EP2441076B1 - Electric cable adapted for ensuring the continuity of power distribution in the event of fire - Google Patents

Description

The present invention relates to an electrical cable adapted to ensure the continuity of electrical distribution in case of fire comprising one or more insulated electrical conductors.

It applies typically, but not exclusively, to the field of fire-resistant and in particular halogen-free security cables, capable of operating for a given period of time in fire conditions, without being a fire propagator or generator. important fumes. These safety cables are in particular power transmission cables or low frequency transmission cables, such as control or signaling cables.

One of the major challenges of the cable industry is the improvement of the behavior and performance of cables in extreme thermal conditions, especially those encountered during a fire. For reasons of safety in particular, it is indeed essential to maximize the capabilities of the cable to withstand fire to ensure continuity of operation, including emergency equipment and evacuation aid.

In case of fire, the cable must be able to withstand the fire in order to operate as long as possible and limit its degradation. A safety cable must also not be dangerous for its environment, that is to say not to spread the fire and not to release toxic fumes and / or opaque when subjected to extreme thermal conditions.

Of the document EP 0 942 439 is known a fire-resistant and halogen-free electrical safety cable comprising a set of insulated electrical conductors, said assembly being surrounded by a outer sheath. Each insulated electrical conductor is formed by an electrical conductor surrounded by a polymeric insulating monolayer obtained from a composition comprising a polymeric material and at least one ceramic-forming filler, said polymeric insulating layer thus being able to convert at least superficially into the ceramic state at high temperatures corresponding to fire conditions. The polymeric material of this single insulating layer is selected from a polysiloxane (polyorganosiloxane) and a copolymer of ethylene, or a mixture thereof.

Other fire-resistant and halogen-free electrical safety cables with electrical conductors surrounded by a two-layer polymeric insulation are also known. For example, the document EP 1 347 464 describes a bilayer insulator adapted to convert at least superficially in the ceramic state at high temperatures corresponding to fire conditions. Each of the layers of the bilayer insulation comprises an ethylene-octene copolymer and a ceramic-forming filler.

However, it has been found that these security cables of the prior art, even if they have good fire resistance properties, are mechanically fragile. More particularly, insulated electrical conductors are sensitive to the various mechanical stresses typically experienced by these cables during their manufacture, transport, handling, installation or connection. In addition, their electrical resistance at high temperature and in a humid medium, in particular according to the IEC 60502-1 standard, is not sufficient because of the presence of ceramic forming charges.

The purpose of the present invention is to overcome the drawbacks of the techniques of the prior art by proposing in particular an easily manipulated electric cable, limiting the risk of degradation mechanically insulated electrical conductors that compose it, while maintaining excellent fire resistance properties meeting the IEC 60331-21 standard and an improved electrical resistance meeting the IEC 60502-1 standard.

The present invention relates to an electrical cable comprising one or more insulated electrical conductors, each of said insulated electrical conductors comprising an electrical conductor surrounded by an insulating layer, preferably an electrically insulating layer, the insulating layer comprising a first polymeric layer (2a) surrounding the electrical conductor, the first layer (2a) being obtained from a first composition comprising a polymer matrix based on thermoplastic polymer, and at least one ceramic forming filler, characterized in that the insulating layer further comprises a second crosslinked polymeric layer (2b) surrounding said first layer, the second layer (2b) being obtained from a second composition comprising a polyolefin-based polymer matrix and comprising substantially neither ceramic-forming filler nor halogenated compound .

• les termes « première composition comprenant une matrice polymère à base de polymère thermoplastique » signifient que le ou les polymères utilisé(s) dans la première composition sont majoritairement un ou des polymères thermoplastiques (en % en poids dans la matrice),
• les termes « deuxième composition comprenant une matrice polymère à base de polyoléfine » signifient que le ou les polymères utilisé(s) dans la deuxième composition sont majoritairement un ou des polyoléfines (en % en poids dans la matrice).

In the following,

• the terms "first composition comprising a polymer matrix based on thermoplastic polymer" mean that the polymer (s) used in the first composition are predominantly one or more thermoplastic polymers (in% by weight in the matrix),
• the terms "second composition comprising a polyolefin-based polymer matrix" mean that the polymer (s) used in the second composition are predominantly one or more polyolefins (in% by weight in the matrix).

The term "halogenated compounds" furthermore means a compound of all kinds comprising at least one halogen element, such as, for example, fluorinated polymers or chlorinated polymers such as polyvinyl chloride (PVC), halogenated plasticizers, halogenated mineral fillers, ... etc.

Thanks to the invention, the second crosslinked polymeric layer (outer layer) based on polyolefin mechanically protects the first polymeric layer (inner layer) based on thermoplastic polymer. This property allows the insulating layer of each isolated electrical conductor to improve the mechanical properties of the cable, including the hardness, resistance to abrasion and tearing of the insulated electrical conductors that compose it, to facilitate the installation of said cable , and make the cable more robust during its manufacture, while ensuring a very good adhesion between the first layer and the second layer of the insulating layer.

More particularly, the insulating layer of the electric cable of the invention has excellent mechanical strength in temperature (or hot creep) meeting the EN 60811-2-1 standard.

In addition, the electrical cable comprising the insulating layer according to the invention meets the IEC 60331-21 standard with excellent fire resistance properties. The electrical conductors are thus protected against fire, or in other words, the electric cable ensures a fire behavior of high quality in terms of at least cohesion electrically insulating ash.

Another advantage of the insulating layer of the electric cable of the invention relates to its electrical resistance. Due to the absence of ceramic forming charge in the outer layer of the insulating layer of the invention, the electrical resistance properties of the cable to high temperature according to IEC 60502-1 are significantly improved.

Another advantage of the insulating layer of the electrical cable of the invention is that it significantly limits the release of toxic fumes when subjected to extreme thermal conditions.

The invention as thus defined finally has the advantage of being economical since it makes it possible to significantly limit, or even completely avoid, the use of polyorganosiloxane in the insulating layer of the isolated electrical conductors, while having very low good fire resistance properties.

The first polymeric layer (or inner layer)

According to the present invention, the thermoplastic polymer of the first composition may be advantageously chosen from olefin polymers, acrylate or methacrylate polymers, vinyl polymers such as, for example, polyvinyl chloride, and fluoropolymers, or one of their mixtures.

By way of preferred example, the olefin polymers are chosen from homopolymers of ethylene; copolymers of ethylene and octene (PEO); copolymers of ethylene and vinyl acetate (EVA); copolymers of ethylene and butyl acrylate (EBA); copolymers of ethylene and methyl acrylate (EMA); copolymers of ethylene and ethyl acrylate (EEA); copolymers of ethylene and butyl acrylate (EBA); copolymers of ethylene and ethyl acrylate (EEA); copolymers of ethylene, propylene and rubber (EPR); copolymers of ethyl propylene diene monomer (EPDM); or a mixture thereof.

In a preferred embodiment, the polymer matrix of the first composition comprises at least 95% by weight of thermoplastic polymer, preferably said polymer matrix comprises only one or more thermoplastic polymers.

In another preferred embodiment, the first composition does not comprise more than 5% by weight of polyorganosiloxane, preferably not more than 2% by weight of polyorganosiloxane, and even more preferably the first composition does not comprise polyorganosiloxane.

The ceramic forming filler used in the first composition allows the first layer to convert at least superficially in the ceramic state at high temperatures corresponding to fire conditions, and thus form a first so-called "ceramizing" layer. This ceramizing layer thus provides sufficient insulation when the second layer (outer layer) has disappeared due to combustion phenomena.

The ceramic forming filler according to the invention may be chosen from a fusible ceramic filler and a refractory filler, or a mixture thereof.

The ceramic forming filler preferably comprises at least one fusible ceramic filler and at least one refractory filler.

More particularly, the fusible ceramic filler has a melting temperature lower than an elevated temperature T, and the refractory filler has a melting temperature higher than said temperature T. This temperature T is advantageously at least 750 ° C., and can reach 1100 ° C.

The fusible ceramic filler may be at least one mineral filler selected from boron oxides (eg B ₂ O ₃ ), anhydrous zinc borates (eg 2ZnO 3B ₂ O ₃ ) or hydrated borates (eg 4ZnO B ₂ O ₃ H ₂ O or 2ZnO 3B ₂ O ₃ 3.5H ₂ O), anhydrous boron phosphates (eg BPO ₄ ) or hydrated, or one of their precursors. By way of example, calcium borosilicates may be mentioned as boron oxide precursor.

This fusible ceramic filler typically has a melting point below 500 ° C and gives rise to an amorphous phase (e.g., a glass) when the temperature exceeds 500 ° C.

The refractory filler may be at least one mineral filler selected from magnesium oxides (eg MgO), calcium oxides (eg CaO), silicon oxides (eg SiO ₂ or quartz), aluminum oxides (eg Al ₂ O ₃ ), chromium oxides (eg Cr ₂ O ₃ ), zirconium oxides (eg ZrO ₂ ) and phyllosilicates such as, for example, montmorillonites, sepiolites, illites, attapulgites, talcs, kaolins or micas (eg muscovite mica 6 SiO ₂ - 3 Al ₂ O ₃ - K ₂ O - 2H ₂ O), or a mixture thereof.

Preferably, the ceramic forming filler consists of two refractory fillers such as, for example, muscovite mica and calcium oxide CaO or one of its precursors (eg calcium carbonate CaCO ₃ ), and a fusible ceramic filler. such as, for example, a boron oxide precursor.

The amount of ceramic-forming fillers can be defined in that the first composition comprises at least 90 parts by weight of said fillers per 100 parts by weight of polymer, preferably at most 250 parts by weight of said fillers per 100 parts by weight of polymers in order to limit the problems of rheologies in the composition.

More particularly, the amount of fusible ceramic filler can range from 5 to 100 parts by weight, preferably from 20 to 80, and the amount of refractory filler can range from 50 to 200 parts by weight, preferably from 70 to 120 parts by weight. weight per 100 parts by weight of polymers in the first composition.

In a preferred embodiment, the first composition is not crosslinked, or in other words the first layer formed around the electrical conductor is uncrosslinked.

Moreover, and in a particular embodiment, the first polymeric layer (or inner layer) does not comprise halogenated compound.

The second cross-linked polymeric layer (or outer layer)

The second crosslinked polymeric layer is distinct from the first polymeric layer because it is said to be "non-ceramizing" since it does not substantially comprise any ceramic-forming filler. The term "substantially" means that the second composition may further comprise a ceramic forming filler but as an additive. As a result, the second layer can not have the properties of being converted at least superficially into the ceramic state at high temperatures corresponding to fire conditions, for example, for example when the second composition comprises less than 50 parts by weight. ceramic forming charge.

The polyolefin of the second composition may be advantageously chosen from homopolymers and copolymers of ethylene, or a mixture thereof.

As a preferred example of homopolymers of ethylene, low density polyethylene (LDPE) can be mentioned.

The copolymers of ethylene can be advantageously chosen from copolymers of ethylene and octene (PEO); copolymers of ethylene and vinyl acetate (EVA); the copolymers of ethylene and butyl acrylate (EBA); copolymers of ethylene and methyl acrylate (EMA); copolymers of ethylene and ethyl acrylate (EEA); copolymers of ethylene, propylene and rubber (EPR); and copolymers of ethylene propylene diene monomer (EPDM); or a mixture thereof. Copolymers of ethylene and vinyl acetate (EVA) as the preferred ethylene copolymer may be mentioned.

Preferably, the polymer matrix of the second composition is distinct from the polymer matrix of the first composition.

In a preferred embodiment, the polymer matrix of the second composition comprises at least 95% by weight of polyolefin, preferably said polymer matrix comprises only one or more polyolefins.

In another preferred embodiment, the second composition does not comprise more than 5% by weight of polyorganosiloxane, preferably not more than 2% by weight of polyorganosiloxane, and even more preferably the second composition does not comprise polyorganosiloxane.

According to a first variant, the second composition may further comprise at least one mineral filler different from a ceramic forming filler.

The inorganic filler may be a hydrated flame retardant mineral filler, chosen in particular from metal hydroxides such as, for example, magnesium dihydroxide (MDH) or aluminum trihydroxide (ATH). The flame retardant inorganic fillers employed mainly act physically by decomposing endothermically, which results in lowering the temperature of the insulating layer and limiting the propagation of the flames along the cable.

The mineral filler may also be a carbonate, such as calcium carbonate.

The amount of mineral fillers can be defined in that the second composition comprises at least 90 parts by weight of said fillers per 100 parts by weight of polymer, preferably at most 200 parts by weight of said fillers per 100 parts by weight of polymers in order to to limit the problems of rheologies in the composition.

The second crosslinked polymeric layer of this first variant is particularly advantageous when associated with a first non-crosslinked polymeric layer comprising, as a ceramic-forming filler, only one or more refractory filler (s).

According to a second variant, the second layer is said to be "uncharged", or in other words the second layer, in addition to not including a ceramic-forming filler, does not comprise a hydrated flame retardant mineral filler, and more particularly not mineral charge.

Crosslinking of the second composition to obtain the second crosslinked layer can be carried out by conventional crosslinking techniques well known to those skilled in the art such as, for example, silane crosslinking in the presence of a crosslinking agent, peroxide crosslinking under the action of heat, or photochemically crosslinking such as irradiation under beta radiation, or irradiation under ultraviolet radiation in the presence of a photoinitiator. The silane crosslinking in the presence of a crosslinking agent in the second composition is preferred since it avoids the use of specific additional equipment such as lamps or irradiation chambers for cross-linking under radiation, or salt bath lines or steam tubes for peroxide crosslinking.

In a particularly preferred embodiment, the second composition comprises only the polymer matrix, and, if necessary, the components intended to crosslink said second composition such as, for example, a crosslinking agent, and thus form the second crosslinked layer. The latter is therefore an uncharged crosslinked layer.

Whether they are the first polymeric layer and / or the second polymeric layer of the invention, they may contain additives that are well known to those skilled in the art, for example surface-treatment agents, antioxidants, waxes, etc. .etc.

Method of manufacturing the insulating layer

The method of manufacturing the (electrically) insulating layer, and more generally the electric cable, is well known to those skilled in the art.

The preferred technique for shaping the first and second compositions is extrusion using an extruder.

The first and second compositions may be extruded in two successive steps or concomitantly. In the latter case, we speak of co-extrusion.

The crosslinking of the second layer is typically carried out after the extrusion shaping of the second composition.

In the case where the first layer is also crosslinked, the crosslinking step is typically either directly after the extrusion forming step of the first composition or after the extrusion forming step of the second composition.

The first and second layers of the invention are preferably directly in contact with each other, or in other words the insulating layer comprises no intermediate layer between the first layer and the second layer. The insulating layer can then be defined as a "bilayer".

The outer sheath

The electrical cable of the invention may further comprise an outer sheath surrounding the isolated electrical conductor or conductors. This outer sheath is well known to those skilled in the art. It can burn completely locally and turn into residual ash under the effect of the high temperatures of a fire without spreading the fire.

The material that composes the outer sheath may be, for example, a polyolefin-based polymer matrix and at least one hydrated flame retardant mineral filler selected in particular from metal hydroxides such as, for example, magnesium dihydroxide or aluminum trihydroxide.

The outer sheath may be a tubular sheath or a so-called "jamming" sheath, these two types of sheath being well known to those skilled in the art. The tubular sheath is preferred to ensure a circular shape of the cross section of the cable, while the sheath is preferred when the insulated electrical conductors are arranged in parallel to each other in the same plane. In all cases, the outer sheath is conventionally obtained by extrusion.

The electric cable

According to a first variant, when the electric cable comprises an outer sheath as defined above, the electric cable may further comprise voids provided between the outer sheath on the one hand, and the isolated electrical conductor or conductors go. In this case, and to ensure a cylindrical shape to the cable over its entire length, the outer sheath is preferably tubular.

According to a second variant, when the electric cable comprises an outer sheath as defined above, the electric cable may further comprise a stuffing material (or stuffing) between the outer sheath on the one hand, and the isolated electrical conductor or conductors on the other hand.

This stuffing material is well known to those skilled in the art and is intended to ensure a cylindrical shape to the cable over its entire length.

It is typically extruded around the isolated electrical conductor (s). The stuffing consists for example of a polyolefin-based polymer matrix in which mineral fillers such as for example calcium carbonate have been added, and particularly hydrated flame retardant fillers as described above. To obtain greater ash cohesion of the stuffing material, the use of hydrated flame retardant mineral fillers combined with phyllosilicate mineral fillers is preferred.

According to a third variant, when the electric cable comprises an outer sheath as defined above, the outer sheath may be jamming, especially when the electric cable does not comprise any empty space or stuffing material.

According to another characteristic of the invention, and in order to guarantee a so-called HFFR cable for Anglicism " Halogen-Free Flame Retardant", the electrical cable, or in other words the elements that make up said electric cable, preferably does not comprise halogenated compounds.

More particularly, the first polymeric layer (or inner layer) and the second crosslinked polymeric layer (or outer layer) do not comprise a halogenated compound.

Method of manufacturing the insulating layer

1. i. former la couche isolante telle que décrite ci-avant autour d'un conducteur électrique,
2. ii. optionnellement, assembler au moins deux conducteurs électriques isolés tels qu'obtenus à l'étape i,
3. iii. optionnellement, extruder un matériau bourrant tel que défini ci-avant autour du ou des conducteurs électriques isolés de l'étape i ou ii, et
4. iv. optionnellement, extruder une gaine extérieure telle que définie ci-avant autour du ou des conducteurs électriques isolés de l'étape i, ii, ou iii.

Another object according to the invention is a method of manufacturing an electric cable as described above according to the invention, characterized in that it comprises the steps of:

1. i. forming the insulating layer as described above around an electrical conductor,
2. ii. optionally, assembling at least two insulated electrical conductors as obtained in step i,
3. iii. optionally, extruding a stuffing material as defined above around the isolated electrical conductor (s) of step i or ii, and
4. iv. optionally, extruding an outer sheath as defined above around the isolated electrical conductor (s) of step i, ii, or iii.

In a particular embodiment according to the invention, the thickness of the first layer (inner layer) ranges from 0.10 mm to 1.50 mm and the thickness of the second layer (outer layer) is in turn from 0.05 mm to 1.50 mm, especially when the (transverse) section of the electrical conductor ranges from 1.5 mm ² to 4 mm ² .

According to a first variant of this embodiment, when the (transversal) section of the electrical conductor is 1.5 mm ² , the thickness of the first layer is preferably from 0.30 mm to 0.80 mm, and more preferably to 0.60 mm. In this case, the thickness of the second layer is preferably 0.10 mm to 0.50 mm.

According to a second variant of this embodiment, when the (transversal) section of the electrical conductor is 2.5 mm ² , the thickness of the first layer is preferably from 0.30 mm to 0.90 mm. In this case, the thickness of the second layer is preferably 0.10 mm to 0.60 mm.

According to a third variant of this embodiment when the (transversal) section of the electrical conductor is 4 mm ² , the thickness of the first layer is preferably from 0.35 mm to 1 mm. In this case, the thickness of the second layer is preferably 0.10 mm to 0.70 mm.

• La figure 1 représente une vue schématique en coupe transversale d'un câble électrique selon un premier mode de réalisation conforme à l'invention.
• La figure 2 représente une vue schématique en coupe transversale d'un câble électrique selon un deuxième mode de réalisation conforme à l'invention.
• La figure 3 représente une vue schématique en coupe transversale d'un câble électrique selon un troisième mode de réalisation conforme à l'invention.

Other features and advantages of the present invention will appear in the light of the examples which follow and the appended figures, said examples and figures being given for illustrative and not limiting.

• The figure 1 is a schematic cross-sectional view of an electric cable according to a first embodiment according to the invention.
• The figure 2 is a schematic cross-sectional view of an electric cable according to a second embodiment according to the invention.
• The figure 3 is a schematic cross-sectional view of an electric cable according to a third embodiment according to the invention.

For the sake of clarity, the same elements have been designated by identical references in this figure. Similarly, only essential elements for understanding the invention have been shown schematically, and this without respect of the scale.

The electric cable shown on the figure 1 comprises three insulated electrical conductors 1,2a, 2b and an outer sheath 3 surrounding all of the three insulated electrical conductors assembled in particular in twist, the insulated electrical conductors being of substantially circular cross section.

Each of the three insulated conductors consists of an electrical conductor 1 surrounded by a first insulating layer 2a (inner layer) and a second insulating layer 2b (outer layer) directly in contact with said first insulating layer 2a. The first and the second insulating layer 2a, 2b are as defined in the present invention.

The outer sheath 3 provides empty spaces 4 between it and all the insulated electrical conductors that it surrounds. This outer sheath 3 is tubular since it has an annular shape in cross section.

The outer sheath 3 is made from a flame retardant composition comprising a polymer matrix based on polyolefin.

The electric cable shown on the figure 2 comprises five insulated electrical conductors 1,2a, 2b or 1,2b and an outer sheath 3 surrounding all five electrical insulated conductors, the insulated electrical conductors being of substantially circular cross section.

Four of the five insulated electrical conductors 1,2a, 2b are respectively surrounded by a first insulating layer 2a (inner layer) and by a second insulating layer 2b (outer layer) directly in contact with said first insulating layer 2a. The first and the second insulating layer 2a, 2b are as defined in the present invention.

The isolated electrical conductor 1,2c remaining is typically grounded. It comprises an electrical conductor surrounded by an insulating layer 2c of polymeric type. This layer may be a monolayer or a bilayer, for example of the same nature as the first layer 2a and / or the second layer 2b of the invention.

The five insulated conductors are assembled, and in particular twisted, around a reinforcing rod 5.

A stuffing material 6 surrounds all five isolated electrical conductors.

Finally, an outer sheath 3 is extruded around all five electrical insulated conductors and the stuffing material.

The cylindrical shape, or in other words the circular cross-section, of the electrical cable of the invention as shown in FIGS. Figures 1 and 2 is not limiting.

The electric cable may also have a so-called "flat" cross-section as illustrated on the figure 3 . The figure 3 represents an electric cable according to the invention in which the insulated electrical conductors 1,2a, 2b, four in number in this embodiment, are arranged in parallel with each other in the same longitudinal median plane P of the cable electric. The set of insulated electrical conductors thus formed forms a strip of insulated electrical conductors, this strip being covered with an outer sheath 3 in order to maintain the insulated electrical conductors 1,2a, 2b in the longitudinal median plane P.

Examples

Electrical cables have been made with electrical conductors surrounded by different types of insulating layers according to the prior art and according to the invention. The structure and nature of these cables are detailed in Table 1 below, broken down into two tables 1a and 1b. Each of the electrical cables comprises N insulated electrical conductors including an electrical conductor connected to the ground. The N-1 electrical conductors are detailed in table la, while said insulated electrical conductor grounded is detailed in Table 1b.

The electric cable structure as such, which can be taken into account for the understanding of Tables 1a and 1b, is the one shown on the figure 2 .

• les termes « Couche thermoplastique céramisante 1 » font référence à une couche obtenue à partir d'un matériau non réticulé d'EVA comportant de 100 à 200 parties en poids d'un mélange de deux charges réfractaires telles que du mica muscovite (50 à 150 parties en poids) et du CaO (5 à 50 parties en poids), et de 5 à 50 parties en poids de borate de zinc, les parties en poids étant exprimées par rapport à 100 parties en poids d'EVA ;
• les termes « Couche thermoplastique céramisante 2 » font référence à une couche obtenue à partir d'un matériau non réticulé de PEO comportant de 100 à 200 parties en poids d'oxyde de magnésium et de 5 à 50 parties en poids de borate de zinc, les parties en poids étant exprimées par rapport à 100 parties en poids de PEO ;
• les termes « Couche thermoplastique céramisante 3 » font référence à une couche obtenue à partir d'un matériau non réticulé de PEO comportant de 100 à 200 parties en poids de mica muscovite et de 5 à 50 parties en poids de borate de zinc, les parties en poids étant exprimées par rapport à 100 parties en poids de PEO ;
• les termes « Couche thermoplastique céramisante 4 » font référence à une couche obtenue à partir d'un matériau non réticulé de PEO comportant de 100 à 200 parties en poids d'oxyde de magnésium (MgO), les parties en poids étant exprimées par rapport à 100 parties en poids de PEO ;
• les termes « Couche silicone » font référence à une couche obtenue à partir d'un matériau réticulé de polyorganosiloxane commercialisé par la société Wacker sous la référence R502/75 ;
• le terme « XLPE non chargé » fait référence à un matériau réticulé de polyéthylène non chargé commercialisé par la société BOREALIS sous la référence Visico 4423 ;
• les termes « XEVA chargé » font référence à un matériau réticulé d'EVA comportant des charges ignifugeantes, commercialisé par la société Padanaplast sous la référence Cogegum GFR 360 ;
• les termes « XLPE chargé » font référence à un matériau réticulé de polyéthylène comportant des charges ignifugeantes, commercialisé par la société Padanaplast sous la référence Cogegum GFR 325 ;
• les termes « Cohésion 1 » font référence à un matériau bourrant (ou bourrage) HFFR, commercialisé par la société CONDOR sous la référence CC420 ;
• les termes « Cohésion 2 » font référence à un matériau bourrant (ou bourrage) HFFR, commercialisé par la société CONDOR sous la référence Confill D-F0704;
• les termes « Epaisseur du bourrage » font référence à l'épaisseur du bourrage compris entre la périphérie interne de la gaine extérieure et la périphérie externe de la couche isolante du conducteur électrique isolé ;
• les termes « Gaine HFFR » font référence à un matériau HFFR non réticulé de polyoléfine commercialisé par la société Polyone sous la référence ECCOH 5860.

In Table 1:

• the term "ceramizing thermoplastic layer 1" refers to a layer obtained from an uncrosslinked EVA material comprising from 100 to 200 parts by weight of a mixture of two refractory fillers such as muscovite mica (50 to 150 parts by weight) and CaO (5 to 50 parts by weight), and from 5 to 50 parts by weight of zinc borate, parts by weight being based on 100 parts by weight of EVA;
• "Ceramicizing thermoplastic layer 2" refers to a layer obtained from an uncrosslinked PEO material having from 100 to 200 parts by weight of magnesium oxide and from 5 to 50 parts by weight of zinc borate, the parts by weight being expressed relative to 100 parts by weight of PEO;
• "Ceramicizing thermoplastic layer 3" refers to a layer obtained from an uncrosslinked PEO material having from 100 to 200 parts by weight of muscovite mica and from 5 to 50 parts by weight of zinc borate, the parts by weight being expressed relative to 100 parts by weight of PEO;
• "Ceramicizing thermoplastic layer 4" refers to a layer obtained from an uncrosslinked PEO material having from 100 to 200 parts by weight of magnesium oxide (MgO), the parts by weight being expressed relative to 100 parts by weight of PEO;
• the term "silicone layer" refers to a layer obtained from a crosslinked polyorganosiloxane material marketed by Wacker under the reference R502 / 75;
• the term "uncharged XLPE" refers to an uncured polyethylene crosslinked material marketed by the company BOREALIS under the reference Visico 4423;
• the terms "charged XEVA" refer to an EVA cross-linked material having flame retardant fillers, marketed by Padanaplast under the reference Cogegum GFR 360;
• the terms "charged XLPE" refer to a polyethylene crosslinked material having flame retardant fillers, sold by Padanaplast under the reference Cogegum GFR 325;
• the terms "Cohesion 1" refer to a stuffing material (or stuffing) HFFR, sold by CONDOR under the reference CC420;
• the terms "Cohesion 2" refer to a stuffing material (or stuffing) HFFR, sold by CONDOR under the reference Confill D-F0704;
• "Thickness of the stuffing" refers to the thickness of the stuffing between the inner periphery of the outer sheath and the outer periphery of the insulating layer of the insulated electrical conductor;
• the terms "HFFR sheath" refer to an uncrosslinked polyolefin HFFR material marketed by Polyone under the reference ECCOH 5860.

Fire resistance tests

Each of the cables referenced 1 to 7 in Table 1 will undergo fire resistance tests. The fire resistance tests are carried out according to the following two standards: IEC 60331-21 and DIN 4102-12.

The IEC 60331-21 standard consists of subjecting an electrical cable to its nominal voltage when it is suspended horizontally over a flame of at least 750 ° C for a fixed period but without mechanical stress. This period is checked whether there is a short-circuit or breakage of the electrical conductors. The test is successful when there is no short circuit or breakage of the electrical conductors during the test and the next 15 minutes. The electrical cable that has passed the test for 30 minutes is then classified FE30. When it passes the test for 90 minutes or 180 minutes, it is respectively classified FE90 and FE180.

DIN 4102-12 consists in subjecting an electrical cable with its fixing devices in an oven with a minimum length of 3 meters for a specified period of time according to a standard temperature curve (ISO 834). In addition, the electrical cable and its fasteners are subject to the maximum permissible weight and specified loads. Electrical conductors are under their operating voltage must not break or give rise to short circuits otherwise the test would be considered a failure. The electrical cable having passed the test for 30 minutes at 842 ° C is then classified E30. When it passes the test for 60 minutes at 945 ° C or for 90 minutes at 1006 ° C, it is then respectively classified E60 and E90. This type of test close to the reality of a fire relates not only to the electric cable but also to the fastening systems of said cable.

Table 2 below shows the very satisfactory results of the fire resistance tests of the electric cables according to the present invention (cables referenced 1 to 5 and 9 to 11) in accordance with the IEC 60331-21 standard. It can also be noted that even without jamming, the cable referenced 3 according to the present invention satisfactorily satisfies this standard.

In addition, the presence of a jam makes it easier to satisfy the DIN 4102-12 standard (cables referenced 1, 2, 4, 5, 10 and 11).

Furthermore, very satisfactory results are observed with the cables referenced 9 to 11, the respective inner layers of which comprise, as a ceramic forming filler, only a refractory filler.

In view of the results of the cables referenced 10 and 11, it can also be seen that the combination on the one hand, of an inner layer comprising, as a ceramic-forming filler, only a refractory filler, and on the other hand a crosslinked outer layer based on a charged ethylene polymer comprising in particular a fire-retardant filler, make it possible to satisfy in a particularly surprising manner the DIN 4102-12 standard.

Finally, the cables referenced 1 to 5 and 9 to 11 have fire resistance properties at least equivalent to or even better than the cable referenced 6, the cost of which is much higher (because of the presence of polyorganosiloxane in the insulating layers of electrical conductors).

Electrical resistance test

The cables referenced 2, 4 and 8 in Table 1 will undergo electrical resistance tests, the outer sheaths of said cables being previously removed. Electrical resistance tests are performed according to IEC 60502-1 (paragraph 17.2).

The IEC 60502-1 standard consists of immersing a ring of insulated electrical conductors with a minimum length of 5 meters in water at the maximum temperature of the electrical conductors in normal operation (eg 90 ° C) for at least 1 hour before 'trial. Then a DC voltage between 80V and 500V is applied between the ring of isolated electrical conductors and water for a sufficient time (between 1 and 5 minutes).

dans laquelle :

• p est la résistivité transversale en Ohm.m,
• R = résistance d'isolement en Ohm,
• L = longueur du conducteur isolé en m,
• D = diamètre exterieur de l'enveloppe isolante en mm, et
• d = diamètre intérieur de l'enveloppe isolante en mm.

Finally, the transverse resistivity is calculated from the insulation resistance according to the following formula: $$\mathrm{\rho }=\mathrm{2}\mathrm{\pi RL}/\ln \left(\mathrm{D}/\mathrm{d}\right)$$

in which :

• p is the transverse resistivity in Ohm.m,
• R = insulation resistance in Ohm,
• L = length of insulated conductor in m,
• D = outer diameter of the insulating envelope in mm, and
• d = inside diameter of the insulating envelope in mm.

Table 3 below shows the very satisfactory results of the electrical resistance tests of the electric cables according to the present invention (cables referenced 2, 4 and 10) unlike the cable referenced 8 according to the prior art. <b><u> Table 3 </ u></b> Cable reference 2 4 8 10 ρ (Ohm.m) at 90 ° C > 1.10 ⁸ 2.10 ¹² 6.10 ⁶ > 1.10 ⁷

Hot creep under load test

The standard NF EN 60811-2-1 describes the measurement of the hot flow of a material under load. The corresponding test is commonly referred to as the Anglicism Hot Set Test.

It concretely consists of ballasting one end of a test piece of material with a mass corresponding to the application of a stress equivalent to 0.2 MPa, and placing the assembly in an oven heated to 200 +/- 1 ° C. a duration of 15 minutes. At the end of this period, the hot elongation under load of the test piece, expressed in%, is recorded. The suspended mass is then removed, and the test piece is kept in the oven for another 5 minutes. longer remaining permanent, also called remanence, is then measured before being expressed in%.

It is recalled that the more a material is crosslinked, the longer the values of elongation and remanence will be low. It is also specified that in the case where a test piece breaks during the test, under the combined action of the mechanical stress and the temperature, the test result would then logically be considered a failure.

This test was carried out on the insulating layer of the N-1 electrical conductors of the cables referenced 1 to 11. The results are summarized in Table 4 below.

It is noted that the insulating layers in accordance with the invention (cables referenced 1 to 5 and 9 to 11) successfully pass the standard NF EN 60811-2-1, in that the elongation under load and the remanence are respectively lower. at 175% and 25%. Even if the double-layer insulation of the cable referenced 6 also passes satisfactorily this standard, it is worth remembering that it has lower fire resistance properties than the cables of the invention while being less economical since comprising polyorganosiloxanes.

Claims (21)

1. An electric cable, comprising one or several insulated electric conductors, each of said electric conductors including an electric conductor surrounded by an insulating layer, the insulating layer comprising a first polymeric layer (2a) of the ceramizing layer type surrounding the electric conductor, the first layer (2a) being obtained from a first composition comprising a polymeric matrix based on a thermoplastic polymer, and at least one ceramic-forming filler, characterized in that the insulating layer further comprises a second crosslinked polymeric layer (2b) surrounding said first layer, the second layer (2b) being obtained from a second composition comprising a polymeric matrix based on polyolefin and substantially not comprising any ceramic-forming filler or any halogenated compound.
2. The cable according to claim 1, characterizing that the thermoplastic polymer of the first composition is selected from olefin polymers, acrylate or methacrylate polymers, vinyl polymers, and fluorinated polymers, or one of their mixtures.
3. The cable according to claim 1 or 2, characterized in that the ceramic-forming filler is selected from a meltable ceramic filler and a refractory filler, or one of their mixtures.
4. The cable according to claim 3, characterized in that the meltable ceramic filler has a melting temperature less than a temperature T of at least 750°C.
5. The cable according to claim 3 or 4, characterized in that the meltable ceramic filler is at least one mineral filler selected from among boron oxides, anhydrous or hydrated zinc borates, anhydrous or hydrated zinc phosphates and one of their precursors.
6. The cable according to claim 3, characterized in that the refractory filler has a melting temperature greater than a temperature T of at least 750°C.
7. The cable according to claims 3 or 6, characterized in that the refractory filler is at least one mineral filler selected from among magnesium oxides, calcium oxides, silicon oxides, aluminium oxides, chromium oxides, zirconium oxides, and phyllosilicates.
8. The cable according to any of the preceding claims, characterized in that the first composition comprises at least 90 parts by weight of ceramic-forming filler for 100 parts by weight of polymer.
9. The cable according to any of the preceding claims, characterized in that the first composition comprises at most 250 parts by weight of ceramic-forming filler for 100 parts by weight of polymer.
10. The cable according to any of the preceding claims, characterized in that the first composition comprises from 5 to 100 parts by weight of meltable ceramic filler for 100 parts by weight of polymer.
11. The cable according to any of claims 3 to 10, characterizing that the first composition comprises from 50 to 200 parts by weight of refractory filler for 100 parts by weight of polymer.
12. The cable according to any of the preceding claims, characterized in that the first layer (2a) is not crosslinked.
13. The cable according to any of the preceding claims, characterized in that the polyolefin of the second composition is selected from homopolymers and copolymers of ethylene, or one of their mixtures.
14. The cable according to any of the preceding claims, characterized in that the first composition and/or the second composition does not comprise more than 5% by weight of polyorganosiloxane.
15. The cable according to any of the preceding claims, characterized in that the crosslinking of the second composition in order to obtain the second crosslinked layer (2b) is silane crosslinking in the presence of a crosslinking agent in the second composition.
16. The cable according to any of claims 1 to 7, characterized in that it further comprises an outer sheath (3) surrounding the insulated electric conductor(s).
17. The cable according to claim 8, characterized in that it further comprises a stuffing material (6) between the outer sheath (3) on the one hand, and the insulated electric conductor(s) on the other hand.
18. The cable according to any of the preceding claims, characterized in that it does not comprise any halogenated compounds.
19. The cable according to any of claims 3 to 18, characterized in that the first composition only comprises a refractory filler as a ceramic-forming filler.
20. The cable according to any of claims 3 to 18, characterized in that the first composition comprises at least two refractory fillers as a ceramic-forming filler.
21. The cable according to any of the preceding claims, characterized in that the second composition further comprises a mineral filler different from the ceramic-forming filler.

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