Anti-ultraviolet high-wear-resistance polyurea composite coating as well as preparation method and application thereof

Abstract

The invention discloses an anti-ultraviolet high-wear-resistance polyurea composite coating as well as a preparation method and application thereof, and relates to the technical field of corrosion and protective coatings. The preparation method of the polyurea composite coating comprises the following steps: adding an amino trialkoxy silane coupling agent into an alkyl alcohol solvent, and heating and stirring for hydrolysis reaction to obtain a silane modified modifier; adding the nanoparticles into a silane modified modifier for surface modification to obtain surface modified nanoparticles; and adding polyurea resin and a curing agent into the surface modified nanoparticles, and uniformly mixing. The modified particles are added into the polyurea resin as a filler, so that the compatibility of the nano particles and the polyurea resin is improved, the agglomeration phenomenon of the nano particles is improved, the dispersity of the nano particles is improved, the mechanical property of the coating is enhanced, the internal defects of the coating are reduced, and the compactness of the coating is improved; finally, the modified epoxy coating shows excellent ultraviolet aging resistance and wear resistance, and has important application in the field of corrosion and protection of maritime work equipment.

Description

Technical Field

[0001] The present invention belongs to the technical field of corrosion and protection coatings, and particularly relates to an anti-ultraviolet and highly wear-resistant polyurea composite coating, a preparation method thereof, and an application thereof. Background Art

[0002] The long-term and stable service of offshore equipment and ships is the guarantee for the development of marine resources. However, offshore equipment has been in service in a harsh environment of high salt, high humidity, high temperature and strong ultraviolet radiation for a long time. Corrosion and its coupled damage are one of the main factors causing its shortened life and safety accidents. Practice has proved that organic coatings play an important role in protecting marine engineering equipment and extending its service life. Among them, polyurea coatings have received extensive attention due to their excellent corrosion resistance, weather resistance and mechanical properties, and have broad application prospects in the construction field and the marine engineering field. However, during the curing and service processes, pores and cracks will occur in the coating. At the same time, in the actual application process, due to the influence of complex factors such as mechanical wear and seawater erosion, the polyurea coating will be locally damaged, resulting in a significant reduction in its service life, and further shortening the service life of offshore equipment. Therefore, how to reduce the internal defects of the coating while improving the wear resistance, and then extend the service life of offshore equipment is a scientific and technological problem that needs to be solved urgently by those skilled in the art.

[0003] To solve the problem of insufficient wear resistance of polyurea coatings, the existing solution is to directly add wear-resistant nanoparticles into the coating resin. For example, Patent CN112876960A proposes a wear-resistant and anti-freezing coating for icebreaking ships, which adds functional fillers (aluminum oxide powder) and ultraviolet absorbers to the polyurea polyurethane system, achieving the advantages of high hardness, good temperature resistance and cold resistance, good stability, toughness, impact resistance, wear resistance and anti-freezing. However, the compatibility between inorganic fillers and polyurea resin is poor. Therefore, directly adding inorganic fillers will make the organic resin incompatible internally, there will be weak regions at the filler / resin interface, which will damage the integrity of the coating internal structure and lead to a decline in the comprehensive protection performance of the coating. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects and deficiencies of the existing polyurea coatings, and provide a preparation method of a polyurea composite coating, which can increase the dispersion and compatibility of nanoparticles in the polyurea resin system.

[0005] Another purpose of the present invention is to provide a polyurea composite coating.

[0006] Another purpose of the present invention is to provide the application of the above polyurea composite coating in the preparation of protective materials for marine engineering equipment.

[0007] Another purpose of the present invention is to provide a polyurea composite coating, which has the characteristics of few internal defects and high compactness, and improves the anti-ultraviolet aging performance and wear resistance of the coating.

[0008] The above object of the present invention is achieved by the following technical solutions:

[0009] The present invention protects a preparation method of a polyurea composite coating, comprising the following steps:

[0010] S1, adding an amino trialkoxysilane coupling agent to an alkyl alcohol solvent, adjusting the pH to 3 - 5, and then heating and stirring for a hydrolysis reaction to obtain a silane-modified modifier;

[0011] S2, adding nanoparticles to the silane-modified modifier for surface modification to obtain surface-modified nanoparticles;

[0012] S3, adding a polyurea resin and a curing agent to the surface-modified nanoparticles and mixing evenly to obtain the polyurea composite coating.

[0013] In the preparation method of the polyurea composite coating of the present invention, the amino trialkoxysilane coupling agent forms polyhydroxy groups after hydrolysis, performs silylation surface modification on the nanoparticles, and the excess hydroxy groups will further react with adjacent groups to form a network structure, greatly improving the compatibility between the nanoparticles and the polyurea resin, reducing the internal defects of the coating, and enhancing the anti-ultraviolet aging performance and wear resistance of the coating. At the same time, the amino groups grafted on the surface of the nanoparticles can also react with the isocyanate groups in the polyurea resin, further integrating the nanoparticles with the coating as a whole, and finally enabling the polyurea coating to exhibit excellent anti-ultraviolet aging performance and wear resistance.

[0014] Furthermore, the present invention uses an alkyl alcohol solvent to dissolve the silane coupling agent and simultaneously controls and adjusts the pH to 3 - 5, which can hydrolyze the silicon-oxygen bond to form hydroxy groups while retaining the amino groups on the silane chain, facilitating the reaction between the amino groups and the isocyanate groups in the polyurea resin, and enhancing the anti-ultraviolet aging performance and wear resistance of the polyurea coating.

[0015] Among them, nanomaterials have small size effect, surface effect, quantum size effect, etc. Research shows that adding a small amount of inorganic nanomaterials to an organic coating can improve the wear resistance, anti-corrosion property, anti-fouling property, and water resistance of the coating. The present invention optimizes the performance of the composite coating by combining nanoparticles and an amino trialkoxysilane coupling agent and changing the surface properties of the nanoparticles; among them, the nanoparticles are derived from industrial production with reliable quality; the amino trialkoxysilane coupling agent has diverse advantages. Since the surface of the modified nanomaterials is grafted with amino groups and silyl groups, the compatibility between the nanomaterials and the polyurea resin is increased, the dispersibility of the nanomaterials is improved, the pores during the coating curing process are filled, the denseness and crosslinking density of the coating are enhanced, the time for the corrosive medium to reach the metal surface is prolonged, and finally the long-term corrosion resistance of the coating is increased.

[0016] Optionally, the alkyl alcohol solvent is a C2-C4 alkyl alcohol, including but not limited to ethanol and / or isopropanol.

[0017] Optionally, the acid solution includes but not limited to oxalic acid solution, hydrochloric acid solution or sulfuric acid solution.

[0018] In some embodiments, in step S1, the hydrolysis temperature is 40-60°C and the hydrolysis time is 0.5-2 h.

[0019] Preferably, the amino trialkoxysilane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane or N-(β-aminoethyl)-γ-aminopropyltriethoxysilane.

[0020] In some embodiments, in step S2, the ratio of the mass of the nanoparticles to the volume of the amino trialkoxysilane coupling agent is 0.5-4 g / mL.

[0021] In some embodiments, in step S2, the surface modification temperature is 40-60°C and the reaction time is 2-6 h.

[0022] In some embodiments, in step S2, the material of the nanoparticles is at least one of alumina, silica, magnesia, zinc oxide, silicon carbide or zirconia.

[0023] In some embodiments, in step S2, the particle size of the nanoparticles is 10-1000 nm.

[0024] The present invention can regulate the number of grafted groups on the surface of the nanoparticles by adjusting the dosage ratio of the nanoparticles and the amino trialkoxysilane coupling agent, thereby improving the coating performance.

[0025] In some embodiments, in step S3, the mass ratio of the polyurea resin to the surface-modified nanoparticles is 1:(0.015-0.1).

[0026] Optionally, the curing agent is an isocyanate curing agent, including but not limited to hexamethylene diisocyanate-based polyisocyanate.

[0027] In some embodiments, in step S3, the dosage of the curing agent accounts for 30-50 wt% of the polyurea coating, preferably 38-42 wt%. The specific amount of the curing agent used in the invention can be cured at room temperature, thus increasing the operability of the coating.

[0028] Optionally, in step S2, a diluent is further added to the polyurea coating, and the mass ratio of the polyurea coating to the diluent is 1:(0.5-0.85).

[0029] Optionally, the diluent is at least one of propylene glycol methyl ether acetate, n-butyl acetate or xylene.

[0030] The present invention protects a polyurea composite coating, which is made by the preparation method of the polyurea composite coating.

[0031] The present invention protects the application of a polyurea composite coating in the preparation of protective materials for ocean engineering equipment.

[0032] The present invention protects a polyurea composite coating, which is formed by curing after the polyurea composite coating is coated on the surface of a metal substrate.

[0033] Optionally, the curing temperature is 5°C to 60°C, and the curing time is 48h to 168h.

[0034] Optionally, the metal substrate is at least one of carbon steel, aluminum alloy, titanium alloy, magnesium alloy or copper alloy.

[0035] Optionally, the thickness of the polyurea composite coating is 30 to 200 μm.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] The present invention provides a polyurea composite coating and its preparation method. After hydrolysis, the amino trialkoxysilane coupling agent performs silylation surface modification on the nanoparticles, greatly improving the compatibility between the nanoparticles and the polyurea resin, reducing the internal defects of the coating, and enhancing the anti-ultraviolet aging performance and wear resistance of the coating.

[0038] The present invention provides a polyurea composite coating. Due to the improved compatibility between the surface-modified nanoparticles and the polyurea resin, the internal defects of the coating can be filled; at the same time, the amino groups grafted on the surface of the nanoparticles can also react with the isocyanate groups in the polyurea resin, further integrating the nanoparticles with the coating as a whole, making the polyurea coating exhibit excellent anti-ultraviolet aging performance and wear resistance. Description of the Drawings

[0039] Figure 1 For the Al of Example 1 of the present invention 2 O 3 -M modified polyurea composite coating and the Al of Comparative Example 2 2 O 3 Morphology structure diagram of the modified polyurea composite coating.

[0040] Figure 2 For the wear resistance test result diagrams of the polyurea composite coatings prepared in Example 1 and Comparative Examples 1 and 2 of the present invention.

[0041] Figure 3This is the surface roughness test and coating wear measurement diagram of the polyurea composite coatings prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0042] Figure 4 This is the electrochemical impedance spectroscopy diagram of the polyurea composite coatings prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. Specific Embodiments

[0043] The present invention will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventional raw material reagents purchased.

[0044] The following examples and comparative examples include the following raw materials:

[0045] Polyurea resin: F520, Shenzhen Feiyang Junyan New Materials Co., Ltd.

[0046] Curing agent: Hexamethylene diisocyanate-based polyisocyanate, HT-600, Shenzhen Feiyang Junyan New Materials Co., Ltd.

[0047] Amino silane coupling agent: γ-Aminopropyltriethoxysilane, KH550, Shanghai Macklin Biochemical Co., Ltd.

[0048] Example 1

[0049] A preparation method of a polyurea composite coating includes the following steps:

[0050] (1) Prepare surface-modified alumina nanoparticles (Al 2 O 3 -M) grafted with amino and silane groups:

[0051] Specifically: Add 2 mL of amino silane coupling agent to 100 mL of absolute ethanol to obtain an amino silane coupling agent dilution. Another 100 mL of absolute ethanol is added dropwise with 0.5 mol / L oxalic acid solution to adjust the pH to 3, then 2 mL of the silane coupling agent dilution is added. After stirring and hydrolyzing in a water bath at 45 °C for 1 h, 1 g of nano-alumina (average particle size 100 nm) particles are added, and stirring continues in a water bath at 45 °C for 4 h. Then, the alumina white solid is filtered and separated, placed in a drying oven at 60 °C for 24 h to obtain the modified alumina block, and finally the block is ground to obtain the modified alumina powder.

[0052] (2) Prepare surface-modified alumina-modified polyurea composite coating:

[0053] Specifically: 3% of modified nano-aluminum oxide by the mass fraction of the polyurea coating was added to 35 wt% of the diluent propylene glycol methyl ether acetate (PMA) of the polyurea coating, and the modified alumina powder was fully dispersed using ultrasonic oscillation to obtain a milky white suspension; then the polyurea resin and the curing agent of the polyurea coating were sequentially added to the suspension according to a mass ratio of 3:2, and then it was stirred at 1500 rpm for 150 s using a planetary gravity mixer to mix it evenly, obtaining an Al 2 O 3 -M modified polyurea composite coating.

[0054] (3) Coating the film layer:

[0055] Specifically: The surface-modified alumina-modified polyurea composite coating obtained in step (2) was coated on the surface of a carbon steel substrate that had been surface-treated (polished with 220-mesh abrasive, and the surface oil and impurities were removed by ultrasonic cleaning with a degreasing solution and pure water, and finally the surface residual moisture was removed and then dried in an oven). After drying and curing at 60 °C for 4 days, an Al 2 O 3 -M modified polyurea composite coating was obtained on the carbon steel surface. The dry film thickness of the Al 2 O 3 -M modified polyurea composite coating was 100 ± 20 μm.

[0056] Example 2

[0057] A preparation method of a polyurea composite coating, which is different from that of Example 1 in that:

[0058] The nano-particles in this example were silica nano-particles; the preparation method of the surface-modified nano-particles included the following steps:

[0059] 2 mL of an amino-silane coupling agent was added to 100 mL of absolute ethanol to obtain a diluted amino-silane coupling agent solution. Another 100 mL of absolute ethanol was added dropwise with a 0.5 mol / L oxalic acid solution to adjust the pH to 3, and then 2 mL of the diluted silane coupling agent solution was added. After stirring and hydrolyzing in a water bath at 45 °C for 1 h, 1 g of nano-silica (100 nm) particles was added, and stirring was continued in a water bath at 45 °C for 4 h. Then, the silica solid was filtered and separated, placed in a drying oven at 60 °C for 24 h, and after drying, the modified silica block was obtained. Finally, after grinding the block, modified silica powder (SiO 2 -M) was obtained.

[0060] Example 3

[0061] A preparation method of a polyurea composite coating, which is different from that of Example 1 in that:

[0062] The nano-particles in this example were magnesium oxide nano-particles; the preparation method of the surface-modified nano-particles included the following steps:

[0063] 2 mL of an amino-silane coupling agent was added to 100 mL of absolute ethanol to obtain a diluted solution of the amino-silane coupling agent. Separately, 0.5 mol / L of oxalic acid solution was added dropwise to 100 mL of absolute ethanol to adjust the pH to 3, and then 2 mL of the diluted silane coupling agent solution was added. After hydrolysis with stirring in a water bath at 45 °C for 1 h, 1 g of nano-magnesium oxide (100 nm) particles were added, and stirring was continued in a water bath at 45 °C for 4 h. Then, the magnesium oxide solid was separated by filtration, placed in a drying oven at 60 °C for drying for 24 h, and finally, the obtained block was ground to obtain modified magnesium oxide powder (MgO-M).

[0064] Example 4

[0065] A method for preparing a polyurea composite coating, which is different from Example 1 in that:

[0066] In this example, the nanoparticles used were zinc oxide nanoparticles; the preparation method of the surface-modified nanoparticles included the following steps:

[0067] 2 mL of an amino-silane coupling agent was added to 100 mL of absolute ethanol to obtain a diluted solution of the amino-silane coupling agent. Separately, 0.5 mol / L of oxalic acid solution was added dropwise to 100 mL of absolute ethanol to adjust the pH to 3, and then 2 mL of the diluted silane coupling agent solution was added. After hydrolysis with stirring in a water bath at 45 °C for 1 h, 1 g of nano-zinc oxide (100 nm) particles were added, and stirring was continued in a water bath at 45 °C for 4 h. Then, the zinc oxide solid was separated by filtration, placed in a drying oven at 60 °C for drying for 24 h, and finally, the obtained block was ground to obtain modified zinc oxide powder (ZnO-M).

[0068] Example 5

[0069] A method for preparing a polyurea composite coating, which is different from Example 1 in that:

[0070] In this example, the nanoparticles used were silicon carbide nanoparticles; the preparation method of the surface-modified nanoparticles included the following steps:

[0071] 2 mL of an amino-silane coupling agent was added to 100 mL of absolute ethanol to obtain a diluted solution of the amino-silane coupling agent. Separately, 0.5 mol / L of oxalic acid solution was added dropwise to 100 mL of absolute ethanol to adjust the pH to 3, and then 2 mL of the diluted silane coupling agent solution was added. After hydrolysis with stirring in a water bath at 45 °C for 1 h, 1 g of nano-silicon carbide (100 nm) particles were added, and stirring was continued in a water bath at 45 °C for 4 h. Then, the silicon carbide solid was separated by filtration, placed in a drying oven at 60 °C for drying for 24 h, and finally, the obtained block was ground to obtain modified silicon carbide powder (SiC-M).

[0072] Example 6

[0073] A preparation method of a polyurea composite coating, different from Example 1 in that:

[0074] In this example, the nanoparticles are zirconia nanoparticles; the preparation method of the surface-modified nanoparticles includes the following steps:

[0075] Add 2 mL of amino silane coupling agent to 100 mL of absolute ethanol to obtain a diluted amino silane coupling agent solution. Take another 100 mL of absolute ethanol, add 0.5 mol / L oxalic acid solution dropwise to adjust the pH to 3, then add 2 mL of the diluted silane coupling agent solution. After hydrolyzing with stirring in a water bath at 45 °C for 1 h, add 1 g of zirconia nanoparticles (100 nm) and continue stirring in a water bath at 45 °C for 4 h. Then, filter and separate the zirconia solid, place it in a drying oven at 60 °C for drying for 24 h to obtain the modified zirconia bulk. Finally, grind the bulk to obtain modified zirconia powder (ZrO 2 -M).

[0076] Comparative Example 1

[0077] A preparation method of a polyurea coating, which does not contain surface-modified nanoparticles in this comparative example, includes the following steps:

[0078] (1) Prepare polyurea coating:

[0079] Specifically: Mix polyurea resin, curing agent, and diluent propylene glycol monomethyl ether acetate (PMA) with a mass ratio of 6:4:3.5, and then use a planetary gravity mixer to stir at 1500 rpm for 150 s to mix them evenly to obtain polyurea coating.

[0080] (2) Coat the film layer:

[0081] Specifically: Coat the polyurea coating obtained in step (1) on the surface of a carbon steel substrate that has been surface-treated (polished with 220-mesh abrasive, ultrasonically cleaned with degreasing liquid and pure water to remove oil stains and impurities on the surface, and finally dried in an oven after removing the residual surface moisture). After drying and curing at 60 °C for 4 days, a polyurea coating is obtained on the carbon steel surface, and the dry film thickness of the coating is 100 ± 20 μm.

[0082] Comparative Example 2

[0083] A preparation method of a polyurea composite coating, in which the nanoparticles in this comparative example are not surface-modified, includes the following steps:

[0084] (1) Prepare surface-modified alumina-modified polyurea composite coating:

[0085] Specifically: Add nano-aluminum oxide accounting for 3% of the mass fraction of the polyurea coating into propylene glycol methyl ether acetate (PMA) diluent accounting for 35% of the mass fraction of the polyurea coating. Use ultrasonic oscillation to fully disperse the alumina powder to obtain a milky white suspension; then add the polyurea resin and curing agent of the polyurea coating into the suspension in sequence according to a mass ratio of 3:2, and then use a planetary gravity mixer to stir at 1500 rpm for 150 s to mix them evenly to obtain Al 2 O 3 modified polyurea composite coating.

[0086] (2) Coating film layer:

[0087] Specifically: Coat the alumina-modified polyurea composite coating obtained in step (1) on the surface of a carbon steel substrate that has been surface-treated (polished with 220-mesh abrasive, ultrasonically cleaned with a degreasing solution and pure water to remove oil stains and impurities on the surface, and finally dried in an oven after removing the residual moisture on the surface). After drying and curing at 60 °C for 4 days, an Al 2 O 3 modified polyurea composite coating is obtained on the carbon steel surface. The dry film thickness of the Al 2 O 3 modified polyurea composite coating is 100 ± 20 μm.

[0088] Performance test

[0089] Perform the following characterizations and tests on Example 1 and Comparative Examples 1-2:

[0090] 1. Microscopic morphology characterization of the composite coating

[0091] Place the Al 2 O 3 -M modified polyurea composite coating prepared in Example 1 and the Al 2 O 3 modified polyurea composite coating prepared in Comparative Example 2 under a scanning electron microscope for observation, and the obtained morphological structure is as Figure 1 shown.

[0092] It can be seen that compared with the un-surface-modified nanoparticles in Comparative Example 2, the agglomeration phenomenon of the surface-modified alumina nanoparticles in the polyurea coating of the present invention is improved and the dispersibility is enhanced.

[0093] 2. Wear resistance and surface roughness test of the coating

[0094] 2.1 Wear resistance

[0095] Perform wear resistance tests on the coatings prepared in Example 1, Comparative Example 1, and Comparative Example 2 according to the standard of GB / T 1768-2006 using a Taber abrasion tester with a load of 10 N.

[0096] The results are as Figure 2 shown. After 2000 wear rotations, the wear loss of the pure polyurea coating (PU) is about 90.9 mg, and that of the Al 2 O 3 -modified polyurea composite coating (PU-Al 2 O 3 ) is about 78.6 mg, and that of the Al 2 O 3 -M modified polyurea composite coating (PU-Al 2 O 3 -M) is about 70.3 mg. Compared with the pure polyurea coating, the wear resistance of the Al 2 O 3 -M modified polyurea composite coating is improved by 22.6%.

[0097] 2.2 Surface roughness and wear measurement

[0098] The surface roughness of the samples after the above wear resistance test was measured using a roughness profiler, and then the wear amount of the coating was measured. The results are as Figure 3 shown.

[0099] It can be seen that the wear amount of the pure polyurea coating in Comparative Example 1 is about 15.75, and that of the Al 2 O 3 -modified polyurea composite coating in Comparative Example 2 is about 9.37, and that of the Al 2 O 3 -M modified polyurea composite coating in Example 1 is about 7.34. The above results show that the wear resistance of the Al 2 O 3 -M modified polyurea composite coating is significantly improved compared with the pure polyurea coating.

[0100] 3. Electrochemical impedance spectroscopy experiment of the coating after UV aging

[0101] The coatings prepared in Example 1, Comparative Example 1, and Comparative Example 2 were acceleratedly aged for 168 h (7 d), 336 h (14 d), 672 h (28 d), and 1008 h (42 d) using a UVB ultraviolet lamp (313 nm, 60 W) according to the ISO16474–2021 standard; subsequently, the coatings prepared in Example 1, Comparative Example 1, and Comparative Example 2 after UV aging for different times were placed in a 3.5 wt.% sodium chloride solution for electrochemical impedance testing. The impedance modulus results are as Figure 3 shown.

[0102] It can be seen that the low-frequency impedance modulus of Example 1 always remains at 10 11 Ω·cm 2Above, the low-frequency impedance modulus of Comparative Example 1 began to decrease significantly after 672 h of aging and finally decreased to 10 9 ~10 10 Ω·cm 2 , and the low-frequency impedance modulus of Comparative Example 2 also began to decrease after 1008 h of aging. It shows that the corrosion resistance of the Al 2 O 3 -M modified polyurea coating is improved by two orders of magnitude compared with the pure polyurea coating, indicating that the Al 2 O 3 -M modified polyurea coating has excellent anti-ultraviolet aging performance and long-term corrosion resistance.

[0103] Similarly, after ultraviolet aging the polyurea composite coatings of Examples 2-6, electrochemical impedance spectroscopy experiments were carried out on the coatings. The polyurea composite coatings of each example showed wear resistance and anti-ultraviolet aging performance comparable to those of Example 1.

[0104] The above examples of the present invention are merely illustrations for clearly explaining the present invention and are not intended to limit the embodiments of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a polyurea composite coating, characterized in that: The following steps are involved: S1, adding an aminotrialkoxysilane coupling agent to an alkyl alcohol solvent, adjusting the pH to 3-5, heating and stirring for hydrolysis reaction to obtain a silane-modified modifier; S2, adding a silane modification agent to the nanoparticles for surface modification to obtain surface-modified nanoparticles; S3, adding polyurea resin and curing agent to the surface modified nanoparticles and mixing them evenly to obtain the polyurea composite coating.

2. The method for preparing the polyurea composite coating according to claim 1, characterized in that: The aminotrialkoxysilane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane or N-(β-aminoethyl)-γ-aminopropyltriethoxysilane.

3. The method for preparing the polyurea composite coating according to claim 1, characterized in that: In step S1, the hydrolysis temperature is 40-60°C.

4. The method for preparing the polyurea composite coating according to claim 1, characterized in that: The ratio of the mass of the nanoparticles to the volume of the aminotrialkoxysilane coupling agent is 0.5-4 g / mL.

5. The method for preparing the polyurea composite coating according to claim 1, characterized in that: In step S2, the surface modification temperature is 40-60°C, and the reaction time is 2-6 hours.

6. The method for preparing the polyurea composite coating according to claim 1, characterized in that: The material of the nanoparticles is at least one of aluminum oxide, silicon oxide, magnesium oxide, zinc oxide, silicon carbide or zirconium oxide.

7. The method for preparing the polyurea composite coating according to claim 1, characterized in that: In step S3, the mass ratio of the polyurea resin to the surface-modified nanoparticles is 1:(0.015-0.1).

8. A polyurea composite coating, characterized in that: The polyurea composite coating is prepared by the preparation method of any one of claims 1 to 7.

9. Use of the polyurea composite coating according to claim 8 in preparing protective materials for marine engineering equipment.

10. A polyurea composite coating, characterized in that: The polyurea composite coating according to claim 8 is at least partially coated on the surface of a metal substrate and then cured.

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