Patent ID: 7241505

Claim:
Hybrid sol comprising: [SiO x (OH) y ] n particles, where 0<y<4 and 0<x<2, which consist of a mixture of a first fraction of particles having a particle size of 4–15 nm and a second fraction of particles having a mean particle size of 20–60 nm where the weight ratio between the first fraction and the second fraction is from 10:1 to 2:1, water and a solvent, wherein the sol is obtained by a process comprising: hydrolytic polycondensation of tetraalkoxysilanes in an aqueous, solvent-containing medium by addition of the tetraalkoxysilanes to the aqueous, solvent-containing medium, resulting in a hydrolysis mixture comprising silicon oxide hydroxide particles having a particle size of 4–15 nm, followed by addition to the hydrolysis mixture of a monodisperse silicon oxide hydroxide sol essentially in the form of discrete particles having a mean particle size of 20–60 nm and a maximum standard deviation of 20%, said addition being at least 5 minutes after addition of the tetraalkoxysilanes to the aqueous, solvent-containing medium.