A high-pressure resistant modified polyester powder coating material and a preparation method thereof

Abstract

The present application relates to the technical field of polyester coating material preparation, and particularly relates to a high-pressure-resistant modified polyester powder coating material and a preparation method thereof, the material comprises, by mass fraction, a hydroxyl end group polyester resin, a caprolactam-based blocked polyisocyanate, a microencapsulated tin-free latent catalyst, a sheet mica powder, spherical silicon dioxide, boron nitride, a modified layered double hydroxide, and a phosphacene compound, and is combined with a leveling agent, a degassing agent, a wetting agent, and a dispersing agent. The modified layered double hydroxide is obtained through co-precipitation-calcination-oleate intercalation reconstruction-silicon dioxide coating-mercapto silane grafting. The microencapsulated catalyst is obtained through F-T hard wax hot melt spraying and cooling to form capsules and grading. The material can significantly reduce pores and interface defects, inhibit ion migration and partial discharge, improve breakdown stability and insulation reliability in a humid heat environment, and simultaneously consider coating film leveling and construction stability.

Description

Technical Field

[0001] This invention relates to the field of polyester coating material preparation technology, specifically to a high-pressure resistant modified polyester powder coating material and its preparation method. Background Technology

[0002] Powder coatings are widely used for the protection of metal components due to their solvent-free nature, high efficiency, and ease of achieving thick coatings and dense films. In the field of surface insulation protection for electrical equipment and high-voltage components, coatings, in addition to meeting corrosion resistance and appearance requirements, must also possess high dielectric strength, volume resistivity, and long-term insulation stability, and be able to suppress partial discharge and breakdown failure under humid, hot, polluted, and electric field coupling conditions. However, existing powder coating materials are mostly designed for general protection, and when directly applied to high-voltage scenarios, they often struggle to balance the control of thick-film defects with the consistency of electrical performance. Among existing insulating powder systems, epoxy or epoxy-modified systems, while possessing high crosslinking density and initial insulation performance, lack sufficient weather resistance and thermal cycling reliability, making them prone to powdering, brittleness, or interfacial debonding, thus forming electric field concentration points and inducing partial discharge. Polyester systems have good weather resistance and toughness, but traditional polyester powders mainly focus on appearance and corrosion resistance optimization, lacking a structured design for high-voltage insulation failure mechanisms. Especially under thick coating conditions, they are more susceptible to the amplification of pores and interface defects, resulting in fluctuations in breakdown voltage and partial discharge initiation voltage, making it difficult to meet high reliability requirements.

[0003] The critical shortcomings of high-pressure resistant coatings often stem from defects such as micropores, gas traps, filler agglomeration, and interfacial voids. With thick coatings, the gas escape path is longer; if the powder contains water, volatiles, or is insufficiently degassed, micropore nuclei can easily remain inside the coating. Curing shrinkage and thermal stress can further promote the evolution of defects into microcracks or interfacial debonding zones, forming localized high-field distortions and becoming initiation points for partial discharges. On the other hand, some curing systems are at risk of premature reaction during processing or storage, easily generating gel particles or uneven cross-linking. Gel points significantly reduce breakdown consistency and amplify inter-batch differences. In humid, hot, and polluted environments, coatings are also prone to tracking and the expansion of tracking carbonization channels. Furthermore, if fillers added to improve thermal conductivity and corona resistance are not sufficiently dispersed and controlled at the interface, they may introduce new interfacial defects and stress concentrations, further weakening the electrical stability.

[0004] In summary, existing technologies generally suffer from problems such as difficulty in suppressing defects in thick coatings, insufficient insulation reliability under humid and hot conditions, and uncontrolled reactions and poor consistency during processing and storage. There is an urgent need for a high-voltage resistant modified polyester powder coating solution that takes into account both material structure design and processing technology control in order to achieve long-term stable insulation protection under high voltage conditions. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to provide a high-pressure resistant modified polyester powder coating material and its preparation method. The material comprises, by weight, hydroxyl-terminated polyester resin, caprolactam-based blocked polyisocyanate, microencapsulated tin-free latent catalyst, lamellar mica powder, spherical silica, boron nitride, modified layered double hydroxide, and phosphazene compounds, along with leveling agents, degassing agents, wetting agents, and dispersants. The modified layered double hydroxide is obtained through co-precipitation—calcination—oleate intercalation reconstruction—silica coating—thiol silane grafting; the microencapsulated catalyst is obtained through Fischer-Tropsch hard wax hot melt spray cooling encapsulation and fractionation. Under thick coating conditions, this material can significantly reduce porosity and interface defects, inhibit ion migration and partial discharge, improve breakdown stability and insulation reliability in humid and hot environments, while also ensuring coating leveling and application stability.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A high-pressure resistant modified polyester powder coating material comprises the following components by weight: 55-68 parts hydroxyl-terminated polyester resin, 6-12 parts blocked polyisocyanate, 0.05-0.25 parts microencapsulated tin latent catalyst, 6-15 parts lamellar mica powder, 8-18 parts spherical silica, 1-5 parts boron nitride, 2-4 parts modified layered double hydroxide, 0.5-3 parts phosphazene compound, 0.6-1.2 parts leveling agent, 0.2-0.6 parts degassing agent, 0.5-1 part wetting agent, and 0.5-2 parts dispersant.

[0007] Preferably, the modified layered double hydroxide is prepared by the following steps: S11. Accurately weigh 7-10 parts by weight of magnesium nitrate hexahydrate and 3-4 parts by weight of aluminum nitrate nonahydrate, and add them to 45-100 parts by weight of deionized water. Stir at 400-600 rpm until completely dissolved to obtain metal salt solution A. Weigh 4-6 parts by weight of sodium hydroxide and 1-2 parts by weight of sodium carbonate, and add them to 40-60 parts by weight of deionized water. Stir at 400-600 rpm until completely dissolved to obtain alkali solution B. Add solution A and alkali solution B simultaneously dropwise at 25-30℃ in a co-current manner to a reactor pre-filled with 20-60 parts by weight of deionized water. Adjust the dropping rate of alkali solution B to stabilize the pH of the system at 9.8-10.3, and maintain the stirring speed at 600-900 rpm. After the addition is complete, continue stirring at 25-30℃ for 30-40 minutes to ensure sufficient nucleation and obtain a uniform coprecipitate slurry. S12. The uniform coprecipitated slurry obtained in step S11 is heated to 70-80℃ and aged for 8-18 h. During the aging process, stirring is maintained at 300-500 rpm to promote crystal growth and improve the layered structure. After aging, the slurry is cooled to below 40℃, and solid-liquid separation is performed by centrifugation. The precipitate is washed with deionized water until the conductivity of the filtrate is ≤200μS / cm. The washed filter cake is dried with hot air at 80-110℃ for 8-12 h to obtain the carbonate-type layered double hydroxide precursor. S13. The carbonate-type layered double hydroxide precursor obtained in step S12 is placed in a muffle furnace and calcined under a nitrogen atmosphere. The heating rate is controlled at 3-8℃ / min. After heating to 430-480℃, it is held for 1-3 hours and then naturally cooled to room temperature to obtain layered bimetallic oxide. S14. Take 5-10 parts of the layered bimetallic oxide obtained in step S13 and add it to 90-100 parts of a mixed solvent of ethanol / deionized water. The mass ratio of ethanol to water is controlled at 60-80:40-20. Disperse the mixture at 800-1200 rpm for 10-30 min at 25-30℃. Then add 1-1.2 parts of sodium oleate as an intercalation anion source. Under nitrogen protection, heat the system to 60-70℃ and maintain it for 6-24 h. During this period, adjust the pH to 9.0-10.0 with sodium hydroxide solution. After the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the hydrophobic intercalated layered bimetallic oxide. S15. Add 5-10 parts of the hydrophobic intercalated layered double hydroxide obtained in step S14 to 80-100 parts of ethanol / water mixed solvent, with the mass ratio of ethanol to water controlled at 70-90:10-30, and disperse at 800-1200 rpm for 10-30 min at 25-35℃; add 15-25% ammonia water to stabilize the pH of the system at 9.0-10.0, and then add tetraethyl orthosilicate dropwise, so that the silica coating accounts for 3-12% of the mass of the hydrophobic intercalated layered double hydroxide. After the dropwise addition is completed, continue to react at 30-40℃ for 2-6 h. After the reaction is completed, filter and wash with ethanol 3-4 times, and then wash with deionized water until the conductivity of the aqueous phase filtrate is ≤200 μS / cm. Vacuum dry at 100-120℃ for 2-6 h to obtain silica-coated hydrophobic intercalated layered double hydroxide. S16. Take 5-10 parts of the silica-coated hydrophobic intercalated layered double hydroxide obtained in step S15 and disperse it in 60-100 parts of anhydrous ethanol. Control the temperature at 25-40℃ and stir at 600-1000 rpm for 10-20 min. Then add 0.05-0.2 parts of 3-mercaptopropyltrimethoxysilane and 0.8-1.5 parts of deionized water to provide the trace water source required for condensation. Adjust the pH of the system to 4.0-5.0 with glacial acetic acid and continue to react at 30-40℃ for 1-4 h. After the reaction is completed, filter and wash with ethanol 2-3 times to remove unreacted silane. Then vacuum dry at 110-120℃ for 4-8 h to obtain the modified layered double hydroxide.

[0008] Preferably, the microencapsulated tin latent catalyst is prepared through the following steps: S21. Melting and Homogenizing: Weigh 5.5-7 parts of Fischer-Tropsch hard wax by weight and heat it to 120-140℃. Mechanically stir at 300-600 rpm until completely melted. Add 2.5-4 parts of Bi / Zr catalyst and 0.2-0.8 parts of flow aid in sequence, and continue stirring for 20-40 min to make the system uniform and free of visible particle agglomeration, thus obtaining the melt material. S22. Spray cooling encapsulation: The molten material is fed into a spray granulator and atomized using a pressure nozzle. The atomization pressure is set to 0.2-0.6 MPa, the cooling air temperature to 10-25℃, the inlet temperature to 120-150℃, and the outlet temperature to 25-35℃, so that the droplets can be rapidly solidified during flight to form spherical wax shell microcapsules. S23. Grading and post-processing: Collect the microcapsule particles obtained in step S22 and control the particle size by air classification to ensure that the D50 of the finished microcapsule powder is controlled within 10-25 µm; mix 5-10 parts of the graded microcapsule powder with 0.03-0.12 parts of fumed silica in a high-speed mixer and mix at 800-1200 rpm for 2-5 min to ensure that the fumed silica is uniformly adsorbed on the surface of the microcapsules to reduce the risk of agglomeration and clumping, thereby obtaining the microencapsulated Wuxi latent catalyst.

[0009] Preferably, in step S21, the Bi / Zr catalyst is a mixture of bismuth neodecanoate and zirconium acetylacetonate in a mass ratio of 2-3:1; the flow aid is one or more of dipropylene glycol dibenzoate and diisononyl phthalate.

[0010] Preferably, the lamellar mica powder is selected from one or more of muscovite powder and phlogopite powder, the particle size D50 of the lamellar mica powder is 10-30 μm, and the particle size-to-thickness ratio is 10-80; the spherical silica is selected from one or more of spherical fused silica, spherical quartz silica, and spherical silica micro powder, the spherical silica has a sphericity ≥0.9, a particle size D50 of 5-20 μm, a SiO2 content ≥99.5%, and a moisture content <0.1%.

[0011] Preferably, the boron nitride is selected from one or more of hexagonal boron nitride and cubic boron nitride; the boron nitride has a particle size D50 of 1-15 μm, a thermal conductivity of not less than 30 W / (m·K), and a volume resistivity of not less than 1×10⁻⁶. 14 Ω·cm, and moisture content ≤0.3%.

[0012] Preferably, the phosphazene compound is selected from one or more of cyclotriphosphazene and cyclotetraphosphazene.

[0013] Preferably, the blocked polyisocyanate is further limited to caprolactam-based blocked polyisocyanates; the leveling agent is further limited to acrylate-based leveling agents; the degassing agent is further limited to benzoin isopropyl ether; the dispersant is further limited to polyurethane-based dispersants; and the wetting agent is further limited to titanate-based wetting agents.

[0014] A method for preparing a high-pressure resistant modified polyester powder coating material, comprising the following steps: S1. Dry the lamellar mica powder, spherical silica, boron nitride and modified layered double hydroxide at 100-110℃ for 2-4 h, and seal the resulting dried powder for later use under RH≤50% conditions; S2. Add hydroxyl-terminated polyester resin, lamellar mica powder, spherical silica and boron nitride to a high-speed mixer and premix at 800-1500 rpm for 3-5 min to obtain masterbatch A; S3. Blocked polyisocyanate, phosphazene compound, microencapsulated tin latent catalyst, leveling agent, wetting agent and dispersant are added to a high-speed mixer at ≤40℃ and premixed at 600-1200 rpm for 2-4 min to obtain masterbatch B; S4. Add masterbatch A to a twin-screw extruder for melt extrusion, and perform vacuum degassing in the middle of the extrusion section, with the vacuum degree set to -0.07 to -0.095 MPa; S5. Add masterbatch B and the dried modified layered double hydroxide of S1 to the side feed of the extrusion section, so that the melt temperature is ≤115℃ and then discharge, press into tablets and cool. S6. The cooled sheet is crushed and graded to obtain a powder coating material, with the powder particle size controlled to D50=35-55μm; S7. The degassing agent is added to the powder coating material obtained in S6 by post-mixing, and mixed at 600-1000 rpm for 1-3 min at ≤40℃ to obtain the high-pressure resistant modified polyester powder coating material.

[0015] Preferably, in step S4, the temperatures of each zone of the twin-screw extruder are: 75-85℃ in the first zone, 85-95℃ in the second zone, 95-100℃ in the third zone, 105-110℃ in the fourth zone, and 110-115℃ in the fifth zone.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes the addition crosslinking of hydroxyl-terminated polyesters and blocked polyisocyanates to form a dense interpenetrating network. Combined with microencapsulated latent catalysts, vacuum degassing, and post-processing side feeding, this effectively reduces premature reactions, gel points, and micropore air trapping defects during extrusion and curing, thereby improving the density and breakdown consistency of the coating under thick coating conditions. Lamellar mica and spherical silica construct a "shielding-interstitial" composite framework, while boron nitride provides thermal field homogenization and hot spot resistance, synergistically reducing local electric field concentration and suppressing the initiation and propagation of partial discharge. Layered double hydroxides, after intercalation with hydrophobicity, silica coating, and silane grafting, retain ion-trapping capabilities while reducing moisture absorption and ion migration risks. Combined with the arc / tracking resistance of phosphazenes, the coating maintains high insulation reliability and long-term stability under humid, hot, polluted, and arc-impact conditions. Attached Figure Description

[0017] Figure 1 This is a flow chart of the preparation process of the high-pressure resistant modified polyester powder coating material described in this invention; Figure 2 This is a flow chart of the preparation process of the modified layered double hydroxide described in this invention; Figure 3 This is a flow chart of the preparation process of the microencapsulated tin latent catalyst described in this invention. Detailed Implementation

[0018] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Please see Figure 1-3 The present invention provides a technical solution: Example 1 This embodiment provides a high-pressure resistant modified polyester powder coating material, which comprises the following components by weight (one part by weight is defined as 100g):

[0020] The hydroxyl-terminated polyester resin is designated as Uralac® P 1550. This resin serves as the continuous phase and main film-forming substance of the coating, providing hydroxyl functional groups for addition curing with the unblocked isocyanate groups to form a cross-linked network with high cohesive energy and impart toughness and interfacial adhesion to the coating. It works synergistically with blocked polyisocyanates to achieve "gas-free" addition curing, reducing the probability of forming micropores and local weak points in thick coatings. At the same time, it forms a "resin-inorganic skeleton" composite structure with mica / spherical silica / boron nitride to homogenize the electric field and stress.

[0021] The blocked polyisocyanate is further specified as a caprolactam-based blocked polyisocyanate, specifically VESTAGON® B 1530. This component acts as a crosslinking agent, undergoing deblocking and releasing isocyanate groups during curing and heating. These groups rapidly add to polyester hydroxyl groups to form urethane bonds, constructing a dense crosslinked network and improving the coating's heat resistance, swelling resistance, and the complete curing of thick films. The key reaction can be illustrated by the following formula: R-NCO+R′-OH→R-NH-COO-R′; The reaction pathway itself does not produce gaseous byproducts, therefore, in conjunction with vacuum degassing and degassing agents, it can significantly reduce bubble nuclei. Simultaneously, this system suppresses unfavorable side reactions through raw material drying and low melt temperature control, thereby reducing micropores and weak points caused by carbon dioxide precipitation. The side reactions are shown below: R-NCO + H2O → R-NH2 + CO2↑; The lamellar mica powder is muscovite powder with a particle size D50 of 15 μm and a sheet diameter-to-thickness ratio of 10-80. This component, as a lamellar high-insulation shielding filler, forms a parallel / semi-parallel orientation structure under melt flow shearing, significantly extending the migration paths of water vapor, ions, and charge carriers and reducing local electric field concentration, thereby suppressing partial discharge initiation and tracking. It synergistically forms a dense framework of "lamellar shielding - spherical interstitial filling" with spherical silica, reducing the porosity of thick coatings and interfacial voids. When synergistically with modified layered double hydroxides, mica extends the migration path while layered double hydroxides reduce the concentration of migratable ions, and the two together reduce the risk of leakage and tracking in humid and hot environments.

[0022] The spherical silica is spherical fused silica, with a sphericity ≥0.9, a particle size D50 of 10 μm, a SiO2 content ≥99.5%, and a moisture content <0.1%. This component achieves dense filling of gaps through its spherical high packing characteristics, reducing the density of micropores and local defects in the coating film, thereby improving breakdown consistency; its low moisture absorption and low ionic impurity characteristics help maintain high volume resistivity; it synergistically forms a "dense packing + tortuous path" with mica, further reducing the possibility of charge and water film penetration under humid and hot conditions; and it synergistically improves the dispersion and melt flow uniformity of inorganic phases with leveling agents, wetting agents, and dispersants, thereby reducing surface shrinkage cavities, pinholes, and other electric field sharp point defects.

[0023] The boron nitride is hexagonal boron nitride with a particle size D50 of 15 μm, a thermal conductivity of not less than 30 W / (m·K), and a volume resistivity of not less than 1×10⁻⁶. 14 Ω·cm, and moisture content ≤0.3%; This component provides a thermally conductive channel while maintaining high insulation, reducing local hot spots and thermo-electric coupling amplification effects under the action of an electric field, thereby suppressing the driving force of partial discharge propagation and electrical tree growth. It works synergistically with spherical silica to achieve "densification + thermal uniformity", reducing the tendency of thermal degradation and carbonization caused by hot spots. When synergistically with phosphazene compounds, thermal uniformity reduces the peak value of local thermal shock of electric arc / electric trace, which is conducive to the formation of a more continuous protective phase on the surface of phosphazene and delays the propagation of carbonization channels.

[0024] The phosphazene compound is a cyclotriphosphazene, specifically a hexaphenoxycyclotriphosphazene; This component tends to form a phosphorus-containing inorganic or glassy protective structure under arc / tracking thermal shock, inhibiting the continuous expansion of carbonized conductive channels and improving arc and tracking resistance. The representative reaction pathway is "the transformation of the phosphazene structure from P=N to P=O and P–O–P networks under thermal / oxygen action," specifically: (P=N)n+O2→(P=O, POP)n; Meanwhile, it can delay the construction of electrical tracking channels in synergy with mica sheet shielding, and improve the continuity and adhesion stability of the surface protective phase in synergy with modified layered double hydroxides.

[0025] The leveling agent is further specified as an acrylate leveling agent, specifically Resiflow P-67; The degassing agent is further specified as benzoin isopropyl ether; The dispersant is further defined as a polyurethane dispersant, specifically DISPERBYK-163; The wetting agent is further specified as a titanate wetting agent, specifically Ken-React CAPOW L38 / H; The modified layered double hydroxide is prepared by the following steps: S11. Accurately weigh 7 parts by weight of magnesium nitrate hexahydrate and 3 parts by weight of aluminum nitrate nonahydrate, and add them to 80 parts by weight of deionized water. Stir at 400 rpm until completely dissolved to obtain metal salt solution A. Weigh 4 parts by weight of sodium hydroxide and 2 parts by weight of sodium carbonate, and add them to 60 parts by weight of deionized water. Stir at 400 rpm until completely dissolved to obtain alkali solution B. Add solution A and alkali solution B simultaneously dropwise at 25°C in a co-current manner to a reactor pre-filled with 20 parts by weight of deionized water. Adjust the dropping rate of alkali solution B to stabilize the pH of the system at 9.8, and maintain the stirring speed at 600 rpm. After the addition is complete, continue stirring at 25°C for 30 min to ensure sufficient nucleation and obtain a uniform coprecipitate slurry. S12. The uniform coprecipitated slurry obtained in step S11 is heated to 70℃ and aged for 10 h. During the aging process, the mixture is stirred at 500 rpm to promote crystal growth and improve the layered structure. After aging, the mixture is cooled to below 40℃, and solid-liquid separation is performed by centrifugation. The precipitate is washed with deionized water until the conductivity of the filtrate is ≤200 μS / cm. The washed filter cake is dried with hot air at 80℃ for 12 h to obtain the carbonate-type layered double hydroxide precursor. S13. The carbonate-type layered double hydroxide precursor obtained in step S12 is placed in a muffle furnace and calcined under a nitrogen atmosphere. The heating rate is controlled at 5℃ / min. After heating to 480℃, it is held for 3 hours and then naturally cooled to room temperature to obtain layered bimetallic oxide. S14. Take 10 parts of the layered bimetallic oxide obtained in step S13 and add it to 100 parts of ethanol / deionized water mixed solvent. The mass ratio of ethanol to water is controlled at 70:30. Disperse the mixture at 800 rpm for 30 min at 25 °C. Then add 1.2 parts of sodium oleate as an intercalation anion source. Under nitrogen protection, heat the system to 70 °C and maintain it for 20 h. During this period, adjust the pH to 9.5 with sodium hydroxide solution. After the reaction is completed, cool to room temperature, filter, wash and dry to obtain hydrophobic intercalated layered bimetallic oxide. S15. Add 7 parts of the hydrophobic intercalated layered double hydroxide obtained in step S14 to 100 parts of ethanol / water mixed solvent, with the mass ratio of ethanol to water controlled at 70:30, and disperse at 800 rpm for 30 min at 25℃; add 25% ammonia water to stabilize the pH of the system at 9.0, and then add tetraethyl orthosilicate dropwise, so that the silica coating amount accounts for 8% of the mass of the hydrophobic intercalated layered double hydroxide (the amount of tetraethyl orthosilicate used is 1.9 parts). After the dropwise addition is completed, continue to react at 40℃ for 4 h. After the reaction is completed, filter, wash with ethanol 4 times, and then wash with deionized water until the conductivity of the aqueous phase filtrate is ≤200 μS / cm. Dry under vacuum at 100℃ for 4 h to obtain silica-coated hydrophobic intercalated layered double hydroxide. S16. Take 5 parts of the silica-coated hydrophobic intercalated layered double hydroxide obtained in step S15 and disperse it in 100 parts of anhydrous ethanol. Control the temperature at 25℃ and stir at 1000 rpm for 20 min. Then add 0.2 parts of 3-mercaptopropyltrimethoxysilane and 1 part of deionized water to provide the trace water source required for condensation. Adjust the pH of the system to 5.0 with glacial acetic acid and continue to react at 40℃ for 3 h. After the reaction is completed, filter and wash with ethanol 3 times to remove unreacted silane. Then dry under vacuum at 110℃ for 5 h to obtain the modified layered double hydroxide.

[0026] While retaining the adsorption / exchange capacity of layered materials for migratable anions and acidic residues, the interlayer water activity and hygroscopicity are reduced by oleate intercalation, a water-proof isolator barrier is formed by silica coating and an interface state that is conducive to capturing charge carriers is introduced, and the interface stability with the polymer network is enhanced by mercaptosilane grafting, thereby reducing interface debonding voids and agglomeration defects.

[0027] Its key chemical synergy with blocked polyisocyanates can be illustrated by the "addition of mercapto to isocyanate": R-NCO+R′-SH→R-NH-CO-SR′; This reaction makes it easier for the modified layered double hydroxide to be "chemically anchored" into the cross-linked network during the curing process, reducing the porosity and electric field sharpness around the particles; at the same time, its ion trapping and silica coating synergistically reduce ion migration and leakage channel formation under humid and hot conditions, thereby improving volume resistivity and anti-scratching stability.

[0028] The microencapsulated tin latent catalyst is prepared through the following steps: S21. Melting and homogenizing: Weigh 7 parts of Fischer-Tropsch hard wax (Sasolwax C105) by weight, heat to 130℃, and mechanically stir at 400 rpm until completely melted; add 2.5 parts of Bi / Zr catalyst and 0.2 parts of flow aid in sequence, and continue stirring for 30 min to make the system uniform and free of visible particle agglomeration, thus obtaining the melt material; S22. Spray cooling encapsulation: The molten material is fed into a spray granulator and atomized using a pressure nozzle. The atomization pressure is set to 0.2 MPa, the cooling air temperature to 25°C, the inlet temperature to 130°C, and the outlet temperature to 35°C, so that the droplets can quickly solidify during flight to form spherical wax shell microcapsules. S23. Grading and post-processing: Collect the microcapsule particles obtained in step S22 and control the particle size by air classification to ensure that the D50 of the finished microcapsule powder is controlled within 10-25 µm; mix 10 parts of the graded microcapsule powder with 0.12 parts of fumed silica in a high-speed mixer and mix at 800 rpm for 5 min to ensure that the fumed silica is uniformly adsorbed on the surface of the microcapsules to reduce the risk of agglomeration and clumping, thereby obtaining the microencapsulated Wuxi latent catalyst.

[0029] The Bi / Zr catalyst is a mixture of bismuth neodecanoate and zirconium acetylacetonate in a mass ratio of 2:1; the flow aid is dipropylene glycol dibenzoate.

[0030] The microencapsulated Wuxi latent catalyst is used to achieve reaction timing control of "latent in the processing stage and released in the curing stage": during the extrusion and storage stages, the wax shell inhibits catalyst migration and premature reaction, reducing the probability of gel point formation; during the curing stage, the wax shell melts and releases the catalyst, increasing the reaction rate and conversion rate inside the thick film, and reducing dielectric loss fluctuations caused by residual hydroxyl groups and unreacted isocyanates. Its synergistic effect is reflected in ensuring "fast and uniform" curing together with blocked polyisocyanates, and in avoiding local unsealing / local crosslinking during the extrusion stage together with the subsequent side feeding and low melt temperature.

[0031] This embodiment also discloses a method for preparing a high-pressure resistant modified polyester powder coating material, including the following steps: S1. Dry the lamellar mica powder, spherical silica, boron nitride and modified layered double hydroxide at 110℃ for 4h, and seal the resulting dried powder for later use under RH≤50% conditions; S2. Add hydroxyl-terminated polyester resin, lamellar mica powder, spherical silica and boron nitride to a high-speed mixer and premix at 1500 rpm for 3 min to obtain masterbatch A; S3. Blocked polyisocyanate, phosphazene compound, microencapsulated tin latent catalyst, leveling agent, wetting agent and dispersant are added to a high-speed mixer at ≤40℃ and premixed at 800 rpm for 4 min to obtain masterbatch B; S4. Add masterbatch A to a twin-screw extruder for melt extrusion, and perform vacuum degassing in the middle section of the extrusion, with the vacuum degree set to -0.095 MPa; the twin-screw extruder is a co-rotating twin-screw extruder with a screw length-to-diameter ratio of 36 and a screw speed set to 350 rpm; masterbatch A is added using a main feed method, with the main feed rate set to 15 kg / h; the temperatures of each zone of the twin-screw extruder are: zone 1: 85℃, zone 2: 95℃, zone 3: 100℃, zone 4: 105℃, and zone 5: 115℃; S5. Masterbatch B and the dried modified layered double hydroxide from S1 are added to the side feed in the later stage of extrusion to make the melt temperature ≤115℃ before being discharged, pressed into tablets, and cooled. The side feed point is located in the later stage after the vacuum exhaust port, at a distance of 8 screw elements after the vacuum port. Masterbatch B is added by metering side feed, with the side feed rate set at 2.2 kg / h. During the extrusion process, the melt temperature measured by the thermocouple inserted at the die head is used as the control criterion, and the melt temperature at the die head is controlled not to exceed 115℃. S6. The cooled sheet is pulverized and classified to obtain a powder coating material. After classification, the particle size distribution of the powder is controlled as D10=14 μm, D50=45 μm, and D90=95 μm, and the mass fraction of fine powder with a particle size less than 10 μm is controlled as 3.0%. When the mass fraction of fine powder is higher than 3.0%, the classification cut-off point is adjusted upward and the material is returned to the mill until the mass fraction of fine powder returns to 3.0%. S7. The degassing agent is added to the powder coating material obtained in S6 by post-mixing, and mixed at 1000 rpm for 3 min at ≤40℃ to obtain the high-pressure resistant modified polyester powder coating material.

[0032] Example 2: This example differs from Example 1 in that, in Example 2, the high-pressure resistant modified polyester powder coating material comprises the following components by weight (one part by weight is defined as 100g):

[0033] The remaining steps are exactly the same as in Example 2 and Example 1.

[0034] Example 3: This example differs from Example 1 in that, in Example 3, the high-pressure resistant modified polyester powder coating material comprises the following components by weight (one part by weight is defined as 100g):

[0035] The remaining steps are exactly the same as in Example 3 and Example 1.

[0036] Comparative Example Comparative Example 1: The only difference between Comparative Example 1 and Example 1 is that the use of modified layered double hydroxides was omitted in Comparative Example 1, while the remaining steps are exactly the same in Comparative Example 1 and Example 1.

[0037] Comparative Example 2: The only difference between Comparative Example 2 and Example 1 is that the use of microencapsulated tin latent catalyst and blocked polyisocyanate was omitted in Comparative Example 2. The remaining steps are exactly the same in Comparative Example 2 and Example 1.

[0038] Comparative Example 3: The only difference between Comparative Example 3 and Example 1 is that the use of boron nitride, spherical silicon dioxide, and phosphazene compounds was omitted in Comparative Example 3. The remaining steps are exactly the same in Comparative Example 3 and Example 1.

[0039] Performance testing The powders obtained in Examples 1, 2, 3, and Comparative Examples 1-3 were electrostatically sprayed onto the surface of sandblasted and degreased steel plate substrates. The dry film thickness was controlled at 400 μm ± 20 μm. The substrates were then cured at 180 ℃ for 15 min, cooled to 23 ℃, and placed in an environment of 23 ℃ and 50% relative humidity for 24 h before electrical performance testing. Thickness was measured at multiple points using a film thickness gauge, and the average value was taken. For each electrical performance and abrasion resistance test, at least five samples were used to calculate the mean and standard deviation.

[0040] Dielectric strength was measured according to the method specified in GB / T 1408.1-2016 (equivalent to IEC 60243-1), using a ball-to-ball electrode under power frequency conditions with a uniform voltage increase until breakdown, and the breakdown field strength was calculated. Partial discharge initiation voltage (PDIV) was determined according to GB / T 7354-2018 (Partial Discharge Measurement) with circuit configuration and calibration, using a 50 Hz AC voltage increase and an apparent discharge quantity of 10 pC as the criterion. Volume resistivity was tested according to GB / T 31838.2-2019 (DC Method Volume Resistivity / Volume Resistivity), and results were given for normal conditions (23 ℃, 50%RH) and damp heat aging (85 ℃, 85%RH, 168 h) followed by a 2 h cooling period. Tracking resistance was determined according to GB / T 4207-2022, and the tracking index (CTI) was compared. Abrasion resistance was determined according to GB / T 1768-2006 (rotational abrasion rubber wheel method), and the mass loss after a specified number of revolutions was recorded. The relevant test results are shown below:

[0041] As can be seen from the above, the three sets of embodiments provided by this invention are significantly superior to the three sets of comparative examples in terms of high voltage resistance. The dielectric strengths of Examples 1-3 are 42.5, 45.8, and 44.1 kV / mm, respectively, and the PDIVs are 11.0, 12.4, and 11.7 kV, respectively, all significantly higher than those of Comparative Examples 1-3 (dielectric strength 35.2 / 18.6 / 31.7 kV / mm, PDIV 8.6 / 5.1 / 7.3 kV). This difference can be attributed to the improved thick film curing conversion rate and spatial uniformity, as well as the reduced defect density. The addition reaction between the hydroxyl polyester and caprolactam-blocked isocyanate during the curing stage forms a urethane cross-linked structure. The timing regulation of the release of the microcapsule latent catalyst during the processing stage and the release during the curing stage further reduces the localized reaction and gel point formation during the extrusion stage, thereby reducing the number of micropores and interfacial voids inside the thick coating film, weakening local electric field distortion, and raising the partial discharge initiation threshold. At the same time, the sheet shielding effect of mica and the interstitial compaction effect of spherical molten silica together extend the carrier migration path and improve dielectric uniformity at the microscale, providing a structural basis for the synchronous improvement of dielectric strength and PDIV.

[0042] Comparative Example 2 exhibited the most significant performance degradation after the removal of the blocked isocyanate and microencapsulated latent catalyst (dielectric strength 18.6 kV / mm, PDIV 5.1 kV, normal volume resistivity 5.4 × 10⁻⁶). 13 (Ω·cm, abrasion mass loss 60mg / 1000 rpm). This result indicates that the formation of the cross-linked network not only determines the mechanical load-bearing capacity of the coating, but also directly affects the defect sensitivity of electrical properties. Insufficient cross-linking or uneven curing leads to an increase in free volume, a decrease in interfacial bonding force, and an enrichment of micro-defects, making breakdown more likely to be dominated by defects and accompanied by a decrease in volume resistivity, thus resulting in a synergistic deterioration of electrical properties and abrasion resistance.

[0043] In Comparative Example 1, when only the modified layered double hydroxide was removed, the normal volume resistivity remained at 2.5 × 10⁻⁶. 15 Ω·cm, but decreased to 2.0×10 after damp heat aging. 13 The CTI decreased from 600 V to 400 V, and the PDIV also decreased from 11.0 kV to 8.6 kV. This characteristic of "maintaining normal operating conditions but collapsing under humid heat" indicates that the modified layered double hydroxide has a decisive contribution to environmental adaptability. Its intercalation hydrophobicity and silica coating reduce moisture absorption and electrolyte ingress, while interfacial grafting enhances the stability of the filler-matrix interface, thereby inhibiting ion migration and water film conduction under humid heat conditions, and slowing down the formation of leakage tracking and tracking carbonization channels. After removing this component, the above-mentioned inhibition mechanism is lost, resulting in a significant decrease in volume resistivity and tracking threshold under humid heat, which is reflected in the reduction of PDIV.

[0044] In Comparative Example 3, after removing boron nitride, spherical silica, and phosphazene, the dielectric strength, PDIV, and CTI decreased to 31.7 kV / mm, 7.3 kV, and 450 V, respectively, while the wear resistance mass loss increased to 55 mg / 1000 rpm, and the wet heat volume resistivity remained at 1.2 × 10⁻⁶. 14 The results are on the order of Ω·cm. This indicates that the composition of this coating primarily affects the comprehensive pathway of "densification—thermal field homogenization—surface anti-tracking". Spherical silica has a direct effect on interstitial densification and wear resistance; boron nitride reduces local hot spots and thermal-electric coupling amplification effects through thermally conductive channels, thus making it easier to suppress partial discharge propagation under adverse conditions; phosphazene tends to form phosphorus-containing protective structures, which helps to increase the tracking propagation barrier and improve CTI. When all three are missing, the coating is more susceptible to the effects of micro-defects and local thermal peaks, resulting in a simultaneous decline in breakdown, partial discharge, and tracking performance.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-pressure resistant modified polyester powder coating material, characterized in that, The product comprises the following components by weight: 55-68 parts hydroxyl-terminated polyester resin, 6-12 parts blocked polyisocyanate, 0.05-0.25 parts microencapsulated tin latent catalyst, 6-15 parts lamellar mica powder, 8-18 parts spherical silica, 1-5 parts boron nitride, 2-4 parts modified layered double hydroxide, 0.5-3 parts phosphazene compound, 0.6-1.2 parts leveling agent, 0.2-0.6 parts degassing agent, 0.5-1 part wetting agent, and 0.5-2 parts dispersant.

2. The high-pressure resistant modified polyester powder coating material according to claim 1, characterized in that, The modified layered double hydroxide is prepared by the following steps: S11. Accurately weigh 7-10 parts by weight of magnesium nitrate hexahydrate and 3-4 parts by weight of aluminum nitrate nonahydrate, and add them to 45-100 parts by weight of deionized water. Stir at 400-600 rpm until completely dissolved to obtain metal salt solution A. Weigh 4-6 parts by weight of sodium hydroxide and 1-2 parts by weight of sodium carbonate, and add them to 40-60 parts by weight of deionized water. Stir at 400-600 rpm until completely dissolved to obtain alkali solution B. Add solution A and alkali solution B simultaneously dropwise at 25-30℃ in a parallel flow to a reactor pre-filled with 20-60 parts by weight of deionized water. Adjust the dropping rate of alkali solution B to stabilize the pH of the system at 9.8-10.3, and maintain the stirring speed at 600-900 rpm. After the addition is complete, continue stirring at 25-30℃ for 30-40 minutes to ensure sufficient nucleation and obtain a uniform co-precipitated slurry. S12. The uniform coprecipitated slurry obtained in step S11 is heated to 70-80℃ and aged for 8-18 h. During the aging process, stirring is maintained at 300-500 rpm to promote crystal growth and improve the layered structure. After aging, the slurry is cooled to below 40℃, and solid-liquid separation is performed by centrifugation. The precipitate is washed with deionized water until the conductivity of the filtrate is ≤200μS / cm. The washed filter cake is dried with hot air at 80-110℃ for 8-12 h to obtain the carbonate-type layered double hydroxide precursor. S13. The carbonate-type layered double hydroxide precursor obtained in step S12 is placed in a muffle furnace and calcined under a nitrogen atmosphere. The heating rate is controlled at 3-8℃ / min. After heating to 430-480℃, it is held for 1-3 hours and then naturally cooled to room temperature to obtain layered bimetallic oxide. S14. Take 5-10 parts of the layered bimetallic oxide obtained in step S13 and add it to 90-100 parts of a mixed solvent of ethanol / deionized water. The mass ratio of ethanol to water is controlled at 60-80:40-20. Disperse the mixture at 800-1200 rpm for 10-30 min at 25-30℃. Then add 1-1.2 parts of sodium oleate as an intercalation anion source. Under nitrogen protection, heat the system to 60-70℃ and maintain it for 6-24 h. During this period, adjust the pH to 9.0-10.0 with sodium hydroxide solution. After the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the hydrophobic intercalated layered bimetallic oxide. S15. Add 5-10 parts of the hydrophobic intercalated layered double hydroxide obtained in step S14 to 80-100 parts of ethanol / water mixed solvent, with the mass ratio of ethanol to water controlled at 70-90:10-30, and disperse at 800-1200 rpm for 10-30 min at 25-35℃; add 15-25% ammonia water to stabilize the pH of the system at 9.0-10.0, and then add tetraethyl orthosilicate dropwise, so that the silica coating accounts for 3-12% of the mass of the hydrophobic intercalated layered double hydroxide. After the dropwise addition is completed, continue to react at 30-40℃ for 2-6 h. After the reaction is completed, filter and wash with ethanol 3-4 times, and then wash with deionized water until the conductivity of the aqueous phase filtrate is ≤200μS / cm. Vacuum dry at 100-120℃ for 2-6 h to obtain silica-coated hydrophobic intercalated layered double hydroxide. S16. Take 5-10 parts of the silica-coated hydrophobic intercalated layered double hydroxide obtained in step S15 and disperse it in 60-100 parts of anhydrous ethanol. Control the temperature at 25-40℃ and stir at 600-1000 rpm for 10-20 min. Then add 0.05-0.2 parts of 3-mercaptopropyltrimethoxysilane and 0.8-1.5 parts of deionized water to provide the trace water source required for condensation. Adjust the pH of the system to 4.0-5.0 with glacial acetic acid and continue to react at 30-40℃ for 1-4 h. After the reaction is completed, filter and wash with ethanol 2-3 times to remove unreacted silane. Then vacuum dry at 110-120℃ for 4-8 h to obtain the modified layered double hydroxide.

3. The high-pressure resistant modified polyester powder coating material according to claim 1, characterized in that, The microencapsulated tin latent catalyst is prepared through the following steps: S21. Melting and Homogenizing: Weigh 5.5-7 parts of Fischer-Tropsch hard wax by weight and heat it to 120-140℃. Mechanically stir at 300-600 rpm until completely melted. Add 2.5-4 parts of Bi / Zr catalyst and 0.2-0.8 parts of flow aid in sequence, and continue stirring for 20-40 min to make the system uniform and free of visible particle agglomeration, thus obtaining the melt material. S22. Spray cooling encapsulation: The molten material is fed into a spray granulator and atomized using a pressure nozzle. The atomization pressure is set to 0.2-0.6 MPa, the cooling air temperature to 10-25℃, the inlet temperature to 120-150℃, and the outlet temperature to 25-35℃, so that the droplets can quickly solidify during flight to form spherical wax shell microcapsules. S23. Grading and post-processing: Collect the microcapsule particles obtained in step S22 and control the particle size by air classification to ensure that the D50 of the finished microcapsule powder is controlled within 10-25 µm; mix 5-10 parts of the graded microcapsule powder with 0.03-0.12 parts of fumed silica in a high-speed mixer and mix at 800-1200 rpm for 2-5 min to ensure that the fumed silica is uniformly adsorbed on the surface of the microcapsules to reduce the risk of agglomeration and clumping, thereby obtaining the microencapsulated Wuxi latent catalyst.

4. The high-pressure resistant modified polyester powder coating material according to claim 3, characterized in that, In step S21, the Bi / Zr catalyst is a mixture of bismuth neodecanoate and zirconium acetylacetonate in a mass ratio of 2-3:1; the flow aid is one or more of dipropylene glycol dibenzoate and diisononyl phthalate.

5. The high-pressure resistant modified polyester powder coating material according to claim 1, characterized in that, The lamellar mica powder is selected from one or more of muscovite powder and phlogopite powder, and the particle size D50 of the lamellar mica powder is 10-30 μm, and the particle size-to-thickness ratio is 10-80; the spherical silica is selected from one or more of spherical fused silica, spherical quartz silica, and spherical silica micro powder, and the spherical silica has a sphericity ≥0.9, a particle size D50 of 5-20 μm, a SiO2 content ≥99.5%, and a moisture content <0.1%.

6. The high-pressure resistant modified polyester powder coating material according to claim 1, characterized in that, The boron nitride is selected from one or more of hexagonal boron nitride and cubic boron nitride; the boron nitride has a particle size D50 of 1-15 μm, a thermal conductivity of not less than 30 W / (m·K), and a volume resistivity of not less than 1×10⁻⁶. 14 Ω·cm, and moisture content ≤0.3%.

7. The high-pressure resistant modified polyester powder coating material according to claim 1, characterized in that, The phosphazene compounds are selected from one or more of cyclotriphosphazenes and cyclotetraphosphazenes.

8. The high-pressure resistant modified polyester powder coating material according to claim 1, characterized in that, The blocked polyisocyanate is further limited to caprolactam-based blocked polyisocyanates; the leveling agent is further limited to acrylate-based leveling agents; the degassing agent is further limited to benzoin isopropyl ether; the dispersant is further limited to polyurethane-based dispersants; and the wetting agent is further limited to titanate-based wetting agents.

9. A method for preparing a high-pressure resistant modified polyester powder coating material, used to prepare the high-pressure resistant modified polyester powder coating material according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Dry the lamellar mica powder, spherical silica, boron nitride and modified layered double hydroxide at 100-110℃ for 2-4 h, and seal the resulting dried powder for later use under RH≤50% conditions; S2. Add hydroxyl-terminated polyester resin, lamellar mica powder, spherical silica and boron nitride to a high-speed mixer and premix at 800-1500 rpm for 3-5 min to obtain masterbatch A; S3. Blocked polyisocyanate, phosphazene compound, microencapsulated tin latent catalyst, leveling agent, wetting agent and dispersant are added to a high-speed mixer at ≤40℃ and premixed at 600-1200 rpm for 2-4 min to obtain masterbatch B; S4. Add masterbatch A to a twin-screw extruder for melt extrusion, and perform vacuum degassing in the middle of the extrusion section, with the vacuum degree set to -0.07 to -0.095 MPa; S5. Add masterbatch B and the dried modified layered double hydroxide of S1 to the side feed of the extrusion section, so that the melt temperature is ≤115℃ and then discharge, press into tablets and cool. S6. The cooled sheet is crushed and graded to obtain a powder coating material, with the powder particle size controlled to D50=35-55μm; S7. The degassing agent is added to the powder coating material obtained in S6 by post-mixing, and mixed at 600-1000 rpm for 1-3 min at ≤40℃ to obtain the high-pressure resistant modified polyester powder coating material.

10. The method for preparing a high-pressure resistant modified polyester powder coating material according to claim 9, characterized in that, In step S4, the temperatures of each zone of the twin-screw extruder are as follows: zone 1 is 75-85℃, zone 2 is 85-95℃, zone 3 is 95-100℃, zone 4 is 105-110℃, and zone 5 is 110-115℃.

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