Influence of different deinking efficiency of waterbased flexographic ink from model cellulose surfaces and sheets

The influence of UV-light, temperature, atmospheric environment and storage time on the ink detachment of water-based flexographic ink printed on model cellulose surfaces was investigated using an impinging jet cell equipment. The printed surfaces were deinked using a NaOH solution (pH = 10) and the deinking process was monitored using a microscope equipped with a CCD camera. Images were collected at different time intervals during the detachment process and image analysis was used to quantify the ink detachment from the surface. Hand sheets, (the same pulp as used for model surface preparation) were also printed and stored under the same conditions, after which they were reslushed and deinked. The deinking efficiency of the recycled sheets was evaluated using brightness and ERIC (Effective Residual Ink Concentration) values. It was shown that UV-light had a negative effect on ink detachment both from the model cellulose surfaces and from the hand sheets. At storage temperatures of 55°C, (dark conditions were used) a large negative effect was observed for the cellulose surfaces while only a small effect on the ink detachment could be seen for the hand sheets. Ink detachment from the hand sheets became more difficult when increasing the storage temperature above 55°C, as detected as a decrease in brightness of the recycled and deinked sheets. A further increase in the storage temperature to 105°C gave poorer ink detachment efficiency than storage under UV-light for the hand sheets. Air had a more negative effect on ink detachment than nitrogen.