EXPANSION MOLDING PROCESS OF POLYPROPYLENE RESIN IN MOLD

PURPOSE:To minimize the diviation of dimension-shrinkage factor of a product by a method in which after a mold has been filled with the prefoamed particle of polypropylene resin in the state of compression, the prefoamed particle is heated and adhesively melted under the steam pressure equal to the filling pressure in compression process or less. CONSTITUTION:After a mold has been filled with the prefoamed particle of polypropylene resin in the state of compression, said particle is heated and adhesively melted under the lower steam pressure than the filling pressure for compressing said particle, whereby the object foamed and molded in the mold is obtained. The steam pressure for adhesively melting the prefoamed particle is preferably 1.8kg/cm or higher. The filling pressure for compressing the prefoamed particle is preferably in the range of 2.0-5.0kg/cm . The prefoamed particle to be used has two melting points in the measurement of differential scanning calorimeter process, and the melting peak calory QH due to the melting point of high temperature side in two molting points is preferably 1.0-3.1cal/g.