Temperature-resistant waterproof polyurethane coating and preparation method thereof

Abstract

The invention discloses a temperature-resistant waterproof polyurethane coating and a preparation method thereof, and belongs to the technical field of polyurethane coatings, the temperature-resistant waterproof polyurethane coating comprises the following components by mass: 80-90 parts of a polyurethane prepolymer, 1-1.5 parts of a reinforcing filler, 2-3 parts of a composite curing agent and 7-9 parts of polyether glycol; the polyurethane prepolymer is prepared by the following steps: stirring and mixing a fluororubber grafted solution and polyester polyol in a reaction kettle, heating to 70-80 DEG C under the protection of nitrogen, adding an isocyanate mixture, and stirring and reacting for 2-3 hours to obtain the polyurethane prepolymer; according to the temperature-resistant waterproof polyurethane coating prepared by the preparation method disclosed by the invention, the-NCO group is terminated, so that the coating has good stability before curing, is not easy to react with moisture in air and has good moisture resistance before curing, and the fluororubber, the reinforcing filler and the polyurethane waterproof coating are mixed, so that a cross-linked network of the cured polyurethane waterproof coating is enhanced; the mechanical property and the temperature resistance of the cured polyurethane waterproof coating are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane coatings, and specifically relates to a heat-resistant and waterproof polyurethane coating and a preparation method thereof. Background Art

[0002] Polyurethane is a polymer with a carbamate structure formed on the main chain of the molecule after the polyaddition reaction of diisocyanate and polyol. Polyurethane coatings prepared by dissolving polyurethane in solvent have good adhesion, wear resistance, waterproofness and weather resistance, and are widely used in industrial infrastructure, residential and public buildings.

[0003] However, the highly active -NCO group contained in the polyurethane prepolymer is extremely easy to react with moisture in the air. Due to the strong activity of -NCO, it can react rapidly with hydroxyl-containing compounds even in the absence of a catalyst, resulting in poor storage stability of the polyurethane coating after unsealing. The reaction also produces carbon dioxide gas, which causes bulging of the polyurethane coating, reduces its temperature and humidity resistance, and affects the mechanical properties of the polyurethane coating.

[0004] A Chinese invention patent application with publication number CN108300253A discloses a modified one-component polyurethane waterproof coating. By adding polyethyleneimine hydrogel, a coupling agent, gellan gum and low-order saturated fatty acids to the one-component polyurethane waterproof coating, the binding force within the system is improved to avoid the reaction of the one-component polyurethane waterproof coating with water molecules in the air. However, in this solution, the polyethyleneimine hydrogel reacts chemically with the carbon dioxide generated during the curing process of the polyurethane waterproof coating, and the problem of the reaction of the -NCO group with moisture in the air is not solved. In addition, the addition of the hydrogel also reduces the heat resistance and mechanical properties of the polyurethane waterproof coating.

[0005] In the application field of polyurethane waterproof coating on metal surface, the metal surface is prone to oxidation reaction with water molecules, thereby accumulating water molecules, making it easy for the polyurethane waterproof coating to react with the water molecules on the metal surface to produce carbon dioxide when coated on the metal surface, thereby reducing the mechanical properties and temperature and humidity resistance of the polyurethane waterproof coating. Summary of the invention

[0006] The first purpose of the present invention is to solve the problem that the polyurethane waterproof coating is easy to react with moisture and has poor moisture resistance before curing, and to provide a heat-resistant and waterproof polyurethane coating and a preparation method thereof.

[0007] The second purpose of the present invention is to solve the problem that polyurethane waterproof coatings are easily reacted with moisture on the surface of metal materials when used on metal materials, thereby reducing the performance of polyurethane waterproof coatings, and to provide a heat-resistant and waterproof polyurethane coating and a preparation method thereof.

[0008] The present invention blocks -NCO groups by a blocking agent to improve the stability of the polyurethane waterproof coating before curing, and strengthens the cross-linking network of the polyurethane waterproof coating after curing by mixing fluororubber and reinforcing filler with the polyurethane waterproof coating to improve the mechanical properties and temperature resistance of the cured polyurethane waterproof coating.

[0009] The purpose of the present invention can be achieved through the following technical solutions: A heat-resistant and waterproof polyurethane coating, comprising the following components in parts by mass: 80-90 parts of polyurethane prepolymer, 1-1.5 parts of reinforcing filler, 2-3 parts of composite curing agent and 7-9 parts of polyether diol.

[0010] The polyurethane prepolymer is prepared by the following steps: The fluororubber grafting solution and polyester polyol are stirred and mixed in a reaction kettle for 8-10 hours to obtain fluororubber polyester polyol. Under nitrogen protection, the fluororubber polyester polyol is heated to 70-80° C., and then the isocyanate mixture is added and stirred for reaction for 2-3 hours to obtain a polyurethane prepolymer.

[0011] Furthermore, the usage ratio of the fluororubber grafting solution, the polyester polyol and the isocyanate mixture is 4-6g:40-50g:35-40g.

[0012] Further, the fluororubber grafting solution is prepared by the following steps: Mix benzoyl peroxide and methacrylic acid in a reaction kettle, dissolve liquid fluororubber raw rubber in ethyl acetate, then add it into the reaction kettle, heat it to 80-90°C and react for 6-8h to obtain a fluororubber grafting solution.

[0013] Furthermore, the usage ratio of benzoyl peroxide, methacrylic acid, liquid fluororubber raw rubber and ethyl acetate is 10-12g:10-12g:5-8g:30-40mL.

[0014] Further, the polyester polyol is prepared by the following steps: In a reaction kettle, ethylene glycol and dimethyl terephthalate are mixed, heated to 195-205° C., stirred and reacted for 2-3 hours, cooled to 115-125° C., neopentyl glycol, isophthalic acid and sebacic acid are added to the reaction kettle, heated to 200-220° C., stirred and reacted for 7-8 hours, and polyester polyols are obtained by vacuum distillation.

[0015] Furthermore, the usage ratio of ethylene glycol, dimethyl terephthalate, neopentyl glycol, isophthalic acid and sebacic acid is 10-15g: 10-20g: 10-15g: 8-12g: 10-15g.

[0016] Further, the isocyanate mixture is prepared by the following steps: In a reaction kettle, isophorone diisocyanate and ethyl acetate are mixed, isophorone diamine is added dropwise, the temperature is raised to 55-65° C., and the reaction is carried out for 2-3 hours to obtain an isocyanate mixture.

[0017] Furthermore, the usage ratio of isophorone diisocyanate, ethyl acetate and isophorone diamine is 12-15g:30-40g:0.1-0.15g.

[0018] Further, the reinforcing filler is prepared by the following steps: In a reaction kettle, chitosan is dissolved in a 2wt% acetic acid solution, quartz sand is added, ultrasonic dispersion is performed for 4-6 hours, glutaraldehyde is added, the temperature is raised to 60-70°C and stirred for 20-24 hours, a precipitate is obtained by filtering, the precipitate is washed, and dried to obtain a reinforcing filler.

[0019] Furthermore, the usage ratio of chitosan, acetic acid solution, quartz sand and glutaraldehyde is 2-3 g: 100-120 mL: 2-3 g: 5-8 mL.

[0020] Further, the composite curing agent is prepared by the following steps: In a reaction kettle, silane coupling agent A-1100 was added dropwise to methanol, and bisphenol AF and tetrabutylammonium hydrogen sulfate were added after stirring for 30-40 minutes, and stirred until dissolved to obtain a composite curing agent.

[0021] Furthermore, the usage ratio of methanol, silane coupling agent A-1100, bisphenol AF and tetrabutylammonium hydrogen sulfate is 5-6g: 0.5-0.8g: 0.6-0.8g: 0.4-0.6g.

[0022] A method for preparing a heat-resistant and waterproof polyurethane coating comprises the following steps: The polyether diol, reinforcing filler, composite curing agent and polyurethane prepolymer are stirred and mixed in a reaction kettle, and the temperature is raised to 80-90° C. to react for 2-3 hours to obtain a heat-resistant and waterproof polyurethane coating.

[0023] A method for using a heat-resistant and waterproof polyurethane coating comprises the following steps: After applying the heat-resistant and waterproof polyurethane coating to the metal substrate, bake it at 180-200℃ for 20-30 minutes to cure it.

[0024] Beneficial effects of the present invention: The heat-resistant and waterproof polyurethane coating prepared by the present invention has good stability before curing by blocking the -NCO group, is not easy to react with moisture in the air, and has good moisture resistance before curing. Fluororubber and reinforcing filler are mixed with the polyurethane waterproof coating to enhance the cross-linking network of the polyurethane waterproof coating after curing, thereby improving the mechanical properties and temperature resistance of the polyurethane waterproof coating after curing.

[0025] The heat-resistant and waterproof polyurethane coating prepared by the present invention unblocks the -NCO group through high-temperature curing, and at the same time evaporates the moisture on the surface of the metal material at high temperature. The moisture evaporates during the coating process, reduces the generation of bubbles during the coating curing process, increases the contact area between the heat-resistant and waterproof polyurethane coating and the metal material, and improves the bonding strength of the heat-resistant and waterproof polyurethane coating.

[0026] The invention prepares polyester polyol containing benzene rings to improve the heat resistance of polyester polyol, introduces fluororubber grafting solution whose solvent is ethyl acetate into polyester polyol, disperses the fluororubber grafting solution in polyester polyol through ethyl acetate, thereby dispersing fluororubber in the fluororubber grafting solution in polyurethane prepolymer, utilizes vulcanization and curing of fluororubber to make fluororubber fill pores formed by curing of polyurethane, and the vulcanized and cross-linked fluororubber reduces the water molecule permeability of polyurethane coating, thereby improving the waterproof performance of cured polyurethane coating.

[0027] The present invention compounds quartz sand whose main component is silicon dioxide with chitosan through the crosslinking effect of glutaraldehyde. Chitosan contains hydroxyl groups and has strong activity. The silanol groups on the surface of silicon dioxide can form hydrogen bonds with hydroxyl groups in polyester polyols, thereby improving the dispersibility of reinforcing fillers in polyurethane prepolymers, enriching the network system of polyurethane coatings, and improving the mechanical strength and temperature resistance of polyurethane coatings. DETAILED DESCRIPTION

[0028] 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 described embodiments 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 creative work are within the scope of protection of the present invention.

[0029] Embodiment 1: A heat-resistant and waterproof polyurethane coating is prepared by the following steps: S1. In a reactor, 10 g of ethylene glycol and 10 g of dimethyl terephthalate were mixed, heated to 195° C., stirred and reacted for 2 h, cooled to 115° C., 10 g of neopentyl glycol, 8 g of isophthalic acid and 10 g of sebacic acid were added to the reactor, heated to 200° C., stirred and reacted for 7 h, and distilled under reduced pressure to obtain polyester polyol.

[0030] S2. Mix 10 g of benzoyl peroxide and 10 g of methacrylic acid in a reactor, dissolve 5 g of liquid fluororubber raw rubber in 30 mL of ethyl acetate, then add the mixture into the reactor, heat to 80° C. and react for 6 h to obtain a fluororubber grafting solution.

[0031] S3. In a reaction kettle, 12 g of isophorone diisocyanate and 30 g of ethyl acetate were mixed, and 0.1 g of isophorone diamine was added dropwise. The temperature was raised to 55° C., and the reaction was carried out for 2 h to obtain an isocyanate mixture.

[0032] S4. In a reaction kettle, 4 g of fluororubber grafting solution and 40 g of polyester polyol were stirred and mixed for 8 h to obtain fluororubber polyester polyol. Under nitrogen protection, the fluororubber polyester polyol was heated to 70° C., and 35 g of isocyanate mixture was added and stirred for reaction for 2 h to obtain a polyurethane prepolymer.

[0033] S5. Dissolve 2 g of chitosan in 100 mL of 2 wt% acetic acid solution in a reactor, add 2 g of quartz sand, and disperse by ultrasonic for 4 h. Add 5 mL of glutaraldehyde, raise the temperature to 60 °C and stir for 20 h. Filter to obtain a precipitate, wash the precipitate with ethanol and deionized water, and dry at 60 °C for 10 h to obtain a reinforced filler.

[0034] S6. In a reaction kettle, add 0.5 g of silane coupling agent A-1100 dropwise into 5 g of methanol, stir for 30 min, then add 0.6 g of bisphenol AF and 0.4 g of tetrabutylammonium hydrogen sulfate, and stir until dissolved to obtain a composite curing agent.

[0035] S7. In a reaction kettle, 7 g of polyether diol, 1 g of reinforcing filler, 2 g of composite curing agent and 80 g of polyurethane prepolymer are stirred and mixed, and then the temperature is raised to 80° C. and reacted for 2 h to obtain a heat-resistant and waterproof polyurethane coating.

[0036] Embodiment 2: A heat-resistant and waterproof polyurethane coating is prepared by the following steps: S1. In a reactor, 12.5 g of ethylene glycol and 15 g of dimethyl terephthalate were mixed, heated to 200° C., stirred and reacted for 2.5 h, cooled to 120° C., 12.5 g of neopentyl glycol, 10 g of isophthalic acid and 12.5 g of sebacic acid were added to the reactor, heated to 210° C., stirred and reacted for 7.5 h, and polyester polyol was obtained by vacuum distillation.

[0037] S2. Mix 11 g of benzoyl peroxide and 11 g of methacrylic acid in a reactor, dissolve 6.5 g of liquid fluororubber raw rubber in 35 mL of ethyl acetate, then add the mixture into the reactor, heat to 85°C and react for 7 h to obtain a fluororubber grafting solution.

[0038] S3. In a reaction kettle, 13.5 g of isophorone diisocyanate and 35 g of ethyl acetate were mixed, and 0.125 g of isophorone diamine was added dropwise. The temperature was raised to 60° C., and the reaction was carried out for 2.5 h to obtain an isocyanate mixture.

[0039] S4. In a reaction kettle, 5 g of the fluororubber grafting solution and 45 g of polyester polyol were stirred and mixed for 9 hours to obtain fluororubber polyester polyol. Under nitrogen protection, the fluororubber polyester polyol was heated to 75° C., 37.5 g of the isocyanate mixture was added, and the mixture was stirred and reacted for 2.5 hours to obtain a polyurethane prepolymer.

[0040] S5. Dissolve 2.5 g of chitosan in 110 mL of 2 wt% acetic acid solution in a reactor, add 2.5 g of quartz sand, and disperse ultrasonically for 5 h. Add 6.5 mL of glutaraldehyde, raise the temperature to 65 ° C and stir for 22 h. Filter to obtain a precipitate, wash the precipitate with ethanol and deionized water, and dry at 65 ° C for 11 h to obtain a reinforced filler.

[0041] S6. In a reaction kettle, add 0.65 g of silane coupling agent A-1100 dropwise into 5.5 g of methanol, stir for 35 min, then add 0.7 g of bisphenol AF and 0.5 g of tetrabutylammonium hydrogen sulfate, and stir until dissolved to obtain a composite curing agent.

[0042] S7. In a reaction kettle, 8 g of polyether diol, 1.25 g of reinforcing filler, 2.5 g of composite curing agent and 85 g of polyurethane prepolymer were stirred and mixed, and then the temperature was raised to 85° C. and reacted for 2.5 h to obtain a heat-resistant and waterproof polyurethane coating.

[0043] Embodiment 3: A heat-resistant and waterproof polyurethane coating is prepared by the following steps: S1. In a reactor, 15 g of ethylene glycol and 20 g of dimethyl terephthalate were mixed, heated to 205° C., stirred and reacted for 3 h, cooled to 125° C., 15 g of neopentyl glycol, 12 g of isophthalic acid and 15 g of sebacic acid were added to the reactor, heated to 220° C., stirred and reacted for 8 h, and distilled under reduced pressure to obtain polyester polyol.

[0044] S2. Mix 12 g of benzoyl peroxide and 12 g of methacrylic acid in a reactor, dissolve 8 g of liquid fluororubber raw rubber in 40 mL of ethyl acetate, then add the mixture into the reactor, heat to 90° C. and react for 8 h to obtain a fluororubber grafting solution.

[0045] S3. In a reaction kettle, 15 g of isophorone diisocyanate and 40 g of ethyl acetate were mixed, and 0.15 g of isophorone diamine was added dropwise. The temperature was raised to 65° C., and the reaction was carried out for 3 h to obtain an isocyanate mixture.

[0046] S4. In a reaction kettle, 6 g of the fluororubber grafting solution and 50 g of polyester polyol were stirred and mixed for 10 h to obtain fluororubber polyester polyol. Under nitrogen protection, the fluororubber polyester polyol was heated to 80° C., 40 g of the isocyanate mixture was added, and the mixture was stirred and reacted for 3 h to obtain a polyurethane prepolymer.

[0047] S5. Dissolve 3 g of chitosan in 120 mL of 2 wt% acetic acid solution in a reactor, add 3 g of quartz sand, and disperse by ultrasonic for 6 h. Add 8 mL of glutaraldehyde, raise the temperature to 70 °C and stir for 24 h. Filter to obtain a precipitate, wash the precipitate with ethanol and deionized water, and dry at 70 °C for 12 h to obtain a reinforced filler.

[0048] S6. In a reaction kettle, add 0.8 g of silane coupling agent A-1100 dropwise into 6 g of methanol, stir for 40 min, add 0.8 g of bisphenol AF and 0.6 g of tetrabutylammonium hydrogen sulfate, and stir until dissolved to obtain a composite curing agent.

[0049] S7. In a reaction kettle, 9 g of polyether diol, 1.5 g of reinforcing filler, 3 g of composite curing agent and 90 g of polyurethane prepolymer are stirred and mixed, and then the temperature is raised to 90° C. and reacted for 3 hours to obtain a heat-resistant and waterproof polyurethane coating.

[0050] Principle of the invention: The invention prepares polyester polyol containing benzene rings to improve the heat resistance of polyester polyol, introduces fluororubber grafting solution whose solvent is ethyl acetate into polyester polyol, disperses the fluororubber grafting solution in polyester polyol through ethyl acetate, thereby dispersing fluororubber in the fluororubber grafting solution in polyurethane prepolymer, utilizes vulcanization and curing of fluororubber to make fluororubber fill pores formed by curing of polyurethane, and the vulcanized and cross-linked fluororubber reduces the water molecule permeability of polyurethane coating, thereby improving the waterproof performance of cured polyurethane coating.

[0051] The invention prepares an isocyanate mixture by using isophorone diisocyanate. Isocyanate belongs to aliphatic polyurethane and is more water-resistant, easy to store and not prone to yellowing. Ethyl acetate is used as a solvent and does not react with isophorone diisocyanate. The solvent has high fluidity and improves the fluidity of the coating during coating.

[0052] The present invention compounds quartz sand whose main component is silicon dioxide with chitosan under the cross-linking effect of glutaraldehyde. Chitosan contains hydroxyl groups and has strong activity. The silanol groups on the surface of silicon dioxide can form hydrogen bonds with hydroxyl groups in polyester polyols, thereby improving the dispersibility of reinforcing fillers in polyurethane prepolymers, enriching the network system of polyurethane coatings, and improving the mechanical strength and temperature resistance of polyurethane coatings.

[0053] The invention uses a blocking agent polyether diol to block the -NCO group of the polyurethane prepolymer, thereby improving the stability of the polyurethane prepolymer in the air and the moisture resistance of the polyurethane coating before use. When the -NCO group is unblocked at a high temperature of 200°C, moisture on the surface of the substrate to be coated is removed, thereby increasing the contact area between the polyurethane coating and the substrate surface. At the same time, the high temperature also triggers the start of the vulcanization reaction of the fluororubber. The coating cured at high temperature has higher thermal stability, so that the cured polyurethane coating has good temperature resistance.

[0054] Comparative Example 1: The difference from Example 1 is that in S2, no liquid fluororubber raw rubber is added to obtain a polyurethane coating.

[0055] Comparative Example 2: The difference from Example 1 is that in S4, the isocyanate mixture is replaced by a mixture of 12 g of commercially available isocyanate and 30 g of ethyl acetate to prepare a polyurethane coating.

[0056] Comparative Example 3: The difference from Example 1 is that in S7, quartz sand is used to replace the reinforcing filler to prepare the polyurethane coating.

[0057] The sources of some reagents in the embodiments and comparative examples of the present invention are as follows: Benzoyl peroxide and methacrylic acid were purchased from Sigma-Aldrich.

[0058] Liquid fluororubber raw rubber was purchased from Jiangsu Guanfu New Material Technology Co., Ltd.

[0059] Isophorone diisocyanate was purchased from Shandong Liang New Material Technology Co., Ltd.

[0060] Isophorone diamine was purchased from Jinan Shanhai Chemical Technology Co., Ltd.

[0061] Bisphenol AF was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0062] Tetrabutylammonium hydrogen sulfate was purchased from Chengdu Kelon Chemical Co., Ltd.

[0063] The SiO2 in quartz sand is ≥99.5-99.9%, Fe2O3 ≤0.001%, and the particle size is 0.005-0.01mm.

[0064] Commercially available isocyanate was purchased from Chengdu Chengying Technology Co., Ltd.

[0065] The remaining reagents were commercially available.

[0066] The performance of the polyurethane coatings prepared in Example 1 to Example 3 and Comparative Examples 1 to Comparative Examples 3 was tested. The polyurethane coating was coated on a steel plate with a coating thickness of 50 μm and cured at 200° C. for 30 min to obtain a polyurethane waterproof coating.

[0067] The tensile strength, elongation at break and water absorption of the polyurethane waterproof coating were tested according to the GB / T19250-2013 method. The polyurethane waterproof coating was then heat treated at 80°C for 180 hours, and the tensile strength and elongation at break were tested. The tensile strength retention and elongation at break retention were calculated. The results are shown in Table 1: Table 1: Polyurethane waterproof coating performance test results project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength (Mpa) 5.36 5.41 5.43 4.25 5.24 3.58 Elongation at break (%) 683 687 692 634 668 595 Water absorption (%) 2.36 2.34 2.33 4.02 2.65 3.96 Tensile strength retention rate (%) 98.4 98.6 98.7 92.4 89.3 84.2 Retention rate of elongation at break (%) 97.6 97.9 98.1 91.3 88.7 82.4 It can be seen from Table 1 that the polyurethane waterproof coating prepared by the present invention has good mechanical properties, low water absorption, high retention rate of tensile strength and elongation at break under long-term heat treatment, and good temperature resistance.

[0068] In Comparative Example 1, since no liquid fluororubber raw rubber was added, the obtained polyurethane coating lacked rubber system curing, the curing network was not tight, the mechanical properties were reduced, and the water absorption rate was increased.

[0069] In Comparative Example 2, since the isocyanate mixture was replaced by commercially available isocyanate and ethyl acetate, the tensile strength retention rate and elongation at break retention rate of the obtained polyurethane coating were reduced, indicating that the isocyanate mixture of the present invention has a better improvement on the heat resistance of the polyurethane coating.

[0070] In Comparative Example 3, since the surface of the quartz sand was not modified, the dispersibility of the quartz sand in the polyurethane coating was poor, and the polyurethane coating formed after curing had poor mechanical properties and significantly reduced heat resistance.

[0071] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention.

Claims

1. A heat-resistant and waterproof polyurethane coating, characterized in that: By mass, it contains the following components: 80-90 parts of polyurethane prepolymer, 1-1.5 parts of reinforcing filler, 2-3 parts of composite curing agent and 7-9 parts of polyether diol; The polyurethane prepolymer is prepared by the following steps: The fluororubber grafting solution and polyester polyol are stirred and mixed in a reaction kettle for 8-10 hours to obtain fluororubber polyester polyol. Under nitrogen protection, the fluororubber polyester polyol is heated to 70-80° C., and then the isocyanate mixture is added and stirred for reaction for 2-3 hours to obtain a polyurethane prepolymer.

2. A heat-resistant and waterproof polyurethane coating according to claim 1, characterized in that: The usage ratio of the fluororubber grafting solution, polyester polyol and isocyanate mixture is 4-6g:40-50g:35-40g.

3. A heat-resistant and waterproof polyurethane coating according to claim 2, characterized in that: The fluororubber grafting solution is prepared by the following steps: Mix benzoyl peroxide and methacrylic acid in a reaction kettle, dissolve liquid fluororubber raw rubber in ethyl acetate, then add it into the reaction kettle, heat it to 80-90°C and react for 6-8h to obtain a fluororubber grafting solution.

4. A heat-resistant and waterproof polyurethane coating according to claim 3, characterized in that: The usage ratio of the benzoyl peroxide, methacrylic acid, liquid fluororubber raw rubber and ethyl acetate is 10-12g:10-12g:5-8g:30-40mL.

5. The heat-resistant and waterproof polyurethane coating according to claim 2, characterized in that: The polyester polyol is prepared by the following steps: In a reaction kettle, ethylene glycol and dimethyl terephthalate are mixed, heated to 195-205° C., stirred and reacted for 2-3 hours, cooled to 115-125° C., neopentyl glycol, isophthalic acid and sebacic acid are added to the reaction kettle, heated to 200-220° C., stirred and reacted for 7-8 hours, and polyester polyols are obtained by vacuum distillation.

6. A heat-resistant and waterproof polyurethane coating according to claim 5, characterized in that: The usage ratio of ethylene glycol, dimethyl terephthalate, neopentyl glycol, isophthalic acid and sebacic acid is 10-15g: 10-20g: 10-15g: 8-12g: 10-15g.

7. The heat-resistant and waterproof polyurethane coating according to claim 2, characterized in that: The isocyanate mixture is prepared by the following steps: In a reaction kettle, isophorone diisocyanate and ethyl acetate are mixed, isophorone diamine is added dropwise, the temperature is raised to 55-65° C., and the reaction is carried out for 2-3 hours to obtain an isocyanate mixture; The usage ratio of isophorone diisocyanate, ethyl acetate and isophorone diamine is 12-15g:30-40g:0.1-0.15g.

8. The heat-resistant and waterproof polyurethane coating according to claim 1, characterized in that: The reinforcing filler is prepared by the following steps: Dissolve chitosan in a 2wt% acetic acid solution in a reaction kettle, add quartz sand, perform ultrasonic dispersion for 4-6h, add glutaraldehyde, heat to 60-70°C and stir for 20-24h, filter to obtain a precipitate, wash the precipitate, and dry to obtain a reinforcing filler; The usage ratio of the chitosan, the acetic acid solution, the quartz sand and the glutaraldehyde is 2-3 g: 100-120 mL: 2-3 g: 5-8 mL.

9. The heat-resistant and waterproof polyurethane coating according to claim 1, characterized in that: The composite curing agent is prepared by the following steps: In a reaction kettle, add silane coupling agent A-1100 dropwise into methanol, stir for 30-40 minutes, then add bisphenol AF and tetrabutylammonium hydrogen sulfate, stir until dissolved to obtain a composite curing agent; The usage ratio of the methanol, the silane coupling agent A-1100, the bisphenol AF and the tetrabutylammonium hydrogen sulfate is 5-6g: 0.5-0.8g: 0.6-0.8g: 0.4-0.6g.

10. The method for preparing a heat-resistant and waterproof polyurethane coating according to claim 1, characterized in that: The preparation method comprises the following steps: The polyether diol, reinforcing filler, composite curing agent and polyurethane prepolymer are stirred and mixed in a reaction kettle, and the temperature is raised to 80-90° C. to react for 2-3 hours to obtain a heat-resistant and waterproof polyurethane coating.