Nanofibrillated cellulose as a coating agent

To determine the potential of nanofibrillated cellulose (NFC) for use as a coating material, the characteristics of several NFC-coated samples on a synthetic fibre sheet were studied. Two water-based printing methods were used to characterize the change in print quality and prepared two types of NFC by two different physical treatment methods. Various coat weights were applied onto synthetic fibre sheets and the printability of the coated sheets was evaluated by ink absorption rates and print density. Ink pigment penetration was characterized with a confocal laser scanning microscope and a scanning electron microscope, with chemical analysis of samples using focused ion beam. The contact angle and the ink penetration rates decreased with increased coat weight of NFC. This result is the opposite of what the Lucas-Washburn equation would predict. For pigment-based flexographic inks, ink pigments were captured at the NFC layer. For dye-based inks, the ink components penetrated and moved through the NFC-coated layer. For ink-jet printing, the print quality improved with the NFC coating. Synthetic fibre sheets coated with NFC can improve printing resolution and ink density, especially for pigment-type inks. ((Source: TAPPI J., Nov. 2010)