Effect of KI Concentration in Correcting Tank on Optical Properties of PVA Polarizing Film

Polarizer is a key component of the liquid crystal display panel, and the optical properties mainly include transmittance, degree of polarization and chromaticity. Polarizer is made of a multilayer optical film, in which the PVA polarizing film is the core structure for realizing the polarization of the whole polarizer. PVA polarizing film is commonly manufactured through a multi-step craft, including rinsing, dyeing, stretching and correcting. The correction process has a significant impact on the final apparent color and optical properties of the polarizer. In this study, the KI concentration in the correcting tank, ranging from 1% to 3%, was systematically investigated. With the increase in KI concentration, the Raman vibration peak at 160 cm−1representingI5−ions gradually weakened, while the Raman vibration peak at 110 cm−1representingI3−ions gradually increased, indicating that the KI in the correcting tank changed the chemical equilibrium of polyiodide ions in PVA. Then abundant chromophoreI5−ions were consumed andI3−ions generated, so that the apparent color of PVA polarizing film gradually changed from dark blue to dark gray, and the chromaticitya-value andb-value gradually increased. The change in the concentration of dichroic species (I5−andI3−) in PVA polarizing film had directly affected its transmittance in the visible range. From the UV-Vis transmittance spectrum of PVA polarizing film, when theI5−ions were consumed andI3−ions generated, the transmittance of PVA polarizing film in the region of 675–525 nm wavelength increased gradually while the polarization degree also increased.Keywords:PVA polarizing film;correction process;transmittance;chromaticity;degree of polarization