Coating coverage and coating holdout (limited penetration of coating color into the base paper) are essential properties of coating layers. Almost all quality parameters of coated papers are influenced by these parameters. Of special interest are these properties for single coated papers and for the precoat of multiple coated papers. Different methods are used to characterize these properties. For example, the so called burnout-test is used to estimate the coating coverage. Paper cross sections, analyzed with scanning electron microscopy (SEM) or optical microscopy are used to estimate the penetration of coating color into the base paper. But all methods are limited in some way. SEM is limited by a small sample size and the results obtained do not represent the coating layer in total. The burnout test gives only relative results coating layer thickness cannot be determined accurately.
A method, developed at the Institute for Paper, Pulp and Fiber Technology of Graz University of Technology allows a representative analysis of coating structures of coated papers at high resolutions. The automated serial sectioning method STRUCSOP provides a 3D model of the investigated paper sample, which can be further processed with especially developed advanced image analysis routines.
This analysis routine will be used in this proposed research project to answer open questions regarding coating coverage and coating holdout. The main goal is the development of characteristic parameters, which can be used as a quality measure for coating layers. Paper samples of the project partners will be analyzed to characterize the effects of different coating formulations, coating application systems as well as the effect of pre- and post-calendering on coating structures.