| 摘要 |
PURPOSE: To enable formation of a foam having a small compressive permanent strain by forming an intermediate foam at specified values of the average particle diameter of a foaming agent, the decomposition ratio of the agent, the pressure and temperature for a primary mold, and then carrying out the secondary expansion of the article. CONSTITUTION: This method of producing a polyolefin foam comprises the first step of forming an intermediate foam, by filling a primary mold with an expandable composition containing polyolefin, a cross linking agent and a foaming agent having an average particle diameter of 1-9μm, pressurizing the mold at 50-100kg/cm<2> and heating it to a temperature lower by 30-40 deg.C than the one-minute half-life temperature of the cross linking agent to decompose a portion of the foaming agent so that the decomposition rate may become (9 to 12)×(100/final expansion ratio) thereby inducing foaming, and depressurizing the primary mold when the temperature is high, to allow the primary expansion followed by taking an expanded article out of the mold, thus obtaining an intermediate foam. In the second step, the intermediate foam is placed in a secondary mold having dimensions and a shape corresponding to those of a final foam, and the mold is heated under normal pressure to decompose the remaining cross linking and foaming agents and allow the secondary expansion, thus producing a final foam having an expansion ratio of 15 or greater. |
