Flow Properties of Carbon Black Dispersed Printing Ink

Flow properties of carbon black (CB) dispersed printing inks were studied. In oscillatory rheological measurements, printing inks showed pseudo sol-gel transition behavior, and critical gel concentration (Wgel) was determined. Wgel was applied as an index to express fluidity of the printing inks, since Wgel was found to show fairly good correlation with BET surface area that is known as a major factor of the fluidity. Moreover, Wgel showed better correlation with CB's external surface area that was determined from electron microscopy and that from mercury porosimetry. Furthermore, Wgel showed the best correlation with CB's specific surface area of the effective volume fraction calculated from relative viscosity in steady state rheological measurements by using a semi empirical model. These results showed that the network structure at Wgel is constructed of complex particle made up of CB and polymer-adsorbed layer on it, not from CB's primary particle as understood generally.