Patent Publication Number: US-2016236487-A1

Title: Printing machine for plates

Description:
The present invention relates to a printing machine for plates or sheets, in particular for cardboard, of the type as recited in the preamble of the first claim. 
     Printing machines for various types of board or sheets, such as cardboard, in particular compact, corrugated or honeycomb cardboard, are known in the prior art. 
     In particular, digital printing has recently been increasingly used for this purpose. 
     For example, corrugated cardboard can be printed using two different methods. 
     A first method consists of printing one sheet, called the liner sheet, which, once printed, is glued to the remaining sheets to form the corrugated cardboard. 
     This method achieves good quality printing. However, the liner sheet may be damaged during the process to make the corrugated cardboard. Moreover, with this process, the printing step is always followed by another process and it is impossible to manufacture stocks of corrugated cardboard to be printed upon request. This undoes some of the benefits of flexibility and speed which characterize digital printing. 
     A second method consists of printing the assembled corrugated cardboard. 
     This process has considerable advantages in terms of flexibility and speed of processing, especially when digital printing is used. 
     Moreover, printing is not followed by another process that could undermine the quality of printing. 
     However, the prior art mentioned above has several significant drawbacks. 
     In particular, the cardboard is not always perfectly flat, as it should be to achieve good printing. 
     Moreover, like other composite boards such as polymer board or board made of other materials, cardboard has a high bending strength and low mass, and so does not lie flat under its own weight or stay flat when laid down. 
     The above drawbacks negatively affect the quality of printing on cardboard and similar materials. 
     In this situation the technical purpose of the present invention is to develop a printing machine for plates, and a printing process, able to substantially overcome the inconveniences mentioned above. 
     Within the scope of said technical purpose an important aim of the invention is to provide a printing machine for stiff or flexible board which achieves high quality printing. 
     Another important aim of the invention is to provide a printing machine for plates which permits high speed and flexibility of printing. 
     A further aim of the invention is to provide a printing machine for plates which is straightforward and economical. 
     The technical purpose and specified aims are achieved by a printing machine for plates as claimed in the appended claim  1 . 
     Preferred embodiments are described in the dependent claims. 
    
    
     
       The characteristics and advantages of the invention are clearly evident from the following detailed description of a preferred embodiment thereof, with reference to the accompanying drawings, in which: 
         FIG. 1 a    shows the printing machine according to the invention in a first position; 
         FIG. 1 b    shows the printing machine according to the invention in a second position; 
         FIG. 1 c    shows the printing machine according to the invention in a third position; 
         FIG. 1 d    shows the printing machine according to the invention in a fourth position; 
         FIG. 1 e    shows the printing machine according to the invention in a fifth position; 
         FIG. 1 f    shows the printing machine according to the invention in a sixth position; and 
         FIG. 2  shows a portion of the machine in a partial section view. 
     
    
    
     With reference to said drawings, reference numeral  1  globally denotes the printing machine according to the invention. 
     It is suitable for printing on board  10 , in particular lightweight and sufficiently stiff board, more in detail the machine is suitable for printing on cardboard, more in particular on compact, corrugated or honeycomb cardboard. Other suitable materials include other types of cardboard and paper, polymer board, such as correx or other types, composite board, for example with a polymer core and paper liner sheets, rigid board, and so on. 
     The printing machine  1  comprises printing means  2 , suitable to print at least a portion of a main surface of extension of the board  10 , and conveyor means  3  suitable to convey the board  10  along a feed path  1   a  and to supply and free the printing means  2 . 
     In particular the printing means  2  consist of a digital printer, in particular of the inkjet type. It may be of the scanning mode type, i.e. with printheads that move perpendicularly to the feed path  1   a,  or of the single pass type, i.e. with fixed printheads aligned perpendicularly with respect to the feed path  1   a.    
     In either case, the printing means  2  define a printing area  1   b,  that is to say an area, preferably flat, in which the board is printed, and which is thus arranged along the feed path  1   a.  In particular the width of the printing area  1   b  is appropriately equal to the maximum width of the board  10  that can be processed by the machine and its length along the feed path  1   a  is variable. 
     The conveyor means  3  are thus suitable to supply and free said printing area  1   b  to permit the positioning of the portion of the board  10  to be printed inside said printing area  1   b.  As is known, digital printers print one portion of the board  10  at a time, and feeding may be performed at intervals, in particular for scanning mode printers, or continuously, in particular for single pass printers. 
     The conveyor means  3  comprise at least one conveyor belt  4  which occupies at least part of the printing area  1   b,  and has a breathable surface layer  4   a.  It preferably consists of a continuous conveyor belt or other type of conveyor. The surface layer  4   a  is breathable owing to the intrinsic properties of the material, for example fabric, or owing to perforations, as illustrated in  FIG. 2 . 
     The conveyor means  3  also comprise, preferably connected to the conveyor belt  4 , suction means  5 , suitable to draw in air through the surface layer  4   a  thus defining a suction surface  4   b.    
     The suction surface  4   b  is appropriately above the suction means  5  and is suitable to hold the board  10  in a flat position. It is also arranged in proximity to or in correspondence with said printing surface  1   b.    
     The dimensions of the suction surface  4   b  are such to permit said surface to hold the board  10  flat without any deformation or bending of the board  10  that would cause the latter to be separated from the suction surface  4   b.  In particular, for the cardboard said length may be comprised between 30 cm and 80 cm. 
     The suction means  5  preferably comprise a vacuum pump  5   a  connected to ducts  5   b  ending in holes  5   c  or apertures in correspondence with the breathable surface layer  4   a  ( FIG. 2 ). 
     Moreover, the suction means  5  appropriately comprise partialization means  8  of the suction surface  4   b,  suitable to alter the size or the position of the suction surface  4   b.  They are preferably suitable to alter the size of the suction surface  4   b  in a direction perpendicular to the feed path  1   a  and parallel to the suction plane  4   b,  so that the width of the suction surface  4   b  is identical to the width of the board  10 , in the direction shown. 
     The partialization means  8  may act by means of a mobile, non-breathable element which obstructs the holes  5   c.  They may also act in a direction parallel to the feed path  1   a  and may serve to move the suction surface, as described in detail below. 
     The conveyor means  3  also appropriately comprise alignment means  6  or levelling means of the board  10  on the suction surface  4   b,  arranged in correspondence with the opposite surface of the board  10  with respect to the surface layer  4   a  and suitable to make the board  10  adhere to the suction surface  4   b,  substantially at least along the entire area of the suction surface  4   b.    
     The alignment or levelling means  6  are thus suitable to eliminate any irregularities in the board  3  with respect to the surface layer  4   a,  such as raised areas, various deformations, bending, bulging. Moreover, the alignment means only need to act initially for a first portion of the board  10 , after which the suction surface  4   b  will have enough force to hold the board in the correct position. 
     In particular the alignment means  6  comprise a plate  6   a  which is substantially a counter-profile of the suction surface  4   b  and transfer means  6   b  for moving the plate  6   a,  such as a sliding block with actuators, suitable to move the latter so as to guarantee the adhesion of the board  10  to the suction surface. In particular, the plate  6   a  moves vertically and moves downwards to press on the board  10 . In detail, it acts when the first part of the board  10  is placed on the suction surface  4   b,  as explained below. 
     The plate  6   a  may also comprise sliding means such as in particular rolls, ball-bearings, rollers, wheels or slides suitable to permit the most badly deformed parts of the board  10  to slide, without being damaged, when the board  10  slides beneath said plate  6   a.  The plate  6   a  is also preferably suitable to facilitate the maintenance of the board  10  in the flat position, after the action exerted by the transfer means  6   b,  as described more fully below. 
     Moreover the printing machine  1  comprises transfer means  7  suitable to move the suction surface  4   b  with respect to the printing area  1   b,  along the feed path  1   a.    
     Said movement has the important advantage of always maintaining the board  10  in contact with the whole of the suction surface  4   b,  so that even in the initial and final stages of printing on the board  10  the latter is always completely flat. 
     The maximum transfer stroke is preferably at least equal to the length, along the feed path  1   a,  of the suction surface  4   b.    
     This is achieved by moving the suction area  4   b  along the feed path  1   a,  or by moving the printing means  2 , in particular the printheads, or even by moving both. 
     Preferably, the transfer means  7  comprise a carriage  7   a  including said conveyor belt  4  and at least part of said suction means, as illustrated in  FIGS. 1 a   - 1   f.  The carriage  7   a  is thus suitable to translate in the direction of the feed path  1   a,  in particular in the first and/or final stage of the printing process, so as to also permit printing on the initial and final portion of the board  10 , advantageously without ever freeing the suction surface  4   b,  even partially, and thus without any loss of the vacuum. The carriage  7   a  may also comprise other similar sliding planes  7   b,  suitable to permit the transfer of the board  10 . 
     Alternatively, the transfer means  7  may comprise means for moving the suction means  5  only, which thus define a movement of the suction surface  4   b,  the portion of conveyor belt  4  of which varies continuously. The movement of the suction surface  4   b  may be achieved through partialization means  8  which act parallel to the feed path  1   a  and are suitable to move the suction surface  4   b.    
     The functioning of the printing machine  1  described above in a structural sense, is as follows. It defines an innovative printing process for plates  10  and other similar materials. 
     The process consists of first placing the board  10  on the printing machine  1 . 
     The printing machine  1  may be installed downstream or upstream of other processing stations of the board  10 , in particular of compact, corrugated, honeycomb or similar types of board. 
     First of all the adjustments to the machine  1  are performed, such as adjustments to the partialization means  8  which are arranged so that the width of the suction surface  4   b  substantially coincides with the width of the board  10 . The length of the board  10  is instead usually greater, even by up to several metres. 
     The board  10  travels along the feed path  1  and reaches the conveyor belt  4  arranged on the carriage  7   a.  The board  10  is then placed on the suction surface  4   b  so as to come into contact therewith, while the plate  6   a,  which is part of the alignment means  6 , is in a raised position ( FIG. 1 a   ). 
     At this point the process consists of the step of aligning the board  10  with respect to the suction surface  4   b,  by acting in correspondence with the opposite surface of the board  10  with respect to the surface layer  4   a,  so as to make the board  10  adhere to the suction surface  4   b,  to cover the whole area of the suction surface  4   b.    
     In detail, the alignment means  6  are activated so that the plate  6   a  at least moves the board  10  towards the suction surface  4   b  so that the surface of the board  10  and the suction surface  4   b  are perfectly overlapping and contiguous ( FIG. 1 b   ). In particular, the board  10  stops at approx. 1 cm, or at a distance that has been appropriately selected depending on the material of which the board  10  is made, so that the vacuum created on the suction surface  4   b  pulls on the board  10  so as to align and flatten it. 
     In this situation, it is extremely advantageous that substantially the whole of the suction surface  4   b  is always covered by the board  10 , so that there are no suction areas which are not covered by the board  10 . Such areas could indeed cause a notable loss of suction force. 
     Next the plate  6   a  is raised slightly, for example by about 1 cm, so as to continue to partially align the board  10  ( FIG. 1 c   ), in particular by means of the sliding means described. Moreover the suction surface  4   b  is moved with respect to said printing area  1   b  along the feed path  1   a.  Said movement may be performed in the initial phase only, in the final phase only, or in both, as in the preferred embodiment. 
     In particular, the carriage  7   a  initially moves the suction surface  4   b  underneath the printing area  1   b  ( FIG. 1 c   ). 
     The printing means  2  print the first part of the board  10  and, once it has been printed, the board  10  is transferred further along the feed path  1   a  so that the area immediately after it can be printed. 
     During these operations there is no need for the plate  6   a  to repeat the initial movement to continuously align the board  10  along the suction surface  4   b.  The force of the suction surface  4   b  is in fact sufficient to hold the board  10  in the correct position and aligned. 
     However, in this step the plate  6   a  helps to align the board  10  ( FIG. 1 d   ). 
     Lastly, the final portion of the board  10  reaches the suction surface  4   b  ( FIG. 1 e   ). 
     In this position the conveyor belt  4  stops so that the board  10  remains on the suction surface  4   a  without ever leaving the suction surface clear. Moreover, in this position, the transfer means  7  and in particular the carriage  7   a  may be used to end printing ( FIG. 1 f   ). 
     The entire movement of the board  10  is advantageously performed by means of the conveyor belt  4  and the transfer means  7 , with the board  10  never leaving the suction surface  4   b  free, so as to always maintain the two in close contact and avoid any loss of the vacuum. 
     After printing, the transfer means can convey the board  10  to subsequent workstations or storage areas. 
     The invention achieves some important advantages. 
     With the printing machine  1 , the board  10  is always perfectly flat  10  or in any case adheres to the suction surface  4   b,  regardless of its shape. 
     Said advantage is due in particular to the presence of the alignment means  6 , the suction surface  4   a  and the fact that the board  10  adheres to the suction surface  4   b  along the entire area of said surface. 
     Moreover, owing to the presence of the transfer means  7 , printing can even be performed on the initial and end portions of the board  10 . This advantage is fundamental for full-bleed printing without borders. 
     Consequently, with the printing machine  1  printing of a high quality is achieved because the board is always flat, and the process is fast and flexible thanks to the use of digital printing means. 
     The printing machine  1  is also straightforward and economical. 
     Modifications and variations may be made to the invention described herein without departing from the scope of the inventive concept as expressed in the independent and dependent claims. 
     All the elements as described herein may be replaced with equivalent elements and the scope of the invention as claimed in the independent and dependent claims includes all other materials, shapes and dimensions.