METHOD FOR IMPROVING IMPULSE BREAKDOWN STRENGTH OF ELECTRICAL INSULATING MATERIALS

摘要

The present invention provides a method for improving impulse destructive strength of an electrical insulating material which is characterized by employing, as the electrical insulating material, a random copolymer of a styrene series monomer and ethylene or a combination of ethylene and another ethylenic unsaturated monomer, or a composition in which the copolymer is blended with an ethylene series polymer, the copolymer being prepared by introducing, into a reaction system, the styrene series monomer selected from the group of styrene and single-ring substituted styrenes, ethylene or the combination of ethylene and the ethylenic unsaturated monomer and a polymerization initiator, the latter being introduced thereinto separately from at least the styrene series monomer, and subjecting these monomers to a high-pressure radical copolymerization under a polymerization pressure of 500 to 4,000 kg/cm2 at a polymerization temperature of 50 DEG to 400 DEG C., the aforesaid polymer or composition satisfying the following (a) and (b): (a) a content of the styrene series monomer in the copolymer or the composition being within the range of 0.01 to 1 mol %; and (b) a crystallinity of the copolymer or the composition being 30% or more in accordance with X-ray diffraction.