Elastic base material for spraying automobile cover as well as preparation method and application of elastic base material

Abstract

The invention relates to the field of automobile clothing, and discloses an elastic base material for spraying an automobile clothing as well as a preparation method and application thereof, the elastic base material for spraying the automobile clothing comprises a polyurethane prepolymer, modified polydimethylsiloxane, a photoinitiator and an alcohol solvent; the polyurethane prepolymer is prepared from polycarbonate diol, modified fluorine-containing diol, isocyanate, 2, 2-dimethylolbutyric acid and modified nano silicon dioxide as raw materials, the modified fluorine-containing diol and the modified nano silicon dioxide are connected to a polyurethane main chain, pentaerythritol triacrylate is used as an end-capping reagent, and p-hydroxyanisole is used as a polymerization inhibitor, so that the polyurethane prepolymer is prepared. A polyurethane prepolymer and sulfydryl-terminated modified polydimethylsiloxane react under the action of a photoinitiator to form a heavy cross-linked network, so that the elastic base material is endowed with excellent mechanical properties, antifouling properties, thermal stability and flame retardance.

Description

Technical Field

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

[0002] With the rapid development of the automobile industry, cars have become an indispensable means of transportation in people's daily lives, and with it comes wear and damage to the exterior of cars. In order to protect the car body, people often use car covers to protect the vehicle. Thermoplastic polyurethane material is a high-performance elastomeric material with good mechanical properties, chemical resistance, weather resistance and wear resistance. In the field of car covers, polyurethane materials are widely used to manufacture various types of car covers due to their unique performance advantages. At present, car covers are mainly made of polyurethane particles into thin films, which are then artificially heated and stretched to be attached to the car body. Due to the process of artificial heating and stretching, the polyurethane film has stress, which makes the polyurethane film easy to collapse at the corners in the later stage. In order to avoid the collapse of the polyurethane film caused by stress, the car cover paint can be sprayed directly on the car body by spraying technology to obtain a more beautiful invisible car cover.

[0003] The prior art polyurethanes using water as a dispersion system have the advantages of being environmentally friendly, low toxicity, and safe. However, water is used as a solvent in aqueous polyurethane emulsions, and the latent heat of evaporation of water is higher than that of commonly used organic solvents. At the same solid content, the water in aqueous polyurethane evaporates more slowly than the solvent in solvent-based polyurethane, and the drying time is long, which makes it difficult to meet the fast-paced production requirements of modern production lines. In order to solve this problem, most of the research focuses at home and abroad are focused on increasing the solid content of aqueous polyurethane to reduce the water volatilization load, shorten the film formation and drying time. However, high solid content and low viscosity are always contradictory in the synthesis of high-solid content aqueous polyurethane. The synthesized aqueous polyurethane with a high solid content is easy to gel, which brings inconvenience to the production, storage, and use of the material. In addition, the chemical and solvent resistance of aqueous polyurethane is poor, the hardness is low, and the surface gloss is not high, which seriously affects the application of aqueous polyurethane in the field of car cover materials.

[0004] The current car cover materials are still prone to scratches, scrapes, and wear, and their mechanical properties need to be further improved. In addition, since the polyurethane structure contains a large number of polar groups, its surface energy is extremely large, and it is easy to fall dust and dirt, which pollutes its surface, affecting its appearance, resulting in poor application experience and limiting its promotion and application. The existing technology achieves the flame retardant effect of car cover by adding additional liquid or solid flame retardants. The added flame retardant is often added in a large amount. While ensuring the flame retardant performance, it has a significant adverse effect and decrease on the mechanical properties of the material itself. Moreover, the flame retardant is very likely to migrate to the surface of the material at high temperature, resulting in a decrease in the flame retardant effect, which limits its large-scale production and application. Summary of the invention

[0005] In order to solve the deficiencies mentioned in the above-mentioned background technology, the purpose of the present invention is to provide an elastic substrate for automobile spray cover, a preparation method and application thereof, and prepare the elastic substrate by using polyurethane prepolymer, modified polydimethylsiloxane, photoinitiator and alcohol solvent to replace the existing aqueous solvent to increase the solvent volatilization rate during the preparation of the cover, while giving the elastic substrate excellent mechanical properties, anti-fouling properties, thermal stability and flame retardant properties.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] An elastic substrate for automobile spray coating, comprising the following components by weight: 55-70 parts of polyurethane prepolymer, 5-10 parts of modified polydimethylsiloxane, 1-3 parts of photoinitiator, and 40-60 parts of alcohol solvent; the modified polydimethylsiloxane is prepared by esterification reaction of hydroxyl-terminated polydimethylsiloxane and 3-mercaptopropionic acid;

[0008] The polyurethane prepolymer comprises the following components in parts by weight: 40-55 parts of polycarbonate diol, 30-50 parts of isocyanate, 10-20 parts of modified fluorine-containing diol, 10-30 parts of 2,2-dihydroxymethylbutyric acid, 2-5 parts of modified nano-silicon dioxide, 2-7 parts of catalyst, 10-25 parts of pentaerythritol triacrylate, 3-8 parts of p-hydroxyanisole, and 20-35 parts of solvent;

[0009] The modified fluorinated diol is prepared by an amidation reaction between pentadecafluorooctanoic acid and 2-amino-2-methyl-1,3-propanediol to obtain a terminal hydroxyl fluorinated diol, and then the terminal hydroxyl fluorinated diol and phenylphosphoryl dichloride are further subjected to a substitution reaction to obtain the modified nano-silicon dioxide. The modified nano-silicon dioxide is prepared by modifying nano-silicon dioxide using isopropoxy tris(ethylenediamino-N-ethoxy) titanate.

[0010] Preferably, the preparation method of the modified polydimethylsiloxane comprises the following steps: placing hydroxyl-terminated polydimethylsiloxane, 3-mercaptopropionic acid and p-toluenesulfonic acid in a reactor, stirring and reacting at 110-125° C. for 7-8 hours, and vacuum dehydrating to prepare the modified polydimethylsiloxane.

[0011] Preferably, the method for preparing the modified fluorinated diol comprises the following steps:

[0012] (1) dissolving pentafluorooctanoic acid and 2-amino-2-methyl-1,3-propanediol in a mixed solution of dichloromethane and methanol, then adding 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline to dissolve, stirring the mixed solution in the dark for 8 to 12 hours, and after the reaction is completed, removing the solvent by rotary evaporation, mixing the obtained solid with diethyl ether, grinding it, filtering it, and washing it to prepare a terminal hydroxyl fluorinated diol;

[0013] (2) Phenylphosphoryl dichloride and terminal hydroxyl fluorinated diol are added to a reactor containing tetrahydrofuran, and the mixture is stirred at room temperature for 5 to 7 hours. During the reaction, triethylamine is added in batches to remove the hydrogen chloride produced by the reaction. After the reaction is completed, the mixture is filtered, rotary evaporated, and dried to prepare a modified fluorinated diol.

[0014] Preferably, in step (2), the molar ratio of phenylphosphoryl dichloride to terminal hydroxyl fluorinated diol is 1:2 to 2.7.

[0015] Preferably, the preparation method of the modified nano-silica comprises the following steps: taking nano-silica into a reactor, adding toluene solvent for ultrasonic dispersion, then adding isopropoxy tris(ethylenediamino-N-ethoxy) titanate, placing at 65-75° C. for stirring reaction for 4-6 hours, and after the reaction is completed, centrifuging, washing and drying to prepare modified nano-silica.

[0016] Preferably, the method for preparing the polyurethane prepolymer comprises the following steps:

[0017] Polycarbonate diol and a catalyst are placed in a reactor, nitrogen is introduced into the reaction, the temperature is raised to 75-85°C, isocyanate is added to react for 1-1.5 hours, and then modified fluorinated diol and 2,2-dihydroxymethylbutyric acid are added to react for 2.5-3 hours. After the reaction is completed, the temperature is lowered to 25-40°C, modified nano-silica is added, and then pentaerythritol triacrylate, a catalyst, p-hydroxyanisole and a solvent are added to the reactor, and the reaction is continued at 55-70°C for 2-4 hours to prepare a polyurethane prepolymer.

[0018] Preferably, the photoinitiator is dimethyl benzoate; and the alcohol solvent is one or more combinations of ethanol, isopropanol, and n-propanol.

[0019] Preferably, the isocyanate is one of isophorone diisocyanate, hexamethylene diisocyanate and dicyclohexylmethane diisocyanate; the catalyst is dibutyltin dilaurate; and the solvent is ethyl acetate.

[0020] The method for preparing the elastic substrate for automobile spray coating comprises the following steps: uniformly mixing parts by weight of polyurethane prepolymer, modified polydimethylsiloxane, photoinitiator and alcohol solvent to obtain the elastic substrate for automobile spray coating.

[0021] An application of the elastic substrate for automobile spray coating as described above in the field of automobile films / covers.

[0022] Beneficial effects of the present invention:

[0023] The invention uses polyurethane prepolymer, modified polydimethylsiloxane, photoinitiator and alcohol solvent to prepare elastic substrate, alcohol solvent replaces existing aqueous solvent to improve solvent volatilization rate in the process of car cover preparation, fast drying speed, and effectively improves the production efficiency of car cover, wherein modified polydimethylsiloxane is mercapto-terminated modified polydimethylsiloxane prepared by esterification reaction of hydroxyl-terminated polydimethylsiloxane and 3-mercaptopropionic acid; polyurethane prepolymer is polycarbonate diol, modified fluorine-containing diol, isocyanate, 2,2-dihydroxy The invention relates to a novel fluorinated diol prepared from methyl butyric acid, modified nano-silica, pentaerythritol triacrylate and p-hydroxyanisole as raw materials, wherein the modified fluorinated diol is prepared by amidation reaction of pentafluorooctanoic acid and 2-amino-2-methyl-1,3-propanediol to generate a terminal hydroxyl fluorinated diol, and then a substitution reaction is carried out between the hydroxyl group in the structure of the terminal hydroxyl fluorinated diol and phenylphosphoryl dichloride to synthesize the terminal hydroxyl modified fluorinated diol, which can be used as a chain extender to be connected to the main chain of the polyurethane, thereby introducing phosphorus element to achieve the purpose of improving the flame retardancy of the substrate, and at the same time The introduction of organic fluorine into polyurethane can endow the substrate with extremely low surface free energy and excellent hydrophobicity, thereby enhancing the antifouling property and surface self-cleaning ability of the substrate; the modified nano-silica is prepared by modifying nano-silica with amino groups on the surface by using isopropoxy tri(ethylenediamino-N-ethoxy) titanate, and the modified nano-silica is connected to the main chain of polyurethane to endow the substrate with good thermal stability and mechanical properties; the invention uses pentaerythritol triacrylate as a capping agent and p-hydroxyanisole as a polymerization inhibitor to synthesize a hyperbranched polyurethane prepolymer containing multiple vinyl end-cappings, provides a large number of cross-linking sites, and then generates a mercapto-ene click reaction with a mercapto-end-modified polydimethylsiloxane under the action of a photoinitiator, forms a heavily cross-linked network through alternating propagation and chain transfer reactions under ultraviolet light curing, is conducive to the formation of a hydrophobic surface, has a synergistic effect on flame retardancy, and can enhance the thermal stability and mechanical stability of the substrate at the same time, so that the external force received can be dispersed along the network structure, thereby improving the mechanical properties of the substrate. DETAILED DESCRIPTION

[0024] 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.

[0025] Embodiment 1 A method for preparing modified polydimethylsiloxane comprises the following steps:

[0026] 10 g of hydroxyl-terminated polydimethylsiloxane, 0.42 g of 3-mercaptopropionic acid and 0.12 g of p-toluenesulfonic acid were placed in a reactor, stirred and reacted at 120° C. for 8 h, and vacuum-dehydrated to prepare modified polydimethylsiloxane.

[0027] Embodiment 2 A method for preparing a modified fluorinated diol comprises the following steps:

[0028] (1) 4.15 g of pentadecafluorooctanoic acid and 1.2 g of 2-amino-2-methyl-1,3-propanediol were dissolved in a mixed solution of 100 mL of dichloromethane and 50 mL of methanol, and then 4.98 g of 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline was added to dissolve, and the mixed solution was stirred to react for 12 h in the dark. After the reaction was completed, the solvent was removed by rotary evaporation, and the obtained solid was mixed with diethyl ether and ground, filtered, and washed to prepare a terminal hydroxyl fluorinated diol;

[0029] (2) 1 g of phenylphosphoryl dichloride and 6.4 g of terminal hydroxyl fluorinated diol were added to a reactor containing 100 mL of tetrahydrofuran, and the mixture was stirred at room temperature for 6 h. During the reaction, 1.1 g of triethylamine was added in batches to remove the hydrogen chloride produced by the reaction. After the reaction was completed, the mixture was filtered, rotary evaporated, and dried to obtain a modified fluorinated diol.

[0030] Embodiment 3 A method for preparing modified nano-silicon dioxide comprises the following steps:

[0031] Take 0.65g of nano-silica in a reactor, add 70mL of toluene solvent and ultrasonically disperse it evenly, then add 3.2g of isopropoxy tris(ethylenediamino-N-ethoxy) titanate, place it at 75°C and stir to react for 5h. After the reaction is completed, centrifuge, wash and dry to prepare modified nano-silica.

[0032] Example 4 An elastic substrate for automobile spray coating comprises the following components in parts by weight: 57 parts of polyurethane prepolymer, 5 parts of modified polydimethylsiloxane prepared in Example 1, 1 part of photoinitiator benzoin dimethyl ether, and 42 parts of alcohol solvent isopropyl alcohol;

[0033] The preparation method of the elastic substrate for automobile spray coating is as follows: parts by weight of polyurethane prepolymer, modified polydimethylsiloxane, photoinitiator and alcohol solvent are uniformly mixed to obtain the elastic substrate for automobile spray coating.

[0034] The preparation method of the polyurethane prepolymer comprises the following steps:

[0035] 42 parts of polycarbonate diol and 1 part of dibutyltin dilaurate were placed in a reactor, nitrogen was passed through the reaction, the temperature was raised to 80° C., 30 parts of isophorone diisocyanate were added and reacted for 1 hour, then 10 parts of the modified fluorinated diol prepared in Example 2 and 11 parts of 2,2-dihydroxymethylbutyric acid were added and reacted for 3 hours, after the reaction was completed, the temperature was lowered to 30° C., 2 parts of modified nano-silica prepared in Example 3 were added, then 10 parts of pentaerythritol triacrylate, 1 part of dibutyltin dilaurate, 3 parts of p-hydroxyanisole and 21 parts of ethyl acetate were added to the reactor, and the reaction was continued at 60° C. for 4 hours to prepare a polyurethane prepolymer.

[0036] Example 5 An elastic substrate for automobile spray coating comprises the following components in parts by weight: 64 parts of polyurethane prepolymer, 7 parts of modified polydimethylsiloxane prepared in Example 1, 2 parts of photoinitiator benzoin dimethyl ether, and 52 parts of alcohol solvent ethanol;

[0037] The preparation method of the elastic substrate for automobile spray coating is as follows: parts by weight of polyurethane prepolymer, modified polydimethylsiloxane, photoinitiator and alcohol solvent are uniformly mixed to obtain the elastic substrate for automobile spray coating.

[0038] The preparation method of the polyurethane prepolymer comprises the following steps:

[0039] 47 parts of polycarbonate diol and 3 parts of dibutyltin dilaurate were placed in a reactor, nitrogen was passed through the reaction, the temperature was raised to 80° C., 41 parts of isophorone diisocyanate were added and reacted for 1 hour, then 14 parts of the modified fluorinated diol prepared in Example 2 and 20 parts of 2,2-dihydroxymethylbutyric acid were added and reacted for 3 hours, after the reaction was completed, the temperature was lowered to 30° C., 4 parts of the modified nano-silica prepared in Example 3 were added, then 17 parts of pentaerythritol triacrylate, 2 parts of dibutyltin dilaurate, 5 parts of p-hydroxyanisole and 28 parts of ethyl acetate were added to the reactor, and the reaction was continued at 60° C. for 4 hours to prepare a polyurethane prepolymer.

[0040] Example 6 An elastic substrate for automobile spray coating comprises the following components in parts by weight: 68 parts of polyurethane prepolymer, 10 parts of modified polydimethylsiloxane prepared in Example 1, 3 parts of photoinitiator benzoin dimethyl ether, and 55 parts of alcohol solvent n-propanol;

[0041] The preparation method of the elastic substrate for automobile spray coating is as follows: parts by weight of polyurethane prepolymer, modified polydimethylsiloxane, photoinitiator and alcohol solvent are uniformly mixed to obtain the elastic substrate for automobile spray coating.

[0042] The preparation method of the polyurethane prepolymer comprises the following steps:

[0043] 55 parts of polycarbonate diol and 4 parts of dibutyltin dilaurate were placed in a reactor, nitrogen was passed through the reaction, the temperature was raised to 80° C., 50 parts of isophorone diisocyanate were added and reacted for 1 hour, then 18 parts of the modified fluorinated diol prepared in Example 2 and 30 parts of 2,2-dihydroxymethylbutyric acid were added and reacted for 3 hours, after the reaction was completed, the temperature was lowered to 30° C., 5 parts of modified nano-silica prepared in Example 3 were added, then 23 parts of pentaerythritol triacrylate, 2 parts of dibutyltin dilaurate, 7 parts of p-hydroxyanisole and 32 parts of ethyl acetate were added to the reactor, and the reaction was continued at 60° C. for 4 hours to prepare a polyurethane prepolymer.

[0044] Comparative Example 1 An elastic substrate for automobile spray coating comprises the following components in parts by weight: 68 parts of polyurethane prepolymer, 10 parts of hydroxyl-terminated polydimethylsiloxane, 3 parts of photoinitiator benzoin dimethyl ether, and 55 parts of alcohol solvent n-propanol;

[0045] The preparation method of the elastic substrate for automobile spray coating is as follows: parts by weight of polyurethane prepolymer, hydroxyl-terminated polydimethylsiloxane, photoinitiator and alcohol solvent are uniformly mixed to obtain the elastic substrate for automobile spray coating.

[0046] The preparation method of the polyurethane prepolymer is the same as that in Example 6.

[0047] Comparative Example 2 An elastic substrate for automobile spray coating comprises the following components in parts by weight: 68 parts of polyurethane prepolymer, 10 parts of modified polydimethylsiloxane prepared in Example 1, 3 parts of photoinitiator benzoin dimethyl ether, and 55 parts of alcohol solvent n-propanol;

[0048] The preparation method of the elastic substrate for automobile spray coating is as follows: parts by weight of polyurethane prepolymer, modified polydimethylsiloxane, photoinitiator and alcohol solvent are uniformly mixed to obtain the elastic substrate for automobile spray coating.

[0049] The preparation method of the polyurethane prepolymer comprises the following steps:

[0050] 55 parts of polycarbonate diol and 4 parts of dibutyltin dilaurate were placed in a reactor, nitrogen was passed through the reaction, the temperature was raised to 80° C., 50 parts of isophorone diisocyanate were added and reacted for 1 hour, then 18 parts of 1,4-butanediol and 30 parts of 2,2-dihydroxymethylbutyric acid were added and reacted for 3 hours, after the reaction was completed, the temperature was lowered to 30° C., 5 parts of modified nano-silica prepared in Example 3 were added, then 23 parts of pentaerythritol triacrylate, 2 parts of dibutyltin dilaurate, 7 parts of p-hydroxyanisole and 32 parts of ethyl acetate were added to the reactor, and the reaction was continued at 60° C. for 4 hours to prepare a polyurethane prepolymer.

[0051] Comparative Example 3 An elastic substrate for automobile spray coating comprises the following components in parts by weight: 68 parts of polyurethane prepolymer, 10 parts of modified polydimethylsiloxane prepared in Example 1, 3 parts of photoinitiator benzoin dimethyl ether, and 55 parts of alcohol solvent n-propanol;

[0052] The preparation method of the elastic substrate for automobile spray coating is as follows: parts by weight of polyurethane prepolymer, modified polydimethylsiloxane, photoinitiator and alcohol solvent are uniformly mixed to obtain the elastic substrate for automobile spray coating.

[0053] The preparation method of the polyurethane prepolymer comprises the following steps:

[0054] 55 parts of polycarbonate diol and 4 parts of dibutyltin dilaurate were placed in a reactor, nitrogen was passed through the reaction, the temperature was raised to 80°C, 50 parts of isophorone diisocyanate were added and reacted for 1 hour, then 18 parts of the modified fluorinated diol prepared in Example 2 and 30 parts of 2,2-dihydroxymethylbutyric acid were added and reacted for 3 hours, then 23 parts of pentaerythritol triacrylate, 2 parts of dibutyltin dilaurate, 7 parts of p-hydroxyanisole and 32 parts of ethyl acetate were added to the reactor, and the reaction was continued at 60°C for 4 hours to prepare a polyurethane prepolymer.

[0055] Performance Testing

[0056] The elastic substrates prepared in Examples 4-6 and Comparative Examples 1-3 were sprayed on the surface of the automobile body by spraying. After curing, the coatings were peeled off after 7 days, and performance tests were performed: the tensile strength and elongation at break were measured according to GB / T 528-2009; the tear strength was measured according to GB / T529-2008; the Shore D hardness was measured according to GB / T 531-1999; the hydrophobicity was tested by a contact angle meter; the thermal performance was tested by a thermogravimetric analyzer, the heating rate was 20°C / min, and the heating range was from room temperature to 700°C; the flame retardant performance was evaluated by the limiting oxygen index, and the data results are shown in Table 1.

[0057] Table 1 Test results of sample performance

[0058]

[0059]

[0060] As can be seen from the data in Table 1, the elastic substrate prepared by the embodiment 4-6 of the present invention has excellent mechanical properties, thermal stability and flame retardant properties, and the water contact angle is greater than 150 °, with super hydrophobic surface, strong antifouling ability. Wherein in comparative example 1, hydroxyl-terminated polydimethylsiloxane is not modified, and it is measured that mechanical properties, water contact angle, thermal decomposition temperature and limiting oxygen index are reduced compared with embodiment 4-6, and the reason is that hydroxyl-terminated polydimethylsiloxane is not modified by sulfhydryl end-capping, so as not to react with polyurethane prepolymer to form a heavy cross-linked network, resulting in its various performance reductions; in comparative example 2, modified fluorinated diol is replaced by 1,4-butanediol in equal amounts, and it is measured that hydrophobic properties and flame retardant properties are reduced compared with embodiment 4-6, and the reason is that fluorine element and phosphorus element are not introduced, and modified nano silicon dioxide is not added in comparative example 3, and it is measured that mechanical properties and thermal decomposition temperature are significantly reduced compared with embodiment 4-6, indicating that the addition of modified nano silicon dioxide can improve the mechanical properties and thermal stability of substrate.

[0061] 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. An elastic substrate for automobile spray coating, characterized in that: The invention comprises the following components by weight: 55-70 parts of polyurethane prepolymer, 5-10 parts of modified polydimethylsiloxane, 1-3 parts of photoinitiator, and 40-60 parts of alcohol solvent; the modified polydimethylsiloxane is prepared by esterification reaction of hydroxyl-terminated polydimethylsiloxane and 3-mercaptopropionic acid; The polyurethane prepolymer comprises the following components in parts by weight: 40-55 parts of polycarbonate diol, 30-50 parts of isocyanate, 10-20 parts of modified fluorine-containing diol, 10-30 parts of 2,2-dihydroxymethylbutyric acid, 2-5 parts of modified nano-silicon dioxide, 2-7 parts of catalyst, 10-25 parts of pentaerythritol triacrylate, 3-8 parts of p-hydroxyanisole, and 20-35 parts of solvent; The modified fluorinated diol is prepared by an amidation reaction between pentadecafluorooctanoic acid and 2-amino-2-methyl-1,3-propanediol to obtain a terminal hydroxyl fluorinated diol, and then the terminal hydroxyl fluorinated diol and phenylphosphoryl dichloride are further subjected to a substitution reaction to obtain the modified nano-silicon dioxide. The modified nano-silicon dioxide is prepared by modifying nano-silicon dioxide using isopropoxy tris(ethylenediamino-N-ethoxy) titanate.

2. The elastic substrate for automobile spray coating according to claim 1, characterized in that: The preparation method of the modified polydimethylsiloxane comprises the following steps: taking hydroxyl-terminated polydimethylsiloxane, 3-mercaptopropionic acid and p-toluenesulfonic acid in a reactor, stirring and reacting at 110-125° C. for 7-8 hours, and vacuum dehydrating to prepare the modified polydimethylsiloxane.

3. The elastic substrate for automobile spray coating according to claim 1, characterized in that: The preparation method of the modified fluorinated diol comprises the following steps: (1) dissolving pentafluorooctanoic acid and 2-amino-2-methyl-1,3-propanediol in a mixed solution of dichloromethane and methanol, then adding 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline to dissolve, stirring the mixed solution in the dark for 8 to 12 hours, and after the reaction is completed, removing the solvent by rotary evaporation, mixing the obtained solid with diethyl ether, grinding it, filtering it, and washing it to prepare a terminal hydroxyl fluorinated diol; (2) Phenylphosphoryl dichloride and terminal hydroxyl fluorinated diol are added to a reactor containing tetrahydrofuran, and the mixture is stirred at room temperature for 5 to 7 hours. During the reaction, triethylamine is added in batches to remove the hydrogen chloride produced by the reaction. After the reaction is completed, the mixture is filtered, rotary evaporated, and dried to prepare a modified fluorinated diol.

4. The elastic substrate for automobile spray coating according to claim 3, characterized in that: In the step (2), the molar ratio of phenylphosphoryl dichloride to terminal hydroxyl fluorinated diol is 1:2 to 2.

7.

5. The elastic substrate for automobile spray coating according to claim 1, characterized in that: The preparation method of modified nano silicon dioxide comprises the following steps: taking nano silicon dioxide into a reactor, adding toluene solvent for ultrasonic dispersion, then adding isopropoxy tris(ethylenediamino-N-ethoxy) titanate, stirring and reacting at 65-75° C. for 4-6 hours, and after the reaction is completed, centrifuging, washing and drying to prepare modified nano silicon dioxide.

6. The elastic substrate for automobile spray coating according to claim 1, characterized in that: The preparation method of the polyurethane prepolymer comprises the following steps: Polycarbonate diol and a catalyst are placed in a reactor, nitrogen is introduced into the reaction, the temperature is raised to 75-85°C, isocyanate is added to react for 1-1.5 hours, and then modified fluorinated diol and 2,2-dihydroxymethylbutyric acid are added to react for 2.5-3 hours. After the reaction is completed, the temperature is lowered to 25-40°C, modified nano-silica is added, and then pentaerythritol triacrylate, a catalyst, p-hydroxyanisole and a solvent are added to the reactor, and the reaction is continued at 55-70°C for 2-4 hours to prepare a polyurethane prepolymer.

7. The elastic substrate for automobile spray coating according to claim 1, characterized in that: The photoinitiator is dimethyl benzoate; the alcohol solvent is one or more combinations of ethanol, isopropanol and n-propanol.

8. The elastic substrate for automobile spray-coated car cover according to claim 1, characterized in that: The isocyanate is one of isophorone diisocyanate, hexamethylene diisocyanate and dicyclohexylmethane diisocyanate; the catalyst is dibutyltin dilaurate; and the solvent is ethyl acetate.

9. A method for preparing an elastic substrate for automobile spray coating as claimed in any one of claims 1 to 8, characterized in that: The following steps are involved: The polyurethane prepolymer, modified polydimethylsiloxane, a photoinitiator and an alcohol solvent are uniformly mixed in parts by weight to obtain an elastic substrate for spraying car covers.

10. Use of the elastic substrate for automobile spray-coated car cover according to any one of claims 1 to 8 in the field of automobile films / car covers.

Images