Conductive carbon blacks | additives feature
Peter Mapleston reviews the latest developments in specialty carbon blacks for adding electrical conductivity to plastics
Controlling conductivity with carbon blacks
Carbon black producers have been busy developing specialty grades to increase the electrical conductivity of thermoplastics compounds for a variety of applications. These include cables, EMI shielding, electronics packaging, automotive components, battery applications and ATEX equipment. Conductive carbon blacks are not all the same,
as established suppliers in particular are quick to point out.
AkzoNobel highlights the advantages of its Ketjenblack-EC grades over other blacks in semi-conductive compounds for the wire and cable market. It says that its grades can be dosed at relatively low levels to achieve an acceptable conduc- tivity (see table). “This low addition level also guaran- tees that the contribution of ‘side’ products, such as metals, sulphur or grit, is low,” says Ted Kampen, technical sales manager for polymer additives in the EMEIA areas. “Although the Ketjenblack EC grades already are among the purest in the market, they still contain very low levels of impurities,” he says. But in the fi nal end-product this level is two to three times lower than with standard blacks. Producers of power cables, especially high and
extremely high voltage cables, are demanding increas- ingly clean products, Kampen notes. “It seems that nowadays impurities dictate the quality and lifetime of the cable, for that reason aspects such as ‘ions’ and ‘grit’ are frequently specifi ed product aspects. Ions potentially can migrate to other layers in the cable, such as the insulator, whilst grit may lead to unwant- ed ‘protrusion’ effects, and both aspects have a negative impact on the cable quality.” Kampen also points out that
temperature development during
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compounding of KB-EC grades is little different from that with “low structure” blacks. This is important, because high compounding temperatures can affect the quality of the semi-con compound, he says. To further optimize processing of high surface
blacks like the Ketjenblack-EC grades, industry has developed technologies to improve the wettability of the blacks. The contact between the polymer and the carbon black aggregates can be positively manipulated by such means as compound temperature optimiza- tion; selection of polymer grades with the correct viscosity, compounding time and energy; and the addition of non-migrating processing aids.
Cabot Carbon will be discussing optimization of conductivity with next generation November 2014 | COMPOUNDING WORLD 29
High-voltage
cable applica- tions require high-purity conductive
carbon blacks
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