EP3398194A1

EP3398194A1 - Fire-resistant insulating layer for a cable

Info

Publication number: EP3398194A1
Application number: EP16829295.1A
Authority: EP
Inventors: Franck Gyppaz; Stéphanie HOAREAU; Vincent BLANC
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2015-12-29
Filing date: 2016-12-29
Publication date: 2018-11-07
Anticipated expiration: 2036-12-29
Also published as: EP3398194B1; WO2017115052A1; FR3046288A1; FR3046288B1; ES2881290T3

Abstract

The present invention relates to a cable comprising at least one elongate conductive element (1) surrounded by at least one insulating layer (2, 2a) obtained from a polymer composition comprising a polymeric material and a cocktail of fillers, characterised in that the cocktail of fillers comprises: - a first silicate, - a second silicate, the second silicate being different from the first silicate, - a third silicate, the third silicate being different from the first silicate and second silicate, and - an oxide of an alkaline-earth metal.

Description

Fire-resistant insulation layer for cable

The present invention relates to a cable comprising at least one elongated conductive element surrounded by at least one insulating layer resistant to fire.

It applies typically, but not exclusively, to the field of fire-resistant, and in particular halogen-free, safety cables capable of operating for a given period of time in fire conditions, without, however, being a fire spreader or generator of 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 delay the spread of flames on the one hand, and resist fire on the other hand to ensure continuity of operation.

A significant slowdown in the progression of the flames, it is as much time gained to evacuate the places and / or to implement appropriate means of extinction. 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 release toxic fumes and / or opaque when subjected to extreme thermal conditions.

From EP-0 942 439 is known a fireproof and halogen-free electrical safety cable comprising a set of insulated electrical conductors, said assembly being surrounded by an outer 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 the state of ceramics at high temperatures corresponding to fire conditions. The polymeric material of this single insulating layer is selected 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 optimum fire resistance properties, and remains relatively expensive when a polysiloxane is chosen as the insulating material.

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

The present invention relates to a cable comprising at least one elongate conductive element surrounded by at least one insulating layer obtained from a polymer composition comprising a polymer material and a charge cocktail, characterized in that the charge cocktail comprises:

a first silicate,

a second silicate, the second silicate being different from the first silicate,

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

an oxide of an alkaline earth metal.

Thanks to the invention, the cable has a very good fire resistance, and in particular reduces significantly or even prevent the formation of inflamed droplets during the 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 requirements of the NF C 32-070 CR1 (2001) standard and the EN50200 (2006) standard.

The invention as defined in this way 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. The first silicate

The first silicate of the charge cocktail can be a phyllosilicate, such as, for example, mica.

The charge cocktail may comprise from 20 to 40% by weight of first silicate based on the total weight of charge cocktail in the polymer composition.

The second silicate

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

The second silicate of the charge cocktail may in particular be of lamellar type.

The second silicate may comprise magnesium silicate, such as, for example, talc.

The charge cocktail can comprise from 20 to 40% by weight of second silicate relative to the total weight of charge cocktail in the polymer composition.

The third silicate

The third silicate of the charge cocktail may be a compound comprising aluminum silicate, in particular of lamellar type.

The third silicate may be selected from montmorillonite, bentonite, kaolinite, hectorite, halloysite, and a mixture thereof.

As a preferred example of a third silicate, there may be mentioned a nanoclay, functionalized or otherwise. More particularly, it can be surface treated with quaternary ammonium cations.

The charge cocktail may comprise from 5 to 30% by weight of third silicate based on the total weight of charge cocktail in the polymer composition. The oxide of an alkaline earth metal

The oxide of an alkaline earth metal may be a compound different from the first and second silcates.

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

Preferably, the alkaline earth metal oxide may be of high purity, in order to improve the electrical resistivity of the cable of the invention.

"High purity" is understood to mean an alkaline earth metal oxide having a purity (by calcination) of at least 96.0%, preferably at least 98.0%, and particularly preferably at least 99.0%.

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

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

For example, the oxide of an alkaline earth metal may be a magnesium oxide (MgO).

The charge cocktail may comprise from 20 to 40% by weight of an alkaline earth metal oxide based on the total weight of charge cocktail in the polymer composition.

The cocktail of charges

The cocktail of charges may include, relative to the total weight of cocktail of charges:

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 alkaline earth metal oxide. The polymer material

The polymer material of the invention comprises one or more polymer (s), the term polymer being 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 , ..atc).

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 polymeric material, or in other words the polymer matrix of the polymeric composition, may 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 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 polymer (s) olefin, and particularly preferably more than 90% by weight of olefin polymer (s), based on the total weight of polymer material in the polymer composition. Preferably, the polymeric material is composed solely of one or more olefin polymer (s).

For example, the polymeric material of the invention may comprise one or more olefin polymers selected from 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 (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 an ethylene-octene copolymer (PEO) or a copolymer of ethylene and butene (PEB); and one of their mixtures. The polymer material of the invention may further comprise a graft polymer, in particular grafted with polar functions.

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

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

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

In a preferred embodiment, the polymeric material may comprise one or more ethylene polymer (s).

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

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

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

The polymer composition

The polymer composition of the invention may comprise at least 30% by weight of said charge cocktail relative to the total weight of the polymer composition.

In addition, the polymer composition may comprise at least 30% by weight of said polymer material relative to the total weight of the polymer composition. In order to optimize the fire resistance of the cable of the invention, the polymer composition may have a Mooney viscosity of at least 50, and preferably at least 55. The polymer composition may have a Mooney viscosity of at most 100, and preferably at most 90.

Mooney viscosity (ML1 + 4, 100 ° C) is expressed in Mooney units

(Me) and can easily be determined by the NFT 43005 standard.

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

The insulating layer of the invention surrounds the elongated conductive member, thereby forming an insulated elongated conductive member.

It can be easily shaped by extrusion around the elongated conductive member. This is called an extruded layer.

Preferably the insulating layer is a so-called thermoplastic layer, or in other words a non-crosslinked layer.

By "non-crosslinked" is meant a layer whose gel level according to ASTM D2765-01 (xylene extraction) is at most 20%, preferably at most 10%, preferably at most 5%. %, and particularly preferably 0%.

The insulating layer of the invention may advantageously 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 according to the invention, the thickness of insulating layer may range from 0.10 mm to 2.00 mm. In a preferred embodiment, the insulating layer may be in direct physical contact with the elongate conductive member.

In a first embodiment, the elongated conductive member may be surrounded by the insulating layer of the invention as a single insulating layer. This is called "monolayer" insulation.

In a second embodiment, the elongated conductive element may be surrounded by at least two insulating layers comprising:

the insulating layer of the invention as an inner layer, and

- Another insulating layer as an outer layer, the outer layer surrounding the inner layer.

The outer layer surrounding the inner layer then forms a so-called "bilayer" insulation.

The outer layer may be more particularly a crosslinked layer by techniques well known to those skilled in the art.

In the present invention, the crosslinked layer can easily be characterized by determining its gel level according to ASTM D2765-01. More particularly, said crosslinked layer may advantageously have a gel level, according to ASTM D2765-01 (xylene extraction), of at least 50%, preferably at least 70%, preferably at least 80% by weight. %, and particularly preferably at least 90%.

Preferably, the outer layer is a crosslinked layer or not, based on an olefin polymer, and more particularly based on an ethylene polymer.

The thickness of the outer layer can range from 0.05 to 2.00 mm.

Preferably, the thickness of the outer layer may be less than or equal to the thickness of the inner layer.

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" is understood to mean 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.

When the elongated conductive element is of the electric type, it may be a single conductor such as for example a metal wire, or a multiconductor 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.

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

In a particular embodiment, the cable may comprise at least two elongate conductive elements, each elongated conductive element being surrounded by at least the insulating layer of the invention.

The cable of the invention may further comprise a protective sheath surrounding one or more elongated conductive element (s) insulated (s).

In other words, when the cable of the invention comprises a single insulated elongated conductive member, the protective sheath surrounds the single, elongated insulated conductive member. When the cable of the invention comprises a plurality of elongate insulated conductive elements, the protective sheath surrounds all of said insulated elongated conductive elements.

The protective sheath of the invention may be a sheath of the tubular type or the stuffing type.

The term "tubular sheath" means a tube-shaped sheath comprising a substantially identical thickness all along said tube. The tubular sheath may be more or less tight around all the insulated conductors so as to immobilize all of said insulated conductors inside said sheath. The tubular sheath is very simple and quick to perform since it requires a pressure at the exit of the extruder smaller than that required for the manufacture of a stuffing sheath.

The term "plugging sheath" means a sheath that fills the interstices between isolated electrical conductors whose volumes are accessible.

The protective sheath may be conventionally based on one or more olefin polymers, optionally with 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 the "Halogen-Free Flame Retardant" anglicism according to IEC 60754 Parts 1 and 2 (2011).

When the cable comprises a protective sheath, it may further comprise a stuffing element positioned along the cable between the protective sheath and the at least one elongate conductive element (s), stuffing element which may further surround the at least one elongated conductive member (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), with optionally at least one flame retardant filler such as, for example, trihydroxide. aluminum (ATH), magnesium dihydroxide (MDH), chalk. Preferably, the stuffing element is a so-called "HFFR" element for the Anglicism "Halogen-Free Flame Retardant" according to IEC 60754 Parts 1 and 2 (2011).

In order to guarantee a so-called HFFR cable for the "Halogen-Free Flame Retardant" anglicism, the cable of the invention, or in other words the elements that make up said cable, such as, for example, the protective sheath, do not include / preferably comprise no halogenated compounds according to I EC 60754 Parts 1 and 2 (2011). These halogenated compounds can be of any kind, such as, for example, fluorinated polymers or chlorinated polymers such as polyvinyl chloride (PVC), halogenated plasticizers, halogenated mineral fillers, etc. Other features and advantages of the present invention will appear in the light of the description of non-limiting 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.

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.

The electric cable shown in FIG. 1 comprises two electrical conductors 1, each electrical conductor being surrounded by a single insulating layer 2 according to the invention.

A protective sheath 3 of tubular type surrounds all of the two insulated electrical conductors.

A stuffing element 4 is positioned between the protective sheath 3 and the set of insulated electrical conductors. The stuffing element 4 further surrounds all the insulated electrical conductors.

The electric cable shown in Figure 2 comprises three electrical conductors 1, a first insulating layer 2a (inner layer) around each electrical conductor 1, a second insulating layer 2b (outer layer) around each first insulating layer 2a.

The inner layer is an insulating layer according to the invention, while the outer layer is a conventional crosslinked polyethylene layer.

A protective sheath 3 of tubular type surrounds all three isolated electrical conductors.

Blank spaces 5 are formed between the protective sheath 3 and all the insulated electrical conductors that surround it.

The set of layers, packing elements and sheaths shown in Figures 1 and 2 are elements obtained by extrusion. The sheath of protection 3 is a conventional sheath made from a flame retardant composition based on polyolefin. The stuffing element 4 is a conventional stuffing element also made from a flame retardant composition based on polyolefin.

Exem pies

Table 1 below gathers a polymer composition according to the invention with:

a polymeric material consisting of three different polymers, namely: Polymer 1, Polymer 2 and Polymer 3; and

- A cocktail of charges consisting of four different charges, namely: Silicate 1, Silicate 2, Silicate 3 and metal oxide.

Table 1

The origin of the different constituents listed in Table 1 is as follows:

Polymer 1 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 2 is a low density polyethylene, with a density of 0.900 g / cm ³ , marketed by Polimeri Europa under the reference Clearflex FFDO;

Polymer 3 is a maleic anhydride grafted polyethylene with a density of 0.912 g / cm ³ sold by the company MPB under the reference

Cohesive LL15M;

Silicate 1 is a silicate of the mica type, sold by the company Keyser and Mackay under the reference Mica SX300;

Silicate 2 is a talc-type silicate, marketed by the company Univar under the reference Mistron HAR, with a specific surface area of

22 m ² / g (BET method according to DIN ISO 9277);

Silicate 3 is a lamellar silicate of the montmorillonite type, sold by BYK under the reference Cloisite 20;

- Metal oxide is an oxide of a alkaline earth metal of the magnesium oxide type (MgO) of pharmaceutical grade, marketed by 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 marketed by Clariant under the reference Wax PE 520; and

- Antioxidant is an antioxidant marketed by society

Chemtura under the reference Naugard XL1.

In order to verify the fire resistance of the composition of the invention in operational configuration, an insulating layer according to the invention has been implemented in different types of cables (see Tables 2 and 3 below) to be tested against standards NF C 32-070 CR1 (2001) and EN50200 (2006).

Table 2 below groups together three cables of substantially identical structure, comprising an insulating layer obtained from the polymer composition of Table 1.

More particularly, the cables 1 to 3 of Table 2 include: two electrical conductors surrounded respectively by a bilayer insulation, said bilayer insulation comprising an inner insulating layer according to the invention obtained from the polymer composition of Table 1,

a stuffing element surrounding the two insulated electrical conductors, and a tubular type protective sheath surrounding the two insulated electrical conductors as well as the stuffing element.

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

HFFR1 is a crosslinked extruded HFFR layer based on polyolefin, obtained from reference SX522 sold by the company AEI;

- HFFR2 is an extruded filling element HFFR based polyolefin (s) loaded (s), obtained from FR4890 marketed by Borealis; and - HFFR3 is an extruded sheath HFFR based polyolefin (s) loaded (s), obtained from ECCOH reference 5860 sold by the company Polyone. Table 3 below groups together two cables of substantially identical structure, comprising an insulating layer obtained from the polymer composition of Table 1.

More particularly, the cables 4 and 5 of Table 3 include:

ten pairs of electrical conductors (i.e. twenty electrical conductors), each electrical conductor being surrounded by a bilayer insulation, said two-layer insulation comprising an inner insulating layer according to the invention obtained from the polymer composition of Table 1,

a tubular type protective sheath surrounding the twenty insulated electrical conductors, and

empty spaces formed between the protective sheath and the insulated electrical conductors.

Table 3 The origin of the elements collected in Table 3 is as follows:

- HFFR4 is a crosslinked extruded layer HFFR based polyolefin (s) loaded (s), obtained from the reference Casico FR 4802 sold by Borealis; and

- HFFR5 is an extruded sheath HFFR based on polyolefin (s), obtained from Megolon S-540 marketed by the company Alphagary.

Preparation process

In a first step, the polymer composition of Table 1 is extruded, using a conventional single screw extruder, around each electrical conductor, thereby forming the inner layer of the bilayer insulation.

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

In a second step, the outer layer of the bilayer insulation of each electrical conductor is conventionally extruded around the inner layer.

The bilayer insulation can be extruded in two successive stages (so-called "tandem" extrusion), but it can also be extruded by coextrusion (one and the same extrusion head).

In a third step, the rest of the constituent elements of the cables 1 to 5 are extruded successively, namely:

- the stuffing element when it exists, and

- the protective sheath.

Test used

The cables 1 to 3 are subjected to the test according to standard NF C 32-070 CR1 (2001), the results being collated in table 2. The standard NF C 32-070 CR1 (2001) indicates in particular a threshold of fire resistance. 65 minutes (min) to validate the performance.

Cables 4 and 5 are tested according to EN50200 (2006), the results are shown in Table 3. EN50200 (2006) indicates in particular a fire resistance threshold of 120 minutes (min) to validate the performance.

The results clearly show that a cable comprising the insulating layer of the invention, whatever its structure, makes it possible to advantageously satisfy different fire resistance standards, in particular the NFC 32-070 CR1 (2001) and EN50200 (2006) standards. , exhibiting significant fire resistance.

Claims

A cable comprising at least one elongate conductive element (1) surrounded by at least one insulating layer (2, 2a) obtained from a polymer composition comprising a polymeric material and a charge cocktail, characterized in that the charges includes:

a first silicate,

a second silicate, the second silicate being different from the first silicate,

an oxide of an alkaline earth metal.

2. Cable according to claim 1, characterized in that the cocktail of charges comprises, relative to the total weight of charge cocktail:

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 alkaline earth metal oxide.

3. Cable according to claim 1 or 2, characterized in that the first silicate is a phyllosilicate.

4. Cable according to any one of the preceding claims, characterized in that the second silicate is a compound comprising magnesium silicate.

5. Cable according to any one of the preceding claims, characterized in that the third silicate is a compound comprising aluminum silicate.

Cable according to any one of the preceding claims, characterized in that the alkaline earth metal oxide has a purity (by calcination) of at least 96.0%, and preferably at least 98%. , 0%.

7. Cable according to any one of the preceding claims, characterized in that the oxide of an alkaline earth metal is magnesium oxide (MgO).

8. Cable according to any one of the preceding claims, characterized in that the polymer composition comprises at least 30% by weight of said cocktail of charges relative to the total weight of the polymer composition.

9. Cable according to any one of the preceding claims, characterized in that the polymer material comprises one or more polymer (s) ethylene.

10. Cable according to any one of the preceding claims, characterized in that the polymer composition comprises at least

30% by weight of said polymer material relative to the total weight of the composition.

11. Cable according to any one of the preceding claims, characterized in that the polymer composition has a Mooney viscosity of at least 50.

12. Cable according to any one of the preceding claims, characterized in that the insulating layer is a non-crosslinked layer.

13. Cable according to any one of the preceding claims, characterized in that the insulating layer is an electrically insulating layer.

14. Cable according to any one of the preceding claims, characterized in that the insulating layer is directly in physical contact with the elongated conductive element.

15. Cable according to any one of the preceding claims, characterized in that the cable comprises at least two elongate conductive elements, each elongated conductive element being surrounded by at least the insulating layer.

16. Cable according to any one of the preceding claims, characterized in that the cable further comprises a protective sheath (3) surrounding one or more elongated conductive element (s) isolated (s).