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
1997-11-10
1999-11-16
Yoon, Tae
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, 524863, 528 38, 528901, C08L 8308, C08L 8305, C08G 7726
Patent
active
059859946
DESCRIPTION:
BRIEF SUMMARY
The invention relates to aqueous dispersions of organopolysiloxanes which following removal of water can be converted into elastomers, to processes for their preparation and to their use as sealing and coating materials.
Environmental protection measures are increasingly dictating the avoidance of organic solvents in chemical formulations. As a consequence, aqueous systems are finding application more and more.
Aqueous dispersions of organopolysiloxanes per se are widely known. The basic structure of such dispersions, which vulcanize even at room temperature to form elastomers, is composed of a linear polymer, a crosslinking component and a crosslinking catalyst. In general, the initial charge to the reaction vessel is an aqueous emulsion of polydiorganosiloxanes whose end groups contain condensable groups. These high molecular weight polysiloxanes are either emulsified directly or, usually, are prepared in emulsion by customary techniques by polymerization, condensation and equilibration from linear or cyclic, low molecular weight polysiloxanes. The polymer emulsion is then generally mixed with a crosslinking component and condensation catalyst, in each case in bulk or as an emulsion, and with further constituents, such as fillers, adhesion promoters, etc., the catalyst comprising almost exclusively (organo)metallic compounds.
The (organo)metallic catalysts employed virtually without exception as catalysts have the disadvantage that on the one hand they impair both the storage stability of the unvulcanized compositions and the stability of the vulcanized elastomers, and on the other hand they are regarded as toxicologically objectionable. In many of the prior developments, the highly complex, time-consuming and therefore costly preparation of the aqueous emulsions constitutes a disadvantage. These problems result principally from the emulsion polymerization, emulsion condensation or equilibration of the polydiorganosiloxanes to be employed, which takes up reaction time and must be carried out prior to the preparation of the end product by mixing in the other constituents. A further disadvantage of the majority of aqueous emulsions known to date is their low solids content. It is a high solids content, however, which is the precondition for low or insignificant shrinkage during vulcanization, which is desirable for most areas of application.
For example, German Application DE 42 17 561 (Wacker-Chemie GmbH; filed on May 27, 1992) or the corresponding U.S. application having the serial number U.S. Ser. No. 08/056,088 describes aqueous dispersions of organopolysiloxanes, comprising condensable organopolysiloxane, silicone resin, polyvinyl alcohol, (organo)metallic catalyst and amino-functional substances, which dispersions can be used to obtain transparent vulcanizates.
Additionally, U.S. Pat. No. 5,045,231 (Wacker-Chemie GmbH; published on Sep. 3, 1991) or the corresponding DE-A 39 32 025 claims aqueous dispersions of organopolysiloxanes, comprising condensable organopolysiloxanes, (organo)metallic catalysts, organopolysiloxane resins and diorganosilanolates, it being possible for the solids content of the dispersions to be up to 90%.
In DE-B 1037707 (Dow Corning; published on Aug. 28, 1958) a process for the preparation of emulsions of high molecular weight organopolysiloxanes is disclosed which starts from an emulsion of low molecular weight siloxanes. The desired molecular size is achieved with the aid of strongly acidic or alkaline catalysts. These emulsions do not lead to elastomers.
According to U.S. Pat. No. 5,004,771 (Rhone Poulenc; published on Apr. 2, 1990) or in the corresponding EP-A 365 439, the acidic condensation of a terminally OH-blocked polydiorganosiloxane is carried out in aqueous emulsion. After neutralizing the polymer emulsion, the further constituents, such as methylsiliconate solution and nonsiliceous fillers, but not compounds containing basic nitrogen, are added. The emulsions described, which have a solids content of less than 90%, do not give rise to elastomers.
U.S. Pat. No. 4,8
REFERENCES:
patent: 3294725 (1966-12-01), Findlay et al.
patent: 4894412 (1990-01-01), Okada et al.
patent: 5000861 (1991-03-01), Yang
patent: 5004771 (1991-04-01), Feder et al.
patent: 5045231 (1991-09-01), Braun et al.
patent: 5140061 (1992-08-01), Feder
U.S. application No. 08/056,088, Braun et al., filed May 27, 1992.
U.S. application No. 08/342,192, Oberneder et al., filed Nov. 26, 1993.
"Ullmann's Encyclopedia of Industrial Chemistry", Urban & Schwarzenberg, Munich, Berlin, 3rd edition, vol. 1, p. 720ff.
Braun Rudolf
Braunsperger Karl
Heinrich Alfred
Oberneder Stefan
Soellradl Herbert
Wacker-Chemie GmbH
Yoon Tae
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