Pre-expanded polypropylene resin beads and process for producing same

A process for processing a polypropylene resin in-mold foamed product whose surface inherent resistance that is measured in accordance with JIS K6911 after the polypropylene resin in-mold formed product is kept in a room conditioned at a temperature of 23° C. under 50% humidity for 24 hours is 5×1011Ω or less,

• the process comprising the steps of:
• 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 C6 to C24 fatty acid and/or a polyglycerin monoester of a C6 to C24 fatty acid and (B) a glycerin diester of a C6 to C24 fatty acid(s) and/or a polyglycerin diester of a C6 to C24 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 to produce pre-expanded polypropylene resin beads;
• and
• filling a mold with the pre-expanded polypropylene resin beads and heating the pre-expanded polypropylene resin beads in the mold.