External additive for electrostatically charged image developing toner

Abstract

An external additive for electrostatically charged image developing toner is provided. The additive includes 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 silicone oil. The fine silica particles fulfill 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. The external additive does not react or has no interaction with an organic photoreceptor and therefore change in quality does not occur or the photoreceptor is not scraped. Furthermore, it has a good flowability and therefore adhesion of a toner to the photoreceptor does not occur.

Dependencies are inferred from the claim text.