超臨界微細發泡射出成型製程特性之研究

Study on the Characteristics of MuCell Injection Molding Process

鍾明修(Ming-Hsiu Chung)

指導教授 ： 陳夏宗

中原大學/工學院/機械工程研究所/博士(2006年)

https://doi.org/10.6840/cycu200600433

摘要

超臨界微細發泡射出成型製程(MuCell Process)是新近發展出具有革新性綠色成型之技術，是具有節省材料、減少成型壓力、減少收縮翹曲及縮短成型周期等提升產品品質之先進成型製程。然截至目前為止，針對成型條件對製程特性與機械性質之影響仍未有系統性之研究。此外，利用MuCell所成型出來之產品在表面都會有氣泡流痕，不能當作A級表面的外觀面，會影響產品之應用範圍。
本研究係針對PC塑膠材料，搭配超臨界微細發泡射出成型製程，利用符合ASTM規範之拉伸與衝擊試片模具進行成型實驗，針對不同成型條件對MuCell製程成型品之機械性質以及發泡密度的影響做一詳盡之研究。實驗中並擷取模穴內之壓力，利用發泡之理論公式來計算氣泡大小，並與實驗量測值做一比較。另一方面，利用油壓及機構等可變幾何模穴設計的方式，針對不同模具結構設計做發泡特性之比較，藉以控制該模具內之壓力降，使熔膠發泡之密度能控制的更均勻，以改善成品之表面品質。最後再利用超臨界微細發泡成型時會在成品表面會形成氣泡流痕之特性，希望透過表面氣泡流痕控制，藉以提昇反光效果及均勻度，並應用於反射片之產品。
研究結果顯示針對MuCell超臨界微細發泡射出成型製程，減重比在10%~20%之間，氣泡的尺寸可以控制在50 μm以下，對於拉伸強度之影響，1.2 mm試片的平均抗拉強度降低約8%，2.5 mm試片的平均抗拉強度降低不到6 %，而衝擊強度則有明顯的提升；成型過程中模穴壓力也比傳統射出製程之模穴壓力要降低許多，1.2 mm試片之模穴壓力降低20~25%，2.5 mm試片之模穴壓力降低可以達到70%。同時利用發泡理論公式所估算之氣泡大小與實驗結果差異都在20%以內，發泡理論可以提供氣泡尺寸分布之趨勢。另外在本研究中使用可變幾何之模具機構設計，可以使熔膠波前穩定流動，得以控制發泡狀態及表面氣泡流痕分布，使可變幾何模具成品的氣泡尺寸及氣泡分布更均勻，表面反光效果比沒有壓力控制的成品提升10%以上。水平可變幾何模具含熱澆道系統成品有最好的反光效果，已經接近背光模組的光學規格要求，具有取代背光模組中之反射片及擴散片之潛力，達到縮短製程週期及節省成本的效益。

關鍵字

可變幾何模具 ； 機械性質 ； 超臨界微細發泡射出成型 ； 發泡密度

並列摘要

In the supercritical fluid microcellular injection molding process (MuCell Process), the polymer melt is first mixed with controlled SCF, followed by cavity filling, creating millions of micron-sized voids within the solidified parts. Benefits associated with this microcellular foaming process include significant reductions in part weight, processing temperature, clamping force, shrink/warpage, dimensional instability, and cooling/cycle.
The first of this study is to study the effects of process conditions on the mechanical properties of PC parts injection molded via microcellular foaming. Tensile test specimens used specimens of 2.5 mm and 1.2 mm thickness. For Izod impact tests specimens of 3.2mm thickness were used. And the second part of this study is to study the effects of different mold designs of variable geometry mold. With these processes, the cavity pressure, the skin thickness, cell size, cell density and surface property can be controlled.
Microcellular process reduces the tensile strength of 1.2 mm parts by 8 %, and 2.5 mm parts by6 %, the Izod impact energy value increased 180~400 %. And the light reflection brightness of injection expanding parts surface increase more then 10 % by convectional injection molding parts. The microcellular process can reduce the cavity pressure, the thickness 1.2 mm parts reduced 20 ~ 25 %, and the thickness 2.5 mm parts reduced more then 70%. With the variable geometry mold, the cavity pressure can be controlled. The surface quality, cell size and cell density also can be controlled, and can getting more uniform distribution. The surfaces reflect effect with the pressure controlled parts increase more then 10 % by convectional injection molding parts.

並列關鍵字

MuCell Process ； Mechanical Properties ； Cell Density ； Variable Geometry Mold

參考文獻

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