Patent ID: 7704552

Claim:
In the process of producing a chemically treated siliceous tiller by contacting an acidic aqueous suspension of amorphous precipitated silica with a coupling agent, optionally in the presence of a surfactant and/or a water-miscible solvent, to form an acidic aqueous suspension of chemically treated precipitated silica, and recovering said chemically treated precipitated silica, the improvement comprising: (a) providing an acidic aqueous suspension of amorphous precipitated silica having a pH of 2.5 or less, (b) treating the precipitated silica with a coupling agent comprising a combination of: (i) mercaptoorganometallic compound and (ii) non-sulfur organometallic compound, the weight ratio of (i) to (ii) being at least 0.05:1, under conditions which result in essentially complete hydrolysis of any alkoxy groups associated with the coupling agent, thereby to produce chemically treated precipitated silica, (c) raising the pH of the acidic aqueous suspension of chemically treated precipitated silica to from 3 to 10 with acid neutralizing agent that does not adversely affect the chemically treated precipitated silica, and (d) separating chemically treated precipitated silica from the aqueous suspension while retaining in the aqueous phase substantially all of any alcohol by-product produced by hydrolysis of alkoxy groups associated with the coupling agent, said chemically treated precipitated silica having a carbon content of greater than 1 weight percent, a mercapto content of greater than 0.15 weight percent, a Silane Conversion Index of at least 0.3 and a Standard Reinforcement Index of at least 4, as measured using the Standard Compounding Protocol.