Application of polyurethane precursors comprising pyrazole-blocking waterborne polyurethane dispersion and recycled polyol to optical poly(ethylene terephthalate) films

초록

In this study, we investigated the application of polyurethane (PU) coating on poly(ethylene terephthalate) (PET) films for optical film applications using pyrazole-blocked waterborne PU dispersion (PUD) (PUDpy) and PET-recycled polyol. Real time Fourier transform infrared spectroscopy, dynamic mechanical analysis, ultra-micro hardness tests, ellipsometry and ultraviolet–visible spectroscopy were used to analyse the deblocking process for PUDpy, the reaction between PUDpy and polyol and the optical properties of the PU-coated PET film. The PU-coated PET films prepared in this study were clear, smooth and transparent enough for optical film applications. The deblocking of pyrazole and activation of isocyanate (NCO) groups started at 100 °C and ended at 180 °C, and the PU reaction between the activated NCO and polyol started immediately after NCO activation and lasted up to a maximum operation temperature of 240 °C. Notably, the PU reaction continued even after cooling to room temperature (25 °C), thereby necessitating a post-curing process to achieve complete curing. As the polyol content in the coating layer increased, the refractive index increased, whereas the coating layer hardness decreased. The evaluation of the compositional effects of the PUDpy:polyol precursor solution indicated that the optimal optical and mechanical properties of the PU-coated PET film were achieved when equal amounts of PUDpy and polyol were used in the precursor solution.

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