US Patent 7086722 Ink cartridge

An ink cartridge includes an ink pack 21 which discharges ink from an ink outlet 22 upon reception of pressure by air pressure; an outer case 20a, 20b which houses the ink pack 21 therein with the ink outlet 22 exposed so that the ink pack 21 can be pressurized by the air pressure, and includes a pressurized air inlet 23 that is connectable to an air source for pressurizing the ink pack 21; and a pressure adjusting unit 30 which is housed in the outer case and discharges air in the outer case to the outside so that pressure in space of the outer case is kept at a setting value.