Weather-resistant insulating powder, method for preparing the same, and use thereof

Abstract

The application discloses weather-resistant insulating powder and a preparation method and application thereof, and relates to the technical field of powder coating. The weather-resistant insulating powder provided by the application comprises phenolic epoxy resin, toughened epoxy resin, dicyandiamide, curing accelerator, spherical alumina, fumed silica, composite filler, antioxidant and auxiliary agent. The weather-resistant insulating powder can adapt to the protection requirements of the insulating coating under the comprehensive working conditions of high temperature, cold-heat cycle and the like in the interior of a new energy automobile driving motor, realizes the multiple performance synergies of high temperature-resistant grade of the coating, cold-heat cycle cracking resistance and high insulating strength, the preparation process can be completely adapted to the existing powder coating double-screw extrusion production line, and the insulating protection requirements of metal parts such as a stator, a rotor, a busbar and a sensor support in the interior of an automobile engine can be met.

Description

Technical Field

[0001] This application relates to the field of powder coating technology, and in particular to a weather-resistant insulating powder, its preparation method, and its application. Background Technology

[0002] Epoxy powder coatings are widely used in the insulation protection of core components such as drive motors, high-voltage busbars, and power batteries in new energy vehicles due to their excellent adhesion, electrical insulation properties, chemical corrosion resistance, and mechanical strength. Pure epoxy powder coatings based on phenolic epoxy resin have long dominated the electric drive insulation powder market due to their high crosslinking density, good heat resistance, and outstanding insulation properties. As the core component for power output, the drive motor of a new energy vehicle operates at high speeds and generates a large amount of heat, with operating temperatures often reaching 150℃-180℃. Under extreme conditions such as rapid acceleration, the operating temperature of the drive motor can reach over 200℃. Because the internal magnetic ring of the drive motor must withstand complex electromagnetic environments and high-temperature shocks, under extreme conditions such as rapid acceleration, the insulation performance of the magnetic ring often deteriorates after a period of operation, leading to motor performance degradation and even short-circuit faults and other safety hazards. This complex service environment places stringent requirements on the comprehensive performance of insulating powder coatings.

[0003] Currently, ordinary pure epoxy powder coatings exhibit significant performance shortcomings in practical applications. After curing, epoxy resin forms a three-dimensional cross-linked network structure with high cross-linking density and high internal stress, making it inherently brittle. During repeated hot and cold cycles inside an engine, the difference in thermal expansion coefficients between the coating and the metal substrate leads to alternating thermal stress at the interface. The brittle epoxy coating struggles to absorb stress energy through effective deformation, making it highly susceptible to microcrack formation. Once microcracks form, they not only directly weaken the coating's insulation resistance and withstand voltage but also provide channels for the penetration of corrosive media such as water vapor, further accelerating the delamination of the coating-substrate interface and ultimately causing insulation failure. To improve the toughness of epoxy coatings, the industry commonly employs methods such as introducing carboxyl-terminated nitrile butadiene rubber, polyurethane elastomers, and core-shell rubber particles into the epoxy system. This toughening method absorbs impact energy by forming a dispersed structure of the toughening phase within the matrix, but its toughening mechanism dictates that it must come at the cost of sacrificing the coating's glass transition temperature and cross-linking density.

[0004] On the other hand, to improve the insulation strength and thermal conductivity of the coating, existing formulations typically require the addition of large amounts of inorganic functional fillers. However, inorganic fillers have high surface energy and poor compatibility with the organic epoxy resin matrix; the interfacial bonding between the two relies solely on weak physical adsorption and van der Waals forces. Under high temperature and repeated stress, the filler-resin interface is prone to debonding, forming micropores. These pores continuously expand during thermal cycling, eventually becoming crack initiation points and breakdown pathways.

[0005] To address the aforementioned technical shortcomings, there is an urgent need to improve existing technologies. Summary of the Invention

[0006] In view of this, this application provides a weather-resistant insulating powder, its preparation method and application. The weather-resistant insulating powder achieves a balance between high temperature resistance, resistance to thermal cycling cracking and high insulation strength. It solves common industry problems in traditional epoxy insulating powder coatings, such as sacrificing the glass transition temperature for toughening modification and weak interfacial bonding between inorganic fillers and resin matrix leading to debonding. The product has excellent heat resistance, insulation and wear resistance, and the preparation process is compatible with existing powder coating production equipment.

[0007] In the first aspect, this application provides a weather-resistant insulating powder, the technical solution of which is as follows: A weather-resistant insulating powder, comprising, by weight parts, the following raw materials: The mixture contains 60-90 parts of phenolic epoxy resin, 10-40 parts of toughened epoxy resin, 8-35 parts of dicyandiamide, 0.1-2 parts of curing accelerator, 20-90 parts of spherical alumina, 15-50 parts of fumed silica, 10-50 parts of composite filler, 0.5-5 parts of antioxidant, and 1-5 parts of additives.

[0008] Optionally, the weather-resistant insulating powder, by weight, comprises the following raw materials: The mixture contains 70-80 parts of phenolic epoxy resin, 20-30 parts of toughened epoxy resin, 15-25 parts of dicyandiamide, 0.5-1.5 parts of curing accelerator, 30-60 parts of spherical alumina, 25-35 parts of fumed silica, 20-30 parts of composite filler, 1-3 parts of antioxidant, and 2-4 parts of additives.

[0009] Optionally, the method for preparing the toughened epoxy resin includes the following steps: Trimethylolpropane and 2,2-dimethylolpropionic acid were mixed and subjected to a polycondensation reaction to obtain hyperbranched polyester polyol. A ring-opening reaction was carried out by mixing a fluorinated alcohol, epichlorohydrin, and tetrabutylammonium bromide to obtain a fluorinated chloro alcohol. The fluorinated chloro alcohol and sodium hydroxide were mixed and subjected to a ring-closing reaction to obtain a fluorinated monoepoxide compound. The hyperbranched polyester polyol, fluorinated monoepoxide compound, bisphenol A diglycidyl ether, and boron trifluoride ethylamine are mixed and then subjected to a grafting reaction to obtain a toughened epoxy resin.

[0010] Optionally, the mass ratio of trimethylolpropane to 2,2-dimethylolpropionic acid is 1:1.5~6.

[0011] Optionally, the polycondensation reaction is carried out under a nitrogen atmosphere at a temperature of 140-160°C for 3-6 hours.

[0012] Optionally, the mass-to-volume ratio of the fluorinated alcohol, epichlorohydrin, and tetrabutylammonium bromide is 1 g : (0.8~2.5) mL : (0.005~0.03) g, and the fluorinated alcohol is selected from one or two of 1H,1H,2H,2H-perfluorooctanol or 1H,1H,2H,2H-perfluorodecanol.

[0013] Optionally, the ring-opening reaction is carried out at a temperature of 80-100°C for 4-8 hours.

[0014] Optionally, the mass ratio of the fluorochlorool to sodium hydroxide is 1:0.1~0.25.

[0015] Optionally, the closed-loop reaction is carried out at a temperature of 40-60°C for 2-4 hours.

[0016] Optionally, the mass ratio of the hyperbranched polyester polyol, the fluorinated monoepoxide, the bisphenol A diglycidyl ether, and the boron trifluoride ethylamine is 1:0.05~0.25:2~6:0.005~0.02.

[0017] Optionally, the grafting reaction is carried out at a temperature of 100-130°C for 3-6 hours.

[0018] Optionally, the method for preparing the composite filler includes the following steps: After mixing flake boron nitride with an aqueous sodium hydroxide solution, ultrasonic treatment was performed to obtain hydroxylated flake boron nitride. The hydroxylated flake boron nitride, fluorinated silane coupling agent, epoxy silane coupling agent, and ethanol aqueous solution are mixed and then subjected to a grafting reaction to obtain a composite filler.

[0019] Optionally, the mass-to-volume ratio of the flake boron nitride to the sodium hydroxide aqueous solution is 1 g: (5~15) mL, and the volume concentration of the sodium hydroxide aqueous solution is 8%~20%.

[0020] Optionally, the ultrasonic treatment is performed at a temperature of 60-80°C for 2-6 hours and at a power of 100-500W.

[0021] Optionally, the mass-to-volume ratio of the hydroxylated flake boron nitride, the fluorinated silane coupling agent, the epoxy silane coupling agent, and the ethanol aqueous solution is 1 g : (0.02~0.15) g : (0.02~0.2) g : (8~20) mL, the volume concentration of the ethanol aqueous solution is 70%~90%, the fluorinated silane coupling agent is selected from one or more of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, or 1H,1H,2H,2H-perfluorooctyltrichlorosilane, and the epoxy silane coupling agent is selected from one or more of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0022] Optionally, the grafting reaction is carried out under stirring conditions, wherein the stirring speed is 200~500 r / min, the temperature is 50~70℃, and the time is 4~8 h.

[0023] Optionally, the phenolic epoxy resin has an epoxy equivalent of 170~230 g / eq and a softening point of 75~95℃.

[0024] Optionally, the curing accelerator is selected from one or more of 2-methylimidazole, 2-phenylimidazole, or 2-ethyl-4-methylimidazole.

[0025] Optionally, the average particle size of the spherical alumina is 2~20 μm.

[0026] Optionally, the specific surface area of ​​the fumed silica is 150~300m². 2 / g.

[0027] Optionally, the antioxidant is selected from one or more of antioxidant 1010, antioxidant 1076 or antioxidant 245.

[0028] Optionally, the additive is selected from one or both of butyl acrylate homopolymer and benzoin.

[0029] Secondly, this application provides a method for preparing the weather-resistant insulating powder described in the foregoing scheme, comprising the following steps: Phenolic epoxy resin, toughened epoxy resin, dicyandiamide, curing accelerator, spherical alumina, fumed silica, composite filler, antioxidant and additives are mixed and then subjected to melt extrusion to obtain extruded material. The extruded material is compressed into tablets and cooled to obtain thin sheet material; After the thin sheet material is crushed, it is passed through a 170-200 mesh standard sieve to obtain the weather-resistant insulating powder.

[0030] Optionally, the melt extrusion process is carried out using a twin-screw extruder, with the temperature of zone I of the extruder being 75~90℃, the temperature of zone II being 95~110℃, the die head temperature being 105~125℃, the screw speed being 200~400 rpm, and the length-to-diameter ratio of the twin-screw extruder being 36~48:1.

[0031] Thirdly, this application provides the application of the weather-resistant insulating powder described in the foregoing scheme in the coating of the surface of metal parts inside an automobile engine.

[0032] The weather-resistant insulating powder provided in this application achieves a deep synergy of coating heat resistance, toughness, and insulation, effectively addressing the problems of traditional epoxy insulating powder coatings where toughening modification sacrifices the glass transition temperature and where weak interfacial bonding between inorganic fillers and the resin matrix leads to debonding. Compared to existing technologies, this weather-resistant insulating powder features high temperature resistance, outstanding resistance to thermal cycling cracking, stable insulation strength, and a preparation process adaptable to existing powder coating production equipment. It can meet the long-term reliable protection requirements of internal metal components of new energy vehicle drive motors under combined high-temperature and thermal cycling conditions, possessing significant practical value and industrial application potential. Detailed Implementation

[0033] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific implementation methods described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0034] In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operating state; while "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative purposes and do not impose numerical requirements or establish an order.

[0035] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0036] In this application, "at least one" means one or more, and "more than one" means two or more. "One or more", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0037] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0038] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0039] In a first aspect, this application discloses a weather-resistant insulating powder, which, by mass parts, comprises the following raw materials: The mixture contains 60-90 parts of phenolic epoxy resin, 10-40 parts of toughened epoxy resin, 8-35 parts of dicyandiamide, 0.1-2 parts of curing accelerator, 20-90 parts of spherical alumina, 15-50 parts of fumed silica, 10-50 parts of composite filler, 0.5-5 parts of antioxidant, and 1-5 parts of additives.

[0040] In some embodiments, the weather-resistant insulating powder comprises, by weight, the following raw materials: The mixture contains 60-90 parts of phenolic epoxy resin, 10-40 parts of toughened epoxy resin, 8-35 parts of dicyandiamide, 0.1-2 parts of curing accelerator, 20-90 parts of spherical alumina, 15-50 parts of fumed silica, 10-50 parts of composite filler, 0.5-5 parts of antioxidant, and 1-5 parts of additives.

[0041] In some embodiments, the phenolic epoxy resin has an epoxy equivalent of 170~230 g / eq and a softening point of 75~95℃.

[0042] It should be noted that, in this application, the phenolic epoxy resin, as the core component of the coating matrix resin, plays a role in providing high crosslinking density and a heat-resistant skeleton. Each repeating unit in the molecular structure of phenolic epoxy resin contains more than two epoxy groups, and after curing, it can form a crosslinking density much higher than that of ordinary bisphenol A type epoxy resin, which can ensure that the coating has excellent glass transition temperature and long-term heat resistance.

[0043] This application ensures that the resin has suitable reactivity and melt viscosity by limiting the epoxy equivalent of the phenolic epoxy resin. If the epoxy equivalent is too low, the crosslinking density will be too high, resulting in increased coating brittleness. If the epoxy equivalent is too high, the crosslinking density will be insufficient, resulting in decreased heat resistance and chemical resistance.

[0044] By limiting the softening point of the phenolic epoxy resin, this application can ensure that the resin is plasticized synchronously with other components in the melt extrusion process, avoiding uneven extrusion mixing due to an excessively high softening point or agglomeration of materials in the premixing stage due to an excessively low softening point.

[0045] In some embodiments, the method for preparing the toughened epoxy resin includes the following steps: Trimethylolpropane and 2,2-dimethylolpropionic acid were mixed and subjected to a polycondensation reaction to obtain hyperbranched polyester polyol. A ring-opening reaction was carried out by mixing a fluorinated alcohol, epichlorohydrin, and tetrabutylammonium bromide to obtain a fluorinated chloro alcohol. The fluorinated chloro alcohol and sodium hydroxide were mixed and subjected to a ring-closing reaction to obtain a fluorinated monoepoxide compound. The hyperbranched polyester polyol, fluorinated monoepoxide compound, bisphenol A diglycidyl ether, and boron trifluoride ethylamine are mixed and then subjected to a grafting reaction to obtain a toughened epoxy resin.

[0046] It should be noted that in this application, the toughened epoxy resin is formed by condensation polymerization of trimethylolpropane as the core and 2,2-dimethylolpropionic acid as the chain extender monomer. The number of hydroxyl groups doubles with each generation, resulting in a highly branched spherical molecular configuration. The generation number is controlled between 2 and 4 generations. Due to the incomplete filling of the branched chains, a large number of nanoscale vacancies exist within the molecule. When the coating is subjected to thermal cycling or external forces, these vacancies can absorb stress energy through reversible deformation, effectively inhibiting the initiation and propagation of microcracks. Its toughening mechanism differs from the energy dissipation mode of the island structure in traditional rubber toughening and does not rely on the introduction of a low-modulus second phase. Therefore, the hyperbranched rigid framework does not reduce the overall crosslinking density and glass transition temperature of the coating. The fluorinated monoepoxide compound is prepared by reacting a fluorinated alcohol with epichlorohydrin. Its terminal epoxy groups undergo ring-opening etherification with the peripheral hydroxyl groups of the hyperbranched core during the grafting reaction, anchoring the covalent bonds of the fluorinated side chains to the periphery of the hyperbranched molecule. The CF bond energy in the fluorinated side chain is much higher than that of the CH bond. The molecular chain segments are rigid and have low cohesive energy density, which can effectively reduce the surface energy of the resin and enhance the affinity with the interface of the fluorinated filler.

[0047] In some embodiments, the mass ratio of trimethylolpropane to 2,2-dimethylolpropionic acid is 1:1.5~6.

[0048] It should be noted that by limiting the ratio of trimethylolpropane to 2,2-dimethylolpropionic acid, this application can precisely control the hyperbranching generation within a reasonable range of 2 to 4 generations. When the mass ratio is 1:1.5, the theoretical hyperbranching generation of the polycondensation reaction is approximately 2 generations, with approximately 12 terminal hydroxyl groups and a molecular weight of approximately 1500 to 2000; when the mass ratio is 1:6, the theoretical hyperbranching generation is approximately 3 to 4 generations, with approximately 48 terminal hydroxyl groups and a molecular weight of approximately 5000 to 6000.

[0049] In some embodiments, the polycondensation reaction is carried out under a nitrogen atmosphere at a temperature of 140-160°C for 3-6 hours.

[0050] It should be noted that this application, by limiting the temperature and time of the polycondensation reaction, can promote the full esterification polycondensation reaction between hydroxyl and carboxyl groups. A temperature of 140-160℃ is the suitable range for the esterification polycondensation of 2,2-dimethylolpropionic acid. Below 140℃, the esterification reaction rate is too slow, the polycondensation reaction is incomplete, and the acid value remains above 10 mg KOH / g after 6 hours. Above 160℃, 2,2-dimethylolpropionic acid may undergo a decarboxylation side reaction, releasing CO2 gas, disrupting the stoichiometric balance of the reaction system, leading to a wider molecular weight distribution of the product and a deviation of the number of terminal hydroxyl groups from the design value. By limiting the reaction time to 3-6 hours, this application can ensure a carboxyl group conversion rate greater than 98%, with the product terminally composed mainly of hydroxyl groups rather than residual carboxyl groups, ensuring the efficiency of subsequent grafting of epoxy groups and the controllability of the product structure.

[0051] In this application, a nitrogen atmosphere can eliminate oxygen in the reaction system, prevent the product from oxidizing and discoloring at high temperatures, and ensure the color stability of the toughened epoxy resin, making it suitable for the application requirements of light-colored powder coatings.

[0052] In some embodiments, the mass-to-volume ratio of the fluorinated alcohol, epichlorohydrin, and tetrabutylammonium bromide is 1 g : (0.8~2.5) mL : (0.005~0.03) g, and the fluorinated alcohol is selected from one or two of 1H,1H,2H,2H-perfluorooctanol or 1H,1H,2H,2H-perfluorodecanol.

[0053] It should be noted that, in this application, the fluorinated carbon chain length of the fluorinated alcohol is moderate, so as not to cause excessively long chain segments that lead to crystallization or a significant decrease in compatibility with the epoxy resin matrix.

[0054] This application ensures a proper excess of epichlorohydrin relative to the fluorinated alcohol by limiting the amount of epichlorohydrin used to 0.8-2.5 mL per gram of fluorinated alcohol. This promotes a positive shift in the equilibrium of the ring-opening etherification reaction between hydroxyl and epoxy groups, achieving a hydroxyl conversion rate of over 95% in the fluorinated alcohol. If the amount of epichlorohydrin used is less than 0.8 mL / g, the fluorinated alcohol reaction is incomplete, and the remaining unreacted fluorinated alcohol cannot be converted into a fluorinated monoepoxide in the subsequent ring-closing step, resulting in insufficient introduction of the fluorinated component. If the amount used is greater than 2.5 mL / g, the excess epichlorohydrin needs to be removed by additional distillation in subsequent purification, increasing process costs and solvent recovery burden.

[0055] This application ensures a moderate phase transfer catalytic efficiency by limiting the amount of tetrabutylammonium bromide to 0.5%~3% of the mass of the fluorinated alcohol. If the amount of catalyst is too small, the ring-opening reaction rate will be too slow, and the conversion rate will be less than 80% within 8 hours; if the amount is too large, it will increase the difficulty of subsequent water washing and purification, and trace amounts of residual catalyst may affect the pH environment of the subsequent ring-closing reaction.

[0056] In some embodiments, the ring-opening reaction is carried out at a temperature of 80-100°C for 4-8 hours.

[0057] It should be noted that by limiting the temperature of the ring-opening reaction, this application can ensure that the liquid phase reaction proceeds smoothly and avoids the large-scale volatilization of epichlorohydrin into the gas phase caused by the temperature exceeding 100°C. This would reduce the concentration of epichlorohydrin in the liquid phase and decrease the reaction rate. At the same time, the volatilized epichlorohydrin may undergo gas-phase homopolymerization side reactions during the condensation and reflux process to generate oligomers.

[0058] This application ensures that the hydroxyl groups in fluorinated alcohols are fully converted into fluorinated chlorohydrin intermediates by limiting the reaction time to 4-8 hours, and the reaction endpoint is set when the residual amount of fluorinated alcohol is less than 2% as monitored by gas chromatography.

[0059] In some embodiments, the mass-to-volume ratio of the fluorochlorool and sodium hydroxide is 1:0.1~0.25.

[0060] It should be noted that by limiting the amount of sodium hydroxide used, this application ensures that sodium hydroxide is in equimolar to slightly excess relative to the chloromethylene group in the fluorochlorohydrin molecule, allowing the dehydrochlorination ring-closing reaction to proceed fully. Sodium hydroxide reacts with the secondary hydroxyl group and the chloromethylene group to produce sodium chloride and water, and the epoxy three-membered ring recloses, with a ring-closing conversion rate exceeding 90%. If the amount of sodium hydroxide used is less than 0.1 g / g of the fluorochlorohydrin, dehydrochlorination is incomplete, leaving residual chloromethylene groups in the product, and the amount of epoxy groups generated is insufficient. If the amount used is greater than 0.25 g / g, the excess alkali may catalyze the hydrolysis and ring-opening side reaction of the already generated epoxy groups, thus reducing the epoxy value of the product.

[0061] In some embodiments, the closed-loop reaction is carried out at a temperature of 40-60°C for 2-4 hours.

[0062] It should be noted that by limiting the low-temperature conditions of the ring-closing reaction, this application can avoid the hydrolysis and ring-opening side reactions of the newly formed epoxy groups under alkaline conditions caused by excessively high temperatures. Epoxy groups are temperature-sensitive in alkaline aqueous solutions; when the temperature exceeds 60°C, the rate of the ring-opening side reaction increases significantly, and some epoxy groups irreversibly convert to diol structures, causing the epoxy equivalent of the fluorinated monoepoxide compound to deviate from the theoretical value by more than 10%. A temperature of 40-60°C balances the ring-closing reaction rate and the stability of the epoxy groups, and the dehydrochlorination reaction can be brought to near completion within 2-4 hours.

[0063] In some embodiments, the mass ratio of the hyperbranched polyester polyol, the fluorinated monoepoxide, the bisphenol A diglycidyl ether, and the boron trifluoride ethylamine is 1:0.05~0.25:2~6:0.005~0.02.

[0064] It should be noted that by limiting the amount of fluorinated monoepoxy compound used, this application can control the fluorine content in the toughened epoxy resin to 1%~5%. If the fluorine content is less than 1%, the enrichment effect of the fluorine-fluorine affinity driven interface is not significant; if the fluorine content is more than 5%, the fluorinated side chains are too dense, the surface energy of the toughened epoxy resin drops to below 20mN / m, the compatibility with the phenolic epoxy main resin decreases, phase separation occurs after the coating is cured, and cracking occurs preferentially at the interface after thermal cycling, which reduces the overall reliability of the coating.

[0065] This application, by limiting the amount of bisphenol A diglycidyl ether, can fully cap the hydroxyl groups around the hyperbranched core, thereby controlling the epoxy equivalent of the final product to 350~550 g / eq. By limiting this epoxy equivalent range, this application can ensure that the activity of the toughened epoxy resin participating in the crosslinking reaction during the curing process matches that of the phenolic epoxy main resin, avoiding uneven curing rate and local defects in the crosslinking network caused by excessive differences in the reactivity of the epoxy groups of the two resins.

[0066] This application ensures a balance between Lewis acid catalytic efficiency and reaction controllability by limiting the amount of boron trifluoride ethylamine used. If the catalyst is too little, the grafting reaction rate will be too slow, and the grafting rate will be less than 70% after 6 hours; if the catalyst is too much, the reaction will be hot and the local temperature will exceed the limit, resulting in a wider molecular weight distribution of the product, thermal polymerization of some epoxy groups, and the epoxy equivalent of the product will exceed the target range.

[0067] In some embodiments, the grafting reaction is carried out at a temperature of 100-130°C for 3-6 hours.

[0068] In some embodiments, the method for preparing the composite filler includes the following steps: After mixing flake boron nitride with an aqueous sodium hydroxide solution, ultrasonic treatment was performed to obtain hydroxylated flake boron nitride. The hydroxylated flake boron nitride, fluorinated silane coupling agent, epoxy silane coupling agent, and ethanol aqueous solution are mixed and then subjected to a grafting reaction to obtain a composite filler.

[0069] It should be noted that in this application, the composite filler uses lamellar boron nitride as the substrate, which can simultaneously provide insulation, thermal conductivity, and self-lubrication and wear resistance. Lamellar boron nitride has a hexagonal layered structure similar to graphite, with B and N atoms within the layers arranged in a sp... 2 Hybridized covalent bonds form a six-membered ring plane, with weak van der Waals forces binding the layers. h-BN is a wide-bandgap semiconductor (approximately 5.9 eV), exhibiting excellent electrical insulation and a volume resistivity reaching 10⁻⁶. 14 The thermal conductivity of h-BN is above Ω·cm. Simultaneously, the thermal conductivity along the basal plane can reach 300~400 W / (m·K), effectively conducting Joule heat generated during motor operation and reducing coating thermal resistance. Furthermore, h-BN has weak interlayer van der Waals forces, making it prone to interlayer slippage under frictional shear forces, forming a continuous transfer film on the grinding surface and providing self-lubricating and wear-resistant properties. However, the surface of lamellar boron nitride is extremely chemically inert, with almost no active functional groups on the basal plane. Only a small number of dangling bonds exist at the edges of the lamellar layers due to mechanical breakage. This results in poor compatibility with the epoxy resin matrix. When used directly, the filler-resin interface exhibits weak physical adsorption, making it prone to interfacial debonding under high temperature and stress, forming micro-cracks along the filler surface.

[0070] In this application, during the coating heating and curing process, the fluorinated side chains of the toughening epoxy resin and the fluorinated silane coupling agent segments on the surface of the composite filler recognize each other, migrate in a directional manner, and accumulate at the interface between the filler and the resin due to the driving force of fluorine-fluorine affinity, forming a dense fluorinated enriched layer. This enriched layer can enhance the interfacial bonding strength between the filler and the resin matrix.

[0071] This application utilizes ultrasonic treatment with sodium hydroxide aqueous solution to achieve the desired effect. - Nucleophilic attack on the BN bonds on the boron nitride surface introduces active B-OH groups at lamellar edges and basal defect sites, achieving a hydroxylation density of 0.5–2.0 hydroxyl groups / nm. 2 This provides sufficient and uniformly distributed chemical anchoring sites for subsequent coupling agent grafting. Through mixed grafting modification of fluorinated silane coupling agents and epoxy silane coupling agents, fluorinated segments and epoxy reactive groups are simultaneously anchored on the surface of hydroxylated boron nitride via Si-OB covalent bonds, thereby realizing the construction of interfacial anchoring function. This fundamentally solves the technical defects of traditional inorganic fillers that rely solely on physical adsorption and have unreliable interfacial bonding.

[0072] In some embodiments, the mass-to-volume ratio of the flake boron nitride to the sodium hydroxide aqueous solution is 1 g: (5~15) mL, and the volume concentration of the sodium hydroxide aqueous solution is 8%~20%.

[0073] It should be noted that by limiting the amount and concentration of the sodium hydroxide aqueous solution, this application can ensure that the sodium hydroxide aqueous solution fully wets the surface of the boron nitride sheet. When the concentration is 8%~20%, the sodium hydroxide solution... - At a suitable concentration, the surface hydroxylation reaction rate and the hydrolysis rate of the BN bond on the boron nitride basal surface reach equilibrium. If the concentration is below 8%, OH... - The concentration was insufficient for efficient attack on BN bonds; after 6 hours of ultrasonic treatment, the hydroxylation density remained below 0.5 hydroxylation atoms / nm. 2 Insufficient grafting sites for the coupling agent; if the concentration is higher than 20%, then OH... - Excessive concentration leads to over-etching of the boron nitride flake edges, damage to the integrity of the flake structure, thinning of the flake thickness, and even perforation. This results in the loss of the barrier and load-bearing functions of the flake filler, significantly reducing its contribution to the coating's insulation strength and wear resistance.

[0074] In some embodiments, the ultrasonic treatment is performed at a temperature of 60-80°C for 2-6 hours and at a power of 100-500W.

[0075] It should be noted that, by limiting the temperature, time, and power of the ultrasonic treatment, this application can utilize the localized high-temperature and high-pressure micro-regions generated by the ultrasonic cavitation effect to promote micro-cleavage between boron nitride layers and activation of surface BN bonds, thereby increasing the active surface area and accelerating the OH... -Mass transfer and diffusion to the boron nitride surface improve the uniformity and efficiency of the surface hydroxylation reaction. Temperature control at 60-80℃ can increase the hydroxylation reaction rate without causing excessive solvent evaporation and resulting in changes in the liquid-solid ratio. Ultrasonic power of 100-500W ensures a moderate frequency of cavitation bubble generation and collapse, effectively utilizing the cavitation effect without causing excessive fragmentation of the sheets due to severe cavitation impacts, thus maintaining the aspect ratio of the plate-like boron nitride at 10:1 or higher.

[0076] In some embodiments, the mass-to-volume ratio of the hydroxylated flake boron nitride, the fluorinated silane coupling agent, the epoxy silane coupling agent, and the ethanol aqueous solution is 1 g : (0.02~0.15) g : (0.02~0.2) g : (8~20) mL, and the volume concentration of the ethanol aqueous solution is 70%~90%.

[0077] It should be noted that this application ensures that the coupling agents form a complete grafted coverage on the boron nitride surface in the form of a monolayer or oligolayer by limiting the dosage of the two coupling agents. If the dosage is too low, the grafting density will be insufficient, and a large number of bare areas will remain on the boron nitride surface, so the chemical bond anchoring function can only be partially realized. If the dosage is too high, the concentration of the coupling agent in the solution will be too high, and the self-condensation reaction rate between the silanol groups of its hydrolysis products will exceed the heterogeneous condensation reaction rate with B-OH on the boron nitride surface. A large number of silsesquioxane oligomers or gel particles will be generated in the solution and deposited on the filler surface, forming a physical adsorption layer with weak bonding with the boron nitride substrate rather than a covalently bonded grafted layer. This layer is easily peeled off under the subsequent melt extrusion shear force, which reduces the reliability of the interface modification.

[0078] In some embodiments, the fluorinated silane coupling agent is selected from one or more of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, or 1H,1H,2H,2H-perfluorooctyltrichlorosilane, and the epoxy silane coupling agent is selected from one or more of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0079] It should be noted that, in this application, the fluorinated carbon chain of the fluorinated silane coupling agent has the same length as the fluorinated carbon chain of the fluorinated monoepoxide compound in the toughened epoxy resin. During the curing process, the fluorinated side chains of the resin and the fluorinated segments on the filler surface migrate directionally due to thermodynamically driven mutual recognition, forming a uniform, dense, and defect-free fluorinated enriched layer at the filler-resin interface, with a thickness of approximately 5-20 nm.

[0080] In some embodiments, the grafting reaction is carried out under stirring conditions, wherein the stirring speed is 200~500 r / min, the temperature is 50~70℃, and the time is 4~8 h.

[0081] It should be noted that by limiting the temperature and time of the grafting reaction to 50-70℃ and 4-8h, this application can promote the full condensation reaction between the silanol groups of the coupling agent hydrolysis product and the B-OH on the boron nitride surface, generating stable Si-OB covalent bonds, with a grafting efficiency of over 80%. Below 50℃, the activation energy of the condensation reaction is insufficient, and the reaction rate is too slow; after 8h, the grafting efficiency is still below 50%. Above 70℃, lateral condensation polymerization may occur between the grafted coupling agent and the free coupling agent in the solution, forming a dense polysiloxane network that wraps around the filler surface. Although the grafting amount appears to increase, some of the coupling agent is not anchored by covalent bonds but exists in a physically entangled form, which may be partially peeled off under the subsequent melt extrusion shear force.

[0082] In some embodiments, the average particle size of the dicyandiamide is 2-10 μm.

[0083] It should be noted that, in this application, the dicyandiamide, as a latent curing agent, can maintain chemical inertness during room temperature storage and melt extrusion stages, and release curing activity during coating baking and curing stages.

[0084] In some embodiments, the curing accelerator is selected from one or more of 2-methylimidazole, 2-phenylimidazole, or 2-ethyl-4-methylimidazole.

[0085] It should be noted that in this application, the curing accelerator acts as a catalyst in the dicyandiamide curing system, thereby reducing the curing temperature. When dicyandiamide is used alone as a curing agent, its epoxy ring-opening curing reaction requires a temperature above 200°C to proceed fully, and the curing time is more than 30 minutes, resulting in high energy consumption and unsuitability for some temperature-sensitive substrates. After adding an imidazole accelerator, the active hydrogen at the 1-position NH or the lone pair electrons of the 3-position tertiary nitrogen atom on the imidazole ring can nucleophilically attack the epoxy group, forming an alkoxy anion active intermediate, which initiates an anionic chain polymerization reaction, thereby lowering the curing initiation temperature and shortening the curing time.

[0086] In some embodiments, the average particle size of the spherical alumina is 2~20 μm.

[0087] It should be noted that, in this application, the spherical alumina serves as both a thermally conductive and reinforcing filler, thereby improving the thermal conductivity and mechanical strength of the coating. The spherical morphology possesses the lowest specific surface area and optimal flowability within the resin matrix. Compared to irregular angular fillers, it effectively reduces the melt viscosity of highly filled systems, improving melt extrusion processability and the electrostatic spraying fluidization properties of powder coatings.

[0088] In some embodiments, the specific surface area of ​​the fumed silica is 150~300 m².2 / g.

[0089] It should be noted that in this application, the fumed silica acts as a thixotropic agent and anti-sagging agent, enabling it to construct a three-dimensional thixotropic network during the coating melting and solidification stage, and preventing coating sagging at vertical surfaces and edges. The original fumed silica particles have a particle size of 7-20 nm and are interconnected through hydrogen bonds between surface silanol groups to form chain-like aggregates, constructing a reversible physical cross-linked network in the coating melt. This cross-linked network is temporarily destroyed under high shear force during spraying, ensuring good powder flowability. Simultaneously, during solidification and heating, the shear force disappears, the network rapidly recovers, and the coating viscosity increases, effectively preventing the molten coating from sagging along vertical surfaces and sharp edges under gravity, ensuring uniform coverage and corner protection on complex-shaped components.

[0090] In some embodiments, the antioxidant is selected from one or more of antioxidant 1010, antioxidant 1076, or antioxidant 245.

[0091] In some embodiments, the additive is selected from one or both of butyl acrylate homopolymer and benzoin.

[0092] It should be noted that, in this application, the butyl acrylate homopolymer serves as a leveling agent, which can reduce the surface tension of the coating, promote full leveling of the coating during the melting and curing stage, and eliminate surface defects such as orange peel and pinholes.

[0093] In this application, the benzoin is used as a degassing agent, which can eliminate bubbles and pinhole defects caused by curing reaction or volatile release during the curing process of thick coating.

[0094] Secondly, this application discloses a method for preparing weather-resistant insulating powder, comprising the following steps: Phenolic epoxy resin, toughened epoxy resin, dicyandiamide, curing accelerator, spherical alumina, fumed silica, composite filler, antioxidant and additives are mixed and then subjected to melt extrusion to obtain extruded material. The extruded material is compressed into tablets and cooled to obtain thin sheet material; After the thin sheet material is crushed, it is passed through a 170-200 mesh standard sieve to obtain the weather-resistant insulating powder.

[0095] In some embodiments, the melt extrusion process is carried out using a twin-screw extruder. The temperature in zone I of the extruder is 75~90℃, the temperature in zone II is 95~110℃, the die temperature is 105~125℃, the screw speed is 200~400 rpm, and the length-to-diameter ratio of the twin-screw extruder is 36~48:1. This application ensures that the material is fully plasticized and mixed without prematurely initiating a cross-linking reaction by limiting the temperature of each extrusion zone to no more than 130℃.

[0096] The preparation method of this application adopts a melt extrusion process. By controlling the extrusion temperature and screw speed, the uniform dispersion of each component is ensured. At the same time, dicyandiamide and imidazole curing accelerators do not undergo substantial curing and cross-linking reactions during extrusion, ensuring the storage stability of the powder. The entire process is fully adaptable to existing twin-screw extrusion production lines for powder coatings and is easy to scale up for industrial production.

[0097] Thirdly, this application discloses the application of weather-resistant insulating powder in the coating of metal parts inside automobile engines. The coating is carried out using conventional electrostatic spraying or fluidized bed dip coating processes, and then cured by baking at 180~200℃.

[0098] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0099] Example 1

[0100] This embodiment provides a method for preparing weather-resistant insulating powder, including the following steps: 75g phenolic epoxy resin (epoxy equivalent 200g / eq, softening point 85℃), 25g toughened epoxy resin, 20g dicyandiamide (average particle size 6μm), 0.8g 2-methylimidazole, 45g spherical alumina (average particle size 10μm), and 30g fumed silica (specific surface area 220m²) were mixed. 2 25g of composite filler, 2g of antioxidant 1010, 2g of butyl acrylate homopolymer and 1.5g of benzoin were added to a high-speed mixer and stirred at 900r / min for 3min. Then, the mixture was fed into a twin-screw extruder for melt extrusion. The temperature of the extruder zone I was 85℃, the temperature of zone II was 105℃, the die head temperature was 115℃, the screw speed was 300r / min, and the length-to-diameter ratio was 40:1 to obtain the extruded material. The extruded material is pressed into a sheet with a thickness of 1.5 mm by a tablet press and then cooled to room temperature by air cooling to obtain the sheet material. The thin sheet material is coarsely crushed by a pulverizer, then finely crushed by a micro pulverizer, and finally passed through a 180-mesh standard sieve to obtain the weather-resistant insulating powder.

[0101] The method for preparing the toughened epoxy resin includes the following steps: 10g of trimethylolpropane and 30g of 2,2-dimethylolpropionic acid were added to a reactor and heated to 150°C under a nitrogen atmosphere for 5 hours to carry out a polycondensation reaction, thereby obtaining hyperbranched polyester polyol. 10 g of 1H,1H,2H,2H-perfluorooctanol, 15 mL of epichlorohydrin and 0.15 g of tetrabutylammonium bromide were added to a reaction flask and the ring-opening reaction was carried out at 90 °C and 300 r / min for 6 h to obtain a fluorochloro alcohol. The fluorinated chloro alcohol and 2g of sodium hydroxide were added to a reaction flask and the ring-closing reaction was carried out at 50°C for 3 hours. The mixture was washed with water until neutral and dried to obtain a fluorinated monoepoxide. 10g of the hyperbranched polyester polyol, 1.5g of the fluorinated monoepoxide compound, 40g of bisphenol A diglycidyl ether and 0.2g of boron trifluoride ethylamine were added to a reaction flask and grafted at 115℃ and 250r / min for 5h to obtain toughened epoxy resin.

[0102] The method for preparing the composite filler includes the following steps: 10g of flake boron nitride (average particle size 20μm, thickness 300nm) and 100mL of sodium hydroxide aqueous solution (volume concentration 12%) were added to a reaction flask and sonicated at 70℃ and 300W for 4h. The mixture was then filtered, washed with deionized water until neutral, and dried under vacuum at 80℃ for 3h to obtain hydroxylated flake boron nitride. 10g of the hydroxylated flake boron nitride, 0.8g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1.2g of γ-glycidyl etheroxypropyltrimethoxysilane, and 150mL of ethanol aqueous solution (80% v / v) were added to a reaction flask. The grafting reaction was carried out at 60℃ and 350r / min for 6h. The mixture was washed twice with anhydrous ethanol and dried under vacuum at 60℃ for 3h to obtain the composite filler.

[0103] The powder coating of this embodiment was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70kV. The substrate was then cured in an oven at 200℃ for 15 minutes to obtain an insulating coating with a thickness of 400μm.

[0104] Example 2

[0105] This embodiment provides a method for preparing weather-resistant insulating powder, including the following steps: 80g of phenolic epoxy resin (epoxy equivalent 180g / eq, softening point 90℃), 20g of toughened epoxy resin, 25g of dicyandiamide (average particle size 4μm), 1.5g of 2-phenylimidazole, 55g of spherical alumina (average particle size 15μm), and 35g of fumed silica (specific surface area 260m²) were mixed. 2Add 20g of composite filler, 1.5g of antioxidant 1076, 1.5g of butyl acrylate homopolymer and 0.5g of benzoin to a high-speed mixer, stir at 1100r / min for 2.5min, and then feed it into a twin-screw extruder for melt extrusion. The temperature of the extruder zone I is 80℃, the temperature of zone II is 100℃, the die head temperature is 110℃, the screw speed is 350r / min, and the length-to-diameter ratio is 44:1 to obtain the extruded material. The extruded material is pressed into a sheet with a thickness of 1.2 mm by a tablet press and then cooled to room temperature by air cooling to obtain the sheet material. The thin sheet material is coarsely crushed by a pulverizer, then finely crushed by a micro pulverizer, and finally passed through a 200-mesh standard sieve to obtain the weather-resistant insulating powder.

[0106] The method for preparing the toughened epoxy resin includes the following steps: 10g of trimethylolpropane and 45g of 2,2-dimethylolpropionic acid were added to a reactor and heated to 155°C under a nitrogen atmosphere for 4.5h to carry out a polycondensation reaction, thereby obtaining hyperbranched polyester polyol. 10 g of 1H,1H,2H,2H-perfluorodecyl alcohol, 18 mL of epichlorohydrin and 0.2 g of tetrabutylammonium bromide were added to a reaction flask and the ring-opening reaction was carried out at 95 °C and 350 r / min for 5 h to obtain a fluorochloro alcohol. The fluorinated chloro alcohol and 2.5g sodium hydroxide were added to a reaction flask and the ring-closing reaction was carried out at 55°C for 2.5h. The mixture was washed with water until neutral and dried to obtain a fluorinated monoepoxide. 10g of the hyperbranched polyester polyol, 2.0g of the fluorinated monoepoxide compound, 50g of bisphenol A diglycidyl ether and 0.15g of boron trifluoride ethylamine were added to a reaction flask and grafted at 120℃ and 300r / min for 4h to obtain toughened epoxy resin.

[0107] The method for preparing the composite filler includes the following steps: 10g of flake boron nitride (average particle size 30μm, thickness 200nm) and 120mL of sodium hydroxide aqueous solution (volume concentration 15%) were added to a reaction flask and sonicated at 400W and 75℃ for 3h. The mixture was then filtered, washed with deionized water until neutral, and dried under vacuum at 80℃ for 3h to obtain hydroxylated flake boron nitride. 10g of the hydroxylated flake boron nitride, 1.2g of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, 1.5g of β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 160mL of ethanol aqueous solution (85% v / v) were added to a reaction flask. The mixture was stirred at 400r / min and grafted at 55℃ for 7h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 60℃ for 3h to obtain the composite filler.

[0108] Example 3

[0109] This embodiment provides a method for preparing weather-resistant insulating powder, including the following steps: 70g phenolic epoxy resin (epoxy equivalent 220g / eq, softening point 78℃), 30g toughened epoxy resin, 15g dicyandiamide (average particle size 8μm), 0.5g 2-ethyl-4-methylimidazole, 35g spherical alumina (average particle size 8μm), and 25g fumed silica (specific surface area 180m²) were mixed. 2 Add 30g of composite filler, 3g of antioxidant 245, 2.5g of butyl acrylate homopolymer and 1g of benzoin to a high-speed mixer, stir at 700r / min for 4min, and then feed it into a twin-screw extruder for melt extrusion. The temperature of the extruder zone I is 90℃, the temperature of zone II is 110℃, the die head temperature is 120℃, the screw speed is 250r / min, and the length-to-diameter ratio is 36:1 to obtain the extruded material. The extruded material is pressed into a sheet with a thickness of 1.8 mm by a tablet press and then cooled to room temperature by air cooling to obtain the sheet material. The thin sheet material is coarsely crushed by a pulverizer, then finely crushed by a micro pulverizer, and finally passed through a 170-mesh standard sieve to obtain the weather-resistant insulating powder.

[0110] The method for preparing the toughened epoxy resin includes the following steps: 10g of trimethylolpropane and 20g of 2,2-dimethylolpropionic acid were added to a reactor and heated to 145°C under a nitrogen atmosphere for 5.5h to carry out a polycondensation reaction, thereby obtaining hyperbranched polyester polyol. 10 g of 1H,1H,2H,2H-perfluorooctanol, 12 mL of epichlorohydrin and 0.1 g of tetrabutylammonium bromide were added to a reaction flask and the ring-opening reaction was carried out at 85 °C and 250 r / min for 7 h to obtain a fluorochloro alcohol. The fluorinated chloro alcohol and 1.5g sodium hydroxide were added to a reaction flask and the ring-closing reaction was carried out at 45°C for 3.5h. The mixture was washed with water until neutral and dried to obtain a fluorinated monoepoxide. 10g of the hyperbranched polyester polyol, 1.0g of the fluorinated monoepoxide compound, 30g of bisphenol A diglycidyl ether and 0.25g of boron trifluoride ethylamine were added to a reaction flask and grafted at 105℃ and 200r / min for 6h to obtain toughened epoxy resin.

[0111] The preparation method of the composite filler includes the following steps: 10g of flake boron nitride (average particle size 15μm, thickness 400nm) and 80mL of sodium hydroxide aqueous solution (volume concentration 10%) are added to a reaction flask, ultrasonically treated at 200W and 65℃ for 5h, filtered, washed with deionized water until neutral, and vacuum dried at 80℃ for 3h to obtain hydroxylated flake boron nitride. 10g of the hydroxylated flake boron nitride, 0.5g of 1H,1H,2H,2H-perfluorooctyltrichlorosilane, 1.0g of γ-glycidyl etheroxypropyltriethoxysilane, and 120mL of ethanol aqueous solution (75% by volume) were added to a reaction flask. The mixture was stirred at 250r / min and the temperature was controlled at 65℃ for 5h for grafting reaction. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 60℃ for 3h to obtain the composite filler.

[0112] Comparative Example 1 This comparative example provides a method for preparing weather-resistant insulating powder. The difference from Example 1 is that ordinary flake boron nitride is used directly as a filler, while the other raw materials and steps are the same.

[0113] Comparative Example 2 This comparative example provides a method for preparing weather-resistant insulating powder. The difference from Example 1 is that ordinary bisphenol A type epoxy resin is used instead of toughening epoxy resin, and the amount of phenolic epoxy resin is adjusted to 100g. The remaining raw materials and steps are the same.

[0114] Comparative Example 3 This comparative example provides a method for preparing weather-resistant insulating powder, comprising the following steps: 75g phenolic epoxy resin (epoxy equivalent 200g / eq, softening point 85℃), 25g toughened epoxy resin, 20g dicyandiamide (average particle size 6μm), 0.8g 2-methylimidazole, 45g spherical alumina (average particle size 10μm), and 30g fumed silica (specific surface area 220m²) were mixed. 2 25g of composite filler, 2g of antioxidant 1010, 2g of butyl acrylate homopolymer and 1.5g of benzoin were added to a high-speed mixer and stirred at 900r / min for 3min. Then, the mixture was fed into a twin-screw extruder for melt extrusion. The temperature of the extruder zone I was 85℃, the temperature of zone II was 105℃, the die head temperature was 115℃, the screw speed was 300r / min, and the length-to-diameter ratio was 40:1 to obtain the extruded material. The extruded material is pressed into a sheet with a thickness of 1.5 mm by a tablet press and then cooled to room temperature by air cooling to obtain the sheet material. The thin sheet material is coarsely crushed by a pulverizer, then finely crushed by a micro pulverizer, and finally passed through a 180-mesh standard sieve to obtain the weather-resistant insulating powder.

[0115] The method for preparing the toughened epoxy resin includes the following steps: 10g of trimethylolpropane and 30g of 2,2-dimethylolpropionic acid were added to a reactor and heated to 150°C under a nitrogen atmosphere for 5 hours to carry out a polycondensation reaction, thereby obtaining hyperbranched polyester polyol. 10 g of 1H,1H,2H,2H-perfluorooctanol, 15 mL of epichlorohydrin and 0.15 g of tetrabutylammonium bromide were added to a reaction flask and the ring-opening reaction was carried out at 90 °C and 300 r / min for 6 h to obtain a fluorochloro alcohol. The fluorinated chloro alcohol and 2g of sodium hydroxide were added to a reaction flask and the ring-closing reaction was carried out at 50°C for 3 hours. The mixture was washed with water until neutral and dried to obtain a fluorinated monoepoxide. 10g of the hyperbranched polyester polyol, 1.5g of the fluorinated monoepoxide compound, 40g of bisphenol A diglycidyl ether and 0.2g of boron trifluoride ethylamine were added to a reaction flask and grafted at 115℃ and 250r / min for 5h to obtain toughened epoxy resin.

[0116] The method for preparing the composite filler includes the following steps: 10g of flake boron nitride (average particle size 20μm, thickness 300nm) and 100mL of sodium hydroxide aqueous solution (volume concentration 12%) were added to a reaction flask and sonicated at 70℃ and 300W for 4h. The mixture was then filtered, washed with deionized water until neutral, and dried under vacuum at 80℃ for 3h to obtain hydroxylated flake boron nitride. 10g of the hydroxylated flake boron nitride, 2.0g of γ-glycidyl etheroxypropyltrimethoxysilane and 150mL of ethanol aqueous solution (80% by volume) were added to a reaction flask and the grafting reaction was carried out at 60℃ and 350r / min for 6h. The mixture was washed twice with anhydrous ethanol and dried under vacuum at 60℃ for 3h to obtain the composite filler.

[0117] Comparative Example 4 This comparative example provides a method for preparing weather-resistant insulating powder, comprising the following steps: 75g phenolic epoxy resin (epoxy equivalent 200g / eq, softening point 85℃), 25g toughened epoxy resin, 20g dicyandiamide (average particle size 6μm), 0.8g 2-methylimidazole, 45g spherical alumina (average particle size 10μm), and 30g fumed silica (specific surface area 220m²) were mixed. 225g of composite filler, 2g of antioxidant 1010, 2g of butyl acrylate homopolymer and 1.5g of benzoin were added to a high-speed mixer and stirred at 900r / min for 3min. Then, the mixture was fed into a twin-screw extruder for melt extrusion. The temperature of the extruder zone I was 85℃, the temperature of zone II was 105℃, the die head temperature was 115℃, the screw speed was 300r / min, and the length-to-diameter ratio was 40:1 to obtain the extruded material. The extruded material is pressed into a sheet with a thickness of 1.5 mm by a tablet press and then cooled to room temperature by air cooling to obtain the sheet material. The thin sheet material is coarsely crushed by a pulverizer, then finely crushed by a micro pulverizer, and finally passed through a 180-mesh standard sieve to obtain the weather-resistant insulating powder.

[0118] The method for preparing the toughened epoxy resin includes the following steps: 10g of trimethylolpropane and 30g of 2,2-dimethylolpropionic acid were added to a reactor and heated to 150°C under a nitrogen atmosphere for 5 hours to carry out a polycondensation reaction, thereby obtaining hyperbranched polyester polyol. 10g of the hyperbranched polyester polyol, 40g of bisphenol A diglycidyl ether, and 0.2g of boron trifluoride ethylamine were added to a reaction flask, and the grafting reaction was carried out at 115℃ and 250r / min for 5h to obtain toughened epoxy resin. The method for preparing the composite filler includes the following steps: 10g of flake boron nitride (average particle size 20μm, thickness 300nm) and 100mL of sodium hydroxide aqueous solution (volume concentration 12%) were added to a reaction flask and sonicated at 70℃ and 300W for 4h. The mixture was then filtered, washed with deionized water until neutral, and dried under vacuum at 80℃ for 3h to obtain hydroxylated flake boron nitride. 10g of the hydroxylated flake boron nitride, 0.8g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1.2g of γ-glycidyl etheroxypropyltrimethoxysilane, and 150mL of ethanol aqueous solution (80% v / v) were added to a reaction flask. The grafting reaction was carried out at 60℃ and 350r / min for 6h. The mixture was washed twice with anhydrous ethanol and dried under vacuum at 60℃ for 3h to obtain the composite filler.

[0119] The performance of the weather-resistant insulating powders and their cured coatings in Examples 1-3 and Comparative Examples 1-4 was tested, and the test results are shown in Table 1. Among them: Glass transition temperature (Tg) test of coating: The coating sample was peeled off from the metal substrate, and 8-12 mg was weighed and placed in a DSC crucible. Under a nitrogen atmosphere, the temperature was increased from room temperature to 250°C at 20°C / min. After eliminating the thermal history, the temperature was cooled to room temperature, and then increased to 250°C at 20°C / min. The midpoint temperature of the glass transition step in the second heating curve was taken as Tg. Three samples were tested in each group, and the average value was taken. Withstand voltage test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70 kV. The coating was cured in a 200℃ oven for 15 min to obtain an insulating coating with a thickness of 400 μm. During the test, the aluminum alloy substrate was used as the grounding electrode, and a cylindrical brass electrode with a diameter of 25 mm was placed on the coating surface as the high-voltage electrode. The sample was immersed in silicone oil at 25℃ to prevent surface flashover. A 50 Hz AC power frequency voltage was applied and increased uniformly at a rate of 500 V / s until the coating broke down (current suddenly increased to over 10 mA or voltage suddenly dropped), and the breakdown voltage value was recorded. Withstand voltage Eb = Ub / t, where Eb is the withstand voltage (kV / mm), Ub is the breakdown voltage (kV), and t is the coating thickness (mm). Five samples were tested in each group, and the average value was taken. Volume resistivity test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70 kV. The substrate was then cured in a 200℃ oven for 15 min to obtain an insulating coating with a thickness of 400 μm. The sample size was 100 mm × 100 mm. During the test, a circular aluminum electrode with a diameter of 50 mm was vapor-deposited onto the coating surface as the main electrode, and a ring-shaped aluminum electrode with an inner diameter of 54 mm and an outer diameter of 74 mm was vapor-deposited on its outer side as a protective electrode. The aluminum alloy substrate was used as the counter electrode. The sample was placed in a shielded box, and a 500 V DC voltage was applied. After 1 min, the volume resistivity value was read. The volume resistivity was calculated using the following formula: ρv = Rv × Aeff / t, where ρv is the volume resistivity (Ω·cm), Rv is the measured volume resistivity (Ω), and Aeff is the effective area of ​​the main electrode (cm²). 2 ), where t is the coating thickness (cm). Three samples were tested in each group, and the average value was taken. Bond strength test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70 kV. The substrate was cured in a 200℃ oven for 15 min to obtain an insulating coating with a thickness of 400 μm. The sample size was 50 mm × 50 mm. Before testing, the coating surface was lightly sanded with 400-grit sandpaper and cleaned with anhydrous ethanol. A 20 mm diameter aluminum alloy pull-out post was vertically bonded to the coating surface using a two-component epoxy resin adhesive and cured at room temperature for 24 h. A sharp blade was used to scrape the coating through the circumference of the pull-out post to the substrate surface to eliminate interference from the surrounding coating. The sample was fixed on the pull-out tester, ensuring the pull-out post was coaxial with the direction of the tensile force. A uniform tensile force of 0.2 MPa / s was applied until the pull-out post detached, and the maximum tensile force F at failure was recorded. The bond strength σ = F / A, where σ is the bond strength (MPa), F is the maximum tensile force (N), and A is the bonding area of ​​the pull-out post (mm²). 2 Five samples were tested in each group, and the average value was taken. Corner coverage test: Powder coating was applied to the surface of a right-angle aluminum alloy test plate by electrostatic spraying at a voltage of 70kV. The plate was then cured in a 200℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400μm. The coating thickness at the right-angle vertex and the coating thickness in the flat area 20mm from the right-angle vertex were measured using a low-magnification microscope. The corner coverage was calculated using the following formula: Corner coverage = (Coating thickness at right-angle vertex / Coating thickness in the flat area) × 100%. Three samples were tested in each group, and the average value was taken. Abrasion resistance test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70kV. The substrate was then cured in a 200℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400μm. The coating was cut into circular samples with a diameter of 100mm. Under a load of 1kg, the coating surface was worn for 3000 revolutions using a CS17 grinding wheel. Abrasion debris was cleaned from the grinding wheel surface every 1000 revolutions. Before and after the test, the samples were placed in a desiccator for 24 hours to equilibrate, and then weighed using an analytical balance. The abrasion amount was calculated as: pre-test mass - post-test mass, expressed in mg. Three samples were tested in each group, and the average value was taken. Flame retardancy test: Powder coating was applied to the surface of fiberglass cloth by electrostatic spraying at a voltage of 70kV. The coating was then cured in a 200℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400μm. The coated samples were then cut into 125mm × 13mm specimens. The specimens were held vertically and a flame was applied to them for 10 seconds using a Bunsen burner with a flame height of 20mm. The flame was then removed, and the flaming time was recorded. Immediately after combustion ceased, the flame was applied again for 10 seconds, and the second flaming time and the flameless time were recorded. The flame retardancy rating was determined based on the total combustion time (10 ignitions) of each group of 5 specimens. If the flaming time of a single specimen did not exceed 10 seconds, the total combustion time of the 5 specimens did not exceed 50 seconds, and no molten droplets ignited the degreased cotton below, the rating was V-0. High and low temperature cycling test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70 kV. The substrate was cured in a 200℃ oven for 15 min to obtain an insulating coating with a thickness of 400 μm. The coated sample was placed in a high and low temperature alternating test chamber and maintained at -50℃ for 6 h, followed by a temperature increase of 5℃ / min to 120℃ and maintenance for 6 h as one cycle, for a total of 80 cycles. After the cycles, the samples were removed and left at room temperature for 2 h to observe for cracking, blistering, or peeling of the coating. The adhesion strength of the coating after the cycles was determined according to the above-described adhesion strength test method. Three samples were tested in each group, and the average value was taken. Coolant resistance test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70kV. The coating was cured in a 200℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400μm. The coated sample was then immersed in a constant-temperature coolant at 80℃ for 7 days. After removal, the coating was observed for cracking, peeling, blistering, or discoloration. After drying, the withstand voltage strength was measured according to the above-described withstand voltage test method to assess whether the insulation withstand voltage performance met the requirements. Three samples were tested in each group, and the average value was taken. Water resistance test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70 kV. The coating was cured in a 200℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400 μm. The coated sample was then immersed in deionized water at a constant temperature of 60℃ for 720 hours. The sample was then removed and observed for blistering, peeling, and discoloration. The coating performance after immersion was evaluated according to the adhesion and compressive strength test methods described above. Three samples were tested in each group, and the average value was taken. Moisture and heat resistance test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70 kV. The substrate was cured in a 200℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400 μm. The coated sample was then placed in a constant temperature and humidity test chamber and kept at 85℃ and 85% relative humidity for 2000 hours. The sample was then removed and observed for cracking, blistering, peeling, and discoloration. The bonding strength was measured according to the bonding strength test method described above. Three samples were tested in each group, and the average value was taken. Salt spray test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70kV. The substrate was cured in a 200℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400μm. Two intersecting scratches, 40mm in length and penetrating to the metal substrate surface, were then made on the coating surface using a sharp blade. The samples were placed in a salt spray test chamber using a 5% sodium chloride aqueous solution with a pH of 6.5-7.2 and a chamber temperature of 35℃. After 1000 hours of continuous spraying, the samples were removed and the width of rust expansion at the scratches and the presence of blistering or peeling of the coating were observed. Three samples were tested in each group, and the average value was taken. Thermo-oxidative aging test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70 kV. The substrate was cured in a 240℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400 μm. The coated samples were then placed in a hot air circulating oven and kept at a constant temperature of 240℃ for 1000 hours. After cooling at room temperature, the coating was observed for cracking, chalking, and peeling. The insulation performance retention rate of the coating after aging was evaluated according to the aforementioned withstand voltage strength test method and volume resistivity test method. Three samples were tested in each group, and the average value was taken. Theoretical specific gravity test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70kV. The coating was cured in a 200℃ oven for 15 minutes to obtain an insulating coating with a thickness of 400μm. The cured coating was completely peeled off the substrate, and a thin film of approximately 2cm × 2cm was cut. The mass m (accurate to 0.1mg) was weighed on an analytical balance. The thickness of the film was measured using a thickness gauge, and the surface area S was calculated. The theoretical specific gravity was calculated using the following formula: ρ = m / (S × t), where ρ is the theoretical specific gravity (g / cm³). 3 m is the mass of the coated sheet (g), and S is the area of ​​the coated sheet (cm²). 2 ), where t is the coating thickness (cm). Five samples were tested in each group, and the average value was taken. Microcrack density test: Powder coating was applied to the surface of an aluminum alloy substrate by electrostatic spraying at a voltage of 70 kV. The substrate was cured in a 200℃ oven for 15 min to obtain an insulating coating with a thickness of 400 μm. The coated sample was cut into 10 mm × 10 mm pieces. Before testing, a platinum conductive layer of approximately 10 nm thickness was sprayed onto the coating surface to eliminate the charging effect. The sample was placed on the scanning electron microscope stage, and the cross-sectional or surface morphology of the coating was observed at 5000x magnification under conditions of accelerating voltage of 10 kV and working distance of approximately 10 mm. Ten non-overlapping fields of view were randomly selected for imaging. A 50 μm × 50 μm square counting frame was superimposed on each SEM image, and the total number of microcracks within the frame was counted (cracks shorter than 1 μm were not counted). The microcrack density ρcr = ΣNi / (10 × A), where ρcr is the microcrack density (cracks / mm²). 2 ΣNi represents the total number of cracks counted across 10 fields of view, and A represents the area of ​​a single counting frame (0.0025 mm²). 2 Three samples were tested in each group, and the average value was taken.

[0120] Table 1 Performance Test Results

[0121] It should be noted that weather resistance, or climate resistance in full, refers to the coating's ability to resist damage from various climate temperature differences and other factors when exposed to the natural environment for a long time, and to resist aging and failure.

[0122] The technical solutions provided by the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A weather-resistant insulating powder, characterized in that, By mass parts, it includes the following components: The mixture contains 60-90 parts of phenolic epoxy resin, 10-40 parts of toughened epoxy resin, 8-35 parts of dicyandiamide, 0.1-2 parts of curing accelerator, 20-90 parts of spherical alumina, 15-50 parts of fumed silica, 10-50 parts of composite filler, 0.5-5 parts of antioxidant, and 1-5 parts of additives.

2. The weather-resistant insulating powder according to claim 1, characterized in that, By mass parts, it includes the following components: The mixture contains 70-80 parts of phenolic epoxy resin, 20-30 parts of toughened epoxy resin, 15-25 parts of dicyandiamide, 0.5-1.5 parts of curing accelerator, 30-60 parts of spherical alumina, 25-35 parts of fumed silica, 20-30 parts of composite filler, 1-3 parts of antioxidant, and 2-4 parts of additives.

3. The weather-resistant insulating powder according to claim 1 or 2, characterized in that, The method for preparing the toughened epoxy resin includes the following steps: Trimethylolpropane and 2,2-dimethylolpropionic acid were mixed and subjected to a polycondensation reaction to obtain hyperbranched polyester polyol. A ring-opening reaction was carried out by mixing a fluorinated alcohol, epichlorohydrin, and tetrabutylammonium bromide to obtain a fluorinated chloro alcohol. The fluorinated chloro alcohol and sodium hydroxide were mixed and subjected to a ring-closing reaction to obtain a fluorinated monoepoxide compound. The hyperbranched polyester polyol, fluorinated monoepoxide compound, bisphenol A diglycidyl ether, and boron trifluoride ethylamine are mixed and then subjected to a grafting reaction to obtain a toughened epoxy resin.

4. The weather-resistant insulating powder according to claim 3, characterized in that, The mass ratio of trimethylolpropane to 2,2-dimethylolpropionic acid is 1:1.5~6; and / or The polycondensation reaction is carried out under a nitrogen atmosphere at a temperature of 140-160°C for 3-6 hours; and / or The mass-to-volume ratio of the fluorinated alcohol, epichlorohydrin, and tetrabutylammonium bromide is 1 g : (0.8~2.5) mL : (0.005~0.03) g, wherein the fluorinated alcohol is selected from one or two of 1H,1H,2H,2H-perfluorooctanol or 1H,1H,2H,2H-perfluorodecanol; and / or The ring-opening reaction is carried out at a temperature of 80-100°C for a time of 4-8 hours; and / or The mass ratio of the fluorochlorool to sodium hydroxide is 1:0.1~0.25; and / or The closed-loop reaction is carried out at a temperature of 40-60°C for 2-4 hours; and / or The mass ratio of the hyperbranched polyester polyol, the fluorinated monoepoxide compound, the bisphenol A diglycidyl ether, and the boron trifluoride ethylamine is 1:0.05~0.25:2~6:0.005~0.02; and / or The grafting reaction is carried out at a temperature of 100-130°C for 3-6 hours.

5. A weather-resistant insulating powder according to claim 1 or 2, characterized in that, The method for preparing the composite filler includes the following steps: After mixing flake boron nitride with an aqueous sodium hydroxide solution, ultrasonic treatment was performed to obtain hydroxylated flake boron nitride. The hydroxylated flake boron nitride, fluorinated silane coupling agent, epoxy silane coupling agent, and ethanol aqueous solution are mixed and then subjected to a grafting reaction to obtain a composite filler.

6. The weather-resistant insulating powder according to claim 5, characterized in that, The mass-to-volume ratio of the sheet-like boron nitride to the sodium hydroxide aqueous solution is 1 g: (5~15) mL, and the volume concentration of the sodium hydroxide aqueous solution is 8%~20%; and / or The ultrasonic treatment is performed at a temperature of 60-80℃ for 2-6 hours and at a power of 100-500W; and / or The mass-to-volume ratio of the hydroxylated flake boron nitride, the fluorinated silane coupling agent, the epoxy silane coupling agent, and the ethanol aqueous solution is 1 g : (0.02~0.15) g : (0.02~0.2) g : (8~20) mL, and the volume concentration of the ethanol aqueous solution is 70%~90%. The fluorinated silane coupling agent is selected from one or more of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, or 1H,1H,2H,2H-perfluorooctyltrichlorosilane. The epoxy silane coupling agent is selected from one or more of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and / or The grafting reaction is carried out under stirring conditions, with a stirring speed of 200~500 r / min, a temperature of 50~70℃, and a time of 4~8 h.

7. A weather-resistant insulating powder according to claim 1 or 2, characterized in that, The phenolic epoxy resin has an epoxy equivalent of 170~230 g / eq and a softening point of 75~95℃; and / or The curing accelerator is selected from one or more of 2-methylimidazole, 2-phenylimidazole, or 2-ethyl-4-methylimidazole; and / or The average particle size of the spherical alumina is 2~20 μm; and / or The specific surface area of ​​the fumed silica is 150~300 m². 2 / g; and / or The antioxidant is selected from one or more of antioxidant 1010, antioxidant 1076, or antioxidant 245; and / or The additive is selected from one or both of butyl acrylate homopolymer and benzoin.

8. A method for preparing a weather-resistant insulating powder according to any one of claims 1 to 7, characterized in that, Includes the following steps: Phenolic epoxy resin, toughened epoxy resin, dicyandiamide, curing accelerator, spherical alumina, fumed silica, composite filler, antioxidant and additives are mixed and then subjected to melt extrusion to obtain extruded material. The extruded material is compressed into tablets and cooled to obtain thin sheet material; After the thin sheet material is crushed, it is passed through a 170-200 mesh standard sieve to obtain the weather-resistant insulating powder.

9. The method for preparing a weather-resistant insulating powder according to claim 8, characterized in that, The melt extrusion process is carried out using a twin-screw extruder. The temperature of zone I of the extruder is 75~90℃, the temperature of zone II is 95~110℃, the die head temperature is 105~125℃, the screw speed is 200~400 rpm, and the length-to-diameter ratio of the twin-screw extruder is 36~48:

1.

10. The application of the weather-resistant insulating powder according to any one of claims 1 to 7 in the coating of the surface of internal metal parts of an automobile engine.

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