Hydrophobic silica powder, process for preparing the same and toner composition for electrophotographic containing the same

The invention relates to a hydrophobic silica powder which is unprecedentedly insensitive to environmental humidity with which electrophotographic toner can possess stable electro static charge that leads to stable quality of printed image. The hydrophobic silica powder has the following physicochemical properties; - average primary particle size (D) is 30 - 2000 nm, - B * D < 430 nm, whilst B stands for weight % of adsorbed water vapor on silica (100 weight %) when the partial pressure of water to the equilibrium vapor pressure of water at 25°C is 80 % and D stands for average primary particle size (nm) of the silica powder, - B / C < 2.7, whilst C stands for weight % of adsorbed water vapor on silica (100 weight %) when the partial pressure of water to the equilibrium vapor pressure of water at 25°C is 20 %, and - carbon content > 0.30 wt.-%.