Semi-conducting polymer compositions for the preparation of wire and cable
Compositions comprising a polyolefin polymer and an expanded graphite exhibit uniform conductivity over a broad range of temperature. In one embodiment, the polyolefin polymer is polypropylene or polyethylene homopolymer or a polypropylene or polyethylene copolymer. The compositions provide uniform conductivity and can be used as a conductive formulation for medium and high voltage cable components.
1. A composition comprising a polyolefin polymer, a carbon black, and an expanded graphite having a BET surface area of at least 250 m 2 /g to about 1500 m 2 /g.
2. The composition of claim 1 in which polyolefin polymer is a polypropylene homopolymer or a polyethylene homopolymer.
3. The composition of claim 1 in which the polyolefin polymer is a polypropylene copolymer comprising at least about 50 mole percent units derived from propylene and the remainder from units derived from at least one α-olefin comprising up to about 20 carbon atoms.
4. The composition of claim 1 in which the polyolefin polymer is a polyethylene copolymer comprising at least about 50 mole percent units derived from ethylene and the remainder from units derived from at least one α-olefin having up to 20 carbon atoms.
5. The composition of claim 1 wherein the expanded graphite is dispersed in an ethylene vinyl acetate resin.
6. The composition of claim 1 in which the polyolefin polymer is linear low density polyethylene.
7. The composition of claim 1 wherein the carbon black is present in an amount from less than about 0.01 wt % to about 50 wt % of the composition.
8. The composition of claim 1 in which the expanded graphite comprises between about 0.1 and 35 percent of the total weight of the composition.
9. The composition of claim 1 in which the composition provides uniform conductivity over a temperature range of 15-160 C.
10. A power cable comprising a semi-conductive shield layer in which the shield layer comprises a polyolefin polymer, a carbon black, and an expanded graphite having a BET surface area of at least 250 m 2 /g to about 1500 m 2 /g.
11. The power cable of claim 10 in which the polyolefin polymer is a polypropylene homopolymer or a polyethylene homopolymer.
12. The power cable of claim 10 in which the polyolefin polymer is a polypropylene copolymer comprising at least about 50 mole percent units derived from propylene and the remainder from units derived from at least one α-olefin comprising up to about 20 carbon atoms.
13. The power cable of claim 10 in which the polyolefin polymer is a polyethylene copolymer comprising at least about 50 mole percent units derived from ethylene and the remainder from units derived from at least one α-olefin having up to 20 carbon atoms.
14. The power cable of claim 10 in which the expanded graphite comprises between about 1 and 15 percent of the total weight of the composition.
15. The power cable of claim 10 in which the semi-conductive shield layer provides uniform conductivity over a temperature range of 15-160 C.
16. A semi-conducting composition comprising (i) a polyolefin polymer and (ii) about 1 to about 15 wt %, based on the weight of the composition of an expanded graphite having a BET surface area greater than 250 m 2 /g, and (iii) carbon black.
17. The composition of claim 1 in which the polyolefin polymer comprises ethylene and at least one unsaturated ester of 4 to about 20 carbon atoms, and the ester is present in an amount of about 10 to about 60 percent by weight.
18. The composition of claim 1 comprising an antioxidant.
19. The composition of claim 18 wherein the antioxidant is a quinoline.