Method for preparing modified polyester by recycling polyester release film

Abstract

The invention relates to a method for preparing modified polyester, in particular to a method for preparing modified polyester by recycling a polyester release film. The invention aims to solve the problems that an organic silicon coating of the organic silicon polyester release film needs to be washed off before the two treatment modes, and then the organic silicon polyester release film is further treated, so that water resource waste and pollution are caused in the cleaning process. The modified polyester is composed of a recycled organosilicon polyester release film, a diacid monomer, a diol monomer, a catalyst, a heat stabilizer and an antioxidant. The invention belongs to the technical field of polyester release film recovery.

Description

Technical Field

[0001] The invention relates to a method for preparing modified polyester, and belongs to the technical field of polyester release film recycling. Background Art

[0002] Since silicone release films are widely used and used in large quantities, and are usually used in process protection and discarded immediately after use, a large number of waste silicone release films are generated. If they are not handled properly, they will bring great pressure to environmental protection. The main raw material for producing silicone release films is PET, which has excellent creep resistance, fatigue resistance, and friction resistance. It is a material with high recycling value. If it is recycled and modified, the economic benefits will definitely be considerable. Therefore, the recycling and modification of silicone release films has very important social significance and economic value.

[0003] At present, there are two main methods for recycling PET materials: physical recycling and chemical recycling. Physically recycled PET raw materials have certain limitations in use. Most recycled PET resins can only be used to make non-food packaging or textiles. Therefore, many companies tend to use chemical methods to treat waste PET, decomposing it into raw materials or intermediates for making PET resins, so as to achieve the purpose of complete reuse. However, before these two treatment methods, the silicone polyester release film needs to be washed off the silicone coating before further treatment, and the washing process will cause waste and pollution of water resources. Therefore, by directly degrading the recycled polyester release film, converting it into smaller molecules or intermediate raw materials, and then copolymerizing and modifying the polyester, it can be recycled and reused, which not only protects the environment but also generates certain economic value. Summary of the invention

[0004] The present invention aims to solve the problem that the silicone polyester release film needs to be washed to remove the silicone coating before further treatment in both treatment methods, which will cause water waste and pollution during the washing process, and further proposes a method for recycling and reusing the polyester release film to prepare modified polyester.

[0005] The technical solution adopted by the present invention to solve the above problems is: the modified polyester of the present invention is composed of recycled silicone polyester release film, diacid monomer, diol monomer, catalyst, heat stabilizer and antioxidant.

[0006] Furthermore, the mass fraction of the recycled silicone polyester release film is 30-50 parts, the mass fraction of the diacid monomer is 80-110 parts, the mass fraction of the diol monomer is 90-120 parts, the mass fraction of the catalyst is 0.13-0.25 parts, the mass fraction of the heat stabilizer is 0.03-0.1 parts, and the mass fraction of the antioxidant is 0.05-0.1 parts.

[0007] Furthermore, the diacid monomer is composed of one or more of phthalic acid, isophthalic acid, terephthalic acid, glutaric acid, azelaic acid, and adipic acid.

[0008] Furthermore, the diol monomer is composed of one or more of ethylene glycol, 1,4-cyclohexanedimethanol, butanediol, neopentyl glycol, and propylene glycol.

[0009] Furthermore, the catalyst is composed of one or more of zinc acetate, chromium acetate, tin acetate, cadmium acetate, antimony glycolate, and germanium oxide.

[0010] Furthermore, the heat stabilizer is composed of one or more of trimethyl phosphate, triphenyl phosphate, phosphorous acid, and phosphoric acid.

[0011] Furthermore, the antioxidant is composed of one or more of 2,6-di-tert-butylphenol and 3,3-thiodipropionate.

[0012] The steps of the preparation method of the present invention include:

[0013] Step 1, weighing the recycled silicone polyester release film, ethylene glycol, and a catalyst, adding them into a Polytex-1L polyester synthesis device, stirring at a set temperature, and performing a degradation reaction for 6-8 hours;

[0014] Step 2: After the degradation is completed, the system is cooled to 40-50°C, and the diacid and diol monomers are weighed and added to the polyester synthesis reactor for stirring; at the same time, the heat stabilizer and antioxidant are weighed and placed in the storage tank of the synthesis device for standby use;

[0015] After strictly deoxygenating the synthesis system by "nitrogen-vacuuming", nitrogen was introduced, followed by stirring and heating the system to the set temperature. During this period, the pressure in the reactor continued to increase, and the esterification pressure valve was adjusted to maintain the system pressure at 400 kPa;

[0016] Step 3, when water starts to be discharged from the esterification tower, the reactor enters the esterification stage; the esterification pressure valve is adjusted to slowly reduce the system pressure to normal pressure, and when the temperature at the top of the esterification tower is lower than 100°C, the esterification stage is ended, and the esterification time is 2-3h;

[0017] Step 4: Use nitrogen to pressurize the heat stabilizer and antioxidant in the storage tank into the reactor to enter the pre-condensation stage. Heat the system to the set temperature, turn on the vacuum pump and adjust the polycondensation pressure valve to slowly reduce the system pressure to low pressure. When the pressure in the reactor drops below 20Pa, the pre-condensation stage ends. The pre-condensation time is 0.5-1h;

[0018] Step 5: When the motor power reaches 45W, the final polycondensation stage of the polyester is ended;

[0019] Step 6: turn off the vacuum pump and stop stirring, pass nitrogen until the pressure in the reactor is slightly higher than normal pressure, squeeze out the synthesized polyester, discharge the material, cut into pellets and dry.

[0020] Furthermore, in step 1, the motor speed is 25 Hz and the set temperature is 170-190°C;

[0021] The set temperature in step 2 is 210-260°C;

[0022] The set temperature in step 4 is 270-280°C.

[0023] The beneficial effects of the present invention are as follows: the present invention provides a technical solution for preparing modified polyester by recycling and reusing polyester release film, by firstly using ethylene glycol to degrade the PET release film, then using diacid and diol monomers to copolymerize the degraded PET, and at the same time introducing silicone segments into the modified polyester chain structure, to prepare modified polyester with excellent flexibility, which not only reduces the environmental pollution caused by traditional treatment but also generates certain economic value. Example

[0024] Embodiment 1

[0025] The modified polyester includes 40g of recycled silicone polyester release film, 50g of terephthalic acid, 30g of isophthalic acid, 100g of ethylene glycol, 20g of 1,4-cyclohexanedimethanol, 0.2g of zinc acetate, 0.05g of trimethyl phosphate, and 0.08g of 3,3-thiodipropionate;

[0026] The preparation steps of the modified polyester include:

[0027] Step 1, weighing 30g of recycled silicone polyester release film, 100g of ethylene glycol, and 0.2g of zinc acetate, adding them into a Polytex-1L polyester synthesis reactor, performing degradation reaction at 190°C and normal pressure for 6h, and cooling to 40°C after the degradation is completed;

[0028] Step 2, weigh 50g of terephthalic acid, 30g of isophthalic acid, and 20g of 1,4-cyclohexanedimethanol, add them to the polyester synthesis reactor and stir; at the same time, weigh 0.05g of trimethyl phosphate and 0.08g of 3,3-thiodipropionate and place them in the storage tank of the synthesis device for standby use. After the synthesis system is strictly deoxygenated by the "nitrogen-vacuum" operation, nitrogen is introduced to make the system have an initial pressure of 150kPa, then the system is stirred and heated to 260°C, the speed of the stirring motor is 25Hz, during which the pressure in the reactor continues to rise, and the esterification pressure valve is adjusted to maintain the system pressure at 400kPa;

[0029] Step 3, when water starts to be discharged from the esterification tower, the reactor enters the esterification stage; the esterification pressure valve is adjusted to slowly reduce the system pressure from 400 kPa to normal pressure, and when the temperature at the top of the esterification tower is lower than 100°C, the esterification stage is ended, and the esterification time is 2 hours;

[0030] Step 4, using nitrogen to pressurize 0.05g of trimethyl phosphate and 0.08g of 3,3-thiodipropionate weighed from the storage tank into the reactor to enter the pre-polycondensation stage; heating the system to 280°C, turning on the vacuum pump and adjusting the polycondensation pressure valve to slowly reduce the system pressure from normal pressure to low pressure, and ending the pre-polycondensation stage after the pressure in the reactor drops below 20Pa, and the pre-polycondensation time is 0.5h;

[0031] Step 5: When the motor power reaches 45W, the final polycondensation stage of the polyester is ended;

[0032] Step 6: turn off the vacuum pump and stop stirring, pass nitrogen until the pressure in the reactor reaches 130 kPa, squeeze out the synthesized polyester, discharge the material, cut into pellets and dry.

[0033] Embodiment 2

[0034] The modified polyester includes 30g of recycled silicone polyester release film, 90g of terephthalic acid, 80g of ethylene glycol, 10g of butanediol, 0.15g of chromium acetate, 0.03g of triphenyl phosphate, and 0.05g of 2,6-di-tert-butylphenol;

[0035] The preparation steps of the modified polyester include:

[0036] Step 1, weighing 30g of recycled silicone polyester release film, 80g of ethylene glycol, and 0.15g of chromium acetate, adding them into a Polytex-1L polyester synthesis reactor, performing degradation reaction at 170°C and normal pressure for 8h, and cooling to 50°C after the degradation is completed;

[0037] Step 2, weighing 90g of terephthalic acid and 10g of butanediol, adding them to a polyester synthesis reactor and stirring; at the same time, weighing 0.03g of triphenyl phosphate and 0.05g of 2,6-di-tert-butylphenol and placing them in a storage tank of a synthesis device for standby; after strictly deoxygenating the synthesis system by "nitrogen-vacuuming" operation, nitrogen was introduced to make the system have an initial pressure of 150kPa, and then the system was stirred and heated to 240°C, the speed of the stirring motor was 25Hz, during which the pressure in the reactor continued to increase, and the esterification pressure valve was adjusted to maintain the system pressure at 400kPa;

[0038] Step 3, when water starts to be discharged from the esterification tower, the reactor enters the esterification stage; the esterification pressure valve is adjusted to slowly reduce the system pressure from 400 kPa to normal pressure, and when the temperature at the top of the esterification tower is lower than 100°C, the esterification stage is ended, and the esterification time is 3 hours;

[0039] Step 4: Use nitrogen to pressurize 0.03 g of triphenyl phosphate and 0.05 g of 2,6-di-tert-butylphenol weighed from the storage tank into the reactor to enter the pre-condensation stage; heat the system to 270°C, turn on the vacuum pump and adjust the condensation pressure valve to slowly reduce the system pressure from normal pressure to low pressure. After the pressure in the reactor drops below 20 Pa, the pre-condensation stage is ended, and the pre-condensation time is 1 hour;

[0040] Step 5: When the motor power reaches 45W, the final polycondensation stage of the polyester is ended;

[0041] Step 6: turn off the vacuum pump and stop stirring, pass nitrogen until the pressure in the reactor reaches 130 kPa, squeeze out the synthesized polyester, discharge the material, cut into pellets and dry.

[0042] Embodiment 3

[0043] The modified polyurethane comprises 35g of recycled silicone polyester release film, 50g of terephthalic acid, 38g of phthalic acid, 80g of ethylene glycol, 20g of 1,4-cyclohexanedimethanol, 0.03g of antimony glycol, 0.15g of tin acetate, 0.1g of phosphorous acid, and 0.07g of 3,3-thiodipropionate;

[0044] The preparation steps of the modified polyurethane include:

[0045] Step 1, weighing 35g of recycled silicone polyester release film, 80g of ethylene glycol, 0.15g of tin acetate, and 0.03g of ethylene glycol antimony, adding them into a Polytex-1L polyester synthesis reactor, performing degradation reaction at 180°C and normal pressure for 7h, and cooling to 40°C after the degradation is completed;

[0046] Step 2, weighing 50g of terephthalic acid, 38g of phthalic acid, and 20g of 1,4-cyclohexanedimethanol, adding them to the polyester synthesis reactor and stirring; at the same time, weighing 0.1g of phosphorous acid and 0.07g of 3,3-thiodipropionate and placing them in the storage tank of the synthesis device for standby; after strictly deoxygenating the synthesis system by "nitrogen-vacuuming" operation, nitrogen is introduced to make the system have an initial pressure of 150kPa, then stirring and heating the system to 240°C, the speed of the stirring motor is 25Hz, during which the pressure in the reactor continues to rise, and the esterification pressure valve is adjusted to maintain the system pressure at 400kPa;

[0047] Step 3, when water starts to be discharged from the esterification tower, the reactor enters the esterification stage; the esterification pressure valve is adjusted to slowly reduce the system pressure from 400 kPa to normal pressure, and when the temperature at the top of the esterification tower is lower than 100°C, the esterification stage is ended, and the esterification time is 3 hours;

[0048] Step 4, using nitrogen to pressurize 0.1g of phosphorous acid and 0.07g of 3,3-thiodipropionate weighed from the storage tank into the reactor to enter the pre-polycondensation stage; heating the system to 270°C, turning on the vacuum pump and adjusting the polycondensation pressure valve to slowly reduce the system pressure from normal pressure to low pressure, and ending the pre-polycondensation stage after the pressure in the reactor drops below 20Pa, and the pre-polycondensation time is 0.5h;

[0049] Step 5: When the motor power reaches 45W, the final polycondensation stage of the polyester is ended;

[0050] Step 6: turn off the vacuum pump and stop stirring, pass nitrogen until the pressure in the reactor reaches 130 kPa, squeeze out the synthesized polyester, discharge the material, cut into pellets and dry.

[0051] Embodiment 4

[0052] The modified polyurethane comprises 50 g of recycled silicone polyester release film, 110 g of terephthalic acid, 100 g of ethylene glycol, 20 g of neopentyl glycol, 0.2 g of cadmium acetate, 0.05 g of ethylene glycol antimony, 0.1 g of phosphoric acid, and 0.1 g of 2,6-di-tert-butylphenol;

[0053] The preparation steps of the modified polyurethane include:

[0054] Step 1, weighing 50g of recycled silicone polyester release film, 100g of ethylene glycol, 0.2g of cadmium acetate, and 0.05g of ethylene glycol antimony, adding them into a Polytex-1L polyester synthesis reactor, performing degradation reaction at 190°C and normal pressure for 6h, and cooling to 40°C after the degradation is completed;

[0055] Step 2, weighing 110g of terephthalic acid and 20g of neopentyl glycol, adding them to a polyester synthesis reactor and stirring; at the same time, weighing 0.1g of phosphoric acid and 0.1g of 2,6-di-tert-butylphenol and placing them in a storage tank of a synthesis device for standby; after strictly deoxygenating the synthesis system by "nitrogen-vacuuming" operation, nitrogen was introduced to make the system have an initial pressure of 150kPa, and then the system was stirred and heated to 250°C, the speed of the stirring motor was 25Hz, during which the pressure in the reactor continued to rise, and the esterification pressure valve was adjusted to maintain the system pressure at 400kPa;

[0056] Step 3, when water starts to be discharged from the esterification tower, the reactor enters the esterification stage; the esterification pressure valve is adjusted to slowly reduce the system pressure from 400 kPa to normal pressure, and when the temperature at the top of the esterification tower is lower than 100°C, the esterification stage is ended, and the esterification time is 3 hours;

[0057] Step 4: Use nitrogen to pressurize 0.1 g of phosphoric acid and 0.1 g of 2,6-di-tert-butylphenol weighed from the storage tank into the reactor to enter the pre-condensation stage; heat the system to 270°C, turn on the vacuum pump and adjust the condensation pressure valve to slowly reduce the system pressure from normal pressure to low pressure. After the pressure in the reactor drops below 20 Pa, the pre-condensation stage is ended, and the pre-condensation time is 1 hour;

[0058] Step 5: When the motor power reaches 45W, the final polycondensation stage of the polyester is ended;

[0059] Step 6: turn off the vacuum pump and stop stirring, pass nitrogen until the pressure in the reactor reaches 130 kPa, squeeze out the synthesized polyester, discharge the material, cut into pellets and dry.

[0060] Embodiment 5

[0061] The modified polyurethane comprises 40g of recycled silicone polyester release film, 80g of terephthalic acid, 10g of glutaric acid, 10g of azelaic acid, 90g of ethylene glycol, 15g of propylene glycol, 0.06g of ethylene glycol antimony, 0.1g of germanium oxide, 0.06g of trimethyl phosphate, and 0.1g of 3,3-thiodipropionate;

[0062] The preparation steps of the modified polyurethane include:

[0063] Step 1, weighing 40g of recycled silicone polyester release film, 90g of ethylene glycol, 0.1g of germanium oxide, and 0.06g of ethylene glycol antimony, adding them into a Polytex-1L polyester synthesis reactor, performing degradation reaction at 170°C and normal pressure for 7h, and cooling to 50°C after the degradation is completed;

[0064] Step 2, weigh 80g of terephthalic acid, 10g of glutaric acid, 10g of azelaic acid, and 15g of propylene glycol, add them to the polyester synthesis reactor and stir; at the same time, weigh 0.06g of trimethyl phosphate and 0.1g of 3,3-thiodipropionate and place them in the storage tank of the synthesis device for standby; after strictly deoxygenating the synthesis system by "nitrogen-vacuuming" operation, nitrogen is introduced to make the system have an initial pressure of 150kPa, then stir and heat the system to 240°C, the speed of the stirring motor is 25Hz, during which the pressure in the reactor continues to rise, and the esterification pressure valve is adjusted to maintain the system pressure at 400kPa;

[0065] Step 3, when water starts to be discharged from the esterification tower, the reactor enters the esterification stage; the esterification pressure valve is adjusted to slowly reduce the system pressure from 400 kPa to normal pressure, and when the temperature at the top of the esterification tower is lower than 100°C, the esterification stage is ended, and the esterification time is 3 hours;

[0066] Step 4, using nitrogen to pressurize 0.06g of trimethyl phosphate and 0.1g of 3,3-thiodipropionate weighed from the storage tank into the reactor to enter the pre-polycondensation stage; heating the system to 270°C, turning on the vacuum pump and adjusting the polycondensation pressure valve to slowly reduce the system pressure from normal pressure to low pressure, and ending the pre-polycondensation stage after the pressure in the reactor drops below 20Pa, and the pre-polycondensation time is 0.5h;

[0067] Step 5: When the motor power reaches 45W, the final polycondensation stage of the polyester is ended;

[0068] Step 6: turn off the vacuum pump and stop stirring, pass nitrogen until the pressure in the reactor reaches 130 kPa, squeeze out the synthesized polyester, discharge the material, cut into pellets and dry.

[0069] Embodiment 6

[0070] The modified polyurethane comprises 30 g of recycled silicone polyester release film, 92 g of terephthalic acid, 13 g of adipic acid, 90 g of ethylene glycol, 0.02 g of germanium oxide, 0.1 g of zinc acetate, 0.04 g of phosphoric acid, and 0.09 g of 2,6-di-tert-butylphenol.

[0071] The preparation steps of the modified polyurethane include:

[0072] Step 1, weighing 30g of recycled silicone polyester release film, 90g of ethylene glycol, 0.1g of zinc acetate, and 0.02g of germanium oxide, adding them into a Polytex-1L polyester synthesis reactor, performing degradation reaction at 170°C and normal pressure for 8h, and cooling to 40°C after the degradation is completed;

[0073] Step 2, weigh 92g of terephthalic acid and 13g of adipic acid, add them to the polyester synthesis reactor and stir; at the same time, weigh 0.04g of phosphoric acid and 0.09g of 2,6-di-tert-butylphenol and place them in the storage tank of the synthesis device for standby; after strictly deoxygenating the synthesis system by "nitrogen-vacuuming" operation, nitrogen is introduced to make the system have an initial pressure of 150kPa, then stir and heat the system to 260°C, the speed of the stirring motor is 25Hz, during which the pressure in the reactor continues to rise, and the esterification pressure valve is adjusted to maintain the system pressure at 400kPa;

[0074] Step 3, when water starts to be discharged from the esterification tower, the reactor enters the esterification stage; the esterification pressure valve is adjusted to slowly reduce the system pressure from 400 kPa to normal pressure, and when the temperature at the top of the esterification tower is lower than 100°C, the esterification stage is ended, and the esterification time is 2 hours;

[0075] Step 4: Use nitrogen to pressurize 0.04g phosphoric acid and 0.09g 2,6-di-tert-butylphenol weighed from the storage tank into the reactor to enter the pre-condensation stage. Heat the system to 280°C, turn on the vacuum pump and adjust the condensation pressure valve to slowly reduce the system pressure from normal pressure to low pressure. When the pressure in the reactor drops below 20Pa, the pre-condensation stage is ended. The pre-condensation time is 0.5h.

[0076] Step 5: When the motor power reaches 45W, the final polycondensation stage of the polyester is ended;

[0077] Step 6: turn off the vacuum pump and stop stirring, pass nitrogen until the pressure in the reactor reaches 130 kPa, squeeze out the synthesized polyester, discharge the material, cut into pellets and dry.

[0078] PET release film is now widely used in printing, packaging, sealing material film, waterproof material, adhesive products and other industries. With the rapid development of the industry, a series of challenges have also emerged, such as environmental issues and resource shortages. By degrading the PET release film with ethylene glycol and then adding diacid and diol monomers for copolymerization modification, the recovery rate of the PET release film is improved, while the use of PET raw materials is reduced, promoting environmental protection and the sustainable development of the circular economy.

[0079] The modified polyesters obtained in Examples 1 to 6 were tested for performance, wherein the comparative case was polyethylene terephthalate (PET) prepared under the same process, and the results are shown in the following table:

[0080]

[0081]

[0082] Intrinsic viscosity test: The polyester was dissolved in phenol / tetrachloroethane (m / m=50:50) solution, and the intrinsic viscosity was measured using an Ubbelohde viscometer in a glass thermostatic water bath at 25°C. The intrinsic viscosity was calculated according to the following formula, where η sp —Specific viscosity; t1—solution flow time (s); t0—solvent flow time (s); [η]—intrinsic viscosity (dL / g); c—copolyester solution concentration (g / dL).

[0083]

[0084] Glass transition temperature test: In N2 atmosphere, the polyester was subjected to DSC test using a differential scanning calorimeter. The test temperature was from room temperature to 300°C, and the heating rate was 5°C / min.

[0085] Melting temperature test: In N2 atmosphere, the polyester was subjected to DSC test using a differential calorimeter scanner. The test temperature was from room temperature to 300°C, and the heating rate was 5°C / min.

[0086] Crystallinity test: In N2 atmosphere, the polyester was subjected to DSC test using a differential scanning calorimeter. The test temperature was from room temperature to 300°C, and the heating rate was 5°C / min.

[0087] Tensile strength test: electronic universal testing machine is used according to the standard CB / T 1040

[0088] Elongation at break test: electronic universal testing machine is used according to the standard CB / T 1040

[0089] From the results in the above table, it can be seen that the modified polyester made from recycled PET release film has better toughness than PET, but the glass transition temperature, melting temperature and tensile strength are significantly reduced. The present invention provides a new technical solution for preparing modified polyester by recycling polyester release film, further promoting environmental protection and economic circular development.

[0090] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

[0091] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0092] The synthesis of the modified polyester in Example 1 is shown below:

[0093]

[0094] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing modified polyester by recycling polyester release film, characterized in that: The modified polyester consists of a recycled organic silicon polyester release film, a diacid monomer, a diol monomer, a catalyst, a heat stabilizer and an antioxidant.

2. The method for preparing modified polyester by recycling polyester release film according to claim 1, characterized in that: The mass fraction of the recycled silicone polyester release film is 30-50 parts, the mass fraction of the diacid monomer is 80-110 parts, the mass fraction of the diol monomer is 90-120 parts, the mass fraction of the catalyst is 0.13-0.25 parts, the mass fraction of the heat stabilizer is 0.03-0.1 parts, and the mass fraction of the antioxidant is 0.05-0.1 parts.

3. The method for preparing modified polyester by recycling polyester release film according to claim 1, characterized in that: The diacid monomer is composed of one or more of phthalic acid, isophthalic acid, terephthalic acid, glutaric acid, azelaic acid and adipic acid.

4. The method for preparing modified polyester by recycling polyester release film according to claim 1, characterized in that: The diol monomer is composed of one or more of ethylene glycol, 1,4-cyclohexanedimethanol, butanediol, neopentyl glycol and propylene glycol.

5. The method for preparing modified polyester by recycling polyester release film according to claim 1, characterized in that: The catalyst is composed of one or more of zinc acetate, chromium acetate, tin acetate, cadmium acetate, antimony glycolate and germanium oxide.

6. The method for preparing modified polyester by recycling polyester release film according to claim 1, characterized in that: The heat stabilizer is composed of one or more of trimethyl phosphate, triphenyl phosphate, phosphorous acid and phosphoric acid.

7. The method for preparing modified polyester by recycling polyester release film according to claim 1, characterized in that: The antioxidant is composed of one or more of 2,6-di-tert-butylphenol and 3,3-thiodipropionate.

8. The method for preparing modified polyester by recycling polyester release film according to claim 1, characterized in that: The preparation steps specifically include: Step 1, weighing the recycled silicone polyester release film, ethylene glycol, and a catalyst, adding them into a Polytex-1L polyester synthesis device, stirring at a set temperature, and performing a degradation reaction for 6-8 hours; Step 2: After the degradation is completed, the system is cooled to 40-50°C, and the diacid and diol monomers are weighed and added to the polyester synthesis reactor for stirring; at the same time, the heat stabilizer and antioxidant are weighed and placed in the storage tank of the synthesis device for standby use; After strictly deoxygenating the synthesis system by "nitrogen-vacuuming", nitrogen was introduced, followed by stirring and heating the system to the set temperature. During this period, the pressure in the reactor continued to increase, and the esterification pressure valve was adjusted to maintain the system pressure at 400 kPa; Step 3, when water starts to be discharged from the esterification tower, the reactor enters the esterification stage; the esterification pressure valve is adjusted to slowly reduce the system pressure to normal pressure, and when the temperature at the top of the esterification tower is lower than 100°C, the esterification stage is ended, and the esterification time is 2-3h; Step 4: Use nitrogen to pressurize the heat stabilizer and antioxidant in the storage tank into the reactor to enter the pre-condensation stage. Heat the system to the set temperature, turn on the vacuum pump and adjust the polycondensation pressure valve to slowly reduce the system pressure to low pressure. When the pressure in the reactor drops below 20Pa, the pre-condensation stage ends. The pre-condensation time is 0.5-1h; Step 5: When the motor power reaches 45W, the final polycondensation stage of the polyester is ended; Step 6: turn off the vacuum pump and stop stirring, pass nitrogen until the pressure in the reactor is slightly higher than normal pressure, squeeze out the synthesized polyester, discharge the material, cut into pellets and dry.

9. The method for preparing modified polyester by recycling polyester release film according to claim 8, characterized in that: In step 1, the motor speed is 25Hz and the set temperature is 170-190℃; The set temperature in step 2 is 210-260°C; The set temperature in step 4 is 270-280°C.

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