ADDITIVES | THERMALLY CONDUCTIVE


THERMALLY CONDUCTIVE | ADDITIVES


good thermal conductivity enhancer for medium conductivity levels (1-3 W/m.K) but adds that ATH can also be a cost-effective alternative that is completely free of abrasion problems. Its applicability is, in part, due to better under- standing of component design. Not that long ago, Ihmels says potential users were seeking com- pounds with very high thermal conductivity values in the range of 5-15 W/m.K or even more. Today much lower values are required, which he attributes to smarter design of the final parts. “1-3 W/m.K is often requested today,” he says. There are also TC applications emerging in the


field of electric vehicles – housings and gap fillers in battery packs and modules for example – where flame retardancy requirements are also being discussed. “The challenge is to offer both proper- ties, flame retardancy and thermal conductivity, in a single formulation,” he says. Among mainstream TC fillers, only metal


hydrates provide a flame retardancy effect, accord- ing to Ihmels. When other fillers are used to generate TC, he says additional FR additives must be included and this can lead to negative effects due to very high filling levels. Furthermore, he points out that additives such as magnesium oxide (MgO), silica and especially aluminium oxide (Al2


O3 ) show high abrasion on tooling, MgO and


aluminium nitride are moisture-sensitive (AlN can decompose to release ammonia), and boron nitride (BN) is costly, difficult to process and provides highly anisotropic thermal conductivity. In a presentation prepared by Ihmels and given by his colleague Kerry Smith (Product Manager – Americas) at Conductive Plastics 2018, Ihmels


Formulation Material removal rate (µm/h)


PA6/ Martoxid TM-4250


Visualization (arrows show flow direction)


5.6


PA6 / Al2SiO5


42.8


Table 1: Comparison of slit die wear for two different formulations of TC PA6 containing aluminium oxide and aluminosilicate fillers. Visualisations were created via chromatic confocal microscopy (3-D surface screening)


Source: Huber


Figure 1: Effect on thermal conductivity of an HDPE (TC 0.5 W/m.K) of various fillers (Apyral is an Al(OH)3


, Nabalox NO 325 is an Al2O3 Source: Nabaltec .)


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