Polyimide / polytetrafluoroethylene composite anticorrosive film containing self-repairing adhesive layer and preparation method thereof

Abstract

The application discloses a polyimide / polytetrafluoroethylene composite anticorrosive film containing a self-repairing adhesive layer and a preparation method thereof, and relates to a polyimide / polytetrafluoroethylene composite anticorrosive film and a preparation method thereof. In order to solve the problems that the existing PTFE anticorrosive layer is difficult to be firmly bonded with a base material, the adhesive layer is easily damaged by a corrosive medium, and the self-repairing capability is lacked, the anticorrosive film is composed of an adhesive layer 1, a supporting layer, an adhesive layer 2 and a surface layer which are sequentially stacked from inside to outside; the surface layer is a polytetrafluoroethylene film which is subjected to a single-side sodium naphthalene solution chemical etching treatment and has a thickness of 80-200 microns; the adhesive layer 1 and the adhesive layer 2 are both fluorine-containing self-repairing adhesives; the solid part of the fluorine-containing self-repairing adhesive includes an epoxy hard segment and a fluorine-containing polyurethane soft segment, wherein the mass ratio of the fluorine-containing polyurethane soft segment to the epoxy hard segment is 0.33-3:1, and a cross-linking network is formed through a reversible Diels-Alder reaction with a bismaleimide. The application belongs to the technical field of composite anticorrosive films and functional film materials.

Description

Technical Field

[0001] This invention relates to a polyimide / polytetrafluoroethylene composite anticorrosive film and its preparation method, belonging to the technical field of composite anticorrosive films and functional film materials. Background Technology

[0002] Polytetrafluoroethylene (PTFE) has extremely low surface energy, excellent chemical corrosion resistance and electrical insulation, and is a commonly used anti-corrosion material in the fields of chemical equipment lining and anti-stick coating. However, its non-polar, difficult-to-wet and difficult-to-adhere surface makes it difficult to bond firmly with metals or other polymers.

[0003] To improve the bonding strength between PTFE and adhesives, surface modification techniques are commonly used in industry, with chemical etching and plasma treatment containing sodium complexes being the most prevalent. Chemical sodium etching typically uses sodium-ammonia or sodium-naphthalene complex solutions, which can significantly reduce the F / C ratio of the PTFE surface and introduce polar functional groups such as hydroxyl and carbonyl groups, increasing the surface energy from approximately 16 mN / m to over 60 mN / m, thereby enabling it to form strong interfacial bonds with polar adhesives.

[0004] Polyimide film, with its excellent heat resistance, mechanical strength, and chemical stability, is widely used as a base film for flexible printed circuit boards, an electrical insulating layer, and a high-temperature structural material. Public information shows that polyimide film exhibits almost no dimensional change within a temperature range of -196℃ to 300℃, has high glass transition temperature and thermal decomposition temperature, and a tensile strength generally exceeding 100MPa. It also possesses good resistance to acids, alkalis, and organic solvents, making it ideal as a support layer material for demanding applications.

[0005] In the existing technology, there are literatures on directly bonding untreated PTFE with special adhesives to avoid the use of dangerous sodium etching solutions. However, such systems are mostly based on modified epoxy or fluororubber, and their corrosion resistance mainly depends on the inertness of the thick PTFE coating and the adhesive itself. They lack self-healing function, are sensitive to defects such as scratches and pinholes, and are prone to blistering and debonding along the interface after the corrosive medium penetrates.

[0006] On the other hand, the applicant has developed a fluorinated adhesive that combines corrosion resistance and self-healing properties. This adhesive is achieved by combining fluorinated polyurethane soft segments and epoxy hard segments, and introducing a reversible crosslinking structure of furan / bismaleimide. While maintaining excellent bond strength and flexibility, the adhesive layer can achieve self-healing at certain temperatures, significantly improving the reliability of the bonding interface in harsh media. However, this technology mainly focuses on the adhesive itself and has not yet been combined with membrane materials such as PTFE and polyimide to construct an overall composite anti-corrosion membrane structure.

[0007] Existing polyimide / fluoropolymer composite films are mostly used for electronic insulation or high-temperature conveyor belts. They are typically formed into an integral layered structure through melt co-extrusion or coating, which does not adequately consider secondary adhesion to metal substrates, corrosion protection, and self-healing synergistic design. Therefore, it is necessary to develop a polyimide / PTFE composite anti-corrosion film with a reasonable structure, simple construction, and strong interfacial adhesion, excellent corrosion resistance, and self-healing function for long-term protection of metal or plastic components. Summary of the Invention

[0008] To address the problems of existing PTFE anti-corrosion layers being difficult to firmly bond with the substrate, the adhesive layer being easily damaged by corrosive media, and lacking self-healing ability, this invention proposes a polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer and its preparation method.

[0009] The technical solution adopted by the present invention to solve the above problems is as follows: The polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer of the present invention is composed of an adhesive layer 1, a support layer, an adhesive layer 2 and a surface layer stacked sequentially from the inside to the outside; The surface layer is a polytetrafluoroethylene film chemically etched with sodium naphthalene solution on one side, with a thickness of 80-200μm; The support layer is a heat-resistant film with a thickness of 10-100μm; Both adhesive layer 1 and adhesive layer 2 are fluorinated self-healing adhesives. The solid part of the fluorinated self-healing adhesive includes epoxy hard segments and fluorinated polyurethane soft segments, wherein the mass ratio of fluorinated polyurethane soft segments to epoxy hard segments is 0.33-3:1, and furan groups are introduced into the molecular chain to form a cross-linked network through a reversible Diels-Alder reaction with bismaleimide.

[0010] Furthermore, the fluorinated polyurethane soft segment is a prepolymer obtained by reacting a fluorinated diol with a diisocyanate in the presence of a catalyst, and then reacting it with furfurylamine. The raw materials include, by molar amount, a fluorinated diol, a diisocyanate, and furfurylamine. The molar ratio of diisocyanate to fluorinated diol is 1-2:1, and the molar ratio of furfurylamine to diisocyanate is 0.5-1.2:1. Fluorinated diols are one or more of the following: perfluorooctyl-1,3-propanediol, perfluoropolyether diol, 2,2,3,3-tetrafluoro-1,4-butanediol, hydroxyl-terminated fluorinated diol FA800, and hydroxyl-terminated fluorinated diol LV80. Diisocyanate is at least one of alicyclic or aliphatic diisocyanates, such as hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

[0011] Furthermore, the epoxy hard segment is composed of a furanyl-containing epoxy prepolymer formed by the reaction of epoxy resin and furfurylamine; Epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin and fluorinated epoxy resin, with an epoxy value of 0.2-0.6 eq / 100g and a molar ratio of furfurylamine to epoxy groups of 0.4-1:1.

[0012] Furthermore, the molar ratio of bismaleimide to furan groups in the adhesive molecular chain in the fluorinated self-healing adhesive is 0.3-0.8:1.

[0013] Furthermore, the thickness of adhesive layer 1 is 5-50 μm, the thickness of adhesive layer 2 is 10-50 μm, and the mass fraction of fluorine element in adhesive layer 1 and adhesive layer 2 is 5-40%, and the total solid content is 30-70 wt%.

[0014] Furthermore, the support layer is a polyimide film with a glass transition temperature of not less than 250°C and a tensile strength of not less than 100 MPa.

[0015] Furthermore, the surface layer is a single-sided sodium naphthalene etched PTFE film, obtained by immersing in an ether or ether alcohol solvent containing sodium-naphthalene complex at 20-70℃ for 10-300s, followed by water washing, neutralization and drying. After etching, the F / C atomic ratio on the PTFE surface is reduced to below 0.2, and polar groups are introduced.

[0016] Furthermore, the adhesive layer 1 also contains 0.5-5 wt% organosilane coupling agent and rust-preventive pigment.

[0017] The steps of the method for preparing a polyimide / polytetrafluoroethylene composite anticorrosive film containing a self-healing adhesive layer according to the present invention include: Step 1: Immerse the PTFE film in sodium naphthalene etching solution at 20-70℃ for 10-300s, then wash with alcohol, wash with water, neutralize and dry to obtain a single-sided treated PTFE surface layer. Step 2: Prepare a fluorinated self-healing adhesive solution by mixing a fluorinated polyurethane prepolymer solution and an epoxy prepolymer solution at a mass ratio of 0.33-3:1, adding bismaleimide and necessary additives to form an adhesive coating solution. Step 3: The adhesive coating liquid is evenly coated on one side of the support layer, and the solvent is removed by drying at 60-90℃ to obtain adhesive layer 2. The adhesive layer 2 is then hot-pressed with the PTFE surface layer at 80-150℃ for 0.1-5MPa for 5-60min to form an intermediate composite film of PTFE / adhesive layer 2 / support layer. Step 4: Apply adhesive coating liquid to the other side of the support layer, and dry it to form adhesive layer 1, thus obtaining the composite anti-corrosion film.

[0018] Furthermore, in step 3, the hot pressing temperature is 100-140℃ and the time is 10-30 min, so that the bismaleimide and furan group undergo a Diels-Alder crosslinking reaction. The composite anti-corrosion film obtained in step 4 can be bonded to the substrate by secondary hot pressing at 80-130℃ to obtain an integral anti-corrosion structural component.

[0019] The beneficial effects of this invention are as follows: By treating PTFE with sodium naphthalene, the surface polarity and roughness are significantly improved, the F / C ratio is significantly reduced, and polar groups such as hydroxyl, carbonyl, and unsaturated carbon-carbon bonds are introduced. This greatly improves the wettability and chemical bonding of PTFE to polar fluorinated adhesives, creating a high-strength, corrosion-resistant interface between PTFE and adhesive layer 2. The polyimide support layer possesses high tensile strength, low coefficient of thermal expansion, and excellent heat and chemical resistance. It maintains dimensional stability under high temperature, thermal cycling, and mechanical loads, providing reliable mechanical support for the overall composite film and preventing creep, warping, and cracking of a single PTFE layer during use. The fluorinated self-healing adhesive undergoes reversible Diels-Alder crosslinking via furan / bismaleimide. Under conditions of 80-150℃, the polymer segments at scratches or microcracks reflow and re-crosslink under thermal excitation, thereby restoring the continuity and shielding performance of the adhesive layer and significantly extending its anti-corrosion life. The PTFE surface layer provides excellent chemical resistance and a low-friction surface; the polyimide layer provides mechanical strength and heat resistance; the fluorinated self-healing adhesive layer combines adhesion, flexibility, corrosion protection, and self-healing functions. The four layers work synergistically, enabling the composite membrane to maintain high peel and shear strength even after 96 hours of neutral salt spray, acid and alkali immersion, and organic solvent environments. Furthermore, after scratches, appropriate heat treatment can restore most of its strength. This composite membrane can be continuously produced in rolls in the factory. On-site application only requires hot-pressing the adhesive layer 1 with the pre-treated substrate at 80-130℃ to complete the anti-corrosion layer installation, avoiding on-site adhesive mixing and spraying. It is suitable for rapid anti-corrosion construction of large storage tanks, pipelines, and complex structural components. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a multi-layer composite anti-corrosion material structure; Figure 2 It is a SEM image of the debonded interface; Figure 2 (a) is the PTFE peeling area. Figure 2 (b) is the dividing line area. Figure 2 (c) is the adhesive body area, (d) is the element distribution image of the debonding interface, and (e) and (g) are the PTFE peeling areas; Figure 3 These are SEM images of the scratches and after repair; Figure 3 (a) and Figure 3 (c) SEM image of the damaged area of ​​the adhesive film after scratching. Figure 3 (b) SEM image of the damaged area after treatment at 130℃ for 30 min. Figure 3 (d) SEM image of the damaged area after treatment at 130℃ for 15 min. Detailed Implementation

[0021] A polyimide / polytetrafluoroethylene composite anticorrosive film with a self-healing adhesive layer, the anticorrosive film being composed of an adhesive layer 1, a support layer, an adhesive layer 2, and a surface layer arranged sequentially from the inside out. The surface layer is a polytetrafluoroethylene (PTFE) film chemically etched with a sodium naphthalene solution on one side. The substrate thickness of the PTFE film is 80-200 μm, preferably 120 μm. Only one side of the PTFE film is etched and modified with a sodium naphthalene complex to form a treated surface and an untreated surface, wherein the treated surface is used for bonding with the adhesive layer 2.

[0022] The support layer is disposed between adhesive layer 1 and adhesive layer 2, and serves to provide mechanical support and dimensional stability for the composite anti-corrosion film. The support layer is a film material with high strength and heat resistance, including but not limited to one or more composites of polyimide film, aramid film, polybenzimidazole film, non-melting aromatic polyamide paper, or metal foil. Preferably, the support layer is a polyimide film with a thickness of 10-100 μm, preferably 20-50 μm, a glass transition temperature of not less than 250°C, and a tensile strength of not less than 100 MPa, to ensure good mechanical properties and dimensional stability under high temperature and thermal cycling conditions.

[0023] The adhesive layer 1 is located on the side of the composite anti-corrosion film closest to the protected substrate and is used to bond the composite anti-corrosion film to the metal or plastic substrate. The adhesive layer 1 uses a self-healing fluorinated adhesive formulation. If necessary, coupling agents, rust-inhibiting pigments, etc., can be further introduced into this adhesive system to improve the interfacial adhesion and corrosion resistance with the substrate.

[0024] The adhesive layer 2 is located between the support layer and the surface layer, and is used to firmly bond the support layer to the PTFE surface layer treated with sodium naphthalene. The adhesive layer 2 also adopts a self-healing fluorinated adhesive formulation, and its chemical structure is basically the same as that of the adhesive layer 1. However, the solid content, viscosity and filler content can be appropriately adjusted according to the interfacial wettability and stress matching requirements with PTFE and support layer, so as to balance the interfacial bonding strength and the flexibility of the adhesive layer.

[0025] In some embodiments, adhesive layer 1 and adhesive layer 2 are both cured products of a fluorinated self-healing adhesive as claimed in the patent application. The solid portion of the fluorinated self-healing adhesive is composed of epoxy hard segments and fluorinated polyurethane soft segments, wherein the mass ratio of fluorinated polyurethane soft segments to epoxy hard segments is 0.33-3:1. The soft segment portion provides excellent resistance to media penetration and flexibility through the fluorinated polyurethane, while the hard segment portion provides high strength and heat resistance through the epoxy resin. The ratio of soft to hard segments can be adjusted according to the requirements of peel strength, shear strength, and self-healing efficiency in different application scenarios.

[0026] The fluorinated polyurethane soft segment is formed by polycondensation of a fluorinated diol and a diisocyanate, followed by a reaction with furfurylamine to introduce furan groups. Specifically, the fluorinated diol is selected from one or more of perfluorooctyl-1,3-propanediol, perfluoropolyether diol, 2,2,3,3-tetrafluoro-1,4-butanediol, self-developed hydroxyl-terminated fluorinated diols FA800 and LV80, with hydroxyl groups at both ends of the molecular chain and a hydroxyl value of 126 (FA800) or 155 (LV80). The diisocyanate is at least one of diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, or dicyclohexylmethane diisocyanate, preferably isophorone diisocyanate. The molar ratio of diisocyanate to fluorinated diol is 1-2:1. By controlling this ratio, the hardness and crosslinking density of the polyurethane segments can be adjusted, thereby achieving a reasonable balance between the strength and flexibility of the adhesive layer.

[0027] In some embodiments, in the step of synthesizing the fluorinated polyurethane prepolymer, one or more of methanol, isopropanol, tetrahydrofuran, N,N-dimethylformamide, or N,N-dimethylacetamide are used as solvents. The solvents are ultra-dry solvents or solvents treated with molecular sieves to remove water, and the amount used is 2-4 times the mass of the fluorinated diol. The catalyst is at least one of dibutyltin dilaurate, stannous chloride, or stannous octoate, and its addition amount is 0.05%-0.2% of the total mass of the fluorinated diol and diisocyanate; preferably, dibutyltin dilaurate is used as the catalyst alone, and the addition amount is 0.1%-0.15%. The isocyanate-terminated fluorinated polyurethane prepolymer is obtained by reacting at 60-80℃ under inert gas protection (such as nitrogen) for 3-6 hours. Then, furfurylamine is added dropwise at room temperature to react with the -NCO groups in the prepolymer. The molar ratio of furfurylamine to diisocyanate is 0.5-1.2:1, thereby introducing furan groups into the polyurethane chain segments to obtain a fluorinated polyurethane prepolymer solution containing furan groups.

[0028] The epoxy hard segment is composed of a furan-based epoxy prepolymer formed by the reaction of epoxy resin and furfurylamine. The epoxy resin is selected from one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and fluorinated epoxy resin, with an epoxy value of 0.2-0.6 eq / 100g, preferably epoxy resin E-51 (epoxy value approximately 0.51 eq / 100g). The epoxy resin solvent is also selected from one or more of methanol, isopropanol, tetrahydrofuran, N,N-dimethylformamide, or N,N-dimethylacetamide, preferably N,N-dimethylacetamide, and is used in an amount 2-4 times the mass of the epoxy resin to ensure its complete dissolution.

[0029] In preparing the epoxy prepolymer, the epoxy resin and solvent are first vacuum dried at 110°C to remove water, then cooled to room temperature under nitrogen protection. Furfurylamine is then added, and the temperature is raised to 70-90°C. The mixture is stirred for 6-10 hours to allow the active amino groups in the furfurylamine to undergo ring-opening addition to the epoxy groups, initially introducing furan groups. Subsequently, the system temperature is raised to 130-160°C, and the reaction continues for 4-8 hours. After the reaction is complete, the mixture is cooled to room temperature to obtain a furan-containing epoxy prepolymer solution. The molar ratio of furfurylamine to epoxy groups is controlled at 0.4-1:1, preferably 0.5-0.8:1, to introduce an appropriate amount of furan groups onto the epoxy molecular chain, balancing crosslinking activity and resin properties.

[0030] The above-mentioned fluorinated polyurethane prepolymer and epoxy prepolymer are mixed at a mass ratio of 0.33-3:1, and then a bismaleimide curing agent is added. The molar ratio of bismaleimide to furan groups in the mixture is 0.3-0.8:1, preferably 0.5:1. After the mixture is stirred evenly under nitrogen protection or other air-isolated conditions, it is coated onto the surface of a substrate and then heated, dried, and thermocured. This causes the furan groups and maleimide double bonds to undergo a Diels-Alder reaction, forming a three-dimensional cross-linked network containing reversible DA bonds, thereby obtaining a cured fluorinated self-healing adhesive with both high corrosion resistance and self-healing ability.

[0031] In some embodiments, the thickness of both adhesive layer 1 and adhesive layer 2 is 5-50 μm, with adhesive layer 1 being thinner to ensure stress matching with the metal or plastic substrate, typically 5-30 μm; adhesive layer 2 is preferably 10-50 μm thick to ensure the formation of a continuous and dense adhesive layer with the PTFE surface layer. The mass fraction of fluorine in the cured adhesive is 5-40%, and the total solid content is 30-70 wt%. By adjusting the fluorine and solid content, a balance can be achieved between corrosion resistance, application flowability, and curing shrinkage.

[0032] In some embodiments, 0.5-5 wt% of an organosilane coupling agent, such as aminopropyltriethoxysilane or epoxypropoxysilane, may be added to the adhesive layer 1 to improve the chemical bonding ability with the metal oxide layer or polar plastic surface; 0.5-15 wt% of an anti-rust pigment, such as zinc phosphate or zinc molybdate, may also be added to enhance the barrier ability of the interface area against chloride ions and acid and alkali media.

[0033] The single-sided sodium naphthalene treatment of the surface layer is accomplished by immersing the PTFE film in an ether or ether alcohol solvent containing a sodium-naphthalene complex. The solvent can be tetrahydrofuran, monoethylene glycol dimethyl ether, diethylene glycol dimethyl ether, or other commonly used low-boiling-point ether solvents. Specifically, the PTFE film is immersed at 20-70°C for 10-300 seconds, then removed and rinsed sequentially with alcohol solvents ethanol, isopropanol, and deionized water. Residual alkaline components are neutralized in a dilute acid solution, and finally dried at 50-80°C. After this treatment, the surface of the treated PTFE changes from white to light brown or dark brown, the surface F / C atomic ratio is significantly reduced, and polar functional groups such as hydroxyl, carbonyl, and carbon-carbon unsaturated bonds are introduced. Simultaneously, microscopic roughness and pores are formed, which facilitates the wetting, penetration, and mechanical intercalation of the adhesive, thereby significantly improving the bonding strength between PTFE and adhesive layer 2. The untreated surface retains the inherent low surface energy characteristics of PTFE and is used as an external anti-corrosion layer.

[0034] The present invention also provides a method for preparing the above-mentioned composite anticorrosive film, comprising at least the following steps: Step 1: Select a PTFE film with a thickness of 80-200 μm, immerse part or one side of it in a sodium-naphthalene complex solution, and maintain it at 20-70℃ for 10-300 s to allow the PTFE surface layer to undergo a reduction-defluorination reaction. After treatment, it is successively washed with alcohol, water, and acid to neutralize, and then dried with hot air or vacuum to obtain a PTFE surface layer with an etched layer on only one side.

[0035] Step Two: Following the aforementioned proportions and process conditions of fluorinated diol, diisocyanate, furfurylamine, epoxy resin, and bismaleimide, first prepare a furan-based fluorinated polyurethane prepolymer solution in a solvent, then prepare a furan-based epoxy prepolymer solution. Next, mix the two prepolymers at a mass ratio of 0.33-3:1, add bismaleimide and necessary coupling agents, rust-inhibiting pigments, leveling agents, defoamers, and other additives, and stir until homogeneous to obtain a suitable fluorinated self-healing adhesive coating liquid. Adjust the solvent dosage as needed to ensure the coating liquid viscosity is suitable for scraping, rolling, or extrusion coating processes.

[0036] Step 3: Spread the polyimide or other high-strength film support layer onto a flat substrate. Apply the fluorinated self-healing adhesive coating liquid evenly to one side using a scraper or roller coating method. Dry at 60-90℃ to remove most of the solvent and form an adhesive layer 2 with a thickness of 10-50μm. Then, align and laminate the PTFE surface layer treated with sodium naphthalene on one side with the treated side facing the adhesive layer 2 to the support layer. Hot press at 80-150℃ and 0.1-5MPa for 5-60 minutes to allow the adhesive layer 2 to fully flow, wet, cross-link, and cure with the PTFE treated surface, resulting in a three-layer composite structure of PTFE / adhesive layer 2 / support layer. Preferred hot pressing conditions are 100-140℃, 0.3-1MPa, and 10-30 minutes.

[0037] Step 4: In the above three-layer composite structure, a fluorine-containing self-healing adhesive coating liquid is applied again to the other side of the support layer, and dried at 60-90℃ to form an adhesive layer 1 with a thickness of 5-30μm, thereby obtaining a composite anti-corrosion film product consisting of adhesive layer 1 / support layer / adhesive layer 2 / PTFE surface layer from the inside out.

[0038] The present invention also provides an anti-corrosion structural component, which includes a metal or plastic substrate and the aforementioned composite anti-corrosion film bonded to its surface. The composite anti-corrosion film is bonded to the substrate surface via an adhesive layer 1, with the PTFE surface layer facing the corrosive medium environment, serving as an anti-corrosion layer for the exposed surface.

[0039] To obtain the aforementioned anti-corrosion structural component, the surface of the metal substrate is preferably subjected to sandblasting, shot blasting, or chemical roughening treatment, followed by degreasing, rust removal, and drying. If necessary, a thin primer or coupling agent can be applied to improve the interfacial stability between the adhesive layer 1 and the substrate. Then, the composite anti-corrosion film is laid on the pretreated substrate surface and hot-pressed at 80-130℃ and 0.1-1MPa for 10-60 minutes to soften and flow the adhesive layer 1, allowing it to fully impregnate the rough surface structure of the substrate under pressure. After cooling, a firmly bonded integral anti-corrosion layer is formed. For temperature-sensitive plastic substrates, the hot-pressing temperature can be appropriately reduced and the time extended, or an infrared / hot air heating method combined with pressure rollers can be used to complete the bonding.

[0040] The composite anti-corrosion membrane and its anti-corrosion structural components of this invention can be widely used in marine engineering equipment, chemical storage tanks and pipeline linings, surface protection of aerospace structural components, and insulating anti-corrosion layers for electronic devices. When corrosive media penetrate or mechanical scratches cause localized damage to the adhesive layer, appropriate heat preservation at 80-150℃ can trigger the breakage and recombination of reversible Diels-Alder bonds in furan-maleimide, causing the adhesive layer in the microcracked or scratched area to flow, heal, and re-crosslink, thereby achieving self-repair of the anti-corrosion layer and extending the service life of the overall anti-corrosion structural components.

[0041] Example Example 1 This embodiment discloses a method for preparing a polyimide / polytetrafluoroethylene composite anticorrosive film containing a self-healing adhesive layer, comprising the following steps: Step 1: Add 13.09 g of hydroxyl-terminated fluorinated diol LV80 to a four-necked flask, dry under vacuum at 110 °C for 2 h to remove water, and cool to 70 °C under nitrogen protection; add 30 mL of N,N-dimethylacetamide (DMAC) and 4.02 g of isophorone diisocyanate (IPDI), and add 0.03 g of dibutyltin dilaurate dropwise while stirring. React at 70 °C for 4 h to obtain a -NCO-terminated fluorinated polyurethane prepolymer solution; after cooling to room temperature, add 1.76 g of furfurylamine dropwise, and stir at room temperature for 12 h to obtain a furan-containing fluorinated polyurethane prepolymer solution.

[0042] Step 2: Take another 12.27g of E-51 epoxy resin, remove water under vacuum at 110℃ for 2h, cool to room temperature, add 30mL of N,N-dimethylacetamide and 3.34g of furfurylamine, react at 80℃ for 8h, and then reflux at 140℃ for 6h to obtain a furanyl epoxy prepolymer solution.

[0043] Step 3: Mix 2.5g of fluorinated polyurethane prepolymer solution with 5.6g of epoxy prepolymer solution, add 0.96g of bismaleimide, and stir for 60min to obtain a fluorinated self-healing adhesive coating liquid with a solid content of about 40wt%.

[0044] Step 4: Select a 120μm thick, untreated double-sided PTFE film and cut it into 300mm × 300mm sheets. Prepare a sodium-naphthalene / diethylene glycol dimethyl ether (DEGDME) complex solution under an inert atmosphere: dissolve metallic sodium in DEGDME, add an equimolar amount of naphthalene, and stir until the solution is a clear, dark green color. The concentration of metallic sodium in the resulting solution should be controlled at 0.4 mol / L. Completely immerse one side of the PTFE film in the above sodium-naphthalene complex solution, controlling the solution temperature at 50±2℃ for 60 seconds, while keeping the other side out of contact with the solution. After removing the film, immediately rinse thoroughly with anhydrous ethanol to remove residual complexes, then wash with deionized water until the pH of the washing solution is close to neutral. Immerse the film in a 1wt% dilute hydrochloric acid solution for 1 minute to neutralize any residual alkaline components, wash again with deionized water, and finally dry in a 60℃ hot air oven for 1 hour to obtain a PTFE film with only one side etched, the treated surface being light brown. Step 5: Select a 25μm thick polyimide (PI) film as the support layer, cut it to the same size as the PTFE film, wipe it with anhydrous ethanol to remove oil, and dry it at 60℃ for 30 minutes.

[0045] Step Six: Lay the PI film flat on a clean glass plate. Use a precision scraper to evenly coat one side of the PI film with self-healing fluorinated adhesive coating liquid A, adjusting the scraper gap to achieve a wet film thickness of approximately 40 μm. Place the coated PI film in an 80℃ hot air oven to dry for 1 hour, allowing the solvent to largely evaporate, resulting in an adhesive layer 2 with a dry film thickness of approximately 20 μm. After removing the dry film, stack the PTFE film treated with sodium naphthalene on one side with the PI film, ensuring the PTFE-treated side faces the adhesive layer 2, and align their edges. Place the stacked PTFE / adhesive layer 2 / PI assembly in a flatbed hot press, sandwiching PTFE release films on both sides. Set the hot pressing temperature to 120℃, the surface pressure to 0.5 MPa, and the holding time to 20 min. After hot pressing, slowly cool to below 50℃ while the pressure is not fully released, then remove the composite film to obtain a three-layer intermediate film with a structure of PTFE / adhesive layer 2 / PI.

[0046] Step 7: Flip the above three intermediate films so that the uncoated PI surface is facing up, and repeat the coating and drying operations to form an adhesive layer 1 with a dry film thickness of about 15μm on the other side of the PI, thus obtaining a four-layer composite anti-corrosion film 1 of adhesive layer 1 / PI / adhesive layer 2 / PTFE.

[0047] Step 8: Select Q235 carbon steel plate (100mm×25mm×2mm) as the metal substrate, and sandblast it with brown corundum until the surface roughness Ra is 3.0-5.0μm. Then wipe it with acetone to remove oil, and dry it at 60℃ for 30min for later use. Apply one side of the adhesive layer 1 of the composite anti-corrosion film 1 obtained in Example 1 to the surface of the pretreated steel plate, ensuring that there are no obvious bubbles and wrinkles. Place the coated steel plate in a flat plate hot press, with silicone pads and release film sandwiched on both sides. Set the hot pressing temperature to 110℃, the pressure to 0.5MPa, and hold the pressure for 30min. Then cool it to room temperature under pressure and take out the sample to obtain the metal substrate anti-corrosion structural component 1.

[0048] Example 2 This embodiment discloses a method for preparing a polyimide / polytetrafluoroethylene composite anticorrosive film containing a self-healing adhesive layer. LV80 in Example 1 is replaced with hydroxyl-terminated fluorinated diol FA800, and the amounts of diisocyanate, furfurylamine, and bismaleimide are adjusted according to stoichiometry to prepare a self-healing adhesive with high chain segment rigidity. The thickness of the polyimide support layer is selected as 50 μm, and the thicknesses of adhesive layers 1 and 2 are each approximately 20 μm. The remaining PTFE etching and lamination conditions are the same as in Example 1.

[0049] Example 3 This embodiment discloses a method for preparing a polyimide / polytetrafluoroethylene composite anticorrosive film containing a self-healing adhesive layer. Compared with Embodiments 1-2, this embodiment has a higher ratio of soft to hard segments, greater adhesive layer flexibility, and the composite anticorrosive film is bonded to a glass fiber reinforced polypropylene substrate. The specific steps are as follows: Step 1: Weigh 12.55g of FA800 into a four-necked flask, dry under vacuum at 110℃ for 2h, cool to 70℃ under nitrogen purging, and stir at 150r / min. Add 30mL of DMAc under continuous nitrogen protection and adjust the stirring speed to 300r / min. Add 3.13g of IPDI, followed by slowly adding 0.02g of dibutyltin dilaurate. Maintain the reaction at 70℃ for 4h, cool to room temperature, and obtain a fluorinated polyurethane prepolymer solution.

[0050] Step 2: Weigh 10.74g of E-51 epoxy resin into another four-necked flask, dry it under vacuum at 110℃ for 2 hours to remove water, then cool it to room temperature by purging with nitrogen. Add 30mL of DMAc to dissolve it, stirring at 150r / min. Add 2.93g of furfurylamine, heat to 80℃ and react for 8 hours, then heat to 140℃ and reflux for 6 hours. Cool to room temperature to obtain the epoxy prepolymer solution.

[0051] Step 3: Weigh 5.30g of fluorinated polyurethane prepolymer solution and 3.06g of epoxy prepolymer solution into a beaker, mix them evenly, add 0.69g of bismaleimide, and stir for 60min under nitrogen protection to obtain self-healing fluorinated adhesive coating solution C with high soft segment content.

[0052] Step 4: Following the procedure in Example 1, using a 120μm thick PTFE film as the substrate, immerse it in a sodium-naphthalene / DEGDME solution at 50℃ for 60s, followed by alcohol washing, water washing, acid washing, neutralization, and drying to obtain a single-sided etched PTFE film.

[0053] Step 5: Select a PI film with a thickness of 50 μm, cut it, wipe it with anhydrous ethanol, and dry it at 60℃ for 30 min. Apply adhesive coating solution C to one side of the PI film, with a wet film thickness of about 50 μm, and dry it in an oven at 80℃ for 1.5 h to obtain an adhesive layer 2 with a dry film thickness of about 25 μm. Stack a single-sided treated PTFE film with the above PI film, with the treated side facing the adhesive layer 2, and hot press it at 120℃ and 0.4 MPa for 25 min. After cooling, a PTFE / adhesive layer 2 / PI intermediate film is obtained. Turn the intermediate film over and apply adhesive coating solution C to the other side of the PI surface, with a wet film thickness of about 30 μm. Dry it in an oven at 80℃ for 1 h to obtain an adhesive layer 1 with a dry film thickness of about 15 μm, thus obtaining the composite anti-corrosion film 3.

[0054] Step Six: Select a glass fiber reinforced polypropylene (GF-PP) sheet (100mm×25mm×3mm) as the plastic substrate. Activate its surface for 30 seconds using corona discharge or flame treatment, then spray a very thin layer of isocyanate-based primer (HDI trimer solution) and let it stand at room temperature for 30 minutes. Attach one side of the adhesive layer 1 of the composite anti-corrosion film 3 to the surface of the pre-treated GF-PP sheet, place it in a hot press, set the hot pressing temperature to 100℃ and the pressure to 0.3MPa, hold the pressure for 20 minutes, and remove it after cooling to room temperature to obtain the plastic substrate anti-corrosion structural component 3, which will be used for subsequent testing.

[0055] Comparative Example 1 The example discloses a method for preparing a polyimide / polytetrafluoroethylene composite anticorrosive film containing a self-healing adhesive layer. The fluorinated diol is replaced with fluorine-free polypropylene glycol to obtain a fluorine-free self-healing adhesive. The amounts of diisocyanate, furfurylamine and bismaleimide are adjusted according to stoichiometry. The remaining PTFE etching and lamination conditions are the same as in Example 1.

[0056] Comparative Example 2 This comparative example uses the same self-healing fluorinated adhesive A and PI support layer as in Example 1, but the PTFE film is not treated with sodium naphthalene to investigate the effect of PTFE surface modification on adhesion and corrosion resistance.

[0057] Performance testing Shear strength testing was conducted according to GB / T 7124-2008, "Determination of Tensile Shear Strength of Adhesives (Rigid-Rigid Materials)". Sample dimensions: For metal substrate samples, 100mm × 25mm × 2mm steel plates were used, with an overlap length of 12.5mm between the two plates; the adhesive layer 1 of the composite anti-corrosion film was located within the overlap area, and samples were prepared under the hot-pressing conditions of each embodiment / comparative example; samples were placed at 23±2℃ and 50±5% relative humidity for 24 hours before testing; a tensile load was applied at a speed of 5mm / min on a universal testing machine, and the maximum tensile shear strength was recorded. Plastic substrate GF-PP samples were prepared using the same method, with identical overlap lengths, and tested under the same conditions.

[0058] The T-peel strength test was conducted according to the methodology outlined in GB / T 2792-2014, "Test Method for 180° Peel Strength of Pressure-Sensitive Adhesive Tapes". The composite anti-corrosion film was first hot-pressed onto the steel plate surface and cut into 150mm × 25mm strip specimens. Approximately 50mm of the unbonded portion of the composite film was left at the free end of the steel plate as the peeling end. Using a T-peel fixture on a universal testing machine, the film was peeled at a speed of 100mm / min, and the steady-state peel force was recorded and converted to N / 25mm.

[0059] The neutral salt spray test was conducted according to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The steel plate anti-corrosion structural components were sealed at the edges and placed in a neutral salt spray chamber; the salt solution concentration was 5wt% NaCl, pH was 6.5-7.2, and the test temperature was 35±2℃; the test times were 96h and 240h respectively. After the test, the coating surface and scratched areas were observed for blistering, corrosion, or peeling, and the peel strength and shear strength were retested. Plastic substrate samples underwent only a 96h neutral salt spray test to examine interfacial adhesion stability.

[0060] The self-healing test was conducted on the anti-corrosion structural components of the steel plate. A scratch instrument was used to scratch a 100 μm wide, penetrating the PTFE surface layer and cutting into the adhesive layer 2 along the length of the composite anti-corrosion film. The scratch length was 30 mm. Immediately after scratching, the sample was left to stand at 23℃ and 50% relative humidity for 2 hours, and the initial peel strength and scratch morphology were recorded. The sample was then placed in a 130℃ oven for 30 minutes, then transferred to 80℃ for 2 hours, and then cooled to room temperature. The scratch healing was observed using an optical microscope, and the T-type peel strength and shear strength were retested.

[0061] The test results are shown in the table below:

[0062] Test results show that sodium naphthalene-treated PTFE and fluorinated self-healing adhesives maintain high bond strength and interfacial stability in both the initial state and after salt spray treatment. The fluorinated soft segments significantly improve the corrosion resistance and compatibility with PTFE, while the bismaleimide-furan reversible crosslinking structure endows the adhesive with significant heat-triggered self-healing capabilities. In contrast, irreversible crosslinking adhesives and untreated PTFE systems exhibit virtually no self-healing behavior. By adjusting the ratio of fluorinated polyurethane soft segments to epoxy hard segments, a balance can be achieved between high bond strength and high flexibility, adapting to the corrosion protection requirements of different substrates such as metals and engineering plastics.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer, characterized in that, The anti-corrosion membrane is composed of an adhesive layer 1, a support layer, an adhesive layer 2, and a surface layer stacked sequentially from the inside out. The surface layer is a polytetrafluoroethylene film chemically etched with sodium naphthalene solution on one side, with a thickness of 80-200μm; The support layer is a heat-resistant film with a thickness of 10-100μm; Both adhesive layer 1 and adhesive layer 2 are fluorinated self-healing adhesives. The solid part of the fluorinated self-healing adhesive includes epoxy hard segments and fluorinated polyurethane soft segments, wherein the mass ratio of fluorinated polyurethane soft segments to epoxy hard segments is 0.33-3:1, and furan groups are introduced into the molecular chain to form a cross-linked network through a reversible Diels-Alder reaction with bismaleimide.

2. The polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer according to claim 1, characterized in that, Fluorinated polyurethane soft segments are prepolymers obtained by reacting fluorinated diols and diisocyanates in the presence of a catalyst, followed by a reaction with furfurylamine. The raw materials, by molar amount, include fluorinated diols, diisocyanates, and furfurylamine. The molar ratio of diisocyanate to fluorinated diol is 1-2:1, and the molar ratio of furfurylamine to diisocyanate is 0.5-1.2:

1. Fluorinated diols are one or more of the following: perfluorooctyl-1,3-propanediol, perfluoropolyether diol, 2,2,3,3-tetrafluoro-1,4-butanediol, hydroxyl-terminated fluorinated diol FA800, and hydroxyl-terminated fluorinated diol LV80. Diisocyanate is at least one of alicyclic or aliphatic diisocyanates, such as hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

3. The polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer according to claim 1, characterized in that, The epoxy hard segment is composed of a furanyl-containing epoxy prepolymer formed by the reaction of epoxy resin and furfurylamine. Epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin and fluorinated epoxy resin, with an epoxy value of 0.2-0.6 eq / 100g and a molar ratio of furfurylamine to epoxy groups of 0.4-1:

1.

4. The polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer according to claim 1, characterized in that, The molar ratio of bismaleimide to furan groups in the adhesive molecular chain in fluorinated self-healing adhesives is 0.3-0.8:

1.

5. The polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer according to claim 1, characterized in that, The thickness of adhesive layer 1 is 5-50 μm, the thickness of adhesive layer 2 is 10-50 μm, and the mass fraction of fluorine in adhesive layer 1 and adhesive layer 2 is 5-40%, and the total solid content is 30-70 wt%.

6. The polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer according to claim 1, characterized in that, The support layer is a polyimide film with a glass transition temperature of not less than 250℃ and a tensile strength of not less than 100 MPa.

7. The polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer according to claim 1, characterized in that, The surface layer is a single-sided sodium naphthalene etched PTFE film, obtained by immersing in ether or ether alcohol solvents containing sodium-naphthalene complexes at 20-70℃ for 10-300s, followed by water washing, neutralization and drying. After etching, the F / C atomic ratio on the PTFE surface is reduced to below 0.2, and polar groups are introduced.

8. The polyimide / polytetrafluoroethylene composite anti-corrosion film containing a self-healing adhesive layer according to claim 1, characterized in that, The adhesive layer 1 also contains 0.5-5 wt% organosilane coupling agent and rust-preventive pigment.

9. A method for preparing an anti-corrosion film according to any one of claims 1 to 8, characterized in that, The specific steps include: Step 1: Immerse the PTFE film in sodium naphthalene etching solution at 20-70℃ for 10-300s, then wash with alcohol, wash with water, neutralize and dry to obtain a single-sided treated PTFE surface layer; Step 2: Prepare a fluorinated self-healing adhesive solution by mixing a fluorinated polyurethane prepolymer solution and an epoxy prepolymer solution at a mass ratio of 0.33-3:1, adding bismaleimide and necessary additives to form an adhesive coating solution. Step 3: The adhesive coating liquid is evenly coated on one side of the support layer, and the solvent is removed by drying at 60-90℃ to obtain adhesive layer 2. The adhesive layer 2 is then hot-pressed with the PTFE surface layer at 80-150℃ for 0.1-5MPa for 5-60min to form an intermediate composite film of PTFE / adhesive layer 2 / support layer. Step 4: Apply adhesive coating liquid to the other side of the support layer, and dry it to form adhesive layer 1, thus obtaining the composite anti-corrosion film.

10. The method for preparing a polyimide / polytetrafluoroethylene composite anticorrosive film containing a self-healing adhesive layer according to claim 9, characterized in that, In step 3, the hot pressing temperature is 100-140℃ and the time is 10-30 min, so that the bismaleimide and furan group undergo the Diels-Alder crosslinking reaction; The composite anti-corrosion film obtained in step 4 can be bonded to the substrate by secondary hot pressing at 80-130℃ to obtain an integral anti-corrosion structural component.

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