Anti-yellowing automobile composite film and preparation method thereof

Abstract

The invention relates to an anti-yellowing automobile composite film and a preparation method thereof, and belongs to the technical field of high polymer materials. The yellow-resistant automobile composite film is prepared from the following components in parts by weight: 60 to 70 parts of PVC (Polyvinyl Chloride) master batch, 10 to 20 parts of TPU (Thermoplastic Polyurethane) master batch, 1 to 2 parts of plasticizer, 0.5 to 0.8 part of flatting agent, 0.1 to 2 parts of yellowing-resistant modifier and 0.1 to 2 parts of modified flame retardant, sym-triazine cyanuric chloride and a benzotriazole intermediate in the anti-yellowing modifier absorb ultraviolet rays and reduce yellowing of the ultraviolet rays on the composite material, and maleimide groups, maleic anhydride and isocyanurate rings for increasing the crosslinking density cooperate with one another, so that the heat resistance of the material is improved, and the yellowing is reduced; phosphorus and nitrogen main chains of phosphonitrilic chloride trimer in the modified flame retardant have a conjugation effect, so that a protective film is formed, oxygen is isolated, and the phosphonitrilic chloride trimer and nitrogen are synergistically flame-retardant; the anti-yellowing automobile composite film prepared by the invention not only has excellent ultraviolet absorption performance, heat resistance and anti-yellowing effects, but also has a good flame retardant effect.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a yellowing-resistant automobile composite film and a preparation method thereof. Background Art

[0002] With the advancement of science and technology and the vigorous development of industry, cars have become the main choice for people's daily travel. In order to protect the car's body paint, many car owners choose to stick a protective film on the car body. This type of film can not only protect but also decorate the car body and is easy to remove, which is in sharp contrast to traditional chemical paint treatments such as glazing, coating, and spray painting.

[0003] Car protective films are mainly made of PVC and TPU. PVC needs to be replaced after about two years of use due to its poor yellowing resistance. During the replacement process, the car paint may be scratched due to adhesive removal. In addition, although TPU protective films have a certain yellowing resistance, with the increase in actual application requirements, the yellowing resistance of the film itself no longer meets the requirements. More importantly, TPU materials themselves have a certain degree of flammability, burn quickly and release a large amount of heat, and are difficult to extinguish themselves during the combustion process. At the same time, they are accompanied by billowing smoke, which not only accelerates the spread of the fire, but also seriously threatens the safety of personnel and public property, and poses a risk to social stability that cannot be ignored. Therefore, the development of automotive composite materials with excellent yellowing resistance and flame retardancy has important practical significance and application value. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a yellowing-resistant automotive composite film and a preparation method thereof.

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

[0006] A yellowing-resistant automotive composite film comprises the following raw materials in parts by weight: 60-70 parts of PVC masterbatch, 10-20 parts of TPU masterbatch, 1-2 parts of plasticizer, 0.5-0.8 parts of leveling agent, 0.1-2 parts of yellowing-resistant modifier, and 0.1-2 parts of modified flame retardant;

[0007] The plasticizer is di(2-ethylhexyl) phthalate;

[0008] The leveling agent is polydimethylsiloxane.

[0009] The anti-yellowing modifier is prepared by the following method:

[0010] Step A1: 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole, dichloromethane, NaOH solution and tetrabutylammonium bromide are mixed and stirred at room temperature for 30 minutes; cyanuric chloride is evenly dispersed in 20 mL of dichloromethane, and the mixture is poured into the mixture, first reacted in a brine ice bath for 2 hours, then heated to 25° C., and continued to react for 2 hours, and then saturated sodium chloride is added, stirred, washed, and dried to obtain a benzotriazole compound;

[0011] Further, the dosage ratio of 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole, dichloromethane, NaOH solution, tetrabutylammonium bromide, cyanuric chloride, and saturated sodium chloride is 3.5-3.7 g: 20-25 mL: 2.5-3 mL: 0.02 g: 1.0 g: 10-15 mL, and the mass fraction of NaOH solution is 50%;

[0012] Step A2: Evenly mix the benzotriazole compound, dioxane and anhydrous potassium carbonate, reflux and slowly dropwise add 3-vinylaniline and 1,4-dioxane for 1 hour, cool to room temperature, filter, and distill under reduced pressure to obtain an intermediate;

[0013] Further, the usage ratio of benzotriazole compound, dioxane, anhydrous potassium carbonate, 3-vinylaniline, and 1,4-dioxane is 0.01-0.02 mol: 15 mL: 1.38 g: 1.18-1.31 g: 10 mL;

[0014] Step A3: N-phenylmaleimide and benzoyl peroxide are dispersed uniformly in xylene, and then maleic anhydride, the intermediate and 1-oxiranylmethyl-3,5-diallyl isocyanurate are added and stirred uniformly. Under nitrogen protection, the mixture is heated to 90° C. and reacted for 4.5 hours. The mixture is distilled under reduced pressure, cooled, washed, filtered, and vacuum dried to obtain a yellowing resistance modifier.

[0015] Furthermore, the usage ratio of N-phenylmaleimide, benzoyl peroxide, xylene, maleic anhydride, intermediate, and 1-oxiranylmethyl-3,5-diallyl isocyanurate is 3-5 g: 0.16 g: 70 mL: 4-6 g: 10-15 g: 6-8 g.

[0016] The modified flame retardant is prepared by the following method:

[0017] Step B1: Stir 4-penten-1-ol and chloroform under nitrogen protection, cool to -6°C, add hexachlorocyclotriphosphazene and triethylamine, heat to 60°C for reaction for 5h, wait until the temperature drops to room temperature, wash, rotary evaporate, and dry at 60°C to obtain a compound;

[0018] Further, the usage ratio of 4-penten-1-ol, chloroform, hexachlorocyclotriphosphazene, and triethylamine is 2.52-2.74 g: 40-60 mL: 1.56-1.89 g: 0.08-0.12 mol;

[0019] Step B2: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, N,N-dimethylformamide and the compound are mixed, stirred at 150° C. for 9 hours, filtered, washed, and vacuum dried at 60° C. for 24 hours to obtain a modified flame retardant;

[0020] Furthermore, the usage ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, N,N-dimethylformamide, and the compound is 0.15-0.25 mol:40-60 mL:0.03-0.05 mol.

[0021] A yellowing-resistant automotive composite film and a preparation method thereof, specifically comprising the following steps:

[0022] S1: Mix PVC masterbatch, TPU masterbatch, plasticizer, leveling agent, anti-yellowing modifier and modified flame retardant for 1 hour, and dry at 80-90°C to obtain a pre-material;

[0023] S2: placing the pre-material into a casting device to prepare a casting film, that is, a yellowing-resistant automotive composite film; the temperature of the first feeding section of the screw extruder in the casting device is 150-165°C, the temperature of the second mixing section is 160-175°C, the temperature of the third mixing section is 165-180°C, the temperature of the fourth high mixing section is 170-185°C, the temperature of the fifth calculation section is 170-195°C, the temperature of the sixth discharge section is 180-195°C, the filter screen temperature of the casting device is 190-210°C, the elbow temperature is 195-215°C, the die connection temperature is 185-210°C, and the die temperature is set to 185-230°C.

[0024] Beneficial effects of the present invention:

[0025] The present invention adds independently developed yellowing-resistant modifiers and modified flame retardants in the preparation of the yellowing-resistant automobile composite film, which not only gives it excellent ultraviolet absorption performance, heat resistance, and yellowing resistance effects, but also makes it have good flame retardant properties, effectively inhibits the combustion process, prolongs the service life of the material, reduces the possibility of fire, and effectively protects human health.

[0026] The anti-yellowing modifier prepared by the invention comprises the following steps: firstly, the chlorine atom of cyanuric chloride reacts with the hydroxyl group of 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole to generate a benzotriazole compound; then, the chlorine atom of the benzotriazole compound reacts with the amino group of 3-vinylaniline to generate an intermediate; and finally, the intermediate, maleic anhydride, N-phenylmaleimide and 1-oxiranylmethyl-3,5-diallyl isocyanurate are copolymerized to synthesize the anti-yellowing modifier. The s-triazine cyanuric chloride in the anti-yellowing modifier contains a conjugated π electron system and an ortho-substituent, which can effectively absorb ultraviolet rays and convert them into heat energy through intramolecular reactions, thereby preventing oxidation and chain scission caused by ultraviolet rays, avoiding yellowing of materials caused by ultraviolet rays, extending their service life and enhancing their stability. In addition, the s-triazine structure can efficiently absorb sunlight ultraviolet rays and release energy in the form of heat energy or harmless low-energy radiation, avoiding photophysical and photochemical decomposition caused by ultraviolet excitation; at the same time, the conjugated double bonds and aromatic rings of the benzotriazole intermediate can efficiently absorb ultraviolet rays of different wavelengths and convert them into It is heat energy or light energy, which can significantly reduce the yellowing of composite materials caused by ultraviolet rays and improve their aging resistance. In addition, the maleimide group can enhance the intermolecular force, increase the glass transition temperature and melting point of the material, increase the rigidity and heat resistance of the molecular chain, and reduce the yellowing of the material caused by high-temperature thermal aging. The six-membered ring structure of 1-oxiranylmethyl-3,5-diallyl isocyanurate has no active hydrogen, which gives the isocyanurate ring good thermal stability and hydrolysis stability, increases the cross-linking density of polyurethane molecules, improves the heat resistance of the material, and cooperates with maleic anhydride to reduce the possibility of yellowing of the material due to high temperature.

[0027] The modified flame retardant prepared by the present invention first utilizes the chlorine atom of hexachlorocyclotriphosphazene and the hydroxyl group of 4-pentene-1-ol to react to generate a compound; secondly, the carbon-carbon double bond of the compound is reacted with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to synthesize the modified flame retardant. The flame retardant has a good flame retardant effect. During the combustion process, the phosphorus and nitrogen main chains in the hexachlorocyclotriphosphazene show a conjugated effect, which gives it excellent thermal stability and chemical stability, making it difficult to be oxidized and open-ringed. The phosphorus element forms a phosphoric acid or polyphosphoric acid protective film to isolate oxygen and inhibit combustion. The nitrogen element releases non-combustible gas, dilutes the oxygen concentration during combustion, and further inhibits combustion. At the same time, the hexachlorocyclotriphosphazene absorbs a large amount of heat during combustion, slows down the temperature rise of the material, and improves the flame retardant performance. At high temperature, it forms a glassy or stable foam covering layer, which is heat-insulating and oxygen-isolating to prevent the escape of combustible gases. Among them, the phosphorus-nitrogen flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, as a phosphaphenanthrene compound with high thermal stability, promotes the formation of a dense and continuous carbon layer during combustion, effectively isolates oxygen, blocks heat and combustible gas exchange, inhibits combustion, and synergizes with nitrogen to achieve flame retardancy and extend its service life. In addition, the modified flame retardant prepared by the present invention is halogen-free, helps to reduce pollution to the environment and damage to the ecosystem, is harmless to human health, and achieves sustainable development. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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] Example 1

[0030] A yellowing-resistant automotive composite film and a preparation method thereof, specifically comprising the following steps:

[0031] S1: Weigh the raw materials by weight, 60 parts of PVC masterbatch, 10 parts of TPU masterbatch, 1 part of plasticizer, 0.5 parts of leveling agent, 0.1 parts of anti-yellowing modifier (prepared in this example), and 0.1 parts of modified flame retardant (prepared in this example), mix and stir the PVC masterbatch, TPU masterbatch, di(2-ethylhexyl) phthalate, polydimethylsiloxane, anti-yellowing modifier and modified flame retardant for 1 hour, and dry at 80° C. to obtain a pre-material;

[0032] S2: putting the pre-material into a casting device to prepare a casting film, that is, a yellowing-resistant automotive composite film; the temperature of the first feeding section of the screw extruder in the casting device is 150°C, the temperature of the second mixing section is 160°C, the temperature of the third mixing section is 165°C, the temperature of the fourth high mixing section is 170°C, the temperature of the fifth calculation section is 170°C, the temperature of the sixth discharge section is 180°C, the filter screen temperature of the casting device is 190°C, the elbow temperature is 195°C, the die connection temperature is 185°C, and the die temperature is set to 185°C;

[0033] The anti-yellowing modifier is prepared by the following method:

[0034] Step A1: 3.5 g of 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole, 20 mL of dichloromethane, 2.5 mL of NaOH solution and 0.02 g of tetrabutylammonium bromide were mixed and stirred at room temperature for 30 min; 1.0 g of cyanuric chloride was evenly dispersed in 20 mL of dichloromethane, and the mixture was poured into the mixture, first reacted in a brine ice bath for 2 h, then heated to 25° C., and continued to react for 2 h, and then 10 mL of saturated sodium chloride was added, stirred, washed, and dried to obtain a benzotriazole compound, wherein the mass fraction of the NaOH solution was 50%;

[0035] Step A2: 0.01 mol benzotriazole compound, 15 mL dioxane and 1.38 g anhydrous potassium carbonate were mixed evenly, refluxed and slowly added dropwise 1.18 g 3-vinylaniline and 10 mL 1,4-dioxane over 1 h, cooled to room temperature, filtered, and distilled under reduced pressure to obtain an intermediate;

[0036] Step A3: 3 g of N-phenylmaleimide and 0.16 g of benzoyl peroxide were evenly dispersed in 70 mL of xylene, and then 4 g of maleic anhydride, 10 g of the intermediate and 6 g of 1-oxiranylmethyl-3,5-diallyl isocyanurate were added and stirred evenly. Under nitrogen protection, the mixture was heated to 90° C. for reaction for 4.5 h, and the mixture was distilled under reduced pressure, cooled, washed, filtered, and vacuum dried to obtain a yellowing-resistant modifier;

[0037] The modified flame retardant is prepared by the following method:

[0038] Step B1: Stir 2.52 g of 4-penten-1-ol and 40 mL of chloroform under nitrogen protection, cool to -6°C, add 1.56 g of hexachlorocyclotriphosphazene and 0.08 mol of triethylamine, heat to 60°C for reaction for 5 h, wait until the temperature drops to room temperature, wash, rotary evaporate, and dry at 60°C to obtain a compound;

[0039] Step B2: 0.15 mol 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 40 mL N,N-dimethylformamide and 0.03 mol compound were mixed, stirred at 150° C. for 9 h, filtered, washed, and vacuum dried at 60° C. for 24 h to obtain a modified flame retardant.

[0040] Example 2

[0041] A yellowing-resistant automotive composite film and a preparation method thereof, specifically comprising the following steps:

[0042] S1: Weigh the raw materials by weight, 65 parts of PVC masterbatch, 15 parts of TPU masterbatch, 1.5 parts of plasticizer, 0.6 parts of leveling agent, 1 part of anti-yellowing modifier (prepared in this example), and 1 part of modified flame retardant (prepared in this example), mix the PVC masterbatch, TPU masterbatch, di(2-ethylhexyl) phthalate, polydimethylsiloxane, anti-yellowing modifier and modified flame retardant for 1 hour, and dry at 85° C. to obtain a pre-material;

[0043] S2: putting the pre-material into a casting device to prepare a casting film, i.e., a yellowing-resistant automotive composite film; the temperature of the first feeding section of the screw extruder in the casting device is 158°C, the temperature of the second mixing section is 168°C, the temperature of the third mixing section is 173°C, the temperature of the fourth high mixing section is 178°C, the temperature of the fifth calculation section is 183°C, the temperature of the sixth discharge section is 188°C, the filter screen temperature of the casting device is 200°C, the elbow temperature is 205°C, the die connection temperature is 197°C, and the die temperature is set to 208°C;

[0044] The anti-yellowing modifier is prepared by the following method:

[0045] Step A1: 3.6 g of 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole, 22 mL of dichloromethane, 2.7 mL of NaOH solution and 0.02 g of tetrabutylammonium bromide were mixed and stirred at room temperature for 30 min; 1.0 g of cyanuric chloride was evenly dispersed in 20 mL of dichloromethane, and the mixture was poured into the mixture, first reacted in a brine ice bath for 2 h, then heated to 25° C., and continued to react for 2 h, and then 12 mL of saturated sodium chloride was added, stirred, washed, and dried to obtain a benzotriazole compound, wherein the mass fraction of the NaOH solution was 50%;

[0046] Step A2: 0.015 mol benzotriazole compound, 15 mL dioxane and 1.38 g anhydrous potassium carbonate were mixed evenly, refluxed and slowly added dropwise 1.24 g 3-vinylaniline and 10 mL 1,4-dioxane over 1 h, cooled to room temperature, filtered, and distilled under reduced pressure to obtain an intermediate;

[0047] Step A3: 4 g of N-phenylmaleimide and 0.16 g of benzoyl peroxide were evenly dispersed in 70 mL of xylene, and then 5 g of maleic anhydride, 12 g of the intermediate and 7 g of 1-oxiranylmethyl-3,5-diallyl isocyanurate were added and stirred evenly. Under nitrogen protection, the mixture was heated to 90° C. for reaction for 4.5 h, and the mixture was distilled under reduced pressure, cooled, washed, filtered, and vacuum dried to obtain a yellowing-resistant modifier.

[0048] The modified flame retardant is prepared by the following method:

[0049] Step B1: Stir 2.63 g of 4-penten-1-ol and 50 mL of chloroform under nitrogen protection, cool to -6°C, add 1.7 g of hexachlorocyclotriphosphazene and 0.1 mol of triethylamine, heat to 60°C for reaction for 5 h, wait until the temperature drops to room temperature, wash, rotary evaporate, and dry at 60°C to obtain a compound;

[0050] Step B2: Mix 0.2 mol 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 50 mL N,N-dimethylformamide and 0.04 mol compound, stir at 150°C for 9 h, filter, wash, and vacuum dry at 60°C for 24 h to obtain a modified flame retardant.

[0051] Example 3

[0052] A yellowing-resistant automotive composite film and a preparation method thereof, specifically comprising the following steps:

[0053] S1: Weigh the raw materials by weight, including 70 parts of PVC masterbatch, 20 parts of TPU masterbatch, 2 parts of plasticizer, 0.8 parts of leveling agent, 2 parts of anti-yellowing modifier (prepared in this embodiment), and 2 parts of modified flame retardant (prepared in this embodiment), mix and stir the PVC masterbatch, TPU masterbatch, di(2-ethylhexyl) phthalate, polydimethylsiloxane, anti-yellowing modifier and modified flame retardant for 1 hour, and dry at 90° C. to obtain a pre-material;

[0054] S2: putting the pre-material into a casting device to prepare a casting film, i.e., a yellowing-resistant automotive composite film; the temperature of the first feeding section of the screw extruder in the casting device is 165°C, the temperature of the second mixing section is 175°C, the temperature of the third mixing section is 180°C, the temperature of the fourth high mixing section is 185°C, the temperature of the fifth calculation section is 195°C, the temperature of the sixth discharge section is 195°C, the filter screen temperature of the casting device is 210°C, the elbow temperature is 215°C, the die connection temperature is 210°C, and the die temperature is set to 230°C;

[0055] The anti-yellowing modifier is prepared by the following method:

[0056] Step A1: 3.7 g of 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole, 25 mL of dichloromethane, 3 mL of NaOH solution and 0.02 g of tetrabutylammonium bromide were mixed and stirred at room temperature for 30 min; 1.0 g of cyanuric chloride was evenly dispersed in 20 mL of dichloromethane, and the mixture was poured into the mixture, first reacted in a brine ice bath for 2 h, then heated to 25° C., and continued to react for 2 h, and then 15 mL of saturated sodium chloride was added, stirred, washed, and dried to obtain a benzotriazole compound, wherein the mass fraction of the NaOH solution was 50%;

[0057] Step A2: 0.02 mol benzotriazole compound, 15 mL dioxane and 1.38 g anhydrous potassium carbonate were mixed evenly, refluxed and slowly added dropwise 1.31 g 3-vinylaniline and 10 mL 1,4-dioxane over 1 h, cooled to room temperature, filtered, and distilled under reduced pressure to obtain an intermediate;

[0058] Step A3: 5 g of N-phenylmaleimide and 0.16 g of benzoyl peroxide were evenly dispersed in 70 mL of xylene, and then 6 g of maleic anhydride, 15 g of the intermediate and 8 g of 1-oxiranylmethyl-3,5-diallyl isocyanurate were added and stirred evenly. Under nitrogen protection, the mixture was heated to 90° C. for reaction for 4.5 h, and the mixture was distilled under reduced pressure, cooled, washed, filtered, and vacuum dried to obtain a yellowing-resistant modifier;

[0059] The modified flame retardant is prepared by the following method:

[0060] Step B1: Stir 2.74 g of 4-penten-1-ol and 60 mL of chloroform under nitrogen protection, cool to -6°C, add 1.89 g of hexachlorocyclotriphosphazene and 0.12 mol of triethylamine, heat to 60°C for reaction for 5 h, wait until the temperature drops to room temperature, wash, rotary evaporate, and dry at 60°C to obtain a compound;

[0061] Step B2: 0.25 mol 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 60 mL N,N-dimethylformamide and 0.05 mol compound were mixed, stirred at 150° C. for 9 h, filtered, washed, and vacuum dried at 60° C. for 24 h to obtain a modified flame retardant.

[0062] Comparative Example 1

[0063] This comparative example is a yellowing-resistant automotive composite film, which differs from Example 3 in that an equal amount of [2-hydroxy-4-(octyloxy)phenyl]phenyl ketone is used to replace the yellowing-resistant modifier prepared in Example 3, and the rest are the same.

[0064] Comparative Example 2

[0065] This comparative example is a yellowing-resistant automotive composite film, which differs from Example 3 in that an equal amount of modified flame retardant magnesium hydroxide is used to replace the modified flame retardant prepared in Example 3, and the rest are the same.

[0066] Performance test: The yellowing-resistant automotive composite films prepared in Examples 1-3 and Comparative Examples 1-2 were cut into standard test sizes, and irradiated with UVA340Lamp ultraviolet aging lamps to test the yellowing resistance level for a total of 144 hours. The yellowing resistance level was divided into 1-5 levels, and the higher the level, the better the yellowing resistance effect. Among them, level 4 is yellowing resistance, and level 5 is no yellowing at all; in an environment of high temperature (70°C) and low temperature (-20°C) reciprocating cycle, the deformation rate of the yellowing-resistant automotive composite film was tested, with 12 hours as a cycle and a total duration of 144 hours; the vertical burning performance was tested using the GB / T2048-1996 plastic burning performance test method; the test results are shown in the following table:

[0067]

[0068] It can be seen from the test data in the table that the yellowing-resistant automotive composite film prepared in Example 1 has excellent ultraviolet absorption performance, heat resistance, and yellowing resistance. It can also be seen from the above table that the yellowing-resistant automotive composite film prepared in the present invention has a good flame retardant effect.

[0069] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a yellowing-resistant automotive composite film, characterized in that: The following steps are involved: S1: Weigh the raw materials by weight, including 60-70 parts of PVC masterbatch, 10-20 parts of TPU masterbatch, 1-2 parts of plasticizer, 0.5-0.8 parts of leveling agent, 0.1-2 parts of anti-yellowing modifier, and 0.1-2 parts of modified flame retardant; mix and stir the PVC masterbatch, TPU masterbatch, plasticizer, leveling agent, anti-yellowing modifier and modified flame retardant for 1 hour, and dry at 80-90°C to obtain a pre-material; S2: placing the pre-material into a casting device to prepare a casting film, i.e., a yellowing-resistant automotive composite film; the temperature of the first feeding section of the screw extruder in the casting device is 150-165°C, the temperature of the second mixing section is 160-175°C, the temperature of the third mixing section is 165-180°C, the temperature of the fourth high mixing section is 170-185°C, the temperature of the fifth calculation section is 170-195°C, the temperature of the sixth discharging section is 180-195°C, the filter screen temperature of the casting device is 190-210°C, the elbow temperature is 195-215°C, the die connection temperature is 185-210°C, and the die temperature is set to 185-230°C.

2. The method for preparing a yellowing-resistant automotive composite film according to claim 1, characterized in that: The anti-yellowing modifier is prepared by the following method: Step A1: 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole, dichloromethane, NaOH solution and tetrabutylammonium bromide are mixed and stirred at room temperature for 30 minutes; cyanuric chloride is evenly dispersed in 20 mL of dichloromethane, and the mixture is poured into the mixture, first reacted in a brine ice bath for 2 hours, then heated to 25° C., and continued to react for 2 hours, and then saturated sodium chloride is added, stirred, washed, and dried to obtain a benzotriazole compound; Step A2: Evenly mix the benzotriazole compound, dioxane and anhydrous potassium carbonate, reflux and slowly dropwise add 3-vinylaniline and 1,4-dioxane for 1 hour, cool to room temperature, filter, and distill under reduced pressure to obtain an intermediate; Step A3: N-phenylmaleimide and benzoyl peroxide are dispersed evenly in xylene, and then maleic anhydride, the intermediate and 1-oxiranylmethyl-3,5-diallyl isocyanurate are added and stirred evenly. Under nitrogen protection, the mixture is heated to 90° C. for reaction for 4.5 hours, and the mixture is distilled under reduced pressure, cooled, washed, filtered, and dried in vacuo to obtain a yellowing-resistant modifier.

3. The method for preparing a yellowing-resistant automotive composite film according to claim 2, characterized in that: In step A1, the dosage ratio of 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole, dichloromethane, NaOH solution, tetrabutylammonium bromide, cyanuric chloride, and saturated sodium chloride is 3.5-3.7 g: 20-25 mL: 2.5-3 mL: 0.02 g: 1.0 g: 10-15 mL, and the mass fraction of NaOH solution is 50%.

4. The method for preparing a yellowing-resistant automotive composite film according to claim 2, characterized in that: In step A2, the usage ratio of benzotriazole compound, dioxane, anhydrous potassium carbonate, 3-vinylaniline and 1,4-dioxane is 0.01-0.02 mol: 15 mL: 1.38 g: 1.18-1.31 g: 10 mL.

5. The method for preparing a yellowing-resistant automotive composite film according to claim 2, characterized in that: In step A3, the usage ratio of N-phenylmaleimide, benzoyl peroxide, xylene, maleic anhydride, intermediate, and 1-oxiranylmethyl-3,5-diallyl isocyanurate is 3-5 g: 0.16 g: 70 mL: 4-6 g: 10-15 g: 6-8 g.

6. The method for preparing a yellowing-resistant automotive composite film according to claim 1, characterized in that: The modified flame retardant is prepared by the following method: Step B1: Stir 4-penten-1-ol and chloroform under nitrogen protection, cool to -6°C, add hexachlorocyclotriphosphazene and triethylamine, heat to 60°C for reaction for 5h, wait until the temperature drops to room temperature, wash, rotary evaporate, and dry at 60°C to obtain a compound; Step B2: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, N,N-dimethylformamide and the compound are mixed, stirred at 150° C. for 9 hours, filtered, washed, and vacuum dried at 60° C. for 24 hours to obtain a modified flame retardant.

7. The method for preparing a yellowing-resistant automotive composite film according to claim 6, characterized in that: In step B1, the usage ratio of 4-penten-1-ol, chloroform, hexachlorocyclotriphosphazene and triethylamine is 2.52-2.74 g: 40-60 mL: 1.56-1.89 g: 0.08-0.12 mol.

8. The method for preparing a yellowing-resistant automotive composite film according to claim 6, characterized in that: In step B2, the usage ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, N,N-dimethylformamide, and compound is 0.15-0.25 mol:40-60 mL:0.03-0.05 mol.

9. The method for preparing a yellowing-resistant automotive composite film according to claim 1, characterized in that: The plasticizer is di(2-ethylhexyl) phthalate and the leveling agent is polydimethylsiloxane.

10. A yellowing-resistant automotive composite film, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 9.

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