Inorganic hollow particle, process for producing the same, and composition containing the same

Abstract

The present invention herein provides fine inorganic hollow powder having a high hollowness rate, which can be incorporated into, for instance, a low dielectric rubber or resin composition. The inorganic hollow powder has an average hollowness rate of higher than 70% by volume and an average particle size ranging from 3 to 20 μm and the powder preferably has an average hollowness rate ranging from 75 to 85% by volume, an average particle size ranging from 5 to 15 μm, a maximum particle size of not more than 25 μm, a specific surface area of not more than 10 m/g, an average sphericity degree of not less than 0.90 and a purity of not less than 99% by mass. The inorganic hollow powder can be prepared by a method comprising the steps of forming a flame using a burner provided with at least a triplet-tubular portion comprising, in order from the outermost side, a combustion-improving gas-supply pipe, a combustible gas-supply pipe and an inorganic raw powder-supply pipe assembled together; injecting, into the flame at a high discharge speed, inorganic raw powder having a specific particle size through the inorganic raw powder-supply pipe, while the powder is entrained with a carrier gas having a specific relative humidity, to thus subject the powder to a heat-treatment.