Corrosion-resistant protective varnish for automobile air-inlet grille and preparation method of corrosion-resistant protective varnish

Abstract

The invention discloses a corrosion-resistant protective varnish for an automobile air-inlet grille and a preparation method of the corrosion-resistant protective varnish, and relates to the technical field of coatings. The corrosion-resistant protective varnish comprises a base coat varnish and a top coat varnish; copper sulfate pentahydrate, dopamine hydrochloride, hydrogen peroxide, aminocyclotriphosphazene and the like are used as raw materials in the prime coat varnish; in the topcoat varnish, aminated bimetal MOF, epoxy polyethylene glycol dopamine, dopa 4-phosphate and the like with specific mass ratio and molecular weight are used as raw materials. The primer varnish and the topcoat varnish synergistically generate excellent corrosion resistance, and meanwhile, the paint has excellent adhesive force and heat resistance.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a corrosion-resistant protective clear coat for automotive air intake grilles and its preparation method. Background Technology

[0002] With the continuous development of the automotive industry, the requirements for car air intake grilles are constantly increasing. They are not only used for surface decoration, but also play a certain role in protection, ventilation and heat dissipation.

[0003] While automotive grilles possess high strength, they are not highly corrosion-resistant. Therefore, current technologies typically modify their surface to improve corrosion resistance. However, current protective coatings often suffer from the following drawbacks: First, the use of a single clear coat results in poor interaction with the grille surface, leading to poor coating adhesion and reduced durability. Second, the coating often lacks heat resistance. Since automotive grilles are components with heat dissipation functions, poor heat resistance of the clear coat can cause coating peeling, thus reducing corrosion resistance and other properties.

[0004] In summary, the development of a corrosion-resistant protective varnish for automotive air intake grilles and its preparation method is of great significance in addressing the aforementioned issues. Summary of the Invention

[0005] The purpose of this invention is to provide a corrosion-resistant protective clear coat for automotive air intake grilles and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A corrosion-resistant protective clear coat for automotive air intake grilles, the corrosion-resistant protective clear coat comprising a primer clear coat and a topcoat clear coat; The raw materials of the primer clear varnish include the following components: by mass, 1.2-1.5 parts copper sulfate pentahydrate, 1.8-2.2 parts dopamine hydrochloride, 2-2.4 parts hydrogen peroxide, 0.5-0.7 parts aminocyclotriphosphazene, 15-17 parts ethanol aqueous solution, and 900-1000 parts TRIS buffer solution; The raw materials for the topcoat varnish include the following components: by weight, 25-35 parts hydroxyl acrylic resin, 20-32 parts thermosetting acrylic resin, 0.3-0.5 parts leveling agent, 0.03-0.1 parts defoamer, 15-22 parts curing agent, 0.5-1.7 parts ultraviolet absorber, 3-5 parts composite additive, and 15-25 parts solvent.

[0007] In a further embodiment, the TRIS buffer is a 50mM tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a pH of 8.5; the ethanol-water solution is an ethanol-water solution with a volume ratio of 20:80; and the hydrogen peroxide is a 30% (w / w) hydrogen peroxide aqueous solution.

[0008] A more optimized method for preparing the composite additive is as follows: Step 1: Add chromium nitrate nonahydrate and copper nitrate hexahydrate to N,N-dimethylformamide-water solution, add 2-aminopyromellitic acid and polyvinylpyrrolidone, stir at room temperature for 30-50 min, keep warm at 150-170℃ for 3-5 h, cool to room temperature, centrifuge, wash and dry to obtain aminated bimetallic MOF; Step 2: Under a nitrogen atmosphere, amino-modified bimetallic MOF, epoxy-modified polyethylene glycol dopamine, dopamine 4-phosphate, and triethylamine are added to an N,N-dimethylformamide aqueous solution and reacted at 50~70℃ for 5~8h. After cooling to room temperature, the mixture is purified and dried to obtain the composite additive.

[0009] In a more optimized manner, the mass ratio of aminated bimetallic MOF, epoxy polyethylene glycol dopamine, and dopamine 4-phosphate in the raw materials of the composite additive is (6~9):(4~6):(1~1.7); the mass of triethylamine is 0.1wt%~0.3wt% of the total mass of the aminated bimetallic MOF.

[0010] Ideally, the molecular weight of the epoxy-based polyethylene glycol dopamine is 200-500.

[0011] In a more optimized manner, the raw materials of the aminated bimetallic MOF include the following components: by mass, 0.8 to 1.3 parts of chromium nitrate nonahydrate, 2.5 to 4 parts of copper nitrate hexahydrate, 1 to 1.3 parts of 2-aminopyromellitic acid, and 0.5 to 1.2 parts of polyvinylpyrrolidone.

[0012] More preferably, the hydroxyl acrylic resin includes one or more of PAR-1153-75 and PAR-1137-75; the viscosity of the thermosetting acrylic resin is 2000~4000 mPa·s / 25℃.

[0013] More preferably, the curing agent is an aliphatic isocyanate trimer; the solvent includes one or more of xylene, butyl acetate, and propylene glycol methyl ether acetate.

[0014] A more optimized method for preparing a corrosion-resistant protective clear coat for automotive air intake grilles includes the following steps: Step 1: Add copper sulfate pentahydrate to TRIS buffer solution and stir evenly at room temperature. Then add dopamine hydrochloride and hydrogen peroxide to obtain solution A. Add aminocyclotriphosphazene to ethanol aqueous solution and stir evenly at room temperature to obtain solution B. Mix solution A and solution B and stir to obtain primer varnish. Step 2: Add hydroxyl acrylic resin and thermosetting acrylic resin to the solvent and stir at high speed until uniform. Then add leveling agent, defoamer, UV absorber and composite additive, stir at low speed until uniform. Finally add curing agent, stir, filter and obtain topcoat varnish. When using, first apply a base coat of clear varnish and let it dry, then apply a top coat of clear varnish and let it dry.

[0015] Ideally, the amount of the primer varnish applied is 15-25 mL / m², and the amount of the topcoat varnish applied is 60-120 mL / m².

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are: This application uses a primer clear coat and a top coat clear coat containing specific components, which are sequentially applied to the surface of the car's air intake grille. The two work together to produce excellent corrosion resistance, while also exhibiting excellent adhesion and heat resistance.

[0017] The primer clear coat is composed of copper sulfate pentahydrate, dopamine hydrochloride, and aminocyclotriphosphazene as raw materials. In the alkaline environment of the TRIS buffer solution, dopamine hydrochloride undergoes self-polymerization under the oxidative catalysis of hydrogen peroxide to form polydopamine. The catechol groups in the polydopamine molecule can improve adhesion to the substrate. Simultaneously, the copper element in the copper sulfate pentahydrate chelates with polydopamine and passivates the substrate surface, further preventing the penetration of corrosive media and improving corrosion resistance. Furthermore, aminocyclotriphosphazene provides specific heat resistance properties, ensuring the coating interface remains stable even at high temperatures.

[0018] However, although the primer clear coat has a certain interfacial bonding and passivation ability, it still lacks sufficient corrosion protection. Therefore, to solve this problem, the proposed solution involves applying a topcoat clear coat after the primer clear coat has dried, forming a dense three-dimensional network that provides corrosion protection. The topcoat clear coat uses a resin base and incorporates a composite additive consisting of an aminated bimetallic MOF, epoxy-based polyethylene glycol dopamine, and dopamine 4-phosphate. The aminated bimetallic MOF is composed of chromium and copper bimetals. Chromium acts as the rigid framework of the MOF, and its standard electrode potential is lower than that of copper. When corrosive media penetrates, the potential difference between chromium and copper forms a composite passivation film. Epoxy-based polyethylene glycol dopamine grafts onto the surface of the bimetallic MOF through a ring-opening reaction, while simultaneously forming specific coordination interactions with copper and chromium, further improving adhesion. The amphiphilic nature of polyethylene glycol also enhances the compatibility of the composite additive with the resin base, ensuring stable dispersion. It is important to note that... The molecular weight of epoxy-based polyethylene glycol dopamine should not be too large, as excessively large molecular weight can lead to thermal oxidation and breakage of PEG segments at high temperatures, significantly reducing the effectiveness of the composite additive. Based on this, this application further introduces dopamine-4-phosphate to provide thermal stability and corrosion protection. Through the coordination of catechol groups with the metal of the MOF, the structural stability of the composite additive in the resin matrix is ​​improved. By introducing phosphate groups, on the one hand, physical protection can be formed on the surface of the metal matrix, thus providing a certain degree of corrosion resistance; on the other hand, the phosphate groups can act as chelating ligands for metal ions, inhibiting their activity and thereby inhibiting the thermal oxidative degradation of the resin matrix, synergistically improving heat resistance stability.

[0019] In summary, both primer and topcoat varnishes work synergistically to improve adhesion, corrosion resistance, and heat resistance, and neither can be omitted. Applying only primer varnish lacks sufficient corrosion protection, making the coating susceptible to corrosive media, leading to rust and blistering, and decreased adhesion and heat resistance. Applying only topcoat varnish, on the other hand, lacks the bonding force of polydopamine to the chromium-plated substrate and the passivation effect of copper, resulting in significantly reduced coating adhesion, increased susceptibility to interlayer delamination and interfacial corrosion, and consequently, decreased corrosion resistance and adhesion. Furthermore, the lack of aminocyclotriphosphazene reduces heat resistance. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that the following quantities are by weight, and there are no special restrictions on the manufacturers of the raw materials involved in this invention. Exemplary examples include: dopamine hydrochloride (CAS No. 62-31-7); aminocyclotriphosphazene (hexa(p-aminophenoxy)cyclotriphosphazene) CAS No. 13441-26-4; copper sulfate pentahydrate (CAS No. 7758-99-8); chromium nitrate nonahydrate (CAS No. 13548-38-4); copper nitrate hexahydrate (CAS No. 13478-38-1); 2-aminopyromellitic acid (CAS No. 489-96-3); polyvinylpyrrolidone (CAS No. 9003-39-8); and hydroxyl acrylic resin. PAR-1153-75 (hydroxyl acrylic resin for automotive OEM); the thermosetting acrylic resin is YZ-S105 thermosetting acrylic resin with a viscosity of 3000 mPa·s / 25℃; the leveling agent is BYK-354 polyacrylate surface additive; the defoamer is BYK-390; the curing agent is aliphatic polyisocyanate, model HT-100; the ultraviolet absorber is EV-81; the epoxy polyethylene glycol dopamine has a molecular weight of 400 and a product number of P026003; dopamine 4-phosphate (CAS No. 101141-95-1); the epoxy polyethylene glycol dopamine has a molecular weight of 5000 and a product number of P026003; and other raw materials are commercially available.

[0022] The material of the car's air intake grille is PC (polycarbonate) / ABS (acrylonitrile-butadiene-styrene copolymer) with electroplated bright chrome.

[0023] Example 1: A method for preparing a corrosion-resistant protective clear coat for automotive air intake grilles, comprising the following steps: Pre-preparation: (1) 1.1 parts of chromium nitrate nonahydrate and 3.2 parts of copper nitrate hexahydrate were added to a 50wt% N,N-dimethylformamide-water solution, 1.15 parts of 2-aminopyromellitic acid and 0.8 parts of polyvinylpyrrolidone were added, stirred at room temperature for 40 min, kept at 160℃ for 4 h, cooled to room temperature, centrifuged, washed and dried to obtain an aminated bimetallic MOF; (2) Under nitrogen atmosphere, an aminated bimetallic MOF, epoxy polyethylene glycol dopamine (molecular weight 400), dopamine 4-phosphate and triethylamine (the amount of triethylamine introduced is 0.2wt% of the total mass of the aminated bimetallic MOF) were added to a 50wt% N,N-dimethylformamide-water solution in a mass ratio of 7.5:5:1.3, reacted at 60℃ for 6.5 h, cooled to room temperature, purified and dried to obtain a composite additive; Step 1: Add 1.3 parts of copper sulfate pentahydrate to 950 parts of TRIS buffer (50mM tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, pH 8.5), stir at room temperature for 10 min, then add 2 parts of dopamine hydrochloride and 2.2 parts of hydrogen peroxide (30% hydrogen peroxide aqueous solution) to obtain solution A; add 0.6 parts of aminocyclotriphosphazene to 16 parts of ethanol aqueous solution (ethanol-water aqueous solution with a volume ratio of 20:80), stir at room temperature for 10 min to obtain solution B; mix solutions A and B, stir, and obtain the primer varnish; Step 2: Add 30 parts of hydroxyl acrylic resin and 26 parts of thermosetting acrylic resin to 20 parts of solvent (xylene, butyl acetate, and propylene glycol methyl ether acetate in a mass ratio of 5:4:1) and disperse at 1350 RPM for 15 min. Then add 0.4 parts of leveling agent, 0.07 parts of defoamer, 1.1 parts of UV absorber, and 4 parts of composite additive and disperse at 400 RPM for 40 min. Finally, add 18 parts of curing agent, stir, and filter through a 10 μm filter to obtain a clear topcoat. When using, first apply the primer clear coat to the surface of the car's air intake grille at a rate of 20 mL / m²; dry at 60°C for 90 minutes; then apply the topcoat clear coat to the surface at a rate of 90 mL / m²; dry at 80°C for 60 minutes. This process forms a corrosion-resistant protective coating.

[0024] Example 2: A method for preparing a corrosion-resistant protective clear coat for automotive air intake grilles, comprising the following steps: Pre-preparation: (1) 1.1 parts of chromium nitrate nonahydrate and 3.2 parts of copper nitrate hexahydrate were added to a 50wt% N,N-dimethylformamide-water solution, 1.15 parts of 2-aminopyromellitic acid and 0.8 parts of polyvinylpyrrolidone were added, stirred at room temperature for 40 min, kept at 160℃ for 4 h, cooled to room temperature, centrifuged, washed and dried to obtain an aminated bimetallic MOF; (2) Under nitrogen atmosphere, an aminated bimetallic MOF, epoxy polyethylene glycol dopamine (molecular weight 400), dopamine 4-phosphate and triethylamine (the amount of triethylamine introduced is 0.2wt% of the total mass of the aminated bimetallic MOF) were added to a 50wt% N,N-dimethylformamide-water solution in a mass ratio of 6:4:1, reacted at 60℃ for 6.5 h, cooled to room temperature, purified and dried to obtain a composite additive; Step 1: Add 1.3 parts of copper sulfate pentahydrate to 950 parts of TRIS buffer (50mM tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, pH 8.5), stir at room temperature for 10 min, then add 2 parts of dopamine hydrochloride and 2.2 parts of hydrogen peroxide (30% hydrogen peroxide aqueous solution) to obtain solution A; add 0.6 parts of aminocyclotriphosphazene to 16 parts of ethanol aqueous solution (ethanol-water aqueous solution with a volume ratio of 20:80), stir at room temperature for 10 min to obtain solution B; mix solutions A and B, stir, and obtain the primer varnish; Step 2: Add 30 parts of hydroxyl acrylic resin and 26 parts of thermosetting acrylic resin to 20 parts of solvent (xylene, butyl acetate, and propylene glycol methyl ether acetate in a mass ratio of 5:4:1) and disperse at 1350 RPM for 15 min. Then add 0.4 parts of leveling agent, 0.07 parts of defoamer, 1.1 parts of UV absorber, and 4 parts of composite additive and disperse at 400 RPM for 40 min. Finally, add 18 parts of curing agent, stir, and filter through a 10 μm filter to obtain a clear topcoat. When using, first apply the primer clear coat to the surface of the car's air intake grille at a rate of 20 mL / m²; dry at 60°C for 90 minutes; then apply the topcoat clear coat to the surface at a rate of 90 mL / m²; dry at 80°C for 60 minutes. This process forms a corrosion-resistant protective coating.

[0025] Example 3: A method for preparing a corrosion-resistant protective clear coat for automotive air intake grilles, comprising the following steps: Pre-preparation: (1) 1.1 parts of chromium nitrate nonahydrate and 3.2 parts of copper nitrate hexahydrate were added to a 50wt% N,N-dimethylformamide-water solution, 1.15 parts of 2-aminopyromellitic acid and 0.8 parts of polyvinylpyrrolidone were added, stirred at room temperature for 40 min, kept at 160℃ for 4 h, cooled to room temperature, centrifuged, washed and dried to obtain an aminated bimetallic MOF; (2) Under nitrogen atmosphere, an aminated bimetallic MOF, epoxy polyethylene glycol dopamine (molecular weight 400), dopamine 4-phosphate and triethylamine (the amount of triethylamine introduced is 0.2wt% of the total mass of the aminated bimetallic MOF) were added to a 50wt% N,N-dimethylformamide-water solution in a mass ratio of 9:6:1.7, reacted at 60℃ for 6.5 h, cooled to room temperature, purified and dried to obtain a composite additive; Step 1: Add 1.3 parts of copper sulfate pentahydrate to 950 parts of TRIS buffer (50mM tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, pH 8.5), stir at room temperature for 10 min, then add 2 parts of dopamine hydrochloride and 2.2 parts of hydrogen peroxide (30% hydrogen peroxide aqueous solution) to obtain solution A; add 0.6 parts of aminocyclotriphosphazene to 16 parts of ethanol aqueous solution (ethanol-water aqueous solution with a volume ratio of 20:80), stir at room temperature for 10 min to obtain solution B; mix solutions A and B, stir, and obtain the primer varnish; Step 2: Add 30 parts of hydroxyl acrylic resin and 26 parts of thermosetting acrylic resin to 20 parts of solvent (xylene, butyl acetate, and propylene glycol methyl ether acetate in a mass ratio of 5:4:1) and disperse at 1350 RPM for 15 min. Then add 0.4 parts of leveling agent, 0.07 parts of defoamer, 1.1 parts of UV absorber, and 4 parts of composite additive and disperse at 400 RPM for 40 min. Finally, add 18 parts of curing agent, stir, and filter through a 10 μm filter to obtain a clear topcoat. When using, first apply the primer clear coat to the surface of the car's air intake grille at a rate of 20 mL / m²; dry at 60°C for 90 minutes; then apply the topcoat clear coat to the surface at a rate of 90 mL / m²; dry at 80°C for 60 minutes. This process forms a corrosion-resistant protective coating.

[0026] Comparative Example 1: A single side was coated with clear varnish; the rest was the same as in Example 1; the specific differences are as follows: Pre-preparation: (1) 1.1 parts of chromium nitrate nonahydrate and 3.2 parts of copper nitrate hexahydrate were added to a 50wt% N,N-dimethylformamide-water solution, 1.15 parts of 2-aminopyromellitic acid and 0.8 parts of polyvinylpyrrolidone were added, stirred at room temperature for 40 min, kept at 160℃ for 4 h, cooled to room temperature, centrifuged, washed and dried to obtain an aminated bimetallic MOF; (2) Under nitrogen atmosphere, an aminated bimetallic MOF, epoxy polyethylene glycol dopamine (molecular weight 400), dopamine 4-phosphate and triethylamine (the amount of triethylamine introduced is 0.2wt% of the total mass of the aminated bimetallic MOF) were added to a 50wt% N,N-dimethylformamide-water solution in a mass ratio of 7.5:5:1.3, reacted at 60℃ for 6.5 h, cooled to room temperature, purified and dried to obtain a composite additive; Step 1: Add 30 parts of hydroxyl acrylic resin and 26 parts of thermosetting acrylic resin to 20 parts of solvent (xylene, butyl acetate, and propylene glycol methyl ether acetate in a mass ratio of 5:4:1) and disperse at 1350 RPM for 15 min. Then add 0.4 parts of leveling agent, 0.07 parts of defoamer, 1.1 parts of UV absorber, and 4 parts of composite additive and disperse at 400 RPM for 40 min. Finally, add 18 parts of curing agent, stir, and filter through a 10 μm filter to obtain a clear topcoat. When using, apply the clear varnish to the surface of the car's air intake grille at a rate of 90 mL / m²; dry at 80°C for 60 minutes to form a corrosion-resistant protective coating.

[0027] Comparative Example 2: In the primer clear coat, the aminocyclotriphosphazene was replaced with 3-aminopropyltriethoxysilane; the rest was the same as in Example 1; the specific differences are as follows: Step 1: Add 1.3 parts of copper sulfate pentahydrate to 950 parts of TRIS buffer (50mM tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, pH 8.5), stir at room temperature for 10 min, then add 2 parts of dopamine hydrochloride and 2.2 parts of hydrogen peroxide (30% hydrogen peroxide aqueous solution) to obtain solution A; add 0.3 parts of 3-aminopropyltriethoxysilane to 16 parts of ethanol aqueous solution (ethanol-water aqueous solution with a volume ratio of 20:80), stir at room temperature for 10 min to obtain solution B; mix solutions A and B and stir to obtain the primer varnish.

[0028] Comparative Example 3: In the topcoat varnish, the aminated bimetallic MOF was replaced with a single chromium MOF; the rest was the same as in Example 1; the specific difference was: Pre-preparation: (1) 4.3 parts of chromium nitrate nonahydrate were added to 50wt% N,N-dimethylformamide-water solution, 1.15 parts of 2-aminotrimethylammonium phosphate and 0.8 parts of polyvinylpyrrolidone were added, stirred at room temperature for 40 min, kept at 160℃ for 4 h, cooled to room temperature, centrifuged, washed and dried to obtain aminated bimetallic MOF; (2) Under nitrogen atmosphere, aminated bimetallic MOF, epoxy polyethylene glycol dopamine (molecular weight 400), dopamine 4-phosphate and triethylamine (the amount of triethylamine introduced is 0.2wt% of the total mass of aminated bimetallic MOF) were added to 50wt% N,N-dimethylformamide-water solution at a mass ratio of 7.5:5:1.3, reacted at 60℃ for 6.5 h, cooled to room temperature, purified and dried to obtain composite additive.

[0029] Comparative Example 4: The molecular weight (400) of epoxy-based polyethylene glycol dopamine in the topcoat varnish was adjusted to (5000); the rest was the same as in Example 1; the specific differences are as follows: Pre-preparation: (1) 1.1 parts of chromium nitrate nonahydrate and 3.2 parts of copper nitrate hexahydrate were added to a 50wt% N,N-dimethylformamide-water solution, along with 1.15 parts of 2-aminopyromellitic acid and 0.8 parts of polyvinylpyrrolidone. The mixture was stirred at room temperature for 40 min, kept at 160℃ for 4 h, cooled to room temperature, centrifuged, washed, and dried to obtain an aminated bimetallic MOF; (2) Under a nitrogen atmosphere, the aminated bimetallic MOF, epoxy polyethylene glycol dopamine (molecular weight 5000), dopamine 4-phosphate, and triethylamine (the amount of triethylamine introduced was 0.2wt% of the total mass of the aminated bimetallic MOF) were added to a 50wt% N,N-dimethylformamide-water solution in a mass ratio of 7.5:5:1.3. The mixture was reacted at 60℃ for 6.5 h, cooled to room temperature, purified, and dried to obtain a composite additive.

[0030] Comparative Example 5: The topcoat varnish did not contain dopa-4-phosphate; otherwise, it was the same as Example 1; the specific differences are as follows: Pre-preparation: (1) 1.1 parts of chromium nitrate nonahydrate and 3.2 parts of copper nitrate hexahydrate were added to a 50wt% N,N-dimethylformamide aqueous solution, along with 1.15 parts of 2-aminopyromellitic acid and 0.8 parts of polyvinylpyrrolidone. The mixture was stirred at room temperature for 40 min, kept at 160℃ for 4 h, cooled to room temperature, centrifuged, washed, and dried to obtain an aminated bimetallic MOF; (2) Under a nitrogen atmosphere, the aminated bimetallic MOF, epoxy polyethylene glycol dopamine (molecular weight 400), and triethylamine (the amount of triethylamine introduced was 0.2wt% of the total mass of the aminated bimetallic MOF) were added to a 50wt% N,N-dimethylformamide aqueous solution at a mass ratio of 8.5:5. The mixture was reacted at 60℃ for 6.5 h, cooled to room temperature, purified, and dried to obtain a composite additive.

[0031] Performance Test 1: The corrosion-resistant protective coatings obtained in Examples 1-3 and Comparative Examples 1-5 were subjected to relevant performance tests. (1) Adhesion test was performed according to the standard method of GB / T 9286-2021 to obtain adhesion A; the coating was subjected to cyclic heat treatment, with the temperature increased to 120℃ at a rate of 2℃ / min and then decreased to 25℃ at a rate of 2℃ / min; the cycle was repeated 200 times. After the cycle was completed, the sample was placed under standard environmental conditions for 24 hours to recover, and the adhesion was tested again according to GB / T 9286-2021 to obtain adhesion B; the above test results were graded, and the adhesion grade decreased from small to large. (2) In accordance with the standard method of GB / T 31588.1-2015, the corrosion resistance test was carried out in cycle B, with a salt spray deposition rate of 1 mL / h to 2 mL / h and a total time of 840 h; the test results are shown in the table below.

[0032] Conclusion: As can be seen from the data in the table above, this application improves the heat resistance, adhesion and corrosion resistance of the product through the synergistic effect of primer varnish and topcoat varnish. Data from Comparative Example 1 shows that a single topcoat clear varnish, lacking a primer clear varnish, significantly reduces coating adhesion, and this adhesion decreases significantly after 200 thermal cycles. Data from Comparative Example 2 shows that adjusting the aminocyclotriphosphazene in the primer clear varnish to 3-aminopropyltriethoxysilane results in a lack of heat-resistant functional groups and reduced interlayer adhesion. Data from Comparative Example 3 shows that adjusting the aminated bimetallic MOF in the topcoat clear varnish to a single chromium MOF reduces overall performance. Data from Comparative Example 4 shows that adjusting the molecular weight of epoxy polyethylene glycol dopamine in the topcoat clear varnish from 400 to 5000 causes the PEG segments to easily break down due to thermal oxidation, resulting in reduced overall performance. Data from Comparative Example 5 shows that without dopamine-4-phosphate in the topcoat clear varnish, the lack of phosphate ester and dopamine significantly reduces the stability of the composite additive, decreases the bonding strength with the base resin, and reduces overall performance.

[0033] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A corrosion-resistant protective varnish for automotive air intake grilles, characterized in that: The corrosion-resistant protective varnish includes a primer varnish and a topcoat varnish; The raw materials of the primer clear varnish include the following components: by mass, 1.2-1.5 parts copper sulfate pentahydrate, 1.8-2.2 parts dopamine hydrochloride, 2-2.4 parts hydrogen peroxide, 0.5-0.7 parts aminocyclotriphosphazene, 15-17 parts ethanol aqueous solution, and 900-1000 parts TRIS buffer solution; The raw materials for the topcoat varnish include the following components: by weight, 25-35 parts hydroxyl acrylic resin, 20-32 parts thermosetting acrylic resin, 0.3-0.5 parts leveling agent, 0.03-0.1 parts defoamer, 15-22 parts curing agent, 0.5-1.7 parts ultraviolet absorber, 3-5 parts composite additive, and 15-25 parts solvent.

2. The corrosion-resistant protective varnish for automotive air intake grilles according to claim 1, characterized in that: The preparation method of the composite additive is as follows: Step 1: Add chromium nitrate nonahydrate and copper nitrate hexahydrate to N,N-dimethylformamide-water solution, add 2-aminopyromellitic acid and polyvinylpyrrolidone, stir at room temperature for 30-50 min, keep warm at 150-170℃ for 3-5 h, cool to room temperature, centrifuge, wash and dry to obtain aminated bimetallic MOF; Step 2: Under a nitrogen atmosphere, amino-modified bimetallic MOF, epoxy-modified polyethylene glycol dopamine, dopamine 4-phosphate, and triethylamine are added to an N,N-dimethylformamide aqueous solution and reacted at 50~70℃ for 5~8h. After cooling to room temperature, the mixture is purified and dried to obtain the composite additive.

3. The corrosion-resistant protective varnish for automotive air intake grilles according to claim 2, characterized in that: In the raw materials of the composite additive, the mass ratio of aminated bimetallic MOF, epoxy polyethylene glycol dopamine, and dopamine 4-phosphate is (6~9):(4~6):(1~1.7); the mass of triethylamine is 0.1wt%~0.3wt% of the total mass of aminated bimetallic MOF.

4. The corrosion-resistant protective varnish for automotive air intake grilles according to claim 3, characterized in that: The molecular weight of the epoxy-based polyethylene glycol dopamine is 200-500.

5. The corrosion-resistant protective varnish for automotive air intake grilles according to claim 3, characterized in that: The raw materials of the aminated bimetallic MOF include the following components: by mass, 0.8-1.3 parts of chromium nitrate nonahydrate, 2.5-4 parts of copper nitrate hexahydrate, 1-1.3 parts of 2-aminopyromellitic acid, and 0.5-1.2 parts of polyvinylpyrrolidone.

6. The corrosion-resistant protective varnish for automotive air intake grilles according to claim 1, characterized in that: The hydroxyl acrylic resin includes one or more of PAR-1153-75 and PAR-1137-75; the viscosity of the thermosetting acrylic resin is 2000~4000 mPa·s / 25℃.

7. The corrosion-resistant protective varnish for automotive air intake grilles according to claim 1, characterized in that: The curing agent is an aliphatic isocyanate trimer; the solvent includes one or more of xylene, butyl acetate, and propylene glycol methyl ether acetate.

8. The method for preparing a corrosion-resistant protective clear coat for automotive air intake grilles according to claim 1, characterized in that: Includes the following steps: Step 1: Add copper sulfate pentahydrate to TRIS buffer solution and stir evenly at room temperature. Then add dopamine hydrochloride and hydrogen peroxide to obtain solution A. Add aminocyclotriphosphazene to ethanol aqueous solution and stir evenly at room temperature to obtain solution B. Mix solution A and solution B and stir to obtain primer varnish. Step 2: Add hydroxyl acrylic resin and thermosetting acrylic resin to the solvent and stir at high speed until uniform. Then add leveling agent, defoamer, UV absorber and composite additive, stir at low speed until uniform. Finally add curing agent, stir, filter and obtain topcoat varnish. When using, first apply a base coat of clear varnish and let it dry, then apply a top coat of clear varnish and let it dry.

9. The method for preparing a corrosion-resistant protective clear coat for automotive air intake grilles according to claim 1, characterized in that: The amount of the primer varnish applied is 15~25 mL / m²; the amount of the topcoat varnish applied is 60~120 mL / m².

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