A film-forming substance and its preparation method, and fluoropolymer coatings, their preparation methods and applications.

Abstract

This invention relates to a film-forming substance and its preparation method, as well as a fluoropolymer coating, its preparation method, and its application. The film-forming substance is a fluoropolymer; the fluoropolymer is poly(vinylidene fluoride-tetrafluoroethylene) (P(VDF-TFE)-OH) with active hydroxyl groups at the ends of its molecular chain. The fluoropolymer coating includes a rust-converting agent, a stabilizer, an organic solvent, a filler, a film-forming aid, and the film-forming substance. The beneficial effects of this invention are: it can produce a fluoropolymer coating that integrates top and bottom layers, providing excellent rust-resistant coating, good weather resistance, and a long effective protection period.

Description

Technical Field

[0001] This invention belongs to the field of anti-corrosion coating technology, specifically relating to a film-forming substance and its preparation method, as well as fluoropolymer coatings, their preparation methods, and applications. Background Technology

[0002] Corrosion is the most significant form of damage to metallic materials, which can drastically shorten their service life and even cause catastrophic accidents. In 2015, the Chinese Academy of Engineering launched a major consulting project, "Research on Corrosion Status and Control Strategies in my country" (Hou Baorong, China Corrosion Cost Survey Report [M]. 2017: Science Press). This project conducted a special investigation on the corrosion status, corrosion costs, and control measures of more than 30 key industries in five major sectors in my country. The results showed that in 2014, the total corrosion cost of various industries in my country accounted for approximately 3.34% of the GDP that year, exceeding RMB 2.1 trillion. Among these costs, the corrosion cost of steel accounted for a relatively large proportion.

[0003] After steel structures corrode, applying a coating for secondary protection is a relatively economical and common maintenance method. To ensure the coating's protective effect, rigorous rust removal is usually required before applying primer, intermediate coat, and topcoat. This multi-step, time-consuming process leads to high overall costs, substandard coating quality, and potential health risks for workers. For rusted structures like iron towers requiring high-altitude work, the efficiency and quality of traditional methods are even more difficult to guarantee, and significant operational risks remain. Furthermore, the rigorous rust removal process can cause steel thinning, reducing load-bearing capacity. Therefore, developing a combined primer and topcoat coating with excellent protective properties that can be applied even with rust present has significant application value.

[0004] Rust-resistant coatings are mainly classified into three types based on their working principle: conversion-type, stabilizing-type, and penetrating-type. Conversion-type coatings generally contain inorganic acids (mainly phosphoric acid), organic acids (tannic acid, etc.), or mixed acids, which can react with harmful components in rust such as ferric hydroxide (Fe(OH)3), forming stable compounds that have good adhesion to the steel substrate. Stabilizing-type coatings typically contain components that can form stable complexes with rust (such as phosphates, chromates, etc.), thus making the entire rust layer a stable and protective filler component in the coating. Penetrating-type coatings mainly utilize penetrants and low-molecular-weight film-forming substances to allow the coating system to penetrate into the rust layer, thereby completely sealing the rust layer and preventing further corrosion. Research on rust-resistant coatings in my country has a history of over 40 years, but their adhesion and weather resistance are generally insufficient, resulting in limited application; most are only used as primers. Zibo Zhongya Special Anticorrosion Co., Ltd. has developed a primer-topcoat coating that can be applied to areas with rust (Chinese Invention Patent, CN202010084817.7). The film-forming substance is a product of suspension polymerization of liquid fluororubber and chlorinated rubber, with a small amount of tannic acid added as a conversion agent. Through its good penetration performance and the rust conversion effect of tannic acid, the coating can achieve a certain effect of applying coating to areas with rust.

[0005] Fluoropolymer coatings (fluorocarbon paints) are recognized worldwide for their excellent properties, including weather resistance, resistance to high and low temperatures, resistance to chemical media, and abrasion resistance. However, because fluoropolymers have weak adhesion to most materials, they require a dedicated primer and can only be used as topcoats.

[0006] Therefore, starting from fluororesin, a film-forming substance and its preparation method are proposed, as well as fluororesin coatings, their preparation methods and applications, so that the fluororesin coatings can be made into a base and topcoat combined coating with rust coating, good weather resistance and long effective protection period. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention proposes a film-forming substance and its preparation method, as well as a fluororesin coating, its preparation method, and its application. This coating has good bonding ability with rust and excellent weather resistance, and can achieve rust-resistant coating with both the substrate and the surface in harsh corrosive environments.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] In one aspect, the present invention provides a film-forming substance, wherein the film-forming substance is a hydroxyl-terminated fluoropolymer; wherein the hydroxyl-terminated fluoropolymer is polyvinylidene fluoride-tetrafluoroethylene (P(VDF-TFE)-OH) with active hydroxyl groups at the ends of its molecular chain.

[0010] In a preferred embodiment of this solution, the hydroxyl-terminated fluoropolymer is prepared by free radical polymerization initiated by a terminally functionalized benzoyl initiator.

[0011] In a preferred embodiment of this solution, the terminal functional group of the benzoyl initiator is tetrahydropyran ether.

[0012] Tetrahydropyran is an introduced protecting group that is removed only after the synthesis of the fluoropolymer is complete, in order to avoid the premature formation of highly reactive hydroxyl groups.

[0013] In a preferred embodiment of this solution, the number-average molecular weight of the hydroxyl-terminated fluoropolymer is approximately 30,000.

[0014] This invention also provides a method for preparing a film-forming substance, comprising the following steps:

[0015] Step A: Preparation of 4-tetrahydropyran ether benzoyl peroxide;

[0016] Step B: After liquefying the vinylidene fluoride and tetrafluoroethylene monomers, transfer them to an acetonitrile solvent containing benzoyl peroxide 4-tetrahydropyran ether to complete the free radical polymerization and obtain the polymer product;

[0017] Step C: Dissolve the obtained polymer product in tetrahydrofuran solution, add acidic mixture, react at 40-50℃ for 3 hours, precipitate and dry the obtained product to obtain hydroxyl-terminated fluoropolymer.

[0018] In a preferred embodiment of this solution, the acidic mixture is a mixture of 3M hydrochloric acid and acetic acid, and the volume ratio of 3M hydrochloric acid to acetic acid is 1:5 to 10.

[0019] In a preferred embodiment of this solution, the method for preparing 4-tetrahydropyran ether benzoyl peroxide includes the following steps:

[0020] S11, methyl 4-hydroxybenzoate, dihydropyran and pyridine ρ-benzenesulfonate were added to dichloromethane solvent in a molar ratio of 5:5:1, and the reaction was stirred for 10 hours. Then the reaction mixture was diluted, washed, extracted, dried and purified by column washing to obtain intermediate product one.

[0021] S12, Dissolve intermediate product one in a mixed solvent of methanol and water, add alkali to carry out saponification reaction, and obtain intermediate product two;

[0022] Wherein, the alkali is sodium hydroxide or potassium hydroxide, and the molar ratio of intermediate product one to alkali is 1:3;

[0023] S13, under low temperature conditions, the intermediate product dicyclohexylcarbodiimide (DCCI) was dissolved in dichloromethane, and 30% hydrogen peroxide aqueous solution was added. After stirring at room temperature for 1 to 3 hours, the mixture was adjusted to neutral, methanol and reaction byproducts were removed, and the mixture was washed and dried under reduced pressure to obtain a white product, namely 4-tetrahydropyran ether benzoyl peroxide.

[0024] Intermediate product one is methyl 4-tetrahydropyranose benzoate, and intermediate product two is 4-tetrahydropyranose benzoic acid.

[0025] On the other hand, the present invention also provides a fluoropolymer coating, comprising a rust converter, a stabilizer, an organic solvent, a filler, a defoamer, a film-forming aid, and the aforementioned film-forming substances.

[0026] In a preferred embodiment of this solution, by weight, the rust converter comprises 10-20 parts, the stabilizer 3-10 parts, the organic solvent 20-30 parts, the filler 5-10 parts, the defoamer 0.1-1.0 parts, the film-forming aid 2-4 parts, the drying agent 0.5-2 parts, and the film-forming substance 30-50 parts.

[0027] In a preferred embodiment of this solution, the rust-converting agent is a mixture of phosphoric acid and tannic acid;

[0028] The stabilizer is a mixture of zinc metaborate and aluminum tripolyphosphate;

[0029] The organic solvent is a mixture of xylene, butyrolactone, and isophorone;

[0030] The filler is a mixture of fumed silica and rutile titanium dioxide;

[0031] The defoamer is tributyl phosphate;

[0032] The film-forming aid is dodecyl alcohol ester;

[0033] The drying agent is cobalt naphthenate.

[0034] In a preferred embodiment of this solution, the mass ratio of tannic acid to phosphoric acid is 1:2-3;

[0035] The volume ratio of butyrolactone, xylene and isophorone is 1:1 to 2:3 to 5;

[0036] The mass ratio of aluminum tripolyphosphate to zinc metaborate is 1:1 to 2;

[0037] The mass ratio of fumed silica to rutile titanium dioxide is 1:1 to 2.

[0038] In a preferred embodiment of this solution, by weight, the hydroxyl-terminated fluoropolymer is 37 parts, phosphoric acid is 12 parts, tannic acid is 6 parts, xylene is 5 parts, butyrolactone is 5 parts, isophorone mixed solvent is 20 parts, fumed silica is 3 parts, rutile titanium dioxide is 3 parts, aluminum tripolyphosphate is 2 parts, zinc metaborate is 3 parts, dodecyl alcohol ester is 3 parts, cobalt naphthenate is 1 part, and tributyl phosphate is 0.3 parts.

[0039] This aspect also provides a method for preparing the above-mentioned fluoropolymer coating, comprising the following steps:

[0040] Step 1: Dissolve the hydroxyl-terminated fluoropolymer in xylene and a portion of isophorone, stir for 5-15 minutes, add a portion of fumed silica and rutile titanium dioxide, stir for 15-30 minutes to obtain mixture A;

[0041] Step 2: Mix phosphoric acid and tannic acid with butyrolactone and stir for 10-20 minutes. Add aluminum tripolyphosphate, zinc metaborate and the remaining fumed silica and stir for 20-40 minutes to obtain mixture B.

[0042] Step 3: Mix mixture A with mixture B and stir at high speed for 20-40 minutes to obtain mixture C;

[0043] Step 4: Mix cobalt naphthenate with dodecyl alcohol ester and the remaining isophorone, and stir for 10-20 minutes to obtain mixture D;

[0044] Step 5: Mix mixture D with mixture C, add defoamer, and stir for 10-15 minutes to obtain a fluoropolymer coating that can be used for both rust-resistant coating and topcoat application.

[0045] On the other hand, the present invention also provides a method for applying the above-mentioned fluoropolymer coating: directly applying it to the surface of a rusted steel structure.

[0046] This invention also provides a method for preparing hydroxyl-terminated fluoropolymers, starting from the synthesis of an initiator, and including three main steps: synthesis of benzoyl peroxide 4-tetrahydropyran ether (BPO initiator), preparation of hydroxyl-terminated fluoropolymers (film-forming substances), and mixing of a coating system (hydroxyl-terminated fluoropolymer coating).

[0047] Step S1, Synthesis of 4-tetrahydropyran ether benzoyl peroxide:

[0048] S11, methyl 4-hydroxybenzoate, dihydropyran and pyridine ρ-benzenesulfonate were added to dichloromethane solvent in a molar ratio of 5:5:1, and the reaction was stirred for 10 hours. Then the reaction mixture was diluted, washed, extracted, dried and purified by column washing to obtain intermediate product one.

[0049] S12, Dissolve intermediate product one in a mixed solvent of methanol and water, add alkali to carry out saponification reaction, and obtain intermediate product two;

[0050] Wherein, the alkali is sodium hydroxide or potassium hydroxide, and the molar ratio of intermediate product one to alkali is 1:3;

[0051] S13, under low temperature conditions, intermediate product 2 and dicyclohexylcarbodiimide (DCCI) are dissolved in dichloromethane, and 1 to 1.5 times the weight of intermediate product 2 in 30% hydrogen peroxide aqueous solution is added. After stirring at room temperature for 1 to 3 hours, the mixture is adjusted to neutral, and methanol is removed under reduced pressure at 40°C. The product is washed in dichloromethane and filtered to remove reaction byproducts, and then washed with brine and dried under reduced pressure at 60°C to obtain a white product, namely 4-tetrahydropyran ether benzoyl peroxide.

[0052] Step S2, Preparation of hydroxyl-terminated fluoropolymer:

[0053] S21, in a reactor, benzoyl 4-tetrahydropyran ether peroxide is dissolved in acetonitrile (solvent). VDF and TFE monomers are liquefied and then introduced into separate volumetric transition containers. The liquid monomers are vaporized and automatically enter the reactor. The mixture is reacted at 90-100°C for 3-6 hours to release unreacted residual monomers. After removing the solvent by vacuum distillation, the mixture is vacuum dried to obtain a white powdered copolymer, which is P(VDF-TFE) with tetrahydropyran ether at the end.

[0054] S22, the copolymer product obtained by S21 is dissolved in tetrahydrofuran, mixed acid solution is added, and after reacting at 40-50℃ for 3 hours, the tetrahydropyran methyl is removed, and the resulting product is precipitated and dried to obtain hydroxyl-terminated fluoropolymer.

[0055] The mixed acid solution is a mixture of 3M hydrochloric acid and acetic acid with a volume ratio of 1:5 to 10, and the volume ratio of the mixed acid solution to tetrahydrofuran is 1:2 to 6.

[0056] S23, in order to obtain pure hydroxyl-terminated P(VDF-TFE) resin, the product (hydroxyl-terminated fluoropolymer) is purified by neutralization and desalting to remove excess acid and salt produced after neutralization.

[0057] Step S3: Preparation of hydroxyl-terminated fluoropolymer coating:

[0058] S31, dissolve the hydroxyl-terminated fluoropolymer in xylene and part of isophorone, stir for 5-15 minutes, add all of the rutile titanium dioxide and half of the fumed silica, stir for 15-30 minutes to obtain mixture A (fluoropolymer solution with filler).

[0059] S32, mix phosphoric acid and tannic acid with butyrolactone, stir for 10-20 minutes, add aluminum tripolyphosphate, zinc metaborate and the remaining half of the fumed silica, stir for 20-40 minutes to obtain mixture B (rust conversion solution);

[0060] S33, Mix mixture A with mixture B and stir for 20-40 minutes to obtain mixture C (the main component of rust-converting fluoropolymer coating);

[0061] S34, mix cobalt naphthenate with dodecyl alcohol ester and the remaining isophorone, stir for 10-20 minutes to obtain mixture D (auxiliary film-forming liquid for rust-converting fluororesin coating);

[0062] S35: Mix mixture D with mixture C, add 0.3% defoamer, and stir for 30-60 minutes to obtain a hydroxyl-terminated fluoropolymer coating that can be applied to both the top and bottom layers and is suitable for rust-resistant coating.

[0063] In a preferred embodiment of this scheme, in step S21, the molar ratio of VDF and TFE monomers is 15:1 to 1.5.

[0064] In a preferred embodiment of this solution, the formulation of the hydroxyl-terminated fluoropolymer coating, by mass fraction, comprises: 37% hydroxyl-terminated fluoropolymer, 12% phosphoric acid, 6% tannic acid, 5% xylene, 5% butyrolactone mixed solvent, 20% isophorone, 3% fumed silica, 3% rutile titanium dioxide, 3% dodecyl ester, 2% aluminum tripolyphosphate, 3% zinc metaborate, 1% cobalt naphthenate, and 0.3% tributyl phosphate.

[0065] It should be noted that:

[0066] The main function of rutile titanium dioxide is to improve the mechanical properties of coatings, and it can also be used as a white pigment.

[0067] The main function of fumed silica is to prevent the sedimentation of solids, while also increasing the hardness and anti-sagging properties of coatings.

[0068] Isophorone, butyrolactone, and dodecyl alcohol ester mainly function as solvents, penetrants, viscosity modifiers, leveling agents, and antifreeze agents.

[0069] It should be noted that hydroxyl-terminated fluoropolymer coatings have higher reactivity than traditional fluorocarbon coatings with ether or ester side chains, and can undergo a certain degree of complexation reaction with rust.

[0070] The beneficial effects of this invention are as follows: First, a benzoyl initiator with a special molecular structure is synthesized. Then, a medium molecular weight polyvinylidene fluoride-tetrafluoroethylene (P(VDF-TFE)-OH) fluororesin with hydroxyl-terminated ends is prepared by free radical polymerization as a film-forming substance. Finally, auxiliary components such as rust converter, solvent, and filler are added to produce a high-performance topcoat weather-resistant coating that can be applied with rust.

[0071] Therefore, this solution can chemically modify fluororesin by attaching highly reactive groups, which not only enhances its adhesion to rust and metal substrates, but also improves the chemical bonding force within the macromolecules and between the macromolecules and other small molecules. With the combined action of rust converters and stabilizers, a topcoat and base coat with excellent weather resistance and long effective protection period can be produced. It has the characteristics of excellent anti-corrosion effect and convenient construction, and has broad application prospects. Attached Figure Description

[0072] Figure 1 Flowchart for the preparation of hydroxyl-terminated fluoropolymer coatings for rust-resistant coatings.

[0073] Figure 2 The macroscopic morphology of the rust-coated hydroxyl fluoropolymer coating after different periods of salt spray testing. Detailed Implementation

[0074] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0075] Example 1

[0076] Preparation of free radical initiators:

[0077] Step 1: Dissolve 10 g of methyl 4-hydroxybenzoate in 300 ml of dichloromethane solution, add 5 g of dihydropyran and 1 g of p-phenylmethylsulfonic acid pyridine salt; after reacting for 10 hours, wash the reaction mixture with brine, extract with ether and dry under vacuum; then wash the obtained product in a silica column with an organic mixture to obtain intermediate product 1: methyl 4-tetrahydropyran ether benzoate;

[0078] The organic mixture is ethyl acetate / hexane in a volume ratio of 1:1.

[0079] Step 2: Saponify intermediate 1, which is dissolved in a mixture of water and methanol (volume ratio 1:1), with sodium hydroxide to obtain intermediate 2: 4-tetrahydropyran ether benzoic acid.

[0080] The molar ratio of intermediate product 2 to sodium hydroxide is 1:3;

[0081] Step 3: At 0°C, add 40 g of intermediate product 2 to a mixed solution containing 1 g of DCCI in dichloromethane and 3 ml of hydrogen peroxide aqueous solution (30%). After stirring at room temperature for 1.5 hours, adjust the pH of the mixture to 7, and remove methanol by vacuum distillation at 40°C. Wash the product in dichloromethane and filter to remove reaction byproducts, then wash it in water and brine respectively. Remove water and solvent by vacuum distillation at 40°C, and dry to obtain a white solid product: benzoyl 4-tetrahydropyran ether peroxide.

[0082] Example 2

[0083] Preparation of hydroxyl-terminated fluoropolymers:

[0084] Step 1: Add 4 g of benzoyl 4-tetrahydropyran ether peroxide prepared in Example 1 and 300 ml of acetonitrile to a 700 ml reactor; transfer and freeze 300 ml of VDF and 20 ml of TFE into the reactor via a liquid nitrogen cooling device in a high vacuum pipeline driven by an oil pump and dissolve them in acetonitrile solvent; place the reactor in an oil bath at 90°C, stop the reaction after 3 hours and release the residual monomer; remove the solvent acetonitrile by vacuum distillation, and the obtained product is dried under vacuum to obtain a white powder copolymer: P(VDF-TFE) with 4-tetrahydropyran ether at the end;

[0085] Step 2: Dissolve 50 g of P(VDF-TFE) with 4-tetrahydropyran ether at the end in 500 ml of tetrahydrofuran, and add 20 ml of 3M hydrochloric acid and 150 ml of acetic acid; stir the mixed solution at 40 °C for 3 hours, add potassium carbonate solution for neutralization reaction; after removing potassium salt, concentrate the solution under vacuum, and precipitate it in methanol. Dry the solid product under vacuum to obtain hydroxyl-terminated fluoropolymer.

[0086] The number-average molecular weight of the hydroxyl-terminated fluoropolymer should be 30,000.

[0087] Example 3

[0088] Preparation of hydroxyl-terminated fluoropolymer coatings:

[0089] Step 1: Dissolve 40g of the hydroxyl-terminated fluoropolymer obtained in Example 2 in 5ml xylene and 15ml isophorone, stir for 10 minutes, add 1.6g of fumed silica and 3.2g of rutile titanium dioxide, stir for 20 minutes to obtain mixture A;

[0090] Step 2: Mix 7.5 ml of phosphoric acid and 6 g of tannic acid with 4 ml of butyrolactone and stir for 15 minutes. Add 2 g of aluminum tripolyphosphate, 3.2 g of zinc metaborate and 1.6 g of fumed silica and stir for 30 minutes to obtain mixture B.

[0091] Step 3: Mix mixture A with mixture B and stir at high speed for 30 minutes to obtain mixture C;

[0092] Step 4: Mix 1.1 g of cobalt naphthenate with 3.2 g of dodecyl alcohol ester, 1 ml of butyrolactone and 5 ml of isophorone, and stir for 15 minutes to obtain mixture D;

[0093] Step 5: Mix mixture D with mixture C, add 0.3 g of defoamer tributyl phosphate, and stir for 40 minutes to obtain a fluoropolymer coating suitable for rust-resistant coating.

[0094] Example 4

[0095] Preparation of hydroxyl-terminated fluoropolymer coatings:

[0096] Step 1: Dissolve 37g of the hydroxyl-terminated fluoropolymer obtained in Example 2 in 5ml xylene and 15ml isophorone, stir for 10 minutes, add 1.5g of fumed silica and 3g of rutile titanium dioxide, stir for 20 minutes to obtain mixture A;

[0097] Step 2: Mix 12 ml of phosphoric acid and 6 g of tannic acid with 4 ml of butyrolactone and stir for 15 minutes. Add 2 g of aluminum tripolyphosphate, 3 g of zinc metaborate and 1.5 g of fumed silica and stir for 30 minutes to obtain mixture B.

[0098] Step 3: Mix mixture A with mixture B and stir at high speed for 30 minutes to obtain mixture C;

[0099] Step 4: Mix 1 gram of cobalt naphthenate with 3 g of dodecyl alcohol ester, 1 ml of butyrolactone and 5 ml of isophorone, and stir for 15 minutes to obtain mixture D;

[0100] Step 5: Mix mixture D with mixture C, add 0.3 g of tributyl phosphate, and stir for 50 minutes to obtain a fluoropolymer coating suitable for rust-resistant coating.

[0101] Experimental Example

[0102] The coating obtained according to the steps in Example 3 was applied to the rusted carbon steel surface. After drying, a salt spray aging test was conducted according to GB / T10125-2021 standard. After 720 hours, the surface morphology of the coating showed no significant change. Simultaneously, the adhesion and protective effects of the coating of this invention and a domestically produced fluorine-containing rust-resistant coating were compared after different periods of salt spray testing according to GB / T 31586.1-2015 and GB / T 1766-2008 standards. The results are shown in Tables 1 and 2. It can be seen that the coating of this invention exhibited a blistering, rusting, cracking, and peeling index of 0 after the 720-hour salt spray test, demonstrating superior protective effect compared to the comparative product. Although the adhesion index of the coating of this invention after drying was lower than that of the comparative product, it maintained excellent stability during the 720-hour salt spray aging test. The comparative product initially had higher adhesion, but it rapidly decreased after salt spray aging, dropping to 60% of the adhesion of the coating of this invention after 720 hours. The experimental results demonstrate that the overall performance of the coating of this invention is superior to that of the comparative product.

[0103] The macroscopic morphology of rust-resistant hydroxyl-terminated fluoropolymer coatings after different periods of salt spray testing is as follows: Figure 2 As shown.

[0104] Table 1. Salt spray test coating defect rating table of the coating of this invention and a fluorine-containing rust-inducing coating of a domestic manufacturer.

[0105]

[0106] Table 2. Salt spray test adhesion data comparing the coating of this invention with a fluorine-containing rust-resistant coating from a domestic manufacturer.

[0107]

[0108] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A fluoropolymer coating, characterized in that: This includes rust converters, stabilizers, organic solvents, fillers, film-forming aids, drying agents, defoamers, and film-forming substances; The film-forming substance is a hydroxyl-terminated fluoropolymer; the hydroxyl-terminated fluoropolymer is polyvinylidene fluoride-tetrafluoroethylene (P(VDF-TFE)-OH) with active hydroxyl groups at the end of the molecular chain, which is prepared by functionalized benzoyl-initiated free radical polymerization. By weight, the rust converter comprises 10-20 parts, the stabilizer 3-10 parts, the organic solvent 20-30 parts, the filler 5-10 parts, the film-forming aid 2-4 parts, the drying agent 0.5-2 parts, the defoamer 0.1-1 parts, and the film-forming substance 30-50 parts.

2. The fluoropolymer coating according to claim 1, characterized in that: The rust-converting agent is a mixture of phosphoric acid and tannic acid; The stabilizer is a mixture of zinc metaborate and aluminum tripolyphosphate; The organic solvent is a mixed solution of xylene, butyrolactone, and isophorone; The fillers are fumed silica and rutile titanium dioxide; The film-forming aid is dodecyl alcohol ester; The drying agent is cobalt naphthenate; The defoamer is tributyl phosphate.

3. The fluoropolymer coating according to claim 2, characterized in that: The mass ratio of tannic acid to phosphoric acid is 1:2~3, based on parts by mass. The volume ratio of butyrolactone, xylene and isophorone is 1:1~2:3~5; The mass ratio of aluminum tripolyphosphate to zinc metaborate is 1:1~2; The mass ratio of fumed silica to rutile titanium dioxide is 1:1~2.

4. The fluoropolymer coating according to claim 2, characterized in that: By weight, the hydroxyl-terminated fluoropolymer comprises 37 parts, phosphoric acid 12 parts, tannic acid 6 parts, a mixed solvent of xylene, butyrolactone and isophorone 30 parts, fumed silica 3 parts, rutile titanium dioxide 3 parts, aluminum tripolyphosphate 2 parts, zinc metaborate 3 parts, dodecyl alcohol ester 3 parts, cobalt naphthenate 1 part, and tributyl phosphate 0.3 parts.

5. The fluoropolymer coating according to claim 3, characterized in that, The preparation of the film-forming substance includes the following steps: Step A: Preparation of 4-tetrahydropyran ether benzoyl peroxide; Step B: After liquefying the vinylidene fluoride and tetrafluoroethylene monomers, transfer them to an acetonitrile solvent containing benzoyl peroxide 4-tetrahydropyran ether to complete the free radical polymerization and obtain the polymer product; Step C: Dissolve the obtained polymer product in tetrahydrofuran solution, add a mixture of 3M hydrochloric acid and acetic acid with a volume ratio of 1:5~10, react at 40~50℃ for 3 hours, precipitate and dry the obtained product to obtain hydroxyl-terminated fluoropolymer.

6. The fluoropolymer coating according to claim 5, characterized in that, The preparation method of the 4-tetrahydropyran ether benzoyl peroxide includes the following steps: S11, methyl 4-hydroxymethylbenzoate, dihydropyran and pyridine ρ-benzenesulfonate were added to dichloromethane solvent in a molar ratio of 5:5:1, and the reaction was stirred for 10 hours. Then the reaction mixture was diluted, washed, extracted, dried and purified by column washing to obtain intermediate product one. S12, Dissolve intermediate product one in a mixed solvent of methanol and water, add alkali to carry out saponification reaction, and obtain intermediate product two; Wherein, the alkali is sodium hydroxide or potassium hydroxide, and the molar ratio of intermediate product one to alkali is 1:3; S13, under low temperature conditions, the intermediate product dicyclohexylcarbodiimide (DCCI) was dissolved in dichloromethane, and 30% hydrogen peroxide aqueous solution was added. After stirring at room temperature for 1 to 3 hours, the mixture was adjusted to neutral, methanol and reaction byproducts were removed, and the mixture was washed and dried under reduced pressure to obtain a white product, namely 4-tetrahydropyran ether benzoyl peroxide.

7. A method for preparing the fluoropolymer coating according to any one of claims 4 to 6, characterized in that, Includes the following steps: Step 1: Dissolve the hydroxyl-terminated fluoropolymer in xylene and a portion of isophorone, stir for 5-15 minutes, add a portion of fumed silica and rutile titanium dioxide powder, stir for 15-30 minutes to obtain mixture A; the hydroxyl-terminated fluoropolymer is polyvinylidene fluoride-tetrafluoroethylene (P(VDF-TFE)-OH) with active hydroxyl groups at the end of the molecular chain, prepared by functionalized benzoyl-initiated free radical polymerization. Step 2: Mix phosphoric acid and tannic acid with butyrolactone and stir for 10-20 minutes. Add aluminum tripolyphosphate, zinc metaborate and the remaining fumed silica and stir for 20-40 minutes to obtain mixture B. Step 3: Mix mixture A with mixture B and stir at high speed for 20-40 minutes to obtain mixture C; Step 4: Mix cobalt naphthenate with dodecyl alcohol ester and the remaining isophorone, and stir for 10-20 minutes to obtain mixture D; Step 5: Mix mixture D with mixture C, add defoamer tributyl phosphate, and stir for 10-15 minutes to obtain a fluoropolymer coating that can be used for both rust-resistant coating and topcoat application.

8. The method for applying a fluoropolymer coating according to claim 7, characterized in that, The preparation of the hydroxyl-terminated fluoropolymer includes the following steps: Step A: Preparation of 4-tetrahydropyran ether benzoyl peroxide; Step B: After liquefying the vinylidene fluoride and tetrafluoroethylene monomers, transfer them to an acetonitrile solvent containing benzoyl peroxide 4-tetrahydropyran ether to complete the free radical polymerization and obtain the polymer product; Step C: Dissolve the obtained polymer product in tetrahydrofuran solution, add a mixture of 3M hydrochloric acid and acetic acid with a volume ratio of 1:5~10, react at 40~50℃ for 3 hours, precipitate and dry the obtained product to obtain hydroxyl-terminated fluoropolymer.

9. The method for applying a fluoropolymer coating according to claim 8, characterized in that, The preparation method of the 4-tetrahydropyran ether benzoyl peroxide includes the following steps: S11, methyl 4-hydroxymethylbenzoate, dihydropyran and pyridine ρ-benzenesulfonate were added to dichloromethane solvent in a molar ratio of 5:5:1, and the reaction was stirred for 10 hours. Then the reaction mixture was diluted, washed, extracted, dried and purified by column washing to obtain intermediate product one. S12, Dissolve intermediate product one in a mixed solvent of methanol and water, add alkali to carry out saponification reaction, and obtain intermediate product two; Wherein, the alkali is sodium hydroxide or potassium hydroxide, and the molar ratio of intermediate product one to alkali is 1:3; S13, under low temperature conditions, the intermediate product dicyclohexylcarbodiimide (DCCI) was dissolved in dichloromethane, and 30% hydrogen peroxide aqueous solution was added. After stirring at room temperature for 1 to 3 hours, the mixture was adjusted to neutral, methanol and reaction byproducts were removed, and the mixture was washed and dried under reduced pressure to obtain a white product, namely 4-tetrahydropyran ether benzoyl peroxide.

10. A method for applying a fluoropolymer coating according to any one of claims 1-6, characterized in that: Apply directly to the surface of a rusty steel structure.

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