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

摘要

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;$\[ {\text{SF1 = (L}}^{\text{2}}\text{/A) ×(π/4) × 100} \]$$\[ {\text{SF2 = (P}}^{\text{2}}\text{/A) × (1/4π) × 100} \]$ 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.