| 摘要 |
PROBLEM TO BE SOLVED: To stabilize expansion in mold by controlling scatter of peak ration of polyolefin resin pre-expanded particles to 1.2 or less in standard deviation, and to improve scatters of molding cycle and dimension of a molded article. SOLUTION: When the polyolefin resin pre-expanded particles are used to expansion in mold, the peak ratio calculated from differential scanning calorimetry is controlled to 1.2 or less in standard deviation as a parameter representing crystalline condition of the resin. Furthermore, in a gas discharge step of depressurizing expansion, increase in the peak ratio with the time of discharge is depressed by a method to raise a temperature in a pressure vessel gradually and continuously, or a method not to keep regular pressure in the pressure vessel but to raise it gradually and continuously when using an expanding agent effective on lowering melting point of polyolefin resins. Thus the pre- expanded particles in which scatter among the crystalline particles is small can be manufactured.
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