A weatherable black polyester powder coating and a method for its preparation

Abstract

The present application relates to the technical field of powder coating, in particular to a weather-resistant black polyester powder coating and a preparation method thereof. The present application overcomes the problems of light-heat synergistic degradation of the coating and the difficulty in achieving leveling and toughness. The coating composition of the present application comprises a carboxyl polyester resin, a curing agent, modified carbon black, fluorosilicon modified hyperbranched polyester, modified barium sulfate and an additive; by constructing a thermal barrier and free radical capture layer on the surface of the carbon black, and cooperating with the rare earth oxide in the matrix, an "interface-matrix" full-space synergistic anti-aging system is established, solving the problem of light-heat synergistic degradation of black coating; at the same time, by using the wettability of hyperbranched resin and the stepwise pre-dispersion process, the agglomeration and leveling problem of high pigment carbon black are solved.

Description

Technical Field

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

[0002] Polyester powder coatings are widely used in outdoor architectural aluminum profiles, outdoor furniture, and transportation facilities due to their excellent mechanical properties and decorative effects. However, black powder coatings face two significant technical challenges under long-term outdoor exposure:

[0003] First, there is the issue of photothermal synergistic degradation. Although black pigments have a strong ability to absorb ultraviolet light, their high absorption rate in the visible and infrared bands will cause the surface temperature of the coating to rise sharply. This "hot spot effect" will accelerate the thermo-oxidative aging of the polyester resin matrix. At the same time, the bonding force between carbon black particles and the resin matrix interface will gradually fail during the thermal expansion and contraction cycle, resulting in premature loss of gloss, chalking, and discoloration (whitening) of the coating.

[0004] Secondly, there is a contradiction between leveling and toughness under high pigment filling. In order to obtain high blackness and high hiding power, it is often necessary to increase the amount of carbon black or use high-structure carbon black, which will significantly increase the viscosity of the molten system, resulting in poor leveling (orange peel appearance); and because carbon black particles have a large specific surface area, they are very easy to agglomerate, and the agglomerates become stress concentration points, which greatly reduces the impact resistance and flexibility of the coating.

[0005] Existing solutions typically involve simply adding UV absorbers or antioxidants. However, these small-molecule additives are prone to volatilization during high-temperature curing or migration and loss during later use, failing to fundamentally solve the photothermal aging and dispersion problems at the carbon black-resin interface. Therefore, developing a black powder coating that can address pigment-resin interface stability while also ensuring leveling and weather resistance is of great significance.

[0006] To address this, a weather-resistant black polyester powder coating and its preparation method are proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a weather-resistant black polyester powder coating and its preparation method.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] Unless otherwise specified, all parts in this invention are by weight.

[0010] This invention provides a method for preparing a weather-resistant black polyester powder coating. The method is as follows: 3-6 parts of modified carbon black, 2-4 parts of fluorosilicone-modified hyperbranched polyester, and 10% of the total weight of matrix resin are added to a high-speed mixer and mixed at 1500 rpm for 8-15 minutes, controlling the material temperature at 50-60℃. Frictional heat is used to initially soften the hyperbranched resin and wet the carbon black, resulting in a mixture. The mixture is then subjected to a first extrusion granulation using a twin-screw extruder, with the extruder zone one temperature at 90℃ and zone two at 110℃, to obtain a black masterbatch. The black masterbatch is then mixed with the remaining 90% of the matrix resin. 3 parts of curing agent β-hydroxyalkylamide, 20-25 parts of modified filler and additives are added to a mixer and mixed at 1000 rpm for 3 minutes. Then, the mixture is extruded and granulated a second time through a twin-screw extruder. The temperature of the first zone is 90℃, the temperature of the second zone is 110℃, and the temperature of the third zone is 130℃ (reaction control zone to avoid local overheating). The screw speed is 350 rpm (to ensure shear force but not too high) to obtain the extruded material. After the extruded material is pressed, water-cooled and crushed, it enters an air classifier mill. The main mill speed is 7000 rpm and the classifier speed is 3500 rpm. After passing through a 180-mesh sieve, a black polyester powder coating is obtained.

[0011] The modified filler was obtained by composite modification of barium sulfate with nano-cerium oxide and titanate.

[0012] Preferred method for preparing modified carbon black is as follows: Polydopamine-coated carbon black is dispersed in ethanol, 3 parts of 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate are added, and triethylamine catalyst is added to adjust the system to weak alkalinity. The reaction is carried out at 60°C and 600 rpm for 8-10 h. After filtration, the mixture is washed three times with anhydrous ethanol, dried under vacuum at 80°C for 12 h, and then ground and sieved to obtain modified carbon black.

[0013] Preferred method for preparing polydopamine-coated carbon black is as follows: 50 parts of high-pigment carbon black (Orion Carbon Black FW200) are dispersed in 500 parts of an ethanol-water solution (ethanol:water volume ratio of 4:1), ultrasonically dispersed for 30 min, ammonia water is added to adjust the pH to 9, and 15 parts of tetraethyl orthosilicate are added dropwise at 800 rpm and 40℃. After reacting for 4 h, the mixture is centrifuged, washed with water, and dried to obtain silica-coated carbon black; the silica-coated carbon black is dispersed in 500 parts of Tris-HCl buffer (pH=8.5), and 2-3 parts of dopamine hydrochloride are added. The mixture is reacted at room temperature and a stirring speed of 600 rpm for 18-22 h. Dopamine is oxidized and self-polymerized on the surface to form a PDA layer. After centrifugation and washing with water, polydopamine-coated carbon black is obtained.

[0014] The preferred method for preparing fluorosilicone-modified hyperbranched polyester is as follows: In a four-necked flask equipped with a stirrer and a condenser, add 1 part trimethylolpropane and 3 parts succinic anhydride, and react at 135-145℃ under nitrogen protection until the acid value reaches 230 mg KOH / g to obtain a carboxyl-terminated intermediate; cool to 110℃, add 6 parts bisphenol A diglycidyl ether, and add 0.1% tetrabutylammonium bromide as a catalyst, reacting for 3 hours to obtain a terminal epoxy group hyperbranched polyester. The polymer was cooled to 100°C, and 0.5 parts of perfluorohexyl ethanol and 0.5 parts of carboxypropyl-terminated polydimethylsiloxane (CAS: 158465-59-9) were added dropwise. 0.05% of 1,8-diazabicycloundec-7-ene was added as a strong base catalyst. The mixture was stirred at 400 rpm for 4 hours. Fluorosilicone segments were grafted to the hyperbranched ends by the reaction of epoxy groups with hydroxyl / carboxyl groups. The product was cooled and pulverized to obtain fluorosilicone-modified hyperbranched polyester.

[0015] Preferred method for preparing modified filler is as follows: 100 parts of precipitated barium sulfate (CAS: 7727-43-7, particle size 0.5-0.8μm) are dispersed in 800 parts of deionized water and ultrasonically dispersed for 20 min. 2 parts of cerium nitrate hexahydrate are added and stirred to dissolve. 5 parts of urea are added as a precipitant. The temperature is raised to 90-100℃ and the reaction is carried out at a constant temperature of 500 rpm for 4 h. The ammonia gas generated by urea hydrolysis induces the uniform nucleation and deposition of nano-cerium oxide on the surface of barium sulfate. The mixture is filtered, washed with water until neutral, and dried at 105℃ to obtain inorganic modified barium sulfate loaded with nano-cerium oxide. The inorganic modified barium sulfate is added to a high-speed mixer and heated to 80℃. 1.5 parts of titanate coupling agent (model NDZ-201, isopropyltris(dioctyl pyrophosphoryloxy) titanate) are added by spraying. The stirring speed is increased to 2000 rpm and the mixture is mixed and modified for 15 min. After discharge, the mixture is pulverized to obtain the modified filler.

[0016] Preferably, the matrix resin is a weather-resistant carboxylated polyester resin (Zhanxin CRYLCOAT 4659-0); the additives consist of 0.8 parts leveling agent and 0.4 parts benzoin (CAS: 119-53-9).

[0017] Another aspect of the present invention provides a weather-resistant black polyester powder coating, wherein the black polyester powder coating is prepared by any of the above preparation methods; the raw materials for preparing the black polyester powder coating include modified carbon black, fluorosilicone modified hyperbranched polyester, matrix resin, curing agent, modified filler and additives.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. This invention blocks the aging path at its source by constructing a "silica-polydopamine-hindered amine" composite structure on the surface of carbon black. The dense nano-silica layer acts as a thermal barrier, effectively suppressing the "hot spot effect" generated after carbon black particles absorb heat, thus preventing thermo-oxidative degradation of the resin matrix due to localized overheating. Simultaneously, the hindered amine light stabilizer chemically grafted onto the outermost layer can be selectively enriched at the most vulnerable pigment-resin interface, capturing free radicals generated by ultraviolet excitation immediately. This dual mechanism of "physical insulation + chemical quenching" prevents microcracks and peeling at the interface.

[0020] 2. This invention establishes two lines of defense against aging through the synergistic effect of modified carbon black and modified barium sulfate. In addition to the targeted protection of modified carbon black at the pigment interface, this invention creatively utilizes nano-cerium oxide-modified barium sulfate to fill the resin matrix. The nano-cerium oxide, with its redox potential cycling characteristics, can continuously and efficiently quench free radicals that escape to the depths of the matrix. This full-coverage anti-aging system, from the "point" (carbon black interface) to the "surface" (resin matrix), overcomes the defects of single antioxidants, such as easy migration and volatility, ensuring that the coating can maintain high gloss retention and mechanical strength even under long-term outdoor exposure.

[0021] 3. To address the issues of orange peel and agglomeration in high-blackness coatings, this invention employs a unique strategy combining a step-by-step pre-dispersion process with material modification. Utilizing the extremely low melt viscosity of fluorosilicone-modified hyperbranched polyester, polydopamine-modified carbon black is fully wetted during the pre-plasticization stage, breaking up pigment agglomerates. Simultaneously, the long-chain alkyl titanate on the surface of modified barium sulfate acts as an internal lubricant during extrusion, significantly reducing the system's melt viscosity. This combination of "internal and external lubrication" and "pre-dispersion" results in excellent flowability of the coating during the curing and leveling stage, eliminating surface defects and achieving a delicate, uniform, high-blackness appearance.

[0022] 4. This invention changes the traditional model where fillers merely serve as physical fillers, constructing a toughening network through chemical bonding. During curing, the active hydrogen on the modified carbon black surface reacts chemically with the terminal epoxy groups of the fluorosilicone hyperbranched polyester, forming a deformable "flexible buffer layer" around the rigid inorganic particles. When the coating is subjected to external impact or bending, this flexible layer effectively absorbs and dissipates impact energy, hindering crack propagation. This design solves the inherent brittleness of highly filled black powder coatings from a microstructural perspective without reducing the coating's hardness.

[0023] 5. The fluorosilicone-modified hyperbranched polyester introduced in this invention has surface migration characteristics. During the coating curing process, the low surface energy fluorosilicone segments automatically migrate and accumulate on the outermost surface of the coating, forming a dense hydrophobic and oleophobic protective film. This not only gives the coating a self-cleaning effect similar to a lotus leaf, making it difficult for dust and dirt to adhere and easy to be washed away by rainwater, keeping the coating looking new for a long time; at the same time, the hydrophobic surface can also effectively block the penetration of water and corrosive media, delaying the hydrolytic aging process of the base resin, and making it exhibit superior protective performance in humid, rainy and other harsh climatic environments. Attached Figure Description

[0024] Figure 1 The graph shows the test results of gloss retention and impact strength retention rate in Examples 1-4 of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Please see Figure 1 This invention provides a weather-resistant black polyester powder coating and its preparation method, the technical solution of which is as follows:

[0027] Example 1

[0028] 50 parts of high-pigment carbon black were dispersed in 500 parts of an ethanol-water solution (ethanol:water volume ratio of 4:1), and ultrasonically dispersed for 30 min. Ammonia was added to adjust the pH to 9. At 800 rpm and 40℃, 15 parts of tetraethyl orthosilicate were added dropwise. After reacting for 4 h, the mixture was centrifuged, washed with water, and dried to obtain silica-coated carbon black. The silica-coated carbon black was then dispersed in 500 parts of Tris-HCl buffer (pH=8.5), and 2 parts of dopamine hydrochloride were added. The mixture was then reacted at room temperature. The mixture was stirred at 600 rpm for 18 h, centrifuged and washed with water to obtain polydopamine-coated carbon black. The polydopamine-coated carbon black was dispersed in ethanol, and 3 parts of 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate were added. Triethylamine catalyst was added to adjust the system to weak alkalinity. The mixture was stirred at 60℃ and 600 rpm for 8 h. After filtration, the mixture was washed three times with anhydrous ethanol, dried under vacuum at 80℃ for 12 h, ground, and passed through a 300-mesh sieve to obtain modified carbon black.

[0029] In a four-necked flask equipped with a stirrer and a condenser, 1 part of trimethylolpropane and 3 parts of succinic anhydride were added. The mixture was reacted at 135°C under nitrogen protection until the acid value reached 230 mg KOH / g, yielding a carboxyl-terminated intermediate. The temperature was lowered to 110°C, and 6 parts of bisphenol A diglycidyl ether were added. 0.1% of tetrabutylammonium bromide was added as a catalyst, and the reaction was carried out for 3 hours to obtain a terminal epoxy hyperbranched polymer. The temperature was lowered to 100°C, and 0.5 parts of perfluorohexyl ethanol and 0.5 parts of carboxypropyl-terminated polydimethylsiloxane were added dropwise. 0.05% of 1,8-diazabicycloundec-7-ene was added as a strong base catalyst, and the mixture was stirred at 400 rpm for 4 hours. After cooling, the product was pulverized to obtain a fluorosilicone-modified hyperbranched polyester.

[0030] 100 parts of precipitated barium sulfate were dispersed in 800 parts of deionized water and ultrasonically dispersed for 20 min. 2 parts of cerium nitrate hexahydrate were added and stirred to dissolve. 5 parts of urea were added as a precipitant. The temperature was raised to 90℃ and the reaction was carried out at a constant temperature of 500 rpm for 4 h. The mixture was filtered, washed with water until neutral, and dried at 105℃ to obtain inorganic modified barium sulfate loaded with nano-cerium oxide. The inorganic modified barium sulfate was added to a high-speed mixer and heated to 80℃. 1.5 parts of the titanate coupling agent isopropyltris(dioctylpyrophosphoryloxy) titanate were added by spraying. The stirring speed was increased to 2000 rpm and the mixture was mixed and modified for 15 min. After discharge, the mixture was pulverized to obtain the modified filler with a particle size D90 < 10 μm.

[0031] Three parts of modified carbon black, two parts of fluorosilicone-modified hyperbranched polyester, and 10% of the total weight of matrix resin were added to a high-speed mixer and mixed at 1500 rpm for 8 minutes, with the material temperature controlled at 50℃, to obtain a mixture. The mixture was then subjected to a first extrusion granulation using a twin-screw extruder, with the extruder zone one temperature at 90℃ and zone two at 110℃, to obtain a black masterbatch. The black masterbatch, along with the remaining 90% of the matrix resin, three parts of curing agent β-hydroxyalkylamide, 20 parts of modified filler, and additives, were added to a mixer and mixed at 1000 rpm for 3 minutes. After initial processing, the material undergoes a second extrusion granulation using a twin-screw extruder. The temperatures in zones one (90℃), two (110℃), and three (130℃) are set at 350 rpm, yielding the extruded material. This material is then processed through tableting, water cooling, and crushing before entering an air classifier mill. The main mill operates at 7000 rpm, and the classifier operates at 3500 rpm. The material is then passed through an 180-mesh sieve to obtain a black polyester powder coating. The base resin is a weather-resistant carboxylated polyester resin, with a total usage of 60 parts. The additives consist of 0.8 parts of leveling agent BYK-361N and 0.4 parts of benzoin.

[0032] Example 2

[0033] The preparation method and parameters were the same as in Example 1, except that when preparing polydopamine-coated carbon black, 2.2 parts of dopamine hydrochloride were added and the reaction was carried out for 19 hours; when preparing modified carbon black, 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate was added and the reaction was carried out for 8.5 hours; the reaction temperature for preparing the carboxyl-terminated intermediate was 138°C; and the temperature was raised to 95°C for preparing inorganic modified barium sulfate loaded with nano-cerium oxide. The amount of modified carbon black was 4 parts, the amount of fluorosilicone-modified hyperbranched polyester was 2.5 parts, the mixing time of the mixture was 10 minutes, the material temperature was controlled at 55°C, and the amount of modified filler was 22 parts.

[0034] Example 3

[0035] The preparation method and parameters of Example 1 were followed, except that when preparing polydopamine-coated carbon black, 2.6 parts of dopamine hydrochloride were added and the reaction was carried out for 20 hours; when preparing modified carbon black, 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate was added and the reaction was carried out for 9 hours; the reaction temperature for preparing the carboxyl-terminated intermediate was 142°C; and the temperature was raised to 95°C for preparing inorganic modified barium sulfate loaded with nano-cerium oxide. The amount of modified carbon black was 5 parts, the amount of fluorosilicone-modified hyperbranched polyester was 3 parts, the mixing time of the mixture was 12 minutes, the material temperature was controlled at 55°C, and the amount of modified filler was 23.5 parts.

[0036] Example 4

[0037] The preparation method and parameters of Example 1 were followed, except that when preparing polydopamine-coated carbon black, 3 parts of dopamine hydrochloride were added and the reaction was carried out for 22 hours; when preparing modified carbon black, 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate was added and the reaction was carried out for 10 hours; the reaction temperature for preparing the carboxyl-terminated intermediate was 145°C; and when preparing inorganic modified barium sulfate loaded with nano-cerium oxide, the temperature was raised to 100°C for the reaction. The amount of modified carbon black was 6 parts, the amount of fluorosilicone-modified hyperbranched polyester was 4 parts, the mixing time of the mixture was 15 minutes, the material temperature was controlled at 60°C, and the amount of modified filler was 25 parts.

[0038] Comparative Example 1

[0039] The preparation method and parameters of Example 1 are the same, except that an equal amount of unmodified high-pigment carbon black is used instead of modified carbon black.

[0040] Comparative Example 2

[0041] The preparation method and parameters of Example 1 are the same, except that the step of "grafting 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate" is omitted in the preparation of modified carbon black, and an equal amount of 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate is added to the coating formulation.

[0042] Comparative Example 3

[0043] The preparation method and parameters of Example 1 are the same, except that the step of "hydrolysis of tetraethyl orthosilicate to coat silica" is omitted in the preparation of modified carbon black, and polydopamine coating and 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate grafting are performed directly on the high pigment carbon black.

[0044] Comparative Example 4

[0045] The preparation method and parameters of Example 1 are the same, except that the "polydopamine coating" and subsequent steps are omitted in the preparation of modified carbon black, and only silica is used to coat the carbon black.

[0046] Comparative Example 5

[0047] The preparation method and parameters of Example 1 were used, except that no fluorosilicone-modified hyperbranched polyester was added.

[0048] Comparative Example 6

[0049] The preparation method and parameters of Example 1 are the same, except that the step of "dropping perfluorohexyl ethanol and carboxypropyl-terminated polydimethylsiloxane" is omitted in the preparation of hyperbranched polyester, that is, only the terminal epoxy hyperbranched polymer is used.

[0050] Comparative Example 7

[0051] The preparation method and parameters of Example 1 were used, except that the fluorosilicone modified hyperbranched polyester was replaced with the commercially available leveling agent Hyperlev F81.

[0052] Comparative Example 8

[0053] The preparation method and parameters of Example 1 are the same, except that an equal amount of ordinary precipitated barium sulfate is used instead of the modified filler.

[0054] Comparative Example 9

[0055] The preparation method and parameters of Example 1 are the same, except that the step of "reacting cerium nitrate and urea to deposit nano-cerium oxide" is omitted in the preparation process of the modified filler, and the precipitated barium sulfate is directly treated with titanate coupling agent.

[0056] Comparative Example 10

[0057] The preparation method and parameters of Example 1 are the same, except that in the preparation process of the modified filler, no in-situ deposition reaction is carried out. Instead, nano-cerium oxide powder (20nm) is physically mixed with precipitated barium sulfate and then modified with titanate.

[0058] Comparative Example 11

[0059] The preparation method and parameters of Example 1 are the same, except that when preparing the black polyester powder coating, all components are added to the mixer at one time and then mixed, and then subjected to twin-screw extrusion.

[0060] Comparative Example 12

[0061] The preparation method and parameters of Example 1 are the same, except that when preparing black polyester powder coating, fluorosilicone modified hyperbranched polyester is not added during the first extrusion granulation to prepare masterbatch, but is added during the second extrusion. The masterbatch consists only of modified carbon black and matrix resin.

[0062] Experimental Example 1: Impact Resistance and Leveling Test

[0063] The prepared powder coating was sprayed onto the phosphated cold-rolled steel plate (film thickness 60-80μm) using an electrostatic spray gun. The workpiece was placed in an oven for curing at 200℃ for 15min and then naturally cooled to room temperature to obtain the test sample.

[0064] Impact resistance was tested according to GB / T 1732-2020 standard using a paint film impact tester. The maximum height at which the coating did not crack or peel was recorded, with a height variation of 5cm for each test.

[0065] Observe the leveling properties under a standard light source (PCI grade, 1-10, with 10 being the best).

[0066] The results are shown in Table 1.

[0067] Table 1 Impact resistance and leveling tests of Examples 1-4 and Comparative Examples 1-12

[0068]

[0069] Experiment Example 2: Corrosion Resistance Test

[0070] Water contact angle: The static contact angle of deionized water on the coating surface was measured using a contact angle meter. The average value was taken from 5 test points.

[0071] The acid and alkali resistance properties were tested in accordance with GB / T 9274-1988. The acid resistance test was performed by immersion in 5% H2SO4 solution for 168 hours; the alkali resistance test was performed by immersion in 5% NaOH solution for 168 hours. The evaluation criteria were to observe whether there was blistering, rusting, peeling, or discoloration.

[0072] The results are shown in Table 2.

[0073] Table 2 Corrosion resistance test results of Examples 1-4 and Comparative Examples 1-12

[0074]

[0075] Experiment Example 3 Weather Resistance Test

[0076] Referring to GB / T 14522-2008, QUV-B (313nm lamp) was used, with an irradiance of 0.68W / m², and a condensation cycle (4h UV / 60℃ + 4h condensation / 50℃) for a test duration of 1000h.

[0077] The color change rating is assessed according to GB / T 1766-2008 (0 is the best, no color change; 5 is the worst).

[0078] The gloss retention rate is calculated as follows: gloss retention rate = (gloss after aging / initial gloss) × 100%; gloss is measured using a 60° gloss meter in accordance with GB / T9754-2007.

[0079] The results are shown in Table 3.

[0080] Table 3 Weather resistance test results of Examples 1-4 and Comparative Examples 1-12

[0081]

[0082] As shown in Tables 1-3, in Examples 1-4, this application introduces a "thermal barrier + free radical capture" mechanism at the pigment interface by constructing a multi-layer coating structure on the carbon black surface, which suppresses the "hot spot effect" unique to black coatings from the source. Combined with the modified filler loaded with nano-cerium oxide in the matrix, a comprehensive free radical reduction network is formed from "point" (pigment interface) to "surface" (resin matrix), breaking through the bottleneck of easy migration and rapid failure of traditional antioxidants. By introducing fluorosilicone modified hyperbranched polyester, efficient "internal wetting" of carbon black and "soft and hard bonding" toughening after curing are achieved. This not only solves the defects of high viscosity and easy cracking of high blackness system, but also endows the coating with super hydrophobic self-cleaning and corrosion resistance through the surface enrichment of fluorosilicone segments. Finally, through the stepwise extrusion process of "masterbatch method", the nanoscale dispersion of pigment carbon black is achieved with the assistance of hyperbranched resin. Example 3 achieves the best balance in reaction time, temperature and component ratio, and produces the best powder coating performance.

[0083] In Comparative Example 1, no carbon black modification was performed. Due to the extreme difficulty in dispersing high-pigment carbon black, severe agglomeration occurred, resulting in extremely low gloss. Furthermore, the lack of protection led to severe matrix degradation due to the photothermal effect of the carbon black, significantly reducing gloss retention and causing extremely poor impact strength. This demonstrates the necessity of carbon black modification. In Comparative Example 2, physically mixed 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate exhibited an initial gloss comparable to Example 1, but significantly reduced weather resistance. The physically added 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate migrated / volatilized during curing or aging, failing to provide the sustained free radical scavenging ability at the interface as chemical grafting did. This resulted in free radicals being unable to be captured in the later stages of aging, leading to resin chain breakage, thus demonstrating the necessity of chemical grafting. In Comparative Example 3, the absence of a silica thermal barrier layer significantly reduced weather resistance. The "hot spots" formed after the carbon black absorbed heat directly accelerated the aging of the interfacial resin, demonstrating the thermal barrier effect of the "inorganic coating layer." In Comparative Example 4, the absence of polydopamine as a coupling interlayer, with only silica, resulted in poor interfacial compatibility between carbon black and the polyester matrix (inorganic-organic interface defects). Acidic media easily peeled off along the interfacial gaps and could not effectively graft 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate, leading to stress concentration and poor dispersion. This demonstrates the crucial role of the polydopamine layer as a "bridge".

[0084] In Comparative Example 5, without the addition of fluorosilicone-modified hyperbranched polyester, the high-filler system had excessively high viscosity, making leveling impossible and lacking flexible buffering, resulting in extreme brittleness; simultaneously, the contact angle was significantly reduced, and hydrophobicity was lost. In Comparative Example 6, the hyperbranched polymer lacked fluorosilicone segments, losing its hydrophobic function. Although leveling and impact resistance were acceptable (the hyperbranched structure itself has a wetting effect), the high surface energy resulted in poor stain resistance, and the easy penetration of moisture led to slightly lower weather resistance than in Example 1. In Comparative Example 7, the fluorosilicone-modified hyperbranched polyester was replaced with the commercially available leveling agent Hyperlev F81. The wetting ability of the pigment was far inferior to that of the hyperbranched structure (volume steric hindrance effect), resulting in mediocre dispersibility, lower gloss than in Example 1, and a lack of chemical bonding toughening, leading to weaker impact resistance.

[0085] In Comparative Example 8, using an equal amount of ordinary precipitated barium sulfate to replace the modified filler resulted in mediocre performance, lacking the lubrication of titanate esters and exhibiting slightly higher viscosity; it also lacked the free radical capture properties of CeO2, leading to poorer long-term weather resistance compared to Example 1. In Comparative Example 9, directly treating the precipitated barium sulfate with a titanate ester coupling agent yielded a good appearance, but the lack of internal free radical quenchers significantly reduced gloss retention. In Comparative Example 10, physically mixing nano-cerium oxide powder with precipitated barium sulfate followed by titanate ester modification resulted in the nano-CeO2 readily agglomerating; physical mixing failed to achieve uniform dispersion, and the resulting agglomerates not only reduced gloss but also became centers for photocatalytic aging, making the in-situ deposition effect less effective.

[0086] In Comparative Example 11, when preparing the black polyester powder coating, all components were added to the mixer at once and then extruded using a twin-screw extruder. Without pre-dispersion with masterbatch, the high-pigment carbon black could not open up, resulting in insufficient blackness, low gloss, and decreased mechanical properties due to agglomeration points, demonstrating the necessity of a step-by-step process. In Comparative Example 12, the addition of fluorosilicone-modified hyperbranched polyester reduced the effectiveness. Although fluorosilicone-modified hyperbranched polyester was used, it was not utilized to wet the carbon black in the first step, missing the optimal opportunity for "pre-wetting," and the carbon black dispersion remained poor, demonstrating the importance of pre-treating the carbon black with fluorosilicone-modified hyperbranched polyester.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a weather-resistant black polyester powder coating, characterized in that: The preparation method is as follows: modified carbon black, fluorosilicone modified hyperbranched polyester, and part of the matrix resin are added to a high-speed mixer and mixed to obtain a mixture; the mixture is subjected to a first extrusion granulation through a twin-screw extruder to obtain a black masterbatch; the black masterbatch is added to a mixer with the remaining matrix resin, curing agent, modified filler, and additives, and mixed, and then subjected to a second extrusion granulation through a twin-screw extruder to obtain an extrudate; the extrudate is subjected to tableting, water cooling, crushing, and then fed into an air classifier mill and sieved to obtain the black polyester powder coating; The modified carbon black is prepared as follows: high-pigment carbon black is dispersed in an ethanol-water solution, ultrasonically dispersed, ammonia is added to adjust the pH value, tetraethyl orthosilicate is added dropwise, and after reaction, it is centrifuged, washed with water, and dried to obtain silica-coated carbon black; the silica-coated carbon black is dispersed in Tris-HCl buffer solution, dopamine hydrochloride is added and reacted for 18-22 h, centrifuged and washed with water to obtain polydopamine-coated carbon black; the polydopamine-coated carbon black is dispersed in ethanol, 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate is added and reacted for 8-10 h, filtered, washed with anhydrous ethanol, vacuum dried, ground and sieved to obtain the modified carbon black; The modified filler is obtained by composite modification of barium sulfate with nano-cerium oxide and titanate ester; the preparation method of the modified filler is as follows: precipitated barium sulfate is added to deionized water and ultrasonically dispersed, cerium nitrate hexahydrate is added and stirred to dissolve, urea is added, the temperature is raised to 90-100℃ and reacted, then filtered, washed with water until neutral, and dried to obtain inorganic modified barium sulfate; the inorganic modified barium sulfate is added to a high-speed mixer, heated and then mixed and modified by adding titanate ester coupling agent by spraying, and then pulverized after discharge to obtain the modified filler.

2. The method for preparing a weather-resistant black polyester powder coating according to claim 1, characterized in that: The preparation method of the fluorosilicone modified hyperbranched polyester is as follows: Trimethylolpropane and succinic anhydride are added to a four-necked flask and reacted at 135-145℃ under nitrogen protection to obtain an intermediate; after cooling, bisphenol A diglycidyl ether is added, followed by the addition of tetrabutylammonium bromide to react and obtain a terminal epoxy hyperbranched polymer; after cooling, perfluorohexyl ethanol and carboxypropyl-terminated polydimethylsiloxane are added dropwise and stirred to react; after cooling, the mixture is pulverized to obtain the fluorosilicone modified hyperbranched polyester.

3. The method for preparing a weather-resistant black polyester powder coating according to claim 1, characterized in that: The matrix resin is a weather-resistant carboxylated polyester resin; the additives consist of a leveling agent and benzoin.

4. A weather-resistant black polyester powder coating, characterized in that: The black polyester powder coating is prepared by the preparation method according to any one of claims 1-3; the raw materials for preparing the black polyester powder coating include modified carbon black, fluorosilicone modified hyperbranched polyester, matrix resin, curing agent, modified filler and additives.

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