a high-quality stretched PET carrier film 22, onto which, in the exemplary embodiment, a thin layer 24 of a UV-curable lacquer is applied over the entire surface. A UV-curable embossing lacquer 26 is then applied over the entire surface of the (partially or fully cured) lacquer layer 24, which is embossed using a process called "casting," ideally without pre-curing.

[0072] Sub-areas 28A and 28B are each provided with an alignment structure 32 over their entire surface. The alignment structure 32 consists, for example, of a multitude of adjacent, parallel grooves that enable the orientation of liquid crystal molecules. For example, these grooves form an aperiodic lattice with a mean period length of 0.2 µm to 2.0 m, preferably from 350 nm to 800 nm, and a profile depth of 50 nm to 600 nm, preferably from 200 nm to 400 nm. Smaller profile depths are also conceivable, for example, in the range of 50 nm. The longitudinal direction of these grooves represents the orientation direction of the alignment structure.

[0073] As can be seen in Figures 2 and 3, the orientation of the alignment structure 32 differs in sub-areas 28A and 28B. For example, sub-area 28A has a multitude of parallel grooves rotated by -45° from the perpendicular, while sub-area 28B has a multitude of parallel grooves rotated by +45° from the perpendicular (indicated by the hatching in Fig. 3b). The parallel grooves are spaced at varying intervals.

[0074] Unlike periodic spacing, aperiodic spacing of the alignment-promoting grooves does not have a simple, regular relationship between the distances between adjacent grooves. This minimizes or even completely prevents constructive interference of the light reflected from neighboring grating lines and thus the formation of a superimposed diffraction pattern. It has been shown that the alignment properties of the alignment structure are not affected by the aperiodic arrangement, particularly in the form of variations in spacing.

[0075] In the exemplary embodiment, the sub-area 28A is arranged in a grid-like pattern in the form of a multitude of repeating image elements (small “25”) in front of the background formed by the sub-area 28B with a different orientation, here orthogonal to it (“wallpaper motif”).

[0076] A thin layer 30 of a nematic liquid crystalline material doped with a dichroic fluorescent dye is applied in a motif-like pattern (large “25”) to the alignment structure 32, in particular by printing. For increased edge sharpness, it may be advantageous to apply the edges or borders of the motif with a reduced basis weight.

[0077] Dichroic fluorescent dyes can either absorb light or exhibit no polarization-dependent light absorption, depending on the polarization of a UV light source. DDUV F375 (from Colour Synthesis Solutions Ltd.) is an example of a dichroic fluorescent dye. Fluorescent dyes with a 9,10-diphenylanthracene fluorophore or a coumarin fluorophore are also particularly well-suited. Depending on the choice of fluorescent dye, the motif layer may appear colorless under normal lighting. Upon irradiation with UV light (365 nm), a yellow fluorescence, for example, becomes visible. The dichroic fluorescent dye can be contained in the liquid crystalline material, for example, in a proportion of up to 5 wt.%, preferably up to 2 wt.%, particularly preferably more than 0.1 wt.% and up to 1 wt.%, based on the total formulation of the nematic liquid crystalline material.

[0078] The motif applied using the nematic liquid-crystalline material can advantageously have a high line thickness. In particular, the dimensions of the motif produced by the liquid-crystalline material can be chosen such that they are significantly, preferably many times, larger than the dimensions of the image elements formed by the sub-region 28 A of the alignment structure 32.

[0079] After the application of the liquid crystal layer 30, the nematic liquid crystals in sub-regions 28A and 28B align homogeneously according to the specified orientation structure 32. The dichroic fluorescent dyes align with the liquid crystals in a nematic liquid crystal matrix. Accordingly, the embedded dichroic fluorescent dye also exhibits a preferred orientation.

[0080] The liquid crystal motif layer 30 thus exhibits regions corresponding to sub-regions 28A and 28B, in which not only the orientation of the liquid crystals but also the orientation of the dichroic fluorescent dye differs. The orientation thus obtained is fixed, if necessary after physical drying to remove any solvents, by crosslinking the liquid crystal layer 30 with UV irradiation.

[0081] A single- or multi-layer embossing lacquer 34 is applied to the resulting layer sequence. A relief structure 38, e.g., a hologram structure, a micromirror structure, a subwavelength grating, or a combination of these structures, is embossed in this lacquer and subsequently provided with a reflection-enhancing coating, for example, a metallization 36. Recesses (not shown), for example, in the form of negative lettering, can be introduced into the preferably vapor-deposited metal layer 36 (e.g., made of aluminum) by partial demetallization. The recesses can be created using an etching process or a washing process. When using a washing process, soluble wash inks are printed onto the metal layer before its application. These wash inks are then washed off along with the PVD layer substances deposited on them after vapor deposition.When using an etching process, the PVD coating process is carried out first, followed by the printing and structuring of a resist varnish. The PVD layer is then removed from the unprotected areas using an etchant. The remaining resist varnish can either remain on the PVD layer or be removed using suitable solvents.

[0082] As an alternative to metal layers, the relief structure 38 can also be provided with a high-refractive-index layer. Examples of suitable high-refractive-index materials are CaS, CrÜ2, ZnS, TiCl or SiO2. xSimilarly, thin-film elements with a color-shifting effect, in particular trilay structures with the layer sequence absorber / dielectric / reflector, can be applied to the relief structure 38 by means of a PVD coating process and, if necessary, provided with recesses. Such thin-film elements are based in particular on viewing-angle-dependent interference effects due to multiple reflections in the different sublayers of the element.

[0083] The resulting product can be directly coated with a primer layer and heat-sealable lacquer and applied, for example, to a substrate such as paper. The carrier film 22 can be removed after application to the substrate or remain in the assembly as a cover film. The latter configuration is used particularly when applying security elements that are intended to cover through openings in the object to be secured. For example, in the case of a T-LEAD (Longlasting Economical Anticopy Device) strip (where T stands for "transfer"), unlike an L-LEAD strip, any carrier film that may be present is generally removed after application to the security paper or document. L-LEAD configurations are used particularly when applying security elements that are intended to cover through openings in the object to be secured.

[0084] Prior to applying the heat-seal varnish, further machine-readable and / or decorative layers can be applied to the possibly partially demetallized embossing varnish layer 34, particularly also in overlap with the metallization 36. The heat-seal varnish can also contain machine-readable markers, such as magnetic, electrically conductive, phosphorescent, or fluorescent substances.

[0085] Any isotropic transparent layers can also be used between the embossing lacquer 26 (“liquid crystal layer assembly”), which is provided with the alignment structure 32 and the liquid crystal layer 30, and the second embossing lacquer assembly 34 (“reflector assembly”), which is provided with the metallization 36 as a reflection-enhancing coating – and thus in the optical path. For example, in cases where the security element 20 is composed of sub-elements (liquid crystal layer assembly and reflector assembly) that are manufactured separately, an isotropic transparent laminating adhesive can be used. If, for example, the interlayer adhesion is insufficient, a one- or two-layer primer assembly can also be used.

[0086] The layered structure can alternatively be further processed, for example, into a so-called patch or individual security element. For this purpose, another film, such as a thin PET film (e.g., 6 µm), can be laminated onto the layered structure. A support film for the subsequent cutting or die-cutting process can then be laminated onto the side of the carrier film 22, while the surface of the aforementioned thin PET film can be coated with primer and heat-seal varnish. After pre-cutting or die-cutting the outlines and removing the backing material, the pre-fabricated individual security elements (patches) can then be applied to a substrate.Methods for producing such a security element transfer material and methods for transferring a security element from the security element transfer material onto a valuable item are described, for example, in publication WO 2010 / 031543 Al, the disclosure content of which is incorporated into the present application in this respect.

[0087] Fig. 4 shows a top view of a single security element 40 as it appears when viewed without any aids. Viewed without aids, the security element 40 exhibits the appearance of a metallic, shiny, optically variable microstructure, in this embodiment a relief image 44 in the shape of a coat of arms created using micromirrors (Fig. 4a). When such a security element 40 is viewed with a circular polarizing filter 42, the image motif 46 created by the liquid crystal layer 30 can be made visible and appears in this area as the symbol “25” brightly against a dark background 50 (Fig. 4b). Rotating the polarizing filter does not change the appearance.

[0088] Another image can be revealed when viewing the security element with a (not shown) linear polarizing filter (or a circular polarizing filter viewed from the back, i.e., "reversed"), which is placed directly on the area to be viewed (incident light is linearly polarized, reflected light must pass through the polarizing filter again). In this case, the metallic-coated areas forming the background 50 appear bright without the liquid crystal layer, while the viewer 48 initially perceives the image 46 created by the liquid crystal layer 30 as dark against a light background 50 when first orienting the linear polarizing filter.

[0089] When the linear polarizing filter is rotated, the brightness of the image 46 produced by the liquid crystal layer 30 changes. With a 45° rotation, the brightness in the area of ​​the liquid crystal layer 30 is reversed, so that the image 46 appears with little or no contrast to the background 50, which is not covered with the liquid crystal layer 30 and also appears bright (Fig. 4d). With a further 45° rotation (90° from the first position), the image produced by the liquid crystal layer 30 appears dark again (Fig. 4c). Regardless of the position of the linear polarizer, the two areas 28A and 28B always appear equally bright or equally dark when rotated by 90°.

[0090] Since in the exemplary embodiment the sub-areas 28A (small “25”) have an orientation rotated by 90° to the sub-area 28B (background), in the case that the dichroic fluorescent dye absorbs light depending on polarization, when irradiated with polarized UV light either the dichroic fluorescent dye in the sub-areas 28A or, with other polarization, the sub-area 28B forming the background can absorb UV light and be excited to fluoresce.

[0091] Dichroic fluorescent dyes typically contain light-emitting molecular components, resulting in the emission of linearly polarized light (in the visible wavelength range). Since the emitted radiation is thus polarized, it can also be "switched" using a linear polarizing filter. This proves advantageous when irradiated with an isotropic (unpolarized) light source.

[0092] When irradiated with isotropic UV light (with a wavelength matched to the dichroic fluorescent dye, preferably radiation with a wavelength of 365 nm) and viewed without aids, all areas containing dichroic fluorescent dye (in the exemplary embodiment, the image motif 46 generated by the liquid crystal layer 30) glow, regardless of the orientation in areas 28A, 28B, in the fluorescent color of the dichroic fluorescent dye (e.g. yellow; Fig. 4e).

[0093] When viewed through a linear polarizing filter (where the polarizing filter is preferably positioned between the observer and the substrate, not between the UV source and the substrate, since most commercial polarizing filters absorb UV light), an additional brightness difference can be perceived between the sub-areas 28A (small “25”) and the sub-area 28B (background) (Fig. 4f, first position of the polarizing filter), which reverses when the polarizing filter is rotated by 90° (Fig. 4g, second position of the polarizing filter).

[0094] In the situation shown in Fig. 4g, the background corresponding to sub-area 28B appears with no or only slight contrast to the area of ​​the safety element 40, which is not covered with the liquid crystal layer 30 and also appears dark. The small characters are used here to define the larger character (the dashed outline serves only to illustrate the image motif 46 formed by the liquid crystal layer 30). In general, if the polarizing filter is oriented in one polarization direction, it is transparent, meaning the corresponding area appears bright; if the polarizing filter is oriented at an angle of 90° to the polarization direction, the corresponding area appears dark.

[0095] The metallically coated areas of the security element 40 forming the background 50, without the liquid crystal layer 30 doped with the dichroic fluorescent dye, appear dark in all viewing situations. When using a linear polarizing filter in front of a UV light source, care must be taken to ensure that the polarizing filter is selected so that it is sufficiently transparent and sufficiently polarizing for the corresponding UV light. A particular advantage of the described design, however, is that the polarizing filter does not have to be placed directly on the light source and, for example, polarized spectacle lenses can also serve as the verification medium.

[0096] The (optically important) steps in the production of the security element begin with the first embossing. The motif made of nematic liquid crystal material 30 is applied, in particular printed, onto the alignment structure 32 created by this process. The alignment structures are filled in this area by the nematic liquid crystals (profile depth of preferred alignment structures e.g. 200 nm, layer thickness of the nematic liquid crystal layer e.g. 1 pm). With a suitable choice of the refractive index of the UV embossing varnish 26, the embossing structure optically disappears.

[0097] Ideally, the refractive indices of the adjacent materials are matched so that no sharp refractive index jumps occur that would make the orientation pattern permanently visible even without aids. Since liquid crystal layers have an orientation-dependent refractive index (e.g., n = 1.57, with An = 0.14), the UV embossing varnish 26 is preferably selected such that its refractive index lies between the two orientation-dependent refractive indices of the liquid crystal layer 30.

[0098] If the nematic liquid crystal layer is not to be visible when viewing the safety element without aids, the alignment quality of the alignment structure 32 should also be comparable to 28A and 28B in all areas.

[0099] While for applications where a layer of nematic liquid crystalline material is present without the addition of a dichroic (fluorescence) dye, the thickness of the liquid crystal layer should be maintained relatively precisely in order to achieve the appropriate birefringence (preferably on metallic substrates by forming an X / 4 layer for wavelengths from the intended wavelength range), the layer thickness plays only a very minor role for the polarization of the emitted fluorescence light.

[0100] Furthermore, the substrate of undoped nematic liquid crystal layers must reflect light in at least a non-depolarized form. This is not necessary when using dichroic fluorescent dyes. If the substrate is absorbing, the fluorescent light emitted in that direction is indeed absorbed, but the light emitted in the corresponding direction still reaches the observer.

[0101] While light scattering without polarization conservation renders the features produced with nematic liquid-crystalline material unrecognizable, the impairment of the effect is also less pronounced with doped nematic liquid-crystalline material. Light can be scattered arbitrarily here. Only light in the wavelength range of fluorescence emission must not be scattered in conjunction with depolarization. For this light, metallic reflection (polarization conservation) or absorption is advantageous.

[0102] Birefringent films, or films whose birefringence is not precisely specified or whose birefringence is strongly wavelength-dependent, should generally be avoided between the viewer and the reflector for polarization features. However, if such films cannot be avoided, the resulting interference effects can be prevented or at least minimized, as explained below. If the dichroic fluorescent layer is positioned above the birefringent film, while an absorbing layer for the fluorescence wavelength is located below the film, the function is not impaired. Even in cases where the fluorescent layer must be located below the birefringent film, its influence is minimal. Thus, isotropic (UV) light does not undergo any problematic changes when passing through an optically anisotropic medium. After excitation of the fluorescence, the emitted light is linearly polarized.However, since only one pass through the film is required, the influence of the film is less than with effects based solely on nematic liquid crystalline materials.

[0103] In the step following the coating with liquid crystal material, UV embossing lacquer 34 is applied over the entire surface (in the exemplary embodiment in two stages) for the actual embossing, e.g., of a hologram or micromirror motif 44. The nematic liquid crystal layer 30 is thus embedded between UV lacquer layers. In addition to the nematic motif, the embossing lacquer layer 34 is applied directly to the existing embossing 32 or the embossing lacquer 26. If the refractive indices are similar (i.e., differ by no more than 0.1 and, in particular, by no more than 0.05 in the visible spectrum), the "A-alignment" embossing or alignment structure 32 also disappears optically.

[0104] The liquid crystal layer 30 and the second embossing varnish layer 34 can have different refractive indices. Ideally, the refractive indices are also matched here so that no sharp changes in refractive index occur.

[0105] It is possible to limit the initial impression to the area where the nematic liquid crystalline material is to be printed (to avoid registration variations). However, this limitation necessitates an inserter step when printing the liquid crystalline material, which can result in increased scrap.

[0106] Regardless, an inserter operation may also be necessary to prevent the welds (embossing tool with alignment motif and embossing tool with motif of the relief structure) from interfering with the motif and causing mutual problems due to build-up.

[0107] According to an alternative embodiment, not shown here, a further fluorescent motif can be provided that does not exhibit any special polarization effects. This further fluorescent motif can even be formed with the same dichroic fluorescent dye if it is used in an isotropic medium (e.g., a transparent or colored printing ink). A particular advantage of this embodiment is that, without a polarizing filter, all fluorescent areas cannot be distinguished. However, when viewed through a linear polarizing filter with sub-areas 28A and 28B, two of the three areas (sub-areas 28A, 28B, and the area without a preferred direction) can be alternately switched between light and dark by changing the position of the linear polarizing filter.

[0108] According to the invention, the nematic liquid-crystalline material is applied to the alignment layer only partially as a motif. It is therefore generally possible to print further areas of nematic liquid-crystalline material onto the alignment layer using another printing unit. The printing can also be carried out in different layer thicknesses. Furthermore, registered printing of the nematic liquid-crystalline material across multiple printing units is fundamentally possible. The alignment layer can also contain different, arbitrary orientations in specific areas without additional effort, so that independently oriented areas of liquid-crystalline material with and without dichroic fluorescent dye can be produced.

[0109] When a first latent motif made of nematic liquid-crystalline material doped with a dichroic fluorescent dye and a second (third) latent motif made of only nematic liquid-crystalline material are printed onto an alignment layer, only one overall motif is observed when a circular polarizing filter is applied: regardless of the orientation of the alignment structures and regardless of the position of the polarizing filter, all nematic-printed areas appear bright. However, when irradiated with (isotropic) UV light, only the areas containing the dichroic fluorescent dye fluoresce. The areas without the dichroic fluorescent dye always remain dark.

[0110] Fig. 5 shows an embodiment of a security element with a structured alignment layer in which the liquid crystal layer is applied in partial image motifs. As can be seen in Figures 5b and 5c, which each show an enlarged view of the alignment structures of one of the partial image motifs 66, 68 described in more detail below, the orientation direction of the alignment structure 62 differs in the sub-areas 64A, 64B, and 64C. For example, sub-area 64A has a plurality of parallel grooves rotated by -45° from the perpendicular, sub-area 64B, which forms a background for both partial image motifs 66, 68, has a plurality of parallel grooves rotated by +45°, and sub-area 64C has a plurality of horizontal parallel grooves.Sub-area 64A is arranged in a grid pattern as a multitude of repeating image elements (“0”) against the background formed by sub-area 64B, with an orthogonal alignment orientation to it. Sub-area 64C, in turn, is arranged in a grid pattern as a multitude of repeating image elements (“5”) against the background formed by sub-area 64B, with an alignment orientation rotated by 45° relative to it. A thin layer 30 of nematic liquid-crystalline material is applied to the alignment structure 62 in a motif-like manner within a first sub-image motif 66 (“0”) such that the liquid-crystalline material, doped with a dichroic fluorescent dye, is homogeneously oriented according to the alignment structure 62 only within the area of ​​the alignment layer encompassing sub-areas 64A and 64B.In addition, a thin layer 78, preferably designed as an X / 4 layer for light from the intended wavelength range, is applied in a motif-like manner in a further partial image motif 68 ("5") above the alignment structure 62 in the sub-areas 64B, 64C, such that the nematic liquid crystalline material (without dichroic fluorescent dye) is homogeneously oriented according to the alignment structure 62 only in the area of ​​the alignment layer comprising sub-areas 64B, 64C. The partial image motifs 66 and 68 form a first and a third latent motif, respectively.

[0111] The optical effects of the security element 60 shown in Fig. 5, perceptible with and without aids, are shown in Fig. 6. Fig. 6a shows a top view of the security element 60 of Fig. 5 as it appears when viewed with a circular polarizer. When viewed with a circular polarizing filter, the overall image motif 76 (composed of two partial image motifs 66, 68) generated by the liquid crystal layer 30 can be made visible and appears in this area as the (composite) symbol “50” bright against a dark background 70. Rotating the circular polarizing filter does not change the appearance.

[0112] Further motifs can be made visible when viewing the security element 60 with a linear polarizing filter (or a circular polarizing filter viewed from the back). In this case, the metallically coated areas without a liquid crystal layer appear bright, while with an initial orientation (position) of the linear polarizing filter in the area of ​​the nematic (undoped) liquid crystal layer 78, the viewer perceives sub-area 64B as a large image element (large "5") as dark and sub-area 64C as a bright motif in the form of raster-like arranged small image elements (small "5") (Fig. 6b). Simultaneously, in the area of ​​the nematic liquid crystal layer 30 doped with the dichroic fluorescent dye, the viewer perceives the image motif 66 produced by the liquid crystal layer 30 as entirely dark. The background 70 formed by the area without a liquid crystal layer appears bright.

[0113] When the linear polarizing filter is rotated, the relative brightnesses change and, with a rotation of 45°, are reversed in the area of ​​the liquid crystal layer 30, so that the partial image motif 66 now appears with no or only slight contrast to the background 70, which does not have a liquid crystal layer and also appears bright. Regardless of the position of the linear polarizer, the two partial areas 64A and 64B, with their orientation rotated by 90° relative to each other, always appear equally bright or equally dark in this area of ​​the security element 60.

[0114] In the area of ​​liquid crystal layer 78, the relative brightnesses are also reversed upon a rotation of 45°. Accordingly, only the small image elements formed by sub-area 64C become visible as a dark (fourth) motif, whose outline, indicated by a dashed line, is defined by the area of ​​liquid crystal layer 78. The background corresponding to sub-area 64B appears, as for sub-image motif 66, with no or only slight contrast to the background 70 (Fig. 6c), which does not contain either of the liquid crystal layers 30 or 78 and also appears bright.

[0115] When irradiated with isotropic UV light (with a wavelength matched to the dichroic fluorescent dye) and viewed without aids, all areas containing the dichroic fluorescent dye (in the exemplary embodiment, the image motif 66 generated by the liquid crystal layer 30) glow, regardless of orientation in areas 64A, 64B, in the fluorescent color of the dichroic fluorescent dye (Fig. 6d). In the area of ​​the liquid crystal layer 78 indicated by the dashed outline, the safety element 60 remains dark.

[0116] When viewing the security element irradiated with isotropic UV light through a linear polarizing filter, a brightness difference can be observed between the sub-areas 64A (small "0") and the background sub-area 64B (Fig. 6e), which reverses to a second position when the polarizing filter is rotated by 90° (Fig. 6f). In the situation shown in Fig. 6e, the background corresponding to sub-area 64B appears with no or only slight contrast to the dark-appearing area of ​​the security element 60 that is not covered with the doped liquid crystal layer 30. The small characters are used here to define the larger character (the dashed outline serves only to illustrate the sub-image 66 formed by the liquid crystal layer 30).

[0117] An effect similar to the optical effect described above can be produced according to an embodiment not shown by first printing all areas intended to contain a birefringent layer with a layer of nematic liquid-crystalline material to which a dichroic fluorescent dye has been added. Subsequently, a UV absorber layer is printed over the areas that are not intended to fluoresce upon irradiation with UV light. The behavior of these areas upon irradiation with UV light thus corresponds to that of an area of ​​liquid-crystalline material that is not doped with a dichroic fluorescent dye.

[0118] Another embodiment of a security element, in which the alignment structure in the sub-areas forming the second latent motif has three different orientation directions, is shown in Fig. 8. As can be seen in particular in Fig. 8b, which shows an enlarged view of the alignment structure 82 of the security element 80, the orientation directions in the sub-areas 84A, 84B, 84C are each rotated by 45° relative to each other.

[0119] The alignment structure 82 consists, for example, of a plurality of adjacent, parallel grooves with varying spacing, which enable the orientation of liquid crystal molecules. Thus, sub-region 84A has a plurality of parallel grooves rotated by -45° from the perpendicular, sub-region 84C has a plurality of horizontal parallel grooves, and sub-region 84B has a plurality of parallel grooves rotated by +45° from the perpendicular. In the exemplary embodiment, sub-region 84A and sub-region 84C are arranged in a grid pattern as a plurality of repeating image elements ("PL" and "10," respectively) in front of the background formed by sub-region 84B, which has a different aligning orientation. In the exemplary embodiment, these grooves in sub-regions 82A, 82B, and 82C each form an aperiodic lattice (in Fig.8b (indicated by the hatching) with a mean period length of 0.2 µm to 2.0 pm and a profile depth of 200 nm to 600 nm. However, it is also possible to provide the groove spacing with a fixed period, so that the alignment structure 82 forms a periodic grid in one or more, in particular all, sub-areas.

[0120] A thin layer 30 of doped nematic liquid crystal material is applied in a motif-like pattern (“€”) above the alignment structure 82, as described in connection with Fig. 2. For optimal contrast (when viewing the safety element 80 with a linear polarizer), the nematic liquid crystal layer 30, doped with the dichroic fluorescent dye, forms an X / 4 layer for light from the intended wavelength range.

[0121] When viewed through a circular polarizing filter, all regions 84A, 84B, and 84C of the liquid crystal layer 30 appear bright. It is not possible to distinguish their orientations. When viewed through a linear polarizing filter, the two regions with their orientations rotated by 90° relative to each other (subregions 84A and 84B) always appear equally bright or equally dark. They are indistinguishable. Subregion 84C, whose orientation structure 82 has an orientation direction that forms a 45° angle with the orientation directions of subregions 84A and 84B, appears maximally dark when the two aforementioned subregions are maximally bright, and vice versa (not shown).

[0122] Fig. 9 shows a top view of the safety element 80 in the section shown in Fig. 8b, as it appears when irradiated with unpolarized UV light. When irradiated with isotropic UV light (e.g., radiation with a wavelength of 365 nm) and viewed without aids, all areas with dichroic fluorescent dye (in the exemplary embodiment, the image motif 86 generated by the liquid crystal layer 30) glow with the same brightness, regardless of orientation, in areas 84A, 84b, 84C, in the fluorescent color of the dichroic fluorescent dye (Fig. 9a).

[0123] When viewed through a linear polarizing filter, the area at the 0° angle appears particularly bright (sub-area 84A or sub-area 84B) when the area at the 90° angle (sub-area 84B or sub-area 84A) appears particularly dark (Fig. 9b or Fig. 9d). The area at the 45° angle appears at a medium brightness.

[0124] When the linear polarizing filter is rotated 45° from one of these positions, sub-area 84C appears at maximum brightness (Fig. 9c) or maximum darkness (not shown), depending on whether the polarizing filter is oriented in the polarization direction after rotation or at an angle of 90° to the polarization direction, while sub-areas 84A and 84B appear at medium brightness. The metallically coated areas of the safety element 80 forming the background 90, excluding the liquid crystal layer 30 doped with the dichroic fluorescent dye, appear dark in all viewing situations.

[0125] The outlines of sub-areas 84A and 84C shown with solid lines in Figures 9c and 9d serve only to illustrate the image elements formed by these areas and are not perceptible as such when viewed through a polarizer.

[0126] A particular advantage of the described designs is that they contain different latent motifs which can be made visible depending on the choice of polarizing filter used as an aid and the lighting conditions. In particular, in addition to a "macroscopic," easily recognizable motif, very sharply defined "microscopic" motifs, visible especially only when illuminated with a special radiation source, can also be created, since the resolution of the polarizing motif is no longer determined solely by the printing accuracy, but also by the accuracy of the structuring.

[0127] Furthermore, the invention offers a more visually appealing appearance than known latent security features based on liquid crystals. If a security feature is visually interesting to the viewer, the likelihood increases that they will pay more attention to the security feature and the valuable item it secures, thereby achieving a greater security effect.

[0128] Since the different patterns could be confusing depending on which side of the (circular) polarizing filter is viewed through which the security element is seen, the expected pattern can be stylized on the top side of the polarizing filter used as a verification medium. On the side of a circular polarizing filter that corresponds in effect to a linear polarizing filter (an "inverted" circular polarizing filter), or on a linear polarizing filter, all patterns achievable by rotating the polarizing filter, with or without UV light irradiation, can also be stylized.

[0129] To verify the optical effects produced solely by the nematic liquid crystal layer, both the incident and emitted light must be polarized, which can be achieved by applying a polarizing filter. However, other variations are also conceivable. For example, the light source illuminating the viewing area can emit polarized light. In this case, the observer can place the polarizing filter at any point between themselves and the object being verified, e.g., in the form of polarizing glasses. [Reference symbol list]

[0130] 10 banknote

[0131] 12 safety threads

[0132] 14 window areas

[0133] 16 T transfer element

[0134] 20 safety elements

[0135] 22 carrier film

[0136] 24, 26 embossing varnish

[0137] 28A, 28B Sub-areas

[0138] 30 Liquid crystal layer

[0139] 32 Alignment structure

[0140] 34 embossing varnish

[0141] 36 Metallization

[0142] 38 Relief structure

[0143] 40 safety elements

[0144] 42 Polarizer

[0145] 44 Relief image

[0146] 46 Image motif

[0147] 48 viewers

[0148] 50 Background

[0149] 52 Substrat

[0150] 60 safety elements

[0151] 62 Alignment structure

[0152] 64A, 64B, 64C Sub-areas

[0153] 66, 68 partial image motifs

[0154] 70 Background

[0155] 78 Liquid crystal layer

[0156] 80 safety element

[0157] 82 Alignment structure

[0158] 84A, 84B, 84C Sub-areas 86 Image motif 90 Background

Claims

Patent claims 1. Security element for securing valuables, with a motif layer based on a liquid crystalline material designed and intended to form a latent motif, characterized in that the security element comprises a first embossed lacquer layer arranged on a carrier film, a motif layer partially present on the first embossed lacquer layer based on a nematic liquid crystalline material and a second embossed lacquer layer present over the entire surface in one or more layers, wherein the nematic liquid crystalline material contains at least one dichroic fluorescent dye whose emission of polarized light depends on its orientation, wherein the surface of the first embossing lacquer layer facing the nematic liquid crystalline material is provided with an embossing which has at least two areas with alignment structures of different orientations to form a second latent motif, wherein the nematic liquid crystalline material is homogeneously aligned by the motif-forming areas in the form of the second latent motif with each of different orientations, so that the second latent motif formed by the different alignment structures is recognizable by emission of polarized light, wherein the motif layer in the form of a first latent motif is arranged in certain areas directly on the first embossing varnish layer and overlapping with the areas forming the second latent motif, and wherein the second embossing lacquer layer is provided with an embossing to create a micro-optical relief structure and a reflection-enhancing coating.

2. Safety element according to claim 1, characterized in that the at least one dichroic fluorescent dye has a polarization-dependent absorption of light which depends on its orientation.

3. Security element according to claim 1 or 2, characterized in that the embossing of the first embossing lacquer layer for the formation of the second latent motif has two areas with alignment structures of orthogonal orientation.

4. Security element according to one of claims 1 to 3, characterized in that the embossing of the first embossing lacquer layer for the formation of the second latent motif has at least three areas with alignment structures of different orientation directions, wherein the orientation directions assume angles relative to each other which are selected from the group consisting of 45°, 90° and 135°.

5. Safety element according to one of the above claims, characterized in that the first embossed lacquer layer is present over the entire surface.

6. Safety element according to one of the above claims, characterized in that the alignment structures are in the form of fine grooves or channels through which the molecules of the nematic liquid crystalline material and the molecules of the at least one dichroic fluorescent dye contained in the nematic liquid crystalline material are aligned.

7. Safety element according to one of the above claims, characterized in that at least one of the alignment structures in the motif-forming areas forms an aperiodic grid.

8. Safety element according to one of the above claims, characterized in that the refractive index of the first and / or the second embossing lacquer layer lies in the visible spectrum between the orientation-dependent refractive indices of the motif layer.

9. Safety element according to one of the above claims, characterized in that the refractive indices of the first embossed lacquer layer and the second embossed lacquer layer are in The visible spectrum differs by no more than 0.1, in particular by no more than 0.

05. 10 Security element according to one of the above claims, characterized in that the first latent motif contains one or more first image elements and the second latent motif contains a plurality of second image elements, wherein the first and second image elements comprise alphanumeric characters, patterns or codes, wherein the second image elements are preferably arranged in a grid.

11. Safety element according to one of the above claims, characterized in that the micro-optical relief structure is formed by a diffractive structure, in particular a one- or two-dimensional periodic diffractive structure, by a matte structure, by a subwavelength structure, in particular a subwavelength grating or a moth-eye structure, and / or by a non-diffractive microstructure, in particular an arrangement of micromirrors or microlenses.

12. Data carrier with a security element according to one of claims 1 to 11, wherein the data carrier is in particular a security document or an identification card.

13. Method for manufacturing a security element for securing valuables, comprising a motif layer of liquid crystalline material designed and intended to generate a latent motif, wherein the method A first embossing lacquer layer is applied to a carrier film to form an alignment layer for the homogeneous orientation of a liquid crystalline material. the first embossing varnish layer is embossed to create at least two areas with alignment structures of different orientations in order to form a second latent motif, and the embossing varnish is cured, A motif layer based on a nematic liquid crystalline material in the form of a first latent motif is applied directly onto the first embossing varnish layer in certain areas and overlapping with the areas forming the second latent motif, wherein the nematic liquid crystalline material has at least one dichroic Contains a fluorescent dye whose emission of polarized light depends on its orientation, wherein the nematic liquid crystalline material is aligned by the alignment structures of the motif-forming areas with different, homogeneous orientations, so that the second latent motif formed by the different alignment structures is recognizable by emission of polarized light, the nematic liquid crystalline material is hardened by exposure to radiation, and A single or multi-layer second embossing varnish layer is applied over the entire surface of the carrier film with the motif layer, the second embossing varnish layer is provided with an embossing to create a micro-optical relief structure and is then provided with a reflection-enhancing coating.

14. Method according to claim 13, characterized in that the first embossing lacquer layer is embossed without pre-curing, wherein, prior to the application of the first embossing lacquer layer, a further lacquer layer is preferably applied to the carrier film and at least partially cured.

15. Method according to claim 13 or 14, characterized in that the nematic liquid crystalline material is physically dried before being exposed to radiation.

16. Method according to at least one of claims 13 to 15, characterized in that the first embossing lacquer layer is applied over the entire surface.

17. Method according to at least one of claims 13 to 16, characterized in that the first and / or the second embossing varnish layer and / or the motif layer is printed.

Images