PRECIPITATED SILICA, A PROCESS TO MAKE IT, AND ITS USE

摘要

The invention relates to a process to make precipitated silica, the precipitated silica so obtained, and the use of this silica as a filler material in elastomers. The process involves the steps of: charging a reactor with an aqueous medium; heating the reactor contents to 60-90 DEG C; dosing water glass (SiO2/Na2O weight ratio about 3.3, containing 15-25 % w/w of SiO2) at a rate of 60-80 g/min; dosing sulfuric acid (15-25 % w/w) simultaneously with the water glass, so that the pH during the precipitation of the silica is from 8-10. On conclusion of the dosing, allowing the reaction mixture to after-react at said pH for 3-45 minutes. Subsequently dosing sulfuric acid in 5-20 minutes, so that the pH is lowered to 6-8. Dosing water glass at about the same rate as before for about 20-60 minutes. Simultaneously dosing sulfuric acid to ensure that the pH is kept constant at 6-8. When the water glass dosing is stopped, continuing to dose sulfuric acid for 10-30 minutes, so that the pH is lowered to 3-5.5. Removing the precipitated silica from the reactor, washing it in a conventional way, drying it in a conventional way, optionally compacting it and packing it. The resulting precipitated silica is characterized by DBP oil absorption of 140-230 ml/100g, a BET surface area of 100-220 m<2>/g, a CTAB surface area of 100-200 m<2>/g, and a Hg-intrusion peak maximum of 0.065 to 0.095 ml/(g•nm).