Preparation method and application of high-voltage GIS / GIL epoxy composite material based on short-chain grafted cross-linked network
By constructing a short-linked crosslinked network, the problem of synergistic performance improvement of epoxy composites for high-voltage GIS/GIL under high electric field, large temperature gradient and mechanical stress was solved. The uniformity and stability of the material were achieved, and the electrothermal-mechanical properties and yield were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HEBEI UNIV OF TECH
- Filing Date
- 2025-12-29
- Publication Date
- 2026-04-28
AI Technical Summary
Existing epoxy composite materials for high-voltage GIS/GIL struggle to achieve synergistic improvement in electrical, thermal, and mechanical properties under high electric fields, large temperature gradients, and mechanical stress. Furthermore, defects in filler dispersibility and casting processes lead to uneven material properties and the risk of partial discharge.
A preparation method based on short-linked branch crosslinking network was adopted. By constructing a dynamic and static combined short-linked branch semi-interpenetrating crosslinking network, combined with the hard and soft segment structures of polyurethane prepolymer, the dispersibility of alumina filler was improved. The uniformity and stability of the material were achieved by vacuum gravity casting and gradient cooling process.
It significantly improves the electrothermal-mechanical properties of the material, reduces the dielectric constant, increases the breakdown field strength and thermal conductivity, enhances the toughness and rigidity of the material, meets the long-term service requirements of high-voltage equipment, and improves the yield and production efficiency.
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Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of epoxy composite materials for high-pressure GIS / GIL, and relates to a method for preparing high-pressure GIS / GIL epoxy composite materials and their applications, particularly a method for preparing high-pressure GIS / GIL epoxy composite materials based on short-linked crosslinked networks and their applications. Background Technology
[0002] In the global energy transition driven by the "dual-carbon" strategy, ultra-high voltage (UHV) and extra-high voltage (UHV) transmission technologies, as the core hub of the new power system, directly determine the safety and stability of the energy network through their operational reliability. Gas-insulated switchgear (GIS) and gas-insulated transmission lines (GIL), as key equipment for realizing large-capacity power transmission and transformation, are rapidly iterating and upgrading towards compact design, high-power transmission, and high voltage levels. The basic material for the insulating components such as basin insulators and post insulators inside this equipment is epoxy composite material, whose formula mainly consists of bisphenol A epoxy resin, alumina filler, and curing agent. Having to withstand the multi-field coupling effects of "high electric field (≥50kV / mm), large temperature gradient (-40~120℃), and strong mechanical stress (≥100MPa)" for a long time, the coordinated reliability of its electrical properties (insulation, breakdown resistance), thermal properties (thermal conductivity, heat resistance), and mechanical properties (rigidity, toughness) has become the core factor restricting the development of equipment to higher voltage levels.
[0003] In recent years, researchers have significantly improved certain properties of epoxy composites by modifying the epoxy matrix formed by epoxy resin monomers and curing agents from different perspectives. However, they often fall into the trap of optimizing a single property leading to the deterioration of multiple properties, thus failing to achieve engineering applications to date. For example, improving the toughness of epoxy composites by adding nano-rubber, core-shell particles, and introducing flexible segments sacrifices the dielectric strength and mechanical stiffness of the composite.
[0004] In terms of improving insulation performance, the main methods include adding nanofillers and modifying the surface of fillers to construct deep traps. However, these methods often cause filler agglomeration, which in turn leads to interface defects and reduces mechanical properties.
[0005] The most common way to improve thermal conductivity is to introduce high thermal conductivity fillers such as boron nitride. However, this often leads to a sudden increase in dielectric constant and inevitably introduces a large number of interfaces, reducing the power frequency breakdown strength of the material and increasing dielectric loss.
[0006] For alumina fillers in epoxy composites used in GIS / GIL, agglomeration is inevitable due to their small particle size (approximately 10 μm) and large specific surface area. Using filler dispersion methods such as silane coupling agents increases the manufacturing complexity of basin-type insulators and offers limited improvement in agglomeration.
[0007] Although polyurethane prepolymer (PPU) has a block structure of "rigid isocyanate segment + flexible polyether segment", it provides a new approach to overcome the problem of mutually exclusive properties of epoxy resin. The aromatic ring conjugated system of its rigid segment can improve the material stiffness and optimize the phonon transport path, while the random curl conformation of the flexible segment endows it with crack propagation resistance and the ability to suppress the growth of electrical trees.
[0008] However, polyurethane prepolymers are currently often used in conjunction with diamine curing agents. The -NH2 group of the diamine curing agent preferentially reacts with the isocyanate group (-NCO) of the polyurethane prepolymer to form urea bonds (-NH-CO-NH-) and undergoes chain extension. Subsequently, the amine curing agent and epoxy groups undergo ring-opening to form an epoxy crosslinking network containing imino groups (-NH-) and ester bonds (-COO-). The small amount of -NCO remaining at both ends of the long polyurethane (PU) molecular chains generated by chain extension reacts with the hydroxyl groups of the epoxy resin to form urethane bonds. At this point, the long molecular chains are branched onto the epoxy crosslinking network, forming a grafted semi-interpenetrating crosslinking network with physical interpenetration as the main component and chemical grafting as a secondary component.
[0009] However, the urea bonds (-NH-CO-NH-) generated by the chain extension reaction have strong polarity, which leads to an increase in the dielectric constant of the material. In an electric field, this can easily cause uneven electric field distribution on the surface of the insulation component, exacerbating the risk of partial discharge. In addition, the strong reactivity of amine curing agents causes the polyurethane rigid segments to aggregate disorderly due to rapid reaction. The non-uniform distribution in the rigid phase region becomes a scattering center for phonon transmission, resulting in a decrease in thermal conductivity. Furthermore, amine curing agents react rapidly with epoxy resin, resulting in a short gel time, which cannot meet the casting process requirements of GIS / GIL insulation components.
[0010] To address the aforementioned problems, this invention proposes a method for preparing high-pressure GIS / GIL epoxy composite materials based on short-linked crosslinked networks. Summary of the Invention
[0011] This invention addresses the shortcomings of existing technologies by proposing a method for preparing and applying high-voltage GIS / GIL epoxy composite materials based on short-linked branch crosslinking networks. By constructing a "dynamic-static combined" short-linked branch semi-interpenetrating crosslinking network, the invention synergistically enhances the electrical, thermal, and mechanical properties of the epoxy resin matrix by combining the hard segments (aromatic ring conjugated structure) and soft segments (polyether chain flexible structure) of the polyurethane prepolymer (PPU). Furthermore, it improves the dispersion of Al2O3 filler in the EP matrix, further achieving synergistic enhancement of the electrical, thermal, and mechanical properties of epoxy composite materials for high-voltage GIS / GIL. Finally, it further improves the casting process of epoxy insulation components, ensuring material uniformity and eliminating internal stress, thereby increasing yield and long-term service stability.
[0012] The above-mentioned objective of this invention is achieved through the following technical solution: A method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked crosslinked networks includes the following steps: Step 1: Prepare experimental raw materials and perform pretreatment to ensure reaction purity and compatibility; Step 2: Prepare a uniform casting masterbatch PPU-EP-MTHPA to initially form a short-linked branch semi-interpenetrating network; Step 3: Based on the uniform casting masterbatch PPU-EP-MTHPA obtained in Step 2, prepare a uniform casting masterbatch Al2O3-PPU-EP-MTHPA to ensure optimized filler dispersion; Step 4: Vacuum gravity casting is performed on the uniform casting masterbatch Al2O3-PPU-EP-MTHPA obtained in Step 3. Step 5: For the Al2O3-PPU-EP-MTHPA that has been gravity-cast in Step 4, perform segmented curing and internal stress relief to ensure material uniformity and stability, and finally obtain epoxy composite material samples or GIS / GIL pot insulators based on short-linked cross-linked networks.
[0013] Furthermore, the specific steps of step 1 include: 1.1 Preparation of experimental materials: Bisphenol A epoxy resin EP, type E-51, epoxy equivalent 182-192 g / eq, moisture ≤0.01%; Polyurethane prepolymer PPU, PPG and MDI are synthesized at a mass ratio of 1:1.9-2.1, with an NCO content of 5.0-5.2% and a molecular chain length ≤50nm; Methyltetrahydrophthalic anhydride (MTHPA), purity ≥99%, moisture ≤0.005%; Al₂O₃ filler, particle size D50 = 15-18 μm, specific surface area 5-8 m² / g. 2 / g, surface hydroxyl content ≥0.8mmol; Accelerator, N,N-dimethylbenzylamine (BDMA), purity ≥98%, addition amount 0.2-0.3 phr; Mold coating: Nano-Al2O3 ceramic coating, thickness 50-80nm, surface roughness Ra≤0.02μm 1.2 Pretreatment of experimental materials; Furthermore, the specific method of step 1.2 is as follows: Bisphenol A epoxy resin EP pretreatment: The EP is dried at 78-82℃ and -0.09MPa vacuum for 4 hours to remove low molecular weight impurities; the moisture content is monitored in real time by an online Karl Fischer moisture analyzer to ensure that the moisture content is ≤0.005% before being discharged for use. Pretreatment of polyurethane prepolymer (PPU): Add the polyurethane prepolymer (PPU) to a three-necked flask and dry it at 80℃ and -0.09MPa vacuum for 4 hours to remove low molecular weight impurities; the moisture content is monitored using a Karl Fischer moisture analyzer, and it is usable when the moisture content is ≤0.005%; Al2O3 pretreatment: Add Al2O3 to a dryer and dry with hot air at 115-120℃ for 3 hours to remove surface adsorbed water; then transfer it to a plasma treatment instrument for 10 minutes to activate surface hydroxyl groups and enhance hydrogen bonding with PPU soft segments. Mold pretreatment: Spray nano-Al2O3 ceramic coating on the inner wall of the sample mold and the basin insulator mold, and cure at 180-185℃ for 1.9-2.1h to form a dense non-stick layer; after curing, place the mold in a constant temperature oven and preheat at 115-125℃ to avoid the formation of air bubbles in the material due to temperature difference during pouring.
[0014] Furthermore, the specific steps of step 2 include: 2.1 Add the pretreated EP and MTHPA to a planetary mixer at a mass ratio of 100:84-88; set the mixing temperature to 55-65℃ and disperse for 18-22 minutes at a stirring speed of 450-550 r / min. 2.2 Add the pretreated PPU to the material in step 2.1, while keeping the temperature at 55-65℃. Rotate the agitator and the dispersing paddle simultaneously at a speed of 200-250 r / min and disperse for 30-35 min.
[0015] 2.3 Degas the material from step 2.2 under vacuum at -0.1MPa for 30-40 minutes, keeping the temperature at 80-85℃. At this time, the stirring paddle and the dispersing paddle stop rotating, so that the short-linked branch semi-interpenetrating network is initially formed. Furthermore, the specific method for step 3 is as follows: Add pretreated Al2O3 and BDMA accelerator to the uniform casting masterbatch PPU-EP-MTHPA obtained in step 2. Set the temperature to 120-125℃. First, use a dispersion paddle and a stirring paddle to perform high-speed shear dispersion at 1000r / min for 5min. Then, switch the dispersion paddle and stirring paddle to stir at 450-550r / min and perform ultrasonic dispersion at 30kHz and 500W for 20-25min. All of this process is carried out in a vacuum environment of -0.1MPa.
[0016] Furthermore, the specific steps of step 4 include: 4.1 Fix the mold, which has been preheated to 115-125℃, at the casting position, turn on the mold vacuum system and evacuate at -0.095MPa for 10 minutes to remove residual air from the mold; 4.2 Keep the casting masterbatch at 115-125℃ and slowly inject it into the mold through a 120℃ constant temperature insulated pipe, with the casting rate controlled at 50mL / min.
[0017] Furthermore, the specific steps of step 5 include: 5.1 Pre-curing: Transfer the mold into a constant temperature oven and keep it at 138-142℃ for 3.9-4.1 hours to allow the material to initially cross-link and form a stable short-linked branched network structure. 5.2 Primary curing: Heat to 158-162℃ for 5.9-6.1 hours. After this process, the curing degree of the epoxy composite material can reach 95%, but there is a certain internal stress. 5.3 Post-curing: Heat to 178-182℃ and hold for 1.9-2.1 hours to eliminate residual curing stress inside the material; 5.4 Gradient cooling: The furnace is cooled to room temperature at a rate of less than or equal to 5℃ / h to avoid thermal stress cracks caused by sudden temperature changes; finally, the mold is removed to obtain epoxy composite material samples or GIS / GIL pot insulators based on short-linked cross-linked networks.
[0018] An epoxy composite material sample or GIS / GIL pot insulator finished product obtained by a method for preparing high voltage GIS / GIL epoxy composite material based on short-link crosslinked network is applied in high voltage GIS / GIL.
[0019] The advantages and beneficial effects of this invention are as follows: This invention proposes a method for preparing high-pressure GIS / GIL epoxy composites based on short-linked branched crosslinking networks. Addressing the shortcomings of existing epoxy composite modification methods, it achieves multi-dimensional advantages through "short-linked branched semi-interpenetrating networks + precise process control," as detailed below: (1) Overcoming performance incompatibilities and achieving synergistic improvement of electric heating engines Compared to pure EP and existing modified systems, the core performance of the 15phr PPU / 250phr Al2O3 / EP system of this invention is significantly improved: Electrical properties: Breakdown field strength 39.7 kV / mm (8.8% improvement over pure EP), volume resistivity 4.69 × 10⁻⁶ 16Ω·cm (improved by nearly one order of magnitude), power frequency dielectric constant 5.0 (reduced by 0.65 compared to Al2O3 / EP), dielectric loss 0.00295 (≤0.003, meeting high voltage equipment standards); Thermal properties: room temperature thermal conductivity 1.573 W / (m·K) (17% higher than Al2O3 / EP), 90℃ thermal conductivity 1.361 W / (m·K) (31.1% improvement in thermal stability), glass transition temperature 110.9℃ (≥110℃, meeting high-temperature service requirements); Mechanical properties: Tensile strength 84.44 MPa (37.2% higher than pure EP), elongation at break 1.87% (78.1% higher than Al2O3 / EP), fracture energy 928.2 J / m 2 (2010% improvement over Al2O3 / EP) — Achieving synergistic optimization of "insulation-thermal conductivity-rigidity-toughness".
[0020] (2) Compatible with GIS / GIL large-scale casting process By using an anhydride curing agent and precise temperature control, the gelation time of the casting masterbatch is extended to 2.5 hours (meeting the requirements for casting large-size insulators), solving the process pain point of short gelation time of amine curing agents; The vacuum gravity casting + gradient degassing process can be used to prepare GIS / GIL pot insulators with a diameter ≥1.5m and a thickness ≥50mm, increasing the yield from the current 70% to 95%. The mold's nano-coating and gradient cooling design can prevent sticking and thermal stress cracks, reduce subsequent processing steps, and lower production costs by 15%.
[0021] (3) Excellent dispersibility and performance stability of the filler Plasma-ultrasound-shear synergistic dispersion reduces Al2O3 agglomeration rate to ≤5%, reduces interface defects by 40%, and reduces batch performance fluctuations to ≤3% (far lower than the existing 10% fluctuation range). The chemical grafting structure of the short-linked branch network ensures that after 100 cycles at -40~120℃, the breakdown field strength decreases by ≤5%, the thermal conductivity decreases by ≤3%, and no cracks are generated, meeting the long-term service requirements of high-voltage equipment.
[0022] (4) Great potential for industrialization All raw materials are industrially mass-produced products (such as E-51 EP, PPU, Al2O3), with no scarce or high-cost components, and the raw material costs are on par with existing systems; The process equipment (twin-screw mixer, ultrasonic disperser, vacuum casting line) are all general-purpose equipment in the polymer materials industry, requiring no new special equipment and requiring low investment in modification; in addition, it can be extended to other high-voltage insulation fields such as high-voltage cable terminals and transformer insulation components, with a wide range of application scenarios. Detailed Implementation
[0023] The structure of the present invention will be further illustrated by the following embodiments. It should be noted that these embodiments are descriptive and not limiting.
[0024] A method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked crosslinked networks includes the following steps: Step 1: Prepare experimental raw materials and perform pretreatment to ensure reaction purity and compatibility; The specific steps of step 1 include: 1.1 Preparation of experimental materials: Bisphenol A epoxy resin (EP), type E-51, epoxy equivalent 182-192 g / eq, moisture ≤0.01%; Polyurethane prepolymer (PPU) is synthesized from PPG (molecular weight 1000) and MDI at a mass ratio of 1:2, with an NCO content of 5.0-5.2% and a molecular chain length ≤50nm. Methyltetrahydrophthalic anhydride (MTHPA), purity ≥99%, moisture ≤0.005%; Al2O3 filler, particle size D50=15-18μm, specific surface area 5-8m². 2 / g, surface hydroxyl content ≥0.8mmol; Accelerator, N,N-dimethylbenzylamine (BDMA), purity ≥98%, addition amount 0.2-0.3 phr; Mold coating (for demolding): Nano-Al2O3 ceramic coating, thickness 50-80nm, surface roughness Ra≤0.02μm In this embodiment, all raw materials have been industrially produced, resulting in good economic efficiency.
[0025] 1.2 Pretreatment of experimental materials; EP pretreatment: Dry the EP at 80℃ and -0.09MPa vacuum for 4 hours to remove low molecular weight impurities (such as unreacted monomers and trace amounts of moisture); monitor the moisture content in real time using an online Karl Fischer moisture analyzer to ensure that the moisture content is ≤0.005% before discharging for later use; PPU pretreatment: Add polyurethane prepolymer (PPU) to a three-necked flask and dry at 80℃ and -0.09MPa vacuum for 4 hours to remove low molecular weight impurities (such as unreacted monomers and trace amounts of moisture); use a Karl Fischer moisture analyzer to monitor the moisture content, and it is usable when the moisture content is ≤0.005%; Al2O3 pretreatment: Add Al2O3 to a dryer and dry with hot air at 120℃ for 3 hours to remove surface adsorbed water; then transfer it to a plasma treatment instrument (power 500W, argon atmosphere) for 10 minutes to activate surface hydroxyl groups (hydroxyl content increased by 20%) and enhance hydrogen bonding with PPU soft segments. In this embodiment, plasma treatment of alumina filler is rarely used in industry. Plasma can activate the hydroxyl groups on the surface of alumina, making it easier for alumina to combine with the -O- groups of PPU, thereby improving dispersibility. For details on the principle, please refer to the "Interfacial Buffering Mechanism of PPU in Improving Al2O3 Dispersion" at the end of this article.
[0026] Mold pretreatment: Spray nano-Al2O3 ceramic coating on the inner wall of the sample mold and the basin insulator mold, and cure at 180℃ for 2 hours to form a dense non-stick layer; after curing, place the mold in a constant temperature oven and preheat at 120℃ to avoid the material from generating bubbles due to temperature difference during pouring.
[0027] Step 2: Prepare a uniform casting masterbatch PPU-EP-MTHPA to initially form a short-linked branch semi-interpenetrating network; The specific method for step 2 is as follows: 2.1 Add the pretreated EP and MTHPA to a planetary mixer at a mass ratio of 100:85; set the mixing temperature to 60℃ (advantage: at this temperature the reaction rate between epoxy resin and curing agent MTHPA is slow, and it has both fluidity and processability), and disperse for 20 minutes using a stirring paddle speed of 500r / min.
[0028] 2.2 Add the pretreated PPU to the material in 2.1, while maintaining the temperature at 60℃. Rotate both the agitator and the dispersion paddle simultaneously at 200 r / min for 30 min. (The dispersion paddle is turned on because the agitator provides good dispersion in the horizontal direction but cannot adequately disperse in the vertical direction. The dispersion paddle compensates for this deficiency, allowing the short chains of PPU in the planetary mixer to be fully grafted onto all the crosslinking networks of the epoxy resin, initially forming a short-chain grafted semi-interpenetrating crosslinking network.) 2.3 The material from 2.2 was subjected to vacuum degassing at -0.1 MPa for 30 minutes, while maintaining the temperature at 80°C. At this time, the stirring paddle and dispersing paddle stopped rotating (the temperature is controlled at 80°C because at this temperature, the reaction between epoxy and curing agent increases slightly, and some epoxy groups open the ring, generating hydroxyl groups. At the same time, at this temperature, the -O- groups of PPU can react with hydroxyl groups and then graft onto the crosslinking network of epoxy resin. Degassing is to avoid microscopic bubble defects and improve the overall performance of the material, and stopping the stirring is to prevent the shear force of rotation from physically blocking the grafting reaction of the polyurethane prepolymer). This allows the short-linked grafted semi-interpenetrating network to initially form. Step 2 forms the basis for the formation of the short-linked semi-interpenetrating cross-linked network, overcoming performance incompatibilities and achieving synergistic performance enhancement of the electric heating engine. The specific mechanism is described in the triple enhancement mechanism for synergistic performance enhancement.
[0029] Step 3: Based on the uniform casting masterbatch PPU-EP-MTHPA obtained in Step 2, prepare a uniform casting masterbatch Al2O3-PPU-EP-MTHPA masterbatch to ensure optimized filler dispersion; The specific method for step 3 is as follows: Pretreated Al2O3 (200-300 phr, preferably 250 phr) and BDMA accelerator were added to the homogeneous casting masterbatch PPU-EP-MTHPA obtained in step 2 (the accelerator was added later because its addition would accelerate the reaction rate of the system and shorten the process window). The temperature was set to 120℃ (because the viscosity of the material system would increase significantly after adding alumina filler, raising the temperature would reduce the fluidity of the material and facilitate better dispersion of the filler). First, a high-speed shear dispersion at 1000 r / min was applied using a dispersion paddle and a stirring paddle for 5 min (to break up large agglomerates), then the dispersion paddle and stirring paddle were switched to 500 r / min for stirring + 30 kHz, 500 W for ultrasonic dispersion for 20 min (to achieve uniform dispersion). In addition, all of this process was carried out under vacuum (-0.1 MPa).
[0030] In this embodiment, step 3 mainly involves first rapidly dispersing the macroscopic agglomeration of the packing material, and then using a combination of a dispersing paddle and a stirring paddle in conjunction with ultrasonic dispersion to achieve uniform dispersion of the packing material in the material tank in both horizontal and vertical directions. Furthermore, the plasma treatment of the packing material during raw material pretreatment enables synergistic dispersion through "plasma-ultrasound-shearing," significantly reducing the packing agglomeration rate compared to traditional processes.
[0031] Step 4: Vacuum gravity casting is performed on the uniform casting masterbatch Al2O3-PPU-EP-MTHPA obtained in Step 3. The specific steps of step 4 include: 4.1 Fix the mold, which has been preheated to 120℃, at the casting position, turn on the mold vacuum system (-0.095MPa) and evacuate for 10 minutes to remove residual air from the mold; 4.2 Keep the casting masterbatch at 120℃ and slowly inject it into the mold through a 120℃ constant temperature insulated pipe. The pouring rate should be controlled at 50mL / min (to avoid turbulence that could cause air bubbles to be trapped). Step 5: For the Al2O3-PPU-EP-MTHPA that has been gravity-cast in Step 4, perform segmented curing and internal stress relief to ensure material uniformity and stability, and finally obtain epoxy composite material samples or GIS / GIL pot insulators based on short-linked cross-linked networks.
[0032] The specific steps of step 5 include: 5.1 Pre-curing: Transfer the mold into a constant temperature oven and keep it at 140℃ for 4 hours to allow the material to initially cross-link and form a stable short-linked branched network structure. 5.2 Primary Curing: Heat to 160℃ for 6 hours. After this process, the curing degree of the epoxy composite material can reach 95%, but there is a certain internal stress. 5.3 Post-curing: Heat to 180℃ and hold for 2 hours to eliminate residual curing stress inside the material; 5.4 Gradient cooling: The furnace is cooled to room temperature at a rate of 5℃ / h to avoid thermal stress cracks caused by sudden temperature changes; finally, the mold is removed to obtain epoxy composite material samples or GIS / GIL pot insulators based on short-linked cross-linked networks.
[0033] In this embodiment, the performance of the epoxy composite material is determined not only by the formulation but also by the curing process. The previous curing process is to further shape the short-chain branched semi-interpenetrating network, stabilize the structure, and fully utilize the function of the short-chain branched semi-interpenetrating network. The temperature setting is mainly to allow the polyurethane prepolymer (short chain) to graft onto the epoxy crosslinking network as much as possible, while avoiding excessively high temperatures that would cause the epoxy network to cure too quickly and result in a low grafting rate.
[0034] Example 1: 15phr PPU / 250phr Al2O3 / EP system (optimal ratio) Raw material ratio: Bisphenol A epoxy resin (E-51) 100 phr, MTHPA 85 phr, PPU 15 phr, Al2O3 250 phr, BDMA 0.2 phr.
[0035] Preparation steps: The process parameters of “Step 1 - Step 5” of this invention shall be strictly followed, wherein the Al2O3 pretreatment adopts plasma activation (500W, 10min), the masterbatch dispersion adopts 30kHz ultrasound (500W), and the curing process is 140℃×4h+160℃×6h+180℃×2h;
[0036] Example 2: Comparison of different PPU concentrations (verification of the optimal ratio) With the Al2O3 addition amount kept at 250 phr, the PPU concentration was varied (5 phr, 10 phr, 15 phr, 20 phr), and the core performance (breakdown field strength, fracture energy, thermal conductivity, dielectric constant) was tested. The results are shown in the table below:
[0037] As shown in the table, when the PPU concentration is 15 phr, the breakdown field strength, fracture energy, and thermal conductivity of the material all reach their peak values, and the dielectric constant is the lowest, proving that 15 phr is the optimal PPU concentration.
[0038] The innovation of this invention lies in: 1. This invention breaks through the mutually exclusive relationship of epoxy resin's "insulation-thermal conductivity-toughness-heat resistance" properties, and achieves a synergistic improvement of all four properties; 2. This invention improves the dispersibility of Al2O3 filler in EP matrix, eliminates interfacial defects, and simultaneously enhances the thermal conductivity and insulation properties of the material; 3. The present invention is designed to be compatible with the curing process of GIS / GIL large-scale casting, ensuring material uniformity and eliminating internal stress, thereby improving yield and long-term service stability.
[0039] The working principle of this invention is: Performance synergistic enhancement mechanism (triple enhancement mechanism) 1. Block copolymer PPU combines both flexibility and rigidity. The role of PPU hard segments: The aromatic rings in PPU form a conjugated structure, which on the one hand optimizes the phonon transport path (reducing phonon scattering) and improves the thermal conductivity of the material by 17%; on the other hand, it can increase the bandgap of EP and suppress carrier injection; at the same time, it can construct deep traps to effectively capture carriers, thereby increasing the breakdown field strength by 8.8% and the volume resistivity by nearly one order of magnitude. Function of PPU soft segments: Through the "flexible bridging" effect, flexible segments can slip and elastically deform under stress, alleviating stress concentration; at the same time, they can hinder crack propagation, increasing fracture energy by 70.5% and elongation at break by 41.5%. 2. The "rigid-flexible synergy" mechanism of short-link semi-interpenetrating networks The short-link grafting network, mainly based on chemical grafting, can avoid the polar defects of urea bonds generated by amine curing agents, thereby reducing the power frequency dielectric constant by 0.28 (from 3.94 to 3.66); at the same time, the network uniformity is improved and the internal stress is reduced by 25%.
[0040] 3. PPU improves the "interfacial buffering" mechanism of Al2O3 dispersion The ether bonds (-O-) of the PPU soft segment can form hydrogen bonds with the hydroxyl groups (-OH) on the Al2O3 surface, constructing a "flexible buffer layer" on the Al2O3 surface. On the one hand, this inhibits Al2O3 aggregation and eliminates interfacial voids; on the other hand, it alleviates the thermal expansion mismatch between Al2O3 and EP, avoiding interfacial microcracks. Ultimately, this results in a 17% increase in thermal conductivity and a 3.2 kV / mm increase in breakdown field strength compared to Al2O3 / EP.
[0041] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.
Claims
1. A method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked branched crosslinking networks, characterized in that: Includes the following steps: Step 1: Prepare experimental raw materials and perform pretreatment to ensure reaction purity and compatibility; Step 2: Prepare a uniform casting masterbatch PPU-EP-MTHPA to initially form a short-linked branch semi-interpenetrating network; Step 3: Based on the uniform casting masterbatch PPU-EP-MTHPA obtained in Step 2, prepare a uniform casting masterbatch Al2O3-PPU-EP-MTHPA to ensure optimized filler dispersion; Step 4: Vacuum gravity casting is performed on the uniform casting masterbatch Al2O3-PPU-EP-MTHPA obtained in Step 3. Step 5: For the Al2O3-PPU-EP-MTHPA that has been gravity-cast in Step 4, perform segmented curing and internal stress relief to ensure material uniformity and stability, and finally obtain epoxy composite material samples or GIS / GIL pot insulators based on short-linked cross-linked networks.
2. The method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked branch crosslinking network according to claim 1, characterized in that: The specific steps of step 1 include: 1.1 Preparation of experimental materials: Bisphenol A epoxy resin EP, type E-51, epoxy equivalent 182-192 g / eq, moisture ≤0.01%; Polyurethane prepolymer PPU, PPG and MDI are synthesized at a mass ratio of 1:1.9-2.1, with an NCO content of 5.0-5.2% and a molecular chain length ≤50nm; Methyltetrahydrophthalic anhydride (MTHPA), purity ≥99%, moisture ≤0.005%; Al₂O₃ filler, particle size D50 = 15-18 μm, specific surface area 5-8 m² / g. 2 / g, surface hydroxyl content ≥0.8mmol; Accelerator, N,N-dimethylbenzylamine (BDMA), purity ≥98%, addition amount 0.2-0.3 phr; Mold coating: Nano-Al2O3 ceramic coating, thickness 50-80nm, surface roughness Ra≤0.02μm 1.2 Pretreatment of experimental materials.
3. The method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked crosslinked network according to claim 2, characterized in that: The specific method for step 1.2 is as follows: Bisphenol A epoxy resin EP pretreatment: The EP is dried at 78-82℃ and -0.09MPa vacuum for 4 hours to remove low molecular weight impurities; the moisture content is monitored in real time by an online Karl Fischer moisture analyzer to ensure that the moisture content is ≤0.005% before being discharged for use. Pretreatment of polyurethane prepolymer (PPU): Add the polyurethane prepolymer (PPU) to a three-necked flask and dry it at 80℃ and -0.09MPa vacuum for 4 hours to remove low molecular weight impurities; the moisture content is monitored using a Karl Fischer moisture analyzer, and it is usable when the moisture content is ≤0.005%; Al2O3 pretreatment: Add Al2O3 to a dryer and dry with hot air at 115-120℃ for 3 hours to remove surface adsorbed water; It was then transferred to a plasma treatment instrument for 10 minutes to activate the surface hydroxyl groups and enhance the hydrogen bonding with the PPU soft segments. Mold pretreatment: Spray nano-Al2O3 ceramic coating on the inner wall of the sample mold and the basin insulator mold, and cure at 180-185℃ for 1.9-2.1h to form a dense non-stick layer; after curing, place the mold in a constant temperature oven and preheat at 115-125℃ to avoid the formation of air bubbles in the material due to temperature difference during pouring.
4. The method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked branch crosslinking network according to claim 1, characterized in that: The specific steps of step 2 include: 2.1 Add the pretreated EP and MTHPA to a planetary mixer at a mass ratio of 100:84-88; set the mixing temperature to 55-65℃ and disperse for 18-22 minutes at a stirring speed of 450-550 r / min. 2.2 Add the pretreated PPU to the material in step 2.1, while controlling the temperature to remain at 55-65℃. Rotate the agitator and the dispersing paddle simultaneously at a speed of 200-250 r / min and disperse for 30-35 min. 2.3 Degas the material from step 2.2 under vacuum at -0.1MPa for 30-40 minutes, keeping the temperature at 80-85℃. At this point, the stirring paddle and dispersing paddle stop rotating, allowing the short-linked semi-interpenetrating network to initially take shape.
5. The method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked crosslinked network according to claim 1, characterized in that: The specific method for step 3 is as follows: Add pretreated Al2O3 and BDMA accelerator to the uniform casting masterbatch PPU-EP-MTHPA obtained in step 2. Set the temperature to 120-125℃. First, use a dispersion paddle and a stirring paddle to perform high-speed shear dispersion at 1000r / min for 5min. Then, switch the dispersion paddle and stirring paddle to stir at 450-550r / min and perform ultrasonic dispersion at 30kHz and 500W for 20-25min. All of this process is carried out in a vacuum environment of -0.1MPa.
6. The method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked crosslinked network according to claim 1, characterized in that: The specific steps of step 4 include: 4.1 Fix the mold, which has been preheated to 115-125℃, at the casting position, turn on the mold vacuum system and evacuate at -0.095MPa for 10 minutes to remove residual air from the mold; 4.2 Keep the casting masterbatch at 115-125℃ and slowly inject it into the mold through a 120℃ constant temperature insulated pipe, with the casting rate controlled at 50mL / min.
7. The method for preparing high-pressure GIS / GIL epoxy composite material based on short-linked branch crosslinking network according to claim 1, characterized in that: The specific steps of step 5 include: 5.1 Pre-curing: Transfer the mold into a constant temperature oven and keep it at 138-142℃ for 3.9-4.1 hours to allow the material to initially cross-link and form a stable short-linked branched network structure. 5.2 Primary curing: Heat to 158-162℃ for 5.9-6.1 hours. After this process, the curing degree of the epoxy composite material can reach 95%, but there is a certain internal stress. 5.3 Post-curing: Heat to 178-182℃ and hold for 1.9-2.1 hours to eliminate residual curing stress inside the material; 5.4 Gradient cooling: The furnace is cooled to room temperature at a rate of less than or equal to 5℃ / h to avoid thermal stress cracks caused by sudden temperature changes; finally, the mold is removed to obtain epoxy composite material samples or GIS / GIL pot insulators based on short-linked cross-linked networks.
8. The epoxy composite material sample or GIS / GIL pot insulator product obtained by the method for preparing high voltage GIS / GIL epoxy composite material based on short-link crosslinked network according to any one of claims 1-7 is used in high voltage GIS / GIL.