Color-coated fingerprint-resistant steel plate and production method thereof

Abstract

The invention discloses a color-coated fingerprint-resistant steel plate, which comprises a substrate, and a color-coated layer and a fingerprint-resistant layer which are respectively arranged on the upper surface and the lower surface of the substrate, and is prepared by the following steps: 1) cleaning the substrate; (2) the face, to be subjected to color coating, of the base plate is subjected to passivation treatment through a chromium-free passivation solution, and the other face, to be provided with the fingerprint-resistant layer, of the base plate is subjected to surface treatment through desalted water; performing baking; (3) the obtained passivated surface is coated and cured with polyurethane primer, and a color-coated bottom layer is obtained; 4) finely coating polyester colored paint on the surface of the color-coated bottom layer; roller-coating one surface treated by the desalted water with a fingerprint-resistant coating; curing the substrate subjected to double-sided coating to obtain a composite substrate of which one surface is colored and the other surface is provided with a fingerprint layer; the color-coated surface of the obtained color-coated fingerprint-resistant plate product can be used for a building appearance surface, the color-coated fingerprint-resistant plate product is high in weather resistance and attractive in color, the binding force between a fingerprint-resistant surface film and a base body is high, a good protection effect on base body metal is achieved, the quality of industrial batch products is stable, and the color-coated fingerprint-resistant plate product is suitable for application and popularization.

Description

Technical Field

[0001] This invention belongs to the field of coated steel plate technology, specifically relating to a color-coated fingerprint-resistant steel plate and its production method. Background Technology

[0002] As an environmentally friendly, energy-saving, and easily processed new material, color-coated steel sheets have been widely used in construction, home appliances, and decoration. With the continuous improvement of requirements for the uses and quality of color-coated products, their applications are becoming increasingly widespread. Light steel buildings, house structures, and high-rise curtain walls are beginning to use color-coated products directly on a large scale. Color-coated steel sheets can usually be formed in one step, with a colored coating, eliminating the need for chemical anti-corrosion treatment or spraying processes. This effectively solves problems such as VOC emissions and the discharge of wastewater and waste residue containing heavy metals caused by subsequent coating processes. Among these, color-coated products have seen a continuous increase in market usage in recent years due to their unique appearance, aesthetics, and weather resistance.

[0003] Hot-dip galvanized fingerprint-resistant steel sheet is a high-value-added product made from cold-rolled steel sheet as the base material. After hot-dip galvanizing, a 1-3μm thick organic composite resin film is coated onto the surface. Fingerprint-resistant steel sheet boasts advantages such as attractive appearance, high corrosion resistance, excellent fingerprint resistance, good electrical conductivity, resistance to blackening, scratch resistance, and high chemical stability. Furthermore, the fingerprint-resistant film exhibits strong adhesion to the substrate, providing excellent protection for the base metal. It has been widely used in home appliances, construction, and other fields.

[0004] Currently, existing color-coated steel sheets and hot-dip galvanized fingerprint-resistant steel sheets belong to two main product categories. Color-coated steel sheets have brighter and more aesthetically pleasing colors and better corrosion resistance, but are more expensive. Hot-dip galvanized fingerprint-resistant steel sheets are more suitable for non-surface surfaces with lower corrosion resistance requirements, and in some fields, they are easier to process than color-coated sheets, while being relatively cheaper. Further exploration of a simple and efficient way to prepare steel sheet products with one side color-coated and the other side fingerprint-resistant has significant research and application value. Summary of the Invention

[0005] The main objective of this invention is to provide a color-coated fingerprint-resistant steel plate with a structure in which one side is color-coated and the other side is fingerprint-resistant; it has strong weather resistance, beautiful color, strong adhesion between the fingerprint-resistant film and the substrate, good protection for the base metal, and wide applicability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a color-coated fingerprint-resistant steel sheet, the color-coated fingerprint-resistant steel sheet comprising a substrate and a color coating layer and a fingerprint-resistant layer respectively disposed on its upper and lower surfaces; the specific preparation method includes the following steps: 1) Substrate cleaning; the substrate is degreased and rinsed; 2) Surface treatment; The surface to be coated is passivated with a chromium-free passivation solution, and the fingerprint-resistant surface is treated with desalinated water; then the substrates treated on both sides are baked. 3) Initial coating of the colored surface; The surface to be coated in step 2) is coated with and cured with polyurethane primer to obtain the color coating underlayer; 4) Double-sided fine coating; A fine coating of polyester paint is applied to the surface of the color-coated base layer; A fingerprint-resistant coating is applied to one side after desalination treatment by roller coating. The steel plate with double-sided coating is cured in a fine coating oven to obtain a composite substrate with one side color coating and the other side fingerprint layer. 5) Cooling and winding; During cooling, the cooling water circulation volume needs to be increased, and the circulation volume should be controlled at 100-120m³. 3 / h; After the steel plate cools to a temperature below 40℃, the hardness of the lower coating layer of the color-coated surface is increased to prevent pressure marks on the color-coated surface due to the high hardness of the fingerprint-resistant surface after winding; then winding is performed.

[0007] In the above scheme, the substrate can be made of pure zinc galvanized steel sheet or high-aluminum zinc-aluminum-magnesium hot-dip galvanized steel sheet.

[0008] Furthermore, the main components and their mass percentages in the coating of the high-aluminum-zinc-aluminum-magnesium hot-dip galvanized steel sheet include: aluminum 53-56%, zinc 40-43%, and magnesium 1.6-2.4%; its surface roughness is large, resulting in better coating adhesion.

[0009] In the above scheme, the degreasing step adopts a step-by-step degreasing process, and the concentration of the alkali solution decreases progressively; the alkali solution can be one or more of sodium hydroxide, potassium hydroxide, etc.

[0010] Furthermore, the stepwise degreasing process includes: firstly, degreasing the substrate once in an alkaline solution at 55-65°C and a concentration of 1.2-1.6 wt% (4-9 s); then, degreasing it a second time in an alkaline solution at 50-60°C and a concentration of 0.5-1.3 wt% (4-8 s).

[0011] In the above scheme, the rinsing step is a three-stage rinsing process, wherein the rinsing solution temperature used in the first stage is 55-60℃, the rinsing solution temperature used in the second stage is 50-60℃, and the rinsing solution temperature used in the third stage is 40-50℃.

[0012] Furthermore, in the three-stage rinsing process, the rinsing solution temperature is decreased progressively.

[0013] Furthermore, the conductivity of the rinsing solution is controlled to be less than 500 µS / cm.

[0014] Furthermore, the rinsing solution is desalinated water (1-5 mg / L).

[0015] In the above scheme, the components and their mass percentages in the chromium-free passivation solution include: 0.2-1.2% fluorotitanic acid, 1.3-2.4% phosphate, 4-6% acrylic resin; the remainder is water.

[0016] In the above scheme, the amount of passivation solution coated is controlled to be 1-2 g / m. 2 .

[0017] Further, the baking temperature in step 2) is 75-105℃.

[0018] In the above scheme, the coating thickness formed by the polyurethane paint is 4-6μm; the curing temperature is 224-232℃.

[0019] Furthermore, the upper viscosity (Zahn#4 cup) of the polyurethane coating is controlled to be 12-15 s / 35℃.

[0020] In the above scheme, the temperature of the steel plate during the curing process described in step 3) is 224-241℃.

[0021] In the above scheme, the thickness of the polyester paint coating formed by the polyester paint is 15-17μm.

[0022] Furthermore, the upper viscosity (Zahn#4 cup) of the polyester varnish is controlled to be 16-18 s / 35℃.

[0023] In the above scheme, the main component of the fingerprint-resistant coating is water-based polyurethane resin, with an effective solid content of 48-55%.

[0024] In the above scheme, the thickness of the fingerprint-resistant layer is 1-3μm.

[0025] Furthermore, in the roll coating step, the coating roller pressure is controlled at 120-150 kg, the material-adhesive roller speed ratio is controlled at 50-70%, and the coating roller speed ratio is controlled at 120-160%.

[0026] Furthermore, the steel plate temperature during the curing (fine coating and baking) process in step 4) is 224-241℃.

[0027] Furthermore, in the curing process described in step 4), the fine coating baking oven is divided into three or more (preferably five) temperature zones for temperature control; the temperature of the last zone is 230 + 1.62 × TV (T is the strip thickness in mm; V is the strip speed in meters per minute), and the oven temperature of each preceding zone decreases by 15-25°C from the last zone.

[0028] Furthermore, the strip speed is 100-150 meters per minute.

[0029] Furthermore, the thickness of the strip is 0.3-0.8 mm.

[0030] Furthermore, in the winding step, the winding tension is adjusted according to the strip thickness: when the strip thickness is below 0.6mm, the winding tension is 32-36 N / m. 2 Control; when the strip thickness is greater than 0.6mm, the coiling tension should be 30-34N / m. 2 control.

[0031] The fingerprint-resistant steel plate prepared according to the above scheme includes a substrate and a color coating layer and a fingerprint-resistant layer respectively disposed on its upper and lower surfaces; the color coating layer is not less than 20 micrometers and its performance meets the national standard GB / T12754; the fingerprint-resistant surface can meet the performance of 240h salt spray level 6 or above for flat plates.

[0032] This invention involves a two-coat, two-bake process on a color-coated steel sheet production line. First, the substrate (pure zinc-galvanized steel coil or high-aluminum zinc-aluminum-magnesium hot-dip galvanized steel coil) such as steel strip is degreased and cleaned in multiple stages, then passivated on one side (the color-coated side), and the other side is treated with desalination water (to ensure the coating effect of the subsequent fingerprint-resistant layer). Then, the first color-coated undercoat (primer) is applied. Next, by adjusting the fine coating machine, the topcoat (polyester paint) of the color-coated product is applied to the front side, and the fingerprint-resistant resin is applied to the back side. After curing and cooling, the product is rolled into a finished product.

[0033] The resulting fingerprint-resistant color-coated steel sheet has a color-coated surface suitable for building facades, exhibiting strong weather resistance and attractive colors. The fingerprint-resistant film has strong adhesion to the substrate, providing good protection for the base metal. Furthermore, its processability in some areas surpasses that of traditional color coatings, and its price is relatively lower. Products manufactured using the fingerprint-resistant color-coated steel sheet produced by this invention exhibit stable quality in industrial-scale production, with good batch-to-batch consistency.

[0034] Compared with the prior art, the beneficial effects of the present invention include: 1) The fingerprint-resistant surface is first treated with desalination water coating, without the need for passivation treatment. This ensures stable rotation of the coating roller on the fingerprint-resistant surface to guarantee the stability of the strip in this area, and will not cause any changes to the strip substrate after drying. 2) First, a primer is sprayed and baked onto the surface to be coated with color paint using a pre-coating machine. Then, a fine coating machine is used to coat the surface with color paint and a fingerprint-resistant layer, thus creating a composite substrate with a color coating on one side and a fingerprint layer on the other. 3) The topcoat (polyester paint) and fingerprint resistant coating of the color-coated surface need to be cured simultaneously in the fine coating baking oven. The temperature process of the plate is controlled by combining the strip thickness and strip speed, which can effectively ensure the curing effect of the color-coated surface and the fingerprint-resistant surface.

[0035] 4) The winding process adjusts the winding tension according to the strip thickness, which can effectively improve the problems of interlayer scratches and slippage caused by the contact between the color-coated surface and the fingerprint-resistant surface, resulting in loose winding and collapse. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of a color-coated fingerprint-resistant board; Figure 2 This is a schematic diagram of the process layout for the color coating unit; Figure 3 The image shows the morphology of the color-coated fingerprint-resistant steel plate obtained in Comparative Example 5. In the diagram, 1. steel plate substrate, 2. fingerprint-resistant layer, 3. passivation layer, 4. primer layer, and 5. topcoat layer. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] In the following embodiments, the color-coated fingerprint-resistant steel sheet is prepared using a conventional two-coat, two-bake color-coating unit. The specific preparation method includes the following steps: 1) Cleaning the substrate: The substrate used is a high-aluminum, zinc-aluminum-magnesium hot-dip galvanized substrate produced by Wuhan Iron and Steel Group's full-process technology (the main components and contents of the coating are: aluminum 53-56wt%, zinc 40-43wt%, magnesium 1.6-2.4wt%). The substrate is placed in an alkaline solution (sodium hydroxide solution) with a temperature of 55-65℃ and a mass concentration of 1.2-1.6% for a first degreasing for 4-7 seconds; then it is placed in an alkaline solution (sodium hydroxide solution) with a temperature of 50-60℃ and a mass concentration of 0.5-1.2% for a second degreasing for 4-7 seconds to remove emulsion, zinc ash, rust-preventive oil, impurities and other contaminants from the substrate surface. The substrate is then rinsed three times in a rinsing tank. The temperature of the first rinsing solution (using demineralized water, 1-5 mg / L, the same below) is 55-60℃, the temperature of the second rinsing solution (using demineralized water) is 50-60℃, and the temperature of the third rinsing solution (using demineralized water) is 40-50℃. After three rinsings, the alkaline solution on the substrate surface can be removed and impurities and other contaminants can be thoroughly removed. After the above degreasing and cleaning treatment, there is no oil, impurities, alkaline solution, or other residues on the substrate surface that would affect subsequent processes, thus completing the cleaning process. 2) Passivation: One side of the cleaned substrate (the colored side) is passivated by a coating roller containing a passivation solution. The components and their mass percentages of the chromium-free passivation solution are as follows: fluorotitanic acid 0.2-1.2%, phosphate 1.3-2.4%, acrylic resin 4-6%, and the remainder is water. The curing temperature of the passivation layer is 70-100℃, and the coating amount of the passivation solution is controlled at 1-2 g / m². 2 And control the Ti level at 3-9 mg / m³ 2 The fingerprint-resistant side needs to be coated with desalinated water to ensure that the strip is located in the center of the coating and operates stably. 3) Apply primer: Apply polyester paint to the front side of the passivated substrate. Specifically, apply polyurethane primer to the front side (the side to be colored) on the primary coating machine. The coating is cured at 224-232℃, and the steel plate temperature is 224-241℃, forming a colored paint with a thickness of 4-6μm. The fingerprint-resistant side does not need a coating. Raise the lifting roller to ensure the strip passes through the plate. 4) Topcoat application: After the primer has cured, apply polyester paint to its surface, specifically on the front side using a fine coating machine, with a coating thickness of 15-17μm. The side of the substrate requiring a fingerprint-resistant layer is coated with a water-based polyurethane resin coating with an effective solids content of 50%, and a coating thickness of 1-3μm. The coating roller pressure is controlled at 120-150kg, the material-adhesive roller speed ratio is controlled at 50-70%, and the coating roller speed ratio is controlled at 120-160% to ensure the fingerprint-resistant film thickness is qualified. Then, the coated steel plates (plate temperature 224-241℃) are cured. The curing process uses a segmented heating process, including 5 temperature zones. The furnace temperature of the last zone is 230 + 1.62 × TV (T is the strip thickness in mm; V is the strip speed in m / min). Each subsequent zone decreases the temperature by 20℃. The strip thickness is 0.3-0.8mm, and the strip speed is 100-150m / min.

[0039] 5) Cooling (circulating water volume controlled at 100-120m³) 3 / h; strip temperature not exceeding 40℃), air dry, coil, the coiling tension is adjusted according to the strip thickness: when the strip thickness is below 0.6mm, the coiling tension is 32-36N / m 2 Control; when the strip thickness is greater than 0.6mm, the coiling tension should be 30-34N / m. 2 Control measures to prevent interlayer scratches and slippage caused by contact between the colored coating and the fingerprint-resistant surface, which can lead to interlayer loosening and collapse; vertical packaging for warehousing.

[0040] Example 1 The product produced in August 2025 has a total film thickness of 20 micrometers on the front, is a medium gray polyester color-coated product with a fingerprint-resistant back, and a thickness of 0.5×1000mm. The thickness is TDC51D+AM C5. The unit speed is 150m / min, the furnace temperature is set according to the unit standard, and the production is carried out according to the above method of the present invention. The main process control conditions are shown in Table 1, and the product performance test results are shown in Table 2.

[0041] Table 1 Production Process Table

[0042] Table 2. Performance test results of the color-coated fingerprint-resistant steel sheet obtained in Example 1.

[0043] Example 2 The product produced in August 2025 has a total film thickness of 20 micrometers on the front, is a scarlet polyester color-coated product with a fingerprint-resistant back, and a thickness of 0.4×1200mm (TDC51D+AM C5). The unit speed is 150 meters / minute, the furnace temperature is set according to the unit standard, and the production was carried out according to the above method. The main process control conditions are shown in Table 3, and the product performance test results are shown in Table 4.

[0044] Table 3 Production Process Table

[0045] Table 4. Performance test results of the color-coated fingerprint-resistant steel sheet obtained in Example 2.

[0046] Example 3 The front-side total film thickness is 20 micrometers, and the back-side is a sea-blue polyester color-coated fingerprint-resistant product with a thickness of 0.6×1100mm (TDC51D+AM C5). The unit speed is 130 meters / minute, and the furnace temperature is set according to the unit standard. The production was carried out according to the above method of the present invention. The main process control conditions are shown in Table 5, and the product performance test results are shown in Table 6.

[0047] Table 5 Production Process Table

[0048] Table 6. Performance test results of the color-coated fingerprint-resistant steel sheet obtained in Example 3.

[0049] Comparative Example 1 If a conventional hot-dip galvanizing unit is used to produce color-coated fingerprint-resistant products, it cannot perform color-coated surface coating because the hot-dip galvanizing unit only has one coating machine.

[0050] If fingerprint-resistant products are coated on a conventional color coating unit using normal processes, the following problems may occur: 1) The fingerprint-resistant surface cannot be properly coated due to the passivation layer being applied first during the color coating process; 2) Inappropriate baking oven temperature may result in incomplete curing of the color-coated surface or over-baking and embrittlement of the fingerprint-resistant surface, affecting performance; 3) If the cooling temperature after fine coating is too high, the fingerprint-resistant surface will have high hardness, resulting in indentations on the color-coated surface; 4) If the winding tension is too low, interlayer scratches and slippage may occur after the color-coated surface comes into contact with the fingerprint-resistant surface, leading to interlayer loosening and collapse.

[0051] Comparative Example 2 A color-coated fingerprint-resistant steel plate is prepared in a manner similar to that of Example 1, except that the upper and lower surfaces of the strip are passivated simultaneously in step 1).

[0052] The results showed that the fingerprint-resistant liquid could not effectively adhere to the surface of the steel strip, and the thickness of the fingerprint-resistant film formed was less than 1 micrometer, which did not meet the product performance requirements.

[0053] Comparative Example 3 A color-coated fingerprint-resistant steel plate is prepared in a manner similar to that of Example 1, except that step 4) uses a one-stage baking temperature of 235°C.

[0054] The results show that using the above method will lead to over-curing of the fingerprint-resistant surface, resulting in aging, and the 500-hour damp heat resistance ΔE4.2 will fail the test. Comparative Example 4 A color-coated fingerprint-resistant steel plate is prepared in a manner similar to that of Example 1, except that step 4) uses a single-stage furnace temperature and the curing temperature (fine coating baking temperature) of the steel plate is 218°C.

[0055] The results show that the above method will result in incomplete curing and cross-linking of the coating surface, with a MEK score of 62, which is unqualified (the standard requires a score greater than 100).

[0056] Comparative Example 5 A color-coated fingerprint-resistant steel sheet is prepared in a manner largely the same as in Example 1, except that when producing this type of product with a thickness of 0.8 mm, the winding tension is set to 38 N / m. 2 .

[0057] The results show that the above method leads to excessive interlayer friction, and the back steel damages the surface of the front coating (see...). Figure 3 ).

[0058] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for preparing a color-coated fingerprint-resistant steel sheet, characterized in that, Includes the following steps: 1) Substrate cleaning; the substrate is degreased and rinsed; 2) Surface treatment; Passivate the side of the substrate to be coated with color using a chromium-free passivation solution, and treat the other side of the substrate to be coated with a fingerprint-resistant layer using a desalination water solution; Bake the substrate after both treatments. 3) Initial coating of the colored surface; The passivated surface obtained in step 2) is coated with and cured with polyurethane primer to obtain a color coating underlayer; 4) Double-sided fine coating; A fine coating of polyester paint is applied to the surface of the color-coated base layer; A fingerprint-resistant coating is applied to one side after desalination treatment by roller coating; The substrate with double-sided coating is cured to obtain a composite substrate with one side coated with color and the other side having a fingerprint layer. 5) Cool the resulting composite substrate and roll it up.

2. The preparation method according to claim 1, characterized in that, The degreasing step employs a step-by-step degreasing process, with the concentration of the alkali solution decreasing progressively.

3. The preparation method according to claim 2, characterized in that, The stepwise degreasing process includes: firstly, degreasing is carried out in an alkaline solution at 55-65℃ with a concentration of 1.2-1.6 wt%; then, a second degreasing is carried out in an alkaline solution at 50-60℃ with a concentration of 0.5-1.3 wt%.

4. The preparation method according to claim 1, characterized in that, The rinsing process involves three stages of rinsing; the first stage uses a rinsing solution with a temperature of 55-60℃, the second stage uses a rinsing solution with a temperature of 50-60℃, and the third stage uses a rinsing solution with a temperature of 40-50℃.

5. The preparation method according to claim 1, characterized in that, The chromium-free passivation solution contains the following components and their mass percentages: 0.2-1.2% fluorotitanic acid, 1.3-2.4% phosphate, 4-6% acrylic resin; the remainder is water.

6. The preparation method according to claim 1, characterized in that, The baking temperature in step 2) is 75-105℃.

7. The preparation method according to claim 1, characterized in that, Step 4) The curing process adopts a segmented temperature control process; wherein, the furnace temperature of the last segment = 230 + 1.62 × TV, T is the strip thickness in mm; V is the strip speed in m / min; the furnace temperature is set in three or more segments, and the furnace temperature decreases by 15-25℃ for each segment from the last segment to the previous segment.

8. The preparation method according to claim 1, characterized in that, The main component of fingerprint-resistant coatings is water-based polyurethane resin, with an effective solid content of 48-55%.

9. The preparation method according to claim 1, characterized in that, The cooling process uses a circulating water volume of 100-120m³. 3 / h; The winding steps are adjusted according to the strip thickness: when the strip thickness is below 0.6mm, the winding tension is 32-36N / m. 2 Control; when the strip thickness is greater than 0.6mm, the coiling tension should be 30-34N / m. 2 control.

10. The color-coated fingerprint-resistant steel sheet prepared by the preparation method according to any one of claims 1 to 9, characterized in that, It includes a substrate and a color coating and a fingerprint-resistant layer respectively disposed on its upper and lower surfaces.

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