Precipitated silicas with particular pore size distribution
Precipitated silicas useful, for example, as fillers in elastomer mixtures or vulcanizates have a particularly broad pore size distribution of the pores with a pore diameter smaller than that of the maximum of the derivative of the pore volume distribution function, and have simultaneously very low microporosity and high rubber activity.
1. A precipitated silica, having the following physicochemical parameters:
a relative breadth γ of pore size distribution of
4.0-10.0 (g nm)/ml,
a BET surface area of
90-320 m 2 /g,
a CTAB surface area of
100-200 m 2 /g,
a Sears number V 2 of
26-40 ml/(5 g), and
Sears number V 2 /CTAB ratio of
0.16-0.28 ml/(5 m 2 ).
2. The precipitated silica according to claim 1 , wherein the BET/CTAB ratio is ≧0.9 and ≦1.6.
3. The precipitated silica according to claim 1 , wherein a zeta potential at pH 5 is from −12 to −30 mV.
4. The precipitated silica according to claim 1 , wherein an oil adsorbency measured as DBP number is from 200 to 330 g/(100 g).
5. The precipitated silica according to claim 1 , wherein an Al 2 O 3 content is from 0.001 to 5% by weight.
6. The precipitated silica according to claim 1 , which is in the form of a granulated material, and wherein a (Ro-Tap) sieve residue on a 300 μm sieve is at least 80% by weight.
7. The precipitated silica according to claim 1 , which is in the form of a granulated material, and wherein a <75 μm (Ro-Tap) sieve fraction is at most 10% by weight.
8. The precipitated silica according to claim 1 , having a carbon content of from 0.1 to 20.0% by weight.
9. The precipitated silica according to claim 1 , which has a Sears number V 2 of 28-40 ml/(5 g).
10. The precipitated silica according to claim 1 , which has a Sears number V 2 of 30-40 ml/(5 g).
11. The precipitated silica according to claim 1 , which has a Sears number V 2 of 32-40 ml/(5 g).
12. The precipitated silica according to claim 1 , which has a Sears number V 2 of 34-40 ml/(5 g).
13. The precipitated silica according to claim 1 , which has a Sears number V 2 of 36-40 ml/(5 g).
14. The precipitated silica according to claim 1 , which has a Sears number V 2 of 38-40 ml/(5 g).
15. An elastomer mixture, a vulcanizable rubber mixture or a vulcanizate, comprising the precipitated silica according to claim 1 .
16. A vulcanizable rubber mixture or vulcanizate, comprising:
at least one precipitated silica according to claim 1 , as filler.
17. A tire, comprising:
at least one precipitated silica according to claim 1 .
18. A process for producing the precipitated silica according to claim 1 , comprising in succession:
a) using an aqueous solution of at least one member selected from the group consisting of an alkali metal silicate, an alkaline earth metal silicate, an organic base, an inorganic base and mixtures thereof as initial charge, the alkali number of the initial charge being from 20 to 40,
b) simultaneously metering into said initial charge alkali metal silicate, alkaline earth metal silicate or mixtures thereof and an acidifier with stirring at from 55 to 85° C. until a viscosity rises,
c) stopping the feed for from 35 to 85 minutes,
d) simultaneously feeding alkali metal silicate, alkaline earth metal silicate or mixtures thereof and acidifier at a temperature of from 55 to 85° C., until a solids content of from 90 to 140 g/l has been reached,
g) continuing stirring of a resultant suspension for from 1 to 120 minutes at from 80 to 98° C.,
h) acidifying said suspension with an acidifier to a pH of from 2.5 to 5.0, and
i) filtering of said suspension to obtain said precipitated silica and drying of said precipitated silica.