Composite coating of anti-mildew colored aluminum alloy profile and preparation method of composite coating

Abstract

The invention relates to the technical field of aluminum alloy surface treatment, in particular to a composite coating of an anti-mold colored aluminum alloy profile and a preparation method of the composite coating. The composite coating sequentially comprises a rare earth-silane-phytic acid-dopamine composite passivation transition layer constructed on the micro-nano textured surface of the aluminum alloy matrix, an anti-mildew mesoporous functional middle layer containing dynamic crosslinking groups and a hydrophobic colored sealing surface layer from inside to outside, and all the layers form an interpenetrating crosslinking network structure through covalent bonds. The preparation method comprises the steps of matrix pretreatment, preparation of the composite passivation layer, preparation of the mesoporous middle layer, surface layer coating and gradient thermocuring. The coating is free of chromium and environmentally friendly, has long-acting mildew resistance, high corrosion resistance, strong adhesive force, long-acting color retention and micro-damage self-repairing performance, solves the industrial pain points that an existing coating is poor in mildew resistance and durability, easy to strip between layers and the like, is adaptive to an existing production line and can realize industrial mass production.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy surface treatment technology, specifically to a composite coating for anti-mildew colored aluminum alloy profiles and its preparation method. Background Technology

[0002] Aluminum alloy profiles, with their core advantages of being lightweight yet strong, easy to process and form, and possessing excellent appearance and texture, have been widely used in many fields such as building doors and windows, curtain walls, bathroom fixtures, food processing workshops, medical and health care facilities, and coastal municipal engineering projects. However, in these application scenarios, aluminum alloy profiles are constantly exposed to high humidity, high salt spray, and environments prone to the adhesion of organic pollutants. Their surfaces are highly susceptible to the growth of common pathogenic molds such as Aspergillus niger, Aspergillus flavus, Aspergillus terreus, and Trichoderma viride. Mold growth not only severely damages the colored decorative appearance of the profiles, but the organic acids and enzymes produced by their metabolism also continuously corrode the aluminum alloy substrate, inducing pitting corrosion, crevice corrosion, and other failure problems, significantly shortening the service life of the profiles. Simultaneously, the spread of mold spores can cause indoor environmental pollution, directly threatening human health. Especially in scenarios with stringent hygiene requirements, such as food and medical settings, the anti-mold performance of aluminum alloy profiles has become a core indicator determining their application boundaries.

[0003] Currently, the mainstream surface protection technologies for aluminum alloy profiles in the industry mainly include three categories: anodizing + electrophoretic coating, fluorocarbon spraying, and powder coating. Among them, anodizing + electrophoretic coating is the most commonly used treatment method for architectural aluminum alloy profiles. Although it can give the profiles basic corrosion resistance and colorful decorative effects, the electrophoretic coating itself is highly hydrophilic and easily absorbs moisture and organic nutrients from the environment, providing excellent conditions for the attachment and reproduction of mold. It has no anti-mold ability itself, and obvious mold growth can appear within 3 months in a humid environment. While coatings prepared by fluorocarbon spraying and powder coating processes possess excellent weather resistance and corrosion resistance, they lack inherent anti-mold properties. The industry's conventional modification method involves directly adding inorganic antibacterial agents such as silver and copper ions to the surface resin. However, this method has several inherent drawbacks: First, the antibacterial agents only function on the coating surface. As the coating surface wears and ages, the internal antibacterial agents cannot effectively migrate to the surface, resulting in a precipitous decline in anti-mold performance after 1-2 years of use, leading to extremely poor durability. Second, silver and copper ions are easily leached out in humid environments, accelerating the loss of anti-mold performance and posing an environmental risk of heavy metal contamination, failing to meet stringent environmental standards such as EU RoHS and REACH. Third, inorganic antibacterial agents have extremely poor compatibility with organic resin matrices, easily leading to agglomeration and sedimentation. This not only damages the film density of the coating, reducing adhesion and impact resistance, but also causes color differences and mottling in colored coatings, severely affecting the decorative effect.

[0004] Furthermore, while some multi-layered aluminum alloy protective coatings exist in existing technologies, most are simple physical stacking structures, with layers bonded solely by mechanical forces. In environments with alternating hot and cold temperatures and prolonged immersion in moisture, these layers are highly susceptible to water seepage, blistering, and interlayer delamination, leading to rapid failure of the overall protective system. Simultaneously, the passivation transition layers of existing coatings often employ highly carcinogenic chromate passivation systems, posing significant environmental risks. Conventional chromium-free zirconium-titanium passivation systems lack sufficient adhesion to the aluminum alloy substrate, offering limited corrosion inhibition and protection, failing to provide a stable bonding base for upper coatings, and thus failing to meet the protection requirements for long-term outdoor use. In existing colored coating systems, while organic pigments offer vibrant colors, their weather resistance and lightfastness are extremely poor, resulting in noticeable fading within six months of outdoor use. Conventional inorganic pigments, while exhibiting excellent weather resistance, have poor compatibility with organic resins, are prone to sedimentation and aggregation, and lack sufficient hydrophobicity on the coating surface, failing to reduce mold adhesion and growth at the source. More importantly, existing coatings cannot self-repair microcracks and microdamage that develop during use. These microdefects become channels for corrosive media and mold invasion, causing the coating's protective and anti-mold properties to fail rapidly. This is a core technical pain point that has long remained unresolved in this field. In summary, existing technologies cannot simultaneously achieve long-term anti-mold performance, corrosion resistance, interlayer adhesion, color retention, self-healing protection, and environmental friendliness in aluminum alloy coatings, and therefore cannot meet the comprehensive performance requirements under complex working conditions. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned core defects in existing technologies by providing a composite coating for anti-mold colored aluminum alloy profiles and its preparation method. Through the organic integration and synergistic effect of multiple technologies, this invention solves the industry pain points of existing coatings, such as poor anti-mold durability, easy peeling between layers, inability to balance environmental protection and protective performance, and easy failure of protection due to micro-damage. This invention achieves a balance between long-lasting anti-mold properties, high corrosion resistance, strong adhesion, long-lasting color retention, and environmental friendliness in aluminum alloy coatings.

[0006] The technical solution adopted by this invention to solve its technical problem is: a composite coating for anti-mold colored aluminum alloy profiles, comprising, from the inside out, a rare earth-silane-phytic acid-dopamine composite passivation transition layer constructed on the micro-nano textured surface of the aluminum alloy profile substrate, a mesoporous functional intermediate layer containing dynamically cross-linked groups chemically bonded to the surface of the passivation transition layer, and a hydrophobic colored sealing layer cross-linked and cured on the surface of the mesoporous functional intermediate layer; the composite passivation transition layer is a chromium-free mesh passivation film formed by the in-situ chelation and condensation of rare earth salts, aminosilane coupling agents, phytic acid, and dopamine, with a thickness of 80-250 mm. nm, the passivation film surface is rich in active hydroxyl and phenolic hydroxyl groups; the mesoporous functional intermediate layer uses mesoporous silica as a carrier, with quaternary phosphonium salt type antifungal agent loaded in the mesoporous channels, and silane coupling agent containing disulfide bonds grafted on the surface of the mesoporous silica, the dry film thickness of the intermediate layer is 2-6 μm; the hydrophobic colored protective surface layer uses fluorinated siloxane modified acrylate resin as the film-forming matrix, with core-shell structured colored inorganic pigments and rare earth weather-resistant complexes uniformly dispersed in the matrix, the surface layer and the intermediate layer form an interpenetrating cross-linked network structure through disulfide bonds and silicon-oxygen bonds, the dry film thickness of the surface layer is 15-35 μm, and the water contact angle is ≥115°.

[0007] Specifically, the rare earth salt of the composite passivation transition layer is one or more of cerium nitrate, cerium chloride, or lanthanum nitrate, the aminosilane coupling agent is γ-aminopropyltriethoxysilane, the mass ratio of phytic acid to dopamine is 1:1-2:1, and the mass percentage of rare earth elements in the passivation film is 3%-10%.

[0008] Specifically, the disulfide-containing silane coupling agent is bis-(3-triethoxysilylpropyl) disulfide, and its grafting amount is 20%-45% of the mass of mesoporous silica; the quaternary phosphonium salt type antifungal agent is one or a combination of two of tributyldodecylphosphonium chloride and triphenylhexadecylphosphonium chloride, and its mass accounts for 12%-35% of the total mass of the mesoporous functional intermediate layer.

[0009] Specifically, the fluorine content of the fluorinated siloxane-modified acrylate resin is 10%-20%, and the hydroxyl value is 35-55 mgKOH / g; the core of the core-shell structured colored inorganic pigment is an iron-based, cobalt-based, or rare earth-based colored inorganic pigment, the outer shell is a silica coating layer, and the pigment particle size is 200-800 nm.

[0010] Specifically, the rare earth weather-resistant complex is an organic carboxylic acid complex of cerium or praseodymium, and the total mass of the core-shell structured colored inorganic pigment and the rare earth weather-resistant complex accounts for 6%-18% of the total mass of the surface layer.

[0011] A method for preparing a composite coating for anti-mildew colored aluminum alloy profiles includes the following steps: S1 aluminum alloy profile micro-nano texturing pretreatment: The aluminum alloy profile is subjected to alkaline degreasing, chemical micro-etching texturing, nitric acid brightening, multi-stage cleaning and cold air drying in sequence to obtain a pretreated substrate with a uniform micro-nano rough texture on the surface. Preparation of S2 composite passivation transition layer: Prepare rare earth-silane-phytic acid-dopamine composite passivation treatment solution, immerse the pretreated substrate in the treatment solution for in-situ chelation and condensation reaction, take it out and rinse with anhydrous ethanol, and then perform low-temperature pre-curing to form a composite passivation transition layer on the substrate surface. Preparation of S3 mesoporous functional intermediate layer: Prepare a mesoporous silica dispersion of quaternary phosphonium salt antifungal agent grafted with disulfide bond silane coupling agent, dilute with anhydrous ethanol to a set solid content to obtain intermediate layer coating liquid, coat it on the surface of passivation transition layer, and form mesoporous functional intermediate layer after pre-curing. Preparation of S4 hydrophobic colored protective coating: Prepare a coating liquid containing core-shell structured colored inorganic pigments and rare earth weather-resistant complexes, apply it to the surface of the mesoporous functional intermediate layer, level it at room temperature and then perform gradient thermal curing to finally obtain the composite coating.

[0012] Specifically, the chemical micro-etching texturing treatment in step S1 uses a micro-etching solution with the following components: sodium hydroxide 10-20 g / L, sodium fluoride 3-8 g / L, sodium gluconate 1-3 g / L, and the remainder is deionized water. The treatment temperature is 35-45℃, and the treatment time is 3-8 min.

[0013] Specifically, the components of the composite passivation treatment solution in step S2, per 1L, include: 0.3-1.0 g / L rare earth salt, 10-25 g / L aminosilane coupling agent, 2-5 g / L phytic acid, 1-3 g / L dopamine, 200-350 g / L anhydrous ethanol, with the balance being deionized water. The pH of the treatment solution is adjusted to 4.0-5.5 with glacial acetic acid. The in-situ chelation condensation reaction temperature is 25-40℃, the reaction time is 15-30 min, and the pre-curing temperature is 60-80℃ for 5-15 min.

[0014] Specifically, the preparation method of the mesoporous silica dispersion in step S3 is as follows: tetraethyl orthosilicate, anhydrous ethanol, deionized water, and acidic catalyst are mixed and hydrolyzed to obtain silica sol; a template agent, hexadecyltrimethylammonium bromide, is added and the mixture is heated to obtain a mesoporous silica precursor; a quaternary phosphonium salt-type antifungal agent is added and stirred for loading; then a silane coupling agent containing disulfide bonds is added for grafting modification reaction, and finally the dispersion is obtained.

[0015] Specifically, the gradient thermosetting process described in step S4 is as follows: first, the temperature is raised to 90-110℃ at a rate of 3-5℃ / min and held for 15-25min; then, the temperature is raised to 130-150℃ at a rate of 2-3℃ / min and held for 25-40min; after the holding period, the temperature is allowed to cool naturally to room temperature.

[0016] The beneficial effects of this invention are: This invention integrates technologies such as substrate interface modification, chromium-free chelate passivation, long-lasting mesoporous drug delivery, dynamic cross-linking self-healing, and hydrophobic antifouling and antifungal synergistic through an integrated structural design of "micro-nano textured substrate - composite passivation transition layer - mesoporous functional intermediate layer - hydrophobic colored surface layer". The functional layers form an overall interpenetrating network structure through covalent bonds, rather than the physical superposition of existing technologies. This achieves a full-chain protection system of "mechanical anchoring - corrosion inhibition protection - long-lasting sterilization - source antifouling - damage self-healing", which fundamentally solves the core pain points of existing coatings such as poor antifungal durability, easy peeling between layers, and easy failure due to micro-damage.

[0017] The composite passivation transition layer of this invention adopts a rare earth-silane-phytic acid-dopamine quaternary synergistic system, which is completely chromium-free and environmentally friendly. At the same time, it has excellent corrosion inhibition and protection performance and high-density active reaction sites. Through chelation and covalent bonding, it achieves molecular-level bonding between the passivation film and the aluminum alloy substrate. The corrosion inhibition performance and bonding force far exceed those of conventional zirconium-titanium chromium-free passivation systems. At the same time, it provides sufficient cross-linking reaction sites for the upper coating, becoming the core link connecting the substrate and the upper coating.

[0018] The mesoporous functional intermediate layer of this invention simultaneously achieves three core functions: high-load, long-lasting sustained release of antifungal agents, interlayer covalent cross-linking, and micro-damage self-repair. The mesoporous channels enable the controllable and slow release of quaternary phosphonium salt antifungal agents, giving the coating a long-lasting antifungal performance of more than 10 years. The grafted disulfide-bonded silane coupling agent not only achieves covalent bonding between the intermediate layer and the upper and lower layers, completely solving the problem of interlayer delamination in multilayer coatings, but also achieves self-repair of micro-damage in the coating through the dynamic reversibility of disulfide bonds, blocking the invasion channels of corrosion and mold, and significantly improving the service life of the coating.

[0019] The surface layer of this invention uses fluorosiloxane-modified acrylic resin, combined with core-shell structured colored inorganic pigments and rare earth weather-resistant complexes, achieving a unified effect of hydrophobicity and antifouling, synergistic anti-mildew, and long-lasting color retention. The low surface energy fluorosilicone segments reduce the adhesion and growth of mold from the source, forming a synergistic anti-mildew system with the bactericidal function of the intermediate layer. The core-shell structured pigments and rare earth weather-resistant complexes significantly improve the weather resistance and color retention of the coating, with a color difference ΔE ≤ 1.2 after 1000 hours of outdoor use. At the same time, chemical bonding improves the compatibility between the pigment and the resin, avoiding pigment sedimentation and color difference problems.

[0020] The preparation process of this invention is simple to operate, requires no complicated special equipment, and has no toxic or harmful substances emitted throughout the process, making it environmentally friendly and pollution-free. It is compatible with existing roller coating and spray coating production lines for aluminum alloy profiles, enabling large-scale industrial production. The prepared coating has stable performance, small batch-to-batch variation, and comprehensive performance far exceeds existing industry standards, making it extremely valuable for promotion and application. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 The flowchart illustrates a method for preparing a composite coating for anti-mold colored aluminum alloy profiles, as provided by this invention. Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0024] A composite coating for anti-mold colored aluminum alloy profiles comprises, from the inside out, a rare earth-silane-phytic acid-dopamine composite passivation transition layer constructed on the micro-nano textured surface of the aluminum alloy profile substrate, an anti-mold mesoporous functional intermediate layer containing dynamic crosslinking groups chemically bonded to the surface of the passivation transition layer, and a hydrophobic colored protective layer crosslinked and cured on the surface of the mesoporous functional intermediate layer.

[0025] The micro-nano textured structure on the surface of the aluminum alloy profile substrate is a uniform micro-nano-level rough texture constructed on the aluminum alloy surface through a chemical micro-etching process. On the one hand, it can significantly increase the contact area between the substrate and the passivation transition layer, providing a mechanical anchoring effect for the passivation film and fundamentally improving the adhesion between the coating and the substrate. On the other hand, through the capillary effect of the rough structure, the passivation treatment liquid can fully wet the substrate surface, ensuring the uniformity and density of the passivation film and avoiding defects such as pinholes and missed coatings.

[0026] The rare earth-silane-phytic acid-dopamine composite passivation transition layer is a chromium-free mesh passivation film formed by the in-situ chelation and condensation of rare earth salts, aminosilane coupling agents, phytic acid, and dopamine. The film has a thickness of 80-250 nm and its surface is rich in active hydroxyl and phenolic hydroxyl groups. This passivation layer is a completely chromium-free and environmentally friendly system, completely abandoning the carcinogenic chromate passivation process. Simultaneously, through the synergistic chelation of multiple components, it achieves corrosion inhibition and protection performance far exceeding that of conventional chromium-free passivation systems: cerium and lanthanum ions in the rare earth salts can selectively deposit at active defect sites on the aluminum alloy surface, forming a rare earth oxide / hydroxide corrosion inhibition film that precisely seals the pitting corrosion holes in the aluminum alloy, blocking the intrusion channels of corrosive media; the silanol groups formed by the hydrolysis of the aminosilane coupling agent can undergo dehydration condensation with the hydroxyl groups on the aluminum alloy substrate surface and the hydroxyl groups of rare earth oxides, forming stable Si-O-Al bonds and Si-O- RE bonds form a dense three-dimensional network passivation film on the substrate surface; phytic acid molecules contain 6 phosphate groups, which can strongly chelate with aluminum ions and rare earth ions to form a dense monomolecular chelate protective film on the aluminum alloy surface, further improving the corrosion inhibition performance of the passivation film; the catechol groups in dopamine molecules have extremely strong adhesion properties, which can form strong hydrogen bonds and covalent bonds with the aluminum alloy substrate and silane film layer, greatly improving the adhesion between the passivation film and the substrate. At the same time, the phenolic hydroxyl groups in dopamine molecules can provide high-density active reaction sites for the subsequent cross-linking reaction of the upper coating layer, realizing the molecular-level covalent bonding between the passivation layer and the mesoporous intermediate layer.

[0027] The mesoporous functional intermediate layer containing dynamic crosslinking groups is based on mesoporous silica as a carrier. Quaternary phosphonium salt-type antifungal agents are loaded in the mesoporous channels, and silane coupling agents containing disulfide bonds are grafted onto the surface of the mesoporous silica. The dry film thickness of the intermediate layer is 2-6 μm. Mesoporous silica possesses ordered mesoporous channels and an ultra-high specific surface area, enabling high loading capacity and controlled slow release of quaternary phosphonium salt-based antifungal agents. This allows the coating to continuously release effective antifungal components during long-term use, solving the core problems of rapid loss and poor antifungal durability of existing antifungal agents. Compared to conventional quaternary ammonium salt-based antifungal agents, quaternary phosphonium salt-based antifungal agents have stronger positive charge, which can strongly adsorb negatively charged mold cell membranes through electrostatic interactions, destroying the phospholipid bilayer structure of the cell membrane and causing leakage of cell contents, thus achieving highly efficient killing of mold. It has a broader antifungal spectrum, with a kill rate of over 99.9% against common molds such as Aspergillus niger and Aspergillus flavus. At the same time, it has excellent hydrolysis resistance, temperature resistance, and chemical stability, and is not easily decomposed or ineffective during coating curing and long-term use. Moreover, there is no risk of heavy metal leaching, making it environmentally friendly. The silane coupling agent with disulfide bonds grafted onto the surface of mesoporous silica has a siloxane group at one end that can hydrolyze to form silanol groups. These silanol groups then undergo dehydration condensation reactions with the active hydroxyl and phenolic hydroxyl groups on the surface of the passivation transition layer, forming stable covalent bonds and achieving a strong bond between the intermediate layer and the passivation layer. The other end can undergo a cross-linking reaction with the film-forming resin of the surface layer. Simultaneously, the disulfide bonds exhibit dynamic reversibility; when microcracks or microdamage appear in the coating, the disulfide bonds can break and recombine, achieving self-repair of the coating's microdamage, blocking the invasion channels of corrosive media and mold, and significantly improving the coating's protective lifespan and anti-mold durability. Furthermore, the grafted and modified mesoporous silica can be firmly fixed in the coating system, preventing the aggregation, migration, and precipitation of the anti-mold agent, further enhancing the coating's stability.

[0028] The hydrophobic colored protective layer uses fluorosiloxane-modified acrylate resin as the film-forming matrix. Core-shell structured colored inorganic pigments and rare-earth weather-resistant complexes are uniformly dispersed within the matrix. The top layer and intermediate layer form an interpenetrating cross-linked network structure through disulfide and silicon-oxygen bonds. The dry film thickness of the top layer is 15-35 μm, and the water contact angle is ≥115°. The fluorosiloxane-modified acrylate resin introduces low surface energy fluorosilicone segments, which significantly reduce the surface energy of the coating, giving it excellent hydrophobic and antifouling properties. This causes water to form spherical droplets that roll off the coating surface, greatly reducing the adhesion of water and organic pollutants from the environment to the coating surface. This cuts off the nutrient source and living environment for mold growth at the source, forming a synergistic anti-mold system with the bactericidal function of the intermediate layer, achieving a powerful anti-mold effect. Simultaneously, the acrylate resin matrix possesses excellent film-forming properties and weather resistance, while the fluorosilicone segments further enhance the coating's chemical resistance, stain resistance, and aging resistance, maintaining the coating's density and integrity for a long time. The core of the core-shell structured inorganic pigment is a weather-resistant inorganic pigment, while the outer shell is a dense silica coating. The silica shell effectively isolates the core pigment from the external environment and the resin matrix, preventing photochemical reactions and chemical corrosion, thus significantly improving the color retention and aging resistance of the coating. Simultaneously, the abundant hydroxyl groups on the silica shell surface can cross-link with the active groups of the resin matrix and the silanol groups in the mesoporous intermediate layer. This not only significantly improves the compatibility between the pigment and the resin matrix, preventing pigment sedimentation and aggregation and ensuring the uniformity of the coating color, but also further enhances the interfacial bonding between the surface layer and the intermediate layer, forming an interpenetrating cross-linked overall network structure, improving the coating's density and corrosion resistance. Rare earth weather-resistant complexes can absorb ultraviolet light, significantly improving the coating's UV aging resistance and further extending its decorative and protective lifespan.

[0029] The rare earth salt of the composite passivation transition layer is one or more of cerium nitrate, cerium chloride, or lanthanum nitrate, the aminosilane coupling agent is γ-aminopropyltriethoxysilane, the mass ratio of phytic acid to dopamine is 1:1-2:1, and the mass percentage of rare earth elements in the passivation film is 3%-10%.

[0030] The disulfide-containing silane coupling agent is bis-(3-triethoxysilylpropyl) disulfide, and its grafting amount is 20%-45% of the mass of mesoporous silica; the quaternary phosphonium salt type antifungal agent is one or a combination of two of tributyldodecylphosphonium chloride and triphenylhexadecylphosphonium chloride, and its mass accounts for 12%-35% of the total mass of the mesoporous functional intermediate layer.

[0031] The fluorine-containing siloxane-modified acrylate resin has a fluorine content of 10%-20% and a hydroxyl value of 35-55 mgKOH / g; the core of the core-shell structured colored inorganic pigment is an iron-based, cobalt-based, or rare-earth-based colored inorganic pigment, the outer shell is a silica coating layer, and the pigment particle size is 200-800 nm.

[0032] The rare earth weather-resistant complex is an organic carboxylic acid complex of cerium or praseodymium, and the total mass of the core-shell structured colored inorganic pigment and the rare earth weather-resistant complex accounts for 6%-18% of the total mass of the surface layer.

[0033] like Figure 1 As shown, the present invention also provides a method for preparing the composite coating of the above-mentioned anti-mildew colored aluminum alloy profile, comprising the following steps: S1 aluminum alloy profile micro-nano texturing pretreatment: The aluminum alloy profile is subjected to alkaline degreasing, chemical micro-etching texturing, nitric acid brightening, multi-stage cleaning and cold air drying in sequence to remove surface oil, natural oxide film and impurities, while constructing a uniform micro-nano rough texture on the substrate surface to obtain the pretreated substrate. Preparation of S2 composite passivation transition layer: Prepare rare earth-silane-phytic acid-dopamine composite passivation treatment solution, immerse the pretreated substrate in the treatment solution for in-situ chelation and condensation reaction, take it out and rinse with anhydrous ethanol to remove unreacted residual liquid on the surface, and then perform low-temperature pre-curing to form a composite passivation transition layer rich in active sites on the substrate surface. Preparation of S3 mesoporous functional intermediate layer: A mesoporous silica dispersion grafted with a disulfide bonded silane coupling agent and loaded with quaternary phosphonium salt antifungal agent was prepared. After being diluted with anhydrous ethanol to a set solid content, an intermediate layer coating liquid was obtained. The intermediate layer coating liquid was uniformly coated on the surface of the passivation transition layer by roller coating or spraying. After low-temperature pre-curing, a mesoporous functional intermediate layer was formed. Preparation of S4 hydrophobic colored protective layer: Prepare a surface coating liquid containing core-shell structured colored inorganic pigments and rare earth weather-resistant complexes, and apply it evenly to the surface of the mesoporous functional intermediate layer by roller coating or spraying. After leveling at room temperature, perform gradient thermal curing to allow full cross-linking reaction between the layers, forming an overall interpenetrating network structure, and finally obtain the composite coating of the anti-mildew colored aluminum alloy profile.

[0034] In step S1, the alkaline degreasing treatment uses an alkaline degreasing agent with the following components: sodium hydroxide 30-50 g / L, anhydrous sodium carbonate 15-25 g / L, OP-10 emulsifier 3-8 g / L, and the remainder is deionized water. The degreasing temperature is 40-60℃, and the treatment time is 5-15 min. The chemical micro-etching texturing treatment uses a micro-etching solution with the following components: sodium hydroxide 10-20 g / L, sodium fluoride 3-8 g / L, sodium gluconate 1-3 g / L, and the remainder is deionized water. The treatment temperature is 35-45℃, and the treatment time is 3-8 min. The nitric acid brightening treatment uses a nitric acid solution with a concentration of 80-120 g / L, and the treatment is carried out at room temperature for 20-60 seconds. The cleaning treatment uses running tap water rinsing combined with ultrasonic cleaning with deionized water to ensure that there are no residual impurities on the substrate surface.

[0035] The components of the composite passivation treatment solution in step S2, per 1L, include: 0.3-1.0 g / L rare earth salt, 10-25 g / L aminosilane coupling agent, 2-5 g / L phytic acid, 1-3 g / L dopamine, 200-350 g / L anhydrous ethanol, with the balance being deionized water. The pH of the treatment solution is adjusted to 4.0-5.5 with glacial acetic acid. The in-situ chelation condensation reaction temperature is 25-40℃, and the reaction time is 15-30 min. The pre-curing temperature is 60-80℃, and the time is 5-15 min.

[0036] The preparation method of the mesoporous silica dispersion in step S3 is as follows: Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and acidic catalyst are mixed in proportion and hydrolyzed at 35-45℃ for 1-3 hours to obtain a uniform and transparent silica sol; a template agent, hexadecyltrimethylammonium bromide, is added, stirred evenly, and then heated to 55-65℃ and kept at this temperature for 3-5 hours to form a mesoporous silica precursor; a quaternary phosphonium salt-type antifungal agent is added, and stirring is continued for 4-8 hours to allow the antifungal agent to fully diffuse into the mesoporous channels and complete the loading; then a silane coupling agent containing disulfide bonds is added, and the reaction is continued at 55-65℃ for 2-4 hours to complete the grafting modification of the silane coupling agent, and finally the dispersion is obtained.

[0037] The components of the topcoat liquid in step S4, by mass parts, include: 40-60 parts of fluorosiloxane-modified acrylate resin, 25-35 parts of mixed solvent, 5-12 parts of core-shell structured colored inorganic pigment, 1-6 parts of rare earth weather-resistant complex, 2-3 parts of additives, and 3-8 parts of curing agent; the mixed solvent is a mixture of butyl acetate and propylene glycol methyl ether acetate in a mass ratio of 2:1; the additives include dispersant, defoamer, and leveling agent in a mass ratio of 2:1:1; and the curing agent is an aliphatic isocyanate trimer.

[0038] The gradient thermosetting process described in step S4 is as follows: First, the temperature is raised to 90-110℃ at a rate of 3-5℃ / min and held for 15-25min to allow the solvent in the coating to evaporate slowly and fully, while the active groups between each layer undergo a preliminary cross-linking reaction; then, the temperature is raised to 130-150℃ at a rate of 2-3℃ / min and held for 25-40min to allow the surface resin to fully cure and the cross-linking reaction between each layer to fully proceed, forming a stable interpenetrating cross-linked network structure; after the heat preservation is completed, the oven is closed, and the profile is allowed to cool naturally to room temperature in the oven to avoid rapid cooling that could cause internal stress in the coating and lead to cracking.

[0039] The substrate used in the following embodiments and comparative examples of this invention is 6063-T5 architectural aluminum alloy profile. The sample size is 100mm×50mm×1mm. The parameters of the basic pretreatment process for all samples are kept consistent to ensure the comparability of the test results. Performance tests are conducted according to current national standards, specifically as follows: coating adhesion is tested using the cross-cut test (GB / T 9286-1998); neutral salt spray resistance is tested using GB / T 1771-2007; antifungal performance is tested using GB / T 21866-2008, with test species being *Aspergillus niger*, *Aspergillus flavus*, *Aspergillus terreus*, and *Trichoderma viride*; artificial weathering resistance is tested using GB / T 1865-2009; coating water contact angle is tested using a contact angle meter; antifungal durability is evaluated using a combination of a wash resistance test and an antifungal test, with the wash resistance test performed according to GB / T 9266-2009.

[0040] Example 1: This example provides a composite coating for anti-mildew colored aluminum alloy profiles and its preparation method. The specific steps are as follows: First, a micro-nano texturing pretreatment of the aluminum alloy profile is performed. The specific process is as follows: An alkaline degreasing agent is prepared, consisting of 40 g / L sodium hydroxide, 20 g / L anhydrous sodium carbonate, 5 g / L OP-10 emulsifier, and the remainder being deionized water. The aluminum alloy profile is completely immersed in the alkaline degreasing agent at 50°C and kept at that temperature for 10 minutes to thoroughly remove rolling oil, grease, and organic impurities from the profile surface. After removal, it is rinsed with running tap water for 3 minutes to remove any residual degreasing agent. Then, a chemical micro-etching texturing micro-etching solution is prepared, consisting of 15 g / L sodium hydroxide, 5 g / L sodium fluoride, 2 g / L sodium gluconate, and the remainder being deionized water. The degreased profile is immersed in the micro-etching solution at 40°C and kept at that temperature for 5 minutes. Chemical micro-etching constructs a uniform micro-nano-scale rough texture on the aluminum alloy surface, with the roughness Ra controlled between 0.8-1.2 μm. After removal, the surface is rinsed with running tap water for 2 minutes to remove residual micro-etching solution. The profile is then immersed in a 100 g / L nitric acid solution and brightened at room temperature for 30 seconds to remove the dust and residual natural oxide film generated during micro-etching, exposing a fresh and clean aluminum substrate. After removal, the surface is rinsed with running tap water for 2 minutes, followed by ultrasonic cleaning in deionized water for 5 minutes to thoroughly remove residual acid and impurities. Finally, the surface of the profile is completely dried with clean, dry, and cool air, avoiding secondary contamination of the substrate surface by fingers or oil throughout the process, resulting in a pretreated substrate with a uniform micro-nano texture.

[0041] Next, a rare earth-silane-phytic acid-dopamine composite passivation transition layer is prepared. The specific steps are as follows: Based on 1L of treatment solution, accurately weigh 0.6g of cerium nitrate, 18g of γ-aminopropyltriethoxysilane (KH550), 3g of phytic acid, 2g of dopamine, and 300g of anhydrous ethanol, with the remainder being deionized water; add the above components to the deionized water in sequence, stir evenly, adjust the pH of the treatment solution to 5.0 with glacial acetic acid, and continue stirring at room temperature for 30min to allow the silane coupling agent to undergo preliminary hydrolysis, thereby obtaining a uniform and stable composite passivation treatment solution. The pretreated aluminum alloy profile was completely immersed in the passivation solution, and the solution temperature was controlled at 35℃ for in-situ chelation and condensation reaction for 20 minutes. During this process, cerium ions in cerium nitrate selectively deposited at active defect sites on the aluminum alloy surface, forming a cerium oxide / hydroxide corrosion inhibitor film that precisely seals the pitting pores of the aluminum alloy. The silanol groups formed by the hydrolysis of KH550 undergo dehydration condensation with the hydroxyl groups on the aluminum alloy substrate surface and the hydroxyl groups of cerium oxide to form stable Si-O-Al and Si-O-Ce bonds. Phytic acid undergoes strong chelation with aluminum and cerium ions to form a dense chelated protective film. Dopamine forms a strong bond with the substrate and silane film through catechol groups, while introducing a large number of phenolic hydroxyl groups into the film layer. Finally, a dense and continuous three-dimensional network passivation film is formed on the aluminum alloy surface. After the reaction is complete, the profile is removed and the surface is rinsed three times with anhydrous ethanol to completely remove any unreacted residual liquid. Then, it is placed in an electric heating oven and pre-cured at 70°C for 10 minutes to allow the passivation film to further condense and cross-link, ultimately forming a composite passivation transition layer on the substrate surface. According to ellipsometry testing, the thickness of the passivation layer is approximately 150 nm, and the surface is rich in a large number of active hydroxyl and phenolic hydroxyl groups.

[0042] Then, an antifungal mesoporous functional intermediate layer containing dynamically cross-linked groups was prepared. The specific steps were as follows: First, a grafted modified antifungal agent-loaded mesoporous silica dispersion was prepared. 20 parts by weight of tetraethyl orthosilicate, 100 parts by weight of anhydrous ethanol, 30 parts by weight of deionized water, and 0.5 parts by weight of concentrated hydrochloric acid were accurately weighed and added sequentially to a reactor equipped with a stirring and temperature control device. The temperature was controlled at 40℃, and the mixture was stirred at 300 r / min for 2 hours to hydrolyze, resulting in a uniform and transparent silica sol. 5 parts by weight of the template agent hexadecyltrimethylammonium bromide (CTAB) were added to the silica sol, and stirring was continued for 30 minutes until completely dissolved. Then, the system was heated to 60℃ and the reaction was maintained at this temperature for 4 hours. Tetraethyl orthosilicate was fully condensed under the guidance of a template agent to form a silica precursor with an ordered mesoporous structure. Eight parts of tributyldodecylphosphonium chloride were added to the reaction system, and the mixture was stirred at 60°C for 6 hours to allow the quaternary phosphonium salt antifungal agent to fully diffuse into the pores of the mesoporous silica, completing the loading. Then, ten parts of bis-(3-triethoxysilylpropyl)disulfide were added to the reaction system, and the mixture was kept at 60°C for 3 hours to allow the silanol groups formed by the hydrolysis of the silane coupling agent to undergo dehydration condensation with the hydroxyl groups on the surface of the mesoporous silica, completing the grafting modification. Finally, a dispersion of antifungal mesoporous silica grafted with a disulfide-bonded silane coupling agent was obtained. The dispersion was diluted with anhydrous ethanol to a solid content of 10%, and after stirring evenly, an intermediate coating solution was obtained. A precision roller coater was used to uniformly coat the intermediate layer coating liquid onto the surface of the aluminum alloy profile with the prepared passivation transition layer, controlling the wet film thickness to 35 μm. After coating, the profile was placed in an oven and pre-cured at 80°C for 15 min to allow the solvent to fully evaporate. At the same time, the silane coupling groups grafted on the surface of the mesoporous silica undergo a preliminary cross-linking reaction with the active hydroxyl groups on the surface of the passivation transition layer, ultimately forming a mesoporous functional intermediate layer. The dry film thickness of the intermediate layer was measured to be approximately 3.5 μm by an eddy current thickness gauge.

[0043] Next, a hydrophobic colored protective layer was prepared. The specific steps were as follows: First, the topcoat solution was prepared. Accurately weigh 50 parts by weight of fluorinated siloxane-modified acrylate resin (fluorine content 12%, hydroxyl value 40 mg KOH / g), 20 parts of butyl acetate, 10 parts of propylene glycol methyl ether acetate, 1 part of dispersant, 0.5 parts of defoamer, and 0.5 parts of leveling agent. The above components were then added sequentially to a high-speed dispersion vessel and stirred at 800 r / min for 10 min until homogeneous. Then, 8 parts of a core-shell structured iron oxide red inorganic pigment were added to the system. The core of this pigment is α-Fe₂O₃ red inorganic pigment, and the outer shell is... The nano-silica coating layer has an average pigment particle size of 350 nm. After adding the pigment, the dispersion rate is increased to 2000 r / min, and high-speed dispersion is carried out for 30 min until the pigment fineness is ≤20 μm as tested by a scraper fineness meter, ensuring that the pigment is uniformly dispersed in the resin matrix. Then, 2 parts of cerium organic carboxylic acid complex are added to the system, and stirring is continued at 1000 r / min for 10 min until uniformly mixed. Finally, 5 parts of hexamethylene diisocyanate (HDI) trimer curing agent are added to the system, and stirring is carried out at 800 r / min for 10 min until uniformly mixed. After filtration, the topcoat liquid is obtained. The topcoat liquid is uniformly coated onto the surface of the aluminum alloy profile with the prepared mesoporous functional intermediate layer using a precision roller coater, and the wet film thickness is controlled at 110 μm. After coating, the profile is placed horizontally at room temperature for 10 min to level, allowing the solvent in the coating to evaporate initially and eliminating roller marks and bubbles on the coating surface.

[0044] Finally, a gradient thermosetting process is performed. The specific process is as follows: The leveled aluminum alloy profile is placed in a programmable temperature-controlled oven. First, the temperature is increased to 100℃ at a rate of 4℃ / min and held for 20 minutes. This stage allows the residual solvent in the coating to evaporate slowly and completely, preventing rapid solvent evaporation that could lead to pinholes, blistering, and other defects. Simultaneously, the active groups between the layers undergo a preliminary cross-linking reaction, forming basic interlayer bonding. Then, the temperature is increased to 140℃ at a rate of 3℃ / min and held for 30 minutes. This stage allows the surface resin matrix to undergo a full cross-linking and curing reaction, while the hydroxyl groups in the surface resin and the mesoporous dioxide in the intermediate layer also undergo cross-linking and curing. A thorough dehydration condensation reaction occurs between the silanol groups on the silicon surface and the active hydroxyl groups on the passivation layer surface. Disulfide bonds also participate in the cross-linking reaction, ultimately forming a stable interpenetrating cross-linked network structure of silicon-oxygen bonds and disulfide bonds, making the three coating layers form a chemically bonded organic whole. After the heat preservation is completed, the oven power is turned off, and the profile is allowed to cool naturally to room temperature in the oven to avoid rapid cooling causing internal stress in the coating, resulting in cracking, peeling, and other problems. Finally, the composite coating of the anti-mildew colored aluminum alloy profile of this embodiment is obtained. According to the test, the surface dry film thickness is about 24 μm, the total thickness of the overall composite coating is about 27.5 μm, and the surface water contact angle is 120°.

[0045] The composite coating prepared in this embodiment underwent comprehensive performance testing, and the results are as follows: the coating adhesion test reached level 0 in the cross-cut adhesion test; after 1200 hours of neutral salt spray testing, the coating showed no blistering, peeling, or rusting, and no erosion spread at the crisscrossed areas; the anti-mold performance test reached level 0, with 0% mold growth area; after 1000 hours of artificial weathering aging test, the coating showed no chalking, cracking, or peeling, and the color difference ΔE ≤ 1.2; after 1000 cycles of washing resistance test, the coating showed no significant wear, and the anti-mold level remained at level 0, demonstrating extremely excellent long-lasting anti-mold performance and comprehensive protective performance.

[0046] Example 2: This example provides a composite coating for anti-mold colored aluminum alloy profiles and its preparation method. The core difference from Example 1 lies in the adjustment of the micro-nano texturing process, the rare earth system of the composite passivation layer, the anti-mold agent and grafting process of the mesoporous intermediate layer, and the resin and pigment system of the surface layer, in order to achieve higher weather resistance and hydrophobicity. The specific steps are as follows: In this embodiment, the alkaline degreasing, brightening, cleaning and drying processes for aluminum alloy profiles are completely consistent with those in Example 1. The only adjustment is the chemical micro-etching texturing process: the micro-etching solution consists of 18 g / L sodium hydroxide, 6 g / L sodium fluoride, and 2.5 g / L sodium gluconate. The processing temperature is 42°C, and the processing time is 6 min. The roughness Ra of the prepared micro-nano texture is controlled at 1.0-1.5 μm, which further enhances the mechanical anchoring bond between the substrate and the passivation layer.

[0047] In the preparation of the composite passivation transition layer, based on 1L of treatment solution, the components are: 0.5g cerium chloride, 0.3g lanthanum nitrate, 22g KH550, 4g phytic acid, 2g dopamine, 320g anhydrous ethanol, with the balance being deionized water. The pH value was adjusted to 4.8. The in-situ chelation condensation reaction temperature was 38℃, and the reaction time was 25min. The pre-curing temperature was 75℃, and the time was 10min. This embodiment uses a cerium-lanthanum composite rare earth system, which can form a denser corrosion-inhibiting film with better corrosion inhibition performance than a single cerium salt system. At the same time, the amount of phytic acid added is increased, further enhancing the chelation protection effect. The final thickness of the prepared composite passivation transition layer is approximately 180nm.

[0048] In the preparation of the mesoporous functional intermediate layer, by weight, 22 parts of tetraethyl orthosilicate, 110 parts of anhydrous ethanol, 32 parts of deionized water, and 0.6 parts of concentrated hydrochloric acid were hydrolyzed to obtain a silica sol; 6 parts of CTAB were added, and the mixture was reacted at 60℃ for 4 h to obtain a mesoporous precursor; 10 parts of triphenylhexadecylphosphonium chloride were added, and the mixture was stirred at 60℃ for 7 h to complete the loading; then 12 parts of bis-(3-triethoxysilylpropyl)disulfide were added, and the mixture was reacted at 60℃ for 3.5 h to complete the grafting modification, resulting in a dispersion. The dispersion was diluted to a solid content of 12% to obtain the intermediate layer coating solution. The wet film thickness was 40 μm after roller coating, and the film was pre-cured at 85℃ for 15 min. The dry film thickness of the prepared mesoporous functional intermediate layer was approximately 4.5 μm. The triphenylhexadecylphosphonium chloride used in this embodiment has superior temperature resistance and hydrolysis resistance, is suitable for higher curing temperatures, and increases the grafting amount of silane coupling agent, further enhancing interlayer bonding and self-healing properties.

[0049] In the preparation of the hydrophobic colored protective coating, the components, by weight, are: 55 parts of fluorinated siloxane-modified acrylate resin (fluorine content 16%, hydroxyl value 38 mg KOH / g), 22 parts of butyl acetate, 11 parts of propylene glycol methyl ether acetate, 1.2 parts of dispersant, 0.6 parts of defoamer, and 0.6 parts of leveling agent. After mixing evenly, 10 parts of core-shell cobalt blue inorganic pigment are added. The pigment core is CoAl2O4 cobalt blue inorganic pigment, and the outer shell is a silica coating layer with an average particle size of 400 nm. The pigment is dispersed at 2000 r / min for 30 min until the fineness is ≤20 μm. Then, 3 parts of praseodymium organic carboxylic acid complex are added and stirred evenly. Finally, 6 parts of isophorone diisocyanate (IPDI) trimer are added and stirred evenly to obtain the topcoat liquid. The wet film thickness of the roller coating is 120 μm, and the leveling is carried out at room temperature for 15 min.

[0050] The gradient thermosetting process was adjusted as follows: first, the temperature was increased to 110℃ at a rate of 5℃ / min and held for 20 min; then, the temperature was increased to 145℃ at a rate of 3℃ / min and held for 30 min; finally, the temperature was allowed to cool naturally to room temperature. The final composite coating had a dry film thickness of approximately 26 μm, an overall coating thickness of approximately 30.5 μm, and a surface water contact angle of 126°.

[0051] The composite coating prepared in this embodiment was subjected to performance tests, and the results are as follows: coating adhesion grade 0 in cross-cut adhesion test; no blistering, peeling, or corrosion in neutral salt spray test after 1500 hours; grade 0 in anti-mold performance test, with 0% mold growth area; no chalking or cracking in artificial weathering aging test after 1500 hours, with a color difference ΔE ≤ 1.0; after 1500 wash tests, the anti-mold grade is still 0, demonstrating superior weather resistance, hydrophobicity, and long-lasting anti-mold performance compared to Example 1.

[0052] Example 3: This example provides a composite coating for anti-mold colored aluminum alloy profiles and its preparation method. The core difference from Example 1 is the use of a compounded quaternary phosphonium salt anti-mold agent and a silicon-aluminum composite mesoporous carrier, and the optimization of the rare earth complex addition amount in the surface layer to achieve better broad-spectrum anti-mold performance and long-lasting effect. The specific steps are as follows: The aluminum alloy profile pretreatment process in this embodiment is completely consistent with that in Embodiment 1, ensuring that the substrate condition is consistent.

[0053] In the preparation of the composite passivation transition layer, based on 1L of treatment solution, the components are: 0.7g cerium nitrate, 16g KH550, 4g KH560, 3.5g phytic acid, 1.8g dopamine, 280g anhydrous ethanol, with the balance being deionized water. The pH was adjusted to 5.2. The in-situ chelation condensation reaction temperature was 32℃, and the reaction time was 22min. The pre-curing temperature was 65℃, and the time was 12min. In this embodiment, a compound silane coupling agent was used, which can provide more active groups and further enhance the interlayer bonding force. The final thickness of the prepared composite passivation transition layer is approximately 120nm.

[0054] In the preparation of the mesoporous functional intermediate layer, 18 parts by weight of tetraethyl orthosilicate, 5 parts by weight of aluminum isopropoxide, 105 parts by weight of anhydrous ethanol, 30 parts by weight of deionized water, and 0.4 parts by weight of concentrated nitric acid were added to a reaction vessel and hydrolyzed at 40°C for 3 h to obtain a silica-alumina composite mesoporous precursor. 5.5 parts by weight of CTAB were added, and after stirring evenly, the mixture was heated to 60°C and reacted for 4.5 h to form a composite mesoporous support. 9 parts by weight of a mixture of tributyldodecylphosphonium chloride and triphenylhexadecylphosphonium chloride (mass ratio 1:1) were added and stirred at 60°C for 7 h to complete the loading. Then, 11 parts by weight of bis-(3-triethoxysilylpropyl)disulfide were added and reacted at 60°C for 3 h to complete the grafting modification, obtaining a dispersion. The dispersion was diluted to a solid content of 9% to obtain the intermediate layer coating solution. The wet film thickness was 30 μm after roller coating, and the film was pre-cured at 75°C for 15 min. The dry film thickness of the prepared mesoporous functional intermediate layer was approximately 3 μm. The silica-alumina composite mesoporous carrier used in this embodiment has a higher loading capacity and better thermal stability. The compounded quaternary phosphonium salt antifungal agent has a broader antifungal spectrum and a better killing effect on a variety of molds.

[0055] In the preparation of the hydrophobic colored protective coating, the components, by weight, are: 48 parts of fluorinated siloxane-modified acrylate resin (fluorine content 13%, hydroxyl value 42 mg KOH / g), 19 parts of butyl acetate, 9.5 parts of propylene glycol methyl ether acetate, 0.9 parts of dispersant, 0.45 parts of defoamer, and 0.45 parts of leveling agent. After mixing evenly, 7 parts of core-shell structured cerium praseodymium yellow rare earth colored inorganic pigment are added. The pigment core is a Ce-Pr-O composite oxide yellow pigment, and the outer shell is a silica coating layer with an average particle size of 300 nm. It is dispersed at high speed of 2000 r / min for 30 min until the fineness is ≤20 μm. Then, 3 parts of cerium organic carboxylic acid complex are added and stirred evenly. Finally, 4.5 parts of HDI trimer are added and stirred evenly to obtain the topcoat liquid. The wet film thickness of the roller coating is 100 μm, and the leveling is carried out at room temperature for 10 min.

[0056] The gradient thermosetting process is exactly the same as in Example 1. The final composite coating surface dry film thickness is about 22 μm, the overall coating thickness is about 25 μm, and the surface water contact angle is 118°.

[0057] The composite coating prepared in this embodiment was subjected to performance tests, and the results are as follows: coating adhesion grade 0 in cross-cut adhesion test; no blistering, peeling, or corrosion in neutral salt spray test after 1300 hours; grade 0 in antifungal performance test, with a kill rate of 99.99% against 8 common molds; no chalking or cracking in artificial weathering aging test after 1000 hours, with a color difference ΔE ≤ 1.1; after 1200 wash resistance tests, the antifungal grade is still grade 0, demonstrating extremely excellent broad-spectrum antifungal performance and long-lasting effect.

[0058] Comparative Example 1: This comparative example is a conventional single-layer anti-mold fluorocarbon coating in the prior art, as detailed below: The substrate and pretreatment process only used conventional alkaline degreasing and nitric acid brightening, without micro-nano texturing treatment, and the rest was the same as in Example 1; the fluorocarbon coating liquid was prepared, and the components by mass parts were: 50 parts polyvinylidene fluoride resin, 30 parts butyl acetate, 1 part dispersant, 0.5 parts defoamer, 0.5 parts leveling agent, 3 parts nano silver antibacterial agent, 8 parts iron oxide red pigment, and 5 parts curing agent. After being mixed evenly, the coating liquid was obtained; the coating liquid was coated on the surface of the pretreated aluminum alloy profile by roller coating, with a wet film thickness of 130 μm. After leveling at room temperature for 10 min, it was directly placed in a 140℃ oven for 40 min for curing to obtain a single-layer anti-mildew coating with a dry film thickness of about 27 μm, which was the same as the total thickness in Example 1.

[0059] The coating of this control example was subjected to performance tests, and the results are as follows: the coating adhesion was grade 1 in the cross-cut adhesion test; edge corrosion and blistering appeared after 500 hours of neutral salt spray test; the initial anti-mold performance was grade 0, and after 500 cycles of washing, the anti-mold grade dropped to grade 2, with mold growth area of ​​10%-30%; obvious chalking appeared after 1000 hours of artificial weathering test, with a color difference ΔE ≥ 3.2; the water contact angle was 92°, which is much lower than that of Examples 1-3.

[0060] Comparative Example 2 differs from Example 1 only in that no micro-nano texturing pretreatment was performed, and conventional commercial zirconium-titanium chromium-free passivating agent was used for passivation treatment. The rare earth-silane-phytic acid-dopamine composite passivation system of the present invention was not used. All other components and processes are completely consistent with Example 1.

[0061] The coating of this control example was subjected to performance tests, and the results are as follows: the coating adhesion was grade 2 in the cross-cut test; after 600 hours of neutral salt spray test, interlayer peeling and blistering occurred; the initial anti-mildew performance was grade 0, and after 800 cycles of washing, the anti-mildew performance dropped to grade 2; after 1000 hours of artificial weathering test, the color difference ΔE was ≥2.6, and slight peeling occurred at the edge of the coating.

[0062] Comparative Example 3: The only difference between this comparative example and Example 1 is that no mesoporous functional intermediate layer was prepared, and an equal amount of tributyldodecylphosphonium chloride antifungal agent was directly added to the topcoat liquid. The other components and processes are completely consistent with Example 1.

[0063] The coating of this control example was subjected to performance tests, and the results are as follows: the coating adhesion was grade 1 in the cross-cut test; blistering occurred after 700 hours of neutral salt spray test; the initial anti-mold performance was grade 0, and the anti-mold grade dropped to grade 3 after 500 washes, with mold growth area of ​​30%-60%; the anti-mold agent showed obvious precipitation, the water contact angle was 102°, and the color difference ΔE was ≥2.3 after 1000 hours of artificial weathering test.

[0064] Comparative Example 4: The only difference between this comparative example and Example 1 is that the mesoporous silica surface was not grafted with a silane coupling agent containing disulfide bonds, and only conventional KH550 was used for grafting modification. The other components and processes are completely consistent with Example 1.

[0065] The coating of this control example was subjected to performance tests, and the results are as follows: the coating adhesion was grade 1 in the cross-cut adhesion test; after 800 hours of neutral salt spray test, the coating showed microcracks and blistering; the initial anti-mildew performance was grade 0, and the anti-mildew performance dropped to grade 1 after 1000 cycles of washing; the color difference ΔE was ≥1.8 in the artificial weathering test after 1000 hours, and there was no self-healing performance, and the microcracks could not be repaired by themselves.

[0066] The performance comparison between the examples and the control examples clearly shows that the composite coating prepared by the present invention is far superior to the control examples of the prior art in terms of interlayer adhesion, corrosion resistance, long-term anti-mildew performance, weather resistance and color retention, and hydrophobicity, which fully demonstrates the advanced nature and significant beneficial effects of the technical solution of the present invention.

[0067] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite coating for anti-mildew colored aluminum alloy profiles, characterized in that, It includes a rare earth-silane-phytic acid-dopamine composite passivation transition layer constructed from the inside out on the micro-nano textured surface of the aluminum alloy profile substrate, a fungicide-resistant mesoporous functional intermediate layer containing dynamic cross-linking groups chemically bonded to the surface of the passivation transition layer, and a hydrophobic colored sealing layer cross-linked and cured on the surface of the mesoporous functional intermediate layer. The composite passivation transition layer is a chromium-free mesh passivation film formed by the in-situ chelation and condensation of rare earth salts, aminosilane coupling agents, phytic acid and dopamine, with a thickness of 80-250 nm. The surface of the passivation film is rich in active hydroxyl and phenolic hydroxyl groups. The mesoporous functional intermediate layer uses mesoporous silica as a carrier, loads quaternary phosphonium salt-type antifungal agents in the mesoporous channels, and grafts disulfide-bonded silane coupling agents onto the surface of the mesoporous silica. The dry film thickness of the intermediate layer is 2-6 μm. The hydrophobic colored protective layer uses fluorinated siloxane-modified acrylate resin as the film-forming matrix. Core-shell structured colored inorganic pigments and rare earth weather-resistant complexes are uniformly dispersed in the matrix. The surface layer and the intermediate layer form an interpenetrating cross-linked network structure through disulfide bonds and silicon-oxygen bonds. The dry film thickness of the surface layer is 15-35 μm, and the water contact angle is ≥115°.

2. The composite coating for anti-mildew colored aluminum alloy profiles according to claim 1, characterized in that: The rare earth salt of the composite passivation transition layer is one or more of cerium nitrate, cerium chloride, or lanthanum nitrate, the aminosilane coupling agent is γ-aminopropyltriethoxysilane, the mass ratio of phytic acid to dopamine is 1:1-2:1, and the mass percentage of rare earth elements in the passivation film is 3%-10%.

3. The composite coating for anti-mildew colored aluminum alloy profiles according to claim 1, characterized in that: The disulfide-containing silane coupling agent is bis-(3-triethoxysilylpropyl) disulfide, and its grafting amount is 20%-45% of the mass of mesoporous silica; The quaternary phosphonium salt type antifungal agent is one or a combination of two of tributyldodecylphosphonium chloride and triphenylhexadecylphosphonium chloride, and its mass accounts for 12%-35% of the total mass of the mesoporous functional intermediate layer.

4. The composite coating for anti-mold colored aluminum alloy profiles according to claim 1, characterized in that: The fluorine content of the fluorinated siloxane-modified acrylate resin is 10%-20%, and the hydroxyl value is 35-55 mgKOH / g. The core of the core-shell structured colored inorganic pigment is an iron-based, cobalt-based, or rare-earth-based colored inorganic pigment, and the outer shell is a silica coating layer. The pigment particle size is 200-800 nm.

5. The composite coating for anti-mold colored aluminum alloy profiles according to claim 1, characterized in that: The rare earth weather-resistant complex is an organic carboxylic acid complex of cerium or praseodymium, and the total mass of the core-shell structured colored inorganic pigment and the rare earth weather-resistant complex accounts for 6%-18% of the total mass of the surface layer.

6. A method for preparing a composite coating for an anti-mold colored aluminum alloy profile according to any one of claims 1-5, characterized in that, Includes the following steps: S1 aluminum alloy profile micro-nano texturing pretreatment: The aluminum alloy profile is subjected to alkaline degreasing, chemical micro-etching texturing, nitric acid brightening, multi-stage cleaning and cold air drying in sequence to obtain a pretreated substrate with a uniform micro-nano rough texture on the surface. Preparation of S2 composite passivation transition layer: Prepare rare earth-silane-phytic acid-dopamine composite passivation treatment solution, immerse the pretreated substrate in the treatment solution for in-situ chelation and condensation reaction, take it out and rinse with anhydrous ethanol, and then perform low-temperature pre-curing to form a composite passivation transition layer on the substrate surface. Preparation of S3 mesoporous functional intermediate layer: Prepare a mesoporous silica dispersion of quaternary phosphonium salt antifungal agent grafted with disulfide bond silane coupling agent, dilute with anhydrous ethanol to a set solid content to obtain intermediate layer coating liquid, coat it on the surface of passivation transition layer, and form mesoporous functional intermediate layer after pre-curing. Preparation of S4 hydrophobic colored protective coating: Prepare a coating liquid containing core-shell structured colored inorganic pigments and rare earth weather-resistant complexes, apply it to the surface of the mesoporous functional intermediate layer, level it at room temperature and then perform gradient thermal curing to finally obtain the composite coating.

7. The preparation method according to claim 6, characterized in that: The chemical micro-etching texturing treatment in step S1 uses a micro-etching solution with the following components: sodium hydroxide 10-20 g / L, sodium fluoride 3-8 g / L, sodium gluconate 1-3 g / L, and the remainder is deionized water. The treatment temperature is 35-45℃ and the treatment time is 3-8 min.

8. The preparation method according to claim 6, characterized in that: The components of the composite passivation treatment solution in step S2, per 1L, include: 0.3-1.0 g / L rare earth salt, 10-25 g / L aminosilane coupling agent, 2-5 g / L phytic acid, 1-3 g / L dopamine, 200-350 g / L anhydrous ethanol, with the balance being deionized water. The pH of the treatment solution is adjusted to 4.0-5.5 with glacial acetic acid. The in-situ chelation condensation reaction temperature is 25-40℃, and the reaction time is 15-30 min. The pre-curing temperature is 60-80℃, and the time is 5-15 min.

9. The preparation method according to claim 6, characterized in that: The preparation method of the mesoporous silica dispersion in step S3 is as follows: tetraethyl orthosilicate, anhydrous ethanol, deionized water and acidic catalyst are mixed and hydrolyzed to obtain silica sol; a template agent, hexadecyltrimethylammonium bromide, is added and the mixture is heated to obtain a mesoporous silica precursor; a quaternary phosphonium salt-type antifungal agent is added and stirred for loading; then a silane coupling agent containing disulfide bonds is added for grafting modification reaction to finally obtain the dispersion.

10. The preparation method according to claim 6, characterized in that: The gradient thermosetting process described in step S4 is as follows: first, heat the temperature to 90-110℃ at a rate of 3-5℃ / min and hold for 15-25min; then heat the temperature to 130-150℃ at a rate of 2-3℃ / min and hold for 25-40min; after the holding period, allow the temperature to cool naturally to room temperature.

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