Abstract:
An inkjet printhead and a method for increasing the shelf life thereof are herein disclosed. The inkjet printhead has one or more nozzles for dispensing a colorant. These nozzles are fluidically connected to a reservoir. A first colorant substantially fills the nozzles while a second colorant is reserved in the reservoir.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to a method and apparatus for reducing nozzle failure in printheads that have been stored or otherwise unused for extended periods. 
   BACKGROUND OF THE INVENTION 
   Most inkjet printers dispense colorants or inks that are comprised of a dye and/or a pigment that is either dissolved or suspended in a volatile solvent. When the print head of the printer deposits the colorants on a recording media such as paper or film, the solvents in the colorants quickly evaporate, leaving the dyes and/or pigments behind on the recording media. 
   During the manufacturing process printheads for inkjet printers must be tested. Accordingly, it is customary to provide an inkjet printhead with a dye and/or pigment based colorant that will be dispensed from the printhead as a test to ensure that the printhead functions properly. It may also be necessary to include a colorant with a printhead so that a printer in which the printhead is installed may be tested. 
   However, where colorants are allowed to remain in a printhead for extended periods of time, it is often the case that the volatile solvents that make up the colorants will at least partially evaporate, leaving within the nozzles of the print head a residue of particles or a precipitate.  FIGS. 1   a - 1   c  illustrate how the evaporation of a volatile solvent from the colorant can result in the malfunction of the printhead. 
     FIG. 1   a  is a schematic view of a typical nozzle  12  in an inkjet printhead  10 . As will be readily understood by those skilled in the art, a printhead  10  typically includes multiple nozzles  12 , each of which is connected to a reservoir (not shown) by a conduit  14 . Generally, a single conduit  14  will supply colorant  13  to multiple nozzles  12 . In a thermal inkjet printhead, a small resistor  16  will be provided adjacent to the opening of the nozzle  12 . The resistor  16  ejects colorant  13  from the nozzle  12  by rapidly raising the temperature of the colorant  13  so as to cause the solvent thereof to boil. The rapid expansion of the boiling solvent ejects a droplet (not shown) of colorant  13  from the opening of the nozzle  12  in a known manner. Other types of inkjet printheads may utilize a piezoelectric element in lieu of the resistor  16 . 
   The printhead  10  illustrated in  FIG. 1   a  represents a printhead that has been newly filled with the colorant  13 .  FIG. 1   b , represents a printhead  10  that has been stored for a period of time. Over time the solvents present in the colorant  13  begin to evaporate as represented by arrows  18 . The evaporation of the solvents from the colorant  13  concentrates the pigments and/or dyes present in the colorant  13 . As more time passes, the pigments and/or dyes begin to form a solid accretion  2 . As can be seen in  FIG. 1   c , the accretion  2  has grown to the point where it blocks the nozzle  12 , thereby preventing its proper functioning. 
   In order to retard the evaporation of the solvents from a colorant, it is common to either cover the nozzles of a printhead with tape or else to ensure that the printhead is otherwise covered with a cap. While such methods do slow the evaporation of solvents from the colorant, simply covering a nozzle is not sufficient to prevent the formation of accretions in a nozzle where the printhead is placed in storage for an extended period of time. Accordingly, there is a recognized need for a method and/or and apparatus that will prevent the formation of accretions in the nozzles of the printhead, particularly where the printhead must be stored for extended periods of time either before it is used or between uses. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1   a - 1   c  are a schematic time-lapse depiction of a prior art printhead wherein solvents in a colorant evaporate to form an accretion in a nozzle; 
       FIG. 2  is a schematic representation of an exemplary printhead having a low concentration colorant inserted into a nozzle according to the present invention; 
       FIG. 3  is a schematic representation of an exemplary printhead and colorant supply system for operating a printhead such as that illustrated in  FIG. 2 ; and, 
       FIG. 4  is a schematic representation of an exemplary printhead such as that illustrated in  FIG. 2  and further including an exemplary nozzle priming system. 
   

   DETAILED DESCRIPTION 
   In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, exemplary embodiments in which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and equivalents thereof. 
     FIG. 2  is a schematic representation of an exemplary printhead  20  having a single nozzle  22  formed therein. Note that in practice, inkjet printhead  20  would have multiple nozzles  22 . However, for the sake of clarity, this description will demonstrate a printhead having only a single nozzle. 
   Colorants are supplied to the nozzle  22  through a conduit  24 . The conduit  24  is fluidically connected to a reservoir (not shown) that provides a continuous supply of a colorant  26 . While the exemplary methods and apparatuses herein may apply to any printhead or printing mechanism that utilizes a colorant  26  that comprises a volatile solvent, this description focuses on an exemplary thermal inkjet printhead embodiment. A resistor  28  is electrically connected to a controller via conductor  30 . The controller (not shown) applies a current to the resistor  28 , which boils the solvent in the colorant  26  immediately adjacent to the resistor  28 . The boiling of the solvents creates a vapor bubble whose expansion ejects a droplet of the colorant  26  from the nozzle  22  so as to form an image on a recording media (not shown). 
   Because it may be necessary to test the printhead  20  after its manufacture, or test a printer (not shown) in which the printhead  20  has been installed, a first, dilute colorant  26   a  is inserted into the printhead  20  so as to substantially fill the nozzle  22 . Note that the first colorant  26   a  must fill that portion of the nozzle  22  immediately adjacent to its opening. The first colorant  26   a  may also fill some portion of or the entire conduit  24  as well. Preferably, a second, more concentrated colorant  26   b  is placed in a reservoir  32  (see  FIG. 3 ) and reserved separately therein. However, in certain applications, the second colorant  26   b  may be injected into the conduit  24  of the printhead  20  after the first colorant  26   a  has been inserted therein. 
   It has been found that the number of malfunctioning nozzles  22  present in a printhead  20  is directly related to both the concentration of the colorant  26  and to the length of time that the printhead  20  is in storage. Accordingly, the insertion of a first, more dilute colorant  26   a  directly into the nozzle  22  adjacent the opening thereof results in fewer malfunctioning nozzles  22  over a given period of time. Thus, as the solvents in the first colorant  26   a  will likely continue to evaporate, the lower concentration of dyes and/or pigments in the first colorant  26   a  results in the slower growth of accretions in the opening of the nozzle  22 . 
   In certain embodiments, the first colorant  26   a  is simply a more dilute version of the more concentrated second colorant  26   b . Once the printhead  20  has been manufactured, the first colorant  26   a  is inserted through the conduit  24  into the nozzle  22 . The second colorant  26   b  is then injected into the reservoir  32 . While the concentration of dyes and/or pigments in the first colorant  26   a  is lower than that of the second colorant  26   b , the concentration is sufficient to allow the printhead  20  to be tested, as is commonly the practice, and yet yields fewer malfunctioning nozzles  22  after storage of the printhead  20  for a given period of time. 
   In certain other embodiments, the second colorant  26   b  is inserted into the printhead  20  at least part way into the conduit  24  but possibly also partly into the nozzle  22 , keeping in mind that the first colorant  26   a  is to occupy the majority of the nozzle  22 , and possibly all of the nozzle  22 . Note that the dimensions of the conduit  24  in the nozzle  22  are such that the colorants  26   a  and  26   b  will not be significantly mixed together. Accordingly, it is possible for colorants  26   a  and  26   b , differing only in their concentration is of dyes and/or pigments, to coexist side-by-side for extended periods of time without any significant mixing. 
   In some instances it may be preferable to utilize dissimilar colorants  26   a  and  26   b . As used herein, the term “dissimilar” should be taken to include colorants  26  comprising different combinations and concentrations of solvents, and coloring agents such as dyes and/or pigments. By way of example only, in some instances it may be desirable to utilize a colorant  26   a  that has a different hue, or for that matter a completely different color, than the colorant  26   b . To further prevent mixing of the colorants  26   a ,  26   b  it may be desirable to select solvents for the respective colorants that are dissimilar or even immiscible with one another. Alternatively, it may be desirable to select a solvent or mixture of solvents for use in the colorant  26   a  that have a relatively low volatility. 
     FIG. 3  illustrates an apparatus for implementing the present invention. In this embodiment, nozzles  22  are formed in a nozzle orifice plate  23 . Colorant is supplied to the nozzles  22  in the nozzle orifice plates  23  through a conduit  24 . As can be seen in  FIG. 3 , the conduit  24  may be sized so as to include a modicum of storage place for colorants  26 . The conduit  24  is fluidically connected to a colorant delivery system  31 . The colorant delivery system  31  includes a colorant supply reservoir  32  that is connected to the conduit  24  by a line  33  that passes through a pump  34  and a valve  36 . Note that in some embodiments the colorant delivery system  31  may be located remotely from the printhead  20 . In other embodiments, the ink delivery system  31  may be formed as an integral part of the printhead  20 . It is to be understood therefore that line  33  is to be construed to include any coupling mechanism for connecting the reservoir  32  to the conduit  24 . 
   During normal operation, pump  34  is actuated to move colorant from the reservoir  32  through the line  33  into the conduit  24 . The valve  36  may be operated to selectively open and close the line  33 , thereby permitting or preventing, as the case may be, the flow of colorant from the reservoir  32  into the conduit  24 . The colorant  26  flows through the conduit  20  either due to the force of gravity or as the pump  34  has pressurized the colorant  26  in the conduit  24 . 
   As part of the manufacturing process, or as part of a “mothballing” procedure, the apparatus illustrated in  FIG. 3  will have a predetermined quantity of the first colorant  26   a  inserted into the conduit  24  as represented by fill line  27 . The amount of the first colorant  26   a  inserted into the conduit  24  is sufficient to allow one or more required tests of the printhead  20  and to ensure that the nozzles  22  remain substantially filled with the first colorant  26   a . A port or other access point (not shown) may be provided in the printhead  20  so as to allow the injection of a quantity of the first colorant  26   a  into the conduit  24  at the time of manufacture or later, after the printhead  20  has been installed in a printer. Such port or other access point may then be closed in some manner. 
   In certain exemplary embodiments, multiple reservoirs  32  may be used. In the illustrated embodiment, the printhead  20  is prepared for printing an image on recording media by actuating the colorant delivery system  31  to withdraw the first colorant  26   a  from the printhead  20  and into a first reservoir  32 . Once the first colorant  26   a  has been removed from the printhead  20 , the reservoir  32  containing the first colorant  26   a  is uncoupled from the colorant delivery system  31  and a second reservoir  32 , this one having the second colorant  26   b  contained therein, is coupled to the colorant delivery system  31 . The colorant delivery system  31  is then actuated to provide the second colorant  26   b  to the printhead  20  for printing. The first colorant  26   a  may be conserved in the first reservoir  32  or may be discarded. Where it is desirable to “mothball” the printhead  20 , the colorant delivery system  31  may be actuated to withdraw the second colorant  26   b  from the printhead  20  back into its reservoir  32  for conservation. Thereafter, the first colorant  26   a  may be reintroduced into the printhead  20  by coupling a reservoir  32  having the first colorant  26   a  contained therein to the colorant delivery system  31 . The colorant delivery system  31  will then be actuated to reintroduce the first colorant  26   a  into the printhead  20 . 
   The nozzles  22  of the printhead  20  may be closed as by capping or taping and as seems appropriate given the application to which the printhead  20  will be put. The printhead  20  may then be placed into storage or otherwise inactivated. Note that the printhead  20  may be detached from the line  33  and stored apart from the reservoir  32 , pump  34  and valve  36 , may be installed in a printer along with the reservoir  32 , pump  34 , and valve  36  for storage, or a combination of the reservoir  32 , pump  34  and valve  36  may be stored together with the printhead  20  in an integral package. For the purposes of the present application, the term “storage” should be taken to mean the reservation of the printhead  20  at a location remote from a printer or an extended period of inactivity where the printhead  20  is installed in a printer. The second colorant  26   b  may be retained entirely within the reservoir  32 , leaving only the first colorant  26   a  in the conduit  24 . Alternatively, the second colorant  26   b  can be inserted into the conduit  24  behind and up to the first colorant  26   a  up to line  27  as shown in  FIG. 3 . 
   Where the printhead  20  is currently in use but is to undergo a period of prolonged in activity, a mothballing procedure may be performed upon the printhead  20 . During such a procedure, relatively concentrated colorant  26   b  present in the conduit  24  and nozzles  22  is either ejected or is withdrawn into the reservoir  32  by means of the pumping action of the pump  34  through line  33 . Thereafter, dilute colorant  26   a  may be inserted into the conduit  24  through the aforementioned port so as to substantially fill the nozzles  22 . In an alternate embodiment, and as it is likely that some quantity of concentrated colorants  26   b  may be retained within the conduit  24  and nozzles  22 , a compatible solvent not having a dye and/or pigments included therein may be inserted into the conduit  24  to be mixed with the second colorant  26   b  remaining in the conduit  24  by means of pulsing the pump  34  as described herein above. Alternatively, the pure solvents added to the conduit  24  may be drawn through the conduit  24  and expelled from the nozzles  22  by the normal operation of the nozzles  22 , the nozzles  22  being operated so as to draw sufficient quantities of the pure solvents into the nozzles  22  to reduce the incidence of malfunction in the nozzles  22  when the printhead  20  is installed and/or reactivated. 
   Upon installation of the printhead  20  in a printer, or upon reactivation of the printhead  20  in a printer, printing of an image upon recording media may commence using the first colorant  26   a . The use of a dilute mixture of the second colorant  26   b  as the first colorant  26   a  may allow the printhead  20  to begin printing in such a way as to produce images of an acceptable quality where the color, hue, and/or intensity of the first colorant  26   a  is near enough to satisfy the image quality requirements expected of images printed using the second colorant  26   b . Alternatively, one or more test images or patterns may be printed for the express purpose of exhausting the supply of the first colorant  26   a  within the printhead  20  prior to the start of printing using the desired second colorant  26   b.    
   The apparatus illustrated in  FIG. 3  may also be operated in such a way as to mix the first and second colorants  26   a ,  26   b  prior to the start of printing by the printhead  20 . In this embodiment, the first colorant  26   a  is a dilute version of the second colorant  26   b . Upon installation of the printhead  20  in a printer, or upon reactivation of the printhead  20  after a period of inactivity, valve  36  is opened and pump  34  is operated so as to alternatively pump the second colorant  26   b  from the reservoir  32  into the conduit  24  and to withdraw the first colorant  26   a  from the conduit  24  into the reservoir  32 , thereby effectively mixing the first and second colorants  26   a  and  26   b . In order to ensure that the colorant  26  used to print an image on a recording media retains a desired color intensity, the second colorant  26   b  contained within the reservoir  32  may be highly concentrated or the reservoir  32  may be over-filled, the concentration and/or volume of the second colorant  26   b  being such that the addition of a quantity of the dilute first colorant  26   a  does not significantly affect desired colorant properties such as intensity, hue, or the like. 
     FIG. 4  illustrates another exemplary embodiment that includes a colorant delivery system  31 , a printhead  20 , and a nozzle priming system  40 . As described above, the ink delivery system  31  includes a reservoir  32  that is fluidically coupled to the conduit  24  of the printhead  20  by means of line  33 . While in the embodiment illustrated in  FIG. 4 , no pump or valve has been included in line  33 , such may be added where warranted by the application under consideration. The nozzles  22  of the printhead  20  are included in the nozzle orifice plate  23 . See  FIG. 3 . As illustrated, the printhead  20  is filled up to fill line  27  with a first colorant  26   a . While  FIG. 4  does illustrate that the conduit  24  is at least partially filled with the first colorant  26   a , it must be kept in mind that all that is required is that the nozzles of the nozzle orifice plate  23  be partially or substantially filled with the dilute, first colorant  26   a . The more concentrated second colorant  26   b  is contained within the reservoir  32  of the ink delivery system  31  and is supplied, upon demand, to the printhead  20  through line  33 . The nozzle priming system  40  comprises a priming cap  42  that is constructed and arranged to fit snugly over the nozzle orifice plate  23 , preferably forming a seal thereover. The priming cap  42  is connected through a pump  44  to a priming reservoir  46  by means of line  48 . 
   In operation, the printhead  20  is first installed in a printer or is reactivated after a period of inactivity; pump  44  is actuated to draw the first colorant  26   a  from the nozzle orifice plate  23  and conduit  24  of the printhead  20  and into the priming cap  42 . The first colorant  26   a  is then deposited into the priming reservoir  46 . In this embodiment, once the first colorant  26   a  is removed from the printhead  20  and deposited in the priming reservoir  46 , it will not be reused. It is to be understood however that the first colorant  26   a  may be reused where so desired. 
   As the first colorant  26   a  is drawn from the printhead  20 , the action of the pump  44  will simultaneously draw the second colorant  26   b  from the reservoir  32  into the condiut  24  and subsequently into the nozzles of the nozzle orifice plate  23 . At this point, the printhead  20  is ready to begin printing an image using the second colorant  26   b.    
   Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Many adaptations of the invention will be apparent to those of ordinary skill in the art. Accordingly, this application is intended to cover any adaptations or variations of the invention. It is manifestly intended that this invention be limited only by the following claims and equivalents thereof.