Date of Award

5-2004

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

Albert Co

Third Committee Member

M. Clayton Wheeler

Abstract

The appearance and performance of paper coatings and paints depends on leveling and flow properties right after application. To obtain a good quality, irregularities in the coating layer must level or smooth to a significant extent before drying, curing, or absorption "locks" them in place. Spray coating has the potential to be a major non-contact coating method for paper. Even though there has been some work on the leveling of scratches in coating layers, little has done to understand the leveling of droplet on paper. The goal of this work is to characterize the leveling of coating defects and drops on porous media. A non-linear model including evaporation and absorption effects is proposed to predict the leveling of coating defects on a porous media. Instead of including shear-shinning in the model, the goal is to use a Newtonian model, and select the correct viscosity to use in some manner. The results of this model are compared quantitatively to experiments. Results are also compared to a linear model that allows leveling to occur for an amount of time that depends on the evaporation or absorption rate. A number of coating systems were used to understand leveling rate. The coatings systems with pigment suspensions show a good correlation between experimental data and theoretical predictions. However, the coating systems with significant elastic properties give an underprediction. A linear model is found to give poor predictions. The spreading and leveling of coating drops is measured on papers with different roughnesses, porositites and absorption rates. The comparisions between final spreading and several models in the literature are given. The models from the literature presented here take into account the kinetic energy of the drop but the importance according to the substrates characteristics such as porosity, roughness and surface energy is small. As a consequence, they do not predict the experimental results, but do predict the important trends.

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