Fire resistant and/or retardant composition

Abstract

The present invention relates to a fire resistant and/or retardant composition comprising a starch, at least one starch plasticiser, at least one first alkali silicate and at least one phyllosilicate; a method for preparing the fire resistant and/or retardant composition; a device chosen from among a power and/or telecommunications cable, and an accessory for a power and/or telecommunications cable, the cable comprising at least one fire resistant and/or retardant layer of the fire resistant and/or retardant composition, and the cable accessory comprising at least one fire resistant and/or retardant layer of the fire resistant and/or retardant composition; as well as a method for manufacturing such a device.

Claims

1. A fire-resistant and/or fire-retardant composition comprising: at least one first alkaline silicate, starch, at least one plasticizer of the starch, and at least one phyllosilicate, said phyllosilicate representing an amount of greater than 10% by weight with respect to the total weight of the fire-resistant and/or fire-retardant composition.

2. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein the plasticizer of the starch is chosen from aliphatic polyols.

3. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein the starch and the plasticizer of the starch represent from 15% to 80% by weight with respect to the total weight of said fire-resistant and/or fire-retardant composition layer.

4. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein the phyllosilicate is chosen selected from the group consisting of sepiolites, palygorskites, attapulgites, kalifersites, loughlinites, falcondoites, montmorillonites, illites, talcs, and micas.

5. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein the phyllosilicate represents at least 20% by weight with respect to the total weight of the fire-resistant and/or fire-retardant composition.

6. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein the phyllosilicate represents at most 50% by weight with respect to the total weight of the fire-resistant and/or fire-retardant composition.

7. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein said fire-resistant and/or fire-retardant composition additionally comprises a second alkaline silicate different from the first alkaline silicate.

8. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein said fire-resistant and/or fire-retardant composition comprises: a first alkaline silicate having a SiO.sub.2/M.sub.2O molar ratio ranging from 1.5 to 2.6, and a second alkaline silicate having a SiO.sub.2/M′.sub.2O molar ratio of greater than 2.6, it being understood that M′ is identical to M, and M and M′ are chosen from a sodium atom and a potassium atom.

9. The fire-resistant and/or fire-retardant composition as claimed in claim 7, wherein said fire-resistant and/or fire-retardant composition comprises from 1% to 20% by weight of first and second alkaline silicates, with respect to the total weight of the fire-resistant and/or fire-retardant composition.

10. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein said fire-resistant and/or fire-retardant additionally comprises inorganic fibers.

11. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein said fire-resistant and/or fire-retardant composition additionally comprises zinc borate.

12. The fire-resistant and/or fire-retardant composition as claimed in claim 1, wherein said fire-resistant and/or fire-retardant composition has a viscosity of at least 1000 Pa.Math.s, at 25° C., and with a shear rate of at most 3000 s.sup.−1.

13. A process for the preparation of the fire-resistant and/or fire-retardant composition as defined in claim 1, wherein said fire-resistant and/or fire-retardant composition comprises at least one stage i) of mixing the starch, the plasticizer of the starch, the phyllosilicate and the first alkaline silicate.

14. A device chosen from a power and/or telecommunications cable and an accessory for a power and/or telecommunications cable, wherein said cable comprises at least one fire-resistant and/or fire-retardant layer, and said cable accessory is coated with a fire-resistant and/or fire-retardant layer, each obtained from a fire-resistant and/or fire-retardant composition as defined in claim 1.

15. The process for the manufacture of the device as claimed in claim 14, wherein said process comprises at least the following stages: 1) the preparation of fire-resistant and/or fire-retardant composition includes at least one stage i) of mixing the starch, the plasticizer of the starch, the phyllosilicate and the first alkaline silicate; and 2) the extrusion of the fire-resistant and/or fire-retardant composition prepared in stage 1): either around one or more elongated conductive elements and/or around an internal layer of a power and/or telecommunications cable, or around a cable accessory.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0173] FIG. 1 represents a diagrammatic view of an electric cable according to an embodiment of the present invention.

[0174] For reasons of clarity, only the components essential for the understanding of the invention have been represented diagrammatically in these FIGURES, this being done without observing a scale.

[0175] The electric cable 10A, illustrated in FIG. 1, corresponds to a fire-resistant electric cable of K25 or RZ1K type.

[0176] This electric cable 10A comprises four elongated electrically conductive elements 100, each being insulated with an electrically insulating layer 200, and, successively and coaxially around these four elongated insulated electrically conductive elements (100, 200), a fire-resistant and/or fire-retardant layer 300 as defined in the invention surrounding the four elongated insulated electrically conductive elements (100, 200) and an external sheath 400 of HFFR type surrounding the fire-resistant and/or fire-retardant layer 300. The fire-resistant and/or fire-retardant layer 300 is as defined in the invention and is advantageously provided in the form of an extruded layer.

[0177] The following examples make it possible to illustrate the present invention. They do not have a limiting nature with regard to the overall scope of the invention as presented in the claims.

EXAMPLES

[0178] The starting materials used in the examples are listed below: [0179] approximately 50% by weight aqueous solution of a first sodium silicate of “water glass” type, from Simalco, sodium silicate with a SiO.sub.2/Na.sub.2O molar ratio of approximately 2.0, [0180] approximately 38% by weight aqueous solution of a second sodium silicate of “water glass” type, from Simalco, sodium silicate with a SiO.sub.2/Na.sub.2O molar ratio of approximately 3.4, [0181] glycerol, Roquette Freres, Reference 8400, [0182] mica, Imerys, Mica MKT, [0183] modified starch, Roquette Freres, Pregeflo CH40, [0184] basalt fibers, Basaltex, product: BCS17-12.7-KV05/1, [0185] zinc borate, Borax, Firebreak ZB.

[0186] Unless indicated otherwise, all these starting materials were used as received from the manufacturers.

Example 1: Preparation of a Fire-Resistant Cable in Accordance with the Invention

[0187] A fire-resistant and/or fire-retardant composition was prepared in the following way: 4000 g of an 84% by weight solution of glycerol in water were mixed with 1000 g of a 50% by weight aqueous solution of a first sodium silicate and 1000 g of a 38% by weight aqueous solution of a second sodium silicate, to form a liquid composition.

[0188] Separately, 4800 g of mica, 2000 g of modified starch and 400 g of zinc borate were mixed to form a solid composition.

[0189] The liquid composition was added to a planetary mixer, followed by 200 g of basalt fibers, then followed by the solid composition, to form a resulting composition.

[0190] The resulting composition was mixed in the mixer for 3 minutes until said fire-resistant and/or fire-retardant composition was obtained in the form of a homogeneous paste.

[0191] The fire-resistant and/or fire-retardant composition thus obtained was extruded around a cable comprising 5 copper conductors with a section of 1.5 mm.sup.2, each of the conductors being surrounded with an electrically insulating layer based on XLPE. On conclusion of the stage of extrusion around the cable, a fire-resistant and/or fire-retardant layer surrounding the insulated conductors is obtained.

[0192] The fire-resistant and/or fire-retardant layer formed has a thickness of 0.7 mm.

[0193] The assembly obtained is subsequently covered by hot extrusion with a protective polymer sheath based on an HFFR mixture produced by Nexans based on polyethylene and on flame-retardant fillers, said sheath having a thickness of approximately 1.54 mm. A cable 10A in accordance with the invention was thus obtained. The flame performance qualities of the cable 10A are determined according to the standard EN50399. 15 cable sections positioned on a vertical ladder are exposed to a flame with a power of 20 kW for 20 min. A comparative cable 2, identical to the cable 10A except that it does not comprise a fire-resistant and/or fire-retardant layer and that its sheath has a thickness of 1.42 mm, was also tested under the same conditions.

[0194] The results are given in table 1 below:

TABLE-US-00001 TABLE 1 Parameters Cable 10A Cable 2, comparative       pHRR (kW) 23.0 661.8 Time to the pHRR (s) 792.0 876.0       .sup. THR (MJ) 11.8 110.9        .sup. SPR (m.sup.2/s) 0.0 0.7         TSP (m.sup.2) 8.0 149.6 Class according to EN 50399 B2 s1 d0 E/F s2 d2

[0195] In this table, the acronym HRR corresponds to the expression “Heat Release Rate”, which provides information on the heat release rate, the acronym THR corresponds to the expression “Total Heat Release”, which provides information on the amount of heat released during the combustion, the acronym SPR corresponds to the expression “Smoke Production Rate”, which provides information on the smoke production rate, and the acronym TSP corresponds to the expression “Total Smoke Production”, which provides information on the total amount of smoke produced.

[0196] These results demonstrate that the cable 10A in accordance with the invention, unlike the comparative cable 2 not forming part of the invention, exhibits the maximum fire protection properties from the viewpoint of the requirements of the European standard EN 50399.