Method for manufacturing surface-treated gas-phase-process silica particle, surface-treated gas-phase-process silica particle, and toner external additive for electrostatic charge image development

A method for manufacturing a surface-treated gas-phase-process silica particle, the method comprising steps of:

• (A1):
• adding 1,3-divinyl-1,1,3,3-tetramethyldisilazane to a raw material gas-phase-process silica particle and introducing a vinyldimethylsilyl group on a surface of the raw material gas-phase-process silica particle to obtain a preliminarily treated silica particle;
• and
• (A2):
• adding hexamethyldisilazane to the preliminarily treated silica particle and introducing a trimethylsilyl group on a surface of the preliminarily treated silica particle to obtain a surface-treated gas-phase-process silica particle.

A surface-treated gas-phase-process silica particle, comprising a gas-phase-process silica particle having a surface treated with 1,3-divinyl-1,1,3,3-tetramethyldisilazane and hexamethyldisilazane, wherein

• a BET specific surface area of the surface-treated gas-phase-process silica particle is 30 m2/g or more and less than 400 m2/g,
• a proportion of particles with 1.5 μm or more in the surface-treated gas-phase-process silica particle is less than 10%, the proportion being determined from a particle size distribution on a volumetric basis by a laser diffraction method,
• a hydrophobicity degree with methanol of the surface-treated gas-phase-process silica particle is 68% or more and 78% or less, and
• when 1 part by mass of the surface-treated gas-phase-process silica particle and 100 parts by mass of a polyester resin particle having a volumetric median diameter of 5 to 8 μm are mixed to form a mixture, an aggregation degree of the mixture is to be 20% or less.