SEMICONDUCTIVE POLYOLEFIN COMPOSITION COMPRISING CARBONACEOUS STRUCTURES, POWER CABLE COMPRISING THE SAME AND USE THEROF

Abstract

The invention relates to a semiconductive polyolefin composition comprising, (A) 80 to 99.5 wt. % of an olefin polymer base resin based on the total weight of the semiconductive polyolefin composition; (B) 0.1 to 10.0 wt. % of first carbonaceous structures based on the total weight of the semiconductive polyolefin composition; (C) 0.2 to 15.0 wt. % of carbon black and/or second carbonaceous structures based on the total weight of the semiconductive polyolefin composition; and (D) optionally additives; wherein the combined amount of components (B) and (C) is at least 0.3 wt. % and not more than 15.0 wt. % based on the total weight of the semiconductive polyolefin composition; and wherein the semiconductive polyolefin composition has an electrical percolation threshold of not more than 5 wt. % of the combined amount of components (B) and (C) dispersed in the olefin polymer base resin (A), the electrical percolation threshold being defined as the critical concentration in wt. % of the components (B) and (C) in the olefin polymer base resin (A) where an exponential increase in electrical conductivity is observed; wherein the polyolefin composition has a conductivity of at least 1.Math.10.sup.−7 S/cm determined according to Broadband Dielectric Spectroscopy for a percolation threshold of 1.0 wt. % or lower and 2-point electrical measurements for a percolation threshold of more than 1.0 wt. %; and wherein components (A) to (D) add up to 100 wt. %.

Claims

1. A semiconductive polyolefin composition comprising (A) 80 to 99.5 wt. % of an olefin polymer base resin based on the total weight of the semiconductive polyolefin composition; (B) 0.1 to 10.0 wt. % of first carbonaceous structures based on the total weight of the semiconductive polyolefin composition; (C) 0.2 to 15.0 wt. % of carbon black and/or second carbonaceous structures based on the total weight of the semiconductive polyolefin composition; and (D) optionally additives; wherein the combined amount of components (B) and (C) is at least 0.3 wt. % and not more than 15.0 wt. % based on the total weight of the semiconductive polyolefin composition; and wherein the semiconductive polyolefin composition has an electrical percolation threshold of not more than 5 wt. % of the combined amount of components (B) and (C) dispersed in the olefin polymer base resin (A), the electrical percolation threshold being defined as the critical concentration in wt. % of the components (B) and (C) in the olefin polymer base resin (A) where an exponential increase in electrical conductivity is observed; wherein the polyolefin composition has a conductivity of at least 1.Math.10.sup.−7 S/cm determined according to Broadband Dielectric Spectroscopy for a percolation threshold of 1.0 wt. % or lower and 2-point electrical measurements for a percolation threshold of more than 1.0 wt. %; and wherein components (A) to (D) add up to 100 wt. %.

2. The semiconductive polyolefin composition according to claim 1, wherein the first carbonaceous structures (B) are selected from the group consisting of graphene, modified graphene, reduced graphite worm-like structures, carbon nanotubes, modified carbon nanotubes or combinations thereof.

3. The semiconductive polyolefin composition according to claim 1, wherein component (C) comprises only carbon black; or wherein component (C) comprises only second carbonaceous structures; or wherein the second carbonaceous structures are selected from the group consisting of graphene, modified graphene, reduced graphite worm-like structures, or combinations thereof.

4. The semiconductive polyolefin composition according to claim 1, wherein the weight ratio between components (B) and (C) is in the range of 9:1 to 1:20.

5. The semiconductive polyolefin composition according to claim 1, wherein the olefin polymer base resin (A) is present in an amount of 85 to 99.5 wt. % based on the total weight of the semiconductive polyolefin composition.

6. The semiconductive polyolefin composition according to claim 1, wherein the first carbonaceous structures (B) are present in an amount of 0.1 to 9.0 wt. %, based on the total weight of the semiconductive polyolefin composition.

7. The semiconductive polyolefin composition according to claim 1, wherein the carbon black and/or the second carbonaceous structures (C) are present in an amount of 0.2 to 12.5 wt. %, based on the total weight of the semiconductive polyolefin composition.

8. The semiconductive polyolefin composition according to claim 1, wherein the combined amount of components (B) and (C) is at least 0.4 wt. %, based on the total weight of the semiconductive polyolefin composition; and/or wherein the combined amount of components (B) and (C) is not more than 12.5 wt. %, based on the total weight of the semiconductive polyolefin composition.

9. The semiconductive polyolefin composition according to claim 1, wherein the semiconductive polyolefin composition has an electrical percolation threshold of not more than 4 wt. % of the combined amount of components (B) and (C) dispersed in the olefin polymer base resin (A).

10. The semiconductive polyolefin composition according to claim 1, wherein the polyolefin composition has a conductivity of at least 1.Math.10.sup.−6 S/cm determined according to Broadband Dielectric Spectroscopy for a percolation threshold of 1.0 wt. % or lower and 2-point electrical measurements for a percolation threshold of more than 1.0 wt. %.

11. The semiconductive polyolefin composition according to claim 1, wherein the olefin polymer base resin (A) is selected from the group consisting of ethylene homopolymer, propylene homopolymer, copolymer of ethylene with at least one C3 to C8 α-olefin as comonomer and copolymer of propylene with at least ethylene or one C4 to C8 α-olefin as comonomer.

12. The semiconductive polyolefin composition according to claim 1, wherein the olefin polymer base resin (A) comprises a copolymer of ethylene with at least one comonomer selected from unsaturated esters or a heterophasic propylene copolymer.

13. Semiconductive polyolefin composition according to claim 1 comprising (A) 90 to 99.5 wt. % of the olefin polymer base resin based on the total weight of the semiconductive polyolefin composition; (B) 0.2 to 2.0 wt. % of the first carbonaceous structures based on the total weight of the semiconductive polyolefin composition; and (C) 0.2 to 10 wt. % of carbon black and/or the second carbonaceous structures, preferably of carbon black, based on the total weight of the semiconductive polyolefin composition; wherein the combined amount of components (B) and (C) is at least 0.5 wt. %, based on the total weight of the semiconductive polyolefin composition; wherein the semiconductive polyolefin composition has an electrical percolation threshold of 1 wt. % or lower of the combined amount of components (B) and (C) dispersed in the olefin polymer base resin (A); and wherein the polyolefin composition has a conductivity of at least 1.Math.10.sup.−5 S/cm determined according to Broadband Dielectric Spectroscopy for a percolation threshold of 1.0 wt. % or lower and 2-point electrical measurements for a percolation threshold of more than 1.0 wt.

14. A power cable comprising a semiconductive layer which comprises the semiconductive polyolefin composition as defined in claim 1.

15. A method for making a power cable, comprising forming a semiconductive layer around a conductor, wherein the semiconductive layer is formed from the semiconductive polyolefin composition of claim 1.

16. The semiconductive polyolefin composition according to claim 1, wherein the weight ratio between components (B) and (C) is in the range of 8:1 to 1:15.

17. The semiconductive polyolefin composition according to claim 1, wherein the olefin polymer base resin (A) is present in an amount of 87 to 99.5 wt. % based on the total weight of the semiconductive polyolefin composition.

18. The semiconductive polyolefin composition according to claim 1, wherein the first carbonaceous structures (B) are present in an amount of 0.2 to 6.0 wt. % based on the total weight of the semiconductive polyolefin composition.

19. The semiconductive polyolefin composition according to claim 1, wherein the carbon black and/or the second carbonaceous structures (C) are present in an amount of 0.5 to 11 wt. % based on the total weight of the semiconductive polyolefin composition.

20. The semiconductive polyolefin composition according to claim 1, wherein the combined amount of components (B) and (C) is at least 1.0 wt. % based on the total weight of the semiconductive polyolefin composition; and/or wherein the combined amount of components (B) and (C) is not more than 11 wt. % based on the total weight of the semiconductive polyolefin composition.

Description

EXAMPLE SECTION

1. Materials

Polymer Base Resins

Polypropylene (PP)

[0098] The polypropylene (PP) used in the examples is HC300BF, which is an isotactic propylene homopolymer having a{circumflex over ( )}n MFR.sub.2 (230° C./2.16 kg) of 3.3 g/10 min (Isotacticity Index: 98%), commercially available from Borealis AG.

High Density Polyethylene (HDPE)

[0099] In all examples using HDPE the polyolefin base resin was a Ziegler-Natta catalyzed HDPE being a unimodal high density copolymer of ethylene and 1-butene (comonomer content of 0.8 mol %), which is prepared by a low pressure polymerization process in a gas phase reactor and which has a density of 962 kg/m.sup.3 and an MFR.sub.2 (2.16 kg, 190° C.) of 12 g/10 min. The HDPE was obtained from Borealis AB.

Ethylene-Butyl Acrylate (EBA)

[0100] The ethylene-butyl acrylate (EBA) used in the examples is an ethylene-butyl acrylate copolymer (butyl acrylate content of 17 wt. %, density of 925.5 kg/m.sup.3; MFR.sub.2=7 g/10 min), which was obtained from Borealis Antwerp.

Low Density Polyethylene (LDPE)

[0101] In all examples using LDPE the olefin polymer base resin was a standard low density polyethylene (LDPE). The LDPE was obtained from Borealis AB, it was produced in a tubular reactor, having an MFR.sub.2 (2.16 kg, 190° C.) of 2 g/10 min and density of 922.5 kg/m.sup.3.

Carbonaceous Structures

[0102] Carbonaceous structure 1 (CS1) was obtained by Cabot Corporation, Boston, Mass., USA. CS1 (GPX-404) is a carbonaceous structure forming clusters or worm-like structures and is obtained from Cabot Corporation, Boston, Mass., USA. CS1 can be obtained by the process as described in WO2019/070514.

[0103] Carbon Nanostructures (CNS) (CS2) Athlos were obtained by Cabot Corporation, Boston, Mass., USA.

[0104] The properties of the carbonaceous structures are summarized in Table 1.

TABLE-US-00001 Sample BET (m.sup.2/g) Volatile (%) Form Density (g/L) CS1 674 5.4 Worms  8 CS2 200 N/A N/A 135

Carbon Black

[0105] Vulcan XC500 (CB1) was obtained by Cabot Corporation, Boston, Mass., USA. Vulcan XCMax (CB2) was obtained by Cabot Corporation, Boston, Mass., USA. CSX-254 Carbon Black (CB3) was obtained by Cabot Corporation, Boston, Mass., USA.

[0106] Denka Black Carbon Black (CB4) was obtained by Denka Corporation, Japan.

2. Measurement Methods and Procedures

Melt Flow Rate

[0107] The MFR.sub.2 was measured with 2.16 kg load at 190° C. for polyethylene and at 230° C. for polypropylene according to ISO 1133. MFR.sub.21 was measured with 21.6 kg load at 190° C. for polyethylene and at 230° C. for polypropylene according to ISO 1133.

Polymer Density

[0108] The polymer density is measured according to the density immersion method described in ISO 1183.

Density of Carbonaceous Structures

[0109] Densities are determined using a method similar to ASTM D7481-09, i.e. weighing a specified volume of material after at least three taps.

BET Surface Area

[0110] BET is determined using ASTM D6556-04.

Volatility

[0111] Volatilities are determined using thermogravimetric analysis under nitrogen.

Particle Size Distribution (PSD)

[0112] PSD is determined by scanning electron microscopy without statistical analysis.

Electrical Percolation Threshold

[0113] The electrical percolation threshold as defined above was determined as follows:

[0114] The electrical conductivity of each of the samples comprising different amounts of the filler is calculated as the reciprocal of the electrical resistivity measured above:

[00001]$\sigma =\frac{1}{\rho }$

[0115] The obtained values of the electrical conductivity are plotted against the values of the amount of the filler. The percolation threshold was determined from the plot as the critical (minimum) concentration in wt % of the reduced graphite oxide worm-like structures (b) in the olefin polymer base resin (a) where an exponential increase (at least 2-3 order of magnitude) in electrical conductivity is observed, as will be shown below.

Conductivity

[0116] The conductivity is the electrical conductivity above the percolation threshold in situations where the network is fully developed and, despite further addition of the filler, the change in electrical conductivity is minimal (within an order of magnitude). Thus, the post-percolation conductivity is determined from the plot at the area of the curve, where the exponential growth of the electrical conductivity has stopped and the curve has flattened.

Compounding

[0117] Filled polyolefin compositions having incorporated carbonaceous structures and/or carbon black were prepared as follows:

[0118] All samples were produced using a Brabender mixer (Plasticoder PLE-331). The mixer was preheated (180° C. for polyethylene-based resins, 210° C. for polypropylene-based resins) prior to the addition of the resin. The rotation speed was set to 10 rpm. The resin was added first followed by the filler. As soon as all the components were added, the rotation speed was increased to 50 rpm and kept for 10 minutes. After the mixing was done, the composition was pelleted and samples were prepared for the relevant tests.

3. Results

[0119] In the following Tables properties of the obtained semi-conductive polyolefin compositions are shown.

TABLE-US-00002 TABLE 2 Filler 1 Amount Filler 2 Amount Conductivity Material (wt %) (wt %) (S/cm) CE1 PP CS1 0.2 1.66E−17 0.5 1.39E−17 1.0 1.93E−16 1.5 3.27E−09 2.0 6.55E−07 2.5 2.92E−04 3.5 0.00243 4.0 0.00518 5.0 0.00354 IE1 PP CS1 CB2 1.2 2.8 3.97E−06 2.0 2.0 7.48E−04 2.8 1.2 0.00638 3.6 0.4 0.00707 IE2 PP CS1 CB1 1.2 2.8 1.55E−07 2.0 2.0 3.71E−04 2.8 1.2 6.95E−04 3.6 0.4 6.94E−04 IE3 PP CS1 CB3 2.0 2.0 2.23E−4  2.8 1.2 0.00247 3.6 0.4 0.00498 IE4 PP CS1 CB4 2.0 2.0 3.85E−04 2.8 1.2 0.00237 3.6 0.4 0.00997

TABLE-US-00003 TABLE 3 Filler 1 Filler 2 Filler 3 Amount Amount Amount Conductivity Material (wt %) (wt %) (wt %) (S/cm) CE2 HDPE CS1 0.25 2.64E−17 0.5 6.07E−17 1.0 5.80E−16 1.5 3.08E−06 2.0 6.15E−06 2.5 4.10E−04 3.0 5.66E−04 4.0 0.00288 5.0 0.02019 CE3 HDPE CB4 1.0 1.34E−16 IE5 HDPE CS1 CS2 0.75 0.25 0.00283 0.5 0.5 0.07128 0.25 0.75 0.0498  IE6 HDPE CS1 CS2 CB4 0.5 0 0.5 1.16E−15 0.375 0.25 0.375 4.08E−05 0.25 0.5 0.25 0.00438 0.125 0.75 0.125 0.08198

TABLE-US-00004 TABLE 4 Filler 1 Filler 2 Filler 3 Amount Amount Amount Conductivity Material (wt %) (wt %) (wt %) (S/cm) CE4 HDPE CS2 0.05 1.14E−10 0.1 4.05E−05 0.125 2.46E−04 0.15 1.62E−04 0.2 5.74E−03 0.5 3.25E−03 1.0 1.50E−02 1.5 1.63E−02 2.0 4.07E−02 IE7 HDPE CS2 CB4 0.25 0.75 6.91E−03 0.5 0.5 8.67E−02 0.75 0.25 7.92E−02 CE5 HDPE CB3 1 1.69E−16 IE8 HDPE CS2 CB3 0.25 0.75 2.39E−02 0.5 0.5 4.81E−02 0.75 0.25 3.00E−01 CE6 EBA CS2 0.1 3.25E−10 0.5 4.15E−04 0.75 1.40E−03 1.0 1.64E−02 CE7 EBA CB4 1 5.84E−16 IE9 EBA CS2 CB4 0.25 0.75 1.38E−03 0.5 0.5 8.16E−02 0.75 0.25 1.05E−01 CE8 LDPE CS2 0.1 4.70E−16 0.5 4.42E−04 0.75 1.39E−03 1.0 1.31E−02 CE9 LDPE CB4 1.0 4.70E−17 IE10 LDPE CS2 CB4 0.25 0.75 9.39E−05 0.5 0.5 4.43E−03 0.75 0.25 3.24E−03

[0120] As can be derived from the inventive examples the combination of a first carbonaceous structure with carbon black and/or a second carbonaceous structure provides advantageous conductivity with low filler loading. In particular is shown by IE1-IE4 and IE6-IE10 that the amount of carbon black can be significantly reduced which has i.a. a positive effect on the processing properties of the respective semiconductive polyolefin compositions.

[0121] A similar effect can be observed by the combination of first and second carbonaceous structures as demonstrated in IE5. IE5 shows that the combination of two carbonaceous structures according to the invention allows the reduction of the amount of in particular CS1 used in the semiconductive polyolefin composition while having good conductivity. This has also a positive effect on the processing.

[0122] Although the present invention has been described with reference to various embodiments, those skilled in the art will recognize that changes may be made without departing from the scope of the invention. It is intended that the detailed description be regarded as illustrative, and that the appended claims including all the equivalents are intended to define the scope of the invention.