Characterizing Porous Absorption in Recycled Packaging Paper Grades
Characterizing porous absorption in recycled paper requires measuring dynamic capillary wicking and pore size distribution to control ink set times and glue bonds.
Flexographic Ink Drying
Solidification Process
Solidification of a liquid ink layer into a dry film on the surface of a moving web prevents the printed image from smudging or transferring during subsequent processing. In package printing, flexographic ink drying must occur almost instantaneously to match the high speeds of modern narrow-web or wide-web presses. The process relies on either the evaporation of water or solvent carriers, or the cross-linking of monomers under ultraviolet radiation.
Achieving a complete cure before the web reaches the rewinder prevents the printed surfaces from sticking together.
Evaporation Control
High velocity air dryers supply heat to the printed web, driving off volatile components without overheating the delicate paperboard or plastic film. This phase of flexographic ink drying depends on the balance between air temperature, nozzle velocity, and the solvent retention of the substrate. If the air velocity is too low, solvent vapors build up near the web surface, which slows the rate of evaporation and causes ink transfer.
Conversely, excessive heat can cause the substrate to shrink or warp, ruining the alignment of subsequent colors. The mechanical adjustments of the dryer must therefore be calibrated to match the specific speed of each production run.
Substrate Influence
The porosity of the paperboard determines how much ink vehicle is absorbed, directly influencing the required drying energy. Uncoated boards absorb water-based vehicles rapidly, which speeds up the initial setting of the ink. In contrast, coated boards or films require more active heat and air flow to complete flexographic ink drying because the non-porous surface forces the solvent to escape entirely through evaporation.