微結構射出成形過程的數值模擬分析

Abstract

近年來，如何成形更細小、更高深寬比的微結構一直是塑膠微成形的重點，然而在微射出成形過程高溫、高壓的環境中，要直接觀察到熔融塑料的流動情形或量測內部狀態非常困難。本研究的目的是要利用數值模擬分析的方式，模擬在微射出成形中，結晶型與非結晶型熔融塑料(PP與PMMA)的流動情況，並且得到在不同時間點，指定區域的溫度場、壓力場等，以及在實際微射出成形中無法直接量測的資訊，以提供作為微射出成形過程中材料高次構造的形成之分析的參考。 模擬結果顯示，利用數值模擬的方式可以明確得到微射出成形時熔融塑料的各項狀態資訊。在模穴充填方面，熔融塑料會因模壁冷卻與流體特性的關係，由模壁至模穴中央可明顯分辨出表面固化層、剪切層與核心層三部分；在微結構模穴充填方面，可發現在微結構尺寸為10μm時，PP與PMMA皆是以噴泉流的方式充填微結構。微結構入口處模穴厚度方向的壓力分佈並不對稱於微結構模穴厚度的中間線；而熔膠在進入微結構後，冷卻速率會大幅提高，使熔膠很快就降至熔點或是Tg之下；微結構充填速度約為主流道內的百分之一，但是其最大剪應變率卻高達主流道的四倍。

In recent years, how to form smaller and higher-aspect-ratio of micro structures has been the focus of plastic-forming. It is hard to directly observe the flow condition and measure the internal state of molten plastic in the process of micro-injection molding, because of high temperature and high pressure. The purpose of this study is to obtain the information which can not be directly obtained in the process of micro- injection molding by numerical simulation analysis. The information of molten plastic in the process of micro-injection molding can be obtained in numerical simulation result. The simulation results show that it, consist of the surface layer, the middle layer, and the core layer formed from the lateral surface to the interior, can be found in the base-plate of the injection molded. In the microstructure with 10 μm thickness, the flow condition of molten plastic is fountain flow. The pressure distributions in thickness direction in a micro-cavity are not symmetrical to the center line of the thickness. The temperature of molten plastic decreases fast, and becomes lower than melting temperature or Tg in a short time after the melt filling into the micro-cavity. Although the filling speed of the molten plastic in the micro-cavity is low to be about 1% of that in the major cavity, the maximum shear rate of the melt in the micro-cavity is high to be four times of that in the major cavity.