PREVIOUSLY EXPANDED PARTICLE OF UNCROSSLINKED STRAIGHT CHAIN LOW-DENSITY POLYETHYLENE AND ITS PREPARATION

摘要

PURPOSE:To obtain the titled previously expanded particles having improved oil and weather resistance, etc., by releasing a dispersion of an uncrosslinked straight chain low-density polyethylene having a specific melting point and density and a volatile foaming agent in a dispersion medium from a vessel to a low- pressure atmosphere in a specific temperature range simultaneously in dispersing the polyethylene and the volatile foaming agent in the dispersion medium. CONSTITUTION:A volatile foaming agent, e.g. propane, is mixed with an uncrosslinked straight chain low-density polyethylene (a copolymer of ethylene with a 3-8C alpha-olefin) haing =115 deg.C melting point and 0.915-0.950g/cm3 density, and the resultant mixture is then dispersed in a dispersion medium, e.g. fine particulate magnesium oxide, in a closed vessel. One end of the vessel is then opened while keeping the dispersion in a temperature range 10 deg.C lower than the melting point of the particles -5 deg.C higher than the melting point thereof, and the dispersion is simultaneously released from the vessel to a low-pressure atmosphere to give the aimed previously expanded particles having 0.01-0.3g/cm3 bulk density, =60% closed cell content and 1,000 cells/mm.2. USE:Packaging, shock absorbing, building materials, etc.