Stock material or miscellaneous articles – Composite – Of silicon containing
Patent
1989-06-14
1991-07-23
Marquis, Melvyn I.
Stock material or miscellaneous articles
Composite
Of silicon containing
428447, 524265, B32B 906
Patent
active
050342789
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to compositions which are useful in low to high voltage insulation because of their resistance to water trees.
BACKGROUND ART
Power cables insulated with extruded dielectrics are known to suffer from shortened life when installed underground where water contact is likely. The shortened life has been attributed to the formation of water trees, which occur when an organic polymeric material is subjected to an electrical field over a long period of time in the presence of water in liquid or vapor form. The net result is a reduction in the dielectric strength of the insulation.
Many solutions have been proposed for increasing the resistance of organic insulating materials to degradation by water treeing. These include, for example, the addition to polyethylene of (i) a polar copolymer such as a copolymer of ethylene and vinyl acetate; (ii) a voltage stabilizer such as dodecanol; and (iii) a filler, e.g., clay. These solutions all have shortcomings of some kind such as an increaser in dielectric loss, i.e., the power factor or volatility.
DISCLOSURE OF THE INVENTION
An object of this invention, therefore, is to provide a water tree resistant composition adapted for use in low to high voltage insulation, which does not depend on the use of those modifying additives, known to increase dielectric loss or volatility, to achieve acceptable treeing resistance.
Other objects and advantages will become apparent hereinafter.
According to the present invention, the above object is met by a water tree resistant composition comprising: to about 0.925 gram per cubic centimeter and a melt index in the range of 0.1 to about 5 grams per 10 minutes or a copolymer of ethylene and one or more alpha-olefins, each having 3 to 8 carbon atoms, said copolymer having a density in the range of about 0.880 to about 0.915 gram per cubic centimeter and a melt index in the range of about 0.1 to about 10 grams per 10 minutes; and ##STR2## wherein R=alkyl having 1 to 4 carbon atoms, acyl having 1 to 4 carbon atoms, or trimethyl silyl, and each R is alike or different weight based on the total weight of the composition.
DETAILED DESCRIPTION
The homopolymer of ethylene can be prepared by the conventional high pressure process described in the Introduction to Polymer Chemistry, Stille, Wiley and Sons, New York, 1962, at pages 149 to 151. The density of the homopolymer is in the range of about 0.915 to about 0.925 gram per cubic centimeter. The melt index, as determined under ASTM D-1238, Condition E (measured at 190.degree. C.), is in the range of about 0.1 to about 5 grams per 10 minutes and is preferably in the range of about 1 to about 3 grams per 10 minutes.
The copolymer of ethylene and one or more alpha-olefins, each having 3 to 8 carbon atoms, has a density in the range of about 0.880 to about 0.915 gram per cubic centimeter and a melt index in the range of about 0.1 to about 10 grams per 10 minutes, preferably about 1 to about 5 grams per 10 minutes. The copolymer can be produced in the presence of a catalyst system containing chromium and titanium or a catalyst system containing a catalyst precursor comprising magnesium, titanium, a halogen, and an electron donor together with one or more aluminum containing compounds. The former can be made in accordance with the disclosure of U.S. Pat. No. 4,101,445 and the latter, which is preferred, can be prepared as described in U.S. Pat. No. 4,302,565.
Suitable alpha-olefin comonomers are exemplified by propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. The portion of the copolymer attributed to the comonomer, other than ethylene, is in the range of about 5 to about 50 percent by weight based on the weight of the copolymer and is preferably in the range of about 10 to about 40 percent by weight.
The polysiloxanes useful in the practice of the invention are organomodified polydimethyl siloxanes. They have the following formula: ##STR3## wherein R=alkyl having 1 to 4 carbon atoms, acyl having 1 to 4 carbon atoms, or trimethyl silyl, and
REFERENCES:
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patent: 4689362 (1987-08-01), Dexter
patent: 4708082 (1987-10-01), Godlewski
patent: 4931492 (1990-06-01), Foster et al.
Bresch Saul R.
Marquis Melvyn I.
Union Carbide Chemicals and Plastics Technology Corporation
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