An approach to the basic processes of ink absorption into paper coatings is made by considering the way in which oil is absorbed into kaolin-based layers (50 microns thick), formed on flexible polyester substrates. Oil layers are applied to these layers by use of an IGT printability tester . The change in gloss level with time after application of the oil film is used as a method for determining the time taken for an oil film of known thickness to be absorbed.
The capillary penetration equation of Washburn is used as a basis to explore the relationship between the physical properties of the oils and the structure of the coatings.
The basic structure of one coating is also determined by the method of mercury porosimetry and is related to the oil absorption rate by use of the equation of Millington & Quirk for the permeability of the layer.