A kind of colorless transparent polyimide film and preparation method thereof

Abstract

The invention discloses a colorless transparent polyimide film and a preparation method thereof. The polyimide film is composed of a diamine monomer containing 3,3'-bis(4-nitrophenoxy) benzidine and a dianhydride monomer containing 4,4'-bis(3,4-dicarboxylphenoxy)benene dianhydride, wherein a molar fraction of the 3,3'-bis(4-nitrophenoxy) benzidine in the diamine monomer is not less than 90%; a molar fraction of 4,4'-bis(3,4-dicarboxylphenoxy)benene dianhydride in the dianhydride monomer is not less than 82%; a molar ratio of the diamine monomer to the dianhydride monomer is (0.94-0.99):1. According to the polyimide film prepared by the invention, monomers containing fluorine or aliphatic cycles are not used, and the obtained film has excellent colorless and transparent property, and is high in mechanical strength, small in coefficient of thermal expansion and excellent in heat resistance.

Description

technical field [0001] The invention relates to the field of preparation of heat-resistant polymer films, in particular to a colorless and transparent polyimide film and a preparation method thereof. Background technique [0002] At present, colorless and transparent polyimide film (PI film) is mainly obtained by introducing fluorine-containing groups or alicyclic groups into the polyimide molecular chain. Due to the introduction of fluorine atoms, the distance between the molecular chains of the fluorine-containing aromatic PI film is increased, which hinders the formation of intermolecular charge transfer complexes (CTC). The large electronic energy level band gap greatly improves the light transmittance of the material. The introduction of alicyclic groups can destroy the conjugated structure on the main chain of the molecule, and also make it difficult to form charge transfer complexes between molecular chains, which improves the transparency of alicyclic PI (Ren Xiaolo...

AI Technical Summary

Problems solved by technology

[0003] At present, PI films are roughly divided into two categories: (1) Introducing fluorine-containing groups (such as fluorine substituents and trifluoromethyl substituents) into the polyimide structure can obtain colorless and transparent polyimide films, But at the same time, there are also certain defects, such as fluorine-containing monomers are generally expensive and the preparation process is very complicated; the introduction of fluorine will also lead to a decrease in the mechanical properties of the film, a decrease in thermal stability, poor adhesion, and affinity with other substrates. (2) The synthesis of colorless and transparent polyimide through alicyclic monomers will also bring a series of problems, and its mechanical strength is generally low, and its tensile strength is generally less than 100 MPa

The preparation of colorless and transparent polyimide films by the above two methods limits the application of such materials in high-performance flexible solar cell backplanes, flexible displays, and optical waveguide materials in the field of optical communications.