Thickness Behavior of Biaxially Stretched PET Film in the Transverse Stretching Zone of a Tenter

摘要

An uneven thickness distribution can cause serious problems in practical applications. In this report the deformation and thickness behavior of poly (ethylene terephthalate) (PET) film during transverse stretching in a tenter is discussed. The experiments were performed in a pilot plant with extrusion, casting, machine direction (MD) stretching, transverse direction (TD) stretching and thermosetting and winding processes. The thickness distribution of the PET film was measured after uniaxial orientation (MD stretched) and again after biaxial orientation (TD stretched in the tenter). The thickness behavior during the transverse stretching in the tenter was calculated by a finite element method (FEM), assuming a rigid-plastic or elastic-plastic constitutive law with parameters determined from the tensile stress-strain measurements. The tensile stress-strain tests were performed on MD stretched film in the transverse stretching direction. The FEM analysis was carried out using the measured initial thickness distribution of the uniaxially oriented film (MD stretched). It was estimated from this analysis that the (TD) stretching of the film in the tenter initiated near the tenter clip (edge of film), spread to the center of the film and then finally moved from the center to the edge of the film under the experimental conditions of this study. Good agreement was obtained between the experimental and predicted FEM results for the final film thickness distribution after transverse stretching.