A weather-resistant powder coating for doors and windows and its preparation method

Abstract

This invention relates to the field of coating technology, specifically to a weather-resistant powder coating for doors and windows and its preparation method. The coating comprises polyester resin, β-hydroxyalkylamide curing agent, titanium dioxide, barium sulfate, and gradient shell nano-zinc oxide powder. The gradient shell consists of a silane layer, a triazine ring interface structure, hindered amine light-stabilizing groups, and an organic shell, which enhances the dispersibility and UV shielding function of the nanoparticles through chemical bonding. The preparation method includes masterbatch premixing, melt extrusion, and grinding and sieving. Tests show that the coating exhibits high gloss retention, minimal color difference, and excellent corrosion resistance and mechanical properties after artificial aging.

Description

Technical Field

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

[0002] Currently, powder coatings for doors and windows need to withstand long-term corrosion from ultraviolet rays, humidity, temperature changes, and salt spray in outdoor environments, making weather resistance a key performance indicator. Traditional weather-resistant powder coatings widely rely on the physical addition of small-molecule ultraviolet absorbers (such as benzotriazoles) and hindered amine light stabilizers (HALS). These additives undergo melt extrusion (temperatures often exceeding 100°C) and high-temperature curing (approximately 160°C) stages during coating processing. Due to the lack of chemical bonding between small-molecule additives and the resin matrix, they are prone to migration, volatilization, or thermal degradation under heat, leading to a decrease in effective content. During long-term ultraviolet aging (such as QUV testing), the coating film exhibits rapid yellowing (increased ΔE value) and loss of specular gloss due to the degradation of its ultraviolet shielding function, affecting the durability of the appearance of doors and windows.

[0003] In addition, to compensate for the shortcomings of organic UV absorbers, the industry has attempted to introduce inorganic nanomaterials (such as nano-zinc oxide) as UV shielding agents, utilizing their wide bandgap properties to reflect or absorb ultraviolet rays. However, the small particle size and large specific surface area of ​​nanoparticles, along with their inherent high surface energy, make them prone to agglomeration in non-polar resin systems, forming micron-sized secondary particles. These agglomerates not only reduce UV shielding efficiency but also induce localized stress concentration during coating formation, leading to surface defects such as haze, orange peel, and uneven gloss, severely damaging the overall appearance consistency of door and window profiles. Simultaneously, these agglomerates can become penetration channels for corrosive media (such as moisture and chloride ions), accelerating substrate corrosion and weakening the mechanical properties of the coating (such as impact resistance and adhesion).

[0004] Existing improvement methods include surface treatment of nanoparticles with silane coupling agents to enhance compatibility with resins; however, a single silane layer is insufficient to completely suppress particle re-agglomeration under complex processing conditions (such as extrusion shearing and high-temperature curing), and lacks a long-term UV resistance mechanism. Some solutions attempt to directly mix small-molecule HALS with nanoparticles, but HALS is easily migrated and lost during processing, failing to efficiently quench free radicals locally at the interface, leading to increased powdering after UV aging. Therefore, existing technologies face a dual challenge: first, how to achieve long-term stable dispersion of nanoparticles in resins to avoid fluctuations in appearance and mechanical properties caused by agglomeration; and second, how to ensure that the UV stabilization function does not migrate or lose during processing and service, thereby synergistically improving weather resistance and corrosion resistance. This has become a technical bottleneck in the development of high-performance powder coatings for doors and windows. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a weather-resistant powder coating for doors and windows and its preparation method, so as to solve the problems of yellowing, loss of gloss, inconsistent appearance and insufficient corrosion resistance caused by the easy migration and loss of ultraviolet stabilizers and poor dispersibility of nanomaterials in existing weather-resistant powder coatings for doors and windows.

[0006] To achieve the above objectives, the present invention provides a weather-resistant powder coating for doors and windows, which is prepared from the following raw materials in parts by weight: 520-529 parts polyester resin, 50 parts β-hydroxyalkylamide curing agent, 250 parts titanium dioxide, 150 parts barium sulfate, 6-15 parts gradient shell nano zinc oxide powder, 5-10 parts leveling agent, 2-6 parts degassing agent and 1-5 parts polyethylene wax.

[0007] Furthermore, the gradient shell nano-zinc oxide powder includes a nano-zinc oxide core and a gradient shell coating the surface of the nano-zinc oxide core, wherein the gradient shell includes:

[0008] A silane layer formed from 3-aminopropyltriethoxysilane;

[0009] Triazine ring interface structure formed using cyanuric chloride as a bridging agent;

[0010] The hindered amine light-stabilizing group is covalently fixed to the triazine ring interface structure; and the outer organic shell is formed by stepwise grafting of monoamine polyether JEFFAMINE M-1000, monoamine polyether JEFFAMINE M-2070 and monoaminopropyl-terminated polydimethylsiloxane.

[0011] Preferably, the silane layer is formed by surface treatment of the nano-zinc oxide core with 3-aminopropyltriethoxysilane, and the mass ratio of the nano-zinc oxide core to the 3-aminopropyltriethoxysilane is 100:1.5-3 by mass.

[0012] Preferably, the triazine ring interface structure is formed by the reaction of cyanuric chloride with amino groups on the surface of the silane layer in the presence of N,N-diisopropylethylamine, and based on the total mass of 100 parts of the nano zinc oxide core and the silane layer, the cyanuric chloride is 3-6 parts and the N,N-diisopropylethylamine is 3-6 parts.

[0013] Preferably, the hindered amine photostable group is introduced by 4-amino-2,2,6,6-tetramethylpiperidine, and the 4-amino-2,2,6,6-tetramethylpiperidine is 1-2 parts by mass, based on the total of 100 parts of the nano zinc oxide core and the silane layer.

[0014] Preferably, based on the total of 100 parts by weight of the nano zinc oxide core and the silane layer, the monoamine polyether JEFFAMINE M-1000 is 2-4 parts, the monoamine polyether JEFFAMINE M-2070 is 3-5 parts, and the single-terminated aminopropyl-capped polydimethylsiloxane is 3-6 parts, and the monoamine polyether JEFFAMINE M-1000, the monoamine polyether JEFFAMINE M-2070 and the single-terminated aminopropyl-capped polydimethylsiloxane are grafted in the order described above.

[0015] Preferably, the gradient shell nano-zinc oxide powder is prepared by the following steps:

[0016] S1. After drying the zinc oxide nanoparticles, disperse them in anhydrous ethanol. Add 3-aminopropyltriethoxysilane prehydrolysate dropwise to the dispersion to react and obtain the dispersion, thereby obtaining silanized zinc oxide nanoparticles.

[0017] S2. Under nitrogen protection, silanized nano-zinc oxide powder is dispersed in anhydrous tetrahydrofuran. N,N-diisopropylethylamine solution and cyanuric chloride solution are added sequentially at 0-5℃ to form a triazine ring interface structure. Then, 4-amino-2,2,6,6-tetramethylpiperidine is added and reacted. Then, monoamine polyether JEFFAMINE M-1000, monoamine polyether JEFFAMINE M-2070 and monoaminopropyl-terminated polydimethylsiloxane are added sequentially for grafting reaction. After the reaction is completed, the powder is washed and dried to obtain gradient shell nano-zinc oxide powder.

[0018] Furthermore, the present invention also provides a method for preparing a weather-resistant powder coating for doors and windows, comprising the following steps:

[0019] P1. Polyester resin, gradient shell nano zinc oxide powder and leveling agent are mixed and melt-extruded, cooled and then pressed and crushed to obtain masterbatch sheets;

[0020] P2. The masterbatch sheet, polyester resin, β-hydroxyalkylamide curing agent, titanium dioxide, barium sulfate, leveling agent, degassing agent and polyethylene wax are dry mixed and melt extruded. The extrudate is cooled, pressed into sheets and crushed.

[0021] P3. Grind the crushed sheets into powder and sieve to obtain weather-resistant powder coatings for doors and windows.

[0022] Preferably, in step P1, dry mixing is performed at 1500 rpm for 2 minutes; during melt extrusion, the temperature of the twin-screw extruder barrel from the feeding section to the die head is 90℃, 100℃, 105℃, and 105℃ respectively, and the screw speed is 300 rpm.

[0023] Preferably, in step P2, dry mixing is performed at 1500 rpm for 3 minutes; during melt extrusion, the temperature of the twin-screw extruder barrel from the feeding section to the die head is 95℃, 105℃, 110℃, and 110℃ respectively, the screw speed is 250 rpm, and the material residence time in the machine is controlled to not exceed 60 seconds.

[0024] Preferably, in step P3, the powder discharge temperature is controlled to be no higher than 40°C, and the powder is passed through a 120-mesh sieve.

[0025] Furthermore, the present invention also provides a coating method for door and window profiles, wherein a weather-resistant powder coating for doors and windows is sprayed onto the surface of the door and window profile substrate by electrostatic spraying and cured to obtain a coating film.

[0026] Preferably, the door and window profile substrate is an aluminum alloy sheet, the spraying voltage is 60kV, the dry film thickness is 70μm, and the curing conditions are 160℃ for 10min and cooling for 24h after curing.

[0027] The beneficial effects of this invention are:

[0028] This invention achieves a significant improvement in the weather resistance and overall performance of powder coatings through the surface silanization and gradient shell design of nano-zinc oxide. After silanization, the reactive amino groups introduced into the surface of the nano-zinc oxide enhance its chemical compatibility with polyester resin, effectively inhibiting particle agglomeration and resulting in a dense and smooth surface structure of the coating film. This leads to high initial gloss and low roughness, thus improving its decorative properties.

[0029] Using cyanuric chloride as a bridging agent, a triazine ring interface structure is constructed on the surface of nanoparticles, and hindered amine light-stabilizing groups (such as 4-amino-2,2,6,6-tetramethylpiperidine derivatives) are covalently fixed, anchoring the light-stabilizing function near the UV shielding agent. This design reduces the migration and heat loss of the light stabilizer during melt extrusion and high-temperature curing, persistently inhibits UV-induced free radical degradation of polymer chains, delays yellowing and gloss loss of the coating, and improves outdoor color stability.

[0030] By stepwise grafting short-chain monoamine polyethers (such as JEFFAMINE M-1000), long-chain monoamine polyethers (such as JEFFAMINE M-2070), and single-terminated aminopropyl-terminated polydimethylsiloxane, a gradient shell structure from the inside to the outside is formed on the surface of nanoparticles. The inner polyether segments improve the wettability and dispersibility of the particles with the resin, the middle polyether provides steric hindrance to inhibit secondary agglomeration, and the outer siloxane segments impart hydrophobic barrier properties, synergistically reducing the penetration of media such as water vapor and salt spray, and enhancing the corrosion resistance and water resistance of the coating film.

[0031] The silane layer and triazine ring structure on the surface of nano-zinc oxide synergistically inhibit its photocatalytic activity, while also exerting a synergistic effect of UV shielding and free radical quenching, reducing the photo-oxidative degradation of the polyester matrix. The internal interface of the coating is more firmly bonded, defects are reduced, and mechanical properties such as impact resistance are improved, achieving a balance between decorative and protective properties and extending the service life of doors and windows in harsh environments. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0033] Example 1:

[0034] I. Raw material source, model, and parameter description

[0035] The zinc oxide nanopowder used in this embodiment is zinc oxide powder sold by Sigma-Aldrich, with a particle size ≤50 nm and product number 544906; the monoaminopropyl-terminated polydimethylsiloxane is monoaminopropyl-terminated polydimethylsiloxanes-asymmetric from Gelest, product code MCR-A11, with a viscosity of 8-12 cSt and a molecular weight of 800-1000; the polyether monoamine is JEFFAMINE M-1000 and JEFFAMINE M-2070 from Huntsman, both of which are monoamine polyethers; the ultra-weather-resistant polyester resin for the powder coating is CRYLCOAT 4442-2 from Allnex; the β-hydroxyalkylamide curing agent is PRIMID XL-552 from EMS-GRILTECH; the titanium dioxide is Ti-Pure R-706 from Chemours; and the barium sulfate is Blanc Fixe from Solvay. N; the leveling agent used was BYK-3900P from BYK Corporation; the degassing agent used was benzoin sold by Sigma-Aldrich, product number B8681; the polyethylene wax used was Licowax PE520 from Clariant Corporation. Anhydrous ethanol, deionized water, and anhydrous tetrahydrofuran were all commercially available analytical grade reagents or higher.

[0036] II. Preparation of Gradient Shell Nanoscale Zinc Oxide Powder

[0037] Step S1: Weigh 100g of zinc oxide nanoparticles and dry them in a 120℃ oven for 2 hours. Transfer the dried powder to a 1L three-necked flask, add 400g of anhydrous ethanol, and pre-stir at 600rpm for 10 minutes. Then, ultrasonically disperse the powder at 300W for 30 minutes to obtain a zinc oxide nanoparticle ethanol dispersion. Add 10g of anhydrous ethanol and 2g of deionized water to a beaker, and add 2g of... 3-Aminopropyltriethoxysilane was magnetically stirred at 25°C for 30 min to obtain an aminosilane pre-hydrolyzed solution. The nano-zinc oxide ethanol dispersion was heated to 60°C, and all the aminosilane pre-hydrolyzed solution was added dropwise over 10 min with stirring at 600 rpm. The reaction was continued at a constant temperature of 60°C for 1 h, then the temperature was lowered to 50°C and stirred for aging for 10 h. After cooling to 25°C, the solid was collected by vacuum filtration or centrifugation at 8000 rpm for 10 min. The solid was washed three times with anhydrous ethanol and once with anhydrous tetrahydrofuran. The solid was then dried in a vacuum drying oven at 60°C for 24 h to obtain silanized nano-zinc oxide powder.

[0038] Step S2: Add 100g of silanized nano-zinc oxide powder and 600g of anhydrous tetrahydrofuran to a three-necked flask. Disperse the mixture ultrasonically at 300W for 20min under nitrogen protection, then place it in an ice-water bath to stabilize the system temperature at 0-5℃. Separately, dissolve 4g of cyanuric chloride in 100g of anhydrous tetrahydrofuran and 4g of N,N-diisopropylethylamine in 20g of anhydrous tetrahydrofuran in a beaker. First, add all the N,N-diisopropylethylamine solution to the reaction flask at once, then add all the cyanuric chloride solution dropwise over 20min. Maintain the temperature at 0-5℃ and stir for 2h, then raise the temperature to 25℃ and stir for 2h. Next, add a solution prepared from 1g of 4-amino-2,2,6,6-tetramethylpiperidine and 50g of anhydrous tetrahydrofuran, and raise the temperature to 40℃ and stir for 4h. After lowering the temperature to 30℃, add 3g of monoamine polyether JEFFAMINE. A solution of M-1000 and 60g of anhydrous tetrahydrofuran was added dropwise and stirred at 30°C for 3 hours. The temperature was then raised to 50°C, and a solution of 3g of monoamine polyether JEFFAMINE M-2070 and 80g of anhydrous tetrahydrofuran was added, and the temperature was maintained at 50°C for 4 hours. The temperature was then raised again to 60°C, and a solution of 4g of monoaminopropyl-terminated polydimethylsiloxane and 80g of anhydrous tetrahydrofuran was added, and the temperature was maintained at 60°C for 4 hours. The temperature was lowered to 25°C, and 50g of aqueous ethanol solution (2wt% water content) was added to the reaction system. The mixture was stirred for 15 minutes to quench the reaction. After the reaction, the solid was collected by filtration and washed twice with anhydrous tetrahydrofuran and twice with anhydrous ethanol. The solid was then dried in a vacuum drying oven at 60°C for 24 hours to obtain gradient shell nano-zinc oxide powder.

[0039] III. Preparation of Weather-Resistant Powder Coatings for Doors and Windows

[0040] Step P1: Weigh 100g of ultra-weather-resistant polyester resin and add it to a high-speed mixer. Add 10g of gradient shell nano zinc oxide powder and 1g of leveling agent. Dry mix at 1500rpm for 2min. Then feed the mixture into a twin-screw extruder. Set the temperature of the barrel from the feeding section to the die head to 90℃, 100℃, 105℃ and 105℃ respectively. Set the screw speed to 300rpm. After the extrudate is cooled to 25℃ by the cooling belt, it is pressed into sheets and crushed into masterbatch sheets.

[0041] Step P2: Weigh 111g of masterbatch flakes, 425g of ultra-weather-resistant polyester resin, 50g of β-hydroxyalkylamide curing agent, 250g of titanium dioxide, 150g of barium sulfate, 7g of leveling agent, 4g of degassing agent, and 3g of polyethylene wax. Add them to a high-speed mixer and dry mix at 1500rpm for 3min. Feed the dry mixture into a twin-screw extruder, setting the barrel temperature from the feeding section to the die head to 95℃, 105℃, 110℃, and 110℃ respectively, and the screw speed to 250rpm. Control the material residence time in the machine to not exceed 60s. After the extrudate is cooled to 25℃ by the cooling belt, it is pressed into sheets and crushed. The crushed sheets are pulverized by an air classifier mill, controlling the powder outlet temperature to not exceed 40℃, and then passed through a 120-mesh sieve to obtain a weather-resistant powder coating for doors and windows.

[0042] IV. Spray curing

[0043] Weather-resistant powder coating for doors and windows was applied to the surface of aluminum alloy sheet using electrostatic spraying at a voltage of 60kV and a dry film thickness of 70μm. The coating was then cured in an oven at 160℃ for 10 minutes and cooled for 24 hours to obtain the coating film.

[0044] Example 2:

[0045] I. The source, type, and parameters of the raw materials are the same as in Example 1.

[0046] II. Preparation of Gradient Shell Nano-Zinc Oxide Powder: Based on Example 1, in step S1, 2g of 3-aminopropyltriethoxysilane was adjusted to 1.5g of 3-aminopropyltriethoxysilane, and the remaining conditions were the same as in Example 1; in step S2, 4g of cyanuric chloride was adjusted to 3g of cyanuric chloride, 4g of N,N-diisopropylethylamine was adjusted to 3g of N,N-diisopropylethylamine, 3g of monoamine polyether JEFFAMINE M-1000 was adjusted to 2g of monoamine polyether JEFFAMINE M-1000, and 3g of monoamine polyether JEFFAMINE M-2070 was adjusted to 5g of monoamine polyether JEFFAMINE M-2070, 4g of single-ended aminopropyl-terminated polydimethylsiloxane was adjusted to 6g of single-ended aminopropyl-terminated polydimethylsiloxane; the amount of anhydrous tetrahydrofuran used in the preparation of each solution, the dropping method, the temperature program, the washing and drying conditions were the same as in Example 1, and the gradient shell nano zinc oxide powder of Example 2 was obtained.

[0047] III. Preparation of weather-resistant powder coatings for doors and windows and IV. Spraying and curing: The remaining conditions are the same as in Example 1.

[0048] Example 3:

[0049] I. The source, type, and parameters of the raw materials are the same as in Example 1.

[0050] II. Preparation of gradient shell nano-zinc oxide powder: Based on Example 1, in step S1, 2g of 3-aminopropyltriethoxysilane was adjusted to 3g of 3-aminopropyltriethoxysilane, and the remaining conditions were the same as in Example 1; in step S2, 3g of monoamine polyether JEFFAMINE M-1000 was adjusted to 4g of monoamine polyether JEFFAMINE M-1000, and 4g of monoaminopropyl-terminated polydimethylsiloxane was adjusted to 3g of monoaminopropyl-terminated polydimethylsiloxane. The amounts of other substances, the amount of anhydrous tetrahydrofuran used in the preparation of each solution, the dropping method, the temperature program, and the washing and drying conditions were the same as in Example 1, thus obtaining the gradient shell nano-zinc oxide powder of Example 3.

[0051] III. Preparation of weather-resistant powder coatings for doors and windows and IV. Spraying and curing: The remaining conditions are the same as in Example 1.

[0052] Example 4:

[0053] I. The source, type, and parameters of the raw materials are the same as in Example 1.

[0054] II. Preparation of gradient shell nano zinc oxide powder: The remaining conditions are the same as in Example 1.

[0055] III. Preparation of weather-resistant powder coating for doors and windows: In step P1, the amount of gradient shell nano zinc oxide powder added was adjusted from 10g to 15g, and the other conditions were the same as in Example 1, to obtain masterbatch sheet; In step P2, 116g masterbatch sheet, 420g ultra-weather-resistant polyester resin, 50g β-hydroxyalkylamide curing agent, 250g titanium dioxide, 150g barium sulfate, 7g leveling agent, 4g degassing agent, and 3g polyethylene wax were weighed, and the other conditions were the same as in Example 1, to obtain weather-resistant powder coating for doors and windows.

[0056] IV. Spray curing: The remaining conditions are the same as in Example 1.

[0057] Example 5:

[0058] I. The source, type, and parameters of the raw materials are the same as in Example 1.

[0059] II. Preparation of gradient shell nano-zinc oxide powder: Based on Example 1, in step S2, 4g of cyanuric chloride was adjusted to 6g of cyanuric chloride, 4g of N,N-diisopropylethylamine was adjusted to 6g of N,N-diisopropylethylamine, and 1g of 4-amino-2,2,6,6-tetramethylpiperidine was adjusted to 2g of 4-amino-2,2,6,6-tetramethylpiperidine. The amounts of the remaining substances, the amount of anhydrous tetrahydrofuran used in the preparation of each solution, the dropping method, the temperature program, and the washing and drying conditions were the same as in Example 1, thus obtaining the gradient shell nano-zinc oxide powder of Example 5.

[0060] III. Preparation of weather-resistant powder coating for doors and windows: In step P1, the amount of gradient shell nano zinc oxide powder added was adjusted from 10g to 6g, and the other conditions were the same as in Example 1, to obtain masterbatch sheet; In step P2, 107g masterbatch sheet, 429g ultra-weather-resistant polyester resin, 50g β-hydroxyalkylamide curing agent, 250g titanium dioxide, 150g barium sulfate, 7g leveling agent, 4g degassing agent, and 3g polyethylene wax were weighed, and the other conditions were the same as in Example 1, to obtain weather-resistant powder coating for doors and windows.

[0061] IV. Spray curing: The remaining conditions are the same as in Example 1.

[0062] Comparative Example 1:

[0063] The difference from Example 1 is that in step P1, 10g of gradient shell nano zinc oxide powder is replaced with 10g of zinc oxide nano powder, and the other conditions are the same as in Example 1.

[0064] Comparative Example 2:

[0065] The difference from Example 1 is that in step P1, 10g of gradient shell nano zinc oxide powder is replaced with 10g of silanized nano zinc oxide powder, and the other conditions are the same as in Example 1.

[0066] Comparative Example 3:

[0067] The difference from Example 1 is that in step S2, the solution prepared by 1g of 4-amino-2,2,6,6-tetramethylpiperidine and 50g of anhydrous tetrahydrofuran is not added, while the other conditions are the same as in Example 1.

[0068] Comparative Example 4:

[0069] The difference from Example 1 is that in step S2, the order of adding monoamine polyether JEFFAMINE M-1000, monoamine polyether JEFFAMINE M-2070 and monoaminopropyl-terminated polydimethylsiloxane is adjusted to add monoamine polyether JEFFAMINE M-2070 first, then monoaminopropyl-terminated polydimethylsiloxane, and finally monoamine polyether JEFFAMINE M-1000. The other conditions are the same as in Example 1.

[0070] Comparative Example 5:

[0071] The difference from Example 1 is that in step S2, instead of adding 4g of a solution prepared by single-terminated aminopropyl-terminated polydimethylsiloxane and 80g of anhydrous tetrahydrofuran, 80g of anhydrous tetrahydrofuran is added at the corresponding stage, and the other conditions are the same as in Example 1.

[0072] Comparative Example 6:

[0073] The difference from Example 1 is that in step S2, instead of adding 3g of the solution prepared by monoamine polyether JEFFAMINE M-2070 and 80g of anhydrous tetrahydrofuran, 80g of anhydrous tetrahydrofuran is added at the corresponding stage, and the other conditions are the same as in Example 1.

[0074] Performance testing:

[0075] Sample preparation and conditioning: Weather-resistant powder coatings for doors and windows prepared in Examples 1-5 and Comparative Examples 1-6 were used to prepare coating test panels according to the electrostatic spraying and curing conditions of Example 1. The substrate was an aluminum alloy sheet (150mm×70mm×1mm) conforming to the requirements of GB / T 9271-2008 "Standard Test Panels for Paints and Varnishes". Before spraying, the sheet was degreased with anhydrous ethanol and dried in an oven at 80℃ for 10min. The spraying voltage was 60kV, and the dry film thickness was controlled at (70±3)μm. The dry film thickness was measured according to GB / T13452.2-2008. After curing, the test panels were placed at a temperature of (23±2)℃ and a relative humidity of (50±5)% for 24h. At least 3 parallel test panels were prepared for each sample, and the average value was taken.

[0076] Artificial accelerated weathering: Artificial aging was conducted according to GB / T 23987-2009; UVA-340 lamps were used, and the irradiance was set to 0.89 W / (m²). 2•nm) (at 340nm), the cycle program is 8h UV irradiation (blackboard temperature 60℃) + 4h condensation (50℃), the cumulative exposure time is 1000h; the 60° mirror gloss before and after the test is determined according to GB / T 9754-2025, and 3 positions are selected for measurement and average for each test board; the color and color difference are determined according to GB / T 11186-2025, and ΔE is calculated using the CIE Lab system; the chalking grade is rated according to GB / T 1766-2008 "Rating Method for Aging of Paint and Varnish Coatings"; the gloss retention rate is calculated as (gloss after exposure / gloss before exposure) × 100%.

[0077] Neutral Salt Spray Test: The neutral salt spray (NSS) test was conducted according to GB / T 10125-2021. A straight scratch with a length of 60 mm and a width of 1 mm was prepared on the surface of the coating film of the test plate using a scratcher, penetrating to the substrate. The test plate was placed in a salt spray chamber at a test temperature of (35±2)℃. The spray solution was a 5% sodium chloride solution with a pH adjusted to 7.0. The salt spray deposition rate was controlled at 1.5 mL / (80 cm²). 2 Spray continuously for 1000 hours. After the test, rinse gently with deionized water and place at (23±2)℃ for 24 hours. Use vernier calipers to randomly select 5 points on the scratch to measure the width of corrosion spread on one side and take the average value.

[0078] Impact resistance: conducted according to GB / T 1732-2020; under the conditions of (23±2)℃ and (50±5)% relative humidity, the test panel is placed flat on an anvil with the paint film facing upward, and a 1kg hammer and a standard impactor are used to gradually increase the drop height. The criteria for qualification are no cracking or peeling of the paint film. The maximum drop height (cm) without damage is recorded.

[0079] Surface roughness of the coating: Tested according to GB / T 1031-2009; a stylus-type roughness tester was used, with a cutoff length of 0.8 mm and an evaluation length of 4.0 mm. Ra was measured at five randomly selected locations on the surface of each test plate, and the average value was taken. The test results are recorded in Table 1.

[0080] Table 1 Performance Test Results

[0081]

[0082] As can be seen from the data in Table 1, the weather-resistant powder coating for doors and windows prepared by this invention can still maintain a high mirror gloss, small color difference, and low chalking level after accelerated weathering aging. It also exhibits minimal corrosion spread in the neutral salt spray scratch test and combines good impact resistance with low surface roughness. This may be because: using cyanuric chloride as a bridging agent, 3-aminopropyltriethoxysilane and 4-amino-2,2,6,6-tetramethylpiperidine are synergistically introduced into the surface of nano-zinc oxide, which weakens the photocatalytic activity of nano-zinc oxide and exerts free radical quenching and photostabilizing effects. Simultaneously, the gradient shell constructed from monoamine polyether JEFFAMINE M-1000, monoamine polyether JEFFAMINE M-2070, and monoaminopropyl-terminated polydimethylsiloxane improves particle dispersion and interfacial wetting, making the coating film denser and with fewer defects, thus achieving a balance between decorative and protective properties.

[0083] As can be seen from the data in Example 1 and Comparative Example 1 in Table 1, when the nano-zinc oxide was not modified with a gradient shell, the initial gloss and gloss retention of the coating decreased, the color difference increased, and the chalking level increased. Simultaneously, the unilateral corrosion propagation of scratches intensified, accompanied by decreased impact resistance and increased surface roughness. The main reason for this is likely that unmodified nano-zinc oxide is prone to agglomeration and the formation of micro-defects, and its photocatalytic activity is more likely to induce chain segment breakage and surface chalking in the polyester matrix. Therefore, simply introducing nano-zinc oxide cannot achieve a stable weather-resistant protective effect; synergistic suppression of failure through surface chemistry and shell structure is necessary.

[0084] As can be seen from the data in Table 1 for Example 1 and Comparative Example 2, after surface treatment of nano-zinc oxide with only 3-aminopropyltriethoxysilane, the appearance and corrosion resistance of the coating film are improved compared to Comparative Example 1. However, it is still difficult to simultaneously maintain gloss, color difference, and chalking after accelerated aging. It is speculated that the reason is that although the single silane layer improves the compatibility between inorganic particles and polyester resin, it lacks the quenching effect of 4-amino-2,2,6,6-tetramethylpiperidine free radicals introduced by cyanuric chloride as a bridge and the dispersing and stabilizing effect of monoamine polyether JEFFAMINE M-2070, resulting in insufficient interface control.

[0085] As can be seen from the data in Table 1 for Example 1 and Comparative Example 3, when 4-amino-2,2,6,6-tetramethylpiperidine is not introduced into the gradient shell nano-zinc oxide, the initial appearance of the coating film remains good, but the gloss retention rate decreases, the color difference increases, and the chalking grade rises after weathering aging. The main reason may be that after the hindered amine photostable groups are missing, the free radical chain reaction is difficult to terminate in time, the polyester backbone is more prone to oxidative degradation, and a loose chalking layer is formed on the surface, which in turn causes enhanced scattering and color drift. It can be seen that the composite modification of hindered amine photostable groups and nano-zinc oxide has an unexpected synergistic effect, which can simultaneously suppress gloss loss and chalking.

[0086] As can be seen from the data in Table 1 for Example 1 and Comparative Example 4, when the order of adding the gradient shell nano-zinc oxide was changed, and the nano-zinc oxide powder was not pre-dispersed with the ultra-weather-resistant polyester resin to form a masterbatch, the surface roughness of the coating increased, leading to a decrease in initial gloss. Corrosion propagation under salt spray scratches and color difference after aging also intensified. It is speculated that this is because the particles are more prone to secondary agglomeration during the melting and mixing stage, resulting in an incomplete gradient shell structure, uneven interfacial wetting, and an increase in micropore defects, thereby simultaneously weakening both decorative properties and shielding protection.

[0087] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 5 and 6, after removing either the single-ended aminopropyl-terminated polydimethylsiloxane or the monoamine polyether JEFFAMINE M-2070, the corrosion propagation of the coating under salt spray scratch conditions increased, accompanied by a decrease in gloss retention and impact resistance, and an increase in surface roughness. This may be because the single-ended aminopropyl-terminated polydimethylsiloxane provides a low surface energy and hydrophobic shielding layer, making it easier for moisture to penetrate along the interface after its absence; while the monoamine polyether JEFFAMINE M-2070 provides dispersion stability and flexible buffering, reducing particle stability after its absence. Therefore, the bi-segment gradient construction of the polyether and siloxane segments achieves a synergistic interfacial effect greater than the sum of its parts (1+1>2).

[0088] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for producing a weather-resistant powder coating for doors and windows, characterized by, Includes the following steps: P1. Polyester resin, gradient shell nano zinc oxide powder and leveling agent are mixed and melt-extruded, cooled and then pressed and crushed to obtain masterbatch sheets; P2. The masterbatch sheet, polyester resin, β-hydroxyalkylamide curing agent, titanium dioxide, barium sulfate, leveling agent, degassing agent and polyethylene wax are dry mixed and melt extruded. The extrudate is cooled, pressed into sheets and crushed. P3. Grind the crushed sheet material into powder and sieve it to obtain a weather-resistant powder coating for doors and windows; The weather-resistant powder coating for doors and windows, by weight, is prepared from the following raw materials: 520-529 parts polyester resin, 50 parts β-hydroxyalkylamide curing agent, 250 parts titanium dioxide, 150 parts barium sulfate, 6-15 parts gradient shell nano zinc oxide powder, 5-10 parts leveling agent, 2-6 parts degassing agent, and 1-5 parts polyethylene wax. The gradient shell nano-zinc oxide powder includes a nano-zinc oxide core and a gradient shell coating the surface of the nano-zinc oxide core. The gradient shell includes: a silane layer formed of 3-aminopropyltriethoxysilane; a triazine ring interface structure formed with cyanuric chloride as a bridging agent; a hindered amine photostable group covalently fixed on the triazine ring interface structure; and an outer organic shell formed by stepwise grafting of monoamine polyether JEFFAMINE M-1000, monoamine polyether JEFFAMINE M-2070, and monoaminopropyl-terminated polydimethylsiloxane. The silane layer is formed by surface treatment of the nano zinc oxide core with 3-aminopropyltriethoxysilane, and the mass ratio of the nano zinc oxide core to the 3-aminopropyltriethoxysilane is 100:1.5-3 by mass. The triazine ring interface structure is formed by the reaction of cyanuric chloride with amino groups on the surface of the silane layer in the presence of N,N-diisopropylethylamine. Based on the total mass of 100 parts of nano zinc oxide core and silane layer, the cyanuric chloride is 3-6 parts and the N,N-diisopropylethylamine is 3-6 parts. The hindered amine photostable group is introduced by 4-amino-2,2,6,6-tetramethylpiperidine, and the 4-amino-2,2,6,6-tetramethylpiperidine is 1-2 parts by mass, based on the total of 100 parts of the nano zinc oxide core and the silane layer. Based on a total of 100 parts by weight of nano-zinc oxide core and silane layer, the monoamine polyether JEFFAMINE M-1000 is 2-4 parts, the monoamine polyether JEFFAMINE M-2070 is 3-5 parts, and the single-terminated aminopropyl-capped polydimethylsiloxane is 3-6 parts. The monoamine polyether JEFFAMINE M-1000, the monoamine polyether JEFFAMINE M-2070, and the single-terminated aminopropyl-capped polydimethylsiloxane are grafted in the order described above. The gradient shell nano-zinc oxide powder is prepared by the following steps: S1. After drying the zinc oxide nanoparticles, disperse them in anhydrous ethanol to obtain a dispersion. Add 3-aminopropyltriethoxysilane prehydrolysate dropwise to the dispersion to react and obtain silanized zinc oxide nanoparticles. S2. Under nitrogen protection, silanized nano-zinc oxide powder is dispersed in anhydrous tetrahydrofuran. N,N-diisopropylethylamine solution and cyanuric chloride solution are added sequentially at 0-5℃ to form a triazine ring interface structure. Then, 4-amino-2,2,6,6-tetramethylpiperidine is added and reacted. Then, monoamine polyether JEFFAMINE M-1000, monoamine polyether JEFFAMINE M-2070 and monoaminopropyl-terminated polydimethylsiloxane are added sequentially for grafting reaction. After the reaction is completed, the powder is washed and dried to obtain gradient shell nano-zinc oxide powder.

2. The method for preparing weather-resistant powder coating for doors and windows according to claim 1, characterized in that, In step P1, dry mixing is performed at 1500 rpm for 2 minutes; during melt extrusion, the temperature of the twin-screw extruder barrel from the feeding section to the die head is 90℃, 100℃, 105℃, and 105℃ respectively, and the screw speed is 300 rpm; in step P2, dry mixing is performed at 1500 rpm for 3 minutes; during melt extrusion, the temperature of the twin-screw extruder barrel from the feeding section to the die head is 95℃, 105℃, 110℃, and 110℃ respectively, and the screw speed is 250 rpm, and the material residence time in the machine is controlled not to exceed 60 seconds; in step P3, the powder outlet temperature is controlled not to exceed 40℃, and the powder passes through a 120-mesh sieve.

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