Viscoelastic Property Loss in Aqueous Coated Paperboard Converting
Moisture and thermal stress during converting plasticize aqueous latex coatings, reducing storage modulus and causing fold delamination unless web tension is optimized.
Paperboard Plasticization
Moisture Control
Hygroscopic conditioning modifies folding boxboard and linerboard by introducing controlled water molecules into the cellulose matrix to prevent cracking during creasing. Paperboard plasticization operates on the principle that bound water acts as a molecular lubricant between adjacent cellulose fibres, lowering the stiffness threshold under mechanical stress. Mills achieve this balance during the final press and calendering stages by applying measured steam profiles directly to the web.
Excessive water addition induces dimensional instability and reduces structural rigidity, whereas insufficient moisture yields a brittle substrate prone to fracturing along score lines.
Crease Tolerance
Folding cartons require precise angular deflection without surface rupture, a mechanical property directly dependent on internal moisture distribution. Paperboard plasticization prevents liner delamination during high speed die cutting operations by increasing the elongation at break of the outer plies. Substrates intended for pharmaceutical packaging demand tight tolerances on residual water content to maintain dead fold characteristics without compromising burst strength.
Converting plants measure this performance through standard bending resistance tests that evaluate the force required to deflect a creased sample through a specific angle.
Conversion Stress
High speed printing presses and rotary die cutters subject heavy packaging substrates to severe tensile and shear loads. Paperboard plasticization mitigates the risk of web breaks on multi unit offset lines by enhancing the internal bond strength of the multi ply sheet. Operators adjust dryer temperatures and dampening units on press to preserve the intended moisture equilibrium established at the paper mill.
Thermal degradation during infrared drying removes the protective moisture sheath, reversing the plasticizing effect and causing immediate cracking on subsequent creasing stations.