A magnetically driven highly dispersed self-healing coating, its preparation method and application on the underwater metal surface

Abstract

The present invention discloses a magnetically driven highly dispersed self-healing coating, its preparation method and application on the underwater metal surface. The preparation steps specifically include: preparation of functional magnetic response self-healing microcapsules; preparation of magnetic highly dispersed self-healing polyurethane coatings; purification pretreatment and bionic structuring pretreatment of the metal substrate surface; the magnetic polyurethane coating is coated on the metal substrate surface in a spatialized magnetic field and homogenized by a self-leveling method, and cured in the spatial magnetic field region. Through the spatial magnetization difference, the present invention drives the magnetic microcapsules to be uniformly distributed in the coating, localizes the utility of the functional microcapsules, and enhances the timeliness of multifunctional repair and the adhesion of the coating. The present invention uniformly incorporates functional self-healing microcapsules into the polyurethane coating, not only making the coating multifunctional, but also having the functions of anti-fouling, anti-corrosion and self-healing, breaking through the technical bottleneck of microcapsule agglomeration, and effectively improving the service life of the coating.

Description

Technical Field

[0001] The present invention belongs to the technical field of the application of self - repairing coatings for underwater metal surfaces. Background Art

[0002] Metal corrosion has caused serious harm in aspects such as economic development, resource environment, and social security. Due to its unique factors such as pH, humidity, salinity, and marine organisms, the marine environment is extremely likely to cause metal corrosion, and the economic losses caused by metal corrosion exceed two trillion yuan every year. Coating metal materials can effectively prevent corrosion, that is, coating a layer with anti - corrosion performance on the metal surface, such as polyurethane coatings, silicone coatings, and graphene coatings. These coatings isolate corrosive media through physical shielding, effectively inhibit the occurrence of corrosion, and improve economic benefits.

[0003] However, during service, changes in the environment and mechanical forces will cause cracks to grow in the coating. Once cracks appear on the surface of a single coating and cannot be repaired in time, it will accelerate the damage of the coating, greatly reducing the service life of the coating. The concept of microcapsules provides a new idea for solving this problem. Adding self - repairing microcapsules to the coating can effectively repair coating cracks within a certain range. It can respond intelligently when stimulated by cracks, release repair agents to form a crack protection layer, and effectively improve the service life of the coating. How to apply self - repairing microcapsules with both anti - corrosion and anti - fouling properties in the coating to achieve long - term and stable protection needs further consideration.

[0004] During actual service, there is an indefinite and random distribution of functional self - repairing microcapsules in the coating, making the feedback regulation path in the corrosion area complex, with a long response time, forming a "maze effect", and it is difficult to achieve effective and timely repair of the crack area. Therefore, achieving a uniform distribution of functional self - repairing microcapsules in the coating has become a key issue in improving the anti - corrosion performance of the coating. The present invention will break through the technical bottleneck of microcapsule agglomeration in the coating, providing ideas for further improving the service life of the coating. Summary of the Invention

[0005] In view of the above - mentioned deficiencies in the prior art, to overcome the defect of the short service life of the coating caused by uneven distribution of microcapsules and single function in the existing coating technology, the present invention provides a magnetically - driven highly - dispersed self - repairing coating and its preparation method, and the technical solution adopted is as follows:

[0006] A preparation method of a magnetically - driven highly - dispersed self - repairing coating, the specific steps are as follows:

[0007] Step 1: Carry out in - situ polymerization reaction on a reaction system containing conductive polyaniline, magnetically - driven medium source Fe 3 O 4 , tung oil, and emulsifier OP - 10 to obtain functional magnetically - responsive self - repairing microcapsules:

[0008] 1) 400 ml of deionized water was measured and placed in a 500 ml beaker. A stirring bar was placed in the beaker and a magnetic stirrer was placed. 2 g of sodium alginate was weighed and slowly added to the 400 ml of deionized water along a vortex of distilled water. A glass rod was used to stir to separate the agglomerated parts in the beaker. After stirring with a magnetic stirrer for 10 to 15 min, the beaker was sealed with a sealing film and allowed to stand for 12 h for full swelling, thereby obtaining a 0.5 wt% sodium alginate solution;

[0009] 2) Take 0.1% OP-10 emulsifier of sodium alginate solution and place it in a tissue crusher and stir at 5000 rpm for 5 to 10 minutes. Weigh the core material tung oil and magnetic nanoparticles Fe in a mass ratio of 1:0.2:0.018. 3 O 4 , antifouling agent PANI, add the above materials into a tissue crusher in turn, stir at 5000 rpm for 5-10 min, pour out the oil-in-water emulsion and skim off the foam on the surface to obtain an oil-in-water emulsion A containing conductive polyaniline and ferrosoferric oxide.

[0010] 3) 400 ml of a 5 wt % calcium chloride solution is prepared and placed on a magnetic stirrer for thorough stirring, and at the same time, the water-in-oil emulsion A is dripped into the calcium chloride solution through a syringe or sprayed into the calcium chloride solution along the solution stirring vortex with a nano-spray gun to form a solution B, wherein sodium alginate and calcium chloride react to form a calcium alginate core-shell structure, and other substances do not react, and tung oil, polyaniline and Fe 3 O 4 Encapsulated with calcium alginate.

[0011] 4) Solution B was filtered step by step with filter screens of 50 to 200 meshes, washed three times with deionized water, and then the temperature was stabilized at -60°C, freeze-dried for 12 hours, and functional magnetic responsive self-healing microcapsules were obtained after grinding.

[0012] Step 2: reacting a mixed system comprising polyurethane prepolymer, ethyl acetate, MOCA, and functional magnetic response self-healing microcapsules to obtain a magnetic highly dispersed self-healing polyurethane coating:

[0013] 1) Weighing polyurethane prepolymer and ethyl acetate in a mass ratio of 1:1, weighing out 0.5wt% to 3wt% of the total mass of functional magnetic response self-healing microcapsules and placing them in a beaker, dropping ethyl acetate into the mixture and stirring and ultrasonicating for 10 to 15 minutes to mix, preheating the polyurethane prepolymer at 70° C. to a uniform flow state, adding the prepolymer to the solution and stirring sufficiently, then sealing the beaker with a sealing film, stirring and ultrasonicating for 10 to 20 minutes to make the microcapsules fully and evenly distributed in the mixed liquid;

[0014] 2) Heat the MOCA reagent (curing agent) to 120 °C to melt it, and add the MOCA reagent to the above mixed solution according to the mass ratio of MOCA: polyurethane prepolymer of 100:18, and stir and ultrasonically mix for 5 - 10 min again to obtain a magnetic highly dispersed self-healing polyurethane coating.

[0015] Step 3: Perform purification pretreatment and bionic structuring pretreatment on the surface of the metal substrate:

[0016] 1) Select emery with a particle size of 80 - 120 mesh, perform sandblasting on both sides of the metal material to remove rust stains on the metal surface, and wipe with alcohol to remove oil stains on the metal surface.

[0017] 2) Using the tree frog toe as a bionic prototype, imitate the adsorption force advantage of the tree frog toe, construct a cubic grid model imitating the tree frog toe structure in CAD, etch through a laser marking machine according to the uniformly distributed cubic aligned grids and cubic misaligned grids to create a structural magnetization difference, and drive the dispersion of magnetic response microcapsules through a magnetic field; the size parameters of the bionic cubic grid are set as follows: length L = 300 - 500 μm, width W = 50 - 150 μm, depth D = 25 - 100 μm, and optimize.

[0018] Step 4: Set the spatial regionalized magnetic field:

[0019] Place two cylindrical permanent magnets parallel to both sides of the metal substrate respectively, with the laser-etched metal surface close to the N pole of the magnetic field. The distance between both sides of the metal substrate material and the permanent magnets is 0.5 - 2.5 cm. The etched surface is magnetized under the action of the magnetic field to form a spatial magnetization difference.

[0020] Step 5: Coating the magnetic highly dispersed self-healing polyurethane coating on the surface of the metal base in the spatialized magnetic field and homogenizing it by the self-leveling method, and curing it in the spatial magnetic field region to obtain a magnetically driven highly dispersed self-healing coating.

[0021] The coating application methods include but are not limited to at least one of drop coating, high-pressure spraying, and electrostatic spraying. Before coating, place the coating in an ultrasonic environment for 5 min to mix evenly, suck a constant mass of the coating with a coating device and evenly coat it on the surface of the pretreated sample. Make the surface thickness of the coating consistent by the self-leveling method. Keep a constant speed during the coating process to avoid generating bubbles. Immediately check whether there are bubbles on the coating surface after coating, and use a syringe needle to break the bubbles to ensure the uniformity of the coating. After complete drying, the magnetic polyurethane coating is prepared.

[0022] Furthermore, in step 1, the particle size of the magnetic nanoparticles Fe 3 O 4 is preferably 5 - 60 nm.

[0023] Furthermore, the thickness of the magnetically driven highly dispersed self-healing coating layer obtained in Step 5 is 10 - 80 μm.

[0024] Application of the magnetically driven highly dispersed self-healing coating on the underwater metal surface.

[0025] Beneficial effects of the present invention:

[0026] (1) By incorporating magnetic nanoparticles Fe 3 O 4 into the self-healing microcapsules, constructing a spatial magnetization difference through a strong adhesion structure imitating the tree frog's toes, driving the magnetic microcapsules to be evenly distributed in the coating, breaking through the technical bottleneck of microcapsule agglomeration, enabling the functional microcapsules to fully exert the anti-fouling, anti-corrosion and self-healing effects, enhancing the coating adhesion, and effectively improving the service life of the coating.

[0027] (2) The present invention incorporates the anti-fouling material conductive polyaniline into the magnetic microcapsules, which can continue to prevent fouling of the coating after the self-healing of the damaged coating is completed, effectively protecting the coating. Incorporating the functional self-healing microcapsules evenly into the polyurethane coating not only makes the coating multifunctional, but also has the functions of anti-fouling, anti-corrosion and self-healing. Description of the drawings

[0028] Figure 1 is a step flow chart of the preparation of a magnetically driven highly dispersed self-healing coating and its application method on the underwater metal surface;

[0029] Figure 2 is a step flow chart of the preparation of functional magnetic-responsive self-healing microcapsules;

[0030] Figure 3 is a step flow chart of the preparation of a magnetic highly dispersed self-healing polyurethane coating;

[0031] Figure 4 is a step flow chart of the pretreatment of the metal substrate material.

[0032] Figure 5 is an etching diagram of the bionic cubic sequential grid of the metal substrate;

[0033] Figure 6 is an etching diagram of the bionic cubic staggered grid of the metal substrate;

[0034] Figure 7 is an SEM diagram of the prepared functional self-healing microcapsules;

[0035] Figure 8 is a magnetic polyurethane self-healing coating prepared under the action of a spatial magnetic field;

[0036] Figure 9The magnetic polyurethane coating prepared under the condition of no spatial magnetic field intervention;

[0037] Figure 10 The corrosion situation schedule of the coatings prepared in Example 1, Example 2, Example 3 and Comparative Example 1;

[0038] Figure 11 The pollutant adhesion rate diagrams of the coatings prepared in Example 1, Example 2, Example 3 and Comparative Example 1;

[0039] Figure 12 The schematic diagram of the self-healing mechanism during the dispersion of magnetic response microcapsules and the application of the coating. Detailed implementation manners

[0040] The technical solution of the present invention will be further explained and illustrated below in the form of specific embodiments. The implementation of the present invention is not limited to the following embodiments, and any form of variation and / or change made to the present invention will fall within the protection scope of the present invention.

[0041] Example 1:

[0042] Refer to Figures 1 to 4 In this example, a preparation method of a magnetically driven highly dispersed self-healing coating is as follows:

[0043] Step 1: Perform an in-situ polymerization reaction on a reaction system containing conductive polyaniline, a magnetic drive medium source Fe 3 O 4 , tung oil, and emulsifier OP-10 to obtain functional magnetic response self-healing microcapsules.

[0044] Among them, conductive polyaniline PANI is added as an antifouling component to the core material of the microcapsules to make the self-healing microcapsules multifunctional, and at the same time, magnetic nanoparticles Fe 3 O 4 are added as a magnetic drive medium source;

[0045] (1) Prepare a 0.5 wt% sodium alginate solution 12 h in advance for sufficient swelling. Measure 0.1% of the volume of the sodium alginate solution of the OP-10 emulsifier, and place it in a tissue homogenizer with the prepared sodium alginate solution and stir at 5000 rpm for 5 - 10 min. Weigh the core material tung oil, magnetic nanoparticles Fe 3 O 4 , and antifouling agent PANI according to the mass ratio of 1:0.2:0.018. Add the above materials to the tissue homogenizer in sequence, stir at 5000 rpm for 5 - 10 min, pour out the oil-in-water emulsion and skim off the surface foam to obtain an oil-in-water emulsion A containing conductive polyaniline and magnetite.

[0046] (2) Prepare a 5 wt% calcium chloride solution. Drop the oil-in-water emulsion A into the calcium chloride solution through syringes with needle apertures of 0.16 mm and 0.11 mm to form solution B and solution C. Spray the oil-in-water emulsion A into the calcium chloride solution through a nano spray gun to form solution D. Among them, sodium alginate and calcium chloride react to form a calcium alginate core-shell structure, and other substances do not react. Tung oil, polyaniline, and Fe 3 O 4 will be encapsulated by calcium alginate;

[0047] (3) Filter, wash, and freeze-dry solutions B, C, and D for 12 h respectively, and then grind them to obtain functional magnetic-responsive self-healing microcapsules with three particle sizes.

[0048] Step 2: React a mixed system containing polyurethane prepolymer, ethyl acetate, MOCA, and functional magnetic-responsive self-healing microcapsules to obtain a magnetically highly dispersed self-healing polyurethane coating:

[0049] (1) Add the polyurethane prepolymer heated at 70 °C and ethyl acetate to a beaker in a mass ratio of 1:1, and respectively add 0.5 wt% of the functional magnetic-responsive self-healing microcapsules prepared from solutions B, C, and D. Seal the beaker mouth with a sealing film, stir, and then ultrasonically mix evenly.

[0050] (2) Heat the MOCA reagent to 120 °C, and add MOCA to the above mixed solution according to the mass ratio of polyurethane prepolymer:MOCA = 100:18, and then stir and ultrasonically mix evenly again to obtain a magnetically driven highly dispersed self-healing coating.

[0051] Refer to Figures 10 to 12 , and drop the obtained coating onto the pretreated metal sample in a magnetic field environment and let it stand and dry to obtain a magnetically driven highly dispersed self-healing coating sample. The average particle sizes of the microcapsules finally obtained from solutions B, C, and D are measured to be 221 μm, 159 μm, and 74 μm respectively. After the salt spray test of 3.5 wt% NaCl in a constant temperature environment of 47 °C, for the magnetic-responsive coating containing self-healing microcapsules with an average particle size of 74 μm, the corrosion start time is 528 h, the attachment area of the adherents is 1.72%, and the self-healing rate reaches 58.4 ± 0.12. Rust spots appear on the magnetic-responsive coating containing self-healing microcapsules with an average particle size of 159 μm at 144 h, but the attachment area of its pollutants reaches 6.72%, and the self-healing rate is 41.4% ± 0.08. Rust spots appear on the magnetic-responsive coating containing self-healing microcapsules with an average particle size of 221 μm at 384 h, and the attachment area of its pollutants reaches 3.91%, and the self-healing rate is only 40.4 ± 0.07. It shows that the magnetic polyurethane coating containing self-healing microcapsules with a particle size of 74 μm prepared in this example has excellent corrosion resistance and anti-fouling performance, and at the same time has a good self-healing rate effect.

[0052] In the present invention, the self - healing rate calculation formula is

[0053]

[0054] where n represents the number of parallel specimens and m represents the number of scratches selected for each specimen.

[0055] Example 2

[0056] (1) Functional magnetic - responsive self - healing microcapsules prepared from Solution D in Example 1 were used.

[0057] (2) Polyurethane prepolymer heated at 70 °C and ethyl acetate were added to four beakers in a mass ratio of 1:1. Functional magnetic - responsive self - healing microcapsules with contents of 0.5 wt%, 1 wt%, 2 wt%, and 3 wt% were respectively added. The mouths of the beakers were sealed with sealing film, and after stirring, they were ultrasonically mixed evenly.

[0058] (3) The MOCA reagent was heated to melt at 120 °C. According to the mass ratio MOCA: polyurethane prepolymer = 18:100, the MOCA reagent was added to the above - mentioned mixed solution and stirred and ultrasonically mixed again to obtain magnetic - driven highly - dispersed self - healing coatings with different contents of functional self - healing microcapsules.

[0059] Refer to Figures 10 to 12 , and the obtained coatings were drop - coated onto pretreated metal specimens in a magnetic field environment and left to stand and dry to obtain magnetic - driven highly - dispersed self - healing coating specimens. After salt spray testing with 3.5% NaCl in a constant - temperature environment of 47 °C, the times when corrosion points appeared on the magnetic polyurethane self - healing coatings with self - healing microcapsule contents of 0.5 wt%, 1 wt%, 2 wt%, and 3 wt% were 528 h, 720 h, 240 h, and 912 h respectively, and the attached areas of pollutants were 1.72%, 1.51%, 1.46%, and 0.67% respectively. Further, the self - healing rates of the coatings were measured to be 58.4% ± 0.12, 78.3% ± 0.22, 95.1% ± 0.79, and 95.9% ± 1.27 respectively. It shows that the magnetic - driven highly - dispersed self - healing coating with a self - healing microcapsule content of 3 wt% prepared in this example has significantly improved corrosion resistance and anti - fouling performance, and at the same time has a significant advantage in self - healing effect, greatly increasing the service life of the coating.

[0060] Example 3

[0061] Refer to Figures 4 to 6 , Step 1: Perform purification pretreatment and bionic structuring pretreatment on the surface of the metal substrate:

[0062] 1) Emery with a particle size of 80 - 120 mesh was selected to perform sandblasting treatment on both sides of the metal material to remove rust stains on the metal surface, and then wiped with alcohol to remove oil stains on the metal surface.

[0063] 2) Using the tree frog toe as a bionic prototype, imitating the adsorption force advantage of the tree frog toe, a cubic grid model is constructed in CAD by imitating the structure of the tree frog toe. The laser marking machine is used to etch according to the uniformly distributed cubic sequential grid and cubic staggered grid to create a structural magnetization difference, and the magnetic response microcapsules are dispersed by magnetic field driving. The size parameters of the bionic cubic grid are set as follows: length L = 300 - 500 μm, width W = 50 - 150 μm, depth D = 25 - 100 μm, and optimization is carried out.

[0064] Step 2: Setting of the spatially regionalized magnetic field:

[0065] Two cylindrical permanent magnets are respectively placed parallel to both sides of the metal substrate. The laser-etched metal surface is close to the N pole of the magnetic field. The distance between both sides of the metal substrate material and the permanent magnet is 0.5 - 2.5 cm. The etched surface is magnetized under the action of the magnetic field to form a spatial magnetization difference.

[0066] Step 3: The coating obtained in Example 2 is respectively drop-coated onto the metal sample after bionic cubic staggered grid etching and the metal sample after bionic cubic sequential grid etching in a magnetic field environment, and left to stand and dry to obtain two types of magnetically driven highly dispersed self-healing coating samples.

[0067] Refer to Figure 8 and Figure 9 , and the results show that the aggregation phenomenon of the magnetic response self-healing microcapsules after bionic cubic staggered grid etching is relatively significant compared to the coating after bionic cubic sequential grid etching, and the anti-corrosion performance and anti-fouling performance are poor.

[0068] Comparative example:

[0069] (1) The preparation of the functional self-healing microcapsules is the same as in Example 2.

[0070] (2) The preparation of the magnetic polyurethane coating is the same as in Example 2.

[0071] (3) The metal substrate of the coating is only subjected to purification treatment. Emery with a particle size of 80 - 120 meshes is selected to sandblast both sides of the metal material to remove the rust on the metal surface, and then wiped with alcohol to remove the oil stain on the metal surface. The prepared magnetic polyurethane coating is immediately directly coated onto the metal substrate in a magnetic field-free environment, and left to stand until completely dry to obtain a coating sample without magnetic field intervention.

[0072] Refer to Figures 10 to 12, after the salt spray test of 3.5% NaCl in a constant temperature environment of 47°C, the time for the appearance of corrosion points of the magnetically driven highly dispersed self-healing coatings with self-healing microcapsule contents of 0 wt%, 0.5 wt%, 1 wt%, 2 wt%, and 3 wt% was 96 h, 144 h, 192 h, 432 h, and 528 h respectively, and the attached areas of their pollutants were 31.55%, 1.81%, 1.43%, 1.22%, and 1.14% respectively. The self-healing rates of the coatings were further measured to be 54.0% ± 0.10, 73.2% ± 0.15, 89.3% ± 0.33, and 93.6% ± 0.61 respectively. It can be seen that the magnetically driven highly dispersed self-healing coatings with magnetic field intervention show obvious advantages in terms of anti-fouling, anti-corrosion, and self-healing performance. The magnetic particles are evenly distributed under the action of the spatially structured magnetic field, and the service life of the coating is significantly improved.

[0073] As Figure 12 shown, the mechanism for the above effects of the present invention is that the bionic wet adhesion microstructures on the metal iron sheet will be magnetized under an external magnetic field ("×" represents the magnetic induction lines of the external magnetic field), and the magnetic domains inside the metal present a paramagnetic state (↓), and each microstructure forms a new magnetic source. For the thick and short samples, the density of the magnetic induction lines (·) of the demagnetizing field in the middle region is denser than that at the edge of the demagnetizing field, and the magnetic induction lines in opposite directions will weaken the magnetic field intensity. Therefore, during the magnetization process, the magnetic induction intensity on each new magnetic source shows a trend of being low in the middle and high around. The magnetic field force at the position with a large magnetic induction intensity is large, and the magnetic microcapsules are adsorbed on the boss structure. This causes the magnetic microcapsules in the fluid to change their movement trajectories under the action of the magnetic field. The magnetic microcapsules tend to adhere to the edges of the microstructures on the metal surface in the magnetic field, mainly distributed on the boss structures, showing good dispersibility. When multiple microcapsules in the coating approach the new magnetic source, they are magnetized, and the like-named magnetic poles formed repel each other, thus generating the "Barkhausen jump" phenomenon, resulting in a jumping displacement on the metal substrate plane, causing the magnetic microcapsules to disperse from each other, thereby enhancing the dispersion degree of the microcapsules on the entire metal plane.

[0074] Due to the viscous resistance in the vertical direction during the sedimentation process of the magnetic response microcapsules in the coating and the viscous resistance in the horizontal direction during the displacement process on the metal substrate plane, the jumping motion of the microcapsules is restricted within a certain distance. In addition, due to the action of its own gravity, the microcapsules drive the coating to better combine with the metal substrate, making the magnetic response self-healing coating have excellent protective performance.

[0075] The above embodiments are the preferred embodiments with better effects of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a magnetically driven highly dispersed self-healing coating, characterized in that, the specific steps of the method are as follows: Step 1: Carry out in-situ polymerization reaction on a reaction system containing conductive polyaniline, magnetic drive medium source Fe 3 O 4 , tung oil, and emulsifier OP-10 to obtain functional magnetic-responsive self-healing microcapsules: 1) Measure 400 ml of deionized water and place it in a 500 ml beaker. After putting a magnetic stir bar, place the beaker on a magnetic stirrer. Weigh 2 g of sodium alginate and slowly add sodium alginate to 400 ml of deionized water along the vortex of the distilled water stirring. Use a glass rod to stir to separate the agglomerated parts in the beaker. After stirring with a magnetic stirrer for 10 - 15 min, seal it with a sealing film and let it stand for 12 h for sufficient swelling to obtain a 0.5 wt% sodium alginate solution; 2) Measure OP-10 emulsifier with a volume of 0.1% of the sodium alginate solution, and place it with the prepared sodium alginate solution in a tissue homogenizer and stir at 5000 rpm for 5 - 10 min; Weigh the core materials tung oil, magnetic nanoparticles Fe 3 O 4 , and conductive polyaniline according to the mass ratio of 1:0.2:0.

018. Add the above materials to the tissue homogenizer in sequence, stir at 5000 rpm for 5 - 10 min, pour out the oil-in-water emulsion and skim off the surface foam to obtain the oil-in-water emulsion A containing conductive polyaniline and magnetite; 3) Prepare 400 ml of a 5 wt% calcium chloride solution and place it on a magnetic stirrer for full stirring. At the same time, drop the water-in-oil emulsion A into the calcium chloride solution through a syringe or spray it into the calcium chloride solution along the vortex of the solution stirring with a nano spray gun to form solution B; 4) Filter solution B through a series of filter meshes, the mesh number of the filter mesh is 50 - 200 meshes, wash it three times with deionized water, then keep the temperature stable at -60 °C, freeze-dry for 12 h, and grind to obtain functional magnetic-responsive self-healing microcapsules; Step 2: React a mixed system containing a polyurethane prepolymer, ethyl acetate, MOCA, and functional magnetic-responsive self-healing microcapsules to obtain a magnetically highly dispersed self-healing polyurethane coating: 1) Weigh the polyurethane prepolymer and ethyl acetate according to the mass ratio of polyurethane prepolymer to ethyl acetate of 1:

1. Weigh out functional magnetic-responsive self-healing microcapsules accounting for 0.5 wt% - 3 wt% of the total mass and place them in a beaker. Drop in ethyl acetate, stir and ultrasonicate for 10 - 15 min to mix evenly. Preheat the polyurethane prepolymer to a uniformly flowing state at 70 °C, add it to the above solution and stir thoroughly. Then seal the beaker mouth with a sealing film, stir and ultrasonicate for 10 - 20 min to make the microcapsules evenly distributed in the mixed liquid; 2) Heat the MOCA reagent to 120 °C to melt it, and add the MOCA reagent to the above mixed solution according to the ratio of MOCA:polyurethane prepolymer mass ratio of 100:18, stir and ultrasonicate again for 5 - 10 min to obtain a magnetically highly dispersed self-healing polyurethane coating; Step 3: Perform purification pretreatment and bionic structuring pretreatment on the surface of the metal substrate: 1) Select emery with a particle size of 80 - 120 meshes, perform sandblasting on both sides of the metal material to remove the rust on the metal surface, and wipe it with alcohol to remove the oil stain on the metal surface; 2) Using the tree frog toe as a bionic prototype, establish a cubic grid model imitating the tree frog toe structure in CAD, etch it through a laser marking machine according to the uniformly distributed cubic in-line grid and cubic offset grid to create a structural magnetization difference, and drive the magnetic-responsive microcapsules to disperse through a magnetic field; the size parameters of the bionic cubic grid are set as follows: length L = 300 - 500 μm, width W = 50 - 150 μm, depth D = 25 - 100 μm, and optimize it; Step 4: Set up a spatially regionalized magnetic field: Place two cylindrical permanent magnets parallel to each other on both sides of the metal substrate. The laser-etched metal surface is close to the N pole of the magnetic field. The distance between the two sides of the metal substrate material and the permanent magnet is 0.5 - 2.5 cm. The etched surface is magnetized under the action of the magnetic field, forming a spatial magnetization difference. Step 5: Coating the magnetic highly-dispersed self-healing polyurethane coating on the surface of the metal base in the spatial magnetic field and homogenizing it by the self-leveling method, and curing it in the spatial magnetic field region to obtain a magnetically-driven highly-dispersed self-healing coating.

2. The method for preparing the magnetically-driven highly-dispersed self-healing coating according to claim 1, characterized in that In Step 1, the particle size of magnetic nanoparticles Fe 3 O 4 is 5 to 60 nm.

3. The method for preparing the magnetically-driven highly-dispersed self-healing coating according to claim 1, characterized in that the coating method in step 5 includes drop coating, high-pressure spraying, and electrostatic spraying.

4. The method for preparing the magnetically-driven highly-dispersed self-healing coating according to claim 1, characterized in that before coating in step 5, the coating is placed in an ultrasonic environment for 5 minutes to be homogenized. A constant mass of the coating is sucked by a coating device and evenly coated on the surface of the pretreated sample. The surface thickness of the coating is made uniform by the self-leveling method. The coating process is kept at a constant speed to avoid the generation of bubbles. After the coating is completed, immediately check whether there are bubbles on the surface of the coating, and use a syringe needle to break the bubbles to ensure the uniformity of the coating. After it is completely dried, the preparation is completed.

5. The magnetically-driven highly-dispersed self-healing coating prepared by the method according to any one of claims 1 - 4.

6. The magnetically-driven highly-dispersed self-healing coating according to claim 5, characterized in that the thickness of the coating is 10 - 80 μm.

7. The application of the magnetically-driven highly-dispersed self-healing coating according to claim 5 on the underwater metal surface.

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