Surface coating process of color steel plate

Abstract

This application relates to the field of color steel plate technology, specifically disclosing a surface coating process for color steel plates, including the following steps: S1, the corrugated raised areas of the steel plate surface are sanded, then uniformly coated with an ethyl cellulose solution, heated to 75-85℃ and dried for 5-10 minutes, then uniformly coated with an epoxy resin solution, and after drying and curing, an ethyl cellulose film and an epoxy resin film are sequentially attached to the steel plate surface to obtain a semi-finished product; S2, a topcoat is uniformly coated on the surface of the semi-finished product, and after the topcoat dries to form a film, a finished color steel plate is obtained; it has the advantages of easy coating, stable coating adhesion, uniform surface film thickness, and good impact resistance of the raised areas of the steel plate surface.

Description

Technical Field

[0001] This application relates to the field of color steel sheet technology, and more specifically, it relates to a surface coating process for color steel sheets. Background Technology

[0002] Color-coated steel sheet, also known as pre-painted steel sheet, is a type of steel sheet with an organic coating. It has advantages such as good decorative properties, energy saving and environmental protection, easy forming, and low cost, and is widely used in construction, building construction and other fields.

[0003] During the manufacturing process of color-coated steel sheets, steel plates are generally pressed into the desired shape, commonly a corrugated shape with a raised center and flat ends, to facilitate overlapping between sheets. After pressing, colored paint is applied to decorate the steel sheet. Because the surface of the steel sheet is relatively smooth, paint does not adhere easily. Therefore, to improve adhesion, a high-viscosity paint is needed to adhere to the surface of the color-coated steel sheet. However, high-viscosity paint has poor flowability and is not easy to apply evenly. If a paint with good flowability is used, although it is easy to apply evenly, after being applied to the surface of the steel sheet, the paint at the raised positions tends to flow to the flat ends, especially at the junction of the raised and flat positions, where paint tends to accumulate, resulting in uneven film thickness on the surface of the color-coated steel sheet. In some areas, the film may even be too thin, which not only easily leads to problems such as blistering and cracking during the drying process due to poor adhesion, but also affects the impact resistance of some areas of the color-coated steel sheet surface. The surface of color-coated steel sheets is often subjected to large impacts, whether it is hail, sandstorms, or hurricanes. A uniform and impact-resistant paint film can protect the color-coated steel sheet, thereby extending its service life.

[0004] Therefore, how to prepare a color steel plate that is easy to coat with paint, has stable paint adhesion, uniform surface film thickness, and good impact resistance is a problem that needs to be solved. Summary of the Invention

[0005] In order to prepare a color steel plate that is easy to coat with paint, has stable paint adhesion, uniform surface film thickness, and good impact resistance at the raised parts of the steel plate surface, this application provides a surface coating process for color steel plates.

[0006] This application provides a surface coating process for color-coated steel sheets, which adopts the following technical solution:

[0007] A surface coating process for color steel sheets includes the following steps:

[0008] S1. The corrugated raised areas on the surface of the steel plate are sanded, then coated with ethyl cellulose solution, heated to 75-85℃ and dried for 5-10 minutes, then coated with epoxy resin solution, and dried and cured. The surface of the steel plate is successively coated with ethyl cellulose film and epoxy resin film to obtain a semi-finished product.

[0009] S2. Apply a topcoat evenly to the surface of the semi-finished product. After the topcoat dries and forms a film, the finished color steel plate is obtained.

[0010] By adopting the above technical solution, the surface roughness of the corrugated raised surface of the steel plate is increased after sanding. Combined with the viscosity of the ethyl cellulose solution, the ethyl cellulose solution with good fluidity can adhere more stably to the corrugated raised surface of the steel plate and is not easy to flow on the surface of the color steel plate, so as to avoid the liquid coating at the raised position from sliding to both ends.

[0011] By limiting the heating temperature and time, the ethanol solvent in the ethyl cellulose solution gradually evaporates. After coating with epoxy resin, the highly fluid epoxy resin can stably adhere to the surface of the ethyl cellulose film. Finally, the highly fluid topcoat can stably adhere to the epoxy resin surface, thus ensuring stable adhesion of the topcoat to the steel plate surface. This allows for better adhesion of the topcoat to the corrugated and raised areas of the steel plate surface, achieving the effects of easy coating application, stable coating adhesion, and uniform surface film thickness. At the same time, the ethyl cellulose film, epoxy resin film, and topcoat film can improve the impact resistance of the steel plate surface, giving the color steel plate a good impact resistance effect.

[0012] Preferably, the ethyl cellulose solution is composed of an ethyl cellulose ethanol solution, carboxymethyl chitosan particles, and polyethyleneimine in a mass ratio of 1:0.2-0.5:0.02-0.05.

[0013] By employing the above technical solution, ethyl cellulose ethanol solution, carboxymethyl chitosan particles, and polyethyleneimine are combined. Since carboxymethyl chitosan particles are water-soluble but alcohol-insoluble, they are dispersed in the ethyl cellulose ethanol solution. Polyethyleneimine, being soluble in ethanol, is also dispersed in the ethyl cellulose solution. The amino groups in polyethyleneimine attract and connect with the carboxyl groups in carboxymethyl chitosan, allowing the carboxymethyl chitosan particles to adhere relatively stably to the ethyl cellulose solution. As the ethanol gradually evaporates, the carboxymethyl chitosan particles easily absorb moisture from the external environment, causing the ethanol-insoluble particles to float easily on the surface of the ethyl cellulose film. Moisture will not evaporate under elevated temperatures of 75-85 degrees Celsius. After coating with epoxy resin, the relatively rough surface structure formed by the carboxymethyl chitosan particles, combined with the bonding effect between ethyl cellulose and the epoxy resin, ensures good adhesion stability of the highly fluid epoxy resin on both corrugated and flat steel plates. This guarantees easy coating while ensuring uniform thickness distribution and good film adhesion.

[0014] Preferably, the epoxy resin liquid comprises the following raw materials in parts by weight:

[0015] 50-70 parts epoxy resin, 5-15 parts elastic filler, 5-10 parts polyethylene glycol ethanol solution, 0.1-0.3 parts defoamer, 1-2 parts dispersant, 20-30 parts amine curing agent, and 15-20 parts water.

[0016] By adopting the above technical solution, when the epoxy resin solution is coated onto the surface of the ethyl cellulose membrane, the ethanol in the polyethylene glycol ethanol solution can partially dissolve the ethyl cellulose, ensuring that the polyethyleneimine and carboxymethyl chitosan particles can come into contact with the water in the epoxy resin solution. The water solubility and viscosity of polyethyleneimine and carboxymethyl chitosan, combined with the cross-linking and bonding of the carboxyl groups in carboxymethyl chitosan with the hydroxyl groups in polyethylene glycol and the amino groups in the curing agent, improve the bonding effect between the ethyl cellulose membrane and the epoxy resin membrane. Furthermore, combined with the cross-linking and curing effect of polyethyleneimine and epoxy resin, the bonding stability between the epoxy resin membrane and the ethyl cellulose membrane is further improved, thereby improving the bonding stability of the topcoat on the steel plate surface.

[0017] The combination of polyethylene glycol ethanol solution and water improves the fluidity of epoxy resin, making the epoxy resin liquid easier to apply while ensuring stable coating adhesion. This prevents flow accumulation on the steel plate surface, which could affect the uniformity of the film thickness. The combination of elastic filler and dispersant, with the elastic filler exhibiting good impact resistance, ensures that the paint film on the steel plate surface and the shape of the steel plate itself are not easily affected by impacts, thus extending the service life of the color steel plate.

[0018] Preferably, the elastic filler is prepared by the following method:

[0019] Weigh polyurethane granules and heat them to 170-190℃ for 5-10 seconds. Then, uniformly spray silicon nitride fibers onto the surface of the polyurethane granules. The mass ratio of polyurethane granules to silicon nitride fibers is 1:0.1-0.25. After drying and dispersion, the loading material is obtained.

[0020] Polyvinyl alcohol solution is uniformly sprayed onto the surface of the load material. The mass ratio of polyurethane particles to polyvinyl alcohol solution is 1:0.2-0.5. After drying and dispersing, the finished elastic filler is obtained.

[0021] By adopting the above technical solution, the heating temperature and time of polyurethane particles are limited, so that the surface of the polyurethane particles is partially melted. After melting, they adhere to the surface of silicon nitride fibers. By utilizing the elasticity and resilience of polyurethane particles, combined with the high strength of silicon nitride fibers and the strength and toughness of polyvinyl alcohol film, the epoxy resin film has good impact resistance, is not easy to scratch the paint film, and is not easy to be damaged by external environmental particles, causing deformation or film rupture of the color steel plate.

[0022] The combination of polyvinyl alcohol solution, polyethylene glycol ethanol solution, amine curing agent, and polyethyleneimine not only improves the cross-linking stability of elastic particles in epoxy resin solution, but also, by utilizing the hydroxyl groups in polyvinyl alcohol, polyethylene glycol, amine curing agent, and polyethyleneimine, further enhances the cross-linking adhesion between the epoxy resin film and the ethyl cellulose film, and improves the strength and toughness of the epoxy resin film. This results in more stable adhesion of the epoxy resin solution to the surface of the steel plate coated with ethyl cellulose solution, preventing liquid flow caused by corrugations and ensuring uniformity of film thickness. Consequently, the color steel plate possesses advantages such as easy coating, stable coating adhesion, uniform surface film thickness, and good impact resistance.

[0023] Preferably, the silicon nitride fiber is composed of silicon nitride fiber filaments and EVA in a mass ratio of 1:0.2-0.4.

[0024] By adopting the above technical solution and utilizing the softening and hot-melting effect of EVA, the EVA easily softens and melts after the surface temperature of the hot-melting polyurethane particles reaches the melting point of EVA. This improves the bonding effect between the polyurethane particles and the surface of the silicon nitride fiber, thereby enhancing the elasticity and resilience of the elastic particles. This not only improves the bonding stability between the topcoat and the steel plate but also enhances the impact resistance of the color steel plate. In the high-temperature environment of summer, the easy softening and hot-melting of EVA further improves the bonding effect between the epoxy resin film and the ethyl cellulose film. This ensures that the topcoat, epoxy resin film, and ethyl cellulose film are less likely to detach from the steel plate surface during prolonged use, thus extending the service life of the color steel plate.

[0025] Preferably, the topcoat comprises the following raw materials in parts by weight:

[0026] The ingredients are: 60-80 parts hydroxyl acrylic resin, 8-16 parts toughening filler, 5-10 parts pigment, 1-3 parts dispersant, 0.1-0.2 parts defoamer, 10-20 parts solvent, 0.5-1 part antioxidant, 0.5-1 part UV stabilizer, 50-60 parts HDI type trimer curing agent, and 20-40 parts anhydrous butyl acetate.

[0027] By adopting the above technical solution, the solvent in the topcoat, the polyethylene glycol ethanol solution in the epoxy resin liquid, and water all contribute to the fluidity of the coating, making it easy to apply.

[0028] The combination of hydroxyl acrylic resin, epoxy resin, and polyethylene glycol ethanol solution allows the topcoat to adhere better to the epoxy resin film surface. The hydroxyl groups in the polyethylene glycol further enhance the adhesion between the topcoat and the epoxy resin film, resulting in stable adhesion of the topcoat to the steel plate surface and reducing the likelihood of bubbles and cracks. After the topcoat is applied, the bonding effect between the hydroxyl acrylic resin and the surface substances of the epoxy resin film prevents the topcoat from flowing, thus ensuring a more uniform topcoat film thickness.

[0029] The combination of toughening fillers and elastic particles, with their good elasticity, resilience and toughness, can improve the impact resistance of color steel plates.

[0030] Preferably, the solvent is one or more of ethanol and isopropanol.

[0031] By adopting the above technical solution, ethanol and isopropanol can promote the dissolution of polyvinyl alcohol on the surface of elastic filler in epoxy resin film and ensure the coating effect of topcoat.

[0032] Preferably, the toughening filler is prepared by the following method:

[0033] EVA melt is weighed and evenly sprayed onto the surface of carbon fiber, and then polyetheretherketone (PEEK) particles are evenly sprayed on. The mass ratio of EVA melt, carbon fiber and PEEK particles is 1:1-2:0.5-1. After drying and dispersing, the finished product is obtained.

[0034] By adopting the above technical solution, EVA melt, carbon fiber, and polyetheretherketone (PEEK) particles are combined. The viscosity of the EVA melt facilitates the adhesion of the PEEK particles to the carbon fiber surface. The elasticity and resilience of the PEEK particles and EVA, combined with the toughness of the carbon fiber, improve the impact resistance of the topcoat, thereby extending the service life of the color steel plate.

[0035] Preferably, the polyetheretherketone (PEEK) particles are prepared by modifying PEEK microparticles with ethyl cellulose solution.

[0036] By adopting the above technical solution, polyetheretherketone (PEEK) microparticles and ethyl cellulose solution are combined. The viscosity of the ethyl cellulose solution facilitates adhesion to the surface of the PEEK microparticles. Since ethyl cellulose is soluble in ethanol, the toughening filler in the topcoat gradually dissolves the ethyl cellulose on the surface of the PEEK particles, increasing the viscosity and thus improving the adhesion stability of the toughening filler in the topcoat, thereby improving the strength and impact resistance of the paint film.

[0037] Preferably, the defoamer is an organosilicone defoamer.

[0038] By adopting the above technical solution, the topcoat is less prone to bubble formation, improving the uniformity of the film layer and enhancing its adhesion stability.

[0039] In summary, this application has the following beneficial effects:

[0040] 1. After the corrugated raised surface of the steel plate is sanded, the surface roughness is increased, allowing the ethyl cellulose solution with good fluidity to adhere more stably to the corrugated raised surface of the steel plate. After coating with epoxy resin, the epoxy resin with good fluidity can adhere stably to the surface of the ethyl cellulose film. Finally, the topcoat with good fluidity can adhere stably to the epoxy resin surface, achieving the effect of easy coating application, stable coating adhesion, and uniform surface film thickness. At the same time, the ethyl cellulose film, epoxy resin film, and topcoat film can improve the impact resistance of the steel plate surface, giving the color steel plate a good impact resistance effect.

[0041] 2. The toughening filler in the topcoat film is mainly used to resist impact and minimize damage to the surface of the topcoat film. The high strength of carbon fiber combined with the high strength of polyetheretherketone (PEEK) particles helps to resist impact. The elasticity and resilience of PEEK particles and EVA, combined with the elastic filler in the epoxy resin film, further buffer the impact, making it difficult for the impact to be transmitted to the steel plate surface and cause irreversible damage. This protects the color steel plate and extends its service life.

[0042] 3. The combination of polyvinyl alcohol solution, polyethylene glycol ethanol solution, amine curing agent, and polyethyleneimine not only improves the cross-linking stability of elastic particles in epoxy resin solution, but also, by utilizing the hydroxyl groups in polyvinyl alcohol, polyethylene glycol, amine curing agent, and polyethyleneimine, further enhances the cross-linking adhesion between the epoxy resin film and the ethyl cellulose film, and improves the strength and toughness of the epoxy resin film. This allows the epoxy resin solution to adhere more stably to the surface of the steel plate coated with ethyl cellulose solution, preventing liquid flow due to corrugations and ensuring uniformity of film thickness. Consequently, the color steel plate possesses advantages such as easy coating, stable coating adhesion, uniform surface film thickness, and good impact resistance. Detailed Implementation

[0043] The present application will be further described in detail below with reference to the embodiments.

[0044] Example of preparation of ethyl cellulose solution

[0045] Preparation Example 1: The ethyl cellulose solution was prepared by the following method:

[0046] Weigh out ethyl cellulose and place it in anhydrous ethanol and stir until the ethyl cellulose is completely dissolved to obtain a 0.8% ethyl cellulose ethanol solution.

[0047] Add 0.36 kg of carboxymethyl chitosan particles and 0.04 kg of polyethyleneimine to 1 kg of ethyl cellulose ethanol solution, mix and stir until polyethyleneimine dissolves and carboxymethyl chitosan particles are evenly dispersed with an average particle size of 2-4 μm to obtain ethyl cellulose solution.

[0048] Preparation Example 2: The difference between this preparation example and Preparation Example 1 is that:

[0049] Add 0.2 kg of carboxymethyl chitosan particles and 0.02 kg of polyethyleneimine to 1 kg of ethyl cellulose ethanol solution, mix and stir until polyethyleneimine dissolves and carboxymethyl chitosan particles are evenly dispersed to obtain ethyl cellulose solution.

[0050] Preparation Example 3: The difference between this preparation example and Preparation Example 1 is that:

[0051] Add 0.5 kg of carboxymethyl chitosan particles and 0.05 kg of polyethyleneimine to 1 kg of ethyl cellulose ethanol solution, mix and stir until polyethyleneimine dissolves and carboxymethyl chitosan particles are evenly dispersed to obtain ethyl cellulose solution.

[0052] Example of preparation of elastic filler

[0053] Preparation Example 4: The elastic filler was prepared by the following method:

[0054] 0.3 kg of EVA was heated to 100°C and completely melted. It was then evenly sprayed onto the surface of 1 kg of silicon nitride fiber. After drying and dispersing until the silicon nitride fibers did not stick together or agglomerate, silicon nitride fiber was obtained.

[0055] Weigh polyurethane granules and heat them to 180℃ for 8 seconds. The average particle size of the polyurethane granules is 18-20μm. Then, 0.2kg of silicon nitride fiber is uniformly sprayed onto the surface of 1kg of polyurethane granules. The average length of the silicon nitride fiber is 5-8μm and the diameter is 10-20nm. After drying and dispersion, the loading material is obtained.

[0056] 0.3 kg of polyvinyl alcohol solution (5% by mass) was uniformly sprayed onto the surface of a 1 kg load material. After drying and dispersing, the finished elastic filler was obtained with an average particle size of 15-17 μm.

[0057] Preparation Example 5: The difference between this preparation example and Preparation Example 4 is that:

[0058] 0.2 kg of EVA was heated to 100°C and completely melted. It was then evenly sprayed onto the surface of 1 kg of silicon nitride fiber. After drying and dispersing until the silicon nitride fibers did not stick together or agglomerate, silicon nitride fiber was obtained.

[0059] Weigh polyurethane granules, heat them to 170℃ for 10 seconds, then uniformly spray 0.1 kg of silicon nitride fiber onto the surface of 1 kg of polyurethane granules, and after drying and dispersion, obtain the loading material.

[0060] 0.2 kg of polyvinyl alcohol solution (5% by mass) was uniformly sprayed onto the surface of a 1 kg load material. After drying and dispersing, the finished elastic filler was obtained.

[0061] Preparation Example 6: The difference between this preparation example and Preparation Example 4 is that:

[0062] 0.4 kg of EVA was heated to 100°C and completely melted. It was then evenly sprayed onto the surface of 1 kg of silicon nitride fiber. After drying and dispersing until the silicon nitride fibers did not stick together or agglomerate, silicon nitride fiber was obtained.

[0063] Weigh out polyurethane granules, heat them to 190℃ for 5 seconds, then uniformly spray 0.25 kg of silicon nitride fiber onto the surface of 1 kg of polyurethane granules, and after drying and dispersion, obtain the loading material.

[0064] A 0.5 kg polyvinyl alcohol solution (a 5% by mass aqueous solution) is uniformly sprayed onto the surface of a 1 kg load material. After drying and dispersing, the finished elastic filler is obtained.

[0065] Preparation example of epoxy resin liquid

[0066] The dispersant in the following raw materials was purchased from Guangdong Huajie Chemical Co., Ltd., brand BYK, model DISPERBYK-2070; other raw materials are commercially available.

[0067] Preparation Example 7: The epoxy resin liquid was prepared by the following method:

[0068] Weigh out 60 kg of epoxy resin, 10 kg of elastic filler, 8 kg of polyethylene glycol ethanol solution, 0.2 kg of defoamer, 1.5 kg of dispersant, 25 kg of amine curing agent, and 18 kg of water, mix and stir evenly to obtain epoxy resin liquid; the epoxy resin is epoxy resin E51; the elastic filler is the elastic filler prepared in Preparation Example 4, the polyethylene glycol ethanol solution has a mass fraction of 20%, the polyethylene glycol is polyethylene glycol 2000, the ethanol is anhydrous ethanol with a mass fraction of 99%; the defoamer is an organosilicon defoamer; the amine curing agent is triethylenetetramine.

[0069] Preparation Example 8: The difference between this preparation example and Preparation Example 7 is that:

[0070] Weigh 50 kg of epoxy resin, 5 kg of elastic filler, 5 kg of polyethylene glycol ethanol solution, 0.1 kg of defoamer, 1 kg of dispersant, 20 kg of amine curing agent, and 15 kg of water, mix and stir evenly to obtain epoxy resin liquid; the elastic filler used is the elastic filler prepared in Preparation Example 5.

[0071] Preparation Example 9: The difference between this preparation example and Preparation Example 7 is that:

[0072] Weigh 70 kg of epoxy resin, 15 kg of elastic filler, 10 kg of polyethylene glycol ethanol solution, 0.3 kg of defoamer, 2 kg of dispersant, 30 kg of amine curing agent, and 20 kg of water, mix and stir evenly to obtain epoxy resin liquid; the elastic filler used is the elastic filler prepared in Preparation Example 6.

[0073] Preparation example of toughening filler

[0074] Preparation Example 10: The toughening filler was prepared by the following method:

[0075] 1.5 kg of ethyl cellulose solution was uniformly sprayed onto the surface of 1 kg of polyetheretherketone (PEEK) microparticles. After drying and dispersion until the PEEK microparticles did not stick together or agglomerate, PEEK particles were obtained. The average particle size of the PEEK microparticles was 3-5 μm, the mass fraction of the ethyl cellulose solution was 0.5%, and the solvent was anhydrous ethanol.

[0076] EVA was heated to 100°C and stirred until completely melted to obtain EVA melt.

[0077] Weigh 1 kg of EVA melt and spray it evenly onto the surface of 1.6 kg of carbon fiber. The average length of the carbon fiber is 6-8 μm. Then, spray 0.8 kg of polyetheretherketone particles evenly. After drying and dispersing, the finished product is obtained with an average particle size of 15-18 μm.

[0078] Preparation Example 11: The difference between this preparation example and Preparation Example 10 is that:

[0079] Weigh 1 kg of EVA melt and spray it evenly onto the surface of 1 kg of carbon fiber. The average length of the carbon fiber is 8-10 μm. Then, spray 0.5 kg of polyetheretherketone granules evenly. After drying and breaking up, the finished product is obtained.

[0080] Preparation Example 12: The difference between this preparation example and Preparation Example 10 is that:

[0081] Weigh 1kg of EVA melt and spray it evenly onto the surface of 2kg of carbon fiber. The average length of the carbon fiber is 8-10μm. Then, spray 1kg of polyetheretherketone granules evenly. After drying and breaking up, the finished product is obtained.

[0082] Preparation example of topcoat

[0083] The hydroxyl acrylic resin in the following raw materials was purchased from Jining Sanshi Biotechnology Co., Ltd.; the dispersant was BYK-163 from BYK (Germany); the antioxidant was purchased from Qingdao Jiedejia New Material Technology Co., Ltd.; the HDI-type trimer curing agent was purchased from Jiangsu Renen Environmental Protection Technology Co., Ltd.; and other raw materials and equipment were all commercially available.

[0084] Preparation Example 13: The topcoat was prepared using the following method:

[0085] The following ingredients were prepared: 70 kg of hydroxyl acrylic resin, 14 kg of toughening filler, 8 kg of pigment, 2 kg of dispersant, 0.15 kg of defoamer, 15 kg of solvent, 0.85 kg of antioxidant, 1 kg of UV stabilizer, 55 kg of HDI-type trimer curing agent, and 30 kg of anhydrous butyl acetate. The toughening filler was the toughening filler prepared in Preparation Example 10. The pigment was carbon black. The defoamer was an organosilicon defoamer, and the solvent was ethanol. The antioxidant was antioxidant AN245DW, and the UV stabilizer was UV absorber UV123.

[0086] Weigh out hydroxyl acrylic resin, toughening filler, pigment, solvent, dispersant, defoamer, antioxidant, and UV stabilizer, mix and stir evenly to obtain a preliminary mixture;

[0087] Weigh out HDI type trimer curing agent and anhydrous butyl acetate, mix and stir evenly, then add the initial mixture and mix evenly to obtain the topcoat.

[0088] Preparation Example 14: The difference between this preparation example and Preparation Example 13 is that:

[0089] The following ingredients were prepared: 60 kg of hydroxyl acrylic resin, 8 kg of toughening filler, 5 kg of pigment, 1 kg of dispersant, 0.1 kg of defoamer, 10 kg of solvent, 0.5 kg of antioxidant, 0.5 kg of UV stabilizer, 50 kg of HDI type trimer curing agent, and 20 kg of anhydrous butyl acetate; the toughening filler was prepared in Preparation Example 11.

[0090] Preparation Example 15: The difference between this preparation example and Preparation Example 13 is that:

[0091] The following ingredients were prepared: 80 kg of hydroxyl acrylic resin, 16 kg of toughening filler, 10 kg of pigment, 3 kg of dispersant, 0.2 kg of defoamer, 20 kg of solvent, 1 kg of antioxidant, 1 kg of UV stabilizer, 50 kg of HDI type trimer curing agent, and 40 kg of anhydrous butyl acetate. The solvent was isopropanol, and the toughening filler was the toughening filler prepared in Preparation Example 12.

[0092] Example

[0093] Example 1: A surface coating process for color steel sheets:

[0094] S1. The corrugated and raised areas on the surface of the steel plate are sanded with sandpaper for 5 minutes. Then, the entire surface of the steel plate is uniformly coated with the ethyl cellulose solution prepared in Example 1. The plate is heated to 80°C and dried for 8 minutes. Then, the epoxy resin liquid prepared in Example 7 is uniformly coated on the plate. After drying and curing, the ethyl cellulose solution forms an ethyl cellulose film with an average thickness of 3-5 μm, and the epoxy resin liquid forms an epoxy resin film with an average thickness of 24-26 μm, thus obtaining a semi-finished product.

[0095] S2. The topcoat prepared in Example 13 is uniformly coated on the surface of the semi-finished product. After the topcoat dries, it forms a topcoat film with an average thickness of 22-26 μm, thus obtaining the finished color steel plate.

[0096] Example 2: The difference between this example and Example 1 is that:

[0097] S1. The corrugated raised areas on the surface of the steel plate are sanded with sandpaper for 5 minutes. Then, the entire surface of the steel plate is uniformly coated with the ethyl cellulose solution prepared in Preparation Example 2. The plate is heated to 75°C and dried for 10 minutes. Then, the epoxy resin liquid prepared in Preparation Example 8 is uniformly coated on the plate. After drying and curing, the ethyl cellulose solution forms an ethyl cellulose film, and the epoxy resin liquid forms an epoxy resin film, thus obtaining a semi-finished product. S2. The topcoat prepared in Preparation Example 14 is uniformly coated on the surface of the semi-finished product. After the topcoat dries, it forms a topcoat film, thus obtaining the finished color steel plate.

[0098] Example 3: The difference between this example and Example 1 is that:

[0099] S1. The corrugated raised areas on the surface of the steel plate are sanded with sandpaper for 5 minutes. Then, the entire surface of the steel plate is uniformly coated with the ethyl cellulose solution prepared in Preparation Example 3. The plate is heated to 85°C and dried for 5 minutes. Then, the epoxy resin liquid prepared in Preparation Example 9 is uniformly coated on the surface. After drying and curing, the ethyl cellulose solution forms an ethyl cellulose film, and the epoxy resin liquid forms an epoxy resin film, thus obtaining a semi-finished product. S2. The topcoat prepared in Preparation Example 15 is uniformly coated on the surface of the semi-finished product. After the topcoat dries, it forms a topcoat film, thus obtaining the finished color steel plate.

[0100] Example 4: The difference between this example and Example 1 is that:

[0101] No carboxymethyl chitosan microparticles or polyethyleneimine were added to the ethyl cellulose solution raw material.

[0102] Example 5: The difference between this example and Example 1 is that:

[0103] The average particle size of carboxymethyl chitosan microparticles in the ethyl cellulose solution raw material is 80-100 nm.

[0104] Example 6: The difference between this example and Example 1 is that:

[0105] No polyethylene glycol ethanol solution was added to the epoxy resin solution.

[0106] Example 7: The difference between this example and Example 1 is that:

[0107] In the preparation process of elastic particles in epoxy resin solution, no polyvinyl alcohol solution was added.

[0108] Example 8: The difference between this example and Example 1 is that:

[0109] No silicon nitride fiber was added during the preparation process of elastic particles in epoxy resin liquid.

[0110] Example 9: The difference between this example and Example 1 is that:

[0111] No toughening fillers were added to the topcoat, and the solvent was water.

[0112] Example 10: The difference between this example and Example 1 is that:

[0113] No polyether ether ketone particles were added to the toughening filler raw materials in the topcoat.

[0114] Comparative Example

[0115] Comparative Example 1: The difference between this comparative example and Example 1 is that:

[0116] A topcoat is directly applied to the surface of the steel plate, and after the topcoat dries, the finished color steel plate is obtained.

[0117] Comparative Example 2: This comparative example differs from Example 1 in that:

[0118] The surface of the steel plate is coated with epoxy resin liquid and topcoat in sequence, forming an epoxy resin film and a topcoat film on the surface of the steel plate respectively, thus obtaining the finished color steel plate.

[0119] Performance testing

[0120] 1. Coating effect inspection

[0121] Finished color steel sheets were prepared using the preparation methods of Examples 1-3 and 6, respectively. During the coating process of ethyl cellulose solution, epoxy resin liquid, and topcoat, the coating or coating effect was evaluated and the score was recorded.

[0122] Low coating resistance, almost no adhesion or accumulation problems 10 points → High coating resistance, adhesion, agglomeration, and accumulation problems, unable to spread evenly 1 point.

[0123] 2. Adhesion effect test

[0124] Finished color steel sheets were prepared using the preparation methods of Examples 1-10 and Comparative Examples 1-2, respectively. The coating adhesion was tested in accordance with the testing methods of GB / T12754-2019 Color Coated Steel Sheets and Strips.

[0125] Peel the paint film off the surface of the color steel plate at a 90° angle and observe whether the film layers separate. If the film layers do not separate, it means that the ethyl cellulose film, epoxy resin film and topcoat film are adhered stably. If they separate, it means that the adhesion is unstable. If they separate, record the length of the separation.

[0126] 3. Film uniformity detection

[0127] Finished color steel plates were prepared using the preparation methods of Examples 1-10 and Comparative Examples 1-2, respectively. The uniformity of the film layer surface thickness was measured, and the smoothness uniformity score was recorded. The scoring criteria for smoothness uniformity are as follows: smooth and flat with no slope on the film layer surface 10 points → poor smoothness and severe unevenness of film layer thickness 1 point. The film layer thickness observation includes the junction between the corrugated position and the two end plane positions, as well as the top of the corrugated position and both sides of the corrugated position. The total number of voids, bubbles, and cracks in Examples 1-3 and Comparative Example 1 were also recorded.

[0128] 4. Impact resistance test

[0129] Finished color steel sheets were prepared using the preparation methods of Examples 1-10 and Comparative Examples 1-2, respectively. The impact resistance of the paint film was tested according to GB / T1732-2020, and the data were recorded. During the test, the drop was 2 cm and multiples of 2 cm each time.

[0130] Table 1 Performance Test Table

[0131]

[0132] As can be seen from Examples 1-3 and Table 1, the surface coating of the color steel plate prepared in this application is not only easy to apply, but also has high adhesion. It is not easy for the layers to separate during peeling, indicating that the bonding effect between the layers is good. At the same time, the surface uniformity of the film layer is high, and it is not easy for some parts to be thick and some parts to be thin. It has good impact resistance, which makes the color steel plate have a long service life.

[0133] Combining Examples 1 and 4-10 with Table 1, it can be seen that in Example 4, the ethyl cellulose solution raw material did not contain carboxymethyl chitosan microparticles and polyethyleneimine. Compared with Example 1, Example 4 had poorer adhesion, a greater delamination distance, a lower uniformity score, and poorer impact resistance. This indicates that the combination of carboxymethyl chitosan microparticles and polyethyleneimine can not only improve the bonding effect between the ethyl cellulose film and the epoxy resin film, thereby improving the adhesion and bonding stability between layers, but also ensure impact resistance.

[0134] In Example 5, the average particle size of carboxymethyl chitosan microparticles in the ethyl cellulose solution raw material was 80-100 nm. Compared with Example 1, the adhesion of Example 5 was worse than that of Example 1, the delamination distance was greater than that of Example 1, the uniformity score was lower than that of Example 1, and the impact resistance was worse than that of Example 1. This indicates that the particle size of carboxymethyl chitosan microparticles is too small, and they are easily completely covered in the ethyl cellulose film, which affects the contact between the carboxymethyl chitosan microparticles and the moisture in the epoxy resin solution. As a result, the bonding effect between the ethyl cellulose film and the epoxy resin film is affected, which can easily affect the adhesion stability and the service life of the color steel plate.

[0135] In Example 6, no polyethylene glycol ethanol solution was added to the epoxy resin solution. Compared to Example 1, Example 6 showed poorer adhesion, a greater delamination distance, a lower uniformity score, and poorer impact resistance. This indicates that the ethanol in the polyethylene glycol ethanol solution can partially dissolve ethyl cellulose, facilitating the exposure of carboxymethyl chitosan microparticles floating on the surface. Furthermore, the size of the carboxymethyl chitosan microparticles and the thickness of the ethyl cellulose film limit ensure that the carboxymethyl chitosan microparticles are exposed on the surface of the ethyl cellulose film and in contact with the epoxy resin solution. While the water in the epoxy resin solution dissolves the carboxymethyl chitosan microparticles, the hydroxyl groups in polyethylene glycol, combined with the amino groups in polyethyleneimine and the epoxy resin, further enhance the crosslinking degree of the epoxy resin, thereby further improving the adhesion between the epoxy resin film and the ethyl cellulose film, resulting in a longer service life for the color steel plate.

[0136] Example 7 describes the preparation process of elastic particles in epoxy resin solution without the addition of polyvinyl alcohol solution. Compared to Example 1, Example 7 shows poorer adhesion, greater delamination distance, lower uniformity score, and poorer impact resistance. This indicates that the combination of polyvinyl alcohol solution, polyethylene glycol, epoxy resin, and amine curing agent can improve the crosslinking stability of elastic particles in epoxy resin, thereby improving the impact resistance and paint film adhesion stability of the color steel plate.

[0137] In Example 8, the preparation process of elastic particles in epoxy resin liquid was carried out without the addition of silicon nitride fiber. Compared with Example 1, the adhesion of Example 8 was worse than that of Example 1, the delamination distance was greater than that of Example 1, the uniformity score was lower than that of Example 1, and the impact resistance was worse than that of Example 1. This shows that the combination of silicon nitride fiber and EVA can improve the strength and impact resistance of elastic pigments, thereby improving the impact resistance of the paint film on the surface of the color steel plate and giving the color steel plate a longer service life.

[0138] In Example 9, no toughening filler was added to the topcoat, and the solvent was water. Compared with Example 1, the adhesion of Example 9 was worse than that of Example 1, the delamination distance was greater than that of Example 1, the uniformity score was lower than that of Example 1, and the impact resistance was worse than that of Example 1. This indicates that the addition of toughening filler can improve impact resistance, and ethanol as a solvent facilitates the dissolution of polyvinyl alcohol on the surface of the elastic filler in the epoxy resin film, so that the topcoat adheres more stably to the surface of the epoxy resin film, thereby improving the adhesion stability of the paint film on the surface of the color steel plate.

[0139] In Example 10, no polyetheretherketone (PEEK) particles were added to the toughening filler raw material in the topcoat. Compared to Example 1, Example 10 showed poorer adhesion, a greater delamination distance, a lower uniformity score, and poorer impact resistance. This indicates that PEEK particles can improve the impact resistance of the paint film. Furthermore, the ethyl cellulose on the surface of the PEEK particles gradually dissolves under the action of ethanol solvent, increasing its viscosity and thus improving the adhesion stability of the toughening filler in the topcoat. This results in a paint film on the surface of the color steel plate with higher strength and better impact resistance.

[0140] Based on Example 1 and Comparative Examples 1-2, and in conjunction with Table 1, it can be seen that the steel plate surface of Comparative Example 1 only has a topcoat film. Compared with Example 1, the adhesion of Comparative Example 1 is worse than that of Example 1, the delamination distance is greater than that of Example 1, the uniformity score is lower than that of Example 1, and the impact resistance is worse than that of Example 1. This indicates that the topcoat directly covering the surface of the color steel plate not only easily affects the adhesion stability, but also easily affects the impact resistance, thus affecting the service life of the color steel plate.

[0141] In Comparative Example 2, no ethyl cellulose film was added to the surface of the steel plate. Compared with Example 1, Comparative Example 2 had poorer adhesion, a greater delamination distance, a lower uniformity score, and poorer impact resistance. This indicates that after the ethyl cellulose film is applied to the corrugated and raised surface of the steel plate, it facilitates the adhesion of epoxy resin while binding the free-flowing epoxy resin, making it less prone to migration during the drying and curing process. This ensures the uniformity of the paint film surface and gives the paint film better adhesion.

[0142] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A surface coating process for color steel sheets, characterized in that, Includes the following steps: S1. The corrugated raised areas on the surface of the steel plate are sanded, then coated with ethyl cellulose solution, heated to 75-85℃ and dried for 5-10 minutes, then coated with epoxy resin solution, and dried and cured. The surface of the steel plate is successively coated with ethyl cellulose film and epoxy resin film to obtain a semi-finished product. S2. Apply topcoat evenly to the surface of the semi-finished product. After the topcoat dries and forms a film, the finished color steel plate is obtained. The ethyl cellulose solution is composed of an ethyl cellulose ethanol solution, carboxymethyl chitosan particles, and polyethyleneimine in a mass ratio of 1:0.2-0.5:0.02-0.

05. The epoxy resin liquid comprises the following raw materials in parts by weight: 50-70 parts epoxy resin, 5-15 parts elastic filler, 5-10 parts polyethylene glycol ethanol solution, 0.1-0.3 parts defoamer, 1-2 parts dispersant, 20-30 parts amine curing agent, and 15-20 parts water.

2. The surface coating process for color steel sheets according to claim 1, characterized in that, The elastic filler is prepared by the following method: Weigh polyurethane granules and heat them to 170-190℃ for 5-10 seconds. Then, uniformly spray silicon nitride fibers onto the surface of the polyurethane granules. The mass ratio of polyurethane granules to silicon nitride fibers is 1:0.1-0.

25. After drying and dispersion, the loading material is obtained. Polyvinyl alcohol solution is uniformly sprayed onto the surface of the load material. The mass ratio of polyurethane particles to polyvinyl alcohol solution is 1:0.2-0.

5. After drying and dispersing, the finished elastic filler is obtained.

3. The surface coating process for color steel sheets according to claim 2, characterized in that, The silicon nitride fiber is composed of silicon nitride fiber filaments and EVA in a mass ratio of 1:0.2-0.

4.

4. The surface coating process for color steel sheets according to claim 1, characterized in that, The topcoat comprises the following raw materials in parts by weight: The ingredients are: 60-80 parts hydroxyl acrylic resin, 8-16 parts toughening filler, 5-10 parts pigment, 1-3 parts dispersant, 0.1-0.2 parts defoamer, 10-20 parts solvent, 0.5-1 part antioxidant, 0.5-1 part UV stabilizer, 50-60 parts HDI type trimer curing agent, and 20-40 parts anhydrous butyl acetate.

5. The surface coating process for color steel sheets according to claim 4, characterized in that, The solvent is one or more of ethanol and isopropanol.

6. The surface coating process for color steel sheets according to claim 4, characterized in that, The toughening filler is prepared by the following method: EVA melt is weighed and evenly sprayed onto the surface of carbon fiber, and then polyetheretherketone (PEEK) particles are evenly sprayed on. The mass ratio of EVA melt, carbon fiber and PEEK particles is 1:1-2:0.5-1. After drying and dispersing, the finished product is obtained.

7. The surface coating process for color steel sheets according to claim 6, characterized in that, The polyetheretherketone (PEEK) particles are prepared by modifying PEEK microparticles with ethyl cellulose solution.

8. The surface coating process for color steel sheets according to claim 4, characterized in that, The defoamer is an organosilicone defoamer.

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