High-voltage direct current cable insulation and semiconductive shield

1. High-voltage direct current cable semiconductive shield comprising: a blend of or which is made from a blend of

(a) at least one ethylene copolymer having a density of less than about 0.900 grams/cubic centimeter, a melt index of from about 0.5 to about 10 grams/10 minutes, a crystallinity of less than about 10 percent and a catalyst residue of less than about 1000 ppm;

(b) a carbon black having a low level of ionic species;

(c) at least one polar polymer modifier in an amount effective to provide a semiconductive shield made with the blend with an enhanced field conductivity and enhanced space charge leakage at high fields relative to a semiconductive shield made with a blend which does not include a polar polymer modifier; and

(d) at least one ion scavenger in an amount effective to reduce ionic mobility relative to a semiconductive shield made with a blend, which does not include an ion scavenger.

2. A high-voltage direct current cable semiconductive shield according to claim 1 , wherein the ethylene copolymer is selected from the group consisting of

(a) ethylene/alpha olefin copolymers and

(b) nonpolar, low crystalline ethylene copolymers selected from the group consisting of ethylene/propylene copolymer and ethylene/styrene copolymer and mixtures thereof.

3. The high-voltage direct current semiconductive shield of claims 1 or 2 , wherein the blend further includes at least one heat stabilizer.

4. The high-voltage direct current semiconductive shield of claim 3 , wherein

(a) the polar polymer modifier is selected from the group consisting of (i) a polymer having a density of less than 0.900 grams/cubic centimeter with at least one side group selected from the group consisting of hydroxyl, carboxyl, styrenic; (ii) a polymer having a density of less than 0.900 grams/cubic centimeter and at least one side group which is a residue of maleic anhydride, vinyl acetate or vinyl acrylate; (iii) a polylactone resin and; (iv) mixtures thereof, and

(b) the ion scavenger has at least one chelating group.

5. The high-voltage direct current semiconductive shield of claim 3 , wherein the ethylene copolymer is crosslinked.

6. The high-voltage direct current semiconductive shield of any of claims 1 or 2 , wherein

(a) the polar polymer modifier is selected from the group consisting of (i) a polymer having a density of less than 0.900 grams/cubic centimeter with at least one side group selected from the group consisting of hydroxyl, carboxyl, styrenic; (ii) a polymer having a density of less than 0.900 grams/cubic centimeter and at least one side group which is a residue of maleic anhydride, vinyl acetate or vinyl acrylate; (iii) a polylactone resin and; (iv) mixtures thereof, and

(b) the ion scavenger has at least one chelating group.

7. The high-voltage direct current semiconductive shield as recited in claim 6 , wherein the ion scavenger is selected from the group consisting of 1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine, poly[[6-[1,1,3,3-tetramethylbutyl)amino]-s-triazine-2,4-diyl] [2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]] N,N′-bis(0-hydroxybenzal) oxalydihydride, barbituric acid, tertiary phosphorous acid ester of a thiobisphenol, and N,N′-diphenyuloxamid, and mixtures thereof.

8. The high-voltage direct current semiconductive shield of claim 6 , wherein the ethylene copolymer is crosslinked.

9. The high-voltage direct current semiconductive shield of any one of claims 1 , 2 , or 7 , wherein the ethylene copolymer is crosslinked.