FR3066637A1 - FIRE RESISTANT CABLE - Google Patents

Abstract

The present invention relates to a cable comprising at least one elongated conductive element (1) surrounded by at least: - a first polymeric layer (2) obtained from a first composition comprising a first polymer material and a first charge, and - a second polymeric layer (3) obtained from a second composition comprising a second polymeric material and a second filler, characterized in that: - said first filler comprises at least a first oxide of an alkaline earth metal oxide type, and said second filler comprises at least a first silicate and a second silicate, the second silicate being different from the first silicate.

Description

Fire resistant cable

The present invention relates to a cable comprising at least one elongated conductive element surrounded by at least two polymeric fire-resistant layers.

It typically, but not exclusively, applies to the field of fire-resistant safety cables, in particular halogen-free, capable of operating for a given period of time under fire conditions, without however being a fire propagator or significant smoke generator.

These safety cables are in particular energy transport cables or low frequency transmission cables, such as control or signaling cables.

One of the major challenges of the cable industry is improving the behavior and performance of cables under extreme thermal conditions, especially those encountered during a fire. For essentially safety reasons, it is indeed essential to maximize the cable's capacities to delay the propagation of flames on the one hand, and to resist fire on the other hand in order to ensure continuity of operation.

Significantly slowing the progression of the flames means that time is saved for evacuating the premises and / or for implementing appropriate extinguishing measures. In the event of a fire, the cable must be able to withstand the fire in order to function 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 give off toxic and / or opaque fumes when it is subjected to extreme thermal conditions.

Document EP-0 942 439 discloses a fire-resistant and halogen-free electrical safety cable comprising a set of insulated electrical conductors, said set being surrounded by an external sheath. Each insulated electrical conductor is formed by an electrical conductor surrounded by an insulating layer obtained from a composition comprising a polymeric material and at least one ceramic-forming filler, said insulating layer thus being able to convert at least superficially into it. state of ceramic at high temperatures corresponding to fire conditions. The polymeric material of this single insulating layer is chosen from a polysiloxane, an ethylene copolymer, and their mixture.

However, it has been found that this safety cable of the prior art does not have optimal fire resistance properties, and remains relatively expensive when a polysiloxane is chosen as the insulating material.

The object of the present invention is to overcome the drawbacks of the techniques of the prior art by proposing in particular a cable having excellent fire resistance properties while limiting the risks of mechanical degradation of the electrical conductor or conductors which compose it, even at high temperature.

The subject of the present invention is a cable comprising at least one elongated conductive element surrounded by at least:

a first polymeric layer obtained from a first composition comprising a first polymeric material and a first filler, and

a second polymeric layer obtained from a second composition comprising a second polymeric material and a second filler, characterized in that:

said first charge comprises at least one first oxide of the oxide type of an alkaline earth metal, and

- Said second filler comprises at least a first silicate and a second silicate, the second silicate being different from the first silicate.

Thanks to the invention, the cable has very good fire resistance, and in particular makes it possible to significantly reduce or even avoid the formation of flaming droplets during combustion of the cable. The mechanical properties of the cable of the invention are also improved which allows it to continue to operate even at high temperatures.

The cable of the invention advantageously satisfies the conditions of the following standards:

- standard NF C32-070 CRl (2001),

- standard DIN4102-12 with the performance requirements E30, E60, E90, and

- standard NBN 713020 Addendum 3 with the performance requirements Rf60, Rf90 and Rfl20.

The invention as defined also has the advantage of being economical since it makes it possible to significantly limit or even avoid the use of polysiloxane in the insulating layer, while having very good resistance properties. fire.

1, The first polymeric layer

1.1 The first charge

The oxide of an alkaline earth metal advantageously makes it possible to improve the electrical resistivity properties at high temperature of the first polymeric layer under the conditions of a fire.

Preferably, the oxide of an alkaline earth metal can be of high purity.

The term "high purity" means an oxide of an alkaline earth metal having a purity (by calcination) of at least 96.0%, preferably at least 98.0%, and in a particularly preferred manner at least 99.0%.

The oxide of a high purity alkaline earth metal advantageously limits the presence of electrically conductive compound (s), in particular in the form of impurity (s). The impurities may contain, for example, heavy metals. Preferably, the oxide of an alkaline earth metal can comprise at most 30 ppm of heavy metals, and preferably less than 10 ppm of heavy metals.

In a preferred embodiment, the oxide of an alkaline earth metal has a melting temperature of at least 1500 ° C, preferably at least 2000 ° C, and particularly preferably at least 2500 ° C .

As a preferred example, the first oxide of the first charge can be magnesium oxide (MgO).

The first charge can also comprise a second oxide different from the first oxide.

Preferably, the second oxide can be silicon dioxide (SiO ₂ ).

The first charge can comprise from 50 to 90% by weight of the first oxide relative to the total weight of the first charge.

The first charge can comprise from 10 to 30% by weight of the second oxide relative to the total weight of the first charge.

1.2 The first polymer material

The first polymer material of the invention comprises one or more polymer (s), the term polymer can be understood by 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 polymer can be of the thermoplastic or elastomer type, and can be crosslinked by techniques well known to those skilled in the art.

In a particular embodiment, the first polymer material, or in other words the polymer matrix of the first composition, can comprise one or more olefin polymers, and preferably one or more ethylene polymers. An olefin polymer is conventionally a polymer obtained from at least one olefin monomer.

More particularly, the first polymer material can comprise more than 30% by weight of olefin polymer (s), preferably 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 of olefin polymer (s), relative to the total weight of the first polymer material in the first composition. Preferably, the first polymer material is composed only of one or more olefin polymer (s).

By way of example, the first polymer material of the invention may comprise one or more olefin polymers, and preferably one or more ethylene polymer (s), chosen from a linear low density polyethylene (LLDPE); very low density polyethylene (VLDPE); low density polyethylene (LDPE); medium density polyethylene (MDPE); high density polyethylene (HDPE); an elastomeric ethylenepropylene (EPM) copolymer; 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 a copolymer of ethylene and octene (PEO) or a copolymer of ethylene and butene (PEB); and one of their mixtures. The preferred ethylene polymer is the copolymer of ethylene and octene (PEO), or a mixture of copolymers of ethylene and octene (PEO).

The first polymer material of the invention can also comprise a grafted polymer, in particular grafted with polar functions.

This grafted polymer advantageously makes it possible to improve the mechanical properties of the first polymer layer.

By way of example, the grafted polymer can be a maleic anhydride grafted olefin polymer, and in particular a maleic anhydride grafted ethylene polymer.

When a grafted polymer is added to the first polymeric material, the first polymeric material may comprise from 1 to 20% by weight of said grafted polymer, and preferably from 1 to 15% by weight of said grafted polymer, relative to the total weight of the first polymeric material in the first composition.

The first polymeric material can have a melt flow index (known as "Melt Flow Index"), in grams / 10 minutes according to ISO 1133 at 190 ° C / 2.16 kg, ranging from 1.0 at 5.

When the composition comprises a mixture of two different olefin polymers, in particular a mixture of ethylene and octene copolymers, the melt flow indices of these two polymers are different.

The first composition of the invention may comprise at least 30% by weight of said first polymer material, and preferably at least 40% by weight of said first polymer material, relative to the total weight of the first composition.

1.3 The first composition

The first composition can comprise from 20 to 60% by weight of the first oxide relative to the total weight of the first composition. Preferably, the first composition can comprise from 30 to 50% by weight of the first oxide relative to the total weight of the first composition.

The first composition can comprise from 5 to 30% by weight of the second oxide relative to the total weight of the first composition. Preferably, the first composition can comprise from 5 to 20% by weight of the second oxide relative to the total weight of the first composition.

In another preferred embodiment, the first composition may comprise at least 30% by weight of said first charge, and preferably at least 40% by weight of said first charge, relative to the total weight of the first composition.

In another preferred embodiment, the first composition may comprise at least 30% by weight of said first polymer material, and preferably at least 40% by weight of said first polymer material, relative to the total weight of the first composition.

In order to optimize the fire resistance of the cable of the invention, the first composition can have a Mooney viscosity of at least 40, and preferably at least 50. The first composition can have a Mooney viscosity of at most 100, and preferably at most 90.

The Mooney viscosity (ML1 + 4, 160 ° C) is expressed in Mooney units (Me) and can be easily determined by standard NFT 43005.

The first composition may typically further include additives in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the first polymeric material in the first composition. Additives are well known to those skilled in the art and can for example be chosen from protective agents (eg anti-UV, anti-copper), implementing agents (eg plasticizers, lubricants), pigments, and antioxidants.

1.4 Characteristics of the first polymer layer

The first pelymeric ceuche can enteur had one or more lightened conductive element (s).

The first pelymeric layer may be an electrically insulating layer.

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), preferably at most 1.10 ' ⁸ S / m, and preferably at most 1.10' ¹³ S / m (at 25 ° C).

In a particular embodiment, the thickness of the first polymer layer can range from 0.05 mm to 2.0 mm, and preferably from 0.1 mm to 1.0 mm.

In a particular embodiment, the first polymeric layer can be crosslinked or uncrosslinked.

In the present invention, the term “non-crosslinked” is intended to mean a layer whose gel rate according to standard ASTM D2765-01 (xylene extraction) is at most 20%, preferably at most 10%, preferably not more than 5%, and particularly preferably 0%.

In the present invention, the term “crosslinked” is intended to mean a layer whose gel rate according to standard ASTM D2765-01 (extraction with xylene) is at least 50%, preferably at least 80%, and so particularly preferred by at least 90%.

2. The second polymeric layer

2.1 The second charge

2.1.1 The first silicate

The first silicate can be chosen from phyllosilicates, compounds comprising magnesium silicate, compounds comprising aluminum silicate, and one of their mixture.

Preferably, the first silicate can be a phyllosilicate. More particularly, the phyllosilicate can be mica.

The second filler can comprise from 20 to 40% by weight of first silicate relative to the total weight of the second filler.

2.1.2 The second silicate

The second silicate can be a compound with a high specific surface, in particular at least 10 m ² / g, and preferably at least 20 m ² / g. The specific surface is conventionally determined by the BET method according to DIN ISO 9277.

The second silicate can in particular be of the lamellar type.

More particularly, the second silicate can be chosen from phyllosilicates, compounds comprising magnesium silicate, compounds comprising aluminum silicate, and one of their mixture.

Preferably, the second silicate can be a compound comprising magnesium silicate.

More particularly, the compound comprising magnesium silicate can be talc.

The second filler can comprise from 20 to 40% by weight of second silicate relative to the total weight of the second filler.

2.1.3 Other compounds in the second composition

In a preferred embodiment, the second charge can also comprise:

- an oxide of an alkaline earth metal, and / or

a third silicate, the third silicate being different from the first silicate and from the second silicate.

The oxide of an alkaline earth metal advantageously makes it possible to improve the mechanical cohesion properties of the second polymeric layer after combustion under the effect of a flame.

Preferably, the oxide of an alkaline earth metal of the second polymeric layer can be of high purity, in order to improve the electrical resistivity of the cable of the invention.

The term "high purity" means an oxide of an alkaline earth metal having a purity (by calcination) of at least 96.0%, preferably at least 98.0%, and in a particularly preferred manner at least 99.0%.

The oxide of a high purity alkaline earth metal advantageously limits the presence of electrically conductive compound (s), in particular in the form of impurity (s). The impurities may contain, for example, heavy metals. Preferably, the oxide of an alkaline earth metal can comprise at most 30 ppm of heavy metals, and preferably less than 10 ppm of heavy metals.

In a preferred embodiment, the oxide of an alkaline earth metal has a melting temperature of at least 1500 ° C, preferably at least 2000 ° C, and particularly preferably at least 2500 ° C .

Preferably, the oxide of an alkaline earth metal can be magnesium oxide (MgO).

The third silicate can be chosen from phyllosilicates, compounds comprising magnesium silicate, compounds comprising aluminum silicate, and one of their mixture.

Preferably, the third silicate can be a compound comprising aluminum silicate, in particular of the lamellar type.

More particularly, the third silicate can be chosen from montmorillonite, bentonite, kaolinite, hectorite, halloysite, and one of their mixtures.

Preferably, the compound comprising aluminum silicate can be montmorillonite.

As a preferred example of a third silicate, mention may be made of a nanoclay, functionalized or not. More particularly, it can be treated at the surface with cations of the quaternary ammonium type.

The second filler can comprise from 5 to 30% by weight of third silicate relative to the total weight of the second filler in the second composition.

In another preferred embodiment, the second load can comprise, relative to the total weight of the second load:

- from 20 to 40% by weight of first silicate,

- from 20 to 40% by weight of second silicate,

- from 5 to 30% by weight of third silicate, and

from 20 to 40% by weight of oxide of an alkaline earth metal.

2.2 The second polymer material

The second polymer material comprises one or more polymer (s), the term polymer can be understood by any type of polymer well known to those skilled in the art such as homopolymer or copolymer (eg block copolymer, random copolymer, terpolymer, etc. .etc).

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

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

More particularly, the second polymeric material may comprise more than 30% by weight of olefin polymer (s), preferably 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 of olefin polymer (s), relative to the total weight of the second polymeric material in the second composition. Preferably, the second polymer material is only composed of one or more olefin polymer (s).

By way of example, the second polymer material of the invention may comprise one or more olefin polymers, and preferably one or more ethylene polymer (s), chosen from a linear low density polyethylene (LLDPE); very low density polyethylene (VLDPE); low density polyethylene (LDPE); medium density polyethylene (MDPE); high density polyethylene (HDPE); an ethylenepropylene elastomeric copolymer (EPM); 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 a copolymer of ethylene and octene (PEO) or a copolymer of ethylene and butene (PEB); and one of their mixtures.

The second polymer material of the invention can also comprise a grafted polymer, in particular grafted with polar functions.

This grafted polymer advantageously makes it possible to improve the mechanical cohesion properties of the second layer after combustion under the effect of a flame.

By way of example, the grafted polymer can be a maleic anhydride grafted olefin polymer, and in particular a maleic anhydride grafted ethylene polymer.

When a grafted polymer is added to the second polymeric material, the second polymeric material may comprise from 1 to 20% by weight of said grafted polymer, and preferably from 5 to 15% by weight of said grafted polymer, relative to the total weight of the second polymeric material in the second composition.

The second polymeric material may comprise a mixture of at least two different ethylene polymers, and more particularly may comprise a mixture of a homopolymer of ethylene and a copolymer of ethylene and vinyl acetate (EVA) .

Preferably, the second polymeric material can comprise from 50 to 80% by weight of EVA and from 20 to 50% by weight of an ethylene homopolymer, relative to the total weight of the second polymeric material in the second composition.

The second composition may comprise at least 30% by weight of the second polymeric material, preferably at least 50% by weight of the second polymeric material, and preferably at least 60% by weight of the second polymeric material, relative to the total weight of the second composition.

2.3 The second composition

The second composition can comprise at least 30% by weight of said second filler relative to the total weight of the second composition.

In a preferred embodiment, the second composition may comprise at least 30% by weight of said second polymeric material relative to the total weight of the second composition.

In order to optimize the fire resistance of the cable of the invention, the second composition can have a Mooney viscosity of at least 50, and preferably at least 55. The second composition can have a Mooney viscosity of at most 100, and preferably at most 90.

The Mooney viscosity (ML1 + 4, 160 ° C) is expressed in Mooney units (Me) and can be easily determined by standard NFT 43005.

The second composition may typically further include additives in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the second polymeric material in the second composition. Additives are well known to those skilled in the art and can for example be chosen from protective agents (eg anti-UV, anti-copper), implementing agents (eg plasticizers, lubricants), pigments, and antioxidants.

2.4 Characteristics of the second polymeric layer

The second polymeric layer may preferably surround the first polymeric layer.

The second polymeric layer can advantageously be non-crosslinked.

In the present invention, the term “non-crosslinked” is intended to mean a layer whose gel rate according to standard ASTM D2765-01 (xylene extraction) is at most 20%, preferably at most 10%, preferably not more than 5%, and particularly preferably 0%.

In another preferred embodiment, the second polymeric layer is an electrically insulating layer.

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), preferably at most 1.10 ' ⁸ S / m, and preferably at most 1.10' ¹³ S / m (at 25 ° C).

In a particular embodiment, the thickness of the second polymeric layer can range from 0.05 mm to 2.0 mm, and preferably from 0.1 mm to 1.0 mm.

3. Otherfs) nappies)

The cable according to the invention can also comprise a third polymeric layer.

The third polymer layer may preferably surround the second polymer layer.

Preferably, the third polymeric layer can be crosslinked.

In the present invention, the term “crosslinked” is intended to mean a layer whose gel rate according to standard ASTM D2765-01 (extraction with xylene) is at least 50%, preferably at least 80%, and so particularly preferred by at least 90%.

In a preferred embodiment, the third polymeric layer is an electrically insulating layer.

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), preferably at most 1.10' ^{4 * * * 8} S / m, and preferably at most 1.10 ^'13 S / m (at 25 ° C).

In another particular embodiment, the third polymeric layer does not comprise halogenated compounds. Preferably, the third polymeric layer is a so-called “HFFR” layer for “Hatogen-Free Ftame Retardant” anglicism according to standard IEC 60754 Parts 1 and 2 (2011).

The third polymeric layer may comprise one or more olefin polymer (s) and preferably one or more ethylene polymer (s)

In a particular embodiment, the thickness of the third polymeric layer can range from 0.05 mm to 2 mm, and preferably from 0.1 mm to 1.0 mm.

4. The cable

The invention finds a particularly advantageous, but not exclusive, application in the field of energy or telecommunication cables intended to remain operational for a defined time when they are subjected to high heat and / or directly to flames.

In the present invention, the term "cable" means an electrical and / or optical cable, intended for the transport of energy and / or for 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.

When the elongated conductive element is of the electrical type, it may be a single conductor such as for example a metallic wire, or a multiconductor such as a plurality of metallic wires, twisted or not.

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

The cross section of the electrical conductor can range from 0.5 mm ² to more than 240 mm ² .

The first polymeric layer can be in direct physical contact with the elongated conductive element.

In a preferred embodiment, the second polymeric layer may surround the first polymeric layer.

When the cable also has a third polymeric layer, the third polymeric layer may surround the first polymeric layer and / or the second polymeric layer.

The cable of the invention may also comprise a protective sheath surrounding one or more elongated conductive element (s) insulated by at least the first polymeric layer, the second polymeric layer, and optionally the third polymeric layer, said three layers being in accordance with the invention.

More particularly, when the cable of the invention comprises a single conductive element insulated by at least the first polymeric layer, the second polymeric layer, and optionally the third polymeric layer, the protective sheath surrounds the single elongated and thus insulated conductive element .

When the cable of the invention comprises several elongated conductive elements insulated by at least the first polymeric layer, the second polymeric layer, and optionally the third polymeric layer, the protective sheath surrounds all of said elongated and thus insulated conductive elements.

The protective sheath of the invention can be a sheath of the tubing type or of the tamping type.

“Tubing sheath” is understood to mean a tube-shaped sheath comprising a substantially identical thickness all along said tube. The tubular sheath can be more or less tight around all of the insulated conductors as previously described, so as in particular to immobilize all of said insulated conductors inside said sheath.

The tubing sheath is very simple and quick to produce since it requires less pressure at the outlet of the extruder than that necessary for the manufacture of a stuffing sheath.

The term "stuffing sheath" means a sheath which fills the interstices, when they exist, between the electrical conductors insulated by at least the first polymeric layer and the second polymeric layer, the volumes of which are accessible.

In a particular embodiment, the thickness of the protective sheath can range from 0.05 mm to 3 mm, and preferably from 0.5 mm to 2.0 mm.

The protective sheath can conventionally be based on one or more olefin polymer (s), with optionally at least one flame-retardant filler such as aluminum trihydroxide (ATH), magnesium dihydroxide (MDH), the chalk. Preferably, the protective sheath is a so-called "HFFR" sheath for Anglicism "Hatogen-Free Ftame Retardant" according to standard IEC 60754 Parts 1 and 2 (2011).

When the cable comprises a protective sheath, it may also comprise a stuffing element positioned along the cable between the protective sheath and the insulated elongated conductive element (s), the stuffing element which can also surround the insulated elongated conductive element (s).

The stuffing element is well known to those skilled in the art and may for example be based on one or more olefin polymer (s), optionally with at least one flame retardant filler such as, for example, trihydroxide. aluminum (ATH), magnesium dihydroxide (MDH), chalk. Preferably, the stuffing element is an element called "HFFR. For Anglicism "Hatogen-Free Ftame Retardant" according to standard IEC 60754 Parts 1 and 2 (2011).

In order to guarantee a so-called HFFR cable for “Hatogen-Free Ftame Retardant” anglicism, the cable of the invention, or in other words the elements which make up said cable such as for example the protective sheath, does not include / preferably include no halogenated compounds according to IEC 60754 Parts 1 and 2 (2011). These halogenated compounds can be of all kinds, such as for example fluorinated polymers or chlorinated polymers such as polyvinyl chloride (PVC), halogenated plasticizers, halogenated mineral fillers, etc.

Other characteristics and advantages of the present invention will appear in the light of the description of nonlimiting examples of cables according to the invention made 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.

2 shows a schematic cross-sectional view of an electric cable according to a second embodiment according to the invention.

For reasons of clarity, only the essential elements for the understanding of the invention have been represented diagrammatically, and this without respecting the scale.

The electrical cable shown in FIG. 1 comprises two electrical conductors 1, each electrical conductor being successively surrounded by a first polymeric layer 2 and a second polymeric layer 3, both according to the invention.

A protective sheath 5 of stuffing type surrounds all of the two conductors insulated by the two polymer layers of the invention.

A packing element 6 is positioned between the protective sheath 5 and all of the electrical conductors insulated by the two polymer layers of the invention. The stuffing element 6 also surrounds all of the electrical conductors insulated by the two polymer layers of the invention.

The electric cable shown in Figure 2 has three electrical conductors 1, successively surrounded by a first polymeric layer 2 and a second polymeric layer 3, both according to the invention. In addition, a third polymeric layer 4 surrounds the second polymeric layer of each of the electrical conductors.

A tubing type protective sheath 5 surrounds all three electrical conductors insulated by the three polymer layers.

Empty spaces 7 are provided between the protective sheath 5 and all of the electrical conductors insulated by the three polymer layers that it surrounds.

All of the layers, packing elements and sheaths shown in FIGS. 1 and 2 are elements obtained by extrusion. The protective sheath 5 is a conventional sheath produced from a flame-retardant composition based on polyolefin. The packing element 6 is a conventional packing element also produced from a flame-retardant composition based on polyolefin.

Examples

Table 1 below brings together the constituents of a first polymer composition according to the invention with:

- a first polymer material consisting of Polymer 1; and

- a first charge consisting of two different charges, namely: Oxide 1 and Oxide 2.

^1st Composition Parts by weight (phr) of the constituents per 100 parts by weight of ¹ polymer material in the composition ^era % by weight of the constituents in the ^1st composition % by weight of the charges in the ^1st charge 1 ^st polymer material Polymer 1 75 35.7 Polymer 2 20 9.5 Polymer 3 5 2.4 ^Being Charge Oxide 1 90 42.9 81.8 Oxide 2 20 9.5 18.2 Total 210 100 100

Table 1

The origin of the various constituents collected in Table 1 is as follows:

- Polymer 1 is a copolymer of ethylene and octene (PEO) with a density of 0.880-0.884 g / cm ³ , sold by the company EXXONMOBIL under the reference EXACT 8203;

- Polymer 2 is a copolymer of ethylene and octene (PEO), with a density of 0.882 g / cm ³ , and marketed by the company EXXONMOBIL under the reference EXACT 8201;

- Polymer 3 is polyethylene grafted with maleic anhydride, with a density of 0.912 g / cm ³ , sold by the company Polieco - MPB under the reference Coesive LL15M;

- Oxide 1 is an oxide of an alkaline earth metal of the magnesium oxide type (MgO), sold by the company Van Mannekus under the reference MgO AK98, with a purity of 97.9%; and

- Oxide 2 is a silicon dioxide (SiO ₂ ) sold by the company EVONIK under the reference Aerosil R.974.

Table 2 below brings together the constituents of a second composition according to the invention with:

a second polymer material made up of three different polymers, namely: Polymer 10, Polymer 20 and Polymer 30; and

a second charge consisting of four different charges, namely: Silicate 10, Silicate 20, Silicate 30 and Oxide 10.

^2nd Composition Parts by weight (per) of the constituents per 100 parts by weight of the ^2nd polymer material in the ^2nd composition % by weight of the constituents in the ^2nd polymer composition % by weight of the charges in the ^2nd charge 2θΓΪ1θ Polymeric material Polymer 10 60 23.3 Polymer 20 30 11.7 Polymer 30 10 3.9 2θΓΠΘ charge Silicate 10 45 17.5 29.4 Silicate 20 45 17.5 29.4 Silicate 30 18 7.0 11.8 Oxide 10 45 17.5 29.4 additives plasticizer 1 0.4 antioxidant 3 1.2 Total 257 100 100

Table 2

The origin of the various constituents collected in Table 2 is as follows:

- Polymer 10 is a copolymer of ethylene and vinyl acetate (EVA), with a density of 0.950 g / cm ³ , sold by the company Exxon Mobil under the reference Elvax 2803;

- Polymer 20 is a low density polyethylene, with a density of 0.900 g / cm ³ , sold by the company Polimeri Europa under the reference Clearflex FFDO;

- Polymer 30 is a grafted polyethylene of maleic anhydride, with a density of 0.912 g / cm ³ , sold by the company Polieco - MPB under the reference Coesive LL15M;

- Silicate 10 is a silica of the mica type, sold by the company Keyser and Mackay under the reference Mica SX300;

- Silicate 20 is a lamellar silicate of the talc type, sold by the company Univar under the reference Mistron HAR, with a specific surface of 22 m ² / g (BET method according to DIN ISO 9277);

- Silicate 30 is a lamellar silicate of the montmorillonite type, sold by the company BYK under the reference Cloisite 20;

Oxide 10 is an oxide of an alkaline earth metal of the magnesium oxide type (MgO) of pharmaceutical grade, marketed by the company SCORA under the reference MgO PE light, with a purity (by calcination) of 99.0%, and a melting temperature of about 2800 ° C;

- Plasticizer is a wax sold by the company Clariant under the reference Wax PE 520; and

- Antioxidant is an antioxidant marketed by the company Chemtura under the reference Naugard XL1.

In order to verify the fire resistance of the compositions of the invention in operational configuration, the polymer layers in accordance with the invention were used in different types of cables (see tables 3 and 4 below) in order to be tested. with regard to the following standards:

- NF C 32-070 CRI (2001),

- DIN4102-12 with performance E30, E60, E90, and

- NBN 713020 Addendum 3 with performance Rf60, Rf90, Rfl20.

Table 3 below presents a cable comprising a first polymeric layer obtained from the first composition of table 1, and a second polymeric layer obtained from the second composition of table 2.

More particularly, the cable 1 of table 3 comprises:

- four electrical conductors respectively surrounded by a three-layer insulation, said three-layer insulation comprising a first polymeric layer according to the invention, obtained from the first polymer composition of Table 1, a second polymeric layer according to the invention, obtained from the second composition of Table 2, and a third polymer layer according to a particular embodiment of the invention,

a stuffing element surrounding the four insulated electrical conductors, and

- a tamping type protective sheath surrounding the four insulated electrical conductors as well as the tamping element.

Cable 1 Number of insulated electrical conductors 4 Cross-section of an electrical copper conductor (mm ² ) 1.5 the polymeric layer ^era / Thickness (mm) Composition according to table 1 / 0.5 ^2nd polymeric layer / Thickness (mm) Composition according to table 2 / 0.2 ^3rd polymeric layer / Thickness (mm) HFFR1 / 0.3 Total thickness (mm) of insulation 1.0 Stuffing element Yes: HFFR2 Thickness (mm) of the HFFR3 protective tubing 1.3 Outside diameter of the electric cable 14.2 NF C 32-070 CRI test (2001) 65 mins DIN4102-12 test Performance E90 90 mins NBN test 713020 120 mins

Addendum 3 Performance Rfl20

Table 3

The origin of the elements gathered in table 3 is as follows:

- HFFR1 is an HFFR extruded layer based on charged polyolefin (s), the polyolefin (s) being of the copolymer (s) type of ethylene and vinyl acetate (EVA), and the filler being at least one flame retardant filler of the aluminum trihydroxide type;

- HFFR2 is an HFFR extruded packing element. based on charged polyolefin (s), the polyolefin (s) being of the copolymer (s) type of ethylene and vinyl acetate (EVA), and the filler being at least one flame retardant filler of the type aluminum trihydroxide; and

- HFFR3 is an HFFR extruded sheath based on charged polyolefin (s), the polyolefin (s) being of the copolymer (s) type of ethylene and vinyl acetate (EVA), and the filler being at least one flame retardant filler of the aluminum trihydroxide type.

Preparation process

Firstly, the first composition of table 1 is extruded, using a conventional single screw extruder, around each electrical conductor, thus forming the first insulating polymeric layer.

The temperature profile ranges from 90 to 200 ° C, and the extruder has eight heating zones.

In a second step, the second composition of table 2 is conventionally extruded around the first polymeric layer, thus forming the second insulating polymeric layer.

In a third step, a third layer as defined in the invention, when it exists, is extruded around the two previous layers.

The two-layer or three-layer insulation can be extruded in several successive stages, but it can also be extruded by co-extrusion (a single extrusion head).

The rest of the constituent elements of the cable 1 is extruded successively or in tandem, namely:

- the stuffing element when it exists, and

- the protective sheath.

Test used

Cable 1 is subject to:

- the test according to standard NF C 32-070 CRI (2001),

- the test according to DIN4120-12, and

- the test according to standard NBN 713020 Addendum 3, the results of these tests being collated in table 3.

Standard NF C 32-070 CRI (2001) indicates in particular a fire resistance threshold of 65 minutes (min) to validate the performance.

The DIN4120-12 standard indicates in particular a fire resistance threshold of 30, 60 and 90 minutes (min) to validate the performance E30, E60 and E90 respectively.

NBN standard 713020 Addendum 3 indicates in particular a fire resistance threshold of 60, 90 and 120 minutes (min) to validate the performance rf60, rf90 and rfl20 respectively.

The results clearly show that a cable comprising the two polymer layers of the invention, whatever its structure, makes it possible to advantageously satisfy various standards of fire resistance, in particular the standards NF C 32-070 CRI (2001), DIN4102- 12 (E90), and NBN 713020 Addendum 3 (Rfl20), with significantly improved fire resistance.

Claims (17)

1. Cable comprising at least one elongated conductive element (1) surrounded by at least: a first polymeric layer (2) obtained from a first composition comprising a first polymeric material and a first filler, and - a second polymeric layer (3) obtained from a second composition comprising a second polymeric material and a second filler, characterized in that: said first charge comprises at least one first oxide of the oxide type of an alkaline earth metal, and - Said second filler comprises at least a first silicate and a second silicate, the second silicate being different from the first silicate. 2. Cable according to claim 1, characterized in that the first oxide is magnesium oxide (MgO). 3. Cable according to claim 1 or 2, characterized in that the first charge further comprises a second oxide different from the first oxide. 4. Cable according to claim 3, characterized in that the second oxide is silicon dioxide (SiO ₂ ). 5. Cable according to any one of the preceding claims, characterized in that the first composition comprises from 20 to 60% by weight of the first oxide relative to the total weight of the first composition. 6. Cable according to any one of claims 3 to 5, characterized in that the first composition comprises from 5 to 30% by weight of the second oxide relative to the total weight of the first composition. 7. Cable according to any one of the preceding claims, characterized in that the first composition comprises at least 30% by weight of said first charge, and preferably 40% by weight of said first charge, relative to the total weight of the first composition. 8. Cable according to any one of the preceding claims, characterized in that the first polymeric material comprises one or more polymer (s) of ethylene. 9. Cable according to any one of the preceding claims, characterized in that the first polymer material comprises at least one copolymer of ethylene and octene. 10. Cable according to any one of the preceding claims, characterized in that the second charge further comprises an oxide of an alkaline earth metal. 11. Cable according to claim 10, characterized in that the oxide of an alkaline earth metal is magnesium oxide (MgO). 12. Cable according to any one of the preceding claims, characterized in that the second charge also comprises a third silicate, the third silicate being different from the first silicate and from the second silicate. 13. Cable according to claim 12, characterized in that the second load comprises, relative to the total weight of the second load: - from 20 to 40% by weight of first silicate, - from 20 to 40% by weight of second silicate, - from 5 to 30% by weight of third silicate, and - from 20 to 40% by weight of oxide of an alkaline earth metal. 14. Cable according to claim 2 or 11, characterized in that the oxide of an alkaline earth metal has a purity (by calcination) of at least 5 96.0%, and preferably at least 98%. 15. Cable according to any one of the preceding claims, characterized in that the first polymeric layer (2) is an electrically insulating layer. 16. Cable according to any one of the preceding claims, 10 characterized in that the second polymeric layer (3) is an electrically insulating layer. 17. Cable according to any one of the preceding claims, characterized in that the second polymeric layer (3) surrounds the first polymeric layer (2).