Patent ID: 7559636

Claim:
An ink tank comprising: an ink accommodation portion; an ink supply port; and a valve unit installed in an ink path between said ink accommodation portion and said ink supply port, wherein, when a negative pressure in said ink supply port exceeds a predetermined level, said valve unit opens the ink path temporarily to introduce ink from said ink accommodation portion to said ink supply port, wherein said valve unit has a valve member formed of an elastic material and a valve case accommodating the valve member, the valve member having a cylindrical portion and an opening formed at a free end of the cylindrical portion, the cylindrical portion being formed to increase in diameter toward the free end, and wherein the free end of the cylindrical portion is pressed against a surface of the valve case to close the ink path, and an angle formed by an inner surface of the free end of the cylindrical portion and the surface of the valve case with which the valve member engages is an acute angle so that the free end of the cylindrical portion is forced to expand in diameter when the cylindrical portion is pressed against the surface of the valve case.