Ink cartridge, ink cartridge manufacturing method, and printing apparatus

An ink cartridge comprising:

• an ink pack unit having a bag member and a rib member, the bag member housing ink and shrinking in volume housing the ink as a remaining amount of the ink decreases, the rib member having a flat plate shape and being fixed to the bag member so as to move along with shrinkage of the bag member;
• a head unit coupled to the ink pack unit and connected to a printing apparatus;
• and
• a case unit that houses the ink pack unit and the head unit such that a part of the head unit is exposed,
• wherein the ink pack unit has a surface fixed to an inner surface of the case unit, the surface being opposite to a portion to which the rib member is fixed of the bag member,
• the case unit has a through hole penetrating inside and outside,
• the rib member has a projection provided so as to protrude outside from the through hole when the remaining amount of the ink becomes smaller than a predetermined value,
• the rib member and the head unit are formed using a first material having a predetermined bending strength to prevent deformation of the rib member and the head unit when connected to the printing apparatus, and
• the case unit is formed using a second material different from the first material.