A combination of flaky and spherical boron nitride particles is boosting thermal conductivity significantly.
Hexagonal boron nitride (hBN or α-BN) is a synthetic, high-polymer material with graphite-like sheet structure. However, in contrast to graphite, there are covalent bondings between the atoms and the electrons are localized resulting in high electrical resistivity and white color. Furthermore, hBN is an excellent thermal conductor; it is chemically inert and stable up to 1.000 °C.
„The thermal conductivity is increased by a factor of 3 to 4 with TCF boron nitride in the plane.“
The hexagonal platy lamellar structure of boron nitride is responsible for the high anisotropy of thermal conductivity. The in-plane thermal conductivity ranges up to 300 W/m ·K, while through-plane thermal conductivity shows values of about 30 to 40 W/m ·K. Since platelets usually align themselves in flow direction of polymer masses, this has to be regarded if BN-filled plastics are designed.
A comparison with alumina fillers shows the directional differences. However, the high thermal conductivity potential of boron nitride at substantially lower filling rates becomes obvious also. The high anisotropy of boron nitride platelets (flakes) might be disadvantageous in particular applications, such as thermal interface materials, silicones as well as impregnation and potting resins.
High-Cool TCF spherical boron nitride agglomerates overcome this shortcoming by keeping BN particles in a random orientation and by making in consequence the material rather isotropic. The through-plane thermal conductivity is increased by factor 3 to 4.
BNF grades are fillers with high aspect ratios of 2:1 up to 30:1 and a flaky morphology. The products are offered with median sizes varying from 5 µm up to 25 µm. Particle size, distribution and low specific surface areas allow an excellent thermal management profile and provide good workability at low viscosities in polymers equally. BNF flakes perfectly meet the requirements for injection molding and high-shear processing. The BNF portfolio includes standard surface treatments for essential polymer systems. Compatibilizing of the particle surface to specific customer needs can be rendered on request.
BNS grades are randomized agglomerates of boron nitride platelets with spherical shape. Since natural crystalline orientation of hBN is overridden, particles show a rather isotropic behavior. The spherical agglomerates have uniform size and a narrow distribution. Median particle sizes of the various products range from 65 µm to 180 µm. The specific surface area is kept on a very low level.
BNS grades exhibit outstanding workability, high flowability and excellent rheological properties in thermosets and thermoplastics. If BNF and BNS particles are combined in one plastic matrix, the alignment of flaky BNF with the flow direction will be suspended. The through-plane conductivity is significantly enhanced.Read more