Surfactant Migration Impact on Dynamic Surface Tension in Hardwood Stock
Residual surfactant migration in hardwood stock depresses dynamic surface tension below forty millinewtons per meter, triggering jetting print defects.
Capillary Absorption Rate
Fluid Dynamics
Liquid transport measurements quantify the velocity at which a fluid migrates through the porous network of a paper or board substrate. This capillary absorption rate determines how quickly aqueous or solvent based carriers leave the surface to penetrate the inter fibre spaces. Control of this property is necessary for ensuring that inks set at the correct depth without causing excessive strike through or feathering.
Structural Influence
Pore diameter and the connectivity of the internal void space act as the primary drivers of fluid movement within the sheet. A high capillary absorption rate indicates a more open structure where liquids move rapidly under the influence of surface tension. Internal sizing agents modify the contact angle of the fibres to slow this process and prevent the substrate from becoming overly saturated.
Operational Consequence
Offset printing requires a balanced intake of the fountain solution and ink oils to maintain image clarity. If the capillary absorption rate exceeds the specified range for a given press speed, the resulting print may appear dull or washed out due to the loss of pigment into the base sheet. Converting operations involving water based adhesives also rely on this metric to time the formation of the bond between paper layers.
A mismatch between the absorption speed and the set time of the glue leads to weak seals or board warping.