Patent GB-1083114-A (GB)
Title: Dielectric compositions
IPC: C08L23/00
Filed: 1964-08-26
Abstract: <PICT:1083114/C3/1> A dielectric composition comprises a solid polyolefin (e.g. low- or high-density polyethylene or polypropylene, which may contain minor amounts of rubbery polymers or copolymers of isobutylene or isoprene) having dispersed therein a blend of a highly aromatic non-volatile hydrocarbon oil or low-melting hydrocarbon and a voltage stabilizing additive which is a halogenated polycyclic aromatic compound or a substituted aromatic hydrocarbon having an electron acceptor group and an electron donor group potentially bound together by a reversibly transferable proton.  Several suitable hydrocarbon oils are specified, and the low-melting hydrocarbon may be o-terphenyl. The oil or the o-terphenyl may be mixed with m- or p-terphenyl, diphenyl, anthracene, or phenanthrene. The additive may be a chlorinated diphenyl or triphenyl, a mixture thereof, a brominated polyphenyl such as 4,41-dibromodiphenyl, a polychlorinated or polybrominated naphthalene or anthracene; 2,4,6-trinitrotoluene, 2-nitro- or 2,4-dinitro-diphenylamine, o-nitroanisole, 2,4- or 2,6-dinitrotoluene, o-nitrodiphenyl, aminodiphenyl, 2-nitroaniline, anthranilonitrile, 1-fluoro-2-nitrobenzene, or mixtures thereof, or mixtures thereof with diphenylamine; or mixtures of diphenylamine with at least one of m-dinitrobenzene, 3- or 4-nitroaniline, 3- or 4-nitrotoluene, or o- or p-nitrochlorobenzene. The polyolefin compositions may contain the usual additives such as carbon black, antioxidants, heat stabilizers, and ozone resistance stabilizers, and may have been cross-linked with peroxides (e.g. dicumyl peroxide, 2,5 - bis - (t - butylperoxy) - 2,5 - dimethylhexane, or 2,5-dimethyl-2,5-di-(t-butylperoxy)-hexyne-3) or by irradiation of from 10-15 megarads.  From 5 to 50 parts of stabilizing additive per 100 parts of aromatic oil or o-terphenyl can be used, and from 1-10% by weight of the mixture in the polyolefin.  The polyolefin composition may contain carbon black and be used as a strand shield or cable jacket, e.g. a strand shield composition may be an ethylene-ethyl acrylate copolymer containing carbon black, and a weatherproof cable jacket may comprise polyethylene containing finely divided carbon.  In Example 1, a semi-conducting polyethylene strand shield 2, Fig. 1, is extruded over a 61-strand bare copper conductor 1, and a polyethylene insulation 3 containing an antioxidant, a mixture of polychlorinated polyphenyls and a non-volatile highly aromatic oil is extruded thereover.  A shield 4 is applied over insulation 3 by helically serving semi-conducting nylon tapes and 0.004-inch thick copper tape thereover, and a protective lead coating 5 and a black polyethylene weather-proof jacket 6 are extruded thereover. The 2 1/2 -inch diameter cable is suitable for 69 kv. grounded neutral service at a rating of 45,000 kv.A.  The greater ability of polyethylene with additives to withstand A.C. voltage is shown by tests.  A table showing a number of oil/additive combinations for addition to polyethylene is given.  Example XXXII describes a strand shielding comprising ethylene-ethyl acrylate copolymer containing semi-conducting carbon black and a mixture of polychlorinated polyphenyls and a non-volatile highly aromatic oil.