Process for the continuous preparation of HTV silicone compositi

Details Process for the continuous preparation of HTV silicone compositi Process for the continuous preparation of HTV silicone compositi

1993-06-10

2000-09-26

Dawson, Robert

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...

524588, 524860, 525474, C08K 334

Patent

active

061243922

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for the continuous preparation of hot vulcanizing silicone compositions based on diorgano(poly)siloxanes, which are called HTV (high temperature vulcanizing) silicone compositions by experts. These HTV silicone compositions differ from RTV (room temperature vulcanizing) silicone compositions in respect of the temperature during the vulcanization operation. While the HTV silicone compositions vulcanize only at a temperature elevated with respect to room temperature via a free radical reaction or addition reaction, vulcanization of one-component RTV silicone compositions even takes place at room temperature via a condensation reaction with atmospheric moisture, that is to say water. One-component RTV silicone compositions contain reinforcing fillers in amounts of not more than 10% by weight. In contrast, the content of reinforcing filler in HTV silicone compositions is at least 20% by weight. To distinguish between HTV and RTV silicone compositions, reference may also be made, for example, to Winnacker, Kuchler, Volume 6, Anorganische Technologie II (Inorganic Technology II), 4th Edition, 1982, Carl Hanser Verlag Munich Vienna, pages 842 and 845, J. Bittera, Kautschuk, Gummi, Kunststoffe, Volume 39 No. 1/86 or J. C. Weis in Progress of Rubber Technology, edited by S. H. Morell, Elsevier Applied Science Publishers Ltd., England, 1984 pages 85-106.
According to EP-A-234,226 and the corresponding U.S. Pat. No. 4,737,561, a process is known for the continuous preparation of one-component RTV silicone compositions in which the diorgano(poly)siloxane to be crosslinked, filler(s) and possibly either catalyst(s) or crosslinking agents and possibly some or all of the auxiliaries optionally to be used are combined in a first step in a continuously operating closed mixer, and in a second step the crosslinking agents and/or catalyst(s) which have not been added in the first step are metered into the resulting composition in an oscillating pilgrim-step kneader and the composition is homogenized and degassed in this kneader.
HTV silicone compositions differ from RTV silicone compositions above all in the following points: compositions
This different consistency can already be seen from the different methods of viscosity measurement. The Mooney viscometers customary in the rubber-processing industry are thus employed for HTV compositions, while rotary viscometers and pressing-out apparatuses are used for RTV compositions.
HTV silicone compositions according to the current prior art are therefore prepared almost exclusively discontinuously by mixing the starting substances in kneaders, internal mixers or mixing roll mills.
According to EP-B-258,159, a process is known for the continuous preparation of master mixtures in the form of homogeneous and thick pastes, to later obtain hot vulcanizable silicone elastomers, a continuous twin-screw kneader being charged with a polysiloxane base polymer and a power batch. The power batch is preferably silicone dioxide having a density of more than 0.1 kg/l.
Disadvantageously, because of the varying intake properties, product properties which are not constant with respect to time result in this process. Long mixing zones are needed to achieve a positive speck evaluation, which unavoidably leads to increased apparatus complexity and increased residence times. There is also the risk of high wear on machinery and contamination of the product by abraded metal.
The object of the invention is to provide a process for the continuous preparation of HTV silicone compositions which avoids the disadvantages of the prior art.
This object is achieved by a process for the continuous preparation of HTV silicone compositions, which comprises mixing and homogenizing 100 parts by weight of diorgano(poly)siloxane which has a viscosity of 50 to 100,000 Pas at 25.degree. C. with at least 20 parts by weight of finely divided silicon dioxide which has a tamped density of more than 0.01 kg/l in an oscillating single-shaft pilgrim-step kneader.
It is possible to obtain HTV sil

REFERENCES:
patent: 4737561 (1988-04-01), Stary et al.

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