Patent ID: 9376322
Filing Date: 2016-06-28
CPC Classification: B82Y,C01B,C01P,C08K

Claim Text:
1. A process for producing colloidal silica particles, the process comprising (I) and (II): (I): adding an acid to a silica sol including colloidal silica particles so that the silica sol has a pH of 0 to 2.0, the colloidal silica particles including at least one polyvalent metal element M selected from a group consisting of iron, aluminum, zinc, zirconium, titanium, tin, and lead in an average content of 0.001 to 0.02 in terms of an M/Si molar ratio, and having an average primary particle diameter of 5 to 40 nm; and aging the sol at 0 to 40° C. for 0.5 to 100 hours; and (II): contacting the acidic silica sol obtained in (I) with a strongly acidic cation-exchange resin in the hydrogen form at a pH of 0 to 2.0, and further contacting the sol with a strongly basic anion-exchange resin in the hydroxy form, wherein the content of the polyvalent metal element M present in an outermost layer of the colloidal silica particles is 0 to 0.003 atom per square nanometer (nm