A flame-retardant polyurethane coating, its preparation method, and its application in the field of unmanned aerial vehicles (UAVs).

Abstract

This invention discloses a flame-retardant polyurethane coating, its preparation method, and its application in the field of unmanned aerial vehicles (UAVs), relating to the field of flame-retardant coating technology. The flame-retardant polyurethane coating comprises the following raw materials in parts by weight: 25-30 parts polyether polyol, 15-20 parts isocyanate, 0.1-0.2 parts catalyst, 4-6 parts 2,2-dimethylolpropionic acid, 1-1.5 parts crosslinking agent, 4-6 parts flame retardant and anti-aging agent, 0.3-0.5 parts defoamer, 0.5-0.8 parts dispersant, 5-8 parts silica, and 70-80 parts deionized water. The flame-retardant polyurethane coating prepared by this invention exhibits excellent tensile strength, anti-aging properties, and flame-retardant properties.

Description

Technical Field

[0001] This invention relates to the field of flame retardant coating technology, specifically to a flame retardant polyurethane coating, its preparation method, and its application in the field of unmanned aerial vehicles (UAVs). Background Technology

[0002] With the rapid development of unmanned aerial vehicles (UAVs) in military reconnaissance, emergency rescue, logistics transportation, agricultural and forestry plant protection, and industrial inspection, their service environments are becoming increasingly complex, placing higher demands on the protective coatings on their surfaces. During flight, UAVs are exposed to prolonged environmental conditions including ultraviolet radiation, fluctuating temperature and humidity, rain erosion, sand and dust abrasion, and chemical corrosion. They also need to withstand takeoff and landing impacts, vibration loads, and localized stress concentrations. Therefore, strict requirements are placed on the mechanical strength, weather resistance, and flame retardant properties of the coating materials. Polyurethane coatings have seen rapid development in recent years due to their low volatile organic compound emissions, excellent physical properties, and environmental friendliness. However, traditional polyurethane resins still suffer from insufficient mechanical properties, weather resistance, and flame retardant performance.

[0003] Chinese invention patent application CN112646475A discloses a method for preparing and applying flame-retardant, wear-resistant, and low-VOC polyurethane coatings. The method involves adding polyester diol, isocyanate, and dibutyltin dilaurate to a reaction vessel and stirring at 75-90°C to obtain a polyurethane prepolymer. Then, hydrophilic chain extender dimethylolpropionic acid, nitrogen-phosphorus intumescent flame retardant, and acetone solvent are added to the polyurethane prepolymer, and the mixture is stirred at 70-90°C for 1-2 hours. Next, triethylamine and water are added and emulsified for 20-60 minutes. Then, substance A and terminal epoxy polyether silicone oil are added, the pH is adjusted to 6.5, and the mixture is stirred at 70-80°C to obtain a flame-retardant, wear-resistant, and low-VOC polyurethane coating. The resulting polyurethane film exhibits a low flaming time and good drip resistance, but its mechanical properties are still insufficient. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a flame-retardant polyurethane coating.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A flame-retardant polyurethane coating comprises the following raw materials in parts by weight: 25-30 parts polyether polyol, 15-20 parts isocyanate, 0.1-0.2 parts catalyst, 4-6 parts 2,2-dimethylolpropionic acid, 1-1.5 parts crosslinking agent, 6-8 parts triethylamine, 4-6 parts flame retardant and antioxidant, 0.3-0.5 parts defoamer, 0.5-0.8 parts dispersant, 5-8 parts silica, and 70-80 parts deionized water; The flame retardant and antioxidant is prepared by the following method: S1: The reaction of oleylamine with 2-hydroxy-4-(methacryloyloxy)benzophenone yields intermediate 1, the structural formula of which is as follows:

[0006] S2: Intermediate 1 reacts with L-cysteine ​​to give intermediate 2, the reaction structure of which is as follows:

[0007] S3: Intermediate 2 reacts with 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide to obtain a flame retardant and antioxidant. Its reaction structure is as follows:

[0008] In step S1, the molar ratio of oleylamine to 2-hydroxy-4-(methacryloyloxy)benzophenone is (1.05-1.1):1.

[0009] In step S2, the molar ratio of intermediate 1 to L-cysteine ​​is 1:(1.1-1.15).

[0010] In step S3, the molar ratio of intermediate 2 to 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide is (2.08-2.1):1.

[0011] The crosslinking agent is prepared by the following method: N1: N,N,N',N'-Tetra(p-aminophenyl)p-phenylenediamine reacts with 6-maleimide hexanoic acid to give a tetraamide compound, the structural formula of which is as follows:

[0012] N2: Tetraamide compounds react with furfuryl alcohol to form crosslinking agents. The reaction structure is as follows:

[0013] In step N1, the molar ratio of N,N,N',N'-tetra(p-aminophenyl)p-phenylenediamine to 6-maleimide hexanoic acid is 1:4.1; in step N2, the molar ratio of the tetraamide compound to furfuryl alcohol is 1:4.2.

[0014] The isocyanate is one of diphenylmethane-4,4'-diisocyanate and 2,4-toluene diisocyanate; the catalyst is one of dibutyltin dilaurate and stannous octoate.

[0015] The defoamer is BYK-011; the dispersant is BYK-190.

[0016] A method for preparing a flame-retardant polyurethane coating includes the following steps: (1) Weigh out the following by weight: 25-30 parts of polyether polyol, 15-20 parts of isocyanate, 0.1-0.2 parts of catalyst, 4-6 parts of 2,2-dimethylolpropionic acid, 1-1.5 parts of crosslinking agent, 6-8 parts of triethylamine, 4-6 parts of flame retardant and antioxidant, 0.3-0.5 parts of defoamer, 0.5-0.8 parts of dispersant, 5-8 parts of silica, and 70-80 parts of deionized water; (2) Stir and mix the polyether polyol, isocyanate and catalyst, heat and react, add 2,2-dimethylolpropionic acid and react, then add crosslinking agent and continue the reaction to obtain polyurethane prepolymer; (3) Stir deionized water, polyurethane prepolymer and triethylamine together, then add flame retardant and anti-aging agent, defoamer, dispersant and silica in sequence and stir to obtain flame retardant polyurethane coating.

[0017] Application of a flame-retardant polyurethane coating in the field of drones.

[0018] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include: The flame-retardant polyurethane coating provided by this invention has excellent tensile strength, anti-aging properties and flame-retardant properties. Attached Figure Description

[0019] Figure 1 The 1H NMR spectrum of the flame retardant and antioxidant prepared in step S3 of Example 1; Figure 2 This is a high-resolution mass spectrum of the flame retardant and antioxidant prepared in step S3 of Example 1; Figure 3 The 1H NMR spectrum of the crosslinking agent prepared by step N2 in Example 4; Figure 4 This is a high-resolution mass spectrum of the crosslinking agent prepared in step N2 of Example 4. Detailed Implementation

[0020] The following description, in conjunction with specific embodiments, provides further details, but the present invention is not limited to these embodiments.

[0021] Example 1: Preparation of flame retardant and antioxidant: S1: 300 ml of anhydrous acetonitrile, 0.105 mol of oleylamine, and 0.1 mol of 2-hydroxy-4-(methacryloyloxy)benzophenone were added to a reaction vessel, stirred and mixed, heated to 40 °C, and reacted for 6 h. The mixture was then distilled under reduced pressure at 40 °C for 1 h. Recrystallization was performed using 180 ml of a mixed solution of acetone and n-hexane (acetone to n-hexane volume ratio 1:9). The solution was filtered and dried under vacuum at 50 °C for 10 h to obtain intermediate 1. Its 1H NMR data are as follows:1 H NMR (400 MHz, Chloroform- d ) δ 11.74 (s, 1H), 7.79 -7.71 (m, 2H), 7.67 (d, J = 8.5 Hz, 1H), 7.56 - 7.45 (m, 3H), 7.05 (dd, J =8.5, 1.9 Hz, 1H), 6.84 (d, J = 1.9 Hz, 1H), 5.33 (t, J = 5.5 Hz, 2H), 4.60 (tt, J = 6.0, 4.8 Hz, 1H), 2.89 - 2.61 (m, 5H), 2.06 - 1.96 (m, 4H), 1.54 -1.43 (m, 2H), 1.38 - 1.22 (m, 22H), 1.08 (d, J = 7.3 Hz, 3H), 0.92 - 0.84 (m,3H); HRMS (m / z): 550.3824[M+H] + ; S2: Under nitrogen protection, 400 ml of anhydrous ethanol, 0.1 mol of intermediate 1, 0.11 mol of L-cysteine, and 3 g of photoinitiator 184 were added to a reaction vessel and stirred for 30 min. The mixture was then irradiated under 300 W UV light for 10 min at 25 °C with stirring, followed by vacuum distillation at 45 °C for 1 h. 300 ml of toluene was added and stirred until homogeneous. The mixture was washed with deionized water (3 × 100 ml), dried with 30 g of anhydrous magnesium sulfate, filtered, and then vacuum distilled at 70 °C for 2 h to obtain intermediate 2. Its 1H NMR spectrum data are as follows: 1 H NMR (400 MHz, Chloroform- d) δ 11.74 (s, 1H), 11.39 (s, 1H), 7.79 - 7.71 (m, 2H), 7.67 (d, J= 8.5 Hz, 1H), 7.58 - 7.45 (m, 3H), 7.05 (dd, J = 8.5, 1.9 Hz, 1H), 6.84 (d,J = 1.9 Hz, 1H), 4.60 (tt, J = 6.0, 4.8 Hz, 1H), 3.61 (q, J = 1.5 Hz, 3H), 3.03 - 2.61 (m, 8H), 1.61 - 1.43 (m, 6H), 1.40 - 1.22 (m, 24H), 1.08 (d, J =7.3 Hz, 3H), 0.93 - 0.84 (m, 3H); HRMS (m / z): 671.4025[M+H] + ; S3: Add 1000 ml of anhydrous acetonitrile, 0.208 mol of intermediate 2, and 0.22 mol of triethylamine to a reaction vessel, stir and mix well. Add 0.1 mol of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide in batches (each batch is divided into 5 batches, with an interval of 10 min between each batch). Heat to 70℃ and react for 7 h. Cool to room temperature, filter, distill under reduced pressure at 45℃ for 1 h, and purify by column chromatography with a mixed solution of ethyl acetate and petroleum ether as the eluent (the volume ratio of ethyl acetate to petroleum ether is 2:3). Distill under reduced pressure at 50℃ for 2 h to obtain the flame retardant and antioxidant. Its 1H NMR spectrum is shown below. Figure 1 As shown, the data is as follows: 1 H NMR (400MHz, Chloroform- d) δ 11.74 (s, 2H), 11.45 (s, 2H), 7.78 - 7.71 (m, 4H), 7.67(d, J = 8.5 Hz, 2H), 7.58 - 7.44 (m, 6H), 7.05 (dd, J = 8.5, 1.9 Hz, 2H), 6.84 (d, J = 1.9 Hz, 2H), 5.45 (d, J = 9.3 Hz, 2H), 4.60 (tt, J = 6.0, 4.8Hz, 2H), 4.05 (s, 10H), 2.99 - 2.60 (m, 16H), 1.60 - 1.43 (m, 12H), 1.40 -1.23 (m, 48H), 1.08 (d, J = 7.3 Hz, 6H), 0.93 - 0.84 (m, 6H); its high-resolution mass spectrum is shown below. Figure 2 As shown, HRMS (m / z): 1565.7669 [M+H] + .

[0022] Example 2: Preparation of flame retardant and antioxidant: S1: Add 300 ml of anhydrous acetonitrile, 0.108 mol of oleylamine, and 0.1 mol of 2-hydroxy-4-(methacryloyloxy)benzophenone to a reaction vessel, stir and mix well, heat to 45 °C, react for 5.5 h, distill under reduced pressure at 40 °C for 1 h, recrystallize using 180 ml of a mixed solution of acetone and n-hexane (volume ratio of acetone to n-hexane is 1:9), filter, and dry under vacuum at 50 °C for 10 h to obtain intermediate 1; S2: Under nitrogen protection, 400 ml of anhydrous ethanol, 0.1 mol of intermediate 1, 0.112 mol of L-cysteine ​​and 3 g of photoinitiator 184 were added to the reaction vessel and stirred for 30 min. The mixture was then irradiated under 300 W UV light at 25 °C for 15 min with stirring, and then distilled under reduced pressure at 45 °C for 1 h. 300 ml of toluene was added and stirred until well mixed. The mixture was washed with deionized water (3 × 100 ml), dried with 30 g of anhydrous magnesium sulfate, filtered, and distilled under reduced pressure at 70 °C for 2 h to obtain intermediate 2. S3: Add 1000 ml of anhydrous acetonitrile, 0.209 mol of intermediate 2, and 0.22 mol of triethylamine to the reaction vessel, stir and mix well, then add 0.1 mol of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide in batches (each batch is divided into 5 batches, with an interval of 10 min between each batch), heat to 75℃, react for 6 h, cool to room temperature, filter, distill under reduced pressure at 45℃ for 1 h, purify by column chromatography, using a mixed solution of ethyl acetate and petroleum ether as the eluent (the volume ratio of ethyl acetate to petroleum ether is 2:3), distill under reduced pressure at 50℃ for 2 h to obtain the flame retardant and antioxidant.

[0023] Example 3: Preparation of flame retardant and antioxidant: S1: Add 300 ml of anhydrous acetonitrile, 0.11 mol of oleylamine, and 0.1 mol of 2-hydroxy-4-(methacryloyloxy)benzophenone to a reaction vessel, stir and mix well, heat to 50 °C, react for 5 h, distill under reduced pressure at 40 °C for 1 h, recrystallize using 180 ml of a mixed solution of acetone and n-hexane (volume ratio of acetone to n-hexane is 1:9), filter, and dry under vacuum at 50 °C for 10 h to obtain intermediate 1; S2: Under nitrogen protection, 400 ml of anhydrous ethanol, 0.1 mol of intermediate 1, 0.115 mol of L-cysteine ​​and 3 g of photoinitiator 184 were added to the reaction vessel and stirred for 30 min. The mixture was then irradiated under 300 W UV light at 25 °C for 20 min with stirring, and then distilled under reduced pressure at 45 °C for 1 h. 300 ml of toluene was added and stirred until well mixed. The mixture was washed with deionized water (3 × 100 ml), dried with 30 g of anhydrous magnesium sulfate, filtered, and distilled under reduced pressure at 70 °C for 2 h to obtain intermediate 2. S3: Add 1000 ml of anhydrous acetonitrile, 0.21 mol of intermediate 2, and 0.22 mol of triethylamine to the reaction vessel, stir and mix well, then add 0.1 mol of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide in batches (each batch is divided into 5 batches, with an interval of 10 min between each batch), heat to 80℃, react for 5 h, cool to room temperature, filter, distill under reduced pressure at 45℃ for 1 h, purify by column chromatography, using a mixed solution of ethyl acetate and petroleum ether as the eluent (the volume ratio of ethyl acetate to petroleum ether is 2:3), distill under reduced pressure at 50℃ for 2 h to obtain the flame retardant and antioxidant.

[0024] Example 4: Preparation of crosslinking agent: N1: 200 ml of anhydrous acetonitrile, 0.041 mol of 6-maleimide hexanoic acid, 0.041 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, 0.004 mol of 1-hydroxybenzotriazole, and 0.041 mol of 4-dimethylaminopyridine were added to a reaction vessel and stirred for 20 min. Then, 0.01 mol of N,N,N',N'-tetra(p-aminophenyl)p-phenylenediamine was added, and the mixture was reacted at 25 °C for 12 h. After filtration, 250 ml of deionized water was added and stirred to precipitate the precipitate. The precipitate was then filtered and washed with a mixed solution of tetrahydrofuran and deionized water (volume ratio of tetrahydrofuran to deionized water was 1:9) (2 × 25 ml). The mixture was then dried under vacuum at 60 °C for 12 h to obtain the tetraamide compound. Its 1H NMR spectrum data are as follows: 1 H NMR (400 MHz, DMSO- d 6) δ 9.72 (s, 4H), 7.57 - 7.49 (m, 8H), 7.24 (s, 4H), 7.20 - 7.12 (m, 8H), 6.71 (s, 8H), 3.81 - 3.63 (m, 8H), 2.33(t, J = 8.3 Hz, 8H), 1.76 - 1.56 (m, 16H), 1.46 - 1.35 (m, 8H); HRMS (m / z): 1245.5343[M+H] + ; N2: 150 ml of dichloromethane, 0.01 mol of tetraamide compound, and 0.042 mol of furfuryl alcohol were added to a reaction vessel. Under nitrogen protection, the mixture was stirred and refluxed for 24 h. After cooling to room temperature, 300 ml of anhydrous diethyl ether was added and stirred to precipitate the precipitate. The precipitate was filtered, washed with anhydrous diethyl ether (2 × 20 ml), and dried under vacuum at 40 °C for 8 h to obtain the crosslinking agent. Its 1H NMR spectrum is shown below. Figure 3 As shown, the data is as follows: 1 H NMR (400 MHz, DMSO- d6) δ 9.72 (s, 4H), 7.58 - 7.49 (m, 8H), 7.24 (s,4H), 7.20 - 7.12 (m, 8H), 6.39 (ddt, J = 8.5, 1.7, 0.8 Hz, 4H), 6.28 (ddd, J= 8.4, 5.9, 1.7 Hz, 4H), 5.09 (tt, J = 5.8, 0.9 Hz, 4H), 4.44 (d, J = 12.3Hz, 4H), 4.02 (dd, J = 11.0, 6.2 Hz, 4H), 3.92 (dd, J = 11.0, 6.2 Hz, 4H),3.62 (dt, J = 12.4, 6.9 Hz, 4H), 3.52 (dt, J = 12.3, 6.9 Hz, 4H), 3.13 (td, J = 6.0, 1.7 Hz, 4H), 3.00 (dd, J = 6.3, 1.7 Hz, 4H), 2.33 (t, J = 8.3 Hz, 8H), 1.73 - 1.53 (m, 16H), 1.49 - 1.33 (m, 8H); its high-resolution mass spectrum is shown below. Figure 4 As shown, HRMS (m / z): 1637.6815 [M+H] + .

[0025] Example 5 Preparation of flame-retardant polyurethane coating (1) Weigh out: 25g of polyether polyol, 15g of isocyanate (diphenylmethane-4,4'-diisocyanate), 0.1g of catalyst (dibutyltin dilaurate), 4g of 2,2-dimethylolpropionic acid, 1g of crosslinking agent (prepared in Example 4), 6g of triethylamine, 4g of flame retardant and antioxidant (prepared in Example 1), 0.3g of defoamer (BYK-011), 0.5g of dispersant (BYK-190), 5g of silica, and 70g of deionized water; (2) Stir the polyether polyol, isocyanate and catalyst for 20 min, heat to 70℃ and react for 3 h, add 2,2-dimethylolpropionic acid and react for 1 h, add crosslinking agent and continue to react for 2 h, cool to room temperature to obtain polyurethane prepolymer; (3) Stir deionized water, polyurethane prepolymer and triethylamine at 500 r / min for 20 min, then add flame retardant and anti-aging agent, defoamer, dispersant and silica in sequence, and stir at 800 r / min for 30 min to obtain flame retardant polyurethane coating.

[0026] Example 6 Preparation of flame-retardant polyurethane coating (1) Weigh out: 28g of polyether polyol, 19g of isocyanate (2,4-toluene diisocyanate), 0.16g of catalyst (stannous octoate), 5g of 2,2-dimethylolpropionic acid, 1.2g of crosslinking agent (prepared in Example 4), 7g of triethylamine, 5g of flame retardant and antioxidant (prepared in Example 2), 0.4g of defoamer (BYK-011), 0.6g of dispersant (BYK-190), 7g of silica, and 75g of deionized water; (2) Stir the polyether polyol, isocyanate and catalyst for 20 min, heat to 75℃ and react for 2.5 h, add 2,2-dimethylolpropionic acid and react for 1 h, add crosslinking agent and continue to react for 2 h, cool to room temperature to obtain polyurethane prepolymer; (3) Stir deionized water, polyurethane prepolymer and triethylamine at 500 r / min for 20 min, then add flame retardant and anti-aging agent, defoamer, dispersant and silica in sequence, and stir at 800 r / min for 30 min to obtain flame retardant polyurethane coating.

[0027] Example 7 Preparation of Flame-Retardant Polyurethane Coating (1) Weigh out: 30g of polyether polyol, 20g of isocyanate (2,4-toluene diisocyanate), 0.2g of catalyst (stannous octoate), 6g of 2,2-dimethylolpropionic acid, 1.5g of crosslinking agent (prepared in Example 4), 8g of triethylamine, 6g of flame retardant and antioxidant (prepared in Example 3), 0.5g of defoamer (BYK-011), 0.8g of dispersant (BYK-190), 8g of silica, and 80g of deionized water; (2) Stir the polyether polyol, isocyanate and catalyst for 20 min, heat to 80℃ and react for 2 h, add 2,2-dimethylolpropionic acid and react for 1 h, add crosslinking agent and continue to react for 2 h, cool to room temperature to obtain polyurethane prepolymer; (3) Stir deionized water, polyurethane prepolymer and triethylamine at 500 r / min for 20 min, then add flame retardant and anti-aging agent, defoamer, dispersant and silica in sequence, and stir at 800 r / min for 30 min to obtain flame retardant polyurethane coating.

[0028] Comparative Example 1 The raw material composition and preparation method of the flame-retardant polyurethane coating are basically the same as those in Example 6, except that the flame-retardant antioxidant is replaced with an equal weight of the flame-retardant antioxidant prepared by the following method: The preparation method of the flame retardant and antioxidant is basically the same as that in Example 2, except that 2-hydroxy-4-(methacryloyloxy)benzophenone in step S1 is replaced with an equimolar amount of 4-methacryloyloxybenzophenone.

[0029] Comparative Example 2 The raw material composition and preparation method of the flame-retardant polyurethane coating are basically the same as those in Example 6, except that the flame-retardant antioxidant is replaced with an equal weight of the flame-retardant antioxidant prepared by the following method: The preparation method of the flame retardant and antioxidant is basically the same as that in Example 2, except that 2-hydroxy-4-(methacryloyloxy)benzophenone in step S1 is replaced with 0.21 mol, the reaction temperature is 60℃, and the reaction time is 15 h.

[0030] The structural formula of the flame retardant and antioxidant is as follows:

[0031] Comparative Example 3 The raw material composition and preparation method of the flame-retardant polyurethane coating are basically the same as those in Example 6, except that the flame-retardant antioxidant is replaced with an equal weight of the flame-retardant antioxidant prepared by the following method: The preparation method of the flame retardant and anti-aging agent is basically the same as that in Example 2. The difference is that the 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide in step S3 is replaced with 0.2 mol of 5,5-dimethyl-2-chloro-1,3,2-dioxaphosphacaprolactone phosphate.

[0032] Comparative Example 4 The raw material composition and preparation method of the flame-retardant polyurethane coating are basically the same as those in Example 6, except that the crosslinking agent is replaced with an equal weight of a crosslinking agent prepared by the following method: The preparation method of the crosslinking agent is basically the same as that in Example 4, except that N,N,N',N'-tetra(p-aminophenyl)p-phenylenediamine in step N1 is replaced with 0.02 mol of bis(4-aminophenyl)aniline (CAS: 4117-90-2); and furfuryl alcohol in step N2 is replaced with 0.021 mol.

[0033] Comparative Example 5 The raw material composition and preparation method of the flame-retardant polyurethane coating are basically the same as those in Example 6, except that the crosslinking agent is replaced with an equal weight of a crosslinking agent prepared by the following method: The preparation method of the crosslinking agent is basically the same as that in Example 4, except that 6-maleimide hexanoic acid in step N1 is replaced with an equimolar amount of 11-maleamido undecanoic acid.

[0034] Comparative Example 6 The raw material composition and preparation method of the flame-retardant polyurethane coating are basically the same as those in Example 6, except that the crosslinking agent is replaced with an equal weight of a crosslinking agent prepared by the following method: N1: 200 ml of anhydrous acetonitrile, 0.041 mol of 6-maleimide hexanoic acid, 0.041 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, 0.004 mol of 1-hydroxybenzotriazole, and 0.041 mol of 4-dimethylaminopyridine were added to a reaction vessel and stirred for 20 min. Then, 0.01 mol of N,N,N',N'-tetra(p-aminophenyl)p-phenylenediamine was added, and the mixture was reacted at 25 °C for 12 h. After filtration, 250 ml of deionized water was added and stirred to precipitate the precipitate. The precipitate was then filtered and washed with a mixed solution of tetrahydrofuran and deionized water (volume ratio of tetrahydrofuran to deionized water was 1:9) (2 × 25 ml). The mixture was then dried under vacuum at 60 °C for 12 h to obtain the tetraamide compound. N2: Add 150 ml of anhydrous acetonitrile, 0.01 mol of tetraamide compound and 0.042 mol of 3-aminopropanol to a reaction vessel, stir and mix well, react at 45 °C for 6 h, cool to room temperature, add 300 ml of anhydrous diethyl ether and stir to precipitate, filter, wash with anhydrous diethyl ether (2 × 20 ml), and vacuum dry at 40 °C for 8 h to obtain the crosslinking agent.

[0035] The polyether polyol used in the embodiments and comparative examples of this application is CHE-303, produced by Changhua Chemical Technology Co., Ltd.; the silica is HDS100, produced by Shandong Hongruitong New Material Technology Co., Ltd.

[0036] The flame-retardant polyurethane coatings prepared in Examples 5-7 and Comparative Examples 1-6 of this application were subjected to anti-aging and flame-retardant performance tests.

[0037] Sample preparation: The flame-retardant polyurethane coating was poured into a polytetrafluoroethylene mold (120mm×30mm×1.5mm) and cured for 7 days under standard curing conditions (temperature 23℃, humidity 50%). The coated sample was then demolded.

[0038] Anti-aging performance test: The samples were placed in a QUV accelerated aging test chamber for aging tests, with an ultraviolet wavelength of 340nm and an irradiance of 0.76W / m. 2 The sample was aged at 60℃ for 1200 hours, and the tensile properties of the sample before and after aging were tested.

[0039] Tensile property test: The specimen was cut into dumbbell shape 1 and tested according to GB / T 19250-2013 standard.

[0040] Flame retardant performance test: The coated sample is vertically clamped in a glass jar containing nitrogen and oxygen in a certain ratio. The upper end of the sample is ignited with a propane igniter. The sample burns steadily from top to bottom for 3 minutes. The minimum volume fraction of oxygen required to support the sample burning to 50 mm is determined (if the burning length is less than 50 mm within 30 minutes, the oxygen concentration is increased; if the burning length exceeds 50 mm, the oxygen concentration is decreased). This is the limiting oxygen index of the sample.

[0041] Table 1 Performance Test Table

[0042] As can be seen from the data in Examples 5-7 in Table 1, the flame-retardant polyurethane coating prepared by the present invention has excellent tensile strength, anti-aging properties and flame-retardant properties.

[0043] The flame-retardant and antioxidant agent added to the flame-retardant polyurethane coating prepared in this invention is based on a symmetrical phosphoramide structure, and incorporates benzophenone, ortho- and ortho-phenolic hydroxyl groups, thioethers, carboxyl groups, and secondary amines. The carboxyl groups and secondary amines in the flame-retardant and antioxidant agent can strongly interact with isocyanate or hydrogen bonding sites in the polyurethane system, allowing the flame-retardant and antioxidant agent to embed into the polyurethane network structure, enhancing intermolecular cohesion, effectively reducing the migration and volatilization of small-molecule flame-retardant and antioxidant agents, and improving the long-term flame-retardant and aging-resistant stability of the coating. Regarding flame retardancy: the phosphoramide structure in the flame-retardant and antioxidant agent molecule decomposes upon heating, releasing inert gases such as NH3 to dilute oxygen, while simultaneously generating phosphoric acid or polyphosphoric acid. This catalyzes the dehydration and carbonization of the material surface to form a dense, heat-insulating carbon layer, and interrupts the combustion reaction in the gas phase by capturing combustion free radicals, thereby improving the flame-retardant performance of the coating. In terms of anti-aging: the intramolecular hydrogen bond formed by the carbonyl group and the ortho-phenolic hydroxyl group in the flame retardant and anti-aging agent molecule undergoes excited-state intramolecular proton transfer after absorbing ultraviolet radiation, rapidly dissipating ultraviolet energy as heat, thereby effectively inhibiting the generation of polymer photo-oxidative free radicals; the thioether can effectively delay the thermo-oxidative aging of the material by decomposing the peroxides generated during polymer aging and blocking the propagation stage of the free radical chain oxidation reaction. The symmetrical phosphoramide core enables the carbonyl group, phenolic hydroxyl group, thioether, carboxyl group and secondary amine to present an ordered spatial distribution, forming a multiple synergistic effect of flame retardancy, anti-aging and interface enhancement, improving the tensile properties, anti-aging properties and flame retardant properties of the coating.

[0044] The flame retardant and antioxidant added in Comparative Example 2 has a larger molecular weight and more complex structure, making it more prone to phase separation in the polyurethane system. This reduces its effective volume fraction in the material, hindering the full realization of the synergistic effect of anti-aging and flame retardancy. The flame retardant and antioxidant used in Comparative Example 3 has a smaller molecular weight and poorer migration resistance, affecting its anti-aging performance.

[0045] The crosslinking agent added to the flame-retardant polyurethane coating prepared by this invention has a four-arm structure, and simultaneously introduces a rigid benzene ring, alkyl chain, and a dynamic six-membered ring and hydroxyl group generated by the Diels-Alder reaction. The hydroxyl group in the crosslinking agent molecule reacts with the unreacted isocyanate group in the polyurethane prepolymer. Its four-arm structure can increase the crosslinking density, construct a dense three-dimensional crosslinking network structure in the system, enhance the overall cohesion of the coating, and thus improve the mechanical properties of the coating. The benzene ring provides a rigid skeleton, restricts the free rotation of chain segments, increases local hard domains, and effectively improves impact resistance. The flexible alkyl chain increases the degree of freedom of chain segments, alleviates the stress concentration of the crosslinking network, and improves the mechanical properties of the coating. The Diels-Alder six-membered ring, as a dynamic reversible bond, can partially break and recombine under stress or heat conditions, absorb and alleviate stress concentration, and thus endow the coating with good mechanical properties. The four-arm topology of the crosslinking agent provides efficient crosslinking density, the benzene ring provides rigid support, the alkyl chain provides flexible transition, and the Diels-Alder dynamic six-membered ring endows the network with reversible adjustment capability, forming a composite crosslinking network of "static strong crosslinking + dynamic adjustable crosslinking" with the polyurethane matrix, thereby improving the mechanical properties of the coating. In Comparative Example 5, the alkyl chain in the flame retardant was too long, which led to a reduction in intermolecular forces, thus reducing the tensile strength of the coating.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A flame-retardant polyurethane coating, characterized in that, The ingredients include the following parts by weight: 25-30 parts polyether polyol, 15-20 parts isocyanate, 0.1-0.2 parts catalyst, 4-6 parts 2,2-dimethylolpropionic acid, 1-1.5 parts crosslinking agent, 6-8 parts triethylamine, 4-6 parts flame retardant and antioxidant, 0.3-0.5 parts defoamer, 0.5-0.8 parts dispersant, 5-8 parts silica, and 70-80 parts deionized water; The flame retardant and antioxidant is prepared by the following method: S1: The reaction of oleylamine with 2-hydroxy-4-(methacryloyloxy)benzophenone yields intermediate 1. S2: Intermediate 1 reacts with L-cysteine ​​to give intermediate 2. S3: Intermediate 2 reacts with 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide to obtain a flame retardant and anti-aging agent; The structural formula of the flame retardant and antioxidant is as follows: ； The crosslinking agent has the following structural formula: 。 2. The flame-retardant polyurethane coating according to claim 1, characterized in that, In step S1, the molar ratio of oleylamine to 2-hydroxy-4-(methacryloyloxy)benzophenone is (1.05-1.1):

1.

3. The flame-retardant polyurethane coating according to claim 1, characterized in that, In step S2, the molar ratio of intermediate 1 to L-cysteine ​​is 1:(1.1-1.15).

4. The flame-retardant polyurethane coating according to claim 1, characterized in that, In step S3, the molar ratio of intermediate 2 to 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide is (2.08-2.1):

1.

5. The flame-retardant polyurethane coating according to claim 1, characterized in that, The crosslinking agent is prepared by the following method: N1: N,N,N',N'-Tetra(p-aminophenyl)p-phenylenediamine reacts with 6-maleimide hexanoic acid to give a tetraamide compound. N2: Tetraamide compounds react with furfuryl alcohol to form crosslinking agents.

6. The flame-retardant polyurethane coating according to claim 5, characterized in that, In step N1, the molar ratio of N,N,N',N'-tetra(p-aminophenyl)p-phenylenediamine to 6-maleimide hexanoic acid is 1:4.1; in step N2, the molar ratio of the tetraamide compound to furfuryl alcohol is 1:4.

2.

7. The flame-retardant polyurethane coating according to claim 1, characterized in that, The isocyanate is one of diphenylmethane-4,4'-diisocyanate and 2,4-toluene diisocyanate; the catalyst is one of dibutyltin dilaurate and stannous octoate.

8. The flame-retardant polyurethane coating according to claim 1, characterized in that, The defoamer is BYK-011; the dispersant is BYK-190.

9. A method for preparing a flame-retardant polyurethane coating according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Weigh out the following by weight: 25-30 parts of polyether polyol, 15-20 parts of isocyanate, 0.1-0.2 parts of catalyst, 4-6 parts of 2,2-dimethylolpropionic acid, 1-1.5 parts of crosslinking agent, 6-8 parts of triethylamine, 4-6 parts of flame retardant and antioxidant, 0.3-0.5 parts of defoamer, 0.5-0.8 parts of dispersant, 5-8 parts of silica, and 70-80 parts of deionized water; (2) Stir and mix the polyether polyol, isocyanate and catalyst, heat and react, add 2,2-dimethylolpropionic acid and react, then add crosslinking agent and continue the reaction to obtain polyurethane prepolymer; (3) Stir deionized water, polyurethane prepolymer and triethylamine together, then add flame retardant and anti-aging agent, defoamer, dispersant and silica in sequence and stir to obtain flame retardant polyurethane coating.

10. The application of the flame-retardant polyurethane coating according to any one of claims 1-8 in the field of unmanned aerial vehicles (UAVs).

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