electrical & electronic | Thermal management
Right: Sabic has extended its Konduit thermally conductive
product line with two new
cost optimised grades for lighting
applications
company said it was to invest €50m to double capacity at the Hi-Bis operation at Bitterfeld in Germany, a joint venture with Mitsui of Japan. Apec is manufactured at Bayer’s plant at Antwerp. Last year, SABIC Innovative Plastics
announced two new additions to its Konduit range of thermally conductive plastics for production of heat sinks and luminaire housings. The Konduit PX13012 and PX11311U grades are electrically insulating compounds with a particular focus on cost reduction. “Unlike other appliance and electronics categories, in which consumers and end-users are willing to pay a premium for a better product, purchas- ing decisions in the lighting category are highly price-driven,” says Venugopal Koka, Director of Electrical and Lighting Marketing for SABIC’s Innovative Plastics business. Available only in black, the cost-optimised Konduit PX13012 grade offers high levels of thermal conductiv- ity along with improved mechanical performance, including a 50% increase in tensile strength and impact and 55% improvement in elongation at break. It is said to be suitable for use in hybrid polymer/metal or all-polymer heat sink designs. Konduit PX11311U is a white grade offering good thermal conductivity and improved UV performance, elongation at break and heat-shock performance across the temperature range from -40°C to +85°C. With a refl ectivity of up to 92%, it can be used for heat sinks and refl ectors.
Additive solutions
Right: This heat sink is
produced using a PA compound with Silatherm mineral
additive from HPF
All of these thermally conductive compounds rely on the use of additives to provide the required thermal management. Thermally conductive additives differ widely in price and performance, so users need to be sure they know what they need. For example, the use of metallic fi bres and powders is quite widespread where a high degree of thermal conductivity is required, but these products also increase electrical conductivity and this, of course, may not always be desirable. As a result, an expanding variety of electrically insulating mineral fi llers are gaining a foothold in the market. The potential
downside is that they often need to be used at high addition rates – possibly close to 60% – which can have a signifi cant impact on the mechanical properties of fi nished parts.
32 INJECTION WORLD | March 2015
Carbon has long been used to improve thermal conductivity. Daniele Bonacchi, a polymer application scientist at Imerys Graphite and Carbon (formerly Timcal), says that graphite is the best solution for thermally conductive plastics when electrical insulation is not required. He says graphite has proven to be more effective and economical than other solutions; it has a very high thermal conductivity and is affordable. “When graphite is added to a compound it gives an anisotropic thermal conductivity that can be maximised for an effi cient thermal management,” he says. For products such as heat sinks for LED lamps,
where ribs are usually present, high anisotropy can be an advantage as the thermal energy is more effi ciently removed away from the heat source. In the case of extruded heat exchangers such as cooling pipes, low aspect ratio graphite grades are preferred. For weight-saving solutions, Imerys has developed a special graphite called C-Therm that gives high thermal conductivity at low concentration. An alternative to graphite, when low conductivity is targeted, is conductive carbon black. The high structure of conductive carbon black is important to decrease the number of thermal contacts that are detrimental to the fi nal conductivity, while the higher carbon black crystal- linity improves the performance of the fi nal material. “The low thermal conductivity of the fi nal compound compared to the intrinsic
conductivity of the fi ller can be explained as the phonons do not pass as easily through interfaces (particle-particle or particle- polymer) as electrons do with tunnelling for electrical conductivity,” Bonacchi notes. “The contacts represent a large obstacle for thermal conduc- tivity and if more contacts are present more obstacles have to be passed by phonons that carry thermal energy.”
The high structure of the carbon black also increases its
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