Crosslinkable polymer composition and cable with advantageous electrical properties
A cross-linked polymer composition includes a cross-linked polyolefin. Peroxide in an amount of less than 35 mmol —O—O—/kg polymer composition may be included in the polymer composition prior to crosslinking the polyolefin. Suitable polyolefins that can be cross-linked in the polymer composition include an unsaturated LDPE homopolymer and an unsaturated LDPE copolymer of ethylene with one or more comonomers. Such unsaturated LDPE polymer can contain vinyl groups, and the total amount of vinyl groups present in the unsaturated LDPE can be higher than 0.05/1000 carbon atoms. The cross-linked polymer composition can be used, for example, in producing a cross-linkable and cross-linked article such as a cross-linkable and cross-linked direct current (DC) or other type of power cable.
1. A crosslinked DC power cable which comprises a conductor which is surrounded by at least an inner semi conductive layer comprising a first semiconductive composition, an insulation layer consisting of a polymer composition that has been crosslinked, and an outer semiconductive layer comprising a second semiconductive composition, in that order,
wherein the polymer composition of said insulation layer consists of, prior to crosslinking, a polyolefin, an antioxidant, a peroxide and a scorch retarder, wherein said peroxide is present in an amount of 10.0 to 28 mmol —O—O—/kg polymer composition, and
wherein the polyolefin is, prior to crosslinking, an unsaturated LDPE copolymer of ethylene with 1,7-octadiene, and
wherein the unsaturated LDPE copolymer contains vinyl groups and the total amount of vinyl groups present in the unsaturated LDPE is higher than 0.54/1000 carbon atoms and 0.82/1000 carbon atoms or less,
wherein the polymer composition has an electrical conductivity of 45 fS/m or less, and
wherein the peroxide is dicumylperoxide,
wherein the antioxidant is 4,4′-thiobis(2-tertbutyl-5-methylphenol),
wherein the scorch retarder is 2,4-diphenyl-4-methyl-1-pentene,
wherein the amount of antioxidant is 0.08 wt %,
wherein the amount of the scorch retarder is from 0.05 wt % to 0.18 wt % relative to the total amount of the polymer composition.
2. The crosslinked DC power cable according to claim 1 , wherein the polymer composition has an electrical conductivity of 40 fS/m or less.
3. The crosslinked DC power cable according to claim 1 , wherein the polymer composition has an electrical conductivity of 0.5 to 35 fS/m.
4. The crosslinked DC power cable according to claim 1 , wherein the polymer composition has a PENT (Pennsylvania Notch Test) life time of 800 hours or more, when measured according to PENT test under load at 2 MPa and at ageing temperature of 70° C.
5. The crosslinked DC power cable according to claim 1 , wherein the polymer composition has a Stress at Break at 70° C. of 12.0 MPa or more, or at −10° C. of 30.0 MPa or more.
6. The crosslinked DC power cable according to claim 1 , wherein the polymer composition has a Strain at break (%) at 70° C. of 450% or more, or at −10° C. of 400% or more.
7. The crosslinked DC power cable according to claim 1 wherein the polyolefin comprises a total amount of carbon-carbon double bonds/1000 carbon atoms of more than 0.4/1000 carbon atoms.
8. The crosslinked DC power cable as claimed in claim 1 , wherein the scorch retarder is present in the polymer composition of said insulation layer prior to crosslinking.