Low shrinkage petg composite heat shrink film

Abstract

The present application relates to the field of heat shrinkable film, in particular to a low shrinkage force PETG composite heat shrinkable film. The PETG composite heat shrinkable film comprises an upper surface layer, an inner core layer and a lower surface layer arranged in turn from top to bottom. The upper surface layer and the lower surface layer are both PETG films, and the inner core layer is a PETG / PBAT composite film. The PETG composite shrinkable film designed by the present application can maintain a low shrinkage stress while ensuring strength, and its thermal stability is enhanced, so that it can shrink more uniformly during interface shrinkage, thereby avoiding the phenomenon of local deformation or poor arc-shaped shrinkage.

Description

Technical Field

[0001] This invention relates to the field of heat shrink film, and more specifically to a low-shrinkage PETG composite heat shrink film. Background Technology

[0002] Heat shrink film refers to labels used to wrap around the outside of containers, including plastic bottles and glass bottles. Heat shrink film has good gloss, adhesion, and shrinkage properties. Because of its gloss and shrinkage, the packaging designs on containers are more vivid and stand out on supermarket shelves, creating an unexpected shelf effect, and is therefore widely used in container packaging.

[0003] The main materials used for heat shrink film in labeling include polyvinyl chloride (PVC), polyethylene terephthalate-1,4-cyclohexanediol (PETG), and oriented polystyrene (OPS). PVC heat shrink film has characteristics such as high tensile strength, high elongation, good self-adhesion, and high transparency, but it also has the drawback of easily generating highly toxic dioxins during recycling and poor environmental performance, leading to its gradual ban. OPS heat shrink film has characteristics such as high strength, high rigidity, shape stability, good gloss and transparency, and is easy to process, easy to color, has good printability, and extremely high printing resolution, but it is more expensive and requires special ink solvents. PETG heat shrink film has characteristics such as being non-toxic, odorless, high strength, high heat shrinkage rate, good optical properties, mechanical elongation, and aesthetically pleasing packaging effects, leading to the rapid growth in the use of OPS and PETG heat shrink films.

[0004] Currently, the requirements for PETG composite heat shrink film on the market usually focus on how to balance shrinkage stress and shrinkage force. Introducing fillers such as nano silica or talc can disperse shrinkage stress, but adding too much will cause a significant decrease in strength and heat shrinkage rate. In addition, due to the large amount of additives added, it is easy to cause local deformation or arc-shaped poor shrinkage when the interface shrinks. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a low-shrinkage PETG composite heat-shrink film.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a low-shrinkage PETG composite heat shrink film, comprising an upper surface layer, an inner core layer and a lower surface layer arranged sequentially from top to bottom; the upper surface layer and the lower surface layer are both PETG films, and the inner core layer is a PETG / PBAT composite film.

[0008] The PETG / PBAT composite film, by weight, includes the following components:

[0009] 60-80 parts PETG resin, 20-40 parts PBAT resin, 1-3 parts plasticizer and 0.2-0.6 parts chain extender.

[0010] The PETG film, by weight, comprises the following components:

[0011] 100 parts PETG resin, 3-7 parts anti-blocking agent, 2-6 parts lubricant, 1-2 parts antioxidant and 0.5-1 part light stabilizer.

[0012] Preferably, the thickness ratio of the upper surface layer, the inner core layer, and the lower surface layer is 1-3:6:1-3.

[0013] Preferably, the density of the PETG resin is 1.22-1.31 g / cm³. 3 More preferably, it is 1.27 g / cm³. 3 Melt index is 8-12 g / 10 min (230℃, 2.16 kg).

[0014] Preferably, the density of the PBAT resin is 1.18-1.22 g / cm³. 3 The melt index is 2-5 g / 10 min (190℃, 2.16 kg).

[0015] Preferably, the plasticizer is one or more of epoxidized soybean oil, epoxidized linseed oil, tributyl citrate, and acetylated tributyl citrate.

[0016] Preferably, the chain extender is phthalic anhydride and 2,2'-bis(2-oxazoline) in a mass ratio of 1.1-1.5:1.

[0017] Preferably, the anti-blocking agent is modified nano-silica, and the preparation method includes:

[0018] S1. Surface treatment:

[0019] Weigh out nano-silica powder, coupling agent KH-550 and ethanol solution, mix them, heat to 60-80℃, reflux for 2-6 hours, filter and dry to obtain aminated nano-silica;

[0020] S2, Activation Reaction:

[0021] Weigh out tris(2-carboxyethyl) isocyanurate and add it to dichloromethane. After stirring evenly in an ice-water bath, nitrogen gas is introduced as a protective gas, N,N'-dicyclohexylcarbodiimide (DCC) is added, and the mixture is stirred for 0.5-1 h. Then, the temperature is raised to room temperature, and N-hydroxysuccinimide (NHS) is added and stirred for 1-2 h to obtain the activated reaction solution.

[0022] S3, Modification reaction:

[0023] Aminated nano-silica was added to the activation reaction solution and stirred for 5-10 hours under the protection of nitrogen at room temperature. After the reaction was completed, the solvent was removed under reduced pressure, washed with water 2-3 times, and dried to obtain modified nano-silica.

[0024] Preferably, in the preparation process of the aminated nano silica, the particle size of the nano silica is 50±10nm, the mass fraction of the ethanol solution is 30-60wt%, and the mass ratio of silica nanopowder, coupling agent KH-550 and ethanol solution is 1:0.1-0.3:5-10.

[0025] Preferably, in the preparation process of the modified nano-silica, the mass ratio of aminated nano-silica, tris(2-carboxyethyl)isocyanurate, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide and dichloromethane is 1:0.25-0.45:0.5-0.8:0.76-0.98:5-10.

[0026] Preferably, the lubricant is one or a mixture of zinc stearate, calcium stearate, polyethylene wax, and paraffin wax.

[0027] Preferably, the antioxidant is obtained by mixing a primary antioxidant and a secondary antioxidant at a mass ratio of 1:1.2-3.6; wherein the primary antioxidant is one of antioxidant 1010, antioxidant 1076, and antioxidant 1098; and the secondary antioxidant is antioxidant 168. More preferably, the primary antioxidant is antioxidant 1010, and the secondary antioxidant is antioxidant 168.

[0028] Preferably, the light stabilizer is one or a mixture of UV-622, UV-770, UV-944, UV-326, UV-328, and UV-1577. More preferably, it is UV-622.

[0029] Secondly, the present invention provides a method for preparing a low-shrinkage PETG composite heat-shrink film, comprising the following steps:

[0030] Step 1: Weigh the raw materials for the upper surface layer, lower surface layer and inner core layer respectively, and dry them in an oven at 70-80℃ until constant weight;

[0031] Step 2: After mixing the raw materials of each layer separately, they are fed into different twin-screw extruders and melt-granulated in a temperature range of 250-290℃ to obtain upper surface masterbatch, lower surface masterbatch and inner core masterbatch respectively.

[0032] Step 3: The three materials obtained in Step 2 are added to three extruders and then cast into sheets after being compounded by a die. The sheets are first subjected to biaxial stretching and then rapidly cooled and shaped to obtain a low-shrinkage PETG composite heat shrink film.

[0033] Preferably, in step 3, the extrusion molding temperature is: 200-240℃ for the upper surface layer, 240-260℃ for the inner core layer, and 200-240℃ for the lower surface layer.

[0034] Preferably, in step 3, the biaxial stretching process includes longitudinal stretching (MDO) and transverse stretching (TDO); wherein, the stretching temperature of longitudinal stretching is 85-90℃ and the stretching ratio is 1.5-3 times; the stretching temperature of transverse stretching is 105-110℃ and the stretching ratio is 3-4.5 times; and the rapid cooling and setting temperature is 35-50℃.

[0035] Preferably, in step 3, the thickness of the obtained antistatic PETG heat shrink film is 40-60 μm.

[0036] The beneficial effects of this invention are as follows:

[0037] 1. This invention prepares a PETG composite heat-shrinkable film, comprising upper and lower surface layers and a middle inner core layer. The upper and lower surface layers are composed of the same PETG film, while the inner core layer is a PETG / PBAT composite film. The PETG composite shrinkable film designed by this invention can maintain low shrinkage stress while ensuring strength, and enhances its thermal stability, enabling more uniform body shrinkage during interfacial shrinkage, thereby avoiding local deformation or poor arc-shaped shrinkage.

[0038] 2. This invention designs the composition of all three layers of the PETG composite heat shrink film. In addition to PETG resin, the inner core layer also contains PBAT resin, plasticizer, and chain extender to enhance the heat resistance and strength of the film. The upper and lower surface layers contain anti-blocking agents and additives based on PETG resin. The anti-blocking agent enhances the melt flow, mechanical properties, and thermal stability of the film, and also makes the thermal conductivity of the shrink film more uniform, reducing uneven shrinkage caused by local overheating, ultimately making the shrinkage of the composite film more uniform and balanced.

[0039] 3. The anti-blocking agent added to the upper and lower surface films in this invention is modified nano-silica, obtained through surface modification treatment of nano-sized silica. Specifically, the surface of silica is first aminated, and then amidated with tris(2-carboxyethyl) isocyanurate through a DCC / NHS system to obtain a core-shell structure containing amide groups and isocyanurate coated with organic matter. The modified nano-silica, as an anti-blocking agent, has significantly enhanced compatibility with PETG resin, resulting in better performance of PETG film strength, thermal stability, and shrinkage balance. Detailed Implementation

[0040] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0041] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0042] The present invention will be further described below with reference to the following embodiments.

[0043] Example 1

[0044] A low-shrinkage PETG composite heat shrink film includes an upper surface layer, an inner core layer, and a lower surface layer arranged sequentially from top to bottom; wherein the thickness ratio of the upper surface layer, the inner core layer, and the lower surface layer is 2:6:2.

[0045] The inner core layer is a PETG / PBAT composite film. The PETG / PBAT composite film, by weight, includes the following components:

[0046] 70 parts PETG resin, 30 parts PBAT resin, 2 parts plasticizer and 0.4 parts chain extender.

[0047] The density of PETG resin is 1.27 g / cm³. 3The melt flow index is 10 g / 10 min (230℃, 2.16 kg); the density of PBAT resin is 1.2 g / cm³. 3 The melt index is 3.2 g / 10 min (300℃, 1.2 kg); the plasticizer is epoxidized soybean oil; the chain extender is phthalic anhydride and 2,2'-bis(2-oxazoline) in a mass ratio of 1.3:1.

[0048] Both the upper and lower surfaces are made of PETG film. The PETG film, by weight, comprises the following components:

[0049] 100 parts PETG resin, 5 parts anti-blocking agent, 4 parts lubricant, 1 part antioxidant and 0.6 parts light stabilizer.

[0050] The density of PETG resin is 1.27 g / cm³. 3 The melt index is 10 g / 10 min (230℃, 2.16 kg); the lubricant is zinc stearate; the antioxidant is obtained by mixing antioxidant 1010 and antioxidant 168 at a mass ratio of 1:2.4; the light stabilizer is UV-622.

[0051] The anti-blocking agent is modified nano-silica, and its preparation method includes:

[0052] S1. Weigh 1g of 50±10nm nano silica powder, 0.2g of coupling agent KH-550 and 10g of 40wt% ethanol solution, mix them, heat to 70℃, reflux for 4h, filter and dry to obtain aminated nano silica.

[0053] S2. Weigh 0.35g of tris(2-carboxyethyl)isocyanurate and add it to 10g of dichloromethane. Stir well under an ice-water bath, then introduce nitrogen as a protective gas, add 0.5-0.8g of N,N'-dicyclohexylcarbodiimide (DCC), stir for 1h, then heat to room temperature, add 0.87g of N-hydroxysuccinimide (NHS), and stir for 1.5h to obtain the activated reaction solution.

[0054] S3. Add 1g of aminated nano-silica to the activation reaction solution, stir for 8 hours under the protection of nitrogen at room temperature. After the reaction is completed, remove the solvent under reduced pressure, wash with water 3 times, and dry to obtain modified nano-silica.

[0055] The preparation method of the above-mentioned low-shrinkage PETG composite heat-shrink film includes the following steps:

[0056] Step 1: Weigh the raw materials for the upper surface layer, lower surface layer and inner core layer respectively, and dry them in a 75℃ oven until constant weight;

[0057] Step 2: After mixing the raw materials of each layer separately, they are fed into different twin-screw extruders and melt-granulated in a temperature range of 250-290℃ to obtain upper surface masterbatch, lower surface masterbatch and inner core masterbatch respectively.

[0058] Step 3: Pour the three masterbatches obtained in Step 2 into a three-layer co-extrusion blown film machine and press and extrude them in sequence. The extrusion temperatures are: 220℃ for the upper surface layer, 250℃ for the inner core layer, and 220℃ for the lower surface layer. After that, the film undergoes biaxial stretching treatment. The longitudinal stretching temperature is 90℃ with a stretching ratio of 2.5 times, and the transverse stretching temperature is 110℃ with a stretching ratio of 4 times. Then, it is rapidly cooled to 45℃ for setting to obtain a low-shrinkage PETG composite heat-shrinkable film with a thickness of 50μm.

[0059] Example 2

[0060] A low-shrinkage PETG composite heat shrink film includes an upper surface layer, an inner core layer, and a lower surface layer arranged sequentially from top to bottom; wherein the thickness ratio of the upper surface layer, the inner core layer, and the lower surface layer is 1:6:1.

[0061] The inner core layer is a PETG / PBAT composite film. The PETG / PBAT composite film, by weight, includes the following components:

[0062] 60 parts PETG resin, 20 parts PBAT resin, 1 part plasticizer and 0.2 parts chain extender.

[0063] The density of PETG resin is 1.27 g / cm³. 3 The melt flow index is 10 g / 10 min (230℃, 2.16 kg); the density of PBAT resin is 1.2 g / cm³. 3 The melt index is 3.2 g / 10 min (300℃, 1.2 kg); the plasticizer is epoxidized linseed oil; the chain extender is phthalic anhydride and 2,2'-bis(2-oxazoline) in a mass ratio of 1.1:1.

[0064] Both the upper and lower surfaces are made of PETG film. The PETG film, by weight, comprises the following components:

[0065] 100 parts PETG resin, 3 parts anti-blocking agent, 2 parts lubricant, 1 part antioxidant and 0.5 parts light stabilizer.

[0066] The density of PETG resin is 1.27 g / cm³. 3 The melt index is 10 g / 10 min (230℃, 2.16 kg); the lubricant is calcium stearate; the antioxidant is obtained by mixing antioxidant 1076 and antioxidant 168 in a mass ratio of 1:1; the light stabilizer is UV-770.

[0067] The anti-blocking agent is modified nano-silica, and its preparation method includes:

[0068] S1. Weigh 1g of 50±10nm nano silica powder, 0.1g of coupling agent KH-550 and 5g of 30wt% ethanol solution, mix them, heat to 60℃, reflux for 2h, filter and dry to obtain aminated nano silica.

[0069] S2. Weigh 0.25g of tris(2-carboxyethyl)isocyanurate and add it to 5g of dichloromethane. Stir well under an ice-water bath, then introduce nitrogen as a protective gas, add 0.5g of N,N'-dicyclohexylcarbodiimide (DCC), stir for 0.5h, then heat to room temperature, add 0.76g of N-hydroxysuccinimide (NHS), and stir for 1h to obtain the activated reaction solution.

[0070] S3. Add 1g of aminated nano-silica to the activation reaction solution, stir for 5h under the protection of nitrogen at room temperature. After the reaction is completed, remove the solvent under reduced pressure, wash twice with water, and dry to obtain modified nano-silica.

[0071] The preparation method of the above-mentioned low-shrinkage PETG composite heat-shrink film includes the following steps:

[0072] Step 1: Weigh the raw materials for the upper surface layer, lower surface layer and inner core layer respectively, and dry them in a 70℃ oven until constant weight;

[0073] Step 2: After mixing the raw materials of each layer separately, they are fed into different twin-screw extruders and melt-granulated in a temperature range of 250-290℃ to obtain upper surface masterbatch, lower surface masterbatch and inner core masterbatch respectively.

[0074] Step 3: Pour the three masterbatches obtained in Step 2 into a three-layer co-extrusion blown film machine and press and extrude them in sequence. The extrusion temperatures are: 200℃ for the upper surface layer, 240℃ for the inner core layer, and 200℃ for the lower surface layer. After that, the film undergoes biaxial stretching treatment. The longitudinal stretching temperature is 85℃ with a stretching ratio of 1.5 times, and the transverse stretching temperature is 105℃ with a stretching ratio of 3 times. Then, the film is rapidly cooled to 35℃ for setting, resulting in a low-shrinkage PETG composite heat-shrinkable film with a thickness of 40μm.

[0075] Example 3

[0076] A low-shrinkage PETG composite heat shrink film includes an upper surface layer, an inner core layer, and a lower surface layer arranged sequentially from top to bottom; wherein the thickness ratio of the upper surface layer, the inner core layer, and the lower surface layer is 3:6:3;

[0077] The inner core layer is a PETG / PBAT composite film. The PETG / PBAT composite film, by weight, includes the following components:

[0078] 80 parts PETG resin, 40 parts PBAT resin, 3 parts plasticizer and 0.6 parts chain extender.

[0079] The density of PETG resin is 1.27 g / cm³. 3 The melt flow index is 10 g / 10 min (230℃, 2.16 kg); the density of PBAT resin is 1.2 g / cm³. 3 The melt index is 3.2 g / 10 min (300℃, 1.2 kg); the plasticizer is tributyl citrate; the chain extender is phthalic anhydride and 2,2'-bis(2-oxazoline) in a mass ratio of 1.5:1.

[0080] Both the upper and lower surfaces are made of PETG film. The PETG film, by weight, comprises the following components:

[0081] 100 parts PETG resin, 7 parts anti-blocking agent, 6 parts lubricant, 2 parts antioxidant and 1 part light stabilizer.

[0082] The density of PETG resin is 1.27 g / cm³. 3 The melt index is 10 g / 10 min (230℃, 2.16 kg); the lubricant is polyethylene wax; the antioxidant is obtained by mixing antioxidant 1098 and antioxidant 168 at a mass ratio of 1:3.6; the light stabilizer is UV-326.

[0083] The anti-blocking agent is modified nano-silica, and its preparation method includes:

[0084] S1. Weigh 1g of 50±10nm nano silica powder, 0.3g of coupling agent KH-550 and 10g of 60wt% ethanol solution, mix them, heat to 80℃, reflux for 6h, filter and dry to obtain aminated nano silica.

[0085] S2. Weigh 0.45g of tris(2-carboxyethyl)isocyanurate and add it to 10g of dichloromethane. Stir well under an ice-water bath, then introduce nitrogen as a protective gas, add 0.8g of N,N'-dicyclohexylcarbodiimide (DCC), stir for 1h, then heat to room temperature, add 0.98g of N-hydroxysuccinimide (NHS), stir for 2h to obtain the activated reaction solution;

[0086] S3. Add 1g of aminated nano-silica to the activation reaction solution, stir for 10h under the protection of nitrogen at room temperature. After the reaction is completed, remove the solvent under reduced pressure, wash with water 3 times, and dry to obtain modified nano-silica.

[0087] The preparation method of the above-mentioned low-shrinkage PETG composite heat-shrink film includes the following steps:

[0088] Step 1: Weigh the raw materials for the upper surface layer, lower surface layer and inner core layer respectively, and dry them in an 80℃ oven until constant weight;

[0089] Step 2: After mixing the raw materials of each layer separately, they are fed into different twin-screw extruders and melt-granulated in a temperature range of 250-290℃ to obtain upper surface masterbatch, lower surface masterbatch and inner core masterbatch respectively.

[0090] Step 3: Pour the three masterbatches obtained in Step 2 into a three-layer co-extrusion blown film machine and press and extrude them in sequence. The extrusion temperatures are: 240℃ for the upper surface layer, 260℃ for the inner core layer, and 240℃ for the lower surface layer. After that, the film undergoes biaxial stretching treatment. The longitudinal stretching temperature is 90℃ with a stretching ratio of 3 times, and the transverse stretching temperature is 110℃ with a stretching ratio of 4.5 times. Then, the film is rapidly cooled to 50℃ for setting, resulting in a low-shrinkage PETG composite heat-shrinkable film with a thickness of 60μm.

[0091] Comparative Example 1

[0092] A PETG composite heat-shrinkable film differs from Example 1 in that the composition of the upper and lower PETG film layers is different, with the anti-blocking agent replaced by nano-silica powder. The PETG film, by weight, comprises the following components:

[0093] 100 parts PETG resin, 5 parts nano silica powder, 4 parts lubricant, 1 part antioxidant and 0.6 parts light stabilizer.

[0094] Comparative Example 2

[0095] A PETG composite heat-shrinkable film differs from Example 1 in that the composition of the upper and lower PETG film layers is different, and the anti-blocking agent is replaced with aminated nano-silica. The preparation process of the aminated nano-silica is the same as in Example 1. The PETG film, by weight, comprises the following components:

[0096] 100 parts PETG resin, 5 parts aminated nano silica, 4 parts lubricant, 1 part antioxidant and 0.6 parts light stabilizer.

[0097] Comparative Example 3

[0098] A PETG composite heat-shrinkable film differs from Example 1 in that the upper and lower PETG film compositions are different. The anti-blocking agent is replaced with a mixture of nano-silica and tris(2-carboxyethyl) isocyanurate, with a mass ratio of nano-silica to tris(2-carboxyethyl) isocyanurate of 1:0.35. The PETG film comprises the following components by weight:

[0099] 100 parts PETG resin, 3.7 parts nano silica, 1.3 parts tris(2-carboxyethyl) isocyanurate, 4 parts lubricant, 1 part antioxidant and 0.6 parts light stabilizer.

[0100] Experimental testing

[0101] The heat shrinkage rate, strength, and heat resistance of the PETG composite heat shrink films prepared in Example 1 and Comparative Examples 1-3 were tested.

[0102] The tensile strength and elongation at break are tested according to the standard ASTM D638 (tensile speed 50 mm / min).

[0103] The test of heat shrinkage rate and shrinkage stress is based on the standard ISO 14616 (hot air treatment at 110°C for 20 seconds).

[0104] The Vicat heat resistance temperature is tested according to the standard ISO 306:2013 (heating rate of 50℃ / h).

[0105] The test results are shown in Table 1 below:

[0106] Table 1. Test results of PETG composite heat shrink film

[0107]

[0108] As can be seen from Table 1 above, the PETG composite heat shrink film prepared in Example 1 has higher transverse tensile strength and heat shrinkage rate than the comparative example, indicating that it has high mechanical strength and can perfectly fit complex contours; while the shrinkage stress is the smallest, indicating that it has better shrinkage balance, reducing stress while maintaining a high shrinkage rate, achieving more uniform shrinkage, and avoiding label wrinkles or cracks caused by local stress concentration.

[0109] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0110] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A low-shrinkage PETG composite heat-shrink film, characterized in that, It includes an upper surface layer, an inner core layer, and a lower surface layer arranged from top to bottom; the upper and lower surface layers are both PETG films, and the inner core layer is a PETG / PBAT composite film. The PETG / PBAT composite film, by weight, includes the following components: 60-80 parts PETG resin, 20-40 parts PBAT resin, 1-3 parts plasticizer and 0.2-0.6 parts chain extender; The PETG film, by weight, comprises the following components: 100 parts PETG resin, 3-7 parts anti-blocking agent, 2-6 parts lubricant, 1-2 parts antioxidant and 0.5-1 part light stabilizer; The anti-blocking agent is modified nano-silica, and its preparation method includes: S1. Weigh out nano-silica powder, coupling agent KH-550 and ethanol solution, mix them, heat to 60-80℃, reflux for 2-6 hours, filter and dry to obtain aminated nano-silica. S2. Weigh tris(2-carboxyethyl)isocyanurate and add it to dichloromethane. Stir evenly under an ice-water bath, then introduce nitrogen as a protective gas, add N,N'-dicyclohexylcarbodiimide, stir for 0.5-1 h, then heat to room temperature, add N-hydroxysuccinimide, stir for 1-2 h to obtain the activated reaction solution. S3. Add the aminated nano-silica to the activation reaction solution and stir for 5-10 hours under the protection of nitrogen at room temperature. After the reaction is completed, remove the solvent under reduced pressure, wash with water 2-3 times, and dry to obtain modified nano-silica.

2. The low-shrinkage PETG composite heat-shrink film according to claim 1, characterized in that, The thickness ratio of the upper surface layer, the inner core layer, and the lower surface layer is 1-3:6:1-3.

3. The low-shrinkage PETG composite heat-shrink film according to claim 1, characterized in that, The plasticizer is one or more of epoxidized soybean oil, epoxidized linseed oil, tributyl citrate, and acetylated tributyl citrate; the lubricant is one or more of zinc stearate, calcium stearate, polyethylene wax, and paraffin wax.

4. The low-shrinkage PETG composite heat-shrink film according to claim 1, characterized in that, The chain extender is phthalic anhydride and 2,2'-bis(2-oxazoline) in a mass ratio of 1.1-1.5:

1.

5. The low-shrinkage PETG composite heat-shrink film according to claim 1, characterized in that, In the preparation process of the aminated nano silica, the particle size of the nano silica is 50±10nm, the mass fraction of the ethanol solution is 30-60wt%, and the mass ratio of silica nanopowder, coupling agent KH-550 and ethanol solution is 1:0.1-0.3:5-10.

6. The low-shrinkage PETG composite heat-shrink film according to claim 1, characterized in that, In the preparation of the modified nano-silica, the mass ratio of aminated nano-silica, tris(2-carboxyethyl)isocyanurate, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide and dichloromethane is 1:0.25-0.45:0.5-0.8:0.76-0.98:5-10.

7. The low-shrinkage PETG composite heat-shrink film according to claim 1, characterized in that, The antioxidant is obtained by mixing a primary antioxidant and a secondary antioxidant at a mass ratio of 1:1.2-3.6; wherein the primary antioxidant is one of antioxidant 1010, antioxidant 1076, and antioxidant 1098; and the secondary antioxidant is antioxidant 168.

8. The low-shrinkage PETG composite heat-shrink film according to claim 1, characterized in that, The light stabilizer is one or a mixture of UV-622, UV-770, UV-944, UV-326, UV-328, and UV-1577.

9. A method for preparing the low-shrinkage PETG composite heat-shrink film according to claim 1, characterized in that, Includes the following steps: Step 1: Weigh the raw materials for the upper surface layer, lower surface layer and inner core layer respectively, and dry them in an oven at 70-80℃ until constant weight; Step 2: After mixing the raw materials of each layer separately, they are fed into different twin-screw extruders and melt-granulated in a temperature range of 250-290℃ to obtain upper surface masterbatch, lower surface masterbatch and inner core masterbatch respectively. Step 3: The three materials obtained in Step 2 are added to three extruders and then cast into sheets after being compounded by a die. The sheets are first subjected to biaxial stretching and then rapidly cooled and shaped to obtain a low-shrinkage PETG composite heat shrink film.

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