多層膜共擠出時的模流特性及膜內結構狀態

Abstract

摘要

塑膠薄膜為高分子產業的一項重要產品，為了提高塑膠薄膜製品的價值與獨特性，近年來的發展朝向功能性多層膜演進，然而多層膜製品的品質與功能受其膜厚均勻性、層界以及層內結構狀態等所影響。 本研究的目的為探討多層膜共擠出時的模流特性，以掌握改善膜層厚度均勻性和層界品質的關鍵，並釐清超多層膜界面滑移產生之機制及膜層厚度限制對於層內結構的影響。 研究中使用高速攝影法即場觀察各種模溫和擠出流量下的模具內的合流行為以及界面不穩定流動現象，同時量測流動方向上的模壁壓力變化；實驗結果並配合有限元素軟體POLYFLOW進行模擬驗證。本研究對象的多層膜包括PC/PMMA以及PP/PA兩種組合，共擠出的多層膜使用光學顯微鏡進行膜層結構的觀察。並計算模壁上剪切應力之變化以分析界面滑移之成因。 側邊即場觀察及模擬結果顯示，當共擠出之兩種塑膠的黏度差距較大時，擠出成品的橫切面較為平穩，而黏度差距相近時則較易有亂流的情況產生。擠出流量差距越大，則包覆現象會越發嚴重。超多層共擠出實驗中，界面結合性差的PP/PA組在低流量時界面滑移主要受界面層數之影響，越多的層數越容易產生顯著地滑移現象；高擠出流量時則不論層數多寡皆有顯著之滑移現象產生。界面結合性優良的PC/PMMA組則較不受流量多寡影響，但在高層數時亦有界面滑移之現象產生，但相比PP/PA組則較不顯著。

Abstract

Polymer film is a major product of the polymer industry. Recent years have seen the development of multi-layer films, which are more valuable and useful than other polymer films. The quality and functionality of multi-layer films are influenced by the uniformity of the thickness of their layers, the number of interfaces within them and the structure of each layer. This investigation examines the characteristics of polymer flow inside a mold and the formation of the internal structure of layers in the film during co-extrusion. The results thus obtained will be used to improve the uniformity of layer thickness and the quality of the interfaces among the layers. Also, the effect of the limiting layer thickness on the internal structure of the layers is analyzed, and the mechanism of interfacial slip between interfaces is elucidated. An experiment in which a multi-layer film is co-extruded is carried out; the first purpose is to observe the flow of the polymer melts at the confluence in the die, and the second is to measure the variation in pressure in the die wall along the flow, and thereby evaluate the flow shear stresses. The interfacial instability is recorded using a camera through an observation window on the die wall. The flow and the stress field were analyzed during co-extrusion using POLYFLOW software. The experimental materials were observed under an optical microscope. Multilayer film co-extrusion experiments were conducted to measure the decreases in flow pressure on the mold wall in the direction of the flow to evaluate the flow shear stresses. The experimental results herein reveal that two materials with significantly different viscosities have a smooth interface. As the difference between the viscosities declines, the generation of turbulence in the interface becomes easier. A large difference between the flow rates of two co-extrusion materials induced a clear encapsulation phenomenon. In the multi-layer co-extrusion experiment, the extrusion rate was experimentally increased to increase the pressure within the flow. Based on the experimental results, when the shear stress reaches a threshold, a large number of interfaces cause interfacial slip, reducing the shear stress. Increasing the number of interfaces increases the interfacial slip. A PP/PA co-extruded film is more likely to exhibit slippage than is a PC/PMMA co-extruded film, because of the poor binding force at the PP/PA interfaces.