模內氣體反壓技術應用於超臨界微細發泡共射出成型產品之表皮層厚度控制與機械性質研究

Study of Skin/Core Distribution and Part Mechanical Properties During Microcellular Co-Injection Molding Process Using Gas Counter Pressure

林威佐(Wei-Zuo Lin)

指導教授 ： 陳夏宗 ； 許政行

中原大學/工學院/機械工程研究所/碩士(2015年)

https://doi.org/10.6840/cycu201500818

摘要

微細發泡射出成型(Microcellular Injection Molding)具有節省材料、降低成型壓力、減少收縮翹曲及縮短成型週期等優點，是能提升產品品質之革新性綠色先進成型技術。然而利用微發泡成型之產品在表面會有氣泡流痕，使得產品外表不美觀，影響產品之應用範圍。如將微發泡技術與傳統共射出成型(Co-Injection Molding)結合，利用無發泡材料做為表皮層，將能改善微發泡成型產品之外觀缺陷。而核心材料則使用超臨界流體型成物理發泡，並利用其低黏度特性可達到降低射出壓力、減重、減少收縮等目的。結合微細發泡射出成型與共射出成型兩種製程優點之微細發泡共射出成型(Microcellular Co-Injection Molding)，將能生產出外觀佳、質量輕、節能省料之環保產品。
本研究係針對射出成型製程，以PP塑膠為微細發泡共射出成型之表皮材料，將超臨界流體氮氣注入PP塑膠做為核心材料，使產品內部產生物理性發泡。量測產品之重量、抗拉強度、表面光澤度、表皮層厚度變化，利用品質工程(Quality Engineering)分析各種成型條件對上述機械性質之影響，以期能在面對減重、強度、外觀等不同的品質需求時找出穩健設計(Robust decision)。實驗第一部分為傳統成型、微發泡成型、微發泡共射成型之比較，接著利用料溫、模溫、射速、冷卻時間、射料切換延遲時間、核心材料穿透率為控制因子，應用田口方法進行優化參數設計。第二部分對經過優化參數設計之組別使用模內氣體反壓法(Gas Counter Pressure)，探討模內氣體反壓技術對於產品重量、抗拉強度、表面光澤度、表皮層厚度之影響。
透過實驗可以發現，在產品重量上以傳統成型最重，微發泡成型最輕，微發泡共射成型居中，搭配模內氣體反壓技術時因抑制核心料發泡，會使產品重量提升；在產品之抗拉強度方面以傳統成型最佳，微發泡成型最差，而微發泡共射成型介於其中，且搭配模內氣體反壓技術能有效提高抗拉強度；在產品表面光澤度部分，微發泡共射成型由於擁有內部保壓效果，光澤度最佳，且搭配模內氣體反壓技術時能再大幅提高，而傳統成型次之，微發泡成型因產品表面佈滿流痕，光澤度最低；使用模內氣體反壓技術會使微細發泡共射出成型產品之表皮層厚度增加。
研究結果顯示，微細發泡共射出成型揉合了無發泡材料與發泡材料之優點，產品具有優異的表面品質與不錯的抗拉強度、減重效果。依照產品需求能以成型參數做簡單調控，也可使用模內氣體反壓技術做進一步控制。模內氣體反壓技術雖會降低減重效果，但對於產品之抗拉強度、光澤度有正面提昇，並能改變產品之表皮層厚度。

關鍵字

微細發泡共射出成型 ； 模內氣體反壓技術 ； 品質工程

並列摘要

Microcellular Injection Molding can shorten the molding cycle, save material, reduce the molding pressure, and reduce part shrinkage and warpage. However, flow marks on the part surface cause surface quality issue and reduce the applicability of the products. Microcellular Co-Injection Molding combines the advantages of both microcellular injection molding and co-injection molding. Using non-foaming material as skin layer can improve the surface quality of products, while the core layer material still uses supercritical fluid to form physical foaming bubbles. Therefore, it can produce good-appearance, lightweight, environmentally friendly, and material-and-energy-saving products.
This study is about Microcellular Co-Injection Molding, using PP plastic as skin layer material and PP plastic mixed by supercritical nitrogen fluid as the core layer material to make physical foaming inside. The measurements comprised tensile strength, part weight, surface gloss, and skin layer thickness of the products. Then, the Taguchi methods was used to analyze data, identify the effect of molding parameters, and finally find out the robust design parameters for mechanical properties described above. In addition, Gas Counter Pressure (GCP) technology was combined with microcellular co-injection molding to discuss the effect of GCP on the mechanical properties.
The results show that microcellular co-injection molding products exhibit the advantages of the non-foaming and foaming plastics. They have excellent surface quality, good tensile strength, and good weight reduction. This can be simply controlled by molding parameters, or it can be further controlled by using GCP technology. Although GCP lowers the part weight reduction, it positively enhances the tensile strength and surface gloss, and it can also be used to change the skin layer thickness.

並列關鍵字

Microcellular Co-Injection Molding ； Gas Counter Pressure ； Quality Engineering

參考文獻

18. 鍾明修，”超臨界微細發泡射出成型製程特性之研究”，中原大學博士論文 (2006)。

3. A. T. Balevski, et al., United States patent 4092385 (1978).

4. M. G. Guergov, et al., United States Patent 5441680 (1995).

5. M. G. Guergov, et al., United States patent 5716561 (1998).

8. S. C. Chen, P. S. Hsu, and Y. W. Lin, “Establishment of Gas Counter Pressure Technology and Its Application to Improve the Surface Quality of Microcellular Injection Molded Parts” , International Polymer Processing, Vol. 26, No. 3, pp. 275-282 (2011).