ELECTRIC CABLE HAVING IMPROVED THERMAL CONDUCTIVITY

Abstract

The invention relates to a cable comprising at least one electrically insulating layer obtained from a polymer composition comprising at least one polypropylene-based thermoplastic polymer material and at least one inorganic filler chosen from silicates, boron nitride, carbonates, and a mixture thereof, and to a process for preparing said cable.

Claims

1. Electric cable comprising: at least one elongated electrically conducting element; and at least one electrically insulating layer obtained from a polymer composition comprising at least one polypropylene-based thermoplastic polymer material and at least one inorganic filler, wherein the inorganic filler is chosen from silicates, boron nitride, carbonates, and a mixture thereof.

2. Cable according to claim 1, wherein the silicates are aluminum silicates chosen from kaolins and any other mineral or clay comprising predominantly kaolinite.

3. Cable according to claim 1, wherein the carbonates are chosen from chalk, calcium carbonate, magnesium carbonate, limestone and any other material comprising predominantly calcium carbonate or magnesium carbonate.

4. Cable according to claim 1, wherein the inorganic filler represents from 2% to 40% by weight, relative to the total weight of the polymer composition.

5. Cable according to claim 1, wherein the inorganic filler is chosen from kaolins, chalk, and a mixture thereof.

6. Cable according to claim 1, wherein the polypropylene-based thermoplastic polymer material comprises a P.sub.1 propylene homopolymer or copolymer.

7. Cable according to claim 6, wherein the P.sub.1 propylene copolymer is a random propylene copolymer or a heterophasic propylene copolymer.

8. Cable according to claim 7, wherein the heterophasic copolymer comprises a thermoplastic phase of propylene type and a thermoplastic elastomer phase of the type copolymer of ethylene and of an .sub.2 olefin.

9. Cable according to claim 6, wherein the polypropylene-based thermoplastic polymer material comprises a random propylene copolymer and a heterophasic propylene copolymer.

10. Cable according to claim 6, wherein the P.sub.1 propylene copolymer(s) represent(s) at least 50% by weight, relative to the total weight of the polypropylene-based thermoplastic polymer material.

11. Cable according to claim 6, wherein polypropylene-based thermoplastic polymer material also comprises a P.sub.2 olefin homopolymer or copolymer, the olefin being chosen from ethylene and an .sub.3 olefin.

12. Cable according to claim 11, wherein the P.sub.2 olefin homopolymer or copolymer is a low-density polyethylene.

13. Cable according to claim 11, wherein the P.sub.2 olefin homopolymer or copolymer represents from 10% to 50% by weight, relative to the total weight of the polypropylene-based thermoplastic polymer material.

14. Cable according to claim 1, wherein the polymer composition of the invention also comprises a dielectric liquid.

15. Cable according to claim 14, wherein the dielectric liquid comprises a mineral oil and at least one polar compound of the type benzophenone, acetophenone, or a derivative thereof.

16. Cable according to claim 1, wherein the electrically insulating layer is a non-crosslinked layer.

17. Electric cable comprising: at least one elongated electrically conducting element and at least one non-crosslinked electrically insulating layer obtained from a polymer composition comprising at least one polypropylene-based thermoplastic polymer material; and at least one inorganic filler, wherein the non-crosslinked electrically insulating layer has a thermal conductivity of at least 0.235 W/m.K at 40 C., and preferably of at least 0.240 W/m.K at 40 C.

18. Process for the manufacture of an electric cable as defined in claim 17, wherein said process comprises: at least one step 1) of extruding the polymer composition around an elongated electrically conducting element, so as to obtain an electrically insulating layer surrounding said elongated electrically conducting element.

Description

EXAMPLES

[0138] 1. Polymer Compositions

[0139] Compositions I1, I2 and I3 in accordance with the invention, i.e. comprising at least one polypropylene-based thermoplastic polymer material and at least chalk as inorganic filler, were compared to comparative compositions C1 and C2, the composition C2 corresponding to a composition for forming a layer of XLPE and the composition C1 corresponding to a composition comprising a polypropylene-based thermoplastic polymer material identical to that used for the compositions of the invention I1, I2 and I3 (C1 thus not comprising an inorganic filler as defined in the invention).

[0140] Table 1 below collates polymer compositions of which the amounts of the compounds are expressed in percentages by weight, relative to the total weight of the polymer composition.

TABLE-US-00001 TABLE 1 Polymer compositions C1 (*) C2 (*) I1 I2 I3 Low-density polyethylene 0 98.1 0 0 0 Heterophasic propylene 100 0 100 100 100 copolymer Peroxide 0 1.6 0 100 100 Dielectric liquid 6 0 6 6 6 Inorganic filler: chalk 0 0 11.8 26.6 45.6 Antioxidant 0.3 0.3 0.3 0.3 0.3 (*) Comparative compositions which are not part of the invention

[0141] The origin of the compounds of Table 1 is as follows:

[0142] low-density linear polyethylene sold by the company Ineos under the reference BPD2000;

[0143] heterophasic copolymer sold by the company Basell Polyolefins under the reference Adflex Q 200F;

[0144] dielectric liquid comprising approximately 5.7% by weight of a mineral oil sold by the company Nynas under the reference Nytex 810; and approximately 0.3% by weight of benzophenone sold by the company Sigma-Aldrich under the reference B9300;

[0145] antioxidant sold by the company Ciba under the reference Irganox B 225 which comprises an equimolar mixture of Irgafos 168 and Irganox 1010 (for C1, I1 and I2) or sold by the company BASF under the reference Irgastab kV10 (for C2); and

[0146] inorganic filler (chalk) sold under the reference Omya EXH1 for chalk.

[0147] 2. Preparation of the Non-Crosslinked Layers

[0148] The compositions collated in Table 1 are used as follows. For the compositions C1, I1, I2 and I3, the dielectric liquid and the antioxidant were mixed with stirring at approximately 75 C., in order to form a dielectric liquid. The dielectric liquid was then mixed with the heterophasic copolymer in a container, then the resulting mixture and the inorganic filler were mixed using a twin-screw extruder (Berstorff twin screw extruder) at a temperature of approximately from 145 to 180 C., then melted at approximately 200 C. (screw speed: 80 revolutions/min). The resulting homogenized and molten mixture was then cooled and formed into granules. The granules were then hot-pressed so as to form layers in the form of plates.

[0149] Each of the polymer compositions C1, C2, I1, I2 and I3 were thus prepared in the form of layers 1 mm thick for evaluating their mechanical properties and also in the form of layers 8 mm thick for carrying out thermal conductivity measurements.

[0150] These compositions C1, C2, I1, I2 and I3 were then compared from the point of view of their mechanical properties (tensile strength/elongation at break before and after ageing at 135 C. for 240 hours) and of their thermal conductivity.

[0151] The tensile strength (TS) and elongation at break (EB) tests were carried out on the materials according to Standard NF EN 60811-1-1, using an instrument sold under the reference 3345 by the company Instron.

[0152] The results corresponding to each of these tests are reported in Table 2 (mechanical properties) below:

TABLE-US-00002 TABLE 2 Properties C1 (*) C2 (*) I1 I2 I3 TS (MPa) 17.1 23.4 18.6 17.5 14.9 EB (%) 777 501.5 715 683 648 TS after ageing (MPa) 18.4 23.7 19.1 16.4 12.9 EB after ageing (%) 677 522.5 664 634 586 (*) Comparative compositions which are not part of the invention

[0153] All of these results show that the incorporation of an inorganic filler as defined in the invention into a polypropylene matrix is not prejudicial to the mechanical properties of the thermoplastic polymer material that can be used in accordance with the invention as electrically insulating layer of a medium-voltage or high-voltage power cable, said cable retaining very good mechanical properties in terms of tensile strength and of elongation at break, including after ageing (Table 2).

[0154] The thermal conductivity tests were carried out on the materials according to the method well known under the term Transient Plane Source or TPS and using an instrument sold under the reference Hot Disk TPS 2500S by the company Thermoconcept.

[0155] The results corresponding to these tests are reported in Table 3 (thermal conductivity) below:

TABLE-US-00003 TABLE 3 Properties C1 (*) I1 I2 I3 Conductivity at 40 C. 0.229 0.243 0.263 0.305 (W/m .Math. K) (*) Comparative composition which is not part of the invention

[0156] The thermal conductivity results show that the presence of an inorganic filler as defined in the invention in a polypropylene matrix results in an electrically insulating layer having a thermal conductivity greater than that of an electrically insulating layer in which there is no inorganic filler.