Water-based metal oriented emulsion special for automobile original factory 3C1B and preparation method of finish paint of water-based metal oriented emulsion

Abstract

The invention belongs to the technical field of water-based emulsions, and particularly relates to a water-based automobile original factory 3C1B special metal oriented emulsion and a preparation method of finish paint of the water-based automobile original factory 3C1B special metal oriented emulsion. The preparation method of the metal finish paint comprises the following steps that Q1, the metal oriented emulsion, aluminum powder pigment dispersion liquid, 2-ethylhexanol and melamine resin are added into a reaction container to be evenly mixed; and Q2, adding a thickening agent, DMEA and water into the reaction container, and uniformly mixing to obtain the metal finishing paint. The metal finishing coat and the floating coat are good in adsorption and combination performance, and a formed coating film is flat and smooth and is excellent in appearance, interlayer adhesive force, water resistance, heat and humidity resistance, flexibility and stone impact resistance.

Description

Technical Field

[0001] This invention belongs to the field of water-based emulsion technology, specifically relating to a water-based automotive original 3C1B metal-oriented emulsion and its topcoat preparation method. Background Technology

[0002] With increasing global awareness of environmental protection, the control of volatile organic compound (VOC) emissions has become a core issue for sustainable development in various industrial sectors. Among them, the painting process in the automotive manufacturing industry is a key source of VOC emissions, and its environmental upgrading is particularly urgent.

[0003] The 3C1B (3 Coats, 1 Baking) process, as an advanced coating technology, significantly reduces the number of baking cycles by applying three coats followed by a single baking process, thereby reducing energy consumption and VOC emissions and shortening the production cycle. It has become a major development trend in the automotive original equipment coating (OEM) industry. However, the 3C1B process places extremely high demands on the coating materials. Because only one baking is performed, each coating (primer, intermediate coat, and topcoat) must achieve synergistic curing under the same curing conditions, and the layers must possess excellent adhesion, compatibility, and stability to avoid defects such as interlayer peeling and pinholes.

[0004] Currently, water-based coatings for automotive painting have become a key means of reducing VOCs. Water-based cationic electrophoretic coatings are commonly used for primers, and research on water-based intermediate and topcoats has also made some progress (e.g., Japanese Patent Application Laid-Open Nos. 2002-294148, 2003-105257, and Chinese Patents CN1357582A, CN102977752A, etc., have proposed technical solutions for water-based intermediate coatings). However, research in the field of metal directional coatings specifically for the 3C1B process is lacking. The main difficulties lie in the poor compatibility with intermediate coatings and solving the problem of smoothness. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a water-based automotive original 3C1B metal directional emulsion and its topcoat preparation method. The metal topcoat of this invention has good adsorption and bonding with the intermediate coating, resulting in a smooth and flat coating film with excellent appearance, interlayer adhesion, water resistance, damp heat resistance, flexibility, and stone chip resistance.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] A method for preparing a water-based automotive OEM 3C1B metal-oriented emulsion includes the following steps:

[0008] S1. Preparation of the first monomer emulsion and the second monomer emulsion, specifically including the following steps:

[0009] S101. To prepare the first monomer emulsion, by mass parts, 30-42 parts water, 0.3-1 parts emulsifier, 1-5 parts ethylene glycol dimethacrylate, 2-8 parts phosphate methacrylate, 1-5 parts styrene, 10-20 parts methyl methacrylate, 20-30 parts ethyl acrylate and 15-30 parts n-butyl acrylate are mixed and stirred to obtain the first monomer emulsion;

[0010] S102. To prepare the second monomer emulsion, by mass parts, 10-30 parts water, 0.1-0.6 parts emulsifier, 0.01-0.1 parts ammonium persulfate, 3-8 parts methacrylic acid, 3-10 parts 2-hydroxyethyl acrylate, 2-7 parts styrene, 2-10 parts methyl methacrylate, 1-5 parts ethyl acrylate and 5-10 parts n-butyl acrylate are mixed and stirred to obtain the second monomer emulsion.

[0011] S2. Add 140-150 parts of water and 0.5-0.8 parts of emulsifier to the reaction vessel and stir evenly. After heating, add 0.8-1.2% of the total mass of the first monomer emulsion and 5-6 parts of ammonium persulfate aqueous solution to the reaction vessel, and then maintain the temperature and react.

[0012] S3. Add all the remaining first monomer emulsion to the reaction vessel and then ripen it.

[0013] S4. Add all of the second monomer emulsion to the reaction vessel and then ripen it. After ripening, add 35-45 parts of dimethylethanolamine aqueous solution to the reaction vessel and cool it. After filtration, the metal-oriented emulsion is obtained.

[0014] Furthermore, the concentration of the ammonium persulfate aqueous solution is 5-7%, and the concentration of the dimethylethanolamine aqueous solution is 4-6%.

[0015] Furthermore, the temperature for heating in step S2 is 75-85°C.

[0016] Furthermore, the remaining first monomer emulsion mentioned in step S3 is added to the reaction vessel by dropping over a period of 2-4 hours.

[0017] Furthermore, the maturation time in step S3 is 1-1.5 hours, and the maturation time in step S4 is 1-1.5 hours.

[0018] Furthermore, the filtration in step S4 uses an 80-120 mesh filter cloth.

[0019] Furthermore, the solids concentration of the metal-oriented emulsion is 28-32%.

[0020] Furthermore, the metal-oriented emulsion has an acid value of 30-35 mgKOH / g and a hydroxyl value of 22-26 mgKOH / g.

[0021] A method for preparing a water-based automotive original 3C1B special metallic topcoat includes the following steps:

[0022] Q1. By mass, add 120-140 parts of metal-oriented emulsion, 55-65 parts of aluminum powder pigment dispersion, 30-40 parts of 2-ethylhexanol and 30-40 parts of melamine resin into the reaction vessel and mix evenly.

[0023] Q2. Then add 0.1-0.5 parts thickener, 0.2-0.8 parts DMEA and 40-80 parts water to the reaction vessel, mix well and obtain the metallic topcoat.

[0024] Furthermore, the melamine resin is SAIMEL 325 melamine resin.

[0025] Furthermore, the solid content of the metallic paint is 40%, and the pH value is 8.0.

[0026] Furthermore, the viscosity of the metallic paint, measured at 20°C using a Ford cup No. 4, is 60 seconds.

[0027] Furthermore, the solid content concentration of the aluminum powder pigment dispersion is 5-8%.

[0028] Furthermore, the thickener is a polyacrylic acid-based thickener.

[0029] Furthermore, the thickener is PRIMALASE-60 polyacrylic acid thickener.

[0030] The beneficial effects of this invention are:

[0031] 1. In this invention, the hydroxyl groups provided by 2-hydroxyethyl acrylate can improve the bonding force between the metal topcoat and the intermediate coating, and can adsorb with the hydroxyl groups of the intermediate coating to form hydrogen bonds, thus significantly improving the interfacial bonding force.

[0032] 2. The emulsion prepared using methacrylate phosphate monomer in this invention has wetting and dispersing properties for aluminum powder pearlescent pigments. The polar ends of the phosphate groups form chemical adsorption with the surface of the aluminum powder, reducing interfacial tension and allowing the aluminum powder to be uniformly dispersed and directionally adsorbed on the surface of the emulsion particles. Furthermore, the long-chain structure of the phosphate forms a three-dimensional barrier on the surface of the aluminum powder, preventing particle agglomeration and ensuring that the metallic pigments remain parallel in the wet film, thereby improving the metallic shimmer effect and gloss of the coating film.

[0033] 3. This invention optimizes the smoothness of metallic topcoat during wet-on-wet coating. The metallic oriented emulsion adopts a stepwise polymerization process, first adding 1% of the first monomer emulsion to initiate the reaction, and then adding the remaining portion to form a core-shell structure. The hydrophilic groups of the shell layer preferentially contact the intermediate coating, while the hydrophobic groups of the core layer support the orientation of the aluminum powder, achieving dual optimization of interlayer compatibility and surface smoothness. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0035] The emulsifier used in this invention is AQUALON KH-10 surfactant manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd. of Japan; the melamine resin is SAIMEL 325 melamine resin manufactured by Cytec Kogyo Co., Ltd. of Japan; the thickener is PRIMALASE-60 polyacrylic acid tackifier manufactured by Rohm & Haas Co., Ltd.; the water is deionized water; and all other raw materials used are commercially available unless otherwise specified.

[0036] Example 1

[0037] Preparation of metal-oriented emulsions

[0038] S101. To prepare the first monomer emulsion, by mass parts, 42 parts water, 0.7 parts emulsifier, 2.1 parts ethylene glycol dimethacrylate, 3 parts phosphate methacrylate, 2.8 parts styrene, 16.1 parts methyl methacrylate, 28 parts ethyl acrylate and 21 parts n-butyl acrylate are mixed and stirred to obtain the first monomer emulsion.

[0039] S102. To prepare the second monomer emulsion, by mass parts, 18 parts water, 0.31 parts emulsifier, 0.03 parts ammonium persulfate, 5.1 parts methacrylic acid, 5 parts 2-hydroxyethyl acrylate, 3 parts styrene, 6 parts methyl methacrylate, 1.8 parts ethyl acrylate and 9 parts n-butyl acrylate are mixed and stirred to obtain the second monomer emulsion.

[0040] S2. Add 140 parts of deionized water and 0.5 parts of emulsifier to the reaction vessel, stir and mix in a nitrogen stream, heat to 80°C, then add 1% of the total mass of the first monomer emulsion and 5.3 parts of a 6% ammonium persulfate aqueous solution to the reaction vessel, and maintain at 80°C for 15 min.

[0041] S3. After 3 hours, add the remaining first monomer emulsion dropwise into the reaction vessel and maintain the temperature at 80°C. After the addition is complete, let it mature for 1 hour.

[0042] S4. After 1 hour, add all the second monomer emulsion dropwise into the reaction vessel and let it mature for 1 hour. After maturation, slowly add 40 parts of a 5% dimethylethanolamine aqueous solution into the reaction vessel and cool to 30°C. Filter with 100-mesh nylon cloth to obtain a metal-oriented emulsion with a solid content of 30%. The average particle size of the metal-oriented emulsion is 100 nm, the acid value is 33 mg KOH / g, and the hydroxyl value is 25 mg KOH / g.

[0043] The average particle size was measured using a submicron particle size distribution measuring device, "COULTER N4 type," diluted with deionized water, and measured at 20°C.

[0044] Preparation of metallic topcoat

[0045] Q1. Add 130 parts of metal-oriented emulsion, 62.2 parts of aluminum powder pigment dispersion, 35 parts of 2-ethylhexanol and 37.5 parts of melamine resin into the reaction vessel and mix thoroughly.

[0046] Q2. Then add 0.3 parts thickener, 0.6 parts DMEA and 60 parts water to the reaction vessel, mix well, and obtain a metallic topcoat with a pH of 8.0, a solid content concentration of 40%, and a viscosity of 60 seconds measured by Ford cup No.4 at 20°C.

[0047] Example 2

[0048] Preparation of metal-oriented emulsions

[0049] S101. To prepare the first monomer emulsion, by mass parts, 35 parts water, 0.8 parts emulsifier, 3 parts ethylene glycol dimethacrylate, 5 parts phosphate methacrylate, 3 parts styrene, 15 parts methyl methacrylate, 25 parts ethyl acrylate and 25 parts n-butyl acrylate are mixed and stirred to obtain the first monomer emulsion.

[0050] S102. To prepare the second monomer emulsion, by mass parts, 20 parts water, 0.4 parts emulsifier, 0.05 parts ammonium persulfate, 5 parts methacrylic acid, 6 parts 2-hydroxyethyl acrylate, 5 parts styrene, 7 parts methyl methacrylate, 3 parts ethyl acrylate and 8 parts n-butyl acrylate are mixed and stirred to obtain the second monomer emulsion.

[0051] S2. Add 145 parts of deionized water and 0.7 parts of emulsifier to the reaction vessel, stir and mix in a nitrogen stream, heat to 80°C, then add 1% of the total mass of the first monomer emulsion and 5.5 parts of a 6% ammonium persulfate aqueous solution to the reaction vessel, and maintain at 80°C for 20 min.

[0052] S3. After 3 hours, add the remaining first monomer emulsion dropwise into the reaction vessel and maintain the temperature at 80°C. After the addition is complete, let it mature for 1 hour.

[0053] S4. After 1 hour, add all the second monomer emulsion dropwise into the reaction vessel and let it mature for 1 hour. After maturation, slowly add 40 parts of a 5% dimethylethanolamine aqueous solution into the reaction vessel and cool to 30°C. Filter with 100-mesh nylon cloth to obtain a metal-oriented emulsion with a solid content of 30%. The average particle size of the metal-oriented emulsion is 100 nm, the acid value is 33 mg KOH / g, and the hydroxyl value is 25 mg KOH / g.

[0054] Preparation of metallic topcoat

[0055] Q1. Add 130 parts of metal-oriented emulsion, 60 parts of aluminum powder pigment dispersion, 35 parts of 2-ethylhexanol and 35 parts of melamine resin into the reaction vessel and mix well.

[0056] Q2. Then add 0.3 parts thickener, 0.5 parts DMEA and 50 parts water to the reaction vessel, mix well, and obtain a metallic topcoat with a pH of 8.0, a solid content concentration of 40%, and a viscosity of 60 seconds measured by Ford cup No.4 at 20°C.

[0057] Example 3

[0058] S101. To prepare the first monomer emulsion, by mass parts, 30 parts water, 0.3 parts emulsifier, 1 part ethylene glycol dimethacrylate, 2 parts phosphate methacrylate, 1 part styrene, 10 parts methyl methacrylate, 20 parts ethyl acrylate and 15 parts n-butyl acrylate are mixed and stirred to obtain the first monomer emulsion.

[0059] S102. To prepare the second monomer emulsion, by mass parts, 10 parts water, 0.1 parts emulsifier, 0.01 parts ammonium persulfate, 3 parts methacrylic acid, 3 parts 2-hydroxyethyl acrylate, 2 parts styrene, 2 parts methyl methacrylate, 1 part ethyl acrylate and 5 parts n-butyl acrylate are mixed and stirred to obtain the second monomer emulsion.

[0060] S2. Add 140 parts of deionized water and 0.5 parts of emulsifier to the reaction vessel, stir and mix in a nitrogen stream, heat to 75°C, then add 1.2% of the total mass of the first monomer emulsion and 5 parts of a 6% ammonium persulfate aqueous solution to the reaction vessel, and maintain at 75°C for 20 min.

[0061] S3. After 3 hours, add the remaining first monomer emulsion dropwise into the reaction vessel and maintain the temperature at 75°C. After the addition is complete, let it mature for 1 hour.

[0062] S4. After 1 hour, all the second monomer emulsion was added dropwise to the reaction vessel and then allowed to mature for 1 hour. After maturation, 35 parts of a 5% dimethylethanolamine aqueous solution were slowly added to the reaction vessel and cooled to 30°C. The mixture was then filtered through an 80-mesh nylon cloth to obtain a metal-oriented emulsion with a solid content of 32%. The average particle size of the metal-oriented emulsion was 120 nm, the acid value was 33 mg KOH / g, and the hydroxyl value was 25 mg KOH / g.

[0063] Preparation of metallic topcoat

[0064] Q1. Add 120 parts of metal-oriented emulsion, 55 parts of aluminum powder pigment dispersion, 30 parts of 2-ethylhexanol and 30 parts of melamine resin into the reaction vessel and mix well.

[0065] Q2. Then add 0.1 parts thickener, 0.2 parts DMEA and 40 parts water to the reaction vessel, mix well, and obtain a metallic topcoat with a pH of 7.8, a solid content concentration of 38%, and a viscosity of 60 seconds measured by Ford cup No.4 at 20°C.

[0066] Example 4

[0067] S101. To prepare the first monomer emulsion, by mass parts, 42 parts water, 1 part emulsifier, 5 parts ethylene glycol dimethacrylate, 8 parts phosphate methacrylate, 5 parts styrene, 20 parts methyl methacrylate, 30 parts ethyl acrylate and 30 parts n-butyl acrylate are mixed and stirred to obtain the first monomer emulsion.

[0068] S102. To prepare the second monomer emulsion, by mass parts, 30 parts water, 0.6 parts emulsifier, 0.1 parts ammonium persulfate, 8 parts methacrylic acid, 10 parts 2-hydroxyethyl acrylate, 7 parts styrene, 10 parts methyl methacrylate, 5 parts ethyl acrylate and 10 parts n-butyl acrylate are mixed and stirred to obtain the second monomer emulsion.

[0069] S2. Add 150 parts of deionized water and 0.8 parts of emulsifier to the reaction vessel, stir and mix in a nitrogen stream, heat to 85°C, then add 0.8% of the total mass of the first monomer emulsion and 6 parts of a 6% ammonium persulfate aqueous solution to the reaction vessel, and maintain at 85°C for 20 min.

[0070] S3. After 3 hours, add the remaining first monomer emulsion dropwise into the reaction vessel and maintain the temperature at 85°C. After the addition is complete, let it mature for 1 hour.

[0071] S4. After 1 hour, all the second monomer emulsion was added dropwise to the reaction vessel and then allowed to mature for 1 hour. After maturation, 45 parts of a 5% dimethylethanolamine aqueous solution were slowly added to the reaction vessel and cooled to 30°C. The mixture was then filtered through a 120-mesh nylon cloth to obtain a metal-oriented emulsion with a solid content of 28%. The average particle size of the metal-oriented emulsion was 80 nm, the acid value was 33 mg KOH / g, and the hydroxyl value was 25 mg KOH / g.

[0072] Preparation of metallic topcoat

[0073] Q1. Add 140 parts of metal-oriented emulsion, 65 parts of aluminum powder pigment dispersion, 40 parts of 2-ethylhexanol and 40 parts of melamine resin into the reaction vessel and mix evenly.

[0074] Q2. Then add 0.5 parts thickener, 0.8 parts DMEA and 80 parts water to the reaction vessel, mix well, and obtain a metallic topcoat with a pH of 8.2, a solid content concentration of 42%, and a viscosity of 60 seconds measured by Ford cup No.4 at 20°C.

[0075] Comparative Example 1

[0076] The difference between Comparative Example 1 and Example 1 is that the first monomer emulsion in Comparative Example 1 does not contain phosphate methacrylate. The specific steps of Comparative Example 1 are as follows:

[0077] Preparation of metal-oriented emulsions

[0078] S101. To prepare the first monomer emulsion, by mass parts, 42 parts water, 0.72 parts emulsifier, 2.1 parts ethylene glycol dimethacrylate, 2.8 parts styrene, 16.1 parts methyl methacrylate, 28 parts ethyl acrylate and 21 parts n-butyl acrylate are mixed and stirred to obtain the first monomer emulsion.

[0079] S102. To prepare the second monomer emulsion, by mass parts, 18 parts water, 0.31 parts emulsifier, 0.03 parts ammonium persulfate, 5.1 parts methacrylic acid, 5.1 parts 2-hydroxyethyl acrylate, 3 parts styrene, 6 parts methyl methacrylate, 1.8 parts ethyl acrylate and 9 parts n-butyl acrylate are mixed and stirred to obtain the second monomer emulsion.

[0080] S2. Add 140 parts of deionized water and 0.52 parts of emulsifier to the reaction vessel, stir and mix in a nitrogen stream, heat to 80°C, then add 1% of the total mass of the first monomer emulsion and 5.3 parts of a 6% ammonium persulfate aqueous solution to the reaction vessel, and maintain at 80°C for 15 min.

[0081] S3. After 3 hours, add the remaining first monomer emulsion dropwise into the reaction vessel and maintain the temperature at 80°C. After the addition is complete, let it mature for 1 hour.

[0082] S4. After 1 hour, add all of the second monomer emulsion dropwise into the reaction vessel and let it mature for 1 hour. After maturation, slowly add 40 parts of a 5% dimethylethanolamine aqueous solution into the reaction vessel and cool to 30°C. Filter with 100-mesh nylon cloth to obtain a metal-oriented emulsion with a solid content of 30%. The average particle size of the metal-oriented emulsion is 100 nm, the acid value is 33 mg KOH / g, and the hydroxyl value is 25 mg KOH / g.

[0083] Preparation of metallic topcoat

[0084] Q1. Add 130 parts of metal-oriented emulsion, 62.2 parts of aluminum powder pigment dispersion, 35 parts of 2-ethylhexanol and 37.5 parts of melamine resin into the reaction vessel and mix thoroughly.

[0085] Q2. Then add 0.3 parts thickener, 0.6 parts DMEA and 60 parts water to the reaction vessel, mix well, and obtain a metallic topcoat with a pH of 8.0, a solid content concentration of 40%, and a viscosity of 60 seconds measured by Ford cup No.4 at 20°C.

[0086] II. Performance Testing

[0087] The coating performance of the metallic topcoats prepared in Examples 1-4 and Comparative Example 1 was tested, and the specific testing methods are as follows:

[0088] On cold-rolled steel plates that have undergone zinc perphosphate formation treatment, electrophoretic coatings were prepared and applied using a pre-made coating material with a dry film thickness of 20 μm. The coating was then heated at 170°C for 30 minutes to cure, thus producing a test substrate.

[0089] In a coating environment of 23°C and 75% humidity, a special intermediate coat was applied to the test substrate using a rotary atomizing coating machine, with a dry film thickness of 30 μm. Next, after pre-drying (pre-heating) at 80°C for 5 minutes, the metallic topcoat from the example was applied to the water-based intermediate coat film using the rotary atomizing coating machine, with a dry film thickness of 15 μm, and then pre-dried (pre-heated) at 80°C for 10 minutes. Finally, a self-made acid epoxy 2K clear coat was applied to the water-based metallic topcoat, with a dry film thickness of 40 μm. After standing for 7 minutes, the substrate was heated at 140°C for 30 minutes to create a test panel.

[0090] in:

[0091] Water absorption rate of coating (%):

[0092] The water-based intermediate coating is applied to aluminum foil used for measuring the water absorption rate of the coating film. The water absorption rate (%) of the intermediate coating film is calculated by dividing (the mass of the coating after flash-drying and immersion in water W1 - the mass of the coating after flash-drying W2) by the mass of the coating after flash-drying W2 using the test method and calculation formula. The lower the water absorption rate, the less water is contained in the water-based intermediate coating film.

[0093] Smoothness:

[0094] The evaluation was conducted using long-wave (LW) values ​​measured using a Wave Scan (trade name, manufactured by BYK Gardner). Long-wave (LW) values ​​are amplitude indicators of surface roughness at wavelengths of approximately 600–1,000 μm; the smaller the measured value, the smoother the surface finish.

[0095] Visibility:

[0096] The evaluation was conducted using the short wave (SW) values ​​measured using the aforementioned Wave Scan. The short wave (SW) value is an amplitude index of surface roughness with a wavelength of 100–600 μm; the smaller the measured value, the higher the sharpness of the coating surface.

[0097] Metallic glitter (FF):

[0098] For each test plate, the L value (lightness) at 15° and 110° angles of light was measured using a multi-angle spectrophotometer MA-68 (trade name, manufactured by X-Rite). The FF value was then calculated using the following formula.

[0099] FF value = L value at a viewing angle of 15° / L value at a viewing angle of 110°. The larger the FF value, the greater the change in L value (brightness) caused by the viewing angle (viewing angle), and the better the metallic luster.

[0100] Water resistance:

[0101] The test panel was immersed in warm water at 40°C for 240 hours, then removed and dried at 20°C for 12 hours. The multi-layered coating on the test panel was then scored into a grid pattern, with the scoring extending to the substrate, creating 100 checkerboard patterns measuring 2mm × 2mm. Next, transparent tape was applied to the surface, and after rapid peeling off the tape at 20°C, the residual state of the checkerboard coating was examined. The evaluation criteria for water resistance are as follows.

[0102] ◎: 100 checkerboard-pattern coating residues remain, and the edges of the checkerboard patterns are intact.

[0103] ○: 100 checkerboard-pattern coating residues remain, but the edges of the checkerboard patterns are incomplete.

[0104] △: 90-99 checkerboard coating residues

[0105] ×: The number of residual checkerboard coating particles is less than 89.

[0106] Stone-breaking resistance:

[0107] A test plate was placed on the specimen holding platform of the "JA-400" type flake testing machine (trade name, manufactured by Suga Testing Machine Co., Ltd., chipping resistance testing device). At -20°C, 50g of No. 7 granite chips were blown at a distance of 30cm with compressed air at 0.392MPa (4kgf / cm2) to impact the test plate at a 45° angle. Then, the resulting test plate was washed with water, dried, and a cloth tape (manufactured by Nichiban Co., Ltd.) was attached to the coating surface. After peeling it off, the degree of scratches on the coating film was visually observed, and the evaluation was carried out according to the following criteria.

[0108] ◎: The scratches are extremely small, and the electrophoretic surface and the base steel plate are not exposed.

[0109] ○: The scratches are small, and the electrophoretic surface and the base steel plate are not exposed.

[0110] △: The scratch is small, but the electrophoretic surface or the base steel plate is exposed.

[0111] ×: The scratches are quite large, and the base steel plate is clearly exposed.

[0112] The test data are shown in Table 1.

[0113] Table 1

[0114]

[0115]

[0116] As can be seen from the data in Table 1, the metallic topcoat and intermediate coating in this invention have good adsorption and bonding properties, resulting in a smooth and flat coating with excellent appearance, as well as superior interlayer adhesion, water resistance, damp heat resistance, flexibility, and stone impact resistance.

[0117] A comparison of Examples 1-4 with Comparative Example 1 shows that the metal-oriented emulsion in Comparative Example 1 lacks phosphate methacrylate monomers, resulting in a coating film formed by the metal-setting paint prepared in Comparative Example 1 exhibiting poor gloss, water absorption, smoothness, developability, and metallic shimmer. This is because the long-chain structure of the phosphate ester forms a three-dimensional barrier on the surface of the aluminum powder, preventing particle agglomeration and ensuring that the metallic pigments remain parallel in the wet film, thereby enhancing the metallic shimmer effect and gloss of the coating film.

Claims

1. A method for preparing a water-based automotive original equipment manufacturer (OEM) 3C1B metal-oriented emulsion, characterized in that, Includes the following steps: S1. Preparation of the first monomer emulsion and the second monomer emulsion, specifically including the following steps: S101. To prepare the first monomer emulsion, by mass parts, 30-42 parts water, 0.3-1 parts emulsifier, 1-5 parts ethylene glycol dimethacrylate, 2-8 parts phosphate methacrylate, 1-5 parts styrene, 10-20 parts methyl methacrylate, 20-30 parts ethyl acrylate and 15-30 parts n-butyl acrylate are mixed and stirred to obtain the first monomer emulsion; S102. To prepare the second monomer emulsion, by mass parts, 10-30 parts water, 0.1-0.6 parts emulsifier, 0.01-0.1 parts ammonium persulfate, 3-8 parts methacrylic acid, 3-10 parts 2-hydroxyethyl acrylate, 2-7 parts styrene, 2-10 parts methyl methacrylate, 1-5 parts ethyl acrylate and 5-10 parts n-butyl acrylate are mixed and stirred to obtain the second monomer emulsion. S2. Add 140-150 parts of water and 0.5-0.8 parts of emulsifier to the reaction vessel and stir evenly. After heating, add 0.8-1.2% of the total mass of the first monomer emulsion and 5-6 parts of ammonium persulfate aqueous solution to the reaction vessel, and then maintain the temperature and react. S3. Add all the remaining first monomer emulsion to the reaction vessel and then ripen it. S4. Add all of the second monomer emulsion to the reaction vessel and then ripen it. After ripening, add 35-45 parts of dimethylethanolamine aqueous solution to the reaction vessel and cool it. After filtration, the metal-oriented emulsion is obtained.

2. The preparation method of a water-based automotive original 3C1B metal-oriented emulsion according to claim 1, characterized in that, The temperature for heating in step S2 is 75-85℃.

3. The preparation method of a water-based automotive original 3C1B metal-oriented emulsion according to claim 1, characterized in that, The remaining first monomer emulsion mentioned in step S3 is added to the reaction vessel by dropping over a period of 2-4 hours.

4. The preparation method of a water-based automotive original 3C1B metal-oriented emulsion according to claim 1, characterized in that, The maturation time in step S3 is 1-1.5 hours, and the maturation time in step S4 is 1-1.5 hours.

5. The method for preparing a water-based automotive original 3C1B specific metal-oriented emulsion according to claim 1, characterized in that, The filtration described in step S4 uses an 80-120 mesh filter cloth.

6. The method for preparing a water-based automotive original 3C1B specific metal-oriented emulsion according to claim 1, characterized in that, The solids concentration of the metal-oriented emulsion is 28-32%.

7. A method for preparing a water-based automotive original 3C1B special metallic topcoat, wherein the metallic topcoat is prepared using the metal-oriented emulsion as described in claim 1, characterized in that, The preparation method of the metallic topcoat includes the following steps: Q1. By mass, add 120-140 parts of metal-oriented emulsion, 55-65 parts of aluminum powder pigment dispersion, 30-40 parts of 2-ethylhexanol and 30-40 parts of melamine resin into the reaction vessel and mix evenly. Q2. Then add 0.1-0.5 parts thickener, 0.2-0.8 parts DMEA and 40-80 parts water to the reaction vessel, mix well and obtain the metallic topcoat.

8. The method for preparing a water-based automotive original 3C1B special metallic topcoat according to claim 7, characterized in that, The solid content of the metallic topcoat is 38-42%, and the pH value is 7.8-8.

2.

9. The method for preparing a water-based automotive original 3C1B special metallic topcoat according to claim 7, characterized in that, The solid content concentration of the aluminum powder pigment dispersion is 5-8%.

10. The method for preparing a water-based automotive original 3C1B special metallic topcoat according to claim 7, characterized in that, The thickener is a polyacrylic acid-based thickener.

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