PRINTING MACHINE WITH A TWIN PRINTING UNIT AND METHOD FOR OPERATING SUCH A PRINTING MACHINE
This application claims the priority, under 35 U.S.C. § 119, of German Patent applications DE 10 2017 212 183.1, filed Jul. 17, 2017 and DE 10 2017 222 700.1, filed Dec. 14, 2017; the prior applications are herewith incorporated by reference in their entirety. The invention relates to a printing machine for printing on a web of printing material, the printing machine including a plurality of in-line flexographic printing units disposed in a plane accessible to a machine operator. The invention also relates to a method for operating a printing machine for printing on a web of printing material. Printing machines constructed or used for packaging printing are faced with more and more demanding challenges in terms of productivity, ease of operation, and maximum production variability. For instance, a printing machine is expected to produce as little waste as possible, for instance when it is reconfigured between print jobs. Common machine constructions for packaging printing, in particular flexographic printing, are web-fed printing machines of in-line construction including a plurality of cylinders and rollers for guiding a printing material between different process levels (for instance printing and drying). That means that a web section of considerable length is present in the machine and a corresponding amount of unusable products may be created. Machines for the printing and rotary die-cutting of folding box blanks in an in-line process have become known in the art, for instance from European Patent EP 1 731 277 B1, corresponding to U.S. Pat. No. 7,690,099. Those web-fed printing machines include multiple printing units to print on a web-shaped substrate, potentially using different printing processes. The web of printing material is subsequently subjected to further processing, e.g. die-cutting embossing, varnishing, etc. German Patent DE 103 43 411 B4, corresponding to U.S. Publication No. 2006/0156934, discloses a rotary printing machine including a plurality of printing units that may be equipped with so-called sleeves for a quick job change. For that purpose, a motor is provided to move the axles of the sleeves into a change position in which the axles are easily accessible. Once the sleeves have been changed, the sleeves and the axles are jointly returned from the change position to an operating position. A disadvantage of those prior art machines is that the printing operation needs to be stopped for a sleeve change, resulting in times of standstill and affecting the productivity of the machine. If a color change is required, longer periods of standstill are required. In addition, start-up waste, i.e. a printed web section that is unusable, is created after every standstill. It is accordingly an object of the invention to provide a printing machine with a twin printing unit and a method for operating such a printing machine, which overcome the hereinafore-mentioned disadvantages of the heretofore-known machines and methods of this general type and which are suitable for quick and easy job changes with as little waste as possible. With the foregoing and other objects in view there is provided, in accordance with the invention, a printing machine for printing on a web of printing material, in particular a web made of paper, cardboard, or plastic, including a plurality of flexographic printing units in an in-line configuration. Due to this in-line configuration, the printing machine may be expanded as desired. The flexographic printing units are disposed in a plane that is accessible to the operator, in particular in a level and horizontal plane and at a level that is easily accessible to the operator in an ergonomic way. Every two flexographic printing units advantageously form a double printing station. The two flexographic printing units of a printing station have a common impression cylinder. This printing station construction may be referred to as a twin printing unit or double ink deck (DID) in contrast to a so-called single ink deck (SID). In accordance with a preferred embodiment, the two flexographic printing units of a respective double printing station may be operated in an alternate way. This enables continuous production, i.e. an on-the-fly job change. Alternatively, the two flexographic printing units may be operated together. In accordance with an advantageous further development of the printing machine of the invention, the two flexographic printing units of each double printing station are disposed to be mirror-symmetrical relative to the common impression cylinder. While one flexographic printing unit is printing, the other flexographic printing unit may undergo set-up or maintenance operations. In accordance with a particularly advantageous and thus preferred embodiment, a drier is provided downstream of every double printing station. An advantage of this configuration is that once ink has been applied, the applied amount of ink may be dried completely, allowing the web of printing material to be diverted in a trouble-free way without smearing. Alternatively, a provision is made for every double printing station to include at least one drier, preferably two or four driers. It is also preferred that the drier is a UV drier or that the driers are UV driers. It is further preferred that the common impression cylinder of a respective double printing station is a cooling cylinder. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for every double printing station to include the following elements successively disposed along the circumference or on the periphery of the cooling cylinder in the direction of printing material transport: a flexographic printing unit; one or two UV driers; a flexographic printing unit; and one or two UV driers. It is furthermore advantageous if a respective flexographic printing unit is equipped with an ink application device and a flexographic cylinder with a print sleeve carrying the printing master. In practice, it has been found to be advantageous for the diameter of a respective impression cylinder to be smaller than 1000 mm (in the case of hot-air drying). In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for at least one further flexographic printing unit to be provided in addition to the plurality of flexographic printing units and in the form of a single printing station. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for the single printing station to be disposed upstream of the plurality of printing units or for the single printing station to be disposed downstream of the plurality of flexographic printing units. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for the single printing station to be disposed downstream of the double printing station or downstream of a last double printing station as viewed in the direction of printing material transport. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for the impression cylinder of the single printing station to be embodied as a cooling cylinder and for the following elements to be successively disposed along the circumference or on the periphery of the cooling cylinder in the direction of printing material transport: a flexographic printing unit; and one or two UV driers. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for a section—or all sections—of the web of printing material a) between two double printing stations and/or b) between the double printing station—or a last double printing station—and the single printing station, to run in a second plane substantially located beneath the first plane. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for the length of the section of the printing material or of all sections of the printing material to be smaller than the length of the printing material in a double printing station. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for the web of printing material in every double printing unit to form a loop extending from the second plane and being open in a downward direction. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for the loop to run around the impression cylinder and around at least two or three guide rollers disposed between the first plane and the second plane. In accordance with a particularly advantageous and thus preferred embodiment, a provision is made for the last double printing station to be followed by a single printing station and a hot-air drier succeeding one another in the direction of printing material transport. With the objects of the invention in view, there is also provided a method for operating a printing machine as described above for printing on a web of printing material. In accordance with the invention, a maximum of one flexographic printing unit of the two flexographic printing units of a respective double printing station is activated to print on the web of printing material. The respective other flexographic printing unit, i.e. the inactive printing unit of a double printing station, may advantageously be subjected to set-up or maintenance operations or may be in an inactive stand-by position. Set-up operations may, for instance, include a printing sleeve change or an ink change. This is an easy way to use and exchange special colors. Maintenance operations may for instance include a blade change on the doctor blade. In a particularly advantageous and thus preferred further development of the method of the invention, the flexographic printing units of a respective double printing station may be activated and deactivated in an in-register way to enable on-the-fly flexographic printing unit changes upon a job change. This means that when a printing station is switched from one flexographic printing unit to the other flexographic printing unit to implement a job change, the flexographic printing units of the different printing stations are synchronized with each other so as to avoid the production of waste in between jobs and to allow the web of printing material to be continuously printed on. Alternatively, a method of the invention may also include provisions for both flexographic printing units of a printing station to be activated and to print on the web of printing material. In accordance with this alternative, a machine that has four printing stations, for instance, may print eight colors instead of just four. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a printing machine with a twin printing unit and a method for operating such a printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. As far as it makes sense from a technical point of view, combinations of the invention as described above and of the advantageous further developments of the invention likewise form advantageous further developments of the invention. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Further advantages and embodiments of the invention that are advantageous in structural and functional terms will become apparent from the dependent claims and the description of exemplary embodiments with reference to the appended figures. Referring now to the figures of the drawings in detail and first, particularly, to The inspection systems 14, the flexographic printing units 11, the embossing unit 12 and the die-cutting/creasing unit 13 are connected to a control unit 22 in terms of data communication and may be actuated by the control unit 22. Like the printing machine 100 in The construction of a respective printing station 10 is shown in more detail in The switch from one print job to the next print job is made in an event-driven way. The triggering event may be a specified printing time, a specified length of the web of substrate that has been printed on, a specified number of printed copies, a change of material, or an initiating operation by the machine operator. Due to such an event-driven control of the printing machine 100 by using a control unit 22, the printing machine 100 is capable of preparing for the next print jobs while processing a current print job and of processing the next print jobs in sequence. Both stations are constructed as so-called short web stations: if UV inks are used, the drier path may be chosen to be much shorter; UV driers may in particular be disposed on the circumference of a (central) impression cylinder in a space-saving way. As compared to the thermal drying process of water-based inks (see The DID station 31 includes the following elements in the direction of printing material transport: a deflection roller 20 for the web 1, a central impression cylinder 16, a first flexographic printing unit 11 (including a flexographic printing cylinder 15 and an ink application device 21 with, for instance, a screen cylinder) assigned to the impression cylinder, one or (as shown) two driers 19, a second flexographic printing unit 11, one or (as shown) two further driers 19, and two deflection rollers 20. The driers are preferably UV driers. Such a station is capable of applying two colors at the same time. The SID station 30 includes the following elements in the direction of printing material transport: two deflection rollers 20 for the web 1, a central impression cylinder 16, a first flexographic printing unit 11 (including a flexographic printing cylinder 15 and an ink application device 21 such as a screen cylinder) assigned to the impression cylinder 16, one or (as shown) two driers 19, and a deflection roller 20. The driers are preferably UV driers. Such a station is capable of applying one color. The other unit of the station may at the same time (i.e. on the fly) be subjected to changeover operations such as a plate and/or color change. The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
A printing machine for printing on a web of printing material includes a plurality of in-line flexographic printing units disposed in a plane that is accessible to a machine operator. Every two flexographic printing units of the plurality of flexographic printing units together form a double printing station and the two flexographic printing units of a respective double printing station have a common impression cylinder. A method of operating a printing machine is also provided. 1. A printing machine for printing on a web of printing material, the printing machine comprising:
a plurality of in-line flexographic printing units disposed in a plane accessible to a machine operator; every two of said flexographic printing units of said plurality of flexographic printing units together forming a double printing station; and said two flexographic printing units of a respective double printing station having a common impression cylinder. 2. The printing machine according to 3. The printing machine according to 4. The printing machine according to 5. The printing machine according to 6. The printing machine according to 7. The printing machine according to a flexographic printing unit, one or two UV driers, another flexographic printing unit and one or two other UV driers are disposed along said circumference of said cooling cylinder in every double printing station in a direction of printing material transport. 8. The printing machine according to 9. The printing machine according to 10. The printing machine according to 11. The printing machine according to 12. The printing machine according to said single printing station is disposed upstream of said plurality of flexographic printing units or said single printing station is disposed downstream of said plurality of flexographic printing units. 13. The printing machine according to 14. The printing machine according to said single printing station has an impression cylinder being a cooling cylinder having a circumference; and a flexographic printing unit and one or two UV driers are successively disposed along said circumference of said cooing cylinder in said direction of printing material transport. 15. The printing machine according to said plane is a first plane; and a section or all sections of the web of printing material are disposed in a second plane located substantially beneath said first plane and disposed at least one of: a) between two double printing stations or b) between a double printing station or a last double printing station and said single printing station. 16. The printing machine according to 17. The printing machine according to 18. The printing machine according to 19. The printing machine according to 20. A method of operating a printing machine, the method comprising the following steps:
providing a plurality of in-line flexographic printing units disposed in a plane accessible to a machine operator, every two of the flexographic printing units of the plurality of flexographic printing units together forming a double printing station, and the two flexographic printing units of a respective double printing station having a common impression cylinder; and activating and printing with a maximum of one flexographic printing unit of the two flexographic printing units of a respective double printing station. 21. The method for operating a printing machine according to 22. The method for operating a printing machine according to CROSS-REFERENCE TO RELATED APPLICATION
BACKGROUND OF THE INVENTION
Field of the Invention
Description of the Related Art
SUMMARY OF THE INVENTION
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
DETAILED DESCRIPTION OF THE INVENTION