Flow visualization and operating limits of tensioned-web-over slot die coating process |
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| Authors: | Jaewook Nam Marcio S Carvalho |
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| Affiliation: | 1. Coating Process Fundamentals Program, Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA;2. Department of Mechanical Engineering, Pontifícia Universidade Cat ólica do Rio de Janeiro, Rua Marques de Sâo Vicente 225, Gávea, Rio de Janeiro, RJ 22453-900, Brazil;1. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 813 Ferst Dr, Atlanta, GA 30332, United States;2. School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 778 Atlantic Dr, Atlanta, GA 30332, United States;1. Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, MA 01003, United States;2. School of Mechanical Engineering, Changwon National University, 20, Changwondaehak-ro, Uichang-gu, Changwon-si, Kyungnam-do 51140, Republic of Korea;1. Department of Materials Engineering, Ming Chi University of Technology, New Taipei City 24301, Taiwan;2. Institute of Nuclear Energy Research, Taoyuan 32546, Taiwan;3. Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan;1. Department of Chemical Engineering, Faculty of Engineering & Informatics, R&KT Centre in Advanced Materials Engineering, University of Bradford, BD7 1DP, United Kingdom;2. Films R&D Centre, Toyobo Co. Ltd., Otsu, Japan |
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| Abstract: | Tensioned-web-over-slot die (TWOSD) coating is one of the most successful high-speed liquid coating process. It deploys elastohydrodynamic interaction to control the distance between the moving substrate and the coating die lip surface in order to be able to coat an ultra-thin liquid layer. However, flow instabilities that come from the gas–liquid interface and micro vortices inside the flow may lead to coating defects. Therefore, the range of operating conditions of uniform coating is limited.Nam and Carvalho 1] proposed a two-dimensional computational model to examine the role of the elastohydrodynamic interaction between the liquid and flexible substrate in tensioned-web-over-slot die (TWOSD) coating process, with the goal of predicting the operability limits of the process.Here, we use flow visualization on a laboratory-scale TWOSD coating apparatus to study limit flow states which are related to various flow instabilities and appearance of vortex in the flow. The visualizations show the progression of flow states beyond critical flow parameters which cannot be predicted by the model as three-dimensional features of these limit flow states. Furthermore, the critical flow rates, that define the operability window of the process, were determined experimentally and were used to validate the computational model. |
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