materials feature | Thermal conductivity
Data was presented that showed graphene increased the thermal conductivity of polypropylene more than carbon black. “In-house testing has confi rmed the performance
benefi ts of graphenes but also identifi ed the importance of delivering them in the appropriate form,” he said. Electrical conductivity of compounds is highly depend- ent on additive morphology and the quality of disper- sion. Cabot is developing materials that can be processed easily in conventional equipment. Many plastics producers and independent com- pounders are busy advancing and expanding their
portfolios of thermally conductive plastics to meet the growing demand from the LED lighting industry and other markets.
Compound growth The LED lighting market is expected to grow annually at 34% from 2010-2016, according to PolyOne. The market will amount to almost US$94 billion by 2020. LED lamp costs are expected to drop by 55%, and luminaires by 30%, by 2017. In many cases aluminium heat sinks are over-engi- neered, claims Philippe Chabanne, market manager for electrical & electronics at PolyOne Engineered Materi- als Europe. “While the thermal conductivity of a specialty plastic is signifi cantly lower than aluminium, with proper design, it can still manage heat just as effectively as aluminium.”
Chabanne says that PolyOne continues to see opportunities for manufacturers to replace metal in electronics applications requiring thermal manage- ment. “The advantages for the manufacturer include an ability to reduce weight and structural complexity, to control more of the logistics and value chain, to create new designs, and ultimately to lower total cost to manufacture while maintaining application perfor- mance,” he says.
Not all graphites are the same; particle size, fl ake morphology and the intrinsic anisotropic thermal conductivity of graphite introduce a strong anisotropy in the thermal conductivity of a material. Bar chart shows in-plane and through-plane thermal conductivity of injection moulded HDPE plaques loaded with different Imerys graphite grades
PolyOne is collaborating with others to develop and test new grades of Therma-Tech thermally conductive plastics to replace thermosets and metal for functional heat sink printed circuit boards. “These specialty plastics must combine fl ame resistance, dielectric properties and resistance to high temperatures so that they can withstand lead-free refl ow soldering in surface mount technology (SMT) during assembly of electronics components,” Chabanne says. They also have to effectively manage heat build-up generated by higher- heat producing electronic components, and act as a heat dissipater in assembled systems. Excess tempera- ture is a major cause of failure in electronic systems. Another major compounder, RTP has developed specialty compounds with thermally conductive and EMI shielding properties, also intended for replacement of metal housings used in various E&E applications. “Our newest compounds actually exceed the thermal conductivity of stainless steel,” says Neil Hardwick, conductive products marketing manager. He says the company offers compounds with conductivities as high as 35 W/mK; these contain metal fi ller. Compounds containing mineral fi llers have conductivities up to around 12 W/mK.
Cabot’s test results comparing the thermal conductivity of PP containing 6 and 10 wt% of carbon black and graphene. Measurements on compression moulded discs using ASTM E1461 Flash method
22 COMPOUNDING WORLD | February 2015
Hardwick says RTP has been pushing thermally conductive compounds for around two years, but it is only now that signifi cant commercialisation of fi nished
www.compoundingworld.com
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