Date of Award

5-2001

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor

Douglas W. Bousfield

Second Committee Member

Joseph Aspler

Third Committee Member

Patrice Aurenty

Abstract

Filaments are formed at the exit of rolling nips in some coating and printing operations. The filament size distribution can determine product quality such as gloss. The average filament size is linked to operational difficulties such as misting. The filament size distribution of various fluids and inks is characterized and compared to theoretical model. A high-speed video camera is used to visualize the exit of a rolling nip. The size distribution of the filaments is characterized with image analysis. A laboratory print tester is used with the high speed camera to characterize the size of the defects right after printing. The rheological properties are obtained using a cone and plate rheometer. A novel test is developed characterize the fluids cavitation pressure using a mechanical tester and a closed syringe. Elongational properties are obtained with a falling bob technique. Fluid rheology has a strong influence on filamentation. The cavitation results do not give a direct correlation with filament volume. The elongational properties of the fluids have a strong effect on filamentation but in a complex manner. As printing speed or ink film thickness increases, the filaments increase in average size and in their size distribution. The nip loading does not have a large effect on filament size nor the size distribution. Porous substrates reduces or eliminates the “remains” within the detectable limit. An empirical correlation is developed to link average filament volume to dimensionless parameters of Reynolds number, Deborah number, and Trouton’s ratio. Reasonable correlations are obtained for specific groups of fluids but low correlation is found for the entire fluid set. A physical model is proposed to predict the occurrence of filamentation and the filament volume. Theoretical predictions are compared to the experimental filament volume for all fluids. The results indicate that a small number of cavities that are formed actually coalesce to form filaments. By altering this fraction linearly with the Trouton ratio, the filament volumes are predicted. The Newtonian model including the elongational effects predicts the filament volume best. The persistent wide scatter in the results compared to the model or the empirical correlation implies that at least one other parameter affects the filamentation process.

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