Patent Publication Number: US-2005132910-A1

Title: Gravure printing cylinder

Description:
The invention relates to a gravure printing cylinder comprising a block carrier having a peripheral surface to which a metallic gravure layer is applied.  
      The block carrier of a gravure printing cylinder has heretofore, in view of the high mechanical loads, been formed by a steel cylinder having an axle firmly welded thereto or thereinto. A nickel layer having a thickness of 2 μm for example, is applied to the peripheral surface of the steel cylinder, and this nickel layer carries in turn one or more copper layers serving as the gravure layer, for example, a layer of priming copper, on which a separating layer with a thickness of 1 μm and then another copper layer having a thickness of about 60 to 120 μm is applied, the so-called form copper or Ballad skin. The ink-receiving pits of the gravure printing cylinder are engraved electromechanically, chemically or by means of a laser into the form copper and, after gravure, the cylinder is chrome-plated.  
      Since the steel gravure printing cylinder has a considerable weight, in particular in case of large printing length and width, suitable equipment such as cranes, manipulators, robots and the like are used for handling the gravure printing cylinder, when the cylinder is to be exchanged, for example.  
      It is an object of the invention to provide a gravure printing cylinder which can be handled more easily.  
      To achieve this object, according to the invention, the block carrier is formed by a self-supporting sleeve made of carbon fiber composite material and supported on disks.  
      By replacing the conventional steel cylinder with a cylinder that consists essentially of carbon fiber composite material and has a substantially lower weight, the handling is greatly facilitated, so that a cylinder change may easily be carried out by the operating personal by hand, even in case of large printing widths of, for example, 1 to 2 m or more and also in case of large cylinder diameters of 10 to 20 cm, for example. Thus, expensive equipment can be dispensed with and, moreover, the cylinder change operation can be accelerated.  
      EP-A-1 025 996 discloses already a printing plate cylinder for a flexographic printing machine, wherein the cylinder has a sleeve made of carbon fiber composite material with a wound structure of carbon fibers, the cylinder being supported on two disks. The printing plates are then fixed on this cylinder either directly or with use of a sleeve thrust thereupon. Although, in case of a gravure printing cylinder, the gravure layer is formed directly on the surface of the block carrier and the line pressure in the print process is approximately 10 times higher than in case of a flexographic printing machine, it has turned out, surprisingly, that the mechanical requirements can be met by a sleeve of carbon fiber composite material even for a gravure printing cylinder.  
      Advantageous embodiments of the invention are indicated in the dependent claims.  
      The disks carrying the sleeve may also be made of carbon fiber-reinforced plastics or, alternatively, of steel or aluminum. They may either be flush with the ends of the sleeve or may be somewhat offset inwardly for better controlling the distortions occurring in the print process. Optionally, the two disks are additionally connected by an internal tube made of carbon fiber reinforced plastics, glass fiber-reinforced plastics, steel or aluminum. This stabilizes the gravure printing cylinder as a whole and, in addition, provides a good guidance when, in the event of a cylinder change, the gravure printing cylinder is thrust onto a supporting or clamping axle of a printing machine.  
      In the gravure printing cylinder according to the invention, the layers of nickel, copper, etc. are formed on the carbon fiber composite material either directly or by means of a primer layer, e.g. galvanically or by powder or plasma spray coating.  
      In addition to a considerable weight reduction and a shortening of the set-up times for the gravure printing machine achieved thereby, the invention has the further advantage that a gravure printing cylinder made of carbon fiber composite material has a spectrum of Eigenfrequencies which is clearly different from that of a steel cylinder and has a greater distance from the excitation frequencies occurring in a printing machine, so that smoother running properties and, due to the high rigidity and the good damping properties of the carbon fiber composite material, an improved print quality can also be achieved.  
    
    
      An embodiment example will now be described in conjunction with the drawings, wherein:  
       FIG. 1  is a partially broken-away view of a gravure printing cylinder according to the invention:  
       FIG. 2  is a schematic view of a support axle of a printing machine onto which the gravure printing cylinder shown in  FIG. 1  is to be thrust; and  
       FIG. 3  is a sectional view of the gravure printing cylinder that has been thrust onto the support axle. 
    
    
      The gravure printing cylinder  10  shown in  FIG. 1  has a self-supporting sleeve  12  made of carbon fiber composite material, e.g. carbon fiber-reinforced synthetic resin, which is supported on radial disks  14  in the vicinity of both ends of the cylinder. The annular disks  14 , which themselves may be made carbon fiber-reinforced synthetic resin, are connected to one another in the region of their internal peripheries by a guide tube  16  made of steel, aluminum or fiber-reinforced synthetic resin. The guide tube  16  and the sleeve  12  are separated by a considerable radial spacing which may vary depending on the desired printing length of the gravure printing cylinder  10 . For example, the printing length may vary between 400 and 1100 mm, and the printing width (length of the sleeve  12 ) may be in a range from 800 to 1600 mm.  
      In the example shown, the sleeve  12  has two layers  18 ,  20  of carbon fiber-reinforced material, e.g. an inner layer  18  in which the carbon fibers extend or are wound essentially in circumferential direction or diagonally, and an outer layer  20  in which the carbon fibers are predominantly oriented in axial direction. However, other configurations of the carbon fiber structure as well as single-layer constructions of the sleeve  12  are also conceivable. The overall wall thickness of the sleeve  12  should be more than 4 mm and is in the order or magnitude of 6 to 20 mm, depending on the size of the printing cylinder, so that, in spite of the high line pressure occurring in the gravure printing process, the gravure printing cylinder  10  as a whole has a high distortion resistance and a good dampening behavior.  
      A layer  22  of nickel or another suitable material with a thickness of a few μm is formed on the outer peripheral surface of the sleeve  12 , e.g. galvanically or by spray coating, and, as is conventional for gravure printing cylinders, this layer carries in turn a gravure layer  24  which may for example consist of several layers of different copper alloys. The ink-receiving, printing recesses of the gravure printing cylinder are engraved in the gravure layer  24 , as has been symbolized in  FIG. 1  by the writing “Gravur”. Subsequent to the gravure process, a chrome layer  26  is applied in the usual way.  
      The gravure printing cylinder  10  described above, in spite of its high mechanical strength, has a low weight, which leads to an improved resonance behavior and drastically reduced forces of inertia during the printing operation, and, in the instant of a cylinder change, has the advantage that even gravure printing cylinders for very large printing lengths and printing widths may be handled manually without using a robot or similar equipment.  
       FIG. 2  schematically shows a support axle  28  which serves for supporting the gravure printing cylinder  10  and is supported in a frame of a printing machine, which has not been shown, by means of bearings  30  so as to be driven for rotation. In two positions corresponding to the positions of the disks  14  in  FIG. 1 , the supporting axle  28  has mechanical or hydraulic clamping devices  32  for the gravure printing cylinder  10 . When the cylinder is to be exchanged, the bearing at one end of the support axle  28  is removed, so that the support axle is held in the printing machine in cantilever fashion, as has been shown in  FIG. 2 . Then, the printing cylinder  10  may easily be pushed by hand onto the support axle with its guide tube  16  and is then fixed by means of the clamping devices  32 , as has been shown in  FIG. 3 . After closing and locking the bearing  30  on the left side in  FIG. 3 , the printing machine is again ready for printing after a very short set-up time.