A kind of ultra-thick polyimide film and its preparation method and graphite sheet

Abstract

The invention discloses an ultra-thick polyimide film and a preparation method thereof. The preparation method comprises: dissolving surface-modified carbon nanotubes and inorganic fillers in an organic solvent and stirring evenly; then adding a diamine monomer After the diamine monomer is dissolved, add the dianhydride monomer in batches, and finally add a cross-linking type end-capping agent to defoam to obtain a polyamic acid resin; then add a dehydrating agent and a catalyst to mix evenly to obtain a precursor resin, which , high temperature imidization and cross-linking, annealing and heat setting. The ultra-thick polyimide film is carbonized, graphitized, and calendered to obtain a single-layer graphite sheet with a thickness of 45-130 μm, which solves the problem of excessive expansion of the ultra-thick PI film in the industry during high-temperature graphitization. Obtain the technical difficulty of monolayer thick graphite flake.

Description

technical field [0001] The invention belongs to the technical field of polyimide, and in particular relates to an ultra-thick polyimide film, a preparation method thereof and a graphite sheet. Background technique [0002] With the rapid development of microelectronics technology, especially the upgrading of communication technology from "4G" to "5G", the introduction of high frequency, the continuous improvement of hardware integration, the continuous miniaturization of chips, and the doubling of the number of networked devices and antennas have resulted in equipment With the continuous increase of power consumption and heat generation, the heat dissipation of components has become a bottleneck problem faced by communication terminal equipment in the "5G" era. [0003] After the high-performance PI film is carbonized and graphitized at high temperature, a thermally conductive graphite sheet with a thermal conductivity several times that of copper can be obtained, which is t...

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Problems solved by technology

[0004] However, the increase in thickness will bring a series of problems to the production of PI film. First, at the end of the polymerization process of the traditional PI film precursor resin, the amine groups and acid anhydrides at both ends of the molecular chain will still react slowly, resulting in difficult control of the reaction end point. The molecular weight of the resin fluctuates during storage and transportation, which affects the quality stability. In order to reduce the molecular weight change, the resin is generally stored at an ultra-low temperature of about -20°C after the polymerization reaction, but too low a temperature will cause the apparent viscosity of the resin to be too large. The leveling of the resin during coating is reduced, resulting in uneven thickness of the cast film and increased defects; secondly, the ultra-low temperature resin has strict requirements on catalyst activity and dosage, and it is difficult to be used to prepare ultra-thick PI films; finally, exceeding The degree of expansion of PI film with a thickness of 90 μm is difficult to control during the high-temperature graphitization process, especially in the Z-axis direction. It is easy to cause excessive foaming, which cannot be calendered to obtain high-density products, and significantly reduces thermal conductivity. At the same time, excessive expansion will also cause graphite flakes. Many appearance defects such as layering, falling powder, cracking, etc., affect the surface quality and process application of the final product

[0005] Patent CN201610825198.6 discloses a method of preparing water-based carbon black modified polyimide film through thermal imidization; Device; patent CN102093715A discloses a carbon nanotube-reinforced PI film and fiber thermal imidization preparation method, the carbon nanotube length of 10-10000 microns used is too long, will produce a lot of winding, affect the comprehensive performance of the film

The above patents all use the thermal imidization method to prepare PI films, which cannot obtain films with uniform structure and high in-plane orientation, and are not suitable for the preparation of thermally conductive graphite sheets, especially thick graphite sheets.

[0006] Patents CN201510409013.9 and CN201610726723.9 use the blending method to disperse inorganic particles such as oxides and inorganic acid salts in the resin, prepare polyimide films through chemical imidization, and finally obtain graphite sheets by high-temperature treatment. This method produces The PI film cannot control the excessive expansion of the normal direction during the graphitization process, so the film thickness generally does not exceed 90 μm, and it is impossible to obtain a thick graphite sheet with excellent performance.

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