Hayao Ishitani

Development of radiation crosslinking process for high voltage power cable

Abstract This work has been done to develop an electron beam crosslinking process for high voltage power cable by solving problems of the foaming and discharge breakdown of thick polyethylene insulation during irradiation. When a polyethylene plaque (d=0.92, MI=1.0) of 4 mm thick corresponding to the wall of 6.6 kV cable was irradiated by 1.5 MeV electrons, the temperature went up to 95°C and foaming was observed at a dose of 20 Mrad. On the other hand, irradiation of 24 Mrad was required for sufficient heat resistance (75% gel formation) of polyethylene. Although an addition of conventional polyfunctional monomers reduced the crosslinking dose (10 – 12 Mrad), discharge breakdown occured at relatively low doses. The present work reveals that both foaming and discharge breakdown are efficiently prevented by the use of dipropargyl succinate (DPS). A 6.6 kV type cable specimen insulated with polyethylene containing 2 phr of DPS was irradiated by 1.5 MeV electrons. While the cable had properties comparable to those of a steam cured one, very few voids were observed in the insulation.

Radiation cross-linked polyolefin-insulated wire

Abstract Because radiation cross-linked polyolefin has excellent mechanical heat resistance, its application limit can be expanded extremely by improving the resistance against heat oxidation and flame. This paper is concerning a halogen free radiation cross-linked polyolefin-insulated wire having excellent heat resistance and flameretardant property, which is used for appliances.

The unique processing of rubber-insulated wires by radiation

Abstract Ethylene-propylene rubbers are able to be crosslinked (vulcanized) by high energy radiation. The radiation-induced crosslinking of ethylene-propylene copolymer or ethylene-propylene-diene terpolymer depends upon the ethylene/propylene ratio, the molecular weight of the polymer, the unsaturating degree of terpolymer and kinds of tercomponents. The mechanical properties of the crosslinked rubber were affected mainly by the E/P ratio and the molecular weight, and improved by blending of low density polyethylene or ethylene-vinylacetate copolymer. Aging of the rubber, due to kinds and contents of tercomponents, was mostly determined by addition of antioxidants to the compound. We developed EP rubber compounds for wire insulation crosslinked by electron beam radiation and applied to the insulation cores of the ships cables, in the place of the wire vulcanized conventionally by the pressurized steam in the continuous vulcanizer. The rubber compounds are consisted of ethylene-propylene-diene terpolymer with high ethylene contents, ethylene-vinylacetate copolymer and antioxidants. The high-ethylene polymers are supplied in the shape of pellets, and antioxidants were added to the compounds by means of dry blending of concentrates in which antioxidants are mixed into pellets of ethylene copolymer. The EP rubbers were covered on the copper wire by the extruder, used to plastic material, and irradiated with the electron beam from an accelerator. These insulated cores manufactured on radiation processing had the excellent properties, particularly aging and electrical properties. Further, they are more simply colored. Therefore, they will be considered to be used to other applications. This method of manufacturing of the rubber-insulated wires made it possible to reduce both the material costs by simple compounding and the operating costs by radiation-induced crosslinking, to compare with the conventional compounding and vulcanizing process, in which the materials are compounded with the openroll, the Banbury mixer or others and the wires coated with these materials are vulcanized with the steam pressured vessel, the continuous catenary vulcanizer or others.