Abstract:
A compact printing unit includes a plate cylinder, an impression cylinder, and an ink applicator roller in a printing press, in particular a label printing press. In the printing unit, the plate cylinder is disengageable from cylinders contacting the plate cylinder for the purpose of format variation. The plate cylinder is pivotable about the impression cylinder about a pivot axis which is parallel to the axis of rotation of the impression cylinder and a distance between the axes of rotation of the plate cylinder and the impression cylinder is variable. A printing press and a method of producing labels or self-adhesive labels in a printing press are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2007 045 876.4, filed Sep. 25, 2007; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a printing unit including a plate cylinder, an impression cylinder and an ink applicator roller. In the printing unit, a plate which is received on the plate cylinder is capable of being brought into contact and engaged with the ink applicator roller. The plate cylinder and the impression cylinder form a printing nip for printing on a substrate. Moreover, the invention relates to a printing press including such a printing unit and a method of producing labels or self-adhesive labels in a printing press. 
         [0003]    Printing machines or printing presses which are constructed or used for printing labels or packaging face increasingly high requirements in terms of efficiency and ease of operation. At the same time, they need to offer maximum variability in the range of products they produce. One aspect is to produce as little waste as possible, for example when the printing press is changed from one print job to another, even from one printing process to another or from one printing length to another. Common in-line narrow-web printing presses constructed for label printing, in particular for printing self-adhesive labels, frequently have a configuration wherein printing material or substrates are guided by a plurality of cylinders and rollers between different process levels (for example for printing and drying). That means that a web section of considerable length is stored in the printing press. Consequently, a lot of waste may be produced. A label printing press which can be switched between different printing processes is described in International Publication No. WO 2005/028202 A1, corresponding to U.S. Patent Application Publication No. US 2006/0156934 A1. A new machine construction, which ensures that a comparatively short web section is stored in the printing press, requires first and foremost a printing unit configuration which, on one hand, provides the desired variability in terms of printing processes and printing lengths and, on the other hand, a short web path. 
         [0004]    Cylinders are frequently supported so as to pivot for the purpose of engaging and disengaging individual cylinders. German Published, Non-Prosecuted Patent Application DE 44 35 986 A1 discloses an offset printing unit including a corresponding apparatus for engaging and disengaging a blanket cylinder. An optimum pressure can be set and printing material of different thickness can be accommodated by displacing pivot arms. An offset printing unit of variable printing length is described, for example, in European Patent Application EP 1101 611 A1, corresponding to U.S. Pat. No. 6,694,877. Spindle drives pivot support arms about an axis in order to move the axes of rotation of the plate cylinder, the blanket cylinder, and the impression cylinder away from and towards each other. Printing cylinders and blanket cylinders of different format can be installed into the printing unit. 
         [0005]    British Patent 1,147,778, corresponding to U.S. Pat. No. 3,443,516 A1, describes an embodiment of an offset printing unit in a sheet-fed printing press wherein the blanket cylinder is pivotable about the axis of rotation of the plate cylinder through the use of a support arm, for engagement and disengagement purposes. The blanket cylinder can simultaneously be disengaged from the plate cylinder in a superimposed radial movement. 
       SUMMARY OF THE INVENTION 
       [0006]    It is accordingly an object of the invention to provide a printing unit of compact construction, a printing press and a method of producing labels or self-adhesive labels in a printing press, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which a plate cylinder is disengageable from cylinders contacting the plate cylinder for the purpose of format variation. 
         [0007]    With the foregoing and other objects in view there is provided, in accordance with the invention, a printing unit, comprising a plate cylinder, which may also be referred to as a master cylinder, an impression cylinder, and an ink applicator roller. In the printing unit of the invention, a plate received on the plate cylinder is engageable so as to be brought into contact with the ink applicator roller while the plate cylinder and impression cylinder form a nip to print on a substrate. The plate cylinder is pivotable about a pivot axis which is parallel to the axis of rotation of the impression cylinder, and a distance between the axes of rotation of the plate cylinder and the impression cylinder is variable. 
         [0008]    In accordance with another feature of the invention, the pivot axis may, in particular, be within the contour of the impression cylinder. In addition or as an alternative, when the plate cylinder is pivoted about the pivot axis, the impression cylinder may at least partly be located in a circle segment limited by a line defined by the movement of the axis of rotation of the plate cylinder. In other words, the plate cylinder is pivotable about the impression cylinder, and not away from the impression cylinder. The pivot axis may be located within the plate cylinder or behind the plate cylinder, as viewed from the axis of rotation of the plate cylinder. The distance between the axes of rotation may be varied along a linear or straight path. Depending on the actual embodiment of the printing unit of the invention, the impression cylinder and/or the ink applicator roller may be received with an axis of rotation which is supported to be fixed to the frame and stationary or displaceable. 
         [0009]    In particular, an element receiving the plate cylinder is pivotable, with the distance between the receiving location of the plate cylinder and the pivot axis being variable. A combination of the two degrees of freedom of movement or adjustment options provides the possibility of carrying out format adjustments and of effecting impression throw-on and throw-off as well as engagement between the plate cylinder and the ink applicator roller to supply ink to the plate cylinder. The printing unit of the invention does not require much installation space and is cost-efficient because it is formed of only a few components. 
         [0010]    In accordance with a further feature of the invention, which is particularly advantageous for label printing, the printing unit may be constructed to implement a flexographic printing process or a letterpress printing process or a gravure process. 
         [0011]    In accordance with an added feature of the invention, the pivot axis of the plate cylinder preferably extends along the central axis of the impression cylinder or coincides with the central axis of the impression cylinder. As another preferred feature, the position in space of the axis of rotation of the plate cylinder is displaceable. The position in space of the axis of rotation of the impression cylinder may be stationary. The position in space of the axis of rotation of the ink applicator roller and of potential further components of an inking unit of the printing unit of the invention may be displaceable. 
         [0012]    In accordance with an additional feature of the invention, the printing unit of the invention may include a mechanical adjustment system or an adjustment actuation system for carrying out the pivoting movement and the distance variation of the impression cylinder in a coupled way. In this manner, simplified operation of the adjustment is achieved at a high degree of automation, thus increasing cost-effectiveness. 
         [0013]    In accordance with yet another feature of the invention, in the printing unit of the invention, the plate cylinder may be received in the printing unit so as to be removable. Plate cylinders of different diameter may be receivable in the printing unit. As an alternative, intermediate sleeves of different diameters may be receivable on the plate cylinder. 
         [0014]    In accordance with yet a further preferred feature of the invention, when the impression cylinder and the plate cylinder are engaged with each other in the printing position, the axes of rotation of the plate cylinder and of the impression cylinder in the printing unit of the invention are located in a vertical plane in such a way that the printing nip is located in the upper tangential point of the impression cylinder (which is preferred) or of the plate cylinder. The impression cylinder may form the center of the printing unit. 
         [0015]    In accordance with yet an added feature of the invention, the printing unit includes a dryer device acting on a substrate which is located on the impression cylinder. In accordance with concrete embodiments, the dryer device may, for example, be a UV dryer unit, an infrared dryer unit, or a hot-air dryer unit. As an advantageous consequence, process levels of a printing press which is equipped with the printing unit of the invention may be combined to achieve a short web path through the printing press. 
         [0016]    In accordance with yet an additional feature of the invention, the printing unit may be constructed in such a way as to be operated in a first direction of rotation of the impression cylinder to print on a front side of the printing substrate and in a second direction of rotation counter to the first direction of rotation to print on a back side of the printing substrate. 
         [0017]    In accordance with again another feature of the invention, the impression cylinder and/or the plate cylinder of the printing unit of the invention may be drivable by a separate drive. 
         [0018]    With the objects of the invention in view, there is also provided a printing press, in particular a label printing press. In accordance with the invention, the printing press is distinguished by at least one printing unit in accordance with the invention having features or combinations of features as set forth herein. The printing press is preferably of in-line construction and/or of modular construction with respect to individual subassemblies, in particular the printing units or printing unit groups, including their support structures. 
         [0019]    In accordance with another feature of the invention, the substrate may be web-shaped. In particular, the web may be a multi-layer web of material, in particular a material for self-adhesive labels on a carrier web. The printing press may be a web-fed printing press. It may include a transport device for moving the web-shaped substrate through the printing press. The printing press may be a so-called narrow-web printing press. The width of the web to be printed may be less than 900 mm, in particular less than 515 mm. Typical widths of embodiments of narrow-web printing presses in accordance with the invention are in particular 330 mm and 280 mm. The printing press of the invention may include a plurality of printing units, in particular four printing units for multicolor printing. The printing press may include a plurality of printing units constructed in accordance with the invention. Short web paths through the press are possible due to the advantageous configuration of the cylinders of the printing unit of the invention. Consequently, the amount of waste can advantageously be reduced. Faster make-ready and register adjustments become possible. 
         [0020]    In accordance with a further feature of the invention, embodiments of the printing press of the invention which are particularly suited for label printing may include a straight path of the web-shaped substrate through a plurality of printing units of the invention. The straight path of the web-shaped substrate may be horizontal. 
         [0021]    In accordance with an added feature of the invention, a printing press according to the invention may in addition include individual ones or combinations of the following features: a printing unit of the invention may be received on a frame wall with one or more integrated drives. The printing press may include receiving elements for alternately receiving modules which are connectible and removable to carry out different printing processes or to treat/finish the substrate. Printing processes may include, in particular, flexographic printing, gravure, letterpress printing, offset printing, direct or indirect planographic printing, foil stamping, screen printing, inkjet printing, or xerographic printing. Types of treatment or processing in particular include punching, cutting, diecutting, perforating, creasing, folding, or varnishing. In other words, the printing press may include a (standardized or neutral) interface for receiving printing unit or processing unit components which are connectible to the printing press. In particular, components which may be used by all of these units or which may complete these units to make them functional may directly be parts of the printing press. The order of the individual printing units and/or processing units may be selected and adapted in accordance with the print job. 
         [0022]    In accordance with an additional feature of the invention, the printing unit of the invention may be received by a bearing element in a support element which is at least partially made of rock, in particular natural rock or a compound including natural rock. A printing press including a support element which is at least partly made of rock is described in German Published, Non-Prosecuted Patent Application DE 10 2006 042 884 A1 and in co-pending U.S. Patent Application Publication No. US 2008/0063458 A1, claiming the priority of the German Patent Application. Both applications and the entire content of their disclosure are explicitly included by reference herein. 
         [0023]    With the objects of the invention in view, there is concomitantly provided a method of producing labels or self-adhesive labels in a printing press. In accordance with the invention, a printing press having features or combinations of features as set forth herein is operated to process a web-shaped substrate which is suited for producing labels or self-adhesive labels. In accordance with a preferred embodiment, a web-fed printing press is operated in which the path of the web-shaped substrate runs straight, in particular horizontally, through a plurality of printing units. In the process, individual color separations of a multicolor print are printed into each other in a wet-on-wet process. A drying process after completion of the multicolor print is optional. 
         [0024]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0025]    Although the invention is illustrated and described herein as embodied in a printing unit, a printing press and a method of producing labels or self-adhesive labels in a printing press, 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. 
         [0026]    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 
         [0027]      FIG. 1  is a diagrammatic, side-elevational view of a preferred embodiment of the printing unit in accordance with the invention, illustrating degrees of freedom of movement; 
           [0028]      FIG. 2  is a side-elevational view of a first embodiment of the printing unit in accordance with the invention with coupled degrees of freedom; 
           [0029]      FIG. 3  is a side-elevational view of a second embodiment of the printing unit in accordance with the invention with coupled degrees of freedom; 
           [0030]      FIG. 4  is a longitudinal-sectional view of a preferred embodiment of a printing press according to the invention; 
           [0031]      FIG. 5  is a longitudinal-sectional view of the printing press shown in  FIG. 4  in an operating configuration including a straight and horizontal web path; 
           [0032]      FIG. 6A  is a front-elevational view and  FIGS. 6B-6D  are side-elevational views of an embodiment of a frame module for two printing units; 
           [0033]      FIGS. 7A and 7B  are side-elevational views illustrating a web path through an embodiment of the printing unit in accordance with the invention for front-side printing and back-side printing and simultaneous UV drying; 
           [0034]      FIGS. 8A and 8B  are side-elevational views illustrating a web path through an embodiment of the printing unit in accordance with the invention for front-side printing and back-side printing and simultaneous UV drying in an alternative configuration different from that of  FIGS. 7A and 7B ; and 
           [0035]      FIGS. 9A and 9B  are side-elevational views illustrating a web path through an embodiment of the printing unit in accordance with the invention for front-side printing and back-side printing and simultaneous hot-air drying in an alternative configuration different from those of  FIGS. 7A ,  7 B,  8 A and  8 B. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen an embodiment of a printing unit  10  in accordance with the invention for flexographic printing. The printing unit  10  includes a master cylinder or plate cylinder  12 , an impression cylinder  14  and an ink applicator roller  16 , which, to be more precise, is a screen roller. The cylinders are rotatable about their respective axes of symmetry. The impression cylinder  14  and the ink applicator roller  16  are fixed to a frame of the printing press. The impression cylinder  14  is disposed at the center of the printing unit  10 . A rocker  18  or support arm, in particular just or precisely one rocker  18 , is used to pivot the plate cylinder  12  about the axis of rotation of the impression cylinder  14  in a pivoting movement  20 . The rocker  18  is supported in the axis of rotation of the impression cylinder  14 . The rocker  18  can operate on the drive side of the plate cylinder  12  so that an operator can access the plate cylinder on the operator side for the purpose of changing format. The rocker  18  has a linear guide  22  so that a linear distance variation  24  between the plate cylinder  12  and the impression cylinder  14  is carried out by a displacement of a position in space of the axis of rotation of the plate cylinder  12  (without tilting the axis). This embodiment represents a simple printing unit construction providing simple and accurate printing cylinder adjustment. 
         [0037]    In accordance with a non-illustrated refinement, the impression cylinder  14  has an integrated cooling system. In addition, due to its configuration, it may be accessible in at least three positions for drying a printed substrate on the impression cylinder  14  (also see the description below with reference to  FIGS. 7A ,  7 B,  9 A and  9 B). 
         [0038]    In order to provide for a practical implementation of the pivoting movement, one of the actuators listed below may be used to move the rocker: a threaded drive with manual adjustment or a threaded drive with motor adjustment, a pneumatic cylinder, a hydraulic cylinder, a gearwheel with a pinion with manual adjustment or a gearwheel with a pinion with motor adjustment, a worm and a worm gear with manual adjustment or a worm with a worm gear with motor adjustment; a toothed belt with manual adjustment or a toothed belt with motor adjustment, or a thrust crank rocker with manual adjustment/motor adjustment with a threaded spindle, in pneumatic or hydraulic cylinder adjustment as well as in manual adjustment with a rack and a gearwheel manually or by motor. 
         [0039]    In order to provide for a practical implementation of the distance variation, in particular in a linear movement, one of the actuators listed below may be used to move the linear pushing element: a spindle-type lifting gear with manual adjustment, a spindle-type lifting gear with motor adjustment, a threaded spindle with manual adjustment, a threaded spindle with motor adjustment, a rack and a gearwheel with manual adjustment, a rack and a gearwheel with motor adjustment, a pneumatic cylinder, a hydraulic cylinder, or a push crank rocker with manual adjustment/motor adjustment with a threaded spindle, in pneumatic or hydraulic cylinder adjustment as well as in manual adjustment with a rack and a gearwheel manually or by motor. 
         [0040]    The actuators listed above may be embodied as a combination of manual and automatic actuating elements. In other words, the adjustment may be made manually, partly automatically, or fully automatically. 
         [0041]      FIG. 2  illustrates a first embodiment of the printing unit  10  in accordance with the invention. The printing unit  10  has coupled degrees of freedom for the pivoting movement  20  and the linear distance variation  24 . In order to disengage the plate cylinder  12  from the ink applicator roller  16  and at the same time to increase the distance of the axis of rotation relative to the impression cylinder  14 , the rocker  18  is moved through the use of an actuating element  26  which may, for example, be an actuator from among the list given above. The axis of the plate cylinder  12  is guided in a connecting link or coulisse  28  and is subjected to the force of a restoring element  30 , for example a tension spring, having a force component directed towards the coulisse  28 . 
         [0042]      FIG. 3  diagrammatically illustrates a second embodiment of the printing unit  10  in accordance with the invention with coupled degrees of freedom for the pivoting movement  20  and the linear distance variation  24 . In order to modify the absolute position of the plate cylinder  12  relative to the impression cylinder  14  and to the ink applicator roller  16 , a connecting link slider with an actuator  26 , which may be one of the actuators listed above, is provided. The axis of the plate cylinder  12  is subjected to the force of a restoring element  30 , for example a tension spring, having a force component directed towards the connecting link or coulisse  28 . 
         [0043]      FIG. 4  illustrates a view of a preferred embodiment of a printing press  32  in accordance with the invention, in this case a label printing press in accordance with the invention, of in-line construction with printing units  10  in accordance with the invention following each other in the horizontal direction. The label printing press processes a web-shaped substrate  34 . The substrate is unwound from a reel of substrate  36  in a feeding section  38  of the printing press  32  and is fed through the printing press  32  along a path. The printing press  32  has a plurality of frame modules  40 , namely three frame modules  40  in the given example. In this embodiment, each frame module  40  receives two printing units  10  or one printing unit  10  and one processing unit  42 , in this case a diecutting unit for cutting the labels out of the web-shaped substrate  34 . The individual processing stations are followed by a delivery section  44  in which the finished products are wound onto a label reel  46 . The feeding section  38 , the frame modules  40  and the delivery section  44  are connected in such a way that they can be removed or separated from each other. That is to say, the printing press  32  is of modular construction. 
         [0044]    The representation of the individual printing units  10  in  FIG. 4 , in this case flexographic printing units, includes chambered doctor blades  48  in addition to the plate cylinders  12 , impression cylinders  14  and ink applicator rollers  16 . Furthermore, the printing units  10  in the printing press  32  have various drying devices: UV drying devices  50  are associated with the impression cylinders  14  downstream at the respective printing nip of the printing unit  10  to be able to dry the printed substrate  34  directly on the impression cylinder  14 . The printing units  10  also include web-guiding rollers  52  for guiding the web-shaped substrate  34 . The fifth printing unit  10  includes a hot-air drying device  54  for both the upper side and the lower side of the substrate  34 . The hot-air drying device  54  is provided downstream of the fifth printing unit  10 . The web-shaped substrate is guided through the hot-air drying device  54 . The individual printing units  10  and the processing unit  42  are fixed to the frame modules  40  of the printing press  32  by a receiving element  56 . By way of example, the second printing unit  10  is operated to print on the back side of the substrate. 
         [0045]      FIG. 5  illustrates a printing press in a machine construction corresponding to  FIG. 4  with an operative configuration having a straight and horizontal web path to carry out a wet-on-wet multicolor printing operation. Starting from the reel of substrate  36  in the feeding section  38 , the web-shaped substrate  34  is moved through the printing units  10  received on the frame modules  40  on a straight and horizontal path  58  of web travel. A hot-air drying device  60  and a UV drying device  62  are provided upstream of the processing unit  42  and downstream of the fifth printing unit  10 . Depending on the drying process which is suitable for the printing inks that have been used in the press, the printed substrate  34  may be dried by hot air (to expel solvents) or UV light (for hardening). The finished labels are stored on a label reel  46  in the delivery section  44 . 
         [0046]    In each one of the printing units  10 , the respective printing nip, which is formed by the plate cylinder  12  and the impression cylinders  14  and through which the web-shaped substrate  34  is passed, is located at an upper tangential point of the impression cylinder  14 . Although not explicitly illustrated in  FIG. 5 , to provide format variability, the position of the ink applicator roller  16  and other inking unit components, in particular of the chambered doctor blade  48 , can be adjusted to be able to accommodate different printing lengths, for example by receiving plate cylinders  12  of different diameters. The plate cylinder  12  is always in contact or engaged with the impression cylinder  14  at the upper tangential point of the impression cylinder  14 . 
         [0047]      FIGS. 6A to 6D  refer to an embodiment of a frame module  40  for two printing units  10  in accordance with the invention.  FIG. 6A  is a view of the frame module  40 . The frame module  40  includes a support element in the form of a side wall  64  made of rock, to be precise a single piece of natural rock, in particular granite, or a monolith. There are four driving interfaces  66  for the printing unit modules to be received. A mechanical interface is formed by a respective receiving element  56 . The side wall  64  made of rock rests on two base foot profiles  68 . The frame module  40  can be aligned through the use of leveling elements  70 .  FIGS. 6B to 6D  are side views of the frame module  40 . Separate integrated drives in the form of motors  72  are attached to the back of the side wall  64  made of rock and are accessible through the drive interfaces  66 . A process module  74 , which includes printing unit or processing unit components, can be received on a receiving element  56  so as to be connectible and removable. An additional component module  76 , which for example includes a hot-air drying device, may be received underneath the receiving element  56  on the frame module  40  so as to be connectible and removable. For this purpose, the receiving element  56  may include, for example, linear guides or rails for the process module  74  and/or the additional component module  76  to be slid on. 
         [0048]      FIGS. 7A and 7B  are used to explain the path of web travel of the substrate  34  for front-side printing and back-side printing with simultaneous UV drying in an embodiment of the printing unit  10  of the invention. The substrate  34  is guided through the printing unit  10  in a direction of substrate transport  78 . In  FIG. 7A , the impression cylinder  14  is operated to rotate in a first direction of rotation  80  for front-side printing. The web-shaped substrate  34 , which is guided by the web-guiding rollers  52 , partly wraps around the impression cylinder  14 . The impression cylinder  14  and the plate cylinder  12  form a printing nip at the upper tangential point. A printing form received on the plate cylinder  12  is supplied with ink by the ink applicator roller  16 , which in turn receives ink from the chambered doctor blade  48 . Downstream of the printing nip as viewed in the direction of transport  78  of the substrate (right-hand exiting side) there is a UV drying device  50  for drying the substrate  34  as it is still located on the impression cylinder  14 . As is shown in  FIG. 7B , for back-side printing, the guide rollers  82  guide the substrate across the printing unit  10  in such a way that the substrate reaches the printing nip formed between the plate cylinder  12  and the impression cylinder  14  from the opposite direction as compared to  FIG. 7A . The impression cylinder  14  rotates in a second direction of rotation  84 . As compared to the situation illustrated in  FIG. 7A , a UV drying device  50  is located at a different position downstream of the printing nip as viewed in the direction of transport  78  of the substrate (left-hand exiting side). The UV drying device  50  dries the substrate  34  while it is still located on the impression cylinder  14 . 
         [0049]      FIGS. 8A and 8B  illustrate an alternative configuration of the path of web travel through an embodiment of the printing unit  10  in accordance with the invention for front-side printing and back-side printing with simultaneous UV drying. Both the configuration for front-side printing shown in  FIG. 8A  and the configuration for back-side printing shown in  FIG. 8B  correspond to  FIGS. 7A and 7B . The same reference numerals are used and reference may be made to the description of  FIGS. 7A and 7B .  FIGS. 8A and 8B  illustrate an embodiment in which a UV drying device  50  is directed to the lower tangential point of the impression cylinder  14 . In this embodiment, the printing unit  10  can advantageously be operated with one and the same UV drying device  50  for both front-side printing as shown in  FIG. 8A  (with a first direction of rotation  80 ) and back-side printing as shown in  FIG. 8B  (with a second direction of rotation  84 ). For this purpose, in both modes of operation, the web-shaped substrate  34  wraps around the impression cylinder  14  far enough for the substrate  34  to be dried directly on the impression cylinder  14  in the lower tangential point. For front-side printing, further web-guiding rollers  86  are provided in addition to one of the two web-guiding rollers  52 , whereas for back-side printing, the web-shaped substrate is guided by the other one of the two web-guiding rollers of the printing unit  10 . 
         [0050]      FIGS. 9A and 9B  illustrate the path of web travel through an embodiment of the printing unit  10  in accordance with the invention for front-side printing and back-side printing with simultaneous UV drying in an alternative configuration which is different from that of  FIGS. 7A ,  7 B,  8 A and  8 B. Both the configuration for front-side printing shown in  FIG. 9A  and the configuration for back-side printing shown in  FIG. 9B  correspond to  FIGS. 7A and 7B . The same reference numerals are used and reference may be made to the description of  FIGS. 7A and 7B .  FIGS. 9A and 9B  illustrate an embodiment in which a hot-air drying device  54  is provided below the impression cylinder  14 . This drying device  54  can be used to dry both sides of the web-shaped substrate both in front-side printing ( FIG. 9A ) and in back-side printing ( FIG. 9B ). Further web-guiding rollers  86  are provided to guide the web-shaped substrate  34  through the hot-air drying device  54 . The web-shaped substrate  34  is fed to the hot-air drying device  54  from the original entry side of the substrate  34  into the printing unit  10 . In other words, the hot-air drying device  54  is operated in the same direction or orientation in both cases.