ADDITIVES | ELECTRICALLY CONDUCTIVE
which the company says is the only plant to use the process in the US, is expected to commence production in the second half of 2024 and will provide North American compounders with a domestic source. The acetylene gas-based production process is
Right: Beki- Shield stainless steel fibres are supplied in granular form for
compounding applications
cleaner and, due to the more uniform feedstock than oil-based or furnace black processes, results in improved batch-to-batch consistency. The purity of the black pigment is higher, with very low traces of heavy metals or polycyclic aromatic hydrocar- bons (PAH). And Orion says the acetylene black material has a much lower moisture content when compared with the furnace black materials. In addition, because the yield of the acetylene process is very high, the resulting product carries lower carbon dioxide emissions per tonne com- pared to alternative carbon blacks. “While the new acetylene-based conductive additives plant was spurred by increasing EV market demand for lithium-ion batteries, it will also benefit compounders for engineering plastics applications,” says Jennifer S Stroh PhD, Orion’s Director of Specialties Sales and Marketing Americas. Orion’s acetylene-based blacks for compound- ing include the powder form Printex Y50A grade and the bead form XPB 711. The latter is an experimental grade, which offers lower dusting levels. One of the primary applications for XPB 711 is in extra- high voltage (EHV) power cables, which require good conductivity, smooth surfaces, and high cleanli- ness (attributed to low ionic and particulate impurities). The smoother surface is said to reduce the risk of electrical stress and water tree failures. According to Kevin Milks,
Marketing Manager for Polymers and Batteries at Orion, because XPB 711 is an acetylene-based
product, it also provides a more consistent conductivity.
K A E
Both XPB 711 and Orion’s Printex HV grade, which is not acetylene based, are used in high voltage cables. This is an application that demands optimisation of both oil absorption number (OAN) and statistical thickness surface area (STSA). The highest conductivity blacks in Orion’s range are its superconductive black products, such as Printex XE2B. These additives are used commercially in multiple applications, including EMI shielding and ESD applications.
16 COMPOUNDING WORLD | February 2023
Metallic options Beki-Shield stainless steel fibres, produced by Belgium’s Bekaert, are used as a conductive additive in polymers for applications ranging from electrostatic dissipation through to EMI shielding. The fibres are available as granular grains for conventional compounding production or as continuous bundles, which are typically used in pultrusion. EVs are a growing area for these conductive additives, which can provide parts offering 30-80 dB EMI shielding. Electrification of vehicles, together with the
increase in the number of sensors in the vehicles, is creating more EMI shielding requirements, accord- ing to Sam Matthews, Market Manager for Conduc- tive Solutions at Bekaert in North America. The use of higher-powered batteries in EVs
presents an opportunity for shielding compounds. While, in the past, electric vehicles have used metal housings that inherently have EMI shielding, these are likely to be replaced with plastics in the push to make EVs lighter. Plastic housings have the benefit of design freedom, but they need additives to supply EMI shielding. The move to 5G for commu- nication also raises the requirements for shielding in device housings. “In communications and EVs, people are looking for higher shielding effectiveness. The high conductivity of stainless-steel fibres requires very low loadings. Below 3 volume% is typical, which is ±20 weight% depending on your polymer; this is significantly lower than carbon black,” says Mat- thews (Figure 3). “The fibres are around 6mm long, so even after
some breakage in the compounding process, it is easier to create a conductive network with a fibre than with a carbon black particle,” he explains, adding that compounding process settings are critical and should be optimised for a particular application.
At these low loadings, the metal fibres have little
effect on mechanical properties, such as tensile strength and flexural modulus, and little effect on shrinkage or warp, so they can be processed in the same moulds as non-conductive plastics. Another advantage of the low loading is that compounds can be easily colored. Matthews says combinations of glass fibres or other additives with stainless-steel fibers are often employed to provide improved mechanical properties with high conductivity. In addition to stainless steel fibers for electrical conductivity, Bekaert is currently working on the development of new metal alloys and materials to enhance thermal conductivity and to impart magnetic properties.
www.compoundingworld.com
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