Abstract
Paper is a multilayer structure of fibers with numerous micro-scale pores. Almost all the pores in paper consist of tortuous capillarylike tubes that are continuously interconnected.
Therefore, paper is permeable and can absorb liquids and gases. The most obvious utilization of the tortuous capillary structure of paper are filter paper, blotting paper, and so on. Furthermore, paper-converting operations involve penetration into the voids of paper by coating, adhesives, ink, and so on. In these processes, liquids such as wax, paraffins, silicones, and oilbased ink are applied to paper in non-aqeous form, whereas latex, silicon emulsions, and waterbased ink are basically aqueous liquids.
The fundamental theory of the wetting and penetration phenomena of paper holds for both aqueous and nonaqueous liquids.
However, in the aqueous case, fiber swelling and wetting cause deviations from the clasical theory of the penetration of porous media. This paper includes the two kind of penetration phenomena such as an oil-based ink for nonaqueous liquid and water based coating colour for aqueous liquid.
