Porous Structure of Paper Coatings - A Comparison of Mercury Porosimetry and Stain-Imbibition Methods of Measurement, 1995 Coating Conference Proceedings

Lidia Larrondo and Sylvie St-Amour

PAPRICAN

Clevys Monasterios

Phoenix International Life Sciences Inc

Stain-imbibition and mercury porosimetry have been used to characterize the porous structure of coated paper samples. The porous structure of both the substrate and the coating layer have been determined. The two methods provided the same total void fraction of the sample but different void fraction values of the constituent parts. For the samples investigated here, stain-imbibition gave about 10% higher coating void fractions than mercury porosimetry, and mercury porosimetry about 10% higher substrate void fractions than stain-imbibition. The values obtained with these methods were substantially smaller than the void fraction values estimated from basis weight and thickness measurements. The latter considers all sample pores, both open and closed. The void fraction values obtained with stain-imbibition and mercury porosimetry are given by the pores which are accessible to the saturating fluid, staining ink and mercury. The conclusion from the results reported here is that the simple stain-imbibition test previously reported is supported by the much more elaborate technique of mercury porosimetry. However, where both techniques are available we have a powerful tool for characterizing the porous structure of coated paper samples. The effect of the coating layer on the substrate porous structure can be investigated with these two

methods.