Electrical insulation for transmission cables - comprising mixt. of high and low pressure polyethylene foamed with aromatic sulphohydrazide

摘要

Electrical insulation for transmission cables, esp. HF transmission cables, consists of polyethylene chemically foamed with an aromatic sulphohydride of formula: H2N-HN-SO2-R-SO2-NH-NH2 (R = aromatic gp). It is produced by incorporating into a melt contg. 100 pts. polyethylene (10-90 pts. high pressure polyethylene and 90-10 pts. low pressure) 0.5-1.5 pts. oxybis (benzene sulphohydrazide) in which the sulphohydrazide gps. are linked to the gp. R in posns. other than 4,4'. This acts as a blowing agent. Pref. the blowing agent is 3,3'-oxybis(benzene sulphohydrazide.). The compsn. pref. contains 0.6-0.9 pts. aromatic sulphohydrazide. The compsn. produces uniform foam which gives more consistent electrical properties. In an example 0.75 pts. of an aromatic sulphohydrazide (pref. 3,3'-oxybis (benzene sulphohydrazide)) were incorporated at 135-150 degrees C into a mixt. of 50 pts. high pressure polyethylene (density 0.918, melt index 0.5) and 50 pts. low pressure polyethylene (density 0.960, melt index 0.3), using a kneader or mill. The prod. was then granulated.