A new method for measuring the liquid permeability of coated and uncoated papers and boards

A new permeation apparatus is described to measure the liquid permeability of coated and uncoated paper samples. The technique can also be applied to other consolidated porous and laminate materials and removes the artefacts of random pinholes whilst relating directly to liquid permeation rather than the more commonly used air/gas permeation. Measurements from three example papers are shown, and the equivalent permeation radii and Darcy permeabilites are calculated. Liquid permeability is compared with both air permeability using the Bendtsen method and mercury porosimetry data for the same samples. Each method is shown to indicate different properties of the porous structures, i.e. porosity and equivalent intrusion diameter alone are not necessarily representative of the saturated permeability characteristics of a porous sample. Furthermore, the permeability of low permeable coated grades is underestimated using the commonly applied air method due to compression of the air causing non-linearity of the pressure gradient. It is necessary to consider network structures including connectivity and pore size and shape distributions in order to correlate porosimetry with liquid permeation properties of differing samples.