Use of Chilled Die Lips to Improve Production Rates in Extrusion of PE

Extrusion rates of polyethylene are limited by the onset of surface defects in the extrudates, which are variously termed sharkskin, melt fracture and so on. Several expedients are effective in relieving this problem. We report here that extrudate surface distortion can be eliminated under some conditions by cooling the die, at normal melt extrusion temperatures. This technique appears to be generally effective for LLDPE and HDPE. The process has been patented [10] for polymers with narrow molecular weight distributions.