US 5,846,311 AGranted

Process for the preparation of precipitated silica, new precipitated silicas containing zinc and their use for the reinforcement of elastomers

AssigneeRhone-Poulenc Chimie

InventorsYves Bomal, Yvonick Chevallier, Evelyne Prat

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Abstract

The invention relates to a new process for the preparation of precipitated silica which has a good dispersibility and very satisfactory reinforcing properties. It also relates to new precipitated silicas which are in the form of powder, of substantially spherical beads or of granules, these silicas being characterized by the fact that they have a CTAB specific surface of between 90 and 250 m.sup.2 /g, a DOP oil uptake lower than 300 ml/100 g, a pore distribution such that the pore volume consisting of the pores whose diameter is between 175 and 275 .ANG. represents less than 50% of the pore volume consisting of the pores of diameters smaller than or equal to 400 .ANG., a zinc content of between 1 and 5% by weight and by the fact that the number N of molecules of stearic acid consumed per nm.sup.2 of silica surface, when stearic acid is reacted with the said silica in xylene for 2 hours at 120.degree. C., is at least 1. The invention also relates to the use of the said silicas as reinforcing fillers for elastomers especially for improving their rheological properties.

Claims25

Dependent claims

A process for preparing precipitated silica comprising reacting a silicate with an acidifying agent to produce a suspension of precipitated silica and, then, separating and drying the suspension, wherein the precipitation is carried out by the steps comprising:

(i) forming an initial base stock comprising the silicate of alkali metal M and M.sub.2 O, said stock initially having a silicate concentration (expressed as SiO.sub.2 ) lower than about 20 g/l,
(ii) adding the acidifying agent to said base stock until at least about 5% of the quantity of M.sub.2 O present in said base stock is neutralized, and
(iii) adding simultaneously additional acidifying agent and silicate to said base stock such that the ratio of the quantity of silicate added (expressed as SiO.sub.2)/the quantity of silicate present in the initial base stock (expressed as SiO.sub.2 ) is greater than about 4 and at most about 100, wherein said process further comprises one of the following two operations (a) or (b):
(a) adding at least one zinc compound and then a basic agent to the base stock after stage (iii), said separation comprising a filtration to obtain a cake and disintegration of the cake, said disintegration being optionally performed in the presence of at least one aluminum compound, or
(b) adding simultaneously additional silicate and at least one zinc compound to the base stock after stage (iii), and said separation comprising a filtration to obtain a cake and the disintegration of the cake, the disintegration being optionally performed in the presence of at least one aluminum compound.

2 more elements

Dependencies are inferred from the claim text.