Structural Breakdown
The fragile porous structure of a silica-based coating layer on paperboard breaks down when subjected to excessive pressure or moisture. Occurrences of silica matrix collapse destroy the microscopic pockets designed to absorb inks and liquid varnishes, leading to poor print resolution and slow drying times. This structural failure is a major concern for manufacturers of specialty coated papers used in high-resolution printing.
Physical Process
Synthetic silica particles are formulated into coatings to create a highly porous network with a large surface area for rapid ink absorption. When the coated paperboard passes through high-pressure nip rollers or calendering stacks, the mechanical force can crush these porous agglomerates. This compression flattens the open pores, reducing the volume of space available to capture the liquid carrier of the ink.
The paperboard is then unable to absorb the ink quickly, causing wet inks to smear or transfer to the opposite side of the sheet during stacking.
Print Consequence
Loss of porosity also reduces the gloss and color density of the final print, as the ink pigments sit on the surface instead of being bound in the coating. Preventing this collapse requires careful control of the roller pressure and the use of hard, structured fillers that resist compression.
