Abstract:
The present invention overcomes the problem of filter blockage created by bubble accumulation underneath the filter of previous printheads with a filter carrier and filter that reduces air bubble blockage of the filter. Namely, air bubble blockage of the filter is avoided by trapping more bubbles in a designated area with a horizontal ink flow, relative to the substrate. In addition to the filter carrier and filter, the printing device further includes an outer housing, a substrate and an ink conduit. The substrate has a back surface and a front surface with ink ejection chambers formed thereon. The ink conduit has a distal end proximate to the back surface of the substrate. The ink conduit, the outer housing and the substrate define an ink flow path to the ink ejection chambers and a bubble accumulation chamber in communication with the ink flow path such that buoyancy will tend to move bubbles that accumulate in the ink flow path into the bubble accumulation chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to U.S. patent application Ser. No. 08/742,253, filed Oct. 31, 1996, entitled “PRINT CARTRIDGE COUPLING AND RESERVOIR ASSEMBLY FOR USE IN AN INKJET PRINTING SYSTEM WITH AN OFF-AXIS INK SUPPLY”. The foregoing commonly assigned patent applications are herein incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to inkjet printers and, more particularly, to an inkjet printer having a scanning printhead with an ink delivery system that utilizes a filter carrier to protect a filter from being blocked by air bubbles in an inkjet printhead.  
         BACKGROUND OF THE INVENTION  
         [0003]    Thermal inkjet hardcopy devices such as printers, graphics plotters, facsimile machines and copiers have gained wide acceptance. These hardcopy devices are described by W. J. Lloyd and H. T. Taub in “Ink Jet Devices,” Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. The basics of this technology are further disclosed in various articles in several editions of the Hewlett-Packard Journal [Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994)], incorporated herein by reference. Inkjet hardcopy devices produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes the paper.  
           [0004]    An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes “dot locations”, “dot positions”, or pixels”. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.  
           [0005]    Inkjet hardcopy devices print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.  
           [0006]    The typical inkjet printhead (i.e., the silicon substrate, structures built on the substrate, and connections to the substrate) uses liquid ink (i.e., dissolved colorants or pigments dispersed in a solvent). It has an array of precisely formed orifices or nozzles attached to a printhead substrate that incorporates an array of ink ejection chambers, which receive liquid ink from the ink reservoir. Each chamber is located opposite the nozzle so ink can collect between it and the nozzle. The ejection of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements. When electric printing pulses heat the inkjet firing chamber resistor, a small portion of the ink next to it vaporizes and ejects a drop of ink from the printhead. Properly arranged nozzles form a dot matrix pattern. Properly sequencing the operation of each nozzle causes characters or images to be printed upon the paper as the printhead moves past the paper.  
           [0007]    The ink cartridge containing the nozzles is moved repeatedly across the width of the medium to be printed upon. At each of a designated number of increments of this movement across the medium, each of the nozzles is caused either to eject ink or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed movement across the medium can print a swath approximately as wide as the number of nozzles arranged in a column of the ink cartridge multiplied times the distance between nozzle centers. After each such completed movement or swath the medium is moved forward the width of the swath, and the ink cartridge begins the next swath. By proper selection and timing of the signals, the desired print is obtained on the medium.  
           [0008]    A concern with inkjet printing is the sufficiency of ink flow to the paper or other print media. Print quality is a function of ink flow through the printhead. Too little ink on the paper or other media to be printed upon produces faded and hard-to-read documents.  
           [0009]    Inkjet printheads are typically attached to a housing or body of a print cartridge. The inkjet printhead ink is fed from an internal ink reservoir integral to the print cartridge or from an “off-axis” ink supply which feeds ink to the print cartridge via tubes connecting the print cartridge and ink supply. A print cartridge having an “off-axis” ink supply usually also has a very small internal ink reservoir. In either case, the housing has an ink conduit for supplying ink from an internal ink reservoir to the printhead.  
           [0010]    Ink is then fed to the various vaporization chambers either through an elongated hole formed in the center of the bottom of the substrate, “center feed”, or around the outer edges of the substrate, “edge feed”. In center feed the ink then flows through a central slot in the substrate into a central manifold area formed in a barrier layer between the substrate and a nozzle member, then into a plurality of ink inlet channels, and finally into the various ink vaporization chambers. In edge feed ink from the ink reservoir flows around the outer edges of the substrate into the ink inlet channels and finally into the ink vaporization chambers. Inkjet printheads are very sensitive to particulate contamination. To deal with this problem, a filter is typically disposed in the ink fluid path between the reservoir of ink and the printhead.  
           [0011]    In either center feed or edge feed, the flow path from the ink reservoir to the printhead inherently provides restrictions on ink flow to the ink vaporization chambers. A concern with inkjet printing is the sufficiency of ink flow to the paper or other print media. Print quality is a function of ink flow through the printhead. Too little ink on the paper or other media to be printed upon produces faded and hard-to-read documents.  
           [0012]    Inkjet printheads are typically attached to a housing or body of a print cartridge, which contains an ink reservoir. The housing has a conduit for supplying ink from the ink reservoir to the printhead. Inkjet printheads are very sensitive to particulate contamination. To deal with this problem, a filter is typically disposed between the reservoir of ink and the printhead. A filter is attached to the inside of the housing, separating the ink delivery portion of the housing into two regions—one upstream and one downstream of the filter. This type of design has a number of drawbacks.  
           [0013]    First, the housing material tends to be selected for structural rigidity and high heat deflection. Fillers (such as glass fibers) are typically included to enhance these properties. Such materials tend to be difficult surfaces to which to attach a filter and effect a complete seal around the perimeter of the filter. If the seal is not complete, bubbles or particulates may slip past the filter and block the ink channels or nozzles.  
           [0014]    One method to improve upon this is to provide a second plastic material by insert molding to rigid outer housing. However insert molding is very expensive and the outer rigid housing must be adapted to be compatible with insert molding. The separation the filter staking from the cartridge housing would provide more freedom of material selection for both the cartridge housing and a good heat staking material for the filter carrier. Moreover, the filter staking process is greatly simplified when it can be performed external to the cartridge housing is done outside a pen body. All of these difficulties are even further compounded by the advent of a new design that provides a jet impinging flow of ink to cool the printhead. This design makes the molding of the rigid housing very difficult.  
           [0015]    Another problem that occurs during the life of the print element is air out gassing. Air builds up between the filter and the printhead during operation of the printhead. Ink delivery systems are capable of releasing gasses and generating bubbles, thereby causing systems to get clogged and degraded by bubbles. In the design of a good ink delivery system, it is important that techniques for eliminating or reducing bubble problems be considered. Therefore, another problem that occurs during the life of the print element is air out-gassing. Air builds up between the filter and the printhead during operation of the printhead. For printers that have a high use model, it would be preferable to have a larger volume between the filter and the printhead for the storage of air. For low use rate printers, this volume would be reduced.  
           [0016]    There is a need for high speed printing devices, such as desktop printers, large format printers, facsimile machines and copiers. In the past, printheads have not had the ability to operate at high speed ink ejection rates required for high speed printing rates due to lack of the ability to remove the large amount of heat generated.  
           [0017]    Accordingly, there is a need for a new filter carrier for protecting a filter from being blocked by air bubbles in an inkjet printhead operating at high speed printing rates.  
         SUMMARY OF THE INVENTION  
         [0018]    The present invention is a printing device including a filter carrier with a filter. The present invention overcomes the problem of filter blockage created by bubble accumulation underneath the filter of previous printheads with a filter carrier and filter that reduces air bubble blockage of the filter. Namely, air bubble blockage of the filter is avoided by trapping more bubbles in a designated area. In addition to the filter carrier and filter, the printing device further includes an outer housing, a substrate and an ink conduit. The substrate has a back surface and a front surface with ink ejection chambers formed thereon. The ink conduit has a distal end proximate to the back surface of the substrate. The ink conduit, the outer housing and the substrate define an ink flow path to the ink ejection chambers and a bubble accumulation chamber in communication with the ink flow path such that buoyancy will tend to move bubbles that accumulate in the ink flow path into the bubble accumulation chamber.  
           [0019]    The filter carrier is located within the print cartridge towards the back of the substrate. An ink conduit is defined by the walls of filter carrier, narrow ink slots on a bottom surface of the filter carrier and the walls of the cartridge body. The ink slots define conduit openings that are adjacent to the bottom surface of the filter carrier. The conduit openings on each side of the filter carrier can define the narrow ink slots. The bottom surface of the filter carrier is preferably flat and provides ink flow through the slots over the bottom surface in a horizontal direction, relative to the substrate. The bottom surface of the filter carrier is substantially aligned in a direction parallel to the back surface of substrate. The slots include openings that face the inner walls and are above the back surface of substrate.  
           [0020]    The ink slots direct the flow of ink along the side of substrate through a gap between the back of the substrate and the bottom surface of the filter carrier. As the fluid flows from the ink conduit and through the slots, it impinges on the substrate, thereby causing heat transfer from the substrate into the ink. This happens as the ink flows toward the drop ejection chambers where the warm ink is ejected onto media. Since the bottom surface of the filter carrier is substantially aligned in a direction parallel to the back surface of substrate, the ink flows horizontally out of the slots, relative the substrate. This in turn helps trap more bubbles in bubble accumulation chambers. In addition, the warming of the ink in the bubble accumulation chambers may be reduced and heat transfer between substrate and the ink can be improved.  
           [0021]    The filter divides the ink delivery portion of the housing into upstream and downstream sections such that ink flows from the upstream portion through the filter to the downstream portion and to the printhead. The separation the filter staking from the cartridge housing provides more freedom of material selection for both the cartridge housing and a good heat staking material for the filter carrier. The separation also greatly simplifies the molding of the rigid cartridge housing. Also, the filter staking process is greatly simplified when it is performed external to the cartridge housing. The present invention also provides the ability to have an adjustable air warehouse volume to accommodate various out-gassing rates of different print usages cartridge usages. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The present invention can be further understood by reference to the following description and attached drawings that illustrate the preferred embodiment. Other features and advantages will be apparent from the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.  
         [0023]    [0023]FIG. 1 is a perspective view of one embodiment of an inkjet printer incorporating the present invention.  
         [0024]    [0024]FIG. 2 is a perspective view of a single print cartridge showing the flexible electric circuit and its electrical contact pads and also showing the fluid interconnect to the carriage.  
         [0025]    [0025]FIG. 3 is another perspective view of a single print cartridge showing the printhead portion on the bottom surface of the cartridge and the fluid interconnect to the carriage.  
         [0026]    [0026]FIG. 4 is a cross-sectional, perspective view along line A-A of the print cartridge of FIG. 2 showing the print cartridge connected to the fluid interconnect on the carriage.  
         [0027]    [0027]FIG. 5 is a simplified perspective view of the back side of the printhead assembly.  
         [0028]    [0028]FIG. 6 is a perspective view the of print cartridge of FIG. 2 showing the headland area where the substrate and flex tape is attached.  
         [0029]    [0029]FIG. 7 is a cross-sectional view along line B-B of FIG. 2 showing the flow of ink to the ink ejection chambers in an edge feed printhead using an embodiment of the present invention.  
         [0030]    [0030]FIG. 8 is a cross-sectional view along line B-B of FIG. 2 showing the flow of ink to the ink ejection chambers in an edge feed printhead using an embodiment of the present invention.  
         [0031]    [0031]FIG. 9 is a cross-sectional view along line B-B of FIG. 2 showing the flow of ink to the ink ejection chambers in a center feed printhead using an embodiment of the present invention  
         [0032]    [0032]FIG. 10 is a cross-sectional view along line A-A of FIG. 5 illustrating the location of the filter carrier of the present invention in the print cartridge.  
         [0033]    [0033]FIG. 11 is a side elevational view of the filter carrier of the present invention.  
         [0034]    [0034]FIG. 11A is a cross-sectional view along line A-A of FIG. 11. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    While the present invention will be described below in the context of an off-axis printer having an external ink source, it should be apparent that the present invention is equally useful in an inkjet printer which uses on-axis inkjet print cartridges having an ink reservoir integral with the print cartridge. FIG. 1 is a perspective view of one embodiment of an inkjet printer  10 , with its cover removed, suitable for utilizing the present invention. Generally, printer  10  includes a tray  12 A for holding virgin paper. When a printing operation is initiated, a sheet of paper from tray  12 A is fed into printer  10  using a sheet feeder, then brought around in a U direction to now travel in the opposite direction toward tray  12 B. The sheet is stopped in a print zone  14 , and a scanning carriage  16 , supporting one or more print cartridges  18 , is then scanned across the sheet for printing a swath of ink thereon. After a single scan or multiple scans, the sheet is then incrementally shifted using a conventional stepper motor and feed rollers to a next position within the print zone  14 , and carriage  16  again scans across the sheet for printing a next swath of ink. When the printing on the sheet is complete, the sheet is forwarded to a position above tray  12 B, held in that position to ensure the ink is dry, and then released.  
         [0036]    The carriage  16  scanning mechanism may generally include a slide rod  22 , along which carriage  16  slides and a flexible electrical cable (not shown), which transmits electrical signals from the printer&#39;s microprocessor to electrical contacts on the carriage  16 . Also shown is a coded strip  24 , which is optically detected by a photo detector on carriage  16  for precisely spatially positioning carriage  16 . A motor (not shown), connected to carriage  16  is used for transporting carriage  16  along slide rod  22  across print zone  14 .  
         [0037]    The features of inkjet printer  10  also include an ink delivery system for providing ink to the print cartridges  18  and ultimately to the ink ejection chambers in the printheads from an off-axis ink supply station  30  containing replaceable ink supply cartridges  31 ,  32 ,  33 , and  34 , which may be pressurized or at atmospheric pressure. For color printers, there will typically be a separate ink supply cartridge for black ink, yellow ink, magenta ink, and cyan ink. Four tubes  36  carry ink from the four replaceable ink supply cartridges  31 - 34  to the print cartridges  18 .  
         [0038]    [0038]FIG. 2 is a perspective view of one embodiment of a print cartridge  18 . The printhead nozzle array is at location  58 . An integrated circuit chip  78  provides feedback to the printer regarding certain parameters of print cartridge  18 . A flexible electrical tape circuit  80  contains electrical contact pads  86 , electrical leads  84  (shown in FIG. 5) and nozzles  82  (shown in FIG. 3) laser ablated through tape  80 . The flexible electrical tape circuit  80  is affixed to the printhead substrate  88  and to the barrier layer  104  to form a printhead assembly  83 . Printhead assembly  83  is then secured to print cartridge  18  as described below with respect to FIG. 7. The contact pads  86  align with and engage electrical contacts (not shown) on carriage  16  when the print cartridge  18  is installed in carriage  16 . Preferably, the electrical contacts on carriage  16  are resiliently biased toward print cartridge  18  to ensure a reliable contact.  
         [0039]    A septum elbow  71  routes ink from the carriage  16  to the septum  52  and supports the septum. An air vent  74  formed in the top of print cartridge  18  is used by a pressure regulator located in print cartridge  18  and described below. In an alternative embodiment, a separate regulator may be connected between the off-axis ink supply and each print cartridge  18 . When the print cartridges  18  are installed in carriage  16 , the print cartridges  18  are in fluid communication with an off-carriage ink supply  31 - 34  that is releasably mounted in ink supply station  30 .  
         [0040]    [0040]FIG. 3 illustrates the bottom side of print cartridge  18 . Two parallel rows of offset nozzles  82  are laser ablated through tape  80 .  
         [0041]    [0041]FIG. 4 is a cross-sectional perspective view of print cartridge  18 , with tape  80  removed, taken along line A-A in FIG. 2. A shroud  76  surrounds the hollow needle  60  to prevent inadvertent contact with needle  60  and also to help align septum  52  with needle  60  when installing print cartridge  18  in carriage  16 . Shroud  76  is shown having an inner conical or tapered portion  75  to receive septum  52  and center septum  52  with respect to needle  60 . A plastic conduit  62  leads from the needle  60  to chamber  61  via hole  65 .  
         [0042]    Embodiments of scanning carriages and print cartridges are described in U.S. patent application Ser. No. 08/706,121, now U.S. Pat. No. 5,996,155 filed Aug. 30, 1996, entitled “Inkjet Printing System with Off-Axis ink Supply Having ink Path Which Does Not Extend above Print Cartridge,” which is herein incorporated by reference.  
         [0043]    A regulator valve (not shown) within print cartridge  18  regulates pressure by opening and closing an inlet hole  65  to an internal ink chamber  61  of print cartridge  18 . When the regulator valve is opened, the hollow needle  60  is in fluid communication with an ink chamber  61  internal to the cartridge  18 . The needle  60  extends through a self-sealing hole formed in through the center of the septum  52 . The hole is automatically sealed by the resiliency of the rubber septum  52  when the needle is removed.  
         [0044]    For a description of the design and operation of the regulator see U.S. patent application Ser. No. 08/706,121, now U.S. Pat. No. 5,966,155 filed Aug. 30, 1996, entitled “Inkjet Printing System with Off-Axis Ink Supply Having Ink Path Which Does Not Extend above Print Cartridge,” which is herein incorporated by reference.  
         [0045]    [0045]FIG. 5 shows a simplified schematic of the printhead assembly  83  shown in FIGS. 2 and 3. Electrical leads  84  are formed on the back of tape  80  and terminate in contact pads  86  for engaging electrical contacts on carriage  16 . The other ends of electrical leads  84  are bonded through windows  87  to terminals of a substrate  88  on which are formed the various ink ejection chambers and ink ejection elements. The ink ejection elements may be heater resistors or piezoelectric elements.  
         [0046]    A demultiplexer on substrate  88  demultiplexes the incoming electrical signals applied to contact pads  86  and selectively energizes the various ink ejection elements to eject droplets of ink from nozzles  82  as printhead  83  scans across the print zone. In one embodiment, the dots per inch (dpi) resolution is 600 dpi, and there are 512 nozzles  82 .  
         [0047]    [0047]FIG. 6 is perspective view of the print cartridge  18  with the printhead assembly  83  removed. An adhesive/sealant is applied to headland areas  174  and  176  and along the top of headland walls  178  and  179  to secure the printhead assembly  83  to the print cartridge body  110 . The adhesive/sealant at areas  174  and  176  squishes upward to secure the ends of the substrate  88  to the print cartridge body  110  and insulates the electrical leads  84  on the back of tape  80  so they will not be shorted by ink in the vicinity of the electrical leads  84 .  
         [0048]    [0048]FIG. 7 is a cross-sectional view along line B-B of FIG. 2 showing the flow of ink  92  from the ink chamber  61  within print cartridge  18  to ink ejection chambers  94  in an edge feed printhead using one embodiment of the present invention. Elements identified with the same numerals as in other figures may be identical and will not be redundantly described.  
         [0049]    The barrier layer  104 , the flexible tape  80  and substrate  88  define the ink inlet channels  132  and ink vaporization chambers  94 . Energization of the ink ejection elements  96  and  98  cause a droplet of ink  101 ,  102  to be ejected through the nozzles  82  associated with the ink ejection chambers  94 . The conductor portion of the flexible tape  80  is glued with adhesive  108  to the plastic print cartridge body  110 . For a description of the barrier layer defining the ink inlet channels  132 , the ink vaporization chambers  94 , the heater resistors  96 ,  98  within the ink vaporization chambers  94  and the electrical circuitry of the printhead, see U.S. patent application Ser. No. 08/962,031, filed Oct. 31, 1997, entitled “Ink Delivery System for High Speed Printing;” The plastic body  110  of print cartridge  18  is formed such that the ink conduit  63  directs the flow of ink as arrow  92  from ink chamber  61  within the print cartridge  18  towards the back of the substrate  88 . Ink conduit  63  is defined by the walls of filter carrier  200 , narrow ink slots  162 ,  163  on a bottom surface  165 , and the walls of cartridge body  110 . The ink slots  162 ,  163  define conduit openings  166 ,  167  (as shown in FIG. 8) that are adjacent to the bottom surface  165 . The conduit openings  166 ,  167  on each side of the filter carrier  200  can define the narrow ink slots  162  and  163 , as shown in FIG. 8. The bottom surface  165  is preferably flat and provides ink flow through the slots  162 ,  163  over the bottom surface in a horizontal direction, relative to the substrate  88 , as shown by arrow  92 . The bottom surface  165  is substantially aligned in a direction parallel to the back surface of substrate  88 . Slots  162 ,  163  include openings  166 ,  167  that face the inner walls and are above the back surface of substrate  88 .  
         [0050]    Ink slots  162 ,  163  direct the flow of ink as shown by arrow  92  along the side of substrate  88  through a gap between the back of the substrate  88  and the bottom surface  165  of the filter carrier  200 . As the fluid flows from the ink conduit  63  and through the slots  162 ,  163 , it impinges on the substrate  88 , thereby causing heat transfer from the substrate  88  into the ink. This happens as the ink flows toward the drop ejection chambers where the warm ink is ejected onto media. Since the bottom surface  165  is substantially aligned in a direction parallel to the back surface of substrate  88 , the ink flows horizontally out of the slots  162 ,  163 , relative the substrate  88 . This in turn helps trap more bubbles  112  in bubble accumulation chambers  168 ,  170 .  
         [0051]    Inkjet printheads are very sensitive to particulate contamination. To deal with this problem, a filter  202  is preferably used between the reservoir of ink  61  and the printhead  83 . The filter  202  prevents particulate contaminates from flowing from the ink reservoir  61  to the printhead  83  and clogging the printhead nozzles  82 .  
         [0052]    Another problem that occurs during the life of the print element is air out-gassing. Air builds up between the filter  202  and the printhead  83  during operation of the printhead. Shown in FIG. 7 are bubble accumulation chambers  168 ,  170  defined and formed by the walls of filter carrier  200  and the walls of cartridge body  110 . As the ink heats up, the solubility of air in the ink decreases, and air defuses out of the ink in the form of bubbles  112 . In order for these bubbles  112  to not restrict the flow of ink, bubble accumulation chambers  168 ,  170  are formed in the print cartridge body to accumulate these bubbles. Since the ink flows horizontally out of the slots  162 ,  163 , relative the substrate  88  more bubbles  112  are trapped in bubble accumulation chambers  168 ,  170 .  
         [0053]    The bubble accumulation chambers  168 ,  170  are positioned above substrate  88  relative to a gravitational frame of reference when the printhead is mounted in the printing system. In the embodiment depicted by FIG. 7, two bubble accumulation chambers  168 ,  170  are formed on opposite sides of conduit  63 . One chamber  168  is formed between wall  163  and an outer portion of the printhead housing  110 . Another chamber  170  is formed between wall  162  and an outer portion of printhead housing  110 .  
         [0054]    A space between each slot  162 ,  163  and a distal end of conduit  63  defines a bubble escape opening. The bubble escape opening communicates between the ink flow path and the bubble accumulation chamber. In the embodiment depicted. Since the bottom surface  165  is substantially aligned in a direction parallel to the back surface of substrate  88  bubbles  112  are prevented from interfering with the flow of ink  92  through ink conduit  63  and around the edges of substrate  88  into the inlet channels  132  and then into ink ejection chambers  94 .  
         [0055]    For printers that have an intended high use rate, it would be preferable to have a larger volume between the filter and the printhead for the storage of air. For low use rate printers, this volume could be reduced. The filter carrier  200  height can be adjusted to readily provide varying volumes for bubble accumulation chambers  168 ,  170  depending on the anticipated out-gassing. In the preferred embodiment, these bubble accumulation chambers  168 ,  170  each have a capacity of 2 to 3 cubic centimeters; however, the capacity can be greater than or less than this preferred volume depending on the anticipated out-gassing. An acceptable range is approximately 1 to 5 cubic centimeters. Bubble accumulation chambers  168 ,  170  extend along the length of substrate  88  to be in fluid communication with all the ink channels  132  formed in barrier layer  104  on substrate  88 .  
         [0056]    The mesh size of filter  202  is sufficiently small that while ink may pass through the passages of the mesh, air bubbles under normal atmospheric pressure will not pass through the mesh passages that are wetted by the ink. As a result, the mesh also serves the function of an air check valve for the print cartridge.  
         [0057]    Ink passes from reservoir  61  through conduit  63  and out of the distal opening in conduit  63 . In a preferred embodiment, the ink flow  92  is in a first direction substantially perpendicular to substrate  88 . The ink flow exits the distal end of conduit  63  in this first direction, and then is redirected in a second direction substantially parallel to substrate  88 . In the embodiment depicted in FIG. 7, the ink forms a bifurcated flow pattern, wherein substantially half of the ink passes in the second direction, and the remaining ink passes in a third direction that is substantially opposite to the second direction. Laterally extending portions of the bottom surface  165  increase the heat transfer and direct the flow of ink in the second and third directions.  
         [0058]    The laterally extending portions  167  work in cooperation with the ink slots  16 ,  163  to channel the ink flow path  92  around substrate  88  to maximize heat transfer to the ejected in droplets. In other words, this geometry minimizes the amount of heat transferred from substrate  88  to the ink contained in the bubble accumulation chambers. The laterally extending portions provide a converging geometry for the ink flow path to better direct ink in the flow path.  
         [0059]    Bubble escape openings can be used to allow bubbles to escape from the ink flow path to the bubble accumulation chambers to prevent bubbles from occluding or substantially increasing flow resistance in the ink flow path.  
         [0060]    [0060]FIG. 8 is perspective view of the print cartridge  18  with the tape  80  removed along with substrate  88  to ink slotsl 62  and  163 , ink conduit  63 , and chambers  168  and  170 . In one embodiment, the preferred length of substrate  88  is approximately one-half inch. An adhesive/sealant is applied to headland areas  174  and  176 , and the assembly of FIG. 7 is then secured to the print cartridge  18  as shown in FIG. 3. The adhesive/sealant at areas  174  and  176  squishes upward to secure the ends of the substrate  881  to the print cartridge body and insulate the conductive traces on the back of tape  80  so that they will not be shorted by any ink in the vicinity of the conductors. An adhesive/sealant along the top of headland walls  178  and  179  secures the tape  80  to the print cartridge body.  
         [0061]    [0061]FIG. 9 is a cross-sectional view along line B-B of FIG. 2 showing a bifurcated flow of ink to the ink ejection chambers in a center feed printhead using another embodiment of the present invention. FIG. 9 shows a center feed printhead using impinging flow, wherein an ink flow path, shown by arrow  92 , is formed by one end of filter carrier  200  and the inner wall of cartridge body  110 . Flow director  169  then directs the ink flow  92  toward the central ink slot  87  in substrate  88 . The flow director  169  helps the ink  92  to run along a larger surface area of substrate  88 .  
         [0062]    A central bubble accumulation chamber  171  is shown which accumulates bubbles  112  which have out-diffused from the ink as the ink is heated by substrate  88 . Bubble accumulation chamber  171  is positioned substantially above substrate  88  relative to a gravitational frame of reference to collect bubbles generated proximate to a back surface of substrate  88 . A laterally extending flow director  169  is positioned above ink feed slot. A bubble escape opening is defined between flow director  169  and the bottom surface  165  of the filter carrier  200 . Bubbles that are generated in the ink flow path  92  escape through the bubble escape opening and to the bubble accumulation chamber. An opening is provided between the fluid director  169  and the bottom surface  165  to allow bubbles to escape into bubble accumulation chamber  169 . Also, since the bottom surface  165  is substantially aligned in a direction parallel to the back surface of substrate  88 , the ink flows horizontally out of the slots  162 ,  163 , relative the substrate  88 . This in turn helps trap more bubbles  112  in bubble accumulation chamber  169 . Hence, bubbles  112  will not interfere with the flow of ink  92  through ink conduit  63 ′ and into ink ejection chambers  94 . The fluid director  169  also reduces the warming of the ink in the bubble accumulation chamber  171  and improves heat transfer between substrate  88  and the ink. The complete structure of the printhead illustrated in FIG. 9 would be readily understood by one skilled in the art.  
         [0063]    The added heat withdrawn from the substrate due to the novel filter carrier  200  allows the printhead to operate at higher speeds without adversely affecting the print quality. The enhanced thermal performance does not rely on any attachments to the substrate, such as a heat exchanger. Such attachments would likely be much more complex and costly. The print cartridge may be a single-use disposable cartridge, a refillable cartridge, or a cartridge connected to an external ink supply.  
         [0064]    [0064]FIG. 10 is a cross-sectional view along line A-A of FIG. 5 illustrating the location of the filter carrier  200  of the present invention in the print cartridge  18 . Filter carrier  200  is supported in cartridge  18  by support surfaces  190 ,  192 . Filter carrier  200  is also supported walls  162 ,  163 , which were described above. The position of the filter screen  202  is also shown.  
         [0065]    Referring to FIGS. 11 and 11A, filter screen  202  is attached to the top surface  204  of filter carrier  1100  through heat staking (heat and pressure welding), adhesives or other bonding processes, to form a leak-proof seal between the filter screen  202  and filter carrier  200 . The filter carrier  1100  of FIGS. 11 and 11A has similar elements and is similar to filter carrier  200  of FIGS.  7 - 9 , but alternatively has straight walls, as opposed to angled walls of filter carrier  200  of FIGS.  7 - 9 . All filter carriers are preferably made of a plastic such as polypropylene or high density polyethylene, or other suitable material. Filter screen  202  is attached to the top surface  204  of filter carrier  200  through preferably heat staking (heat and pressure welding), or alternatively, adhesives or other bonding processes, to form a leak-proof seal between the filter screen  202  and filter carrier  200 . The filter screen  202  is formed of a material, which is permeable to the ink to be stored within the ink reservoir, and compatible with the plastic of material from which the filter carrier  200  is fabricated. A preferred material for the filter screen  202  is a section of finely woven stainless steel mesh, the periphery edges of which are attached to the top surface  204  of filter carrier  200  by heat staking. The mesh has a nominal passage dimension of 15 microns between adjacent mesh strands, and has a typical thickness of less than 0.005 inches.  
         [0066]    The filter carrier  200  is inserted into the cartridge body  110  such that the bottom surfaces  208 ,  210  of filter carrier  200  rest on cartridge body surfaces  190 ,  192 , respectively, and lower surface  212  of the snout portion  214  of filter carrier  200  is connected to the bottom surface  165 , which has ink slots  162 ,  163  formed therethrough. The inside of the filter carrier  200  has square corners for ink to wick up in the event that air fills the filter standpipe. The manufacture of the square corners is facilitated by slits  216 . Tabs  218  hold filter screen  202  in place during the heat staking process to filter carrier  200 . The sloping surface  220  of filter carrier  200  helps prevent trapping of air during the cartridge filling process. Grooves  222  are provided to prevent distortion during the molding process for filter carrier  200 .  
         [0067]    The filter carrier  200  has a carrier seal  206  on all sides to engage a housing seal surface disposed on the inside walls of the housing  18  to define a seal zone that separates chamber  61  from the region in fluid communication with printhead and make a leak proof seal around the filter carrier  200  and the cartridge body  110 . The carrier seal  206  is adapted to deform upon installation of the filter carrier  200  in the housing  110  and provide a reliable seal.  
         [0068]    Another problem that occurs during the life of the print element is air out gassing. Air builds up between the filter and the printhead during operation of the printhead. For printers that have a high use model, it would be preferable to have a larger volume between the filter and the printhead for the storage of air. For low use rate printers, this volume would be reduced. The present invention also addresses this problem. The filter carrier  200  height can be adjusted to readily provide varying volumes for chambers  168 ,  170  depending on the anticipated out-gassing.  
         [0069]    The mesh passage size is sufficiently small that while ink may pass through the passages of the mesh, air bubbles under normal atmospheric pressure will not pass through the mesh passages, which are wetted by the ink. The required air bubble pressure necessary to permit bubbles to pass through the mesh, in this embodiment, about 30 inches of water, is well above that experienced by the pen under any typical storage, handling or operational conditions. As a result, the mesh also serves the function of an air check valve for the print cartridge.  
         [0070]    The present invention allows a wide range of product implementations other than that illustrated in FIG. 2. For example, such ink delivery systems may be incorporated into an inkjet printer used in a facsimile machine. While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made within departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.