Electric treatment for hydrophilic ink deinking

Hydrophilic inks have been widely used due to higher printing speed, competitive cost and healthy non-organic solvent. However, it causes problems in both product quality and process runnability due to the hydrophilic surface wettability, strong negative surface charge and sub-micron size. Electric treatment was shown to be able to increase the ink sizes from 60 nm to 700 nm through electrocoagulation and electrophoresis. In addition, electric treatment assisted flotation could reduce effective residual ink concentration (ERIC) by 90 ppm, compared with only 20 ppm by traditional flotation. Furthermore, the effect of electric treatment alone on ink separation was investigated by two anode materials, graphite and stainless steel. Both of them could remove hydrophilic inks with less than 1% yield loss via electroflotation and electrophoresis. But graphite is a better material as anode because graphite reduced ERIC by additional 100 ppm. The yield loss of flotation following electric treatment was also lower by 17% if graphite was the anode material. The difference between the two electrode materials resulted from electrocoagulation and ink redeposition during electric treatment. An electric pretreatment-flotation-hyperwashing process was conducted to understand the deinking performance in condition similar to paper mill, and the ERIC was reduced from 950 ppm to less than 400 ppm.