Water-based metal primer for vehicles and preparation method of water-based metal primer

Abstract

The invention relates to the technical field of automotive primer, in particular to automotive water-based metal primer and a preparation method thereof. Comprising the following raw materials in parts by weight: 40 to 60 parts of modified water-based acrylic resin, 1 to 3 parts of nonionic polyurethane thickening agent, 5 to 10 parts of aluminum paste, 1 to 5 parts of nano titanium dioxide / graphene oxide composite filler, 0.1 to 0.5 part of cocamidopropyl betaine and 0.1 to 0.3 part of polydimethylsiloxane. In the design, the surface tension of the modified water-based acrylic resin is reduced by introducing an organic silicon chain segment, so that the wetting of a paint film on a base material is promoted; the silicon dioxide nanoparticles construct a three-dimensional network structure, endow the system with high thixotropy, maintain viscosity stability at a low shear rate, and effectively inhibit a vertical surface sagging phenomenon. The nonionic polyurethane thickener is grafted by gamma-aminopropyltrimethoxysilane to introduce hydrophobic groups, a dynamic hydrogen bond network is formed, and the system is endowed with the shear thinning characteristic, so that the stability and adhesive force of the coating are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of automotive primers, and more specifically, to an aqueous metallic automotive primer and a preparation method thereof. Background Art

[0002] Metallic primers play an important role in automobile manufacturing. They not only need to provide good adhesion and anti-corrosion protection, but also need to be compatible with subsequent coatings. Traditional solvent-based coatings are restricted due to their high volatile organic compound (VOC) emissions, while waterborne coatings, because of their low or zero VOC emissions, have gradually become an ideal choice for environmentally friendly and high-performance painting. Compared with traditional solvent-based products, aqueous metallic primers can reduce environmental pollution while maintaining or even improving performance indicators such as weather resistance, abrasion resistance, and aesthetics.

[0003] However, due to the fact that the surface tension of existing aqueous metallic primers is greater than that of solvent-based paints, and their high heat of vaporization and specific heat capacity are also relatively high, they are prone to sagging during the spraying process. In view of this, we propose an aqueous metallic automotive primer and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide an aqueous metallic automotive primer and a preparation method thereof, so as to solve the problem that existing aqueous metallic primers are prone to sagging during the spraying process due to the fact that their surface tension is greater than that of solvent-based paints, and their high heat of vaporization and specific heat capacity are also relatively high, which is mentioned in the above background art.

[0005] To achieve the above purpose, the present invention provides an aqueous metallic automotive primer, which comprises the following raw materials: 40 - 60 parts by weight of modified aqueous acrylic resin, 1 - 3 parts by weight of non-ionic polyurethane thickener, 5 - 10 parts by weight of aluminum 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 aqueous acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion; The non-ionic polyurethane thickener is prepared by end-capping a polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane to graft-modify the end-capped polyurethane prepolymer.

[0006] Preferably, in the modified aqueous acrylic resin, the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.0 - 4.0.

[0007] Preferably, in the non-ionic polyurethane thickener, the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.01 - 0.03.

[0008] Preferably, the preparation steps of the modified waterborne acrylic resin are as follows: Mix the acrylic copolymer base material with the epoxy resin E-20 emulsion, add sodium dodecyl sulfate in an amount of 2%-4% by mass of the acrylic copolymer base material, and pre-emulsify for 20-30 min at a speed of 600-800 rpm using a high-speed disperser to obtain a mixed solution; transfer the mixed solution to a reaction kettle, and under nitrogen protection, heat it to 75-85 °C at a rate of 1-2 °C per minute, and stir at a speed of 300-500 rpm for 1-2 h to form an acrylic-epoxy composite emulsion; Add the organosilicon / silica hybrid powder to deionized water, and ultrasonically disperse it at a power of 100-200 W for 20-30 min to form a hybrid suspension; Add the hybrid suspension to the acrylic-epoxy composite emulsion, and simultaneously dropwise add an aqueous ammonium persulfate solution. The dropping time is 1-2 h, raise the temperature to 80-85 °C, and stir and react at a speed of 300-500 rpm for 4-6 h under nitrogen protection; After the reaction is completed, cool the reaction system to 40-50 °C, adjust the pH of the reaction system to 8.0-8.5 with ammonia water having a mass percentage concentration of 20%-25%, and then filter through a 180-200 mesh filter screen to obtain the modified waterborne acrylic resin.

[0009] The epoxy groups (-O-CH2-CH(O)-CH2) in the epoxy resin (E-20) can undergo a ring-opening reaction with the silanol groups (Si-OH) of the organosilicon / silica hybrid under alkaline conditions to form stable Si-O-C bonds (siloxane-carbon bonds); this structure significantly improves the hardness and wear resistance of the resin; at the same time, the polar groups (such as hydroxyl groups 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 chain segments, effectively reducing the water absorption rate of the coating and preventing metal substrate corrosion caused by water penetration; the silica nanoparticles fill the microscopic pores of the coating to form a dense barrier, and in cooperation with the chemical inertness of the epoxy resin, can resist corrosion media such as salt spray and acid rain; the Si-O bond energy of the organosilicon / silica hybrid is high (about 444 kJ / mol), which can resist ultraviolet degradation and delay the yellowing and powdering of the coating; the rigid benzene ring structure of the epoxy resin enhances the high-temperature stability of the coating.

[0010] Preferably, the mass percentage concentration of the aqueous ammonium persulfate solution is 3%-8%.

[0011] Preferably, the preparation steps of the non-ionic polyurethane thickener are as follows: Add dehydrated polypropylene glycol, diisocyanate and dibutyltin dilaurate into a reaction kettle, heat up to 70 - 80 °C and stir at a speed of 300 - 400 rpm for a prepolymerization reaction for 2 - 3 h; After the prepolymerization reaction is completed, add fatty alcohol polyoxyethylene ether according to the molar ratio of isocyanate groups to fatty alcohol polyoxyethylene ether in the prepolymer being 1:1, and continue to stir and react at 60 - 70 °C at a speed of 400 - 500 rpm for 1 - 2 h; after the reaction is completed, cool the reaction system to 40 - 50 °C at a rate of 1 - 2 °C per minute to obtain a blocked polyurethane prepolymer; Add γ-aminopropyltrimethoxysilane to the blocked polyurethane prepolymer, and stir and react at 60 - 70 °C at a speed of 400 - 500 rpm for 1 - 2 h; after the reaction is completed, cool to room temperature to obtain a non-ionic polyurethane thickener.

[0012] The non-ionic polyurethane thickener forms a dynamic three-dimensional network structure through association, endowing the primer with a balance of high shear viscosity (anti-sagging during construction) and low shear viscosity (anti-settling during storage); the non-ionic structure makes it insensitive to pH value, and it does not contain organic solvents and heavy metals, meeting the environmental protection requirements of waterborne coatings; at the same time, it has good compatibility with components such as waterborne acrylic resin and aluminum paste, avoiding water separation or flocculation.

[0013] After the hydrophobic groups (such as fatty alcohol polyoxyethylene ether) in the thickener are modified with γ-aminopropyltrimethoxysilane, the adhesion between the coating and the metal substrate can be improved, and water penetration can be reduced, thereby enhancing corrosion resistance, providing good fluidity and leveling property, reducing surface defects of the coating film (such as orange peel and brush marks), and at the same time reducing splashing during the spraying process; through the graft modification of the silane coupling agent, the thickener can form chemical bonding with the nano-titanium dioxide / graphene oxide filler, prevent the filler from settling, and extend the storage stability of the coating.

[0014] Preferably, the diisocyanate is isophorone diisocyanate or diphenylmethane diisocyanate.

[0015] On the other hand, the present invention provides a preparation method of a waterborne metallic primer for vehicles, which is used to prepare the above-mentioned waterborne metallic primer for vehicles, and includes the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 40 - 60 parts by weight of modified waterborne acrylic resin, 1 - 3 parts by weight of non-ionic polyurethane thickener, 5 - 10 parts by weight of aluminum paste, 1 - 5 parts by weight of nano-titanium dioxide / graphene oxide composite filler, 0.1 - 0.5 parts by weight of coconut oil amide propyl betaine, and 0.1 - 0.3 parts by weight of polydimethylsiloxane; S1.2, mix aluminum powder slurry and deionized water in a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800-1000rpm for 5min, then stir at a speed of 300-500rpm for 10-15min to evenly disperse the aluminum powder; then add polydimethylsiloxane, continue to stir at a speed of 300-500rpm for 5-10min, filter with a 200-mesh sieve to obtain pre-dispersed aluminum powder slurry; S1.3, mixing the nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, using a high-speed disperser to disperse at a speed of 1000-1500 rpm for 20-30 min, and filtering with a 300-mesh sieve after dispersion to obtain a pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4, add the modified waterborne acrylic resin into a stirring kettle, stir at a speed of 300-500 rpm for 5-10 min, add deionized water to adjust the viscosity of the resin, and 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 material, and stir at a speed of 300-500rpm for 10-15min; then add a non-ionic polyurethane thickener dissolved in 40-50℃ water, and stir at a speed of 300-500rpm for 10-15min; add deionized water to adjust the solid content of the paint, and filter the paint with a 200-300 mesh sieve to obtain a water-based metallic primer for vehicles.

[0016] The rigid particles of nano-titanium dioxide can increase 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 characteristics of graphene give the coating excellent toughness and effectively reduce stress cracking; the two-dimensional layer structure of graphene oxide can form a dense physical barrier, effectively blocking the penetration of water, oxygen and corrosive ions; in addition, the nano-scale dispersion of composite fillers can increase the contact area between the coating and the metal substrate and improve adhesion.

[0017] Preferably, in S1.4, the viscosity of the resin is adjusted to a coating-4 cup viscosity of 30-50 seconds.

[0018] Preferably, in S1.5, deionized water is added to adjust the solid content of the paint to 30%-40%.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. In the waterborne metallic primer for vehicles and its preparation method, the modified waterborne acrylic resin reduces the surface tension of the resin system by introducing organosilicon segments, thereby reducing the interfacial tension difference between the paint film and the substrate during spraying and promoting uniform wetting. In addition, the silica nanoparticles form a three-dimensional network through physical interactions in the system, endowing high thixotropy, maintaining a relatively high viscosity at low shear rates, and effectively inhibiting the sagging phenomenon on vertical surfaces. At the same time, the rigid crosslinked network of epoxy resin shortens the surface drying time of the paint film and reduces the influence of high evaporation heat on the film-forming process, thus improving the overall performance of the paint film.

[0020] 2. In the waterborne metallic primer for vehicles and its preparation method, the nonionic polyurethane thickener forms a hydrophilic segment by end-capping with fatty alcohol polyoxyethylene ether to ensure compatibility with the modified waterborne acrylic resin. At the same time, a hydrophobic group is introduced by grafting with γ-aminopropyltrimethoxysilane to form a dynamic hydrogen bond network, endowing the system with shear thinning characteristics (i.e., the viscosity rapidly decreases under high shear force during spraying), thereby improving the atomization efficiency. After spraying, the shear force disappears and the viscosity quickly recovers, effectively inhibiting the fluidity of the paint film on vertical surfaces and ensuring the stability and adhesion of the coating. Detailed implementation mode

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] The present invention provides a waterborne metallic primer for vehicles, comprising 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 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 acrylic-epoxy composite emulsion; The nonionic polyurethane thickener is prepared by end-capping a polyurethane prepolymer with fatty alcohol polyoxyethylene ether and grafting and modifying the end-capped polyurethane prepolymer by adding γ-aminopropyltrimethoxysilane.

[0023] The synthesis steps of the silicone / silica hybrid are as follows: Mix tetraethyl orthosilicate with a silicone precursor (SiO2 accounts for 30%-40% of the total weight), add ethanol and deionized water, and then add dilute hydrochloric acid with a mass percentage concentration of 0.1 mol / L; Under nitrogen protection, heat to 60-70 °C and continuously stir at a speed of 300-500 rpm for 6-8 h. After a stable hybrid sol is formed, let it stand and age at room temperature for 24 h; After the aging is completed, use a rotary evaporator to remove the solvent, and then vacuum dry at 80-100 °C and -0.08-0.1 MPa for 12 h until the residual solvent and moisture are completely removed; Grind the dried hybrid into fine powder (particle size less than 100 μm) through a mechanical grinder to obtain the silicone / silica hybrid powder.

[0024] The preparation steps of the modified waterborne acrylic resin are as follows: Mix the acrylic copolymer base material with the epoxy resin E-20 emulsion, add sodium dodecyl sulfate accounting for 2%-4% of the mass of the acrylic copolymer base material, and pre-emulsify with a high-speed disperser at a speed of 600-800 rpm for 20-30 min to obtain a mixed solution; Transfer the mixed solution to a reaction kettle, under nitrogen protection, heat to 75-85 °C at a rate of 1-2 °C per minute, and stir at a speed of 300-500 rpm for 1-2 h to form an acrylic-epoxy composite emulsion; Add the silicone / silica hybrid powder to deionized water and ultrasonically disperse it at a power of 100-200 W for 20-30 min to form a hybrid suspension; Add the hybrid suspension to the acrylic-epoxy composite emulsion, and at the same time dropwise add an aqueous ammonium persulfate solution with a mass percentage concentration of 3%-8%. The dropping time is 1-2 h, raise the temperature to 80-85 °C, and stir and react at a speed of 300-500 rpm under nitrogen protection for 4-6 hours; After the reaction is completed, cool the reaction system to 40-50 °C, adjust the pH of the reaction system to 8.0-8.5 with ammonia water with a mass percentage concentration of 20%-25%, and then filter through a 180-200 mesh filter screen to obtain the modified waterborne acrylic resin.

[0025] The acrylic copolymer base material is prepared by mixing hydroxyethyl methacrylate, butyl acrylate, and styrene in a mass ratio of 2:3:1.

[0026] The preparation steps of the non-ionic polyurethane thickener are as follows: Add dehydrated polyoxypropylene glycol, diisocyanate, and dibutyltin dilaurate to a reaction kettle, heat to 70-80 °C and stir at a speed of 300-400 rpm for a prepolymerization reaction for 2-3 h; After the prepolymerization reaction is completed, fatty alcohol polyoxyethylene ether is added according to the molar ratio of isocyanate groups to fatty alcohol polyoxyethylene ether in the prepolymer of 1:1, and the reaction is continued to stir at a speed of 400-500 rpm at 60-70 °C for 1-2 h; after the reaction is completed, the reaction system is cooled to 40-50 °C at a rate of 1-2 °C per minute to obtain a blocked polyurethane prepolymer; γ-aminopropyltrimethoxysilane is added to the blocked polyurethane prepolymer, and the reaction is stirred at a speed of 400-500 rpm at 60-70 °C for 1-2 h; after the reaction is completed, it is cooled to room temperature to obtain a non-ionic polyurethane thickener.

[0027] The dehydrated polypropylene glycol is obtained by vacuum dehydrating polypropylene glycol at 100-110 °C for 1-2 h.

[0028] The diisocyanate is isophorone diisocyanate or diphenylmethane diisocyanate, preferably isophorone diisocyanate.

[0029] Example 1: An aqueous automotive metal primer and its preparation method, comprising the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 40 parts by weight of modified aqueous acrylic resin, 2 parts by weight of non-ionic polyurethane thickener, 8 parts by weight of aluminum paste, 3 parts by weight of nano-titanium dioxide / graphene oxide composite filler, 0.3 parts by weight of cocamidopropyl betaine, and 0.2 parts by weight of polydimethylsiloxane; S1.2. Mix the aluminum paste and deionized water according to a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800 rpm for 5 min, then stir at a speed of 500 rpm for 15 min to uniformly disperse the aluminum powder; then add polydimethylsiloxane, continue to stir at a speed of 500 rpm for 10 min, and filter through a 200-mesh sieve to obtain a pre-dispersed aluminum paste; S1.3. Mix the nano-titanium dioxide / graphene oxide composite filler and deionized water according to a mass ratio of 1:9, disperse at a speed of 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain a pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4. Add the modified aqueous acrylic resin to a stirring kettle, stir at a speed of 500 rpm for 10 min, add deionized water, adjust the viscosity of the resin to 50 seconds of the coating-4 cup viscosity, and adjust the pH of the resin to 8.0 with dimethylethanolamine at the same time; S1.5. Add the pre-dispersed aluminum paste and the nano-titanium dioxide / graphene oxide composite filler into the resin base material, and stir for 15 min at a speed of 500 rpm; then add the non-ionic polyurethane thickener dissolved in water at 50 °C, and stir for 15 min at a speed of 500 rpm; add deionized water to adjust the solid content of the paint to 40%, and filter the paint through a 300-mesh sieve to obtain the waterborne metallic primer for vehicles.

[0030] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion, and the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.5; the non-ionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane for graft modification of the end-capped polyurethane prepolymer, and the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.02.

[0031] Example 2: A waterborne metallic primer for vehicles and its preparation method, comprising the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 50 parts by weight of modified waterborne acrylic resin, 2 parts by weight of non-ionic polyurethane thickener, 8 parts by weight of aluminum paste, 3 parts by weight of nano-titanium dioxide / graphene oxide composite filler, 0.3 parts by weight of cocamidopropyl betaine, and 0.2 parts by weight of polydimethylsiloxane; S1.2. Mix the aluminum paste and deionized water in a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800 rpm for 5 min, and then stir at a speed of 500 rpm for 15 min to uniformly disperse the aluminum powder; then add polydimethylsiloxane, continue to stir at a speed of 500 rpm for 10 min, and filter through a 200-mesh sieve to obtain the pre-dispersed aluminum paste; S1.3. Mix the nano-titanium dioxide / graphene oxide composite filler and deionized water in a mass ratio of 1:9, disperse with a high-speed disperser at a speed of 1200 rpm for 25 min, and filter through a 300-mesh sieve after dispersion to obtain the pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4. Add the modified waterborne acrylic resin into the stirring kettle, stir at a speed of 500 rpm for 10 min, add deionized water, adjust the viscosity of the resin to 50 s of the coating-4 cup viscosity, and adjust the pH of the resin to 8.0 with dimethylethanolamine at the same time; S1.5. Add the pre-dispersed aluminum paste and the nano-titanium dioxide / graphene oxide composite filler into the resin base material, and stir at a speed of 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50 °C, and stir at a speed of 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint through a 300-mesh sieve to obtain the waterborne metallic primer for vehicles.

[0032] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion, and the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.5; the non-ionic polyurethane thickener is prepared by blocking the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane for graft modification of the blocked polyurethane prepolymer, and the mass ratio of the blocked polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.02.

[0033] Example 3: A waterborne metallic primer for vehicles and its preparation method, comprising the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 60 parts by weight of modified waterborne acrylic resin, 2 parts by weight of non-ionic polyurethane thickener, 8 parts by weight of aluminum paste, 3 parts by weight of nano-titanium dioxide / graphene oxide composite filler, 0.3 parts by weight of cocamidopropyl betaine, and 0.2 parts by weight of polydimethylsiloxane; S1.2. Mix the aluminum paste and deionized water according to a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800 rpm for 5 min, and then stir at a speed of 500 rpm for 15 min to uniformly disperse the aluminum powder; then add polydimethylsiloxane, continue to stir at a speed of 500 rpm for 10 min, and filter through a 200-mesh sieve to obtain the pre-dispersed aluminum paste; S1.3. Mix the nano-titanium dioxide / graphene oxide composite filler and deionized water according to a mass ratio of 1:9, disperse at a speed of 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain the pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4. Add the modified waterborne acrylic resin into a stirring kettle, stir at a speed of 500 rpm for 10 min, add deionized water, adjust the viscosity of the resin to 50 s of the coating-4 cup viscosity, and adjust the pH of the resin to 8.0 with dimethylethanolamine at the same time; S1.5. Add the pre-dispersed aluminum paste and the nano-titanium dioxide / graphene oxide composite filler into the resin base material, and stir at a speed of 500 rpm for 15 min. Then add the non-ionic polyurethane thickener dissolved in water at 50 °C, and stir at a speed of 500 rpm for 15 min. Add deionized water to adjust the solid content of the paint to 40%, and filter the paint through a 300-mesh sieve to obtain the waterborne metallic primer for vehicles.

[0034] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion, and the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.5. The non-ionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane for graft modification of the end-capped polyurethane prepolymer, and the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.02.

[0035] Example 4: A waterborne metallic primer for vehicles and its preparation method, comprising the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 60 parts by weight of modified waterborne acrylic resin, 1 part by weight of non-ionic polyurethane thickener, 8 parts by weight of aluminum paste, 3 parts by weight of nano-titanium dioxide / graphene oxide composite filler, 0.3 part by weight of cocamidopropyl betaine, and 0.2 part by weight of polydimethylsiloxane; S1.2. Mix the aluminum paste and deionized water according to a mass ratio of 1:1, add cocamidopropyl betaine, disperse at a high speed of 800 rpm for 5 min first, and then stir at a speed of 500 rpm for 15 min to uniformly disperse the aluminum powder. Subsequently, add polydimethylsiloxane, continue to stir at a speed of 500 rpm for 10 min, and filter through a 200-mesh sieve to obtain the pre-dispersed aluminum paste; S1.3. Mix the nano-titanium dioxide / graphene oxide composite filler and deionized water according to a mass ratio of 1:9, disperse with a high-speed disperser at a speed of 1200 rpm for 25 min, and filter through a 300-mesh sieve after dispersion to obtain the pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4. Add the modified waterborne acrylic resin into a stirring kettle, stir at a speed of 500 rpm for 10 min, add deionized water, adjust the viscosity of the resin to 50 s of the cup-4 viscosity, and adjust the pH of the resin to 8.0 with dimethylethanolamine at the same time; S1.5. Add the pre-dispersed aluminum paste and the nano-titanium dioxide / graphene oxide composite filler into the resin base material, and stir at a speed of 500 rpm for 15 min. Then add the non-ionic polyurethane thickener dissolved in water at 50 °C, and stir at a speed of 500 rpm for 15 min. Add deionized water to adjust the solid content of the paint to 40%, and filter the paint through a 300-mesh sieve to obtain the waterborne metallic primer for vehicles.

[0036] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion, and the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.5. The non-ionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane for graft modification of the end-capped polyurethane prepolymer. The mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.02.

[0037] Example 5: A waterborne metallic primer for vehicles and its preparation method, including the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 60 parts by weight of modified waterborne acrylic resin, 3 parts by weight of non-ionic polyurethane thickener, 8 parts by weight of aluminum paste, 3 parts by weight of nano-titanium dioxide / graphene oxide composite filler, 0.3 parts by weight of cocamidopropyl betaine, and 0.2 parts by weight of polydimethylsiloxane; S1.2. Mix the aluminum paste and deionized water according to a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800 rpm for 5 min, and then stir at a speed of 500 rpm for 15 min to uniformly disperse the aluminum powder. Subsequently, add polydimethylsiloxane, continue to stir at a speed of 500 rpm for 10 min, and filter through a 200-mesh sieve to obtain the pre-dispersed aluminum paste; S1.3. Mix the nano-titanium dioxide / graphene oxide composite filler and deionized water according to a mass ratio of 1:9, disperse at a speed of 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain the pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4. Add the modified waterborne acrylic resin into a stirring kettle, stir at a speed of 500 rpm for 10 min, add deionized water, adjust the viscosity of the resin to 50 s of the coating-4 cup viscosity, and adjust the pH of the resin to 8.0 with dimethylethanolamine at the same time; S1.5. Add the pre-dispersed aluminum paste and the nano-titanium dioxide / graphene oxide composite filler into the resin base material, and stir at a speed of 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50 °C, and stir at a speed of 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint through a 300-mesh sieve to obtain the waterborne metallic primer for vehicles.

[0038] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion, and the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.5; the non-ionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane for graft modification of the end-capped polyurethane prepolymer, and the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.02.

[0039] Example 6: A waterborne metallic primer for vehicles and its preparation method, including the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 60 parts by weight of modified waterborne acrylic resin, 3 parts by weight of non-ionic polyurethane thickener, 5 parts by weight of aluminum paste, 1 part by weight of nano-titanium dioxide / graphene oxide composite filler, 0.1 part by weight of cocamidopropyl betaine, and 0.1 part by weight of polydimethylsiloxane; S1.2. Mix the aluminum paste and deionized water according to a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800 rpm for 5 min, and then stir at a speed of 500 rpm for 15 min to uniformly disperse the aluminum powder; then add polydimethylsiloxane, continue to stir at a speed of 500 rpm for 10 min, and filter through a 200-mesh sieve to obtain the pre-dispersed aluminum paste; S1.3. Mix the nano-titanium dioxide / graphene oxide composite filler and deionized water according to a mass ratio of 1:9, disperse at a speed of 1200 rpm for 25 min using a high-speed disperser, and filter through a 300-mesh sieve after dispersion to obtain the pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4. Add the modified waterborne acrylic resin into a stirring kettle, stir at a speed of 500 rpm for 10 min, add deionized water, adjust the viscosity of the resin to 50 s of the cup-4 viscosity, and adjust the pH of the resin to 8.0 with dimethylethanolamine at the same time; S1.5. Add the pre-dispersed aluminum powder paste and the nano-titanium dioxide / graphene oxide composite filler into the resin base material, and stir at a speed of 500 rpm for 15 min; then add the non-ionic polyurethane thickener dissolved in water at 50 °C, and stir at a speed of 500 rpm for 15 min; add deionized water to adjust the solid content of the paint to 40%, and filter the paint through a 300-mesh sieve to obtain the waterborne metallic primer for vehicles.

[0040] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion, and the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:4.0; the non-ionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane for graft modification of the end-capped polyurethane prepolymer, and the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.02.

[0041] Example 7: A waterborne metallic primer for vehicles and its preparation method, comprising the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 60 parts by weight of modified waterborne acrylic resin, 3 parts by weight of non-ionic polyurethane thickener, 5 parts by weight of aluminum powder paste, 1 part by weight of nano-titanium dioxide / graphene oxide composite filler, 0.1 part by weight of cocamidopropyl betaine, and 0.1 part by weight of polydimethylsiloxane; S1.2. Mix the aluminum powder paste and deionized water according to a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800 rpm for 5 min, and then stir at a speed of 500 rpm for 15 min to uniformly disperse the aluminum powder; then add polydimethylsiloxane, continue to stir at a speed of 500 rpm for 10 min, and filter through a 200-mesh sieve to obtain the pre-dispersed aluminum powder paste; S1.3. Mix the nano-titanium dioxide / graphene oxide composite filler and deionized water according to a mass ratio of 1:9, disperse with a high-speed disperser at a speed of 1200 rpm for 25 min, and filter through a 300-mesh sieve after dispersion to obtain the pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4. Add the modified waterborne acrylic resin into a stirring kettle, stir at a speed of 500 rpm for 10 min, add deionized water, adjust the viscosity of the resin to 50 s of the coating-4 cup viscosity, and adjust the pH of the resin to 8.0 with dimethylethanolamine at the same time; S1.5. Add the pre-dispersed aluminum paste and the nano-titanium dioxide / graphene oxide composite filler into the resin base material, and stir for 15 min at a speed of 500 rpm. Then add the non-ionic polyurethane thickener dissolved in water at 50 °C, and stir again for 15 min at a speed of 500 rpm. Add deionized water to adjust the solid content of the paint to 40%, and filter the paint through a 300-mesh sieve to obtain the waterborne metallic primer for vehicles.

[0042] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion, and the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.0. The non-ionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane for graft modification of the end-capped polyurethane prepolymer, and the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.02.

[0043] Example 8: A waterborne metallic primer for vehicles and its preparation method, comprising the following steps: S1.1. Weigh the following raw materials in parts by weight respectively: 60 parts by weight of modified waterborne acrylic resin, 3 parts by weight of non-ionic polyurethane thickener, 5 parts by weight of aluminum paste, 1 part by weight of nano-titanium dioxide / graphene oxide composite filler, 0.1 part by weight of cocamidopropyl betaine, and 0.1 part by weight of polydimethylsiloxane; S1.2. Mix the aluminum paste and deionized water according to a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800 rpm for 5 min, and then stir at a speed of 500 rpm for 15 min to uniformly disperse the aluminum powder. Subsequently, add polydimethylsiloxane, continue to stir at a speed of 500 rpm for 10 min, and filter through a 200-mesh sieve to obtain the pre-dispersed aluminum paste; S1.3. Mix the nano-titanium dioxide / graphene oxide composite filler and deionized water according to a mass ratio of 1:9, disperse with a high-speed disperser at a speed of 1200 rpm for 25 min, and filter through a 300-mesh sieve after dispersion to obtain the pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4. Add the modified waterborne acrylic resin into a stirring kettle, stir at a speed of 500 rpm for 10 min, add deionized water, adjust the viscosity of the resin to 50 s of the cup-4 viscosity, and at the same time adjust the pH of the resin to 8.0 with dimethylethanolamine; S1.5. Add the pre-dispersed aluminum paste and the nano-titanium dioxide / graphene oxide composite filler into the resin base material, and stir for 15 min at a speed of 500 rpm; then add the non-ionic polyurethane thickener dissolved in water at 50 °C, and stir again for 15 min at a speed of 500 rpm; 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 waterborne metallic primer for vehicles.

[0044] Among them, the modified waterborne acrylic resin is composed of an organosilicon / silica hybrid grafted acrylic-epoxy composite emulsion, and the mass ratio of the organosilicon / silica hybrid to the acrylic-epoxy composite emulsion is 1:3.0; the non-ionic polyurethane thickener is prepared by end-capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding γ-aminopropyltrimethoxysilane to graft-modify the end-capped polyurethane prepolymer, and the mass ratio of the end-capped polyurethane prepolymer to γ-aminopropyltrimethoxysilane is 1:0.03.

[0045] Comparative Example 1: Using the method of Example 5, directly use the acrylic-epoxy composite emulsion as the waterborne acrylic resin, and do not use the waterborne acrylic resin prepared by grafting the acrylic-epoxy composite emulsion with the organosilicon / silica hybrid.

[0046] Comparative Example 2: Using the method of Example 5, directly use polyurethane as the thickener, and do not use the thickener prepared by graft-modifying the end-capped polyurethane prepolymer with γ-aminopropyltrimethoxysilane.

[0047] Comparative Example 3: Using the method of Example 5, in the step of preparing the non-ionic polyurethane thickener, do not add fatty alcohol polyoxyethylene ether.

[0048] During the preparation process of a waterborne metallic primer for vehicles, by adding the modified waterborne acrylic resin and the non-ionic polyurethane thickener, the performance index test items and test standards of the obtained waterborne metallic primer for vehicles are as follows: Measurement of anti-sagging performance: According to the national standard GB / T 9264-2012, use a sagging tester to scrape and form parallel wet films with different thicknesses, and observe the maximum critical wet film thickness without sagging after vertically placing the test panel, so as to evaluate the anti-sagging performance of the coating; the thixotropic index (TI) is determined by a rotational rheometer to measure the viscosity ratio of the coating at low shear rates (such as 0.1 s⁻¹) and high shear rates (such as 10 s⁻¹), characterizing the thixotropy and anti-sagging ability of the coating; a higher critical wet film thickness indicates that the maximum thickness of the coating formed in one time is larger, and the anti-sagging performance is better; the higher the TI value, the higher the viscosity of the coating at low shear rates, the stronger the thixotropy, and the less likely to sag during construction.

[0049] Adhesion measurement: According to the national standard GB / T 9286-1998, a grid with a spacing of 1 mm is scratched on the coating surface using a cross cutter (the scratch depth reaches the substrate). After using 3M tape to pick it up, the adhesion grade is evaluated according to the coating peeling area; the grade is divided into 0-5 levels, with 0 level indicating no peeling (the best) and 5 level indicating the worst.

[0050] Through the above standards, the waterborne metallic automotive primers prepared in Examples 1-8 and Comparative Examples 1-3 were tested, and the obtained data are shown in Table 1: Table 1 Performance data of waterborne metallic automotive primers in Examples 1-8 and Comparative Examples 1-3 It can be seen from Examples 1-3 that when other components in the waterborne metallic automotive primer remain unchanged and the weight parts of the modified waterborne acrylic resin continuously increase, the critical wet film thickness, thixotropic index, and adhesion grade of the waterborne metallic automotive primer continuously increase.

[0051] After the resin ratio is increased, the proportion of the film-forming substance in the system increases, and the crosslinking network formed during the drying process of the coating film is denser, allowing a thicker wet film to remain stable before curing; the organosilicon / silica hybrid in the resin forms a rigid skeleton through physical crosslinking, improving the anti-sagging property of the wet film and increasing the critical thickness; At a high resin content, the fatty alcohol polyoxyethylene ether chain segment of the thickener forms a denser physical entanglement with the hydroxyl / carboxyl group of the resin, and the ability to recover viscosity after shear thinning is enhanced.

[0052] The nano-titanium dioxide / graphene oxide composite filler adsorbs resin molecular chains through a high specific surface area and forms a three-dimensional network through physical interactions, further strengthening the thixotropy; the organosilicon hybrid improves the wettability of the resin to the metal substrate, and the epoxy group forms a chemical bond with the metal surface, significantly improving the adhesion; graphene oxide binds to the resin through π-π bonds, and at the same time its lamellar structure is embedded in the coating-substrate interface, enhancing the mechanical anchoring effect.

[0053] Furthermore, by comparing Examples 3-5, it can be seen that when other components in the waterborne metallic automotive primer remain unchanged and the weight parts of the non-ionic polyurethane thickener continuously increase, the critical wet film thickness and thixotropic index of the waterborne metallic automotive primer continuously increase.

[0054] Non-ionic polyurethane thickeners form a network structure through association, significantly enhancing the pseudoplastic rheological properties of the system; as the dosage of the thickener increases, the viscosity decreases at high shear rates, facilitating construction; the viscosity quickly recovers at low shear rates, preventing sagging, making it difficult for the wet film to sag during vertical surface construction and allowing for the application of thicker wet films; the thickener molecules associate with the emulsion particles and the surface of the filler, forming a tight physical cross-linked network, enhancing the anti-settling and anti-running ability of the wet film; under high shear forces, the associated network dissociates temporarily and the viscosity decreases; after stopping shear, the network is quickly rebuilt, the viscosity recovers, and the thixotropy index increases, indicating an increase in the strength of the network structure and requiring a higher external force to initiate flow.

[0055] It can be seen from the comparison between Example 6 and Example 7 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, thixotropy index, and adhesion grade of the automotive waterborne metallic primer continuously increase.

[0056] When the proportion of the acrylic-epoxy composite emulsion increases, the epoxy groups in the epoxy resin react with the active hydroxyl groups to form a denser three-dimensional cross-linked network, significantly improving the mechanical strength of the coating (such as hardness and impact resistance), while enhancing 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 grafted and modified and embedded in the resin chain, and its siloxane bond (Si-O) can form a stable chemical bond with the surface of the metal substrate, further enhancing the adhesion.

[0057] The increase in the acrylic-epoxy composite emulsion will improve the leveling and wetting properties of the resin; the polar characteristics of the epoxy resin (such as hydroxyl groups and ether bonds) can reduce the surface tension of the system, making the coating easier to spread on the metal surface and reducing shrinkage holes and pinhole defects; the rigid particles of the organosilicon / silica hybrid form a physical support structure during the curing process of the coating, inhibiting the shrinkage of the wet film during drying, thereby increasing the critical wet film thickness.

[0058] Furthermore, it can be seen from the comparison between Example 7 and Example 8 that: as the mass ratio of the blocked polyurethane prepolymer to γ-aminopropyltrimethoxysilane in the non-ionic polyurethane thickener increases, the critical wet film thickness and thixotropy index of the automotive waterborne metallic primer continuously increase.

[0059] Polyurethane thickeners form a dynamic associative network with latex particles, pigments, etc. in the coating through hydrophobic groups (such as silane-modified hydrophobic segments), thus achieving the thickening effect; when the silane grafting amount increases, the density of hydrophobic groups at the ends of the thickener molecular chains increases, enhancing the associative interaction 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; while at rest, the network is rapidly rebuilt and the viscosity recovers, thus increasing the thixotropic index; in addition, the chemical bonding effect of silane makes the associative network more stable, accelerating the recovery speed after shearing and significantly improving the thixotropy.

[0060] According to the above test experiments, Example 5 is taken as the optimal example; By comparing Example 5 with Comparative Example 1, it can be seen that directly using the acrylic-epoxy composite emulsion as the waterborne acrylic resin significantly reduces the critical wet film thickness, thixotropic index and adhesion grade of the automotive waterborne metallic primer; when directly using the acrylic-epoxy composite emulsion, the crosslinked network is loose, and the mechanical anchoring and chemical bonding between the paint film and the substrate are insufficient, resulting in a decrease in the adhesion grade; in the unmodified emulsion, there is a microphase separation between the epoxy resin and the acrylic phase, resulting in poor internal structure uniformity; in addition, due to the lack of dynamic rheological regulation, the thixotropic index is significantly reduced, and sagging or uneven film thickness is likely to occur during painting; 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 directly used, resulting in a decrease in the critical value of the wet film thickness.

[0061] By comparing Example 5 with Comparative Example 2, it can be seen that directly using polyurethane as the thickener significantly reduces the critical wet film thickness and thixotropic index of the automotive waterborne metallic primer; the ordinary polyurethane thickener causes the viscosity of the coating system to be too low at high shear rates, resulting in problems such as sagging and dripping during the construction process. This is mainly because its viscosity decreases under the action of shear force and the viscosity recovers slowly after the shear force disappears, affecting the thixotropic properties of the coating.

[0062] By comparing Example 5 with Comparative Example 3, it can be seen that when fatty alcohol polyoxyethylene ether is not added in the preparation step of the non-ionic polyurethane thickener, the thixotropic index of the automotive waterborne metallic primer is significantly reduced; the non-ionic 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 associative action, and without it, it cannot be effectively adsorbed on the surface of latex or pigments, resulting in a loose or even broken network structure; the destruction of the associative structure will significantly reduce the high-shear viscosity (thixotropy) of the coating during construction, manifested as easy sagging of the coating film and poor anti-settling property.

[0063] 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 by the above embodiments, and the above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A water-based metallic primer for vehicles, characterized in that: The invention comprises 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 slurry, 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 a silicone / silicon dioxide hybrid grafted with an acrylic-epoxy composite emulsion; The nonionic polyurethane thickener is prepared by capping the polyurethane prepolymer with fatty alcohol polyoxyethylene ether and adding gamma-aminopropyltrimethoxysilane to graft the capped polyurethane prepolymer.

2. The automotive water-based metallic primer according to claim 1, characterized in that: In the modified waterborne acrylic resin, the mass ratio of the organosilicon / silicon dioxide hybrid to the acrylic acid-epoxy composite emulsion is 1:3.0-4.

0.

3. The automotive water-based metallic primer according to claim 1, characterized in that: In the nonionic polyurethane thickener, the mass ratio of the blocked polyurethane prepolymer to the gamma-aminopropyltrimethoxysilane is 1:0.01-0.

03.

4. The automotive water-based metallic primer according to claim 2, characterized in that: The preparation steps of the modified waterborne acrylic resin are as follows: The acrylic copolymer base material and the epoxy resin E-20 emulsion are mixed, sodium dodecyl sulfate of 2%-4% by mass of the acrylic copolymer base material is added, and pre-emulsified at a speed of 600-800 rpm for 20-30 minutes using a high-speed disperser to obtain a mixed solution; the mixed solution is transferred to a reaction kettle, and under nitrogen protection, the temperature is increased to 75-85° C. at a rate of 1-2° C. per minute, and stirred at a speed of 300-500 rpm for 1-2 hours to form an acrylic-epoxy composite emulsion; Adding the organosilicon / silicon dioxide hybrid powder into deionized water, and ultrasonically dispersing it at a power of 100-200 W for 20-30 min to form a hybrid suspension; Add the hybrid suspension to the acrylic-epoxy composite emulsion, and simultaneously drip an aqueous solution of ammonium persulfate for 1-2 hours, raise the temperature to 80-85°C, and stir the mixture at a speed of 300-500 rpm for 4-6 hours under nitrogen protection; After the reaction is completed, the reaction system is cooled to 40-50° C., the pH of the reaction system is adjusted to 8.0-8.5 with 20%-25% by mass concentration of ammonia water, and then filtered through a 180-200 mesh filter to obtain a modified water-based acrylic resin.

5. The vehicle water-based metallic primer according to claim 4, characterized in that: The mass percentage concentration of the ammonium persulfate aqueous solution is 3%-8%.

6. The automotive water-based metallic primer according to claim 3, characterized in that: The preparation steps of the nonionic polyurethane thickener are as follows: Add the dehydrated polyoxypropylene glycol, diisocyanate and dibutyltin dilaurate into a reaction kettle, raise the temperature to 70-80°C and stir at 300-400 rpm for prepolymerization for 2-3 hours; After the prepolymerization reaction is completed, fatty alcohol polyoxyethylene ether is added according to the molar ratio of isocyanate group to fatty alcohol polyoxyethylene ether in the prepolymer of 1:1, and the reaction is continued at 60-70°C at a speed of 400-500rpm for 1-2h; after the reaction is completed, the reaction system is cooled to 40-50°C at a speed of 1-2°C per minute to obtain a blocked polyurethane prepolymer; Add γ-aminopropyltrimethoxysilane to the blocked polyurethane prepolymer, stir and react at 60-70° C. and 400-500 rpm for 1-2 hours; after the reaction is completed, cool to room temperature to obtain a nonionic polyurethane thickener.

7. The vehicle water-based metallic primer according to claim 6, characterized in that: The diisocyanate is isophorone diisocyanate or diphenylmethane diisocyanate.

8. A method for preparing a water-based metallic primer for a vehicle, for preparing the water-based metallic primer for a vehicle as claimed in any one of claims 1 to 7, characterized in that: The preparation method of the automotive water-based metallic primer is as follows: S1.1, weigh the following raw materials in parts by weight respectively: 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 slurry, 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 and deionized water in a mass ratio of 1:1, add cocamidopropyl betaine, first disperse at a high speed of 800-1000rpm for 5min, then stir at a speed of 300-500rpm for 10-15min to evenly disperse the aluminum powder; then add polydimethylsiloxane, continue to stir at a speed of 300-500rpm for 5-10min, filter with a 200-mesh sieve to obtain pre-dispersed aluminum powder slurry; S1.3, mixing the nano-titanium dioxide / graphene oxide composite filler with deionized water at a mass ratio of 1:9, using a high-speed disperser to disperse at a speed of 1000-1500 rpm for 20-30 min, and filtering with a 300-mesh sieve after dispersion to obtain a pre-dispersed nano-titanium dioxide / graphene oxide composite filler; S1.4, add the modified waterborne acrylic resin into a stirring kettle, stir at a speed of 300-500 rpm for 5-10 min, add deionized water to adjust the viscosity of the resin, and 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 material, and stir at a speed of 300-500rpm for 10-15min; then add a non-ionic polyurethane thickener dissolved in 40-50℃ water, and stir at a speed of 300-500rpm for 10-15min; add deionized water to adjust the solid content of the paint, and filter the paint with a 200-300 mesh sieve to obtain a water-based metallic primer for vehicles.

9. The method for preparing the automotive water-based metallic primer according to claim 8, characterized in that: In S1.4, the viscosity of the resin is adjusted to a coating viscosity of 4 cups for 30-50 seconds.

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

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