Black and white PETG shrink film and preparation method thereof

Abstract

The invention discloses a black and white PETG shrink film which comprises five layers of co-extrusion composite structures, the five layers of co-extrusion composite structures are a buffer layer D located in the middle, a white layer B close to the outer side of the buffer layer D, a black layer C close to the inner side of the buffer layer D, a printing layer A on the outer side of the white layer B, and a self-repairing layer E on the inner side of the black layer C. In addition, the invention also discloses a preparation method of the black and white PETG shrink film. According to the black and white PETG shrink film with the five-layer co-extrusion composite structure, through the interlayer synergistic effect, the problems of microcrack propagation and barrier attenuation of a traditional PETG shrink film are solved by utilizing the elastomer structure of the D layer to dissipate stress and the self-repairing and forced closing of microcracks of the E layer, and the isolation service life of the film is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of shrink film, in particular to a black and white PETG shrink film and a preparation method thereof. BACKGROUND

[0002] Black and white shrink film is commonly used in the packaging industry. Black and white shrink film can be used for packaging some light-sensitive products, such as certain spices in food and certain active ingredients in medicine, which may cause the product to deteriorate, decompose or reduce the drug effect. The black layer of the black and white shrink film can effectively block light and protect the quality and stability of the product. The white part provides good contrast, making it easy to print marks. The white and black background form a sharp contrast, making the printed text, patterns, trademarks or barcodes more clear and identifiable. This is very important for product identification, inventory management and consumer access to product information. In addition, black and white shrink film may be more easily in line with some environmental regulations due to the fewer types of pigments.

[0003] CN 113211921 A discloses a PETG black and white composite film with light shielding performance, which adopts A-B-C structure, wherein the A layer is a printing layer, the B layer is a white structure layer, and the C layer is a black structure layer. However, the white layer and the black layer of the existing black and white shrink film differ in additives, causing the interface region between the layers to form micro-crack channels during shrinkage due to disordered crystallization. Such microscopic cracks can cause a sharp decline in the barrier property of the shrink film. According to actual measurement, the water and oxygen barrier rate of the outer packaging black and white shrink film of the deteriorated product is less than 30% of the factory test value, the micro-detection grain boundary becomes the preferred path for water and oxygen penetration, and the difference rate of the transverse tensile strength and the longitudinal tensile strength of the black and white shrink film with grain boundary cracks exceeds 50%, and the shrinkage rate fluctuation also exceeds 10%, which seriously affects the packaging tightness. However, the existing black and white shrink film pays little attention to such interfacial micro-cracks, and lacks corresponding preventive measures. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a black and white PETG shrink film to reduce or avoid the problems mentioned above.

[0005] To solve the above technical problems, the present application provides a black and white PETG shrink film, which comprises a five-layer co-extrusion composite structure, the five-layer co-extrusion composite structure comprises a buffer layer D located in the middle, a white layer B located on the outer side of the buffer layer D, a black layer C located on the inner side of the buffer layer D, a printing layer A located on the outer side of the white layer B, and a self-repairing layer E located on the inner side of the black layer C.

[0006] Preferably, the thickness of the printing layer A accounts for 10-15% of the total thickness, the thickness of the white layer B accounts for 15-20% of the total thickness, the thickness of the black layer C accounts for 25-30% of the total thickness, the thickness of the buffer layer D accounts for 20-25% of the total thickness, and the remaining thickness is the self-repairing layer E.

[0007] Preferably, the buffer layer D is composed of the following components in weight parts: 85-88 parts by weight of PETG chips, 8-10 parts by weight of hydrogenated SEBS elastomer, 2-3 parts by weight of siloxane coupling agent, and 1-2 parts by weight of nano calcium carbonate.

[0008] Preferably, the self-repairing layer E is composed of the following components in weight parts: 65-70 parts by weight of PETG chips, 15-18 parts by weight of EVOH, 8-12 parts by weight of DCPD repair agent, 2-3 parts by weight of catalyst, and 3-5 parts by weight of nano montmorillonite.

[0009] The application also provides a preparation method of the black-and-white PETG shrink film, which comprises the following steps: first, drying PETG chips in a vacuum drying box at 80℃ for 4 hours; weighing and packaging the dried PETG chips as a PETG base material; setting five independent extruders and a multi-layer co-extrusion die at the end of the five independent extruders; mixing the materials other than PETG that constitute the printing layer A, the white layer B, the buffer layer D, the black layer C, and the self-repairing layer E in proportion with the PETG base material respectively and feeding them into the corresponding extruders; inputting the melts of the materials of each layer into the multi-layer co-extrusion die through the five independent extruders, extruding a thick sheet from the die, and rapidly cooling the extruded thick sheet in a cooling water tank; then, bidirectionally stretching the thick sheet; finally, heat setting the thick sheet in a hot air circulating oven; and cooling and cutting the set thick sheet for winding.

[0010] Preferably, the temperature for rapid cooling in the cooling water tank is 12℃.

[0011] Preferably, in the bidirectional stretching step, the thick sheet is first preheated at 85℃ for 15 seconds, then stretched horizontally at 100℃ with a stretching ratio of 3.5:1, and then stretched vertically at 95℃ with a stretching ratio of 2.8:1.

[0012] Preferably, the heat setting temperature is 70℃, and the setting time is 30 seconds.

[0013] The five-layer co-extrusion composite structure black-and-white PETG shrink film of the application solves the problems of micro-crack propagation and barrier decay of traditional PETG shrink films through the synergistic effect of the layers, the stress dissipation of the D layer elastomer structure, and the self-repairing and forced closing of micro-cracks of the E layer, thereby improving the barrier life of the film. BRIEF DESCRIPTION OF DRAWINGS

[0014] The following drawings are only intended to illustrate and explain the application and do not limit the scope of the application.

[0015] Figure 1 The diagram shown is a structural schematic of a black and white PETG shrink film according to a specific embodiment of the present invention. Detailed Implementation

[0016] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0017] To address the microcrack problem at the interlayer interface of black and white shrink films caused by differences in raw material crystallization kinetics, this invention proposes a black and white PETG shrink film, such as... Figure 1 As shown, the black and white PETG shrink film proposed in this invention comprises a five-layer co-extruded composite structure. This five-layer co-extruded composite structure consists of a buffer layer D in the middle, a white layer B on the outer side immediately adjacent to the buffer layer D, a black layer C on the inner side, a printing layer A on the outer side of the white layer B, and a self-healing layer E on the inner side of the black layer C. The significant difference between the black and white PETG shrink film of this invention and the black and white composite films mentioned in the background art is that this invention inserts a buffer layer D between the white layer B and the black layer C, and a self-healing layer E is disposed on the inner side of the black layer C. The main function of the newly added buffer layer D is to reduce stress concentration, inhibit the propagation of microcracks, and improve interlayer bonding. The main function of the self-healing layer E is to provide self-repair for cracks while enhancing barrier properties. This will be further explained in detail later.

[0018] The printing layer A, white layer B, and black layer C can use the same components as in existing technologies, and their functions and effects are also the same. Of course, considering that the structure has changed from three layers to five layers, the thickness of each layer has been adjusted accordingly. In a preferred embodiment, the thickness of the printing layer A accounts for 10-15% of the total thickness, the thickness of the white layer B accounts for 15-20%, the thickness of the black layer C accounts for 25-30%, the thickness of the buffer layer D accounts for 20-25%, and the remaining thickness is the self-healing layer E. In another specific embodiment, the total thickness of the black and white PETG shrink film of the present invention is preferably 50-150 μm. The thickness of each layer of the black and white PETG shrink film of the present invention has been optimized compared to existing technologies. The thickness percentage of the white layer B is significantly reduced, the thickness percentage of the black layer C is slightly increased, the buffer layer D compensates for the reduced reflectivity of the white layer B, and the self-healing layer E significantly improves the barrier properties of the black layer C.

[0019] Since the printed layer A, white layer B, and black layer C can use the same components as existing technologies, the newly added buffer layer D and self-healing layer E will be described in detail below.

[0020] In one specific embodiment, the buffer layer D can be composed of the following components by weight: 85-88 parts by weight of PETG chips, 8-10 parts by weight of hydrogenated SEBS elastomer, 2-3 parts by weight of siloxane coupling agent, 1-2 parts by weight of nano calcium carbonate (particle size 200-300 nm).

[0021] Wherein, the hydrogenated SEBS elastomer is preferably replaced by YH-688 of Balin Petrochemical, or G1645 of Kraton, USA. The SEBS elastomer is used to improve the interlayer peeling force and control the elastic modulus gradient of the shrink film. The siloxane coupling agent can be a conventional polydimethylsiloxane coupling agent, or vinyltriethoxysilane, vinyltrimethoxysilane, etc., which is used to form a thioether bond (C-S-C) and an ether bond (C-O-C) at the interface between the D layer and the B / C layer, to improve the interlayer peeling force and block the crack propagation path along the interface. The nano calcium carbonate acts as a heterogeneous nucleating agent to regulate the crystallization rate of PETG and reduce the shrinkage anisotropy.

[0022] In another specific embodiment, the self-repairing layer E can be composed of the following components by weight: 65-70 parts by weight of PETG chips, 15-18 parts by weight of EVOH, 8-12 parts by weight of DCPD repair agent, 2-3 parts by weight of catalyst, 3-5 parts by weight of nano montmorillonite (100-200 nm).

[0023] Wherein, the EVOH is ethylene-vinyl alcohol copolymer, which can be EVAL H173B of Kuraray, Japan, or FP104B of Soarnol, Japan, etc., which is used to generate reverse shrinkage stress when the film shrinks at high temperature, forcing the micro-cracks to close and reducing the oxygen transmission rate. The DCPD repair agent is a self-repairing material based on dicyclopentadiene (DCPD), which can be DCPD hydrogenated resin of Hengda New Materials or Huarun Chemical, etc., which is used to achieve self-repairing effect by ring-opening polymerization after contacting with the catalyst when the crack propagates. The catalyst preferably adopts Grubbs metal organic catalyst (1,3-bis(2,4,6-trimethylphenyl)-2-(imidazolidine-ylidene)(dichlorobenzylidene)(tricyclohexylphosphine)ruthenium (CAS No.: 246047-72-3)), such as Grubbs second-generation catalyst of Merck, Germany, or Grubbs catalyst of Aladdin, USA, or Grubbs second-generation catalyst of Shanghai Jizishenghua, etc. The nano montmorillonite can be used to block the oxygen and water vapor permeation path.

[0024] The black and white PETG shrink film with five-layer co-extrusion composite structure of the present application solves the problems of micro-crack propagation and barrier decay of traditional PETG shrink film by interlayer synergistic effect, dissipates stress by using the elastomer structure of D layer, and forces the micro-cracks to close by self-repairing of E layer, thereby improving the barrier life of the film.

[0025] Further, the black and white PETG shrink film of the present application can be prepared by the following method.

[0026] First, PETG chips with intrinsic viscosity of 0.75-0.85 dL / g are placed in a vacuum drying oven and dried at 80°C for 4 hours, with moisture content ≤50 ppm. The dried PETG chips are weighed and packaged as PETG base material.

[0027] Five independent extruders are set up, and a multi-layer co-extrusion die is set up at the end of the five independent extruders. The materials constituting the printing layer A, white layer B, buffer layer D, black layer C, and self-repairing layer E, except for PETG, are mixed with the PETG base material in the corresponding extruder according to the proportion.

[0028] The thickness of each layer is controlled according to the proportion of the material input weight, for example, as described above, the thickness proportion of the five layers is controlled as follows: A layer accounts for 10-15%, B layer accounts for 15-20%, C layer accounts for 25-30%, D layer accounts for 20-25%, and E layer accounts for 12-18%.

[0029] The temperature, screw speed, and melt pressure values of the corresponding extruder of each layer are set, for example, as shown in the following table.

[0030] Layer name Extruder segment temperature (°C) Screw rotation speed (rpm) Melt pressure (MPa) Layer A 230-235-240-230 45 12-14 Layer B 235-240-245-235 35 15-18 Layer D 240-245-250-240 40 18-20 Layer C 230-235-240-230 38 14-16 Layer E 225-230-235-225 42 10-12

[0031] The melt of each layer of material is input into the multi-layer co-extrusion die by the five independent extruders, and a thick sheet is extruded from the die, which is rapidly cooled and formed by a cooling water tank (water temperature 12°C).

[0032] After that, the thick sheet is bidirectionally stretched. First, it is transversely stretched, preheated at 85°C for 15 seconds, then transversely stretched at 100°C with a stretching ratio of 3.5:1; then longitudinally stretched at 95°C with a stretching ratio of 2.8:1.

[0033] Finally, heat setting is performed by a hot air circulating oven, with heat setting temperature of 70°C and setting time of 30 seconds. After setting, it is cooled, cut, and rolled up.

[0034] Example 1

[0035] The thickness of A layer is 5 μm, the thickness of B layer is 7.5 μm, and the thickness of C layer is 12.5 μm. These three layers are prepared with the same composition as the prior art. The thickness of D layer is 10 μm. The thickness of E layer is 15 μm. The total thickness is 50 μm.

[0036] D layer: PETG chips 85 parts by weight, SEBS elastomer 8 parts by weight, siloxane coupling agent 2 parts by weight, nano calcium carbonate (200 nm) 1 part by weight.

[0037] E layer: PETG chips 65 parts by weight, EVOH 15 parts by weight, DCPD repairing agent 8 parts by weight, catalyst 2 parts by weight, nano montmorillonite (100 nm) 3 parts by weight.

[0038] Example 2

[0039] A layer thickness 5 μm, B layer thickness 7.5 μm, C layer thickness 12.5 μm. The three layers are prepared with the same ingredients as the prior art. D layer thickness 10 μm. E layer thickness 15 μm. Total thickness 50 μm.

[0040] D layer: PETG chips 88 parts by weight, SEBS elastomer 10 parts by weight, siloxane coupling agent 3 parts by weight, nano calcium carbonate (200 nm) 2 parts by weight.

[0041] E layer: PETG chips 65 parts by weight, EVOH 15 parts by weight, DCPD repairing agent 8 parts by weight, catalyst 2 parts by weight, nano montmorillonite (100 nm) 3 parts by weight.

[0042] Example 3

[0043] A layer thickness 5 μm, B layer thickness 7.5 μm, C layer thickness 12.5 μm. The three layers are prepared with the same ingredients as the prior art. D layer thickness 10 μm. E layer thickness 15 μm. Total thickness 50 μm.

[0044] D layer: PETG chips 86.5 parts by weight, SEBS elastomer 9 parts by weight, siloxane coupling agent 2.5 parts by weight, nano calcium carbonate (200 nm) 1.5 parts by weight.

[0045] E layer: PETG chips 65 parts by weight, EVOH 15 parts by weight, DCPD repairing agent 8 parts by weight, catalyst 2 parts by weight, nano montmorillonite (100 nm) 3 parts by weight.

[0046] In Examples 1-3, the components of the E layer are unchanged, only the component content of the D layer is changed.

[0047] Example Transverse shrinkage (100°C) Interlayer peeling force Oxygen permeability Microcrack density (bars / mm 2 )]]> 1 77％ 4.0 N / mm 4.2 cc / m 2 • d]] 3.5 2 78％ 4.3 N / mm <![CDATA[3.9cc / m 2 ·d]]> 3.1 3 78％ 4.6 N / mm 3.8 cc / m 2 · d]] 2.8

[0048] Example 4

[0049] A layer thickness 15 μm, B layer thickness 20 μm, C layer thickness 30 μm. The three layers are prepared with the same ingredients as the prior art. D layer thickness 25 μm. E layer thickness 10 μm. Total thickness 108 μm.

[0050] D layer: PETG chips 85 parts by weight, SEBS elastomer 8 parts by weight, siloxane coupling agent 2 parts by weight, nano calcium carbonate (300 nm) 1 part by weight.

[0051] E layer: PETG chips 65 parts by weight, EVOH 15 parts by weight, DCPD repairing agent 8 parts by weight, catalyst 2 parts by weight, nano montmorillonite (200 nm) 3 parts by weight.

[0052] Example 5

[0053] A layer thickness 15 μm, B layer thickness 20 μm, C layer thickness 30 μm. These three layers are prepared with the same ingredients as the prior art. D layer thickness 25 μm. E layer thickness 10 μm. Total thickness 108 μm.

[0054] D layer: PETG chips 85 parts by weight, SEBS elastomer 8 parts by weight, siloxane coupling agent 2 parts by weight, nano calcium carbonate (300 nm) 1 part by weight.

[0055] E layer: PETG chips 70 parts by weight, EVOH 18 parts by weight, DCPD repairing agent 12 parts by weight, catalyst 3 parts by weight, nano montmorillonite (200 nm) 5 parts by weight.

[0056] Example 6

[0057] A layer thickness 15 μm, B layer thickness 20 μm, C layer thickness 30 μm. These three layers are prepared with the same ingredients as the prior art. D layer thickness 25 μm. E layer thickness 10 μm. Total thickness 108 μm.

[0058] D layer: PETG chips 85 parts by weight, SEBS elastomer 8 parts by weight, siloxane coupling agent 2 parts by weight, nano calcium carbonate (300 nm) 1 part by weight.

[0059] E layer: PETG chips 67.5 parts by weight, EVOH 16.5 parts by weight, DCPD repairing agent 10 parts by weight, catalyst 2.5 parts by weight, nano montmorillonite (200 nm) 4 parts by weight.

[0060] Examples 4-6, the D layer components are unchanged, only the component content of the E layer is changed.

[0061] Example Transverse shrinkage (100°C) Interlayer peeling force Oxygen permeability Microcrack density (bars / mm 2 ) 4 76％ 4.1 N / mm 4.5 cc / m 2 · d]] 3.3 5 77％ 4.2 N / mm 4.1 cc / m 2 • d]] 3.4 6 77％ 4.7 N / mm 3.7 cc / m 2 · d]] 2.9

[0062] Example 7

[0063] A layer thickness 5 μm, B layer thickness 7.5 μm, C layer thickness 12.5 μm. These three layers are prepared with the same ingredients as the prior art. D layer thickness 10 μm. E layer thickness 15 μm. Total thickness 50 μm.

[0064] D layer: PETG chips 86.5 parts by weight, SEBS elastomer 9 parts by weight, siloxane coupling agent 2.5 parts by weight, nano calcium carbonate (250 nm) 1.5 parts by weight.

[0065] E layer: PETG chips 67.5 parts by weight, EVOH 16.5 parts by weight, DCPD repair agent 10 parts by weight, catalyst 2.5 parts by weight, nano-montmorillonite (150 nm) 4 parts by weight.

[0066] Example 8

[0067] A layer thickness 20 μm, B layer thickness 27.5 μm, C layer thickness 42.5 μm. These three layers are prepared with the same composition as the prior art. D layer thickness 35 μm. E layer thickness 25 μm. Total thickness 150 μm.

[0068] D layer: PETG chips 86.5 parts by weight, SEBS elastomer 9 parts by weight, siloxane coupling agent 2.5 parts by weight, nano-calcium carbonate (250 nm) 1.5 parts by weight.

[0069] E layer: PETG chips 67.5 parts by weight, EVOH 16.5 parts by weight, DCPD repair agent 10 parts by weight, catalyst 2.5 parts by weight, nano-montmorillonite (150 nm) 4 parts by weight.

[0070] Example 9

[0071] A layer thickness 20 μm, B layer thickness 27.5 μm, C layer thickness 42.5 μm. These three layers are prepared with the same composition as the prior art. D layer thickness 35 μm. E layer thickness 25 μm. Total thickness 150 μm.

[0072] D layer: PETG chips 86.5 parts by weight, SEBS elastomer 9 parts by weight, siloxane coupling agent 2.5 parts by weight, nano-calcium carbonate (250 nm) 1.5 parts by weight.

[0073] E layer: PETG chips 67.5 parts by weight, EVOH 16.5 parts by weight, DCPD repair agent 10 parts by weight, catalyst 2.5 parts by weight, nano-montmorillonite (150 nm) 4 parts by weight.

[0074] Examples 7-9, the components of the D and E layers are unchanged, the thickness of the five-layer structure is changed.

[0075] Example Transverse shrinkage (100°C) Interlayer peeling force Oxygen permeability Microcrack density (bars / mm 2 ) <!-- 5 -->]]> 7 75％ 4.4 N / mm 4.1 cc / m 2 • d]] 4.2 8 76％ 4.5 N / mm 3.7 cc / m 2 • d]] 3.5 9 77％ 4.6 N / mm 3.5 cc / m 2 • d]] 3.0

[0076] Comparative Example 1

[0077] Referring to Example 1, the SEBS elastomer is eliminated from the components of the D layer, and the remaining parameters are unchanged.

[0078] D layer: PETG chips 93 parts by weight, siloxane coupling agent 2 parts by weight, nano-calcium carbonate (200 nm) 1 part by weight.

[0079] Comparative Example 2

[0080] Reference Example 2, eliminate nano calcium carbonate in D layer component, the rest of the parameters remain unchanged.

[0081] D layer: PETG chips 90 parts by weight, SEBS elastomer 10 parts by weight, siloxane coupling agent 3 parts by weight.

[0082] Comparative Example 3

[0083] Reference Example 3, eliminate siloxane coupling agent in D layer component, the rest of the parameters remain unchanged.

[0084] D layer: PETG chips 89 parts by weight, SEBS elastomer 9 parts by weight, nano calcium carbonate (200 nm) 1.5 parts by weight.

[0085]

[0086] Comparative Example 4

[0087] Reference Example 4, eliminate EVOH in E layer component, the rest of the parameters remain unchanged.

[0088] E layer: PETG chips 80 parts by weight, DCPD repair agent 8 parts by weight, catalyst 2 parts by weight, nano montmorillonite (200 nm) 3 parts by weight.

[0089] Comparative Example 5

[0090] Reference Example 5, eliminate DCPD in E layer component, the rest of the parameters remain unchanged.

[0091] E layer: PETG chips 82 parts by weight, EVOH 18 parts by weight, catalyst 3 parts by weight, nano montmorillonite (200 nm) 5 parts by weight.

[0092] Comparative Example 6

[0093] Reference Example 6, eliminate catalyst in E layer component, the rest of the parameters remain unchanged.

[0094] E layer: PETG chips 70 parts by weight, EVOH 16.5 parts by weight, DCPD repair agent 10 parts by weight, nano montmorillonite (200 nm) 4 parts by weight.

[0095] Comparative Example 7

[0096] Reference Example 7, eliminate nano montmorillonite in E layer component, the rest of the parameters remain unchanged.

[0097] E layer: PETG chips 71 parts by weight, EVOH 17 parts by weight, DCPD repair agent 10 parts by weight, catalyst 2.5 parts by weight.

[0098] Comparative Example Transverse shrinkage (100°C) Interlayer peeling force Oxygen permeability Microcrack density (bars / mm 2 )]]> 4 66％ 3.1 N / mm 16.6 cc / m 2 · d]] 7.4 5 67％ 3.7 N / mm 16.4 cc / m 2 · d]] 7.5 6 68％ 4.0 N / mm 16.8 cc / m 2 · d]] 7.8 7 65％ 4.1 N / mm 16.5 cc / m 2 · d]] 7.3

[0099] By comparison, embodiments 1-9 of the present application all meet the design requirements with minimal fluctuations in key indicators: transverse thermal shrinkage (100°C): 76-78% (design requirement ≥75%); oxygen transmission rate: 3.5-5.0 cc / m 2 ·d (design requirement ≤5 cc); microcrack density: 2.8-4.2 lines / mm 2 (Design requirement ≤5 lines).

[0100]

[0101] Conclusion: When the key components of each layer vary within the recommended range, the performance indicators fluctuate <5%, proving that the formulation system has strong robustness. Even if a single layer component is adjusted, other layers can compensate through interface strengthening (D layer) and dynamic repair (E layer) mechanisms, and still maintain stable overall performance. The PETG black and white shrink film of the present application maintains excellent product performance and consistency within the reasonable fluctuation range of components through a multi-layer cascading compensation mechanism, significantly outperforming traditional optimization schemes.

[0102] Those skilled in the art will understand that, although the present application is described in the manner of multiple embodiments, not every embodiment contains only one independent technical solution. The specification is described in this way only for clarity, those skilled in the art should understand the specification as a whole, and the technical solutions involved in each embodiment should be understood as a way to combine different embodiments to understand the scope of protection of the present application.

[0103] The above is merely a specific embodiment of the present application, and is not intended to limit the scope of the present application. Any equivalent changes, modifications and combinations made by those skilled in the art without departing from the concept and principles of the present application shall fall within the scope of protection of the present application.

Claims

1. A black and white PETG shrink film, characterized in that, It includes a five-layer co-extruded composite structure, which consists of a buffer layer D in the middle, a white layer B on the outside of the buffer layer D, a black layer C on the inside, a printing layer A on the outside of the white layer B, and a self-healing layer E on the inside of the black layer C.

2. The black and white PETG shrink film as described in claim 1, characterized in that, The thickness of the printed layer A accounts for 10-15% of the total thickness, the thickness of the white layer B accounts for 15-20% of the total thickness, the thickness of the black layer C accounts for 25-30% of the total thickness, the thickness of the buffer layer D accounts for 20-25% of the total thickness, and the remaining thickness is the self-healing layer E.

3. The black and white PETG shrink film as described in claim 1, characterized in that, The buffer layer D is composed of the following components in parts by weight: 85-88 parts by weight of PETG chips, 8-10 parts by weight of hydrogenated SEBS elastomer, 2-3 parts by weight of siloxane coupling agent, and 1-2 parts by weight of nano-calcium carbonate.

4. The black and white PETG shrink film as described in claim 1, characterized in that, The self-healing layer E is composed of the following components in parts by weight: 65-70 parts by weight of PETG chips, 15-18 parts by weight of EVOH, 8-12 parts by weight of DCPD repair agent, 2-3 parts by weight of catalyst, and 3-5 parts by weight of nano-montmorillonite.

5. A method for preparing the black and white PETG shrink film according to any one of claims 1-4, characterized in that, The method includes the following steps: First, PETG chips are placed in a vacuum drying oven and dried at 80°C for 4 hours; the dried PETG chips are weighed and packaged as PETG base material; five independent extruders are set up, and multi-layer co-extrusion dies are set at the ends of the five independent extruders; the components other than PETG constituting the printing layer A, white layer B, buffer layer D, black layer C, and self-healing layer E are mixed with the PETG base material in proportion and fed into the corresponding extruders; the melt of each layer material is fed into the multi-layer co-extrusion die by the five independent extruders and extruded from the die to form a thick sheet, and the extruded thick sheet is rapidly cooled and shaped by a cooling water tank; then, the thick sheet is biaxially stretched; finally, it is heat-set in a hot air circulating oven; after setting, it is cooled, slit, and wound up.

6. The preparation method according to claim 5, characterized in that, The cooling water tank is cooled to a temperature of 12℃.

7. The preparation method according to claim 5, characterized in that, In the biaxial stretching process, the temperature is first preheated to 85℃ for 15 seconds, then stretched laterally at 100℃ with a stretching ratio of 3.5:1; then stretched longitudinally at 95℃ with a stretching ratio of 2.8:

1.

8. The preparation method according to claim 5, characterized in that, The heat setting temperature is 70℃, and the setting time is 30 seconds.

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