先進低介電環保型光固化樹酯開發及其3D列印應用

Abstract

光固化3D列印是一種以光聚合反應為基礎的成型技術，作為先進的積層製造（AM）技術之一，因其出色的成型精度和快速的成型效率，近年來開始備受矚目且被廣泛應用於工業製造、電子產業及生物醫學等各領域。目前適合此技術的主要列印材料為光固化樹酯，它是由光起始劑、光固化預聚物、反應單體和其他添加劑組成的複合樹酯，其中光固化聚胺酯因其獨特的分子結構，可透過調節軟鏈段與硬鏈段之間比例或微相分離程度的差異，賦予其多變化的材料性能，如彈性體、耐磨性、高抗拉強度及良好熱穩定性等特性。隨著高速傳輸的電子訊號需求日益劇增，對於訊號保真度的要求也越來越高，低介電係數聚合物在此類的電子產品中扮演著重要角色，當前最常見的低介電係數材料有聚醯亞胺（PI）、聚四氟乙烯（PTFE）及液晶高分子（LCP），然而這些高分子因其固有分子結構上的限制，大多以薄膜及平面電路基板等硬質材料形式使用，且不利於作為3D列印技術材料，為了克服上述問題以滿足軟性電子產品需求，迫切需要開發兼具低Dk及具可3D列印的光固化高分子材料，這些先進材料將可能徹底改變下一代電子產品的型態及其生產方式，為次世代的電子設備提供更高的製程靈活性和生產效率。 本論文研究核心建立以LCD 3D光固化列印技術為研究平台，在第二章中開發了一種專為3D列印技術使用的低Dk光固化樹酯，將帶有非極性及立體障礙功能之金剛烷二醇導入光固化聚胺酯分子主鏈中，藉此增加基質的自由體積，進而改善光固化聚胺酯固有的高介電特性，實驗結果已顯著優於常用的PCB材料（High Tg FR-4），同時也提升光固化聚胺酯材料整體熱穩定性與機械性質。然而，光固化樹酯材料成品與其他熱固型聚合物一樣，一旦固化反應，將產生永久性塑膠廢棄物，其降解效率和回收能力遠不及熱塑型塑膠或超分子塑膠，僅能透過研磨後用作填料或以燃燒方式銷毀，為解決這個問題，在第三章開發可降解回收型的3D列印光固化樹酯，採用受阻脲鍵（Hindered Urea Bond，HUB）來設計用於可回收的光固化聚胺酯彈體，能在溫和條件下可重新解離回異氰酸酯和受阻胺，藉由導入類似1-(tert-butyl)-1-ethyl urea（TBEU）之結構來合理設計含HUB的動態聚脲熱固性材料，故在環境永續保護及成本效益上將有很大助益。最後在第四章中，將金剛烷結構導入含有HUBs的PUUA分子鏈中，所研製出之PUUA-ADO光固化樹酯具有基本的自修復能力外，在磨耗測試及刮痕測試亦展現優異的耐磨耗特性，因此除了可運用於電子元件材料，其高強度機械性質、優異的高硬度及耐磨耗性，亦可作為環保型耐磨耗性塗料，同時賦予物體表面抗腐蝕的保護功能，並可藉由加熱方式使受損漆面恢復原貌，達到自修復之功能。

The photocurable three-dimensional (3D) printing technology is based on photopolymerization reactions. This technology has received extensive attention in industrial manufacturing, electronics, and biomedical engineering because of its excellent forming accuracy and rapid forming efficiency. The printing material most compatible with this technology is photopolymerizable resin, which consists of photoinitiator, photocurable prepolymer, reactive monomer, and other additives. Photocurable polyurethane can be endowed with various properties, such as elastomeric behavior, wear resistance, high tensile strength, and good thermal stability, by adjusting the ratio of its soft segments to hard segments or through microphase separation. The increasing demand for high-speed transmission of electronic signals is accompanied by the stringent requirement of signal fidelity. Low-dielectric-constant (low-Dk) polymers, such as polyimide, polytetrafluoroethylene, and liquid crystal polymer, play a crucial role in such electronic products. However, owing to their inherent molecular structures, these polymers are mostly used in the form of rigid materials such as films and flat circuit boards; they are not suitable for use as 3D printing materials. To overcome these problems, developing photocurable polymers that exhibit low dielectric constants and can be used in 3D printing is imperative. The study focuses on liquid crystal display LCD 3D printing technology. Chapter 2 describes the development of a low-dielectric-constant photocurable resin specifically designed for 3D printing. Adamantane having the properties of nonpolarity and steric hindrance was introduced into the main chain of polyurethane, thereby increasing the free volume of the matrix and improving the inherently high dielectric properties of the photocurable polyurethane. The experimental results indicated that the newly developed photocurable resin performed significantly better than the commonly used printed circuit board materials (high-glass-transition-temperature FR-4) and enhanced the thermal stability and mechanical properties of the photocurable polyurethanes. However, similar to other thermoset polymers, photocured products produce plastic waste after the curing reaction is completed. Their degradation efficiency and recyclability are far inferior to those of thermoplastic plastics or supramolecular plastics. They can only be used as fillers after grinding or can be destroyed by burning. To address these drawbacks, a degradable and recyclable photocurable resin for 3D printing was engineered, the development of which is described in Chapter 3. Recyclable photocurable polyurethane elastomers were designed using hindered urea bonds (HUBs); they can be re-dissociated into isocyanates and hindered amines under mild conditions. Dynamic polyurea thermosetting materials containing HUBs can be rationally designed by introducing a compound with a structure similar to that of 1-(tert-butyl)-1-ethyl urea. This provides major advantages in terms of environmental sustainability and cost-effectiveness. Finally, Chapter 4 describes the introduction of adamantane into the molecular chain of polyurethane urea acrylate containing hindered urea bonds. The developed polyurethane urea acrylate–adamantane photocurable resin exhibits not only the basic ability to self-repair but also excellent performance in abrasion and scratch resistance tests. In addition to its potential use in electronic components, this resin can be used as an eco-friendly, abrasion-resistant coating because of its high mechanical strength, outstanding hardness, and excellent abrasion resistance. Moreover, it protects surfaces from corrosion and can restore damaged paint by heating, thus exhibiting self-repair abilities.