Drawing Forces and Film Properties in Semi-Sequentially Stretched Polypropylene

The relationship between biaxial stretching and oriented polypropylene film properties is studied. Initial films have been made with a 6×6 areal draw ratio (ADR) while reducing the transverse direction (TD) drawing speed and maintaining the machine direction (MD) speed. Slowing the TD speed increases the final TD drawing force and produces anisotropic film shrinkage. Varying the draw ratios in both directions creates anisotropic tensile properties. By changing both drawing speeds and draw ratios, films with similar shrinkage but differing tensile properties have been made.