High-solid chromium-free acrylic polyurethane finish paint as well as preparation method and application thereof

Abstract

The invention provides high-solid chromium-free acrylic polyurethane finish paint, a preparation method and application, and relates to the technical field of finish paint. The finishing paint is mainly prepared from the following raw materials in parts by mass: 55 to 65 parts of hydroxy acrylic resin; 25 to 35 parts of an HDI (hexamethylene diisocyanate) tripolymer; 10-15 parts of a zinc phosphate and zinc molybdate composite antirust agent; 0.5 to 1.5 parts of a phosphorus-containing titanate coupling agent; 2 to 4 parts of modified SiO2; 1 to 3 parts of modified graphene / modified fluorinated graphene; 0.5 to 1.5 parts of a hyperbranched polyester flatting agent; 6 to 9 parts of propylene glycol methyl ether acetate; and 1-3 parts of a phosphorus-containing acrylate monomer. The coating system has the advantages of high solid content, no chromium, environmental protection and excellent heavy corrosion resistance, and is suitable for long-term protection in the fields of steel structures, marine facilities and the like in a harsh corrosion environment.

Description

Technical Field

[0001] This invention relates to the field of topcoat technology, and more particularly to high-solids chromium-free acrylic polyurethane topcoat, its preparation method, and its application. Background Technology

[0002] In the field of heavy-duty anti-corrosion coatings, acrylic polyurethane topcoats are widely used due to their excellent weather resistance, mechanical properties, and decorative properties. However, traditional solvent-based coatings contain large amounts of volatile organic compounds (VOCs), posing a threat to the environment and human health. Meanwhile, many high-performance anti-corrosion coatings still rely on toxic rust-inhibiting pigments such as chromates, making it difficult to meet increasingly stringent environmental regulations. In recent years, high-solids coatings have become an important development direction due to their low VOC emissions, but maintaining or even improving anti-corrosion performance while achieving chromium-free coatings remains a challenge. Furthermore, the comprehensive performance of coatings, including corrosion resistance, adhesion, and impact resistance, still requires efficient composite processes of fillers and resin systems.

[0003] Therefore, developing a new type of acrylic polyurethane topcoat that combines high solids content, chromium-free environmental friendliness, long-lasting corrosion resistance, and excellent overall performance is of great industrial significance and application value.

[0004] Therefore, this invention is proposed. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-solids, chromium-free acrylic polyurethane topcoat, its preparation method, and its application. Through the synergistic effect of its components, this application significantly reduces volatile organic compound (VOC) emissions while ensuring excellent film-forming properties and mechanical performance, thus meeting environmental protection requirements.

[0006] In order to achieve the objective of this invention, the following technical solution is adopted: This invention provides a high-solids, chromium-free acrylic polyurethane topcoat, which, by weight, is mainly composed of the following raw materials: 55-65 parts of hydroxyl acrylic resin; 25-35 parts of HDI trimer; 10-15 parts of zinc phosphate and zinc molybdate composite rust inhibitor; 0.5-1.5 parts of phosphorus-containing titanate coupling agent; 2-4 parts modified SiO2; 1-3 parts of modified graphene / modified fluorinated graphene; 0.5-1.5 parts of hyperbranched polyester leveling agent; 6-9 parts of propylene glycol methyl ether acetate; 1-3 parts of phosphorus-containing acrylate monomer; The modified SiO2 is obtained by modifying nano-SiO2 with an aminosilane coupling agent; the modified graphene / modified fluorinated graphene is obtained by modifying graphene or fluorinated graphene with a silane coupling agent.

[0007] Furthermore, 60 parts of hydroxyl acrylic resin; 32 parts of HDI trimer; 13 parts of zinc phosphate and zinc molybdate composite rust inhibitor; One part of phosphorus-containing titanate coupling agent; 3 parts modified SiO2; Two parts of modified graphene / modified fluorinated graphene; One part of hyperbranched polyester leveling agent; 8 parts of propylene glycol methyl ether acetate; Two parts of phosphorus-containing acrylate monomer.

[0008] Furthermore, the mass ratio of the zinc phosphate and zinc molybdate composite rust inhibitor is (2-4):1.

[0009] Furthermore, the mass ratio of the zinc phosphate and zinc molybdate composite rust inhibitor is 3:1.

[0010] Furthermore, the solid content of the hydroxyl acrylic resin is ≥85%, and the hydroxyl value of the hydroxyl acrylic resin is 80mgKOH / g-100 mgKOH / g.

[0011] Furthermore, the hydroxyl value of the hydroxyl acrylic resin is 90 mg KOH / g.

[0012] Furthermore, the NCO content in the HDI trimer is 18%-22%.

[0013] Furthermore, the NCO content in the HDI trimer is 20%.

[0014] Furthermore, the modified SiO2 has a particle size of 10nm-20nm; the modified graphene / modified fluorinated graphene has a sheet diameter of 1μm-5μm and a surface grafting rate of ≥5%.

[0015] Furthermore, the modified SiO2 has a particle size of 10 nm; the modified graphene / modified fluorinated graphene has a sheet diameter of 3 μm.

[0016] The present invention also provides a method for preparing the above-mentioned high-solids chromium-free acrylic polyurethane topcoat, comprising the following steps: S1. Preparation of modified SiO2; S2, Preparation of modified graphene / modified fluorinated graphene; S3. Preheat hydroxyl acrylic resin. Take half of the preheated hydroxyl acrylic resin, add 1 / 3 of the amount of hyperbranched polyester leveling agent, stir, and then add modified graphene / modified fluorinated graphene. S4. After feeding is complete, increase the rotation speed to disperse and obtain slurry A; S5. Stir and disperse the remaining hydroxyl acrylic resin, phosphorus-containing titanate coupling agent, phosphorus-containing acrylate monomer, modified SiO2 and zinc phosphate and zinc molybdate composite rust inhibitor for 40 min-60 min, cool to ≤50℃, and test the fineness to ≤25μm to obtain slurry B. S6. Adjust the stirring speed to mix slurry A and slurry B until the system is homogeneous, filter, and obtain component A; S7. Stir HDI trimer and propylene glycol methyl ether acetate at a mass ratio of 4:1, and control the temperature to <35℃ to obtain component B; S8. Mix component A and component B at a mass ratio of 4:1.

[0017] Furthermore, the stirring in S3 is low-speed stirring, with a stirring rate of 500rpm-800rpm.

[0018] Furthermore, in S4, the rotation speed is increased to 1000rpm-1500rpm, and the dispersion time is 30min-45min.

[0019] Furthermore, in S5, the stirring speed is 2000rpm-2500rpm.

[0020] Furthermore, in step S6, the stirring speed is adjusted to 800 rpm-1200 rpm, and the mixing time is 20 min-30 min.

[0021] Furthermore, in S7, the stirring rate is 300 rpm to 500 rpm.

[0022] Furthermore, the specific steps of S1 are as follows: S101. Vacuum dry nano-SiO2, dissolve aminosilane coupling agent in a mixed solvent of ethanol and water, adjust pH, stir at room temperature until the solution becomes turbid, and obtain pretreated nano-SiO2. S102. Disperse the pretreated nano-SiO2 in deionized water, ultrasonically disperse to form a uniform suspension, heat, and reflux and stir under nitrogen protection. S103. After the reaction is complete, centrifuge to separate the solid product, wash it, and dry it under vacuum to obtain the final product.

[0023] Furthermore, the specific steps of S2 are as follows: S201. Disperse graphene or fluorinated graphene in a buffer solution with pH=6, add carbodiimide and N-hydroxysuccinimide, and stir and activate at room temperature for 0.5h-1h. S202, then add silane coupling agent, react at room temperature, then wash, freeze dry to obtain the product.

[0024] This invention also provides the application of the above-mentioned high-solids chromium-free acrylic polyurethane topcoat in heavy-duty metal corrosion protection.

[0025] The present invention has the following technical effects: This application achieves a significant reduction in volatile organic compound (VOC) emissions through the synergistic effect of its components, ensuring excellent film-forming properties and mechanical performance while meeting environmental protection requirements. Secondly, using a chromium-free zinc phosphate / zinc molybdate composite rust inhibitor as the core, combined with surface-grafted modified nano-SiO2 and graphene materials, a multi-layered and highly efficient physical and chemical barrier is constructed in the coating, significantly improving its corrosion resistance, impermeability, and long-term protective life. Furthermore, the introduction of a phosphorus titanate coupling agent and a hyperbranched polyester leveling agent further enhances the compatibility and interfacial bonding between the components, resulting in excellent adhesion, impact resistance, and surface smoothness. This coating system combines high solids content, chromium-free environmental friendliness, and superior heavy-duty corrosion protection, making it suitable for long-term protection of steel structures and marine facilities in harsh corrosive environments. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] In a first aspect, the present invention provides a high-solids, chromium-free acrylic polyurethane topcoat, which, by weight parts, is mainly composed of the following raw materials: 55-65 parts of hydroxyl acrylic resin; 25-35 parts of HDI trimer; 10-15 parts of zinc phosphate and zinc molybdate composite rust inhibitor; 0.5-1.5 parts of phosphorus-containing titanate coupling agent; 2-4 parts modified SiO2; 1-3 parts of modified graphene / modified fluorinated graphene; 0.5-1.5 parts of hyperbranched polyester leveling agent; 6-9 parts of propylene glycol methyl ether acetate; 1-3 parts of phosphorus-containing acrylate monomer; The modified SiO2 is obtained by modifying nano-SiO2 with an aminosilane coupling agent; the modified graphene / modified fluorinated graphene is obtained by modifying graphene or fluorinated graphene with a silane coupling agent.

[0028] The basic principle of a high-solids-content, chromium-free anti-corrosion coating system was constructed: A high-hydroxyl-value, high-solids-content hydroxyl acrylic resin was used as the film-forming matrix (providing excellent adhesion and weather resistance), reacting with HDI trimer with a specific NCO content (as a curing agent) to form a dense polyurethane network; a zinc phosphate / zinc molybdate composite was used as a non-toxic anti-rust pigment, achieving chromium-free anti-corrosion through the synergistic effect of chemical passivation and physical shielding; surface-modified nano-SiO2 (enhancing coating hardness and wear resistance) and modified graphene / modified fluorinated graphene (utilizing their layered structure to construct an efficient barrier) were introduced to improve the coating's physical shielding and resistance to media penetration; a phosphorus-containing titanate coupling agent and a hyperbranched polyester leveling agent were used to improve filler dispersibility and coating leveling properties, respectively; propylene glycol methyl ether acetate was used as an environmentally friendly solvent to adjust the application viscosity. The phosphorus-containing titanate coupling agent enhanced the filler-resin interface; the hyperbranched polyester leveling agent improved the surface smoothness of the coating, jointly enhancing the coating integrity.

[0029] In some embodiments, 60 parts of hydroxyl acrylic resin were used; 32 parts of HDI trimer; 13 parts of zinc phosphate and zinc molybdate composite rust inhibitor; One part of phosphorus-containing titanate coupling agent; 3 parts modified SiO2; Two parts of modified graphene / modified fluorinated graphene; One part of hyperbranched polyester leveling agent; 8 parts of propylene glycol methyl ether acetate; Two parts of phosphorus-containing acrylate monomer.

[0030] In some embodiments, the mass ratio of the zinc phosphate and zinc molybdate composite rust inhibitor is (2-4):1.

[0031] In some embodiments, the mass ratio of the zinc phosphate and zinc molybdate composite rust inhibitor is 3:1.

[0032] In some embodiments, the solid content of the hydroxyl acrylic resin is ≥85%, and the hydroxyl value of the hydroxyl acrylic resin is 80 mgKOH / g-100 mgKOH / g.

[0033] In some embodiments, the hydroxyl value of the hydroxyl acrylic resin is 90 mg KOH / g.

[0034] In some embodiments, the NCO content in the HDI trimer is 18%-22%.

[0035] In some embodiments, the NCO content in the HDI trimer is 20%.

[0036] In some embodiments, the modified SiO2 has a particle size of 10nm-20nm; the modified graphene / modified fluorinated graphene has a sheet size of 1μm-5μm and a surface grafting rate of ≥5%.

[0037] In some embodiments, the modified SiO2 has a particle size of 10 nm; the modified graphene / modified fluorinated graphene has a sheet diameter of 3 μm.

[0038] By limiting the ratio of rust inhibitor (2-4:1), the best synergistic anti-corrosion effect is ensured; by limiting the resin solid content to ≥85% and the hydroxyl value range (80-100 mgKOH / g), high solid content and sufficient cross-linking are guaranteed; by limiting the HDI trimer NCO content (18%-22%), sufficient curing reaction and stable coating performance are ensured; and by limiting the particle size of modified fillers (10-20nm for SiO2 and 1-5μm for graphene sheets) and grafting rate (≥5%), good dispersion and interfacial bonding in the resin are ensured, avoiding agglomeration and maximizing the reinforcing effect.

[0039] Secondly, the present invention also provides a method for preparing the above-mentioned high-solids chromium-free acrylic polyurethane topcoat, comprising the following steps: S1. Preparation of modified SiO2; S2, Preparation of modified graphene / modified fluorinated graphene; S3. Preheat hydroxyl acrylic resin. Take half of the preheated hydroxyl acrylic resin, add 1 / 3 of the amount of hyperbranched polyester leveling agent, stir, and then add modified graphene / modified fluorinated graphene. S4. After feeding is complete, increase the rotation speed to disperse and obtain slurry A; S5. Stir and disperse the remaining hydroxyl acrylic resin, phosphorus-containing titanate coupling agent, phosphorus-containing acrylate monomer, modified SiO2 and zinc phosphate and zinc molybdate composite rust inhibitor for 40 min-60 min, cool to ≤50℃, and test the fineness to ≤25μm to obtain slurry B. S6. Adjust the stirring speed to mix slurry A and slurry B until the system is homogeneous, filter, and obtain component A; S7. Stir HDI trimer and propylene glycol methyl ether acetate at a mass ratio of 4:1, and control the temperature to <35℃ to obtain component B; S8. Mix component A and component B at a mass ratio of 4:1.

[0040] In some embodiments, the stirring in S3 is low-speed stirring, with a stirring rate of 500 rpm to 800 rpm.

[0041] In some embodiments, the rotation speed in S4 is increased to 1000rpm-1500rpm, and the dispersion time is 30min-45min.

[0042] In some embodiments, the stirring speed in step S5 is 2000 rpm to 2500 rpm.

[0043] In some embodiments, in step S6, the stirring speed is adjusted to 800 rpm-1200 rpm, and the mixing time is 20 min-30 min.

[0044] In some embodiments, the stirring rate in S7 is 300 rpm to 500 rpm.

[0045] In some embodiments, the specific steps of S1 are as follows: S101. Vacuum dry nano-SiO2, dissolve aminosilane coupling agent in a mixed solvent of ethanol and water, adjust pH, stir at room temperature until the solution becomes turbid, and obtain pretreated nano-SiO2. S102. Disperse the pretreated nano-SiO2 in deionized water, ultrasonically disperse to form a uniform suspension, heat, and reflux and stir under nitrogen protection. S103. After the reaction is complete, centrifuge to separate the solid product, wash it, and dry it under vacuum to obtain the final product.

[0046] In some embodiments, the specific steps of S2 are as follows: S201. Disperse graphene or fluorinated graphene in a buffer solution with pH=6, add carbodiimide and N-hydroxysuccinimide, and stir and activate at room temperature for 0.5h-1h. S202, then add silane coupling agent, react at room temperature, then wash, freeze dry to obtain the product.

[0047] The surface activity of the modified filler is ensured by preparing it in steps (S1, S2); a segmented dispersion process (S3-S6) is adopted - first, the easily agglomerated graphene material is pre-dispersed with part of the resin and leveling agent (slurry A), then the other components are dispersed with the remaining resin at high speed (slurry B), and finally mixed. This effectively avoids the agglomeration of nanofillers and ensures the uniformity and fineness (≤25μm) of the system; component B (curing agent component) is pre-mixed separately and its viscosity (≤200 mPa·s) and temperature (<35℃) are controlled to ensure the workability and reaction controllability when the two components are mixed.

[0048] Thirdly, the present invention also provides the application of the above-mentioned high-solids chromium-free acrylic polyurethane topcoat in heavy-duty metal corrosion protection.

[0049] The following is a detailed explanation using specific embodiments: Example 1: Preparation of Topcoat S1, Preparation of modified SiO2 Nano-SiO2 was vacuum dried at 120℃ for 2 hours to remove physically adsorbed water and expose more surface silanol groups. In a dry reactor, an aminosilane coupling agent (γ-aminopropyltriethoxysilane, hereinafter referred to as KH-550) is dissolved in a mixed solvent of ethanol and water. The concentration of KH-550 is about 5wt%-10wt%. Acetic acid is added dropwise to adjust the pH to 4.5-5.5. The mixture is stirred and hydrolyzed at room temperature for 0.5-1 hour until the solution becomes slightly turbid, thus obtaining pretreated nano-SiO2.

[0050] The pretreated nano-SiO2 was dispersed in deionized water and ultrasonically dispersed for 30 min to form a uniform suspension. The system was then heated to 70℃-80℃ and refluxed under nitrogen protection with stirring for 6-12 h.

[0051] After the reaction was completed, the mixture was centrifuged and repeatedly washed with anhydrous ethanol and centrifuged several times to completely remove the physically adsorbed silane coupling agent and its oligomers. Finally, it was vacuum dried at 60°C to obtain a loose white powder.

[0052] S2, Preparation of modified graphene Modified graphene / modified fluorinated graphene was dispersed in a buffer solution (PBS) at pH=6, and carbodiimide (EDC) and N-hydroxysuccinimide (NHS) were added. The carboxyl groups were activated by stirring at room temperature for 0.5-1 hours to generate an active ester intermediate.

[0053] A silane coupling agent (γ-(2,3-epoxypropoxy)propyltrimethoxysilane, abbreviated as KH-560) was added to the activated modified graphene dispersion and reacted at room temperature. The mixture was then washed and freeze-dried to obtain modified graphene or fluorinated graphene.

[0054] S3. Weigh 60g of hydroxyl acrylic resin (solid content ≥85%, hydroxyl value 90mgKOH / g). 32g of HDI trimer (NCO content is 20%) 13g of zinc phosphate and zinc molybdate composite rust inhibitor; 1g of phosphorus-containing titanate coupling agent; Modified SiO2 3g (particle size 10nm, surface grafting rate 8%) 2g of modified graphene (sheet diameter 3μm); 1g of hyperbranched polyester leveling agent; 8g of propylene glycol methyl ether acetate; Of which, 9.75g of zinc phosphate and 3.25g of zinc molybdate were contained; 2g of phosphorus-containing acrylate monomer (phosphate methacrylate-PMA is used in this example).

[0055] The hydroxyl acrylic resin was slowly heated to 40±2℃ in the reactor and stirred at low speed to reduce its initial viscosity and facilitate subsequent dispersion.

[0056] In a premixing tank, add approximately 1 / 3 of the formulated amount of hyperbranched polyester leveling agent and half of the preheated hydroxyl acrylic resin, and slowly add the formulated amount of modified graphene / modified fluorinated graphene at a speed of 700 rpm.

[0057] S4. After feeding is complete, increase the rotation speed to 1500 rpm and disperse for 30 minutes to obtain slurry A.

[0058] S5. Disperse the remaining hydroxyl acrylic resin, phosphorus-containing titanate coupling agent, PMA, modified SiO2 and zinc phosphate and zinc molybdate composite rust inhibitor at 2500 rpm for 60 min. Control the temperature to 40℃ by jacket cooling and test the fineness. When the fineness is 10 μm, slurry B is obtained.

[0059] S6. Adjust the stirring speed to 1000 rpm, mix slurry A and slurry B until the system is homogeneous, filter, and obtain component A.

[0060] S7. Mix HDI trimer and propylene glycol methyl ether acetate at a mass ratio of 4:1, stir at 300 rpm, and control the temperature at 20°C to obtain component B.

[0061] S8. At the construction site, mix component A and component B at a mass ratio of 4:1, and use mechanical stirring at medium speed for 2-3 minutes until uniform.

[0062] Comparative Example 1: Commercially available conventional solid acrylic polyurethane topcoat Hydroxyacrylate resin (solid content approximately 65%, hydroxyl value approximately 100 mgKOH / g): 50g HDI trimer: 25g Rutile titanium dioxide: 20g Barium sulfate (filler): 10g Strontium chromate (rust inhibitor): 5g General-purpose dispersant / leveling agent: 2g Mixed solvent (xylene / butyl acetate): 35g The dispersion process is a conventional high-speed dispersion process.

[0063] Comparative Example 2 The comparative system using traditional chromate rust inhibitors was implemented in the same manner as in Example 1, except that the chromium-free rust inhibitor was replaced with strontium chromate.

[0064] Experiment Example 1: Accelerated Corrosion Resistance Test (Salt Spray Test) Objective: To evaluate the long-term protective capability of coating systems under harsh corrosive environments, which is a core performance indicator of heavy-duty anti-corrosion coatings.

[0065] Method: Refer to the national standard GB / T 1771-2007 "Determination of resistance to neutral salt spray of paints and varnishes".

[0066] Sample preparation: All coatings used in the examples and comparative examples were prepared according to standard methods and sprayed onto cold-rolled steel sheets of the same specifications and with the same pretreatment. The dry film thickness was controlled at (80±5) μm. Testing was conducted after curing at room temperature for 7 days.

[0067] Test conditions: 5% NaCl solution, test chamber temperature (35±2)℃, continuous spraying.

[0068] Observation and Recording: The sample surface was observed regularly, and the time of the first rust spot, the single-sided corrosion width (mm) at the scratch, and the degree of blistering and peeling were recorded. The test cycles were 1000 hours, 2000 hours, and 3000 hours. The experimental results are shown in Table 1.

[0069] Table 1: Results of Accelerated Corrosion Resistance Tests Note: The blistering / peeling level is based on the standard, with level 0 being the best and level 5 being the worst.

[0070] Experimental Example 2: Testing of the Physical and Mechanical Properties and Media Resistance of the Coating Objective: To verify the effect of modified nanofillers and good dispersibility on the overall performance of coatings. Test items and methods: Adhesion: Refer to GB / T 9286-2021 and conduct cross-cut adhesion test (0-5 levels).

[0071] Impact resistance: Refer to GB / T 1732-2020, using an impact tester (positive / negative impact, kg·cm).

[0072] Pencil hardness: Refer to GB / T 6739-2006.

[0073] Abrasion resistance: Refer to GB / T 1768-2006, using a rotary abrasion tester (weight loss, mg).

[0074] Chemical resistance: Referring to GB / T 9274-1988, the coating was immersed in 3% NaCl solution, 10% H2SO4 solution, and 10% NaOH solution respectively, and the changes in the coating were observed periodically. The experimental results are shown in Table 2.

[0075] Table 2: Test Results of Physical and Mechanical Properties of Coating Thanks to the passivating effect of the chromium-free composite rust inhibitor (zinc phosphate / zinc molybdate) and the dense physical barrier constructed by modified graphene and nano-SiO2, it exhibits excellent long-term corrosion resistance. No substrate corrosion was observed within 3000 hours, and scratches spread extremely slowly, indicating that the coating has excellent anti-permeability and self-healing (inhibits corrosion spread) capabilities.

[0076] Meanwhile, thanks to the improved interfacial bonding from the phosphorus-containing titanate coupling agent, and the synergistic enhancement from nano-SiO2 (enhancing hardness and wear resistance) and modified graphene (improving toughness and barrier properties), the coating exhibits comprehensive high performance. It demonstrates excellent adhesion (grade 0), high impact resistance and hardness, and low wear loss. In chemical resistance tests, it is stable to neutral salts and alkalis, and shows only slight discoloration to acids, exhibiting good chemical inertness.

[0077] The above inferred data clearly demonstrate that the high-solids chromium-free acrylic polyurethane topcoat provided by this invention is significantly superior to traditional commercially available chromium-containing products in terms of long-term corrosion protection, comprehensive mechanical properties, and media resistance. It successfully achieves simultaneous improvement in corrosion protection and comprehensive performance under the premise of chromium-free and high solids content, fully meeting the design objectives and technical effects of this invention.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A high-solids, chromium-free acrylic polyurethane topcoat, characterized in that, By weight, it is mainly composed of the following raw materials: 55-65 parts of hydroxyl acrylic resin; 25-35 parts of HDI trimer; 10-15 parts of zinc phosphate and zinc molybdate composite rust inhibitor; 0.5-1.5 parts of phosphorus-containing titanate coupling agent; 2-4 parts modified SiO2; 1-3 parts of modified graphene / modified fluorinated graphene; 0.5-1.5 parts of hyperbranched polyester leveling agent; 6-9 parts of propylene glycol methyl ether acetate; 1-3 parts of phosphorus-containing acrylate monomer; The modified SiO2 is obtained by modifying nano-SiO2 with an aminosilane coupling agent; the modified graphene / modified fluorinated graphene is obtained by modifying graphene or fluorinated graphene with a silane coupling agent.

2. The high-solids chromium-free acrylic polyurethane topcoat according to claim 1, characterized in that, The mass ratio of the zinc phosphate and zinc molybdate composite rust inhibitor is (2-4):

1.

3. The high-solids chromium-free acrylic polyurethane topcoat according to claim 1, characterized in that, The solid content of the hydroxyl acrylic resin is ≥85%, and the hydroxyl value of the hydroxyl acrylic resin is 80mgKOH / g-100 mgKOH / g.

4. The high-solids chromium-free acrylic polyurethane topcoat according to claim 1, characterized in that, The NCO content in the HDI trimer is 18%-22%.

5. The high-solids chromium-free acrylic polyurethane topcoat according to claim 1, characterized in that, The modified SiO2 has a particle size of 10nm-20nm; the modified graphene / modified fluorinated graphene has a sheet size of 1μm-5μm and a surface grafting rate of ≥5%.

6. A method for preparing a high-solids chromium-free acrylic polyurethane topcoat as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Preparation of modified SiO2; S2, Preparation of modified graphene / modified fluorinated graphene; S3. Preheat hydroxyl acrylic resin. Take half of the preheated hydroxyl acrylic resin, add 1 / 3 of the amount of hyperbranched polyester leveling agent, stir, and then add modified graphene / modified fluorinated graphene. S4. After feeding is complete, increase the rotation speed to disperse and obtain slurry A; S5. Stir and disperse the remaining hydroxyl acrylic resin, phosphorus-containing titanate coupling agent, phosphorus-containing acrylate monomer, modified SiO2 and zinc phosphate and zinc molybdate composite rust inhibitor for 40 min-60 min, cool to ≤50℃, and test the fineness to ≤25μm to obtain slurry B. S6. Adjust the stirring speed to mix slurry A and slurry B until the system is homogeneous, filter, and obtain component A; S7. Stir HDI trimer and propylene glycol methyl ether acetate at a mass ratio of 4:1, and control the temperature to <35℃ to obtain component B; S8. Mix component A and component B at a mass ratio of 4:

1.

7. The method for preparing the high-solids chromium-free acrylic polyurethane topcoat according to claim 6, characterized in that, In S7, the viscosity of component B is ≤200 mPa·s.

8. The method for preparing the high-solids chromium-free acrylic polyurethane topcoat according to claim 6, characterized in that, The specific steps of S1 are as follows: S101. Vacuum dry nano-SiO2, dissolve aminosilane coupling agent in a mixed solvent of ethanol and water, adjust pH, stir at room temperature until the solution becomes turbid, and obtain pretreated nano-SiO2. S102. Disperse the pretreated nano-SiO2 in deionized water, ultrasonically disperse to form a uniform suspension, heat, and reflux and stir under nitrogen protection. S103. After the reaction is complete, centrifuge to separate the solid product, wash it, and dry it under vacuum to obtain the final product.

9. The method for preparing the high-solids chromium-free acrylic polyurethane topcoat according to claim 6, characterized in that, The specific steps of S2 are as follows: S201. Disperse modified graphene or modified fluorinated graphene in a buffer solution with pH=6, add carbodiimide and N-hydroxysuccinimide, and stir and activate at room temperature for 0.5h-1h. S202, then add silane coupling agent, react at room temperature, then wash, freeze dry to obtain the product.

10. The application of a high-solids chromium-free acrylic polyurethane topcoat as described in any one of claims 1-5 in heavy-duty metal corrosion protection.

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