Patent ID: 8129020

Claim:
A method of producing heat-expanded microspheres, comprising the steps of: feeding a gas containing a plurality of heat-expandable microspheres, each heat-expandable microsphere comprising a shell of thermoplastic resin and a blowing agent encapsulated therein having a boiling point not higher than the softening point of the thermoplastic resin, and the plurality of heat-expandable microspheres having an average particle size from 1 to 100 micrometer, through a gas-introducing tube equipped with a dispersion nozzle on an outlet thereof and fixed inside a hot gas flow which includes a turbulent hot gas flow, and then jetting the gas from the dispersion nozzle; making the gas collide with a collision plate fixed on a downstream position of the dispersion nozzle in order to disperse the heat-expandable microspheres in the hot gas flow; and bringing the dispersed heat-expandable microspheres into contact with the hot gas flow, the temperature difference between a maximum temperature and a minimum temperature of the hot gas flow of which does not exceed 40 degree.C., and heating them at a temperature not lower than the expansion initiating temperature of the heat-expandable microspheres and thus expanding the same such that the heat-expanded microspheres have a void fraction not higher than 0.70, where the void fraction is a physical property value for evaluating packing efficiency of a bulk volume of the heat-expanded microspheres, the void fraction representing the ratio of void in the bulk volume of the heat-expanded microspheres.