Effect of fluorination on haze reduction in transparent polyimide films for flexible substrates

Abstract

High transmittance is an important parameter for polyimide (PI) films used as flexible display substrates. However, thermal treatment during film fabrication can cause an undesired phenomenon affecting color change in the films, which is called haze. Until now, haze formation in PI films has remained mostly unexplored, suggesting that originates in the composition. In this work, the effect of fluorination on haze reduction was investigated. Both experiments and density functional theory calculations suggest that a high degree of fluorination of PI repeating units results in weaker intra/intermolecular conjugations between polymer chains and higher haze resistance in the following order: one fluorinated group (-1.43 eV)>two fluorinated groups (-0.76 eV)>three fluorinated groups (-0.52 eV)>four fluorinated groups (-0.43 eV). The differences in the haze resistance can influence on haziness in the PI films by thermal gradient inside a lab scale cavity in a furnace. The obtained results indicate that slow heat transfer facilitates the manufacturing process to obtain high transparency in PI films. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44375.