Water-based metallic primer for vehicle and preparation method thereof

Abstract

The present application relates to the technical field of automotive primer, in particular to an automotive water-based metal primer and a preparation method thereof, comprising the following raw materials: modified water-based acrylic resin 40-60 parts by weight, non-ionic polyurethane thickener 1-3 parts by weight, aluminum powder slurry 5-10 parts by weight, nano titanium dioxide / graphene oxide composite filler 1-5 parts by weight, cocamide propyl betaine 0.1-0.5 parts by weight, and polydimethylsiloxane 0.1-0.3 parts by weight. In the design, the modified water-based acrylic resin reduces the surface tension by introducing the organic silicon chain segment, thereby promoting the wetting of the paint film to the substrate; the three-dimensional network structure is constructed by the silicon dioxide nanoparticles, and the system is given high thixotropy, so as to keep the viscosity stability at low shear rate and effectively inhibit the vertical face sagging phenomenon. The non-ionic polyurethane thickener introduces the hydrophobic group by grafting gamma-aminopropyl trimethoxysilane, forms a dynamic hydrogen bond network, and gives the system the shear thinning characteristics, so as to ensure the stability and adhesion of the coating.

Description

Technical Field

[0001] This invention relates to the field of automotive primer technology, and more specifically, to a water-based metallic primer for automobiles and its preparation method. Background Technology

[0002] Metallic primers play a crucial role in automobile manufacturing, requiring not only excellent adhesion and corrosion protection but also compatibility with subsequent coatings. Traditional solvent-based coatings are limited by their high volatile organic compound (VOC) emissions, while water-based coatings, with their low or zero VOC emissions, are gradually becoming the ideal choice for environmentally friendly and high-performance coatings. Compared to traditional solvent-based products, water-based metallic primers reduce environmental pollution while maintaining or even improving performance indicators such as weather resistance, abrasion resistance, and aesthetics.

[0003] However, existing water-based metallic primers have a higher surface tension than solvent-based paints, and their high heat of vaporization and specific heat capacity also make them prone to sagging during the spraying process. In view of this, we propose a water-based metallic primer for automobiles and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a water-based metallic primer for automobiles and its preparation method, in order to solve the problem mentioned in the background art that existing water-based metallic primers are prone to sagging during the spraying process because their surface tension is greater than that of solvent-based paints, and their own high heat of vaporization and specific heat capacity are also higher.

[0005] To achieve the above objectives, the present invention provides a water-based metallic primer for automobiles, comprising the following raw materials: 40-60 parts by weight of modified water-based acrylic resin, 1-3 parts by weight of nonionic polyurethane thickener, 5-10 parts by weight of aluminum powder paste, 1-5 parts by weight of nano-titanium dioxide / graphene oxide composite filler, 0.1-0.5 parts by weight of cocamidopropyl betaine, and 0.1-0.3 parts by weight of polydimethylsiloxane;

[0006] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion.

[0007] Nonionic polyurethane thickeners are prepared by end-capping polyurethane prepolymers with fatty alcohol polyoxyethylene ethers and then grafting γ-aminopropyltrimethoxysilane onto the end-capped polyurethane prepolymers.

[0008] Preferably, in the modified waterborne acrylic resin, the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.0-4.0.

[0009] Preferably, in the nonionic polyurethane thickener, the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.01-0.03.

[0010] Preferably, the preparation steps of the modified waterborne acrylic resin are as follows:

[0011] The acrylic copolymer base material is mixed with epoxy resin E-20 emulsion, and 2%-4% sodium dodecyl sulfate by weight of the acrylic copolymer base material is added. The mixture is pre-emulsified for 20-30 minutes using a high-speed disperser at 600-800 rpm to obtain a mixture. The mixture is then transferred to a reactor and heated to 75-85°C at a rate of 1-2°C per minute under nitrogen protection. The mixture is stirred at 300-500 rpm for 1-2 hours to form an acrylic-epoxy composite emulsion.

[0012] Add the organosilicon / silica hybrid powder to deionized water and ultrasonically disperse it for 20-30 minutes at a power of 100-200W to form a hybrid suspension.

[0013] Add the hybrid suspension to the acrylic-epoxy composite emulsion, and simultaneously add an aqueous solution of ammonium persulfate dropwise over a period of 1-2 hours. Raise the temperature to 80-85°C and stir the mixture at 300-500 rpm for 4-6 hours under nitrogen protection.

[0014] After the reaction is complete, the reaction system is cooled to 40-50℃, and the pH of the reaction system is adjusted to 8.0-8.5 with ammonia water with a mass percentage concentration of 20%-25%. Then, the system is filtered through a 180-200 mesh filter to obtain the modified waterborne acrylic resin.

[0015] Under alkaline conditions, the epoxy groups (-O-CH2-CH(O)-CH2) in the epoxy resin (E-20) can undergo ring-opening reactions with the silanol groups (Si-OH) of the organosilicon / silica hybrid to generate stable Si-OC bonds (silicon-oxygen-carbon bonds). This structure significantly improves the hardness and wear resistance of the resin. At the same time, the polar groups (such as hydroxyl and carboxyl groups) of the epoxy resin form hydrogen bonds or chemical bonds with the metal substrate, greatly improving the adhesion of the primer to the metal surface. The organosilicon component introduces hydrophobic siloxane segments, effectively reducing the water absorption rate of the coating and preventing water penetration that leads to corrosion of the metal substrate. Silica nanoparticles fill the micropores of the coating, forming a dense barrier, which, together with the chemical inertness of the epoxy resin, can resist corrosive media such as salt spray and acid rain. The high bond energy of the Si-O bonds in the organosilicon / silica hybrid (approximately 444 kJ / mol) can resist ultraviolet degradation and delay the yellowing and chalking of the coating. The rigid benzene ring structure of the epoxy resin enhances the high-temperature stability of the coating.

[0016] Preferably, the mass percentage concentration of the ammonium persulfate aqueous solution is 3%-8%.

[0017] Preferably, the preparation steps of the nonionic polyurethane thickener are as follows:

[0018] Dehydrated polyoxypropylene glycol, diisocyanate and dibutyltin dilaurate are added to a reactor, heated to 70-80℃ and stirred at 300-400 rpm for 2-3 hours for prepolymerization.

[0019] After the prepolymerization reaction is completed, fatty alcohol polyoxyethylene ether is added at a molar ratio of 1:1 between isocyanate groups and fatty alcohol polyoxyethylene ether in the prepolymer. The reaction is continued to be stirred at 400-500 rpm at 60-70℃ for 1-2 hours. After the reaction is completed, the reaction system is cooled to 40-50℃ at a rate of 1-2℃ per minute to obtain the end-capped polyurethane prepolymer.

[0020] γ-aminopropyltrimethoxysilane was added to the end-capped polyurethane prepolymer and stirred at 400-500 rpm for 1-2 hours at 60-70℃. After the reaction was completed, the mixture was cooled to room temperature to obtain a nonionic polyurethane thickener.

[0021] Nonionic polyurethane thickeners form a dynamic three-dimensional network structure through association, giving the primer a balance between high shear viscosity (anti-sagging during application) and low shear viscosity (anti-settling during storage); the nonionic structure makes it insensitive to pH value and free of organic solvents and heavy metals, meeting the environmental protection requirements of water-based coatings; at the same time, it has good compatibility with water-based acrylic resins, aluminum powder pastes and other components, avoiding water separation or flocculation.

[0022] After modification with γ-aminopropyltrimethoxysilane, the hydrophobic groups (such as fatty alcohol polyoxyethylene ethers) in thickeners can improve the adhesion between the coating and the metal substrate and reduce water penetration, thereby improving corrosion resistance, providing good flowability and leveling, reducing surface defects in the coating film (such as orange peel and brush marks), and reducing splattering during the spraying process. Through graft modification with silane coupling agents, thickeners can form chemical bonds with nano-titanium dioxide / graphene oxide fillers, preventing filler sedimentation and extending the storage stability of the coating.

[0023] Preferably, the diisocyanate is isophorone diisocyanate or diphenylmethane diisocyanate.

[0024] On the other hand, the present invention provides a method for preparing a water-based metallic primer for automobiles, for producing the above-mentioned water-based metallic primer for automobiles, comprising the following steps:

[0025] S1.1 Weigh the following raw materials in parts by weight: 40-60 parts by weight of modified waterborne acrylic resin, 1-3 parts by weight of nonionic polyurethane thickener, 5-10 parts by weight of aluminum powder paste, 1-5 parts by weight of nano titanium dioxide / graphene oxide composite filler, 0.1-0.5 parts by weight of cocamidopropyl betaine, and 0.1-0.3 parts by weight of polydimethylsiloxane.

[0026] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800-1000 rpm for 5 min, then stir at 300-500 rpm for 10-15 min to ensure uniform dispersion of aluminum powder; then add polydimethylsiloxane, continue stirring at 300-500 rpm for 5-10 min, filter through a 200-mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0027] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse using a high-speed disperser at a speed of 1000-1500 rpm for 20-30 minutes, and filter using a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0028] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 300-500 rpm for 5-10 minutes. Add deionized water to adjust the viscosity of the resin, and at the same time adjust the pH of the resin to 8.0-8.5 with dimethylethanolamine.

[0029] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 300-500 rpm for 10-15 min; then add the non-ionic polyurethane thickener dissolved in water at 40-50℃, and stir at 300-500 rpm for 10-15 min; add deionized water to adjust the solid content of the paint, and filter the paint using a 200-300 mesh sieve to obtain a water-based metallic primer for automobiles.

[0030] The rigid particles of nano-titanium dioxide can improve the surface hardness of the coating, while its semiconductor properties can passivate the metal surface and reduce the oxidation reaction rate, thereby enhancing the corrosion resistance and wear resistance of the coating. The interlayer slip properties of graphene endow the coating with excellent toughness and effectively reduce stress cracking. The two-dimensional sheet structure of graphene oxide can form a dense physical barrier, effectively blocking the penetration of water, oxygen and corrosive ions. In addition, the nanoscale dispersion of composite fillers can increase the contact area between the coating and the metal substrate and improve adhesion.

[0031] Preferably, in step S1.4, the viscosity of the resin is adjusted to a Forte 4 cup viscosity of 30-50 seconds.

[0032] Preferably, in step S1.5, deionized water is added to adjust the solid content of the paint to 30%-40%.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. In the water-based metallic primer and its preparation method for this vehicle, the modified water-based acrylic resin reduces the surface tension of the resin system by introducing organosilicon segments, thereby reducing the difference in interfacial tension between the paint film and the substrate during the spraying process and promoting uniform wetting. In addition, silica nanoparticles form a three-dimensional network in the system through physical interactions, which endows it with high thixotropy and maintains high viscosity at low shear rates, effectively suppressing vertical sagging. At the same time, the rigid cross-linking network of epoxy resin shortens the surface drying time of the paint film and reduces the impact of high evaporation heat on the film formation process, thereby improving the overall performance of the paint film.

[0035] 2. In the water-based metallic primer and its preparation method, the nonionic polyurethane thickener forms hydrophilic segments through fatty alcohol polyoxyethylene ether end-capping, ensuring compatibility with the modified water-based acrylic resin. At the same time, hydrophobic groups are introduced through γ-aminopropyltrimethoxysilane grafting to form a dynamic hydrogen bond network, giving the system shear-thinning properties (i.e., viscosity decreases rapidly under high shear force during spraying), thereby improving atomization efficiency. After spraying, the shear force disappears, and the viscosity recovers rapidly, effectively inhibiting the flow of the paint film on the vertical plane and ensuring the stability and adhesion of the coating. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention provides a water-based metallic primer for automobiles, comprising the following raw materials: 40-60 parts by weight of modified water-based acrylic resin, 1-3 parts by weight of nonionic polyurethane thickener, 5-10 parts by weight of aluminum powder paste, 1-5 parts by weight of nano-titanium dioxide / graphene oxide composite filler, 0.1-0.5 parts by weight of cocamidopropyl betaine, and 0.1-0.3 parts by weight of polydimethylsiloxane;

[0038] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion.

[0039] Nonionic polyurethane thickeners are prepared by end-capping polyurethane prepolymers with fatty alcohol polyoxyethylene ethers and then grafting γ-aminopropyltrimethoxysilane onto the end-capped polyurethane prepolymers.

[0040] The synthesis steps of the organosilicon / silica hybrid are as follows: Tetraethyl orthosilicate is mixed with an organosilicon precursor (SiO2 accounts for 30%-40% of the total weight), ethanol and deionized water are added, and then dilute hydrochloric acid with a mass percentage concentration of 0.1 mol / L is added; under nitrogen protection, the temperature is raised to 60-70℃ and stirred continuously at 300-500 rpm for 6-8 hours until a stable hybrid sol is formed, and then aged at room temperature for 24 hours; after aging, the solvent is removed by rotary evaporator, and then vacuum dried at 80-100℃ and -0.08-0.1 MPa for 12 hours until the residual solvent and moisture are completely removed; the dried hybrid is ground into fine powder (particle size less than 100 μm) by mechanical pulverizer to obtain organosilicon / silica hybrid powder.

[0041] The preparation steps of the modified waterborne acrylic resin are as follows:

[0042] The acrylic copolymer base material is mixed with epoxy resin E-20 emulsion, and 2%-4% sodium dodecyl sulfate by weight of the acrylic copolymer base material is added. The mixture is pre-emulsified for 20-30 minutes using a high-speed disperser at 600-800 rpm to obtain a mixture. The mixture is then transferred to a reactor and heated to 75-85°C at a rate of 1-2°C per minute under nitrogen protection. The mixture is stirred at 300-500 rpm for 1-2 hours to form an acrylic-epoxy composite emulsion.

[0043] Add the organosilicon / silica hybrid powder to deionized water and ultrasonically disperse it for 20-30 minutes at a power of 100-200W to form a hybrid suspension.

[0044] Add the hybrid suspension to the acrylic-epoxy composite emulsion, and simultaneously add an aqueous solution of ammonium persulfate with a mass percentage concentration of 3%-8% dropwise over a period of 1-2 hours. Raise the temperature to 80-85℃ and stir the mixture at 300-500 rpm for 4-6 hours under nitrogen protection.

[0045] After the reaction is complete, the reaction system is cooled to 40-50℃, and the pH of the reaction system is adjusted to 8.0-8.5 with ammonia water with a mass percentage concentration of 20%-25%. Then, the system is filtered through a 180-200 mesh filter to obtain the modified waterborne acrylic resin.

[0046] The acrylic copolymer base material is a mixture of hydroxyethyl methacrylate, butyl acrylate, and styrene in a mass ratio of 2:3:1.

[0047] The preparation steps for nonionic polyurethane thickeners are as follows:

[0048] Dehydrated polyoxypropylene glycol, diisocyanate and dibutyltin dilaurate are added to a reactor, heated to 70-80℃ and stirred at 300-400 rpm for 2-3 hours for prepolymerization.

[0049] After the prepolymerization reaction is completed, fatty alcohol polyoxyethylene ether is added at a molar ratio of 1:1 between isocyanate groups and fatty alcohol polyoxyethylene ether in the prepolymer. The reaction is continued to be stirred at 400-500 rpm at 60-70℃ for 1-2 hours. After the reaction is completed, the reaction system is cooled to 40-50℃ at a rate of 1-2℃ per minute to obtain the end-capped polyurethane prepolymer.

[0050] γ-aminopropyltrimethoxysilane was added to the end-capped polyurethane prepolymer and stirred at 400-500 rpm for 1-2 hours at 60-70℃. After the reaction was completed, the mixture was cooled to room temperature to obtain a nonionic polyurethane thickener.

[0051] The dehydrated polypropylene glycol is produced by vacuum dehydration of polypropylene glycol at 100-110℃ for 1-2 hours.

[0052] The diisocyanate is isophorone diisocyanate or diphenylmethane diisocyanate, preferably isophorone diisocyanate.

[0053] Example 1: A water-based metallic primer for automobiles and its preparation method, comprising the following steps:

[0054] S1.1 Weigh the following raw materials by weight: 40 parts modified waterborne acrylic resin, 2 parts nonionic polyurethane thickener, 8 parts aluminum powder paste, 3 parts nano titanium dioxide / graphene oxide composite filler, 0.3 parts cocamidopropyl betaine, and 0.2 parts polydimethylsiloxane.

[0055] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800 rpm for 5 min, then stir at 500 rpm for 15 min to make the aluminum powder uniformly dispersed; then add polydimethylsiloxane, continue to stir at 500 rpm for 10 min, filter through a 200 mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0056] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse at 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0057] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 500 rpm for 10 min. Add deionized water and adjust the viscosity of the resin to the viscosity of Fort-4 cup for 50 seconds. At the same time, adjust the pH of the resin to 8.0 with dimethylethanolamine.

[0058] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50°C, and stir at 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint using a 300-mesh sieve to obtain the water-based metallic primer for automobiles.

[0059] The modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion, with a mass ratio of organosilicon / silica hybrid to acrylic-epoxy composite emulsion of 1:3.5. The nonionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and then grafting and modifying the end-capped polyurethane prepolymer with γ-aminopropyltrimethoxysilane, with a mass ratio of end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane of 1:0.02.

[0060] Example 2: A water-based metallic primer for automobiles and its preparation method, comprising the following steps:

[0061] S1.1 Weigh the following raw materials by weight: 50 parts modified waterborne acrylic resin, 2 parts nonionic polyurethane thickener, 8 parts aluminum powder paste, 3 parts nano titanium dioxide / graphene oxide composite filler, 0.3 parts cocamidopropyl betaine, and 0.2 parts polydimethylsiloxane.

[0062] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800 rpm for 5 min, then stir at 500 rpm for 15 min to make the aluminum powder uniformly dispersed; then add polydimethylsiloxane, continue to stir at 500 rpm for 10 min, filter through a 200 mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0063] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse at 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0064] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 500 rpm for 10 min. Add deionized water and adjust the viscosity of the resin to the viscosity of Fort-4 cup for 50 seconds. At the same time, adjust the pH of the resin to 8.0 with dimethylethanolamine.

[0065] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50°C, and stir at 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint using a 300-mesh sieve to obtain the water-based metallic primer for automobiles.

[0066] The modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion, with a mass ratio of organosilicon / silica hybrid to acrylic-epoxy composite emulsion of 1:3.5. The nonionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and then grafting and modifying the end-capped polyurethane prepolymer with γ-aminopropyltrimethoxysilane, with a mass ratio of end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane of 1:0.02.

[0067] Example 3: A water-based metallic primer for automobiles and its preparation method, comprising the following steps:

[0068] S1.1 Weigh the following raw materials by weight: 60 parts modified waterborne acrylic resin, 2 parts nonionic polyurethane thickener, 8 parts aluminum powder paste, 3 parts nano titanium dioxide / graphene oxide composite filler, 0.3 parts cocamidopropyl betaine, and 0.2 parts polydimethylsiloxane.

[0069] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800 rpm for 5 min, then stir at 500 rpm for 15 min to make the aluminum powder uniformly dispersed; then add polydimethylsiloxane, continue to stir at 500 rpm for 10 min, filter through a 200 mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0070] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse at 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0071] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 500 rpm for 10 min. Add deionized water and adjust the viscosity of the resin to the viscosity of Fort-4 cup for 50 seconds. At the same time, adjust the pH of the resin to 8.0 with dimethylethanolamine.

[0072] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50°C, and stir at 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint using a 300-mesh sieve to obtain the water-based metallic primer for automobiles.

[0073] The modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion, with a mass ratio of organosilicon / silica hybrid to acrylic-epoxy composite emulsion of 1:3.5. The nonionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and then grafting and modifying the end-capped polyurethane prepolymer with γ-aminopropyltrimethoxysilane, with a mass ratio of end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane of 1:0.02.

[0074] Example 4: A water-based metallic primer for automobiles and its preparation method, comprising the following steps:

[0075] S1.1 Weigh the following raw materials by weight: 60 parts modified waterborne acrylic resin, 1 part nonionic polyurethane thickener, 8 parts aluminum powder paste, 3 parts nano titanium dioxide / graphene oxide composite filler, 0.3 parts cocamidopropyl betaine, and 0.2 parts polydimethylsiloxane.

[0076] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800 rpm for 5 min, then stir at 500 rpm for 15 min to make the aluminum powder uniformly dispersed; then add polydimethylsiloxane, continue to stir at 500 rpm for 10 min, filter through a 200 mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0077] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse at 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0078] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 500 rpm for 10 min. Add deionized water and adjust the viscosity of the resin to the viscosity of Fort-4 cup for 50 seconds. At the same time, adjust the pH of the resin to 8.0 with dimethylethanolamine.

[0079] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50°C, and stir at 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint using a 300-mesh sieve to obtain the water-based metallic primer for automobiles.

[0080] The modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion, with a mass ratio of organosilicon / silica hybrid to acrylic-epoxy composite emulsion of 1:3.5. The nonionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and then grafting and modifying the end-capped polyurethane prepolymer with γ-aminopropyltrimethoxysilane, with a mass ratio of end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane of 1:0.02.

[0081] Example 5: A water-based metallic primer for automobiles and its preparation method, comprising the following steps:

[0082] S1.1 Weigh the following raw materials by weight: 60 parts modified waterborne acrylic resin, 3 parts nonionic polyurethane thickener, 8 parts aluminum powder paste, 3 parts nano titanium dioxide / graphene oxide composite filler, 0.3 parts cocamidopropyl betaine, and 0.2 parts polydimethylsiloxane.

[0083] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800 rpm for 5 min, then stir at 500 rpm for 15 min to make the aluminum powder uniformly dispersed; then add polydimethylsiloxane, continue to stir at 500 rpm for 10 min, filter through a 200 mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0084] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse at 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0085] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 500 rpm for 10 min. Add deionized water and adjust the viscosity of the resin to the viscosity of Fort-4 cup for 50 seconds. At the same time, adjust the pH of the resin to 8.0 with dimethylethanolamine.

[0086] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50°C, and stir at 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint using a 300-mesh sieve to obtain the water-based metallic primer for automobiles.

[0087] The modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion, with a mass ratio of organosilicon / silica hybrid to acrylic-epoxy composite emulsion of 1:3.5. The nonionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and then grafting and modifying the end-capped polyurethane prepolymer with γ-aminopropyltrimethoxysilane, with a mass ratio of end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane of 1:0.02.

[0088] Example 6: A water-based metallic primer for automobiles and its preparation method, comprising the following steps:

[0089] S1.1 Weigh the following raw materials by weight: 60 parts modified waterborne acrylic resin, 3 parts nonionic polyurethane thickener, 5 parts aluminum powder paste, 1 part nano titanium dioxide / graphene oxide composite filler, 0.1 parts cocamidopropyl betaine, and 0.1 parts polydimethylsiloxane.

[0090] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800 rpm for 5 min, then stir at 500 rpm for 15 min to make the aluminum powder uniformly dispersed; then add polydimethylsiloxane, continue to stir at 500 rpm for 10 min, filter through a 200 mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0091] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse at 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0092] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 500 rpm for 10 min. Add deionized water and adjust the viscosity of the resin to the viscosity of Fort-4 cup for 50 seconds. At the same time, adjust the pH of the resin to 8.0 with dimethylethanolamine.

[0093] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50°C, and stir at 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint using a 300-mesh sieve to obtain the water-based metallic primer for automobiles.

[0094] The modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion, with a mass ratio of organosilicon / silica hybrid to acrylic-epoxy composite emulsion of 1:4.0. The nonionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and then grafting γ-aminopropyltrimethoxysilane to modify the end-capped polyurethane prepolymer, with a mass ratio of end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane of 1:0.02.

[0095] Example 7: A water-based metallic primer for automobiles and its preparation method, comprising the following steps:

[0096] S1.1 Weigh the following raw materials by weight: 60 parts modified waterborne acrylic resin, 3 parts nonionic polyurethane thickener, 5 parts aluminum powder paste, 1 part nano titanium dioxide / graphene oxide composite filler, 0.1 parts cocamidopropyl betaine, and 0.1 parts polydimethylsiloxane.

[0097] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800 rpm for 5 min, then stir at 500 rpm for 15 min to make the aluminum powder uniformly dispersed; then add polydimethylsiloxane, continue to stir at 500 rpm for 10 min, filter through a 200 mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0098] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse at 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0099] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 500 rpm for 10 min. Add deionized water and adjust the viscosity of the resin to the viscosity of Fort-4 cup for 50 seconds. At the same time, adjust the pH of the resin to 8.0 with dimethylethanolamine.

[0100] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50°C, and stir at 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint using a 300-mesh sieve to obtain the water-based metallic primer for automobiles.

[0101] The modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion, with a mass ratio of organosilicon / silica hybrid to acrylic-epoxy composite emulsion of 1:3.0. The nonionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and then grafting and modifying the end-capped polyurethane prepolymer with γ-aminopropyltrimethoxysilane, with a mass ratio of end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane of 1:0.02.

[0102] Example 8: A water-based metallic primer for automobiles and its preparation method, comprising the following steps:

[0103] S1.1 Weigh the following raw materials by weight: 60 parts modified waterborne acrylic resin, 3 parts nonionic polyurethane thickener, 5 parts aluminum powder paste, 1 part nano titanium dioxide / graphene oxide composite filler, 0.1 parts cocamidopropyl betaine, and 0.1 parts polydimethylsiloxane.

[0104] S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800 rpm for 5 min, then stir at 500 rpm for 15 min to make the aluminum powder uniformly dispersed; then add polydimethylsiloxane, continue to stir at 500 rpm for 10 min, filter through a 200 mesh sieve to obtain pre-dispersed aluminum powder slurry;

[0105] S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse at 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler.

[0106] S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 500 rpm for 10 min. Add deionized water and adjust the viscosity of the resin to the viscosity of Fort-4 cup for 50 seconds. At the same time, adjust the pH of the resin to 8.0 with dimethylethanolamine.

[0107] S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50°C, and stir at 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint using a 300-mesh sieve to obtain the water-based metallic primer for automobiles.

[0108] The modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion, with a mass ratio of organosilicon / silica hybrid to acrylic-epoxy composite emulsion of 1:3.0. The nonionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and then grafting γ-aminopropyltrimethoxysilane to modify the end-capped polyurethane prepolymer, with a mass ratio of end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane of 1:0.03.

[0109] Comparative Example 1: The method of Example 5 was used, and the acrylic-epoxy composite emulsion was used directly as the waterborne acrylic resin, instead of the waterborne acrylic resin prepared by grafting the acrylic-epoxy composite emulsion with an organosilicon / silica hybrid.

[0110] Comparative Example 2: The thickener prepared by directly using polyurethane as a thickener, without grafting modification of the end-capped polyurethane prepolymer with γ-aminopropyltrimethoxysilane, was prepared using the method of Example 5.

[0111] Comparative Example 3: The method of Example 5 was used, but no fatty alcohol polyoxyethylene ether was added in the preparation step of the nonionic polyurethane thickener.

[0112] The performance indicators and testing standards of a waterborne metallic primer for automobiles, obtained by adding modified waterborne acrylic resin and nonionic polyurethane thickener during the preparation process, are as follows:

[0113] Sagging resistance test: According to the national standard GB / T 9264-2012, a sag tester was used to form parallel wet films of different thicknesses by scraping. After placing the test plate vertically, the maximum critical wet film thickness without sagging was observed to evaluate the anti-sagging performance of the coating. Thixotropic index (TI) is the ratio of the viscosity of the coating at low shear rates (e.g., 0.1 s⁻¹) and high shear rates (e.g., 10 s⁻¹) measured by a rotational rheometer, which characterizes the thixotropic properties and anti-sagging ability of the coating. A higher critical wet film thickness indicates that the maximum thickness of the coating film formed in one application is greater, and the better the anti-sagging performance. A higher TI value indicates that the coating has higher viscosity at low shear rates, stronger thixotropy, and is less prone to sagging during application.

[0114] Adhesion test: According to the national standard GB / T 9286-1998, a grid with a spacing of 1mm is made on the coating surface using a cross-cutting tool (the depth of the scratches extends to the substrate). After the coating is removed using 3M tape, the adhesion level is evaluated based on the area of ​​coating peeling off. The level is divided into 0-5, with level 0 indicating no peeling (best) and level 5 indicating the worst.

[0115] The water-based metallic primers for automobiles prepared in Examples 1-8 and Comparative Examples 1-3 were tested according to the above standards, and the data obtained are shown in Table 1:

[0116] Table 1 Performance data of waterborne metallic primers for automobiles in Examples 1-8 and Comparative Examples 1-3

[0117]

[0118] As can be seen from Examples 1-3, when the other components in the waterborne metallic primer for automobiles remain unchanged and the weight of the modified waterborne acrylic resin is continuously increased, the critical wet film thickness, thixotropic index, and adhesion grade of the waterborne metallic primer for automobiles are continuously improved.

[0119] With the increase of resin ratio, the proportion of film-forming substances in the system increases, and the cross-linking network formed during the coating drying process is more compact, allowing a thicker wet film to remain stable before curing; the organosilicon / silica hybrid in the resin forms a rigid skeleton through physical cross-linking, which improves the anti-sagging property of the wet film and increases the critical thickness.

[0120] With high resin content, the fatty alcohol polyoxyethylene ether segments of the thickener form a denser physical entanglement with the hydroxyl / carboxyl groups of the resin, enhancing its ability to recover viscosity after shear thinning.

[0121] Nano-titanium dioxide / graphene oxide composite filler adsorbs resin molecular chains through high specific surface area, forming a three-dimensional network through physical interaction, further enhancing thixotropy; organosilicon hybrids improve the wettability of resin to metal substrates, while epoxy groups form chemical bonds with the metal surface, significantly improving adhesion; graphene oxide binds to resin through π-π bonds, and its sheet structure is embedded in the coating-substrate interface, enhancing the mechanical anchoring effect.

[0122] Furthermore, a comparison of Examples 3-5 shows that when other components in the waterborne metallic primer for automobiles remain unchanged, and the weight percentage of the nonionic polyurethane thickener is continuously increased, the critical wet film thickness and thixotropic index of the waterborne metallic primer for automobiles continuously increase.

[0123] Nonionic polyurethane thickeners form a network structure through association, significantly enhancing the pseudoplastic rheological properties of the system. With increasing thickener dosage, viscosity decreases at high shear rates, facilitating application; viscosity recovers rapidly at low shear rates, preventing sagging and minimizing drooping of the wet film during vertical application, allowing for thicker wet film coatings. Thickener molecules associate with emulsion particles and filler surfaces, forming a tight physical cross-linked network, improving the wet film's resistance to sedimentation and flow. Under high shear stress, the associated network temporarily dissociates, reducing viscosity; after shearing ceases, the network rapidly rebuilds, viscosity recovers, and the thixotropic index increases, indicating enhanced network strength and requiring higher external forces to initiate flow.

[0124] A comparison of Examples 6 and 7 shows that as the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion in the modified waterborne acrylic resin increases, the critical wet film thickness, thixotropic index, and adhesion grade of the waterborne metallic primer for automobiles continuously improve.

[0125] When the proportion of acrylic-epoxy composite emulsion increases, the epoxy groups in the epoxy resin react with the active hydroxyl groups to form a tighter three-dimensional cross-linked network, which significantly improves the mechanical strength of the coating (such as hardness and impact resistance) and enhances the chemical bonding ability between the coating and the metal substrate (such as hydrogen bonds and van der Waals forces). In addition, the organosilicon / silica hybrid is embedded in the resin chain through graft modification, and its siloxane bonds (Si-O) can form stable chemical bonds with the surface of the metal substrate, further improving the adhesion.

[0126] The addition of acrylic-epoxy composite emulsion improves the leveling and wettability of the resin; the polar characteristics of epoxy resin (such as hydroxyl and ether bonds) can reduce the surface tension of the system, making the coating easier to spread on the metal surface and reducing pinhole and crater defects; the rigid particles of organosilicon / silica hybrid form a physical support structure during the coating curing process, inhibiting the shrinkage of the wet film during the drying process, thereby increasing the critical wet film thickness.

[0127] Furthermore, a comparison between Examples 7 and 8 shows that as the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane in the nonionic polyurethane thickener increases, the critical wet film thickness and thixotropic index of the waterborne metallic primer for automobiles continuously improve.

[0128] Polyurethane thickeners achieve their thickening effect by forming a dynamic associative network with latex particles and pigments in coatings through hydrophobic groups (such as silane-modified hydrophobic segments). As the silane grafting amount increases, the density of hydrophobic groups at the ends of the thickener molecular chains increases, enhancing the association with other hydrophobic components in the coating and forming a more stable network structure. Under high shear conditions, the network is destroyed, and the viscosity decreases. However, at rest, the network is rapidly rebuilt, the viscosity recovers, and the thixotropic index increases. Furthermore, the chemical bonding of silanes makes the associative network more stable, accelerates the recovery speed after shearing, and significantly improves thixotropy.

[0129] Based on the above test experiments, Example 5 is considered the optimal example.

[0130] A comparison of Example 5 and Comparative Example 1 shows that: directly using acrylic-epoxy composite emulsion as the waterborne acrylic resin significantly reduces the critical wet film thickness, thixotropic index, and adhesion grade of the waterborne metallic primer for automobiles; when directly using acrylic-epoxy composite emulsion, the crosslinking network is loose, and the mechanical anchoring and chemical bonding between the paint film and the substrate are insufficient, resulting in a reduced adhesion grade; in the unmodified emulsion, there is microphase separation between the epoxy resin and the acrylic phase, resulting in poor internal structural uniformity; in addition, due to the lack of dynamic rheological control, the thixotropic index is significantly reduced, making it easy for sagging or uneven film thickness to occur during coating; at the same time, the composite fillers such as nano-titanium dioxide / graphene oxide are unevenly dispersed, and the fillers are prone to agglomeration when used directly, resulting in a reduction in the critical wet film thickness value.

[0131] A comparison of Example 5 and Comparative Example 2 shows that: directly using polyurethane as a thickener significantly reduces the critical wet film thickness and thixotropic index of the water-based metallic primer for automobiles; ordinary polyurethane thickeners cause the viscosity of the coating system to be too low at high shear rates, which easily leads to problems such as sagging and dripping during construction. This is mainly because its viscosity decreases under shear force, and the viscosity recovers slowly after the shear force disappears, affecting the thixotropic properties of the coating.

[0132] As can be seen from Example 5 and Comparative Example 3, in the preparation steps of the nonionic polyurethane thickener, the thixotropic index of the water-based metallic primer for automobiles is significantly reduced when fatty alcohol polyoxyethylene ether is not added. The nonionic polyurethane thickener associates with components such as latex particles and pigments in the coating through hydrophobic groups (such as the hydrophobic segments of fatty alcohol polyoxyethylene ether). When fatty alcohol polyoxyethylene ether is not added, its hydrophobic end is the key to the association. Without it, it cannot be effectively adsorbed onto the surface of latex or pigment, resulting in a loose network structure or even breakage. The destruction of the association structure will significantly reduce the high shear viscosity (thixotropy) of the coating during construction, which manifests as easy sagging and poor anti-settling properties of the coating film.

[0133] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A water-based metallic primer for automobiles, characterized in that, The product contains the following raw materials: 40-60 parts by weight of modified waterborne acrylic resin, 1-3 parts by weight of nonionic polyurethane thickener, 5-10 parts by weight of aluminum powder paste, 1-5 parts by weight of nano titanium dioxide / graphene oxide composite filler, 0.1-0.5 parts by weight of cocamidopropyl betaine, and 0.1-0.3 parts by weight of polydimethylsiloxane. Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted with an acrylic-epoxy composite emulsion. Nonionic polyurethane thickeners are prepared by end-capping polyurethane prepolymers with fatty alcohol polyoxyethylene ethers and grafting the end-capped polyurethane prepolymers with γ-aminopropyltrimethoxysilane. The preparation steps of the modified waterborne acrylic resin are as follows: The acrylic copolymer base material is mixed with epoxy resin E-20 emulsion, and 2%-4% sodium dodecyl sulfate by weight of the acrylic copolymer base material is added. The mixture is pre-emulsified for 20-30 minutes using a high-speed disperser at 600-800 rpm to obtain a mixture. The mixture is then transferred to a reactor and heated to 75-85°C at a rate of 1-2°C per minute under nitrogen protection. The mixture is stirred at 300-500 rpm for 1-2 hours to form an acrylic-epoxy composite emulsion. Add the organosilicon / silica hybrid powder to deionized water and ultrasonically disperse it for 20-30 minutes at a power of 100-200W to form a hybrid suspension. Add the hybrid suspension to the acrylic-epoxy composite emulsion, and simultaneously add an aqueous solution of ammonium persulfate dropwise over a period of 1-2 hours. Raise the temperature to 80-85°C and stir the mixture at 300-500 rpm for 4-6 hours under nitrogen protection. After the reaction is complete, the reaction system is cooled to 40-50℃, and the pH of the reaction system is adjusted to 8.0-8.5 with ammonia water with a mass percentage concentration of 20%-25%. Then, it is filtered through a 180-200 mesh filter to obtain the modified waterborne acrylic resin. The synthesis steps of the organosilicon / silica hybrid are as follows: Tetraethyl orthosilicate is mixed with an organosilicon precursor, ethanol and deionized water are added, and then dilute hydrochloric acid with a concentration of 0.1 mol / L is added; under nitrogen protection, the temperature is raised to 60-70℃ and stirred continuously at a speed of 300-500 rpm for 6-8 hours until a stable hybrid sol is formed, and then aged at room temperature for 24 hours; after aging, the solvent is removed by rotary evaporator, and then vacuum dried at 80-100℃ and 0.08-0.1 MPa for 12 hours until the residual solvent and water are completely removed; the dried hybrid is ground into fine powder by mechanical pulverizer to obtain organosilicon / silica hybrid powder.

2. The water-based metallic primer for automobiles according to claim 1, characterized in that, In the nonionic polyurethane thickener, the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.01-0.

03.

3. The water-based metallic primer for automobiles according to claim 2, characterized in that, The mass percentage concentration of the ammonium persulfate aqueous solution is 3%-8%.

4. The water-based metallic primer for automobiles according to claim 1, characterized in that, The preparation steps of the nonionic polyurethane thickener are as follows: Dehydrated polyoxypropylene glycol, diisocyanate and dibutyltin dilaurate are added to a reactor, heated to 70-80℃ and stirred at 300-400 rpm for 2-3 hours for prepolymerization. After the prepolymerization reaction is completed, fatty alcohol polyoxyethylene ether is added at a molar ratio of 1:1 between isocyanate groups and fatty alcohol polyoxyethylene ether in the prepolymer. The reaction is continued to be stirred at 400-500 rpm at 60-70℃ for 1-2 hours. After the reaction is completed, the reaction system is cooled to 40-50℃ at a rate of 1-2℃ per minute to obtain the end-capped polyurethane prepolymer. γ-aminopropyltrimethoxysilane was added to the end-capped polyurethane prepolymer and stirred at 400-500 rpm for 1-2 hours at 60-70℃. After the reaction was completed, the mixture was cooled to room temperature to obtain a nonionic polyurethane thickener.

5. The water-based metallic primer for automobiles according to claim 4, characterized in that, The diisocyanate is isophorone diisocyanate or diphenylmethane diisocyanate.

6. A method for preparing a water-based metallic primer for automobiles, used to produce the water-based metallic primer for automobiles as described in any one of claims 1-5, characterized in that, The preparation method of the water-based metallic primer for automobiles is as follows: S1.1 Weigh the following raw materials in parts by weight: 40-60 parts by weight of modified waterborne acrylic resin, 1-3 parts by weight of nonionic polyurethane thickener, 5-10 parts by weight of aluminum powder paste, 1-5 parts by weight of nano titanium dioxide / graphene oxide composite filler, 0.1-0.5 parts by weight of cocamidopropyl betaine, and 0.1-0.3 parts by weight of polydimethylsiloxane. S1.2 Mix aluminum powder slurry with deionized water at a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at high speed of 800-1000 rpm for 5 min, then stir at 300-500 rpm for 10-15 min to ensure uniform dispersion of aluminum powder; then add polydimethylsiloxane, continue stirring at 300-500 rpm for 5-10 min, filter through a 200-mesh sieve to obtain pre-dispersed aluminum powder slurry; S1.3 Mix nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, disperse using a high-speed disperser at a speed of 1000-1500 rpm for 20-30 minutes, and filter using a 300-mesh sieve after dispersion to obtain pre-dispersed nano-titanium dioxide / graphene oxide composite filler. S1.4 Add the modified waterborne acrylic resin to the mixing tank and stir at 300-500 rpm for 5-10 minutes. Add deionized water to adjust the viscosity of the resin, and at the same time adjust the pH of the resin to 8.0-8.5 with dimethylethanolamine. S1.5 Add the pre-dispersed aluminum powder slurry and nano-titanium dioxide / graphene oxide composite filler to the resin base and stir at 300-500 rpm for 10-15 min; then add the non-ionic polyurethane thickener dissolved in water at 40-50℃, and stir at 300-500 rpm for 10-15 min; add deionized water to adjust the solid content of the paint, and filter the paint using a 200-300 mesh sieve to obtain a water-based metallic primer for automobiles.

7. The method for preparing a water-based metallic primer for automobiles according to claim 6, characterized in that, In step S1.4, the viscosity of the resin is adjusted to 30-50 seconds of the Forte 4 cup viscosity.

8. The method for preparing a water-based metallic primer for automobiles according to claim 6, characterized in that, In step S1.5, deionized water is added to adjust the solid content of the paint to 30%-40%.

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