Process for the manufacture of an electric cable by extrusion of a composition based on a propylene polymer and on a dielectric liquid

A process for the manufacture of an electric cable having at least one elongated electrically conducting element and at least one extruded thermoplastic layer surrounding said elongated electrically conducting element, said process employing a device comprising at least one extruder containing a barrel, a screw and an extruder head, said method comprising steps of:

• i) a stage of introduction of a composition comprising:
• at least one thermoplastic polymer in a solid form chosen from a propylene homopolymer and a propylene copolymer, and
• at least one dielectric liquid, said dielectric liquid representing an amount of less than 15% by weight, with respect to a total weight of the composition, into a first zone of the screw, denoted feed zone, located at an inlet of the extruder;
• ii) a stage during which the composition resulting from stage i) is conveyed from the feed zone towards one or more intermediate zones of the screw, making possible transportation of the composition towards the head of the extruder located at an outlet of the extruder and gradual melting of the thermoplastic polymer;
• and
• iii) a stage of application, at the head of the extruder, of the composition resulting from stage ii) around the elongated electrically conducting element,
• wherein, the barrel is a grooved barrel and the screw is a barrier screw, wherein said barrier screw has at least one barrier zone with a secondary thread with a greater pitch than a main thread, and with a height lower than said main thread, sufficient to separate the molten polymer from the polymer which is still solid.