Patent ID: 8889328

Claim:
A developer cartridge containing developer suitable to develop an electrostatic latent image when the developer is dispensed from the cartridge to a development carrier of a development device, the developer satisfying the requirements of 0.85≦Q60/Q600 and 10≦Q600≦20, where Q60 (−μC/g) represents a charge amount of the developer when a sample made by adding the developer to a carrier in the form of spheres of a Cu—Zn base which has a saturation magnetization of 60 to 70 Am 2 /kg such that the concentration of the developer is 5% by weight is shaken for 60 seconds, and Q600 (−μC/g) represents a charge amount of the developer when shaken for 600 seconds under the same conditions; wherein the developer comprises a developer base particle and hydrophobic silica as external additive particles attached to the surface of the developer base particle, the developer base particle comprises 100 plus or minus 10% parts by weight of an amorphous polyester resin, 0.41 to 0.91 parts by weight of a metal complex of salicylic acid, 0.75 to 2.25 parts by weight of a polyester resin having a quaternary ammonium salt, and the developer fluidity is 80% or more, wherein the fluidity is the average value of G=(X/2+3Y/10+Z/10)×100, where X represents the weight of the developer on a sieve with openings of 150 μm, Y represents the weight of the developer on a sieve with openings of 75 μm, and Z represents the weight of the developer on a sieve with openings of 45 μm, when the three sieves each with openings of 45 μm, 75 μm, 150 μm are stacked in this order, and 2 g of the developer is placed on the sieve with openings of 150 μm as a top sieve, followed by vibration at an amplitude of 0.8 mm for 95 seconds.