| 摘要 |
Disclosed herein is a method for producing a foamed board based on a polystyrenic resin by foam-extruding a foamable composition obtained by incorporating a foaming agent into the polystyrenic resin, which comprises using, as a raw resin, a polystyrenic resin in which a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is at least 3.2, the z average molecular weight is at least 5 x 10 5, and the MFR is 1-10 g/10 min, or a polystyrenic resin in which a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is lower than 3.2, the z average molecular weight is at least 5 x 10 5, and a slope value of storage elastic modulus, G' at a circular frequency, .omega. within a range of from 10-1 to 10 1 (rad/sec) falls within a range of 0.8-1.2 as determined by dynamic viscoelasticity measurement in which vibrating strain is given under temperature conditions of 220.degree.C.
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