Ink Release from Printed Surfaces – New Methodology and Initial Insights to the True Mechanisms Behind Ink Detachment

Abstract

The aim of this study was to develop and test a new equipment for evaluating the mechanism behind ink detachment from printed model surfaces. The equipment developed for this purpose consisted of an impinging jet cell, a printed model cellulose surface and a microscope equipped with a CCD camera for image collection. By applying image analysis to images of the printed surfaces at different time intervals, during the detachment studies, it was possible to quantify the ink detachment from the surface. Mechanistic studies of offset ink and flexographic ink detachment were also performed with the new equipment. Results show that the flexographic inks seem to be removed by a washing process in which the printed image is gradually removed from the surface. For the offset print the results are quite different. In order to remove the printed offset ink it is necessary to have a certain hydrodynamic shear in combination with a swelling of the cellulose surface. This swelling seems to create a relative movement between the ink and the cellulose surface. In solutions with higher ionic strength no offset ink is removed.

These results are in line with earlier assumptions about the deinking mechanisms but in the present work these processes are actually shown for the first time.