Method for manufacturing an electrical cable by controlled cooling

Abstract

The invention relates to a method for manufacturing a cable comprising at least one elongated electrically conductive element, a first semiconductor layer surrounding the elongated electrically conductive element, an electrically insulating thermoplastic layer surrounding the first semiconductor layer, and a second semiconductor layer surrounding the electrically insulating thermoplastic layer, said electrically insulating thermoplastic layer being obtained from an electrically insulating composition comprising at least one thermoplastic polymer (e.g., a propylene polymer), said method employing controlled cooling of the cable after extrusion of the aforementioned layers. Figure for the abstract: Fig. 1

Description

Title of the invention: Method for manufacturing an electrical cable by controlled cooling

[0001] The invention relates to a method for manufacturing a cable comprising at least one elongated electrically conductive element, a first semiconducting layer surrounding the elongated electrically conductive element, an electrically insulating thermoplastic layer surrounding the first semiconducting layer, and a second semiconducting layer surrounding the electrically insulating thermoplastic layer, said electrically insulating thermoplastic layer being obtained from an electrically insulating composition comprising at least one thermoplastic polymer (e.g., a propylene polymer), said method employing controlled cooling of the cable after extrusion of the aforementioned layers.

[0002] The invention typically but not exclusively applies to electrical cables intended for the transport of energy, in particular to medium voltage power cables (in particular from 6 to 45-60 kV) or high voltage power cables (in particular above 60 kV, and up to 400 kV), whether direct current or alternating current, in the fields of aerial, submarine, or terrestrial electricity transport.

[0003] A medium or high voltage power transmission cable preferably comprises, from the inside to the outside: - an elongated electrically conductive element, particularly made of copper or aluminum, - an internal semiconductor layer surrounding said elongated electrically conductive element, - an electrically insulating layer surrounding said internal semiconductor layer, - an external semiconductor layer surrounding said electrically insulating layer, - possibly an electrical screen surrounding said outer semiconductor layer, and - possibly an electrically insulating protective sheath surrounding said electrical screen.

[0004] It is known to manufacture cables in which the electrically insulating layer is a cross-linked polyethylene (XLPE) polymer layer. The process thus comprises a step of extruding the polymer composition around the elongated electrically conductive element, a cross-linking step, and a step of cooling the cable by contacting the cable with water at room temperature. Crosslinking promotes the cohesion of the layer material during the cooling stage.

[0005] Thermoplastic polymers such as polypropylene have also been tested as a replacement for XLPE, in particular to promote the recycling of raw materials, and to avoid the scorch phenomenon that can occur during crosslinking.

[0006] By way of example, international application WO02 / 47092 describes a method for manufacturing a cable comprising a step of applying by extrusion an inner semiconductor layer, an electrically insulating layer based on a propylene polymer, and an outer semiconductor layer, around an elongated electrically conductive element, and a step of cooling the cable by passing the cable through a cooling channel in which a suitable liquid, such as water, is placed, maintained at a temperature of 12 to 15°C. The electrically insulating layer thus obtained may then exhibit morphological defects (microcavities, microcracks) which can induce the occurrence of partial discharges, and increase the risk of electrical breakdown.

[0007] The object of the present invention is therefore to overcome the disadvantages of prior art techniques by proposing a method for manufacturing an electrical cable, in particular medium or high voltage, based on thermoplastic polymer(s) such as propylene polymer(s), said method being easy to implement, inexpensive, and leading to a homogeneous thermoplastic layer, i.e. avoiding the formation of morphological defects (microcavities, microcracks) within said thermoplastic layer.

[0008] The goal is achieved by the invention which will be described below.

[0009] The invention relates first to a method for manufacturing an electrical cable comprising at least one elongated electrically conductive element, an internal semiconducting layer surrounding the elongated electrically conductive element, an electrically insulating thermoplastic layer surrounding the internal semiconducting layer, and an external semiconducting layer surrounding the electrically insulating thermoplastic layer, said electrically insulating thermoplastic layer comprising at least one thermoplastic polymer, said method being characterized in that it comprises at least the following steps: i) apply by extrusion in this order: the inner semiconductor layer, the electrically insulating thermoplastic layer, and the outer semiconductor layer, around the elongated electrically conductive element, ii) cool the external semiconductor layer thus extruded in step i) by contacting it with a first medium maintained at a temperature Ti ranging from approximately 60 to 140°C for a sufficient time so that the thermoplastic layer The insulating material reaches a temperature T2 such that Te - 25 °C < T2 and T2 ≤ Te + 25 °C

[0010] Tc being the crystallization temperature of the thermoplastic polymer, and iii) cool the cable thus obtained in step ii) by bringing it into contact with a second medium maintained at a temperature T3 less than or equal to 50°C.

[0011] The process of the invention is simple to implement, inexpensive, and does not require complex equipment. It makes it possible to obtain a cable capable of operating at temperatures above 70°C, just like XLPE-based cables. Furthermore, it has the advantages of using thermoplastic polymers (i.e., which are recyclable) and of resulting in a homogeneous electrically insulating thermoplastic layer, i.e., in which the formation of morphological defects (microcavities, microcracks) is reduced or even prevented.

[0012] Indeed, during the manufacture of thermoplastic cables (i.e., comprising at least one thermoplastic or non-crosslinked electrically insulating layer), and particularly during the cooling stage, the risk of morphological defects becomes significant due to the absence of crosslinking, which generally contributes to the cohesion of the layer. This risk is even greater when the thermoplastic polymer(s) used in the layer have a high melting point, as is the case, for example, with propylene polymer. Thus, with conventional cooling, the electrically insulating thermoplastic layer begins to crystallize in the innermost zone near the elongated electrically conductive element, and in the outermost zone near the external semiconducting layer, since these zones lose heat more rapidly.This cooling then leads to an internal zone of the thermoplastic layer that is not crystallized and is subjected to physical forces from the already crystallized zones, promoting the formation of morphological defects.

[0013] Thanks to the process of the invention, and in particular thanks to the presence of steps ii) and iii), the electrically insulating thermoplastic layer crystallizes from the internal zone, and the risk of formation of morphological defects within this layer is reduced, or even avoided. Step i)

[0014] During step i), the three layers of the cable, i.e. the inner semiconductor layer, the electrically insulating thermoplastic layer, and the outer semiconductor layer are applied by extrusion around the elongated electrically conductive element.

[0015] The electrically insulating thermoplastic layer is preferably obtained from an electrically insulating composition comprising at least the thermoplastic polymer material.

[0016] The internal semiconductor layer can be obtained from a first semiconductor composition.

[0017] The outer semiconductor layer can be obtained from a second semiconductor composition.

[0018] During this step i), the first semiconducting composition is extruded around the elongated electrically conducting element to form the inner semiconducting layer; the electrically insulating composition comprising at least one thermoplastic polymer is extruded around the inner semiconducting layer to form the electrically insulating thermoplastic layer; and the second semiconducting composition is extruded around the electrically insulating thermoplastic layer to form the outer semiconducting layer.

[0019] Step i) can be carried out by techniques well known to those skilled in the art, for example using an extruder.

[0020] During step i), the first and second semiconducting compositions, and the electrically insulating composition are in a molten state, and preferably pass under pressure through a die, in particular in the extruder head.

[0021] During step i), at least the electrically insulating composition at the extruder outlet is said to be "non-crosslinked". The temperature and the processing time within the extruder are optimized accordingly.

[0022] At the extruder outlet, we therefore obtain a cable comprising at least one elongated electrically conductive element, an extruded internal semiconducting layer surrounding the elongated electrically conductive element, an extruded electrically insulating thermoplastic layer surrounding the internal semiconducting layer, and an extruded external semiconducting layer surrounding the electrically insulating thermoplastic layer.

[0023] During step i), the temperature within the extruder is preferably higher than the melting temperature of the major polymer or of the polymer having the highest melting temperature, among the polymers used in the different compositions to be implemented.

[0024] This step i) can be carried out at an extrusion temperature Te ranging from approximately 170°C to approximately 240°C, and preferably ranging from approximately 180°C to approximately 220°C.

[0025] According to a preferred embodiment of the invention, step i) comprises the following substeps: i') extrude a first semiconductor composition, this first semiconductor composition possibly being cross-linked, around the elongated electrically conductive element, (i) extrude the electrically insulating composition comprising at least one thermoplastic polymer, around the internal semiconducting layer, i'") extrader a second semiconducting composition, this second semiconducting composition being cross-linked, around the electrically insulating thermoplastic layer.

[0026] Substep i') allows the formation of the internal semiconducting layer surrounding said elongated electrically conductive element.

[0027] Substep i”) enables the formation of the electrically insulating thermoplastic layer surrounding said internal semiconducting layer.

[0028] Substep i'”) enables the formation of the external semiconducting layer surrounding said electrically insulating thermoplastic layer.

[0029] The substeps i'), i”), and i'”) are preferably concurrent, step i) is then a co-extrusion step.

[0030] Each of the substeps i'), i”), and i”') can be carried out at an extrusion temperature Te ranging from approximately 170°C to approximately 240°C, and preferably ranging from approximately 180°C to approximately 220°C. Step ii)

[0031] Step ii) allows the external semiconductor layer extruded in step i) to be cooled in a controlled manner. Indeed, thanks to this step ii), a progressive cooling from the inside of the cable to the outside is achieved.

[0032] In particular, this controlled cooling after the extrusion step i) makes it possible to maintain at the outermost surface of the cable a temperature higher than the crystallization temperature of the thermoplastic polymer.

[0033] Thanks to this step ii), the too rapid crystallization of the external zones of the electrically insulating thermoplastic layer (zones close to the internal semiconducting layer and the external semiconducting layer) is avoided, and said step ii) makes it possible to reduce, or even avoid, the formation of morphology defects during cooling.

[0034] The temperature T2 represents a temperature close to the crystallization temperature of the thermoplastic polymer.

[0035] During the contact in step ii), said outer semiconducting layer (and thus at least the outermost surface of the cable) can be cooled from the extrusion temperature Te to a temperature T4 greater than or equal to about 80°C; and maintained at a temperature T'4 greater than or equal to about 80°C, T'4 being greater than or equal to Tb until the electrically insulating thermoplastic layer reaches the temperature T2 as defined in the invention.

[0036] The temperature T4 is preferably greater than or equal to approximately 90°C, T4 being able to be greater than or equal to Tb and particularly preferably greater than or equal to approximately 100°C.

[0037] The temperature T'4 is preferably greater than or equal to approximately 90°C, and in a way particularly preferred at approximately 100°C or higher.

[0038] The temperatures T4 and T'4 can be identical or different, and preferably identical.

[0039] In a preferred embodiment, step ii) is carried out by bringing the external semiconductor layer into contact with a cooling fluid (as a first medium) selected from liquids and gases of cooling, such as water, nitrogen, silicone oil, carbon dioxide, air, compressed air, or ethylene glycol.

[0040] Water and nitrogen are preferred as cooling fluids.

[0041] During step ii), the temperature Ti preferably goes from about 90 to 120°C.

[0042] In a particular embodiment of the invention, step ii) is carried out to a cooling rate (for example to go from extrusion temperature Te to temperature T'4) ranging from 1 to 20°C per minute approximately, and preferably ranging from 2 to 10°C per minute approximately.

[0043] The cooling rate can be implemented using a thermostatic control device for the cooling fluid.

[0044] Step ii) can be carried out at a pressure ranging from approximately 1 to 15 bars, and preferably from approximately 5 to 12 bars.

[0045] The duration of step ii) depends on the diameter and structure of the cable.

[0046] Step ii) can last from about 1 minute to about 1 hour, and preferably 20 minutes approximately 45 minutes.

[0047] According to a preferred embodiment of the invention, the temperature T2 is such that Te - 25 °C < T2 and T2 < Te + 20 °C

[0048] Tc being the crystallization temperature of the thermoplastic polymer, the temperature T2 can be greater than or equal to Tb

[0049] When the electrically insulating composition comprises several thermoplastic polymers, the temperature Tc corresponds to the crystallization temperature of the thermoplastic polymer having the highest crystallization temperature or to the crystallization temperature of the mixture of thermoplastic polymers.

[0050] In the present invention, the crystallization temperature Tc is determined by digital scanning calorimeter (DSC).

[0051] According to a particularly preferred embodiment of the invention, step ii) is carried out by passing said cable from step i) through a cooling conduit or tube comprising said cooling fluid.

[0052] In particular, said cooling conduit or tube is continuously supplied with said cooling fluid. The latter therefore circulates continuously in said cooling conduit or tube.

[0053] The cooling tube or conduit is preferably made of metal such as, for example steel.

[0054] According to another embodiment of the invention, step ii) is carried out by passing said cable from step i) through one or more cooling tanks continuously supplied with the cooling fluid, in particular to maintain a constant temperature of the cooling tanks.

[0055] Each of the cooling tanks can include a cooling fluid maintained at a different temperature depending on the tanks, the temperature being decreasing from tank to tank, for example the temperature of successive tanks is 90°C, 80°C and 65°C. Step iii)

[0056] While step ii) represents surface cooling, step iii) represents mass cooling.

[0057] In particular, once the electrically insulating thermoplastic layer reaches the temperature T2 as defined in the invention, the cable can be cooled by contacting a second medium maintained at a temperature less than or equal to 50°C.

[0058] Generally, this step iii) allows the cable to be cooled to ambient temperature (i.e., 18-30°C). At the end of step iii), the cable thus obtained is ready to be put into service and / or used in various applications.

[0059] In a preferred embodiment, step iii) is carried out by bringing the cable of step ii) into contact with a cooling fluid (as a second medium) selected from liquids and gases of cooling, such as water, nitrogen, silicone oil, carbon dioxide, air, compressed air, or ethylene glycol.

[0060] Water and nitrogen are preferred as cooling fluids.

[0061] During step iii), the temperature T3 preferably goes from about 10 to 40°C.

[0062] According to a particularly preferred embodiment of the invention, step iii) is carried out by passing said cable of step ii) through a cooling conduit or tube comprising said cooling fluid.

[0063] In particular, said cooling conduit or tube is continuously supplied with said cooling fluid. The latter therefore circulates continuously in said cooling conduit or tube.

[0064] The cooling tube or conduit is preferably made of metal such as, for example, steel. The electrically insulating composition

[0065] The thermoplastic polymer can have a crystallization temperature Tc ranging from approximately 100 to 140°C, and preferably from approximately 105 to 125°C.

[0066] The thermoplastic polymer can have a melting temperature Tf ranging from approximately 140 to 165°C, and preferably from approximately 145 to 165°C.

[0067] The thermoplastic polymer can be chosen from propylene polymers.

[0068] According to a preferred embodiment of the invention, the thermoplastic polymer is a propylene polymer.

[0069] The thermoplastic polymer, or thermoplastic polymers when there are several, preferably represents at least about 50% by weight, preferably about 60 to 95% by weight, and particularly preferably about 100% by weight, relative to the total weight of polymer(s) in the electrically insulating composition.

[0070] The thermoplastic polymer can be a homopolymer or a copolymer of propylene Pb and preferably a copolymer of propylene Pb

[0071] The homopolymer of propylene Pi preferably has an elastic modulus ranging from approximately 1250 to 1600 MPa.

[0072] In the present invention, the elastic modulus or Young's modulus of a polymer (known by the English term "Tensile Modulus") is well known to those skilled in the art and can be easily determined according to ISO 527-1, -2 (2012). ISO 527 has a first part, designated "ISO 527-1", and a second part, designated "ISO 527-2", specifying the test conditions relating to the general principles of the first part of ISO 527.

[0073] The propylene homopolymer Pi can represent at least 10% by weight, and preferably 15 to 30% by weight, relative to the total weight of polymer(s) in the electrically insulating composition.

[0074] Examples of propylene Ph copolymers include propylene and olefin copolymers, the olefin being chosen in particular from ethylene and an olefin ai different from propylene.

[0075] The ethylene or olefin ai different from the propylene of the propylene and olefin copolymer represents preferably at most about 45% by mole, particularly preferably at most about 40% by mole, and more particularly preferably at most about 35% by mole, relative to the total number of moles of propylene and olefin copolymer.

[0076] The mole percentage of ethylene or olefin ai in the propylene copolymer Pi can be determined by nuclear magnetic resonance (NMR), for example according to the method described in Masson et al., Int. J. Polymer Analysis & Characterization, 1996, Vol.2, 379-393.

[0077] The olefin ai, different from propylene, may correspond to the formula CH2=CH-R1, in which R1 is a linear or branched alkyl group having from 2 to 12 carbon atoms, in particular chosen from the following olefins: 1-butene, 1-Pentene, 4-Methyl-l-Pentene, 1-Hexene, 1-Octene, 1-Decene, 1-Dodecene, and a mixture thereof.

[0078] Propylene-ethylene copolymers are preferred as a propylene Pb copolymer

[0079] The propylene Pi copolymer can be a homophasic propylene copolymer or a heterophasic propylene copolymer.

[0080] In the invention, the homophasic propylene copolymer Pi preferably has an elastic modulus ranging from approximately 600 to 1200 MPa, and particularly preferably ranging from approximately 800 to 1100 MPa.

[0081] The homophasic propylene copolymer Pi is advantageously a statistical propylene copolymer Pb

[0082] The ethylene or olefin ai different from the propylene of the homophasic propylene copolymer Pi preferably represents at most about 20% by mole, particularly preferably at most about 15% by mole, and more particularly preferably at most about 10% by mole, relative to the total number of moles of the homophasic propylene copolymer Pi.

[0083] The ethylene or olefin ai different from the propylene of the homophasic propylene copolymer Pi can represent at least 1% by mole about, relative to the total number of moles of homophasic propylene copolymer Pi.

[0084] As an example of a statistical propylene Pp copolymer, one can cite that marketed by the company Borealis under the reference Bormed® RB 845 MO or that marketed by the company Total Petrochemicals under the reference PPR3221.

[0085] The heterophasic (or heterophase) propylene copolymer Pi may comprise a propylene-type thermoplastic phase and a thermoplastic elastomer phase of the ethylene-a2 olefin copolymer type.

[0086] The olefin a2 of the thermoplastic elastomer phase of the heterophase propylene copolymer Pi can be propylene.

[0087] The thermoplastic elastomer phase of the heterophasic propylene copolymer Pi may represent at least approximately 20% by weight, and preferably at least approximately 45% by weight, relative to the total weight of the heterophasic propylene copolymer P i-

[0088] The heterophasic propylene copolymer Pi preferably has an elastic modulus ranging from approximately 50 to 1200 MPa, and particularly preferably: either an elastic modulus ranging from approximately 50 to 550 MPa, and more particularly preferably ranging from approximately 50 to 300 MPa; or an elastic modulus ranging from approximately 600 to 1200 MPa, and more particularly preferably ranging from approximately 800 to 1200 MPa.

[0089] As an example of a heterophasic propylene copolymer, mention may be made of the heterophasic propylene copolymer marketed by LyondellBasell. under the reference Adflex® Q 200 F, or the heterophasic copolymer marketed by LyondellBasell under the reference Moplen EP®2967.

[0090] The homopolymer or copolymer of propylene Pi may have a melting temperature above about 110°C, preferably above about 130°C, particularly preferably above about 135°C, and more particularly preferably from about 140 to 170°C.

[0091] The homopolymer or copolymer of propylene Pi can have a crystallization temperature ranging from approximately 90 to 130°C, and preferably from approximately 100 to 120°C.

[0092] The homopolymer or copolymer of propylene Pi can have an enthalpy of fusion ranging from approximately 20 to 100 J / g.

[0093] The homopolymer of propylene Pi preferably has an enthalpy of fusion of approximately 80 to 90 J / g.

[0094] The homophasic propylene copolymer Pi preferably has an enthalpy of fusion of approximately 40 to 90 J / g, and particularly preferably of 50 to 85 J / g.

[0095] The heterophasic propylene copolymer Pi preferably has an enthalpy of fusion ranging from approximately 20 to 50 J / g.

[0096] The homopolymer or copolymer of propylene Pi can have a melt flow index ranging from 0.5 to 3 g / 10 min; in particular determined at approximately 230°C with a charge of approximately 2.16 kg according to ASTM D1238-00, or ISO 1133.

[0097] The homophasic propylene copolymer Pi preferably has a melt flow index of 1.0 to 2.75 g / 10 min, and more preferably of 1.2 to 2.5 g / 10 min; in particular determined at approximately 230°C with a charge of approximately 2.16 kg according to ASTM D1238-00, or ISO 1133.

[0098] The heterophasic propylene copolymer Pi can have a melt flow index of 0.5 to 3 g / 10 min, and preferably of 0.6 to 1.2 g / 10 min about; in particular determined at about 230°C with a charge of about 2.16 kg according to ASTM D1238-00, or ISO 1133.

[0099] The homopolymer or copolymer of propylene Pi can have a density ranging from approximately 0.81 to 0.91 g / cm3; in particular determined according to ISO 1183A (at a temperature of 23 °C).

[0100] The propylene Pi copolymer preferably has a density of 0.85 to 0.91 g / cm3, and particularly preferably of 0.87 to 0.91 g / cm3; in particular determined according to ISO 1183A (at a temperature of 23°C).

[0101] The electrically insulating composition may comprise several propylene polymers, in particular several different propylene Pi copolymers, including two different propylene Pi copolymers, said propylene Pi copolymers being as defined above.

[0102] In particular, the electrically insulating composition may comprise a homophasic propylene copolymer (as the first propylene copolymer Pi) and a heterophasic propylene copolymer (as the second propylene copolymer Pi), or two different heterophasic propylene copolymers.

[0103] When the electrically insulating composition comprises a homophasic propylene copolymer and a heterophasic propylene copolymer, said heterophasic propylene copolymer preferably has an elastic modulus ranging from approximately 50 to 300 MPa.

[0104] According to one embodiment of the invention, the two heterophasic propylene copolymers have different elastic moduli. Preferably, the electrically insulating composition comprises a first heterophasic propylene copolymer having an elastic modulus ranging from approximately 50 to 550 MPa, and particularly preferably from approximately 50 to 300 MPa; and a second heterophasic propylene copolymer having an elastic modulus ranging from approximately 600 to 1200 MPa, and more particularly preferably from approximately 800 to 1200 MPa.

[0105] Advantageously, the first and second heterophasic propylene copolymers have a flow index as defined in the invention.

[0106] These combinations of propylene Pi copolymers can advantageously improve the physico-chemical and mechanical properties of the electrically insulating layer.

[0107] According to a preferred embodiment of the invention, the propylene P i copolymer or the propylene Pi copolymers when there are several, represent(s) at least about 50% by weight, preferably about 55 to 100% by weight, and particularly preferably about 60 to 85% by weight, relative to the total weight of polymer(s) in the electrically insulating composition.

[0108] The homophasic propylene copolymer Pi can represent at least 20% by weight, and preferably from 25 to 70% by weight, relative to the total weight of polymer(s) in the electrically insulating composition.

[0109] The heterophasic propylene copolymer Pi or the heterophasic propylene copolymers Pi when there are several, can represent from 5 to 100% by weight about, preferably from 25 to 95% by weight about, and particularly preferably from 60 to 80% by weight about, relative to the total weight of polymer(s) in the electrically insulating composition.

[0110] The electrically insulating composition may further comprise a homopolymer or a copolymer of P2 olefin.

[0111] Said homopolymer or olefin copolymer P2 is preferably different from said propylene polymer or said propylene homopolymer or copolymer Pi (or said propylene homopolymers or copolymers Pi).

[0112] The olefin of the olefin copolymer P2 can be selected from ethylene and an olefin a3 corresponding to the formula CH2=CH-R2, in which R2 is a linear or branched alkyl group having from 1 to 12 carbon atoms.

[0113] The olefin a3 is preferably selected from the following olefins: propylene, 1-butene, isobutylene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and a mixture thereof.

[0114] The olefin a3 of the propylene, 1-hexene or 1-octen type is particularly preferred.

[0115] The combination of Pi and P2 polymers makes it possible to obtain an electrically insulating layer exhibiting good mechanical properties, particularly in terms of elastic modulus, and electrical properties.

[0116] The homopolymer or copolymer of olefin P2 is preferably an ethylene polymer.

[0117] The ethylene polymer preferably comprises at least about 80 mole percent of ethylene, particularly preferably at least about 90 mole percent of ethylene, and more particularly preferably at least about 95 mole percent of ethylene, relative to the total number of moles of the ethylene polymer.

[0118] According to a preferred embodiment of the invention, the ethylene polymer is low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, or high-density polyethylene, and preferably high-density polyethylene; in particular according to ISO 1183A (at a temperature of 23°C). High-density polyethylene improves the thermal conductivity of the electrically insulating layer.

[0119] The ethylene polymer preferably has an elastic modulus of at least 400 MPa, and particularly preferably of at least 500 MPa.

[0120] In the present invention, the expression "low density" means having a density ranging from approximately 0.91 to 0.925 g / cm3, said density being measured according to ISO 1183A (at a temperature of 23°C).

[0121] In the present invention, the expression "medium density" means having a density ranging from approximately 0.926 to 0.940 g / cm3, said density being measured according to ISO 1183A (at a temperature of 23°C).

[0122] In the present invention, the expression "high density" means having a density ranging from 0.941 to 0.965 g / cm3, said density being measured according to ISO 1183A (at a temperature of 23 °C).

[0123] According to a preferred embodiment of the invention, the homopolymer or copolymer of olefin P2 represents approximately 5 to 50% by weight, and particularly preferably approximately 10 to 40% by weight, relative to the total weight of polymer(s) in the electrically insulating composition.

[0124] According to a particularly preferred embodiment of the invention, the com The electrically insulating layer comprises two propylene Pi copolymers, such as a homophasic propylene copolymer and a heterophasic propylene copolymer, or two different heterophasic propylene copolymers; and a homopolymer or copolymer of olefin P2, such as an ethylene polymer. This combination of propylene Pi copolymers and a homopolymer or copolymer of olefin P2 further improves the mechanical properties of the electrically insulating layer while ensuring good thermal conductivity.

[0125] When the electrically insulating composition comprises several thermoplastic polymers, the set of thermoplastic polymers in the electrically insulating composition preferably forms a thermoplastic polymer material.

[0126] Said thermoplastic polymer material is preferably heterophase (i.e., it comprises several phases). The presence of several phases generally arises from the mixing of two different polyolefins, such as a mixture of different propylene polymers or a mixture of a propylene polymer and an ethylene polymer.

[0127] In the invention, the "multiple thermoplastic polymers" may be several propylene polymers as defined in the invention, or a mixture of a propylene polymer as defined in the invention, and other thermoplastic polymer(s) which are not necessarily propylene polymers.

[0128] The thermoplastic polymer material may represent at least about 50% by weight, preferably at least about 70% by weight, and particularly preferably at least about 80% by weight, relative to the total weight of the electrically insulating composition.

[0129] The electrically insulating composition of the invention is a thermoplastic composition. It is therefore not crosslinkable. In particular, the thermoplastic polymer material is not crosslinkable.

[0130] In other words, the electrically insulating composition preferably does not include crosslinking agents, silane-type coupling agents, peroxides, and / or additives that enable crosslinking. Indeed, such agents degrade the propylene polymer(s), and thus the thermoplastic polymer material.

[0131] The electrically insulating composition is preferably recyclable.

[0132] The electrically insulating composition may include one or more additives.

[0133] The additives may be selected from processing aids such as lubricants, compatibilizing agents, coupling agents, antioxidants, anti-UV agents, water treeing inhibitors, pigments, and mixtures thereof.

[0134] Antioxidants help protect the electrically insulating composition from thermal stresses generated during the cable manufacturing or operating stages. cable operation.

[0135] The antioxidants are preferably chosen from among hindered phenols, thioesters, sulfur-based antioxidants, phosphorus-based antioxidants, amine-type antioxidants, and a mixture thereof.

[0136] Examples of hindered phenols include l,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine (Irganox® MD 1024), pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox® 1010), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox® 1076), l,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (Irganox® 1330), 4,6-bis(octylthiomethyl)-o-cresol (Irgastab® KV10 or Irganox® 1520), the 2,2'-thiobis(6-tert-butyl-4-methylphenol) (Irganox® 1081), 2,2'-thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (Irganox® 1035), tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate (Irganox® 3114), 2,2'-oxamido-bis(ethyl-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Naugard XL-1), or 2,2'-methylenebis(6-tert-butyl-4-methylphenol).

[0137] Examples of sulfur-based antioxidants include thioethers such as didodecyl-3,3'-thiodipropionate (Irganox® PS800), distearyl thiodipropionate or dioctadecyl-3,3'-thiodipropionate (Irganox® PS802), bis[2-methyl-4-{3-n-alkyl (C12 or CM) thiopropionyloxy]-5-tert-butylphenyl]sulfide, thiobis-[2-tert-butyl-5-methyl-4,l-phenylene]bis[3-(dodecylthio)propionate], or 4,6-bis(octylthiomethyl)-o-cresol (Irganox® 1520 or Irgastab® KV10).

[0138] Examples of phosphorus-based antioxidants include tris(2,4-di-tert-butyl-phenyl)phosphite (Irgafos® 168) or bis(2,4-di-tert-but-tylphenyl)pentaerythritol diphosphite (Ultranox® 626).

[0139] Examples of amine-type antioxidants include phenylenediamines (e.g., paraphenylenediamines such as 1PPD or 6PPD), styrene diphenylamine, diphenylamines, the 4- ( 1 -methyl 1-1 -phenylethyl 1) -N- [4- ( 1 -methyl 1-1 -phenylethyl 1)phenyl]aniline (Naugard 445), mercaptobenzimidazoles, or 2,2,4-trimethyl-1,2-dihydroquinoline polymerized (TMQ).

[0140] As examples of usable antioxidant mixtures according to the invention, Irganox B 225, which comprises an equimolar mixture of Irgafos 168 and Irganox 1010 as described above, may be cited.

[0141] The electrically insulating composition may comprise from 0.01 to 5% by weight about, and preferably from 0.1 to 2% by weight about, of additives, relative to the total weight of the electrically insulating composition.

[0142] The electrically insulating composition may further comprise a dielectric liquid.

[0143] The dielectric liquid may comprise at least one liquid selected from a mineral oil (e.g. naphthenic oil, paraffinic oil or aromatic oil), a vegetable oil (e.g. soybean oil, linseed oil, rapeseed oil, corn oil or castor oil), a synthetic oil such as an aromatic hydrocarbon (alkylbenzene, alkylnaphthalene, alkylbiphenyl, alkyldiarylethylene, etc.), a silicone oil, an ether, an organic ester, and an aliphatic hydrocarbon, and preferably from a mineral oil (e.g. naphthenic oil, paraffinic oil or aromatic oil), a vegetable oil (e.g. soybean oil, linseed oil, rapeseed oil, corn oil or castor oil), a synthetic oil such as an aromatic hydrocarbon (alkylbenzene, alkylnaphthalene, alkylbiphenyl, alkyldiarylethylene, etc.), a silicone oil, and an aliphatic hydrocarbon.

[0144] The liquid composing the dielectric liquid (respectively the dielectric liquid) is generally liquid at approximately 20-25°C.

[0145] The dielectric liquid may comprise at least about 70% by weight of the liquid composing the dielectric liquid, preferably at least about 80% by weight, and particularly preferably at least about 90% by weight of the liquid composing the dielectric liquid, relative to the total weight of the dielectric liquid.

[0146] Mineral oil is preferred as a liquid included in the dielectric liquid.

[0147] The dielectric liquid particularly preferably comprises at least one mineral oil, and at least one polar compound of the benzophenone, acetophenone, or one of their derivatives type.

[0148] Mineral oil is preferably chosen from naphthenic oils and paraffinic oils.

[0149] Mineral oil is obtained from the refining of crude oil.

[0150] According to a particularly preferred embodiment of the invention, the oil mineral includes a paraffinic carbon (Cp) content ranging from approximately 45 to 65 atomic percent, a naphthenic carbon (Cn) content ranging from approximately 35 to 55 atomic percent, and an aromatic carbon (Ca) content ranging from approximately 0.5 to 10 atomic percent.

[0151] In a particular embodiment, the polar compound of the benzophenone, acetophenone, or one of their derivatives constitutes at least approximately 2.5% by weight, preferably at least approximately 3.5% by weight, and most preferably at least approximately 4% by weight, relative to the total weight of the dielectric liquid. The polar compound improves the dielectric strength of the electrically insulating layer.

[0152] The dielectric liquid may comprise at most about 20% by weight, and preferably at most about 15% by weight, of a polar compound of the benzophenone, acetophenone or one of their derivatives type, relative to the total weight of the dielectric liquid. This maximum quantity ensures moderate, or even low, dielectric losses (e.g., less than approximately 103), and also prevents the migration of the dielectric liquid out of the electrically insulating layer.

[0153] According to a preferred embodiment of the invention, the polar compound of the benzophenone, acetophenone or one of their derivatives type is chosen from benzophenone, dibenzosuberone, fluorenone and anthrone. Benzophenone is particularly preferred.

[0154] The dielectric liquid can represent from 1% to 20% by weight approximately, preferably from 2% to 15% by weight approximately, and particularly preferably from 3% to 12% by weight approximately, relative to the total weight of the electrically insulating composition. The first semiconductor composition

[0155] The first semiconductor composition may comprise at least one thermoplastic polymer as defined in the invention and at least one electrically conductive charge in sufficient quantity to make the internal semiconductor layer semiconductor.

[0156] Preferably, the first semiconductor composition comprises at least about 6% by weight of electrically conductive charge, preferably at least about 10% by weight of electrically conductive charge, preferably at least about 15% by weight of electrically conductive charge, and even more preferably at least about 25% by weight of electrically conductive charge, relative to the total weight of the first semiconductor composition.

[0157] The first semiconductor composition may comprise at most about 45% by weight of electrically conductive charge, and preferably at most about 40% by weight of electrically conductive charge, relative to the total weight of the first semiconductor composition.

[0158] The electrically conductive charge can be carbon black. The second semiconductor composition

[0159] The second semiconductor composition may comprise at least one thermoplastic polymer as defined in the invention and at least one electrically conductive charge in sufficient quantity to make the outer semiconductor layer semiconductor.

[0160] Preferably, the second semiconductor composition comprises at least about 6% by weight of electrically conductive charge, preferably at least about 10% by weight of electrically conductive charge, preferably at least about 15% by weight of electrically conductive charge, and even more preferably at least about 25% by weight of electrically conductive charge, relative to the total weight of the second semiconductor composition.

[0161] The second semiconductor composition may comprise at most about 45% by weight of electrically conductive charge, and preferably at most about 40% by weight of electrically conductive charge, relative to the total weight of the second semiconductor composition.

[0162] The electrically conductive charge can be carbon black. Other steps in the process of the invention

[0163] The process of the invention may further include a step i0), prior to step i) (i.e. before extrusion), of preparing the electrically insulating composition.

[0164] At the end of step i0) a homogeneous electrically insulating composition is obtained and it can then be extruded around the internal semiconducting layer according to step i), to obtain the electrically insulating thermoplastic layer.

[0165] Step i0) may include: melting the thermoplastic polymer.

[0166] When the electrically insulating composition comprises several constituents, step i0) may include mixing the different constituents of the electrically insulating composition, and melting the thermoplastic polymer.

[0167] Step i0) is preferably carried out at a temperature of approximately 170°C to 240°C, and particularly preferably from approximately 180°C to 220°C.

[0168] Step i0) is preferably carried out using an extruder or an internal mixer, and preferably an extruder.

[0169] According to one embodiment of the invention, the extruder implementing step i0) of the process of the invention is a single-screw extruder. It therefore comprises a single screw.

[0170] The extruder may be equipped with at least one feed hopper connected to the extruder and configured to introduce or inject constituents of the electrically insulating composition into the extruder.

[0171] According to a preferred embodiment of the invention, step i0) comprises the following substeps: ioi) a substep of introducing, particularly at room temperature, the electrically insulating composition comprising said thermoplastic polymer into a first zone of the screw, called the feed zone, and located at the inlet of the extruder, and iœ) a substep during which the electrically insulating composition of substep iOi) is brought from the feeding zone to one or more intermediate zones of the screw allowing the transport of the electrically insulating composition to the extruder head located at the exit of the extruder and the gradual melting of the thermoplastic polymer.

[0172] The thermoplastic polymer of the electrically insulating composition is of preference introduced into the extruder during substep iOi) in solid form, and particularly preferably in the form of granules.

[0173] Substep iOi) can be carried out by means of a feed hopper.

[0174] When the electrically insulating composition comprises several polymers, all the polymers of the electrically insulating composition are preferably introduced during substep iOi) in solid form, and particularly preferably in the form of granules.

[0175] Substep iOi) can be implemented at a pressure of at most 5 bar, preferably at most 3 bar, and preferably at most 1.5 bar. In a particularly preferred embodiment, substep iOi) is implemented at atmospheric pressure, namely at a pressure of approximately 1 bar.

[0176] Before substep iOi) of introducing the thermoplastic polymer (respectively several polymers) into the extruder, said thermoplastic polymer (respectively several polymers) may be preheated (respectively may be preheated) to a temperature ranging from 40°C to 100°C.

[0177] Substep i02) then allows said thermoplastic polymer to be melted.

[0178] When the electrically insulating composition comprises several polymers, substep i02) allows the polymers to be mixed and melted.

[0179] During substep i02), the electrically insulating composition is brought (continuously) from the feeding zone to one or more intermediate zones of the screw allowing the transport of the electrically insulating composition to the extruder head located at the exit of the extruder, and the gradual melting of the polymer(s).

[0180] The intermediate zones are located between the feeding zone and the extruder head.

[0181] The intermediate zones may include one or more heating zones, allowing the temperature in the extruder to be controlled.

[0182] The molten state (melting) is reached when the thermoplastic polymer (respectively the several polymers) is heated (respectively are heated) to a temperature greater than or equal to its melting temperature.

[0183] Substep i02) can be carried out at a temperature ranging from approximately 170°C to 240°C, and particularly preferably from approximately 180°C to 220°C.

[0184] Substep i02) can be carried out at a pressure ranging from 1 to 300 bar.

[0185] According to a particularly preferred embodiment of the invention, the extruder comprises a barrier screw and / or a grooved barrel. The use of a specific barrel (i.e., grooved barrel) and / or a specific screw (i.e., barrier screw) makes it possible to obtain a homogeneous electrically insulating composition that is easy to extrude, while avoiding or limiting the formation of structural defects in the electrically insulating layer obtained.

[0186] When step i0) is carried out using an extruder, the next step i) consists of recovering the electrically insulating composition formed in one or more intermediate zones of the extruder and bringing it to the level of the extruder head to apply it around the internal semiconducting layer.

[0187] The process of the invention does not include a preferred crosslinking step for the electrically insulating layer obtained in step i). Indeed, thermoplastic polymers such as propylene polymers degrade under the action of crosslinking and / or in the presence of crosslinking agents such as peroxides.

[0188] When the electrically insulating composition includes one or more additives and / or a dielectric liquid, these may be introduced into the extruder during substep iOi).

[0189] The dielectric liquid and / or additives, and the thermoplastic polymer can be brought into contact in the feed hopper or in the extruder, in particular in the feed zone; and preferably in the feed hopper.

[0190] The contacting of the dielectric liquid and / or additives, and the thermoplastic polymer can be carried out at a temperature ranging from approximately 15°C to 80°C, and preferably at room temperature.

[0191] In the present invention, the expression "ambient temperature" means a temperature ranging from approximately 15 to 35°C, and preferably ranging from approximately 20 to 25°C.

[0192] The contacting of said dielectric liquid and / or additives with the thermoplastic polymer is preferably carried out at a pressure of at most 5 bar, preferably at most 3 bar, and preferably at most 1.5 bar. In a particularly preferred embodiment, the contacting is carried out at atmospheric pressure, namely approximately 1 bar.

[0193] The substep iOi) allows the dielectric liquid and / or one or more additives to be brought into contact with the thermoplastic polymer.

[0194] According to a first embodiment of the process of the invention, substep i01), or the contacting of said dielectric liquid and / or additives, and the thermoplastic polymer, does not include a step of impregnating the thermoplastic polymer with the dielectric liquid. In other words, the dielectric liquid is not completely absorbed by the thermoplastic polymer, particularly before the melting of the thermoplastic polymer according to substep i02). Indeed, a conventional impregnation step can be lengthy and requires a minimum quantity of dielectric liquid (approximately 10-15% by weight of the total mass of the electrically insulating composition).

[0195] In a second variant of the process of the invention, the contacting includes a step of impregnating the thermoplastic polymer with the dielectric liquid. In this case, prior to the introduction of the electrically insulating composition comprising said thermoplastic polymer into a first zone of the screw, a sub-step of impregnation of the thermoplastic polymer by the dielectric liquid takes place to form an impregnated thermoplastic polymer or an impregnated thermoplastic polymer material which is then introduced into said first zone. The electrically insulating thermoplastic layer

[0196] The electrically insulating thermoplastic layer of the cable of the invention is a non-crosslinked layer.

[0197] In the invention, the expression "non-crosslinked layer" or "thermoplastic layer" means a layer whose gel content according to ASTM D2765-01 (xylene extraction) is at most about 30%, preferably at most about 20%, particularly preferably at most about 10%, more particularly preferably at most 5%, and even more particularly preferred of 0%.

[0198] In a particular embodiment, the electrically insulating thermoplastic layer has a tensile strength (RT) of at least 8.5 MPa, preferably of at least about 10 MPa, and particularly preferably of at least about 12 MPa, before aging (according to IEC 20-86).

[0199] In a particular embodiment, the electrically insulating thermoplastic layer has an elongation at break (ER) of at least about 250%, preferably of at least about 300%, and particularly preferably of at least about 350%, before aging (according to IEC 20-86).

[0200] In a particular embodiment, the electrically insulating thermoplastic layer has a tensile strength (RT) of at least 8.5 MPa, preferably of at least about 10 MPa, and particularly preferably of at least about 12 MPa, after aging (according to IEC 20-86.

[0201] In a particular embodiment, the electrically insulating thermoplastic layer has an elongation at break (ER) of at least about 250%, preferably of at least about 300%, and particularly preferably of at least about 350%, after aging (according to IEC 20-86).

[0202] Tensile strength (RT) and elongation at break (ER) (before or after aging) can be carried out according to Standard NF EN 60811-1-1, in particular using a device marketed under reference 3345 by the company Instron.

[0203] Aging is generally carried out at 135°C for 240 hours (or 10 days).

[0204] The electrically insulating thermoplastic layer of the cable of the invention is preferably a recyclable layer.

[0205] The electrically insulating thermoplastic layer of the invention is a layer extradited.

[0206] The electrically insulating thermoplastic layer of the invention may comprise at least the thermoplastic polymer, optionally one or more additives, and a dielectric liquid, the aforementioned ingredients being as defined in the invention.

[0207] The proportions of the different ingredients in the electrically insulating thermoplastic layer can be identical to those described in the invention for these same ingredients in the electrically insulating composition.

[0208] The electrically insulating thermoplastic layer has a variable thickness depending on the type of cable envisaged. The thickness depends in particular on the size of the elongated electrically conductive element.

[0209] The electrically insulating layer of the invention preferably has a thickness of at least approximately 4 mm, particularly preferably ranging from approximately 5 to 50 mm, and even more particularly preferably ranging from approximately 6 to 30 mm. With such thicknesses, it is all the more important to ensure homogeneous cooling of the cable after extrusion to prevent the appearance of morphological defects.

[0210] In the present invention, "electrically insulating layer" means a layer whose electrical conductivity can be at most 1.108 S / m (siemens per meter), preferably at most 1.109 S / m, and particularly preferably at most 1.10 10 S / m, measured at approximately 25°C in direct current.

[0211] In the present invention, the term "semiconductor layer" means a layer whose electrical conductivity may be strictly greater than 1 x 10⁸ S / m (siemens per meter), preferably of at least 1 x 10³ S / m, and preferably may be less than 1 x 10³ S / m, measured at 25°C in direct current. The cable

[0212] The cable of the invention relates more particularly to the field of electrical cables operating in direct current (DC) or alternating current (AC).

[0213] The elongated electrically conductive element is preferably positioned in the center of the cable.

[0214] The elongated electrically conductive element can be a single-core conductor such as, for example, a metal wire or a multi-core conductor such as a plurality of twisted or untwisted metal wires.

[0215] The elongated electrically conductive element may be made of aluminium, aluminium alloy, copper, copper alloy, or any combination thereof.

[0216] The electrically insulating layer more particularly has a lower electrical conductivity than the semiconductor layer. More particularly, the electrical conductivity of the semiconductor layer may be at least 10 times greater than the electrical conductivity of the electrically insulating layer, preferably at least 100 times greater than the electrical conductivity of the electrically insulating layer, and particularly preferably at least 1000 times greater than the electrical conductivity of the electrically insulating layer.

[0217] In a particular embodiment, the inner semiconductor layer, the electrically insulating layer, and the outer semiconductor layer constitute a three-layer insulation. In other words, the electrically insulating layer is in direct physical contact with the inner semiconductor layer, and the outer semiconductor layer is in direct physical contact with the electrically insulating layer.

[0218] The inner semiconductor layer (respectively the outer semiconductor layer) is preferably a thermoplastic layer or a non-crosslinked layer.

[0219] The cable may further comprise an outer protective sheath surrounding the electrically insulating layer (or the outer semiconducting layer).

[0220] The outer protective sheath may be in direct physical contact with the electrically insulating layer (or the external semiconducting layer).

[0221] The outer protective sheath may be an electrically insulating sheath.

[0222] The electrical cable may further comprise an electrical screen (e.g., metallic) surrounding the outer semiconductor layer. In this case, the electrically insulating sheath surrounds said electrical screen, and the electrical screen is between the electrically insulating sheath and the outer semiconductor layer.

[0223] This metallic screen may be a so-called "wire" screen composed of a set of copper or aluminum conductors arranged around and along the outer semiconducting layer; a so-called "ribbon" screen composed of one or more conductive copper or aluminum metal ribbons, possibly laid in a helix around the outer semiconducting layer; or a conductive aluminum metal ribbon laid longitudinally around the outer semiconducting layer and sealed with adhesive in the overlapping areas of said ribbon; or a so-called "waterproof" screen of the metal tube type, possibly composed of lead or a lead alloy and surrounding the outer semiconducting layer. This last type of screen notably provides a barrier against moisture that tends to penetrate the electrical cable radially.

[0224] The metallic screen of the electric cable of the invention may comprise a screen called "wire" and a screen called "waterproof" or a screen called "wire" and a screen called "ribboned".

[0225] All types of metallic screens can play the role of grounding the electrical cable and can thus carry fault currents, for example in the event of a short circuit in the network concerned.

[0226] Other layers, such as layers that swell in the presence of moisture, can be added between the second semiconductor layer and the metallic screen, these layers to ensure longitudinal water tightness of the electrical cable. Brief description of the drawings

[0227] [Fig-1] The [Fig. 1] represents a device for implementing a method according to the invention.

[0228] For reasons of clarity, only the essential elements for understanding the invention have been represented schematically, and this without regard to scale.

[0229] In [Fig. 1], the device 1 comprises a container 2 which can be fed with granules of a thermoplastic polymer such as a propylene polymer, a container 3 which can be fed with a dielectric liquid, a feed hopper 4 which can be fed at room temperature with the granules of the thermoplastic polymer contained in the container 2 and with the dielectric liquid contained in the container 3, and an extruder 5 comprising a grooved barrel 6 and / or a barrier screw 7, as well as an extruder head 8.The thermoplastic polymer granules and the dielectric liquid are fed via the feed hopper 4 into a feed zone 9 of the screw (according to step i0), and then conveyed from the feed zone 9 to one or more intermediate zones 10. These intermediate zones 10 allow the electrically insulating composition to be transported to the extruder head 8, located at the outlet of the extruder 5, and the thermoplastic polymer to be gradually melted. Finally, at the extruder head 8, the electrically insulating composition is applied around the internal semiconducting layer. Immediately after extrusion, the cable is conveyed to a progressive cooling device.

Claims

Demands

1. A method for manufacturing an electrical cable comprising at least one elongated electrically conductive element, an inner semiconducting layer surrounding the elongated electrically conductive element, an electrically insulating thermoplastic layer surrounding the inner semiconducting layer, and an outer semiconducting layer surrounding the electrically insulating thermoplastic layer, said electrically insulating thermoplastic layer comprising at least one thermoplastic polymer, said method being characterized in that it comprises at least the following steps: i) applying by extrusion, in that order, the inner semiconducting layer, the electrically insulating thermoplastic layer, and the outer semiconducting layer, around the elongated electrically conductive element,ii) cool the external semiconducting layer thus extruded in step i) by contacting it with a first medium maintained at a temperature Ti ranging from approximately 60 to 140°C for a sufficient time so that the electrically insulating thermoplastic layer reaches a temperature T2 such that Te - 25°C < T2 and T2 ≤ Te + 25°C, Tc being the crystallization temperature of the thermoplastic polymer, and iii) cool the cable thus obtained in step ii) by contacting it with a second medium maintained at a temperature T3 less than or equal to 50°C.

2. A method according to claim 1, characterized in that step i) is carried out at an extrusion temperature Te ranging from 170°C to 240°C.

3. A process according to claim 1 or 2, characterized in that the thermoplastic polymer is a propylene polymer.

4. A method according to any one of the preceding claims, characterized in that the thermoplastic polymer represents at least 50% by weight approximately, relative to the total weight of polymer(s) in the electrically insulating composition.

5. A method according to any one of the preceding claims, characterized in that the temperature Ti of step ii) ranges from 90 to 120°C.

6. A method according to any one of the preceding claims, characterized in that step ii) is carried out at a cooling rate of 1 to 20°C per minute.

7. A method according to any one of the preceding claims, characterized in that step ii) is carried out at a pressure ranging from 1 to 15 bars.

8. A method according to any one of the preceding claims, characterized in that the temperature T2 of step ii) is such that Te - 25 °C < T2 and T2 < Te + 20 °C, Tc being the crystallization temperature of the thermoplastic polymer.

9. A method according to any one of the preceding claims, characterized in that step ii) is carried out by bringing the external semiconductor layer into contact with a cooling fluid selected from liquids and gases such as water, nitrogen, silicone oil, carbon dioxide, air, compressed air, or ethylene glycol.

10. A method according to any one of the preceding claims, characterized in that step ii) is carried out: - by passing said cable of step i) through a cooling conduit or tube continuously supplied with a cooling fluid, or - by passing said cable of step i) through one or more cooling tanks continuously supplied with a cooling fluid.

11. A method according to claim 2 or any one of claims 3 to 10 taken in combination with claim 2, characterized in that during contact in step ii), said external semiconducting layer is cooled from the extrusion temperature Te to a temperature T4 greater than or equal to 80°C; and maintained at a temperature T'4 greater than or equal to 80°, until the electrically insulating thermoplastic layer reaches temperature T2.

12. A method according to any one of the preceding claims, characterized in that it further comprises a step i0), prior to step i), of preparing the electrically insulating composition using a single-screw extruder, step i0) comprising the following substeps: i0i) a substep of introducing the electrically insulating composition comprising said thermoplastic polymer into a first zone of the screw, referred to as the feed zone, located at the inlet of the extruder, i02) a substep in which the electrically insulating composition of substep i0i) is conveyed from the feed zone to one or more intermediate zones of the screw enabling transport

13.

14.

15. from the electrically insulating composition to the extruder head located at the extruder outlet and the gradual melting of the thermoplastic polymer. A method according to any one of the preceding claims, characterized in that the electrically insulating layer is a non-crosslinked layer. A process according to any one of the preceding claims, characterized in that the thermoplastic polymer has a melting temperature Tf ranging from 140 to 165°C. A process according to any one of the preceding claims, characterized in that the thermoplastic polymer has a crystallization temperature Tc ranging from 100 to 140°C.

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