DIELECTRIC COMPOSITIONS

1,169,855. Polymer compositions. ALLIED CHEMICAL CORP. 6 March, 1968 [10 March, 1967], No. 10990/68. Heading C3P. [Also in Division H1] Solid electrically insulating compositions and articles having high thermal conductivity and a power factor which is substantially stable to moisture comprise oriented particles of boron nitride of at least 99% purity dispersed in a matrix of a thermoplastic polymer. The platelike boron nitride particles, at least 40 microns in size are mixed with at least 25% by volume of the substantially uniform polymer particles, and the composition is shaped under heat and pressure whereby the plates orient themselves perpendicular to the direction of pressure. Particle sizes are so selected that each boron nitride particle is coated with polymer. The polymer may be polyethylene, chlorinated polyethylene, PVC, polyvinylidene chloride, polyvinyl acetate, polyvinyl butyrate, PTFE, polychlorotrifluoroethylene, cellulose triacetate, cellulose acetate butyrate, polymethyl methacrylate and other acrylic resins, polystyrene, polycarbonates, polysulphones, polypropylene or moisture-resistant polyamides.