Precipitated silicas, a process for their preparation and their use in vulcanizable rubber mixtures

A vulcanizable rubber mixture comprising, based on 100 parts of Rubber, from 5 to 100 parts of a precipitated silica having a CTAB surface area, in accordance with ASTM D 3765-92, of 200 to 400m.sup.2 /g, a DBP index, in accordance with ASTM D 2414, between 230 and 380 ml/100 g as powder and 180-250 g/100 g as granulate, a silanol group density, V.sub.2 -NaOH consumption, of 20 to 30 ml and the following macroproe size distribution which is typical of the surface area range involved, determined by means of Hg porosimetry (DIN 66 133) for specific pore size intervals (incremental mode of application):

• ______________________________________ CTAB surface CTAB surface CTAB surface area range:
• area range:
• area range:
• 200-250 m.sup.2 /g 250-300 m.sup.2 /g 300-400 m.sup.2 /g Pore size interval ›nm! Hg consumption in ml/g of silica ______________________________________ 10-20 0.27-0.49 0.35-0.50 0.32-0.42 20-30 0.22-0.32 0.15-0.30 0.17-0.22 30-40 0.15-0.21 0.12-0.17 0.12-0.15 40-50 0.11-0.16 0.09-0.12 0.08-0.11 50-60 0.08-0.12 0.06-0.10 0.06-0.09 ______________________________________
• and produced by reacting sulphuric acid with an alkali metal silicate solution,
• which process comprises:
• acidifying water at a temperature from 30.degree. to 90.degree. C. to a pH of 5 to 5.9 by adding small amounts of sulphuric acid;
• introducing simultaneously said alkali metal silicate solution and sulphuric acid in to said acidified water to precipitate silica, the pH of the solution being kept constant at 5 to 5.9 and the reaction solution being agitated during the entire process;
• suspending the introduction of said alkali metal silicate and sulphuric acid when it is detected that the viscosity of the reaction solution increases to halt the precipitation of silica;
• after an interval of 30 to 120 minutes, resuming the introduction of alkali metal silicate and sulphuric acid into the reaction solution until the concentration of silica reaches from 40 to 60 g/liter, thereby producing a silica suspension.

A precipitated silica having its surface modified with an organolsilane, wherein said silica has a CTAB surface area, in accordance with ASTM D 3765-92, of 200 to 400 m.sup.2 /g, a DBP index, in accordance with ASTM D 2414, between 230 and 380 ml/100 g as powder and 180-250 g/100 g as granulate, a silanol group density, V.sub.2 -NaOH consumption, of 20 to 30 ml and the following macroproe size distribution which is typical of the surface area range involved, determined by means of Hg porosimetry (DIN 66 133) for specific pore size intervals (incremental mode of application):

• ______________________________________ CTAB surface CTAB surface CTAB surface area range:
• area range:
• area range:
• 200-250 m.sup.2 /g 250-300 m.sup.2 /g 300-400 m.sup.2 /g Pore size interval in nm Hg consumption in ml/g of silica ______________________________________ 10-20 0.27-0.49 0.35-0.50 0.32-0.42 20-30 0.22-0.32 0.15-0.30 0.17-0.22 30-40 0.15-0.21 0.12-0.17 0.12-0.15 40-50 0.11-0.16 0.09-0.12 0.08-0.11 50-60 0.08-0.12 0.06-0.10 0.06-0.09 ______________________________________
• and produced by reacting sulphuric acid with an alkali metal silicate solution,
• which process comprises:
• acidifying water at a temperature from 30.degree. to 90.degree. C. to a pH of 5 to 5.9 by adding small amounts of sulphuric acid;
• introducing simultaneously said alkali metal silicate solution and sulphuric acid in to said acidified water to precipitate silica, the pH of the solution being kept constant at 5 to 5.9 and the reaction solution being agitated during the entire process;
• suspending the introduction of said alkali metal silicate and sulphuric acid when it is detected that the viscosity of the reaction solution increases to halt the precipitation of silica;
• after an interval of 30 to 120 minutes, resuming the introduction of alkali metal silicate and sulphuric acid into the reaction solution until the concentration of silica reaches from 40 to 60 g/liter, thereby producing a silica suspension,
• wherein said organosilane is a member selected from the group consisting of the formulas I, II and III
• ›R.sub.n.sup.1 -(RO).sub.3-n Si-(alk).sub.m -(ar).sub.p !.sub.q ›B!(I)
• or
• R.sub.n.sup.1 (RO).sub.3-n Si-(alkyl) (II)
• R.sub.n.sup.1 (RO).sub.3-n Si(alkenyl) (III)
• wherein
• B represents --SCN, --SH, --Cl, --NH.sub.2 (if q=1) or --X.sub.x -- (if q=2)
• R and R.sup.1 represent an alkyl group with 1 to 4 carbon atoms or a phenyl group, wherein all R and R.sup.1 groups may be identical or different,
• n is 0, 1 or 2,
• alk represents a divalent, straight-chain or branched hydrocarbon group with 1 to 6 carbon atoms,
• m is 0 or 1,
• ar represents an arylene group with 6 to 12 carbon atoms,
• p is 0 or 1, with the proviso that p and n are not simultaneously 0,
• x is a number from 2 to 8,
• alkyl represents a monovalent, straight-chain or branched saturated hydrocarbon group with 1 to 20 carbon atoms,
• alkenyl represents a monovalent, straight-chain or branched unsaturated hydrocarbon group with 2 to 20 carbon atoms.