兩平板間液體轉移之研究

Abstract

凹版轉印技術(gravure offset printing)以其高輸出速率與不錯的解析度而聞名，現今此一技術更將拓展到印刷電子上。然而其未達100 %轉移率使得凹版內的導電膠無法完全由凹版中轉移到目標基材上，使得印刷成品出現像是斷線、汙點之類的缺陷，可能造成短路或是斷路等狀況，降低產品的良率。 為了解決此一問題，本研究利用兩分離平板間的液橋對凹版轉印的過程作近似，並探討其於上下兩板上之接觸線的移動機制和接觸角的變化。其中兩板間的液滴使用甘油。為了觀察其接觸線和接觸角，吾人將定量的甘油(或甘油水溶液)置於兩平板間，接觸至一定距離後再移動上板拉伸液橋使其一分為二。過程由CCD攝影機拍攝下來，並使用程式記錄液橋之三相接觸線和接觸角的變化。通常，接觸線的移動與否與液體於基材上的後退角有關；實驗結果指出，接觸角在液橋拉伸過程中會先下降到一個最小值再上升，此最小值與拉伸速度存在一關係式。且當接觸角上升到液體在基材上的後退角時，邊界便會停滯不動。此一停滯的寬度也會隨著速度的增加而增加。這一個停滯的寬度與速度的變化趨勢，就會在不同基材組合下對轉移率就會造成不同的影響。 若能將相同的實驗結論套用在實際的凹版轉印研究上，便可找出提升轉移率的方法，使相關技術之缺陷減少、增加產品良率，以達到提升其競爭力、造福人群之目的。

In recent years, gravure offset printing has received great attention for its high throughput rate and fine quality for printed electronics. However, as the dimensions of printed features decrease, the ink left over in the patterned gravures usually dries quickly and leads to defects, such as undesired dots or broken lines. These defects not only deteriorate the printing quality but also shorten the life time of gravures. One way to solve this problem is to increase the transfer ratio, which is the volumetric ratio of the liquid transferred from the gravure to target media. To study the fundamental physics of liquid transfer phenomena in the printing process, a liquid bridge is used in this study for its simple geometry. The stretching process of a liquid bridge between two separating large plates is recorded by a CCD camera. Image analyses are performed to obtain the transient interfacial profiles of liquid bridges. From the experiment results, we observe that the contact angle first decrease to a minimum value even below the receding angle, and then increase until the liquid bridge breaks up. The minimum contact angle has an exponential relationship with the top plate’s velocity. Furthermore, the boundaries on both sides stop receding when the contact angle increases to the receding angle. Also, when the top plate’s velocity increases, the boundaries stop at larger values. This phenomenon makes the transfer ratio vary differently in different substrates combination.