EP4264644A1

EP4264644A1 - Process for manufacturing an electrical cable having improved thermal conductivity

Info

Publication number: EP4264644A1
Application number: EP21851613.6A
Authority: EP
Inventors: Gabriele Perego; Christelle Mazel; Claire GRANGER
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2020-12-18
Filing date: 2021-12-15
Publication date: 2023-10-25
Also published as: CN116711030A; FR3118274B1; FR3118274A1; WO2022129782A1; US20240096522A1

Abstract

The invention relates to a process for manufacturing a cable comprising at least one electrically insulating layer obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene and polyethylene, at least one dielectric liquid, and at least one thermally conductive inorganic filler, said process implementing the preliminary mixing of the thermally conductive inorganic filler with the polyethylene.

Description

Title of the invention: Process for manufacturing an electric cable with improved thermal conductivity

The invention relates to a process for manufacturing a cable comprising at least one electrically insulating layer obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene and polyethylene, at least one dielectric liquid, and at at least one thermally conductive inorganic nanofiller, said method comprising premixing the thermally conductive inorganic nanofiller with the polyethylene.

The invention applies typically but not exclusively to electric cables intended for the transport of energy, in particular to medium voltage (in particular from 6 to 45-60 kV) or high voltage (in particular greater than 60 kV, and up to 400 kV), whether in direct or alternating current, in the fields of air, submarine, or land electricity transmission.

The invention applies in particular to electric cables having improved thermal conductivity.

A medium or high voltage power transmission cable preferably comprises, from the inside to the outside:

- an elongated electrically conductive element, in particular 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 outer semiconductor layer surrounding said insulating layer,

- optionally an electric screen surrounding said outer semi-conducting layer, and

- Optionally an electrically insulating protective sheath surrounding said electrical screen. International application WO2019072388A1 discloses a cable comprising an electrically insulating layer obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene and boron nitride having a particle size distribution D50 of at over 3 p.m. More particularly, the electrically insulating layer is manufactured by impregnating the dielectric liquid in the polymer material in order to obtain granules of polymer material impregnated with said dielectric liquid, mixing the granules with a powder of boron nitride having a particle size distribution D50 of at most 15 μm in order to form a polymer composition, then extruding the polymer composition around the core of the cable. However, the thermal conductivity properties of the electrically obtained layer are not optimized. Furthermore, the incorporation of boron nitride or other inorganic fillers in a polymer material is generally difficult to implement due to the presence of agglomerates, which makes the process sometimes long and/or requiring specific equipment which increase the cost of cable production.

The object of the present invention is therefore to overcome the drawbacks of the techniques of the prior art by proposing a method of manufacturing an electric cable, in particular at medium or high voltage, based on propylene polymer(s), said process being easy to implement, inexpensive, not requiring complex equipment, and being able to lead to a cable, being able to operate at temperatures above 70° C., and having improved thermal conductivity properties, while guaranteeing good mechanical properties, particularly in terms of elongation at break and tensile strength.

The object is achieved by the invention which will be described below.

The first subject of the invention is a method for manufacturing an electric cable comprising at least one elongated electrically conductive element and at least one electrically insulating layer obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene and polyethylene, at least one dielectric liquid, and at least one thermally conductive inorganic nanofiller, said method being characterized in that it comprises at least the following steps: i) mixing the nanoscale thermally conductive inorganic nanofiller with an ethylene polymer to form a nanofilled ethylene polymer, ii) mixing the nanofilled ethylene polymer with at least one propylene polymer, to form a nanofilled thermoplastic polymer material, ill) mixing the nanofilled thermoplastic polymer material with the dielectric liquid to form a polymer composition, and iv) extruding the polymer composition around the elongated electrically conductive member.

The method of the invention is simple to implement, inexpensive, and it does not require complex equipment. It also makes it possible to obtain a cable that can operate at temperatures above 70°C, and has improved thermal conductivity properties, while guaranteeing good mechanical properties.

The dispersion of the inorganic nanofiller in the ethylene polymer during step i) before bringing it into contact with the propylene polymer according to step ii) makes it possible to promote the dispersion of the inorganic nanofiller within the thermoplastic polymer material , to promote the creation of several levels of percolation, and to improve the thermal conductivity of the layer thus obtained.

Step i)

Step i) includes mixing the inorganic nanofiller with the ethylene polymer.

This step i) can be carried out at a temperature ranging from approximately 140° C. to approximately 240° C., and preferably from approximately 160° C. to approximately 220° C.

Step i) is advantageously carried out with a mixer suitable for mixing several solids, such as for example a single-screw extruder, a twin-screw extruder, in particular co-rotating or counter-rotating, a buss co-kneader, or a closed mixing device.

This step i) can last from approximately 1 min to approximately 1 hour, and preferably from approximately 5 minutes to approximately 30 minutes.

The duration of step i) depends on the type of mixing device used. In the case of an extrusion device, we will rather speak of residence time and not of duration strictly speaking. The thermally conductive inorganic nanocharqe

At the end of step i), the thermally conductive inorganic nanofiller preferably represents from 20% to 80% by weight approximately, and in a particularly preferred manner from 40% to 75% by weight approximately, relative to the total weight of the nanofilled ethylene polymer (i.e. ethylene polymer and thermally conductive inorganic nanofiller).

The thermally conductive inorganic nanofiller may have a thermal conductivity of at least 1 W/mk approximately at 20°C, and preferably of at least 5 W/mk approximately at 20°C.

In the present invention, the thermal conductivity is preferably measured according to the method well known under the anglicism “Transient Plane Source or TPS”. Advantageously, the thermal conductivity is measured using a device marketed under the reference HOT DISK TPS 2500S by the company THERMOCONCEPT.

The thermally conductive inorganic nanofiller can be chosen from silicates, boron nitride, carbonates, metal oxides, and one of their mixtures, and preferably from silicates, carbonates, metal oxides, and one of their mixtures.

A mixture of thermally conductive inorganic nanofillers is preferably a mixture of two or three of said thermally conductive inorganic nanofillers.

Among the silicates, mention may be made of aluminum, calcium or magnesium silicates.

Aluminum silicates are preferred.

The aluminum silicates can be chosen from kaolins and any other mineral or clay mainly comprising kaolinite.

In the present invention, the expression "any other mineral or clay mainly comprising kaolinite" means any other mineral or clay comprising at least 50% by weight approximately, preferably at least 60% by weight approximately, and more preferably at least less than 70% by weight approximately, of kaolinite, relative to the total weight of the mineral or the clay. Kaolins, in particular calcined kaolin, are preferred.

Among the carbonates, mention may be made of chalk, calcium carbonate (e.g. aragonite, vaterite, calcite, or a mixture of at least two of the aforementioned compounds), magnesium carbonate, limestone, or any other mineral mainly comprising calcium carbonate or magnesium carbonate.

In the present invention, the expression "any other mineral mainly comprising calcium carbonate or magnesium carbonate" means any other mineral comprising at least 50% by weight approximately, preferably at least 60% by weight approximately, and preferably still at least 70% by weight approximately, of calcium carbonate or magnesium carbonate, relative to the total weight of the mineral.

Chalk and calcium carbonate are preferred.

Among the metal oxides, mention may be made of aluminum oxide, a hydrated aluminum oxide, magnesium oxide, silicon dioxide, or zinc oxide.

In the present invention, aluminum oxide, also well known as "alumina", is a chemical compound with the formula AI2O3.

The hydrated aluminum oxide or hydrated alumina can be a monohydrated or polyhydrated aluminum oxide, and preferably monohydrated or trihydrated.

Examples of aluminum oxide monohydrate include boehmite, which is the gamma polymorph of AIO(OH) or Al2O3.H2O; or the diaspore, which is the alpha polymorph of AIO(OH) or Al2O3.H2O.

By way of example of aluminum oxide polyhydrate, and preferably trihydrate, mention may be made of gibbsite or hydrargillite, which is the gamma polymorph of AI(OH)s; bayerite which is the alpha polymorph of AI(OH)s; or nordstrandite, which is the beta polymorph of AI(OH)s.

Hydrated aluminum oxide is also well known as "aluminum oxide hydroxide" or "alumina hydroxide".

Aluminum oxide, magnesium oxide, and silicon dioxide are preferred. The aluminum oxide (respectively magnesium oxide) is preferably calcined aluminum oxide (respectively calcined magnesium oxide).

The silicon dioxide is preferably fumed silica, the expression “fused silica” being well known under the Anglicism “fumed silica”.

According to a particularly preferred embodiment of the invention, the thermally conductive inorganic nanofiller is chosen from kaolins, chalk, a calcined magnesium oxide, fumed silica, and a calcined aluminum oxide.

The thermally conductive inorganic nanofiller of the invention is a filler of nanometric dimension.

The thermally conductive inorganic nanofiller(s) of the invention typically have at least one of their dimensions of nanometric size (10 ⁻⁹ meters).

More particularly, the nanofiller(s) of the invention (i.e. one or more elementary particles) can have at least one of their dimensions of at most 1000 nm (nanometers) approximately, preferably of at least more than approximately 900 nm, preferably at most approximately 800 nm, preferably at most approximately 600 nm, and more preferably at most approximately 400 nm.

In addition, the nanofiller(s) of the invention can have at least one of their dimensions of at least approximately 1 nm, and preferably of at least approximately 5 nm.

Preferably, the nanofiller(s) of the invention may have at least one of their dimensions ranging from approximately 1 to 800 nm, and particularly preferably from approximately 5 to 600 nm.

The use of nanometric thermally conductive inorganic filler nanoparticles makes it possible to improve the thermal conductivity of the polymer composition.

By considering several nanoparticles of thermally conductive inorganic filler according to the invention, the term “dimension” represents the distribution of sizes D50, this distribution being conventionally determined by methods well known to those skilled in the art. The dimension of the thermally conductive nanofiller(s) according to the invention may for example be determined by microscopy, in particular by scanning electron microscope (SEM) or by transmission electron microscope (TEM), or by laser diffraction.

The D50 size distribution is preferably measured by laser diffraction, for example using a laser beam diffraction particle sizer. The D50 size distribution indicates that 50% by volume of the particle population has an equivalent sphere diameter less than the given value.

The thermally conductive inorganic nanofiller can be "treated" or "untreated", and preferably "treated".

“Treated thermally conductive inorganic nanofiller” means a thermally conductive inorganic nanofiller that has undergone a surface treatment, or in other words, a surface-treated thermally conductive inorganic nanofiller. Said surface treatment makes it possible in particular to modify the surface properties of the thermally conductive inorganic nanofiller, for example to improve the compatibility of the thermally conductive inorganic nanofiller with the thermoplastic polymer material, and in particular with the ethylene polymer.

In a preferred embodiment, the thermally conductive inorganic nanofiller of the invention is silanized, or in other words is processed to obtain a silanized thermally conductive inorganic nanofiller.

The surface treatment used to obtain the silanized thermally conductive inorganic nanofiller is in particular a surface treatment from at least one silane compound (with or without coupling agent), this type of surface treatment being well known to man of career.

Thus, the silanized thermally conductive inorganic nanofiller of the invention may comprise siloxane and/or silane groups at its surface. Said groups can be of the vinylsilane, alkylsilane, epoxysilane, methacryloxysilane, acryloxysilane, aminosilane or mercaptosilane type.

The silane compound used to obtain the silanized thermally conductive inorganic nanofiller can be chosen from:

- alkyltrimethoxysilane or alkyltriethoxysilane, such as for example octadecyltrimethoxysilane (OdTMS - C18), octyl(triethoxy)silane (OTES - C8), methyl trimethoxysilane, hexadecyl trimethoxysilane,

- vinyltrimethoxysilane or vinyltriethoxysilane,

- methacryloxylsilane or acryloxysilane, such as for example 3-methacryloxypropyl methyldimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-acryloxypropyl trimethoxysilane, and

- one of their mixtures

The thermally conductive inorganic nanofiller may have a specific surface according to the BET method ranging from 1 to 1000 m ² /g approximately, preferably from 50 to 750 m ² /g approximately, and in a particularly preferred manner from 100 to 500 m ² /g about.

In the present invention, the specific surface area of the inorganic thermally conductive inorganic filler nanofiller can be easily determined according to DIN 9277 (2010).

The star polymer

The ethylene polymer can be an ethylene homo- or copolymer.

When the ethylene polymer is an ethylene copolymer, it may be a copolymer of ethylene and an olefin chosen 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. The olefin is preferably from the following olefins: propylene, 1-hexene and 1-octene.

The ethylene polymer preferably comprises at least about 80% by mole of ethylene, more preferably at least about 90% by mole of ethylene, and more particularly preferably at least about 95% by mole of ethylene. , based on the total number of moles of the ethylene polymer.

According to a preferred embodiment of the invention, the ethylene polymer is a low density polyethylene, a linear low density polyethylene, a medium density polyethylene, or a high density polyethylene, and preferably a linear low density polyethylene; in particular according to the ISO 1183A standard (at a temperature of 23°C). Indeed, such a linear low density polyethylene facilitates step i), ie the dispersion of the nanofiller in the ethylene polymer. The ethylene polymer preferably has an elastic modulus of at least 200 MPa, and particularly preferably at least 250 MPa.

In the present invention, the elastic modulus or Young's modulus of a polymer (known under the anglicism "Tensile Modulus") is well known to those skilled in the art, and can be easily determined according to the ISO 527-1 standard. , -2 (2012). The ISO 527 standard presents a first part, denoted “ISO 527-1”, and a second part, denoted “ISO 527-2” specifying the test conditions relating to the general principles of the first part of the ISO 527 standard.

In the present invention, the expression “low density” means having a density ranging from 0.91 to 0.925 g/cm ³ approximately, said density being measured according to the ISO 1183A standard (at a temperature of 23° C.).

In the present invention, the expression “medium density” means having a density ranging from 0.926 to 0.940 g/cm ³ approximately, said density being measured according to the ISO 1183A standard (at a temperature of 23° C.).

In the present invention, the expression “high density” means having a density ranging from 0.941 to 0.965 g/cm ³ , said density being measured according to the ISO 1183A standard (at a temperature of 23° C.).

The ethylene polymer preferably represents from 20% to 80% by weight approximately, and particularly preferably from 25% to 60% by weight approximately, relative to the total weight of the nanocharged ethylene polymer (i.e. of the polymer of ethylene and thermally conductive inorganic nanofiller).

Step ii)

Step ii) comprises mixing the nanofilled ethylene polymer obtained in step i) with at least one propylene polymer, to form a nanofilled thermoplastic polymer material.

This step ii) makes it possible to form a thermoplastic polymer material having several levels of percolation.

This step ii) can be carried out at a temperature ranging from approximately 180° C. to approximately 240° C., and preferably from approximately 200° C. to approximately 220° C.

Step ii) is advantageously carried out with a mixer suitable for mixing several solids, such as for example a single-screw extruder, a twin-screw, in particular co-rotating or counter-rotating, a buss co-kneader, or a closed mixing device.

This step ii) may have a residence time ranging from approximately 1 min to approximately 1 hour, and preferably from approximately 5 minutes to approximately 30 minutes.

The combination of ethylene and propylene polymers makes it possible to obtain a thermoplastic polymer material with good mechanical properties, particularly in terms of elastic modulus, and electrical properties.

The propylene polymer

During step ii), the propylene polymer (or the propylene polymers when there are several of them) is (are) used in an amount such that it (they) represent(s) preferably at least 50% by weight approximately, particularly preferably from 55% to 90% by weight approximately, and more particularly preferably from 60% to 85% by weight approximately, relative to the total weight of the thermoplastic polymer material based polypropylene and polyethylene.

The propylene polymer can be a propylene Pi homopolymer or copolymer, and preferably a propylene Pi copolymer.

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

The propylene homopolymer Pi can represent at least 10% by weight, and preferably 15 to 30% by weight, relative to the total weight of the thermoplastic polymer material based on polypropylene and polyethylene.

Mention may be made, as examples of copolymers of propylene Pi, of copolymers of propylene and of olefin, the olefin being chosen in particular from ethylene and an olefin ai other than propylene. The ethylene or the olefin ai different from the propylene of the copolymer of propylene and olefin preferably represents at most 45% by mole approximately, in a particularly preferred manner at most 40% by mole approximately, and more particularly preferably at most 35% by mole, relative to the total number of moles of copolymer of propylene and olefin.

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.

The olefin ai different from propylene can correspond to the formula CH2=CH-R ¹ , in which R ¹ is a linear or branched alkyl group having from 2 to 12 carbon atoms, chosen in particular from the following olefins: 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and a mixture thereof.

Propylene and ethylene copolymers are preferred as the propylene Pi copolymer.

The propylene copolymer Pi can be a homophasic propylene copolymer or a heterophasic propylene copolymer, and preferably a homophasic propylene copolymer.

In the invention, the homophasic propylene copolymer Pi preferably has an elastic modulus ranging from approximately 600 to 1200 MPa, and in a particularly preferred manner ranging from approximately 800 to 1100 MPa.

The homophasic propylene copolymer Pi is advantageously a random copolymer of propylene Pi.

The ethylene or the olefin ai different from the propylene of the homophasic propylene copolymer Pi preferably represents at most 20% by mol approximately, in a particularly preferred manner at most 15% by mol approximately, and more particularly preferably at most 10% in mole approximately, relative to the total number of moles of the homophasic propylene copolymer Pi. The ethylene or the olefin ai different from the propylene of the homophasic propylene copolymer Pi can represent at least 1% by mole, relative to the total number of moles of homophasic propylene copolymer Pi.

By way of example of a random copolymer of propylene Pi, mention may be made of 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.

The heterophasic (or heterophase) propylene copolymer Pi may comprise a thermoplastic phase of the propylene type and a thermoplastic elastomer phase of the copolymer type of ethylene and an olefin ci2.

The olefin 012 of the thermoplastic elastomer phase of the heterophasic propylene copolymer Pi may be propylene.

The thermoplastic elastomer phase of the heterophasic propylene copolymer Pi can represent at least 20% by weight approximately, and preferably at least 45% by weight approximately, relative to the total weight of the heterophasic propylene copolymer Pi.

The heterophasic propylene copolymer Pi preferably has an elastic modulus ranging from approximately 50 to 1200 MPa, and in a particularly preferred manner: either an elastic modulus ranging from approximately 50 to 550 MPa, and more particularly preferably ranging from 50 to 300 MPa about ; or an elastic modulus ranging from approximately 600 to 1200 MPa, and more particularly preferably ranging from approximately 800 to 1200 MPa.

By way of example of a heterophasic propylene copolymer, mention may be made of the heterophasic propylene copolymer marketed by the company LyondelIBasell under the reference Adflex® Q 200 F, or the heterophasic copolymer marketed by the company LyondelIBasell under the reference EP®2967.

The propylene homopolymer or copolymer Pi may have a melting point above approximately 110° C., preferably above approximately 130° C., in a particularly preferred manner above approximately 135° C., and more particularly preferably ranging from 140 to 170°C approximately.

The propylene Pi homopolymer or copolymer can have an enthalpy of fusion ranging from approximately 20 to 100 J/g. The propylene homopolymer P1 preferably has an enthalpy of fusion ranging from approximately 80 to 90 J/g.

The homophasic propylene copolymer Pi preferably has an enthalpy of fusion ranging from approximately 40 to 90 J/g, and in a particularly preferred manner ranging from 50 to 85 J/g.

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

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

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

The heterophasic propylene copolymer Pi can have a melt index ranging from 0.5 to 1.3 g/10 min, and preferably ranging from 0.6 to 1.2 g/10 min approximately; in particular determined at approximately 230° C. with a load of approximately 2.16 kg according to the ASTM D1238-00 standard, or the ISO 1133 standard.

The propylene Pi homopolymer or copolymer can have a density ranging from approximately 0.81 to 0.92 g/cm ³ ; in particular determined according to the ISO 1183A standard (at a temperature of 23°C).

The propylene copolymer Pi preferably has a density ranging from 0.85 to 0.91 g/cm ³ , and in a particularly preferred manner ranging from 0.87 to 0.91 g/cm ³ ; in particular determined according to the ISO 1183A standard (at a temperature of 23°C).

Step ii) can implement several propylene polymers.

In this embodiment, step ii) comprises mixing the nanofilled ethylene polymer obtained in step i) with several propylene polymers, to form a nanofilled thermoplastic polymer material.

The propylene polymers may be several different propylene Pi copolymers, in particular two different propylene Pi copolymers, said propylene Pi copolymers being as defined above. In particular, step ii) can implement a homophasic propylene copolymer (as the first propylene Pi copolymer) and a heterophasic propylene copolymer (as the second propylene Pi copolymer), or two heterophasic propylene copolymers different.

When a homophasic propylene copolymer and a heterophasic propylene copolymer are used, said heterophasic propylene copolymer preferably has an elastic modulus ranging from approximately 50 to 300 MPa.

According to one embodiment of the invention, the two heterophasic propylene copolymers have a different elastic modulus. Preferably, a first heterophasic propylene copolymer has an elastic modulus ranging from 50 to 550 MPa approximately, and in a particularly preferred manner ranging from 50 to 300 MPa approximately; and a second heterophasic propylene copolymer has an elastic modulus ranging from approximately 600 to 1200 MPa, and more particularly preferably ranging from approximately 800 to 1200 MPa.

Advantageously, the first and second heterophasic propylene copolymers have a melt index as defined in the invention.

These combinations of propylene copolymers Pi can advantageously make it possible to improve the mechanical properties of the electrically insulating layer. In particular, the combination makes it possible to obtain optimized mechanical properties of the electrically insulating layer, in particular in terms of elongation at break, and flexibility; and/or makes it possible to form a more homogeneous electrically insulating layer, in particular promotes the dispersion of the dielectric liquid in the thermoplastic polymer material based on polypropylene and polyethylene of said electrically insulating layer.

Furthermore, the combination of propylene Pi copolymers with an ethylene polymer makes it possible to further improve the mechanical properties of the electrically insulating layer, while guaranteeing good thermal conductivity.

According to a preferred embodiment of the invention, the propylene Pi copolymer or the propylene Pi copolymers when there are several of them, represent(s) at least 50% by weight approximately, preferably from 55 to 90% by weight. weight approximately, and particularly preferably from 60 to 90% by weight approximately, per relative to the total weight of the thermoplastic polymer material based on polypropylene and polyethylene.

The homophasic propylene copolymer Pi can represent at least 30% by weight, and preferably from 40 to 80% by weight, relative to the total weight of the thermoplastic polymer material based on polypropylene and polyethylene.

The heterophasic propylene copolymer Pi or the heterophasic propylene copolymers Pi when there are several of them, can represent from 1 to 50% by weight approximately, preferably from 5 to 45% by weight approximately, and in such a way particularly preferred from 10 to 50% by weight approximately, relative to the total weight of the thermoplastic polymer material based on polypropylene and polyethylene.

The ethylene polymer preferably represents from 5% to 50% by weight approximately, and particularly preferably from 10% to 40% by weight approximately, relative to the total weight of the thermoplastic polymer material based on polypropylene and polyethylene.

Step iii)

Step iii) comprises mixing the nanofilled thermoplastic polymer material obtained in step ii) with the dielectric liquid to form a polymer composition.

This step iii) makes it possible to bring the dielectric liquid possibly comprising one or more additives into contact with the nanocharged thermoplastic polymer material.

Step iii) is preferably carried out at a temperature ranging from 170° C. to 240° C. approximately, and in a particularly preferred manner from 180° C. to 220° C. approximately.

Step iii) is preferably carried out using an extruder.

The extruder preferably includes a screw.

According to one embodiment of the invention, the extruder implementing step iii) of the method of the invention is a single-screw extruder. It therefore comprises a single screw. The extruder may be provided with at least one feed hopper connected to the extruder and configured to introduce or inject constituents into the extruder.

According to a particularly preferred embodiment of the invention, step iii) is carried out according to the following sub-steps: iii-1) introducing the dielectric liquid into an extruder by means of a feed hopper, iii-2 ) introducing the nanocharged thermoplastic polymer material [from step ii)], in particular in the form of granules, into the extruder by means of the feed hopper, iii-3) mixing the dielectric liquid and the thermoplastic polymer material nanocharged within the extruder, in order to form the polymer composition, and iii-4) melting the thermoplastic polymer material.

During step iii), the dielectric liquid and the nanofilled thermoplastic polymer material are preferably brought into a first zone of the screw, called the feed zone (sub-steps iii-1 and iii-2)).

The feed zone or first zone of the screw is located in particular at the entrance to the extruder.

The resulting mixture can then be brought from the feed zone to one or more intermediate zones of the screw allowing the transport of the polymer composition to the head of the extruder located at the outlet of the extruder, and the gradual melting of the thermoplastic polymer material (substeps iii-3) and iii-4)).

Sub-step iii-1) (respectively sub-step iii-2) can be implemented at a pressure of at most 5 bars, preferably at most 3 bars, and preferably at most 1 .5 bars. In a particularly preferred embodiment, sub-step iii-1) (respectively sub-step iii-2) is carried out at atmospheric pressure, namely at a pressure approximately equal to 1 bar.

Before sub-step iii-2) of introducing the nanofilled thermoplastic polymer material into the extruder, said nanofilled thermoplastic polymer material may be heated beforehand to a temperature ranging from 40° C. to 100° C.

According to a preferred embodiment, the sub-steps iii-1) and iii-2) are concomitant. In other words, the dielectric liquid is introduced at the same time that the nanofilled thermoplastic polymer material in solid form in the feed zone, through the hopper of the extruder.

During sub-steps iii-3) and iii-4), the polymer composition is brought (continuously) from the feed zone to one or more intermediate zones of the screw allowing the transport of the composition towards the head of the extruder located at the exit of the extruder, and the gradual melting of the polymer.

The intermediate zones are located between the feed zone and the extruder head.

The intermediate zones can include one or more heating zones, making it possible to control the temperature in the extruder.

The molten (melting) state is reached when the thermoplastic polymer material is heated to a temperature greater than or equal to its melting temperature.

According to a particularly preferred embodiment of the invention, sub-steps iii-3) and iii-4) are concomitant.

Sub-step iii-4) [respectively sub-step iii-3)] can be carried out at a temperature ranging from 170° C. to 240° C. approximately, and in a particularly preferred manner from 180° C. to 220° C. approximately .

Sub-step iii-4) [respectively sub-step iii-3)] can be carried out at a pressure ranging from 1 to 300 bars.

The dielectric liquid and the nanocharged thermoplastic polymer material 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.

The bringing into contact of the charged dielectric liquid and of the thermoplastic polymer material can be carried out at a temperature ranging from 15° C. to 80° C. approximately, and preferably at room temperature.

In the present invention, the expression “ambient temperature” means a temperature varying from 15 to 35° C. approximately, and preferably varying from 20 to 25° C. approximately.

The bringing into contact is preferably carried out at a pressure of at most 5 bars, preferably of at most 3 bars, and preferably of at most 1.5 bars. In a mode of particularly preferred embodiment, the contacting is carried out at atmospheric pressure, namely approximately equal to 1 bar.

Sub-step iii-3) or bringing the dielectric liquid and the nanocharged thermoplastic polymer material into contact preferably does not include a step of impregnating the nanocharged thermoplastic polymer material with the dielectric liquid. In other words, the dielectric liquid is not completely absorbed by the nanocharged thermoplastic polymer material, in particular before the melting of the nanocharged thermoplastic polymer material according to sub-step iii-4). Indeed, a conventional impregnation step is long and requires a minimum amount of dielectric liquid (approximately 10-15% relative to the total mass of the polymer composition).

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 sleeve (i.e. grooved sleeve) and/or a specific screw (i.e. barrier screw) makes it possible to obtain a homogeneous composition that is easy to extrude, while avoiding or limiting the formation of structural defects in the thermoplastic electrically insulating layer obtained.

At the end of step iii), the dielectric liquid forms an intimate mixture with the nanocharged thermoplastic polymer material.

The dielectric liquid

The dielectric liquid can comprise at least one liquid chosen from a mineral oil (eg naphthenic oil, paraffinic oil or aromatic oil), a vegetable oil (eg soybean oil, linseed oil, rapeseed oil, corn oil or castor oil ), a synthetic oil such as an aromatic hydrocarbon (alkylbenzene, alkylnaphthalene, alkylbiphenyl, alkydiarylethylene, etc.), a silicone oil, an ether-oxide, an organic ester, and an aliphatic hydrocarbon, and preferably from a mineral oil (eg naphthenic oil, paraffinic oil or aromatic oil), a vegetable oil (eg soybean oil, linseed oil, rapeseed oil, corn oil or castor oil), a synthetic oil such as an aromatic hydrocarbon ( alkylbenzene, alkylnaphthalene, alkylbiphenyl, alkydiarylethylene, etc.), a silicone oil, and an aliphatic hydrocarbon. The liquid composing the dielectric liquid is generally liquid at around 20-25°C.

The dielectric liquid may comprise at least approximately 70% by weight of the liquid making up the dielectric liquid, and preferably at least 80% by weight approximately of the liquid making up the dielectric liquid, relative to the total weight of the dielectric liquid.

Mineral oil is preferred as the liquid composing the dielectric liquid.

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

The mineral oil is preferably chosen from naphthenic oils and paraffinic oils.

Mineral oil is obtained from the refining of crude oil.

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

In a particular embodiment, the polar compound of benzophenone, acetophenone type or one of their derivatives represents at least 2.5% by weight approximately, preferably at least 3.5% by weight approximately, and in a particularly preferred manner at least 4% by weight approximately, relative to the total weight of the dielectric liquid. The polar compound makes it possible to improve the dielectric strength of the electrically insulating layer.

The dielectric liquid may comprise at most 30% by weight approximately, preferably at most 20% by weight approximately, and even more preferably at most 15% by weight approximately, of polar compound of the benzophenone or acetophenone type or one of their derivatives, for relative to the total weight of the dielectric liquid. This maximum quantity makes it possible to guarantee moderate or even low dielectric losses (eg less than approximately 10' ³ ), and also to prevent migration of the dielectric liquid out of the electrically insulating layer. According to a preferred embodiment of the invention, the polar compound of benzophenone or acetophenone type or one of their derivatives is chosen from benzophenone, dibenzosuberone, fluorenone and anthrone. Benzophenone is particularly preferred.

One or more additives may form part of the constituents of the dielectric liquid, of the charged dielectric liquid, or of the polymer composition.

Additives may be selected from processing aids such as lubricants, compatibilizers, coupling agents, antioxidants, anti-UV agents, antioxidants, anti-copper agents, anti-treeing agents of water, pigments, and a mixture thereof.

The antioxidants make it possible to protect the polymer composition from the thermal stresses generated during the stages of manufacture of the cable or operation of the cable.

The antioxidants are preferably selected from hindered phenols, thioesters, sulfur-based antioxidants, phosphorus-based antioxidants, amine-type antioxidants, and a mixture thereof.

Examples of hindered phenols include 1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine (Irganox® MD 1024), pentaerythritol tetrakis(3-(3, 5-di-te/'t-butyl-4-hydroxyphenyl)propionate) (Irganox® 1010), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox® 1076), 1,3,5-trimethyl-2,4,6-tris(3,5-di-te/'t-butyl-4-hydroxybenzyl)benzene (Irganox® 1330), 4,6-bis(octylthiomethyl) -o-cresol (Irgastab® KV10 or Irganox® 1520), 2,2'-thiobis(6-te/'t-butyl-4-methylphenol) (Irganox® 1081), 2,2'-thiodiethylene bis[ 3-(3,5-di-te/ -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-te/'t-butyl-4-hydroxyphenyl)propionate) (Naugard XL-1), or 2,2'-methylenebis(6 -te/'t-butyl-4-methylphenol).

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 C14) thiopropionyloxy}-5-te/'t-butylphenyl]sulphide, thiobis-[2-te/7-butyl-5 - methyl-4,1-phenylene] bis [3-(dodecylthio)propionate], or 4,6-bis(octylthiomethyl)-o-cresol (Irganox® 1520 or Irgastab® KV10).

Examples of phosphorus-based antioxidants include tris(2,4-di-te/i-butyl-phenyl)phosphite (Irgafos® 168) or bis(2,4-di-te /i-Butylphenyl)pentaerythritol diphosphite (Ultranox® 626).

Examples of amine-type antioxidants include phenylene diamines (e.g. paraphenylene diamines such as 1 PPD or 6PPD), diphenylamine styrene, diphenylamines, 4-(1-methyl-1-phenylethyl)- N-[4-(1-methyl-1-phenylethyl)phenyl]aniline (Naugard 445), mercapto benzimidazoles, or polymerized 2,2,4-trimethyl-1,2 dihydroquinoline (TMQ).

As examples of mixtures of antioxidants which can be used according to the invention, mention may be made of Irganox B 225 which comprises an equimolar mixture of Irgafos 168 and Irganox 1010 as described above.

The antioxidant can represent from 3% to 25% by weight approximately, and preferably from 5% to 20% by weight approximately, relative to the total weight of the dielectric liquid.

The polymer composition

The thermoplastic polymer material of the polymer composition of the electrically insulating layer of the cable of the invention is preferably heterophase (i.e. it comprises several phases). The presence of several phases generally comes from the mixture of two different polyolefins, such as a mixture of a propylene polymer and an ethylene polymer, or a mixture of different propylene polymers.

At the end of step iii), a polymer composition comprising at least said thermoplastic polymer material, said dielectric liquid, and said thermally conductive inorganic filler is obtained.

The polymer composition of the electrically insulating layer of the invention is a thermoplastic polymer composition. It is therefore not reticulum labiate.

In particular, the polymer composition does not include crosslinking agents, silane-type coupling agents, peroxides and/or additives which allow crosslinking. Indeed, such agents degrade the thermoplastic polymer material based on polypropylene and polyethylene. The polymer composition is preferably recyclable.

The polymer composition may comprise at least 1% by weight approximately, preferably at least 2% by weight approximately, more preferably at least 5% by weight approximately, and more particularly preferably at least 10% by weight approximately, of thermally conductive inorganic filler relative to the total weight of the polymer composition.

The polymer composition may comprise at most 50% by weight approximately, particularly preferably at most 40% by weight approximately, and more particularly preferably at most 30% by weight approximately, thermally conductive inorganic filler relative to the total weight of the polymer composition.

The polymer composition may typically comprise from 0.01 to 5% by weight approximately, and preferably from 0.1 to 2% by weight approximately, of additives, relative to the total weight of the thermoplastic polymer material based on polypropylene and polyethylene .

The dielectric liquid represents from 1% to 20% by weight approximately, preferably from 2 to 15% by weight approximately, and in a particularly preferred manner from 3 to 12% by weight approximately, relative to the total weight of the polymer composition.

The thermoplastic polymer material based on polypropylene and polyethylene can represent at least 50% by weight approximately, preferably at least 70% by weight approximately, and in a particularly preferred manner at least 80% by weight approximately, relative to the total weight of the polymer composition.

The method may further comprise, before step iii), a step io) of preparing the dielectric liquid.

During step io), the dielectric liquid can be prepared by mixing the different constituents of the dielectric liquid.

Step io) can then be carried out by mixing the mineral oil with the polar compound.

Stage io) can be carried out at a temperature ranging from approximately 20° C. to approximately 100° C., in particular in order to guarantee a homogeneous mixture of the mineral oil with the polar compound. One or more of the additives as defined in the invention can be added during step io), i), ii), or iii).

When the additive is an antioxidant, it is preferably added during step io).

In other words, step io) comprises mixing the liquid making up the dielectric liquid, optionally the polar compound, with at least one antioxidant.

When the antioxidant is present, step io) comprises mixing the mineral oil with optionally the polar compound, and with the antioxidant.

Step io) is optional. In other words, the various constituents of the dielectric liquid can be mixed with the nanocharged thermoplastic polymer material without prior step io).

Step iv)

At the end of step iii) a homogeneous polymer composition is obtained and it can then be extruded around the elongated electrically conductive element according to step iv), to obtain an electrically insulating layer (extruded) surrounding said electrically elongated conductor.

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

When step iii) is carried out by means of an extruder, step iv) consists in recovering the polymer composition formed in one or more intermediate zones of the extruder and brought to the level of the head of the extruder for the applied around the elongated electrically conductive element.

During step iv), the composition comprising the nanocharged thermoplastic polymer material in the molten state and the dielectric liquid passes in particular under pressure through a die.

During step iv), the polymer composition at the extruder outlet is said to be

"non-crosslinked", the temperature as well as the processing time within the extruder being optimized accordingly.

On leaving the extruder, a layer is therefore obtained extruded around said electrically conductive element, which may or may not be in direct physical contact with said elongated electrically conductive element. The method of the invention preferably does not include a step of crosslinking the layer obtained in step iv).

The electrically insulating layer and/or the semi-conductive layer(s) of the electric cable of the invention can be obtained by successive extrusion or by co-extrusion.

The different compositions can be extruded one after the other to successively surround the elongated electrically conductive element, and thus form the different layers of the electric cable of the invention.

They can alternatively be extruded concomitantly by co-extrusion using a single extruder head, co-extrusion being a process well known to those skilled in the art.

During step iv), the temperature within the extrusion device is preferably higher than the melting temperature of the majority polymer or of the polymer having the highest melting temperature, among the polymers used in the composition to be enforce.

This step iv) can be carried out at a temperature ranging from approximately 180° C. to approximately 240° C., and preferably ranging from approximately 200° C. to approximately 220° C.

The electrically insulating layer

The electrically insulating layer of the cable of the invention is a non-crosslinked layer or in other words a thermoplastic layer.

In the invention, the expression "uncrosslinked layer" or "thermoplastic layer" means a layer whose gel content according to the ASTM D2765-01 standard (xylene extraction) is at most approximately 30%, preferably at most approximately 20%, particularly preferably at most approximately 10%, more particularly preferably at most 5%, and even more particularly preferably 0%.

In one embodiment of the invention, the electrically insulating layer, preferably non-crosslinked, has a thermal conductivity of at least 0.30 W/mK at 40° C., preferably of at least 0.31 W/ mK at 40°C, particularly preferably at least 0.32 W/mK at 40°C, more preferably at least 0.33 W/mK at 40°C, even more particularly preferably at least 0.34 W/mK at 40°C, and even more preferably at least 0.35 W/mK at 40°C.

In a particular embodiment, the electrically insulating layer, preferably non-crosslinked, has a tensile strength (RT) of at least 8.5 MPa, preferably of at least approximately 10 MPa, and particularly preferably of at least approximately 15 MPa, before aging (according to standard CEI 20-86).

In a particular embodiment, the electrically insulating layer, preferably non-crosslinked, has an elongation at break (ER) of at least approximately 250%, preferably of at least approximately 300%, and particularly preferably of at least approximately 350%, before aging (according to standard CEI 20-86).

In a particular embodiment, the electrically insulating layer, preferably non-crosslinked, has a tensile strength (RT) of at least 8.5 MPa, preferably of at least approximately 10 MPa, and particularly preferably of at least approximately 15 MPa, after aging (according to standard CEI 20-86).

In a particular embodiment, the electrically insulating layer, preferably non-crosslinked, has an elongation at break (ER) of at least approximately 250%, preferably of at least approximately 300%, and particularly preferably of at least approximately 350%, after aging (according to standard CEI 20-86).

The tensile strength (RT) and the 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 the reference 3345 by the company Instron.

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

The electrically insulating layer of the cable of the invention is preferably a recyclable layer.

The electrically insulating layer of the invention may be an extruded layer, in particular by methods well known to those skilled in the art.

The electrically insulating layer has a variable thickness depending on the type of cable envisaged. In particular, when the cable according to the invention is a medium voltage cable, the thickness of the electrically insulating layer is typically approximately 4 to 5.5 mm, and more particularly approximately 4.5 mm. When the cable in accordance with the invention is a high voltage cable, the thickness of the electrically insulating layer typically varies from 17 to 18 mm (for voltages of the order of approximately 150 kV) and to go up to thicknesses ranging approximately 20 to 25 mm for voltages above 150 kV (high voltage cables). The aforementioned thicknesses depend on the size of the elongated electrically conductive element.

In the present invention, the term "electrically insulating layer" means a layer whose electrical conductivity can be at most ^1.10'8 S/m (siemens per meter), preferably at most ^1.10'9 S/m, and particularly preferably at most ^1.10'1 ° S/m, measured at approximately 25° C. in direct current.

The electrically insulating layer of the invention may comprise at least the thermoplastic polymer material based on polypropylene and polyethylene, at least the thermally conductive inorganic filler, and the dielectric liquid, the aforementioned ingredients being as defined in the invention.

The proportions of the various ingredients in the electrically insulating layer may be identical to those as described in the invention for these same ingredients in the polymer composition.

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

The cable

The electrically insulating layer of the invention may surround the elongated electrically conductive element.

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

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

The elongated electrically conductive member can be aluminum, aluminum alloy, copper, copper alloy, or a combination thereof. According to a preferred embodiment of the invention, the electric cable comprises:

- at least one semiconductor layer surrounding the elongated electrically conductive element, and

- an electrically insulating layer as defined in the invention.

The electrically insulating layer more particularly has an electrical conductivity lower than that of the semi-conducting layer. More particularly, the electrical conductivity of the semiconductor layer can 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 in a particularly preferably at least 1000 times greater than the electrical conductivity of the electrically insulating layer.

The semiconductor layer may surround the electrically insulating layer. The semiconductor layer can then be an outer semiconductor layer.

The electrically insulating layer may surround the semiconductor layer. The semiconductor layer can then be an internal semiconductor layer.

The semiconductor layer is preferably an inner semiconductor layer.

The electrical cable of the invention may further comprise another semi-conducting layer.

Thus, in this embodiment, the cable of the invention may comprise:

- at least one elongated electrically conductive element, preferably positioned in the center of the cable,

- a first semiconductor layer surrounding the elongated electrically conductive element,

- an electrically insulating layer surrounding the first semiconductor layer, and

- a second semiconductor layer surrounding the electrically insulating layer, the electrically insulating layer being as defined in the invention.

In the present invention, the term "semiconducting layer" means a layer whose electrical conductivity can be strictly greater than 1.10 ^-8 S/m (siemens per meter), preferably at least 1.10' ³ S/m, and preferably may be less than 1×10 ³ S/m, measured at 25° C. in direct current. In a particular embodiment, the first semiconductor layer, the electrically insulating layer and the second semiconductor layer constitute a three-layer insulation. In other words, the electrically insulating layer is in direct physical contact with the first semiconductor layer, and the second semiconductor layer is in direct physical contact with the electrically insulating layer.

The first semiconductor layer (respectively the second semiconductor layer) is preferably obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene as defined in the invention, and optionally at least one electrically conductive load as defined in the invention.

The electrically conductive filler preferably represents an amount sufficient for the layer to be semiconductive.

Preferably, the polymer composition at least 6% by weight approximately of electrically conductive filler, preferably at least 10% by weight approximately of electrically conductive filler, preferably at least 15% by weight approximately of electrically conductive filler, and even more preferably at least least 25% by weight of electrically conductive filler, relative to the total weight of the polymer composition.

The polymer composition may comprise at most 45% by weight approximately of electrically conductive filler, and preferably at most 40% by weight approximately of electrically conductive filler, relative to the total weight of the polymer composition.

The first semiconductor layer (respectively the second semiconductor layer) is preferably a thermoplastic layer or an uncrosslinked layer.

The cable may further comprise an outer protective sheath surrounding the electrically insulating layer (or the second semi-conducting layer if it exists).

The outer protective sheath may be in direct physical contact with the electrically insulating layer (or the second semi-conductor layer if it exists). The outer protective sheath may be an electrically insulating sheath.

The electrical cable may further comprise an electrical screen (e.g. metal) surrounding the second semi-conducting layer. In this case, the electrically insulating sheath surrounds said electrical shield and the electrical shield is between the electrically insulating sheath and the second semi-conducting layer.

This metallic screen can be a so-called "wired" screen composed of a set of copper or aluminum conductors arranged around and along the second semi-conducting layer, a so-called "ribboned" screen composed of one or more ribbons metal conductors in copper or aluminum possibly placed in a helix around the second semi-conductive layer or a metal conductive strip in aluminum placed longitudinally around the second semi-conductive layer and sealed with glue in the areas of overlapping portions of said tape, or of a so-called "sealed" screen of the metal tube type optionally composed of lead or lead alloy and surrounding the second semi-conductor layer. This last type of screen makes it possible in particular to act as a barrier to moisture which tends to penetrate the electrical cable in the radial direction.

The metal screen of the electric cable of the invention may comprise a so-called "wired" screen and a so-called "watertight" screen or a so-called "wired" screen and a so-called "taped" screen.

All types of metal screens can play the role of earthing the electric cable and can thus carry fault currents, for example in the event of a short circuit in the network concerned.

Other layers, such as layers that swell in the presence of humidity, can be added between the second semi-conducting layer and the metal screen, these layers making it possible to ensure the longitudinal watertightness of the electric cable.

Brief description of the drawings

[Fig. 1] Figure 1 shows a device for implementing a method according to the invention. For reasons of clarity, only the essential elements for the understanding of the invention have been represented schematically, and this without respecting the scale.

In FIG. 1, the device 1 comprises a container 2 which can be supplied with granules of a nanofilled thermoplastic polymer material based on polyethylene and polypropylene (i.e. ethylene polymer + thermally conductive inorganic filler; previously mixed with a polymer of propylene), a container 3 which can be supplied with a dielectric liquid, a supply hopper 4 which can be supplied at ambient temperature with the granules of nanocharged thermoplastic polymer material contained in the container 2 and with the dielectric liquid contained in the container 3, and an extruder 5 comprising a grooved sleeve 6 and/or a barrier screw 7, as well as an extruder head 8. The granules of nanocharged thermoplastic polymer material and the dielectric liquid are introduced via the supply hopper 4 into a zone feed 9 of the screw according to step iii), then brought from the feed zone 9 to one or more intermediate zones ires 10 allowing the transport of the polymer composition to the head of the extruder 8 located at the outlet of the extruder 5 and the gradual melting of the nanocharged thermoplastic polymer material, said intermediate zones 10 being located between the feed zone 9 and the extruder head 8. Finally, at the level of the extruder head 8, the polymer composition is applied around an elongated electrically conductive element.

Example

Nanocharged polyethylene

A nanofilled polyethylene was prepared as follows: a linear low density polyethylene LLDPE sold under the trade name BPD 3642 by Ineos was mixed with alumina sold under the trade name Timal 17 by Alteo using a twin-screw extruder (“Leistritz twin screw extruder”) at a temperature of approximately 165 to 180° C., then melted at approximately 200° C. (screw speed: 15 revolutions/min), to form a filled polyethylene comprising 36.5 % by weight of polyethylene and 63.5% by weight of alumina, based on weight total filled polyethylene. The alumina used has a D50 of approximately 400 nm and a specific surface area of approximately 8 m ² /g.

Polymer composition

A layer in accordance with the invention, i.e. obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene and polyethylene, at least one dielectric liquid, and at least one thermally conductive inorganic filler was prepared from the way detailed below.

Table 1 below collates the amounts of the compounds present in the polymer composition in accordance with the invention which are expressed in percentages by weight, relative to the total weight of the polymer composition.

[Tables 1]

The origin of the compounds in Table 1 is as follows:

- Random propylene copolymer marketed by the company Total Petrochemicals under the reference PPR3221;

- Heterophase propylene copolymer marketed by the company Basell Polyolefins under the reference Adflex® Q 200 F;

- Linear low-density polyethylene marketed by the company Ineos under the reference BPD3642 YB;

- Antioxidant marketed by Ciba under the reference Irganox® B 225 comprising an equimolar mixture of Irgafos® 168 and Irganox® 1010; and

- Dielectric liquid comprising 95.0% by weight of an oil marketed by Nynas under the reference BNS 28 and 5.0% by weight of benzophenone.

Uncured layer

The following constituents: mineral oil, antioxidant and benzophenone of the polymer composition referenced in Table 1, are measured out and mixed with stirring at approximately 75° C., in order to form a dielectric liquid.

The nanofilled polyethylene is then mixed in a container with the following constituents: heterophase propylene copolymer, additional linear low density polyethylene, and random propylene copolymer of the polymer composition referenced in Table 1 and dielectric liquid as prepared above. Then, the resulting mixture is homogenized using a twin-screw extruder (“Leistritz twin screw extruder”) at a temperature of approximately 165 to 180°C, then melted at approximately 200°C (screw speed: 15 rpm).

The homogenized and molten mixture is then put into the form of granules.

The granules were then hot pressed to form a layer in the form of a plate.

The polymer composition was thus prepared in the form of a layer 1 mm thick for the evaluation of its mechanical properties and also of a layer 8 mm thick to perform the thermal conductivity measurements.

The tensile strength (RT) and elongation at break (ER) tests were carried out on the materials according to Standard NF EN 60811 -1 -1, using a device marketed under reference 3345 by the Instron company.

The thermal conductivity tests were carried out on the materials according to the well-known method under the anglicism "Transient Plane Source or TPS" and using a device marketed under the reference HOT DISK TPS 2500S by the company THERMOCONCEPT.

The results corresponding to each of these tests are reported in Table 2 below:

[Tables 2]

All of these results show that the incorporation of a thermally conductive inorganic nanofiller as defined in the invention in an ethylene polymer according to the process of the invention improves the properties of thermal conductivity while guaranteeing good properties. mechanical, particularly in terms of tensile strength and elongation at break, including after ageing.

Claims

34 Claims

[Claim 1] A method of manufacturing an electric cable comprising at least one elongated electrically conductive element and at least one electrically insulating layer obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene and polyethylene, at least one dielectric liquid, and at least one thermally conductive inorganic nanofiller, said method being characterized in that it comprises at least the following steps: i) mixing the nanometric thermally conductive inorganic nanofiller with an ethylene polymer to form a polymer of nanofilled ethylene, ii) mixing the nanofilled ethylene polymer with at least one propylene polymer, to form a nanofilled thermoplastic polymer material, ill) mixing the nanofilled thermoplastic polymer material with the dielectric liquid to form a polymer composition, and iv ) extruding the polymer composition around the electrical element elongated conductor only.

[Claim 2] Process according to claim 1, characterized in that step i) is carried out at a temperature ranging from 140°C to 240°C.

[Claim 3] Process according to claim 1 or 2, characterized in that step i) is carried out with a mixer suitable for mixing several solids, such as for example a single-screw extruder, a twin-screw extruder, a buss co-kneader, or a closed mixing device.

[Claim 4] Process according to any one of the preceding claims, characterized in that at the end of step i), the thermally conductive inorganic nanofiller represents from 20% to 80% by weight, relative to the total weight nanocharged ethylene polymer.

[Claim 5] Process according to any one of the preceding claims, characterized in that the thermally conductive inorganic nanofiller is chosen from silicates, boron nitride, carbonates, metal oxides, and one of their mixtures. 35

[Claim 6] Process according to any one of the preceding claims, characterized in that the thermally conductive inorganic nanofiller has at least one of its dimensions ranging from 1 to 800 nm.

[Claim 7] Process according to any one of the preceding claims, characterized in that step ii) is carried out at a temperature ranging from 180°C to 240°C.

[Claim 8] Process according to any one of the preceding claims, characterized in that step ii) is carried out with a mixer suitable for mixing several solids, such as for example a single-screw extruder, a twin-screw extruder, a co-kneader buss, or a closed mixing device.

[Claim 9] Process according to any one of the preceding claims, characterized in that during step ii), the propylene polymer is used in an amount such that it represents at least 50% by weight, with respect to to the total weight of the thermoplastic polymer material based on polypropylene and polyethylene.

[Claim 10] Process according to any one of the preceding claims, characterized in that the propylene polymer is a propylene Pi copolymer chosen from a homophasic propylene copolymer and a heterophasic propylene copolymer.

[Claim 11] Process according to any one of the preceding claims, characterized in that step iii) is carried out according to the following sub-steps: iii-1) introducing the dielectric liquid into an extruder by means of a hopper feeding, iii-2) introducing the nanocharged thermoplastic polymer material, in particular in the form of granules, into the extruder by means of the feed hopper, iii-3) mixing the dielectric liquid and the nanocharged thermoplastic polymer material within of the extruder, to form the polymer composition, and iii-4) melting the thermoplastic polymer material.

[Claim 12] Process according to claim 11, characterized in that the sub-steps iii-1) and iii-2) are implemented at a pressure of at most 5 bars.

[Claim 13] Process according to claim 11 or 12, characterized in that substeps iii-3) and iii-4) are concomitant.

[Claim 14] Process according to any one of Claims 11 to 13, characterized in that the dielectric liquid and the nanofilled thermoplastic polymer material are brought into contact in the feed hopper or in the extruder. [Claim 15] Process according to Claim 14, characterized in that the bringing into contact of the dielectric liquid and of the nanocharged thermoplastic polymer material is carried out at a temperature ranging from 15 to 80°C and at a pressure of at most 5 bars.