technical paper | Carbon black
cost effective for less demanding applications Secondary features can often infl uence selection: Fine particle, high porosity (jet black colour; strong UV protection)
Coarse particle, low surface area (easier to disperse; better fl ow for moulding and impact resistance)
Wire and cable performance factors: For wire and cable applications, carbon black is used in three layers: conductor shield, insulation shield and jacket- ing. The performance needs are described below. High conductivity - determined by the morphology of the carbon black. Highly structured, low surface area blacks give good conductivity balanced with easy dispersion
Figure 9: Percolation curves for carbon blacks Key areas of concern are:
Dispersability, to avoid potential weak points in the pipe and maximise UV protection Smoothness of extrusion surfaces Excellent chemical purity, low in ash and for water pipes, low polycyclic aromatic hydrocarbons For potable water pipe, organoleptic properties must also be taken into consideration
Film: Carbon black is widely used for fi lm in agricul- tural and industrial applications: Provides opacity to a fi lm either to hide contents or to prevent light transmission Opacity is increased by fi ner particle size and porosity, but structure has little effect Increases the weatherability of a fi lm, which is impor- tant for long-term outdoor use. Good dispersion and cleanliness are important to
reduce defects and weak points in the fi lm - especially during blowing process < 30 nm grades are used for fi lms where extended UV resistance is not critical (eg mulch fi lm, pond liners) < 25 nm grades are recommended for maximum UV weatherability protection (eg silage stretch wrap, geomembranes)
Conductive applications: Carbon black can be used to impart conductivity to dissipate static electricity and in shielding for power cables and to protect sensitive electronics or prevent the build up of charge. Primary features: Fine/high-structure/porous products provide conductivity at lower loadings Coarser medium-structure carbon blacks are more
44 COMPOUNDING WORLD | November 2013
Dispersion - low surface area and soft beads make for easier dispersion and processing
Age resistance - low ash and sulphur levels reduce moisture absorption, increasing service life Surface smoothness - low residue gives fewer surface defects, lower scrap reject rate
Strippability - controlled structure to modify strip force, high cleanliness to prevent residue on underlying insulation
UV protection - fi ne primary particle size, less than 20 nm, maximises UV protection and service life
Summary There are a large number of carbon blacks commer- cially available and this can make the choice for any application challenging. To select the best carbon black, the performance needs must be defi ned and the carbon black property-performance relationship understood.
More information Dr Natalie Harris is NA technical service manager with Birla Carbon. She acknowledges the support of the following people in the writing of this article: Dr Richard Abbott, Dr Romeo Baccay, Dr Garth Brown, Christy Klinkler, Bruce McDonald, Brent Speer and Dr Deepak Tandon. The paper was originally presented at AMI’s Thermoplastics Concentrates 2012 conference. Birla Carbon is a leading global manufacturer and supplier of carbon black additives. It was formed following the acquisition of Columbian Chemicals by the Carbon Black business of Aditya Birla Group. Paul Hoffmann, commercial/marketing director at Birla Carbon, will give a presentation on “Carbon black market trends for the plastics industry” at the Thermoplastics Concentrates 2014 conference that takes place in Coral Springs, Florida, USA, on 28-30 January. For details, go to:
http://bit.ly/Conc14.
www.birlacarbon.com
www.compoundingworld.com
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