BINARY SYSTEM DEVELOPER

摘要

PURPOSE: To provide a developer which contains specific toner and carrier, has good chargeability without charge control agent, scatters less toner, and excels in the quality of image. CONSTITUTION: A binary system developer contains toner and carrier. A toner particle contains a resin for fixing, magnetic powder dispersed in the resin, and a mold releasing agent. The resin for fixing contains a resin having an anion polar group. The magnetic powder is contained at a ratio of 0.1-5 weight parts for 100 weight parts of the resin for fixing. The mold releasing agent contains polypropylene having the average molecular weight of 7000 or more, and the polypropylene is contained at a ratio of 0.1-6 weight parts for 100 weight parts of the resin for fixing. A particle of carrier has a core particle and a covering layer. The core particle is composed of a magnetic material expressed by a formula MOFe2 O3 (M is a metal such as Cu, Zn.). The covering layer contains alkylated melamine resin and acryl denatured silicone resin. The average molecular weight M of the alkylated melamine resin is expressed by an expression of M>=1100C-400, wherein C is the number of carbons in an alkyl group.