INORGANIC HOLLOW POWDER, PROCESS FOR PRODUCING THE INORGANIC HOLLOW POWDER, AND COMPOSITION COMPRISING THE INORGANIC HOLLOW POWDER

摘要

This invention provides an inorganic hollow powder which has high purity and, at the same time, has been subjected to further size reduction and enhanced percentage hollowness. Specifically, the inorganic hollow powder has an average particle diameter of 1 to 5 µm, a maximum particle diameter of not more than 20 µm, a standard deviation of particle size distribution of not more than 3 µm, and an average percentage hollowness of 35 to 70% by volume. The inorganic hollow powder is produced by supplying an inorganic starting material powder having a specific surface area of not less than 500 m²/g and an average particle diameter of not more than 7 µm into a flame formed by a burner comprising at least a triple pipe part comprising, for example, a supporting gas supply pipe, a combustible gas supply pipe, and an inorganic starting material powder supply pipe provided in that order from the outer side at a delivery rate of not less than 80 m/s through the inorganic starting material powder supply pipe. The inorganic hollow powder, when incorporated into rubber or resin, is useful for lowering in permittivity, for example, in multilayered printed boards, electric wire covering materials, and semiconductor sealing materials.