Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1997-05-02
1999-01-19
Glass, Margaret W.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
578 17, 578 18, 578 38, C08L 8308
Patent
active
058614591
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The field of the present invention is that of silicone compositions which can be hardened by cross-linking and which are usable especially as a mastic or any other sealing material, or for forming any type of coating for example in paintings.
More specifically, the invention relates to an aqueous silicone dispersion which forms an adhesive elastomer by removing especially water and optionally alcohol and/or carboxylic acid, using a polycondensation mechanism which intervenes advantageously at ambient temperature.
PRIOR ART
The silicones or polyorganosiloxanes, such as .alpha.,.omega.-(dihydroxy)polydiorganosiloxane, are known to enter into the composition of standard silicone mastics which further include cross-linking agents of the alkyltrialkoxysilane type, polycondensation catalysts of the tin salt type and fillers. Such compositions have not proved to be very convenient in their use for carrying out sealing joints, films or coatings for example, since their pasty and viscous states render their handling and their placing in a given shape difficult.
Moreover, these compositions have the disadvantage in that they are not dispersible or soluble in water which complicates their use, particularly because the tools used for their application are not in fact easily washable in water.
Furthermore, these compositions have also the disadvantage in that they are not << paintable >>; the paints do not stick on.
In order to alleviate these serious faults, systems of formation of mastic or cross-linkable film have been developed from an aqueous emulsion based on silicone oil capable of being cross-linked into an elastomer by condensation (water removal for example).
Although of a more practical application, these aqueous silicone emulsions have raised a certain number of technical difficulties:
stability in storage,
hardening times too long,
mediocre mechanical properties (hardness, elasticity),
thixotropy flaws,
weak adhesion properties on usual supports.
Various prior art propositions have attempted to satisfy, in vain, such specifications.
It is thus known from the German patent application No 2 912 431, of a polyorganosiloxane latex obtained from an emulsion, within which the polymerisation of a cyclic organosiloxane intervenes leading to a polysiloxane with OH terminals. This emulsion also includes an organo-functional trialkyoxysilane which is useful as a cross-linking agent. These known compositions do not give satisfaction in what concerns the stability of the emulsion and the adhesive properties.
The German patent application No. 3 019 655 describes a silicone emulsion which, after water removal, may be converted into an elastomer under ambient conditions. This silicone emulsion also includes amorphous silica which is introduced in the form of a colloidal dispersion. Now, such silica dispersions are not particularly stable and so the pH of the mixture is a critical parameter which is very difficult to fix. Furthermore, the incorporation of silica is at the origin of a certain inhomogeneity in the hardness of the obtainable cross-linked elastomer. This is due to the fact that the silica has in fact a tendency to react in a parasite fashion with the reactive OH terminals of the silicone oil.
In other prior propositions, the siliceous filler is sodium silicate (U.S. Pat. No. 4,244,849) or powdered amorphous silica (FR No. 2 463 163).
These last three patents teach that in order to obtain a monocomponent emulsion which is stable in storage, it is necessary to fix its pH at values equal to or greater than 8.5 or 9, preferably 10. However, the processes according to these patents do not live up to the expectations of the technical field as regards stability and mechanical and adhesive properties.
German patent application No 2 943 832 describes a silicone emulsion which differs from that which is the subject of the German patent application No 3 019 655 studied above only by a higher dry matter content (>60%). A great disadvantage of this emulsion is that it must have a pH great
REFERENCES:
patent: 4191817 (1980-03-01), Schiller et al.
patent: 4559385 (1985-12-01), Huhn et al.
patent: 5204432 (1993-04-01), Saito et al.
patent: 5336419 (1994-08-01), Coffindaffer et al.
Cardinaud Denis
Feder Michel
Fischer Christian
Glass Margaret W.
Rhone-Poulenc Chimie
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