Multiple laser engraving

Abstract

The invention relates to a method and a device for producing a printing plate by means of laser engraving. The device (200) comprises: means for subdividing an engraved image (212) to be produced on a surface of the printing plate (210) into at least two image sections (214, 216) by defining at least one section boundary (218) between the at least two image sections (214, 216); means (230, 240, 242, 244, 252) for engraving the surface of the printing plate (210) using at least two laser engraving units (230), wherein the means (230, 240, 242, 244, 252) for engraving the surface of the printing plate (210) are configured such that each of the at least two image sections (214, 216) is simultaneously engraved by one of the at least two laser engraving units (230). The object of providing a method and a device for producing a printing plate by means of laser engraving in which a reduction in engraving time can be achieved by using a plurality of laser engraving units, irrespective of the nature of the engraved image to be produced, is achieved for the device (200) in that the means (252) for subdividing the engraved image (212) is configured to define the at least one section boundary (218) such that at least a portion of the at least one section boundary (218) passes through an engraving region (220) of the engraved image.

Description

[0001] Multiple laser engraving

[0002] The invention relates to a method for producing printing forms by laser engraving. Furthermore, the invention relates to a device or system for producing printing forms by laser engraving, a computer program product, and a use of a printing form.

[0003] Printing plates, especially for flexographic printing, but also for gravure printing, are increasingly being produced using laser engraving. This involves removing material from the surface of the printing plate by locally heating the surface material with a laser beam to such an intense degree that it evaporates. This creates an engraved image on the surface of the printing plate, which, depending on the printing process, represents a kind of mirrored negative of the final printed image. The laser engraving process is characterized by the high precision required for the production of such printing plates.

[0004] In flexographic printing, a distinction can be made between solid areas, halftone areas, and white areas with regard to the print image. In a solid area, the surface of the printing form prints across the entire surface of the substrate. Examples of solid areas include the letters and other typographic characters of a text to be printed, as well as the lines of a line drawing to be printed. In a halftone area, on the other hand, the surface of the printing form has a screen, so that only the individual screen dots of the halftone area print onto the substrate, but not the entire surface of the halftone area. The screen dots are usually circular, but can also take on other shapes. Overlaps between the individual screen dots are also possible. Examples of halftone areas include halftone images to be printed. In a white area, the entire surface of the substrate remains unprinted.Examples of white areas include the areas between individual typographic characters in printed text, the areas between individual lines in line drawings, and the spaces between text, line drawings, and halftone images. The term white area is used regardless of whether a white substrate such as paper or a different colored substrate is used. In addition to paper, suitable substrates include cardboard, paperboard, rubber, and various plastics, such as PE, PET, PVC, PS, PP, and PC.

[0005] In accordance with the three possible areas of a printed image in flexographic printing just described, three different areas can also be distinguished with regard to the engraving image on printing plates produced by laser engraving. In this regard, it should be noted that flexographic printing is a form of relief printing, which means that raised or elevated elements of the surface of the printing plate print on the substrate, while non-raised or depressed elements of the surface of the printing plate leave the substrate unprinted. In order to create a white area in the subsequent printed image, material must be removed from the entire surface of the printing plate during engraving. Furthermore, to create a halftone area, material must be removed from part of the surface of the printing plate during engraving in such a way that a screening with individual screen dots is created.The halftone dots can represent both raised and recessed elements of the printing form's surface. Finally, to create a solid area, the surface of the printing form must remain completely unengraved during engraving, so that no material is removed from the surface, especially not partial material.

[0006] In this context, in the context of the present patent application, a full engraving area is understood to be an area of ​​the engraving image in which a full-surface engraving of the printing form takes place. Furthermore, a raster engraving area is understood to be an area of ​​the engraving image in which a partial engraving takes place to generate raster dots. Finally, a free area is understood to be an area of ​​the engraving image in which no engraving, in particular not even a partial engraving, takes place. Full engraving areas and raster engraving areas are referred to by the generic term engraving area. This means that in the context of the present patent application, an engraving area is understood to be an area of ​​the engraving image in which a full-surface engraving and / or a partial engraving takes place to generate raster dots.

[0007] In contrast to flexographic printing, in gravure printing, raised or elevated elements of the printing form's surface remain unprinted, while non-raised or recessed elements of the printing form's surface print the printing material. A special feature of gravure printing is that all elements of the print image to be printed, including text and line drawings, are rasterized. Therefore, a gravure printing form produced by laser engraving only has raster engraving areas and blank areas. The raster engraving areas correspond to the printed areas in the final printed image, while the blank areas correspond to the white areas.

[0008] Since the production of printing plates using laser engraving is very time-consuming, regardless of whether they are for flexographic printing or gravure printing, solutions that enable a reduction in engraving time have always been sought. For this purpose, it is already known from the state of the art for engraving printing cylinders for gravure printing to divide the engraved image to be created on the surface of the printing plate into several image sections by defining section boundaries between the image sections. The printing plates are then engraved by several laser engraving units, with each of the previously defined image sections being engraved simultaneously by one laser engraving unit.

[0009] However, as European patent application EP 2058122 A1 shows, for example, section boundaries for simultaneous engraving by multiple laser engraving units can currently only be defined by free areas of the engraved image. This is partly due to the fact that the properties of the individual laser engraving units are not necessarily perfectly identical due to unavoidable deviations such as manufacturing tolerances, which also affects the engraving results in the individual image sections. For example, the intensity or power of the lasers may differ slightly. Since it is therefore possible for the individual image sections to be engraved in slightly different ways, section boundaries that do not run through a free area may be visually recognizable in the subsequent printed image.This is especially true when the section boundary runs through a raster engraving area, as the human eye is very sensitive to even slight differences in the raster when perceiving rasterized areas. On the other hand, however, inaccuracies can also arise in the positioning of the laser engraving units. In the worst case, these inaccuracies can lead to the material on the surface of the printing form not being removed at certain points along a section boundary, for example when engraving a full engraving area using multiple laser engraving units. Instead, raised areas are created at these points, which lead to ink removal on the printing substrate within a white area during subsequent printing, thus making the section boundary directly visible.

[0010] Consequently, an engraved image that does not have a continuous free area cannot be engraved simultaneously by multiple laser engraving units according to the current state of the art, meaning that no reduction in engraving time is possible in this case. Furthermore, for an engraved image that has continuous free areas only close to the edge of the engraved image, the potential reduction in engraving time is minimal, since the size of the individual image sections that are engraved simultaneously by each laser engraving unit differs greatly, meaning that a comparatively large image section can still only be engraved simultaneously by a single laser engraving unit. In such cases, simultaneous engraving by multiple laser engraving units is often completely dispensed with due to the minimal time savings.

[0011] Against this background, the present invention is based on the object of providing a method for producing printing forms by laser engraving, in which a reduction in engraving time can be achieved when using multiple laser engraving units, regardless of the nature of the engraved image to be created. Furthermore, the invention aims to provide a corresponding device or system for producing printing forms by laser engraving, a corresponding computer program product, and an advantageous use of a printing form produced by the method.

[0012] According to a first teaching of the invention, the above-mentioned object is achieved by a method for producing a printing form by laser engraving. The method comprises:

[0013] Dividing an engraving image to be produced on a surface of the printing form into at least two image sections by defining at least one section boundary between the at least two image sections;

[0014] Engraving the surface of the printing form using at least two laser engraving units, wherein each of the at least two image sections is engraved simultaneously by one of the at least two laser engraving units.

[0015] The solution to the problem is achieved for such a method in that, when dividing the engraving image, the at least one section boundary is defined such that at least one section of the at least one section boundary runs through an engraving area of ​​the engraving image.

[0016] Within the scope of the invention, it was recognized that a reduction in engraving time when using multiple laser engraving units can be achieved by, contrary to the prior art, at least one section of the at least one section boundary defined when dividing the engraving image running through an engraving region of the engraving image. The term "at least one section boundary running 'through' an engraving region means that the at least one section boundary has at least one intersection point with an edge of the engraving region. Because at least one section boundary runs through an engraving region of the engraving image, for example, even an engraving image that does not have a continuous free region can be engraved simultaneously by multiple laser engraving units. This has not been possible with the prior art methods described above.Furthermore, for example, an engraved image that has continuous free areas only near the edge of the engraved image can be engraved within a shorter engraving time than previously possible, since the size differences between the individual image sections, each engraved simultaneously by a single laser engraving unit, can be reduced. Overall, the method according to the invention thus makes it possible to shorten the engraving time when using multiple laser engraving units, regardless of the nature of the engraved image to be created.

[0017] In a preferred embodiment of the method, the at least one section boundary is defined such that at least a portion of the at least one section boundary runs through a raster engraving area of ​​the engraved image. As initially indicated, a section boundary running through a raster engraving area is not possible in the described prior art methods. Because at least a portion of the at least one section boundary runs through a raster engraving area of ​​the engraved image, in particular an engraved image whose engraving areas are exclusively raster engraving areas can be engraved simultaneously by multiple laser engraving units. Such engraved images include, for example, all conceivable engraved images for gravure printing as well as engraved images for flexographic printing whose associated print image does not have any white areas.

[0018] In a further preferred embodiment of the method, at least one action is carried out which leads to a reduction in the optical perceptibility of the at least one section boundary in the subsequent printed image. The at least one action carried out can in particular relate to the subdividing of the engraving image. For example, the at least one action carried out relates to the definition of the at least one section boundary. However, other actions are also conceivable which do not relate to the definition of the at least one section boundary. By carrying out the at least one action which leads to a reduction in the optical perceptibility of the at least one section boundary in the subsequent printed image, the course of the at least one section boundary in the subsequent printed image is not so easily recognizable to the human eye.

[0019] In a further preferred embodiment of the method, an overlap region surrounding the section boundary is defined along at least one section of the at least one section boundary, in which the at least one section boundary runs through an engraving region of the engraving image, in which overlap region the two adjacent image sections overlap. When engraving the surface of the printing form, the overlap region is engraved by both laser engraving units, which are respectively assigned to the two adjacent image sections. This makes it possible to ensure that the course of the at least one section boundary is not so easily recognizable to the human eye in the subsequent printed image, for example if the properties of the individual laser engraving units are not perfectly identical due to manufacturing tolerances, or if there are inaccuracies in the positioning of the laser engraving units.

[0020] In a further preferred embodiment of the method, a gradual transition between the engraving depths of the two laser engraving units takes place in at least one partial area of ​​the overlapping area, which lies within an engraving area of ​​the engraving image. The engraving depth of a laser engraving unit is understood to mean the material removal caused by this laser engraving unit in a direction perpendicular and / or tangential to the engraved surface of the printing form. The engraving depth can be varied, for example, via the intensity of the laser, the wavelength of the laser, the power of the laser, or the irradiation time of the surface of the printing form. A gradual transition between the engraving depths of the two laser engraving units in the overlapping area is understood to mean that the engraving depth of the first laser gradually decreases within the overlapping area and the engraving depth of the second laser increases accordingly.For example, it can be a continuous or a step-by-step, gradual transition. Preferably, the total engraving depth, i.e., the sum of the engraving depths of both laser engraving units, remains constant. By ensuring a gradual transition between the engraving depths of the two laser engraving units in at least a portion of the overlapping area that lies within an engraving area of ​​the engraving image, it is possible to prevent raised areas from forming along the section boundary in a fully engraved area of ​​the engraving image. These raised areas could lead to ink removal on the substrate within a white area in the subsequent printed image, thus making the section boundary directly visible.In a raster engraving area of ​​the engraving image, a more uniform transition can be achieved between the two adjacent image sections, so that the course of at least one section boundary is not so easily recognizable to the human eye in the subsequent printed image.

[0021] In a further preferred embodiment of the method, in at least one partial area of ​​the overlapping area that lies within a raster engraving area of ​​the engraved image, at least one depressed element of the surface of the printing form, which lies within one of the two adjacent image sections of the engraved image, is engraved by the laser engraving unit assigned to the respective other image section. If the printing form is intended for gravure printing, the depressed element of the surface of the printing form can be, for example, a printing depression of the surface of the printing form. Furthermore, if the printing form is intended for flexographic printing, the depressed element of the surface of the printing form can be, for example, a non-printing depressed element of a raster engraving area.By engrave- ing at least one recessed element located within one of the two adjacent image sections of the engraved image by the laser engraving unit assigned to the other image section, a more smooth transition between the two adjacent image sections can be achieved, so that the contour of at least one section boundary is not as easily recognizable to the human eye in the subsequent printed image. This is especially true if the properties of the individual laser engraving units are not perfectly identical due to manufacturing tolerances, or if there are inaccuracies in the positioning of the laser engraving units.

[0022] The overlapping area can, for example, have a width of up to 200 mm, preferably in the range of 0.1 mm to 50 mm, particularly preferably in the range of 0.5 mm to 20 mm, in a direction perpendicular and / or tangential to the section boundary. This width is sufficient to achieve the effects just described. Smaller widths lead to greater time savings during simultaneous engraving with multiple laser engraving units. Conversely, larger widths reduce the visual perceptibility of the at least one section boundary in the subsequent printed image.

[0023] In a further preferred embodiment of the method, the at least one section boundary is defined such that the length of the direct connecting line between the point at which the at least one section boundary enters an engraving area and the point at which the at least one section boundary exits this engraving area is reduced compared to the maximum possible length. The length of the direct connecting line is preferably reduced to a minimum. By reducing the length of the direct connecting line, preferably to a minimum, it can be achieved that the at least one section boundary, based on its entire length, runs through an engraving area only in relatively short sections, such that the optical perceptibility of the at least one section boundary in the subsequent printed image is reduced.In a further preferred embodiment of the method, in at least one section of the at least one section boundary, in which the at least one section boundary runs through a raster engraving area of ​​the engraving image, the at least one section boundary is defined such that the at least one section boundary is curved, wavy, jagged and / or otherwise deviates from a continuous straight line. In this context, a continuous straight line is understood to mean a straight line that completely traverses a contiguous raster engraving area without changing direction. Section boundaries that run along a continuous straight line within a raster engraving area are comparatively easy for the human eye to recognize in the subsequent printed image.As a result of the at least one section boundary running in at least one section of the at least one section boundary in a curved, wavy, jagged and / or otherwise deviating from a continuous straight line through a raster engraving area of ​​the engraving image, it can consequently be achieved that the optical perceptibility of the at least one section boundary in the subsequent printed image is reduced.

[0024] In a further preferred embodiment of the method, in at least one section of the at least one section boundary, in which the at least one section boundary runs through a raster engraving area of ​​the engraving image, the at least one section boundary is defined such that the at least one section boundary runs along an inner contour of the raster engraving area. In this context, an inner contour of a raster engraving area is understood to mean an abrupt transition within a raster engraving area between two areas with different rasterization.In flexographic printing, an inner contour of a screen engraving area can be formed, for example, by a transition from an area in which the size and / or spacing of the screen dots each assumes a first value to produce a first halftone color, to an area in which the size and / or spacing of the screen dots each assumes a second value to produce a second halftone color. However, variations with regard to any other screening parameters are also conceivable. In gravure printing, an inner contour of a screen engraving area can, for example, also be formed by a transition from an area in which the recess depth of the printing depressions assumes a first value to produce a first ink application, to an area in which the recess depth of the printing depressions assumes a second value to produce a second ink application.By having at least one section boundary run along an inner contour of the raster engraving area in at least one section boundary, the optical perceptibility of the at least one section boundary in the subsequent printed image is reduced. This is due to the fact that the inner contour of the raster engraving area is already perceived as a kind of boundary, so the course of the at least one section boundary along the inner contour is not as visually noticeable.

[0025] In a further preferred embodiment of the method, the at least one section boundary is defined in at least one portion of the at least one section boundary such that the at least one section boundary runs along an edge between an engraving area and a free area or along an edge between a full engraving area and a raster engraving area. In the former case, the engraving area can be a full engraving area or a raster engraving area. Just like contours within a raster engraving area, the aforementioned edges are also perceived by the human eye as a type of boundary.The fact that the at least one section boundary runs along an edge between an engraving area and a free area or along an edge between a full engraving area and a raster engraving area in at least one section of the at least one section boundary thus reduces the visual perceptibility of the at least one section boundary in the subsequent printed image. In a further preferred embodiment of the method, the at least one section boundary is defined in at least one section of the at least one section boundary based on a user input. For example, a user can define the course of the at least one section boundary themselves, at least in sections. It is also conceivable for possible courses of the at least one section boundary to be displayed to the user on a display unit, wherein the user selects one of the displayed courses by means of a suitable user input.By defining the at least one section boundary in at least one section based on user input, a user who initiates or controls the process can influence the definition of the at least one section boundary. For example, the user can define the at least one section boundary in such a way that the at least one section boundary is not easily recognizable to the human eye in the subsequent printed image.

[0026] In a further preferred embodiment of the method, the method is designed such that at least one of the following conditions is met: along at least one section of the at least one section boundary, in which the at least one section boundary runs through an engraving area of ​​the engraving image, an overlap area surrounding the section boundary is defined, in which the two adjacent image sections overlap, wherein when engraving the surface of the printing form, the overlap area is engraved by both laser engraving units, which are respectively assigned to the two adjacent image sections;the at least one section boundary is defined such that the length of the direct connecting line between the point at which the at least one section boundary enters an engraving area and the point at which the at least one section boundary exits this engraving area is reduced compared to the maximum possible length; in at least one section of the at least one section boundary in which the at least one section boundary runs through a raster engraving area of ​​the engraving image, the at least one section boundary is defined such that the at least one section boundary is curved, wavy, jagged and / or otherwise deviates from a continuous straight line;In at least one section of the at least one section boundary, in which the at least one section boundary runs through a raster engraving area of ​​the engraving image, the at least one section boundary is defined such that the at least one section boundary runs along an inner contour of the raster engraving area; In at least one section of the at least one section boundary, the at least one section boundary is defined such that the at least one section boundary runs along an edge between an engraving area and a free area or along an edge between a full engraving area and a raster engraving area;the at least one section boundary is defined in at least one section of the at least one section boundary based on user input. Compliance with each of the aforementioned conditions individually results in the optical perceptibility of the at least one section boundary in the subsequent printed image being reduced, as can be seen from the previous explanations. However, it is sufficient that at least one condition is met to achieve the aforementioned effect. In principle, however, at least two, at least three, or more than three of the aforementioned conditions can also be met. The more conditions are met simultaneously, the more the optical perceptibility of the at least one section boundary is reduced in the subsequent printed image.;

[0027] In a further preferred embodiment of the method, a representation of the engraving image is displayed on at least one display unit together with a representation of the at least one section boundary or at least together with a representation of a preliminary profile of the at least one section boundary. This makes it easier for a user to control the method. In particular, the definition of the at least one section boundary is simplified for the user if the user receives visual feedback about the engraving image and the at least one section boundary or at least a preliminary profile of the at least one section boundary via the at least one display unit.

[0028] In a further preferred embodiment of the method, the at least two laser engraving units are movable independently of one another in at least one spatial direction. The at least one spatial direction is, in particular, an axial direction of a cylindrical printing form. The independent mobility of the at least two laser engraving units in at least one spatial direction ensures that the at least two laser engraving units can engrave the respective image sections independently of one another when engraving the printing form. For example, each laser engraving unit can traverse free areas occurring within the image section it is to process in the axial direction independently of the other laser engraving units, so that an overall reduction in the engraving time can be achieved.

[0029] In a further preferred embodiment of the method, each of the at least two laser engraving units comprises at least one dedicated laser source. A dedicated laser source in this context is understood to mean a physically independent laser source that is exclusively assigned to the respective laser engraving unit and can be moved independently together with this laser engraving unit. Furthermore, each of the at least two laser engraving units in this embodiment comprises at least one dedicated modulator. A dedicated modulator in this context is understood to mean a physically independent modulator that is exclusively assigned to the respective laser engraving unit and can be moved independently together with this laser engraving unit.Because each of the at least two laser engraving units comprises at least one of its own laser source and at least one of its own modulator, it is achieved that the at least two laser engraving units can engrave the respective image sections independently of one another when engraving the surface of the printing form, thus achieving an overall reduction in the engraving time.

[0030] In a further preferred embodiment of the method, the laser sources of the at least two laser engraving units are fiber laser sources. This allows for high beam quality and a virtually maintenance-free design of the laser sources.

[0031] In an alternative embodiment of the method, the laser sources of the at least two laser engraving units are CCh laser sources. This also allows the engraving of materials such as silicones, which cannot be engraved with fiber lasers.

[0032] In a further preferred embodiment of the method, the modulators of the at least two laser engraving units are acousto-optical modulators. This allows for particularly precise modulation of the laser beam and thus a correspondingly accurate engraving result when engraving the printing form.

[0033] In a further preferred embodiment of the method, each of the at least two laser engraving units comprises at least one lens. In particular, each of the at least two laser engraving units comprises at least one separate lens. In this context, a separate lens is understood to be a physically independent lens that is exclusively assigned to the respective laser engraving unit and can be moved independently together with this laser engraving unit. By using lenses in the laser engraving units, the resolution of the engraving images can be increased and thus the sharpness of the engraving result can be improved. By using separate lenses for each of the at least two laser engraving units, the at least two laser engraving units can engrave the respective image sections independently of one another when engraving the printing form, thereby shortening the engraving time overall.In a further preferred embodiment of the method, the at least two laser engraving units are essentially identical. This means that the at least two laser engraving units have the same structure with the same components, and that their properties differ only through unavoidable deviations such as manufacturing tolerances. Because the at least two laser engraving units are essentially identical, a particularly uniform engraving result can be achieved. In particular, this also makes it possible to ensure that section boundaries between individual image sections of the engraved image are not as easily recognizable to the human eye in the subsequent printed image.

[0034] In a further preferred embodiment of the method, a printing form for flexographic printing is produced. In an alternative embodiment of the method, a printing form for gravure printing is produced. In both flexographic printing and gravure printing, a reduction in engraving time can be achieved by using multiple laser engraving units, regardless of the nature of the engraved image to be created.

[0035] In a further preferred embodiment of the method, the surface of the printing form to be engraved consists at least partially of rubber. Preferably, the surface of the printing form to be engraved consists entirely of rubber. Particularly in flexographic printing, rubber is widely used as a material for the surface of the printing form to be engraved and meets the applicable requirements. Because the surface of the printing form to be engraved consists at least partially, preferably entirely, of rubber, the method according to the invention can be used to produce corresponding printing forms for flexographic printing.

[0036] In an alternative embodiment of the method, the surface of the printing form to be engraved consists at least partially of metal or plastic.

[0037] Preferably, the surface of the printing form to be engraved consists entirely of metal or plastic. In the case of metal, this is particularly copper, chromium, or zinc. Metal, especially copper, chromium, or zinc, and plastic are widely used as materials for the surface of the printing form to be engraved, particularly in gravure printing, and they meet the applicable requirements. Because the surface of the printing form to be engraved consists at least partially, preferably entirely, of metal or plastic, the method according to the invention can be used to produce corresponding printing forms for gravure printing.

[0038] In another preferred embodiment of the method, the printing form is a sleeve. This is understood to be a cylindrical sleeve whose outer surface is engraved by laser engraving and serves as the printing surface during subsequent printing. Sleeves are widely used as printing forms in both flexographic printing and gravure printing. Because the printing form is a sleeve, corresponding printing forms can be produced using the method according to the invention.

[0039] In an alternative embodiment of the method, the printing form is a printing cylinder. This is understood to be a cylindrical body whose outer surface is engraved by laser engraving and serves as the printing surface in the subsequent printing process. Printing cylinders are also still widely used in both flexographic and gravure printing. Because the printing form is a printing cylinder, corresponding printing forms can be produced using the method according to the invention.

[0040] In a further alternative embodiment of the method, the printing form is at least one flexible printing plate that is fixed to a fixing cylinder. The at least one flexible printing plate can be fixed to the fixing cylinder, for example, by means of a material bond, magnetically, and / or by means of negative pressure. The flexible printing plate fixed in this way therefore has an outer surface that, for the purpose of engraving, corresponds to the outer surface of a cylindrical printing form. Subsequent printing then usually takes place in a planar geometry, which means that the at least one printing plate is no longer fixed to a fixing cylinder, for example. Because the printing form is at least one flexible printing plate that is fixed to a fixing cylinder, the method according to the invention can also be used for the production of printing plates, which are also widely used in flexographic printing.

[0041] The first teaching also specifies a method for producing at least two associated printing forms for multi-color printing. Each of the at least two associated printing forms is produced by the method described so far according to the first teaching, wherein, at least in areas in which the engraving areas of at least two engraving images overlap when the engraving images to be generated on the respective surfaces of the printing forms are placed on top of one another, the at least one section boundary of each engraving image involved in the overlap is defined such that the at least one section boundary is, at least in sections, not congruent with a section boundary of another engraving image involved in the overlap. In multi-color printing, the finished multi-color print image is created by the print images of several colors superimposing one another.If several section boundaries of the respective engraving images coincide within an engraving area, this can be relatively easy to visually detect in the subsequent printed image. By defining at least one section boundary of each engraving image involved in the overlap, at least in areas where the engraving areas of at least two engraving images overlap when the engraving images to be created on the respective surfaces of the printing forms are placed on top of one another, the optical perceptibility of the at least one section boundary in the subsequent printed image is reduced. This applies in particular if the engraving areas mentioned are raster engraving areas.According to a second teaching of the invention, the above-mentioned object is achieved by a device or system for producing a printing form by laser engraving. The device or system comprises:

[0042] Means for dividing an engraving image to be produced on a surface of the printing form into at least two image sections by defining at least one section boundary between the at least two image sections;

[0043] Means for engraving the surface of the printing form using at least two laser engraving units, wherein the means for engraving the surface of the printing form are configured such that each of the at least two image sections is engraved simultaneously by one of the at least two laser engraving units.

[0044] The object is achieved for such a device or such a system in that the means for dividing the engraving image are configured to define the at least one section boundary such that at least a portion of the at least one section boundary runs through an engraving area of ​​the engraving image.

[0045] For example, the device according to the second teaching is a laser engraving machine with an integrated processing unit. For example, the system according to the second teaching is a laser engraving machine that is connected to an external processing unit. The external processing unit can be a

[0046] Control computer. For example, the means for dividing the engraving image comprise a processor, in particular a processor of the integrated or external computing unit. For example, the means for engraving the surface of the printing form comprise at least two laser engraving units, means for positioning the at least two laser engraving units relative to the surface of the printing form, and control means. In an exemplary case in which the printing form has a cylindrical shape, the means for positioning comprise, for example, a motor that rotates the printing form about a longitudinal axis, such that in this way the at least two laser engraving units are positioned in the circumferential direction relative to an outer surface of the printing form.Furthermore, the positioning means comprise, for example, at least two longitudinal drives, which displace the at least two laser engraving units parallel to an axial direction of the printing form, thereby positioning the at least two laser engraving units in the axial direction relative to an outer surface of the printing form. For example, the control means comprise at least one processor, in particular a processor of the integrated or external processing unit, and at least one control unit of the laser engraving machine, which controls the laser engraving units, the motor, and the longitudinal drive such that the printing form is engraved according to the engraving image to be generated.

[0047] As already explained in connection with the first teaching, by having at least one section of the at least one section boundary run through an engraving area of ​​the engraving image, it is possible overall to achieve that, regardless of the nature of the engraving image to be produced, the engraving time can be shortened when using several laser engraving units.

[0048] In particular, the device or system according to the second teaching carries out a method according to the first teaching and is configured to carry out such a method. All method features described within the first teaching are hereby also deemed to be disclosed for the device or system according to the second teaching. This is to be understood as meaning that the device or system according to the second teaching is configured to implement the method features described within the first teaching and / or has means for implementing the method features described within the first teaching.

[0049] In a preferred embodiment of the device or system, the device or system comprises means for at least partially defining the at least one section boundary based on a user input. This ensures that a user who initiates or controls the method can influence the definition of the at least one section boundary, as already explained in connection with the first teaching.

[0050] In a further preferred embodiment of the device or system, the device or system further comprises means for displaying the engraving image together with a representation of the at least one section boundary, or at least together with a representation of a preliminary profile of the at least one section boundary, on at least one display unit. This makes it easier for a user to control the method according to the first teaching when it is carried out by the device or system according to the second teaching.

[0051] In a further preferred embodiment of the device or system, the device or system further comprises at least one dedicated laser source and at least one dedicated modulator for each of the at least two laser engraving units. This ensures that the at least two laser engraving units can engrave the respective image sections independently of one another when engraving the surface of the printing form, thus achieving an overall reduction in engraving time, as already explained in connection with the method according to the first teaching.

[0052] According to a third teaching of the invention, the above-mentioned object is achieved for a computer program product in that the computer program product comprises instructions which, when the program is executed by a processor, cause a device or a system according to the second teaching to execute a method according to the first teaching. The processor can, for example, be a processor of an integrated processing unit within a device according to the second teaching or a processor of an external processing unit within a system according to the second teaching. As already explained, the execution of the method according to the first teaching by a device or a system according to the second teaching means that, regardless of the nature of the engraving image to be generated, the engraving time can be shortened by using multiple laser engraving units.

[0053] According to a fourth teaching of the invention, the above-mentioned object for the use of a printing form is achieved in that at least one printing form produced by a method according to the first teaching is used for packaging, label, decorative and / or magazine printing. Packaging printing in this context includes in particular the printing of food and beverage packaging, and label printing in particular the printing of labels for food and beverage packaging. Decorative printing includes, for example, the printing of adhesive films, napkins, wallpapers and latex balloons. Magazine printing also includes, in particular, newspaper printing. For the aforementioned printing applications, it is customary to divide the engraving image of the printing form into several image sections.However, in simultaneous engraving by multiple laser engraving units, the section boundaries could previously only be defined by free areas of the engraving image, so the realized time savings depended, among other things, on the nature of the engraving image. By using the printing plates produced by a process according to the first teaching for packaging, label, decorative, and / or magazine printing, a reduction in engraving time can now be achieved in these printing applications regardless of the nature of the engraving image to be created.

[0054] In the following, the invention will be explained in more detail using exemplary embodiments, with reference also to the drawing. The drawing shows in

[0055] Fig. 1 is a schematic flow diagram of a method according to the first

[0056] Teaching of the invention,

[0057] Fig. 2 is a schematic representation of a device according to the second

[0058] Teaching of the invention, Fig. 3A to 31 a schematic representation of an overlap area according to a preferred embodiment of the invention (Fig. 3A), as well as exemplary engraving depths of two laser engraving units for this engraving area (Fig. 3B, 3D, 3F, 3H) and the resulting engraving profiles of the printing form (Fig. 3C, 3E, 3G, 31),

[0059] Fig. 4A and 4B show a schematic representation of an overlapping area according to a further preferred embodiment (Fig. 4A), as well as an exemplary assignment of recessed elements of the surface of the printing form to two different laser engraving units (Fig. 4B),

[0060] Fig. 5A to 5E are schematic representations of section boundaries defined in various ways according to preferred embodiments of the invention, and

[0061] Fig. 6 is a schematic representation of four superimposed

[0062] Engraving images for a multi-color print including the respectively defined section boundaries according to the first teaching of the invention.

[0063] Fig. 1 shows a schematic flow diagram of a method according to the first teaching of the invention. The illustrated method comprises a step (110) in which the engraved image to be generated on a surface of a printing form is divided into at least two image sections by defining at least one section boundary. The method further comprises a step (120) in which the surface of the printing form is engraved using at least two laser engraving units, wherein each of the at least two image sections defined in step (110) is engraved simultaneously by one of the at least two laser engraving units. When dividing (110) the engraved image, the at least one section boundary is defined such that at least a portion of the at least one section boundary runs through an engraving region of the engraved image.This allows the engraving time to be shortened when using multiple laser engraving units, regardless of the nature of the engraving image to be created.

[0064] The method shown in Fig. 1 or at least one of the method steps shown can be implemented by various means, such as hardware, firmware, at least one processor, at least one circuit associated with the execution of software. For example, one or more of the method steps shown can be effected by instructions of a computer program product. For this purpose, the instructions can be stored in a memory and executed by a processor. The instructions can be loaded from the memory onto a computing unit such as an integrated circuit, an integrated processor, a computer, a laptop computer, a tablet computer or a smartphone in order to effect execution of the method when the program is executed by a processor of the computing unit.When executing the method, the computing unit can interact with a device such as a laser engraving machine. For this purpose, the computing unit can be integrated into the device or be an external computing unit, in particular a control computer.

[0065] Fig. 2 shows a schematic representation of a device according to the second teaching of the invention. The device is a laser engraving machine (200). The laser engraving machine (200) processes a cylindrical printing form (210), in this case a sleeve (210), by means of laser engraving. An engraving image (212) is generated on the printing form (210), which is also schematically illustrated in Fig. 2, in which exemplary engraving regions (220, 221, 222) of the engraving image are shown as hatched areas and an exemplary free region (228) of the engraving image are shown. The laser engraving machine comprises two laser engraving units (230), a control unit (240), a motor (242), a longitudinal drive (244) for each of the two laser engraving units (230), and an integrated computing unit (250). The integrated computing unit (250) comprises a control computer (251) with a processor (252) and a memory (253), a display unit (254) and an input unit (255).

[0066] The laser engraving machine (200) shown in Fig. 2 is configured to perform a method according to the first teaching of the invention. For this purpose, the laser engraving machine (200) comprises corresponding means, as explained below.

[0067] First, the laser engraving machine (200) divides the engraving image (212) to be generated on the outer surface of the printing form (210) into two image sections (214, 216) by defining a section boundary (218) between the two image sections (214, 216). The division of the engraving image (212) is performed by the processor (252) of the integrated processing unit (250). For this purpose, a program can be loaded from the memory (253). Subsequently, the laser engraving machine (200) engraves the outer surface of the printing form (210) using the two laser engraving units (230), with each of the two image sections (214, 216) being engraved simultaneously by one of the two laser engraving units (230). When dividing the engraving image, the section boundary is defined in such a way that at least one section of the at least one section boundary runs through an engraving area of ​​the engraving image.This allows a reduction in engraving time by using the two laser engraving units (230), regardless of the nature of the image to be engraved. The example in Fig. 2 shows a situation in which the section boundary (218) was defined such that the section (218a) of the section boundary (218) runs through the engraving area (221) of the engraved image (212). This results in two image sections (214, 216) of at least approximately equal size, thus reducing the engraving time.

[0068] The exemplary engraving areas (220, 221, 222) in Fig. 2 are full engraving areas. However, they could equally well have been raster engraving areas, which would correspond to a situation in which the section boundary is defined such that a portion of the section boundary runs through a raster engraving area of ​​the engraving image. In general, engraving areas, which can be both full engraving areas and raster engraving areas, are shown as hatched areas in the figures. Engraving areas that are specifically raster engraving areas are shown as dotted areas.

[0069] In the embodiment of the laser engraving machine (200) shown in Fig. 2, the means for subdividing the engraving image (212) comprise the processor (252) of the integrated computing unit (250). The means for engraving the surface of the printing form (210) comprise the two laser engraving units (230), the motor (242), the longitudinal drives (244) of the two laser engraving units (230), the processor (252) of the integrated computing unit (250), and the control unit (240). The laser engraving units (230) generate laser beams by means of laser sources (231) and modulators (232) to create the engraving image on the surface of the printing form (210). The motor (242) rotates the printing form (210) about the cylindrical longitudinal axis (260), so that in this way the two laser engraving units (230) are positioned in the circumferential direction (262) relative to the outer surface of the printing form (210).The longitudinal drives (244) move the laser engraving units (230) on a guide rail (238) parallel to the axial direction (260) of the printing form (210), thereby positioning the two laser engraving units (230) in the axial direction (260) relative to the outer surface of the printing form (210). The control unit (240) communicates with the processor (242) and controls the laser engraving units (230), in particular the modulators (232), as well as the motor (242) and the longitudinal drives (244) such that the surface of the printing form (210) is engraved according to the engraving image (212) to be engraved.

[0070] The laser engraving machine (200) shown in Fig. 2 has an integrated computing unit (250). However, the computing unit (250) could also be an external computing unit of a laser engraving machine, thus creating a system according to the second teaching. The external computing unit can be, among other things, a control computer. Although only two image sections (214, 216) and two laser engraving units (230) are shown in Fig. 2, the invention can also be readily implemented with any number of more than two image sections and more than two laser engraving units. The number of laser engraving units should be at least as large as the number of image sections into which the engraving image is divided.If the number of available laser engraving units is greater than the number of image sections, it is possible that excess laser engraving units are not involved in the method according to the invention and are located, for example, in a parking position on the guide rail (238).

[0071] The laser engraving machine (200) shown in Fig. 2 is configured to define the section boundary (218) in at least one section of the section boundary (218) based on a user input. As a means for defining the section boundary (218) based on a user input in at least one section of the section boundary (218), the laser engraving machine (200) comprises, in addition to the processor (252), the input unit (255). The input unit (255) here comprises, for example, a computer mouse and a computer keyboard. For example, it is conceivable that various possible courses of the section boundary are first determined by the processor (252) and displayed to a user on the display unit (254). The user can then make an input to select a section boundary.Additionally, it is conceivable that the user can manually adjust the section boundary in areas where the course of the section boundary is particularly important, for example by drawing the course of the section boundary into a representation of the engraving image (212) on the display unit (254) using the computer mouse. The user input detected by the input unit (255) is then taken into account by the processor (252) in the final definition of the section boundary (218). This ensures that a user who initiates or controls the implementation of a method according to the invention on the laser engraving machine (200) can influence the definition of the section boundary (218).

[0072] The laser engraving machine (200) shown in Fig. 2 is further configured to display a representation of the engraving image (212) together with a representation of the section boundary (218) or at least together with a representation of a preliminary course of the at least one section boundary (218) on at least one display unit (254). As a corresponding means for this purpose, the laser engraving machine (200) comprises the display unit (254) in addition to the processor (252). The display unit (254) displays a preliminary course of the section boundary (218) while the engraving image (212) is being subdivided. This simplifies the definition of the section boundary (218) for the user, since the user receives visual feedback about the course of the section boundary (218) provisionally defined by the user.Furthermore, the display unit (254) can also display the defined course of the section boundary (218) during the engraving of the surface of the printing form (210), thereby making it easier for the user to control and monitor the implementation of a method according to the invention on the laser engraving machine (200).

[0073] As shown in Fig. 2, the two laser engraving units (230) are movable independently of one another in the axial direction (260) of the printing form (210). For this purpose, the two laser engraving units (230) each comprise a longitudinal drive (244). Each longitudinal drive (244) can be controlled independently of the other longitudinal drive (244) and can move its associated laser engraving unit (230). This ensures that the two laser engraving units can engrave the respective image sections independently of one another when engraving the surface of the printing form. For example, each laser engraving unit (230) can traverse the free areas (228a, 228b) between the engraving areas (220, 221, 222) within the respective image section (214, 216) to be processed in the axial direction (260) independently of the other laser engraving unit (230), so that an overall reduction in engraving time can be achieved. As shown in Fig.As further shown in Figure 2, the laser engraving machine (200) comprises a separate laser source (231) and a separate modulator (232) for each of the two laser engraving units (230). This allows the two laser engraving units (230) to engrave the respective image sections (214, 216) independently of one another when engraving the surface of the printing form (210), thus achieving an overall reduction in engraving time.

[0074] In the laser engraving machine (200) shown in Fig. 2, the laser sources (231) of the two laser engraving units (230) are fiber laser sources (231). This allows for high beam quality and a virtually maintenance-free design of the laser sources (231). However, other laser sources, such as CO2 laser sources, are also conceivable. This also allows for the engraving of materials such as silicones, which cannot be engraved with fiber lasers.

[0075] In the laser engraving machine (200) shown in Fig. 2, the modulators (232) of the two laser engraving units (230) are acousto-optical modulators (232). This allows for particularly precise modulation of the laser beams generated by the laser sources (231) and thus a correspondingly accurate engraving result when engraving the workpiece (210).

[0076] Furthermore, each laser engraving unit (230) of the laser engraving machine (200) shown in Fig. 2 includes its own lens (not shown). This increases the resolution of the engraving image (212) and thus improves the sharpness of the engraving result.

[0077] In the laser engraving machine (200) shown in Fig. 2, the two laser engraving units (230) are essentially identical. Specifically, both laser engraving units (230) are constructed in the same way from the same components. The properties of the two laser engraving units (230) therefore differ only through unavoidable deviations, such as manufacturing tolerances of the components. The components shown here are a fiber laser source (231), an acousto-optical modulator (232), and a longitudinal drive (244), whereby the two laser engraving units (230) can each also have several other components not shown, such as a lens. Because the two laser engraving units (230) are essentially identical, a particularly uniform engraving result can be achieved.

[0078] The printing form (210) shown in Fig. 2 is a printing form (210) for flexographic printing. However, it would also be conceivable for the printing form (210) to be a printing form (210) for gravure printing. In both flexographic and gravure printing, regardless of the nature of the engraving image, a reduction in engraving time can be achieved by using multiple laser engraving units (230).

[0079] The surface to be engraved on the printing form (210) shown in Fig. 2 consists entirely of rubber. However, it would also be conceivable for the surface of the printing form (210) to be at least partially made of metal or plastic. There are no limitations regarding the materials that can be processed with the laser engraving machine (200).

[0080] The printing form (210) shown in Fig. 2 is a sleeve (210). However, the printing form (210) could also be a printing cylinder or at least one flexible printing plate fixed to a fixing cylinder. The laser engraving machine (200) is equally suitable for the production of sleeves, printing cylinders, and flexible printing plates. Regardless of the nature of the engraved image to be created, a reduction in engraving time can be achieved by using the two laser engraving units (230).

[0081] Figures 3A to 31 serve to illustrate an overlap region surrounding the section boundary according to a preferred embodiment of the invention, as well as the advantages that can be achieved thereby. The following explanations in connection with Figures 3A to 31 relate, by way of example, to flexographic printing. First, Fig. 3A shows an exemplary engraving region (220) of an engraving image (212) in a plan view. The engraving region (220) here is, by way of example, a full engraving region (220). Furthermore, a section boundary (218) has been defined, which runs through the full engraving region (220) in the section (218a). The section boundary (218) divides the engraving image (212) into the two image sections (214, 216). In addition, an x-direction and a y-direction for the engraving image (212) have been defined, as shown in Fig. 3A. The y-direction runs parallel to the section boundary (218) and the x-direction perpendicular to it.Points x0 and x2 correspond to the positions of the two edges of the full engraving area (220) in the x-direction, and point xi corresponds to the position of the section boundary (218) in the x-direction. As Fig. 3A now shows, an overlap area (224) surrounding the section boundary has been defined along the section (218a) of the section boundary (218). The two image sections (214, 216) overlap in the overlap area (224). The overlap area (224) lies within the full engraving area (220) of the engraving image (212). Furthermore, the overlap area (224) has a width of Ax perpendicular to the course of the section boundary (218), which here is 5 mm by way of example.

[0082] The advantages of the overlap region (224) can be understood in this example using Figures 3B to 3I. Fig. 3B shows a diagram in which the position in the x-direction is plotted on the abscissa and the engraving depth T of the two laser engraving units that are assigned to the two adjacent image sections (214, 216) of the engraving image (212) from Fig. 3A when engraving the corresponding printing form is plotted on the ordinate. The positions x0, xi and X2 correspond to those in Fig. 3A. Fig. 3B initially shows a situation in which no overlap region has been defined. Furthermore, Fig. 3B shows a situation that corresponds to perfect positioning of the two laser engraving units in relation to the surface of the printing form. Accordingly, a sudden transition takes place between the engraving depths (301, 302) of the two laser engraving units at the position xi of the section boundary (218).The position xi, at which the engraving depth (301) of the first laser engraving unit drops abruptly from T = To to T = 0, corresponds exactly to the position xi, at which the engraving depth (302) of the second laser engraving unit increases abruptly from T = 0 to T = To.

[0083] Fig. 3C shows the resulting engraving profile of the corresponding printing form. The engraving profile is represented as a cross-section through the surface of the printing form, with the z-direction defined perpendicular to the surface of the printing form and the x-direction corresponding to that in Figures 3A and 3B. Due to the perfect positionability of the laser engraving units, the engraving profile has raised elements (311, 312) corresponding to the engraving depth T = 0 in Fig. 3B, as well as an intermediate recessed element (313) corresponding to the engraving depth T = To in Fig. 3B. With this engraving profile, the desired print image can be realized in this example.

[0084] Figures 3D and 3E show a situation in which no overlap area has been defined, but the positionability of the two laser engraving units is not perfect due to inaccuracies. In practice, such inaccuracies can arise, for example, because the longitudinal drives of the laser engraving units do not have infinitely high accuracy, or because a measurement tolerance occurs when detecting the axial position of the printing form. The imperfect positionability of the two laser engraving units is expressed in Fig. 3D by the fact that the area between position xT and position X2', in which the engraving depth (302) of the second laser engraving unit assumes the value T = To, is shifted slightly to the right compared to the original area between xi and X2 (cf. Fig. 3B).Consequently, no material removal occurs in the area between position xi of the section boundary (218) and position xi' when engraving the surface of the printing form. In the resulting engraving profile, shown in Fig. 3E, an additional raised element (314) appears between position xi and position xi'. In flexographic printing, this additional raised element (314) is inked and causes an undesired ink application to the printing substrate, making the section boundary (218) immediately visible in the printed image.

[0085] In contrast, Figures 3F, 3G, 3H, and 3I each show a situation in which an overlap region has been defined, as explained in connection with Fig. 3A. First, for Figures 3F and 3G, perfect positioning of the two laser engraving units is again assumed. Fig. 3F shows a corresponding diagram with the engraving depth T as the ordinate and the position in the x-direction as the abscissa. The overlap region with the width Ax is located symmetrically around the position xi of the section boundary (218). Thus, the overlap region begins at the position xi - 1^2 and ends at the position xi + Ax / 2. In the overlap region, a gradual transition now takes place between the engraving depths (301, 302) of the two laser engraving units. Specifically, the engraving depth (301) of the first laser engraving unit continuously increases from T = 0 to T = To, while the engraving depth (302) of the first laser engraving unit continuously decreases from T = To to T = 0. Fig.Figure 3G shows the resulting engraving profile. When engraving the surface of the printing form, the overlapping area is engraved by both laser engraving units, each assigned to the two adjacent image sections (214, 216) in Figure 3A. Due to the perfect positioning of the laser engraving units, the engraving profile is exactly the same as in Figure 3C. Once again, this engraving profile allows the desired print image to be realized in this example.

[0086] Finally, Figures 3H and 3I again show a situation in which the positioning of the two laser engraving units is not perfect due to inaccuracies. This imperfect positioning is expressed in Fig. 3H by the fact that the area between position xi' - 1^2 and position X2', in which the engraving depth (302) of the second laser engraving unit continuously increases from T = 0 to T = To and finally assumes the constant value T = To, is slightly shifted to the right compared to the original area between xi - Ax / 2 and X2 (cf. Fig. 3F). However, due to the gradual transition between the engraving depths (301, 302) of the two laser engraving units in the overlap area, material removal also occurs in the area between position xi of the section boundary (218) and position xi' when engraving the surface of the printing form, unlike in Fig. 3E. In the resulting engraving profile, which is shown in Fig.As shown in Fig. 31, an additional element (315) therefore appears. Although this additional element (315) does not have a height z = 0 like the recessed element (313) (cf. Fig. 3G), the additional element (315) is nevertheless not a raised element that is provided with ink in flexographic printing. As Fig. 31 shows, the height zi of the additional element (315) is significantly lower than the height zo of the raised elements (311, 312). Consequently, unlike in Fig. 3E, there is no undesired ink application to the printing substrate, and accordingly, the section boundary (218) is also not visible in the printed image.

[0087] The comments on Figures 3A to 31 can therefore be summarized as follows: Even if the positioning of the two laser engraving units is not perfect, the gradual transition between the engraving depths of the two laser engraving units in the overlap area can prevent the section boundary from becoming visible, thus achieving the desired print image. In the case of perfect positioning, no significant change, in particular no deterioration of the print image, occurs.

[0088] Figures 4A and 4B serve to illustrate an overlap region surrounding the section boundary according to a further preferred embodiment of the invention, as well as the advantages achievable thereby. The following explanations in connection with Figures 4A and 4B relate, by way of example, to gravure printing, but are also transferable to flexographic printing. First, Fig. 4A shows an exemplary raster engraving region (220) of an engraved image (212) in a plan view. Furthermore, a section boundary (218) can be seen, which has been defined such that it runs through the raster engraving region (220) in the section (218a). The section boundary (218) divides the engraved image (212) into the two image sections (214, 216). As Fig. 4A now shows, an overlap region (224) surrounding the section boundary has been defined along the section (218a) of the section boundary (218). In the overlap area (224) the two image sections (214, 216) overlap.The overlap area (224) lies within the raster engraving area (220) of the engraved image (212). When engraving the surface of the printing form, the image section (214) is engraved by a first laser engraving unit, while the image section (216) is engraved by a second laser engraving unit. The overlap area (224) is engraved by both laser engraving units, which are respectively assigned to the two adjacent image sections (214, 216). The overlap area (224) here has, as an example, a width of 1 mm in a direction perpendicular to the section boundary (218), although larger width values ​​are also readily conceivable.

[0089] Fig. 4B shows an enlarged section of the overlap region (224) from Fig. 4A. In the example described here, recessed elements (226a, 226b) are engraved into the surface of the printing form. In this respect, only a partial engraving of the surface of the printing form takes place to generate halftone dots. The recessed elements (226a, 226b) are printing depressions in the surface of the printing form, which in gravure printing are also called cells (226a, 226b). The individual recessed elements are only indicated in Fig. 4A insofar as the halftone engraving region (220) is schematically shown as a dotted area. In the enlarged view of Fig. 4B, the recessed elements (226a, 226b) have a circular shape by way of example. Fig. 4B now further shows an exemplary assignment of the respective recessed elements (226a, 226b) to the two laser engraving units involved in the engraving of the image sections (214, 216).In this case, recessed elements (226a) engraved by the first laser engraving unit assigned to the image section (214) are schematically represented as circles with a broken contour. In contrast, recessed elements (226b) engraved by the second laser engraving unit assigned to the image section (216) are schematically represented as circles with a continuous contour. As can be seen in Fig. 4B, in the overlap region (224), those recessed elements (226a) located within the image section (216) are engraved by the first laser engraving unit assigned to the image section (214). In contrast, those recessed elements (226b) located within the image section (214) are engraved by the second laser engraving unit assigned to the image section (216).By engrave the recessed elements (226a, 226b) located within one of the two adjacent image sections (214, 216) in the overlapping area (224) by the laser engraving unit assigned to the other image section, a more uniform transition between the two image sections (214, 216) can be achieved, so that the course of the section boundary (218) is not so easily recognizable to the human eye in the subsequent printed image. This applies in particular if the properties of the individual laser engraving units are not perfectly identical due to manufacturing tolerances, or if there are inaccuracies in the positioning of the laser engraving units.

[0090] Figs. 5A to 5E each show schematic representations of section boundaries defined in various ways according to preferred embodiments of the invention. Depending on the nature of the engraving image, it may be advantageous to define at least one section boundary in a specific way.

[0091] First, Fig. 5A shows a preferred embodiment of the invention, in which the section boundary (218) is defined such that the length of the direct connecting line between the point (219a) at which the section boundary (218) penetrates the engraving area (221) and the point (219b) at which the section boundary (218) exits this engraving area (221) is reduced compared to the maximum possible length. If the section boundary for the engraving image (212) shown in Fig. 5A were defined along a vertical line exactly in the middle of the engraving image (212), the section boundary in this case would run through the engraving area (221) in a comparatively long section based on its entire length. This case would be the case for the engraving image shown in Fig.5A also corresponds to the maximum possible length of the direct connecting line between the point at which the section boundary enters the engraving area (221) and the point at which the section boundary exits the engraving area (221). Instead, however, the section boundary (218) has been defined here such that it is shifted to the left relative to the vertical line exactly in the center of the engraving image (212). As a result, the section boundary (218) enters the engraving area (221) at point (219a) and exits the engraving area (221) again at point (219b), whereby the length of the direct connecting line between point (219a) and point (219b) is reduced compared to the maximum possible length.This ensures that the section boundary (218), based on its entire length, only runs through the engraving area (221) in a relatively short section (218b), so that the optical perceptibility of the section boundary (218) in the subsequent printed image is reduced.

[0092] Furthermore, Fig. 5B shows a preferred embodiment of the invention in which, in the portion (218c) of the section boundary (218) in which the section boundary (218) runs through the raster engraving area (221) of the engraving image (212), the section boundary (218) is defined such that the section boundary (218) runs in a wavy manner. However, it would also be conceivable for the section boundary (218) in the portion (218c) to be curved, jagged, and / or otherwise deviate from a continuous straight line. This reduces the optical perceptibility of the section boundary (218) in the subsequent printed image.

[0093] Furthermore, Fig. 5C shows a preferred embodiment of the invention in which, in the portion (218d) of the section boundary (218) in which the section boundary (218) runs through the raster engraving area (220) of the engraving image (212), the section boundary (218) is defined such that the section boundary runs along an inner contour of the raster engraving area (220). For this purpose, Fig. 5C shows an exemplary engraving image (212) with a raster engraving area (220) that has an inner contour. Specifically, the raster engraving area (220) is composed of a first area (220a) and a second area (220b), wherein these two areas (220a, 220b) of the raster engraving area (220) each have a different rasterization. The different rasterization here consists, for example, in the fact that the distance between the raster points in the two areas (220a, 220b) takes on different values. In Fig.5C, the different rasterization is schematically indicated by depicting the two regions (220a, 220b) as areas with different dot patterns. The abrupt transition at the boundary between the regions (220a, 220b) represents an inner contour of the raster engraving region (220), and the section boundary (218) runs along this inner contour in the section (218d). This reduces the optical perceptibility of the section boundary (218) in the subsequent printed image, since the inner contour of the raster engraving region (220) is perceived by the human eye as a kind of boundary anyway.

[0094] In this context, the laser engraving machine (200) shown in Fig. 2 is configured to define the section boundary (218) shown in Fig. 50 in the portion (218d) of the section boundary (218) such that the section boundary (218) runs along the inner contour of the raster engraving area (220). As a means for defining the section boundary (218) along the inner contour, the processor (252) is configured to recognize and take into account inner contours in raster engraving areas of the engraving image when defining the section boundary (218). This also ensures that the section boundary (218) is not so easily recognizable to the human eye in the subsequent printed image.

[0095] Furthermore, Fig. 5D shows a preferred embodiment of the invention, in which the section boundary (218) is defined in the portions (218e, 218f, 218g) of the section boundary (218) such that the section boundary (218) runs along an edge between an engraving area (220, 221) and a free area (228) or along an edge between a full engraving area (220) and a raster engraving area (221). For this purpose, Fig. 5D shows an exemplary engraving image (212) with an engraving area (220), a raster engraving area (221), and a free area (228). The engraving area (220) here is, by way of example, a full engraving area (220). As shown in Fig. 5D, the section boundary (218) in the portion (218e) of the section boundary (218) was defined such that the section boundary (218) runs along the edge between the full engraving area (220) and the free area (228).Furthermore, the section boundary (218) in section (218f) of the section boundary (218) was defined such that the section boundary (218) runs along the edge between the full engraving area (220) and the raster engraving area (221). Finally, the section boundary (218) in section (218g) of the section boundary (218) was defined such that the section boundary (218) runs along the edge between the raster engraving area (221) and the free area (228). The definition of the section boundary shown here reduces the optical perceptibility of at least one section boundary in the subsequent printed image, since the edges between the areas (220, 221, 228) of the engraving image (212) are perceived by the human eye as a type of boundary anyway.

[0096] In this context, the laser engraving machine (200) shown in Fig. 2 is configured such that the section boundary (218) shown in Fig. 50 is defined in the sections (218e, 218f, 218g) of the section boundary (218) such that the section boundary (218) runs along an edge between an engraving area (220, 221) and a free area (228) or along an edge between a full engraving area (220) and a raster engraving area (221). As a means for defining the section boundary (218) along the respective edge, the processor (252) is configured to recognize and take into account corresponding edges of the engraving image when defining the section boundary (218). This also ensures that the section boundary (218) is not so easily recognizable to the human eye in the subsequent printed image.

[0097] Finally, Fig. 5E shows a preferred embodiment of the invention in which the section boundary (218) is defined in a portion of the section boundary (218) based on a user input. Fig. 5E shows an engraving image (212) consisting of a contiguous raster engraving area (220). Here, the user has specified the shown course of the section boundary (218), whereby the engraving image (212) is divided into the image sections (214, 216) and can be engraved simultaneously by multiple laser engraving units. The portion in which the section boundary (218) was defined based on a user input here comprises the entire section boundary (218). By defining the section boundary (218) based on a user input, it is achieved, among other things, that a user who initiates or controls a method according to the first teaching of the invention can influence the definition of the at least one section boundary.

[0098] Fig. 6 shows a schematic representation of four superimposed engraving images (212) assigned to four related printing forms for multi-color printing, including the respectively defined section boundaries (218k, 218l, 218m, 218n) according to the first teaching of the invention. The representation with the superimposed engraving images was chosen in order to be able to more easily show the course of the section boundaries (218k, 218l, 218m, 218n) in relation to one another. The individual engraving images (212) of the four colors each have identical dimensions as well as common engraving areas (220, 221, 222) and a common white area (228). The common engraving areas (220, 221, 222) result from the fact that here each engraving image (212) of the four colors has an engraving area to be engraved. The common white area (228) results from the fact that each engraving image (212) of the four colors has a white area that is not to be engraved.In the common engraving areas (220, 221, 222) of the engraving images (212), the finished multi-coloured print image is created by the individual print images of the four colours superimposing each other. As Fig. 6 shows, at least in the area (221) in which the engraving areas (220, 221, 222) of at least two engraving images (212) overlap when the engraving images (212) to be generated on the respective surfaces of the printing forms are placed on top of one another, the section boundary (218k, 2181, 218m, 218n) of each engraving image (212) involved in the overlap is defined such that the section boundary (218k, 2181, 218m, 218n) is not congruent with a section boundary (218k, 2181, 218m, 218n) of another engraving image (212) involved in the overlap. This reduces the optical perceptibility of the section boundaries (218k, 2181, 218m, 218n) in the subsequent printed image.To produce the four associated printing forms for a multi-colour print, each printing form is produced by a method according to the first teaching, such as the method schematically shown in Fig. 1.

[0099] The printing plates produced using the methods according to the first teaching as described here can be used particularly advantageously for packaging, label, decorative, and / or magazine printing. This allows a reduction in engraving time in these printing applications, regardless of the nature of the engraving image to be produced.

Claims

Patent claims: Method for producing a printing form by means of laser engraving, wherein the method (100) comprises: (110) Subdividing an engraving image to be produced on a surface of the printing form into at least two image sections by defining at least one section boundary between the at least two image sections; Engraving (120) the surface of the printing form using at least two laser engraving units, wherein each of the at least two image sections is engraved simultaneously by one of the at least two laser engraving units; characterized in that, when subdividing the engraved image, the at least one section boundary is defined such that at least one section of the at least one section boundary passes through an engraving area of ​​the engraved image. A method according to claim 1, characterized in that the at least one section boundary is defined such that at least one section of the at least one section boundary passes through a raster engraving area of ​​the engraved image. A method according to claim 1 or 2, characterized in that, along at least one section of the at least one section boundary, in which the at least one section boundary passes through an engraving area of ​​the engraved image, an overlap region surrounding the section boundary is defined. is defined by the fact that the two adjacent image sections overlap, whereby when engraving the surface of the printing form, the overlap area is engraved by both laser engraving units, each assigned to one of the two adjacent image sections.

4. Method according to claim 3, characterized in that in at least one partial area of ​​the overlap area which lies within an engraving area of ​​the engraving image, a gradual transition takes place between the engraving depths of the two laser engraving units.

5. Method according to claim 3, characterized in that in at least one partial area of ​​the overlap area which lies within a raster engraving area of ​​the engraving image, at least one recessed element of the surface of the printing form which lies within one of the two adjacent image sections of the engraving image is engraved by the laser engraving unit which is assigned to the other image section.

6. Method according to any one of claims 1 to 5, characterized in that the at least one section boundary is defined such that the length of the direct connecting line between the point at which the at least one section boundary enters an engraving area and the point at which the at least one section boundary exits this engraving area is reduced compared to the maximum possible length.

7. Method according to any one of claims 1 to 6, characterized in that in at least one section of the at least one section boundary, in which the at least one section boundary passes through a raster engraving area of ​​the engraving image, the at least one section boundary is defined in such a way that the at least one section boundary is curved, wavy, jagged and / or otherwise deviates from a continuous straight line.

8. Method according to one of claims 1 to 7, characterized in that in at least one section of the at least one section boundary, in which the at least one section boundary passes through a raster engraving area of ​​the engraving image, the at least one section boundary is defined such that the at least one section boundary runs along an inner contour of the raster engraving area.

9. Method according to any one of claims 1 to 8, characterized in that the at least one section boundary in at least one section of the at least one section boundary is defined based on a user input.

10. Method according to any one of claims 1 to 9, characterized in that a representation of the engraving image together with a representation of the at least one section boundary or at least together with a representation of a preliminary course of the at least one section boundary is displayed on at least one display unit.

11. Method according to any one of claims 1 to 10, characterized in that each of the at least two laser engraving units comprises at least one separate laser source and at least one separate modulator. A method according to any one of claims 1 to 11, characterized in that a printing form for flexographic printing is produced. A method according to any one of claims 1 to 12, characterized in that the surface of the printing form to be engraved consists at least partially, preferably entirely, of rubber.A method for producing at least two related printing plates for multicolor printing, characterized in that each of the at least two related printing plates is produced by a method according to one of claims 1 to 13, wherein, at least in areas where the engraving areas of at least two engraving images overlap when the engraving images to be produced on the respective surfaces of the printing plates are superimposed, the at least one section boundary of each engraving image involved in the overlap is defined such that the at least one section boundary is not at least partially congruent with a section boundary of another engraving image involved in the overlap. A device or system for producing a printing plate by means of laser engraving, in particular for carrying out a method according to one of claims 1 to 14, wherein the device (200) or the system comprises: Means (252) for dividing an engraving image (212) to be produced on a surface of the printing form (210) into at least two image sections (214, 216) by defining at least one section boundary (218) between the at least two image sections (214, 216); Means (230, 240, 242, 244, 252) for engraving the surface of the printing form (210) using at least two laser engraving units (230), wherein the means (230, 240, 242, 244, 252) for engraving the surface of the printing form (210) are configured such that each of the at least two image sections (214, 216) is engraved simultaneously by one of the at least two laser engraving units (230); characterized in that the means (252) for subdividing the engraving image (212) are configured to define the at least one section boundary (218) such that at least one section of the at least one section boundary (218) passes through an engraving area (220) of the engraving image. Computer program product comprising instructions which, when the program is executed by a processor, cause a device (200) or a system according to claim 15 to execute a method according to any one of claims 1 to 14.Use of at least one printing form (210) produced by a method according to one of claims 1 to 14 for packaging, label, decoration and / or magazine printing.

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