The development in the field of electronics and microelectronics has greatly promoted the research on thermally conductive polymer film materials. However, there is a lack of systematic study on both the analyzing technology of thermal conductivity and the testing methods suitable for polymer films. The light/laser flash analysis (LFA) is the most representative method in transient analysis technique. In this paper, the basic principle, testing conditions and application scope of LFA method were systematically introduced. Thermally conductive polyimide films were taken as the representative examples to analyze the key factors on the testing results in detail, including the film thickness, surface quality, pretreatment conditions, instrument parameters, and data analyzing and processing. In addition, the application of LFA method for testing thermal conductivity along different directions of polymer film materials was further discussed. The results show that the thickness accuracy, surface quality, and transparency of the samples will affect the test results, and the pretreatment methods such as gold sputtering or graphite spraying can effectively improve the test accuracy. In addition, the parameter setting and data processing of the testing instrument will affect the shape of temperature-time curve and the fitting results. Thus, it is necessary to reasonably select the appropriate testing conditions according to the characteristics of polymer film samples.

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 .

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.

Polyimide (PI) has attracted wide attention in the field of new high-temperature energy storage dielectric materials because of its excellent properties. Compared with inorganic/PI composite dielectric materials, all-organic PI composite dielectric materials can maintain excellent mechanical properties while obtaining high dielectric permittivity and high energy storage density. This paper firstly discussed the key parameters affecting the energy storage characteristics of polymer dielectric materials, including dielectric permittivity, dielectric loss, breakdown field strength, energy storage density, charge/discharge efficiency, and heat resistance. And then introduced the key factors and development trends affecting the energy storage characteristics of all-organic PI composite dielectric materials from physical blending and chemical blending, respectively. Finally, the problem of how to effectively improve the high-temperature energy storage characteristics of all-organic PI composite dielectric materials was summarized and the future development direction was proposed.

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.

With the miniaturization and light-weighting of electronic equipment, graphite films with high thermal conductivity attract extensive attention. In this paper, a series of nanocomposite films were prepared by copolymerizing p-phenylenediamine (p-PDA) with 4,4′-oxybisbenzenamine (ODA) and 1,2,4,5-benzenetetracarboxylic anhydride (PMDA), and various two-dimensional carbon nanomaterials, including graphene oxide (GO), reduced graphene oxide (rGO), and graphene (GP), were added via mechanical mixing. And then corresponding graphite films were obtained after high-temperature sintering of polyimide films at 2 850℃, the morphology and crystal type of graphite films were analyzed. The results show that graphite films with two-dimensional carbon nanomaterials are flat, they exhibit more flexible, higher degree of graphitization, and larger crystal size, and the lamellar spacing is closer to the ideal graphite. In particular, the horizontal thermal conductivity and vertical thermal conductivity of graphite film containing 2% of GO nanosheets is 1 207 W/(m·K) and 8.38 W/(m·K), respectively. It is concluded that GO nanosheets can induce graphitization of polyimide films under high temperature, and the graphite sheet sintered shows excellent thermal conductivity.

In order to further clarify the key properties of matrix resin in semiconducting shielding materials, three different types of semiconducting shielding materials at home and abroad were selected, and their microstructure characteristic, mechanical properties, electrical properties, and rheological properties were tested. The results show that the volume resistivity of each shielding material is low, and the temperature stability of resistivity is good. The acrylate content of the imported shielding material matrix resin is higher, polarity is greater, and the mechanical toughness is better. At the same time, the pseudoplasticity of the imported shielding material is stronger. In a certain shear rate range, the viscosity of the material can be reduced by increasing the shear rate appropriately, and the energy consumption can be reduced by increasing the fluidity, and then the production efficiency can be improved. Based on the results of the experimental analysis, the polarity or ester content of the material is proposed as a key parameter to reflect the matrix resin in the semiconductive shielding material.

A semi-alicyclic polyimide resin (TFCPI) and the derived colorless and transparent polyimide film (TFCPI-0) were prepared by one-step high-temperature polycondensation using 1S,2R,4S,5R-hydrogenated pyromellitic dianhydride (H-PMDA) and a fluoro-containing aromatic diamine 2,2′-bis(trifluoromethyl)benzidine (TFMB). Then, a series of colorless and transparent polyimide/SiO₂ composite films with different loading amounts of nano-sized silica fillers were prepared via mechanical blending method by mixing TFCPI matrix with dispersion liquid of colloidal nano-silica/N,N-dimethylacetamide (DMAC). The results show that the loading amounts of nano-silica in the composite films can reach to 25%. The derived composite film TFCPI-25 shows the optical transmittance at the wavelength of 450 nm (T₄₅₀) and yellow index (b*) values of 87.5% and 1.56, respectively, which are slightly inferior to those of TFCPI-0 (T₄₅₀=88.5%, b^*=0.91). The 5% weight loss temperatures (T_5%) and glass transition temperature (T_g) of TFCPI-25 is at the same level with that of TFCPI-0. However, the storage modulus of TFCPI-25 at 50℃ (E′₅₀) and its linear coefficient of thermal expansion (CTE) in the range of 50-250℃ is 4.86 GPa and 30.9×10^-6 K^-1, respectively, which are obviously superior to those of TFCPI-0 (E′₅₀=3.02 GPa, CTE=39.6×10^-6 K^-1).

In order to analyze the influence of natural ester insulating oil on the insulating properties of power transformers, at first, the winding wave processes of a 110 kV natural ester insulating oil and a mineral insulating oil power transformers with the same insulation structure were calculated, and the longitudinal insulation margins of the two transformers were obtained. And then, the winding potential with linear distribution under power frequency and the nonlinear winding potential calculated by wave process were used as excitation sources respectively, the composite electric field of the two insulating oil transformers main insulation were simulated, and their distribution characteristics were compared and analyzed. At last, the main insulation margins of the two insulating oil transformers were calculated by using the whole-region electric flux line scanning method, and in view of the weak main insulation strength of natural ester insulating oil transformer, the structure was improved and the improvement effect was analyzed. The results show that through adding insulation paper boards and adjusting the size of oil ducts, the minimum insulation margin of the improved natural ester insulating oil transformer increases by 15.8%, which meets the requirements of main insulation strength, which provides a reference for developing large natural ester insulating oil transformer and optimizing its structure.

To research the strain characteristic and its measurement method of encapsulation insulation for dry-type air-core reactor, the methods of making test model, embedding sensor and strain gauge, and calculating strain were studied. A test model was made and a test system was built, and the internal strain of encapsulation was studied during the process of reducing temperature and applying current at different low temperatures. The results show that the circumferential thermal expansion coefficient of the encapsulation insulation is less than the axial thermal expansion coefficient and there is anisotropy, which makes the circumferential strain larger than the axial strain. During the process of reducing temperature, negative strain is produced by circumferential shrinkage of the encapsulation insulation, which decreases gradually with the temperature decreasing, the decline rate gradually slows down in the same cabin temperature, and the value increases significantly with the increase of temperature decline amplitude in different cabin temperatures. The axial strain is positive when the cabin temperature is higher, which gradually changes to a negative value with the temperature decreasing, and the change law also changes from gradually increasing to gradually decreasing with the temperature decreasing. During the process of reducing temperature, the circumferential and axial strains have negative jumps many times, resulting in shrinkage micro-cracks. The strain change during process of applying current is contrast to the process of reducing temperature, with the increase of temperature, the circumferential strain increases gradually, the axial strain decreases rapidly, and neither strain jumps. By calculating the maximum thermal stress, it is further verified that the circumferential compression stress is larger than the compression strength of the epoxy glass fiber, resulting in the damage of encapsulated insulation.