Surface Distortion
Fine localized surface deformities appear as miniature ripples or puckers across paperboard sheets following water-based ink or coating application. The defect designated as micro-cockling stems from uneven localized hygroexpansion of cellulose fibers during wet printing and subsequent non-uniform drying. This defect affects surface smoothness and gloss uniformity, ending where overall structural sheet curling dominates fine surface rippling.
Hygroexpansional Strain
Absorbing water from aqueous inks causes individual wood fibers to swell up to twenty percent in diameter while expanding minimally in length. When water-based ink deposition varies across graphic areas, localized expansion forces push against adjacent dry fiber networks, forcing paperboard surfaces to pucker at millimeter scale. High-speed hot air drying locks these localized stress patterns into place before fibers relax back to original dimensions.
Coated paperboard grades with low surface porosity resist water vehicle penetration, reducing localized fiber swelling. Uncoated or lightly sized paper stocks exhibit higher susceptibility when exposed to heavy aqueous coating weights or dense ink coverage.
Substrate Selection
Selecting high-internal-bond paperboard with uniform fiber orientation minimizes localized cockling during multi-pass aqueous printing. Inkjet and flexographic printers adjust dryer temperature curves and ink limits to mitigate surface rippling. Uniform moisture profiles preserve surface flatness for downstream lamination.
