Semiconductive polymer composition for electric power cables

Abstract

The invention provides a novel semiconductive polymer composition with improved smoothness and dispersibility of carbon black when compounding the polymer composition and feasible balance with other properties such as volume resistivity. The semiconductive polymer composition comprises (a) from 30 to 90 wt % of a polymer component, (b) from 10 to 70 wt % of carbon black and the carbon black (b) has a mass pellet strength (MPS) according to ASTM D1937-13 of from 50 to 250 N. The invention further relates to a process for preparing the semiconductive polymer composition comprising the steps of: i) introducing 30-90 wt % of a polymer component as defined above and 0-8 wt % additives in a mixer device and mixing the polymer component and additives at elevated temperature such that a polymer melt is obtained; ii) adding 10-70 wt % of a carbon black as defined above to the polymer melt and further mixing of the polymer melt.

1 - 20 . (canceled) 
     
     
         21 . A semiconductive polymer composition comprising
 (a) from 30 to 90 wt % of a polymer component,   (b) from 10 to 70 wt % of carbon black and   wherein the carbon black (b) has a mass pellet strength (MPS) according to ASTM D1937-13 of from 50 to 250 N.   
     
     
         22 . The semiconductive polymer composition according to  claim 21 , wherein the carbon black (b) has an average value of individual pellet hardness (CSAV) according to ASTM D5230-13 of from 5 to 30 cN. 
     
     
         23 . The semiconductive polymer composition according to  claim 21 , wherein the carbon black (b) has an average value of individual pellet hardness for the 5 hardest pellets (M5H) according to ASTM D5230-13 of from 10 to 40 cN. 
     
     
         24 . The semiconductive polymer composition according to  claim 21 , wherein the carbon black (b) has an average pellet size according to ASTM D1511-12 of from 0.1 to 5 mm. 
     
     
         25 . The semiconductive polymer composition according to  claim 21  wherein the carbon black (b) has one or more of the following characteristics:
 a BET surface area (STSA value), measured by nitrogen adsorption according to ASTM D 6556-10 of from 20 to 60 m 2 /g; 
 an iodine adsorption number measured according to ASTM D1510-13, method A of from 20 to 60 g/kg; 
 a DBP oil absorption number measured according to ASTM D2414-13 of from 100 to 150 cm 3 /100 g. 
 
     
     
         26 . The semiconductive polymer composition according to  claim 21  wherein the composition has a surface smoothness measured according to the surface smoothness analysis using a tape sample as described herein of
 not more than 200 particles/m 2  having a width of larger than 150 μm, and/or 
 not more than 9 particles/m 2  having a width of larger than 200 μm. 
 
     
     
         27 . The semiconductive polymer composition according to  claim 21  wherein said carbon black (b) is furnace carbon black. 
     
     
         28 . The semiconductive polymer composition according to  claim 21 , wherein said polymer component (a) comprises an alpha-olefin polymer. 
     
     
         29 . The semiconductive polymer composition according to  claim 21 , wherein said polymer component (a) comprises a homopolymer of a C 2-12  alpha-olefin or a copolymer of a C 2-8  alpha-olefin with one or more comonomers of an C 3-30  alpha-olefin. 
     
     
         30 . The semiconductive polymer composition according to  claim 21 , wherein polymer component (a) is selected from a branched ethylene homo- or copolymer and a linear ethylene homo- or copolymer. 
     
     
         31 . The semiconductive polymer composition according to  claim 21 , wherein said polymer component (a) comprises at least one polyunsaturated comonomer. 
     
     
         32 . The semiconductive polymer composition according to  claim 21 , wherein said polymer component (a) comprises at least one polar comonomer. 
     
     
         33 . The semiconductive polymer composition according to  claim 32 , wherein said polar comonomer is selected from: vinyl carboxylate esters, such as vinyl acetate and vinyl pivalate, (meth)acrylates, such as methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate and hydroxyethyl(meth)acrylate, olefinically unsaturated carboxylic acids, such as (meth)acrylic acid, maleic acid and fumaric acid, (meth)acrylic acid derivatives, such as (meth)acrylonitrile and (meth)acrylic amide, vinyl ethers, such as vinyl methyl ether and vinyl phenyl ether. 
     
     
         34 . The semiconductive polymer composition according to  claim 32  wherein the content of polar comonomer in said polymer component (a) is from 0.5 to 35 wt %, based on the total amount of said polymer component (a). 
     
     
         35 . The semiconductive polymer composition according to  claim 21  which has a MFR 21 , of from 1.0 g/10 min to 15 g/10 min, measured according to ISO 1133 at 125° C. and a load of 21.6 kg. 
     
     
         36 . The semiconductive polymer composition according to  claim 32 , which is cross-linkable via radical reaction or via silane groups. 
     
     
         37 . A process for preparing a semiconductive polymer composition comprising the steps of:
 i) introducing 30-90 wt % of the polymer component (a) as defined in  claims 21  and 0-8 wt % additives in a mixer device and mixing the polymer component and additives at elevated temperature such that a polymer melt is obtained;   ii) adding 10-70 wt % of a carbon black as defined in  claim 21  and further mixing of the polymer melt to obtain a semiconductive polymer mixture,   iii) extruding and pelletising the obtained polymer mixture.   
     
     
         38 . An electric power cable comprising a conductor surrounded by one or more layers, wherein at least one of said one or more layers is a semiconductive layer, which comprises a semiconductive polymer composition as defined in  claim 21 . 
     
     
         39 . The electric power cable according to  claim 38 , wherein at least one of the inner and outer semiconductive layer(s) comprises a semiconductive polymer composition as defined in  claim 21 .