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EP-4742276-A1 - PREPARATION OF AN ELECTRICAL CABLE BY CONTINUOUS EXTRUSION OF A THERMOPLASTIC INSULATING LAYER AND A THERMOPLASTIC OUTER SHEATH

EP4742276A1EP 4742276 A1EP4742276 A1EP 4742276A1EP-4742276-A1

Abstract

The present invention relates to a method for the continuous manufacture of an electrical cable (1) comprising an elongated electrically conductive element (2), an insulating layer (3) surrounding said elongated electrically conductive element; and a sheath (4) surrounding said insulating layer, and wherein: - the insulating layer (3) is extruded around said elongated electrically conductive element (2), from a first non-crosslinkable thermoplastic polymer composition C1; and - the sheath (4) is extruded around the insulating layer (3) , from a second non-crosslinkable thermoplastic polymer composition C2, distinct from composition C1.

Inventors

  • PEREGO, GABRIELE
  • CACCIOTTI, MAURO
  • SADIK, Tarik

Assignees

  • Nexans

Dates

Publication Date
20260513
Application Date
20251110

Claims (11)

  1. A method for the continuous manufacture of an electrical cable (1) comprising an elongated electrically conductive element (2), an insulating layer (3) surrounding said elongated electrically conductive element; and a sheath (4) surrounding said insulating layer, and wherein: - the insulating layer (3) is extruded around said elongated electrically conductive element (2), from a first non-crosslinkable thermoplastic polymer composition C1; and - the sheath (4) is extruded around the insulating layer (3) , from a second non-crosslinkable thermoplastic polymer composition C2, distinct from composition C1.
  2. Method according to claim 1, wherein the thermoplastic polymer sheath (4) is in direct contact with the thermoplastic insulating layer (3).
  3. A process according to claim 1 or 2, wherein the first composition C1 is a non-crosslinkable thermoplastic composition containing a propylene (PP) polymer.
  4. A method according to any one of claims 1 to 3, wherein the second composition C2 is a composition containing an ethylene polymer (PE), preferably an HDPE.
  5. A method according to any one of claims 1 to 4, which is carried out on a continuous production line, comprising successive stations through which the elongated electrically conductive element is conveyed at constant speed and without stopping time, and where the following steps are implemented: Step a: the insulating layer (3) is extruded around said elongated electrically conductive element (2) in a first extruder, from the first thermoplastic composition C1 Step b: the extruded insulating layer (3) obtained at the outlet of the first extruder is subjected to cooling means; Step c: the thermoplastic polymer sheath (4) is extruded around the insulating layer (3) as obtained after cooling in step b, in a second extruder, from the second thermoplastic composition C2.
  6. A process according to claim 5, wherein composition C2 has a melting point lower than that of composition C1
  7. A method according to claim 5 or 6, wherein the cooling means of step b comprise contacting the extruded insulating layer with water.
  8. A method according to claim 7 wherein, after step b and prior to step c, the extruded insulating layer (3) which has been brought into contact with water is dried, preferably under a stream of air.
  9. A method according to any one of claims 4 to 8, wherein the extruded polymer sheath (4) obtained at the outlet of the second extruder is subjected to cooling means, these cooling means typically including bringing the extruded polymer sheath (4) into contact with water.
  10. A method according to any one of claims 1 to 4, which is carried out on a continuous production line, comprising successive stations through which the elongated electrically conductive element is conveyed at constant speed and without stopping time, and where the following steps are implemented: Step 1: the insulating layer (3) and the sheath (4) surrounding this insulating layer are co-extruded around said elongated electrically conductive element (2) in the same extrusion head, from the first thermoplastic composition C1 for the insulating layer and from the second thermoplastic composition C2 for the sheath; Step 2: The elongated electrically conductive element (2) fitted with the insulating layer (3) and the sheath (4) obtained at the outlet of the extrusion head of step 1 is subjected to cooling means.
  11. Electrical cable (1) capable of being obtained according to the process according to any one of claims 1 to 10.

Description

The present invention relates to the field of preparing electrical cables having an elongated electrically conductive element coated with a polymer insulating layer, itself coated with a polymer sheath. More specifically, the invention relates to an extrusion process allowing the layer and sheath to be applied continuously. The invention typically, but not exclusively, applies to electrical cables intended for the transport of energy, and in particular to low voltage power cables (i.e. carrying a direct or alternating current typically having a voltage less than or equal to 6 kV), and which can for example be used in the fields of aerial, submarine, terrestrial, or aeronautical electricity transport. A low-voltage power transmission cable preferably includes: an elongated electrically conductive element (for example a wire or a set of wires twisted together), especially made of copper or aluminum; an electrically insulating polymer layer surrounding said elongated electrically conductive element; and preferably an electrically insulating protective sheath surrounding said electrically insulating layer. The present invention relates to cables of this type comprising a polymer insulating layer, covered by a polymer sheath. Historically, the insulating layers of such cables were made of polyethylene, particularly cross-linked polyethylene (XLPE), which offers the advantage of being easy to handle and providing good electrical properties for the insulating layer. Cross-linking also imparts good physical properties to the polyethylene. In particular, XLPE-based cables can be used at operating temperatures of up to 90°C in continuous mode due to the cross-linking, whereas the operating temperature of an LDPE-based cable generally does not exceed 70°C in continuous mode. However, cross-linked polyethylene has some drawbacks. In addition to being difficult to recycle (cross-linking causes polyethylene to lose its thermoplastic properties), XLPE cross-linked polyethylene requires a cross-linking (vulcanization) step, which limits the production speed of XLPE-based cables. Typically, for the production of an XLPE-based insulating layer around an elongated electrically conductive element, the insulating layer being formed must remain in a vulcanization chamber where the crosslinking of the layer takes place in order to reach a sufficient level of crosslinking. The required cross-linking must first be achieved before applying the protective sheath around the insulating layer. Therefore, the production speed of cross-linked XLPE cables is limited by the rate at which cross-linking occurs in the vulcanization chambers. The need for vulcanization chambers also results in a larger installation footprint. Furthermore, using a crosslinkable composition to prepare the insulating layer introduces a risk of premature crosslinking in the extruder, with associated overheating that must be avoided. Otherwise, premature crosslinking often necessitates a production line shutdown for extruder cleaning. These considerations also limit production speed. Furthermore, by employing a crosslinked insulating layer, the process involves verification steps to ensure that adequate crosslinking is achieved, which complicates the process (which involves not only extrusion, but also a subsequent step to verify the layer obtained), resulting in increased process costs. These difficulties are inherent to the use of crosslinked polyethylene. Reducing the size of the vulcanization chambers is hardly feasible, nor is decreasing the residence time of the layer being crosslinked within the chambers, particularly if one wishes to avoid any risk of incomplete crosslinking or fluctuation in the crosslinking rate of the applied XLPE. As a result, XLPE-based low-voltage cable production lines have limited capacity and production speed. One aim of the present invention is to provide a new method for increasing the production speed of low voltage cables and the capacity of production lines for such cables. To this end, it is proposed according to the present invention to apply by extrusion a non-crosslinkable thermoplastic polymer layer, to form a non-crosslinked insulating layer, and to apply on this non-crosslinked insulating layer another thermoplastic layer, which thus forms a sheath around the insulating layer, which makes it possible to consider a continuous application method of the two applied thermoplastic layers. More specifically, according to a first aspect, the present invention relates to a method for the continuous manufacture of an electrical cable comprising an elongated electrically conductive element, an insulating layer surrounding said elongated electrically conductive element, and a sheath surrounding said insulating layer, and wherein: the insulating layer (3) is extruded around said elongated electrically conductive element (2), from a first non-crosslinkable thermoplastic polymer composition C1; and The sheath is extruded around the in