Security element with a luminescent security feature

Abstract

The invention relates to a security element (14) for safeguarding security papers, value documents, and other data carriers using a luminescent security feature. According to the invention, the luminescent security feature contains a luminescent iris printing (34) with a color gradient between at least two different luminescent shades.

Description

[0001] Security element with luminescent security feature

[0002] The invention relates to a security element for protecting security papers, valuable documents, and other data carriers with a luminescent security feature. The invention also relates to a method for producing such a security element and to a valuable document or security document with such a security element.

[0003] Data storage devices, such as valuables or identification documents, as well as other valuable items such as branded goods, are often provided with security features for security purposes. These allow the authenticity of the data storage devices to be verified and also serve as protection against unauthorized reproduction. In this context, luminescent substances are known to be used to protect valuables or identification documents. The presence of the luminescent substances can then be verified using a UV lamp, for example.

[0004] For example, from document EP 1 567358 B2, security prints with several areas are known which show the same color impression under white light, but which show different color impressions in luminescence upon additional UV excitation.

[0005] Furthermore, it is known that the color impressions of luminescent printing inks generally change due to aging and environmental factors, and that both the intensities and color impressions of different luminescences can change at different rates. The choice of motifs for luminescent features on valuable and security documents is therefore limited, as motifs whose appearance changes significantly over time due to insufficient color stability cannot be used.

[0006] Based on this, the object of the invention is to overcome the disadvantages of the prior art and, in particular, to provide a security element of the type mentioned at the outset with a high level of forgery security and an attractive visual appearance.

[0007] Summary of the invention:

[0008] 1. (First aspect of the invention): Security element for securing security papers, value documents and other data carriers with a luminescent security feature, characterized in that the luminescent security feature contains a luminescent iris print with an unscreened color gradient between at least two different luminescent color tones.

[0009] 2. (Preferred embodiment): Security element according to paragraph 1, characterized in that the luminescent security feature contains, in addition to the luminescent iris print, a body-coloured iris print with an unscreened colour gradient between at least two different body colours.

[0010] The body-color iris print can, in particular, occupy the same surface area as the luminescent iris print or overlap with its surface area. The luminescent iris print is, in particular, arranged above and / or below the body-color iris print; a juxtaposition of the two prints is also possible. Finally, the two iris prints can also be produced using printing inks that contain both a body color and a luminescent ink, so that the two iris prints are formed by the same printing layer.

[0011] Instead of the term "luminescent iris print," the term "luminescent color gradient" is often used in this description, and the term "body color gradient" is often used instead of "body color print." In the present invention, an iris print always consists of an unscreened color gradient between at least two different color tones, thus, in particular, it does not contain any dot or line screening.

[0012] 3. (Preferred embodiment): Security element according to paragraph 2, characterized in that the luminescent iris print has a brightness gradient inverted to the body color print.

[0013] 4. (Preferred embodiment): Security element according to paragraph 2 or 3, characterized in that the luminescent iris print has the same color gradient as the body-color iris print, or that the luminescent iris print has a color gradient opposite or complementary to the color gradient of the body-color iris print.

[0014] 5. (Preferred embodiment): Security element according to at least one of paragraphs 1 to 4, characterized in that the luminescent security feature contains, in addition to the luminescent iris print, a motif printed with body colors, wherein the luminescent iris print is preferably printed with a pixel or line offset to the body color motif.

[0015] 6. (Preferred embodiment): Security element according to at least one of paragraphs 1 to 5, characterized in that the luminescent iris print is arranged over the body-coloured iris print or the body-coloured motif, wherein preferably the body-coloured iris print or the body-coloured motif is printed with colour-neutral colours (in particular white, grey or black) or light pastel colours.

[0016] 7. (Preferred embodiment): Security element according to at least one of paragraphs 1 to 5, characterized in that the luminescent iris print is arranged below the body-coloured print or the body-coloured motif.

[0017] The color gradient of the body color iris printing and / or the luminescent printing can also create the appearance of a pseudo-3D effect.

[0018] 8. (Second aspect of the invention): Method for producing a security element according to one of paragraphs 1 to 7, in which a luminescence iris print with an unscreened color gradient between at least two different luminescence color tones is applied to a substrate, wherein the luminescence iris print is preferably applied in a single printing unit.

[0019] 9. (Preferred embodiment): Method according to paragraph 8, characterized in that a body-color iris print with an unscreened color gradient between at least two different body-color tones is applied, in particular printed, to the substrate above or below the luminescent iris print and / or a body-color motif is applied, in particular printed, to the substrate above or below the luminescent iris print. In a preferred embodiment, which is particularly easy to implement, for example, in banknote printing, the luminescent iris print and the body-color iris print are printed onto the substrate using separate printing plates. In principle, however, it is also possible to create a luminescent iris by admixing various luminescent colors with body colors that exhibit a body-color iris under normal lighting.

[0020] Alternatively, luminescent iris printing and body-color iris printing can also be initially produced on separate substrates and then laminated onto each other. This is particularly suitable for the production of passports or cards.

[0021] 10. (Third aspect of the invention): A valuable document or security document with a security element according to any one of paragraphs 1 to 7.

[0022] The value document can be, in particular, a banknote, a certificate, a voucher, a check, a high-value ticket, or high-value product packaging for brand protection. The security document can be, in particular, an identification card, such as an ID card, a data page for an ID document, a bank card, a credit card, a passport, or a driver's license.

[0023] Preferably, one of the following printing processes is used within the scope of the invention: i) Background printing (offset / Nyloprint) is used with particular advantage, optimally registered by printing in a super-simultaneous printing press with multiple printing units, ii) alternatively, inkjet processes, screen printing, and intaglio printing can be used. In screen printing or intaglio printing, a true color iris can be achieved, for example, via ink dosing systems or an iris in the ink fountain or screen. In the inkjet process, multi-color heads can be used, in which the corresponding color patterns are generated during the flight of the inkjet droplets. Particular advantages here are the customizability in the card sector and the tamper protection in a multi-layer system.

[0024] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0025] They show:

[0026] Fig. 1 is a schematic representation of a banknote with two security elements according to the invention,

[0027] Fig. 2 in (a) and (b) the appearance of the first security element of Fig. 1 under normal lighting and under UV light,

[0028] Fig. 3 in (a) and (b) the appearance of the second security element of Fig. 1 under normal lighting and under UV light,

[0029] Fig. 4 in (a) and (b) each schematically shows the layer structure of a security element according to the invention, Fig. 5 schematically illustrates a printing process advantageously used to produce a color iris,

[0030] Fig. 6 shows, by way of example, the color locations of the luminescence of some encapsulated luminescent pigments which can be used according to the invention in a CIE-LAB ab diagram,

[0031] Fig. 7 in (a) and (b) a security element according to a further embodiment of the invention, and

[0032] Fig. 8 the composition of a uniformly appearing fluorescent color tone by an alternating arrangement of opposing fluorescent color gradient lines.

[0033] The invention will now be explained using the example of securing banknotes. Figure 1 shows a schematic representation of a banknote 10 provided with two security elements 12, 14 according to the invention. Figures 2 and 3 show the appearance of the security element 12 and the security element 14, respectively, under normal and UV illumination in more detail.

[0034] Referring initially to Fig. 2, the first security element 12 represents a pure luminescence security feature that is not detectable under normal illumination 20 without UV excitation on the substrate of the banknote 10, as schematically illustrated in Fig. 2(a). When illuminated with UV light 22, however, the security element 12 exhibits a conspicuous luminescence emission, namely the luminescence-his schematically illustrated in Fig. 2(b), which shows an unscreened color gradient from cobalt blue luminescence emission at the left edge 12-L of the security element to white luminescence in the center 12-M and back again to cobalt blue luminescence emission at the right edge 12-R of the security element.

[0035] With reference to Fig. 3, the second security element 14 represents a combination security feature that already displays an image motif under normal illumination 20. As schematically illustrated in Fig. 3(a), the image motif visible under standard illumination is a body-color iris with an unscreened color gradient from white body color at the left edge 14-L of the security element to cobalt blue body color in the center 14-M and back again to white body color at the right edge 14-R of the security element. When illuminated with UV light 22, the security element 14 displays the same luminescence emission as the security element 12, namely the luminescence iris schematically illustrated in Fig. 3(b), which ranges from cobalt blue luminescence emission at the left edge 14-L to white luminescence in the center 14-M and back to cobalt blue luminescence emission at the right edge 14-R.When switching between normal illumination and UV illumination, the security element 14 therefore displays a color iris with identical color change but inverted brightness progression.

[0036] Figure 4 shows schematically the layer structure of a security element according to the invention with a combination security feature in cross section, wherein Fig. 4(a) shows a currently preferred structure and Fig. 4(b) shows a likewise advantageous, alternative structure.

[0037] With reference to Fig. 4(a), in a first step, a body color layer 32 with a body color iris is printed onto a substrate 30, for example, the banknote paper of a banknote, in the manner described in more detail below. Subsequently, in a second step, a luminescent color layer 34 with a luminescent iris is printed onto the body color layer 32. The luminescent color layer 34 itself is visually transparent or at least translucent and therefore essentially only appears upon UV excitation.

[0038] As shown in Fig. 4(b), the luminescent ink layer 34 can be printed not only above, but also below the body color layer 32. However, due to lower ink consumption, printing above the body color layer according to Fig. 4(a) is currently preferred. In all variants, the print motif is advantageously applied using a printing plate in Nyloprint, wet offset printing, or alternatively, using screen printing (water-based or UV-curing).

[0039] In both variants shown in Fig. 4, the intensity of the luminescence can be varied by modulating the line width used in banknote printing; this is also possible through screen area modulation. In addition to the preferred color gradient generation in one printing unit, it is also possible to create a luminescent color gradient effect by overprinting two differently coated ink units and different area coverage on the printing plate.

[0040] Figure 5 schematically illustrates a printing process advantageously used to produce a color iris. Two different printing inks A, B are applied to two inking rollers 40, 42, transferred to a mixing roller 44, and there rubbed together by means of so-called rubbing rollers acting on the surfaces of the rollers, so that the printing inks A, B are mixed with one another at their boundaries. The color gradient ABAB ... present on the mixing roller 44 is then transferred in a conventional manner, optionally via further ink transfer rollers, to a desired target substrate 46, for example the banknote paper of a banknote. The principle illustrated in Fig. 5 has long been used for solid colors A, B. However, such a color iris printing of mixed colors of fluorescent inks in one printing unit or inking unit was previously not possible or even impossible due to the different printing properties of the base fluorescent pigments.could only be used under the most difficult conditions for a small number of sheets due to the need for frequent cleaning and wiping of the printing plate and rollers.

[0041] Surprisingly, the inventors have now discovered that, with the help of special, coordinated luminescent pigments, a luminescent color gradient with luminescent colors A and B can also be printed using a principle as shown in Fig. 5. In the special luminescent pigments mentioned, the pigments for the emission colors red, green, and blue are coated with a uniform shell material and are therefore essentially equally printable regardless of the emission color. Furthermore, the encapsulated luminescent pigments also exhibit virtually identical stability and aging properties due to the uniform shell material. Therefore, even if the emission intensity of the pigments decreases over time, the reduction occurs concurrently for the different colored pigments, so that the mixed colors produced by the pigments, and thus also a color gradient, remain virtually unchanged.The decreasing emission intensity over time can be compensated, for example, by a higher intensity of UV excitation radiation.

[0042] With the encapsulated luminescent pigments mentioned, a wide range of colors can be selected. Figure 6 shows, by way of example, the color coordinates 62 of the luminescence of some encapsulated luminescent pigments usable according to the invention in a CIE-LAB ab diagram 60. The a-axis describes the green or red component of a color (negative values ​​represent green, positive values ​​represent red), while the b-axis indicates the blue or yellow component of a color (negative values ​​represent blue, positive values ​​represent yellow). In addition to the color coordinates 62 shown, essentially all color coordinates within the area 64 can be achieved by color mixing of the associated pigments.

[0043] With the encapsulated luminescent pigments, all mixed colors occurring in a luminescent iris can be generated directly and without any screening for the first time. Due to the virtually identical aging properties, the color impression of the luminescent iris remains unchanged over time, except for a possible decrease in brightness.

[0044] The brightness of a luminescent color is primarily determined by the illuminance of the UV lamp and the concentration of the encapsulated luminescent pigments in the printing ink. The concentration is also preferably selected to ensure good printability in the substrate. For example, the ink application rate can be approximately 1 g / m². 2 The substrate used advantageously has no or only very low intrinsic fluorescence.

[0045] With the encapsulated luminescent pigments, fluorescent color gradients starting from different fluorescent colors can be printed together in a single printing unit. Due to the consistent pigment coating, the print quality in security printing for large runs, such as those required in banknote printing, can be maintained in both Nyloprint and wet offset printing processes without leading to color drift or deterioration in print quality. In particular, with the encapsulated luminescent pigments, it is possible to set a specific color change per distance (hereinafter also referred to as AE / cm) for a color change along an x-axis (for example, along a horizontally positioned banknote) within a printing plate or inking unit, while maintaining the same printability. For a gentle color change, for example, printing is carried out with AE / cm of 5; however, for good distinguishability, AE / cm is advantageously between 10 and 70.

[0046] For example, two luminescent colors, such as a strong green and a strong red, can have an AE of 100 (a = -50 for green and a = +50 for red with the same b and L). If these two colors are separated in the color box by color wedges spaced 2 cm apart, for example, a color gradient with an AE / cm value of 50 is created.

[0047] In this way, long-term stable, luminescent color gradients can be created that, on the one hand, are stable in banknote production, meaning they can be printed over a large number of sheets without color change and without line or dot gain. On the other hand, their chemical-physical stability does not age, or only slightly and evenly, so that a printed luminescent color gradient remains recognizable even after exposure to external stimuli (such as heat, temperature, or light). Furthermore, the colors mixed with the encapsulated luminescent pigments exhibit significantly less color change than conventional color pigments used in security printing, even after exposure to external stimuli such as chemicals (e.g., acids) or sunlight. Surprisingly, it has also been shown that attractive "fluoroaddons" can be produced particularly easily with encapsulated luminescent pigments.This means that an additional print motif is created for an existing banknote design made up of body colors, visible in daylight, by applying at least one additional printing unit's ink fountains with at least one, technically optimal three, and a maximum of five different fluorescent inks. This additional print motif is also provided with at least one color iris by rubbing.

[0048] It is particularly advantageous if the body colours have a more pastel-like appearance in their overall appearance; this can be achieved either by applying a small amount of colour to the substrate, by using a high proportion of white in the body colours or by using a small area of ​​the body colours on the substrate.

[0049] From a printing technology perspective, printing fluorescent inks is challenging, as the consistent luminosity of the print motif can only be verified with additional effort (e.g., a UV calibration booth or fluorescence densiometer). The risk of back-contamination in other printing units is also a risk for printers. For this reason, the present invention particularly preferably separates body-color printing from UV-fluorescent printing. This is possible, for example, by printing the fluorescent ink first (as a UV-LED ink) in a super-simultaneous 12-color press, and then printing the conventionally oxidatively drying body colors on top after UV curing.

[0050] In another, equally advantageous variant, the body color is printed as a UV-LED ink on a super-simultaneous 12-color press, and after UV curing, the conventional oxidatively drying fluorescent ink is printed on top. The latter variant has the advantage of allowing the use of a lower concentration of the fluorescent ink, since both the UV excitation and the absorption of the underlying body color are lower than with the former.

[0051] Another possibility is to separate the printing steps of body ink and fluorescent ink in time, for example by passing them through the same machine twice after the first printing layer has dried or by printing on different printing units.

[0052] Figure 7 shows a security element 70 according to a further embodiment of the invention. The security element 70 represents a combination security feature that, under normal illumination 20, exhibits a body color iris ranging from red through orange and yellow to white from the left edge 70-L to the right edge 70-R, as schematically illustrated in Fig. 7(a). Upon illumination with UV light 22, the security element 70 exhibits a luminescence iris that ranges from cobalt-blue luminescence emission at the left edge 70-L to white luminescence in the center 70-M and back to cobalt-blue luminescence emission at the right edge 70-R, as shown in Fig. 7(b).With hybrid illumination, i.e., simultaneous illumination with daylight 20 and UV light 22, the interaction of the body and luminescent colors involved results in a complex color gradient with a color impression that ranges from magenta at the left edge 70-L through yellow in the center 70-M to light blue at the right edge 70-R of the security element, as schematically shown in Fig. 7(c) (the complex color gradients can only be inadequately reproduced in the black-and-white patent drawings). Within the scope of the invention, luminescent color gradients can also be generated in multiple printing units. As illustrated in Fig. 8, for example, two opposing fluorescent color gradients 80, 82 can be printed alternately as narrow lines. Lines 80, for example, show a fluorescent color gradient from red via orange and yellow to white, while lines 82 generate the reverse fluorescent color gradient from white via yellow and orange to red.At normal viewing distance (>25 cm), the lines 80, 82 cannot be resolved with the naked eye and for an observer, a mixed, orange fluorescent color impression 84 results. Only with optical aids, for example a magnifying glass or a microscope, can it be seen that the orange color tone of the surface 84 is actually created by two different opposing color gradients 80, 82.

[0053] By dividing the lines into two alternating lines, a stable fluorescent color gradient impression can be achieved in a smaller space. A motif design can be created by cutting out or thickening individual alternating lines. This also creates the macroscopic effect of the color gradient changing several times at short intervals, with significantly shorter intervals possible than with a single printing unit.

[0054] In the figures, only simple rectangular color gradients were shown for illustration purposes, but it is understood that a luminescent iris and / or a body color iris can be designed in particular in the form of motifs, patterns or characters, for example in the form of characters or guilloches.

Claims

Patent claims 1. Security element for securing security papers, value documents and other data carriers with a luminescent security feature, characterized in that the luminescent security feature contains a luminescent iris print with an unscreened color gradient between at least two different luminescent color tones.

2. Security element according to claim 1, characterized in that the luminescent security feature contains, in addition to the luminescent iris print, a body color print with an unscreened color gradient between at least two different body color tones.

3. Security element according to claim 2, characterized in that the luminescence iris print has a brightness gradient inverted to the body color print.

4. Security element according to claim 2 or 3, characterized in that the luminescent iris print has the same color gradient as the body color print, or that the luminescent iris print has a color gradient opposite or complementary to the color gradient of the body color print.

5. Security element according to at least one of claims 1 to 4, characterized in that the luminescent security feature comprises, in addition to the luminescent print, a printed with body colours motif, wherein the luminescent iris print is preferably printed with a pixel or line offset to the body color motif.

6. Security element according to at least one of claims 1 to 5, characterized in that the luminescent iris print is arranged above the body-color iris print or the body-color motif, wherein preferably the body-color iris print or the body-color motif is printed with color-neutral colors or light pastel colors.

7. Security element according to at least one of claims 1 to 5, characterized in that the luminescent iris print is arranged below the body-color iris print or the body-color motif.

8. A method for producing a security element according to one of claims 1 to 7, wherein a luminescent iris print with an unscreened color gradient between at least two different luminescent color tones is applied to a substrate, wherein the luminescent iris print is preferably applied in a single printing unit.

9. The method according to claim 8, characterized in that a body color iris print with an unscreened color gradient between at least two different body color tones is applied, in particular printed, to the substrate above or below the luminescent iris print and / or a body color motif is applied, in particular printed, to the substrate above or below the luminescent iris print.

10. A value document or security document with a security element according to one of claims 1 to 7.

Images