超臨界微細發泡射出成型反壓機制建立並應用於流變特性研究

Study on the Establishment of Counter Pressure Technology in Mucell Injection Molding Process and Its Application to Rheological Characterization

林鈺婉(Yu-Wan Lin)

指導教授 ： 陳夏宗

中原大學/工學院/機械工程研究所/博士(2008年)

https://doi.org/10.6840/cycu200800319

摘要

超臨界微細發泡射出成型具有製品輕量化及製程節能環保之優點，然而製品外觀品質不佳且製程控制不易，氣泡的分布與尺寸的控制是影響製品品質的關鍵之一，但超臨界流體會隨在熔膠注入模穴後因壓力或溫度的變化而達到過飽和狀態，導致氣核產生與氣泡成長，進而影響熔膠的流動以及後續的製程控制，因此了解含超臨界流體的熔膠之流變行為顯得相當重要。
本研究針對超臨界流體混合高分子熔體在射出成型過程中的流變行為進行探討。建立氣體反壓機制並應用於Mucell射出成型，達到控制氣泡成長與抑制發泡之效果，並求得混合熔體抑制發泡後之黏度變化。不同模溫(185、195、205℃)與射出速度(5、10、15mm/s)之參數條件下進行聚苯乙烯熔膠溶有濃度0.4wt%超臨界氮氣在狹縫流道內之Mucell流變量測，研究結果顯示，使用氣體反壓50bar~200bar可降低熔體黏度最高達30%，若氣體反壓200~300bar則因高於臨界發泡壓力，可得到未發泡熔體黏度降低率約32%~49%，但未能降低射出壓力。
將真實黏度以Power Law Model進行解析配置，由於剪切率介於3000~11000s-1為剪稀薄效應之高剪切率範圍，因此可得到相當近似的解析曲線。

關鍵字

超臨界微細發泡 ； 流變行為 ； 氣體反壓法 ； 臨界發泡壓力

並列摘要

Microcellular (Mucell) injection molded products have advantages of weight reducing and green manufacturing process. However, defective appearance caused by bubble deformation is a visible flaw. The major approach to improve Mucell product quality is control of bubble distribution and uniformity of bubble size. SCF nucleation and bubble growth which begin above saturation point as a result of pressure drop influence polymer melt flowing and product shaping, so that it’s necessary to understand rheological behavior of melt mixed with supercritical fluid (SCF) during Mucell injection molding process.
The purpose of this study is to investigate rheological characteristics of melt dissolved SCF under restrained growth by Gas Counter Pressure (GCP) Technology in Mucell injection molding process. A slit cavity is designed to measure pressure drop of polystyrene (PS) mixed with 0.4wt% supercritical nitrogen (SCN2) under different mold temperature (185, 195, and 205℃) and injection speed (5, 10, and 15mm/s). In addition, different level of GCP is also used to affect SCF variation during injection process. Compared with convention injection molding process without GCP, melt viscosity of GCP from 50 to 200bar is maximally reducing to 70%. Non-nucleation mixture melt obtained by using GCP of 300bar has 32~49% lower viscosity but changeless injection pressure.
Finally, Power Law Model is chosen to do curve fitting from measured real viscosity. The result shows the model is proper to express shear thinning viscosity variation with shear rate from 3000 to 11000 s-1 in this study.

並列關鍵字

Microcellular Injection Molding ； Critical Nucleation Pressure ； Rheological Characterization ； Gas Counter Pressure Technology

參考文獻

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