Thickness Behavior of Biaxially Oriented PET Film in the Transverse Stretching Zone of Tenter
Toshiro Yamada, Yukinori Nasu, Takayuki Iwasaki
Dept. of Chemistry & Chem. Eng., Kanazawa University
Japan

Keywords: Film, Thickness, FEM

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The unevenness of thickness causes serious problems in practical applications. Though the thickness uniformity of film is very important, few papers have been reported. Especially, very few reports on the thickness behavior of film in the production process have been published. The authors have researched on the deformation behavior of film in a tenter. In this report is discussed the thickness behavior of poly(ethylene terephthalate) (PET) film during the transverse stretching in the tenter.
The experiments were made by a pilot plant, which was composed of extrusion, casting, machine direction (MD) stretching, transverse direction (TD) stretching, thermosetting and winding processes, as follows: First the TD thickness distribution of uniaxially oriented PET film (MD stretched film) before the tenter was measured as an initial thickness distribution of film. Then the uniaxially oriented film was transversely stretched in the tenter. The TD thickness distribution of biaxially oritented film after the tenter was measured.
The authors tried to predict the thickness behavior during the transverse stretching in the tenter by a finite element method (FEM). The analysis with FEM was made under the assumption that the constitutive law of film obeys rigid-plastic or elastic-plastic bodies whose parameters were determined from the stress-strain relations of film obtained by the tensile testing machine. The stress-strain curves of film were obtained from the transverse stretching of MD stretched film by the pilot plant using the tensile testing machine. The FEM analysis was carried out in consideration of initial thickness distribution of uniaxially oriented film. It was estimated from this analysis that the stretching of film began near the tenter clip (edge of film) and spread to the center of film and then finally moved from the center to the edge of film during transverse stretching in the tenter under the experimental conditions of this report.
The good agreement of TD film thickness distributions after transverse stretching was obtained between experimental and predicted results by FEM.