A color coated steel plate with gradient temperature control and antibacterial wear-resistant function and a preparation method thereof

Abstract

The present application provides a kind of gradient temperature control and antibacterial wear-resistant function's color coated steel plate and its preparation method, color coated steel plate includes metal base material and sequentially coated on at least one surface of metal base material on chemical conversion coating, primer layer and topcoat layer;Topcoat layer is by including the coating prepared from material of fluorine modified polysiloxane, primer layer includes first thermal conductivity modifier and first multi-scale ceramic reinforcing phase, first thermal conductivity modifier is by high thermal conductivity component and low thermal conductivity component is mixed and constitutes by first mass ratio;Topcoat layer includes second thermal conductivity modifier and second multi-scale ceramic reinforcing phase, second thermal conductivity modifier is by high thermal conductivity component and low thermal conductivity component is mixed and constitutes by second mass ratio;Primer layer and / or topcoat layer also include nano silver antibacterial agent;The preparation method of the present application is by adjusting the stepwise temperature rising process of roll coating production line drying furnace, combined with specific gas flow guide, realizes the construction of filler directional migration and gradient structure.

Description

Technical Field

[0001] This invention belongs to the technical field of metal material surface treatment, and in particular relates to a color-coated steel sheet with gradient temperature control, antibacterial and wear-resistant functions and its preparation method. Background Technology

[0002] Color-coated steel sheets are widely used in building envelopes, appliance housings, and other fields due to their excellent formability, decorative properties, and corrosion resistance. As applications expand towards high-end and specialized sectors, such as medical facilities, food processing equipment, and electronic heat dissipation components, higher demands are placed on the comprehensive performance of the materials. In addition to basic protective functions, they also require composite functions such as temperature control, surface antibacterial properties, and wear resistance.

[0003] Existing technical solutions often focus on a single performance. To achieve antibacterial properties, antibacterial agents are usually added directly to the coating, but this can easily lead to uneven dispersion and poor durability. To improve wear resistance, hard particles are often added, but this may affect the toughness of the coating. In addition, although the concept of functionally graded materials has been developed in the field of materials science, its typical preparation processes, such as powder metallurgy and laser cladding, are generally limited by complex processes, large equipment investment, and difficulty in continuous production. These processes are fundamentally different from the continuous roll coating production lines mainly used in the color-coated steel sheet industry in terms of technical principles and equipment requirements, making it impossible to achieve industrial application. Summary of the Invention

[0004] To address the technical problems of existing color-coated steel sheets having limited functionality and difficulty in achieving synergy, one objective of this invention is to provide a color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions. Another objective of this invention is to provide a method for preparing the aforementioned color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions.

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

[0006] A color-coated steel sheet with gradient temperature control, antibacterial and wear-resistant functions includes a metal substrate and a chemical conversion coating, a primer layer, and a topcoat layer sequentially coated on at least one surface of the metal substrate. The primer layer contains a first thermal conductivity modifier and a first multi-scale ceramic reinforcing phase. The first thermal conductivity modifier is composed of a high thermal conductivity component and a low thermal conductivity component mixed in a first mass ratio of 3:7. The topcoat layer contains a second thermal conductivity modifier and a second multi-scale ceramic reinforcing phase. The second thermal conductivity modifier is composed of the high thermal conductivity component and the low thermal conductivity component mixed in a second mass ratio of 7:3. The primer layer and / or the topcoat layer also contain a nano-silver antibacterial agent. Both the first multi-scale ceramic reinforcing phase and the second multi-scale ceramic reinforcing phase contain ceramic particles of different sizes, including coarse particles, fine particles, and nanoparticles.

[0007] In this invention, a continuous thermal conductivity gradient is constructed in the thickness direction of the coating by the difference in the ratio of high thermal conductivity components to low thermal conductivity components in the primer layer and the topcoat layer (i.e., the ratio of high thermal conductivity components to low thermal conductivity components in the primer layer is 3:7, and the ratio of high thermal conductivity components to low thermal conductivity components in the topcoat layer is 7:3).

[0008] In this invention, the primer layer and / or topcoat layer further contain a nano-silver antibacterial agent, which can provide a more durable antibacterial function for the primer layer and / or topcoat layer.

[0009] In this invention, both the first and second multi-scale ceramic reinforcing phases contain a variety of gradations of coarse, fine, and nanoparticles, which can form a support-filling-reinforcing composite structure in the corresponding coating, thereby improving the hardness and wear resistance of the corresponding coating.

[0010] In this invention, preferably, the high thermal conductivity component is boron nitride and the low thermal conductivity component is hollow glass microspheres, wherein boron nitride has high thermal conductivity and hollow glass microspheres have low thermal conductivity. Therefore, the combination and ratio adjustment of the two can create a thermal conductivity gradient.

[0011] In this invention, preferably, the coarse particles are alumina particles with a particle size of 2-3 μm, the fine particles are zirconium oxide particles with a particle size of 0.5-1 μm, and the nanoparticles are silicon carbide particles with a particle size of 50-200 nm. The alumina and zirconium oxide particles have high hardness and can provide the main wear-resistant skeleton for the first and second multi-scale ceramic reinforcing phases, while the silicon carbide particles can strengthen the interface between the resin matrix and the micron-sized particles, improving toughness.

[0012] In this invention, preferably, the mass ratio of coarse particles, fine particles and nanoparticles is (4-5):(3-4):(1-2). This gradation ratio can achieve close packing and optimal mechanical property transfer in the coating. More preferably, the mass ratio of coarse particles, fine particles and nanoparticles is 5:3:2.

[0013] In this invention, preferably, the film-forming matrix of the primer layer and the topcoat layer is a saturated polyester resin; to ensure uniform dispersion of each functional filler in the resin matrix and good coating leveling performance and appropriate curing speed, the primer layer further includes a first dispersant, a first leveling agent and a first catalyst; the topcoat layer further includes a second dispersant, a second leveling agent and a second catalyst.

[0014] Specifically, preferably, the first dispersant is a silane coupling agent, the first leveling agent is an organosilicon leveling agent, and the first catalyst is an organotin catalyst; wherein, the silane coupling agent can have the effect of surface modification on the multi-scale ceramic reinforcing phase to improve compatibility with the resin, preferably, the silane coupling agent is KH-550, the organosilicon leveling agent is BYK-333, and the organotin catalyst is dibutyltin dilaurate (DBTDL).

[0015] Specifically, preferably, the second dispersant is a high-molecular-weight carboxylic acid dispersant, the second leveling agent is a fluorinated polysiloxane leveling agent, and the second catalyst is a compound of organotin and organobismuth catalysts. The high-molecular-weight carboxylic acid dispersant meets the dispersion requirements of the topcoat system, the fluorinated polysiloxane leveling agent provides superior surface leveling and anti-sticking effects, and the compound of organotin and organobismuth catalysts better matches the thicker film layer and higher curing temperature requirements of the topcoat. Preferably, the high-molecular-weight carboxylic acid dispersant is BYK-163, the fluorinated polysiloxane leveling agent is EFKA-3777, and the compound of organotin and organobismuth catalysts is DBTDL and bismuth isooctanoate compounded in a 1:1 mass ratio. Therefore, the topcoat layer of the present invention is a topcoat coating prepared from materials including a special fluorinated polysiloxane material.

[0016] In this invention, preferably, a back coating layer is also applied to the other surface of the metal substrate. The back coating layer comprises an epoxy resin film-forming matrix, a nano-silver antibacterial agent, a third dispersant, a third leveling agent, and a polyamide curing agent. The back coating layer mainly provides back protection and additional antibacterial function for the color-coated steel sheet.

[0017] Specifically, preferably, the third dispersant is a polyurethane-modified dispersant, and the third leveling agent is a silicone-modified acrylate leveling agent. More preferably, the polyurethane-modified dispersant is BYK-110, the silicone-modified acrylate is BYK-358N, and the polyamide curing agent is 650 low molecular weight polyamide.

[0018] To achieve the second objective of this invention, the following technical solution is adopted:

[0019] A method for preparing a color-coated steel sheet with gradient temperature control, antibacterial and wear-resistant functions as described above includes the following steps:

[0020] S1. Clean the surface of the metal substrate, apply a chemical conversion treatment solution and dry it to form a chemical conversion coating.

[0021] S2. The prepared primer coating is applied to the chemical conversion coating and then placed in a primer drying oven for stepped heating and curing to form a primer layer. The primer drying oven is divided into an inlet section, a middle section and an outlet section along the direction of the board's movement. The temperature of the inlet section is set to be lower than that of the middle section and lower than that of the outlet section.

[0022] S3. Apply the prepared topcoat coating onto the cured primer layer, and then enter the topcoat drying oven for stepped heating and curing to form the topcoat layer. The topcoat drying oven is also divided into an inlet section, a middle section and an outlet section along the direction of the board's movement. The temperature of the inlet section is set to be lower than that of the middle section, and the temperature of the middle section is set to be lower than that of the outlet section.

[0023] During the curing process of the primer and topcoat layers of this invention, by controlling the lower temperature of the inlet section, the coating maintains suitable fluidity for a longer period of time. This causes the thermal conductivity modifier and multi-scale ceramic reinforcing phase to undergo directional migration and alignment along the heat flow direction under the influence of gravity and the heat flow directed vertically towards the coating surface by the gas guiding device in the drying oven. This migration results in a gradient distribution of high thermal conductivity components and low thermal conductivity components, as well as ceramic particles of different sizes, in the coating thickness direction. Subsequently, under the high temperature environment of the outlet section, the resin rapidly cross-links and cures, fixing the formed gradient structure in the coating, thereby constructing a gradient of thermal conductivity and structure.

[0024] Preferably, in step S2, the inlet temperature of the primer drying oven is 180-195℃, the middle temperature is 195-210℃, and the outlet temperature is 210-230℃; in step S3, the inlet temperature of the topcoat drying oven is 185-200℃, the middle temperature is 200-220℃, and the outlet temperature is 220-240℃. The above temperature settings can ensure that the polyester resin system flows appropriately, the filler migrates in a directional manner, and finally achieves complete curing.

[0025] Preferably, the preparation of the primer coating includes: mixing the first multi-scale ceramic reinforcing phase with a silane coupling agent for surface treatment, mixing with a first solvent and a silane coupling agent as a first dispersant and ultrasonically dispersing, then adding the first thermal conductivity modifier, nano-silver antibacterial agent, saturated polyester resin, first leveling agent and first catalyst, stirring evenly and adjusting the viscosity before filtering;

[0026] The preparation of the topcoat includes: mixing the second multi-scale ceramic reinforcing phase with a silane coupling agent for surface treatment, mixing with a second solvent and a second dispersant and ultrasonically dispersing, then adding the second thermal conductivity modifier, nano-silver antibacterial agent, saturated polyester resin, a second leveling agent and a second catalyst, stirring evenly and adjusting the viscosity before filtering.

[0027] The beneficial effects of this invention are:

[0028] This invention creates a thermal conductivity gradient in the coating thickness direction by differentiating the thermal conductivity modifiers in the primer and topcoat layers, achieving synergistic thermal management of surface insulation and internal heat conduction. The gradation structure of the multi-scale ceramic reinforcing phase and surface modification treatment enable the coating to achieve good hardness and wear resistance. By optimizing the dispersion process, the antibacterial components are uniformly distributed and stably combined in the coating, achieving a long-lasting antibacterial effect.

[0029] The preparation method of the present invention is based on the existing roller coating production line with process adjustments. By controlling the stepped temperature rise curing and directional solidification, the functional gradient structure is constructed without changing the main production equipment, thus solving the compatibility problem between the functional material preparation process and the continuous production line. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the color-coated steel plate structure with gradient temperature control, antibacterial and wear-resistant functions of the present invention.

[0031] Figure label:

[0032] 1. Metal substrate; 2. Chemical conversion coating; 3. Primer layer; 4. Topcoat layer; 5. Backcoat layer. Detailed Implementation

[0033] The invention can be further understood through the specific embodiments given below, but they are not intended to limit the invention. Example 1

[0034] This embodiment 1 provides a color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions. The raw material formula composition of the color-coated steel sheet is shown in Table 1:

[0035] Table 1. Raw material formula for color-coated steel sheet with gradient temperature control, antibacterial and wear-resistant functions in Example 1

[0036]

[0037] In Table 1, the dibutyltin dilaurate catalyst and the bismuth isooctanoate catalyst in the topcoat layer are compounded in a 1:1 ratio, and the total amount of the two is 0.4 parts by weight.

[0038] This embodiment 1 provides a method for preparing the coatings of each paint layer in a color-coated steel sheet with gradient temperature control, antibacterial and wear-resistant functions, including the following steps:

[0039] Preparation of primer coating:

[0040] Alumina, zirconium oxide, silicon carbide particles were mixed with 0.7 parts by weight of silane coupling agent KH-550 and surface treated in a high-speed mixer at 1500 rpm for 30 min.

[0041] The treated ceramic powder was mixed with an appropriate amount of mixed solvent (xylene:butanol = 1:1) and 1.4 parts by weight of KH-550, and then treated in an ultrasonic disperser at 300W power for 60 minutes.

[0042] Add thermal conductivity modifier (boron nitride: hollow glass microspheres = 3:7, total 11 parts by weight) and nano silver antibacterial agent, and continue ultrasonic treatment for 30 minutes;

[0043] Add saturated polyester resin, BYK-333 leveling agent and DBTDL catalyst, stir at low speed of 500 rpm for 60 min, control the temperature below 35℃, adjust the viscosity with solvent to 28s (25℃) of Fort-4 cup, and filter through a 3μm filter for later use.

[0044] Preparation of topcoat:

[0045] Alumina, zirconium oxide, silicon carbide particles were mixed with 0.65 parts by weight of silane coupling agent KH-550 and surface treated in a high-speed mixer at 1500 rpm for 30 min.

[0046] The treated ceramic powder was mixed with a mixed solvent (xylene:butanol:butyl acetate = 7:2:1) and BYK-163 dispersant, and ultrasonically treated at 300W for 60min.

[0047] Add thermal conductivity modifier (boron nitride: hollow glass microspheres = 7:3, total 14 parts by weight) and nano silver antibacterial agent, and continue ultrasonic treatment;

[0048] Add saturated polyester resin, EFKA-3777 leveling agent and compound catalyst (DBTDL and bismuth isooctanoate, 0.2 parts by weight each), stir at low speed, adjust the viscosity to 28-32s (25℃) of Fort-4 cup, filter and set aside.

[0049] Preparation of backing paint:

[0050] Epoxy resin, nano silver antibacterial agent, BYK-110 dispersant, BYK-358N leveling agent, polyamide 650 curing agent, and mixed solvent (xylene: n-butanol: cyclohexanone = 5:3:2) were directly mixed and stirred at 500 rpm for 60 min. The temperature was controlled below 30℃. The viscosity was adjusted to 28 s (25℃) at Forecast cup 4. Filter and set aside.

[0051] The preparation method of the color-coated steel sheet with gradient temperature control, antibacterial and wear-resistant functions in Example 1 includes the following steps:

[0052] S1, 0.5mm hot-dip galvanized steel sheet is uncoiled, alkaline washed and degreased, washed with water and dried with hot air. Nippon RC300 chemical coating liquid is then rolled onto the treated steel sheet and dried at 130℃ for 45s to form a chemical coating of about 2μm.

[0053] S2, two-roller coated primer, dry film thickness 11μm. Enters primer drying oven (oven length 20m), oven temperature is controlled in three sections: inlet section (0-10m) 190℃, middle section (7-14m) 200℃, outlet section (14-20m) 220℃, hot air is blown vertically onto the board surface, the passage time is about 90s;

[0054] S3, three-roll coating topcoat, dry film thickness 16μm. Enter the topcoat drying oven (oven length 30m), the oven temperature is divided into three sections: inlet section (0-10m) 195℃, middle section (10-20m) 210℃, outlet section (20-30m) 235℃, the passage time is about 120s.

[0055] S4. Apply back coating to the back of the steel plate by roller, with a dry film thickness of 6.5μm, and cure using the residual heat of the production line;

[0056] S5. Post-processing: Cooling, film application, and winding to obtain the finished product. Example 2

[0057] This embodiment 2 provides a color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions. The difference between this embodiment and embodiment 1 is that the ratio of thermal conductivity regulator is different. The ratio of thermal conductivity regulator in this embodiment 2 is: in the primer layer: boron nitride: hollow glass microspheres = 2:8; in the topcoat layer: boron nitride: hollow glass microspheres = 8:2.

[0058] The remaining components, dosages, preparation methods of each paint layer and color-coated steel sheet are the same as in Example 1, and will not be repeated here. Example 3

[0059] This embodiment 3 provides a color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions. The difference between this embodiment and embodiment 1 is that the gradation ratio of the multi-scale ceramic reinforcing phase is different. The gradation ratio of the multi-scale ceramic reinforcing phase in this embodiment 3 is as follows: the mass ratio of the primer layer and the topcoat layer is: alumina:zirconia:silicon carbide = 5:3:2. Specifically, the alumina, zirconia and silicon carbide in the primer layer are 10, 6 and 4 parts by weight, respectively; the alumina, zirconia and silicon carbide in the topcoat layer are 9, 5.4 and 3.6 parts by weight, respectively.

[0060] The remaining components, dosages, preparation methods of each paint layer and color-coated steel sheet are the same as in Example 1, and will not be repeated here. Example 4

[0061] This embodiment 4 provides a color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions. The difference between this and embodiment 1 is that:

[0062] The film-forming matrix of both the primer and topcoat layers was replaced with an aliphatic polyurethane resin with a solid content of 75%. Correspondingly, the catalyst of the primer layer was replaced with an organotin catalyst suitable for polyurethane, and the catalyst of the topcoat layer was replaced with an amine compound catalyst. The leveling agent was also replaced with a model that is compatible with polyurethane.

[0063] The remaining components, dosages, preparation methods of each paint layer and color-coated steel sheet are the same as in Example 1, and will not be repeated here. Example 5

[0064] This embodiment 5 provides a color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions. The difference between this and embodiment 1 is:

[0065] The color-coated steel sheet in this embodiment 5 does not contain a back paint layer, and neither the primer nor the topcoat layer contains nano-silver antibacterial agent; it only exhibits gradient temperature control and wear resistance functions.

[0066] The remaining components, dosages, preparation methods of each paint layer and color-coated steel sheet (excluding the back paint layer) are the same as in Example 1, and will not be repeated here.

[0067] Comparative Example 1

[0068] Comparative Example 1 provides a conventional antibacterial color-coated sheet with a structure similar to that of Example 1. The difference from Example 1 is that no thermal conductivity modifier or multi-scale ceramic reinforcing phase is added to the primer and topcoat layers; 5 parts by weight of silica matting agent with a single particle size of about 1 μm is added; the amount of nano-silver antibacterial agent added is the same as in Example 1; the coating is dispersed by conventional mechanical stirring; and the curing is carried out using a constant temperature process of 200°C.

[0069] Comparative Example 2

[0070] Comparative Example 2 provides a conventional wear-resistant color-coated sheet with a structure similar to that of Example 1, but without the addition of thermal conductivity modifiers and nano-silver antibacterial agents to the primer and topcoat layers; 20 parts by weight of silicon carbide particles with a single-scale particle size of about 5 μm are added, and the coating and curing process are the same as in Comparative Example 1.

[0071] Comparative Example 3

[0072] Comparative Example 3 provides a color-coated sheet with a non-gradient ratio design. Its product composition is the same as that of Example 1. The difference from Example 1 is that the thermal conductivity modifier used in the primer layer and the topcoat layer has the same ratio, which is boron nitride: hollow glass microspheres = 5:5.

[0073] The remaining components, dosages, preparation methods of each paint layer and color-coated steel sheet are the same as in Example 1, and will not be repeated here.

[0074] Comparative Example 4

[0075] Comparative Example 4 provides a color-coated sheet with a non-directional solidification process. Its product composition is the same as that of Example 1. The difference between Example 1 and Example 2 is that the preparation process is different. The curing of the primer layer and the topcoat layer are both carried out using a conventional constant temperature process. The temperature of the drying oven is uniformly set to 215°C, with no step heating or special gas flow.

[0076] The remaining components, dosages, preparation methods of each paint layer and color-coated steel sheet are the same as in Example 1, and will not be repeated here.

[0077] Performance Description

[0078] Performance tests were conducted on the color-coated (steel) sheets of Examples 1-5 and Comparative Examples 1-4. The test items included: gradient temperature control performance, antibacterial performance, and wear resistance.

[0079] The gradient temperature control performance test used an infrared thermal imager to observe the surface temperature of each of the above-mentioned colored (steel) plates under the action of a local heat source;

[0080] The antibacterial performance test was conducted in accordance with the standard GB / T 21866-2008, using Staphylococcus aureus and Escherichia coli as test bacteria to test the above-mentioned color-printed (steel) plates.

[0081] The wear resistance test was conducted by measuring the wear weight loss of each of the above-mentioned colored (steel) plates, referring to the Taber wear resistance test (CS-10 wheel, 500g load).

[0082] The performance test results and analysis of the color-coated (steel) sheets of Examples 1-5 and Comparative Examples 1-4 are as follows:

[0083] Gradient temperature control performance test: Under the same heating conditions, the surface high-temperature area of ​​Examples 1-4 was reduced by an average of about 40% compared with Comparative Examples 1-4, and the heat was transferred to the substrate more rapidly. This indicates that the thermal conductivity gradient constructed by the primer layer (thermal conductivity modifier ratio 3:7 or 2:8) and the topcoat layer (ratio 7:3 or 8:2) effectively achieves the goal of "surface insulation and internal heat conduction".

[0084] The surface temperature distribution of Comparative Example 3 (all ratios are 5:5) is similar to that of ordinary color-coated steel sheets, verifying the necessity of gradient ratio.

[0085] Although Comparative Example 4 (constant temperature curing) has the same components, its thermal management performance is significantly lower than that of Example 1 due to the lack of a directional solidification process and insufficient filler gradient distribution.

[0086] Antibacterial performance test: The antibacterial rates of Examples 1-4 were all higher than 99.9%. After performing Taber abrasion tests on each color-printed (steel) plate to simulate wear, the antibacterial rates of Examples 1-4 remained above 99.5%, indicating that the nano-silver antibacterial agent was firmly bonded in the coating and had a long-lasting antibacterial effect;

[0087] Although the initial antibacterial rate of Comparative Example 1 (traditional antibacterial board) reached 99%, after the same wear, the antibacterial rate dropped to about 85%, indicating that its antibacterial agent is easily lost due to wear.

[0088] Wear resistance test: The average wear weight loss of Examples 1-4 was 4.2-4.8 mg / 1000 rpm, which was much lower than that of Comparative Example 1 (conventional plate, about 15 mg / 1000 rpm) and Comparative Example 2 (single-reinforced phase wear-resistant plate, about 8 mg / 1000 rpm).

[0089] The hardness of the coated pencils in Examples 1-4 all reached 2H, indicating that the gradation design of the multi-scale ceramic reinforcing phase (alumina / zirconia / silicon carbide) formed an effective "support-filler" composite structure, which improved hardness while ensuring good wear resistance.

[0090] Although hard particles were added to Comparative Example 2, its wear resistance was only slightly improved due to the lack of multi-scale synergy and good interfacial bonding.

[0091] Comprehensive analysis: The test results and analysis above show that the color-coated steel sheet provided by the present invention can integrate three functions: gradient temperature control, long-lasting antibacterial properties, and high wear resistance. Its performance advantages are reflected in the following aspects: In terms of formulation, functional synergy is achieved through gradient thermal conductivity regulator ratio and multi-scale reinforcing phase gradation; in terms of process, the above-mentioned formulation is structurally ordered through directional solidification technology compatible with existing production lines.

[0092] 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 gradient temperature control and antibacterial and wear-resistant functions, comprising a metal substrate and a chemical conversion coating, a primer layer, and a topcoat layer sequentially coated on at least one surface of the metal substrate; characterized in that, The primer layer contains a first thermal conductivity modifier and a first multi-scale ceramic reinforcing phase. The first thermal conductivity modifier is composed of a high thermal conductivity component and a low thermal conductivity component mixed in a first mass ratio of 3:

7. The high thermal conductivity component is boron nitride, and the low thermal conductivity component is hollow glass microspheres; The topcoat layer contains a second thermal conductivity modifier and a second multi-scale ceramic reinforcing phase. The second thermal conductivity modifier is composed of the high thermal conductivity component and the low thermal conductivity component mixed at a second mass ratio of 7:

3. The primer layer and / or the topcoat layer further contain a nano-silver antibacterial agent; Both the first multi-scale ceramic reinforcing phase and the second multi-scale ceramic reinforcing phase contain ceramic particles of different sizes, including coarse particles, fine particles, and nanoparticles. The coarse particles are alumina particles with a particle size of 2-3 μm, the fine particles are zirconium oxide particles with a particle size of 0.5-1 μm, and the nanoparticles are silicon carbide particles with a particle size of 50-200 nm. The preparation method of the color-coated steel sheet with gradient temperature control, antibacterial and wear-resistant functions includes the following steps: S1. Clean the surface of the metal substrate, apply a chemical conversion treatment solution and dry it to form a chemical conversion coating. S2. The prepared primer coating is applied to the chemical conversion coating and then placed in a primer drying oven for stepped heating and curing to form a primer layer. The primer drying oven is divided into an inlet section, a middle section and an outlet section along the direction of the board's movement. The temperature of the inlet section is set to be lower than that of the middle section and lower than that of the outlet section. S3. Apply the prepared topcoat coating onto the cured primer layer, and then enter the topcoat drying oven for stepped heating and curing to form the topcoat layer. The topcoat drying oven is also divided into an inlet section, a middle section and an outlet section along the direction of the board's movement. The temperature of the inlet section is set to be lower than that of the middle section, and the temperature of the middle section is lower than that of the outlet section. During the curing process of the primer layer and the topcoat layer, by controlling the lower temperature of the inlet section, the coating maintains suitable fluidity for a longer period of time, thereby causing the first thermal conductivity modifier, the second thermal conductivity modifier, the first multi-scale ceramic reinforcing phase and the second multi-scale ceramic reinforcing phase to undergo directional migration and alignment along the heat flow direction under the action of gravity and the heat flow perpendicular to the coating surface guided by the gas guiding device in the drying oven.

2. The color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions according to claim 1, characterized in that, The mass ratio of coarse particles, fine particles and nanoparticles is (4-5):(3-4):(1-2).

3. The color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions according to claim 1, characterized in that, The film-forming matrix of the primer layer and the topcoat layer is saturated polyester resin; the primer layer further includes a first dispersant, a first leveling agent and a first catalyst; the topcoat layer further includes a second dispersant, a second leveling agent and a second catalyst.

4. The color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions according to claim 3, characterized in that, The first dispersant is a silane coupling agent, the first leveling agent is an organosilicon leveling agent, and the first catalyst is an organotin catalyst; the second dispersant is a high molecular weight carboxylic acid type dispersant, the second leveling agent is a fluorinated polysiloxane leveling agent, and the second catalyst is a compound of organotin and organobismuth catalysts.

5. The color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions according to claim 1, characterized in that, It also includes a back coating layer coated on the other surface of the metal substrate, the back coating layer comprising an epoxy resin film-forming matrix, a nano-silver antibacterial agent, a third dispersant, a third leveling agent, and a polyamide curing agent.

6. A method for preparing a color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Clean the surface of the metal substrate, apply a chemical conversion treatment solution and dry it to form a chemical conversion coating. S2. The prepared primer coating is applied to the chemical conversion coating and then placed in a primer drying oven for stepped heating and curing to form a primer layer. The primer drying oven is divided into an inlet section, a middle section and an outlet section along the direction of the board's movement. The temperature of the inlet section is set to be lower than that of the middle section and lower than that of the outlet section. S3. Apply the prepared topcoat coating onto the cured primer layer, and then enter the topcoat drying oven for stepped heating and curing to form the topcoat layer. The topcoat drying oven is also divided into an inlet section, a middle section and an outlet section along the direction of the board's movement. The temperature of the inlet section is set to be lower than that of the middle section, and the temperature of the middle section is set to be lower than that of the outlet section.

7. The method for preparing color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions according to claim 6, characterized in that, In step S2, the inlet temperature of the primer drying oven is 180-195℃, the middle temperature is 195-210℃, and the outlet temperature is 210-230℃; in step S3, the inlet temperature of the topcoat drying oven is 185-200℃, the middle temperature is 200-220℃, and the outlet temperature is 220-240℃.

8. The method for preparing color-coated steel sheet with gradient temperature control and antibacterial and wear-resistant functions according to claim 6, characterized in that, The preparation of the primer coating includes: mixing the first multi-scale ceramic reinforcing phase with a silane coupling agent for surface treatment, mixing with a first solvent and a silane coupling agent as a first dispersant and ultrasonically dispersing, then adding the first thermal conductivity regulator, nano-silver antibacterial agent, saturated polyester resin, first leveling agent and first catalyst, stirring evenly and adjusting the viscosity before filtering; The preparation of the topcoat includes: mixing the second multi-scale ceramic reinforcing phase with a silane coupling agent for surface treatment, mixing with a second solvent and a second dispersant and ultrasonically dispersing, then adding the second thermal conductivity modifier, nano-silver antibacterial agent, saturated polyester resin, a second leveling agent and a second catalyst, stirring evenly and adjusting the viscosity before filtering.

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