Measurements of Absolute Birefringence of Biaxially Oriented Films and Sheets On-Line or Off-Line

Abstract

In this paper, we discuss the development and use of a birefringence technique for on-line or off-line quantitative measurement of orientation in transparent films, sheets, bottles, etc. Absolute values of birefringence are measured in two directions using a technique based on an incident multi-wavelength double beam and a photodiode array assembly, combined with in-house developed software. Both machine and transverse direction birefringence (relative to the normal direction) are measured quasi-simultaneously. Film and sheet thicknesses from 10 microns to 10 mm were tested and birefringence values from 0.0005 to 0.25 were measured. The technique was tested on different materials and under different conditions and several applications will be discussed.