EP3329496A1

EP3329496A1 - Cable comprising a cross-linked foam insulating layer

Info

Publication number: EP3329496A1
Application number: EP16757695.8A
Authority: EP
Inventors: Marcelo DANTAS PAIXAO; Birane Toure; Laurent Keromnes; Encarnacion GONZALEZ CALVO; Laura QUIN
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2015-07-27
Filing date: 2016-07-21
Publication date: 2018-06-06
Also published as: FR3039697B1; WO2017017354A1; FR3039697A1

Abstract

The present invention relates to a cable (1, 2) comprising an elongate conductive element (11, 21) encircled by at least one electrically insulating cross-linked foam first layer (12, 22) obtained from a first composition comprising a first polymer, a first cross-linking agent able to liberate at least one gas during its decomposition to obtain the first layer and optionally a nucleation agent, characterised in that it furthermore comprises an extruded layer (13, 22) that is impermeable to said gas that is liable to be given off during the decomposition of the first cross-linking agent to obtain the first layer.

Description

Cable comprising a foamed and reticulated insulating layer

The present invention relates to a cable comprising at least one electrically insulating layer foamed and crosslinked.

It applies typically, but not exclusively, to the fields of low voltage power cables, especially less than 6kV, whether DC or AC.

No. 5,455,392 discloses an electrical cable comprising a central conductor surrounded by a polyethylene foamed and crosslinked insulating material, a film of polyethylene terephthalate (PET) being wound around this insulating material. The electrical cable further comprises an insulated electrical wire twisted around the central conductor, and positioned in the thickness of the insulating material.

However, this foamed and crosslinked insulating material has non-optimized dielectric and mechanical properties, particularly in the field of low voltage cables, and the manufacturing process of this cable is very restrictive with many manufacturing steps.

The object of the present invention is to overcome the drawbacks of the prior art techniques by proposing a cable comprising at least one electrically insulating layer foamed and crosslinked, simple and fast to manufacture, while ensuring good dielectric and mechanical properties at the level of the electrically insulating layer.

The present invention relates to a cable comprising an elongated conductive element surrounded by at least a first foamed and crosslinked electrically insulating layer, obtained from a first composition comprising a first polymer material, a first crosslinking agent capable of releasing at least a gas during its decomposition to obtain the first layer, and optionally a nucleating agent, characterized in that it further comprises an extruded layer impervious to said gas that may be released during the decomposition of the first crosslinking agent to obtain the first layer. The invention advantageously has a cable comprising a foamed and crosslinked layer, which is light while having a good mechanical strength as well as good dielectric properties.

The term "impervious to said gas likely to be released during the decomposition of the first crosslinking agent" means a layer which allows less than 5 bars to pass, and preferably less than 2 bars (see 1 bar = 1 g cm. ^"1" cm ^"2 bar ^{" 1} ) the carbon dioxide or methane permeability test (test carried out at 20 ° C under a pressure gradient of 3 bar), using an Ox-type apparatus -Tran 2/61 of the company Mocon.

More particularly, the extruded layer is impermeable to methane

(CH ₄ ).

The term "extruded layer" means an extruded layer along the cable, by techniques well known to those skilled in the art.

The term "foamed layer" means a layer comprising gas bubbles, or in other words pores containing gas. The foamed layer conventionally has a porosity ranging from 5 to 80% by volume, relative to the total volume of the first composition (before foaming).

The foamed layer of the invention may be preferably a layer whose variation in density (expressed as a percentage) may be at least 5% (in absolute value), preferably at least 10% (in absolute value) , and particularly preferably at least 20% (in absolute value).

In the present invention, the variation of the density of the foamed layer is calculated as follows: 100 x (d 1-d 2) / d 2, where d 1 is the density of the foamed layer and d 2 is the density of the layer not foamed (intended to form the foamed layer), the foamed layer being distinguished only from the unfoamed layer in that it further comprises gas bubbles.

The variation in the density makes it possible to give the decrease in the density of the foamed layer relative to said unfoamed layer, and is typically expressed by a negative value.

For example, a density change of 10% (in absolute value) means a change of -10%, or in other words a decrease in density of 10% from the unfoamed layer to the foamed layer.

1. First embodiment: a bilayer insulation

In a first embodiment, the extruded layer is a second electrically insulating layer (i.e. second layer), in particular different from the first electrically insulating layer (i.e. first layer), and surrounding the first electrically insulating layer. The first electrically insulating layer may be called the "inner layer", and the second electrically insulating layer may be called the "outer layer".

More particularly, the term "a second layer different from the first layer" a second layer obtained from a different composition of the first layer. By way of example, the second layer comprises a different polymer material from that of the first layer and / or an additional additive with respect to the composition of the first layer.

In a particularly preferred embodiment, the second layer may be in direct physical contact with the first layer, thereby forming a "bilayer" electrical insulation.

1.1. The second layer

The second layer may be obtained from a second composition comprising a second polymer material, at least one filler having a shape factor strictly greater than 1, and optionally a second crosslinking agent.

The second extruded layer is impervious to the gas that may be released during the decomposition of the first crosslinking agent to obtain the first layer.

Preferably, the second layer is a crosslinked layer, the crosslinking being carried out by techniques well known to those skilled in the art. As such, there may be mentioned for example peroxide crosslinking under the action of heat; silane crosslinking in the presence of a crosslinking agent; crosslinking by electron beams, gamma rays, X-rays, or microwaves; photochemically crosslinking such as irradiation under beta radiation, or irradiation under ultraviolet radiation in the presence of a photoinitiator.

The peroxide crosslinking under the action of heat is preferred in the first embodiment. In this case, the second composition further comprises an organic peroxide as the second crosslinking agent. This type of crosslinking is easy to implement and is very economical.

The peroxide crosslinking is conventionally carried out under the action of heat, for example by immersing the second layer in a bath of salt, at a temperature sufficient to decompose all the organic peroxide in the time interval corresponding to the heat treatment of crosslinking. .

"Fully decomposed" means a sufficient time of decomposition to obtain a second layer with a hot creep under load (percentage elongation) of not more than 175% according to IEC 60811-507 ("Hot Set Test") .

1.1.1. The second polymeric material

The second polymeric material of the invention may comprise one or more polymer (s), the term "polymer" being understood as any type of polymer well known to those skilled in the art such as homopolymer or copolymer (eg block copolymer, random copolymer, terpolymer, etc.).

The second polymer material is conventionally derived from the covalent linking of a large number of identical or different monomer units, and more particularly from the covalent linking of more than 40 identical or different monomer units.

The polymer may be of the thermoplastic or elastomeric type, and may be crosslinked by techniques well known to those skilled in the art.

In a particular embodiment, the second polymeric material, or in other words the polymer matrix of the second composition, may comprise one or more olefin polymers (ie polyolefin), and preferably one or more ethylene polymers. and / or or more propylene polymers. An olefin polymer is conventionally a polymer obtained from at least one olefin monomer.

More particularly, the second polymer material comprises more than 50% by weight of olefin polymer (s), preferably more than 70% by weight of olefin polymer (s), and more preferably more than 90% by weight. weight of olefin polymer (s), based on the total weight of polymer material. Preferably, the second polymeric material is composed solely of one or more olefin polymer (s), and preferably one or more ethylene polymer (s).

By way of example, the second polymeric material of the invention may comprise one or more olefin polymers chosen from a linear low density polyethylene (LLDPE); a very low density polyethylene (VLDPE); low density polyethylene (LDPE); medium density polyethylene (MDPE); high density polyethylene (HDPE); an ethylene-propylene elastomeric copolymer (EPR); an ethylene propylene diene monomer terpolymer (EPDM); a copolymer of ethylene and vinyl ester such as a copolymer of ethylene and vinyl acetate (EVA); a copolymer of ethylene and acrylate such as a copolymer of ethylene and butyl acrylate (EBA) or a copolymer of ethylene and methyl acrylate (EMA); a copolymer of ethylene and alpha-olefin such as an ethylene-octene copolymer (PEO) or a copolymer of ethylene and butene (PEB); a functionalized olefin polymer; polypropylene; a copolymer of propylene; and one of their mixtures.

The second composition of the invention may comprise at least 20% by weight of second polymeric material, preferably at least 30% by weight of second polymeric material, and particularly preferably at least 40% by weight of second polymeric material, relative to the total weight of the second composition. 1.1.2. The load having a form factor strictly greater than 1

Said filler is preferably of the lamellar type. It preferably has a form factor of at least 10, preferably at least 100, and particularly preferably at least 200. The form factor is typically the ratio between the smallest dimension of the load (such as, for example, the thickness of the load for a lamellar load) and the largest dimension of said load (such as, for example, the length load for a slat load).

In a particular embodiment, the load is a micrometric load.

Micrometric charges typically have at least one of their micrometer size dimensions (10 ^-6 meters).

By "dimension" is meant the number-average size of all the micrometric charges of a given population, this dimension being conventionally determined by methods well known to those skilled in the art.

The size of the micrometric charges according to the invention may for example be determined by microscopy, in particular by transmission electron microscope (TEM).

The average number of micrometric charges may in particular be at most 400 μm, preferably at most 300 μm, and more preferably at most 100 μm.

Particularly preferably, the number average size of the micrometric charges is at least 1 μm and at most 100 μm, preferably at least 1 μm and at most 50 μm, and particularly preferably at least 1 μm and not more than 3 μm.

As an example of a micrometric charge having a form factor strictly greater than 1, mention may be made of natural montmorillonite modified with a quaternary ammonium salt, sold by BYK KOMETRA under the reference Cloisite 20.

This nanometric load comprises sets of agglomerated lamellae whose average number of agglomerates is as defined above.

The average number of unit lamellae of this load can be about 1 nm for its thickness (the smallest dimension), and 200 nm for its length (largest dimension). The second composition of the invention may comprise a sufficient amount of filler (s) having a form factor strictly greater than 1, to optimize the gas impermeability properties of the second layer.

By way of example, the second composition can comprise from 0.1 to

30 parts by weight, preferably from 2 to 20 parts by weight, and particularly preferably from 5 to 15 parts by weight, filler (s) having a form factor of strictly greater than 1, per 100 parts by weight of the second polymeric material in the second composition.

1.1.3. The second crosslinking agent

The second crosslinking agent may be necessary when the second layer is a crosslinked layer.

Peroxide crosslinking under the action of heat is preferred. The second crosslinking agent may be chosen from an organic peroxide well known to those skilled in the art.

By way of example, the organic peroxide may be chosen from dicumyl peroxide (DCP), tert-butyl cumyl peroxide (TBCP), and a mixture thereof.

Preferably, the second crosslinking agent may have a half-life time lower than that of the first crosslinking agent (determined at the same temperature).

The second composition may comprise a sufficient amount of one or more crosslinking agents to obtain said crosslinked layer.

By way of example, the second composition may comprise from 0.01 to 10.0 parts by weight of second crosslinking agent per 100 parts by weight of second polymeric material.

Preferably, especially when using an organic peroxide-type crosslinking agent, the second composition may advantageously comprise at most 5.0 parts by weight of the second crosslinking agent, and preferably at most 2.0 parts by weight. weight of the second crosslinking agent, per 100 parts by weight of second material polymer in the second composition.

When the second layer is a crosslinked layer, the crosslinking of this layer can be easily characterized by its "Hot Set Test" according to the IEC 60811-507 standard, with a hot creep under load (percentage elongation) of at most 175 %.

1.2. The first layer

The first foamed and crosslinked layer is obtained from a first composition comprising a first polymer material, a first crosslinking agent capable of releasing at least one gas during its decomposition to obtain the first layer, and optionally a nucleating agent.

The thickness of the first layer may advantageously be greater than or equal to the thickness of the second layer. Preferably, the thickness of the first layer may be 2 to 4 times greater than the thickness of the second layer, and particularly preferably the thickness of the first layer is about 3 times greater than the thickness of the first layer. second layer.

The first layer is on the one hand a crosslinked layer thanks to the first crosslinking agent, in particular under the action of a rise in temperature which will break down the crosslinking agent in order to crosslink the first polymer material, and on the other hand a foamed layer thanks to the gas released during the decomposition of the first crosslinking agent, to foam the first composition and thus obtain a foamed layer.

Crosslinking under the action of heat is preferred in the first embodiment. This type of crosslinking is easy to implement and is very economical.

1.2.1. The first polymer material

The first polymeric material of the first composition may be the same or different from the second polymeric material of the second composition.

The first polymeric material may be a polymeric material as previously described for the second polymeric material. Preferably, the first polymeric material may be identical to the second polymeric material.

In a particularly advantageous embodiment, the first layer and the second layer are extruded layers.

The first and second layers can be extruded successively, with the same extruder comprising a single extrusion head. More particularly, the first layer is first extruded around the elongate conductive member during a first pass in an extruder, and then the second layer is then extruded around the first layer during a second pass in said extruder. .

Preferably, the first layer and the second layer are extruded at the same time. This is called coextrusion or coextruded layers. Coextrusion can then be typically performed using two extruders feeding a single extrusion head. More particularly, the first layer and the second layer exit from their respective extruder simultaneously by one and the same extrusion head, thus at the same time surrounding the elongated conductive member.

1.2.2. The first crosslinking agent

The first crosslinking agent included in the first layer has a dual role: it allows both the crosslinking of the first polymer material, especially under the action of heat, and the foaming of the first composition by releasing at least one gas.

Thus, during the decomposition of the first crosslinking agent under the effect of an increase in temperature, the first crosslinking agent releases at least one gas, this gas thus forming bubbles inside the first polymer material. The bubbles thus formed are then advantageously retained by the second layer impervious to said gas.

When the first crosslinking agent will decompose, the first composition will more particularly be foamed before being crosslinked. In other words, it will more particularly foam before it can obtain a creep under load (percentage extension) of at most 175% according to IEC 60811-507. Preferably, the gas to be released by the first crosslinking agent is methane or carbon dioxide.

In addition, the first crosslinking agent may have a decomposition temperature that is compatible with the processing temperatures, in particular the extrusion temperatures, of the first composition. In other words, the crosslinking of the first polymer material should preferably not take place during the implementation of the first composition, in particular during the extrusion of the first composition.

The first crosslinking agent may advantageously be an organic peroxide, this type of compound releasing methane during its decomposition.

The organic peroxide may be selected from dicumyl peroxide (DCP), tertiary butyl cumyl peroxide (TBCP), and a mixture thereof.

Other organic peroxides may be chosen provided that the decomposition temperature is compatible with the temperature at which the first composition is used, in particular in an extruder.

The peroxide crosslinking is conventionally carried out under the action of heat, for example by immersing the first layer in a salt bath at a temperature sufficient to decompose all of the organic peroxide in the time interval corresponding to the heat treatment of crosslinking. .

"Fully decomposed" means a sufficient time of decomposition to obtain a first layer with a hot creep under load (percentage elongation) of not more than 175% according to IEC 60811-507 ("Hot Set Test") .

The first composition may comprise a sufficient amount of one or more first crosslinking agents to provide said foamed and crosslinked layer.

By way of example, the first composition may comprise from 0.01 to 10.0 parts by weight of first crosslinking agent, and preferably from 1.0 to 5.0 parts by weight of first crosslinking agent, per 100 parts by weight of first polymeric material.

The crosslinking of the first foamed and crosslinked layer can be easily characterized by its "Hot Set Test" according to IEC 60811-507, with a hot creep under load (percentage elongation) of at most 175%.

The foaming, or expansion, of the first foamed and crosslinked layer may be characterized by its degree of expansion determined according to the difference in density measurement between the unfoamed layer and the layer after foaming. The density can be easily determined by techniques well known to those skilled in the art, such as for example by immersing in ethanol the first layer before foaming and after foaming, according to standard IEC 60811-606.

1.2.3. The nucleating agent

The nucleating agent advantageously makes it possible to refine the gas bubbles formed during the decomposition of the first crosslinking agent.

The nucleating agent may advantageously be talc, such as, for example, Talc referenced MISTROCELL supplied by the company IMERYS.

The first composition may comprise a sufficient amount of one or more nucleating agents to achieve the desired properties.

By way of example, the first composition may comprise from 0.01 to 10.0 parts by weight of nucleating agent, and preferably from 1.0 to 5.0 parts by weight of nucleating agent, per 100 parts by weight of first polymeric material.

2. Second embodiment: a single-layer insulation

In a second embodiment, the extruded layer is the first foamed and crosslinked electrically insulating layer.

More particularly, the extruded layer is therefore the first foamed and crosslinked electrically insulating layer obtained from the first composition comprising the first polymer material, the first crosslinking agent, and optionally the nucleating agent.

To simplify the description of this second embodiment, the first foamed and crosslinked electrically insulating layer will be called "electrically insulating layer foamed and crosslinked", the first composition will be called "composition", the first polymeric material will be called "polymeric material", and the first crosslinking agent will be called "crosslinking agent", in the following description of this second embodiment.

This extruded layer is impervious to the gas that may be released during the decomposition of the crosslinking agent to obtain the foamed and crosslinked electrically insulating layer.

Preferably, the cable comprises only said electrically insulating layer foamed and crosslinked as a single electrically insulating layer.

In a particularly preferred manner, the cable comprises said foamed and crosslinked electrically insulating layer as the single layer of the cable surrounding the elongated conductive element.

Said layer is on the one hand a crosslinked layer through said crosslinking agent, in particular under the action of a temperature rise which will break down the crosslinking agent in order to crosslink the polymer material, and on the other hand a foamed layer thanks to the gas released during the decomposition of said crosslinking agent, to foam the composition and thus obtain a foamed layer.

Crosslinking under the action of heat is preferred in the second embodiment. This type of crosslinking is easy to implement and is very economical.

In addition, said layer is itself impervious to the gas that may be released during the decomposition of said crosslinking agent to obtain the electrically insulating layer foamed and crosslinked.

2.1. The polymer material

The polymeric material of the extruded layer may advantageously comprise at least one polymer having a Mooney viscosity ML (1 + 4) at 125 ° C. of at least 10 MU (Mooney Unit), preferably at least 15 MU, and particularly preferably at least 20 MU. The viscosity of said polymer may be at most 100 MU, and preferably at most 50 MU. More particularly, the polymeric material of the extruded layer may have a Mooney viscosity ML (1 + 4) at 125 ° C of at least 10 MU (Mooney Unit), preferably at least 15 MU, and particularly preferably at least 20 MU. The viscosity of said polymeric material may be at most 100MU, and preferably at most 50MU.

The Mooney viscosity can be classically measured according to the IS0289-1 standard.

The polymeric material may be a polymeric material as previously described for the second polymeric material in the first embodiment.

Preferably, the polymeric material is an elastomeric material, in particular of the amorphous rubber type.

For example, the polymeric material may comprise at least one polymer selected from EPDM, EVA, and a mixture thereof.

The composition of this second embodiment may comprise at least 20% by weight of polymeric material, preferably at least 30% by weight of polymeric material, and particularly preferably at least 40% by weight of polymeric material, with respect to total weight of the composition.

In this second embodiment, the Mooney ML (1 + 4) viscosity at 125 ° C of the composition (i.e., uncrosslinked and unfoamed composition) may be at least 10 MU (Mooney Unit). The viscosity of said composition may be at most 100 MU, and preferably at most 50 MU.

It can be measured according to the IS0289-1 standard, using an MV2000 device from Alpha Technologies. The Mooney MV2000 consists of a thermo-regulated chamber, in which is placed the composition, and a rotor plane rotating at constant speed within the compound (2 rev / min). Mooney viscosity or consistency is proportional to the amount of torque exerted by the material on the rotor. It is given in Mooney or Mooney Units points (with 1MU = 8.3 × 10 ^-2 Nm) The indicated viscosity value ML (1 + 4) is measured at 125 ° C.

2.2. The crosslinking agent The crosslinking agent included in the layer of the cable corresponding to the second embodiment has a dual role: it allows both the crosslinking of the polymer material, in particular under the action of heat, and the foaming of the composition by releasing at least one gas.

Thus, during the decomposition of said crosslinking agent under the effect of an increase in temperature, the crosslinking agent releases at least one gas, this gas thus forming bubbles inside the polymer material. The bubbles thus formed are then advantageously retained in situ, inside the electrically insulating layer foamed and crosslinked which is a layer impervious to said gas. More particularly, the bubbles are retained by the presence of the polymer having a Mooney viscosity ML (1 + 4) at 125 ° C. of at least 10 MU, combined with the presence of fillers having a form factor strictly greater than 1, making this layer is intrinsically impervious to gases.

When said crosslinking agent will decompose, the composition will more particularly be foamed before being crosslinked. In other words, it will more particularly foam before it can obtain a creep under load (percentage extension) of at most 175% according to IEC 60811-507.

Preferably, the gas to be released by the crosslinking agent is methane or carbon dioxide.

In addition, said crosslinking agent may have a decomposition temperature compatible with the processing temperatures, especially the extrusion temperatures, of the first composition. In other words, the crosslinking of the polymer material should preferably not take place during the implementation of the composition, in particular during the extrusion of the composition.

Said crosslinking agent may advantageously be an organic peroxide, this type of compound releasing methane during its decomposition.

The organic peroxide can be chosen from dicumyl peroxide

(DCP), tert-butyl cumyl peroxide (TBCP), and a mixture thereof. Other organic peroxides may be selected subject to having a decomposition temperature compatible with the processing temperature of the composition, in particular in an extruder.

The peroxide crosslinking is conventionally carried out under the action of heat, for example by dipping the layer in a bath of salt, at a temperature sufficient to decompose all the organic peroxide in the time interval corresponding to the heat treatment of crosslinking.

The term "fully decomposed" means a sufficient time of decomposition to obtain a layer with a hot creep under load (percentage elongation) of at most 175% according to IEC 60811-507 ("Hot Set Test").

The composition may comprise a sufficient amount of one or more crosslinking agents to provide said foamed and crosslinked layer.

By way of example, the composition may comprise from 0.01 to 10.0 parts by weight of said crosslinking agent, and preferably from 1.0 to 5.0 parts by weight of said crosslinking agent, per 100 parts by weight of polymeric material.

The crosslinking of the foamed and crosslinked layer can be easily characterized by its "Hot Set Test" according to the IEC 60811-507 standard, with a hot creep under load (percentage elongation) of at most 175%.

The foaming, or expansion, of the foamed and crosslinked layer may be characterized by its degree of expansion determined according to the difference in density measurement between the unfoamed layer and the layer after foaming. The density can be easily determined by techniques well known to those skilled in the art, such as for example by immersing in ethanol the layer before foaming and after foaming, according to standard IEC 60811-606.

2.3. The nucleating agent

The nucleating agent may be that described in the first embodiment. 3. The first and second embodiments

The compositions of the present invention, whether those of the first embodiment or the second embodiment, may further comprise one or more additives well known to those skilled in the art, especially in an amount of from 0.1 to 20. % by weight in the composition (relative to the total weight of the composition).

For example:

protective agents, such as antioxidants, anti-UV, anti-copper agents, anti-tree water agents,

processing agents, such as plasticizers, lubricants, oils, waxes or paraffins,

- compatibilizing agents,

coupling agents, such as silane-based compounds or compounds of the maleic anhydride graft polymer type,

- roasting retarders,

pigments,

- crosslinking catalysts,

crosslinking coagents such as triallyl cyanurates,

thermal stabilizers, and

- one of their mixtures.

More particularly, the antioxidants make it possible to protect the composition of the thermal stresses generated during the steps of manufacturing the electrical cable or operating said cable.

The antioxidants are preferably chosen from:

hindered phenolic antioxidants such as tetrakismethylene (3,5-di-t-butyl-4-hydroxy-hydrocinnamate) methane, octadecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate 2,2'-thiodiethylene bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,2'-thiobis (6-t-butyl-4-methylphenol), 2,2'-Methylenebis (6-t-butyl-4-methylphenol), 1,2-bis (3,5-di-t-butyl-4-hydroxyhydrocinnamoyl) hydrazine, and 2,2'-oxamido bis (ethyl 3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate); thioethers such as 4,6-bis (octylthiomethyl) -o-cresol, bis [2-methyl-4- {3-n-alkyl (C 12 or C 14) thiopropionyloxy} -5-t-butylphenyl] sulfide and Thiobis- [2-t-butyl-5-methyl-4,1-phenylene] bis [3- (dodecylthio) propionate];

sulfur-based antioxidants such as Dioctadecyl-3,3'-thiodipropionate or Didodecyl-3,3'-thiodipropionate;

phosphorus-based antioxidants such as phosphites or phosphonates, for instance Tris (2,4-di-tert-butylphenyl) phosphite or bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite; and

amine-type antioxidants such as phenylene diamines

(IPPD, 6PPD ....), and 2,2,4-trimethyl-1,2-dihydroquinoline polymerized (TMQ), the latter type of antioxidant being particularly preferred in the composition of the invention.

TMQs can have different grades, namely:

a so-called "standard" grade with a low degree of polymerization, that is to say with a residual monomer level greater than 1% by weight and having a residual NaCl content that may range from 100 ppm to more than 800 ppm (parts per million mass);

a so-called "high degree of polymerization" grade with a high degree of polymerization, that is to say with a residual monomer level of less than

1% by weight and having a residual NaCl content ranging from 100 ppm to more than 800 ppm;

a so-called "low residual salt" grade with a residual NaCl content of less than 100 ppm.

The type of antioxidant and its level in the composition of the invention are conventionally chosen as a function of the maximum temperature experienced by the polymers during the production of the mixture and during their use, in particular by extrusion, as well as according to the maximum duration. exposure to this temperature.

The crosslinking catalysts are intended to assist in crosslinking, in particular for "silane" crosslinking type condensation reactions. The crosslinking catalyst may be selected from Lewis acids; the Brönsted acids; and tin catalysts such as dibutyltin dilaurate (DBTL).

The thermal stabilizers can be chosen from metal oxides, such as, for example, zinc oxide (ZnO). Depending on the type of polymeric material used, the metal oxide may act as a thermal stabilizer, but may also improve the electrical properties of the crosslinked layer. The metal oxide may be added to the crosslinkable polymer composition in an amount ranging from 1.0 to 10.0 parts by weight per 100 parts by weight of polymeric material.

The compositions of the present invention, whether those of the first embodiment or the second embodiment, may further comprise one or more fillers.

The filler of the invention may be a mineral or organic filler. It can be chosen from a fire-retardant filler, an inert filler (or non-combustible filler), and a mixture thereof.

By way of example, the flame-retardant filler may be a hydrated filler, chosen in particular from metal hydroxides such as, for example, magnesium dihydroxide (MDH) or aluminum trihydroxide (ATH). These flame retardant fillers act mainly physically by decomposing endothermically (e.g., release of water), which results in lowering the temperature of the layer and limiting the propagation of flames along the electric cable. In particular, we speak of flame retardancy properties, well known under the Anglicism "flame retardant".

The inert filler (ie non-combustible filler) can be, for its part, calcium carbonate (CaCO ₃ ), chalk, talc or clay (eg kaolin).

The charge may also be an electrically conductive charge chosen in particular from carbonaceous charges. By way of example, electrically conductive filler may be carbon blacks, graphenes, carbon nanotubes. In order to guarantee a so-called "electrically insulating" layer, the electrically conductive filler may be used in small quantities to improve the dielectric properties of an electrically insulating layer, without it becoming a semiconductor. The electrically conductive filler may also be used to color the layer and / or to increase the stability of the ultraviolet ray layer. By way of example, the appropriate amount of electrically conductive filler may be less than 8% by weight in the composition, and preferably at most 5% by weight in the composition (relative to the total weight of the composition).

The polymer composition may comprise at least 1% by weight of filler (s), preferably at least 10% by weight of filler (s), and preferably at most 50% by weight of filler (s), relative to the weight total of the composition.

According to another characteristic of the invention, and in order to guarantee a cable called "Halogen-Free" or more specifically "HFFR" for the Anglicism "Halogen-Free Flame Retardant", the cable, or in other words the elements that make up said cable preferably do not comprise halogenated compounds. These halogenated compounds may be of any kind, such as, for example, fluorinated polymers or chlorinated polymers such as polyvinyl chloride (PVC), polyvinylidene chloride, halogenated plasticizers, halogenated mineral fillers, etc.

4. The cable

The cable of the invention is preferably an electrical and / or optical cable, intended for the transmission of energy and / or the transmission of data.

More particularly, this type of cable comprises one or more elongated conductive element (s) of the electrical and / or optical type, surrounded by at least the crosslinked layer according to the invention.

In the present invention, the first foamed and crosslinked electrically insulating layer may surround one or more elongated conductive member (s), isolated or not, along the cable. The elongated conductive member may preferably be in a central position (in cross-section of the cable) in the cable.

In a particularly preferred embodiment, the cable of the invention is an electrical cable comprising one or more elongated electrical conductive elements.

The elongate electrical conductor may be a single-body conductor such as for example a wire, or a multi-body conductor such as a plurality of metal wires, twisted or not.

The elongated electrical conductor may be made from a metallic material chosen in particular from aluminum, an aluminum alloy, copper, a copper alloy, and one of their combinations.

In a particular embodiment, the electrical cable may be a low-voltage cable comprising an elongate electrical conductor surrounded solely by one or more electrically insulating layers, or surrounded by at least one electrically insulating layer, the latter being surrounded by one or more several semiconductor layers.

In the present invention, the term "electrically insulating layer" means a layer whose electrical conductivity can be at most 1.10 ^"9 S / m (siemens per meter) (at 25 ° C), and preferably at most 1.10 ^"13 S / m (at 25 ° C).

In the present invention, the term "semiconductor layer" means a layer whose electrical conductivity can be at least 1.10 ^"9 S / m (siemens per meter), preferably at least 1.10 ^{" 3} S / m and preferably may be less than 1.10 ³ S / m (at 25 ° C).

Other features and advantages of the present invention will become apparent in the light of the description of non-limiting examples of an electric cable according to the invention, with reference to the figures.

Figure 1 shows a schematic cross-sectional view of an electric cable according to a first embodiment according to the invention. FIG. 2 represents a schematic cross-sectional view of an electric cable according to a second embodiment in accordance with the invention.

For the sake of clarity, only the essential elements for understanding the invention have been shown schematically, and this without respect of the scale.

FIG. 1 represents a cross-sectional view of an electric cable 1 comprising a bilayer insulation according to the invention.

The electric cable 1 is of the low-voltage cable type, and comprises an elongated central electrical conductor element 11, in particular made of copper or aluminum. The electric cable 1 further comprises two layers arranged successively and coaxially around this conductive element 11, namely:

a first layer 12 electrically insulating, foamed and crosslinked, called "inner layer", according to the invention, and

a second cross-linked electrically insulating layer 13, called an "outer layer", according to the invention, whose thickness is less than that of the inner layer.

The inner layer 12 is in direct physical contact with the electrical conducting element 11, and the outer layer 13 is in direct physical contact with the inner layer 12.

FIG. 2 represents a cross-sectional view of an electric cable 2 comprising a single-layer insulation according to the invention.

The electric cable 2 is of the low-voltage cable type, and comprises an elongate central electrical conductor element 21, in particular made of copper or aluminum. The electric cable 2 further comprises a single layer 22, according to the invention, directly in physical contact with the electrical conductive element 21. This layer 22 is an electrically insulating layer, foamed and crosslinked, impervious to gases.

5. Example of a two-layer insulation according to the invention

A two-layer insulation according to the invention is detailed below. 5.1. First composition to obtain an electrically insulating first layer foamed and crosslinked

Table 1 below collates the compounds used to produce a first extruded, foamed and crosslinked electrically insulating layer, in accordance with the invention.

The amounts of the compounds are expressed in parts by weight per 100 parts by weight of polymeric material in the first composition.

The polymeric material in Table 1 is composed solely of

LDPE.

Table 1

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

- First polymer material is a LDPE marketed by Inéos under the reference BPD 2000;

The first crosslinking agent is an organic peroxide of the tert-butyl cumyl peroxide type (TBCP), sold by the company Arkema under the reference Luperox 801, whose half-life time is 0.4 minutes at 200 ° C. (measured in decane);

Nucleating agent is talc marketed by the company IMERYS under the reference Mistrocell.

5.2. Second composition for obtaining a second electrically insulating crosslinked layer, impermeable to methane

Table 2 below collates the compounds used to produce a second electrically insulating extruded, crosslinked and impermeable to gas layer, according to the invention.

The amounts of the compounds are expressed in parts by weight per 100 parts by weight of polymeric material in the second composition. The polymeric material in Table 2 is composed solely of

LDPE.

Table 2 The origin of the compounds in Table 2 is as follows:

Second polymeric material is a LDPE marketed by Inéos under the reference BPD 2000;

The second crosslinking agent is an organic peroxide of the dicumyl peroxide type (DCP), sold by the company Arkema under the reference Luperox DCP, whose half-life time is 0.26 minutes at 200 ° C. (measured in decane). );

- Lamellar charge is natural montmorillonite modified with a quaternary ammonium salt, marketed by BYK Kometra under the Cloisite 20 reference, whose D50 dimensions are between 3 pm and 10 pm (set of agglomerated lamellae); and

- Flame retardant charge is magnesium dihydroxide (MDH) marketed by MARTINSWERK under the reference Magnifin H 10.

5.3. Preparation of the two-layer insulation

In a first step, the composition C1 is introduced into a Brabender-type extruder in order to extrude this composition around a single-strand copper electrical conductor (ie a single strand) of diameter 1.12 mm, to form a cable with a first insulating layer.

In a second step, the composition C2 is introduced into the same extruder in order to extrude this composition around the first layer insulation, to form a second insulating layer around the first insulating layer.

The temperature profiles used for the respective extrusion of the first composition and the second composition are collated in the following Table 3:

Table 3

Once the two layers are extruded around the conductive element, the cable comprising the bilayer insulation is immersed in a salt bath at 220 ° C. for a duration corresponding to the longest t90, in this case that of the inner layer. namely 41 seconds, in order to foam the first layer, and to crosslink the first and second layers.

5.4. Characterization of crosslinked layers

Properties Inner layer Outer layer

(foamed layer

and crosslinked) crosslinked)

Thickness (in millimeters) 1.2 mm 0.4 mm

Hot Set Test: creep at 110 110 hot under load (in

percentage)

Time required for 40.2 s 28.2 s

have 90% of the peroxide that

decomposed

second)

Variation of the total diameter + 26%

(percentage)

Density variation (in - 38%

percentage)

Table 4

The crosslinking of the inner layer and the outer layer is characterized by the "Hot Set Test" according to IEC 60811-507 (15 min at 200 ° C).

The time required to have 90% of the peroxide which has decomposed is determined using an MDR rheometer of ALPHA Technologies which makes it possible to measure the kinetics of decomposition of the peroxide in the mixture at a given temperature.

The variation of the total diameter is the variation of the total diameter of the cable (conducting element together with its two layers) before foaming and after foaming. This variation was measured with a graduated magnifier (profile projector).

The variation of the density of the foamed layer, expressed as a percentage, is calculated as follows: 100 x (d 1-d 2) / d 2, where d 1 is the density of the foamed layer and d 2 is the density of the layer not foamed (intended to form the foamed layer), the foamed layer being distinguished only from the unfoamed layer in that it further comprises gas bubbles.

More particularly, the variation of the density makes it possible to express the decrease in the density of the unfoamed layer once it has been foamed. The density variation is thus expressed with a negative value. To estimate the density, specimens are made from the unfoamed layer (intended to form the foamed layer) and the foamed layer, these specimens being of the rectangular type, cut longitudinally in the insulating layer and having a mass that can go from 1 gram minimum to 5 grams maximum.

The copper is removed from the test pieces and their length is measured with calipers. The mass of the foamed and unfoamed specimens is determined by a precision balance.

The density is determined as follows:

The total section of the cable (in cm ² ) is determined with the calculation from IEC 60811-501 according to the equation S = TT x (D-δ) x δ where D is the total diameter of the cable (in cm ), and δ is the thickness of the insulation (in cm), where D and δ are measured using a graduated magnifier (profile projector).

We then deduce the volume, then the density of the specimen with the equation V = S x L, in which d = m / V with V being the volume of the specimen (in cm ³ ), L being the length of the test piece measured at vernier caliper (in cm), m being the mass of the test piece (in g), and d being the density (g / cm ³ ).

6. Example of a single-layer insulation according to the invention

A single layer insulation according to the invention is detailed below.

6.1. Composition for electrically insulating single-layer foamed and crosslinked insulation, methane impermeable

Table 5 below summarizes the compounds used to produce an electrically insulating layer extruded, foamed and crosslinked, and impermeable to gas, according to the invention.

The amounts of the compounds are expressed in parts by weight per 100 parts by weight of polymeric material in the composition.

The polymeric material in Table 5 is composed solely of an elastomer. Composition C3

Polymeric material 100

Inert load 80

Thermal stabilizer 2

Implementing Agent 1 1

Antioxidant 1

Implementing Agent 2 20

Crosslinking agent 9

Table 5

The origin of the compounds in Table 5 is as follows:

Polymeric material is an elastomer (synthetic amorphous rubber) of the EPDM type comprising 53% by weight of ethylene and 6% by weight of ethyldiene norbornene (ENB), sold by the company DSM under the reference Keltan 2340; it has an ML (1 + 4) viscosity at 125 ° C of 25 MU;

Inert load is calcium carbonate (CaCO ₃ );

Thermal stabilizer is zinc oxide (ZnO);

- Implementing Agent 1 is zinc stearate used as a lubricant;

Antioxidant is an antioxidant of the TMQ type marketed by Flectol;

- Processing Agent 2 is a paraffin oil used as a plasticizer;

- Crosslinking agent comprises an organic peroxide dicumyl peroxide type (DCP) up to 40% by weight on a calcium carbonate type carrier, and is marketed by Arkema under the reference Luperox DC 40; the half-life time of this peroxide is 0.26 minutes at 200 ° C (measured in decane);

The Mooney viscosity ML (1 + 4) at 125 ° C of the composition C3 is 14 MU. This viscosity was measured according to IS0289-1 standard, using an MV2000 device from Alpha Technologies. 6.2. Preparation of monolayer insulation

Composition C3 is introduced into a Fairex-type extruder to be extruded around a single-stranded copper conductor (i.e., a single strand) of 1.12 mm diameter to form a single-layer insulation cable.

The temperature profile of the extruder is summarized in Table 6 below:

Table 6

Once the layer is extruded around the conductive element, the cable comprising the single insulating layer is immersed in a bath of salt at 220 ° C. for 26 seconds (time corresponding to the t90 of the organic peroxide of the composition C3), in order to foam and crosslink said insulating layer.

6.3. Characterization of crosslinked layers

Properties Foam layer

and reticulated

Thickness (in millimeters) 3 mm

Hot Set Test: hot creep under 125%

charge (in percentage)

Time required to have 90% of the 26s

peroxide that has broken down (in

second) Variation of the total diameter (in + 21% percentage)

Density variation (in - 30%

percentage)

Table 7

The properties measured in Table 7 were measured according to what has been described for the properties measured in Table 4.

Claims

A cable (1, 2) comprising an elongate conductive member (11, 21) surrounded by at least a first foamed and crosslinked electrically insulating layer (12, 22) obtained from a first composition comprising a first polymeric material, a first crosslinking agent capable of releasing at least one gas during its decomposition to obtain the first layer, and optionally a nucleating agent, characterized in that it further comprises an extruded layer (13, 22) impervious to said gas likely to be released during the decomposition of the first crosslinking agent to obtain the first layer.

2. Cable according to claim 1, characterized in that the extruded layer is a second layer (13) electrically insulating, surrounding the first layer (12).

3. Cable according to claim 2, characterized in that the second layer (13) is in direct physical contact with the first layer (12).

4. Cable according to claim 2 or 3, characterized in that the second layer (13) is a crosslinked layer.

5. Cable according to any one of claims 2 to 4, characterized in that the second layer (13) is obtained from a second composition comprising a second polymer material, at least one load having a shape factor strictly greater at 1, and optionally a second crosslinking agent.

6. Cable according to claim 5, characterized in that the load is a micrometric load.

7. Cable according to claim 5 or 6, characterized in that the charge is natural montmorillonite modified with a quaternary ammonium salt.

8. Cable according to any one of claims 5 to 7, characterized in that the second composition comprises from 0.1 to 30 parts by weight of filler having a form factor strictly greater than 1, per 100 parts by weight of the second. polymeric material.

9. Cable according to any one of claims 5 to 8, characterized in that the second polymer material comprises at least one olefin polymer.

10. Cable according to any one of claims 5 to 9, characterized in that the second crosslinking agent is an organic peroxide.

11. Cable according to any one of claims 5 to 10, characterized in that the second crosslinking agent has a half-life time lower than that of the first crosslinking agent.

12. Cable according to any one of the preceding claims, characterized in that the first layer (12) is an extruded layer.

13. Cable according to claim 1, characterized in that the extruded layer is the first layer (22) foamed and crosslinked.

Cable according to claim 13, characterized in that the first polymer material comprises at least one polymer having a Mooney viscosity ML (1 + 4) at 125 ° C of at least 10 MU, and preferably at least 15 MU.

15. Cable according to claim 14, characterized in that the first polymer material comprises at least one polymer selected from an EPDM, an EVA, and a mixture thereof.

16. Cable according to any one of the preceding claims, characterized in that the first crosslinking agent is an organic peroxide.

17. Cable according to any one of the preceding claims, characterized in that the first layer (12, 22) has a density variation of at least 5% (in absolute value).

18. Cable according to any one of the preceding claims, characterized in that the extruded layer (13, 22) passes less than 5 bar to the carbon dioxide or methane permeability test (test carried out at 20 ° C under a pressure gradient of 3 bar).