CABLE WITH ADVANTAGEOUS ELECTRICAL PROPERTIES

Abstract

A cable comprising one or more conductors surrounded by at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein said insulation layer comprises at least 90 wt % of a polymer composition, said polymer composition comprising (I) 80.0 to 99.9 wt % of an LDPE homopolymer or copolymer; and (II) 0.1 to 20.0 wt % of: (i) an ultra-high molecular weight polyethylene having a Mw of at least 1,000,000; or (ii) a single site catalysed medium density polyethylene (MDPE) having a density of 925 to 940 kg/m.sup.3 or a single site catalysed linear low density polyethylene (LLDPE) having a density of 910 to 925 kg/m.sup.3.

Claims

1. A cable comprising one or more conductors surrounded by at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein said insulation layer comprises at least 90 wt % of a polymer composition, said polymer composition comprising (I) 80.0 to 99.9 wt % of an LDPE homopolymer or copolymer; and (II) 0.1 to 20.0 wt % of: (i) an ultra-high molecular weight polyethylene having a Mw of at least 1,000,000; or (ii) a single site catalyzed medium density polyethylene (MDPE) having a density of 925 to 940 kg/m.sup.3 or a single site catalyzed linear low density polyethylene (LLDPE) having a density of 910 to 925 kg/m.sup.3.

2. A cable comprising one or more conductors surrounded by at least an inner semiconductive layer, a crosslinked insulation layer and an outer semiconductive layer, in that order, wherein said insulation layer comprises at least 90 wt % of a polymer composition, said polymer composition comprising (I) 80.0 to 99.9 wt % of an LDPE homopolymer or copolymer; and (II) 0.1 to 20.0 wt % of a single site catalyzed medium density polyethylene (MDPE) having a density of 925 to 940 kg/m.sup.3 or a single site catalyzed linear low density polyethylene (LLDPE) having a density of 910 to 925 kg/m.sup.3.

3. The cable of claim 1, wherein the polymer composition of the insulation layer has a conductivity of 10 fS/m or less, when measured according to DC conductivity method as described under Method A.

4. The cable of claim 1, wherein the polymer composition of the insulation layer has a conductivity of 20.0 fS/m or less (determination method C (80 kV, 70 C.)).

5. The cable of claim 1, wherein the polymer composition of the insulation layer has a conductivity of 10.0 fS/m or less (determination method D (60 kV, 70 C.)).

6. A cable comprising one or more conductors surrounded by at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein said insulation layer comprises at least 90 wt % of a polymer composition, said polymer composition comprising (I) 80.0 to 99.9 wt % of an LDPE homopolymer or copolymer having a density of 927 to 940 kg/m.sup.3; and (II) 0.1 to 20.0 wt % of an ultra-high molecular weight polyethylene having a Mw of at least 1,000,000.

7. The cable of claim 1, wherein the conductivity of the polymer composition of the insulation layer is 1.010.sup.14 S/cm or less, when measured according to DC conductivity method as described under Methods B.

8. The cable of claim 1, wherein the insulation layer is not crosslinked.

9. The cable of claim 1, having a direct current (DC) power cable.

10. The cable of claim 1, wherein the component (II) is a SSC MDPE.

11. The cable of claim 1, wherein the component (II) is MDPE and this forms 4.0 to 15.0 wt % of the polymer composition.

12. The cable of claim 1, wherein the component (II) is an LLDPE and this forms 1.5 to 6 wt % of the polymer composition.

13. The cable of claim 1, wherein the component (II) is an UHMWPE and this forms 5.0 to 10.0 wt % of the polymer composition.

14. The cable of claim 1, wherein the component (II) is the MDPE having a density of 930 to 937 kg/m.sup.3 and an MFR.sub.2 of 0.5 to 3.0 g/10 min.

15. A process for producing a cable comprising the steps of: applying on one or more conductors, an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein the insulation layer comprises a polymer composition of claim 1, and optionally crosslinking the insulation layer.

16. The cable of claim 1, wherein the conductivity of the polymer composition of the insulation layer is of 5.0 fS/m or less when measured according to DC conductivity method as described under Method A.

17. The cable of claim 1, wherein the conductivity of the polymer composition of the insulation layer is 15.0 fS/m or less (determination method C (80 kV, 70 C.)).

18. The cable of claim 1, wherein the conductivity of the polymer composition of the insulation layer is 5.0 fS/m or less (determination method D (60 kV, 70 C.)).

19. The cable of claim 1, wherein the conductivity of the polymer composition of the insulation layer is 1.010.sup.16 S/cm or less when measured according to DC conductivity method as described under Methods B.

20. The cable of claim 9, wherein the direct current (DC) power cable operates at or is capable of operating at 320 kV or more.

Description

[0212] The invention will now be defined with reference to the following non limiting examples and figures.

[0213] FIG. 1 shows the Conductivity vs. stress at 70 C. for XLPE and SSC-MDPE modified XLPEs.

[0214] FIG. 2 shows conductivity vs UHMWPE content.

[0215] In FIG. 3 a visual representation of the results shown on Table 5 can be seen.

[0216] From these results we can see that the DC conductivity drops by 2 orders of magnitude when the pure LDPE is modified.

Determination Methods

[0217] Unless otherwise stated in the description or experimental part the following methods were used for the property determinations.
Wt %: % by weight

Melt Flow Rate

[0218] The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR is determined at 190 C. for polyethylene and at 230 C. for polypropylene. MFR may be determined at different loadings such as 2.16 kg (MFR.sub.2) or 21.6 kg (MFR.sub.21).

Molecular Weight

[0219] Mz, Mw, Mn, and MWD are measured by Gel Permeation Chromatography (GPC) according to the following method:
The weight average molecular weight Mw and the molecular weight distribution (MWD=Mw/Mn wherein Mn is the number average molecular weight and Mw is the weight average molecular weight; Mz is the z-average molecular weight) is measured according to ISO 16014-4:2003 and ASTM D 6474-99. A Waters GPCV2000 instrument, equipped with refractive index detector and online viscosimeter was used with 2GMHXL-HT and 1G7000HXL-HT TSK-gel columns from Tosoh Bioscience and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert-butyl-4-methyl-phenol) as solvent at 140 C. and at a constant flow rate of 1 mL/min. 209.5 L of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with at least 15 narrow MWD polystyrene (PS) standards in the range of 1 kg/mol to 12 000 kg/mol. Mark Houwink constants were used as given in ASTM D 6474-99. All samples were prepared by dissolving 0.5-4.0 mg of polymer in 4 mL (at 140 C.) of stabilized TCB (same as mobile phase) and keeping for max. 3 hours at a maximum temperature of 160 C. with continuous gentle shaking prior sampling in into the GPC instrument.

Comonomer Contents

a) Comonomer Content in Random Copolymer of Polypropylene:

[0220] Quantitative Fourier transform infrared (FTIR) spectroscopy was used to quantify the amount of comonomer. Calibration was achieved by correlation to comonomer contents determined by quantitative nuclear magnetic resonance (NMR) spectroscopy. The calibration procedure based on results obtained from quantitative .sup.13C-NMR spectroscopy was undertaken in the conventional manner well documented in the literature.
The amount of comonomer (N) was determined as weight percent (wt %) via:

N=k1(A/R)+k2

wherein A is the maximum absorbance defined of the comonomer band, R the maximum absorbance defined as peak height of the reference peak and with k1 and k2 the linear constants obtained by calibration. The band used for ethylene content quantification is selected depending if the ethylene content is random (730 cm.sup.1) or block-like (as in heterophasic PP copolymer) (720 cm.sup.1). The absorbance at 4324 cm.sup.1 was used as a reference band.

b) Quantification of Alpha-Olefin Content in Linear Low Density Polyethylenes and Low Density Polyethylenes by NMR Spectroscopy:

[0221] The comonomer content was determined by quantitative 13C nuclear magnetic resonance (NMR) spectroscopy after basic assignment (J. Randall JMSRev. Macromol. Chem. Phys., C29(2&3), 201-317 (1989). Experimental parameters were adjusted to ensure measurement of quantitative spectra for this specific task.
Specifically solution-state NMR spectroscopy was employed using a Bruker AvanceIII 400 spectrometer. Homogeneous samples were prepared by dissolving approximately 0.200 g of polymer in 2.5 ml of deuterated-tetrachloroethene in 10 mm sample tubes utilising a heat block and rotating tube oven at 140 C. Proton decoupled 13C single pulse NMR spectra with NOE (powergated) were recorded using the following acquisition parameters: a flip-angle of 90 degrees, 4 dummy scans, 4096 transients an acquisition time of 1.6 s, a spectral width of 20 kHz, a temperature of 125 C, a bilevel WALTZ proton decoupling scheme and a relaxation delay of 3.0 s. The resulting FID was processed using the following processing parameters: zero-filling to 32k data points and apodisation using a gaussian window function; automatic zeroth and first order phase correction and automatic baseline correction using a fifth order polynomial restricted to the region of interest.
Quantities were calculated using simple corrected ratios of the signal integrals of representative sites based upon methods well known in the art.
c) Comonomer content of polar comonomers in low density polyethylene

(1) Polymers Containing >6 wt % Polar Comonomer Units

[0222] Comonomer content (wt %) was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy. Below is exemplified the determination of the polar comonomer content of ethylene ethyl acrylate, ethylene butyl acrylate and ethylene methyl acrylate. Film samples of the polymers were prepared for the FTIR measurement: 0.5-0.7 mm thickness was used for ethylene butyl acrylate and ethylene ethyl acrylate and 0.10 mm film thickness for ethylene methyl acrylate in amount of >6 wt %. Films were pressed using a Specac film press at 150 C., approximately at 5 tons, 1-2 minutes, and then cooled with cold water in a not controlled manner. The accurate thickness of the obtained film samples was measured.
After the analysis with FTIR, base lines in absorbance mode were drawn for the peaks to be analysed. The absorbance peak for the comonomer was normalised with the absorbance peak of polyethylene (e.g. the peak height for butyl acrylate or ethyl acrylate at 3450 cm.sup.1 was divided with the peak height of polyethylene at 2020 cm.sup.1). The NMR spectroscopy calibration procedure was undertaken in the conventional manner which is well documented in the literature, explained below.
For the determination of the content of methyl acrylate a 0.10 mm thick film sample was prepared. After the analysis the maximum absorbance for the peak for the methylacrylate at 3455 cm.sup.1 was subtracted with the absorbance value for the base line at 2475 cm.sup.1 (A.sub.methylacrylate-A.sub.2475). Then the maximum absorbance peak for the polyethylene peak at 2660 cm.sup.1 was subtracted with the absorbance value for the base line at 2475 cm.sup.1 (A.sub.2660-A.sub.2475). The ratio between (A.sub.methylacrylate-A.sub.2475) and (A.sub.2660-A.sub.2475) was then calculated in the conventional manner which is well documented in the literature.
The weight-% can be converted to mol-% by calculation. It is well documented in the literature.
Quantification of copolymer content in polymers by NMR spectroscopy
The comonomer content was determined by quantitative nuclear magnetic resonance (NMR) spectroscopy after basic assignment (e.g. NMR Spectra of Polymers and Polymer Additives, A. J. Brandolini and D. D. Hills, 2000, Marcel Dekker, Inc. New York). Experimental parameters were adjusted to ensure measurement of quantitative spectra for this specific task (e.g 200 and More NMR Experiments: A Practical Course, S. Berger and S. Braun, 2004, Wiley-VCH, Weinheim). Quantities were calculated using simple corrected ratios of the signal integrals of representative sites in a manner known in the art.

(2) Polymers Containing 6 wt. % or Less Polar Comonomer Units

[0223] Comonomer content (wt. %) was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy. Below is exemplified the determination of the polar comonomer content of ethylene butyl acrylate and ethylene methyl acrylate. For the FT-IR measurement a film samples of 0.05 to 0.12 mm thickness were prepared as described above under method 1). The accurate thickness of the obtained film samples was measured.
After the analysis with FT-IR base lines in absorbance mode were drawn for the peaks to be analysed. The maximum absorbance for the peak for the comonomer (e.g. for methylacrylate at 1164 cm.sup.1 and butylacrylate at 1165 cm.sup.1) was subtracted with the absorbance value for the base line at 1850 cm.sup.1 (A.sub.polar comonomer-A.sub.1850). Then the maximum absorbance peak for polyethylene peak at 2660 cm.sup.1 was subtracted with the absorbance value for the base line at 1850 cm.sup.1 (A.sub.2660-A.sub.1850). The ratio between (A.sub.comonomer-A.sub.1850) and (A.sub.2660-A.sub.1850) was then calculated. The NMR spectroscopy calibration procedure was undertaken in the conventional manner which is well documented in the literature, as described above under method 1).
The weight-% can be converted to mol-% by calculation. It is well documented in the literature.
Below is exemplified how polar comonomer content obtained from the above method (1) or (2), depending on the amount thereof, can be converted to micromol or mmol per g polar comonomer as used in the definitions in the text and claims:
The millimoles (mmol) and the micro mole calculations have been done as described below.
For example, if 1 g of the poly(ethylene-co-butylacrylate) polymer, which contains 20 wt % butylacrylate, then this material contains 0.20/M.sub.butylacrylate (128 g/mol)=1.5610.sup.3 mol. (=1563 micromoles).
The content of polar comonomer units in the polar copolymer C.sub.polar comonomer is expressed in mmol/g (copolymer). For example, a polar poly(ethylene-co-butylacrylate) polymer which contains 20 wt. % butyl acrylate comonomer units has a C.sub.polar comonomer of 1.56 mmol/g. The used molecular weights are: M.sub.butylacrylate=128 g/mole, M.sub.ethylacrylate=100 g/mole, M.sub.methylacrylate=86 g/mole).

Density

[0224] Low density polyethylene (LDPE): The density was measured according to ISO 1183-2.

The sample preparation was executed according to ISO 1872-2 Table 3 Q (compression moulding).
Low pressure process polyethylene: Density of the polymer was measured according to ISO 1183/1872-2B.

Method for Determination of the Amount of Double Bonds in the Polymer Composition or in the Polymer

A) Quantification of the Amount of Carbon-Carbon Double Bonds by IR Spectroscopy

[0225] Quantitative infrared (IR) spectroscopy was used to quantify the amount of carbon-carbon doubles (CC). Calibration was achieved by prior determination of the molar extinction coefficient of the CC functional groups in representative low molecular weight model compounds of known structure.
The amount of each of these groups (N) was determined as number of carbon-carbon double bonds per thousand total carbon atoms (CC/1000C) via:

N=(A14)/(ELD)

were A is the maximum absorbance defined as peak height, E the molar extinction coefficient of the group in question (l.Math.mol.sup.1.Math.mm.sup.1), L the film thickness (mm) and D the density of the material (g.Math.cm.sup.1).
The total amount of CC bonds per thousand total carbon atoms can be calculated through summation of N for the individual CC containing components.
For polyethylene samples solid-state infrared spectra were recorded using a FTIR spectrometer (Perkin Elmer 2000) on compression moulded thin (0.5-1.0 mm) films at a resolution of 4 cm.sup.1 and analysed in absorption mode.
1) Polymer Compositions Comprising Polyethylene Homopolymers and Copolymers, Except Polyethylene Copolymers with >0.4 wt % Polar Comonomer
For polyethylenes three types of CC containing functional groups were quantified, each with a characteristic absorption and each calibrated to a different model compound resulting in individual extinction coefficients: [0226] vinyl (RHCH2) via 910 cm.sup.1 based on 1-decene [dec-1-ene] giving E=13.13 l.Math.mol.sup.1.Math.mm.sup.1 [0227] vinylidene (RRCCH2) via 888 cm.sup.1 based on 2-methyl-1-heptene [2-methyhept-1-ene] giving E=18.24 l.Math.mol.sup.1.Math.mm.sup.1 [0228] trans-vinylene (RCHCHR) via 965 cm.sup.1 based on trans-4-decene [(E)-dec-4-ene] giving E=15.14 l.Math.mol.sup.1.Math.mm.sup.1
For polyethylene homopolymers or copolymers with <0.4 wt % of polar comonomer linear baseline correction was applied between approximately 980 and 840 cm.sup.1.
2) Polymer Compositions Comprising Polyethylene Copolymers with >0.4 wt % Polar Comonomer

[0229] For polyethylene copolymers with >0.4 wt % of polar comonomer two types of CC containing functional groups were quantified, each with a characteristic absorption and each calibrated to a different model compound resulting in individual extinction coefficients: [0230] vinyl (RCH=CH2) via 910 cm.sup.1 based on 1-decene [dec-1-ene] giving E=13.13 l.Math.mol.sup.1.Math.mm.sup.1 [0231] vinylidene (RRCCH2) via 888 cm.sup.1 based on 2-methyl-1-heptene [2-methyl-hept-1-ene] giving E=18.24 l.Math.mol.sup.1.Math.mm.sup.1

EBA:

[0232] For poly(ethylene-co-butylacrylate) (EBA) systems linear baseline correction was applied between approximately 920 and 870 cm.sup.1.

EMA:

[0233] For poly(ethylene-co-methylacrylate) (EMA) systems linear baseline correction was applied between approximately 930 and 870 cm.sup.1.

3) Polymer Compositions Comprising Unsaturated Low Molecular Weight Molecules

[0234] For systems containing low molecular weight CC containing species direct calibration using the molar extinction coefficient of the CC absorption in the low molecular weight species itself was undertaken.

B) Quantification of Molar Extinction Coefficients by IR Spectroscopy

[0235] The molar extinction coefficients were determined according to the procedure given in ASTM D3124-98 and ASTM D6248-98. Solution-state infrared spectra were recorded using a FTIR spectrometer (Perkin Elmer 2000) equipped with a 0.1 mm path length liquid cell at a resolution of 4 cm.sup.1.
The molar extinction coefficient (E) was determined as l.Math.mol.sup.1.Math.mm.sup.1 via:

E=A/(CL)

where A is the maximum absorbance defined as peak height, C the concentration (mol.Math.l.sup.1) and L the cell thickness (mm).
At least three 0.18 mol.Math.l.sup.1 solutions in carbondisulphide (CS.sub.2) were used and the mean value of the molar extinction coefficient determined.

DC Conductivity Methods

Method A

[0236] The plaques are compression moulded from pellets of the test polymer composition. The final plaques have a thickness of 1 mm and size of 200200 mm. The conductivity measurement can be performed using a test polymer composition which does not comprise or comprises the optional crosslinking agent. In case of no crosslinking agent, the conductivity is measured from a non-crosslinked plaque sample using the below procedure. If the test polymer composition comprises the crosslinking agent, then the crosslinking occurs during the preparation of the plaque samples, whereby the conductivity is then measured according to the below procedure from the resulting crosslinked plaque sample. Crosslinking agent, if present in the polymer composition prior to crosslinking, is preferably a peroxide, as herein.

[0237] The plaques are press-moulded at 130 C. for 12 min while the pressure is gradually increased from 2 to 20 MPa. Thereafter the temperature is increased and reaches 180 C. after 5 min. The temperature is then kept constant at 180 C. for 15 min during which the plaque becomes fully crosslinked by means of the peroxide, if present in the test polymer composition. Finally the temperature is decreased using the cooling rate 15 C./min until room temperature is reached when the pressure is released. The plaques are immediately after the pressure release wrapped in metallic foil in order to prevent loss of volatile substances.

[0238] If the plaque is to be degassed (i.e. if it is crosslinked) it is placed in a ventilated oven at atmospheric pressure for 24 h at 70 C. Thereafter the plaque is again wrapped in metallic foil in order to prevent further exchange of volatile substances between the plaque and the surrounding.

[0239] A high voltage source is connected to the upper electrode, to apply voltage over the test sample. The resulting current through the sample is measured with an electrometer. The measurement cell is a three electrodes system with brass electrodes. The brass electrodes are equipped with heating pipes connected to a heating circulator, to facilitate measurements at elevated temperature and provide uniform temperature of the test sample. The diameter of the measurement electrode is 100 mm. Silicone rubber skirts are placed between the brass electrode edges and the test sample, to avoid flashovers from the round edges of the electrodes.

[0240] The applied voltage was 30 kV DC meaning a mean electric field of 30 kV/mm. The temperature was 70 C. The current through the plaque was logged throughout the whole experiments lasting for 24 hours. The current after 24 hours was used to calculate the conductivity of the insulation.

[0241] This method and a schematic picture of the measurement setup for the conductivity measurements has been thoroughly described in a publication presented at the Nordic Insulation Symposium 2009 (Nord-IS 09), Gothenburg, Sweden, Jun. 15-17, 2009, page 55-58: Olsson et al, Experimental determination of DC conductivity for XLPE insulation.

DC Conductivity Method B (Values in S/cm)

Broadband Dielectric Spectroscopy (BDS)

[0242] Samples (40100 mm) were made by hot pressing at 250 C. and 100 kN press force. Spacers with a thickness of 0.1 mm were used to control thickness. Disk-shaped samples were then cut out of the plaques.
All measurements were performed on disk-shaped samples with 40 mm diameter and 0.1 mm thickness. The conductivity measurements were obtained by the use of dielectric spectrometer.
Broadband Dielectric Spectroscopy (BDS) was performed using a Novocontrol alpha spectrometer in a frequency range of 10.sup.2 to 10.sup.7 Hz, at different temperatures in the range 253-383K with an error of 0.1K, at atmospheric pressure and under nitrogen atmospher.

[0243] For selected temperatures frequency scans were also performed to investigate the local and ion dynamics. The sample cell consisted of two silver-coated electrodes 40 mm in diameter and the sample with a thickness of about 0.1 mm. The complex dielectric permittivity *=i, where ist he real and is the imaginary part, is generally a function of frequency, , temperature T, and pressure P.sup.1, although here only the frequency and temperature dependencies have been investigated. The complex dielectric conductivity * can be also calculated from the complex dielectric function * as *=i.sub.f*, (.sub.f is the permittivity of free space, 8.854 pF/m) where conductivity can also be analysed in a real and an imaginary part: *=+i!. This means the conductivity data are effectively an alternative representation of the permittivity, nevertheless focusing on different features of the dielectric behaviour as we will discuss below. The analysis has been made using the empirical equation of Havriliak and Negami.sup.2

[00001]$\frac{{\mathrm{.Math.}}^{*}\left(,T,P\right)-\mathrm{.Math.}\left(T,P\right)}{\mathrm{.Math.}\left(T,P\right)}=\frac{1}{{\left[1+\left(i.Math..Math.{}_{\mathrm{HN}}\left(T,P\right)\right).Math.a\right]}^{}}$

where .sub.HN(T,P) is the characteristic relaxation time in this equation, (T,P) is the relaxation strength of the process under investigation, .sub. is the dielectric permittivity at the limit of high frequencies, and , (0<, 1) describe, respectively, the symmetrical and asymmetrical broadening of the distribution of relaxation times. The relaxation times at maximum loss (.sub.max) presented herein have been analytically obtained by fitting the relaxation spectra with the Havriliak-Negami (HN) equation as follows:

[00002]${}_{\max }={{}_{\mathrm{HN}}\left[\frac{\sin \left(\frac{}{2.Math.\left(1+\right)}\right)}{\sin \left(\frac{}{2.Math.\left(1+\right)}\right)}\right]}^{-1/}$

DC Conductivity Method C

[0244] Method A is repeated but the applied voltage was 80 kV DC meaning a mean electric field of 80 kV/mm.

DC Conductivity Method D

[0245] Method A is repeated but the applied voltage was 60 kV DC meaning a mean electric field of 60 kV/mm.

Experimental Part

[0246] The following materials are used in the examples:
LDPE1, an LDPE homopolymer of density 922 kg/m.sup.3 and MFR.sub.2 of 2.0 g/10 min.
LDPE2LDPE homopolymer having the properties of table 1:
UHMWPE1 Mw =4.610.sup.6 Da viscosity number 2200 (ISO1628-3).
The UHMWPE polymer is a homopolymer.
MDPE1a single site copolymer of ethylene with of density 930 kg/m.sup.3 and MFR.sub.2 of 2.2 g/10 min.
MDPE2a single site copolymer of ethylene with of density 935 kg/m.sup.3 and MFR.sub.2 of 1.2 g/10 min.
SSC LLDPEa single site copolymer of ethylene with of density 918 kg/m.sup.3 and MFR.sub.2 of 1.5 g/10 min.
Compounding of the polymer compositions: Each polymer component of a test polymer composition were added as separate pellets to a pilot scale extruder (Prism TSE 24TC) together with additives, if not present in the pellets, other than the crosslinking agent. The obtained mixture was meltmixed in conditions given in the below table and extruded to pellets in a conventional manner.
The crosslinking agent, herein peroxide, if present, was added on to the pellets and the resulting pellets were used for the experimental part. CrosslinkiNg conditions are defined in the conductivity tests.

EXAMPLE 1

Crosslinked Blends

[0247] The following blends are prepared:
Results are shown in FIG. 1 and summarised in table 4. As can be seen, both MDPE modified crosslinked blends exhibit extremely low stress dependence, with conductivity below 10 fS/m at 80 kV/mm. For comparison, the material with 0% MDPE exhibits more than 10 times higher conductivity

TABLE-US-00001 TABLE 4 Wt % Conductivity Conductivity Conductivity SSC- [fS/m].sup.2 [fS/m].sup.4 [fS/m].sup.3 Material MDPE (30 kV/mm) (60 kV/mm) (80 kV/mm) CE1 0 14.2 49.6 IE1 15 0.2 3.8 8.1 IE2 15 0.3 2.5 7.3 .sup.1Method A (30 kV) .sup.3Method C (80 KV) .sup.4Method D (60 KV)

EXAMPLE 2

Not Crosslinked

[0248] All blends were prepared on the Prism compounding unit described above.
These results are presented in FIG. 3.

EXAMPLE 3

Non Crosslinked

[0249] The mixtures in table 6 were prepared by melt mixing the components at 160 C. for 10 minutes in a Haake mini twin screw extruder followed by hot pressing at 250 C. and 100 kN press force. Film samples are 40100 mm. Spacers with a thickness of 0.1 mm were used to control thickness. Disk-shaped samples were then cut out of the films.
Spacers with a thickness of 0.1 mm was used to control thickness.

TABLE-US-00002 TABLE 6 CE3 IE5 LDPE2 wt % 100 95 UHMWPE wt % 5 DC Conductivity (S/cm)* 1.64E12 6.11E15 *(method B)
In FIG. 2 a visual representation of the results in Table 6 can be seen. From these results we can see that the DC conductivity drops by 2 orders of magnitude when the pure LDPE is modified with UHMWPE. In this example, all measurements were performed on disk-shaped samples with 40 mm diameter and 0.1 mm thickness.