Aviation sand corrosion and rain corrosion resistant polyurethane protective film and preparation method thereof
A polyurethane protective film for aviation is prepared by polymerizing cyclic carbonate-based perfluoromonomers and aminothiobisphenol monomers, and modified silica and functional cross-linking agents are introduced to form a cross-linked network. This solves the wear and corrosion problems of the polyurethane protective film under high-altitude and high-speed flight conditions and improves its anti-aging and sand and rain erosion resistance.
Patent Information
- Application Number
- CN202510928873.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-07
- Publication Date
- 2025-09-16
AI Technical Summary
Existing aviation polyurethane protective films are susceptible to sand erosion and rain erosion under high-altitude and high-speed flight conditions, causing wear and corrosion. They are also prone to powdering and yellowing under strong sunlight, resulting in performance degradation.
Polyurethane is prepared by polymerizing cyclic carbonate-based perfluoromonomers and aminothiobisphenol monomers, and a cross-linked network is formed by modified silica and functional cross-linking agents. Organic nickel complexes are combined to dissipate the excited state energy of photosensitive chromophores and improve anti-aging properties. Fluorine atoms and carbon-carbon double bonds are introduced to enhance hydrophobicity and cross-linking degree, and modified silica is added to improve wear resistance.
The impact resistance, abrasion resistance and rain erosion resistance of the polyurethane protective film are improved, the service life is extended and the risk of photodegradation is reduced.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of polymer materials, in particular to a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation and a preparation method thereof. Background Art
[0002] Dust erosion refers to the phenomenon of progressive wear on the surface of a material caused by loose dust particles flowing across the surface of the material within a certain speed and scale range. With the development of the aviation industry, the flight speed of aircraft has been increasing. Aircraft are susceptible to erosion by sand particles and scouring by rainwater under high-altitude and high-speed flight conditions, causing wear and corrosion to the aircraft surface. Organic membrane materials have easy plasticity and buffering effects. Using organic membrane materials to protect aircraft surfaces has been a research direction in recent years. Polyurethane is a new type of organic material between rubber and plastic. It has great softness and elasticity, good wear resistance and corrosion resistance, and is an ideal material for preparing aircraft protective films. However, during the service process, aircraft will be exposed to strong sunlight for a long time. The polyurethane film is prone to powdering and yellowing, resulting in a decrease in the performance of the polyurethane film. Therefore, it is necessary to develop an aviation-grade polyurethane protective film with excellent anti-aging properties and resistant to sand and rain erosion. Summary of the Invention
[0003] The purpose of the present invention is to provide a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation and a preparation method thereof, so as to solve the problems existing in the prior art.
[0004] In order to solve the above technical problems, the present invention provides the following technical solutions: A sand-erosion and rain-erosion-resistant polyurethane protective film for aviation, comprising: polyurethane prepared by polymerizing a cyclic carbonate-based perfluoromonomer and an aminothiobisphenol monomer; modified silica prepared by polymerizing and coating 1,1,3,3-tetramethyl-1,3-disiloxanediol and vinylphosphonyl chloride on the surface of silica; and uniformly mixing the polyurethane, a functionalized crosslinking agent, the modified silica, and nickel chloride hexahydrate, curing the mixture in a mold, and then demolding the mixture. The aminothiobisphenol monomer is prepared by reacting 2,2'-thiobis(4-chlorophenol) and diaminobutene; The cyclic carbonate-based perfluoromonomer is prepared by reacting 1,4-bis(2',3'-epoxypropyl)perfluorobutane and carbon dioxide; The functionalized cross-linking agent is prepared by diazotizing 4-mercaptoaniline and reacting the 4-mercaptoaniline with 6-mercapto-2-naphthol.
[0005] A method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation, comprising the following steps: (1) Adding a cyclic carbonate perfluoromonomer and an aminothiobisphenol monomer in a molar ratio of 1:1 to N,N-dimethylformamide (11 to 13 times the mass of the cyclic carbonate perfluoromonomer), and adding 1,5,7-triazabicyclo[4.4.0]dec-5-ene (0.03 to 0.05 times the mass of the cyclic carbonate perfluoromonomer), stirring at 138 to 142°C and 200 to 300 r / min for 24 to 25 hours under nitrogen protection, and drying at 57 to 63°C for 7 to 8 hours under vacuum conditions to obtain a polyurethane; (2) 6-mercapto-2-naphthol and tetrahydrofuran were mixed at a mass ratio of 1:(5~6) to prepare a 6-mercapto-2-naphthol solution; 4-mercaptoaniline and hydrochloric acid aqueous solution were mixed at a mass ratio of 1:(8~10) with an equal molar amount of 6-mercapto-2-naphthol, and sodium nitrate aqueous solution with a mass of 2~3 times that of 4-mercaptoaniline was added dropwise at a constant speed within 3 minutes at 0~2°C and 200~300r / min stirring conditions, and the stirring reaction was continued for 1~1.2h. 6-mercapto-2-naphthol solution was added dropwise at a constant speed within 5 minutes, and the stirring reaction was continued for 2~2.2h. The pH was adjusted to 7~7.2 with sodium hydroxide aqueous solution, and the mixture was dried at 68~72°C under vacuum conditions for 8~10h to obtain a functional cross-linking agent; (3) 1,1,3,3-tetramethyl-1,3-disiloxanediol and acetonitrile were mixed at a mass ratio of 1:(5~6) to prepare a silanediol solution; silica, vinylphosphonyl chloride (1.1~1.3 times the molar amount of 1,1,3,3-tetramethyl-1,3-disiloxanediol), and acetonitrile were mixed at a mass ratio of 1:(3~4):(30~36), ultrasonically dispersed for 1~1.2h, heated to 78~80℃, and under nitrogen protection, 300~500r / min stirring conditions, the silanediol solution was added dropwise at a uniform speed within 5min, and the stirring reaction was continued for 16~18h, filtered, washed with anhydrous ethanol and deionized water 3~5 times each, and dried at 68~72℃ under vacuum conditions for 9~10h to obtain modified silica; (4) The polyurethane, functional cross-linking agent, modified silica, azobisisobutyronitrile, nickel chloride hexahydrate and N,N-dimethylformamide were mixed evenly, stirred at 50-60 r / min for 8-10 min at room temperature, poured into a polytetrafluoroethylene mold, allowed to stand at 78-82 °C for 3-4 h, dried at 66-70 °C under vacuum conditions for 9-11 h, cooled and demolded to obtain a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
[0006] As an optimization, the preparation method of the amino thiobisphenol monomer in step (1) is as follows: 2,2'-thiobis(4-chlorophenol) and toluene are mixed uniformly in a mass ratio of 1:(6~7) to prepare a thiobisphenol reaction solution; 2 times the molar amount of 2,2'-thiobis(4-chlorophenol) diaminobutene, triethylamine, and toluene are mixed uniformly in a mass ratio of 1:(0.03~0.05):(10~12), and the thiobisphenol reaction solution is added dropwise at a uniform rate within 10 minutes at 40~50°C and 300~500r / min stirring conditions, and the stirring reaction is continued for 2~3h, and the mixture is dried at 50~60°C under vacuum conditions for 8~10h to prepare an amino thiobisphenol monomer; The reaction process is as follows: .
[0007] As an optimization, the preparation method of the cyclic carbonate-based perfluoromonomer in step (1) is as follows: 1,4-bis(2',3'-epoxypropyl)perfluorobutane, potassium iodide, and ethanol are uniformly mixed in a mass ratio of 1:(0.01-0.02):(3-4), placed in a high-pressure reactor, introduced with carbon dioxide gas to maintain the pressure at 1.2-1.4 MPa, stirred at 110-120°C and 300-500 r / min for 1-1.2 h, cooled to room temperature, and then discharged to obtain a cyclic carbonate-based perfluoromonomer; The reaction process is as follows: .
[0008] As an optimization, the molar concentration of the hydrochloric acid aqueous solution in step (2) is 2 mol / L.
[0009] As an optimization, the mass fraction of the sodium nitrate aqueous solution in step (2) is 8% to 10%.
[0010] As an optimization, the molar concentration of the sodium hydroxide aqueous solution in step (2) is 2 mol / L.
[0011] As an optimization, the reaction process of the functionalized cross-linking agent in step (2) is as follows:
[0012] As an optimization, the particle size of the silicon dioxide in step (3) is 2000 mesh, and the manufacturer is Shandong Wanhua Tianhe New Materials Co., Ltd.
[0013] As an optimization, the addition amounts of the polyurethane, functionalized crosslinking agent, modified silica, azobisisobutyronitrile, nickel chloride hexahydrate, and N,N-dimethylformamide in step (4) are: 98-102 parts of polyurethane, 6-7 parts of functionalized crosslinking agent, 4-5 parts of modified silica, 0.1-0.2 parts of azobisisobutyronitrile, 2-3 parts of nickel chloride hexahydrate, and 220-230 parts of N,N-dimethylformamide.
[0014] Compared with the prior art, the present invention has the following beneficial effects: When preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation, the present invention comprises the following steps: reacting 2,2'-thiobis(4-chlorophenol) and diaminobutene to obtain an aminothiobisphenol monomer; reacting 1,4-bis(2',3'-epoxypropyl)perfluorobutane and carbon dioxide to obtain a cyclocarbonate-based perfluoromonomer; polymerizing the cyclocarbonate-based perfluoromonomer and the aminothiobisphenol monomer to obtain polyurethane; diazotizing 4-mercaptoaniline and reacting it with 6-mercapto-2-naphthol to obtain a functional crosslinking agent; polymerizing and coating 1,1,3,3-tetramethyl-1,3-disiloxanediol and vinylphosphonyl chloride on the surface of silicon dioxide to obtain modified silicon dioxide; and uniformly mixing the polyurethane, the functional crosslinking agent, the modified silicon dioxide, and nickel chloride hexahydrate, curing the mixture in a mold, and then demolding the mixture to obtain the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
[0015] First, the chlorine atom on 2,2'-thiobis(4-chlorophenol) reacts with the amino group on diaminobutene to prepare an aminothiobisphenol monomer, and an amino group is introduced into the aminothiobisphenol monomer; the epoxy group of 1,4-bis(2',3'-epoxypropyl)perfluorobutane is subjected to a cycloaddition reaction with carbon dioxide to convert the epoxy group into a cyclocarbonate group to prepare a cyclocarbonate-based perfluoromonomer; the cyclocarbonate group on the cyclocarbonate-based perfluoromonomer is polymerized with the amino group on the aminothiobisphenol monomer to prepare a polyurethane, and a fluorine atom, a carbon-carbon double bond, and a 2,2'-thiobisphenol structure are introduced into the polyurethane molecular chain; the 2,2'-thiobisphenol structure can be complexed with the nickel atom provided by nickel chloride hexahydrate to form an organic nickel complex, which can effectively transfer the excited state energy of the photosensitive chromophore in the polymer and dissipate it in a harmless form, thereby preventing the polymer from undergoing photodegradation reaction, and can endow the aviation sand and rain erosion resistant polyurethane protective film with excellent properties. Good anti-aging performance; at the same time, a cross-linked network is formed between the polyurethane molecular chains, which inhibits the relative slip between the polyurethane molecular chains and improves the impact resistance of the aviation sand erosion and rain erosion resistant polyurethane protective film. When the aircraft is flying, the leading edge of the wing is easily eroded by dust, sand and gravel, and hail in the airflow, causing wear on the aircraft surface. By improving the impact resistance of the aviation sand erosion and rain erosion resistant polyurethane protective film, the energy generated by the impact is dissipated, and the sand erosion resistance and rain erosion resistance of the aviation sand erosion and rain erosion resistant polyurethane protective film are improved; the introduction of fluorine atoms can reduce surface energy, improve the hydrophobicity of the film material, and improve the rain erosion resistance of the aviation sand erosion and rain erosion resistant polyurethane protective film; the carbon-carbon double bonds introduced in the polyurethane molecular chain can react with the thiol group on the functional cross-linking agent to form a cross-linked network structure, further improving the cross-linking degree, improving the impact resistance, dissipating the energy generated by the impact, and improving the sand erosion resistance and rain erosion resistance of the aviation sand erosion and rain erosion resistant polyurethane protective film.
[0016] Secondly, 4-mercaptoaniline is diazotized and then reacted with 6-mercapto-2-naphthol to obtain a functional cross-linking agent; two mercapto groups and an azonaphthol structure are introduced into the functional cross-linking agent; the azonaphthol structure undergoes tautomerism under the action of ultraviolet light, dissipating the ultraviolet light energy in a harmless form, further improving the anti-aging performance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation; the mercapto groups on the functional cross-linking agent can react with the carbon-carbon double bonds on the polyurethane molecular chain and the modified silica to form a cross-linking network, thereby improving the sand-erosion resistance and rain-erosion resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation.
[0017] Finally, the Si-OH bond on 1,1,3,3-tetramethyl-1,3-disiloxanediol and the P-Cl bond on vinylphosphonyl chloride were dehydrochlorinated and polymerized, and then coated on the surface of silica to produce modified silica. Phosphorus, Si-O bonds, and carbon-carbon double bonds were introduced onto the surface of the modified silica. The introduction of phosphorus and Si-O bonds improves the flame retardancy of the aviation-grade sand-erosion and rain-erosion-resistant polyurethane protective film. The introduction of carbon-carbon double bonds allows the modified silica to react with the thiol groups on the functionalized crosslinker, forming more crosslinking sites and enhancing the film's sand-erosion and rain-erosion resistance. Silica is an inorganic non-metallic material with excellent wear, fire, and high-temperature resistance. Surface modification of silica enhances its compatibility with polyurethane, reduces silica agglomeration, and fully utilizes the advantages of silica, further enhancing the film's sand-erosion and rain-erosion-resistant flame retardancy. DETAILED DESCRIPTION
[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.
[0019] Example 1:
[0020] A method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation, comprising the following steps: (1) 2,2'-thiobis(4-chlorophenol) and toluene were mixed at a mass ratio of 1:6 to prepare a thiobisphenol reaction solution; 2 times the molar amount of 2,2'-thiobis(4-chlorophenol) diaminobutene, triethylamine and toluene were mixed at a mass ratio of 1:0.03:10, and the thiobisphenol reaction solution was added dropwise at a constant speed within 10 minutes at 40°C and 300 r / min stirring conditions, and the stirring reaction was continued for 3 hours. Under vacuum conditions, it was dried at 50°C for 10 hours to prepare an aminothiobisphenol monomer; 1,4-bis(2',3'-epoxypropyl)perfluorobutane, potassium iodide and ethanol were mixed at a mass ratio of 1:0.01:3 and placed In a high-pressure reactor, carbon dioxide gas was introduced to maintain the pressure at 1.2 MPa, and the reaction was stirred at 110° C. and 300 r / min for 1.2 hours. The product was cooled to room temperature and then discharged to obtain a cyclic carbonate-based perfluoromonomer; the cyclic carbonate-based perfluoromonomer and the aminothiobisphenol monomer were added in a molar ratio of 1:1 to N,N-dimethylformamide (11 times the mass of the cyclic carbonate-based perfluoromonomer), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (0.03 times the mass of the cyclic carbonate-based perfluoromonomer) was added, and the reaction was stirred at 138° C. and 200 r / min for 25 hours under nitrogen protection, and dried at 57° C. under vacuum conditions for 8 hours to obtain a polyurethane; (2) 6-mercapto-2-naphthol and tetrahydrofuran were mixed at a mass ratio of 1:5 to prepare a 6-mercapto-2-naphthol solution; 4-mercaptoaniline and a 2 mol / L hydrochloric acid aqueous solution were mixed at a mass ratio of 1:8 to prepare a 6-mercapto-2-naphthol solution; at 0°C and 200 r / min, an 8% sodium nitrate aqueous solution with a mass fraction twice that of the 4-mercaptoaniline was added dropwise at a constant speed within 3 minutes, and the stirring reaction was continued for 1.2 hours; the 6-mercapto-2-naphthol solution was added dropwise at a constant speed within 5 minutes, and the stirring reaction was continued for 2.2 hours; the pH was adjusted to 7 with a 1 mol / L sodium hydroxide aqueous solution, and the solution was dried at 68°C under vacuum conditions for 10 hours to prepare a functional cross-linking agent; (3) 1,1,3,3-tetramethyl-1,3-disiloxanediol and acetonitrile were mixed in a mass ratio of 1:5 to prepare a silanediol solution; silica, vinylphosphonyl chloride (1.1 times the molar amount of 1,1,3,3-tetramethyl-1,3-disiloxanediol), and acetonitrile were mixed in a mass ratio of 1:3:30, ultrasonically dispersed for 1 hour, heated to 78 ° C, and under nitrogen protection, stirred at 300 r / min, the silanediol solution was added dropwise at a uniform speed within 5 minutes, and the stirring reaction was continued for 18 hours. The solution was filtered, washed with anhydrous ethanol and deionized water for 3 times each, and dried at 68 ° C for 10 hours under vacuum conditions to obtain modified silica; (4) Weigh 98 parts of polyurethane, 6 parts of functionalized crosslinking agent, 4 parts of modified silica, 0.1 parts of azobisisobutyronitrile, 2 parts of nickel chloride hexahydrate, and 220 parts of N,N-dimethylformamide by mass; mix the polyurethane, functionalized crosslinking agent, modified silica, azobisisobutyronitrile, nickel chloride hexahydrate, and N,N-dimethylformamide evenly, stir at 50 r / min for 10 minutes at room temperature, pour into a polytetrafluoroethylene mold, let stand at 78°C for 4 hours, dry at 66°C under vacuum conditions for 11 hours, cool and demold, and obtain a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
[0021] Example 2:
[0022] A method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation, comprising the following steps: (1) 2,2'-thiobis(4-chlorophenol) and toluene were mixed evenly at a mass ratio of 1:6.5 to prepare a thiobisphenol reaction solution; 2 times the molar amount of 2,2'-thiobis(4-chlorophenol) diaminobutene, triethylamine, and toluene were mixed evenly at a mass ratio of 1:0.04:11, and the thiobisphenol reaction solution was added dropwise at a constant speed within 10 minutes at 45°C and 400 r / min stirring conditions, and the stirring reaction was continued for 2.5 hours. Under vacuum conditions, it was dried at 55°C for 9 hours to obtain an aminothiobisphenol monomer; 1,4-bis(2',3'-epoxypropyl)perfluorobutane, potassium iodide, and ethanol were mixed evenly at a mass ratio of 1:0.015:3.5. The reaction mixture was placed in a high-pressure reactor, and carbon dioxide gas was introduced to maintain the pressure at 1.3 MPa. The mixture was stirred at 115° C. and 400 r / min for 1.1 h, and the mixture was discharged after cooling to room temperature to obtain a cyclic carbonate-based perfluoromonomer. The cyclic carbonate-based perfluoromonomer and the aminothiobisphenol monomer were added in a molar ratio of 1:1 to N,N-dimethylformamide (12 times the mass of the cyclic carbonate-based perfluoromonomer), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (0.04 times the mass of the cyclic carbonate-based perfluoromonomer) was added. The mixture was stirred at 140° C. and 250 r / min for 24.5 h under nitrogen protection, and dried at 60° C. under vacuum conditions for 7.5 h to obtain a polyurethane. (2) 6-mercapto-2-naphthol and tetrahydrofuran were mixed at a mass ratio of 1:5.5 to prepare a 6-mercapto-2-naphthol solution; 4-mercaptoaniline and a 2 mol / L hydrochloric acid aqueous solution were mixed at a mass ratio of 1:9, and a 9% sodium nitrate aqueous solution (2.5 times the mass of 4-mercaptoaniline) was added dropwise at a constant speed within 3 minutes at a stirring condition of 1°C and 250 r / min. The stirring reaction was continued for 1.1 hours. The 6-mercapto-2-naphthol solution was added dropwise at a constant speed within 5 minutes. The stirring reaction was continued for 2.1 hours. The pH was adjusted to 7.1 with a 1 mol / L sodium hydroxide aqueous solution. The solution was dried at 70°C under vacuum conditions for 9 hours to prepare a functional cross-linking agent. (3) 1,1,3,3-tetramethyl-1,3-disiloxanediol and acetonitrile were mixed at a mass ratio of 1:5.5 to prepare a silanediol solution; silica, vinylphosphonyl chloride (1.2 times the molar amount of 1,1,3,3-tetramethyl-1,3-disiloxanediol), and acetonitrile were mixed at a mass ratio of 1:3.5:33 to prepare a silanediol solution; the mixture was ultrasonically dispersed for 1.1 hours, heated to 79°C, and under nitrogen protection, the silanediol solution was added dropwise at a constant speed within 5 minutes at a stirring rate of 400 r / min. The reaction was continued by stirring for 17 hours, filtered, washed with anhydrous ethanol and deionized water 4 times each, and dried at 70°C under vacuum conditions for 9.5 hours to prepare modified silica; (4) Weigh 100 parts of polyurethane, 6.5 parts of functionalized crosslinking agent, 4.5 parts of modified silica, 0.15 parts of azobisisobutyronitrile, 2.5 parts of nickel chloride hexahydrate, and 225 parts of N,N-dimethylformamide by mass; mix the polyurethane, functionalized crosslinking agent, modified silica, azobisisobutyronitrile, nickel chloride hexahydrate, and N,N-dimethylformamide evenly, stir at 55 r / min for 9 minutes at room temperature, pour into a polytetrafluoroethylene mold, let stand at 80°C for 3.5 hours, dry at 68°C under vacuum conditions for 10 hours, cool and demold, and obtain a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
[0023] Example 3:
[0024] A method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation, comprising the following steps: (1) 2,2'-thiobis(4-chlorophenol) and toluene were mixed evenly in a mass ratio of 1:7 to prepare a thiobisphenol reaction solution; 2 times the molar amount of 2,2'-thiobis(4-chlorophenol) diaminobutene, triethylamine, and toluene were mixed evenly in a mass ratio of 1:0.05:12, and the thiobisphenol reaction solution was added dropwise at a constant speed within 10 minutes at 50°C and 500 r / min stirring conditions, and the stirring reaction was continued for 2 hours. Under vacuum conditions, it was dried at 60°C for 8 hours to obtain an aminothiobisphenol monomer; 1,4-bis(2',3'-epoxypropyl)perfluorobutane, potassium iodide, and ethanol were mixed evenly in a mass ratio of 1:0.02:4. The method comprises placing the cyclic carbonate perfluoromonomer in a high-pressure reactor, introducing carbon dioxide gas to maintain the pressure at 1.4 MPa, stirring and reacting at 120° C. and 500 r / min for 1 hour, cooling to room temperature and discharging the product to obtain a cyclic carbonate perfluoromonomer; adding the cyclic carbonate perfluoromonomer and the aminothiobisphenol monomer in a molar ratio of 1:1 to N,N-dimethylformamide (13 times the mass of the cyclic carbonate perfluoromonomer), adding 1,5,7-triazabicyclo[4.4.0]dec-5-ene (0.05 times the mass of the cyclic carbonate perfluoromonomer), stirring and reacting at 142° C. and 300 r / min for 24 hours under nitrogen protection, and drying at 63° C. under vacuum conditions for 7 hours to obtain a polyurethane; (2) 6-mercapto-2-naphthol and tetrahydrofuran were mixed at a mass ratio of 1:6 to prepare a 6-mercapto-2-naphthol solution; 4-mercaptoaniline and a 2 mol / L hydrochloric acid aqueous solution were mixed at a mass ratio of 1:10, and a 10% sodium nitrate aqueous solution with a mass fraction of 3 times the mass of 4-mercaptoaniline was added dropwise at a constant speed within 3 minutes at a stirring condition of 2°C and 300 r / min. The stirring reaction was continued for 1 hour. The 6-mercapto-2-naphthol solution was added dropwise at a constant speed within 5 minutes. The stirring reaction was continued for 2 hours. The pH was adjusted to 7 with a 1 mol / L sodium hydroxide aqueous solution. The solution was dried at 72°C under vacuum conditions for 8 hours to prepare a functional cross-linking agent. (3) 1,1,3,3-tetramethyl-1,3-disiloxanediol and acetonitrile were mixed in a mass ratio of 1:6 to prepare a silanediol solution; silica, vinylphosphonyl chloride (1.3 times the molar amount of 1,1,3,3-tetramethyl-1,3-disiloxanediol), and acetonitrile were mixed in a mass ratio of 1:4:36, ultrasonically dispersed for 1.2 hours, heated to 80°C, and under nitrogen protection, stirred at 500 r / min, the silanediol solution was added dropwise at a uniform speed within 5 minutes, and the stirring reaction was continued for 16 hours, filtered, washed with anhydrous ethanol and deionized water 5 times each, and dried at 72°C under vacuum conditions for 9 hours to obtain modified silica; (4) Weigh 102 parts of polyurethane, 7 parts of functionalized crosslinking agent, 5 parts of modified silica, 0.2 parts of azobisisobutyronitrile, 3 parts of nickel chloride hexahydrate, and 230 parts of N,N-dimethylformamide by mass; mix the polyurethane, functionalized crosslinking agent, modified silica, azobisisobutyronitrile, nickel chloride hexahydrate, and N,N-dimethylformamide evenly, stir at 60 r / min for 8 minutes at room temperature, pour into a polytetrafluoroethylene mold, let stand at 82°C for 3 hours, dry at 70°C under vacuum conditions for 9 hours, cool and demold, and obtain a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
[0025] Comparative Example 1: The difference between the preparation method of the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation in Comparative Example 1 and Example 2 lies in the difference in step (1). Step (1) is modified as follows: 1,4-di(2',3'-epoxypropyl)perfluorobutane, potassium iodide, and ethanol are uniformly mixed in a mass ratio of 1:0.015:3.5, placed in a high-pressure reactor, and carbon dioxide gas is introduced to maintain the pressure at 1.3 MPa. The reaction is stirred at 115°C and 400 r / min for 1.1 h, and the material is discharged after cooling to room temperature. To prepare a cyclic carbonate perfluoromonomer, the cyclic carbonate perfluoromonomer and 1,6-hexanediamine were added in a molar ratio of 1:1 to N,N-dimethylformamide (12 times the mass of the cyclic carbonate perfluoromonomer), followed by the addition of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (0.04 times the mass of the cyclic carbonate perfluoromonomer). The mixture was stirred at 140°C and 250 rpm under nitrogen for 24.5 hours, and dried at 60°C under vacuum for 7.5 hours to prepare a polyurethane. The remaining steps were the same as in Example 2.
[0026] Comparative Example 2: The preparation method of the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation of Comparative Example 2 differs from that of Example 2 in that step (1) is different. Step (1) is modified as follows: 2,2'-thiobis(4-chlorophenol) and toluene are mixed evenly in a mass ratio of 1:6.5 to prepare a thiobisphenol reaction solution; 2 times the molar amount of 2,2'-thiobis(4-chlorophenol) diaminobutene, triethylamine and toluene are mixed evenly in a mass ratio of 1:0.04:11, and the thiobisphenol reaction solution is added dropwise at a uniform speed within 10 minutes at 45°C and 400 r / min stirring conditions, and the stirring reaction is continued for 2.5 hours. Under vacuum conditions, it is dried at 55°C for 9 hours to prepare an aminothiobisphenol monomer; 2,2'-hexane-1,6-diyldioxirane The mixture was uniformly mixed with potassium iodide and ethanol in a mass ratio of 1:0.015:3.5, placed in an autoclave, and carbon dioxide gas was introduced to maintain the pressure at 1.3 MPa. The mixture was stirred at 115°C and 400 rpm for 1.1 hours. The mixture was cooled to room temperature and then discharged to obtain a cyclocarbonate monomer. The cyclocarbonate monomer and the aminothiobisphenol monomer were added in a molar ratio of 1:1 to N,N-dimethylformamide (12 times the mass of the cyclocarbonate monomer), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (0.04 times the mass of the cyclocarbonate monomer) was added. The mixture was stirred at 140°C and 250 rpm for 24.5 hours under nitrogen protection, and dried at 60°C under vacuum for 7.5 hours to obtain a polyurethane. The remaining steps were the same as in Example 2.
[0027] Comparative Example 3: The method for preparing the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation in Comparative Example 3 differs from that in Example 2 in that step (2) is omitted and step (4) is modified as follows: 100 parts of polyurethane, 4.5 parts of modified silica, 2.5 parts of nickel chloride hexahydrate, and 225 parts of N,N-dimethylformamide are weighed, by mass; the polyurethane, modified silica, nickel chloride hexahydrate, and N,N-dimethylformamide are uniformly mixed, stirred at 55 rpm for 9 minutes at room temperature, poured into a polytetrafluoroethylene mold, allowed to stand at 80°C for 3.5 hours, dried at 68°C under vacuum for 10 hours, cooled, and demolded to obtain the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation. The remaining steps are the same as those in Example 2.
[0028] Comparative Example 4: The method for preparing the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation in Comparative Example 4 differs from that in Example 2 in that step (3) is omitted and step (4) is modified as follows: 100 parts of polyurethane, 6.5 parts of a functionalized crosslinking agent, 4.5 parts of silicon dioxide, 0.15 parts of azobisisobutyronitrile, 2.5 parts of nickel chloride hexahydrate, and 225 parts of N,N-dimethylformamide are weighed in parts by mass; the polyurethane, functionalized crosslinking agent, silicon dioxide, azobisisobutyronitrile, nickel chloride hexahydrate, and N,N-dimethylformamide are uniformly mixed, stirred at room temperature at 55 rpm for 9 minutes, poured into a polytetrafluoroethylene mold, allowed to stand at 80°C for 3.5 hours, dried at 68°C under vacuum for 10 hours, cooled and demolded, to obtain a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation. The remaining steps are the same as those in Example 2.
[0029] Test Example 1 Sand erosion resistance test Test method: The wear resistance of the examples and comparative examples was tested according to GB / T 23988-2009. The results are shown in Table 1.
[0030] Table 1
[0031] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 1, it can be found that the aviation sand-erosion and rain-erosion resistant polyurethane protective film prepared by the present invention has good sand-erosion resistance.
[0032] By comparison, the wear resistance of Examples 1 to 3 is greater than that of Comparative Example 1, indicating that the chlorine atom on 2,2'-thiobis(4-chlorophenol) reacts with the amino group on diaminobutene to prepare an aminated thiobisphenol monomer, and an amino group is introduced into the aminated thiobisphenol monomer; the cyclic carbonate group on the cyclic carbonate perfluoromonomer is polymerized with the amino group on the aminated thiobisphenol monomer to prepare a polyurethane, and a carbon-carbon double bond and a 2,2'-thiobisphenol structure are introduced into the polyurethane molecular chain; the 2,2'-thiobisphenol structure can be complexed with the nickel atom provided by nickel chloride hexahydrate to form an organic nickel complex, so that a cross-linked network is formed between the polyurethane molecular chains, thereby inhibiting the polyurethane molecules from forming cross-linked networks. The relative slip between chains improves the impact resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation. When the aircraft is flying, the leading edge of the wing is susceptible to erosion by dust, sand, and hail in the airflow, causing wear on the aircraft surface. By improving the impact resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation, the energy generated by the impact is dissipated, and the sand-erosion resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation is improved; the carbon-carbon double bonds introduced in the polyurethane molecular chain can react with the thiol groups on the functionalized cross-linking agent to form a cross-linked network structure, further improving the degree of cross-linking, improving the impact resistance, dissipating the energy generated by the impact, and improving the sand-erosion resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation.
[0033] By comparison, the wear resistance of Examples 1 to 3 is greater than that of Comparative Example 3, indicating that the functionalized crosslinking agent is prepared by reacting 4-mercaptoaniline with 6-mercapto-2-naphthol after diazotization; two mercapto groups are introduced into the functionalized crosslinking agent; the mercapto groups on the functionalized crosslinking agent can react with the carbon-carbon double bonds on the polyurethane molecular chain and the modified silica to form a crosslinked network, thereby improving the sand erosion resistance of the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
[0034] By comparison, the wear resistance of Examples 1 to 3 is greater than that of Comparative Example 4, indicating that the Si-OH bond on 1,1,3,3-tetramethyl-1,3-disiloxanediol and the P-Cl bond on vinylphosphonyl chloride are dehydrochlorinated and polymerized, and then coated on the surface of silica to produce modified silica. Carbon-carbon double bonds are introduced on the surface of the modified silica. The introduction of carbon-carbon double bonds enables the modified silica to react with the thiol groups on the functionalized crosslinking agent, forming more crosslinking sites and improving the sand erosion resistance of the aviation-grade sand-erosion and rain-erosion-resistant polyurethane protective film. Silica is an inorganic non-metallic material with good wear resistance. Surface modification of silica enhances the compatibility between silica and polyurethane, reduces silica agglomeration, and fully utilizes the advantages of silica, further enhancing the sand erosion resistance of the aviation-grade sand-erosion and rain-erosion-resistant polyurethane protective film.
[0035] Test Example 2 Rain erosion resistance test Test Method: Rain erosion resistance of Examples and Comparative Examples was tested according to ASTM G73. Samples of Examples and Comparative Examples were cut into 20 x 20 cm dimensions and attached to a circular disk. The samples were subjected to a maximum impact velocity of 160 m / s and a rainfall rate of 48 mm / h. The samples were repeatedly passed through a circular path and impacted with the liquid. The mass loss of the samples after 12 hours was measured. The results are shown in Table 2.
[0036] Table 2
[0037] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 2, it can be found that the aviation sand erosion and rain erosion resistant polyurethane protective film prepared by the present invention has good rain erosion resistance.
[0038] By comparison, the mass loss of Examples 1 to 3 is less than the mass loss of Comparative Examples 1 to 2, indicating that the chlorine atom on 2,2'-thiobis(4-chlorophenol) reacts with the amino group on diaminobutene to prepare an aminated thiobisphenol monomer, and an amino group is introduced into the aminated thiobisphenol monomer; the epoxy group of 1,4-bis(2',3'-epoxypropyl)perfluorobutane is subjected to a cycloaddition reaction with carbon dioxide to convert the epoxy group into a cyclocarbonate group to prepare a cyclocarbonate-based perfluoromonomer; the cyclocarbonate group on the cyclocarbonate-based perfluoromonomer is polymerized with the amino group on the aminated thiobisphenol monomer to prepare a polyurethane, and a fluorine atom, a carbon-carbon double bond, and a 2,2'-thiobisphenol structure are introduced into the polyurethane molecular chain; the 2,2'-thiobisphenol structure can be reacted with nickel chloride hexahydrate. The nickel atoms provided are complexed to form an organic nickel complex, and at the same time, a cross-linked network is formed between the polyurethane molecular chains, which inhibits the relative slip between the polyurethane molecular chains, improves the impact resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation, dissipates the energy generated by rain impact, and improves the rain erosion resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation; the introduction of fluorine atoms can reduce surface energy, improve the hydrophobicity of the film material, and improve the rain erosion resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation; the carbon-carbon double bonds introduced in the polyurethane molecular chain can react with the thiol groups on the functionalized cross-linking agent to form a cross-linked network structure, further improve the cross-linking degree, improve the impact resistance, dissipate the energy generated by rain impact, and improve the rain erosion resistance of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation.
[0039] By comparison, the mass loss of Examples 1 to 3 is less than the mass loss of Comparative Example 3, indicating that the functionalized crosslinking agent is prepared by reacting 4-mercaptoaniline with 6-mercapto-2-naphthol after diazotization; two mercapto groups are introduced into the functionalized crosslinking agent; the mercapto groups on the functionalized crosslinking agent can react with the carbon-carbon double bonds on the polyurethane molecular chain and the modified silica to form a crosslinked network, thereby improving the impact resistance, dissipating the energy generated by rain impact, and improving the rain erosion resistance of the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
[0040] By comparison, the mass loss of Examples 1 to 3 is less than that of Comparative Example 4, indicating that the Si-OH bond on 1,1,3,3-tetramethyl-1,3-disiloxanediol and the P-Cl bond on vinylphosphonyl chloride are dehydrochlorinated and polymerized, and then coated on the surface of silica to prepare modified silica, and carbon-carbon double bonds are introduced on the surface of the modified silica. The introduction of the carbon-carbon double bonds enables the modified silica to react with the thiol group on the functionalized cross-linking agent to form more cross-linking sites, thereby improving impact resistance, dissipating the energy generated by rain impact, and improving the rain erosion resistance of the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
[0041] Test Example 3 Anti-aging performance test Testing method: According to GB / T 1040, the examples and comparative examples were cut into standard strips and their tensile strength (M) was measured. The standard strips were irradiated with a xenon arc lamp for 7 days, and the tensile strength (N) of the standard strips after UV aging was measured. The change in tensile strength of the examples and comparative examples before and after UV aging was calculated as follows: Tensile strength change = (original tensile strength (M) of the strip - tensile strength (N) after UV aging) / original tensile strength (M) of the strip × 100%. The results are shown in Table 3.
[0042] Table 3
[0043] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 3, it can be found that the aviation sand erosion and rain erosion resistant polyurethane protective film prepared by the present invention has good anti-aging performance.
[0044] By comparison, the rate of change of tensile strength in Examples 1 to 3 is less than that in Comparative Example 1, indicating that the chlorine atom on 2,2'-thiobis(4-chlorophenol) reacts with the amino group on diaminobutene to prepare an aminated thiobisphenol monomer, and an amino group is introduced into the aminated thiobisphenol monomer; the cyclic carbonate group on the cyclic carbonate perfluoromonomer is polymerized with the amino group on the aminated thiobisphenol monomer to prepare a polyurethane, and a 2,2'-thiobisphenol structure is introduced into the polyurethane molecular chain; the 2,2'-thiobisphenol structure can be complexed with the nickel atom provided by nickel chloride hexahydrate to form an organic nickel complex, which can effectively transfer the excited state energy of the photosensitive chromophore in the polymer and dissipate it in a harmless form, thereby protecting the polymer from photodegradation reaction, and can impart excellent anti-aging properties to the sand and rain erosion resistant polyurethane protective film for aviation.
[0045] By comparison, the change rate of tensile strength of Examples 1 to 3 is less than that of Comparative Example 3, indicating that the functionalized crosslinking agent is prepared by reacting 4-mercaptoaniline with 6-mercapto-2-naphthol after diazotization; an azonaphthol structure is introduced into the functionalized crosslinking agent; the azonaphthol structure undergoes tautomerism under the action of ultraviolet light, dissipating the ultraviolet light energy in a harmless form, thereby further improving the anti-aging performance of the sand and rain erosion resistant polyurethane protective film for aviation.
[0046] Test Example 4 Flame retardant performance test Test method: The examples and comparative examples were prepared into standard specimens according to GB / T 2406.2, and the limiting oxygen index of the standard specimens was tested. The results are shown in Table 4.
[0047] Table 4
[0048] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 4, it can be found that the aviation sand erosion and rain erosion resistant polyurethane protective film prepared by the present invention has good flame retardant properties.
[0049] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Example 4, indicating that the Si-OH bond on 1,1,3,3-tetramethyl-1,3-disiloxane diol and the P-Cl bond on vinylphosphonyl chloride are dehydrochlorinated and polymerized, and then coated on the surface of silica to prepare modified silica, and phosphorus element and Si-O bond are introduced into the surface of modified silica. The introduction of phosphorus element and Si-O bond can improve the flame retardant properties of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation. Silica is an inorganic non-metallic material with good fire resistance and high temperature resistance. The surface modification of silica enhances the compatibility between silica and polyurethane, reduces the agglomeration problem of silica, gives full play to the advantages of silica, and further enhances the flame retardant ability of the sand-erosion and rain-erosion resistant polyurethane protective film for aviation.
[0050] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. A sand-erosion and rain-erosion-resistant polyurethane protective film for aviation, characterized in that: The sand and rain erosion resistant polyurethane protective film for aviation is prepared by polymerizing a cyclic carbonate-based perfluoromonomer and an aminothiobisphenol monomer to obtain polyurethane; polymerizing 1,1,3,3-tetramethyl-1,3-disiloxanediol and vinylphosphonyl chloride to coat the surface of silicon dioxide to obtain modified silicon dioxide; and uniformly mixing the polyurethane, a functionalized crosslinking agent, the modified silicon dioxide, and nickel chloride hexahydrate, curing the mixture in a mold, and then demolding the mixture. The aminothiobisphenol monomer is prepared by reacting 2,2'-thiobis(4-chlorophenol) and diaminobutene; The cyclic carbonate-based perfluoromonomer is prepared by reacting 1,4-bis(2',3'-epoxypropyl)perfluorobutane and carbon dioxide; The functionalized cross-linking agent is prepared by diazotizing 4-mercaptoaniline and reacting the 4-mercaptoaniline with 6-mercapto-2-naphthol.
2. A method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation, characterized in that: The preparation method of the sand-erosion and rain-erosion-resistant polyurethane protective film for aviation comprises the following preparation steps: (1) Adding a cyclic carbonate perfluoromonomer and an aminothiobisphenol monomer in a molar ratio of 1:1 to N,N-dimethylformamide (11 to 13 times the mass of the cyclic carbonate perfluoromonomer), and adding 1,5,7-triazabicyclo[4.4.0]dec-5-ene (0.03 to 0.05 times the mass of the cyclic carbonate perfluoromonomer), stirring at 138 to 142°C and 200 to 300 r / min for 24 to 25 hours under nitrogen protection, and drying at 57 to 63°C for 7 to 8 hours under vacuum conditions to obtain a polyurethane; (2) 6-mercapto-2-naphthol and tetrahydrofuran were mixed at a mass ratio of 1:(5~6) to prepare a 6-mercapto-2-naphthol solution; 4-mercaptoaniline and hydrochloric acid aqueous solution were mixed at a mass ratio of 1:(8~10) with an equal molar amount of 6-mercapto-2-naphthol, and sodium nitrate aqueous solution with a mass of 2~3 times that of 4-mercaptoaniline was added dropwise at a constant speed within 3 minutes at 0~2°C and 200~300r / min stirring conditions, and the stirring reaction was continued for 1~1.2h. 6-mercapto-2-naphthol solution was added dropwise at a constant speed within 5 minutes, and the stirring reaction was continued for 2~2.2h. The pH was adjusted to 7~7.2 with sodium hydroxide aqueous solution, and the mixture was dried at 68~72°C under vacuum conditions for 8~10h to obtain a functional cross-linking agent; (3) 1,1,3,3-tetramethyl-1,3-disiloxanediol and acetonitrile were mixed at a mass ratio of 1:(5~6) to prepare a silanediol solution; silica, vinylphosphonyl chloride (1.1~1.3 times the molar amount of 1,1,3,3-tetramethyl-1,3-disiloxanediol), and acetonitrile were mixed at a mass ratio of 1:(3~4):(30~36), ultrasonically dispersed for 1~1.2h, heated to 78~80℃, and under nitrogen protection, 300~500r / min stirring conditions, the silanediol solution was added dropwise at a uniform speed within 5min, and the stirring reaction was continued for 16~18h, filtered, washed with anhydrous ethanol and deionized water 3~5 times each, and dried at 68~72℃ under vacuum conditions for 9~10h to obtain modified silica; (4) The polyurethane, functional cross-linking agent, modified silica, azobisisobutyronitrile, nickel chloride hexahydrate and N,N-dimethylformamide were mixed evenly, stirred at 50-60 r / min for 8-10 min at room temperature, poured into a polytetrafluoroethylene mold, allowed to stand at 78-82 °C for 3-4 h, dried at 66-70 °C under vacuum conditions for 9-11 h, cooled and demolded to obtain a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation.
3. The method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation according to claim 2, characterized in that: The preparation method of the amino thiobisphenol monomer in step (1) is as follows: 2,2'-thiobis(4-chlorophenol) and toluene are mixed uniformly in a mass ratio of 1:(6~7) to prepare a thiobisphenol reaction solution; 2 times the molar amount of 2,2'-thiobis(4-chlorophenol), diaminobutene, triethylamine and toluene are mixed uniformly in a mass ratio of 1:(0.03~0.05):(10~12), and the thiobisphenol reaction solution is added dropwise at a uniform speed within 10 minutes at 40~50°C and 300~500r / min stirring conditions, and the stirring reaction is continued for 2~3h, and the mixture is dried at 50~60°C under vacuum conditions for 8~10h to prepare the amino thiobisphenol monomer.
4. The method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation according to claim 2, characterized in that: The preparation method of the cyclic carbonate-based perfluoromonomer in step (1) is as follows: 1,4-bis(2',3'-epoxypropyl)perfluorobutane, potassium iodide and ethanol are uniformly mixed in a mass ratio of 1:(0.01-0.02):(3-4), placed in a high-pressure reactor, introduced with carbon dioxide gas to maintain the pressure at 1.2-1.4 MPa, stirred at 110-120° C. and 300-500 r / min for 1-1.2 h, cooled to room temperature and then discharged to obtain a cyclic carbonate-based perfluoromonomer.
5. The method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation according to claim 2, characterized in that: The molar concentration of the hydrochloric acid aqueous solution in step (2) is 2 mol / L.
6. The method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation according to claim 2, characterized in that: The mass fraction of the sodium nitrate aqueous solution in step (2) is 8% to 10%.
7. The method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation according to claim 2, characterized in that: The molar concentration of the sodium hydroxide aqueous solution in step (2) is 2 mol / L.
8. The method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation according to claim 2, characterized in that: The particle size of the silicon dioxide in step (3) is 2000 mesh.
9. The method for preparing a sand-erosion and rain-erosion-resistant polyurethane protective film for aviation according to claim 2, characterized in that: The addition amounts of the polyurethane, functionalized crosslinking agent, modified silica, azobisisobutyronitrile, nickel chloride hexahydrate, and N,N-dimethylformamide in step (4) are: 98-102 parts of polyurethane, 6-7 parts of functionalized crosslinking agent, 4-5 parts of modified silica, 0.1-0.2 parts of azobisisobutyronitrile, 2-3 parts of nickel chloride hexahydrate, and 220-230 parts of N,N-dimethylformamide.