Electricity: conductors and insulators – Conduits – cables or conductors – Conductive armor or sheath
Reexamination Certificate
2000-04-25
2001-09-18
Kopec, Mark (Department: 1751)
Electricity: conductors and insulators
Conduits, cables or conductors
Conductive armor or sheath
C252S511000
Reexamination Certificate
active
06291772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to compositions of matter useful as shields in power cables and to shields and power cables utilizing the composition.
2. Description of the Related Art
Semiconductive shields have been used in power cables as shields for the cable conductor and insulation for many years. A conductor shield is typically extruded over the cable conductor to provide a layer of intermediate conductivity between the conductor and cable insulation in the power cable. A shield is also typically provided over the insulation. Conventional compositions for these shields include a base polymer as the predominant component of the composition compounded with, carbon black to provide conductivity for the composition and various additives including antioxidants, processing aids or lubricants and curing agents.
Examples of polymer compositions used as shields in power cables are found in the disclosures of U.S. Pat. Nos. 4,612,139 and 4,305,846 to Kawasaki et al., U.S. Pat. No. 4,857,232 to Burns, Jr., U.S. Pat. No. 3,849,333 to Lloyd et al., and U.S. Pat. No. 5,889,117 to Flenniken, the disclosures of which are hereby incorporated by reference.
As previously mentioned, one common additive to cable shield compositions is an antioxidant. Conventional antioxidants used in shielding compositions for power cables include stearically hindered phenols and amines such as polymerized 1,2-dihydro-2,2,4-trimethylquinoline, octadecyl, 3,5 diterbutyl-4-hydroxyhydrocinnamate, 4,4′-thio-bis-(3-methyl-6-tert-butylphenol), thiodithylene-'bis-(3,5-ditert-butyl-4-hydroxy) hydrocinnamate, distearyl-thio-dispropionate, and mixtures of these compounds. The antioxidant components are generally included in the shield compositions in amounts significantly less than 1.0% by weight, typically less than 0.7%, by weight, of the shield compositions. The antioxidants function as stabilizers to prevent degradation of the polymer composition over time due to temperature.
SUMMARY OF THE INVENTION
The present invention is based upon the discovery that a particular antioxidant additive when incorporated in a conductor shield composition in particular amounts, significantly improves the performance of a cable shield composition. More specifically, the invention is based upon the discovery that the use of polymerized trimethylquinoline as the antioxidant additive for the conductor shield composition in amounts significantly higher than conventionally used in shield compositions, results in a cable shield exhibiting improved performance over cable shields formed with other antioxidant additives including trimethylquinolines. In particular, the composition of the invention exhibits superior performance over time as demonstrated by accelerated cable life testing (ACLT) as compared to shielding compositions which use conventional antioxidant additives in conventional amounts.
The invention, therefore, is a composition matter suitable for use in electric cables as a cable shield, comprising at least one base polymer, conductive carbon black in an amount which is sufficient to give the composition an electrical resistivity below 500 &OHgr;m, and an antioxidant additive comprised of polymerized trimethylquinoline in an amount which is greater than 0.7% by weight of the composition, and preferably at least 1.0% by weight of the composition. Polymerized 1,2-dihydro-2,2,4-trimethylquinoline having a melting point of about 60° C. is most preferred as the antioxidant additive for use in the composition of this invention.
In addition to the composition matter, the invention includes a semiconductive shield for the conductor or insulation in a power cable formed by extruding the composition over the conductor or insulation of the power cable and the resulting power cable which employs the composition as a shield.
Further features of the invention will become evident to those of skill in the art upon reading the detailed description of the invention which follows.
REFERENCES:
patent: 3849333 (1974-11-01), Lloyd et al.
patent: 4305846 (1981-12-01), Jennings
patent: 4612139 (1986-09-01), Kawasaki et al.
patent: 4857232 (1989-08-01), Burns, Jr.
patent: 5889117 (1999-03-01), Flenniken
patent: 6013202 (2000-01-01), Easter et al.
Easter Mark R.
Freestone James
Blank Rome Comisky & McCauley LLP
General Cable Technologies Corporation
Kopec Mark
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