Process for the production of power cable

A process for the co-extrusion of an outer layer, a middle layer, and an inner layer, each layer comprising a thermoplastic resin, around a conductive medium in three extruders, one extruder for each layer, connected by a triple crosshead, each of said extruders having an extrusion zone comprising a die plate and, downstream of the die plate, a die, and, downstream of the extrusion zone, a common crosslinking zone, comprising passing the thermoplastic resins through the extrusion zones, under extrusion conditions including an extrusion temperature in the range of at least 150 degrees C. to below the decomposition temperature of the organic peroxide referred to hereinafter, and passing the extrudate into the crosslinking zone, under crosslinking conditions, the improvement comprising introducing an organic peroxide having a half life of one minute at a temperature of about 150 to about 200 degrees C. into the middle layer extruder into injection zone 15 of FIG. 1 of the drawing.

A process for the co-extrusion of an outer semiconductive and/or jacketing layer, an insulating middle layer, and an inner semiconductive layer, the middle layer comprising a polyethylene and the inner and outer layers comprising polyethylene and an organic peroxide, around a conductive medium in three extruders, one extruder for each layer, connected by a triple crosshead, each of said extruders having an extrusion zone comprising a die plate and, downstream of the die plate, a die, and, downstream of the extrusion zone, a common crosslinking zone, comprising passing the polyethylene through the extrusion zones, under extrusion conditions including an extrusion temperature in the range of at least 150 degrees C. to about 170 degrees C., but below the decomposition temperature of the organic peroxide referred to hereinafter, and passing the extrudate into the crosslinking zone, under crosslinking conditions, the improvement comprising introducing an organic peroxide having a half life of one minute at a temperature of about 150 to about 200 degrees C. into the middle layer extruder into injection zone 15 of FIG. 1 of the drawing, but in close proximity to the die plate, said organic peroxide being introduced in an amount in the range of about 1 to about 5 parts by weight of organic peroxide per 100 parts by weight of resin.