The Application of Injection Molding Technique to Optimize the Replication of Micro Structure for Light Guide Plates

Abstract

[[abstract]]本研究主要目的在探討LCD背光模組之重要元件－導光板其微結構的轉寫性，為使轉寫高度達到與微結構模仁有最佳的一致性，符合光學設計所需之效果及商業價值，在射出成型上必需考量避免殘留應カ、流痕、收縮、翹曲、積風等成型不良之因素，於此前提下嘗試各種射出參數對成型的影響性，其中鲜為人所探討的背壓壓力於本研究中發現對殘留應力及轉寫高度均有顯著的影響。 眾所皆知，不論運用何種實驗設計法，其所設定的初始條件攸關實驗的效益與成敗，綜觀各文獻中從未將背壓壓力列入轉寫高度之控制因子而加以研究，其所尋得最具影響力之參數大多為料溫、模溫與保壓壓力。本研究發現背壓壓力相較於保壓壓力對導光板微結構轉寫性更具有影響力，並以此為較佳的初始條件，尋求成品達到強健化之目標。 在研究中應用強健型成型參數迴歸搜尋法，先以田口方法之最佳化參數為初始值，進而搜尋強健參數點，最後得到ㄧ最佳化且具有強健型的射出成型參數，結果證實在初始參數的設定下其轉寫率為89.6%，經強健型成型參數迴歸搜尋法提升至95.3%，顯見此方法可以有效增加導光板微結構之轉寫率，並能促進業界生產導光板之良率。[[abstract]]This research aims to investigate how to enhance the effort of replicating the micro-structures of light guided plates (LGP), which is an important component in the LCD back light module. To make the best unity of replicating the micro-structures between the injection part and the mold insert, and to fulfill all the requirement considered by the optical design and commercial issue, process of injection-molding LGP must consider to avoid many defeats, such as residual stress, flow mark, shrinkage, warp and void. Thus, several process parameters influencing the molding quality especially including the back pressure setting, which is seldom discussed in the past studies, have been conducted in this research. The experimental results show that back pressure has noticeable influence on residual stress and the replication performance. As is well known, the experimental results conducted by design of experiment methods highly depend whether important factors have been selected. After reviewing a few research literatures, the back pressure is seldom chosen in the controlled factor. Instead, parameters such as the melt temperature, mold temperature, and packing pressure are most concerned. This study reveals that the back pressure is more effective than the packing pressure in the replication of LGP’s micro-structures. For the sake of controlling process quality, this factor is important to the searching of robust process parameters setting. In this study, a regression model based searching method of robust parameters setting has been applied to molding LGP. Firstly, the initial values of process parameters are determined with the optimal combinations using Taguchi method. Then, the robust parameters setting are found by the applied searching method. The experimental results for verification show that the replication rate of height of the micro-structures has been improved to 95.3% (the original is 89.6%). The method is also apparent to effectively improve the yielding rate of LGP manufacture