PRODUCTION OF PREFOAMED PARTICLES

PURPOSE:A composition consisting of polymer particles containing a volatile foaming agent and a dispersant is discharged out of a tightly sealed vessel in a specific range of the discharge rate, thus producing prefoamed particles with uniform extent of foaming and uniform bubble number without breakage and deformation. CONSTITUTION:After polymer particles, preferably of an olefinic polymer are made to contain a volatile foaming agent such as an aliphatic or alicyclic hydrocarbon or halogenated hydrocarbon in an amount of 0.04-0.33mol/mol of the polymer particles, the resultant particles are dispersed in a dispersant which does not dissolve the polymer particles such as water, ethylene glycol, methanol or the like, in a tightly sealed vessel. Then, under an atmosphere lower than the inside of the vessel in pressure, the composition is discharged at a rate of 0.5-3kg/min/mm. defined by the equation to give the objective prefoamed particles. The above discharge rate is controllable, when the pressure of an inorganic gas in the vessel 1, land diameter phi of the discharge orifice 2 and land length 1 are varied.