Preparation and Properties of Inherently Black Polyimide Films with Extremely Low Coefficients of Thermal Expansion and Potential Applications for Black Flexible Copper Clad Laminates

Abstract

In the current work, a series of black polyimide (PI) films with excellent thermal and dimensional stability at elevated temperatures were successfully developed. For this purpose, two aromatic diamines including 4,4′-iminodianline (NDA) and 2-(4-aminophenyl)-5- aminobenzimidazole (APBI) were copolymerized with pyromellitic dianhydride (PMDA) to afford PIs containing imino groups (–NH–) in the molecular structures. The referenced PI film, PI-ref, was simultaneously prepared from PMDA and 4,4′-oxydianiline (ODA). The introduction of imino groups endowed the PI films with excellent blackness and opaqueness with the optical transmittance lower than 2% at the wavelength of 600 nm at a thickness of 25 μm and lightness (L*) below 10 for the CIE (Commission International Eclairage) Lab optical parameters. Meanwhile, the introduction of rigid benzimidazole units apparently improved the thermal and dimensional stability of the PI films. The PI-d film based on PMDA and mixed diamines (NDA:APBI = 70:30, molar ratio) showed a glass transition temperature (Tg) of 445.5 °C and a coefficient of thermal expansion (CTE) of 8.9 × 10−6/K in the temperature range of 50 to 250 °C, respectively. It is obviously superior to those of the PI-a (PMDA-NDA, Tg = 431.6 °C; CTE = 18.8 × 10−6/K) and PI-ref (PMDA-ODA, Tg = 418.8 °C; CTE: 29.5 × 10−6/K) films.

Research Progress and Application of Polyimide-Based Nanocomposites

“…For instance, Kapton™, with a thickness of 80 μm, exhibits a brown color, and its cut-off wavelength (initial wavelength corresponding to light transmittance exceeding 1%, λ 0 ) locates as long as 455 nm. A 50 μm Kapton™ obtains light transmittance (T%) of merely 80.9% at 760 nm [ 54 ]. The deep color of PI films results from the formation of intra- and intermolecular charge transfer complexes (CTCs, as plotted in Figure 2 ) between aromatic dianhydrides (electron acceptors) and diamines (electron donors), causing strong filtration in the visible region.…”

Research progress in thermal expansion behavior of polyimide films

“…聚酰亚胺的化学分子结构与薄膜的热膨胀行为 有重要关系，分子主链的刚性与柔性、线性与弯曲程 度等直接影响薄膜的线性或体积热膨胀 [35][36][37][38][39] . 同时， 分子主链的化学结构与薄膜的取向、 结晶或堆积情况 紧密相关，因此在分析聚酰亚胺薄膜的热膨胀行为…”

Synthetic strategies for highly transparent and colorless polyimide film

“…For example, the 80‐μm‐thick Kapton™ is deep yellow with a cut‐off wavelength ( λ 0 ) as high as 455 nm 59 . Even the 50‐μm‐thick Kapton™ transmits only 80.9% at 760 nm 60 . The reason for deep color of PI films is the formation of charge transfer complexes (CTCs in Figure 1) between diamines (electron donors) and aromatic dianhydrides (electron acceptors) with strong absorption in the UV–Vis region.…”