Study On The Preparation Of Thermocontrolled Polyimide Films By Thermidization And Its Carbonation-graphitization

In order to meet the increasingly high heat dissipation requirements of electronic equipment,it is imperative to develop flexible heat management materials with high thermal conductivity.Polyimide based high thermal conductivity graphite films are widely accepted and have great potential as a class of heat management materials in this field.Currently,thermal controlled polyimide（PI）films,the precursor materials used to prepare high thermal conductivity graphite films,are mostly imported and produced using chemical imide methods with high technical barriers,complex processes,and high costs.The preparation of thermally controlled polyimide films by thermal imidization is the optimal strategy to achieve import substitution of this material and reduce costs.However,the polyimide films prepared by thermal amination method have the problems of low orientation,low comprehensive properties,and difficulty in preparing high-quality and high thermal conductivity graphite films.In order to solve the above problems,this paper systematically studied the preparation process of polyimide films by thermal amination,and prepared high-performance thermally controlled polyimide films and flexible and highly conductive graphite films by adding inorganic fillers（CQ1）and high-quality carbon source graphene（GN）.Firstly,the effects of different film preparation processes and imidization methods on the properties of polyimide films were discussed,and the optimal process was selected for subsequent research;Then,the effects of different molar ratios of diamine monomers（PDA/ODA）on the properties of PI thin films were studied;Based on this,the molar ratios of different dianhydride monomers（BPDA/PMDA）were optimized;Based on the optimal molar ratio of diamine to dianhydride,the process flow of thermal imidization was adjusted to obtain thermally controlled polyimide films with excellent comprehensive properties;Finally,based on the above research,the effects of the addition of CQ1 and graphene（GN）on the microstructure,flexibility,and thermal conductivity of graphite films were investigated.The main conclusions of this article are as follows:（1）The film preparation and imidization methods were discussed,and the optimal method was selected for subsequent research.The experimental results showed that higher PAA viscosity（100-150Pa.s）,thinner film thickness,and higher imidization temperature（390℃）significantly improved the mechanical properties and aggregate structure of polyimide;Furthermore,the comparison of the imidization process between the muffle furnace and the infrared drying oven shows that the imidization process in the infrared drying oven is more stable and does not cause overheating;At the same time,the effects of various support methods such as glass plate,iron frame,full frame and half frame,and needle plate clamp on the performance of PI film were compared and studied.From the perspective of mechanical properties and aggregate structure,the needle plate clamp has the best support effect on PI film.（2）Based on the above optimized process,the regulation and influence behaviors of diamine PDA/ODA and dianhydride BPDA/PMDA molar ratios were systematically studied.The research shows that with the increase of PDA ratio,PI molecules have stronger rigidity,smaller chain spacing,and higher in-plane orientation,but the elongation at break decreases.When the molar ratio of PDA/ODA is 3:7,the comprehensive properties of the polyimide film are optimal,with a tensile strength of 169.8 MPa and an elongation at break of 59.3%.On this basis,a dianhydride monomer with a multi benzene ring structure,BPDA,was introduced to improve the in-plane carbon content of the benzene ring structure carbon formed by inking in the PI film system.It was found that when the molar ratio of BPDA to PMDA was 3:7,the PI film had the best properties,with a tensile strength of 164.6MPa and an elongation at break of 38.1%.Subsequently,the heat treatment process was optimized to produce high-performance PI films with a tensile strength of 205.9MPa and a fracture elongation of 48.1%.（3）The comprehensive properties of graphite films derived from Process-1 to Process-3 PI films with the best performance were compared.Based on the optimal PI films,CQ1 and graphene were introduced to investigate the effects of CQ1 and graphene on the structure,flexibility,and thermal conductivity of graphite films.The results show that the blank polyimide cornerstone ink film has a good graphitized layered structure,with a graphitization degree of over 92%.The resulting graphite film exhibits excellent thermal conductivity,but it exhibits greater brittleness on the macro level.After adding a small amount of CQ1,the layered structure and thermal conductivity of the graphite film were significantly improved.Its thermal conductivity can reach 1729.6 W·m^-1·K^-1at room temperature and 1981.7 W·m^-1·K^-1at 80℃.Due to the high regularity of the layered structure of graphite,the degree of graphitization has been determined to be 98%.However,the graphite film also exhibits brittle characteristics.Because CQ1 generates gas at high temperatures,excessive CQ1 content can disrupt this high regularity,resulting in a significant increase in flexibility and a significant decrease in thermal conductivity;With the increase in the amount of graphene added,the surface vesicular structure of the graphite film becomes fuller and more uniform,and it also has a better graphite layered structure.The degree of graphitization is above 90%.The rolled graphite film has excellent flexibility,with a thermal conductivity of 1377.5 W·m^-1·K^-1at room temperature and 1670.0 W·m^-1·K^-1at 80℃.