Dynamic Z Direction Tensile Stress Propagation in Recycled Fibers during High Speed Creasing
High speed creasing generates Z-direction tensile stress waves that fracture short recycled fibers unless matrix clearance absorbs elastic strain energy.
Penetration Velocity
Fluid Absorption
Rate at which a liquid infiltrates the porous structure of a paper or board substrate determines the drying time and adhesion of inks and coatings. This penetration velocity depends on the surface energy of the fibers, the viscosity of the liquid, and the average pore size of the web. Laboratory testing often employs ultrasonic or optical methods to track the liquid front over time.
Coating Influence
Sizing agents applied during the papermaking process reduce the rate of liquid absorption by rendering the fiber surfaces hydrophobic. Alkyl ketene dimer or alkenyl succinic anhydride can be added to the pulp slurry to control this behavior. Without adequate sizing, water-based inks would penetrate too quickly, causing the fibers to swell and distorting the printed image.
Proper calibration of these chemical additions ensures that the sheet retains its dimensional stability during printing. The balance of sizing also prevents the board from absorbing too much atmospheric moisture during storage.
Print Performance
Ink mileage and print sharpness are direct consequences of how the liquid interacts with the surface coatings. Low velocity keeps the ink pigment on the surface, yielding high optical density and crisp images. Wet ink can transfer to the next sheet in the stack if the velocity is too low.