Effects on ink setting in flexographic printing: Coating polarity and dot gain

摘要

Ink transfer and the subsequent ink setting are processes that depend on the physical properties of the ink and the substrate, and on the press settings. To gain a better understanding of the effects of these factors on printing performance, four coating layers were prepared using calcium carbonates of different particle sizes and latices of different polarities. The coating layers were printed with a water-based flexographic ink in a laboratory printing press under different printing pressures. Measurements were made using a white light interference profi-lometer, an optical densitometer, and an atomic absorption spectrophotometer to characterize the size and shape of an individual halftone dot, the print density of the halftone print, and the amount of ink transferred, respectively. It was found that the coating layer based on a latex of higher polarity gave a higher print density even though there was no significant increase in ink transfer. A non-linear relationship between physical dot enlargement and printing pressure was observed, due to increasing printing form deformation. The proposed mathematical model taking into account elastic deformations reveals the relationship between dot enlargement on the printing form and the printing pressure. The results of the measurements agree qualitatively with the theoretical predictions.