PL-2 Polarization Light for Preform (PET Preform Stress Viewer)
Many of the defects found in PET container preforms can be detected by using the PL-2. Preforms viewed in polarized light exhibit a colored birefringence pattern.
The birefringence is a result of the polymer flow lines (molecular orientational strain) produced during the injection moulding process.
The colored pattern observed with preform held at 45° to the polarizing axis is known as an isochromatic fringe indicating the amount of birefringence.