Application of optical spectroscopy to paper production

Fluorescence from paper following excitation by either ultraviolet or visible light gives information on the chemical composition of the paper. This can be used for on-line monitoring of the paper during production. Such measurements can be performed non-intrusively at sampling rates high enough to give a sub-millimeter resolution at paper webs moving at velocities higher than 20 meters per second. Two types of fluorescence meters, operating at different wavelengths, have been constructed. Together with an optical speedometer they have been tested at newsprint producing paper mills. A fluorescence based method for scanning cross-directional newsprint profiles in the laboratory has been developed. From these measurements the relative shrinkage of the paper during drying can be calculated using time-frequency analysis.