SEMICONDUCTIVE POLYETHYLENE COMPOSITION

Abstract

The invention relates semiconductive polyethylene composition, for use in power cables, with improved processability compared to other available semiconductive polymer compositions. This invention relates to a cable with a layer comprising the semiconductive polyethylene composition.

Claims

1. A semiconductive polyethylene composition comprising: a. a very low density polyolefin, having a density of less than or equal to 910 kg/m.sup.3, b. an amount of at least 20 wt % of carbon black, wherein said polyolefin comprises: i. a first polyolefin fraction with density in the range of 885 to 920 kg/m.sup.3 and MFR.sub.2 in the range of 15 to 50 g/10 min, ii. a second polyolefin fraction with density in the range of 840 to 880 kg/m.sup.3 and MFR.sub.2 in the range of 0.5 to 10 g/10 min, and the amounts of the first and second fraction of polyolefin are present in an amount of at least 10 wt % of the polyolefin.

2. The semiconductive polyethylene composition according to claim 1, wherein: a. the polyolefin comprises: i. a first polyolefin fraction with density of in the range 890 to 910 kg/m.sup.3 and MFR.sub.2 in the range of 20 to 40 g/10 min, ii. a second polyolefin fraction with density of 860 to 875 kg/m.sup.3 and MFR.sub.2 in the range of 0.5 to 5 g/10 min.

3. The semiconductive polyethylene composition according to claim 1, wherein the amount of polyolefin in the semiconductive polyethylene composition is from 40 to 75 wt % of the semiconductive polyethylene composition.

4. The semiconductive polyethylene composition according to claim 1, wherein the plastomer has a MFR.sub.2 in the range of 5 to 25 g/10 min.

5. The semiconductive polyethylene composition according to claim 1, wherein the semiconductive polyethylene composition comprises an ethylene polar copolymer.

6. The semiconductive polyethylene composition according to claim 1, wherein the MFR2 of the polyolefin and the ethylene polar copolymer differ less than 15 g/10 min.

7. The semiconductive polyethylene composition according to claim 1, wherein the ethylene polar copolymer has an MFR2 in the range of 5 to 50 g/10 min.

8. The semiconductive polyethylene composition to according to claim 1, wherein the polyethylene composition comprises an amount of 30 to 45 wt % of carbon black.

9. The semiconductive polyethylene composition according to claim 1, wherein the gel count in the polyolefin for above 1000 m is below 100 gels/kg.

10. The semiconductive polyethylene composition according to claim 1, wherein the semiconductive polyethylene composition has less than 5 pips/m.sup.2 that are >0.150 mm.

11. A cable comprising at least one semiconducting layer comprising the semiconductive polyethylene composition according to claim 1.

12. The cable according to claim 11, wherein the at least one semiconducting layer is an inner semiconducting layer.

13. The cable according to claim 11, wherein said cable is a DC cable.

Description

EXAMPLES

Pressure of INNER SEMICON DURING CABLE EXTRUSION

[0126] The construction of the cables is 50 mm.sup.2 stranded Al-conductor and 5.5 mm thick insulation. The inner and outer semiconductive layers have a thickness of 0.9 and 0.8 mm, respectively. The cable line is a 1+2 system, thus one extrusion head for the inner semicon (semicon is used as an abbreviation for a semiconductive layer in a cable), and another for the insulation +outer semicon. The pressure of the molten semiconductive composition before the screen pack in the extruder during production of cables is noted.

[0127] The materials were extruded on a 45 mm Maillefer extruder with a temperature profile of 75/105/110/120/130/130/130 C. profile at a line speed of 1.6 m/min.

TABLE-US-00001 TABLE 1 Processability of semiconductive polyethylene compositions. Comparative Inventive Unit example 2 example 1 Nonpolar ethylene-octene copolymer wt % 24.54 with a density of 897 kg/m.sup.3 and an MFR2 of 1.6 g/10 min, Engage 8440 available from DOW Nonpolar ethylene-octene copolymer wt % 36.81 with an density of 885 kg/m3 and an MFR.sup.2 of 30 g/10 min, Engage 8401 available from DOW Queo 0230 wt % 50.7 Queo 2M137 wt % 12.4 EBA 17 wt % wt % 5.25 EBA 14 wt % 5 TMQ wt % 0.65 0.65 Denka Black wt % 33 31 Melt pressure of inner semicon Bar 165 150 during cable extrusion

[0128] The inventive sample shows a lower melt pressure compared to the comparative example. As can be remembered from Table 1 the base resin used in the comparative example have a much higher gel count content compared to the base resins in the inventive example. With the increased number of gels a higher percentage of the comparative formulation will interact with the melt screen in the extruder, leading to the higher noted pressure compared to the inventive example.

[0129] Samples of various base resin are prepared and measured according to gel count content measurement.

TABLE-US-00002 TABLE 2 Gel count in base resin/kg Gel-check Gel-check Gel-check Gel-check Base Resin 100-300 m 300-600 m 600-1000 m 1000-m Engage 8100 35925 7902 352 160 Engage 8402 38391 3925 757 368 Queo 0210 103 50 7 0 Queo SM137 1527 305 96 27 Queo 8201 432 220 89 46 Queo 0230 440 157 13 0 Non-polar 338454 69110 5893 621 ethylene-butene copolymer (Borstar technology)

[0130] As it can be seen from the table 2 there is a big variance in the number of gels in the different materials regarding the number of gels.

Compounding of Semiconductive Examples

[0131] All examples of semiconductive polyethylene composition were compounded on a Busskneader MK. The compounding were done according to the steps of [0132] i) introducing base resins and TMQ in a mixer device and mixing the polymer component and additives at elevated temperature such that a polymer melt is obtained; [0133] ii) adding the carbon black to the polymer melt and further mixing of the polymer melt.

TABLE-US-00003 TABLE 3 Surface smoothness analysis (SSA) of the semiconductive compound reported as pips per m.sup.2 Comparative 1 Inven- Inven- Component Function wt % tive 1 tive 2 Engage 8402 Plastomer 51 Engage 8100 Plastomer 12 Queo 0230 Plastomer 50.7 Queo 2M137 Plastomer 12.4 Queo 0210 Plastomer 63 EBA 17 wt % Polar 5 5 5.25 ethylene copolymer TMQ Antioxidant 0.65 0.65 0.65 Denka Black Conductive 30.9 31 31 filler MFR.sub.21 measured 3.1 3.6 at 125 C. SSA SSA > 0.150 mm 5.46 1.91 4.3

[0134] As can be seen in table 3, the inventive examples using base resin with lower gel count content results in a smoother semiconductive material.

[0135] The compositions of inventive example 2 and comparative example 1 are bleed out on a 60 mm Maillefer tripplehead extruder. A 80 mesh melt screen was used to remove eventual contaminants in the melt. With bleed out means that no conductor was used and only the polymer melt is extruded from the cable extruder.

TABLE-US-00004 TABLE 4 Processability of semiconductive polyethylene compositions. Melt Temperature Melt pressure Extrudate p1 p2 Output Material (Rpm) ( C.) (bar) (bar) (Kg/h) Inventive 2 15 126.4 313 226 16.93 20 127.8 339 246 22.49 25 129.1 362 263 28.69 40 136.7 407 298 48.35 Comparative 1 15 126.3 323 228 17.18 20 128.0 346 248 22.34 25 129.3 382 275 29.22 40 137.9 426 311 48.44

[0136] The RPM values are relevant for the size of the extruder used and it can be seen that the melt pressure is increased with 4-5% for the formulation with higher gel count content. This is due to gels will be filtered in the melt screen. P1 and P2 in table 4 mean the pressure before and after the die.