Preparation and Properties of Intrinsically Black Polyimide Films with CIE Lab Color Parameters Close to Zero and High Thermal Stability for Potential Applications in Flexible Printed Circuit Boards

Abstract

Black polymer films with high thermal stability are highly desired in flexible electrical and electronic fields. Conventional black polymer films based on high-temperature resistant polymers and black inorganic dyes are usually suffered from the poor electrical and tensile properties. In the current work, a series of intrinsically black polyimide (BPI) films with International Commission on Illumination (CIE) Lab optical parameters close to zero and high thermal stability have been designed and prepared. For this purpose, an electron-rich aromatic diamine, 4,4′-iminodianiline (NDA), was copolymerized with 1,4-phenylenediamine (PDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (sBPDA) to afford a series of poly(amic acid) (PAA) solutions, which were then thermally dehydrated to provide the final BPI films at elevated temperatures up to 400 °C in air. The molar fraction of NDA in the total diamine monomers was 0 for BPI-0 (sBPDA-PDA), 10% for BPI-1, 20% for BPI-2, 30% for BPI-3, 40% for BPI-4, 50% for BPI-5, and 100% for BPI-6. For comparison, two referenced polyimide (PI) films, including PI-ref1 and PI-ref2, were prepared according to a similar procedure. The former was derived from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) and the latter was from PMDA and NDA. The BPI films exhibited an increasing degree of blackness with the increasing contents of NDA units in the polymer films. For example, the BPI-6 (sBPDA-NDA) film exhibited the optical transmittance of 1.4% at a wavelength of 650 nm (T650), which was obviously lower than those of PI-ref1 (T650 = 74.6%) and PI-ref2 (T650 = 3.6%). In addition, the BPI-6 film showed the CIE Lab parameters of 0.39 for L*, 2.65 for a*, 0.66 for b*, and haze of 1.83, which was very close to the criterion of “pure blackness” for polymer films (L* = a* = b* = 0). At last, incorporation of the NDA units in the rigid-rod BPI-0 (BPDA-PDA) film slightly deteriorated the high-temperature dimensional stability of the derived BPI films. BPI-6 film showed a linear coefficient of thermal expansion (CTE) value of 34.8 × 10−6/K in the temperature range of 50 to 250 °C, which was higher than those of the BPI-0 (CTE = 12.3 × 10−6/K), PI-ref1 (CTE = 29.5 × 10−6/K), and PI-ref2 (CTE = 18.8 × 10−6/K) films. Nevertheless, the BPI films maintained good thermal stability with the 5% weight loss temperatures (T5%) higher than 590 °C, and the glass transition temperatures (Tg) higher than 340 °C.

Intrinsically Colored Polyimide Films Prepared by Embedding Chromophores on the Polymer Backbones

“…[1][2][3][4] Polyimides with different optical properties can be applied in different fields. For example, colorless and transparent PIs can be used in flexible substrates; [5] black PIs can be used in shielding materials; [6] and colored PIs can be used for color filters. [7] For color filters, polymer-based ones are better than their glass-based counterparts in terms of their advantages of being lighter in weight and less prone to cracking.…”

A facile in‐situ fabrication of black polyimide films with ultrahigh electrical properties

“…Currently, black fillers such as carbon‐based materials and organic dyes are added to PI acid‐based resins 8–11 . However, the addition of fillers results in the aggregation of filler particles and conductivity characteristics, leading to a reduction in the mechanical and electrical insulation properties of PI films.…”

“…Currently, black fillers such as carbon-based materials and organic dyes are added to PI acid-based resins. [8][9][10][11] However, the addition of fillers results in the aggregation of filler particles and conductivity characteristics, leading to a reduction in the mechanical and electrical insulation properties of PI films. Additionally, it is crucial to select a suitable composition of fillers and dispersion method to prepare BPI films with superior electrical properties, following the performance requirements outlined in the Chinese national standard GB/T 13555-2017 for FCCL based on PI.…”

Polyimide Films Based on β-Cyclodextrin Polyrotaxane with Low Dielectric and Excellent Comprehensive Performance

“…Nonetheless, the constraints inherent in millimeterwave communication, such as limited transmission distance, severe signal attenuation, and susceptibility to obstruction, pose formidable challenges to the effective deployment of wireless data transmission in these frequency bands. Addressing these challenges necessitates a rigorous analysis of signal delay time, a parameter calculable through a defined equation [8][9][10]. This scholarly exploration seeks to elucidate the intricate interplay between dielectric materials, transmission frequencies, and the associated challenges encountered in the pursuit of advancing wireless communication technologies.…”