Patent ID: 8785508

Claim:
A process for producing pre-expanded polypropylene resin beads, comprising: introducing polypropylene resin particles, water, a dispersion agent, and a foaming agent in a pressure-resistant vessel, so as to prepare an aqueous dispersion, wherein the polypropylene resin particles has a polypropylene resin composition including (A) a glycerin monoester of a C 6 to C 24 fatty acid and/or a polyglycerin monoester of a C 6 to C 24 fatty acid and (B) a glycerin diester of a C 6 to C 24 fatty acid(s) and/or a polyglycerin diester of a C 6 to C 24 fatty acid(s), in such a manner that a weight ratio [=(A)/(B)] between (A) and (B) is not less than 1.3 but not more than 10, and a total content [=(A)+(B)] is not less than 0.3 parts by weight but not more than 5 parts by weight with respect to 100 parts by weight of the polypropylene resin; pressuring the aqueous dispersion at a temperature range of a melting point of the polypropylene resin particles ±20° C., so as to cause the polypropylene resin particles to contain the foaming agent; and releasing the aqueous dispersion into a low pressure atmosphere whose pressure is lower than inside the pressure resistant vessel.