Patent Application
20180186168
The invention relates to an anti-counterfeit carrier having a series of optical security elements. The invention also relates to a method for producing an anti-counterfeit carrier having a series of optical security elements.
Optically variable elements are used for protection against the forgery of products, documents and identity documents. Optical security elements contain structures in very high resolution that produce special optical effects. Such structures are difficult to copy and in most cases cannot be represented by normal printing technology. Optical security elements can contain structures that are visible to, and verifiable by, the naked eye and structures that require simple or special readers to be checked. Optical security elements are largely known and are used in a wide range of applications. Optical security elements include, for example, holograms, kinegrams and lithograms. The structures contained in optically variable elements can be holograms, specifically rainbow holograms, transmission holograms, reflection holograms, 2D holograms, 3D holograms, Fourier holograms, Fresnel holograms, volume holograms and kinoforms. Such holograms can either be directly optically produced or be calculated on a computer. Furthermore, diffractive structures can be contained, in particular diffraction gratings. Refractive structures can be contained, such as Fresnel lenses or blazed gratings. Scattering elements can be contained, such as diffusers. Numerous further structures that can be contained in optically variable elements are described in the literature. The various structures can be partially overlaid so as to be able to accommodate two or more effects in the same region of the optically variable element. The different structures can be used to form graphic elements, such as guilloches, logos, images, lines, areas etc. Furthermore, text elements can be produced, such as lettering, numerical or alphanumerical serial numbers, microprints. Furthermore, functional elements can be formed, such as barcodes or other machine-readable structures. The different structures and elements are cleverly combined to form an overall design for the optical security element that, as far as possible, meets all the requirements of the optical security element with respect to security, functionality and aesthetic impression.
Optical security elements can be produced in a replication process. To this end, a master embossing stamp having a special overall design is established in a complex manner. Such master embossing stamps can be produced in an electron beam lithography method or in a dot matrix method, wherein high resolutions can be achieved. In the case of electron beam lithography, resolutions of up to only a few nanometers can be achieved. In the case of the dot matrix method or other interference methods, diffraction gratings having a grating constant of up to only a few 100 nanometers can be produced. Daughter embossing stamps can in turn be produced from the master embossing stamp, and further daughter embossing stamps from the former. The embossing stamps are then used in an embossing process to emboss a relatively large number of optically variable elements. In such an embossing process, the optically variable elements produced are all substantially identical.
The closest prior art is considered to be the document WO 2013/127650 A1, disclosed in which is an anti-counterfeit carrier having at least one metallized layer into which at least one optically variable element is introduced, wherein the at least one optically variable element has a non-individual embossed structure and the at least one optically variable element has an individual laser-lithographic structure with a resolution of below 20 μm.
The invention is based on the object of rendering carriers having a series of optical security elements even more secure against forgery and to provide a method for their production.
The object with respect to the carrier is achieved by way of an anti-counterfeit carrier having the features of claim 1. Preferred developments are the subject matter of the dependent product claims.
The term carrier is to be understood here in a very general manner. Carriers can be deformable strips, in particular a stripe-type, multi-layer foil, an adhesive strip or stiff strips. What the carriers have in common is that their length and their width are significantly greater than their thickness. The anti-counterfeit carriers according to the invention can adopt a wide variety of forms, in particular can be multi-part, in other words comprise a plurality of individual carrier units. They can be designed in particular as self-adhesive labels or hot-seal material. The label shape or the shape of a hot-seal stamp can be arbitrary, for example circular, oval, polygonal with rounded corners etc. In the case of the hot-seal material, the overall design can also be designed in the form of a long strip that is sealed onto the substrate over its entire length. Such strips are known from entrance tickets, travel tickets or banknotes.
It has surprisingly been found that the security against the forgery of carriers of a series of optical security elements can be increased by adding an optical tilt effect to at least two, a plurality of or each of the optical security elements. This can be done in a manner according to the invention by combining or connecting an embossed structure with a lithographic structure. Arranged along the carrier is a series of optical security elements. A series is here understood to mean at least two optical security elements, but it can also include three, four or any higher number of security elements. They can all be different from one another or some of them can be different. The carrier is preferably dividable between the optical security elements, with the result that each individual optical security element can be used further as an adhesive or hot-sealing label, Holospot®, Priospot®, VeoMark® or the like. In the case of a hot seal foil, dividability is not necessary for further processing in a sealing process.
The carrier has at least one metallized layer, which can be a metallized foil or a metallized lacquer. Other forms of metallized layer also feasible.
The carrier can be first embossed then metallized, or the other way around. The relief of the emboss is here embossed into the metal layer. The metal layer is not destroyed by the embossing and serves as a reflective layer. The light that is diffracted by the embossed structure is reflected back into space. The metallized layer is embossed by embossing a series of non-individual motifs, preferably of mutually identical or at least largely identical motifs. Each of the non-individual motifs forms part of in each case one of the optical security elements. A respective other component of the optical security element is the individual motif. The individual motif differs for each security element in the series.
A series is here understood to be an arrangement. The series can be an arrangement of security elements arranged one next to the other along the carrier. The series has two, three or any higher number of security elements or motifs. The security elements in the series, however, do not need to be arranged immediately next to one another, and instead other security elements can also be arranged within the series. The security elements can be arranged next to one another in a linear manner or in a circular manner or some other way.
The tilt effect between the non-individual motif and the individual motif of each security element manifests in that, at specific viewing angles, the individual motif comes to the foreground for the viewer, and at other viewing angles, the non-individual motif comes to the the foreground for the viewer and appears to be overlaying the individual motif.
A motif is here considered individual if it differs in the series of the optical security elements according to the invention from all motifs of the other security elements or at least from most of them. The individual motifs are different, preferably different in pairs. Such an individual motif can be a serial number or a barcode that contains a serial number, among other things. A non-individual motif is that part of the optical security element that has been embossed by a single master embossing stamp during the production of a series of optical security elements of the non-individual motif. In other words, the non-individual motif is the same or identical in each optical security element. According to the prior art, the non-individual motif of the embossing structure is destroyed or rendered invisible by the individual motif of the lithography structure, because the diffracted light in the locations of the material that are demetallized in the lithographic method is not reflected back. This gives the appearance that the non-individual motif of the embossing structure is overlaid or overprinted by the individual motif of the laser-lithographic structure.
According to the invention, the metallized layer is provided with a diffractive surface structure at a location where the non-individual motif is embossed. Diffractive is to be understood here to mean that the non-individual motif is populated with one or more diffraction gratings along its metallized surface such that, depending on the viewing angle and the illumination, the non-individual motif becomes visible by way of a shimmer. The diffraction gratings generally have grating constants of 400 nm to a few μm to efficiently diffract visible light. The diffractive surface structure thus utilizes the principle of diffraction of the incident light, wherein the light has, depending on the wavelength, diffraction maxima of different orders in different reflection angles, such that when viewing the diffractive surface structure obliquely, a rainbow-type shimmering effect occurs at viewing angles that coincide with the diffraction angles, but not at all viewing angles.
According to the invention, the non-individual motif is overlaid with an individual motif in the same metallized layer. An individual motif is introduced by laser lithography into the metallized layer, and the individual motif has cutouts that are preferably not processed by laser lithography. The cutouts form at least a partial motif, but possibly even the entire non-individual motif, and the cutouts are arranged in register on the individual motif.
In register is here understood to mean that the individual and the non-individual motifs of a security element are arranged exactly, or exactly save for register deviations, with respect to one another. The motifs can here be offset relative to one another from security element to security element at most by the register deviation. The magnitude of the register deviation, which is also referred to as register offset, will be explained further below.
In laser lithography, a structure to be exposed is transferred into a substrate using a laser beam. The structure to be exposed is specified or calculated using a computer and is present in the form of image or vector data. The image or vector data are used by the laser lithography apparatus for controlling the position of the laser beam relative to the substrate and for controlling the intensity and the duration of action of the laser beam that is incident on the substrate. In laser lithography, several methods have become established. For one, a writing beam can be fixed in space and the substrate can be moved relative thereto. Alternatively, the substrate can be fixed in space and the writing beam can be moved relative thereto. Furthermore, both substrate and laser beam can be moved. It is also possible for the writing beam to be modulated using a spatial light modulator and to expose a relatively large area of the substrate at once in this way. In this principle, writing beam and substrate can also be moved.
In laser lithography, the resolution is limited by the wavelength used and by the optical unit used. In order to be able to produce structures with as high a resolution as possible, small wavelengths are therefore used with preference. Suitable wavelengths are in the range of 0.2 μm to 10 μm, preferably in the range of 0.2 μm to 1 μm. Smaller wavelengths are likewise possible. At these wavelengths, structures can be produced that are effective in the range of the visible light (wavelength approximately 0.4 μm to 0.7 μm). Diffraction gratings having grating constants in the order of magnitude of the visible light can be produced in this way, which have large diffraction angles and can therefore be perceived particularly well.
Optical security elements produced using laser lithography can be fully individualized in terms of design during production. All structures can be configured individually. This can be done using numerical or alphanumerical serial numbers or by way of individual graphic elements such as images or guilloches.
Substrate materials used for laser lithography are, as in the embossed optical security elements, metallized foils or metallized lacquers, among others. In this case, the laser beam can be set in terms of wavelength, intensity, pulse duration, shape and writing energy such that the substrate material becomes demetallized at specific predefined locations and as a result becomes transparent or semi-transparent. This is done either by ablating the metal layer, by displacing the metal layer towards the edges of the exposed location or by converting the metal layer into a transparent or semi-transparent oxide layer. A mixture of the three stated effects can also take place. The demetallization can be aligned in register with the other structures which can be produced by laser lithography, because it can be introduced in the same exposure process. Since demetallization in laser lithography is effected in principle with the high resolution of the laser lithographic process, highly resolved demetallized structures can be produced therewith. This includes microprint, scattering structures, gray levels or gray-level wedges. Such gray levels can be produced by suitable rasterization in a halftone method, wherein only a specific portion of the area is demetallized in rasterized fashion in an area. In the case of gray-level wedges, the demetallized area portion gradually increases in the area by adapting the rasterization.
In addition to complete demetallization, reducing the thickness of the metal layer is also possible in laser lithography by exactly setting the laser energy introduced during the writing process. By reducing the thickness of the metal layer, the light transmittance of the metal layer increases. This can also be used to produce gray levels and gray wedges.
The production of optical security elements with highly resolving laser lithography is subject to certain limitations. For example, the base resolution is limited by the wavelength used of the writing laser and by the optical unit used. Since in mass production, high writing speeds and thus a high throughput are intended to be achieved, it is desirable to further reduce the resolution since in that case larger areas can be exposed in shorter time periods. Typical base resolutions used here are 0.5 μm to 5 μm. In laser lithography, a limited resolution should thus be assumed. When producing diffracting structures, such as e.g. gratings or holograms, not all diffraction angles can be achieved due to the limited resolution. Furthermore, the phase or amplitude modulation to be achieved with laser lithography in the material is not ideal, such that the theoretically maximum possible diffraction efficiency of the diffractive structures is not achieved.
The individual motif is produced here for example such that the regions that make up the individual motif are processed by laser lithography such that the metallized layer is demetallized. As a result, the motif becomes transparent, and dark or different-colored areas located under the metal layer can optically come to the fore, with the result that, when the optical security element is viewed, the individual motif is recognizable in principle. According to the invention, however, the individual motif has cutouts. These are regions that are not processed by laser lithography, in other words they continue to be metallized and thus reflect the incident light. The idea here is that the cutouts occupy exactly those areas that are not used by the non-individual motif of the embossed structure. As a result, the at least one optical security element is formed by a stacked arrangement of the non-individual motif with the individual motif.
The non-individual motif preferably has fine lines. Fine is to be understood here to mean that the width of the line is less than 250 μm, preferably between 50 μm and 100 μm. The line width is selected such that the lines are still sufficiently wide to receive a diffractive structure and also to produce a diffraction effect. The area occupied by the non-individual motif should be small, preferably less than 25%. The diffractive surface structure of the metallized layer preferably remains completely unchanged even by the individual motif that has been applied by laser lithography.
The non-individual motif can be a pattern of fine lines, such as concentric rings or a diamond pattern. The non-individual motif can be a letter, a word, a logo or a symbol. If the motif contains larger areas, only the outlines of these areas should form the motif, so that the motif overall is made up only of fine lines.
The invention is based on both the non-individual motif and the individual motif remaining recognizable in at least one optical security element. Due to the above-described arrangement, surprisingly a type of tilt effect occurs for the viewer of the optical security element. At a viewing angle and illumination at which the non-individual motif of the embossed structure does not shimmer, the individual motif of the laser-lithographic structure comes to the foreground and is readable by a human viewer almost in a disruption-free manner, as if the cutouts were not present. This is because the cutouts are practically not noticeable to the viewer due to the low line width of the non-individual motif.
However, at a viewing angle and illumination at which the non-individual motif of the embossed structure does shimmer, the non-individual motif of the embossed structure comes to the foreground and, to the human viewer, appears to be located over the individual motif of the laser lithographic structure. The two views are swapped when the optical security element is tilted.
In order to produce the anti-counterfeit carrier according to the invention having at least one optical security element, a resolution of a laser lithographic method is necessary to be able to apply the cutouts in the order of magnitude of less than 250 μm, and also very good registration accuracy between the non-individual motifs and the individual motifs is necessary. To this end, the position of the non-individual motif must be marked during the production method, e.g. using a registration mark, and the individual motif must be introduced into the metallized layer in exact register according to the marked position using the laser lithographic method.
If the registration accuracy is not present during production, the non-individual motif is partially destroyed or rendered invisible by the individual motif of the laser lithographic method, and the tilt effect is not, or at least not fully, effective. During production, production tolerances may occur, i.e. slight register offsets between the non-individual motif of the embossed structure and the individual motif of the laser lithographic structure can destroy the tilt effect. Such production tolerances are preferably taken into consideration when designing the security elements.
If the maximum register deviation of the production process between the two motifs is known, the maximum register deviation can be added to the line width of the non-individual motif of the embossed structure. The line width is increased by the absolute value of the maximum deviation. The cutouts of the laser lithographic structure, however, retain their original width, i.e. are designed as if the lines of the non-individual motif of the embossed structure had not been widened. If during the production method the position of the individual motif of the laser lithographic structure deviates from the position of the non-individual motif of the embossed structure, then the line of the non-individual motif of the embossed structure is still present at the cutouts. The tilt effect continues to be effective. A disadvantage of this is of course that the lines are widened. It is still possible with this method and the widening of the lines to compensate for minor register deviations. The register deviations should be in the range of +/−100 μm, preferably +/−50 μm.
To take into consideration the production tolerances when designing the motifs, alternatively the register deviation is added to the width of the cutouts of the laser lithographic structure. If during the production method the position of the individual motif of the laser lithographic structure deviates from the position of the non-individual motif of the embossed structure, then the line of the non-individual motif of the embossed structure is still present at the larger cutouts. The tilt effect continues to be effective here as well.
The high resolution of the laser lithography method and the high demands in terms of registration accuracy represent a significant obstacle to forging the optical security elements.
With respect to the method, the object is achieved by way of a method having the features of claim 11.
The object is achieved by way of a method for producing an anti-counterfeit carrier having at least one optical security element by the optical security element producing an optical tilt effect by way of a non-individual motif being embossed into a metallized layer, and by a diffractive surface structure being produced on the non-individual motif in the process, and by an individual motif being introduced into the metallized layer by laser lithography, and by cutouts being produced in the individual motif in the process that form at least a partial motif of the non-individual motif. The cutouts are arranged in exact register on the non-individual motif. Here, initially a non-individual motif is embossed into the metallized layer, for example in the form of concentric rings, another mathematical pattern or a logo. A stamp is used herefor, preferably a master embossing stamp, which continuously embosses, for example, non-individual motifs into the metallized layer along an elongate carrier at specific intervals. The stamp is here designed exactly such that a surface structure is introduced in the metallized layer that produces a diffraction grating in visible light or an overlay of a plurality of diffraction gratings in visible light. The diffraction grating produces a shimmering effect and causes the non-individual motif to become visible at specific viewing angles that correspond to the diffraction angle of different orders.
Preferably, a further, but individual motif is subsequently burned into the same metallized layer by laser lithography. However, the metallized layer is treated by laser lithography such that the surface structure of the non-individual motif remains intact and at the same time only the interspaces between the concentric lines or other lines of the non-individual motif are treated by laser lithography. The lines of the individual motif and the areas of the individual motif that are treated by laser lithography have significantly greater dimensions, i.e. in the millimeter range, and are thus dominantly visible when viewing the optical security element outside the diffraction angles.
The invention will be described on the basis of four exemplary embodiments in 17 figures, in which:
In
If the optical security element 6 according to
In order to still produce the tilt effect according to the invention, the lines of the non-individual motif 2 are uniformly widened around a register deviation along their entire perimeter. The lines which have been widened by the register deviation are illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 210 982.8 | Jun 2015 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/063716 | 6/15/2016 | WO | 00 |
