Modeling of lateral thickness variation in a liquid curtain with edge guide, 2012 Advanced Coating Fundamentals Symposium

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Edge guides are commonly used in curtain coating. The goal of this work is to understand their influence to curtain stability. A method of modeling large area liquid curtain is proposed which is based on the integration of momentum equation in the curtain thickness direction. Comparison with experimental data found in the literatures show that the model is reasonably accurate. Based on the developed model, a parametric study was carried out numerically. For a Newtonian fluid and non-lubricated edge guide, the results show that liquid viscosity and the edge guide wettability can have strong influence on minimum curtain thickness and curtain uniformity. Based on the location of the thickness minimum, it is proposed that edge detachment and film splitting are responsible for curtain breakage from edge guide. For low wettability edge guide, a wave pattern in the curtain can be initiated and propagates toward the center of the curtain. This can certainly cause uneven coat weight distribution in the machine cross direction.