Electrophoretic paint and low-temperature integrated painting method for whole vehicle

Abstract

This invention relates to the field of coating technology, and more particularly to an electrophoretic coating and a method for low-temperature integrated coating of vehicles. The electrophoretic coating provided by this invention significantly reduces the curing temperature to 130-140℃ by optimizing the resin and curing agent systems, resulting in energy savings of over 15% compared to traditional electrophoretic coating curing systems. Furthermore, the curing agent system of this invention is stable at room temperature, avoiding the storage safety hazards of traditional isocyanate systems. It can also synergistically catalyze at low temperatures, achieving rapid cross-linking and excellent film performance. In addition, the B1B2-based low-temperature integrated coating process for vehicles provided by this invention, utilizing the aforementioned electrophoretic coating in combination with low-temperature adhesive materials, low-temperature first-layer color paint, and low-temperature second-layer color paint, not only solves the problem of color difference between the vehicle body and plastic parts, but also reduces energy consumption, saves time, achieves cost reduction and efficiency improvement, and promotes green transformation, demonstrating promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to an electrophoretic coating and a method for low-temperature integrated coating of a whole vehicle. Background Technology

[0002] With the nation's increasing emphasis on environmental protection and energy conservation, green and energy-saving technologies have become the main direction of development for the modern automotive industry. While ensuring high decorative properties and corrosion resistance, automotive painting is also moving towards the use of environmentally friendly materials and processes. Currently, the painting process accounts for a very high proportion of energy consumption in vehicle production, typically around 80% of the total energy consumption of the four main vehicle manufacturing processes, with the majority of this energy consumption coming from spraying and baking operations. Therefore, developing more energy-efficient and environmentally friendly painting technologies has become a key focus for major automakers.

[0003] Traditional coating processes commonly employ a "three-coat, two-bake" (3C2B) process, the core flow of which is: electrophoretic primer → intermediate coat spraying → intermediate coat drying → color paint spraying → flash drying → clear coat spraying → clear coat drying. This process requires two high-temperature baking cycles, consuming significant energy and generating substantial VOCs (volatile organic compounds) through solvent evaporation, placing considerable pressure on the environment. To alleviate these issues, the industry has gradually developed a "three-coat, one-bake" (3C1B) process. This process reduces energy consumption and VOC emissions to some extent by eliminating one baking step. Currently, 3C1B has been applied in multiple vehicle models, becoming a relatively mature and environmentally friendly coating solution. However, this process still relies on high-temperature baking, and its energy efficiency still needs improvement.

[0004] Based on this, the B1B2 coating process was developed. This process, based on water-based coating technology, combines the intermediate coat and color coat into a single spray application and achieves integrated baking. The entire process is as follows: B1 color coat spraying → B2 color coat spraying → pre-drying → clear coat spraying → clear coat baking. Compared to the traditional 3C2B and 3C1B processes, B1B2 is more energy-efficient and environmentally friendly. By reducing the number of baking cycles and optimizing the process flow, the B1B2 process can significantly reduce energy consumption and VOC emissions, meeting current national requirements for green manufacturing. This process eliminates the intermediate coat and intermediate coat sanding steps, reducing production line complexity and improving efficiency. It also reduces material and equipment inputs and lowers labor costs, which is significant for controlling overall vehicle manufacturing costs. This process is suitable for various vehicle models and complex body structures, especially when applying the intermediate coat and top coat in an integrated manner, effectively avoiding the problem of the body and exterior parts being painted separately due to high-temperature baking.

[0005] However, another point of concern is that, in terms of coating materials, current resin systems mostly rely on epoxy or polyester resins. These materials have low curing efficiency at low temperatures, resulting in problems such as insufficient coating hardness (e.g., pencil hardness below H) and poor corrosion resistance. Although the use of lightweight fillers such as calcium carbonate or talc can reduce weight, it often sacrifices the mechanical strength of the coating. Furthermore, inaccurate formulation adjustments can lead to poor leveling and orange peel effects.

[0006] The root cause of these problems lies in the disconnect between material formulation and process, and the lack of systematic optimization, which leads to resource waste and inefficiency.

[0007] Therefore, how to improve the B1B2 coating process, further reduce production energy consumption, and improve production efficiency has become an urgent problem to be solved. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides an electrophoretic coating and a method for low-temperature integrated coating of the entire vehicle.

[0009] In a first aspect, the present invention provides an electrophoretic coating, which, by weight, comprises: 85-100 parts of a first aqueous resin, 5-10 parts of a curing agent, and 5-10 parts of a first filler; The first aqueous resin includes aqueous resins having hydroxyl groups and aqueous resins having carboxyl groups; The curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole.

[0010] In some embodiments of the present invention, the weight ratio of the furan-maleic anhydride adduct, the blocked isocyanate, and the 2-methylimidazole is (3-4):1:(0.25-0.4).

[0011] In some embodiments of the present invention, the aqueous resin having hydroxyl groups is 50-55 parts by weight, and the aqueous resin having carboxyl groups is 35-45 parts by weight.

[0012] In some embodiments of the present invention, the aqueous resin having hydroxyl groups in the electrophoretic coating includes an epoxy resin, wherein the epoxy equivalent of the epoxy resin is 400-600.

[0013] In some embodiments of the present invention, the aqueous resin having carboxyl groups includes an acrylic resin, wherein the acid value of the acrylic resin is 40-70 mg KOH / g.

[0014] In some embodiments of the present invention, the electrophoretic coating further includes a first neutralizing agent, the content of which is such that the pH of the electrophoretic coating is 8.0-8.5.

[0015] In some embodiments of the present invention, the electrophoretic coating further includes a first functional additive.

[0016] In some embodiments of the present invention, the electrophoretic coating further includes water, the content of which is such that the solid content of the electrophoretic coating is 12-18%.

[0017] In some embodiments of the present invention, the first neutralizing agent includes an amine neutralizing agent.

[0018] In some embodiments of the present invention, the first functional additive includes one or more of leveling agents, anti-settling agents, thixotropic agents, thickeners, defoamers, silane coupling agents, or weather-resistant enhancers.

[0019] In some embodiments of the present invention, by weight, it comprises: 50-55 parts of an aqueous resin having hydroxyl groups, 35-45 parts of an aqueous resin having carboxyl groups, 5-10 parts of a curing agent, 5-10 parts of a first filler, 1-2 parts of a leveling agent, 1.3-2 parts of an anti-settling agent, a first neutralizing agent, and water. The curing agent comprises a furan-maleic anhydride adduct, a blocked isocyanate, and 2-methylimidazole in a weight ratio of (3-4):1:(0.25-0.4); The electrophoretic coating has a pH of 8.0-8.5 and a solid content of 12-18%.

[0020] Secondly, the present invention provides an application of the electrophoretic coating as described in the first aspect in the field of vehicle coating.

[0021] Thirdly, the present invention provides a method for low-temperature integrated coating of a vehicle, comprising the following steps: (1) The car body is electrophoresed with the electrophoretic coating as described in the first aspect, then dried for the first time, then sealed with adhesive, and then dried for the second time; The temperature of the first drying is 130-140℃, and the temperature of the second drying is 85-100℃; The plastic parts are assembled onto the car body after the second drying process to form the parts to be sprayed. (2) The coating is completed by sequentially applying the first layer of color paint, the second layer of color paint, color paint leveling, pre-drying, clear varnish spraying, clear varnish leveling, and the third drying to the part to be sprayed. The temperature for the third drying process is 85-100℃.

[0022] In some embodiments of the present invention, the first layer of paint comprises, by weight, parts of: 24-44 parts of the second waterborne resin, 4-7 parts of the crosslinking agent, and 10-35 parts of the second filler; The crosslinking agent includes methyl etherified high-imino melamine resin and high-methyl etherified melamine-formaldehyde resin; The weight ratio of the methyl etherified high-imino melamine resin to the high-methyl etherified melamine-formaldehyde resin is (1.5-5):1.

[0023] In some embodiments of the present invention, the second aqueous resin comprises, by weight, 3-5 parts of aliphatic polyurethane acrylate hybrid resin, 10-15 parts of aliphatic polyurethane-acrylic acid hybrid dispersion, 4-5 parts of aqueous acrylic copolymer, 10-15 parts of aqueous polyurethane dispersion, and 2-4 parts of aqueous aliphatic self-crosslinking polyurethane resin.

[0024] In some embodiments of the present invention, the first layer of paint further includes coloring pigments.

[0025] In some embodiments of the present invention, the first layer of paint further includes a second neutralizing agent, the amount of which makes the pH of the first layer of paint 8.0-8.5.

[0026] In some embodiments of the present invention, the first layer of paint further includes a second functional additive.

[0027] In some embodiments of the present invention, the first layer of paint further includes water, the amount of which makes the solid content of the first layer of paint 12-18%.

[0028] In some embodiments of the present invention, the second neutralizing agent includes an amine neutralizing agent.

[0029] In some embodiments of the present invention, the second functional additive includes one or more of the following: defoamer, dispersant, wetting agent, thixotropic agent, cosolvent, thickener, rheology modifier, leveling agent, or slip agent.

[0030] In some embodiments of the present invention, the first layer of paint comprises, by weight, 3-5 parts of aliphatic polyurethane acrylate hybrid resin, 10-15 parts of aliphatic polyurethane-acrylic hybrid dispersion, 4-5 parts of waterborne acrylic copolymer, 10-15 parts of waterborne polyurethane dispersion, 2-4 parts of waterborne aliphatic self-crosslinking polyurethane resin, 4-7 parts of crosslinking agent, 10-35 parts of filler, 15-30 parts of coloring pigment, 9-20 parts of second functional additive, second neutralizer, and water; The crosslinking agent comprises methyl etherified high-imino melamine resin and high-methyl etherified melamine-formaldehyde resin in a weight ratio of (1.5-5):1. The pH of the first layer of paint is 8.0-8.5, and the solid content of the first layer of paint is 12-18%.

[0031] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: (1) The electrophoretic coating provided by the present invention significantly reduces the curing temperature of the electrophoretic coating by optimizing the resin system and using a curing agent system formed by furan-maleic anhydride adduct, blocked isocyanate and 2-methylimidazole, making it as low as 130-140℃. This saves more than 15% energy compared with the traditional electrophoretic coating curing system. Moreover, the curing agent system of the present invention is stable at room temperature, avoiding the storage safety hazards of the traditional isocyanate system. At the same time, it can synergistically catalyze at low temperature to achieve rapid cross-linking. The coating film has excellent performance and is suitable for coating scenarios with high energy consumption and environmental protection requirements, such as the automotive field.

[0032] (2) The low-temperature integrated coating process for the whole vehicle based on B1B2 provided by the present invention solves the problem of color difference between the body and plastic parts; at the same time, by using the above-mentioned electrophoretic coating, combined with low-temperature adhesive material, low-temperature first layer color paint material and low-temperature second layer color paint material, energy consumption is significantly reduced and time is saved, achieving cost reduction and efficiency improvement and green transformation, and has good application prospects. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the low-temperature integrated coating method for the whole vehicle described in Application Example 1 of the present invention. Detailed Implementation

[0034] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0035] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0037] In a first aspect, the present invention provides an electrophoretic coating, which, by weight, comprises: 85-100 parts of a first aqueous resin, 5-10 parts of a curing agent, and 5-10 parts of a first filler. The first aqueous resin includes aqueous resins having hydroxyl groups and aqueous resins having carboxyl groups; The curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole.

[0038] The weight parts of the first waterborne resin can be 85 parts, 88 parts, 90 parts, 95 parts, 97 parts or 100 parts, etc., but are not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0039] The amount of curing agent added can be 5, 6, 7, 8, 9 or 10 parts by weight, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0040] The weight of the first packing material can be 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0041] It should be noted that furan-maleic anhydride adducts refer to the reaction of furan and maleic anhydride via a concerted mechanism to yield an addition product with a six-membered ring structure. The specific reaction equation is as follows:

[0042] This invention significantly reduces the curing temperature of electrophoretic coatings to 130-140℃ by optimizing the resin system and using a curing agent system formed by furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole. This results in energy savings of more than 15% compared to traditional electrophoretic coating curing systems. Furthermore, the compounded curing agent system is stable at room temperature, avoiding the storage safety hazards of traditional isocyanate systems. It can also synergistically catalyze at low temperatures to achieve rapid crosslinking, resulting in excellent paint film performance. This invention is suitable for coating scenarios with high energy consumption and environmental protection requirements, such as the automotive industry.

[0043] Specifically, 2-methylimidazole, as a highly efficient latent catalyst, can significantly reduce the deblocking temperature of blocked isocyanate components. When heated to approximately 130-140°C, the imidazole groups are preferentially activated, promoting the rapid deblocking of isocyanate (-NCO) groups and cross-linking reactions with functional groups such as hydroxyl (-OH) in the resin system. Under heating and alkaline conditions, furan-maleic anhydride adducts can undergo ring-opening esterification reactions with carboxyl (-COOH) functional groups provided by the resin system, forming a dense cross-linked network. This reaction pathway itself requires relatively low activation energy, making it suitable for low-temperature curing. These two curing pathways are not isolated; while 2-methylimidazole catalyzes the deblocking and cross-linking of isocyanates, it may also promote the reaction between the anhydride and carboxyl groups. The two curing mechanisms occur simultaneously and mutually promote each other at 130-140°C, achieving a cross-linking rate much faster than a single curing agent system and a more complete reaction degree. This significantly reduces the curing temperature while ensuring excellent adhesion, hardness, and corrosion resistance of the paint film.

[0044] In this invention, the first filler includes, but is not limited to, titanium dioxide and carbon black, which can improve the weather resistance, abrasion resistance, and corrosion resistance of the paint film. Those skilled in the art can select other fillers according to their needs. Simultaneously, it also serves as a coloring pigment for tinting the paint film.

[0045] In some embodiments of the present invention, the weight ratio of the furan-maleic anhydride adduct, the blocked isocyanate, and the 2-methylimidazole is (3-4):1:(0.25-0.4), for example, 3:1:0.25, 3.5:1:0.3, 4:1:0.4, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0046] The present invention improves the low-temperature curing effect and ensures the quality of the coating film by further controlling the weight ratio of furan-maleic anhydride adduct, the blocked isocyanate and the 2-methylimidazole. If too much furan-maleic anhydride adduct is added, there will be an excess of anhydride groups in the system. After curing, the anhydride groups that have not participated in the ring-opening esterification reaction are prone to hydrolysis in a humid environment, which will destroy the cross-linking network of the paint film and cause a significant decrease in the water resistance and corrosion resistance of the paint film. At the same time, the excess adduct will increase the viscosity of the resin system, reduce the penetration and construction stability of electrophoretic application, and cause appearance defects such as uneven paint film thickness and sagging. It will also compete with the isocyanate cross-linking system for resin functional groups, weaken the synergistic effect of the two curing paths, and lead to poor paint film flexibility. If too little is added, the ring-opening esterification reaction with the carboxyl groups of the resin will be insufficient, the density of the paint film cross-linking network will be insufficient, and the adhesion, hardness and abrasion resistance of the paint film achieved by this reaction will be greatly reduced. At the same time, relying solely on the isocyanate cross-linking system will result in the loss of the synergistic curing effect at low temperatures, the cross-linking rate will be slowed down, the paint film will be insufficiently cured, and the scratch resistance and chemical resistance will be difficult to meet the standards.

[0047] If too much closed-type isocyanate is added, the excess isocyanate groups will react with trace amounts of moisture in the system after unsealing, generating carbon dioxide bubbles, resulting in appearance defects such as pinholes, craters, and blistering in the paint film. At the same time, excessive cross-linking of the paint film increases brittleness, reduces impact resistance and flexibility, and makes the paint film prone to cracking and delamination. It also increases the risk of unsealing trace amounts of isocyanate during storage at room temperature, reduces the storage stability of electrophoretic coatings, and increases raw material costs. If too little is added, the cross-linking reaction with hydroxyl groups in the resin system will be insufficient, resulting in a low overall cross-linking density of the paint film. The salt spray resistance and chemical resistance of the paint film achieved by this reaction will be greatly reduced, and the paint film will be prone to powdering and peeling after film formation. At the same time, the cross-linking reaction kinetics at low temperatures are insufficient, making it impossible to achieve the design goal of rapid curing at 130-140℃, reducing curing efficiency and making it difficult to adapt to the production rhythm of automotive coating production lines.

[0048] Excessive addition of 2-methylimidazole can lead to overly strong catalytic activity, causing an excessively low desealing temperature for the blocked isocyanate, and even micro-desealing during room temperature storage. This can trigger premature reactions between the isocyanate and system components, resulting in gelation and delamination of the electrophoretic coating, severely compromising storage stability. During the curing stage, an excessively rapid and uneven catalytic reaction rate generates significant internal stress within the paint film, making it prone to cracking and delamination, especially at stress concentration points such as the edges and corners of the substrate. Furthermore, excessive residual imidazole groups reduce the film's weather resistance, leading to yellowing and affecting appearance consistency. Insufficient addition, on the other hand, results in inadequate catalytic efficiency, failing to fully deseale the blocked isocyanate within the 130-140℃ low-temperature range. This hinders the cross-linking reaction between hydroxyl groups and isocyanate, leading to incomplete curing. Simultaneously, the auxiliary promoting effect on the anhydride and carboxyl groups disappears, completely eliminating the synergistic effect of the two curing pathways. Ultimately, this manifests as poor film adhesion, low hardness, substandard corrosion resistance and scrub resistance, and a significantly slower curing rate, failing to meet the demands of high-efficiency production lines.

[0049] In some embodiments of the present invention, the first aqueous resin in the electrophoretic coating comprises 50-55 parts of aqueous resin with hydroxyl groups, such as 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, or 55 parts; the weight of the aqueous resin with carboxyl groups is 35-45 parts, such as 35 parts, 38 parts, 40 parts, 42 parts, or 45 parts, but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0050] In this invention, by further optimizing the resin system ratio and appropriately matching the curing agent system, the crosslinking speed can be effectively improved, the reaction can be made more complete, the curing temperature can be reduced, and the excellent performance of the coating film can be guaranteed.

[0051] In some embodiments of the present invention, the hydroxyl-containing resin includes an epoxy resin, wherein the epoxy equivalent of the epoxy resin is 400-600, such as 400, 450, 500, 550 or 600, but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0052] In some embodiments of the present invention, the resin having carboxyl groups includes acrylic resin, and the acid value of the acrylic resin is 40-70 mg KOH / g, such as 40 mg KOH / g, 50 mg KOH / g, 60 mg KOH / g or 70 mg KOH / g, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0053] In some embodiments of the present invention, the electrophoretic coating further includes a first neutralizing agent, the content of which is such that the pH of the electrophoretic coating is 8.0-8.5, such as 8.0, 8.1, 8.2, 8.3, 8.4 or 8.5, but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0054] In this invention, the first neutralizing agent is used to maintain the pH of the system, promote resin curing, and improve the stability of the paint film.

[0055] In some embodiments of the present invention, the electrophoretic coating further includes a first functional additive.

[0056] In some embodiments of the present invention, the electrophoretic coating further includes water, the content of which is such that the solid content of the electrophoretic coating is 12-18%, such as 12%, 13%, 14%, 15%, 16%, 17% or 18%, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0057] In some embodiments of the present invention, the first neutralizing agent includes an amine neutralizing agent.

[0058] In some embodiments of the present invention, the first functional additive includes one or more of leveling agents, anti-settling agents, thixotropic agents, thickeners, defoamers, silane coupling agents, or weather-resistant enhancers.

[0059] In this invention, the first functional additives are all additives conventionally used in the art. Those skilled in the art can add and adjust the addition ratio according to their needs, and no special restrictions are imposed here. For example, the leveling agent can be polyether-modified polydimethylsiloxane; the anti-settling agent can be bentonite; and the thixotropic agent can be fumed silica, etc.

[0060] In some embodiments of the present invention, the product comprises, by weight: 50-55 parts of an aqueous resin having hydroxyl groups, 35-45 parts of an aqueous resin having carboxyl groups, 5-10 parts of a curing agent, 5-10 parts of a first filler, 1-2 parts of a leveling agent, 1.3-2 parts of an anti-settling agent, a first neutralizing agent, and water. The curing agent comprises a furan-maleic anhydride adduct, a blocked isocyanate, and 2-methylimidazole in a weight ratio of (3-4):1:(0.25-0.4); The electrophoretic coating has a pH of 8.0-8.5 and a solid content of 12-18%.

[0061] Secondly, the present invention provides an application of the electrophoretic coating as described in the first aspect in the field of vehicle coating.

[0062] Thirdly, the present invention provides a method for low-temperature integrated coating of a vehicle, comprising the following steps: (1) The car body is electrophoresed with the electrophoretic coating as described in the first aspect, then dried for the first time, then sealed with adhesive, and then dried for the second time; The temperature of the first drying is 130-140℃, and the temperature of the second drying is 85-100℃; The plastic parts are assembled onto the car body after the second drying process to form the parts to be sprayed. (2) The coating is completed by sequentially applying the first layer of color paint, the second layer of color paint, color paint leveling, pre-drying, clear varnish spraying, clear varnish leveling, and the third drying to the part to be sprayed. The temperature for the third drying process is 85-100℃.

[0063] The first drying temperature can be selected from 130℃, 132℃, 134℃, 136℃, 138℃ or 140℃, etc.; the second drying temperature can be selected from 85℃, 90℃, 95℃ or 100℃, etc.; the third drying temperature can be selected from 85℃, 90℃, 95℃ or 100℃, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0064] This invention proposes a low-temperature integrated coating process for the entire vehicle based on B1B2, which solves the problem of color difference between the vehicle body and plastic parts. At the same time, by utilizing the electrophoretic coating described in the first aspect, combined with low-temperature adhesive material, low-temperature first layer color paint material and low-temperature second layer color paint material, energy consumption is significantly reduced and time is saved, achieving cost reduction, efficiency improvement and green transformation, and has good application prospects.

[0065] The low-temperature adhesive material (used for sealing the vehicle body to prevent leaks, rust, and corrosion), the low-temperature first coat paint material, and the low-temperature second coat paint material can be commercially available or prepared using methods known to those skilled in the art. No specific limitations are imposed. For example, the low-temperature adhesive material was purchased from Idoco. The low-temperature second coat paint material was purchased from Axalta, with the following models: Hercion GA WB Obsidian Black MBC; Hercion GA WB Crystal White SBC.

[0066] More specifically, the first layer of paint spraying includes the first layer of paint spraying on the outer panel; The second layer of paint spraying includes the second layer of paint spraying on the inner panel and the second layer of paint spraying on the outer panel in sequence. The clear varnish spraying process includes sequential spraying of the inner clear varnish panel and the outer clear varnish panel.

[0067] In some embodiments of the present invention, the first layer of paint comprises, by weight, parts of: 24-44 parts of the second waterborne resin, 4-7 parts of the crosslinking agent, and 10-35 parts of the second filler; The crosslinking agent includes methyl etherified high-imino melamine resin and high-methyl etherified melamine-formaldehyde resin; The weight ratio of the methyl etherified high-imino melamine resin to the high-methyl etherified melamine-formaldehyde resin is (1.5-5):1.

[0068] The weight parts of the second waterborne resin can be 24 parts, 30 parts, 35 parts, 38 parts, 40 parts or 44 parts, etc., but are not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0069] The amount of crosslinking agent added can be 4, 5, 6 or 7 parts by weight, but is not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0070] The weight of the second filler can be 10 parts, 15 parts, 20 parts, 25 parts, 30 parts or 35 parts, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0071] The weight ratio of the methyl etherified high-imino melamine resin to the high-methyl etherified melamine-formaldehyde resin can be 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0072] In this invention, methyl etherified high-imino melamine resin and high-methyl etherified melamine-formaldehyde resin are used as crosslinking agents. By limiting the addition ratio of the two, the drying temperature of the first layer of paint (i.e., the B1 layer of base paint) is effectively reduced, while the curing speed is accelerated, thereby reducing energy consumption.

[0073] If too little methyl etherified high-imino melamine resin is added, it will lead to insufficient cross-linking activity, preventing rapid cross-linking with the functional groups of the second waterborne resin under low-temperature conditions. This will not only fail to achieve the design goal of low-temperature drying of the first layer of paint, but will also prolong drying time, increase energy consumption, and result in low cross-linking density of the paint film, significantly reducing adhesion and hardness. Subsequent interlayer bonding with the second layer of paint will be insufficient, easily leading to interlayer peeling and paint detachment. Simultaneously, the scratch resistance and chemical resistance of the paint film will deteriorate, failing to meet the basic protective requirements of the base coat in automotive painting. Excessive crosslinking can lead to an excessively rapid and intense crosslinking reaction, resulting in poor leveling, orange peel, pinholes, and craters in the paint film during low-temperature drying, affecting the uniformity of the car body paint finish. Furthermore, excessive crosslinking increases brittleness and reduces impact resistance, making the paint film prone to cracking at corners and bends on the car body. In addition, excessive high-imino components can reduce the storage stability of the coating system, leading to gelation and delamination, while also increasing raw material costs. It may also reduce the water resistance of the paint film, causing it to whiten and lose gloss when exposed to humid environments for extended periods.

[0074] If too little highly methylated melamine-formaldehyde resin is added, it will lead to decreased compatibility of the coating system, poor dispersion uniformity of the second water-based resin and crosslinking agent, and appearance defects such as particles and pitting in the paint film after spraying, affecting the decorative effect of the first layer of color paint. At the same time, its role in assisting crosslinking and improving the density of the paint film cannot be fully utilized, resulting in insufficient water resistance, weather resistance, and chemical resistance of the paint film, making it difficult to resist the erosion of rainwater and car wash liquid during automobile use. In addition, the overall crosslinking rate cannot be effectively adjusted, which easily leads to uneven curing of the first layer of color paint and fluctuations in paint film performance. Excessive amounts of certain components can slow down the cross-linking reaction rate, making it difficult to keep up with the production cycle of the first layer of paint drying at low temperatures, thus extending the production line cycle and increasing energy consumption. Furthermore, excessive amounts of highly methylated components can lead to a higher gloss level in the paint film, which can result in color differences and uneven gloss when combined with the second layer of paint, affecting the overall coating quality of the car body. It can also cause the paint film to have an excessively high cross-linking density, resulting in poor flexibility, insufficient impact resistance, and a tendency to crack. Additionally, excessive components may not fully participate in the cross-linking reaction and remain in the paint film, leading to accelerated aging and chalking of the paint film after long-term use.

[0075] This invention also improves the performance of the coating film while ensuring cost by adding an appropriate amount of filler (i.e., extender pigment). For example, the filler can be natural hydrated magnesium silicate to improve the coating's abrasion resistance and scratch resistance; or barium sulfate to improve the coating's hardness, chemical resistance, and insulation properties. Those skilled in the art can choose different fillers according to their needs, and no special limitations are imposed here.

[0076] It should be noted that "high methyl etherification" in high methyl etherification melamine-formaldehyde resin refers to a degree of etherification greater than 80%.

[0077] In some embodiments of the present invention, the second aqueous resin comprises, by weight, 3-5 parts of aliphatic polyurethane acrylate hybrid resin, 10-15 parts of aliphatic polyurethane-acrylic acid hybrid dispersion, 4-5 parts of aqueous acrylic copolymer, 10-15 parts of aqueous polyurethane dispersion, and 2-4 parts of aqueous aliphatic self-crosslinking polyurethane resin.

[0078] The aliphatic polyurethane acrylate hybrid resin can be in parts by weight of 3, 4, or 5, etc. The weight parts of the aliphatic polyurethane-acrylic hybrid dispersion can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, etc. The waterborne acrylic copolymer can be in parts by weight of 4, 4.5, or 5, etc. The waterborne polyurethane dispersion can be in parts by weight of 10, 11, 12, 13, 14, or 15, etc. The waterborne aliphatic self-crosslinking polyurethane resin can be in parts by weight of 2, 3, or 4, but is not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0079] This invention effectively improves the final quality by selecting suitable resin components and controlling the appropriate addition ratio. Specifically, aliphatic polyurethane-acrylate hybrid resin provides excellent weather resistance, abrasion resistance, and adhesion, enhancing the mechanical properties of the coating; aliphatic polyurethane-acrylic hybrid dispersion provides excellent flexibility, impact resistance, and chemical resistance, enhancing coating adhesion; waterborne acrylic copolymer improves the directional alignment of aluminum powder, improving the gloss and weather resistance of the paint film; waterborne polyurethane dispersion imparts excellent elasticity, abrasion resistance, and hydrolysis resistance to the paint film; and waterborne aliphatic self-crosslinking polyurethane resin improves the hardness and chemical resistance of the paint film, making it suitable for baking-type systems.

[0080] In some embodiments of the present invention, the first layer of paint further includes coloring pigments.

[0081] In this invention, the coloring pigments include, but are not limited to, one or more of iron oxide yellow, iron oxide red, carbon black, and carbon black. Those skilled in the art may add other types of pigments as needed, and no special limitations are imposed herein.

[0082] In some embodiments of the present invention, the first layer of paint further includes a second neutralizing agent, the content of which makes the pH of the first layer of paint 8.0-8.5, such as 8.0, 8.1, 8.2, 8.3, 8.4 or 8.5, but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0083] In some embodiments of the present invention, the first layer of paint further includes a second functional additive.

[0084] In some embodiments of the present invention, the first layer of paint further includes water, the content of which makes the solid content of the first layer of paint 12-18%, such as 12%, 13%, 14%, 15%, 16%, 17% or 18%, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0085] In some embodiments of the present invention, the second neutralizing agent includes an amine neutralizing agent.

[0086] In some embodiments of the present invention, the second functional additive includes one or more of the following: defoamer, dispersant, wetting agent, thixotropic agent, cosolvent, thickener, leveling agent, rheology modifier, or slip agent.

[0087] In this invention, the second functional additives are all additives conventionally used in the art. Those skilled in the art can add and adjust the addition ratio according to their needs, and no special restrictions are imposed here. Exemplarily, defoamers include, but are not limited to, polyether siloxane copolymers; dispersants include, but are not limited to, copolymers containing pigment affinity groups; wetting agents include, but are not limited to, isotridecyl alcohol and polyether-modified siloxanes; thixotropic agents include, but are not limited to, fumed silica; cosolvents include, but are not limited to, one or more of ethylene glycol monobutyl ether, ethanol, and 2-ethylhexanol; thickeners include, but are not limited to, high molecular weight polyacrylates; rheology modifiers include, but are not limited to, refined lithium montmorillonite clay; leveling agents include, but are not limited to, polyether-modified siloxanes; and slip agents include, but are not limited to, polytetrafluoroethylene wax emulsions.

[0088] In some embodiments of the present invention, the first layer of paint comprises, by weight, 3-5 parts of aliphatic polyurethane acrylate hybrid resin, 10-15 parts of aliphatic polyurethane-acrylic hybrid dispersion, 4-5 parts of waterborne acrylic copolymer, 10-15 parts of waterborne polyurethane dispersion, 2-4 parts of waterborne aliphatic self-crosslinking polyurethane resin, 4-7 parts of crosslinking agent, 10-35 parts of second filler, 15-30 parts of coloring pigment, 9-20 parts of second functional additive, second neutralizer, and water; The crosslinking agent comprises methyl etherified high-imino melamine resin and high-methyl etherified melamine-formaldehyde resin in a weight ratio of (1.5-5):1. The pH of the first layer of paint is 8.0-8.5, and the solid content of the first layer of paint is 12-18%.

[0089] This invention does not impose any special limitations on the preparation methods of the above-mentioned coating layers. The following is an exemplary method for preparing an electrophoretic coating, comprising: (1) Stir the first water-based resin at 40-50℃ and 300-500rpm for 30-40 minutes to form a uniform and transparent resin matrix; then slowly add the first functional additive and the first filler while stirring to fully disperse the components; then transfer the stirred material to a grinding mill and grind it to a fineness of ≤15μm using 0.3-0.8mm zirconium beads as the grinding medium to obtain a uniform and stable resin mixture. (2) Cool the resin mixture to below 35°C, slowly add the prepared curing agent, and stir continuously at 300-400 rpm for 60-90 minutes to fully disperse the curing agent and resin mixture, forming a stable, gel-free, and non-layered electrophoretic coating stock solution; then, add deionized water to adjust the solid content to 12-18%, and adjust the pH value to 8.0-8.5 with a neutralizing agent, continue stirring for 30 minutes, and let stand for 24 hours to obtain the electrophoretic coating.

[0090] The following is an exemplary method for preparing a first layer of paint, comprising: (1) Mix water, cosolvent, dispersant and part of wetting agent thoroughly, then add rheology modifier, second filler, coloring pigment, part of defoamer and second neutralizer, and keep the pH of the system at 8-9 to obtain pre-dispersion; Keep stirring throughout the process, and adjust the stirring speed as needed. (2) Transfer the pre-dispersed liquid to a grinding mill and use 0.8-1.2 mm zirconia beads as grinding media for grinding. Adjust the speed during the grinding process until the fineness of the slurry is ≤15 μm. During this period, monitor the outlet temperature of the sand mill to ≤45℃ to prevent resin degradation. (3) Add the second water-based resin, crosslinking agent, thickener, remaining wetting agent, slip agent and remaining defoamer to the ground slurry, and then adjust the viscosity to 25-35s / 25℃ by adding cosolvent and / or water. Retest the pH value. If it deviates from 8.0-9.0, add the second neutralizing agent to ensure the stability of the coating performance. Keep stirring throughout the process, and adjust the stirring speed as needed.

[0091] To make the technical problems solved, technical solutions, and beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0092] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with conventional techniques or conditions in the art, techniques or conditions described in the literature, or product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0093] Example 1 This embodiment provides an electrophoretic coating, comprising, by weight: 52 parts of epoxy resin (epoxy equivalent 500); 40 parts of acrylic resin (acid value 60 mg KOH / g); 8 parts curing agent; Leveling agent (polyether-modified polydimethylsiloxane): 1.5 parts; Anti-settling agent (bentonite) 1 part; Thixotropic agent (fumed silica) 0.7 parts: First filler (titanium dioxide and carbon black, weight ratio 9:1) 8 parts; Neutralizing agent (dimethylethanolamine) 3 parts; Deionized water: appropriate amount, used for dilution to achieve a solid content of 15% for the electrophoretic coating; The curing agent comprises furan-maleic anhydride adduct (purchased from Aladdin), blocked isocyanate (purchased from Covestro, product number: BL3370MPA), and 2-methylimidazole in a weight ratio of 3.5:1:0.3.

[0094] The electrophoretic coating in this embodiment refers to the method listed in the specific implementation details, specifically as follows: (1) Stir epoxy resin and acrylic resin at 45°C and 400 rpm for 35 minutes to form a uniform and transparent resin matrix; then slowly add leveling agent, dust suppressant, thixotropic agent and first filler while stirring to fully disperse each component; then transfer the stirred material to a grinding mill and grind it to a fineness of ≤15μm using 0.3-0.8mm zirconium beads as grinding media to obtain a uniform and stable resin mixture; (2) Cool the resin mixture to below 35°C, slowly add the prepared curing agent, and stir continuously at 350 rpm for 80 minutes to fully disperse the curing agent and resin mixture, forming a stable, gel-free, and non-layered electrophoretic coating stock solution; then, add deionized water to adjust the solid content to 15%, and adjust the pH value to 8.0-8.5 with a neutralizing agent, continue stirring for 30 minutes, and let stand for 24 hours to obtain the electrophoretic coating.

[0095] Example 2 This embodiment provides an electrophoretic coating, which differs from Embodiment 1 only in that the curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole in a weight ratio of 3:1:0.25.

[0096] Example 3 This embodiment provides an electrophoretic coating, which differs from Embodiment 1 only in that the curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole in a weight ratio of 4:1:0.4.

[0097] Example 4 This embodiment provides an electrophoretic coating, which differs from Embodiment 1 only in that the curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole in a weight ratio of 6:1:0.3.

[0098] Example 5 This embodiment provides an electrophoretic coating, which differs from Embodiment 1 only in that the curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole in a weight ratio of 1:1:0.3.

[0099] Example 6 This embodiment provides an electrophoretic coating, which differs from Embodiment 1 only in that the curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole in a weight ratio of 3.5:2:0.3.

[0100] Example 7 This embodiment provides an electrophoretic coating, which differs from Embodiment 1 only in that the curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole in a weight ratio of 3.5:0.1:0.3.

[0101] Example 8 This embodiment provides an electrophoretic coating, which differs from Embodiment 1 only in that the curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole in a weight ratio of 3.5:1:0.6.

[0102] Example 9 This embodiment provides an electrophoretic coating, which differs from Embodiment 1 only in that the curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole in a weight ratio of 3.5:1:0.1.

[0103] Comparative Example 1 This comparative example provides an electrophoretic coating that differs from Example 1 only in that it does not contain furan-maleic anhydride adducts, but the weight ratio of blocked isocyanate and 2-methylimidazole remains unchanged.

[0104] Comparative Example 2 This comparative example provides an electrophoretic coating that differs from Example 1 only in that it does not contain a blocked isocyanate, but the weight ratio of furan-maleic anhydride adduct to 2-methylimidazole remains unchanged.

[0105] Comparative Example 3 This comparative example provides an electrophoretic coating that differs from Example 1 only in that 2-methylimidazole is not added, but the weight ratio of furan-maleic anhydride adduct to blocked isocyanate remains unchanged.

[0106] Comparative Example 4 This comparative example provides an electrophoretic coating, whose raw material composition, by weight, is as follows: Epoxy resin (epoxy equivalent 450) 55 parts; Acrylic resin (acid value 50 mg KOH / g) 35 parts; Curing agent (blocked isocyanate, purchased from Covestro, product number: BL3125SN) 10 parts; Leveling agent (polyether-modified polydimethylsilane) 1.2 parts; Dust suppressant (bentonite) 0.8 parts; First filler (titanium dioxide and carbon black, weight ratio 10:1) 7 parts; Neutralizing agent (triethanolamine) 2.5 parts; Use an appropriate amount of deionized water to make the content of the electrophoretic coating 16%.

[0107] Electrophoretic coating performance testing First, referring to the GB1727-1992 standard, the treated tinplate was connected to the electrodes and immersed in the electrophoretic coating. The electrophoresis parameters were: electrophoresis voltage 80V, electrophoresis time 30S, electrode spacing 10cm, and electrophoresis temperature 25℃.

[0108] 1. Curing temperature test: Place the electrophoretic tinplate in an oven and test the minimum temperature required to form a stable paint film within a baking time of 0.5 hours. 2. Pencil hardness: Measured according to Q / JL J130020 standard; 3. Paint film impact: Measured according to GB / T 1732 standard; 4. Paint film flexibility: Measured according to GB / T 1731 standard; 5. Adhesion (1mm cross-cut): Measured according to Q / JL J174010 standard; 6. Adhesion (scratch test): Measured according to Q / JL J174010 standard; 7. Cupping: Measured according to GB / T 9753 standard; 8. Gasoline resistance: Tested according to Q / JL J130009 standard; 9. Moisture resistance: Tested according to Q / JL J174008 standard; 10. Edge coverage: Measured according to Q / JL J130005 standard; 11. Corrosion resistance: Tested according to Q / JL J130006 standard; 12. Stone impact resistance was measured according to standard Q / JLJ174006; 13. Water resistance was measured according to standard Q / JLJ130018; 14. Acid resistance was measured according to standard Q / JLJ130009; 15. Alkali resistance was measured according to standard Q / JLJ130009; The test results are shown in Table 1.

[0109] Table 1

[0110]

[0111] Continued from Table 1

[0112]

[0113] Continued from Table 1

[0114] Examples 1-3 of this invention utilize the synergistic crosslinking of furan-maleic anhydride, blocked isocyanate, and 2-methylimidazole, along with precise catalysis, to achieve low-temperature curing at 135-140℃, with all performance characteristics meeting the test standards. Examples 4-9, due to excessive or insufficient amounts of a single curing agent component, exhibit uneven crosslinking networks or reduced density, resulting in a slight decrease in some properties. Comparative Examples 1-3 lack any curing agent component, have no synergistic crosslinking system, and fail to cure at low temperatures (requiring 165-180℃), leading to significant deterioration in various properties. Comparative Example 4 is a conventional single isocyanate system without synergistic catalysis, exhibiting a high curing temperature (170℃) and weaker performance.

[0115] Application Example 1 This application example provides a method for integrated low-temperature coating of a vehicle, and its process flow diagram is as follows: Figure 1 As shown, it includes: (1) The car body is electrophoresed with the electrophoretic coating described in Example 1, then dried at 140°C for the first time, then coated with adhesive, and then dried at 90°C for the second time; The plastic parts are assembled onto the car body after the second drying process to form the parts to be sprayed. (2) The coating is completed by sequentially spraying the outer panel with the first layer of colored paint, spraying the inner panel with the second layer of colored paint, spraying the outer panel with the second layer of colored paint, leveling the colored paint, pre-drying, spraying the inner panel with clear varnish, spraying the outer panel with clear varnish, leveling the clear varnish, and drying the third layer of paint on the part to be sprayed. The pre-drying temperature is 90°C; the third drying temperature is 95°C.

[0116] The adhesive material used for applying the glue was provided by Edoco. The composition of the first layer of paint is shown in Table 2: Table 2

[0117]

[0118] The second coat of paint was Hercion GA WB Crystal White SBC, supplied by Axalta. The varnish is Hercion GA High Performance 2K Varnish, and the Hercion GA High Performance 2K Varnish Hardener are both provided by Axalta. The specific proportions are formulated according to the manufacturer's instructions.

[0119] Comparative Application Example 1 This comparative application example provides a method for integrated vehicle painting, including: (1) The car body was electrophoresed with the electrophoretic coating described in Comparative Example 4, then dried at 170°C for the first time, then sealed with adhesive, and then dried at 155°C for the second time. The plastic parts are assembled onto the car body after the second drying process to form the parts to be sprayed. (2) The coating is completed by sequentially spraying the outer panel with the first layer of colored paint, spraying the inner panel with the second layer of colored paint, spraying the outer panel with the second layer of colored paint, leveling the colored paint, pre-drying, spraying the inner panel with clear varnish, spraying the outer panel with clear varnish, leveling the clear varnish, and drying the third layer of paint on the part to be sprayed. The pre-drying temperature is 90°C; the third drying temperature is 140°C.

[0120] The adhesive material used for applying the glue was provided by Edoco. The first coat of paint consists of Hercion GA WB Deep Grey BC1, Hercion GA WB White BC1, and Hercion GA BC1 Hardener, all provided by Axalta. The specific mixing ratio should be followed according to the manufacturer's mixing instructions. The second coat of paint was Hercion GA WB Crystal White SBC, supplied by Axalta. The varnish is Hercion GA High Performance 2K Varnish, and the Hercion GA High Performance 2K Varnish Hardener are both provided by Axalta. The specific proportions are formulated according to the manufacturer's instructions.

[0121] The performance quality of the topcoat (color paint + clear coat) in Comparative Application Example 1 and Comparative Application Example 1 is shown in Table 3.

[0122] Among them, average gloss: measured in accordance with GB / T 9754 standard; Orange peel results and DOI (freshness index): both were obtained by orange peel analyzer. Pencil hardness: Measured according to Q / JL J130020 standard; Interlayer compatibility: Adhesion (cross-cut test): measured according to Q / JL J174010 standard; Adhesion (scratch test): measured according to Q / JL J174010 standard; The test results are shown in Table 3.

[0123] Table 3

[0124] As shown in Table 3, apart from the baking temperature required for curing, the performance parameters of Application Example 1 and Comparative Application Example 1 are basically the same. This indicates that the performance of the low-temperature integrated paint meets the standard and can be cured at a lower temperature compared with conventional paint, which can effectively reduce energy consumption.

[0125] The following table shows the performance evaluation of the whole vehicle paint film corresponding to Use Case 1 and Comparative Application Example 1.

[0126] Table 4

[0127]

[0128] Wherein, ED represents the electrophoretic paint film layer; BC1 represents the first color paint layer; BC2 represents the second color paint layer; and CC represents the clear coat layer.

[0129] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0130] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrophoretic coating, characterized in that, By weight, the electrophoretic coating comprises: 85-100 parts of a first water-based resin, 5-10 parts of a curing agent, and 5-10 parts of a first filler; The first aqueous resin includes aqueous resins having hydroxyl groups and aqueous resins having carboxyl groups; The curing agent includes furan-maleic anhydride adduct, blocked isocyanate, and 2-methylimidazole.

2. The electrophoretic coating according to claim 1, characterized in that, The weight ratio of the furan-maleic anhydride adduct, the blocked isocyanate, and the 2-methylimidazole is (3-4):1:(0.25-0.4).

3. The electrophoretic coating according to claim 1 or 2, characterized in that, In the electrophoretic coating, the waterborne resin with hydroxyl groups is 50-55 parts by weight, and the waterborne resin with carboxyl groups is 35-45 parts by weight. And / or, the aqueous resin having hydroxyl groups includes an epoxy resin, wherein the epoxy equivalent of the epoxy resin is 400-600. And / or, the aqueous resin having a carboxyl group includes an acrylic resin, the acrylic resin having an acid value of 40-70 mg KOH / g.

4. The electrophoretic coating according to any one of claims 1-3, characterized in that, The electrophoretic coating further includes a first neutralizing agent, the content of which is such that the pH of the electrophoretic coating is 8.0-8.5; And / or, the electrophoretic coating further includes a first functional additive; And / or, the electrophoretic coating further includes water, the content of which is such that the solid content of the electrophoretic coating is 12-18%.

5. The electrophoretic coating according to claim 4, characterized in that, The first neutralizing agent includes amine neutralizing agents; And / or, the first functional additive includes one or more of the following: leveling agent, anti-settling agent, thixotropic agent, thickener, defoamer, silane coupling agent, or weather-resistant enhancer.

6. The electrophoretic coating according to claim 1, characterized in that, By weight, it comprises: 50-55 parts of waterborne resin with hydroxyl groups, 35-45 parts of waterborne resin with carboxyl groups, 5-10 parts of curing agent, 5-10 parts of first filler, 1-2 parts of leveling agent, 1.3-2 parts of anti-settling agent, first neutralizing agent and water; The curing agent comprises a furan-maleic anhydride adduct, a blocked isocyanate, and 2-methylimidazole in a weight ratio of (3-4):1:(0.25-0.4); The electrophoretic coating has a pH of 8.0-8.5 and a solid content of 12-18%.

7. The application of the electrophoretic coating as described in any one of claims 1-6 in the field of vehicle coating.

8. A method for integrated low-temperature coating of a vehicle, characterized in that, The method includes the following steps: (1) The car body is electrophoretically coated with the electrophoretic coating as described in any one of claims 1-6, then dried for the first time, then sealed with adhesive, and then dried for the second time; The temperature of the first drying is 130-140℃, and the temperature of the second drying is 85-100℃; The plastic parts are assembled onto the car body after the second drying process to form the parts to be sprayed. (2) The coating is completed by sequentially applying the first layer of color paint, the second layer of color paint, color paint leveling, pre-drying, clear varnish spraying, clear varnish leveling, and the third drying to the part to be sprayed. The temperature for the third drying process is 85-100℃.

9. The method according to claim 8, characterized in that, The first layer of paint comprises, by weight: 24-44 parts of the second waterborne resin, 4-7 parts of the crosslinking agent, and 10-35 parts of the second filler; The crosslinking agent includes methyl etherified high-imino melamine resin and high-methyl etherified melamine-formaldehyde resin; The weight ratio of the methyl etherified high-imino melamine resin to the high-methyl etherified melamine-formaldehyde resin is (1.5-5):

1.

10. The method according to claim 9, characterized in that, By weight, the second waterborne resin comprises 3-5 parts of aliphatic polyurethane acrylate hybrid resin, 10-15 parts of aliphatic polyurethane-acrylic acid hybrid dispersion, 4-5 parts of waterborne acrylic copolymer, 10-15 parts of waterborne polyurethane dispersion and 2-4 parts of waterborne aliphatic self-crosslinking polyurethane resin. And / or, the first layer of paint further includes coloring pigments; And / or, the first layer of paint further includes a second neutralizing agent, the amount of which makes the pH of the first layer of paint equal to 8.0-8.5; And / or, the first layer of paint further includes a second functional additive; And / or, the first layer of paint also includes water, the amount of which makes the solid content of the first layer of paint 12-18%.

11. The method according to claim 10, characterized in that, The second neutralizing agent includes amine neutralizing agents; And / or, the second functional additive includes one or more of the following: defoamer, dispersant, wetting agent, thixotropic agent, cosolvent, thickener, rheology modifier, leveling agent, or slip agent.

12. The method according to claim 9, characterized in that, By weight, the first layer of paint comprises 3-5 parts of aliphatic polyurethane acrylate hybrid resin, 10-15 parts of aliphatic polyurethane-acrylic hybrid dispersion, 4-5 parts of waterborne acrylic copolymer, 10-15 parts of waterborne polyurethane dispersion, 2-4 parts of waterborne aliphatic self-crosslinking polyurethane resin, 4-7 parts of crosslinking agent, 10-35 parts of second filler, 15-30 parts of coloring pigment, 9-20 parts of second functional additive, second neutralizer and water; The crosslinking agent comprises methyl etherified high-imino melamine resin and high-methyl etherified melamine-formaldehyde resin in a weight ratio of (1.5-5):

1. The pH of the first layer of paint is 8.0-8.5, and the solid content of the first layer of paint is 12-18%.

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