A color coated steel plate with heat insulation, antibacterial and super-hydrophobic functions and a preparation method thereof

Abstract

The present application provides a kind of color coated steel sheet with heat insulation, antibacterial and super-hydrophobic function, including metal substrate and sequentially arranged on at least one surface of metal substrate chemical conversion layer and primer layer, composite functional topcoat layer is arranged on primer layer;Composite functional topcoat layer includes film-forming resin, near-infrared reflective composite pigment, dual-mode antibacterial agent and fluorinated nanosilica;The topcoat layer in the color coated steel sheet of the present application has heat insulation, antibacterial capacity and super-hydrophobic self-cleaning function simultaneously;The present application also provides a preparation method of color coated steel sheet, comprising the following steps: surface pretreatment is carried out to metal substrate, and chemical conversion layer is formed;Coat primer on chemical conversion layer and carry out first solidification, form primer layer;Coat topcoat coating on primer layer, then carry out multi-temperature zone gradient solidification, form composite functional topcoat layer;The preparation method of the present application adopts multi-temperature zone gradient solidification process, controls the temperature of different solidification stages, and constructs stable functional structure.

Description

Technical Field

[0001] This invention belongs to the technical field of color-coated steel sheets, and in particular relates to a color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions and its preparation method. Background Technology

[0002] Color-coated steel sheets are widely used in construction, home appliances, transportation and other fields. With increasing usage requirements, especially in special places such as hospitals and food factories, color-coated sheets are required to have multiple functions: first, heat insulation to reduce indoor energy consumption or equipment surface temperature; second, antibacterial function to prevent bacterial growth; and third, self-cleaning function to reduce surface contamination and lower cleaning costs.

[0003] Most current pre-coated steel sheets possess only a single function. Although some technologies attempt to add different fillers to coatings to achieve multiple functions, they often face several problems: different functional fillers are difficult to disperse evenly in the resin; functions may interfere with each other, for example, hard particles added to increase hardness may damage the surface smoothness and be detrimental to hydrophobicity; more importantly, traditional functional coating processes are mostly constant-temperature curing or simple two-stage curing, which cannot precisely control the orderly distribution of multiple functional fillers in the coating thickness direction, resulting in poor functional synergy and unstable performance. In addition, some complex processes that can build gradient structures (such as powder metallurgy) are incompatible with the efficient and continuous roll coating production lines in the pre-coated steel sheet industry, making industrialization difficult. Summary of the Invention

[0004] To solve the above-mentioned technical problems, one object of the present invention is to provide a color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions, and another object of the present invention is to provide a method for preparing the color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions.

[0005] To achieve the first objective of this invention, the following technical solution is adopted:

[0006] A color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions includes a metal substrate and a chemical conversion layer and a primer layer sequentially disposed on at least one surface of the metal substrate. A composite functional topcoat layer is disposed on the primer layer. The film-forming resin of the composite functional topcoat layer is a fluorocarbon resin or a silicon-modified polyester resin. The composite functional topcoat layer includes a near-infrared reflective composite pigment, a dual-mode antibacterial agent and fluorinated nano-silica.

[0007] In this invention, the film-forming resin in the composite functional topcoat layer can provide the topcoat layer with good weather resistance and durability matrix. In this invention, the preferred film-forming resin is fluorocarbon resin or silicone-modified polyester resin.

[0008] In this invention, the near-infrared reflective pigment in the composite functional topcoat layer can effectively adjust the optical properties of the pigment and enhance its reflectivity in the near-infrared band.

[0009] In this invention, preferably, the near-infrared reflective composite pigment is a core-shell structured TiO2@SiO2 composite pigment, where the SiO2 shell helps to improve the dispersion stability and weather resistance of the pigment.

[0010] In this invention, the dual-mode antibacterial agent in the composite functional topcoat layer can improve the antibacterial performance of the topcoat layer. Preferably, the dual-mode antibacterial agent is a composite of silver-loaded silica and nitrogen-doped titanium dioxide. The silver-loaded silica provides contact antibacterial action based on the release of silver ions, while the nitrogen-doped titanium dioxide can generate reactive oxygen species under light irradiation, achieving photocatalytic antibacterial action. The combination of the two can achieve synergistic effects, broaden the antibacterial spectrum, and enhance durability.

[0011] In this invention, fluorinated nano-silica in the composite functional topcoat layer is used to construct the necessary micro-roughness on the surface of the topcoat layer and introduce low surface energy substances, thereby achieving the superhydrophobic self-cleaning function of the topcoat layer.

[0012] Preferably, the content of each component in the composite functional topcoat layer, by weight, is as follows:

[0013] Film-forming resin: 50-70 parts;

[0014] Near-infrared reflective composite pigment: 15-25 parts;

[0015] Dual-mode antibacterial agent: 5-8 parts;

[0016] Fluorinated nano-silica: 3-5 parts.

[0017] In this invention, by using the above-mentioned weight ratio, the film-forming properties, mechanical properties and processing properties of the composite functional topcoat layer can be effectively guaranteed.

[0018] Preferably, the composite functional topcoat layer further includes a dispersant and a leveling agent, wherein the content of the dispersant is 1-3 parts by weight and the content of the leveling agent is 1-2 parts.

[0019] In this invention, the dispersant in the composite functional topcoat layer ensures that the above-mentioned multifunctional filler can be uniformly dispersed in the film-forming resin, and the leveling agent in the composite functional topcoat layer ensures that the above-mentioned multifunctional filler has good leveling properties in the topcoat layer.

[0020] Preferably, the other surface of the metal substrate is provided with a back coating.

[0021] In this invention, the back coating mainly serves as corrosion protection and basic protection, and its specific composition can adopt the conventional back coating system in the field.

[0022] Preferably, the film-forming resin of the primer layer is epoxy resin or polyurethane resin, and its main function is to enhance the adhesion between the primer layer system and the metal substrate and provide basic anti-corrosion protection.

[0023] To achieve the second objective of this invention, the following technical solution is adopted:

[0024] A method for preparing a color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions as described above includes the following steps:

[0025] S1. The metal substrate is pretreated on the surface, then chemically converted and dried to form a chemical conversion layer;

[0026] S2. Apply a primer to the chemical conversion layer and perform a first curing to form a primer layer;

[0027] S3. Preparation of composite functional topcoat: Fluorocarbon resin or silicon-modified polyester resin, near-infrared reflective composite pigment, dual-mode antibacterial agent, fluorinated nano-silica, additives and solvent are mixed and dispersed and ground to obtain topcoat coating.

[0028] S4. Apply the topcoat coating onto the primer layer, and then perform multi-temperature gradient curing to form a composite functional topcoat layer.

[0029] The multi-temperature gradient curing process includes a solvent evaporation stage, a resin crosslinking and leveling stage, and a functional building stage, which are performed sequentially, with the peak metal plate temperature increasing sequentially in each stage.

[0030] Preferably, the multi-temperature gradient curing specifically involves: a peak metal plate temperature of 110-160°C during the solvent evaporation stage; a peak metal plate temperature of 170-210°C during the resin crosslinking and leveling stage; and a peak metal plate temperature of 210-260°C during the functional building stage.

[0031] Preferably, in step S2, the peak temperature of the first cured metal plate is 200-224°C.

[0032] Preferably, in step S3, the fineness of the coating after dispersion and grinding is ≤15μm; in step S4, the dry film thickness of the composite functional topcoat layer is controlled at 15-25μm.

[0033] The core of the preparation method of the color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions of the present invention lies in the "multi-temperature gradient curing" after the topcoat layer is applied. The curing process is not a single temperature, but is divided into three stages with the temperature increasing in sequence: the solvent evaporation stage, the resin cross-linking and leveling stage and the functional construction stage.

[0034] Specifically:

[0035] The peak metal plate temperature during the solvent evaporation stage is controlled at 110-160℃. The purpose is to allow the solvent to evaporate slowly, avoid coating defects such as pinholes and orange peel caused by excessive evaporation, and allow the filler to initially stabilize in the system.

[0036] During the resin crosslinking and leveling stage, the peak metal plate temperature rises to 170-210℃. At this temperature, the resin begins to fully crosslink, the coating achieves good leveling, and the change in system viscosity creates conditions for the migration of functional fillers.

[0037] The peak metal plate temperature during the functional construction stage is further increased to 210-260℃. This high-temperature stage promotes the complete curing of the resin to form a robust coating film, and specifically drives low surface energy components such as fluorinated nano silica to migrate to the coating surface and complete the final enrichment and positioning, thereby stably constructing a microstructure with heat insulation, antibacterial and superhydrophobic properties.

[0038] Therefore, the entire gradient curing process can be precisely achieved in a multi-temperature zone oven on a continuous production line.

[0039] The beneficial effects of this invention are:

[0040] The present invention relates to a color-coated steel sheet with heat insulation, antibacterial, and superhydrophobic functions. Near-infrared reflective composite pigments, a dual-mode antibacterial agent, and fluorinated nano-silica are compounded in a weather-resistant resin, and the proportions of each component are optimized to allow a single topcoat layer to simultaneously perform all three functions. The selection and proportioning of the near-infrared reflective composite pigments ensure efficient solar heat reflection and insulation; the dual-mode antibacterial agent provides long-lasting and broad-spectrum antibacterial properties through the synergistic effect of contact sterilization and photocatalysis; and fluorinated nano-silica is key to constructing a stable superhydrophobic surface.

[0041] The method for preparing color-coated steel sheets with heat insulation, antibacterial and superhydrophobic functions of the present invention includes a multi-temperature gradient curing process. By precisely controlling the temperature and time of different curing stages, the functional fillers, especially fluorinated nano-silica, are effectively guided to migrate and accumulate on the surface within the coating, thereby forming a stable functional gradient structure at the microscopic level. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of the color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions of the present invention.

[0043] The attached figures are labeled as follows: 1. Metal substrate; 2. Chemical conversion layer; 3. Back coating layer; 4. Primer layer; 5. Composite functional topcoat layer; 6. Polyethylene protective film. Detailed Implementation

[0044] The invention can be further understood through the specific embodiments given below, but they are not intended to limit the invention. Example 1

[0045] This embodiment 1 provides a color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions. The raw material formula of the color-coated steel sheet is shown in Table 1:

[0046]

[0047] The preparation method of the color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions in Example 1 includes the following steps:

[0048] S1. Substrate pretreatment and chemical conversion:

[0049] A 0.5mm thick hot-dip aluminum-zinc steel sheet is selected as the metal substrate 1. After uncoiling, alkaline washing and degreasing, and water washing, a double-sided roller coating chemical conversion treatment is carried out at 50℃ using a chromium-free passivation solution, and then hot air drying is performed to form a double-sided chemical conversion layer 2.

[0050] S2. Primer and back coat application and curing:

[0051] The above-mentioned epoxy primer is applied to the front side of the steel plate using a roller coating method, and an epoxy back coat is applied to the back side. The dry film thickness of the front primer is controlled to be about 8 μm, and the dry film thickness of the back coat is about 5 μm. The plate is then placed in an oven for co-curing, with the peak metal plate temperature (PMT) controlled at 210°C and the curing time at about 60 seconds. After exiting the oven, the plate is cooled in a water cooling section.

[0052] S3. Preparation of composite functional topcoat:

[0053] According to the topcoat formulation in Table 1, PVDF resin powder, TiO2@SiO2, silver-loaded SiO2 / N-TiO2, F-SiO2, dispersant and part of the solvent were put into a high-speed disperser and pre-dispersed at 1500 rpm for 30 min. Then, the mixture was transferred to a sand mill for grinding until the fineness of the slurry was ≤12 μm. A leveling agent was added, and the viscosity of the coating was adjusted to 45 seconds (25℃) with the remaining solvent. After filtration, the topcoat coating was obtained.

[0054] S4. Topcoat Application and Gradient Curing: A three-roll reverse coating machine is used to apply the topcoat layer over the cured primer coating, controlling the dry film thickness to 20μm. The coating is then subjected to gradient curing in a three-zone curing oven.

[0055] Zone 1 (solvent evaporation stage): Control the peak plate temperature of the board in this zone to 140-150℃, and the time is about 8 seconds;

[0056] Second zone (resin cross-linking and leveling stage): control the peak plate temperature to 190-200℃, and the time is about 18s;

[0057] Third zone (functional construction phase): control the peak board temperature (PMT) to 240-250℃, with a transit time of approximately 25 seconds;

[0058] S5. Post-processing: After the sheet material exits the furnace, it is successively cooled to room temperature by air cooling and water quenching. After online testing confirms that the coating thickness, color difference, and other indicators are qualified, a polyethylene protective film 6 is applied to the coating surface, and finally, it is rolled up. Example 2

[0059] This embodiment 2 provides a color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions. The raw material formula composition of the color-coated steel sheet is shown in Table 2:

[0060]

[0061] In the preparation method of the color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions in Example 2, the substrate pretreatment and single-sided chemical conversion steps are the same as in Example 1. The difference from Example 1 is that only the front primer is coated, with a dry film thickness of approximately 7 μm, and the PMT curing temperature is 205°C for 55 seconds; the grinding fineness requirement for the topcoat layer is the same as in Example 1, the dry film thickness of the topcoat layer is 18 μm, and the gradient curing parameters are adjusted as follows:

[0062] Peak board temperature in Zone 1: 130-140℃, time 7s; Peak board temperature in Zone 2: 180-190℃, time 20s; Peak board temperature in Zone 3 (PMT): 230-240℃, time 28s.

[0063] The post-processing for S5 is the same as in Example 1, but a back-side coating is not required. Example 3

[0064] This embodiment 3 provides a color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions. The raw material formula composition of the color-coated steel sheet is shown in Table 3:

[0065]

[0066] In the preparation method of the color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions in Example 3, the primer, back coat system and process, and substrate pretreatment are the same as in Example 1; the topcoat preparation and coating process are the same as in Example 1, and the dry film thickness is controlled at 22 μm. The gradient curing parameters are the same as in Example 1. Example 4

[0067] Example 4 provides a color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions. The raw material formula of the color-coated steel sheet is shown in Table 4:

[0068]

[0069] In the preparation method of the color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions in Example 4, the primer system and process are the same as in Example 2; the topcoat preparation and coating process are the same as in Example 2, and the dry film thickness is 16μm; the gradient curing parameters are the same as in Example 2.

[0070] Comparative Example 1

[0071] Comparative Example 1 provides a common heat-insulating color-coated sheet, which differs from Example 1 in that the topcoat layer uses only 20 parts by weight of common rutile titanium dioxide and PVDF resin, without adding antibacterial agents and F-SiO2, and the amount of additives is the same. The product contains a back coating and is cured using conventional single-temperature zone (PMT 230℃, 60s). The rest is the same as Example 1, and will not be repeated here.

[0072] Comparative Example 2

[0073] Comparative Example 2 provides a common antibacterial color-coated plate, which differs from Example 1 in that the topcoat layer uses PVDF resin, 20 parts by weight of common titanium dioxide, and 6 parts by weight of common silver-loaded zeolite antibacterial agent, without adding F-SiO2. The product contains a backcoat, and the curing process is the same as Comparative Example 1. The rest is the same as Example 1, and will not be described again here.

[0074] Comparative Example 3

[0075] Comparative Example 3 provides ordinary color-coated steel sheets with the same topcoat formulation as Example 1. The product includes a backcoat layer and is cured using the same single-temperature zone curing process (PMT 230℃, 60s) as Comparative Example 1, without the gradient curing step.

[0076] Comparative Example 4

[0077] Comparative Example 4 provides a standard color-coated steel sheet. Compared with Example 1, the topcoat formulation does not include F-SiO2 (4 parts by weight), but its parts are added to the PVDF resin (i.e., the resin is 64 parts). The product contains a backcoat, and the curing process is the same gradient curing process as in Example 1.

[0078] Performance testing

[0079] Performance tests were conducted on the color-coated (steel) sheets of Examples 1-4 and Comparative Examples 1-4, respectively. The test items included: thermal insulation performance, antibacterial performance, and surface hydrophobicity. The specific test methods were as follows:

[0080] Thermal insulation performance test: Referring to the principle of thermal performance testing of building envelope, a xenon lamp aging chamber (spectral matching degree AM1.5) was used to simulate solar radiation. The radiation intensity was set to 1000W / m². After continuous irradiation for 30 minutes, an infrared thermometer was used to measure and record the temperature at the center point of the non-irradiated surface of the sample. The temperature rise difference compared to that of an ordinary white paint coating under the same conditions was calculated. The smaller the difference, the better the thermal insulation performance.

[0081] Antimicrobial performance testing: According to JIS Z 2801:2010, Antimicrobial Processed Products - Test Methods for Antimicrobial Properties. Representative bacterial species *Escherichia coli* (ATCC 8739) and *Staphylococcus aureus* (ATCC 6538) were selected, with an inoculum size of approximately (3.0–4.0) × 10⁻⁶. 5 The antibacterial rate was calculated by colony counting after the sample surface was in contact with the sample for 24 hours at CFU / mL.

[0082] Surface hydrophobicity testing includes static water contact angle testing and roll-off angle testing, wherein:

[0083] Static water contact angle: Using an optical contact angle meter, a 5 μL droplet of deionized water was placed on a flat surface of the sample at room temperature, and the equilibrium contact angle was read and recorded by goniometric method. Five different points were tested for each sample and the average value was taken.

[0084] Roll-off angle: Fix the sample on an adjustable tilt platform, add 20 μL of deionized water at a fixed height above the surface, slowly increase the tilt angle of the platform, and record the critical angle at which the water droplet begins to roll off steadily.

[0085] The performance test results of this invention are shown in Table 5:

[0086]

[0087] Performance test results analysis:

[0088] According to the test results in Table 5:

[0089] Regarding thermal insulation performance: The back-side temperature rise of Examples 1-4 under simulated solar radiation was significantly lower than that of Comparative Examples 1 and 2 (traditional single-function panels). This indicates that the core-shell structure near-infrared reflective composite pigment (TiO2@SiO2) used in this invention has excellent solar heat reflection capability and can effectively block heat transfer. The thermal insulation performance of Comparative Examples 3 and 4 is comparable to that of Examples 1-4, indicating that the performance mainly depends on the pigment itself and has low dependence on the curing process.

[0090] Regarding antibacterial performance: The samples with added dual-mode antibacterial agent (silver-loaded SiO2 / N-TiO2), including Examples 1-4 and Comparative Examples 2-4, all showed a high antibacterial rate of greater than 99.9%, meeting the antibacterial standard. This indicates that the antibacterial agent is well dispersed and has stable activity in the selected resin system, and its "dual-mode" mechanism of contact sterilization and photocatalysis synergy is effective. Comparative Example 1, on the other hand, did not have this function because no antibacterial agent was added.

[0091] Regarding superhydrophobic properties:

[0092] When both fluorinated nano-silica (F-SiO2) and gradient curing processes are used (as in Examples 1-4), the coating can achieve a static water contact angle greater than 150° and a low roll-off angle less than 10°, thus achieving stable superhydrophobicity.

[0093] The contact angle of Comparative Example 3 (with F-SiO2 but without gradient curing) was only 128°, indicating that without the driving force of the gradient curing process, F-SiO2 could not fully migrate to the surface and form an ideal micro-rough structure, thus failing to achieve superhydrophobicity.

[0094] Comparative Example 4 (without F-SiO2 but with gradient curing) had a contact angle of only 96°, which is within the normal hydrophobic range. This proves that even with a gradient process, superhydrophobicity cannot be achieved without the low surface energy material and roughness building blocks provided by fluorinated nano silica.

[0095] In summary, this invention, through a specific ratio of three functional components—near-infrared reflective composite pigment, dual-mode antibacterial agent, and fluorinated nano-silica—combined with a multi-temperature gradient curing process, successfully synergistically constructs a triple function of heat insulation, antibacterial and superhydrophobic in a single coating. It also demonstrates that the gradient curing process is a crucial step in driving the directional migration of F-SiO2, thereby constructing a stable superhydrophobic surface structure.

[0096] The above description is merely an embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions, comprising a metal substrate and a chemical conversion layer and a primer layer sequentially disposed on at least one surface of the metal substrate, characterized in that, A composite functional topcoat layer is provided on the primer layer; the film-forming resin of the composite functional topcoat layer is fluorocarbon resin or silicon-modified polyester resin; the composite functional topcoat layer includes near-infrared reflective composite pigment, dual-mode antibacterial agent and fluorinated nano-silica. The composite functional topcoat layer is formed by multi-temperature gradient curing, which includes a solvent evaporation stage, a resin crosslinking and leveling stage, and a functional building stage, with the peak metal plate temperature increasing sequentially in each stage. Specifically, the peak metal plate temperature in the solvent evaporation stage is 110-160℃; the peak metal plate temperature in the resin crosslinking and leveling stage is 170-210℃; and the peak metal plate temperature in the functional building stage is 210-260℃. The near-infrared reflective composite pigment is a core-shell structured TiO2@SiO2 composite pigment, and the dual-mode antibacterial agent is a composite of silver-loaded silicon dioxide and nitrogen-doped titanium dioxide. By weight, the content of each component in the composite functional topcoat layer is as follows: Film-forming resin: 50-70 parts; Near-infrared reflective composite pigment: 15-25 parts; Dual-mode antibacterial agent: 5-8 parts; Fluorinated nano-silica: 3-5 parts.

2. The color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions according to claim 1, characterized in that, The composite functional topcoat layer also includes a dispersant and a leveling agent. By weight, the content of the dispersant is 1-3 parts and the content of the leveling agent is 1-2 parts.

3. The color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions according to any one of claims 1-2, characterized in that, The film-forming resin of the primer layer is epoxy resin or polyurethane resin.

4. A method for preparing a color-coated steel sheet with heat insulation, antibacterial and superhydrophobic functions as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: S1. The metal substrate is pretreated on the surface, then chemically converted and dried to form a chemical conversion layer; S2. Apply a primer to the chemical conversion layer and perform a first curing to form a primer layer; S3. Preparation of composite functional topcoat: Fluorocarbon resin or silicon-modified polyester resin, near-infrared reflective composite pigment, dual-mode antibacterial agent, fluorinated nano-silica, additives and solvent are mixed and dispersed and ground to obtain topcoat coating. S4. Apply the topcoat coating onto the primer layer, and then perform multi-temperature gradient curing to form a composite functional topcoat layer.

5. The method for preparing color-coated steel sheets with heat insulation, antibacterial and superhydrophobic functions according to claim 4, characterized in that, In step S2, the peak temperature of the first cured metal plate is 200-224℃.

6. The method for preparing color-coated steel sheets with heat insulation, antibacterial and superhydrophobic functions according to claim 4, characterized in that, In step S3, the fineness of the coating after dispersion and grinding is ≤15μm; in step S4, the dry film thickness of the composite functional topcoat layer is controlled at 15-25μm.

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