Dimensional Expansion
Hydroscopic dimensional expansion measures how paperboard increases in caliper after absorbing moisture from ambient air or liquid contact. Caliper variation compromises print registration and folding carton assembly lines when moisture penetrates exposed edges. Uncoated folding boxboard typically exhibits greater caliper growth than heavily coated equivalents because mineral layers restrict lateral fibre movement.
Board machines set initial moisture targets between four and six percent to balance converting performance against post press distortion risks. Production facilities evaluate this physical response using micrometers calibrated to standard pressure specifications before converting operations commence.
Moisture Gradient
Hydrolysed starch additives and internal sizing chemicals modify how rapidly water molecules migrate into cellulose matrices during conversion processes. Wet end chemistry controls fibre bonding density, which directly dictates total void volume available for liquid retention. Excessively high relative humidity in finishing departments forces moisture into board edges, initiating localized swelling before die cutting occurs.
Converters adjust press nip pressures to compensate for minor caliper variations across large format production runs.
Caliper Tolerance
Finished packaging components require stringent thickness consistency to ensure reliable performance on high speed automated filling lines. Excessive caliper growth causes jamming in cartoning machinery designed for strict dimensional envelopes. Quality control protocols specify maximum acceptable swelling percentages following standardized water immersion tests to prevent structural failure in refrigerated supply chains.
Precise moisture barriers applied during extrusion lamination protect sensitive substrates from environmental humidity fluctuations.
