Patent Application
20160303889
The invention relates to a security element for a document of value and/or a security document, which is disposed on a transparent layer, for example, a film, wherein the security element has a first periodic, optical structure on the first side of the transparent layer and a second periodic, optical structure on the second side, which is disposed opposite the first side of the transparent layer. The invention further relates to a document of value and/or a security document comprising such a security element.
It is already known to provide documents of value and/or security documents, such as bank notes, chip cards, personal identification documents, passports, tickets, checks, and the like, with a transparent layer, for example, a film. Such a transparent film can contain, for example, a protective layer or a “see-through” element as the security element.
Security elements, which are high-quality elements that provide protection against copying, require either complex manufacturing or production process, such as, for example, the hologram, special pigments that are customized and often expensive, or other production-related aids for manufacturing and depicting variable information or effects. In particular, elements that provide protection against copying, which have a so-called tilt effect when viewed from different viewing angles, are known. When these elements are digitally reproduced, i.e., copied, said elements generate interference effects, which are also referred to as moiré patterns. Due to the higher resolution of digital scanners, however, reproduction results are continuously improving. As a result, the forgery-proofness of such security elements is limited. Furthermore, the manufacture of such elements is complex and cost-intensive, since a surface structure and imprinting and laser inscription are required.
Document EP 1 780 681 B1 makes known a security element for protection against copying, in which a substantially transparent substrate is provided, on the first side of which a halftone line structure having a first frequency is applied and on the second side of which a marking substance is applied. The marking substance has two different regions, wherein the first region contains a second halftone line structure having a second frequency, and the second region contains a third halftone line structure having a third frequency. The halftone line structures form a (partial) coating of the substrate. When the structures of the various halftone line structures, which have different frequencies, are placed on top of one another and looked through, a moiré pattern is observed. The solution according to the prior art is relatively complicated and includes only a few possibilities with respect to the image design. The verification of the security element is therefore difficult to carry out.
The problem addressed by the present invention is therefore that of creating a security element, which enables a copy-protection element to be manufactured in a low-cost and simple manner, and which also has greater protection against forgery. With regard to the document of value and/or security document, the problem is that of enabling this to be equipped with such a security element in a simple and low-cost manner.
The aforementioned problem is solved by a security element having the features of claim 1.
In particular, the security element has a first periodic, optical structure, for example a grid of lines or a grid of points, which forms a first coating on the first side of the transparent layer, and a second periodic, optical structure, for example a grid of lines or a grid of points, which forms a second coating on the second side, which is disposed opposite the first side of the transparent layer, wherein the first optical structure and the second optical structure are disposed to as to overlap such that, as viewed by outside observer at a certain, predetermined viewing angle relative to the surface of the transparent layer provided with the coatings or at the lighting angle of the light source used for verification, preferably a UV lamp, said structures show a color-changing effect, wherein the first coating has a first color and the second coating has at least one second color, which is different from the first color.
The security element according to the invention therefore advantageously provides a color-changing effect, which can be achieved in a low-cost and simple manner merely by using printing technology. Surface structuring is not necessary. The solution according to the invention makes use of the development of the technology such that it is now possible to achieve printing having highly exact register on different sides of a layer, for example, different sides of a film, by means of a suitable turning device. When the optical structures having different suitable colors that are visible to the observer (first color, second color) are printed on both sides, tilting the security element results in an increasing superposition of the colors or an increasing separation of the colors, which are disposed on the two sides of the transparent layer. As a result, a color-tone change (color change effect) is achieved that is dependent on the viewing angle or the lighting angle. The security element according to the invention is characterized by a high level of protection against forgery, due to the high requirements with respect to the accuracy of the register of the structures, and is suitable, in particular, for increasing the protection against forgery for ID1/ID3 plastic cards having a multilayer design. The security element according to the invention, as an element that provides protection against copying, has a high level of protection against forgery, in particular, when the color of the first coating and the color of the second coating are difficult to separate. Furthermore, the spatial separation of the colors of the first coating and the second coating results in a visible color change, which has a 3D effect (tilt effect) due to the structure of the security element. This tilt effect disappears after copying or scanning, since the levels of the first and the second coating are combined in one level.
It is also advantageous that the security element according to the invention can be easily verified without any further tools. Therefore, this is a security element for the first level of inspection.
The term “color” as used in the context of the present invention refers to the individual visual perception (surface color) of the security element, which is brought about by the reflection, absorption and/or emission of electromagnetic radiation on and/or in the security element and which is perceived by an observer upon viewing the security element from a certain angle. The color and, correspondingly, the color change of the optical structures can be defined, e.g., in the RGB, CMYK or HSV color spaces or in the CIELAB color space for surface colors or, for self-illuminating colors, in the CIE xy color space.
The color that is visible to the observer results from a combination of additive and/or subtractive color mixing of the color of the first layer and the color of the second layer, when the coating facing the observer is transparent. In this case, an additive color mixing results, in particular, for electromagnetic radiation of a certain wavelength range, which is emitted by the first coating and/or the second coating and also plays a role for the structural elements of the first optical structure and the second optical structure, which lie next to one another as observed from the particular viewing angle. Subtractive color mixing occurs with all classical colors (absorption colors) and is significant, in particular, for the structural elements having an absorption color, in each case, which are located on top of one another as observed from the particular viewing angle.
In another exemplary embodiment, the coating facing the observer is substantially not transparent, in particular not for UV light and/or visible light. In the case of intransparency to visible light, a color change effect can occur, at least as observed from a certain, predetermined viewing angle, in that the optical structure of the coating facing away from the observer at least partially disappears, as it were, underneath the optical structure of the coating facing the observer and, therefore, is not involved in the additive and/or subtractive color mixing. The color impression presented to the outside observer is therefore determined, substantially or completely, by the optical structure of the coating facing the observer. As an alternative, when the coating facing the observer is not transparent to UV light, the coating facing away from the observer can be excited by being illuminated from the side with a UV light source, which luminesces this coating, wherein this luminescence is perceived by the observer.
With respect to the transparency of the transparent layer disposed between the first optical structure and the second optical structure, it is necessary that the layer be transparent primarily for at least a sub-range of the visible wavelength range (380 nm to 780 nm) or the UV wavelength range. If a colorant (e.g., a pigment) is used for the first optical structure and/or the second optical structure, which is excited in a wavelength range outside of the visible wavelength range, it is necessary that the transparent layer also be transparent for this excitation wavelength range, which is preferably in the IR wavelength range or in the UV wavelength range.
In one exemplary embodiment, the transparent layer can be composed of two or more films or other layers. In this case, the films or other layers, which carry the first optical structure and the second optical structure, may need to be combined with highly exact register in the manufacture of the security element.
Reference is hereby also made to the difference from the halftone line structures disclosed in the prior art. With regard for the known security element, the only differences relate to the structure of the elements located on top of one another, which said elements generate the moiré pattern due to the frequency differences. A color change effect is not observed in this case. Nothing is found in document EP 1 780 681 B1 regarding the behavior of the security element in terms of the surface color.
The color change effect that is achieved becomes particularly clear to the observer when the first optical structure and the second optical structure are disposed relative to one another such that the elements of the first optical structure, e.g., the lines of the first optical structure, fully overlap the elements of the second optical structure, e.g., the lines of the second optical structure, as observed from a certain, predetermined angular range of viewing or illumination. This means that, in this angular range of viewing, the observer perceives a subtractive and/or additive color mixing of the colors of the two structures when the coating facing the observer is transparent, or, when the structure located closer to the observer completely or nearly completely absorbs the light used for the observation, the observer only perceives black elements of the first optical structure, while the second structure is no longer visible or is only partially visible. When the security element is tilted by a certain, predetermined angle out of this angular range of viewing, which depends on the thickness of the substrate and the undercut portion of the elements of the second optical structure relative to the elements of the first optical structure and can be adjusted, the second optical structure, which is located underneath, becomes visible to the observer without influence by the first optical structure, and therefore a color change takes place. At this tilt angle, the observer therefore perceives the color of the second optical structure.
The problem according to the invention is therefore also solved by a security element, which is disposed on a layer, which is transparent in the visible and UV wavelength ranges, for example, a film, wherein the security element has a first periodic, optical structure in the form of a grid of lines or a grid of points, which forms a first coating on the first side of the transparent layer, and a second periodic, optical structure in the form of a grid of lines or a grid of points, which forms a second coating on the second side, which is disposed opposite the first side of the transparent layer, wherein the first optical structure and the second optical structure are disposed to as to overlap such that these exhibit a color changing effect for an outside observer as viewed from a certain, predetermined viewing angle and under UV radiation, wherein the first coating contains a first color, which is not transparent for UV light, and pigments, which have a visible chromatic or achromatic surface color, and the second coating has at least one second color, which is different from the first color and contains luminescent pigments, wherein the first optical structure and the second optical structure are disposed relative to one another such that the elements of the first optical structure fully overlap the elements of the second optical structure as viewed from a certain, predetermined angular range of viewing or illumination.
It is advantageous when, in a preferred exemplary embodiment, the thickness of the transparent layer is in a range from 50 μm to 800 μm, preferably in the range from 70 μm to 250 μm, particularly preferably in the range from 100 μm to 150 μm. Since the tilting of the security element, which is necessary for the color change effect to occur, is dependent on the film thickness and the separation of the structural elements, e.g., the lines or the points, of the first optical structure and/or the second optical structure, this layer thickness is particularly well suited for the desired color change effect in combination with the usual line separations of a grid of lines or a grid of points.
In addition, the color change effect can be perceived particularly clearly by the observer when the first optical structure and the second optical structure are each designed as a grid of lines and when these grids of lines extend parallel to one another, at least in sections.
With regard to the perceptibility of the color change effect, it is furthermore advantageous when the separation between two adjacent structural elements, e.g., between two lines or two points, of the first optical structure and/or the second optical structure is 0.1-fold to 100-fold the thickness of the transparent layer, preferably 0.5-fold to 10-fold the thickness of the transparent layer, particularly preferably 0.5-fold to 3-fold the thickness of the transparent layer.
For the same reason, it is advantageous when the width of the structural elements, e.g., the width of the lines or the points of the first optical structure and/or the second optical structure is 0.1-fold to 100-fold the thickness of the transparent layer, preferably 0.5-fold to 10-fold the thickness of the transparent layer. For example, the width of the structural elements in a 100 μm-thick film, as the transparent layer, can be approximately 100 μm to 200 μm.
It is furthermore advantageous when the color separation of the first and/or the at least one second color between the state before and after the color change has a predetermined, sufficient value, preferably a value of ΔE>10. Complementary colors are best suited. When the colors are too similar, a color change (dE>10) cannot be detected. In this context, in another exemplary embodiment, the first color and the at least one second color can be designed as metameric colors, i.e., can achieve the same color impression before and/or after tilting. The difference between the colors can be detected only by disposing a filter between the security element and the observer, wherein the filter absorbs a predetermined wavelength range of the light and thereby makes the color change effect visible.
With regard to the detectability of the security feature or with regard to a reliable verification, it is advantageous when the first optical structure and/or the second optical structure, in totality, contain information in the form of an image and/or text and/or numbers. In particular, it is preferable for the information to be a personalization. The term “personalization” refers to information in the form of an image and/or text and/or numbers, which is unique or individualized, e.g., for the owner of the document of value and/or security document comprising the security element, or for the document of value or security document itself. Such a personalization can be, for example, a serial number, e.g., of a bank note, the picture or personal data, or the like, of the document owner, e.g., the owner of the passport, or a ticket number.
Particularly preferably, the first optical structure and/or the second optical structure are applied by means of a printing process, e.g., by means of offset lithography, letterpress printing, rotogravure, soft-ground etching, and/or digital printing, preferably by means of intaglio printing, by means of an offset printing process, or by means of an inkjet printing process. These printing processes are very low-cost alternatives to the manufacture of a security feature according to the invention. The inkjet printing process, in particular, is advantageous in terms of applying a personalization that changes with each security element. In this context, it is advantageous, for example, when either the first optical structure or the second optical structure is designed as a fixed grid of lines, for example. The respective other optical structure is then calculated and, correspondingly, is likewise printed as a grid of lines, for example, such that, of the at least two bits of information that are depicted at various tilt angles, one bit of information contains personalization, for example, the picture of the document owner.
In another exemplary embodiment, the first coating comprises pigments, which have a visible chromatic or achromatic surface color, and the second coating has luminescent pigments. Particularly preferably, the first coating additionally comprises luminescent pigments, which preferably emit electromagnetic radiation having a wavelength, which differs from the wavelength of the luminescent pigments of the second coating. A high level of protection against forgery can be achieved as a result. Within the scope of the present invention, the term “luminescence” is intended to refer to the phenomena of both fluorescence as well as phosphorescence.
The luminescent pigments, in particular fluorescent pigments, that are used are, for example, host lattices doped with rare earth metals, for example, with ytterbium, praseodymium, neodymium, europium, terbium, cerium, dysprosium, holmium, thulium, samarium-doped garnets, perovskites, oxides, sulfides, oxysulfides, phosphates, silicates, fluorides, nitrides or selenides, optionally with traces of heavy metals, such as, for example, silver, copper, manganese. Furthermore, organic luminescent materials can be used, for example, rhodamines, perylene dyes, isoindolinones, quinophthalones, oxazinones, coumarins, perinone dyes. The manufacture of such luminescent materials is known to a person skilled in the art and is described, for example, in the document WO 81/03508 A1. Commercially available luminescent pigments are, for example, LUMILUX CD 740 and LUMILUX Green CD 702 from Honeywell, Paliosecure Gelb from BASF, and Cartax from Clariant. Other luminescent materials can also be found in the “Phosphor Handbook”, 2nd Edition, ISBN-13 978-0849335648, or the book “Optical Document Security”, 3rd Edition, ISBN-13 978-1580532587.
The aforementioned problem is also solved by a document of value and/or a security document having an above-described security element. The advantages of the invention, which also apply similarly to the particular document of value and/or security document, have been presented above.
The security element can be obtained particularly easily when this security element is disposed in a window of the document of value and/or security document.
The invention is explained in the following on the basis of exemplary embodiments and with reference to the figures. All the features that are described and/or graphically depicted form the subject matter of the invention, either alone or in any combination, independently of their wording in the claims or their back-references.
Schematically in the drawings:
The first grid of lines 10 and the second grid of lines 20 are depicted in a simplified manner in each of
In the first exemplary embodiment, which is shown in
However, as soon as the security element is tilted relative to the observer, the light beam 1 passes through the lines of the first grid of lines 10, in a range that is dependent on the tilt angle, and reaches the lines of the second grid of lines 20 (see line of view 8). The colors of the optical structures lying on top of one another therefore affect one another in this range, such that, according to the laws of subtractive color mixing, the observer sees regions having an orange color as viewed from an angle. This color-tone change from red or yellow to orange produces the above-described color change effect.
The exemplary embodiment shown in
The grids of lines 10, 20 of the exemplary embodiments depicted in
Exemplary embodiments are depicted in
The pigments used in the first grid of lines 10′ in
Similarly to
A second grid of lines 40, which is located directly underneath the first grid of lines 30, is disposed, in the fifth and sixth exemplary embodiments, such that the lines of the second grid of lines 40 and 40′ are completely covered by the lines of the first grid of lines 30 in a state in which the observer looks perpendicularly onto the surface of the substrate 1 (see line of view 14 in each case). From this angle and in a small region about this angle, the observer therefore sees only black lines.
From a certain, predetermined angle α relative to the normal line, which results from the thickness d of the film 1′ and the length of the “undercut portion” z of the second grid of lines 40 and 40′ relative to the first grid of lines 30 according to
α=arctan(z/d) (1)
the observer can look past the lines of the first grid of lines 30, on the side (see lines of view 18, 19), and thereby see the grid of lines 40 located thereunder, which emits light in the red wavelength range, for example, under UV radiation. As the tilt having an angle>α increases, the observer therefore sees an increasing portion of red color, i.e., in this exemplary embodiment, the color change takes place at an angle α. For example, the thickness of the film 1′ is d=100 μm and the undercut portion is z=100 μm, thereby resulting in an angle of α=45°. In a first alternative exemplary embodiment, d=100 μm, z=30 μm and, therefore, α=16.7°, and in a second exemplary embodiment, d=100 μm, z=58 μm and, therefore, α=30.1°.
Depending on the materials selected for the film 1′, it is necessary to also account for Snell's law, i.e., the law of refraction, in the calculation of the angle (critical angle) at which the color change effect occurs; Snell's law states that a light ray bends relative to the normal in media that are optically denser than air (i.e., having an index of refraction n>1), according to the formula
sin α1/sin α2=n2/n1
wherein n1 is the index of refraction for air, n2 is the index of refraction of the material of the film (n2=1.58 in the case of PC used as the material of the film 1′), α1 is the angle of the line of view relative to the normal in air, and α2 is the angle of the line of view relative to the normal in the material of the film.
The parameters mentioned above with respect to the fifth exemplary embodiment can also be provided, similarly, for the exemplary embodiment shown in
The exemplary embodiment shown in
The films 1′ of the exemplary embodiments 3 to 7 must also be transparent for the UV wavelength range in order to permit an excitation of the pigments of the lines of the second grid of lines 20′, 40, 40′, 40″. The following film materials PC, PET, PETG, PVC, PE and PA, preferably PC, are preferably suitable for this.
In another exemplary embodiment, rather than changing the position of the observer (cf. lines of view 14, 15, 18 and 19) of the exemplary embodiments according to
The exemplary embodiments according to
In the view depicted in
After the identification card 50 is tilted by an angle of, e.g., at least 45° in the clockwise direction (see
In an analogous manner, when the identification card 50 is tilted by an angle of at least 45°, for example, in the counterclockwise direction (see
The colors that are suitable for the above-described exemplary embodiments are depicted in
The first dot, “red”, is the color of the first grid of lines 10, 10′ of the first to fourth exemplary embodiments (
The second dot, “green”, is the color of the second grid of lines 20′ of the third and fourth exemplary embodiment (
In another exemplary embodiment, the first coating and/or the second coating could be additionally provided with pigments, which emit, reflect, or absorb electromagnetic radiation in the wavelength range that is not visible to the human eye. These pigments contain an additional security element, which is preferably machine-readable.
The above-presented exemplary embodiments show a security element, which can be manufactured in a simple and low-cost manner, and which offers a high level of protection against forgery by copying, in particular, due to the three-dimensional nature thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 111 054.9 | Nov 2012 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/073970 | 11/15/2013 | WO | 00 |
