Ductile flame-retardant polyamide compositions and uses thereof, in particular for railways

Abstract

The present invention relates to a flame-retardant composition comprising: ((a) from 30 to 85 wt%, for example from 33 to 83 wt%, in particular from 50 to 78.9 wt%, of at least one semicrystalline aliphatic polyamide having an inherent viscosity ranging from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to ISO 307:2007 but using m-cresol instead of sulphuric acid, a temperature of 20°C and a concentration of 0.5 wt%; (b) from 10 to 30 wt%, for example from 10 to 25 wt%, for example from 14 to 25 wt%, for example from 14 to 22 wt%, for example from 17 to 22 wt% of at least one phosphinate flame retardant; (c) from 5 to 20 wt%, in particular from 5 to 15 wt% of at least one functionalised polyolefin; (d) from 2 to 8 wt%, in particular from 2 to 6 wt% of at least one plasticiser; (e) from 0 to 10 wt%, in particular from 0.1 to 5 wt% of at least one additive.

Description

[0001] DESCRIPTION

[0002] TITLE OF INVENTION: DUCTILE FLAME-RETARDANT POLYAMIDE COMPOSITIONS AND THEIR USE, PARTICULARLY FOR RAILWAY APPLICATIONS

[0003] The present invention relates to ductile flame-retardant polyamide compositions and their use, in particular for railway applications and the preparation of tubes, in particular corrugated tubes.

[0004] The railway sector tends to use materials with high mechanical resistance and good resistance to aging.

[0005] More recently, materials used in trains must meet technical requirements in terms of fire resistance. These requirements depend on the type of object and its use in the train. The EN 45545 standard sets different specifications depending on the material category. Polyamide tubes correspond to categories R22 and R23.

[0006] Products are classified according to their oxygen limit index as well as the density and toxicity of the fumes they generate during combustion. Three classifications HL1, HL2 or HL3 can be achieved depending on their fire properties.

[0007] The higher this classification, the more the product can be used in a wide range of trains, whereas a product classified as HL1 cannot be used in an underground metro, for example.

[0008] The HL2 category today covers the majority of the existing market and is the target audience in general, which means in particular a measurement of limit oxygen level (LOI) > 28.

[0009] Beyond this fire resistance, the materials used in trains are also subject to numerous mechanical stresses which cover the following properties:

[0010] - Flexibility: the modulus must be between 500 and 1200 MPa,

[0011] - Flexibility / Pliability: Ability to deform a tube without crunching, associated with behavior at the plasticity threshold (low stress and high elongation)

[0012] - Breaking strength: the elongation at break in tension must be greater than 100%

[0013] - Impact resistance over a temperature range down to -30°C,

[0014] - Resistance to fatigue.

[0015] These properties must be maintained over time. The products must therefore be able to withstand accelerated thermal aging for several days at 150°C.

[0016] Finally, the implementation by extrusion of the polyamide must remain easy, which limits the viscosity that the formulation can present.

[0017] The prior art already describes flame-retardant formulations such as in application US20170037198 which describes formulations for the railway sector focusing specifically on a PA12 matrix.

[0018] However, these formulations do not meet all the requirements listed above, particularly for mechanical properties. Still in the railway field, international application WO 2013 / 092302 deals with polyamides reinforced with glass fiber and flame retardant with a melamine derivative.

[0019] Finally, application US 2007 / 0021535 combines the use of phosphinate, melamine cyanurate and polyol as a flame retardant for a polyamide.

[0020] However, the same drawbacks relating to the above-listed requirements, particularly for mechanical properties, remain.

[0021] New products must therefore be developed to provide good protection for equipment and passengers in the event of fire.

[0022] A more advanced formulation presenting an improved compromise, in particular an optimum, between mechanical resistance and fire resistance is therefore necessary.

[0023] The present invention therefore relates to a flame-retardant composition comprising by weight:

[0024] (a) from 30 to 85% by weight, in particular from 33 to 83% by weight, in particular from 50 to 78.9% by weight, of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass,

[0025] (b) from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight of at least one phosphinate flame retardant,

[0026] (c) from 5 to 20% by weight, in particular from 5 to 15% by weight of at least one functionalized polyolefin,

[0027] (d) from 2 to 8% by weight, in particular from 2 to 6% by weight of at least one plasticizer,

[0028] (e) from 0 to 10% by weight, in particular from 0.1 to 5% by weight of at least one additive.

[0029] The inventors have therefore found that a semi-crystalline aliphatic polyamide, in particular proportions and having a particular inherent viscosity, associated with at least one phosphinate-type flame retardant, a functionalized polyolefin and a plasticizer, all three in an equally particular proportion, with optionally an additive, allowed the constitution of a composition meeting all the requirements listed above.

[0030] The viscosity of the semi-crystalline aliphatic polyamide matrix is ​​essential in particular for fatigue resistance. An inherent viscosity that is too low, i.e. less than 1.2, will not be sufficiently resistant to fatigue. Compositions based on semi-crystalline aliphatic polyamide with a viscosity of less than 1.2 would thus have insufficient mechanical properties for the intended application, in particular for an application as a tube, in particular corrugated, for a railway application. Compositions based on semi-crystalline aliphatic polyamide with a viscosity of less than 1.2 would in particular have insufficient fatigue resistance. Fatigue resistance can in particular be measured by a Ross Flex test as described in the examples.Compositions in accordance with the invention, namely comprising in particular a semi-crystalline aliphatic polyamide with a viscosity greater than 1.2, advantageously make it possible to satisfy this test, that is to say to prepare bars which are not broken after 400,000 cycles, according to the Ross Flex test described in the examples.

[0031] Too high a viscosity, particularly above 1.6, will no longer allow the composition to be shaped, particularly in the form of a corrugated tube.

[0032] Compositions based on semi-crystalline aliphatic polyamide with a viscosity in particular greater than 1.6 could not in particular be extruded at usual forming temperatures, in particular at temperatures less than or equal to 350°C, preferably less than or equal to 320°C, preferably between 170°C and 300°C, for example between 200 and 280°C. Such compositions would have to be extruded at significantly higher temperatures and / or with higher shear rates, which would have the consequence of impacting in particular the fire resistance properties of the resulting tube, the flame retardant being at least partially, or even totally, degraded under such processing conditions. These compositions would thus have insufficient fire resistance properties for the intended application, in particular for an application as a tube, in particular corrugated, for a railway application.Compositions based on semi-crystalline aliphatic polyamide with too high a viscosity, in particular greater than 1.6, would in particular have a limiting oxygen level (LOI) lower than the value sought to satisfy standard EN 45545 for categories R22 and R23. Compositions in accordance with the invention, namely comprising in particular a semi-crystalline aliphatic polyamide with a viscosity of less than 1.6, preferably less than 1.5, preferably strictly less than 1.5, advantageously make it possible to satisfy this test, as illustrated in the examples.

[0033] The plasticizer range allows the composition to have a sufficiently low modulus without compromising cold impact resistance.

[0034] Compositions comprising less than 2% by weight of plasticizer relative to the total weight of the composition could thus have insufficient mechanical properties for the intended application, in particular for an application as a tube, in particular corrugated, for a railway application. Compositions comprising less than 2% by weight of plasticizer relative to the total weight of the composition could in particular have too high a tensile modulus, in particular a tensile modulus greater than 1200 MPa, this parameter being measured as described in the examples. Compositions in accordance with the invention, namely comprising in particular at least 2% by weight of plasticizer relative to the total weight of the composition, advantageously make it possible to achieve satisfactory mechanical properties, in particular a tensile modulus less than 1200 MPa, this parameter being measured as described in the examples.Compositions comprising more than 8% by weight of plasticizer relative to the total weight of the composition could have insufficient mechanical properties for the intended application, in particular for an application as a tube, in particular corrugated, for a railway application. Compositions comprising more than 8% by weight of plasticizer relative to the total weight of the composition could have in particular a cold notched impact strength of less than 5 kJ / m. 2 , this parameter being measured as described in the examples. Compositions in accordance with the invention, namely comprising in particular up to 8% by weight of plasticizer relative to the total weight of the composition, advantageously make it possible to achieve satisfactory mechanical properties, in particular a cold notched impact strength greater than or equal to 5 kJ / m 2 , this parameter being measured as described in the examples.

[0035] The range of functionalized polyolefin makes it possible to obtain good fatigue resistance and / or good cold impact resistance, without excessively increasing the fire sensitivity of said composition. Compositions comprising less than 5% by weight of functionalized polyolefin relative to the total weight of the composition would thus have insufficient mechanical properties for the intended application, in particular for an application as a tube, in particular corrugated, for a railway application. Compositions comprising less than 5% by weight of functionalized polyolefin relative to the total weight of the composition would in particular have a cold notched impact resistance of less than 5 kJ / m 2, this parameter being measured as described in the examples. Compositions in accordance with the invention, namely comprising in particular at least 5% by weight of functionalized polyolefin relative to the total weight of the composition, advantageously make it possible to achieve satisfactory mechanical properties, in particular a cold notched impact strength greater than or equal to 5 kJ / m 2 , this parameter being measured as described in the examples.

[0036] Compositions comprising more than 20% by weight of functionalized polyolefin relative to the total weight of the composition would also have insufficient fire resistance properties for the intended application, in particular for an application as a tube, in particular corrugated, for a railway application. Compositions comprising more than 20% by weight of functionalized polyolefin relative to the total weight of the composition would in particular have a limiting oxygen level (LOI) lower than the value sought to satisfy standard EN 45545 for categories R22 and R23. Compositions in accordance with the invention, namely comprising in particular a functionalized polyolefin in a content of less than 20% by weight, relative to the total weight of the composition, advantageously make it possible to satisfy this test, as illustrated in the examples.The range of flame retardant as defined according to the invention makes it possible to obtain sufficient fire resistance, and in particular to obtain compositions having in particular a limiting oxygen level (LOI) higher than the value sought to satisfy the EN 45545 standard for categories R22 and R23, while maintaining satisfactory mechanical properties, in particular without excessively weakening the product. Compositions comprising less than 10% by weight of flame retardant relative to the total weight of the composition generally do not make it possible to achieve the value sought to satisfy the EN 45545 standard for categories R22 and R23, as defined in the examples. Compositions comprising more than 30% by weight of flame retardant relative to the total weight of the composition could have insufficient mechanical properties, in particular a cold notched impact strength of less than 5 kJ / m. 2, this parameter being measured as described in the examples. Compositions in accordance with the invention, namely comprising in particular up to 30% by weight of flame retardant relative to the total weight of the composition, preferably up to 25% by weight, in particular up to 22% by weight, advantageously make it possible to achieve satisfactory mechanical properties, in particular a cold notched impact strength greater than or equal to 5 kJ / m 2 , this parameter being measured as described in the examples.

[0037] It is therefore a compromise, in particular an optimum, which can only be achieved by the particular selection of the ranges of the different constituents of the composition. Advantageously, said composition is intended for a railway application.

[0038] The invention also covers the use of compositions as defined according to the invention for the manufacture of flame-retardant articles, in particular tubes, intended for railway applications, and in particular intended for applications in trains.

[0039] Regarding semi-crystalline aliphatic polyamide (a)

[0040] The compositions of the invention comprise at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, as determined according to ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass.

[0041] According to one embodiment, the compositions of the invention comprise at least one semi-crystalline aliphatic polyamide having an inherent viscosity strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by weight. Said at least one semi-crystalline aliphatic polyamide (a) is present in a content ranging from 30 to 85% by weight, in particular from 33 to 83% by weight, in particular from 50 to 78.9% by weight, relative to the total weight of the composition.

[0042] Semi-crystalline polyamide is understood to mean a material which is generally solid at room temperature and which softens when the temperature increases, in particular after passing its glass transition temperature (Tg), and which can exhibit a clear melting when passing its so-called melting temperature (Tf), and which becomes solid again when the temperature decreases below its crystallization temperature.

[0043] Tg, Te and Tf are determined by differential scanning calorimetry (DSC) according to standard 11357-2:2013 and 11357-3:2013 respectively.

[0044] The number-average molecular mass Mn of said semi-crystalline polyamide is preferably in a range from 10,000 to 85,000, in particular from 10,000 to 60,000, preferably from 10,000 to 50,000, even more preferably from 12,000 to 50,000.

[0045] The nomenclature used to define polyamides is described in ISO 1874-1:2011 “Plastics - Polyamide (PA) materials for molding and extrusion - Part 1: Designation”, particularly on page 3 (tables 1 and 2) and is well known to those skilled in the art.

[0046] The term polyamide includes both homopolyamides and copolyamides.

[0047] Said at least one aliphatic semi-crystalline polyamide is obtained from the polycondensation of at least one lactam, or from the polycondensation of at least one amino acid, or from the polycondensation of at least one diamine X with at least one dicarboxylic acid Y or from their mixtures.

[0048] When said at least one aliphatic semi-crystalline polyamide is obtained from the polycondensation of at least one lactam, said at least one lactam may be chosen from a C6 to C18 lactam, preferably a C9 to C18 lactam, more preferably a C10 to C18 lactam, more preferably a C10 to C11 lactam. A C8 to C18 lactam is in particular decanolactam, undecanolactam.

[0049] When said at least one aliphatic semi-crystalline polyamide is obtained from the polycondensation of at least one lactam, it can therefore comprise a single lactam or several lactams.

[0050] When said at least one aliphatic semi-crystalline polyamide is obtained from the polycondensation of at least one amino acid, said at least one amino acid may be chosen from a C6 to C18 amino acid, preferably a C9 to C18 amino acid, more preferably a C10 to C18 amino acid, more preferably a C10 to C11 amino acid. A C6 to C18 amino acid is in particular 9-aminononanoic acid, 10-aminodecanoic acid and 11-aminoundecanoic acid as well as its derivatives, in particular N-heptyl-11-aminoundecanoic acid.

[0051] When said at least one aliphatic semi-crystalline polyamide is obtained from the polycondensation of at least one amino acid, it can therefore comprise a single amino acid or several amino acids.

[0052] Advantageously, said aliphatic semi-crystalline polyamide is obtained from the polycondensation of a single amino acid and said amino acid is chosen from 10-aminodecanoic acid and 11-aminoundecanoic acid, advantageously 11-aminoundecanoic acid.

[0053] When said at least one aliphatic semi-crystalline polyamide is obtained from the polycondensation of at least one C4-C36, preferably C6-C18, preferably C6-C12, more preferably C10-C12, diamine X with at least one C4-C36, preferably C6-C18, preferably C6-C12, more preferably C10-C12, diacid Y, then said at least one X diamine is an aliphatic diamine and said at least one Y diacid is an aliphatic diacid.

[0054] The diamine can be linear or branched. Advantageously, it is linear.

[0055] Said at least one C4-C36 diamine X may in particular be chosen from 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 1,12-dodecamethyldiamine, 1,13-tridecarnethylenediamine, 1,14-tetradecamethylenediamine, 1,16-hexadecamethylenediamine and 1,18-octadecamethylenediamine, octadecenediamine, eicosanediamine, docosanediamine and diamines obtained from fatty acids.

[0056] Advantageously, said at least one diamine X is C6-C18 and chosen from 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 1,12-dodecamethylenediamine, 1,13-tridecamethylenediamine, 1,14-tetradecamethylenediamine, 1,16-hexadecamethylenediamine and 1,18-octadecamethylenediamine.

[0057] Advantageously, said at least one diamine X in C6 to C12, is in particular chosen from 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 1,12-dodecamethylenediamine.

[0058] Advantageously, the diamine X used is C10 to C12, in particular chosen from 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 1,12-dodecamethylenediamine. Said at least one C4 to C36 dicarboxylic acid Y may be chosen from succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, octadecanedioic acid, and diacids obtained from fatty acids.

[0059] The diacid can be linear or branched. Advantageously, it is linear.

[0060] Advantageously, said at least one dicarboxylic acid Y is C6 to C18 and is chosen from adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, octadecanedioic acid.

[0061] Advantageously, said at least one dicarboxylic acid Y is C6 to C12 and is chosen from adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid.

[0062] Advantageously, said at least one dicarboxylic acid Y is C10 to C12 and is chosen from sebacic acid, undecanedioic acid, dodecanedioic acid.

[0063] When said aliphatic semi-crystalline polyamide is obtained from the polycondensation of at least one diamine X with at least one dicarboxylic acid Y, it can therefore comprise a single diamine or several diamines and a single dicarboxylic acid or several dicarboxylic acids. Advantageously, said aliphatic semi-crystalline polyamide is obtained from the polycondensation of a single diamine X with a single dicarboxylic acid Y.

[0064] In one embodiment, said at least one polyamide is a long-chain polyamide having a number of carbons per nitrogen atom greater than or equal to 8, in particular greater than or equal to 9, in particular greater than or equal to 10.

[0065] In another embodiment, said at least one semi-crystalline aliphatic polyamide is chosen from polyamide PA610, PA612, PA1010, PA1012 and PAU.

[0066] Advantageously, said at least one semi-crystalline aliphatic polyamide is chosen from polyamides PA1010, PA1012 and PAU, in particular PAU.

[0067] According to one embodiment, the semi-crystalline aliphatic polyamide of the invention may be a poly ether block amide (PEBA).

[0068] Poly ether block amide (PEBA) are copolymers with amide units (Bal) and polyether units (Ba2), said amide unit (Bal) corresponding to an aliphatic repeating unit chosen from a unit obtained from at least one amino acid or a unit obtained from at least one lactam, or an XY unit obtained from polycondensation:

[0069] - at least one diamine, said diamine being chosen from a linear or branched aliphatic diamine, and - at least one dicarboxylic acid, said diacid being an aliphatic diacid, said polyether units (Ba2) being in particular derived from at least one polyalkylene ether polyol, in particular a polyalkylene ether diol.

[0070] According to one embodiment, the semi-crystalline aliphatic polyamide according to the invention is not a poly ether block amide (PEBA).

[0071] According to one embodiment, the semi-crystalline aliphatic polyamide according to the invention is not a PA12.

[0072] Regarding the phosphinate flame retardant (b)

[0073] A composition according to the invention must contain a quantity of phosphinate type flame retardant (b) sufficient to give said composition the desired fire resistance properties, and in particular a classification at risk level HL2, or even HL3, according to standard EN 45545, and preferably a classification at risk level HL2 according to standard EN 45545.

[0074] Said at least one phosphinate flame retardant (b) may be present in a content of at least 10% by weight, for example at least 14% by weight, for example at least 15% by weight, for example at least 17% by weight, relative to the total weight of the composition.

[0075] Too low a quantity of phosphinate flame retardant (b) does not allow sufficient fire resistance properties to be achieved, and in particular does not allow classification at risk level HL2, or even HL3 according to standard EN 45545, and in particular classification at risk level HL2 according to standard EN 45545.

[0076] The phosphinate flame retardant (b) must also not be present in excessively high proportions, at the risk of negatively impacting the mechanical properties. Thus, the phosphinate flame retardant (b) is generally present in a content of at most 40% by weight, typically up to 30% by weight, relative to the total weight of the composition.

[0077] Too high a quantity of phosphinate flame retardant (b) can have negative consequences on the mechanical properties, and in particular reduce the breaking strength and / or the impact strength and / or the fatigue resistance.

[0078] According to one embodiment, the phosphinate flame retardant (b) is present in a content ranging from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight, relative to the total weight of the composition. For example, said at least one phosphinate flame retardant (b) may be present in a content ranging from 14 to 20% by weight relative to the total weight of the composition.

[0079] The flame retardant is in particular a metal salt chosen from a metal salt of phosphinic acid, a metal salt of diphosphinic acid, a polymer containing at least one metal salt of phosphinic acid, a polymer containing at least one metal salt of diphosphinic acid. The flame retardant may also be a mixture of the aforementioned flame retardants. The flame retardant agent may also be chosen from the metal salt of phosphinic acid of the following formula (I) and the metal salt of diphosphinic acid of the following formula (II):

[0080] [Chem 1] with

[0081] RI and R2, independently of each other, denote a linear or branched C1-C6 alkyl group, or an aryl group;

[0082] R3 represents a linear or branched C1-C10 alkylene, C6-C10 arylene, C6-C10 alkylarylene, or C6-C10 arylalkylene group,

[0083] M is an ion of Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K and / or a protonated amine base m denotes an integer from 1 to 4, n denotes an integer from 1 to 4, x denotes an integer from 1 to 4, n and m being chosen so that the salt is neutral, i.e. it does not carry an electric charge.

[0084] Preferably, M represents a calcium, magnesium, aluminum or zinc ion.

[0085] Preferably, R1 and R2, independently of each other, denote a methyl, ethyl, n-propyl, iso-propyl, n-butyl, tert-butyl, n-pentyl and / or phenyl group.

[0086] Preferably, R3 represents a methylene, ethylene, n-propylene, iso-propylene, n-butylene, tert-butylene, n-pentylene, n-octylene, n-dodecylene group; phenylene, naphthylene; methylphenylene, ethylphenylene, tert-butylphenylene, methylnaphthylene, ethylnaphthylene, tert-butylnaphthylene; phenylmethylene, phenylethylene, phenylpropylene, or phenylbutylene.

[0087] According to one embodiment, the flame retardant may be an aluminum diethyl phosphinate. Examples of such compounds include the product Exolit OP1311 marketed by Clariant. With regard to the functionalized polyolefin (c)

[0088] A composition according to the invention must contain a quantity of functionalized polyolefin sufficient to give said composition the mechanical properties sought for the intended application, in particular good fatigue resistance.

[0089] Said at least one functionalized polyolefin (c) is present from 5 to 20% by weight, in particular from 5 to 15% by weight, relative to the total weight of the composition.

[0090] The functionalized polyolefin may be a polymer of alpha olefins having reactive units (the functionalities); such reactive units are acid, anhydride, or epoxy functions. For example, non-functionalized polyolefins grafted or co- or terpolymerized by unsaturated epoxides such as glycidyl (meth)acrylate, or by carboxylic acids or the corresponding salts or esters such as (meth)acrylic acid (which may be neutralized totally or partially by metals such as Zn, etc.) or by carboxylic acid anhydrides such as maleic anhydride may be mentioned.

[0091] A non-functionalized polyolefin is typically a homopolymer or copolymer of alpha olefins or diolefins, such as, for example, ethylene, propylene, butene-1, octene-1, butadiene. Examples include:

[0092] - homopolymers and copolymers of polyethylene, in particular LDPE, HDPE, LLDPE (linear low density polyethylene), VLDPE (very low density polyethylene) and metallocene polyethylene.

[0093] - homopolymers or copolymers of propylene.

[0094] - ethylene / alpha-olefin copolymers such as ethylene / propylene, EPR (abbreviation of ethylene-propylene-rubber) and ethylene / propylene / diene (EPDM).

[0095] - styrene / ethylene-butene / styrene (SEBS), styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), styrene / ethylene-propylene / styrene (SEPS) block copolymers.

[0096] - copolymers of ethylene with at least one product chosen from salts or esters of unsaturated carboxylic acids such as alkyl (meth)acrylate (for example methyl acrylate), or vinyl esters of saturated carboxylic acids such as vinyl acetate (EVA), the proportion of comonomer being able to reach 40% by weight.

[0097] A functionalized polyolefin is, for example, a PE / EPR blend, the weight ratio of which can vary widely, for example between 40 / 60 and 90 / 10, said blend being co-grafted with an anhydride, in particular maleic anhydride, according to a grafting rate of, for example, 0.01 to 5% by weight.

[0098] The functionalized polyolefin can be chosen from the following (co)polymers, grafted with maleic anhydride or glycidyl methacrylate, in which the grafting rate is for example from 0.01 to 5% by weight: - PE, PP, copolymers of ethylene with propylene, butene, hexene, or octene containing for example from 35 to 80% by weight of ethylene;

[0099] - ethylene / alpha-olefin copolymers such as ethylene / propylene, EPR (abbreviation of ethylene-propylene-rubber) and ethylene / propylene / diene (EPDM).

[0100] - styrene / ethylene-butene / styrene (SEBS), styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), styrene / ethylene-propylene / styrene (SEPS) block copolymers.

[0101] - ethylene and vinyl acetate (EVA) copolymers, containing up to 40% by weight of vinyl acetate;

[0102] - ethylene and alkyl (meth)acrylate copolymers, containing up to 40% by weight of alkyl (meth)acrylate;

[0103] - ethylene vinyl acetate (EVA) and alkyl (meth)acrylate copolymers, containing up to 40% by weight of comonomers.

[0104] The functionalized polyolefin can also be chosen from ethylene / propylene copolymers with a majority of propylene grafted with maleic anhydride then condensed with mono-amine polyamide (or a polyamide oligomer) (products described in EP-A-0342066).

[0105] The functionalized polyolefin may also be a co- or terpolymer of at least the following units: (1) ethylene, (2) alkyl (meth)acrylate or saturated carboxylic acid vinyl ester and (3) anhydride such as maleic anhydride or (meth)acrylic acid or epoxy such as glycidyl (meth)acrylate.

[0106] As examples of functionalized polyolefins of the latter type, the following copolymers may be mentioned, where ethylene preferably represents at least 60% by weight and where the ter monomer (the function) represents, for example, from 0.1 to 10% by weight of the copolymer:

[0107] - ethylene / alkyl (meth)acrylate / (meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers;

[0108] - ethylene / vinyl acetate / maleic anhydride or glycidyl methacrylate copolymers;

[0109] - ethylene / vinyl acetate or alkyl (meth)acrylate / (meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers.

[0110] In the above copolymers, (meth)acrylic acid can be salified with Zn or Li.

[0111] The term "alkyl (meth)acrylate" means C1 to C8 alkyl methacrylates and acrylates, and may be selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate and ethyl methacrylate.

[0112] Furthermore, the aforementioned functionalized polyolefins can also be crosslinked by any suitable process or agent (diepoxy, diacid, peroxide, etc.); the term functionalized polyolefin also includes mixtures of the aforementioned polyolefins with a difunctional reagent such as diacid, dianhydride, diepoxy, etc. capable of reacting with them or mixtures of at least two functionalized polyolefins capable of reacting with each other.

[0113] The above-mentioned copolymers can be copolymerized in a statistical or block manner and have a linear or branched structure.

[0114] The molecular weight, MFI index, and density of these polyolefins can also vary widely, as those skilled in the art will appreciate. MFI, short for Melt Flow Index, is the melt flow index. It is measured according to ASTM 1238.

[0115] In one embodiment, the polyolefin is crosslinked.

[0116] According to one embodiment, the functionalized polyolefin can be chosen from homopolymers and copolymers of polyethylene, in particular LDPE, HDPE, LLDPE (linear low density polyethylene), VLDPE (very low density polyethylene) and metallocene polyethylene, and in particular from VLDPE (very low density polyethylene).

[0117] Examples of such compounds include the product Orevac IM800 marketed by the company SK Functional Polymer.

[0118] According to one embodiment, the functionalized polyolefin may be chosen from ethylene / alkyl (meth)acrylate / (meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers; ethylene / vinyl acetate / maleic anhydride or glycidyl methacrylate copolymers; ethylene / vinyl acetate or alkyl (meth)acrylate / (meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers.

[0119] Examples of such compounds include the Lodater AX8900 product marketed by SK Functional Polymer.

[0120] Regarding the plasticizer (d)

[0121] Said at least one plasticizer (e) may be present from 2 to 8% by weight, in particular from 2 to 6% by weight, relative to the total weight of the composition.

[0122] The plasticizer may be a plasticizer commonly used in compositions based on polyamide(s). Advantageously, a plasticizer is used which has good thermal stability so that fumes do not form during the stages of mixing the different polymers and transforming the composition obtained.

[0123] In particular, this plasticizer may be chosen from: benzene sulfonamide derivatives such as n-butyl benzene sulfonamide (BBSA), the ortho and para isomers of ethyl toluene sulfonamide (ETSA), N-cyclohexyl toluene sulfonamide and N-(2-hydroxypropyl) benzene sulfonamide (HP-BSA), hydroxybenzoic acid esters such as 2-ethylhexyl para-hydroxybenzoate (EHPB) and 2-decylhexyl para-hydroxybenzoate (HDPB), tetrahydrofurfuryl alcohol esters or ethers such as oligoethyleneoxy-tetrahydrofurfuryl alcohol, and citric acid or hydroxymalonic acid esters, such as oligoethyleneoxymalonate.

[0124] A preferred plasticizer is n-butyl benzene sulfonamide (BBSA).

[0125] Another particularly preferred plasticizer is N-(2-hydroxy-propyl) benzene sulfonamide (HP-BSA). This has the advantage of preventing the formation of deposits on the screw and / or the extrusion die ("die tears") during an extrusion processing step. A mixture of plasticizers can of course be used.

[0126] Regarding additives (e)

[0127] Said at least one additive (f) may be present from 0 to 10% by weight, in particular from 0.1 to 5% by weight, relative to the total weight of the composition.

[0128] The at least one additive may be selected from stabilizers, colorants, processing aids, surfactants, nucleating agents, pigments, brighteners, antioxidants, lubricants, waxes, flame retardant synergists, or a mixture thereof.

[0129] Advantageously, the at least one additive is chosen from antioxidants, colored pigments and flame retardant synergists, in particular melamine-based nitrogen synergists.

[0130] For example, the stabilizer may be a UV stabilizer, an organic stabilizer or more generally a combination of organic stabilizers, such as a phenol-type antioxidant (for example of the type of irganox® 245 or 1098 or 1010 from BASF), a phosphite-type antioxidant (for example irgafos® 126 or Irgafos® 168 from BASF) and possibly other stabilizers such as a HALS, which stands for Hindered Amine Light Stabilizer (for example Tinuvin® 770 from BASF), a UV stabilizer (for example Tinuvin® 312 from BASF), a phosphorus-based stabilizer. It is also possible to use amine-type antioxidants such as Naugard® 445 from Crompton or polyfunctional stabilizers such as Nylostab® S-EED from Clariant.

[0131] This stabilizer can also be a mineral stabilizer, such as a copper-based stabilizer. Examples of such mineral stabilizers include copper halides and acetates. Alternatively, other metals such as silver may be considered, but these are known to be less effective. These copper-based compounds are typically combined with alkali metal halides, particularly potassium.

[0132] The flame retardant synergist agents are in particular as described in WO2005121234.

[0133] They can be chosen from nitrogen synergists and phosphorus / nitrogen synergists. The nitrogen synergists preferably include benzoguanamine, tris(hydroxyethyl)isocyanurate, allantoin, glycoluril, melamine, melamine cyanurate, dicyandiamide, guanidine, carbodiimides.

[0134] The nitrogen synergists preferably comprise melamine condensation products. For example, the melamine condensation products are melem, melam or melon, or such compounds with a higher condensation rate, or a mixture thereof, and, for example, can be prepared by the process described in U.S. 5,985,960.

[0135] The phosphorus / nitrogen synergists may include reaction products of melamine with phosphoric acid or with condensed phosphoric acids, or include reaction products of condensation products of melamine with phosphoric acid or condensed phosphoric acids, or include a mixture of the specified products.

[0136] In one embodiment, the additives are chosen from antioxidants, colored pigments and flame retardant synergists, in particular nitrogen synergists, in particular based on melamine.

[0137] Regarding the composition

[0138] According to one embodiment, the flame-retardant composition comprises by weight:

[0139] (a) from 30 to 85% by weight, in particular from 33 to 83% by weight, in particular from 50 to 78.9% by weight, of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass,

[0140] (b) from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight, for example from 14 to 20% by weight of at least one phosphinate flame retardant,

[0141] (c) from 5 to 20% by weight, in particular from 5 to 15% by weight of at least one functionalized polyolefin,

[0142] (d) from 2 to 8% by weight, in particular from 2 to 6% by weight of at least one plasticizer,

[0143] (e) from 0 to 10% by weight, in particular from 0.1 to 5% by weight of at least one additive, the sum of constituents (a) to (e) being equal to 100% by weight.

[0144] According to one embodiment, the flame-retardant composition comprises by weight:

[0145] (a) from 30 to 85% by weight, in particular from 33 to 83% by weight, in particular from 50 to 78.9% by weight, of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass,

[0146] (b) from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight, for example from 14 to 20% by weight of at least one phosphinate flame retardant,

[0147] (c) from 5 to 20% by weight, in particular from 5 to 15% by weight of at least one functionalized polyolefin,

[0148] (d) from 2 to 8% by weight, in particular from 2 to 6% by weight of at least one plasticizer,

[0149] (e) from 0 to 10% by weight, in particular from 0.1 to 5% by weight of at least one additive, said composition being excluding PA12.

[0150] According to one embodiment, the flame-retardant composition comprises by weight:

[0151] (a) from 30 to 85% by weight, in particular from 33 to 83% by weight, in particular from 50 to 78.9% by weight, of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass,

[0152] (b) from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight, for example from 14 to 20% by weight of at least one phosphinate flame retardant,

[0153] (c) from 5 to 20% by weight, in particular from 5 to 15% by weight of at least one functionalized polyolefin,

[0154] (d) from 2 to 8% by weight, in particular from 2 to 6% by weight of at least one plasticizer,

[0155] (e) from 0 to 10% by weight, in particular from 0.1 to 5% by weight of at least one additive, said composition being excluding PA12 and the sum of constituents (a) to (e) being equal to 100% by weight.

[0156] In one embodiment, said composition comprises by weight:

[0157] (a) from 50 to 78.9% by weight of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass,

[0158] (b) from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight, for example from 14 to 20% by weight of at least one phosphinate flame retardant, (c) from 5 to 20% by weight, in particular from 5 to 15% by weight of at least one functionalized polyolefin,

[0159] (d) from 2 to 8% by weight, in particular from 2 to 6% by weight of at least one plasticizer,

[0160] (e) from 0 to 10% by weight, in particular from 0.1 to 5% by weight of at least one additive, said composition being excluding PA12 and the sum of constituents (a) to (e) being equal to 100% by weight.

[0161] In another embodiment, said composition comprises by weight:

[0162] (a) from 50 to 78.9% by weight of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass,

[0163] (b) from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight, for example from 14 to 20% by weight of at least one phosphinate flame retardant,

[0164] (c) from 5 to 15% by weight of at least one functionalized polyolefin,

[0165] (d) from 2 to 8% by weight, in particular from 2 to 6% of at least one plasticizer,

[0166] (e) from 0 to 10% by weight, in particular from 0.1 to 5% by weight of at least one additive, said composition being for example excluding PA12 and the sum of the constituents (a) to (e) being for example equal to 100% by weight.

[0167] In yet another embodiment, said composition comprises by weight:

[0168] (a) from 50 to 78.9% by weight of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass,

[0169] (b) from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight, for example from 14 to 20% by weight of at least one phosphinate flame retardant,

[0170] (c) from 5 to 15% by weight of at least one functionalized polyolefin,

[0171] (d) from 2 to 8% by weight, in particular from 2 to 6% by weight of at least one plasticizer,

[0172] (e) from 0 to 10% by weight, in particular from 0.1 to 5% by weight of at least one additive, said composition being for example excluding PA12 and the sum of the constituents (a) to (e) being for example equal to 100% by weight.

[0173] In yet another embodiment, said composition comprises by weight: (a) from 50 to 78.9% by weight of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of from 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular ranging from 1.30 to 1.48, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass,

[0174] (b) from 10 to 30% by weight, for example from 10 to 25% by weight, for example from 14 to 25% by weight, for example from 14 to 22% by weight, for example from 17 to 22% by weight of at least one phosphinate flame retardant,

[0175] (c) from 5 to 15% by weight of at least one functionalized polyolefin,

[0176] (d) from 2 to 8% by weight, in particular from 2 to 6% by weight of at least one plasticizer,

[0177] (e) from 0.1 to 5% by weight of at least one additive, said composition being for example excluding PA12 and the sum of the constituents (a) to (e) being for example equal to 100% by weight.

[0178] In all such embodiments, the invention also covers said compositions wherein the term "comprises" is replaced by the term "consisting of".

[0179] The expression "said composition being excluding PA12" means, within the meaning of the invention, that the composition comprises less than 5% by weight of PA12, relative to its total weight, in particular comprises less than 2% by weight, in particular less than 1% by weight, in particular less than 0.5% by weight, in particular 0% by weight.

[0180] In particular, in all embodiments, the invention also covers compositions for which the sum of constituents (a) to (e) is equal to 100% by weight.

[0181] In a first variant of all these embodiments, said composition is free of melamine. It may in particular comprise less than 5% by weight of melamine, in particular less than 2% by weight of melamine, or even 0% by weight of melamine, relative to the total weight of said composition.

[0182] Melamine means both melamine and melamine cyanurate or a nitrogen compound based on melamine.

[0183] It is obvious that in this case the flame retardant cannot be melamine or melamine cyanurate or a nitrogen compound based on melamine.

[0184] The presence or absence of melamine depends on the processing temperature of the product and in the case of a high temperature, the melamine will be too sensitive to the temperature.

[0185] The use of melamine as a flame retardant is not possible when using polymers such as those targeted according to the invention, namely semi-crystalline aliphatic polymers having an inherent viscosity of between 1.2 and 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, as determined according to standard ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass.

[0186] The conditions of use of such semi-crystalline aliphatic polymers, in particular in terms of temperature and / or shear, in fact lead to a degradation of such flame retardants and consequently to insufficient fire resistance properties.

[0187] It is therefore not possible to obtain compositions having both the fire resistance properties and the mechanical properties sought according to the invention using melamine as a flame retardant.

[0188] On the contrary, the inventors discovered that only compositions comprising a phosphinate-type flame retardant (b) made it possible to obtain a compromise, in particular an optimum, improved one between mechanical resistance and fire resistance.

[0189] According to one embodiment, the compositions of the invention may comprise less than 50% by weight, in particular less than 30% by weight, in particular less than 20% by weight, in particular less than 10% by weight, in particular less than 5% by weight of PEBA as defined previously.

[0190] In particular, according to one embodiment, a composition of the invention may in particular comprise less than 1% by weight of PEBA, in particular less than 0.5% by weight of PEBA, or even 0% by weight of PEBA, relative to the total weight of said composition.

[0191] In a second variant of these embodiments, said composition is free of PEBA. According to one embodiment, the compositions of the invention may comprise less than 40% by weight, in particular less than 30% by weight, in particular less than 20% by weight, in particular less than 10% by weight, in particular less than 5% by weight of reinforcing fibers as defined below.

[0192] In particular, according to one embodiment, a composition of the invention may in particular comprise less than 1% by weight of reinforcing fibers, in particular less than 0.5% by weight of reinforcing fibers, or even 0% by weight of reinforcing fibers, relative to the total weight of said composition. In a third variant of all these embodiments, said composition is devoid of reinforcing fibers.

[0193] In a fourth variant of all these embodiments, said composition is free of melamine and PEBA.

[0194] In a fifth variant of all these embodiments, said composition is free of melamine and reinforcing fibers.

[0195] In a sixth variant of all these embodiments, said composition is free of PEBA and reinforcing fibers.

[0196] In a seventh variant of all these embodiments, said composition is free of melamine, PEBA and reinforcing fibers. According to one embodiment, the compositions of the invention may comprise less than 50% by weight, in particular less than 30% by weight, in particular less than 20% by weight, in particular less than 10% by weight, in particular less than 7.5% by weight, in particular less than 5% by weight of PA12 as defined above.

[0197] In particular, according to one embodiment, a composition of the invention may in particular comprise less than 1% by weight of PA12, in particular less than 0.5% by weight of PA12, or even 0% by weight of PA12, relative to the total weight of said composition.

[0198] In one embodiment, said composition is intended for a railway application.

[0199] Regarding PEBAs that may be excluded

[0200] Poly ether block amide (PEBA) are copolymers with amide units (Bal) and polyether units (Ba2), said amide unit (Bal) corresponding to an aliphatic repeating unit chosen from a unit obtained from at least one amino acid or a unit obtained from at least one lactam, or an XY unit obtained from polycondensation:

[0201] - at least one diamine, said diamine being chosen from a linear or branched aliphatic diamine or an aromatic diamine or a mixture thereof, and

[0202] - at least one dicarboxylic acid, said diacid being chosen from an aliphatic diacid or an aromatic diacid, said polyether units (Ba2) being in particular derived from at least one polyalkylene ether polyol, in particular a polyalkylene ether diol.

[0203] Regarding the possibly excluded reinforcing fibers.

[0204] The reinforcing fibers can in particular be chosen from reinforcing fibers of mineral, organic or plant origin.

[0205] Among the fibers of mineral origin, we can cite carbon fibers, glass fibers, basalt fibers or basalt-based fibers, silica fibers, or silicon carbide fibers for example. Among the fibers of organic origin, we can cite fibers based on thermoplastic or thermosetting polymer, such as semi-aromatic polyamide fibers, aramid fibers or polyolefin fibers for example. Among the fibers of plant origin, we can cite natural fibers based on flax, hemp, lignin, bamboo, silk, especially spider silk, sisal, and other cellulosic fibers, in particular viscose.

[0206] In one embodiment, said composition after implementation has a limiting oxygen level (LOI) > 28.

[0207] According to another aspect, the present invention relates to a tube, in particular partly corrugated, comprising at least one layer consisting of a composition as defined above. Said tube may be single-layer or multi-layer.

[0208] It can be partly smooth or completely smooth. A smooth tube is used in particular for the circulation of pressurized gas.

[0209] It can also be partly ringed.

[0210] A corrugated tube is used in particular to serve as a cable conduit.

[0211] The term "partly corrugated" means that the pipe has a corrugated tubular shape along part of its length. The corrugated portion may form a single portion or several portions of the structure, in which case two corrugated portions are separated by a smooth portion.

[0212] The ringed part(s) allow(s) to increase the deformation and extension capacity of the tubular structure, particularly in areas where small angles are required.

[0213] Advantageously, the tubular structure is ringed over at least 10% of its length.

[0214] Advantageously, the tubular structure is ringed over a proportion of 10 to more than 90% of its length.

[0215] Advantageously, the tubular structure is ringed over a proportion of 20 to 90% of its length.

[0216] Advantageously, the tubular structure is ringed over a proportion of 30 to more than 90% of its length.

[0217] Advantageously, the tubular structure is ringed over a proportion of 40 to more than 90% of its length.

[0218] Advantageously, the tubular structure is ringed over a proportion of 50 to more than 90% of its length.

[0219] Advantageously, the tubular structure is ringed over a proportion of 60 to more than 90% of its length.

[0220] Advantageously, the tubular structure is ringed over a proportion of 70 to more than 90% of its length.

[0221] Advantageously, the tubular structure is ringed over a proportion of 80 to more than 90% of its length.

[0222] Advantageously, the tubular structure is ringed over a proportion of more than 90% of its length.

[0223] According to yet another aspect, the present invention relates to the use of a composition as defined above, for the manufacture of fireproof articles for railways, in particular for trains.

[0224] Advantageously, said articles are intended for the interior or exterior of trains.

[0225] In one embodiment, said articles are obtained by extrusion.

[0226] Advantageously, the article obtained by extrusion is a corrugated tube serving as a cable conduit or a smooth tube allowing the circulation of pressurized fluid, in particular pressurized gas, in particular compressed air. According to another aspect, the present invention relates to the use of a composition as defined above, for the protection of a part made entirely or partly of metal.

[0227] Preferably, the invention relates to this use for conferring on the metal-based material, on which it is applied, electrical insulation and anti-corrosion properties.

[0228] For the purposes of the present invention, the term “metal-based material” means metal elements made entirely or partly of metal or plastic or elastic materials containing metal fibers.

[0229] Therefore, the use according to the invention aims to confer electrical insulation and anti-corrosion properties to a part comprising a part comprising metal, said part of which is coated with said composition.

[0230] These elements can have very diverse forms: cable, wire, tube, container, film or plate, preferably a tube.

[0231] According to yet another aspect, the present invention relates to a method for preparing an article for railways comprising a step of extruding a composition as defined above.

[0232] EXAMPLES

[0233] The compositions in Table 1 were prepared by melt blending the polymer granules with flame retardants, polyolefins, plasticizers, and additives. This blending was carried out by compounding on a 40 mm diameter co-rotating twin-screw extruder with a flat temperature profile (T°) at 250°C. The screw speed was 300 rpm and the throughput was 70 kg / h.

[0234] The polyamide(s), polyolefins, and additives are introduced into the compounding process in the main hopper. The flame retardant is added to the molten polymer, in the middle of the screw via a side feeder. The plasticizer is also introduced into the molten polymer via a pump.

[0235] The compositions were then injected at a temperature of 250°C to obtain the samples to be tested.

[0236] The compositions (samples) of the invention and comparative ones were tested with a measurement of the limiting oxygen index carried out according to the ISO 4589-2:2017 standard on test pieces of dimension 80x10x4 mm.

[0237] The density of smoke during combustion is measured according to ISO 5659-2:2017 on plates measuring 75x75x1 mm. The maximum opacity is recorded during a 10-minute combustion.

[0238] The toxicity of fumes is measured according to standard NF X70-100-l:2006 on a 30g sample at a temperature of 600°C.

[0239] The inherent viscosity (IV) was determined according to ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass. The impact strength was determined according to ISO 179:leA:2010 (Charpy impact) on notched bars of size 80mm x 10mm x 4mm, at a temperature of 23°C + / - 2°C under a relative humidity of 50% + / - 10% and at -30°C + / -2°C under a relative humidity of 50% + / - 10% on dry samples.

[0240] The tensile modulus, stress at 50% strain and at break and elongation at break were measured at 23°C according to ISO 527-1:2012 on dry sample. For the applications targeted by the invention, the target properties are: modulus < 1200 MPa, elongation at break > 100%, stress at 50% strain < 40 MPa, stress at break < 50 MPa.

[0241] The machine used is an INSTRON 5966. The crosshead speed is 1 mm / min for modulus measurement and 50 mm / min for stress at 50% strain and at break and elongation at break. The test conditions are 23°C + / - 2°C, on dry samples.

[0242] Fatigue resistance is measured by a Ross Flex test on 10 bars of dimension 150 x 20 x 2 mm without notch. The measurement was carried out as follows:

[0243] Number of cycles: 400,000

[0244] Temperature: -10°C

[0245] Bending frequency: 100 cycles / min

[0246] Bending Angle: 60°

[0247] Conditioning of test tubes: 7 days at 70°C

[0248] After 400,000 cycles, the bars obtained from the formulations of the invention E1 to E6 are not broken, whereas those obtained from the comparative compositions CEI, CE3 and CE4 are. [Table 1]

[0249] [Table 2] Orevac® IM800: VLDPE (very low density polyethylene) grafted with maleic anhydride (SK functional polymer).

[0250] Lotader® AX8900: copolymer of ethylene, methyl acrylate and glycidyl methacrylate (Et / MA / GMA - 68 / 24 / 8 by weight) (SK functional polymer).

[0251] Renol® black AF 34132010-ZA: black masterbatch marketed by Clariant.

[0252] Anox® TL 91: antioxidant marketed by SI group.

[0253] Exolit® OP1311 is a Clariant product (flame retardant based on aluminum diethyl phosphinate).

[0254] Melapur MC25 is a BASF product (melamine cyanurate-based flame retardant)

[0255] BBSA (benzyl butyl sulfonamide)

[0256] Fire resistance: The EN 45545 standard sets different specifications depending on the material category. Polyamide tubes correspond to categories R22 and R23, whose fire requirements are as follows (Table 3):

[0257] [Table 3]

[0258] Products are therefore classified according to their oxygen limit index as well as the density and toxicity of the fumes they generate during combustion. Three hazard level classifications (HL1, HL2 or HL3) can be achieved depending on their fire properties.

[0259] The higher this classification, the more the polyamide grade can be used in a large type of train, whereas a product classified as HL1 cannot be used in an underground metro, for example.

[0260] CIT: Conventional Toxicity Index. The examples show in particular the influence of inherent viscosity as well as the influence of the range of plasticizer and other constituents on the mechanical criteria and in particular for fatigue resistance and cold impact. Corrugated tubes with an external diameter of 32 mm were extruded at 230°C with the formulations of examples according to the invention E1 to E6. These confirm the mechanical performance and fire resistance of these products.

Claims

Tl CLAIMS Flame-retardant composition comprising by weight: (a) from 30 to 85% by weight, for example from 33 to 83% by weight, in particular from 50 to 78.9% by weight, of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, in particular strictly less than 1.5, in particular from 1.30 to 1.48, as determined according to ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by weight, (b) 10 to 30% by weight, for example 10 to 25% by weight, for example 14 to 25% by weight, for example 14 to 22% by weight, for example 17 to 22% by weight of at least one phosphinate-type flame retardant, (c) from 5 to 20%, in particular from 5 to 15% of at least one functionalized polyolefin, (d) 2 to 8%, in particular 2 to 6% of at least one plasticizer,(e) from 0 to 10%, in particular from 0.1 to 5% of at least one additive. Composition according to claim 1, characterized in that the semi-crystalline aliphatic polyamide (a) is obtained by polycondensation: of at least one amino acid in Cg to Cis, preferably an amino acid in Cg to Cis, more preferably in Cio to Cis, in particular in Cio to Cn, or of at least one lactam in Cg to Cis, preferably an amino acid in Cg to Cis, more preferably in Cio to Cis, in particular in Cio to Cn, or of at least one diamine X in C^Cgg, preferably Cg-Ci8, preferably Cg-Ci2, more preferably C10-C12, with at least one dicarboxylic acid Y in C^Cgg, preferably Cg-Ci8, preferably Cg-Cu, more preferably C10-C12.Composition according to claim 1 or 2, characterized in that the polyamide is a long-chain polyamide having a number of carbons per nitrogen atom greater than or equal to 8, in particular greater than or equal to 9, in particular greater than or equal to 10. Composition according to claim 3, characterized in that said long-chain polyamide is selected from PA610, PA612, PA1010, PA1012 and PAU.

5. Composition according to claim 4, characterized in that said at least one semi-crystalline aliphatic polyamide is selected from PA1010, PA1012 and PAU, in particular PAU.

6. Composition according to any one of claims 1 to 5, characterized in that the flame retardant is a metal salt selected from a metal salt of phosphinic acid, a metal salt of diphosphinic acid, a polymer containing at least one metal salt of phosphinic acid, a polymer containing at least one metal salt of diphosphinic acid.

7. Composition according to any one of claims 1 to 6, characterized in that the additives are selected from antioxidants, colour pigments and flame retardant synergists, in particular nitrogen synergists, especially melamine-based.

8. Composition according to any one of claims 1 to 7, characterized in that it is devoid of polyether block amides (PEBA).

9. Composition according to any one of claims 1 to 8, characterized in that it is devoid of reinforcing fiber.

10. Composition according to any one of the preceding claims, comprising by weight: (a) from 33 to 83%, in particular from 50 to 78.9%, of at least one semi-crystalline aliphatic polyamide having an inherent viscosity of 1.2 to 1.6, in particular from 1.2 to 1.5, in particular from 1.3 to 1.5, as determined according to ISO 307:2007 but using m-cresol instead of sulfuric acid, a temperature of 20°C and a concentration of 0.5% by mass, (b) 10 to 25% by weight, in particular 14 to 20% by weight of at least one phosphinate-type flame retardant, (c) from 5 to 20%, in particular from 5 to 15% of at least one functionalized polyolefin, (d) 2 to 8%, in particular 2 to 6% of at least one plasticizer, (e) from 0 to 10%, in particular from 0.1 to 5% of at least one additive, said composition being to the exclusion of PA12 and the sum of constituents (a) to (e) being equal to 100% by weight.

11. Tube, in particular partly corrugated, comprising at least one layer made of a composition as defined in any one of claims 1 to 10.

12. Use of a composition as defined in claims 1 to 10, for the manufacture of flame-retardant articles for railways, in particular for trains.

13. Use according to claim 112, characterized in that the articles are intended for use inside or outside trains.

14. Use according to claim 12 or 13, characterized in that the articles are obtained by extrusion.

15. Use according to claim 14, characterized in that the article obtained by extrusion is a corrugated tube used as a cable conduit or a smooth tube allowing the circulation of gas under pressure.

16. Use of a composition as defined in claims 1 to 10, for the protection of a part made entirely or partly of metal.

17. Method for preparing a railway article comprising an extrusion step of a composition as defined in any one of claims 1 to 10.

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