Expanded polypropylene resin beads and process for the production thereof

摘要

A process for the production of expanded beads, including kneading a base resin containing a polypropylene resin and having a tensile modulus of at least 1,200 MPa together with a mixture of a coloring agent and a thermoplastic polymer having a tensile modulus lower than that of the base resin to form a kneaded mixture including a matrix of the base resin and a multiplicity of domains dispersed in the matrix and each containing the thermoplastic polymer and the coloring agent. The kneaded mixture is formed into resin particles, then treated with an organic peroxide to modify surfaces of the resin particles therewith. Foaming and expanding of the surface-modified resin particles gives expanded beads having an inside region surrounded by a surface region. The heat of fusion of a high temperature peak of the surface region is lower than that of the inside region.