Precision Coating Die Design for Suspensions: Organic/Inorganic Particles in Micro/Nano Scale

• Main Authors: Lin, Yu-Yan, 林育彥
• Other Authors: Liu, Ta-Jo
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/67278430716893472625

碩士 === 國立清華大學 === 化學工程學系 === 98 === Coating solutions with a significant amount of solid particles added are not unusual for many industrial applications. Products such as backlit films, diffusers for LCD panels, CIGS solar cells are just a few examples. Two issues arise for delivering such solutions, i.e. the solutions may have yield stress and particle sedimentations may appear in the manifolds for conventional coat-hanger or T-dies. There are experimental evidences that clearly indicate that particle sedimentation can be serious in the manifold on the die. A die that can maintain relatively high shear ratse in the manifold can improve this precipitation problem. The purpose of this research is to design a coat-hanger die which has a shallow manifold with rectangular cross-sectional area. Therefore, flow field with high shear rate can be achieved. Due to the high cost of traditional coat-hanger die, this research also propsed a new idea-using two easily-replaced shims to make a die, this design can effectively reduce the cost of manufacture. Both the theoretical modeling and the experimental verifications were carried out for die design. The coating solutions were assumed to obey the Bingham viscoplastic model. A mathematical model based on the 1D lubrication approximation, 2D Hele-Shaw flow and 3D flow simulations were developed to predict the performance of the new design, the computer-aided solutions by the finite difference (FDM) and the finite element method (FEM) could be obtain. The performance of the design based on the lubrication approach is in agreement with the 3D simulation and experimental results, therefore the new die can develop uniform flow and no stagnent zone can exist in the end of the manifold, so that the sedimentation can be avoided. We also compared the sedimentation and uniformity of our design to a commercial T-die and fishtail die experimentally, the results indicated the performance of our design is excellent, sedimentation and uniformity problem appeared in both the T die and fishtail die. The design of our research can be applied to the wet coating process of CIGS solar cell & TCO films.