SURFACE-MODIFIED SPHERICAL SILICA POWDER AND METHOD FOR PRODUCING THE SAME

PROBLEM TO BE SOLVED: To provide a highly hydrophobic spherical silica powder which ensures a very small increase in the moisture content even at high temperature and high humidity.SOLUTION: The spherical silica powder has a hydrophobicity degree distribution in which a hydrophobicity degree A at the time when 100 mass% of the spherical silica powder settles in a methanol titration method and a hydrophobicity degree B at the time when 5 mass% of the spherical silica powder settles satisfy the formula (1), 65%≤A, and the formula (2), A-B≤15%, and under test conditions of high temperature and high humidity (50°C and 70%), an increasing amount of the moisture content of the spherical silica powder before the test and after 24 hours is ≤0.02 mass%. In a method for producing the spherical silica powder, a space factor in a reaction vessel is confined to 0.85-0.99, water and a surface modifier are sprayed on a raw material silica powder having a moisture content of ≤0.20 mass%, and the raw material spherical silica powder is surface-modified while being suspended in gas.