A kind of heat-insulating polyurethane protective film and preparation method thereof

Abstract

The invention relates to a heat-insulating polyurethane protective film and a preparation method thereof, and belongs to the technical field of polymer materials. The invention uses polytetramethylene glycol, 4,4'-dicyclohexylmethane diisocyanate, dibutyltin dilaurate, 1,4-butanediol, and modified hollow glass microspheres as raw materials to prepare a heat-insulating polyurethane protective film. The invention comprises the following steps: firstly uniformly mixing 4,4'-dicyclohexylmethane diisocyanate and the modified hollow glass microspheres; then adding polytetramethylene glycol and a catalyst dibutyltin dilaurate to carry out polymerization to obtain a prepolymer containing the modified hollow glass microspheres; then adding a chain extender 1,4-butanediol to carry out a chain extension reaction to obtain a heat-insulating polyurethane; and finally thermally curing the heat-insulating polyurethane to obtain a heat-insulating polyurethane protective film. The preparation method of the invention is simple and easy to scale up. The prepared polyurethane protective film not only has good mechanical strength and heat resistance, but also has flame retardancy.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a heat-insulating polyurethane protective film and a preparation method thereof. Background Art

[0002] Polyurethane is a polymer compound synthesized by the reaction of polyisocyanate and polyol. It has good wear resistance, elasticity, and waterproof properties. The thermal conductivity of polyurethane is relatively low, so it is also widely used in the field of thermal insulation material technology. However, the heat resistance of polyurethane materials is poor. When the temperature is high, the polyurethane molecular chain may break, resulting in a decrease in mechanical properties and weakened elasticity, which in turn affects the service life of the polyurethane material.

[0003] Hollow glass microspheres are a lightweight, high-strength inorganic non-metallic material with a hollow interior, resulting in extremely low thermal conductivity. Composite polyurethane materials with even better thermal insulation properties can be produced by compounding polyurethane and hollow glass microspheres. However, the interfacial compatibility between hollow glass microspheres and polyurethane is poor, and the mechanical properties of the polyurethane material will be reduced after compounding. Based on this, the present invention provides a thermal insulating polyurethane protective film and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide a heat-insulating polyurethane protective film and a preparation method thereof, which are used to solve the problem that the interface compatibility between hollow glass microspheres and polyurethane is poor, and the mechanical properties of the polyurethane material will be reduced after compounding.

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

[0006] A heat-insulating polyurethane protective film comprises the following raw materials in parts by mass: 65-70 parts of polytetramethylene glycol, 35-40 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.01-0.012 parts of dibutyltin dilaurate, 14-16 parts of 1,4-butanediol, and 3 parts of modified hollow glass microspheres;

[0007] A method for preparing a heat-insulating polyurethane protective film comprises the following steps:

[0008] The first step is to weigh 65-70 parts of polytetramethylene glycol, 35-40 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.01-0.012 parts of dibutyltin dilaurate, 14-16 parts of 1,4-butanediol, and 3 parts of modified hollow glass microspheres by mass;

[0009] The second step is to add 4,4'-dicyclohexylmethane diisocyanate and modified hollow glass microspheres into a reaction container, stir and mix them evenly, then add dibutyltin dilaurate and polytetramethylene ether glycol into the reaction container, and introduce nitrogen to exhaust the air in the reaction container, and then react at a temperature of 80-100°C for 4 hours to obtain a prepolymer containing modified hollow glass microspheres;

[0010] Step 3: Cool the reaction system to 50-60°C, then add 1,4-butanediol to the reaction vessel, and react at 50-60°C for 2 hours to obtain thermal insulation polyurethane;

[0011] Step 4: Pour the heat-insulating polyurethane into a PTFE mold and heat-cure it for 24 hours to obtain a heat-insulating polyurethane protective film.

[0012] Furthermore, the molecular weight of the polytetramethylene ether glycol used is 1000.

[0013] Furthermore, in the second step, the stirring and mixing speed condition is 300-400 rpm, and the stirring and mixing time condition is 4 hours.

[0014] Furthermore, the thermal curing condition in the fourth step is 80°C.

[0015] Furthermore, the modified hollow glass microspheres are prepared by the following steps:

[0016] Step 1: N-(4-hydroxyphenyl)maleimide, triethylamine, and tetrahydrofuran were mixed in a three-necked flask, and magnetic stirring was started. A carbon tetrachloride solution of dimethyl phosphite was added to the three-necked flask, and the mixture was reacted at room temperature for 4 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 1;

[0017] Step 2: 3-mercaptopropyltriethoxysilane, intermediate 1, sodium ethoxide, and tetrahydrofuran were mixed in a three-necked flask, magnetic stirring was started, and the mixture was reacted at room temperature for 24 hours. After the reaction, the solvent was removed by rotary evaporation, and the remaining solid was purified by silica gel column chromatography to obtain intermediate 2;

[0018] Step 3: Mix the intermediate 2, hollow glass microspheres, and ethanol solution in a three-necked flask, install a condenser and a thermometer, turn on the magnetic stirring, add glacial acetic acid to the three-necked flask to adjust the pH of the system to 4, and then react at a temperature of 50-60°C for 2h. After the reaction is completed, filter, wash the obtained solid with deionized water, and dry it to obtain modified hollow glass microspheres.

[0019] Furthermore, the carbon tetrachloride solution of dimethyl phosphite used in step 1 is prepared from 0.06 mol dimethyl phosphite and 10 mL carbon tetrachloride.

[0020] Furthermore, the amount ratio of N-(4-hydroxyphenyl)maleimide, triethylamine, tetrahydrofuran, and carbon tetrachloride solution of dimethyl phosphite used in step 1 is 0.05 mol: 0.06-0.08 mol: 40-50 mL: 22.54 g.

[0021] Furthermore, the amount ratio of 3-mercaptopropyltriethoxysilane, intermediate 1, sodium ethoxide, and tetrahydrofuran used in step 2 is 0.03 mol: 0.03 mol: 0.4 g: 30-40 mL.

[0022] Furthermore, the ethanol solution used in step 3 is an ethanol aqueous solution with a volume fraction of 90%.

[0023] Furthermore, the usage ratio of the intermediate 2, hollow glass microspheres, and ethanol solution used in step 3 is 5-6 g: 5 g: 60-80 mL.

[0024] Beneficial effects of the present invention:

[0025] 1) The present invention uses polytetramethylene glycol, 4,4'-dicyclohexylmethane diisocyanate, dibutyltin dilaurate, 1,4-butanediol, and modified hollow glass microspheres as raw materials to prepare a heat-insulating polyurethane protective film. The present invention comprises the following steps: first, 4,4'-dicyclohexylmethane diisocyanate and the modified hollow glass microspheres are uniformly mixed; then, polytetramethylene glycol and a catalyst, dibutyltin dilaurate, are added to carry out polymerization to obtain a prepolymer containing the modified hollow glass microspheres; then, a chain extender, 1,4-butanediol, is added to carry out a chain extension reaction to obtain a heat-insulating polyurethane; and finally, the heat-insulating polyurethane is thermally cured to obtain a heat-insulating polyurethane protective film. The preparation method of the present invention is simple, the ratio is easily controlled, and the prepared heat-insulating polyurethane protective film has good mechanical strength and heat-insulating properties.

[0026] 2) The present invention uses N-(4-hydroxyphenyl)maleimide and dimethyl phosphite as raw materials, utilizes dimethyl phosphite to react with carbon tetrachloride to produce dimethyl chlorophosphite by Atherton-Todd reaction, and then the dimethyl chlorophosphite reacts with the hydroxyl group of N-(4-hydroxyphenyl)maleimide to produce intermediate 1 by esterification reaction, then uses intermediate 1 and 3-mercaptopropyltriethoxysilane as raw materials, utilizes the double bond of intermediate 1 and the mercapto group of 3-mercaptopropyltriethoxysilane to produce Michael addition reaction under the catalysis of sodium ethoxide to produce intermediate 2, and finally utilizes intermediate 1 to produce intermediate 2 by esterification reaction. The silicon-oxygen bond of intermediate 2 is grafted onto hollow glass microspheres through an alcoholysis reaction to obtain a modified hollow glass microsphere. The surface of the modified hollow glass microsphere of the present invention is loaded with intermediate 2 with an organophilic structure, which effectively improves the compatibility of the modified hollow glass microspheres in polyurethane materials. The benzoheterocyclic structure in intermediate 2 can enhance the rigidity of the polymer molecular chain and hinder the movement of the polymer molecular chain, thereby improving the heat resistance of the polyurethane protective film. In addition, intermediate 2 also has a phosphate structure, which can give the polyurethane protective film good flame retardancy and improve the safety performance of the polyurethane protective film.

[0027] 3) The preparation method of the polyurethane heat-insulating protective film of the present invention is simple and easy to scale up. The prepared polyurethane protective film not only has good mechanical strength and heat resistance, but also has flame retardancy and good safety performance. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0029] Example 1

[0030] A modified hollow glass microsphere is prepared by the following steps:

[0031] Step 1: 0.05 mol N-(4-hydroxyphenyl)maleimide, 0.06 mol triethylamine, and 40 mL tetrahydrofuran were mixed in a three-necked flask, and magnetic stirring was turned on. 22.54 g of a solution prepared by 0.06 mol dimethyl phosphite and 10 mL carbon tetrachloride was added to the three-necked flask, and the mixture was reacted at room temperature for 4 h. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 1;

[0032] Step 2: 0.03 mol 3-mercaptopropyltriethoxysilane, 0.03 mol intermediate 1, 0.4 g sodium ethoxide, and 30 mL tetrahydrofuran were mixed in a three-necked flask, magnetic stirring was turned on, and the mixture was reacted at room temperature for 24 h. After the reaction, the solvent was removed by rotary evaporation, and the remaining solid was purified by silica gel column chromatography to obtain intermediate 2;

[0033] Step 3. Mix 5 g of intermediate 2, 5 g of hollow glass microspheres, and 60 mL of 90% volume fraction ethanol aqueous solution in a three-necked flask, install a condenser and a thermometer, turn on magnetic stirring, add glacial acetic acid to the three-necked flask to adjust the pH of the system to 4, and then react at a temperature of 50 ° C for 2 h. After the reaction is completed, filter, wash the resulting solid with deionized water, and dry it to obtain modified hollow glass microspheres.

[0034] Example 2

[0035] A modified hollow glass microsphere is prepared by the following steps:

[0036] Step 1: 0.05 mol N-(4-hydroxyphenyl)maleimide, 0.07 mol triethylamine, and 45 mL tetrahydrofuran were mixed in a three-necked flask, and magnetic stirring was turned on. 22.54 g of a solution prepared by 0.06 mol dimethyl phosphite and 10 mL carbon tetrachloride was added to the three-necked flask, and the mixture was reacted at room temperature for 4 h. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 1;

[0037] Step 2: 0.03 mol 3-mercaptopropyltriethoxysilane, 0.03 mol intermediate 1, 0.4 g sodium ethoxide, and 35 mL tetrahydrofuran were mixed in a three-necked flask, magnetic stirring was turned on, and the mixture was reacted at room temperature for 24 h. After the reaction, the solvent was removed by rotary evaporation, and the remaining solid was purified by silica gel column chromatography to obtain intermediate 2;

[0038] Step 3: Mix 5.5 g of intermediate 2, 5 g of hollow glass microspheres, and 70 mL of 90% by volume ethanol aqueous solution in a three-necked flask, install a condenser and a thermometer, turn on magnetic stirring, add glacial acetic acid to the three-necked flask to adjust the pH of the system to 4, and then react at a temperature of 55 ° C for 2 h. After the reaction is completed, filter, wash the resulting solid with deionized water, and dry it to obtain modified hollow glass microspheres.

[0039] Example 3

[0040] A modified hollow glass microsphere is prepared by the following steps:

[0041] Step 1: 0.05 mol N-(4-hydroxyphenyl)maleimide, 0.08 mol triethylamine, and 50 mL tetrahydrofuran were mixed in a three-necked flask, and magnetic stirring was turned on. 22.54 g of a solution prepared by 0.06 mol dimethyl phosphite and 10 mL carbon tetrachloride was added to the three-necked flask, and the mixture was reacted at room temperature for 4 h. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 1;

[0042] Step 2: 0.03 mol 3-mercaptopropyltriethoxysilane, 0.03 mol intermediate 1, 0.4 g sodium ethoxide, and 40 mL tetrahydrofuran were mixed in a three-necked flask, magnetic stirring was turned on, and the mixture was reacted at room temperature for 24 h. After the reaction, the solvent was removed by rotary evaporation, and the remaining solid was purified by silica gel column chromatography to obtain intermediate 2;

[0043] Step 3: Mix 6 g of intermediate 2, 5 g of hollow glass microspheres, and 80 mL of 90% volume fraction ethanol aqueous solution in a three-necked flask, install a condenser and a thermometer, turn on magnetic stirring, add glacial acetic acid to the three-necked flask to adjust the pH of the system to 4, and then react at a temperature of 60°C for 2 h. After the reaction is completed, filter, wash the resulting solid with deionized water, and dry it to obtain modified hollow glass microspheres.

[0044] Example 4

[0045] A heat-insulating polyurethane protective film, comprising the following raw materials in parts by mass: 65 parts of polytetramethylene glycol, 35 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.01 parts of dibutyltin dilaurate, 14 parts of 1,4-butanediol, and 3 parts of the modified hollow glass microspheres obtained in Example 1;

[0046] A method for preparing a heat-insulating polyurethane protective film comprises the following steps:

[0047] The first step is to weigh 65 parts of polytetramethylene glycol, 35 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.01 parts of dibutyltin dilaurate, 14 parts of 1,4-butanediol, and 3 parts of the modified hollow glass microspheres obtained in Example 1;

[0048] In the second step, 4,4'-dicyclohexylmethane diisocyanate and the modified hollow glass microspheres obtained in Example 1 were added to a reaction vessel, stirred at a speed of 300 rpm for 4 hours to mix uniformly, and then dibutyltin dilaurate and polytetramethylene ether glycol were added to the reaction vessel, and nitrogen was introduced to exhaust the air in the reaction vessel. After that, the reaction was carried out at a temperature of 80°C for 4 hours to obtain a prepolymer containing modified hollow glass microspheres;

[0049] Step 3: Cool the reaction system to 50°C, then add 1,4-butanediol to the reaction vessel and react at 50°C for 2 hours to obtain thermal insulation polyurethane;

[0050] The fourth step is to pour the heat-insulating polyurethane into a PTFE mold and heat-cure it at a temperature of 80°C for 24 hours to obtain a heat-insulating polyurethane protective film.

[0051] Wherein, the molecular weight of the polytetrahydrofuran ether glycol used in this embodiment is 1000.

[0052] Example 5

[0053] A heat-insulating polyurethane protective film, comprising the following raw materials in parts by mass: 67.5 parts of polytetramethylene glycol, 37.5 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.011 parts of dibutyltin dilaurate, 15 parts of 1,4-butanediol, and 3 parts of the modified hollow glass microspheres obtained in Example 2;

[0054] A method for preparing a heat-insulating polyurethane protective film comprises the following steps:

[0055] The first step is to weigh 67.5 parts of polytetramethylene glycol, 37.5 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.011 parts of dibutyltin dilaurate, 15 parts of 1,4-butanediol, and 3 parts of the modified hollow glass microspheres obtained in Example 2 in parts by mass;

[0056] In the second step, 4,4'-dicyclohexylmethane diisocyanate and the modified hollow glass microspheres obtained in Example 2 were added to a reaction vessel, stirred at a speed of 350 rpm for 4 hours to mix evenly, and then dibutyltin dilaurate and polytetramethylene ether glycol were added to the reaction vessel, and nitrogen was introduced to exhaust the air in the reaction vessel. Then, the mixture was reacted at a temperature of 90°C for 4 hours to obtain a prepolymer containing modified hollow glass microspheres;

[0057] Step 3: Cool the reaction system to 55°C, then add 1,4-butanediol to the reaction vessel and react at 55°C for 2 hours to obtain thermal insulation polyurethane;

[0058] The fourth step is to pour the heat-insulating polyurethane into a PTFE mold and heat-cure it at a temperature of 80°C for 24 hours to obtain a heat-insulating polyurethane protective film.

[0059] Wherein, the molecular weight of the polytetrahydrofuran ether glycol used in this embodiment is 1000.

[0060] Example 6

[0061] A heat-insulating polyurethane protective film, comprising the following raw materials in parts by mass: 70 parts of polytetramethylene glycol, 40 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.012 parts of dibutyltin dilaurate, 16 parts of 1,4-butanediol, and 3 parts of the modified hollow glass microspheres obtained in Example 3;

[0062] A method for preparing a heat-insulating polyurethane protective film comprises the following steps:

[0063] The first step is to weigh 70 parts of polytetramethylene glycol, 40 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.012 parts of dibutyltin dilaurate, 16 parts of 1,4-butanediol, and 3 parts of the modified hollow glass microspheres obtained in Example 3 in parts by mass;

[0064] In the second step, 4,4'-dicyclohexylmethane diisocyanate and the modified hollow glass microspheres obtained in Example 3 were added to a reaction vessel, stirred at a speed of 400 rpm for 4 hours to mix uniformly, and then dibutyltin dilaurate and polytetramethylene ether glycol were added to the reaction vessel, and nitrogen was introduced to exhaust the air in the reaction vessel. After that, the reaction was carried out at a temperature of 100°C for 4 hours to obtain a prepolymer containing modified hollow glass microspheres;

[0065] Step 3: Cool the reaction system to 60°C, then add 1,4-butanediol to the reaction vessel and react at 60°C for 2 hours to obtain thermal insulating polyurethane;

[0066] The fourth step is to pour the heat-insulating polyurethane into a PTFE mold and heat-cure it at a temperature of 80°C for 24 hours to obtain a heat-insulating polyurethane protective film.

[0067] Wherein, the molecular weight of the polytetrahydrofuran ether glycol used in this embodiment is 1000.

[0068] Comparative Example 1

[0069] The “modified hollow glass microspheres obtained in Example 3” used in Example 6 were replaced with unmodified hollow glass microspheres, and the other conditions and preparation steps remained unchanged.

[0070] A heat-insulating polyurethane protective film comprises the following raw materials in parts by mass: 70 parts of polytetramethylene glycol, 40 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.012 parts of dibutyltin dilaurate, 16 parts of 1,4-butanediol, and 3 parts of hollow glass microspheres;

[0071] A method for preparing a heat-insulating polyurethane protective film comprises the following steps:

[0072] The first step is to weigh 70 parts of polytetramethylene glycol, 40 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.012 parts of dibutyltin dilaurate, 16 parts of 1,4-butanediol, and 3 parts of hollow glass microspheres according to their mass ratio;

[0073] The second step is to add 4,4'-dicyclohexylmethane diisocyanate and hollow glass microspheres into a reaction vessel, stir at a speed of 400 rpm for 4 hours to mix evenly, then add dibutyltin dilaurate and polytetramethylene ether glycol into the reaction vessel, and introduce nitrogen to exhaust the air in the reaction vessel, and then react at a temperature of 100 ° C for 4 hours to obtain a prepolymer containing modified hollow glass microspheres;

[0074] Step 3: Cool the reaction system to 60°C, then add 1,4-butanediol to the reaction vessel and react at 60°C for 2 hours to obtain thermal insulating polyurethane;

[0075] The fourth step is to pour the heat-insulating polyurethane into a PTFE mold and heat-cure it at a temperature of 80°C for 24 hours to obtain a heat-insulating polyurethane protective film.

[0076] Wherein, the molecular weight of the polytetrahydrofuran ether glycol used in this comparative example is 1000.

[0077] Comparative Example 2

[0078] This comparative example is a commercially available polyurethane thermal insulation film.

[0079] The thermal insulation polyurethane protective films of Examples 4-6 and Comparative Example 1 were subjected to performance tests together with the commercially available polyurethane thermal insulation film of Comparative Example 2. The thermal conductivity of each component material was tested in accordance with the national standard GB / T 10294, the oxygen limiting index of each component material was tested in accordance with the national standard GB / T 2048, and the tensile strength of each component material was tested in accordance with GB / T 528. After aging at a temperature of 130° C. for 4 hours, the materials were retested. The test results are shown in Table 1:

[0080] Table 1

[0081]

[0082] As can be seen from Table 1, the thermal conductivity coefficients of the thermal insulating polyurethane protective films of the present invention in Examples 4-6 are all lower than those of the commercially available polyurethane thermal insulating films, indicating that the thermal insulating polyurethane protective films of the present invention have better thermal insulation performance, and the limiting oxygen index is higher than that of the commercially available polyurethane protective films, indicating that the thermal insulating polyurethane protective films of the present invention have better flame retardant properties. In addition, the thermal insulating polyurethane protective films of the present invention have better tensile strength than the commercially available polyurethane thermal insulating films, and are less affected by high-temperature aging, indicating that the thermal insulating polyurethane protective films of the present invention have better strength and heat resistance.

[0083] The above is a detailed introduction to a heat-insulating polyurethane protective film and a preparation method thereof provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best way, and also enables any technician in this field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combination method. It should be pointed out that for ordinary technicians in this technical field, the present invention can also be improved and modified without departing from the principles of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention can be combined with each other in any way. The reason why these combinations are not exhaustively described in this specification is simply for the sake of omitting space and saving resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A heat-insulating polyurethane protective film, characterized in that: The method comprises the following raw materials in parts by weight: 65-70 parts of polytetramethylene glycol, 35-40 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.01-0.012 parts of dibutyltin dilaurate, 14-16 parts of 1,4-butanediol, and 3 parts of modified hollow glass microspheres; Wherein, the modified hollow glass microspheres are prepared by the following steps: Step 1: N-(4-hydroxyphenyl)maleimide, triethylamine, and tetrahydrofuran were mixed in a container and stirred evenly. A carbon tetrachloride solution of dimethyl phosphite was added to the container, and the mixture was reacted at room temperature for 4 hours to obtain intermediate 1. Step 2: 3-mercaptopropyltriethoxysilane, intermediate 1, sodium ethoxide, and tetrahydrofuran were mixed in a container, stirred evenly, and reacted at room temperature for 24 hours to obtain intermediate 2; Step 3: Mix the intermediate 2, hollow glass microspheres, and ethanol solution in a container, stir evenly, add glacial acetic acid to the container to adjust the pH of the system to 4, and then react at a temperature of 50-60° C. for 2 h to obtain modified hollow glass microspheres; Modified hollow glass microspheres surface loaded with organophilic structure intermediate 2.

2. The heat-insulating polyurethane protective film according to claim 1, characterized in that: The carbon tetrachloride solution of dimethyl phosphite used in step 1 is prepared from 0.06 mol of dimethyl phosphite and 10 mL of carbon tetrachloride.

3. The heat-insulating polyurethane protective film according to claim 1, characterized in that: The amount ratio of N-(4-hydroxyphenyl)maleimide, triethylamine, tetrahydrofuran, and carbon tetrachloride solution of dimethyl phosphite used in step 1 is 0.05 mol: 0.06-0.08 mol: 40-50 mL: 22.54 g.

4. The heat-insulating polyurethane protective film according to claim 1, characterized in that: The amount ratio of 3-mercaptopropyltriethoxysilane, intermediate 1, sodium ethoxide, and tetrahydrofuran used in step 2 is 0.03 mol: 0.03 mol: 0.4 g: 30-40 mL.

5. The heat-insulating polyurethane protective film according to claim 1, characterized in that: The ethanol solution used in step 3 is an ethanol aqueous solution with a volume fraction of 90%.

6. The heat-insulating polyurethane protective film according to claim 1, characterized in that: The amount ratio of the intermediate 2, hollow glass microspheres, and ethanol solution used in step 3 is 5-6 g: 5 g: 60-80 mL.

7. A method for preparing a heat-insulating polyurethane protective film according to any one of claims 1 to 6, characterized in that: The following steps are involved: The first step is to weigh 65-70 parts of polytetramethylene glycol, 35-40 parts of 4,4'-dicyclohexylmethane diisocyanate, 0.01-0.012 parts of dibutyltin dilaurate, 14-16 parts of 1,4-butanediol, and 3 parts of modified hollow glass microspheres by mass; The second step is to add 4,4'-dicyclohexylmethane diisocyanate and modified hollow glass microspheres into a reaction container, stir and mix them evenly, then add dibutyltin dilaurate and polytetramethylene ether glycol into the reaction container, and introduce nitrogen to exhaust the air in the reaction container, and then react at a temperature of 80-100°C for 4 hours to obtain a prepolymer containing modified hollow glass microspheres; Step 3: Cool the reaction system to 50-60°C, then add 1,4-butanediol to the reaction vessel, and react at 50-60°C for 2 hours to obtain thermal insulation polyurethane; Step 4: Pour the heat-insulating polyurethane into a PTFE mold and heat-cure it for 24 hours to obtain a heat-insulating polyurethane protective film.

8. The method for preparing a heat-insulating polyurethane protective film according to claim 7, characterized in that: The molecular weight of the polytetrahydrofuran diol used is 1000.

9. The method for preparing a heat-insulating polyurethane protective film according to claim 7, characterized in that: In the second step, the stirring and mixing speed condition is 300-400 rpm, and the stirring and mixing time condition is 4 hours.

10. The method for preparing a heat-insulating polyurethane protective film according to claim 7, characterized in that: The heat curing condition in the fourth step is 80°C.

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