A coating for galvanized steel sheet and a method for preparing the same

Abstract

The present application belongs to the technical field of paint, and particularly relates to a kind of paint for galvanized sheet and its preparation method.The present application uses graphene oxide, carbon nanotube to modify molybdenum disulfide.Compared with the inert structure of molybdenum disulfide nanosheet, graphene oxide sheet layer contains a large number of oxygen-containing functional groups, and the modification of molybdenum disulfide nanosheet by graphene oxide can effectively improve the dispersion of molybdenum disulfide nanosheet in water-based polyurethane paint.In the process of grafting reaction between graphene oxide and modified molybdenum disulfide nanosheet, the addition of one-dimensional structure carbon nanotube can effectively prevent the aggregation of nanosheet layer during the reaction process, thereby ensuring the uniform modification of molybdenum disulfide nanosheet;and, carbon nanotube has high specific strength and specific modulus, its addition can form an interactive network with graphene oxide and molybdenum disulfide nanosheet, greatly improving the mechanical properties and corrosion resistance of water-based polyurethane coating.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a coating for galvanized steel sheets and its preparation method. Background Technology

[0002] Metallic materials are a crucial foundation of modern industry and technology, finding wide application across various fields. However, they are also susceptible to corrosion. This occurs when metallic materials undergo electrochemical reactions with surrounding substances such as oxygen, water, acids, alkalis, and salts, leading to deterioration of the metal's surface properties and even severe damage. Metal corrosion not only reduces the reliability of materials and the safety and lifespan of engineering facilities but also results in resource waste and environmental pollution.

[0003] Metal corrosion is related to many factors, such as the composition, structure, shape, and surface condition of the metal material, as well as environmental conditions, such as the properties of the corrosive substance, temperature, humidity, pH, and redox potential. Furthermore, metal corrosion is a highly complex process; different metals exhibit different corrosion patterns under different environmental conditions. Therefore, to prevent or mitigate metal corrosion, it is essential to first fully understand its principles and mechanisms, and then propose corresponding protective measures and methods for different metal materials under varying environmental conditions.

[0004] Today, with the continuous development of technology and the increasing demands of enterprises, people have researched and invented many methods to prevent metal corrosion. These include: selecting materials with excellent corrosion resistance; applying a protective coating to the metal surface; adding substances that can slow down the corrosion rate; using electrochemical methods to protect the metal substrate; designing new alloy materials and modifying the properties of existing materials; controlling necessary environmental conditions; and monitoring and predicting real-time changes in metal corrosion. It is essential to fully utilize the advantages of each method while mitigating its disadvantages, and to select the appropriate protection scheme based on the specific circumstances.

[0005] Metal protection is crucial for preventing metal corrosion and encompasses a series of measures and methods to slow down, inhibit, or prevent corrosion of metals in specific environments. The goal of metal protection is to ensure that metals can operate stably and reliably for extended periods in various environments, thereby reducing damage caused by corrosion and extending the service life of metallic materials.

[0006] To improve the corrosion resistance of metals, a coating is often applied to their surface. Among these, polyurethane coatings are the most commonly used. The preparation of polyurethane resin coatings typically involves the reaction of isocyanates with polyols. This reaction produces polymer chains, forming a robust polyurethane structure. The coating is applied to the substrate surface, and the polyurethane chains generated by the reaction form a protective film. For example, CN120795774A discloses an easy-to-apply, one-component polyurethane waterproof coating and its preparation method. The raw materials include: polyol, plasticizer, solid filler, isocyanate, catalyst, and solvent; the polyol includes polyether diol and polyether triol; the plasticizer includes tributyl acetylacetate; and the catalyst includes bismuth neodecanoate catalyst and dimorpholine diethyl ether (DMDEE) catalyst. By combining the bismuth neodecanoate catalyst and the dimorpholine diethyl ether (DMDEE) catalyst, the viscosity of the waterproof coating is effectively reduced, facilitating application; at the same time, the drying speed of the waterproof coating is increased. Although the above-mentioned patented technology improves the mechanical properties of the coating, it uses toxic and expensive chemical reagents, resulting in high costs, which does not meet the requirements of green chemistry development. Summary of the Invention

[0007] The purpose of this invention is to address the above-mentioned problems by providing a coating for galvanized steel sheets and its preparation method. The coating of this invention has properties such as easy application, weather resistance, high adhesion, and strong salt spray resistance, and has broad application prospects.

[0008] The technical solution of this invention is implemented as follows:

[0009] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0010] (1) Modified molybdenum disulfide nanosheets were prepared by modifying molybdenum disulfide nanosheets with an aminosilane coupling agent;

[0011] (2) First, prepare a dispersion of 10-20 wt% graphene oxide and catalyst, then add carbon nanotubes and modified molybdenum disulfide nanosheets. After reacting for a period of time, add the remaining graphene oxide and continue the reaction to obtain graphene oxide modified molybdenum disulfide nanosheets.

[0012] (3) A coating for galvanized steel sheets is prepared by mixing water-based polyurethane dispersion, graphene oxide modified molybdenum disulfide nanosheets and coating additives evenly.

[0013] Molybdenum disulfide nanosheets exhibit unique sliding properties and excellent corrosion resistance at the microscale, along with good insulation properties, enabling their widespread application in harsh environments. Their layered structure forms an effective barrier, preventing harmful substances and corrosive media from easily eroding the substrate. However, because the nanomaterials have at least one dimension smaller than 100 nm, directly adding them to waterborne polyurethane presents technical challenges such as dispersion difficulties and easy agglomeration.

[0014] To address the aforementioned issues, this invention modifies molybdenum disulfide using graphene oxide and carbon nanotubes. The macroscopic structure of graphene oxide is similar to that of molybdenum disulfide nanosheets, both exhibiting a two-dimensional sheet structure with a high aspect ratio. Compared to the inert structure of molybdenum disulfide nanosheets, the basal surface and edges of graphene oxide sheets are covered with numerous oxygen-containing functional groups such as carboxyl and epoxy groups. These polar groups are hydrophilic, making the originally hydrophobic graphene framework highly hydrophilic. Modifying inert molybdenum disulfide nanosheets with hydrophilic graphene oxide can effectively improve the dispersion performance of molybdenum disulfide nanosheets in waterborne polyurethane coatings.

[0015] First, molybdenum disulfide nanosheets were modified using an aminosilane coupling agent, introducing amino and alkane chains onto their surface. The alkane chains exhibit steric hindrance, which can, to some extent, prevent the molybdenum disulfide nanosheets from stacking themselves. Subsequently, after reacting with the oxygen-containing functional groups on the surface of graphene oxide, graphene oxide is uniformly distributed on the surface of the molybdenum disulfide nanosheets, preventing the re-stacking of the nanosheet layers. One end of the aminosilane coupling agent is bonded to the molybdenum disulfide nanosheets via silicon-oxygen bonds, while the amino group at the other end chemically reacts or strongly interacts with the oxygen-containing functional groups on the graphene oxide. This transforms the molybdenum disulfide nanosheets from a free filler into a strongly chemically bonded component with graphene oxide, significantly improving the dispersibility of molybdenum disulfide. Furthermore, during the grafting reaction between graphene oxide and the modified molybdenum disulfide nanosheets, a small amount of one-dimensional carbon nanotubes were also added. One-dimensional carbon nanotubes act as physical separators between unreacted molybdenum disulfide (MoD) sheets, effectively preventing agglomeration during the reaction and ensuring uniform modification of the MoD nanosheets. Graphene oxide and MoD nanosheets are two-dimensional sheet materials, while carbon nanotubes are one-dimensional tubular materials. Adding a small amount of carbon nanotubes allows them to interweave between the nanosheets; furthermore, carbon nanotubes possess high specific strength and specific modulus, enabling them to form an interactive network with graphene oxide and MoD nanosheets, significantly improving the mechanical properties and corrosion resistance of waterborne polyurethane coatings.

[0016] In one embodiment, the specific process steps of step (1) are as follows: the aminosilane coupling agent and molybdenum disulfide nanosheets are dispersed in a solvent, and after the reaction, the modified molybdenum disulfide nanosheets are obtained by filtration, washing and drying.

[0017] In one embodiment, the mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets is (0.1-0.4):1. Specifically, the mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets can be 0.1:1, 0.2:1, 0.3:1, or 0.4:1. Particularly, it can be (0.2-0.3):1. Insufficient aminosilane coupling agent will not effectively cover the surface of the molybdenum disulfide sheets, resulting in low grafting density and insufficient steric hindrance effect. Excessive aminosilane coupling agent will not only easily lead to self-condensation but also prevent the uniform dispersion of small amounts of graphene oxide on the surface of the molybdenum disulfide nanosheets, thus reducing the modification effect.

[0018] In one embodiment, the aminosilane coupling agent is one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-diethylenetriaminopropyltrimethoxysilane, 3-diethylenetriaminopropyltriethoxysilane, 3-diethylenetriaminopropylmethyldimethoxysilane, and 3-diethylenetriaminopropylmethyldiethoxysilane. Specifically, 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane with suitable reactivity can be selected.

[0019] In one embodiment, the solvent is a mixed solvent of ethanol and deionized water in a volume ratio of (0.5-5):1. Specifically, the volume ratio of ethanol to deionized water can be 0.5:1, 1:1, 2:1, 3:1, 4:1, or 5:1.

[0020] In one embodiment, the reaction temperature is 55-65°C and the reaction time is 2-3 hours. Specifically, the reaction temperature is 60°C and the reaction time is 2.5 hours.

[0021] In one embodiment, the specific process steps of step (2) are as follows: 10-20wt% of graphene oxide and catalyst are dispersed in a solvent, then carbon nanotubes and modified molybdenum disulfide nanosheets are added, stirred evenly, and after reacting for a period of time, the remaining graphene oxide is added to continue the reaction. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets are obtained.

[0022] The surface of molybdenum disulfide nanosheets modified with aminosilane coupling agents is grafted with a large number of amino groups, while the surface of graphene oxide is rich in functional groups such as carboxyl and epoxy groups. When the modified molybdenum disulfide nanosheets are mixed with graphene oxide, a reaction occurs between the amino groups and the oxygen-containing functional groups. If all the graphene oxide is added at once or too much is added initially, the dispersion of the modified molybdenum disulfide itself is relatively limited. In the early stage of the reaction, the local concentration is too high, and the newly added graphene oxide does not have time to disperse before reacting with the modified molybdenum disulfide nanosheets. Some molybdenum disulfide nanosheets have a high concentration of graphene oxide loaded on them, while others do not have enough time to react with the graphene oxide, resulting in a decrease in the grafting efficiency of the modified molybdenum disulfide. Adding a small amount of graphene oxide first can reduce the grafting rate and allow the modified molybdenum disulfide to be fully and uniformly loaded with graphene oxide. After the reaction has been going on for a period of time, adding the remaining graphene oxide can better promote the reaction between graphene oxide and modified molybdenum disulfide, so that the graphene oxide is evenly dispersed on the surface of each molybdenum disulfide nanosheet and its dispersion performance is improved.

[0023] In one embodiment, the mass ratio of graphene oxide, carbon nanotubes, and modified molybdenum disulfide nanosheets is (0.05-0.2):(0.05-0.2):1. Further, the mass ratio of graphene oxide, carbon nanotubes, and modified molybdenum disulfide nanosheets is (0.08-0.18):(0.08-0.18):1; particularly, it can be (0.1-0.15):(0.1-0.15):1. The present invention uses relatively small amounts of graphene oxide and carbon nanotubes because although graphene oxide has good dispersibility, its mechanical properties are poor, and pure graphene oxide is a conductor; if it directly contacts the metal substrate, it will act as a cathode, accelerating metal corrosion. A suitable amount of graphene oxide and carbon nanotubes can better balance the dispersion of molybdenum disulfide and the reinforcing effect of the coating.

[0024] Adding one-dimensional carbon nanotubes and two-dimensional graphene oxide-modified molybdenum disulfide to waterborne polyurethane effectively improves the coating's salt spray resistance by constructing a highly efficient physical barrier and enhancing interfacial bonding. The one-dimensional carbon nanotubes, interspersed between the two-dimensional layers, fill the micropores, making the coating denser. Their layered two-dimensional structure extends the penetration path of corrosive media, greatly enhancing the coating's shielding properties and delaying the time it takes for corrosive agents to reach the substrate. This significantly improves the coating's density, hydrophobicity, and adhesion, ensuring that the coating does not blister or peel off in long-term salt spray environments, maintaining its structural integrity.

[0025] In one embodiment, the solvent is deionized water. The amount of deionized water used is not particularly limited. Specifically, the mass-to-volume ratio of modified molybdenum disulfide nanosheets to deionized water is 8 mg: (0.1-10) mL.

[0026] In one embodiment, the catalyst is a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). Specifically, the mass ratio of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS), and graphene oxide is (1.2-1.6):(0.8-1.1):1; more specifically, it can be (1.3-1.5):(0.9-1.0):1. By adding the catalyst, the reaction potential energy can be reduced, thus better promoting the bonding of graphene oxide with modified molybdenum disulfide.

[0027] In one embodiment, the reaction time is 4-8 hours, and the continued reaction time is 20-30 hours. The reaction temperature is not particularly limited; in particular, it can be carried out at room temperature.

[0028] In one embodiment, the solid content of the aqueous polyurethane dispersion is 50-70%.

[0029] In one embodiment, the mass ratio of graphene oxide-modified molybdenum disulfide nanosheets to the aqueous polyurethane dispersion is (5-10):100. Specifically, it can be 5:100, 6:100, 7:100, 8:100, 9:100, or 10:100. Further, it can be (5.5-8.5):100. An appropriate amount of graphene oxide-modified molybdenum disulfide nanosheets can be better dispersed in the aqueous polyurethane matrix resin, enhancing the coating performance. Generally, as the amount of graphene oxide-modified molybdenum disulfide nanosheets increases, salt spray resistance improves; however, excessive amounts may lead to dispersion difficulties, causing salt spray resistance to plateau or even decrease, while coating adhesion will significantly decrease. Within the above-mentioned ratio range, the mechanical properties and corrosion resistance of the coating can be balanced, preventing excessive filler from affecting coating adhesion.

[0030] In one embodiment, the coating additive is one or more of the following: anti-settling agent, defoamer, wetting and dispersing agent.

[0031] In one embodiment, the mass ratio of coating additive to aqueous polyurethane dispersion is (3-6):100.

[0032] In one embodiment, the mass ratio of the anti-settling agent, defoamer, wetting and dispersing agent to the aqueous polyurethane dispersion is (1-2):(1-2):(1-2):100. Specifically, it can be (1.2-1.7):(1.2-1.7):(1.2-1.7):100.

[0033] In one embodiment, the anti-settling agent is one or more of BYK420, BYK425, and BYK430.

[0034] In one embodiment, the defoamer is an organosilicone defoamer or a mineral oil defoamer. Specifically, it can be a polyether-modified organosilicone.

[0035] In one embodiment, the wetting and dispersing agent is one or more of sodium polyacrylate, ammonium polyacrylate, and polyphosphate. Specifically, it can be sodium polyacrylate.

[0036] On the other hand, the present invention also provides a coating for galvanized steel sheets prepared by the above method. This coating has excellent mechanical properties, is easy to apply, and has good weather resistance, and has broad application prospects in the field of coatings, especially in the field of anti-corrosion coatings for galvanized steel sheets.

[0037] Beneficial effects:

[0038] Molybdenum disulfide nanosheets were modified using an aminosilane coupling agent, introducing amino and alkane chains onto their surface. Subsequently, after reacting with oxygen-containing functional groups on the surface of graphene oxide, graphene oxide was uniformly distributed on the surface of the molybdenum disulfide nanosheets, preventing the recombination of the molybdenum disulfide nanosheet layers. One end of the aminosilane coupling agent is bonded to the molybdenum disulfide nanosheets via silicon-oxygen bonds, while the amino group at the other end chemically reacts or strongly interacts with the oxygen-containing functional groups on the graphene oxide. This transforms the molybdenum disulfide nanosheets from a free filler into a strongly chemically bonded component with the graphene oxide, significantly improving the dispersibility of molybdenum disulfide. Furthermore, a small amount of one-dimensional carbon nanotubes was added during the grafting reaction of graphene oxide with the modified molybdenum disulfide nanosheets. Graphene oxide and molybdenum disulfide nanosheets are two-dimensional sheet materials, while carbon nanotubes are one-dimensional tubular materials. Adding a small amount of carbon nanotubes allows them to be interspersed between nanosheet layers. Furthermore, carbon nanotubes have high specific strength and specific modulus, and their addition can form an interactive network with graphene oxide and molybdenum disulfide nanosheets, significantly improving the mechanical properties and corrosion resistance of waterborne polyurethane coatings. Detailed Implementation

[0039] To better illustrate the purpose, technical solution, and advantages of this application, the following will provide further explanation in conjunction with specific embodiments. In the following embodiments and comparative examples, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0040] Performance testing: Parallel experiments were conducted to test the paint film adhesion (GB / T 5210-2006) and salt spray resistance (GB / T 1771-2007) of the galvanized sheet coatings prepared in the following examples and comparative examples.

[0041] Example 1

[0042] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0043] (1) The aminosilane coupling agent 3-aminopropyltrimethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 65°C for 2 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.4:1.

[0044] (2) 20wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 8 hours. Then, the remaining graphene oxide was added and the reaction was continued for 20 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.18:0.05:1. The mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL. The mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0045] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK420, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred again until homogeneous to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent, and aqueous polyurethane dispersion was 5:1:1:2:100. The coating film adhesion was tested to be 5.1 MPa, and the salt spray resistance was 680 h.

[0046] Example 2

[0047] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0048] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 55°C for 3 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.1:1.

[0049] (2) 10wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 4 hours. Then, the remaining graphene oxide was added and the reaction was continued for 30 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.05:0.17:1; the mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL; and the mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0050] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK425, defoamer polyether-modified organosilicon, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred evenly again to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent, and aqueous polyurethane dispersion was 9:2:2:1:100. The coating film adhesion was tested to be 4.7 MPa, and the salt spray resistance was 840 h.

[0051] Example 3

[0052] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0053] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 60°C for 2.5 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.25:1.

[0054] (2) 15wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 6 hours. Then, the remaining graphene oxide was added and the reaction was continued for 25 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.12:0.1:1. The mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL. The mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0055] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK420, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred until homogeneous to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent, and aqueous polyurethane dispersion was 10:1.7:1.2:1.7:100. The coating film adhesion was tested to be 4.5 MPa, and the salt spray resistance was 870 h.

[0056] Example 4

[0057] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0058] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 58°C for 2.8 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.2:1.

[0059] (2) 13wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 5 hours. Then, the remaining graphene oxide was added and the reaction was continued for 27 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.1:0.1:1; the mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL; and the mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0060] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK425, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred evenly again to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent to aqueous polyurethane dispersion was 5.5:1:2:2:100. The coating film adhesion was tested to be 5.3 MPa, and the salt spray resistance was 670 h.

[0061] Example 5

[0062] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0063] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 60°C for 2.5 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.25:1.

[0064] (2) 15wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 6 hours. Then, the remaining graphene oxide was added and the reaction was continued for 25 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.12:0.2:1. The mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL. The mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0065] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK420, defoamer polyether-modified organosilicon, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred evenly again to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent to aqueous polyurethane dispersion was 8.2:1.7:1.2:1.7:100. The coating film adhesion was tested to be 5.0 MPa, and the salt spray resistance was 790 h.

[0066] Example 6

[0067] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0068] (1) The aminosilane coupling agent 3-aminopropyltrimethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 55°C for 2 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.15:1.

[0069] (2) 19wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 4 hours. Then, the remaining graphene oxide was added and the reaction was continued for 20 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.18:0.17:1; the mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL; and the mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0070] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK420, defoamer polyether-modified organosilicon, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred evenly again to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent to aqueous polyurethane dispersion was 6:1.2:1.1:1.3:100. The coating film adhesion was tested to be 4.8 MPa, and the salt spray resistance was 730 h.

[0071] Example 7

[0072] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0073] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 60°C for 2.5 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.25:1.

[0074] (2) 15wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 6 hours. Then, the remaining graphene oxide was added and the reaction was continued for 25 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.2:0.1:1. The mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL. The mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0075] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK420, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred evenly again to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent to aqueous polyurethane dispersion was 8.2:1.7:1.2:1.7:100. The coating film adhesion was tested to be 4.7 MPa, and the salt spray resistance was 830 h.

[0076] Example 8

[0077] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0078] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 57°C for 2.6 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.26:1.

[0079] (2) 14wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 5.5 h. Then the remaining graphene oxide was added and the reaction was continued for 26 h. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.13:0.09:1. The mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL. The mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0080] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK425, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred again until homogeneous to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent to aqueous polyurethane dispersion was 7:1.4:1.6:1.8:100. The coating film adhesion was tested to be 4.8 MPa, and the salt spray resistance was 790 h.

[0081] Example 9

[0082] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0083] (1) The aminosilane coupling agent 3-aminopropyltrimethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 62°C for 2.3 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.3:1.

[0084] (2) 17wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 7 hours. Then, the remaining graphene oxide was added and the reaction was continued for 23 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.16:0.15:1; the mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL; and the mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0085] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK425, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred evenly again to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent to aqueous polyurethane dispersion was 6.5:1.8:1.8:1.1:100. The coating film adhesion was tested to be 4.9 MPa, and the salt spray resistance was 750 h.

[0086] Example 10

[0087] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0088] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 60°C for 2.5 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.25:1.

[0089] (2) 15wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 6 hours. Then, the remaining graphene oxide was added and the reaction was continued for 25 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.12:0.1:1. The mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL. The mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0090] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK420, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred evenly again to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent to aqueous polyurethane dispersion was 8.2:1.7:1.2:1.7:100. The coating film adhesion was tested to be 5.5 MPa, and the salt spray resistance was 850 h.

[0091] Comparative Example 1

[0092] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0093] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 60°C for 2.5 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.25:1.

[0094] (2) 85wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then carbon nanotubes and modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 6 hours. Then, the remaining graphene oxide was added and the reaction was continued for 25 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets was 0.12:0.1:1. The mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL. The mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0095] (3) Graphene oxide-modified molybdenum disulfide nanosheets were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK420, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred again until homogeneous to obtain a coating for galvanized steel sheets. The mass ratio of graphene oxide-modified molybdenum disulfide nanosheets, anti-settling agent, defoamer, wetting and dispersing agent, and aqueous polyurethane dispersion was 8.2:1.7:1.2:1.7:100. The coating film adhesion was tested to be 3.6 MPa, and the salt spray resistance was 570 h.

[0096] Comparative Example 2

[0097] A method for preparing a coating for galvanized steel sheets includes the following steps:

[0098] (1) The aminosilane coupling agent 3-aminopropyltriethoxysilane and molybdenum disulfide nanosheets were dispersed in a mixed solvent of ethanol and deionized water in a volume ratio of 1:1. After reacting at 60°C for 2.5 h, the mixture was filtered, washed and dried to obtain modified molybdenum disulfide nanosheets. The mass ratio of aminosilane coupling agent to molybdenum disulfide nanosheets was 0.25:1.

[0099] (2) 15wt% graphene oxide and catalysts 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were dispersed in deionized water, and then modified molybdenum disulfide nanosheets were added. The mixture was stirred evenly and reacted for 6 hours. Then, the remaining graphene oxide was added and the reaction was continued for 25 hours. After filtration, washing and drying, graphene oxide modified molybdenum disulfide nanosheets were obtained. The mass ratio of graphene oxide to modified molybdenum disulfide nanosheets was 0.12:1; the mass-volume ratio of modified molybdenum disulfide nanosheets to deionized water was 8 mg:1 mL; and the mass ratio of EDC, NHS and graphene oxide was 1.3:1:1.

[0100] (3) Graphene oxide-modified molybdenum disulfide nanosheets and carbon nanotubes were dispersed in deionized water, and an aqueous polyurethane dispersion (60% solid content) was added. The mixture was stirred and dispersed, and then anti-settling agent BYK420, defoamer polyether-modified silicone, and wetting and dispersing agent sodium polyacrylate were added. The mixture was then stirred until homogeneous to obtain a coating for galvanized steel sheets. The mass ratio of carbon nanotubes to modified molybdenum disulfide nanosheets was 0.1:1; the mass ratio of graphene oxide-modified molybdenum disulfide nanosheets to carbon nanotubes, and the mass ratio of anti-settling agent, defoamer, wetting and dispersing agent to aqueous polyurethane dispersion was 8.2:1.7:1.2:1.7:100. The coating film adhesion was tested to be 4.1 MPa, and the salt spray resistance was 610 h.

[0101] As can be seen from the above examples and comparative examples, this invention uses an aminosilane coupling agent to modify molybdenum disulfide nanosheets, introducing amino and alkane chains onto their surface. The alkane chains have a steric hindrance effect, which can, to some extent, prevent the molybdenum disulfide nanosheets from stacking themselves. Subsequently, after reacting with the oxygen-containing functional groups on the surface of graphene oxide, graphene oxide is uniformly distributed on the surface of the molybdenum disulfide nanosheets, preventing the recombination of the molybdenum disulfide nanosheet layers and improving the dispersion performance of inert molybdenum disulfide in aqueous polyurethane. One end of the aminosilane coupling agent is bonded to the molybdenum disulfide nanosheets through silicon-oxygen bonds, while the amino group at the other end undergoes a chemical reaction or strong interaction with the oxygen-containing functional groups on the graphene oxide. This makes the molybdenum disulfide nanosheets no longer free fillers, but rather forms a strong chemical bond with graphene oxide, significantly improving the dispersibility of molybdenum disulfide. Furthermore, during the grafting reaction between graphene oxide and the modified molybdenum disulfide nanosheets, this invention also adds a small amount of one-dimensional carbon nanotubes. One-dimensional carbon nanotubes act as physical separators between unreacted molybdenum disulfide (MoD) sheets, effectively preventing agglomeration during the reaction and ensuring uniform modification of the MoD nanosheets. Graphene oxide and MoD nanosheets are two-dimensional sheet materials, while carbon nanotubes are one-dimensional tubular materials. Adding a small amount of carbon nanotubes allows them to interweave between the nanosheets; furthermore, carbon nanotubes possess high specific strength and specific modulus, enabling them to form an interactive network with graphene oxide and MoD nanosheets, significantly improving the mechanical properties and corrosion resistance of waterborne polyurethane coatings.

[0102] Specifically, in Example 10, 15 wt% graphene oxide was added initially, and the remaining 85 wt% graphene oxide was added after a period of reaction. In contrast, in Comparative Example 1, too much graphene oxide was added initially. The newly added graphene oxide reacted with the modified molybdenum disulfide nanosheets before it could disperse, resulting in some molybdenum disulfide nanosheets having a higher concentration of graphene oxide, while others did not have enough time to react with the graphene oxide, leading to a decrease in the grafting efficiency of the modified molybdenum disulfide. This indicates that adding a small amount of graphene oxide initially can reduce the grafting rate, allowing the modified molybdenum disulfide to be fully and uniformly loaded with graphene oxide. Adding the remaining graphene oxide after a period of reaction can better promote the reaction between graphene oxide and modified molybdenum disulfide, ensuring that the graphene oxide is uniformly dispersed on the surface of each molybdenum disulfide nanosheet and improving its dispersion performance.

[0103] Compared to Example 10, Comparative Example 2 did not add carbon nanotubes during the reaction of graphene oxide and modified molybdenum disulfide nanosheets. Instead, it added an equal amount of carbon nanotubes during the final blending process. In this case, it failed to prevent the stacking of the sheet-like structures, resulting in reduced filler dispersibility. The above examples and comparative examples demonstrate that by adjusting the feeding method of graphene oxide and carbon nanotubes, molybdenum disulfide nanosheets can be better modified, improving their dispersion performance in waterborne polyurethane, enabling them to better construct a reinforcing and barrier network, and improving the corrosion resistance and adhesion of the coating.

[0104] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing a coating for a galvanized sheet, characterized by, Includes the following steps: (1) Modified molybdenum disulfide nanosheets were prepared by modifying molybdenum disulfide nanosheets with an aminosilane coupling agent; (2) First, prepare a dispersion of 10-20 wt% graphene oxide and catalyst, then add carbon nanotubes and modified molybdenum disulfide nanosheets. After reacting for a period of time, add the remaining graphene oxide and continue the reaction to obtain graphene oxide modified molybdenum disulfide nanosheets; the mass ratio of graphene oxide, carbon nanotubes and modified molybdenum disulfide nanosheets is (0.05-0.2):(0.05-0.2):1; (3) Mix the aqueous polyurethane dispersion, graphene oxide modified molybdenum disulfide nanosheets and coating additives evenly to obtain a coating for galvanized steel sheets; the mass ratio of graphene oxide modified molybdenum disulfide nanosheets to aqueous polyurethane dispersion is (5-10):

100.

2. The method of claim 1, wherein the coating for a galvanized sheet is prepared by adding 0.1 to 0.5 parts by weight of the compound of formula (1) to 100 parts by weight of a base paint. The specific process steps of step (1) are as follows: the aminosilane coupling agent and molybdenum disulfide nanosheets are dispersed in a solvent, and after the reaction, they are filtered, washed and dried to obtain modified molybdenum disulfide nanosheets.

3. The method of producing a coating for a galvanized sheet according to claim 2, characterized by, In step (1), the aminosilane coupling agent is one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-diethylenetriaminopropyltrimethoxysilane, 3-diethylenetriaminopropyltriethoxysilane, 3-diethylenetriaminopropylmethyldimethoxysilane, and 3-diethylenetriaminopropylmethyldiethoxysilane.

4. The method of claim 2, wherein the coating for a galvanized sheet is prepared by adding 0.1 to 0.5 parts by weight of the compound of claim 1 to 100 parts by weight of a base paint. The reaction temperature in step (1) is 55-65℃.

5. The method of claim 2, wherein the coating for a galvanized sheet is prepared by adding 0.1 to 0.3 parts by weight of the compound of claim 1 to 100 parts by weight of a base paint. The reaction time in step (1) is 2-3 hours.

6. The method of claim 1, wherein the coating for a galvanized sheet is prepared by adding 0.1 to 0.5 parts by weight of the compound of claim 1 to 100 parts by weight of a base paint. The catalyst in step (2) is a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide.

7. The method of claim 1, wherein the coating for a galvanized sheet is prepared by adding 0.1 to 0.5 parts by weight of the compound of claim 1 to 100 parts by weight of a base paint. In step (2), the reaction time is 4-8 hours, and the reaction time continues for 20-30 hours.

8. The method of claim 1, wherein the coating for a galvanized sheet is prepared by adding 0.1 to 0.5 parts by weight of the compound of claim 1 to 100 parts by weight of a base paint. In step (3), the coating additive is one or more of the following: anti-settling agent, defoamer, wetting and dispersing agent.

9. The method for preparing a coating for galvanized steel sheets as described in claim 1, characterized in that, In step (3), the mass ratio of coating additive to waterborne polyurethane dispersion is (3-6):

100.

10. A coating for galvanized steel sheets, characterized in that, The coating for galvanized steel sheets is prepared by any one of claims 1-9.