1. Field of the Invention
This invention relates to a method for producing embossing plates, in particular steel intaglio printing plates.
2. Description of Related Art
For producing embossing plates, in particular steel intaglio printing plates, as are usually employed for printing high-quality printed products such as papers of value, bank notes or the like one has hitherto resorted to having the embossing plates produced in an elaborate method by an artist. A picture motif made available to the artist is converted into a line pattern whereby lines of different width, depth and a different number per unit area represent the gray levels of the original. Using a chisel, the artist brings this motif in time-consuming hand labor into the metal plate, for example steel or copper. The thus produced plates are characterized by their high quality with respect to use in steel intaglio printing. However the possibilities of correction are extremely low for the artist during production of the plate. If this original plate is damaged or lost, no identical plate can be produced since each plate is an individual production.
It is also known to perform the engraving of a printing cylinder by machine. As described in EP 0 076 868 B1 for example, cups are brought into the printing form which represent the gray level value of a master depending on their screen width and engraving depth. Light tones and tone-dependent changes in the master are produced by varying the focal value of the electron beam in the printing form, whereby cups of different volume can arise.
From DE 30 08 176 C2 it is also known to use a laser for engraving a printing cylinder. An original is scanned and the resulting signal used via an analog-to-digital converter for controlling the laser with which engraved cups of defined depth and extension are brought into the printing cylinder.
When the original is broken down into gray-level values represented on the printing plate by cups, the essential components necessary for steel intaglio printing are lost, since this technique is only able to transfer ink to the print carrier point by point. Steel intaglio printing, however, is characterized by the fact that a continuous linear printing pattern tangible with the inking is transferred to the print carrier, characterized in particular by its filigreed design.
The objective of the invention is accordingly to propose a method permitting simple and automated production of embossing plates, in particular steel intaglio printing plates.
The invention is based on the finding that it is possible to treat a two-dimensional line original graphically such that the existing lines are interpreted as areas. These areas are limited by edges, these edges defining a desired contour of the area. Starting out from this desired contour one determines a tool track along which an engraving tool can be guided such that material is removed within the area limited by the desired contour. The engraving tool is controlled such that the material within the desired contour is removed in the form of continuous or interrupted lines or grooves in a certain depth profile. This depth profile can be determined by a depth value that is constant or varies within the desired contour.
The inventive method preferably makes use of a data processing system which makes it possible to acquire, store and process two-dimensional line originals. The two-dimensional line original, which is for example produced in a computer or read in via input devices, can be processed with the ad of a suitable computer program so as to yield track data for controlling an engraving tool along a tool track. For this purpose one defines in a first working step from the two-dimensional line original a plane element which consists for example of a single line of the line original. The edge enclosing the line then defines a desired contour with is intersection-free. To produce the engraving one associates a depth profile with the interior of the plate element as the desired depth for the engraving, and then calculates from the desired contour data and the associated desired depth a tool track along which the engraving tool is guided and removes material within the plane element in a predetermined, non-random manner.
This procedure is then repeated for each individual plane element to be engraved so that an engraving tool track can be determined for the entire area to be engraved, composed of the sum of the individual plane elements to be engraved.
Using this method one can considerably increase the speed for producing the embossing plate. Furthermore, errors during engraving are excluded by the exact guidance of the engraving tool so that a multiplicity of embossing plates can be produced with the same exactness. In addition the method offers simple possibilities of correction by changing the data of the line drawing. The exact reproducibility of the engraving to be brought in furthermore permits printing plates to be produced directly without any need for a galvanic shaping process. Several engraving tools can thereby also engrave several plates simultaneously. Furthermore several, possibly different, engraving tools can also be controlled such that they process a plate simultaneously, thereby optimizing the processing time.
Further advantages and advantageous embodiments will be explained with reference to the following figures, in which a true-to-scale representation was dispensed with for the sake of clearness.
As shown in
Since different engraving tools can be used for engraving the plate, it is clear that data of the particular engraving tool also enter into the calculation of the tool track. If a laser beam is used, the width of the beam acting on the embossing plate can be included in the calculation for example. If a mechanical chisel is used, the chisel form, in particular the form of the point or its radius of curvature, is of essential importance for calculating the tool track.
The engraving tool is controlled subsequent to the determination of the tool track such that it moves within area 4, does not hurt desired contour 5 during engraving and removes area 4 at predetermined desired depth 6.
In a specific embodiment, shown in
Since the width of the material removed with the engraving tool is limited, one can define via the line drawings plane elements with a size which cannot be removed completely if the engraving tool is guided only along the desired contour lines. A very simple form of line drawing is shown by way of example in FIG. 3. Via the line drawing of FIG. 3(a) one defines plane element 8 having contour line 9. When tool track 13 is now calculated on the basis of these given data, as shown in FIG. 3(b), the engraving tool cannot in one cycle completely remove the area to be removed, depending on the dimensioning of area 8 and the form of the engraving tool.
For rotating 14 chisel these relations are shown in perspective in FIG. 4. Corresponding relations for a laser beam 35 generated by a laser beam source 34 are shown in
As to be seen in FIG. 5(a), it is necessary in this case also to consider residual area 16 not removable in the first step when calculating the tool track for removing area 8. For removing residual area 16 one can determine different tool tracks depending on the desired engraving results. Thus the tool track can, as shown in FIG. 5(b), first extend along the desired contour and residual area 16 then be removed in a meander shape, the engraving tool removing the residual area continuously in meander-shaped track 17 within area 16. FIG. 5(c) shows a further possibility whereby residual area 16 is removed by guidance of the engraving tool along tool tracks which are similar in the mathematical sense to tool track 12 first calculated, i.e. tool tracks 18, 19 and 20 correspond to tool track 12 in form but have a different dimension from tool track 12. Particularly in the case of curved contour lines, residual area 16 can accordingly be removed using tool tracks which extend contour-parallel, i.e. are equidistant from the contour line at each point.
As to be seen in FIG. 6(a) in a cross section through embossing plate 15, one calculated from contour line 9 a tool track along which the engraving tool was guided, thereby producing engraved line 28 enclosing residual area 16 yet to be engraved. To remove residual area 16 one can use any method but preferably one of the above-described. Regardless of the particular method one produces at the base of the residual area engraving a defined roughness structure determined by the offset and form of the engraving tool. FIG. 6(b) shows such a roughness structure, whereby a tapered, rotating graver was used for engraving, removing the embossing plate at defined depth T. The chisel used had diameter D on the surface emerging from the embossing plate and was offset inward by the amount d/2 during removal of the residual area, while the offset is ¾ d in the example shown in FIG. 6(c). The engraving tool was moved in accordance with the tool tracks shown in FIG. 5(c) in both examples.
The described surface structuring at the base of the engraved area has several advantages for producing steel intaglio printing plates. Using steel intaglio printing plates one could hitherto print only limited line widths, due to the fact that the steel intaglio printing ink can only be brought into engravings of the plate which have a certain maximum width. This obstacle is eliminated by the newly proposed engraving since one can now adjust the roughness as a base pattern at the base of the engraving to serve as an ink trap for a steel intaglio printing ink brought in. This ink can thus be held even in very wide engraved lines so that it is now possible for the first time to print wide lines by steel intaglio printing. As shown in FIGS. 6(b) and 6(c), the roughness of the base can be controlled via the size of the engraving tool offset. Since different offset widths of the chisel can also be considered in the calculation of the tool track, the roughness can be different at the base in different areas of the residual area and thus the engraved line or area be superimposed with an additional modulation of the roughness of the base pattern. It is thus also possible to bring further information into an engraved line solely by selectively producing the roughness of the base pattern.
Since transparent inks are usually employed in steel engraving, a different color effect within a line can be produced on the document to be printed with the aid of the different engravings within a line. This color effect can be improved further in particular if the engraving already produced is provided in a further method step with a second engraving whose desired depth has a different definition from that of the first engraving.
The tapered edges of line drawing 19 can be rendered exactly by a suitable choice of chisel form. It is possible to use a single fine chisel for the engraving, or rework the tapered edges with a fine chisel after engraving the area with a coarse chisel. As an alternative to this possibility one can also adapt the depth profile to the requirements of area 19 to be engraved. In this case the depth profile is preset such that the engraving tool removes less material at the tapered edges so that, in particular if a rotating mechanical chisel is used, the chisel emerges ever further out of the material to be processed and due to the conic form therefore the removed line becomes narrower. These two techniques can also be used for exact engraving of corners or edges.
For determining the tool track one generally combines a determined desired contour with an engraving depth profile according to the inventive method, thus determining from these two data a tool track along which the engraving tool is guided, so that the material can be removed in accordance with the line drawing at the depth corresponding to the depth profile. The depth profile, i.e. the desired depth, can be preset for each individual engraved line or for the engraving altogether as a constant. Desired depths can also be different for individual engraved lines or parts of engraved lines, so that the particular tool track is accordingly modulated. In addition it is possible to use different engraving tools of like or different kinds in successive method steps in order to produce the desired engraving result. If rotating mechanical chisels are used it is especially advantageous to use different chisel points, forms and sizes, so that optimal embossing plates can be produced in this way.
By producing and using different chisel forms and sizes one can influence the embossing result in a variety of ways. Precisely the form and size of the embossing tool determine the form of the thus produced engraving cross-sectional area, depending on the penetration depth of the engraving tool into the plate.
The inventive method offers the crucial advantage that engraving can be performed with exact line control even with extremely small engraving areas or lines. The desired depths which can be reached with the inventive method are preferably between 10 and 150 microns, whereby the desired depths can also be preset by different gray-level values of the line original.
If the original is formed for example by a uniform line pattern, e.g. a guilloche, one can bring in visible information, for example a portrait, by varying the line depth, line width, line density or contour by the method described above. Instead of visually recognizable information, however, one can also bring in different, for example machine-readable, information in this way.
Although the use of different engraving tools already provides a wealth of possibilities for bringing into the embossing plate substructures in the form of defined roughness structures at the base of the engraving, as shown in
The inventive method can of course also be employed if a negative image of the line original is to be produced. As shown in
Number | Date | Country | Kind |
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196 24 131 | Jun 1996 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCTEP97/03120 | 6/16/1997 | WO | 00 | 4/2/1999 |
Publishing Document | Publishing Date | Country | Kind |
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WO9748555 | 12/24/1997 | WO | A |
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