Deinking of inkjet digital nonimpact printing

Abstract

Pigmented nonimpact (inkjet) printing is a concern in conventional flotation deinking, due to the problems associated with the hydrophilic, submicron-size pigment particles of the ink. Preliminary experiments were conducted to evaluate the efficiency of a conventional flotation deinking process in detaching those inkjet particles from the fiber surfaces and network. A Denver D-12 laboratory flotation cell was used to test 100% old newsprint paper (ONP) with the ISO brightness target set to 58, which makes a paper recyclable. The inkjet-printed ONP was floated to 47 ISO brightness by the INGEDE Method 11. It was enhanced to 50 ISO brightness using flotation, with the addition of nonionic surfactant for better repulping. In addition, a patented electric field technology was used for further improving the floated ISO brightness to 52.5—yet still short of the 58 target for recycling. This improvement was reached with small air bubble sizes, which are more likely to collide and interact with ink particles, causing additional ink to be brought up to the surface of the water pool. The increasing problem of deinkability from digital nonimpact inkjet printing means that additional technical efforts are needed to overcome the crossroad between environmental concerns and technological progress. Papermills, inkjet suppliers, printer manufacturers, and academic and industrial deinkers should take collective action to meet the challenges to future success.