Ceramic coating for metal door and preparation method thereof

Abstract

The invention discloses a ceramic coating for a metal door and a preparation method of the ceramic coating, and relates to the technical field of coatings. The prepared ceramic coating is prepared from sodium silicate, methyltrimethoxysilane, modified polyacrylate emulsion, modified silicon dioxide, glass powder, sodium fluosilicate, a dispersing agent, a flatting agent and pure water. The modified polyacrylate emulsion is obtained by polymerizing a phosphorus-containing monomer and a vinyl monomer to generate polyacrylate, carrying out sulfonyl chlorination on the polyacrylate, reacting with 5-chloromethyl-2-pyrimidinamine, and emulsifying; the preparation method comprises the following steps: polymerizing aniline on the surface of pretreated silicon dioxide, reacting with 1-benzothiophene-5-carbonyl chloride, salinizing with diphenyl iodide trifluoromethanesulfonate and copper acetate, and reacting with bis (2-ethynylphenyl) sulfane to obtain the silicon dioxide. The prepared ceramic coating has good corrosion resistance, antibacterial property and ageing resistance, and the performance of the metal door is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of high-performance coatings, and particularly to a ceramic coating with high performance for metal doors and a preparation method thereof. Background Art

[0002] In the field of manufacturing and application of metal doors, the selection of surface coatings has a crucial impact on the durability, aesthetics, and functionality of products. Traditional metal doors mostly use organic coatings or ordinary metal coatings for surface treatment. However, with the progress of industrial technology and the increasing requirements of users for product performance, the limitations of traditional coatings have gradually emerged; while ceramic coatings, as a new type of surface treatment material, have gradually attracted attention; ceramic coatings have been widely used in many industrial fields due to their excellent high-temperature resistance, wear resistance, corrosion resistance, and good insulation performance; in the application of metal doors, ceramic coatings can not only provide more durable surface protection, but also enhance the overall performance of products through their unique physical and chemical properties.

[0003] Although ceramic coatings have many advantages, such as high-temperature resistance, non-stickiness, corrosion resistance, and beautiful appearance, they also have some disadvantages. Among them, the most important disadvantage is the brittleness of the ceramic coating and relatively poor wear resistance. Under the conditions of high-frequency use and outdoor light, the coating may be worn, resulting in the exposure of the metal substrate, thus losing its original corrosion resistance and non-stickiness;

[0004] In order to overcome these disadvantages, ceramic coatings need to have stronger anti-corrosion performance, anti-ultraviolet aging performance, and antibacterial performance. Anti-corrosion performance can extend the service life of the coating and protect the substrate from corrosion. Anti-ultraviolet aging performance can ensure that the coating still maintains its performance and appearance after long-term exposure to the outdoor environment. Antibacterial performance can effectively prevent the growth of microorganisms such as bacteria and molds on the surface of the coating, and keep the coating clean and hygienic. Summary of the Invention

[0005] The purpose of the present invention is to provide a ceramic coating with high performance for metal doors and a preparation method thereof to solve the problems existing in the prior art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A ceramic coating for metal doors, the ceramic coating comprising sodium silicate, methyltrimethoxysilane, modified polyacrylate emulsion, modified silica, glass powder, sodium fluorosilicate, dispersant, leveling agent, and pure water.

[0008] The modified polyacrylate emulsion is obtained by polymerizing a phosphorus-containing monomer and a vinyl monomer to form polyacrylate, subjecting the polyacrylate to sulfonyl chlorination, reacting it with 5-chloromethyl-2-pyrimidinamine, and then emulsifying the product.

[0009] The silica is obtained by polymerizing aniline on the surface of pretreated silica, reacting it with 1-benzothiophene-5-carbonyl chloride, subjecting it to diphenyliodonium trifluoromethanesulfonate and copper acetate salification, and then reacting it with bis(2-ethynylphenyl)sulfane.

[0010] A preparation method of a ceramic coating for a metal door includes the following preparation steps:

[0011] (1) React vinyl diphenylphosphine with fuming sulfuric acid to obtain a phosphorus-containing monomer;

[0012] (2) Polymerize methyl acrylate, the phosphorus-containing monomer, and styrene to obtain polyacrylate;

[0013] (3) React the polyacrylate with chlorosulfonic acid and thionyl chloride to obtain a pre-modified polyacrylate; react the pre-modified polyacrylate with 5-chloromethyl-2-pyrimidinamine to obtain a modified polyacrylate; emulsify the modified polyacrylate with an emulsifier to obtain a modified polyacrylate emulsion;

[0014] (4) React silica with 3-[3-(trimethoxysilyl)propoxy]aniline to obtain pretreated silica; polymerize aniline on the surface of the pretreated silica to obtain polyaniline-based silica; react the polyaniline-based silica with 1-benzothiophene-5-carbonyl chloride to obtain benzothiophene-based silica;

[0015] (5) React the benzothiophene-based silica with diphenyliodonium trifluoromethanesulfonate and copper acetate to obtain thiophene salt silica; react the thiophene salt silica with ethanol and sodium ethoxide to obtain pre-modified silica;

[0016] (6) Mix the pre-modified silica, copper chloride, acetonitrile, triethylamine, and diethyl iodobenzoate, and dropwise add a bis(2-ethynylphenyl)sulfane solution at a dropping rate of 0.6 mL / min; after the dropping is completed, continue stirring for 30 - 40 min, and obtain modified silica through filtration, washing, and drying at room temperature;

[0017] (7) Weigh the following components: sodium silicate, methyltrimethoxysilane, modified polyacrylate emulsion, modified silica, glass powder, sodium fluorosilicate, dispersant, leveling agent, pure water; stir the above components at 50 - 60 °C for 30 min, then mix them in a high-speed mixer for 60 - 70 min, and grind them with a grinder. After the fineness reaches 40 - 50 μm, a ceramic coating is obtained.

[0018] As an optimization, the preparation method of the phosphorus-containing monomer in step (1) is as follows: at 0 °C, vinyl diphenylphosphine and fuming sulfuric acid are mixed at a mass ratio of 1:(2 - 2.5), stirred at 0 °C for 2 h, heated to room temperature and then stirred for 16 - 18 h, and then cooled to 0 °C. Pure water is added dropwise at a rate of 1 mL / min, and the addition amount of pure water is 15 - 20 times that of vinyl diphenylphosphine; 7.5 M sodium hydroxide solution is used to adjust the pH to 7, filtered and recrystallized with pure water at 4 °C, filtered and washed with n-pentane 3 - 4 times, and dried at room temperature to obtain the phosphorus-containing monomer; the fuming sulfuric acid contains 25 wt% sulfur trioxide.

[0019] As an optimization, the preparation method of the polyacrylate in step (2) is as follows: methyl acrylate, phosphorus-containing monomer, styrene, and N,N-dimethylformamide are mixed at a mass ratio of 1:(0.6 - 0.8):(0.1 - 0.2):(20 - 30). Under nitrogen protection, it is heated to 90 °C, then benzoyl peroxide with a mass of 0.01 times that of methyl acrylate is added and stirred for 90 min. Then, benzoyl peroxide with a mass of 0.01 times that of methyl acrylate is added again and stirred for 90 min. After stirring, it is vacuum dried at 80 °C for 12 h to obtain polyacrylate.

[0020] As an optimization, the preparation method of the modified polyacrylate emulsion in step (3) is as follows: polyacrylate, chlorosulfonic acid, thionyl chloride, phosphorus trichloride, and N,N-dimethylformamide are mixed at a mass ratio of 1:(0.2 - 0.3):(0.2 - 0.3):(0.06 - 0.08):(30 - 40), heated to 55 °C and reacted for 2 h, cooled to room temperature, an ice-water mixture with a mass 3 - 4 times that of N,N-dimethylformamide is added, filtered and washed with pure water at 4 °C 3 - 4 times, and vacuum dried to obtain pre-modified polyacrylate; the pre-modified polyacrylate, 5-chloromethyl-2-pyrimidinamine, dichloromethane, and triethylamine are mixed at a mass ratio of 1:(0.2 - 0.3):(20 - 30):(0.2 - 0.3), reacted at room temperature for 5 - 6 h. After the reaction, modified polyacrylate is obtained by rotary evaporation under reduced pressure; the modified polyacrylate, emulsifier, pure water, and ethylene glycol monobutyl ether are weighed at a mass ratio of 1:0.3:40:5. After the modified polyacrylate and ethylene glycol monobutyl ether are mixed for 5 min, the emulsifier and pure water are added, and they are mixed evenly at 70 °C and 1000 r / min to obtain the modified polyacrylate emulsion; the emulsifier is OP-10.

[0021] As an optimization, the preparation method of the benzothiophene-based silica in step (4) is as follows: Mix silica, 3-[3-(trimethoxysilyl)propoxy]aniline, and absolute ethanol in a mass ratio of 1:(5 - 6):(50 - 60), ultrasonically oscillate for 20 - 30 min, heat up to 50 °C, stir for 1 - 2 h, filter and wash with pure water 3 - 4 times, and dry at 60 °C for 6 - 8 h to obtain pretreated silica; at 2 - 4 °C, mix the pretreated silica and a 2 wt% aqueous solution of polyvinylpyrrolidone, add a 0.6 mol / L hydrochloric acid aqueous solution, aniline, and ammonium persulfate, and continue stirring for 5 - 6 h, filter and wash with absolute ethanol 3 - 4 times, and dry at 60 °C for 6 - 8 h to obtain polyaniline-based silica. The mass ratio of the pretreated silica, aniline, the 2 wt% aqueous solution of polyvinylpyrrolidone, the 0.6 mol / L hydrochloric acid aqueous solution, and ammonium persulfate is 1:(0.5 - 0.6):(50 - 60):(25 - 30):(0.3 - 0.5); mix the polyaniline-based silica, 1-benzothiophene-5-carbonyl chloride, N,N-dimethylformamide, and triethylamine in a mass ratio of 1:(0.1 - 0.2):(20 - 30):(0.2 - 0.3), heat up to 70 - 80 °C and stir for 2 - 3 h, filter and wash with absolute ethanol 3 - 4 times, and dry at room temperature for 6 - 8 h to obtain benzothiophene-based silica; the mesh number of the silica is 325 mesh.

[0022] As an optimization, the preparation method of the pre-modified silica in step (5) is as follows: Mix benzothiophene-based silica, diphenyliodonium trifluoromethanesulfonate, and copper acetate in a mass ratio of 1:(0.2 - 0.3):0.02 to obtain a mixture. Place the mixture in a ball mill and mix for 30 min. The ball-to-material ratio of the ball mill is 1:1, and the rotation speed of the ball mill is 300 r / min. After the ball milling is completed, take it out, stir at 130 - 140 °C for 30 min, and the stirring speed is 500 - 600 r / min. After the stirring is completed, wash with dichloromethane 5 - 6 times and dry at 60 °C for 6 - 8 h to obtain thiophene salt silica; mix the thiophene salt silica, ethanol, and sodium ethoxide in a mass ratio of 1:(20 - 30):(0.3 - 0.4), stir at room temperature for 2 h, and obtain pre-modified silica after filtration, washing, and drying at room temperature.

[0023] As an optimization, the bis(2-ethynylphenyl)sulfane solution in step (6) is obtained by mixing bis(2-ethynylphenyl)sulfane and acetonitrile in a mass ratio of 1:5; the mass ratio of the pre-modified silica, copper(I) chloride, acetonitrile, triethylamine, diethyl 2-iodobenzoate, and the bis(2-ethynylphenyl)sulfane solution is 1:(0.2 - 0.3):(20 - 30):(0.3 - 0.4):0.2:0.5.

[0024] As an optimization, the dosages of the components described in step (7) are as follows: by mass parts, 20 - 30 parts of sodium silicate, 1 - 2 parts of methyltrimethoxysilane, 20 - 30 parts of modified polyacrylate emulsion, 10 - 15 parts of modified silica, 10 - 15 parts of glass powder, 1 - 2 parts of sodium fluorosilicate, 1 - 2 parts of dispersant, 1 - 2 parts of leveling agent, and 20 - 30 parts of pure water.

[0025] As an optimization, the solid content of the sodium silicate described in step (7) is 34%; the mesh number of the glass powder is 3000 mesh, the model of the dispersant is BYK - 2100, and the model of the leveling agent is BYK - 310.

[0026] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0027] The ceramic coating for metal doors prepared by the present invention comprises sodium silicate, methyltrimethoxysilane, modified polyacrylate emulsion, modified silica, glass powder, sodium fluorosilicate, dispersant, leveling agent, and pure water; the modified polyacrylate emulsion is obtained by polymerizing a phosphorus - containing monomer and vinyl monomers to form polyacrylate, sulfonyl chlorinating the polyacrylate, reacting with 5 - chloromethyl - 2 - pyrimidinamine, and then emulsifying; the silica is obtained by polymerizing aniline on the surface of pretreated silica, reacting with 1 - benzothiophene - 5 - carbonyl chloride, salifying with diphenyliodonium trifluoromethanesulfonate and copper acetate, and then reacting with bis(2 - ethynylphenyl) sulfide.

[0028] First, the phosphorus - containing monomer and vinyl monomers are polymerized by free - radical initiation to form polyacrylate; the phosphorus - containing monomer is vinyl diphenylphosphine containing a sodium sulfonate functional group, and the sodium sulfonate functional group becomes sulfonyl chloride in the presence of chlorosulfonic acid and thionyl chloride. The sulfonyl chloride reacts with the amino group on 5 - chloromethyl - 2 - pyrimidinamine to form a sulfadiazine structure, which has an inhibitory effect on most Gram - negative and Gram - positive bacteria and can provide good antibacterial properties for the coating. In addition, the phosphorus element and nitrogen element can cooperate in flame retardancy to provide a certain flame - retardant performance for the coating;

[0029] Secondly, silica is pretreated with a silane coupling agent containing an aniline functional group, and aniline is polymerized on the surface of the pretreated silica to generate polyaniline with conductive properties. Polyaniline has reversible oxidation-reduction properties and can oxidize metals to form a dense passivation layer, inhibiting the further corrosion of metals, thereby protecting the metal substrate and providing good anti-corrosion performance for the coating; 1-benzothiophene-5-carbonyl chloride introduces a benzothiophene functional group on the silica surface through the reaction of acyl chloride and the secondary amino group on polyaniline. The benzothiophene functional group generates an aryl sulfonium salt in the presence of diaryliodonium salt, and then undergoes ring-opening under alkaline conditions to obtain a thioether containing a terminal alkyne. Then, in the presence of an oxidant and a catalyst, it undergoes a coupling reaction with bis(2-ethynylphenyl)sulfane, and the arylthio group and the diynyl group generate a large conjugated structure, which has a good absorption effect on ultraviolet light, thereby providing good anti-ultraviolet aging ability for ultraviolet light.

[0030] Finally, sodium silicate, methyltrimethoxysilane, modified polyacrylate emulsion, modified silica, glass powder, sodium fluorosilicate, dispersant, leveling agent, and pure water are mixed to obtain a ceramic coating. The chloromethyl structure in the modified polyacrylate emulsion can react with the polyaniline on the surface of the modified silica, thereby increasing the crosslinking sites, further improving the density of the coating, and enhancing the mechanical properties.

[0031] The ceramic coating provided by the present invention can greatly improve the corrosion resistance, antibacterial property, and anti-aging property of metal doors, and solve the problems existing in metal doors exposed to various environments for a long time. Specific Embodiments

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] In the following examples and comparative examples, the solid content of the sodium silicate is 34%, purchased from Qingdao Gulf Group; the mesh number of the glass powder is 3000 mesh, purchased from Fuhua Mineral Materials Co., Ltd.; the model of the dispersant is BYK-2100, purchased from BYK Chemie GmbH; the model of the leveling agent is BYK-310, purchased from BYK Chemie GmbH; the solution of bis(2-ethynylphenyl)sulfane is obtained by mixing bis(2-ethynylphenyl)sulfane and acetonitrile in a mass ratio of 1:5; the fuming sulfuric acid contains 25 wt% sulfur trioxide; the mesh number of the silica is 325 mesh; the emulsifier is OP-10.

[0034] Example 1:

[0035] A preparation method of a ceramic coating for a metal door, the preparation method of the ceramic coating comprising the following preparation steps:

[0036] (1) At 0 °C, vinyl diphenylphosphine and fuming sulfuric acid are mixed at a mass ratio of 1:2, stirred at 0 °C for 2 h, heated to room temperature and stirred for 18 h, then cooled to 0 °C, and pure water is added dropwise at a rate of 1 mL / min. The addition amount of pure water is 15 times that of vinyl diphenylphosphine; the pH is adjusted to 7 with 7.5 M sodium hydroxide solution, filtered and recrystallized with pure water at 4 °C, filtered and washed 3 times with n-pentane, and dried at room temperature to obtain a phosphorus-containing monomer;

[0037] (2) Methyl acrylate, phosphorus-containing monomer, styrene, and N,N-dimethylformamide are mixed at a mass ratio of 1:0.6:0.1:20. Under nitrogen protection, the temperature is raised to 90 °C, then benzoyl peroxide with a mass 0.01 times that of methyl acrylate is added and stirred for 90 min. Then, benzoyl peroxide with a mass 0.01 times that of methyl acrylate is added again and stirred for 90 min. After stirring, vacuum drying is carried out at 80 °C for 12 h to obtain polyacrylate;

[0038] (3) Polyacrylate, chlorosulfonic acid, thionyl chloride, phosphorus trichloride, and N,N-dimethylformamide are mixed at a mass ratio of 1:0.2:0.2:0.06:30, heated to 55 °C and reacted for 2 h, cooled to room temperature, and an ice-water mixture with a mass 3 times that of N,N-dimethylformamide is added. Filtered and washed 4 times with pure water at 4 °C, and vacuum dried to obtain pre-modified polyacrylate; Pre-modified polyacrylate, 5-chloromethyl-2-pyrimidinamine, dichloromethane, and triethylamine are mixed at a mass ratio of 1:0.2:20:0.2, reacted at room temperature for 6 h. After the reaction, modified polyacrylate is obtained by rotary evaporation under reduced pressure; Weigh modified polyacrylate, emulsifier, pure water, and ethylene glycol monobutyl ether at a mass ratio of 1:0.3:40:5. After mixing modified polyacrylate and ethylene glycol monobutyl ether for 5 min, add emulsifier and pure water, and mix well at 70 °C and 1000 r / min to obtain a modified polyacrylate emulsion;

[0039] (4) Mix silicon dioxide, 3-[3-(trimethoxysilyl)propoxy]aniline, and absolute ethanol in a mass ratio of 1:5:50, ultrasonically oscillate for 30 min, heat up to 50 °C, stir for 2 h, filter and wash with pure water 4 times, and dry at 60 °C for 8 h to obtain pretreated silicon dioxide; Weigh pretreated silicon dioxide, aniline, 2 wt% polyvinylpyrrolidone aqueous solution, 0.6 mol / L hydrochloric acid aqueous solution, and ammonium persulfate in a mass ratio of 1:0.5:50:25:0.3; At 4 °C, mix the pretreated silicon dioxide and 2 wt% polyvinylpyrrolidone aqueous solution, add 0.6 mol / L hydrochloric acid aqueous solution, aniline, and ammonium persulfate, and continue stirring for 6 h, filter and wash with absolute ethanol 4 times, and dry at 60 °C for 8 h to obtain polyaniline-based silicon dioxide; Mix polyaniline-based silicon dioxide, 1-benzothiophene-5-carbonyl chloride, N,N-dimethylformamide, and triethylamine in a mass ratio of 1:0.1:20:0.2, heat up to 80 °C and stir for 3 h, filter and wash with absolute ethanol 4 times, and dry at room temperature for 8 h to obtain benzothiophene-based silicon dioxide;

[0040] (5) Mix benzothiophene-based silicon dioxide, diphenyliodonium trifluoromethanesulfonate, and copper acetate in a mass ratio of 1:0.2:0.02 to obtain a mixture. Place the mixture in a ball mill and mix for 30 min. The ball-to-material ratio of the ball mill is 1:1, and the rotation speed of the ball mill is 300 r / min. After the ball milling is completed, take it out, stir at 140 °C for 30 min, and the stirring speed is 600 r / min. After the stirring is completed, wash with dichloromethane 6 times and dry at 60 °C for 8 h to obtain thiophene salt silicon dioxide; Mix thiophene salt silicon dioxide, ethanol, and sodium ethoxide in a mass ratio of 1:20:0.3, stir at room temperature for 2 h, and obtain pre-modified silicon dioxide after filtration, washing, and drying at room temperature;

[0041] (6) Mix pre-modified silicon dioxide, cuprous chloride, acetonitrile, triethylamine, and diethyl iodobenzoate, and dropwise add bis(2-ethynylphenyl)sulfane solution at a dropping rate of 0.6 mL / min; After the dropping is completed, continue stirring for 40 min, and obtain modified silicon dioxide after filtration, washing, and drying at room temperature; The mass ratio of pre-modified silicon dioxide, cuprous chloride, acetonitrile, triethylamine, diethyl iodobenzoate, and bis(2-ethynylphenyl)sulfane solution is 1:0.2:20:0.3:0.2:0.5;

[0042] (7) Weigh the following components: By mass fraction, 20 parts of sodium silicate, 1 part of methyltrimethoxysilane, 20 parts of modified polyacrylate emulsion, 10 parts of modified silicon dioxide, 10 parts of glass powder, 1 part of sodium fluorosilicate, 1 part of dispersant, 1 part of leveling agent, and 20 parts of pure water; Stir the above components at 60 °C for 30 min, then mix in a high-speed mixer for 70 min, and after grinding by a grinder until the fineness reaches 50 μm, obtain a ceramic coating.

[0043] Example 2:

[0044] A preparation method of a ceramic coating for a metal door, the preparation method of the ceramic coating comprising the following preparation steps:

[0045] (1) At 0 °C, vinyl diphenylphosphine and fuming sulfuric acid are mixed at a mass ratio of 1:2.3, stirred at 0 °C for 2 h, heated to room temperature and stirred for 17 h, then cooled to 0 °C, and pure water is added dropwise at a rate of 1 mL / min. The addition amount of pure water is 17 times that of vinyl diphenylphosphine; the pH is adjusted to 7 using 7.5 M sodium hydroxide solution, filtered and recrystallized using pure water at 4 °C, filtered and washed 3 times with n-pentane, and dried at room temperature to obtain a phosphorus-containing monomer;

[0046] (2) Methyl acrylate, phosphorus-containing monomer, styrene, and N,N-dimethylformamide are mixed at a mass ratio of 1:0.7:0.15:25. Under nitrogen protection, the temperature is raised to 90 °C, then benzoyl peroxide at 0.01 times the mass of methyl acrylate is added and stirred for 90 min. Then benzoyl peroxide at 0.01 times the mass of methyl acrylate is added again and stirred for 90 min. After stirring, it is dried under vacuum at 80 °C for 12 h to obtain polyacrylate;

[0047] (3) Polyacrylate, chlorosulfonic acid, thionyl chloride, phosphorus trichloride, and N,N-dimethylformamide are mixed at a mass ratio of 1:0.25:0.25:0.07:35, heated to 55 °C and reacted for 2 h, cooled to room temperature, an ice-water mixture 3 times the mass of N,N-dimethylformamide is added, filtered and washed 3 times with pure water at 4 °C, and dried under vacuum to obtain pre-modified polyacrylate; pre-modified polyacrylate, 5-chloromethyl-2-pyrimidinamine, dichloromethane, and triethylamine are mixed at a mass ratio of 1:0.25:25:0.25, reacted at room temperature for 5.5 h. After the reaction, modified polyacrylate is obtained by rotary evaporation under reduced pressure; modified polyacrylate, emulsifier, pure water, and ethylene glycol monobutyl ether are weighed at a mass ratio of 1:0.3:40:5. After mixing the modified polyacrylate and ethylene glycol monobutyl ether for 5 min, the emulsifier and pure water are added, and mixed evenly at 70 °C and 1000 r / min to obtain a modified polyacrylate emulsion;

[0048] (4) Mix silicon dioxide, 3-[3-(trimethoxysilyl)propoxy]aniline, and absolute ethanol in a mass ratio of 1:5.5:57, ultrasonically oscillate for 25 min, heat up to 50 °C, stir for 1.5 h, filter and wash with pure water 3 times, and dry at 60 °C for 7 h to obtain pretreated silicon dioxide; Weigh pretreated silicon dioxide, aniline, 2 wt% polyvinylpyrrolidone aqueous solution, 0.6 mol / L hydrochloric acid aqueous solution, and ammonium persulfate in a mass ratio of 1:0.55:56:27:0.4; At 3 °C, mix the pretreated silicon dioxide and 2 wt% polyvinylpyrrolidone aqueous solution, add 0.6 mol / L hydrochloric acid aqueous solution, aniline, and ammonium persulfate and continue stirring for 5.5 h, filter and wash with absolute ethanol 3 times, and dry at 60 °C for 7 h to obtain polyaniline-based silicon dioxide; Mix polyaniline-based silicon dioxide, 1-benzothiophene-5-carbonyl chloride, N,N-dimethylformamide, and triethylamine in a mass ratio of 1:0.15:25:0.25, heat up to 76 °C and stir for 2.5 h, filter and wash with absolute ethanol 3 times, and dry at room temperature for 7 h to obtain benzothiophene-based silicon dioxide;

[0049] (5) Mix benzothiophene-based silicon dioxide, diphenyliodonium trifluoromethanesulfonate, and copper acetate in a mass ratio of 1:0.25:0.02 to obtain a mixture. Place the mixture in a ball mill and mix for 30 min. The ball-to-material ratio of the ball mill is 1:1, and the rotation speed of the ball mill is 300 r / min. After the ball milling is completed, take it out, stir at 135 °C for 30 min, and the stirring speed is 550 r / min. After the stirring is completed, wash with dichloromethane 5 times and dry at 60 °C for 7 h to obtain thiophene salt silicon dioxide; Mix thiophene salt silicon dioxide, ethanol, and sodium ethoxide in a mass ratio of 1:25:0.35, stir at room temperature for 2 h, and obtain pre-modified silicon dioxide after filtration, washing, and drying at room temperature;

[0050] (6) Mix pre-modified silicon dioxide, copper(I) chloride, acetonitrile, triethylamine, and diethyl iodobenzoate, and dropwise add bis(2-ethynylphenyl)sulfane solution at a dropping rate of 0.6 mL / min; After the dropping is completed, continue stirring for 30 min, and obtain modified silicon dioxide after filtration, washing, and drying at room temperature; The mass ratio of pre-modified silicon dioxide, copper(I) chloride, acetonitrile, triethylamine, diethyl iodobenzoate, and bis(2-ethynylphenyl)sulfane solution is 1:0.25:25:0.35:0.2:0.5;

[0051] (7) Weigh the following components: By mass fraction, 23 parts of sodium silicate, 1.5 parts of methyltrimethoxysilane, 25 parts of modified polyacrylate emulsion, 12 parts of modified silicon dioxide, 13 parts of glass powder, 1 part of sodium fluorosilicate, 2 parts of dispersant, 2 parts of leveling agent, and 25 parts of pure water; Stir the above components at 55 °C for 30 min, then mix in a high-speed mixer for 65 min, and after grinding with a grinder until the fineness reaches 45 μm, obtain a ceramic coating.

[0052] Example 3:

[0053] A preparation method of a ceramic coating for a metal door, the preparation method of the ceramic coating comprising the following preparation steps:

[0054] (1) At 0 °C, vinyl diphenylphosphine and fuming sulfuric acid are mixed at a mass ratio of 1:2.5, stirred at 0 °C for 2 h, heated to room temperature and then stirred for 16 h, and then cooled to 0 °C. Pure water is added dropwise at a rate of 1 mL / min, and the addition amount of pure water is 20 times that of vinyl diphenylphosphine; 7.5 M sodium hydroxide solution is used to adjust the pH to 7, filtered and recrystallized with pure water at 4 °C, filtered and washed with n-pentane 4 times, and dried at room temperature to obtain a phosphorus-containing monomer;

[0055] (2) Methyl acrylate, phosphorus-containing monomer, styrene, and N,N-dimethylformamide are mixed at a mass ratio of 1:0.8:0.2:30. Under nitrogen protection, the temperature is raised to 90 °C, and then benzoyl peroxide 0.01 times the mass of methyl acrylate is added and stirred for 90 min. Then, benzoyl peroxide 0.01 times the mass of methyl acrylate is added and stirred for 90 min. After stirring, it is vacuum dried at 80 °C for 12 h to obtain polyacrylate;

[0056] (3) Polyacrylate, chlorosulfonic acid, thionyl chloride, phosphorus trichloride, and N,N-dimethylformamide are mixed at a mass ratio of 1:0.3:0.3:0.08:40, heated to 55 °C and reacted for 2 h, cooled to room temperature, and an ice-water mixture 4 times the mass of N,N-dimethylformamide is added. Filtered and washed with pure water at 4 °C 3 times, and vacuum dried to obtain pre-modified polyacrylate; Pre-modified polyacrylate, 5-chloromethyl-2-pyrimidinamine, dichloromethane, and triethylamine are mixed at a mass ratio of 1:0.3:30:0.3, reacted at room temperature for 5 h, and after the reaction, modified polyacrylate is obtained by rotary evaporation under reduced pressure; Modified polyacrylate, emulsifier, pure water, and ethylene glycol butyl ether are weighed at a mass ratio of 1:0.3:40:5. After mixing the modified polyacrylate and ethylene glycol butyl ether for 5 min, the emulsifier and pure water are added, and mixed evenly at 70 °C and 1000 r / min to obtain a modified polyacrylate emulsion;

[0057] (4) Mix silicon dioxide, 3-[3-(trimethoxysilyl)propoxy]aniline, and absolute ethanol in a mass ratio of 1:6:60, ultrasonically oscillate for 20 min, heat up to 50 °C, stir for 1 h, filter and wash with pure water 3 times, and dry at 60 °C for 8 h to obtain pretreated silicon dioxide; Weigh pretreated silicon dioxide, aniline, 2 wt% polyvinylpyrrolidone aqueous solution, 0.6 mol / L hydrochloric acid aqueous solution, and ammonium persulfate according to a mass ratio of 1:0.6:60:30:0.5; At 2 °C, mix the pretreated silicon dioxide and 2 wt% polyvinylpyrrolidone aqueous solution, add 0.6 mol / L hydrochloric acid aqueous solution, aniline, and ammonium persulfate, and continue stirring for 5 h, filter and wash with absolute ethanol 3 times, and dry at 60 °C for 6 h to obtain polyaniline-based silicon dioxide; Mix polyaniline-based silicon dioxide, 1-benzothiophene-5-carbonyl chloride, N,N-dimethylformamide, and triethylamine in a mass ratio of 1:0.2:30:0.3, heat up to 70 °C and stir for 2 h, filter and wash with absolute ethanol 3 times, and dry at room temperature for 6 h to obtain benzothiophene-based silicon dioxide;

[0058] (5) Mix benzothiophene-based silicon dioxide, diphenyliodonium trifluoromethanesulfonate, and copper acetate in a mass ratio of 1:0.3:0.02 to obtain a mixture. Place the mixture in a ball mill and mix for 30 min. The ball-to-material ratio of the ball mill is 1:1, and the rotation speed of the ball mill is 300 r / min. After the ball milling is completed, take it out, stir at 130 °C for 30 min, and the stirring speed is 500 r / min. After the stirring is completed, wash with dichloromethane 5 times and dry at 60 °C for 6 h to obtain thiophene salt silicon dioxide; Mix thiophene salt silicon dioxide, ethanol, and sodium ethoxide in a mass ratio of 1:30:0.4, stir at room temperature for 2 h, and obtain pre-modified silicon dioxide after filtration, washing, and drying at room temperature;

[0059] (6) Mix pre-modified silicon dioxide, copper(I) chloride, acetonitrile, triethylamine, and diethyl iodobenzoate, and dropwise add bis(2-ethynylphenyl)sulfane solution at a dropping rate of 0.6 mL / min; After the dropping is completed, continue stirring for 30 min, and obtain modified silicon dioxide after filtration, washing, and drying at room temperature; The mass ratio of pre-modified silicon dioxide, copper(I) chloride, acetonitrile, triethylamine, diethyl iodobenzoate, and bis(2-ethynylphenyl)sulfane solution is 1:0.3:30:0.4:0.2:0.5;

[0060] (7) Weigh the following components: by mass fraction, 30 parts of sodium silicate, 2 parts of methyltrimethoxysilane, 30 parts of modified polyacrylate emulsion, 15 parts of modified silicon dioxide, 15 parts of glass powder, 2 parts of sodium fluorosilicate, 2 parts of dispersant, 2 parts of leveling agent, and 30 parts of pure water; Stir the above components at 50 °C for 30 min, then mix in a high-speed mixer for 60 min, and after grinding with a grinder until the fineness reaches 40 μm, obtain a ceramic coating.

[0061] Comparative Example 1:

[0062] The preparation method of the ceramic coating in Comparative Example 1 is different from that in Example 2 in that step (3) is modified as follows: Weigh polyacrylate, emulsifier, pure water, and ethylene glycol monobutyl ether according to a mass ratio of 1:0.3:40:5. After mixing the modified polyacrylate and ethylene glycol monobutyl ether for 5 min, add the emulsifier and pure water, and mix well at 70 °C and 1000 r / min to obtain a modified polyacrylate emulsion.

[0063] Comparative Example 2:

[0064] The preparation method of the ceramic coating in Comparative Example 2 is different from that in Example 2 in that steps (5) to (6) are not included, and step (4) is modified as follows: Mix silicon dioxide, 3-[3-(trimethoxysilyl)propoxy]aniline, and absolute ethanol according to a mass ratio of 1:5.5:57, ultrasonically oscillate for 25 min, heat up to 50 °C, stir for 1.5 h, filter and wash with pure water 3 times, and dry at 60 °C for 7 h to obtain pretreated silicon dioxide; Weigh pretreated silicon dioxide, aniline, 2 wt% polyvinylpyrrolidone aqueous solution, 0.6 mol / L hydrochloric acid aqueous solution, and ammonium persulfate according to a mass ratio of 1:0.55:56:27:0.4; At 3 °C, mix the pretreated silicon dioxide and 2 wt% polyvinylpyrrolidone aqueous solution, add 0.6 mol / L hydrochloric acid aqueous solution, aniline, and ammonium persulfate, and continue to stir for 5.5 h, filter and wash with absolute ethanol 3 times, and dry at 60 °C for 7 h to obtain modified silicon dioxide.

[0065] Comparative Example 3:

[0066] The preparation method of the ceramic coating in Comparative Example 3 is different from that in Example 2 in that steps (4) to (6) are not included, and step (7) is modified as follows: Weigh the following components: By mass, 23 parts of sodium silicate, 1.5 parts of methyltrimethoxysilane, 25 parts of modified polyacrylate emulsion, 12 parts of silicon dioxide, 13 parts of glass powder, 1 part of sodium fluorosilicate, 2 parts of dispersant, 2 parts of leveling agent, and 25 parts of pure water; Stir the above components at 55 °C for 30 min, then mix in a high-speed mixer for 65 min, and grind through a grinder. After the fineness reaches 45 μm, a ceramic coating is obtained.

[0067] Test Example 1:

[0068] Test for corrosion resistance:

[0069] Testing method: The ceramic coatings prepared in the examples and comparative examples were sprayed on the surface of tinplate by means of compressed air and cured into films at room temperature. The pressure of the air compressor was 0.9 MPa, the nozzle diameter was 1.5 mm, the spraying angle was 45°, the coating thickness was 30 μm, and it was dried at room temperature for 24 h. The corrosion resistance of the coating was tested according to the standard GB T1763-1979. The chemical reagent selected was 20 wt% sodium hydroxide solution, the testing time was 20 days, the appearance of the coating was recorded, and the results are shown in Table 1.

[0070] Table 1

[0071] Coating appearance Coating appearance Example 1 No blistering, rusting, peeling Comparative Example 1 No blistering, rusting, peeling Example 2 No blistering, rusting, peeling Comparative Example 2 No blistering, rusting, peeling Example 3 No blistering, rusting, peeling Comparative Example 3 Blistering

[0072] From the comparison of the experimental data of Examples 1-3 and Comparative Examples 1-3 in Table 1, it can be found that the ceramic coating prepared by the present invention has good corrosion resistance.

[0073] By comparison, the appearance of the coatings in Examples 1-3 is better than that of the coating in Comparative Example 3, indicating that using a silane coupling agent containing an aniline functional group to pretreat silica, polymerizing aniline on the surface of the pretreated silica to generate polyaniline with electrical conductivity, and polyaniline has reversible oxidation-reduction properties, can oxidize metals to form a dense passivation layer, inhibit the further corrosion of metals, thereby protecting the metal substrate and providing good anti-corrosion performance for the coating.

[0074] Test Example 2:

[0075] Testing of antibacterial properties:

[0076] Testing method: The ceramic coatings prepared in the examples and comparative examples were sprayed on the surface of tinplate by means of compressed air and cured into films at room temperature. The pressure of the air compressor was 0.9 MPa, the nozzle diameter was 1.5 mm, the spraying angle was 45°, the coating thickness was 30 μm, and it was dried at room temperature for 24 h. Referring to the standard GB / T21866—2008, the antibacterial properties of the coating were tested. The results are shown in Table 2.

[0077] Table 2

[0078] Antibacterial rate (%) Antibacterial rate (%) Example 1 96.74 Comparative Example 1 35.47 Example 2 97.03 Comparative Example 2 96.32 Example 3 97.16 Comparative Example 3 96.21

[0079] From the comparison of the experimental data of Examples 1-3 and Comparative Examples 1-3 in Table 2, it can be found that the ceramic coating prepared by the present invention has good antibacterial properties.

[0080] By comparison, the antibacterial rates of Examples 1 to 3 are greater than that of Comparative Example 1, indicating that the phosphorus-containing monomer and the vinyl monomer are polymerized by free radical initiation to generate polyacrylate; the phosphorus-containing monomer is vinyl diphenyl phosphine containing a sodium sulfonate functional group, and the sodium sulfonate functional group is converted into sulfonyl chloride in the presence of chlorosulfonic acid and thionyl chloride, and the sulfonyl chloride reacts with the amino group on 5-chloromethyl-2-pyrimidineamine to generate a sulfadiazine structure, which has an inhibitory effect on most Gram-negative bacteria and Gram-positive bacteria, and can provide a good antibacterial effect for the coating.

[0081] Test Example 3:

[0082] Test of anti-ultraviolet aging performance:

[0083] Test method: The ceramic coating obtained in the embodiment and the comparative example was sprayed on the surface of the tinplate sheet by compressed air, and cured at room temperature to form a film. The pressure of the air compressor was 0.9 MPa, the nozzle diameter was 1.5 mm, the spraying angle was 45°, the coating thickness was 30 μm, and it was dried at room temperature for 24 hours. The anti-aging performance of the coating was tested using a QUV ultraviolet accelerated aging tester in accordance with the test method specified in Q / JLY J7110279, and the test time was 1200 hours. The impact resistance of the coating before and after ultraviolet aging was determined in accordance with standard GB / T 1732.1993, and the retention rate of the impact strength was calculated. The results are shown in Table 3.

[0084] Table 3

[0085]

[0086]

[0087] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 3, it can be found that the ceramic coating prepared by the present invention has good anti-ultraviolet aging performance.

[0088] The retention rates of Examples 1 to 3 are greater than those of Comparative Examples 2 to 3, indicating that the silica is pretreated using a silane coupling agent containing an aniline functional group, aniline is polymerized on the surface of the pretreated silica to generate polyaniline, 1-benzothiophene-5-carbonyl chloride introduces a benzothiophene functional group on the silica surface through a reaction between the acyl chloride and the secondary amine group on the polyaniline, the benzothiophene functional group generates an aryl sulfide salt in the presence of a diaryl iodonium salt, and then the benzothiophene functional group is ring-opened under alkaline conditions to obtain a sulfide containing a terminal alkyne, and then a coupling reaction is carried out with bis(2-ethynylphenyl)sulfane in the presence of an oxidant and a catalyst, the aryl sulfide group and the diacetyl group generate a large conjugated structure, which has a good absorption effect on ultraviolet rays, thereby providing good resistance to ultraviolet aging for ultraviolet rays.

[0089] Since metal doors are exposed to various environments for a long time, their performance is likely to decline due to problems such as corrosion and aging. Moreover, the selling price of metal doors is high and users expect a long service life. How to improve the corrosion resistance and anti-aging performance of metal doors has always been a pain point in the industry. The ceramic coating provided by the present invention can greatly improve the corrosion resistance, antibacterial property and anti-aging performance of metal doors, solve the technical problems existing in the long-term exposure of metal doors to various environments, and has remarkable technical effects and extremely high economic value.

[0090] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims concerned.

Claims

1. A ceramic coating for metal doors, characterized in that: The ceramic coating comprises sodium silicate, methyltrimethoxysilane, modified polyacrylate emulsion, modified silicon dioxide, glass powder, sodium fluorosilicate, dispersant, leveling agent and pure water; The modified polyacrylate emulsion is obtained by polymerizing phosphorus-containing monomers and vinyl monomers to generate polyacrylate, and then reacting the polyacrylate with 5-chloromethyl-2-pyrimidinamine after sulfonyl chloride, and then emulsifying. The silicon dioxide is obtained by polymerizing aniline on the surface of pretreated silicon dioxide, reacting with 1-benzothiophene-5-carbonyl chloride, salifying with diphenyl iodine trifluoromethanesulfonate and copper acetate, and reacting with bis(2-ethynylphenyl)sulfane.

2. A method for preparing a ceramic coating for a metal door, characterized in that: The method comprises the following preparation steps: (1) reacting vinyl diphenyl phosphine and fuming sulfuric acid to obtain a phosphorus-containing monomer; (2) polymerizing methyl acrylate, phosphorus-containing monomers, and styrene to obtain polyacrylate; (3) reacting polyacrylate, chlorosulfonic acid and thionyl chloride to obtain pre-modified polyacrylate; reacting the pre-modified polyacrylate and 5-chloromethyl-2-pyrimidinamine to obtain modified polyacrylate; emulsifying the modified polyacrylate with an emulsifier to obtain a modified polyacrylate emulsion; (4) reacting silica and 3-[3-(trimethoxysilyl)propoxy]aniline to obtain pretreated silica; polymerizing aniline on the surface of the pretreated silica to obtain polyaniline-based silica; reacting polyaniline-based silica and 1-benzothiophene-5-carbonyl chloride to obtain benzothiophene-based silica; (5) reacting benzothiophene silica, diphenyliodonium trifluoromethanesulfonate, and copper acetate to obtain thiophene salt silica; reacting thiophene salt silica, ethanol, and sodium ethoxide to obtain pre-modified silica; (6) pre-modified silica, cuprous chloride, acetonitrile, triethylamine, and diethyl iodophenyl are mixed, and the bis(2-ethynylphenyl)sulfane solution is added dropwise at a rate of 0.6 mL / min; after the addition is completed, stirring is continued for 30-40 min, and the modified silica is obtained by filtering, washing, and drying at room temperature; (7) Weigh the following components: sodium silicate, methyltrimethoxysilane, modified polyacrylate emulsion, modified silica, glass powder, sodium fluorosilicate, dispersant, leveling agent, and pure water; stir the above components at 50-60° C. for 30 min, then mix them in a high-speed mixer for 60-70 min, grind them in a grinder until the fineness reaches 40-50 μm, and obtain a ceramic coating.

3. The method for preparing a ceramic coating for a metal door according to claim 2, characterized in that: The preparation method of the phosphorus-containing monomer in step (1) is as follows: at 0°C, vinyl diphenyl phosphide and fuming sulfuric acid are mixed in a mass ratio of 1:(2-2.5), stirred at 0°C for 2h, heated to room temperature and stirred for 16-18h, then cooled to 0°C, and pure water is added dropwise at a rate of 1mL / min, wherein the amount of pure water added is 15-20 times that of vinyl diphenyl phosphide; pH is adjusted to 7 using 7.5M sodium hydroxide solution, filtered and recrystallized using pure water at 4°C, filtered and washed 3-4 times with n-pentane, and dried at room temperature to obtain the phosphorus-containing monomer; the fuming sulfuric acid contains 25wt% of sulfur trioxide.

4. The method for preparing a ceramic coating for a metal door according to claim 2, characterized in that: The preparation method of the polyacrylate in step (2) is as follows: methyl acrylate, phosphorus-containing monomer, styrene and N,N-dimethylformamide are mixed in a mass ratio of 1:(0.6-0.8):(0.1-0.2):(20-30), and the mixture is heated to 90° C. under nitrogen protection, and then benzoyl peroxide in an amount of 0.01 times the mass of methyl acrylate is added and stirred for 90 minutes, and benzoyl peroxide in an amount of 0.01 times the mass of methyl acrylate is continuously added and stirred for 90 minutes. After the stirring is completed, the mixture is vacuum dried at 80° C. for 12 hours to obtain the polyacrylate.

5. The method for preparing a ceramic coating for a metal door according to claim 2, characterized in that: The preparation method of the modified polyacrylate emulsion in step (3) is as follows: polyacrylate, chlorosulfonic acid, thionyl chloride, phosphorus trichloride, N,N-dimethylformamide are mixed in a mass ratio of 1:(0.2-0.3):(0.2-0.3):(0.06-0.08):(30-40) were mixed, heated to 55°C for reaction for 2h, cooled to room temperature, and an ice-water mixture of 3-4 times the mass of N,N-dimethylformamide was added, filtered and washed with 4°C pure water for 3-4 times, and vacuum dried to obtain a pre-modified polyacrylate; the pre-modified polyacrylate, 5-chloromethyl-2-pyrimidinamine, dichloromethane, and triethylamine were mixed in a mass ratio of 1:(0.2-0.3 ):(20-30):(0.2-0.3) mixed, reacted at room temperature for 5-6h, after the reaction was completed, the modified polyacrylate was obtained by reduced pressure rotary evaporation; the modified polyacrylate, emulsifier, pure water and ethylene glycol butyl ether were weighed in a mass ratio of 1:0.3:40:5, the modified polyacrylate and ethylene glycol butyl ether were mixed for 5min, and then the emulsifier and pure water were added, and mixed at 70°C and 1000r / min to obtain a modified polyacrylate emulsion; the emulsifier was OP-10.

6. The method for preparing a ceramic coating for a metal door according to claim 2, characterized in that: The preparation method of the benzothienyl silica in step (4) is as follows: silica, 3-[3-(trimethoxysilyl)propoxy]aniline and anhydrous ethanol are mixed in a mass ratio of 1:(5-6):(50-60), ultrasonically vibrated for 20-30 min, heated to 50° C., stirred for 1-2 h, filtered and washed with pure water for 3-4 times, and dried at 60° C. for 6-8 h to obtain pretreated silica; at 2-4° C., the pretreated silica and a 2wt% aqueous solution of polyvinyl pyrrolidone are mixed, 0.6 mol / L aqueous hydrochloric acid solution, aniline and ammonium persulfate are added, and stirring is continued for 5-6 h, filtered and washed with anhydrous ethanol for 3-4 times, and dried at 60° C. for 6-8 h to obtain polyphenylene oxide. The mass ratio of amino silica, pretreated silica, aniline, 2wt% polyvinyl pyrrolidone aqueous solution, 0.6mol / L hydrochloric acid aqueous solution and ammonium persulfate is 1:(0.5-0.6):(50-60):(25-30):(0.3-0.5); polyaniline silica, 1-benzothiophene-5-carbonyl chloride, N,N-dimethylformamide and triethylamine are mixed in a mass ratio of 1:(0.1-0.2):(20-30):(0.2-0.3), heated to 70-80°C and stirred for 2-3h, filtered and washed with anhydrous ethanol for 3-4 times, and dried at room temperature for 6-8h to obtain benzothienyl silica; the mesh number of the silica is 325 mesh.

7. The method for preparing a ceramic coating for a metal door according to claim 2, characterized in that: The preparation method of the pre-modified silica in step (5) is as follows: benzothiophene silica, diphenyl iodine trifluoromethanesulfonate, and copper acetate are mixed in a mass ratio of 1: (0.2-0.3): 0.02 to obtain a mixture, and the mixture is placed in a ball mill for mixing for 30 minutes, the ball-to-material ratio of the ball mill is 1: 1, and the ball mill speed is 300r / min. After the ball milling is completed, the mixture is taken out, stirred at 130-140°C for 30 minutes, and the stirring speed is 500-600r / min. After the stirring is completed, it is washed with dichloromethane for 5-6 times, and dried at 60°C for 6-8h to obtain thiophene salt silica; thiophene salt silica, ethanol, and sodium ethoxide are mixed in a mass ratio of 1: (20-30): (0.3-0.4), stirred at room temperature for 2h, filtered, washed, and dried at room temperature to obtain pre-modified silica.

8. The method for preparing a ceramic coating for metal doors according to claim 2, characterized in that: The bis(2-ethynylphenyl)sulfane solution in step (6) is obtained by mixing bis(2-ethynylphenyl)sulfane and acetonitrile in a mass ratio of 1:5; the mass ratio of the pre-modified silica, cuprous chloride, acetonitrile, triethylamine, diethyl iodophenyl, and bis(2-ethynylphenyl)sulfane solution is 1:(0.2-0.3):(20-30):(0.3-0.4):0.2:0.

5.

9. The method for preparing a ceramic coating for a metal door according to claim 2, characterized in that: The amounts of the components in step (7) are as follows: by mass: 20-30 parts of sodium silicate, 1-2 parts of methyltrimethoxysilane, 20-30 parts of modified polyacrylate emulsion, 10-15 parts of modified silicon dioxide, 10-15 parts of glass powder, 1-2 parts of sodium fluorosilicate, 1-2 parts of dispersant, 1-2 parts of leveling agent, and 20-30 parts of pure water.

10. The method for preparing a ceramic coating for a metal door according to claim 2, characterized in that: In step (7), the solid content of the sodium silicate is 34%; the mesh size of the glass powder is 3000 meshes, the dispersant model is BYK-2100, and the leveling agent model is BYK-310.

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