Patent Application
20220105743
The invention relates to a security element, a method for producing a security element, as well as a security document with a security element.
Optically active security elements are used in particular on security documents, such as for instance banknotes, passports, identity cards, check cards, credit cards, visas or certificates, for both information and decorative purposes. Such security elements on the one hand increase the protection against forgery, for example vis-à-vis modern color copying and other reproduction systems, and on the other hand can be easily and clearly recognized by the layperson, with the result that the layperson can clearly determine the authenticity of a security document provided with such a security element and can thus recognize forgeries or manipulations.
For this purpose, security elements often have light-diffracting, diffractive structures such as for example holograms. These security elements offer the observer effects that are optically variable when the security element is tilted. Optically variable thin-film elements which, when tilted, give the observer different color impressions, in particular as color changes, are also often used as security elements. However, such security elements are nowadays to be found on a multitude of security documents, such as for example banknotes, with the result that the layperson now hardly pays attention to them in everyday use, whereby forgeries or manipulations are recognized less often, in particular by laypeople.
The object of the invention is now to provide a security element, as well as a method for producing a security element, which is characterized by a novel optically variable effect which differs from the known optically variable effects described previously.
This object is achieved by a security element with a first volume hologram layer which spans a coordinate system with the coordinate axes x and y perpendicular to each other in an unbent state of the security element, wherein a first volume hologram is introduced into the first volume hologram layer in at least one first area, wherein the first volume hologram is formed such that a first item of information is visible for an observer in a first observation situation in a first predefined bent state of the security element and is not visible in the first observation situation in the unbent state of the security element or vice versa. This object is further achieved by a method for producing a security element with a first volume hologram layer, in particular according to one of claims 1 to 43, wherein the method comprises the following steps: a) providing the first volume hologram layer; b) arranging a first master with a first surface structure on the first volume hologram layer; c) exposing the first master and the first volume hologram layer by means of coherent light, wherein the first volume hologram introduced into the first volume hologram layer in this way is formed such that a first item of information is visible for an observer in a first observation situation in a first predefined bent state of the security element and is not visible in the first observation situation in the unbent state of the security element or vice versa. This object is also achieved by a security document with a security element according to one of claims 1 to 43.
The invention is based on the recognition that, by the forming of the above-specified volume hologram layer, an optically variable effect can be generated which differs from the above-named known optically variable effects. Whereas in the case of previous security elements an optically variable effect appeared during a tilting of the security elements, here an optically variable effect is produced by a bending of the security element, with the result that, for example, an item of information only becomes visible for the observer, in the bent state of the security element. This produces a surprising novel impression on an observer, which differs from the known optically variable effects. In particular, the optically variable effect which is to be seen during bending, clearly differs from an optical effect of the volume hologram during tilting. Depending on the design of the volume hologram, the optically variable effect according to the invention can occur, for example, both in the case of a “bending towards” and in the case of a “bending away”. The curiosity of the observer is hereby awakened, whereby the security element is observed more often and forgeries are thus recognized more often. Because the optically variable effect occurs only during bending (and not during tilting) of the security element, a clear identification of the effect, which is further characterized by being highly memorable, is made possible in particular for the layperson. The observer can for example intuitively check the authenticity of a security document with the security element according to the invention by bending. Here, it is advantageous that in particular security documents such as for example identity documents, passport documents, visas, banknotes or securities are flexible or bendable and are also often bent in everyday use, with the result that attention to this optical effect is further increased for users of the security documents with the security element according to the invention. The protection against forgery is further increased by the security element according to the invention, as a forger now also has to take into consideration a bent state of the security element during a potential counterfeiting. Furthermore, because of the volume hologram, the security element cannot be copied by molding a surface relief.
Unlike embossed holograms, in which the item of information is applied only as a relief to the surface of a film and via which incident light is diffracted—in a “volume hologram” in particular the items of information are stored in the material volume. In this material volume as recording medium, via a modulation of at least two coherent waves, superimposition of these waves occurs. The resulting interference patterns are stored in the material volume of the volume hologram in so-called Bragg planes and contain the holographic information as a variation of the refractive index of the material. During reconstruction of the volume hologram, the stored information of the object wave is read. During bending on a volume hologram, the Bragg condition applies, with the result that a volume hologram can be reconstructed only by reference beams with quite specific angles of incidence and wavelengths. The Bragg condition is n λ=2d sin θ, wherein n is a natural number, λ the wavelength and d the distance between the Bragg planes. The complementary angle θ is called the Bragg angle or glancing angle and is calculated from the angle of incidence measured from the perpendicular as follows: θ=90−α.
By “bending” is meant here the deformation of an object in a specific manner by exertion of a force. By “bending” of a security element is therefore meant the exertion of force on the security element, wherein the shape of the security element is changed or can be changed by the application of force. A bent security element thus has a changed geometry in comparison with the unbent security element. Furthermore, by “bending” is also meant a kinking, with the result that a bent security element can have one or more kink points or kink lines, at which the security element is sharply or abruptly bent.
By “bent state” of the security element is meant here a bent security element. This means that the shape of a security element in a bent state has been changed by the application of force. Preferably, the security element is curved or kinked in the bent state and is flat or plane in the unbent state.
By “predefined” is meant here a predetermined value or range of values, or a predetermined shape or geometry. Thus, for example, a security element in a predefined bent state conforms to the shape of a parabola, wherein the parameters describing the parabola for the predefined bent state are fixed within tolerance limits.
By “observation situation” is meant here the positional relationships of the observer, an illumination device and the security element to each other. This means that in a specific observation situation the positional relationships to each other do not change. Thus, for example, the distances or angular relationships of the observer, the illumination device and the security element to each other remain substantially identical in a specific observation situation.
By “visible” is meant here that the item of information is recognizable for the observer, in particular under normal lighting conditions and at a normal observation distance. By “not visible” is meant here that the item of information is not recognizable for the observer, in particular under normal lighting conditions and at a normal observation distance. Preferably, by “not visible” is also meant only slightly visible. Thus it is possible that the “not visible” information is only slightly recognizable for the observer, in particular in comparison with the “visible” information.
By “area” is meant here in each case a defined surface area of a layer, which is occupied during observation perpendicular to a plane spanned by the first volume hologram layer. Preferably, the defined surface area occupied by the area is determined in the unbent state of the security element.
Further advantageous embodiments of the invention are described in the dependent claims.
It is possible that the first volume hologram is formed such that at least one second item of information is visible for the observer in the first observation situation in at least one second predefined bent state of the security element and is not visible in the first observation situation in the unbent state of the security element or vice versa. It is hereby achieved that a second item of information becomes visible for the observer in the first observation situation in a second predefined bent state of the security element. Preferably, the first and the second items of information complement each other here, with the result that, for an inexperienced observer, an image that is logically to be expected, or a sequence of images that is logically to be expected, arises from the combination of the first and second items of information. The first item of information can here be visible in the first and in the second predefined bent state. Thus, the observer can for example see a closed blossom in the first bent state of the security element and an opened blossom in the second bent state of the security element. Thus, it is possible that a motif which is recognizable for the observer in the first bent state of the security element changes during bending of the security element into the second bent state. A picture story, for example, can hereby be produced for the observer, which is also intuitive and self-explanatory for the layperson. During bending, the observer is “rewarded” by the discovery of the picture story. Furthermore, the protection against forgery is further increased, as a forger now has to consider several bent states. An example of such a picture story is an image which is put together piece by piece, like a puzzle, during bending.
Advantageously, in the first and/or the at least one second predefined bent state the security element is bent around the x-axis and/or the y-axis. Thus it is possible that in the first and/or the at least one second predefined bent state the security element is bent around a horizontal and/or vertical axis of the security element. By a bending around the x-axis and/or y-axis is also meant a bending relative to a line parallel to one of these axes.
Preferably, in the first and/or the at least one second predefined bent state the security element is bent towards the observer, in particular such that the security element has a concave shape in the first and/or the at least one second predefined bent state, and/or the security element is bent away from the observer, in particular such that the security element has a convex shape in the first and/or the at least one second predefined bent state.
It is further possible that the first and/or the at least one second predefined bent state of the security element approximately conforms to the shape of a half-parabola or of a parabola.
Preferably, the security element has at least one bending line around which the security element is bent in the first and/or the at least one second predefined bent state of the security element. Preferably the bending line lies in the at least one first area, in which the first volume hologram is introduced into the first volume hologram layer.
It is further possible that the thickness of the security element is reduced in an area of the bending line. Thus it is possible that the thickness of the first volume hologram layer is reduced in the area of the bending line, preferably by at least 1 μm, by preference by at least 2.5 μm, further preferably by at least 5 μm, even further preferably by at least 10 μm. It is also possible that the thicknesses of one or more further layers of the security element, in particular a carrier layer and/or a protective varnish layer, are reduced in the area of the bending line. It is further possible that at least one of the layers of the security element is not present in the area of the bending line, with the result that the thickness of the security element is reduced hereby. It is further possible that perforations or other local holes in the security element and/or the security document are arranged in the area of the bending line. The width of the area with reduced thickness of the security element is preferably between 5 μm and 10 mm, preferably between 50 μm and 5 mm, further preferably between 100 μm and 5 mm. It is hereby possible that the security element is bent along a bending line, the position of which on the security element is predefined by the reduction in thickness.
It is further possible that the security element is bent symmetrically or asymmetrically with respect to the bending line in the first and/or the at least one second predefined bent state.
By “symmetrically” is preferably meant here a geometric symmetry, with the result that the security element symmetrically bent in the first and/or the at least one second predefined bent state can be mapped onto itself by movement.
Thus it is possible that the security element symmetrically bent in the first and/or the at least one second predefined bent state is bent as a mirror image with respect to the bending line. By “asymmetrically” is preferably meant here a bending in the first and/or the at least one second bent state which is not symmetrical.
It is also possible that the angles enclosed between a surface of the security element and one of the coordinate axes x or y are different on both sides of the bending line in the first and/or the at least one second predefined bent state of the security element when the security element is observed parallel to a plane spanned by the coordinate axes x and y.
Preferably, the angles enclosed between a surface of the security element and one of the coordinate axes x or y are substantially identical on both sides of the bending line in the unbent state of the security element when the security element is observed parallel to a plane spanned by the coordinate axes x and y, in particular the angles differ by less than 5°, preferably by less than 2.5°, further preferably by less than 1°.
It is further possible that, if the Laplace operator Δ is applied to a surface of the security element described by a function F(x,y), a predefined limit value is exceeded in the first and/or the at least one second predefined bent state of the security element and is not exceeded in the unbent state, wherein the function F(x,y) describes the distance from the surface of the security element to a two-dimensional reference surface spanned by the coordinate axes x and y. It is also possible that if the Laplace operator Δ is applied to the function F(x,y), a further predefined limit value is not exceeded in the first and/or the at least one second predefined bent state of the security element, with the result that if the Laplace operator Δ is applied to the function F(x,y), the first and/or the at least one second predefined bent state is determined by a range of values which lies between the predefined limit value and the further predefined limit value.
According to a further preferred embodiment example, the bending radius in the first and/or the at least one second predefined bent state of the security element lies between 1 mm and 100 mm, preferably between 2 mm and 50 mm, further preferably between 4 mm and 30 mm.
By “bending radius” is meant here the radius r of the largest circle which lies tangential to the bending line or the bending point, and at the same time has no points of intersection with the security element and/or security document. An unbent, flat security element consequently has an infinite bending radius.
It is further advantageous that the bending radius in the first and the at least one second predefined bent state of the security element differs by at least 2 mm, preferably 5 mm, further preferably 10 mm.
Furthermore, it is expedient that the security element is bendable, preferably easily and reversibly bendable, in particular that the shape of the security element can be changed by application of force, preferably small application of force.
Preferably, in the direction of the coordinate axis x or y around which the security element is bent in the first and/or the at least one second predefined bent state, the security element has a length of at least 5 mm, preferably of at least 10 mm, further preferably of at least 20 mm, even further preferably of at least 50 mm.
Advantageously, the security element has an areal extent in the unbent state of the security element of at least 5 mm×1 mm, preferably of at least 10 mm×2 mm, even further preferably of at least 50 mm×10 mm.
According to a further preferred embodiment example, in the at least one first area the first volume hologram has two or more first zones, wherein the two or more first zones in the first predefined bent state of the security element provide the first item of information for the observer in the first observation situation. It is hereby possible that the first item of information is generated in the first observation situation by the two or more first zones of the at least one first area.
It is further possible that in the at least one first area the first volume hologram has two or more second zones, wherein the two or more second zones in the at least one second predefined bent state of the security element provide the at least one second item of information for the observer in the first observation situation. It is hereby possible that the at least one second item of information is generated in the first observation situation by the two or more second zones of the at least one first area.
It is advantageous here if the two or more first zones and/or the two or more second zones have a length in the unbent state of the security element of at least 5 μm, preferably 50 μm, even further preferably 500 μm in the direction of one of the coordinate axes x and/or y.
It is further possible that the two or more first zones and/or the two or more second zones have an areal extent in the unbent state of the security element of at least 5 μm×5 μm, preferably of 50 μm×50 μm, even further preferably of 500 μm×500 μm.
It is further expedient if the two or more first zones and/or the two or more second zones are arranged according to a grid.
Here it is possible that the grid is a one-dimensional grid, in particular a line grid, or a two-dimensional grid, in particular a dot grid. By dot grid is also meant here a pixel grid of square, in particular rectangular or quadratic areas of surface.
It is further possible that the two or more first zones and/or the two or more second zones are gridded in each other. It is thus possible that the two or more first zones are arranged alternating with the two or more second zones, and that the two or more first zones are arranged adjacent to the two or more second zones.
Furthermore, it is possible that the grid width is smaller than the resolution limit of the naked human eye, in particular that the grid width is smaller than 300 μm, preferably smaller than 150 μm.
Advantageously, the two or more first zones and/or the two or more second zones are arranged on both sides of the bending line. Thus it is possible, for example, that at least one of the first zones lies on a first side of the bending line and at least one of the first zones lies on a second side of the bending line.
Preferably, in the first predefined bent state of the security element the two or more first zones and/or in the at least one second predefined bent state of the security element the two or more second zones are visible for the observer in the first observation situation at different illumination angles or observation angles.
By observation angle is meant the angle enclosed between the plane spanned by the first volume hologram layer in the unbent state and the observation direction of an observer. Likewise, by illumination angle is meant the angle enclosed between the plane spanned by the first volume hologram layer in the unbent state and the illumination direction of an illumination device. If the security element is bent, in the two or more first and/or second zones the observation angle and the illumination angle thus change for the respective zone.
According to a further preferred embodiment example, the first volume hologram layer has Bragg planes formed by refractive index variations.
Advantageously, at least one of the parameters: distance between the Bragg planes and alignment of the Bragg planes differs in the two or more first zones and/or in the two or more second zones. It is hereby made possible, for example, that the two or more first zones and/or the two or more second zones appear in different colors for the observer. It is further determined, for example, by the alignment of the Bragg planes, whether the two or more first zones and/or the two or more second zones are visible for the observer in the first and/or at least one second predefined bent state.
It is advantageous here if the distance between the Bragg planes differs by more than 5 nm, preferably more than 10 nm, even further preferably by more than 20 nm, and/or if the angles enclosed by the Bragg planes and the first volume hologram layer differ by more than 2°, preferably by more than 5°, further preferably by more than 10°, even further preferably by more than 20°.
Preferably, the alignments of the Bragg planes in the two or more first zones are substantially identical to each other in the first predefined bent state of the security element. It can hereby be achieved that each of the two or more first zones contributes to generating the first item of information in the first observation situation in the first predefined bent state of the security element. Furthermore, this has the consequence that the alignments of the Bragg planes in the two or more first zones are not identical to each other in the flat state.
It is further possible that the alignments of the Bragg planes in the two or more second zones are substantially identical to each other in the second predefined bent state of the security element. It can hereby be achieved that each of the two or more second zones contributes to generating the at least one second item of information in the first observation situation in the at least one second predefined bent state of the security element. Furthermore, this has the consequence that the alignments of the Bragg planes in the two or more second zones are not identical to each other in the flat state.
Furthermore, it is possible that in the first predefined bent state of the security element in the two or more first zones and/or in the at least one second predefined bent state in the two or more second zones of the security element the angles enclosed between the normals to the Bragg planes and the direction of the incident light are substantially identical to the angles enclosed between the normals to the Bragg planes and the direction of the light reflected and/or diffracted by the Bragg planes.
Preferably, for producing a security element a first master is used, which is generated starting from a bent intermediate master, wherein the bending of the bent intermediate master corresponds to the bending of the first and/or of the at least one second predefined bent state of the security element. The intermediate master can, for example, be a film with a holographically exposed photoresist, wherein the film is bent during the holographic exposure corresponding to the bending of the first and/or of the at least one second predefined bent state of the security element.
It is further possible that a first master is used, which is produced by means of distorting optics, in particular cylindrical lenses. Here, the distorting optics expose the first master such that the first volume hologram introduced into the first volume hologram layer by means of the first master is formed such that the first and/or the at least one second item of information is visible for an observer in a first observation situation in the first and/or the at least one second predefined bent state of the security element and is not visible in the first observation situation in the unbent state of the security element or vice versa.
It is further possible that for producing a security element a first master is used, which contains a computer-generated hologram (CGH), wherein this CGH is calculated for a curved surface area corresponding to the bending of the first and/or of the at least one second predefined bent state of the security element. The curvature of the bent security element is thus compensated for in the calculated CGH.
It is also possible that a first master is used, the first surface structure of which comprises a Kinegram®, a symmetrical grating, an asymmetrical grating, in particular a blazed grating, a binary grating, a multi-level phase grating, isotropic or anisotropic matte structures, a retroreflective structure, a macrostructure with a (substantially) refractive effect, in particular a microprism structure or a micromirror, in particular Fresnel-like or also otherwise designed freeform surfaces, or combinations thereof. In addition, grating structures with statistically varying parameters (grating period, profile shape, grating depth, azimuthal alignment) can advantageously be provided here. In particular, blazed gratings are suitable, the flank angles of which are designed for the illumination and observation angles of the corresponding zones of the security element in the first and/or at least one second predefined bent state.
Here the depth t of the blazed gratings is preferably optimized for the wavelength for which the first volume hologram is designed, according to the following formula:
t=n×λ/2 with: n∈N
At the same time, however, the depth t should preferably not be greater than the period of the blazed gratings.
Furthermore, it is advantageous that a first master is used, which has at least two partial areas, which reflect or diffract incident light into at least two different zones of the first volume hologram layer.
Preferably, the first surface structure of the first master differs in the at least two partial areas, in particular in at least one of the parameters: profile shape, grating depth, grating period and azimuthal angle.
It is possible that the first master has a symmetrical grating structure in a first partial area and a first asymmetrical grating structure in a second partial area, wherein the grating periods and/or grating depths of the grating structures in the first and second partial areas differ.
It is further possible that the first master has a second asymmetrical grating structure in a third partial area, wherein the grating periods and/or grating depths of the first and second asymmetrical grating structures differ.
It is advantageous that the first volume hologram layer and the first master are exposed by coherent light beams of different wavelengths and/or different directions of incidence.
The coherent light beam advantageously passes through the first volume hologram layer and is diffracted or reflected at the first surface structure of the first master. Here the master is, in particular, the object to be reconstructed.
It makes sense that the first master is arranged on the first volume hologram layer directly or with the interposition of a transparent optical medium.
Preferably, the exposure is effected with laser light with a power density in the range from 0.5 to 5 W/cm2 or with an energy density in the range from 5 to 50 mJ/cm2, particularly preferably with a power density in the range from 1 to 3 W/cm2 or with an energy density in the range from 10 to 30 mJ/cm2.
It is further expedient that after the exposure the first volume hologram layer is fixed by curing, in particular by means of UV radiation.
According to a further preferred embodiment example, a second volume hologram is introduced into the first volume hologram layer in at least one second area.
Preferably, the second volume hologram is formed such that a third item of information is visible in the first observation situation in the unbent state of the security element. It is hereby possible that the observer in the first observation situation perceives the third item of information, for example an image of a sun, in the unbent state of the security element and perceives the first item of information, for example an image of a cloud and a sun, in the first bent state of the security element.
Advantageously, the at least one first area and the at least one second area are gridded in each other, in particular the at least one first area is arranged alternating with the at least one second area and the at least one first area is arranged adjacent to the at least one second area.
It is also possible that the security element has a third volume hologram in a second volume hologram layer. It is thus possible that the method further comprises the following steps, which are carried out in particular after steps a) to c): d) applying a second volume hologram layer; e) arranging a second master with a second surface structure on the second volume hologram layer; f) exposing the second master and the second volume hologram layer by means of coherent light, with the result that in this way a third volume hologram is introduced into the second volume hologram layer.
Preferably, in the unbent state of the security element the first volume hologram layer and the second volume hologram layer are arranged one above the other during observation perpendicular to a plane spanned by the first volume hologram layer of the security element.
Furthermore, it is possible to arrange further volume hologram layers, in particular a third, fourth, fifth volume hologram layer one above another, like the first and the second volume hologram layers. Thus it is possible that the security element has at least one third volume hologram in at least one second volume hologram layer.
It is further possible that the first volume hologram in the first volume hologram layer and the third volume hologram in the second volume hologram layer are aligned with register accuracy relative to each other.
It is further advantageous that the third volume hologram is formed such that a fourth item of information is visible for an observer in the first observation situation in a third predefined bent state of the security element and is not visible in the first observation situation in the unbent state of the security element or vice versa. It is hereby possible, for example, that the security element shows the first item of information and/or the at least one second item of information in the first observation situation in the first and/or at least one second bent state and shows the fourth item of information in the first observation situation in the third bent state. For example, the first and/or at least one second item of information can be recognizable in the case of a concavely bent shape of the security element and the third item of information can be visible in the case of a convexly bent shape of the security element. However, it is also possible that the second volume hologram is formed such that a fifth item of information is visible in the first observation situation in the unbent state of the security element. It is hereby possible that the observer perceives the fifth item of information in the first observation situation in the unbent state of the security element and perceives the first item of information in the first bent state of the security element.
With respect to possible embodiments of the second master and/or further masters, as well as the steps of arranging the second master and exposing the second master and/or further masters and the second and/or further volume hologram layers, reference is made here to the corresponding embodiments relating to the first master.
Furthermore, it is advantageous if, in at least one third area, the security element comprises a relief structure selected from the group: diffractive grating, Kinegram® or hologram, blazed grating, binary grating, multi-level phase grating, linear grating, cross grating, hexagonal grating, asymmetrical or symmetrical grating structure, retroreflective structure, in particular binary or continuous Fresnel-type freeform surfaces, diffractive or refractive macrostructure, in particular lens structure or microprism structure, microlens, microprism, zero-order diffraction structure, moth-eye structure or anisotropic or isotropic matte structure, or a superimposition or combinations of two or more of the above-named relief structures. Further, grating structures with statistically varying parameters (grating period, profile shape, grating depth, azimuthal alignment) can in addition preferably be provided.
It is hereby possible to combine the first and/or at least one second and/or fourth items of information, which are visible depending on a bending of the security element, in particular in the first and/or at least one second and/or third predefined bent state of the security element, with optical effects produced by the relief structures, the visibility of which has no, or only a slight dependence on a bending. The effect is hereby achieved, for example, that an optical effect produced by the relief structures, in particular by diffractive lenses, and/or by binary or continuous freeform surfaces and/or by a retroreflective structure, is visible in the unbent state of the security element, and is complemented by the first item of information in the first bent state, wherein the characteristic appearance of the optical effect produced by the relief structure does not change, or changes only slightly, in the first predefined bent state.
It is further possible here that the security element comprises a replication varnish layer. The replication varnish layer consists, for example, of a thermoplastic varnish, into which a relief structure is molded by means of heat and pressure by the action of a stamping tool. It is further also possible that the replication varnish layer is formed by a UV-crosslinkable varnish and the relief structure is molded into the replication varnish layer by means of UV replication. The relief structure is molded onto the uncured replication varnish layer by the action of a stamping tool and the replication varnish layer is cured before and/or directly during and/or after the molding by irradiation with UV light. Preferably, the relief structure is molded into the replication varnish layer in the at least one third area. It is further advantageous that the replication varnish layer has a layer thickness between 0.2 μm and 4 μm, preferably 0.3 μm and 2 μm, further preferably 0.4 μm and 1.5 μm.
Preferably, the security element has a reflective layer in at least one fourth area. The reflective layer is preferably a metal layer made of aluminum, chromium, gold, copper, silver or an alloy of such metals which is vapor-deposited under vacuum in a layer thickness of 0.01 μm to 0.15 μm. The reflective layer can, however, also in principle be a non-metal layer. The reflective layer can be a printed or high-resolution structured color layer or another layer which absorbs radiation, in particular in the visible spectral range. The reflective layer is formed, in particular, as a color layer. The color layer is, in particular, produced by means of the HD-Demet process.
The reflective layer can be applied over the whole surface or also only in areas, in particular as a partial metallization. For this, the reflective layer can, for example, be applied over the whole surface and then removed again in areas of the surface by means of known structuring processes (for example by means of etch resist, by means of photoresist, by means of washing processes). Such a partial metallization can, for example, be a KINEGRAM® or a metallic nanotext.
Preferably, the reflective layer is formed gridded. According to a preferred embodiment example, the partially metalized reflective layer is formed in the form of a grid. Alternatively, the gridded reflective layer can also be non-metallic and, in particular, consist of a printed or high-resolution structured color layer.
Preferably, the at least one first and/or second and/or third and/or fourth areas are aligned with register accuracy relative to each other. Particularly preferably, the items of information which the respective areas represent complement each other here.
By register or registration and register accuracy or registration accuracy is meant a positional accuracy of two or more elements and/or layers relative to each other. The register accuracy is to range within a predetermined tolerance and be as low as possible. At the same time, the register accuracy of several elements and/or layers relative to each other is an important feature in order to increase the process reliability. The positionally accurate positioning can be effected in particular by means of sensorially, preferably optically, detectable registration marks or register marks. These registration marks or register marks can either represent specific separate elements or areas or layers or themselves be part of the elements or areas or layers to be positioned.
The first volume hologram in the first volume hologram layer can also preferably be formed not over the whole surface, but in the form of a grid, i.e. only in areas. It is thus possible that the first volume hologram is arranged according to a grid. Advantageously, the first volume hologram is arranged such that the respective areas of the first volume hologram are arranged congruent in register with the metalized areas of the reflective layer. Preferably, the first volume hologram is here arranged below the reflective layer, in particular with respect to the observation direction of the security element. It is further advantageous if the grid of the first volume hologram is formed as a line grid. In the unbent state of the security element the reflective layer thus covers the first volume hologram, whereby the first volume hologram is substantially not visible. On the other hand, in the first and/or at least one second predefined bent state of the security element the reflective layer no longer completely covers the first volume hologram, with the result that the first volume hologram becomes visible or at least partially visible.
Preferably, a transparent spacing layer is arranged between the first volume hologram layer and the reflective layer, in particular between the first volume hologram layer and the reflective layer that is partially metalized and/or formed gridded.
According to a further preferred embodiment example the security element has two reflective layers in the form of a grid, preferably partially metalized, between which a transparent spacing layer is preferably arranged. Furthermore, a further spacing or varnish layer can be arranged between the reflective layers and the volume hologram layer.
The two reflective layers are preferably arranged offset relative to each other, such that the transparent areas of one reflective layer are covered by the existing or present, in particular the metalized, areas of the other reflective layer, in particular during observation perpendicular to a plane spanned by the first volume hologram layer in the unbent state of the security element. The two reflective layers are, so to speak, positioned “with a gap” relative to each other. The two reflective layers are thereby arranged with respect to each other such that in the unbent state of the security element they completely cover the underlying, for example whole-surface, first volume hologram, with the result that the first volume hologram is therefore substantially not visible for the observer. On the other hand, in the first and/or at least one second predefined bent state of the security element the reflective layers no longer cover the first volume hologram, with the result that the latter becomes visible or at least partially visible. By transparent areas in connection with in the form of a grid is meant in the present case, in particular, areas where the reflective layer is not present.
The grid of the reflective layer and/or of the reflective layers and/or of the first volume hologram is advantageously a regular grid. However, it is also possible that it is an irregular grid.
The grid of the reflective layer and/or of the reflective layers and/or the grid of the first volume hologram is preferably formed as a line grid. The lines of the line grid preferably run parallel to the bending line of the security element. The line widths and/or the line spacings are between 1 μm and 50 μm, preferably between 2 μm and 10 μm.
For adaptation to the bending line, it can be necessary that the line widths and/or line spacings of the grid of the reflective layer and/or of the reflective layers and/or the grid of the first volume hologram are not constant, but vary. Preferably, the line widths and/or line spacings vary perpendicularly to the bending line, in particular depending on the bending of the first and/or of the at least one second bent state of the security element.
In particular, the line widths and the line spacings of the grid of the reflective layer and/or of the reflective layers and the layer thickness of the transparent spacing layer are selected such that the effect of the visibility of the first volume hologram is maximized in the first and/or at least one second predefined bent state, for example in the case of a predetermined bending radius, of the security element.
It is advantageous if the layer thickness of the transparent spacing layer substantially corresponds to the grid periods of the line grids of the reflective layers or of the reflective layer. Preferably, the line widths and/or the line spacings are between 1 μm and 50 μm, preferably between 2 μm and 10 μm.
It is advantageous if the spacing layer has a layer thickness between 1 μm and 50 μm, preferably between 2 μm and 10 μm. The lines of the line grids of the two reflective layers preferably run parallel to the bending line of the security element.
It is also possible, instead of a transparent spacing layer with a constant layer thickness, to provide a transparent spacing layer the thickness of which varies. Both a continuous variation of the layer thickness and a stepped, discrete variation of the layer thickness are possible. It is thereby possible to improve the effect of the visibility of the first volume hologram in the first and/or at least one second predefined bent state, and also the effect of the invisibility in the flat state. In particular, the thickness of the spacing layer changes perpendicularly to the bending line. It is advantageous if the spacing layer has the greatest layer thickness in the area of the bending line or along the bending line, and the layer thickness decreases or becomes smaller with distance from the bending line. This means in particular that a greater layer thickness of the spacing layer is provided in the area of small bending angles and a smaller layer thickness of the spacing layer is provided in the area of larger bending angles. The decrease can be both continuous and stepped.
In principle, however, it is further also possible that the reflective layer and/or the reflective layers are formed by a transparent reflective layer, preferably a thin or finely structured metallic layer or a dielectric HRI (high refractive index) or LRI (low reflective index) layer. Such a dielectric reflective layer consists, for example, of a vapor-deposited layer made of a metal oxide or metal sulfide, e.g. titanium oxide etc. with a thickness of 10 nm to 150 nm.
It is further also possible to provide three or more superimposed, structured reflective layers, and two or more transparent spacing layers. This makes possible a better visibility of the volume hologram in the bent state and a greater observation angle range in which the volume hologram is not visible in the flat state.
In a further embodiment, the structured reflective layer is, or the structured reflective layers are, provided not over the whole surface, but only partially over the underlying volume hologram. This makes it possible, in particular, that an area of the volume hologram is also visible in the flat state, with the result that the observer's attention is directed towards the security element. An ever greater part of the volume hologram then becomes visible during bending.
In a further variant, one of the reflective layers is formed as a line grid, whereas the other reflective layer is formed as a gridded layer of extensive grid elements. The formation of Moiré effects through the two layers that are arranged spaced apart and one above the other is utilized here. The geometric shapes of the two reflective layers as well as their dimensions result through mathematical calculation, for example by means of software for the calculation of Moiré effects. As first target value, it is for example predetermined during the calculation that the Moiré effect in the flat state of the security element produces a completely or almost completely non-transparent surface area. The underlying volume hologram is thereby covered in the flat state, and thus not visible or almost not visible. As second target value, it is for example predetermined that in the superimposed reflective layers the Moiré effect in the bent state of the security element produces windows or transparent areas which have specific geometric shapes. In these transparent areas the underlying volume hologram becomes visible.
In a further embodiment example, instead of the structured reflective layer or the structured reflective layers, a structured absorption layer or two spaced-apart absorption layers can also be provided. The above-named embodiments relating to the reflective layer or the reflective layers also apply correspondingly to the absorption layer.
It is also conceivable that only a single grid is used to cover the volume hologram in the flat state. This has the advantage that no register accuracy would be necessary, as in the case of the two or more metal grids. The reflective layer or a metal grid is present here substantially as flanks. The reflective layer is formed, in particular, in the form of flanks. The reflective layer extends not only in the xy-plane, but also in the z-direction. The reflective layer formed in the form of flanks, or the flanks have a similar effect to the louvers in a so-called “privacy filter” for computer screens. The light can pass through the reflective layer substantially perpendicularly, i.e. in the z-direction. As soon as a critical angle g is exceeded, the flanks of the reflective layer almost completely block the light coming from the volume hologram. However, for smaller angles the intensity of the volume hologram is also already reduced as at the critical angle g the light can only pass out of a few points of the volume hologram.
The production of such a reflective layer or such a metal grid results in particular from a louver-like or cup-shaped structure being replicated. The height H of the louvers or cup edges can be between 1 μm and 50 μm, preferably between 2 μm and 20 μm, and particularly preferably between 2 μm and 10 μm. The distance between the louvers or cup edges should preferably be less than or equal to 10×H, better less than 5×H and even better less than 2×H. In a further step, the replicated structure is then vapor-deposited over the whole surface with a reflective layer, preferably with a thin metal layer, for example in a thickness of 20 nm to 30 nm, in particular with aluminum. In a demetalizing step, the reflective layer and/or the metal layer is then removed again in areas. The metal is substantially removed only in the recesses between the louvers or the walls of the “microcups” i.e. only from the “bottom” of the structures. Elements formed substantially in the form of flanks or a reflective layer formed in the form of flanks remain. The demetalizing step can in principle be carried out with all known demetalizing processes.
Advantageously, the at least one third and/or fourth area forms a graphic element, in particular a motif, image, symbol, logo and/or alphanumeric character.
It is further possible that the at least one first area forms a frame around the at least one third and/or fourth area. It is also possible that the at least one first area completely surrounds the at least one third and/or fourth area. Alternatively, it is also possible that the at least one third and/or the fourth area completely surrounds the at least one first and/or second area.
Furthermore, it is expedient that the first and/or the at least one second and/or the third and/or the fourth item of information represents one or more symbols, logos, motifs, images, signs or alphanumeric characters.
Preferably, the first and/or second volume hologram layer has a layer thickness between 3 μm and 100 μm, preferably between 10 μm and 30 μm.
It is further expedient if the first and/or second and/or further volume hologram layers are formed from a photopolymer, in particular from Omni DX 796 (DuPont), silver halide emulsions or dichromatic gelatin.
Preferably, the security element, at least before application to a substrate, for example the security document, comprises a carrier layer, in particular a transparent carrier layer. Preferably, the carrier layer consists of a self-supporting film made of PET (=polyethylene terephthalate), PEN (=polyethylene naphthalate) or BOPP (=biaxially oriented polypropylene) and has a thickness between 5 μm and 250 μm, preferably between 10 μm and 50 μm. After application to the substrate, for example the security document, it is possible to remove the carrier layer.
Alternatively, however, the security element can also be generated directly on the substrate. For example, the volume hologram can be produced directly during the production of polymer banknotes or polymer banknote substrates. In particular, the volume hologram layer and optionally even further layers can be applied directly to the substrate under and/or over the volume hologram layer in each case by known printing processes such as screen printing, gravure printing, offset printing or inkjet printing and the volume hologram layer can be exposed directly on the substrate.
It is further possible that the security element comprises at least one protective varnish layer and/or at least one sealing layer and/or at least one adhesion-promoting layer and/or at least one barrier layer and/or at least one stabilizing layer and/or at least one adhesive layer, in particular comprising acrylates, PVC, polyurethane or polyester.
Using such a security element, a security document can be created which is formed in particular as an identity document, passport document, visa, credit card, banknote, security or the like.
The security element can also lie over a transparent window area of a security document. This can, for example, be a transparent area of a polymer or hybrid banknote or a punched or laser-cut hole in a paper banknote. Here, it is possible, for example via a suitable gridding of the structures in the master, to integrate two volume holograms into the volume hologram layer which show different optical effects when observed from the front and the rear side of the security document in the bent state. These different optical effects can either be to be seen if the bending is kept identical, thus at one time convex and at one time concave. The different effects can, however, also be to be seen if the bending is inverted when the security document is turned over, i.e. the same bend shape—convex or concave—is present when observed from the front and the rear side.
Embodiment examples of the invention are explained below by way of example with the aid of the accompanying figures which are not drawn to scale.
The security document 2 consists of a flexible, elastic or non-elastic substrate 17, on which the security element 1 is arranged. The substrate 17 is preferably a substrate made of paper material which is provided with printing, and into which further security features, such as for example water marks or security threads, are introduced and/or to which these are applied. In particular, the substrate 17 or the security document 2 can be a paper banknote or a paper visa. However, it is also possible that the substrate 17 is a plastic film or a laminate consisting of one or more paper and/or plastic layers. Examples of plastic films for polymer banknotes, in particular made of BOPP are e.g. the substrate Guardian® from Innovia or Safeguard® from De La Rue or also Tyvek® from Dupont. Examples of laminates made of paper and plastic layers, also called hybrid substrates, are for example Durasafe® from Landquart or “Hybrid” from Giesecke & Devrient. The thickness of the carrier substrate 17, in particular if it is a banknote, is between 6 μm and 150 μm, preferably between 15 μm and 50 μm.
The security document 2, as shown in
Preferably, the security element 1 is applied to the security document 2 by means of stamping, in particular by means of cold or hot stamping. It has proved successful here if the security element 1 is provided on a transfer film, with the result that an application of the security element 1 to a security document 2 can be effected by means of stamping. Such a transfer film has at least one security element 1, wherein the at least one security element 1 is arranged detachable from a carrier layer in the form of a carrier film of the transfer film. Starting from the carrier layer of the transfer film, a detachment layer is usually present here, in order to be able to detach the security element 1 from the carrier layer after stamping. The security element 1 can be fixed to the security document 2 by means of an adhesive layer, in particular made of a cold or hot-melt adhesive.
Alternatively, the security element can also be provided on a laminating film, wherein the application is effected by lamination and the carrier layer remains on the security element.
It is also conceivable to produce the security element 1 directly on the security document 2. In particular, the volume hologram layer 11 and optionally even further layers can be applied directly to the substrate 17 under and/or over the volume hologram layer 11 in each case by known printing processes such as screen printing, gravure printing, offset printing or inkjet printing and the volume hologram layer can be exposed directly on the substrate 17.
The security element 1 fixed on the security document 2 is applied to the security document 2 such that it adapts to changes in shape and/or geometry of the security document 2. In particular, the security element 1 is bendable, with the result that the shape of the security element 1 is changed or can be changed by the application of force. If, for example, the security document 2 shown in
In the following, the difference between a tilting and a bending of the security element 1 is first illustrated with reference to
On the other hand, if the security element 1 is bent towards the observer 7, with the result that a concave shape of the security element 1 results, the observation angles change inversely.
As shown by
It is further possible to describe the bent state of the security element 1, described above in particular via geometric characteristics, via the mathematical Laplace function. Thus it is possible that, if the Laplace operator Δ is applied to a surface of the security element 1 described by a function F(x,y), a predefined limit value G is exceeded in the bent state of the security element 1 and is not exceeded in the unbent state, wherein the function F(x,y) describes the distance from the surface of the security element 1 to a two-dimensional reference surface area spanned by the coordinate axes x and y. For example, for a security element 1 in an unbent state ΔF(x,y)<G applies and for a security element 1 in the bent state ΔF(x,y)>G applies. Preferably, the value of ΔF(x,y) is compared with the predefined limit value G here.
The volume hologram layer 11 is preferably a layer made of a photopolymer, in particular of Omni DX 796 from DuPont, Wilmington, USA. It is further also possible that the volume hologram layer 11 is formed from a silver halide emulsion or dichromatic gelatin. The layer thickness of the volume hologram layer 11 is preferably between 3 μm and 100 μm, in particular between 10 μm and 30 μm.
A volume hologram 11v is introduced into the volume hologram layer 11. The volume hologram 11v has a periodic modulation of the refractive index which, in
This three-dimensional refractive index pattern can be produced by a holographic interference arrangement, for example by a structure in which a coherent light beam, in particular a laser source, is deflected on a master with a surface structure arranged on the volume hologram layer 11. The light beam striking the volume hologram layer 11 in order to introduce the volume hologram 11v is first refracted at the volume hologram layer 11 and then deflected at the master by diffraction at the surface structure. The deflected beams represent the object wave which interferes with the reference wave incorporated by the incident light beam and triggers a local polymerization in the volume hologram layer 11. As a result of the polymerization, the refractive index of the volume hologram layer 11 is changed locally. The refractive index variations are localized in the Bragg planes 12.
As shown in
As shown in
Through the parameter: distance between the Bragg planes in the zones 10a, 10b and 10c, for example, the color of the light 14 diffracted and/or reflected by the respective zones 10a, 10b and 10c for the observer 7 can also be determined. It is hereby made possible, for example, that the light diffracted and/or reflected by the zones 10a, 10b and 10c appears in the same color or in different colors for the observer 7. For different colors, it is advantageous if the distance between the Bragg planes differs by more than 2 nm, preferably more than 10 nm, even further preferably by more than 20 nm. If the distance between the Bragg planes in the zone 10a is, for example, approximately 260 nm, the light diffracted and/or reflected by the zone 10a appears green to the observer. On the other hand, in the case of a distance between the Bragg planes in the zone 10b of, for example, approximately 320 nm, the light diffracted and/or reflected by the zone 10b appears red to the observer.
The zones 10a, 10b and 10c can produce a common item of information for the observer, for example an image, wherein each zone 10a, 10b and 10c produces a part of the image. However, it is also possible that the zones 10a, 10b and 10c each produce an individual item of information for the observer. For example, the zone 10a can produce a letter for the observer 7 in one color and the zone 10b can produce a further letter for the observer 7 in a further color.
In the unbent state of the security element 1 the zones 10a, 10b and 10c shown in
Furthermore, the bent state of the security element, as shown in
The individual bending variants 801 shown in
It is further possible that a detachment layer is applied to the carrier layer 16 first, before the volume hologram layer 11 is printed on, cast or applied using a doctor blade. The detachment layer can be provided in order to facilitate the subsequent detachment of the carrier layer from the volume hologram layer.
It is further possible that the security element 1 comprises at least one protective varnish layer and/or at least one sealing layer and/or at least one adhesion-promoting layer and/or at least one barrier layer and/or at least one stabilizing layer and/or at least one adhesive layer, in particular comprising acrylates, PVC, polyurethane or polyester.
As shown in
The master 18 is here designed such that the volume hologram to be inscribed in the volume hologram layer 11 by means of the master 18 makes an item of information visible for an observer in an observation situation in a predefined bent state of the security element 1 and makes it not visible in the first observation situation in the unbent state of the security element or vice versa.
Such a master 18 can, for example, be generated starting from a bent intermediate master, wherein the bending of the bent intermediate master corresponds to the bending of the predefined bent state of the security element 1. Thus an intermediate master is first generated by means of holographic exposure, wherein the intermediate master is present in the predefined bent state. Starting from this bent intermediate master, a flat master 18 with the surface structure is then created, which is arranged on the volume hologram layer 11.
The flat master 18 can also have an in particular Fresnel-like cylindrical lens structure as surface structure, wherein the curvature of the Fresnel lens compensates for the bending of the security element 1. The surface of the security element 1, which is covered with the Fresnel-like cylindrical lens structure as surface structure, lights up completely in the predefined bent state.
It is further also possible to produce the master 18 by means of distorting optics, in particular by means of cylindrical lenses. During the holographic production of a flat master, the beam path is here distorted by means of distorting optics such that the volume hologram to be inscribed in the volume hologram layer 11 is visible for the observer only in the bent state.
As shown in
It is further possible that the master 18 has at least two partial areas which reflect or diffract incident light into at least two different zones of the volume hologram layer 11. The partial areas are here designed such that they reflect and/or diffract the incident light at a predetermined angular position which is determined such that the desired alignment of the Bragg planes forms in the volume hologram layer 11. The angular positions into which the at least two partial areas reflect and/or diffract the incident light beam are thus different for one thing and, for another thing also depend on the angular position at which the coherent light beam 19 is radiated onto the at least two partial areas. The desired orientation of the Bragg planes 12 in the predefined bent state of the security element 1, as well as the structure of a predetermined holographic exposure device here determine the deflection angle of the at least two partial areas. By deflection angle is meant here the angle by which the surface structure of the master 18 in the respective partial area deflects a perpendicularly incident light beam from the surface normal by reflection and/or diffraction.
Preferably, the surface structures of the master 18 comprise a Kinegram®, linear or crossed sinusoidal grating, anisotropic or isotropic matte structures, lens structures, Fresnel-like freeform surfaces, kinoform structures or computer-generated holograms, a symmetrical grating, an asymmetrical grating, in particular a blazed grating, microstructures with a predominantly refractive effect such as for example micromirrors, a binary grating, a multi-level phase grating or combinations thereof. Further, grating structures with statistically varying parameters (grating period, profile shape, grating depth, azimuthal alignment) can be provided here. In particular, blazed gratings or microstructures with a predominantly refractive effect are suitable, the flank angles of which are designed for the illumination and observation angles of the corresponding zones of the security element in the predefined bent state.
It can be provided that the volume hologram layer 11 and the master 18 are exposed by coherent light beams 19, in particular by light beams generated by a laser, of different wavelengths and/or different angles of incidence. In this way it can be achieved that the items of information produced by the volume hologram appear in different colors and/or are visible in the case of different observation situations in the bent state of the security element.
It can be provided that the surface structures of the master 18 in part provide no information. The areas of the master 18 which provide no information can, for example, be used as background structure. Such background structures can, for example, be formed such that scattered light and/or disruptive reflections are reduced. This can be achieved in that the areas of the master 18 which contain no image information are formed as a moth-eye structure, in particular crossed grating structures (quadratic or hexagonal) or statistical structures with a high number of lines or spatial frequencies (for example more than 2000 lines/mm, in particular more than 3000 lines/mm) and/or as a mirror and/or as a matte structure and/or as a scatter grating. Anti-reflective structures or structures further optimized specifically for the purpose can also be used for this.
Preferably, the surface structure of the master 18 differs in the at least two partial areas, in particular the surface structure of the master 18 differs in at least one of the parameters: profile shape, grating depth, grating period and azimuthal angle in the at least two partial areas, wherein these parameters can also be defined via statistical distribution functions.
It can further be provided that the master 18 has a symmetrical grating structure in a first partial area and a first asymmetrical grating structure in a second partial area, in particular a blazed grating, wherein the grating periods and/or grating depths of the grating structures in the first and second partial areas differ. Further, the master 18 can have a second asymmetrical grating structure, in particular a blazed grating, in a third partial area, wherein the grating periods and/or the grating depths of the first and second asymmetrical grating structures differ. It is thus possible, for example, that the grating period is 600 lines/mm in the first partial area, the grating period is 300 lines/mm in the second partial area and is 100 lines/mm in the third partial area.
After curing of the volume hologram layer 11, as shown in
Thus
As shown in
The reflective layer is preferably a metal layer made of aluminum, chromium, gold, copper, silver or an alloy of such metals which is vapor-deposited under vacuum in a layer thickness of 0.01 μm to 0.15 μm. The reflective layer is here preferably applied over the whole surface first. Then the reflective layer is removed again in areas of the surface by means of known structuring processes (by means of etch resist, by means of photoresist, by means of washing processes), with the result that a partial metallization occurs in the areas 50. As shown in
The volume hologram which in the bent state produces the item of information 29 in the form of the three-dimensional impression of the motif can, for example, be a CGH which has been calculated for a curved surface area such as is present in the bent state. Alternatively, this volume hologram can also be a 3D hologram which is based on a master which, as explained above, is based on an intermediate master exposed curved.
If, as shown in
The security element 1 preferably has a replication varnish layer into which a relief structure is molded. The replication varnish layer consists, for example, of a thermoplastic varnish into which the relief structure is molded by means of heat and pressure through the action of a stamping tool. It is further also possible that the replication varnish layer is formed by a UV-crosslinkable varnish and the relief structure is molded into the replication varnish layer by means of UV replication. The relief structure is molded onto the uncured replication varnish layer through the action of a stamping tool and the replication varnish layer is cured directly during or after the molding, through irradiation with UV radiation. Such a replication varnish layer in particular has a layer thickness between 0.1 μm and 20 μm, preferably 0.2 μm and 10 μm, further preferably 0.4 μm and 5 μm. It is further possible here that the security element 1 has a reflective layer, in particular in the area 50. The reflective layer is preferably a metal layer made of aluminum, chromium, gold, copper, silver or an alloy of such metals which is vapor-deposited under vacuum in a layer thickness of 0.01 μm to 0.15 μm.
The varnish layer 17l1 is preferably a protective varnish layer. The varnish layer 17l1 is preferably transparent and has a layer thickness between 0.1 μm and 10 μm, preferably between 0.3 μm and 1 μm, further preferably between 0.5 μm and 1 μm. The varnish layer 17l2 is preferably a transparent spacing layer, which is arranged between the volume hologram layer 11 and the reflective layer 17r. The varnish layers 17l1 and 17l2 preferably comprise PMMA (=polymethyl methacrylate), PVC, acrylate or carnauba wax.
The reflective layer 17r is preferably a metal layer made of aluminum, chromium, gold, copper, silver or an alloy of such metals which is vapor-deposited under vacuum in a layer thickness of 0.01 μm to 0.15 μm. Alternatively, the reflective layer 17r can also be a printed or high-resolution structured color layer or another layer which absorbs radiation in the visible spectral range. As shown in
A volume hologram 11v is introduced into the volume hologram layer 11. As shown in
The adhesive layer 15 preferably comprises acrylates, PVC (=polyvinyl chloride), PUR (=polyurethane) or polyester and further preferably has a layer thickness between 0.1 μm and 20 μm, preferably between 0.1 μm and 10 μm, further preferably between 0.5 μm and 5 μm, even further preferably between 0.8 μm and 3 μm. The adhesive layer shown in
With respect to the design of the substrate 17, reference is made here to the above statements.
In the unbent state of the security element 1 shown in
On the other hand, in the predefined bent state of the security element 1 shown in
Preferably, the line widths and line spacings of the grids of the reflective layer 17r and/or of the volume hologram 11v and the layer thickness of the transparent spacing layer 17l2 are selected such that the visibility of the volume hologram 11v is maximized in the predefined bent state of the security element 1. As shown in
The line widths and line spacings of the grids of the reflective layer 17r and the corresponding line widths and line spacings of the volume hologram 11v are determined by geometric construction or mathematical calculation. These are based on the parameters defined in
In a variant, the spacing layer or the varnish layer 17l2 can be provided, as shown in
The advantage is that, due to the variation in the thickness of the spacing layer, the line widths and line spaces of the grids of the reflective layer 17r can be formed more uniform and the volume hologram 11v is thereby clearly visible at all points in the bent state and, in addition, the appearance of the metallization is more uniform.
In a variant, it can also be provided to provide the spacing layer or the varnish layer 17l2 not as a layer with a constant thickness or continuously varying thickness, but rather as a stepped layer, see
In a further variant, it can be provided to use two or more spacing layers 17l2, 17l3 instead of a single spacing layer 17l2, and two or more partial reflective layers 17r1, 17r2 instead of a single partial reflective layer, see
As shown in
As shown in
In the unbent state of the security element 1 shown in
On the other hand, in the predefined bent state of the security element 1 shown in
Preferably, the line widths and line spacings of the grids of the reflective layers 17r1 and 17r2 and the layer thicknesses of the spacing layers 17l2 and 17l3 are selected such that the visibility of the volume hologram 11v is maximized in the predefined bent state of the security element 1. It is advantageous here if the layer thicknesses of the spacing layers 17l2 and 17l3 substantially correspond to the grid period of the line grids of the reflective layers 17r1 and 17r2. It is further possible that the line widths and/or line spacings vary, in particular depending on the predefined bent state of the security element 1. The line widths and spaces of the two line grids are in particular again determined by geometric construction, as described previously, or by calculation. As shown in
In a variant, the spacing layers 17l2 and 17l3 can be provided, as shown in
In a further variant, it can also be provided to use three or more reflective layers instead of two reflective layers 17r1 and 17r2. Because at least three reflective layers are present, the line widths can be selected smaller and the line spacings larger. The volume hologram is thereby more visible in the bent state and less visible in the unbent state.
With respect to the further design of the layers 17r1 and 17r2 and the design of the layers 11, 15 and 17, reference is made here to the above statements.
After the reflective layer 17r′ formed in the form of flanks is formed, another varnish layer can be applied to the reflective layer 17r′. The single-ply reflective layer 17r′ can then be combined with a volume hologram layer 11 and applied to a flexible substrate 17, such as a paper banknote (
This layer 68 can be an adhesive layer and/or an adhesion-promoter layer. However, the layer 68 can also be dispensed with.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102016104300.1 | Mar 2016 | DE | national |
| 102016109632.6 | May 2016 | DE | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16083207 | Sep 2018 | US |
| Child | 17477986 | US |
