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.
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 xe2x80x9cInk Supply With Air Diffusion Barrier for Unsaturated Ink,xe2x80x9d 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.
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.