黏土含量在聚丙烯/蒙脫土和聚苯乙烯/蒙脫土奈米複合材料的微細發泡射出成型品熱/流變/翹曲性質之研究

本研究先以兩種不同的基材，結晶性材料之聚丙烯（PP）與非結晶性材料之聚苯乙烯（GPPS），經傳統射出與超臨界流體微細發泡射出成型製成塑膠盒子，以二氧化碳﹙CO2﹚和氮氣（N2）作為發泡劑，探討兩種基材與兩種氣體之發泡微結構特性（SEM）與收縮/翹曲變形（Shrinkage/Warpage）之影響。研究結果顯示，在收縮/翹曲變形性質方面，兩種基材隨著兩種氣體的含量增加都能有效的降低其收縮/翹曲變形量。在氣泡結構方面，兩種基材之氣泡大小會隨著氣體含量的增加而有變小的情形，也可有效的提升氣泡密度。接著研究聚丙烯/蒙脫土和聚苯乙烯/蒙脫土奈米複合材料，利用傳統射出成型與超臨界流體微細發泡射出成型製成塑膠盒子，探討改變聚丙烯之蒙脫土含量（0、1、3、5、7、9 wt%）和聚苯乙烯之蒙脫土含量（0、0.5、1、2、3 wt%）對熱性質、氣泡微結構特性、收縮/翹曲變形（Shrinkage/Warpage）以及PVT性質之影響，並藉由田口法實驗找出影響收縮/翹曲變形之最佳化參數。研究結果顯示，在氣泡微結構方面，得知氣泡大小會隨著蒙脫土含量的增加而有變小的趨勢，並提高了氣泡密度。熱性質方面，添加適量的蒙脫土可有效提升奈米複合材料的熔融溫度（Tm）與熱裂解溫度（Td）。收縮/翹曲變形性質方面，隨著蒙脫土含量的增加可有效降低其收縮/翹曲變形量。PVT性質方面，奈米複合材料在射出成型時，從熔融狀態到凝固成型，中間過程體積變化小，故奈米複合材料有較好的尺寸安定性及較小的收縮翹曲行為，加工成型性比基材好。田口法實驗方面，在傳統與微細發泡射出結果皆顯示模具溫度與冷卻時間是最具影響力的製程參數。採用田口法實驗之最佳化參數，對傳統與微細發泡射出成型品收縮/翹曲變形作一探討，找出影響變形量最低之最佳化參數。

關鍵字

聚丙烯；聚苯乙烯；蒙脫土；超臨界流體微細發泡射出成型；翹曲變形

並列摘要

Conventional injection molding parts may cause shrinkage/warpage problem after cooling due to the uneven wall thickness, uneven cooling, or long flow ratio. In this study, both microcellular injection molding and polymer nanocomposites are used to improve the warpage problem over the conventional molding process. Moreover, the polymer nanocomposites foam has smaller cell size and larger cell density compared to those by neat polymer foam. Foam with small cell size would help the warpage problem. So using polymer nanocomposites foam to improve the warpage problem is the goal of this project. A rectangular box is used for this study which has shrinkage/warpage problem along the long side wall. Semi-crystalline polypropylene (PP), amorphous polystyrene (PS), and PP/clay nanocomposites are used in this study. The results show the microcellular injection molding can improve the shrinkage/warpage problem of the box. However, PS foam has less shrinkage/warpage than that of PP. And the addition of clay into PP also helps the shrinkage/warpage problem. The PP/clay foam has the same level of shrinkage/warpage of the box as the PS foam does. In order to get the least shrinkage/warpage of the rectangular box, Taguchi method is used to investigate the effects of melt temperature, packing pressure, cooling time, injection speed, and mold temperature on the shrinkage/warpage of the box. The results showe that mold temperature is the most important factor in affecting the shrinkage/warpage of the box both on conventional and microcellular injection molding.