In-line monitoring of the conversion in photopolymerized acrylate coatings on polymer foils using NIR spectroscopy

Near-infrared (NIR) reflection spectroscopy was used to monitor the conversion of double bonds in acrylate coatings after irradiation with UV light or electron beams. Quantitative analysis of the spectroscopic data was performed either with a chemometric method on the basis of the PLS algorithm or according to the Beer-Lambert law. FTIR spectroscopy was used for calibration. In-line monitoring of the conversion in pilot-scale was carried out on clear and pigmented coatings, which were applied to polymer foils or paper by roll coating. Useful data were obtained from layers with a thickness from 4 g/m2 upwards and at line speeds of at least up to 120 m/min. It was shown that any change of the irradiation dose or other parameters such as inertization leads to an immediate response in the conversion record. Similar investigations were also performed on layers of UV-curable adhesives on the basis of acrylic hot-melts.