Hot vulcanizable polyorganosilox compounds for use especially in the manufacture of electrical wires or cables

Description

[0001] The present invention relates to hot-vulcanizable polyorganosiloxane compositions in silicone elastomers, that is, compositions vulcanizable at material temperatures generally between 100° and 200°C, and potentially up to 250°C. The invention further relates to the use of these compositions, in particular for the production of primary sheaths or insulators used in the construction of fire-protected electrical wires or cables. Finally, the invention relates to fire-protected electrical wires or cables manufactured using identical compositions.

[0002] The term "electrical wire" refers to an electrotechnical component used to carry electricity, in order to transmit energy or information, and which consists of an electrically conductive material, either single-strand or multi-strand, surrounded by an insulating sheath. The interior of an electrical wire is called the "core" of the wire.

[0003] By "conductor" or "single conductor" we mean an element composed of a core and its insulating sheath.

[0004] By "electrical cable" we mean an electrotechnical component used for the transport of electricity, in order to transmit energy or information and which consists of several electrically distinct and mechanically joined conductors with possibly an external shield.

[0005] An electrical cable consists of one or more single conductors (generally made of copper or aluminum); each of these conductors is protected by a primary sheath or insulation made of one or more concentric layers of an insulating material. Around this sheath (or sheaths, in the case of a cable with multiple single conductors) are one or more filler elements and / or one or more reinforcing elements, typically made of glass fibers and / or mineral fibers. An outer sheath, which may consist of one or more outer layers, is also usually present. In the case of a multi-conductor electrical cable, the filler element(s) and / or reinforcing element(s), arranged around the single conductors (each with its own primary insulation), form a common sheath for all the conductors.

[0006] The terms "fire-protected electrical wires or cables" or "fire-resistant safety electrical wires or cables" refer to electrical wires or cables that must guarantee high-quality fire performance in terms of, at a minimum, ash cohesion and flame resistance. The characteristics required of fire-protected electrical wires or cables are subject to legal regulations in many countries, and rigorous standards have been established.

[0007] The present invention typically, but not exclusively, applies to the field of "fire-protected electrical wires or cables," that is, wires or cables that are fire-resistant and capable of operating for a given period of time under fire conditions, without propagating the fire or generating significant smoke. These fire-protected electrical wires or cables are, in particular, power transmission or low-frequency transmission wires or cables. One of the major challenges for the cable industry is improving the behavior and performance of cables under extreme thermal conditions, especially those encountered during a fire.Indeed, when the performance of the materials constituting the insulating sheaths is insufficient, the overheating of the conductive wires included in an electrical wire or cable leads to the formation of electric arcs or short circuits which can cause ignition and combustion of these wires, thus propagating the fire.

[0008] Thus, for safety reasons, it is indeed essential to maximize the capacity of the wire or electrical cable to delay the spread of flames on the one hand, and to resist fire on the other, in order to ensure continuity of operation, particularly for devices vital to the safety of people such as an alarm system, an elevator, a landline telephone, in order to allow emergency services to intervene under better conditions.

[0009] A fire-resistant safety electrical wire or cable must also not be dangerous to its environment, that is, it must not release toxic and / or opaque fumes when subjected to extreme thermal conditions.

[0010] A fire-resistant safety wire or cable requires materials that exhibit good cohesion of the residue after combustion during a fire to ensure sufficient insulation of the metallic conductor, preventing power outages. The required fire resistance and imposed constraints are summarized in the French standard NF C 32-070 CR1, which concerns the operating time of burning cables under defined conditions. Fire resistance is achieved through the production of ash, which must have a certain cohesion to maintain sufficient insulation for cable operation. This test involves subjecting a test specimen of the cable or wire to the heat flux of an electric furnace heated to approximately 900°C and verifying its electrical functionality during the test. The specimen is also subjected to tensile stress and mechanical shocks.A test is considered satisfactory if indicator lamps, connected to cables supplied at a nominal voltage, are not switched off at the end of the test period.

[0011] The aforementioned standard can only be met for electrical wires or cables whose primary insulating materials have been specifically studied with regard to their non-propagation of fire.

[0012] To ensure the integrity of the insulation of flexible electrical wires or cables during a fire, the cable industry has used two technologies: fire-resistant mica tapes or silicone elastomers that transform into ceramic.

[0013] Robust but rigid, mica tape-based insulation is easy to implement on an industrial scale, offering an effective and robust insulating sheath when covered with cross-linked polyethylene. The drawback is that cables manufactured using this technique are rigid and much more difficult to strip and connect.

[0014] Silicone elastomer insulation is an effective alternative to mica tapes. Its direct extrusion onto conductors provides a good balance between fire resistance and ease of installation. Furthermore, unlike materials made from organic polymers, silicone materials exposed to high temperatures in the presence of oxygen form a silica-based ash, which has the advantage of being insulating. This intrinsic property of silicone materials has facilitated their use in electrical wires and cables. Indeed, after combustion, it is the silica residue that maintains the insulating function of the conductor while delaying the volatilization of decomposition products, reducing the amount of volatile substances available for combustion in the gaseous phase and thus decreasing the amount of heat available at the surface of the wire or cable.The silica residue also helps to insulate the surface of the conductor from the incident heat flux. However, this silica layer, obtained from a silicone material, does not exhibit sufficient cohesion and disintegrates at the slightest impact. Thus, in an electrical wire or cable, the properties of a protective layer made of silicone material alone, even one enriched with silica, are not sufficient to classify that wire or cable as a fire-resistant safety wire or cable according to the French standard NF C 32-070 CR1.

[0015] To overcome this drawback, prior art described hot-vulcanizable polyorganosiloxane compositions in silicone elastomers comprising a polyorganosiloxane polymer crosslinked by peroxide catalysis, flux-type and / or lamellar fillers which may or may not be combined with platinum and metal oxides to produce, in the event of a fire, an insulating, cohesive ash-like substance, thus extending the operating time of cables in a fire. Document EP-A-0 467 800 is a case in point, proposing the use of both zinc oxide (ZnO) as a flux and mica (as a lamellar filler), possibly combined with a platinum compound and / or metal oxides such as titanium oxide and iron oxide.

[0016] Another technical solution is described in patent application WO 01 / 34696, in which hot-vulcanizable polyorganosiloxane compositions in silicone elastomers contain: 100 parts of an ingredient a) consisting of at least one polyorganosiloxane polymer, 5 to 80 parts of at least one reinforcing filler, 0.2 to 8 parts of an organic peroxide, 8 to 30 parts of mica, 6 to 20 parts of zinc oxide, 0 to 15 parts of at least one additive commonly used in the field of hot-vulcanizable polyorganosiloxane compositions, said compositions being characterized in that they also contain, as other mandatory ingredients: 0.0010 to 0.02 parts of platinum, a platinum compound and / or a platinum complex, 2 to 10 parts of titanium oxide, and 50 to 120 parts of an ingredient i) consisting of at least one packing charge.

[0017] Other useful compositions are described in patent application WO01 / 34705, which describes hot-vulcanizable polyorganosiloxane compositions in silicone elastomers with improved fire behavior, containing: a) at least one polyorganosiloxane polymer; b) at least one reinforcing filler; c) an organic peroxide; d) mica; e) zinc oxide; f) possibly at least one additive commonly used in the field of hot-vulcanizable polyorganosiloxane compositions; said compositions being characterized in that they also contain, as other mandatory ingredients: g) platinum, a platinum compound and / or a platinum complex; h) titanium oxide; i) at least one packing filler; and j) at least one mineral species belonging to the wollastonite group.

[0018] Finally, patent application WO2004 / 064081 describes the use of hot-vulcanizable polyorganosiloxane compositions in silicone elastomers containing: a) at least one polyorganosiloxane polymer; b) at least one reinforcing filler; c) an organic peroxide; d) mica; e) zinc oxide; f) optionally at least one additive commonly used in the field of hot-vulcanizable polyorganosiloxane compositions; g) platinum, a platinum compound and / or a platinum complex; h) titanium oxide; i) at least one packing filler; and j) optionally at least one mineral species belonging to the wollastonite group, said compositions being characterized in that the packing charges i) consist of aluminum hydroxide powders Al(OH) 3 surface treated.

[0019] Other hot-vulcanizable polyorganosiloxane compositions in silicone elastomers are described in US 2010 / 0105823 A1.

[0020] Thus, prior art electrical wires or cables bearing the "safety" designation require the use of cables whose primary insulating materials have been specifically studied with regard to their fire-retardant properties. These primary insulating materials, based on silicone elastomers, are most often obtained from a polyorganosiloxane composition that crosslinks either at high temperature under the action of organic peroxides, or crosslinks at room temperature or under heat through polyaddition reactions in the presence of a metallic catalyst.

[0021] A ready-to-use mixture is a composition of hot-vulcanizable polyorganosiloxanes (EVCs) that serve as a precursor to silicone insulating material. An EVC composition typically includes, in proportions that depend on the desired final properties: oils and / or polyorganosiloxane gums with siloxyl functions having vinylated groups, preferably at the end of the chain, reinforcing fillers, in particular combustion silicas; possibly a plasticizer or an anti-structure agent (which slows down the evolution of viscosity during storage); a curing component in sufficient quantity to harden the composition either at room temperature or under the action of heat, and a thermal stabilizing system.

[0022] These mixtures are supplied as one or more components and can be formulated directly by the user according to the specific properties required. After plasticization by kneading, these ready-to-use EVC mixtures are applied by extrusion for wiring metallic wires or conductors. Specifically, in the production of a sheath or primary insulation for a single conductor, the ready-to-use EVC mixture is then deposited around each conductor and subsequently cross-linked into silicone elastomer by heating to a material temperature ranging from 100°C to 250°C. The resulting silicone material is then described as "annealed." The thicknesses of silicone insulation materials are small (no more than a few millimeters for some cables).However, flame resistance properties are still sought and are evaluated according to the IEC 60707 standard and more specifically by the UL 94V standard, which is the standard applied by American Underwriters Laboratories to test the flammability and fire safety of silicone insulation. Self-extinguishing capability is characterized by measuring the time a test specimen remains ignited after two successive applications of a Bunsen burner flame. The thinner the sample being tested, the more demanding the test is for the material.

[0023] However, the ready-to-use EVC mixtures or hot-vulcanizable polyorganosiloxane compositions in silicone elastomers available so far are not entirely satisfactory. Indeed, these compositions have the disadvantage of exhibiting sticky properties, thus complicating their handling (or "processability") during industrial preparation or their extrusion in the manufacture of electrical wires or cables.

[0024] Another problem encountered with these compositions is related to the requirements imposed to achieve a performance level that meets the French standard NF C 32-070 CR1. Indeed, prior art dictates that EVC compositions must contain a significant amount of mineral particles so that the residue after material degradation retains sufficient integrity to ensure proper electrical operation. To have a real impact, the levels of inorganic fillers introduced into a ready-to-use EVC mixture are most often exceeding 50% by weight relative to the total weight of the mixture. This results in high viscosity or consistency of these ready-to-use EVC mixtures, which places significant stress on industrial equipment, particularly during the extrusion stage.Ease of implementation, or "processability," is therefore an important criterion, especially in the context of an industrial process. Indeed, when used in the manufacture of a conductor (consisting of a core and an insulating sheath), ready-to-use EVC mixtures are first kneaded to "plasticize the paste," then they are extruded to place the insulating material around the conductive core and cross-linked by heating to allow the final hardening of the insulating material.

[0025] Another problem associated with these high levels of fillers present in the silicone material matrix is ​​an increase in the density of the resulting material and, consequently, in the weight of the safety wires and cables. This runs counter to user demand for increasingly lightweight safety wires and cables. Furthermore, the mechanical properties, particularly the elongation at break, of these highly filled silicone materials are compromised.

[0026] Another important additive for improving the fire behavior of silicone materials is platinum (Pt) or platinum derivatives. The addition of platinum, preferably in the presence of silica, improves the thermal stability and fire behavior of silicone materials. It is now known that the presence of platinum and silica in silicone materials increases the silicone residue level after combustion.

[0027] Although a small amount of platinum is required in absolute terms, to meet the extreme conditions according to the French standard NF C 32-070 CR1 and prior art, it is important to add: 56 ppm of platinum metal and more than 50% by weight of mineral fillers in the composition described in the example of patent application EP 1 238 007, 25 ppm of platinum metal and more than 50% by weight of mineral fillers in the composition described in the example of patent application EP 2 004 741, or 10 ppm of platinum metal and more than 50% by weight of mineral fillers in the composition described in the example of patent application EP 2 099 848.

[0028] The very high cost of platinum is prompting the safety cable industry to find technical alternatives requiring less platinum in silicone materials used for insulating safety electrical cables and wires without deteriorating the thermal resistance properties of the silicone material and while complying with the standard.

[0029] Therefore, the ready-to-use EVC mixtures or hot-vulcanizable polyorganosiloxane (EVC) compositions that serve as precursors to silicone insulating materials for safety-critical electrical wires and cables, as offered so far, are not entirely satisfactory and still require improvements, particularly in: a) obtain more cohesive ash, which will lead to longer cable operating times in the event of a fire, b) reduce the density of the silicone insulating material obtained from ready-to-use EVC mixtures in order to lighten the weight of safety electrical wires and cables, preferably to a density of less than 1.3, c) ensure that the viscosity of the ready-to-use EVC mixture is sufficiently low so that it is easily handled and allows good processability with the tools used in the manufacture of safety electrical wires and cables, d) reduce the platinum content used to improve thermal stability to values ​​below 10 ppm or even below 5 ppm, and e) obtain good self-extinguishing or flame-resistance performance of the elastomers obtained from ready-to-use mixtures according to the protocol defined by the reference "The Underwriters Laboratories" (UL 94V),Fourth edition, June 18, 1991.

[0030] One aim of the present invention is therefore the development of hot-vulcanizable polyorganosiloxane compositions in silicone elastomers which are capable, even when used for the sole purpose of producing the primary insulation, of giving electrical wires and cables a very high quality fire behavior marked, at least, by the achievement of good ash cohesion allowing to satisfy the standard "NF C 32-070 CR1" and to provide improvements with regard to the properties sought and listed in points b) to e) above.

[0031] A composition C comprising has now been found, and this constitutes the first object of the present invention: (A) for 100 parts by weight of at least one polyorganosiloxane polymer A having at least two C2-C6 alkenyl groups per molecule bonded to silicon, (B) between 1 and 30 parts by weight of at least one mineral B consisting of a mixture of hydromagnesite with the molecular formula Mg5(CO3)4(OH)2·4H2O and huntite with the molecular formula Mg3Ca(CO3)4, (C) from 0.1 ppm to 200 ppm, expressed as a percentage of the total weight of elemental platinum metal relative to the total weight of composition C, of ​​at least one thermal stabilizer D for improving resistance to degradation of silicone elastomers at temperatures above 800°C, selected from the group consisting of: platinum metal, a platinum compound, a platinum complex, and mixtures thereof, and (D) a curing component E in sufficient quantity to harden the composition.

[0032] Composition C of polyorganosiloxane(s) which is curable into a silicone elastomer is particularly useful as an insulator in an electrical wire or cable.

[0033] Thus, the Applicant discovered that the use of at least one mineral B consisting of a mixture of hydromagnesite with the empirical formula Mg5(CO3)4(OH)2·4H2O, and huntite with the empirical formula Mg3Ca(CO3)4 in the composition according to the invention leads to a good compromise in the application of electrical wires or cables and allows: to obtain more cohesive ash, which will lead to longer cable operating times in the event of a fire, good extrudability and improved ease of implementation (or "processability") of the composition compared to prior art compositions, and no longer exhibiting the harmful sticky properties of the prior art, thus allowing easier handling, which is an important advantage for industrial implementation, to reduce the density of the silicone insulating material obtained from ready-to-use EVC mixtures in order to lighten the weight of safety electrical wires and cables and achieve low densities below 1.3, to reduce the platinum content used to improve thermal stability to values ​​below 10 ppm or even below 5 ppm,and to obtain good self-extinguishing or flame-resistance performance of elastomers obtained from ready-to-use mixtures according to the protocol defined by the reference "The Underwriters Laboratories" (UL 94V), fourth edition of June 18, 1991.

[0034] Hydromagnesite, with the empirical formula Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O, is a mineral with a lamellar structure, the dimensions of the primary particle are on the order of 2 to 5µm in diagonal D and, for example, 200 nm in thickness d and a form factor of 1:20.

[0035] Huntite, with the chemical formula Mg3Ca(CO3)4, is a mineral with a lamellar structure, the dimensions of the primary particle are on the order of 1 to 2µm in diagonal D, for example 50 nm in thickness d and a form factor of 1:20.

[0036] The Mohs hardness of hydromagnesite and huntite is in the order of 1 to 2 and the aspect ratio is for example greater than or equal to 1:20. Hydromagnesite and huntite generally occur as aggregates of lamellar primary particles with a size generally between 1 and 15 µm with a thickness between 100 and 500 nm.

[0037] The thermal stabilizer D contains platinum, which may be in the form of: metallic (elemental) platinum, chloroplatinic acid (e.g., hexachloroplatinic acid H₂PtCl₆), hydrated chloroplatinic acid H₂PtCl₆·6H₂O (as described in US patent 2,823,218), or in the form of platinum and organic compounds: such as platinum and vinyl organosiloxane complexes (e.g., the Karstedt complex, see US patent 3,775,452), complexes such as those with the formula (PtCl₂, olefin)₂ and H(PtCl₃, olefin) described in US patent 3,159,601, where olefin represents ethylene, propylene, butylene, cyclohexene, or styrene, and platinum chloride complexes. and cyclopropane described in U.S. patent US-A-3,159,662 or Pt-carbene type complexes such as those described in patent application EP1866364-A1.

[0038] Another advantage of the composition according to the invention is the amount of platinum used as a thermal stabilizer D can be reduced to quantities less than 10 ppm, 9 ppm or 5 ppm relative to the total weight of the composition.

[0039] Thus, according to an advantageous embodiment, the composition C is characterized in that it comprises from 0.00001 to 0.0009 part, or from 0.1 ppm to 9 ppm, expressed as a weight of elemental platinum metal relative to the total weight of the composition C and at least one thermal stabilizer D enabling improved resistance against the degradation of silicone elastomers under the effect of temperatures above 800°C and which is chosen from the group consisting of: platinum metal, a platinum compound, a platinum complex and their mixtures.

[0040] According to a preferred embodiment, the invention therefore relates to a composition Cincluding: (A) for 100 parts by weight of at least one polyorganosiloxane polymer A (B) containing at least two alkenyl groups per molecule, in C2-C6 bonded to silicon, (B) between 1 and 30 parts by weight of at least one mineral B which consists of a mixture of hydromagnesite with the empirical formula Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O, and huntite with the empirical formula Mg 3 Ca(CO 3 ) 4 , (C) from 0.1 ppm to 200 ppm, expressed as weight of elemental platinum metal relative to the total weight of the composition C, of at least one thermal stabilizer D enabling improved resistance against the degradation of silicone elastomers under the effect of temperatures above 800°C and which is selected from the group consisting of: platinum metal, a platinum compound, a platinum complex and mixtures thereof, (D) a curing component Ein sufficient quantity to harden the composition, (E) from 0 to 200 parts by weight, preferably from 0.5 to 120 parts by weight and even more preferably from 0.5 to 50 parts by weight of at least one fusible charge F having a softening point between 300°C and 900°C, (F) of 0 to 250 parts by weight and preferably of 0.1 to 100 parts by weight and even more preferably of 0.5 to 50 parts by weight of at least one refractory mineral charge G, (G) from 0 to 300 parts by weight, preferably from 1 to 100 parts by weight and even more preferably from 1 to 80 parts by weight of at least one flame-retardant mineral filler Hchosen from the group consisting of: magnesium hydroxide Mg(OH) 2, aluminium hydroxide Al(OH) 3 which may have been surface treated with an organoakoxysilane or an organosilazane, and mixtures thereof, and (H) from 0 to 20 parts by weight, preferably from 0.1 to 15 parts by weight and even more preferably from 0.5 to 10 parts by weight of a zinc oxide.

[0041] Polyorganosiloxane polymer A can be linear or branched. For example, the polymer polyorganosiloxane A may consist of: of siloxyl motifs of general formula (1') : R n SiO (4-n) / 2 and at least two siloxyl motifs of general formula (II'):Z x R y SiO (4-xy) / 2 ∘ formulas in which the various symbols have the following meaning: the symbols R, identical or different, each represent a non-hydrolyzable hydrocarbon group, this radical being: an alkyl radical having 1 to 5 carbon atoms or a haloalkyl radical having 1 to 5 carbon atoms and containing 1 to 6 chlorine and / or fluorine atoms, a cycloalkyl and halocycloalkyl radical having 3 to 8 carbon atoms and containing 1 to 4 chlorine and / or fluorine atoms, an aryl, alkylaryl or haloaryl radical having 6 to 8 carbon atoms and containing 1 to 4 chlorine and / or fluorine atoms, or a cyanoalkyl radical having 3 to 4 carbon atoms; ∘ the symbols Z, identical or different, each represent an alkenyl group in C2 to C6; ∘ n = an integer equal to 0, 1, 2 or 3; ∘ x = an integer equal to 1, 2 or 3 and preferably equal to 1, ∘ y = an integer equal to 0, 1, or 2;and ∘ the sum x + y = 1, 2 or 3. ;

[0042] For illustrative purposes, the following organic radicals (R) can be cited among those directly bonded to silicon atoms: methyl; ethyl; propyl; isopropyl; butyl; isobutyl; n-pentyl; t-butyl; chloromethyl; dichloromethyl; α-chloroethyl; α,β-dichloroethyl; fluoromethyl; difluoromethyl; α,β-difluoroethyl; 3,3,3-trifluoropropyl; trifluorocyclopropyl; 4,4,4-trifluorobutyl; 3,3,4,4,5,5-hexafluoropentyl; β-cyanoethyl; γ-cyanopropyl; phenyl: p-chlorophenyl; m-chlorophenyl; 3,5-dichlorophenyl; trichlorophenyl; tetrachlorophenyl; o-, p- or m-tolyl; α,α,α-trifluorotolyte; xylyls such as 2,3-dimethylphenyl and 3,4-dimethylphenyl.

[0043] Preferably, the organic radicals R linked to silicon atoms are methyl radicals, phenyl radicals, these radicals may possibly be halogenated or even cyanoalkyl radicals.

[0044] The Z symbols are alkenyls which are preferably vinyl or allyl groups.

[0045] As concrete examples of siloxyl formula patterns (I') Examples of formulas that can be cited include: (CH3)2SiO2 / 2, (CH3)(C6H5)SiO2 / 2, (C6H5)2SiO2 / 2, (CH3)(C2H5)SiO2 / 2, (CH3CH2CH2-)(CH3)SiO2 / 2, (CH3)3SiO1 / 2 and (CH3)(C6H5)2SiO1 / 2.

[0046] As concrete examples of siloxyl formula patterns (II') Examples of formulas that can be cited include: (CH3)(C6H5)(CH2=CH)SiO1 / 2, (CH3)(CH2=CH)SiO2 / 2 and (CH3)2(CH2=CH)SiO1 / 2.

[0047] For example, the polyorganosiloxane polymer A may contain from 0.01 to 4% by weight of vinyl group. When these polyorganosiloxane polymers APolyorganosiloxane polymers with viscosities at 25°C ranging from 1,000 to 1,000,000 mPa·s are referred to as "oils," but their viscosity can also exceed 1,000,000 mPa·s, in which case they are referred to as "gums." In the compositions according to the present invention, the polyorganosiloxane polymers may be oils, gums, or mixtures thereof. These oils and gums are commercially available from silicone manufacturers or can be produced using known techniques.

[0048] According to a preferred embodiment, the organosiloxane polymer A presents per molecule at least 2 vinyl groups linked to different silicon atoms, located in the chain, at chain ends or in the chain and at chain ends, and whose other organic radicals linked to the silicon atoms are chosen from the group made up of the radicals: methyl, ethyl and phenyl.

[0049] The thermal stabilizerD The material used to improve the resistance of silicone elastomers to degradation at temperatures exceeding 800°C is chosen from the group consisting of: platinum metal, a platinum compound, a platinum complex, and mixtures thereof. Platinum may be in the form of: of metallic (elemental) platinum, chloroplatinic acid (for example hexachloroplatinic acid H2PtCl6), platinum complexes and organic products such as platinum and vinyl organosiloxane complexes (for example the Karstedt complex), complexes such as those of formula (PtCl2, olefin)2 and H(PtCl3, olefin) where the olefin represents ethylene, propylene, butylene, cyclohexene or styrene, platinum chloride and cyclopropane complexes or platinum carbene type complexes (such as those described for example in patent application EP1235836-A2).

[0050] The fuse load Ftypically has a softening point between 300°C and 900°C. It can be chosen from boron oxides (e.g., B₂O₃), anhydrous zinc borates (e.g., 2ZnO₃B₂O₃) or hydrated zinc borates (e.g., 4ZnO₃B₂O₃H₂O or 2ZnO₃B₂O₃3.5H₂O), and anhydrous boron phosphates (e.g., BPO₄) or hydrated boron phosphates, or one of their precursors, which can be boron oxide or a calcium borosilicate, recycled and ground aluminosilicate-based glass such as Fillite®< 160W marketed by Omya, hollow or solid glass microspheres such as those in the Sphériglass®< range (in particular Sphériglass®< 7010 CP01, Sphériglass®< 5000 CP01, Sphériglass®< 2000 CP01). and Sphériglass ®< 3000 CP01) marketed by Potters Industries, feldspars such as products in the Microspar ®< range such as Microspar ®< 1351 600, Microspar ®< 1351 600MST sold by Quarzwerke, hydrated calcium borates, or a mixture of these fillers.

[0051] The use as a fusible charge F of solid glass microspheres of type Sphériglass ®< 7010 CP01 or Sphériglass ®< 5000 CP01 marketed by Potters Industries is particularly preferred.

[0052] According to a preferred embodiment, the fusible load F is chosen from the group consisting of: boron oxide, zinc borates, boron phosphates, ground glasses, glasses in the form of beads, calcium borates and their mixtures.

[0053] The refractory mineral charge Gmay be at least one mineral filler chosen from among magnesium oxides (e.g. MgO), calcium oxides (e.g. CaO), silicon oxides (e.g. a precipitated or pyrogenated silica SiO2 which is preferably surface treated to make it hydrophobic by techniques known in the field of silicones or a quartz), aluminium oxides or aluminas (e.g. Al2O3), chromium oxides (e.g. Cr2O3), titanium oxides, iron oxides, zirconium oxides (e.g. ZrO2), nano-clays including the 3 subfamilies of phyllosilicates, polysilicates and layered double hydroxides (montmorillonites, sepiolites, illites, attapulgites, talcs, kaolins, micas) and their mixtures.

[0054] According to a preferred embodiment, the refractory charge Gis chosen from the group consisting of: magnesium oxides, calcium oxides, silica, quartz, montmorillonites, talcs, kaolins, micas and their mixtures.

[0055] A combination of refractory charges G is particularly preferred and consists of an association: of at least one refractory charge G1 chosen from the group consisting of a silicon oxide (e.g., a precipitated or pyrogenated silica SiO2, preferably surface-treated to make it hydrophobic using techniques known in the field of silicones), quartz, phyllosilicates such as montmorillonites, sepiolites, illites, attapulgites, talcs, kaolins or micas (e.g., muscovite mica 6 SiO2 - 3 Al2O5 - K2O - 2H2O) and their mixtures, and at least one refractory charge G2chosen from the group consisting of: magnesium oxides (e.g. MgO), calcium oxides (e.g. CaO), aluminium oxides or aluminas (e.g. Al2O3), chromium oxides (e.g. Cr2O3), zirconium oxides (e.g. ZrO2) and their mixtures.

[0056] When such a combination of refractory charges G refractory charges are used G1 are preferably present at a rate of 10 to 150 parts by weight per 100 parts by weight of polyorganosiloxane polymer A and the refractory charges G2 are preferably present at a rate of 0.5 to 100 parts by weight per 100 parts by weight of polyorganosiloxane polymer ASilicon oxides, such as silica, have the advantage of being widely used as reinforcing fillers in silicones. They are generally selected from combustion silicas and precipitated silicas. They have a specific surface area, measured using BET methods, of at least 20 m² / g, preferably greater than 100 m² / g, and an average particle size of less than 0.1 micrometer (µm). These silicas can preferably be incorporated as is or after being treated with organosilicon compounds commonly used for this purpose.These compounds include methylpolysiloxanes such as hexamethyldisiloxane and octamethylcyclotetrasiloxane; methylpolysilazanes such as hexamethyldisilazane and hexamethylcyclotrisilazane; chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane, and dimethylvinylchlorosilane; and alkoxysilanes such as dimethyldimethoxysilane, dimethylvinylethoxysilane, and trimethylmethoxysilane. During this treatment, the silicas can increase their initial weight by up to 20%, preferably around 10%.

[0057] The fire-retardant mineral filler H is chosen from the group consisting of: magnesium hydroxide Mg(OH)₂, aluminum hydroxide Al(OH)₃ which may have been surface-treated with an organoakoxysilane or an organosilazane, and mixtures thereof. Such a filler often has a particle size greater than 0.1 µm.

[0058] Concrete examples of organoalkoxysilanes include: methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, rethyltrimethoxysilane, n-propyltrimethoxysilane, vinyltrimethoxysilane, vinyltri(2-methoxyethoxy)silane, vinyltriacetoxysilane, allyltrimethoxysilane, butenyltrimethoxysilane, hexenyltrimethoxysilane, gamma-methacryloxyproyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, trimethylmethoxysilane, and trimethylethoxysilane.

[0059] Concrete examples of organosilazane include: hexamethyldisilazane or divinyltetramethyldisilazane.

[0060] Preferably, the flame-retardant mineral filler H is aluminum trihydroxide treated with an organoalkoxysilane.

[0061] The compositions according to the present invention may also contain, as an optional ingredient, at least one mineral speciesI belonging to the wollastonite group. The wollastonite group includes the following mineral species: calcium metasilicate (CaSiO3) or wollastonite; mixed calcium-sodium metasilicate (NaCa2HSi3O9) or pectolite; and mixed calcium-manganese metasilicate [CaMn(SiO3)2] or bustamite. Of course, a mixture of these different species can be used. Preferably, the mineral species I is a wollastonite. Wollastonite exists in two forms: wollastonite itself, which chemists designate as α-CaSiO3, which is commonly found in nature; and pseudo-wollastonite or β-CaSiO3. More preferably, α-CaSiO3 wollastonite is used. Mineral species I belonging to the wollastonite group can be untreated on the surface or treated with an organosilicon compound of the type mentioned above in connection with aluminum hydroxide powder.

[0062] Mineral species I may be present at a rate of 2 to 20 parts by weight per 100 parts by weight of polyorganosiloxane A.

[0063] According to a preferred embodiment, the composition C is characterized in that the hardening component E East : at least one organic peroxide (a-1), or a component (a-2) consisting of: a) at least one polyorganosiloxane (II) having, per molecule, at least two hydrogen atoms bonded to silicon, and preferably at least three hydrogen atoms bonded to silicon, and b) an effective amount of at least one polyaddition catalyst (III) and preferably chosen from the group consisting of platinum, a platinum compound, a platinum complex and mixtures thereof.

[0064] When the curing component E is an organic peroxide (a-1),Composition C is hardenable at high temperatures (generally between 100 and 200°C) under the action of organic peroxides. The polyorganosiloxane or gum used in such compositions, called EVC, is then essentially composed of siloxyl units (V), possibly associated with units (VI) in which the remainder Z represents an alkenyl group at C2-C6 and where x is equal to 1. Such EVCs are described, for example, in US-A-3,142,655, 3,821,140, ​​3,836,489 and 3,839,266 patents.

[0065] The polyorganosiloxane constituent of these EVC compositions advantageously has a viscosity at 25°C of at least 300,000 mPa.s and preferably between 1 million and 30 million mPa.s and even more.

[0066] Organic peroxide (a-1)It could be any of those that act as vulcanizing agents towards silicone elastomer-forming compositions. It may therefore be any of the peroxides or per esters which are known to be used with silicone elastomers, for example ditert-butyl peroxide, benzoyl peroxide, tert-butyl peracetate, dicumyl peroxide, 2,5-dimethylhexane 2,5-diperbenzoate and bis(t-butylperoxy)-2,5-dimethyl-2,5-hexane, monochlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, bis(2,4-dichlorobenzoyl peroxide), tert-butyl peracetate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and 2,2-bis(t-butylperoxy)-p-diisopropylbenzene.

[0067] Preferably, organic peroxide (a-1)is chosen from the group consisting of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane or "Peroxide L", dicumyl peroxide or "Peroxide D", bis(2,4-dichlorobenzoyl) peroxide or "Peroxide E", and their mixtures.

[0068] In general, when organic peroxide (a-1) is present in the composition, 0.05 to 10 parts by weight per 100 parts by weight of at least one polyorganosiloxane polymer are added A .

[0069] The composition according to the invention may also contain, as a semi-reinforcing filler, at least one polyorganosiloxane (V) resin, preferably comprising at least one alkenyl residue in its structure. These polyorganosiloxane (V) resins are well-known and commercially available branched organopolysiloxane oligomers or polymers. They may be in the form of formulations or solutions, preferably siloxane. They have, in their structure, at least two different motifs chosen from those of formula R 3 SiO 0.5 (motif M), R 2 SiO (motif D), RSiO 1.5 (motif T) and SiO 2 (motif Q), at least one of these motifs being a T or Q motif. The R radicals are identical or different and are chosen from linear or branched C1-C6 alkyl radicals, C2-C4 phenyl, 3,3,3-trifluoropropyl alkenyl radicals, and hydroxyl groups.Examples include methyl, ethyl, isopropyl, tert-butyl, and n-hexyl radicals as alkyl R-radicals, and vinyl radicals as alkenyl R-radicals. In another particular mode, polyorganosiloxane (V) resin contains 0.1 to 20% by weight of alkenyl group(s) in its structure, said structure exhibiting identical or different M-type siloxyl motifs, identical or different T-type siloxyl motifs, and / or Q-type siloxyl motifs, and possibly D-type siloxyl motifs.

[0070] The composition according to the invention may also contain at least one thermal resistance additive J such as, for example, iron octoate, cerium octoate or mixtures thereof.

[0071] In the extrusion manufacturing of electrical cables or wires, the choice of peroxide will depend in practice on the process used to cure the elastomer (vulcanization process). When the vulcanization process operates in the absence of pressure (for example, hot air and / or infrared radiation oven), the preferred peroxide is monochlorobenzoyl peroxide and / or 2,4-dichlorobenzoyl peroxide. When the vulcanization process operates in the presence of pressure (for example, steam tube), the preferred peroxide is bis(t-butylperoxy)-2,5-dimethyl-2,5-hexane.

[0072] In the case of compositions C crosslinking by polyaddition reactions called RTV, the polyorganosiloxane polymer A carrier of alkenyl-silyl groups advantageously exhibits a viscosity at 25°C of no more than 10,000 mPa.s and, preferably, between 200 and 5,000 mPa.s.

[0073] In the case of compositions C crosslinking by polyaddition reactions called LSR, the polyorganosiloxane polymer A carrier of alkenyl-silyl groups advantageously exhibits a viscosity at 25°C greater than 1,000 mPa.s, preferably in the range from a value greater than 5,000 mPa.s to 200,000 mPa.s.

[0074] In the case of compositions C crosslinking by polyaddition reactions called polyaddition EVC, the polyorganosiloxane polymer A carrier of alkenyl-silyl groups advantageously exhibits a viscosity at 25°C greater than 300,000 mPa.s and preferably between 1 million mPa.s and 30 million mPa.s or even more.

[0075] In the case of polyorganosiloxane compositions C called RTV, LSR or EVC polyaddition, the component (a-2) will be advantageously constituted: a) of at least one polyorganosiloxane (II) having, per molecule, at least two hydrogen atoms bonded to silicon, and preferably at least three hydrogen atoms bonded to silicon, and b) an effective amount of at least one polyaddition catalyst (III) and preferably chosen from the group consisting of platinum, a platinum compound, a platinum complex and mixtures thereof.

[0076] Examples of polyorganosiloxane (II) We can mention those who understand: siloxyl motifs of formula (II-1) : H d L e SiO 4 − d + e 2 wherein: the L groups, identical or different, each represent a monovalent hydrocarbon group having from 1 to 15 carbon atoms, such as, for example, an alkyl group having from 1 to 8 included carbon atoms, optionally substituted by at least one halogen atom, advantageously chosen from the methyl, ethyl, propyl, and 3,3,3-trifluoropropyl groups, or an aryl group advantageously chosen from a xylyl, tolyl, or phenyl radical, d is an integer equal to 1 or 2, e is an integer equal to 0, 1, or 2, the sum of d + e is equal to 1, 2, or 3, and optionally siloxyl motifs of formula (II-2) : L g SiO 4 − g 2 in which the L groups have the same meaning as above and g is equal to 0, 1, 2 or 3.

[0077] The dynamic viscosity at 25°C of this polyorganosiloxane (II) is preferably at least equal to 10 mPa·s and preferably it is between 20 and 10000 mPa·s. Polyorganosiloxane (II)can be formed solely from formula patterns (II-1) or include additional formulaic patterns (II-2) Polyorganosiloxane (II) may exhibit a linear, branched, cyclic, or network structure.

[0078] Examples of siloxyl motifs with the formula (II-1) Examples of siloxyl motifs with the formula H(CH3)2SiO1 / 2, HCH3SiO2 / 2, and H(C6H5)SiO2 / 2 are: H(CH3)2SiO2 / 2. (II-2) are: (CH 3 ) 3 SiO 1 / 2, (CH 3 ) 3 SiO 1 / 2 (CH 3 ) 2 SiO 2 / 2 and (CH 3 )(C 6 H 5 )SiO 2 / 2.

[0079] Useful examples of polyorganosiloxane (II) linear compounds include: dimethylpolysiloxanes with hydrogenodimethylsilyl ends, motif copolymers of (dimethyl)(hydrogenomethyl)polysiloxanes with trimethylsilyl ends, motif copolymers of (dimethyl)(hydrogenomethyl) polysiloxanes with hydrogenodimethylsilyl ends, and hydrogenomethylpolysiloxanes with trimethylsilyl ends,

[0080] Polyorganosiloxane (II) may possibly be a mixture of a dimethylpolysiloxane with hydrogenodimethylsilyl ends and a polyorganosiloxane bearing at least 3 SiH (hydrogenosiloxyl) functions.

[0081] The ratio of the number of hydrogen atoms bonded to silicon in polyorganosiloxane (II) on the total number of alkenyl unsaturation groups in the polyorganosiloxane polymer A is generally between 0.4 and 10, preferably between 0.6 and 5.

[0082] According to a preferred embodiment, polyorganosiloxane (II) is a polyorganohydrogenosiloxane having at least 2 hydrogen atoms per molecule bonded to different silicon atoms and whose organic radicals bonded to the silicon atoms are chosen from the group consisting of the radicals: methyl, ethyl, phenyl and their combinations.

[0083] The polyaddition catalyst (III)is preferably chosen from the group consisting of platinum, a platinum compound, a platinum complex, and mixtures thereof. In this case, the polyaddition catalyst (III) will also be the thermal stabilizer D, thus playing a dual role as a polyaddition catalyst and thermal stabilizer, improving resistance against the degradation of silicone elastomers under temperatures exceeding 800°C.

[0084] The polyaddition catalyst (III) The material used to improve the resistance of silicone elastomers to degradation at temperatures exceeding 800°C is chosen from the group consisting of: platinum metal, a platinum compound, a platinum complex, and mixtures thereof. Platinum may be in the form of: of metallic (elemental) platinum, of chloroplatinic acid (for example hexachloroplatinic acid H2PtCl6); of platinum complexes and organic products such as platinum complexes and vinyl organosiloxanes (for example the Karstedt complex), complexes such as those of formula (PtCl2, olefin)2 and H(PtCl3, olefin) where the olefin represents ethylene, propylene, butylene, cyclohexene or styrene, platinum chloride and cyclopropane complexes or platinum carbene type complexes (such as those described for example in patent application EP1235836-A2).

[0085] In addition to the mandatory ingredients specified above, the compositions according to the present invention may optionally also contain one or more auxiliary additive(s) f) such as in particular a pigment f5) for manufacturing colored wires and cables.

[0086] For the preparation of the compositions according to the invention, the various ingredients are intimately mixed using devices well known in the silicone elastomer industry, the order of incorporation being able to be arbitrary.

[0087] Furthermore, the invention, in a second object, relates to the use of composition C according to the invention and as described above for the production of the primary sheaths or insulators of the single conductors used in the construction of fire-protected electrical wires or cables.

[0088] The invention, in a third object, relates to electrical wires or cables which are manufactured using polyorganosiloxane compositions according to the first object of the invention.

[0089] In such an application, the deposition of a composition C according to the invention around each single conductor can be carried out using conventional methods, particularly extrusion processes. The resulting deposit is then cross-linked by heating to form the primary silicone elastomer insulator. The heating time obviously varies with the material temperature and any working pressure. It is generally on the order of a few seconds to several minutes between 100 and 120 °C and a few seconds between 180 and 200 °C. It is possible to deposit several layers simultaneously using tandem extrusion equipped, for example, with a right-angle head or co-extrusion.

[0090] Another object of the invention relates to a fire-protected electrical wire or cable comprising at least one conductive element (1) surrounded by at least one primary insulating layer (2)characterized in that said primary insulating layer (2) consists of a material obtained by hardening said composition C according to the invention and as described above possibly by a heater providing a material temperature ranging from 80°C to 250°C.

[0091] According to a preferred embodiment, the material obtained by hardening said composition C according to the invention at a density less than 1.30.

[0092] The electrical wire or cable according to the invention may further comprise an outer sheath surrounding the insulated electrical conductor(s). This outer sheath is well known to those skilled in the art. It can burn completely locally and be reduced to residual ash under the effect of the high temperatures of a fire without propagating the fire. The material composing the outer sheath may, for example, be a polyolefin-based polymer matrix and at least one hydrated flame-retardant mineral filler, chosen in particular from among metal hydroxides such as, for example, magnesium dihydroxide or aluminum trihydroxide. The outer sheath is conventionally obtained by extrusion.

[0093] According to a preferred embodiment, the fire-protected electrical wire or cable according to the invention is characterized in that the primary insulating layer (2)is formed by deposition around the conductive element (1) of said composition C by an extrusion technique and by heating means so as to obtain a material temperature ranging from 80°C to 250°C until the said composition hardens C.

[0094] Another object of the invention relates to a method for manufacturing an electrical wire or cable according to the invention and as described above, characterized in that it comprises the steps of: i. form around an electrical conductor at least one primary insulating layer (2)which consists of a material obtained by hardening said composition C possibly by heating providing a material temperature ranging from 80°C to 250°C, ii. optionally, assemble at least two insulated electrical conductors as obtained in step i, and iii. optionally, extrude an outer sheath as defined above around the insulated electrical conductor(s) of step i or ii.

[0095] The following examples are given for illustrative purposes only and cannot be considered as a limitation of the scope of the invention. EXAMPLES

[0096] 1) Constituents: Polyorganosiloxane A1 = a polydimethylsiloxane blocked at each of its two ends by a dimethylvinylsiloxy motif, and having a viscosity of 20 million mPa·s at 25°C; Polyorganosiloxane A2= a poly(dimethyl)(methylvinyl)-siloxane blocked at both ends by a trimethylsiloxy motif, containing 720 ppm of vinyl groups in the chain, having a viscosity of 20 million mPa·s at 25°C; Mineral B1 = natural mixture of Huntite and Hydromagnesite corresponding to the commercial grade Ultracarb LH15 from MINELCO, Mineral B2 = natural mixture of Huntite [(Mg3Ca(CO3)4)] and Hydromagnesite [Mg5(CO3)4(OH)2.4H2O] corresponding to the commercial grade Ultracarb® < 1250 from MINELCO, Mineral species I1 = Wollastonite Mineral species I2 Magnesium carbonate, a product of the Luvomag® range (C013 series, sold by Lehmanns Voss & Co). Stabilizer D1 : solution in divinyltetramethyldisiloxane of a 10 wt% platinum complex liganded by divinyltetramethyldisiloxane (Karstedt complex); Hardening component E1= 2,4-Dichlorobenzoyl peroxide; Refractory charge G'1 : fumed silica (specific surface area 150 m² / g) Refractory charge G'2 : Fumed silica surface-treated with octamethyltetrasiloxane. Refractory charge. G'3 = crystalline silica (Sikron® E600 marketed by SiBELCO); Refractory charge G'4 = talc (MISTRON® HAR marketed by Imerys Talc); Refractory charge G'5 = talc (MISTRON® R10 marketed by Imerys Talc); Refractory charge G'6 = mica (Concord® grade 325); Refractory charge G'7 = mica (Mica MAS 10 ®<); Refractory filler G'8 = MgO (Luvomag® < N 050 marketed by Lehmann & Voss & Co.) Refractory charge G'9 = Treated kaolin (Burgess® 2211 marketed by Burgess Pigment Co.); Refractory charge G'10= CaO (Caloxol® PG marketed by Omya UK Chemicals); Refractory charge G'11 = TiO2 (Aeroxide® < TiO2 P25 marketed by Evonik); MEMO: γ-methacryloxypropyltrimethoxysilane Additive 1 = Rhodorsil ®< RP 110 ST (di(hydroxydimethylsiloxy) polydimethylsiloxane oil marketed by Bluestar Silicones France SAS); Additive 2 = RG 150 HTS (phenylated silicone oil marketed by Bluestar Silicones France SAS); Additive 3 = RP130 Vi (vinyl and hydroxylated silicone oil marketed by Bluestar Silicones France SAS), Additive J1 = iron ethyl-2 hexanoate. 2) Preparation ofCompositions: In a Z-arm mixer, the components of the compositions (except the hardening component) are mixed for 1 hour at room temperature (23°C). The resulting mixture is then processed in a roller mixer, and the hardening component is added. The tested compositions are described in Table 1 below.

[0097] The ease of implementation (or "processability") of the resulting mixture is assessed at the roller mixer. The mixture is evaluated according to the following scale: 0 = very sticky mixture not suitable for use on rollers; 1-2 = sticky, the mixture is difficult to work with on rollers; 3-4 = slightly sticky; 5 = non-sticky, the mixture is easily worked with rollers. Table 1: Components of the compositions Components Compositions calculated as a mass percentage relative to the sum of the polyorganosiloxanes A1 and A2 C-1 C-2 C-3 I-1 I-2 I-3 I-4 Polyorganosiloxane A2 98,54 33,87 100 25,73 25,73 100 100 Polyorganosiloxane A1 1,46 66,13 74,27 74,27 Mineral B1 4,50 4,50 22.33 11.17 Mineral B2 11.17 Mineral species I1 3,33 Thermal stabilizer D1 (amount of platinum in ppm relative to the total weight of the composition) 12 ppm 20 ppm 20ppm 5 ppm 5 ppm 20 ppm 20ppm refractory charge G'1 13,65 12,56 42,76 42,76 refractory charge G'2 18,38 24 24 24 refractory charge G'3 33,30 96 96 96 refractory charge G'4 12,01 refractory charge G'5 12,02 6,00 refractory charge G'6 7,71 refractory charge G'7 0,80 1,78 refractory charge G'8 3,01 3,00 refractory charge G'9 26,64 refractory charge G'10 0,29 refractory charge G'11 1,68 2,01 MEMO 0,69 0.4 0,46 0,46 0.4 0.4 Zinc oxide H1 4,40 4,93 4,50 4,50 Cerium hydroxide 0,87 1,95 Additive J1 0,63 0,39 0.4 0.4 0.4 Additive 1 4,36 2,90 1.0 3,93 3,93 1 1 Additive 2 3,02 3,02 Additive 3 RP130 We 1,94 Hardening component E1 1,48 2,00 1.5 2,62 2,62 1,50 1,50 3) Characterization of the compositions:

[0098] (1i) A fraction of the homogeneous mass obtained on the mixer is used to measure the mechanical properties of the silicone elastomer resulting from the hot vulcanization of the polyorganosiloxane composition. To do this, the homogeneous mass fraction retained for this purpose is then vulcanized under pressure for 8 minutes at 115°C, using a suitable mold to obtain 2 mm thick plates. This yields plates in the unannealed (NR) state. A fraction of the plates is then annealed for 4 hours at 200°C (R) and then aged for 10 days at 200°C. Standardized samples are then taken from all of these plates, and the following properties are measured: Shore A hardness (DSA) according to DIN 53505, tensile strength (RR) in MPa according to AFNOR NF T 46002, elongation at break (AR) in % according to the previous standard, elastic modulus (Mod 100%) at 100% elongation in MPa according to the previous standard.

[0099] The density of the silicone elastomer in the unannealed state (NR) is still measured by operating according to the indications of the AFNOR NF T 46030 standard.

[0100] (2i) Another portion of the homogeneous mass obtained in the mixer is cut into strips to feed the extruder for manufacturing an electrical cable. The cable is manufactured using a standard construction consisting of a 2.8 mm diameter cable comprising a 1.05 mm diameter copper core, around which a 0.875 mm thick silicone elastomer sheath or primary insulation is extruded. The cable thus obtained at the extruder outlet is vulcanized in a hot-air infrared oven at a temperature of approximately 250°C (providing a material temperature of approximately 110°C - 130°C) for 1 to 3 minutes. Standardized samples are then taken from the cable to measure the ash cohesion under an electrical voltage of 500 volts according to standard NF C 32-070 CR1. The results obtained are shown in Table 2 below.The mention of the term "NC" means that the test was inconclusive and is classified as "not classified" (NC). Table 2: Mechanical and cohesive properties of the ash. Composition C-1 Composition C-2 Composition I-1 Composition I-2 Density of silicone elastomer in the unannealed state (NR) 1,23 1,42 1,26 1,28 Mechanical properties of silicone elastomer in the unannealed (NR) state DSA (pt) 75 62 71 71 RR (MPa) 8 6,8 8,5 8,1 AR (%) 240 406 331 324 Mod 100% 3,4 3,7 Ease of implementation (or "processability") 4 4 5 5 Mechanical properties after thermal aging (10 days at 200°C) DSA (pt) 79 70 84 85 RR (MPa) 7.2 6.7 6,1 6,0 AR (%) 140 143 190 172 Ash cohesion under 500V according to standard NFC 32070 CR1 Time in minutes NC 70 >90 >90

[0101] (3i) The flame resistance tests of the elastomers obtained are carried out according to the international standard IEC 60707 defined by Underwriters Laboratories. More specifically, the protocol used to evaluate the compositions presented in Table 1 corresponds to the UL 94V standard, which consists of vertically exposing a vulcanized elastomer specimen, 127 mm long, 12.7 mm wide, and with a thickness specified in the tests below, to a flame. This specimen is thus subjected to two successive exposures, each lasting 10 seconds, to a flame of approximately 900°C calibrated according to the requirements of the aforementioned standard. For each exposure, the extinction times T1 and T2 are recorded. A ranking is then established: The "V0" rating is the highest, corresponding to a material that is difficult to ignite and does not produce flaming droplets during the test. For the "V1" rating, the material is more easily flammable but also does not produce flaming droplets during the test. For the "V2" rating, in addition to being more easily flammable than V0, flaming droplets may occur during the test. For even more flammable materials, the rating "NC" (not classified) is given.

[0102] The results obtained are shown in Table 3 below. Table 3. Composition C-3 Composition I-3 Composition I-4 Flame resistance tests (UL94V) Ranking NC V0 V0 Specimen thickness = 3 mm; annealed elastomer Ranking NC V0 V0-V1 Specimen thickness = 2 mm; annealed elastomer Ranking NC V1 V1 Specimen thickness = 2 mm; unannealed elastomer

[0103] The compositions according to the invention exhibit better self-extinguishing or flame resistance performance when hardened into elastomers.

[0104] It should be noted that a comparative composition was tested with a mineral species I2 = Magnesium Carbonate, product of the Luvomag ®< range (series C013, sold by the company Lehmanns Voss & Co) but that the results were not satisfactory and were classified as "not classified" (NC).

Claims

1. Composition C comprising: (A) per 100 parts by weight of at least one polyorganosiloxane polymer A having per molecule at least two silicon-bonded alkenyl groups, (B) between 1 and 30 parts by weight of at least one mineral B that consists of a mixture of hydromagnesite of empirical formula Mg5(CO3)4(OH)2·4H2O and huntite of empirical formula Mg3Ca(CO3)4, (C) from 0.1 ppm to 200 ppm, expressed as weight of elemental platinum metal relative to the total weight of composition C, of at least one thermal stabilizer D for improving the resistance to degradation of silicone elastomers under the influence of temperatures greater than 800°C and that is selected from the group consisting of: platinum metal, a platinum compound, a platinum complex and mixtures thereof, and (D) a curing component E in an amount sufficient to cure the composition.

2. Composition C according to Claim 1 comprising: (A) per 100 parts by weight of at least one polyorganosiloxane polymer A having per molecule at least two silicon-bonded alkenyl groups, (B) between 1 and 30 parts by weight of at least one mineral B that consists of a mixture of hydromagnesite of empirical formula Mg5(CO3)4(OH)2·4H2O and huntite of empirical formula Mg3Ca(CO3)4, (C) from 0.1 ppm to 200 ppm, expressed as weight of elemental platinum metal relative to the total weight of composition C, of at least one thermal stabilizer D for improving the resistance to degradation of silicone elastomers under the influence of temperatures greater than 800°C and that is selected from the group consisting of: platinum metal, a platinum compound, a platinum complex and mixtures thereof, (D) a curing component E in an amount sufficient to cure the composition, (E) from 0 to 200 parts by weight, preferably from 0.5 to 120 parts by weight and even more preferably from 0.5 to 50 parts by weight, of at least one fusible filler F having a softening point of between 300°C and 900°C, (F) from 0 to 250 parts by weight and preferably from 0.1 to 100 parts by weight and even more preferably from 0.5 to 50 parts by weight of at least one refractory mineral filler G, (G) from 0 to 300 parts by weight, preferably from 1 to 100 parts by weight and even more preferably from 1 to 80 parts by weight, of at least one flame-retardant mineral filler H selected from the group consisting of: magnesium hydroxide Mg(OH)2, aluminium hydroxide Al(OH)3 that has optionally been surface-treated with an organoalkoxysilane or organosilazane, and mixtures thereof, and (H) from 0 to 20 parts by weight, preferably from 0.1 to 15 parts by weight and even more preferably from 0.5 to 10 parts by weight, of zinc oxide.

3. Composition C according to either one of the preceding claims, characterized in that curing component E is: - at least one organic peroxide (a-1), or - a component (a-2) consisting of: a) at least one polyorganosiloxane (II) having, per molecule, at least two silicon-bonded hydrogen atoms, and preferably at least three silicon-bonded hydrogen atoms, and b) an effective amount of at least one polyaddition catalyst (III), preferably selected from the group consisting of platinum, a platinum compound, a platinum complex and mixtures thereof.

4. Composition C according to either one of Claims 1 and 2, characterized in that it comprises from 0.00001 to 0.0009 parts, i.e. from 0.1 ppm to 9 ppm, expressed as weight of elemental platinum metal relative to the total weight of composition C, and of at least one thermal stabilizer D for improving the resistance to degradation of silicone elastomers under the influence of temperatures greater than 800°C and that is selected from the group consisting of: platinum metal, a platinum compound, a platinum complex and mixtures thereof.

5. Composition C according to Claim 2, wherein the fusible filler F is selected from the group consisting of: boron oxide, zinc borates, boron phosphates, ground glasses, glasses in bead form, calcium borates and mixtures thereof.

6. Composition C according to Claim 2, wherein the refractory mineral filler G is selected from the group consisting of: magnesium oxides, calcium oxides, silica, quartz, montmorillonites, talcs, kaolins, micas and mixtures thereof.

7. Composition C according to Claim 1, wherein the polyorganosiloxane polymer A has per molecule at least 2 vinyl groups bonded to different silicon atoms located within the chain, at chain ends or within the chain and at chain ends, and in which the other organic radicals bonded to the silicon atoms are selected from the group consisting of the radicals: methyl, ethyl and phenyl.

8. Composition C according to Claim 3, wherein the polyorganosiloxane (II) is a polyorganohydrogenosiloxane having per molecule at least 2 hydrogen atoms bonded to different silicon atoms and in which the organic radicals bonded to the silicon atoms are selected from the group consisting of the radicals: methyl, ethyl, phenyl and combinations thereof.

9. Use of composition C as described in any one of the preceding claims for producing coverings or primary insulation of single-core wiring or cabling within the structure of fire-protected electric wires or cables.

10. Fire-protected electric wire or electric cable comprising at least one conducting element (1) surrounded by at least one primary insulating layer (2), characterized in that said primary insulating layer (2) consists of a material obtained by curing said composition C as defined in any one of Claims 1 to 8, optionally by heating providing a material temperature in the range from 80°C to 250°C.

11. Fire-protected electric wire or electric cable according to Claim 10, characterized in that the primary insulating layer (2) is formed by depositing said composition C around the conducting element (1) by an extrusion technique and by heating so as to obtain a material temperature in the range from 80°C to 250°C until said composition C has cured.

12. Process for producing an electric wire or cable as described in Claim 10 or 11, characterized in that it comprises the steps of: i. forming around an electrical conductor at least one primary insulating layer (2) that consists of a material obtained by curing said composition C as defined in any one of Claims 1 to 8, optionally by heating providing a material temperature in the range from 80°C to 250°C, ii. optionally, joining together at least two insulated electrical conductors as obtained in step i, and iii. optionally, extruding an outer sheath surrounding the insulated electrical conductor(s) around the insulated electrical conductor(s) from step i or ii.