1. Field of the Invention
The present invention relates to an ink tank, and specifically to a structure that prevents ink leakage from an ink tank used in an ink jet printing apparatus that ejects ink for printing. The ink tank according to the present invention can be used not only in common printers but also in apparatuses such as copy machines, facsimile machines with communication systems, and word processors with printing sections, as well as industrial printing apparatuses combined with various processing apparatuses.
2. Related Art of the Invention
Ink jet printing apparatuses are based on what is called non-impact printing scheme and have various advantages: the ink jet printing apparatus can achieve high-speed printing, print various print media, and reduce possible noise during printing. Thus, the ink jet printing apparatus is commonly used to make up a printing mechanism for printers, word processors, facsimile machines, copiers, and the like.
In the ink jet printing apparatuses, an ink tank in which ink to be supplied to a print head for ink ejection is stored is in many cases removably used. Specifically, for example, when the stored ink is consumed and exhausted, the ink tank is replaced with another. Thus, the ink tank is of a cartridge type and is often independently distributed and handled as a commercial product.
A conventional ink tank of such cartridge type may present a problem that ink leakage occurs. Various measures against the problem have been provided. In one aspect of the ink leakage, ink may leak through an air communication hole formed, for example, for adjustment of negative pressure in the ink tank. For example, if the posture of the ink tank during physical distribution is such that a surface of the ink tank in which the air communication hole is formed is located below, the ink is likely to leak through the air communication hole depending on the relationship between a change in pressure in the tank and the atmospheric pressure at the time. Furthermore, if the ink tank is subjected to a relatively great impact during handling, a similar pressure change occurs to make the ink likely to leak.
Japanese Patent Laid-Open No. Hei 1-93365 (1989) describes a structure that prevents the ink leakage. Japanese Patent Laid-Open No. Hei 1-93365 (1989) describes an ink tank housing an absorber to hold the ink, being provided with a truncated cone-like projecting portion located on a back surface of a cover member making up a tank case and away from the absorber, and having a hole passing through the projecting portion to be an air communication hole. A groove is formed along a root portion of the projecting portion so that the ink leaking from the absorbing member is trapped by the capillary force of the groove, to limit a movement of the ink to the through-hole in the projecting portion.
Japanese Patent Laid-Open No. 2006-150679 describes another structure that prevents the ink leakage. Japanese Patent Laid-Open No. 2006-150679 describes an ink tank including no projecting portion projecting into the tank as in Japanese Patent Laid-Open No. Hei 1-93365 but a hole formed directly in the cover member of the ink tank and serving as an air communication hole. A groove is formed at a given distance from the air communication hole so as to surround the communication hole so that the ink is trapped by the capillary force of the groove. Japanese Patent Laid-Open No. 2006-150679 also describes that the groove is extended to a position where the groove contacts the absorber so that the trapped ink is finally returned to the absorber.
However, when, for example, the ink tank in Japanese Patent Laid-Open No. Hei 1-93365 (1989) is subjected to relatively intense vibration, the ink trapped in the groove around the projecting portion may fly off and enter the air communication hole.
FIGS. 1A to 1C are views illustrating this problem. The figures show vertical sectional views of the ink tank. Specifically, FIG. 1A shows a part of the ink tank in which a print element board 1500 making up a print head is integrally attached to a tank case 1400. An absorber 1700 is housed in the tank case 1400. The ink held by the absorber 1700 is supplied to the print element board 1500 via an ink channel 1401 as an ejection operation or the like is performed. In FIG. 1A, a cover member 1800 makes up the tank case below the absorber 1700. The cover member 1800 includes a truncated conical projecting portion 1817 and a rib 1809. The rib 1809 contacts the absorber 1700 to form a space 1402 between the truncated conical projecting portion 1817 and the absorber 1700. As described in Japanese Patent Laid-Open No. Hei 1-93365, a groove 1813 is formed along the root portion of the truncated conical projecting portion 1817, forming an air communication hole 1801, that is, the groove 1813 is formed at a position not away from the projecting portion 1817.
However, in the case that the groove 1813 is not formed away from the truncated conical projecting portion 1817, the ink trapped in the groove 1813 may fly off and enter the air communication hole 1801. For example, variation in environmental temperature or the like may change the pressure in the ink tank to cause the ink to leak and flow from the absorber 1700 toward the cover member 1800. As shown in FIG. 1B, the flowing ink is trapped in the groove 1813 and can thus be prevented from reaching the air communication hole. However, if a relatively great impact is made on the ink tank, for example, the tank falls down, the ink trapped in the groove 1813 may disperse as shown in FIG. 1C. The ink 1819 may then enter the air communication hole 1801. Upon entering the air communication hole, the ink leaks from an air communication passage outlet through an air communication path formed in a surface of the cover member.
On the other hand, according to Japanese Patent Laid-Open No. 2006-150679, the air communication hole is not formed in the projecting portion. Consequently, the leaking ink basically travels through the member forming the air communication hole and readily enters the air communication hole. Thus, in Japanese Patent Laid-Open No. 2006-150679, the groove is formed at the given distance from the air communication hole to trap the ink.
However, the ink entering the area surrounded by the groove can no longer be trapped and is likely to enter the air communication hole.