Stabilization control method for film thickness and color difference of high-end fluorocarbon building color-coated sheet

Abstract

The invention belongs to the technical field of color-coated sheet production, and particularly relates to a high-end fluorocarbon building color-coated sheet film thickness and color difference stabilization control method which comprises the following steps: 1) performing pretreatment of degreasing, rinsing, surface conditioning and re-rinsing on a base material; (2) passivation is conducted, specifically, a chromium-containing passivation technology is adopted, and after passivation, the weight of a chemical coating film is controlled to be 25-35 mg / m < 2 >; after drying and cooling, the temperature of the base material is 60-70 DEG C; (3) coating, wherein the deviation of the coating temperature is controlled within + / -0.5 DEG C; the RN two-roller reverse coating is adopted, and the roller speed, the roller pressure and the A-P roller gap of the P roller and the A roller are controlled; the viscosity of the coating is controlled, the color difference delta E of the coating is smaller than or equal to 0.5, and delta b * ranges from-0.2 to-0.4; the plate temperature of the color-coated plate in a primary coating curing oven is controlled, and the furnace temperature and the air speed of a fine coating curing oven are controlled, and the cooling water temperature, the spraying pressure and the drying temperature are controlled. The method has the advantages that the technical problems that in high-end fluorocarbon building color-coated plate production, the film thickness control precision is poor and the color difference is unstable for a long time are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of color-coated steel sheet production technology, and particularly relates to a method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated steel sheets. Background Technology

[0002] Fluorocarbon color-coated steel sheets are high-end color-coated products. The surface coating uses PVDF coating, which has superior weather resistance compared to ordinary PE coating. Compared with color-coated steel sheets, fluorocarbon color-coated steel sheets not only have a beautiful appearance and good corrosion resistance, but also have more stable physical and chemical properties. They are currently widely used in key urban projects and landmark buildings.

[0003] Compared to other ordinary polyester products, fluorocarbon color-coated steel sheets typically have a coating thickness of ≥23μm (ordinary polyester ≥20μm). Due to the higher coating thickness, the high viscosity of the fluorocarbon coating itself, and the special nature of the coating process, poor material feeding by the feed rollers during strip coating leads to lower coating accuracy and less stable film thickness control compared to other ordinary polyester products, easily resulting in excessive thickness (standard film thickness range 0~+4μm, target value +2μm). Furthermore, the fluorocarbon resin content in the coating is typically ≥70%, generally employing a two-coat, two-bake process. High-temperature baking is required to cross-link and cure the resin, forming a dense protective layer. However, high temperatures can cause unstable color differences on the sheet surface, easily resulting in a yellowish tint, affecting product appearance and user experience. In addition, excessive film thickness leads to excessive paint consumption, significantly increasing production costs.

[0004] In a certain color-coated steel sheet manufacturer, 30% of the fluorocarbon coating products had a thickness exceeding the tolerance by 1μm, and 16% had a thickness exceeding the tolerance by 2μm or more. Therefore, in the production of fluorocarbon color-coated steel sheets, the industry often encounters problems such as unstable and excessively thick film thickness, which leads to high paint consumption and increased production costs. At the same time, the unstable film thickness also causes color differences in the actual products to exceed the standard, affecting the aesthetics and user experience.

[0005] The industry urgently needs a comprehensive production technology that can simultaneously and stably control film thickness and reduce color difference in order to improve the physical quality of high-end fluorocarbon color-coated sheets, reduce production costs, and enhance market competitiveness. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated steel sheets, solving three interrelated problems that have long existed in the production of high-end fluorocarbon color-coated steel sheets: poor film thickness control accuracy, unstable color difference, and high paint consumption. This method improves the quality of fluorocarbon color-coated steel sheets, significantly reducing color difference problems caused by uneven film thickness; it narrows the total film thickness control range in actual production from the industry-standard 0 to +4 μm to 0 to +1 μm, achieving refined production. It also reduces paint consumption and waste in fluorocarbon products, lowering the paint cost per ton of steel.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels includes the following steps: 1) Substrate pretreatment: The substrate is subjected to spray degreasing, spray rinsing, spray surface conditioning, and finally spray rinsing in sequence. 2) Passivation: A chromium-containing passivation process is adopted, with the chemical coating solution (working tank solution) having a mass concentration of 25%~40%, and the chromium point controlled at AT9~11. After substrate passivation, the chemical coating film weight is controlled at 25~35 mg / m³. 2 After passivation, the drying temperature is 185~190℃, and the substrate temperature after cooling is 60~70℃. 3) Painting: The constant temperature system of the coating machine room is precisely controlled, and the temperature deviation of the coating is controlled within ±0.5℃. Since temperature changes the thermal motion of molecules inside the coating, the thermal motion of molecules inside the coating intensifies when the temperature rises, the distance between molecules increases, the intermolecular force weakens, the relative fluidity is better, and the viscosity of the coating decreases. Therefore, constant temperature control can accurately control the viscosity of the coating and ensure uniform coating thickness. The RN two-roll reverse coating method is adopted, with the P roller speed at 35~60m / min, the A roller speed at 65~85m / min, the roller pressure at 2.0~3.0kN, and the AP roller gap at 1.0~3.0mm. During production, the paint tray temperature control system is running, with the temperature set at 20~35℃. After premixing and stirring the paint, the viscosity is controlled at 120~150 seconds. The color difference ΔE between the paint sample and the standard color swatch is ≤0.5, and the color difference Δb* between the paint sample and the standard color swatch in the yellow-blue phase is controlled within -0.2 to -0.4; in order to offset the influence of the yellowish phase caused by high-temperature curing. 4) Curing oven process: During the initial coating process in the No. 1 curing oven, the board temperature is controlled at 224~232℃. After the fine coating, the temperature in the No. 2 curing oven is controlled at 241~254℃ to ensure the cross-linking and curing effect of the fluorocarbon resin and form a dense coating on the surface. After the fine coating, the temperature of the first stage of the No. 2 curing oven is controlled at 250~280℃, the temperature of the second stage is controlled at 276~291℃, and the temperature of the third and fourth stages is controlled at 309~318℃. The air velocity of the first stage oven is reduced by 20%~25%. 5) Cooling: After the paint film has cured, the cooling water temperature is <40℃, the spraying pressure is 1.3kg≤2.0kg, and the hot air drying temperature after cooling is ≥80℃.

[0008] In step 1), the spray degreasing treatment is to use a degreasing agent to spray degrease the substrate once, with a water temperature of 35~40℃, a degreasing solution concentration of 2%~3.5%, and the free alkalinity controlled at 7~12 after mixing.

[0009] In step 1), the spray rinsing process involves spraying the substrate twice with filtered water at a temperature of 33-38°C.

[0010] In step 1), the spray surface conditioning treatment involves spraying the substrate with a surface conditioning agent once. The surface conditioning liquid has a mass percentage concentration of 3% to 5.5%, a pH value of 3.0 to 3.5, and a water temperature of 35 to 40°C.

[0011] The surface conditioning solution contains nickel salt, hydrofluoric acid, and sulfuric acid, wherein the mass percentage of nickel ions is 2% to 8%, the mass percentage of hydrofluoric acid is 4% to 9%, and the mass percentage of sulfuric acid is 20% to 40%.

[0012] In step 1), the final spray rinsing treatment is to spray the substrate twice with demineralized water at a temperature of 33~38℃.

[0013] In step 4), the wind speed of the first furnace section is 10~20m / s.

[0014] In step 5), the cooling water is demineralized water.

[0015] Compared with the prior art, the beneficial effects of the present invention are: The technical solution of this invention effectively solves the long-standing technical problems of poor film thickness control accuracy and unstable color difference in the production of high-end fluorocarbon architectural color-coated panels by systematically optimizing the complete process flow from substrate pretreatment to coating, curing, and cooling. The specific technical effects are reflected in the following three aspects: 1. The method of this invention significantly improves the uniformity of film thickness distribution, successfully narrowing the total film thickness control target range of fluorocarbon color-coated plates from the traditional "0 to +4μm" to "0 to +1μm", achieving "near-zero deviation" control of film thickness. Actual production data shows that the proportion of products with film thickness exceeding the positive deviation by more than 1μm has decreased significantly from 46.5% per year (of which exceeding 1μm accounts for 30.1%, and exceeding 2μm and above accounts for 16.4%) to 16.1% (of which exceeding 1μm accounts for 13.8%, and exceeding 2μm and above accounts for 2.3%).

[0016] 2. This invention effectively curbs color fluctuations caused by uneven film thickness and uneven curing by precisely controlling the color difference and hue tendency of the coating at the factory, and through a dual guarantee mechanism of constant temperature coating and optimized curing process. After adopting the method of this invention, the average color difference value (ΔE) of the product is steadily reduced from 0.78 to 0.65, and the product hue changes from being prone to yellowing to a stable, bright, high-quality appearance, significantly reducing the rate of defective products.

[0017] 3. The production cost is significantly reduced by using the method of this invention. The improved precision in film thickness control directly leads to precise savings in coatings. Taking the production of fluorocarbon coated products by a certain color-coated steel sheet manufacturer as an example, the coating consumption per ton of steel decreased from 23.62 kg / t to 21.02 kg / t, a reduction of 2.6 kg / t. At the same time, the improved color difference stability leads to a decrease in the defect rate, reducing quality losses. Attached Figure Description

[0018] Figure 1 This is a surface diagram of the original fluorocarbon building color-coated panel.

[0019] Figure 2 This is a surface view of the fluorocarbon building color-coated sheet produced by the method of this invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0021] A method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels includes the following steps: 1) Substrate pretreatment: The substrate is subjected to spray degreasing, spray rinsing, spray surface conditioning, and spray rinsing in sequence.

[0022] The treatment process includes: 1) Spray degreasing: The substrate is degreased once using a degreasing agent at a water temperature of 35-40℃. The degreasing solution concentration is 2%-3.5% by mass, and the free alkalinity (Pt) is controlled at 7-12 after preparation. 2) Spray rinsing: The substrate is rinsed twice using filtered water at a water temperature of 33-38℃ to remove any residual degreasing solution. 3) Spray surface conditioning: The substrate is surface-conditioned once using a surface conditioning agent at a concentration of 3%-5.5%, a pH of 3.0-3.5, and a water temperature of 35-40℃. The surface conditioning agent contains nickel salt, hydrofluoric acid, and sulfuric acid, with nickel ions accounting for 2%-8% by mass, hydrofluoric acid for 4%-9% by mass, and sulfuric acid for 20%-40% by mass. 4) Finally, the substrate is rinsed twice using demineralized water at a water temperature of 33-38℃.

[0023] 2) Passivation: The hexavalent chromium passivation process is adopted, with the chemical coating solution concentration ratio of 25%~40%. The hexavalent chromium point (AT) is 9~11 (obtained by iodometric titration, requiring 9~11 mL of 0.1mol / L Na2S2O3 per 5 mL of bath solution). After substrate passivation, the chemical coating film weight is controlled at 25~35 mg / m². 2 After passivation, the drying temperature is 185~190℃, and the substrate temperature after cooling is 60~70℃. 3) Painting: The constant temperature system of the coating room is precisely controlled to ensure that the temperature of the paint in the paint tray is constant and the temperature control deviation of the paint is controlled within ±0.5℃; the temperature control capability of the system is improved to ensure constant temperature, thereby enhancing the film thickness control capability.

[0024] The RN two-roll reverse coating method is adopted. Roll speeds are as follows: for a linear production speed of 60 m / s, the P roll speed is set at 55 m / min, and the A roll speed is maintained at 75 m / min; for a linear production speed of 50 m / s, the A roll speed is set at 65 m / s, and the P roll speed is set at 45~50 m / min. The roll pressure is set at 2.0 kN, and the AP roll gap is maintained at 2.0 mm.

[0025] After premixing the coating, the viscosity is controlled at 130 seconds (measured with an NK-2 viscosity cup). During production, the constant temperature system of the paint tray is kept running, and the temperature is set at 23℃.

[0026] The color difference ΔE between the paint sample and the standard color swatch should be ≤0.3, and the color difference Δb* between the sample and the standard color swatch in the yellow and blue hues should be controlled within -0.2 to -0.4 to ensure that the color difference of the finished product is stable within the required range.

[0027] The coating process was optimized during production. The coating process parameters are shown in Table 1 compared with those before implementation.

[0028] 4) Curing oven process: During the initial coating process in the No. 1 curing oven, the board temperature is controlled at 224~232℃. After the fine coating, in the No. 2 curing oven, the board temperature is controlled at 241~254℃. After the fine coating, the No. 2 curing oven temperature settings are adjusted in five stages: the temperature of stages one and two is reduced, and the temperature of stages three and four is increased. The air velocity of stage one is reduced by 25%. The temperature of stage one is controlled at 257~272℃, the temperature of stage two is controlled at 276~291℃, and the temperature of stages three and four is controlled at 309~318℃. The air velocity of stage one is set to 15m / s to avoid defects caused by excessively high inlet temperature.

[0029] 5) Cooling: After the paint film cures, surface cooling is performed using demineralized water. The cooling water temperature after curing is <40℃, the spraying pressure is 1.3kg ≤ spray pressure ≤ 2.0kg, and the hot air drying temperature after cooling is ≥80℃. See the image below for the finished color-coated sheet surface. Figure 2 .

[0030] During production, color difference and film thickness data are measured and combined with this data to quickly determine the film thickness trend and make timely adjustments, continuously improving process control capabilities and precisely controlling film thickness. The measured film thickness deviation was 0μ, a significant improvement compared to the previous deviation of 3μ, reducing paint waste and lowering production costs.

[0031] Example 1: Methods for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels, specifically including: 1. Substrate pretreatment: Degreasing solution with free alkalinity (Pt) of 8 and water temperature of 35℃; surface conditioning solution with pH value of 3.2 and water temperature of 35℃; two rinsing steps after degreasing, using filtered water at 38℃; two rinsing steps after surface conditioning, using demineralized water at 36℃.

[0032] 2. Passivation process: Hexavalent chromium passivation is adopted, with a hexavalent chromium point (AT) of 10. The passivation drying temperature is 185℃, and the substrate temperature after cooling is 65℃. The weight of the passivated coating film is 25mg / m². 2 .

[0033] 3. Coating Process: After premixing, the paint viscosity is 120 seconds. The constant temperature system operates stably, and the paint reflux temperature in the paint tray is set at 25℃. A two-roll reverse coating method (RN) is used, with a production line speed of 60m / s. The P roll speed is set to 55m / min, the A roll speed is maintained at 75m / min, the roll pressure is set at 2.0kN, and the AP roll gap is maintained at 2.0mm. 4. Curing process: The temperature of the board at the outlet of the No. 1 curing oven is controlled at 231℃ for the initial coating. After the fine coating, the temperature of the No. 2 curing oven is set in five stages: 260℃, 280℃, 310℃, 310℃ and 290℃. The wind speed of the first stage is set to 15m / s to keep the board temperature at 241℃.

[0034] 5. Cooling process: After curing, the cooling water temperature of the cooling section is set at 35℃, the spray pressure is 1.5kg, and the hot air drying temperature after cooling is 90℃.

[0035] 6. Production speed: The production line speed is set to 65m / min.

[0036] Example 2: Methods for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels, specifically including: 1. Substrate pretreatment: Degreasing solution with free alkalinity (Pt) of 9 and water temperature of 37℃; surface conditioning solution with pH value of 3.0 and water temperature of 36℃; two rinsing steps are set after the degreasing process, using filtered water at 36℃; two rinsing steps are set after the surface conditioning process, using demineralized water at 36℃.

[0037] 2. Passivation process: Hexavalent chromium passivation is adopted, with a hexavalent chromium point (AT) of 9. The passivation drying temperature is 190℃, and the substrate temperature after cooling is 60℃. The weight of the passivated coating film is 30mg / m³. 2 .

[0038] 3. Coating Process: After premixing, the paint viscosity is 130 seconds. The constant temperature system operates stably, and the paint reflux temperature in the paint tray is set at 25℃. A two-roll reverse coating method (RN) is used, with a production line speed of 50m / s. The P roll speed is set to 50m / min, the A roll speed is maintained at 65m / min, the roll pressure is set at 2.0kN, and the AP roll gap is maintained at 2.0mm. 4. Curing process: The temperature of the board at the outlet of the No. 1 curing oven is controlled at 231℃ for the initial coating. After the fine coating, the temperature of the No. 2 curing oven is set in five stages: 260℃, 280℃, 300℃, 300℃ and 290℃. The wind speed of the first stage is set to 15m / s to keep the board temperature at 242℃.

[0039] 5. Cooling process: After curing, the cooling water temperature of the cooling section is set at 30℃, the spray pressure is 1.5kg, and the hot air drying temperature after cooling is 95℃.

[0040] 6. Production speed: The production line speed is set to 50m / min.

[0041] This invention effectively solves the long-standing technical problems of poor film thickness control accuracy and unstable color difference in the production of high-end fluorocarbon architectural color-coated panels by systematically optimizing the complete process flow from substrate pretreatment to coating, curing and cooling.

Claims

1. A method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels, characterized in that, Includes the following steps: 1) Substrate pretreatment: The substrate is subjected to spray degreasing, spray rinsing, spray surface conditioning, and finally spray rinsing in sequence. 2) Passivation: A chromium-containing passivation process is used, with a chemical coating solution concentration of 25%~40%, chromium points controlled at AT9~11, and the chemical coating film weight controlled at 25~35 mg / m² after substrate passivation. 2 After passivation, the drying temperature is 185~190℃, and the substrate temperature after cooling is 60~70℃. 3) Painting: The temperature control system of the coating room is precisely controlled, and the temperature deviation of the coating is controlled within ±0.5℃. The RN two-roll reverse coating method is adopted, with the P roller speed at 35~60m / min, the A roller speed at 65~85m / min, the roller pressure at 2.0~3.0kN, and the AP roller gap at 1.0~3.0mm. During production, the paint tray temperature control system is running, with the temperature set at 20~35℃. After premixing and stirring the paint, the viscosity is controlled at 120~150 seconds. The color difference ΔE between the paint sample and the standard color swatch is ≤0.5, and the color difference Δb* between the paint sample and the standard color swatch in the yellow and blue hues is controlled within -0.2 to -0.

4. 4) Curing oven process: During the initial coating process in the No. 1 curing oven, the board temperature is controlled at 224~232℃. After the fine coating, in the No. 2 curing oven, the board temperature is controlled at 241~254℃. After the fine coating, the temperature of the first stage of the No. 2 curing oven is controlled at 250~280℃, the temperature of the second stage is controlled at 276~291℃, and the temperature of the third and fourth stages is controlled at 309~318℃. The air velocity of the first stage oven is reduced by 20%~25%. 5) Cooling: After the paint film has cured, the cooling water temperature is <40℃, the spraying pressure is 1.3kg≤2.0kg, and the hot air drying temperature after cooling is ≥80℃.

2. The method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels according to claim 1, characterized in that, In step 1), the spray degreasing treatment is to use a degreasing agent to spray degrease the substrate once, with a water temperature of 35~40℃, a degreasing solution concentration of 2%~3.5%, and the free alkalinity controlled at 7~12 after mixing.

3. The method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels according to claim 1, characterized in that, In step 1), the spray rinsing process involves spraying the substrate twice with filtered water at a temperature of 33-38°C.

4. The method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels according to claim 1, characterized in that, In step 1), the spray surface conditioning treatment involves spraying the substrate with a surface conditioning agent once. The surface conditioning liquid has a mass percentage concentration of 3% to 5.5%, a pH value of 3.0 to 3.5, and a water temperature of 35 to 40°C.

5. The method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels according to claim 4, characterized in that, The surface conditioning solution contains nickel salt, hydrofluoric acid, and sulfuric acid, wherein the mass percentage of nickel ions is 2% to 8%, the mass percentage of hydrofluoric acid is 4% to 9%, and the mass percentage of sulfuric acid is 20% to 40%.

6. The method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels according to claim 1, characterized in that, In step 1), the final spray rinsing treatment is to spray the substrate twice with demineralized water at a temperature of 33~38℃.

7. The method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated panels according to claim 1, characterized in that, In step 4), the wind speed of the first furnace section is 10~20m / s.

8. The method for stabilizing and controlling the film thickness and color difference of high-end fluorocarbon architectural color-coated steel sheets according to claim 1, characterized in that, In step 5), the cooling water is demineralized water.

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