Catalyst for the preparation and processing of polyorganosiloxan

Details Catalyst for the preparation and processing of polyorganosiloxan Catalyst for the preparation and processing of polyorganosiloxan

1997-01-23

1998-01-13

Marquis, Melvyn I.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

502102, 502152, 502158, 528 16, 528 17, 556 9, 556 10, 556 11, 556 12, C08G 7706, C07F 708

Patent

active

057081131

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to catalysts for the preparation and processing of polyorganosiloxanes, in particular for the processing of silicone resins, for example for solvent-free preparation of mica insulating materials. The catalysts are silanized organometallic compounds and have a high catalytic activity. Another field of use of the silanized organometallic compounds is acceleration of the curing of silicone rubbers and silicone resins which crosslink by condensation, in particular when used in the form of aqueous formulations.


PRIOR ART

Organosilicon compounds, in particular polyorganosiloxanes, have found a wide field of use because of their specific physical properties. Their use extends from elastic sealing compositions to the production of components for the electrical industry, where particularly high requirements are imposed on the properties of the processed polyorganosiloxanes, such as, for example, in the use of silicone resins as binders in mica insulating materials.
The Patent DE 11 26 467 discloses the principles for the production of insulating materials based on mica using solvent-containing silicone resins or aqueous suspensions. The production of mica insulating materials, preferably with solvent-containing silicone resins with the addition of catalysts, is known. Solutions of aminic, organophosphorus or organometallic compounds are employed as catalysts. Extensive literature references are given in Noll, Chemie u. Technologie der Silicone (Chemistry and Technology of the Silicones) (Noll, Chemie u. Technologie der Silicone, 2nd edition, Weinheim 1968, page 357).
The technology based on an organic solvent was expensive in terms of safety and was displaced by further development in favour of aqueous systems. For this, aqueous suspensions of mica slurry, silicone resin powder, emulsifiers and catalysts are processed to prepregs, and rigid mica insulating materials with silicone resin binders are obtained by subsequent compression moulding.
Pure or mixed, pulverulent or pasty organometallic compounds, such as, for example, the acetylacetonates of aluminium and zinc and reaction products thereof, are preferably used as catalysts for aqueous systems. Although these are largely insoluble, they essentially dissolve in the aqueous suspensions at the low use concentrations. Since the catalytic activity is determined by the content of catalysts contained in the moist mica paper before drying, the better the solubility of the catalyst, the greater the amount added must be. The wastewater obtained thus comprises a large proportion of the catalyst which does not remain in the mica paper and must be worked up expensively. The known catalysts furthermore have a deficient catalytic activity and the mica insulating materials produced with these have a low mechanical strength and too high an absorption of water and therefore impaired electrical properties.
Formulations based on organic solvents are being replaced more and more by emulsions or dispersions for the processing of silicone resins, for example as binders in paints. Mineral acids, for example, are used as catalysts for curing these resin formulations (EP 98 940). This has the disadvantage that neutralization of the catalyst is additionally necessary. The use of toluene solutions of aluminium(III) or iron(III) acetylacetonates is also described (U.S. Pat. No. 3 395 071, EP 342 519). The disadvantages of these catalysts--chiefly pollution of the environment by solvent vapours--are obvious.
In the formulation of silicone rubbers which crosslink by condensation, the nature of the catalysts used is also decisive for the processing properties and the physical characteristic values of the products. Aqueous formulations in particular have recently found wide interest in silicone rubbers which crosslink by condensation (Liles, D. T.: Polym. Mater. Sci. Eng. 66 (1992) pages 172-173). These usually contain organotin compounds as catalysts (EP 354 015, U.S. Pat. No. 5 145 907) and are often used in the form of emulsions. Because of the sur

REFERENCES:
patent: 3419593 (1968-12-01), Willing
patent: 3927052 (1975-12-01), Vizurraga
patent: 4681963 (1987-07-01), Lewis
patent: 5304622 (1994-04-01), Ikai et al.

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