METHOD AND DEVICE FOR PRINTING A SUBSTRATE WITH AN ELECTROLUMINESTIC PRINTING INK AND OF IDENTIFICATION, VALUE OR SECURITY DOCUMENTS COMPLETING SUCH A SUBSTRATE

Description

[0001] The invention relates to a method for printing a substrate of an identification, valuable, or security document. The invention also relates to an identification, valuable, or security document and an intaglio printing device for implementing the method.

[0002] Identification, valuables, or security documents serve to verify the identity of a person or thing or a claim, for example, to payment of money or to the release of a product or provision of a service. The document can be in the form of a banknote. To this end, it must be ensured that the document cannot be imitated, counterfeited, or falsified, or can only be done with considerable effort. The document therefore often contains security features that are extremely difficult or even practically impossible to imitate. For example, the document, e.g., the banknote, is made of a material that is not readily available. Additionally or alternatively, security features or imprints can be created using special inks, for example, luminescent or optically variable inks, optical elements such as tilting images, kinegrams, lens or prism arrays, guilloches, mottled fibers, security threads, and other methods.

[0003] Although many security features exist, many counterfeits of identification, valuables or security documents are still successful.

[0004] To make it more difficult to counterfeit a document, especially a banknote, it is known to print the identification, valuables, or security documents with a printing ink applied to the substrate of the identification, valuables, or security document using an intaglio printing process, a special form of gravure printing. This allows for the generation of very fine print patterns that, after drying, have a slightly raised feel, i.e., protrude above the substrate itself.

[0005] It is also known from DE 103 26 644 A1 that identification, valuables, or security documents can be equipped with an electroluminescent printing ink, for example, by printing. The electroluminescent pigments contained in this printing ink are excited and luminesce when an alternating electric field is applied, and the radiation can be detected again using a suitable testing device. Typically, the electroluminescent printing ink is applied to a substrate using a screen printing process. DE 103 26 644 A1 also mentions the possibility of applying the electroluminescent printing ink using an intaglio printing process, although in practice it has been found that excitation of the electroluminescent printing ink after printing is only rarely possible and mostly by chance.

[0006] WO 98 / 39163 A1 also describes a valuable or security product with luminescent security elements.

[0007] A printing device with an intaglio printing cylinder for printing identification, valuables or security documents with electroluminescent printing ink is known, for example, from EP 1 842 665 A1.

[0008] It is therefore the object of the present invention to provide a method and a device for printing that take the aforementioned disadvantage into account and result in reliably reproducible luminescence. Furthermore, it is the object of the present invention to provide an identification, valuables, or security document produced accordingly.

[0009] This object is achieved by a method having the features of claim 1, by an identification, value or security document having the features of claim 14 and by a device having the features of claim 15. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0010] The process for printing a substrate of an identification, valuables or security document with an electroluminescent printing ink comprises the following steps: Providing an intaglio printing unit with an intaglio printing cylinder which can be driven to rotate in a direction of rotation and which has a surface into which a plurality of depressions for temporarily storing printing ink are introduced, and with a wiping cylinder which interacts with the surface of the intaglio printing cylinder, applying the printing ink to the surface and into the depressions of the intaglio printing cylinder, wiping the surface of the rotating intaglio printing cylinder by moving the wiping cylinder in a direction deviating from the direction of rotation of the intaglio printing cylinder, and applying the substrate to the intaglio printing cylinder and transferring the electroluminescent printing ink introduced into the depressions to the substrate.

[0011] The different directions for printing the electroluminescent ink onto the substrate and for wiping the surface of the intaglio printing cylinder ensure that the ink applied to the substrate actually exhibits the desired luminescence effect when subsequently excited with an alternating electric field. The different directions for wiping the surface of the intaglio printing cylinder and the direction of the printing itself lead to reproducible intensities of the luminescence effect.

[0012] To enhance the luminescence effect, i.e., to enable improved excitation of the electroluminescent printing ink, it is advantageous for the electroluminescent printing ink to be composed of electroluminescent pigments and electrically conductive pigments arranged in an electrically insulated manner. The latter serve to enhance the field. Color pigments can also be added to the printing ink to make it color-identifiable or displayable even in the non-excited state.

[0013] It is advantageous if the ratio of the number of electroluminescent pigments to the number of electrically conductive pigments in the electroluminescent printing ink is between 0.2 and 0.7, preferably between 0.25 and 0.6, most preferably between 0.3 and 0.5, i.e. the ratio of the number of electroluminescent pigments to the number of electrically conductive pigments is 1:5 to 1:1.5, preferably 1:4 to 1:1.7, most preferably 1:3 to 1:2. Both pigment types can be embedded in a matrix that enforces a desired distribution of the pigments. The ratio formed in this way leads to a good intensity of the electroluminescence of the printed printing ink. In particular, the ratio of the narrowest band of 0.3 and 0.5 leads to very good, reproducible results under electrical excitation.

[0014] The intensity of the electroluminescence is also enhanced by the ratio of the average pigment size of the electroluminescent pigments to the average pigment size of the electrically conductive pigments being between 0.4 and 1.0, preferably between 0.5 and 0.9, in particular between 1:1.8 and 1:1.2. The average pigment size of the electroluminescent pigments is between 3 µm and 25 µm, preferably between 5 micrometers and 20 micrometers. It is most preferably between 8 micrometers and 12 micrometers, since particularly reproducible luminescent properties can be observed in this range.

[0015] The plurality of depressions is preferably formed from parallel lines with a line width of between 10 and 50 times the average pigment size of the electroluminescent pigments in the printing ink, preferably between 25 and 40 times. This ensures that the electroluminescent pigments can reliably penetrate the depressions before being transferred to the substrate. The wiping motion, directed in a different direction, forces the electroluminescent pigments and the amplifier pigments into the depressions, which further enhances the subsequent luminescence effect. The spacing between the line depressions is proportional to the intensity of the ink on the substrate and its luminosity. Therefore, a smaller or finer spacing between the lines is chosen to improve the resolution of the printed image.

[0016] The depressions can be created, for example, by etching into the surface of the intaglio printing cylinder. Alternatively or additionally, the depressions can be engraved. The line thickness or line width is at least 120 micrometers, preferably 250 µm - 500 µm, most preferably 320-410 µm. Particularly good and reproducible results can be achieved with line thicknesses between 320 micrometers and 410 micrometers.

[0017] The plurality of recesses preferably have a depth, radially aligned with a rotational axis of the intaglio printing cylinder, of between 4 and 8 times the average pigment size of the electroluminescent pigments, thus ensuring that a sufficient number of luminescent particles are incorporated into the recesses before being transferred to the substrate. The depth is approximately between 40 micrometers and 70 micrometers.

[0018] Preferably, the wiping cylinder wipes the surface in a direction opposite to the rotation of the intaglio printing cylinder. This ensures that the pigments are reliably "penetrated" into the recesses.

[0019] For simplified excitability of the printed substrate, it is useful if the majority of the depressions extend parallel to a rotation axis of the intaglio printing cylinder in the surface, and if, for electroluminescent excitation, two electrodes are placed on the substrate, lying side by side and forming a capacitor, which are aligned perpendicularly or parallel to printing lines caused by the depressions.

[0020] It is also possible that the substrate already comprises two electrodes lying flat side by side, forming a capacitor, before printing, and that the substrate is then aligned during printing such that the electrodes are aligned perpendicular or parallel with respect to the axis of rotation of the intaglio printing cylinder.

[0021] The advantages and effects mentioned in connection with the method according to the invention also apply to the identification, valuables, or security document according to the invention, which comprises at least one substrate or part thereof printed with an electroluminescent printing ink, which was produced using the method according to the invention. The electroluminescent printing ink is applied using an intaglio printing cylinder, in whose surface depressions are formed, comprising a line thickness or line width of at least 120 micrometers.

[0022] The advantages and effects mentioned in connection with the method according to the invention also apply to the intaglio printing device according to the invention.

[0023] It comprises an intaglio printing unit comprising an intaglio printing cylinder that can be driven to rotate in a rotational direction and has a surface into which a plurality of depressions are formed for temporarily storing printing ink. The intaglio printing cylinder has a wiping cylinder that interacts with a surface of the intaglio printing cylinder and is configured to wipe the intaglio printing cylinder in a direction deviating from the rotational direction of the intaglio printing cylinder. The wiping cylinder is configured to laterally rub the surface of the intaglio printing cylinder by moving the wiping cylinder in and against a direction parallel to the rotational axis of the intaglio printing cylinder.

[0024] The printing unit may also be associated with an ink reservoir, which includes an outlet opening for applying the electroluminescent printing ink to the surface of the intaglio printing cylinder and into its recesses. Additionally, a pressure roller may be provided to press the substrate against the surface of the intaglio printing cylinder.

[0025] The method according to the invention for printing a substrate with an electroluminescent printing ink comprises several steps. The specified order of the individual steps is not mandatory.

[0026] Further features, properties, and advantages of the present invention are described in more detail below using embodiments with reference to the accompanying figures. All features described so far and below are advantageous both individually and in any combination. The embodiments described below are merely examples and do not limit the subject matter of the invention. They show: Fig. 1 a schematic detailed view of an intaglio printing device for printing an electroluminescent printing ink onto a substrate of a banknote using an intaglio printing technique, Fig. 2 a substrate partially printed with printing lines of the electroluminescent printing ink, Fig. 3 the printed substrate from Figure 3on which a pair of electrodes of an excitation and / or measuring means is placed, which is aligned parallel with respect to the printing lines, and Fig. 4 the printed substrate from Figure 3 onto which a pair of electrodes of an excitation and / or measuring device is placed, which is aligned perpendicular to the pressure lines.

[0027] In Figure 1An intaglio printing device 100 is shown schematically, which has an intaglio printing unit comprising an intaglio printing cylinder 102 which can be driven to rotate clockwise and has a surface 104 into which a plurality of depressions 106 are introduced for temporarily storing printing ink. The intaglio printing unit also comprises a wiping cylinder 108 which interacts with the surface 104 of the intaglio printing cylinder and is configured to wipe the intaglio printing cylinder 102 in a counterclockwise direction. In addition, the wiping cylinder 108 is configured to laterally rub the surface 104 of the intaglio printing cylinder 102 by moving the wiping cylinder 108 in and against a direction parallel to the rotational axis of the intaglio printing cylinder 102. The printing direction 118 and the wiping direction 120 are illustrated by arrows.

[0028] For the sake of clarity, the other components of the intaglio printing unit have been omitted. However, the printing unit is also assigned an ink reservoir, which includes an outlet opening for applying an electroluminescent printing ink to the surface 104 of the intaglio printing cylinder 102 and into its recesses 106. Additionally, a pressure roller is provided for pressing a substrate 110 to be printed onto the surface 104 of the intaglio printing cylinder 102 so that the printing ink is applied to the substrate 110 or absorbed by it.

[0029] The electroluminescent printing ink comprises electroluminescent pigments and electrically conductive pigments arranged in an electrically insulated manner. Color pigments can also be present to allow the printed result to be seen or optically detected even without excitation by an electric field.

[0030] The ratio of the number of electroluminescent pigments to the number of electrically conductive pigments in the electroluminescent printing ink is presently between 0.2 and 0.7, preferably between 0.25 and 0.6, most preferably between 0.3 and 0.5. The ratio of the average pigment size of the electroluminescent pigments to the average pigment size of the electrically conductive pigments is between 0.4 and 1.0, preferably between 0.5 and 0.9, with the average pigment size of the electroluminescent pigments being between 3 micrometers and 25 micrometers, preferably between 5 micrometers and 20 micrometers, most preferably between 8 micrometers and 12 micrometers, since particularly well-reproducible luminescence properties of the printing lines 112 caused by the depressions 106 can be determined in these ranges.

[0031] The plurality of depressions 106 in the intaglio printing cylinder 102 is formed from mutually parallel lines having a line width of between 10 and 50 times the average pigment size of the electroluminescent pigments of the printing ink, preferably between 25 and 40 times. The plurality of depressions 106 also has a depth, radially aligned with respect to a rotation axis of the intaglio printing cylinder 102, of between 4 and 8 times the average pigment size of the electroluminescent pigments.

[0032] In Figure 2 These parallel printing lines 112 can be seen on the printed substrate 110, with the printing direction 118 being indicated again by the arrow.

[0033] After printing the printing lines 112 using the intaglio printing process, a pair of electrodes 114 can be placed on the substrate 110 or externally aligned for testing or exciting the electroluminescent printing ink, which electrodes are arranged in Figure 3 is oriented such that its substantially rectangular shaped electrodes extend parallel to the pressure lines 112. The resulting semi-circular field lines 114 are also shown. In Figure 4 An improvement is shown wherein the electrode pair 114 is aligned with respect to the printing lines 112 such that its substantially rectangular shaped electrodes extend perpendicularly with respect to the printing lines 112.

[0034] Overall, the Figures 3 and 4In the design shown, care was taken to ensure that the field lines 114 optimally run in the direction of the print lines 112 caused by the depressions 106. This can be achieved through a cleverly selected design of the electrodes with a less straight design of the electroluminescent print itself. The print lines 112 should be present on the substrate 110 where a subsequent test with a sensor will take place, as this will result in the highest "yield" of electroluminescence. Centering the substrate 110 within the test device can be advantageous for this purpose. A field with parallel print lines 112 can be present, for example, where a sorting machine allows open space between the conveyor belts for light emission caused by electroluminescence.

[0035] As a result, the present invention now makes it possible to obtain reliable and reproducible results from electroluminescent prints applied using the intaglio printing process. LIST OF REFERENCE SYMBOLS

[0036] 100Intaglio printing device 102Intaglio printing cylinder 104Surface 106Depressions 108Wiping cylinder 110Substrate 112Printing line 114Electrode pair (capacitor) 116Field lines 118Printing direction 120Wiping direction

Claims

1. A method of printing an electroluminescent ink on a substrate (110) of an identification, value or security document, comprising the steps of: - providing of an intaglio printing unit having an intaglio printing cylinder (102) which can be rotatably driven in a direction of rotation (118) and has a surface (104) in which a plurality of indentations (106) for temporarily storing of printing ink are formed, and having a wiper cylinder (108) interacting with the surface (104) of the intaglio printing cylinder (102), - applying the printing ink to the surface (104) and into the indentations (106) of the intaglio printing cylinder (102), - wiping the surface (104) of the rotating intaglio printing cylinder (102) by moving the wiper cylinder (108) in a direction (120) other than the direction of rotation (118) of the intaglio printing cylinder (102), and - applying the substrate (110) to the intaglio printing cylinder (102) and transferring the electroluminescent ink introduced into the indentations (106) to the substrate (110).

2. The method according to claim 1, characterized in that the electroluminescent printing ink is formed from electroluminescent pigments and electrically conductive pigments arranged electrically insulated from these.

3. The method according to claim 2, characterized in that in the electroluminescent printing ink the ratio of the number of electroluminescent pigments to the number of electrically conductive pigments is between 0.2 and 0.7.

4. The method according to claim 2 or 3, characterized in that in the electroluminescent printing ink the ratio of the number of electroluminescent pigments to the number of electrically conductive pigments is between 0.25 and 0.6.

5. The method according to any one of claims 2 to 4, characterized in that in the electroluminescent printing ink the ratio of the number of electroluminescent pigments to the number of electrically conductive pigments is between 0.3 and 0.5.

6. The method according to any one of claims 2 to 5, characterized in that the ratio of the mean pigment size of the electroluminescent pigments to the mean pigment size of the electrically conductive pigments is between 0.4 and 1.0.

7. The method according to any one of claims 2 to 6, characterized in that the ratio of the mean pigment size of the electroluminescent pigments to the mean pigment size of the electrically conductive pigments is between 0.5 and 0.9.

8. The method according to any one of claims 2 to 7, characterized in that the mean pigment size of the electroluminescent pigments is between 3 micrometres and 25 micrometres.

9. The method according to any one of claims 2 to 8, characterized in that the plurality of indentations (106) is formed from lines running parallel to each other and having a line width of between 10 times and 50 times the mean pigment size of the electroluminescent pigments of the printing ink.

10. The method according to any one of claims 2 to 9, characterized in that the plurality of indentations (106) is formed from lines running parallel to each other and having a line width of between 25 times and 40 times the mean pigment size of the electroluminescent pigments of the printing ink.

11. The method according to claim 9 or 10, characterized in that the plurality of indentations (106) has a depth radially aligned with respect to an axis of rotation of the intaglio printing cylinder (102) of between 4 times and 8 times the mean pigment size of the electroluminescent pigments.

12. The method according to any one of claims 1 to 11, characterized in that the wiper cylinder (108) wipes the surface (104) in a direction of rotation (120) opposite to the direction of rotation (118) of the intaglio printing cylinder (102).

13. The method according to one of claims 1 to 12, characterized in that the plurality of indentations (106) extend parallel with respect to an axis of rotation of the intaglio printing cylinder (102) in the surface (104), and in that, for electroluminescent excitation of the printing ink applied to the substrate (110), two electrodes forming a capacitor and lying flat next to one another are applied, which electrodes are aligned perpendicularly or parallel with respect to printing lines (112) caused by the indentations (106).

14. An identification, value or security document comprising a printed substrate (110) with an electroluminescent printing ink, produced by the method according to any one of claims 1 to 13, wherein the electroluminescent printing ink is applied with an intaglio printing cylinder (102), in the surface (104) of which indentations are made comprising a line thickness or line width of at least 120 micrometers.

15. An intaglio printing press (100) for carrying out the method according to one of claims 1 to 13, having an intaglio printing unit which comprises an intaglio printing cylinder (102) which can be rotatably driven in a direction of rotation (118) and has a surface (104) in which a plurality of indentations (106) for the temporary storage of printing ink are introduced, having a wiper cylinder (108) which interacts with the surface (104) of the intaglio printing cylinder (102), which is arranged to wipe the intaglio printing cylinder (102) against the direction of rotation (118) of the intaglio printing cylinder (102), characterized in that the wiper cylinder (108) is arranged to rub the surface (104) of the intaglio printing cylinder (102) laterally by a movement of the wiper cylinder (108) in and against a direction parallel to the axis of rotation of the intaglio printing cylinder (102).