Development of measurement techniques to characterize the optical properties of transparent films with application in in-mould decoration

Abstract

This paper details the development of appropriate techniques for quantifying and comparing the optical properties of transparent polymer films used in in-mould decoration (IMD) and the effects of heat and strain on these properties. Currently there are no approved methods for optical characterization of transparent films, with most techniques being based on reflectance measurement of printed materials for the graphic arts industry. Original experimentation was therefore required in order to characterize the optical properties of transparent polymer films used in IMD or similar applications and to predict the changes in appearance during the forming process. A range of measurement techniques was utilized to characterize the films and their interaction with light in terms of light scattering and transmission. As a result of the investigation, the optical properties of these films can now be quantified and the changes due to the different mechanisms of softening and crystallization can be separately distinguished.