Understanding of neck-in phenomenon in production of flat polymeric films: A review

Abstract

This review paper summarizes current state of knowledge with respect to unwanted neck-in phenomenon, which occurs during production of flat polymeric films. The effect of draw ratio, Deborah number (i.e. melt relaxation time, melt velocity at the die exit, air-gap), film cooling, second to first normal stress difference ratio at the die exit, uniaxial extensional strain hardening and planar-to-uniaxial extensional viscosity ratio on the neck-in phenomenon is discussed. The paper also summarizes simple analytical equations, which can be used to predict neck-in phenomenon. © 2020 Society of Plastics Engineers. All rights reserved.