Abstract
During a thin film application, the surface of the coating liquid applied to the substrate becomes uneven because of the geometry of the substrate, viscosity of the coating liquid, surface tension, and its contact angle with the substrate. The surface is particularly uneven at the edge corner portion of the substrate and is thicker than the average coating thickness. This study used the volume-of-fluid (VOF) method to examine the surface unevenness of the coating liquid in terms of the contact angle of the substrate surface and sides. After the coating liquid was evenly applied to the substrate, the maximum height of the uneven region of the coating liquid at the edge of the substrate increased as time passed. The point of maximum height moved away from the edge corner portion of the substrate. The coating liquid applied to the substrate with a contact angle less than 90° exhibited a pinning effect in which the contact point was fixed at the edge. The surface unevenness was more pronounced in the absence of the pinning effect than in its presence, due to the effects of the viscosity of the coating fluid and the surface energy of the substrate.
Highlights
During a thin film application, the surface of a substrate is treated with inorganic or organic material in the form of a thin film to endow the substrate surface with high functionality, such as conductivity, magnetic properties, light reflectivity, and anti-corrosion property [1,2]
This study examined coating fluid behavior and surface unevenness in terms of the surface energy
This study examined coating fluid behavior and surface unevenness in terms of the surface of the substrate surface and sides during a thin film coating process
Summary
During a thin film application, the surface of a substrate is treated with inorganic or organic material in the form of a thin film to endow the substrate surface with high functionality, such as conductivity, magnetic properties, light reflectivity, and anti-corrosion property [1,2]. In the case of an unevenly coated lens surface, optical signals cannot be received accurately, and signal processing errors can occur [29] To resolve this problem, the uneven parts on a coated surface can be removed using chemical or mechanical removal technologies [30,31,32]. The uneven parts on a coated surface can be removed using chemical or mechanical removal technologies [30,31,32] These methods need to be performed as an additional process after the coating, and they are time-consuming and expensive. This study uses the VOF method to analyze the coating fluid behavior and surface unevenness at the edge portion of a coated surface, based on the changes in the contact angle of the substrate surface, which is an important factor influencing the surface unevenness
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