應用於可撓式基材之高透明度及高玻璃轉換溫度聚醯亞胺之合成及結構與性質之探討

Abstract

在這近年來，有機面板也逐漸開始受到重視並且蓬勃發展，而這都是由於現在科技趨勢為輕、薄、短小、可撓性。這些成果都是建立在現今的精密捲繞對位技術和轉印塗佈上的蓬勃發展。雖然這些高分子材料有這麼多的優點，然而在其應用上仍然有一些限制存在，例如以PET、PEN 為基版的材料具有較低的水汽阻抗還有其黏著性相對於金屬以及陶瓷材料具有較低的趨勢；另外其玻璃轉換溫度以及較高的熱膨脹係數，也讓現今的可撓性電子元件製程於溫度上受到極大的限制，這也間接影響導電薄膜的電性以及物理性質。而現今市面上具有高玻璃轉換溫度的可撓式PI基板卻沒有良好的透明度，這使得其在應用上有許多限制。 因此一個具有良好熱穩定性質以及高透明的有機可撓式基板是本論文著重的討論點，而所選擇的高分子為聚醯亞胺高分子薄膜，利用其本身就具有的高玻璃轉換溫度的優勢並且加以改良。而研究方向即為：合成各種新穎的高透明高玻璃轉換溫度的聚醯亞胺高分子薄膜。使其於熱性質方面具有良好的表現(玻璃轉換溫度高於230 oC)，以及其薄膜透光率也能達到90%以上，另外在熱傳導係數上也能低於60 ppm/ oC以下。 首先，在這研究實驗中所所選擇的高分子為利用雙胺類以及雙酐類合成的聚醯亞胺。合成中使用到的雙胺類為 BAF、BAPF、BAPP、ODA，雙酐類則為ODPA以及6FDA，其所合成出來的聚醯亞胺為使用加熱脫水閉環的方式，而使用的溶劑則為DMAc。這些聚醯亞胺薄膜因為在其單體中具有醚類以及作為巨大立體障礙的烷基和氟化官能基於其分子鏈中，因此具有高玻璃轉換溫度以及良好的光穿透度。擁有立體障礙的烷基和氟化官能基和醚基的存在會使得電子在分子間以及分子內電荷轉換跳動的機率減少，進而也同時破壞了苯環的堆疊，因此在聚醯亞胺薄膜厚度為60~80μm時，對於可見光範圍的白光穿透度可達到90％。在玻璃轉換溫度方面則可達到超過230 oC以上，而熱裂解溫度則可達到480 oC以上。本研究中所合成出來的色淡6FDA-BAF聚醯亞胺其玻璃轉換溫度達到298oC，並且在800nm仍然有93%的良好光穿透度和良好的透明度以及熱穩定性以及可饒性，可適合應用在可撓性電子元件以及綠能環保元件基版。

In recent year, the organic flexible devices are being intensely pursued because today’s technology trend necessitates lightweight, flexibility, thermal stability, and dielectric properties. In terms of low cost, polymer substrates are preferred over metal foil due to their ease in fabrication based on roll-to-roll process. However, there are several drawbacks and limitations of using a polymer substrate, for example, high water vapor permeation rate (WVTR) on PET or PEN, and low adhesion between polymer and inorganic layer. In addition, low glass transition temperature (Tg) and high coefficient of thermal expansion (CTE) impose great challenges to the mechanical integrity of the flexible devices during and after the fabrication processes. In this study, polyimide is chosen as the flexible substrate for its excellent thermal stability. However, the transmittance of a conventional polyimide is <60%. Thus, the objective of this thesis is to develop novel, flexible polyimide films with high Tg (> 230 oC), high transmittance (> 90%) and low CTE (< 60 ppm/ oC). Polyimide is synthesized by polycondensation reaction of a diamine and a dianhydride via a two-step polymerization, involving the formation of poly(amic-acid) and subsequent thermal imidization. In particular, four different starting diamine monomers: BAF, BAPF, ODA, and BAPP and two starting dianhydride monomers: 6FDA and ODPA are chosen in this study to prepare 8 different polyimides. These polyimide films show high Tg and excellent transmittance due to the incorporation of ether linkage and bulky groups (–CH3 and –CF3). The role of bulky group and ether linkage is to reduce the charge transfer in the inter- and intra-molecular, or to block the stacking of benzene rings. Overall, the transmittance of these polyimides could reach 90% under visible light range for PI with a thickness of 60~80μm. The Tg’s are > 230 oC and Td ‘s reach 480 oC. 6FDA-BAF polyimide possesses high Tg (298oC) and high transmittance (93% at 800nm), and excellent thermal stability. The structure-property relations for these 8 polyimide are also discussed.