Patent ID: 6264907
Filing Date: 2001-07-24
Classification: C01B,C01P,D21H

Abstract:
A process for producing secondary silica particles consisting of aggregated primary silica particles, comprising the steps of:(1) mixing an aqueous alkali silicate solution with first particles difficultly soluble in an alkali and soluble in an acid, so as to form a first slurry containing said first particles, said first particles having an average particle diameter of 0.01 to 10 .mu.m and being present in an amount of 5 to 120% by weight based on the solid (in terms of silica) in said aqueous alkali silicate solution;(2) neutralizing said first slurry with a mineral acid to prepare a second slurry containing second particles wherein silica is deposited on said first particles as a silica layer of secondary particles comprising aggregated primary silica particles; and(3) adding a mineral acid to said second slurry to dissolve said first particles and form a third slurry containing silica particles having a cumulative volume of 4.0 to 6.0 cc/g for pores having a diameter of 10.sup.5 .ANG. or less, that of at least 2.6 cc/g for pores having a diameter of 6,000 to 8.times.10.sup.4 .ANG. and that of at least 1.0 cc/g for pores having a diameter of 200 to 2,000 .ANG.; an oil absorption of 300 to 500 ml/100 g; and an average particle diameter of 5 to 30 .mu.m.