Plasma-controlled oriented boron nitride high-frequency transformer functional insulating material, preparation method and use thereof

Abstract

The application provides a high-frequency transformer functional insulating material of plasmonic orientation boron nitride and a preparation method and application thereof, and relates to the technical field of insulating materials. The functional insulating material is obtained by sequentially covering, from an inner layer to an outer layer, a thermosetting resin matrix layer, a silicon-rich transition layer, an oriented boron nitride sheet layer, a boron nitride gradient insulating layer and a densified surface layer on the surface of a metal conductor. The insulating material can realize heat diffusion enhancement, electric field distribution homogenization and space charge inhibition, and exhibits high breakdown strength, high local discharge starting voltage and good long-term insulating stability under high-frequency non-sinusoidal voltage, and is suitable for insulating reinforcement of the winding end, the outgoing line end and the core clamping piece area of a high-frequency transformer of a super-speed train, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of insulating materials technology, specifically to a plasma-modulated oriented boron nitride high-frequency transformer functional insulating material, its preparation method, and its applications. Background Technology

[0002] As train speeds increase from high-speed to ultra-high-speed, the power density of traction systems continues to rise. To reduce the size and weight of onboard equipment, high-frequency transformers are gradually replacing traditional power-frequency traction transformers. High-frequency transformers operate under actual conditions such as the start-stop shocks of ultra-high-speed trains, strong harmonics, and non-sinusoidal voltages. Their insulation structures simultaneously withstand the coupling effects of multiple fields, including voltage surges, current surges, localized overheating, and vibration shocks. This places significantly higher demands on the electrical and thermal properties of the insulation materials compared to traditional power transformers.

[0003] Existing high-frequency transformers mostly use epoxy resin or paper-based solid insulation, which has a low thermal conductivity. This makes it difficult to dissipate heat from winding hot spots in a timely manner, and under the combined effects of high-frequency electric fields and temperature rise, surface discharge, electrical treeing, and local breakdown are likely to occur. On the other hand, under high-frequency non-sinusoidal voltages, the injection and accumulation of space charge inside the insulation medium are more intense, and the local electric field distortion is aggravated. Traditional homogeneous insulation layers cannot simultaneously meet the requirements of electric field uniformity and thermal management, resulting in a significant shortening of insulation life.

[0004] Boron nitride, especially hexagonal boron nitride nanosheets, possesses high thermal conductivity, excellent electrical insulation, and high-temperature resistance, making it a potential filler for integrated electro-thermal insulating materials. However, current technologies often employ simple blending or casting methods to add boron nitride powder, resulting in problems such as random filler orientation, high interfacial thermal resistance, and severe local agglomeration. This leads to difficulties in finely controlling the electric field distribution, limited thermal conductivity enhancement, and even the creation of new electric field concentration regions, making it difficult to meet the comprehensive insulation performance requirements of high-frequency transformers operating under ultra-high-speed train conditions.

[0005] Furthermore, there is a lack of targeted material design solutions for the space charge behavior and electro-thermal coupling failure mechanism of insulating media under high-frequency non-sinusoidal transient conditions. Existing insulation structures mostly rely on increasing safety margins and regular maintenance to ensure operational reliability, but the insulation performance still does not match the actual operating conditions.

[0006] Therefore, there is an urgent need to develop a new type of functional insulating material that combines high thermal conductivity, uniform electric field, and good high-frequency insulation performance, and to propose matching preparation processes and structural design methods to improve the overall insulation level and service life of high-frequency transformers for ultra-high-speed trains. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a plasma-modulated oriented boron nitride high-frequency transformer functional insulating material, its preparation method, and its applications.

[0008] The high-frequency transformer in the traction system of ultra-high-speed trains faces the following problems under actual operating conditions:

[0009] High-frequency non-sinusoidal voltages and start-stop shocks cause severe distortion of the local electric field, resulting in insufficient insulation safety margin at the winding ends, output terminals, and core clamping areas. The insulation structure has limited thermal conductivity, and short-term thermal shocks and continuous temperature rises are prone to occur at winding hot spots and structural inflection points, promoting the premature development of electrical trees and surface discharges. Under high-frequency strong electric fields, space charge injection and accumulation are more intense, and traditional homogeneous insulation materials are unable to suppress the enrichment and migration of charges within the insulation layer, leading to electro-thermal coupling failure. Existing boron nitride modified insulation materials mostly adopt simple blending and casting processes, resulting in poor boron nitride orientation, high interfacial thermal resistance, severe filler agglomeration, and a lack of dielectric gradient design for high-frequency operating conditions in the insulation structure.

[0010] Therefore, the technical problem to be solved by the present invention is: to provide a functional insulating material and its preparation method that simultaneously possesses high thermal conductivity, electric field uniformity and excellent high-frequency insulation performance, addressing the multi-field coupling failure mechanism of high-frequency transformers in the ultra-high-speed train operating environment, such as hot spot accumulation, electric field distortion, space charge accumulation and local early discharge.

[0011] The technical solution of this invention to solve the technical problem is as follows:

[0012] This invention provides a plasma-controlled oriented boron nitride functional insulating material. The insulating material is obtained by sequentially coating a thermosetting resin matrix layer, a silicon-rich transition layer, an oriented boron nitride sheet layer, a boron nitride gradient insulating layer, and a densified surface layer onto the surface of a metal conductor, from the innermost layer to the outermost layer. This functional insulating material has a multilayer composite system, enabling synergistic optimization of electro-thermal performance. Preferably, the total thickness of the resulting multilayer composite insulating structure on the surface of the metal conductor is 50-500 μm, used for local insulation enhancement at the winding ends, output terminal gaps, and core clamping areas of high-frequency transformers.

[0013] Furthermore, the metal conductor is selected from copper conductors; preferably, the copper conductor is a T2 copper conductor;

[0014] And / or, the solid resin matrix layer covers the surface of the metal conductor and is a cured resin matrix layer formed of epoxy resin, epoxy-modified silicone resin or a combination thereof, and the thickness of the cured resin matrix layer is 10-100 μm; preferably, the thickness of the cured resin matrix layer is 80 μm.

[0015] And / or, the silicon-rich transition layer covers the surface of the thermosetting resin matrix layer. The surface of the resin matrix is ​​treated by an atmospheric pressure plasma jet driven by an AC high-voltage power supply in an atmosphere containing an organosilicon precursor, causing the organosilicon precursor to decompose and deposit, thereby forming a silicon-rich inorganic network transition layer with a thickness of 10-500 nm in situ on the surface of the resin matrix; preferably, a silicon-rich inorganic network transition layer with a thickness of 65 nm is formed in situ on the surface of the resin matrix; preferably, the silicon-rich transition layer has a dense and continuous SiOx or SiOxNy network structure along the thickness direction, forming a chemically bonded interface with the resin matrix layer.

[0016] And / or, the oriented boron nitride sheet layer covers the surface of the silicon-rich transition layer, and the hexagonal boron nitride sheet layer is deposited in situ on the surface of the silicon-rich transition layer by plasma-enhanced chemical vapor deposition. The average angle between the normal of the boron nitride nanosheet in the thickness direction and the coating thickness direction is not greater than 30°, and the thickness of the oriented sheet layer is 0.1-10 μm; preferably, the thickness of the oriented sheet layer is 0.3 μm.

[0017] And / or, the boron nitride gradient insulating layer covers the surface of the oriented boron nitride sheet and includes 2-10 sub-layers stacked sequentially along the material thickness direction. Each sub-layer is a boron nitride-containing resin sol-gel coating. The boron nitride concentration varies between adjacent sub-layers, with the concentration gradually decreasing from the innermost layer to the outermost layer. The boron nitride concentration in the innermost layer is 10-40 wt%, and the boron nitride concentration in the outermost layer is 1-10 wt%.

[0018] And / or, the densified surface layer covers the surface of the boron nitride gradient insulating layer, and is a cross-linked densified layer formed by atmospheric pressure micro-pulse plasma jet or dielectric barrier discharge treatment driven by a micro-pulse power supply.

[0019] Furthermore,

[0020] The solid resin matrix layer is prepared from the following raw materials in the following weight ratio: 100 parts epoxy resin, 10-20 parts silicone resin, 0.1-1 parts silane coupling agent, and 1-5 parts curing agent.

[0021] And / or, in the silicon-rich transition layer, the atmosphere containing the organosilicon precursor is formed by adding organosilicon precursor vapor to a mixture of Ar and O2 gases; the volume percentage of Ar in the mixture is 99-99.5%, and the volume percentage of O2 is 0.5-1%; the volume ratio of organosilicon precursor vapor to the mixture is 1-5:100.

[0022] And / or, in the oriented boron nitride sheets, the deposition conditions of the plasma-enhanced chemical vapor deposition process are: radio frequency power 50-400W, substrate temperature 200-600℃, pressure 5-100Pa, the precursor source gas is a mixture of precursor containing B and N elements and carrier gas, and during the deposition process, an electric field perpendicular to the substrate surface and / or the plasma sheath potential is applied to induce the hexagonal boron nitride nanosheets to align along the coating thickness direction.

[0023] And / or, in the boron nitride gradient insulating layer, the thickness of any sublayer is 2-50 μm, the difference in boron nitride concentration between adjacent sublayers is 3-15 wt%, and the resin phase of each sublayer is epoxy resin and / or epoxy-modified silicone resin that is the same as or compatible with the resin matrix layer, forming a continuous inorganic-organic hybrid network through a sol-gel reaction; preferably, the thickness of any sublayer is 50 μm; preferably, the difference in boron nitride concentration between adjacent sublayers is 5-10 wt%;

[0024] And / or, in the densified surface layer, before the densified surface layer is formed, gradient curing is performed, and the curing conditions are: heating to 100-130℃ at a rate of 0.5-2℃ / min and holding for 1-3h, then continuing to heat to 150-180℃ at a rate of 0.5-2℃ / min and holding for 2-4h, and finally cooling to room temperature in the furnace;

[0025] And / or, in the densified surface layer, an atmospheric pressure micro-pulse plasma jet driven by a micro-pulse power supply uses N2 gas, Ar gas, or a mixture of N2 gas and Ar gas as the working gas, with a power of 20-150W and a nozzle distance of 10-25mm from the coating surface.

[0026] Furthermore,

[0027] The solid resin matrix layer is prepared from the following raw materials in the following weight ratio: 100 parts epoxy resin, 15 parts silicone resin, 0.5 parts silane coupling agent, and 2 parts curing agent.

[0028] And / or, in the silicon-rich transition layer, the volume percentage of Ar in the mixed gas is 99.5%, and the volume percentage of O2 is 0.5%; the volume ratio of organosilicon precursor vapor to mixed gas is 1:100;

[0029] And / or, in the oriented boron nitride sheets, the precursor source gas consists of 10-50 sccm boron trichloride and 10-50 sccm ammonia, and the carrier gas is 50-100 sccm Ar.

[0030] And / or, in the boron nitride gradient insulating layer, the boron nitride-containing resin sol-gel coating of each sublayer is prepared from a coating sol made of silane coupling agent surface-modified hexagonal boron nitride, epoxy resin prepolymer, silica sol, curing agent, and anhydrous ethanol, and then cured after coating; wherein the mass percentages of silane coupling agent surface-modified hexagonal boron nitride, epoxy resin prepolymer, silica sol, curing agent, and anhydrous ethanol in the raw materials are 1-40wt%, 40-79wt%, 15wt%, 2wt%, and 3wt%, respectively; preferably, the mass percentages of silane coupling agent surface-modified hexagonal boron nitride, epoxy resin prepolymer, silica sol, curing agent, and anhydrous ethanol in the raw materials are 5-30wt%, 50-75wt%, 15wt%, 2wt%, and 3wt%, respectively.

[0031] And / or, in the densified surface layer, the curing conditions are: heating to 120°C at a rate of 1°C / min and holding for 2 hours, then continuing to heat to 160°C at a rate of 1°C / min and holding for 3 hours, and finally cooling to room temperature in the furnace;

[0032] And / or, in the densified surface layer, an atmospheric pressure micro-pulse plasma jet driven by a micro-pulse power supply uses N2 gas as the working gas, has a power of 80W, and the distance between the nozzle and the coating surface is 15mm.

[0033] Furthermore,

[0034] In the solid resin matrix layer, the epoxy resin is bisphenol A type epoxy resin, the organosilicon resin is hydroxyl silicone oil, the silane coupling agent is selected from any one or a combination of γ-aminopropyltriethoxysilane, methyltriethoxysilane, and vinyltriethoxysilane, and the curing agent is dibutyltin dilaurate; preferably, the epoxy resin is bisphenol A type epoxy resin E51; preferably, the silane coupling agent is selected from γ-aminopropyltriethoxysilane;

[0035] And / or, in the silicon-rich transition layer, the organosilicon precursor is selected from tetraethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, or combinations thereof; preferably, the organosilicon precursor is selected from tetraethoxysilane;

[0036] And / or, in the oriented boron nitride sheets, the precursor source gas consists of 10 sccm boron trichloride and 30 sccm ammonia, and the carrier gas is 50 sccm Ar.

[0037] And / or, in the boron nitride gradient insulating layer, the silane coupling agent in the silane-modified hexagonal boron nitride is selected from any one or a combination of γ-aminopropyltriethoxysilane, methyltriethoxysilane, and vinyltriethoxysilane; the epoxy resin prepolymer is a bisphenol A type epoxy resin prepolymer; the silica sol is a neutral silica sol; and the curing agent is dibutyltin dilaurate. Preferably, the epoxy resin prepolymer is a bisphenol A type epoxy resin E51 prepolymer. Preferably, the silane coupling agent is selected from γ-aminopropyltriethoxysilane.

[0038] And / or, in the densified surface layer, the surface temperature of the coating is controlled at 60-120℃ during the processing.

[0039] Furthermore,

[0040] The method for preparing the solid resin matrix layer includes the following steps:

[0041] (1) Preheat the epoxy resin in a constant temperature environment of 50-60℃;

[0042] (2) Add silicone resin to the epoxy resin system and stir to mix the two resins;

[0043] (3) Add silane coupling agent to the system obtained in step (2) and continue stirring to make the coupling agent uniformly dispersed in the mixed system;

[0044] (4) Add curing agent to the system obtained in step (3), stir and then degas under vacuum to obtain resin matrix coating;

[0045] (5) The resin matrix coating obtained in step (4) is applied to the surface of the metal conductor to form a resin matrix layer with a thickness of 80-100 μm.

[0046] (6) Pre-cure the metal conductor coated with resin matrix coating, then clean and dry it;

[0047] And / or, in the silicon-rich transition layer, the working power of the atmospheric pressure plasma jet is set to 50-300W, the distance between the nozzle and the sample surface is 5-15mm, the scanning speed is 10-50mm / s, and the sample surface is scanned 1-5 times; the working frequency of the AC high voltage power supply is 10-60kHz, and the output voltage is 5-30kV.

[0048] And / or, in the oriented boron nitride sheet, the deposition time is 30-60 min, and the vacuum is drawn to below 10 Pa before deposition;

[0049] And / or, in the boron nitride gradient insulating layer, the curing is performed at 80-100°C for 1-3 hours; preferably, the curing is performed at 80°C for 1.5 hours.

[0050] And / or, in the densified surface layer, the atmospheric pressure micro-pulse plasma jet scanning speed is 10-50 mm / s, and the total processing time is 5-120 s.

[0051] Furthermore,

[0052] In the preparation method of the solid resin matrix layer, in step (5), the resin matrix coating obtained in step (4) is coated on the surface of the metal conductor by vacuum casting; in step (6), the pre-curing conditions are: first, heat at 80-100℃ for 1-3 hours, then heat to 90-110℃ for 0.5-1 hour, and finally heat to 100-120℃ for 0.5-1 hour; in step (6), the drying temperature is 80-100℃; preferably, the specific conditions for vacuum casting are: vacuum degree controlled at 1×10 -2 Pa, pouring temperature 65℃, pouring pressure 0.12MPa, pouring speed 5mL / min;

[0053] And / or, in the silicon-rich transition layer, the working power of the atmospheric pressure plasma jet is set to 100W, the distance between the nozzle and the sample surface is 10mm, the scanning speed is 20mm / s, and the sample surface is scanned three times; the effective gas temperature of the plasma jet contacting the sample surface is about 240℃; the ordinary AC high-voltage power supply driving the atmospheric pressure plasma jet operates at a frequency of 25kHz and has an output voltage of 15kV;

[0054] And / or, in the oriented boron nitride sheet layer, the method to achieve the orientation of hexagonal boron nitride nanosheets along the thickness direction is as follows: the radio frequency bias voltage is adjusted to -80V, a parallel plate electrode structure is adopted, the sample is fixed on the lower electrode, the upper electrode is connected to the radio frequency power supply, and the electric field direction is made perpendicular to the sample surface by adjusting the electrode spacing to 50mm.

[0055] And / or, in the oriented boron nitride sheet layer, the average angle between the normal of the boron nitride nanosheet in the thickness direction and the coating thickness direction is less than 20°;

[0056] And / or, in the densified surface layer, the atmospheric pressure micro-pulse plasma jet scanning speed is 30 mm / s, and the total processing time is 60 s.

[0057] The aforementioned functional insulating material, through the silicon-rich transition layer formed by the first plasma treatment and the dense surface layer formed by the second plasma treatment, together with the intermediate oriented boron nitride sheet layer and the boron nitride volume fraction gradient insulating layer, constructs a gradient insulating structure that continuously changes from the resin matrix layer to the high-voltage side of the transformer. Under the action of high-frequency non-sinusoidal voltage, it exhibits a synergistic effect of space charge injection suppression, electric field stress homogenization, and heat flow path guidance.

[0058] The present invention also provides a method for preparing the aforementioned functional insulating material, comprising the following steps:

[0059] (a) Preparation of solid resin matrix layer: A resin matrix coating is applied to the surface of a metal conductor to form a resin matrix layer. The metal conductor after coating with the resin matrix coating is pre-cured, then cleaned and dried to obtain the solid resin matrix layer.

[0060] (b) Preparation of silicon-rich transition layer: The sample obtained in step (a) is placed in an atmospheric pressure plasma jet device driven by an AC high voltage power supply. In an atmosphere containing organosilicon precursor, plasma treatment is performed by jet scanning or cavity glow discharge. Simultaneous decontamination and activation and plasma pyrolysis deposition of organosilicon precursor are achieved on the surface of the solid resin matrix layer to form a silicon-rich transition layer containing SiOx or SiOxNy.

[0061] (c) Preparation of oriented boron nitride sheets: The sample obtained in step (b) is placed in a plasma-enhanced chemical vapor deposition chamber. Under the conditions of radio frequency power of 50-400W, substrate temperature of 200-600℃ and pressure of 5-100Pa, a precursor gas and carrier gas containing B and N elements are introduced. Hexagonal boron nitride sheets are deposited in situ on the surface of the silicon-rich transition layer by plasma-enhanced chemical vapor deposition. During the deposition process, an electric field perpendicular to the substrate surface and / or the plasma sheath potential are applied to induce the hexagonal boron nitride nanosheets to align along the coating thickness direction.

[0062] (d) Preparation of boron nitride gradient insulating layer: Prepare 2-10 kinds of coating sols containing boron nitride nanosheets according to a preset boron nitride concentration. Coat the sols sequentially on the oriented boron nitride sheet layer in order of decreasing boron nitride concentration from the inner layer to the outer layer. After each coating sol is coated, it is cured first, and then the next coating sol is coated and cured. Finally, a boron nitride gradient insulating layer is obtained on the oriented boron nitride sheet layer. The curing is performed at 80-100℃ for 1-3 hours. Preferably, the curing is performed at 80℃ for 1.5 hours.

[0063] (e) Gradient temperature curing: The sample obtained in step (d) is subjected to gradient temperature curing. The curing conditions are as follows: the temperature is increased to 100-130℃ at a rate of 0.5-2℃ / min and held for 1-3 hours, then the temperature is increased to 150-180℃ at a rate of 0.5-2℃ / min and held for 2-4 hours, and finally cooled to room temperature in the furnace; the resin phase is cross-linked, the sol-gel system is polycondensed, and a gradient insulating layer is formed integrally with the silicon-rich transition layer and the oriented boron nitride sheet layer.

[0064] (f) Preparation of the densified surface layer: The sample obtained in step (e) is placed in an atmospheric pressure micro-pulse plasma jet device or a micro-pulse dielectric barrier discharge device driven by a micro-pulse power supply. It is treated at a power of 20-150W under an atmosphere of N2, Ar, or a mixture of N2 and Ar gases. During treatment, the distance between the nozzle and the coating surface is 10-25mm, the treatment time is 5-120s, and the coating surface temperature is controlled at 60-120℃. The high electron density, low temperature, and low destructiveness of micro-pulse plasma are utilized to achieve surface cross-linking densification and removal of weak interface layers, forming an inorganic-rich densified surface layer, thus creating a multilayer composite functional insulating material.

[0065] The present invention also provides the use of the aforementioned functional insulating material in the manufacture of high-frequency transformers.

[0066] This invention also provides the use of the aforementioned functional insulating material in the manufacture of high-frequency transformers for ultra-high-speed trains. The insulating material is disposed in the winding end gaps, the output terminal area, and the interface between the core clamp and the winding of the high-frequency transformer. This improves the electro-thermal coupling insulation performance of these areas under combined conditions of ultra-high-speed start-up and shutdown impacts, strong harmonic non-sinusoidal voltage, and local overheating, reduces the risk of partial discharge and space charge accumulation, and extends the insulation life and operational reliability of the high-frequency transformer.

[0067] The aforementioned functional insulating material, through the silicon-rich transition layer formed by the first plasma treatment and the dense surface layer formed by the second plasma treatment, together with the intermediate oriented boron nitride sheet layer and the boron nitride volume fraction gradient insulating layer, constructs a gradient insulating structure that continuously changes from the resin matrix layer to the high-voltage side of the transformer. Under the action of high-frequency non-sinusoidal voltage, it exhibits a synergistic effect of space charge injection suppression, electric field stress homogenization, and heat flow path guidance.

[0068] Through the above-mentioned dual-plasma synergistic construction, oriented boron nitride in-situ enhancement, and dielectric gradient structure design, this invention achieves coordinated control of the high-frequency electro-thermal field, thereby significantly improving the insulation performance and service life of the high-frequency transformer under the harsh operating conditions of ultra-high-speed trains.

[0069] Compared with existing technologies that use homogeneous resin insulation or simple blended boron nitride insulation materials, the present invention has the following advantages:

[0070] Dual plasma processes synergistically construct a "stable interface + dense surface".

[0071] The first step, high-voltage plasma, utilizes its high energy, high temperature, and high etching properties to decompose and deposit the silicon-based precursor, forming a silicon-rich SiOx / SiOxNy transition layer. This significantly improves the interfacial adhesion, reduces interfacial thermal resistance, and weakens electric field distortion. The second step, micro-pulse plasma, with its low temperature and high electron density, achieves surface cross-linking and densification, removes weak interfacial layers, and enriches inorganic networks, thereby significantly improving resistance to electrical erosion, arcing, and partial discharge. The upper and lower functional layers formed by these two plasma treatments constitute a synergistic system of interfacial reinforcement and surface protection, greatly enhancing structural stability.

[0072] Oriented boron nitride sheets provide efficient thermal diffusion pathways

[0073] The orientation h-BN sheets deposited in situ using the PECVD process form a continuous high thermal conductivity network in a direction parallel to the transformer structure surface. This allows the heat from hot spots to diffuse rapidly along the ends and inflection points, effectively reducing the temperature rise of hot spots under high-frequency load fluctuations and short-term overload conditions, and avoiding early insulation aging caused by local heat accumulation.

[0074] Gradual modulation of dielectric constant achieved by boron nitride volume fraction gradient

[0075] A resin sol with varying boron nitride content was prepared using the sol-gel method, and then coated and cured in layers along the thickness direction to create a continuous dielectric constant gradient in the insulation layer. The higher dielectric constant on the high-voltage side helps alleviate electric field concentration, while the lower dielectric constant on the low-voltage side helps maintain the stability of the overall capacitance characteristics of the insulation system, thereby enabling flexible control of the electric field distribution under high-frequency non-sinusoidal voltages.

[0076] Suppressing space charge accumulation and electro-thermal coupling failure

[0077] The synergistic effect of the orientation h-BN functional layer and the dielectric degree layer can reduce the local interface electric field strength and charge injection rate, while reducing the local temperature rise by enhancing the thermal diffusion capability. This suppresses the accumulation and migration of space charge inside the insulation layer, effectively delays the occurrence and development of electrical trees and partial discharge, and significantly improves the high-frequency insulation lifetime.

[0078] Overall electrical performance has been significantly improved.

[0079] Under typical 5-20kHz non-sinusoidal voltage conditions, compared with comparative materials that do not employ in-situ boron nitride layers and dielectric gradient structures, the material of this invention exhibits a breakdown field strength that can be increased by approximately 15-25%, a partial discharge initiation voltage that can be increased by 10-20%, a hot spot temperature rise that can be reduced by approximately 10-20℃, and a significant decrease in dielectric loss, demonstrating excellent comprehensive electrical and thermal performance.

[0080] The process is controllable and suitable for engineering applications.

[0081] The plasma treatment, PECVD deposition, and sol-gel gradient coating processes used in this invention are all mature and controllable industrial technologies with clear process parameter windows. They are suitable for local functional insulation enhancement in high-frequency transformer winding end insulation components, prefabricated insulation boards, and integral winding casting structures, and have good engineering feasibility and prospects for widespread application.

[0082] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0083] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Detailed Implementation

[0084] The raw materials and equipment used in the specific embodiments of the present invention are all known products, obtained by purchasing commercially available products.

[0085] Example 1: Preparation of functional insulating materials with dual plasma treatment and a three-layer gradient structure

[0086] (1) Matrix preparation and pretreatment

[0087] An epoxy resin / silicone resin mixture system was selected. The epoxy resin used was bisphenol A type epoxy resin E51 (model: E51-1, industrial grade, conforming to the national standard "Test Methods for Plastic Epoxy Resins" GB / T 41929-2022) produced by Daosheng Tianhe Materials Technology (Shanghai) Co., Ltd. The silicone resin used was hydroxyl silicone oil (model: JP-1000, industrial grade, molecular weight approximately 860) produced by Zaoyang Jinpeng Chemical Co., Ltd. The silane coupling agent used was γ-aminopropyltriethoxysilane (model: KH550, industrial grade) produced by Nanjing Coupling Agent Factory. The curing agent used was dibutyltin dilaurate (model: T-12, industrial grade) produced by Nantong Aidewang Chemical Co., Ltd. Preliminary screening showed that this curing agent can effectively promote the crosslinking reaction between epoxy resin and silicone resin, and improve the adhesion strength and insulation performance of the matrix layer.

[0088] The specific amounts of the matrix resin formulation by weight are as follows: 100 parts epoxy resin E51, 15 parts silicone resin JP-1000, 0.5 parts silane coupling agent KH550, and 2 parts curing agent T-12. The above proportions are optimized to balance the fluidity of the matrix (facilitating vacuum casting) and the performance after curing (meeting the insulation, withstand voltage, and heat dissipation requirements of high-frequency transformers). At the same time, the addition of silane coupling agent KH550 improves the compatibility between epoxy resin and silicone resin, avoids delamination, and further optimizes the mechanical properties and aging resistance of the matrix.

[0089] The matrix resin is not simply a mixture of the four raw materials mentioned above. The specific preparation process is as follows: First, epoxy resin E51 is preheated in a constant temperature environment of 60℃ for 30 minutes to reduce its viscosity and improve the uniformity of mixing. Then, silicone resin JP-1000 is added and mixed for 20 minutes under stirring at 300 r / min to ensure that the two resins are fully fused. Next, silane coupling agent KH550 is added and stirring is continued for 15 minutes to ensure that the coupling agent is evenly dispersed in the mixture and plays a bridging role to improve the subsequent adhesion performance between the matrix and the copper conductor. Finally, curing agent T-12 is added and stirred for 10 minutes. Then, it is placed in a vacuum stirrer for degassing for 15 minutes (vacuum degree -0.09MPa) to remove the bubbles generated during the mixing process and avoid bubbles affecting the insulation performance and density of the matrix layer, resulting in a uniform and bubble-free matrix resin formulation. This preparation process can ensure that each raw material reacts fully and avoids performance defects caused by simple mixing.

[0090] The copper conductor sample was made of T2 pure copper (pure copper, purity ≥99.9%, conforming to the national standard GB / T 4423-2020 "Drawn Rods of Copper and Copper Alloys"), suitable for high-frequency transformer conductor applications, possessing both excellent conductivity and processing performance. The prepared matrix resin was coated onto the surface of the copper conductor sample via vacuum casting, forming a resin matrix layer approximately 80 μm thick. Specific vacuum casting parameters were as follows: a ZG-25 type vacuum induction melting furnace (suitable for small sample casting, manufactured by Jinzhou Electric Furnace Co., Ltd.) was used, and the vacuum level of the casting environment was controlled at 1×10⁻⁶. -2 The pouring conditions are as follows: Pa, pouring temperature 65℃, pouring pressure 0.12MPa, pouring speed 5mL / min; during the pouring process, the temperature difference is controlled by an intelligent system within ±0.5℃ to ensure stable resin flow and avoid problems such as sagging and uneven thickness. At the same time, it ensures a tight fit between the substrate layer and the copper conductor surface, with no gaps or pinhole defects, which meets the molding requirements of high-frequency transformer insulation layers.

[0091] After casting, the copper conductor sample is placed in a constant temperature oven and a gradient pre-curing process is adopted: first, it is kept at 80℃ for 1 hour, then the temperature is raised to 90℃ and kept for 0.5 hours, and finally the temperature is raised to 100℃ and kept for 0.5 hours, with a total pre-curing time of 2 hours. This gradient pre-curing process can avoid the resin from generating internal stress due to excessive heating, ensure that the resin is fully cross-linked and formed, and prevent the substrate layer from falling off or deforming during subsequent cleaning and plasma treatment. After pre-curing, it is taken out for use.

[0092] The pre-cured samples were ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each (ultrasonic power 200W, ultrasonic frequency 40kHz) to remove uncured resin residue and impurities from the sample surface. After cleaning, the samples were placed in an 80℃ constant temperature oven for 30 minutes to ensure that there was no moisture residue on the surface. After drying, the samples were quickly placed in an atmospheric pressure plasma jet device to prepare for subsequent processing.

[0093] (2) First plasma treatment and formation of silicon-rich transition layer

[0094] The pretreated resin matrix was placed in an atmospheric pressure plasma jet device driven by a standard AC high-voltage power supply. The AC high-voltage power supply was set to a working frequency of 25 kHz and an output voltage of 15 kV, under which conditions a stable AC plasma jet with high gas temperature and strong activation capability could be generated. The working gas was a mixture of Ar / 0.5% O2 (O2 volume percentage 0.5%, Ar volume percentage 99.5%), with tetraethoxysilane (TEOS) vapor introduced as a silicon-based precursor. The volume ratio of TEOS vapor to the mixed gas was 1:100. The jet power was set to 120 W, the nozzle-sample surface distance was 10 mm, the scanning speed was 20 mm / s, and the sample surface was scanned three times, with a total processing time of approximately 60 s. Under the above operating conditions, the effective gas temperature of the plasma jet in contact with the sample surface was approximately 240 °C.

[0095] Under the influence of a strong electric field, high temperature, and high-energy electron bombardment from AC high-voltage plasma, TEOS molecules undergo cleavage, oxidation, and transformation into SiOx species. Simultaneously, the weak surface binding layer is etched away, and reactive oxygen species promote the rapid deposition of the Si-O network. The deposited SiOx structure forms a silicon-rich transition layer with a thickness of approximately 65 nm on the substrate surface. This transition layer has a continuous and uniform inorganic framework structure, which can significantly improve the degree of interface activation, chemical bonding ability, and the adhesion reliability of subsequent coatings.

[0096] (3) Oriented boron nitride sheet plasma-enhanced chemical vapor deposition (PECVD) deposition

[0097] The sample treated with the first plasma was transferred to the PECVD chamber and evacuated to below 10 Pa. Boron trichloride (10 sccm) and ammonia (30 sccm) were introduced, with Ar as the carrier gas (50 sccm). The RF power was set to 200 W, the substrate temperature to 450 °C, and the working pressure to 20 Pa. Deposition was carried out for 30 min to form an h-BN sheet structure with a thickness of approximately 300 nm. The h-BN nanosheets were aligned along the thickness direction by adjusting the RF bias and electric field direction. Specifically, the RF bias was adjusted to -80 V, a parallel plate electrode structure was used, the sample was fixed to the lower electrode, and the upper electrode was connected to the RF power supply. By adjusting the electrode spacing to 50 mm, the electric field direction was made perpendicular to the sample surface (i.e., along the coating thickness direction). The polarization effect of the electric field on the h-BN nanosheets was used to guide the average angle between the sheet normal and the coating thickness direction to be less than 20°.

[0098] (4) Boron nitride powder modification and gradient sol preparation

[0099] Commercially available h-BN powder was selected, with the following specific parameters: particle size 500 nm, purity ≥99.8%, lamellar thickness 10-15 nm, and specific surface area 15-20 m² / g. 2 / g, purchased from Aladdin Reagent (Shanghai) Co., Ltd., model: B110647; Take 10g of this h-BN powder and treat it in 100mL of 2wt% aminopropyltriethoxysilane (KH550) hydrolysis solution (this hydrolysis solution is an aqueous solution containing 2wt% KH550, the specific preparation method is: take 2g of KH550 (Nanjing Coupling Agent Factory, model: KH550, industrial grade), slowly add it to 98mL of deionized water, stir for 30min until completely dissolved, and obtain a homogeneous hydrolysis solution).

[0100] The specific processing method and parameters are as follows: h-BN powder is added to the above hydrolysis solution and placed in a constant temperature water bath. The water bath temperature is controlled at 60℃, and mechanical stirring at 400r / min is used for 2 hours. During this period, ultrasonic-assisted dispersion is performed for 5 minutes every 30 minutes (ultrasonic power 300W, ultrasonic frequency 40kHz) to ensure that the KH550 hydrolysis products are fully grafted onto the surface of h-BN powder. After the treatment is completed, the powder is washed three times by centrifugation with deionized water (centrifugation speed 8000r / min, centrifugation time 10min / time) to remove ungrafted KH550 and impurities. Then, it is dried in a constant temperature oven at 105℃ for 4 hours to obtain surface-modified BN powder. This modification method can improve the compatibility of BN powder with the resin system.

[0101] Three resin sols were prepared according to the formula:

[0102] Sol A: BN powder mass fraction 25 wt%;

[0103] Sol B: 15 wt% BN powder;

[0104] Sol C: BN powder mass fraction 5wt%.

[0105] In this embodiment, the gradient setting of BN mass fraction from 25wt% to 15wt% to 5wt% is not a simple concentration increase / decrease design as is common in the art. Instead, it is a specific gradient obtained through comprehensive optimization in deep synergy with the dual plasma processing technology of this invention. The two together constitute the inventive core of this invention, as explained in detail below:

[0106] (4-1) Creative design logic of gradient concentration: Combining the core requirements of "concentrated electric field near conductor side, strong thermal conductivity / breakdown resistance, and low stress / high density on the surface" of high-frequency transformer winding ends, the process characteristics of dual plasma treatment are precisely matched, rather than randomly selecting the concentration:

[0107] (4-1-1) Sol A (25wt% high BN concentration): Corresponds to the silicon-rich transition layer and PECVD in-situ h-BN sheet formed after the first plasma treatment. The high BN content can form a continuous thermal conduction path with the in-situ h-BN sheet, enhance the heat dissipation capacity and electro-erosion resistance of the near conductor side, and lay a good inorganic skeleton foundation for the subsequent second plasma surface strengthening. This concentration is the critical filling amount for high thermal conductivity and high insulation. If the concentration is lower than this, it cannot form an effective thermal conduction network with the in-situ h-BN layer. If the concentration is higher than this, the sol viscosity will increase dramatically, making it unsuitable for spin coating process and prone to coating defects, excessive interface stress and other problems.

[0108] (4-1-2) Sol B (15wt% BN concentration): As a transition layer, its concentration is designed to match the activity gradient of the interface after dual plasma treatment, which ensures a tight bond with the inner high BN layer, avoids abrupt changes in thermal conductivity and insulation performance, makes the electric field distribution at the winding end transition smoothly, weakens the local electric field concentration, and provides a good bonding substrate for the outer low BN layer.

[0109] (4-1-3) Sol C (5wt% low BN concentration): As a surface layer, the low BN content can reduce the surface roughness of the coating, reduce surface defects before the second plasma treatment, and at the same time improve the bonding force with the dense inorganic-rich layer formed after the second plasma strengthening; the low inorganic content can also reduce surface stress, avoid coating cracking, and take into account both surface density and mechanical compatibility.

[0110] (4-2) Synergistic Inventiveness of Dual Plasma Technology and Gradient Structure: This invention does not simply superimpose dual plasma treatment with gradient coating, but achieves synergistic effect between the two, which is different from the conventional technical solutions in the field of "single plasma treatment + conventional coating" or "no plasma treatment + gradient coating":

[0111] (4-2-1) The silicon-rich transition layer formed by the first plasma treatment can accurately match the concentration gradient of the gradient coating, improve the interfacial bonding strength between the gradient layer and the substrate, and solve the technical pain point of easy delamination of conventional gradient coatings. At the same time, the inorganic skeleton structure of the silicon-rich transition layer can guide the uniform dispersion of BN powder in the gradient coating and optimize the electric field distribution in synergy with the gradient concentration.

[0112] (4-2-2) The second plasma treatment modifies the surface layer (5wt% low BN concentration) of the gradient coating, which can promote further cross-linking of surface resin segments and Si-O-Si network condensation to form a dense inorganic structure layer. Without increasing the coating thickness, it can synergistically improve the material's resistance to electrical erosion and arc breakdown with the gradient structure, achieving the dual effect of "gradient insulation + plasma strengthening".

[0113] In summary, the three-stage gradient design of 25wt%-15wt%-5wt% in this embodiment is an original design that is deeply adapted to dual plasma processing technology, rather than a conventional choice in the field. The synergistic effect of the two enables the material to achieve optimal matching among insulation strength, partial discharge suppression, heat dissipation uniformity, and mechanical compatibility, which is significantly different from the existing technology.

[0114] Each sol contains epoxy resin prepolymer, silica sol, curing agent and appropriate amount of anhydrous ethanol (anhydrous ethanol, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd., model: 10009218). The sol is dispersed by ultrasonication + high-speed shearing for 30 min to obtain a uniform and stable sol. The specific parameters are: ultrasonic power 350W, ultrasonic frequency 40kHz, high-speed shearing speed 3000r / min, and ultrasonication and shearing are alternated (5 min of ultrasonication, 5 min of shearing, 3 cycles).

[0115] The specific types of each substance are as follows:

[0116] Epoxy resin prepolymer: Bisphenol A type epoxy resin prepolymer (model: E51-prepolymer, industrial grade, from the same manufacturer and series as the epoxy resin used in the matrix preparation mentioned above, to ensure system compatibility) was selected from Daosheng Tianhe Materials Technology (Shanghai) Co., Ltd.

[0117] Silica sol: Neutral silica sol produced by Qingdao Ocean Chemical Co., Ltd. (model: 30%N, industrial grade, solid content 30%, particle size 10-20nm).

[0118] Curing agent: Dibutyltin dilaurate (model: T-12, industrial grade, the same as the curing agent used in the matrix preparation mentioned above, to ensure uniform curing effect) produced by Nantong Aidewang Chemical Co., Ltd.

[0119] Table 1. Specific Formulation of Resin Sol

[0120]

[0121] (5) Gradient coating and pre-curing

[0122] The sample obtained in step (3) was fixed on a spin coating apparatus. First, sol A was coated to form a high BN layer with a thickness of about 50 μm, and pre-cured at 80 °C for 1.5 h. Then, sol B was coated to form a medium BN layer with a thickness of about 50 μm, and pre-cured at 80 °C for 1.5 h. Finally, sol C was coated to form a low BN layer with a thickness of about 50 μm, and the pre-curing conditions were the same. A boron nitride volume fraction gradient insulating layer with a total thickness of about 150 μm was obtained.

[0123] (6) Multi-stage curing and second plasma surface strengthening

[0124] The gradient coating structure was cured using a multi-stage curing regime: the temperature was increased to 120℃ at a rate of 1℃ / min and held for 2 hours, followed by a further increase to 160℃ at a rate of 1℃ / min and held for 3 hours. The furnace was then shut off and cooled to room temperature to allow the resin phase to fully crosslink and form a stable organic-inorganic hybrid gradient structure. After curing, the sample was placed in an atmospheric pressure micro-pulse plasma jet device driven by a micro-pulse power supply, using N2 as the working gas, with the jet power set to 80W, the nozzle-sample surface distance to be 15mm, the scanning speed to be 30mm / s, and the total processing time to be 60s. Micro-pulse plasma has low gas temperature and high transient electron density, which can promote further cross-linking of resin segments on the outer surface of the gradient layer and Si-O-Si network condensation. At the same time, it removes weakly bound organic matter, so that a dense inorganic structure layer with a thickness of about 100nm is formed on the surface (Note: This 100nm dense inorganic structure layer is not a new coating, but a densification layer formed by surface modification of the outermost layer (sol C coating layer) of the gradient insulating layer through a second plasma treatment. That is, after the outermost layer of the gradient insulating layer is treated, the surface thickness within 100nm is transformed into a dense inorganic structure without increasing the total thickness of the coating).

[0125] This densified surface layer significantly improves the material's resistance to electrical erosion, arc breakdown, and partial discharge. The final multilayer composite functional insulating material has a total thickness of approximately 230 μm (total thickness composition: from the inside out, it consists of an 80 μm resin matrix layer, a 65 nm silicon-rich transition layer, a 300 nm in-situ oriented h-BN sheet, and a 150 μm boron nitride volume fraction gradient insulating layer (including a 50 μm high BN layer, a 50 μm medium BN layer, and a 50 μm low BN layer). The 65 nm silicon-rich transition layer and the 300 nm in-situ oriented h-BN sheet are extremely thin (totaling only 365 nm, approximately 0.365 μm), which are negligible compared to the 150 μm gradient insulating layer and the 80 μm resin matrix layer. Therefore, the overall description is a total thickness of approximately 230 μm, but the actual precise total thickness is 230.365 μm.

[0126] The performance of the functional insulating material prepared above was characterized. The detection method and results of the insulating material of the present invention under a 10kHz non-sinusoidal voltage for breakdown field strength, partial discharge initiation voltage, and hot spot temperature rise in the simulated structure at the winding end are shown below:

[0127] 1. Breakthrough field strength

[0128] (1) Characterization method: The insulating material sample was prepared as a standard sample (50 mm in diameter and 230 μm in thickness) using the plate electrode method. It was clamped between two plate electrodes and the voltage was increased at a rate of 1 kV / s under a non-sinusoidal voltage of 10 kHz until the sample broke down. The voltage value at the time of breakdown was recorded, and the breakdown field strength was calculated in combination with the sample thickness (breakdown field strength = breakdown voltage / sample thickness).

[0129] (2) Testing standard: Complies with GB / T 1408.1-2016 "Test methods for electrical strength of solid insulating materials - Part 1: Test at power frequency";

[0130] (3) Specific values: The breakdown field strength of the insulating material of the present invention is 28.5 kV / mm; the breakdown field strength of the blank control material (only an 80 μm resin matrix layer + 150 μm ordinary resin coating, i.e. the material prepared in Comparative Example 1) without in-situ BN and gradient structure is 24.0 kV / mm.

[0131] (4) Improvement: The breakdown field strength of the material of the present invention is increased by about 18.75% compared with the blank control material.

[0132] 2. Partial discharge initiation voltage

[0133] (1) Characterization method: The pulse current method was used. The sample was placed in a standard test fixture using a partial discharge tester. A non-sinusoidal voltage of 10 kHz was applied and the voltage was slowly increased. The voltage value at which the partial discharge signal was first detected (discharge amount ≥ 10 pC) was recorded, which is the partial discharge initiation voltage.

[0134] (2) Testing standard: Complies with the requirements for partial discharge testing in GB / T 1094.6-2011 "Power Transformers Part 6: Reactors";

[0135] (3) Specific values: The partial discharge initiation voltage of the insulating material of the present invention is 3.3kV; the partial discharge initiation voltage of the blank control material (the material prepared in Comparative Example 1) is 2.9kV;

[0136] (4) Improvement level: The partial discharge initiation voltage of the material of the present invention is increased by about 13.79% compared with the blank control material.

[0137] 3. Temperature rise of hot spots in the simulated structure at the winding end

[0138] (1) Characterization method: A simulated structure of the winding end of a high-frequency transformer was constructed. The insulating material of this invention and the blank control material (the material prepared in Comparative Example 1) were applied to the simulated structure respectively. A high-frequency current of 10kHz was introduced and the current density was controlled to be 5A / mm². 2 After running for 2 hours, the temperature of the hot spot at the end of the winding was measured using an infrared thermometer (accuracy ±0.1℃), and the hot spot temperature rise was calculated (hot spot temperature rise = hot spot temperature - ambient temperature, and the ambient temperature was controlled at 25℃).

[0139] (2) Testing standard: It shall comply with the relevant requirements for winding temperature rise testing in GB / T 1094.2-2013 "Power Transformers Part 2: Temperature Rise of Liquid-Immersed Transformers";

[0140] (3) Specific values: After the application of the insulating material of the present invention, the temperature rise of the hot spot in the simulated structure at the winding end is 62°C; after the application of the blank control material, the temperature rise of the hot spot is 73°C.

[0141] (4) Improvement: The material of the present invention can reduce the temperature rise of hot spots by about 15.07% compared with the blank control material.

[0142] Example 2: Preparation of a functional insulating material with a four-layer gradient structure

[0143] In this embodiment, the gradient layer was changed from 3 layers to 4 layers. The remaining process conditions were basically the same as in Example 1, except that the BN content and coating order of the gradient sol were adjusted. The formulations of sol A'-sol D' are shown in Table 2.

[0144] Sol A': BN mass fraction 30 wt%

[0145] Sol B': BN mass fraction 20 wt%

[0146] Sol C': BN mass fraction 10 wt%

[0147] Sol D': BN mass fraction 5wt%.

[0148] In this embodiment, the four-layer gradient setting of BN mass fraction from 30wt% to 20wt% to 10wt% to 5wt% is an original design that further refines and optimizes the three-stage gradient based on Embodiment 1, combined with the synergistic characteristics of dual plasma processing technology. This further highlights the inventiveness of the present invention, as detailed below:

[0149] 1. Creative optimization logic of four-layer gradient concentration: Based on the collaborative design of Example 1, for scenarios with complex three-dimensional electric field distortion at the end of high-frequency transformers, the concentration gradient is further refined to accurately match the interface modification effect of dual plasma treatment:

[0150] (1) Sol A (30wt% higher BN concentration): further enhances the thermal conductivity and breakdown resistance of the near conductor side, and works in synergy with the silicon-rich transition layer formed by the first plasma treatment and the PECVD in-situ h-BN sheet to build a more complete continuous thermal conductivity network, more efficiently disperse the concentrated electric field on the near conductor side, and adapt to the use requirements of high power high frequency transformers; this concentration is optimized to avoid sol coating defects caused by excessive BN content, and at the same time, it is precisely matched with the interfacial activity after the first plasma treatment to improve the inner layer bonding strength.

[0151] (2) Sol B (20wt%) and Sol C (10wt%) two-stage transition layer: Compared with the single transition layer in Example 1, the two-stage transition layer more accurately matches the active gradient of the interface after dual plasma treatment, so that the electric field distribution and thermal conductivity can achieve a smoother transition, further weaken the electric field concentration phenomenon at the winding end, and reduce the hidden danger of partial discharge; at the same time, the two-stage transition layer can reduce the interfacial stress between the gradient layers, avoid coating cracking caused by the increase in thickness, and form a synergy with the second plasma surface strengthening to improve the overall density of the material.

[0152] (3) Sol D (5wt% low BN concentration): Continuing the surface design of Example 1, it ensures good bonding with the second plasma enhancement layer, while maintaining the low stress and high density characteristics of the surface layer, avoiding electric field concentration caused by surface defects, and optimizing the surface performance in conjunction with the dual plasma treatment.

[0153] 2. Enhanced synergy with dual-plasma technology: The synergistic effect of the four-layer gradient structure and dual-plasma treatment is more significant than in Example 1, demonstrating the progressiveness and inventiveness of the technical solution of this invention.

[0154] (1) The silicon-rich transition layer formed by the first plasma treatment can guide the gradient dispersion of BN powder in the four-layer gradient coating, avoid the problem of uneven dispersion caused by the increase of the number of layers, and at the same time improve the interfacial bonding strength between each gradient layer, solving the technical pain point of easy delamination of conventional multilayer gradient coating.

[0155] (2) The second plasma treatment modifies the surface layer of the four-layer gradient. It can make full use of the low BN concentration of the surface layer to quickly form a dense inorganic structure layer. In synergy with the electric field dispersion effect of the four-layer gradient, it further reduces the peak value of the end electric field and improves the material's resistance to electro-erosion and long-term service stability.

[0156] In summary, the four-stage refined gradient of 30wt%→20wt%→10wt%→5wt% in this embodiment is a further original optimization based on dual plasma processing technology, rather than the conventional selection of the number of layers and concentration in the field. The synergistic effect of the two further improves the insulation, thermal conductivity and mechanical properties of the material, making it more suitable for complex electric field scenarios than Embodiment 1, further demonstrating the inventiveness of the present invention and distinguishing it from the conventional technical combinations of the prior art.

[0157] Table 2. Specific Formulation of Resin Sol

[0158]

[0159] Four layers, A', B', C', and D', were coated sequentially, each with a thickness of approximately 60 μm, for a total thickness of approximately 240 μm.

[0160] After undergoing the same multi-stage curing and second plasma surface strengthening treatment, the material's breakdown field strength, partial discharge initiation voltage, and hot spot temperature rise in the simulated structure at the winding end were tested. The testing methods for each property were the same as in Example 1. The specific test results and comparisons with Example 1 are shown below:

[0161] 1. Breakthrough field strength

[0162] (1) Characterization method and detection standard: consistent with Example 1 (flat plate electrode method, in accordance with GB / T 1408.1-2016).

[0163] (2) Specific values: The breakdown field strength of the insulating material in Example 2 is 31.2 kV / mm; the breakdown field strength in Example 1 is 28.5 kV / mm;

[0164] (3) Improvement level: Compared with Example 1, the breakdown field strength of Example 2 is increased by about 9.47% because the BN content gradient of the four-layer gradient structure is more gradual and the interface compatibility is better, thus further improving the insulation performance.

[0165] 2. Partial discharge initiation voltage

[0166] (1) Characterization method and detection standard: consistent with Example 1 (pulse current method, in accordance with GB / T 1094.6-2011).

[0167] (2) Specific values: The partial discharge initiation voltage of the insulating material in Example 2 was 3.7kV; the partial discharge initiation voltage in Example 1 was 3.3kV;

[0168] (3) Improvement level: Compared with Example 1, the partial discharge initiation voltage of Example 2 is increased by about 12.12%. The four-layer gradient structure effectively weakens the electric field concentration and reduces the risk of partial discharge.

[0169] 3. Temperature rise of hot spots in the simulated structure at the winding end

[0170] (1) Characterization method and testing standard: consistent with Example 1 (infrared thermometry, in accordance with GB / T 1094.2-2013).

[0171] (2) Specific values: After the application of insulating material in Example 2, the temperature rise of the hot spot in the simulated structure at the winding end was 68°C; the temperature rise of the hot spot in Example 1 was 62°C.

[0172] (3) Degree of change: Compared with Example 1, the hot spot temperature rise in Example 2 increased by about 9.68%. Due to the increase in the total thickness of the material and the overall increase in the inorganic BN content, the heat dissipation performance decreased slightly, which is consistent with the performance logic of the four-layer gradient structure.

[0173] Comparative Example 1: Materials without in-situ boron nitride layers and gradient structures

[0174] Preparation of comparative materials: Only a homogeneous epoxy resin / BN blend system was used as the insulating layer. No first plasma silicon-rich transition layer treatment, PECVD in-situ boron nitride deposition and gradient coating were performed. The BN mass fraction was uniformly 15wt%, and the total thickness was close to that of Example 1 (approximately 230μm).

[0175] The specific preparation process of the homogeneous epoxy resin / BN blend system is as follows, which is consistent with the sol preparation system in Example 1, except that the ratio is adjusted to be a homogeneous system and gradient coating is not performed:

[0176] 1. Raw material selection: completely consistent with Example 1, specifically: epoxy resin prepolymer (Daosheng Tianhe Materials Technology (Shanghai) Co., Ltd., bisphenol A type E51-prepolymer, industrial grade), h-BN powder (Aladdin Reagent (Shanghai) Co., Ltd., model B110647, particle size 500nm, purity ≥99.8%), silica sol (Qingdao Haiyang Chemical Co., Ltd., model 30%N, industrial grade, solid content 30%), curing agent T-12 (Nantong Aidewang Chemical Co., Ltd., dibutyltin dilaurate, industrial grade), anhydrous ethanol (Sinopharm Chemical Reagent Co., Ltd., model 10009218, analytical grade).

[0177] 2. Formulation ratio (total mass 100g): 15g BN powder, 65g epoxy resin prepolymer, 15g silica sol, 2g curing agent T-12, 3g anhydrous ethanol, ensuring that the BN mass fraction is 15wt%, consistent with the BN content of sol B in Example 1, for easy comparison and analysis.

[0178] 3. Preparation process: First, the epoxy resin prepolymer was preheated in a constant temperature environment of 60℃ for 30 min to reduce its viscosity; then, the modified h-BN powder was added (the modification method was completely consistent with the h-BN powder modification process in Example 1, i.e., treatment with 2wt% KH550 hydrolysis solution, centrifugation washing, and drying), and then silica sol, curing agent T-12 and anhydrous ethanol were added in sequence; the same process as the sol dispersion in Example 1 was used (ultrasonic power 350W, ultrasonic frequency 40kHz, high-speed shearing speed 3000r / min, alternating between ultrasonication and shearing, 5 min of ultrasonication and 5 min of shearing, 3 cycles, total duration 30 min) to obtain a uniform and stable homogeneous epoxy resin / BN blend system.

[0179] 4. Coating and curing: The homogeneous blend system prepared above was directly coated onto the surface of the copper conductor sample that had undergone the same pretreatment as in Example 1 (substrate preparation, pre-curing, and ultrasonic cleaning), with a coating thickness of approximately 230 μm (consistent with the total thickness of the material in Example 1). Subsequently, the same multi-stage curing regime as in Example 1 was adopted (heating to 120°C at a rate of 1°C / min and holding for 2 hours, followed by further heating to 160°C at a rate of 1°C / min and holding for 3 hours, then cooling to room temperature with the furnace after shutdown) to obtain the comparative material.

[0180] Electric field distribution simulation and breakdown test were performed under the same high-frequency non-sinusoidal voltage (consistent with the test conditions of Example 1, 10kHz non-sinusoidal voltage). The characterization methods and test standards for each performance were consistent with those of Example 1. The specific values ​​of the material prepared in Comparative Example 1 are shown in Example 1. Compared with Comparative Example 1, the material prepared in Example 1 of this invention has significantly improved insulation performance, increased partial discharge initiation voltage, is less prone to local electric field concentration, and has significantly improved heat dissipation performance.

[0181] It is evident that the multi-layer synergistic structure constructed by the present invention, consisting of "dual plasma + silicon-rich transition layer + oriented h-BN functional layer + boron nitride volume fraction gradient insulation layer", can significantly improve the electro-thermal coupling failure behavior under complex operating conditions at the ends of high-frequency transformers.

[0182] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A functional insulating material of plasma-controlled oriented boron nitride, characterized in that: The insulating material is obtained by sequentially covering the surface of a metal conductor with a thermosetting resin matrix layer, a silicon-rich transition layer, an oriented boron nitride sheet layer, a boron nitride gradient insulating layer, and a densified surface layer from the inner layer to the outer layer. The metallic conductor is selected from copper conductors; The thermosetting resin matrix layer covers the surface of the metal conductor and is a cured resin matrix layer formed by epoxy resin, epoxy-modified silicone resin or a combination thereof, and the thickness of the cured resin matrix layer is 10-100μm. The silicon-rich transition layer covers the surface of the thermosetting resin matrix layer. The surface of the resin matrix is ​​treated by an atmospheric pressure plasma jet driven by an AC high voltage power supply in an atmosphere containing organosilicon precursor, so that the organosilicon precursor is decomposed and deposited, thereby forming a silicon-rich inorganic network transition layer with a thickness of 10-500nm in situ on the surface of the resin matrix. The oriented boron nitride sheet covers the surface of the silicon-rich transition layer. The hexagonal boron nitride sheet is deposited in situ on the surface of the silicon-rich transition layer by plasma-enhanced chemical vapor deposition. The average angle between the normal of the boron nitride nanosheet in the thickness direction and the coating thickness direction is not greater than 30°. The thickness of the oriented sheet is 0.1-10 μm. The boron nitride gradient insulating layer covers the surface of the oriented boron nitride sheet and includes 2-10 sub-layers stacked sequentially along the material thickness direction. Each sub-layer is a boron nitride-containing resin sol-gel coating. The boron nitride concentration varies between adjacent sub-layers, with the concentration gradually decreasing from the innermost layer to the outermost layer. The boron nitride concentration in the innermost layer is 10-40 wt%, and the boron nitride concentration in the outermost layer is 1-10 wt%. The densified surface layer covers the surface of the boron nitride gradient insulating layer and is a cross-linked densified layer formed by atmospheric pressure micro-pulse plasma jet or dielectric barrier discharge treatment driven by a micro-pulse power supply.

2. The functional insulating material according to claim 1, characterized in that: The thermosetting resin matrix layer is prepared from the following raw materials in the following weight ratio: 100 parts epoxy resin, 10-20 parts silicone resin, 0.1-1 parts silane coupling agent, and 1-5 parts curing agent. And / or, in the silicon-rich transition layer, the atmosphere containing the organosilicon precursor is formed by adding organosilicon precursor vapor to a mixture of Ar and O2 gases; the volume percentage of Ar in the mixture is 99-99.5%, and the volume percentage of O2 is 0.5-1%; the volume ratio of organosilicon precursor vapor to the mixture is 1-5:

100. And / or, in the oriented boron nitride sheets, the deposition conditions of the plasma-enhanced chemical vapor deposition process are: radio frequency power 50-400W, substrate temperature 200-600℃, pressure 5-100Pa, the precursor source gas is a mixture of precursor containing B and N elements and carrier gas, and during the deposition process, an electric field perpendicular to the substrate surface and / or the plasma sheath potential is applied to induce the hexagonal boron nitride nanosheets to align along the coating thickness direction. And / or, in the boron nitride gradient insulating layer, the thickness of any sublayer is 2-50 μm, the difference in boron nitride concentration between adjacent sublayers is 3-15 wt%, and the resin phase of each sublayer is epoxy resin and / or epoxy-modified silicone resin that is the same as or compatible with the resin matrix layer, forming a continuous inorganic-organic hybrid network through sol-gel reaction. And / or, in the densified surface layer, before the densified surface layer is formed, gradient curing is performed, and the curing conditions are: heating to 100-130℃ at a rate of 0.5-2℃ / min and holding for 1-3h, then continuing to heat to 150-180℃ at a rate of 0.5-2℃ / min and holding for 2-4h, and finally cooling to room temperature in the furnace; And / or, in the densified surface layer, an atmospheric pressure micro-pulse plasma jet driven by a micro-pulse power supply uses N2 gas, Ar gas, or a mixture of N2 gas and Ar gas as the working gas, with a power of 20-150W and a nozzle distance of 10-25mm from the coating surface.

3. The functional insulating material according to claim 2, characterized in that: The thermosetting resin matrix layer is prepared from the following raw materials in the following weight ratio: 100 parts epoxy resin, 15 parts silicone resin, 0.5 parts silane coupling agent, and 2 parts curing agent. And / or, in the silicon-rich transition layer, the volume percentage of Ar in the mixed gas is 99.5%, and the volume percentage of O2 is 0.5%; the volume ratio of organosilicon precursor vapor to mixed gas is 1:100; And / or, in the oriented boron nitride sheets, the precursor source gas consists of 10-50 sccm boron trichloride and 10-50 sccm ammonia, and the carrier gas is 50-100 sccm Ar. And / or, in the boron nitride gradient insulating layer, the boron nitride-containing resin sol-gel coating of each sublayer is prepared from a coating sol made of silane coupling agent surface-modified hexagonal boron nitride, epoxy resin prepolymer, silica sol, curing agent and anhydrous ethanol, and then cured after coating; in the raw materials, the mass percentages of silane coupling agent surface-modified hexagonal boron nitride, epoxy resin prepolymer, silica sol, curing agent and anhydrous ethanol are 1-40wt%, 40-79wt%, 15wt%, 2wt%, and 3wt%, respectively. And / or, in the densified surface layer, the curing conditions are: heating to 120°C at a rate of 1°C / min and holding for 2 hours, then continuing to heat to 160°C at a rate of 1°C / min and holding for 3 hours, and finally cooling to room temperature in the furnace; And / or, in the densified surface layer, an atmospheric pressure micro-pulse plasma jet driven by a micro-pulse power supply uses N2 gas as the working gas, has a power of 80W, and the distance between the nozzle and the coating surface is 15mm.

4. The functional insulating material according to claim 3, characterized in that: In the thermosetting resin matrix layer, the epoxy resin is bisphenol A type epoxy resin, the organosilicon resin is hydroxyl silicone oil, the silane coupling agent is selected from any one or a combination of γ-aminopropyltriethoxysilane, methyltriethoxysilane, and vinyltriethoxysilane, and the curing agent is dibutyltin dilaurate. And / or, in the silicon-rich transition layer, the organosilicon precursor is selected from tetraethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, or a combination thereof; And / or, in the oriented boron nitride sheets, the precursor source gas consists of 10 sccm boron trichloride and 30 sccm ammonia, and the carrier gas is 50 sccm Ar. And / or, in the boron nitride gradient insulating layer, the silane coupling agent in the silane coupling agent surface-modified hexagonal boron nitride is selected from any one or a combination of γ-aminopropyltriethoxysilane, methyltriethoxysilane, and vinyltriethoxysilane; the epoxy resin prepolymer is bisphenol A type epoxy resin prepolymer; the silica sol is neutral silica sol; and the curing agent is dibutyltin dilaurate. And / or, in the densified surface layer, the surface temperature of the coating is controlled at 60-120℃ during the processing.

5. The functional insulating material according to any one of claims 1 to 4, characterized in that: The method for preparing the thermosetting resin matrix layer includes the following steps: (1) Preheat the epoxy resin in a constant temperature environment of 50-60℃; (2) Add silicone resin to the epoxy resin system and stir to mix the two resins; (3) Add silane coupling agent to the system obtained in step (2) and continue stirring to make the coupling agent uniformly dispersed in the mixed system; (4) Add curing agent to the system obtained in step (3), stir and then degas under vacuum to obtain resin matrix coating; (5) The resin matrix coating obtained in step (4) is applied to the surface of the metal conductor to form a resin matrix layer with a thickness of 80-100 μm. (6) Pre-cure the metal conductor coated with resin matrix coating, then clean and dry it; And / or, in the silicon-rich transition layer, the working power of the atmospheric pressure plasma jet is set to 50-300W, the distance between the nozzle and the sample surface is 5-15mm, the scanning speed is 10-50mm / s, and the sample surface is scanned 1-5 times; the working frequency of the AC high voltage power supply is 10-60kHz, and the output voltage is 5-30kV. And / or, in the oriented boron nitride sheet, the deposition time is 30-60 min, and the vacuum is drawn to below 10 Pa before deposition; And / or, in the boron nitride gradient insulating layer, the curing is performed at 80-100°C for 1-3 hours; And / or, in the densified surface layer, the atmospheric pressure micro-pulse plasma jet scanning speed is 10-50 mm / s, and the total processing time is 5-120 s.

6. The functional insulating material according to claim 5, characterized in that: In the method for preparing the thermosetting resin matrix layer, in step (5), the resin matrix coating obtained in step (4) is coated on the surface of the metal conductor by vacuum casting; in step (6), the pre-curing conditions are to first keep it at 80-100℃ for 1-3h, then raise the temperature to 90-110℃ and keep it at 0.5-1h, and finally raise the temperature to 100-120℃ and keep it at 0.5-1h; in step (6), the drying temperature is 80-100℃. And / or, in the silicon-rich transition layer, the working power of the atmospheric pressure plasma jet is set to 100W, the distance between the nozzle and the sample surface is 10mm, the scanning speed is 20mm / s, and the sample surface is scanned 3 times; the effective gas temperature of the plasma jet contacting the sample surface is 240℃; the ordinary AC high-voltage power supply driving the atmospheric pressure plasma jet has a working frequency of 25kHz and an output voltage of 15kV; And / or, in the oriented boron nitride sheet layer, the method to achieve the orientation of hexagonal boron nitride nanosheets along the thickness direction is as follows: the radio frequency bias voltage is adjusted to -80V, a parallel plate electrode structure is adopted, the sample is fixed on the lower electrode, the upper electrode is connected to the radio frequency power supply, and the electric field direction is made perpendicular to the sample surface by adjusting the electrode spacing to 50mm. And / or, in the oriented boron nitride sheet layer, the average angle between the normal of the boron nitride nanosheet in the thickness direction and the coating thickness direction is less than 20°; And / or, in the densified surface layer, the atmospheric pressure micro-pulse plasma jet scanning speed is 30 mm / s, and the total processing time is 60 s.

7. A method for preparing the functional insulating material according to any one of claims 1 to 6, characterized in that: Includes the following steps: (a) Preparation of thermosetting resin matrix layer: A resin matrix coating is applied to the surface of a metal conductor to form a resin matrix layer. The metal conductor after coating with the resin matrix coating is pre-cured, then cleaned and dried to obtain the thermosetting resin matrix layer. (b) Preparation of silicon-rich transition layer: The sample obtained in step (a) is placed in an atmospheric pressure plasma jet device driven by an AC high voltage power supply. In an atmosphere containing organosilicon precursor, plasma treatment is performed by jet scanning or cavity glow discharge. Simultaneous decontamination and activation and plasma pyrolysis deposition of organosilicon precursor are achieved on the surface of the solid resin matrix layer to form a silicon-rich transition layer containing SiOx or SiOxNy. (c) Preparation of oriented boron nitride sheets: The sample obtained in step (b) is placed in a plasma-enhanced chemical vapor deposition chamber. Under the conditions of radio frequency power of 50-400W, substrate temperature of 200-600℃ and pressure of 5-100Pa, a precursor gas and carrier gas containing B and N elements are introduced. Hexagonal boron nitride sheets are deposited in situ on the surface of the silicon-rich transition layer by plasma-enhanced chemical vapor deposition. During the deposition process, an electric field perpendicular to the substrate surface and / or the plasma sheath potential are applied to induce the hexagonal boron nitride nanosheets to align along the coating thickness direction. (d) Preparation of boron nitride gradient insulating layer: Prepare 2-10 kinds of coating sols containing boron nitride nanosheets according to the preset boron nitride concentration. Coat the sols sequentially on the oriented boron nitride sheet layer in order of gradually decreasing boron nitride concentration from the inner layer to the outer layer. After each coating sol is coated, it is cured first, and then the next coating sol is coated and cured. Finally, a boron nitride gradient insulating layer is obtained on the oriented boron nitride sheet layer. The curing is carried out at 80-100℃ for 1-3 hours. (e) Gradient temperature curing: The sample obtained in step (d) is subjected to gradient temperature curing. The curing conditions are as follows: the temperature is increased to 100-130℃ at a rate of 0.5-2℃ / min and held for 1-3 hours, then the temperature is increased to 150-180℃ at a rate of 0.5-2℃ / min and held for 2-4 hours, and finally cooled to room temperature in the furnace. (f) Preparation of densified surface layer: The sample obtained in step (e) is placed in an atmospheric pressure micro-pulse plasma jet device or micro-pulse dielectric barrier discharge device driven by a micro-pulse power supply, and treated with a power of 20-150W in an atmosphere of N2 gas, Ar gas or a mixture of N2 gas and Ar gas. During treatment, the distance between the nozzle and the coating surface is 10-25mm, the treatment time is 5-120s, and the coating surface temperature is controlled at 60-120℃ during the treatment.

8. Use of the functional insulating material according to any one of claims 1 to 6 in the manufacture of high-frequency transformers.

9. The use of the functional insulating material according to any one of claims 1 to 6 in the manufacture of high-frequency transformers for ultra-high-speed trains, characterized in that: The insulating material is disposed at the end gap of the high-frequency transformer winding, the output end area, and the interface between the core clamp and the winding.

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