| 摘要 |
PURPOSE:To obtain the subject composition having a specific weight average molecular weight and excellent foamability and moldability, causing little generation of carbon in casting and useful for a model having good surface state, etc., by copolymerizing styrene and a specific methacrylic acid ester and impregnating a foaming agent into the copolymer. CONSTITUTION:A monomer mixture containing 55-85wt.% of styrene and 45-15wt.% of a methacrylic acid ester of formula (R is 1-4C alkyl) (e.g. methyl methacrylate) is copolymerized in the presence of a radical polymerization initiator (e.g. lauroyl peroxide) to obtain a copolymer having a weight-average molecular weight of 150,000-350,000. The objective resin composition for foaming is obtained by impregnating <=10wt.% of a foaming agent (e.g. pentane) into the copolymer. A foamed model is prepared by the expansion molding of the resin composition under heating, the model is embedded in a refractory substance and a molten metal is poured on the model to form a cast metal article as the replica of the model by eliminating the model and solidifying the metal. |
