Multilayer sheet coextrusion: Analysis and design

A numerical simulation of multilayer coextrusion flows has been undertaken for polymer melts used in producing multilayered plastic sheets. Viscosity data and other material properties are used for typical melts and adhesives applied in coextrusion. Industrial designs have been employed for feedblock geometry and multimanifold vane flat dies. The analysis is based on the lubrication approximation theory (LAT), which treats the flow locally as fully developed. A Newton‐Raphson iterative scheme is employed to solve the equations for a pressure‐driven flow of N number of layers (N ⩽ 11). For a given total flow rate and flow rate ratios (or correspondingly total sheet thickness and individual layer thicknesses), the solution provides the interface locations and individual pressure drops that each extruder has to supply. The shear stresses at the channel walls are checked as a criterion for proper design. The die design or melt combinations are altered to produce smooth shear stresses with no humps or discontinuities at the points of confluence. A Adiabatic temperature rises are also computed based on the pressure drops in the system. Such an analysis provides a quick qualitative as well as quantitative insight into the proper design and melt combinations for multilayer sheet coextrusion.