Visualization of Flexographic and Offset Ink at Bubble Surfaces, 2000 Recycling Symposium Proceedings

Note: This file can not be downloaded due to file size. To use your free download for this file please call TAPPI’s Member Connection Department.

Andrew P.H. Davies, Steve R. Duke

This paper describes and demonstrates a test method (bubble-suspending flow facility and optical diagnostic technique) to directly image and quantify ink removal rates for single air bubbles. The fundamental research goal is to characterize the rates and behavior of the removal of inks from water using dissolved air flotation (DAF) and flotation deinking processes. A bubble suspending facility is described where bubbles, instead of rising, are suspended in a carefully controlled down flow of water. A bubble injection system creates bubbles with consistent but variable sizes ranging in diameters from 0.2 to 1.7 mm. Stationary bubbles can also be created that do not release from the injector needle tips. The imaging system includes zoom microscope and close-up lenses and two CCD cameras: a 760x480 inspection grade CCD and a 500 frame-per-second digital motion recorder. Suspension of the bubble allows ink and particle adsorption and desorption processes at bubble interfaces to be observed dynamically and at high spatial resolutions. Time series visualizations and images are presented for flexo and offset ink attachment and interaction at the surfaces of bubbles in sodium oleate and calcium chloride solutions at different pH values. Initial imaging studies with the flexo ink show that, as expected, there is no observable ink adsorption. Image sequences show the offset ink adsorbing to bubbles. Some offset ink particles and agglomerates adsorbed to the bubble surface, while others were observed to pass by the bubble without adsorbing.