Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Patent
1990-11-29
1992-10-27
Davis, Jenna L.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
428355, 428413, 428454, C09J16302
Patent
active
051588269
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an insulating tape for manufacturing an insulating sleeve impregnated with a hot-curing epoxy-resin/acid-anhydride-system, for electrical conductors, especially for bars or coils of electrical machines, consisting of a flat, inorganic material of high dielectric strength, such as mica splittings or mica flakes, deposited on a flexible support. This material is bonded to the support and to other sections of the material and optionally to a facing by means of a binder containing an accelerator which promotes the curing reaction of the impregnating resin. The binder/accelerator mixture forms a system that is self-curing at the curing temperature of the impregnating resin.
Such an insulating tape, as known from the German Patent 21 42 571, makes it possible to perform the impregnation process economically, because a non-reactive impregnating resin can be used. This non-reactive impregnating resin does not undergo any change in viscosity, even at the high impregnating temperatures which are required to thoroughly impregnate the insulating sleeve. This is necessary, because only a small portion of the epoxy-resin/acid-anhydride system used as impregnating resin penetrates into the insulating sleeve, while the residue must be used again for new impregnation procedures. For this reason, the insulating tape contains an accelerator which promotes the curing reaction of the impregnating resin, so that the portion of impregnating resin that has penetrated into the insulating sleeve cures within an economically short time.
To be able to store insulating tapes for a long time before the impregnation process, the binder/accelerator mixture is selected, in the case of the known insulating tape, so that there is virtually no curing of this system at room temperature. In addition, the binder/accelerator mixture forms a self-curing system, which cures only at the curing temperatures of the impregnating resin which lie considerably above ambient temperatures. So the binder, which has penetrated between large-surfaces of inorganic material of high dielectric strength and has not been completely absorbed by the impregnating resin, does not remain in an uncured state in the insulation.
In the case of the known insulating tape, cycloaliphatic epoxy resins with an epoxide-equivalent lower than 180 are used as binders, whereby the epoxy groups are the result of the addition of oxygen on double bonds in ring position. As is generally known, these cycloaliphatic epoxy resins do not show any reaction with amine hardeners, or show a much delayed reaction with accelerators. However, when the epoxy-resin/acid-anhydride impregnating system is added, these accelerators develop their full catalytic activity. As accelerators, the known insulating tape contains adducts from vinylcyclohexanedioxide and secondary amines of the molar ratio 1:1, where the secondary nitrogen atom is a part of a hydrogenated ring system, and adducts of the molar ratio 1:1 of vinylcyclohexanedioxide and, in the 1 position, unsubstituted imidazoles.
Recent investigations have shown, however, that vinylcyclohexanedioxide (4-vinyl-1.2. cyclohexanediepoxide) is a harmful substance, because it has been carcinogenic in tests on laboratory animals.
According to the manufacturer, the same judgment is valuable for cycloaliphatic epoxy resin 3(3',4'-epoxycyclohexyl)-7.8-epoxy 2.4-dioxa-spirobicyclo-[5.5]-undecane (epoxide equivalent approx. 162).
The object of the invention is therefore to find a binder/accelerator mixture for insulating tapes of the type described in the beginning, which is physiologically innocuous, according to all tests known to date.
Furthermore, insulating substances are known from DE-A-29 16 954, which consist of an epoxy resin modified by molecular enhancement with an epoxide equivalent of over 200 and an inorganic, powdery filler, such as mica. In addition, these insulating substances contain acid-anhydride hardeners as well as amines as accelerators, such as N-aminoethylpiperazine. The known insulating substance is cast for
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Ihlein Walter
Pollmeier Franz-Josef
Rogler Wolfgang
Davis Jenna L.
Siemens Aktiengesellschaft
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