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materials | Thermally conductive compounds


ment of LEDs and electrical devices. The newest member of the product family, with high mineral reinforcement, is Durethan TP 723-620. “The special feature behind this polyamide 6 is its outstanding thermal conductivity combined with high light reflection and excellent flame retardance,” says Thomas Malek, New Business Development Manager for Lighting Technology in the Lanxess High Performance Materials business unit. “As far as we know, this premium combination of properties makes it absolutely unique in this material class.”


Figure 6: Through-plane thermal conductivity values for an ethylene-octene copolymer elastomer (Engage 8003) reinforced with various levels of Martoxid TM filler. Measurements made using steady state method with a THASYS THA01-1419 (ASTM 1114-06 at 23°C)


Source: Huber


compound´s particle interface,” he says. On the other hand, mechanical properties improve as particle size decreases (Figure 5).


Right: This


modular flange for a drive used in car interior ventilation systems is made from


Durethan BTC 75 H3.0 EF


from Lanxess, which contains 75% mineral reinforcement


Highly loaded Recognising the importance of additive loadings, Huber Engineered Materi- als claims its new Martoxid TM thermally conductive and electri- cally insulating calcined alumini- um oxide-based fillers enable loadings that are much higher than achievable using previous technologies, providing high levels of thermal conductivity for applications such as encapsulating electronic parts and polymeric composites. Despite the high addition rates, Huber says Martoxid TM retains good processing properties. Four series of Martoxid TM fillers have been


Right: This heat sink design by Covestro and Vesuto


maximises performance


from thermally conductive plastics


developed, varying in aspects such as density, coating type and processing characteristics (notably rheological behaviour). For a performance snapshot, Huber highlights Martoxid TM-4250 from the 4000 series, which is aimed at polyamide compounds. A filler loading of 70 wt% can be easily reached, the company says. Already at a 60 wt% loading, the finished compound provides an isotropic thermal conductivity of 1.5 W/m.K and retains good processability and mechan- ical properties.


A number of major polymer makers are playing a part in the thermally conductive compounds arena. Lanxess, for example, continues to expand its range of polyamides for components used in thermal manage-


52 COMPOUNDING WORLD | February 2017 www.compoundingworld.com


Shape matters Because of the shape of the filler particles, the thermal conductivity of the new compound is directionally dependent, reaching 2.5 W/m.K along the direction of flow (determined by the NanoFlash test). This is about 10 times higher than that of the standard 30% glass fibre reinforced polyamide 6, Durethan BKV 30 H2.0. Another cited advantage of the material is its high


tracking resistance: its CTI A value is 600 volts. “Electrical assemblies can therefore be positioned closer together without resulting in shorts or device defects caused by leakage current,” says Malek. And despite the high mineral content, the density of 1.7 g/cm3


is


comparatively low, which the company says means it supports cost-efficient, lightweight component solutions. Lanxess already offers two other thermally conductive polyamides,


Durethan BTC 65 H3.0 EF and BTC 75 H3.0 EF, with high levels of mineral


reinforcement –65 and 75% respectively – (see Compounding World Feb 2016). Their thermal


conductivities are 1.0 and 1.4 W/m.K through the wall thickness, meaning they are on par with polyamides containing boron nitride and aluminium oxide as thermally conductive fillers. The 75% mineral rein- forced Durethan BTC 75 H3.0 EF grade is being used by Robert Bosch to produce modular flanges for drives


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