| 摘要 |
PURPOSE:To obtain a low density and uniform foam free from a deteriorated layer, by a method wherein a primary foam having a specific foaming magnification is taken out of a mold, put into a closed mold having a vacuum drawing equipment, the remaining foaming agent is decomposed and foamed by heating under specific reduced pressure and then cooling is carried out. CONSTITUTION:A foamable resin composition is put into a mold, a foaming agent is gasified after starting of decomposition of a crosslinking agent, primary foaming is performed so that the unfoamed foaming agent may remains by 60-75%, and pressure is eliminated at a high temperature. A primary foam possesses a foaming magnification of 25-40% of that of a final product. The same is put into a closed mold having a vacuum drawing equipment and secondary foaming is performed. The mold is constituted of a top force 2 and a bottom force 3 and the bottom force 3 is of a double force type with an inner force 4. Small holes 5 are provided on the inner and outer forces and a small hole 6 for venting of the outer force is piped to a vacuum equipment through a valve 7. The secondary foaming is performed while reducing pressure in the inside of the mold by putting the primary foam in the mold under a high-temperature state. The remaining foaming agent is decomposed and foamed at a temperature of 160-170 deg.C and a degree of vacuum of 200mm Hg or higher as foaming conditions. At the time of the secondary foaming, talc powder or clay powder is applied to the surface of the inside of the mold beforehand.
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