Recyclable high-barrier multilayer heat-shrinkable film, and preparation method and application thereof

Abstract

The application provides a recyclable full-PO high-barrier multilayer heat-shrinkable film and a preparation method and application thereof and a recycling method, relates to the technical field of packaging materials and plastic resource recycling. The total amount of polyolefins of the recyclable full-PO high-barrier multilayer heat-shrinkable film is more than 90 wt%. The film edge and corner scraps generated in the preparation of the multilayer heat-shrinkable film or the discarded film after use can smoothly enter the "recycling-sorting-regeneration-application" system for recycling and utilization, meanwhile, the film has high oxygen resistance, so that the shelf life of the product can be maximally prolonged, and the loss of aroma and quality can be effectively prevented.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, specifically to a recyclable high-barrier multilayer heat-shrinkable film, its preparation method, application, and recycling method. Background Technology

[0002] Removing harmful substances from packaging materials to provide consumers with safe and recyclable packaging films or bags is an increasingly important issue in the industry. In daily life, plastic waste is often mixed with various household wastes, making it difficult to detect and identify, and impossible to achieve recycling. The same problem exists with multi-layer barrier packaging films in food packaging. Film waste containing polymers such as EVOH, nylon, and PVDC is difficult to disperse into a polyolefin matrix, thus making it impossible to recycle and reuse. Usually, the waste plastic waste can only be landfilled or recycled materials can be made into thick products.

[0003] Currently, in order to reduce the environmental damage caused by plastics and address the plastic waste crisis, many countries are increasing recycling facilities and developing recyclable packaging films to achieve resource recycling. However, these recyclable packaging films or bags are limited to a single material, and single-material packaging cannot achieve a high barrier effect, making it difficult to preserve quality, freshness, flavor, and extend the shelf life of food. Summary of the Invention

[0004] The purpose of this invention is to provide a recyclable, high-barrier, multilayer heat-shrinkable film made entirely of polyolefin (PO), along with its preparation, application, and recycling methods. The multilayer heat-shrinkable film provided by this invention has a structure close to that of single or pure polyolefin (PO) materials, possessing advantages such as high barrier properties against oxygen and water vapor, high shrinkage performance, and good mechanical properties. This can maximize the shelf life of products and effectively prevent the loss of aroma and quality. The film scraps or waste film generated during the preparation of the multilayer heat-shrinkable film can be recycled using existing recycling processes or by adding compatibilizers to achieve recycling and reuse. It can smoothly enter the "recycling-sorting-regeneration-application" system for recycling, reducing the environmental harm caused by plastics, developing recyclable flexible plastic packaging, and actively addressing the plastic waste crisis.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a recyclable, all-PO, high-barrier multilayer heat-shrinkable film, comprising a heat-sealing layer A, a structural layer B, and a barrier layer C; wherein the barrier layer C is disposed between the heat-sealing layer A and the structural layer B;

[0007] The raw materials for preparing the heat-sealing layer A include one or more of the following: plasmid and ethylene-vinyl acetate copolymer;

[0008] The raw materials for preparing structural layer B include one or more of low-density polyethylene, plasmons, and elastomers.

[0009] The raw materials for preparing the barrier layer C include ethylene-vinyl alcohol copolymer;

[0010] The total polyolefin content of the multilayer heat-shrinkable film is above 90 wt%.

[0011] Preferably, the heat-sealing layer A is prepared from a blend of 50-80% by weight of a plasmid and 20-50% by weight of an ethylene-vinyl acetate copolymer.

[0012] Preferably, the weight of the heat-sealing layer A is 20-40% of the total weight of the multilayer heat-shrinkable film;

[0013] The weight of structural layer B is 10-50% of the total weight of the multilayer heat-shrinkable film;

[0014] The weight of the barrier layer C shall not exceed 5% of the total weight of the multilayer heat shrink film.

[0015] Preferably, the multilayer heat shrink film further includes a plurality of adhesive layers D;

[0016] The plurality of adhesive layers D are disposed between the heat-sealing layer A and the structural layer B.

[0017] Preferably, the multilayer heat shrink film further includes several additional layers; the several additional layers are disposed between the heat-sealing layer A and the structural layer B; the raw materials for preparing each additional layer independently include one or more of low-density polyethylene, plasmon, and elastomer.

[0018] Preferably, the total density of the multilayer heat-shrinkable film is less than 1.0 g / cm³. 3 .

[0019] This invention provides a method for preparing the multilayer heat-shrinkable film described above, comprising the following steps:

[0020] The raw materials for each layer of the multilayer heat shrink film are heated and melted separately, and then fed into a multilayer stacking mold according to the structure of the multilayer heat shrink film to obtain a thin blank.

[0021] The preform is sequentially cooled and then folded by a first roll pressing to obtain a folded film preform;

[0022] The folded membrane embryo is sequentially heated and stretched to obtain a membrane bubble;

[0023] The membrane bubble is sequentially subjected to a second roll folding and shaping to obtain a multilayer heat shrink film.

[0024] This invention provides the application of the multilayer heat shrink film described in the above technical solution or the multilayer heat shrink film prepared by the preparation method described in the above technical solution in the packaging field.

[0025] This invention provides a method for recycling the multilayer heat-shrinkable film described in the above-described technical solution or the multilayer heat-shrinkable film prepared by the preparation method described in the above-described technical solution, comprising the following steps:

[0026] The film scraps or waste multilayer heat shrink film generated during the preparation of the multilayer heat shrink film are recycled and reused.

[0027] Preferably, the recycling includes recycling using existing recycling processes or recycling after adding compatibilizers.

[0028] This invention provides a recyclable, high-barrier, all-PO multilayer heat-shrinkable film. The total polyolefin (PO) content of the multilayer heat-shrinkable film provided by this invention is above 90 wt%, approaching the structure of single or pure polyolefin (PO) materials, allowing for recycling. The multilayer heat-shrinkable film provided by this invention has high oxygen barrier properties, which can maximize the shelf life of products and effectively prevent the loss of aroma and quality.

[0029] Preferably, the multilayer heat-shrinkable film provided by the present invention has good mechanical properties, light weight, and excellent optical properties, providing meat and cheese producers with a new alternative packaging solution, thereby replacing the traditional PA, EVOH, PVDC co-extruded multilayer structure, and is recyclable.

[0030] The multi-layer heat shrink film provided by this invention not only improves recyclability, but also reduces carbon emissions by about 25% compared to traditional shrink film products. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the process for preparing a multilayer heat-shrinkable film according to an embodiment of the present invention; Figure 1 In the diagram, 1 represents the extruder, 2 represents the multi-layer stacked die, 3 represents the cooling water ring, 4 represents the first herringbone clamping roller, 5 represents the hot water tank, 6 represents the infrared heating cylinder, 7 represents the film bubble, 8 represents the second herringbone clamping roller, 9 represents the hot roller, 10 represents the cold roller, and 11 represents the take-up roller.

[0032] Figure 2 A schematic cross-sectional view of the multilayer heat-shrinkable film prepared in Example 1;

[0033] Figure 3 A schematic cross-sectional view of the multilayer heat-shrinkable film prepared in Example 2;

[0034] Figure 4 A schematic cross-sectional view of the multilayer heat-shrinkable film prepared in Example 3;

[0035] Figure 5 A schematic cross-sectional view of the multilayer heat-shrinkable film prepared in Example 4;

[0036] Figures 2-5 In the diagram, A represents the heat-sealing layer, D represents the adhesive layer, C represents the barrier layer, B represents the structural layer, and E1, E2, E3, and E4 represent different additional layers. Detailed Implementation

[0037] This invention provides a recyclable, all-PO, high-barrier multilayer heat-shrinkable film, comprising a heat-sealing layer A, a structural layer B, and a barrier layer C; wherein the barrier layer C is disposed between the heat-sealing layer A and the structural layer B;

[0038] The raw materials for preparing the heat-sealing layer A include one or more of the following: plasmid and ethylene-vinyl acetate copolymer;

[0039] The raw materials for preparing structural layer B include one or more of low-density polyethylene, plasmons, and elastomers.

[0040] The raw materials for preparing the barrier layer C include ethylene-vinyl alcohol copolymer;

[0041] The total polyolefin (PO) content of the multilayer heat shrink film is above 90 wt%.

[0042] The multilayer heat-shrinkable film provided by this invention includes a heat-sealing layer A. In this invention, the raw materials for preparing the heat-sealing layer A include one or more of a plastinated element (POP) and ethylene-vinyl acetate copolymer (EVA), preferably a blend of 50-80% by weight of plastinated element (POP) and 20-50% by weight of ethylene-vinyl acetate copolymer (EVA). In this invention, the melt index of the plastinated element (POP) is preferably 0.5-4.0 g / 10 min, more preferably 1.0-2.0 g / 10 min; the density of the plastinated element (POP) is preferably 0.868-0.908 g / cm³. 3 More preferably, it is 0.89~0.905 g / cm³. 3 In this invention, the vinyl acetate (VA) content in the ethylene-vinyl acetate copolymer (EVA) is preferably 5-35%, more preferably 8-20% by mass; the density is preferably 0.93-0.95 g / cm³. 3 .

[0043] In this invention, the total density of the heat-sealing layer A is preferably 0.88~0.91 g / cm³. 3 The weight of the heat-sealing layer A is preferably 20-40% of the total weight of the multilayer heat-shrinkable film, more preferably 25-35%.

[0044] In this invention, the heat-sealing layer A is preferably a multi-layer structure.

[0045] The multilayer heat-shrinkable film provided by this invention includes a structural layer B. In this invention, the structural layer B provides the film with shrinkage properties, puncture resistance, abrasion resistance, and protection against mechanical damage. In this invention, the raw materials for preparing the structural layer B include one or more of low-density polyethylene, plasmons, and elastomers. In this invention, the density of the low-density polyethylene is preferably 0.89~0.92 g / cm³. 3 The low-density polyethylene preferably includes one or more of ultra-low-density polyethylene (ULDPE) and linear low-density polyethylene (LLDPE). In this invention, the density of the plastid (POP) is preferably 0.90~0.908 g / cm³. 3 The plastic body preferably includes one or more of SK Supreme 021S and DOW AFFINITY PL 1881G. In this invention, the density of the elastomer (POE) is preferably 0.85~0.886 g / cm³. 3 The elastomer preferably includes one or more of Mitsui_Tafmer_A-1085S (Mitsui Chemicals 1085) and SK Solumer 891. In a specific embodiment of the present invention, the raw materials for preparing the structural layer B, by weight percentage, include 80% plastomer (POP) and 20% ultra-low density polyethylene (ULDPE).

[0046] In this invention, the weight of the structural layer B is preferably 10-50% of the total weight of the multilayer heat shrink film, more preferably 20-40%.

[0047] In this invention, the structural layer B is preferably a multi-layer structure; the total density of the structural layer B is preferably 0.88~0.92 g / cm³. 3 .

[0048] The multilayer heat-shrinkable film provided by this invention includes a barrier layer C disposed between the heat-sealing layer A and the structural layer B. In this invention, the barrier layer C provides oxygen barrier properties for the film. In this invention, the raw material for preparing the barrier layer C includes ethylene-vinyl alcohol copolymer (EVOH). In this invention, the ethylene content in the ethylene-vinyl alcohol copolymer is preferably 27-48 mol%, more preferably 32-48 mol%; the density of the ethylene-vinyl alcohol copolymer (EVOH) is preferably 1.12-1.20 g / cm³. 3 The melting peak temperature of the ethylene-vinyl alcohol copolymer (EVOH) is preferably 160~190℃; the ethylene-vinyl alcohol copolymer (EVOH) preferably includes one or more of EVAL H171B, EVAL SP292B and Soarnol ET3803RB.

[0049] In this invention, the weight of the barrier layer C preferably does not exceed 5% of the total weight of the multilayer heat shrink film, more preferably 1-5%. This invention limits the content of the barrier layer C to the above range, which is more conducive to the recycling and reuse of the multilayer heat shrink film.

[0050] In this invention, the barrier layer C is preferably a multi-layer structure; the total density of the barrier layer C is preferably 1.12~1.2 g / cm³. 3 .

[0051] In this invention, the multilayer heat-shrinkable film preferably further includes a plurality of adhesive layers D; the plurality of adhesive layers D are disposed between the heat-sealing layer A and the structural layer B. In this invention, the adhesive layers D provide suitable adhesion between the layers of the film. In a specific embodiment of this invention, the adhesive layers D are located between any other layers, such as between the barrier layer C and the structural layer B, and between the barrier layer C and the heat-sealing layer A. In this invention, the raw materials for preparing each adhesive layer D preferably include maleic anhydride-grafted olefin polymers, more preferably one or more of maleic anhydride-grafted polyethylene (PE)-based adhesives, maleic anhydride-grafted elastomer-based adhesives, and maleic anhydride-grafted ethylene-vinyl acetate copolymer (EVA) adhesives, and even more preferably maleic anhydride-grafted elastomer-based adhesives or maleic anhydride-grafted ethylene-vinyl acetate copolymer (EVA) adhesives.

[0052] In this invention, the total weight of the plurality of adhesive layers D is preferably 5-20% of the total weight of the multilayer heat-shrinkable film, more preferably 10-20%; the total density of the adhesive layers D is preferably 0.90-0.92 g / cm³. 3 .

[0053] In this invention, the multilayer heat-shrinkable film further includes several additional layers; these additional layers are disposed between the heat-sealing layer A and the structural layer B. In this invention, the additional layers provide the film with shrinkage properties, overall mechanical strength, and processability. In this invention, the raw materials for preparing each additional layer preferably include one or more of low-density polyethylene, a plasmon, and an elastomer. In this invention, the specific compositions of the low-density polyethylene, plasmon, and elastomer are consistent with those in the structural layer B described above, and will not be repeated here. In this invention, the additional layers have the same composition as the structural layer B, but the quantity and proportion of polymer components composing the additional layers and the structural layer B may differ. In a specific embodiment of this invention, by weight percentage, the raw materials for preparing the additional layers include 80% plasmon (POP) and 20% linear low-density polyethylene (LLDPE).

[0054] In this invention, one or more of the additional layers are preferably disposed between the structural layer B, the barrier layer C, and the heat-sealing layer A. For example, one additional layer is disposed between the barrier layer C and the heat-sealing layer A, while another additional layer is disposed between the structural layer B and the barrier layer C.

[0055] In this invention, the total weight of the additional layer is preferably 10-40% of the total weight of the multilayer heat-shrinkable film, more preferably 20-40%; the total density of the additional layer is preferably 0.88-0.92 g / cm³. 3 .

[0056] In this invention, the additional layer does not impair the recyclability of the multilayer heat-shrinkable film and can be present at any location on the film.

[0057] In this invention, the raw materials for preparing the multilayer heat-shrinkable film preferably include additives. In this invention, the additives preferably include one or more of antistatic agents, colorants, lubricants, processing aids, and anti-blocking agents. In this invention, the mass content of the additives is preferably 1-5%; the total density of the additives is preferably 0.90-0.95 g / cm³. 3 .

[0058] The multilayer heat-shrinkable film provided by the present invention preferably has 5 to 9 layers; the thickness of the multilayer heat-shrinkable film is preferably 30 to 100 µm, more preferably 50 µm. In a specific embodiment of the present invention, the multilayer heat-shrinkable film, from the inner layer to the outer layer, includes: A / D / C / D / B, A / D / C / D / E / E / B, A / E / D / C / D / E / B, A / E / E / D / C / D / B, A / E / D / C / D / E / B, A / E / E / E / D / C / D / E / B, or A / E / E / D / C / D / E / E / B; wherein, A represents a heat-sealing layer, B represents a structural layer, C represents a barrier layer, D represents an adhesive layer, E represents an additional layer, and the symbol " / " represents the boundary between layers.

[0059] In this invention, the total density of the multilayer heat-shrinkable film is preferably less than 1.0 g / cm³. 3 The present invention limits the total density of the multilayer heat-shrinkable film to the above range, enabling floating sorting and separation, which is more conducive to recycling.

[0060] In this invention, the total polyolefin (PO) content of the multilayer heat-shrinkable film is 90 wt% or more, preferably 95 wt%; the total non-polyolefin polymer content of the multilayer heat-shrinkable film is 10 wt% or less. In this invention, the multilayer heat-shrinkable film can shrink to a size at least 30% smaller than its original size after 5 seconds at 85°C.

[0061] In this invention, the multilayer heat shrink film is preferably biaxially oriented in both the transverse and longitudinal directions; the transverse × longitudinal direction of the multilayer heat shrink film preferably has an 8 to 20 times stretch orientation.

[0062] In this invention, the multilayer heat shrink film is preferably in a tubular form. In this invention, the heat shrink bag obtained by self-sealing the multilayer heat shrink film exists in the form of an end-sealed bag, a side-sealed bag, or a V-shaped side-sealed bag; the heat seal strength of the resulting heat shrink bag is 15N or higher.

[0063] This invention provides a method for preparing the multilayer heat-shrinkable film described above, comprising the following steps:

[0064] The raw materials for each layer of the multilayer heat shrink film are heated and melted separately, and then fed into a multilayer stacking mold according to the structure of the multilayer heat shrink film to obtain a thin blank.

[0065] The preform is sequentially cooled and then folded by a first roll pressing to obtain a folded film preform;

[0066] The folded membrane embryo is sequentially heated and stretched to obtain a membrane bubble;

[0067] The membrane bubble is sequentially subjected to a second roll folding and shaping to obtain a multilayer heat shrink film.

[0068] This invention involves heating and melting the raw materials for each layer of a multilayer heat-shrinkable film separately, then feeding them into a multilayer stacking mold according to the structure of the multilayer heat-shrinkable film to obtain a preform. Preferably, the raw materials for each layer of the multilayer heat-shrinkable film are melted separately and then stacked together according to the structure of the multilayer heat-shrinkable film. In this invention, the multilayer stacking mold is preferably circular. Preferably, the preform is formed by extrusion through the die opening of the multilayer stacking mold. In this invention, the thickness of the preform is preferably 500~1500µm, more preferably 800~1200µm.

[0069] After obtaining the preform, the present invention sequentially cools and performs a first roll folding to obtain a folded film preform. In the present invention, the cooling temperature is preferably 5~20℃, more preferably 10℃. In the present invention, the cooling is preferably water cooling. In the present invention, the first roll folding preferably employs a herringbone clamping roll folding method.

[0070] In this invention, the fold diameter of the folded membrane embryo is preferably 45~150mm.

[0071] After obtaining the folded membrane preform, the present invention sequentially heats and stretches the folded membrane preform to obtain a membrane bubble. In the present invention, the heating preferably includes sequential heating in a hot water bath and heating in an infrared heating cylinder. In the present invention, the temperature of the hot water bath heating is preferably 80~93℃, more preferably 90℃; the temperature of the infrared heating cylinder heating is preferably 90~140℃, more preferably 120℃. The present invention achieves the temperature required for biaxial orientation of the membrane preform through heating.

[0072] In this invention, the stretching ratio is preferably 8 to 20 times, more preferably 16 times; specifically, it is preferably 8 to 20 times in the transverse direction × longitudinal direction.

[0073] Preferably, the present invention involves blowing out a membrane bubble after stretching.

[0074] After obtaining the film bubble, the present invention sequentially performs a second roll folding and shaping on the film bubble to obtain a multilayer heat shrinkable film. In the present invention, the second roll folding preferably uses a herringbone clamping roller folding. In the present invention, the fold diameter of the folded film after the second roll folding is preferably 200~500mm.

[0075] In this invention, the setting process includes sequential heat setting and cold setting. Preferably, the heat setting temperature is 40-60°C, more preferably 50°C; the heat setting time is preferably 2-5 seconds; and the heat setting is preferably performed on a hot roller. Preferably, the cold setting temperature is 15-25°C, more preferably 20°C; the cold setting time is preferably 2-5 seconds; and the cold setting is preferably performed on a cold roller.

[0076] Preferably, after the shaping process, the resulting film is placed on a take-up roller, and then printed or directly made into bags according to requirements.

[0077] In this invention, the fold diameter of the multilayer heat shrink film is preferably 200~500mm.

[0078] This invention provides the application of the multilayer heat shrink film described in the above-described technical solution or the multilayer heat shrink film prepared by the above-described preparation method in the packaging field, preferably for food packaging, specifically for meat and cheese packaging. In this invention, the heat-sealing layer A of the multilayer heat shrink film is the innermost layer, which is in direct contact with the product to be packaged; the structural layer B of the multilayer heat shrink film is the outermost layer, providing the film with shrinkage, puncture resistance, abrasion resistance, and protection against mechanical damage; the barrier layer C provides the film with oxygen barrier properties.

[0079] In this invention, the application preferably includes processing the multilayer heat-shrinkable film into a bag for packaging. In this invention, the processing method preferably involves heat-sealing the inner layer of the multilayer heat-shrinkable film itself. In this invention, the bag is preferably open at the top and sealed at the sides and bottom; the bag includes a bottom-sealed bag or a side-sealed bag.

[0080] This invention provides a method for recycling the multilayer heat-shrinkable film described in the above-described technical solution or the multilayer heat-shrinkable film prepared by the preparation method described in the above-described technical solution, comprising the following steps:

[0081] The film scraps or waste multilayer heat shrink film generated during the preparation of the multilayer heat shrink film are recycled and reused.

[0082] In this invention, the recycling and reuse preferably includes recycling using existing recycling processes or recycling after adding compatibilizers.

[0083] In this invention, the film scraps generated during the preparation of the multilayer heat-shrink film or the waste film after consumer use can be recycled in existing recycling processes or recycled and reused by adding compatibilizers. This allows for smooth entry into the "recycling-sorting-regeneration-application" system for recycling. In this invention, the recycling of film scraps refers to the reuse of scraps from the multilayer packaging process as a recycling layer or in the form of polyolefin resin. In this invention, the recycling of waste multilayer heat-shrink film refers to consumers directly disposing of it at designated drop-off points in stores or nearby recycling bins after consumption for easy recycling. Recycled granules can be reformulated into new products that do not suffer from gelation, material brittleness, or poor appearance, thus improving reusability and facilitating the reuse of waste plastics in packaging and container manufacturing.

[0084] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0085] The raw materials used in the examples and comparative examples are shown in Table 1;

[0086] Table 1. Raw materials used in the examples and comparative examples

[0087]

[0088] Mechanical strength was determined according to GB / T 1040.3, including tensile strength and elongation at break. Type 5 specimens with a width of 6 mm were used. The specimen speed was (100±1) mm / min.

[0089] Oxygen permeability shall be determined in accordance with GB / T 1038.

[0090] Transparency and haze shall be determined in accordance with GB / T 2410.

[0091] Heat shrinkage rate, cut length 100mm A smooth, intact, and creased 100mm membrane is used to accurately measure its transverse and longitudinal lengths. The membrane is then immersed in 85℃ warm water for 5 seconds, and its transverse and longitudinal lengths are measured again. The ratio (%) of the difference between the transverse and longitudinal lengths before and after immersion to the transverse and longitudinal lengths before immersion is its transverse and longitudinal shrinkage rate.

[0092] Total density (g / cm³) 3 In this invention, the total density of each layer is the sum of the proportions of each mixture and the densities of that mixture; in this invention, the total density of the membrane is the sum of the total density of each layer and the weight ratio of that layer.

[0093] Examples 1-4 and Comparative Examples 1-3

[0094] The preparation method of multilayer heat shrink film is as follows: Figure 1 As shown:

[0095] The extruder adds various resins according to the film structure, heats and melts them in the extruder 1, and then enters the multi-layer circular stacked mold 2;

[0096] The blank is formed by extrusion through the die orifice, cooled in water at 10°C, and folded by the first herringbone clamping roller 4, with a folded diameter of 65mm.

[0097] The folded film preform enters the hot water tank 5 through the guide rollers and is heated at 90°C, and then enters the infrared heating cylinder 6 and is heated at 120°C to reach the temperature required for biaxial orientation of the film preform;

[0098] The heated membrane preform is stretched and oriented by 16 times in the transverse × longitudinal direction to blow out membrane bubbles 7. The blown membrane bubbles are folded by the second herringbone clamping roller 8, and the fold diameter of the folded membrane is 260mm.

[0099] The folded film is then heated to 50°C by the hot roller 9 for shaping, then cooled to 20°C by the cold roller 10, and finally placed on the take-up roller 11.

[0100] A tubular film with a winding diameter of 250 mm and a thickness of 50 µm is produced.

[0101] The structures, material ratios, and weights of the embodiments and comparative examples are shown in Tables 2-8. Unless otherwise specified, all percentages in the embodiments are by weight, and the comparative examples are commonly used barrier multilayer shrink films in the prior art.

[0102] Table 2. Structure, material ratio, and layer weight ratio of Example 1 ( Figure 2 )

[0103]

[0104] Table 3. Structure, material ratio, and layer weight ratio of Example 2 ( Figure 3 )

[0105]

[0106] Table 4. Structure, material ratio, and layer weight ratio of Example 3 ( Figure 4 )

[0107]

[0108] Table 5. Structure, material ratio, and layer weight ratio of Example 4 ( Figure 5 )

[0109]

[0110] Table 6. Structure, material ratio, and layer weight ratio of Comparative Example 1

[0111]

[0112] Table 7. Structure, material ratio, and layer weight ratio of Comparative Example 2

[0113]

[0114] Table 8. Structure, material ratio, and layer weight ratio of Comparative Example 3

[0115]

[0116] Test case

[0117] The films prepared in the above examples and comparative examples were tested, and the results are shown in Table 9.

[0118] Table 9. Thin film properties of the examples and comparative examples

[0119]

[0120] As can be seen from Table 9, the tensile strength, elongation at break, barrier properties, and shrinkage of the embodiment are close to those of the prior art. The embodiment can achieve the use of PA and PET plastics without maintaining gas barrier properties, and the present invention is suitable for this application.

[0121] The film waste (scraps) of the above embodiments and the film waste (scraps) of the prior art comparative example were recycled and granulated by adding 5 wt% Fusabond® E226 compatibilizer. The recycled granules were then used as the blown film test material of structural layer B in Example 1. The materials used for other layers remained unchanged, the weight ratio of each layer remained unchanged, and the blown film preparation process remained unchanged. The film performance before and after recycling was tested, and the results are shown in Table 10.

[0122] Table 10 Performance of recycled granular films in Examples and Comparative Examples

[0123]

[0124] As can be seen from Table 9, the total density of the films in Examples 1-4 is less than 1 g / cm³. 3 This facilitates the detection and identification of recycled plastics. The film properties, such as mechanical properties, shrinkage rate, barrier properties, and transparency / haze, are close to those of the comparative examples. After adding the additional layer, the mechanical strength of Examples 2-4 is significantly improved compared to Example 1. As can be seen from Table 10, the reprocessed films from recycled film waste in Comparative Examples 1-3 cannot be formed, exhibiting defects such as gelation and poor appearance. The films reprocessed from recycled film waste in Examples 1-4 do not show a significant decrease in mechanical strength, puncture resistance, transparency, shrinkage rate, and oxygen barrier properties compared to the film in Example 1 before recycling, achieving recyclability. The blown film preparation process is completely consistent with the film before recycling in Example 1, requiring no adjustments. Compared with existing comparative films, the multilayer heat-shrinkable film of this invention successfully achieves the production and recycling of high-barrier multilayer heat-shrinkable film with a total polyolefin (PO) content of 95%. In terms of performance, such as high oxygen barrier properties, puncture resistance, good mechanical properties, strong oxygen barrier properties, and excellent optical properties, it remains essentially the same as before recycling. This solves the problem of achieving high barrier properties in single-material packaging. This structure, close to that of a single or pure PO material, allows for the reuse of process scraps from multilayer packaging as a recycling layer or in the form of polyolefin resin. This invention eliminates the need to peel off different plastics, reducing sorting and processing hassles and greatly facilitating recycling. It provides good shelf life and recyclability options for meat and cheese packaging, reducing the carbon footprint by more than 25%.

[0125] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A recyclable high-barrier multilayer heat-shrinkable film, comprising a heat-seal layer (A), a structure layer (B), a barrier layer (C) and several adhesive layers (D); the barrier layer (C) is arranged between the heat-seal layer (A) and the structure layer (B); the heat-seal layer (A) is prepared from 70% plastic body and 30% ethylene-vinyl acetate copolymer; the structure layer (B) is prepared from 80% plastic body and 20% ultra-low density polyethylene; the barrier layer (C) is prepared from ethylene-vinyl alcohol copolymer; the total amount of polyolefin in the multilayer heat-shrinkable film is more than 90 wt%; the weight of the heat-seal layer (A) is 20-40% of the total weight of the multilayer heat-shrinkable film; the weight of the structure layer (B) is 10-50% of the total weight of the multilayer heat-shrinkable film; the weight of the barrier layer (C) is not more than 5% of the total weight of the multilayer heat-shrinkable film.

2. The multilayer heat shrinkable film according to claim 1, characterized in that, The total density of the multilayer heat shrinkable film is less than 1.0 g / cm 3 .

3. The multilayer heat shrinkable film according to claim 1, characterized in that, the several adhesive layers (D) are arranged between the heat-seal layer (A) and the structure layer (B).

4. The multilayer heat shrinkable film according to claim 1, characterized in that, the multilayer heat-shrinkable film further comprises several additional layers; the several additional layers are arranged between the heat-seal layer (A) and the structure layer (B); and each additional layer is independently prepared from one or more of low-density polyethylene, plastic body and elastomer.

5. A preparation method of the multilayer heat-shrinkable film according to any one of claims 1-4, comprising the following steps: heating and melting the raw materials of each layer of the multilayer heat-shrinkable film respectively, and then feeding the multilayer heat-shrinkable film into a multilayer stacking mold to obtain a thin blank; cooling and first roll pressing and folding the thin blank in sequence to obtain a folded film blank; heating and stretching the folded film blank in sequence to obtain a film bubble; second roll pressing and folding and setting the film bubble in sequence to obtain the multilayer heat-shrinkable film.

6. Application of the multilayer heat-shrinkable film according to any one of claims 1-4 or prepared by the preparation method of claim 5 in the field of packaging.

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