A high-hardness color-coated steel sheet and its production method

Abstract

This invention discloses a high-hardness color-coated steel sheet and its production method. The color-coated steel sheet includes a substrate, an intermediate layer on the surface of the substrate, and a top coating layer on top of the intermediate layer. The top coating layer, by weight, comprises 15-25 parts polyvinylidene fluoride, 40-60 parts silane-modified polyester, 10-30 parts pigments and fillers, 1-3 parts modified carbon nitride, 0.5-1 parts leveling agent, and 0.5-1 parts dispersant. The intermediate layer, by weight, comprises 20-30 parts polymethyl methacrylate, 10-15 parts polyvinylidene fluoride-hexafluoropropylene copolymer, and 40-60 parts ethylene-vinyl acetate copolymer. The top coating layer of this invention has good hardness and wear resistance, and a long service life. Simultaneously, the modified carbon nitride enhances the coating's absorption of light and heat, giving the color-coated steel sheet excellent thermal conductivity and insulation properties.

Description

Technical Field

[0001] This invention relates to the field of color-coated steel sheet technology, and in particular to a high-hardness color-coated steel sheet and its production method. Background Technology

[0002] Pre-coated steel sheet, also known as coated steel sheet, organic coated steel sheet, or pre-coated steel sheet, is made by coating or laminating various organic coatings or plastic films onto the surface of metal coils (cold-rolled steel, hot-dip galvanized steel, aluminized steel, high-aluminum alloy steel, stainless steel, etc.). Because the surface coating of pre-coated steel sheet is completed in a metallurgical plant, it can be directly processed into products by users, hence the name "pre-coated coil." Due to its combination of excellent decorative and protective properties of the outer coating with the high strength and easy processing performance of the substrate, pre-coated steel sheet is widely used in construction, home appliances, and the automotive industry.

[0003] In the structure of pre-coated steel sheets, the coating layer is located on the surface and is in direct contact with the external environment. Therefore, the coating material plays a crucial role in the corrosion resistance, stain resistance, and appearance of the pre-coated steel sheet. Improving the coating material can enhance the surface strength and scratch resistance of the pre-coated steel sheet, protecting the surface from damage and ensuring that the overall corrosion resistance, stain resistance, weather resistance, and thermal insulation properties of the pre-coated steel sheet remain unaffected. CN109401507A discloses a high-strength nano-graphene pre-coated steel sheet and its preparation method. The pre-coated steel sheet includes a top coating layer, a base coating layer, a first passivation layer, a substrate, a second passivation layer, and a back coating layer stacked sequentially. Aluminum nitride is modified with triethanolamine and β-hydroxyalkylamide, and then combined with graphene under the action of epoxy resin to form a composite material, improving the overall strength of the top coating layer. Graphene oxide is added to the base coating layer and modified by ultra-high molecular weight polyacrylamide (UHMWPA), which acts as a crosslinking point in the UHMWPA molecules, further improving the strength of the base coating layer. However, although the aluminum nitride in the top coating of this coated plate has undergone modification treatment, it can react violently with water, and may precipitate out and come into contact with water during long-term use, resulting in instability. CN115216197A discloses a color-coated plate and its preparation method. This color-coated plate includes a substrate, a primer layer applied to the top of the substrate, and a fine coating layer applied to the top of the primer layer. The primer layer, by weight, includes 80-95 parts of epoxy resin, 30-45 parts of acrylic, 25-35 parts of acetylene-butyl acrylate copolymer, 10-15 parts of modified lime powder, 5-10 parts of modified graphite powder, 15-25 parts of modified inorganic particles, and 1-5 parts of modified bentonite, forming a primer layer that can enhance the bending strength and scratch resistance of the color-coated plate. However, this method requires high pressure and radiation modification for the lime powder, graphite powder, and inorganic particles, necessitating additional equipment, which is not conducive to industrial mass production.

[0004] Developing color-coated steel sheets with high hardness and structural stability coatings still presents certain challenges. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a high-hardness color-coated steel sheet, comprising a substrate, an intermediate layer on the surface of the substrate, and a top coating layer on top of the intermediate layer.

[0006] The material of the surface coating comprises, by weight parts, the following:

[0007] 15-25 parts polyvinylidene fluoride, 40-60 parts silane-modified polyester, 10-30 parts pigments and fillers, 1-3 parts modified carbon nitride, 0.5-1 part leveling agent, 0.5-1 part dispersant;

[0008] The material of the intermediate layer comprises, by weight, parts of,

[0009] 20-30 parts polymethyl methacrylate, 10-15 parts polyvinylidene fluoride-hexafluoropropylene copolymer, and 40-60 parts ethylene-vinyl acetate copolymer.

[0010] The topcoat formulation of this invention incorporates polyvinylidene fluoride (PVDF) and silane-modified polyester. Due to its highly stable fluorocarbon bonds and unique molecular symmetry, PVDF possesses strong stability and unique UV resistance. The silane-modified polyester backbone features repeating typical Si-O bonds with bond energies as high as 446 kJ / mol, making it less susceptible to the effects of sunlight and ultraviolet radiation. This contributes to the excellent mechanical properties of the topcoat.

[0011] Carbon nitride possesses properties such as high temperature resistance, wear resistance, high electrical conductivity, and theoretically higher hardness than diamond. Its unique band gap structure and photoluminescence properties also give it good UV shielding performance. Compared to direct calcination of precursors rich in carbon and nitrogen, copolymerizing melamine with molecules of similar structure, such as cyanuric acid, followed by calcination, can produce carbon nitride with a larger specific surface area. Furthermore, adding substances that can interact with piperazine rings during the polymerization reaction can further promote polymerization. Dopamine spontaneously polymerizes in alkaline environments to form polydopamine. This invention modifies the surface of carbon nitride with polydopamine after preparation, utilizing the abundant amino, hydroxyl, and benzene ring groups of polydopamine to enhance the interaction between carbon nitride and the coating resin, improving the dispersibility of carbon nitride. However, polydopamine has a certain degree of hydrophilicity, and direct modification may increase the hydrophilicity of the coating. In the preparation of carbon nitride, the copolymer is ground and mixed with copper salt and then calcined to introduce copper into the carbon nitride. The introduction of copper not only enhances the interaction between the modified carbon nitride and the coating resin but also suppresses the drawbacks of the hydrophilicity of polydopamine. Furthermore, based on the copper and polydopamine contained in the modified carbon nitride, the coating's ability to absorb light and heat is enhanced, resulting in excellent thermal conductivity and insulation properties in the color-coated sheet.

[0012] Furthermore, the method for preparing the modified carbon nitride includes, by weight, the following:

[0013] Dissolve 5-10 parts of melamine and 5-10 parts of cyanuric acid in 100-150 parts of dimethyl sulfoxide and stir for 2-5 hours; then add 1-3 parts of 3,4-pyridinedicarboxylic acid and continue the reaction for 3-8 hours, and collect the polymer.

[0014] 5-10 parts of polymer and 0.2-0.5 parts of copper salt are ground and mixed to obtain a mixture, which is then calcined at 400-600℃ for 3-5 hours to obtain an intermediate.

[0015] Mix 5-10 parts of intermediate, 0.3-1 parts of dopamine hydrochloride, and 150-200 parts of the first solvent and adjust the pH to weakly alkaline. Then stir the reaction to obtain modified carbon nitride.

[0016] However, the reaction essentially stops after most of the melamine and cyanuric acid polymerization is completed. Therefore, this invention adds 4-acetaminopyrimidine to further promote the reaction through interaction, enabling the preparation of carbon nitride with a larger specific surface area under the same conditions.

[0017] Furthermore, when adding 3,4-pyridinedicarboxylic acid, 0.1 to 0.2 times the mass of melamine, 4-acetaminopyrimidine is also added.

[0018] Furthermore, the particle size of the mixture is 200-500 mesh.

[0019] Furthermore, the first solvent includes at least one of water, ethanol, acetone, and phosphate buffer solution;

[0020] The term "weakly alkaline" refers to a pH value adjusted to 8.5-9.3.

[0021] Furthermore, the method for preparing the silane-modified polyester includes, by weight, the following:

[0022] 10-30 parts of vinyl benzoate, 50-80 parts of ethylene tert-carbonate, and 0.2-1 parts of initiator are added to 60-150 parts of a second solvent and heated for polymerization. Then, 60-100 parts of silane monomer and 0.1-0.3 parts of catalyst are added and heated again to obtain silane-modified polyester.

[0023] Furthermore, the second solvent includes at least one of toluene and ethyl acetate;

[0024] The silane monomer includes at least one of γ-aminopropyltriethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane;

[0025] The catalyst includes at least one of organotin compounds, titanate compounds, and germanium compounds.

[0026] Furthermore, the pigments and fillers include at least one of calcium carbonate (300-500 mesh), barium sulfate, titanium dioxide, and zinc oxide.

[0027] Furthermore, the leveling agent is an organosilicon-modified polyacrylate leveling agent.

[0028] Furthermore, the dispersant is at least one of sodium polycarboxylate, potassium polyacrylate, and sodium polyacrylate.

[0029] The present invention also provides a method for producing the above-mentioned high-hardness color-coated steel sheet, comprising,

[0030] The intermediate layer material is rolled onto the upper and lower surfaces of the substrate and then cured to obtain an intermediate product.

[0031] The material for the top and bottom coatings of the intermediate product is rolled onto the top and bottom surfaces, and then cured to obtain a high-hardness color-coated sheet.

[0032] It should be noted that polyvinylidene fluoride is also dissolved using a solvent of 1 to 3 times its mass. This solvent can be N,N-dimethylformamide, N-methylpyrrolidone, methyl vinyl ketone, dichloromethane, etc., as the solvent is completely dried and not included in the topcoat material. The type of substrate in this invention is not limited. According to general understanding in the art, the substrate can be one of cold-rolled steel sheet, hot-dip galvanized sheet, aluminized sheet, high-aluminum alloy sheet, stainless steel sheet, etc. The type of initiator used in this invention is not strictly limited and can be selected as needed, as long as it can initiate a free radical reaction. Exemplarily, it can be at least one of dicumyl peroxide, benzoyl peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, potassium persulfate, etc. The type of copper salt used in this invention is not strictly limited and can be at least one of copper sulfate pentahydrate, copper nitrate trihydrate, copper acetate monohydrate, etc.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The formulation of the topcoat of this invention includes polyvinylidene fluoride, silane-modified polyester, and modified carbon nitride, which gives the coating good hardness and wear resistance, and a long service life. At the same time, based on the copper element and polydopamine contained in the modified carbon nitride, the coating's ability to absorb light and heat is enhanced, giving the color-coated plate excellent thermal conductivity and insulation properties. Detailed Implementation

[0035] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0036] The following describes some of the raw materials used in the embodiments and comparative examples of this invention:

[0037] Polymethyl methacrylate, model number ZK5BR, is sourced from Evonik Degussa, Germany.

[0038] Polyvinylidene fluoride-hexafluoropropylene copolymer, grade 2801, is sourced from Arkema, France;

[0039] Ethylene-vinyl acetate copolymer, grade UL15019CC, is sourced from ExxonMobil;

[0040] Polyvinylidene fluoride, grade 4000HD, is sourced from Arkema, France;

[0041] Vinyl benzoate, CAS number 769-78-8;

[0042] Ethylene tert-carbonate, CAS number 51000-52-3;

[0043] 3,4-Pyridinedicarboxylic acid, CAS number 490-11-9;

[0044] 4-Acetaminopyrimidine, CAS number 5221-42-1;

[0045] The leveling agent selected was an organosilicon-modified polyacrylate leveling agent, brand name BYK3700, sourced from BYK Chemical Company of Germany.

[0046] All other unmentioned raw materials are common raw materials. The above content is only for illustrative purposes and should not be construed as a strict limitation of the present invention. Those skilled in the art can directly purchase commercially available raw materials or prepare the same / similar raw materials themselves. These contents will not be repeated in the embodiments.

[0047] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Example 1

[0049] A method for producing high-hardness color-coated steel sheets, comprising the following steps.

[0050] S1. Dissolve 2 kg of polyvinylidene fluoride in 2.5 kg of N-methylpyrrolidone, then mix with 5 kg of silane-modified polyester, 2.5 kg of 350 mesh calcium carbonate, 0.2 kg of modified carbon nitride, 0.08 kg of organosilicon-modified polyacrylate leveling agent, and 0.75 kg of sodium polyacrylate. Heat to 65°C and stir at 150 rpm for 20 min to obtain the topcoat material.

[0051] S2. Mix 2.5 kg of polymethyl methacrylate, 1.3 kg of polyvinylidene fluoride-hexafluoropropylene copolymer, and 5.5 kg of ethylene-vinyl acetate copolymer, and stir at 120°C and 120 rpm for 15 min to obtain the intermediate layer material.

[0052] S3. Preheat a 0.5mm thick Q235 cold-rolled steel sheet to 60°C, then roll-coat the upper and lower surfaces with the intermediate layer material, bake at 130°C for 30s, and air-cool to solidify to obtain the intermediate product.

[0053] S4. A topcoat material is rolled onto the upper and lower surfaces of the intermediate product, followed by baking at 150°C for 30 seconds and air-cooling to cure, resulting in a high-hardness color-coated sheet. The high-hardness color-coated sheet comprises a cold-rolled steel sheet, an intermediate layer on the surface of the cold-rolled steel sheet, and a topcoat on top of the intermediate layer. The thicknesses of the intermediate layer and the topcoat are 30 μm and 50 μm, respectively.

[0054] The preparation method of silane-modified polyester is as follows:

[0055] 2.5 kg of vinyl benzoate, 6.5 kg of ethylene tert-carbonate, and 0.08 kg of azobisisobutyronitrile were added to 12 kg of ethyl acetate and the mixture was heated to 65 °C and polymerized under reflux for 5 h. Then, 8 kg of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane and 0.025 kg of dibutyltin dilaurate were added, and the mixture was heated to 80 °C and reacted under reflux for 2 h to obtain silane-modified polyester.

[0056] The preparation method of modified carbon nitride is as follows:

[0057] T1. Dissolve 80g of melamine and 85g of cyanuric acid in 1200g of dimethyl sulfoxide and stir at 150rpm for 3h; then add 20g of 3,4-pyridinedicarboxylic acid and continue the reaction for 6h. After filtration, dry in a constant temperature oven at 120℃ for 12h to obtain the polymer.

[0058] T2. Grind and mix 75g of polymer and 3g of copper sulfate pentahydrate, then sieve to obtain a mixture with a particle size of 300 mesh. Then transfer it to a muffle furnace with air atmosphere at 450℃ and calcine for 4 hours to obtain an intermediate.

[0059] T3. Mix 75g of intermediate, 8g of dopamine hydrochloride and 1500g of ethanol at 350rpm and adjust the pH to 9.1. Then stir and react for 5h. After filtration, dry in an 80℃ constant temperature oven for 12h to obtain modified carbon nitride.

[0060] Example 2

[0061] The method is basically the same as in Example 1, except that the modified carbon nitride is prepared by...

[0062] T1. Dissolve 80g of melamine and 85g of cyanuric acid in 1200g of dimethyl sulfoxide and stir at 150rpm for 3h. Then add 20g of 3,4-pyridinedicarboxylic acid and 8g of 4-acetaminopyrimidine and continue the reaction for 6h. After filtration, dry in a constant temperature oven at 120℃ for 12h to obtain the polymer.

[0063] T2. Grind and mix 75g of polymer and 3g of copper sulfate pentahydrate, then sieve to obtain a mixture with a particle size of 300 mesh. Then transfer it to a muffle furnace with air atmosphere at 450℃ and calcine for 4 hours to obtain an intermediate.

[0064] T3. Mix 75g of intermediate, 8g of dopamine hydrochloride and 1500g of ethanol at 350rpm and adjust the pH to 9.1. Then stir and react for 5h. After filtration, dry in an 80℃ constant temperature oven for 12h to obtain modified carbon nitride.

[0065] Example 3

[0066] The difference compared to Example 2 is that the amount of 4-acetaminopyrimidine added in step T1 is 12g.

[0067] Example 4

[0068] The difference compared to Example 2 is that the amount of 4-acetaminopyrimidine added in step T1 is 16g.

[0069] Comparative Example 1

[0070] The difference compared to Example 2 is that the amount of 4-acetaminopyrimidine added in step T1 is 6g.

[0071] Comparative Example 2

[0072] The difference compared to Example 2 is that the amount of 4-acetaminopyrimidine added in step T1 is 20g.

[0073] Comparative Example 3

[0074] Compared with Example 1, the difference is that copper sulfate pentahydrate is not added in step T2, and the polymer is ground to 300 mesh and then calcined.

[0075] Comparative Example 4

[0076] Compared with Example 3, the difference is that copper sulfate pentahydrate is not added in step T2, and the polymer is ground to 300 mesh and then calcined.

[0077] Comparative Example 5

[0078] The difference from Example 1 is that in step S1, modified carbon nitride is replaced with carbon nitride.

[0079] The method for preparing carbon nitride is as follows:

[0080] T1. Dissolve 80g of melamine and 85g of cyanuric acid in 1200g of dimethyl sulfoxide and stir at 150rpm for 3h. Then add 20g of 3,4-pyridinedicarboxylic acid and 12g of 4-acetaminopyrimidine and continue the reaction for 6h. After filtration, dry in a constant temperature oven at 120℃ for 12h to obtain the polymer.

[0081] T2. Grind 75g of polymer and sieve it to a particle size of 300 mesh. Then transfer it to a muffle furnace with an air atmosphere at 450℃ and calcine for 4 hours to obtain carbon nitride.

[0082] Comparative Example 6

[0083] The difference from Example 1 is that modified carbon nitride is not added in step S1.

[0084] Test case

[0085] The specific surface area and average pore size of the carbon nitride materials prepared in the examples and comparative examples were tested by nitrogen adsorption-desorption, and the results are shown in Table 1.

[0086] Table 1. Specific surface area and average pore size results of carbon nitride materials

[0087]

[0088] As shown in Table 1, the carbon nitride materials prepared in the embodiments of the present invention have a larger specific surface area and average pore size. Furthermore, Examples 2-4 are significantly larger than Example 1, indicating that the introduction of 4-acetaminopyrimidine promotes the further polymerization of melamine and cyanuric acid, resulting in a polymer with a richer pore structure after calcination. Examples 2-4 and Comparative Examples 1-2 demonstrate that there is a preferred value for the addition of 4-acetaminopyrimidine; too little or too much is detrimental to the improvement of specific surface area and pore size. Comparative Examples 3 and 4 were not ground with copper sulfate pentahydrate after polymer preparation. Correspondingly, compared to Examples 1 and 3, the specific surface area remained almost unchanged, but the pore size decreased significantly. This indicates that the introduction of copper does not cause significant etching of the carbon nitride aggregate, but effectively controls the pore size. The carbon nitride prepared in Comparative Example 5, compared to the modified carbon nitride of Example 3, did not undergo copper and polydopamine modification, indicating that the introduction of polydopamine can slightly increase the specific surface area, but has almost no effect on the pore size. Using carbon nitride materials with a larger specific surface area provides more binding sites, which is beneficial for their good dispersion in topcoat materials.

[0089] The water contact angle of the topcoat of the color-coated steel sheet was tested using a water contact angle tester; the hardness of the topcoat of the color-coated steel sheet was tested according to the standard GB / T 6739-2022 "Determination of Hardness of Paint and Varnish by Pencil Method"; the surface of the topcoat of the color-coated steel sheet was ground using a JM-1 type paint film abrasion tester, and the abrasion resistance was expressed by the weight loss of the topcoat, with the smaller the weight loss, the better the abrasion resistance. The test results are shown in Table 2.

[0090] Table 2. Hardness and weight loss results of the topcoat

[0091]

[0092] As shown in Table 2, the topcoat of Comparative Example 6 without carbon nitride exhibits good hydrophobic properties, with a water contact angle of 140°. The water contact angle of Comparative Example 5, which is not modified with polydopamine, is even lower. Furthermore, compared to Examples 1 and 3, the water contact angles of Comparative Examples 3 and 4 are significantly lower. This is because while polydopamine modification improves the dispersion of modified carbon nitride in the topcoat, the presence of hydrophilic functional groups in polydopamine also increases the hydrophilicity of the topcoat. The introduction of copper strengthens the interaction between modified carbon nitride and polyvinylidene fluoride and silane-modified polyester, making it difficult for hydrophilic groups to distribute on the surface, thus suppressing the drawbacks of polydopamine modification. Simultaneously, the amount of 4-acetaminopyrimidine added also has a certain impact on carbon nitride. Due to the synergistic effect of the polymerization reaction of 4-acetaminopyrimidine, the introduction of copper, and the multiple effects of polydopamine modification, Example 3 exhibits the largest water contact angle, reaching 151°. It can also be seen that the embodiments and comparative examples of the present invention have high hardness, all exceeding the 3H level. This is because polyvinylidene fluoride and silane-modified polyester have high mechanical strength. However, the hardness of comparative example 5 is lower than that of comparative example 6, indicating that directly adding carbon nitride without over-modification with polydopamine may result in poor dispersibility, leading to a decrease in the strength of the topcoat. Example 3 has the highest strength and the lowest weight loss rate because the modified carbon nitride with a large specific surface area can be well dispersed in the topcoat matrix, thereby improving the hardness and wear resistance of the topcoat.

[0093] The thermal insulation temperature difference test was conducted on the color-coated plates prepared in the examples and comparative examples in accordance with HG / T 4341-2012 "Heat-reflective coatings for metal surfaces". The results of the thermal insulation temperature difference of the samples are shown in Table 3.

[0094] Table 3 Insulation Temperature Difference Results

[0095]

[0096] The test results in Table 3 also show that the color-coated sheet prepared in the embodiments of the present invention has good thermal insulation performance. This is due to the good absorption of light and heat by polydopamine and copper in the well-distributed modified carbon nitride, and the good thermal conductivity of carbon nitride itself.

[0097] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-hardness color-coated steel sheet, comprising a substrate, an intermediate layer on the surface of the substrate, and a top coating layer on top of the intermediate layer, characterized in that, The material of the surface coating comprises, by weight, parts thereof. 15-25 parts polyvinylidene fluoride, 40-60 parts silane-modified polyester, 10-30 parts pigments and fillers, 1-3 parts modified carbon nitride, 0.5-1 part leveling agent, 0.5-1 part dispersant; The material of the intermediate layer comprises, by weight, parts of, 20-30 parts polymethyl methacrylate, 10-15 parts polyvinylidene fluoride-hexafluoropropylene copolymer, 40-60 parts ethylene-vinyl acetate copolymer; The method for preparing the modified carbon nitride includes, by weight, the following: Dissolve 5-10 parts of melamine and 5-10 parts of cyanuric acid in 100-150 parts of dimethyl sulfoxide and stir for 2-5 hours; then add 1-3 parts of 3,4-pyridinedicarboxylic acid and continue the reaction for 3-8 hours, and collect the polymer. 5-10 parts of polymer and 0.2-0.5 parts of copper salt are ground and mixed to obtain a mixture, which is then calcined at 400-600℃ for 3-5 hours to obtain an intermediate. Mix 5-10 parts of intermediate, 0.3-1 part of dopamine hydrochloride, and 150-200 parts of the first solvent and adjust the pH to weakly alkaline. Then stir the reaction to obtain modified carbon nitride. The addition of 4-acetaminopyrimidine, at a mass of 0.1 to 0.2 times that of melamine, is also carried out when adding 3,4-pyridinedicarboxylic acid. The particle size of the mixture is 200-500 mesh; The method for preparing the silane-modified polyester includes, by weight, the following: 10-30 parts of vinyl benzoate, 50-80 parts of ethylene tert-carbonate, and 0.2-1 parts of initiator are added to 60-150 parts of a second solvent and heated for polymerization. Then, 60-100 parts of silane monomer and 0.1-0.3 parts of catalyst are added and heated again to obtain silane-modified polyester. The second solvent includes at least one of toluene and ethyl acetate; The silane monomer is N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane; The catalyst includes at least one of organotin compounds, titanate compounds, and germanium compounds.

2. The high-hardness color-coated steel sheet according to claim 1, characterized in that, The first solvent includes at least one of water, ethanol, acetone, and phosphate buffer solution; The term "weakly alkaline" refers to a pH value adjusted to 8.5-9.

3.

3. The high-hardness color-coated steel sheet according to claim 1, characterized in that, The pigments and fillers include at least one of calcium carbonate, barium sulfate, titanium dioxide, and zinc oxide with a mesh size of 300-500.

4. The high-hardness color-coated steel sheet according to claim 1, characterized in that, The leveling agent is an organosilicon-modified polyacrylate leveling agent.

5. The high-hardness color-coated steel sheet according to claim 1, characterized in that, The dispersant is at least one of potassium polyacrylate and sodium polyacrylate.

6. A method for producing high-hardness color-coated steel sheet as described in any one of claims 1 to 5, characterized in that, include, The intermediate layer material is rolled onto the upper and lower surfaces of the substrate and then cured to obtain an intermediate product; The material for the top and bottom coatings of the intermediate product is rolled onto the top and bottom surfaces, and then cured to obtain a high-hardness color-coated sheet.

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