FERRITE CARRIER CORE MATERIAL FOR ELECTROPHOTOGRAPHIC DEVELOPER, FERRITE CARRIER AND PRODUCTION METHODS OF THE SAME, AND ELECTROPHOTOGRAPHIC DEVELOPER USING THE FERRITE CARRIER

摘要

PROBLEM TO BE SOLVED: To provide a ferrite carrier core material for an electrophotographic developer which has an approximately spherical particle shape but has a larger BET specific surface area compared with conventional core particles because of the presence of minute projections and recesses on the surface in spite of having a small particle diameter, and which has an excellent charging property and a long life while preventing carrier scattering from being caused by cracking or chipping of the core material, a ferrite carrier, production methods of the core material and the ferrite carrier, and an electrophotographic developer using the ferrite carrier.SOLUTION: The ferrite carrier core material for an electrophotographic developer, the ferrite carrier and the methods for producing the core material and the ferrite carrier have the following characteristics. The ferrite carrier core material has (1) a ferrite composition containing Sr by 0.5 to 2.5 wt.%, in which the amount of Sr-Fe oxides present therein satisfies a given conditional formula; (2) number distribution of a shape factor SF-2 within a given range; (3) a BET specific surface area of 0.15 to 0.30 m/g; (4) an average particle diameter Dof 20 to 35 m; and (5) magnetization of 50 to 65 Am/kg. An electrophotographic developer using the above ferrite carrier is employed.