Method for preparing a silica suspension in a vulcanisable silicon matrix to form elastomers

Abstract

The invention concerns the preparation of a silica suspension in a silicon fluid, said suspension being used to produce silicon vulcanisable by polyaddition (RTV elastomers). The problem which the invention aims to solve is that of finding a technical compromise between the rheological and mechanical properties of the final RTV. The invention solves the problem by providing a method for preparing a silica suspension treated with hexamethyldisilazane (HMDZ) in a silicon fluid with siloxyl Si-Vinyl function, characterised in that it consists essentially in introducing HMDZ in the preparation medium, before and/or substantially while bringing at least part of the silicon fluid prepared with at least part of the particulate filler used, said introduction being carried out once or several times for a HMDZ fraction corresponding to a proportion not more than 8% by dry weight with respect to the total silica charge and after bringing together the POS and the filler.

Description

[0001] The field of the invention is that of silicone elastomers which can be obtained by polyaddition and the main components of which are silicone polymers and fillers.[0002] More specifically, the present invention relates to the preparation of an intermediate product useful for obtaining these silicone elastomers and consisting of a suspension of a reinforcing filler in a polyorganosiloxane carrying Si-alkenyl--preferably Si-Vi--functional groups capable of reacting by polyaddition with the SiH crosslinking functional groups of another POS.PRIOR ART[0003] A distinction may be made between reinforcing and non-reinforcing fillers in silicone rubbers.[0004] The most widely used reinforcing fillers are preferably pyrogenic silicas having a BET surface area >50 m.sup.2 / g. They owe their reinforcing effect firstly to their morphology and secondly to the hydrogen bonds which form between the silanol groups on the surface of the silicas (3-4.5 SiOH groups / mm.sup.2) and the polyorgano...

AI Technical Summary

Problems solved by technology

Moreover, the bonds between polymers and fillers improve the mechanical properties but may also cause prejudicial premature curing (structuring) of the precursor compositions of the elastomers.

This dispersion causes problems when mixing some of the pulverulent filler with the oil and particular care must be taken in order to obtain a uniform distribution of the fillers in the suspension.

Another difficulty to be overcome is associated with the rheology of the suspensions prepared.

This is because it is clear that introducing a pulverulent particulate filler of very small particle size into the silicone oil necessarily causes an appreciable increase in the viscosity.

However, this characteristic, although it accompanies the achievement of good mechanical properties for the silicon elastomers comprising the suspension as raw material, is prejudicial to the handling and forming of the suspension and of