Confocal Raman Analysis Method to Study Binder Depth Profiles in Coating Layers, 2001 Coating Conference Proceedings

J. Vyörykkä--This work describes a new technique for the analysis of chemical composition of paper coating layers in z-direction. The technique is based on the use of confocal Raman microscopy and an immersion sampling method. In confocal Raman microscopy a pinhole rejects signal emerging out-of-focus zones. This enables measurements of small volume elements. Depth profiles are measured by focusing the laser beam stepwise into a sample and collecting separate Raman spectrum of each layer. Since paper coatings are highly light scattering materials, light penetration into the sample is limited and the spatial resolution is decreased. To improve light penetration and to enhance the spatial resolution, samples were pretreated with refractive index matching fluid that reduces light scattering efficiently. Depth profiles show the Raman intensity of coating components at different depths. By collecting several parallel depth profiles, it is possible to form a Raman map of the distribution of the coating components in the cross section of a sample, e.g. SB-latex-CaCO3 distribution map. In addition to that, the Raman map gives information about the roughness of the coating surface and variations in the coating thickness.