PMMA微透鏡陣列於射出成形中的收縮特性與定位精度

Abstract

塑膠鏡片重量輕，且可以用射出成形方式製作非球面鏡片，利於大量生產並有效的降低生產本。然而在射出成形製程的冷卻過程中，塑膠材料都無法避免產生收縮。不均勻的收縮會導致成形品的精度變差，而影響成像的品質，因此為了提高光學元件的成形品質，主要的思考策略就是要盡力排除或減少不均勻收縮，以增加成形品的精度。 本研究旨在以PMMA作為實驗材料，探討射出成形冷卻過程中不同的冷卻速率設定對於非結晶性塑膠成形品的內部結構狀態及收縮特性的影響，利用光散射法對其進行材料內部結構分析，觀察是否有秩序性結構的形成，以及其與透鏡陣列板的收縮特性之關係。 實驗結果顯示高溫模溫冷卻的成形品在收縮率以及光散射強度皆高於低溫模溫冷卻的成形品，判斷高溫模溫冷卻的成形品因為冷卻速率較慢，內部產生了較多不均勻的分佈的短距離結構，也因此造成收縮率的增加。而對高溫模溫冷卻的成形品以90°C來進行退火可使其短距離結構的分佈變均勻，光散射的強度因此降低，但也因退火而產生了二次收縮，使收縮率上升。 本研究在觀察PMMA成形品之收縮特性以及內部結構分佈方面提供了有效的參考。

Plastic lens has light in weight, and can be formed into a spherical lens by injection molding. These advantages make plastic lenses suitable for mass production, and reduce the production cost. However, the shrinkage of plastic material during cooling process of injection molding is difficult to avoid. Non-uniform shrinkage can cause bad accuracy of the product, and reduce the quality of imaging. To enhance the imaging quality of plastic optical components, the study aims to reduce non-uniform shrinkage, and improve product accuracy. This research investigate the internal structure and shrinkage behavior of amorphous plastic product with different cooling rates by using light scattering and shrinkage measurement. The result would be used to improve the accuracy of injection molding products. The results show that shrinkage and light scattering signal of product with high mold temperature cooling is higher than product with low mold temperature cooling. The phenomenon is because many short distance structures are non-uniform generated in the products with low cooling rate, and cause the shrinkage of product increase. For the product with high mold temperature cooling after annealing, the light scattering signal become lower. The decrement suggests that after annealing, the distribution of short distance structures become more uniform. But the annealing also cause the secondary shrinking and increase the shrinkage of the products. This study offers effective insights on observing shrinkage characteristics and internal structure distribution.