PRODUCTION OF EXPANDABLE THERMOPLASTIC POLYMER PARTICLE

摘要

PURPOSE:To obtain the title polymer particles having a uniform particle diameter distribution in good efficiency by suspending specified thermoplastic polymer particles in an aqueous medium, adding a polymerizable monomer and an easily volatile blowing agent to the dispersion and polymerizing the mixture. CONSTITUTION:A polymerizable monomer (e.g. styrene) containing a radical- generating polymerization initiator (e.g. benzoyl peroxide) is injected through a nozzle into an aqueous dispersing medium and regular vibrational disturbances are applied to the liquid column of the injected polymerizable monomer through a vibrator to form a group of liquid drops of a uniform diameter in the aqueous medium. The drops are polymerized under conditions in which neither association nor additional dispersion of the drops occurs to obtain thermoplastic polymer particles at least 90% of which have a particle diameter which is 0.9-1.1 times as large as the volume-mean particle diameter. These particles in an amount equivalent to 1-60wt.% of the entire polymer at the end of polymerization are suspended in an aqueous medium and a polymerizable monomer is continuously or intermittently added to the dispersion. The polymerization is started, and an easily volatile blowing agent is added to the mixture at any desired point of time between the start of polymerization and its end.