Aluminum-magnesium alloy low-temperature curing fire-retardant powder coating and preparation method thereof

Abstract

The application belongs to the technical field of paint, and discloses an aluminum-magnesium alloy low-temperature curing flame-retardant powder coating and a preparation method thereof, wherein the raw materials of the powder coating include, in terms of weight fractions, 60-70 parts of carboxyl polyester resin, 5-7 parts of beta-hydroxyalkyl amide, 0.55-0.8 parts of curing accelerator, 8-12 parts of phytic acid modified magnesium hydroxide, 2-5 parts of aminated nanocellulose, 3-5 parts of diatomite, 1-1.8 parts of leveling agent and 0.3-0.7 parts of defoaming agent. The application forms a synergistic effect of flame retardation and low smoke by virtue of the high-efficiency flame-retardant characteristics of the phytic acid modified magnesium hydroxide, the three-dimensional network structure constructed by the aminated nanocellulose and the low-smoke function of the modified diatomite, realizes excellent flame-retardant performance, significantly reduces the release of smoke and harmful gas in the combustion process, and meets the stringent requirements in the environmental protection field.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and specifically relates to a low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy and its preparation method. Background Technology

[0002] Aluminum-magnesium alloys, with their excellent lightweight properties, high strength, and good machinability, are widely used in aerospace, rail transportation, electronic equipment, and civilian hardware. However, aluminum-magnesium alloys are chemically reactive, easily forming oxide films on their surfaces, and are extremely sensitive to high temperatures. Prolonged exposure to air or during service can easily lead to oxidation and corrosion. Furthermore, high temperatures can damage their internal structural integrity, resulting in a decline in mechanical properties. Therefore, the requirements for surface protective coatings are extremely stringent. Powder coatings, due to their absence of volatile organic compound release and excellent environmental performance, have become one of the ideal choices for surface protection of aluminum-magnesium alloys.

[0003] However, existing powder coatings suitable for aluminum-magnesium alloys still face many technical bottlenecks. Conventional powder coatings generally have excessively high curing temperatures, far exceeding the safe temperature range that aluminum-magnesium alloys can withstand. This can easily lead to structural damage to the alloy material, failing to balance curing effectiveness with substrate protection. To achieve flame retardant properties, existing coatings often directly add inorganic flame retardants, but these have poor compatibility with the resin matrix and are prone to agglomeration. This not only results in uneven flame retardant performance but also damages the coating's density and mechanical strength, making it difficult to achieve efficient and stable flame retardant effects. Furthermore, existing flame-retardant powder coatings often produce large amounts of smoke and harmful gases during combustion. Summary of the Invention

[0004] The present invention aims to improve at least one technical problem in the prior art.

[0005] The first aspect of this invention provides a low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys, wherein the raw materials, by weight, include: 60-70 parts of carboxylated polyester resin, 5-7 parts of β-hydroxyalkylamide, 0.55-0.8 parts of curing accelerator, 8-12 parts of phytic acid-modified magnesium hydroxide, 2-5 parts of aminated nanocellulose, 3-5 parts of diatomaceous earth, 1-1.8 parts of leveling agent, and 0.3-0.7 parts of defoamer.

[0006] The low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys provided in this application addresses the reactive, easily oxidized, and high-temperature sensitive characteristics of aluminum-magnesium alloys. Through the synergistic formulation of its components, it achieves low-temperature curing, high-efficiency flame retardancy, low smoke and environmental friendliness, and good compatibility with the substrate. Carboxylated polyester resin, as the coating matrix, imparts excellent leveling and superior weather resistance to the coating, providing a stable foundation for the subsequent functional components. Its own properties are also suitable for the low-temperature curing process requirements. β-hydroxyalkylamide, as a crosslinking agent, works synergistically with the carboxylated polyester resin to complete the crosslinking reaction at a lower temperature. This avoids damage to the aluminum-magnesium alloy structure from high temperatures and offers the advantages of being environmentally friendly and residue-free, without corrosive reactions with the aluminum-magnesium alloy surface, ensuring the compatibility of the coating with the substrate. The curing accelerator accelerates the crosslinking reaction process, ensuring rapid coating formation under the set low-temperature curing conditions, improving production efficiency while guaranteeing complete coating curing. Phytic acid-modified magnesium hydroxide is the core flame-retardant component. The modification of magnesium hydroxide with phytic acid not only solves the problem of easy agglomeration of inorganic flame retardants but also allows for uniform dispersion of flame-retardant elements. It combines the char-forming flame-retardant effect of organophosphorus compounds with the heat-absorbing and cooling effect of inorganic magnesium hydroxide, synergistically enhancing the flame-retardant performance of the coating. Aminated nanocellulose can form a stable three-dimensional network structure with phytic acid-modified magnesium hydroxide through intermolecular forces. This network can anchor the flame-retardant components, preventing their migration in the coating, and also enhance the mechanical strength and structural stability of the coating. Simultaneously, the amino functional groups on its surface can coordinate with the hydroxyl groups on the aluminum-magnesium alloy surface, significantly improving the adhesion between the coating and the substrate. Diatomaceous earth, with its porous structure, can adsorb smoke and harmful gases generated during the combustion of the coating, achieving a low-smoke and environmentally friendly effect. Furthermore, its compatibility with the three-dimensional network structure further inhibits smoke diffusion. Leveling agents improve the surface condition during the coating process, ensuring a smooth and even finish and enhancing appearance. Defoamers eliminate air bubbles generated during curing, preventing defects such as pinholes and craters, and ensuring the coating's density and protective properties. The synergistic effect of these components allows the prepared powder coating to meet the low-temperature curing requirements of aluminum-magnesium alloys while also exhibiting excellent flame retardancy, low smoke, adhesion, and weather resistance, making it suitable for surface protection of aluminum-magnesium alloy components.

[0007] The preparation method of the phytic acid-modified magnesium hydroxide includes the following steps: Phytic acid and nano-magnesium hydroxide were mixed and reacted at 60℃-80℃ for 2h-4h to obtain the phytic acid-modified magnesium hydroxide.

[0008] Preferably, the mass ratio of the nano-magnesium hydroxide to the phytic acid is 1:(0.1-0.2).

[0009] The preferred mass ratio of nano-magnesium hydroxide to phytic acid in this application further ensures the modification effect of phytic acid on nano-magnesium hydroxide. Insufficient phytic acid makes it difficult to form a complete modified layer on the surface of nano-magnesium hydroxide, failing to effectively improve its hydrophobicity and compatibility with the resin. Nano-magnesium hydroxide is prone to agglomeration, which not only leads to uneven flame retardant properties of the coating but also damages the coating's density, reducing its mechanical strength and adhesion. Conversely, excessive phytic acid leaves residues in the system. Its hydrophilic groups reduce the coating's water resistance and weather resistance. Furthermore, excessive phytic acid may interact with crosslinking agents or curing accelerators, interfering with the normal low-temperature crosslinking reaction, resulting in incomplete coating curing and affecting overall protective performance.

[0010] Preferably, the particle size of the nano-magnesium hydroxide is 50nm-100nm.

[0011] The preparation method of the aminated nanocellulose includes the following steps: Nanocellulose was mixed with aminosilane and reacted at 60℃-70℃ for 3-5 hours to obtain the aminated nanocellulose.

[0012] Preferably, the mass ratio of the nanocellulose to the aminosilane is 1:(0.08-0.15).

[0013] The preferred mass ratio of nanocellulose to aminosilane in this application further regulates the degree of amination of nanocellulose. When the amount of aminosilane is too small, the number of amino functional groups grafted onto the surface of nanocellulose is insufficient, making it difficult to form stable hydrogen bonds and electrostatic interactions with phytic acid-modified magnesium hydroxide. This results in the inability to construct a dense three-dimensional network structure, significantly reducing the mechanical strength, structural stability, and adhesion to the aluminum-magnesium alloy substrate of the coating. Conversely, if the amount of aminosilane is too large, excess aminosilane will agglomerate on the surface of nanocellulose or form ineffective crosslinks in the system. This not only affects the uniform dispersion of the coating components but also leads to poor surface smoothness. Furthermore, excessive aminosilane may remain in the coating, reducing its weather resistance and chemical resistance, thus failing to meet the long-term protection requirements of aluminum-magnesium alloy components.

[0014] Preferably, the aminosilane includes one of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

[0015] Preferably, the diatomaceous earth is further modified with a silane coupling agent.

[0016] After modification with silane coupling agents, the hydrolyzable groups at one end of the silane coupling agent molecule will undergo a condensation reaction with the hydroxyl groups on the surface of diatomaceous earth to form a stable chemical bond, while the organic functional groups at the other end can have a compatibility effect with the molecular chains of carboxyl polyester resin, which can further enable diatomaceous earth to be uniformly dispersed in the coating system.

[0017] Preferably, the mass ratio of the diatomaceous earth to the silane coupling agent is 1:(0.02-0.08).

[0018] Preferably, the silane coupling agent comprises one of 3-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and bis-[γ-(triethoxysilyl)propyl]tetrasulfide.

[0019] Preferably, the curing accelerator is benzyltrimethylammonium bromide.

[0020] As a quaternary ammonium salt compound, benzyltrimethylammonium bromide can activate the reaction sites of carboxyl and hydroxyalkylamide groups through ion catalysis, reducing the reaction activation energy. This allows the crosslinking reaction, which originally required higher temperatures, to proceed rapidly at lower temperatures, ensuring that the coating is fully cured under the set conditions and improving reaction efficiency.

[0021] A second aspect of this invention provides a method for preparing the above-mentioned low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys, comprising the following steps: The phytic acid-modified magnesium hydroxide and the aminated nanocellulose were added to a high-speed mixer for a first stirring and mixing to obtain mixture A; Add the carboxylated polyester resin, the β-hydroxyalkylamide, the curing accelerator, the diatomaceous earth, the leveling agent, and the defoaming agent to the mixture A, and perform a second stirring and mixing to obtain mixture B; The mixture B is fed into a twin-screw extruder through the feed port for melt extrusion, cooling, tableting, crushing, and sieving to obtain the low-temperature curing flame-retardant powder coating of aluminum-magnesium alloy.

[0022] The first stirring and mixing speed is 3000rpm-3500rpm, and the time is 90s-120s.

[0023] The second stirring and mixing speed is 1000rpm-1500rpm, and the time is 10min-15min.

[0024] The melt extrusion temperature is 85℃-99℃, and the screw speed is 500rpm-550rpm.

[0025] The beneficial effects of this invention are as follows: By leveraging the highly efficient flame-retardant properties of phytic acid-modified magnesium hydroxide, the three-dimensional network structure constructed from aminated nanocellulose, and the low-smoke function of modified diatomaceous earth, this invention achieves a synergistic effect of flame retardancy and low smoke. This results in excellent flame-retardant performance while significantly reducing the release of smoke and harmful gases during combustion, meeting stringent environmental protection requirements. Simultaneously, the synergistic effect of the components further optimizes the adhesion between the coating and the aluminum-magnesium alloy substrate, enhancing the coating's mechanical strength, structural stability, and corrosion resistance. This provides comprehensive and long-lasting surface protection for aluminum-magnesium alloy components, effectively extending their service life and expanding the application scenarios of powder coatings in aluminum-magnesium alloy-related fields. It possesses significant technical value and promising market prospects. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims. Example 1

[0027] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy comprises the following raw materials by weight: 65 parts of carboxylated polyester resin, 6 parts of β-hydroxyalkylamide, 0.65 parts of curing accelerator (benzyltrimethylammonium bromide), 10 parts of phytic acid-modified magnesium hydroxide, 3 parts of aminated nanocellulose, 4 parts of diatomaceous earth, 1.5 parts of leveling agent (polyether-modified polysiloxane), and 0.5 parts of defoaming agent (benzoin).

[0028] The preparation method of phytic acid-modified magnesium hydroxide includes the following steps: Phytic acid and nano-magnesium hydroxide (80 nm particle size) were mixed at a mass ratio of 1:0.15 and added to deionized water to prepare a suspension with a solid content of 20%. The mixture was stirred at 70 °C for 3 h. After the reaction, the solid was washed with deionized water and dried under vacuum at 70 °C to obtain phytic acid modified magnesium hydroxide.

[0029] The preparation method of aminated nanocellulose includes the following steps: Nanocellulose and aminosilane (3-aminopropyltriethoxysilane) were mixed at a mass ratio of 1:0.12 and added to anhydrous ethanol to prepare a dispersion with a solid content of 10%. The mixture was stirred at 65°C for 4 hours. After the reaction, the solid was washed with deionized water and dried under vacuum at 60°C to obtain amino-modified nanocellulose.

[0030] The preparation method of this low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy includes the following steps: Phytic acid-modified magnesium hydroxide and aminated nanocellulose were added to a high-speed mixer for the first stirring and mixing (3200 rpm, 90 s) to obtain mixture A; Add carboxylated polyester resin, β-hydroxyalkylamide, curing accelerator, diatomaceous earth, leveling agent and defoamer to mixture A, and carry out a second stirring and mixing (speed 1200 rpm, time 15 min) to obtain mixture B; Mixture B is fed into a twin-screw extruder through the feed port for melt extrusion (melt extrusion temperature is 95℃, screw speed is 520rpm), cooled, pressed into tablets, crushed, and passed through a 160-mesh sieve to obtain a low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy. Example 2

[0031] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy comprises the following raw materials by weight: 63 parts carboxylated polyester resin, 5.5 parts β-hydroxyalkylamide, 0.58 parts curing accelerator (benzyltrimethylammonium bromide), 9 parts phytic acid modified magnesium hydroxide, 2.5 parts aminated nanocellulose, 3.5 parts diatomaceous earth, 1.2 parts leveling agent (polyether modified polysiloxane), and 0.4 parts defoaming agent (benzoin).

[0032] The preparation method of phytic acid-modified magnesium hydroxide includes the following steps: Phytic acid and nano-magnesium hydroxide (particle size 60 nm) were mixed at a mass ratio of 1:0.12 and added to deionized water to prepare a suspension with a solid content of 20%. The mixture was stirred at 65 °C for 2.5 h. After the reaction, the solid was washed with deionized water and dried under vacuum at 70 °C to obtain phytic acid modified magnesium hydroxide.

[0033] The preparation method of aminated nanocellulose includes the following steps: Nanocellulose and aminosilane (3-aminopropyltrimethoxysilane) were mixed at a mass ratio of 1:0.10 and added to anhydrous ethanol to prepare a dispersion with a solid content of 10%. The mixture was stirred at 62°C for 3.5 h. After the reaction, the solid was washed with deionized water and dried under vacuum at 60°C to obtain amino-modified nanocellulose.

[0034] The preparation method of this low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy includes the following steps: Phytic acid-modified magnesium hydroxide and aminated nanocellulose were added to a high-speed mixer for the first stirring and mixing (3000 rpm for 100 s) to obtain mixture A; Add carboxylated polyester resin, β-hydroxyalkylamide, curing accelerator, diatomaceous earth, leveling agent and defoamer to mixture A, and carry out a second stirring and mixing (speed 1100 rpm, time 10 min) to obtain mixture B; Mixture B is fed into a twin-screw extruder through the feed port for melt extrusion (melt extrusion temperature is 90℃, screw speed is 500rpm), cooled, pressed into tablets, crushed, and passed through a 160-mesh sieve to obtain a low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy. Example 3

[0035] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy comprises the following raw materials by weight: 67 parts of carboxylated polyester resin, 6.5 parts of β-hydroxyalkylamide, 0.7 parts of curing accelerator (benzyltrimethylammonium bromide), 11 parts of phytic acid-modified magnesium hydroxide, 4 parts of aminated nanocellulose, 4.5 parts of diatomaceous earth, 1.6 parts of leveling agent (polyether-modified polysiloxane), and 0.6 parts of defoaming agent (benzoin).

[0036] The preparation method of phytic acid-modified magnesium hydroxide includes the following steps: Phytic acid and nano-magnesium hydroxide (particle size 90 nm) were mixed at a mass ratio of 1:0.18 and added to deionized water to prepare a suspension with a solid content of 20%. The mixture was stirred at 75 °C for 3.5 h. After the reaction, the solid was washed with deionized water and dried under vacuum at 70 °C to obtain phytic acid modified magnesium hydroxide.

[0037] The preparation method of aminated nanocellulose includes the following steps: Nanocellulose with a mass ratio of 1:0.14 was mixed with aminosilane (N-(2-aminoethyl)-3-aminopropyltrimethoxysilane) and added to anhydrous ethanol to prepare a dispersion with a solid content of 10%. The mixture was stirred at 65°C for 4.5 h. After the reaction, the solid was washed with deionized water and dried under vacuum at 60°C to obtain aminated nanocellulose.

[0038] The preparation method of this low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy includes the following steps: Phytic acid-modified magnesium hydroxide and aminated nanocellulose were added to a high-speed mixer for the first stirring and mixing (3400 rpm, 120 s) to obtain mixture A; Add carboxylated polyester resin, β-hydroxyalkylamide, curing accelerator, diatomaceous earth, leveling agent and defoamer to mixture A, and carry out a second stirring and mixing (speed 1300 rpm, time 12 min) to obtain mixture B; Mixture B is fed into a twin-screw extruder through the feed port for melt extrusion (melt extrusion temperature is 98℃, screw speed is 540rpm), cooled, pressed into tablets, crushed, and passed through a 160-mesh sieve to obtain a low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy. Example 4

[0039] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy comprises the following raw materials by weight: 69 parts of carboxylated polyester resin, 5 parts of β-hydroxyalkylamide, 0.75 parts of curing accelerator (benzyltrimethylammonium bromide), 8.5 parts of phytic acid-modified magnesium hydroxide, 2.2 parts of aminated nanocellulose, 3.2 parts of diatomaceous earth, 1.3 parts of leveling agent (polyether-modified polysiloxane), and 0.35 parts of defoaming agent (benzoin).

[0040] The preparation method of phytic acid-modified magnesium hydroxide includes the following steps: Phytic acid and nano-magnesium hydroxide (particle size 55 nm) were mixed at a mass ratio of 1:0.13 and added to deionized water to prepare a suspension with a solid content of 20%. The mixture was stirred at 70 °C for 3 h. After the reaction, the solid was washed with deionized water and dried under vacuum at 70 °C to obtain phytic acid modified magnesium hydroxide.

[0041] The preparation method of aminated nanocellulose includes the following steps: Nanocellulose with a mass ratio of 1:0.09 was mixed with aminosilane (N-(n-butyl)-3-aminopropyltrimethoxysilane) and added to anhydrous ethanol to prepare a dispersion with a solid content of 10%. The mixture was stirred at 60°C for 3.5 h. After the reaction, the solid was washed with deionized water and dried under vacuum at 60°C to obtain aminated nanocellulose.

[0042] The modification of diatomaceous earth with a silane coupling agent is carried out in the following steps: diatomaceous earth and a silane coupling agent (γ-glycidoxypropyltrimethoxysilane) are mixed at a mass ratio of 1:0.05, and then added to anhydrous ethanol to prepare a dispersion with a solid content of 10%. The mixture is stirred and reacted at 55°C for 1.5 hours. After the reaction, the solid product is washed with deionized water and dried under vacuum at 60°C to obtain modified diatomaceous earth.

[0043] The preparation method of this low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy includes the following steps: Phytic acid-modified magnesium hydroxide and aminated nanocellulose were added to a high-speed mixer for the first stirring and mixing (3500 rpm, 90 s) to obtain mixture A; Add carboxylated polyester resin, β-hydroxyalkylamide, curing accelerator, diatomaceous earth, leveling agent and defoamer to mixture A, and carry out a second stirring and mixing (1000 rpm, 15 min) to obtain mixture B; Mixture B is fed into a twin-screw extruder through the feed port for melt extrusion (melt extrusion temperature is 90℃, screw speed is 500rpm), cooled, pressed into tablets, crushed, and passed through a 160-mesh sieve to obtain a low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy. Comparative Example 1

[0044] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of phytic acid-modified magnesium hydroxide used is 7 parts. Everything else is the same as in Example 1. Comparative Example 2

[0045] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of phytic acid-modified magnesium hydroxide used is 13 parts. Everything else is the same as in Example 1. Comparative Example 3

[0046] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of aminated nanocellulose used is 1.5 parts. Everything else is the same as in Example 1. Comparative Example 4

[0047] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that it does not contain aminated nanocellulose. Otherwise, it is the same as Example 1. Comparative Example 5

[0048] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of aminated nanocellulose used is 6 parts. Otherwise, it is the same as Example 1. Comparative Example 6

[0049] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of β-hydroxyalkylamide used is 4 parts. Everything else is the same as in Example 1. Comparative Example 7

[0050] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of β-hydroxyalkylamide used is 8 parts. Everything else is the same as in Example 1. Comparative Example 8

[0051] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of curing accelerator (benzyltrimethylammonium bromide) is 0.9 parts. Everything else is the same as in Example 1. Comparative Example 9

[0052] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of diatomaceous earth used is 2 parts. Everything else is the same as in Example 1. Comparative Example 10

[0053] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that the amount of carboxylated polyester resin used is 58 parts. Everything else is the same as in Example 1. Comparative Example 11

[0054] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that nano-magnesium hydroxide is used instead of phytic acid-modified magnesium hydroxide. Otherwise, it is the same as Example 1. Comparative Example 12

[0055] A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys differs from Example 1 in that it uses nanocellulose instead of aminated nanocellulose. Otherwise, it is the same as Example 1.

[0056] The powder coatings prepared in the examples and comparative examples were sprayed onto the surface of magnesium-aluminum alloy substrates, and the performance of the coatings obtained after curing was tested, as shown in Table 1.

[0057] Table 1

[0058] Referring to the data in Table 1, Comparative Example 1 suffers from an excessively low amount of phytic acid-modified magnesium hydroxide. As a core flame-retardant component, its insufficiency directly leads to a significant weakening of the coating's flame-retardant efficacy and a corresponding decrease in low-smoke effect. Simultaneously, its protective and supporting role in the coating is weakened, resulting in significantly poorer corrosion resistance compared to the examples, failing to achieve the combined high-efficiency flame retardancy and long-term protection of the examples. Comparative Example 2, on the other hand, suffers from an excessively high amount of phytic acid-modified magnesium hydroxide. The excessive inorganic flame retardant is difficult to disperse uniformly in the resin system, instead exhibiting agglomeration. This not only fails to further improve flame-retardant performance but also damages the structural integrity of the coating, leading to a significant reduction in the adhesion between the coating and the aluminum-magnesium alloy substrate, as well as its impact resistance, compared to the examples, and a decline in protective performance.

[0059] In Comparative Example 3, the amount of aminated nanocellulose was insufficient. As the core builder of the three-dimensional network structure, insufficient dosage resulted in a loose and incomplete network structure, failing to effectively anchor the flame-retardant components and enhance the coating structure. Consequently, the mechanical strength, adhesion, and low-smoke effect of the coating were inferior to those of the examples, especially in suppressing smoke diffusion, showing a significant gap compared to the excellent performance of the examples. In Comparative Example 4, no aminated nanocellulose was added, and the three-dimensional network structure could not be formed. The flame-retardant components were prone to migration, and the coating structure lacked support, resulting in a significant decline in all performance aspects. Not only were the mechanical properties and adhesion far lower than those of the examples, but the smoke density was also significantly increased, fully demonstrating the indispensability of aminated nanocellulose in the formulation system of Example 1. In Comparative Example 5, the amount of aminated nanocellulose was too high. Excessive nanocellulose agglomerated in the system, interfering with the uniform dispersion of the components and damaging the density of the coating. This led to a decline in mechanical properties and low-smoke effect compared to the examples, failing to achieve the expected performance optimization.

[0060] In Comparative Example 6, the amount of β-hydroxyalkylamide was too low. As a crosslinking agent, its insufficiency prevented the crosslinking reaction of the carboxylated polyester resin from proceeding fully, resulting in incomplete coating curing and insufficient structural stability. Consequently, the adhesion and corrosion resistance of the coating to the aluminum-magnesium alloy substrate were significantly reduced compared to the examples, failing to form an effective protective barrier. In Comparative Example 7, the amount of β-hydroxyalkylamide was too high. Excessive crosslinking agent led to over-crosslinking of the coating, causing it to become brittle and significantly reducing its impact resistance. It also affected the density of the coating, resulting in weakened corrosion resistance compared to the examples. The balance between curing effect and mechanical properties achieved in the examples was not realized.

[0061] In Comparative Example 8, the excessive amount of curing accelerator caused the crosslinking reaction rate to be too fast. As a result, the coating was prone to micro-defects during the low-temperature curing process, which not only affected the surface hardness of the coating but also its adhesion to the substrate.

[0062] In Comparative Example 9, the amount of diatomaceous earth was insufficient. As a key component for low smoke function, its deficiency significantly weakened the smoke adsorption and suppression effect during the combustion of the coating, and the smoke density was significantly higher than that of the Example.

[0063] In Comparative Example 10, the amount of carboxylated polyester resin was too low. As a base material for the coating, its deficiency resulted in insufficient coating density and structural support. Consequently, the coating's mechanical strength, adhesion, corrosion resistance, and other core properties were significantly inferior to those of the examples, and it could not provide effective surface protection for the aluminum-magnesium alloy.

[0064] The difference between Comparative Example 11 and Example 1 is that the magnesium hydroxide was not modified with phytic acid, and nano-magnesium hydroxide was used directly as the flame retardant component. The unmodified nano-magnesium hydroxide has more hydrophilic groups on its surface, which has poor compatibility with hydrophobic carboxylated polyester resin. It is easy to agglomerate in the coating system, resulting in uneven dispersion of flame retardant elements. This not only makes the flame retardant performance significantly lower than that of the Example, but also destroys the structural density of the coating, causing a decrease in adhesion and impact strength. At the same time, the voids formed by the agglomerates provide channels for smoke and corrosive media, resulting in a significant increase in smoke density and corrosion resistance that is far inferior to that of the Example.

[0065] The difference between Comparative Example 12 and Example 1 is that the nanocellulose was not aminated. Instead, nanocellulose was used directly to replace the aminated nanocellulose. The surface of the unmodified nanocellulose lacks amino functional groups, which makes it impossible to form stable hydrogen bonds and electrostatic interactions with phytic acid-modified magnesium hydroxide. This makes it difficult to build a dense three-dimensional network structure, resulting in the flame retardant components not being effectively anchored and easily migrating. This not only weakens the synergistic effect of flame retardancy and low smoke, but also significantly increases the smoke density compared to the Example. Furthermore, the coating loses the support of the network structure, resulting in a decrease in mechanical strength and adhesion. At the same time, the coordination bonding ability to the aluminum-magnesium alloy matrix is ​​weakened, and the corrosion resistance also declines to some extent.

[0066] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A low-temperature curing flame-retardant powder coating for aluminum-magnesium alloys, characterized in that, The raw materials, by weight, include: 60-70 parts of carboxylated polyester resin, 5-7 parts of β-hydroxyalkylamide, 0.55-0.8 parts of curing accelerator, 8-12 parts of phytic acid-modified magnesium hydroxide, 2-5 parts of aminated nanocellulose, 3-5 parts of diatomaceous earth, 1-1.8 parts of leveling agent, and 0.3-0.7 parts of defoaming agent; The preparation method of the phytic acid-modified magnesium hydroxide includes the following steps: Phytic acid and nano-magnesium hydroxide were mixed and reacted at 60℃-80℃ for 2h-4h to obtain the phytic acid modified magnesium hydroxide. The mass ratio of the nano-magnesium hydroxide to the phytic acid is 1:(0.1-0.2); The preparation method of the aminated nanocellulose includes the following steps: Nanocellulose was mixed with aminosilane and reacted at 60℃-70℃ for 3h-5h to obtain the aminated nanocellulose. The mass ratio of the nanocellulose to the aminosilane is 1:(0.08-0.15).

2. The low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy according to claim 1, characterized in that, The particle size of the nano-magnesium hydroxide is 50nm-100nm.

3. The low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy according to claim 1, characterized in that, The diatomaceous earth has also been modified with a silane coupling agent.

4. The low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy according to claim 1, characterized in that, The curing accelerator is benzyltrimethylammonium bromide.

5. A method for preparing a low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy as described in any one of claims 1 to 4, characterized in that, Includes the following steps: The phytic acid-modified magnesium hydroxide and the aminated nanocellulose were added to a high-speed mixer for a first stirring and mixing to obtain mixture A; Add the carboxylated polyester resin, the β-hydroxyalkylamide, the curing accelerator, the diatomaceous earth, the leveling agent, and the defoaming agent to the mixture A, and perform a second stirring and mixing to obtain mixture B; The mixture B is fed into a twin-screw extruder through the feed port for melt extrusion, cooling, tableting, crushing, and sieving to obtain the low-temperature curing flame-retardant powder coating of aluminum-magnesium alloy.

6. The method for preparing low-temperature curing flame-retardant powder coating for aluminum-magnesium alloy according to claim 5, characterized in that, The first stirring and mixing speed is 3000rpm-3500rpm, and the time is 90s-120s; And / or, the second stirring and mixing speed is 1000rpm-1500rpm, and the time is 10min-15min; And / or, the melt extrusion temperature is 85℃-99℃, and the screw speed is 500rpm-550rpm.

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