Modified hydrotalcite enhanced soluble polytetrafluoroethylene anticorrosive paint and coating preparation method thereof

Abstract

The invention discloses a modified hydrotalcite enhanced soluble polytetrafluoroethylene anticorrosive paint and a coating preparation method thereof, relates to the field of metal surface protection, and solves the technical problems that the interface compatibility of hydrotalcite and soluble polytetrafluoroethylene is poor, and the additive amount of hydrotalcite is limited, so that the barrier corrosion resistance of the coating is poor. According to the invention, hydrotalcite is modified by a specific anionic surfactant, and the modified hydrotalcite is compounded with soluble polytetrafluoroethylene in proportion to prepare the anticorrosive paint; the surface of a metal base material is coated with the paint through electrostatic spraying, and the anticorrosive coating is obtained through high-temperature thermocuring. The interface compatibility of the hydrotalcite and the soluble polytetrafluoroethylene is greatly improved, the high adding amount of the hydrotalcite is achieved, the coating structure is complete, the barrier property of the coating is synergistically enhanced through the effect of the modified hydrotalcite structure and hydroxyl, the process is controllable and suitable for industrial production, and the coating can meet the metal protection requirement in the severe corrosion environment.

Description

Technical Field

[0001] This invention relates to the field of metal surface protection, and in particular to a modified hydrotalcite-reinforced soluble polytetrafluoroethylene anticorrosive coating and its preparation method. Background Technology

[0002] Metallic materials, due to their excellent mechanical properties, are widely used in numerous industrial fields such as petrochemicals, marine engineering, transportation, and construction, serving as core basic materials in industrial production and engineering construction. However, in natural and industrial environments, metallic materials are highly susceptible to corrosion through chemical or electrochemical reactions with media such as water, oxygen, acids, alkalis, and salts. This corrosion not only causes damage to the metallic materials themselves and substantial economic losses but can also lead to serious safety accidents such as equipment failure and structural collapse. Therefore, developing efficient and long-lasting metal corrosion protection technologies and materials has become a critical technical problem urgently needing to be solved in the field of chemical corrosion protection.

[0003] Soluble polytetrafluoroethylene (PFA), as a high-performance fluoropolymer material, exhibits outstanding chemical stability due to the presence of numerous carbon-fluorine bonds with bond energies as high as 485.6 kJ / mol, making it a commonly used base material in the field of anti-corrosion coatings. However, due to the high electronegativity of fluorine atoms, adjacent fluorine atoms in the soluble PFA molecule repel each other to maintain the lowest system energy, resulting in a helical molecular structure. This structure creates numerous pores, which become pathways for corrosive substances such as water and oxygen to penetrate. Consequently, pure soluble PFA coatings have poor physical barrier properties, allowing corrosive substances to easily permeate the coating and contact the metal substrate, significantly reducing their anti-corrosion effect and making it difficult to meet the long-term anti-corrosion requirements of harsh corrosive environments.

[0004] To improve the barrier properties of soluble polytetrafluoroethylene (PTFE) coatings, existing technologies attempt to modify them by adding nanofillers. While using three-dimensional nanoparticles as fillers can extend the transport path of corrosive substances to some extent, the barrier effect is limited and cannot fundamentally solve the problem of pore permeation in soluble PTFE. In contrast, hydrotalcite (LDHs), as an inorganic intercalated functional material with a multi-layered lamellar structure, exhibits excellent barrier potential as a two-dimensional filler. Its lamellar structure allows corrosive substances to form a "zigzag path" during permeation, significantly extending the permeation distance (e.g., ...). Figure 1 As shown in the figure, the abundant hydroxyl groups on the surface of the hydrotalcite nanosheets can form hydrogen bonds with the permeating substances, thereby capturing water molecules. Furthermore, the hydrogen bond network can occupy the voids in the soluble polytetrafluoroethylene coating, inhibiting the free movement of polymer chains and reducing the free volume of the membrane, thus synergistically enhancing the barrier properties of the coating from multiple aspects.

[0005] However, hydrotalcite is an inorganic material, and there is a serious interfacial compatibility problem between it and organic soluble polytetrafluoroethylene (PTFE). This has become a core technical bottleneck restricting the application of hydrotalcite in soluble PTFE anticorrosive coatings. In existing technologies, the maximum addition amount of hydrotalcite to soluble PTFE is only 1%, ensuring the integrity of the coating structure and preventing cracking and powdering. This low addition amount cannot fully utilize the two-dimensional barrier advantages of hydrotalcite, resulting in minimal improvement in the coating's barrier performance. Blindly increasing the addition amount of hydrotalcite can lead to defects such as cracking and peeling due to poor compatibility, thus losing its anticorrosive effect. To address this technical bottleneck, no effective solution has yet been found in this field, making it impossible to achieve a balance between high hydrotalcite addition and the integrity of the soluble PTFE coating. Therefore, there is an urgent need to develop an anticorrosive coating and preparation process that can improve the interfacial compatibility between hydrotalcite and soluble PTFE, achieving high hydrotalcite addition while ensuring coating integrity, in order to enhance the barrier performance and long-term anticorrosive capability of the soluble PTFE coating. Summary of the Invention

[0006] The purpose of this invention is to provide a modified hydrotalcite-reinforced soluble polytetrafluoroethylene anticorrosive coating and its preparation method, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is to provide a modified hydrotalcite-reinforced soluble polytetrafluoroethylene anticorrosive coating, comprising surfactant-modified hydrotalcite and soluble polytetrafluoroethylene; wherein the mass of the surfactant-modified hydrotalcite is 0.1-5% of the mass of the soluble polytetrafluoroethylene; The surfactant is at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, lithium dodecyl sulfate, ammonium dodecyl sulfate, and sodium lauryl ether sulfate.

[0008] The present invention selects surfactants with sulfate or sulfonate groups at the hydrophilic end for the following main reasons: First, the anti-corrosion coating of the present invention requires subsequent high-temperature thermosetting treatment at around 350°C. Sulfate and sulfonate groups themselves can maintain structural stability under this high-temperature condition and will not decompose or change their properties due to high temperature, thus ensuring the modification effect. Second, these groups have suitable molecular sizes. If surfactants with carboxyl groups, such as sodium stearate, are selected, their group size is too large, which will produce obvious steric hindrance and cannot effectively achieve the interfacial connection between hydrotalcite (LDH) and soluble polytetrafluoroethylene (PFA). Third, the surface of the hydrotalcite layer is positively charged. Only anionic surfactants can effectively combine with hydrotalcite through electrostatic interaction, thereby modifying the hydrotalcite and connecting PFA, thus improving the interfacial compatibility between the two.

[0009] Furthermore, the mass of the surfactant-modified hydrotalcite is 4% of the mass of the soluble polytetrafluoroethylene.

[0010] Furthermore, the hydrotalcite is one of magnesium aluminum hydrotalcite, cobalt aluminum hydrotalcite, calcium aluminum hydrotalcite, and zinc aluminum hydrotalcite.

[0011] The second technical solution of the present invention provides a method for preparing the above-mentioned modified hydrotalcite-reinforced soluble polytetrafluoroethylene anticorrosive coating, comprising the following steps: Hydrotalcite and surfactant are mixed in water and reacted at 50-90℃ for 12-24 hours. After the reaction is completed, the mixture is dried to obtain surfactant-modified hydrotalcite. The drying temperature is 40-80℃ and the drying time is 12-24 hours.

[0012] The surfactant-modified hydrotalcite and soluble polytetrafluoroethylene are mixed in an organic solvent, and then dried to remove the solvent, thereby obtaining the modified hydrotalcite-reinforced soluble polytetrafluoroethylene anti-corrosion coating.

[0013] Furthermore, the mass ratio of hydrotalcite to surfactant is 1.2:1 to 5:1, preferably 2:1.

[0014] Furthermore, the organic solvent is anhydrous ethanol.

[0015] The third technical solution of this invention provides a method for preparing a modified hydrotalcite-reinforced soluble polytetrafluoroethylene anti-corrosion coating, comprising the following steps: A modified hydrotalcite-reinforced soluble polytetrafluoroethylene (PTFE) anti-corrosion coating was applied to the surface of a metal substrate using electrostatic spraying. After thermosetting and cooling, a modified hydrotalcite-reinforced soluble PTFE anti-corrosion coating was obtained.

[0016] Furthermore, the thermosetting temperature is 365~375℃, and the time is 0.2~5h.

[0017] Furthermore, the parameters for the electrostatic spraying are: voltage 90~100kV, current 70~80μA. The distance between the spray gun and the metal substrate is preferably 10~15cm.

[0018] The layers of hydrotalcite (LDHs) are primarily composed of metal hydroxides, exhibiting significant amphoteric characteristics and high sensitivity to acidic and alkaline environments. Modification with conventional acidic modifiers (such as some organic acids) easily causes the dissolution of metal ions from the layers, triggering an "acid etching" phenomenon that ultimately leads to the collapse of the hydrotalcite crystal structure. Conversely, strongly alkaline environments cause aluminum ions in the layers to be removed as aluminate ions. The two-dimensional barrier function of hydrotalcite is highly correlated with its layer structure; once the layer structure is damaged, its barrier effect as a two-dimensional material immediately fails.

[0019] The "agglomeration" of inorganic fillers in polymer matrices is a fatal factor in the failure of anti-corrosion coatings. In a soluble polytetrafluoroethylene (PFA) matrix, unmodified hydrotalcite, when added at a concentration exceeding 1%, will agglomerate and generate microcracks. These microcracks become channels for the rapid penetration of corrosive media, resulting in a loss of anti-corrosion barrier effect (as shown in Comparative Example 1). To achieve a high addition amount of hydrotalcite in a PFA matrix while ensuring a crack-free coating with structural integrity, the key lies in eliminating the interfacial compatibility barrier between inorganic hydrotalcite and organic PFA.

[0020] This invention fundamentally solves this problem by modifying hydrotalcite with a specific surfactant. The mechanism of action is as follows: the surfactant has both hydrophilic and organic groups, which can act as a connecting bridge between inorganic hydrotalcite and organic PFA, effectively inhibiting the aggregation of hydrotalcite in the PFA matrix and eliminating interfacial defects between the two. Under the premise of high addition amount, the modified hydrotalcite can be uniformly dispersed in the PFA matrix and act as a "physical cross-linking point" in the system, which not only ensures the compactness of the coating structure, but also gives full play to the two-dimensional barrier advantage of hydrotalcite.

[0021] The fourth technical solution of the present invention provides a modified hydrotalcite-reinforced soluble polytetrafluoroethylene anti-corrosion coating prepared by the above preparation method.

[0022] The two-dimensional sheet-like structure of the modified hydrotalcite of this invention forms a tortuous penetration path in the coating. The hydrogen bond network formed by the surface hydroxyl groups and the penetrating substances can also fill the coating pores and reduce the free volume. The two work together to enhance the barrier performance of the coating. The water vapor transmission rate and oxygen transmission rate of the 4% modified hydrotalcite composite coating are significantly reduced, showing excellent ability to block corrosive media.

[0023] The present invention discloses the following technical effects: This invention effectively solves the technical problem of poor interfacial compatibility between inorganic hydrotalcite and organic polytetrafluoroethylene. By using specific surfactants to directionally modify hydrotalcite, the interfacial bonding force between the two is greatly improved. Even when the amount of hydrotalcite added is increased to 4%, the coating surface can still be smooth and dense, without defects such as cracking or powdering. The coating is tightly bonded to the metal substrate and has good adhesion.

[0024] The process parameters of this invention are controllable, the raw materials are conventional chemical materials, and it is suitable for the industrial production requirements of dry powder electrostatic spraying and high temperature curing. The prepared composite coating takes into account both structural integrity and long-term corrosion resistance, and can meet the use requirements of harsh corrosive environments such as petrochemicals and marine engineering, and has extremely high practical application value. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic diagram comparing the barrier mechanisms of corrosive media under different filler systems.

[0027] Figure 2 The image shows the EDX elemental analysis of the modified magnesium-aluminum hydrotalcite obtained in Example 1.

[0028] Figure 3 The infrared (IR) spectrum (a) and X-ray diffraction (XRD) spectrum (b) of magnesium aluminum hydrotalcite and modified magnesium aluminum hydrotalcite in Example 1 are shown.

[0029] Figure 4 The images show the physical specimen and scanning electron microscope (SEM) image of the 4% modified magnesium aluminum hydrotalcite-PFA composite coating prepared in Example 1.

[0030] Figure 5 The image shows a physical sample of the 4% unmodified magnesium aluminum hydrotalcite-PFA composite coating prepared for Comparative Example 1.

[0031] Figure 6 The graph shows the comparison of water vapor transmission rate (a) and oxygen transmission rate (b) of the coatings prepared in Examples 1, 2, 4, 5, 6 and Comparative Example 2.

[0032] Figure 7 The surface contact angle test diagrams for magnesium aluminum hydrotalcite, modified magnesium aluminum hydrotalcite, PFA, and the 4% modified magnesium aluminum hydrotalcite-PFA composite coating in Example 1 are shown.

[0033] Figure 8 This is a photograph of the coating prepared for Comparative Example 3.

[0034] Figure 9 Bode plot (phase angle-frequency) of composite anti-corrosion coating.

[0035] Figure 10 Bode plot (impedance modulus-frequency) of composite anti-corrosion coating. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0042] Hydrotalcite (LDHs) is an inorganic intercalated functional material with a multilayered lamellar structure. Its chemical formula can be represented as follows: In the formula M 2+ It is a divalent metal cation (such as Mg) 2+ Zn 2+ Co 2+ Ni 2+ M 3+ It is a trivalent metal cation (such as Al) 3+ ,Cr 3+ ,Fe 3+ ); x represents the surface charge, which has a significant impact on the performance of LDHs; m is the number of water molecules between layers, A n- It is anion between layers (such as CO3). 2- Cl - NO 3- ).

[0043] In this invention, the hydrotalcite is one of magnesium aluminum hydrotalcite, cobalt aluminum hydrotalcite, calcium aluminum hydrotalcite, and zinc aluminum hydrotalcite; the ratio of divalent metal ions to trivalent metal ions is 1~5:1.

[0044] In the following embodiments of the present invention, hydrotalcite is synthesized by urea-assisted hydrothermal method, modified by a specific surfactant, and then added to soluble polytetrafluoroethylene powder (PFA). The nanofiller method is used, with hydrotalcite as a filler. The surfactant modification improves the interfacial compatibility between hydrotalcite and soluble polytetrafluoroethylene, thereby increasing the amount of hydrotalcite that can be added and improving the barrier ability of the composite coating.

[0045] The preferred method for preparing modified hydrotalcite is to include the following steps: adding 0.1-3 g of hydrotalcite powder to 50-150 mL of deionized water, followed by adding 0.05-1.5 g of surfactant, stirring and heating at 50-90 °C for 12-24 h, and drying in an oven at 40-80 °C for 12-24 h to obtain modified hydrotalcite.

[0046] The present invention will be further described in detail below with reference to specific embodiments: Example 1: Preparation of 4% Modified Magnesium Aluminum Hydrotalcite-PFA Composite Anti-corrosion Coating (1) Preparation of magnesium aluminum hydrotalcite: Magnesium-aluminum hydrotalcite with a divalent to trivalent metal ion molar ratio of 2:1 was used as the preparation material. 100 mL of deionized water was added to a beaker, followed by 4.22 g of magnesium carbonate, 6.04 g of aluminum chloride hexahydrate, and then 15.02 g of urea. The mixture was stirred thoroughly with a magnetic stirrer until homogeneous. The mixture was transferred to a polytetrafluoroethylene-lined stainless steel high-temperature reactor, sealed, and placed in an oven for hydrothermal reaction at 110℃ for 24 h. After the reaction, the product was washed with deionized water by centrifugation until the filtrate pH reached 7. It was then dried in a 60℃ oven for 12 h, and finally ground into a fine magnesium-aluminum hydrotalcite powder (Mg-Al(CO3)2). 2- LDHs), for backup.

[0047] (2) Modification of magnesium aluminum hydrotalcite: Add 100 mL of deionized water to a beaker, weigh 1 g of the magnesium aluminum hydrotalcite powder prepared above and 0.5 g of sodium dodecyl sulfate (SDS) into it, stir and disperse, then place the beaker in a 70 ℃ constant temperature water bath and stir and heat for 12 h. After the reaction is complete, centrifuge and wash the product until there is no surfactant residue in the filtrate to obtain white powdered modified magnesium aluminum hydrotalcite (SDS@LDHs), which is then dried in a 60 ℃ oven for 12 h for later use.

[0048] (3) Preparation of modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Weigh 25 g of soluble polytetrafluoroethylene (PFA) powder and 1 g of modified magnesium aluminum hydrotalcite powder prepared in step (2) (the mass of modified magnesium aluminum hydrotalcite is 4% of the mass of PFA powder), and add them together to a container containing 50 mL of anhydrous ethanol. Stir thoroughly for 12 h to ensure uniform dispersion. Transfer the dispersion to a 60 ℃ oven and dry for 12 h until the anhydrous ethanol is completely evaporated to obtain dried modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating powder (SDS@LDHs / PFA) for later use.

[0049] (4) Preparation of modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Metal steel plates were selected as the substrate. The surface of the steel plates was first ground to remove rust until fresh metal surfaces were exposed. Then, the plates were repeatedly wiped clean with alcohol swabs and placed in a ventilated place to dry. The composite anti-corrosion coating powder was sprayed onto the treated steel plate surface using electrostatic spraying. The spraying parameters were: voltage 90kV, current 75μA, and distance between the spray gun and the metal plate surface 12cm. The sprayed steel plates were then transferred to a muffle furnace and heated to 370℃ at a heating rate of 4℃ / min. The temperature was maintained for 4 hours and then naturally cooled to room temperature to cure and form a modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating.

[0050] Figure 2 The image shows the EDX diagram of the modified magnesium aluminum hydrotalcite obtained in Example 1, which can intuitively reflect the elemental composition and distribution of the modified hydrotalcite and verify the successful grafting of surfactant onto the surface of hydrotalcite. Figure 3 In the image, (a) shows the IR spectrum of magnesium aluminum hydrotalcite and modified magnesium aluminum hydrotalcite from Example 1, and (b) shows the XRD pattern of magnesium aluminum hydrotalcite and modified magnesium aluminum hydrotalcite from Example 1. The structural changes of hydrotalcite before and after modification can be clearly seen, which confirms that the surfactant modification did not destroy the layered structure of hydrotalcite, thus laying the foundation for its barrier properties.

[0051] Example 2: Preparation of 2% Modified Magnesium Aluminum Hydrotalcite-PFA Composite Anti-corrosion Coating (1)-(2) Same as Example 1; (3) Preparation of modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Weigh 25 g of soluble polytetrafluoroethylene (PFA) powder and 0.5 g of modified magnesium aluminum hydrotalcite powder (the mass of modified magnesium aluminum hydrotalcite is 2% of the mass of PFA powder), and add them together to a container containing 50 mL of anhydrous ethanol. Stir thoroughly for 12 h to ensure uniform dispersion. Transfer the dispersion to a 60 ℃ oven and dry for 12 h until the anhydrous ethanol is completely evaporated to obtain dried modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating powder for later use.

[0052] (4) Preparation of modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Metal steel plates were selected as the substrate. The surface of the steel plates was first ground to remove rust until fresh metal surfaces were exposed. Then, the plates were repeatedly wiped clean with alcohol swabs and placed in a ventilated place to dry. The composite anti-corrosion coating powder was sprayed onto the treated steel plate surface using electrostatic spraying. The spraying parameters were: voltage 95kV, current 80μA, and distance between the spray gun and the metal plate surface 13cm. The sprayed steel plates were then transferred to a muffle furnace and heated to 370℃ at a heating rate of 4℃ / min. The temperature was maintained for 4 hours and then naturally cooled to room temperature to cure and form a modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating.

[0053] Example 3: Preparation of 2% Modified Magnesium Aluminum Hydrotalcite-PFA Composite Anti-corrosion Coating (1) Same as Example 1; (2) Modification of magnesium aluminum hydrotalcite: Add 100 mL of deionized water to a beaker, weigh 1 g of the magnesium aluminum hydrotalcite powder prepared above and 0.5 g of sodium dodecyl sulfonate into it, stir and disperse, then place the beaker in a 70 ℃ constant temperature water bath and stir and heat for 12 h. After the reaction is complete, centrifuge and wash the product until there is no surfactant residue in the filtrate to obtain white powdered modified magnesium aluminum hydrotalcite (SDS@LDHs), which is then dried in a 60 ℃ oven for 12 h for later use.

[0054] (3) Preparation of modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Weigh 25 g of soluble polytetrafluoroethylene (PFA) powder and 0.5 g of modified magnesium aluminum hydrotalcite powder (the mass of modified magnesium aluminum hydrotalcite is 2% of the mass of PFA powder), and add them together to a container containing 50 mL of anhydrous ethanol. Stir thoroughly for 12 h to ensure uniform dispersion. Transfer the dispersion to a 60 ℃ oven and dry for 12 h until the anhydrous ethanol is completely evaporated to obtain dried modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating powder for later use.

[0055] (4) Preparation of modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Metal steel plates were selected as the substrate. The surface of the steel plates was first ground to remove rust until fresh metal surfaces were exposed. Then, the plates were repeatedly wiped clean with alcohol swabs and placed in a ventilated place to dry. The composite anti-corrosion coating powder was sprayed onto the treated steel plate surface using electrostatic spraying. The spraying parameters were: voltage 95kV, current 80μA, and distance between the spray gun and the metal plate surface 13cm. The sprayed steel plates were then transferred to a muffle furnace and heated to 370℃ at a heating rate of 4℃ / min. The temperature was maintained for 4 hours and then naturally cooled to room temperature to cure and form a modified magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating.

[0056] Example 4 The only difference from Example 1 is that the mass of the modified magnesium aluminum hydrotalcite is 1% of the mass of the PFA powder, that is, the mass of the modified magnesium aluminum hydrotalcite powder is 0.25g.

[0057] Example 5 The only difference from Example 1 is that the mass of the modified magnesium aluminum hydrotalcite is 3% of the mass of the PFA powder, that is, the mass of the modified magnesium aluminum hydrotalcite powder is 0.75g.

[0058] Example 6 The only difference from Example 1 is that the mass of the modified magnesium aluminum hydrotalcite is 5% of the mass of the PFA powder. That is, the mass of the modified magnesium aluminum hydrotalcite powder is 1.25g.

[0059] Comparative Example 1: Preparation of 4% Unmodified Magnesium Aluminum Hydrotalcite-PFA Composite Coating (1) Same as Example 1; (2) Preparation of magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Weigh 25g of soluble polytetrafluoroethylene (PFA) powder and 1g of magnesium aluminum hydrotalcite powder prepared in step (1) (the mass of magnesium aluminum hydrotalcite is 4% of the mass of PFA powder), and add them together to a container containing 50 mL of anhydrous ethanol. Stir thoroughly for 12 h to ensure uniform dispersion. Transfer the dispersion to a 60℃ oven and dry for 12 h until the anhydrous ethanol is completely evaporated to obtain dried magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating powder for later use.

[0060] (3) Preparation of magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Metal steel plates were selected as the substrate. The surface of the steel plates was first polished to remove rust until fresh metal surfaces were exposed. Then, the plates were repeatedly wiped clean with alcohol swabs and placed in a ventilated place to dry. The composite anti-corrosion coating powder was sprayed onto the treated steel plate surface using electrostatic spraying. The spraying parameters were: voltage 90kV, current 75μA, and distance between the spray gun and the metal plate surface 12cm. The sprayed steel plates were then transferred to a muffle furnace and heated to 370℃ at a heating rate of 4℃ / min. The temperature was maintained for 4 hours and then naturally cooled to room temperature to cure and form a magnesium-aluminum hydrotalcite-PFA composite anti-corrosion coating.

[0061] Comparative Example 2: Preparation of Pure PFA Coating (1) Pretreatment of pure PFA coating: Weigh 25.00 g of PFA spray powder and dry it in a 60 ℃ oven for 12 h to remove the adsorbed moisture from the powder, and obtain dry pure PFA anti-corrosion coating powder for later use.

[0062] (2) Preparation of pure PFA anti-corrosion coating: Metal steel plates were selected as the substrate. The surface of the steel plates was first polished to remove rust until the fresh metal surface was exposed. Then, the plates were repeatedly wiped clean with alcohol cotton and placed in a ventilated place to dry. The pure PFA anti-corrosion coating powder was sprayed onto the treated steel plate surface using electrostatic spraying. The spraying parameters were: voltage 90kV, current 75μA, and distance between the spray gun and the metal plate surface 12cm. The sprayed steel plates were then transferred to a muffle furnace and heated to 370℃ at a heating rate of 4℃ / min. The temperature was maintained for 4 hours and then allowed to cool naturally to room temperature to cure and form a pure PFA anti-corrosion coating.

[0063] Comparative Example 3: Preparation of Sodium Stearate Modified Magnesium Aluminum Hydrotalcite-PFA Composite Coating (1) Same as Example 1; (2) Modification of magnesium aluminum hydrotalcite: Add 100 mL of deionized water to a beaker, weigh 1 g of the magnesium aluminum hydrotalcite powder prepared above and 0.5 g of sodium stearate into it, stir and disperse, then place the beaker in a 70 ℃ constant temperature water bath and stir and heat for 12 h. After the reaction is complete, centrifuge and wash the product until there is no surfactant residue in the filtrate to obtain white powdered modified magnesium aluminum hydrotalcite, which is then dried in a 60 ℃ oven for 12 h for later use.

[0064] (3) Preparation of magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Weigh 25g of soluble polytetrafluoroethylene (PFA) powder and 1g of magnesium aluminum hydrotalcite powder prepared in step (1) (the mass of magnesium aluminum hydrotalcite is 4% of the mass of PFA powder), and add them together to a container containing 50 mL of anhydrous ethanol. Stir thoroughly for 12 h to ensure uniform dispersion. Transfer the dispersion to a 60℃ oven and dry for 12 h until the anhydrous ethanol is completely evaporated to obtain dried magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating powder for later use.

[0065] (4) Preparation of magnesium aluminum hydrotalcite-PFA composite anti-corrosion coating: Metal steel plates were selected as the substrate. The surface of the steel plates was first polished to remove rust until fresh metal surfaces were exposed. Then, the plates were repeatedly wiped clean with alcohol swabs and placed in a ventilated place to dry. The composite anti-corrosion coating powder was sprayed onto the treated steel plate surface using electrostatic spraying. The spraying parameters were: voltage 90kV, current 75μA, and distance between the spray gun and the metal plate surface 12cm. The sprayed steel plates were then transferred to a muffle furnace and heated to 370℃ at a heating rate of 4℃ / min. The temperature was maintained for 4 hours and then naturally cooled to room temperature to cure and form a magnesium-aluminum hydrotalcite-PFA composite anti-corrosion coating.

[0066] Result: A complete coating could not be obtained.

[0067] Figure 8 This is a photograph of the coating prepared for Comparative Example 3.

[0068] Effect Verification 1: Coating Appearance and Structural Integrity The coatings prepared in Examples 1, 2, 1, and 2 were tested and verified for their appearance, structural integrity, and barrier properties (water vapor transmission rate and oxygen transmission rate). The effects of hydrotalcite modification treatment and the amount of modified hydrotalcite added on the overall performance of the coatings were compared. The specific verification results are as follows: The composite anti-corrosion coatings prepared in Example 1 (4% modified magnesium aluminum hydrotalcite-PFA composite coating) and Example 2 (2% modified magnesium aluminum hydrotalcite-PFA composite coating) both exhibit a smooth and dense surface, free from structural defects such as cracking, powdering, and peeling. The coatings are tightly bonded to the metal substrate and have good adhesion, fully meeting the basic structural requirements of anti-corrosion coatings. Figure 4 The images shown are physical photos and SEM images of the coating obtained in Example 1, which allow for a direct observation of its smooth surface and dense structure.

[0069] Comparative Example 1 (4% unmodified magnesium aluminum hydrotalcite-PFA composite coating) had poor interfacial compatibility between hydrotalcite and PFA because the hydrotalcite was not modified with surfactant. The prepared coating showed obvious cracking and powdering, and the coating structure was completely incomplete. It could not form an effective anti-corrosion protective layer and lost its basic anti-corrosion function. Figure 5 The image shows a physical sample of the coating prepared in Comparative Example 1, clearly showing the cracking and powdering defects of the coating.

[0070] Although the surface of Comparative Example 2 (pure PFA coating) was generally smooth and without obvious cracks or peeling, there were a large number of pores at the microscopic level. These pores became channels for the penetration of corrosive substances such as water and oxygen, which in turn led to the subsequent contact of corrosive substances with the metal substrate.

[0071] Example 2: Barrier Performance of the Coating Barrier performance is the core performance characteristic of anti-corrosion coatings. The coating's ability to block corrosive media is evaluated by testing two key indicators: water vapor transmission rate and oxygen transmission rate. Figure 6 The graph shows a comparison of water vapor transmission rate and oxygen transmission rate for different composite anti-corrosion coatings. The test results indicate that: The water vapor transmission rate of Example 1 was 1.073 g / m³. 2 The oxygen permeability over 24 hours was 6498.87 cm³ / (m²·24h·0.1Mpa), demonstrating excellent barrier properties; the water vapor permeability in Example 2 was 3.949 g / m³. 2 After 24 hours, the oxygen permeability was 9294.61 cm³ / (m²·24h·0.1Mpa), which showed better barrier performance than the pure PFA coating, but was significantly lower than that of Example 1. The pure PFA coating in Comparative Example 2 had significantly higher water vapor permeability and oxygen permeability than Examples 1 and 2, and its barrier performance was the worst among the four groups of samples, failing to effectively block the penetration of corrosive media.

[0072] Figure 7 The surface contact angle diagrams of the magnesium-aluminum hydrotalcite, modified magnesium-aluminum hydrotalcite, and composite coating in Example 1 show that the compatibility between the modified hydrotalcite and PFA is significantly improved, further confirming the effectiveness of the modification process.

[0073] Example 3: Electrochemical Corrosion Protection Test Using a saturated calomel electrode as the reference electrode and a platinum wire electrode as the counter electrode, a carbon steel sheet coated with a composite anti-corrosion coating was immersed in a 1 wt.% NaCl solution for electrochemical impedance spectroscopy testing, and the change of the AC impedance signal of the material over time was observed.

[0074] Figure 9 Bode plot (phase angle-frequency) of composite anti-corrosion coating; Figure 10 The Bode plot (impedance modulus-frequency) for the composite anti-corrosion coating clearly shows the relationship between impedance modulus, phase angle, and frequency. The second time constant in the phase angle plot of the pure PFA film is attributed to the electrochemical corrosion within the film.

[0075] With the addition of LDHs filler, the disappearance of the second phase angle diagram is clearly visible. This indicates that the corrosion resistance of the LDH-doped composite film in 1% NaCl solution is significantly enhanced. The low-frequency modulus value in the Bode plot can quantitatively measure the corrosion resistance performance of the film. Comparing the low-frequency modulus values ​​of the four films, it can be found that the composite film with 4% added hydrotalcite has the highest low-frequency modulus value, indicating that it has the best corrosion resistance performance in 1% NaCl solution.

[0076] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A modified hydrotalcite-reinforced soluble polytetrafluoroethylene anticorrosive coating, characterized in that, The mixture includes surfactant-modified hydrotalcite and soluble polytetrafluoroethylene; the mass of the surfactant-modified hydrotalcite is 0.1-5% of the mass of the soluble polytetrafluoroethylene. The surfactant is at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, lithium dodecyl sulfate, ammonium dodecyl sulfate, and sodium lauryl ether sulfate.

2. The modified hydrotalcite-reinforced soluble polytetrafluoroethylene anticorrosive coating according to claim 1, characterized in that, The mass of the surfactant-modified hydrotalcite is 4% of the mass of the soluble polytetrafluoroethylene.

3. The modified hydrotalcite-reinforced soluble polytetrafluoroethylene anticorrosive coating according to claim 1, characterized in that, The hydrotalcite is one of magnesium aluminum hydrotalcite, cobalt aluminum hydrotalcite, calcium aluminum hydrotalcite, and zinc aluminum hydrotalcite.

4. The method for preparing the modified hydrotalcite-reinforced soluble polytetrafluoroethylene anticorrosive coating as described in any one of claims 1-3, characterized in that, Includes the following steps: Hydrotalcite and surfactant were mixed in water and reacted at 50-90℃ for 12-24 hours. After the reaction was completed, the mixture was dried to obtain surfactant-modified hydrotalcite. The surfactant-modified hydrotalcite and soluble polytetrafluoroethylene are mixed in an organic solvent, and then dried to remove the solvent, thereby obtaining the modified hydrotalcite-reinforced soluble polytetrafluoroethylene anti-corrosion coating.

5. The preparation method according to claim 4, characterized in that, The organic solvent is anhydrous ethanol.

6. A method for preparing a modified hydrotalcite-reinforced soluble polytetrafluoroethylene anti-corrosion coating, characterized in that, Includes the following steps: The modified hydrotalcite-reinforced soluble polytetrafluoroethylene anti-corrosion coating of any one of claims 1-3 is sprayed onto the surface of a metal substrate by electrostatic spraying, followed by thermosetting and cooling to obtain the modified hydrotalcite-reinforced soluble polytetrafluoroethylene anti-corrosion coating.

7. The preparation method according to claim 6, characterized in that, The thermosetting temperature is 365~375℃, and the time is 0.2~5h.

8. The preparation method according to claim 6, characterized in that, The parameters for electrostatic spraying are: voltage 90~100kV, current 70~80μA.

9. The modified hydrotalcite-reinforced soluble polytetrafluoroethylene anti-corrosion coating prepared by the preparation method according to any one of claims 6-8.

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