HYDROUS POLYOLEFIN RESIN COMPOSITION, PREEXPANDED PARTICLES PRODUCED THEREFROM, PROCESS FOR PRODUCING THE SAME, AND EXPANDED MOLDINGS

摘要

A water-containing polyolefin resin composition containing a polyolefin resin and a hydrophilic polymer and having a water content of 1 to 50 % by weight, which is suitable for use in preparation of polyolefin resin pre-expanded particles, and pre-expanded particles of a polyolefin resin prepared by pre-expanding this water-containing polyolefin resin composition and having a an apparent expansion ratio of 5 to 60, a closed cell ratio of 80 to 100 % and an average cell diameter of 50 to 500 mu m. The pre-expanded particles can be prepared without using a volatile blowing agent by dispersing resin particles made of a polyolefin resin composition containing a polyolefin resin and a hydrophilic polymer into an aqueous dispersion medium in a closed vessel to form a dispersion, heating to a temperature of not lower than the softening point of the polyolefin resin to give water-containing resin particles having a water content of 1 to 50 % by weight, and releasing the aqueous dispersion from the closed vessel into an atmosphere of lower pressure than the inner pressure of the closed vessel, thereby expanding the water-containing resin particles. When the releasing of the dispersion from the vessel is conducted after raising the inner pressure to 25 to 75 kg/cm<2>G by introducing nitrogen gas, air or an inorganic gas composed of them as a main component into the vessel, pre-expanded particles capable of providing foams having good physical properties and a high expansion ratio can be obtained.