Quantifying the force of ink attachment in ink removal operations

A Couette device was used to quantify the attachment force of offset-printe d in on a 44 g/m(2) old newspaper. Changes in ink detachment (quantified us ing the effective residual ink concentration, ERIC) measured as a function of the magnitude and duration of the applied stress, print age, presence of repulping chemicals and processing temperature. Ink detachment increased w ith the duration of stress application reaching a plateau after 20 min. For an aged newspaper, treating the sheet for 20 min with a shear force of 35 N/m(2) resulted in ink detachment of only 10%. At 90 N/m(2), ink detachment increased to 34%, and at 150 N/m(2) it reached 60%. The addition of repulp ing chemicals, or increased temperature, increased ink removal at a given a pplied stress. Results were compared with ink removal efficiencies measured in a laboratory and industrial repulper, and with mechanisms of ink detach ment given in the literature.