DE102021004849A1 - Process for producing a substrate with a luminescent element - Google Patents

Abstract

The invention relates to a method for producing a substrate (2), in particular a banknote (2), with a luminescent element (6) designed to emit luminescent radiation, the substrate (2) having a substrate surface (5) and the following Steps are carried out: a) providing (S1) data for a print motif (4) which extends over the substrate surface (5) and is to be reproduced on the substrate (2) by an imprint,b) providing (S2) data for the luminescent element (6) which extends over an element area (7) which is smaller than the substrate area (5) and which is also to be arranged on the substrate (2),c) generating (S3) a map of the substrate area (5 ), which reproduces a local absorption of the luminescence radiation by the print motif (4) andd) determining, on the basis of the map (4), at least one position of the luminescence element (6) within the substrate surface (5), in which in the element surface (7) an expected intensity of the luminescent radiation is optimized.

Description

The invention relates to a method for producing a substrate, in particular a banknote or the like, with a luminescent element.

For substrates to be secured against counterfeiting, in particular banknotes, etc., luminescence elements are known as a supplement to printed motifs, which can be detected with a luminescence sensor of a banknote processing device under certain lighting conditions. In many cases, luminescence is used in the form of phosphorescence, but luminescence in the form of fluorescence is also possible. An example of such a luminescent element as a security feature can be found in WO 2014/184738 A1 .

For the use of a luminescent element, a method for producing a substrate, in particular a bank note or the like, is used, the substrate having a substrate surface. For banknotes, this is the face of the banknote. For this substrate area, data for a print motif is generated, i.e. provided, which is to be reproduced by an imprint (e.g. by offset printing) on the substrate. The print motif usually has several distributed, individual motif components. It extends over the substrate surface, since the print motif covers the substrate surface, e.g. the top surface of a banknote. Data is also provided for a luminescence element to be arranged on the substrate surface. It has an element area smaller than the substrate area. It is also designed to be read out with a luminescence sensor of a predetermined type. This type is usually characterized in that the luminescence sensor has a predetermined subdivision into a number of pixels, in particular a spatial resolution, with a pixel size. A pixel can also be divided into sub-pixels, with the pixel size then referring to the respective sub-pixel.

It has now been found that when checking the substrate, e.g.

The invention is therefore based on the object of specifying a method for producing a substrate with a luminescence element, so that the reliability of reading the luminescence element is improved independently of the specific design of the substrate, e.g. the denomination of a bank note.

The invention is defined in the independent claims. The dependent claims relate to preferred developments.

In the method mentioned at the outset, it is therefore provided that a map of the substrate area is generated, which shows a local absorption of the luminescence radiation by the print motif. In this case, the degree of absorption can preferably be used and/or the intensity and/or color of the print motif and/or reflectance can be used. At least one position for the luminescence element within the substrate area is now determined on the basis of this map, with an expected intensity of the luminescence intensity of the luminescence element being optimized at this position. This intensity represents a contrast.

The observation based on the map makes it surprisingly easy to find an optimized position of the luminescent element, i.e. an optimized arrangement of the element area within the substrate area, which is affected as little as possible by absorption due to superimposed motif components of the print motif. In this way, the readability of the luminescent element is improved. The selection of the position of the luminescence element according to the invention thus achieves good readability of the luminescence element and thus ultimately good protection of the substrate against forgery, regardless of the specific design of the print motif. In particular, it is avoided that a substrate secured with the luminescence element is erroneously classified as a falsification because the luminescence element cannot be correctly identified due to absorption by the motif components.

As will be explained below, this position determination also allows the amount of luminescence dye required to generate the luminescence properties of the luminescence element to be minimized without impairing the detectability of the luminescence element by the luminescence sensor of a predetermined type.

Furthermore, there is the advantage that the printed or applied luminescence motif remains recognizable or legible even with a visual check, for example with a UV hand lamp. If the motif consists, for example, of negative numbers, letters or a coat of arms, the motif can be severely impaired in its perceptibility by partial brightness differences due to partial absorption of the emission radiation by a background print.

In a further development, which has turned out to be particularly simple and economical in terms of computation, the substrate surface is first broken down into surface elements with the pixel size in order to generate the map. The absorption is then averaged for each surface element. In this way, a map is obtained which is made up of surface elements with the pixel size, each surface element having an indication of the absorption of the luminescence radiation. For example, each surface element indicates a degree of absorption for the luminescence radiation.

Provision is preferably made for the substrate surface to be broken down into surface elements with x-times or x-th of a pixel size of the sensor, with x preferably being an integer. The finer the pixels of the absorption map are, the more exactly the prediction, especially the luminescence intensity, corresponds to the subsequent measurement.

For example, a pixel resolution of the card that is at least 3 times higher than the pixel resolution of the sensor is particularly advantageous in order to also take into account possible process tolerances and deviations, such as manufacturing tolerances, such as deviations of the printed phosphor block or luminescent element by e.g. 0.5 mm from the expected position of the non luminescent motif print, or the web transport of the bank note along a sensor, e.g. a tolerance of 0.5 mm.

While print data is processed with 8000 dpi, for example, typical luminescence sensors have a resolution of around 10 to 50 dpi, for example, since it is only checked whether the phosphor block is in the correct position.

The optimization can preferably be carried out by evaluating as a criterion whether the intensity or the contrast exceeds a predetermined threshold value.

When determining the intensity or contrast, a loss of luminescence intensity can be calculated in particular, which (e.g. in each surface element) due to absorption, in particular luminescence, due to print motifs, in particular visually visible print motifs, UV radiation-absorbing or scattering or covering motifs. In a particularly simple type of calculation, the degree of absorption of the individual components of the print motif is considered and used as a measure of the luminescence intensity loss.

A particularly simple optimization is obtained from a computational point of view if areas are first defined in the map by means of a threshold value analysis, in which a luminescence intensity loss, e.g. specified as an absorptivity, exceeds a threshold value.

In many embodiments, the luminescent elements are rectangular in order to provide a luminescent surface, for example in the form of a 1D or 2D barcode.

When specifying a position, it is preferred to also vary an aspect ratio of the element area and/or a rotation of the element area for such a rectangular element area.

Particularly preferably, not only a single possible position is determined on the basis of the map, but several possible positions for the luminescence element are specified at which it can be read with a minimum contrast, i.e. a minimum intensity of the luminescence radiation can be expected. For this purpose, it is preferred that a map is generated that can be superimposed on the print motif and that indicates possible locations and/or dimensions for the arrangement of the luminescence element.

To optimize the possible position or to find the possible positions of the luminescence element, it is further preferred to calculate an area integral, with a luminescence intensity being integrated over the element area, which remains after absorption by the print motif. Here too, in a particularly simple calculation method, only the degree of absorption of the corresponding print motif can be integrated within the element area. This calculation is also carried out in particular on the basis of the simplified print motif.

The optimized position of the luminescent element makes it possible to apply luminescent dye relatively sparingly, in particular in a thin layer, since the impairment caused by the print motif is reduced or completely avoided due to the position optimization. An equally possible possibility for optimization results from the fact that parts of the element area are identified in which the expected intensity drops below a predetermined minimum value due to absorption by the print motif. Recesses are provided in these parts, in which no luminescent dye will be applied. In this way, the need for luminescent dye is further reduced.

Provision is preferably made for the luminescent element to luminesce in a plurality of color channels and for the method to be carried out individually for each of the color channels. For example, the luminescence element can be in the form of a multicolor fluorescent color image or a combination of fluorescent image and phosphorescent image.

Furthermore, the luminescence element can also consist of a substance mixture of individual substances that can be excited differently, so that different emission colors or decay times result depending on the excitation wavelength UVA-UVC and/or NIR.

The luminescence element itself can also consist of at least partially overlapping individual color layers and/or application layers with the same or different physical properties such as emission color and/or decay times.

In an optional embodiment, the luminescence feature can also have a body color that is visually recognizable without excitation with UV or NIR radiation.

It may also be the case that different areas on the banknote are recommended for different luminescent colors. For example, a different range may be recommended for a red fluorescent color than for a yellowish fluorescent color.

Furthermore, it is preferably provided that the position of the luminescence element is determined as a function of an opacity value of the luminescence color, in particular the phosphorescence color. The opacity value is preferably known and can be provided by a database, for example. The opacity value is preferably determined or specified under normal light, ie without UV excitation.

The method according to the invention can be carried out particularly preferably with a software program which contains program code or instructions for execution on a computer, the program code being designed to carry out a method of the type explained when it is executed. Providing the data for the print motif then corresponds to entering a corresponding design for the print motif into the program.

The invention creates an automated decision for the optimal position of the luminescence element for the production. Too low a signal intensity of the printed luminescence element on the predefined print motif, which acts as a background for the luminescence, is avoided. An automated evaluation of the optimal position of the luminescence element with the aim of the strongest luminescence signal is achieved on the basis of the map, which in this sense represents a simulation. It can be generated, for example, using the digital data from the prepress stage and allows the area in which the luminescence element may/should be positioned to be delimited. The optimized position is found, for example, by processing the process steps, e.g. using an automated software package for simulating an overprint with luminescent dyes, preferably as a plug-in in existing preliminary software. In addition to a digital proof of the luminescence element for risk assessment with regard to sufficient intensity of the luminescence, in particular phosphorescence, minimal ink consumption can also be achieved.

If the luminescent feature is not applied in the same process step as the visually visible underprint or overprint motif, experience has shown that there will be register deviations of the individual motifs, for example due to contact and print register tolerances and/or changes in substrate dimensions due to application processes such as intaglio printing or moisture differences with fiber-based substrates. These can be a few mm. Therefore, this is optionally taken into account when finding the optimal position of the luminescence motif.

With the help of the method, it is also possible to evaluate the luminescence image impression as a screen proof, taking into account the influence of underprinted or overprinted colors, for example to recognize whether the image motif of the luminescence image is too severely restricted in terms of its recognizability by the underprinted or overprinted colors.

Optionally, for better visualization, the signal intensity related to the image motif can also be displayed on the screen in false colors, e.g. red for high intensity, blue for low intensity.

Furthermore, you can make a prediction of the signal intensity for different stored sensors. This makes it possible to check whether the signal quality is also sufficient for the sensors at the customer's if the customer has other sensors which, for example, check the phosphorescence after a different time or time interval.

Furthermore, one can optionally calculate the color management and/or color strength with which the color for the luminescence feature is to be printed in order to achieve reliable detection on the sensor. For this purpose, a minimum signal for a predetermined test device, e.g. a hand-held luminescence test device, is calculated for a full tone test field, e.g. outside the print motif, e.g. in the area of the sheet edge of the substrate, which is used by the printer to specify the color control.

• 1 eine Schemadarstellung einer Banknote,
• 2 ein Flussdiagramm, das Schritte in einem Verfahren zur Herstellung der Banknote der 1 zeigt,
• 3 verschiedene Ansichten der Banknote während des Herstellverfahrens,
• 4 eine Darstellung ähnlich der 3 für eine abgewandelte Ausführungsform des Herstellverfahrens,
• 5 eine Darstellung ähnlich der 4 im Falle eines mehrfarbigen Lumineszenzelements,
• 6 eine Weiterbildung zur Reduktion eines Bedarfs an Lumineszenzfarbstoff,
• 7 eine Erläuterung zur Ausführungsform der 6 hinsichtlich einer Farbstoffeinsparung und
• 8 eine Darstellung zur Erläuterung der Ausbildung des Lumineszenzelements als zweidimensionaler Digitalcode.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the accompanying drawings, which also disclose features that are essential to the invention. These embodiments are provided for illustration only and are not to be construed as limiting. For example, a description of an embodiment having a plurality of elements or components should not be construed as implying that all of those elements or components are necessary for implementation. Rather, other embodiments may include alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of different exemplary embodiments can be combined with one another unless otherwise stated. Modifications and variations that are described for one of the embodiments can also be applicable to other embodiments. To avoid repetition, the same or corresponding elements in different figures are denoted by the same reference symbols and are not explained more than once. In the figures show:

• 1 a schematic representation of a banknote,
• 2 a flowchart showing steps in a method of making the banknote of 1 shows,
• 3 different views of the banknote during the manufacturing process,
• 4 a representation similar to that 3 for a modified embodiment of the manufacturing process,
• 5 a representation similar to that 4 in the case of a multicolor luminescent element,
• 6 a further development for reducing the need for luminescent dyes,
• 7 an explanation of the embodiment of the 6 in terms of dye savings and
• 8th a representation to explain the formation of the luminescent element as a two-dimensional digital code.

1 shows a schematic plan view of one side of a banknote 2. It has a printed motif 4 that covers the front surface 5 of the banknote 2. It has several motif elements 4a, 4b, 4c and 4d, which in the present example can contain a denomination, an image element, a frame and a text, purely as an example. A phosphorescence block 6 is also arranged on the front surface 5, which serves as an example for a luminescence element in this description. It covers a block area 7 and cannot be seen with the naked eye. Rather, it is read out with a luminescence sensor and, if necessary, suitably illuminated for this purpose with excitation radiation. Such phosphorescence blocks are known to those skilled in the art. They represent a so-called machine-readable security feature.

To produce the banknote 2, banknote paper is suitably printed on the front side 5. In this case, the print motif 4 is applied, for example, using intaglio printing, and the phosphorescence block 6 is produced by applying suitable phosphorescence inks.

It is therefore also part of the production of the bank note 2 to define the position of the phosphorescence block 6 on the front face 5 of the bank note 2 . For this part of the manufacturing process, the in 2 procedures shown. In it, data for the print motif 4 are first provided in a step S1. In a step S2, the data for the phosphorescence block 6 is provided, for example the size and possibly also specific dimensions of the area that is to be printed with the phosphor dye or the phosphorescence ink. A map of the front face 5 is created in a step S3. This map indicates the local absorption for the phosphorescence radiation due to the print motif 4 . The print motif 4 absorbs the phosphorescence radiation locally differently because of its individual motif components.

In particular, the UV radiation is partially absorbed and/or partially reflected differently on the individual layers, including the deeper layers. The emission of the phosphorescent color is also partially reflected or absorbed by underlying layers.

Since the phosphorescence color is emitted in all spatial directions, in particular perpendicular to the main surface of the banknote, the proportion of phosphorescence color whose emission light radiates in the direction of the interior of the banknote has a significant signal loss for the observer of the banknote. The absorption intensity and/or reflection intensity depends in particular on the color of the underlying background layer and on its absorption spectrum in the range of the emission wavelength of the phosphorescence color.

A sensor with a strong UV light source can also be used for detection, which can also completely radiate through or penetrate the substrate.

Excitation from the back of the substrate and detection of the phosphorescence block 6 from the front of the substrate or the front surface 5 is also possible.

The absorption map thus makes it possible to find possible positions and/or sizes for the phosphorescence block 6 at which impairment by the print motif 4 is not disruptive, for example because absorption of phosphorescence radiation by the print motif 4 remains below a specific threshold value. In the representation of 1 this is given by the outline of the block surface 7 shown in dashed lines.

The phosphorescence block 6 is determined for checking the authenticity of the banknote 2 with a phosphorescence detector or phosphorescence sensor, which is pixellated. It is therefore preferred, in step S3, to generate the map with a resolution that corresponds to the pixel size of the phosphorescence sensor for which the phosphorescence block 6 is designed. This design is in 3 shown. It shows banknote 2 in the top left. In the middle of the left 3 an intermediate method step is shown, in which the front surface 5 of the banknote 2 is divided into surface elements 8, which are ultimately the images of the pixels of a phosphorescence sensor that is used to check the authenticity of the banknote 2.

The front face 5 of the banknote 2 is thus subdivided into surface elements 8 which indicate, for example, the gray value or the color value which is averaged over the respective surface element 8 at the corresponding point on the front surface 5 . The parameters mentioned are examples of specifying the local variation in absorption for the phosphorescence radiation. In the lower representation of the left column of the 3 shows the result of a next intermediate step, which subjects the front side of the map 9, which is divided into surface elements 8, to a threshold value analysis. It is checked for each surface element 8 whether the absorption (or the parameter indicating the absorption, which is shown as a function of location on the map 9) is above or below a threshold value. This results in low-absorbing planar elements 10 and high-absorbing planar elements 11. The low-absorbing planar elements 10 are shown in the bottom left in the diagram 3 drawn white, the highly absorbent surface elements 11 black. Based on this black-and-white map, a surface element that corresponds to the element surface 6 in size and outline is then moved over the map 9 modified in this way in a scanning step 12 . The displacement takes place in an increment which corresponds to the surface elements 8 . The integrated absorption is determined using map 9 for each displacement position. In the embodiment described, it is the threshold-filtered card with exclusively high-absorption surface elements 10 and low-absorption surface elements 11. Of course, this scanning process can also be carried out before the threshold-value filtering of the card 9. As a result of the scanning process 12, which is shown in the lower left of the illustration 2 is symbolized by an arrow, there are areas 14 in which the element surface would experience an absorption that is above a threshold value, and areas 15 in which the Absorption is below a threshold. In order to determine the areas 14, 15, it is checked for the respective displacement position in the scanning step 12 whether the absorption integrated over the element surface in the respective scanning position is above or below a threshold value. If it is below the threshold value, the area covered by the element area in the respective scan position is assigned to area 15, so that area 15 indicates a total of possible positions for the element area. In scan positions in which the integration of the absorption over the element area is above a threshold value, it applies that the scan position and thus the area covered by the element area is assigned to the region 14 . In this way, a map 16 is obtained which, with the area 15, identifies possible positions for the element area.

The illustration in the middle of the right column 3 shows the front face 5 of the banknote 2 with a position “a” of the element face 7 selected within the permissible range 15. The illustration at the bottom right in 3 shows that the area 15 can also be used in that several, for example different, phosphorescence blocks 6 can be used in positions "a", "b" and "c", i.e. different block areas 7a, 7b and 7c in the permissible area 15 can be arranged.

The subdivision of the map 9 into surface elements 8, corresponding to the pixels of the phosphorescence sensor to be used, is optional. It is equally possible to adapt the pixelation to the specific design of the phosphorescence sensor, i.e. whether it is a single-pixel sensor, in relation to which the banknote 2 is moved during the verification process, a matrix sensor, a line sensor, etc.

4 shows a modified embodiment in the illustrations 4A , 4B and 4C the left column of 3 is equivalent to. The difference from the embodiment of 3 lies in the evaluation of the threshold-filtered map 9 according to 4C , which is now not used by a scanning step 12, in which the block area 7 is shifted over the thresholded map, but directly by thresholding in the pixelated map according to FIG 4C (or alternatively also in the map according to 4B ) is applied. In this way, a mapping 16 with permissible areas 15 and impermissible areas 14 is also obtained. However, these areas do not necessarily have the same outline shape as the block area 7. This was the result of the scanning step 12 in the illustration at the top right 3 . Rather, the permissible ranges 15 are now determined solely by the degree of absorption of the print motif 4 on the front surface 5 .

At this point it should be noted that, depending on the effect of the phosphorescence block 6, not only the print motif 4 on the front surface 5 can be taken into account, but also a print motif that is located on the rear surface. This is the case when the phosphorescence block 6 is detected in a transmitted light evaluation. Then the absorption of both the print motif 4 on the front surface 5 and the absorption of a print motif on the back surface of the banknote 2 must be considered. This was done in the evaluation of 4d , which can be seen from the fact that the impermissible areas 14, which are colored black, would not necessarily have been expected at first glance when looking at the front surface 5.

The evaluation of the absorption without a scanning step 12 also has the advantage that the outline and orientation of the phosphorescence block 6 can now be adapted to the available areas of the permissible area 15 . This is advantageous because often only a specific area is required for a phosphorescence block 6, but not a specific outline, for example a specific aspect ratio for a rectangle. 4E shows the result, in which the outline 7 of the phosphorescence block 6, for which only one area was specified, was adjusted in its aspect ratio in such a way that it covers a section that is available in the permissible range 15.

5 shows an image similar to that 4 , but for the case that the bank note is to receive 2 phosphorescence blocks 6 with different colors. The procedure according to 3 or 4 is thus carried out in, for example, three color channels R, G, B, which correspond, for example, to the colors red, green and blue. These color channels correspond to the color channels of the multicolor phosphorescent element. This results in three different possible areas for corresponding phosphorescence blocks 6R, 6G and 6B according to the color channels.

6 shows a further development in which, starting from the mapping 16, not only the aspect ratio of the phosphorescence block 6 is adjusted, but also gaps are provided, located in areas where insufficient phosphorescence would be perceptible due to the print motif.

7 shows the corresponding procedure using the example of the phosphorescence block 6, which first contains a hole-like recess 18, which is located in an area in which the printing element has very strong absorption and also an optional further recess 19 in an area in which the print motif has a slightly weaker but possibly still disturbing absorption. The area integral intensity decreases from left to right. At the same time, ink consumption also decreases, since areas that do not (recess 18) or contribute only slightly (recess 19) to the phosphorescence do not have to be printed.

8th shows by way of example that the phosphorescence block 6 can also be structured in itself, for example in the form of a QR code 20 or another 1D or 2D barcode.

The luminescent color includes color components that exhibit phosphorescence and/or fluorescence properties; these can be organic as well as inorganic coloring substances (dyes, pigments, ...). The ink, which usually luminesces under UV light (excitation, e.g. in the range of 240-380 nm), can be applied using any printing process, e.g. as a UV-curing ink layer (radical or cationic curing) or conventionally drying or oxidatively drying or physically (sticking away) etc . Fix on the substrate or other print layer. Alternatively, the luminescence layer can also be located on or in a film element, which is applied to the print carrier, for example a banknote, for example using a hot or cold embossing process. The luminescence can be detected using a sensor with a brightness signal compared to an unprinted reference.

An "up converter", i.e. a color that is excited in the IR range and then emits in the visible-visible range, can also be understood as a luminescent color. Various paint systems in different shades are available on the market from various manufacturers.

The use of a database that contains the signal intensity of a defined sensor for a luminescent color used in relation to an underlying surface, e.g. a phosphorescent printing color on a printed motif of the banknote, is preferred for the method.

The print motif is characterized in that its coloring correlates with at least one printed body color or a mixture thereof with other body colors of a color manufacturer and their area coverage on the substrate and with a typical ink consumption of 0.1 to 5 g/m2, preferably 0.5 up to 2.0 g/m2, is printed in the full tone field.

In the case of the digital proof, a virtual "digital twin" of a real printed banknote proof print, the real printed product is used to check the luminescence intensity based on at least one substrate color and a color profile specialized with available printing inks.

The signal intensities to be expected under UV excitation are determined by summing up different signal intensities/signal integrals of the different body colors that are printed below or above the luminescent ink or are printed in mixtures with the luminescent ink.

In embodiments, a sensor-specific look-up table is created for each body color that is used as background color and for each visually transparent and/or invisibly luminescent color, as well as for each body color with an integrated specific luminescence color. This look-up table contains at least one piece of information about the hue, which describes the body color, and about a sensor signal under UV light. In general, an extension to any fluorescent color is possible in addition to phosphorescence colors. For this, however, the interaction with a corresponding background hue must be translated in the form of an adapted look-up table for each fluorescence hue. The respective look-up table indicates the reduction in intensity of the fluorescence when combined with different background colors - i.e. a scalar numerical value for each combination. This is possible, for example, in relation to a given fluorescence sensor with a given detector characteristic.

So far, quality control has been carried out on the basis of tests, for example with a stationary luminescence spectrometer; to do this, the intensity signal is read at a specified wavelength. Quality control with a mobile measuring device for luminescent colors can also be used, where different "RGB filters" are used when measuring the fluorescence intensity and thus specific values are generated for the respective filters.

Embodiments enable the achievable signal intensity to be predicted and thus a guarantee for good machine readability, high process reliability and quality control during printing and sufficient visual perceptibility. The method can be used to find an optimal arrangement field for the phosphorescence element in an existing print design, which allows good testing with a measuring device, since the design-related attenuations are minimal or at least very homogeneous in the arrangement field.

• Vorhersage-Variante 1: Die Vorhersage bezieht sich auf die Leuchtkraftstärke einer im separaten Druck aufgebrachten Lumineszenzfarbe im gegeben designten Druckbereich; diese kann wahlweise auf eine Gesamthelligkeit abstellen oder auch getrennt betrachtet auf einzelne Kanäle eines RGB-Sensors oder eines Schwarzweißsensors mit vorgeschaltem Rotfilter/Grünfilter und Blaufilter als RGB-Signalstärke.
• Vorhersage-Variante 2: Die Vorhersage bezieht sich auf die Leuchtkraftstärke im gegebenen Druckdesign, wobei entweder nur eine reine Lumineszenzfarbe (basierend auf einen Lumineszenzfarbstoff) oder eine Mischung aus mindestens zwei Lumineszenzfarben ohne visuell sichtbare Körperfarbe vorliegt.
• Vorhersage-Variante 3: Die Vorhersage bezieht sich auf ein Druckdesign, bei dem die Lumineszenzfarbe in eine visuell sichtbare Körperfarbe des Druckdesigns eingemischt wird, z.B. eine visuell grüne Farbe enthält zusätzlich eine unter UV-Licht gelbliche fluoreszierende Farbe. Damit die optimale Position für diese Lumineszenzfarbe von der Software errechnet werden kann, wird ein Eintrag in einer Datenbank verwendet, der die Signalstärke der gewählten Mischung aus Körperfarbe und Lumineszenzfarbe anhand eines z.B. 1 g/m2 Andrucks bei einem festgelegten Sensor und festgelegter Anregung enthält oder der die Signalstärke über ein Rechenmodell beruhend auf, z.B. Kubelka-Munk-Theorie mit infinitesimale kleinen Schichten von der gewählten Fluoreszenzfarbe und der gewählten Körperfarbe berechnet. Als Modell kann z.B. ein System aus alternierenden fünf Schichten einer Fluoreszenzfarbe und fünf Schichten einer Köperfarbe als gute Näherung für ein reales System betrachtet werden. Dabei wird in jeder der Schichten die Lichtabsorption der angeregten Lumineszenzfarbe durch die Körperfarbe ermittelt, als auch die in tieferen Schichten geringer durchdringende UV-Dosis der Anregungslampe aufgrund der UV-Absorption der darüber liegenden Schichten berücksichtigt.
• Vorhersage-Variante 4: Sollen mehrere verschiedenfarbige Lumineszenzfarben auf einem farbigen Wertpapierdesign integriert werden und für den jeweiligen Lumineszenzfarbstoff/-pigment eine ausreichend gute Signalintensität bei UV-Beleuchtung erzielt werden, muss das Druckdesign in die entsprechenden Farbräume aufgeteilt werden; exemplarisch ist dies in 5 für drei Lumineszenzfarben (Rot, Grün, Blau) durchgeführt. Auch für beliebige Mischfarben ist dies prinzipiell möglich, bedeutet aber im Detail, dass z.B. jeweils eine Look-Up-Tabelle in der Datenbank zuvor auf Basis von eingelesenen realen Messwerten erstellt oder berechnet werden muss, um die entsprechende Bildfilterung durchzuführen. Dies ist aber ein rechnerisch lösbares Problem. Anbei ein Beispiel für die Extraktion (unter der Annahme, eine unter UV-Licht rote Lumineszenz wird von einer roten Köperfarbe weniger beeinflusst, usw.). Für ein großflächiges Lumineszenzsicherheitsmerkmal mit hoher Flächendeckung sieht eine Farbtonsplittung für die Verwendung dreier verschiedener Lumineszenzfarben dann z.B. so aus, wie in der nachfolgenden Abbildung gezeigt. Dadurch erkennt der Designer sehr schnell, in welchen Bereichen er alle drei Lumineszenzfarben auf dem gegeben Untergrund zusammen einsetzen kann oder in welchem Bereich eine Lumineszenzfarbe nicht eingesetzt werden sollte.

The method ultimately predicts a possible position or array for the phosphorescent element. In particular, there are the following variants:

• Prediction variant 1: The prediction relates to the luminosity of a luminescence ink applied in a separate print in the given designed print area; this can either be based on an overall brightness or, viewed separately, on individual channels of an RGB sensor or a black and white sensor with an upstream red filter/green filter and blue filter as RGB signal strength.
• Prediction variant 2: The prediction relates to the luminosity in the given print design, with either just a pure luminescent color (based on a luminescent dye) or a mixture of at least two luminescent colors with no visible body color.
• Prediction variant 3: The prediction relates to a print design in which the luminescent color is mixed into a visually visible body color of the print design, eg a visually green color also contains a yellowish fluorescent color under UV light. So that the software can calculate the optimal position for this luminescence color, an entry in a database is used that contains the signal strength of the selected mixture of body color and luminescence color using, for example, a 1 g/m2 print with a specified sensor and specified excitation or the the signal strength is calculated via a computational model based on, for example, the Kubelka-Munk theory with infinitesimally small layers of the selected fluorescence color and the selected body color. As a model, for example, a system of alternating five layers of fluorescent paint and five layers of twill paint can be considered a good approximation for a real system. In each of the layers, the light absorption of the excited luminescence color is determined by the body color, and the UV dose of the excitation lamp, which penetrates less deeply into deeper layers, is also taken into account due to the UV absorption of the layers above.
• Prediction variant 4: If several differently colored luminescent colors are to be integrated on a colored security design and a sufficiently good signal intensity is to be achieved for the respective luminescent dye/pigment under UV lighting, the print design must be divided into the corresponding color spaces; this is an example in 5 performed for three luminescent colors (red, green, blue). In principle, this is also possible for any mixed colors, but means in detail that, for example, a look-up table in the database must first be created or calculated on the basis of real measured values read in, in order to carry out the corresponding image filtering. However, this is a computationally solvable problem. Here is an example of the extraction (assuming red luminescence under UV light is less affected by red body color, etc.). For a large-area luminescence security feature with high area coverage, a color tone split for the use of three different luminescence colors looks like this, for example, as shown in the figure below. As a result, the designer quickly recognizes in which areas he can use all three luminescent colors together on the given background or in which area a luminescent color should not be used.

A so-called look-up table can be used in particular when creating the map 9 .

The following is an example of a subsurface hue look-up table for the expected phosphorescence intensity that describes the signal loss per pixel.

A look-up table can, for example, based on CIELAB values, Pantone, RGB, XYZ, HUE color space or the color series used, result in a weighting of different color tones. Attached is an example of a phosphorescence signal strength printed on real color series for typical colors in security printing, e.g. as a solid area (100%).

Lookup tables can also be created for smaller area coverages or lower color tone strengths (g/m2) in order to refine the model. Color series, hue, area coverage, hue strength Phosphorescence Signal Strength (au) reference white 100 yellow 100.0000% 1.0 g/m ² 71 green 100.0000% 1.0 g/m ² 66 magenta red 100.0000% 1.0 g/m ² 22 black 100.0000% 1.0 g/m ² 19 red 100.0000% 1.0 g/m ² 17 orange 100.0000% 1.0 g/ ^m2 16 purple 100.0000% 1.0 g/m ² 14

The table shows the phosphor signal strength that can be achieved on different colored backgrounds with 100% area coverage for different intensities/doses/printing quantities of the phosphorescent ink.

A look-up table is generated by converting the digital colors of the digital proof (color spaces XYZ, RGB, CIELab, ...) into analog colors (Pantone shade, color number, color recipe/proofing weight) and vice versa, or only in partial steps among themselves. The look-up tables can also contain other color and substrate properties, such as reflection properties, body color, roughness, gloss, smoothness of the substrate (calendered/uncalendered). In addition, missing data can be obtained by interpolating existing data or weighted by correction factors.

A look-up table can also take into account the print resolution of different printing processes (offset, flexo, screen, inkjet printing).

Reference List

2

bank note

4

print motif

4a-d

motif elements

5

front face

6

phosphorescent block

7, 7a-c

block surface

8,10,11

surface element

S1-S4

Step

9

Map

12

scan cut

14:15

Area

16

mapping

18.19

recess

20

QR code

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2014184738 A1 [0002]

Claims (11)

Method for producing a substrate (2), in particular a bank note (2), with a luminescence element (6) which is designed to emit luminescence radiation, the substrate (2) having a substrate surface (5) and the following steps being carried out: a) providing (S1) data for a print motif (4) which extends over the substrate surface (5) and is to be reproduced on the substrate (2) by an imprint, b) providing (S2) data for the luminescence element (6 ) which extends over an element area (7) which is smaller than the substrate area (5) and which is also to be arranged on the substrate (2), further characterized by c) generating (S3) a map of the substrate area (5) , which reflects a local absorption of the luminescence radiation by the print motif (4) and d) determining, on the basis of the map (4), at least one position of the luminescence element (6) within the substrate area (5), in which in the element area (7 ) an adult rtete intensity of the luminescence radiation is optimized. procedure after claim 1 , characterized in that - the luminescence element (6) is designed for reading out with a luminescence sensor of a predetermined type, the luminescence sensor of a predetermined type having a predetermined subdivision into a plurality of pixels with a pixel size, and - step c) the dismantling of the substrate surface (5) in surface elements (8, 10, 11) with the pixel size and the averaging of a degree of absorption over each surface element (8, 10, 11), so that the map (9) is made up of uniform surface elements (8, 10, 11) with the pixel size is. procedure after claim 1 or 2 , characterized in that in step d) the criterion used for the optimization is that the intensity exceeds a predetermined threshold value. Method according to one of the above claims, characterized in that the element area (7) is rectangular and in step d) an aspect ratio of the element area (7) and/or a rotation of the element area (7) is varied for optimization. Method according to one of the above claims, characterized in that areas in which an absorption degree exceeds a threshold value are defined in the map (9) by means of a threshold value analysis. Method according to one of the above claims, characterized in that a map (16) which can be superimposed on the substrate surface (5) is generated and which indicates possible locations for the arrangement of the luminescence element (6). Method according to one of the above claims, characterized in that an area integral of a luminescence intensity remaining after absorption by the print motif (4) is calculated over the element area (7). Method according to one of the above claims, characterized in that parts of the element surface (7) are identified in which the expected intensity falls below a predetermined minimum value due to absorption by the print motif (4), and in these parts a recess in the luminescent element remains without luminescent dye (6) is provided to minimize the need for luminescent dye. Method according to one of the above claims, characterized in that the luminescent element (6) comprises a 1D or 2D barcode (20) made of luminescent dye. Method according to one of the above claims, characterized in that the luminescence element (6) luminesces in several color channels and the method is carried out individually for each of the color channels. Software program with instructions for execution on a computer, which are designed, when executed, to carry out a method according to one of the above method claims.

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