Process for producing hydrophobized silicon oxide-coated metal oxide particles comprising primary and secondary hydrophobizing steps

A process for producing hydrophobized silicon oxide-coated metal oxide particles, which comprises:

• (a) adding a silicon oxide precursor to a dispersion of metal oxide particles to form a silicon oxide film on the surface of metal oxide particles thereby to obtain a dispersion of silicon oxide-coated metal oxide particles,
• (b) adding a compound represented by the following formula (1) or (2) and a silicon oxide precursor to the above dispersion of silicon oxide-coated metal oxide particles thereby to obtain a dispersion of primarily hydrophobized silicon oxide-coated metal oxide particles,
• R14-nSi(OR2)n (1)
• R33Si—NH—SiR33 (2)
• in the above formulae (1) and (2), R1 is a C1-9 alkyl group, each of R2 and R3 which are independent of each other, is an alkyl group, and n is an integer of from 1to 3,
• (c) adding a silanol-protective agent to the above dispersion of primarily hydrophobized silicon oxide-coated metal oxide particles thereby to obtain a dispersion of secondarily hydrophobized silicon oxide-coated metal oxide particles, and
• (d) drying the above secondarily hydrophobized silicon oxide-coated metal oxide particles thereby to obtain the hydrophobized silicon oxide-coated metal oxide particles.