Expandable methyl methacrylate resin particles, methyl methacrylate resin pre-expanded particles, methyl methacrylate expansion-molded body, and method for producing expandable methyl methacrylate resin particles

A method for producing expandable methyl methacrylate resin particles, comprising the steps of:

• (a) copolymerizing monomers including a methyl methacrylate monomer and an acrylic ester monomer to obtain a copolymer;
• and
• (b) impregnating a blowing agent in the copolymer thus obtained, wherein
• in the step (a),
• an amount of the methyl methacrylate monomer to be added is not less than 91 parts by weight and not more than 99 parts by weight and an amount of the acrylic ester monomer to be added is not less than 1 part by weight and not more than 9 parts by weight, relative to 100 parts by weight of a total amount of the methyl methacrylate monomer and the acrylic ester monomer to be added, and
• in the step (a),
• the monomers are added to an aqueous medium to initiate a polymerization reaction of the monomers, the aqueous medium containing a poorly water-soluble inorganic salt in an amount of not less than 0.08 parts by weight and not more than 0.20 parts by weight relative to 100 parts by weight of the monomers, and
• at a timing when a polymerization conversion rate is not less than 35% and not more than 70%, the poorly water-soluble inorganic salt is added thereto in an amount of not less than 0.08 parts by weight and not more than 0.50 parts by weight relative to 100 parts by weight of the monomers, and
• the expandable methyl methacrylate resin particles have an average particle diameter of 0.6 mm to 1.0 mm.