DUCTILE FLAME-RETARDANT POLYAMIDE COMPOSITIONS AND USES THEREOF, IN PARTICULAR FOR RAILWAYS

1 . A flame-retardant composition comprising, by weight:

(a) from 30% to 85% by weight of at least one semicrystalline aliphatic polyamide having an inherent viscosity ranging from 1.2 to 1.6, as determined according to the standard ISO 307:2007 but while using m-cresol instead of sulfuric acid, a temperature of 20° C. and a concentration of 0.5% by weight,

(b) from 10% to 30% by weight of at least one phosphinate flame retardant,

(c) from 5% to 20% of at least one functionalized polyolefin,

(d) from 2% to 8%, of at least one plasticizer,

(e) from 0 to 10% of at least one additive.

2 . The composition as claimed in claim 1 , wherein the semicrystalline aliphatic polyamide (a) is obtained by polycondensation:

of at least one C 6 to C 18 amino acid, or

of at least one C 6 to C 18 lactam, or

of at least one C 4 -C 36 diamine X with at least one C 4 -C 36 dicarboxylic acid Y.

3 . The composition as claimed in claim 1 , wherein the polyamide is a long-chain polyamide having a number of carbons per nitrogen atom of greater than or equal to 8.

4 . The composition as claimed in claim 3 , wherein said long-chain polyamide is chosen from PA610, PA612, PA1010, PA1012 and PA11.

5 . The composition as claimed in claim 4 , wherein said at least one semicrystalline aliphatic polyamide is chosen from PA1010, PA1012 and PA11.

6 . The composition as claimed in claim 1 , wherein the flame retardant is 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 and a polymer containing at least one metal salt of diphosphinic acid.

7 . The composition as claimed in claim 1 , wherein the additives are chosen from antioxidants, colored pigments and flame retardancy synergists.

8 . The composition as claimed in claim 1 , wherein it is free of polyether block amides (PEBA).

9 . The composition as claimed in claim 1 , wherein it is free of reinforcing fibers.

10 . The composition as claimed in claim 1 , comprising, by weight:

(a) from 33% to 83% of at least one semicrystalline aliphatic polyamide having an inherent viscosity between from 1.2 to 1.6, as determined according to the standard ISO 307:2007 but while using m-cresol instead of sulfuric acid, a temperature of 20° C. and a concentration of 0.5% by weight,

(b) from 10% to 25% by weight of at least one phosphinate flame retardant,

(c) from 5% to 20% of at least one functionalized polyolefin,

(d) from 2% to 8% of at least one plasticizer,

(e) from 0 to 10% of at least one additive,

said composition excluding PA12 and the sum of the constituents (a) to (e) being equal to 100% by weight.

11 . A tube comprising at least one layer consisting of a composition as defined in claim 1 .

12 . A method comprising using a composition as defined in claim 1 for the manufacture of flame-retardant articles for the railroad sector.

13 . The method as claimed in claim 11 , wherein the articles are intended for the interior or exterior of trains.

14 . The method as claimed in claim 12 , wherein the articles are obtained by extrusion.

15 . The method as claimed in claim 14 , wherein the article obtained by extrusion is a corrugated tube used as cable duct or a smooth tube allowing the circulation of pressurized gas.

16 . A method comprising using a composition as defined in claim 1 , for the protection of a part consisting completely or partly of metal.

17 . A process for preparing an article for the railroad sector comprising a step of extruding a composition as defined in claim 1 .