Abstract:
A printing apparatus comprises a jetting assembly including a plurality of nozzles for ejecting droplets on a substrate; an enclosure defining a print zone within which the jetting assembly prints on the substrate, the enclosure including an inlet for introducing a material associated with controlling an environment of the enclosure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Under 35 U.S.C. §119(e)(1), this application claims benefit of Provisional Patent Application No. 60/633,240, entitled “PRINTHEADS AND SYSTEMS USING PRINTHEADS,” filed on Dec. 3, 2004, the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates to printheads and systems using printheads.  
       BACKGROUND  
       [0003]     Ink jet printers typically include an ink path from an ink supply to a nozzle path. The nozzle path terminates in a nozzle opening from which ink drops are ejected. Ink drop ejection is controlled by pressurizing ink in the ink path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electro statically deflected element. A typical printhead includes a reservoir and a jetting assembly. The jetting assembly has an array of ink paths with corresponding nozzle openings and associated actuators, and drop ejection from each nozzle opening can be independently controlled. In a drop-on-demand printhead, each actuator is fired to selectively eject a drop at a specific pixel location of an image as the jetting assembly and a printing substrate are moved relative to one another. In high performance jetting assemblies, the nozzle openings typically have a diameter of 50 microns or less, e.g. around 25 microns, are separated at a pitch of 100-300 nozzles/inch, have a resolution of 100 to 3000 dpi or more, and provide drop sizes of about 1 to 70 picoliters (pl) or less. Drop ejection frequency is typically 10 kHz or more.  
         [0004]     Hoisington et al. U.S. Pat. No. 5,265,315, the entire contents of which is hereby incorporated by reference, describes a jetting assembly having a semiconductor body and a piezoelectric actuator. The assembly body is made of silicon, which is etched to define ink chambers. Nozzle openings are defined by a separate nozzle plate, which is attached to the silicon body. The piezoelectric actuator has a layer of piezoelectric material, which changes geometry, or bends, in response to an applied voltage. The bending of the piezoelectric layer pressurizes ink in a pumping chamber located along the ink path.  
         [0005]     Further examples of jetting assemblies are disclosed in U.S. patent application Ser. No. 10/189,947, entitled “PRINTHEAD,” to Andreas Bibl et al., filed on Jul. 3, 2002, the entire contents of which are hereby incorporated by reference.  
         [0006]     The amount of bending that a piezoelectric material exhibits for a given voltage is inversely proportional to the thickness of the material. As a result, as the thickness of the piezoelectric layer increases, the voltage requirement increases. To limit the voltage requirement for a given drop size, the deflecting wall area of the piezoelectric material may be increased. The large piezoelectric wall area may also require a correspondingly large pumping chamber, which can complicate design aspects such as maintenance of small orifice spacing for high-resolution printing.  
         [0007]     In general, printheads can include one or more jetting assemblies. Printing systems can print in a single pass of the substrate relative to the printhead, or in multiple passes. Printheads can be used to jet inks and/or other fluids, such as materials used for electronic components (e.g., electrically conductive materials) or color filter materials for flat panel displays, for example.  
       SUMMARY  
       [0008]     In a general aspect of the invention, a printing apparatus comprises a jetting assembly including a plurality of nozzles for ejecting droplets on a substrate; an enclosure defining a print zone within which the jetting assembly prints on the substrate, the enclosure including an inlet for introducing a material associated with controlling an environment of the enclosure.  
         [0009]     Embodiments of this aspect of the invention may include one or more of the following features.  
         [0010]     The material is vaporized water, dry air, alcohol, MEK, or a sanitizing agent. The dry air has a pre-determined temperature. The material is adapted to suppress bacterial growth. The material is compatible with the droplets. The printing apparatus further comprises a sensor placed within the enclosure. The sensor is configured to provide a signal that is used to regulate the environment within the enclosure. The enclosure includes an outlet.  
         [0011]     In another general aspect of the invention, a method of printing comprises providing an enclosure defining a print zone, the enclosure including an inlet for introducing a material associated with controlling an environment of the enclosure; positioning a jetting assembly including a plurality of nozzles for ejecting droplets on a substrate within the print zone; and introducing a material associated with controlling the environment of the enclosure through the inlet.  
         [0012]     Embodiments of this aspect of the invention may include one or more of the following features.  
         [0013]     The material is vaporized water, dry air, alcohol, MEK, or a sanitizing agent. The dry air has a pre-determined temperature. The material is adapted to suppress bacterial growth. The material is selected based on the characteristics of the droplets. The method of printing further comprises placing a sensor within the enclosure. The method of printing further comprises configuring the sensor to provide a signal that is used to regulate the environment of the enclosure. The enclosure includes an outlet.  
         [0014]     Among other advantages, the enclosure defines a conditioning print zone in which an environment favorable to the print head nozzles is maintained. For example, the humidity of the print zone can be maintained at a level that minimizes the possibility of the nozzles becoming dry or, alternatively, causing condensation to form on the nozzles. Depending on the characteristics of the ink, other materials (e.g., alcohol, MEK) may be introduced into the enclosure. Thus, the reliability of the print head nozzles is maintained and the need for servicing and replacement is reduced.  
         [0015]     Gaseous materials including hydrogen and nitrogen can also be introduced into the conditioning print zone. Where solvents or hazardous chemicals are used, the enclosure provides operator health and safety benefits.  
         [0016]     Sanitizing agents or other materials to suppress bacterial growth can also be introduced, particularly useful in applications associated with printing on food products. The sanitizing agent is used to maintain a sanitary environment so as not to contaminate products including food or pharmaceuticals.  
         [0017]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.  
     
    
     DESCRIPTION OF DRAWINGS  
       [0018]      FIG. 1  is a perspective view of a printing assembly including a controlled environment enclosure.  
         [0019]      FIG. 2  is a cross-sectional side view of the printing assembly and controlled environment enclosure of  FIG. 1 .  
         [0020]     Like reference symbols in the various drawings indicate like elements. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Referring to  FIGS. 1 and 2 , four print head clusters  10  used as part of a production process in which a substrate  12  is moved by a conveyor  14  beneath the print head clusters. In this embodiment, conveyor  14  supports substrates as wide as one to four feet and is capable of moving at speeds as high as 1600 feet/minute. Each of print head clusters  10  include an array of jetting assemblies, each of which is connected to one or more ink reservoirs. Print head clusters  10  print text or images upon the substrate as it passes beneath the print head clusters. Print head clusters  10  are supported by and movable on one end of a mounting rack  16  positioned over conveyor  14  and attached to a support post  18 .  
         [0022]     An enclosure  19  is positioned between print head clusters  10  and just above the surface of conveyor  14  to define a conditioning print zone  21 . The conditioning print zone provides an environment favorable to the nozzles of the print head clusters such that their reliability is improved. Enclosure  19  includes an inlet  20  connected to a source of material to be introduced in the enclosure.  
         [0023]     For example, in one embodiment, the source of material is vaporized water for providing a desirable level of humidity in the print zone. Providing an environment with greater humidity can extend time for the deposited ink to dry and also prevent the nozzles from becoming dry. When a nozzle has not jetted ink for a substantial amount of time there is a risk that ink will dry and eventually the nozzle will become clogged. A humid environment addresses this problem and can improve the “nozzle open time.” The level of humidity is generally selected based on the type of water-based ink. In contrast to providing humidity, the source of material may be a current of dry air (heated or cooled) passed in front of the print head nozzles to minimize the possibility of condensation forming on the nozzles of the print head clusters. For other types of inks, different materials may be introduced into enclosure  19  through inlet  20 . For example, the source of material introduced into enclosure  19  may be alcohol or MEK. Thus, the reliability of the print head nozzles is maintained and the need for servicing and replacement is reduced.  
         [0024]     In still other embodiments, sanitizing agents or other materials to suppress bacterial growth can also be introduced, particularly useful in applications associated with printing on food products or pharmaceuticals.  
         [0025]     In certain embodiments, a sensor (not shown) can be placed within enclosure  19  to measure conditions within the conditioning print zone. The sensor provides a signal that is used to regulate the environment within enclosure  19  by either increasing/decreasing material being introduced. Thus, a closed loop control system is provided.  
         [0026]     In certain embodiments, the source material is selected to be compatible with the characteristics of the ink; e.g., selecting a source material to be soluble in the selected ink, or selecting a source material which chemically reacts with the selected ink in a desired manner appropriate to the particular printing application.  
         [0027]     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. For example, although four print head clusters were shown supported on mounting rack  16 , in other embodiments, fewer or greater numbers of print head clusters can be positioned on mounting rack  16 . Enclosure  19  can also include additional inlets as well as outlets for controlling the environment in the conditioning print zone.  
         [0028]     Accordingly, other embodiments are within the scope of the following claims.