Production of stable aqueous silica sol.

摘要

A sol of flat silica particles (100-1000 nm in size) is produced by the following steps (a) to (d) from an acidic aqueous sol (S0) of negatively charged silica particles (7-30 nm in diameter) and an aqueous solution (B) of basic aluminum or zirconium salt. (a) mixing 100 parts by weight (as SiO2) of the sol (S0) with 0.2-10 parts by weight (as Al2O3 or ZrO2) of the aqueous solution (B), and adjusting the resulting sol to pH 4-7, thereby yielding a sol (S1), (b) mixing 100 parts by weight (as SiO2) of the sol (S1) with 20-200 parts by weight (as SiO2) of the sol (S0), and adjusting the resulting sol to pH 4-7, thereby yielding a sol (S2), (c) mixing 100 parts by weight (as SiO2) of the sol (S2) with the aqueous solution (B) in an amount corresponding to 2-50% of the amount (as Al2O3 or ZrO2 in parts by weight) added to 100 parts by weight (as SiO2) of the sol (S0) used in step (a), and adjusting the resulting sol to pH 4-7, thereby yielding a sol (S3), and (d) mixing 100 parts by weight (as SiO2) of the sol (S3) with the sol (S0) in an amount corresponding to 10-95% of the amount (as SiO2 in parts by weight) added to 100 parts by weight (as SiO2) of the sol (S1) in step (b), and adjusting the resulting sol to pH 4-7, thereby yielding a sol (S4).