Patent Publication Number: US-7717040-B2

Title: Plate cutting and imaging with same device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   Reference is made to commonly-assigned co-pending U.S. patent application Ser. No. 11/615,025, filed Dec. 22, 2006, entitled HYBRID OPTICAL HEAD FOR DIRECT ENGRAVING OF FLEXOGRAPHIC PRINTING PLATES, by Alon Siman Tov et al., the disclosure of which is incorporated herein. 
   FIELD OF THE INVENTION 
   This invention relates in general to precision cutting of a flexographic plate while positioned on a flexographic imaging device, and in particular to utilizing the flexographic imaging device and high power laser diodes for cutting. 
   BACKGROUND OF THE INVENTION 
   The flexographic plate, using current technologies is imaged (or engraved) using a specially designed flexographic imaging device. Flexographic plates are relatively expensive, therefore flexographic plates will usually accommodate more than one distinct graphical art piece. For example, if a packaging job of a consumer product is requested, the job will usually include several different graphic art pieces, such as the front, back and sides of the package. The imaging of the flexographic plate, will include in this case the imaging of all those graphic art pieces in one imaging step. At this point the imaged flexographic plate comprises several distinct graphic art pieces. Those graphic art pieces are usually cut before they are positioned on a printing press. 
   In current printing technologies, the plate cutting is performed as a post imaging step. Often cutting is done manually on a manual cutting table, using a cutting blade. There are also automatic cutting machines, which receive the cutting geometry for a specific plate from a dedicated workstation. The supplied cutting geometry is translated to machine cutting commands for implementing the actual plate cutting. Cutting the flexographic as an extra step, in addition to the flexographic imaging machine process, is time consuming and costly, and manual cutting may result in lack of precision. 
   SUMMARY OF THE INVENTION 
   Briefly, according to one aspect of the present invention a method for cutting flexographic plates while plate imaging process is performed, comprises the steps of: mounting a flexographic plate on an imaging drum; imaging at least one graphical piece on the flexographic plate; cutting the graphical piece using the imaging device; and removing at least one graphical piece from the imaging device drum. 
   According to one embodiment of the present invention the precise cutting that is proposed by this invention, is based on utilization of the flexographic output device imaging means. At the point that the flexographic plate is fully exposed by the imaging device, the imaged plate is still mounted on the imaging device drum. At this stage, the lasers of the output device are deployed to cut around or mark the cutting of the various graphic art pieces by laser engraving around the proposed cutting piece. This process will yield a very precise cutting of the individual pieces, and will almost finalize the cutting process, before unmounting the flexographic plate from the imaging output device. 
   These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of a flexographic printing plate, illustrating the cutting areas around various graphic art pieces positioned on the flexographic printing plate. 
       FIG. 2  is a sectional schematic view of a flexographic a printing plate, illustrating an area where the plate cutting is performed, elevated ink transfer areas, and blank areas. 
       FIG. 3  is schematic of printhead and an imaging drum, with a flexographic printing plate mounted on the drum. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present description is directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
   In flexographical printing, it is common to image more than one graphical element on a single flexographic printing plate. The graphical elements, which will eventually be separated into more then one flexographical plate piece, may be independently printed on a printing machine at more then one printing session. The main reason for ganging the imaging of the plurality of graphical elements in one imaging session, lies in the high cost of the flexographical plates. 
   The present invention describes methods and apparatus for cutting graphical elements of flexographic plates, during the flexographical plates imaging process. This invention eliminates the need to perform an additional step in flexographical pre press workflow to cut the plate into more than one piece. The plate cutting step is performed today at the stage when the plate is un mounted from the imaging device. The plate cutting today can be done by:
         1. A manual process using a special cutting table using precision tools and cutting blades.   2. Applying a post imaging cutting machine, such a machine is produced by Misomex International of Nashua, N.H. Misomex offers a range of flatbed x-y plotting machines with cutting heads.       

     FIG. 1  illustrates an example of an imaged flexographic plate, with cutting areas according to the present invention. The printing plate  10  shows three different flexographic graphical elements  11 , each element belongs to a distinct printing job. Each graphical element or printing job, is separated by cut areas  12 . The cutting process of the areas  12 , in the present invention, is performed at the imaging stage of the flexographic plate. 
   The same laser engraving means used for imaging the plate, are utilized to produce the cutting areas  12 ,  13 , or  14  while the flexographic printing plate  10  is mounted on the imaging drum  30  as is depicted in  FIG. 3 .  FIG. 3  shows printhead  31 , which is used for imaging of the graphical elements  11  on the flexographic printing plate  10 . Printhead  31  is used for cutting the graphical elements  11 , as well, while printing plate  10  is mounted on the imaging drum  30 . 
   Referring again to  FIG. 1 , plate cutting can be performed in various manners; for example, full cutting as is illustrated in cutting area  14  or partial cutting as is illustrated in  13 . Cutting area  13  illustrates full cutting in the x-axis and partial cutting in the y-axis. The reason for using those various cutting styles depends on the available means for attaching the plate to the imaging device drum. Whenever the attaching means are such that a fully cut piece of plate is firmly attached, for example, plates are held on the drum by a strong vacuum, a full cut can be used. Otherwise partial cut such as illustrated by cutting area  12  or  13  should be used. 
     FIG. 2  illustrates a sectional view of flexographic printing plate  10 . It shows an imaged area  21 , which belongs to an imaged graphical element. On both sides of imaged area  21 , there are additional imaged areas  23 , each belong to a different graphical element. The imaged areas  21  and  23 , are separated by a cutting area  22 . The cutting areas shows that the flexographic plates is engraved as deep as the entire thickness of the printing plate, reaching up to the level of the imaging device drum  20 . 
   The cutting areas  22  can be made by the imaging device in the same imaging step at the same time as the imaging of the graphical elements. The plate cutting can be also performed as a separate step, while the plate is still mounted on the imaging device by utilizing a high power coarse laser as is disclosed in commonly-assigned copending U.S. patent application Ser. No. 11/615,025, or by multiple passes with a lower power laser. Parts of the cutting areas  22  maybe partially cut, as was discussed above. The reason for applying a partial cut is, for firmly attaching the plate pieces to the imaging device drum, to avoid plate staggering or plate pieces leaving the drum. 
   When imaging of more than one graphical element is completed, and there is a need to remove it from the imaging device for further processing; the imaging device is stopped, and the required graphical elements are unmounted from the imaging device drum. This is performed by completing a manual cutting of the thin areas which were originally left uncut. As mentioned above, the partial cut is used when there are no alternative means available for firmly attaching the graphical elements to the imaging device drum. In the case of partial imaging of the flexographic plate, the further imaging of at least one graphical element can be performed by applying an additional imaging pass. 
   It another embodiment of the invention, the flexographic plate is imaged in a first step in. In a second step, the rotation of the drum  30  is slowed and the cutting step in is performed. Slowing the rotation of the drum during the cutting step, reduces the possibility of one of the cut, graphical elements leaving the surface of the drum due to centrifugal forces. 
   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 
   
       
         10  flexographic printing plate 
         11  imaged graphical element or piece 
         12  fully cut area 
         13  partially cut area 
         14  cutting area at which one axis is fully cut, and the other is partially cut 
         20  level of the imaging device drum 
         21  cut around imaged area (elevated ink transfer areas and blank areas are shown) 
         22  cutting areas 
         23  separated imaged areas 
         30  imaging drum 
         31  printhead