Epoxy core surface gas phase fluorination regulation and control method for extra-high voltage direct current wall bushing

Abstract

The invention provides an epoxy core surface gas phase fluorination regulation and control method for an extra-high voltage direct current wall bushing, which comprises the following steps of: using fluorine-containing mixed gas in a closed system; and carrying out surface modification treatment on the epoxy resin-based composite material under the conditions that the reaction temperature is 20-120 DEG C, the temperature gradient is 0.1-5 DEG C / cm, the reaction pressure is 10-200 kPa and the reaction time is 10-180 minutes, so as to obtain the epoxy resin-based composite material with the flashover voltage of 110-120 kV / cm. By regulating and controlling fluorination modification conditions, a chemically bonded gradient fluorination layer is constructed on the surface of the epoxy resin-based composite material, so that the surface charge decay time of the epoxy resin-based composite material is less than or equal to 30s, and interface charge accumulation is remarkably inhibited; the interface bonding strength is greater than or equal to 10MPa; according to the invention, the electric arc resistance is improved by more than or equal to 10%, the flashover voltage is improved by more than or equal to 30%, the problems of electric field distortion and insulation deterioration caused by epoxy resin / SF6 interface charge accumulation are solved, and the long-term operation reliability of the DC bushing in an SF6 gas environment is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of electrical insulation materials technology, specifically to a method for controlling the vapor phase fluorination of epoxy core surfaces for ultra-high voltage direct current through-wall bushings. Background Technology

[0002] As a core component of the national energy strategy, ultra-high voltage direct current (UHVDC) transmission projects rely on their through-wall bushings for crucial insulation, connecting the valve hall to the DC field. Under the harsh conditions of long-term exposure to ≥800kV DC voltage and polarity reversal stress, the gas-solid interface formed by epoxy resin / SF6 experiences dynamic charge imbalance due to material energy level mismatch, leading to a sharp drop in surface flashover voltage and posing a significant threat to power grid safety.

[0003] While epoxy resins possess excellent mechanical strength, their surface polar groups (such as -OH and -COOR) readily adsorb SF6 decomposition products, forming charge traps that significantly hinder charge migration. Simultaneously, the non-uniform surface resistivity distribution causes accumulated charge to induce localized electric field distortion, significantly accelerating the insulation degradation process. Furthermore, their surface resistivity is as high as 10⁻⁶. 16 The charge is Ω, and the radial distribution deviation can reach two orders of magnitude, making it difficult for the charge to dissipate uniformly and further exacerbating the risk of interface insulation.

[0004] While gas-phase direct fluorination technology theoretically improves interfacial properties through CF bonding, industrial practice reveals its inherent limitations: First, high F2 concentrations easily induce epoxy backbone chain breakage (energy barrier only 1.2 eV), leading to a material mass loss rate exceeding 8%. Second, constant fluorination throughout the surface results in uniformly distributed -CF3 groups, which, although reducing surface energy, leads to excessive carrier mobility decay due to over-fluorination. Third, the lack of directional control over the -CF3 configuration results in uneven trap energy level dispersion. The interface between the fluorinated layer and the substrate formed by traditional processes exhibits significant performance abrupt changes, with generally low bonding strength, making it prone to delamination and peeling during thermal cycling. These problems make it difficult for traditional fluorinated layers to meet the core performance requirements of flashover voltage for ultra-high voltage power equipment.

[0005] To overcome the aforementioned limitations, the following issues need to be addressed: first, precisely controlling reaction kinetics to avoid side reactions; second, moderately increasing the chemical bonding density of the fluorinated layer without damaging the main chain structure; and third, achieving synergistic optimization of charge decay time ≤30s and interfacial bonding strength ≥10MPa. Current technologies have not yet established a quantitative mapping model between process parameters (F2 / N2 mixing ratio, temperature gradient, pressure) and interfacial energy level structure.

[0006] Density functional theory (DFT) calculations (based on the B3LYP / 6-311G** basis set) show that conventional isothermal fluorination easily leads to β-fracture at the CO bond in the epoxy backbone (energy barrier only 1.2 eV), while a temperature gradient can redirect the reaction pathway to CH bond fluorination (energy barrier 2.3 eV), reducing the probability of side reactions by 87%. Experiments show that conventional isothermal fluorination (F2 / N2=1:5, 60℃) results in an 8.2% mass loss of epoxy resin. This invention, through a gradient fluorination process (F2 / N2=1:20, gradient 0.5℃ / cm), controls the mass loss to within 1.5%, effectively protecting the integrity of the matrix.

[0007] Based on this, the present invention proposes a method for controlling the gas phase fluorination of epoxy core surface for ultra-high voltage direct current through-wall bushings. By dynamically controlling the gas phase reaction process, a gradient CF bonding layer is constructed on the epoxy surface to improve the insulation performance of the material. Summary of the Invention

[0008] To address the issues of charge accumulation at the epoxy resin-SF6 gas-solid interface, weak bonding strength in traditional coating modifications, and insufficient surface treatment depth in the aforementioned background technologies, the main objective of this invention is to provide a method for controlling the vapor-phase fluorination of the epoxy core surface for UHVDC through-wall bushings. This invention constructs a chemically bonded fluorinated layer with high bonding strength and high CF bond content on the epoxy resin surface through a vapor-phase fluorination reaction, solving the problem of interface insulation performance degradation and significantly improving the long-term operational reliability of UHVDC bushings.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for controlling the vapor-phase fluorination of the epoxy core surface for ultra-high voltage direct current through-wall bushings includes the following steps: S1. Prepare epoxy resin samples for UHVDC bushings and pre-treat the samples. S2. Place the pretreated epoxy resin sample in a sealed reaction chamber and introduce a fluorinated mixed gas for fluorination treatment to obtain an epoxy resin sample with a fluorinated layer on the surface.

[0010] Preferably, the pretreatment includes: cleaning the epoxy resin sample with an organic solvent and drying it under vacuum conditions. Pretreatment of the epoxy resin sample activates its surface properties and enhances its fluorination reactivity.

[0011] Preferably, the pretreatment includes: cleaning the epoxy resin sample with an organic solvent for 15-30 minutes, drying it in a vacuum oven with a vacuum degree ≤100Pa and a temperature of 60-80℃ for 4-8 hours to thoroughly remove solvent residue and adsorbed moisture; and then polishing its surface for 10 minutes to reduce the surface contact angle from more than 80° to 35°, thereby improving the fluorination reaction activity.

[0012] Preferably, the epoxy resin sample includes at least one of a cured epoxy resin impregnated paper composite insulation material sample block or an epoxy resin composite material sample block cured with a curing agent.

[0013] Preferably, the epoxy resin composite material sample cured by the curing agent is bisphenol A type epoxy resin cured with methylhexahydrophthalic anhydride under the action of an accelerator. More preferably, the mass ratio of bisphenol A type epoxy resin to methylhexahydrophthalic anhydride is 100:85, and the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol, with a mass of 0.5-1% of the weight of the epoxy resin.

[0014] Preferably, the fluorinated mixed gas comprises fluorine and nitrogen, with a volume ratio of fluorine to nitrogen of 1:50 to 1:5. More preferably, the volume ratio of fluorine to nitrogen is 1:30 to 1:10. During the fluorination process, the amount of fluorinated mixed gas is precisely metered and dynamically adjusted using a mass flow rate (MFC) controller.

[0015] Preferably, the fluorination treatment temperature is 20-120°C. More preferably, the fluorination treatment temperature is 40-90°C. By adjusting the fluorination temperature, accurate control of the activation energy and reaction rate of the fluorination reaction can be achieved.

[0016] Preferably, the fluorination treatment pressure is 10-200 kPa. More preferably, the fluorination treatment pressure is 50-150 kPa. By controlling the fluorination pressure, the collision frequency of gas molecules and the surface adsorption probability can be effectively adjusted.

[0017] Preferably, the fluorination treatment time is 10-180 min; more preferably, the fluorination treatment time is 30-90 min.

[0018] Preferably, the fluorination treatment further includes: setting and controlling a temperature gradient on the surface of the epoxy resin sample or along a specific direction, said temperature gradient being 0.1-5℃ / cm. Fitting the Arrhenius equation shows that when the temperature gradient > 0.3℃ / cm, the activation energy of the fluorination reaction decreases from 98kJ / mol to 72kJ / mol (R0). 2 =0.96), which significantly accelerates the fluorination rate of surface CH bonds.

[0019] More preferably, the temperature gradient is set along a specific direction such as the thickness direction, radial direction, or axial direction of the epoxy resin-based sample. By controlling the temperature of the epoxy resin-based composite material sample in zones, the synergistic optimization of the gradient structure of the fluorinated layer and heat conduction can be achieved.

[0020] Through the synergistic control of the above fluorination treatment conditions, the CF bond content in the fluorinated layer is ensured to be ≥60% (quantitative analysis by XPS).

[0021] Preferably, the method further includes a post-processing step: after the fluorination treatment is completed, the F2 supply is stopped, and high-purity N2 or other inert gases are continuously supplied to thoroughly purge the reaction chamber to remove residual reaction gases and byproducts. Then, the reaction device and its internal core are safely cooled to room temperature, and finally the fluorinated epoxy resin sample is taken out.

[0022] Preferably, the thickness of the fluorinated layer of the epoxy resin-based sample is ≥0.4μm, and the fluorinated layer is distributed in a gradient from the surface to the substrate, with the surface layer (0-0.05μm) mainly composed of CF3 and CF2 configurations, and the deep layer (0.2-0.5μm) mainly composed of CF configuration.

[0023] Preferably, the fluorinated epoxy resin-based sample has at least one of the following characteristics: The percentage of CF bonds in the fluorinated layer is ≥60%; The surface charge decay time of the fluorinated epoxy resin sample is ≤30s under specific charging conditions; The interfacial bonding strength between the fluorinated layer and the epoxy resin matrix is ​​≥10MPa; The arc resistance time of the fluorinated layer is ≥195s; The average DC flashover voltage of the fluorinated layer is ≥110kV / cm.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a simple, mature, and highly effective gas-phase fluorination modification method. Through direct chemical bonding with the epoxy resin matrix via CF bonds, the interfacial bonding strength is ≥10 MPa. Furthermore, after a 2000-hour accelerated aging test (120℃, 85% RH), the CF bond retention rate of the fluorinated layer is ≥95%, and the interfacial bonding strength attenuation rate is <5%, avoiding the interfacial peeling problem of traditional coating technologies. The integrated structure of the fluorinated layer and the substrate in this invention gives the material excellent anti-aging and crack resistance, significantly improving the insulation margin and service life of ultra-high voltage DC bushings.

[0025] 2. The fluorinated layer formed by this invention has a surface charge decay time of ≤30s. With its high chemical inertness and low surface free energy, it accelerates charge migration and dissipation. At the same time, the high bond energy CF bond (485kJ / mol) can effectively resist arc ablation. The arc resistance time is increased by ≥15% compared with the untreated sample, which greatly improves the insulation performance of the material. It is suitable for charge accumulation suppression and arc damage protection under ultra-high voltage DC environment.

[0026] 3. The modification method of this invention has simple process steps, good controllability, and low economic cost. It avoids the interfacial compatibility problems of traditional coating technologies through gas-phase reaction. This method can achieve batch and uniform fluorination of epoxy resin insulating parts with complex shapes and arbitrary sizes, making it particularly suitable for industrial mass production and commercial applications.

[0027] 4. This invention establishes a three-dimensional synergistic mechanism of gas composition, temperature gradient, and pressure to precisely achieve an axial fluorination concentration gradient (35%→55%); and optimizes the molecular configuration to achieve an interfacial bandgap ≥7.0eV; experiments have confirmed that the flashover voltage of the fluorinated epoxy resin / SF6 interface reaches 117.3kV / cm under ±200kV DC voltage, which is 39.3% higher than that of the untreated group (84.2kV / cm), meeting the stringent requirements of UHVDC bushings for gas-solid interface insulation performance. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the gas-phase fluorination treatment system of the present invention; Figure 2 This is a schematic diagram of the fluorination reaction pathway of the present invention; Figure 3 This is a graph showing the effect of the temperature gradient on the activation energy of the fluorination reaction according to the present invention; Figure 4 This is a graph showing the effect of the F2 / N2 ratio on the CF bond content and charge decay time in an embodiment of the present invention. Figure 5 This is a diagram showing the effect of temperature gradient on interfacial bonding strength and arc resistance of the present invention. Figure 6 This is a comparison diagram of the fluorination treatment conditions in Examples 1-4 of the present invention; Figure 7 This is a diagram showing the CF bond ratio of the fluorinated modified composite materials in Examples 1-4 of this invention; Figure 8 The above figures show the surface charge decay time of the fluorinated modified composite materials in Examples 1-4 of this invention. Figure 9 These are the interfacial bonding strength diagrams of the fluorinated modified composite materials in Examples 1-4 of this invention; Figure 10 The graphs show the improvement in arc resistance of the fluorinated modified composite materials in Examples 1-4 of this invention. Figure 11 This is a comparison curve of the flashover voltage at the interface of fluorinated modified epoxy / SF6 in Examples 1-4 of the present invention; Figure 12 This is a comparison chart of the flashover voltage improvement of the fluorinated modified composite materials in Examples 1-4 of the present invention; Figure 13This is a comparison diagram of the fluorinated layer thickness of the fluorinated modified composite materials in Examples 1-4 of the present invention; Figure 14 This is a comparison chart of the CF bond retention rate of the fluorinated modified composite materials in Examples 1-4 of the present invention after accelerated aging; Figure 15 This is a comparison diagram of the F / C atomic ratio depth distribution of the fluorinated layer in the fluorinated modified composite materials of Examples 1-4 of the present invention. Detailed Implementation

[0029] The sources of some of the raw materials used in this invention are as follows: 1. The epoxy resin sample is an epoxy resin impregnated paper composite material sample (already cured and molded) obtained from the actual UHVDC bushing production line.

[0030] 2. Preparation of epoxy resin samples: Bisphenol A type epoxy resin and methylhexahydrophthalic anhydride were used as curing agents (ratio: epoxy resin: curing agent = 100:85, by weight), and 2,4,6-tris(dimethylaminomethyl)phenol was added as an accelerator (addition amount: 0.5-1% of resin weight). The uniformly mixed system was stirred and degassed under vacuum conditions (<100 Pa), and then poured into a preheated mold. Vacuum casting and curing were performed according to standard curing process to prepare plate-shaped sample blocks with dimensions of 50mm×50mm×5mm.

[0031] 3. Fluorinated gases: F2 gas (purity ≥ 99.8%), N2 gas (purity ≥ 99.999%).

[0032] In the following examples, the epoxy resin samples were prepared as follows: Bisphenol A type epoxy resin and methyl hexahydrophthalic anhydride were mixed evenly with 0.75% (by weight) 2,4,6-tris(dimethylaminomethyl)phenol at a mass ratio of 100:85, and then stirred and degassed under vacuum conditions. The mixture was then poured into a preheated mold and vacuum-cast and cured according to standard curing processes to prepare a plate-shaped sample block with dimensions of 50mm × 50mm × 5mm.

[0033] Example 1: like Figure 1-2 As shown, this invention provides a method for controlling the vapor-phase fluorination of the epoxy core surface for ultra-high voltage direct current through-wall bushings, comprising the following steps: S1. Preprocessing: The prepared epoxy resin sample was ultrasonically cleaned in anhydrous ethanol and acetone for 20 min each, then the surface was dried with high-purity N2 gas flow, and then placed in a vacuum oven and vacuum dried for 6 h at a temperature of 70℃ and a vacuum degree of 50 Pa, and then cooled to room temperature. S2, fluorination treatment: (1) Place the pretreated epoxy resin sample into a sealed Hastelloy reaction chamber, start the vacuum system, pump the pressure inside the chamber to 5Pa, then introduce high-purity N2 gas into the chamber to atmospheric pressure, then pump the vacuum back to 5Pa, repeat the nitrogen replacement process three times to fully purify the environment inside the chamber. (2) The flow rates of fluorine and nitrogen are precisely controlled by MFC, with the flow rates of fluorine and nitrogen being 5 sccm and 100 sccm, respectively; the volume ratio of fluorine to nitrogen is 1:20. (3) Start the temperature control system to raise the temperature in the reaction chamber to 60℃ and keep it constant; at the same time, control and maintain a temperature gradient of 0.5℃ / cm in the thickness direction of the epoxy resin sample through zone temperature control (the temperature of the upper surface is slightly higher than the temperature of the bottom of the sample); control the pressure in the reaction chamber to 100kPa through the pressure control system. (4) Under the set F2 / N2 volume ratio, reaction temperature, reaction pressure and temperature gradient, the epoxy resin sample surface underwent an in-situ non-coating fluorination reaction for 60 min. S3, Post-processing: After the reaction is complete, stop the F2 supply and simultaneously purge the reaction chamber with N2 gas at a flow rate of 100 sccm for 30 minutes to thoroughly remove residual F2 and HF reaction products. After purging, turn off the heating device and allow the reaction chamber to cool down to room temperature under N2 atmosphere protection. Once the sample has completely cooled, open the chamber and remove it to obtain an epoxy resin sample with a fluorinated layer.

[0034] The performance of the prepared fluorinated epoxy resin samples was tested, and the results are shown in Table 1: The fluorinated epoxy resin samples were modified with a fluorinated layer thickness of 0.52 μm. (1) The total atomic percentage of CF bonds (including CF bonds in fluorinated groups such as -CF, -CF2, and -CF3) was 65% (relative to the total carbon atoms); (2) After being charged with +10 kV corona for 30 s, the time required for the surface potential to decay from the peak value to 10% of its peak value was 25 s; (3) The average pull-out bonding strength between the fluorinated layer and the epoxy resin matrix was 1. 2.5MPa; (4) The arc resistance time was 195s, while the arc resistance time of the unfluorinated epoxy resin composite material (blank control group) was 165s. Therefore, the arc resistance performance of the fluorinated epoxy resin composite material in this embodiment was improved by (195-165) / 165×100%=18.2%; (5) The flashover voltage of the fluorinated epoxy resin / SF6 interface reached 117.3kV / cm at ±200kV DC voltage (84.2kV / cm for the unmodified group), and the surface flashover voltage was improved by 39.3%.

[0035] Example 2: This embodiment is basically the same as Embodiment 1, except that the conditions for the fluorination treatment in step S3 are changed, as follows: The volume ratio of F2 / N2 was 1:10, the reaction temperature was 60℃, the temperature gradient along the sample thickness was 0.5℃ / cm, the reaction pressure was 100kPa, and the reaction time was 60min.

[0036] The performance test results of the fluorinated epoxy resin samples are shown in Table 1: The fluorinated epoxy resin samples with a fluorinated layer thickness of 0.41 μm, (1) the total percentage of CF bond atoms is 72%; (2) the decay time of the surface charge to 10% of the peak value is 20s; (3) the average interfacial bonding strength is 11.8 MPa; (4) the arc resistance time is 205s, which is 24.2% higher than that of the blank control group (165s); (5) the surface flashover voltage is increased by 32.1%.

[0037] Example 3: This embodiment is basically the same as Embodiment 1, except that the conditions for the fluorination treatment in step S3 are changed, as follows: The F2 / N2 volume ratio was 1:20, the reaction temperature was 80℃, the temperature gradient along the sample thickness direction was 0.5℃ / cm, the total reaction pressure was 100kPa, and the reaction duration was 60min.

[0038] The performance test results of the fluorinated epoxy resin composite material are shown in Table 1: The fluorinated epoxy resin composite material with fluorinated modification has a fluorinated layer thickness of 0.63 μm; (1) the total percentage of CF bond atoms is 68%; (2) the decay time of surface charge decay to 10% of the peak value is 22s; (3) the average interfacial bonding strength is 13.0 MPa; (4) the arc resistance time is 200s, which is 21.2% higher than that of the blank control group (165s); (5) the surface flashover voltage is increased by 35.7%.

[0039] Example 4: This embodiment is basically the same as Embodiment 1, except that the conditions for the fluorination treatment in step S3 are changed, as follows: The F2 / N2 volume ratio was 1:20, the reaction temperature was 60℃, the reaction pressure was 100kPa, and the reaction time was 60min (without temperature gradient).

[0040] The performance test results of the fluorinated epoxy resin samples are shown in Table 1: The fluorinated layer thickness of the fluorinated epoxy resin sample is 0.38 μm; (1) the total percentage of CF bond atoms is 61%; (2) the charge decay time from surface charge decay to 10% of the peak value is 28 s; (3) the average interfacial bonding strength is 11.5 MPa; (4) the arc resistance time is 185 s, which is 12.1% higher than that of the blank control group (165 s); (5) the surface flashover voltage is increased by 20.5%.

[0041] Through the above Examples 1-4, this invention investigated fluorination treatment conditions such as F2 / N2 volume ratio, temperature gradient, and reaction temperature. Figure 3-6 The effect of fluorination on the epoxy resin reaction was investigated, and the performance of the prepared epoxy resin samples with fluorinated layers was analyzed. 1. The XPS, surface charge decay, interfacial bonding strength, and arc resistance test results of the epoxy resin samples with fluorinated layers prepared in Examples 1-4 are shown in Table 1 and 2. Figure 7-13 .

[0042] Table 1 Performance test results of Examples 1-4

[0043] As shown in Table 1, compared with the epoxy resin sample without surface modification by the method of this invention, the epoxy resin sample modified by the method of this invention has the following characteristics: surface charge decay time ≤30s, significantly inhibiting interfacial charge accumulation; interfacial bonding strength between the fluorinated layer and the matrix ≥10MPa, significantly improving interfacial bonding strength; arc resistance ≥15%, and surface flashover voltage increased by ≥30%, effectively improving the interfacial insulation performance; after 2000h accelerated aging test (120℃, 85%RH)... Figure 14 The fluorinated layer exhibits a CF bond retention rate ≥95% and an interfacial bond strength attenuation rate <5%, extending the service life of the UHVDC bushing. These results fully demonstrate that the present invention, through fluorination modification of the epoxy resin material surface, can solve the problems of electric field distortion and insulation degradation caused by charge accumulation at the epoxy resin / SF6 interface, significantly improving the long-term operational reliability of the DC bushing in an SF6 gas environment. Simultaneously, it verifies the feasibility and advancement of the technical solution of this invention and its enormous potential in improving the interfacial performance of key insulating components in UHVDC bushings.

[0044] 2. The fluorinated epoxy resin samples from Examples 1-4 were cross-sectionally processed using cryo-focused ion beam (Cryo-FIB), and the nanostructure characterization of the fluorinated layer was obtained by XPS depth profiling, as shown in Tables 2-5. Figure 15 .

[0045] Table 2. Characterization of the fluorinated layer nanostructure of the fluorinated epoxy resin sample from Example 1.

[0046] Table 3. Characterization of the nanostructure of the fluorinated layer in the fluorinated epoxy resin sample of Example 2.

[0047] Table 4. Characterization of the nanostructure of the fluorinated layer in the fluorinated epoxy resin sample of Example 3.

[0048] Table 5. Characterization of the fluorinated layer nanostructure of the fluorinated epoxy resin sample from Example 4.

[0049] As shown in Tables 2-5, the gas-phase fluorination method of this invention can form a fluorinated layer structure with gradient changes on the surface of epoxy resin samples. The differences in gradient structures among different embodiments indicate that fluorination process parameters (gas ratio, temperature, etc.) affect the formation of the nano-gradient structure of the fluorinated layer, including different depths of F / C atomic ratios and molecular configuration distributions. Combined with Table 1, it can be seen that the nano-gradient structure of the fluorinated layer is an intrinsic factor affecting the macroscopic properties (electrical, mechanical, arc resistance, etc.) of the epoxy resin samples. Different gradient distributions lead to performance differences, providing a theoretical basis at the microstructural level for optimizing material properties by controlling process parameters.

[0050] It is important to emphasize that the specific parameters and numerical ranges described in this specification (e.g., temperature, pressure, gas flow rate, time, etc.) are based on experimental results of specific epoxy resin systems under laboratory conditions. They are examples provided to better illustrate the invention and are not intended to limit the scope of application of the invention. In actual industrial production, for different grades of epoxy resin, different sizes and structures of sleeve cores, and the specific performance requirements of the application environment, those skilled in the art can and should, under the guidance of the core technical ideas and principles disclosed in this invention, further dynamically optimize and adjust the above-mentioned process parameters through reasonable experimental design (such as orthogonal experiments, response surface methodology, etc.) to obtain the best comprehensive modification effect. All such reasonable adjustments and optimizations based on the core ideas of this invention should be considered to be included within the scope of protection of this invention.

Claims

1. A method for controlling the vapor-phase fluorination of the epoxy core surface for ultra-high voltage direct current through-wall bushings, characterized in that: Includes the following steps: S1. Prepare epoxy resin samples for UHVDC bushings and pre-treat the samples. S2. Place the pretreated epoxy resin sample in a sealed reaction chamber and introduce a fluorinated mixed gas for fluorination treatment to obtain an epoxy resin sample with a fluorinated layer on the surface.

2. The method according to claim 1, characterized in that: The epoxy resin sample includes at least one of a cured epoxy resin impregnated paper composite insulation material sample or an epoxy resin composite material sample cured with a curing agent.

3. The method according to claim 1, characterized in that: The fluorine-containing mixed gas includes fluorine and nitrogen, and the volume ratio of fluorine to nitrogen is 1:50 to 1:

5.

4. The method according to claim 1, characterized in that: The fluorination treatment is carried out at a temperature of 20-120℃, a pressure of 10-200kPa, and a time of 10-180min.

5. The method according to claim 4, characterized in that: The fluorination treatment is carried out at a temperature of 40-90℃, a pressure of 150-150kPa, and a time of 30-90min.

6. The method according to claim 1, characterized in that: The fluorination treatment further includes setting and controlling a temperature gradient on the surface of the epoxy resin sample, wherein the temperature gradient is 0.1-5℃ / cm.

7. The method according to claim 6, characterized in that: The temperature gradient is set along any one of the following directions: thickness, radial direction, or axial direction of the epoxy resin-based sample.

8. The method according to claim 1, characterized in that: The method also includes a post-processing step: after the fluorination treatment is completed, the F2 supply is stopped, and high-purity N2 is continuously supplied to thoroughly purge the reaction chamber to remove residual reaction gases and byproducts. Then, the reaction device and its internal core are safely cooled to room temperature, and finally the fluorinated epoxy resin sample is taken out.

9. The method according to claim 1, characterized in that: The thickness of the fluorinated layer in the fluorinated epoxy resin-based sample is ≥0.4μm.

10. The method according to claim 1, characterized in that: The fluorinated epoxy resin-based sample has at least one of the following properties: The percentage of CF bonds in the fluorinated layer is ≥60%; The surface charge decay time of the fluorinated epoxy resin sample is ≤30s under specific charging conditions; The interfacial bonding strength between the fluorinated layer and the epoxy resin matrix is ​​≥10MPa; The arc resistance time of the fluorinated layer is ≥195s; The average DC flashover voltage of the fluorinated layer is ≥110kV / cm.

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