01. Experimental/Computational Fluid Dynamics

Traditionally, spray painting has been used for painting aircraft and automobiles, but there are issues such as a large amount of paint being wasted due to a low transfer efficiency. The massive waste of paint not only leads to economic problems due to increased costs but also causes environmental issues such as increased energy consumption during disposal. Inkjet technology, which is commonly used for document printing, forms a coating with small amounts of liquid droplets, so applying this technology to painting aircraft and other objects can be expected to reduce paint usage and costs. Typically, the created painted surface forms a smooth surface due to a leveling phenomenon caused by the flow of the paint, but it is known that painting defects such as orange-peel effect and sagging can occur depending on the painting conditions. While research on inkjet technology and the leveling phenomenon is well- known, the relationship between urethane-based resins, which are the main component of aircraft paints, and inkjet technology, as well as leveling, is not understood. In this study, we hypothesize that the film formation process of urethane-based resins using inkjet technology consists of two parts: the flight process from droplet ejection to impact, and the leveling process of the coating film. We evaluate the relationship between the ejection conditions and the appearance of the coating surface. Inkjet technology involves various factors such as the temperature and viscosity of the liquid, and the pressure and frequency of ejection, but particularly, changes in ejection frequency greatly affect the spacing of the generated droplets. Therefore, we show the impact of frequency changes on the coating film based on measurements of the flight process of droplets and the state of the resulting coating surface when the ejection frequency is varied.

Prof.

Kato Koichi

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