Toner cartridge, image forming apparatus and image forming method

A toner cartridge comprising a container body having a toner containing space for containing a toner, and a screw conveyer section provided in the toner containing space of the container body, for conveying the toner toward a toner discharge part for discharging the toner,

• the screw conveyor section facing the toner discharge part,
• the screw conveyer section comprising a rotation shaft having a rotation axis in parallel with a conveying direction of a toner, and a spiral toner conveying blade provided on the rotation shaft,
• the rotation shaft including a first rotation shaft portion, and a second rotation shaft portion concentrically continuing from the first rotation shaft portion and having a diameter smaller than that of the first rotation shaft portion,
• the first rotation shaft portion being provided only at a position facing the toner discharge part,
• the toner conveying blade including a first blade portion formed on the first rotation shaft portion, and a second blade portion formed on the second rotation shaft portion, a pitch of the second blade portion winding around the second rotation shaft portion of the rotation shaft being smaller than a pitch of the first blade portion winding around the first rotation shaft portion of the rotation shaft,
• an effective screw cross-sectional area S1 of the first rotation shaft portion in the screw conveyor section being represented by the following expression (1),
• S
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• =
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• R
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• an effective screw cross-sectional area S2 of the second rotation shaft portion in the screw conveyor section being represented by the following expression (2),
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• 2
• =
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• R
• 2
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• S1, S2, P1 and P2 satisfying the following expression (3),
• P1×S1=P2×S2 (3),
• wherein R denotes an outer diameter of the screw conveyor section, r1 denotes a shaft diameter of the first rotation shaft portion, r2 denotes a shaft diameter of the second rotation shaft portion, P1 denotes the pitch of the first blade portion and P2 denotes the pitch of the second blade portion.