A mass-producible four-coat two-bake topcoat spraying method and topcoat

Abstract

The application provides a mass-producible four-coating and two-baking top paint spraying method and top paint, and belongs to the technical field of vehicle body spraying, and aims to solve the problem of vehicle polishing in the process of multi-layer varnish top paint, the method comprising the following steps: spraying water-based intermediate coating and color paint on the vehicle body treated by electrophoresis in sequence, and performing flash drying treatment; spraying single-component varnish or double-component varnish on the vehicle body, and performing baking treatment; then, polishing the defect points on the vehicle body, spraying double-component varnish, and performing baking treatment again to obtain a four-coating and two-baking top paint vehicle body; the single-component varnish comprises 35-45 parts of acrylic resin, 13-18 parts of first amino resin, 18-23 parts of anti-sagging resin, 5-8 parts of polyester resin, 1.5-2 parts of additive and 15-18 parts of solvent in terms of weight; the double-component varnish comprises a main agent and a curing agent, the main agent comprises 35-47 parts of acrylic resin, 14-24 parts of second amino resin, 16-25 parts of anti-sagging resin, 0.8-1.3 parts of additive and 15-38 parts of solvent; and the curing agent comprises a polyisocyanate curing agent.

Description

Technical Field

[0001] This invention relates to the field of vehicle body painting technology, and in particular to a mass-producible four-coat two-bake topcoat spraying method and topcoat. Background Technology

[0002] Currently, in order to ensure the quality of automotive paint, a multi-layer clear coat process is often used to spray the car body.

[0003] However, the process of applying multiple layers of clear coat and topcoat often requires sanding and finishing the entire vehicle, resulting in low efficiency and an inability to meet the needs of mass production. Summary of the Invention

[0004] In view of this, the present invention proposes a mass-producible four-coat two-bake topcoat spraying method to solve the problem of needing to sand the entire vehicle during the multi-layer clear coat topcoat process.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] In a first aspect, the present invention provides a mass-producible four-coat, two-bake topcoat spraying method, the method comprising:

[0007] Step S1: Spray water-based intermediate coat and color paint sequentially onto the electrophoretic treated car body to form a water-based intermediate coat and a color paint layer, and then perform flash drying treatment.

[0008] Step S2: After the flash-drying process is completed, a single-component or two-component clear coat is sprayed onto the vehicle body to form a first clear coat layer, and then the vehicle body is dried.

[0009] Step S3: After the drying process is completed, the defect points on the vehicle body are sanded, the two-component clear coat is sprayed to form a second clear coat layer, and the drying process is performed again to obtain a four-coat, two-bake topcoat vehicle body.

[0010] The single-component varnish, by weight, comprises: 35-45 parts acrylic resin, 13-18 parts first amino resin, 18-23 parts anti-sagging resin, 5-8 parts polyester resin, 1.5-2 parts additives, and 15-18 parts solvent.

[0011] The two-component varnish comprises a main agent and a curing agent. The main agent comprises: 35-47 parts of the acrylic resin, 14-24 parts of the second amino resin, 16-25 parts of the anti-sagging resin, 0.8-1.3 parts of the additives, and 15-38 parts of the solvent. The curing agent comprises a polyisocyanate curing agent.

[0012] Optionally, in step S2, the main component of the sprayed two-component varnish, by weight, comprises: 35-45 parts of the acrylic resin, 14-18 parts of the second amino resin, 16-23 parts of the anti-sagging resin, 0.8-1.2 parts of the additives, and 28-28 parts of the solvent.

[0013] In step S3, the main component of the two-component varnish sprayed, by weight, comprises: 39-47 parts of the acrylic resin, 18-24 parts of the second amino resin, 19-25 parts of the anti-sagging resin, 1-1.3 parts of the additives, and 15-25 parts of the solvent.

[0014] Optionally, in step S2, the main agent and the curing agent are mixed in a first preset ratio, wherein the first preset ratio is 3.5:1 to 4:1;

[0015] In step S3, the main agent and the curing agent are mixed in a second preset ratio, which is 3:1 to 3.5:1.

[0016] Optionally, the acrylic resin includes one or a mixture of (meth)acrylate, (meth)acrylate, (meth)acrylate, (meth)acrylate, (meth)acrylate, (meth)acrylate, and lauryl methacrylate in any proportion.

[0017] Optionally, the first amino resin includes one or a mixture of multiple types of butylated melamine resin, mixed etherified melamine resin, methylated melamine resin, or methylated hexamethylol melamine resin in any proportion;

[0018] The second amino resin includes one or a mixture of methyl etherified melamine resin and methyl etherified hexamethylol melamine resin in any proportion.

[0019] Optionally, the anti-sagging resin includes one or a mixture of multiple types of modified acrylic resin and polyamide wax paste in any proportion.

[0020] Optionally, the additives include one or a mixture of leveling agents, defoamers, and drying agents in any proportion;

[0021] The leveling agent comprises one or a mixture of multiple types of modified organosilicon, epoxy-modified polyacrylate, and modified organopolysiloxane polyisocyanate; the defoamer comprises one or a mixture of multiple types of polyamide hydrophobic particle polymer and propylene glycol methyl ether acetate; and the drying agent comprises one or a mixture of multiple types of dibutyltin dilaurate and p-toluenesulfonic acid amino salt solution.

[0022] Optionally, the solvent includes one or a mixture of ethyl acetate, solvent oil, ethylene glycol butyl ether acetate, diethylene glycol butyl ether, dimethyl carbonate, isopropanol, and diethyl carbonate in any proportion.

[0023] Optionally, the flash-drying treatment includes flash-drying the vehicle body at 75-80°C for 4-6 minutes;

[0024] The drying process includes baking at 130–150°C for 20–30 minutes.

[0025] Optionally, in step S1, the thickness of the water-based intermediate coat is 9-15 μm, and the thickness of the colored paint is 10-15 μm.

[0026] In step S2, the thickness of the single-component varnish or the two-component varnish is 25-35 μm.

[0027] In step S3, the thickness of the two-component varnish is 35-50 μm.

[0028] Optionally, the thickness of the water-based intermediate coating is 9-15 μm; the thickness of the color paint layer is 10-15 μm; the thickness of the first clear varnish layer is 25-35 μm; and the thickness of the second clear varnish layer is 45-60 μm.

[0029] In a second aspect, the present invention provides a topcoat, comprising:

[0030] A water-based intermediate coating, a color paint layer, a first clear coat layer, and a second clear coat layer are sequentially layered on the surface of the vehicle body; wherein...

[0031] By weight, the first varnish layer is formed by spraying a single-component varnish or a two-component varnish, and the second varnish layer is formed by spraying a two-component varnish.

[0032] The single-component varnish comprises: 35-45 parts acrylic resin, 13-18 parts first amino resin, 18-23 parts anti-sagging resin, 5-8 parts polyester resin, 1.5-2 parts additives and 15-18 parts solvent.

[0033] The two-component varnish comprises a main agent and a curing agent. The main agent comprises: 35-47 parts of the acrylic resin, 14-24 parts of the second amino resin, 16-25 parts of the anti-sagging resin, 0.8-1.3 parts of the additives, and 15-38 parts of the solvent. The curing agent comprises a polyisocyanate curing agent.

[0034] The present invention has the following advantages over the prior art:

[0035] This invention proposes specialized single-component and two-component clear coats. By reducing the weight percentage of additives in the single-component and two-component clear coats, the surface roughness of the resulting paint film is significantly improved after spraying. This facilitates the formation of physical forces between paint layers through hydrogen bonding or mechanical bonding, enhancing interlayer adhesion. Consequently, after the first drying process, the entire vehicle does not need to be sanded; only defective areas on the body need to be sanded. Furthermore, this invention reduces the weight percentage of the first amino resin in the single-component clear coat and the second amino resin in the two-component clear coat. This reduces the crosslinking density after spraying, leaving more active sites. This allows for further chemical reactions during the second drying process in step S3, greatly improving interlayer adhesion. Therefore, a four-coat, two-bake topcoat body can be obtained without sanding the body. Therefore, this invention reduces the amount of sanding on the car body during the entire painting process, and even eliminates sanding after the second drying process, greatly saving time and improving production efficiency to meet the needs of mass production of vehicles. Secondly, because this invention reduces the amount of sanding on the car body, it avoids problems such as excessive paint particles and pinhole defects after sanding. In addition, this invention adopts a four-coat, two-bake topcoat process, which improves the overall appearance, smoothness, gloss, and fullness of the paint surface, significantly enhancing the appearance of the paint surface and surpassing the paint quality level of the traditional 3C2B (three-coat, two-bake) process. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart illustrating the steps of a mass-producible four-coat, two-bake topcoat spraying method according to an embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of a four-coat, two-bake topcoat body according to an embodiment of the present invention. Detailed Implementation

[0039] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, preferred embodiments of the present invention will be described in detail below with reference to examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the present invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and intent. Unless otherwise specified, the materials, reagents, etc., used in the following examples are commercially available.

[0040] In related technologies, the 3C2B (three coats, two bakes) process is commonly used for vehicle body painting. In this process, after the first clear coat is applied and baked, the entire vehicle surface must be sanded to address interlayer adhesion issues. This process is inefficient and labor-intensive. After the second clear coat is applied and baked, defects such as particles and pinholes are prone to appear in the paint film, requiring further sanding. In other words, sanding is necessary after each baking cycle, resulting in a long painting time and a production cycle insufficient for mass production of more than 30 vehicles per hour, making it only suitable for prototype manufacturing. Furthermore, sanding the vehicle body can easily cause defects such as particles and pinholes on the paint surface, affecting paint quality.

[0041] In view of this, this invention proposes a mass-producible four-coat, two-bake topcoat spraying method and topcoat. By improving the adhesion between paint layers, it reduces or even eliminates the need for sanding the vehicle body, thereby saving process time, improving production efficiency, and meeting the needs of mass production of vehicles. Specific implementation details are as follows:

[0042] In a first aspect, the present invention provides a four-coat, two-bake topcoat spraying method. Figure 1 A flowchart illustrating the steps of a mass-producible four-coat, two-bake topcoat spraying method according to an embodiment of the present invention is shown, as follows: Figure 1 As shown, the method includes the following steps:

[0043] Step S1: Spray water-based intermediate coat and color paint sequentially onto the electrophoretic treated car body to form a water-based intermediate coat and a color paint layer, and then perform flash drying treatment.

[0044] Step S2: After the flash-drying process is completed, a single-component or two-component clear coat is sprayed onto the vehicle body to form a first clear coat layer, and then the vehicle body is dried.

[0045] Step S3: After the drying process is completed, the defect points on the vehicle body are sanded, the two-component clear coat is sprayed to form a second clear coat layer, and the drying process is performed again to obtain a four-coat, two-bake topcoat vehicle body.

[0046] The single-component varnish, by weight, comprises: 35-45 parts acrylic resin, 13-18 parts first amino resin, 18-23 parts anti-sagging resin, 5-8 parts polyester resin, 1.5-2 parts additives, and 15-18 parts solvent.

[0047] The two-component varnish comprises a main agent and a curing agent. The main agent comprises: 35-47 parts of the acrylic resin, 14-24 parts of the second amino resin, 16-25 parts of the anti-sagging resin, 0.8-1.3 parts of the additives, and 15-38 parts of the solvent. The curing agent comprises a polyisocyanate curing agent.

[0048] In this embodiment of the invention, a four-coat, two-bake topcoat process is used to paint the vehicle body. First, the vehicle body undergoes electrophoresis treatment to obtain an electrophoretic body. Then, a water-based intermediate coat and a color paint are sequentially sprayed onto the electrophoretic body. The color paint can be any color. After the color paint is applied, the vehicle body undergoes flash-drying treatment. Specifically, the vehicle is moved into a flash-drying oven for leveling and dehydration.

[0049] After flash-drying, a single-component clear coat can be applied to the car body base. It can be used directly after dilution and requires a shorter drying time, thus improving production efficiency. In this embodiment of the invention, to further shorten the process cycle and improve production efficiency, the single-component clear coat comprises: 35-45 parts acrylic resin, 13-18 parts first amino resin, 18-23 parts anti-sagging resin, 5-8 parts polyester resin, 1.5-2 parts additives, and 15-18 parts solvent.

[0050] The additives include one or more of the following: leveling agents, defoamers, and driers, or a mixture of these in any proportion. Leveling agents reduce the surface tension between the single-component clear coat and the vehicle body, ensuring good wetting properties and preventing the formation of surface tension gradients between substances that cause pinholes. They also adjust solvent evaporation rates, reduce viscosity, improve the flowability of the single-component clear coat, and extend leveling time, resulting in a more glossy paint film. Defoamers have a self-defoaming effect, preventing microbubbles and effectively improving the surface of the paint film from bubbling. Driers shorten the curing time of the coating, increase film strength and water resistance, and also facilitate pigment wetting and dispersion, improving the viscoelasticity of the coating.

[0051] In this embodiment of the invention, 1.5 to 2 parts of additives are used. This reduces the amount of additives, especially the amount of leveling agent, which can improve the surface roughness of the formed paint film. This is beneficial for the formation of physical forces between layers in the form of hydrogen bonds or mechanical bonding, thereby enhancing the adhesion between paint layers.

[0052] Therefore, after applying a single-component clear coat as a base coat and drying the vehicle body, there is no need to sand the entire vehicle; only the defective areas on the body need to be sanded. The drying process can include moving the vehicle into a topcoat oven for leveling and curing. Defective areas on the body can be sanded using 2000-grit sandpaper.

[0053] After sanding down the defective areas on the vehicle body, a two-component clear coat can be applied. The two-component clear coat consists of a base agent and a curing agent. The base agent includes 35–47 parts acrylic resin, 14–24 parts second amino resin, 16–25 parts anti-sagging resin, 0.8–1.3 parts additives, and 15–38 parts solvent. The curing agent includes a polyisocyanate curing agent. The curing agent accelerates the film-forming speed of the base agent, improving production efficiency.

[0054] In one example, the polyisocyanate curing agent may include aliphatic polyisocyanates and alicyclic polyisocyanates. Such curing agents do not contain aryl groups, do not produce benzene ring conjugated quinone chromophores, and do not cause yellowing, which is beneficial to the color stability of the paint film.

[0055] Aliphatic polyisocyanates include one or a mixture of hexamethylene diisocyanate and 2,2,4-trimethylhexane diisocyanate in any proportion; alicyclic isocyanates include one or a mixture of dicyclohexylmethylene diisocyanate and isophorone diisocyanate in any proportion.

[0056] After spraying the above two-component clear coat, the resulting paint film has excellent hardness, flexibility and fullness, which greatly improves the quality of the car body paint.

[0057] Furthermore, in this embodiment of the invention, 0.8 to 1.3 parts of additives are used. This reduces the amount of additives, especially the amount of leveling agent, which can improve the surface roughness of the formed paint film. This is beneficial for the formation of physical forces between layers in the form of hydrogen bonds or mechanical bonding, thereby enhancing the adhesion between paint layers.

[0058] Next, the car body is dried. Since the first amino resin in the single-component clear coat has a relatively small weight percentage, which is 13 to 18 parts, the crosslinking density is low when it undergoes an addition polymerization reaction during spraying in step S2, leaving more active sites. This allows for a further chemical reaction during the second drying process of the car body in step S3, which further improves the adhesion between paint layers.

[0059] Therefore, after the drying process is completed, there is no need to polish the entire vehicle to obtain the desired result. Figure 2 The car body shown is coated with four layers of paint and baked with two layers of baking paint.

[0060] In another example, after step S1, i.e., after the flash-drying process, a two-component clear coat can be applied to the car body base. Using a two-component clear coat can result in a paint film with excellent hardness, flexibility, and fullness. Furthermore, in this embodiment of the invention, 0.8 to 1.3 parts of additives are used. This reduces the amount of additives, especially the amount of leveling agent, which can improve the surface roughness of the formed paint film. This facilitates the formation of physical forces between layers through hydrogen bonds or mechanical bonding, thereby enhancing the adhesion between paint layers.

[0061] Therefore, after applying a two-component clear coat and drying the car body, there is no need to sand the entire vehicle; only the defective areas on the car body need to be sanded.

[0062] After sanding down the defective areas on the car body, a two-component clear coat is applied, resulting in a paint film with excellent hardness, flexibility, and fullness, significantly improving the quality of the car body paint.

[0063] Furthermore, in this embodiment of the invention, the two-component varnish contains only 0.8 to 1.3 parts of additives. This reduces the amount of additives, especially the amount of leveling agent, which can improve the surface roughness of the formed paint film. This is beneficial for the layers to form physical forces in the form of hydrogen bonds or mechanical bonding, thereby enhancing the adhesion between paint layers.

[0064] Next, the car body is dried. Since the second amino resin in the two-component clear coat has a relatively small weight percentage, ranging from 14 to 24 parts, the crosslinking density was low during the addition polymerization reaction in step S2, leaving more active sites. This allows for a further chemical reaction during the second drying process of the car body in step S3, further improving the adhesion between paint layers.

[0065] Therefore, after the drying process is completed, there is no need to polish the entire vehicle to obtain a four-coat, two-bake topcoat body.

[0066] Therefore, this invention employs a five-coat, two-bake topcoat process, significantly improving the overall appearance, smoothness, gloss, and fullness of the paint surface. By using a single-component or two-component clear varnish in the base coat and a two-component clear varnish in the top coat, the weight percentage of additives in the single-component and two-component clear varnishes is reduced. This significantly increases the surface roughness of the resulting paint film after the base coat, facilitating the formation of physical forces between paint layers through hydrogen bonding or mechanical bonding, thus enhancing interlayer adhesion. Consequently, after the first drying process, no... The entire vehicle needs to be sanded, but only the defective points on the body need to be sanded. At the same time, the embodiments of the present invention also reduce the weight percentage of the first amino resin in the single-component clear varnish and the weight percentage of the second amino resin in the two-component clear varnish. In this way, after spraying the single-component or two-component clear varnish, the crosslinking density can be reduced, leaving more active sites. This allows for further chemical reactions to occur during the second drying treatment of the body in step S3, greatly improving the adhesion between paint layers. Thus, the body does not need to be sanded, and a four-coat, two-bake topcoat body can be obtained.

[0067] Therefore, in the entire painting process, the embodiments of the present invention reduce the sanding of the car body, and even eliminate the need for sanding after the second drying process, which greatly saves the cycle time of the process, improves production efficiency, and meets the needs of mass production of vehicles. At the same time, since the embodiments of the present invention reduce the sanding of the car body, problems such as more paint particles and the tendency to develop pinhole defects after sanding can be avoided.

[0068] In an optional embodiment, in step S2, the main component of the sprayed two-component varnish, by weight, comprises: 35-45 parts of the acrylic resin, 14-18 parts of the second amino resin, 16-23 parts of the anti-sagging resin, 0.8-1.2 parts of the additives, and 28-28 parts of the solvent.

[0069] In step S3, the main component of the two-component varnish sprayed, by weight, comprises: 39-47 parts of the acrylic resin, 18-24 parts of the second amino resin, 19-25 parts of the anti-sagging resin, 1-1.3 parts of the additives, and 15-25 parts of the solvent.

[0070] In this embodiment of the invention, the main component of the two-component clear varnish used in the primer coating differs from that used in the two-component clear varnish used in the topcoat. Specifically, in step S2, the main component of the two-component clear varnish used in the primer coating includes: 35-45 parts acrylic resin, 14-18 parts second amino resin, 16-23 parts anti-sagging resin, 0.8-1.2 parts additives, and 28-28 parts solvent; in step S3, the main component of the two-component clear varnish used in the topcoat includes: 39-47 parts acrylic resin, 18-24 parts second amino resin, 19-25 parts anti-sagging resin, 1-1.3 parts additives, and 15-25 parts solvent.

[0071] In this way, when applying the primer, a two-component clear coat with a lower content of the second amino resin is used. This reduces the crosslinking density during the addition polymerization reaction of the primer two-component clear coat, leaving more active sites. As a result, in step S3, when the car body is dried for the second time, a further chemical reaction can occur, improving the adhesion between paint layers.

[0072] For the topcoat, a two-component varnish with a slightly higher content of second amino resin is used to ensure the cross-linking density of the final paint film and improve its gloss.

[0073] In addition, when applying the primer, a two-component clear coat with less additives is used to reduce the amount of additives, especially the amount of leveling agent, thereby increasing the surface roughness of the formed paint film. This is beneficial for the formation of physical forces between the layers in the form of hydrogen bonds or mechanical bonding, thus enhancing the adhesion between paint layers.

[0074] For the topcoat, a two-component varnish with a slightly higher content of additives is used to ensure the strength and appearance quality of the final paint film.

[0075] Therefore, the main components of the two-component primer and the two-component topcoat clear coat are further optimized in this embodiment of the invention, which can improve the adhesion between paint layers and ensure the quality of the car body paint surface.

[0076] In one optional embodiment, in step S2, the main agent and the curing agent are mixed in a first preset ratio, wherein the first preset ratio is 3.5:1 to 4:1.

[0077] In step S3, the main agent and the curing agent are mixed in a second preset ratio, which is 3:1 to 3.5:1.

[0078] In this embodiment of the invention, in step S2, the main agent and the curing agent in the two-component clear varnish used for the primer are mixed according to a first preset ratio of 3.5:1 to 4:1. This reduces the amount of curing agent used, so that after the addition polymerization reaction, the acrylic resin in the main agent can retain a large number of unreacted active groups. These active groups can combine with the active groups in the two-component clear varnish sprayed in step S3 to form chemical bonds, thereby greatly enhancing the interlayer adhesion. Thus, it is ensured that after the second drying treatment, there is no need to polish the whole vehicle, avoiding polishing operations, reducing the process cycle time, and meeting the mass production needs of vehicles.

[0079] In step S3, the main agent and curing agent in the two-component clear varnish used for the topcoat are mixed according to a second preset ratio of 3:1 to 3.5:1. This ensures that the main agent in the two-component clear varnish reacts completely, forms a film quickly, and guarantees the quality of the topcoat.

[0080] In one alternative embodiment, the acrylic resin comprises one or a mixture of (meth)acrylate, (meth)acrylate, (meth)acrylate, (meth)acrylate, (meth)acrylate, (meth)acrylate, and lauryl methacrylate in any proportion.

[0081] In the embodiments of the present invention, methyl methacrylate, ethyl methacrylate, propyl methacrylate, hexyl methacrylate, and lauryl methacrylate are all thermosetting resins. The above-mentioned thermosetting resins have good gloss and color retention, water resistance, and chemical resistance, so that the formed paint film has excellent fullness, gloss, hardness, solvent resistance, weather resistance, and does not change color or yellow when baked at high temperature.

[0082] In one optional embodiment, the first amino resin includes one or a mixture of multiple types of butylated melamine resin, mixed etherified melamine resin, methylated melamine resin, or methylated hexamethylol melamine resin in any proportion.

[0083] The second amino resin includes one or a mixture of methyl etherified melamine resin and methyl etherified hexamethylol melamine resin in any proportion.

[0084] In this embodiment of the invention, the use of the first amino resin and the second amino resin can give the formed paint film excellent gloss.

[0085] In one alternative embodiment, the anti-sagging resin comprises one or more of modified acrylic resin and polyamide wax paste in any proportion.

[0086] In this embodiment of the invention, the use of the above-mentioned anti-sagging resin can significantly improve the anti-sagging performance, high gloss and dustproof effect of the paint film.

[0087] In one optional embodiment, the additives include one or a mixture of multiple agents selected from leveling agents, defoamers, and drying agents in any proportion;

[0088] The leveling agent comprises one or a mixture of multiple types of modified organosilicon, epoxy-modified polyacrylate, and modified organopolysiloxane polyisocyanate; the defoamer comprises one or a mixture of multiple types of polyamide hydrophobic particle polymer and propylene glycol methyl ether acetate; and the drying agent comprises one or a mixture of multiple types of dibutyltin dilaurate and p-toluenesulfonic acid amino salt solution.

[0089] In one alternative embodiment, the solvent includes one or a mixture of ethyl acetate, solvent oil, ethylene glycol butyl ether acetate, diethylene glycol butyl ether, dimethyl carbonate, isopropanol, and diethyl carbonate in any proportion.

[0090] In this embodiment of the invention, the solvent described above is not only environmentally friendly, but can also significantly improve the quality of deep surfaces and provide a good product application environment.

[0091] In one alternative embodiment, the polyester resin includes one or a mixture of multiple types of oil-free alkyd resin, modified polyester resin, and saturated polyester in any proportion.

[0092] In the embodiments of the present invention, the use of the above-mentioned polyester resin can significantly improve the physical and mechanical properties of the paint film, especially its toughness, wear resistance, impact resistance and scratch resistance. At the same time, it can also enhance the gloss and color retention and weather resistance of the paint film, and there is no loss of gloss or yellowing after long-term exposure to sunlight.

[0093] In one alternative embodiment, in step S3, after grinding the defect points on the vehicle body, the vehicle body is cleaned with alcohol or isopropyl alcohol.

[0094] After sanding down the defective areas on the car body, you can use alcohol or isopropyl alcohol to clean the car body. This will not only remove dust and foreign objects from the car body, but also keep the car body dry.

[0095] In one optional embodiment, the flash-drying treatment includes flash-drying the vehicle body at 75-80°C for 4-6 minutes;

[0096] The drying process includes baking at 130–150°C for 20–30 minutes.

[0097] In this embodiment of the invention, flash drying treatment can achieve excellent leveling and dehydration of the sprayed water-based intermediate coat and color paint, thus improving the spraying quality; two drying treatments can achieve excellent leveling and curing of the sprayed single-component or two-component clear varnish, further improving the spraying quality.

[0098] In one optional embodiment, in step S1, the thickness of the water-based intermediate coat is 9-15 μm, and the thickness of the colored paint is 10-15 μm.

[0099] In step S2, the thickness of the single-component varnish or the two-component varnish is 25-35 μm.

[0100] In step S3, the thickness of the two-component varnish is 35-50 μm.

[0101] In this embodiment of the invention, the thickness of the water-based intermediate coating is set to 9-15 μm, the thickness of the color paint film is set to 10-15 μm, the thickness of the base coat single-component clear varnish or two-component clear varnish is set to 25-35 μm, and the thickness of the top coat two-component clear varnish is set to 35-50 μm, so as to ensure that the orange peel effect of the car body is achieved at the lowest cost.

[0102] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined to obtain specific implementation methods.

[0103] Secondly, the present invention provides a topcoat obtained by the mass-producible four-coat, two-bake topcoat spraying method provided in the first aspect above. Figure 2 A schematic diagram of a four-coat, two-bake topcoat body provided by an embodiment of the present invention is shown, as follows: Figure 2 As shown, it includes:

[0104] A water-based intermediate coating, a color paint layer, a first clear coat layer, and a second clear coat layer are sequentially layered on the surface of the vehicle body. The first clear coat layer, by weight, is formed by spraying a single-component or two-component clear coat, and the second clear coat layer is formed by spraying a two-component clear coat. The single-component clear coat comprises: 35-45 parts acrylic resin, 13-18 parts first amino resin, 18-23 parts anti-sagging resin, 5-8 parts polyester resin, 1.5-2 parts additives, and 15-18 parts solvent. The two-component clear coat comprises a main agent and a curing agent. The main agent comprises: 35-47 parts of the acrylic resin, 14-24 parts of the second amino resin, 16-25 parts of the anti-sagging resin, 0.8-1.3 parts of the additives, and 15-38 parts of the solvent. The curing agent comprises a polyisocyanate curing agent.

[0105] To enable those skilled in the art to better understand the present invention, the following specific embodiments are used to illustrate the two-component varnish composition and its spraying method provided by the present invention.

[0106] Example 1

[0107] This embodiment 1 provides a single-component clear varnish for primer, with the following composition:

[0108]

[0109] This embodiment 1 also provides a two-component clear varnish for topcoat, comprising a base agent and a curing agent, wherein the ratio of the base agent to the curing agent is 3:1, wherein the curing agent is hexamethylene diisocyanate, and the composition of the base agent is as follows:

[0110]

[0111] A four-coat, two-bake topcoat spraying method includes the following steps:

[0112] Step S1: Spray a water-based intermediate coat on the electrophoretic treated car body with a film thickness of 10μm, then spray black paint with a film thickness of 12μm. After spraying, move the vehicle into a flash drying oven for leveling and dehydration. The flash drying conditions are 80℃ for 5.5min.

[0113] Step S2: After flash drying, the above-mentioned single-component clear coat is sprayed onto the vehicle body with a film thickness of 30μm. After spraying, the vehicle is moved into the topcoat oven for leveling and curing. The drying conditions are 140℃ for 20 minutes.

[0114] Step S3: After drying, use 2000-grit sandpaper to sand the defect points on the car body, then wipe the car body clean with alcohol. Next, spray the above two-component clear coat with a film thickness of 40μm. Then, move the vehicle into the topcoat oven again for leveling and curing. The drying conditions are 140℃ for 20 minutes to obtain a four-coat, two-bake topcoat car body.

[0115] Example 2

[0116] This embodiment 2 provides a two-component clear varnish for primer, comprising a base agent and a curing agent, wherein the ratio of the base agent to the curing agent is 4:1, wherein the curing agent is hexamethylene diisocyanate, and the composition of the base agent is as follows:

[0117]

[0118]

[0119] This embodiment 2 also provides a two-component clear varnish for topcoat, comprising a base agent and a curing agent, wherein the ratio of the base agent to the curing agent is 3:1, wherein the curing agent is hexamethylene diisocyanate, and the composition of the base agent is as follows:

[0120]

[0121] A four-coat, two-bake topcoat spraying method includes the following steps:

[0122] Step S1: Spray a water-based intermediate coat on the electrophoretic treated car body with a film thickness of 10μm, then spray black paint with a film thickness of 12μm. After spraying, move the vehicle into a flash drying oven for leveling and dehydration. The flash drying conditions are 80℃ for 5.5min.

[0123] Step S2: After flash drying, the above-mentioned two-component primer clear coat is sprayed onto the vehicle body with a film thickness of 30μm. After spraying, the vehicle is moved into the topcoat oven for leveling and curing. The drying conditions are 140℃ for 20 minutes.

[0124] Step S3: After drying, use 2000-grit sandpaper to sand the defect points on the car body, then wipe the car body clean with isopropyl alcohol. Next, spray the above-mentioned two-component clear coat with a film thickness of 40μm. Then, move the vehicle into the topcoat oven again for leveling and curing. The drying conditions are 140℃ for 20 minutes to obtain a four-coat, two-bake topcoat car body.

[0125] Comparative Example 1

[0126] The clear coat used for the primer in Comparative Example 1 was BASF UniGloss 1K clear coat, and the clear coat used for the topcoat was BASF ProGloss 2K clear coat.

[0127] A four-coat, two-bake topcoat spraying method includes the following steps:

[0128] Step S1: Spray a water-based intermediate coat on the electrophoretic treated car body with a film thickness of 10μm, then spray black paint with a film thickness of 12μm. After spraying, move the vehicle into a flash drying oven for leveling and dehydration. The flash drying conditions are 80℃ for 5.5min.

[0129] Step S2: After flash drying, the vehicle body is sprayed with the above-mentioned BASF UniGloss 1K clear coat with a film thickness of 30μm. After spraying, the vehicle is moved into the topcoat oven for leveling and curing. The drying conditions are 140℃ for 20min.

[0130] Step S3: After drying, the entire vehicle is sanded with 2000-grit sandpaper. Then, the above-mentioned BASF ProGloss 2K clear coat is sprayed with a film thickness of 40μm. Next, the vehicle is moved into the topcoat oven again for leveling and curing. The drying conditions are 140℃ for 20 minutes to obtain a four-coat, two-bake topcoat body.

[0131] Comparative Example 1 uses BASF UniGloss 1K clear coat as the base coat and BASF ProGloss 2K clear coat as the top coat. After drying, the entire vehicle needs to be sanded, which takes about 3-4 hours.

[0132] Comparative Example 2

[0133] The clear coat used for the primer in Comparative Example 2 was BASF EverGloss 2K clear coat, and the clear coat used for the topcoat was BASF ProGloss 2K clear coat.

[0134] A four-coat, two-bake topcoat spraying method includes the following steps:

[0135] Step S1: Spray a water-based intermediate coat on the electrophoretic treated car body with a film thickness of 10μm, then spray black paint with a film thickness of 12μm. After spraying, move the vehicle into a flash drying oven for leveling and dehydration. The flash drying conditions are 80℃ for 5.5min.

[0136] Step S2: After flash drying, the vehicle body is sprayed with the above-mentioned BASF EverGloss 2K clear coat with a film thickness of 30μm. After spraying, the vehicle is moved into the topcoat oven for leveling and curing. The drying conditions are 140℃ for 20min.

[0137] Step S3: After drying, the entire vehicle is sanded with 2000-grit sandpaper. Then, the above-mentioned BASF ProGloss 2K clear coat is sprayed with a film thickness of 40μm. Next, the vehicle is moved into the topcoat oven again for leveling and curing. The drying conditions are 140℃ for 20 minutes to obtain a four-coat, two-bake topcoat body.

[0138] Comparative Example 2 uses BASF EverGloss 2K clear coat as the base coat and BASF ProGloss 2K clear coat as the top coat. After drying, the entire vehicle needs to be sanded, which takes about 3-4 hours.

[0139] The performance boards were fabricated and tested according to the conditions of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively. The results are compared in Table 1 below:

[0140] Table 1. Performance test results of Example 1, Example 2, Comparative Example 1 and Comparative Example 2

[0141]

[0142]

[0143] As shown in Table 1 above, Examples 1 and 2, while ensuring construction performance, show significant improvements in appearance data such as DOI and orange peel, as well as physical and chemical properties such as adhesion, impact resistance, and resistance to damp heat, all of which are higher than those of Comparative Example 1 and Comparative Example 2.

[0144] Each embodiment in this specification focuses on the differences from other embodiments. For the same or similar parts between the embodiments, please refer to each other.

[0145] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present invention.

[0146] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only 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 terminal device 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 terminal device. 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 terminal device that includes said element.

[0147] The present invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A mass-producible four-coat two-bake finish spray painting method, characterized by, The method comprises: Step S1, sequentially spraying water-based mid-coat and color paint on the electrophoretically treated vehicle body to form a water-based mid-coat layer and a color paint layer, and then performing flash drying treatment; Step S2, after the flash drying treatment is completed, spraying one-component clear paint or two-component clear paint on the vehicle body to form a first clear paint layer, and performing baking treatment; Step S3, after the baking treatment is completed, polishing the defect points on the vehicle body, spraying the two-component clear paint to form a second clear paint layer, and performing the baking treatment again to obtain a four-coat two-baking finish vehicle body; The composition of the one-component clear paint comprises, in parts by weight, 35-45 parts of acrylic resin, 13-18 parts of first amino resin, 18-23 parts of sag-resistant resin, 5-8 parts of polyester resin, 1.5-2 parts of auxiliary agent, and 15-18 parts of solvent; The composition of the two-component clear paint comprises a main agent and a curing agent, and the curing agent comprises a polyisocyanate curing agent; In the step S2, the main agent and the curing agent are mixed according to a first preset ratio, and the first preset ratio is 3.5:1-4:1; the main agent in the sprayed two-component clear paint comprises, in parts by weight, 35-45 parts of acrylic resin, 14-18 parts of second amino resin, 16-23 parts of sag-resistant resin, 0.8-1.2 parts of auxiliary agent, and 28-28 parts of solvent; In the step S3, the main agent and the curing agent are mixed according to a second preset ratio, and the second preset ratio is 3:1-3.5:1; the main agent in the sprayed two-component clear paint comprises, in parts by weight, 39-47 parts of acrylic resin, 18-24 parts of second amino resin, 19-25 parts of sag-resistant resin, 1-1.3 parts of auxiliary agent, and 15-25 parts of solvent.

2. A mass-producible four-coat two-bake finish spray painting method according to claim 1, wherein The acrylic resin comprises one or a plurality of various proportions of mixtures of (methyl) methacrylate, (methyl) acrylate, (methyl) acrylate, (methyl) acrylate, and lauryl methacrylate; The first amino resin comprises one or a plurality of various proportions of mixtures of butyl etherified melamine resin, mixed etherified melamine resin, methyl etherified melamine resin, or methyl etherified hexamethylol melamine resin; The second amino resin comprises one or a plurality of various proportions of mixtures of methyl etherified melamine resin and methyl etherified hexamethylol melamine resin.

3. A mass-producible four-coat two-bake finish spray painting method according to claim 1, wherein The sag-resistant resin comprises one or a plurality of various proportions of mixtures of modified acrylic resin and polyamide wax paste.

4. The mass-producible four-coat two-bake finish spray painting method according to claim 1, wherein The auxiliary agent comprises one or a plurality of various proportions of mixtures of leveling agent, defoaming agent, and drying catalyst; The leveling agent comprises one or a plurality of various proportions of mixtures of modified organosilicon, epoxy-modified polyacrylate, and modified organopolysiloxane polyisocyanate; the defoaming agent comprises one or a plurality of various proportions of mixtures of polyamide hydrophobic particle polymer and propylene glycol methyl ether acetate; and the drying catalyst comprises one or a plurality of various proportions of mixtures of dibutyltin dilaurate and p-toluenesulfonic acid amino salt solution.

5. The mass-producible four-coat two-bake finish spray painting method according to claim 1, wherein The solvent includes one or a mixture of multiple kinds in any proportion of ethyl acetate, solvent oil, ethylene glycol butyl ether acetate, diethylene glycol butyl ether, dimethyl carbonate and isopropyl alcohol and diethyl carbonate.

6. A mass-producible four-coat two-bake finish spray painting method according to claim 1, wherein The flash drying treatment includes flash drying the vehicle body at 75-80 DEG C for 4-6 min. The baking treatment includes baking at 130-150 DEG C for 20-30 min.

7. A mass-producible four-coat two-bake finish spray painting method according to claim 1, wherein The thickness of the aqueous midcoat layer is 9-15 mu m; the thickness of the color paint layer is 10-15 mu m; the thickness of the first clearcoat layer is 25-35 mu m; and the thickness of the second clearcoat layer is 45-60 mu m.

8. A topcoat characterized by, Comprise: An aqueous midcoat layer, a color paint layer, a first clearcoat layer and a second clearcoat layer are sequentially arranged on the surface of the vehicle body, wherein The first clearcoat layer is formed by spraying a single-component clearcoat or a two-component clearcoat, and the second clearcoat layer is formed by spraying a two-component clearcoat; The composition of the single-component clearcoat comprises 35-45 parts of acrylic resin, 13-18 parts of first amino resin, 18-23 parts of anti-sagging resin, 5-8 parts of polyester resin, 1.5-2 parts of auxiliary agent and 15-18 parts of solvent; The composition of the two-component clearcoat comprises a main agent and a curing agent, and the curing agent comprises a polyisocyanate curing agent; In the two-component clearcoat of the first clearcoat layer, the main agent and the curing agent are mixed at a first preset ratio, and the first preset ratio is 3.5:1-4:1; the main agent in the sprayed two-component clearcoat comprises 35-45 parts of acrylic resin, 14-18 parts of second amino resin, 16-23 parts of anti-sagging resin, 0.8-1.2 parts of auxiliary agent and 28-28 parts of solvent; In the two-component clearcoat of the second clearcoat layer, the main agent and the curing agent are mixed at a second preset ratio, and the second preset ratio is 3:1-3.5:1; the main agent in the sprayed two-component clearcoat comprises 39-47 parts of acrylic resin, 18-24 parts of second amino resin, 19-25 parts of anti-sagging resin, 1-1.3 parts of auxiliary agent and 15-25 parts of solvent.

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