AbstractSpecular reflectance infrared spectroscopy is investigated as a potential on-line technique to measure the cure state of an organic polymer on steel strip. White internal polyester, deep red external polyester and pale brown plastisol coatings are studied.
The Fourier transform infrared (FTIR) spectra of coatings were analysed to identify candidate peaks which could be used to follow the curing reactions of the coatings. Corresponding candidate peaks were identified and quantified from specular reflectance infrared (IR) spectra of the coatings. In all instances, candidate peak heights were ratioed against reference peak heights to correct for coating thickness variations in the measurements. The reproducibility of the curves, the effect of paint thickness, the methods to evaluate peak heights and the accuracy of each type of IR method are reported in this thesis.
Transmission spectra were used to construct absorbance ratio/peak metal temperature curves. The parts of the curves corresponding to "over-cured", "cured" and "under-cured" were identified for all three polymer systems. Similar relationships, although less clear cut, appear to apply to reflectance spectra.
Preliminary investigations of an on-line instrument were made using an Oriel Corporation "Merlin" radiometer to amplify and collect chopped and filtered IR signal reflected from the coating. The instrument was arranged to operate in specular reflectance mode.
It is concluded that infrared spectroscopy has the potential to measure polymeric cure state under commercial production conditions.
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