PREEXPANDED PARTICLE OF UNCROSSLINKED STRAIGHT-CHAINLIKE LOW-DENSITY POLYETHYLENE

摘要

PURPOSE:To obtain the titled particles, having a specific crystal structure, moldable without carrying out pretreatment of applying an internal pressure and capable of providing low-density molded bodies having a low water absorption without shrinkage, by expanding an uncrosslinked straight chainlike low- density polyethylene. CONSTITUTION:The aimed particles, capable of exhibiting a crystal structure having two endothermic peaks with the endothermic peak with =5J/g energy on the high temperature side in a DSC curve (a curve obtained by increasing temperature of 1-5mg preexpanded particles to 220 deg.C at 10 deg.C/min heating rate using a differential scanning calorimeter) obtained by differential scanning calorimetry. Furthermore, a base material polymer of the above-mentioned particles is preferably a copolymer of ethylene and 1-butene with 6-9wt.% 1-butene content. The afore-mentioned particles are preferably obtained by adjusting the expansion temperature to =the melting point - 20 deg.C - the melting point - 10 deg.C without heating the polymer particles in a vessel to =the melting end temperature or above.