BLACK MAGNETIC IRON OXIDE PARTICLES FOR MAGNETIC TONER AND PROCESS FOR PRODUCING THE SAME

摘要

Black magnetic iron oxide particles of the present invention having an average particle diameter of 0.1 to 0.3 .mu.m, comprise: black spinel iron oxide particles as core particles; and a surface coat formed on the surface of each core particle, comprising fine spinel iron oxide particles, the content of Fe0 in a surface layer having a thickness of from a surface of each black magnetic iron oxide particle to about 3.5 % per a radius of each black magnetic iron oxide particle, being 8 to 14 % by weight based on the weight of Fe contained in said surface layer. Such black magnetic iron oxide particles not only have a sufficient blackness and excellent electrical properties, flowability and electrification property (charging property), but also exhibit a good compatibility with binder resins such as aromatic vinyl-based resins, acrylic-based resins and copolymer resins thereof, and a good dispersibility in these resins for a magnetic toner.