OPTICAL METHODS FOR MEASURING THE SURFACE QUALITY OF PAPER

The application of IR spectrometry for porosity characterization and c oatweight measurement was investigated. The aim of the coatweight meas urement was to develop a microscale measurement principle. Near infra- red (NIR) reflectance measurement provided information on the porosity of the coating. The results gave a satisfactory correlation with thos e obtained with the extruder method used as a reference for printing i nk absorption. The standard deviation with the IR method was about I u nit, compared with 0.5 units for the reference method. Middle infra-re d (MIR) reflectance measurement gave very good correlations with the c oatweights of papers coated with either china clay or carbonate, or wi th mixtures of the two. The advantages of MIR include strong absorptio n bands with all the main coating material components, sharp absorptio n peaks and low scattering MIR measurement was the most promising meth od in this study for development of a commercial instrument. The metho d can also be used for microscale measurement.