US Patent 7745087 Electrostatic image developer, process cartridge, and image forming apparatus

An electrostatic image developer contains a toner and a carrier having a resin coating layer formed on the surface of a core material containing a ferrite component, wherein a ratio R1/R2 is from 0.88 to 0.92 where R1 is the resistance value (Ω) of the developer having a toner concentration of 2 mass % in a state formed into a magnetic brush, at an applied voltage of 104 V/cm, and R2 is the resistance value (Ω) of the developer having a toner concentration of 12 mass % in a state formed into a magnetic brush, at an applied voltage of 104 V/cm.