Developer supply device and image forming apparatus comprising same

A developer system comprising:

• a partially or wholly deformable developer container removably installed in a developer supply device which holds a developer comprising a toner and a carrier, the developer supply device including a pump that suctions the developer held in the developer container, together with a gas, and that discharges the developer towards a developing unit,
• wherein, the toner comprises an additive which has a volume average particle size of 50 to 500 nm,
• the toner has a weight average particle size of 3 to 8 μm, and satisfies a relationship:
• 1.0≦D4/D1≦1.4,
• where D4 is the weight average particle size of the toner and D1 is the number average particle size of the toner,
• the carrier has a weight average particle size of 20 to 60 μm,
• the developer has a carrier concentration of 1 to 30 wt %, and
• an air layer occupies at least 12% of a capacity of the developer container.

A developer comprising:

• a toner;
• and
• a carrier, the developer being held in a developer container,
• wherein the developer container is partially or wholly deformable,
• the toner includes an additive which has a volume average particle size of 50 to 500 nm,
• the toner has a weight average particle size of 3 to 8 μm, and satisfies a relationship:
• 1.0≦D4/D1≦1.4,
• where D4 is the weight average particle size of the toner and D1 is the number average particle size of the toner,
• the carrier has a weight average particle size of 20 to 60 μm,
• the developer has a carrier concentration of 1 to 30 wt %, and
• an air layer occupies at least 12% of a capacity of the developer container.