Dynamic Measurement of Ink Film Thickness, Pressure and Temperature in Rolling Contacts

The understanding of the dynamics of the nip contact in printing and coating applications is key to the transfer mechanisms. This paper describes a series of experimental trials that have been carried out to obtain the physical characteristics within this contact region. A full-scale printing unit has been instrumented to allow the dynamic measurement of pressure through the nip region on both a solid copper and at the rubber-steel interface of a covered roller. Measurements were made using a dry contact, a Newtonian fluid (oil) and a non-Newtonian fluid (ink). In addition, the fluid film thickness each side of the contact has been measured using non-contact methods providing data on the film thickness and the splitting ratios. The system used incorporated both capacitance and inductive probes, which eliminated the influence of vibration or eccentricity. Finally, the build up of temperature in the contact and rubber layer has been evaluated. The results provide data for assessing the stresses on and within the rollers and comparisons for numerical models. They also give an insight into the mechanisms within the nip contact.