Coating application method and calendering influence on the spatial coating layer formation obtained by an automated serical sectioning method

After an introduction to related research in the field of spatial coating layer formation, a new analysis method, based on a fully automated microtomy process and light microscopy combined with advanced image analysis algorithms, is presented. The concept offers both, a high spatial resolution and a significantly larger sample size than conventional SEM techniques. The concept is based on a light microscope which is attached to a rotary microtome. An embedded paper sample is digitized by means of serial sectioning. Repeatedly, slices are cut off the embedded paper sample and the cut block surface is scanned fully automated. Image analysis software was developed to automatically detect the coating layer. Segmentation of the coating layer is realized by a 3D color segmentation process in the RGB color space instead of a threshold based algorithm. The approach itself is a three-dimensional concept, meaning that for the detection of the coating layer in one slice image also data from the neighboring slices is incorporated. Thus, the algorithm delivers both, detailed and robust coating layer recognition. Single coated LWC papers from a pilot coater were analyzed to compare coating layer formation for blade and curtain coating. Local correlation was used to study the relation between the obtained thickness and topography values of the base paper and the coating layers for both coating methods. The results showed, as expected, in tendency a leveling coat behavior for blade coating and a contour coat behavior for curtain coating. However, especially the curtain coated sample, but also the blade coated sample, was away from the idealized characteristics of a contour or a leveling coat respectively. Studies regarding the effect of calendering on these samples showed that calendering predominantly influences the base sheet topography under the coating layer with a less pronounced effect on the coating layer thickness.