Patent ID: 6447968
Filing Date: 2002-09-10
Classification: G03G

Abstract:
A magnetic toner for developing an electrostatic latent image, comprising magnetic toner particles containing at least a binder resin, a magnetic powder, a wax component and a negative charge control agent, wherein(a) said magnetic powder has magnetic iron oxide particles, 1) the particle surfaces of the magnetic iron oxide particles have been coat-treated with an organic surface modifying agent; said organic surface modifying agent being selected from the group consisting of (i) a silane coupling agent having an alkyl group having 4-16 carbon atoms bonded to a silicon atom and (ii) a titanate compound; 2) the magnetic iron oxide particles before conducting the coat-treated step 1) contain silicon element (Si) in an amount from 0.4 to 2.0% by weight based on the weight of iron element (Fe); 3) the magnetic iron oxide particles before conducting the coat-treated step 1) have an Fe/Si atomic ratio from 1.0 to 4.0 at their outermost surfaces; 4) the magnetic iron oxide particles have a uniform coverage by the organic surface modifying agent of 95% by weight or more; (b) the magnetic toner particles have been produced by suspension polymerization in which a polymerizable monomer composition comprising a polymerizable monomer and the magnetic powder have been dispersed in an aqueous medium to form particles of the polymerizable monomer composition; and the polymerizable monomer in the particles has been polymerized to form magnetic toner particles; (c) the magnetic iron oxide particles are encapsulated by the binder resin in each of the magnetic toner particles; and (d) the magnetic toner particles have shape factors SF-1 and SF-2 as measured by an image analyzer, with a value of SF-1 from 100 to 160, a value of SF-2 from 100 to 140 and a value of (SF-2)/(SF-1) of not more than 1.0.