Boron Nitride in Thermoplastics (for LED Housings)

Abstract

Boron nitride (BN) is increasingly being used as a filler in thermoplastics, primarily to increase the thermal conductivity of the resins. Filler-reinforced plastics are being considered to replace traditionally metal parts in a number of markets, with applications such as under-hood automotive parts, sensors and housings for motors, LEDs, and other electronic devices. When BN powders are used as fillers in resins, the BN-resin composite materials also demonstrate anisotropic properties, largely determined by the orientation of the platy BN crystals in the final part. To overcome this problem of anisotropy, boron nitride powders have been developed which are agglomerates of single crystal. In such agglomerate grades, platy BN crystals are held together to form a larger particle to randomize their orientation. Such BN powder grades, broadly called agglomerate grades, demonstrate more isotropic properties than do single crystal BN grades. One of the biggest challenges of using agglomerate BN grades is to preserve the structure through all the processing steps. In the case of thermoplastics, the BN agglomerates can break down during the extrusion step and/or the molding step. Both the screw configuration during extrusion and the flow configuration during molding determine the extent of shear of the BN agglomerates. The thermal conductivity of single crystal platelet and agglomerate boron nitrides in a thermoplastic resin is examined in this paper to consider and explain the effect of particle morphology. The anisotropic properties will be characterized on BN-plastic composite parts. The effect of screw configuration during extrusion and molding conditions on the thermal conductivity and other physical strength properties will also be examined and the trade-offs will be discussed.