materials feature | Thermal conductivity
Graph by ESK shows in-plane and through- plane conductivity of various additives for thermally conductive compounds
filling levels of under 30% by volume. Furthermore, it is possible to obtain through-plane
conductivity of well over 2 W/m.K; something that ESK says is not possible with rival fillers. In fact, with 3M Boronid Cooling Filler flakes, which are textured agglomerates of platelets that provide a less anisotropic conductivity in space, it is possible to reach 4 W/m.K at a loading of 50% by volume. Despite this high loading, however, processability of compounds remains good. The properties of 3M Boronid Cooling Filler as a dry
lubrication medium, as well as their low hardness (1-2 on the Mohs scale), ensure non-abrasive processing even at the highest filling levels, ESK claims (this is something common to all BN additives in fact). Other additives have a hardness of up to 9, by contrast. ESK offers a range of grades, depending on the
ESK says that a 50% loading of boron nitride in PA can deliver in-plane conductivity up to 10 W/m.K
material into which they are incorporated, the process- ing method, and the application. Additives are in the form of non-agglomerated platelets, “soft” agglomera- tions of platelets, “hard” textured agglomerates in the form of flakes, and bulk agglomerates. The company highlights 3M Boronid Cooling Filler Platelets 15/400, a soft agglomerated version, developed for extrusion
compounding. This zero-dusting grade has a high bulk density and pourability. Power consumption during extrusion is much lower than with alternative, non- lubricating filling materials, the company claims. “Due to the low required filling level when using Cooling Filler Platelets, compound developers still have leeway for combining it with additional secondary filling materials,” noted Armin Kayser, speaking at the Com- pounding World Forum last December in Philadelphia. Additional property requirements like mechanical strength can be achieved by adding glass fibre, for example. According to Kayser, even filling levels of over 50%
can be processed with economic throughputs and process reliably in conventional extrusion systems. Good dispersion is achieved even at such high filling levels. The agglomerates disperse in the melted polymer mass even at low shear rates, breaking down into individual platelets of approximately 15 µm, necessary for achieving high thermal conductivity levels. Simple gravimetric side dosing is sufficient for common compound recipes. Kayser says BN provides potential for cost savings as high as 60% at the moulder, due to the high conduc- tivity of the filler, the low abrasion of the compounds, and their high processability. Saint-Gobain is another company supplying BN for
plastics compounds. It says that, compared with other thermally conductive, electrically insulating ceramic fillers such as aluminium nitride, aluminium oxide, silicon nitride and zinc oxide, HBN has the lowest density and lowest coefficient of friction. Saint-Gobain has over 50 grades of CarboTherm HBN, of which four are suitable for plastics compounds; a fine platelet grade (PCTF5) for thin-wall applications; a free-flowing loosely agglomerated powder (PCTP30D) for cost-sensitive, high-volume applications; a grade with larger platelets where higher conductivity is required (PCTP40); and a premium, high-density
14 COMPOUNDING WORLD | February 2014
www.compoundingworld.com
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