Abstract:
An ink jet printing system including an ink jet print head configured to eject ink drops, a perforated substrate support having a plurality of holes, configured to carry a substrate over a first surface of the perforated substrate support, wherein the ink jet print head and the holes in the perforated substrate support are configured to allow at least a portion of ejected ink drops not received by the substrate to pass through the holes, and a collector disposed beneath the perforated substrate support, configured to collect at least a portion of the ejected ink drops not received by the substrate.

Description:
TECHNICAL FIELD  
       [0001]     This application relates to the field of ink jet printing.  
       BACKGROUND  
       [0002]     Ink jet printing is a non-impact method that produces droplets of ink that are deposited on a substrate such as paper or transparent film in response to an electronic digital signal. In various commercial or consumer applications, there is a general need to provide ink jet images that are printed edge-to-edge on a substrate. There is also a need for printing images on irregular and/or small substrates such as candy and cookies.  
         [0003]     Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. Multiple orifices or nozzles also may be used to increase imaging speed and throughput. The ink is ejected out of orifices and perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the electrically charged ink droplets are passed through an applied electric field that is controlled and switched on and off in accordance with digital data signals. Charged ink droplets are passed through a controllable electric field, which adjusts the trajectory of each droplet in order to direct it to either a gutter for ink deletion and recirculation or a specific location on a recording medium to create images. The image creation is controlled by electronic signals.  
         [0004]     In drop-on-demand systems, a droplet is ejected from an orifice directly to a position on a recording medium by pressure created by, for example, a piezoelectric device, an acoustic device, or a thermal device controlled in accordance with digital data signals. An ink droplet is not generated and ejected through the nozzles of an imaging device unless it is to be placed on the recording medium.  
       SUMMARY  
       [0005]     In one aspect, an ink jet printing system has an ink jet print head configured to eject ink drops, and a perforated substrate support comprising a plurality of holes and configured to carry a substrate over a first surface of the perforated substrate support, and a collector disposed beneath the perforated substrate support. The ink jet print head and the holes in the perforated substrate support are configured to allow at least a portion of ejected ink drops not received by the substrate to pass through the holes, and the collector is configured to collect at least a portion of the ejected ink drops not received by the substrate.  
         [0006]     In another aspect, an ink jet printing system includes an ink jet print head configured to eject ink drops, a perforated substrate support comprising a plurality of holes and configured to carry a substrate over a first surface of the perforated substrate support, a conveying mechanism configured to cause relative movement between the ink jet print head and the perforated substrate support, a collector disposed behind the second surface of the perforated substrate support, and a cleaning station configured to clean the ink fluid captured on perforated substrate support. The ink jet print head and the holes in the perforated substrate support are configured to allow at least a portion of ejected ink drops to pass through the holes, and the collector is configured to collect at least a portion of the ejected ink drops not received by the substrate.  
         [0007]     In yet another aspect, a method for printing an image on a substrate includes placing a substrate over a first surface of a perforated substrate support comprising a plurality of holes, causing relative movement between the substrate and an ink jet print head, disposing ink drops from the ink jet print head on the substrate to form an image, and collecting ink drops disposed outside of the edge of the substrate behind a second surface of the perforated substrate support.  
         [0008]     Implementations of the system may include one or more of the following. The ink jet printing system can further include a conveying mechanism configured to cause relative movement between the ink jet print head and the perforated substrate support. The ink jet printing system can further include an ink absorbing material over the collector adapted to collect ink drops ejected by the ink jet print head. The ink jet printing system can further include a cleaning station configured to remove ink from the perforated substrate support. The ink jet printing system can further include a substrate handling mechanism configured to feed the substrate to the conveying mechanism or to retrieve the substrate from the conveying mechanism. The second surface of the perforated substrate support can be opposite to the first surface of the perforated substrate support. The perforated substrate support can include a cylindrical surface adapted to receive the substrate. The perforated substrate support can include a conveyance belt driven by one or more rollers. The ink jet printing system can further include a print head transport mechanism capable of moving the ink jet print head relative to the substrate. The ink jet printing system can further include one or more sensors configured to detect the location or the orientation of the substrate. The ink jet print head can deliver ink drops to form an image on the substrate. The ink jet print head can print the image full bleed along at least one edge of the substrate.  
         [0009]     Embodiments may include one or more of the following advantages. The disclosed ink jet system is capable of full bleed printing while preventing the contamination of the substrate by the overspray inks. The system provides effective arrangements for collecting and cleaning the overspray inks. Furthermore, the disclosed ink jet system is capable of printing images on small and irregular shaped ink substrates without the need of pre-aligning the substrates before printing.  
         [0010]     Implementations of the method for printing an image can include printing an image that is full bleed along at least one edge of the substrate.  
         [0011]     The details of one or more embodiments are set forth in the accompanying drawing and in the description below. Other features, objects, and advantages of the invention will become apparent from the description and drawings, and from the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  illustrates an ink jet printing system having an ink jet print head and a substrate transport system comprising a perforated substrate support.  
         [0013]      FIG. 2  illustrates an ink jet printing system having an ink jet print head and a substrate transport system comprising a perforated substrate support having a cylindrical surface.  
         [0014]      FIG. 3  is a top view of a substrate over a perforated substrate support in the substrate transport system of  FIG. 1  and  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0015]      FIG. 1  shows an ink jet printing system  10  including an ink jet print head  20 , a controller unit  30  that provides image data and other digital data to the ink jet print head  20 , and an ink reservoir  40  for supplying ink to the ink jet print head  20 . A substrate  50  is transported by a substrate transport system  100 . The substrate transport system  100  includes a conveyor belt  70 , rollers  120  and  130  for driving the conveyor belt  70 , and a motor  110  that can drive the roller  120  under the control of the control unit  30 .  
         [0016]     One or more sensors  150  can detect the position and orientation of the substrate  50 . The detection of the positions of the substrate  50  can be triggered by the edges of the substrate  50 . The detection of the position of the substrate can facilitate the printing of the ink pattern on the substrate  50  from the leading edge and around the edges of the substrate  50 . In another embodiment, the sensors  150  can detect both the position and the orientation of the substrate  50  on the perforated substrate support of the conveyor belt  70 . In response to the signal received from the sensors  150 , the control unit  30  can rotate the input digital image to compensate for the orientation variation of the substrate  50 . As a result, an image can be printed with desired orientation over the substrate  50 .  
         [0017]     At least a portion of the conveyor belt  70  includes a perforated substrate support that includes holes that extend through the belt. The perforated substrate support can include a mesh of metal wires or a plastic sheet punched with holes. Preferably, the holes take a majority of the surface area of the conveyor belt  70  to allow overspray inks to pass through. The openings in the mesh or the punched holes can have dimensions in the range of 0.1 inch to one inch to allow ink drops to pass through while also keeping the substrate  50  flat. The top surface of the perforated substrate support preferably comprises an ink repelling material such as Teflon that helps to prevents ink accumulation in the solid portion of the perforated substrate support. The substrate  50  is carried by the perforated substrate support of the conveyor belt  70  to positions under the ink jet print head  20  to receive ink drops  140  ejected by the ink jet print head  20 . As shown in  FIG. 1 , the substrate  50  can be carried by a flat portion of the conveyor belt  70  when the image is printed on the substrate  50  by the ink jet print head  20 . Alternatively, the perforated substrate support carrying the substrate may be fixed during printing. The image is printed by scanning the ink jet print head over the substrate.  
         [0018]     An example of the perforated substrate support  370  is shown in a top view in  FIG. 3 . The perforated substrate support  370  includes a plurality of holes  310  that occupy a large portion of the area. A substrate  350  is placed over a perforated substrate support  370  spanning over a plurality of holes  310 .  
         [0019]     The disclosed ink jet printing system  10  is capable of producing an image that is full bleed along at least one edge of the substrate  50 . One known problem with full bleed printing is that the inks ejected from the print heads often sprays outside of the substrate along the edges of substrate where the image is printed full bleed to that edge. The overspray inks can contaminate the supporting substrate and the back surface of the substrate if not handled properly.  
         [0020]     In one embodiment, the ink jet printing system  10  includes a collector  90  under the perforated substrate support in the conveyor belt  70 . The overspray ink fluids outside of the edges of the substrate  50  can fall through the through holes of the perforated substrate support and be captured by the collector  90 . The collector  90  can further include absorbent material  95 . The absorbent material  95  can be replaceable or disposable to keep substrate transport mechanism  100  clean. The absorbent material  95  can include man made or natural materials. The absorbent material  95  can also be selected to be most effective in absorbing the specific types of inks used for each batch of substrates: for example, aqueous, solvent types of inks.  
         [0021]     In another embodiment, the ink jet printing system  10  includes a cleaning station  80  that is capable of cleaning the conveyor belt  70  after the printing and after the substrate  50  is received. The cleaning station  80  can include a rubber blade  81  that can blade off the ink accumulated on the conveyor belt  70  and a sponge  82  that can wipe and absorb inks on the conveyor belt  70 . The conveyor belt  70  can be cleaned regularly by wiping, blotting, washing, etc. after printing one or more a batch of substrates  50 .  
         [0022]     The ink jet printing system is particularly useful for printing small and/or irregular shaped substrates such as cookies and candy. The term irregular shape refers to a substrate that has at least one edge that is not straight. The positions and the orientations of the small and/or irregular shaped substrates can be detected by one or more sensors  150 . The ink pattern printed can be full bleed along at least one edge of the substrate  50 . The overspray inks can be captured by the collector  90  without contaminating the undersides of the substrates. The ink pattern can also be automatically adjusted according to the specific orientation of the substrate  50 . The ink jet printing system therefore enables the ink jet printing on irregular shaped substrates without the need for aligning the substrates  50  on the conveyor belt  70 .  
         [0023]     In another embodiment as shown in  FIG. 2 , the ink jet printing system  310  includes an ink jet print head  320 , a controller unit  330  that provides image data and other digital data to the ink jet print head  320 , and ink reservoir  340  for supplying ink to the ink jet print head  320 . A substrate  350  is transported by a substrate transport system  300  that includes a drum platen  370  and a motor  410  that can drive the drum platen  370  under the control of the control unit  330 .  
         [0024]     One or more sensors  450  can detect position and orientation of the substrate  350 . The detection of the positions of the substrate  350  can be triggered by the edges of the substrate  350 . The detection of the position of the substrate can facilitate the printing of the ink pattern on the substrate  350  from the leading edge and around the edges of the substrate  350 . In another embodiment, the sensors  450  can detect both the position and the orientation of the substrate  530  on the perforated substrate support of the drum platen  370 . In response to the signal received from the sensors  450 , the control unit  330  can rotate the input digital image to compensate for the orientation variation of the substrate  350 . As a result, an image can be printed with desired orientation over the substrate  350 .  
         [0025]     The drum platen  370  is bounded by a cylindrical surface adapted to receive the substrate  350 . At least a portion of the drum platen  370  includes a perforated substrate support that includes through holes. The substrate  350  is attached to the perforated substrate support of the drum platen  370  by clamping or vacuum sucking. The substrate  350  is transported to positions under the ink jet print head  320  to receive ink drops  440  ejected by the ink jet print head  320 . The overspray inks passing the through holes of the perforated substrate support are captured by a collector  390  that is fixed under the printing area inside the drum platen  370 . The collector  390  may include ink absorbing materials  395 . The surface of the drum platen can be cleaned regularly by a blade  381  and a sponge  382  when the contaminated area of the surface of the drum platen  370  is rotated to a cleaning station  380 .  
         [0026]     The substrate transport system  300  can further comprise a substrate picking mechanism for feeding the substrate  350  onto the drum platen  370 , and a substrate retrieval mechanism for retrieving the substrate  350  from the drum platen  370 . The released substrates  425  containing images can be held in a substrate tray  420 .  
         [0027]     Substrates compatible with the present invention include natural paper or man-made materials for displaying images including opaque, translucent, or transparent materials. The substrates can also include foods such as cookies, candies, and cakes. The substrates can also comprise plastics, ceramics, stone, metallic substrate, wood, and fabrics. Ink types compatible with the ink jet printing system described include water-based inks, solvent-based inks, and hot melt inks. The colorants in the inks can comprise dye or pigment. Furthermore, the ink jet printing system disclosed is also compatible with delivering other fluids such as polymer solutions, gel solutions, solutions containing particles or low molecular-weight molecules, which may or may not include any colorant.  
         [0028]     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.