模內氣體反壓與動態模溫機制應用於超臨界微細發泡射出成型發泡控制與表面品質影響之研究

Study of Foaming Control and Influence on Surface Quality During Microcellular Injection Molding Process via a Mechanism of Gas Counter Pressure and Dynamic Mold Temperature Variation

許評順(Ping-Shun Hsu)

指導教授 ： 陳夏宗

中原大學/工學院/機械工程研究所/博士(2011年)

https://doi.org/10.6840/cycu201100205

摘要

超臨界流體微細發泡射出成型(Microcellular Injection Molding, MuCell)製程可降低熔融塑膠黏度、減低產品變形量、節能省料等優點，具高度應用潛力。但如何避成型過程因發泡失控引起成品表面缺陷如銀絲痕、渦流紋等以及如何有效控制皮層厚度與氣泡大小均勻度，是未來MuCell技術發展的重要關鍵。本研究係在建立一模穴內氣體反壓(Gas Counter Pressure, GCP)與動態模溫協同控制機制，來控制MuCell射出成型聚苯乙烯(PS)過程中的反壓壓力與模溫，希望藉此來控制熔膠中超臨界流體(Super Critical Fluid, SCF)的發泡過程和品質。在分別控制壓力與模溫以及壓力- 模溫協同控制下，系統化探討SCF濃度、GCP、持壓時間與動態模溫控制對於MuCell成型品表面與發泡品質(皮層分佈、孔徑大小、發泡密度)的影響。
研究結果顯示，僅用GCP時可以有效改善成型品表面品質。當GCP大於100 bar改善效果大於90%。GCP越大，皮層厚度增加，減重效果反而變差，但發泡孔徑隨反壓增加可降至30 μm以下；在持壓時間影響方面，持壓時間越久，發泡密度越低，但孔徑越均勻； SCF濃度增高則可增加發泡密度。僅使用動態模溫控制，當模溫接近PS之Tg點(約96℃)時，可以有效改善成型品表面品質。模溫在90℃至120℃範圍時改善效果可在65%以上；發泡品質方面，高模溫可降低皮層厚度，使減重比增加，但泡孔大小不均勻，發泡密度低。最後，在壓力- 模溫協同控制下，表面品質改善效果大於90%，孔徑在高GCP下可被有效降低，但隨溫度升高而增加，發泡密度在高GCP與高模溫下可明顯提高。雖然高模溫使得發泡孔徑增大，但已提高成核與發泡效果，配合高GCP使發泡均勻性提升。利用壓力-模溫協同控方式已達到創新有效發泡控制，大幅改善MuCell成品表面與發泡品質。

關鍵字

發泡品質 ； 表面粗糙度 ； 動態模溫控制 ； 模穴內氣體反壓 ； 超臨界微細發泡射出成型

並列摘要

Microcellular injection molding (MuCell) offers many advantages such as melt viscosity and warpage reduction as well as material and energy savings. Despite all of the advantages of MuCell process, the uneasy control of foaming process leading to strip-type flow marks (e.g. bright sliver streaks or swirl marks) on the MuCell part surface hinders MuCell’s wide applications. In addition, foaming quality (skin thickness, average cell size and cell density) can’t be control efficiently is also another bottleneck for MuCell parts. The purpose of this study is to develop a foaming control using the Gas Counter Pressure (GCP) combined with mold temperature control technology during MuCell process and to investigate its relevant influence on parts’ surface and foaming qualities.
The results reveal that under GCP control alone, when the GCP is over 100 bar the surface roughness can be improved by 90%. When GCP increases, the skin thickness also increases, the weight reduction decreases and the average cell size can be reduced to about 30µm. Increasing gas holding time the cell density is decreased and the cell size becomes more uniform. The increase in SCF level also increases the cell density. Applying mold temperature control alone, for mold temperature rangeing between 90~120℃(near Tg), the surface roughness improved by 65%. Increasing mold temperature will decrease the skin thickness, however, the cell size becomes non-uniform severely. Combined GCP and mold temperature control simultaneously, thin skin, small and uniform cell size as well as high surface quality can be achieved efficiently.

並列關鍵字

Foam Quality ； Surface Roughness ； Mold Temperature Control ； Gas Counter Pressure ； Microcellular Injection Molding

參考文獻

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