Abstract:
A packaged, degassed printer ink supply is provided, the ink supply including ink-containment vessel, a substantially degassed volume of ink contained within the ink-containment vessel, and a removable, sealable outer protective container having a low permeability to air and surrounding at least part of the ink-containment vessel to define an atmosphere between the ink-containment vessel and the outer protective container. The atmosphere between the ink-containment vessel and outer protective container is modified relative to ambient atmosphere outside of the outer protective container to decrease a diffusion rate of at least one component gas of air into the ink-containment vessel.

Description:
TECHNICAL FIELD 
     The present invention relates generally to packaging of ink supplies. More particularly, the invention relates to a degassed ink supply and a method of packaging an ink supply to maintain the ink in a degassed state. 
     BACKGROUND OF THE INVENTION 
     In contrast to other types of printers, inkjet printers provide fast, high resolution, black-and-white and color printing on a wide variety of media, and at a relatively low cost. As a result, inkjet printers have become one of the most popular types of printers for both consumer and business applications. Nevertheless, inkjet technology must continuously advance to keep pace with ever-increasing customer demands for printers that print faster, at a higher resolution, and at a lower cost. 
     One of the more important components of an inkjet printer is the inkjet printhead, which controls the application of ink to the printing medium (e.g., paper). Generally, an inkjet printhead includes a plurality of ink ejection mechanisms formed on a substrate. Each ink ejection mechanism includes a firing chamber with at least one ejection orifice. Each ink ejection mechanism also includes one or more firing resistors located in the firing chamber. The substrate is connected to an ink cartridge or other ink supply. Channel structures formed on the substrate direct the ink from the ink supply to the firing chambers. Control circuitry, located on the substrate and/or remote from the substrate, supplies current to the firing resistors in selected firing chambers. The ink within the selected chambers is super-heated by the firing resistors, causing the ink in close proximity to the resistors to be vaporized. This forms a bubble that pushes ink through the chamber orifice toward the printing medium in the form of an ink droplet. 
     Due to the many processing steps required to create the various printhead structures on the substrate, the printhead is typically one of the most expensive parts of an inkjet ink delivery system. Furthermore, the cost of the printhead tends to increase with the size of the printhead. For smaller printers, the cost of the printhead may be low enough to allow the use of an integrated ink supply system, in which the printhead is permanently attached to the ink supply. This arrangement necessitates replacing the printhead whenever the ink supply is replaced. Larger printers, however, often use a separate ink supply system, in which the printhead is a separate component from the ink supply. In this arrangement, the ink supply may be replaced without having to replace the printhead, thus significantly cutting the cost of new ink supplies. 
     Although the printhead of a separate ink supply system does not need to be changed with each change of the ink supply, it does periodically require replacement. One of the most common causes of printhead failure is the accumulation of excess air in the printhead. Excess air in the printhead can cause the printhead to fail in several different ways. For example, air that accumulates in the printhead can expand with increases in temperature or altitude, causing ink either to seep out of firing chambers. One of the most common sources of air that accumulates in the printhead is air exsolved in the ink, which can be evolved from the ink by the elevated temperatures commonly found in the printhead due to heat dissipated by the firing resistors. 
     Various solutions have been proposed to overcome the effects of air on the lifetime of inkjet printheads. One effective solution is to print with degassed ink, as described in U.S. patent application Ser. No. 08/758,744, entitled “Ink Supply With Air Diffusion Barrier for Unsaturated Ink,” filed Jan. 11, 2001. The subject matter of that application is incorporated herein by this reference. 
     Degassed ink is ink that has a low concentration of dissolved gases, typically 80% or less of total saturation. When this ink reaches the printhead, it dissolves some air present in the printhead, and thus helps remove air from the printhead. The use of degassed ink may increase printhead life up to 10 times or more compared to the use of non-degassed ink. However, if air diffuses back into a degassed ink supply between manufacturing and use, such as while the ink supply is in storage, the level of saturation will increase. To address this problem, degassed ink may be contained within a relatively impermeable metalized membrane inside of the ink cartridge. However, even this type of packaging system may have portions of higher permeability to air, such as a port or septum through which ink flows out of the membrane. Because of problems with air re-saturation, degassed ink supplies tend to have a relatively short shelf life, creating problems with shipping and storing the supplies. 
     SUMMARY OF THE INVENTION 
     The present invention provides a packaged, degassed ink supply for use in a printer, and provides a method of packaging an ink supply to maintain ink in a degassed state. The packaged ink supply includes an ink-containment vessel, a substantially degassed volume of ink contained within the ink-containment vessel, and a removable, sealable outer protective container having a low permeability to air and surrounding at least part of the ink-containment vessel to define an atmosphere between the ink-containment vessel and the outer protective container. The atmosphere between the ink-containment vessel and outer protective container is modified relative to ambient atmosphere outside of the outer protective container to decrease a diffusion rate of at least one component gas of air into the ink-containment vessel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a packaged ink supply constructed in accordance with the present invention. 
     FIG. 2 is an exploded isometric view of the ink supply and ink supply packaging of FIG.  1 . 
     FIG. 3 is a sectional view of the packaged ink supply of FIG. 1 taken along lines  3 — 3  of FIG.  1 . 
     FIG. 4 is an enlarged sectional view of a first material suitable for use in constructing the packaging of the packaged ink supply of FIG.  1 . 
     FIG. 5 is an enlarged sectional view showing a seam of the packaging of the packaged ink supply of FIG.  1 . 
     FIG. 6 is an enlarged sectional view of a second material suitable for use in constructing the packaging of the packaged ink supply of FIG.  1 . 
     FIG. 7 is a flow diagram demonstrating a method of packaging an ink supply to maintain ink in a degassed state in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of a packaged, degassed ink supply according to the present invention is depicted generally at  10  in FIGS. 1-3. Ink supply  10  includes an ink-containment vessel  12  that houses a volume of degassed ink  14 . The depicted ink-containment vessel  12  includes a generally rigid outer housing  16  and an inner membrane  18  that contains degassed ink  14 . It will be appreciated, however, that any other suitable ink-containment vessel may be used. Packaged ink supply  10  also includes packaging in the form of a removable, outer protective container  20 . Outer protective container  20  is made from a material with a low permeability to air, and is configured to surround any parts of ink-containment vessel  12  that have an unsuitably high permeability to air. Typically, as shown in FIGS. 2 and 3, outer protective container  20  is configured to completely envelop ink-containment vessel  12 . 
     In accordance with the present invention, the atmosphere within the space between ink-containment vessel  12  and outer protective container  20  is modified relative to the atmosphere outside of the protective container to modify the diffusion gradient of at least one component gas of air across ink-containment vessel  12 , and thus to change the rate of diffusion of the gas either into or out of degassed ink  14 . Typically, this is accomplished by sealing the outer protective container about the ink-containment vessel and creating at least a partial vacuum within the outer protective container as will be described further below. 
     To extend the life of an inkjet printhead, it may be desirable to maintain a low concentration of all dissolved gases in degassed ink  14 . Thus, the atmosphere between ink-containment vessel  12  and outer protective container  20  may be modified in a way to decrease diffusion of all component gases of air across ink-containment vessel  12  and into degassed ink  14 . This may be accomplished by partially evacuating the space between ink-containment vessel  12  and outer protective container  20 . The transmission rate of a gas through a medium is given by the equation: 
     
       
           T   x   =P   x   Ap   x   /t   (1) 
       
     
     where T x  is the transmission rate for gas x, P x  is the permeability of the medium to gas x, A is the area of the medium exposed to gas x, P x  is the partial pressure of gas x against the medium, and t is the thickness of the medium. 
     As is evident from this equation, the transmission rate of each component gas of air into degassed ink  14  is directly proportional to the partial pressure of that gas in the space between ink-containment vessel  12  and outer protective container  20 . Thus, by lowering the total gas pressure between ink-containment vessel  12  in this space, the transmission rates of all component gases of air through ink-containment vessel  12  are lowered. 
     The space between ink-containment vessel  12  and outer protective container  20  may be evacuated to any desired pressure. The desired pressure will generally depend upon the permeability of the material from which outer protective container  20  is made, as well as other factors, such as the cost of vacuum packaging to a desired pressure. Typically, the pressure will be in the range of 0.1-0.6 atmospheres, and more typically approximately 0.5 atmospheres, though either higher or lower pressures may be used. Furthermore, while the atmosphere between ink-containment vessel  12  and outer protective container  20 , as described herein, has been modified by partial evacuation, it will be appreciated that it can be modified in other ways. For example, the atmosphere in the space between ink-containment vessel  12  and outer protective container  20  may be modified by purging the atmosphere with a gas that has a low transmission rate across ink-containment vessel  12 . 
     After modifying the atmosphere between ink-containment vessel  12  and outer protective container  20 , the outer protective container is sealed to maintain the modified atmosphere in the area surrounding the ink-containment vessel. Outer protective container  20  may be sealed in any suitable manner that provides an acceptably low rate of diffusion of air into the outer protective container. For example, a chemical adhesive, such as an epoxy with a low permeability to air, may be used to close outer protective container  20 . In the depicted embodiment, however, outer protective container  20  is made at least partially of a material that can be bonded to itself to form a seal, for example via heat fusion, as described in more detail below. 
     Outer protective container  20  may be configured to cover as much of ink-containment vessel  12  as desired. As mentioned above, ink-containment vessel  12  may have some regions of relatively higher permeability to air than other regions. Therefore, it is generally desirable for outer protective container  20  to cover at least these regions. For example, in the depicted embodiment, degassed ink  14  is mostly surrounded by inner membrane  18 . Inner membrane  18  is typically made of a material that is relatively impermeable to air, such as a film containing a metal or metalized foil. Because inner membrane  18  has a low permeability to air, little air diffuses into degassed ink  14  through the inner membrane, even though a relatively large quantity of air may be present between housing  16  (which is typically made of a lower barrier material such as polyethylene) and the inner membrane. 
     However, as best seen in FIG. 3, inner membrane  18  does have an opening  30  that allows ink to flow out of ink-containment vessel  12 . This opening extends through a first septum  32  in housing  16 . First septum  32  typically is made of an elastomeric or plastic material which may have a higher permeability to air than the metalized foil of inner membrane  18 . Thus, first septum  32  may present a more rapid path for diffusion of air into degassed ink  14  than the other parts of ink-containment vessel  12 . Therefore, it is desirable for outer protective container  20  to cover first septum  32 . Similarly, a second septum  34  may be disposed on housing  16  to allow air to be pumped into the area between housing  16  and inner membrane  18  to force ink out of first septum  32 . Second septum  34  also typically is made of an elastomeric or plastic material which may have a higher permeability to air than the metalized foil of inner membrane  18 . Accordingly, second septum  34  also may present a more rapid path for diffusion of air into degassed ink  14  than the parts of ink-containment vessel  12 . Therefore, it is desirable for outer protective container  20  to cover second septum  34 . 
     More often, ink-containment vessel  12  will be completely within outer protective container  20 , as shown in the depicted embodiment. This is advantageous where housing  16  is made of a relatively permeable material, such as polyethylene, in order to prevent air from diffusing through exposed portions of housing  16  and into the space between ink-containment vessel  12  and outer protective container  20 . On the other hand, if housing  20  is made of a relatively impermeable material, it may be desirable to cover only the portion of ink-containment vessel  12  surrounding first septum  32 , rather than the entire ink-containment vessel. 
     Outer protective container  20  may have any suitable design that presents an adequate diffusion barrier to outside air. For example, a rigid enclosure made of a low permeability plastic may be used. In the depicted embodiment, however, outer protective container  20  takes the form of a flexible bag of a sufficient size to enclose ink-containment vessel  12  fully. This flexible bag may be made of any suitable material. 
     FIG. 4 shows generally, at  40 , an enlarged sectional view of one suitable layered material for use in formation of outer protective container  20 . Layered material  40  includes a bondable layer  41  for sealing protective container  20 , and a barrier layer  42  which has a relatively low permeability to air. 
     An intermediate layer  44  may be positioned between bondable layer  41  and barrier layer  42  to strengthen the adherence between bondable layer  41  and barrier layer  42 . Furthermore, an outer layer  46  may be provided to protect barrier layer  42 , or to allow labeling and/or instructions to be printed directly onto outer protective container  20 . The use of an outer printable layer is particularly advantageous as it allows packaged ink supply  10  to be displayed and sold without the use of an outer box or an instructional insert, and thus may lower the cost of the packaged, degassed ink supply  10 . 
     Intermediate layer  44  and outer layer  46  may be made of any suitable material. An example of a suitable material is a plastic, typically a polyamide or polyester such as polyethylene terephthalate. Each of these layers is generally approximately 8-16 micrometers thick, and more typically about 12 micrometers thick, but either layer may have a thickness outside of this range In one typical embodiment, such as that shown in FIG. 4, intermediate layer  44  is formed of a polyamide, and outer printable layer  46  is formed of a polyester such as polyethylene terephthalate. 
     Bondable layer  41  may be made of any suitable material but typically is made from a material that may be fused to itself with heat. An example of one such material is polyethylene. Bondable layer  41  may also have any desired thickness. It may be advantageous, however, to use a relatively thin bondable layer to decrease the spacing of the barrier layers  42  in seam  48 . This decreases the thickness of the fused layer  50  of seam  48  through which air can diffuse, and thus also decreases the diffusion rate of air through seam  48 . Bondable layer  41  is typically 50-100 micrometers thick, and more typically approximately 75 micrometers thick. The thickness of fused layer  50  may be somewhat less than double the thickness of bondable layer  41 , as some thickness may be lost in the fusion process. Similarly, the seam may be made any width W. The thicker the seam, the lower the diffusion rate of air through the seam. Typically, seam  48  will be from 0.5-2 cm wide, and more typically approximately 0.8 cm wide, though it may also have a width outside of this range. 
     Bondable layer  41  may be made of any suitable material but typically is made from a material that may be fused to itself with heat. An example of one such material is polyethylene. Bondable layer  41  may also have any desired thickness. It may be advantageous, however, to use a relatively thin bondable layer to decrease the spacing of the barrier layers  42  in seam  48 . This decreases the thickness of the fused layer  50  of seam  48  through which air can diffuse, and thus also decreases the diffusion rate of air through seam  48 . Bondable layer  41  is typically 50-100 microns thick, and more typically approximately 75 microns thick. The thickness of fused layer  50  may be somewhat less than double the thickness of bondable layer  41 , as some thickness may be lost in the fusion process. Similarly, the seam may be made any width W. The thicker the seam, the lower the diffusion rate of air through the seam. Typically, seam  48  will be from 0.5-2 cm wide, and more typically approximately 0.8 cm wide, though it may also have a width outside of this range. 
     As with bondable layer  41 , barrier layer  42  may be positioned in any desired layer of outer protective container  20 . In the layered material depicted in FIG. 4, barrier layer  42  is positioned between intermediate layer  44  and outer printable layer  46 . Additionally, barrier layer  42  may be made of any suitable material with desired permeability characteristics. An example of a suitable material is a metal foil, such as aluminum foil. It will be appreciated, however, that high barrier plastics, such as polyvinylidene chloride or ethylene vinyl alcohol, may also be used. The barrier layer also may take the form of a film of aluminum or aluminum oxide deposited on a layer of polyethylene terephthalate. The thickness of barrier layer  42  may be selected to give outer protective container  20  desired diffusion characteristics. 
     Generally, it is desirable for outer protective container  20  to allow less than about 1.5 cm 3 /year of air to diffuse therethrough. Aluminum has a very low permeability to the component gases of air, and thus may be used in a very thin layer. Typically, an aluminum barrier layer  42  will have a thickness of 6-10 micrometers, although a barrier layer with a thickness outside this range may also be used. A thin aluminum barrier layer, however, will accommodate a flexible multilayer outer protective container as described herein. 
     FIG. 6 shows generally at  140  an enlarged sectional view of a second layered material suitable for use as outer protective container  20 . Like layered material  40 , layered material  140  includes a bondable layer  141 , a barrier layer  142 , an intermediate layer  144  and an outer layer  146 . However, barrier layer  142  itself is a multilayer structure formed from a barrier film  150  of a material with suitably low permeability deposited upon a substrate layer  152 . 
     Barrier film  150  typically is formed from a material with a low permeability to air, such as aluminum metal or aluminum oxide. Barrier film  150  may be formed on substrate layer  152  in any desired manner, for example by evaporation or sputtering. Barrier film  150  may also have any desired thickness. Because aluminum metal has a very low permeability to air, it may be used in a very thin layer, typically only a few micrometers thick. Similarly, substrate layer  152  may be any desired material and thickness. An example of a typical substrate layer is a flexible polymeric material, such as polyethylene terephthalate (PET), with a thickness of approximately 6-10 micrometers. 
     A method of packaging an ink supply to maintain a volume of ink in a degassed state is shown generally at  200  in FIG.  7 . As indicated, such method involves providing the protective container with a low permeability to air at  210 , inserting a degassed ink supply into the protective container at  220 , sealing the protective container at  230 , and modifying the interior atmosphere of the protective container to achieve a lower partial pressure of at least one component gas of air relative to the atmosphere outside of the protective container at  240 . Thus a packaged ink supply configured to maintain ink in a degassed state may be achieved. 
     To test the effectiveness of outer protective container herein described, an outer protective container with an 8-micrometer thick aluminum foil barrier layer was constructed to completely enclose a 780 cm 3  ink-containment vessel. An ink-containment vessel with 780 cm 3  of ink can hold approximately 20 cm 3  of air at room temperature when fully saturated. The space between the ink-containment vessel and the outer protective container, which had a volume of approximately 100 cm 3 , was pumped down to approximately 0.5 atmospheres. Under these conditions, the outer protective container was found to pass only about 1 cm 3 /year of air into the space between the ink-containment vessel and the outer protective container. At this diffusion rate, degassed ink contained within the ink-containment vessel will maintain an acceptably low level of air saturation for years. In contrast, the ink may last only a few months in the absence of an outer protective container with a modified atmosphere contained therein. Furthermore, when ready for use, the ink-containment vessel may simply be removed from the outer protective container by tearing, cutting or otherwise rupturing the outer protective container. 
     While the present invention has been particularly shown and described with reference to the foregoing depicted embodiments, those skilled in the art will understand that many variations may be made therein without departing from the spirit and scope of the invention as defined in the following claims. The description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application. Where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.