SILICA-BASED SOLS AND THEIR PRODUCTION AND USE

摘要

The invention relates to a process for producing an aqueous silica-based sol which comprises: (a) providing a cationic ion exchange resin having at least part of its ion exchange capacity in hydrogen form; (b) bringing said ion exchange resin in contact with an aqueous alkali metal silicate to form an aqueous slurry; (c) stirring said aqueous slurry until the pH of the aqueous phase is in the range of from 5.0 to 8.0; (d) adjusting the pH of said aqueous phase to above 9.0; and (e) separating said ion exchange resin from the aqueous phase after step (c) or after step (d). The invention also relates to an aqueous silica-based sol obtainable by the processes as well as a process for producing paper which comprises (i) providing an aqueous suspension comprising cellulosic fibres; (j) adding to the suspension one or more drainage and retention aids comprising an aqueous silica-based sol according to the invention; and (k) dewatering the obtained suspension to provide a sheet or web of paper.