POM材料應用超臨界微細發泡射出成型之研究

自塑膠面世以來，使用範圍愈來愈廣，它除了有量產穩定及價格的優勢，許多塑膠材料也兼具高機械強度的特質，能在產品設計上做多方面的運用，但塑膠不易自然分解的環保議題，也日漸受到業界的重視，因此相關節省材料並能維持高分子特性的製程因應而生。本研究希望聚甲醛(POM)射出成型產品，在維持拉伸強度條件下，利用超臨界流體微細發泡之特性取代傳統射出保壓的製程，進而達到減塑的目的。研究分為兩階段並使用田口方法尋找最佳組別，第一階段是以超臨界流體注入相關參數為主軸，設計三種不同參數：超臨界流體注入量、產品減重比與儲料背壓進行實驗。第二階段導入射出成型相關參數：熔膠溫度、模具溫度、螺桿轉速與射出速度，並搭配第一階段最佳的超臨界流體注入量、產品減重比、儲料背壓，最終探討各種參數對拉伸強度之影響。結果顯示第一階段之超臨界流體注入量與拉伸強度成正比；產品減重比於8%時，因氣體發泡的空間過大，造成聚併現象頻繁發生，最終導致氣體半徑過大，拉伸強度降低；儲料背壓170 kgf/cm²時，拉伸強度最高，但在160 kgf/cm²時即接近注入的飽和壓力，持續增壓沒有太大助益；因此第二階段使用之第一階段參數為0.20 wt%超臨界流體注入量與6%產品減重比，以及170 kgf/cm²的儲料背壓。第二階段搭配之參數除了熔膠溫度外，其餘三種因子都成反比現象，熔膠溫度於230 °C時，因冷凝層過薄讓發泡空間足夠，最終造成更多的氣泡聚併，導致拉伸強度下降。透過此實驗我們也發現最佳參數組別的拉伸強度為52.31 MPa與最差參數組別的拉伸強度為40.22 MPa，兩者相差了23%之多，可見參數搭配對於POM使用超臨界微發泡射出成型的重要性。

關鍵字

聚甲醛； POM ；超臨界微細發泡射出成型；田口方法；拉伸強度

並列摘要

The plastic product was used on various application since the it was introduced to the world, however the issue of the plastic not easy to decompose have gradually been payed attention from the industry. The study is focused on, for Polyoxymethylene (POM) injection product, how to reduce material but still maintain its tensile strength by using Microcellular Injection Molding Process to replace the process of controlling holding pressure of traditional plastic injection. This study try to find the optimum combination by using Taguchi-method. The first stage, experiments had been conducted with three different parameters: Supercritical Fluid volume, reduce-weight ratio and screw backpressure. The second stage, conducted with four different parameters of injection: melting temperature, mold temperature, rotational speed of screw, injection speed, and combine with parameters from first stage for studying the impact of tensile strength from all different parameters introduced. The result had shown that SCF volume is directly proportional to tensile strength, with reduce-weight ratio 8%, the tensile strength is reduced due to larger foaming space. The tensile strength is highest at 170 kgf/cm² screw backpressure. Hence the 0.20 wt% SCF volume, 6% reduce-weight ratio and 170 kgf/cm² screw backpressure parameters are used on second stage. The parameters at second stage, except melting temperature, the other three parameters are inverse proportional to tensile strength. However, the tensile strength is dropped if melting temperature is over 230°C. Based on the experiment result, we found that the tensile strength is 52.31 MPa for optimum parameter combination, and 40.22 MPa for worse parameter combination, which is 23% reduction. Hence the experiment concluded that choosing optimal parameters is crucial for obtain great tensile strength while using Microcellular Injection Molding on POM injection application.