Appeal No. 95-2237
Application 08/067,308
to 12.5 is established in the reactors thus
charged,
c) the average residence times in the stages of
the reaction cascade charged with acidic fresh
sol are adjusted in such a manner that an
average particle size of 27-72 nm is obtained in
the last reactor of the cascade.
The examiner relies upon the following references as
evidence of obviousness:
Weldes et al. (Weldes) 3,440,175 Apr. 22, 1969
Leutner et al. (Leutner) 4,336,234 Jun. 22, 1982
Appellants' claimed invention is directed to a continuous
process for the production of aqueous alkaline silica sols
with SiO particles having an average diameter of 27-72 nm.
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The process entails preparing an acidic fresh sol having SiO2
particles with an average diameter of about 2nm by mixing an
alkali silicate solution with a cation exchanger resin in the
H-form, and then adding the acidic fresh sol to a starting
medium containing an aqueous, alkaline, colloidal silica sol
solution having an SiO content of 2-20% by weight and an
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average particle size of 14-27 nm. The continuous process is
carried out in a multi-stage casade reactor by continuously
introducing the acidic fresh sol into the reactor wherein the
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