METHOD FOR PRODUCEING ENGRAVING DATA FOR ENGRAVING PRESSURE CYLINDERS

Description

[0001] The invention relates to a method for generating engraving data for the engraving of printing cylinders and a method for producing printing cylinders of a printing press, as well as a method for printing decorations using such printing cylinders, specifically for the subtractive multi-color analog printing of surface decorations on flat substrates, e.g. foils or paper. The invention also relates to a method for generating print data for the printing of surface decorations, wherein, on the one hand, digital print data for digital printing and, on the other hand, engraving data for the engraving of printing cylinders for multi-color analog printing (of the same decoration) are generated. The invention relates in particular to the printing of decorations for the surface finishing of plate-shaped workpieces, e.g. furniture panels, worktops, floor panels or wall and ceiling cladding panels. The decorations can be, for example, wood decors orThese can be decorations for the reproduction of wood-based materials or other natural or artificial materials, such as stone slabs or the like. For this purpose, decorative papers or decorative films are printed with a specific decoration, and these papers or films are applied to the carrier board in a subsequent process step. However, the invention also encompasses the direct printing of board-shaped materials, such as wood-based panels or other carrier boards.

[0002] In practice, printing on decorative papers or foils is usually done using multi-color analog printing, especially in a (rotary) gravure printing process with several engraved printing cylinders, each inked with a different printing ink. Analog printing with printing cylinders enables particularly cost-effective, high-quality printing, especially in mass production. Separate printing cylinders must be manufactured for each individual design, so such printing processes are generally used for the production of designs in large quantities.

[0003] Alternatively, designs can also be printed using digital printing. The disadvantage of this method for mass production is the significantly higher costs compared to conventional analog printing processes, such as gravure printing. A key advantage of digital printing is the ability to quickly and easily print new designs without the complex production of printing cylinders, making it particularly suitable for small-scale production.

[0004] In practice, a large number of new decorations are constantly being developed, of which only a few then make it into mass production. There is a need to initially produce samples for new decorations in small quantities using digital printing. If it turns out that a certain decoration is to be produced in larger quantities and, for example, transferred to mass or series production, the printing cylinders for this decoration are produced for the gravure printing process. In practice, this raises the problem of comparability between decorations produced using digital printing on the one hand and those produced using analogue printing on the other. Due to the very different characteristics of the respective production processes, the print data generated for digital printing are generally only suitable to a limited extent for analogue printing or for engraving printing cylinders. The results are often not sufficiently comparable.This is due, among other things, to the fact that digital printing usually works with primary colors / scale colors, e.g. in a CMYK color space. In contrast, surface decors are usually printed in conventional gravure printing processes using special colors (mixed colors) that can be adapted to the respective decor for reasons of quality and cost. For example, decors for simulating wooden surfaces are often printed in different shades of brown. This means that very different color separations must usually be used for digital printing on the one hand and gravure printing on the other. In practice, for example, a digital printing separation is first created for a specific decor in a specific color space, e.g. in the CMYK color space. If a decor is to be transferred to mass production, a new gravure separation is created for the corresponding color space.Such gravure separations are very complex in practice and require a significant amount of manual work. During the separation process, color separations for the respective printing inks are created based on a digital data set, e.g., in RGB format. The separation for surface decorations for analog printing is generally performed in such a way that the printing cylinders engraved on the basis of this separation can subsequently print decorations in different shades using different base colors. This means that different color combinations are realized in the printing press using the same printing cylinders by selecting the respective colors.

[0005] The comparability of the decorations initially produced in small quantities for testing using digital printing, on the one hand, with the decorations later produced in mass production using the gravure printing process, on the other, remains problematic. This invention aims to remedy this.

[0006] A method for producing a print decoration for use in different printing processes is known, for example, from EP 3 020 565 B1. In this method, color separations for gravure printing are generated from the digital data set by means of a separation, with a specific color or color mixture being provided for each color channel. The printing rollers or printing cylinders to be used for gravure printing are manufactured from the separated data after their resolution has been reduced, and the mixed colors for each cylinder are defined. Parallel to or subsequent to the production of the printing rollers for gravure printing, the color information separated in the color channels and possibly processed is combined to form a digital print file, i.e. the separation data is combined to form a digital template for digital printing.After converting the digital print file into a format suitable for the digital printer using RIP, a second print design is created on a second substrate using digital printing, forming a pattern. According to EP 3 020 565 B1, this is intended to enable the creation of an identical print design on two substrates using two different printing processes—in this case, gravure printing as an analog, cost-effective printing process, and digital printing—where the print images produced by the two different printing processes should not differ from one another.

[0007] EP 3 470 972 A1 describes a method for the multiple use of digital print data to produce visually and / or haptically high-quality print decorations on a carrier material. First, a high-resolution electronic data set is generated from the print motif, which is then digitally separated into four color channels, specifically in the CMYK color space. Optionally, the color information contained in each color channel is independently processed. The provided, separated color information is combined into a digital print file for a print decoration to be created using the digital printing process. This method is characterized in that position data of at least one provided, separated color component is determined and stored during the creation of the print decoration on the carrier material.

[0008] Furthermore, WO 2010 / 108569 A1 describes a method for producing panel bodies for use in the floor, wall or ceiling area using printed printing papers which are produced with a printing device, wherein the printing device comprises at least one digital printing device for digital printing and at least one gravure printing device for decorative gravure printing, wherein either the digital printing device or the gravure printing device is used to print the decoration depending on the amount of printing paper to be printed.

[0009] Furthermore, US 2016 / 0301829 A1 discloses a method for converting basic colors of a basic color space (e.g. CMYK) into a multi-color space, e.g. CMYKcm color space.

[0010] Based on the prior art, the object of the invention is to provide a method for generating engraving data for engraving printing cylinders of an analogue printing machine, with which an initial production previously created in digital printing can be reproduced economically and with high quality.

[0011] To achieve this object, the invention teaches a method according to claim 1 for generating engraving data for engraving printing cylinders of a printing press for multi-color analogue printing of surface decorations on flat substrates, e.g., foils or papers, comprising the following method steps: a) a layout of a decor is created or made available as a digital data set (e.g. by scanning), b) basic color separations for each individual basic color are created from the data set by separating it into a basic color space with several basic colors, e.g. by a standard digital print separation, c) the basic color separations are optionally converted using a conversion process, e.g. with a raster image processor (RIP), into converted color separations with converted color distribution, which are optionally available as digital print data for transfer to a digital printing machine, d) the converted color separations or alternatively the basic color separations are post-processed by increasing the tonal values ​​for each basic color or each individual basic color separation in such a way that the darkest color tone (i.e. the color tone with the highest tonal value) in the color separation reaches a predetermined maximum tonal value (of e.g.95% or 100%) and the remaining tonal values ​​of the respective color separation are increased accordingly, e.g. linearly increased. The color separations thus post-processed are available or made available as engraving data for engraving the printing cylinders of a printing press for an analogue printing process, e.g., the printing cylinders of a rotary gravure printing press. Printing in the analogue printing process with the printing cylinders is then carried out with the pure or essentially pure basic colors of the basic color space, but in a blended and therefore diluted form.

[0012] In addition, to achieve the object, the invention proposes a method according to claim 2 for generating print data for printing surface decorations, wherein on the one hand digital print data for digital printing and on the other hand engraving data for engraving printing cylinders for multi-colour analogue printing are generated, with the following method steps:a) a layout of a decor is created or made available as a digital data set, b) basic colour separations for each individual basic colour are generated from the data set by means of a separation, e.g. a standard digital printing separation, into a basic colour space with several basic colours, c) the basic colour separations are optionally converted into converted colour separations with converted colour distribution using a conversion process, e.g. using a raster image processor (RIP), whereby the basic colour separations or the converted colour separations are available or made available as digital printing data for transfer to a digital printing press and d) the basic colour separations or the converted colour separations made available for the digital printing press are post-processed by creating a colour separation for each basic colour orthe tonal values ​​of each individual color separation are increased in such a way that the darkest color tone with the highest tonal value in the color separation is raised to a predetermined maximum tonal value and the remaining tonal values ​​of the respective color separation are increased according to a predetermined relationship. whereby the color separations thus post-processed are available or made available as engraving data for the engraving of the printing cylinders of a printing press for an analogue printing process.

[0013] According to this aspect of the invention, both digital printing data and analogue printing data or engraving data for analogue printing are therefore made available for the production of one and the same decoration, e.g., first digital printing data for a sample and then engraving data for analogue printing for series production.

[0014] In principle, this can be a two-color print with two printing cylinders. However, the invention preferably relates to a three-color print, and particularly preferably to a four-color print with four printing cylinders, i.e., with four basic colors in a four-dimensional color space. This can, for example, be a CYMK color space, i.e., preferably working with the four basic colors cyan, yellow, magenta, and black. Alternatively, two, three, four, or more (other) basic colors, e.g., blue, red, yellow, and black, can also be used.

[0015] The invention is based on the finding that, in order to achieve the best possible reproduction of an initial production created in digital printing in analogue printing, it is advantageous to carry out the analogue printing with the same colours or base colours in the same colour space, whereby in analogue printing, however, only blended and consequently diluted colours of this colour space are used.

[0016] According to the invention, the production of printing cylinders for analog or gravure printing is not based on a complex gravure separation designed for special mixed colors, e.g., different shades of brown, but the separation for engraving the cylinders takes place in the same color space as a standard digital printing separation. Preferably, a process is provided with which one and the same decoration can be produced with high comparability both digitally and analogically. This can be achieved, for example, as follows: In production - as usual - a specific layout of a decoration is first made available and created as a digital data set, e.g., digitized by scanning. Such a layout can, for example, initially be available in the RGB color space, which is not suitable for transfer to a printer.

[0017] From this data set, basic color separations for each individual basic color, such as cyan, magenta, yellow, and black, are generated by separating them into a basic color space (e.g., the CMYK color space) with multiple basic colors, e.g., using a standard digital printing separation. This is therefore a separation process common for digital production and digital printing.

[0018] In a preferred embodiment of the method, these basic color separations are subsequently converted into converted color separations, e.g., in an achromatic composition, using a conversion process, in particular by GCR conversion (gray component replacement). Consequently, GCR conversion takes place in the raster image processor (RIP), so that converted color separations in an achromatic composition are available. These can be transferred in a generally known manner to a digital printing press, which prints, for example, with the process colors CMYK or with the basic colors blue, red, yellow, and black. Up to this step, the processing of print data for decor printing in digital printing is conventional; in this step, the print data is converted into an achromatic composition using GCR conversion.Such a GCR converted digital printing separation, which can be passed on to the digital printer without further changes, has the advantage that digital printing is particularly economical, since a higher proportion of black is usually produced.

[0019] According to the invention, this is where engraving data for analogue printing is generated, which enables excellent reproduction of the digital print pattern in analogue printing.

[0020] For this purpose, the exact data that was transferred to the digital printing press is accessed, e.g., the converted color separations generated by GCR conversion in the RIP. The color separations, which are no longer subsequently manipulated in digital printing but are transferred unchanged to the digital printing press, are further processed in preparation for analog printing.

[0021] If conversion (e.g., GCR conversion) is not required for digital printing and the base color separations are therefore passed on to the digital printing press for digital printing, the base color separations are used and post-processed for analog printing as described above. Post-processing for analog printing is always based on the color separations previously submitted to the digital printing press.

[0022] This makes it possible, for example, to first separate a large number of decors for digital printing and then to produce them cost-effectively in small

[0023] to produce large quantities. If a specific decoration is to be reproduced later in analogue printing, the converted data available for digital printing is further processed as follows: The converted color separations (or base color separations) are post-processed for analogue printing by increasing the tonal values ​​for each base color or base color separation in such a way that the darkest color tone in the color separation is increased to a maximum value of at least 90%, preferably at least 95%, e.g. 100%. All tonal values ​​in between are preferably increased linearly. This procedure increases the tonal value information per color separation and therefore per cylinder. This makes it possible to subsequently work with heavily blended, pure base colors, e.g. blended CMYK colors, in analogue printing and in this way to excellently recreate digital printing.The color separations post-processed in the manner described are then made available as engraving data for engraving the printing cylinders of an analog printing press. In production, these printing cylinders are used in analog printing with pure, but blended basic colors of the basic color space (e.g., CMYK). This ensures excellent comparability between the results in analog printing and digital printing. By using the achromatic composition in digital and analog printing, overall ink consumption is reduced and color stability is increased in both processes. Since analog printing uses (pure) blended colors and the predominant detail of the decoration comes from the black separation (due to GCR conversion), a slight shift in register is not immediately visible.

[0024] Within the scope of the invention, the post-processing of the color separations according to feature d) is of particular importance, in which the tonal values ​​and consequently the brightness levels are changed. Such post-processing can utilize known image processing or prepress tools and programs that allow the tonal values ​​of each individual color separation to be manipulated.

[0025] As described, according to the invention, analog printing uses the same inks that were previously used for digital printing during the initial sampling. The inks used for digital printing are referred to as base inks, and the same pure base inks are then preferably used in analog printing, albeit in a blended and thus diluted form. However, it is also possible to work not with 100% pure base inks, but with essentially pure base inks that contain a small proportion of other color components (maximum 10%), preferably maximum 5%, particularly preferably maximum 3%.

[0026] The method according to the invention allows both print data or color separations for digital printing and print data or color separations for engraving the printing cylinders for analog printing, resulting in highly comparable results. This allows a wide variety of designs to be tested in digital printing. If a specific design needs to be reproduced in analog printing at a later date, this can be achieved with outstanding quality using the method described.

[0027] The invention relates, on the one hand, to the generation of engraving data for engraving the printing cylinders (e.g., of a rotary printing press) and, on the other hand, to a method for producing the printing cylinders of a printing press for multi-color analog printing of surface decorations. Consequently, the engraving data generated in the manner described is used for engraving the printing cylinders (e.g., of a rotary gravure printing press).

[0028] Finally, the invention also relates to the printing method itself, i.e., a method for printing decorations using the analogue printing method with printing cylinders produced as described. Furthermore, the invention also relates to a method for printing one and the same decoration using both digital and analogue printing, the respective print data being produced as described. It is particularly important that one and the same decoration is printed in a specific colour space using digital printing, and then, for example, later selected decorations are also printed in the same (or essentially the same) colour space using analogue printing, albeit with blended colours.

[0029] The invention will be explained in more detail below with reference to drawings which merely represent an exemplary embodiment. Fig. 1 shows a layout of a surface decoration, e.g., as a wood reproduction, Fig. 2A, B shows the generation of print data or engraving data using a method known from the prior art, Fig. 3A, B shows the inventive processing or generation of print data for digital printing, and Fig. 4 shows the further processing of the data according to Figur 3A , B for analogue printing.

[0030] The starting point is a Fig. 1 An example of a decor shown as a layout, which can be, for example, a replica of a wooden surface. It is a colored layout that is Fig. 1 is represented only in shades of gray. For this design, a layout 1 is created as a digital data set, for example, by digitizing the original (e.g., scanning it). Such a digital data set cannot be used directly for printing, neither for digital nor analogue printing, so color separation takes place in the so-called prepress stage, i.e., color separations are created for the color space selected for the printing process.

[0031] The Fig. 2A und B show the classic path in decor development up to printing. It is initially carried out according to Fig. 2A a color separation, namely a gravure separation in a special color space that does not use the process colors CYMK for the four printing cylinders, but rather special mixed colors, for example several shades of brown. Fig. 2A The lower four images show the tonal value information or color separations F1, F2, F3 and F4 for the four selected colors and the upper image shows the print image TD, ie the result of printing this gravure separation with pure process colors CMYK, the so-called color play. This color print image TD is in Fig. 2A shown above only in shades of gray. The printed image is unnatural, since in this case the printing is done in CMYK, for example, although the gravure separation is designed for printing with mixed colors (e.g. brown tones). However, such a play of colors is advantageous in the classic technique, so that different color nuances of the decoration can be created with a single set of cylinders with different mixed colors or by exchanging the mixed colors. The drawings show the black print for the color separations F1 to F4, ie the tonal value information in the respective cylinder. In the upper image of the Fig. 2A The print result is indicated, which in practice - contrary to the illustration - is colored.

[0032] Fig. 2B shows the same gravure separation with the same tonal information in the (color separations F1 to F4) or cylinders. However, the upper area now shows the print result TD of this gravure separation with the specially provided mixed colors (e.g. four brown tones), so that the print result TD in Fig. 2B essentially the Fig. 1 Layout 1 shown. It is important that in this case, analogue printing uses special mixed colours, for example, different shades of brown. Fig. 2B shows the color print result above only in grayscale.

[0033] Such a conventional gravure separation according to Fig. 2A , B is associated with considerable effort. If a decoration is first printed in small quantities using digital printing, e.g., in the CMYK color space, and then the same decoration is to be prepared for analog printing, this requires, on the one hand, complex gravure separation, and, on the other hand, reproducibility is problematic.

[0034] For this reason, according to the invention, in the Figuren 3A und 3B and 4 described manner: According to Fig. 3A First, a standard digital printing separation is performed in a base color space commonly used for digital printing, e.g., a CMYK color space. The individual tonal value information F1 to F4, or the individual color separations F1 to F4, are shown as base color separations, as well as the result DD of the digital print in the CMYK color space in the upper image. The color result DD is again shown only in grayscale.

[0035] These basic color separations F1 to F4 according to Fig. 3A However, they are not usually used for digital printing, but are first processed, in particular a GCR conversion in the raster image processor, so that the converted color separations K1 to K4 are Fig. 3B It is a GCR-converted digital printing separation in the same basic color space, e.g. CMYK color space. The individual color separations K1 to K4 show the achromatic composition with an increased black content, ie the color separations F1 to F4 according to Figur 3A are converted into color separations K1 to K4 in an achromatic composition according to Fig. 3B This data is processed in accordance with Fig. 3B can now be transferred directly to a digital printing machine for digital production, so that in digital printing the Fig. 3B The print image DD shown above is created by printing with the four basic colors, e.g., process colors in the CMYK color space. The representation of the color print image DD in Fig. 3B is also limited to a black and white representation or grayscale. The color separations K1 to K4 are displayed as black prints in the usual way.

[0036] For example, if the Fig. 1 or Fig. 3B If the above-depicted decoration or print image DD is to be reproduced at a later date in analogue printing or is to be prepared for analogue printing, the Fig. 3B The data shown, ie the converted color separations K1 to K4, are taken over and post-processed in a special way. For each base color or for each base color separation K1 to K4, the tonal values ​​are increased in such a way that the darkest color tone in the color separation is raised to a maximum value of 100% and the remaining tonal values ​​of the respective color separation are increased linearly. If, for example, within a single color separation the darkest color tone, ie the color tone with the highest tonal value, is raised from its original value of 50% to 100% and thus by a factor of 2, all other tonal values ​​of the same color separation are also raised by this factor of 2. Through this post-processing, the Fig. 4 The post-processed color separations N1 to N4 shown below are generated. This data is used for engraving the four cylinders, and these cylinders are used in the analogue printing press to print with blended, pure base colors. In this way, the originally produced digital print sample DD from Fig. 3B excellently reproduce TD in analogue printing, in the identical colour space, but with blended colours (e.g. blended CMYK colours). Fig. 4 The image above shows the result of the gravure TD with the cylinders engraved on the basis of the color separations N1 to N4 with maximum tonal value correction. Fig. 4 It is evident that the tonal value information per cylinder is increased, making it possible to work with significantly more heavily blended, pure CMYK colors in analog printing, thus closely mimicking digital printing. The maximum tonal value correction in this example ensures that one of the colors, e.g., cyan, is hardly needed or not needed at all.

[0037] Because digital printing is Fig. 3B in pure colors, e.g., CMYK, and the reproduction in analogue printing according to Fig. 4 also in the CMYK color space, the comparability is very good. By using the achromatic composition in digital and analogue printing, the overall ink consumption is reduced and the color stability in both processes is increased. Fig. 4 Please note that the color print result TD is graphically represented only in black and white or grayscale. The color separations N1 to N4 each show the black print, i.e., the tonal value information in the respective cylinder.

[0038] In certain cases, digital printing offers the possibility of already Fig. 3A The basic color separations F1 to F4 shown are to be used for digital printing and consequently transferred to the digital printing machine, so that GCR conversion can be omitted if necessary. In this case, these basic color separations F1 to F4 are also used for the processing essential to the invention in preparation for analogue printing, ie for the Fig. 4 The processing of tonal values ​​described always uses the data that was previously used for the digital printing evaluation.

[0039] Furthermore, as an alternative to the described scale colours in CMYK, other basic colours and, in particular, similar basic colours can be used, e.g., blue, red, yellow and / or black.

[0040] For analog printing, as described above, the same pure process colors are preferably used as those used for digital printing. Optionally, these can be essentially pure, blended process colors that contain a very small proportion of other colors.

Claims

1. A method for generating engraving data for the engraving of printing cylinders of a printing machine for the multi-color analog printing of surface decors on flat substrates, e.g. films or papers, comprising the following method steps: a) a layout (1) of a decor is created or made available as a digital data set, b) base color separations (F1 to F4) for each individual base color are generated from the data set by means of a separation, e.g., a standard digital print separation, into a base color space with multiple base colors, c) the base color separations (F1 to F4) are optionally converted into converted color separations (K1 to K4) with converted color distribution using a conversion method, e.g., using a raster image processor (RIP), which are optionally available as digital print data for transfer to a digital printing machine, d) the base color separations (F1 to F4) or the converted color separations (K1 to K4) are post-processed by increasing the tonal values for each base color or each individual color separation in such a manner that in each case the darkest tone with the highest tonal value in the color separation is raised to a predetermined maximum tonal value, and the remaining tonal values of the respective color separation are increased according to a predetermined relationship, wherein the color separations (N1 to N4) post-processed in this manner are available or made available as engraving data for engraving the printing cylinders of a printing machine for an analog printing method, wherein the printing cylinders are intended for analog printing with pure or substantially pure but blended base colors of the base color space.

2. A method for generating print data for the printing of surface decors on flat substrates, e.g. films or papers, wherein, on the one hand, digital print data for a digital print are generated and, on the other hand, engraving data for the engraving of print cylinders for multi-color analog printing are generated by a method according to claim 1, comprising the following method steps: a) a layout (1) of a decor is created or made available as a digital data set, b) base color separations (F1 to F4) for each individual base color are generated from the data set by means of a separation, e.g., a standard digital print separation, into a base color space with multiple base colors, c) the base color separations (F1 to F4) are optionally converted into converted color separations (K1 to K4) with converted color distribution using a conversion method, e.g., using a raster image processor (RIP), wherein the base color separations (F1 to F4) or the converted color separations (K1 to K4) are available or made available as digital printing data for transfer to a digital printing machine, and d) the base color separations (F1 to F4) made available for the digital printing machine or the converted color separations (K1 to K4) are post-processed by increasing the tonal values for each base color or each individual color separation in such a manner that in each case the darkest tone with the highest tonal value in the color separation is raised to a predetermined maximum tonal value, and the remaining tonal values of the respective color separation are increased according to a predetermined relationship, wherein the color separations (N1 to N4) post-processed in this manner are available or made available as engraving data for engraving the printing cylinders of a printing machine for an analog printing method.

3. The method according to claim 1 or 2 for a three-color or four-color print, wherein three or four base color separations for the three or four base colors are produced by the separation in method step b).

4. The method according to claim 3, wherein as the base colors - blue or blue / green, e.g., cyan (C) - red or red / blue, e.g., magenta (M) - yellow (Y) and / or - black (K) are used, e.g., in a CMYK color space or blue-red-yellow-black color space.

5. The method according to any one of claims 1 to 4, wherein in method step c), the base color separations (F1 to F4) are converted by means of a GCR conversion into converted color separations (K1 to K4) in an achromatic structure using the processing method.

6. The method according to any one of claims 1 to 5, wherein in method step d), in each case the darkest tonal value in the color separations is raised to a predetermined maximum tonal value of at least 90 %, e.g., at least 95 %, preferably 100 %, and the remaining tonal values of the respective color separation are increased accordingly.

7. The method according to any one of claims 1 to 6, wherein in method step d), the remaining tonal values of the respective color separation are increased linearly.

8. A method for producing printing cylinders of a printing machine for multi-color analog printing of surface decors on flat substrates, e.g., films or papers, wherein engraving data are used for engraving the printing cylinders, which engraving data are generated or have been generated by a method according to any one of claims 1 to 7.

9. A method for printing decors in analog printing with printing cylinders, in particular using an intaglio printing method, wherein the printing cylinders are produced by a method according to claim 8.

10. A method for printing decors both in digital printing and in analog printing, wherein the printing data for digital printing on the one hand and for engraving the printing cylinders for multi-color analog printing on the other hand are generated by a method according to any one of claims 2 to 7.

11. The method according to claim 9 or 10, wherein the printing cylinders are used to print with pure or substantially pure, blended base colors of the base color space.