A heat-resistant shrinkable plastic film and a preparation method thereof

Abstract

The present invention discloses a heat-resistant shrinkable plastic film and a preparation method thereof, belonging to the technical field of plastic film production. The preparation process of the heat-resistant shrinkable plastic film is as follows: Modified graphene, ODA and DAPBO are added to DMAc, and stirred until ODA and DAPBO are completely dissolved, and then PMDA is added to obtain a modified polyimide solution; The modified polyimide solution is subjected to leveling, drying and thermal imidization treatment to obtain a heat-resistant shrinkable plastic film. The present invention uses the flexible diamine monomer ODA and PMDA to polymerize to prepare a polyimide heat-resistant shrinkable plastic film. The introduction of the flexible structure diamine can not only improve the toughness of the film, but also reduce the thermal expansion coefficient of the film; The addition of DAPBO introduces oxazole groups into the film. The oxazole groups belong to rigid groups and can significantly reduce the thermal expansion coefficient of the film; Modified graphene is also added during the film preparation process of the present invention, and the modified graphene helps to improve the heat-resistant shrinkage performance of the film.

Description

Technical Field

[0001] The present invention belongs to the technical field of plastic film production, and particularly relates to a heat-resistant shrinkable plastic film and a preparation method thereof. Background Art

[0002] Polyimide (PI for short) is a polymer containing a rigid five-membered imide ring (-CO-N-CO-). Due to strong intermolecular interactions, polyimide has excellent heat-resistant stability and mechanical properties. The excellent heat-resistant stability provides excellent heat shrinkage properties for polyimide films.

[0003] Chinese Patent CN111704798B discloses a high-temperature resistant polyimide film and a preparation method thereof, and this polyimide film is applied in the field of electrical and electronics. This invention selects boron nitride nanosheets with appropriate sizes and modified nano-silica in an appropriate proportion to cooperate with each other, so that the modified nano-silica surrounds the boron nitride nanosheets and is uniformly dispersed in the polyimide, avoiding the agglomeration of boron nitride nanosheets, enabling the film to obtain good high-temperature performance while still maintaining good mechanical properties. Finally, the prepared polyimide film has good high-temperature resistance, mechanical properties and insulation properties.

[0004] Polyimide films are widely used in flexible printed circuit boards. In recent years, with the continuous improvement of the performance of printed circuit boards, there are higher requirements for the heat resistance and mechanical properties of polyimide films, especially the coefficient of thermal expansion (evaluating the heat shrinkage properties of the film). In the above-mentioned prior art, the high-temperature resistance of polyimide films is improved by introducing boron nitride nanosheets, indirectly enhancing the heat shrinkage properties of polyimide films. The purpose of this application is to improve the existing polyimide films and further enhance the heat shrinkage properties of polyimide films. Summary of the Invention

[0005] The purpose of the present invention is to provide a heat-resistant shrinkable plastic film and a preparation method thereof to improve the heat shrinkage properties of the film.

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

[0007] A preparation method of a heat-resistant shrinkable plastic film includes the following steps:

[0008] A1. At room temperature and in a nitrogen atmosphere, modified graphene is added to dimethylacetamide (DMAc), and ultrasonically dispersed for 2 h. Then, 4,4'-diaminodiphenyl ether (ODA) and 2-(4-aminophenyl)-5-aminobenzoxazole (DAPBO) are added, and stirred until ODA and DAPBO are completely dissolved to form a mixed solution. The mixed solution is cooled to 10 °C, and pyromellitic dianhydride (PMDA) is added to the mixed solution, and stirred in an ice-water bath for 24 h, and then vacuum degassed for 2 h to obtain a modified polyimide solution;

[0009] A2. Pour the modified polyimide solution on a glass plate, scrape it flat, place the glass plate in an oven, heat up to remove the organic solvent, and then transfer it to a vacuum drying oven for thermal imidization treatment to obtain a heat-resistant shrinkable plastic film.

[0010] Further, the dosage ratio of DMAc, modified graphene, 4,4'-ODA, DAPBO, and PMDA in step A1 is 4 L: 15 - 20 g: 0.9 - 1.2 moL: 0.10 - 0.15 moL: 1 moL.

[0011] Further, the process of the thermal imidization treatment in step A2 is: 250 °C * 1 h + 300 °C * 1 h + 350 °C * 1 h.

[0012] Further, the preparation process of the modified graphene in step A1 is:

[0013] S1. Add 30% of the total amount of 2,2-bis(hydroxymethyl)propionic acid and 35% of the total amount of p-toluenesulfonic acid to pentaerythritol, heat up to 140 °C, stir and react for 2 h, add the remaining 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid, and continue to react for 2 h to obtain a hydroxyl-terminated branched monomer;

[0014] S2. Mix the hydroxyl-terminated branched monomer, p-toluenesulfonic acid and toluene, add 6-aminocaproic acid, heat up to 140 °C and stir for 5 h. After the reaction is completed, remove the solvent to obtain a modifier;

[0015] S3. Add graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxybenzotriazole to N,N-dimethylformamide, add the modifier at 25 °C, and stir at a constant temperature for 24 h to obtain modified graphene.

[0016] Further, the dosage ratio of pentaerythritol, 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid in step S1 is 0.25 moL: 2.2 - 2.5 moL: 1.2 g.

[0017] Further, the dosage ratio of the hydroxyl-terminated branched monomer, p-toluenesulfonic acid, toluene and 6-aminocaproic acid in step S2 is 5 g: 0.1 g: 80 mL: 7.6 g.

[0018] Further, the dosage ratio of graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 1-hydroxybenzotriazole, N,N-dimethylformamide and the modifier in step S3 is 5 g: 0.5 g: 0.4 g: 100 mL: 3.2 g.

[0019] Further, a heat-resistant shrinkable plastic film is prepared by the above preparation method.

[0020] Advantages of the present invention:

[0021] The present invention uses the flexible diamine monomer 4,4'-diaminodiphenyl ether and pyromellitic dianhydride to polymerize to prepare a polyimide heat-resistant shrinkable plastic film. The introduction of the flexible diamine structure can not only improve the toughness of the plastic film, but also reduce the thermal expansion coefficient of the plastic film. In the process of preparing polyimide in the present invention, 2-(4-aminophenyl)-5-aminobenzoxazole is added, and the oxazole group is introduced into the polyimide plastic film. The oxazole group belongs to a rigid group and can significantly reduce the thermal expansion coefficient of the plastic film, that is, improve the heat-resistant shrinkage performance of the plastic film.

[0022] In the process of preparing polyimide in the present invention, modified graphene is added. The modified graphene is formed by bonding graphene and a modifier. Graphene contains oxygen-containing groups and reacts with the amino group in the modifier to bond. Among them, the introduction of graphene can improve the high-temperature resistance of the plastic film. However, graphene is prone to agglomeration. The present invention uses a modifier with a branched structure to bond with graphene to improve the dispersion performance of graphene, thereby improving the high-temperature resistance of the plastic film, and finally realizing the improvement of the heat-resistant shrinkage performance of the plastic film. Detailed implementation manners

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0024] Example 1

[0025] Prepare modified graphene:

[0026] S1. Add 30% of the total amount of 2,2-bis(hydroxymethyl)propionic acid and 35% of the total amount of p-toluenesulfonic acid to pentaerythritol, heat up to 140 °C, stir and react for 2 h. Then add the remaining 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid, and continue to react for 2 h to obtain a hydroxyl-terminated branched monomer. Among them, the dosage ratio of pentaerythritol, 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid is 0.25 moL: 2.2 moL: 1.2 g.

[0027] S2. Mix the hydroxyl-terminated branched monomer, p-toluenesulfonic acid and toluene, then add 6-aminohexanoic acid, heat up to 140 °C and stir for 5 h. After the reaction is completed, remove the solvent to obtain a modifier. Among them, the dosage ratio of the hydroxyl-terminated branched monomer, p-toluenesulfonic acid, toluene and 6-aminohexanoic acid is 5 g: 0.1 g: 80 mL: 7.6 g.

[0028] S3. Add graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxybenzotriazole to N,N-dimethylformamide. Under the condition of a temperature of 25 °C, add the modifier and stir at a constant temperature for 24 h to obtain modified graphene. Among them, the dosage ratio of graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 1-hydroxybenzotriazole, N,N-dimethylformamide and the modifier is 5 g: 0.5 g: 0.4 g: 100 mL: 3.2 g.

[0029] Example 2

[0030] Preparation of modified graphene:

[0031] S1. Add 30% of the total amount of 2,2-bis(hydroxymethyl)propionic acid and 35% of the total amount of p-toluenesulfonic acid to pentaerythritol, heat up to 140 °C, stir and react for 2 h. Then add the remaining 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid, and continue to react for 2 h to obtain a hydroxyl-terminated branched monomer. Among them, the dosage ratio of pentaerythritol, 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid is 0.25 moL: 2.4 moL: 1.2 g.

[0032] S2. Mix the hydroxyl-terminated branched monomer, p-toluenesulfonic acid and toluene, then add 6-aminohexanoic acid, heat up to 140 °C and stir for 5 h. After the reaction is completed, remove the solvent to obtain a modifier. Among them, the dosage ratio of the hydroxyl-terminated branched monomer, p-toluenesulfonic acid, toluene and 6-aminohexanoic acid is 5 g: 0.1 g: 80 mL: 7.6 g.

[0033] S3. Add graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and 1-hydroxybenzotriazole into N,N-dimethylformamide. Under the condition of a temperature of 25°C, add the modifier and stir at a constant temperature for 24 h to obtain modified graphene. Among them, the dosage ratio of graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 1-hydroxybenzotriazole, N,N-dimethylformamide, and the modifier is 5 g: 0.5 g: 0.4 g: 100 mL: 3.2 g.

[0034] Example 3

[0035] Preparation of modified graphene:

[0036] S1. Mix 30% of the total amount of 2,2-bis(hydroxymethyl)propionic acid and 35% of the total amount of p-toluenesulfonic acid into pentaerythritol, heat up to 140°C, and stir and react for 2 h. Then add the remaining 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid and continue to react for 2 h to obtain a hydroxyl-terminated branched monomer. Among them, the dosage ratio of pentaerythritol, 2,2-bis(hydroxymethyl)propionic acid, and p-toluenesulfonic acid is 0.25 moL: 2.5 moL: 1.2 g.

[0037] S2. Mix the hydroxyl-terminated branched monomer, p-toluenesulfonic acid, and toluene, then add 6-aminohexanoic acid, heat up to 140°C and stir for 5 h. After the reaction is completed, remove the solvent to obtain the modifier. Among them, the dosage ratio of the hydroxyl-terminated branched monomer, p-toluenesulfonic acid, toluene, and 6-aminohexanoic acid is 5 g: 0.1 g: 80 mL: 7.6 g.

[0038] S3. Add graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and 1-hydroxybenzotriazole into N,N-dimethylformamide. Under the condition of a temperature of 25°C, add the modifier and stir at a constant temperature for 24 h to obtain modified graphene. Among them, the dosage ratio of graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 1-hydroxybenzotriazole, N,N-dimethylformamide, and the modifier is 5 g: 0.5 g: 0.4 g: 100 mL: 3.2 g.

[0039] Example 4

[0040] Preparation of heat-resistant shrinkable plastic film:

[0041] A1. At room temperature and in a nitrogen atmosphere, modified graphene prepared in Example 1 was added to dimethylacetamide (DMAc), and ultrasonic dispersion was carried out for 2 h. Then, 4,4'-oxydianiline (4,4'-ODA, 99.95%) and 2-(4-aminophenyl)-5-aminobenzoxazole (DAPBO, 99.95%) were added. After stirring until 4,4'-ODA and DAPBO were completely dissolved, a mixed solution was formed. The mixed solution was cooled to 10 °C, and pyromellitic dianhydride (PMDA, 99.98%) was added to the mixed solution. Stirring was carried out in an ice-water bath for 24 h, and vacuum degassing was carried out for 2 h to obtain a modified polyimide solution; wherein, the dosage ratio of DMAc, modified graphene, 4,4'-ODA, DAPBO, and PMDA was 4 L: 15 g: 0.9 moL: 0.10 moL: 1 moL.

[0042] A2. The modified polyimide solution was poured on a glass plate and leveled. The glass plate was placed in an oven to remove the organic solvent by heating, and then transferred to a vacuum drying oven for thermal imidization treatment. The process of thermal imidization treatment: First, the temperature was raised to 250 °C and kept constant for 1 h; then the temperature was continuously raised to 300 °C and kept constant for 1 h; then the temperature was raised to 350 °C and kept constant for 1 h, thus completing the thermal imidization treatment process, and a brownish-yellow heat-resistant shrinkable plastic film was obtained. The thickness of the film was about 50 μm;

[0043] Through testing the thermal properties of the film, it was obtained that the glass transition temperature was 435 °C, the 5% thermal decomposition temperature was 588 °C, the coefficient of thermal expansion CTE was 3 ppm / K (100 °C - 200 °C), and the thermal shrinkage rate was 0.03% (200 °C, 2 h). It has the characteristics of thermal stability and low expansion coefficient.

[0044] The test results of the mechanical properties of the film: The tensile strength was 140 MPa, the tensile modulus was 3.5 GPa, and the elongation at break was 54%. The mechanical properties are excellent.

[0045] Example 5

[0046] Preparation of heat-resistant shrinkable plastic film:

[0047] A1. At room temperature and in a nitrogen atmosphere, modified graphene prepared in Example 2 was added to dimethylacetamide (DMAc), and ultrasonically dispersed for 2 h. Then, 4,4'-oxydianiline (4,4'-ODA, 99.95%) and 2-(4-aminophenyl)-5-aminobenzoxazole (DAPBO, 99.95%) were added. After stirring until 4,4'-ODA and DAPBO were completely dissolved, a mixed solution was formed. The mixed solution was cooled to 10 °C, and pyromellitic dianhydride (PMDA, 99.98%) was added to the mixed solution. Stirring was carried out in an ice-water bath for 24 h, and vacuum degassing was carried out for 2 h to obtain a modified polyimide solution; wherein, the dosage ratio of DMAc, modified graphene, 4,4'-ODA, DAPBO, and PMDA was 4 L: 18 g: 1.0 moL: 0.12 moL: 1 moL.

[0048] A2. The modified polyimide solution was poured on a glass plate and leveled. The glass plate was placed in an oven to remove the organic solvent by heating, and then transferred to a vacuum drying oven for thermal imidization treatment. The thermal imidization treatment process: First, the temperature was raised to 250 °C and held for 1 h; then the temperature was continuously raised to 300 °C and held for 1 h; then the temperature was raised to 350 °C and held for 1 h, and the thermal imidization treatment process was completed to obtain a brownish-yellow heat-resistant shrinkable plastic film with a film thickness of about 50 μm;

[0049] Testing the thermal properties of the film showed that the glass transition temperature was 4320 °C, the 5% thermal decomposition temperature was 582 °C, the coefficient of thermal expansion CTE was 3 ppm / K (100 °C - 200 °C), and the thermal shrinkage rate was 0.03% (200 °C, 2 h). It has the characteristics of thermal stability and low expansion coefficient.

[0050] The test results of the mechanical properties of the film: The tensile strength was 142 MPa, the tensile modulus was 3.6 GPa, and the elongation at break was 52%. The mechanical properties are excellent.

[0051] Example 6

[0052] Preparation of heat-resistant shrinkable plastic film:

[0053] A1. At room temperature and in a nitrogen atmosphere, the modified graphene prepared in Example 3 was added to dimethylacetamide (DMAc), and ultrasonically dispersed for 2 hours. Then, 4,4'-diaminodiphenyl ether (4,4'-ODA, 99.95%) and 2-(4-aminophenyl) 5-aminobenzoxazole (DAPBO, 99.95%) were added, and stirred until 4,4'-ODA and DAPBO were completely dissolved to form a mixed solution. The mixed solution was cooled to 10° C., and pyromellitic dianhydride (PMDA, 99.98%) was added to the mixed solution. The mixture was stirred in an ice-water bath for 24 hours, and vacuum degassed for 2 hours to obtain a modified polyimide solution; wherein the amount ratio of DMAc, modified graphene, 4,4'-ODA, DAPBO and PMDA was 4L:20g:1.2moL:0.15moL:1moL.

[0054] A2. Pour the modified polyimide solution onto a glass plate, scrape it flat, place the glass plate in an oven, heat it up to remove the organic solvent, and then transfer it to a vacuum drying oven for thermal imidization. The thermal imidization process is as follows: first, heat it up to 250°C and keep it at a constant temperature for 1 hour; then continue to heat it up to 300°C and keep it at a constant temperature for 1 hour; then heat it up to 350°C and keep it at a constant temperature for 1 hour, thus completing the thermal imidization process and obtaining a brown-yellow heat-resistant shrinkable plastic film with a thickness of about 50 μm.

[0055] The thermal properties of the film were tested and found to have a glass transition temperature of 438°C, a 5% thermal decomposition temperature of 582°C, a thermal expansion coefficient of 3ppm / K (100°C-200°C), and a thermal shrinkage of 0.03% (200°C, 2 hours). It has the characteristics of thermal stability and low expansion coefficient.

[0056] The mechanical properties test results of the film are as follows: tensile strength is 144MPa, tensile modulus is 3.5GPa, and elongation at break is 56%. The mechanical properties are excellent.

[0057] Comparative Example 1

[0058] Comparative Example 1 is the control group of Example 4, except that 2-(4-aminophenyl) 5-aminobenzoxazole (DAPBO, 99.95%) in step A1 of Example 4 is replaced with p-phenylenediamine (p-PDA, 99.95%), and the other raw materials and the preparation process remain unchanged. Finally, a brown-yellow heat-resistant shrinkable plastic film is obtained, and the film thickness is about 50 μm;

[0059] The thermal properties of the film were tested and found to have a glass transition temperature of 390°C, a 5% thermal decomposition temperature of 525°C, a thermal expansion coefficient CTE of 13ppm / K (100°C-200°C), and a thermal shrinkage rate of 0.15% (200°C, 2 hours).

[0060] Mechanical property test results of the film: Tensile strength is 136 MPa, tensile modulus is 3.2 GPa, and elongation at break is 51%.

[0061] Comparative Example 2

[0062] Comparative Example 2 is the control group of Example 5. Remove the terminal hydroxyl branched monomer in the preparation of modified graphene in Example 2, and keep the remaining raw materials and preparation process unchanged. The specific preparation process of the modified graphene is as follows. Then, produce the heat-resistant shrinkable plastic film with the prepared modified graphene according to the preparation process in Example 5. Finally, obtain a brownish-yellow heat-resistant shrinkable plastic film with a film thickness of about 50 μm.

[0063] Testing the thermal properties of the film, the glass transition temperature is 410 °C, the 5% thermal decomposition temperature is 578 °C, the coefficient of thermal expansion CTE is 5 ppm / K (100 °C - 200 °C), and the thermal shrinkage rate is 0.06% (200 °C, 2 hours).

[0064] Mechanical property test results of the film: Tensile strength is 115 MPa, tensile modulus is 2.8 GPa, and elongation at break is 54%.

[0065] Preparation of modified graphene:

[0066] S1. Mix p-toluenesulfonic acid and toluene, then add 6-aminohexanoic acid, heat up to 140 °C and stir for 5 h. After the reaction ends, remove the solvent to obtain the modifier. Among them, the dosage ratio of p-toluenesulfonic acid, toluene, and 6-aminohexanoic acid is 0.1 g: 80 mL: 7.6 g.

[0067] S2. Add graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and 1-hydroxybenzotriazole to N,N-dimethylformamide. Under the condition of a temperature of 25 °C, add the modifier and stir at a constant temperature for 24 h to obtain modified graphene. Among them, the dosage ratio of graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 1-hydroxybenzotriazole, N,N-dimethylformamide, and the modifier is 5 g: 0.5 g: 0.4 g: 100 mL: 3.2 g.

[0068] Comparative Example 3

[0069] Comparative Example 3 is the control group of Example 6. Remove the modified graphene prepared in Example 3 in Example 6, and keep the remaining raw materials and preparation process unchanged. Finally, obtain a brownish-yellow heat-resistant shrinkable plastic film with a film thickness of about 50 μm.

[0070] The thermal properties of the film were tested and obtained as follows: the glass transition temperature was 380 °C, the 5% thermal decomposition temperature was 524 °C, the coefficient of thermal expansion CTE was 9 ppm / K (100 °C - 200 °C), and the thermal shrinkage rate was 0.12% (200 °C, 2 hours).

[0071] The test results of the mechanical properties of the film are as follows: the tensile strength was 102 MPa, the tensile modulus was 2.4 GPa, and the elongation at break was 51%.

[0072] It should be noted that in this article, terms such as "including", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such a process, method, article or device.

[0073] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a heat-shrinkable plastic film, characterized in that, It includes the following steps: A1. At room temperature and in a nitrogen atmosphere, add modified graphene to dimethylacetamide, ultrasonically disperse for 2 h, then add 4,4'-diaminodiphenyl ether and 2-(4-aminophenyl)-5-aminobenzoxazole, stir until 4,4'-diaminodiphenyl ether and 2-(4-aminophenyl)-5-aminobenzoxazole are completely dissolved to form a mixed solution. When the mixed solution cools to 10 °C, add pyromellitic dianhydride to the mixed solution, stir in an ice-water bath for 24 h, and perform vacuum degassing for 2 h to obtain a modified polyimide solution. A2. Pour the modified polyimide solution onto a glass plate, scrape it flat, place the glass plate in an oven, raise the temperature to remove the organic solvent, and then transfer it to a vacuum drying oven for thermal imidization treatment to obtain a heat-resistant shrinkable plastic film. Among them, the preparation process of the modified graphene in step A1: S1. Add 30% of the total amount of 2,2-bis(hydroxymethyl)propionic acid and 35% of the total amount of p-toluenesulfonic acid to pentaerythritol, raise the temperature to 140 °C, stir and react for 2 h, add the remaining 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid, and continue to react for 2 h to obtain a hydroxyl-terminated branched monomer. S2. Mix the hydroxyl-terminated branched monomer, p-toluenesulfonic acid and toluene, add 6-aminocaproic acid, raise the temperature to 140 °C and stir for 5 h. After the reaction is completed, remove the solvent to obtain a modifier. S3. Add graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxybenzotriazole to N,N-dimethylformamide. At a temperature of 25 °C, add the modifier and stir at a constant temperature for 24 h to obtain modified graphene.

2. The preparation method of a heat-shrinkable plastic film according to claim 1, characterized in that The dosage ratio of dimethylacetamide, modified graphene, 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzoxazole and pyromellitic dianhydride in step A1 is 4 L: 15 - 20 g: 0.9 - 1.2 moL: 0.10 - 0.15 moL: 1 moL.

3. The preparation method of a heat-shrinkable plastic film according to claim 1, characterized in that, The thermal imidization treatment process in step A2: 250 °C * 1 h + 300 °C * 1 h + 350 °C * 1 h.

4. The preparation method of a heat-shrinkable plastic film according to claim 1, characterized in that, The dosage ratio of pentaerythritol, 2,2-bis(hydroxymethyl)propionic acid and p-toluenesulfonic acid in step S1 is 0.25 moL: 2.2 - 2.5 moL: 1.2 g.

5. The preparation method of a heat-shrinkable plastic film according to claim 1, characterized in that, The mass ratio of the hydroxyl-terminated branched monomer, p-toluenesulfonic acid and 6-aminocaproic acid in step S2 is 5: 0.1: 7.

6.

6. The preparation method of a heat-shrinkable plastic film according to claim 1, characterized in that, The mass ratio of graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxybenzotriazole in step S3 is 5: 0.5: 0.

4.

7. A heat-shrinkable plastic film, characterized in that, It is prepared by the preparation method of a heat-resistant shrinkable plastic film described in any one of claims 1 - 6.