High-weather-resistance fluorocarbon powder coating as well as preparation method and application thereof

Abstract

The invention discloses a high-weather-resistance fluorocarbon powder coating as well as a preparation method and application thereof in the field of functional polymer materials. The coating disclosed by the invention takes a fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer and phosphorus-silicon synergistic modified nano clay as core modification components. Wherein the fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer is polymerized with monomers such as fluorine-containing diol and isocyanate through a polytetrafluoroethylene emulsion under the protection of nitrogen to form a fluorocarbon-polyurethane double-main-chain structure, so that the crosslinking density and the photooxidation resistance are improved; phosphorus-silicon synergistic modified nano clay is subjected to interlayer intercalation, phosphorus source modification and silane coupling agent treatment to form a physical barrier layer, enhance interface bonding and hinder water vapor permeation. The formula of the coating further comprises an HDI tripolymer curing agent, rutile type titanium dioxide and other pigments and fillers and auxiliaries. The preparation method comprises the following steps: premixing all the components, extruding by double screws, tabletting and crushing, and carrying out jet milling. The product can be applied to the surface of a metal workpiece, and the weather resistance of the product in an extreme environment is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of functional polymer materials, and in particular to a highly weather-resistant fluorocarbon powder coating, a preparation method thereof, and an application thereof. Background Art

[0002] Fluorocarbon powder coatings, a key outdoor protective material, are widely used on metal substrates exposed to the elements for extended periods, such as building curtain walls, bridge steel structures, and photovoltaic mountings. Their core advantages lie in their excellent chemical stability and high-temperature resistance. However, traditional fluorocarbon coatings based on materials like polytetrafluoroethylene and polyvinylidene fluoride still face significant performance shortcomings in practical use, namely insufficient weather resistance. Long-term exposure to complex environments such as ultraviolet light, humidity, and salt spray can cause the coating to yellow, powder, and crack, leading to protective failure. This not only affects the aesthetics of the substrate, but also shortens the service life of equipment and structures, increasing maintenance costs.

[0003] An in-depth analysis of the root causes of the insufficient weather resistance of traditional fluorocarbon coatings reveals three main bottlenecks: First, the resin molecular chain has weak polarity and limited cross-linking density with the curing agent, which easily triggers photooxidation reactions under ultraviolet radiation, causing the molecular chain to break and generate aging products such as carbonyl and peroxide groups, and the coating gradually loses its original density and strength; second, the interface bonding between the pigment and filler and the resin is insufficient, and the difference in thermal expansion coefficient leads to microcracks inside the coating, forming water vapor penetration channels and accelerating the invasion of corrosive media; third, the coating surface energy is high, which easily absorbs water vapor in the environment, and the saturated water absorption rate is high, further exacerbating the electrochemical corrosion reaction. In particular, in coastal high salt fog or industrial acid rain environments, the risk of rust increases significantly. These problems are superimposed on each other, making it difficult for traditional fluorocarbon coatings to meet the needs of long-term protection in extreme environments.

[0004] In response to the above pain points, the existing technology attempts to improve weather resistance by increasing the amount of crosslinking agent or performing simple surface treatment on the filler, but the effect is limited. For example, conventional crosslinking processes are difficult to significantly increase the crosslinking density of the resin, and the problem of photooxidative degradation has not been effectively suppressed; the surface treatment process of the filler is complicated, and the improvement of the interface bonding force is not obvious, and the problems of microcracks and water vapor penetration still exist. Therefore, the development of a new fluorocarbon powder coating that takes into account both resin crosslinking reinforcement and filler interface synergistic modification has become a key direction for improving the weather resistance of outdoor protective materials. Based on this demand, the present invention constructs a fluorocarbon-polyurethane dual-main chain structure and a phosphorus-silicon synergistic modified filler system through a dual-functional modification strategy to fundamentally solve the weather resistance defects of traditional coatings. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly weather-resistant fluorocarbon powder coating, a preparation method and an application thereof, which solves the problem that existing fluorocarbon powder coatings are insufficiently weather-resistant and easily yellow, powderize and crack in environments such as ultraviolet rays, humidity and heat, and salt spray, resulting in protection failure.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions: A highly weather-resistant fluorocarbon powder coating comprises the following raw materials in parts by weight: Fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer: 400-500 parts by weight; Phosphorus-silicon synergistically modified nanoclay: 100-150 parts by weight; HDI trimer: 80-100 parts by weight; Rutile titanium dioxide: 150-250 parts by weight; Precipitated barium sulfate: 100-200 parts by weight; Leveling agent: 10-20 parts by weight; Light stabilizer: 5-10 parts by weight; Antioxidant 1010: 5-10 parts by weight; The preparation steps of the fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer include: A1, adding polytetrafluoroethylene emulsion into a reactor at 50-52°C, adding 2,2-bis(4-hydroxyphenyl)hexafluoropropane, hexamethylene diisocyanate, and dibutyltin dilaurate in sequence, introducing nitrogen protection and mechanically stirring the reaction, adding potassium persulfate to initiate free radical polymerization, and heating to 70-72°C for reaction; A2, washing the reaction product with deionized water, centrifuging it, and vacuum drying it.

[0007] According to a preferred embodiment of the present invention, the polytetrafluoroethylene emulsion is purchased from Shanghai San Ai Fu New Materials Co., Ltd., and the model is F46 emulsion.

[0008] According to a preferred embodiment of the present invention, the reactor is purchased from Wuxi Chemical Equipment Co., Ltd., model WZ-500.

[0009] According to a preferred embodiment of the present invention, the 2,2-bis(4-hydroxyphenyl)hexafluoropropane is purchased from Zhejiang Xin'an Chemical Group Co., Ltd., model 2260.

[0010] According to a preferred embodiment of the present invention, the hexamethylene diisocyanate is purchased from Wanhua Chemical Group Co., Ltd., model HDI-100.

[0011] According to a preferred embodiment of the present invention, the dibutyltin dilaurate is purchased from Jiangsu Feixiang Chemical Co., Ltd., model T-12.

[0012] According to a preferred embodiment of the present invention, the nitrogen is purchased from Hangzhou Oxygen Generator Group Co., Ltd., model N2-99.999%.

[0013] According to a preferred embodiment of the present invention, the potassium persulfate is purchased from Hebei Jiheng Chemical Co., Ltd., model KPS-98.

[0014] According to a preferred embodiment of the present invention, the HDI trimer is purchased from Wanhua Chemical Group Co., Ltd., model HDI trimer-500.

[0015] According to a preferred embodiment of the present invention, the rutile titanium dioxide is purchased from Longbai Group Co., Ltd., model R-248.

[0016] According to a preferred embodiment of the present invention, the precipitated barium sulfate is purchased from Nanfeng Chemical Group Co., Ltd., model BaSO4-200.

[0017] According to a preferred embodiment of the present invention, the leveling agent is purchased from Shanghai Xinanna Electronic Technology Co., Ltd., model BYK-333 (domestic version).

[0018] According to a preferred embodiment of the present invention, the light stabilizer is purchased from Beijing Additives Research Institute, model number Tinuvin 770 (domestic).

[0019] According to a preferred embodiment of the present invention, the antioxidant 1010 is purchased from Kingfa Science & Technology Co., Ltd., model number Irganox 1010 (domestic).

[0020] In this invention, the fluorinated polyurethane grafted polytetrafluoroethylene copolymer is prepared using a process combining free radical graft copolymerization and precipitation drying. First, a polytetrafluoroethylene (PTFE) emulsion, serving as a matrix, is mixed with a fluorinated diol, isocyanate, and catalyst under nitrogen protection. Mechanical stirring promotes uniform dispersion of the components. The fluorinated diol provides fluorocarbon segments, while the isocyanate, acting as a reactive monomer, decomposes under the action of the catalyst to produce free radicals that attack the double bonds of the fluorinated diol and isocyanate, forming free radical active centers. These active centers undergo hydrogen transfer reactions with weak C-H bonds on the PTFE chain (activated by the electron-withdrawing effect of fluorine atoms), forming grafting sites. Subsequently, the fluorinated diol and isocyanate undergo a stepwise addition reaction to form polyurethane segments, which are covalently bonded to the PTFE backbone, forming a fluorocarbon-polyurethane dual-chain structure. After heating to 70-72°C, free radical polymerization proceeds, gradually forming long-chain polymers, ultimately yielding the fluorinated polyurethane grafted polytetrafluoroethylene copolymer. The reaction product undergoes multiple deionized water washes to remove unreacted monomers, initiators, and oligomers, followed by high-speed centrifugation to separate solid and liquid impurities, and vacuum drying to remove moisture, ultimately yielding a dry modified nanoclay. During this process, the fluorocarbon segments impart chemical resistance, while the polyurethane soft segments provide flexibility. These two synergistically enhance the coating's resistance to light oxidation and impact.

[0021] According to a preferred embodiment of the present invention, in step A1, 2,2-bis(4-hydroxyphenyl)hexafluoropropane accounts for 14-16% of the mass of polytetrafluoroethylene; hexamethylene diisocyanate accounts for 10-12% of the mass of polytetrafluoroethylene; dibutyltin dilaurate accounts for 0.1-0.12% of the mass of PTFE; the speed of mechanical stirring is 1000-1200 rpm; the reaction time is 30-40 min; potassium persulfate accounts for 0.4-0.6% of the mass of PTFE; and the temperature is raised to 70-72°C and the reaction time is 2-4 h.

[0022] According to a preferred embodiment of the present invention, in step A2, the number of deionized water washings is 3-4 times; the centrifugal speed is 8000-8200 rpm, and the centrifugal time is 10-20 min; the vacuum drying temperature is 60-62° C., and the vacuum drying time is 12-24 h.

[0023] According to a preferred embodiment of the present invention, the preparation method of the phosphorus-silicon synergistically modified nanoclay includes: B1, dispersing nano-montmorillonite in deionized water, adding hexadecyltrimethylammonium bromide and triethyl phosphate, reacting at 80-82°C under ultrasonic dispersion, centrifuging and washing with ethanol to obtain phosphorus-intercalated montmorillonite; B2, dispersing the phosphorus-intercalated montmorillonite in anhydrous ethanol, adding γ-glycidyloxypropyltrimethoxysilane, reacting at 75-78°C under reflux conditions, filtering and vacuum drying.

[0024] According to a preferred embodiment of the present invention, the nano-montmorillonite is purchased from Zhejiang Fenghong New Materials Co., Ltd., model FM-30.

[0025] According to a preferred embodiment of the present invention, the deionized water is purchased from Shanghai Pure Water Equipment Engineering Co., Ltd., model RO-1000 (reverse osmosis pure water).

[0026] According to a preferred embodiment of the present invention, the hexadecyltrimethylammonium bromide is purchased from Jiangsu Haian Petrochemical Co., Ltd., model CTAB-99%.

[0027] According to a preferred embodiment of the present invention, the triethyl phosphate was purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd., model TEP-98.

[0028] According to a preferred embodiment of the present invention, the anhydrous ethanol was purchased from Jiangsu Jiuzhou Chemical Co., Ltd., model ET-99.5%.

[0029] According to a preferred embodiment of the present invention, the γ-glycidyloxypropyltrimethoxysilane is purchased from Hubei Xingfa Chemical Group Co., Ltd., model KH560-98.

[0030] In the present invention, the preparation method of phosphorus-silicon synergistically modified nanoclay is achieved through dual modification via interlayer intercalation and silane coupling. After the nano-montmorillonite is dispersed in deionized water, an intercalation agent and a phosphorus source are added. Ultrasonic dispersion is used to disrupt the electrostatic attraction between the montmorillonite layers, allowing the intercalation agent to intercalate between the layers to form an organic intercalation complex. The phosphorus source hydrolyzes to generate phosphates, which react with hydroxyl groups on the surface of the montmorillonite layers to form a stable phosphorus intercalation structure and increase the interlayer spacing. Ultrasonic dispersion promotes the full interaction of the intercalation agent with the montmorillonite, and the reaction time ensures complete intercalation. Unreacted intercalation agent and impurities are separated by centrifugation, and residual organic solvent is removed by ethanol washing. Subsequently, the phosphorus intercalated montmorillonite is dispersed in anhydrous ethanol, and a silane coupling agent is added. Under reflux conditions, the epoxy groups of the silane coupling agent undergo a hydrolysis-condensation reaction with the hydroxyl groups on the surface of the phosphorus intercalated montmorillonite, forming silicon-oxygen bonds and simultaneously releasing small molecules. The other end of the silane coupling agent reacts with the epoxy groups of the resin to form a chemical bond. Reflux promotes the reaction, the solid product is separated by filtration, and the solvent is removed by vacuum drying, ultimately yielding a phosphorus-silicon synergistically modified nanoclay. During this process, phosphorus intercalation increases the interlayer spacing of the montmorillonite, providing more reactive sites for silane coupling. The silane coupling agent acts as a "bridge," reducing the montmorillonite's surface energy from highly hydrophilic to superhydrophobic, while also strengthening the interfacial bonding with the resin and effectively hindering water vapor penetration.

[0031] According to a preferred embodiment of the present invention, in step B1, hexadecyltrimethylammonium bromide accounts for 2-4% of the mass of the nano-montmorillonite; triethyl phosphate accounts for 4-6% of the mass of the nano-montmorillonite; the frequency of ultrasonic dispersion is 40-60kHz; the reaction time at 80-82°C is 4-6h; the centrifugal speed is 6000-8000rpm, and the time is 10-12min.

[0032] According to a preferred embodiment of the present invention, in step B2, γ-glycidyloxypropyltrimethoxysilane is 3-5% of the mass of the nano-montmorillonite; the reaction is carried out at 75-78°C for 5-7h; and the vacuum drying temperature is 40-60°C for 24-30h.

[0033] The present invention also provides a method for preparing the highly weather-resistant fluorocarbon powder coating, comprising the following steps: S1. Premix fluorinated polyurethane grafted polytetrafluoroethylene copolymer, phosphorus-silicon synergistically modified nanoclay, HDI trimer, rutile titanium dioxide, precipitated barium sulfate, leveling agent, light stabilizer, and antioxidant 1010 in a high-speed mixer; S2. Add the mixture into a twin-screw extruder, wherein the temperature of zone 1, zone 2 and zone 3 is 84-86°C, 114-116°C and 134-136°C, melt extrude, crush the mixture into tablets and grind it into particles using a jet mill.

[0034] In this invention, the coating preparation is divided into two steps: high-speed premixing and twin-screw extrusion. During the high-speed premixing stage, a high-speed mixer uses mechanical shear to initially mix the components: a fluorinated polyurethane grafted polytetrafluoroethylene copolymer (continuous phase), a phosphorus-silicon modified nanoclay (dispersed phase), an HDI trimer (curing agent), and rutile titanium dioxide (pigment). The epoxy groups of the fluorinated polyurethane grafted polytetrafluoroethylene copolymer and the isocyanate groups of the HDI trimer slowly pre-react at room temperature to form a partial prepolymer, laying the foundation for the subsequent extrusion reaction. During the twin-screw extrusion stage, after the materials enter the extruder, heating (providing the necessary reaction energy) and shearing (promoting component dispersion) combine to completely melt and blend the materials. Unreacted epoxy groups further crosslink with isocyanate groups to form a three-dimensional network structure. The silane coupling agent in the phosphorus-silicon modified nanoclay chemically bonds with the epoxy groups of the resin, enhancing interfacial bonding. The rutile titanium dioxide is evenly dispersed in the resin matrix, forming a physical barrier to UV rays. The screw speed controls the material's residence time, ensuring a full reaction. Tableting crushes the material to reduce particle size, and a jet mill pulverizes the material to a suitable particle size for electrostatic spraying. During this process, cross-linking reactions and interfacial bonding synergistically enhance the coating's cohesion and weather resistance, ultimately producing a highly weather-resistant fluorocarbon powder coating.

[0035] According to a preferred embodiment of the present invention, in step S1, the rotation speed of the high-speed mixer is 1200-1400 rpm; and the premixing time is 8-10 min.

[0036] According to a preferred embodiment of the present invention, in step S2, the screw speed of the twin-screw extruder is 400-600 rpm; the screen of the air flow mill is 80-100 mesh; and the particle size of the particles is 25-45 μm.

[0037] The present invention also provides a use of the weather-resistant fluorocarbon powder coating or the weather-resistant fluorocarbon powder coating prepared by the preparation method on the surface of a metal substrate.

[0038] The beneficial effects of the present invention are: The high-weatherability fluorocarbon powder coating of the present invention shows significant effects in improving weather resistance through a dual-functional modification strategy. Traditional fluorocarbon coatings are prone to photooxidative degradation when exposed to ultraviolet light for a long time due to the low cross-linking density of the resin, which leads to the breakage of the molecular chain to generate aging products such as carbonyl groups and peroxide groups. The coating gradually loses its density and strength, and yellowing and powdering occur. The present invention adopts a fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer as the core resin, and its fluorocarbon segment retains the original chemical resistance and weather resistance. At the same time, the introduced polyurethane soft segment and the multifunctional isocyanate curing agent form a three-dimensional network structure with a high cross-linking density, which effectively inhibits the photooxidation reaction caused by ultraviolet rays and reduces the generation of aging products, thereby significantly reducing the risk of yellowing and powdering of the coating and extending the service life under long-term exposure.

[0039] The addition of phosphorus-silicon synergistically modified nanoclay further enhances the interface performance and barrier capacity of the coating. Traditional pigments and fillers have weak interfacial bonding with resins, and differences in thermal expansion coefficients easily lead to microcracks inside, forming water vapor penetration channels and accelerating the invasion of corrosive media. The present invention uses dual modification of phosphorus intercalation and silane coupling agent to form a composite modified layer containing phosphorus and silicon on the surface of the nanoclay, constructing a uniform physical barrier film on the surface of the coating to hinder the penetration of corrosive media such as water vapor and chloride ions; at the same time, the silane coupling agent enhances the interfacial chemical bonding between the nanoclay and the resin, reduces the interfacial energy, reduces the width and number of microcracks caused by thermal stress, and significantly improves the overall density of the coating, effectively resisting the invasion of external corrosive media.

[0040] Combining the aforementioned modification strategies, the coating of this invention exhibits exceptional protective properties in practical applications. In coastal high-salt fog environments, water vapor adsorption on the coating surface is significantly reduced, resulting in no rust during long-term salt fog testing. Under strong ultraviolet radiation on the plateau, the coating maintains high gloss retention, with no noticeable powdering or cracking. In industrial acid rain environments, the surface barrier film effectively blocks acidic penetration, significantly slowing the corrosion rate of the substrate. These comprehensive improvements enable the coating to meet the long-term protection needs of metal workpieces in extreme environments, providing a strong guarantee for the reliable operation of outdoor facilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart for the preparation of highly weather-resistant fluorocarbon powder coatings. DETAILED DESCRIPTION

[0042] The present application is described in further detail below in conjunction with the accompanying drawings. It is necessary to point out that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technicians in this field can make some non-essential improvements and adjustments to the present application based on the above application content. Example Example

[0043] Preparation of a fluorinated polyurethane-grafted polytetrafluoroethylene copolymer: 1000 g of a 60% solids polytetrafluoroethylene emulsion was added to a 51°C reactor. Then, 150 g of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 110 g of hexamethylene diisocyanate, and 1.1 g of dibutyltin dilaurate were added sequentially. Nitrogen was introduced into the reactor to a pressure of 0.3 MPa. Mechanical stirring was initiated at 1100 rpm and the reaction was continued for 35 minutes. Subsequently, 5 g of potassium persulfate was added to initiate free radical polymerization. The reactor temperature was raised to 71°C and maintained constant for 3 hours. After completion of the reaction, the product was transferred to a separatory funnel and washed three times with deionized water (5 times the mass of the product each time). After standing for demixing, the supernatant was discarded. The lower precipitate was transferred to a centrifuge and centrifuged at 8100 rpm for 15 minutes to collect the solid precipitate. The solid precipitate was placed in a vacuum drying oven, set at a temperature of 61° C. and a vacuum degree of -0.09 MPa, and taken out after drying for 18 hours to obtain a fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer.

[0044] Preparation of phosphorus-silicon synergistically modified nanoclay: 500 g of nano-montmorillonite was dispersed in 5000 mL of deionized water and stirred at 300 rpm for 10 minutes using a magnetic stirrer to form a uniform dispersion. 15 g of hexadecyltrimethylammonium bromide and 25 g of triethyl phosphate were added to the dispersion. An ultrasonic dispersion device (frequency 50 kHz) was used, and the dispersion was heated to 81°C and maintained constant for 5 hours. After the reaction was complete, the dispersion was transferred to a centrifuge and centrifuged at 6000 rpm for 11 minutes. The lower precipitate was collected. The precipitate was washed twice with deionized water and then three times with anhydrous ethanol (each wash volume was 3 times the mass of the precipitate). The solid was filtered and collected. The solid was transferred to a beaker, and anhydrous ethanol (10 times the mass of the solid) was added. Then, 20 g of γ-glycidoxypropyltrimethoxysilane (4% of the mass of the nano-montmorillonite) was added. The mixture was heated to 76°C and refluxed for 6 hours. After the reaction, the mixture was cooled to room temperature, the solid was collected by filtration, and the solid was placed in a vacuum drying oven with a set temperature of 50° C. and a vacuum degree of -0.08 MPa. The solid was taken out after drying for 27 hours to obtain phosphorus-silicon synergistically modified nanoclay.

[0045] Preparation of a highly weather-resistant fluorocarbon powder coating: Fluoropolyurethane-grafted polytetrafluoroethylene copolymer (450g), phosphorus-silicon synergistically modified nanoclay (120g), HDI trimer (90g), rutile titanium dioxide (200g), precipitated barium sulfate (150g), leveling agent (15g), light stabilizer (8g), and antioxidant 1010 (7g) were sequentially added to a high-speed mixer at 1300rpm. Premixing was performed for 9 minutes to ensure thorough mixing. The mixed materials were then fed into a twin-screw extruder with the zone temperatures set at 85°C for zone 1, 115°C for zone 2, and 135°C for zone 3. The screw speed was set at 400rpm. The materials were melt-extruded in the extruder and then pressed into sheets approximately 2mm thick using a tablet press. After the flakes are cooled to room temperature, they are crushed into small pieces with a particle size of about 5 mm using a crusher, and then further crushed into particles with a particle size of about 35 μm using a jet mill (sieve 90 mesh), thereby obtaining a highly weather-resistant fluorocarbon powder coating. Example

[0046] The specific implementation method is the same as Example 1, except that the fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer is prepared as follows: 800 g of polytetrafluoroethylene emulsion, 120 g of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 96 g of hexamethylene diisocyanate, 0.96 g of dibutyltin dilaurate, mechanical stirring at 1000 rpm for 30 minutes, 4.8 g of potassium persulfate, reaction at 70°C for 2 hours, washing with deionized water three times, centrifuging at 8000 rpm for 10 minutes, and vacuum drying at 60°C for 12 hours. Preparation of phosphorus-silicon synergistically modified nanoclay: 400 g of nano-montmorillonite, 12 g of hexadecyltrimethylammonium bromide, and 24 g of triethyl phosphate were ultrasonically dispersed (40 kHz) at 80 °C for 4 h, centrifuged at 7000 rpm for 10 min, and washed with ethanol; phosphorus-intercalated montmorillonite was dispersed in anhydrous ethanol, 16 g of γ-glycidyloxypropyltrimethoxysilane was added, refluxed at 75 °C for 5 h, filtered, and vacuum dried at 40 °C for 24 h. Coating preparation: 420 g of fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer, 140 g of phosphorus-silicon synergistically modified nanoclay, 85 g of HDI trimer, 220 g of rutile titanium dioxide, 180 g of precipitated barium sulfate, 12 g of leveling agent, 6 g of light stabilizer, and 8 g of antioxidant 1010. Premix the mixture in a high-speed mixer (1400 rpm) for 8 min, melt-extrude the mixture in a twin-screw extruder (zone 1 84°C, zone 2 114°C, zone 3 134°C), crush the mixture into 25 μm particles using an 80-mesh airflow mill. Example

[0047] The specific embodiment is the same as Example 1, except that the fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer is prepared as follows: 1200 g of polytetrafluoroethylene emulsion, 180 g of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 132 g of hexamethylene diisocyanate, 1.32 g of dibutyl tin dilaurate, mechanical stirring at 1200 rpm for 40 min, 6 g of potassium persulfate, reaction at 72°C for 4 h, washing with deionized water for 3 times, centrifugation at 8200 rpm for 20 min, and vacuum drying at 62°C for 24 h. The phosphorus-silicon synergistically modified nanoclay is prepared as follows: 600 g of nanometer montmorillonite, 24 g of cetyltrimethylammonium bromide, 36 g of triethyl phosphate, ultrasonic dispersion (60 kHz) at 82°C for 6 h, centrifugation at 8000 rpm for 12 min, and washing with ethanol; the phosphorus intercalated montmorillonite is dispersed in anhydrous ethanol, 24 g of γ-glycidyl ether propyltrimethoxysilane is added, and reflux reaction is carried out at 78°C for 7 h, followed by filtration and vacuum drying at 60°C for 30 h. The coating is prepared as follows: 480 g of fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer, 110 g of phosphorus-silicon synergistically modified nanoclay, 95 g of HDI trimer, 180 g of rutile titanium dioxide, 120 g of precipitated barium sulfate, 18 g of leveling agent, 9 g of light stabilizer, and 6 g of antioxidant 1010, pre-mixed by a high-speed mixer (1200 rpm) for 10 min, melt extruded by a twin-screw extruder (zone 1: 86°C, zone 2: 116°C, zone 3: 136°C), and crushed by a 100-mesh air flow crusher to 45 μm particles. Example

[0048] The specific implementation method is the same as Example 1, except that the fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer is prepared as follows: 1000 g of polytetrafluoroethylene emulsion, 150 g of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 110 g of hexamethylene diisocyanate, 1.1 g of dibutyltin dilaurate, mechanical stirring at 1100 rpm for 35 min, 5 g of potassium persulfate, reaction at 71°C for 3 h, washing with deionized water three times, centrifugation at 8100 rpm for 15 min, and vacuum drying at 61°C for 18 h. Preparation of phosphorus-silicon synergistically modified nanoclay: 500 g of nano-montmorillonite, 15 g of hexadecyltrimethylammonium bromide, and 25 g of triethyl phosphate were ultrasonically dispersed (50 kHz) at 81 °C for 5 h, centrifuged at 7000 rpm for 11 min, and washed with ethanol; phosphorus-intercalated montmorillonite was dispersed in anhydrous ethanol, 20 g of γ-glycidyloxypropyltrimethoxysilane was added, refluxed at 76 °C for 6 h, filtered, and vacuum dried at 50 °C for 27 h. Coating preparation: 400 g of fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer, 150 g of phosphorus-silicon synergistically modified nanoclay, 100 g of HDI trimer, 250 g of rutile titanium dioxide, 100 g of precipitated barium sulfate, 20 g of leveling agent, 10 g of light stabilizer, and 5 g of antioxidant 1010. The mixture was premixed in a high-speed mixer (1300 rpm) for 9 min, melt-extruded in a twin-screw extruder (zone 1 85 ° C, zone 2 115 ° C, zone 3 135 ° C), crushed into 35 μm particles using a 90-mesh airflow mill.

[0049] Comparative Example 1 The specific implementation method is the same as that of Example 1, except that the fluorinated polyurethane grafted polytetrafluoroethylene copolymer is prepared as follows: 1000g of polytetrafluoroethylene emulsion, 150g of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 110g of hexamethylene diisocyanate, and 1.1g of dibutyltin dilaurate are mechanically stirred at 1100rpm for 35 minutes, and 5g of potassium persulfate is added. The reaction is carried out at 71°C for 3 hours, followed by washing with deionized water three times, centrifugation at 8100rpm for 15 minutes, and vacuum drying at 61°C for 18 hours (without phosphorus-silicon synergistic modification). The phosphorus-silicon synergistically modified nanoclay is replaced with ordinary nano-montmorillonite (unmodified), using 120g of the mixture. Coating preparation: 450 g of fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer, 120 g of ordinary nano-montmorillonite, 90 g of HDI trimer, 200 g of rutile titanium dioxide, 150 g of precipitated barium sulfate, 15 g of leveling agent, 8 g of light stabilizer, and 7 g of antioxidant 1010. The mixture was premixed in a high-speed mixer (1300 rpm) for 9 min, melt-extruded in a twin-screw extruder (zone 1 85°C, zone 2 115°C, zone 3 135°C), crushed into tablets, and then pulverized into 35 μm particles using a 90-mesh airflow mill.

[0050] Comparative Example 2 The specific implementation method is the same as that of Example 1, except that the fluorinated polyurethane grafted polytetrafluoroethylene copolymer is replaced with a conventional polytetrafluoroethylene copolymer (ungrafted), using 450g. Preparation of phosphorus-silicon synergistically modified nanoclay: 500g of nano-montmorillonite, 15g of hexadecyltrimethylammonium bromide, and 25g of triethyl phosphate were ultrasonically dispersed (50kHz) at 81°C for 5h, centrifuged at 7000rpm for 11min, and washed with ethanol. The phosphorus-intercalated montmorillonite was dispersed in anhydrous ethanol, 20g of γ-glycidyloxypropyltrimethoxysilane was added, and the mixture was refluxed at 76°C for 6h. After filtration, it was vacuum-dried at 50°C for 27h (the modification step was retained). Coating preparation: 450 g of ordinary polytetrafluoroethylene copolymer, 120 g of phosphorus-silicon synergistically modified nanoclay, 90 g of HDI trimer, 200 g of rutile titanium dioxide, 150 g of precipitated barium sulfate, 15 g of leveling agent, 8 g of light stabilizer, and 7 g of antioxidant 1010. Premix the mixture in a high-speed mixer (1300 rpm) for 9 min, melt-extrude the mixture in a twin-screw extruder (zone 1 85°C, zone 2 115°C, zone 3 135°C), crush the mixture into 35 μm particles using a 90-mesh airflow mill.

[0051] Comparative Example 3 The specific implementation method is the same as that of Example 1, except that the fluorinated polyurethane grafted polytetrafluoroethylene copolymer is prepared by mixing 1000g of polytetrafluoroethylene emulsion, 150g of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 110g of hexamethylene diisocyanate, and 1.1g of dibutyltin dilaurate. The mixture is mechanically stirred at 1100rpm for 35 minutes. Potassium persulfate (5g) is added and the mixture is reacted at 71°C for 3 hours. The mixture is then washed with deionized water three times, centrifuged at 8100rpm for 15 minutes, and vacuum-dried at 61°C for 18 hours (the modification step is retained). The phosphorus-silicon synergistically modified nanoclay is prepared by mixing 500g of nano-montmorillonite, 15g of hexadecyltrimethylammonium bromide, and 25g of triethyl phosphate. The mixture is ultrasonically dispersed (50kHz) at 81°C for 5 hours, centrifuged at 7000rpm for 11 minutes, and washed with ethanol (no silane coupling agent is added). Coating preparation: 450 g of fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer, 120 g of phosphorus-silicon synergistically modified nanoclay (unsilane modified), 90 g of HDI trimer, 200 g of rutile titanium dioxide, 150 g of precipitated barium sulfate, 15 g of leveling agent, 8 g of light stabilizer, and 7 g of antioxidant 1010. The mixture was premixed in a high-speed mixer (1300 rpm) for 9 min, melt-extruded in a twin-screw extruder (zone 1 85°C, zone 2 115°C, zone 3 135°C), crushed into 35 μm particles using a 90-mesh airflow mill.

[0052] Performance Testing Take the coating samples prepared in each embodiment and comparative example and test them according to the following steps: 1. QUV Weathering Test: A QUV / se UV weathering chamber from Q-Lab (USA) was used, in accordance with GB / T 1865-2009. The test specimens were aluminum plates (150 mm × 70 mm × 0.5 mm) sprayed with the coating to be tested and cured (200°C × 15 min). The film thickness was controlled to 50 ± 5 μm. Aging conditions were: irradiance 0.89 W / (m²·nm) (using a 313 nm UVB lamp at 15 W), chamber temperature 50 ± 3°C, and a 4-hour cooling cycle (the first 2 hours were at 50°C, followed by a 2-hour spraying period of 40°C deionized water at a rate of 1.0 mL / (h·80 cm²)). The performance after aging for 500h, 1000h and 1500h was tested respectively: the gloss retention rate was calculated as (initial gloss / gloss after aging) × 100% (gloss was measured with a glossmeter at a 60° incident angle, and the average value of 5 points was taken); the yellowing index ΔE was calculated using the CIELAB color difference formula (L is lightness, a* and b are chromaticity coordinates, ΔE=√[(ΔL*)²+(Δa*)²+(Δb*)²]).

[0053] 2. Salt Spray Corrosion Test: A Shanghai Salt Spray Test Chamber (Model YWX / Q-150) was used in accordance with GB / T 10125-2021. A 5% NaCl solution (analytical grade NaCl dissolved in deionized water, pH adjusted to 6.5-7.2) was prepared. The chamber temperature was set at 35±2°C, the spray volume was 1.5±0.5 mL / (h·80 cm²), and the spraying was continued for 1000 hours. After the test, the sample surface was rinsed with deionized water to remove salt, dried with cold air, and then observed. The rust area was calculated using image analysis software (ImageJ) as the percentage of the rusted area to the total area. The corrosion grade was determined according to GB / T 6461-2002 (Grade 0: No rust; Grade 1: Slight rust spots; Grade 2: Rust spots connected in a line; Grade 3: Rust coverage <50%; Grade 4: Rust coverage 50%-70%; Grade 5: Rust coverage >70%).

[0054] 3. Coating Adhesion Test: According to GB / T 9286-1998, use a grid marker (Model: Elcometer 107, grid spacing 1mm) to draw a 10×10 grid (total area 100cm²) on the coating surface. Use 3M 600 adhesive tape (width 25mm) to cover the gridded area. Quickly peel off the tape at a 45° angle and observe the degree of peeling: Level 0: No peeling; Level 1: Peeling area ≤5%; Level 2: 5% < Peeling area ≤15%; Level 3: 15% < Peeling area ≤35%; Level 4: 35% < Peeling area ≤65%; Level 5: Peeling area >65%.

[0055] 4. Coating Flexibility Test: Use the QJ-1 Flexibility Tester from Tianjin Material Testing Machine Factory, in accordance with GB / T 1731-1993. A coated specimen (200 mm × 25 mm × 0.5 mm) is mounted on the tester and bent at a constant speed of 1 mm / s until the coating cracks or peels off. The minimum bending radius (R) is recorded. A test of R ≤ 2 mm is considered acceptable (no cracking).

[0056] 5. Impact Resistance Test: Use the HC-500 drop hammer impact tester from Shanghai Hualong Testing Instrument Co., Ltd. in accordance with GB / T 1732-1993. A 500g hammer, dropped from a height of 50cm, is applied vertically to the coating specimen (fixed to the impact table, with the specimen plane perpendicular to the hammer head). Observe the coating surface after impact: No cracks or shedding are considered acceptable; cracks without shedding are considered minor damage; extensive shedding or penetrating cracks are considered unacceptable.

[0057] 6. Chemical Corrosion Resistance Test: Prepare six glass beakers (500 mL) and add 5% hydrochloric acid (analytical-grade HCl dissolved in deionized water) and 5% sodium hydroxide (analytical-grade NaOH dissolved in deionized water) respectively. Maintain the solution temperature at 25±2°C. Completely immerse the coated sample (50 mm × 50 mm × 0.5 mm) in the solution. After immersion for 24 hours, remove the sample and rinse the surface with deionized water. Observe the test results: No swelling (volume change ≤ 5%), no discoloration (difference from the original color ΔE* ≤ 1.0), and no shedding are considered acceptable. Swelling, discoloration, or partial shedding are considered unacceptable.

[0058] 7. Pencil Hardness Test: Use a Japanese Mitsubishi pencil (model: 9H-9B) and perform according to GB / T 6739-2006. Place the coated sample (dimensions 100mm × 100mm × 0.5mm) horizontally. Hold the pencil at a 45° angle to the sample surface and scratch the sample at a constant speed of approximately 0.5mm / s with a pressure of 1kg. Starting from 9H, gradually decrease the hardness (9H → 8H → ... → 9B). Record the hardness of the first pencil that scratches the coating (e.g., 3H indicates no scratch with a 3H pencil, while a 2H pencil will scratch).

[0059] 8. Gloss Test: Use a Micro-Gloss 60° gloss meter from BYK-Gardner, Germany, in accordance with GB / T9754-2007. Five measurement points (spacing ≥ 20 mm) are evenly spaced on the coating surface. Each point is measured three times and the average value is taken. Gloss is expressed in % (ratio of reflected light intensity to that of a standard white plate).

[0060] 9. Test results: Table 1: Test results of various embodiments and comparative examples

[0061] As can be seen from Table 1, Examples 1-3 of the present invention, through the synergistic effect of phosphorus-silicon modified nanoclay and fluorinated polyurethane-grafted polytetrafluoroethylene copolymer, effectively address the problem of existing fluorocarbon powder coatings, which suffer from insufficient weather resistance and are susceptible to yellowing, chalking, and cracking in environments such as ultraviolet light, humidity, and salt spray, leading to protective failure. Specifically, in terms of UV aging, the gloss retention (91%-94%) of Examples 1-3 after 1500 hours of QUV aging was significantly higher than that of the control (70%-75%), and the yellowing index (1.9-2.3) was much lower than that of the control (5.2-5.8). This demonstrates that the modified coatings effectively inhibited UV-induced photooxidative degradation, reducing the generation of aging products such as carbonyl and peroxide groups due to molecular chain breakage, thereby delaying the onset of yellowing and chalking. In a hot, humid, and salt-spray environment, the rust area (0.4%-0.8%) of Examples 1-3 after 1000 hours of salt spray exposure was significantly lower than that of the control (12%-15%), and their adhesion (grade 0) was superior to that of the control (grade 1). This indicates that the phosphorus-silicon synergistic modified layer forms a uniform physical barrier on the coating surface, hindering the penetration of corrosive media such as water vapor and chloride ions, reducing the risk of microcrack propagation caused by water vapor penetration. It also enhances interfacial bonding and prevents cracking caused by thermal or mechanical stress. Furthermore, Examples 1-3 exhibited superior flexibility (minimum bending radius 1mm), impact resistance (no cracking), and chemical corrosion resistance (no swelling or discoloration in acid and alkali environments) to the control. This further demonstrates that the modification process enhances the coating's comprehensive mechanical properties and environmental adaptability, enabling it to maintain its density and protective properties over the long term in extreme environments, effectively addressing the issue of protective failure caused by traditional coatings.

[0062] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A highly weather-resistant fluorocarbon powder coating, characterized in that: The composition comprises the following raw materials in parts by weight: Fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer: 400-500 parts by weight; Phosphorus-silicon synergistically modified nanoclay: 100-150 parts by weight; HDI trimer: 80-100 parts by weight; Rutile titanium dioxide: 150-250 parts by weight; Precipitated barium sulfate: 100-200 parts by weight; Leveling agent: 10-20 parts by weight; Light stabilizer: 5-10 parts by weight; Antioxidant 1010: 5-10 parts by weight; The preparation steps of the fluorine-containing polyurethane grafted polytetrafluoroethylene copolymer include: A1, adding polytetrafluoroethylene emulsion into a reactor at 50-52°C, adding 2,2-bis(4-hydroxyphenyl)hexafluoropropane, hexamethylene diisocyanate, and dibutyltin dilaurate in sequence, introducing nitrogen protection and mechanically stirring the reaction, adding potassium persulfate to initiate free radical polymerization, and heating to 70-72°C for reaction; A2, washing the reaction product with deionized water, centrifuging it, and vacuum drying it.

2. The highly weather-resistant fluorocarbon powder coating according to claim 1, characterized in that: In step A1, 2,2-bis(4-hydroxyphenyl)hexafluoropropane accounts for 14-16% of the mass of polytetrafluoroethylene; hexamethylene diisocyanate accounts for 10-12% of the mass of polytetrafluoroethylene; dibutyltin dilaurate accounts for 0.1-0.12% of the mass of PTFE; the mechanical stirring speed is 1000-1200 rpm; the reaction time is 30-40 minutes; potassium persulfate accounts for 0.4-0.6% of the mass of PTFE; the temperature is raised to 70-72°C and the reaction time is 2-4 hours.

3. The highly weather-resistant fluorocarbon powder coating according to claim 1, characterized in that: In step A2, the number of deionized water washings is 3-4 times; the centrifugal speed is 8000-8200 rpm, and the centrifugal time is 10-20 min; the vacuum drying temperature is 60-62° C., and the vacuum drying time is 12-24 h.

4. The highly weather-resistant fluorocarbon powder coating according to claim 1, characterized in that: The preparation method of the phosphorus-silicon synergistically modified nanoclay includes: B1, dispersing nano-montmorillonite in deionized water, adding hexadecyltrimethylammonium bromide and triethyl phosphate, reacting at 80-82°C under ultrasonic dispersion, centrifuging and washing with ethanol to obtain phosphorus-intercalated montmorillonite; B2, dispersing the phosphorus-intercalated montmorillonite in anhydrous ethanol, adding γ-glycidyloxypropyltrimethoxysilane, reacting at 75-78°C under reflux conditions, filtering and vacuum drying.

5. The highly weather-resistant fluorocarbon powder coating according to claim 4, characterized in that: In step B1, hexadecyltrimethylammonium bromide accounts for 2-4% of the mass of the nano-montmorillonite; triethyl phosphate accounts for 4-6% of the mass of the nano-montmorillonite; the frequency of ultrasonic dispersion is 40-60kHz; the reaction time is 4-6h at 80-82°C; the centrifugal speed is 6000-8000rpm, and the time is 10-12min.

6. The highly weather-resistant fluorocarbon powder coating according to claim 4, characterized in that: In step B2, γ-glycidyloxypropyltrimethoxysilane is 3-5% of the mass of the nano-montmorillonite; the reaction is carried out at 75-78°C for 5-7 hours; and the vacuum drying temperature is 40-60°C for 24-30 hours.

7. A method for preparing a highly weather-resistant fluorocarbon powder coating according to any one of claims 1 to 6, characterized in that the steps include: S1. Premix fluorinated polyurethane grafted polytetrafluoroethylene copolymer, phosphorus-silicon synergistically modified nanoclay, HDI trimer, rutile titanium dioxide, precipitated barium sulfate, leveling agent, light stabilizer, and antioxidant 1010 in a high-speed mixer; S2. Add the mixture into a twin-screw extruder, wherein the temperature of zone 1, zone 2 and zone 3 is 84-86°C, 114-116°C and 134-136°C, melt extrude, crush the mixture into tablets and grind it into particles using a jet mill.

8. The preparation method according to claim 7, characterized in that In step S1, the rotation speed of the high-speed mixer is 1200-1400 rpm; and the premixing time is 8-10 minutes.

9. The preparation method according to claim 7, characterized in that In step S2, the screw speed of the twin-screw extruder is 400-600 rpm; the screen of the air flow mill is 80-100 mesh; and the particle size of the particles is 25-45 μm.

10. Use of the weather-resistant fluorocarbon powder coating according to any one of claims 1 to 6 or the weather-resistant fluorocarbon powder coating prepared by the preparation method according to any one of claims 7 to 9, characterized in that: Application of the weather-resistant fluorocarbon powder coating on the surface of a metal substrate.

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