Characterization of the pore structure and clay orientation in curtain coating layers using SEM and image analysis

High-speed curtain coating technology is of interest to the paper industry because it can be used to coat paper and paperboard with high-solids colors without using a mechanical metering device that contacts the running web. This premetered coating process avoids the numerous problems, and consequently defects, associated with high shear conditions during metering. Moreover, curtain coating provides excellent coverage and uniform coating. Despite the growing use of this application process, however, very little research has been reported on the structural characteristics of curtain coating layers. In this study, we analyzed the coating structure of commercially produced curtain coated linerboards and papers. Coating structure was characterized using a cross section image analysis technique. Structural parameters of curtain coated papers, such as pore size distribution, particle orientation, and evenness of coating thickness, were evaluated and compared with traditional blade coated papers and film coated papers. Results showed that curtain coating provides a bulkier and more porous structure. Clay particles were aligned more randomly in curtain coating layers, which also showed good coating coverage and uniform coating thickness.