Conductivity Mechanism in Magnetic Brush Developer

Magnetic brush developers, which are a mixture of iron spheres (carriers) and insulator powder (toners), are widely used in the developing process of electrophotographic copying machines. The developer conductivity has a great influence upon copy quality. The electric field dependences of their conductivities are measured under various magnetic fields and toner concentration conditions. It is found that conductivity σ increases abruptly when magnetic field H is applied as: σ∝Hn (n=5-6) and that conduction current I increases abruptly when electric field E is applied as: ln (I)∝E1/2. The conduction mechanism is concluded to be controlled by the Schottky emission from the carrier and by the contact probability between the carriers.