materials | Thermally conductive


Figure 5: Typical characteristics of additives for thermally conductive polymer compounds


Source: Ensinger


Figure 6: Processing challenges of thermally conductive compounds Feature


Process technology High filler content • feeding technology • pelletizing technology


High thermal conductivity • control of process temperature Hardness/abrasion Shear-sensitive fillers Brittleness


Source: Ensinger


identify. “Both materials display an ideal balance between high thermal conductivity, impressive mechan- ical properties and good processing behaviour,” the company says. Thermal conductivity of these compounds is close to being isotropic, Lanxess says. Despite the high mineral content, both compounds are also said to be easy to process using injection moulding. A more recent development from the company is another highly filled polyamide 6 compound currently called Durethan TP723-620 (TP stands for Trial Product). This has anisotropic thermal conductivity: approximately 2.5 W/mK in the direction of flow and approximately 1.4 W/mK perpendicular to it. This compound also offers UL94 V-0 flame retardance with a wall thickness of 0.75 mm, together with enhanced reflectivity of around 85%.


Right:


Desalination plant heat exchanger


tubes manufac- tured in a


PP-graphite


compound by Technoform Kunststoff- profile


52 INJECTION WORLD | May 2016 www.injectionworld.com


• screw design • wear protection • screw configuration • pelletizing technology


Conductive yarns Compounding company Grafe Polymer Technik is also making moves in the area of thermally conductive grades but is beating its own path. Project manager Carlos Caro says: “As a producer of electrically conduc- tive thermoplastic compounds we have been assessing the market in terms of further effects and useful applications. The topic of thermal conductivity has been one of them. Our first activities referred to the increase of thermal conductivity in HDPE for pipes applications. “In 2011 we analysed some benchmarks and came to the special boron nitride products of ESK Ceramics (now 3M). However, due to the fact that many compa- nies like SABIC, Bayer, Schulman, Barlog, Albis, Ensinger and others have been focusing successfully on materials for injection moulding and extrusion, we wanted to take a different approach by inducing a thermally conductive effect on synthetic spinning yarns (PA, PP or PET).” Caro says this was done successfully in 2013, with


Grafe able to produce its own spinning yarn made of PP with a BN content of 25%. “The special preparation of this BN material brings positive aspects for spinning yarns like free flowing behavior, no-dust, low hardness (Mohs 1) and low heat-up during extrusion at higher loadings. The cooling periods are also very short. Most important also is the chance of colouring the materi- als,” he says. “However, the main open issue lies in the fact that the measuring techniques are only focused on parts made via injection moulding or sheet extrusion. Up until now it has not been possible to measure the exact level of thermal conductivity on our PP yarns.” Caro says external research indicates it should be


possible to reach thermal conductivity values over 5 W/ mK at a BN level below 30%. “Additionally, the possibility of production and use of thermally conductive yarns has not been assessed in full by the yarn and smart textiles producers due to the complicated supply chain with many partners and companies in between,” he says. Several suppliers of thermally conducting additives, compounds and finished parts presented their latest


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