A coating for spraying car cover and its preparation method and application

Abstract

The invention relates to the field of car cover coatings, and discloses a coating for automobile spraying car cover, a preparation method and an application thereof. The coating comprises the following components in parts by weight: 50-70 parts of polyester resin, 10-20 parts of stain-resistant resin, 3-7 parts of modifying additives, 1-2 parts of leveling agent, 0.2-0.5 parts of defoaming agent, 1-3 parts of curing agent, 1-5 parts of cross-linking agent and 70-100 parts of solvent; the stain-resistant resin is prepared by using trifluoropropylmethylcyclotrisiloxane, octamethylcyclotetrasiloxane, tetramethyldihydrodisiloxane and vinyltrimethoxysilane as raw materials, and then hydrolyzing and polycondensing with ethyl orthosilicate and tridecafluorooctyltrimethoxysilane in steps; the modifying additive is prepared by using polydopamine as a bridge to introduce amino cage-type silsesquioxane and an antioxidant into a carboxylated carbon nanotube structure. The invention provides the coating with excellent hydrophobicity and oleophobicity by adding the stain-resistant resin and the modifying additive, and the mechanical properties, aging resistance and heat resistance of the coating are all improved.

Description

Technical Field

[0001] The invention belongs to the technical field of car cover coatings, and in particular relates to a coating for automobile spray-coated car covers and a preparation method and application thereof. Background Art

[0002] Car covers are mainly made of TPU materials and are widely used to protect car bodies and original car paint. At present, car covers are mainly made of TPU particles into thin films, which are then artificially heated and stretched to stick to the car body. Due to the process of artificial heating and stretching, the TPU film has stress, which makes the TPU film easy to collapse at the corners in the later stage. In order to avoid the collapse of the TPU film caused by stress, the car cover paint can be sprayed directly on the car body by spraying process to obtain a more beautiful invisible car cover. The coating used for spraying car covers is an effective way to protect cars. Its main purpose is to reduce the erosion of vehicles by ultraviolet radiation, acid rain, dust and various pollutants, and it can also improve the waterproof, antioxidant and scratch resistance of vehicles.

[0003] The coating used for existing car spray covers is easily affected by environmental factors such as high temperature, acid rain, and dust during use, resulting in oxidation, fading, deformation, and other problems on the coating surface, which is prone to scratches, scrapes, and wear, affecting the appearance and life of the vehicle. At the same time, the coating surface is easily contaminated with grease, dust, dirt, etc. during the use of the vehicle, and is difficult to clean, so the coating is required to have good comprehensive properties such as mechanical properties, aging resistance, stain resistance, and heat resistance. Summary of the invention

[0004] In order to solve the deficiencies mentioned in the above-mentioned background technology, the purpose of the present invention is to provide a coating for automobile spray car cover and its preparation method and application. By adding stain-resistant resin and modified additives, the coating is given excellent hydrophobicity and oleophobicity, strong stain resistance, and its mechanical properties, aging resistance and heat resistance are improved.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A coating for spraying car covers, comprising the following components by weight: 50-70 parts of polyester resin, 10-20 parts of stain-resistant resin, 3-7 parts of modifying additives, 1-2 parts of leveling agent, 0.2-0.5 parts of defoaming agent, 1-3 parts of curing agent, 1-5 parts of cross-linking agent, and 70-100 parts of solvent;

[0007] The stain-resistant resin is prepared by using trifluoropropylmethylcyclotrisiloxane, octamethylcyclotetrasiloxane, tetramethyldihydrodisiloxane and vinyltrimethoxysilane as raw materials to obtain terminal methoxy fluorine-containing polysiloxane, which is then hydrolyzed and polycondensed with ethyl orthosilicate and tridecafluorooctyltrimethoxysilane in steps; the modified additive is prepared by using polydopamine as a bridge to introduce amino cage-type silsesquioxane and antioxidant 3,5-di-tert-butyl-4-hydroxybenzylamine into the carboxylated carbon nanotube structure.

[0008] Preferably, the leveling agent is BYK-333; the defoaming agent is Defom 5300; the curing agent is one or more combinations of curing agent N75, curing agent N3600, and curing agent C-2793; the cross-linking agent is trimethylolpropane; and the solvent is one or more combinations of chloroform, toluene, tetrahydrofuran, acetone, ethyl acetate, butyl acetate, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0009] Preferably, the method for preparing the stain-resistant resin comprises the following steps:

[0010] A. Trifluoropropylmethylcyclotrisiloxane, octamethylcyclotetrasiloxane and tetramethyldihydrodisiloxane are placed in a reactor, heated to 70-80° C. under a nitrogen atmosphere, stirred and mixed for 20-30 min, and then trifluoromethanesulfonic acid is added to react for 7-9 h. After the reaction is completed, n-heptane is added to dilute and neutralize the acid in the system, and then filtered and distilled to remove the solvent, and the small molecular weight low-boiling products are removed under reduced pressure at 175-185° C. for 20-30 min to prepare a hydrogen-terminated fluorine-containing polysiloxane;

[0011] B. Put hydrogen-terminated fluorinated polysiloxane in a reactor, add vinyl trimethoxysilane and Karstedt catalyst, and react at 75-90° C. for 8-10 hours. After the reaction is completed, distill and remove the solvent to prepare methoxy-terminated fluorinated polysiloxane;

[0012] C. Take anhydrous ethanol, tetraethyl orthosilicate, terminal methoxy fluorine-containing polysiloxane and tridecafluorooctyltrimethoxysilane in a reactor, heat up to 55-65°C and adjust the system pH to 4-5, mix tetraethyl orthosilicate and deionized water to obtain tetraethyl orthosilicate hydrolyzate, add 2 / 3 of the mass of the tetraethyl orthosilicate hydrolyzate to the reactor for reaction for 2-3h, mix tridecafluorooctyltrimethoxysilane and tetraethyl orthosilicate to obtain a mixed solution, add the mixed solution and the remaining tetraethyl orthosilicate hydrolyzate to the reactor and continue to react for 6-7h. After the reaction is completed, the solvent is removed by reduced pressure distillation to prepare a stain-resistant resin.

[0013] Preferably, in step A, the molar ratio of trifluoropropylmethylcyclotrisiloxane, octamethylcyclotetrasiloxane and tetramethyldihydrogendisiloxane is 2.6-2.8:2.6-2.8:1.

[0014] Preferably, in the step C, the mass ratio of anhydrous ethanol, tetraethyl orthosilicate, terminal methoxy fluorinated polysiloxane and tridecafluorooctyltrimethoxysilane is 6-8:1.5-3:1:0.5-1; the molar ratio of tetraethyl orthosilicate and deionized water in the tetraethyl orthosilicate hydrolyzate is 1:3-4; the molar ratio of tridecafluorooctyltrimethoxysilane and tetraethyl orthosilicate in the mixed solution is 0.4-0.7:1.

[0015] Preferably, the preparation method of the modified additive comprises the following steps:

[0016] (1) Deionized water, propanol, acetonitrile and tetraethylammonium hydroxide are placed in a reactor, stirred and mixed evenly, and then γ-aminopropyltriethoxysilane is added, and the mixture is stirred and reacted at 55 to 70° C. for 20 to 24 hours. After the reaction is completed, the mixture is precipitated, filtered, washed and dried to prepare an amino cage silsesquioxane;

[0017] (2) carbon nanotubes are placed in a mixture of concentrated sulfuric acid and concentrated nitric acid, and reacted at 70-90° C. for 4-6 hours. The product is filtered, washed until neutral and dried. The obtained carboxylated carbon nanotubes are added to a Tris buffer solution and ultrasonically dispersed to obtain a dispersion. Dopamine hydrochloride is dissolved in deionized water and added to the dispersion. The mixture is stirred for reaction for 18-20 hours. After the reaction is completed, the mixture is centrifuged, washed and dried to obtain functionalized carbon nanotubes.

[0018] (3) Functionalized carbon nanotubes, amino cage silsesquioxane and 3,5-di-tert-butyl-4-hydroxybenzylamine are added to a reactor filled with toluene solvent, Tris buffer is added, and the mixture is reacted at 75-85° C. for 5-7 hours. After the reaction is completed, the mixture is cooled to room temperature, the supernatant is removed, the lower precipitate is centrifuged to neutrality, and vacuum dried to prepare a modified additive.

[0019] Preferably, in step (3), the mass ratio of the functionalized carbon nanotubes, the amino cage-type silsesquioxane and the 3,5-di-tert-butyl-4-hydroxybenzylamine is 1:0.2-0.5:0.2-0.6.

[0020] Preferably, the method for preparing the coating for automobile spray-painted car covers comprises the following steps: weighing each raw material by weight, mixing the anti-fouling resin, leveling agent, defoaming agent and solvent evenly, then adding the cross-linking agent and polyester resin and dispersing them evenly, and finally adding the curing agent, stirring and dispersing them evenly to prepare the coating for automobile spray-painted car covers.

[0021] An application of the coating for automobile spray coating as described above, characterized in that the coating is used to prepare automobile invisible coating film and functional film.

[0022] Beneficial effects of the present invention:

[0023] The invention uses trifluoropropylmethylcyclotrisiloxane and octamethylcyclotetrasiloxane as polymerization monomers, tetramethyldihydrodisiloxane as a capping agent, and uses cationic ring-opening polymerization to prepare hydrogen-terminated fluorine-containing polysiloxane, then grafts vinyltrimethoxysilane to the end of the hydrogen-terminated fluorine-containing polysiloxane through hydrosilylation to prepare terminal methoxy fluorine-containing polysiloxane, and then performs step-by-step hydrolysis and polycondensation of the terminal methoxy fluorine-containing polysiloxane with ethyl orthosilicate and tridecafluorooctyltrimethoxysilane to prepare a stain-resistant resin. The step-by-step hydrolysis allows the fluorine-containing long chain to be attached to the surface of silicon dioxide, thereby reducing the number of hydroxyl groups on the surface of silicon dioxide. It can fully polycondense and reduce the probability of self-condensation of the reactants, avoiding agglomeration and resulting in reduced performance. In addition, the fluorine-silicon-containing anti-fouling resin can reduce the surface tension of the coating, making it difficult for oil stains to adhere to the surface, and inhibit the penetration of oil stains into the coating, thereby improving the anti-fouling ability. At the same time, the addition of anti-fouling resin can make the coating form a super-hydrophobic surface, thereby isolating water vapor and making the coating produce an anti-fouling and self-cleaning effect. The silicon-oxygen bond energy in the anti-fouling resin is relatively high, which can improve the heat resistance of the coating, thereby reducing the decomposition and yellowing of the coating at higher temperatures, which is beneficial to increasing the service life of the coating.

[0024] The invention uses the hydrolysis condensation reaction of γ-aminopropyltriethoxysilane to prepare the aminated cage silsesquioxane, then uses dopamine to self-polymerize and deposit on the surface of the carboxylated carbon nanotube to prepare the functionalized carbon nanotube, and finally grafts the aminated cage silsesquioxane and 3,5-di-tert-butyl-4-hydroxybenzylamine to the surface of the functionalized carbon nanotube through the Schiff base reaction to prepare the modified additive. The chelated ring structure of polydopamine can effectively absorb ultraviolet rays, and the aminated cage silsesquioxane and the antioxidant 3,5-di-tert-butyl-4-hydroxybenzylamine are introduced into the carboxylated carbon nanotube structure by using polydopamine as a bridge, so as to give the coating excellent adhesion, hardness and aging resistance. DETAILED DESCRIPTION

[0025] 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.

[0026] Embodiment 1 A method for preparing a stain-resistant resin comprises the following steps:

[0027] A. Take 12.6g of trifluoropropylmethylcyclotrisiloxane, 8g of octamethylcyclotetrasiloxane and 0.14g of tetramethyldihydrodisiloxane in a reactor, heat to 75°C under a nitrogen atmosphere, stir and mix for 30min, then add 0.2mL of trifluoromethanesulfonic acid to react for 8h, add n-heptane to dilute and neutralize the acid in the system after the reaction is completed, then filter and distill to remove the solvent, and reduce the pressure at 180°C for 30min to remove small molecular low-boiling products to prepare a hydrogen-terminated fluorine-containing polysiloxane;

[0028] B. Take 2 g of hydrogen-terminated fluorinated polysiloxane in a reactor, add 7.4 g of vinyltrimethoxysilane and 0.5 mL of Karstedt catalyst, and react at 80° C. for 10 h. After the reaction is completed, distill to remove the solvent to prepare methoxy-terminated fluorinated polysiloxane;

[0029] C. Take 6g of anhydrous ethanol, 2.3g of tetraethyl orthosilicate, 1g of terminal methoxy fluorinated polysiloxane and 0.7g of tridecafluorooctyltrimethoxysilane in a reactor, heat to 60°C and adjust the pH value of the system to 5 with 36% hydrochloric acid by mass, take 4.03g of tetraethyl orthosilicate and 1.2mL of deionized water to mix to obtain tetraethyl orthosilicate hydrolyzate, add 2 / 3 of the mass of the tetraethyl orthosilicate hydrolyzate to the reactor and react for 3h, take 1.12g of tridecafluorooctyltrimethoxysilane and 1g of tetraethyl orthosilicate to mix to obtain a mixed solution, add the mixed solution and the remaining tetraethyl orthosilicate hydrolyzate to the reactor and continue to react for 7h. After the reaction is completed, the solvent is removed by reduced pressure distillation to prepare a stain-resistant resin.

[0030] Embodiment 2 A method for preparing a modified additive comprises the following steps:

[0031] (1) 22.5 mL of deionized water, 10 mL of propanol, 2.5 mL of acetonitrile and 0.5 mL of tetraethylammonium hydroxide were placed in a reactor and stirred to mix evenly. Then, 55 g of γ-aminopropyltriethoxysilane was added and stirred at 65° C. for 24 h. After the reaction was completed, the mixture was precipitated, filtered, washed and dried to prepare an amino cage-type silsesquioxane.

[0032] (2) 0.54 g of tris(hydroxymethyl)aminomethane hydrochloride was dissolved in deionized water, and the pH value of the system was adjusted to 8.5 with 0.1 mol / L sodium hydroxide solution to obtain Tris buffer solution. 2 g of carbon nanotubes were dissolved in a mixture of 90 mL of concentrated sulfuric acid and 30 mL of concentrated nitric acid, and the mixture was placed at 85° C. for reaction for 4 h. The product was filtered and washed to neutrality and dried. 1 g of the obtained carboxylated carbon nanotubes was added to 300 mL of Tris buffer solution and ultrasonically dispersed to obtain a dispersion solution. 0.8 g of dopamine hydrochloride was dissolved in 15 mL of deionized water and added to the dispersion solution. The mixture was stirred for reaction for 18 h. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain functionalized carbon nanotubes.

[0033] (3) Take 1 g of functionalized carbon nanotubes, 0.3 g of amino cage-type silsesquioxane and 0.5 g of 3,5-di-tert-butyl-4-hydroxybenzylamine and add them into a reactor filled with 200 mL of toluene solvent, add 60 mL of Tris buffer, place it at 85 ° C for 6 h, cool to room temperature after the reaction is completed, remove the supernatant, centrifuge the lower layer to neutral precipitation, and vacuum dry to prepare a modified additive.

[0034] Example 3 A coating for spraying car covers comprises the following components in parts by weight: 52 parts of polyester resin, 10 parts of the stain-resistant resin prepared in Example 1, 3 parts of the modifying additive prepared in Example 2, 1 part of leveling agent BYK-333, 0.2 parts of defoaming agent Defom 5300, 1 part of curing agent N75, 1 part of cross-linking agent trimethylolpropane, and 74 parts of solvent ethyl acetate.

[0035] The coating preparation method for the above-mentioned automobile spray car cover comprises the following steps: weighing each raw material by weight, mixing the anti-fouling resin, leveling agent, defoaming agent and solvent evenly, then adding the cross-linking agent and polyester resin and dispersing them evenly, and finally adding the curing agent, stirring and dispersing them evenly to prepare the coating for the automobile spray car cover.

[0036] Example 4 A coating for spraying car covers comprises the following components in parts by weight: 60 parts of polyester resin, 16 parts of the stain-resistant resin prepared in Example 1, 5 parts of the modifying additive prepared in Example 2, 2 parts of leveling agent BYK-333, 0.4 parts of defoaming agent Defom 5300, 2 parts of curing agent N75, 3 parts of cross-linking agent trimethylolpropane, and 87 parts of solvent ethyl acetate.

[0037] The method for preparing the coating for the above-mentioned automobile spray cover is the same as that in Example 3.

[0038] Example 5 A coating for spraying car covers comprises the following components in parts by weight: 68 parts of polyester resin, 20 parts of the stain-resistant resin prepared in Example 1, 7 parts of the modifying additive prepared in Example 2, 2 parts of leveling agent BYK-333, 0.5 parts of defoaming agent Defom 5300, 3 parts of curing agent N75, 4 parts of cross-linking agent trimethylolpropane, and 95 parts of solvent ethyl acetate.

[0039] The method for preparing the coating for the above-mentioned automobile spray cover is the same as that in Example 3.

[0040] Comparative Example 1 A coating for spraying car covers comprises the following components in parts by weight: 68 parts of polyester resin, 7 parts of the modifying additive prepared in Example 2, 2 parts of leveling agent BYK-333, 0.5 parts of defoaming agent Defom 53000, 3 parts of curing agent N75, 4 parts of cross-linking agent trimethylolpropane, and 95 parts of solvent ethyl acetate.

[0041] The method for preparing the coating for the above-mentioned automobile spray cover is the same as that in Example 3.

[0042] Comparative Example 2 A coating for spraying car covers includes the following components in parts by weight: 68 parts of polyester resin, 20 parts of the stain-resistant resin prepared in Example 1, 7 parts of carbon nanotubes, 2 parts of leveling agent BYK-333, 0.5 parts of defoaming agent Defom 5300, 3 parts of curing agent N75, 4 parts of cross-linking agent trimethylolpropane, and 95 parts of solvent ethyl acetate.

[0043] The method for preparing the coating for the above-mentioned automobile spray cover is the same as that in Example 3.

[0044] Comparative Example 3 A coating for automobile spray coating comprises the following components in parts by weight: 68 parts of polyester resin, 20 parts of the stain-resistant resin prepared in Example 1, 2 parts of leveling agent BYK-333, 0.5 parts of defoaming agent Defom 53000, 3 parts of curing agent N75, 4 parts of cross-linking agent trimethylolpropane, and 95 parts of solvent ethyl acetate.

[0045] The method for preparing the coating for the above-mentioned automobile spray cover is the same as that in Example 3.

[0046] Performance Testing

[0047] The coatings for automobile spray car covers prepared in Examples 3-5 and Comparative Examples 1-3 were subjected to performance testing: adhesion test was performed with reference to the national standard GB / T 9286-2021; water contact angle test was performed using a PZ-200SD contact angle meter; the friction resistance number of the coating was measured using a friction tester, and stage friction was performed in the same area, with a fixed friction distance and a fixed number of times (100 times), and contact angle tests were performed at three different positions of the area for 100 times. The average value was taken and the water contact angle test after friction was performed; the elongation at break was tested with reference to the national standard GB / T 1040.3-2006, and the change rate of the elongation at break was tested after aging at 110°C for 168h; an oily marker was used to write and apply, and after seven days, it was wiped with a towel to observe whether there was any residue, and a stain resistance test was performed; the sample was placed in an oven at 180°C, taken out after 24h, and the coating was observed to see if there was any shedding, blistering, yellowing, etc., and a heat resistance test was performed, and the data results are shown in Table 1.

[0048] Table 1 Test results of sample performance

[0049]

[0050]

[0051] It can be seen from the data in Table 1 that the coatings prepared in Examples 3-5 of the present invention have strong adhesion, high hardness, are not easy to break, and have excellent heat aging resistance, hydrophobicity and oleophobicity, and heat resistance. Their water contact angles are all greater than 150°, have super hydrophobic surfaces, and have strong stain resistance. Among them, no anti-fouling resin was added in Comparative Example 1, and its measured water contact angle and water contact angle after friction were significantly lower than those of Examples 3-5, and its heat resistance was worse than that of Examples 3-5, indicating that the silicon-oxygen bonds and fluorine-containing hydrophobic segments in the anti-fouling resin structure can improve the hydrophobicity, friction resistance and heat resistance of the coating; in Comparative Example 2, the modifying additives were replaced with carbon nanotubes in equal amounts, and no modifying additives were added in Comparative Example 3. Its measured coating adhesion, elongation at break, change rate of elongation at break and hardness were lower than those of Examples 3-5. The reason is that no amino cage-type silsesquioxane and antioxidant 3,5-di-tert-butyl-4-hydroxybenzylamine were introduced into the carbon nanotube structure, which resulted in a decrease in its various performances, and the addition of carbon nanotubes can improve the hardness and elongation at break of the coating to a certain extent.

[0052] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0053] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A coating for spraying car covers, characterized in that: The invention comprises the following components by weight: 50-70 parts of polyester resin, 10-20 parts of anti-fouling resin, 3-7 parts of modifying additive, 1-2 parts of leveling agent, 0.2-0.5 parts of defoaming agent, 1-3 parts of curing agent, 1-5 parts of cross-linking agent and 70-100 parts of solvent; The anti-fouling resin is prepared by using trifluoropropylmethylcyclotrisiloxane, octamethylcyclotetrasiloxane, tetramethyldihydrodisiloxane and vinyltrimethoxysilane as raw materials to obtain terminal methoxy fluorine-containing polysiloxane, which is then hydrolyzed and polycondensed with ethyl orthosilicate and tridecafluorooctyltrimethoxysilane in steps; The modified additive is prepared by using dopamine self-polymerization deposition on the surface of carboxylated carbon nanotubes to obtain functionalized carbon nanotubes, and finally grafting amino cage-type silsesquioxane and antioxidant 3,5-di-tert-butyl-4-hydroxybenzylamine onto the surface of the functionalized carbon nanotubes through Schiff base reaction to obtain the modified additive.

2. The coating for automobile spraying car cover according to claim 1, characterized in that: The leveling agent is BYK-333; the defoaming agent is Defom 5300; the curing agent is one or more combinations of curing agent N75, curing agent N3600, and curing agent C-2793; the cross-linking agent is trimethylolpropane; and the solvent is one or more combinations of chloroform, toluene, tetrahydrofuran, acetone, ethyl acetate, butyl acetate, N,N-dimethylformamide, and N,N-dimethylacetamide.

3. The coating for automobile spraying car cover according to claim 1, characterized in that: The preparation method of the stain-resistant resin comprises the following steps: A. Trifluoropropylmethylcyclotrisiloxane, octamethylcyclotetrasiloxane and tetramethyldihydrodisiloxane are placed in a reactor, heated to 70-80°C under a nitrogen atmosphere, stirred and mixed for 20-30 minutes, and then trifluoromethanesulfonic acid is added to react for 7-9 hours. After the reaction is completed, n-heptane is added to dilute and neutralize the acid in the system, and then filtered and distilled to remove the solvent, and the small molecular weight low-boiling products are removed under reduced pressure at 175-185°C for 20-30 minutes to prepare a hydrogen-terminated fluorine-containing polysiloxane; B. Put hydrogen-terminated fluorinated polysiloxane in a reactor, add vinyl trimethoxysilane and Karstedt catalyst, and react at 75-90° C. for 8-10 hours. After the reaction is completed, remove the solvent by distillation to prepare methoxy-terminated fluorinated polysiloxane; C. Take anhydrous ethanol, tetraethyl orthosilicate, terminal methoxy fluorine-containing polysiloxane and tridecafluorooctyltrimethoxysilane in a reactor, heat it to 55-65°C and adjust the pH value of the system to 4-5, mix tetraethyl orthosilicate and deionized water to obtain tetraethyl orthosilicate hydrolyzate, add 2 / 3 of the mass of the tetraethyl orthosilicate hydrolyzate into the reactor to react for 2-3 hours, mix tridecafluorooctyltrimethoxysilane and tetraethyl orthosilicate to obtain a mixed solution, add the mixed solution and the remaining tetraethyl orthosilicate hydrolyzate into the reactor and continue to react for 6-7 hours. After the reaction is completed, the solvent is removed by distillation under reduced pressure to prepare a stain-resistant resin.

4. The coating for automobile spraying car cover according to claim 3, characterized in that: In the step A, the molar ratio of trifluoropropylmethylcyclotrisiloxane, octamethylcyclotetrasiloxane and tetramethyldihydrogendisiloxane is 2.6-2.8:2.6-2.8:

1.

5. The coating for automobile spraying car cover according to claim 3, characterized in that: The mass ratio of anhydrous ethanol, tetraethyl orthosilicate, terminal methoxy fluorinated polysiloxane and tridecafluorooctyltrimethoxysilane in step C is 6-8:1.5-3:1:0.5-1; the molar ratio of tetraethyl orthosilicate and deionized water in the tetraethyl orthosilicate hydrolyzate is 1:3-4; the molar ratio of tridecafluorooctyltrimethoxysilane and tetraethyl orthosilicate in the mixed solution is 0.4-0.7:

1.

6. The coating for automobile spraying car cover according to claim 1, characterized in that: The preparation method of the modified additive comprises the following steps: (1) Deionized water, propanol, acetonitrile and tetraethylammonium hydroxide are placed in a reactor, stirred and mixed evenly, and then γ-aminopropyltriethoxysilane is added, and the mixture is stirred and reacted at 55-70° C. for 20-24 hours. After the reaction is completed, the mixture is precipitated, filtered, washed and dried to prepare an amino cage-type silsesquioxane; (2) Carbon nanotubes are placed in a mixture of concentrated sulfuric acid and concentrated nitric acid, and reacted at 70-90°C for 4-6 hours. The product is filtered, washed until neutral and dried. The obtained carboxylated carbon nanotubes are added to Tris buffer and ultrasonically dispersed to obtain a dispersion. Dopamine hydrochloride is dissolved in deionized water and added to the dispersion. The mixture is stirred for reaction for 18-20 hours. After the reaction is completed, the functionalized carbon nanotubes are prepared by centrifugation, washing and drying. (3) Functionalized carbon nanotubes, amino cage-type silsesquioxane and 3,5-di-tert-butyl-4-hydroxybenzylamine were added to a reactor filled with toluene solvent, Tris buffer was added, and the mixture was reacted at 75-85°C for 5-7 hours. After the reaction was completed, the mixture was cooled to room temperature, the supernatant was removed, the lower precipitate was centrifuged until neutral, and vacuum dried to obtain a modified additive.

7. The coating for automobile spraying car cover according to claim 6, characterized in that: In the step (3), the mass ratio of the functionalized carbon nanotubes, the amino cage-type silsesquioxane and the 3,5-di-tert-butyl-4-hydroxybenzylamine is 1:0.2-0.5:0.2-0.

6.

8. The coating for automobile spraying car cover according to claim 1, characterized in that: The coating preparation method for automobile spray coating comprises the following steps: weighing various raw materials by weight, mixing anti-fouling resin, leveling agent, defoaming agent and solvent evenly, then adding cross-linking agent and polyester resin and dispersing them evenly, and finally adding curing agent, stirring and dispersing them evenly to prepare the coating for automobile spray coating.

9. An application of the coating for spraying car covers according to any one of claims 1 to 8, characterized in that: The coating is used for preparing automobile invisible car cover film.

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