Electrographic developing material and developing method employing said developing material

Claim 1

A developing method for use in repetitive electrophotography which comprises the steps of: (1) stirring a developing material which comprises: (a) electrically insulative toner particles comprising colorant and resin and having a volume resistance of above 10 14 Ω.cm, an average particle diameter of 2 to 30 μm, (b) carrier particles comprising magnetizable particles of average particle diameter of less than 3 μm and a bonding material, said carrier particles having a volume resistance higher than 10 12 Ω.cm and an average particle diameter of 5 to 40 μm, and (c) electrically insulative fine particles composed of metallic oxide and having an average particle diameter of less than 0.1 μm, whereby components (a), (b) and (c) contact each other and whereby said carrier particles are triboelectrically charged to a polarity opposite that of said electrically insulative toner particles through frictional contact therewith, said electrically insulative fine particles are triboelectrically charged to a polarity opposite that of the electrically insulative toner particles through frictional contact therewith and wherein said fine particles are not triboelectrically charged upon frictional contact with said carrier particles, to thereby produce a triboelectrically charged developing material in which said carrier particles and said electrically insulative fine particles are charged to the same polarity, which polarity is opposite that of said electrically insulative toner particles, (2) developing electrostatic latent images into visible images with said electrically insulative toner particles and said electrically insulative fine particles contained in said developing material by: (a) forming a magnetic brush with said developing material, (b) bringing said magnetic brush into sliding contact with said electrostatic latent images, and (3) repeating said developing step while replenishing said developing material which has been consumed, with a replenishing developing material composed of said electrically insulative toner particles and said electrically insulative fine particles.