JPS6438447A - Pre-expanded polypropylene resin particle and its production - Google Patents

Abstract

PURPOSE:To obtain easily without fail the title spherical particles which have a high expansion ratio relative to the particle diameter and excellent in filling property and expansion efficiency and can give a foam free of poor fusion, by expanding talc-containing PP resin particles so that the obtained pre-expanded particles may have a particle diameter and a bulk density both in a specified range. CONSTITUTION:100pts.wt. PP resin (e.g., ethylene/propylene random copolymer) is homogeneously mixed with 0.3-0.001pt.wt. talc by, e.g., dry blending to obtain talc-containing PP resin particles. 100pts.wt. particles formed by finely grinding the talc-containing PP particles to a particle diameter <=1mm with a grinder is mixed with at least 100pts.wt. dispersing medium such as water and at least 0.1pt.wt. dispersing agent such as Al2O3 or CaCO3, and the mixture is heated in a pressure vessel with agitation to a temperature at which the fusion is completed to obtain spherical resin particles of a particle diameter <=300mu. After cooling, these particles are placed in a sealed vessel together with a volatile blowing agent and a dispersant, and heated to a temperature >=a predetermined temperature under agitation, while keeping the pressure inside the vessel at a pressure above or below the vapor pressure of the volatile blowing agent. This mixture is released into a low-pressure atmosphere to obtain the title particles of a particle diameter <=100mu and a bulk density of 0.015-0.045g/cm<3>.