Fire-resistant and water-resistant halogen-free low-voltage cables

ES 2 238 043 T3

DESCRIPTION

Low voltage non-halogen flame retardant and watertight cable.

Background of the invention

Field of the invention

The present invention relates to electrical cables, in particular low voltage electrical cables having improved fire resistance and water resistance.

Description of the prior art

Fire resistant cables are known in the art to include layers of polyolefin containing an organic halide or other fire retardants.

The drawbacks of using halogenated flame retardant compounds, particularly in connection with the manufacture of the above cables and their possible corrosion effect on metal parts of the equipment, are known in the art.

PCT patent WO 99/05688 describes cables with good fire resistance properties, which include a layer of crystalline propylene homopolymer or copolymer mixed with a copolymer of ethylene with at least one α-olefin and possibly a diene.

The above compounds contain a natural magnesium hydroxide in amounts that confer fire retardant properties on the cables.

The above application mentions the possible use of an internal insulation layer that is relatively thick compared to the layer containing the fire retardant.

European patent application EP 0 378 259 describes high voltage connecting cables that include a metal wire surrounded by a first layer of insulation between 0.3 and 1.5 mm thick and that includes a propylene copolymer and therefore at least one other alkene, the first insulation jacket being covered with a second insulation jacket which is not crosslinked and has a thickness of between 1.0 and 3 mm, having a polyvinyl chloride or a vinyl chloride copolymer. The second jacket includes fire retardant additives.

GB 2 294 801 refers to an electrical cable that includes a conduit embedded in a hydrophobic material and surrounded by a layer of fire retardant material. The cable is used in the field of telecommunications in particular.

However, we have found that using a jacket that includes a layer containing the fire retardant as described in PCT WO 99/05688 renders the water resistance of the cable unsatisfactory, not meeting the relevant requirements. Also, when an additional thick insulation layer is used, the cable has fire resistance problems.

We have found that when the cable operates in the presence of moisture, water tends to penetrate the cable and reduce its insulation, causing a cable breakdown.

The invention therefore relates to a low voltage electrical cable, preferably a single conductor cable, which has improved fire resistance and flame spread resistance, does not contain halides and complies with IEC standards, the cable having improved water resistance. The combination is also intended to improve the mechanical properties of the cable and its resistance to short circuits.

The cable according to the invention must have a fire resistance that complies with the following standards: IEC 3323c (March 1992), NFEN 50 266-2 section 4 of February 1999, and NFC 32070 section 2 and 2.2 of March 1991, and the additions A1 of July 1992 and A2 of November 1993, and a water resistance such that it resists salt water (10 g / l NaCl) at 60 ° C at a voltage of 220 V DC for at least ten days, complying with NFC-32-201-2, art. October 2.5, 1998 and NFC-32-201-1 table 3, section October 5, 1998.

We have found that the above problems can be solved by developing a cable that has a double layer, the layers having relative thicknesses such that the cable has at the same time improved fire resistance properties and improved water resistance properties, in both cases complying with the standards cited above.

Description of the invention

The invention provides a fire resistant and water resistant low voltage electrical cable, which includes a conductor and a first internal layer to protect it against water based on a polymer compound that

ES 2 238 043 T3 does not contain any halogens, cross-linked or not, and a second layer consisting of a mixture of crystalline propylene homopolymer or copolymer or a copolymer of ethylene and at least one α-olefin, optionally with a diene, and in an agent having fire retardant properties, the ratio of the thickness of the outer layer and the inner layer being comprised between 1 and 7.

Depending on the cross section of the conductor, the inner layer preferably has a thickness between 0.05 and 1 mm and the outer layer preferably has a thickness between 0.25 and 2 mm.

According to the invention, the inner layer covering the conductor is a layer of an olefin polymer containing no halide, crosslinked or not, preferably chosen from polyolefins and more particularly homopolymers or copolymers, copolymers of an olefin with esters, polyesters , ethylenically unsaturated polyethers, polyether / polyester copolymers, and mixtures thereof.

Polymers can include polyethylene and in particular linear low-density polyethylene (LLDPE), polypropylene, a propylene-ethylene thermoplastic copolymer, ethylene-propylene rubbers (EPR) or ethylene-propylene-diene rubbers (EPDM), natural rubbers, butyl rubbers, copolymers ethylene / vinyl acetate (EVA), ethylene / methacrylate copolymers (EMA), ethylene / ethyl acrylate copolymers (EEA), ethylene / butyl acrylate copolymers (EBA) and ethylene / α-olefin copolymers.

The outer fire retardant layer is preferably a mixture of crystalline propylene homopolymer or copolymer and of a copolymer of ethylene with an α-olefin, possibly with a diene, said copolymers having a narrow molecular weight distribution, characterized by a distribution index molecular weight, defined with the ratio of the molecular weight of average weight MW to the molecular weight of number average Mn, less than 5, preferably between 1.5 and 3.5, as determined by gel permeation chromatography and a fire retardant.

The α-olefins can be α-olefins with the formula:

CH₂ = CH-R where R is a linear or branched alkyl radical having between 1 and 10 carbon atoms.

In particular, it can be propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-dodecene, etc.

The α-olefins are preferably the propylene, 1-hexene and 1-octene radicals.

When the α-olefin is propylene, the copolymers can be characterized by high domain regularity in the sequence of monomer units. In particular, these copolymers have a number of CH2 groups in the sequences - (CH₂)_n-, where n is an integer, with respect to the total number of CH groups₂ less than 5% / mol, preferably less than 1% / mol. This can be determined by NMR analysis using carbon-13. This is known in the art.

When the comonomer is a diene, it generally has 4 to 20 carbon atoms and is preferably chosen from conjugated or unconjugated linear diolefins such as, for example, 1,3-butadiene, 1,4-hexadiene or 1,6-octadiene; Monocyclic or polycyclic dienes such as, for example, 1,4-cyclohexadiene, 5-ethylidene norbornene, 5-methylene-2-norbornene, etc.

According to the invention, the composition of the outer layer is obtained using mixtures of the two polymers containing between 5 and 60% by weight and preferably between 10 and 40% by weight of a crystalline propylene homopolymer or copolymer (a ) and between 40 and 95% by weight of the ethylene / α-olefin copolymer (b) with respect to the total weight of the polymer components of the compound.

The compounds preferably contain, as fire retardants, natural or synthetic aluminum and / or magnesium hydroxide. Natural magnesium oxide can be obtained, for example, by grinding magnesium hydroxide-based minerals such as brucite. Brucite can generally be obtained by mixing with other minerals such as calcite, dragonite, talc or magnesite, often in laminar form between silicate deposits, especially in asbestos, chlorites or schists.

According to the invention, brucite is ground using a wet or dry technique known in the art and in the presence of additives such as polyglycols.

The specific surface area of ​​the ground product is generally between 3 and 20 m²/ g and preferably between 6 and 15 m²/ g.

The ground product can be subjected to a separation process to obtain a range of particle sizes between 1 and 15 μιη, and preferably between 1 and 5 pm. The particle distribution is such that it is less than 10% of the

ES 2 238 043 T3 total number of particles having a particle size less than 1.5 µm and less than 10% of the total number of particles having a particle size greater than 20 µm.

If the fire retardant is of natural origin, it may contain various impurities derived from metal oxides and / or hydroxides such as iron, manganese, calcium, silicon, vanadium, etc.

Magnesium hydroxide obtained by chemical procedures known in the art can also be used, for example by basic precipitation from an aqueous solution containing the Mg ion.²⁺.

Magnesium hydroxide can be used as such or it can be treated with saturated or unsaturated fatty acids containing 8 to 24 carbon acids or metal salts thereof, for example with oleic acid, palmitic acid, stearic acid, isostearic acid , lauric acid, magnesium or zinc stearate, magnesium or zinc oleate.

The particles can also be surface treated with coupling agents such as organic titanates or silanes, such as vinyltriethoxysilane, vinyltriacetylsilane, tetraisopropyltitanate, tetra-n-butyl titanate, etc.

The copolymers (b) of the outer layer are preferably copolymers of ethylene with at least one α-olefin C₃C₁₂, possibly a diene, these copolymers having elastomeric properties characterized by:

- an enthalpy of fusion less than 35 J / g and preferably less than 30 J / g;

- an intrinsic viscosity (η) generally greater than 100 l / kg (1.0 dl / g), and preferably greater than 200 l / kg (2.0 dl / g), determined in tetralin at 135 ° C;

- a Money ML (1 + 4) viscosity at 125 ° C, measured by the ASTM D 1646 standard, generally greater than 10 and preferably between 20 and 90;

- a solubility in pentane at 20 ° C generally greater than 80% by weight; Y

- a permanent adjustment of less than 30% measured one minute after removal of the tension, which allowed an elongation to 20% according to the ASTM D 412 standard.

These copolymers generally have the following composition: 35 to 90 mole% of ethylene, 10 to 65 mole% of α-olefin, preferably propylene, 0.10 mole% of a diene, preferably 1,4-hexadiene or 5-ethylidene norbornene.

When the α-olefin is propylene, the composition of the monomer is preferably as follows: 55 to 80% by weight and preferably 65 to 75% by weight of ethylene, 20 to 45% by weight and preferably 25 to 35% by weight of propylene ; 0 to 10% by weight and preferably 0 to 5% by weight of diene (preferably 5-ethylene-2-norbornene).

A second family of copolymers that can be used in the outer layer are copolymers of ethylene with at least one α-olefin C₄-C₁₂, preferably 1-octene, and possibly a diene, characterized by:

- a density between 0.86 and 0.90 g / cm³;

- an enthalpy of fusion between 30 and 60 J / g;

- a melt flow index measured according to the ASTM D 1238 L standard of between 0.1 and 30 g / 10 minutes, preferably between 0.5 and 5 g / 10 minutes.

These copolymers preferably have the following composition: 75 to 97 mol% and preferably 90 to 95 mol% of ethylene; 3 to 25 mol% and preferably 5 to 10 mol% of α-olefin and 0 to 5 mol% and preferably 0.2 mol% of a diene.

Crystalline propylene homopolymers or copolymers generally have an enthalpy of melt greater than 75 J / g and preferably greater than 85 J / g. Preferably they are chosen between:

- isotactic propylene homopolymers having an isotactic index greater than 80, preferably greater than 90 and in particular greater than 95;

- propylene homopolymers obtained using metallocene catalysts, having a mmmmm pentad concentration greater than 90% as determined by NMR analysis using carbon-13;

- copolymers of propylene with ethylene or an α-olefin having between 4 and 10 carbon atoms and a concentration of ethylene and / or α-olefin of less than 10 mol%;

- Heterophase propylene copolymers that can be obtained by block polymerization of propylene and mixtures of propylene with ethylene and / or an α-olefin having 4 to 10 carbon atoms and containing at least 70% by weight of homopolymers of propylene and crystalline ethylene / propylene copolymers with an isotactic index

ES 2 238 043 T3 greater than 80, the remainder consisting of elastomeric ethylene / propylene copolymers with a propylene content of 30 to 70% by weight; Y

- crystalline propylene homopolymers or copolymers having a syndiotactic structure that can be obtained using metallocene catalysts.

The amount of magnesium hydroxide used as a fire retardant is finally between 10 and 90% by weight and preferably between 30 and 80% by weight with respect to the total weight of the compound.

Other fillers that have flame retardant properties can be used, such as aluminum hydroxide or aluminum trihydrate (Al₂OR₃-3H₂O) or one or more inorganic oxides or salts such as CoO, TiO₂, Sb₂OR₃, ZnO, Fe₂OR₃, CaCO₃ or mixtures thereof.

As indicated above, to improve the compatibility of the magnesium hydroxide with the polymer matrix, coupling agents can be used to improve the interaction between the hydroxyl groups of the magnesium hydroxide and the polyolefin chains.

Coupling agents are preferably chosen from unsaturated silane derivatives, preferably silanes containing at least one ethylenically unsaturated group: epoxides containing one ethylenically unsaturated group, monocarboxylic acids or preferably dicarboxylic acids having at least one ethylenically unsaturated group or derivatives thereof, such as anhydrides or esters.

Silanes include γ-methacryloxypropyltrimethoxysilane, methyltriethoxysilane, tris- (2-methoxyethoxy) methylsilane, dimethyldiethoxysilane, tris- (2-methoxyethoxy) vinyl silane, vinyltromethoxysilane, isyltriethoxysilane, and mixtures of isyltriethoxysylanoxysilane.

Epoxides include glycidyl acrylates, glycidyl methacrylates, the monoglycyl ester of itaconic acid, the glycidyl ester of maleic acid, vinyl glycidyl ether, allyl glycidyl ether, or mixtures thereof.

Monocarboxylic acids or dicarboxylic acids include an ethylenically unsaturated group including maleic acid, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, acrylic acid, methacrylic acid, their esters and anhydrides or mixtures thereof, with maleic anhydride being preferred.

The coupling agent is generally used in amounts between 0.01 and 5% by weight and preferably between 0.05 and 2% by weight relative to the total weight of the base polymer mixture.

These compounds can also contain antioxidants, processing aids, lubricants, pigments, and other fillers.

The compounds are prepared by mixing the polymers and additives by procedures known in the art.

The layers can be applied by extrusion, for example, or by extrusion in two separate stages, consisting of extruding the inner layer onto the conductor in a first stage and the outer layer onto the inner layer in a second stage.

In a preferred embodiment, the two layers are applied in a single step using a so-called "tandem" process, in which two separate extruders are used in series or by coextrusion using a single extrusion head.

The cables according to the invention are designed in particular to be used in environments where there are humidity problems or places for which there are special safety conditions in case of fire, such as public places, storage areas, test areas or work areas that they are prone to receiving flammable products. They have improved short circuit resistance.

The following examples are intended to illustrate the invention without limiting it.

The following composition was prepared:

ES 2 238 043 T3

TABLE I

<td>Composition</td><td>% in weigh</td>

<td>Engage 8003</td><td> 20,9</td>

<td>Moplen EP 1X35 F</td><td> 3,7</td>

<td>Hydrofy G. 1.5 S</td><td> 73,3</td>

<td>Irganox MD 1024</td><td> 0,074</td>

<td>Irganox 1010</td><td> 0,20</td>

<td>Stearic acid</td><td> 0,37</td>

<td>Silane VTMOEO</td><td> 0,74</td>

<td>Peroximon DC</td><td> 0,074</td>

The cable had a cross section of 1.5 mm² and a nominal total insulation thickness of 0.7 mm.

TABLE II

<td>Show</td><td>TO</td><td>B</td><td>C</td>

<td>Composition (Table I)</td><td> 0,7</td><td> 0,5</td><td> 0,2</td>

<td>(Outer layer - mm)</td><td></td><td></td><td></td>

<td>Escorene LL 1004</td><td> 0</td><td> 0,2</td><td> 0,5</td>

<td>(inner layer - mm)</td><td></td><td></td><td></td>

<td>Tensile strength (MPa) *</td><td> 12,2</td><td> 14,2</td><td> 17,6</td>

<td>Elongation at break (%) **</td><td> 110</td><td> 170</td><td> 210</td>

<td>Saltwater aging **</td><td>Not</td><td>Yes</td><td>Yes</td>

<td>(10 days) (NF-C 32-201-2)</td><td></td><td></td><td></td>

<td>Fire spread test</td><td>Yes</td><td>Yes</td><td>Not</td>

<td>(IEC 332.3C of March 1992)</td><td></td><td></td><td></td>

<td>Elongation at break</td><td>Not</td><td>Yes</td><td>Yes</td>

<td>Tension at break</td><td>Not</td><td>Yes</td><td>Yes</td>

* According to standard NF-C 32-201-1, table 1 section 1.1 column 6, October 1998.

** According to standard NF-C 32-201-2, art. 2-5, October 1998 and NF-C 32-201-1, table 3 section 5, October

1998.

Examples A and C are comparative.

Escorene LL 1004 is classified as a linear low density polyethylene. It is an ethylene / 1-butene copolymer produced by Exxon-Mobil with an MFI: 2.8 g / 10 min, a density: 0.918 g / cm³ and a melting point: 121 ° C. Its volume resistivity in direct current is at least 1 * 10¹⁵ ohm * cm.

Engage 8003 is an ethylene / 1-octene copolymer obtained by metallocene catalysis.

The ethylene / 1-octene weight ratio was equal to 82/18 (5.5 molar% 1-octene, density = 0.885 g / cm³; MFI = 1.0 g / 10 minutes; CDI&gt; 70%; AH2m = 55.6 J / g).

Moplen (EP 1X35 HF) is a crystalline propylene / ethylene copolymer (d = 0.900 g / cm³; MFI = 9.0 g / 10 minutes; T_m = 154 ° C; AH2m = 90.6 J / g).

ES 2 238 043 T3

Hydrofy G 1.5 S is a SIMA magnesium hydroxide surface treated with stearic acid and has an aqueous extract conductivity of 290 pS / cm, a specific surface area of ​​10.4 m²/ g; and a particle size distribution expressed in pm of:

TABLE III

<td> 10%</td><td> 50%</td><td> 80%</td>

<td>0.7 (average)</td><td> 2,1</td><td> 6,4</td>

Irganox MD 1024 is an antioxidant from CIBA with the formula:

<img file="ES2238043T3_D0001.tif" />

Irganox 1010 is an antioxidant from CIBA that has the formula:

<img file="ES2238043T3_D0002.tif" />

VTMOEO silane is tris- (2-methoxyethoxy) vinyl silane with the formula CH₂= CH-Si (OCH₂H₄OCH₃)₃ with a purity of not less than 99% by weight.

Peroximon DC is dicumyl peroxide with a purity of not less than 99% by weight and the following formula:

CH3 CH3

II

CJI-. —C - O - O - C - GIL II

CH3 CH3