Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1998-04-10
2000-02-01
Marquis, Melvyn I.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521130, C08J 900
Patent
active
060203897
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a process for the foaming of mixtures of at least bifunctionally-terminated diorganopolysiloxanes, acyloxysilane cross-linking agents, as well as possibly filling materials.
Such organopolysiloxane mixtures, also known as cold-vulcanising, monocomponent silicone rubbers, which possibly also contain suitable additives, pigments, colouring materials, oxidation-, heat- and light-protective pigments, as well as solvents and plasticisers, and, in a state ready for working up, are present in liquid or pasty form, are described as such in FR 1 198 749 or U.S. Pat. No. 3,133,891. The mixtures usually cross-link at room temperature with the take up of water from the surrounding atmosphere to give rubber-elastic polymers. As cross-linkers, there are used tri and higher functional acyloxysilane compounds which, by reaction with the polysiloxane or by hydrolysis, split off carboxylic acids and thus initiate the formation of a macromolecular meshwork. After hardening out has taken place, such masses are characterised by a good inherent adhesion to the most varied material surfaces and by a generally high stability against the action of temperature, light, moisture, as well as chemicals. Because of these properties, monocomponent silicone masses hardening with the splitting off of carboxylic acids are preferably used for sealing purposes.
A disadvantage of the described silicone masses is their low compressibility so that, in the case of use e.g. as packing cord, high application forces on the constructional parts to be sealed are necessary in order to achieve the desired compactness. For this reason, in technology there are often used foamable elastomers based on polyurethanes or on noble metal-catalysed, addition cross-linked silicone masses of vinyl group-containing siloxanes and hydrogen siloxanes for the production of seals. However, the field of use of polyurethane systems is restricted by their limited stability against the action of higher temperatures and also by certain chemical materials. Foamable noble metal-, preponderantly platinum-catalysed addition cross-linking silicone masses, admittedly have a substantially higher temperature stability but have the disadvantage that these products have no or only a very small inherent adhesion to the materials to be sealed. Furthermore, in the reactive state, thus before foaming up and hardening, these systems are extremely susceptible to certain chemical materials, especially sulphur- and nitrogen-containing compounds which, already in the cases of traces, inhibit the catalyst system of these products and can thus suppress their foaming up and hardening. An application of addition cross-linking silicone foam systems to materials which contain such catalyst poisons is thus not possible (cf. EP 0 416 229-A2 and EP 0 416 516-A2).
On the other hand, the initially mentioned acyloxysilane cross-linking silicone masses display a sufficient stability at higher temperatures of use and in the case of chemical stressing. The cross-linking system of these products is insensitive towards sulphur- and nitrogen-containing compounds. Furthermore, acyloxysilane cross-linking silicones display inherent adhesion to many usual, especially silicate materials.
However, the hardening of these monocomponent polysiloxane mixtures cross-linking at room temperature with take up of moisture takes place comparatively slowly since the water necessary for the reaction must diffuse in gaseous form from the surrounding atmosphere into the interior of the mass. Therefore, the speed of the hardening through decreases continuously with progressing reaction into the interior of the mass. In the case of low moisture of the surrounding atmosphere or in the case of an unfavourable ratio of surface to volume of the silicone mass, the reaction can become very slow or, as in vapour-tight sealed off rooms, can also come to a complete stop. Because of this only slow hardening, atmospheric moisture cross-linking acyloxysilane-containing silicone masses cannot be foamed with known p
REFERENCES:
patent: 3133891 (1964-05-01), Ceyzeriat et al.
patent: 5661192 (1997-08-01), Giraud
Heidelberger Bauchemie GmbH
Marquis Melvyn I.
Milstead Mark W.
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