| 摘要 |
A telecommunication cable has as the primary insulation a 4-methylpentene-1 polymer coating having an ash content of less than 0.02% by weight. The polymer may be a copolymer of 4-methylpentene-1 with a minor proportion of a linear 1-olefine having 5 to 18 carbon atoms. The cables may be co-axial or symmetrical. The outer conductor may be lapped aluminium foil or tinned copper braiding and the outside sheath may be of any suitable thermoplastic material e.g. polythene or polypropylene. Methods for producing the polymers having the requisite ash contents are described in Specifications 942,297, and 1,001,801. The polymer may contain 0.05 to 0.5% by weight of an antioxidant e.g. a condensate of three molar proportions of 3-methyl-6-tertiary-butyl-phenol with one molecule of crotonaldehyde or 1,3,5-trimethyl-2,4,6-tri(3,5-di-tertiary butyl 4-hydroxybenzyl)benzene, and 0.05 to 0.5% by weight of a melt stabiliser e.g. dihydroanthracene. The cables may be formed by extrusion. In the embodiment of the invention, the central conductor of copper is surrounded by primary insulation comprising an unstabilised copolymer of 4-methyl-pentene-1 containing 12% by weight of hexene-1 monomer units and less than 0.01% ash content, which is in turn surrounded by the outer conductor of lapped copper foil and has an outside layer of a polyvinyl chloride sheath. The cables are said to be particularly useful as submarine cables. |
