Capillary Condensation

Surface Tension

Strong attractive forces between liquid molecules and the solid substrate wall drive the spontaneous filling of narrow gaps. Small pore diameters provide larger Laplace pressures, which lower the required vapor pressure for transition to the liquid state. Narrow openings fill earlier than wide chambers when humidity rises inside a storage environment.

Converters monitor this shift because the uptake of water modifies the dimensional stability of paper sheets and causes internal swelling. Rapid absorption leads to uneven coating distributions if the web passes through humid air during the drying stage. Surface chemistry dictates the contact angle of the condensate, which modifies the exact pressure at which the filling begins or ends.

Hydrophobic additives reduce the risk of this entrapment by increasing the energy barrier for water penetration into the fibre bulk.

Mechanical Impact

Tensile strength of a paper sheet relies on the bonded fibre network, yet moisture bridges within the structure promote softening that degrades physical resistance. When capillary condensation occurs during storage, the added mass of trapped liquid weakens the hydrogen bonds linking the fibres. Print machines suffer registration errors as the web stretches under the influence of these micro-droplets.

Packaging materials that rely on rigid porosity for barrier function lose their protective capacity once internal condensation reaches a threshold density. Controlled atmospheric storage mitigates these changes by maintaining vapor pressure levels beneath the point where internal meniscus formation compromises the structural performance of the substrate. Constant humidity monitoring acts as the final guard against these phase changes.