Surface Interaction
Liquid movement into the porous structure of paper or board occurs through the interaction of surface tension and pore geometry. Printing operations rely on capillary penetration to anchor inks within the fibre matrix of uncoated stocks. The rate of absorption depends on the diameter of the pores and the viscosity of the fluid.
Measurement Method
Standard testing often involves observing the rise of a liquid against gravity or the rate of lateral spread. Controlling capillary penetration prevents feathering and ensures sharp image definition on corrugated liners. Excessively high rates lead to strike through where the ink becomes visible on the reverse side.
Fibre Chemistry
Sizing agents are added at the wet end of the paper machine to increase the contact angle of water and slow the rate of intake. These chemicals coat the fibres to reduce the effective energy of the surface. Without these additives, the capillary penetration would be too rapid for functional use in liquid packaging.
Internal sizing provides resistance throughout the entire sheet while surface sizing targets the top layers of the paper. This dual approach allows for a precisely controlled absorption rate that meets the requirements of specific offset and inkjet printing processes.
