Tese e Dissertação

Tese: Slot Coating of Particle Suspension

Slot coating process is commonly used in the manufacture of high technology products such as flexible circuits, LCD and OLED displays, among others. The thickness of the coated liquid film depends on the flow rate and substrate velocity. It is very important to study the flow in the coating bead region, because the flow pattern has a strong effect on the quality of the coated film. Most of the available studies on slot coating consider the fluid as a Newtonian liquid. However, coating liquids are usually polymer solutions or particle suspensions. The effect of dissolved polymer molecules in the flow has been analyzed recently. However, the effect of suspended particle remains unknown. The goal of this work is to develop a fundamental understanding of the effect of suspended particles in the flow pattern in a slot coating process. The local changes in particle concentration can lead to great changes in the local liquid viscosity and consequently in the flow and process limits. In this research, the particle suspension is a system composed by a Newtonian liquid as a continuous phase and rigid spherical particles as the dispersed phase. The particle transport equations takes into account the diffusion due to gradients of concentration, viscosity and deformation rates. The particle transport equation together with the mass and momentum conservation equations are used to describe the two-dimensional free surface flow. These equations are solved using the Galerkin/Finite element method. The numerical code was validated by comparing numerical prediction obtained in circular tube flow with the available exact solution. The results obtained in slot coating flow show regions of high and low concentration of particles and its effect of the flow, and the variation of particle concentration in the deposited thin film.

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