POLYOLEFIN COMPOSITION FOR POWER CABLES

Abstract

The present invention relates to a polyolefin composition comprising a polyolefin (A), a fullerene composition (B) which comprises: a C.sub.60 fullerene or a C.sub.60 chemical derivative selected from the group consisting of methanofullerene derivatives, PCBM derivatives, ThCBM derivatives, Prato derivatives, Bingel derivatives, diazoline derivatives, azafulleroid derivatives, ketolactam derivatives, and Diels-Alder derivatives; or a C.sub.70 fullerene or a C.sub.70 chemical derivative selected from the group consisting of methanofullerene derivatives, PCBM derivatives, ThCBM derivatives, Prato derivatives, Bingel derivatives, diazoline derivatives, azafulleroid derivatives, ketolactam derivatives, and Diels-Alder derivatives; or a blend of fullerenes; a master batch, a cable, and uses thereof.

Claims

1-14. (canceled)

15. A polyolefin composition comprising a polyolefin (A), and a fullerene composition (B) which comprises: a C.sub.60 fullerene or a C.sub.60 chemical derivative selected from the group consisting of methanofullerene derivatives, PCBM derivatives, ThCBM derivatives, Prato derivatives, Bingel derivatives, diazoline derivatives, azafulleroid derivatives, ketolactam derivatives, and Diels-Alder derivatives; or a C.sub.70 fullerene or a C.sub.70 chemical derivative selected from the group consisting of methanofullerene derivatives, PCBM derivatives, ThCBM derivatives, Prato derivatives, Bingel derivatives, diazoline derivatives, azafulleroid derivatives, ketolactam derivatives, and Diels-Alder derivatives; or a blend of fullerenes.

16. The polyolefin composition according to claim 15, wherein the fullerene composition (B) is a C.sub.60 fullerene or a C.sub.60 chemical derivative selected from the group consisting of methanofullerene derivatives, PCBM derivatives, ThCBM derivatives, and Prato derivatives; or a C.sub.70 fullerene or a C.sub.70 chemical derivative selected from the group consisting of methanofullerene derivatives, PCBM derivatives, ThCBM derivatives and Prato derivatives.

17. The polyolefin composition according to claim 15, wherein the fullerene composition (B) is a C.sub.60 fullerene or a C.sub.60 chemical derivative selected from the group consisting of methanofullerene derivatives and PCBM derivatives; or a C.sub.70 fullerene or a C.sub.70 chemical derivative selected from the group consisting of methanofullerene derivatives and PCBM derivatives.

18. The polyolefin composition according to claim 15, wherein the fullerene composition (B) is a C.sub.60 fullerene or Phenyl-C.sub.61-butyric acid methyl ester ([60]PCBM); or a C.sub.70 fullerene or Phenyl-C.sub.71-butyric acid methyl ester (the [70]PCBM analogue of [60]PCBM).

19. The polyolefin composition according to claim 18, wherein the fullerene composition (B) is a C.sub.60 fullerene or [60]PCBM.

20. The polyolefin composition according to claim 15, wherein the fullerene composition (B) comprises a blend of fullerenes, wherein said blend may comprises about 80% wt of [60]PCBM, about 20% wt of [70]PCBM, and, optionally, small quantities of chemical derivatives of said higher fullerenes, e.g. higher PCBM.

21. The polyolefin composition according to claim 15, wherein the fullerene composition (B) comprises a blend of fullerenes, wherein said blend may comprises about 65% wt of [60]PCBM, about 30% wt of [70]PCBM, and about 5% wt of chemical derivatives of said higher fullerenes, e.g. higher PCBM.

22. A master batch comprising (i) a matrix polymer and (ii) the fullerene composition (B) according to any of claims 15.

23. A cable or wire comprising a layer which comprises a polyolefin composition according to claim 15.

24. The cable according to claim 23 wherein the cable is a medium, high or extra high voltage cable comprising an inner semiconductive layer, an insulating layer and an outer semiconductive layer.

25. The cable or wire according to claim 24 wherein at least the insulating layer comprises a polyolefin composition according to claim 15.

26. A process for the production of a layer of a cable or wire using a polyolefin composition according to claim 15.

27. A process for the production of a layer of a cable or wire using a masterbatch according to claim 22.

28. A cable or wire comprising a layer which comprises a master batch according to claim 22.

29. The cable or wire according to claim 24 wherein at least the insulating layer comprises a master batch according to claim 22.

Description

EXAMPLES

[0177] The following examples serve to further illustrate the present invention. Unless otherwise specified all the reagents are commercially available or can be produced according to methods well known in the literature.

Inventive Example 1 (IE1)

[0178] A polyolefin composition comprising: a polyolefin (A), a fullerene composition (B) which comprises [60]PCBM

[0179] Phenyl-C.sub.61-Butyric-Acid-Methyl-Ester ([60]PCBM) was used as purchased from Solenne BV (purity>99%).

Inventive Example 2 (IE2)

[0180] A polyolefin composition comprising: a polyolefin (A), a fullerene composition (B) which comprises C.sub.60 fullerene C.sub.60 fullerene was used as purchased from Solenne BV (purity>99%).

[0181] Production and Testing of Compositions

[0182] The polyolefin compositions of the present invention (Inventive Examples 1 and 2, i.e. IE1 and IE2) are tested together with a reference composition comprising 4,4-di(dodecyloxy)benzil (Comparative Example 2) (CE2) described in EP2545114 as voltage stabilizer.

[0183] A polymer without voltage stabilizer is used as base reference material (Comparative Example 1) (CE1).

[0184] The test arrangements are the same for the reference polymers and for the tested fullerene composition.

[0185] A commercially available cross-linkable polyethylene with the grade name, LS4201S, supplied by Borealis, Sweden, which is prepared by high pressure polymerization and had a density of 0.922 g/cm.sup.3 (ISO1872-2/ISO1183-2), MFR.sub.2 (ISO 1133, load 2.16 kg, at 190 C.) of 2 g/10 min is used as base reference (comparative example 1, i.e. CE1) and as the polymer for preparing the compositions of comparative example 2 (CE2) and inventive Examples 1 and 2 (IE1 and IE2).

[0186] The base reference polymer is in a form of pellets which contains dicumyl peroxide as a cross-linking agent. Before use, the pellets are ground to fine powder in a Retsch ZM-1 centrifugal mill with a 500 micrometer sieve. In the cases where voltage stabilizers are added, the powder is impregnated with the stabilizer dissolved in dichloromethane (inventive Example 1 and comparative Example 2), or in chloroform (inventive Example 2), for one hour while agitated manually for about 30 s every 15 minutes. The solvent is then removed by means of rotary evaporation and vacuum oven to obtain a dry powder with a homogeneously distributed voltage stabiliser.

[0187] The test objects are prepared by compression moulding in two steps. In the first step, the polyethylene powder is formed to suitable shapes by melting at 130 C. and 10 kN press force for three minutes followed by 200 kN during another three minutes. A tungsten wire electrode with a diameter of 10 m is then applied between two of the pre-pressed polymer pieces (30 mm14 mm1.5 mm) and fastened with a piece of aluminum tape used as high voltage connection during the electrical treeing tests, as shown in FIG. 1. In the second step the material is first melted at 130 C. during fifteen minutes to reduce the influence of interfaces between the pre-pressed blocks after which the temperature is ramped up to 180 C. and held for fifteen minutes for cross linking to take place. The press force is increased to 200 kN during the cross linking to inhibit the formation of gas filled voids from the cross linking by-products.

[0188] This procedure yield the wire electrode test object illustrated in FIG. 2. To make the thermal history of the test objects as similar as possible, the samples are remelted at 130 C. in an oven and are allowed to cool slowly by switching the oven off.

[0189] Electrical Treeing Evaluation

[0190] Testing of electrical tree initiation field is performed in a setup, illustrated in FIG. 3, under 50 Hz AC voltage ramping regime with a ramp rate of 20 V/s (rms). A 30 kV step-up variable transformer is used as voltage supply. To limit short circuit currents a water resistor of approximately 200 k is connected in series with the tested object.

[0191] The electrical tree initiation tests are performed in transformer oil in a custom made container with optical detection system shown in FIG. 4. The ramp speeds used are measured prior to testing. The treeing process is optically observed using a microscope coupled with a CCD camera, recording the process at 2 frames per second at a resolution of 20481532 pixels allowing detection of trees smaller than 10 m for accurate determination of their initiation. The measurements are performed at ambient conditions.

[0192] The tree initiation field strength at the wire electrode is calculated from the applied voltage level using a simplified field enhancement factor of 21 mm.sup.1. This factor is calculated using 3D numerical simulations of the maximum electrical field in the test object using a finite element based software, Comsol Multiphysics.

[0193] The % improvement of the tree initiation field is calculated from the sum of the scale and the threshold parameter compared to the reference material (CE1) yielded by fitting the dataset to a 3-parameter Weibull distribution, using the maximum likelihood method in the software Minitab version 16.2.4 in accordance with IEEE Std930TM-2004, IEEE Guide for the Statistical Analysis of Electrical Breakdown Data. From every test object, four trees are used for calculating the tree initiation fields and trees growing in the immediate proximity of visible defects in the material or on the wire electrode are censored.

[0194] The gel-content of the crosslinked samples is determined gravimetrically using a solvent extraction technique. The samples (100 mg) are placed in pre-weighed 100 mesh stainless steel baskets, and extracted in 1.1 dm.sup.3 boiling decahydronaphthalene for 6 h. An antioxidant, 10 g Irganox 1076 from BASF, is added to prevent degradation. After 6 h, the solvent is exchanged for 0.9 dm.sup.3 new decahydronaphthalene (pre-heated) and the extraction continued for another two hours. The samples are left to evaporate at room temperature for one week under ventilation and finally dried under vacuum for 72 h at 40 C. After this period a constant weight is reached. The non-soluble fraction left in the baskets is weighed, and the gel-content of the polymers is calculated.

[0195] Results

[0196] From Table 1, it can be seen that the CE2 has roughly the same tree initiation field as inventive example 1 (IE1), and about 10% higher than inventive example 2 (IE2), however when looking at the concentration on a mass scale (wt %), it shall be noted that the inventive example 1 (IE1) has less than a fifth, and inventive example 2 (IE2) less than an eight, respectively, of the amount voltage stabilizer added. It is also seen in Table 2 that the cross-linking performance is in the same range as for the CE1.

TABLE-US-00001 TABLE 1 Number % of conc conc Tree init Difference Increase samples [mmol/kg] [wt %] [kV/mm] to Ref from Ref CE1 56 0 0 296 0 0 CE2 60 10 0.58 376 81 27 IE1 28 1.1 0.1 372 75 25 IE2 20 1 0.072 340 44 15

TABLE-US-00002 TABLE 2 Gel content Material (%) CE1 82 IE1 85 IE2 86