Crystalline easy-to-recycle polyester heat-shrinkable film and preparation method therefor

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

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

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on October 10, 2023, with application number CN202311300538.X and invention name “A crystalline and easily recyclable polyester heat shrinkable film and its preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The invention belongs to the field of heat shrinkable film preparation, and in particular relates to a crystalline easily recyclable polyester heat shrinkable film and a preparation method thereof. Background Art

[0003] Polyethylene terephthalate glycol copolymer (PETG) heat shrink film is widely used in beverage packaging, daily chemical packaging, and battery packaging. It is one of the most widely used plastic products. However, it is not easily degradable and can remain in the environment for hundreds of years under natural conditions. Improper disposal can have serious environmental impacts. To alleviate the problem of plastic pollution and improve the recyclability of PETG film, attention to the recycling and reuse of film products continues to increase.

[0004] However, the film recycling process presents numerous challenges. Bottle flakes are made of polyethylene terephthalate (PET), which is highly crystalline and has a high melting point, while shrinkable labels (made of polyester film) are mostly amorphous PETG. The melting points and crystallinity of the two materials differ significantly, and both materials have densities greater than 1, making it difficult to separate the flakes from the film after crushing. Manual separation of the polyester labels from the bottles is required before crushing and sorting for recycling, increasing labor costs and impacting overall recycling efficiency. Furthermore, the melting points of the two materials differ, with PETG film having a much lower melting point than PET flakes. The PET recycling process requires drying at temperatures above 200°C. At these temperatures, conventional polyester heat-shrinkable film softens and becomes sticky, forming clumps with the PET flakes. This can cause adhesion, bridging, and other problems during the recycling process, leading to blockage in recycling equipment. These clumps must be handled before further processing. These clumps reduce recycling yield and create an additional step for handling the clumps, severely impacting the recovery of PET flakes.

[0005] The recycling methods currently reported mainly start from the synthetic route of modified molecular structure of PETG polyester, which improves the melting point and crystallinity of polyester raw materials, so that the prepared polyester heat shrinkable film has the characteristics of crystallization, making PETG closer to PET. However, this will lead to the reduction of the shrinkage characteristics of the prepared film, which cannot meet the packaging requirements of various scenarios. In addition, the synthetic process is more complicated to change, and energy consumption is increased.

[0006] Summary of the Invention

[0007] The present invention mainly addresses the problems existing in the existing recycling process and the limitations of reducing the shrinkage rate of crystalline films. It improves the melting point of PETG film from the film preparation process route, constructs a porous structure combined with a process to improve the film shrinkage rate, introduces additives to improve the film crystallinity and melting point, and provides a crystalline, easily recyclable polyester heat-shrinkable film with good recycling characteristics, crystallizability, printability, shrinkage, and low shrinkage force, and a preparation method thereof.

[0008] To this end, the present invention provides a crystalline and easily recyclable polyester heat-shrinkable film, wherein the film layer structure of the heat-shrinkable film is a three-layer structure of A / B / A; wherein the raw materials of the A layer are composed of PETG, a functional masterbatch and PET; the raw materials of the B layer are composed of modified PET, PET, a nucleating agent, a chain extender and a foaming agent, and the modified PET is neopentyl glycol (NPG) modified PET.

[0009] Furthermore, by 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%.

[0010] Furthermore, the chain extender is at least one of glycidyl methacrylate or cycloethyl acrylate.

[0011] Furthermore, the nucleating agent is at least one of dibutyl sebacate, ammonium phosphate or sodium benzoate.

[0012] Furthermore, the functional masterbatch is a compound of at least one of silicon dioxide, talc, clay or kaolin and at least one of oleamide or erucamide.

[0013] Furthermore, the foaming agent is at least one of trihydrazinotriazine, barium azodicarboxylate, 4,4'-oxybisphenylsulfonylsemicarbazide or p-toluenesulfonylsemicarbazide.

[0014] The present invention also provides a method for preparing the above-mentioned crystalline easily recyclable polyester heat shrinkable film, comprising the following steps:

[0015] (1) The raw materials of the A layer and the B layer are uniformly mixed in a planetary mixer according to a certain proportion and then dried. The raw materials of the core layer and the surface layer are melt-plasticized in corresponding extruders;

[0016] (2) Setting the ABA three-layer structure, the melt is extruded through the same die head with a die head temperature of 240-270 ° C, and the cast sheet is cooled and formed on a chill roller;

[0017] (3) longitudinally stretching the cast sheet;

[0018] (4) performing a transverse stretching operation;

[0019] (5) pulling and rolling to obtain the crystalline and easily recyclable polyester heat shrinkable film.

[0020] Furthermore, the stretching conditions of step (3) are: after preheating at 85-95°C, the stretching ratio reaches 1-2 times at 80-110°C, and after longitudinal stretching, the film is cooled and set at 50-80°C.

[0021] Furthermore, the stretching conditions of step (4) are: after preheating at 90-110°C, the stretching ratio reaches 4.0-5.5 times at 80-95°C, and after transverse stretching, the film is cooled and set at 70-90°C.

[0022] Furthermore, the thickness of the crystalline and easily recyclable polyester heat shrinkable film is preferably 30-100 μm. Beneficial effects:

[0023] 1. The present invention prepares a foamed, crystallizable, and easily recyclable polyester heat-shrinkable film by adding a suitable foaming agent to the core layer. During processing, a large stretch ratio can expand the cell structure to a certain extent. By shaping and fixing the cell structure, the shrinkage becomes smaller after heating, making the film have a higher heat shrinkage rate than ordinary crystalline films. The film structure of the present invention reduces the film density, thereby reducing the binding force on the packaging during the film shrinkage process, reducing the overall heat shrinkage force of the film, and making the shrinkage process smoother. It can effectively reduce the problems of wrinkles caused by excessive shrinkage of the film during the shrinkage process and deformation of the packaging bottle caused by excessive shrinkage force. At the same time, the foaming agent can reduce the film density, so that more heat-shrinkable film can be obtained with the same amount of polyester chips, which is conducive to cost reduction.

[0024] 2. The present invention adds a chain extender to the core layer, which allows the PETG component in the polyester film to be cross-linked to a limited extent, thereby increasing the molecular weight of the polyester film as a whole. Correspondingly, the melting point of the film is improved to a certain extent, and the overall melting point of the film is brought closer to that of PET while ensuring the thermal shrinkage properties of the polyester film. The addition of an appropriate nucleating agent can accelerate the crystallization rate, increase the crystallization density, and promote the formation of micronized grains during the melting process, thereby improving the overall crystallinity of the film to a certain extent and avoiding the loss of shrinkage properties due to excessive crystallization. The nucleating agent and the chain extender synergistically increase the film's thermal deformation temperature and the material melting point, ensuring that the film label prepared by this method can be recycled together with the PET bottle flakes, and the recycling process does not cause adhesion, bridging, and other blockages in the recycling equipment. At the same time, the nucleating agent can control the size of the pore structure formed by the foaming agent during the melting process. Under an appropriate ratio, it can effectively improve the fogging of the film caused by the pore structure, and improve the overall transparency and light transmittance of the film. The recyclable crystalline film prepared by this method does not require changing the synthesis process of the polyester chips, does not increase the cost of equipment modification and synthesis formula process modification, has a high shrinkage rate, and has strong product applicability.

[0025] 3. The method of the present invention uses a foaming agent, a chain extender, and a nucleating agent, and the three modifying additives have a synergistic effect. An appropriate amount of chain extender can increase the molecular weight, that is, increase the melting point, and increase the crystallinity of the film with the nucleating agent, which can synergistically improve the film recycling characteristics (the recycling process does not stick to the bottle flakes, and bridging affects the recycling efficiency). The foaming agent can increase the film yield (reduce the density) and reduce the film shrinkage force. However, if the bubbles formed by the foaming agent are too large, it will affect the transparency of the film. The nucleating agent can promote the formation of microcrystals, thereby inhibiting the excessive bubbles formed by foaming and improving the overall haze of the film.

[0026] 4. The polyester film prepared by the present invention has a three-layer structure, in which the functional masterbatch added to the surface layer mainly serves to improve the printing and palm-jointing performance of the film. The three-layer structure is all PET-derived materials with similar polarity, strong adhesion between the layers, and no stratification problem. It is a single material, which is conducive to the recyclability of the product.

[0027] Figures in the specification

[0028] FIG1 is a schematic structural diagram of a crystalline, easily recyclable polyester heat-shrinkable film prepared according to an embodiment of the present invention; wherein layer A is a surface layer (printing layer) and layer B is a core layer (porous structure layer). DETAILED DESCRIPTION

[0029] The effects of the crystalline, easily recyclable polyester heat-shrinkable film and the preparation method thereof of the present invention are studied and analyzed through examples and comparative examples.

[0030] The PETG used in the examples and comparative examples is selected from SK Chemical Company of South Korea. S2012, Eastman Chemical Company GN071. Modified PET (NPG-modified PET) was selected from Henan Yuanhong Polymer New Materials Co., Ltd. YH101 and Jiangyin Huahong Chemical Fiber Co., Ltd. WS501. PET was selected from Sinopec Yizheng Chemical Fiber Co., Ltd. FG600 and Henan Yuanhong Polymer New Materials Co., Ltd. YH600.

[0031] Example 1

[0032] (1) Modify the raw materials PET (Henan Yuanhong Polymer New Materials Co., Ltd. YH101), PETG (Korea SK Chemical Co., Ltd. S2012), PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600) and functional masterbatch, nucleating agent, chain extender and foaming agent were dried in a vacuum dryer to remove moisture.

[0033] (2) Various ABA three-layer structure films are prepared according to the composition ratio and preliminarily mixed in a mixer, wherein:

[0034] The A layer comprises the following components by mass percentage: PETG: functional masterbatch (anti-blocking agent SiO2: slip agent erucamide = 1:1): PET = 76.8%: 3.2%: 20%;

[0035] The B layer contains the following components in percentage by mass: modified PET: PET: nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonyl semicarbazide = 1:5) = 57.0%: 32.0%: 2.5%: 4.5%: 4.0%.

[0036] (3) The ingredients are uniformly mixed in a planetary mixer for a mixing time of not less than 1 h. The mixing temperature is controlled at 60°C. The ingredients are fed into a twin-screw extruder for melting and plasticization. The screw diameter is selected to be 90 mm, the aspect ratio is 32, and the temperature is 245°C.

[0037] (4) The ingredients are extruded into the same die head by three extruders according to the ABA structure, and the die head temperature is 247 °C.

[0038] (5) When the melt is extruded into a cast sheet, the ratio of the linear speed of the quenching roller to the melt outflow speed is controlled to be less than or equal to 5, and the temperature of the quenching roller is controlled at 35℃±2℃.

[0039] (6) The cast sheet is longitudinally stretched by single-point stretching using infrared heating. The stretching conditions are as follows: preheating at 90°C and then stretching the sheet to a ratio of 1.5 times at 95°C. After longitudinal stretching, the sheet is cooled at 60°C to set the shape.

[0040] (7) The transverse stretching is performed by oil heating. The stretching conditions are as follows: preheating at 100°C, then stretching the film to a ratio of 5.0 at 85°C. After transverse stretching, the film is cooled and set at 80°C.

[0041] (8) pulling and rolling to obtain a crystalline and easily recyclable polyester heat shrinkable film, wherein the thickness ratio of layer A, layer B and layer A is 6:88:6.

[0042] Example 2

[0043] (1) The raw materials modified PET (WS501 from Jiangyin Huahong Chemical Fiber Co., Ltd.), PETG (GN071 from Eastman Chemical Company), PET (YH600 from Henan Yuanhong Polymer New Materials Co., Ltd.), functional masterbatch, nucleating agent, chain extender and foaming agent were dried in a vacuum dryer to remove moisture.

[0044] (2) Various ABA three-layer structure films are prepared according to the composition ratio and preliminarily mixed in a mixer, wherein:

[0045] The A layer comprises the following components by mass percentage: PETG: functional masterbatch (anti-blocking agent SiO2: slip agent erucamide = 1:1): PET = 76.8%: 3.2%: 20%;

[0046] The B layer contains the following components in percentage by mass: modified PET: PET: nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonyl semicarbazide = 1:5) = 49.0%: 40.0%: 1.0%: 2.0%: 8.0%.

[0047] (3) The ingredients are uniformly mixed in a planetary mixer for a mixing time of not less than 1 h. The mixing temperature is controlled at 60°C. The ingredients are fed into a twin-screw extruder for melting and plasticization. The screw diameter is selected to be 90 mm, the aspect ratio is 32, and the temperature is 255°C.

[0048] (4) The ingredients were extruded into the same die head by three extruders according to the ABA structure, and the die head temperature was 257 °C.

[0049] (5) When the melt is extruded into a cast sheet, the ratio of the linear speed of the quenching roller to the melt outflow speed is controlled to be less than or equal to 5, and the temperature of the quenching roller is controlled at 35℃±2℃.

[0050] (6) The cast sheet was longitudinally stretched using infrared heating for single-point stretching. The stretching conditions were as follows: preheating at 95°C and then stretching the sheet to a ratio of 1.5 times at 85°C. After longitudinal stretching, the sheet was cooled at 60°C for final shaping.

[0051] (7) The transverse stretching is performed by oil heating. The stretching conditions are as follows: preheating at 105°C and then stretching the film to a ratio of 5.5 times at 80°C. After transverse stretching, the film is cooled and set at 80°C.

[0052] (8) pulling and rolling to obtain a crystalline and easily recyclable polyester heat shrinkable film, wherein the thickness ratio of layer A, layer B and layer A is 6:88:6.

[0053] Example 3

[0054] (1) Modify the raw materials PET (Henan Yuanhong Polymer New Materials Co., Ltd. YH101), PETG (Korea SK Chemical Co., Ltd. S2012), PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600) and functional masterbatch, nucleating agent, chain extender and foaming agent were dried in a vacuum dryer to remove moisture.

[0055] (2) Various ABA three-layer structure films are prepared according to the composition ratio and preliminarily mixed in a mixer, wherein:

[0056] The A layer comprises the following components by mass percentage: PETG: functional masterbatch (anti-blocking agent SiO2: slip agent erucamide = 1:1): PET = 76.8%: 3.2%: 20%;

[0057] The B layer contains the following components in percentage by mass: modified PET: PET: nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonyl semicarbazide = 1:5) = 65.4%: 22.6%: 4.0%: 6.0%: 2.0%.

[0058] (3) The ingredients are uniformly mixed in a planetary mixer for a mixing time of not less than 1 h. The mixing temperature is controlled at 60°C. The ingredients are fed into a twin-screw extruder for melting and plasticization. The screw diameter is selected to be 90 mm, the aspect ratio is 32, and the temperature is 240°C.

[0059] (4) The ingredients are extruded into the same die head by three extruders according to the ABA structure, and the die head temperature is 242℃.

[0060] (5) When the melt is extruded into a cast sheet, the ratio of the linear speed of the quenching roller to the melt outflow speed is controlled to be less than or equal to 5, and the temperature of the quenching roller is controlled at 35℃±2℃.

[0061] (6) The cast sheet is longitudinally stretched by single-point stretching using infrared heating. The stretching conditions are as follows: preheating at 90°C, stretching the sheet to a ratio of 1.5 times at 90°C, and cooling the sheet at 60°C to set the shape after longitudinal stretching.

[0062] (7) The transverse stretching is done by oil heating. The stretching conditions are: preheating at 90°C, then stretching the film to a ratio of 4.8 times at 85°C. After transverse stretching, the film is cooled and set at 80°C.

[0063] (8) pulling and rolling to obtain a crystalline and easily recyclable polyester heat shrinkable film, wherein the thickness ratio of layer A, layer B and layer A is 6:88:6.

[0064] Example 4

[0065] (1) Modify the raw materials PET (Henan Yuanhong Polymer New Materials Co., Ltd. YH101), PETG (Korea SK Chemical Co., Ltd. S2012), PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600) and functional masterbatch were dried in a vacuum dryer to remove moisture.

[0066] (2) Various ABA three-layer structure films are prepared according to the composition ratio and preliminarily mixed in a mixer, wherein:

[0067] The A layer comprises the following components by mass percentage: PETG: functional masterbatch (anti-blocking agent SiO2: slip agent erucamide = 1:1): PET = 87.2%: 3.8%: 10%;

[0068] The B layer contains the following components in percentage by mass: modified PET: PET: nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonyl semicarbazide = 1:5) = 57.0%: 32.0%: 2.5%: 4.5%: 4.0%.

[0069] (3) The ingredients are uniformly mixed in a planetary mixer for a mixing time of not less than 1 h. The mixing temperature is controlled at 60°C. The ingredients are fed into a twin-screw extruder for melting and plasticization. The screw diameter is selected to be 90 mm, the aspect ratio is 32, and the temperature is 245°C.

[0070] (4) The ingredients are extruded into the same die head by three extruders according to the ABA structure, and the die head temperature is 247 °C.

[0071] (5) When the melt is extruded into a cast sheet, the ratio of the linear speed of the quenching roller to the melt outflow speed is controlled to be less than or equal to 5, and the temperature of the quenching roller is controlled at 35℃±2℃.

[0072] (6) The cast sheet is longitudinally stretched by single-point stretching using infrared heating. The stretching conditions are as follows: preheating at 90°C and then stretching the sheet to a ratio of 1.5 times at 95°C. After longitudinal stretching, the sheet is cooled at 60°C to set the shape.

[0073] (7) The transverse stretching is performed by oil heating. The stretching conditions are as follows: preheating at 100°C, then stretching the film to a ratio of 5.0 at 85°C. After transverse stretching, the film is cooled and set at 80°C.

[0074] (8) pulling and rolling to obtain a crystalline and easily recyclable polyester heat shrinkable film, wherein the thickness ratio of layer A, layer B and layer A is 6:88:6.

[0075] Example 5

[0076] (1) Modify the raw materials PET (Henan Yuanhong Polymer New Materials Co., Ltd. YH101), PETG (Korea SK Chemical Co., Ltd. S2012), PET (Sinopec Yizheng Chemical Fiber Co., Ltd. FG600) and functional masterbatch, nucleating agent, chain extender and foaming agent were dried in a vacuum dryer to remove moisture.

[0077] (2) Various ABA three-layer structure films are prepared according to the composition ratio and preliminarily mixed in a mixer, wherein:

[0078] The A layer comprises the following components by mass percentage: PETG: functional masterbatch (anti-blocking agent SiO2: slip agent erucamide = 1:1): PET = 66.0%: 4.0%: 30.0%;

[0079] The B layer contains the following components in percentage by mass: modified PET: PET: nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonyl semicarbazide = 1:5) = 60.0%: 28.5%: 3.5%: 5.0%: 3.0%.

[0080] (3) The ingredients are uniformly mixed in a planetary mixer for a mixing time of not less than 1 h. The mixing temperature is controlled at 60°C. The ingredients are fed into a twin-screw extruder for melting and plasticization. The screw diameter is selected to be 90 mm, the aspect ratio is 32, and the temperature is 245°C.

[0081] (4) The ingredients are extruded into the same die head by three extruders according to the ABA structure, and the die head temperature is 247 °C.

[0082] (5) When the melt is extruded into a cast sheet, the ratio of the linear speed of the quenching roller to the melt outflow speed is controlled to be less than or equal to 5, and the temperature of the quenching roller is controlled at 35℃±2℃.

[0083] (6) The cast sheet is longitudinally stretched by single-point stretching using infrared heating. The stretching conditions are as follows: preheating at 90°C and then stretching the sheet to a ratio of 1.5 times at 95°C. After longitudinal stretching, the sheet is cooled at 60°C to set the shape.

[0084] (7) The transverse stretching is performed by oil heating. The stretching conditions are as follows: preheating at 100°C, then stretching the film to a ratio of 5.0 at 85°C. After transverse stretching, the film is cooled and set at 80°C.

[0085] (8) pulling and rolling to obtain a crystalline and easily recyclable polyester heat shrinkable film, wherein the thickness ratio of layer A, layer B and layer A is 6:88:6.

[0086] Comparative Example 1

[0087] The core layer (layer B) in this comparative example contains the following components in percentage by mass: modified PET (YH101 from Henan Yuanhong Polymer New Materials Co., Ltd.): nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonylamino urea = 1:5) = 89.0%: 2.5%: 4.5%: 4.0%. The components of the other layers are the same as those in Example 1, and the preparation method is the same as that in Example 1.

[0088] Comparative Example 2

[0089] The core layer (layer B) in this comparative example contains the following components in percentage by mass: PET (FG600 of Sinopec Yizheng Chemical Fiber Co., Ltd.): nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonyl semicarbazide = 1:5) = 89.0%: 2.5%: 4.5%: 4.0%. The components of other layers are the same as those in Example 1, and the preparation method is consistent with that in Example 1.

[0090] Comparative Example 3

[0091] The core layer (layer B) in this comparative example contains the following components in percentage by mass: modified PET (YH101 from Henan Yuanhong Polymer New Materials Co., Ltd.): PET (FG600 from Sinopec Yizheng Chemical Fiber Co., Ltd.): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonylamino urea = 1:5) = 59.5%: 32.0%: 4.5%: 4.0%. The components of other layers are the same as those in Example 1, and the preparation method is the same as that in Example 1.

[0092] Comparative Example 4

[0093] The core layer (layer B) in this comparative example contains the following components in percentage by mass: modified PET (YH101 from Henan Yuanhong Polymer New Materials Co., Ltd.): PET (FG600 from Sinopec Yizheng Chemical Fiber Co., Ltd.): nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): foaming agent (barium azodicarboxylate: p-toluenesulfonylamino urea = 1:5) = 61.5%: 32.0%: 2.5%: 4.0%. The components of other layers are the same as those in Example 1, and the preparation method is the same as that in Example 1.

[0094] Comparative Example 5

[0095] The core layer (layer B) in this comparative example contains the following components in percentage by mass: modified PET (YH101 from Henan Yuanhong Polymer New Materials Co., Ltd.): PET (FG600 from Sinopec Yizheng Chemical Fiber Co., Ltd.): nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate) = 61.0%: 32.0%: 2.5%: 4.5%. The components of other layers are the same as those in Example 1, and the preparation method is the same as that in Example 1.

[0096] Comparative Example 6

[0097] The core layer (layer B) in this comparative example contains the following components in percentage by mass: modified PET (YH101 of Henan Yuanhong Polymer New Materials Co., Ltd.): PET (FG600 of Sinopec Yizheng Chemical Fiber Co., Ltd.): foaming agent (barium azodicarboxylate: p-toluenesulfonylamino urea = 1:5) = 64.0%: 32.0%: 4.0%. The components of other layers are the same as those in Example 1, and the preparation method is consistent with that in Example 1.

[0098] Comparative Example 7

[0099] The B layer contains the following components in percentage by mass: modified PET (YH101 from Henan Yuanhong Polymer New Materials Co., Ltd.): PET (FG600 from Sinopec Yizheng Chemical Fiber Co., Ltd.): nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonyl semicarbazide = 1:5) = 53.0%: 28.5%: 10.0%: 4.5%: 4.0%.

[0100] Comparative Example 8

[0101] The B layer contains the following components in percentage by mass: modified PET (YH101 from Henan Yuanhong Polymer New Materials Co., Ltd.): PET (FG600 from Sinopec Yizheng Chemical Fiber Co., Ltd.): nucleating agent (dibutyl sebacate: ammonium phosphate: sodium benzoate = 1:1:4): chain extender (glycidyl methacrylate): foaming agent (barium azodicarboxylate: p-toluenesulfonyl semicarbazide = 1:5) = 53.0%: 28.5%: 2.5%: 12.0%: 4.0%.

[0102] Comparative Example 9

[0103] The surface layer (A layer) comprises the following components by mass percentage: PETG (SK Chemical Company, South Korea S2012): Functional masterbatch (anti-blocking agent SiO2: lubricant erucamide = 1:1) = 97.8%: 3.2%. The other layer components are the same as in Example 1, and the preparation method is the same as in Example 1.

[0104] Comparative Example 10

[0105] The surface layer (layer A) comprises the following components by mass percentage: PETG (SKYGREEN, S2012): PET (Yizheng Chemical Fiber, FG600) = 76.8%: 23.2%. Other components and other layer components are the same as in Example 1, and the preparation method is the same as in Example 1.

[0106] Comparative Example 11

[0107] In this comparative example, the cast sheet was stretched transversely, and the stretching conditions were adjusted to: the stretching ratio was 4.0 times. The other layer components were the same as those in Example 1, and the preparation method was the same as that in Example 1.

[0108] Comparative Example 12

[0109] In this comparative example, the cast sheet was longitudinally stretched, and the stretching conditions were adjusted to: the stretching ratio was 1.0 times. The other layer components were the same as those in Example 1, and the preparation method was the same as that in Example 1.

[0110] The high-melting-point, easily recyclable PETG heat-shrinkable films prepared in Examples 1-5 and Comparative Examples 1-10 were tested for thickness, melting point, lumps, shrinkage, shrinkage force, haze, transparency, and wetting tension. Transparency and haze were measured according to the methods in GB / T 2410-2008; wetting tension and other parameters were measured according to the methods in GB / T 14216-2008 / 1S08296:2003. The lumps were tested according to the APR PET CG-02 Critical Guidance: The shrunken, crushed film was oven-dried at 160°C for 0.5 h. The dried, crushed film was then mixed with bottle flakes in a ratio of 1:3, then oven-baked at 210°C for 90 min. The film was considered passed if the mass of the material clumping with the bottle flakes did not exceed 1% of the total mass of the mixture. Otherwise, the film was considered failed. The results are shown in Table 1.

[0111] Table 1 Crystalline and easily recyclable PETG heat shrinkable film

[0112] As can be seen from Table 1, by comparing Examples 1 to 4 and Comparative Example 1, when more modified PET is used in the core layer, the overall shrinkage of the film is improved. However, insufficient PET content in the entire film will result in a lower melting point of the entire film, which cannot pass the agglomeration test and affects the recycling process.

[0113] Compared with Comparative Example 2, when the core layer is not added with modified PET, the core layer is mainly composed of PET, the film almost loses its shrinkage characteristics and its optical properties are significantly reduced.

[0114] Compared with Comparative Examples 3, 4 and 6, Example 1 shows that when no nucleating agent is added to the core layer, the pore structure generated by the foaming agent is uncontrollable, the haze of the film is significantly improved, and the crystallinity of the film is low without the action of the nucleating agent, resulting in failure of the agglomerate test and failure to meet the recycling requirements; when no chain extender is added to the core layer, the overall molecular weight and viscosity of the film cannot be improved, resulting in a low overall melting point of the film, which cannot pass the agglomerate test; when no nucleating agent and chain extender combination is added to the core layer, the film crystallinity is unqualified, the melting point is low, and the agglomerate test cannot be passed, the haze is large, and the recycling requirements cannot be met.

[0115] Compared with Comparative Example 5, in Example 1, when no foaming agent is added to the core layer, the film has no pore structure, will not expand during the stretching process, will not shrink after preheating, and due to the presence of a certain degree of crystallinity in the film, the overall shrinkage rate of the film is relatively low; since no foaming agent is added, the overall density of the film is high, and the corresponding film shrinkage force is large. During application, the film may shrink too quickly, resulting in deformation of the bottle body or shrinkage wrinkles, and the application range of the film is limited.

[0116] Compared with Comparative Example 7, Example 1 shows that when an excessive amount of nucleating agent is added to the core layer, the film crystallization speed is too fast, resulting in an excessively high degree of crystallization of the film, a more obvious increase in the haze of the film, and a significant decrease in the thermal shrinkage performance of the film, which seriously affects the packaging effect; and because the nucleating agent is relatively large, the degree of crystallization is high, and the speed is fast, the expansion of the bubbles formed by the foaming agent is affected, which affects the improvement of the thermal shrinkage performance of the film by the bubble structure.

[0117] Compared with Comparative Example 8, in Example 1, when an excessive amount of chain extender is added to the core layer, the polymer undergoes more crosslinking during melt extrusion, and the film elongation performance is greatly reduced during film production, resulting in the inability to stretch the film.

[0118] Compared with Comparative Example 9, when PET is not added to the surface layer, Example 1 has a lower melting point and crystallinity of the entire film, which may cause the film to fail the agglomeration test and may cause the film to form sticky blocks during the recycling process.

[0119] Compared with Example 10, when the functional masterbatch is not added to the surface layer, the surface friction of the film is too large, the winding is not smooth, the surface tension of the film is insufficient, and the wetting tension is unqualified, resulting in problems such as the film cannot be printed at the back end.

[0120] Compared with Comparative Examples 11 and 12, Example 1 shows that when the transverse stretching performed in the process used is insufficient, the overall shrinkage rate of the film will be low, making the film unable to be used under certain conditions with high shrinkage requirements; when the longitudinal stretching is not performed in the process used, due to the characteristics of the raw materials, the film will stretch after longitudinal preheating and shrinkage, affecting the terminal packaging effect.

[0121] 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 should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation on the present invention. In addition, the technical features involved in the various embodiments of the present invention described above can be combined with each other as long as they do not conflict with each other. In addition, the above are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this technical field without making creative work are within the scope of protection of the present invention.

Claims

1. A crystalline and easily recyclable polyester heat shrinkable film, characterized in that: The film layer structure of the heat shrinkable film is a three-layer porous structure of A / B / A; wherein the raw material of the A layer consists of polyethylene terephthalate copolymer (PETG), functional masterbatch and polyethylene terephthalate (PET); the raw material of the B layer consists of modified PET, PET, nucleating agent, chain extender and foaming agent, and the modified PET is neopentyl glycol (NPG) modified PET; wherein, by mass percentage, in the A layer, PETG: functional masterbatch: PET = 89.4-66.0%: 1.6-4.0%: 10.0-30.0%; in the B layer, 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 functional masterbatch is a compound of at least one of silicon dioxide, talc, clay or kaolin and at least one of oleamide or erucamide; The nucleating agent is composed of dibutyl sebacate, ammonium phosphate and sodium benzoate, and the ratio of dibutyl sebacate: ammonium phosphate: sodium benzoate is 1:1:4; The chain extender is glycidyl methacrylate; The foaming agent consists of barium azodicarboxylate and p-toluenesulfonyl semicarbazide, and the ratio of barium azodicarboxylate to p-toluenesulfonyl semicarbazide is 1:

5.

2. The method for preparing a crystalline and easily recyclable polyester heat shrinkable film according to claim 1, characterized in that: The steps include: (1) the raw materials of the A layer and the B layer are uniformly mixed in a planetary mixer according to a certain proportion and then dried, and melt-plasticized in corresponding extruders according to the mixing of the core layer and the surface layer; (2) Setting the three-layer structure of ABA, the melt is extruded through the same die head with a temperature of 240-270°C, and the cast sheet is cooled and formed on a quenching roller; (3) longitudinally stretching the cast sheet; (4) performing a transverse stretching operation; (5) pulling and rolling up to obtain the crystalline and easily recyclable polyester heat shrinkable film.

3. The method for preparing a crystalline and easily recyclable polyester heat shrinkable film according to claim 2, characterized in that: The stretching conditions of step (3) are: after preheating at 85-95°C, stretching the film at 80-110°C to a ratio of 1-2 times, and cooling and shaping the film at 50-80°C after longitudinal stretching.

4. The method for preparing a crystalline and easily recyclable polyester heat shrinkable film according to claim 3, characterized in that: The stretching conditions of step (4) are: after preheating at 90-110°C, the stretching ratio reaches 4.0-5.5 times at 80-95°C, and after transverse stretching, the film is cooled and set at 70-90°C.

5. The method for preparing a crystalline and easily recyclable polyester heat shrinkable film according to claim 4, characterized in that: The thickness of the crystalline easily recyclable polyester heat shrinkable film is 30-100 μm.

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