Patent Publication Number: US-2004041990-A1

Title: System and method for using flexographic media in an imaging system

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention generally relates to the field of imaging systems, and specifically relates to systems and methods for recording and processing flexographic plates in pre-press imaging  
       [0002] In many pre-press imaging systems, such as imagesetters or platesetters, a plurality of sheets or plates (hereafter referred to as plates) of flexographic recording media are separately exposed by an imaging source. The flexographic media may include sheets of a photo-polymerizable material. Each plate may provide a pattern for a different color (e.g., yellow, magenta, cyan and possibly black), and these plates must be registered with one another during printing of the final multi-color image. The flexographic recording media to be imaged by a pre-press imaging system may be supplied in web form or in discrete plates.  
       [0003] During imaging, a movable optical carriage is typically used to displace a laser system or other imaging source in a slow scan direction along a stationary or moving, curved or planar, media support surface (e.g., an external drum, and internal drum, a flatbed, or other support surface). The imaging source exposes a supply or recording media supported on, and held against, the media support surface. Generally, the imaging source includes an optical system for scanning one or more lasers or other radiation beams, each modulated by a digital information signal, over the recording media to record an image onto the recording media. Generally, the information signal is recorded onto a supply of recording media mounted about the external drum by displacing the imaging source relative to the media support surface, e.g., an external drum. This may be accomplished in a number of ways, including rotation of the external drum in combination with a lateral translation of the imaging source, etc. In certain systems, the external drum is rotated while the imaging source is displaced in discrete steps or continuously along the length of the external drum to record data onto the recording media.  
       [0004] The imaged flexographic plate is then output from the imaging system, and transported to a photo-processing station, where the photo-polymers of the flexographic plate are photo-cured. The flexographic plate is then transported to a chemical processing station in which the non-desired portions of the image are removed from the surface of the plate to form the flexographic relief image for printing.  
       [0005] The use of a separate photo-processing and chemical processing stations require additional floor space as well as handling and separate processing steps, which increase the risk of occurrence of human and other errors. It is desirable to reduce the processing time and to reduce the chance of error in the processing operations in flexographic imaging systems.  
       [0006] There is a need, therefore, for an improved system and method for imaging and processing flexographic media in a pre-press imaging system.  
       SUMMARY OF THE INVENTION  
       [0007] The invention provides an imaging system is disclosed for imaging and photo-processing flexographic media. The imaging system includes an input opening through which flexographic media may be input to the imaging system, an imaging unit, a photo-processing unit, and an output opening. The imaging unit is for imaging the flexographic media that is received through the input opening, and provides imaged flexographic media. The photo-processing unit receives the imaged flexographic media, and photo-processes the imaged flexographic media by illuminating the flexographic media. The photo-processing unit provides photo-processed imaged flexographic media. The photo-processed imaged flexographic media may exit the imaging system through the output opening. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] The following description may be further understood with reference to the accompanying drawings in which:  
     [0009]FIG. 1 shows an illustrative isometric view of an external drum imaging system of the invention together with an output table;  
     [0010]FIG. 2 shows an illustrative isometric view of the imaging system of FIG. 1 in accordance with an embodiment of the invention with the housing removed;  
     [0011]FIG. 3 shows an illustrative side view of the imaging system of FIG. 1 with the housing removed;  
     [0012]FIG. 4 shows an illustrative bottom view of the photo-processing unit of FIG. 3 taken along line  4 - 4  thereof;  
     [0013]FIG. 5 shows a diagrammatic flow chart of an imaging and photo-processing system of the invention;  
     [0014] FIGS.  6 A- 6 D show diagrammatic illustrations of various steps in the photo-processing system of the invention; and  
     [0015]FIG. 7 shows an illustrative side view of the imaging system of a further embodiment of the invention with the housing removed.  
     [0016] The drawings are shown for illustrative purposes only, and are not to scale. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0017] An embodiment of a system of the invention is illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout the drawings. Although the drawings are intended to illustrate an embodiment of the present invention, the drawings are not necessarily drawn to scale.  
     [0018] A flexographic media processing system of the invention may be used with an external drum imaging system that is configured to record digital data onto a flexographic printing plate.  
     [0019] Although described below with regard to an external drum flexographic platesetter, many aspects of the present invention may be used in conjunction with a wide variety of other types of flexographic external drum, internal drum, sleeve or flatbed imaging systems, including imagesetters and the like, without departing from the intended scope of the present invention.  
     [0020] As shown in FIG. 1, in accordance with an embodiment of the invention, a flexographic plate may be placed onto an input tray  30  of an image recorder, such as a platesetter  10  having a housing  4 . The flexographic plate is then imaged, and then photo-processed inside the platesetter  10  in accordance with the invention. The flexographic plate is then output from the platesetter  10  via output port  6  and deposited onto a table  8  in the illustrated embodiment.  
     [0021] The imaging system generally includes a front end computer or workstation (not shown) for the design, layout, editing, and/or processing of digital files representing pages to be printed, a raster image processor (RIP) for further processing the digital pages to provide rasterized page data (e.g., rasterized digital files) for driving an image recorder, and the platesetter  10 , for recording the rasterized digital files onto a printing plate or other recording media. The platesetter  10  records the digital data provided by the RIP onto a supply of flexographic media including a photo-ablatable surface. In the present embodiment, the flexographic printing plate is manually loaded onto a staging area of the platesetter  10  by an operator. Alternately, or in addition to manual loading, the flexographic plate may be provided and loaded onto the platesetter  10  by a media supply or autoloading system, which may accept a plurality of the same size or different size flexographic printing plates.  
     [0022] As shown in FIG. 2, the platesetter  10  includes an external drum  12  having a cylindrical media support surface  14  for supporting the flexographic printing plate  16  (shown in FIG. 3) during imaging. The external drum platesetter  10  further includes a scanning system  18 , coupled to a movable carriage  20 , for recording digital data onto the imaging surface  22  of the printing plate  16  using a single or multiple imaging beams  24  (shown in FIG. 3). The carriage  20  rides along a stable base  26 , and the drum  12  rotates about a drum drive system  28 . The base  26  may be formed of heavy material, such as a polymer-concrete mixture, granite, or the like, to vibrationally isolate the external drum  12  and scanning system  18  from external vibrations.  
     [0023] The flexographic platesetter  10  also includes a photo-processing source  46  that is suspended above the output area of the imaging system by suspension brackets  48  as shown in FIGS. 2 and 3. Generally, during use a plate is positioned on an input tray  30 , and transferred to an imaging area in a direction as indicated at A. After imaging, the plate is transferred from the imaging area to the output area in a direction as indicated at B using transfer belts  32  that are driven by pulleys  34  about pulley shafts  36 . From the output area, the plate may be photo-processed as discussed below in further detail. The plate may then be exited from the platesetter  10  in either of a direction as indicated at C or a direction as indicated at D by rollers  40  that contact the plate after the pulleys  34  and belts  32  are lowered with respect to the rollers  40 . In other embodiments, the plate may be output in a direction as indicated at E by the pulleys  34  and belts  32 .  
     [0024] As shown in FIG. 3, the scanning system  18  is displaced by the movable carriage  20  in a slow scan (axial) direction along the length of the rotating external drum  12  to expose the printing plate  16  in a line-wise manner when a single beam is used or in a section-wise manner for multiple beams. Other types of imaging systems may also be used in the present invention. In an embodiment, the printing plate  16  is loaded onto the external drum  12  while rotating the drum in a first clockwise direction. The external drum  12  is then rotated by a drive system  28  in a clockwise or counterclockwise fast scan direction, typically at a rate of about 100-1000 rpm. The printing plate  16  is then imaged while the drum is rotated in the fast scan direction. Finally, the printing plate  16  is unloaded from the external drum  12  while rotating the drum in the second direction.  
     [0025] In accordance with the embodiment of the invention shown in FIGS.  1 - 3 , the system also includes a photo-processing station  46  within the imaging system  10 . As will be discussed in further detail below, the photo-processing station processes the flexographic plates to set (or selectively harden) the photo polymers in the flexographic media.  
     [0026] As shown in FIG. 3, the flexographic plate  16  is positioned on the input tray  30  above a pair of resilient input nip rollers  50 , one of which may be driven by a drive assembly  52 . The leading edge  38  of the plate  16  is positioned by the input tray  30  to rest substantially between the input nip rollers  50 . The rollers  50  are positioned above the external drum  12 , and are oriented such that the common tangent of the rollers  50  is tangent to the media support surface  14 . The input tray  30  is oriented such that the loading path of the plate  16  extends along a line that is tangent to the external drum  12  at a leading edge clamping mechanism  40 .  
     [0027] A curved input/output guide platen  54 , mounted to a frame member (not shown) of the external drum platesetter  10  may be provided to direct the leading edge  38  of the printing plate  16  toward the leading edge clamping mechanism  40  during the loading of the printing plate  16  onto the external drum  12 . In addition, the curved input/output guide platen  54  is configured to direct the printing plate  16  off of the external drum  12  toward the plate output area after imaging is complete.  
     [0028] During loading of the plate  16 , the drum  12  is rotated until the leading edge clamping mechanism  40  is positioned to receive the leading edge  38  of the plate  16 . A clamping portion  54  of the clamping mechanism  40  is held in an open position by an actuator  56 , exposing registration pins  58 . A trailing edge clamping mechanism  44  is rotated by the drive system  28 , if necessary, to position a clamping bar  60  out of the way of the loading path of the plate  16 . An actuation system  62  for the trailing edge clamping mechanism  44 , and an ironing roller system  64 , may also be retracted away from the media support surface  14  of the external drum  12  out of the way of the loading path. After the leading edge  38  of the plate  16  is properly positioned against the registration pins  58 , the leading edge clamping mechanism is closed, thereby pinching the plate  16  against the external drum  12  while the leading edge  38  remains in contact with the registration pins  58 .  
     [0029] After the leading edge clamping operation, the external drum  12  is rotated a few degrees by the drive system  28 . The ironing roller assembly of the stationary ironing roller system  64  is then extended and positioned against the plate  16  by an actuating system. The plate is drawn around the drum  12  until the trailing edge  42  of the plate  16  is positioned adjacent the trailing edge clamping mechanism  44 . The clamping bar  60  is then positioned over the trailing edge  42  of the plate  16 . If the size of the plate is not known and pre-programmed into the system, a sensor  68  may be used to detect the trailing edge of the plate  16 . The drum and clamping bar  60  are then rotated together, and the clamping bar  60 , which is normally biased away from the drum  12 , is then forced against the drum  12  by the actuation system  62 . Vacuum may also be used to facilitate securing the plate to the drum.  
     [0030] During imaging, the leading edge  38  of the plate  16  is held in position against the media support surface  14  by the leading edge clamping mechanism  40 . Similarly, the trailing edge  42  of the printing plate  16  is held in position against the media support surface  14  by the trailing edge clamping mechanism  44 . Both the trailing edge clamping mechanism  44  and the leading edge clamping mechanism  40  provide a tangential friction force between the printing plate  16  and the external drum  12  sufficient to resist the tendency of the edges of the printing plate  16  to pull out of the clamping mechanisms  40 ,  44 , at a high drum rotational speed. In accordance with the present invention, only a small section (e.g., 6 mm) of the leading and trailing edges  38 ,  42 , is held against the external drum  12  by the leading and trailing edge clamping mechanisms  40 ,  44 , thereby preserving as much of the available imaging area of the printing plate  16  as possible.  
     [0031] During output of the plate  16  from the drum  12 , the drive system  28  rotates the drum  12  in a counterclockwise direction, the trailing edge clamping mechanism  44  is released, and the leading edge clamping mechanism  40  is released. The trailing edge  42  of the plate  16  is guided by the input/output platen  54  toward resilient output nip rollers  70 , one of which may include a drive system  72 . The plate  16  is then received in the output area by the belts  32  which are rotated about pulleys  34  in a direction that causes the top surface of the belts  32  to travel with the plate as it emerges from the imaging area, and thereby carry the plate away from the imaging area.  
     [0032] Once the plate reaches an optionally retractable stop surface, the plate stops moving and the drive system for the pulleys  34  is turned off. In other embodiments, plate advancement may cease responsive to the output of a position sensor in the output area.  
     [0033] As shown in FIGS. 3 and 4, the output area also includes the photo-processing illumination source  46 , which includes a plurality of elongated illumination tubes  80  that are connected in parallel via tracks  82  and  84 . The illumination source  46  is suspended above the belts  40  via brackets  48  with sufficient elevation to permit a flexographic plate to be received in the output area on the belts  40  underneath the source  46 .  
     [0034] As shown in FIG. 5, the imagesetter of the present embodiment begins the imaging and photo-processing system (step  500 ) by transferring a flexographic plate onto an external drum (step  502 ). The system then images the plate while the plate is on the drum using an illumination source such as a laser (step  504 ). The system then removes the plate from the drum and transfers the plate to an output area (step  506 ). The system then exposes the entire plate with a flexographic illumination source (step  508 ), and then outputs the plate to an output opening (step  510 ) before ending (step  512 ).  
     [0035] In particular, and with reference to FIGS.  6 A- 6 D, the flexographic plate  16  includes a thin layer of a carbon material  90 , which may be easily ablated by the writing laser  26 , and a photopolymer layer  92 . As shown in FIG. 6B, when the illumination field  93  from the writing laser  26  contacts the plate  16  in the imaging area, the carbon film is ablated by the laser beam as indicated at  94 . After imaging, the plate is removed from the imaging area, and output to an output area underneath the photo-processing illumination source  46 . The selectively ablated carbon film then acts as a mask during the photo-processing step. Specifically, the illumination field  95  from the illumination source  46  then exposes the portions  96  of the photo-polymer  92  that are associated with the ablated portions of the carbon film, leaving the adjacent portions of the photo-polymer un-exposed. The exposed portions  96  of the photo-polymer film  92 , therefore, become photo-cured and harden to a certain depth as indicated at d as shown in FIG. 6C. Later, the plate may be chemically processed to remove the remaining carbon film as well as the un-cured portions of the plate to a depth again of about d as shown in FIG. 6D to form the final imaged and fully processed flexographic plate. In certain embodiments, the other side of the film (the side that is not imaged) may be photo-cured (or hardened) using an illumination source similar to  46  with no carbon film. This produces a final imaged flexographic plate with additional structural rigidity, and this step may be performed either before or after imaging and photo-processing by the platesetter  10 .  
     [0036] In a further embodiment, a system of the invention may include two illumination sources  100  and  102  similar to source  46  discussed above, one above and one below the imaging output area  104  as shown in FIG. 7. The output area  104  may include belts similar to belts  32  that are discussed above with reference to FIG. 2 except that they must be formed of a clear material. The output area  104  may also include rollers similar to rollers  40  discussed above with reference to FIG. 2.  
     [0037] The system shown in FIG. 7 provides that both sides of a flexographic plate maybe photo-processed processed inside the platesetter, either simultaneously of sequentially. As discussed above, this permits the back (non-imaged) side of the flexographic plate to become photo-cured. If the output area  104  includes rollers similar to rollers  40  discussed above, then the process of photo-curing the non-imaged side of the flexographic plate should involve actuating the rollers during the photo-curing process to move the plate small amount equivalent to about one half of a rotation of the rollers. This will ensure that the non-imaged side of the plate will be uniformly photo-cured.  
     [0038] Those skilled in the art will appreciate that numerous modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the present invention.