塗佈產品如燈箱片、LCD擴散膜、CIGS薄膜太陽能電池、TCO透明導電膜等，其濕式製程所用之塗液皆為含有微奈米固體粒子之多相系統，以此類系統進行濕式塗佈工程時常面臨兩個問題：一是懸浮液系統可能含有屈伏應力，可能造成塗液於模具內流動緩慢或滯留，二是塗液中所含的固體粒子在塗佈模具內發生沉澱的現象。實驗結果顯示模具之分流管越大，粒子在分流管內的沉澱就越嚴重；反之若模具分流管內之流場具有較大之切變率則可改善此問題。本研究之目的為設計一衣架型模具，其分流管為一極淺的矩形，如此可維持模具內之流動維持高切變率。為了改善衣架型模具製作費用昂貴的缺點，本研究提出了組合式模具之設計概念。
本研究內容分為理論模擬與實驗驗證兩部分：理論部分先以巨觀一維之滑潤理論設計模具形狀，再配合有限元素法來模擬模具內二維(2-D Hele-Shaw flow)和三維之流動情況，出口流量分佈及所產生之滯留區，塗液之流變行為假設遵守Bingham 模型。理論模擬之結果顯示以滑潤理論設計之衣架型模具能夠傳遞均勻的液膜且模具內亦無明顯之滯留區存在，模具之幾何形狀具有彈性，可隨著不同之操作流體而做調整，T型模具由於分流管較大故在末端有滯留區的產生，此區域容易發生粒子沉澱之現象。實驗部分以常用之T型模具和魚尾型模具作為對照組，探討流量均勻度和粒子沉澱兩個議題，結果證實本研究所設計之模具能成功解決粒子沉澱之問題且塗膜之均勻度亦非常優越，相對而言T型模具和魚尾型模具則分別具有粒子沉澱和模具尺寸受限制等問題。本研究結果可作為銅銦鎵硒(copper indium gallium selenide, CIGS)太陽能電池與透明導電膜(transparent conductive oxide, TCO)等產品於濕式製程之模具設計參考。

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.

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