PC/PMMA共擠製模內流動現象初步探討

Abstract

高分子多層膜是一種單一結構的薄膜產品，包含了兩種或兩種以上的高分子。可以達到單一素材無法得成的特性。近年隨著有機高分子顯示器以及有機太陽電池的發展，高分子多層膜的應用與品質要求更受到了重視。本研究探討非結晶性塑料PC/PMMA多層膜共擠製時模內的合流行為，以及擠製條件所帶來的影響。研究中設計製作一套共擠製實驗機台與模具。藉由利用模壁上開設的石英觀察窗與照相機來進行實驗觀察與攝影，以對多層共擠出製程中PC及PMMA在模具內的合流部的流動行為及層間界面穩定性進行分析。 實驗的結果得知，熔體界面的穩定情形與熔體溫度、擠出速度、擠出速率比有關。當等速擠出時，由於熔體黏度差異會有包覆現象的產生，隨著擠出速度的提升可改善包覆現象，但模壁剪應力及界面剪切率也會隨之增加而導致界面不穩定的現象。在高速擠出時甚至會產生熔液破裂的情形。提高熔體溫度可降低模壁剪應力，使界面不穩定情形獲得改善。在非等速比方面，增加支流路的擠出速度使得黏度差異變小可使包覆現象獲得改善，但可能會因流速差異而造成界面不穩定現象。在非等溫擠出時，若支流路溫度較高，則黏度差異縮小使得無明顯包覆現象產生，但在非等速比條件下則會因界面剪切率差異擴大而產生界面不穩定現象。若支流路溫度較低，造成黏度差異擴大，會有更嚴重的包覆現象產生，並使界面不穩定情形加劇，若再提高支流路擠出速度則會因剪切率差異過大而導致逆流的現象發生。

Multilayer polymer film is a single-structure film that contains two or more polymer types, and is capable of producing characteristics beyond that of a single-type polymer film. In recent years, with the development of the organic polymer display and organic solar cell, the application of multilayer polymer films and the demand for their quality have received much attention.This study explores the confluence behavior of non-crystalline plastic PC/PMMA multilayer films inside a mold during the coextrusion process, and investigates the effects of the extrusion conditions.This study designed and created a set of machines and molds for the coextrusion experiment.Quartz sight glass and cameras mounted on the mold wall were used to observe and video record the experiment. Both the confluence aspect of the flow behavior of PC and PMMA inside a mold during the multilayer coextrusion process and the stability of the interface layer were analyzed. Experimental results revealed that the stability of the melt interface is related to melt temperature, extrusion speed, and extrusion speed ratio. When the extrusion speed was constant, the envelopment phenomenon due to differences in melt viscosity was observed.The envelopment phenomenon improved as the extrusion speed increased; however, the mold wall shear stress and interface shear rate induced interface instability following the increase in extrusion speed.High-speed extrusion can even generate melt fractures.The increase in melt temperature reduced the wall shear stress,which reduced the interface instability. When the extrusion speed ratio was not constant, increasing the extrusion speed of the branch paths reduced the viscosity variations,and subsequently improved the envelopment phenomenon.However, differences in flow speeds possibly caused the interface to become unstable.When the extrusion temperature was not constant, the branch paths having higher temperatures reduced viscosity differences and generated insignificant envelopment phenomenon.However,under non-constant speed ratios, the increased differences of the interface shear rates resulted in the interface becoming unstable. When the temperatures of the branch paths were lowered, which subsequently increased the viscositydifferences, they generated a more severe envelopment phenomenon that exacerbated the interface instability. When the extrusion speeds of the branch paths were further increased, the reflux phenomenon began to appear due to the significant differences in shear rate.