STABILIZATION MECHANISMS OF WATER-BASED NEWSPRINT INKS

In order to elucidate the fundamental behaviour of flexographic printi ng inks in a deinking environment, a model water-based ink composed of carbon black and an acrylic binder has been developed. This model sys tem reproduces the colloidal properties of. washing deinking dispersio n from flexographically printed newsprint. Experiments with the carbon black-acrylic resin system have shown that water-based inks are very likely to be electrostatically and sterically stabilized. Ionization o f the carboxyl groups in the acrylic resin and the carbon black indica te that the maximum electrostatic contribution to stabilization ranges between a pH of 8 and 10. We have verified the attachment of the acry lic resin onto carbon black with absorption isotherms. The extent of c overage of the acrylic resin onto the carbon black shows the existence of a three-dimensional surface layer that may act as a robust steric stabilizer. Particle diameters in the colloidal range (approximate to 200 nm) have been found for both the carbon black-acrylic resin system and the residual deinking dispersion from flexo newsprint.