Predicting and determining the bending stiffness of thin films and laminates

Three different techniques for experimentally determining the bending stiff ness of flexible films and laminates have been evaluated using a number of different packaging materials. The results showed that a cantilever test wa s the best, giving reliable data for all kinds of films and laminates. A th ree-point bending test proved to be sensitive to misalignment, whereas a be nding under-own-weight test was incapable of handling curled samples and ge nerally gave lower stiffness values. A model for predicting the bending sti ffness of multilayer laminates from the elastic modulus of the constituents was developed and used to examine the influence of layer position and comp osition on the overall bending stiffness. Model calculations showed that th in layers, such as adhesives, print and barrier coatings, can have a large influence on the bending stiffness and that the influence often goes agains t what would be intuitively expected. The calculations also showed that lay er modulus of-ten is less important than layer thickness and that the posit ion of the layer in the laminate can have a major influence on the overall stiffness. Copyright (C) 2001 John Wiley & Sons, Ltd.