Capillary Absorption Testing Standards in Coated Printing Substrates
Substrate capillary absorption speeds govern ink setting rate, dryer energy consumption, and cross-web print defect thresholds across high-speed converting runs.
Dynamic Absorption Rate
Fluid Penetration
Measurement of the speed at which a paper or board substrate pulls a liquid into its internal void structure provides essential data for predicting print run behavior. Known as the dynamic absorption rate, this measurement tracks the interaction between the liquid and the fibrous surface over very short intervals, typically millisecond ranges. It models the behavior of offset inks or aqueous coatings at the moment of contact on a high-speed press.
The measurement stops being relevant once the substrate reaches saturation or when the liquid has fully penetrated the sheet, meaning it focuses entirely on the initial contact phase.
Test Method
Automated test instruments apply a drop of fluid to the paper surface and measure the contact angle change or the volume reduction over time using high-speed cameras. Alternatively, ultrasonic transmitters can measure the attenuation of a sound wave as liquid penetrates the paper structure. These techniques allow paper manufacturers to optimize surface sizing and internal sizing agents.
Press Correlation
Pressrooms rely on this property to ensure that fountain solutions and ink vehicles do not migrate too slowly, which would cause smearing, or too quickly, which would cause strike-through or loss of gloss. When the absorption is too slow, ink from one sheet transfers to the back of the next sheet in the delivery pile.