A stretch sleeve film

Abstract

The application relates to a kind of stretch sleeve films, belonging to the technical field of high-strength cold-stretching sleeve film composition.In order to ensure the comprehensive performance of the film, especially the puncture resistance and tear resistance, a large amount of ultra-low density polyethylene resin and propylene-based elastomer need to be added in the formula, wherein the high content of propylene-based elastomer makes the production cost higher.The application comprises a middle layer and an outer layer, the middle layer composition comprises two kinds of metallocene polyethylene with specific density and MFR and propylene-based elastomer;the outer layer composition is metallocene polyethylene with specific density.The film simultaneously has higher tensile property, puncture resistance, tear resistance and resilience, and lower cost, so that the cold-stretching sleeve film has excellent comprehensive performance.

Description

Technical Field

[0001] A stretchable sleeve membrane, belonging to the technical field of high-strength cold stretchable sleeve membrane compositions. Background Technology

[0002] Cold stretch film is mainly used for packaging and transporting large-volume goods. It is produced by horizontal stretching at room temperature, then vertically covering the item from above to tightly encase it. Currently, cold stretch film production primarily uses three-layer co-extrusion blown film, typically employing ordinary stretch film. However, the puncture and tear resistance of ordinary three-layer co-extrusion cold stretch film is insufficient to meet requirements.

[0003] To ensure the overall performance of the film, especially its puncture and tear resistance, a large amount of ultra-low density polyethylene resin and propylene-based elastomer needs to be added to the formulation. The high content of propylene-based elastomer makes the production cost high, which makes it difficult to widely promote the dedicated stretch sleeve film. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a stretchable sleeve membrane with good puncture and tear resistance and low production cost.

[0005] The technical solution adopted by this invention to solve its technical problem is: a stretchable sheath membrane, characterized in that: it comprises a middle layer and two outer layer structures respectively disposed on both sides of the middle layer; the middle layer, based on 100 parts by weight, has a composition including a density of 0.914 g / cm³. 3 Metallocene polyethylene mLLDPE-B, 10-40 parts, density 0.912-0.916 g / cm³ 3 The outer layer comprises 40-70 parts of metallocene polyethylene mLLDPE-C and 10-30 parts of propylene-based elastomer; the outer layer composition has a density of 0.918-0.920 g / cm³. 3 Metallocene polyethylene mLLDPE-A;

[0006] The density is 0.914 g / cm³. 3 The metallocene polyethylene MFR2.16 has a strength of 0.8 g / 10 min; its density is 0.912~0.916 g / cm³. 3 The MFR2.16 of metallocene polyethylene is 0.2~0.7 g / 10 min.

[0007] mLLDPE-B is characterized by a narrow molecular weight distribution, and its melt curve exhibits three melting peaks, with the highest melting temperature exceeding 120°C. Higher melting peak temperatures in polyethylene materials indicate greater lamellar thickness, reflected in a longer polyethylene molecular chain structure. When these longer chains act as binding molecules, they increase the entanglement between lamellar crystals, improving the material's mechanical properties, particularly the film's tear and puncture resistance. mLLDPE-A utilizes a relatively high-density metallocene polyethylene resin to ensure high tensile strength and prevent tearing during use. The middle layer uses a relatively low-density metallocene polyethylene resin and a propylene-based elastomer to ensure good resilience, puncture and tear resistance, allowing the cold-stretched film to quickly rebound and tightly wrap the contents, while also preventing sharp objects from puncturing the film during transport.

[0008] The aforementioned specifically defined mLLDPE-B has a melt index of 0.8 and a density of 0.914 g / cm³. 3 It has suitable extrusion flowability and molecular weight, and a high comonomer content, which can improve the puncture resistance and tear resistance of the film.

[0009] By selecting ultra-low density polyethylene resins with specific melt indexes, densities, and molecular structures, and by combining complementary specific polyethylene resins for the middle and outer layers, the film can maintain good tear and puncture resistance while reducing the amount of elastomer added. By adding mLLDPE-B to the film formulation, the amount of elastomer used can be reduced by up to 50%.

[0010] Preferably, the melt flow rate of the outer metallocene polyethylene 2.16 kg is 0.9~1.2 g / 10 min.

[0011] Preferably, the outer layer of metallocene polyethylene has a molecular weight distribution of 2.5 to 3.2 and a weight-average molecular weight of 112,000 to 120,000.

[0012] Preferably, the outer metallocene polyethylene layer, when analyzed by thermal crystallization, has a lamellar content of 14% to 16.4% with a thickness of 9.0 nm or more, and a branching point number of 125 to 145 / 10000C.

[0013] Preferably, the density of the middle layer is 0.914 g / cm³. 3 In metallocene polyethylene, the comonomer is 1-hexene.

[0014] More preferably, the density is 0.914 g / cm³. 3 The molar content of hexene in metallocene polyethylene is 3.2~3.5 mol.

[0015] Further preferred, the number of branches is 145~170 / 10000C.

[0016] Preferably, the density of the middle layer is 0.914 g / cm³. 3 The molecular weight distribution of metallocene polyethylene is 3.3~3.8.

[0017] Preferably, the propylene-based elastomer is Vistamaxx 6102FL.

[0018] Preferably, the thickness ratio of any outer layer to the middle layer is 1:3.

[0019] Preferably, the middle layer, based on 100 parts by weight, comprises components with a density of 0.914 g / cm³. 3 40 parts of metallocene polyethylene, density 0.916 g / cm³ 3 30 parts of metallocene polyethylene and 30 parts of propylene-based elastomer.

[0020] Preferably, the middle layer, based on 100 parts by weight, comprises components with a density of 0.914 g / cm³. 3 20 parts of metallocene polyethylene, density 0.912 g / cm³ 3 70 parts of metallocene polyethylene and 10 parts of propylene-based elastomer.

[0021] Under this preferred solution, only 10 parts of propylene-based elastomer are needed to achieve high tensile properties, puncture resistance, tear resistance, and resilience, significantly reducing costs.

[0022] Compared with existing technologies, the beneficial effects of this invention are as follows: By selecting ultra-low density polyethylene resins with specific melt index, density, and molecular structure, and by using complementary specific polyethylene resins for the middle and outer layers, the film can maintain good tear and puncture resistance while reducing the amount of elastomer added. This ensures that the film simultaneously possesses high tensile strength, puncture resistance, tear resistance, and resilience, and at a lower cost, resulting in excellent overall performance for cold-stretched films. By using mLLDPE-B in the film formulation, the amount of elastomer can be reduced by up to 50%, effectively reducing manufacturing costs. Attached Figure Description

[0023] Figure 1 The melting curve of mLLDPE-B in Example 1 is shown below. Figure 1As can be seen, the melt curve of mLLDPE-B used in the examples has three melting peaks, with the highest melting temperature above 120°C. This indicates a large lamellar thickness, which translates to a longer polyethylene sequence structure, i.e., longer polyethylene molecular chains. When the longer polyethylene molecular chains act as binding molecules, they can increase the degree of entanglement between lamellar crystals, which is beneficial to improving the mechanical properties of the material, especially the tear and puncture resistance of the film.

[0024] Figure 2 The melting curve of mLLDPE-C in Comparative Example 1 is shown.

[0025] Figure 3 The melt curve of ultra-low density polyethylene with a middle layer content of 40 parts is shown in Comparative Example 2.

[0026] Figure 4 The melting curve of ultra-low density polyethylene in Comparative Example 5 is shown. Detailed Implementation

[0027] The present invention will be further described below with reference to the embodiments, wherein Embodiment 2 is the preferred embodiment of the present invention.

[0028] Example 1

[0029] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0030] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0031] Middle layer of film: 20 parts metallocene ultra-low density polyethylene mLLDPE-B (density 0.914 cm³) 3 The following components were used: MFR 2.16 (0.8 g / 10 min), molecular weight distribution 3.5, comonomer 1-hexene (3.4 mol% hexene molar content, 158 / 10000 C branched chain number), 10 parts of propylene-based elastomer Exxon Vistamaxx 6102FL, and 70 parts of metallocene polyethylene mLLDPE-C (density 0.912 g / cm³). 3 MFR2.16 is 0.5g / 10min.

[0032] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0033] The film thickness is 120 μm, and the thickness ratio of any outer layer to the middle layer is 1:3.

[0034] Example 2

[0035] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0036] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0037] Middle layer of film: 40 parts metallocene ultra-low density polyethylene mLLDPE-B (density 0.914 cm³) 3 The following components were used: MFR 2.16 (0.8 g / 10 min), molecular weight distribution 3.5, comonomer 1-hexene (3.4 mol% hexene molar content, 158 / 10000 C branched chain number), 30 parts of propylene-based elastomer Exxon Vistamaxx 6102FL, and 30 parts of metallocene polyethylene mLLDPE-C (density 0.916 g / cm³). 3 MFR2.16 is 0.2g / 10min.

[0038] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0039] The thickness setting is the same as in Example 1.

[0040] Example 3

[0041] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0042] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.920 g / cm³) 3MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.8, weight average molecular weight is 116800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 15.0%, and the number of branching points is 140 / 10000C.

[0043] Middle layer of film: 40 parts metallocene ultra-low density polyethylene mLLDPE-B (density 0.914 cm³) 3 The following components were used: MFR 2.16 (0.8 g / 10 min), molecular weight distribution 3.5, comonomer 1-hexene (3.4 mol% hexene molar content, 158 / 10000 C branched chain number), 30 parts of propylene-based elastomer Exxon Vistamaxx 6102FL, and 30 parts of metallocene polyethylene mLLDPE-C (density 0.916 g / cm³). 3 MFR2.16 is 0.2g / 10min.

[0044] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.920 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.8, weight average molecular weight is 116800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 15.0%, and the number of branching points is 140 / 10000C.

[0045] The thickness setting is the same as in Example 1.

[0046] Example 4

[0047] A stretchable sleeve membrane, based on Example 2, has a film thickness of 80 μm and a thickness ratio of 1:3 between any outer layer and the middle layer.

[0048] Example 5

[0049] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0050] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0051] Outer film layer: 100 parts metallocene polyethylene (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 104800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 13.4%, and the number of branching points is 105 / 10000C.

[0052] Intermediate layer of film: 50 parts acrylic elastomer Exxon Vistamaxx 6102FL, 50 parts metallocene polyethylene mLLDPE-C (density 0.916 g / cm³) 3 MFR2.16 is 0.2g / 10min.

[0053] Inner layer of film: 100 parts metallocene polyethylene (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 104800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 13.4%, and the number of branching points is 105 / 10000C.

[0054] The thickness setting is the same as in Example 1.

[0055] Comparative Example 1

[0056] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0057] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0058] Intermediate layer of film: 20 parts acrylic elastomer Exxon Vistamaxx 6102FL, 80 parts metallocene polyethylene mLLDPE-C (density 0.912 g / cm³) 3 MFR2.16 is 0.5g / 10min.

[0059] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0060] The thickness setting is the same as in Example 1.

[0061] Comparative Example 2

[0062] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0063] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.920 g / cm³)3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.8, weight average molecular weight is 116800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 15.0%, and the number of branching points is 140 / 10000C.

[0064] Intermediate layer of film: 50 parts acrylic elastomer Exxon Vistamaxx 6102FL, 50 parts metallocene polyethylene mLLDPE-C (density 0.916 g / cm³) 3 MFR2.16 is 0.2g / 10min.

[0065] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.920 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.8, weight average molecular weight is 116800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 15.0%, and the number of branching points is 140 / 10000C.

[0066] The thickness setting is the same as in Example 1.

[0067] Comparative Example 3

[0068] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0069] Outer layer of film: 100 parts of metallocene polyethylene mLLDPE-A (density 0.920 g / cm3, MFR 2.16 1.0 g / 10 min, molecular weight distribution 2.8, weight average molecular weight 116800, SSA analysis showed that the relative content of lamellar crystals with a thickness of more than 9.0 nm was 15.0%, and the number of branching points was 140 / 10000C).

[0070] Middle layer of film: 40 parts metallocene ultra-low density polyethylene (density 0.914 cm³) 3 The following components were used: MFR 2.16 (0.8 g / 10 min), molecular weight distribution 4.0, comonomer 1-hexene (4.2 mol% hexene molar content), branch number 192 / 10000C; 30 parts of propylene-based elastomer Exxon Vistamaxx 6102FL; and 30 parts of metallocene polyethylene mLLDPE-C (density 0.916 g / cm³). 3 MFR2.16 is 0.2g / 10min.

[0071] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.920 g / cm³) 3MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.8, weight average molecular weight is 116800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 15.0%, and the number of branching points is 140 / 10000C.

[0072] The thickness setting is the same as in Example 1.

[0073] Comparative Example 4

[0074] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0075] Outer film layer: 100 parts metallocene polyethylene (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 104800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 13.4%, and the number of branching points is 105 / 10000C.

[0076] Middle layer of film: 40 parts metallocene ultra-low density polyethylene mLLDPE-B (density 0.914 cm³) 3 The following components were used: MFR 2.16 (0.8 g / 10 min), molecular weight distribution 3.5, comonomer 1-hexene (3.4 mol% hexene molar content, 158 / 10000 C branched chain number), 30 parts of propylene-based elastomer Exxon Vistamaxx 6102FL, and 30 parts of metallocene polyethylene mLLDPE-C (density 0.916 g / cm³). 3 MFR2.16 is 0.2g / 10min.

[0077] Outer film layer: 100 parts metallocene polyethylene (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 104800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 13.4%, and the number of branching points is 105 / 10000C.

[0078] The thickness setting is the same as in Example 1.

[0079] Comparative Example 5

[0080] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0081] Outer film layer: 30 parts metallocene linear low-density polyethylene (density 0.918 g / cm³) 3MFR2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 103600, it is copolymerized from ethylene and hexene, and the number of branching points of the hexene structural unit is 107.5 / 10000C).

[0082] 65 parts ultra-low density polyethylene (density 0.912 g / cm³) 3 MFR2.16 is 1.0 g / 10 min, and molecular weight distribution is 6).

[0083] 5 parts low-density polyethylene (density 0.922 g / cm³) 3 MFR2.16 is 0.6 g / 10 min, molecular weight distribution is 13; it is homopolymerized from ethylene.

[0084] Middle layer of film: 35 parts Exxon Vistamaxx 3020FL, a propylene-based elastomer; 65 parts ultra-low density polyethylene (density 0.912 g / cm³). 3 MFR2.16 is 1.0 g / 10 min, and molecular weight distribution is 6.

[0085] Outer film layer: 30 parts metallocene linear low-density polyethylene (density 0.918 g / cm³) 3 MFR2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 103600, it is copolymerized from ethylene and hexene, and the number of branching points of the hexene structural unit is 107.5 / 10000C).

[0086] 65 parts ultra-low density polyethylene (density 0.912 g / cm³) 3 MFR2.16 is 1.0 g / 10 min.

[0087] 5 parts low-density polyethylene (density 0.922 g / cm³) 3 MFR2.16 is 0.6 g / 10 min, molecular weight distribution is 13; it is homopolymerized from ethylene.

[0088] The film thickness is 120 μm, and the thickness ratio of any outer layer to the middle layer is 3:7.

[0089] Comparative Example 6

[0090] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer. The middle layer is composed of the following components in parts by weight: 60 parts Exceed XP 6026, 30 parts Vistamaxx 3020FL, 10 parts LD2420D, 5 parts cellulose, 2 parts titanium dioxide and 2 parts silicone oil.

[0091] The outer layer is composed of the following components in parts by weight: 88 parts Exceed 1018, 10 parts LD2420D, 2 parts opening agent, 3 parts cellulose, 2 parts titanium dioxide and 3 parts silicone oil.

[0092] The film thickness is set to 80 μm, and the thickness ratio of any outer layer to the middle layer is 1:3.

[0093] Comparative Example 7

[0094] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0095] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0096] Middle layer of film: 70 parts metallocene ultra-low density polyethylene mLLDPE-B (density 0.914 cm³) 3 MFR2.16 is 0.8 g / 10 min, molecular weight distribution is 3.5, comonomer is 1-hexene, hexene molar content is 3.4 mol%, branch number is 158 / 10000C), 30 parts of propylene-based elastomer Exxon Vistamaxx 6102FL.

[0097] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0098] Comparative Example 8

[0099] A stretchable sheath membrane includes a middle layer and outer layers respectively disposed on both sides of the middle layer, each layer comprising:

[0100] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0101] Intermediate layer of film: 30 parts acrylic elastomer Exxon Vistamaxx 6102FL, 70 parts metallocene polyethylene mLLDPE-C (density 0.916 g / cm³) 3 MFR2.16 is 0.2g / 10min.

[0102] Outer film layer: 100 parts metallocene polyethylene mLLDPE-A (density 0.918 g / cm³) 3 MFR 2.16 is 1.0 g / 10 min, molecular weight distribution is 2.6, weight average molecular weight is 114800, SSA analysis shows that the relative content of lamellar crystals with a thickness of 9.0 nm or more is 16.4%, and the number of branching points is 135 / 10000C.

[0103] Performance testing

[0104] The films prepared according to the examples and comparative examples were evaluated for performance using the following methods:

[0105] Thin film tensile properties: tested according to GB / T 13022-1991, using type 5 specimens, with a tensile speed of 200 mm / min.

[0106] Tear resistance of film: tested according to GB / T 11999-1989, using rectangular specimens.

[0107] Impact strength of dart: as per GB / T 9639-2008.

[0108] The performance test results are shown in Table 1 below.

[0109] Table 1 Performance Test Results

[0110] .

[0111] according to Figure 2 , 3 4 and Figure 1 In contrast, the melt curves of the middle layer polyethylene used in the comparative example did not reach three melt peaks, and the highest melt temperature was below 120°C, which also proves that the middle layer is unlikely to have the puncture resistance and tear resistance properties shown in the examples.

[0112] According to the performance test results in Table 1, compared with Comparative Example 1 (without mLLDPE-B), Example 1 showed a significant improvement in film tear resistance and a reduction in cost; compared with Comparative Examples 3 and 4 (without mLLDPE-B) and Comparative Example 4 (without mLLDPE-A), Examples 2 and 3 showed significant improvements in both tensile and tear resistance of the film and a reduction in cost; compared with Comparative Example 6, Example 4 showed significant improvements in both tensile and tear resistance of the film and a reduction in cost; compared with the Comparative Example using Vistamaxx 3020, the tensile properties of the film were significantly improved; compared with Comparative Example 7 (using only propylene-based elastomers and mLLDPE-B) and Comparative Example 8 (using only propylene-based elastomers and mLLDPE-C), both tensile and tear resistance of the film were improved. By using the polyethylene resin with the specific structure and specific formulation combination of this invention, the mechanical properties of cold-stretched films can be significantly improved while reducing production costs.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A stretchable sheath membrane, characterized in that: It includes a middle layer and two outer layers respectively located on both sides of the middle layer; The middle layer, based on 100 parts by weight, comprises components with a density of 0.914 g / cm³. 3 Metallocene polyethylene, 10-40 parts, density 0.912-0.916 g / cm³ 3 40-70 parts of metallocene polyethylene and 10-30 parts of propylene-based elastomer; The outer layer component has a density of 0.918~0.920 g / cm³. 3 The outer layer of metallocene polyethylene has a molecular weight distribution of 2.5 to 3.2 and a weight-average molecular weight of 112,000 to 120,000. According to the thermal analysis of crystallization, the outer layer of metallocene polyethylene has a lamellar content of 14% to 16.4% with a thickness of 9.0 nm or more and a branching point number of 125 to 145 / 10,000°C. The density is 0.914 g / cm³. 3 The metallocene polyethylene MFR2.16 has a strength of 0.8 g / 10 min; its density is 0.912~0.916 g / cm³. 3 The metallocene polyethylene MFR2.16 has a content of 0.2~0.7 g / 10 min; the density of the middle layer is 0.914 g / cm³. 3 The molecular weight distribution of metallocene polyethylene is 3.3~3.

8.

2. The stretchable sleeve membrane according to claim 1, characterized in that: The outer metallocene polyethylene melt flow rate of 2.16 kg is 0.9~1.2 g / 10 min.

3. The stretchable sleeve membrane according to claim 1, characterized in that: The density of the middle layer is 0.914 g / cm³. 3 In metallocene polyethylene, the comonomer is 1-hexene.

4. The stretchable sleeve membrane according to claim 3, characterized in that: The density is 0.914 g / cm³. 3 The molar content of hexene in metallocene polyethylene is 3.2~3.5 mol.

5. The stretchable sleeve membrane according to claim 1, characterized in that: The propylene-based elastomer is Vistamaxx 6102FL.

6. The stretchable sleeve membrane according to claim 1, characterized in that: The thickness ratio of any outer layer to the middle layer is 1:3.

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