Methods for Measuring Dynamic Out-of-Plane Dimensional Stability of Base Paper, 2001 Coating Conference Proceedings

Erik Blohm, Jolanta Borg--A new method to characterize base paper for coating has been developed. The method evaluates the dynamics of the changes in the base paper properties after contact with water (i.e. the liquid phase in the coating color). The characterization was made in specially developed devices in the paper web research machine, LINDA, where changes in surface roughness and compressibility are analyzed. A rapid increase in the surface roughness (within 70 ms) after water application was then noticed whereas the changes in compressibility were comparatively slower. In order to evaluate the method, a number of different paper grades have been examined: fine papers with different degrees of calendering as well as surface-sized and non-surface-sized fine papers. The evaluation also included LWC base paper, (uncalendered and calendered) and wood-containing base paper produced with conventional wet pressing and with extended nip pressing.

The papers were coated on a laboratory scale and the coatings have been evaluated with respect to surface roughness, evenness of the coating layer and gloss. In order to calculate the roughness of the base paper beneath the dry coating layer, a method developed by STFI was used. The base paper properties have also been evaluated with conventional methods.

A good correlation was found between the rapid increase in the surface roughening evaluated with the new method and the results of the laboratory coating trials. A paper that was stable according to the dynamic base paper measurements corresponded to an even mass distribution of the coating layer and vice versa. The method will thus be useful for predicting the performance of base paper when coating.