Abstract:
A method for preparing a printing cylinder includes providing an image bearing printing surface comprising a plurality of cells; applying a filling material into the cells; fixing the filling material in a first group of cells in a first pattern; and removing the filling material from a second group of cells.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to commonly-assigned copending U.S. patent application Ser. No.______ (Attorney Docket No. K000187US01/NAB), filed herewith, entitled REUSABLE PRINTING DEVICE, by Solomon, the disclosure of which is incorporated herein. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates in general to printing, and in particular to a re-usable printing surface having a plurality of cells. 
       BACKGROUND OF THE INVENTION 
       [0003]    In current printing technology the final image is conveyed to a substrate by transferring ink from an image bearing printing surface to the substrate. The image bearing surface generally picks up ink only on the ‘image’ areas, the areas that correspond on the substrate to be inked. The print on the substrate is produced by transferring ink directly or indirectly from an inked-up image bearing surface to the substrate. An example of this technology is a printing plate wherein certain areas of the plate are hydrophobic or hydrophilic. 
         [0004]    In conventional printing systems, the image bearing surface picks up liquid or paste ink, typically from an ink reservoir. The means by which the surface transfers ink to the ‘image’ areas depends upon the particular technology. Printing plates will be used in flexography and offset lithography, whereas specially made cylinders are used in gravure printing. The ink is then transferred to another surface, be it the final product substrate, such as printed paper, or an intermediate medium such as a rubber blanket. 
         [0005]    In digital printing systems, ink is transferred to the substrate in various ways for example, inkjet printing. Digital printing has an advantage over conventional print in its ability to handle variable information. This allows the printer to tailor each print differently. The main drawbacks of digital printing are that it is, in general, significantly more expensive and time consuming than conventional printing processes. 
       SUMMARY OF THE INVENTION 
       [0006]    Briefly, according to one aspect of the present invention a method for preparing a printing cylinder includes providing an image bearing printing surface comprising a plurality of cells; applying a filling material into the cells; fixing the filling material in a first group of cells in a first pattern; and removing the filling material from a second group of cells. 
         [0007]    The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic illustration of a printing block with plurality of printing cells; 
           [0009]      FIG. 2   a  is a schematic illustration of blocked and empty printing cells; 
           [0010]      FIG. 2   b  is a cross-section of several empty printing cells on the printing block surface; 
           [0011]      FIG. 2   c  is a cross-section of several printing cells on the printing block surface wherein some of them are empty, fully filled, or partially filled; 
           [0012]      FIG. 3  is a schematic illustration of a printing block imaging device consisting of an imaging system and a cylinder made printing block the imaging system is adapted to adjust the printing cells content; and 
           [0013]      FIG. 4  is a schematic illustration of an inkjet system adapted to fill the printing cells with blocking material. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The present invention describes a direct printing device containing a surface of printing cells. The printing cells can be filled by selective control thus allowing forming an image to be printed on a substrate. A previously formed image can be erased from printing cells surface and modified forming another image by suitable imaging means. 
         [0015]      FIG. 1  shows a printing cylinder  100 . The printing cylinder  100  contains a printing block  104 . The printing block  104  is covered with an image bearing surface  108 , containing plurality of printing cells. The printing cells are in a form of micro-cavities of holes spread on surface  108 , the printing cells are geometrically arranged for printing. The printing block  104  can be round as is depicted in  FIG. 1  or flat (not shown). The printing block  104  can be made from flexible material. Additionally the round printing block  104  in  FIG. 1  can rotated during imaging or can be fixed into a single position during imaging. 
         [0016]      FIG. 2   a , depicts an illustration of printing cells  200  representing a segment of printing cells out of image bearing surface  108 . The printing cells  200  are divided into two groups of cells, fully filled cells  204  and non-blocked or empty cells  208 . The division of cells into two groups forms an image and transforms printing cells surface into an image bearing surface. The image bearing surface  108  when applied with ink and pressed on a substrate (not shown) will cause the image represented by printing cells  204  and  208  to be printed on the substrate. 
         [0017]    In another arrangement, more than two groups ( 204 ,  208 ) can be formed, where each of the additional groups of cells represent filling of printing cells  200  in levels that may range from non empty to not fully filled printing cells. 
         [0018]      FIG. 2   b  shows a cross-section of several empty printing cells on the printing block surface  212 .  FIG. 2   c  shows the filling level of the printing cells, for example printing cell  216  is fully filled, printing cell  220  is partially filled and printing cell  224  is not filled at all. Similar arrangements can be made by adding additional filling levels. The impact on the printing substrate of the printing cells with various filling will be different and distinct from each other. 
         [0019]    In order to form an image on the image bearing surface  108 , a filling material is applied one the entire surface  108 . The filling material can be a photopolymer that will be cured by ultra violet (UV) light, or the filling material can be a liquid polymer to be solidified by cooling means. Another filling material can a polymer solution that solidifies by vaporization of the solvent, when laser means or other thermal sources area applied. All the printing cells ( 204  and  208 ) are filled with the printing material. The filling material can be applied for example by immersing the entire surface  108  in a filling material reservoir (not shown). The next step is to fix the filling material residing in a selected group of printing cells for example printing cells  204  and removing the filling material (which is not fixed) from printing cells  208 , the removal of the filling material can be performed by an printing block imaging device  300  (shown in  FIG. 3 ), described further in this document. 
         [0020]    Fixing of the filling material can be achieved by applying UV (ultra violet) light in printing cells  204 . Another alternative for fixing the filling material in cells  204  is by applying heat on the filling material in the first group in printing cells  204 . The fixing method depends on the characteristics of the chosen filling material. 
         [0021]    At this stage the image bearing surface  108  represent an image which is ready to be mounted on a printing device (not shown) for printing. The imaging device  300  can integrated into a printing device as a pre-printing step or alternatively can be a standalone system detached from a printing device. The image is formed according to a previously prepared halftone image. The halftone image is typically prepared by a digital front end (DFE) (not shown) server such as Kodak Prinergy, the DFE is capable to process a printing job received in a page description language (PDL) format and rasterizing it into a halftone image or a plurality of halftone images that represent the entire print job, ready for imaging. 
         [0022]    In order to perform printing, the printing block  104  is mounted on a printing device. Printing of the halftone image is initiated, the printing can be performed directly from the printing block  104  to a substrate, or alternatively via an intermediate blanket to the substrate. After printing is completed the printing block  104  is unloaded from the printing device. The printing block  104  is loaded on an imaging device  300  shown in  FIG. 3 , for removal of the filling material from cells  204 . This process will enable reuse of printing block  104  for subsequent printing of new printing jobs. The cleaning of cells  204  or is performed by imaging device  300 . 
         [0023]    The imaging device  300  includes a laser imaging head  304  mounted on carriage  308  in direction  312 , parallel to printing cylinder  100 . The carriage movement is coordinated by screw  316 . The laser imaging head  304  emits laser energy pointed on the cells  204  (filled with filling material). The information which cells are filled with a filling material is provided to imaging head  304  by micro-controller  320 . Micro-controller  320  receives the information on cells  204  from the previously prepared halftone image that had been used to form an image on printing block  104 . The applied laser energy from imaging head  304  is adapted to dissolve the filling material from cells  204 . 
         [0024]    Another embodiment that is used to fill cells  204  with filling material is described in  FIG. 4 .  FIG. 4  shows an inkjet head  404  configured to apply filling material via inkjet means only on cells  204  of surface  108 . In this embodiment there is no need to fill the entire cells of surface  108 , but only the selected cells  204  defined by the halftone image are injected by inkjet head  404  with filling material  408 . The fixing of filling material is preformed selectively to cells  204 . 
         [0025]    In certain embodiments cells  204  will serve as printing cells and cells  208  as non printing cells, in other embodiments cells  208  will be printing cells whereas cells  204  will not print. 
         [0026]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
       PARTS LIST 
       [0027]      100  printing cylinder 
         [0028]      104  printing block 
         [0029]      108  image bearing surface 
         [0030]      200  printing cells 
         [0031]      204  fully filled cells 
         [0032]      208  empty cells 
         [0033]      212  printing block surface 
         [0034]      216  fully filled printing cell 
         [0035]      220  partially filled printing cell 
         [0036]      224  empty printing cell 
         [0037]      300  imaging device 
         [0038]      304  imaging head 
         [0039]      308  carriage 
         [0040]      312  carriage direction 
         [0041]      316  screw 
         [0042]      320  micro-controller 
         [0043]      404  inkjet head 
         [0044]      408  injected filling material