Structural Recovery of Printing Inks Studied by Steady Shear Rheometry

Pseudoplasticity and thixotropy may be the most important rheological properties of printing inks. The viscosity of a printing ink decreases with increasing shear (shear thinning or pseudoplasticity) and with time under a given constant shear (thixotropy). To control these two properties properly, one needs to know what causes them in a microscopic sense. Two experimental techniques used to study structural recovery of inks are presented. Results reported in this paper show that pseudoplastic structure recovers much faster than thixotropic structure. These two structures can be Two experimental techniques used to study structural recovery of inks are presented. Results reported in this paper show that pseudoplastic structure recovers much faster than thixotropic structure. These two structures can be distinguished by the state of pigment particles present in the ink vehicle. The physical significance of pseudoplastic and thixotropic structures and their implications to press performance are discussed.