對茂金屬和齊格拉塔聚乙烯之傳統單螺桿及障壁螺桿之設計與比較

Abstract

Metallocene PE的重要應用之一為薄膜，此種薄膜時具有卓越的物性，但在加工時因其窄分子量分布所引起的低熔融強度、高黏度等造成不少加工的困難。在此我們經由適當之設計螺桿避免膠料過熱的現象，以電腦模擬配合田口法進行螺桿設計為找尋螺桿最佳幾何形狀最有效之方法，節省開發時間並提昇製程操作的穩定性。 以m-PE為加工材料，於固定押出量下根據熔化區長度、螺桿最後一斷面之溫差及螺桿壓力來決定傳統單螺桿，和Maillefer、Barr、雙溝道的Barr、Dray & Lawrence、Kim及Ingen Housz等障壁螺桿之最佳幾何形狀。探討在不同加工條件下，及m-PE和ZN-PE於相同加工條件下於各螺桿於押出性能上之表現，如固體床速度、熔融薄膜厚度、障壁梯板開口大小、熔化效率、單位長度熔化速率、熔化區長度、壓力分布、整體平均溫度等，最後進行模擬與實驗結果之比較，以確認模擬程式之準確性。

Making film is an important m-PE application. The film has good physical properties. But it’s difficult to be processed because that the molecular weight distribution of m-PE is narrow. The narrow molecular weight will be caused a low melt strength and high viscousity. Due to the poor melt strength of m-PE, the screw must be designed properly to avoid the overheat of melt. Computer simulation combined with Taguchi method is the most efficient method for finding the optimal geometry of the barrier screws. It’ll economize the developed time and improve the steady process. The optimal screw geometry of Single Screw ,Maillefer, Barr, Double channel Barr, Dray & Lawrence, Kim and Ingen Housz , with m-PE and ZN-PE as the processing material, can be determined, base on the length of melting zone , temperature difference of last channel section and screw pressure. Subsequently, the effect of processing conditions on the screw performance, such as solid bed velocity, melt film thickness, barrier clearance thickness, melting efficiency, melting rate per unit length, the length of melting zone, pressure build-up, and bulk temperature were discussed. Finally, the simulation results were compared with the experimental results to identify the accuracy of the simulation models.