Surfactant Migration Impact on Dynamic Surface Tension in Hardwood Stock
Residual surfactant migration in hardwood stock depresses dynamic surface tension below forty millinewtons per meter, triggering jetting print defects.
Press Sheet Mottling
Visual Irregularity
Ink density variations across a printed surface result in a clouded or uneven visual texture that detracts from the image quality. This press sheet mottling appears as localized patches of light and dark color in areas that should be uniform. The defect arises from inconsistent ink absorption or variations in the surface topography of the paperboard substrate.
Porosity Variation
Uneven distribution of the coating layer often creates differences in porosity that lead to irregular ink take up. As the ink hits the surface, press sheet mottling develops if some areas absorb the vehicle faster than others, leaving behind different concentrations of pigment. Mechanical issues on the press, such as improper roller pressure or contaminated blankets, can also contribute to this phenomenon.
Quality Assessment
Quality control teams use densitometers and digital image analysis to quantify the severity of the pattern and determine its root cause. Reducing press sheet mottling requires a combination of substrate selection and ink adjustment to ensure a harmonious interaction between the fluid and the fibres. Printers often switch to a more uniform coating or adjust the tack of the ink to mitigate the visual impact of these density fluctuations.
Accurate evaluation of the base sheet smoothness helps prevent these patterns before the production run begins.