In order to relieve the conflict between tight land supply and land acquisition for transmission lines in tight land supply area, we developed a new structural type of composite material insulated tower, which looked like a rocket, and the wires passed through the insulated composite material rocket tower to compress the line corridor to the greatest extent. Besides, the electrical performance of the 110 kV composite rocket tower was systematically studied. The results indicate that the dry lightning impulse voltage of the 110 kV composite rocket tower is 979 kV, the impulse voltage under wet condition is 576 kV, the average value of 1 min wet power frequency flashover voltage is 282 kV, and the power frequency pollution flashover voltage at 0.20 mg/cm² of salt density and 1.00 mg/cm² of gray density is 106.2 kV. Compared with the traditional 110 kV suspension composite insulator iron tower, the lightning impulse voltage value of 110 kV composite rocket tower increases by 78%, the impulse voltage value under wet condition increases by 34%, the 1 min withstand wet power frequency flashover voltage increases by 22.6%, and the pollution flashover voltage value is equivalent. In addition, the line corridor is greatly compressed, and the minimum line corridor width is 1.8 m, which is much smaller than the corridor width value (5.5-7.5 m) of 110 kV iron tower.

The performance of domestic corona-resistant polyimide film as well as the corona-resistant film magnet wire was compared with that of the similar imported products, and then the reliability of domestic corona-resistant film magnet wire in the application process was discussed. The results show that the conventional properties of domestic corona-resistant film and its magnet wire are comparable to those of similar imported products, and the corona resistance performance and initial partial discharge voltage of domestic corona-resistant film magnet wire are better than those of similar imported products. Domestic corona-resistant film magnet wire has excellent manufacturability in the coil forming process, which meets the technical requirements of inverter traction motor applications.

Polyimide is widely used in high-tech fields because of its excellent performance characteristics. In recent years, the new display technology represented by smartphones with foldable screen has greatly promoted the development of optically transparent polyimide materials. In order to understand the technical condition and future development direction of polyimide patents of foreign companies, this work took KOLON, SKC and their related companies as the research object, and deeply analyzed their polyimide film patents applied in China during 2017 to 2022, including the number of applications, disclosure condition, field distribution, etc. The technical route and layout characteristics of transparent polyimide patents were focused, and the structural formula, preparation methods, key performance of representative transparent polyimide films were respectively introduced in detail. The current technological challenges and future breakthrough directions were also summarized.

In this paper, the aggregation properties of molecular chain as well as permittivity of 10 kinds of polyimides containing carbonyl group or sulfone group were characterized. Moreover, microscopic parameters such as theoretical density, free volume fraction, polarizability density, and dipole moment density were calculated based on density functional theory (DFT) and molecular dynamics theory (MD). The results show that the partially crystallized polyimides show relatively high theoretical density and low free volume fraction (FFV), which indicates that the measured results are in good agreement with the theoretical calculations. Compared with using polarizability density, using dipolar moment density, which is highly correlated with the orientation polarization, provides a more accurate prediction of the size of the polyimide dielectric constant in relation to the molecular structure in tests in the frequency range of kHz .

In order to solve the problem of agglomeration and poor dispersion of fillers in high-viscosity poly(amic acid) (PAA), we prepared PAA solution with low viscosity by anhydride hydrolysis method using PAA solution of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) under a high solid content. On this basis, boron nitride/polyimide (BN/PI) composite films with the mass fraction of BN ranging from 0 to 40% were prepared by ultrasonic pulverization pretreatment and high-efficiency ball milling mixing process. The dispersion of fillers and the mechanical properties, heat resistance and thermal conductivity of composite films were systematically investigated. The results show that the low viscosity of PAA and the mixing process improve the dispersibility of fillers and have an important impact on the properties of BN/PI composite films. When the mass fraction of filler is 40%, the tensile strength of the composite film is about 140 MPa, the glass transition temperature is 385.2℃. The maximum thermal conductivity is up to 0.741 W/(m·K), which is 338% higher than that of pure polyimide film.

Improving the performance of dielectric capacitors is one of the effective methods to meet the requirements of miniaturization and integration of circuit components. How to improve the dielectric properties of dielectric composites has attracted extensive attention of researchers. A series of ZIF-67/PVDF composite films were prepared by flowing spread molding using polyvinylidene fluoride (PVDF) as matrix and metal organic frameworks (MOFs), ZIF-67, as filler. The influence of MOF on the microstructure and macroscopic properties of PVDF composites was investigated. The results show that ZIF-67 can induce PVDF to generate more β phase, promote the polarization of matrix, and improve the mechanical and dielectric properties of the composite. When the mass fraction of filler is 5%, the Young's modulus of ZIF-67/PVDF composite film under 40℃ is 1 200 MPa and the breakdown strength is 139.74 kV/mm, both of them are higher than those of pure PVDF. The dielectric constant of ZIF-67/PVDF composite at 100 Hz is 10.39, which is 35.29% higher than that of pure PVDF film, and the dielectric loss can be kept low.

Epoxy resin micro-alumina composite materials with micro-alumina mass fraction of 0, 20%, and 40% were prepared. The effect of micro-alumina filler on the dielectric relaxion behavior of epoxy resin at high temperature was analyzed by dielectric test at room temperature and high temperature and fitting calculation of high temperature dielectric spectra. The results show that the effect of micro-alumina on the dielectric relaxion at high temperature is more obviously than that at room temperature. With the introduction of alumina, the optical frequency dielectric constant increases, while the relaxation strength of relaxion process α shows little change. With the increase of mass fraction of filler, the relaxion time of relaxion process α decreases. Besides, the micro-alumina filler significantly increases the relaxion strength of relaxation process δ. However, with the increase of mass fraction of micro-alumina, the relaxation strength of relaxation process δ decreases, while the relaxation time increases continuously.

With the development of portable electronic devices, there is an increasing demand for thermal management materials with high thermal conductivity and electrical insulation. As a new thermal conductive filler with high conductivity and insulating property, fluorinated graphene (FG) has received extensive attention from the scientific community. In this paper, the preparation method of FG and the relationship between its structure and properties were summarized, the thermal conducting mechanism of FG was analyzed especially, and the latest research progress of FG as functional filler composite modified polyimide (PI) was systematically described. The problems and challenges were summarized and prospected.

Biaxially oriented polypropylene (BOPP) film is a mainstream dielectric material used in power capacitor, there is still a large gap between thermal stability performance of imported BOPP films and that of domestic films. In order to systematically investigate the thermal stability of domestic and imported BOPP film, as well as to reveal the thermal ageing mechanism, we selected typical domestic and imported BOPP film samples, and conducted vacuum thermal ageing test on them for 1 000 h under 80℃ and 120℃, respectively. The changing law of molecular structure, aggregation structure, and electrical properties of the films before and after thermal ageing was compared and analyzed via infrared spectroscopy (FTIR), optical microscope observation, X-ray diffraction (XRD), dynamic thermomechanical analysis (DMA), dielectric spectroscopy, and direct current breakdown strength. The results show that compared with that of imported BOPP films, the crystallinity of domestic films is lower and the force between molecular chains is weaker. The breakdown field strength of domestic films is 5.7% lower than that of imported films. Under the effect of long-term thermal ageing, both BOPP films have undergone recrystallization, including the increase of crystallinity and lamellae size in the crystal region and the increase of free volume and the molecular chains loss scale in the amorphous region. Meanwhile, the change of the aggregate structure leads to the increase of the dielectric loss and the decrease of the breakdown strength at low probability zone of the film after ageing. Moreover, compared with domestic films, the stronger inter-chain forces in imported films effectively inhibit the recrystallization process, and decrease the generation and development of electrical weakness, which makes the imported BOPP films have better long-term thermal stability.

Aimed at the application requirements of polyimide (PI) film materials in the field of high frequency, polyimides containing semi-alicyclic structure were synthesized by the semi-alicyclic diamine 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindan (DAPI) with different aromatic dianhydrides. And their corresponding films were prepared, the correlation between their structure and properties was explored. The results show that polyimides containing semi-alicyclic structure have good solubility and processability, they are soluble in conventional organic solvents such as NMP, DMF, CHC1₃, etc. The corresponding films had good mechanical and thermal properties, their tensile strength ranges from 64.8 MPa to 82.6 MPa, and their glass transition temperature can exceed 487℃. The dielectric constant (D_k) of the PI films is 2.63-4.62 at 1 kHz-1 MHz and 2.46-2.75 at 10 GHz, respectively. The dissipation factor (D_f) is 0.003 1-0.020 5 at 1 kHz-1 MHz and 0.006 6-0.017 4 at 10 GHz, respectively. In particular, the D_k and D_f of the B-PI(BPADA-DAPI) film at 10 GHz is 2.75 and 0.006 6, respectively. It is indicated that the polyimide films with low dielectric constant and low dielectric loss at high frequency can be obtained by the introduction of semi-alicyclic moieties and bisphenol A groups into the main chains.