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External additive for toner for electrophotography, toner for electrophotography, double-component developer for electrophotography, image forming process using the toner, and image-forming apparatus using the toner
External additive for toner for electrophotography, toner for electrophotography, double-component developer for electrophotography, image forming process using the toner, and image-forming apparatus using the toner
An external additive for a toner for electrophotography which contains oxide fine particles which contain silicon, in which the oxide fine particles have a primary particle diameter of 30nm to 300nm in number average, a standard deviation σ of a particle size distribution of the primary particle diameter satisfies a relation of: R/4 ≤ σ ≤ R, in which the R expresses the primary particle diameter,the oxide fine particles are substantially spherical having a circularity SF1 defined as equation (1) of 100 to 130 and a circularity SF2 defined as equation (2) of 100 to 125; ]]> ]]> in the equations, "L" expresses the absolute maximum length of the oxide fine particles; "A" expresses a projected area of the oxide fine particles; and "P" expresses a maximum perimeter of the oxide fine particles.
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