Deinking of Indigo Prints Using High Intensity Ultrasound

This paper investigated the use of ultrasound to deink papers printed using Indigo’s liquid toner, Electroink. In recent years, concerns have been expressed over the difficulty of deinking waste paper produced using the Indigo printing process. Among other problems it was found that the ink particles were too large to be removed using conventional deinking methods.

High-intensity ultrasound was applied to investigate the possibility of fragmenting the ink particles to a size where they could be removed by flotation methods. The effect of temperature and sonication power on the particle size distribution was also studied. Tests were performed on two substrates, a typical paper used with Indigo presses and Indigo’s Sapphire coated paper, treated to help the Electroink bond to the paper. Handsheets were formed from the sonicated pulp and analysed to obtain a particle distribution.

The findings from this work revealed that Indigo inks are not as hard to remove as was previously thought, and the application of ultrasound improves the number of particles removed. Variations in power input and temperature were found to have a significant effect on the results, with most effective cleaning occurring at a higher power and lower temperature.