A crystalline and easily recyclable polyester heat shrinkable film and its preparation method and recycling application

Abstract

The present invention discloses a crystalline, easily recyclable polyester heat-shrinkable film, a preparation method thereof, and a recycling application. The crystalline, easily recyclable polyester heat-shrinkable film comprises the following raw materials: by mass percentage: 55-63% modified PET, 20-63% recycled PET bottle flakes, 5-10% modified copolyether, 1-3% nucleating agent, and 0.1-0.5% auxiliary agent. The modified copolyether is prepared by acylation reaction using terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether and alkenyl acyl halide as raw materials. The present invention, through suitable formula design and supporting preparation process, makes the obtained polyester heat-shrinkable film have a higher melting point and heat shrinkage rate, and obtains suitable crystallinity, so that it can be better recycled together with bottle flake recycled materials with a relatively large proportion of PET components.

Description

Technical Field

[0001] The present invention relates to the field of polyester shrinkage films, in particular to a crystalline and easily recyclable polyester heat shrinkage film and a preparation method and recycling application thereof. Background Art

[0002] Polyester heat shrinkable film is a widely used shrink sleeve label material. This technology usually uses a non-crystalline copolyester resin to extrude a thick sheet through an extruder, and then through one or both of longitudinal and transverse stretching to obtain a film with unidirectional or bidirectional orientation of the polymer chain.

[0003] A typical feature of this heat-shrinkable film is that the oriented film prepared by the above steps can shrink as much as possible to its pre-stretching and orientation state when heated to between 50-100°C, thereby achieving a larger shrinkage rate. Therefore, this technology usually requires the use of non-crystalline copolyester to ensure that crystallization does not occur during the stretching and orientation process of the thick sheet, because crystallization usually "freezes" the movement of the molecular chains, hindering its heat shrinkage ability at 50-100°C and reducing its heat shrinkage rate.

[0004] Another characteristic of heat-shrinkable film is that the oriented film prepared through the above steps exhibits excellent leveling properties when applied to the film surface using one or more commonly used organic solvents, such as 1,4-dioxane, 1,3-dioxolane, and tetrahydrofuran. The film's surface can also be dissolved or swelled using these solvents. This dissolved or swollen surface layer, when placed next to another surface layer, adheres to the film and maintains a certain bond strength even after the solvent evaporates. This method is used in the industry to prepare shrink film into shrink sleeves. This essential step is called "shrunk," and the organic solvent used is called the "shrunk solvent." Generally speaking, amorphous polyester films are easily dissolved or swelled by the "shrunk solvent," and the bond strength of the "shrunk" is sufficient for the application. However, as the film's crystallinity increases, the "shrunk" solvent becomes less able to dissolve or swell the film, resulting in a decrease in "shrunk" strength and impacting subsequent use.

[0005] While the aforementioned non-crystalline copolyester heat-shrinkable film offers numerous advantages, its drawbacks and shortcomings are also evident. First, such shrinkable film is difficult to mix with physically recycled polyester bottle flakes. This refers to the recycled polyester bottle flakes obtained after consumers use the bottles and then through recycling systems, which are then physically processed by crushing, cleaning, and drying. In particular, when the content of physically recycled polyester bottle flakes in the shrinkable film formula exceeds 25%, the film's heat shrinkage rate and grip strength decrease, thus affecting its usability. This performance degradation is essentially due to the fact that physically recycled polyester bottle flakes are crystalline polymers. Mixing such materials into the shrinkable film increases the film's crystallinity, resulting in decreased shrinkage and grip strength.

[0006] Secondly, this type of shrink film is difficult to recycle using physical methods. Because amorphous films lack crystals and have a low softening point, they gradually soften during the aforementioned physical recycling process, causing the recycled bottle flakes to stick together and agglomerate, resulting in the entire recycling system being unable to function properly. While mixing in a large amount of crystalline recycled bottle flakes can help alleviate this agglomeration, as mentioned in the first drawback above, mixing in crystalline polymers can lead to a decrease in the shrinkage and sealing properties of the shrink film, making it difficult to achieve a balance in practical applications.

[0007] As countries around the world pursue environmental protection and a circular economy, more and more food and beverage brands are placing increasing emphasis on packaging materials containing recycled content and being recyclable. Several countries have also established roadmaps requiring packaging materials to contain 30% or more recycled content. In the polyester industry, "recycled content" typically refers to recycled bottles supported by a comprehensive recycling system, and these recycled contents are typically crystalline polyester. For a long time, widely used amorphous copolyester heat shrink film was considered difficult to incorporate 30% physically recycled content and could not be physically recycled. This is inconsistent with the current circular and environmentally friendly model promoted by the plastic packaging industry, which advocates the use of high levels of recycled content and recyclable packaging.

[0008] To address the problem of non-crystalline membranes being unable to use recycled materials in large quantities and being non-recyclable, the industry typically uses chemical methods for recycling and reuse. This chemical method involves chemically depolymerizing used polyester waste at high temperatures to obtain small-molecule monomers or oligomers. These monomers are then purified and then repolymerized at high temperatures to form polyester or industrial polyester. While this chemical recycling method achieves a certain degree of recycling, it adds two energy-intensive depolymerization and repolymerization steps, which clearly contradicts the concept of low-carbon and environmental protection. Summary of the Invention

[0009] In view of this, the object of the present invention is to provide a crystalline and easily recyclable polyester heat-shrinkable film and its preparation method and application. The polyester heat-shrinkable film provided by the present invention can be physically recycled together with polyester bottle flakes and has good heat shrinkage and mechanical properties.

[0010] In order to achieve the above object of the invention, the present invention provides the following technical solutions:

[0011] A crystalline, easily recyclable polyester heat-shrinkable film comprises the following raw materials: by weight, 55-63% modified PET, 20-50% recycled PET bottle flakes, 5-10% modified copolyether, 1-3% nucleating agent, and 0.1-0.5% auxiliary agent.

[0012] In some embodiments of the present invention, the modified PET is prepared by esterification and polymerization of a dibasic acid and a diol, wherein, based on 100 mol% of the total dibasic acid components, the dibasic acid includes at least 0-3 mol% of isophthalic acid and 97-100 mol% of terephthalic acid; based on 100 mol% of the total diol components, the diol includes at least 7-35 mol% of neopentyl glycol, 0-12 mol% of cyclohexanedimethanol and the remaining percentage of ethylene glycol.

[0013] In some embodiments of the present invention, the modified PET has an intrinsic viscosity (IV) of 0.74-0.82 dl / g; a terminal carboxyl content of <35 mol / t; and, in its L*A*B value, B value ≤2.2, and L value >56.

[0014] In some embodiments of the present invention, the modified copolyether is prepared by reacting a hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether with an alkenyl acid halide, and the preparation process comprises the following steps:

[0015] S1: Add terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether into a reaction vessel, heat and reduce pressure to remove water, and then cool to room temperature;

[0016] S2: Add an organic solvent and an amine catalyst to the system obtained in S1, cool it in an ice bath, and start adding the organic solution of the alkenyl acyl halide dropwise. After the addition is complete, continue the reaction for 24 hours;

[0017] S3: The reaction solution obtained in S2 is washed with water until it becomes neutral, and the liquids are separated. The solvent is evaporated from the oil phase under reduced pressure to obtain the modified ethylene oxide-tetrahydrofuran copolyether.

[0018] Furthermore, in S1, the preparation process of the terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether comprises the following steps: adding boron trifluoride ether complex, ethylene glycol and toluene to a three-necked flask, stirring evenly at -25-0°C, and then adding a mixed monomer of ethylene oxide and tetrahydrofuran to react; after reacting for 5-7 hours, adding distilled water, continuing to stir for 10-15 minutes, terminating the reaction, washing the product to neutrality, then distilling off the toluene, and vacuum drying at 70-80°C to obtain a terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether with a relative molecular mass of 3300-3900.

[0019] Furthermore, the molar ratio of ethylene oxide to tetrahydrofuran is 5-8:2-5.

[0020] Furthermore, the heating, depressurization and water removal temperature in S1 is 90-100°C.

[0021] Furthermore, the temperature of the ice bath cooling in S2 is 0-2°C.

[0022] Furthermore, the alkenyl halide in S2 is at least one of acryloyl chloride, crotonoyl chloride, 3-methylcrotonoyl chloride, 3-cis-methyl-isobutylene chloride, (E)-pent-2-enoyl chloride, (E)-hex-2-enoyl chloride, and sorbic acid chloride.

[0023] Furthermore, in the organic solution of alkenyl acyl halide in S2, the mass fraction of alkenyl acyl halide is 2.0-2.2 g / ml.

[0024] Furthermore, the mass ratio of the hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether, the amine catalyst, and the alkenyl acid halide described in S1 and S2, respectively, is 680-700:65-70:40-45.

[0025] Furthermore, the amine catalyst is triethylamine, NN-dimethylcyclohexylamine, N,N-dimethylbenzylamine, N,N-dimethylpyridine, triethylenediamine, trimethylbenzylamine, dimethylethanolamine, etc.

[0026] In some embodiments of the present invention, the nucleating agent is any one of the sodium salt or zinc salt of ethylene-methacrylic acid polymer.

[0027] In some embodiments of the present invention, the auxiliary agent includes a slip agent and / or an anti-sticking agent, the slip agent is oleamide and / or erucamide, and the anti-sticking agent is silica powder, silicon dioxide or talc.

[0028] The present invention provides a method for preparing the above-mentioned crystalline and easily recyclable polyester heat-shrinkable film, comprising the following steps: mixing modified PET, recycled PET bottle flakes, modified ethylene oxide-tetrahydrofuran copolyether, a nucleating agent and an auxiliary agent, melt-extruding, and forming into a cast sheet after rapid cooling; and sequentially longitudinally stretching, transversely stretching and traction-winding the cast sheet to obtain the recyclable polyester heat-shrinkable film.

[0029] Furthermore, the melt extrusion is performed by a twin-screw extruder, and the temperature of the melt extrusion is preferably 240-270° C. In the present invention, the rapid cooling is preferably performed by attaching the extrudate obtained by the melt extrusion to a chilled roller for rapid cooling.

[0030] Furthermore, the longitudinal stretching includes sequentially performing a first preheating longitudinal stretching and a first cooling and shaping on the cast sheet.

[0031] Furthermore, the temperature of the first preheating is 60-80°C, the temperature of the longitudinal stretching is 100-120°C, the stretching ratio is 1.2-2 times, and the temperature of the first cooling and setting is 40-60°C.

[0032] Furthermore, the transverse stretching includes sequentially performing a second preheating transverse stretching and a second cooling and shaping on the longitudinally stretched film.

[0033] Furthermore, the second preheating temperature is 105-110°C, the transverse stretching temperature is 95-100°C, the stretching ratio is 2-3 times, and the second cooling and setting temperature is 50-60°C.

[0034] The present invention also provides the use of the polyester heat shrinkable film in the field of PET bottle label materials after ink cleaning.

[0035] In some embodiments of the present invention, before application, the ink is cleaned with a 1-5% sodium hydroxide solution or a surfactant, and the deinking time is 25-30 seconds.

[0036] Beneficial Effects: Compared to existing technologies, the present invention utilizes a higher percentage of recycled PET bottle flakes, which can significantly improve the crystallinity of the film material and increase the film's tensile strength. Furthermore, the addition of a modified copolyether increases the material's molecular weight, further raising its crystallization temperature. Furthermore, the olefinic groups at both ends of the modified copolyether act as a "bonding" agent, enhancing the compatibility of the crystalline recycled bottle flakes with the modified PET. Furthermore, the modified copolyether, as an amorphous material, imparts a certain amorphous structure to the heat-shrinkable film and a very low glass transition temperature, thereby ensuring a high heat shrinkage rate. Ultimately, the heat-shrinkable film exhibits excellent recyclability and a high heat shrinkage rate. Furthermore, by defining the raw material composition and physical parameters of the modified PET, the present invention utilizes the modified copolyether in conjunction with the heat-shrinkable polyester film, enabling rapid ink elution in the presence of low-concentration alkali solutions or surfactants, enabling efficient recycling. DETAILED DESCRIPTION

[0037] The following will be combined with the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well known to those skilled in the art. Specifically, the nucleating agent is surlyn 8940 (DuPont, USA).

[0039] The following is an exemplary description of the preparation process of the modified ethylene oxide-tetrahydrofuran copolyether used in the examples:

[0040] Modified copolyether-1

[0041] S1: Add 6.8 parts of hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether (relative molecular weight 3350) to a three-necked flask equipped with a mechanical stirrer and a thermometer, heat to 90°C and remove water under reduced pressure for 1.5 hours, then cool to room temperature;

[0042] S2: Add 60 parts of dichloromethane and 0.65 parts of triethylamine to the system obtained in S1, cool to 0°C in an ice bath, and begin to dropwise add 20 parts of a 2.0 g / ml dichloromethane solution of acryloyl chloride. After the addition is complete within 6 hours, continue the reaction for 24 hours.

[0043] S3: The reaction liquid obtained in S2 is washed with water until it becomes neutral, and the liquids are separated. The solvent is evaporated from the oil phase under reduced pressure to obtain the modified ethylene oxide-tetrahydrofuran copolyether-1.

[0044] The preparation process of the hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether described in S1 is as follows:

[0045] 1.2 mol of boron trifluoride ether complex, 1.2 mol of ethylene glycol and 1000 ml of toluene were added to a three-necked flask and stirred evenly at -25°C. Then, 2 mol of a mixed monomer of ethylene oxide and tetrahydrofuran in a molar ratio of 5:5 was added to react. After reacting for 5 hours, distilled water was added and stirring was continued for 10 minutes to terminate the reaction. The product was washed until neutral, and then the toluene was distilled off and vacuum dried at 70°C to obtain the terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether.

[0046] Modified copolyether-2

[0047] S1: Add 6.9 parts of hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether (relative molecular weight 3510) to a three-necked flask equipped with a mechanical stirrer and a thermometer, heat to 95°C and remove water under reduced pressure for 1 hour, then cool to room temperature;

[0048] S2: Add 60 parts of dichloromethane and 0.67 parts of NN-dimethylcyclohexylamine to the system obtained in S1, cool to 1°C in an ice bath, and begin to dropwise add 20 parts of a 2.1 g / ml dichloromethane solution of crotonyl chloride. After the addition is complete within 6 hours, continue the reaction for 24 hours.

[0049] S3: The reaction liquid obtained in S2 is washed with water until it becomes neutral, and the liquids are separated. The solvent is evaporated from the oil phase under reduced pressure to obtain the modified ethylene oxide-tetrahydrofuran copolyether-2.

[0050] The preparation process of the hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether described in S1 is as follows:

[0051] 1.3 mol of boron trifluoride ether complex, 1.3 mol of ethylene glycol and 1000 ml of toluene were added to a three-necked flask and stirred evenly at -15°C. Then, 2 mol of a mixed monomer of ethylene oxide and tetrahydrofuran in a molar ratio of 7:3 was added to react. After reacting for 6 hours, distilled water was added and stirring was continued for 12 minutes to terminate the reaction. The product was washed until neutral, and then the toluene was distilled off and vacuum dried at 75°C to obtain the terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether.

[0052] Modified copolyether-3

[0053] S1: Add 7.0 parts of hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether (relative molecular weight 3760) to a three-necked flask equipped with a mechanical stirrer and a thermometer, heat to 100°C and remove water under reduced pressure for 0.5 h, then cool to room temperature;

[0054] S2: Add 60 parts of ethylene dichloride and 0.70 parts of triethylenediamine to the system obtained in S1, cool to 2°C in an ice bath, and begin to dropwise add 20 parts of a 2.2 g / ml solution of (E)-pent-2-enoyl chloride in ethylene dichloride. Complete the addition within 6 hours and continue the reaction for 24 hours.

[0055] S3: The reaction liquid obtained in S2 is washed with water until it becomes neutral, and the liquids are separated. The solvent is evaporated from the oil phase under reduced pressure to obtain the modified ethylene oxide-tetrahydrofuran copolyether-3.

[0056] The preparation process of the hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether described in S1 is as follows:

[0057] 1.4 mol of boron trifluoride ether complex, 1.4 mol of ethylene glycol and 1000 ml of toluene were added to a three-necked flask and stirred uniformly at 0°C. Then, 2 mol of a mixed monomer of ethylene oxide and tetrahydrofuran in a molar ratio of 8:2 was added to react. After reacting for 7 hours, distilled water was added and stirring was continued for 15 minutes to terminate the reaction. The product was washed until neutral, and then the toluene was distilled off and vacuum dried at 80°C to obtain the terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether. Example 1

[0058] Preparation of crystalline and easily recyclable polyester heat shrinkable film:

[0059] 55% modified PET (intrinsic viscosity IV of 0.74 dl / g, end carboxyl content of 20 mol / t, B value of 2.0, L value of 60), 48.9% recycled PET bottle flakes, 5% modified copolyether-1, 1% nucleating agent, and 0.2% additives (0.1% erucamide and 0.1% silica powder) were added to a high-speed mixer to obtain a mixture. The mixture was fed into a twin-screw extruder for melt extrusion (temperature of 240°C). The extrudate was attached to a chilled roll (temperature of 25-35°C) and rapidly cooled to form a cast sheet.

[0060] The cast sheet was preheated at 60°C for 10 seconds, stretched at 100°C in the longitudinal direction with a stretching ratio of 1.2 times, and then cooled at 60°C for final shaping.

[0061] After longitudinal stretching, the film was preheated at 105°C for 10s, then stretched in the transverse direction at 95°C with a stretching ratio of 2 times, and then cooled at 60°C for setting; then the film was measured online for thickness, and finally pulled and rolled. Example 2

[0062] Preparation of crystalline and easily recyclable polyester heat shrinkable film:

[0063] 59% modified PET (intrinsic viscosity IV of 0.78 dl / g, end carboxyl content of 31 mol / t, B value of 2.1, L value of 64), 41.6% recycled PET bottle flakes, 7% modified copolyether-2, 2% nucleating agent, and 0.4% additives (0.2% erucamide and 0.2% silica powder) were added to a high-speed mixer to obtain a mixture. The mixture was fed into a twin-screw extruder for melt extrusion (temperature of 250°C). The extrudate was attached to a chilled roll (temperature of 25-35°C) and rapidly cooled to form a cast sheet.

[0064] The cast sheet was preheated at 70°C for 10 seconds, stretched in the longitudinal direction at 110°C with a stretching ratio of 1.5 times, and then cooled at 50°C for final shaping.

[0065] After longitudinal stretching, the film was preheated at 105°C for 10s, then stretched in the transverse direction at 95°C with a stretching ratio of 2.5 times, and then cooled at 55°C for setting; then the film was measured online for thickness and finally pulled and rolled. Example 3

[0066] Preparation of crystalline and easily recyclable polyester heat shrinkable film:

[0067] 63% modified PET (intrinsic viscosity IV of 0.80 dl / g, end carboxyl content of 33 mol / t, B value of 1.9, L value of 67), 22.5% recycled PET bottle flakes, 10% modified copolyether-3, 5% nucleating agent, and 0.5% additives (0.2% erucamide and 0.3% silica powder) were added to a high-speed mixer to obtain a mixture. The mixture was fed into a twin-screw extruder for melt extrusion (temperature of 270°C). The extrudate was attached to a chilled roll (temperature of 25-35°C) and rapidly cooled to form a cast sheet.

[0068] The cast sheet was preheated at 80°C for 10 seconds, stretched at 120°C in the longitudinal direction with a stretching ratio of 2, and then cooled at 60°C for final shaping.

[0069] After longitudinal stretching, the film was preheated at 110°C for 10s, then stretched in the transverse direction at 100°C with a stretching ratio of 3 times, and then cooled to 50°C for shaping; then the film was measured online for thickness, and finally pulled and rolled. Comparative Example 1

[0070] Same as Example 3, except that the modified copolyether-3 used is not modified with (E)-pent-2-enoyl chloride. Comparative Example 2

[0071] Same as Example 3, except that modified copolyether-3 is not used.

[0072] Performance Testing

[0073] Tensile strength and elongation at break: tested according to ASTM D882;

[0074] Thermal shrinkage: tested according to ASTM D1204;

[0075] Lump test: refer to the relevant methods of APR PET CG-02 Critical Guidance: dry the shrunken broken film pieces in a 160℃ oven for 0.5h, evenly mix the dried broken film pieces with bottle pieces in a ratio of 1:3, bake in a 210℃ oven for 90min, and take out. If the mass of the material sticky with the bottle pieces does not exceed 1% of the total mass of the mixture, it is considered passed, otherwise it is considered failed.

[0076] The test results are shown in Table 1.

[0077] Table 1 Test results of polyester heat shrinkable films obtained in Examples 1-3 and Comparative Examples 1-2

[0078]

[0079] The test results in Table 1 demonstrate that the present invention, through appropriate formulation design and supporting preparation processes, results in a polyester heat-shrinkable film with a high melting point and suitable crystallinity, enabling it to be recycled with PET bottles. Furthermore, the film exhibits excellent heat shrinkage and mechanical properties. However, the comparative example, which did not use the specified modified copolyether, failed the agglomeration test and was not recyclable enough to be recycled with PET bottle flakes.

Claims

1. A crystalline and easily recyclable polyester heat shrinkable film, characterized in that: The preparation comprises the following raw materials: by weight percentage, 55-63% modified PET, 20-50% recycled PET bottle flakes, 5-10% modified copolyether, 1-3% nucleating agent, and 0.1-0.5% additive; the modified copolyether is prepared by reacting terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether with alkenyl acyl halide, and the preparation process comprises the following steps: S1: Add terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether into a reaction vessel, heat and reduce pressure to remove water, and then cool to room temperature; S2: Add an organic solvent and an amine catalyst to the system obtained in S1, cool it in an ice bath, and start adding the organic solution of the alkenyl acyl halide dropwise. After the addition is complete, continue the reaction for 24 hours; S3: The reaction solution obtained in S2 is washed with water until it becomes neutral, and the liquids are separated. The solvent is evaporated from the oil phase under reduced pressure to obtain the modified ethylene oxide-tetrahydrofuran copolyether.

2. The crystalline and easily recyclable polyester heat shrinkable film according to claim 1, characterized in that: The modified PET is prepared by esterification and polymerization of a dibasic acid and a diol, wherein, based on 100 mol% of the total dibasic acid components, the dibasic acid includes at least 0-3 mol% of isophthalic acid and 97-100 mol% of terephthalic acid; based on 100 mol% of the total diol components, the diol includes at least 7-35 mol% of neopentyl glycol, 0-12 mol% of cyclohexanedimethanol, and the remaining percentage of ethylene glycol.

3. The crystalline and easily recyclable polyester heat shrinkable film according to claim 2, characterized in that: The modified PET has an intrinsic viscosity (IV) of 0.74-0.82 dl / g; a terminal carboxyl content of <35 mol / t; and, in its L*A*B value, a B value ≤2.2 and an L value >56.

4. The crystalline and easily recyclable polyester heat shrinkable film according to claim 1, characterized in that: In S1, the preparation process of the terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether comprises the following steps: adding boron trifluoride etherate complex, ethylene glycol and toluene to a three-necked flask, stirring evenly at -25-0°C, and then adding a mixed monomer of ethylene oxide and tetrahydrofuran to react; after reacting for 5-7 hours, adding distilled water, continuing stirring for 10-15 minutes, terminating the reaction, washing the product until neutral, then distilling off the toluene, and vacuum drying at 70-80°C to obtain a terminal hydroxyl ethylene oxide-tetrahydrofuran copolyether with a relative molecular mass of 3300-3900.

5. The crystalline and easily recyclable polyester heat shrinkable film according to claim 4, characterized in that: The molar ratio of ethylene oxide to tetrahydrofuran is 5-8:2-5.

6. The crystalline and easily recyclable polyester heat shrinkable film according to claim 1, characterized in that: The temperature for heating, reducing pressure and removing water in S1 is 90-100°C; the temperature for ice bath cooling in S2 is 0-2°C; the alkenyl acid halide in S2 is at least one of acryloyl chloride, crotonyl chloride, 3-methylcrotonyl chloride, 3-cis-methyl-isobutylene chloride, (E)-pent-2-enoyl chloride, (E)-hex-2-enoyl chloride, and sorbic acid chloride; and the mass fraction of the alkenyl acid halide in the organic solution is 2.0-2.2 g / ml.

7. The crystalline and easily recyclable polyester heat shrinkable film according to claim 1, characterized in that: The mass ratios of the hydroxy-terminated ethylene oxide-tetrahydrofuran copolyether, the amine catalyst, and the alkenyl acid halide in S1 and S2, respectively, are 680-700:65-70:43-45.

8. The method for preparing the crystalline and easily recyclable polyester heat shrinkable film according to claims 1-7, characterized in that: The method comprises the following steps: mixing modified PET, recycled PET bottle flakes, modified copolyether, a nucleating agent and an additive, performing melt extrusion, and forming into a cast sheet after rapid cooling; and sequentially performing longitudinal stretching, transverse stretching and traction winding on the cast sheet to obtain an easily recyclable polyester heat shrinkable film.

9. The crystalline and easily recyclable polyester heat shrinkable film according to any one of claims 1 to 7 is recycled and used in the field of PET bottle label materials after ink cleaning.

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