Micro-nano network coated loss-controlled fertilizer and efficient preparation method thereof

Abstract

The invention relates to the technical field of controlled-release fertilizers, in particular to a micro-nano network coated controlled-release fertilizer and an efficient preparation method thereof. The micro-nano network coated loss-controlled fertilizer comprises a core material and a composite coating layer coating the surface of the core material, the composite coating layer is composed of a composite base material, a micro-nano reinforced phase and a cross-linking system, the composite base material is a mixture of epoxypropane modified starch and acetic acid activated chitosan, the micro-nano reinforced phase is a mixture of silane coupling agent modified nano silicon dioxide and Na-montmorillonite, the cross-linking system is formed by reaction of a cross-linking agent, and the cross-linking system is a mixture of nano silicon dioxide modified by a silane coupling agent and Na-montmorillonite. The composite coating layer is of a compact micro-nano network structure; by adopting the design of combining the composite coating base material and micro-nano reinforcement, a compact micro-nano network coating structure is formed, the barrier property of a coating layer is greatly improved, the nutrient release rate can be accurately regulated and controlled, the controlled release period is remarkably prolonged, and continuous and stable nutrient supply for crops in the whole growth period is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of controlled-release fertilizers, in particular to a micro-nano network coated controlled-release fertilizer and an efficient preparation method thereof. BACKGROUND

[0002] In agricultural production, low nutrient utilization efficiency of fertilizers is a long-standing key problem. After the application of traditional fertilizers, rapid nutrient loss, volatilization or fixation often occurs, which not only causes resource waste, but also may cause environmental pollution. Controlled-release fertilizers, by constructing a barrier layer through coating technology, delay the release rate of nutrients, and become the core direction to improve nutrient utilization efficiency, which has been widely concerned in agricultural production.

[0003] However, the existing controlled-release fertilizer technology still has many defects to be solved. Some products use single substrate for coating, and the film forming performance is poor, which is difficult to form a dense barrier structure, resulting in too fast nutrient release rate, short controlled-release period, and unable to meet the continuous nutrient demand of crops throughout the growth period. Even if some technologies use composite substrates for coating, due to the lack of effective reinforcement system, the mechanical strength of the coating layer is insufficient, and it is easy to break during transportation, storage and field application, which directly affects the stability of the controlled-release effect.

[0004] At the same time, the existing coating system has poor environmental adaptability and is easily degraded in different soil with different acid-base properties, further shortening the controlled-release period and limiting its application in diversified soil environments. In addition, the core material adaptation range of most controlled-release fertilizers is narrow, and only specific types of fertilizers can be coated, which is difficult to meet the demand of different crops and different planting scenes for fertilizer types. In addition, traditional controlled-release fertilizers often only focus on nutrient controlled-release function, lack of soil water retention properties, and cannot improve soil water conditions in dry or water resource shortage environments, which indirectly affects the absorption efficiency of crops to nutrients, resulting in limited overall fertilizer efficiency improvement. These problems jointly restrict the comprehensive performance and application promotion of existing controlled-release fertilizers, and it is urgent to develop a controlled-release fertilizer with excellent nutrient controlled-release effect, mechanical strength, environmental stability and wide adaptation, and an efficient preparation method thereof. SUMMARY

[0005] The primary object of the present application is to provide a micro-nano network coated controlled-release fertilizer and an efficient preparation method thereof.

[0006] The further object of the present application is to provide a micro-nano network coated controlled-release fertilizer, comprising a core material and a composite coating layer coated on the surface of the core material; the composite coating layer is composed of a composite base material, a micro-nano reinforcing phase and a cross-linking system, the composite base material is a mixture of propylene oxide modified starch and acetic acid activated chitosan, the micro-nano reinforcing phase is a mixture of nano-silicon dioxide modified by a silane coupling agent and sodium-based montmorillonite, the cross-linking system is formed by the reaction of a cross-linking agent, and the composite coating layer has a dense micro-nano network structure; the acetic acid activated chitosan is obtained by treating chitosan with an acetic acid solution, and the nano-silicon dioxide modified by the silane coupling agent is obtained by mixing and treating nano-silicon dioxide and a silane coupling agent; the mass ratio of the composite base material to the core material is 1:20 to 1:16.7, and the mass ratio of the micro-nano reinforcing phase to the composite base material is 1:5 to 1:2.8.

[0007] Preferably, the core material is a compound fertilizer or a urea-formaldehyde resin coated urea.

[0008] Preferably, in the composite base material, the mass ratio of propylene oxide modified starch to acetic acid activated chitosan is 3:2 to 5:7.

[0009] Preferably, the cross-linking agent is a combination of glutaraldehyde and citric acid or a combination of glutaraldehyde and maleic acid; when it is a combination of glutaraldehyde and citric acid, the mass ratio of the two is 3:10 to 5:10; when it is a combination of glutaraldehyde and maleic acid, the mass ratio of the two is 3:12 to 4:13.

[0010] Preferably, in the micro-nano reinforcing phase, the mass ratio of nano-silicon dioxide to sodium-based montmorillonite is 1:1 to 3:2.

[0011] A preparation method of the micro-nano network coated controlled-release fertilizer, comprising the following steps: (1) Raw material preparation: selecting a core material, propylene oxide modified starch, acetic acid activated chitosan, nano-silicon dioxide modified by a silane coupling agent, sodium-based montmorillonite, a cross-linking agent and deionized water; (2) Coating base material pretreatment: adding propylene oxide modified starch and acetic acid activated chitosan into deionized water, constant temperature stirring until the mixture is uniform to form a composite base material solution, adding nano-silicon dioxide modified by a silane coupling agent and sodium-based montmorillonite into the composite base material solution, high-speed stirring and then ultrasonic dispersion to obtain a micro-nano composite coating liquid; (3) Spray coating: putting the core material into a preheating roller coating machine, spraying the micro-nano composite coating liquid to the surface of the preheated core material through a high-pressure sprayer, maintaining negative pressure in the roller and introducing dry air during the spraying process; (4) Cross-linking and curing: spraying a cross-linking agent to the surface of the core material after the spray coating, stirring to make the cross-linking agent fully contact with the composite coating layer, then segmentally heating and curing, and screening and removing the agglomerates and fine powder after cooling to obtain a finished product.

[0012] Preferably, in step (1), the preparation of the silane coupling agent modified nano-silica is as follows: nano-silica is mixed with a silane coupling agent, stirred, and then dried and crushed.

[0013] Preferably, in step (4), the segmented temperature curing is a first low-temperature holding and a second high-temperature holding, the high-temperature holding temperature is higher than the low-temperature holding temperature, the low-temperature holding temperature is 55-60℃, and the high-temperature holding temperature is 70-75℃.

[0014] Preferably, in step (2), the viscosity of the micro-nano composite coating liquid is controlled at 200-250 mPa·s by adjusting the amount of deionized water.

[0015] Preferably, in step (3), the roller speed during the spraying process is 45-50 rpm, and the atomization pressure is 0.3-0.35 MPa.

[0016] Compared with the prior art, the present application has the following advantages: 1. The present application adopts the design of combining composite coating substrates with micro-nano reinforcing phases to form a dense micro-nano network coating structure, which greatly improves the barrier performance of the coating layer, accurately controls the nutrient release rate, significantly prolongs the controlled release period, ensures the continuous and stable nutrient supply of crops throughout the growth period, fundamentally improves the nutrient utilization efficiency, and reduces resource waste.

[0017] 2. The present application optimizes the ratio of micro-nano reinforcing phases and the design of the composite crosslinking system, strengthens the structural stability and mechanical strength of the coating layer, effectively resists extrusion impact during transportation, storage and application, reduces the risk of breakage, ensures the consistency of the controlled release effect of the product in actual application, and meets the requirements of industrial production and application.

[0018] 3. The present application significantly improves the environmental stability of the product by segmenting the control of the composite crosslinking system and the curing process, so that the product can maintain structural integrity in different soil with different acid-base properties, avoid premature degradation, further prolong the effective controlled release time, and broaden the range of applicable soil.

[0019] 4. The micro-nano network structure in the present application also endows the product with excellent soil water retention function, which can adsorb and lock soil water, improve soil water conditions, and synergistically promote the growth and development of crops, thereby significantly improving crop yield. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application. Embodiment 1

[0021] (1) Raw material preparation: the core material is urea-potassium dihydrogen phosphate-potassium chloride compound fertilizer with a particle size of 15 mesh, the mass ratio of nitrogen, phosphorus and potassium is 15:10:15, and the amount is 100 kg; the amount of propylene oxide modified starch is 3 kg, the degree of substitution is 0.3, the amount of acetic acid activated chitosan is 2 kg, the degree of deacetylation is 85, the activation treatment method is to add chitosan into a 2% acetic acid solution, stir at room temperature for 2 hours until completely dissolved, and then stand for defoaming; the amount of nano-silicon dioxide is 0.5 kg, the particle size is 20 nanometers, which is modified by silane coupling agent KH550, the modification process is that nano-silicon dioxide is mixed with 0.05 kg of silane coupling agent KH550, stirred at 80°C for 1 hour, then dried and pulverized; the amount of sodium-based montmorillonite is 0.5 kg, the particle size is 100 nanometers; the amount of glutaraldehyde is 0.3 kg, the mass fraction is 50%; the amount of citric acid is 1 kg; the amount of deionized water is 20 kg.

[0022] (2) Pretreatment of coated substrate: add modified starch and activated chitosan solution into deionized water, stir in a 50°C constant temperature water bath for 30 minutes until completely mixed and uniform, to form a composite substrate solution; add modified nano-silicon dioxide and sodium-based montmorillonite into the solution, stir at high speed of 1500 revolutions per minute for 20 minutes, then use 300 watt ultrasonic dispersion for 15 minutes, the ultrasonic frequency is 25 kilohertz, to ensure uniform dispersion of micro-nano particles without agglomeration, to obtain micro-nano composite coating liquid, control the viscosity of the coating liquid to be 200 millipascal seconds.

[0023] (3) Spray coating: put the compound fertilizer core material into the roller coating machine, adjust the roller speed to 50 revolutions per minute, the temperature in the cylinder is 45°C, preheat the core material for 10 minutes until the temperature is stable; spray the micro-nano composite coating liquid through a high-pressure sprayer, the atomization pressure is 0.3 megapascal, the nozzle diameter is 0.8 millimeter, the spray flow rate is controlled at 0.5 kg per minute, the spray time is 40 minutes; maintain the negative pressure in the cylinder at 0.02 megapascal, and simultaneously introduce dry air, the air flow rate is 2 cubic meters per minute, to promote water evaporation and uniform adhesion of the coating layer.

[0024] (4) Crosslinking and curing: After the spraying is completed, mix glutaraldehyde and citric acid uniformly at a mass ratio of 3:10, slowly spray into the drum, continue to stir for 20 minutes to ensure that the crosslinking agent and the coating layer are in full contact; segment temperature rise and curing, first heat to 60°C for 30 minutes to make the crosslinking reaction proceed preliminarily, then heat to 70°C for 20 minutes to promote the crosslinking reaction to be complete, forming a dense micro-nano network structure; after cooling to room temperature, remove the lumps and fine powder through 12 mesh and 22 mesh screens to obtain the finished product, and the particle size of the finished product is controlled to be 15 mesh.

[0025] This embodiment constructs a basic micro-nano network system, solves the problems of poor film formation and short controlled release period of existing single substrate coating, and provides a benchmark for subsequent performance optimization. Example 2

[0026] Based on the basic formula and preparation process of Example 1, in view of the problems of insufficient barrier property of the coating layer and fast nutrient release rate, the ratio of the composite coating substrate is optimized, and the amount of crosslinking agent is adjusted to adapt to the composition of the substrate, and the remaining parameters remain unchanged.

[0027] The adjusted parameters are as follows: the amount of propylene oxide modified starch is 2 kg, the amount of acetic acid activated chitosan is 3 kg; the total amount of micro-nano reinforcing phase is maintained at 1 kg, and the amount of nano silicon dioxide and sodium-based montmorillonite is still 0.5 kg and 0.5 kg; the crosslinking agent is adjusted to glutaraldehyde 0.4 kg and citric acid 0.8 kg.

[0028] In this embodiment, the amount of chitosan is increased to strengthen the hydrogen bonding of the coating layer, improve the density and barrier property, and the ratio of the crosslinking agent is adjusted to balance the reactivity of the substrate. Example 3

[0029] Based on the high barrier substrate system of Example 2, in view of the problem of insufficient mechanical strength of the coating layer and easy breakage during transportation, the total amount of micro-nano reinforcing phase is increased and the ratio is optimized, and the amount of deionized water is adjusted to maintain the viscosity of the coating liquid, and the remaining preparation process remains unchanged.

[0030] The adjusted parameters are as follows: the amount of nano silicon dioxide is 1 kg, the amount of sodium-based montmorillonite is 0.8 kg, and the total amount of micro-nano reinforcing phase is 1.8 kg; the total amount of coating substrate is maintained at 5 kg, the amount of propylene oxide modified starch is 2 kg, and the amount of acetic acid activated chitosan is 3 kg; the crosslinking agent is adjusted to glutaraldehyde 0.5 kg and citric acid 1 kg; the amount of deionized water is increased to 22 kg to maintain the viscosity of the coating liquid at 250 mPa·s.

[0031] In this embodiment, nano silicon dioxide is filled into the network pores, and montmorillonite layers are used to strengthen the structure support, forming a double protection of substrate barrier + micro-nano reinforcement, and constructing a high-strength dense network system.

[0032] Example 4 Preparation of environment-resistant micro-nano network coated controlled-release fertilizer Based on the high-strength system of Example 3, to solve the problem of easy degradation in acid and alkali soil and insufficient stability, the crosslinking system is optimized and the curing process is adjusted to adapt to the reaction rate, and the remaining parameters remain unchanged.

[0033] The parameters are adjusted as follows: the crosslinking agent is replaced with glutaraldehyde 0.3 kg and maleic acid 1.2 kg; the curing process is adjusted to the first stage 55°C for 35 minutes and the second stage 75°C for 15 minutes; epoxy propane modified starch 2 kg, acetic acid activated chitosan 3 kg, micro-nano reinforcing phase 1.8 kg, deionized water 22 kg.

[0034] This example uses a glutaraldehyde-maleic acid composite crosslinking system to form a synergistic network of aldehyde group crosslinking and ester bond crosslinking, improving acid and alkali degradation resistance, and adjusting the curing process to avoid cracking of the coating layer. Example 5

[0035] Based on the environmental resistance system of Example 4, to solve the problem of existing technology that the core material is only suitable for coated compound fertilizer, the core material type is replaced and the process and substrate dosage are optimized to adapt to smooth surface single nitrogen fertilizer.

[0036] The parameters are adjusted as follows: the core material is urea formaldehyde resin coated urea with particle size 13 mesh, nitrogen content 46%, and dosage 100 kg; the total amount of coated substrate is increased to 6 kg, epoxy propane modified starch 2.5 kg, acetic acid activated chitosan 3.5 kg; the total amount of micro-nano reinforcing phase is 2 kg, nano silicon dioxide 1.2 kg, sodium-based montmorillonite 0.8 kg; crosslinking agent glutaraldehyde 0.4 kg, maleic acid 1.3 kg; deionized water 25 kg; spray pressure 0.35 MPa, roller speed 45 rpm; curing process first stage 58°C for 30 minutes, second stage 72°C for 20 minutes.

[0037] This example enhances the adhesion of the coating layer to the smooth core material by increasing the substrate dosage and adjusting the spray and curing parameters, achieving broad-spectrum adaptation to compound fertilizer and single nitrogen fertilizer.

[0038] Comparative Example 1: Select the urea-potassium dihydrogen phosphate-potassium chloride compound fertilizer in Example 1 as the sample without any coating treatment, corresponding to the existing uncoated fertilizer technology.

[0039] Comparative Example 2: Use single epoxy propane modified starch as the coating material without chitosan and micro-nano reinforcing phase, and the remaining preparation parameters are the same as Example 1: Modified starch 5 kg, glutaraldehyde 0.5 kg, deionized water 20 kg, spray and curing parameters same as Example 1.

[0040] Comparative Example 3: Based on the formulation of Example 1, nano-silica and sodium-based montmorillonite were removed, while the remaining parameters remained unchanged: 3 kg of propylene oxide-modified starch, 2 kg of acetic acid-activated chitosan, 0.3 kg of glutaraldehyde, and 1 kg of citric acid, corresponding to the existing composite coating technology without reinforcement phase.

[0041] Comparative Example 4: Based on the formulation of Example 1, the total amount of crosslinking agent was halved: 0.15 kg of glutaraldehyde and 0.5 kg of citric acid, with the remaining parameters unchanged.

[0042] Comparative Example 5: Based on the formulation of Example 1, the curing process was changed to a one-time heating to 80°C and holding for 50 minutes, without the segmented heating step, and the other parameters remained unchanged.

[0043] Performance testing and results analysis: Test method: (1) Nutrient release rate test: Weigh 5 grams of sample and place it in 500 ml of deionized water. Keep it at a constant temperature of 25°C. Take 5 ml of sample at 1 day, 3 days, 7 days, 14 days, 28 days and 42 days respectively. After filtration, use Kjeldahl method to determine nitrogen content, molybdenum antimony colorimetric method to determine phosphorus content and flame photometry to determine potassium content. Calculate the cumulative nutrient release rate. At the same time, conduct soil culture test. Mix the sample with 2 kg of air-dried soil to maintain soil moisture content of 25%. Regularly test the content of available nitrogen, phosphorus and potassium to simulate the field control effect.

[0044] (2) Mechanical performance test: a pressure testing machine was used with a loading rate of 2 mm per minute. Ten particles were tested in each group, the maximum crushing pressure was recorded, and the average value was taken as the compressive strength to evaluate the transport and storage adaptability.

[0045] (3) Soil water retention rate test: The sample and soil were mixed at a mass ratio of 1:100 and placed in an environment of 25℃ and 60% humidity. The samples were weighed regularly, the changes in soil moisture content were calculated, and the water retention capacity of the blank soil was compared to evaluate the water retention function.

[0046] (4) Field fertilizer efficiency test: Select a 10-square-meter experimental plot, plant corn, set up 3 replicates for each group, apply equal amounts of pure nutrient samples, and do not apply fertilizer to the blank group. Record plant height, number of grains per ear, thousand-grain weight and yield, calculate nutrient utilization rate, and verify the actual field effect.

[0047] The test results are shown in Table 1 below:

[0048] As can be seen from the above test results, the overall performance of the products in each embodiment of the present invention is significantly better than that of the corresponding prior art solutions in the comparative examples.

[0049] (1) The cumulative nutrient release rate of Examples 1 to 5 over 42 days was controlled within the range of 65% to 82%, and the release period could be extended to more than 60 days, which could fully meet the nutrient supply needs of crops throughout their entire growth period. In contrast, the cumulative nutrient release rate of Comparative Examples 1 to 5 over 42 days exceeded 82%. Among them, Comparative Example 1 without coating was close to complete release, and the comparative examples with single substrate, no micro-nano reinforcing phase, and insufficient cross-linking also showed the problem of rapid nutrient loss. This confirms that the synergistic effect of the composite coating substrate, micro-nano reinforcing phase, and composite cross-linking system of the present invention is the key to improving the controlled release effect.

[0050] (2) In terms of mechanical properties, the compressive strength of the products in the examples is all above 1.2 MPa, of which Example 4 reaches 1.8 MPa, which is much higher than the 0.4 to 0.9 MPa of the comparative examples. It can effectively resist the crushing during transportation, storage and application, and meet the mechanical strength requirements of industrial applications. This advantage comes from the dense network structure constructed by the micro-nano reinforced phase and cross-linking system.

[0051] (3) Soil water retention and field fertilizer efficiency also demonstrate the significant advantages of this invention. The 28-day soil water retention rate of Examples 1 to 5 all exceeded 20%, an increase of more than 33% compared to the blank soil, while the highest water retention rate of the comparative example was only 18.9%. Most existing products lack significant water retention function. This invention achieves synergy between water loss control and water retention through the water absorption and locking characteristics of the micro-nano network structure. In field trials, the corn yield increase of the products in the examples ranged from 18.5% to 28.3%, and the nutrient utilization rate ranged from 12.3% to 18.7%, which was 8.3% to 18.1% higher than the yield increase of Comparative Example 1, and 5 to 10 percentage points higher than the nutrient utilization rate of existing similar products. Among them, Example 5 achieved the best yield increase and nutrient utilization rate due to its broad-spectrum adaptation to single nitrogen fertilizer, fully demonstrating the universality and practicality of the technical solution of this invention.

[0052] (4) In summary, this invention is not a simple superposition of existing coating materials, micro-nano particles and curing processes, but a rational combination of optimized substrate ratio, precise matching of reinforcing phase and crosslinking system, and segmented process control. The various technical features support each other to form a complete technical system, enabling the product to have excellent nutrient controlled release, mechanical strength and soil water retention performance, and the technical effect is stable and reproducible.

[0053] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A micro / nano network-coated controlled-release fertilizer, characterized in that, The invention comprises a core material and a composite coating layer covering the surface of the core material. The composite coating layer consists of a composite substrate, a micro / nano reinforcing phase, and a crosslinking system. The composite substrate is a mixture of propylene oxide-modified starch and acetic acid-activated chitosan. The micro / nano reinforcing phase is a mixture of nano-silica modified with a silane coupling agent and sodium-based montmorillonite. The crosslinking system is formed by the reaction of a crosslinking agent. The composite coating layer has a dense micro / nano network structure. The acetic acid-activated chitosan is obtained by treating chitosan with an acetic acid solution. The silane coupling agent-modified nano-silica is obtained by mixing nano-silica with a silane coupling agent. The mass ratio of the composite substrate to the core material is 1:20 to 1:16.7, and the mass ratio of the micro / nano reinforcing phase to the composite substrate is 1:5 to 1:2.

8.

2. The micro / nano network-coated controlled-release fertilizer according to claim 1, characterized in that, The core material is compound fertilizer or urea-formaldehyde resin coated urea.

3. The micro / nano network-coated controlled-release fertilizer according to claim 1, characterized in that, In the composite substrate, the mass ratio of propylene oxide-modified starch to acetic acid-activated chitosan is 3:2 to 5:

7.

4. The micro / nano network-coated controlled-release fertilizer according to claim 1, characterized in that, The crosslinking agent is a combination of glutaraldehyde and citric acid or a combination of glutaraldehyde and maleic acid; when it is a combination of glutaraldehyde and citric acid, the mass ratio of the two is 3:10 to 5:10; when it is a combination of glutaraldehyde and maleic acid, the mass ratio of the two is 3:12 to 4:

13.

5. The micro / nano network-coated controlled-release fertilizer according to claim 1, characterized in that, In the micro-nano reinforced phase, the mass ratio of nano-silica to sodium-based montmorillonite is 1:1 to 3:

2.

6. A method for preparing a micro / nano network-coated controlled-release fertilizer as described in claim 1, characterized in that, Includes the following steps: (1) Raw material preparation: Select core material, propylene oxide modified starch, acetic acid activated chitosan, nano silica modified with silane coupling agent, sodium montmorillonite, crosslinking agent and deionized water; (2) Pretreatment of coating substrate: propylene oxide modified starch and acetic acid activated chitosan are added to deionized water and stirred at constant temperature until they are mixed evenly to form a composite substrate solution. Nano-silica modified with silane coupling agent and sodium montmorillonite are added to the composite substrate solution. The mixture is first stirred at high speed and then ultrasonically dispersed to obtain micro-nano composite coating liquid. (3) Spray coating: The core material is put into the roller coating machine for preheating, and the micro-nano composite coating liquid is sprayed onto the surface of the preheated core material through a high-pressure sprayer. During the spraying process, the negative pressure inside the roller is maintained and dry air is introduced. (4) Crosslinking and curing: Spray crosslinking agent onto the surface of the core material after spray coating, stir to make the crosslinking agent fully contact the composite coating layer, then heat and cure in stages, and after cooling, sieve to remove lumps and fine powder to obtain the finished product.

7. The preparation method according to claim 6, characterized in that, In step (1), the preparation method of the nano-silica modified by silane coupling agent is as follows: nano-silica is mixed with silane coupling agent, stirred and then dried and pulverized.

8. The preparation method according to claim 6, characterized in that, In step (4), the segmented heating and curing consists of a first stage of low-temperature insulation and a second stage of high-temperature insulation. The temperature of the high-temperature insulation is higher than that of the low-temperature insulation. The low-temperature insulation temperature is 55°C to 60°C, and the high-temperature insulation temperature is 70°C to 75°C.

9. The preparation method according to claim 6, characterized in that, In step (2), the viscosity of the micro-nano composite coating liquid is controlled between 200 mPa second and 250 mPa second by adjusting the amount of deionized water.

10. The preparation method according to claim 6, characterized in that, In step (3), the drum speed during the spraying process is 45 to 50 revolutions per minute, and the atomization pressure is 0.3 MPa to 0.35 MPa.

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