Flame retardant magnesium hydroxide HIDROMAG additionally equalizes directional differences and provides a synergistic effect on thermal conductivity.
Thermal Management is one aspect to be observed in designing plastic composites. Flame retardancy in many cases has to be regarded equally. Having in view a lower impact on human health and environment FR-additives should be halogen-free. Magnesium hydroxide is one of the proven and most efficient mineral fillers providing a halogen-free solution.
„More flame resistant with Hidromag combinations based on aluminium oxide or boron nitride.“
In a bench study Hi-Cool TCF products on alumina or boron nitride base have been utilized in combination with a specific grade of Hidromag (LY1, aminosilane-coated) in a PA 6.6 matrix. In the composition an appropriate portion of the thermal conductive filler has been replaced with the intention not to impair the thermal, but to improve the flame retardant properties.
In case of alumina based Hi-Cool TCF AR and AS fillers 10 wt.% of the 70 wt.% total filler load have been substituted. Surprisingly, the tests did not show any disruption of the thermal conductivity, on the contrary a further improving and equalizing effect on the thermal conductivity could be observed.
Flame retardant properties could be lifted according to UL94 vertical test from V2 classification to V1 and glow wire ignitability test (IEC 60695-2-13) GWIT for a 1mm specimen from 700°C to 750°C. Considering the small portion of flame retardant filler in the system, it is conceivable to increase the share up to 20 – 25 wt.% without disturbing the thermal conductivity and simultaneously achieving good flame retardant properties. Furthermore, the introduction of Hidromag magnesium hydroxide in the plastic system offers the opportunity to reduce the overall costs of the compound formulation.
The impact of magnesium hydroxide on thermal conductive and flame retardant properties has been examined in a composite containing 35 wt.% Hi-Cool BNF and 30 wt.% Hidromag LY1 in a PA 6.6 matrix. The filler volume has been kept similar to the blend of 50 wt.% boron nitride flakes in the polyamide 6.6.
The introduction of magnesium hydroxide into the formulation led to a significant increase of thermal conductivity in the through-plane direction, while only a minor impact could be observed for in-plane flow direction. The application of Hidromag magnesium hydroxide enhances remarkably the already strong thermal conductive capabilities of Hi-Cool BNF. The flame retardant effect of magnesium hydroxide in the composition lifts the UL 94 vertical test classification from failure to a V2 passing. The glow wire ignitability test (IEC 60695-2-13) GWIT for a 1mm specimen increased from 725°C to 775°C. Apart from technical aspects the partial replacement of boron nitride in the overall composition by magnesium hydroxide initiates considerable cost cutting options in thermal conductive formulations.