EP4264643A1

EP4264643A1 - Method for manufacturing an electrical cable having improved thermal conductivity

Info

Publication number: EP4264643A1
Application number: EP21847991.3A
Authority: EP
Inventors: Gabriele Perego; Christelle Mazel; Daphné MERLE
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2020-12-18
Filing date: 2021-12-08
Publication date: 2023-10-25
Also published as: US20240096523A1; CN116601725A; WO2022129735A1; FR3118273A1; FR3118273B1

Abstract

The invention relates to a method for manufacturing a cable comprising at least one electrically insulating layer obtained from a polymer composition comprising at least one polypropylene-based thermoplastic polymer material, at least one dielectric liquid, and at least one thermally conductive inorganic filler, wherein said method comprises mixing the thermally conductive inorganic filler with the dielectric liquid to form a filled dielectric liquid before bringing the dielectric liquid into contact with said thermoplastic polymer material.

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, at least one dielectric liquid, and at least one filler thermally conductive inorganic filler, said method comprising mixing the thermally conductive inorganic filler with the dielectric liquid to form a charged dielectric liquid before contacting the dielectric liquid with said polymeric material.

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

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

A medium 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 and/or the formation of agglomerates, which makes the process sometimes long and/or requiring specific equipment which increases the production cost of the cable.

The object of the present invention is therefore to overcome the drawbacks of the techniques of the prior art by proposing a method for manufacturing an electric cable, in particular at medium voltage, based on propylene polymer(s), said method being easy to implement, inexpensive, requiring no complex equipment, and capable of leading to a cable, capable of operating at temperatures above 70°C, and having improved thermal conductivity properties, while guaranteeing good properties electrical, particularly in terms of dielectric 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 , at least one dielectric liquid, and at least one thermally conductive inorganic filler, said method being characterized in that it comprises at least the following steps: i) mixing the dielectric liquid with the thermally conductive inorganic filler conductive, to form a charged dielectric liquid, ii) mixing the charged dielectric liquid with the thermoplastic polymer material to form a polymer composition, and iii) 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 electrical properties.

The dispersion of the thermally conductive inorganic filler in the dielectric liquid during step i), before bringing it into contact with the thermoplastic polymer material according to step ii), makes it possible to promote the dispersion of the thermally conductive inorganic filler within of the polymer material, and to improve the thermal conductivity of the layer thus obtained.

Step i) includes mixing the dielectric liquid with the inorganic filler.

This step i) can be carried out at a temperature ranging from approximately 0° C. to approximately 100° C., and preferably from approximately 20° C. to approximately 80° C. Step i) is generally carried out at room temperature (i.e. from approximately 15 to 35°C).

Step i) is advantageously carried out with a mixer suitable for mixing a powder in a liquid, such as for example a mixer with a turbo agitator (well known under the Anglicism "turbomixer"), a planetary mixer, a mixing device continuous tubing, and/or an ultrasound device.

Mixers with turbo agitator are high-speed cylindrical mechanical agitators, generally having at least one mixing tool (eg blade). They have the particularity of generally operating at high rotational speeds, which will depend on their size. Peripheral speeds generally used range from 20 to 50 m/sec or speeds from 1800 to 2250 revolutions per minute. An example of a planetary mixer can be a “speed mixer” type mixer. This type of mixer is based on a double rotation of a bowl (instead of blade(s)), with high rotation speeds such as for example ranging from 1800 to 2250 revolutions per minute. The combination of centrifugal forces without the presence of a mixing tool (eg blade) acts on several levels and makes it possible to very quickly obtain a mixture without air bubbles. A suitable mixer is, for example, the speed mixer sold under the trade name “SPEEDMIXER DAC 400 FV”.

This step i) can last from approximately 5 min to approximately 10 hours, and preferably from approximately 1 hour to approximately 5 hours.

The thermally conductive inorganic filler

At the end of step i), the thermally conductive inorganic filler can represent from 10% to 75% by weight approximately, preferably from 20% to 70% by weight approximately, and in a particularly preferred way from 30% to 60 % by weight approximately relative to the total weight of the filled dielectric liquid (i.e. of the dielectric liquid and the thermally conductive inorganic filler). Beyond 75% of thermally conductive inorganic filler in the charged dielectric liquid, the thermally conductive inorganic filler penetrates more difficultly into the dielectric liquid.

The thermally conductive inorganic filler may have a thermal conductivity of at least 1 W/m.k approximately at 20°C, and preferably of at least 5 W/m.k 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 filler 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 fillers is preferably a mixture of two or three of said thermally conductive inorganic fillers.

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)3; 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 a calcined aluminum oxide (respectively a 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 filler is chosen from kaolins, chalk, calcined magnesium oxide, fumed silica, and calcined aluminum oxide.

The thermally conductive inorganic filler can be in the form of particles with a size ranging from 0.001 to 6 μm approximately, preferably from 0.02 to 2 μm approximately, in a particularly preferred manner from 0.050 to 1.5 μm approximately, and more particularly preferred from 0.075 to 1.0 μm approximately.

According to a particularly preferred embodiment, the thermally conductive inorganic filler is in the form of nanometric particles, such as for example particles having at least one of their dimensions ranging from approximately 1 to 800 nm, and preferably ranging from 1 to 500 nm approximately, and particularly preferably ranging from 1 to 250 nm approximately. The use of nanoscale thermally conductive inorganic filler particles improves the thermal conductivity of the polymer composition.

By considering several thermally conductive inorganic filler particles according to the invention, the term “dimension” represents the size distribution D50, this distribution being conventionally determined by methods well known to those skilled in the art.

The dimension of the thermally conductive particle(s) according to the invention can for example be determined by microscopy, in particular by scanning electron microscope (SEM), 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 filler can be "treated" or "untreated", and preferably "treated".

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

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

The surface treatment used to obtain the silanized thermally conductive inorganic filler can be a surface treatment from at least one silane compound (with or without a coupling agent), this type of surface treatment being well known to man. of career. Thus, the silanized thermally conductive inorganic filler 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 filler 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 filler may have a specific surface according to the BET method ranging from 1 to 1000 m ² /g approximately, preferably from 10 to 750 cm ² /g approximately, and in a particularly preferred manner from 50 to 500 m ² /g about.

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

The dielectric liquid of step i) 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 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 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 approximately 20-25°C.

The dielectric liquid may comprise at least 70% by weight approximately of the liquid composing the dielectric liquid, preferably at least 80% by weight approximately, and in a particularly preferred manner at least 90% by weight approximately of the liquid composing 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 benzophenone, 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 (lrganox® MD 1024), pentaerythritol tetrakis(3-(3, 5-di-te/i-butyl-4-hydroxyphenyl)propionate) (Irganox® 1010), octadecyl 3-(3,5-di-te/i-butyl-4-hydroxyphenyl)propionate (Irganox® 1076) , 1,3,5-trimethyl-2,4,6-tris(3,5-di-te/7-butyl-4-hydroxybenzyl)benzene (Irganox® 1330), 4,6-bis (octylthiomethyl) -o-cresol (Irgastab® KV10 or Irganox® 1520), 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-te/'t-butyl-4-hydroxyphenyl)propionate) (Naugard XL-1), or 2,2'-methylenebis(6-te/7 - 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/7-butylphenyl]sulfide, thiobis-[2-tert-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-tert-butyl-phenyl)phosphite (Irgafos® 168) or bis(2,4-di-tert-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.

At the end of step i), the dielectric liquid can represent from 25% to 90% by weight approximately, preferably from 30% to 80% by weight approximately, and in a particularly preferred way from 40% to 70% by weight, relative to the total weight of the filled dielectric liquid (i.e. of the dielectric liquid and the thermally conductive inorganic filler).

The method may further comprise, before step i), 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) or ii).

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 thermally conductive inorganic filler without prior step io).

Step ii)

Step ii) comprises mixing the charged dielectric liquid obtained in step i) with the thermoplastic polymer material, to form the polymer composition.

This step makes it possible to bring the charged dielectric liquid, optionally comprising one or more additives, into contact with the thermoplastic polymer material.

Stage ii) 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.

According to a particular embodiment, during step ii), the thermoplastic polymer material based on polypropylene is used in an amount such that it represents from 75% to 97% by weight approximately, and preferably from 80% to 95% by weight approximately, relative to the total weight of the polymer composition.

Step ii) is preferably carried out using an extruder or an internal mixer, and preferably an extruder.

The extruder preferably includes a screw.

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

During step ii), the charged dielectric liquid and the thermoplastic polymer material are preferably brought into a first zone of the screw, called the feed zone (sub-steps ii-1 and ii-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 ii-3) and ii-4)).

Sub-step ii-1) (respectively sub-step ii-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 ii-1) (respectively sub-step ii-2) is carried out at atmospheric pressure, namely at a pressure approximately equal to 1 bar.

Before sub-step ii-2) of introducing the thermoplastic polymer material into the extruder, said thermoplastic polymer material can be preheated to a temperature ranging from 40°C to 100°C.

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

During sub-steps ii-3) and ii-4), the polymer composition is fed (continuously) from the feed zone to one or more intermediate zones of the screw allowing the transport of the composition to the head of the extruder located at the outlet 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 ii-3) and ii-4) are concomitant.

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

The charged dielectric liquid and the 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 of said charged dielectric liquid and of said thermoplastic polymer material 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 particularly preferred embodiment, the contacting is carried out at atmospheric pressure, namely approximately equal to 1 bar. Sub-step ii-3) or bringing the charged dielectric liquid and the thermoplastic polymer material into contact preferably does not include a step of impregnating the thermoplastic polymer material with the dielectric liquid. In other words, the dielectric liquid is not completely absorbed by the thermoplastic polymer material, in particular before the melting of the thermoplastic polymer material according to sub-step ii-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 ii), the charged dielectric liquid forms an intimate mixture with the thermoplastic polymer material.

The thermoplastic polymer material based on polypropylene

The polypropylene-based thermoplastic polymer material may comprise 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.

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.

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

The ethylene or the cci olefin 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 oci olefin other than 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 P1 can be a homophasic propylene copolymer or a heterophasic propylene copolymer, and preferably a heterophasic 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 α-olefin different from the propylene of the homophasic propylene copolymer Pi preferably represents at most 20% by mole approximately, in a particularly preferred manner at most 15% by mole approximately, and more particularly preferred at most approximately 10% by mole, relative to the total number of moles of the homophasic propylene copolymer P1.

The ethylene or olefin α1 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 α2 olefin.

The α2 olefin 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 Moplen EP®2967.

The propylene homopolymer or copolymer Pi may have a melting point above approximately 110° C., preferably above approximately 130° C., particularly preferably 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 Pi 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 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 0.81 to 0.92 g/cm ³ approximately; 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).

The polypropylene-based thermoplastic polymer material may comprise several different propylene Pi copolymers, in particular two different propylene Pi copolymers, said propylene Pi copolymers being as defined above. In particular, the polypropylene-based thermoplastic polymer material may comprise a homophasic propylene copolymer (as the first propylene Pi copolymer) and a heterophasic propylene copolymer (as the second propylene Pi copolymer), or two propylene copolymers different heterophasic.

When the polypropylene-based thermoplastic polymer material 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.

According to one embodiment of the invention, the two heterophasic propylene copolymers have a different elastic modulus. Preferably, the polypropylene-based thermoplastic polymer material comprises a first heterophasic propylene copolymer having an elastic modulus ranging from approximately 50 to 550 MPa, and in a particularly preferred manner ranging 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 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 of said electrically insulating layer.

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 85% by weight approximately, relative to the total weight of the thermoplastic polymer material based on polypropylene. 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 the thermoplastic polymer material based on polypropylene.

The heterophasic propylene copolymer Pi or the heterophasic propylene copolymers Pi when there are several of them, can represent from 5 to 95% by weight approximately, preferably from 25 to 90% by weight approximately, and so particularly preferred from 60 to 80% by weight approximately, relative to the total weight of the thermoplastic polymer material based on polypropylene.

The polypropylene-based thermoplastic polymer material may further comprise a P2 olefin homopolymer or copolymer.

Said P2 olefin homopolymer or copolymer is preferably different from said P2 propylene homopolymer or copolymer.

The olefin of the olefin copolymer P2 can be chosen from ethylene and an α3 olefin corresponding to the formula CH2=CH-R ² , in which R ² is a linear or branched alkyl group having from 1 to 12 carbon atoms .

The α3 olefin is preferably chosen from the following olefins: propylene, 1 - butene, isobutylene, 1 -pentene, 4-methyl-1 -pentene, 1 -hexene, 1 -octene, 1 -decene, 1 -dodecene, and one of their mixtures.

The α3 olefin of the propylene, 1-hexene or 1-octene type is particularly preferred.

The combination of polymers Pi and P2 makes it possible to obtain a thermoplastic polymer material with good mechanical properties, in particular in terms of elastic modulus, and electrical properties.

The P2 olefin homopolymer or copolymer is preferably an ethylene polymer.

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 polyethylene medium density, or a high density polyethylene, and preferably a high density polyethylene; in particular according to the ISO 1183A standard (at a temperature of 23°C). High density polyethylene makes it possible to further improve the thermal conductivity of the polymer composition.

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

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.).

According to a preferred embodiment of the invention, the olefin homopolymer or copolymer P2 represents from 5 to 50% by weight approximately, and in a particularly preferred manner from 10 to 40% by weight approximately, relative to the total weight of the thermoplastic polymer material based on polypropylene.

According to a particularly preferred embodiment of the invention, the thermoplastic polymer material based on polypropylene comprises two copolymers of propylene Pi such as a homophasic propylene copolymer and a heterophasic propylene copolymer or two different heterophasic propylene copolymers; and a P2 olefin homopolymer or copolymer such as an ethylene polymer. This combination of propylene copolymers Pi and an olefin homopolymer or copolymer P2 makes it possible to further improve the properties mechanical properties of the electrically insulating layer, while guaranteeing good thermal conductivity.

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 results from the mixture of two different polyolefins, such as a mixture of different propylene polymers or a mixture of a propylene polymer and an ethylene polymer.

At the end of step ii), 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 cross-linkable.

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.

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. 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 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 .

Step iii)

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

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

When step ii) is carried out by means of an extruder, step iii) 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 iii), the composition comprising the thermoplastic polymer material in the molten state and the charged dielectric liquid passes in particular under pressure through a die.

During step iii), 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.

At the extruder outlet, 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 iii). Indeed, propylene polymers degrade under the action of crosslinking and/or in the presence of crosslinking agents such as peroxides. 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 iii), the temperature within the extrusion device is preferably higher than the melting temperature of the predominant polymer or of the polymer having the highest melting temperature, among the polymers used in the composition to be enforce.

This step iii) can be carried out at a temperature ranging from approximately 180° C. to approximately 240° C., and preferably ranging from approximately 190° 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 preferably 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 in accordance with the invention is a medium voltage cable, the thickness of the electrically insulating layer is typically from 4 to 5.5 mm approximately, and more particularly from 4.5 mm approximately. 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 −10} 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, 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 may 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 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 electrically conductive filler may be carbon black.

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-conducting layer if it exists).

The outer protective sheath may be an electrically insulating sheath. The electric cable may also comprise an electric screen (eg metal) surrounding the second semi-conductor layer. In this case, the electrically insulating sheath surrounds said electric screen and the electric screen 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-conducting 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 thermoplastic polymer material chosen from a homo- and a copolymer of propylene, a container 3 which can be supplied with a charged dielectric liquid (ie dielectric liquid + thermally conductive inorganic filler), a feed hopper 4 which can be fed at ambient temperature with the granules of thermoplastic polymer material contained in the container 2 and with the charged dielectric liquid contained in the container 3, and an extruder 5 comprising a sheath grooved 6 and/or a barrier screw 7, as well as an extruder head 8. The granules of thermoplastic polymer material and the charged dielectric liquid are introduced via the feed hopper 4 into a feed zone 9 of the screw according to step i), then brought from the supply zone 9 to one or more intermediate zones 10 allowing the transport of the polymer composition v towards the head of the extruder 8 located at the outlet of the extruder 5 and the gradual melting of the 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

A charged dielectric liquid L1 comprising 50% by weight of a BNS28 mineral oil from Nynas, and 50% by weight of a Timal 17 alumina from Alteo was prepared by mixing the oil and the alumina at room temperature in a mixer. sold under the trade name “SPEEDMIXER DAC 400 FV” at a speed of rotation ranging from 1800 rpm to 2250 rpm. The mixture causes the oil to heat up. The alumina used has a D50 of approximately 400 nm, and a specific surface area of approximately 8 m ² /g.

Thermal conductivity tests were carried out on the charged dielectric liquid obtained, and by comparison on mineral oil without alumina (also called uncharged dielectric liquid L0).

The table below shows the different thermal conductivities obtained. The thermal conductivity was measured according to the method well known under the Anglicism "Transient Plane Source or TPS" and using a device marketed under the reference HOT DISK TPS 2500S by the company THERMOCONCEPT.

[Tables 1] Polymer compositions

A layer in accordance with the invention, i.e. obtained from a polymer composition C1 comprising at least one thermoplastic polymer material based on polypropylene, at least one dielectric liquid, and at least one thermally conductive inorganic filler was prepared according to a process according to the invention (with prior preparation of a charged dielectric liquid). For comparison, a layer not in accordance with the invention, i.e. obtained from a CO polymer composition comprising at least one thermoplastic polymer material based on polypropylene, at least one dielectric liquid, and at least one thermally conductive inorganic filler, has been prepared according to a method not in accordance with the invention (no prior preparation of a charged dielectric liquid).

Table 2 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 2]

(*) did not feel part rte 'nvenOee

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;

- High-density polyethylene sold under the trade name Eltex® A4009 MFN1325 by the company Ineos and whose density is 0.960 g/cm ³ according to standard ISO 1183A at a temperature of 23° C. (MFI=0.9);

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

- Dielectric liquid comprising 95.6% by weight of an oil marketed by Nynas under the reference BNS 28, and 4.4% by weight of benzophenone.

Uncrosslinked layers

The following constituents: mineral oil, antioxidant and benzophenone of the C0 and C1 polymer compositions referenced in Table 2, are measured out and mixed with stirring at approximately 75° C., in order to form a dielectric liquid.

For the preparation of the layer relating to composition C1, the dielectric liquid thus obtained is then mixed with the thermally conductive inorganic filler using a mixer sold under the trade name "SPEEDMIXER DAC 400 FV" at a speed of rotation ranging from 1800 rpm minute at 2250 rpm and at room temperature, to form a charged dielectric liquid.

The charged dielectric liquid is then mixed with the following constituents: heterophase propylene copolymer, random propylene copolymer, high density polyethylene of the polymer composition referenced in Table 2, in a container. Then, the resulting mixture is homogenized using a twin-screw extruder (“Berstorff twin screw extruder”) at a temperature of approximately 145 to 180°C, then melted at approximately 200°C (screw speed: 80 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 C1 was thus prepared in the form of an 8 mm thick layer to perform thermal conductivity measurements.

For the preparation of the layer relating to the CO composition, the dielectric liquid was not previously mixed with the thermally conductive inorganic filler, before adding the thermoplastic polymer material. In other words, the dielectric liquid obtained is then mixed with the following constituents: heterophase propylene copolymer, random propylene copolymer, high density polyethylene of the CO composition referenced in Table 2 in a container. Then, the resulting mixture and the inorganic filler is homogenized using a twin-screw extruder (“Berstorff twin screw extruder”) at a temperature of approximately 145 to 180°C, then melted at approximately 200°C (speed screws: 80 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 CO polymer composition was thus prepared in the form of an 8 mm thick layer to perform thermal conductivity measurements.

The results are reported in Table 3 below:

[Tables 3]

All of these results show that the prior preparation of a charged dielectric liquid before contact with the thermoplastic polymer material according to the method of the invention improves the thermal conductivity properties of the cable layer.

Claims

35 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, at least one dielectric liquid, and at least one thermally conductive inorganic filler, said method being characterized in that it comprises at least the following steps: i) mixing the dielectric liquid with the thermally conductive inorganic filler, to form a charged dielectric liquid, ii) mixing the charged dielectric liquid with the thermoplastic polymer material to form a polymer composition, and iii) extruding the polymer composition around the elongated electrically conductive member.

[Claim 2] Process according to claim 1, characterized in that step i) is carried out at a temperature ranging from 0°C to 100°C.

[Claim 3] Process according to claim 1 or 2, characterized in that step i) is carried out with a mixer with turbo agitator, a tubular continuous mixing device, a planetary mixer, and/or an ultrasonic 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 filler represents from 10% to 75% by weight, relative to the total weight charged dielectric liquid.

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

[Claim 6] Process according to any one of the preceding claims, characterized in that the thermally conductive inorganic filler is in the form of nanometric particles. 36

[Claim 7] Process according to any one of the preceding claims, characterized in that step ii) is carried out using an extruder or an internal mixer.

[Claim 8] Process according to any one of the preceding claims, characterized in that step ii) is carried out at a temperature ranging from 170°C to 240°C.

[Claim 9] Process according to any one of the preceding claims, characterized in that during step ii), the thermoplastic polymer material based on polypropylene is used in an amount such that it represents from 75% to 97 % by weight relative to the total weight of the polymer composition.

[Claim 10] A method according to any one of the preceding claims, characterized in that the polypropylene-based thermoplastic polymer material comprises a propylene Pi copolymer selected 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 ii) is carried out according to the following sub-steps: ii-1) introducing the charged dielectric liquid into an extruder by means of a hopper feed, ii-2) introducing the thermoplastic polymer material, in particular in the form of granules, into the extruder by means of the feed hopper, ii-3) mixing the charged dielectric liquid and the thermoplastic polymer material within of the extruder, in order to form the polymer composition, and ii-4) melting the thermoplastic polymer material.

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

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

[Claim 14] Process according to any one of Claims 11 to 13, characterized in that the charged dielectric liquid and the material thermoplastic polymer 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 charged dielectric liquid and of the thermoplastic polymer material is carried out at a temperature ranging from 15 to 80°C and at a pressure of at most 5 bars.