Patent ID: 7687214

Claim:
A two-component developer comprising toner particles and carrier particles, wherein: the mixing ratio of the toner particles to the carrier particles is between 1:99 and 15:85 in ratio by weight; the toner particles contain at least a binding resin and a carbon black pigment, a charge control agent and external additives; wherein the external additives contain silica fine powders and do not contain fine powders of titanium oxide; a mean volume particle diameter of the toner particles is between 5.5 μm and 7 μm; a number percent of the toner particles with a mean volume particle diameter of 5 μm or below, with respect to the total toner particles, is in the range up to the limit represented by a numerical expression (1); a volume percent of the toner particles with a mean volume particle diameter between 8 μm and 12.7 μm, with respect to the total toner particles is in the range between an upper limit represented by a numerical expression (2) and a lower limit represented by a numerical expression (3); density of the carbon black pigments in the toner particles is between 8 weight percent and 20 weight percent; carrier particles are resin coated carrier particles; a mean volume particle diameter of the carrier particles is between 35 μm and 65 μm; and y=− 15 x+ 136 (1), n= 15 m− 75 (2), and n= 7 m− 37 (3), in which x represents a mean volume particle diameter; y represents a number percent of toner particles with a mean volume particle diameter of 5 μm or below; m represents a mean volume particle diameter; and n represents a volume percent of toner particles with a mean volume particle diameter between 8 μm and 12.7 μm, respectively, the toner particles consist of first toner particles and second toner particles, wherein said first toner particles and said second toner particles are of different mean volume particle diameters so that a condition a>b is satisfied; in which: a % is the ratio of said first and second toner particles with the smaller mean volume particle diameter and b % is the ratio of the other of said first and second toner particles with the greater mean volume particle diameter, with respect to the toner particles, respectively.