Polymer composition for W and C application with advantageous electrical properties

Abstract

The invention relates to power cable polymer composition which comprises a single site polyethylene (SSPE), a power cable, for example, a high voltage direct current (HV DC), a power cable polymer insulation, use of a polymer composition for producing a layer of a power cable, and a process for producing a power cable.

Claims

1. A non-crosslinked power cable polymer composition consisting essentially of a composition selected from the group consisting of a multimodal single site polyethylene (SSPE) and a multimodal single site polyethylene (SSPE) with one or more antioxidants, wherein the power cable polymer composition is configured to have and has a DC electrical conductivity of 5.0 fS/m or less when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition.

2. A power cable polymer composition according to claim 1, wherein the single site polyethylene has a density of from 930 to 945 kg/m.sup.3.

3. A power cable polymer composition according to claim 1, wherein the power cable polymer composition is a thermoplastic power cable polymer composition.

4. A power cable polymer composition according to claim 1, wherein the power cable polymer composition is a high voltage (HV) and/or extra-high voltage (EHV) power cable polymer composition.

5. A power cable polymer composition according to claim 1, wherein the power cable polymer composition is a high voltage direct current (HV DC) and/or an extra high voltage direct current (EHV DC) power cable polymer composition.

6. A power cable polymer composition according to claim 1, wherein the power cable polymer composition has a DC electrical conductivity of 0.05 to 5.0 fS/m when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition.

7. A power cable polymer composition according to claim 1, wherein the power cable polymer composition has a DC electrical conductivity of 4.0 fS/m or less when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition.

8. A power cable polymer composition according to claim 1, wherein the single site polyethylene is a medium density single site polyethylene (MD SSPE).

9. A power cable comprising a conductor which is surrounded at least by an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein the insulation layer consists of the power cable polymer composition according to claim 1.

10. A power cable polymer insulation consisting of the power cable polymer composition according to claim 1.

11. A power cable polymer composition according to claim 1, wherein the power cable polymer composition has a DC electrical conductivity of 0.01 to 3.0 fS/m when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition.

12. A power cable polymer composition according to claim 1, wherein the power cable polymer composition has a DC electrical conductivity of 0.01 to 2.0 fS/m when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition.

13. A power cable polymer composition according to claim 1, wherein the power cable polymer composition has a DC electrical conductivity of 3.0 fS/m or less when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition.

14. A power cable polymer composition according to claim 1, wherein the power cable polymer composition has a DC electrical conductivity of 2.0 fS/m or less when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition.

15. A power cable polymer composition according to claim 1, wherein the power cable polymer composition has a DC electrical conductivity of 1.0 fS/m or less when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition.

16. A power cable according to claim 9, wherein the power cable is a high voltage direct current (HV DC) power cable and/or an extra high voltage direct current (EHV DC) power cable.

17. A power cable polymer insulation according to claim 10, wherein the power cable polymer insulation is a high voltage direct current (HV DC) power cable polymer insulation and/or an extra high voltage direct current (EHV DC) power cable polymer insulation.

18. A power cable polymer composition according to claim 1, wherein the single site polyethylene is an MDPE having a density of from 930 to 945 kg/m.sup.3 or an HDPE having a density of more than 945 kg/m.sup.3.

19. A power cable polymer composition according to claim 1, wherein the power cable polymer composition consists of the multimodal single site polyethylene.

20. A method for producing a power cable, comprising: polymerizing at least ethylene and one or more comonomer(s) in the presence of a single site catalyst to produce a non-crosslinked power cable polymer composition consisting essentially of a composition selected from the group consisting of a multimodal single site polyethylene (SSPE) and a multimodal single site polyethylene (SSPE) with one or more antioxidants, the power cable polymer composition having a DC electrical conductivity of 5.0 fS/m or less when measured at 70° C. and 30 kV/mm mean electric field on a 1 mm thick plaque sample consisting of the power cable polymer composition and producing the cable with the power cable polymer composition.

21. A method according to claim 20 wherein the power cable comprises a conductor surrounded by at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, said method further comprising: producing at least one layer of the power cable with the power cable polymer composition.

22. A method according to claim 21, wherein the power cable is a direct current (DC) power cable.

23. A method according to claim 21, further comprising: producing the insulation layer with the power cable polymer composition.

24. A method according to claim 21, wherein the insulation layer consists of the power cable polymer composition.

25. A method according to claim 20, wherein said power cable is a direct current (DC) power cable.

Description

EXAMPLE 1

Comparative

(1) A commercially available LDPE, i.e. LE4253 supplied by Borealis Sweden, which is a crosslinkable low density polyethylene having a density of 922 kg/m.sup.3.

EXAMPLE 2

Inventive

(2) Single Site Polyethylene (SSPE)

(3) Single Site Catalyst

(4) A Possible Preparation of a Single Site Catalyst

(5) 16.4 kg methylalumoxane in toluene (30 weight-%, supplied by Albemarle) was mixed with 8.5 kg dry toluene and added to 0.46 kg di(n-benzyl)di(n-butylcyclopentadienyl)hafnium in toluene (67.9 wt %) and stirred at room temperature for 20 min. The obtained solution was added dropwise during 45 min to 10 kg activated silica (commercial silica carrier, XP02485A, having an average particle size 20 μm, supplier: Grace) and stirred at room temperature for 3 hours. The solvents were evaporated off under nitrogen flow at 50° C. to obtain the supported catalyst. The obtained catalyst had an Al/Hf ratio of 200 mol/mol; a Hf-concentration of 0.42 wt % and an Al-concentration of 14.0 wt %.

(6) Single site polyethylene (SSPE): The single site polyethylene (SSPE) of inventive example 2, was prepared with the above single site catalyst and as described below.

(7) Preparation of Polyethylene, i.e. a Single Site Polyethylene (SSPE) of Inventive Example 2

(8) The single site polyethylene was prepared using in addition to prepolymerisation reactor, a slurry-loop reactor as well as a gas phase reactor. The prepolymerisation stage was carried out in slurry in a 50 dm.sup.3 loop reactor under conditions and using feeds of catalyst (as prepared above), monomers, antistatic agent and diluent (propane (C3)) as disclosed in Table 1. The obtained slurry together with the prepolymerised catalyst was introduced into a 500 dm.sup.3 loop reactor to carry out the actual polymerisation. The polymer slurry was withdrawn from the loop reactor and transferred into a flash vessel operated at 3 bar pressure and 70° C. temperature where the hydrocarbons were substantially removed from the polymer. The polymer was then introduced into a gas phase reactor. The conditions and feeds/feed ratio in loop and gas phase polymerisation steps are disclosed in Table 2 and 3

(9) TABLE-US-00001 TABLE 1 Process conditions in the Prepolymerisation (inventive example 2) Example 2 (Inventive) Temperature [° C.] 60 Pressure [bar] 62 Catalyst Feed [g/h] 38 Antistatic feed [g/h] 7 C2 feed [kg/h] 2 C4 feed [g/h] 50 C3 feed [kg/h] 32

(10) TABLE-US-00002 TABLE 2 Process condition in the Loop reactor and properties (inventive example 2) Example 2 (Inventive) Temperature [° C.] 85 Pressure [bar] 58 C2 feed [kg/h] 33 H2 feed [g/h] 7.9 C4 feed [kg/h] 1.7 C3 feed [kg/h] 71 H2/C2 ratio [mol/kmol] 0.55 C4/C2 ratio [mol/kmol] 91 C4/C2 feed ratio [g/kg] 0.05 Production rate [kg/h] 29.9 Split [wt %] 49 MFR.sub.2 [g/10 min] 100 Density [kg/m3] 939

(11) TABLE-US-00003 TABLE 3 Process conditions in the Gas phase reactor and properties (inventive example 2) Example 2 (Inventive) Temperature [° C.] 80 Pressure [bar] 20 C2 feed [kg/h] 39.3 H2 feed [g/h] 0 C4 feed [kg/h] 0 C6 feed [kg/h] 1.2 C2 concentration [mol %] 21.7 H2/C2 ratio [mol/kmol] 0 C4/C2 ratio [mol/kmol] 0 C6/C2 ratio [mol/kmol] C4/C2 feed ratio [g/kg] 0 C6/C2 feed ratio [g/kg] Production rate [kg/h] 32 Split [wt %] 51 MFR.sub.2 [g/10 min] 2.5 Density [kg/m3] 934 For all the tables: C2: ethylene C3: propane H2: hydrogen C4: 1-butene C6: 1-hexene

(12) The powder produced after the multistage polymerisation was compounded and pelletised using an extruder and the medium density polyethylene obtained had a MFR.sub.2=2.2 dg/10 min and a density=935.8 kg/m.sup.3.

EXAMPLE 3

Inventive

(13) The same single site catalyst as in Example 2 was used.

(14) Single site polyethylene (SSPE): The single site polyethylene (SSPE) of inventive example 3 was prepared with the above single site catalyst of Example 2 and as described below.

(15) Preparation of Polyethylene, i.e. a Single Site Polyethylene (SSPE) of Inventive Example 3

(16) Polyethylene was prepared using a slurry-loop reactor as well as a gas phase reactor. The catalyst prepared according to the description above was introduced into a 500 dm.sup.3 loop reactor to carry out the actual polymerisation. The polymer slurry was withdrawn from the loop reactor and transferred into a flash vessel operated at 3 bar pressure and 70° C. temperature where the hydrocarbons were substantially removed from the polymer. The polymer was then introduced into a gas phase reactor. The conditions and feeds/feed ratio in loop and gas phase polymerisation steps are disclosed in Table 4 and 5.

(17) TABLE-US-00004 TABLE 4 Process condition in the Loop reactor and properties (inventive example 3) Example 3 (Inventive) Temperature [° C.] 85 Pressure [bar] 58 C2 feed [kg/h] 32 H2 feed [g/h] 5.7 C4 feed [kg/h] 2.2 C3 feed [kg/h] 108 H2/C2 ratio [mol/kmol] 0.46 C4/C2 ratio [mol/kmol] 115 C4/C2 feed ratio [g/kg] 0.07 Production rate [kg/h] 28 Split [wt %] 54 MFR.sub.2 [g/10 min] 90 Density [kg/m3] 936

(18) TABLE-US-00005 TABLE 5 Process condition in the Gas phase reactor and properties (inventive example 3) Example 3 (Inventive) Temperature [° C.] 80 Pressure [bar] 20 C2 feed [kg/h] 74.4 H2 feed [g/h] 0.9 C4 feed [kg/h] 1.4 C6 feed [kg/h] 3.6 C2 concentration [mol %] 50.2 H2/C2 ratio [mol/kmol] 0.3 C4/C2 ratio [mol/kmol] 8.6 C6/C2 ratio [mol/kmol] 10 C4/C2 feed ratio [g/kg] C6/C2 feed ratio [g/kg] Production rate [kg/h] 28 Split [wt %] 46 MFR.sub.2 [g/10 min] 1.2 Density [kg/m3] 929 For all the tables: C2: ethylene C3: propane H2: hydrogen C4: 1-butene C6: 1-hexene

(19) The powder produced after the multistage polymerisation was compounded and pelletised using an extruder and the medium density polyethylene obtained had a MFR.sub.2=1.2 dg/10 min and a density=930.4 kg/m.sup.3.

(20) TABLE-US-00006 TABLE 6 Polymer compositions and the DC electrical conductivity results: Ex 1 Ex 2 Ex 3 Components comparative inventive inventive crosslinked LDPE 100 (LE4253) SSPE, wt %* 100 SSPE, wt %* 100 DC conductivity, 48 0.2 0.5 fS/m Ref is crosslinked LDPE Ref contained crosslinking agent and was crosslinked as disclosed in DC conductivity method under “Determination methods” and the conductivity was measured from the crosslinked plaques. *The amounts of polymer composition components in table 6 are based on the combined amount of the used polymer composition components. The amount 100 wt % of polymer in table 6 means that this polymer is the sole polymer component.

(21) As can be seen form table 6, the single site polyethylenes (SSPEs) of inventive examples 2 and 3 show excellent low DC conductivity. The single site polyethylenes (SSPEs), in accordance with the present invention, are suitable in the power cable polymer compositions of the invention, e.g. in DC power cables, for example, in HV DC power cables.