Moisture Migration
Dynamic physical processes governing the rapid absorption, distribution, and release of water vapor within fibrous networks are fundamental to the performance of paperboard during conversion. The term transient moisture dynamics describes the rate-dependent behavior of paper sheets as they interact with ambient humidity or aqueous coatings during high-speed processing. This interaction triggers rapid expansion or contraction of the individual cellulose fibres, which leads to dimensional changes in the entire sheet.
Because these changes do not happen instantly, the transient phase can introduce temporary curls or twists in the substrate.
Dimensional Instability
During high-speed printing and folding carton converting, these rapid moisture shifts can cause severe runnability problems. If one side of a paperboard sheet absorbs water from an offset ink or a water-based adhesive faster than the other, the resulting stress imbalance causes the board to warp. This curling can disrupt the feeding mechanism of a folder-gluer or cause misregistration on a multi-color printing press.
Managing these transient effects requires strict humidity control in the converting plant and precise selection of adhesive application rates.
Sorption Rate
The speed of this moisture exchange depends heavily on the surface sizing, coating thickness, and internal porosity of the paperboard. Dense, highly sized sheets slow down the absorption rate, mitigating the immediate structural changes. This resistance allows the material to pass safely through wet converting processes without distorting.
