Recyclable Crystalline Polyester Heat Shrink Film and its Preparation Method

Abstract

Disclosed in the present invention are a crystalline easy-to-recycle polyester heat-shrinkable film and a preparation method therefor. The film layer structure has an A / B / A three-layer structure; the layer A is made from the following raw materials: PETG, functional master batches and PET; and the layer B is made from the following raw materials: modified PET, PET, a nucleating agent, a chain extender and a foaming agent. A proper amount of the chain extender can increase the molecular weight, namely the melting point, and increase the crystallinity of the film together with the nucleating agent, which can synergistically improve the recycling property of the film. The foaming agent can improve the yield of the film and reduce the shrinkage force of the film, and the nucleating agent can promote the formation of microcrystals, thus inhibiting the overall haze increase of the film resulting from overlarge cells formed by foaming. During processing, the cell structure can be expanded due to a high draw ratio, and thus the film can have a higher heat shrinkage rate. In the present invention, an additive is introduced to improve the crystallinity and melting point of the film, and the resulting polyester heat-shrinkable film has the features of good recycling property, crystallizability, printability, shrinkability and low shrinkage force.

Description

1 / 19 Recyclable Crystalline Polyester Heat Shrink Film and its Preparation Method

[01] This application claims priority over the Chinese patent application filed with the National Intellectual Property Administration of China on October 10, 2023, under number CN202311300538.X, entitled Recyclable crystalline polyester heat shrink film and its preparation method, the full content of which is incorporated by reference in this application. TECHNICAL FIELD

[02] The present invention pertains to the field of heat shrink film preparation, specifically relating to a recyclable crystalline polyester heat shrink film and its preparation method. TECHNICAL BACKGROUND

[03] Ethylene terephthalate glycol copolymer (PETG) heat shrink films are widely used in beverage packaging, personal care products, and batteries, being one of the most widely used plastic products. However, their degradation is difficult, and they can remain in the environment for hundreds of years under natural conditions, and their improper treatment can cause serious environmental impacts. To mitigate the problem of plastic pollution and improve the recyclability characteristics of PETG films, there has been a growing interest in the recycling and reuse of these products.

[04] However, there are several problems in the film recycling process. As the bottle material is polyethylene terephthalate (PET), which has high crystallinity and a high melting point, while the shrink labels (composed of polyester film) are generally amorphous PETG, there is a large difference in melting point and crystallinity between the two materials. In addition, both materials have a density greater than 1, making it difficult to separate the bottle and film fragments after shredding. It is necessary to manually separate the polyester labels from the bottles before shredding, and then proceed with sorting and recycling, which increases the costs of manual sorting and affects the overall efficiency of recycling. Simultaneously, due to the inconsistency in the melting points of the two materials, with the melting point of PETG film being significantly lower than that of Petition 870260054003, dated 03 / 06 / 2026, page 9 / 31 2 / 19 PET fragments, and considering that the PET recycling process requires drying at temperatures above 200°C. Under this temperature, conventional polyester heat-shrink films soften and become sticky, forming agglomerates with the PET fragments, causing blockages in recycling equipment due to adhesion and bridging, making it necessary to treat these agglomerates before further processing. Furthermore, the agglomerates reduce the yield of the recycling process and generate an additional processing step, severely affecting the recycling of PET fragments.

[05] Currently reported recycling methods focus primarily on modifying the molecular structure of PETG polyester, increasing the melting point and crystallinity characteristics of the polyester raw material, thus imparting crystallization characteristics to the resulting polyester heat shrink film, making PETG more similar to PET. However, this results in a reduction in the shrinkage characteristics of the resulting film, failing to meet packaging requirements in several scenarios, as well as involving a complex change in the synthesis process and increasing energy consumption. CONTENT OF THE INVENTION

[06] The present invention mainly addresses the problems existing in the current recycling process and the limitations of the shrinkage rate in crystalline films, aiming to increase the melting point of the PETG film through the preparation process, building a porous structure combined with technology to improve the shrinkage rate, and introducing additives to increase the crystallinity and melting point of the film, thus providing a recyclable crystalline polyester heat-shrinkable film and its preparation method, which has good characteristics of recyclability, crystallinity, printability, shrinkage and low shrinkage force.

[07] To this end, the present invention provides a recyclable crystalline polyester heat-shrinkable film, the structure of which consists of three layers A / B / A; wherein layer A is composed of PETG, functional masterbatch and PET; layer B is composed of modified PET, PET, nucleating agent, chain extender and agent Petition 870260054003, dated 03 / 06 / 2026, page 10 / 31 3 / 19 foaming agent, the modified PET being a PET modified with neopentyl glycol (NPG).

[08] Additionally, in mass percentage, layer A contains PETG: functional masterbatch: PET = 89.4-66.0%: 1.6-4.0%: 10.0-30.0%; layer B contains modified PET: PET: nucleating agent: chain extender: foaming agent = 42-65.4%: 30-40%: 0.6-4.0%: 2.0-6.0%: 2.0-8.0%.

[09] Additionally, the chain extender is at least one of glycidyl methacrylate or cyclohexyl acrylate.

[010] Additionally, the nucleating agent is at least one of dibutyl adipate, ammonium salt of phosphoric ester or sodium benzoate.

[011] Additionally, the functional masterbatch is a combination of at least one of silicon dioxide, talc, clay or kaolin and at least one of oleamide or erucamide.

[012] Additionally, the foaming agent is at least one of trihydrazines-triazine, barium azodicarboxylate, 4,4'-oxybis(benzenesulfonyl-aminourea) or ptoluenesulfonyl-aminourea.

[013] The present invention also provides a method for preparing said recyclable crystalline polyester heat-shrinkable film, which includes the following steps:

[014] (1) Mix the materials of layers A and B uniformly in the proportions specified in a planetary mixer, followed by drying, and perform melt plasticization in the corresponding extruders, distinguishing between the mixtures of the central layer and the surface layers;

[015] (2) Set up the ABA three-layer structure, pass the molten material through the same die, with die temperature between 240-270°C, extrude by melting, and cool the molten film on a fast cooling roll for molding;

[016] (3) Perform longitudinal stretching of the molten film;

[017] (4) Perform the transverse stretching operation;

[018] (5) To pull and roll, thus obtaining the said recyclable crystalline polyester heat shrink film.

[019] Additionally, the stretching conditions in step (3) are: after preheating to 85-95°C, stretching at a rate of 1-2 times at 80-110°C, followed by cooling and heat setting at 50-80°C after longitudinal stretching. Petition 870260054003, dated 03 / 06 / 2026, p. 11 / 31 4 / 19

[020] Additionally, the stretching conditions in step (4) are: after preheating to 90-110°C, stretching at a rate of 4.0-5.5 times at 80-95°C, followed by cooling and heat setting at 70-90°C after cross stretching.

[021] Additionally, the thickness of said recyclable crystalline polyester heat shrink film is preferably 30-100 µm. BENEFICIAL EFFECTS:

[022] 1. The present invention, by adding a suitable foaming agent to the central layer, produces a foamed, recyclable crystalline polyester heat-shrinkable film. During processing, the higher stretch ratio can expand the foam cell structure to a certain extent, fixing the cell structure through heat setting, resulting in less shrinkage after heating, allowing this film to have a higher thermal shrinkage rate than common crystalline films. The film structure of the present invention reduces the film density, decreasing the constriction force on the packaged material during shrinkage, reducing the overall thermal shrinkage force of the film, making the shrinkage process smoother, and effectively reducing problems such as wrinkling due to very rapid shrinkage and deformation of the bottle body due to excessive shrinkage force values ​​during the shrinkage process.Simultaneously, the foaming agent can reduce the density of the film, allowing for more heat-shrinkable film to be obtained with the same number of polyester chips, thus reducing costs.

[023] 2. The present invention, through the addition of a chain-extending agent in the central layer, allows the PETG component in the polyester film to be cross-linked in a limited way, increasing the overall molecular weight of the polyester film, and correspondingly raising the melting point of the film. Under the premise of ensuring the thermal shrinkage characteristics of the polyester film, the overall melting point of the film approaches that of PET. The addition of a compatible nucleating agent can accelerate the crystallization rate during the melting process, increase the crystallization density and promote the formation of refined crystalline grains, improving to some extent the overall crystallinity of the film, avoiding the loss of shrinkage characteristics due to excessive crystallization. The agent Petition 870260054003, dated 03 / 06 / 2026, page 12 / 31 5 / 19 The nucleating agent and the chain extension agent act synergistically to raise the thermal deformation temperature and melting point of the material, ensuring that film labels produced by this method can be recycled along with PET bottles without adhesion, bridging, or clogging of recycling equipment. Simultaneously, the nucleating agent can control the size of the cell structure formed by the foaming agent during the melting process, and in appropriate proportions, can effectively improve the haze condition of the film caused by the cell structure, increasing the overall transparency of the film and the light transmission rate. The recyclable crystalline film prepared by this method does not require changes to the polyester chip synthesis process, does not increase the costs of equipment modification and formula synthesis process reform, has a high shrinkage rate, and strong product applicability.

[024] i. The method of the present invention demonstrates a synergistic effect through the use of three modifying additives: a foaming agent, a chain extender, and a nucleating agent. An appropriate amount of chain extender can increase the molecular weight, i.e., increase the melting point, and together with the nucleating agent, increase the crystallinity of the film, synergistically improving the film's recycling characteristics (no adhesion to bottles and no formation of bridges that affect recycling efficiency during the recycling process). The foaming agent can increase the film yield (by reducing density) and reduce the film's shrinkage force. However, very large cells formed by the foaming agent will affect the film's transparency. The nucleating agent can promote the formation of microcrystals, thus inhibiting the formation of very large cells by the foaming agent that would increase the overall turbidity of the film.

[025] ii. The polyester film prepared by the present invention has a three-layer structure, where the functional masterbatch added to the surface layer serves primarily to improve the printing and lamination properties of the film. The three layers are all PET-derived materials, with similar polarity, strong adhesion between the layers, no delamination problems, belonging to a single material, favorable for recycling and circularity of Petition 870260054003, dated 03 / 06 / 2026, page 13 / 31 6 / 19 product. Description of the figures

[026] Figure 1 shows a schematic diagram of the structure of the recyclable crystalline polyester heat-shrinkable film prepared in the embodiment of the present invention; wherein layer A is the surface layer (printing layer), layer B is the core layer (porous structure layer). Specific Implementation Method

[027] Next, through embodiment examples and comparative examples, the effects of the recyclable crystalline polyester heat-shrink film and its preparation method of the present invention are studied and analyzed.

[028] The PETG used in the embodiments and comparative examples was selected from SKYGREEN® S2012 from SK Chemical Co., Ltd. of South Korea and Eastman Chemical Company GN071. The modified PET (NPG-modified PET) was selected from Henan Hongyuan Polymer Materials Co., Ltd. YH101 and Jiangyin Huahong Chemical Fiber Co., Ltd. WS501. The PET was selected from Sinopec Yizheng Chemical Fiber Co., Ltd. FG600 and Henan Hongyuan Polymer Materials Co., Ltd. YH600. Example of Implementation 1

[029] (1) Modified PET raw materials (Henan Hongyuan Polymer Materials Co., Ltd. YH101), PETG (SKYGREEN® S2012 from SK Chemical Co., Ltd. of South Korea), PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600) and functional masterbatch, nucleating agent, chain extending agent and foaming agent were dried in a vacuum dryer to remove moisture.

[030] (2) The various films with three-layer ABA structure were formulated according to the composition proportions and preliminarily mixed in a mixer, where:

[031] Layer A contains the following components in mass percentage: PETG:functional masterbatch (anti-adherent agent S1O2: stearamide slip = 1:1): PET = 76.8%:3.2%:20%;

[032] Layer B contains the following components in mass percent: Modified PET: PET; nucleating agent (dibutyl sebacate:ammonium salt of phosphoric ester:sodium benzoate = 1:1:4); chain extending agent (ester Petition 870260054003, dated 03 / 06 / 2026, page 14 / 31 7 / 19 glycidyl methacrylic acid): foaming agent (barium azodicarboxylate: toluenesulfonyl urea = 1:5) = 57.0%: 32.0%:2.5%:4.5%:4.0%.

[033] (3) The formulation was uniformly mixed in a planetary mixer for not less than 1 h, with the mixing temperature controlled at 60°C, and fed into a twin-screw extruder for melt plasticization, with a screw diameter of 90 mm, an L / D ratio of 32, and a temperature of 245°C.

[034] (4) The formulation was coextruded into an ABA structure using three extruders in a single die, with a die temperature of 247°C.

[035] (5) The casting was extruded into sheet, controlling the ratio between the linear speed of the cooling roll and the exit speed of the casting to be less than or equal to 5, with the cooling roll temperature controlled at 35°C ± 2°C.

[036] (6) Uniaxial stretching was performed using infrared heating, with the sheet being stretched in the longitudinal direction under the following conditions: after preheating at 90°C, stretching at 95°C to a stretch ratio of 1.5 times. After longitudinal stretching, cooling and heat setting at 60°C.

[037] (7) Transverse stretching was performed using oil heating under the following conditions: after preheating at 100°C, stretching at 85°C to a stretch ratio of 5.0 times. After transverse stretching, cooling and heat setting at 80°C.

[038] (8) The film was pulled and wound, obtaining the recyclable crystalline polyester heat shrink film, where the thickness ratio of layers A, B and A was 6:88:6. Example of Implementation 2

[039] (1) Modified PET raw materials (Jiangyin Huahong Chemical Fiber Co., Ltd. WS501), PETG (Eastman Chemical Company GN071), PET (Henan Hongyuan Polymer Materials Co., Ltd. YH600) and functional masterbatch, nucleating agent, chain extending agent and foaming agent were dried in a vacuum dryer to remove moisture.

[040] (2) The various films of the three-layer ABA structure were formulated separately according to the composition proportions and mixed Petition 870260054003, dated 03 / 06 / 2026, page 15 / 31 8 / 19 preliminarily in a mixer, where:

[041] Layer A contains the following components in mass percentage: PETG: functional masterbatch (anti-adherent agent S1O2: erucic acid amide as slip agent = 1:1): PET = 76.8%:3.2%:20%;

[042] Layer B contains the following components in mass percent: Modified PET: PET: nucleating agent (dibutyl sebacate: ammonium salt of phosphoric ester: sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid): foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 49.0%:40.0%:1.0%:2.0%:8.0%.

[043] (3) The formulation was uniformly mixed in a planetary mixer for not less than 1 h, with the mixing temperature controlled at 60°C, and fed into a twin-screw extruder for melt plasticization, with a screw diameter of 90 mm, an L / D ratio of 32, and a temperature of 255°C.

[044] (4) The formulation was coextruded into an ABA structure using three extruders in a single die, with a die temperature of 257°C.

[045] (5) The casting was extruded into sheet, controlling the ratio between the linear speed of the cooling roll and the exit speed of the casting to be less than or equal to 5, with the cooling roll temperature controlled at 35°C ± 2°C.

[046] (6) Uniaxial stretching was performed using infrared heating, with the sheet being stretched in the longitudinal direction under the following conditions: after preheating at 95°C, stretching at 85°C to a stretch ratio of 1.5 times. After longitudinal stretching, cooling and heat setting at 60°C.

[047] (7) Transverse stretching was performed using oil heating under the following conditions: after preheating at 105°C, stretching at 80°C to a stretch ratio of 5.5 times. After transverse stretching, cooling and heat setting at 80°C.

[048] (8) The film was pulled and wound, obtaining the recyclable crystalline polyester heat shrink film, where the thickness ratio of layers A, B and A was 6:88:6. Example of Implementation 3 Petition 870260054003, dated 03 / 06 / 2026, page 16 / 31 9 / 19

[049] (1) Modified PET raw materials (Henan Hongyuan Polymer Materials Co., Ltd. YH101), PETG (SKYGREEN® S2012 from SK Chemical Co., Ltd. of South Korea), PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600) and functional masterbatch, nucleating agent, chain extending agent and foaming agent were dried in a vacuum dryer to remove moisture.

[050] (2) The various films of the three-layer ABA structure were formulated separately according to the composition proportions and preliminarily mixed in a mixer, where:

[051] Layer A contains the following components in mass percentage: PETG: functional masterbatch (anti-adherent agent S1O2: erucic acid amide as slip agent = 1:1): PET = 76.8%:3.2%:20%;

[052] Layer B contains the following components in mass percent: Modified PET: PET: nucleating agent (dibutyl sebacate:ammonium salt of phosphoric ester:sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid): foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 65.4%:22.6%:4.0%:6.0%:2.0%.

[053] (3) The formulation was uniformly mixed in a planetary mixer for not less than 1 h, with the mixing temperature controlled at 60°C, and fed into a twin-screw extruder for melt plasticization, with a screw diameter of 90 mm, an L / D ratio of 32, and a temperature of 240°C.

[054] (4) The formulation was coextruded into an ABA structure using three extruders in a single die, with a die temperature of 242°C.

[055] (5) The casting was extruded into sheet, controlling the ratio between the linear speed of the cooling roll and the exit speed of the casting to be less than or equal to 5, with the cooling roll temperature controlled at 35°C ± 2°C.

[056] (6) Uniaxial stretching was performed using infrared heating, with the sheet being stretched in the longitudinal direction under the following conditions: after preheating at 90°C, stretching at 90°C to a stretch ratio of 1.5 times. After longitudinal stretching, cooling and heat setting at 60°C.

[057] (7) Transverse stretching was performed using oil heating Petition 870260054003, dated 03 / 06 / 2026, p. 17 / 31 10 / 19 under the following conditions: after preheating to 90°C, stretching at 85°C to a stretch ratio of 4.8 times. After cross stretching, cooling and heat setting at 80°C.

[058] (8) The film was pulled and wound, obtaining the recyclable crystalline polyester heat shrink film, where the thickness ratio of layers A, B and A was 6:88:6. Example of Implementation 4

[059] (1) Modified PET raw materials (Henan Hongyuan Polymer Materials Co., Ltd. YH101), PETG (SKYGREEN® S2012 from SK Chemical Co., Ltd. of South Korea), PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600) and functional masterbatch were dried in a vacuum dryer to remove moisture.

[060] (2) The various films of the three-layer ABA structure were formulated separately according to the composition proportions and preliminarily mixed in a mixer, where:

[061] Layer A contains the following components in mass percentage: PETG: functional masterbatch (anti-adherent agent S1O2: erucic acid amide as slip agent = 1:1): PET = 87.2%:3.8%:10%;

[062] Layer B contains the following components in mass percent: Modified PET: PET: nucleating agent (dibutyl sebacate: ammonium salt of phosphoric ester: sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid): foaming agent (barium azodicarboxylate: toluenesulfonyl urea = 1:5) = 57.0%:32.0%:2.5%:4.5%:4.0%.

[063] (3) The formulation was uniformly mixed in a planetary mixer for not less than 1 h, with the mixing temperature controlled at 60°C, and fed into a twin-screw extruder for melt plasticization, with a screw diameter of 90 mm, an L / D ratio of 32, and a temperature of 245°C.

[064] (4) The formulation was coextruded into an ABA structure using three extruders in a single die, with a die temperature of 247°C.

[065] (5) The casting was extruded into sheet metal, controlling the ratio between the linear speed of the cooling roll and the exit speed of the casting to be less than or equal to 5, with the cooling roll temperature controlled at 35°C. Petition 870260054003, dated 03 / 06 / 2026, p. 18 / 31 11 / 19 ± 2°C.

[066] (6) Uniaxial stretching was performed using infrared heating, with the plate being stretched in the longitudinal direction under the following conditions: after preheating at 90°C, stretching at 95°C to a stretch ratio of 1.5 times. After longitudinal stretching, cooling and heat setting at 60°C.

[067] (7) Transverse stretching was performed using oil heating under the following conditions: after preheating at 100°C, stretching at 85°C to a stretch ratio of 5.0 times. After transverse stretching, cooling and heat setting at 80°C.

[068] (8) The film was pulled and wound, obtaining the recyclable crystalline polyester heat shrink film, where the thickness ratio of layers A, B and A was 6:88:6. Example of Implementation 5

[069] (1) Modified PET raw materials (Henan Hongyuan Polymer Materials Co., Ltd. YH101), PETG (SKYGREEN® S2012 from SK Chemical Co., Ltd. of South Korea), PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600) and functional masterbatch, nucleating agent, chain extending agent and foaming agent were dried in a vacuum dryer to remove moisture.

[070] (2) The various films of the three-layer ABA structure were formulated separately according to the composition proportions and preliminarily mixed in a mixer, where:

[071] Layer A contains the following components in mass percentage: PETG: functional masterbatch (anti-adherent agent S1O2: erucic acid amide as slip agent = 1:1): PET = 66.0%:4.0%:30.0%;

[072] Layer B contains the following components in mass percent: Modified PET: PET nucleating agent (dibutyl sebacate: ammonium salt of phosphoric ester: sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid): foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 60.0%:28.5%:3.5%:5.0%:3.0%.

[073] (3) The formulation was uniformly mixed in a planetary mixer for not less than 1 h, with the mixing temperature controlled at 60°C, and fed Petition 870260054003, dated 03 / 06 / 2026, p. 19 / 31 12 / 19 in a twin-screw extruder for melt plasticization, with a screw diameter of 90 mm, an L / D ratio of 32, and a temperature of 245°C.

[074] (4) The formulation was coextruded into an ABA structure using three extruders in a single die, with a die temperature of 247°C.

[075] (5) The casting was extruded into sheet, controlling the ratio between the linear speed of the cooling roll and the exit speed of the casting to be less than or equal to 5, with the cooling roll temperature controlled at 35°C ± 2°C.

[076] (6) Uniaxial stretching was performed using infrared heating, with the plate being stretched in the longitudinal direction under the following conditions: after preheating at 90°C, stretching at 95°C to a stretch ratio of 1.5 times. After longitudinal stretching, cooling and heat setting at 60°C.

[077] (7) Transverse stretching was performed using oil heating under the following conditions: after preheating at 100°C, stretching at 85°C to a stretch ratio of 5.0 times. After transverse stretching, cooling and heat setting at 80°C.

[078] (8) The film was pulled and wound, obtaining the recyclable crystalline polyester heat shrink film, where the thickness ratio of layers A, B and A was 6:88:6. Comparative Example 1

[079] In this comparative example, the central layer (layer B) contains the following components in mass percent: Modified PET (Henan Hongyuan Polymer Materials Co., Ltd. YH101): nucleating agent (dibutyl sebacate:ammonium salt of phosphoric ester:sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid): foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 89.0%:2.5%:4.5%:4.0%, with the components of the other layers identical to those of Embodiment Example 1 and the preparation method consistent with Embodiment Example 1. Comparative Example 2

[080] In this comparative example, the central layer (layer B) contains the following components in mass percentage: PET (Sinopec Yizheng Petition 870260054003, dated 03 / 06 / 2026, page 20 / 31 13 / 19 Chemical Fiber Co., Ltd. FG600): nucleating agent (dibutyl sebacate:ammonium salt of phosphoric ester:sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid): foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 89.0%:2.5%:4.5%:4.0%, with the components of the other layers identical to those of Embodiment Example 1 and the preparation method consistent with Embodiment Example 1. Comparative Example 3

[081] In this comparative example, the central layer (layer B) contains the following components in mass percent: Modified PET (Henan Hongyuan Polymer Materials Co., Ltd. YH101): PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600): Chain extender (methacrylic acid glycidyl ester): Foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 59.5%:32.0%:4.5%:4.0%, with the components of the other layers identical to those of Embodiment Example 1 and the preparation method consistent with Embodiment Example 1. Comparative Example 4

[082] In this comparative example, the central layer (layer B) contains the following components in mass percent: Modified PET (Henan Hongyuan Polymer Materials Co., Ltd. YH101): PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600): nucleating agent (dibutyl sebacate:ammonium salt of phosphoric ester:sodium benzoate = 1:1:4): foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 61.5%:32.0%:2.5%:4.0%, with the components of the other layers identical to those of Embodiment Example 1 and the preparation method consistent with Embodiment Example 1. Comparative Example 5

[083] In this comparative example, the central layer (layer B) contains the following components in mass percentage: modified PET (Henan Hongyuan Polymer Materials Co., Ltd. YH101): PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600): nucleating agent (dibutyl sebacate:ammonium salt of phosphoric ester:sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid) = 61.0%:32.0%:2.5%:4.5%, with the components of the other layers identical to those of Embodiment Example 1 and the method of Petition 870260054003, dated 03 / 06 / 2026, pages 21 / 31 14 / 19 preparation consistent with Achievement Example 1. Comparative Example 6

[084] In this comparative example, the central layer (layer B) contains the following components in mass percentage: modified PET (Henan Hongyuan Polymer Materials Co., Ltd. YH101): PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600): foaming agent (barium azodicarboxylate: toluenesulfonyl urea = 1:5) = 64.0%:32.0%:4.0%, with the components of the other layers identical to those of Embodiment Example 1 and the preparation method consistent with Embodiment Example 1. Comparative Example 7

[085] Layer B contains the following components in mass percent: Modified PET (Henan Hongyuan Polymer Materials Co., Ltd. YH101): PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600): nucleating agent (dibutyl sebacate:ammonium salt of phosphoric ester:sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid): foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 53.0% :28.5%: 10.0% :4.5% :4.0%. Comparative Example 8

[086] Layer B contains the following components in mass percent: Modified PET (Henan Hongyuan Polymer Materials Co., Ltd. YH101): PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600): nucleating agent (dibutyl sebacate:ammonium salt of phosphoric ester:sodium benzoate = 1:1:4): chain extending agent (glycidyl ester of methacrylic acid): foaming agent (barium azodicarboxylate:toluenesulfonyl urea = 1:5) = 53.0% :28.5% :2.5%: 12.0% :4.0%. Comparative Example 9

[087] The surface layer (layer A) contains the following components in mass percent: PETG (SKYGREEN® S2012 from SK Chemical Co., Ltd. of South Korea): functional masterbatch (anti-adherent agent SÍOSÍO2: slip agent erucamide = 1:1) = 97.8%:3.2%. The components of the other layers are identical to those of Embodiment Example 1 and the preparation method is consistent with Embodiment Example 1. Petition 870260054003, dated 03 / 06 / 2026, pages 22 / 31 15 / 19 Comparative Example 10

[088] The surface layer (layer A) contains the following components in mass percentage: PETG (SKYGREEN, S2012): PET (Yizheng Chemical Fiber, FG600) = 76.8%:23.2%. The other components and the components of the other layers are identical to those of Embodiment Example 1, and the preparation method is consistent with Embodiment Example 1. Comparative Example 11

[089] In this comparative example, the molded sheet was subjected to transverse stretching, with the stretching conditions adjusted to: stretch ratio of 4.0 times. The components of the other layers are identical to those of Embodiment Example 1 and the preparation method is consistent with Embodiment Example 1. Comparative Example 12

[090] In this comparative example, the molded sheet was subjected to longitudinal stretching, with the stretching conditions adjusted to: stretch ratio of 1.0 times. The components of the other layers are identical to those of Embodiment Example 1 and the preparation method is consistent with Embodiment Example 1.

[091] High-melting-point recyclable PETG heat-shrink films prepared in Embodiment Examples 1-5 and Comparative Examples 1-10 were tested for thickness, melting point, agglomeration test, shrinkage rate, shrinkage force, turbidity, transparency, and surface tension. Transparency and turbidity were determined according to GB / T 2410-2008; surface tension was determined according to GB / T 142162008 / ISO 8296. 2003; the agglomeration test was partially performed according to APR PET CG-02 Critical Guidance: the fragments of the shrunk film were dried in an oven at 160°C for 0.5 h, the dried fragments were uniformly mixed with bottle fragments in a 1:3 ratio, and then placed in an oven at 210°C for 90 min. The test is considered passed if the mass of the material adhering to the bottle fragments does not exceed 1% of the total mass of the mixture; otherwise, it is considered failed.The results are shown in Table 1. Petition 870260054003, dated 03 / 06 / 2026, pages 23 / 31 16 / 19 Table 1. Recyclable Crystalline PETG Heat Shrink Film Test Items Actual Thickness (µm) Thermal Shrinkage Rate (%) (90°C / 10s) Melting Point (°C) Agglomeration Test Turbidity (%) Transparency (%) Shrinkage Force (N) Surface Tension (µN / m) Longitudinal Transverse Example of Realization 1 40 5 76 231 3.76 98.3 5.7 40 Example of Realization 2 40 3 74 233 3.91 98.3 5.3 40 Example of Realization 3 40 5 78 231 3.55 98.5 5.8 40 Example of Realization 4 40 5 77 231 3.68 98.3 5.7 40 Example of Realization 5 40 4 76 232 3.57 98.4 5.6 40 Comparative Example 1 40 11 79 193 17.5 68.5 6.3 40 Comparative Example 4 40 8 77 197 60.1 6.5 40 Comparative Example 40 0 49 249 8.21 81.0 2.3 40 Petition 870260054003, dated 03 / 06 / 2026, pages 24 / 31 17 / 19 Test Items Actual Thickness (µm) Thermal Shrinkage Rate (%) (90°C / 10s) Melting Point (°C) Agglomeration Test Turbidity (%) Transparency (%) Shrinkage Force (N) Surface Tension (µN / m) Longitudinal Transverse 7 Comparative Example 8 / / / / / / / / / Comparative Example 9 40 6 76 221 X 3.55 98.4 5.8 40 Comparative Example 10 40 5 76 232 3.47 98.1 5.5 38 Comparative Example 11 40 4 68 230 3.78 98.5 5.1 40 Comparative Example 12 40 -2 77 236 3.62 98.3 5.6 40

[092] As can be seen in Table 1, comparing Embodiment Examples 1-4 with Comparative Example 1, when more modified PET is used in the central layer, the overall shrinkage rate of the film increases. However, when the total PET content in the film is insufficient, it results in a lower melting point for the film as a whole, failing the agglomeration test, which affects the recycling process.

[093] Comparing Embodiment Example 1 with Comparative Example 2, when no modified PET is added to the central layer, with PET being the main component of the central layer, the film practically loses its shrinkage characteristics and shows a significant reduction in optical properties.

[094] Comparing Embodiment Example 1 with Comparative Examples 3, 4, and 6, when no nucleating agent is added to the central layer, the structure of the cells formed by the foaming agent becomes uncontrollable, the turbidity of the film increases noticeably, and without the action of the nucleating agent, the crystallinity of the film is low, resulting in failure in the agglomeration test and not meeting the recycling requirements. When no chain-extending agent is added to the central layer, it is not possible to increase the overall molecular weight and viscosity. Petition 870260054003, dated 03 / 06 / 2026, pages 25 / 31 18 / 19 of the film, resulting in a lower melting point for the film as a whole, failing the agglomeration test. When the combination of nucleating agent and chain extender is not added to the central layer, problems such as inadequate film crystallinity, lower melting point, failure in the agglomeration test, and high turbidity occur, failing to meet recycling requirements.

[095] Comparing Embodiment Example 1 with Comparative Example 5, when no foaming agent is added to the central layer, the film does not exhibit a cellular structure, which would not expand during the stretching process, nor would it shrink after preheating. Furthermore, due to a certain crystallinity of the film, the overall shrinkage rate of the film is low. Due to the absence of the foaming agent, the overall density of the film is higher, resulting in a correspondingly higher shrinkage force, which can cause phenomena such as deformation of the bottle body or shrinkage wrinkles during application, thus limiting the range of applications of the film.

[096] Comparing Embodiment Example 1 with Comparative Example 7, when there is an excess of nucleating agent in the central layer, the crystallization rate of the film becomes too fast, resulting in an excessive degree of crystallization. This causes a noticeable increase in the turbidity of the film and a significant reduction in the heat-shrinkable properties, severely affecting the packaging effect. Furthermore, due to the excessive amount of nucleating agent, the high degree and rapid rate of crystallization affect the expansion of the cells formed by the foaming agent, impacting the improvement of the film's heat-shrinkable properties provided by the cell structure.

[097] Comparing Embodiment Example 1 with Comparative Example 8, when there is an excess of chain extender in the central layer, excessive crosslinking occurs during the polymer melt extrusion process, significantly reducing the elongation properties of the film during the production process, resulting in the inability to stretch the film.

[098] Comparing Embodiment Example 1 with Comparative Example 9, when PET is not added to the surface layer, the melting point and overall crystallinity of the film decrease, resulting in failure of the agglomeration test. Petition 870260054003, dated 03 / 06 / 2026, pages 26 / 31 19 / 19, adhesion and clumping phenomena may occur during the recycling process.

[099] Comparing Embodiment Example 1 with Comparative Example 10, when no functional masterbatch is added to the surface layer, the film exhibits excessive surface friction force, resulting in irregular winding, insufficient surface tension and inadequate wetting tension, causing problems such as the inability to print the film.

[0100] Comparing Embodiment Example 1 with Comparative Examples 11 and 12, when transverse stretching in the process is insufficient, a low overall shrinkage rate of the film occurs, making its use impossible in conditions requiring high shrinkage. When there is no longitudinal stretching in the process, due to the characteristics of the raw material, the film exhibits elongation after longitudinal thermal shrinkage, affecting the final effect of the packaging.

[0101] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. It is necessary to clarify that these embodiments are used to aid in understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in each embodiment of the present invention, as described above, can be combined with each other, provided there is no conflict between them. In addition, the above constitutes only part of the embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention. Petition 870260054003, dated 03 / 06 / 2026, pages 27 / 31

Claims

1 / 2 CLAIMS:

1. A QUITE RECYCLABLE CRYSTALLINE POLYESTER HEAT SHRINK FILM, characterized in that the heat shrink film structure has a three-layer porous structure A / B / A; wherein layer A is composed of polyethylene terephthalate (PETG) copolymer, functional masterbatch and polyethylene terephthalate (PET); layer B is composed of modified PET, PET, nucleating agent, chain extending agent and foaming agent, the modified PET being a PET modified with neopentyl glycol (NPG); wherein, in mass percentage, in layer A, PETG:functional masterbatch:PET = 89.4-66.0%:1.6-4.0%:10.0-30.0%; In layer B, modified PET: PET: nucleating agent: chain extender: foaming agent = 42-65.4%:30-40%:0.6-4.0%:2.0-6.0%:2.0-8.0%; The aforementioned functional masterbatch is a composition of at least one compound among silicon dioxide, talc, clay or kaolin, and at least one compound among oleamide or erucamide;The aforementioned nucleating agent is composed of dibutyl adipate, ammonium phosphate ester salt and sodium benzoate, with dibutyl adipate:ammonium phosphate ester salt:sodium benzoate = 1:1:4; The aforementioned chain extending agent is glycidyl methacrylate; The aforementioned foaming agent is composed of barium azodicarboxylate and p-toluenesulfonyl urea, with barium azodicarboxylate:p-toluenesulfonyl urea = 1:

5.

2. METHOD FOR PREPARING EASILY RECYCLABLE CRYSTALLINE POLYESTER HEAT SHRINK FILM, as claimed in claim 1, characterized by comprising the following steps: (1) Uniformly mixing the raw materials of layers A and B in the specified proportions in a planetary mixer, followed by drying, and performing melt plasticization in the corresponding extruders, separating the mixtures of the central layer and the surface layers; (2) Set up the ABA three-layer structure, extrude the molten material through a single die, with die temperature between 240-270°C, and Petition 870260054003, dated 03 / 06 / 2026, page 28 / 31 2 / 2 cool the molten sheet on a fast cooling roll for molding; (3) Perform longitudinal stretching of the sheet; (4) Perform the transverse stretching operation; (5) Perform traction and winding to obtain said easily recyclable crystalline polyester heat shrink film.

3. METHOD OF PREPARING THE EASILY RECYCLABLE CRYSTALLINE POLYESTER HEAT SHRINK FILM, as claimed in claim 2, characterized in that the stretching conditions in step (3) are: after preheating at 85-95°C, stretching at a ratio of 1-2 times at 80-110°C, followed by cooling and heat setting at 50-80°C after longitudinal stretching.

4. METHOD FOR PREPARING EASILY RECYCLABLE CRYSTALLINE POLYESTER HEAT SHRINK FILM, as claimed in claim 3, characterized in that the stretching conditions in step (4) are: after preheating at 90-110°C, stretching at a ratio of 4.0-5.5 times at 80-95°C, followed by cooling and heat setting at 70-90°C after transverse stretching. 5.METHOD FOR PREPARING EASILY RECYCLABLE CRYSTALLINE POLYESTER HEAT SHRINK FILM, as claimed in claim 4, characterized in that the thickness of said easily recyclable crystalline polyester heat shrink film is 30-100 µm. Petition 870260054003, dated 03 / 06 / 2026, pp. 29 / 31.

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