Characterization of Paper Coating Penetration by Laser Scanning Microscopy, 2006 TAPPI Advanced Coating Fundamentals Symposium

The quality of a coating layer, and the efficiency of the coating, depends to a large part on the penetration of the coating into the paper. Methods to characterize this penetration are limited. A new technique is proposed that combines Confocal Laser Scanning Microscopy (CLSM) and image analysis to characterize the coating layer and coating penetration into the substrate. With this technique, it is possible to obtain the information of coating layer thickness variation without any sample destruction and little sample preparation.

In this paper, two methods are proposed to obtain quantitative analysis of coating layer thickness and penetration into the paper. The results are compared to scanning electron microscope (SEM) cross sections. Coatings applied onto plastic calibrate the method and demonstrate the limitations. Both methods give results that are consistent with the SEM results. In addition, a technique is shown that can characterize the penetration of the coating liquid phase into the paper by staining the coating suspension before coating. These steps allow a comparison between the penetration of the liquid phase and the coating pigments. A double staining method is demonstrated where the paper is stained with one dye and the coating layer a second dye. By detecting fluorescence at two different wavelengths, paper and coating locations can be characterized.