Abstract:
A catcher design is provided wherein vacuum channels are added to both sides of the catcher to remove ink from the face of the catcher and from the eyelid seal. An additional fluid port on the catcher allows the additional vacuum channels to maintain an increased level of vacuum. A restriction on the catcher line balances the fluid flow between the catcher and the additional vacuum channels. A scoop can be machined into the catch pan to remove fluid from below the catcher face. A manifold can be used to maintain a vacuum source for the catcher throat and the additional channels, while pulling the unprinted ink back to the fluid system. Finally, a wider eyelid seal can allow purge fluid used during shutdown to clear the channels.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to continuous ink jet printing systems and, more particularly, to a catcher design for a solvent based ink printing system, to prevent ink from wicking out of the catcher throat.  
         BACKGROUND ART  
         [0002]    Ink jet printing systems are known in which a printhead defines one or more rows of orifices which receive an electrically conductive recording fluid from a pressurized fluid supply manifold and eject the fluid in rows of parallel streams. Printers using such printheads accomplish graphic reproduction by selectively charging and deflecting the drops in each of the streams and depositing at least some of the drops on a print receiving medium, while others of the drops strike a drop catcher device.  
           [0003]    Over the years, a number of inkjet printers using binary array continuous inkjet printing have been developed, with continuing improvements in speed, reliability, and ease of use. These printers are used in a variety of print applications, often using aqueous inks. Aqueous inks have a viscosity of approximately 1.0 cps and a surface tension of 42.0 dynes/cm. These inks create a uniform fluid film on the face of the catcher that is controlled and directed at a slot on the bottom of the catcher.  
           [0004]    In spite of advances in aqueous ink technology, solvent inks, such as ethanol or MEK based inks, are preferred for some applications. For example, in applications such as printing on metals or plastics, solvent inks are preferred over aqueous inks as a result of the solvent ink characteristics of being much faster drying and more permanent than aqueous inks. Solvent inks, having a much lower surface tension (approximately 24 dynes/cm) create a fluid film on the face of the catcher that is much more difficult to control.  
           [0005]    As this film enters the throat of the catcher, the ink wicks up away from the throat creating a dripping effect during normal operation. This dripping of ink creates a need for an improved design that will eliminate the wicking of ink.  
           [0006]    It is seen then that there is a need for an improved anti-wicking arrangement which overcomes the problems associated with the prior art.  
         SUMMARY OF THE INVENTION  
         [0007]    This need is met by the anti-wicking catcher design according to the present invention, wherein ink wicking outward on the catcher face is eliminated. The present invention allows a solvent based ink jet printing system to maintain high printhead reliability and reduce the chance for print defects that can be caused by dripping or wicking ink.  
           [0008]    In accordance with one aspect of the present invention, a catcher design is provided wherein vacuum channels are added to both sides of the catcher to remove ink from the face of the catcher and from the eyelid seal. An additional fluid port on the catcher allows the additional vacuum channels to maintain an increased level of vacuum. A restriction on the catcher line balances the fluid flow between the catcher and the additional vacuum channels. A scoop can be machined into the catch pan to remove fluid from below the catcher face. A manifold can be used to maintain a vacuum source for the catcher throat and the additional channels, while pulling the unprinted ink back to the fluid system.  
           [0009]    Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a prior art side view of a printhead, illustrating the trajectory flow of uncharged ink droplets, diverted by the eyelid into the catcher fluid channel, as is done during startup;  
         [0011]    [0011]FIGS. 2, 3 and  4  illustrate various views of the improved catcher design associated with the printhead of FIG. 1, according to the present invention; and  
         [0012]    [0012]FIG. 5 shows the area below the catcher, to further illustrate the improved catcher design according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    The present invention proposes an improved catcher design for controlling the flow of unprinted ink and eliminating wicking our of the catcher throat. In existing printheads, ink drops are deflected onto the face of the catcher. The ink then flows down the face of the catcher, rounding the radius at the bottom of the catcher and entering the catcher throat, from where it can be evacuated. With low surface tension inks, such as solvent based inks, there can be some lateral spreading of the ink as it flows down the catcher face, due to the wicking nature of such inks. An air-ink interface forms inside the catcher throat, with ink filling the inner portion of the catcher throat. As ink is being evacuated from the catcher, the air-ink interface, rather than remaining static, moves in and out, causing air bubbles to occasionally be drawn into the ink. In certain operating conditions, this air-ink interface can become unstable as a result of ingesting air, causing ink to spit out of the catcher throat. Even when the air-ink interface is not so unstable as to spit ink out of the catcher throat, the oscillations of the interface can cause ink to be deposited on the face of the catcher outside the catcher throat, on each side of the impact created by the deflected array of jets. With low surface tension inks that are more prone to spread on the catcher face, and with continued transfers of small amounts of ink onto the catcher face by the oscillations of the air-ink interface in the throat, these ink bulges can spread out as far as the eyelid seal. Ink can then wick up to the charge plate during the Standby condition (when jets of fluid are in catch with the eyelid closed), leading to a charge plate short failure.  
         [0014]    The present invention eliminates this failure by eliminating the ink bulges on the catcher face outside the catcher throat. This is accomplished by means of additional ink removal ports on the front of the catcher. In FIG. 1, there is illustrated a prior art view of a drop generator and catcher assembly  10 . A drop generator  12  is situated in an area above a catcher  14  and charge plate  15 , and an eyelid  16 . When the eyelid is in the open position, ink drops are allowed to exit the printhead. When the eyelid is moved to the closed position, as shown in FIG. 1, the eyelid seal  18  presses against the bottom edge of the catcher plate  20  to contain ink  22  within the printhead on startup and shutdown of the printer system. The uncharged ink droplets flow along a trajectory path indicated by  26  in FIG. 1.  
         [0015]    Referring now to FIGS.  2 - 5 , the present invention eliminates the ink bulges on the catcher face outside the catcher throat by means of additional ink removal ports  30  on the front of the catcher  14 . The ink removal ports eliminate the ink on the face of the catcher through additional vacuum and increased flow at the port. Ink that is below the catcher throat is directed to the additional vacuum port by means of an additional machined channel that is at, for example, a 30 degree angle into the face of the catcher. Ink on the catcher face outside the catcher throat and catcher throat flow channels  34  is drawn into the ink removal port  30  by means of vacuum that is supplied to these ports. The channel  36  from the removal port  30  sends the ink to outlet  38  in the catcher plate  20 . The outlet  38  of the flow channels in the catcher pan, shown in FIG. 4, communicate with fluid channel ports  36  machined into the catcher, as best illustrated in FIG. 2. Angled channels rising from the ink removal port outlets connect with a larger ink flow removal channel  40  machined laterally in the catcher. The outlet  42  of the larger ink removal flow channel  40  can be connected to a vacuum source, not shown. By means of the flow channels  30  which may have scoop-like entrance regions  32 , ink that wicks out onto the catcher face, or is sloshed there by the oscillations of the air-ink interface in the catcher throat, can be removed from the catcher face before it has any adverse effect on printing.  
         [0016]    For the removal of the ink from the catcher face, vacuum can be supplied by any suitable means. For example, in one embodiment of the present invention, the outlet  42  of the ink removal flow channel in the catcher can be connected by a fluid line to the fluid system ink reservoir, which is maintained under vacuum. The ink removed from the catcher face can then be recycled back into the ink reservoir.  
         [0017]    In another embodiment of the present invention, the outlet of the ink removal flow channel in the catcher can be Tee&#39;d into the fluid line that returns ink from the catcher outlet to the ink reservoir. Not only does this approach eliminate the need for an additional fluid return line, it can also help stabilize the air-ink interface in the catcher throat. That is, the oscillations of the air-ink interface can be reduced such that the sloshing of ink out of the catcher throat onto the sides of the catcher face is significantly reduced or eliminated.  
         [0018]    The Tee&#39;d in ink removal ports of this preferred embodiment, stabilize the air-ink interface by serving as an air bleed into the catcher return line. Without such an air bleed in the catcher return line, air needs to be drawn into the catcher return line through the catcher throat, leading to an unstable air-ink interface. While this preferred embodiment serves as an air bleed to stabilize the air-ink interface in the catcher throat, the air ink interface can also be stabilized by the addition of one or more appropriately sized air bleeds ports, that do not also serve to remove ink from the catcher face, into the catcher return line.  
         [0019]    In printheads in which the presence of the problematic ink on the sides of the catcher face in primarily the result of unstable air ink interface in the catcher throat, as opposed to the wicking of ink across the catcher face, (the relative significance of these two effects depends on the ink properties, particularly ink surface tension and viscosity) simple air bleeds in the catcher return line may be an appropriate embodiment of the present invention to deal with the problem. In other printers, ink on the catcher face outside of the catcher throat may be solely the result of ink wicking. In such systems, ink removal ports can be employed which return ink directly back to the ink reservoir without serving as air bleeds into the catcher return line.  
         [0020]    Stabilizing the air-ink interface in the catcher throat by means of the ink removal ports or other air bleeds also allows the printing system to operate at a lower vacuum level than is typically possible. This lower vacuum level reduces the amount of evaporation at the fluid system, reducing the amount of make-up fluid that is needed and also reducing the operating cost of the system. Finally, the lower evaporation rate reduces the amount of volatile organic compounds (VOCs) produced by the system.  
         [0021]    In the preferred embodiment in which the ink removal ports are Tee&#39;d into the catcher return line, proper ink removal from these added ink removal ports and from the catcher throat depend on providing appropriately balanced flow restrictions in these flow channels. If the ink removal ports are too small, there may be insufficient ink removal through these ports to remove ink from the catcher face. The stabilization of the air ink interface in the catcher throat also depends on the appropriate amount of air being drawn in through these ports. If the ink removal ports are too large, the air ink interface in the ink removal ports can become unstable, causing ink to slosh out of these ports. Too large of ink removal ports also results in insufficient ink removal from the catcher throat through the ink return line. The balanced restriction is critical for completing a successful start-up of the system. In inkjet printers that use a purge or flush fluid to remove ink from the catcher throat at shutdown, it is desirable to also flush the ink out of the ink removal ports  30  with the same purge fluid. Failure to flush out these ports could cause ink to dry and plug these ports, making them ineffective.  
         [0022]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that modifications and variations can be effected within the spirit and scope of the invention.