Low-VOC environment-friendly color-coated sheet adsorption material and preparation method thereof

Abstract

The invention discloses a low-VOC (volatile organic compound) environment-friendly color-coated sheet and a preparation method thereof, a substrate is a pretreated galvanized steel sheet or an aluminum-zinc plated steel sheet, the thickness range of the substrate is 0.2-2.0 mm, the surface roughness is controlled to be Ra0.8-Ra1.5 mu m, and the pretreatment sequentially comprises the steps of degreasing, cleaning and passivating; degreasing and cleaning: spraying and cleaning for 3-5 minutes by adopting an alkaline degreasing agent under the conditions that the temperature is 50-60 DEG C and the pH value is 9-11, and then spraying and rinsing with clear water twice; passivation: treating for 2-3 minutes by adopting a passivation solution containing zirconium and titanium metal salts under the conditions that the temperature is 30-40 DEG C and the concentration is 3%-5%, and then drying by using hot air at 80-100 DEG C until the surface water content is lower than 0.5%; the primer comprises the following components in parts by weight: 40-60 parts of waterborne epoxy resin, 10-20 parts of an aliphatic amine curing agent, 5-15 parts of an anti-rust pigment, 10-20 parts of an extender pigment, 2-5 parts of a coalescing agent and 10-20 parts of deionized water; the finish paint is prepared from the following components in parts by weight: 50 to 70 parts of fluorocarbon emulsion, 15 to 25 parts of weather-resistant pigment, 1 to 3 parts of ultraviolet light absorber, 1 to 3 parts of light stabilizer and 5 to 15 parts of deionized water.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly materials, specifically to a low-VOC environmentally friendly color-coated steel sheet and its preparation method. Background Art

[0002] As a type of metal sheet widely used in construction, home appliances, transportation and many other fields, color-coated steel sheets often use a large amount of raw materials such as paints and solvents containing volatile organic compounds in traditional production processes and formulas. Color-coated steel sheets release a variety of volatile organic compounds, such as benzene, toluene, xylene, ethylbenzene, formaldehyde, acetaldehyde, etc., which will be referred to as VOCs in the following text.

[0003] During the production and subsequent use of color-coated steel sheets, these VOCs continue to volatilize and release into the atmosphere, emitting irritating odors. This not only harms the health of workshop operators, causing respiratory diseases and neurological problems, but also participates in atmospheric photochemical reactions, forming secondary pollutants such as ozone and fine particulate matter, seriously impacting air quality. With increasingly stringent environmental regulations, it is urgent to develop low-VOC or even zero-VOC environmentally friendly color-coated steel sheet formulations and preparation processes to reduce the adverse impacts on the environment and humans during the production and use of color-coated steel sheets. Summary of the Invention

[0004] To comprehensively address the VOC pollution problem generated during the production and use of color-coated steel sheets, this invention provides a VOC-friendly formula and preparation method for color-coated steel sheets, thereby reducing VOC emissions during production and use while ensuring that the color-coated steel sheets possess excellent performance.

[0005] To achieve the above objectives, the present invention employs the following technical means:

[0006] A low-VOC environmentally friendly color-coated steel sheet comprises a substrate and a primer and a topcoat sequentially coated on the substrate, wherein:

[0007] The substrate is a pretreated galvanized steel sheet or aluminized zinc steel sheet with a thickness ranging from 0.2 to 2.0 mm and a surface roughness controlled between Ra0.8 and Ra1.5 μm. The pretreatment includes degreasing, cleaning, and passivation steps in sequence.

[0008] Degreasing and cleaning: Use an alkaline degreasing agent to spray and clean for 3-5 minutes at a temperature of 50-60℃ and a pH value of 9-11, followed by two rinses with clean water.

[0009] Passivation: The surface is treated with a passivation solution containing zirconium and titanium metal salts at a temperature of 30-40℃ and a concentration of 3%-5% for 2-3 minutes, and then dried with hot air at 80-100℃ until the surface moisture content is less than 0.5%.

[0010] The primer comprises, by weight, 40-60 parts of waterborne epoxy resin, 10-20 parts of aliphatic amine curing agent, 5-15 parts of anti-rust pigment, 10-20 parts of extender pigment, 2-5 parts of film-forming aid, and 10-20 parts of deionized water.

[0011] The topcoat comprises, by weight, 50–70 parts of fluorocarbon emulsion, 15–25 parts of weather-resistant pigment, 1–3 parts of ultraviolet absorber, 1–3 parts of light stabilizer, and 5–15 parts of deionized water.

[0012] Preferably, the anti-rust pigment is zinc phosphate.

[0013] Preferably, the pigment component is talc.

[0014] Preferably, the film-forming aid is a mixture of dispersant, defoamer and leveling agent.

[0015] Preferably, the weather-resistant pigment is rutile titanium dioxide.

[0016] Preferably, the coating thickness of the primer is controlled at 5-10μm, the coating is performed using a roller coating equipment, the coating speed is set at 50-100m / min according to the production line speed, and after coating, it is dried by hot air circulation at a temperature of 120-150℃ for 3-5 minutes.

[0017] This operation effectively ensures that the primer adheres evenly to the substrate and fully cures and cross-links under appropriate process parameters, forming a solid protective underlayer. This not only meets the requirement of good adhesion to the substrate but also meets the requirements of low-VOC environmentally friendly processing. If the coating thickness, speed, and drying conditions exceed this range, problems such as primer sagging, incomplete curing, poor adhesion, or excessive VOC emissions may occur.

[0018] Preferably, the coating thickness of the topcoat is 15-25μm, and it is applied using a roller coating machine. The coating speed is set at 50-100m / min according to the production line speed. After coating, the topcoat is dried at a temperature of 180-220℃ for 4-6 minutes.

[0019] This combination of process parameters ensures the quality of the topcoat film, allowing its weather resistance, color stability, and other properties to be fully utilized. If the thickness is too thin, it cannot provide sufficient protection and decorative effect, while if it is too thick, it is easy to cause problems such as uneven drying and coating cracking. Furthermore, the precise control of drying temperature and time is crucial for reducing VOC emissions and ensuring the various performance indicators of the topcoat.

[0020] Preferably, the VOC content of the primer system is less than 50 g / L, and the VOC content of the topcoat is less than 30 g / L.

[0021] A method for preparing low-VOC environmentally friendly color-coated steel sheets includes the following steps:

[0022] a. Substrate pretreatment steps: Galvanized steel sheet or aluminum-zinc coated steel sheet is fed into a degreasing tank through an automated conveying equipment for degreasing treatment, and then passed through a rinsing and passivation treatment tank for passivation before being sent to a drying equipment for drying; the degreasing, rinsing, passivation and drying conditions are the same as those described above for substrate pretreatment.

[0023] b. Primer coating and curing: The primer described above is uniformly coated onto the pretreated substrate using a roller coating machine, and the operation is carried out according to the primer coating thickness, speed and drying conditions described above;

[0024] c. Topcoat application and curing: After the primer has cured and cooled to room temperature, the topcoat is applied again using a roller coating machine. The topcoat thickness is 15-25μm. The coating speed is set to 50-100m / min according to the production line speed. After coating, the topcoat is dried at a temperature of 180-220℃ for 4-6 minutes.

[0025] d. Post-processing and inspection steps: After the topcoat has cured, the color-coated panels are allowed to cool naturally. Performance tests such as appearance, coating thickness, adhesion, and corrosion resistance are conducted. Qualified products are cut, packaged, and stored according to specifications. Unqualified products are marked and reworked.

[0026] Preferably, in the degreasing process, the alkaline degreasing agent has a stable composition, which can efficiently remove oil and impurities without leaving any residue on the substrate that would affect the adhesion and corrosion resistance of subsequent coatings; the passivation solution contains a scientifically proportioned ratio of metal salts such as zirconium and titanium, which forms a uniform and dense passivation film that effectively enhances the substrate's own protective capabilities, laying a solid foundation for the adhesion of subsequent coatings. Furthermore, the synergistic effect of each step in the entire preparation process ensures the low VOC environmental protection characteristics and excellent performance of the final color-coated plate.

[0027] Any arbitrary alteration of the degreasing agent or passivation solution, or reversal of the process steps or significant changes in parameters, will disrupt the overall process continuity, leading to adverse consequences such as excessive VOC emissions and substandard performance. For example, incomplete degreasing can result in poor adhesion and blistering in subsequent coatings; poor passivation film quality will damage the substrate's corrosion resistance, affecting the overall lifespan of the color-coated sheet; and inappropriate drying temperature and time can cause poor coating curing and uncontrolled VOC emissions.

[0028] The beneficial effects of this invention patent:

[0029] By fully adopting a water-based coating system, namely water-based epoxy resin primer and fluorocarbon emulsion topcoat, to replace traditional solvent-based coatings containing high VOCs, the use of traditional organic solvents is significantly reduced from the source. At the same time, VOC emissions are reduced by more than 80% compared with traditional processes throughout the entire color-coated sheet production process, making the color-coated sheet production process more environmentally friendly, effectively reducing pollution to the atmospheric environment, and making a positive contribution to improving air quality.

[0030] Water-based epoxy resin primers possess excellent adhesion and rust-preventive properties, forming a tightly adhered and highly rust-preventive undercoat on the substrate surface. This effectively prevents the substrate from rusting and corroding, providing a solid foundation for the entire coating system. Fluorocarbon emulsion topcoats, on the other hand, give the color-coated steel sheets excellent weather resistance and color stability. After long-term outdoor exposure tests, the coating showed no obvious fading or peeling defects, enabling the color-coated steel sheets to maintain good appearance and performance in long-term outdoor use scenarios such as building exterior walls and outdoor equipment housings. This significantly extends the service life of the color-coated steel sheets, reduces resource waste and environmental pollution caused by frequent replacement of sheets, and meets the needs of long-term outdoor use scenarios such as building exterior walls and outdoor equipment housings. Detailed Implementation

[0031] The technical solutions of the present invention will now be clearly and completely described. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the shown orientation or positional relationships and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Example 1:

[0035] A low-VOC environmentally friendly color-coated steel sheet and its preparation method:

[0036] a. Substrate pretreatment steps: Select a 0.5mm thick galvanized steel sheet as the substrate and smoothly feed it into the degreasing tank through an automated conveying system. The degreasing tank is filled with an alkaline degreasing agent. Adjust the temperature of the degreasing agent to 55℃ and the pH value to 10, and spray the substrate for cleaning. The cleaning time lasts for 4 minutes. After degreasing, the substrate is rinsed twice with clean water to thoroughly remove the residual degreasing agent from the surface.

[0037] After rinsing, the substrate enters the passivation treatment tank. The passivation solution is a passivation solution containing zirconium metal salt, with the concentration adjusted to 4% and the temperature controlled at 35°C. The substrate is passivated for 2.5 minutes. After passivation, the substrate is immediately sent to the drying equipment and dried in a hot air environment at 90°C to ensure that the surface moisture content of the substrate is less than 0.5%.

[0038] b. Primer Coating and Curing: Prepare the primer according to the formula, taking 50 parts of water-based epoxy resin, 15 parts of aliphatic amine curing agent, 10 parts of zinc phosphate, 15 parts of talc powder, 3 parts of film-forming aid (the film-forming aid is a combination of dispersant, defoamer, and leveling agent), and 7 parts of deionized water. Mix thoroughly and evenly. Use a roller coating machine to evenly coat the primer onto the pretreated substrate, controlling the coating thickness to 8μm and setting the coating speed to 75m / min. After coating, the substrate enters the curing and drying oven, using hot air circulation, setting the drying temperature to 130℃ and the drying time to 4 minutes to ensure that the primer is fully cured and cross-linked.

[0039] c. Topcoat Coating and Curing: After the primer has cured, the substrate is cooled to room temperature in the cooling section before the topcoat is applied. The topcoat formula consists of 60 parts fluorocarbon emulsion, 20 parts rutile titanium dioxide, 2 parts UV absorber, 2 parts light stabilizer, and 16 parts deionized water. Using the same roller coating equipment, the topcoat is evenly applied over the primer layer, with a coating thickness controlled at 20 μm. The coating speed is the same as the primer, set at 75 m / min. After coating, the topcoat layer enters the topcoat curing and drying oven, with the drying temperature set at 200℃ and the drying time controlled at 5 minutes to ensure good film formation and stable performance of the topcoat.

[0040] d. Post-processing and Inspection Steps: After the color-coated steel sheets have cured and cooled naturally, comprehensive performance testing is conducted. This includes: visual inspection showing a smooth and even surface with vibrant and uniform color; using a coating thickness gauge to measure the thickness of the primer and topcoat, with results meeting the set standards; a cross-cut adhesion test to test the coating adhesion, achieving excellent industry standards; and a salt spray test to test corrosion resistance, showing only slight rust spots on the coating surface after 1200 hours of testing, far superior to traditional color-coated steel sheets. The qualified color-coated steel sheets are then cut, packaged, and stored according to specifications.

[0041] Example 2:

[0042] A low-VOC environmentally friendly color-coated steel sheet and its preparation method:

[0043] a. Substrate pretreatment steps: A 1.0mm thick aluminum-zinc coated steel plate is used as the substrate and is transported to a degreasing tank. The temperature of the alkaline degreasing agent in the degreasing tank is adjusted to 60℃ and the pH value is 9.5. The substrate is sprayed and degreased for 3 minutes, and then rinsed with clean water twice.

[0044] The substrate is placed in a passivation bath using a passivation solution containing titanium metal salt at a concentration of 3.5% and a temperature of 32°C for 2 minutes. After passivation, the substrate is dried under hot air at 85°C.

[0045] b. Primer coating and curing: Prepare the primer by mixing 55 parts of water-based epoxy resin, 12 parts of aliphatic amine curing agent, 8 parts of zinc phosphate, 18 parts of talc powder, 2.5 parts of additives and 4.5 parts of deionized water. After mixing evenly, roll the primer onto the substrate to a thickness of 7 μm at a coating speed of 80 m / min and cure it at 140℃ for 3.5 minutes.

[0046] c. Topcoat application and curing: After cooling, apply the topcoat. The topcoat formula consists of 65 parts fluorocarbon emulsion, 18 parts rutile titanium dioxide, 1.5 parts ultraviolet absorber, 1.5 parts light stabilizer, and 14 parts deionized water. The coating thickness is 22 μm. The coating speed is the same as that of the primer. Curing is carried out at 190℃ for 4.5 minutes.

[0047] d. Post-processing and inspection steps: After cooling, the color-coated steel sheets are tested. All performance indicators are good, there are no defects in appearance, the coating has strong adhesion, excellent corrosion resistance, and meets the requirements of low VOC environmentally friendly color-coated steel sheets. Qualified products are put into storage, and unqualified products are marked for rework.

[0048] By fully adopting a water-based coating system, namely water-based epoxy resin primer and fluorocarbon emulsion topcoat, to replace traditional solvent-based coatings containing high VOCs, the use of traditional organic solvents is significantly reduced from the source. At the same time, VOC emissions are reduced by more than 80% compared with traditional processes throughout the entire color-coated sheet production process, making the color-coated sheet production process more environmentally friendly, effectively reducing pollution to the atmospheric environment, and making a positive contribution to improving air quality.

[0049] Water-based epoxy resin primers possess excellent adhesion and rust-preventive properties, forming a tightly adhered and highly rust-preventive undercoat on the substrate surface. This effectively prevents the substrate from rusting and corroding, providing a solid foundation for the entire coating system. Fluorocarbon emulsion topcoats, on the other hand, give the color-coated steel sheets excellent weather resistance and color stability. After long-term outdoor exposure tests, such as over 1000 hours of salt spray testing and over 2000 hours of accelerated aging testing, the coating still shows no obvious fading or peeling defects. This allows the color-coated steel sheets to maintain good appearance and performance in long-term outdoor use scenarios such as building exteriors and outdoor equipment housings, greatly extending the service life of the color-coated steel sheets and reducing resource waste and environmental pollution caused by frequent replacement of sheets. It also meets the needs of long-term outdoor use scenarios such as building exteriors and outdoor equipment housings.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0051] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A low VOC environmentally friendly color-coated plate, characterized in that: It consists of a substrate and a primer and a topcoat sequentially applied on the substrate, wherein: The substrate is a pre-treated galvanized steel sheet or an aluminum-zinc-plated steel sheet, the thickness of the substrate is in the range of 0.2-2.0 mm, and the surface roughness is controlled at Ra0.8-Ra1.5 μm, and the pre-treatment includes degreasing, cleaning, and passivation treatment steps in sequence; Degreasing and cleaning: Use alkaline degreasing agent to spray and clean for 3-5 minutes at a temperature of 50-60℃ and a pH value of 9-11, and then rinse with two streams of clean water; Passivation: Use a passivation solution containing zirconium and titanium metal salts at a temperature of 30-40°C and a concentration of 3%-5% for 2-3 minutes, then dry with hot air at 80-100°C until the surface moisture content is less than 0.5%; The primer composition includes, by weight, 40-60 parts of waterborne epoxy resin, 10-20 parts of aliphatic amine curing agent, 5-15 parts of anti-rust pigment, 10-20 parts of extender pigment, 2-5 parts of film-forming aid, and 10-20 parts of deionized water; The topcoat composition comprises, by weight, 50-70 parts of fluorocarbon emulsion, 15-25 parts of weather-resistant pigment, 1-3 parts of ultraviolet absorber, 1-3 parts of light stabilizer, and 5-15 parts of deionized water.

2. The low VOC environmentally friendly color-coated plate according to claim 1, characterized in that: The anti-rust pigment component is zinc phosphate.

3. The low VOC environmentally friendly color-coated plate according to claim 1, characterized in that: The extender pigment component is talcum powder.

4. The low VOC environmentally friendly color-coated plate according to claim 1, characterized in that: The film-forming aid component is a mixture of a dispersant, a defoamer and a leveling agent.

5. The low VOC environmentally friendly color-coated plate according to claim 1, characterized in that: The weather-resistant pigment component is rutile titanium dioxide.

6. The low VOC environmentally friendly color-coated plate according to claim 1, characterized in that: The coating thickness of the primer is controlled at 5-10 μm, and the coating is carried out by roller coating equipment. The coating speed is set at 50-100 m / min according to the production line speed. After coating, it is dried by hot air circulation at a drying temperature of 120-150° C. and a drying time of 3-5 minutes.

7. The low VOC environmentally friendly color-coated plate according to claim 1, characterized in that: The coating thickness of the topcoat is 15-25 μm, and the topcoat is coated by roller coating equipment. The coating speed is set at 50-100 m / min according to the production line speed. After coating, the topcoat is dried at a temperature of 180-220° C. for 4-6 minutes.

8. The low VOC environmentally friendly color-coated plate according to claim 1, characterized in that: The VOC content of the primer system is lower than 50 g / L, and the VOC content of the topcoat is lower than 30 g / L.

9. A method for preparing a low-VOC environmentally friendly color-coated plate, characterized in that: The following steps are involved: a. Substrate pretreatment: the substrate is sent to the degreasing tank through an automated conveying device, and the galvanized steel sheet or the aluminum-zinc-coated steel sheet is degreased according to the substrate pretreatment conditions in claim 1, and then rinsed and passivated in a passivation tank, and then sent to a drying device for drying; b. Primer coating and curing: The primer according to claim 1 is evenly coated on the pretreated substrate using a roller coating device, and the coating thickness, speed and drying conditions according to claim 6 are operated; c. Topcoat coating and curing: After the primer is cured and cooled to room temperature, the topcoat according to claim 1 is applied again using a roller coating device, and the coating thickness, speed and drying conditions set in claim 7 are implemented; d. Post-processing and inspection: After the topcoat is cured, the color-coated panels are naturally cooled and subjected to performance tests on appearance, coating thickness, adhesion, and corrosion resistance. Qualified products are cut and packaged according to specifications and stored, while unqualified products are marked and reworked.