Method for preparing corrosion-resistant composite film from acyl fluoride by-product

Abstract

The invention discloses a method for preparing a corrosion-resistant composite film by using an acyl fluoride byproduct, and belongs to the technical field of preparation of corrosion-resistant films on surfaces of steel materials. The method comprises the following steps: by taking a perfluoropropylene oxide (HFPO) acyl fluoride byproduct as a raw material, mixing the raw material with a solvent and an acid-binding agent to prepare a film-forming agent; and double-layer self-assembly of a polyacrylic acid layer and an acyl fluoride by-product film layer is carried out on the surface of the steel by combining a polyacrylic acid mixed solution, and the corrosion-resistant composite film is formed on the surface of the steel after high-temperature curing. According to the invention, the high value of the HFPO byproduct is realized, the dripping time of the copper sulfate of the composite film reaches 298-426 s, and the electrochemical corrosion resistance is excellent; and chromizing and phosphating pollution processes are not needed, the process is simple and convenient, the cost is low, and the method is suitable for steel materials and can be popularized to the field of manufacturing of buildings, automobiles and major equipment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal surface corrosion protection, and particularly relates to a method for preparing a corrosion-resistant composite film by using acyl fluoride by-products. BACKGROUND

[0002] In the process of synthesizing perfluoroepoxypropane (HFPO) from hexafluoropropylene (HFP), various by-products caused by over-oxidation, hydrolysis or isomerization will be produced. Among them, perfluoroacyl fluoride by-products are important for turning waste into treasure due to their reactivity. Their hydrolysis, alcoholysis and aminolysis products and their derivatives are important pharmaceutical and organic synthesis solvents. Therefore, the high-value comprehensive utilization of HFPO by-products is particularly important.

[0003] Steel is widely used in key fields of the national economy such as construction, automobiles, major equipment manufacturing, etc. However, steel is prone to electrochemical corrosion in humid environments, reducing the load-bearing capacity of metal structures. Therefore, effective protection of the steel surface has become the focus of corrosion prevention research. Existing steel corrosion prevention methods mainly include chromizing, phosphating, composite resin coating, etc. Among them, chromizing and phosphating treatment methods face many environmental challenges. Therefore, the development and application of effective corrosion-resistant composite films are of great significance to environmental protection and promoting sustainable development.

[0004] Patent CN112662096A discloses a fluorine-containing corrosion-resistant material and a preparation method thereof. By adjusting 5-20wt% of soluble polytetrafluoroethylene and a composite modifier, a fluorine-containing corrosion-resistant coating with low porosity and high density is synthesized, and has good resistance to strong acid, strong base and strong oxidizing agent oxidation. However, this technology focuses on the preparation of block-shaped corrosion-resistant materials, rather than metal surface composite films, and relies on pure polytetrafluoroethylene resin (PTFE) and fusible polytetrafluoroethylene (PFA) as raw materials. It does not utilize industrial by-products, has high cost, and cannot be directly applied to in-situ corrosion protection treatment of steel surfaces. Patent CN105420735A discloses a super-hydrophobic fluorosilane composite film. By adjusting fluorosilane including tridecafluorooctyltriethoxysilane, heptadecafluorodecyltriethoxysilane and 4-methyltridecafluorodecyltriethoxysilane, a super-hydrophobic layer is prepared, and a hydrophobic corrosion-resistant film is formed on the surface of bronze cultural relics. However, it does not utilize HFPO acyl fluoride by-products, and cannot achieve the goal of resource utilization of by-products.

[0005] Therefore, it is a key problem to be solved in the current industry to develop a composite film preparation method that can not only realize the high-value utilization of HFPO acyl fluoride by-products, but also provide efficient and environmentally friendly corrosion protection for steel materials. SUMMARY

[0006] The present application aims to solve the problems of low utilization rate of HFPO acyl fluoride by-products, poor environmental friendliness and limited application scenarios of existing steel corrosion prevention methods, and provides a method for preparing a corrosion-resistant composite film using acyl fluoride by-products, which realizes the resource utilization and high value of HFPO by-products, and at the same time prepares an environmentally friendly, corrosion-resistant composite film with excellent corrosion resistance and suitable for steel materials, meeting the demand for steel corrosion prevention in the fields of building, automobile and major equipment manufacturing.

[0007] To solve the above technical problems, the technical scheme adopted by the present application is to provide a method for preparing a corrosion-resistant composite film using acyl fluoride by-products, comprising the following steps: (1) Film forming agent preparation: the acyl fluoride by-products generated in the oxidation of hexafluoropropylene to perfluoropropanol are stirred uniformly in an organic solvent, and the long-chain acyl fluoride by-products settled at the bottom are removed by standing and liquid separation, and the clear liquid containing short-chain acyl fluoride by-products is retained; an acid-binding agent is added to the clear liquid, and stirring is carried out until complete dissolution, to obtain a film forming agent; (2) Steel surface functionalization: the pretreated steel is immersed in a polyacrylic acid-ethanol-water mixed solution for 5-10 min, taken out, washed and dried, and a polyacrylic acid film is self-assembled on the surface of the steel; (3) Composite film preparation: the steel with the polyacrylic acid film grown in step (2) is immersed in the film forming agent of step (1) for 5-10 min, and the short-chain acyl fluoride by-products are self-assembled on the surface of the polyacrylic acid film to form a modified corrosion-resistant composite film on the surface of the steel, which is then taken out and dried with hot air; (4) Curing: the steel treated in step (3) is placed in an oven for high-temperature curing, and then naturally cooled, to form a corrosion-resistant composite film on the surface of the steel material.

[0008] The present application utilizes the acyl fluoride by-products generated in the oxidation of hexafluoropropylene to perfluoropropanol for resource utilization, realizes the conversion of "industrial waste" to "high-value corrosion-resistant materials", reduces waste discharge and environmental protection treatment costs, saves raw material costs, and is consistent with the concepts of circular economy and green manufacturing. Through the double-layer structure of the polyacrylic acid film and the self-assembled film of short-chain acyl fluoride by-products, the polyacrylic acid film provides a good adhesion substrate for the upper layer, and the film layer formed by the short-chain acyl fluoride by-products has weather resistance and structural stability, effectively blocking the contact between the corrosion medium and the surface of the steel, so that the composite film can serve stably in a humid and corrosive environment for a long time, significantly improving the electrochemical corrosion resistance of the steel, and effectively prolonging the service life of the steel material.

[0009] As a further description of the above technical solution: the non-polar organic solvent in step (1) is at least one of n-hexane, n-pentane, n-heptane, or cyclohexane. The above non-polar solvent can dissolve short-chain acyl fluoride byproducts well, while long-chain acyl fluoride byproducts will settle to the bottom due to poor solubility. Through a simple static separation operation, long-chain impurities can be easily separated and removed, which not only ensures the purity of the effective short-chain components in the film-forming agent, but also simplifies the impurity separation process, providing a high-purity raw material basis for the subsequent preparation of uniform and corrosion-resistant composite membranes, and improving the efficiency and accuracy of high-value utilization of acyl fluoride byproducts; moreover, the chemical properties of this type of solvent are stable and do not react with acyl fluoride byproducts or acid-binding agents, and can completely retain the active groups of short-chain acyl fluoride byproducts, ensuring the reaction efficiency of subsequent self-assembly with polyacrylic acid membranes.

[0010] As a further description of the above technical solution: In the clarifying liquid of step (1), the volume fraction of perfluoroacyl fluoride byproduct is 1-10%. This can prevent the concentration of perfluoroacyl fluoride byproduct from being too high, which would cause the perfluoroacyl fluoride molecules to aggregate excessively during the subsequent self-assembly process, resulting in pores and cracks in the composite film and preventing the formation of a dense corrosion barrier layer. It can also avoid the situation where the concentration is too low, resulting in insufficient active ingredients and incomplete film coverage, exposing the steel surface to the corrosive medium and losing the anti-corrosion effect.

[0011] As a further description of the above technical solution: In the clarifying liquid described in step (1), the volume fraction of the acid-binding agent is 1-10%, which matches the volume fraction of the perfluoroacyl fluoride byproducts of 1-10% in the clarifying liquid. This can just neutralize the acidic components that may be generated by the acyl fluoride substances in the subsequent reaction. This avoids the acid residue caused by insufficient use of the acid-binding agent (residual acid will damage the steel substrate or weaken the adhesion of the polyacrylic acid film), and also prevents excessive use from causing the film-forming agent system to become too alkaline (excessive alkali may reduce the activity of the acyl fluoride byproducts, or even generate impurities that affect the purity of the film layer), thus ensuring the chemical stability of the film-forming agent. At the same time, this concentration also allows the acid-binding agent to play its role without interfering with the dissolution state of the acyl fluoride byproducts, maintaining the uniformity of the film-forming agent system and laying the foundation for the subsequent self-assembly with the polyacrylic acid film to form a dense composite layer.

[0012] As a further description of the above technical solution: the acid-binding agent is selected from triethylamine, N,N-diisopropylethylamine, or pyridine. All three are weakly basic organic amines, which can gently and efficiently neutralize the acidic substances that may be generated by perfluoroacyl fluoride byproducts in subsequent reactions, avoiding acid residues that corrode the steel substrate or damage the adhesion of the polyacrylic film. At the same time, it will not cause excessive reactions of acyl fluoride byproducts (such as hydrolysis or isomerization) due to excessive alkalinity, and will completely retain its active groups that can self-assemble with the polyacrylic film, ensuring the structural integrity of the composite film. Moreover, its chemical properties are stable. Under subsequent high-temperature curing, it will either remain stable without decomposition or decompose into easily volatile small molecules (such as amines and water), without leaving impurities in the film layer, thus avoiding the formation of corrosive media penetration channels.

[0013] As a further description of the above technical solution: In the polyacrylic acid-ethanol-water mixture in step (2), the mass percentage concentration of polyacrylic acid is 2%~2.5%, and the volume ratio of ethanol to water is 5:2. The concentration of polyacrylic acid is preferably 2.4%, which can avoid the film layer being too thin and the adhesion being weak due to the low concentration (unable to provide a stable substrate for the subsequent fluoride film), and also prevent the solution from becoming viscous and easily agglomerated during self-assembly due to the high concentration (forming pores and affecting the anti-corrosion effect). It can form a base film with uniform thickness and dense structure on the steel surface. The polyacrylic acid uses a mixture of ethanol and water as solvent. Ethanol can improve the solubility of polyacrylic acid and avoid its precipitation and stratification. Water can adjust the polarity so that the polyacrylic acid molecules can be more easily arranged and self-assembled on the steel surface, which can significantly enhance the adhesion between the base film and the steel substrate (reducing the risk of subsequent film layer peeling).

[0014] As a further description of the above technical solution: the pretreatment in step (2) refers to the process of sequentially subjecting the steel to ultrasonic degreasing with alkaline solution, rinsing with deionized water, soaking in anhydrous ethanol, and then air-drying. The alkaline solution can decompose the grease and dirt on the surface of the steel through saponification reaction, and the ultrasonic vibration can penetrate into the tiny crevices on the surface of the steel to remove stubborn oil residue; the subsequent rinsing with deionized water can accurately remove residual alkaline solution, avoiding side reactions between the alkali and polyacrylic acid that damage the film layer; the soaking in anhydrous ethanol can quickly dehydrate and further remove trace impurities, ultimately making the surface of the steel reach a state of "no oil, no residue, dry and clean", which greatly reduces the interfacial resistance between the polyacrylic acid film and the substrate, making it easier for polyacrylic acid molecules to combine through chemical bonds or physical adsorption, reducing the risk of subsequent film layer peeling and wrinkling, laying the foundation for the stable adhesion of the upper acrylic acid by-product film, and indirectly improving the overall corrosion resistance and durability of the composite film.

[0015] As a further description of the above technical solution: the air temperature of the hot air drying in step (3) is 40-60℃, which will not cause the newly self-assembled acyl fluoride by-product film or polyacrylic acid film to soften, deform or decompose due to excessive temperature (avoiding damage to the film structure and the generation of pores), nor will it cause the residual solvent and moisture on the film surface to be difficult to evaporate due to excessive temperature, thus preventing the formation of bubbles due to the evaporation of residual substances during subsequent curing and ensuring the compactness of the composite film.

[0016] As a further description of the above technical solution: the high-temperature curing temperature in step (4) is 110-150℃, and the time is 20-60 min. This can avoid the incomplete cross-linking of polyacrylic acid and short-chain acrylic fluoride by-product membrane caused by low temperature (weak film adhesion, easy to fall off, and unable to form an effective anti-corrosion barrier), and also prevent high temperature from damaging the structure of fluorine-containing groups or causing polyacrylic acid chain segment decomposition (avoiding the formation of pores and embrittlement of the film layer, affecting its ability to block corrosive media), thus laying the foundation for the compactness of the composite membrane.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention directly uses acyl fluoride byproducts from the HFPO production process as the core raw material to prepare a film-forming agent, transforming "industrial waste" into high-value steel corrosion-resistant materials. This reduces resource waste while lowering environmental treatment costs, aligning with the concept of a circular economy. The prepared coated 40Cr steel sheets were verified by the copper sulfate drop test according to GB / T 3824-1999, with a drop duration of 298–426 seconds. Electrochemical testing showed that the corrosion current of the coated 40Cr steel sheets was significantly reduced (corrosion current density from 2.951 × 10⁻⁶ ppm). Reduced to 1× The charge transfer resistance was significantly improved (Rct from 6.38). Increased to 12.50 It can effectively inhibit the electrochemical corrosion of steel; the preparation process does not require polluting processes such as chromating and phosphating, and the solvents and acid-binding agents used are easy to handle; the film layer is compatible with mainstream industrial steel materials such as 40Cr steel, and can be promoted to multiple fields such as construction, automobiles, and heavy equipment, solving the problem of the narrow application scenarios of existing fluorine-based anti-corrosion technologies; the preparation process parameters are easy to control, and no complex equipment is required, which facilitates large-scale production. Attached Figure Description

[0018] Figure 1 This is a comparison image of a bare 40Cr steel sheet (A) and a coated 40Cr steel sheet (B) from Example 1 under a super depth-of-field microscope.

[0019] Figure 2 These are the surface Fourier transform infrared spectra of bare 40Cr steel sheets and the coated 40Cr steel sheets of Example 1.

[0020] Figure 3These are the polarization curves of bare 40Cr steel sheet and the coated 40Cr steel sheet of Example 1.

[0021] Figure 4 The Nyquist spectrum is obtained by fitting the bare 40Cr steel sheet with the coated 40Cr steel sheet of Example 1.

[0022] Figure 5 The Bode amplitude spectrum is obtained by fitting the bare 40Cr steel sheet and the coated 40Cr steel sheet of Example 1.

[0023] Figure 6 The Bode phase spectrum is obtained by fitting the bare 40Cr steel sheet with the coated 40Cr steel sheet of Example 1. Detailed Implementation

[0024] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The embodiments given are only for explaining the present invention and do not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of protection of the claims of the present invention are still within the scope of protection of the claims of the present invention.

[0025] Example 1 This embodiment provides a method for preparing a corrosion-resistant composite film using acyl fluoride byproducts, including the following steps: (1) Preparation of film-forming agent: Add 4 mL of HFPO acyl fluoride byproduct and 100 mL of n-hexane to a 250 mL beaker and stir thoroughly at 150 rpm; after standing and separating the layers, use a separatory funnel to separate and remove the long-chain acyl fluoride byproduct that has settled at the bottom. Add 1 mL of triethylamine acid-binding agent to the retained upper clear liquid (containing short-chain acyl fluoride byproduct) and stir until completely dissolved to obtain the film-forming agent; (2) Preparation of polyacrylic acid-ethanol-water mixture: Take 3 mL of polyacrylic acid aqueous solution (average molecular weight ~3000, mass percentage concentration 50%) and add dropwise 70 mL of ethanol-water mixture. : A polyacrylic acid-ethanol-water mixture (2.4% by mass) was prepared by stirring a 20:50 mixture of solvents. (3) Steel sheet pretreatment: The 40Cr steel sheet (specification 50 mm × 50 mm × 2 mm) is ultrasonically degreased with 10% sodium hydroxide solution for 30 min, rinsed with deionized water 3 times, soaked in anhydrous ethanol for 10 min, and then dried for later use. (4) Functionalization of steel surface: The pretreated 40Cr steel sheet was placed in a polyacrylic acid-ethanol-water mixture for self-assembly. After 5 min, it was taken out and rinsed twice with clean water. It was then dried at 60℃ for 10 min to form a polyacrylic acid film on the steel surface, resulting in a bluish polyacrylic acid film steel sheet. It was then immersed in a film-forming agent and self-assembled at 25℃ for 5 min to form short-chain acrylic fluoride byproducts on the surface of the polyacrylic acid film, forming a modified corrosion-resistant composite film on the steel surface. After removal, it was dried with hot air (air temperature 50℃). (5) Curing: Place the 40Cr steel sheet treated in step (4) in a 120℃ oven for curing for 30 minutes, and then let it cool naturally to room temperature to form a corrosion-resistant composite film on the surface of the 40Cr steel sheet.

[0026] The comparison images of bare 40Cr steel sheets and the coated 40Cr steel sheets prepared in this embodiment under a super depth-of-field microscope show that the surface of the bare 40Cr steel sheet (A) is rough, with obvious scratches and oil residue; the surface of the coated 40Cr steel sheet (B) is uniformly covered with a bluish composite film, without pores or agglomerates, and the film layer is tightly bonded to the substrate, such as... Figure 1 As shown, this demonstrates the excellent uniformity of the composite film formation. FT-IR spectrum ( Figure 2 The results also show that the bare 40Cr steel sheet lacks characteristic peaks of organic functional groups, indicating that there is no polymer film layer on its surface; the polyacrylic acid film shows a peak at 1058.3. The presence of a CO bond stretching vibration peak (corresponding to the ester / ether bond structure of polyacrylic acid) at this point proves that the polyacrylic acid film successfully self-assembled onto the steel sheet surface; the coated 40Cr steel sheet retains the characteristic peak of the polyacrylic acid CO bond (1046.5). Based on the above, a new bending vibration peak (e.g., 853.5) for fluorine-containing groups (CF) is added. 692.2 This demonstrates that the composite film, with its two-layer structure of "polyacrylic acid base film (containing CO functional groups) + acyl fluoride byproduct composite film (containing CF functional groups)," was successfully deposited on the steel sheet surface, providing direct compositional evidence for the subsequent improvement of corrosion resistance.

[0027] Performance testing: Copper sulfate drop test: The copper sulfate drop test was conducted according to GB / T 3824-1999, with a drop duration of 426s, indicating that the composite film can effectively delay the corrosion of the steel sheet.

[0028] Polarization curve test: its polarization curve ( Figure 3 The corrosion potential and electrochemical parameters (Table 1) of the bare 40Cr steel sheet are -0.60V and 2.951× 10⁻⁶V, respectively. The corrosion potential of the coated 40Cr steel sheet shifted positively to -0.54V, and the corrosion current density decreased to 1× This indicates that the composite film can significantly improve the corrosion resistance dynamic barrier of 40Cr steel sheets and slow down the electrochemical corrosion rate.

[0029] Table 1 Electrochemical parameters fitted to polarization curves

[0030] Electrochemical impedance spectroscopy (EIS) analysis: Nyquist spectra of bare 40Cr steel sheet and coated 40Cr steel sheet after fitting ( Figure 4 The impedance fitting parameters (Table 2) show that the impedance semicircle radius of the coated 40Cr steel sheet is much larger than that of the bare 40Cr steel sheet, and its charge transfer resistance... From bare 40Cr steel sheet 6.38 Increased to 12.5 And the added film resistance 215 This demonstrates that the composite membrane can effectively block corrosive media and improve the corrosion resistance of the system; Bode amplitude spectrum ( Figure 5 The results show that the coated 40Cr steel sheet performs well in the high-frequency region ( ~ The impedance modulus (Hz) is significantly higher than that of bare 40Cr steel sheet, indicating that the film layer has excellent insulation and protection capabilities; Bode phase spectrum (Hz) Figure 6 In the study, the peak phase angle of the coated 40Cr steel sheet increased from about 30° to over 50°, and the phase angle plateau was wider, indicating that the composite film can effectively inhibit the charge transfer reaction on the steel sheet surface, further confirming its anti-corrosion performance.

[0031] Table 2. Electrochemical parameters fitted to impedance curves.

[0032] Example 2 This embodiment provides a method for preparing a corrosion-resistant composite film using acyl fluoride byproducts, including the following steps: (1) Preparation of film-forming agent: Add 1 mL of HFPO acyl fluoride byproduct and 100 mL of n-pentane to a 250 mL beaker, stir for 5 min and let stand, and use a separatory funnel to separate and remove the long carbon chain acyl fluoride byproduct that has settled at the bottom; add 1 mL of N,N-diisopropylethylamine to the retained upper clear liquid (containing short chain acyl fluoride byproduct), stir until completely dissolved, and the film-forming agent is obtained; (2) Preparation of polyacrylic acid-ethanol-water mixture: Same as in Example 1; (3) Steel sheet pretreatment: Same as in Example 1; (4) Functionalization of steel surface: The pretreated 40Cr steel sheet was placed in a polyacrylic acid-ethanol-water mixture for self-assembly. After 7 min, it was taken out and rinsed twice with clean water. It was then dried at 60℃ for 10 min to form a polyacrylic acid film on the steel surface, resulting in a bluish polyacrylic acid film steel sheet. It was then immersed in a film-forming agent and self-assembled at 25℃ for 10 min to form a modified corrosion-resistant composite film on the surface of the polyacrylic acid film. After removal, it was dried with hot air (air temperature 60℃). (5) Curing: Place the 40Cr steel sheet treated in step (4) in an oven at 130℃ for 40 minutes and let it cool naturally to room temperature to form a corrosion-resistant composite film on the surface of the 40Cr steel sheet.

[0033] A copper sulfate drop test was conducted according to GB / T 3824-1999, with a drop duration of 328 seconds. The corrosion retardation effect was better than that of bare 40Cr steel sheets, indicating that the composite film can effectively delay the corrosion of steel sheets.

[0034] Example 3 This embodiment provides a method for preparing a corrosion-resistant composite film using acyl fluoride byproducts, including the following steps: (1) Preparation of film-forming agent: Add 2 mL of HFPO acyl fluoride byproduct and 100 mL of n-heptane to a 250 mL beaker, and stir thoroughly at 50 rpm. Let stand, and use a separatory funnel to separate and remove the long-chain acyl fluoride byproduct that has settled at the bottom. Add 5 mL of triethylamine to the retained upper clear liquid (containing short-chain acyl fluoride byproduct), and stir until completely dissolved to obtain the film-forming agent. (2) Preparation of polyacrylic acid-ethanol-water mixture: Same as in Example 1; (3) Steel sheet pretreatment: Same as in Example 1; (4) Functionalization of steel surface: The pretreated 40Cr steel sheet was placed in a polyacrylic acid-ethanol-water mixture for self-assembly. After 10 min, it was taken out and rinsed twice with clean water. It was then dried at 60℃ for 10 min to form a polyacrylic acid film on the steel surface, resulting in a bluish polyacrylic acid film steel sheet. It was then immersed in a film-forming agent and self-assembled at 25℃ for 8 min to form short-chain acrylic fluoride byproducts on the surface of the polyacrylic acid film, forming a modified corrosion-resistant composite film on the steel surface. After removal, it was dried with hot air (air temperature 45℃). (5) Curing: Place the 40Cr steel sheet treated in step (4) in an oven at 110℃ for 60 minutes and let it cool naturally to room temperature to form a corrosion-resistant composite film on the surface of the 40Cr steel sheet.

[0035] The copper sulfate drop test was performed according to GB / T 3824-1999, with a drop duration of 298 seconds.

[0036] Example 4 This embodiment provides a method for preparing a corrosion-resistant composite film using acyl fluoride byproducts, including the following steps: (1) Preparation of film-forming agent: Add 5 mL of HFPO acyl fluoride byproduct and 100 mL of n-hexane to a 250 mL beaker, and stir thoroughly at 250 rpm. After standing, use a separatory funnel to separate and remove the long-chain acyl fluoride byproduct that has settled at the bottom. Add 5 mL of triethylamine to the remaining clear upper layer (containing short-chain acyl fluoride byproduct) and stir until completely dissolved to obtain the film-forming agent. (2) Preparation of polyacrylic acid-ethanol-water mixture: Same as in Example 1; (3) Steel sheet pretreatment: Same as in Example 1; (4) Functionalization of steel surface: The pretreated 40Cr steel sheet was placed in a polyacrylic acid-ethanol-water mixture for self-assembly. After 6 minutes, it was taken out and rinsed twice with clean water. It was then dried at 60°C for 10 minutes to form a polyacrylic acid film on the steel surface, resulting in a bluish polyacrylic acid film steel sheet. It was then immersed in a film-forming agent and self-assembled at 25°C for 9 minutes to self-assemble the short-chain acrylic fluoride byproducts onto the polyacrylic acid film surface, forming a modified corrosion-resistant composite film on the steel surface. After removal, it was dried with hot air (air temperature 40°C). (5) Curing: Place the 40Cr steel sheet treated in step (4) in an oven at 150℃ for 20 minutes and let it cool naturally to room temperature to form a corrosion-resistant composite film on the surface of the 40Cr steel sheet.

[0037] The copper sulfate drop test was performed according to GB / T 3824-1999, with a drop duration of 354 seconds.

[0038] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the present invention.

Claims

1. A method for preparing a corrosion-resistant composite film using acyl fluoride byproducts, characterized in that, The method comprises the following steps: (1) Film forming agent preparation: the acyl fluoride by-product generated by the oxidation of hexafluoropropylene oxide into perfluoroepoxy propane is stirred uniformly in a non-polar organic solvent, and the long carbon chain acyl fluoride by-product settled at the bottom is removed by standing and separating, and the clear liquid containing the perfluoroacyl fluoride by-product is retained; an acid binding agent is added to the clear liquid, and stirring is performed until complete dissolution, thereby obtaining a film forming agent; (2) Steel surface functionalization: the pretreated steel is soaked in a polyacrylic acid-ethanol-water mixed solution for 5-10 min, and then taken out, washed and dried, so as to form a polyacrylic acid film on the surface of the steel by self-assembly; (3) Composite film preparation: the steel with the polyacrylic acid film grown in step (2) is soaked in the film forming agent of step (1) for 5-10 min, so as to form a modified corrosion-resistant composite film on the surface of the steel, and the steel is taken out and dried by hot air; (4) Curing: the steel treated in step (3) is placed in an oven for high-temperature curing, and then naturally cooled, so as to form a corrosion-resistant composite film on the surface of the steel.

2. The method for preparing a corrosion resistant composite film using acyl fluoride by-products according to claim 1, characterized by: The non-polar organic solvent in step (1) is at least one of n-hexane, n-pentane, n-heptane or cyclohexane.

3. The method for preparing a corrosion-resistant composite film using an acyl fluoride by-product according to claim 1 or 2, characterized by: The volume fraction of the perfluoroacyl fluoride by-product in the clear liquid in step (1) is 1-10%.

4. The method for making a corrosion resistant composite film using acyl fluoride byproducts according to claim 3, characterized in that: The volume fraction of the acid binding agent in the clear liquid in step (1) is 1-10%.

5. The method for making a corrosion resistant composite film using acyl fluoride byproducts according to claim 4, wherein: The acid binding agent is selected from triethylamine, N,N-diisopropyl ethylamine or pyridine.

6. The method for making a corrosion resistant composite film using acyl fluoride byproducts according to claim 1, wherein: The mass percentage concentration of polyacrylic acid in the polyacrylic acid-ethanol-water mixed solution in step (2) is 2%-2.5%, and the volume ratio of ethanol to water is 5:

2.

7. The method for making a corrosion resistant composite film using acyl fluoride byproducts according to claim 1, wherein: The pretreatment in step (2) refers to that the steel is sequentially subjected to ultrasonic oil removal with alkali, rinsing with deionized water, soaking in anhydrous ethanol and then naturally air-drying.

8. The method for making a corrosion resistant composite film using acyl fluoride byproducts according to claim 1, wherein: The air temperature for the hot air drying in step (3) is 40-60°C.

9. The method for making a corrosion resistant composite film using acyl fluoride byproducts according to claim 1, wherein: The temperature for the high-temperature curing in step (4) is 110-150°C, and the time is 20-60 min.

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