High-thermal-conductivity epoxy resin composite material for transformer, heat dissipation runner structure and preparation method

Abstract

The invention discloses a transformer high-thermal-conductivity epoxy resin composite material, a heat dissipation runner structure and a preparation method, and belongs to the technical field of high-voltage transformer heat dissipation materials. In order to solve the problem that the service life of equipment is shortened due to insufficient heat-conducting property and overhigh local temperature rise of an existing transformer heat dissipation runner material, an epoxy resin matrix, a boron nitride nanosheet and a curing agent are used as raw material components, and a heat dissipation runner is prepared through a vacuum mixing and casting molding process. According to the scheme, a continuous heat conduction network is constructed by optimizing interface combination of boron nitride nanosheets and a matrix, so that the heat conductivity coefficient of the composite material in the plane direction is larger than or equal to 1.5 W / (m.K), and meanwhile, a gradient casting molding process is adopted to be matched with heat load distribution of different areas of a runner. The material can be used for manufacturing a heat dissipation flow channel of a high-voltage transformer of a pumped storage power station, winding temperature rise can be remarkably reduced, the operation stability and overload capacity of equipment are improved, and the material is suitable for optimizing a heat dissipation system of a 10-20 kV high-power transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage transformer heat dissipation structural materials, and more specifically, to a transformer high-thermal-conductivity epoxy resin composite material, a heat dissipation flow channel structure, and a preparation method. Background Art

[0002] The Chinese patent application with reference to announcement number CN118231117A discloses a high-voltage winding, a high-voltage transformer for a pumped-storage power station, and a manufacturing method. It discloses a heat dissipation channel structure consisting of a trough body and a cover plate. The trough body and the cover plate are made of epoxy resin, and the cover plate and the trough body are covered to form a heat dissipation channel strip. Since the heat dissipation channel strip is located inside the winding, it requires good thermal conductivity to meet the heat dissipation requirements. Epoxy resin-based composite materials are widely used due to their insulation and molding convenience, but their inherent thermal conductivity is low, and there are problems of insufficient thermal conductivity and local overheating, which affect the life and safety performance of the equipment and are difficult to meet the efficient heat dissipation requirements of high-power transformer windings. At the same time, traditional casting processes mostly use uniform filler distribution, which cannot adapt to the difference in thermal load gradients at the inlet, middle section, and outlet of the heat dissipation channel, resulting in excessive temperature rise in local hot spots and accelerated insulation aging. Furthermore, existing flow channel designs (such as straight-through or serpentine channels) reduce heat dissipation efficiency due to fluid retention effects. The manufacturing of complex biomimetic flow channels (such as Tesla valve structures) is limited by material molding precision and interface bonding strength, making them prone to microcracks or delamination defects. These issues stem from a lack of modification technology to optimize the filler-matrix interface, making it difficult to balance high thermal conductivity and high strength requirements; an immature flow channel gradient filling process that prevents precise control of filler distribution; and difficulties controlling material fluidity and curing shrinkage during the molding of complex flow channel structures. Summary of the Invention

[0003] To address the problem that the above-mentioned epoxy resin composite material has a low thermal conductivity coefficient, typically ≤0.2 W / (m·K), which cannot meet the efficient heat dissipation requirements of the high-voltage transformer heat dissipation flow channel, resulting in excessively high winding temperature rise, typically >100 K, and accelerated insulation aging. The present invention provides a high thermal conductivity epoxy resin composite material and its application in a transformer heat dissipation structure.

[0004] To achieve these objectives of the present invention, the present invention provides a high thermal conductivity epoxy resin composite material for a transformer heat dissipation flow channel, comprising the following raw material components in parts by weight: 50-90 parts of an epoxy resin matrix; 10-30 parts of boron nitride nanosheets; and 5-18 parts of a curing agent. The epoxy resin matrix, boron nitride nanosheets, and curing agent are uniformly mixed, and the transformer heat dissipation flow channel is cast.

[0005] Unmodified boron nitride nanosheets are prone to agglomeration due to their surface inertness, resulting in a discontinuous thermal network and low actual thermal conductivity. High filler loading also leads to degraded mechanical properties. Preferably, the boron nitride nanosheets of the present invention are treated as follows: the boron nitride nanosheets are dispersed in anhydrous ethanol, aminosilane (KH550) is added, and the reaction is carried out at 60-80°C for 24 hours; low-temperature plasma treatment is performed at a power of 50-100 W for 10-30 minutes, followed by washing and drying.

[0006] A single boron nitride nanosheet filler is difficult to improve the thermal conductivity in the thickness direction, and the traditional curing process cannot directionally control the filler distribution, resulting in limited heat dissipation efficiency. Preferably, the present invention also includes 1-5 parts of graphite microsheets; the epoxy resin matrix, boron nitride nanosheets, curing agent and graphite microsheets are mixed evenly, the slurry is injected into the mold, and after vacuum casting, it is cured in stages. The curing process is carried out in two stages: a low-temperature pre-curing stage: under the condition of a vertical magnetic field strength of 1-2 T, the slurry is heated to 60-80°C and maintained for 1-2 hours to align the graphite microsheets vertically along the magnetic field direction; a high-temperature final curing stage: after removing the magnetic field, the temperature is raised to 140-160°C and maintained for 2-4 hours to complete the complete curing of the epoxy resin matrix; wherein the direction of the vertical magnetic field is consistent with the thickness direction of the composite material, and the matrix viscosity during the low-temperature pre-curing stage is 50-100 Pa·s.

[0007] Traditional composite material preparation processes result in uneven filler dispersion and high curing shrinkage, leading to stress concentration and microcracks within the flow channel. The composite material preparation method provided by the present invention comprises the following steps: Step 1: Mixing modified boron nitride nanosheets, graphite microsheets, and an epoxy resin matrix under vacuum and negative pressure at a stirring rate of ≥500 rpm for ≥1 hour; Step 2: Adding a curing agent and continuing stirring for 30-60 minutes to form a uniform slurry; Step 3: Injecting the slurry into a mold, vacuum casting, and then curing in sections.

[0008] Uniformly filled flow channels cannot adapt to local heat load differences, and the temperature rise of the inlet section is too high (>15°C), which causes accelerated aging of the insulating material. The present invention provides a heat dissipation flow channel structure based on the composite material, which is divided into an inlet section, a middle section and an outlet section. The flow channel adopts a multi-stage casting molding method for gradient filling, specifically comprising: step one, dividing the composite material slurry into three groups, the first group has a boron nitride nanosheet content of 25%-30%, the second group has a boron nitride nanosheet content of 15%-20%, and the third group has a boron nitride nanosheet content of 5%-10%; step two, dividing the mold into an inlet section, a middle section and an outlet section, the inlet section corresponds to the first group of slurry, the middle section corresponds to the second group of slurry, and the outlet section corresponds to the third group of slurry; step three, using a segmented injection device to inject the corresponding grouped slurry into the inlet section, middle section and outlet section in turn, and the injection pressure is 10-15 MPa, and the holding time between adjacent segments is 20-30 seconds; step four, after the segmented injection is completed, a vacuum casting process is used to form a continuous transition structure at the interface of each segment slurry, and the gradient change rate of the boron nitride nanosheet content in the transition area is 5%-8% / mm; wherein, the ratio of the nozzle diameter of the segmented injection equipment to the cross-sectional width of the corresponding segment flow channel is 1:3-1:5.

[0009] Traditional straight-through flow channels can cause fluid retention and low heat dissipation efficiency, while complex biomimetic flow channels (such as Tesla valves) are prone to delamination defects due to poor molding precision. Preferably, the flow channel of the present invention is a Tesla valve structure, comprising: a main flow channel and a return flow channel, each of which is provided with alternating ridges; the ridges have a pitch-to-height ratio of 1:3-1:5; the inner wall of the flow channel is sequentially coated with a nano-alumina layer and a fluorosilane layer; the nano-alumina layer has a thickness of 5-10 nm; the fluorosilane layer is formed by vacuum vapor deposition at a temperature of 80-100°C for 2-4 hours, wherein the fluorosilane is heptadecafluorodecyltrimethoxysilane.

[0010] Preferably, the preparation method of the present invention comprises the following steps: step 1, preparing a Tesla valve flow channel mold, wherein the interior of the mold is divided into an inlet section, a middle section, and an outlet section; step 2, dividing the composite material slurry into three groups according to the content of boron nitride nanosheets: the first group 25%-30%, the second group 15%-20%, and the third group 5%-10%; step 3, using a segmented injection device to sequentially inject the first group of slurry into the inlet section, the second group of slurry into the middle section, and the third group of slurry into the outlet section, with an injection pressure of 10-15 MPa, and the intervals between adjacent sections are 10-15 MPa. The holding time is 20-30 seconds; in step 4, after the segmented injection is completed, the mold is placed in a vertical magnetic field with a strength of 1-2T and heated to 60-80°C, and maintained for 1-2 hours to allow the graphite microsheets in the slurry to be arranged vertically along the direction of the magnetic field; in step 5, after removing the magnetic field, the temperature is raised to 140-160°C and maintained for 2-4 hours to complete vacuum casting and curing; in step 6, the mold is opened and the cured heat dissipation flow channel assembly is taken out; wherein, the direction of the vertical magnetic field is consistent with the direction of the flow channel thickness; the viscosity of the slurry in step 4 is 50-100 Pa·s; the ratio of the nozzle diameter of the segmented injection equipment to the cross-sectional width of the corresponding segment flow channel is 1:3-1:5.

[0011] The slurry viscosity (50-100 Pa·s) during the magnetic field treatment stage ensures the vertical orientation of the graphite microsheets, and the bending strength of the flow channel after curing is ≥85 MPa, which is suitable for mass production.

[0012] During the segmented injection process, the slurry temperature and flow rate do not match, resulting in interface stratification or uneven filler distribution. Preferably, in step three of the present invention, when injecting at the inlet section, the slurry temperature is 50-60°C and the injection speed is 5-8 mm / s; when injecting at the middle section, the slurry temperature is 40-50°C and the injection speed is 3-5 mm / s; when injecting at the outlet section, the slurry temperature is 30-40°C and the injection speed is 1-3 mm / s; wherein, a transition mixing zone is set at the interface between the inlet section and the middle section slurry, and the length of the transition mixing zone is 3-5 mm.

[0013] During the gradient filling process, the interface of slurries with different boron nitride nanosheet contents is prone to stratification or pores due to viscosity differences, resulting in insufficient interface bonding strength and increased local thermal resistance. Preferably, after the segmented injection is completed, the present invention applies a local temperature gradient control to the interface area, with the inlet section side heated to 70-80°C and the outlet section side cooled to 40-50°C, with a temperature gradient of 5-10°C / mm for 5-10 minutes; an ultrasonic vibration device is used to apply vertical vibration to the interface area, with a vibration time of 30-60 seconds and an amplitude of 1-3 μm; the transducer of the ultrasonic vibration device is in contact with the outer wall of the mold, with a spacing of ≤2 mm, and the vibration direction is consistent with the thickness direction of the runner.

[0014] The present invention has at least the following beneficial effects: By optimizing the boron nitride nanosheet filling ratio (10-30 parts) to the matrix, this composite material achieves an in-plane thermal conductivity of ≥1.5 W / (m·K) and a tensile strength of ≥65 MPa, capable of withstanding the thermomechanical stresses of high-voltage windings. This material can be directly cast to form complex flow channels, avoiding secondary processing that damages the thermal conductivity network. Suitable for 10-20 kV transformers, it reduces winding temperature rise to ≤80 K, extending equipment life.

[0015] 2. This invention introduces -NH2 and -OH functional groups onto the surface of boron nitride nanosheets through aminosilane grafting and plasma activation, improving dispersion uniformity. The resulting composite material achieves a thermal conductivity of 2.0 W / (m·K) or higher at a 25% loading, a tensile strength of >80 MPa, and avoids partial discharge (<5 pC) caused by agglomeration.

[0016] 3. This invention uses a magnetic field to orient graphite microplatelets, forming a vertical heat conduction path. The thermal conductivity through the thickness is ≥1.2 W / (m·K), and the anisotropy ratio (plane / thickness) is optimized to 1.8:1. The staged curing process ensures that the matrix viscosity (50-100 Pa·s) matches the magnetic field strength (1-2 T), preventing filler sedimentation or orientation shift.

[0017] 4. The segmented curing process of the present invention matches the filler orientation requirements and is suitable for the molding of complex structures such as Tesla valves.

[0018] 5. The gradient filling design of this invention achieves thermal conductivity of approximately 2.3 W / (m·K) at the inlet section, 2.0 W / (m·K) at the middle section, and 1.5 W / (m·K) at the outlet. This matches the heat load distribution, reduces the temperature rise of local hot spots by 10-15°C, and increases fluid heat transfer by 30%. A gradient change rate of 5-8% / mm in the transition zone prevents interfacial stress concentration, and the bond strength is ≥15 MPa.

[0019] 6. The Tesla valve structure of the present invention utilizes a ridge plate spacing and height ratio (1:3-1:5) to enhance fluid turbulence and improve heat transfer; the nano-aluminum oxide layer (5-10 nm) increases surface hardness (HV ≥ 200), and the fluorosilane layer has a contact angle of >150°, reducing fluid resistance and dirt adhesion.

[0020] 7. The high-temperature, high-speed injection at the inlet (50-60°C, 5-8 mm / s) ensures high filler slurry fluidity, while the low-temperature, low-speed at the outlet (30-40°C, 1-3 mm / s) reduces turbulence. A spiral mixing head (100-200 rpm) in the transition mixing zone (3-5 mm) achieves a gradient transition of boron nitride nanosheets, with an interfacial porosity of less than 0.2%, avoiding delamination defects.

[0021] 8. After the segmented injection is completed, the present invention uses temperature gradient control (5-10°C / mm) to reduce the interfacial viscosity difference, promote molecular chain diffusion, and increase the interfacial bonding strength to ≥18 MPa; ultrasonic vibration (20-40 kHz) eliminates micropores (porosity <0.1%), reduces interfacial thermal resistance, and avoids delamination defects.

[0022] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below with reference to examples so that those skilled in the art can implement the invention with reference to the description.

[0024] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0025] Example 1 The present invention provides a high thermal conductivity epoxy resin composite material for transformer heat dissipation channels and a preparation method thereof, comprising: The epoxy resin matrix is ​​bisphenol A epoxy resin E-51, with a viscosity of 4000-6000 mPa·s (25°C) and a weight content of 50-90 parts. The boron nitride nanosheets have a particle size of 100-500 nm, a thickness of 2-5 nm, and a weight content of 10-30 parts. The curing agent is methylhexahydrophthalic anhydride (MHHPA) or tetrahydrophthalic anhydride (THPA), with a weight content of 5-18 parts, representing 10-25% of the epoxy resin matrix.

[0026] The mixing process can be performed using a vacuum mixer at a stirring rate of 500-800 rpm for 1-2 hours, with a vacuum level of ≤100 Pa. The casting mold can be made of aluminum alloy or steel, with an inner surface roughness of Ra ≤1.6 μm and a preheat temperature of 60-80°C. The casting pressure is 0.5-1 MPa. After casting, the material is placed in a hot air circulating oven, heated at a rate of 2-5°C / min to 150-160°C, and held at that temperature for 3-4 hours to complete curing.

[0027] Mixing uniformity was tested using a laser particle size analyzer to determine the dispersion of boron nitride nanosheets. A D90 / D10 ratio of ≤3 was considered acceptable. Thermal conductivity was tested in the planar direction using a laser flash method, with a target value of ≥1.5 W / (m·K). Tensile strength was tested using a universal materials testing machine according to ASTM D638, with a target value of ≥75 MPa.

[0028] By controlling the ratio of epoxy resin matrix (50-90 parts) to boron nitride nanosheets (10-30 parts), this composite material achieves a planar thermal conductivity of 1.5 W / (m·K) and a tensile strength of ≥65 MPa, meeting the thermal load (≤180°C) and mechanical strength requirements of the heat dissipation channels of high-voltage transformers. The casting process avoids secondary processing damage to the thermal conductivity network, and the heat dissipation channel molding has a dimensional accuracy of ±0.2 mm, making it suitable for direct fabrication of complex structures such as Tesla valves. A boron nitride nanosheet content of 10-30 parts achieves a balanced thermal conductivity and material toughness, with an elongation at break of ≥3%, avoiding brittle failure caused by high filling.

[0029] Example 2 Based on Example 1, the present invention provides a high-thermal-conductivity epoxy resin composite material for transformer heat dissipation channels and its preparation method. The boron nitride nanosheets are treated as follows: the boron nitride nanosheets are dispersed in anhydrous ethanol (preferably anhydrous ethanol with a purity of ≥99.7%), with a mass ratio of boron nitride nanosheets to ethanol of 1:20-1:50. Aminosilane (KH550) is then added, with the amount of KH550 being 1-3% of the mass of the boron nitride nanosheets. The reaction vessel is a thermostatic oil bath with mechanical stirring, with a reaction temperature of 60-80°C, a reaction time of 24 hours, and a stirring rate of 200-300 rpm.

[0030] The reacted boron nitride nanosheet suspension is washed three times in a centrifuge at 8,000-10,000 rpm to remove unreacted KH550. The washed boron nitride nanosheets are dried in a vacuum oven at 60-80°C for 12 hours. The plasma treatment equipment can be a radio frequency plasma cleaner with a power of 50-100 W and a treatment time of 10-30 minutes. The chamber vacuum is ≤10 Pa, and the gas used is argon (purity ≥99.99%).

[0031] The dispersion uniformity of the treated boron nitride nanosheets in this example was tested by laser particle size analysis, with a D90 / D10 ratio of ≤3. The treated composite material exhibited a planar thermal conductivity of 2.0 W / (m·K) or higher at a 25% loading, a tensile strength of >80 MPa, and avoided partial discharge (<5 pC) due to agglomeration. Plasma treatment parameters (50-100 W, 10-30 minutes) optimized the surface activation, avoided excessive etching that damaged the boron nitride nanosheet structure, and ensured a dielectric strength of ≥20 kV / mm (GB / T 1408).

[0032] Example 3 Based on Example 1, the present invention provides a high thermal conductivity epoxy resin composite material for transformer heat dissipation channels and a preparation method thereof, further comprising: The graphite microplatelets have a thickness of 20-50 nm and a diameter of 5-10 μm, and are mixed in 1-5 parts by weight. The graphite microplatelets and epoxy resin matrix can be mixed using a dual planetary mixer at a stirring rate of 500-800 rpm for 1-2 hours, with a vacuum level of ≤100 Pa. The viscosity of the mixed slurry is measured using a rheometer and controlled to be 50-100 Pa·s (shear rate 0.1 s⁻¹).

[0033] During the low-temperature pre-curing stage, an electromagnet generates a perpendicular magnetic field with a strength of 1-2 T, aligned with the thickness of the composite material. The mold is made of aluminum alloy and preheated to 60-80°C. After slurry injection, the temperature is increased at a rate of 2-5°C / min for 1-2 hours. During the application of the magnetic field, the slurry viscosity is maintained at 50-100 Pa·s in a constant-temperature water bath. If this range is exceeded, 1-5 parts of a reactive diluent, butyl glycidyl ether, is added to the epoxy resin matrix to adjust the slurry viscosity and ensure adequate rotational alignment of the graphite microplatelets.

[0034] After removing the magnetic field, transfer the mold to a hot air circulation oven and heat to 140-160°C at a rate of 2-5°C / min. Hold for 2-4 hours to complete the curing process. After curing, a silicone oil emulsion can be used as the release agent, with a release force of ≤5 kN (hydraulic ejection device). Runner dimensional tolerances are measured using a three-dimensional coordinate measuring machine and maintained within ±0.1 mm.

[0035] In this example, by adding 1-5 parts of graphite microplatelets and combining them with magnetic field alignment, the composite material's through-thickness thermal conductivity is increased to 1.2-1.5 W / (m·K), and the anisotropy ratio (plane / thickness) is optimized to 1.8:1. During the low-temperature pre-curing stage, the slurry viscosity (50-100 Pa·s) is matched to the magnetic field strength (1-2 T), preventing sedimentation or misalignment of the graphite microplatelets. The resulting flexural strength is ≥80 MPa. A high-temperature final curing process ensures complete cross-linking of the matrix, with no bubbles or delamination defects within the flow channels (porosity <0.3%), making it suitable for the manufacture of high-precision heat dissipation structures such as Tesla valves.

[0036] Example 4 The present invention provides a heat dissipation channel structure based on the composite material of any one of Examples 1 to 3 and a method for preparing the same, comprising: In step 1, the composite material slurry was divided into three groups based on boron nitride nanoflake content: Group 1 had a boron nitride nanoflake content of 27% ± 2%, Group 2 had a boron nitride nanoflake content of 18% ± 2%, and Group 3 had a boron nitride nanoflake content of 8% ± 2%. The boron nitride nanoflakes had a particle size of 100-500 nm and a purity of ≥ 99%. Bisphenol A E-51 was used as the epoxy resin matrix, and methylhexahydrophthalic anhydride (MHHPA) was used as the curing agent, added at 17% ± 2% of the resin mass.

[0037] In step 2, the mold is divided into inlet, middle, and outlet sections. The runner cross-sectional width of the inlet section is 10-15 mm, 8-12 mm in the middle section, and 5-8 mm in the outlet section. The segmented injection molding machine uses a three-axis servo injection molding machine, with a nozzle diameter to runner width ratio of 1:3-1:5 (for example, a 3 mm inlet nozzle diameter corresponds to a 9 mm runner width). The injection pressure is 10-15 MPa, and the holding time between adjacent sections is 20-30 seconds. The injection speed is adjusted according to the section: 5-8 mm / s in the inlet section, 3-5 mm / s in the middle section, and 1-3 mm / s in the outlet section.

[0038] The transition mixing zone is 3-5 mm long, and the material is mixed by a spiral mixing head at 100-200 rpm for 10-15 seconds, achieving a gradient of 5-8% / mm in boron nitride nanosheet content. The inner wall roughness of the flow channel is Ra ≤ 0.8 μm (polished) to avoid increased fluid resistance.

[0039] In this example, a gradient filling design is employed. The boron nitride nanosheet content (25%-30%) in the inlet section achieves a thermal conductivity of approximately 2.3 W / (m·K), which decreases to approximately 2.0 W / (m·K) in the middle section and 1.5 W / (m·K) at the outlet (5%-10%). This optimizes the flow channel's heat load distribution and reduces the temperature rise in local hotspots by 10-15°C. The gradient change rate in the transition zone is controlled by a spiral mixing head, at 5-8% / mm. The interfacial bonding strength is ≥15 MPa (ASTM D1002 test), preventing delamination or cracking. The segmented injection parameters (pressure 10-15 MPa, hold pressure 20-30 seconds) ensure a slurry fill density >98% and a flow channel dimensional tolerance of ±0.1 mm, making it suitable for mass production of 10-20 kV pumped-storage power station transformers. After 500 hours of continuous operation in a 10 kV transformer, the winding temperature rise remained stable at ≤80 K.

[0040] Example 5 Based on Example 4, a heat dissipation channel structure and a preparation method thereof of the present invention include: Referring to the flow channel structure disclosed in Chinese patent publication number CN118231117A, the flow channel adopts a Tesla valve structure, with alternating main and return channels. The main channels are 50-100 mm long, 8-15 mm wide, and 3-5 mm deep. The return channels are angled 30-45° from the main channels. The mold is formed using a CNC machined aluminum alloy mold, with the parting line located at the centerline of the spine.

[0041] The ridge height is 3-5 mm, the spacing is 1-1.7 mm, and the ratio of ridge spacing to height is 1:3-1:5. The mold inner surface roughness Ra ≤ 0.8 μm is polished using diamond paste (grain size W1-W3).

[0042] The nanoalumina layer is prepared via a sol-gel method with a sol concentration of 5-10 wt%. After coating, it is calcined at 400-500°C for 1-2 hours, resulting in a layer thickness of 8±2 nm. The fluorosilane layer is deposited using vacuum vapor deposition equipment at a temperature of 80-100°C, a pressure of ≤10 Pa, and a deposition time of 2-4 hours. The fluorosilane is heptadecafluorodecyltrimethoxysilane (CAS 83048-65-1), and the contact angle measured (ASTM D7334) is 150-155°.

[0043] The Tesla valve structure in this embodiment enhances fluid turbulence and improves heat dissipation efficiency through a ridge spacing-to-height ratio of 1:3-1:5. A nano-aluminum oxide layer (5-10 nm) increases the surface hardness of the flow channel to HV ≥ 200 (as measured by a Vickers hardness tester), while a fluorosilane layer with a contact angle of >150° reduces fluid resistance and dirt adhesion.

[0044] Example 6 Based on Example 5, a heat dissipation flow channel structure and preparation method of the present invention is described, wherein the slurry temperature at the inlet section is controlled at 50-60°C, a zoned heating injection molding barrel is selected, the heating power is 1-2 kW, and the injection speed is 5-8 mm / s. The slurry temperature in the middle section is controlled at 40-50°C, the heating power is 0.8-1.5 kW, and the injection speed is 3-5 mm / s. The slurry temperature at the outlet section is controlled at 30-40°C, the heating power is 0.5-1 kW, and the injection speed is 1-3 mm / s. Temperature monitoring is performed using an infrared thermometer.

[0045] A transitional mixing zone, 3-5 mm in length, is established at the interface between the inlet and mid-section slurries. This zone is achieved through a spiral mixing head. The rotating shear and propulsion of the mixing head diffuse the boron nitride nanosheets from high to low concentrations, forming a continuous gradient. The mixing head rotates at 100-200 rpm, with a mixing time of 10-15 seconds. The ratio of the mixing head inner diameter to the runner width is 1:3-1:5. The mixing head can be installed at the nozzle end of the segmented injection molding machine, aligned with the mold inlet section.

[0046] The boron nitride nanosheet content gradient at the slurry interface was measured using EDS surface scanning, with a gradient variation rate of 5-8% / mm. The interfacial bonding strength was tested using a tensile test (ASTM D1002), with a target value of ≥15 MPa. The inner wall roughness of the flow channel was tested to Ra ≤ 0.8 μm.

[0047] This example utilizes segmented temperature and velocity control (50-60°C / 5-8 mm / s at the inlet, 30-40°C / 1-3 mm / s at the outlet) to ensure high filler slurry fluidity and minimize turbulence. A spiral mixing head (100-200 rpm) in the transition mixing zone (3-5 mm) achieves a gradient transition of boron nitride nanosheets, resulting in an interfacial porosity of less than 0.2% and a tensile strength of 15 MPa or greater.

[0048] Example 7 Based on Example 6, after segmented injection, a local temperature gradient is applied to the interface region. The inlet temperature can be set to 70-80°C, and the outlet temperature can be set to 40-50°C, with a temperature gradient of 5-10°C / mm. Temperature control can be achieved using a segmented temperature control module, consisting of an inlet heating unit (70-80°C) and an outlet cooling unit (40-50°C). The temperature control modules can be installed on the outer walls of the inlet and outlet sections of the mold, with the spacing aligned with the runner interface region. The temperature gradient duration can be set to 5-10 minutes, with a heating rate of 2-5°C / min.

[0049] An ultrasonic vibration device is used to apply vertical vibration to the interface area. The vibration frequency can be set to 20-40 kHz, the power can be set to 50-100 W, the vibration time can be set to 30-60 seconds, and the amplitude can be set to 1-3 μm. The transducer of the ultrasonic vibration device can be mounted on the outer wall of the mold, with a spacing of ≤2 mm from the flow channel interface area. The vibration direction is aligned with the flow channel thickness. The contact surface between the transducer and the mold can be coated with thermal conductive silicone grease to ensure effective transmission of vibration energy.

[0050] Interfacial bonding strength was tested using a tensile test (ASTM D1002) with a specimen size of 100 × 10 × 2 mm³ at a tensile rate of 2 mm / min, with a target value of ≥18 MPa. Porosity was determined by observing the interface region under a metallographic microscope (200× magnification) and calculating the average value from five selected fields of view, with a target value of <0.1%. Thermal resistance was tested using the steady-state heat flow method (ASTM D5470) at a test temperature of 25°C and a sample thickness of 5 mm. The target interfacial thermal resistance was ≤0.6 × 10⁻. 4 m²·K / W.

[0051] This embodiment achieves a synergistic effect by controlling the local temperature gradient (5-10°C / mm) and ultrasonic vibration (20-40 kHz, 1-3 μm amplitude) to increase the interfacial bonding strength to ≥18 MPa and reduce the porosity to <0.1%. The assembly position of the temperature control module and ultrasonic transducer (on the mold's outer wall, with a spacing of ≤2 mm) ensures precise energy delivery to the interface, preventing deformation of the flow channel structure (dimensional deviation ≤0.05 mm). This process is compatible with industrial-grade temperature control and ultrasonic equipment, with a single processing time of ≤15 minutes and a yield rate of ≥95%.

[0052] Experimental comparative analysis 1. Experimental Process and Test Methods of Example 1 and Comparative Examples 1 to 3 Sample Preparation: Weigh the raw materials according to each recipe, mix under vacuum, and then inject into a mold. Curing conditions are 150-160°C for 3-4 hours. After demolding, cut into standard specimens (ASTM standard size). Thermal conductivity is determined using the laser flash method (ASTM E1461) with specimen dimensions of 100 × 100 × 2 mm³ and a test temperature of 25°C. Tensile strength and elongation at break are determined using a universal materials testing machine (ASTM D638) at a rate of 2 mm / min and specimen dimensions of 100 × 10 × 2 mm³. Dispersibility is determined using laser particle size analysis (D90 / D10). Thermal stability is determined using thermogravimetric analysis (TGA) at a heating rate of 10°C / min under a nitrogen atmosphere, and the thermal decomposition temperature is recorded.

[0053] Comparative Example 1: Epoxy resin matrix without boron nitride nanosheets Bisphenol A epoxy resin E-51 (90 parts) and methylhexahydrophthalic anhydride (MHHPA, 18 parts) were used, without the addition of boron nitride nanosheets. The mixing process was performed using a vacuum mixer (500 rpm, 1 hour, vacuum ≤ 100 Pa), and the casting conditions were the same as in Example 1. Test results showed a thermal conductivity of only 0.2 W / (m·K), a tensile strength of 60-65 MPa, and an elongation at break of 5-6%. This demonstrates that boron nitride nanosheets are a key factor in improving thermal conductivity, and their appropriate addition can balance mechanical properties.

[0054] Comparative Example 2: Composite material of highly filled boron nitride nanosheets (40 parts) Epoxy resin E-51 (50 parts), untreated boron nitride nanosheets (40 parts), and MHHPA (15 parts). The mixing process was the same as in Example 1. Testing revealed that excessive boron nitride nanosheets resulted in poor dispersibility (D90 / D10 ≥ 8), reduced thermal conductivity to 1.2-1.5 W / (m·K), tensile strength to only 45-50 MPa, and elongation at break to 1-2%. This indicates that while a high loading slightly improves thermal conductivity, it significantly degrades mechanical properties, indicating that the optimal loading range in Example 1 is 10-30 parts.

[0055] Comparative Example 3: Boron nitride nanosheet composite material without surface treatment Epoxy resin E-51 (70 parts), untreated boron nitride nanosheets (25 parts), and MHHPA (14 parts). The process parameters were the same as in Example 1. The results showed that the untreated boron nitride nanosheets had poor dispersibility (D90 / D10 ≥ 6), a thermal conductivity of 0.8-1.0 W / (m·K), and a tensile strength of 55-60 MPa. Comparison of the thermal conductivity (≥1.5 W / (m·K)) and tensile strength (≥65 MPa) of Example 1 demonstrates that surface treatment significantly improves the dispersibility and interfacial bonding of the boron nitride nanosheets, thereby enhancing their overall performance.

[0056] II. Experimental Process and Test Methods of Example 2 and Comparative Examples 4-6 Sample preparation: Epoxy resin, boron nitride nanosheets, and curing agent were mixed according to the respective comparative example formulations. Vacuum stirring was performed followed by casting. Curing conditions were the same as in Example 2 (150-160°C, 3-4 hours). The dispersion of the boron nitride nanosheets was determined using laser particle size analysis (D90 / D10). Thermal conductivity was measured using the laser flash method (ASTM E1461) in the planar direction. Mechanical properties were measured using tensile strength (ASTM D638) and elongation at break.

[0057] Comparative Example 4: Boron nitride nanosheet composite material not subjected to plasma treatment Epoxy resin E-51 (70 parts), aminosilane-treated boron nitride nanosheets (25 parts, chemically grafted only, not plasma treated), and curing agent methylhexahydrophthalic anhydride (MHHPA) (14 parts) were mixed using the same process as in Example 2 (stirring at 500 rpm for 1 hour). Test results showed that the boron nitride nanosheets exhibited inferior dispersion (D90 / D10 = 4-5) compared to Example 2 (D90 / D10 ≤ 3), with thermal conductivity of 1.2-1.4 W / (m·K) and tensile strength of 65-70 MPa. This indicates that chemical grafting alone cannot fully activate the surface of the boron nitride nanosheets, requiring plasma treatment to further optimize dispersion.

[0058] Comparative Example 5: Boron nitride nanosheet composite material treated with low power plasma (30 W) After the boron nitride nanosheets were treated with aminosilane, the plasma treatment power was 30 W (50-100 W in Example 2) for 30 minutes. All other conditions were the same as in Example 2. Testing revealed a dispersibility of D90 / D10 of 3.5-4, a thermal conductivity of 1.5-1.7 W / (m·K), and a tensile strength of 70-75 MPa. This demonstrates that insufficient plasma power resulted in inadequate surface activation, resulting in lower performance than in Example 2 (thermal conductivity ≥ 2.0 W / (m·K)).

[0059] Comparative Example 6: Boron nitride nanosheet composite material treated with short plasma time (5 minutes) The plasma treatment time for the boron nitride nanosheets was shortened to 5 minutes (compared to 10-30 minutes in Example 2), with a power of 100 W. The remaining processes were the same as in Example 2. The results showed that the boron nitride nanosheets had a dispersion of D90 / D10 of 4-4.5, a thermal conductivity of 1.3-1.6 W / (m·K), and a tensile strength of 68-72 MPa. This indicates that the short treatment time resulted in incomplete surface modification and weakened interfacial bonding.

[0060] III. Experimental Process and Test Methods of Example 3 and Comparative Examples 7-9 Sample Preparation: Mix the raw materials according to the recipes in the Examples and Comparative Examples, cast, and cure under the corresponding conditions. Graphite microflakes (particle size 5-10 μm, thickness 20-50 nm) were added in an amount of 5 parts. Thermal conductivity was measured in the plane and through-thickness directions using the laser flash method (ASTM E1461) and the steady-state heat flow method (ASTM D5470), respectively. Mechanical properties were measured using flexural strength (ASTM D790) and porosity (measured using a metallographic microscope). Viscosity was monitored during the pre-curing phase using a rheometer (shear rate 0.1 s⁻¹).

[0061] Comparative Example 7: Composite material without graphite flakes Epoxy resin E-51 (70 parts), boron nitride nanosheets (25 parts), and MHHPA (14 parts) were used. No graphite microplatelets were added. The mixing process was identical to that of Example 3, except that the magnetic field treatment was omitted. The curing process was a single-stage process (directly heating to 140-160°C and holding for 3 hours). Test results showed that the thermal conductivity through the thickness of Comparative Example 7 was only 0.4-0.5 W / (m·K), significantly lower than that of Example 3 (1.2-1.5 W / (m·K)). The flexural strength was 75-80 MPa. This demonstrates that the addition of graphite microplatelets and magnetic field-oriented alignment are essential for improving through-thickness thermal conductivity.

[0062] Comparative Example 8: Composite material with graphite flakes added but no magnetic field treatment Epoxy resin E-51 (70 parts), boron nitride nanosheets (25 parts), and graphite microplatelets (5 parts) were mixed and directly cured (single-stage, 140-160°C, 3 hours) without magnetic field treatment. Testing revealed a thickness-directed thermal conductivity of 0.6-0.8 W / (m·K), an anisotropy ratio (plane / thickness) of 3.5:1, and a flexural strength of 70-75 MPa. Comparison with Example 3 (anisotropy ratio of 1.8:1, flexural strength ≥80 MPa) demonstrates that magnetic field orientation significantly optimizes the alignment and performance of the graphite microplatelets.

[0063] Comparative Example 9: Composite material with single-stage curing process Epoxy resin E-51 (70 parts), boron nitride nanosheets (25 parts), and graphite microplatelets (5 parts) were mixed and heated directly to 140-160°C for 3 hours (without a low-temperature pre-curing stage). Test results showed that the graphite microplatelets settled due to the low matrix viscosity (<50 Pa·s). The through-thickness thermal conductivity was 0.9-1.0 W / (m·K), the flexural strength was 65-70 MPa, and pores (0.5% porosity) were present within the flow channel. This was compared to the two-stage curing process in Example 3 (low-temperature pre-curing with a viscosity of 50-100 Pa·s), demonstrating the critical role of the staged process in maintaining the orientation stability and structural integrity of the graphite microplatelets.

[0064] IV. Experimental Process and Test Methods of Example 4 and Comparative Examples 10-11 Comparative Example 10 used a single slurry (20% boron nitride nanosheets) with no gradient filling. Comparative Example 11 eliminated the spiral mixer and relied on natural diffusion to form the transition. Thermal conductivity was measured using an infrared thermal imager to monitor the surface temperature distribution of the flow channel, and the laser flash method was used to calculate the thermal conductivity of each section. Interfacial bonding strength was measured using a tensile test (ASTM D1002), with specimens taken from the transition zone.

[0065] Comparative Example 10: Uniform filling without gradient design A slurry containing a single boron nitride nanosheet content (20%) was used to fill the entire runner, without any grouping gradient design. The mold runner cross-section width was uniformly 10 mm, injection pressure was 10 MPa, injection speed was 5 mm / s, and no transition mixing zone was treated. Test results showed that the thermal conductivity of the inlet section was 1.8 W / (m·K), heat accumulation at the outlet caused a local temperature rise of 25°C, and the interfacial bonding strength was 10 MPa (ASTM D1002), significantly lower than that of Example 4 (inlet 2.3 W / (m·K), outlet temperature rise ≤15°C, and bonding strength ≥15 MPa).

[0066] Comparative Example 11: Segmented Injection without Spiral Mixing Head The boron nitride nanosheet content grouping was the same as in Example 4, but the spiral mixing head was omitted and the slurry was injected directly. The injection pressure was 10-15 MPa, the holding time was 20-30 seconds, and the transition zone relied on natural diffusion. Testing revealed that the boron nitride nanosheet gradient varied by as much as 15-20% / mm (compared to 5-8% / mm in Example 4), with distinct delamination at the interface. The thermal conductivity fluctuated within ±20%, and the partial discharge was >10 pC (IEC 60270), significantly higher than the <5 pC in Example 4.

[0067] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiment. They can be applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily realized.

Claims

1. A high thermal conductivity epoxy resin composite material for transformer heat dissipation flow channel, characterized in that: The raw material components include the following parts by weight: 50-90 parts of epoxy resin matrix; 10-30 parts of boron nitride nanosheets; 5-18 parts of curing agent.

2. The high thermal conductivity epoxy resin composite material according to claim 1, wherein: The boron nitride nanosheets are treated as follows: the boron nitride nanosheets are dispersed in anhydrous ethanol, aminosilane is added, and the reaction is carried out at 60-80°C for 24 hours; low-temperature plasma treatment is carried out at a power of 50-100 W for 10-30 minutes, and then the boron nitride nanosheets are cleaned and dried.

3. The high thermal conductivity epoxy resin composite material according to claim 1, characterized in that: It also includes 1-5 parts of graphite microsheets; the epoxy resin matrix, boron nitride nanosheets, curing agent and graphite microsheets are mixed evenly, the slurry is injected into the mold, and after vacuum casting, it is cured in sections. The curing process is carried out in two stages: Low-temperature pre-curing stage: Under the condition of a vertical magnetic field strength of 1-2 T, the slurry is heated to 60-80°C and maintained for 1-2 hours to align the graphite microsheets vertically along the magnetic field direction; High temperature final curing stage: After removing the magnetic field, the temperature is raised to 140-160°C and maintained for 2-4 hours to complete the complete curing of the epoxy resin matrix; The direction of the perpendicular magnetic field is consistent with the thickness direction of the composite material, and the matrix viscosity is 50-100 Pa·s during the low-temperature pre-curing stage.

4. A method for preparing the high thermal conductivity epoxy resin composite material according to claim 3, characterized in that: The following steps are involved: Step 1: mixing boron nitride nanosheets, graphite microsheets and epoxy resin matrix under vacuum conditions at a stirring rate of ≥500 rpm for ≥1 hour; Step 2: Add curing agent and continue stirring for 30-60 minutes to form a uniform slurry; Step 3: Inject the slurry into the mold, vacuum cast it, and solidify it in sections.

5. A heat dissipation channel structure of a transformer based on the high thermal conductivity epoxy resin composite material according to claim 3, characterized in that: Divided into inlet section, middle section and outlet section, the runner adopts multi-stage casting method for gradient filling, specifically including: Step 1: Divide the composite material slurry into three groups, wherein the content of boron nitride nanosheets in the first group is 25%-30%, the content of boron nitride nanosheets in the second group is 15%-20%, and the content of boron nitride nanosheets in the third group is 5%-10%. Step 2: Divide the mold into an inlet section, a middle section, and an outlet section. The inlet section corresponds to the first group of slurry, the middle section corresponds to the second group of slurry, and the outlet section corresponds to the third group of slurry. Step 3: Use segmented injection equipment to inject the corresponding grouped slurry into the inlet section, middle section and outlet section in sequence. The injection pressure is 10-15 MPa, and the pressure holding time between adjacent sections is 20-30 seconds. Step 4: After the segmented injection is completed, a vacuum casting process is used to form a continuous transition structure at the interface of each segment of slurry, and the gradient change rate of the boron nitride nanosheet content in the transition area is 5%-8% / mm; Among them, the ratio of the nozzle diameter of the segmented injection equipment to the cross-sectional width of the corresponding segment flow channel is 1:3-1:

5.

6. The heat dissipation channel structure according to claim 5, characterized in that: The flow channel adopts Tesla valve structure, including main flow channel and return flow channel, with alternating ridge plates in the main flow channel and return flow channel; the spacing and height ratio of the ridge plates is 1:3-1:5; The inner wall of the flow channel is sequentially coated with a nano-aluminum oxide layer and a fluorosilane layer; the thickness of the nano-aluminum oxide layer is 5-10 nm; the fluorosilane layer is formed by a vacuum vapor deposition process with a deposition temperature of 80-100°C and a deposition time of 2-4 hours, wherein the fluorosilane is heptadecafluorodecyltrimethoxysilane.

7. A method for preparing the heat dissipation channel structure according to claim 6, characterized in that: The following steps are involved: Step 1: Prepare the Tesla valve flow channel mold, which is divided into an inlet section, a middle section, and an outlet section; Step 2: Divide the composite material slurry into three groups according to the content of boron nitride nanosheets: the first group contains 25%-30%, the second group contains 15%-20%, and the third group contains 5%-10%. Step 3: Use segmented injection equipment to inject the first group of slurry into the inlet section, the second group of slurry into the middle section, and the third group of slurry into the outlet section in sequence. The injection pressure is 10-15 MPa, and the pressure holding time between adjacent sections is 20-30 seconds. Step 4: After the segmented injection is completed, the mold is placed in a vertical magnetic field with a strength of 1-2T and heated to 60-80°C for 1-2 hours to allow the graphite flakes in the slurry to align vertically along the magnetic field direction. Step 5: After removing the magnetic field, heat up to 140-160°C and maintain for 2-4 hours to complete vacuum casting and curing; Step 6: Open the mold and take out the cured heat dissipation channel assembly; The direction of the vertical magnetic field is consistent with the direction of the flow channel thickness; the viscosity of the slurry in step 4 is 50-100 Pa·s; and the ratio of the nozzle diameter of the segmented injection device to the cross-sectional width of the corresponding segment flow channel is 1:3-1:

5.

8. The method for preparing the heat dissipation channel structure according to claim 7, wherein: In step 3, when injecting at the inlet section, the slurry temperature is 50-60°C and the injection speed is 5-8 mm / s; when injecting at the middle section, the slurry temperature is 40-50°C and the injection speed is 3-5 mm / s; when injecting at the outlet section, the slurry temperature is 30-40°C and the injection speed is 1-3 mm / s; Among them, a transition mixing zone is set at the interface between the inlet section and the middle section slurry. The boron nitride nanosheet content gradient change rate in the transition mixing zone is 5%-8% / mm and the length is 3-5 mm.

9. The method for preparing the heat dissipation channel structure according to claim 7, characterized in that: After the segmented injection is completed, a local temperature gradient control is applied to the interface area, with the inlet side heated to 70-80°C and the outlet side cooled to 40-50°C, with a temperature gradient of 5-10°C / mm for 5-10 minutes. Ultrasonic vibration is applied to the interface area with a vertical vibration time of 30-60 seconds, an amplitude of 1-3 μm, and a vibration direction consistent with the thickness direction of the flow channel.