| abstract |
The invention relates to an aqueous sol containing silica-based particles which has an S-value within the range of from 10 to 45 %, a viscosity within the range of from 5 to 40 cP, and a molar ratio of SiO2 to M2O, where M is alkali metal or ammonium, within the range of from 10:1 to 40:1, or a silica content of at least 10 % by weight. The invention further relates to a process for the production of silica-based particles comprising the steps of: (a) acidifying an aqueous silicate solution to a pH of from 1 to 4 to form an acid sol; (b) alkalising the acid sol at an SiO2 content within the range of from 4.5 to 8 % by weight to; (c) allowing particle growth of the alkalised sol for at least 10 minutes, or heat-treating the alkalised sol at a temperature of at least 30 °C; and then (d) alkalising the obtained sol to a pH of at least 10.0. The invention further relates to silica-based particles obtainable by the process, the use of the silica-based particles as drainage and retention aids in the production of paper as well as a process for the production of paper from an aqueous suspension containing cellulosic fibres, and optional filler, in which silica-based particles and at least one charged organic polymer are added to the cellulosic suspension. |