A durable enhanced thermal interface coating, method of manufacture and use

Abstract

This invention discloses a durable thermal interface coating, its preparation method, and its application, belonging to the field of condensation heat transfer technology. The coating comprises a base layer and a top layer. The base layer contains fluorocarbon resin, high thermal conductivity microparticles, nanoparticles, and adhesion-promoting resin, with the nanoparticles filling the sintered pores in the base layer. The top layer contains fluorocarbon resin, sheet-like graphene oxide loaded with nanoparticles, and adhesion-promoting resin. The sheet-like graphene oxide is stacked to form a barrier structure covering the openings of the pores in the top layer, forming a hierarchical sealing effect together with the pore filling in the base layer. The high thermal conductivity microparticles are exposed at their tips and contact the sheet-like graphene oxide to form interfacial thermal bridges. The preparation involves phase separation-induced pore formation, pulsed atomization sedimentation filling, scraping orientation, and gradient sintering to construct a thermally conductive and sealing microstructure. When applied to the metal surface of a steam condensing heat exchanger, this coating enables stable droplet condensation, solving the problems of poor thermal conductivity and insufficient long-term durability of traditional fluorocarbon coatings.

Description

Technical Field

[0001] This invention belongs to the field of condensation heat transfer technology, specifically relating to a durable thermal interface coating, its preparation method, and its application. Background Technology

[0002] Steam condensation heat transfer processes have wide applications in industrial production fields such as chemical engineering, power generation, and refrigeration. Taking the condensation process of steam in a surface condenser as an example, it belongs to the condensation heat transfer in phase change convective heat transfer, that is, steam condenses when it comes into contact with a wall at a temperature below saturation. This condensation mode is mainly divided into film condensation and droplet condensation. Numerous studies have shown that the heat transfer coefficient of droplet condensation is much higher than that of film condensation. Therefore, achieving and maintaining droplet condensation is a key way to enhance condensation heat transfer efficiency.

[0003] Currently, commonly used condensation surface materials in industry are mostly high-surface-energy metals such as copper, aluminum, stainless steel, and titanium. Due to their high surface energy, steam typically condenses into a film on these surfaces, forming a continuous liquid film, which significantly increases the heat transfer resistance. To achieve droplet condensation, the main current technical approach is to coat the high-surface-energy metal substrate with a low-surface-energy fluorocarbon polymer coating, such as tetrafluoroethylene-perfluoroalkoxy ether copolymer, polytetrafluoroethylene, polyvinylidene fluoride, or tetrafluoroethylene-hexafluoropropylene copolymer. These coatings reduce surface energy, causing the condensate to form dispersed droplets on the surface and rapidly detach, thereby significantly improving the condensation heat transfer coefficient.

[0004] However, existing fluorocarbon polymer coating solutions face the dual challenges of poor durability and insufficient thermal conductivity in practical applications, which severely restricts their reliability for long-term service.

[0005] First, regarding thermal conductivity, although fluorocarbon polymers impart hydrophobicity to the surface, they are themselves polymer materials with extremely low thermal conductivity, orders of magnitude lower than that of a thermally conductive metal substrate. This low thermal conductivity coating effectively introduces a significant thermal resistance into the heat transfer path, partially offsetting the heat transfer enhancement effect brought about by droplet condensation.

[0006] Secondly, regarding durability, this type of coating exhibits several failure factors. Firstly, the significant difference in linear expansion coefficients between the fluorocarbon polymer and the metal substrate leads to substantial thermal stress at the interface under thermal cycling conditions, making the coating prone to detaching from the substrate surface. Secondly, and more critically, during the high-temperature baking process of the fluorocarbon polymer coating, solvent evaporation inevitably creates microscopic defects such as nanoscale pinholes within the coating. Over long-term use, vapor molecules penetrate through these pinholes and reach the metal substrate surface, where they nucleate and condense, generating immense capillary pressure at the pinholes. This continuous capillary pressure gradually destroys the adhesive interface between the coating and the substrate, ultimately causing blistering and peeling, completely disabling the droplet condensation function.

[0007] In summary, developing a novel thermal interface coating technology that can maintain excellent droplet condensation performance, possess high thermal conductivity, and effectively solve the long-term durability problem caused by internal pinhole defects has become a key breakthrough urgently needed in this field. Summary of the Invention

[0008] The purpose of this invention is to provide a durable thermal interface coating, its preparation method, and its application, in order to solve the technical problems of poor thermal conductivity, weak adhesion to the metal substrate, and insufficient long-term durability caused by internal pinhole defects in current fluorocarbon coatings for steam condensation.

[0009] This invention provides a durable thermal interface material, comprising a base layer and a top layer above the base layer; the base layer can cover the surface of a substrate to be coated, and the base layer includes a base fluorocarbon resin matrix, highly thermally conductive microparticles dispersed in the base fluorocarbon resin matrix, base nanoparticles, and a base adhesion-promoting resin; the base nanoparticles are composed of a first base nanoparticle and a second base nanoparticle, wherein the first base nanoparticle accounts for 50-80% of the total mass of the base nanoparticles, and the second base nanoparticle accounts for 20-50% of the total mass of the base nanoparticles; the base fluorocarbon resin matrix serves as a film-forming phase to coat the highly thermally conductive microparticles and the base nanoparticles; The high thermal conductivity microparticles have a particle size of less than 2 μm and a mass percentage of 5-10%; the bottom layer nanopowder has a mass percentage of 0.3-1%; the bottom layer adhesion-promoting resin is distributed on the side of the bottom layer fluorocarbon resin matrix close to the substrate to be coated; the top layer covers the side of the bottom layer opposite to the substrate to be coated, and includes a top layer fluorocarbon resin matrix, top layer nanopowder and sheet-like graphene oxide dispersed in the top layer fluorocarbon resin matrix, and a top layer adhesion-promoting resin; the top layer fluorocarbon resin matrix acts as a film-forming phase to coat the top layer nanopowder; the sheet-like graphene oxide has a length of 5-10 μm and is loaded with the top layer nanopowder, and the top layer nanopowder is distributed on the top layer fluorocarbon resin matrix. The layers overlap each other along a direction parallel to the surface of the bottom layer, forming a stacked sheet-like barrier structure. The surface layer adhesion-promoting resin is distributed on the side of the surface layer near the bottom layer, and the surface layer adhesion-promoting resin chemically bonds with the fluorocarbon resin matrix of the bottom layer, so that the surface layer adheres to the bottom layer. The bottom layer nanopowder fills the pores formed in the bottom layer due to the evaporation of the sintering solvent. The sheet-like barrier structure in the surface layer covers the openings of the pores formed in the surface layer due to the evaporation of the sintering solvent. The filling of the pores in the bottom layer by the bottom layer nanopowder and the sealing of the pores in the surface layer by the sheet-like barrier structure both extend from the substrate to the side of the surface layer opposite to the substrate. The layers are arranged sequentially in the direction of the substrate to form a hierarchical sealing structure; the surface of the high thermal conductivity microparticles in the bottom layer is partially exposed from the side of the bottom layer away from the substrate to be coated, and contacts the sheet-like graphene oxide in the top layer to form an interfacial thermal bridge node; the thickness of the bottom layer is 3~35μm, and the thickness of the top layer is 2~15μm; in the top layer, the mass ratio of the top layer nanopowder is 0.5~2%; the amount of the bottom layer adhesion promoting resin is 3~8% of the mass of the bottom layer fluorocarbon resin matrix; the amount of the top layer adhesion promoting resin is 3~8% of the mass of the top layer fluorocarbon resin matrix; the mass ratio of the sheet-like graphene oxide to the loaded top layer nanopowder is (1~5):1.

[0010] Furthermore, both the bottom fluorocarbon resin matrix and the top fluorocarbon resin matrix are selected from one or more of tetrafluoroethylene-perfluoroalkoxy ether copolymer, polytetrafluoroethylene, polyvinylidene fluoride, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0011] Furthermore, the highly thermally conductive microparticles are selected from one or more of copper powder, aluminum powder, nickel powder, silver powder, silicon carbide, aluminum nitride, aluminum oxide, titanium nitride, titanium carbide, and titanium carbonitride.

[0012] Furthermore, the bottom layer nanopowder and the top layer nanopowder are respectively selected from one or more of copper, aluminum, chromium and their oxides, titanium dioxide and zinc oxide.

[0013] Furthermore, both the bottom adhesive promoting resin and the top adhesive promoting resin are selected from one or more of acrylic resin, epoxy resin, polyamide, polyamide-imide, polyurethane, and polyphenylene sulfide.

[0014] Furthermore, the underlying adhesive promoting resin contains polar groups, which can chemically adsorb onto the oxide film on the surface of the substrate to be coated, thereby bonding the underlying fluorocarbon resin matrix to the substrate to be coated.

[0015] Secondly, the present invention provides a method for preparing a durable thermal interface coating, comprising the following steps: S1. Mixing high thermal conductivity microparticles, a first-layer bottom layer nanopowder, a bottom layer adhesion-promoting resin, a bottom layer fluorocarbon resin matrix, and an organic solvent to form a bottom layer coating liquid; wherein the organic solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, butanone, and ethyl acetate, and the amount of the organic solvent is such that the solid content of the bottom layer coating liquid is 15~35wt%; S2. Coating the bottom layer coating liquid onto the surface of the substrate to be coated, and performing staged drying in a phase separation induction atmosphere and at a first temperature range to form a semi-cured bottom layer with pores penetrating to the surface. The average pore size of the openings is 1 / 5 to 1 / 2 of the particle size of the high thermal conductivity microparticles; S3. The second layer of bottom nanoparticles is dispersed in a low-boiling-point volatile solvent to form a suspension, the solid content of the suspension being 1-8 wt%, and applied to the surface of the semi-cured bottom layer by pulsed atomization sedimentation, relying on capillary penetration to allow the nanoparticles to enter the interior of the openings; subsequently, the surface is gently blown with airflow until there is no visible liquid film on the surface, ensuring that the tops of the high thermal conductivity microparticles are exposed and not covered; S4. Heating and sintering curing are performed in a second temperature range, the temperature of the second temperature range being higher than that of the first temperature range, causing the bottom fluorocarbon resin matrix to undergo residual solvent evaporation and resin crosslinking shrinkage during the sintering process, further evolving the openings into a dense structure. The bottom layer nanoparticles are sintered and fixed within the pores, forming a filling effect. Simultaneously, the tips of the highly thermally conductive microparticles are partially exposed from the upper surface of the bottom layer, forming interfacial thermal bridge nodes. S5. Preparation of a sheet-like graphene oxide composite dispersion loaded with surface nanoparticles: Sheet-like graphene oxide is dispersed in deionized water at a mass ratio of 1:50 to 1:200. Surface nanoparticles are added and ultrasonically stirred to load the nanoparticles onto the surface of the sheet-like graphene oxide. Then, the system is gradually replaced from water to an organic solvent compatible with the surface fluorocarbon resin through solvent displacement. The organic solvent is selected from N-methylpyrrolidone, N,N-dimethylformamide, N, One or more of N-dimethylacetamide, acetone, butanone, and ethyl acetate are used; the sheet-like graphene oxide is kept in a liquid-phase dispersion state throughout the process without undergoing complete drying; S6. The composite dispersion is mixed with the top layer fluorocarbon resin, the top layer adhesion promoting resin, the additive, and the supplementary solvent to prepare the top layer coating liquid. The additive is a non-organosilicon leveling agent or a non-organosilicon defoamer. The amount of the additive is 0.3~1% of the mass of the top layer fluorocarbon resin matrix, and the viscosity of the system is adjusted to 250~400 mPa·s; S7. The top layer coating liquid is applied to the upper surface of the bottom layer by a scraping method. Under the action of shear force, the sheet-like graphene oxide is oriented and aligned in a direction parallel to the bottom layer surface to form a wet film; S8.Under an inert atmosphere, the surface layer is sintered and cured using a gradient heating method, starting at a low temperature and then increasing to a high temperature. During the sintering and curing process, the surface layer undergoes solvent evaporation and resin shrinkage. The sheet-like barrier structure formed by the sheet-like graphene oxide-supported surface layer nanopowder covers the openings of the pores formed by the evaporation of the sintering solvent. Simultaneously, the surface layer adhesion promotes chemical bonding between the resin and the exposed fluorocarbon resin matrix of the underlying layer, forming interlayer bonding, ultimately resulting in the thermal interface coating.

[0016] Further, in step S2, the phase separation induction atmosphere is a mixture of supersaturated water vapor and air, and the volume percentage of the supersaturated water vapor is 30-70%; in step S2, the first temperature range is 80-120°C, and in step S4, the second temperature range is 150-160°C, and the temperature of the second temperature range is at least 30°C higher than that of the first temperature range; in step S1, the particle size of the high thermal conductivity microparticles is 0.5-2.0 μm, and the particle size of the bottom nanoparticles is 20-100 nm; in step S3, the low-boiling-point volatile solvent is one or more of ethanol, isopropanol, acetone, or n-hexane.

[0017] Furthermore, the pulse frequency of the pulsed atomization sedimentation in step S3 is 0.5~5Hz, and the deposition amount per pulse is 0.05~0.5mL / cm³. 2 After solvent replacement in step S5, the water content of the system is less than 5 wt%; the scraper moving speed in step S7 is 5~50 mm / s; the heating and sintering time in step S4 is 10~15 min, and the heating rate is 5~15℃ / min; the gradient heating method of first low temperature and then high temperature in step S8 is: first hold at 100~120℃ for 10~15 min, and then heat to 130~150℃ and hold for 10~15 min; the stage drying time in step S2 is 10~20 min; the solvent replacement method in step S5 is: add the organic solvent in batches to the sheet-like graphene oxide aqueous dispersion containing surface nanopowder and perform vacuum distillation to gradually remove water until the water content of the system is less than 5 wt%.

[0018] Thirdly, the present invention also provides an application of a durability-enhanced thermal interface coating in a steam condensing heat exchanger, wherein the thermal interface coating is applied to the surface of metal pipes or plates in the steam condensing heat exchanger, causing steam to condense in droplets on the surface of the thermal interface coating.

[0019] The beneficial effects of this invention are as follows: 1. Significantly improves the vertical thermal conductivity of the coating, solving the thermal conductivity bottleneck of traditional fluorocarbon coatings.

[0020] By introducing highly thermally conductive microparticles into the bottom layer and exposing their tops, they directly contact the sheet-like graphene oxide in the surface layer to form interfacial thermal bridge nodes, thus constructing a highly efficient "point-to-sheet" thermal conductivity network that runs through the bottom and surface layers. This structure effectively overcomes the inherently low thermal conductivity of fluorocarbon resin, significantly reduces the overall thermal resistance of the thermal interface coating, and fully releases the enhanced heat transfer potential of droplet condensation.

[0021] 2. Completely seals microscopic pinhole defects, fundamentally preventing vapor penetration and achieving ultra-long durability.

[0022] By utilizing the bottom layer of nanoparticles to fill the sintered pores, combined with the layered barrier structure formed by the top layer of sheet-like graphene oxide loaded with nanoparticles to cover the openings of the top layer pores, a hierarchical sealing structure is synergistically constructed, sealing the pores step by step from the inside out. This structure completely blocks the microchannels through which vapor molecules penetrate into the metal substrate, thoroughly eliminating failure factors such as coating blistering and peeling caused by capillary pressure at pinholes, and significantly extending the service life of the coating.

[0023] 3. It strengthens the interlayer and multi-level interfacial bonding with the substrate, and has excellent resistance to spalling due to thermal cycling.

[0024] The bottom layer adhesion-promoting resin achieves chemical adsorption with the oxide film on the metal substrate surface through polar groups, ensuring a strong bond between the bottom layer and the top layer adhesion-promoting resin. The top layer adhesion-promoting resin, on the other hand, chemically bonds with the exposed fluorocarbon resin matrix of the bottom layer, fusing the top and bottom layers together. This dual chemical bonding anchoring strategy greatly enhances the coating's resistance to thermal stress caused by differences in thermal expansion coefficients during thermal cycling, effectively preventing cracking and peeling of the coating under frequent temperature changes.

[0025] 4. It ensures a stable and efficient droplet condensation effect, and the overall heat transfer performance remains consistently excellent.

[0026] The top and bottom layers are still based on a low surface energy fluorocarbon resin matrix, giving the coating surface excellent hydrophobic properties, ensuring that steam can stably condense into droplets on it, and the droplets can quickly fall off. At the same time, because internal defects are blocked and interfacial bonding is enhanced, the high heat transfer coefficient of droplet condensation can be maintained for a long time, avoiding the problem of degradation to film condensation due to coating deterioration.

[0027] 5. The preparation method is precise and controllable, and the pre-designed multi-level thermal conductivity and sealing microstructure has been successfully constructed.

[0028] By employing key processes such as phase separation-induced pore formation, pulsed atomization sedimentation for precise filling of nanoparticles, gentle airflow to maintain exposure, shear force field-oriented alignment of sheet-like graphene oxide, and gradient temperature curing, a complete and intricate structure was achieved, including exposed thermally conductive microparticles at the bottom layer, filled pores, oriented sheet-like barrier arrangement at the surface layer, and interlayer chemical bonding. The entire process is ingeniously designed, highly operable, and suitable for industrial-scale production. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. Typically, the components of the embodiments of this invention can be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0032] The features and performance of the present invention will be further described in detail below with reference to embodiments. Example 1 This embodiment provides a durability-enhanced thermal interface coating and its preparation method, as detailed below.

[0033] I. Coating Formulation Base recipe: Bottom layer fluorocarbon resin matrix: tetrafluoroethylene-perfluoroalkoxy ether copolymer (PFA), 10kg; High thermal conductivity microparticles: silver powder, particle size 0.5μm, mass percentage 5%, i.e. 0.526kg (calculated based on total solid content 10.526kg, the same below); Bottom layer nanopowder total mass percentage 0.3%, i.e. 0.032kg; First bottom layer nanopowder (internal doping, percentage 50%): nano alumina, particle size 20nm, 0.016kg; Second bottom layer nanopowder (pore filling, percentage 50%): nano alumina, particle size 20nm, 0.016kg; Bottom layer adhesion promoting resin: epoxy resin, amount is 3% of the bottom layer fluorocarbon resin matrix mass, i.e. 0.3kg; Bottom layer thickness: 3μm.

[0034] Topcoat formulation (based on 10 kg of topcoat fluorocarbon resin matrix): Topcoat fluorocarbon resin matrix: PFA, 10 kg; Topcoat nanopowder: nano zinc oxide, particle size 20 nm, mass percentage 0.5%, i.e. 0.050 kg; Sheet-like graphene oxide: length 5 μm, mass ratio of topcoat nanopowder 1:1, i.e. 0.050 kg; Topcoat adhesion promoting resin: epoxy resin, amount 3% of the mass of topcoat fluorocarbon resin matrix, i.e. 0.3 kg; Additives: non-organosilicon leveling agent (polyacrylate), amount 0.3% of the mass of topcoat fluorocarbon resin matrix, i.e. 0.03 kg; Topcoat thickness: 2 μm.

[0035] II. Preparation Method S1. Preparation of the base coating solution 0.526 kg of silver powder (0.5 μm particle size), 0.016 kg of first-layer nanopowder (nano-alumina, 20 nm particle size), 0.3 kg of epoxy resin, 10 kg of PFA resin, and N-methylpyrrolidone (NMP) organic solvent were mixed and stirred evenly to form the bottom coating solution. The amount of NMP used was such that the solid content of the bottom coating solution was 15 wt%, which means the amount of solvent used was approximately 61.5 kg.

[0036] S2. Undercoat application and semi-curing pore formation The undercoating solution was applied to the surface of the copper substrate and then subjected to staged drying under a phase separation induction atmosphere. The phase separation induction atmosphere was a mixture of supersaturated water vapor and air, with the supersaturated water vapor accounting for 30% of the volume. The first temperature range was 80°C, and the drying time was 10 minutes, forming a semi-cured undercoat with open pores extending to the surface. The average pore size was 1 / 5 of the diameter of the high thermal conductivity microparticles, i.e., 0.1 μm.

[0037] S3. Second bottom layer nanopowder pulsed atomization sedimentation filling 0.016 kg of the second bottom layer nanopowder (nano-alumina, particle size 20 nm) was dispersed in ethanol (boiling point 78℃, not exceeding 80℃) to form a suspension. The solid content of the suspension was 1 wt%, i.e., the amount of ethanol used was 1.584 kg. The nanopowder was applied to the surface of the semi-cured bottom layer using a pulsed atomization deposition method with a pulse frequency of 0.5 Hz and a single pulse deposition amount of 0.05 mL / cm². The nanopowder penetrated into the pores through capillary penetration; subsequently, the surface was gently blown with an airflow until no visible liquid film remained on the surface, ensuring that the top of the silver powder was exposed and not covered.

[0038] S4. Bottom layer heating and sintering curing Sintering and curing were carried out at a second temperature range of 150℃, with a heating rate of 5℃ / min and a sintering time of 10min. The temperature in the second temperature range was at least 30℃ higher than that in the first temperature range (150℃ - 80℃ = 70℃). During the sintering process, the PFA resin underwent residual solvent evaporation and resin cross-linking shrinkage, transforming open pores into denser pores. Nano-alumina was simultaneously sintered and fixed within the pores, forming a bottom layer of nano-powder filling the pores; at the same time, the tips of the silver powder were partially exposed from the upper surface of the bottom layer, forming interfacial thermal bridge nodes. The resulting bottom layer thickness was 3μm.

[0039] S5. Preparation of sheet-like graphene oxide composite dispersions supported on surface layer nanopowders 0.050 kg of sheet-like graphene oxide (5 μm in length) was dispersed in deionized water at a mass ratio of 1:200 (i.e., 10 kg of deionized water was used). 0.050 kg of surface-layer nanoparticles (nano-zinc oxide, 20 nm particle size) were added and ultrasonically stirred to load the nanoparticles onto the surface of the sheet-like graphene oxide. The system was then gradually replaced with NMP through solvent displacement. The solvent displacement method involved adding NMP to the dispersion in batches and performing vacuum distillation to gradually remove water until the water content of the system was below 5 wt%. Throughout the process, the sheet-like graphene oxide was kept in a liquid-phase dispersion state without undergoing complete drying.

[0040] S6. Preparation of Topcoat Solution The above composite dispersion was mixed with 10 kg of PFA fluorocarbon resin for the top layer, 0.3 kg of epoxy resin for the top layer adhesion promoter, 0.03 kg of polyacrylate leveling agent and supplemented NMP solvent to prepare the top layer coating liquid, and the viscosity of the system was adjusted to 250 mPa·s.

[0041] S7. Topcoat application and orientation alignment The topcoat liquid was applied to the upper surface of the substrate using a blade coating method at a blade speed of 5 mm / s. Under shear force, the sheet-like graphene oxide was oriented and aligned in a direction parallel to the substrate surface, forming a wet topcoat film. The thickness of the wet film was controlled to achieve a final topcoat thickness of 2 μm.

[0042] S8. Surface layer gradient temperature sintering and curing Under a nitrogen inert atmosphere, the surface layer was sintered and cured using a gradient heating method, first at a low temperature and then at a high temperature: first, it was held at 100℃ for 10 minutes, and then the temperature was increased to 130℃ and held for 10 minutes. During the sintering and curing process, the surface layer was accompanied by solvent evaporation and resin shrinkage. The sheet-like barrier structure formed by the sheet-like graphene oxide loaded with nano-zinc oxide covered the openings of the pores formed by the evaporation of the sintering solvent in the surface layer. At the same time, the epoxy resin surface layer adhesion promoted the chemical bonding between the resin and the underlying exposed PFA resin matrix, forming interlayer bonding, and finally obtaining a thermal interface coating.

[0043] Example 2 This embodiment provides a durability-enhancing thermal interface coating and its preparation method, as shown below: I. Coating Formulation Bottom layer formulation (based on 10kg of bottom fluorocarbon resin matrix): Bottom fluorocarbon resin matrix: polytetrafluoroethylene (PTFE), 10 kg; high thermal conductivity microparticles: silicon carbide powder, particle size 2.0 μm, mass percentage 10%, i.e. 1.111 kg; bottom nanopowder total mass percentage 1%, i.e. 0.111 kg; first bottom nanopowder (internal doping, 80% percentage): nano titanium dioxide, particle size 100 nm, 0.089 kg; second bottom nanopowder (pore filling, 20% percentage): nano titanium dioxide, particle size 100 nm, 0.022 kg; bottom adhesion promoting resin: polyamide-imide (PAI), amount is 8% of the bottom fluorocarbon resin matrix mass, i.e. 0.8 kg; bottom thickness: 35 μm.

[0044] Topcoat formulation (based on 10 kg of topcoat fluorocarbon resin matrix): Top-layer fluorocarbon resin matrix: PTFE, 10kg; Top-layer nanopowder: nano-chromium powder, particle size 100nm, mass percentage 2%, i.e. 0.204kg; Sheet-like graphene oxide: length 10μm, mass ratio of top-layer nanopowder 5:1, i.e. 1.020kg; Top-layer adhesion promoting resin: PAI, amount is 8% of the mass of the top-layer fluorocarbon resin matrix, i.e. 0.8kg; Additives: non-organosilicon defoamer (polyether), amount is 1% of the mass of the top-layer fluorocarbon resin matrix, i.e. 0.1kg; Top-layer thickness: 15μm.

[0045] II. Preparation Method S1. Preparation of the base coating solution 1.111 kg of silicon carbide powder (particle size 2.0 μm), 0.089 kg of first-layer nanoparticle powder (nano titanium dioxide, particle size 100 nm), 0.8 kg of PAI, 10 kg of PTFE resin, and N,N-dimethylformamide (DMF) organic solvent were mixed and stirred evenly to form the bottom coating solution. The amount of DMF used was such that the solid content of the bottom coating solution was 35 wt%, which means the amount of solvent used was approximately 22.8 kg.

[0046] S2. Undercoat application and semi-curing pore formation The undercoating solution was applied to the surface of the stainless steel substrate and then subjected to phase-separation induction atmosphere. The phase-separation induction atmosphere was a mixture of supersaturated water vapor and air, with supersaturated water vapor accounting for 70% by volume. The first temperature range was 120°C, and the drying time was 20 minutes, forming a semi-cured undercoat with open pores extending to the surface. The average pore size was half the diameter of the high thermal conductivity microparticles, i.e., 1.0 μm.

[0047] S3. Second bottom layer nanopowder pulsed atomization sedimentation filling 0.022 kg of the second bottom layer nanopowder (nano titanium dioxide, 100 nm particle size) was dispersed in n-hexane (boiling point 69℃, not exceeding 80℃) to form a suspension. The solid content of the suspension was 8 wt%, i.e., the amount of n-hexane used was 0.253 kg. The powder was applied to the surface of the semi-cured bottom layer using a pulsed atomization deposition method with a pulse frequency of 5 Hz and a single pulse deposition amount of 0.5 mL / cm². The nanopowder penetrated into the pores through capillary penetration. Subsequently, the surface was gently blown with an airflow until no visible liquid film remained on the surface, ensuring that the top of the silicon carbide powder was exposed and not covered.

[0048] S4. Bottom layer heating and sintering curing Sintering and curing were carried out at a second temperature range of 160℃, with a heating rate of 15℃ / min and a sintering time of 15min. The temperature in the second temperature range was at least 30℃ higher than that in the first temperature range (160℃-120℃=40℃). During the sintering process, the PTFE resin underwent residual solvent evaporation and resin cross-linking shrinkage, transforming open pores into denser pores. Nano-titanium dioxide was simultaneously sintered and fixed within the pores, forming a bottom layer of nano-powder filling the pores; at the same time, the top of the silicon carbide powder was partially exposed from the upper surface of the bottom layer, forming interfacial thermal bridge nodes. The resulting bottom layer thickness was 35μm.

[0049] S5. Preparation of sheet-like graphene oxide composite dispersions supported on surface layer nanopowders 1.020 kg of sheet-like graphene oxide (10 μm in length) was dispersed in deionized water at a mass ratio of 1:50 (51 kg of deionized water). 0.204 kg of surface-layer nanoparticles (nano-chromium powder, 100 nm particle size) were added and ultrasonically stirred to load the nanoparticles onto the surface of the sheet-like graphene oxide. The system was then gradually replaced from water to DMF via solvent displacement. The solvent displacement method involved adding DMF to the dispersion in batches and performing vacuum distillation to gradually remove water until the water content of the system was below 5 wt%. Throughout the process, the sheet-like graphene oxide was kept in a liquid-phase dispersion state without undergoing complete drying.

[0050] S6. Preparation of Topcoat Solution The above composite dispersion was mixed with 10 kg of PTFE fluorocarbon resin for the top layer, 0.8 kg of PAI adhesive-promoting resin for the top layer, 0.1 kg of polyether defoamer, and supplemented DMF solvent to prepare the top layer coating liquid. The viscosity of the system was adjusted to 400 mPa·s.

[0051] S7. Topcoat application and orientation alignment The topcoat liquid was applied to the upper surface of the substrate using a blade coating method at a blade speed of 50 mm / s. Under shear force, the sheet-like graphene oxide was oriented and aligned in a direction parallel to the substrate surface, forming a wet topcoat film. The thickness of the wet film was controlled to achieve a final topcoat thickness of 15 μm.

[0052] S8. Surface layer gradient temperature sintering and curing Under a nitrogen inert atmosphere, the surface layer was sintered and cured using a gradient heating method, first at a low temperature and then at a high temperature: first held at 120℃ for 15 minutes, then heated to 150℃ and held for 15 minutes. During the sintering and curing process, the surface layer experienced solvent evaporation and resin shrinkage. The sheet-like barrier structure formed by the sheet-like graphene oxide loaded with nano-chromium powder covered the openings of the pores formed by the evaporation of the sintering solvent in the surface layer. At the same time, the PAI surface layer adhesion promoted the chemical bonding between the resin and the underlying exposed PTFE resin matrix, forming interlayer bonding, and finally obtaining a thermal interface coating.

[0053] Example 3 This embodiment provides a durability-enhancing thermal interface coating and its preparation method, as shown below: I. Coating Formulation Bottom layer formulation (based on 10kg of bottom fluorocarbon resin matrix): Bottom layer fluorocarbon resin matrix: polyvinylidene fluoride (PVDF), 10 kg; High thermal conductivity microparticles: aluminum nitride powder, particle size 1.25 μm ((0.5+2.0) / 2), mass percentage 7.5%, i.e. 0.811 kg; Bottom layer nanopowder total mass percentage 0.65% ((0.3+1) / 2), i.e. 0.070 kg; First bottom layer nanopowder (internal doping, 65%): nano copper powder, particle size 60 nm, 0.046 kg; Second bottom layer nanopowder (pore filling, 35%): nano copper powder, particle size 60 nm, 0.024 kg; Bottom layer adhesion promoting resin: acrylic resin, amount is 5.5% of the bottom layer fluorocarbon resin matrix mass, i.e. 0.55 kg; Bottom layer thickness: 19 μm ((3+35) / 2) Topcoat formulation (based on 10 kg of topcoat fluorocarbon resin matrix): Surface layer fluorocarbon resin matrix: PVDF, 10kg; Surface layer nanopowder: nano copper powder, particle size 60nm, mass percentage 1.25% ((0.5+2) / 2), i.e. 0.127kg; Sheet-shaped graphene oxide: length 7.5μm ((5+10) / 2), mass ratio with surface layer nanopowder is 3:1 ((1+5) / 2), i.e. 0.381kg; Surface layer adhesion promoting resin: acrylic resin, amount is 5.5% of the surface layer fluorocarbon resin matrix, i.e. 0.55kg; Additives: non-organosilicon leveling agent (polyacrylate), amount is 0.65% of the surface layer fluorocarbon resin matrix, i.e. 0.065kg; Surface layer thickness: 8.5μm ((2+15) / 2).

[0054] II. Preparation Method S1. Preparation of the base coating solution 0.811 kg of aluminum nitride powder (particle size 1.25 μm), 0.046 kg of first-layer nanoparticle powder (nano copper powder, particle size 60 nm), 0.55 kg of acrylic resin, 10 kg of PVDF resin, and N,N-dimethylacetamide (DMAc) organic solvent were mixed and stirred evenly to form the bottom coating solution. The amount of DMAc used was such that the solid content of the bottom coating solution was 25 wt% ((15+35) / 2), that is, the amount of solvent used was approximately 35.2 kg.

[0055] S2. Undercoat application and semi-curing pore formation The undercoating solution was applied to the surface of the aluminum substrate and then dried in stages under a phase separation induction atmosphere. The phase separation induction atmosphere was a mixture of supersaturated water vapor and air, with the supersaturated water vapor accounting for 50% by volume ((30+70) / 2). The first temperature range was 100℃ ((80+120) / 2), and the drying time was 15 min ((10+20) / 2), forming a semi-cured undercoat with open pores extending to the surface. The average pore size was 7 / 20 of the diameter of the high thermal conductivity particles ((1 / 5+1 / 2) / 2=0.35), or approximately 0.44 μm.

[0056] S3. Second bottom layer nanopowder pulsed atomization sedimentation filling 0.024 kg of the second bottom layer nanopowder (nano copper powder, particle size 60 nm) was dispersed in acetone (boiling point 56℃, not exceeding 80℃) to form a suspension. The solid content of the suspension was 4.5 wt% ((1+8) / 2), i.e., the amount of acetone used was 0.509 kg. The powder was applied to the surface of the semi-cured bottom layer using a pulsed atomization deposition method with a pulse frequency of 2.75 Hz ((0.5+5) / 2) and a single pulse deposition amount of 0.275 mL / cm² ((0.05+0.5) / 2). The nanopowder penetrated into the pores through capillary penetration; subsequently, the surface was gently blown with air until no visible liquid film was visible on the surface, ensuring that the top of the aluminum nitride powder was exposed and not covered.

[0057] S4. Bottom layer heating and sintering curing Sintering and curing were carried out at a second temperature range of 155℃ ((150+160) / 2), with a heating rate of 10℃ / min ((5+15) / 2) and a sintering time of 12.5min ((10+15) / 2). The temperature in the second temperature range was at least 30℃ higher than that in the first temperature range (155℃-100℃=55℃). During the sintering process, the PVDF resin underwent residual solvent evaporation and resin cross-linking shrinkage, transforming open pores into dense pores. Simultaneously, nano-copper powder was sintered and fixed within the pores, forming a bottom layer of nano-powder filling the pores. At the same time, the top of the aluminum nitride powder was partially exposed from the upper surface of the bottom layer, forming interfacial thermal bridge nodes. The resulting bottom layer thickness was 19μm.

[0058] S5. Preparation of sheet-like graphene oxide composite dispersions supported on surface layer nanopowders 0.381 kg of sheet-like graphene oxide (7.5 μm in length) was dispersed in deionized water at a mass ratio of 1:125 ((50+200) / 2), meaning 47.6 kg of deionized water was used. 0.127 kg of surface-layer nanoparticles (nano-copper powder, 60 nm particle size) were added and ultrasonically stirred to load the nanoparticles onto the surface of the sheet-like graphene oxide. The system was then gradually replaced with DMAc via solvent displacement. The solvent displacement method involved adding DMAc to the dispersion in batches and performing vacuum distillation to gradually remove water until the water content of the system was below 5 wt%. Throughout the process, the sheet-like graphene oxide was kept in a liquid-phase dispersion state without undergoing complete drying.

[0059] S6. Preparation of Topcoat Solution The above composite dispersion was mixed with 10 kg of PVDF fluorocarbon resin, 0.55 kg of acrylic resin adhesive promoter, 0.065 kg of polyacrylate leveling agent and supplemented DMAc solvent to prepare a topcoat liquid. The viscosity of the system was adjusted to 325 mPa·s ((250+400) / 2).

[0060] S7. Topcoat application and orientation alignment The topcoat liquid was applied to the upper surface of the substrate using a blade coating method. The blade moved at a speed of 27.5 mm / s ((5+50) / 2). Under shear force, the sheet-like graphene oxide was oriented and aligned in a direction parallel to the substrate surface to form a wet topcoat film. The thickness of the wet film was controlled to achieve a final topcoat thickness of 8.5 μm.

[0061] S8. Surface layer gradient temperature sintering and curing Under a nitrogen inert atmosphere, the surface layer was sintered and cured using a gradient heating method, first at a low temperature and then at a high temperature: first, it was held at 110℃ ((100+120) / 2) for 12.5 min ((10+15) / 2), and then the temperature was increased to 140℃ ((130+150) / 2) and held for 12.5 min. During the sintering and curing process, the surface layer was accompanied by solvent evaporation and resin shrinkage. The sheet-like barrier structure formed by the sheet-like graphene oxide loaded with nano-copper powder covered the openings of the pores formed by the evaporation of the sintering solvent in the surface layer; at the same time, the adhesion of the acrylic resin surface layer promoted the chemical bonding between the resin and the exposed PVDF resin matrix at the bottom layer, forming an interlayer bond, and finally a thermal interface coating was obtained.

[0062] Example 4 This embodiment provides a durability-enhancing thermal interface coating and its preparation method, as shown below: I. Coating Formulation Bottom layer formulation (based on 10kg of bottom fluorocarbon resin matrix): Bottom layer fluorocarbon resin matrix: tetrafluoroethylene-hexafluoropropylene copolymer (FEP), 10kg; High thermal conductivity microparticles: titanium nitride powder, particle size 1.8μm, mass percentage 9.2%, i.e. 1.013kg; Bottom layer nanopowder total mass percentage 0.85%, i.e. 0.094kg; First bottom layer nanopowder (internal doping, 70%): nano aluminum powder, particle size 85nm, 0.066kg; Second bottom layer nanopowder (pore filling, 30%): nano aluminum powder, particle size 85nm, 0.028kg; Bottom layer adhesion promoting resin: polyurethane, amount is 6.5% of the bottom layer fluorocarbon resin matrix mass, i.e. 0.65kg; Bottom layer thickness: 28μm.

[0063] Topcoat formulation (based on 10 kg of topcoat fluorocarbon resin matrix): Top-layer fluorocarbon resin matrix: FEP, 10kg; Top-layer nanopowder: nano-aluminum powder, particle size 85nm, mass percentage 1.7%, i.e. 0.173kg; Sheet-like graphene oxide: length 9μm, mass ratio to top-layer nanopowder 4:1, i.e. 0.692kg; Top-layer adhesion promoting resin: polyurethane, amount 6.5% of the top-layer fluorocarbon resin matrix mass, i.e. 0.65kg; Additives: non-organosilicon defoamer (polyether), amount 0.7% of the top-layer fluorocarbon resin matrix mass, i.e. 0.07kg; Top-layer thickness: 12μm.

[0064] II. Preparation Method S1. Preparation of the base coating solution 1.013 kg of titanium nitride powder (particle size 1.8 μm), 0.066 kg of first-layer nanoparticle powder (nano-aluminum powder, particle size 85 nm), 0.65 kg of polyurethane, 10 kg of FEP resin, and ethyl acetate organic solvent were mixed and stirred evenly to form the bottom coating solution. The amount of ethyl acetate used was such that the solid content of the bottom coating solution was 28 wt%, i.e., the amount of solvent used was approximately 30.7 kg.

[0065] S2. Undercoat application and semi-curing pore formation The undercoating solution was applied to the surface of the titanium substrate and then dried in stages under a phase separation induction atmosphere. The phase separation induction atmosphere was a mixture of supersaturated water vapor and air, with the supersaturated water vapor accounting for 55% of the volume. The first temperature range was 108°C, and the drying time was 17 minutes, forming a semi-cured undercoat with open pores extending to the surface. The average pore size was 0.4 times the particle size of the high thermal conductivity particles, i.e., 0.72 μm.

[0066] S3. Second bottom layer nanopowder pulsed atomization sedimentation filling 0.028 kg of the second bottom layer nanopowder (nano-aluminum powder, particle size 85 nm) was dispersed in isopropanol (boiling point 82℃, to be determined according to process suitability) to form a suspension with a solid content of 5.5 wt%, i.e., 0.481 kg of isopropanol was used. This was applied to the surface of the semi-cured bottom layer using a pulsed atomization deposition method with a pulse frequency of 3.5 Hz and a single pulse deposition rate of 0.35 mL / cm². The nanopowder penetrated into the pores via capillary penetration; subsequently, the surface was gently blown with air until no visible liquid film remained, ensuring that the top of the titanium nitride powder was exposed and not covered.

[0067] S4. Bottom layer heating and sintering curing Sintering and curing were carried out at a second temperature range of 157℃, with a heating rate of 12℃ / min and a sintering time of 13min. The temperature in the second temperature range was at least 30℃ higher than that in the first temperature range (157℃-108℃=49℃). During the sintering process, the FEP resin underwent residual solvent evaporation and resin cross-linking shrinkage, transforming open pores into denser pores. Simultaneously, nano-aluminum powder was sintered and fixed within the pores, forming a bottom layer of nano-powder filling the pores. At the same time, the top of the titanium nitride powder was partially exposed from the upper surface of the bottom layer, forming interfacial thermal bridge nodes. The resulting bottom layer thickness was 28μm.

[0068] S5. Preparation of sheet-like graphene oxide composite dispersions supported on surface layer nanopowders 0.692 kg of sheet-like graphene oxide (9 μm in length) was dispersed in deionized water at a mass ratio of 1:100, i.e., 69.2 kg of deionized water was used. 0.173 kg of surface-layer nanoparticles (nano-aluminum powder, 85 nm particle size) were added and ultrasonically stirred to load the nanoparticles onto the surface of the sheet-like graphene oxide. Then, the system was gradually replaced from water to ethyl acetate through solvent displacement. The solvent displacement method was as follows: ethyl acetate was added to the dispersion in batches and vacuum distillation was performed to gradually remove water until the water content of the system was below 5 wt%. Throughout the process, the sheet-like graphene oxide was kept in a liquid-phase dispersion state without undergoing complete drying.

[0069] S6. Preparation of Topcoat Solution The above composite dispersion was mixed with 10 kg of FEP surface fluorocarbon resin, 0.65 kg of polyurethane surface adhesion promoter resin, 0.07 kg of polyether defoamer and supplemented ethyl acetate solvent to prepare the surface coating liquid, and the viscosity of the system was adjusted to 350 mPa·s.

[0070] S7. Topcoat application and orientation alignment The topcoat liquid was applied to the upper surface of the substrate using a blade coating method at a blade speed of 35 mm / s. Under shear force, the sheet-like graphene oxide was oriented and aligned in a direction parallel to the substrate surface, forming a wet topcoat film. The thickness of the wet film was controlled to achieve a final topcoat thickness of 12 μm.

[0071] S8. Surface layer gradient temperature sintering and curing Under a nitrogen inert atmosphere, the surface layer was sintered and cured using a gradient heating method, first at a low temperature and then at a high temperature: first held at 112℃ for 13 minutes, then heated to 145℃ and held for 13 minutes. During the sintering and curing process, the surface layer experienced solvent evaporation and resin shrinkage. The sheet-like barrier structure formed by the sheet-like graphene oxide loaded with nano-aluminum powder covered the openings of the pores formed by the evaporation of the sintering solvent in the surface layer. At the same time, the polyurethane surface layer adhesion promoted the chemical bonding between the resin and the underlying exposed FEP resin matrix, forming interlayer bonding, and finally obtaining a thermal interface coating.

[0072] Example 5 This embodiment provides a durability-enhancing thermal interface coating and its preparation method, with specific results as follows: Bottom layer formulation (based on 10kg of bottom fluorocarbon resin matrix): Bottom fluorocarbon resin matrix: a mixture of PFA and PVDF in a 1:1 mass ratio, 5 kg each, totaling 10 kg; High thermal conductivity microparticles: aluminum powder, 0.8 μm in diameter, accounting for 6.2% by mass, i.e., 0.661 kg; Bottom nanopowder total mass percentage: 0.48%, i.e., 0.051 kg; First bottom nanopowder (internal doping, accounting for 55%): nano zinc oxide, 40 nm in diameter, 0.028 kg; Second bottom nanopowder (pore filling, accounting for 45%): nano zinc oxide, 40 nm in diameter, 0.023 kg; Bottom adhesion promoting resin: polyphenylene sulfide (PPS), used at 4% of the mass of the bottom fluorocarbon resin matrix, i.e., 0.4 kg; Bottom thickness: 10 μm.

[0073] Topcoat formulation (based on 10 kg of topcoat fluorocarbon resin matrix): Top-layer fluorocarbon resin matrix: a mixture of PFA and PVDF in a 1:1 mass ratio, 5 kg each, totaling 10 kg; Top-layer nanopowder: nano zinc oxide, 40 nm particle size, 0.85% by mass, i.e., 0.086 kg; Sheet-like graphene oxide: 6 μm in length, with a mass ratio of 2:1 to the top-layer nanopowder, i.e., 0.172 kg; Top-layer adhesion promoting resin: PPS, used at 4% of the top-layer fluorocarbon resin matrix mass, i.e., 0.4 kg; Additives: non-organosilicon leveling agent (polyacrylate), used at 0.5% of the top-layer fluorocarbon resin matrix mass, i.e., 0.05 kg; Top-layer thickness: 5 μm.

[0074] II. Preparation Method S1. Preparation of the base coating solution 0.661 kg of aluminum powder (0.8 μm particle size), 0.028 kg of first-layer nanopowder (nano zinc oxide, 40 nm particle size), 0.4 kg of PPS, 5 kg of PFA, 5 kg of PVDF resin, and methyl ethyl ketone (MEK) organic solvent were mixed and stirred until homogeneous to form the bottom coating solution. The amount of MEK used was such that the solid content of the bottom coating solution was 20 wt%, which means the amount of solvent used was approximately 43.6 kg.

[0075] S2. Undercoat application and semi-curing pore formation The undercoating solution was applied to the surface of the copper substrate and then subjected to staged drying under a phase separation induction atmosphere. The phase separation induction atmosphere was a mixture of supersaturated water vapor and air, with the supersaturated water vapor accounting for 40% of the volume. The first temperature range was 90°C, and the drying time was 13 minutes, forming a semi-cured undercoat with open pores extending to the surface. The average pore size was 0.3 times the particle size of the high thermal conductivity particles, i.e., 0.24 μm.

[0076] S3. Second bottom layer nanopowder pulsed atomization sedimentation filling 0.023 kg of the second bottom layer nanopowder (nano zinc oxide, 40 nm particle size) was dispersed in a 1:1 volume ratio of ethanol and acetone to form a suspension. The solid content of the suspension was 2.5 wt%, meaning the amount of mixed solvent used was 0.897 kg. The nanopowder was applied to the surface of the semi-cured bottom layer using a pulsed atomization deposition method with a pulse frequency of 1.8 Hz and a single pulse deposition rate of 0.15 mL / cm². The nanopowder penetrated into the pores via capillary penetration. Subsequently, the surface was gently blown with an airflow until no visible liquid film remained, ensuring that the top of the aluminum powder was exposed and not covered.

[0077] S4. Bottom layer heating and sintering curing Sintering and curing were carried out at a second temperature range of 153℃, with a heating rate of 7℃ / min and a sintering time of 11min. The temperature in the second temperature range was at least 30℃ higher than that in the first temperature range (153℃ - 90℃ = 63℃). During the sintering process, the PFA / PVDF mixed resin underwent residual solvent evaporation and resin cross-linking shrinkage, transforming open pores into denser pores. Nano-zinc oxide was simultaneously sintered and fixed within the pores, forming a bottom layer of nanoparticles that filled the pores. At the same time, the tips of the aluminum powder were partially exposed from the upper surface of the bottom layer, forming interfacial thermal bridge nodes. The resulting bottom layer thickness was 10μm.

[0078] S5. Preparation of sheet-like graphene oxide composite dispersions supported on surface layer nanopowders 0.172 kg of sheet-like graphene oxide (6 μm in length) was dispersed in deionized water at a mass ratio of 1:160, i.e., 27.5 kg of deionized water was used. 0.086 kg of surface-layer nanoparticles (nano-zinc oxide, 40 nm particle size) were added and ultrasonically stirred to load the nanoparticles onto the surface of the sheet-like graphene oxide. Then, the system was gradually replaced from water to methyl ethyl ketone (MEK) through solvent displacement. The solvent displacement method was as follows: MEK was added to the dispersion in batches and vacuum distillation was performed to gradually remove water until the water content of the system was below 5 wt%. Throughout the process, the sheet-like graphene oxide was kept in a liquid-phase dispersion state without undergoing complete drying.

[0079] S6. Preparation of Topcoat Solution The above-mentioned composite dispersion was mixed with 5 kg of PFA and 5 kg of PVDF mixed top-layer fluorocarbon resin, 0.4 kg of PPS top-layer adhesion promoter resin, 0.05 kg of polyacrylate leveling agent and supplemented with methyl ethyl ketone solvent to prepare a top-layer coating liquid, and the viscosity of the system was adjusted to 290 mPa·s.

[0080] S7. Topcoat application and orientation alignment The topcoat liquid was applied to the upper surface of the substrate using a blade coating method at a blade speed of 15 mm / s. Under shear force, the sheet-like graphene oxide was oriented and aligned in a direction parallel to the substrate surface, forming a wet topcoat film. The thickness of the wet film was controlled to achieve a final topcoat thickness of 5 μm.

[0081] S8. Surface layer gradient temperature sintering and curing Under a nitrogen inert atmosphere, the surface layer was sintered and cured using a gradient heating method, first at a low temperature and then at a high temperature: first held at 105℃ for 11 min, then heated to 135℃ and held for 11 min. During the sintering and curing process, the surface layer experienced solvent evaporation and resin shrinkage. The sheet-like barrier structure formed by the sheet-like graphene oxide loaded with nano-zinc oxide covered the openings of the pores formed by the evaporation of the sintering solvent in the surface layer. At the same time, the adhesion of the PPS surface layer promoted the chemical bonding between the resin and the underlying exposed PFA / PVDF mixed resin matrix, forming an interlayer bond, and finally obtaining a thermal interface coating.

[0082] Comparative Example 1 I. Coating Formulation Fluorocarbon resin matrix: tetrafluoroethylene-perfluoroalkoxy ether copolymer (PFA), 10 kg; organic solvent: N-methylpyrrolidone (NMP), used in an amount sufficient to achieve a coating liquid-to-solid content of 15 wt% (approximately 61.5 kg). No thermally conductive fillers, nanoparticles, or adhesion-promoting resins are added.

[0083] II. Preparation Method PFA resin was dissolved in NMP and stirred until homogeneous to form a coating solution. The coating solution was applied to the surface of the copper substrate by a blade coating method, dried at 80 °C for 10 min, and then sintered and cured at 150 °C for 10 min to obtain a fluorocarbon coating with a single layer thickness of approximately 5 μm.

[0084] Comparative Example 2 Compared to Example 1, no high thermal conductivity microparticles and sheet-like graphene oxide were added; otherwise, the same as in Example 1 was used.

[0085] Comparative Example 3 Compared to Example 1, no bottom layer nanopowder was filled, and the top layer coating was changed to spraying; otherwise, it was the same as Example 1.

[0086] Experimental Example 1 Coating thermal conductivity and condensation heat transfer performance test Test samples: The coatings prepared in Examples 1-5 and Comparative Examples 1-3 (covering the surface of a 50 mm × 50 mm × 0.5 mm copper plate) were used for thermal conductivity measurement; the same coating was prepared on the outer wall of a φ19 mm × 1 m copper tube for condensation heat transfer measurement.

[0087] Thermal conductivity: The equivalent thermal conductivity of each coating in the vertical direction was measured according to ASTM D5930 (protected hot plate method) at room temperature of 25 °C. Each sample was measured 3 times and the average value was taken.

[0088] Condensation heat transfer coefficient: Coated copper tubes were installed on an open steam condensation test bench. The steam side was saturated steam at 100 ℃, and the cooling water inlet temperature was 30 ℃ with a flow rate of 0.5 m / s. After the system stabilized, the initial condensation heat transfer coefficient (K) was calculated from the cooling water temperature rise and steam condensation rate. Then, the system was run continuously for 1000 h, and the heat transfer coefficient was measured again to calculate the retention rate. The condensation morphology was observed through a viewing window during operation.

[0089] The results are shown in Table 1: Table 1 Thermal conductivity results As shown in Table 1, Examples 1-5, through the thermal bridge formed by the "exposed high thermal conductivity microparticles - sheet-like graphene oxide contact," increased the thermal conductivity of the coating by approximately 10 times compared to pure PFA (Comparative Example 1), significantly improving the initial condensation heat transfer coefficient. Simultaneously, due to the hierarchical sealing structure preventing vapor permeation, the coating maintained droplet condensation with almost no performance degradation after 1000 hours. Comparative Example 2 lacked a thermally conductive network, resulting in limited heat transfer improvement; Comparative Example 3, although possessing a thermally conductive network, lacked pore filling and barriers, allowing vapor to permeate along pinholes, leading to early failure. This directly demonstrates that both the thermally conductive network and the hierarchical sealing are indispensable.

[0090] Experimental Example 2 Test samples: Coatings were prepared on 100 mm × 50 mm × 1 mm copper plates, stainless steel plates, and aluminum plates according to Examples 1-5 and Comparative Examples 1-3.

[0091] Initial adhesion: Perform a 1 mm × 1 mm cross-cut test (100-cross cutter) according to GB / T 9286-1998, and rate the 3M tape after tearing.

[0092] Thermal cycling resistance: Place the same batch of test pieces in a thermal shock chamber, from -40 ℃ (30 min) to 150 ℃ (30 min), with a transition time of ≤30 s, for 100 cycles. Remove and allow to return to room temperature, visually inspect for blistering and cracking, and then grade again by cross-section.

[0093] The results are shown in Table 2: Table 2 Adhesion and heat cycle results As shown in Table 2, the examples and comparative examples 2 and 3 containing adhesion-promoting resins (epoxy, PAI, acrylic, etc.) all achieved strong adhesion between the matrix and the substrate through chemical bonding, exhibiting excellent resistance to thermal cycling. Comparative example 1, containing pure PFA, lacked chemical anchoring, resulting in poor adhesion and easy detachment under thermal stress. This demonstrates that adhesion-promoting resins are key to solving the problem of weak interfacial bonding.

[0094] Experimental Example 3 Test Samples: The coatings of Examples 1 and Comparative Examples 1-3 (prepared on a 0.2 mm thick copper foil, φ30 mm in size) were sealed and covered the mouth of a beaker containing boiling deionized water (coating facing the water vapor). The beaker was continuously heated to maintain boiling. The samples were removed every 24 hours and observed under a 200× metallographic microscope for bubbles or peeling marks with a diameter ≥10 μm. Three samples were used in each group in parallel, and the average time for the first appearance of defects was recorded as the "penetration failure time". If no defects were observed after a cumulative period >3000 hours, it was recorded as >3000 hours.

[0095] The results are shown in Table 3: Table 3 Results of vapor permeation resistance test As shown in Table 3, in Comparative Example 1, the pinholes in the pure PFA, due to the large amount of solvent evaporation, became rapid vapor permeation channels, failing within 20 hours. Comparative Example 3, lacking both bottom-layer nanopowder filling and a surface sheet barrier, could not seal the pinholes, resulting in permeation failure in only 165 hours. Although Comparative Example 2 had bottom-layer pores filled, the lack of oriented stacked sheet graphene oxide on the surface layer prevented the formation of a continuous barrier to block the openings, allowing vapor to still enter the interface through the surface pinholes, leading to bubbling after 480 hours. In contrast, Example 1 of this invention employs a hierarchical sealing method: "bottom-layer nanopowder filling the bottom-layer pores + surface sheet graphene oxide supporting nanopowder layering to block the surface openings." This completely blocks vapor molecules, resulting in no permeation defects after 3000 hours. This irrefutably demonstrates that the hierarchical sealing structure is the decisive factor in granting ultra-long durability.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A durability-enhanced thermal interface coating, characterized in that, Includes the bottom layer and the surface layer above the bottom layer; The bottom layer can cover the surface of the substrate to be coated. The bottom layer includes a bottom fluorocarbon resin matrix, highly thermally conductive microparticles dispersed in the bottom fluorocarbon resin matrix, bottom nanopowder, and bottom adhesion-promoting resin. The bottom nanopowder is composed of a first bottom nanopowder and a second bottom nanopowder, with the first bottom nanopowder accounting for 50-80% of the total mass of the bottom nanopowder and the second bottom nanopowder accounting for 20-50% of the total mass of the bottom nanopowder. The bottom fluorocarbon resin matrix serves as a film-forming phase, coating the highly thermally conductive microparticles and the bottom nanopowder. The highly thermally conductive microparticles have a particle size of less than 2 μm and account for 5-10% of the mass. The bottom nanopowder accounts for 0.3-1% of the mass. The bottom adhesion-promoting resin is distributed on the side of the bottom fluorocarbon resin matrix closest to the substrate to be coated. The top layer covers the side of the bottom layer facing away from the substrate to be coated, and includes a top layer fluorocarbon resin matrix, top layer nanopowder and sheet-like graphene oxide dispersed in the top layer fluorocarbon resin matrix, and a top layer adhesion promoting resin; the top layer fluorocarbon resin matrix serves as a film-forming phase to coat the top layer nanopowder; the sheet-like graphene oxide has a length of 5~10μm and is loaded with the top layer nanopowder, and the top layer nanopowder overlaps with each other in the top layer fluorocarbon resin matrix in a direction parallel to the surface of the bottom layer to form a stacked sheet-like barrier structure; the top layer adhesion promoting resin is distributed on the side of the top layer close to the bottom layer, and the top layer adhesion promoting resin is chemically bonded to the bottom layer fluorocarbon resin matrix, so that the top layer adheres to the bottom layer. The bottom layer nanopowder fills the pores formed by the evaporation of the sintering solvent in the bottom layer, and the sheet-like barrier structure in the surface layer covers the openings of the pores formed by the evaporation of the sintering solvent in the surface layer. The filling of the pores in the bottom layer by the bottom layer nanopowder and the sealing of the pores in the surface layer by the sheet-like barrier structure are arranged sequentially from the substrate to be coated to the side of the surface layer facing away from the substrate to be coated, forming a hierarchical sealing structure. The surface of the high thermal conductivity microparticles in the bottom layer is partially exposed on the side of the bottom layer facing away from the substrate to be coated, and comes into contact with the sheet-like graphene oxide in the top layer to form an interfacial thermal bridge node. The thickness of the bottom layer is 3~35μm, and the thickness of the top layer is 2~15μm; in the top layer, the mass percentage of the top layer nanopowder is 0.5~2%; the amount of the bottom layer adhesion-promoting resin is 3~8% of the mass of the bottom layer fluorocarbon resin matrix; the amount of the top layer adhesion-promoting resin is 3~8% of the mass of the top layer fluorocarbon resin matrix; the mass ratio of the sheet-like graphene oxide to the loaded top layer nanopowder is (1~5):

1.

2. The thermal interface coating according to claim 1, characterized in that, Both the bottom fluorocarbon resin matrix and the top fluorocarbon resin matrix are selected from one or more of tetrafluoroethylene-perfluoroalkoxy ether copolymer, polytetrafluoroethylene, polyvinylidene fluoride, and tetrafluoroethylene-hexafluoropropylene copolymer.

3. The thermal interface coating according to claim 1, characterized in that, The highly thermally conductive microparticles are selected from one or more of copper powder, aluminum powder, nickel powder, silver powder, silicon carbide, aluminum nitride, aluminum oxide, titanium nitride, titanium carbide, and titanium carbonitride.

4. The thermal interface coating according to claim 1, characterized in that, The bottom layer nanopowder and the top layer nanopowder are respectively selected from one or more of copper, aluminum, chromium and their oxides, titanium dioxide and zinc oxide.

5. The thermal interface coating according to claim 1, characterized in that, Both the bottom adhesive promoting resin and the top adhesive promoting resin are selected from one or more of acrylic resin, epoxy resin, polyamide, polyamide-imide, polyurethane, and polyphenylene sulfide.

6. The thermal interface coating according to claim 1, characterized in that, The underlying adhesive promoting resin contains polar groups, which can chemically adsorb onto the oxide film on the surface of the substrate to be coated, thus bonding the underlying fluorocarbon resin matrix to the substrate to be coated.

7. A method for preparing a durability-enhanced thermal interface coating as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. High thermal conductivity microparticles, first-layer bottom layer nanopowder, bottom layer adhesion-promoting resin, bottom layer fluorocarbon resin matrix, and organic solvent are mixed to form a bottom layer coating liquid; the organic solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, butanone, and ethyl acetate, and the amount of the organic solvent is such that the solid content of the bottom layer coating liquid is 15~35wt%; S2. The bottom coating liquid is applied to the surface of the substrate to be coated, and the substrate is dried in stages in the first temperature range under a phase separation induction atmosphere to form a semi-cured bottom layer with openings that extend to the surface. The average pore size of the openings is 1 / 5 to 1 / 2 of the particle size of the high thermal conductivity microparticles. S3. The second layer of bottom nanopowder is dispersed in a low-boiling-point volatile solvent to form a suspension. The solid content of the suspension is 1~8wt%. The suspension is applied to the surface of the semi-cured bottom layer by pulsed atomization sedimentation. The nanopowder enters the pores by capillary penetration. Then, the surface is gently blown with air until there is no visible liquid film on the surface, ensuring that the top of the high thermal conductivity particles is exposed and not covered. S4. Sintering and curing are carried out in the second temperature range, where the temperature is higher than that in the first temperature range. This causes the bottom fluorocarbon resin matrix to undergo residual solvent evaporation and resin cross-linking shrinkage during sintering, further transforming the open pores into denser pores. The bottom nanopowder is simultaneously sintered and fixed within the pores, forming a filling effect of the bottom nanopowder on the pores. At the same time, the tips of the high thermal conductivity microparticles are partially exposed from the upper surface of the bottom layer, forming interfacial thermal bridge nodes. S5. Preparation of a sheet-like graphene oxide composite dispersion loaded with surface nanopowder: Sheet-like graphene oxide is dispersed in deionized water at a mass ratio of 1:50 to 1:

200. Surface nanopowder is added and ultrasonically stirred to load the nanopowder onto the surface of the sheet-like graphene oxide. Then, the system is gradually replaced from water to an organic solvent compatible with the surface fluorocarbon resin through solvent displacement. The organic solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, butanone, and ethyl acetate. Throughout the process, the sheet-like graphene oxide remains in a liquid-phase dispersion state without undergoing complete drying. S6. The composite dispersion is mixed with the top layer fluorocarbon resin, the top layer adhesion promoting resin, the additives and the supplementary solvent to prepare the top layer coating liquid. The additives are non-organosilicon leveling agents or non-organosilicon defoamers. The amount of the additives is 0.3~1% of the mass of the top layer fluorocarbon resin matrix, and the viscosity of the system is adjusted to 250~400 mPa·s. S7. The surface coating liquid is applied to the upper surface of the bottom layer by a scraping method, and the sheet-like graphene oxide is oriented and aligned in a direction parallel to the bottom layer surface under the action of shear force to form a wet surface film. S8. Under an inert atmosphere, the surface layer is sintered and cured using a gradient heating method of first low temperature and then high temperature. During the sintering and curing process, the surface layer undergoes solvent evaporation and resin shrinkage. The sheet-like barrier structure formed by the sheet-like graphene oxide-loaded surface layer nanopowder covers the openings of the pores formed by the evaporation of the sintering solvent in the surface layer. At the same time, the surface layer adhesion promotes the chemical bonding between the resin and the fluorocarbon resin matrix on the exposed surface of the bottom layer, forming interlayer bonding, and finally obtaining the thermal interface coating.

8. The preparation method according to claim 7, characterized in that, The phase separation induction atmosphere in step S2 is a mixture of supersaturated water vapor and air, wherein the volume percentage of the supersaturated water vapor is 30-70%. In step S2, the first temperature range is 80~120℃, and in step S4, the second temperature range is 150~160℃, and the temperature of the second temperature range is at least 30℃ higher than that of the first temperature range. The particle size of the high thermal conductivity microparticles in step S1 is 0.5~2.0μm, and the particle size of the bottom nanoparticles is 20~100nm; the low boiling point volatile solvent in step S3 is one or more of ethanol, isopropanol, acetone or n-hexane.

9. The preparation method according to claim 7, characterized in that, In step S3, the pulse frequency of the pulsed atomization sedimentation is 0.5~5Hz, and the deposition amount per pulse is 0.05~0.5mL / cm³. 2 After the solvent replacement is completed in step S5, the water content of the system is less than 5 wt%; the scraper moving speed in step S7 is 5~50 mm / s. The heating and sintering time in step S4 is 10-15 min, and the heating rate is 5-15℃ / min; the gradient heating method of first low temperature and then high temperature in step S8 is: first hold at 100-120℃ for 10-15 min, and then heat to 130-150℃ and hold for 10-15 min; the stage drying time in step S2 is 10-20 min; The solvent replacement method described in step S5 is as follows: The organic solvent is added in batches to the sheet-like graphene oxide aqueous dispersion containing the surface nanoparticles, and vacuum distillation is performed to gradually remove water until the water content of the system is below 5 wt%.

10. The application of a durability-enhanced thermal interface coating as described in any one of claims 1 to 6 in a steam condensing heat exchanger, characterized in that, The thermal interface coating is applied to the surface of the metal pipes or plates in the steam condensing heat exchanger, causing steam to condense in droplets on the surface of the thermal interface coating.

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