Further exemplary embodiments and advantages of the present invention are explained below by reference to the drawings, in which a depiction to scale and proportion was omitted in order to improve their clarity.
Shown are:
The invention will now be explained using a banknote as an example.
Both the front-side numbering 13 and the reverse-side numbering 15 are introduced from the front 12 of the banknote by the action of a laser beam, so that the engineering outlay for the two-sided numbering is kept low. In the example shown, the front-side numbering 13 is formed by a blackened area in the security paper of the banknote 10. The reverse-side numbering 15 is formed by a demetallized area in an otherwise metallic-appearing patch 16, for example a transfer element or a label having a diffraction optical structure, and in this way, rich in contrast, stands out from its metallic environment.
The structure and the manufacture of the banknote 10 will now be described more precisely with reference to
For labeling, the banknote 10 is impinged on from the front 12 by the radiation 26, 28 of an infrared laser, for example a pulsed or continuous wave Nd:YAG laser. In the recording region 22, the laser radiation 26 is absorbed by the admixed infrared absorber and causes a local blackening 30 of the substrate. Through suitable beam control, for example a computer-controlled positioning of the laser beam, the blackening 30 can be easily produced in the form of the desired serial number 13.
Since the paper substrate 20 is substantially transparent to the radiation of the Nd:YAG laser, at least at low laser intensity, the incident laser radiation 28 passes through (reference number 32) the substrate 20 in the area of the recording layer 24 and is absorbed only on the reverse 14 of the banknote in the recording layer 24. The metal layer of the hologram patch 16 is locally destroyed by the laser radiation, or in any case so changed in its optical properties that a local color or contrast shift 34 is created for the viewer. In order to obtain a serial number 15 that is right reading from the reverse side, the serial number is inscribed from the front side laterally inverted, which can be done easily with computer-based beam control.
In the further exemplary embodiment in
It is understood that, for this purpose, the recording layer 50 is formed so that only part of the laser radiation is absorbed in the recording layer 50 and part passes through the substrate to the reverse-side recording layer 44. Naturally, the areas of the recording layers 44, 50 outside of the overlapping area 52 can be provided with additional identifiers that are applied separately for the front and reverse. Because of the register-based configuration of the identifiers 54, an attempted imitation by inscribing the banknote from the reverse side can easily be recognized as a counterfeit.
In the variation of a banknote 60 shown in
While in the exemplary embodiments described so far, the reverse-side labeling always occurred with the aid of a recording layer, the reverse-side identifier can also be produced in a recording area within the paper substrate, as explained with reference to
In the exemplary embodiment in
Advantageously, the letterpress numbering is not switched mechanically, but rather electrically from one numeral to the next. In this way, the correspondence between the front-side numbering 92 and the reverse-side numbering 94 can be ensured by addressing through a common computing unit. In place of the letterpress numbering, the front-side numbering 92 can also be applied with an inkjet method.
In other embodiments of the present invention, of which a first exemplary embodiment is depicted in
The height of the tangible marking above the surface can be varied within a broad scope through the choice of laser parameters, the substrate material and the relative speed of the laser beam and the banknote during inscription. Typically, a height between 30 μm and about 100 μm is chosen. In addition to producing a tangible substrate protrusion, the laser radiation can also produce a color shift, especially a blackening of the substrate, as indicated by hatching for the marking 114. Whether and to what extent a blackening is produced depends, in addition to the laser parameters, primarily on the composition of the substrate material.
In the exemplary embodiment, the first tangible marking 112 was produced with low laser intensity, so that no blackening of the substrate occurred there. In the area of the reverse-side recording layer 116, a higher laser intensity was used, so that a blackened substrate protrusion 114 is created on the front of the banknote, and a local color and/or contrast change 118 in the recording layer 116 on the reverse. The color and/or contrast change is preferably a blackening of the recording layer. Alternatively, the area 118 of the recording layer 116 can also be lightened by the laser action.
A combination of a tangible substrate protrusion 122 with a smooth recording layer 124 on the front of the substrate, as shown for banknote 120 in
An additional security aspect results when the substrate of the value document is processed such that, when inscribing a reverse-side identifier through the substrate, a hidden image of the inscribed identifier is created on the front and is perceptible only with special aids or under specific viewing conditions. In this way, a counterfeit can be detected through an authenticity test on a second, more complex testing level.
By applying an additional detection layer 142 on the front of the substrate, as illustrated in
The exemplary embodiment in
To manufacture such a see-through register 152, the reverse of the banknote is first provided with an absorbing and opaque coating layer 154, for example a metal or opaque printing layer. The opaque coating layer 154 is partially removed or transformed into a transparent modification by irradiating the banknote from the front side, so that only sub-regions 156 of the coating layer 154 remain on the reverse.
Then the front of the banknote is impinged on by high-intensity laser radiation, so that visible, if appropriate also tangible, identifier areas 158 are produced on the front. The design of the identifier areas 156 and 158 is coordinated so that, together, they result in the desired identifier when looked through, in the exemplary embodiment the numeral “1”. Since both identifier areas 156, 158 are produced with the same laser beam, the register is perfect and thus has a high security value. Moreover, especially for tangible identifiers, it is clearly perceptible that the identifier was lasered.
An infrared laser beam 206 is deflected via two movable mirrors 208, one of the mirrors producing the deflection in the x-direction, and the other mirror the deflection in the y-direction. A plane-field lens 210 focuses the laser beam 206 on the substrate 202, where it produces on the front and/or reverse, in the manner described above, an identifier, here a serial number 204. The substrate 202 moves during the labeling process with a certain speed v. This speed is detected by sensors and transmitted to a computer to control the movement of the mirrors 208 such that the substrate speed v is compensated during inscribing. This labeling method can thus be employed particularly advantageously for the non-contact labeling of value documents that are processed at high speeds, as usual in printing plants.
The substrate 202 can also be marked in another way, for example by means of a matrix of punctiformly emerging laser beams or by means of beams with larger cross-section that are partially covered by a stencil. Such stencils can be automatically variably implemented. If it is not possible or not desired to guide the radiation in line with the substrate speed, it is also possible to label moving substrates by choosing a short exposure time. Beam control through polygon mirrors is also possible.
Depending on the substrate used, CO2 lasers, Nd:YAG lasers or other laser types in the wavelength range from UV to far infrared may be used as the radiation source, the lasers also often working advantageously with frequency doubling or tripling. Preferably, however, laser sources in the near infrared are employed, since this wavelength range is well suited to the absorption properties of the substrates and printing inks used. Depending on the application, the spot size of the laser radiation can be varied from a few micrometers to a few millimeters, for example by changing the distance between the plane-field lens 210 and the substrate 202.
The continuous output of the laser coder used typically lies between a few watts and a few hundred watts. Nd:YAG lasers can be operated with laser diodes for low total output with smaller construction dimensions and high beam quality, or with pump lamps for high outputs. In order to not reduce the speeds of an industrial value document production line, the labelings are advantageously executed with very fast-moving galvanometers, which can guide the beam across the substrate at more than 1000 mm/s, preferably at up to 4000 mm/s. At these speeds, only a small proportion of energy is deposited in the substrate or the coating for each section, so that, advantageously, lamp-pumped Nd:YAG lasers with an output of about 100 watts are employed.
By varying the inscription parameters, such as the laser output, exposure time, spot size, inscription speed, working mode of the laser etc., the labeling results can be varied within a broad scope. For example, the height of the tangible markings produced by the laser can be varied accordingly. Preferably, the tangible markings have a height from 30 to 100 μm. Likewise, the composition of the paper substrate is advantageously adapted to the laser radiation or the laser output used.
The identifiers are undertaken for example with a Nd:YAG laser having a fundamental wavelength of 1064 nm and exhibiting an average output of 26 W and a modulation frequency of 8 kHz. The diameter of the laser beam on the substrate (spot size) is about 100 μm and the traverse speeds of the laser beam across the substrate 250 to 4000 mm/s. The typical height of a tangible identifier thus produced lies between 30 and 80 μm. In individual cases, i.e. especially at low traverse speeds, considerably higher values can also be achieved, for example a height of more than 100 μm at 250 mm/s. The width of the marks normally lies between 0.2 and 0.6 mm.
For a calendered cotton-vellum paper with a density of 90 g/m2, at an inscription speed of 330 mm/s for example, tangible markings result having an average relief height of 70 μm and a line width of about 500 μm. At an inscription speed of 675 mm/s, the relief height achievable at the same line width is merely 40 μm. In a paper composed of a mixture of cotton and plastic fibers having a plastic fiber share of 12.5 weight % and an area weight of 90 g/m2 (so-called Synthek paper), the measurements of the marking produced at 250 mm/s are 65 μm average height and approximately 0.5 mm average width. When the traverse speed was increased to 1000 mm/s, the measurements were 35 μm average height and 0.3 mm average width.
Number | Date | Country | Kind |
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10 2004 022 079.4 | May 2004 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP05/04393 | 4/25/2005 | WO | 00 | 11/12/2007 |