The Preparation And Research Of Polyimide-based Carbon Films

With the continuous development of science and technology, Heat dissipation has become a common challenges encountered in many areas. The graphite film prepared from carbonization and graphitization of polyimide(PI) has excellent thermal conductivity, and becomes the candidate for solving the problem of heat dissipation.The main purpose of this paper is to prepare polyimide-based carbon films with highly ordered structure and good electrical conductivity, and establish the foundation for further preparing graphite material with high thermal conductivity. Polyimide film with excellent performance is an important factor for preparing polyimide-based carbon film and graphite film. This paper focuses on preparation methods of polyimide films.First, the effect of carbonization temperature on carbon film was researched. Second, the impact of different preparation methods on structure and properties of polyimide-based carbon was studied. The methods include formula design, introduction of partial cross-linking structure, preparation of composite membranes doped grapheme and stretch film stretching method. Finally, some PI-based carbon films were selected for the preliminary exploration of graphitization, and the properties of these graphite have been researched. The structure and performance of polyimide-based carbon films and graphite membrane are characterized by X-ray diffraction (XRD), Raman, Scanning electron microscopy (SEM) and electrical conductivity.The results show that when the carbonization temperature is in the range 700℃ to 1000℃, the internal structure ordering of formed carbon film improves, two-dimensional carbon layer structure becomes apparent and surface conductivity increases with the increase of carbonization temperature. Besides, The conductivity of formed carbon film can also improved by increasing carbonization time. For BPDA-ODA-PDA type ternary copolyimide, with the increase of PDA proportion, the rigidity of original PI film increases, the carbon structure ordering of carbon film increases, the compactness of carbon layer is better, and the surface conductivity of carbon film also has a slight improvement. The partial cross-linking PI film was prepared by introducing TAB, and the corresponding carbon film has a higher ordering structure, the two-dimensional carbon layer structure is more cmpelete, the carbon layers become tighter, and the conductivity and thermal conductivity is also higher. The uniaxial thermal drawing has a certain influence on polyimide-based carbon film. Overall, with the improvement of tensile rate of PI film, the internal structural ordering of carbon film increases at first, then decreases, and rising again. Slight stretch is conducive for the improvement of internal structural regularity of carbon film and surface conductivity. The carbon film prepared from PI composite film doped small amount of graphene has a higher carbon structural ordering and surface conductivity. The prepared graphite film also has a higher thermal conductivity. The graphene has inducing action on carbonization and graphitization of PI. However, the excessive doped graphene is not conducive to improving the internal structure ordering of prepared carbon film.