Preparation method of microcapsule-based self-repairing coating, self-repairing coating and light metal alloy

Abstract

The invention relates to the technical field of material surface treatment, and discloses a preparation method of a microcapsule-based self-repairing coating, the self-repairing coating and a light metal alloy. The preparation method of the self-repairing coating comprises the following steps: adding microcapsules into a mixed solution of epoxy resin and a curing agent, and stirring to obtain a coating; the surface of a base body is coated with the paint, and a self-repairing coating is obtained; the preparation method of the microcapsule comprises the following steps: preparing a prepolymer solution which comprises the following components: urea and formaldehyde; preparing an oil-in-water emulsion, namely adding tung oil into a surfactant solution, and emulsifying to obtain the oil-in-water emulsion; and mixing the prepolymer solution and the oil-in-water emulsion to obtain the microcapsule. When the self-repairing coating is damaged, the microcapsules at the damaged part are broken, the core material tung oil is released, the core material flows in the coating and fills the damaged part, and the damaged part is repaired, so that the automatic repairing effect is achieved, the corrosion speed of an alloy matrix is slowed down, and the corrosion resistance is improved.

Description

Technical Field

[0001] The present application relates to the technical field of material surface treatment, for example, to a preparation method of a self-healing coating based on microcapsules, a self-healing coating and a light metal alloy. Background Art

[0002] Light metals represented by aluminum alloys and magnesium alloys have the characteristics of sufficient resources, low price, excellent performance, etc. Therefore, they are widely used in the fields of automobiles, aerospace, biomedicine, electronic products, energy, etc. However, the chemical properties of aluminum alloys and magnesium alloys are active and their corrosion resistance is poor, which greatly limits their wide application in industry. In order to improve the service performance of light metal materials such as aluminum alloys and magnesium alloys, the oxide coating prepared by micro-arc oxidation technology has a strong bonding force with the substrate and can effectively improve the hardness, corrosion resistance, wear resistance and electrical insulation of metal materials. However, during the treatment process of micro-arc oxidation technology, there are phenomena of spark discharge and gas evolution, resulting in a natural porous structure of the formed coating, and corrosion media can still penetrate through the microcracks and micropores on the coating to the substrate, thereby reducing the protection effect on the substrate.

[0003] In related technologies, in order to improve the protection effect on light metal materials such as aluminum alloys and magnesium alloys, an organic coating is applied on the coating after micro-oxidation treatment. The organic coating can effectively prevent corrosion media from penetrating through the microcracks and micropores on the micro-arc oxidation coating to cause corrosion of the substrate.

[0004] However, during the use of the organic coating, microcracks are easily generated under the influence of external factors such as bumps, scratches, and environmental corrosion. If not repaired in time and the cracks expand, it will cause the coating to fail and fall off, thereby causing corrosion of light metal materials such as aluminum alloys and magnesium alloys. Summary of the Invention

[0005] To have a basic understanding of some aspects of the disclosed embodiments, a simple summary is given below. The summary is not a general review, nor is it intended to identify key / important constituent elements or delineate the protection scope of these embodiments, but rather serves as a preface to the subsequent detailed description.

[0006] The embodiments of the present disclosure provide a preparation method of a self-healing coating based on microcapsules, a self-healing coating and a light metal alloy to improve the self-healing effect of the coating provided on the light metal surface.

[0007] In some embodiments, a method for preparing a microcapsule-based self-healing coating is provided, including: Step 1: adding microcapsules into a mixed solution of epoxy resin and curing agent, and stirring to obtain a coating; Step 2: coating the coating on the surface of a substrate to obtain a self-healing coating; wherein, the preparation steps of the microcapsules include: S1. preparing a prepolymer solution, the components of the prepolymer solution including urea and formaldehyde; S2. preparing an oil-in-water emulsion, including adding tung oil into a surfactant solution, and performing emulsification treatment to obtain the oil-in-water emulsion; S3. mixing the prepolymer solution and the oil-in-water emulsion to obtain microcapsules.

[0008] In some embodiments, a microcapsule-based self-healing coating is provided, and the self-healing coating is prepared by using the method for preparing a microcapsule-based self-healing coating as described in any one of the above embodiments.

[0009] In some embodiments, a light metal alloy is provided, and the surface of the light metal alloy includes the microcapsule-based self-healing coating as described in any one of the above embodiments.

[0010] The method for preparing a self-healing coating, the self-healing coating and the light metal alloy provided by the embodiments of the present disclosure can achieve the following technical effects:

[0011] The method for preparing a microcapsule-based self-healing coating provided by the present disclosure adds the already prepared microcapsule glue into a mixed solution of epoxy resin and curing agent to obtain a coating. The coating is coated on the surface of a substrate to obtain a self-healing coating. Since the microcapsules are loaded with the healing agent tung oil, when the self-healing coating is damaged, the microcapsules at the damaged part rupture, releasing the core material tung oil. The core material flows inside the coating and fills the damaged part, finally repairing the damaged part to achieve the effect of automatic repair, slowing down the corrosion rate of the alloy substrate, improving the corrosion resistance, and prolonging the protection time of the coating.

[0012] The above general description and the following description are only exemplary and explanatory, and are not used to limit the present application. Description of the Drawings

[0013] One or more embodiments are exemplarily illustrated by corresponding drawings. These exemplary illustrations and the drawings do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements. The drawings do not constitute a proportional limitation, and among them:

[0014] Figure 1 is a schematic structural diagram of a microcapsule-based self-healing composite coating provided by an embodiment of the present disclosure;

[0015] Figure 2 is a cross-sectional microscopic morphology diagram of a microcapsule-based self-healing composite coating provided by an embodiment of the present disclosure;

[0016] Figure 3 is a schematic structural diagram of the micro-arc oxidation device provided by an embodiment of the present disclosure;

[0017] Figure 4 is a surface topography diagram after repair of the self-healing coating with a 5wt% microcapsule content provided by Embodiment 1 of the present disclosure;

[0018] Figure 5 is a surface topography diagram after repair of the self-healing coating with a 15wt% microcapsule content provided by Embodiment 2 of the present disclosure;

[0019] Figure 6 is a surface topography diagram after repair of the coating with a 0wt% microcapsule content provided by the comparative example of the present disclosure.

[0020] Reference numerals:

[0021] 10 Self-healing composite coating; 110 Substrate; 120 Self-healing coating; 130 Micro-arc oxidation coating;

[0022] 20 Micro-arc oxidation device; 210 Power supply; 220 Electrolytic cell; 230 Wire; 240 Light alloy metal specimen; 250 Stainless steel plate. Detailed implementation manners

[0023] In order to be able to understand the features and technical content of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for reference and illustration only and are not intended to limit the embodiments of the present disclosure. In the following technical description, for the sake of explanation, numerous details are provided to give a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and methods for preparing self-healing coatings may be shown in a simplified manner to simplify the drawings.

[0024] The terms "first", "second", etc. in the specification, claims and above-mentioned drawings of the embodiments of the present disclosure are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so as to implement the embodiments of the present disclosure described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion.

[0025] In the embodiments of the present disclosure, the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "middle", "outer", "front", "rear", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the embodiments of the present disclosure and their embodiments, and are not used to limit that the preparation method, components or parts of the self-healing coating must have a specific orientation, or be constructed and operated in a specific orientation. Moreover, in addition to being used to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0026] In addition, the terms "arrangement", "connection", "fixation" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there can be internal communication between two preparation methods, components or parts of the self-healing coating. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0027] Unless otherwise specified, the term "plural" means two or more.

[0028] In the embodiments of the present disclosure, the character " / " indicates that the objects before and after are in an "or" relationship. For example, A / B means: A or B.

[0029] The term "and / or" is an associative relationship describing objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or, A and B.

[0030] It should be noted that, without conflict, the embodiments and features in the embodiments of the present disclosure can be combined with each other.

[0031] In some embodiments, a method for preparing a microcapsule-based self-healing coating is provided, including: Step 1: Add microcapsules to a mixed solution of epoxy resin and curing agent, and stir to obtain a coating; Step 2: Coat the coating on the surface of a substrate to obtain a self-healing coating; wherein, the preparation steps of the microcapsules include: S1. Prepare a prepolymer solution, and the components of the prepolymer solution include urea and formaldehyde; S2. Prepare an oil-in-water emulsion, including adding tung oil to a surfactant solution, and performing emulsification treatment to obtain the oil-in-water emulsion; S3. Mix the prepolymer solution and the oil-in-water emulsion to obtain microcapsules.

[0032] The preparation method of the microcapsule-based self-healing coating provided by the present disclosure obtains a coating by adding the prepared microcapsule glue into a mixed solution of epoxy resin and a curing agent. Using the mixed solution of epoxy resin and a curing agent as the basis of the coating provides good adhesiveness and mechanical strength. The coating is applied to the surface of the substrate to obtain a self-healing coating. Among them, the process of preparing microcapsules by using urea and formaldehyde solution to prepare a prepolymer solution and then combining it with an oil-in-water emulsion (containing tung oil) that has been emulsified is relatively simple, easy to control, and conducive to large-scale production and application.

[0033] Furthermore, since the microcapsules are loaded with the healing agent tung oil, when the self-healing coating is damaged, the microcapsules at the damaged part rupture, releasing the core material tung oil. The core material flows inside the coating and fills the damaged part, finally repairing the damaged part to achieve the effect of automatic repair, slowing down the corrosion rate of the alloy substrate, improving the corrosion resistance, and extending the protection time of the coating.

[0034] Optionally, the particle size of the microcapsules is less than or equal to 150 μm. By reasonably setting the particle size of the microcapsules, the self-healing effect of the coating is optimized.

[0035] Optionally, in step 1: the mass of the added microcapsules accounts for 0.1 wt% to 15 wt% of the total weight of the coating.

[0036] In this embodiment, the mass of the added microcapsules accounts for greater than or equal to 0.1 wt% and less than or equal to 15 wt% of the total weight of the coating. The addition of microcapsules endows the coating with self-healing ability. When the coating is damaged, the microcapsules can release the core material to repair the damaged part. The coating provided by the present disclosure can achieve self-repair when it is mechanically damaged or environmentally eroded by adding self-healing microcapsules to the epoxy resin, thereby extending the service life of the coating and the light metal alloy substrate. Moreover, the cross-linked structure formed by the epoxy resin and the polyamide curing agent improves the hardness and wear resistance of the coating, making it have better protection in harsh environments.

[0037] Optionally, the specific values of the mass fraction of the added microcapsules include but are not limited to: 0.1 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, 12 wt%, 14 wt% or 15 wt%.

[0038] Optionally, the mass ratio of the epoxy resin to the curing agent is 1:1 to 2:1; by mixing the epoxy resin and the curing agent according to a preset ratio. The epoxy resin has good adhesiveness, chemical resistance, and mechanical properties; the curing agent is used to react with the epoxy resin to form a cross-linked three-dimensional network structure, improving the hardness and heat resistance of the coating.

[0039] Optionally, the mass ratio of the epoxy resin to the curing agent includes but is not limited to: 1:1, 1.5:1, or 2:1.

[0040] Optionally, the epoxy resin is selected from one or more of bisphenol A epoxy resin E-51 and bisphenol A epoxy resin E-44;

[0041] Optionally, the curing agent is selected from one or more of polyamide, triethylenetetramine, and diethylenetriamine.

[0042] Optionally, the methods of coating the coating on the surface of the substrate include but are not limited to: air spraying or brushing, etc. In practical applications, a suitable spraying method can be selected according to requirements such as the thickness of the coating. Among them, by using the method of air spraying to coat the coating on the surface of the substrate, the coating can be quickly and evenly coated on the surface of the substrate to form a uniform coating.

[0043] Optionally, the steps of preparing the prepolymer solution include: mixing urea and formaldehyde solution, stirring and dissolving; adding triethanolamine to the dissolved solution to adjust the pH value of the solution to a first value to obtain a first solution; heating the first solution to obtain the prepolymer solution.

[0044] Optionally, the preset first molar ratio of urea to formaldehyde in the prepolymer solution is 1:2 to 1:1. The specific values of the preset first molar ratio include but are not limited to: 1:2, 1:1.5, or 1:1.

[0045] Optionally, the first value is 7 to 9, and the specific values of the first value include but are not limited to 7, 8, or 9.

[0046] Optionally, the mass fraction of the formaldehyde solution is 37wt% to 40wt%; the specific values of the mass fraction of the formaldehyde solution include but are not limited to: 37wt%, 38wt%, 39wt%, or 40wt%.

[0047] Optionally, the conditions for heating the first solution include: the heating temperature is 60°C to 80°C, and the heating duration is 50min to 80min. Among them, the specific values of the heating temperature include but are not limited to: 60°C, 65°C, 70°C, 75°C, or 80°C. The specific values of the heating duration include but are not limited to: 50min, 60min, 70min, or 80min.

[0048] In this embodiment, urea and formaldehyde are weighed in a molar ratio of 1:1 to 1:2 to control the crosslinking degree of the prepolymer solution and ensure the elasticity and strength of the shell layer. The urea and formaldehyde solutions are loaded into a container and stirred well in the container until the urea is completely dissolved to ensure the uniform distribution of the reactants. Adjusting the pH value helps control the formation rate of the prepolymer, avoiding too fast or too slow reactions and ensuring the stability of the prepolymer structure. Heating promotes the polymerization reaction of urea and formaldehyde to form a prepolymer with an appropriate molecular weight and crosslinked structure. A molar ratio of 1:2 to 1:1 helps form a prepolymer with an appropriate crosslinking degree, enhancing the elasticity and mechanical strength of the microcapsule shell layer, enabling it to better protect the core material and achieve self-healing function during application.

[0049] Optionally, the components of the prepolymer solution further include melamine. The steps for preparing the prepolymer solution include: mixing urea, melamine and formaldehyde solution and stirring to dissolve; adding triethanolamine to the dissolved solution to adjust the pH value of the solution to a third value; heating the second solution to obtain the prepolymer solution.

[0050] In this embodiment, by using urea, melamine and formaldehyde solution, the three can undergo a polycondensation reaction to form a three-dimensional network structure. By adding triethanolamine, the acidic substances in the formaldehyde solution are neutralized and the reaction environment is stabilized. Through the synthesis steps of urea-melamine-formaldehyde prepolymer, a prepolymer solution with good film-forming property and crosslinking property can be obtained. This solution, as the outer shell material for microcapsule preparation, wraps and protects the core material, enabling the microcapsule to have excellent mechanical properties and chemical corrosion resistance.

[0051] Optionally, the preset second molar ratio of urea, melamine and formaldehyde in the prepolymer solution ranges from 3:1:6 to 3:1:12. The specific values of the preset second molar ratio include but are not limited to: 3:1:6, 3:1:7, 3:1:8, 3:1:9, 3:1:10, 3:1:11 or 3:1:12.

[0052] Optionally, the mass fraction of the formaldehyde solution is 37wt% to 40wt%; the specific mass fractions of the formaldehyde solution include but are not limited to: 37wt%, 38wt%, 39wt% or 40wt%.

[0053] Optionally, the steps of performing the heating reaction include: placing the container filled with the solution after pH adjustment in a heating bath, heating it to 60°C to 80°C, and maintaining this temperature for reaction for 50 min to 80 min. During the reaction, the solution needs to be continuously stirred to ensure uniform progress of the reaction. After the reaction, take the container out of the heating bath and let it cool naturally to room temperature for standby. Among them, the specific values of the heating temperature include but are not limited to: 60°C, 65°C, 70°C, 75°C or 80°C. The specific values of the heating duration include but are not limited to: 50 min, 60 min, 70 min or 80 min.

[0054] Optionally, the third value is 7 to 9. By adjusting the pH value of the solution, a stable reaction environment is provided. The specific values of the third value include but are not limited to 7, 8 or 9.

[0055] Optionally, taking the mass of tung oil as M t and the sum of the masses of all components added to the prepolymer solution as M z , M t :M z = 1:1 to 2:1.

[0056] In this embodiment, by reasonably setting M t :M z , the self-healing ability, corrosion resistance, adhesion and wear resistance of the microcapsules are optimized, thereby improving the comprehensive performance of the final coating.

[0057] Specifically, tung oil, as an oily substance, can increase the flexibility and elasticity of the microcapsules. When tung oil is mixed with the sum of the masses of all components added to the prepolymer solution in a ratio of 1:1 to 2:1, a microcapsule wall with good mechanical strength can be formed, which helps the microcapsules to maintain integrity and stability during the preparation and application processes. The ratio of tung oil to the sum of the masses of all components added to the prepolymer solution will affect the thickness and density of the microcapsule wall, and thus affect the release rate of the core material. A higher ratio of tung oil may result in a thinner microcapsule wall and easier rupture to release the core material, while a lower ratio may slow down the release rate. Moreover, when the microcapsules are uniformly dispersed in the mixed solution of epoxy resin and curing agent and a coating is formed, an appropriate ratio of tung oil to urea-formaldehyde resin or melamine-urea-formaldehyde resin can improve the overall corrosion resistance of the coating. And, the self-healing function is achieved by adding microcapsules, reducing the chance of corrosive media penetrating into the substrate.

[0058] Optionally, the steps of adding tung oil to the surfactant solution and performing emulsification treatment to obtain an oil-in-water emulsion include: preparing a surfactant solution with a preset mass fraction; adding tung oil to the surfactant solution and stirring at a preset stirring rate for a preset emulsification duration.

[0059] In this embodiment, a preparation process method for the core material of the microcapsules is provided. Among them, the mass of tung oil added is determined according to the mass ratio relationship between tung oil and melamine-urea-formaldehyde resin. Tung oil is selected as the core material of the microcapsules because tung oil can directly crosslink and cure with oxygen in the atmosphere to form a new coating, playing a role in repairing the coating. And the corresponding mass of tung oil is slowly added to the surfactant solution, and the surfactant is used to reduce the interfacial tension between water and oil to help tung oil disperse in water. A stirrer is used to fully emulsify the tung oil and the surfactant solution for a set time at a preset stirring rate. Stirring can disperse tung oil into tiny droplets to form an oil-in-water emulsion.

[0060] In the embodiment of the present disclosure, a stable oil-in-water emulsion is prepared through the above steps, in which tung oil is dispersed into tiny droplets and wrapped by surfactants. Such an emulsion can be used as the core material for preparing microcapsules to prepare a coating with self-healing function.

[0061] Optionally, during the emulsification process, 1 to 2 drops of n-octanol are added. The addition of n-octanol can effectively eliminate the foam generated during the emulsification process and ensure the stability of the emulsion.

[0062] Optionally, the step of preparing the surfactant solution with a preset mass fraction includes: dissolving the surfactant in deionized water to prepare a solution with a mass fraction of 0.5wt% to 3wt%, and the specifically prepared mass fractions include but are not limited to 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%. The surfactant can reduce the interfacial tension between water and oil to help tung oil disperse in water.

[0063] Optionally, the surfactant includes but is not limited to one or more of sodium dodecylbenzenesulfonate, OP-10 and polysorbate-80.

[0064] Optionally, the value range of the stirring rate is 600r / min to 1200r / min.

[0065] In this embodiment, at a stirring rate of 600r / min to 1200r / min, tung oil can be effectively dispersed into fine oil droplets and fully mixed with the surfactant solution to form a stable oil-in-water emulsion, which helps the subsequent formation and stability of microcapsules. The stirring rate directly affects the size of the oil droplets. In the range of 600r / min to 1200r / min, the size of the oil droplets can be controlled to be suitable for the preparation of microcapsules, which helps the uniformity and self-healing performance of the microcapsules. And by reasonably setting the stirring rate, it helps to prevent the oil droplets from re-aggregating during the emulsification process, maintain the stability of the emulsion, avoid the appearance of large oil droplets or precipitation, and thus improve the uniformity and stability of the microcapsules.

[0066] Optionally, the specific values of the stirring rate include, but are not limited to: 600 r / min, 700 r / min, 800 r / min, 900 r / min, 1000 r / min, 1100 r / min or 1200 r / min.

[0067] Optionally, the value range of the emulsification setting duration is from 20 min to 60 min.

[0068] In this embodiment, the setting duration of 20 min to 60 min provides sufficient time for the emulsification process. Sufficient emulsification time helps to form a more uniform and dense microcapsule wall, ensuring the full mixing of tung oil and surfactant, improving the mechanical strength and durability of the microcapsules, and forming a stable emulsification system. If the emulsification time is too long, it may cause the oil droplets to be too small, affecting the self-healing effect of the microcapsules. If the emulsification time is too short, it may cause the oil droplets to be too large and unevenly distributed.

[0069] Optionally, the specific values of the emulsification setting duration include, but are not limited to: 20 min, 30 min, 40 min, 50 min or 60 min.

[0070] Optionally, the step of mixing the prepolymer solution and the oil-in-water emulsion to obtain microcapsules includes: adding the prepared prepolymer solution to the oil-in-water emulsion and stirring; adding dilute hydrochloric acid to the mixture for the first reaction to adjust the pH value of the mixture to a second value; heating and performing the second reaction, and then cooling; after cooling to room temperature, adding sodium hydroxide to obtain a suspension; performing post-treatment on the suspension to obtain microcapsules.

[0071] In this embodiment, the prepared prepolymer solution is added to the oil-in-water emulsion and stirred evenly to ensure that the prepolymer solution can uniformly coat the surface of the oil droplets to form the shell layer of the microcapsules. Among them, the addition method of the prepolymer solution includes, but is not limited to, a dropper to slowly add the prepolymer solution to the oil-in-water emulsion. By changing the pH value, the reaction conditions are adjusted to promote the dehydration condensation reaction of the prepolymer to form a stable microcapsule shell layer. By heating to the set temperature, the cross-linking reaction of the prepolymer is accelerated. When heating to the set temperature, continuously stirring for the set reaction duration helps to accelerate the cross-linking reaction, form a denser shell layer, and improve the durability and stability of the microcapsules. By slowly cooling, the stress concentration and cracking of the shell layer caused by too rapid temperature change can be avoided, ensuring the integrity of the microcapsules. After cooling to room temperature, adding sodium hydroxide to adjust the pH value to neutral can remove the excess acid in the reaction system, prevent the damage of the acidic environment to the microcapsule core material, and thus optimize the performance of the microcapsules.

[0072] Optionally, the steps for post-treating the suspension include: repeatedly washing the obtained suspension with deionized water and acetone, followed by suction filtration, and drying to obtain microcapsules, so as to obtain pure microcapsules.

[0073] Optionally, the second value is from 3 to 4, and the specific values of the second value include, but are not limited to, 3 or 4.

[0074] Optionally, the conditions for adding dilute hydrochloric acid for the first reaction are that the reaction temperature is 20°C to 25°C, and the set reaction duration is 1 h to 3 h. The specific values of the set reaction duration include, but are not limited to: 1 h, 2 h, or 3 h. The mass fraction of the dilute hydrochloric acid is 8 wt% to 10 wt%, and the specific concentrations include, but are not limited to, 8 wt%, 9 wt%, or 10 wt%.

[0075] Optionally, the conditions for the second reaction include: the reaction temperature is 55°C to 60°C, and the reaction duration is 1.5 h to 2 h. Among them, the reaction temperature of the second reaction includes, but is not limited to, 55°C, 58°C, or 60°C. The specific reaction durations include, but are not limited to, 1.5 h, 1.7 h, 1.9 h, or 2 h.

[0076] Optionally, the conditions for cooling include: the cooling temperature is 20°C to 25°C. Among them, the specific values of the cooling temperature include, but are not limited to, 20°C, 22°C, or 25°C.

[0077] Optionally, the addition amount of sodium hydroxide satisfies that the pH value of the suspension is 7 to 8. The specific pH values are 7 or 8.

[0078] In this embodiment, dilute hydrochloric acid or citric acid is added to the uniformly stirred mixture and continued for 1 h to 3 h to adjust the pH value of the mixture to the second value. Adjusting the pH value to the acidic range can promote the dehydration condensation reaction of the prepolymer, and ultimately form a stable cross-linked network structure. The adjustment time of 1 h to 3 h can ensure the full progress of the reaction, and at the same time avoid the unevenness or rupture of the microcapsule shell layer caused by too rapid change of the pH value. Heat to the set temperature of 55°C to 60°C and continue stirring for the set reaction duration of 1.5 h to 2 h, and then cool. The heating temperature of 55°C to 60°C can accelerate the reaction rate of the functional groups in the prepolymer, promote the cross-linking reaction, and at the same time will not be too high to cause emulsion damage or core material degradation. Continuous stirring can ensure the uniform distribution of the prepolymer in the emulsion and the full progress of the cross-linking reaction to form a strong microcapsule shell layer. The appropriate time can balance the formation speed and strength of the shell layer.

[0079] In some embodiments, the substrate is a substrate with a micro-arc oxidation coating.

[0080] In this embodiment, in combination with Figure 1 the structural schematic diagram of the self-healing composite coating 10 shown in Figure 2Cross-sectional microscopic morphology diagram of the self-healing composite coating 10 shown. The micro-arc oxidation coating 130 is prepared on the surface of the substrate 110 as the bottom layer through the micro-arc oxidation technology. The coating containing self-healing microcapsules is coated on the surface of the micro-arc oxidation coating 130, so as to form a self-healing coating 120 on the upper part of the micro-arc oxidation coating 130. The self-healing coating 120 containing microcapsules seals the micro-arc oxidation coating 130 to prevent the corrosive medium from corroding the alloy substrate through the micropores and microcracks on the micro-arc oxidation coating 130, improving the corrosion resistance of the self-healing composite coating 10. At the same time, the self-healing composite coating 10 has self-healing ability, can repair the microcracks generated by external conditions during service, significantly extends the service life of the coating, and also extends the service time of the light metal material.

[0081] Optionally, the step of preparing the substrate with the micro-arc oxidation coating includes: placing the substrate in the electrolyte, using the substrate as the anode and stainless steel as the cathode, and performing micro-arc oxidation treatment to obtain the substrate with the micro-arc oxidation coating.

[0082] In this embodiment, the oxide coating prepared by the micro-arc oxidation technology has a strong bonding force with the substrate, and can effectively improve the hardness, corrosion resistance, wear resistance, electrical insulation and other properties of the metal material.

[0083] Optionally, the components of the electrolyte include sodium silicate, sodium hydroxide and sodium fluoride. Among them, sodium silicate can also be replaced by sodium phosphate. Sodium fluoride can also be replaced by sodium hexametaphosphate.

[0084] Optionally, the substrate is a magnesium alloy substrate, and the components of the electrolyte include sodium silicate, sodium hydroxide and sodium fluoride. Among them, the mass concentrations of the components are as follows: the mass concentration of sodium silicate ranges from 10 g / L to 30 g / L, the mass concentration of sodium hydroxide ranges from 2 g / L to 5 g / L, and the mass concentration of sodium fluoride ranges from 2 g / L to 10 g / L.

[0085] In this embodiment, by reasonably configuring the mass concentrations of sodium silicate, sodium hydroxide and sodium fluoride in the electrolyte, the dissolution and deposition rates of the coating are changed to improve the denseness of the coating.

[0086] Among them, the specific values of the mass concentration of sodium silicate include but are not limited to: 10 g / L, 15 g / L, 20 g / L, 25 g / L or 30 g / L. The specific values of the mass concentration of sodium hydroxide include but are not limited to: 2 g / L, 3 g / L, 4 g / L or 5 g / L. The specific values of the mass concentration of sodium fluoride include but are not limited to: 2 g / L, 4 g / L, 6 g / L, 8 g / L or 10 g / L.

[0087] Optionally, for the magnesium alloy substrate, the steps of micro-arc oxidation treatment include: according to a preset current density, a preset duty cycle, and a preset frequency, using a preset pulse treatment method, and stopping when the termination voltage reaches 400V. Among them, the preset pulse treatment method includes: a unipolar pulse output method or a bipolar pulse output method. The conditions corresponding to the unipolar pulse output method are as follows: the value range of the preset current density is 0.5A / dm 2 to 3A / dm 2 ; and / or, the value range of the preset duty cycle is 20% to 80%; and / or, the value range of the preset frequency is 100Hz to 1000Hz.

[0088] In this embodiment, by performing micro-arc oxidation treatment according to a preset current density, a preset duty cycle, and a preset frequency, the formation process of the coating can be precisely controlled to control the thickness and density of the coating. The specific values of the preset current density include but are not limited to: 0.5A / dm 2 , 1A / dm 2 , 1.5A / dm 2 , 2A / dm 2 , 2.5A / dm 2 or 3A / dm 2 . The specific values of the preset duty cycle include but are not limited to: 20%, 30%, 40%, 50%, 60%, 70%, or 80%. The specific values of the preset frequency include but are not limited to: 100Hz, 150Hz, 200Hz, 250Hz, 300Hz, 350Hz, 400Hz, 450Hz, 500Hz, 550Hz, 600Hz, 650Hz, 700Hz, 750Hz, 800Hz, 8500Hz, 900Hz, 950Hz, or 1000Hz.

[0089] Optionally, the substrate is an aluminum alloy substrate, and the components of the electrolyte include sodium silicate, sodium hydroxide, and sodium citrate. Among them, the mass concentrations of the respective components are as follows: the value range of the mass concentration of sodium silicate is 15g / L to 20g / L, the value range of the mass concentration of sodium hydroxide is 1g / L to 2g / L, and the value range of the mass concentration of sodium citrate is 5g / L to 7g / L.

[0090] In this embodiment, sodium silicate plays a role in increasing the viscosity of the electrolyte and promoting film formation in the electrolyte. An appropriate concentration of sodium silicate can ensure the stability of the electrolyte and good compatibility with the aluminum alloy substrate, preventing adverse effects of the electrolyte on the substrate. Sodium hydroxide, as an activator, can remove the oxide layer on the surface of the aluminum alloy, improve the activity of the substrate, and is conducive to the formation of a uniform protective film. Sodium citrate, as a complexing agent, can form stable complexes with metal ions in the solution, reduce the deposition of metal ions, and keep the electrolyte clean. Buffering effect: Sodium citrate can also play a buffering role, maintaining the pH value of the electrolyte within an appropriate range, which is conducive to the formation of a high-quality protective film.

[0091] By reasonably configuring the mass concentrations of each component, the uniformity and denseness of the obtained micro-arc oxidation coating thickness can be improved, and the corrosion resistance of the aluminum alloy substrate can be enhanced.

[0092] Among them, the specific values of the mass concentration of sodium silicate include but are not limited to: 15 g / L, 16 g / L, 17 g / L, 18 g / L, or 20 g / L. The specific values of the mass concentration of sodium hydroxide include but are not limited to: 1 g / L, 1.2 g / L, 1.4 g / L, 1.6 g / L, 1.8 g / L, or 2 g / L. The specific values of the mass concentration of sodium citrate include but are not limited to: 5 g / L, 5.5 g / L, 6 g / L, 6.5 g / L, or 7 g / L.

[0093] Optionally, for the aluminum alloy substrate, the steps of micro-arc oxidation treatment include: using a preset pulse treatment method according to a preset current density, a preset duty cycle, and a preset frequency, and maintaining a set treatment duration. Among them, the preset pulse treatment method includes: a unipolar pulse output method or a bipolar pulse output method. The conditions corresponding to the unipolar pulse output method are as follows: the value range of the preset current density is 7 A / dm 2 to 9 A / dm 2 ; and / or, the value range of the preset duty cycle is 20% to 40%; and / or, the value range of the preset frequency is 400 Hz to 600 Hz; and / or, the value range of the set treatment duration is 15 min to 20 min.

[0094] In this embodiment, by performing micro-arc oxidation treatment according to a preset current density, a preset duty cycle, and a preset frequency, the coating formation process can be precisely controlled to control the thickness and denseness of the coating. The specific values of the preset current density include but are not limited to: 7 A / dm 2 , 7.5 A / dm 2 , 8 A / dm 2 , 8.5 A / dm 2 or 9 A / dm 2The specific values of the preset duty ratio include but are not limited to: 20%, 25%, 30%, 35%, or 40%. The specific values of the preset frequency include but are not limited to: 400 Hz, 450 Hz, 500 Hz, 550 Hz, or 600 Hz. The specific values of the set processing duration include but are not limited to: 15 min, 16 min, 17 min, 18 min, 19 min, or 20 min.

[0095] Optionally, before the step of placing the substrate in the electrolyte, it further includes: pre-treating the substrate. The step of pre-treating the substrate includes: degreasing the substrate with acetone. Then, ultrasonic cleaning is performed using anhydrous ethanol. After cleaning, it is dried.

[0096] In this embodiment, the substrate is degreased with acetone to remove the oil stains on the surface of the substrate, improve the bonding degree between the coating and the substrate, and facilitate the growth of the subsequent coating. The substrate is cleaned with anhydrous ethanol in an ultrasonic cleaner to remove the residual acetone and prevent adverse effects on the micro-arc oxidation process. The substrate is dried with a hair dryer to prepare for the subsequent micro-arc oxidation treatment.

[0097] Optionally, an epoxy resin coating containing microcapsules is evenly sprayed on the surface of the micro-arc oxidation coating of the magnesium alloy using an air spraying device. The sprayed coating is placed in an oven and cured according to the curing conditions of the epoxy resin coating. The curing time, temperature, and humidity are determined according to the specific type of coating.

[0098] In some embodiments, a microcapsule-based self-healing coating is provided, and the self-healing coating is prepared by using the preparation method of the microcapsule-based self-healing coating described in any one of the above embodiments.

[0099] The microcapsule-based self-healing coating provided by the present disclosure is prepared by using the preparation method of the microcapsule-based self-healing coating described in any one of the above embodiments. Since the microcapsules of the self-healing coating are loaded with the repair agent tung oil. In the case of damage to the self-healing coating, the microcapsules at the damaged part rupture, releasing the core material tung oil. The core material flows inside the coating and fills the damaged part, finally repairing the damaged part to achieve the effect of automatic repair, slowing down the corrosion rate of the alloy substrate, improving the corrosion resistance, and extending the protection time of the coating.

[0100] Optionally, the self-healing coating 120 is formed on the basis of the micro-arc oxidation coating 130, and thus a composite coating 10 is formed on the surface of the light alloy, combining Figure 1 and Figure 2As shown. The composite coating 10 provided by the embodiments of the present disclosure includes a micro-arc oxidation coating 130 and a self-healing coating 120 doped with self-healing microcapsules. The microcapsules are made of melamine-urea-formaldehyde resin loaded with a repair agent, tung oil. The micro-arc oxidation coating 130 is prepared under the condition of a weakly alkaline electrolyte of silicate. The micro-arc oxidation coating 130 is a coating formed on the surface of the substrate 110 through micro-arc oxidation technology, which can inhibit the filiform corrosion of light metal alloys and provide a buffering time for the curing of the repair agent. Through the synergistic effect of the two, the service life of the coating is extended, and the problem that the surface coating of light metal alloys in the existing technology has poor corrosion resistance under corrosion conditions and cannot be used for a long time is solved. At the same time, the composite coating 10 has self-healing ability and can repair the microcracks generated by external conditions during service, significantly extending the service life of the coating.

[0101] In some embodiments, a light metal alloy is provided, and the surface of the light metal alloy includes a microcapsule-based self-healing coating as described in any of the above embodiments.

[0102] The surface of the magnesium alloy provided by the present disclosure includes a microcapsule-based self-healing coating as described in any of the above embodiments. The self-healing coating can effectively isolate the direct contact between the surface of the light metal alloy and the external corrosion environment, such as oxygen, moisture, salt spray, etc., thereby significantly improving the corrosion resistance of the magnesium alloy. Since the self-healing coating can automatically repair microcracks or defects by releasing the repair agent in the core material when damaged, the service life of the light metal alloy can be extended, and the maintenance frequency and cost can be reduced.

[0103] Optionally, the light metal alloy includes, but is not limited to, magnesium alloy or aluminum alloy.

[0104] Embodiment

[0105] Embodiment 1

[0106] The substrate is made of a magnesium alloy material: AZ31B magnesium alloy sheet

[0107] (1) Preparation of self-healing microcapsules

[0108] Synthesis of melamine-urea-formaldehyde (MUF) prepolymer: Weigh 1.80 g of urea, 1.26 g of melamine and 7.30 g of formaldehyde solution (mass fraction of 37%) and add them into a three-necked flask. After stirring and dissolving, adjust its pH value to 8.0 with triethanolamine, heat up to 70 °C and react for 1 h to obtain a transparent and viscous prepolymer solution, and cool it to room temperature for standby.

[0109] Preparation of core material: Add a sodium dodecylbenzenesulfonate solution with a mass fraction of 2% into a three-necked flask, add 8.64 g of tung oil, emulsify it at a stirring rate of 1000 r / min for 30 min, and then add 1 - 2 drops of n-octanol to defoam, forming a stable oil-in-water emulsion.

[0110] Synthesis of microcapsules: Slowly add the prepolymer solution to the obtained oil-in-water emulsion. After stirring evenly, slowly add dilute hydrochloric acid with a mass fraction of 10% using a peristaltic pump to adjust the pH value of the system to 4.0, heat up to 60 °C, and stir and react for 2 h. After cooling to room temperature, adjust the pH value to 7.0 with sodium hydroxide with a mass fraction of 10%. Wash the obtained suspension repeatedly with deionized water and acetone, filter by suction, and dry to obtain microcapsules.

[0111] (2) Preparation of self-healing coating

[0112] Mix E-51 epoxy resin and polyamide curing agent in a specified ratio of 1:1, add microcapsules with a mass fraction of 5%, stir evenly, and then coat the paint on the surface of the magnesium alloy by air spraying. After curing, a self-healing coating is obtained.

[0113] In this example, the self-healing coating was scratched. After curing for 48 h, as Figure 4 shown, when the microcapsule content is 5%, some defects can already be repaired.

[0114] Example 2

[0115] The base material is selected as a magnesium alloy material: AZ31B magnesium alloy sheet

[0116] (1) Preparation of self-healing microcapsules

[0117] Synthesis of melamine-urea-formaldehyde (MUF) prepolymer: Weigh 1.80 g of urea, 1.26 g of melamine, and 7.30 g of formaldehyde solution (mass fraction of 37%) and add them into a three-necked flask. After stirring and dissolving, adjust its pH value to 8.0 with triethanolamine, heat up to 70 °C and react for 1 h to obtain a transparent and viscous prepolymer solution, and cool it to room temperature for standby.

[0118] Preparation of core material: Add a sodium dodecylbenzenesulfonate solution with a mass fraction of 2% into a three-necked flask, add 8.64 g of tung oil, emulsify it at a stirring rate of 1000 r / min for 30 min, and then add 1 - 2 drops of n-octanol to defoam, forming a stable oil-in-water emulsion.

[0119] Synthesis of microcapsules: The prepolymer solution was slowly added to the obtained emulsion. After stirring evenly, a 10% mass fraction of dilute hydrochloric acid was slowly added using a peristaltic pump to adjust the pH value of the system to 4.0. The temperature was raised to 60 °C, and the mixture was stirred and reacted for 2 h. After cooling to room temperature, the pH value was adjusted to 7.0 using 10% mass fraction of sodium hydroxide. The obtained suspension was repeatedly washed with deionized water and acetone, filtered by suction, and dried to obtain microcapsules.

[0120] (2) Preparation of self-healing coating

[0121] E-51 epoxy resin and polyamide curing agent were mixed in a specified ratio of 1:1, 10% mass fraction of microcapsules was added, and the mixture was stirred evenly. Then, the coating was applied to the surface of the magnesium alloy by air spraying, and a self-healing coating was obtained after curing.

[0122] In this example, the self-healing coating was scratched. After curing for 48 h, as Figure 5 shown. When the microcapsule content was 15%, the scratch was basically completely repaired.

[0123] Example 3

[0124] Combined with Figure 3 shown, the schematic diagram of the micro-arc oxidation device 20 used in the following examples. The micro-arc oxidation device 20 includes a power supply 210, an electrolytic cell 220, and wires 230 connected to the anode and cathode of the power supply 210. The anode is connected to the light alloy metal specimen 240 through the wire 230, and the cathode is connected to the stainless steel plate 250 through the wire 230.

[0125] The substrate is made of magnesium alloy material: AZ31B magnesium alloy sheet

[0126] (1) Preparation of micro-arc oxidation coating

[0127] Substrate and pretreatment: The magnesium alloy sheet was cut into plate specimens of 50 mm × 30 mm × 2 mm, and a hole was drilled in the middle of the upper part of the specimen to facilitate subsequent connection of wires. The specimens were sequentially rinsed with clean water, degreased by alkali washing, pickled, washed with water, and dried for later use. Composition of electrolyte: Na 2 SiO 3 : 20 g / L, NaOH: 2 g / L, NaF: 2 g / L.

[0128] Micro-arc oxidation treatment: The magnesium alloy specimens were subjected to micro-arc oxidation treatment in the above electrolyte. A pulsed power supply was used, the magnesium alloy specimens were connected to the anode, and the 304 stainless steel plate was connected to the cathode. The current was applied in a constant current mode and stopped when the set voltage reached 400 V. The current density was 1 A / dm 2 , the frequency was 500 Hz, and the duty cycle was 50%. After the micro-arc oxidation treatment was completed, the specimens were rinsed with clean water and then placed in a drying oven at 100 °C for drying.

[0129] (2) Preparation of self-healing microcapsules

[0130] Synthesis of melamine-urea-formaldehyde (MUF) prepolymer: Weigh 1.80 g of urea, 1.26 g of melamine and 7.30 g of formaldehyde solution (mass fraction 37%) and add them into a three-necked flask. After stirring and dissolving, adjust the pH value to 8.0 with triethanolamine, heat up to 70 °C and react for 1 h to obtain a transparent and viscous prepolymer solution. Cool it to room temperature for standby.

[0131] Preparation of core material: Add a 2% sodium dodecylbenzenesulfonate solution into a three-necked flask, add 8.64 g of tung oil, emulsify at a stirring rate of 1000 r / min for 30 min, then add 1 - 2 drops of n-octanol to defoam and form a stable oil-in-water emulsion.

[0132] Synthesis of microcapsules: Slowly add the prepolymer solution to the obtained oil-in-water emulsion. After stirring evenly, slowly add 10% dilute hydrochloric acid with a peristaltic pump to adjust the pH value of the system to 4.0, heat up to 60 °C and stir and react for 2 h. After cooling to room temperature, adjust the pH value to 7.0 with 10% sodium hydroxide. Wash the obtained suspension repeatedly with deionized water and acetone, filter by suction, and dry to obtain microcapsules.

[0133] (3) Preparation of micro-arc oxidation composite self-healing coating

[0134] Mix E-51 epoxy resin and polyamide curing agent in a specified ratio of 1:1, add 5% mass fraction of microcapsules, stir evenly, and then coat the coating on the surface of the micro-arc oxidation coating of magnesium alloy by air spraying. After curing, a composite coating is obtained.

[0135] The composite coating obtained in this example includes a micro-arc oxidation coating and an epoxy self-healing coating doped with self-healing microcapsules. The microcapsules use melamine-urea-formaldehyde resin to load the repair agent tung oil. The micro-arc oxidation coating is prepared under the condition of a weakly alkaline electrolyte of silicate. The micro-arc oxidation coating can inhibit the filiform corrosion of magnesium alloy and provide a buffering time for the curing of the repair agent. Through the synergistic effect of the two, the service life of the coating is extended, and the problem that the surface coating of magnesium alloy in the existing technology has poor corrosion resistance and cannot be used for a long time under corrosion conditions is solved.

[0136] Comparative example

[0137] The substrate is made of magnesium alloy material: AZ31B magnesium alloy sheet

[0138] (1) Preparation of self-healing microcapsules

[0139] Synthesis of melamine-urea-formaldehyde (MUF) prepolymer: Weigh 1.80 g of urea, 1.26 g of melamine and 7.30 g of formaldehyde solution (mass fraction 37%) and add them into a three-necked flask. After stirring and dissolving, adjust the pH value to 8.0 with triethanolamine, heat up to 70 °C and react for 1 h to obtain a transparent viscous prepolymer solution, which is cooled to room temperature for standby.

[0140] Preparation of core material: Add a 2% sodium dodecylbenzenesulfonate solution into a three-necked flask, add 8.64 g of tung oil, emulsify at a stirring rate of 1000 r / min for 30 min, then add 1 - 2 drops of n-octanol to defoam and form a stable oil-in-water emulsion.

[0141] Synthesis of microcapsules: Slowly add the prepolymer solution to the obtained emulsion. After stirring evenly, slowly add 10% dilute hydrochloric acid with a peristaltic pump to adjust the pH value of the system to 4.0, heat up to 60 °C, stir and react for 2 h. After cooling to room temperature, adjust the pH value to 7.0 with 10% sodium hydroxide. Wash the obtained suspension repeatedly with deionized water and acetone, filter by suction, and dry to obtain microcapsules.

[0142] (2) Preparation of coating

[0143] Mix E-51 epoxy resin and polyamide curing agent in a specified ratio of 1:1, without adding microcapsules, stir evenly, and then coat the magnesium alloy surface with the coating by air spraying. After curing, a coating is obtained.

[0144] In this example, the coating without microcapsules is used as a blank control group. After the coating is scratched and cured for 48 h, as Figure 6 shown, the coating does not have a self-healing effect.

[0145] By comparing the self-healing coatings obtained in the above Example 1, Example 2 and Example 3 with the coatings of the comparative example, it can be seen that the scratches of the composite coating with added microcapsules are repaired, indicating that the polymer generated by the repair agent tung oil has successfully filled the scratches. And as the content of microcapsules increases, the number of microcapsules broken during scratching also increases, and the more repair agent that can act on the cracks of the coating, the self-healing effect is improved, and the protection time of the coating is extended.

[0146] The above description and the drawings sufficiently illustrate embodiments of the present disclosure so that those skilled in the art can practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Unless explicitly required, individual components and functions are optional, and the order of operations may vary. Parts and features of some embodiments may be included in or substituted for parts and features of other embodiments. Embodiments of the present disclosure are not limited to the structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method for preparing a self-healing coating based on microcapsules, characterized in that: include: Step 1: adding microcapsules to a mixed solution of epoxy resin and curing agent, stirring, and obtaining a coating; Step 2: applying the coating to the surface of the substrate to obtain a self-healing coating; Wherein, the preparation steps of the microcapsules include: S1. preparing a prepolymer solution, wherein the components of the prepolymer solution include urea and formaldehyde; S2. Preparing an oil-in-water emulsion, comprising adding tung oil to a surfactant solution, and emulsifying the solution to obtain the oil-in-water emulsion; S3. Mixing the prepolymer solution and the oil-in-water emulsion to obtain microcapsules.

2. The method for preparing the self-repairing coating according to claim 1, characterized in that: In step 1: The mass of the added microcapsules accounts for 0.1wt% to 15wt% of the total weight of the coating; Preferably, the mass ratio of epoxy resin to curing agent is 1:1 to 2:1; Preferably, the epoxy resin is selected from one or more of bisphenol A epoxy resin E-51 and bisphenol A epoxy resin E-44; Preferably, the curing agent is selected from one or more of polyamide, triethylenetetramine and diethylenetriamine.

3. The method for preparing the self-repairing coating according to claim 1, characterized in that: The S1 includes: Mix urea and formaldehyde solution and stir to dissolve; adding triethanolamine to the dissolved solution to adjust the pH value of the solution to a first value to obtain a first solution; heating the first solution to obtain the prepolymer solution; Preferably, the preset first molar ratio of urea to formaldehyde in the prepolymer solution is: 1:2 to 1:1; Preferably, the first value is 7 to 9; Preferably, the mass fraction of the formaldehyde solution is 37wt% to 40wt%; Preferably, the conditions for heating the first solution include: a heating temperature of 60° C. to 80° C., and a heating duration of 50 min to 80 min.

4. The method for preparing the self-repairing coating according to claim 1, characterized in that: The components of the prepolymer solution also include melamine, and the S1 includes: Mix urea, melamine and formaldehyde solution and stir to dissolve; adding triethanolamine to the dissolved solution to adjust the pH value of the solution to a third value to obtain a second solution; heating the second solution to obtain the prepolymer solution; Preferably, the preset second molar ratio of urea, melamine and formaldehyde in the prepolymer solution is: 3:1:6 to 3:1:12; Preferably, the third value is 7 to 9; Preferably, the mass fraction of the formaldehyde solution is 37wt% to 40wt%; Preferably, the conditions for heating the second solution include: a heating temperature of 60° C. to 80° C., and a heating duration of 50 min to 80 min.

5. The method for preparing the self-repairing coating according to claim 3 or 4, characterized in that: The mass of tung oil is M t , the sum of the mass of all components added to the prepolymer solution is M z , M t :M z =1:1 to 2:

1.

6. The method for preparing a self-repairing coating according to any one of claims 1 to 4, characterized in that: In S2, The surfactant is selected from one or more of sodium dodecylbenzene sulfonate, OP-10 and polysorbate-80; and / or, The mass fraction of the surfactant solution is 0.5wt% to 3wt%; and / or, The emulsification treatment conditions include: a stirring rate of 600 r / min to 1200 r / min, and an emulsification time of 20 min to 60 min.

7. The method for preparing a self-repairing coating according to any one of claims 1 to 4, characterized in that: The S3 includes: Adding the prepared prepolymer solution into the oil-in-water emulsion and stirring to obtain a mixed solution; Adding dilute hydrochloric acid to the mixed solution for a first reaction, and adjusting the pH value of the mixed solution to a second value; heating and performing a second reaction, and then cooling; After cooling to room temperature, sodium hydroxide was added to obtain a suspension; post-treating the suspension to obtain microcapsules; Preferably, the second value is 3 to 4; Preferably, the conditions of the first reaction include: the reaction temperature is 20°C to 25°C, and the reaction time is set to 1h to 3h; Preferably, the mass fraction of the dilute hydrochloric acid is 8wt% to 10wt%; Preferably, the conditions of the second reaction include: a reaction temperature of 55°C to 60°C, and a reaction duration of 1.5h to 2h; Preferably, the cooling conditions include: the cooling temperature is 20°C to 25°C; Preferably, the amount of sodium hydroxide added is such that the pH value of the suspension is 7 to 8.

8. The method for preparing a self-repairing coating according to any one of claims 1 to 4, characterized in that: The substrate is a substrate with a micro-arc oxidation coating; Preferably, the substrate is selected from one or more of a magnesium alloy sheet and an aluminum alloy sheet.

9. A self-healing coating based on microcapsules, characterized in that: The self-healing coating is prepared by the method for preparing a microcapsule-based self-healing coating according to any one of claims 1 to 8.

10. A light metal alloy, characterized in that: The surface of the light metal alloy comprises the self-healing coating as claimed in claim 9.

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