Electricity: conductors and insulators – Insulators
Reexamination Certificate
2001-06-20
2003-04-15
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Insulators
C174S13800J, C174S1400CR, C174S176000, C427S385500, C427S386000, C427S387000, C427S393400
Reexamination Certificate
active
06548763
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to Appln. No. 00810540.5 filed in Europe on Jun. 20, 2000; the entire content of which is hereby incorporated by reference.
The present invention relates to casting compositions based on polymeric matrix resins for producing self-healing electrical insulators, especially in the form of moldings and coatings in the field of high-voltage insulators for outdoor use, and to the electrical insulators produced in accordance with the invention.
1. Technical Field
High-voltage insulators based on polymeric matrix resins for outdoor use are known per se. For outdoor applications, use is traditionally made of insulators based on glass and ceramic materials. In recent years, polymeric insulants as well have been able to capture a steadily increasing market share. Outdoor insulators are employed in large numbers both in association with high-voltage lines and in the medium-voltage sector, in particular as base insulators. Further fields of use are outdoor power switches, measuring transducers, leadthroughs, overvoltage protectors, and in switchgear construction.
In recent years the use of polymeric materials, such as silicones (RTV, HTV) or ethylene-propylene rubber (EPR, EPDM), and also casting resin systems based on epoxy resins and polyurethanes, has been on the increase. Of the polymeric materials, however, only silicones have achieved general acceptance in the art, silicones being superior to the other polymeric materials on account of their inherent pronounced hydrophobicity and, in particular, the inherent hydrophobicity regain. The high price of silicones, however, is a significant brake on their use in the art.
The polymeric materials mentioned, such as ethylene-propylene rubber or casting resin systems based on epoxy resins and polyurethanes, possess no intrinsic hydrophobicity regain and, moreover, have a significantly lower hydrophobicity. Furthermore, these materials undergo relatively severe degradation due to thermal and oxidative influences, especially UV radiation. There is therefore a need for improved polymeric materials which in terms of their mechanical properties are better than silicones and are suitable for producing electrical insulators which combine an enhanced hydrophobicity with the property of hydrophobicity regain without any marked alteration or weakening in their mechanical properties. Polymeric materials thus improved could be used, for example, to produce inexpensive epoxy resins, and to produce electrical insulators.
Where polymeric materials, such as ethylene-propylene rubber or casting resin systems based on epoxy resins and polyurethanes, for example, are used as high-voltage insulators outdoors and the surface is bedewed, the insulating effect is substantially dependent on the water-repelling effect (hydrophobicity) of this surface. In the case of highly hydrophobic surfaces, as generally occur with silicones, dew deposits are formed as individual droplets separate from one another. Where there is a loss of hydrophobicity, coherent film deposits form on the insulator surface under moist conditions. Markedly increased currents flow through these film deposits, and may possibly lead to instances of sparkover of the insulator, or at any rate may cause accelerated thermal and/or oxidative damage to the polymer matrix. Owing to the polar nature of the epoxy resin matrix, epoxy resin surfaces, and a large number of other thermosetting resin surfaces, lack sufficient water-repelling properties. Therefore, the use of epoxy resins and related materials is substantially restricted to interior applications.
2. Prior Art
The literature appears not to contain any references to the intrinsic modification of casting resin systems in which the casting resin systems are endowed with additional hydrophobicity and the property of hydrophobicity regain and at the same time there is little or no alteration to the mechanical properties.
The U.S. Pat. No. 4,537,803 proposes adding a polymerizable silicone oil to the epoxy resin mixture. U.S. Pat. No. 5,306,747 relates to the addition of a modified silicone oil which is able to react chemically with the resin system. The addition of silicones to the epoxy resin mixture or to other thermosetting systems has the disadvantage, fundamentally, that the physical properties, the reactivity, the flow properties, and the processing properties of the matrix are altered in such a way that, for example, separation phenomena or electrical discharges occur in cavities. U.S. Pat. No. 5,306,747 gives the silicone oil terminal hydroxyphenyl groups and incorporates it chemically into the matrix. The principal disadvantage of this method, as the patent describes, lies in the deterioration in mechanical properties that accompanies increasing chain length of the silicone oil introduced. Additionally, as a result of the direct incorporation of the hydrophobic constituents into the resin matrix, this method does not provide any regain of the hydrophobicity, since the hydrophobicity regain is tied to the diffusion of freely mobile, low molecular mass silicone oligomers.
DESCRIPTION OF THE INVENTION
It has now been found that casting compositions based on polymeric matrix resins for producing self-healing electrical insulators are obtained if encapsulated, selected, water-repelling compounds are added to the polymeric matrix resins prior to their curing. Cured casting compositions based on polymeric matrix resins comprising inventively encapsulated water-repelling compounds exhibit good hydrophobicity and also a pronounced hydrophobicity regain without any marked changes in the mechanical properties. There is no phase separation. It is found in particular that when the capsule material breaks down, which is simultaneous with the thermal and/or oxidative degradation of the cured matrix surface, the encapsulated, water-repelling compound(s) is (are) released, and so diffuse(s) to the direct surface. In doing so, these compounds penetrate the surface and are also able to penetrate into any degraded and/or superimposed external layers that are formed, so that the oxidative and/or thermal degradation of the surface is accompanied in each case by the re-establishment of the hydrophobicity, or self-healing. This process of self-healing continues for as long as the surface subject to erosion comprises the casting composition of the invention. The life expectancy of products produced from the casting compositions of the invention is, accordingly, significantly prolonged. The casting compositions of the invention make it possible to combine excellently the good mechanical properties of inexpensive thermosetting materials with the properties of hydrophobicity and hydrophobicity regain.
The present invention is defined in the claims. The present invention relates in particular to a liquid or pastelike casting composition based on a polymeric matrix resin or a mixture of such resins for producing self-healing electrical insulators, and this casting composition is characterized in that it comprises in uniform distribution a selected hydrophobicizing compound or a mixture of such compounds in encapsulated form.
The casting compositions of the invention are especially suitable for producing moldings and coatings in the field of electrical insulators, especially high-voltage insulators, in particular for outdoor use. It is also possible to use these insulators in interior installations.
In this sense the present invention relates to the use of the casting compositions of the invention to produce moldings and coatings in the field of electrical insulators, especially high-voltage insulators, and, in particular, high-voltage insulators for outdoor use.
The invention further relates to the electrical insulators produced from the casting compositions of the invention.
The invention further relates to a process for preparing the casting compositions of the invention.
According to the invention, suitable casting compositions in liquid or pastelike form include polymeric materials, such as thermosettable
Kaltenborn Uwe
Rocks Jens
ABB Research Ltd
Nguyen Chau N.
Walkenhorst W. David
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