Polyethylene heavy packaging film

Abstract

The invention discloses a polyethylene heavy packaging film, and belongs to the technical field of polyethylene heavy packaging films. According to the technical scheme, the cable comprises an inner layer, a middle layer and an outer layer, wherein the inner layer comprises the following components in parts by weight: 10-25 parts of high-pressure polyethylene resin, 20-40 parts of metallocene polyethylene resin I and 50-70 parts of metallocene polyethylene resin II; the middle layer is prepared from the following components in parts by weight: 10 to 40 parts of high-density polyethylene resin, 10 to 50 parts of metallocene polyethylene resin I, 20 to 50 parts of metallocene polyethylene resin II and 0.06 to 0.1 part of hexahydrophthalic acid metal salt compound; the outer layer comprises the following components in parts by weight: 10-25 parts of high-pressure polyethylene resin, 20-40 parts of metallocene polyethylene resin I and 50-70 parts of metallocene polyethylene resin II. According to the polyethylene heavy packaging film, the thickness of the polyethylene heavy packaging film is reduced and the comprehensive performance of the polyethylene heavy packaging film is improved under the condition that no elastomer is added.

Description

Technical Field

[0001] The invention relates to the technical field of polyethylene heavy packaging films, and in particular to a polyethylene heavy packaging film. Background Art

[0002] Polyethylene heavy packaging film is a new type of packaging film. Usually, the packaging film that can carry 10-50kg of solid particles or powdered materials is called heavy packaging film, which is generally a 25kg packaging bag. Polyethylene heavy packaging bags have the advantages of high packaging automation, good sealing, excellent moisture and anti-fouling performance, good aging resistance, and extended storage time of goods. Early polyethylene heavy packaging bags were mainly made of general linear polyethylene and low-density polyethylene resin blends, but the thickness was relatively thick, about 150-200μm, the production cost was high, and the total amount of waste after the material was unpacked and used was high.

[0003] Chinese invention patent CN111483196B discloses a three-layer co-extruded heavy packaging film preparation method, which provides a heavy packaging film with good mechanical properties, but a high content of polyolefin elastomer is added to its formula. The average price of polyolefin elastomer is currently above 20,000 yuan / ton, while the average price of polyethylene resin is less than 10,000 yuan / ton. Therefore, adding a high content of polyolefin elastomer to the formula will greatly increase the production cost; at the same time, the patent does not specify the thickness of the heavy packaging film prepared by it. Chinese invention patent CN115635750A discloses a low-temperature resistant three-layer co-extruded heavy packaging film, which provides a heavy packaging film with high strength, but the film thickness is 160μm. At the same time, adding a high content of polyolefin elastomer makes the material and cost in the production process higher, and more waste will be generated after use; in addition, adding a high content of LDPE resin and LLDPE resin in the invention will reduce the mechanical properties of the film.

[0004] Therefore, in view of the above-mentioned problems existing in the existing polyethylene heavy packaging film, it is necessary to develop a new formula for three-layer co-extruded polyethylene heavy packaging film to prepare a polyethylene heavy packaging film with higher comprehensive performance without adding polyolefin elastomers with higher production costs. Summary of the invention

[0005] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and provide a polyethylene heavy packaging film, which can reduce the thickness of the polyethylene heavy packaging film and improve its comprehensive performance without adding elastomers through the formula design of the inner, middle and outer three layers and the optimization of each component in the formula.

[0006] The technical solution of the present invention is:

[0007] A polyethylene heavy packaging film comprises three layers, an inner layer, a middle layer and an outer layer, wherein the inner layer comprises the following components in parts by weight: 10-25 parts of high-pressure polyethylene resin (LDPE), 20-40 parts of metallocene polyethylene resin 1 (mPE1), and 50-70 parts of metallocene polyethylene resin 2 (mPE2); the middle layer comprises the following components in parts by weight: 10-40 parts of high-density polyethylene resin (HDPE), 10-50 parts of metallocene polyethylene resin 1, 20-50 parts of metallocene polyethylene resin 2, and 0.06-0.1 parts of hexahydrophthalic acid metal salt compounds, preferably 0.06 parts of hexahydrophthalic acid metal salt compounds; the outer layer comprises the following components in parts by weight: 10-25 parts of high-pressure polyethylene resin, 20-40 parts of metallocene polyethylene resin 1, and 50-70 parts of metallocene polyethylene resin 2.

[0008] Preferably, the high-density polyethylene resin is a copolymer of ethylene and 1-hexene, with a density of 0.952-0.956 g / cm 3 , the melt index is 8-12g / 10min; preferably, the density of the high-density polyethylene resin is 0.954g / cm 3 , the melt index is 10g / 10min.

[0009] Preferably, the density of the high pressure polyethylene resin is 0.920-0.926 g / cm 3 , the melt index is 0.3-0.8g / 10min; preferably, the density of the high pressure polyethylene resin is 0.924g / cm 3 , the melt index is 0.5g / 10min.

[0010] Preferably, the density of the metallocene polyethylene resin is 0.917-0.921 g / cm 3 , the melt index is 0.8-1.1 g / 10 min; preferably, the density of the metallocene polyethylene resin is 0.918 g / cm 3 , the melt index is 1.0g / 10min; the density of metallocene polyethylene resin II is 0.913-0.915g / cm 3 , the melt index is 0.7-0.9 g / 10 min; preferably, the density of metallocene polyethylene resin II is 0.914 g / cm 3 , the melt index is 0.8g / 10min.

[0011] Preferably, the metallocene polyethylene resin 2 is subjected to a crystallization thermal fractionation analysis using DSC, wherein the content of lamellae with a thickness of more than 9 nm is 22-30%, and the content of lamellae with a thickness of less than 6 nm is 48-55%.

[0012] Preferably, the molecular weight and distribution of the metallocene polyethylene resin II are tested by GPC, and its weight average molecular weight is greater than 130,000, wherein the content of the portion with a weight average molecular weight above 1,000,000 is greater than 0.35%. The higher the molecular weight and the greater the content of the high molecular weight portion, the more beneficial it is to improve the mechanical properties of the material.

[0013] Preferably, the comonomer of the metallocene polyethylene resin II is analyzed by carbon nuclear magnetic resonance, and the molar percentage of the comonomer is 3.20-3.60 mol%.

[0014] Preferably, the hexahydrophthalic acid metal salt compound is calcium hexahydrophthalate. Through experiments, it is found that adding hexahydrophthalic acid metal salt compounds can improve the tear resistance and puncture resistance of polyethylene heavy packaging film.

[0015] Preferably, the polyethylene heavy-duty packaging film of the present invention is produced by three-layer co-extrusion, the thickness ratio of the inner, middle and outer layers is 1:(2-3):1, and the total thickness of the polyethylene heavy-duty packaging film is 120 μm.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The invention provides a three-layer polyethylene heavy packaging film, which reduces the thickness of the polyethylene heavy packaging film and improves its comprehensive performance without adding an elastomer through the formula design of the inner, middle and outer three layers and the optimization of each component in the formula. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with embodiments.

[0019] Example 1

[0020] The polyethylene heavy packaging film of this embodiment includes three layers, inner, middle and outer layers, wherein the inner layer includes the following components in parts by weight: 20 parts of LDPE resin, density 0.924 g / cm 3 , melt index 0.5g / 10min; mPE1 resin 20 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38%, molar percentage of comonomer 3.38 mol%.

[0021] The middle layer includes the following components by weight: 30 parts of HDEP resin, density 0.954g / cm 3 , melt index 10g / min; mPE1 resin content 30 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 40 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flake crystals with thickness above 9nm 25%, content of flake crystals with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.38mol%; 0.06 parts of calcium hexahydrophthalate.

[0022] The outer layer includes the following components by weight: 20 parts of LDPE resin, density 0.924g / cm 3 , melt index 0.5g / 10min; mPE1 resin 20 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.38mol%.

[0023] Three-layer co-extrusion, the thickness ratio of the inner, middle and outer layers is 1:2:1, and the total thickness of the polyethylene heavy packaging film is 120μm.

[0024] Example 2

[0025] The polyethylene heavy packaging film of this embodiment includes three layers, inner, middle and outer layers, wherein the inner layer includes the following components in parts by weight: 15 parts of LDPE resin, density 0.926 g / cm 3 , melt index 0.5g / 10min; mPE1 resin 30 parts, density 0.921g / cm 3 , melt index 1.0g / 10min; mPE2 resin 55 parts, density 0.913g / cm 3 , melt index 0.7g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.40mol%.

[0026] The middle layer includes the following components by weight: 20 parts of HDEP resin, density 0.952g / cm 3, melt index 8g / min; mPE1 resin content 30 parts, density 0.921g / cm 3 , melt index 1.0g / 10min; mPE2 resin 50 parts, density 0.913g / cm 3 , melt index 0.7g / 10min, content of flake crystals with thickness above 9nm 25%, content of flake crystals with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.40mol%; 0.08 parts of calcium hexahydrophthalate.

[0027] The outer layer includes the following components by weight: 15 parts of LDPE resin, density 0.926g / cm 3 , melt index 0.5g / 10min; mPE1 resin 30 parts, density 0.921g / cm 3 , melt index 1.0g / 10min; mPE2 resin 55 parts, density 0.913g / cm 3 , melt index 0.7g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.40mol%.

[0028] Three-layer co-extrusion, the thickness ratio of the inner, middle and outer layers is 1:2:1, and the total thickness of the polyethylene heavy packaging film is 120μm.

[0029] Example 3

[0030] The polyethylene heavy packaging film of this embodiment includes three layers, inner, middle and outer layers, wherein the inner layer includes the following components in parts by weight: 25 parts of LDPE resin, density 0.920 g / cm 3 , melt index 0.3g / 10min; mPE1 resin 20 parts, density 0.917g / cm 3 , melt index 1.1g / 10min; mPE2 resin 55 parts, density 0.915g / cm 3 , melt index 0.9g / 10min, content of flakes with thickness above 9nm 29%, content of flakes with thickness below 6nm 50%, weight average molecular weight 148000, content of part with molecular weight above 1000000 0.42, molar percentage of comonomer 3.26mol%.

[0031] The middle layer includes the following components by weight: 40 parts of HDEP resin, density 0.956g / cm 3 , melt index 12g / 10min; mPE1 resin content 10 parts, density 0.917g / cm 3, melt index 1.1g / 10min; mPE2 resin 50 parts, density 0.915g / cm 3 , melt index 0.9g / 10min, content of flake crystals with thickness above 9nm 29%, content of flake crystals with thickness below 6nm 50%, weight average molecular weight 148000, content of part with molecular weight above 1000000 0.42, molar percentage of comonomer 3.26mol%; 0.1 part of calcium hexahydrophthalate.

[0032] The outer layer includes the following components by weight: 25 parts of LDPE resin, density 0.920g / cm 3 , melt index 0.3g / 10min; mPE1 resin 20 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 55 parts, density 0.915g / cm 3 , melt index 0.9g / 10min, content of flakes with thickness above 9nm 29%, content of flakes with thickness below 6nm 50%, weight average molecular weight 148000, content of part with molecular weight above 1000000 0.42, molar percentage of comonomer 3.26mol%.

[0033] Three-layer co-extrusion, the thickness ratio of the inner, middle and outer layers is 1:2:1, and the total thickness of the polyethylene heavy packaging film is 120μm.

[0034] Comparative Example 1

[0035] The difference from Example 1 is that calcium hexahydrophthalate is not added to the middle layer.

[0036] Comparative Example 2

[0037] The polyethylene heavy packaging film of Comparative Example 2 comprises three layers, the inner layer, the middle layer and the outer layer, wherein the inner layer comprises the following components in parts by weight: 20 parts of LDPE resin, a density of 0.924 g / cm 3 , melt index 0.5g / 10min; mPE1 resin 20 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; low-density mPE resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, 50% flake content with thickness above 9nm, 27% flake content with thickness below 6nm, weight average molecular weight 138000, content of part with molecular weight above 1000000 is 0.07, and molar percentage of comonomer is 4.15mol%.

[0038] The middle layer includes the following components by weight: 30 parts of HDEP resin, density 0.954g / cm 3 , melt index 10g / min; mPE1 resin content 30 parts, density 0.918g / cm3 , melt index 1.0g / 10min; low-density mPE resin 40 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, 50% flake crystal content with thickness above 9nm, 27% flake crystal content with thickness below 6nm, weight average molecular weight 138000, content of part with molecular weight above 10000000 0.07, molar percentage of comonomer 4.15mol%; 0.06 parts of calcium hexahydrophthalate.

[0039] The outer layer includes the following components by weight: 20 parts of LDPE resin, density 0.924g / cm 3 , melt index 0.5g / 10min; mPE1 resin 20 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; low-density mPE resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, 50% flake content with thickness above 9nm, 27% flake content with thickness below 6nm, weight average molecular weight 138000, content of part with molecular weight above 1000000 is 0.07, and molar percentage of comonomer is 4.15mol%.

[0040] Three-layer co-extrusion, the thickness ratio of the inner, middle and outer layers is 1:2:1, and the total thickness of the polyethylene heavy packaging film is 120μm.

[0041] Comparative Example 3

[0042] The polyethylene heavy packaging film of Comparative Example 3 comprises three layers, the inner layer, the middle layer and the outer layer, wherein the inner layer comprises the following components in parts by weight: 20 parts of LDPE resin, a density of 0.917 g / cm 3 , melt index 1.0g / 10min; mPE1 resin 20 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38%, molar percentage of comonomer 3.38 mol%.

[0043] The middle layer includes the following components by weight: 30 parts of HDEP resin, density 0.954g / cm 3 , melt index 10g / min; mPE1 resin content 30 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 40 parts, density 0.914g / cm 3, melt index 0.8g / 10min, content of flake crystals with thickness above 9nm 25%, content of flake crystals with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.38mol%; 0.06 parts of calcium hexahydrophthalate.

[0044] The outer layer includes the following components by weight: 20 parts of LDPE resin, density 0.917 g / cm3, melt index 1.0 g / 10 min; 20 parts of mPE1 resin, density 0.918 g / cm 3 , melt index 1.0g / 10min; mPE2 resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.38mol%.

[0045] Three-layer co-extrusion, the thickness ratio of the inner, middle and outer layers is 1:2:1, and the total thickness of the polyethylene heavy packaging film is 120μm.

[0046] Comparative Example 4

[0047] The polyethylene heavy packaging film of Comparative Example 4 comprises three layers, the inner layer, the middle layer and the outer layer, wherein the inner layer comprises the following components in parts by weight: 20 parts of LDPE resin, a density of 0.924 g / cm 3 , melt index 0.5g / 10min; mPE1 resin 20 parts, density 0.924g / cm 3 , melt index 0.6g / 10min; mPE2 resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38%, molar percentage of comonomer 3.38 mol%.

[0048] The middle layer includes the following components by weight: 30 parts of HDEP resin, density 0.954g / cm 3 , melt index 10g / min; mPE1 resin content 30 parts, density 0.924g / cm 3 , melt index 0.6g / 10min; mPE2 resin 40 parts, density 0.914g / cm 3, melt index 0.8g / 10min, content of flake crystals with thickness above 9nm 25%, content of flake crystals with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.38mol%; 0.06 parts of calcium hexahydrophthalate.

[0049] The outer layer includes the following components by weight: 20 parts of LDPE resin, density 0.924g / cm 3 , melt index 0.5g / 10min; mPE1 resin 20 parts, density 0.924g / cm 3 , melt index 0.6g / 10min; mPE2 resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.38mol%.

[0050] Three-layer co-extrusion, the thickness ratio of the inner, middle and outer layers is 1:2:1, and the total thickness of the polyethylene heavy packaging film is 120μm.

[0051] Comparative Example 5

[0052] The polyethylene heavy packaging film of Comparative Example 5 comprises three layers, the inner layer, the middle layer and the outer layer, wherein the inner layer comprises the following components in parts by weight: 20 parts of LDPE resin, a density of 0.924 g / cm 3 , melt index 0.5g / 10min; mPE1 resin 20 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38%, molar percentage of comonomer 3.38 mol%.

[0053] The middle layer includes the following components by weight: 30 parts of HDEP resin, density 0.950g / cm 3 , melt index 14g / min; mPE1 resin content 30 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 40 parts, density 0.914g / cm 3, melt index 0.8g / 10min, content of flake crystals with thickness above 9nm 25%, content of flake crystals with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.38mol%; 0.06 parts of calcium hexahydrophthalate.

[0054] The outer layer includes the following components by weight: 20 parts of LDPE resin, density 0.924g / cm 3 , melt index 0.5g / 10min; mPE1 resin 20 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; mPE2 resin 60 parts, density 0.914g / cm 3 , melt index 0.8g / 10min, content of flakes with thickness above 9nm 25%, content of flakes with thickness below 6nm 51%, weight average molecular weight 138000, content of part with molecular weight above 1000000 0.38, molar percentage of comonomer 3.38mol%.

[0055] Three-layer co-extrusion, the thickness ratio of the inner, middle and outer layers is 1:2:1, and the total thickness of the polyethylene heavy packaging film is 120μm.

[0056] Comparative Example 6 (Example 1 in CN114454578A)

[0057] Polyethylene heavy packaging film outer layer: mPE resin 50 parts, density 0.924g / cm 3 , melt index 1.1g / 10min, relative content of 9nm thick or above flakes 15%; ultra-low density polyethylene resin 25 parts, density 0.910g / cm 3 , melt index 1.0g / 10min; LDPE resin 25 parts, density 0.920g / cm 3 , melt index 1.0g / 10min.

[0058] Polyethylene heavy packaging film middle layer: mPE resin 80 parts, density 0.924g / cm 3 , melt index 1.1g / 10min, relative content of 9nm thick or above flakes 15%; LDPE resin 20 parts, density 0.920g / cm 3 , melt index 1.0g / 10min.

[0059] Inner layer of polyethylene heavy packaging film: 16.7 parts of ultra-low density polyethylene resin, density 0.910g / cm 3 , melt index 1.0g / 10min; LDPE resin 50 parts, density 0.920g / cm 3 , melt index is 1.0g / 10min; mPE resin 33.3 parts, density 0.924g / cm3 , melt index 1.1g / 10min, relative content of flakes above 9nm thickness 15%

[0060] The thickness ratio of the inner, middle and outer layers is 1:1:1, and the total thickness is 120μm.

[0061] Comparative Example 7 (Example 1 in CN115635750A)

[0062] Inner layer of polyethylene heavy packaging film: 25 parts of LDPE resin, density 0.920g / cm 3 , melt index 1.0g / 10min; mLLDPE resin 39 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; LLDPE resin 30 parts, 0.920g / cm3, melt index 0.5g / 10min; propylene elastomer 5 parts, density 0.900g / cm 3 , melt index 0.5g / 10min; 1 part of processing aid.

[0063] Polyethylene heavy packaging film middle layer: LDPE resin 20 parts, density 0.920g / cm 3 , melt index 1.0g / 10min; mLLDPE resin 50 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; LLDPE resin 0.920g / cm 3 , melt index 0.5g / 10min.

[0064] Polyethylene heavy packaging film outer layer: LDPE resin 20 parts, density 0.920g / cm 3 , melt index 1.0g / 10min; mLLDPE resin 40 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; LLDPE resin 29 parts, density 0.920g / cm 3 , melt index 0.5g / 10min; 1 part of masterbatch.

[0065] The inner, middle and outer thickness ratio is 1:2:1, and the total thickness is 160μm.

[0066] Comparative Example 8 (Example 6 in CN115635750A)

[0067] Inner layer of polyethylene heavy packaging film: 39 parts of mPE resin, density 0.918g / cm 3 , melt index 1.0g / 10min; LLDPE resin 25 parts, density 0.920g / cm 3 , melt index 1.0g / 10min; LDPE resin 20 parts, density 0.924g / cm 3, melt index 0.8g / 10min; propylene elastomer 10 parts, density 0.900g / cm 3 , melt index 0.5g / 10min.

[0068] Polyethylene heavy packaging film middle layer: mPE resin 50 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; LLDPE resin 20 parts, density 0.920g / cm 3 , melt index 1.0g / 10min; LDPE resin 20 parts, density 0.924g / cm 3 , melt index 0.8g / 10min; propylene elastomer 15 parts, density 0.900g / cm 3 , melt index 0.5g / 10min; 1 part of processing aid.

[0069] Polyethylene heavy packaging film outer layer: mPE resin 40 parts, density 0.918g / cm 3 , melt index 1.0g / 10min; LLDPE resin 25 parts, density 0.920g / cm 3 , melt index 1.0g / 10min; LDPE resin 20 parts, density 0.924g / cm 3 , melt index 0.8g / 10min; propylene elastomer 15 parts, density 0.900g / cm 3 , melt index 0.5g / 10min.

[0070] The inner, middle and outer thickness ratio is 1:2:1, and the total thickness is 120μm.

[0071] The performance of the polyethylene heavy packaging films prepared in Examples 1-3 and Comparative Examples 1-8 was evaluated according to the following method:

[0072] Tensile properties: According to GB / T 1040.3-2006, 5-type splines, tensile speed is 200mm / min;

[0073] Tear resistance: According to GB / T 11999-1989, using rectangular specimens;

[0074] Drop impact strength: according to GB / T 9639-2008.

[0075] The test results are shown in Table 1-2:

[0076] Table 1

[0077]

[0078] Table 2

[0079]

[0080] As can be seen from Table 1-2, the absence of calcium hexahydrophthalate in the middle layer of the packaging film of Comparative Example 1 will result in low tear resistance and drop impact strength of the polyethylene heavy packaging film. This is mainly because calcium hexahydrophthalate is added to the example, which increases the crystal orientation of the polyethylene during film processing, thereby improving the tear resistance and puncture resistance of the film. 3 The resin has a higher comonomer content than mPE2 in the embodiment. Theoretically, the higher the comonomer content of the resin with similar indicators, the higher the puncture resistance and tear resistance of the processed film will be. However, through structural analysis, it is found that the mPE2 resin in Comparative Example 2 has a low polymer content and a low comonomer content in the high molecular weight part. As a result, although its comonomer content is high, the performance of the final prepared film is not improved. The LDPE resin used in Comparative Example 3 has a low density and a large melt index, resulting in a decrease in the mechanical properties of the film. The mPE1 resin used in Comparative Example 4 has an increased density, resulting in a decrease in the longitudinal tearing and dart drop impact strength of the film. The HDPE resin used in Comparative Example 5 has a reduced density, resulting in a decrease in the transverse tearing and transverse tensile properties of the film. Comparative Example 6 does not add HDPE resin, resulting in low film tensile strength and transverse tearing performance. Comparative Examples 7 and 8 add propylene-based elastomers, but due to the addition of more LLDPE resin, the dart drop impact strength is low. At the same time, the film thickness of Comparative Example 7 is high, the production cost is increased, and it cannot be thinned and strengthened.

[0081] The present invention uses a low-density metallocene polyethylene resin with a specific molecular structure. Although its comonomer content is relatively low, it has the particularity of different thickness lamellae distribution and molecular weight distribution, breaking the rule that resins with the same index have low comonomer content and poor mechanical properties. The packaging film processed with the resin has higher comprehensive performance, which exceeds the level of resins with the same index and high comonomer content.

Claims

1. A polyethylene heavy packaging film, characterized in that: It includes three layers, inner, middle and outer layers, wherein the inner layer includes the following components by weight: 10-25 parts of high pressure polyethylene resin, 20-40 parts of metallocene polyethylene resin I, and 50-70 parts of metallocene polyethylene resin II; The middle layer comprises the following components in parts by weight: 10-40 parts of high-density polyethylene resin, 10-50 parts of metallocene polyethylene resin 1, 20-50 parts of metallocene polyethylene resin 2, and 0.06-0.1 parts of hexahydrophthalic acid metal salt compound; The outer layer comprises the following components in parts by weight: 10-25 parts of high pressure polyethylene resin, 20-40 parts of metallocene polyethylene resin 1, and 50-70 parts of metallocene polyethylene resin 2.

2. The polyethylene heavy packaging film according to claim 1, characterized in that: The high-density polyethylene resin is a copolymer of ethylene and 1-hexene, and has a density of 0.952-0.956 g / cm 3 , the melt index is 8-12g / 10min.

3. The polyethylene heavy packaging film according to claim 1, characterized in that: The density of the high pressure polyethylene resin is 0.920-0.926 g / cm 3 , the melt index is 0.3-0.8g / 10min.

4. The polyethylene heavy packaging film according to claim 1, characterized in that: The density of the metallocene polyethylene resin is 0.917-0.921 g / cm 3 , the melt index is 0.8-1.1g / 10min; the density of metallocene polyethylene resin II is 0.913-0.915g / cm 3 , the melt index is 0.7-0.9g / 10min.

5. The polyethylene heavy packaging film according to claim 1, characterized in that: In the metallocene polyethylene resin II, the content of platelets with a thickness of more than 9 nm is 22-30%, and the content of platelets with a thickness of less than 6 nm is 48-55%.

6. The polyethylene heavy packaging film according to claim 5, characterized in that: The weight average molecular weight of the metallocene polyethylene resin II is greater than 130,000, wherein the content of the part with a weight average molecular weight of more than 1,000,000 is greater than 0.35%.

7. The polyethylene heavy packaging film according to claim 6, characterized in that: The molar percentage of the comonomer in the metallocene polyethylene resin II is 3.20-3.60 mol%.

8. The polyethylene heavy packaging film according to claim 1, characterized in that: The hexahydrophthalic acid metal salt compound is calcium hexahydrophthalate.

9. The polyethylene heavy packaging film according to claim 1, characterized in that: The thickness ratio of the inner, middle and outer layers of the polyethylene heavy packaging film is 1:(2-3):1, and the total thickness of the polyethylene heavy packaging film is 120 μm.

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