Abstract:
An improved print head includes a die coating apparatus to die coat the cable. Thus the wire or cable would pass through a die coating apparatus instead of the reservoir of ink described in the above-identified patents. Die coating the cable offers increased control of the amount of ink that adheres to the cable and thus facilitates the production of a high resolution final image on the print medium. Die coating also increases the speed at which an image can be printed on the print medium. Lastly, die coating will enable the print head to be a closed system, minimizing the presence of dirt and dust particles in the ink.

Description:
BACKGROUND 
       [0001]    One known printer technology includes a print head that (1) immerses a wire in a reservoir of pigmented liquid material (e.g., ink) for a period of time sufficient to allow the wire to be coated with ink, (2) places the coated wire in close proximity to a print medium, and (3) directs a stream of air to contact the coated wire and thereby causes at least some of the ink on the wire to be deposited onto the print medium. The speed of the wire, the proximity of the wire to the print medium, and the force of the air stream may be digitally controlled by a processor, controller, microprocessor, or other computing device to ensure that a desired image resolution is achieved. By forming a print head with multiple wires; multiple, differently colored ink reservoirs; and multiple air streams, and by controlling and coordinating the metering of the ink and the position of the print head in relation to the print medium, a digital image can be created on a large-sized print medium. U.S. Pat. Nos. 5,944,893; 5,972,111; 6,089,160; 6,090,445; 6,190,454; 6,319,555; 6,398,869; and 6,786,971 describe this printer technology in greater detail and are incorporated herein by reference. 
         [0002]      FIG. 1  is a perspective view of one embodiment of the above-identified prior art single color ink injector, generally indicated at  10 , for depositing paint, ink, dye, or other liquid pigmented material that could be used for painting or printing onto a print medium to which a motor  14  is attached. A pulley  13  having a circumscribing groove  38  defined therein is secured to a shaft  15  of motor  14 . An elongate frame member  32  depends from and is secured to print medium  12  and extends into a reservoir of ink  24 . A rotatable or stationary guide  34  is attached to a distal end  37  of elongate frame member  32 . Guide  34  is illustrated as a cylindrical, non-rotatable member having a groove  40  circumscribing guide  34  in which a wire cable  36 , can slide during rotation of wheel  13 . Wire cable  36  is described in greater detail in the above-identified patents. Wire cable  36  is disposed in groove  38  circumscribing the wheel  13  and in groove  40  circumscribing guide  34 . 
         [0003]    An elongate reservoir retaining member  16  is attached to plate  12  and includes a flange  18  defining a notch  20  between the flange  18  and elongate reservoir retaining member  16 . Notch  20  is configured to receive a top lip  22  of ink reservoir  24 . A bottom plate  26  is secured to a distal end  28  of elongate reservoir retaining member  16  with a threaded nut  31  that is threaded onto a threaded shaft  33 . Threaded shaft  33  is secured to distal end  28  of elongate reservoir retaining member  16 . Bottom plate  26  abuts against the bottom  30  of the ink reservoir  24  and holds it between flange  18  and bottom plate  26 . 
         [0004]    An air supply hose  42  is secured to a nozzle body  44  and supplies air through a nozzle orifice  46  that is aimed at a portion of cable  36 . A cable guide  48  defining a longitudinal slot  50  is positioned proximate nozzle orifice  46 . Cable  36  rides within slot  50  and is thus held in relative position to nozzle orifice  46  so that air passing therethrough does not substantially move cable  36  from in front of nozzle orifice  46  or cause cable  36  to substantially vibrate. 
         [0005]    Rotation of shaft  15  is controlled by a controller, generally indicated at  57 , comprising circuitry  54  in a module  56  that receives signals from a signal generating device  52 , such as a personal computer employing a microprocessor or other devices that can supply discrete signals to instruct selective rotation of the shaft  15  of the motor. Circuitry  54  receives a signal(s) from generating device  52  and rotates shaft  15  of the motor according to the signal(s). 
         [0006]    In operation, ink contained in reservoir  24  is picked up by cable  36  and advanced by rotation of wheel  13 , indicated by the arrow, in front of nozzle orifice  46 . Air that is blown through nozzle orifice  46  disperses or pulls ink from cable  36  toward the print medium. Depending on the viscosity of the ink, the cross-sectional diameter of cable  36 , and the diameter of wheel  13 , a relatively precise amount of ink can be deposited on print medium. Such an apparatus may produce images having a resolution of approximately 50 dpi or better. 
       SUMMARY 
       [0007]    The present application is directed to a method of more accurately applying a uniform coating of pigmented liquid material into the wire. 
         [0008]    The present application is directed to increasing the speed at which the above-identified printer technology can print digital images. 
         [0009]    The present application is directed to forming a closed system for the above-identified printer technology. 
         [0010]    An improved print head includes a die coating apparatus to die coat the cable. Thus the wire or cable would pass through a die coating apparatus instead of the reservoir of ink described in the above-identified patents. Die coating the cable offers increased control of the amount of ink that adheres to the cable and thus facilitates the production of a high resolution final image on the print medium. Die coating also increases the speed at which an image can be printed on the print medium. Lastly, die coating will enable the print head to be a closed system, minimizing the presence of dirt and dust particles in the ink. 
         [0011]    One embodiment of a method of printing with the improved print head involves die coating at least a portion of an exterior surface of a cable with a pigmented material. An air stream is directed at the portion of the cable coated with the pigmented material. The force of air in the air stream causes a metered amount of the pigmented material to be removed from the exterior surface of the cable and to be deposited onto a print medium that is placed in close proximity to the cable. Advancement of the cable through the air stream is electronically controlled. 
         [0012]    One embodiment of an apparatus for digitally printing a high resolution image on a print medium includes a support structure, a carriage associated with and movable in at least one direction relative to the support structure, and a plurality of paint injectors secured to the carriage. Each of the paint injectors includes a motor having a rotatable shaft, a wheel rotatable by the shaft, an idler, and an elongate segment disposed around at least a portion of the wheel and a portion of the idler. The elongate segment is advanceable by the wheel and has a quantity of pigmented material die coated onto at least a portion of it. The paint injectors also each include at least one fluid nozzle positioned and oriented for directing a jet of fluid toward at least a portion of the elongate segment to remove an amount of pigmented material from the elongate segment and direct the amount toward a surface of a print medium. A controller that is electronically connected to each motor controls the rotation of each wheel and controls the position of the carriage relative to the support structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of one embodiment of the prior art single color paint injector. 
           [0014]      FIG. 2  is a schematic view of one embodiment of a paint injector in which a die coats the cable with ink. 
           [0015]      FIG. 3  is an expanded schematic of the die of  FIG. 2 . 
           [0016]      FIG. 4  is a cross-sectional view of the die of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    As is described in greater detail in U.S. Pat. Nos. 5,944,893; 5,972,111; 6,089,160; 6,090,445; 6,190,454; 6,319,555; 6,398,869; and 6,786,971, ink clings to the cable during its advance through the ink reservoir, thereby forming a coating of ink on the cable. The thickness of this coating is at least partly controlled by the viscosity of the ink in the reservoir. When highly viscous inks, such as those preferred when forming signage capable of outdoor use, are used, the coating on the cable is very thick. The thickness of the coating on the cable at least partly dictates the size of the ink droplet that is deposited on the print medium. More specifically, when small diameter ink droplets are deposited on the print medium, the final image has a high resolution. Conversely, when larger diameter ink droplets are deposited on the print medium, the final image has a low resolution. Thus when highly viscous inks are used in the printer described in the above-identified patents, the resulting image has a low resolution. 
         [0018]    The above-identified patents provide no means for controlling the thickness of the coating other than to regulate the viscosity of the ink in the ink reservoir. Thus these patents fail to describe a printer capable of printing high resolution images using highly viscous inks, such as those highly durable inks preferably used to form outdoor signage. The inventors of the present invention recognized that it would be desirable to have an apparatus for and method of printing a higher resolution image when using highly durable, higher viscosity inks. 
         [0019]      FIG. 2  is a perspective view of one embodiment of a print head  10   2  including a die  102 . A pulley  13  having a circumscribing groove  38  defined therein is secured to a shaft  15  of motor  14 . An elongate frame member  32  is secured to an ink pan  100 . A rotatable or stationary guide  34  is attached to a distal end  37  of elongate frame member  32 . Guide  34  is illustrated as a cylindrical, non-rotatable member having a groove  40  circumscribing guide  34  in which a wire cable  36 , can slide during rotation of wheel  13 . Wire cable  36  is disposed in groove  38  circumscribing the wheel  13  and in groove  40  circumscribing guide  34 . Die  102  is secured to ink pan  100  or print head  10   2 . 
         [0020]    An elongate ink pan retaining member  16  is attached to plate  12  and includes a flange  18  defining a notch  20  between the flange  18  and elongate reservoir retaining member  16 . Notch  20  is configured to receive a top lip  22  of ink reservoir  24 . A bottom plate  26  is secured to a distal end  28  of elongate reservoir retaining member  16  with a threaded nut  31  that is threaded onto a threaded shaft  33 . Threaded shaft  33  is secured to distal end  28  of elongate reservoir retaining member  16 . Bottom plate  26  abuts against the bottom  30  of the ink pan  100  and holds it between flange  18  and bottom plate  26 . 
         [0021]    An air supply hose  42  is secured to a nozzle body  44  and supplies air through a nozzle orifice  46  that is aimed at a portion of cable  36 . A cable guide  48  defining a longitudinal slot  50  is positioned proximate nozzle orifice  46 . Cable  36  rides within slot  50  and is thus held in relative position to nozzle orifice  46  so that air passing therethrough does not substantially move cable  36  from in front of nozzle orifice  46  or cause cable  36  to substantially vibrate. 
         [0022]    Rotation of shaft  15  is controlled by a controller, generally indicated at  57 , comprising circuitry  54  in a module  56  that receives signals from a signal generating device  52 , such as a personal computer employing a microprocessor or other devices that can supply discrete signals to instruct selective rotation of the shaft  15  of the motor. Circuitry  54  receives a signal(s) from generating device  52  and rotates shaft  15  of the motor according to the signal(s). 
         [0023]    In operation, ink is fed into die  102  via a tube (not shown). The ink is then deposited onto cable  36  and advanced by rotation of wheel  13 , indicated by the arrow, in front of nozzle orifice  46 . Air that is blown through nozzle orifice  46  disperses or pulls ink from cable  36  toward the print medium. Depending on the viscosity of the ink, the cross-sectional diameter of cable  36 , and the diameter of wheel  13 , a relatively precise amount of ink can be deposited on print medium. Such an apparatus may produce images having a resolution of approximately 50 dpi or better. 
         [0024]      FIGS. 3 and 4  are expanded schematic and cross-sectional views of die  102 . 
         [0025]    The present inventors recognized that die coating the cable facilitates the use of highly viscous inks to produce high resolution images. Because the die meters and controls the thickness of the coating of ink on the cable, smaller diameter ink droplets can be deposited on the print medium, resulting in the creation of a higher resolution image. Thus the incorporation of a die-coating system in the printer described in U.S. Pat. Nos. 5,944,893; 5,972,111; 6,089,160; 6,090,445; 6,190,454; 6,319,555; 6,398,869; and 6,786,971 permits the user to produce a high resolution image using highly viscous inks. 
         [0026]    Further, the speed of the cable&#39;s advance through the air stream affects the quantity of ink injected into the air stream. The faster the cable is advancing, the less ink is deposited on the print medium, and the slower the cable is advancing, the greater the amount of ink is deposited on the print medium. The speed of the cable is at least partly determined by the speed at which the cable can be pulled through the ink reservoir, which is largely dictated by the viscosity of the ink in reservoir. By replacing the ink reservoir with a die coating apparatus, the speed at which the cable advances can be increased without significantly affecting the resolution of the final image or the ability to use highly viscous inks. Thus the overall efficiency of the printer can be increased. 
         [0027]    Lastly, the use of a die coating apparatus in the printer enables the print head to be formed as a closed system. By creating a closed system in the print head, the presence of dirt and dust particles in the ink is minimized, resulting in a higher resolution image. In contrast, the ink reservoirs described in the above-identified prior art patents were topless cans whose contents were freely exposed to dirt and dust. 
         [0028]    As used herein, the term “cable” is meant to include the use of a wire, a cable formed of multiple wires, a rod, a saw tooth wheel, or variations thereof. 
         [0029]    As used herein, the term “ink” is meant to include any pigmented material, including, but not limited to, inks, dyes, paints, or other similarly pigmented liquids. Inks that can be printed in the printer of the present invention include inks having a viscosity between about 200 and about 2000. This is a still significantly higher viscosity than can be jetted though conventional ink jet printers. A list of exemplary commercially available inks that fall within this range includes: 3M Process Color Series 700, 3M Process Color Series 880-00, 3M Process Color Series 880i, 3M Process Color Series 990, 3M Scotchlite Transparent Screen Printing Ink Series 2900, 3M Screen Printing Ink Series 1900, 3M Screen Printing Ink Series 9700UV, Nazdar 3500 Series UV Vinex Screen Ink, Avery Dennison Series 4930 Series Inks (10 year-1 Component Solvent Ink*), Sericol UVTS Series Ink, Nazdar UVTS Series Ink, Avery Dennison® UVTS-Sericol Ultraviolet Curable Printing Inks, Avery Dennison® UVTS-NazDar Ultraviolet Curable Printing Inks, Kiwalite KT Series Screen Process Ink, Avery Dennison® 10TS SeriesTwo-Component Printing Inks For Traffic Sign Products, Sericol Sinvacure UV Curable Screen Ink, Avery Dennison® 7TS Series Inks One Component Solvent Ink System For Traffic Sign Products, and Ink Dezyne VP-000 Series Vinyl Plus Screen Ink. 
         [0030]    As used herein, the term “print medium” is meant to include any print medium known in the art, including but not limited to paper, plastic, synthetic paper, metal foil, vinyl, and films, and variations thereof. 
         [0031]    Any die coating apparatus known to those of skill in the art can be used in the printer of the present invention, including but not limited to, carbide tipped dies; doghouse-type wiper dies; solid dies; universal-type assemblies for square, rectangular, and ribbon wire; split dome dies for round and rectangular wire; crosshead centering dies, and rod die assemblies. Some exemplary die coating manufacturers include Bettner Wire Coating Dies and C.W. Braebender. 
         [0032]    Further, multiple print heads each including a die coating apparatus may be used to form a printer capable of printing a high-resolution multi-color image. 
         [0033]    Various modifications and alterations of the present invention will become apparent to those skilled in the art without departing from the spirit and scope of the invention.