| abstract |
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 (S 0 ) of negatively charged silica particles (7-30 nm in diameter) and an aqueous solution (B) of basic aluminum or zirconium salt. n (a) mixing 100 parts by weight (as SiO 2 ) of the sol (S 0 ) with 0.2-10 parts by weight (as Al 2 O 3 or ZrO 2 ) of the aqueous solution (B), and adjusting the resulting sol to pH 4-7, thereby yielding a sol (S 1 ), n (b) mixing 100 parts by weight (as SiO 2 ) of the sol (S 1 ) with 20-200 parts by weight (as SiO 2 ) of the sol (S 0 ), and adjusting the resulting sol to pH 4-7, thereby yielding a sol (S 2 ), n (c) mixing 100 parts by weight (as SiO 2 ) of the sol (S 2 ) with the aqueous solution (B) in an amount corresponding to 2-50% of the amount (as Al 2 O 3 or ZrO 2 in parts by weight) added to 100 parts by weight (as SiO 2 ) of the sol (S 0 ) used in step (a), and adjusting the resulting sol to pH 4-7, thereby yielding a sol (S 3 ), and n (d) mixing 100 parts by weight (as SiO 2 ) of the sol (S 3 ) with the sol (S 0 ) in an amount corresponding to 10-95% of the amount (as SiO 2 in parts by weight) added to 100 parts by weight (as SiO 2 ) of the sol (S 1 ) in step (b), and adjusting the resulting sol to pH 4-7, thereby yielding a sol (S 4 ). |