Muddasir Khan

Date of Award

8-2010

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

Douglas W. Bousfield

Second Committee Member

David Neivandt

Third Committee Member

Michael Mason

Abstract

During conventional lithographic printing, fountain solutions are added to a printing plate with a roll before the inking roll. Fountain solution plays a critical role in maintaining trouble free press operation. This water layer is needed to prevent ink from transferring to the non-image area. While printing is a common operation, it is not clear if the ink displaces a water film from the image area due to some flow, or if the water layer ruptures and flows away from the image area. Liquid film behavior at the nip region was studied. Experiments were done on laboratory scale rolls that form the rolling nip device. Images were taken at the nip region by using a digital camera. Rolls were pressed together with a known nip loading pressure. Roll rotation was controlled by a computer. Images show that water comes out from the nip region in the form of droplets scattered all over the roll for many different conditions. When the rolls were covered with a smooth plastic film, thin lines of drops are seen. Glycerol-water solution did not form drops but came out in a ribbing pattern. The pressure recorded at the nip exit is close to the vapor pressure of water. Therefore, cavitation of water at the nip exit must lead to disturbances that generate drops instead of a smooth film. An evaporation experiment was attempted to characterize the stability of thin films. A thin film of water, a surfactant solution in water of sodium dodecyl sulfate (SDS), Isopropyl alcohol and fountain solution were evaporated over different substrates such as a lithographic plate, a Teflon coated foil and a plastic sheet. The sample was kept on a weigh balance during the test. These liquid films were evaporated in a region surrounded a by a thin wire rim. The weight difference between the film rupture point and the dry system is used to characterize an average rupture thickness. The rupture of these films is modeled with the thin film equations accounting for surface forces. Films rupture at thicknesses much larger than what is expected. This may be due to fluid leakage, vibrations in the lab, or non-level surfaces. The model and experiments show steps that can be taken to improve the experiments.

Download

Files over 10MB may be slow to open. For best results, right-click and select "save as..."

Share