Patent ID: 7083888

Claim:
An external additive for electrostatically charged image developing toner, comprising spherical hydrophobic fine silica particles having primary particles with a particle diameter of from 0.01 to 5 μm and having been treated with a compound selected from the group consisting of a quaternary ammonium salt compound, a fluoroalkyl-group- containing betaine compound, and a fluoroalkenyl-group- containing betaine compound, said fine silica particles fulfilling the following conditions (i) and (ii): (i) When an organic compound which is liquid at room temperature and has a dielectric constant of from 1 to 40 F/m and fine silica particles are mixed in a weight ratio of 5:1 and shaken, the fine silica particles disperse uniformly in the organic compound; and (ii) The quantity of primary particles remaining as primary particles when methanol is evaporated under heating by means of an evaporator from a dispersion prepared by dispersing the fine silica particles in methanol and thereafter the particles are held at a temperature of 100° C. for 2 hours, represents at least 20% of the quantity of primary particles originally present, wherein said hydrophobic fine silica particles have been obtained by the step (A) of introducing an R 2 SiO 3/2 unit (wherein R 2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) onto the surfaces of hydrophilic fine silica particles comprising an SiO 2 unit to obtain first hydrophobic fine silica particles; and the step (B) of introducing an R 1 3 SiO 1/2 unit (wherein R 1 's may be the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms) onto the surfaces of the first hydrophobic fine silica particles.