Melamine glazing powder and preparation method thereof

Abstract

The invention discloses melamine glazing powder and a preparation method thereof, and belongs to the technical field of melamine glazing resin. The method is used for solving the technical problems that in the prior art, a melamine glazing powder synthesis process is poor in surface brightness and smoothness and is not resistant to high temperature. The preparation method of the melamine glazing powder comprises the following steps: uniformly mixing and ball-milling a primary material, a lubricant, a curing agent, hybrid resin and poly-2, 2 '-(m-phenyl)-5, 5'-bis-benzimidazole to prepare the melamine glazing powder. Wherein methyl acrylate and divinylbenzene are subjected to suspension copolymerization to synthesize a suspension copolymer; 4-chloromethylstyrene is cross-linked with the suspension copolymer, and composite resin is prepared; and hydrolyzing tetraethyl orthosilicate in the composite resin to prepare the hybrid resin. When melamine and formaldehyde are subjected to polycondensation, p-toluenesulfonamide is adopted for modification, so that the smoothness and the brightness value of the prepared melamine glazing powder are improved. The melamine glazing powder prepared by the invention has the advantages of high surface brightness and smoothness and high temperature resistance.

Description

Technical Field

[0001] The invention relates to the technical field of melamine overprint resins, and in particular to a melamine overprint powder and a preparation method thereof. Background Art

[0002] Melamine varnish, also known as melamine varnish resin, is primarily produced by the reaction of formaldehyde and melamine to form melamine-formaldehyde resin, followed by drying and ball milling. Melamine varnish has a variety of uses: 1. It can be used in the manufacturing process of melamine tableware. During the pressing process, dusting the surface with melamine varnish significantly improves the finish and wear resistance of the finished product. 2. Melamine varnish can serve as a bonding medium when used with printed paper to create a clear and durable pattern on the tableware surface. 3. Melamine varnish can also be used in the electrical appliance industry and grinding wheel polishing industry to enhance glossiness, corrosion resistance, and wear resistance.

[0003] Patent application CN111704783A discloses a process for preparing a glazing powder. A formaldehyde solution, melamine, hexamethylenetetramine, and alginate are blended and reacted to form a prepolymer. The prepolymer is then ground, aged, cured, and ball-milled with nano-silica to obtain a finished product. Nano-silica is then added to the prepolymer to improve the mechanical properties of the glazing powder. However, when melamine glazing powder is sprayed onto the surface of a molded part, its surface brightness and smoothness are also important properties that require consideration. Furthermore, improving the high-temperature resistance of melamine glazing powder is a pressing technical issue.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a melamine overprinting powder and a preparation method thereof, so as to solve the technical problems of poor surface brightness and smoothness and poor high temperature resistance in the synthesis process of melamine overprinting powder in the prior art.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing a melamine varnish comprises the following steps: According to weight parts, 70-80 parts of the initial material, 0.5-1.5 parts of the lubricant, 0.05-0.15 parts of the curing agent, 3-10 parts of the hybrid resin and 1-5 parts of the poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole are mixed and ball-milled to prepare a melamine varnish.

[0007] Furthermore, the preparation method of the hybrid resin comprises the following steps: A1. Replace the air in the autoclave with nitrogen and evacuate the autoclave to -0.7-0.5 MPa. Add deionized water, initiator, methyl acrylate, and divinylbenzene to the autoclave and react at 55-65°C for 50-60 minutes. The polymerization reaction is considered complete to obtain a product. Centrifuge the product and dry it to a constant weight to synthesize a suspension copolymer. Methyl acrylate and divinylbenzene are suspended and copolymerized to prepare a spherical cross-linked copolymer, which is a synthetic suspension copolymer. The reaction formula is as follows:

[0008] A2. Adding the suspension copolymer and anhydrous ferric chloride to deionized water and blending them, then adding 4-chloromethylstyrene dropwise until the addition is complete to obtain a product; reacting the product at 35-45° C. for 1-2 hours, then stopping the reaction, and filtering through a 10-20 μm coarse filter membrane to remove solid anhydrous ferric chloride to prepare a composite resin; Using anhydrous ferric chloride as a catalyst, the chlorine on 4-chloromethylstyrene can react with the benzene ring to undergo Friedel-Crafts alkylation reaction, the reaction formula of which is as follows:

[0009] A3. A composite resin, tetraethyl orthosilicate, and deionized water are mixed and stirred at 45-50° C. for 2-3 hours to obtain a reactant; triethylamine is added to the reactant to adjust the pH value of the reactant to 7-8, and the reaction is continued with stirring at room temperature for 5-6 hours to obtain a product; the product is transferred to a dialysis bag with a molecular weight cutoff of 800-1000 to remove unreacted raw materials, and dried to finally prepare a hybrid resin.

[0010] With the composite resin as the reaction space, tetraethyl orthosilicate is in situ hydrolyzed in the composite resin to synthesize silica nanoparticles, thereby preparing the hybrid resin.

[0011] Furthermore, in step A1, the usage ratio of deionized water, initiator, methyl acrylate and divinylbenzene is 200 mL: 0.5-1 g: 50-100 g: 60-80 g.

[0012] Furthermore, in step A2, the usage ratio of the suspension copolymer, anhydrous ferric chloride, 4-chloromethylstyrene and deionized water is 20-30 mL:0.5-1 g:10-20 mL:100 mL.

[0013] Furthermore, in step A3, the weight ratio of the composite resin, tetraethyl orthosilicate and deionized water is 10:0.1-0.5:5; and the drying temperature is 70-75°C.

[0014] Furthermore, the preparation method of the initial material comprises the following steps: S1. NaOH solution is added dropwise to formaldehyde to adjust the pH to 8-9, and then melamine is added to obtain a reactant; the reactant is heated to 90-100° C. and reacted at this temperature for 50-60 minutes to obtain intermediate 1; S2. Continue to add 0.1 mol / L NaOH solution dropwise to 150-300 g of intermediate 1 to make the pH value of intermediate 1 8-9, then add p-toluenesulfonamide, and continue to react at 90-100 ° C for 30-50 min to obtain a material; the material is naturally cooled to room temperature to obtain an initial material.

[0015] Formaldehyde, melamine and p-toluenesulfonamide react in sequence to synthesize the initial material. The reaction formula is as follows:

[0016] Furthermore, in step S1, the ratio of formaldehyde to melamine is 30-60 mL:125-250 g; and in step S2, the ratio of intermediate 1 to p-toluenesulfonamide is 150-300 g:17-34 g.

[0017] As another aspect of the present invention, a method for preparing melamine varnish powder is provided to prepare melamine varnish powder.

[0018] The present invention has the following beneficial effects: 1. The melamine varnish prepared in the present invention is obtained by co-grinding a starting material, a hybrid resin, poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole, and related additives. Melamine and formaldehyde undergo polycondensation to form only long linear molecules, thereby producing the starting material. The present invention uses p-toluenesulfonamide to modify the synthesized starting material, forming a three-dimensional network structure. This reduces the amount of formaldehyde in the starting material, thereby lowering the molecular weight of the synthesized melamine varnish and improving the fluidity of the starting material. This allows the melamine varnish prepared in the present invention to be evenly coated on the surface of melamine molded parts, improving their smoothness and brightness.

[0019] 2. The present invention improves the mechanical properties of the prepared melamine varnish by doping it with a hybrid resin and poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole. A spherical suspension copolymer is synthesized from methyl acrylate monomer and divinylbenzene monomer. The benzene ring structure contained in the suspension copolymer is utilized to introduce 4-chloromethylstyrene monomer via a Friedel-Strauss alkylation reaction. The macromolecular chains are cross-linked, and the cross-linking bridges are evenly distributed, thereby increasing the density of the prepared composite resin. The composite resin prepared by suspension copolymerization in the present invention is a spherical adsorption resin. The cavity structure within the composite resin serves as the reaction chamber, and tetraethyl orthosilicate is hydrolyzed in situ within the composite resin to synthesize silica nanoparticles. By loading the composite resin with silica, the mechanical strength of the prepared composite resin is improved. Poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole itself has excellent heat resistance. This invention adds a trace amount of poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole to the prepared melamine overprinting powder to improve its heat resistance. The melamine overprinting powder doped with the hybrid resin and poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole retains its gloss after being boiled in high-temperature water. DETAILED DESCRIPTION

[0020] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0021] The anhydrous ferric chloride used in Examples 1-3 of the present invention was purchased from Shanghai Tengqian Biotechnology Co., Ltd., with a particle size of 300-400 mesh; the poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole used in Examples 4-6 of the present invention was purchased from Changzhou Puwei Composite Materials Technology Co., Ltd.; the nano-scale silicon dioxide used in Comparative Example 2 of the present invention was purchased from Zhejiang Manli Nanotechnology Co., Ltd., with the product number ML-SiO2 and a specification of 7nm.

[0022] Example 1 This embodiment provides a method for preparing a hybrid resin for melamine overprint varnish, comprising the following steps: A1. Prepare a 500mL stainless steel autoclave, replace the air in the autoclave with nitrogen, and evacuate the autoclave to -0.5MPa. Add 200mL of deionized water and 0.5g of benzoyl peroxide (initiator) to the autoclave, followed by 50g of methyl acrylate and 60g of divinylbenzene. React at 55°C for 50 minutes, and the polymerization reaction is considered complete to obtain the product. Centrifuge the product at 2000 rpm for 5 minutes and then dry at 65°C to constant weight to synthesize a suspension copolymer.

[0023] A2. Add 20 mL of the suspension copolymer, 0.5 g of anhydrous ferric chloride, and 100 mL of deionized water, based on parts by weight, to a 200 mL three-necked flask. Then, add 10 mL of 4-chloromethylstyrene dropwise within 2 minutes to produce a product. The product is reacted at 35°C for 1 hour, after which the reaction is terminated. The product is filtered through a 10 μm coarse filter membrane and the deionized water is removed by rotary evaporation at 90°C to produce a composite resin.

[0024] A3. 10 parts by weight of the composite resin, 0.1 parts of tetraethyl orthosilicate, and 5 parts of deionized water were added to a beaker and stirred at 45°C for 2 hours to obtain a reactant. Triethylamine was then added to the reactant to adjust the pH to 7, and the reaction was continued with stirring at room temperature for 5 hours to obtain a product. The product was transferred to a dialysis bag with a molecular weight cutoff of 800 to remove unreacted raw materials, and then dried at 70°C to constant weight to obtain a hybrid resin.

[0025] Example 2 This embodiment provides a method for preparing a hybrid resin for melamine overprint varnish, comprising the following steps: A1. Prepare a 500mL stainless steel autoclave, replace the air in the autoclave with nitrogen, and evacuate the autoclave to -0.6MPa. Add 200mL of deionized water and 0.8g of benzoyl peroxide (initiator) to the autoclave, followed by 80g of methyl acrylate and 70g of divinylbenzene. React at 60°C for 55 minutes, and the polymerization reaction is considered complete to obtain the product. Centrifuge the product at 2500 rpm for 6 minutes and then dry at 68°C to constant weight to synthesize a suspension copolymer.

[0026] A2. Add 25 mL of the suspension copolymer, 0.6 g of anhydrous ferric chloride, and 100 mL of deionized water, based on parts by weight, to a 200 mL three-necked flask. Then, add 15 mL of 4-chloromethylstyrene dropwise within 3 minutes to produce a product. The product is reacted at 40°C for 1.5 hours, after which the reaction is stopped. The solid anhydrous ferric chloride is removed by filtration using a 20 μm coarse filter membrane, and the deionized water is removed by rotary evaporation at 80°C to produce a composite resin.

[0027] A3. 10 parts by weight of the composite resin, 0.3 parts of tetraethyl orthosilicate, and 5 parts of deionized water were added to a beaker and stirred at 48°C for 2.5 hours to obtain a reactant. Triethylamine was then added to the reactant to adjust the pH to 8, and the reaction was continued with stirring at room temperature for 5.5 hours to obtain a product. The product was transferred to a dialysis bag with a molecular weight cutoff of 900 to remove unreacted raw materials, and then dried at 72°C to constant weight to obtain a hybrid resin.

[0028] Example 3 This embodiment provides a method for preparing a hybrid resin for melamine overprint varnish, comprising the following steps: A1. Prepare a 500mL stainless steel autoclave, replace the air in the autoclave with nitrogen, and evacuate the autoclave to -0.7MPa. Add 200mL of deionized water and 1g of benzoyl peroxide (initiator) to the autoclave, followed by 100g of methyl acrylate and 80g of divinylbenzene. React at 65°C for 60 minutes, and the polymerization reaction is considered complete to obtain the product. Centrifuge the product at 3000 rpm for 10 minutes and then dry at 70°C to constant weight to synthesize a suspension copolymer.

[0029] A2. Add 30 mL of the suspension copolymer, 1 g of anhydrous ferric chloride, and 100 mL of deionized water, based on parts by weight, to a 200 mL three-necked flask. Then, add 20 mL of 4-chloromethylstyrene dropwise within 5 minutes to produce a product. The product is reacted at 45°C for 2 hours, after which the reaction is terminated. The solid anhydrous ferric chloride is removed by filtration using a 20 μm coarse filter membrane, and the deionized water is removed by rotary evaporation at 80°C to produce a composite resin.

[0030] A3. 10 parts by weight of the composite resin, 0.5 parts of tetraethyl orthosilicate, and 5 parts of deionized water were added to a beaker and stirred at 50°C for 3 hours to obtain a reactant. Triethylamine was then added to the reactant to adjust the pH to 8, and the reaction was continued with stirring at room temperature for 6 hours to obtain a product. The product was transferred to a dialysis bag with a molecular weight cutoff of 1000 to remove unreacted raw materials, and then dried at 75°C to constant weight to obtain a hybrid resin.

[0031] Example 4 This embodiment provides a method for preparing a melamine overprint varnish, comprising the following steps: S1: Add 30 mL of formaldehyde to a 500 mL slurry kettle. The pH of the formaldehyde is then adjusted to 8 using a 0.1 mol / L NaOH solution. 125 g of melamine is then added to the kettle to obtain a reactant. The reactant is heated to 90°C and stirred with a stirrer for 50 minutes to obtain Intermediate 1. 0.1 mol / L NaOH solution is then added dropwise to the slurry kettle to adjust the pH of Intermediate 1 to 8. 17 g of p-toluenesulfonamide is then added and the reaction is continued at 90°C for 30 minutes to obtain the material. Heating is then stopped and the material is cooled to 40°C using circulating water to obtain the initial material.

[0032] S2. According to weight parts, 70 parts of the initial material, 0.5 parts of lubricant polyethylene wax, 0.05 parts of curing agent phthalic anhydride, 3 parts of the hybrid resin prepared in Example 1 and 1 part of poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole were mixed evenly and ball-milled to 500 mesh to prepare melamine varnish.

[0033] Example 5 This embodiment provides a method for preparing a melamine overprint varnish, comprising the following steps: S1: 50 mL of formaldehyde was added to a 500 mL slurry kettle. The pH of the formaldehyde was then adjusted to 8.6 using a 0.1 mol / L NaOH solution. 200 g of melamine was then added to the kettle to obtain a reactant. The reactant was heated to 97°C with stirring and allowed to react at this temperature for 58 minutes to obtain Intermediate 1. NaOH solution was then added dropwise to the slurry kettle until the pH of Intermediate 1 reached 89. 28 g of p-toluenesulfonamide was then added and the reaction continued at 93°C for 40 minutes to obtain the product. Heating was then stopped and the product was cooled to 45°C using circulating water to obtain the initial product.

[0034] S2. According to weight parts, 75 parts of the starting material, 1 part of the lubricant, 0.1 part of the curing agent phthalic anhydride, 6 parts of the hybrid resin prepared in Example 2 and 3 parts of poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole were mixed evenly and ball-milled to 450 mesh to prepare a melamine varnish.

[0035] Example 6 This embodiment provides a method for preparing a melamine overprint varnish, comprising the following steps: S1 and 60 mL of formaldehyde were added to a 500 mL slurry kettle. The pH of the formaldehyde was then adjusted to 9 using a 0.1 mol / L NaOH solution. 250 g of melamine was then added to the kettle to obtain a reactant. The reactant was heated to 100°C with stirring and allowed to react at this temperature for 60 minutes to obtain Intermediate 1. NaOH solution was then added dropwise to the slurry kettle until the pH of Intermediate 1 reached 9. 34 g of p-toluenesulfonamide was then added and the reaction continued at 100°C for 50 minutes to obtain the product. Heating was then stopped and the product was cooled to 50°C using circulating water to obtain the initial product.

[0036] S2. According to weight parts, 80 parts of the initial material, 1.5 parts of the lubricant, 0.15 parts of the curing agent phthalic anhydride, 10 parts of the hybrid resin prepared in Example 3 and 5 parts of poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole were mixed evenly and ball-milled to 400 mesh to prepare a melamine varnish.

[0037] Comparative Example 1 The difference between this comparative example and Example 6 is that, when preparing the hybrid resin, step A2 is omitted; 30 mL of the suspension copolymer and 20 mL of 4-chloromethylstyrene are mixed to obtain the prepared composite resin.

[0038] Comparative Example 2 The difference between this comparative example and Example 6 is that, when preparing the hybrid resin, nano-scale silicon dioxide is used instead of tetraethyl orthosilicate of the same mass.

[0039] Comparative Example 3 The difference between this comparative example and Example 6 is that when preparing the melamine overprint varnish, in step S1, 34 g of p-toluenesulfonamide is added to the intermediate 1 and mixed to obtain the initial material.

[0040] Comparative Example 4 The difference between this comparative example and Example 6 is that in step S2, when preparing the melamine varnish, the same mass of epoxy resin E44 is used instead of poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole.

[0041] Performance testing: 1. The hybrid resins prepared in Examples 1-3 and Comparative Examples 1-2 were sequentially placed in a dedicated crucible for thermal stability testing. Nitrogen was used as the protective gas during the test. The heating rate in the test procedure was 10°C / min. The initial thermal decomposition temperature was determined as the temperature at which the sample mass loss reached 5%. This was used to evaluate the thermal stability of the synthesized hybrid resins.

[0042] 2. According to ASTM D638-2003 "Determination of Tensile Properties of Plastics", the hybrid resins prepared in Examples 1-3 and Comparative Examples 1-2 were prepared into test strips. The test strips were placed in a universal testing machine for tensile testing. The crossbeam movement speed of the fixture during tensile testing was 10 mm / min.

[0043] 3. The hybrid resins prepared in Examples 1-3 and Comparative Examples 1-2 were successively prepared into 80 mm × 15 mm × 3.8 mm strips. The impact strength of the hybrid resins prepared in Examples 1-3 and Comparative Examples 1-2 was tested using a Charpy impact tester. The specific test results are shown in the table below: Table 1. Sample performance test data

[0044] Data analysis: By comparing and analyzing the data in the above table, the hybrid resins added to the melamine varnish of the present invention all have excellent thermal stability. The hybrid resins synthesized in Examples 1-3 all have excellent thermal stability, which is manifested in the T 5%The value is relatively high. However, in Comparative Example 2, an equal mass of tetraethyl orthosilicate is replaced with nano-silica; tetraethyl orthosilicate is in situ hydrolyzed inside the synthesized hybrid resin to generate silica, thereby better encapsulating the silica inside the hybrid resin, thereby significantly improving the thermal stability of the prepared hybrid resin.

[0045] The hybrid resins synthesized in Examples 1-3 of the present invention all exhibited high mechanical properties, as demonstrated by high tensile strength and impact strength values. However, in Comparative Example 1, the suspension copolymer was not cross-linked with 4-chloromethylstyrene, and no cross-linking bridges were formed, thereby increasing the density of the prepared composite resin, resulting in decreased tensile strength and impact strength values ​​for the synthesized hybrid resins.

[0046] 4. The melamine overprint varnishes prepared in Examples 4-6 and Comparative Examples 3-4 were sequentially sprayed onto melamine molded parts and then pressed at a temperature of 170°C and a time of 20 MPa. The molds were then opened, the parts removed, and their glossiness (A, B, C, and D, with A being the brightest and D the worst), appearance (spotted or smooth), and water-boiling results (gloss loss, glossy but partially peeled, or unchanged) were measured.

[0047] Table 2. Sample performance test data

[0048] Data analysis: The melamine varnish prepared in Examples 4-6 of the present invention and Comparative Examples 3-4, when sprayed onto the surface of melamine molded parts, all have good brightness and a smooth surface appearance; the parts have good high temperature resistance and remain bright after being boiled in water, especially the melamine varnish prepared in Example 6, whose brightness remains unchanged after being boiled in water.

[0049] However, in Comparative Example 3, when preparing the melamine overprint varnish, no p-toluenesulfonamide was added to the initial material for modification. Doping with p-toluenesulfonamide can transform long linear molecules into a three-dimensional network structure, resulting in poor flowability, reduced gloss, and speckled appearance in the melamine molded parts. In Comparative Example 4, when preparing the melamine overprint varnish, an equivalent mass of epoxy resin E44 was used in place of poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole. Compared to epoxy resins, poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole has poorer thermal stability. Therefore, the melamine overprint varnish prepared in Comparative Example 4 lost its gloss after boiling.

[0050] The above contents are merely examples and explanations of the structure of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

[0051] Throughout this specification, references to terms such as "one embodiment," "example," and "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0052] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a melamine varnish, characterized in that: The following steps are involved: According to weight parts, 70-80 parts of the initial material, 0.5-1.5 parts of the lubricant, 0.05-0.15 parts of the curing agent, 3-10 parts of the hybrid resin and 1-5 parts of the poly-2,2'-(m-phenyl)-5,5'-bisbenzimidazole are mixed and ball-milled to prepare a melamine varnish.

2. The method for preparing a melamine varnish according to claim 1, characterized in that: The preparation method of the hybrid resin comprises the following steps: A1. Replace the air in the autoclave with nitrogen and evacuate the autoclave to -0.7-0.5 MPa. Add deionized water, initiator, methyl acrylate, and divinylbenzene to the autoclave and react at 55-65°C for 50-60 minutes. The polymerization reaction is considered complete to obtain a product. Centrifuge the product and dry it to a constant weight to synthesize a suspension copolymer. A2. Adding the suspension copolymer and anhydrous ferric chloride to deionized water and blending them, then adding 4-chloromethylstyrene dropwise until the addition is complete to obtain a product; reacting the product at 35-45° C. for 1-2 hours, then stopping the reaction, filtering through a 10-20 μm coarse filter membrane to remove solid anhydrous ferric chloride, and then rotary evaporating to remove deionized water to obtain a composite resin; A3. The composite resin, tetraethyl orthosilicate, and deionized water are mixed and stirred at 45-50° C. for 2-3 hours to obtain a reactant; triethylamine is added to the reactant to adjust the pH value of the reactant to 7-8, and the reaction is continued with stirring at room temperature for 5-6 hours to obtain a product; the product is transferred to a dialysis bag with a molecular weight cutoff of 800-1000 to remove unreacted raw materials, and dried to finally prepare a hybrid resin.

3. The method for preparing a melamine varnish according to claim 2, characterized in that: In step A1, the usage ratio of deionized water, initiator, methyl acrylate and divinylbenzene is 200 mL: 0.5-1 g: 50-100 g: 60-80 g.

4. The method for preparing a melamine varnish according to claim 2, characterized in that: In step A2, the amount ratio of the suspension copolymer, anhydrous ferric chloride, 4-chloromethylstyrene and deionized water is 20-30 mL:0.5-1 g:10-20 mL:100 mL.

5. The method for preparing a melamine varnish according to claim 2, characterized in that: In step A3, the weight ratio of the composite resin, tetraethyl orthosilicate and deionized water is 10:0.1-0.5:5; and the drying temperature is 70-75°C.

6. The method for preparing a melamine varnish according to claim 1, characterized in that: The preparation method of the initial material comprises the following steps: S1. NaOH solution is added dropwise to formaldehyde to adjust the pH to 8-9, and then melamine is added to obtain a reactant; the reactant is heated to 90-100° C. and reacted at this temperature for 50-60 minutes to obtain intermediate 1; S2. Continue to add 0.1 mol / L NaOH solution dropwise to 150-300 g of intermediate 1 to make the pH value of intermediate 1 8-9, then add p-toluenesulfonamide, and continue to react at 90-100 ° C for 30-50 min to obtain a material; the material is naturally cooled to room temperature to obtain an initial material.

7. The method for preparing a melamine varnish according to claim 6, characterized in that: In step S1, the ratio of formaldehyde to melamine is 30-60 mL:125-250 g; in step S2, the ratio of intermediate 1 to p-toluenesulfonamide is 150-300 g:17-34 g.

8. A melamine varnish, characterized in that: The melamine varnish is prepared by the preparation method of any one of claims 1 to 7.

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