Effect of ink transfer on print mottle in shrink films

The gravure printing process is considered a pioneer in long run package printing jobs, offering exceptional print quality teamed with high quantities. Shrink films, primarily polyvinyl chloride (PVC) and polyethylene terephthalate-glycol modified (PET-G) are extensively printed using the rotogravure printing process. The intricacies of the printing process and the complex nature of the interactions between the substrate, ink, and printing press, if not studied and controlled, can contribute to unnecessary variation and degradation in print quality. Printability not only can be approximated in the dimensions of densitometry and spectrophotometry, but can also be gauged by print defects such as mottle. This study investigates the effect of process parameters, viz., line screen, ink viscosity, printing speed, and impression roller hardness on print mottle, and explores a way to minimize the same. Design of experiments were generated and analyzed through analysis of variance, main and interaction effects. Furthermore, a regression model was generated to predict the print mottle. The predicted values from the model were in close agreement with the press results. The optimization of process parameters resulted in reduction of print mottle in solid printed areas by 34% and 51% on PET-G and PVC, respectively.