Abstract:
A system for coating printing materials with coating fluids and a method for operating the system include, in a first step, coating printing material with a first coating fluid using a coating device of the system and keeping a first feed device of the system connected to the coating device for feeding the first coating fluid to the coating device using the first feed device. In a second step following the first step, printing material is coated with a second coating fluid using the coating device and a second feed device of the system is kept connected to the coating device for feeding the second coating fluid to the coating device using the second feed device. In a third step carried out after the first step and, at least to some extent, during the second step, the first feed device is flushed through with a cleaning fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2008 053 340.8, filed Oct. 27, 2008; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a method for operating a system for coating printing materials with coating fluids and to a system for coating printing materials with coating fluids which is suitable for implementing the method. 
     Printing materials, that is sheets or webs, for example of paper or board, are coated with coating fluids, for example printing inks or varnishes. For that purpose, use is made of systems which include a printing press or varnishing machine and peripheral devices assigned to the machine. Disposed in the machine is a coating device, through the use of which the fluid is metered and transferred to the printing material. Such a coating device can include a chamber-type doctor and one or more rollers. The peripheral device can include a vessel in which there is a supply of fluid. In addition, it can include a pump and connecting hoses in order to pump the fluid from the vessel into the chamber-type doctor. 
     Such a system is described in German Utility Model DE 29616686 U1. The prior art system has a first circuit for emulsified varnish and a second circuit for UV varnish. A metering device can be supplied as desired with the emulsified varnish and the UV varnish and a cleaning fluid reservoir can be incorporated into the first or second circuit, through the use of appropriate activation of control valves. 
     A further coating system for printing materials is described in German Published, Non-Prosecuted Patent Application DE 102 46 946 A1. The system has circulation lines for the coating fluid, into which a liquid cleaning medium can also be introduced. 
     In the known systems, the cleaning is comparatively time-consuming and cumbersome. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a printing material coating system and a method for operating the system, which overcome the hereinafore-mentioned disadvantages of the heretofore-known systems and methods of this general type and with which quick and simple cleaning is achieved. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a system for coating printing materials with coating fluids. The method comprises, in a first step, coating printing material with a first coating fluid using a coating device of the system while keeping a first feed device of the system connected to the coating device for feeding the first coating fluid to the coating device with the first feed device. In a second step following the first step, printing material is coated with a second coating fluid using the coating device while keeping a second feed device of the system connected to the coating device for feeding the second coating fluid to the coating device with the second feed device. In a third step carried out after the first step and at least to some extent during the second step, the first feed device is flushed through with a cleaning fluid. 
     This method permits automated cleaning of the first feed device during a printing operation that is running with the incorporation of the second feed device. This is very user-friendly and maintenance time is saved. 
     In accordance with another mode of the method of the invention, the coating device is separated from the first feed device and connected to the second feed device, between the first step and the second step. In a further mode, the first feed device is short-circuited, between the first step and the third step. In this case, a check can be made to see whether the short-circuiting of the first feed device has been carried out correctly in that, through the use of at least one pump belonging to the first feed device, a vacuum is generated in the latter and that vacuum is monitored through the use of a sensor, with any incorrectness of the short-circuiting being detected on the basis of a drop in or lack of buildup of the vacuum. In this case, provision can also be made for the first feed device to be flushed through with the cleaning fluid only when the correctness of the short-circuiting has been confirmed by the checking. 
     With the objects of the invention in view, there is also provided a system for coating printing materials with coating fluids. The system comprises a coating device for coating the printing materials with a first coating fluid and a second coating fluid, a first feed device for feeding the first coating fluid to the coating device, a second feed device for feeding the second coating fluid to the coating device, and a device for simultaneously:
         closing a first circuit for a cleaning fluid, the first circuit incorporating the first feed device, and   forming a second circuit for the second coating fluid, the second circuit incorporating the second feed device and the coating device.       

     Through the use of this system, the method according to the invention can be carried out in such a way that quick and simple cleaning is ensured. 
     In accordance with another feature of the system of the invention, the device for closing the first circuit is a connecting link for short-circuiting two lines belonging to the first circuit. The connecting link can be constructed to be compatible with connections of the two lines, which are disposed at an interface. It is possible for there to be a monitoring device which monitors whether or not the connecting link has been connected correctly to the two lines. In this case, the first circuit can have at least one pump for pumping the first coating fluid, and the monitoring device can have a sensor for detecting a drop in or lack of buildup of a vacuum generated by the pump. In a further feature, the device for closing the first circuit is a control valve device for short-circuiting two lines belonging to the first circuit. This control valve device can be disposed immediately before an interface of the two lines which is formed by connections. 
     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 material coating system and a method for operating the system, 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. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a schematic and diagrammatic, longitudinal-sectional view of a first exemplary embodiment of the invention, having a coating system with two fluid circuits, of which one is short-circuited through the use of a control valve device in a cleaning mode; and 
         FIG. 2  is a view similar to  FIG. 1  of a second exemplary embodiment having a coating system with two fluid circuits, of which one is short-circuited through the use of a connecting link in a cleaning mode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now in detail to  FIGS. 1 and 2  of the drawings, in which mutually corresponding elements and components are indicated by the same designations, there is seen a portion of a printing press  1  and a supply device  2  disposed beside the printing press, which together form a system  3  for coating preferably sheet printing materials. The figure shows a varnishing unit  4  belonging to the printing press  1 , in which a coating device  5  is disposed. The coating device  5  is located in the interior of the printing press between lateral frame walls  6  and includes a non-illustrated engraved roll as a metering device having a chamber-type doctor  7  resting thereon and a collecting trough  8  disposed underneath. The supply device  2  is substantially not located between the frame walls  6  and includes a first feed device  9  for a first coating fluid, for example UV varnish, and a second feed device  10  for a second coating fluid, for example emulsified varnish. 
     The first feed device  9  includes a first container  11  for storing the first coating fluid and a second container  12  for storing a cleaning fluid. The second feed device  10  includes a third container  13  for storing the second coating fluid and a fourth container  14  for storing a cleaning fluid, which can be the same as in the second container  12  or preferably another one. Hose-like or tube-like lines  15  for delivering the fluids from the containers  11  to  14  dip into the respective fluid, and just such lines  16  for conveying the fluids back into the containers  11  to  14  open above the respective fluid level, which is indicated in the drawing. 
     Each feed device  9 ,  10  has a first pump  17  for the delivery of the respective coating fluid to the coating device  5 , which is carried out during the printing operation, and a second pump  18  for conveying non-printed, excess coating fluid from the coating device  5  back into the respective container  11  or  13 . The four pumps  17 ,  18  are each reversible pumps, that is to say pumps having a delivery direction which can be changed. 
     An interface  19  for liquid lines is disposed on one frame wall  6 . The interface  19  includes connections  20 , through which a feed line  21  of the chamber-type doctor  7  and a return line  22  from the collecting trough  8  can be connected to a feed line  23  and a return line  24  belonging to the first feed device  9 . Furthermore, the interface  19  includes connections  25 , through which the feed line  21  and the return line  22  can be connected to a feed line  26  and a return line  27  belonging to the second feed device  10 . The feed lines  23 ,  26  are connected to the first pumps  17  of the feed devices  9 ,  10 , and the return lines  24 ,  27  are connected to the second pumps  18 . The connections  20 ,  25  can be constructed as half-couplings of quick-closure couplings, with complementary half-couplings being located on the hose-like lines  21 ,  22  of the coating device  5 . The designation “ 28 ” designates selection or directional control valves, which are integrated into the part of the line system respectively lying between the containers  11 ,  12  and  13 ,  14  and the pumps  17 ,  18 . 
     Following the preceding description of the common features of the two exemplary embodiments, the special features of the exemplary embodiment according to  FIG. 1  will be described in more detail below. 
     In the system  3  illustrated in  FIG. 1 , selection or directional control valves  29  are integrated into the lines  23 ,  24  of the first feed device  9 , and selection or directional control valves  30  are integrated into the lines  26 ,  27  of the second feed device  10 . A connecting line  31  is disposed between the directional control valves  29 , and a connecting line  32  is disposed between the directional control valves  30 . 
     In a first switching position of the directional control valves  29 , the first coating fluid flows from the feed line  23  through one directional control valve  29  into the feed line  21  and from the return line  22  through the other directional control valve  29  into the return line  24 . In a second switching position of the directional control valves  29 , the cleaning fluid flows from the feed line  23  through the two directional control valves  29  and the connecting line  31  located in between into the return line  24 . The two lines  21 ,  22  can be detached from the connections  20  by the operator during conversion of the printing press  1  and coupled to the connections  25  of the other feed device  10 . Instead, however, provision can also be made for the operator to replace the contaminated lines  21 ,  22  during the conversion, that is to say to remove them from the printing press  1  and to connect the coating device  5  to the connections  25  of the second feed device  10  through the use of new lines  21 ,  22 . 
     Following the conversion, in a first switching position of the directional control valves  30 , the second coating fluid can flow from the feed line  26  through one directional control valve  30  into the feed line  21  and from the return line  22  through the other directional control valve  30  into the return line  27 . In a second switching position of the directional control valves  30  belonging to the second feed device  10 , the cleaning fluid flows from the feed line  26  through one directional control valve  30  into the connecting line  32  and from the latter through the other directional control valve  30  into the return line  27 . 
     The directional control valves  29 ,  30  of the two feed devices  9 ,  10  are disposed in the immediate vicinity of the connections  20 ,  25  and can be fixed to the frame wall  6  on which the interface  19  is disposed. The four directional control valves  29 ,  30  together form a control valve device  33  and, including the connecting lines  31 ,  32 , can form a single spool valve having a corresponding number of switching positions, which is advantageous with regard to a compact construction and the ability to be operated remotely. The directional control valves  29 ,  30  can, however, also be constructed as ball valves which are separate from one another and can be operated by hand. 
     In the system  3  illustrated in  FIG. 2 , there is a connecting link  34 , which is a piece of hose or tube. This connecting link  34  has a half-coupling at each of its two ends, which can be coupled to the connections  20 ,  25 . In the simplest case, if the connections  20 ,  25  are formed as hose connectors, ends of the hoses of the connecting link  34 , which can be plugged onto these hose connectors, form their half-couplings. 
     In a first operating mode, which is shown in  FIG. 2 , the lines  21 ,  22  of the coating device  5  are detached from the connections  25  of the second feed device  10  and are connected to the connections  20  of the first feed device  9 , and the connections  25  of the second feed device  10  are connected to each other through the connecting link  34 , so that the cleaning fluid can flow from the feed line  26  through the connecting link  34  into the return line  27 . In this case, the cleaning fluid does not flow through the coating device  5 , since the two lines  26 ,  27  are short-circuited with each other by the connecting link  34 . 
     In a second operating mode, which is not illustrated in the drawing, the two lines  21 ,  22  of the coating device  5  are no longer connected to the connections  20  of the first feed device  9  but instead to the connections  25  of the second feed device  10 , and the connecting link  34  is coupled to the connections  20 , in order to connect the two lines  23 ,  24  to each other. In this case, the cleaning fluid flows from the feed line  23  through the connecting link  34  into the return line  24  of the first feed device  9 . 
     The feed devices  9 ,  10  in each case include a monitoring device  35 , which is used to monitor whether the connecting link  34  has been connected correctly to the respective connections  20  or  25 . The monitoring device  35  registers leaks in the connection of the connecting link  34  and is disposed within the line system between the pumps  17 ,  18  and the respective connections  20  and  25  and more precisely in the respective return line  24  and  27 . The monitoring device  35  includes a sensor  36  for detecting the vacuum generated in the return line  24  or  27  by the first pump  17 . 
     A pneumatic valve  37  functioning as a venting device is likewise integrated into the respective return line  24  and  27 . There is an electronic device controller  38  for each feed device  9 ,  10 , which receives and processes signals from the sensor  36  and activates the pumps  17 ,  18 , their motors and the pneumatic valve  37 . The device controllers  38  have a control link to a central control device belonging to the printing press  1 . 
     The operation of the systems shown in  FIGS. 1 and 2  will be described below. 
     If, in the system illustrated in  FIG. 1  and in the system illustrated in  FIG. 2 , the printing press  1  is printing, the first feed device  9  together with the coating device  5  forms a first circuit  39  for the first coating fluid from the first container  11 . The first circuit  39  is indicated symbolically in the drawing. In this case, the delivery direction of the first pump  17  and the flow path of the directional control valve  28  integrated into the line  15  belonging to the first container  11  are set in such a way that the first pump  17  sucks the first coating fluid out of the first container  11  through the line  15  and pumps it into the chamber-type doctor  7  through the feed line  23  and the feed line  21 . Some of the first coating fluid pumped into the chamber-type doctor  7  is passed on by the chamber-type doctor  7  to the engraved roll and consequently printed. The remaining part of the first coating fluid pumped into the chamber-type doctor  7  runs out of the chamber-type doctor  7  into the collecting trough  8  and is sucked out of the latter by the second pump  18  through the return line  22  and the return line  24 . In the system  3  shown in  FIG. 1 , in this case the directional control valves  29  are switched through from the feed line  23  into the feed line  21  and from the return line  22  into the return line  24 , with the flow path through the connecting line  31  being shut off. The second pump  18  pumps the excess first coating fluid back into the first container  11  through the line  16  belonging to the latter, with the directional control valve  28  of the line  16  having been switched to a setting permitting the flow from the return line  24  into this line  16 . The pumps  17 ,  18  of the first feed device  9  therefore circulate the first coating fluid in the first circuit  39 . Thus, the control valve device  33  and the connecting link  34  each form a device for closing a first circuit  39 . 
     During this running printing operation, the second feed device  10  forms a second circuit  40  for the cleaning fluid from the fourth container  14 . The cleaning fluid is circulated in the second circuit  40  chronologically parallel with the circulation of the first coating fluid in the first circuit  39 , in order to flush clean the second feed device  10  not participating in the printing operation. In this case, the feed line  26  and the return line  27  are short-circuited with each other at their ends which are not connected to the coating device  5 . This short-circuiting in the system  3  shown in  FIG. 1  is effected by an appropriate setting of the control valve device  33 , more precisely the directional control valves  30 , and in the system  3  shown in  FIG. 2  by the connecting link  34  connected to the connections  25 . In this case, the directional control valves  30  are set in such a way that they free a flow path of the cleaning fluid from the feed line  26  through the connecting line  32  into the return line  27  and shut off flow paths of the cleaning fluid to the connections  25 , so that no cleaning fluid can escape from the latter. 
     In the system  3  illustrated in  FIG. 2 , the hermetic coupling of the connecting link  34  is checked before the cleaning fluid is circulated in the second feed device  10 . For the purpose of carrying out this checking, firstly residues of the second coating fluid from the feed line  26  and the return line  27  are pumped back into the third container  13 , with the two pumps  17 ,  18  being operated with mutually opposite delivery directions. Accordingly, the fluid residues are sucked out of the feed line  26  by the first pump  17  and conveyed into the third container  13  through the line  15  belonging to the latter. The directional control valve  28  of the line  15  of the third container  13  in this case is switched to an appropriate setting. At the same time, the varnish or fluid residues are sucked out of the return line  27  by the second pump  18  and conveyed back into the third container  13  through the line  16  belonging to the latter. 
     Given correct seating of the connecting link  34 , in this case a vacuum is generated in the line system formed from the feed line  26 , the return line  27  and the connecting link  34 , and is detected by the sensor  36 . If this intended vacuum is built up within that line system, it is ensured that the connecting link  34  is connected properly to the connections  25 . 
     Otherwise, extraneous or parasitic air would penetrate into the line system in the region of the connections  25  and lead to a drop in the vacuum, which would be detected by the sensor  36  and signaled to the device controller  38 . The device controller  38  is able to indicate to the operator, acoustically or visually, that the connecting link  34  has not yet been coupled up correctly, so that the operator can carry out an appropriate correction. 
     If the connecting link  34  is seated correctly and the fluid residues have been pumped out of the lines  26 ,  27 , the directional control valves  28  are changed over and the delivery direction of the first pump  17  is changed over, so that the cleaning fluid from the fourth container  14  is now circulated in the second circuit  40 , in order to clean the latter thoroughly. During the circulation of the cleaning fluid, the pumps  17 ,  18  operate with the delivery direction being the same as each other, so to speak in tandem operation. This takes place during the printing operation running with the use of the first feed device  9 . It is only in order to connect the connecting link  34  to the connections  25  that any interruption to the printing operation is necessary. This can be carried out, for example, during the conversion of the printing press  1  from one print job to another. The two exemplary embodiments according to  FIGS. 1 and 2  do not differ from each other with respect to the circulation of the cleaning fluid in the short-circuited second circuit  40 . 
     Once the second feed device  10  has been cleaned to the greatest extent, its first pump  17  is reversed again, so that the latter attempts to suck the feed line  26  empty. In this case, the pumps  17 ,  18  once more run with mutually opposite delivery directions. A vacuum is produced in the line system, is detected by the sensor  36  and signaled to the device controller  38 , whereupon the latter opens the pneumatic valve  37 , so that ambient air flows into the line system and the latter is emptied completely. Compressed air can also be used to assist the emptying, instead of the ambient air. 
     The two structurally identical feed devices  9 ,  10  can be used alternately for the printing operation. In each case the feed device  9  or  10 , which is not participating actively in the printing operation, is flushed through with the cleaning fluid during the printing operation that is running by using the other feed device.