A waterborne metallic coating and a method for preparing the same

Abstract

The present application relates to the technical field of paint, in particular to a kind of water-based metal paint and its preparation method, by weight parts includes: water-based modified acrylic resin 30~60 parts, fluorine silicon phosphorus hybrid nano penetrating agent 3~10 parts, composite crosslinking agent 3~8 parts, metal pigment 5~20 parts, nano filler 3~15 parts, substrate wetting agent 0.5~2 parts, orientation agent 0.5~2 parts, corrosion inhibitor 0.2~1 part, cosolvent 2~5 parts, defoaming agent 0.2~1 part, dispersing agent 0.5~2 parts, deionized water 10~25 parts.The present application relies on the chemical anchoring of fluorine silicon phosphorus hybrid nano penetrating agent, physical penetration, triple synergistic effect of nano roughening, and is matched with water-based modified acrylic resin modified by organic silicon and phosphate double, so that the adhesion of paint on the surface of aluminum material is improved, and the peeling, peeling, blistering and delamination phenomenon of paint on the surface of aluminum material is avoided.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to a water-based metallic coating and its preparation method. Background Technology

[0002] Aluminum and its alloys are widely used in defense, aerospace, transportation, instrumentation, machinery, electronic devices, and home decoration due to their excellent corrosion resistance, electrical and thermal conductivity, and ease of processing and forming. However, aluminum is chemically highly reactive and readily oxidizes when directly exposed to air, rapidly forming a dense aluminum oxide film on its surface. This oxide film is inert to atmospheric corrosion, providing basic protection, but it is precisely this inertness that makes it difficult for coatings to adhere firmly to aluminum surfaces. Traditionally, the industry has used solvent-based coatings and powder coatings to coat aluminum profiles for protection and decoration. However, oil-based coatings release volatile organic compounds such as benzene and aldehydes during production, formulation, and application, seriously impacting human health and the environment. With increasingly stringent environmental regulations, water-based coatings, which use water instead of solvents, have been recognized as green coatings and have become the mainstream direction for industry development.

[0003] However, when existing water-based coatings are applied to aluminum, the high surface tension of water, which has poor wetting properties on the substrate, necessitates the addition of a substrate wetting agent to reduce surface tension and ensure effective coating spread on the aluminum surface. Furthermore, after the water-based coating is applied to the aluminum surface, poor adhesion between the water-based metal coating and the aluminum substrate leads to problems such as coating peeling and blistering. Therefore, a new type of water-based metal coating needs to be designed. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a water-based metal coating and its preparation method.

[0005] The technical solution adopted in this invention is as follows: a water-based metallic coating, comprising, by weight: 30-60 parts of water-based modified acrylic resin, 3-10 parts of fluorosilicone-phosphorus hybrid nano-penetrating agent, 3-8 parts of composite crosslinking agent, 5-20 parts of metallic pigment, 3-15 parts of nanofiller, 0.5-2 parts of substrate wetting agent, 0.5-2 parts of orientation agent, 0.2-1 parts of corrosion inhibitor, 2-5 parts of co-solvent, 0.2-1 parts of defoamer, 0.5-2 parts of dispersant, and 10-25 parts of deionized water; wherein the water-based modified acrylic resin is a dual-modified acrylic resin of organosilicon and phosphate ester; wherein the fluorosilicone-phosphorus hybrid nano-penetrating agent is a hybrid nanoparticle with a core of 20-50nm nano-silica, a surface bonded with fluorinated alkyl chains, phosphate groups, and silane coupling agent segments.

[0006] As a further description of the above technical solution: The composite crosslinking agent is composed of an aqueous amino resin and a blocked isocyanate, wherein the mass ratio of the aqueous amino resin to the blocked isocyanate is 2-4:1; the aqueous amino resin is a methyl etherified melamine-formaldehyde resin or a mixed etherified melamine resin; and the blocked isocyanate is a methyl ethyl ketone oxime or an ε-caprolactam-blocked polymethylene polyphenyl isocyanate.

[0007] As a further description of the above technical solution: The preparation method of the fluorosilicon-phosphorus hybrid nano-penetrating agent includes the following steps: Amination of nano-silica surface: Nano-silica sol was added to anhydrous ethanol and ultrasonically dispersed for 15 min. The mass ratio of nano-silica sol to anhydrous ethanol was 1:6-8. Then, 0.15-0.25 times the mass of nano-silica and 3-aminopropyltriethoxysilane were added and reacted at 60 °C for 6 h. After centrifugation, washing and vacuum drying, amination of nano-silica was obtained. RAFT-polymerized grafted fluorophosphorus copolymer: First, aminated nano-silica is added to anhydrous ethanol and mixed, with a mass ratio of aminated nano-silica to anhydrous ethanol of 1:9-11. Then, 0.03-0.04 times the mass of aminated nano-silica, 2.0-2.5 times the mass of functional monomers, and 0.015-0.025 times the total mass of functional monomers, are added sequentially. Then, nitrogen is used to deoxygenate for 30 min, and the reaction is carried out at 70℃ for 12 h. After centrifugation, washing, and vacuum drying, grafted hybrid particles are obtained. Hydrolysis and condensation: The grafted hybrid particles are added to an ethanol-water solution for mixing. The mass ratio of the grafted hybrid particles to the ethanol-water solution is 1:12-14. The pH is adjusted to 9-10 with ammonia. The mixture is stirred at room temperature for 2 hours. After centrifugation, washing and drying, the fluorosilicon-phosphorus hybrid nano-penetrating agent is obtained.

[0008] As a further description of the above technical solution: The functional monomer is composed of perfluorooctyl ethyl acrylate and methacryloxyethyl phosphate, wherein the mass ratio of perfluorooctyl ethyl acrylate to methacryloxyethyl phosphate is 1:0.8-1.2; and the mass ratio of ethanol to water in the ethanol-water solution is 7:3.

[0009] As a further description of the above technical solution: The metallic pigment is an aqueous aluminum-silver paste with a surface coated with an organic phosphate passivation layer and a particle size of 10~40μm.

[0010] As a further description of the above technical solution: The nanofiller is hydrophobically modified nano-silica with a particle size of 20~80nm, which has been treated with an organosilane coupling agent on its surface; the substrate wetting agent is a polyether-modified polysiloxane surfactant, and the model is BYK-349.

[0011] As a further description of the above technical solution: The orientation agent is a polyamide wax paste, model AQH-800; the corrosion inhibitor is sodium nitrite; the co-solvent is one of dipropylene glycol butyl ether (DPnB), propylene glycol methyl ether (PM), and dipropylene glycol methyl ether (DPM); the defoamer is a polyether-modified polysiloxane defoamer, model DefomW-0506; and the dispersant is a high molecular weight block copolymer dispersant, model G-7190.

[0012] A method for preparing a water-based metallic coating, comprising the following steps: S1. Premixing: Add 60% to 80% of the total amount of deionized water to the dispersion vessel, add dispersant and defoamer while stirring at 300 to 500 r / min, and stir for 5 to 10 min; S2. Nanofiller dispersion: Add nanofiller, increase the stirring speed to 800~1200 r / min, and disperse for 15~30 min until the fineness is ≤20μm; S3. Mixing resin and penetrating agent: Reduce stirring speed to 400~600r / min, add water-based modified acrylic resin, and stir for 10min; then slowly add fluorosilicone-phosphorus hybrid nano-penetrating agent, and continue stirring for 15min until uniform. S4. Addition of functional additives: Add the substrate wetting agent and 50%~70% co-solvent in sequence, and stir for 5~10 minutes; S5. Adding crosslinking agent: Add the composite crosslinking agent and stir for 5-10 minutes; S6. Adjusting viscosity: Add the remaining deionized water to adjust the viscosity to 30~60s to obtain the main paint; S7. Addition of metallic pigments: Premix the metallic pigments with the remaining co-solvent, add the main paint while stirring at a low speed of 200~400r / min, then add the orientation agent and corrosion inhibitor, and stir for 10~15min; S8: Filtration: Filter with a 150~200 mesh filter to obtain water-based metal coating.

[0013] As a further description of the above technical solution: In step S3, the fluorosilicon-phosphorus hybrid nano-penetrating agent is pre-wetted with 10%~20% co-solvent before being added.

[0014] The present invention has the following beneficial effects: 1. This invention relies on the synergistic effect of chemical anchoring, physical penetration, and nano-roughening of fluorosilicone-phosphorus hybrid nano-penetrating agents, combined with water-based modified acrylic resin with dual modification of organosilicon and phosphate ester, to improve the adhesion of coatings on aluminum surfaces. This avoids peeling, flaking, blistering, and delamination of coatings on aluminum surfaces, and completely solves the industry problem of poor adhesion and rapid failure of traditional water-based coatings on aluminum surfaces under humid and hot environments. The coating and the substrate achieve molecular-level chemical bonding, and the interfacial bonding strength is far superior to that of physically adsorbed coatings.

[0015] 2. The fluorinated alkyl chains in the fluorosilicon-phosphorus hybrid nano-penetrating agent of this invention impart extremely low surface tension to the coating. Combined with the small size effect of 20-50nm nanoparticles, it can directly penetrate the dense inert alumina layer naturally formed on the surface of aluminum materials. Traditional complex pretreatment processes such as acid washing, alkali washing, deoxidation, phosphating, and hexavalent chromium chromating can be used to achieve a strong bond between the coating and the aluminum substrate. On the one hand, it saves the cost of pretreatment equipment, agents, and labor, thereby reducing construction costs. On the other hand, it avoids the use of strong acids, strong alkalis, and toxic chromates, eliminating environmental pollution and construction safety risks from the source.

[0016] 3. This invention uses water-based aluminum silver paste with an organic phosphate passivation layer on the surface, combined with sodium nitrite corrosion inhibitor and polyamide wax paste orienting agent to form a three-dimensional stable system, which can completely block the oxidation and hydrogen evolution reaction between aluminum powder and water-based system, and thoroughly overcome the core pain points of poor storage stability and poor decorative effect of water-based metal coatings.

[0017] 4. The three-dimensional dense cross-linked network formed by the composite cross-linking agent of this invention, combined with the filling and reinforcing effect of nanofillers, enables the coating film to have excellent scratch resistance, wear resistance, acid and alkali resistance, solvent resistance and good mechanical stability. It can protect the aluminum substrate from environmental corrosion for a long time, while maintaining an aesthetically pleasing metallic decorative effect, and meet the usage needs of different application scenarios. Detailed Implementation

[0018] The present invention provides a water-based metallic coating, comprising, by weight parts: 30-60 parts of water-based modified acrylic resin, which is an acrylic resin modified by both organosilicon and phosphate ester.

[0019] 3-10 parts of a fluorosilicon-phosphorus hybrid nano-penetrating agent are used. The fluorosilicon-phosphorus hybrid nano-penetrating agent consists of hybrid nanoparticles with a core of 20-50 nm silica, a surface-bonded fluorinated alkyl chain, phosphate groups, and silane coupling agent segments. The preparation method of the fluorosilicon-phosphorus hybrid nano-penetrating agent includes the following steps: Amination of nano-silica surface: Nano-silica sol was added to anhydrous ethanol and ultrasonically dispersed for 15 min. The mass ratio of nano-silica sol to anhydrous ethanol was 1:6-8. Then, 0.15-0.25 times the mass of nano-silica and 3-aminopropyltriethoxysilane were added and reacted at 60 °C for 6 h. After centrifugation, washing and vacuum drying, amination of nano-silica was obtained. RAFT-polymerized grafted fluorophosphorus copolymer: First, aminated nano-silica is added to anhydrous ethanol and mixed, with a mass ratio of aminated nano-silica to anhydrous ethanol of 1:9-11. Then, 0.03-0.04 times the mass of aminated nano-silica, 2.0-2.5 times the mass of functional monomers, and 0.015-0.025 times the total mass of functional monomers are added sequentially. Then, nitrogen is used to deoxygenate for 30 min, and the reaction is carried out at 70℃ for 12 h. After centrifugation, washing, and vacuum drying, grafted hybrid particles are obtained.

[0020] Hydrolysis and condensation: The grafted hybrid particles are added to an ethanol-water solution for mixing. The mass ratio of the grafted hybrid particles to the ethanol-water solution is 1:12-14. The pH is adjusted to 9-10 with ammonia. The mixture is stirred at room temperature for 2 hours. After centrifugation, washing and drying, the fluorosilicon-phosphorus hybrid nano-penetrating agent is obtained.

[0021] The functional monomers consist of perfluorooctyl ethyl acrylate and methacryloxyethyl phosphate, with a mass ratio of perfluorooctyl ethyl acrylate to methacryloxyethyl phosphate of 1:0.8-1.2; the mass ratio of ethanol to water in the aqueous ethanol solution is 7:3.

[0022] The composite crosslinking agent consists of 3-8 parts, which is composed of water-based amino resin and blocked isocyanate. The mass ratio of water-based amino resin to blocked isocyanate is 2-4:1. The water-based amino resin is methyl etherified melamine-formaldehyde resin or mixed etherified melamine resin. The blocked isocyanate is methyl ethyl ketone oxime or ε-caprolactam blocked polymethylene polyphenyl isocyanate.

[0023] 5-20 parts of metallic pigment, which is an aqueous aluminum silver paste with an organic phosphate passivation layer on the surface and a particle size of 10-40 μm.

[0024] 3-15 parts of nanofiller, which is hydrophobically modified nano-silica with a particle size of 20-80 nm, and the surface is treated with organosilane coupling agent.

[0025] 0.5 to 2 parts of substrate wetting agent, which is a polyether-modified polysiloxane surfactant with model number BYK-349.

[0026] 0.5 to 2 parts of orientation agent, which is polyamide wax paste and model AQH-800.

[0027] 0.2 to 1 part of corrosion inhibitor, the corrosion inhibitor is sodium nitrite.

[0028] The co-solvent consists of 2-5 parts, and the co-solvent is one of dipropylene glycol butyl ether (DPnB), propylene glycol methyl ether (PM), or dipropylene glycol methyl ether (DPM).

[0029] 0.2 to 1 part of defoamer, which is a polyether-modified polysiloxane defoamer with the model name DefomW-0506.

[0030] 0.5 to 2 parts of dispersant, which is a high molecular weight block copolymer dispersant with model number G-7190.

[0031] 10-25 parts deionized water.

[0032] A method for preparing a water-based metallic coating, comprising the following steps: S1. Premixing: Add 60% to 80% of the total amount of deionized water to the dispersion vessel, add dispersant and defoamer while stirring at 300 to 500 r / min, and stir for 5 to 10 min; S2. Nanofiller dispersion: Add nanofiller, increase the stirring speed to 800~1200 r / min, and disperse for 15~30 min until the fineness is ≤20μm; S3. Mixing the resin and penetrating agent: Reduce the stirring speed to 400~600r / min, add the water-based modified acrylic resin, and stir for 10min; then slowly add the fluorosilicone-phosphorus hybrid nano-penetrating agent (the fluorosilicone-phosphorus hybrid nano-penetrating agent is pre-wetted with 10%~20% co-solvent before being added), and continue stirring for 15min until uniform. S4. Addition of functional additives: Add the substrate wetting agent and 50%~70% co-solvent in sequence, and stir for 5~10 minutes; S5. Adding crosslinking agent: Add the composite crosslinking agent and stir for 5-10 minutes; S6. Adjusting viscosity: Add the remaining deionized water to adjust the viscosity to 30~60s to obtain the main paint; S7. Addition of metallic pigments: Premix the metallic pigments with the remaining co-solvent, add the main paint while stirring at a low speed of 200~400r / min, then add the orientation agent and corrosion inhibitor, and stir for 10~15min; S8: Filtration: Filter with a 150~200 mesh filter to obtain water-based metal coating.

[0033] The coating system of this invention achieves efficient penetration and firm adhesion to the oxide layer on the surface of aluminum materials through multi-level and multi-mechanism synergistic effects. The complete mechanism of adhesion enhancement is systematically explained below, starting from the surface characteristics of aluminum materials.

[0034] Characteristics and challenges of aluminum surface oxide layers The oxide film (Al2O3) that naturally forms on aluminum in the air is about 2-10 nm thick, with a dense structure and abundant hydroxyl groups (—Al—OH) and oxygen bridges (—Al—O—Al—). This oxide layer has high chemical inertness and low surface energy (about 40-50 mN / m), while the surface tension of water-based coatings is usually as high as 70 mN / m or more, making it difficult for the coating to wet and spread.

[0035] Chemical bonding mechanism: This invention achieves chemical bonding with aluminum through two pathways: (1) Phosphate anchoring provided by fluorosilicon-phosphorus hybrid nanoparticles: The phosphate groups (-PO4H2) on the surface of the fluorosilicon-phosphorus hybrid nano-penetrating agent partially ionize into -PO4 in water. 2- or -HPO4 - , with Al on the surface of alumina 3+ A coordination substitution reaction occurs, forming a PO-Al covalent bond. Further, the phosphate group reacts with the adjacent Al group... 3+ It forms a bidentate or tripentate chelate structure, which is far more stable than ordinary hydrogen bonds or van der Waals forces. The bond energy of this chemical bond is about 300~400 kJ / mol, which is much greater than the physical adsorption energy (about 10~50 kJ / mol). Therefore, it can resist the erosion of water molecules and other media, giving the coating excellent water-resistant adhesion.

[0036] (2) Carboxyl and hydroxyl groups provided by water-based modified acrylic resin: The water-based modified acrylic resin of this invention contains carboxyl groups (—COOH) and hydroxyl groups (—OH). The carboxyl groups can undergo esterification with the hydroxyl groups on the surface of alumina, or directly react with Al. 3+ Aluminum carboxylate coordination bonds are formed. Hydroxyl groups can form ether bonds through hydrogen bonding or condensation with surface hydroxyl groups. These polar groups have a high density in the resin (controlled by monomer ratio), which can produce a multi-point anchoring effect, so that even if individual bonds break, the overall adhesion is still maintained.

[0037] Physical penetration mechanism: The natural oxide film of aluminum is not completely dense; it contains numerous nanoscale micropores (pore size approximately 1-10 nm, porosity approximately 5%-15%). This invention utilizes the following design to achieve physical permeation: (1) Low surface tension drives permeation: The perfluoroalkyl chains (such as -CF3) on the surface of fluorosilicon-phosphorus hybrid nanoparticles have extremely low surface energy (approximately 6-8 mN / m). When introduced into coating systems, the overall surface tension can be reduced to 20-25 mN / m. According to Young's equation, the reduction in surface tension decreases the contact angle θ, making it easier for the coating to spread and penetrate into micropores.

[0038] (2) Nanoparticle size matching: The average particle size of the fluorosilicon-phosphorus hybrid nanoparticle penetrating agent is 45 nm, much larger than the micropores of the oxide film (1-10 nm), so the particles themselves cannot enter the micropores. However, the fluorocarbon segments on the particle surface are flexible molecular chains, about 2-5 nm in length, which can extend into the micropores like tentacles, drawing the resin components deep into the pores. After curing, these molecular chains form anchor points within the pores, producing a pinning effect.

[0039] Interface roughening and mechanical interlocking mechanism: (1) Micro-roughening of nanofillers: The nano-SiO2 (particle size 20-80 nm) and fluorosilicon-phosphorus hybrid nano-penetrating agent (particle size 45 nm) added in this invention are uniformly distributed at the coating-substrate interface after coating curing, forming micro-protrusions with a height of 20-80 nm, thus increasing the interface roughness. According to the mechanical interlocking theory, the increase in interface roughness can significantly increase the actual contact area and provide a structural basis for mechanical interlocking, thereby enhancing the interlocking effect between the coating and the substrate, effectively improving the interfacial bonding strength, and preventing the coating from peeling off along the interface under external force. These uniformly distributed micro- and nano-protrusions do not damage the original structural properties of the substrate, nor do they introduce additional defects; the adhesion is improved solely through interface morphology control.

[0040] (2) Rigid core effect of penetrant: The nano-SiO2 core of the fluorosilicon-phosphorus hybrid nano-penetrating agent is a rigid sphere, which is not easily deformed under external force. When the coating is subjected to peel stress, these rigid particles act as stress concentration and crack pinning agents, forcing the cracks to deflect around the particles, lengthening the crack propagation path, and thus increasing the peel resistance.

[0041] Cross-linked networks enhance cohesive strength: This invention utilizes a composite crosslinking agent (amino resin and blocked isocyanate) to react with the hydroxyl and carboxyl groups in a water-based modified acrylic resin, forming a high-density three-dimensional network structure. The cohesive strength of the crosslinked coating is significantly improved, and no coating chipping occurs at the cut edges during cross-cut testing. Furthermore, the silanol groups (Si-OH) on the surface of the fluorosilicon-phosphorus hybrid nano-penetrating agent can also participate in the crosslinking reaction, chemically bonding the penetrating agent to the resin network and avoiding the long-term performance degradation caused by the migration of small molecule additives.

[0042] Based on the above mechanisms, the complete path by which this invention achieves enhanced adhesion can be summarized as follows: Wetting stage: The fluorocarbon segments of the substrate wetting agent and the fluorosilicone-phosphorus hybrid nano-penetrating agent work together to reduce surface tension, enabling the coating to spread rapidly and penetrate into the micropores of the oxide film.

[0043] Anchoring stage: The phosphate groups of the fluorosilicon-phosphorus hybrid nano-penetrating agent and the carboxyl groups of the resin chemically bond with the alumina surface, forming multi-point anchoring.

[0044] Filling stage: The molecular chains of water-based modified acrylic resin are guided into the depths of micropores by the tentacles of fluorosilicone-phosphorus hybrid nano-penetrating agents, and form mechanical interlocking after curing.

[0045] Enhancement stage: Nanoparticles and fluorosilicon-phosphorus hybrid nano-penetrating agents form a micro-rough structure at the interface, increasing the contact area; cross-linked networks improve the cohesive strength of the coating.

[0046] Long-term effect: Fluorosilicon-phosphorus hybrid nano-penetrating agents are chemically bonded to the cross-linked network and will not migrate or precipitate, exhibiting excellent resistance to boiling water and salt spray.

[0047] Example 1 Coating components: 40 parts of water-based modified acrylic resin, 5 parts of fluorosilicone-phosphorus hybrid nano-penetrating agent, 5 parts of composite crosslinking agent (methyl etherified melamine-formaldehyde resin: ε-caprolactam blocked polymethylene polyphenyl isocyanate = 3:1), 10 parts of water-based passivating aluminum silver paste, 8 parts of hydrophobic modified nano silica, 1 part of polyether modified polysiloxane surfactant, 1 part of polyamide wax paste, 0.5 parts of sodium nitrite corrosion inhibitor, 3 parts of dipropylene glycol butyl ether, 0.5 parts of polyether modified polysiloxane defoamer, 1 part of high molecular weight block copolymer dispersant, and 20 parts of deionized water.

[0048] Preparation method: Premix: Add 14 parts of deionized water to the dispersion vessel, add dispersant and defoamer while stirring at 400 r / min, and stir for 8 min until uniform; Nanofiller dispersion: Add hydrophobically modified nano-silica, disperse at 1000 r / min for 20 min, and control the fineness to 15 μm; Mixing the resin and penetrating agent: Adjust the speed to 500 r / min, add water-based modified acrylic resin and stir for 10 min; add fluorosilicone-phosphorus hybrid nano-penetrating agent wetted with 0.5 parts dipropylene glycol butyl ether and stir for 15 min; Functional additives: Add substrate wetting agent and the remaining 2 parts of dipropylene glycol butyl ether, and stir for 8 minutes; Crosslinking agent addition: Add composite crosslinking agent and stir for 8 minutes; Viscosity adjustment: Add 6 parts of deionized water and adjust the viscosity to 40s to obtain the main paint; Adding metallic pigments: Premix water-based passivated aluminum silver paste with 0.5 parts of dipropylene glycol butyl ether, add it to the main paint at a low speed of 300 r / min, then add the orientation agent and corrosion inhibitor, and stir for 12 min; Filtration: Filtered through a 180-mesh filter to obtain the coating of Example 1.

[0049] Example 2 Coating components: 50 parts of water-based modified acrylic resin, 8 parts of fluorosilicone-phosphorus hybrid nano-penetrating agent, 6 parts of composite crosslinking agent (methyl etherified melamine-formaldehyde resin: ε-caprolactam blocked polymethylene polyphenyl isocyanate = 3:1), 15 parts of water-based passivating aluminum silver paste, 10 parts of hydrophobic modified nano silica, 1.2 parts of polyether-modified polysiloxane surfactant, 1.5 parts of polyamide wax paste, 0.6 parts of sodium nitrite corrosion inhibitor, 4 parts of dipropylene glycol butyl ether, 0.6 parts of polyether-modified polysiloxane defoamer, 1.2 parts of high molecular weight block copolymer dispersant, and 18 parts of deionized water.

[0050] Preparation method: Premix: Add 14.4 parts of deionized water to the dispersion vessel, add dispersant and defoamer while stirring at 450 r / min, and stir for 9 min until uniform; Nanofiller dispersion: Add hydrophobically modified nano silica, disperse at 1100 r / min for 25 min, and control the fineness to 18 μm; Mixing resin and penetrating agent: Adjust the speed to 550 r / min, add water-based modified acrylic resin and stir for 10 min; add fluorosilicone-phosphorus hybrid nano-penetrating agent wetted with 0.6 parts of dipropylene glycol butyl ether and stir for 15 min; Functional additives addition: Add substrate wetting agent and the remaining 3 parts of dipropylene glycol butyl ether, and stir for 9 minutes; Crosslinking agent addition: Add composite crosslinking agent and stir for 9 minutes; Viscosity adjustment: Add 3.6 parts of deionized water and adjust the viscosity to 45s to obtain the main paint; Adding metallic pigments: Premix water-based passivated aluminum silver paste with 0.4 parts of dipropylene glycol butyl ether, add it to the main paint at a low speed of 350 r / min, then add the orientation agent and corrosion inhibitor, and stir for 14 min; Filtration: Filtered through a 180-mesh filter to obtain the coating of Example 2.

[0051] Example 3 Coating components: 45 parts of water-based modified acrylic resin, 6 parts of fluorosilicone-phosphorus hybrid nano-penetrating agent, 5 parts of composite crosslinking agent (methyl etherified melamine-formaldehyde resin: ε-caprolactam blocked polymethylene polyphenyl isocyanate = 3:1), 12 parts of water-based passivating aluminum silver paste, 9 parts of hydrophobic modified nano silica, 1 part of polyether modified polysiloxane surfactant, 1.2 parts of polyamide wax paste, 0.5 parts of sodium nitrite corrosion inhibitor, 3.5 parts of dipropylene glycol butyl ether, 0.5 parts of polyether modified polysiloxane defoamer, 1 part of high molecular weight block copolymer dispersant, and 22 parts of deionized water.

[0052] Preparation method: Premix: Add 17.6 parts of deionized water to the dispersion vessel, add dispersant and defoamer while stirring at 400 r / min, and stir for 8 min until uniform; Nanofiller dispersion: Add hydrophobically modified nano-silica, disperse at 1000 r / min for 20 min, and control the fineness to 16 μm; Mixing the resin and penetrating agent: Adjust the speed to 500 r / min, add water-based modified acrylic resin and stir for 10 min; add fluorosilicone-phosphorus hybrid nano-penetrating agent wetted with 0.5 parts dipropylene glycol butyl ether and stir for 15 min; Functional additives: Add substrate wetting agent and the remaining 2 parts of dipropylene glycol butyl ether, and stir for 8 minutes; Crosslinking agent addition: Add composite crosslinking agent and stir for 8 minutes; Viscosity adjustment: Add 4.4 parts of deionized water and adjust the viscosity to 42s to obtain the main paint; Adding metallic pigments: Premix water-based passivated aluminum silver paste with 1 part dipropylene glycol butyl ether, add it to the main paint at a low speed of 300 r / min, then add the orienting agent and corrosion inhibitor, and stir for 12 min; Filtration: Filtered through a 180-mesh filter to obtain the coating of Example 3.

[0053] Comparative Example 1 Coating components: Without the addition of fluorosilicon-phosphorus hybrid nano-penetrating agents, the remaining components are completely consistent with those in Example 2.

[0054] Preparation method: The preparation process of Example 2 was followed, but the step of adding the fluorosilicon-phosphorus hybrid nano-penetrating agent was omitted, and the remaining rotation speed, time and temperature remained unchanged.

[0055] Comparative Example 2 Coating components: The common silane coupling agent KH-550 was used to replace the fluorosilicon-phosphorus hybrid nano-penetrating agent, and the dosage was the same as in Example 2. The remaining components were completely consistent with those in Example 2.

[0056] Preparation method: The preparation process of Example 2 was followed, except that the fluorosilicon-phosphorus hybrid nano-penetrating agent was replaced with KH-550, while the rotation speed, time, and temperature remained unchanged.

[0057] Comparative Example 3 Coating components: Unpassivated ordinary aluminum silver paste was used instead of water-based passivated aluminum silver paste, and the remaining components were completely consistent with those in Example 2.

[0058] Preparation method: The preparation process of Example 2 was followed, except that the water-based passivated aluminum silver paste was replaced with ordinary aluminum silver paste, while the rotation speed, time, and temperature remained unchanged.

[0059] Test method: Standardized Sample Preparation Procedures: Substrate selection: Use 6063 aluminum alloy template (50mm×100mm×1mm), without any pretreatment such as pickling, deoxidation, chromating, or phosphating. Wipe the surface with anhydrous ethanol to remove oil and let it air dry naturally for later use.

[0060] Spraying application: Use air spraying method, spray gun nozzle diameter 1.0mm, spraying pressure 0.3-0.4MPa, wet film thickness controlled at 60-80μm, leveling at room temperature for 10min.

[0061] Curing conditions: Bake at 120℃ for 30 min, cool naturally to room temperature, and cure for 7 days in a standard environment of 23±2℃ and 50±5% humidity to obtain the dry film sample to be tested (dry film thickness 25±3μm).

[0062] Cross-cut adhesion test (GB / T9286-1998): Test equipment: Cross-cut tester (blade spacing 1mm), 3M 600 transparent tape, magnifying glass (4x). Experimental steps: Use a cross-cutting tool to vertically cut a 6-row, 6-column uniform grid on the coating surface, with the cuts extending to the aluminum alloy substrate. Use a brush to clean the surface of the grid, then firmly stick the tape to the grid area and press it down with your fingers; Tear the tape vertically at a uniform speed, completing the peeling process within 1 second; Use a 4x magnifying glass to observe the coating peeling in the grid area.

[0063] Evaluation criteria: Grade 0: The cut edges are completely smooth, and there is no loose material within the mesh. Level 1: Minor detachment at the intersection, with a detachment area ≤ 5%; The higher the level, the more severe the shedding; level 0 is the optimal level.

[0064] Water boiling resistance test (GB / T1733-1993): Test instrument: Constant temperature water bath (accuracy ±1℃) Experimental steps: Completely immerse the cured sample in boiling water at 100℃ for 4 hours. Remove the sample, blot the surface moisture with filter paper, and let it sit at room temperature for 2 hours; Retest the cross-cut adhesion according to GB / T9286-1998, and observe the blistering, peeling, flaking, and discoloration of the paint film.

[0065] Evaluation criteria: No blistering, no peeling, no falling off, and adhesion remaining at level 0 is qualified; blistering, falling off, and adhesion reduction are unqualified.

[0066] Neutral salt spray test (GB / T 10125-2021): Test instrument: Neutral salt spray test chamber Test conditions: Sodium chloride solution concentration 5 ± 0.1%, pH value 6.5 - 7.2, test temperature 35 ± 1°C, continuous spraying, sedimentation rate 1 - 2 mL / 80 cm²h.

[0067] Test steps: Seal the edges of the test panel with paraffin and place it with the test surface tilted upward at 15° - 30°; Spray continuously for 240 h. After the test, take out the test panel, gently rinse the salt stains on the surface with clean water, and air dry for observation; Record the rusting, blistering, falling off, and the width of scratch corrosion expansion of the test panel.

[0068] Evaluation criteria: No rusting, no blistering, no falling off, and corrosion expansion width ≤ 0.5 mm is excellent; large - area rusting, blistering, and falling off are unqualified.

[0069] Pencil hardness test (GB / T 6739 - 2006): Test instruments: Pencil hardness tester (load 750 g), Zhonghua high - grade drawing pencils (6B - 6H) Test steps: Sharpen the pencil until the cylindrical lead is exposed, and sand it until the end face is flat; The hardness tester makes an angle of 45° with the coating surface, and is pushed forward uniformly for 3 mm. Test 5 places with the same hardness; Take the highest pencil hardness that does not scratch the coating as the test result.

[0070] Evaluation criteria: No scratches and no indentations are qualified.

[0071] Impact resistance test (GB / T 1732 - 1993): Test instrument: Film impact tester (weight of the hammer 1 kg, impact height 50 cm) Test steps: Place the test panel with the coating facing up on the base of the impact tester; The weight falls freely from a height of 50 cm and impacts the center of the test panel; Observe the impact area with a 4 - fold magnifying glass and check for cracking and falling off.

[0072] Evaluation criteria: No cracks, no falling off, and no wrinkling are passed; cracks and falling off are failed.

[0073] Storage stability test of metallic pigments: Test equipment: sealed glass bottle, constant temperature oven (accuracy ±1℃) Experimental steps: Fill a 500mL sealed glass bottle with all the paint, ensuring no air is left inside. Store in a sealed oven at 45℃ for 7 days; Remove the bottle and let it cool to room temperature. Observe whether the bottle is swollen, whether the coating is separated, and whether the coating film has turned black.

[0074] Evaluation criteria: No tank bulging, no stratification, and no blackening indicate stability; tank bulging, blackening, and gas separation indicate instability.

[0075] VOC content determination (GB / T23984-2009): Experimental instruments: Gas chromatograph, moisture analyzer Experimental steps: Sampling was performed according to standards to determine the volatile matter and moisture content in the coating. The content of volatile organic compounds was determined by gas chromatography, and the VOC value was calculated after deducting moisture.

[0076] Evaluation criteria: VOC ≤ 80g / L is considered environmentally compliant.

[0077] Coating gloss (GB / T9754-2007): Testing instrument: Gloss meter (60°) Test procedure: After calibrating the instrument, test 3 points on the sample surface and take the average value.

[0078] Evaluation criteria: Metallic luster ≥90 GU is considered excellent.

[0079] The experimental data are shown in Table 1: Adhesion and oxide layer penetration performance analysis, combined with Table 1, shows that the initial cross-cut adhesion of Examples 1-3 was grade 0, and the adhesion remained at grade 0 after soaking in boiling water at 100℃ for 4 hours; the initial adhesion of Comparative Example 1 (without fluorosilicone-phosphorus hybrid nano-penetrating agent) was grade 3, which decreased to grade 4 after boiling in water for 4 hours; the initial adhesion of Comparative Example 2 (using ordinary silane coupling agent KH-550 to replace fluorosilicone-phosphorus hybrid nano-penetrating agent) was grade 2, which decreased to grade 3 after boiling in water for 4 hours. The fluorosilicon-phosphorus hybrid nano-penetrating agent used in this invention achieves efficient penetration and strong interfacial anchoring of aluminum oxide layers through a triple synergistic mechanism of physical penetration, chemical anchoring, and nano-roughening. The fluoroalkyl chains impart extremely low surface energy to the material, and combined with the 20-50nm nano-size effect, it can rapidly penetrate the dense alumina layer on the aluminum surface. The phosphate groups can chelate with alumina and the aluminum matrix to form stable covalent bonds. The nano-SiO core can microscopically roughen the substrate surface, significantly increasing the interlocking contact area between the coating and the substrate. Simultaneously, the combination of organosilicon and phosphoric acid... The carboxyl and phosphate ester polar groups contained in the ester-modified acrylic resin further enhance the interfacial bonding between the coating and the substrate, ultimately achieving Grade 0 ultimate adhesion. However, in Comparative Example 1, due to the absence of a penetrating agent, the coating could not penetrate the aluminum oxide layer and only formed physical adsorption with the substrate, resulting in extremely poor adhesion. In Comparative Example 2, the ordinary silane coupling agent KH-550 contained only a single silane group and lacked fluorine and phosphorus functional chains and nano-roughening structure, which could not efficiently penetrate the aluminum oxide layer. The interfacial bonding between the coating and the substrate was weak, and the adhesion and water resistance were significantly reduced.

[0080] Analysis of water-boiling and salt spray corrosion resistance, as shown in Table 1, revealed that Examples 1-3 showed no rust or blistering after 240 hours of neutral salt spray testing, and the paint film showed no abnormalities after immersion in boiling water at 100°C for 4 hours. Comparative Example 1 showed severe rust and large-area coating peeling after 240 hours of salt spray testing, and the paint film delaminated after 4 hours of boiling in water. Comparative Example 2 showed moderate rust and blistering after 240 hours of salt spray testing, and the adhesion decreased significantly after 4 hours of boiling in water. The coating of this invention achieves chemical bonding between the coating and the aluminum substrate through a fluorosilicon-phosphorus hybrid nano-penetrating agent, fundamentally preventing moisture penetration along the coating interface. Combined with a composite crosslinking agent forming a three-dimensional dense crosslinked network, it effectively blocks the intrusion of moisture and salt spray corrosion media. The synergistic protective effect of sodium nitrite corrosion inhibitor endows the coating with excellent water-boiling and salt spray resistance. Comparative Example 1, lacking a penetrating agent, has no chemical bonding between the coating and the substrate, allowing rapid penetration of moisture and corrosive media, directly leading to coating blistering and peeling, and severe corrosion of the substrate. Comparative Example 2 uses a common silane coupling agent, resulting in weak interfacial bonding. After high-temperature boiling, the interface fails, allowing corrosive media to easily penetrate the coating under salt spray conditions, significantly reducing its anti-corrosion performance.

[0081] Analysis of the storage stability of metallic pigments, as shown in Table 1, reveals that in Examples 1-3, after 7 days of storage in a sealed environment at 45℃, the coatings showed no can bulging or blackening, and the gloss at 60° remained above 90 GU. In Comparative Example 3, which used unpassivated ordinary aluminum silver paste, severe can bulging, blackening of the coating, and complete loss of gloss occurred after 7 days of storage under the same conditions. This invention utilizes a water-based special aluminum silver paste with a surface-coated silica or organophosphate passivation layer, effectively isolating aluminum powder from direct contact with the water-based system. Combined with sodium nitrite corrosion inhibitor, it blocks the oxidation and hydrogen evolution reaction of aluminum powder. Simultaneously, a polyamide wax paste orienting agent guides the metallic pigments to arrange in a parallel and orderly manner, enhancing metallic gloss while reducing particle contact and ensuring long-term stability of the metallic pigments in the water-based system. In Comparative Example 3, the unpassivated aluminum silver paste directly contacted water, rapidly undergoing an oxidation and hydrogen evolution reaction. The generated hydrogen gas caused can bulging, and the alumina generated from the oxidation of aluminum powder led to blackening of the coating and complete loss of gloss.

[0082] Analysis of the physical and mechanical properties of the coating, as shown in Table 1, reveals that Examples 1-3 achieved a pencil hardness of 2H and passed all impact resistance tests (1kg×50cm); Comparative Example 1 had a pencil hardness of only HB and failed the impact resistance test; Comparative Examples 2-3 had a pencil hardness of H-2H and passed the impact resistance test. The hydrophobic modified nano-silica in the coating of this invention effectively fills the internal voids of the coating. Combined with the high crosslinking density structure formed by the composite crosslinking agent, resin, and penetrating agent, it significantly improves the cohesive strength, hardness, and impact resistance of the coating. Furthermore, the flexible segments of the organosilicon-modified acrylic resin can buffer impact stress and prevent coating cracking. Comparative Example 1, lacking a penetrating agent, had insufficient crosslinking and low cohesiveness, resulting in a significant decrease in hardness and impact resistance. Although the crosslinking state of the coatings in Comparative Examples 2-3 was normal, the interfacial bonding between the coating and the substrate was weak, making them prone to performance failure during long-term use.

[0083] Environmental performance (VOC) analysis, as shown in Table 1, revealed that the VOC content of Examples 1-3 was 68-72 g / L, while the VOC content of Control Groups 1-3 was 69-75 g / L. All experimental groups used water as the main dispersion medium and did not add harmful volatile solvents such as benzene or aldehydes. The VOC content was far below the national standard limit (≤80 g / L). In particular, the embodiments of this invention, due to the excellent compatibility between the fluorosilicone-phosphorus hybrid nano-penetrating agent and the water-based modified acrylic resin, reduced the amount of co-solvent added, resulting in even lower VOC content. Furthermore, the coatings do not contain highly toxic and harmful substances such as hexavalent chromium, fully meeting the requirements for green and environmentally friendly coatings and adaptable to the high-end environmentally friendly coating application needs in the construction, automotive, and electronics industries.

[0084] Analysis of the coating gloss performance, as shown in Table 1, reveals that the 60° mirror gloss of Examples 1-3 are 92 GU, 95 GU, and 93 GU, respectively, exhibiting a strong metallic texture and excellent decorative appearance. Comparative Example 1 has a gloss of 76 GU, and Comparative Example 2 has a gloss of 81 GU, both resulting from insufficient interfacial bonding and decreased coating smoothness. Comparative Example 3, due to the use of unpassivated aluminum silver paste, suffers from blackened and disordered aluminum powder oxidation, resulting in a gloss of only 32 GU, completely losing its metallic decorative effect. This invention guides the parallel and orderly arrangement of metallic pigments through an orienting agent, combined with passivated aluminum silver paste and a highly dense film-forming system, enabling the coating to possess high gloss and a uniform metallic texture, meeting the requirements for high-end aluminum decorative coatings.

[0085] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-based metallic coating, characterized in that, The product comprises, by weight parts: 30-60 parts of water-based modified acrylic resin, 3-10 parts of fluorosilicone-phosphorus hybrid nano-penetrating agent, 3-8 parts of composite crosslinking agent, 5-20 parts of metallic pigment, 3-15 parts of nanofiller, 0.5-2 parts of substrate wetting agent, 0.5-2 parts of orientation agent, 0.2-1 parts of corrosion inhibitor, 2-5 parts of co-solvent, 0.2-1 parts of defoamer, 0.5-2 parts of dispersant, and 10-25 parts of deionized water; wherein the water-based modified acrylic resin is a dual-modified acrylic resin of organosilicon and phosphate ester; wherein the fluorosilicone-phosphorus hybrid nano-penetrating agent is a hybrid nanoparticle with a core of 20-50nm nano-silica bonded to the surface with fluorinated alkyl chains, phosphate groups and silane coupling agent segments.

2. The water-based metallic coating according to claim 1, characterized in that, The composite crosslinking agent is composed of an aqueous amino resin and a blocked isocyanate, wherein the mass ratio of the aqueous amino resin to the blocked isocyanate is 2-4:1; the aqueous amino resin is a methyl etherified melamine-formaldehyde resin or a mixed etherified melamine resin; and the blocked isocyanate is a methyl ethyl ketone oxime or an ε-caprolactam-blocked polymethylene polyphenyl isocyanate.

3. The water-based metallic coating according to claim 1, characterized in that, The preparation method of the fluorosilicone-phosphorus hybrid nano-penetrating agent includes the following steps: Amination of nano-silica surface: Nano-silica sol was added to anhydrous ethanol and ultrasonically dispersed for 15 min. The mass ratio of nano-silica sol to anhydrous ethanol was 1:6-8. Then, 0.15-0.25 times the mass of nano-silica and 3-aminopropyltriethoxysilane were added and reacted at 60 °C for 6 h. After centrifugation, washing and vacuum drying, amination of nano-silica was obtained. RAFT-polymerized grafted fluorophosphorus copolymer: First, aminated nano-silica is added to anhydrous ethanol and mixed, with a mass ratio of aminated nano-silica to anhydrous ethanol of 1:9-11. Then, 0.03-0.04 times the mass of aminated nano-silica, 2.0-2.5 times the mass of functional monomers, and 0.015-0.025 times the total mass of functional monomers, are added sequentially. Then, nitrogen is used to deoxygenate for 30 min, and the reaction is carried out at 70℃ for 12 h. After centrifugation, washing, and vacuum drying, grafted hybrid particles are obtained. Hydrolysis and condensation: The grafted hybrid particles are added to an ethanol-water solution for mixing. The mass ratio of the grafted hybrid particles to the ethanol-water solution is 1:12-14. The pH is adjusted to 9-10 with ammonia. The mixture is stirred at room temperature for 2 hours. After centrifugation, washing and drying, the fluorosilicon-phosphorus hybrid nano-penetrating agent is obtained.

4. The water-based metallic coating according to claim 3, characterized in that, The functional monomer is composed of perfluorooctyl ethyl acrylate and methacryloxyethyl phosphate, wherein the mass ratio of perfluorooctyl ethyl acrylate to methacryloxyethyl phosphate is 1:0.8-1.2; and the mass ratio of ethanol to water in the ethanol-water solution is 7:

3.

5. The water-based metallic coating according to claim 1, characterized in that, The metallic pigment is an aqueous aluminum-silver paste with a surface-coated organic phosphate passivation layer and a particle size of 10~40μm.

6. The water-based metallic coating according to claim 1, characterized in that, The nanofiller is hydrophobically modified nano-silica with a particle size of 20-80 nm, and its surface has been treated with an organosilane coupling agent; the substrate wetting agent is a polyether-modified polysiloxane surfactant.

7. The water-based metallic coating according to claim 1, characterized in that, The orientation agent is a polyamide wax paste; the corrosion inhibitor is sodium nitrite; the co-solvent is one of dipropylene glycol butyl ether (DPnB), propylene glycol methyl ether (PM), and dipropylene glycol methyl ether (DPM); the defoamer is a polyether-modified polysiloxane defoamer, specifically model DefomW-0506; and the dispersant is a high molecular weight block copolymer dispersant.

8. A method for preparing a water-based metallic coating, used to prepare the water-based metallic coating according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Premixing: Add 60% to 80% of the total amount of deionized water to the dispersion vessel, add dispersant and defoamer while stirring at 300 to 500 r / min, and stir for 5 to 10 min; S2. Nanofiller dispersion: Add nanofiller, increase the stirring speed to 800~1200 r / min, and disperse for 15~30 min until the fineness is ≤20μm; S3. Mixing resin and penetrating agent: Reduce stirring speed to 400~600r / min, add water-based modified acrylic resin, and stir for 10min; then slowly add fluorosilicone-phosphorus hybrid nano-penetrating agent, and continue stirring for 15min until uniform. S4. Addition of functional additives: Add the substrate wetting agent and 50%~70% co-solvent in sequence, and stir for 5~10 minutes; S5. Adding crosslinking agent: Add the composite crosslinking agent and stir for 5-10 minutes; S6. Adjusting viscosity: Add the remaining deionized water to adjust the viscosity to 30~60s to obtain the main paint; S7. Addition of metallic pigments: Premix the metallic pigments with the remaining co-solvent, add the main paint while stirring at a low speed of 200~400r / min, then add the orientation agent and corrosion inhibitor, and stir for 10~15min; S8: Filtration: Filter with a 150~200 mesh filter to obtain water-based metal coating.

9. The method for preparing a water-based metallic coating according to claim 8, characterized in that, In step S3, the fluorosilicon-phosphorus hybrid nano-penetrating agent is pre-wetted with 10%~20% co-solvent before being added.

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