A cold sleeve film and a preparation method thereof

Abstract

The present application relates to the technical field of composite film, and provides a cold sleeve film and a preparation method thereof.The present application uses different grades of metallocene polyethylene in the outer layer, the middle layer and the inner layer, and controls the proportion thereof, so that the tensile strength and the puncture resistance of the cold sleeve film can be improved;The present application adds ethylene-vinyl acetate copolymer and elastomer in the middle layer, so that the resilience and the clamping force of the film can be improved;The present application also adds an opening slip agent in the outer layer and the inner layer to prevent the film from sticking, and adds a processing aid in the outer layer, the middle layer and the inner layer, so that the processing performance of the film can be improved.The present application also provides a preparation method of the cold sleeve film described in the above scheme, and small angle (10-20 degrees) and slow speed (5%-20%) are used in the upper traction rotation, so that the film surface can be flat, the winding can be neat, the end surface can be flat, and the problem of affecting the downstream use can be solved.

Description

Technical Field

[0001] This invention relates to the field of composite membrane technology, and in particular to a cold-coated membrane and its preparation method. Background Technology

[0002] Cold-stretch sleeve film, also known as cold-stretch tubing film, allows for the wrapping of goods without heating. Its high resilience and clamping force tightly encase the entire packaged item, creating a transparent package. Cold-stretch sleeve film is an economical and flexible packaging method that ensures cargo safety, provides excellent visual appeal, high packaging efficiency, and also offers waterproof and dustproof protection.

[0003] Cold-stretch film can replace cardboard boxes for home appliance packaging, significantly reducing packaging costs and reliance on cardboard. For a production base with 10 million units, using cold-stretch film often saves over 30% in packaging costs compared to cardboard boxes (based on a conservative median). At a saving of 1 yuan per unit, this translates to 10 million yuan in packaging cost savings annually; at 10 yuan per unit (savings for large appliances often exceed 10 yuan per unit), this amounts to 100 million yuan in packaging cost savings annually. Basically, home appliances with a length and width of at least 400mm can be packaged using vertical cold-stretch film; for smaller sizes or those requiring six-sided closure, horizontal cold-stretch film can be used. Therefore, most home appliances are suitable for cold-stretch film packaging. However, the variety of cold-stretch films currently available is still limited, and there is an urgent need to develop new cold-stretch film products.

[0004] In addition, in the current cold-rolled film production process, in order to achieve a flat film surface, a large angle and high speed are usually selected in the upper traction rotation. Although this method can achieve a flat film surface, it will cause the edge to shift and the winding to be uneven, which will affect the downstream use. Summary of the Invention

[0005] In view of this, the present invention provides a cold-rolled film and a method for preparing the same. The cold-rolled film provided by the present invention has good mechanical properties, which can meet packaging requirements. Furthermore, in the preparation of the cold-rolled film, the upward traction is carried out at a small angle and a slow speed, which can achieve neat winding and flat end face.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A cold-shelter film comprises an outer layer, a middle layer, and an inner layer stacked sequentially; the outer layer comprises the following raw materials in parts by weight: 10-90 parts of a first metallocene polyethylene, 30-60 parts of a second metallocene polyethylene, 1-10 parts of an opening slip agent, and 0.5-1 part of a processing aid; the first metallocene polyethylene has a melt index of 1 g / 10 min and a density of 0.918 g / cm³. 3The second metallocene polyethylene has a melt index of 1.9 g / 10 min and a density of 0.913 g / cm³. 3 ;

[0008] The middle layer comprises the following raw materials in parts by weight: 10-80 parts of third metallocene polyethylene, 10-60 parts of ethylene-vinyl acetate copolymer, 10-60 parts of elastomer, and 0.5-1 part of processing aid; the third metallocene polyethylene has a melt index of 0.5 g / 10 min and a density of 0.912 g / cm³. 3 ;

[0009] The inner layer comprises the following raw materials in parts by weight: 10-90 parts of fourth metallocene polyethylene, 20-70 parts of fifth metallocene polyethylene, 1-10 parts of opening slip agent, and 0.5-1 part of processing aid; the fourth metallocene polyethylene has a melt index of 0.8 g / 10 min and a density of 0.914 g / cm³. 3 The fifth metallocene polyethylene has a melt index of 0.85 g / 10 min and a density of 0.92 g / cm³. 3 .

[0010] Preferably, the first metallocene polyethylene is grade 1018MF; the second metallocene polyethylene is grade SP1520H; the third metallocene polyethylene is grade XP7052; the fourth metallocene polyethylene is grade 8784MK; and the fifth metallocene polyethylene is grade 5100.

[0011] Preferably, the processing aids used in the outer, middle, and inner layers have a melt index of 4.0–5.0 g / 10 min and a density of 0.910–0.930 g / cm³. 3 The melt index of the slip agent used in the outer and inner layers is 1.0–3.0 g / 10 min, and the density is 0.930–0.950 g / cm³. 3 .

[0012] Preferably, the ethylene-vinyl acetate copolymer has a melt index of 1.5 g / 10 min and a density of 0.936 g / cm³. 3 The vinyl acetate content in the ethylene-vinyl acetate copolymer is 16 wt%; the melt index of the elastomer is 3 g / 10 min, and the density is 0.862 g / cm³. 3 .

[0013] Preferably, the ethylene-vinyl acetate copolymer is grade EVA630; and the elastomer is grade 6102.

[0014] Preferably, the processing aid used in the outer, middle and inner layers is grade PE103-001; the opening slip agent used in the outer and inner layers is grade SAB-808.

[0015] Preferably, based on the total mass of the outer layer, middle layer, and inner layer (100%), the mass fraction of the outer layer is 20%–25%, the mass fraction of the middle layer is 50%–60%, and the mass fraction of the inner layer is 20%–25%.

[0016] The present invention also provides a method for preparing the cold jacket film described in the above-mentioned scheme, comprising the following steps:

[0017] The raw materials for the outer, middle, and inner layers are melted and plasticized, and then co-extruded and blown to obtain a primary film.

[0018] The primary film is sequentially subjected to upper traction rotation, corona treatment, lower traction, and winding to obtain the cold-rolled film; the upper traction rotation has an upward rotation angle of 10 to 20 degrees and a rotation speed of 5% to 20%.

[0019] Preferably, the corona treatment further includes sequentially printing, drying, and punching the corona-treated film.

[0020] Preferably, the co-extrusion blown film extruder includes an outer layer extruder, a middle layer extruder, and an inner layer extruder; each of the outer layer extruder, middle layer extruder, and inner layer extruder is provided with 5 heating zones, which are numbered 1 to 5 according to the order in which the raw materials pass through; the temperatures of zones 1 to 5 of the outer layer extruder are 165-175℃, 170-180℃, 170-180℃, 170-180℃, and 170-180℃ respectively; the temperatures of zones 1 to 5 of the middle layer extruder are 165-175℃, 180-190℃, 180-190℃, 180-190℃, and 180-190℃ respectively; and the temperatures of zones 1 to 5 of the inner layer extruder are 165-175℃, 170-180℃, 170-180℃, 170-180℃, and 170-180℃ respectively.

[0021] This invention provides a cold-coating film comprising an outer layer, a middle layer, and an inner layer stacked sequentially; the outer layer comprises the following raw materials in parts by weight: 10-90 parts of a first metallocene polyethylene, 30-60 parts of a second metallocene polyethylene, 1-10 parts of an opening slip agent, and 0.5-1 part of a processing aid; the first metallocene polyethylene has a melt index of 1 g / 10 min and a density of 0.918 g / cm³. 3 The second metallocene polyethylene has a melt index of 1.9 g / 10 min and a density of 0.913 g / cm³. 3The middle layer comprises the following raw materials in parts by weight: 10-80 parts of third metallocene polyethylene, 10-60 parts of ethylene-vinyl acetate copolymer, 10-60 parts of elastomer, and 0.5-1 part of processing aid; the third metallocene polyethylene has a melt index of 0.5 g / 10 min and a density of 0.912 g / cm³. 3 The inner layer comprises the following raw materials in parts by weight: 10-90 parts of fourth metallocene polyethylene, 20-70 parts of fifth metallocene polyethylene, 1-10 parts of opening slip agent, and 0.5-1 part of processing aid; the fourth metallocene polyethylene has a melt index of 0.8 g / 10 min and a density of 0.914 g / cm³. 3 The fifth metallocene polyethylene has a melt index of 0.85 g / 10 min and a density of 0.92 g / cm³. 3 This invention uses different grades of metallocene polyethylene in the outer, middle, and inner layers, and controls their proportions to improve the tensile strength and puncture resistance of the cold-coated film. The addition of ethylene-vinyl acetate copolymer and elastomer to the middle layer improves the film's resilience and holding power. Furthermore, the addition of an opening slip agent to the outer and inner layers prevents film adhesion, and the addition of processing aids to the outer, middle, and inner layers improves the film's processing performance.

[0022] This invention also provides a method for preparing the cold-coated film described above. After obtaining a primary film through co-extrusion blown film, the invention sequentially performs upward traction rotation, corona treatment, downward traction, and winding to obtain the cold-coated film. The upward traction rotation angle is controlled at 10–20 degrees, and the rotation speed at 5%–20%. Traditional methods, in order to achieve a smooth film surface, typically control the upward traction rotation speed above 50% and the upward traction angle above 270 degrees. While this achieves a smooth film surface, it can lead to issues such as edge misalignment and uneven winding, affecting downstream use. This invention breaks with traditional thinking by using a small angle (10–20 degrees) and a slow rotation speed (5%–20%) in the upward traction rotation. This ensures a smooth film surface while achieving neat winding and a flat end face, solving the problems affecting downstream use. Detailed Implementation

[0023] This invention provides a cold-coating film comprising an outer layer, a middle layer, and an inner layer stacked sequentially; the outer layer comprises the following raw materials in parts by weight: 10-90 parts of a first metallocene polyethylene, 30-60 parts of a second metallocene polyethylene, 1-10 parts of an opening slip agent, and 0.5-1 part of a processing aid; the first metallocene polyethylene has a melt index of 1 g / 10 min and a density of 0.918 g / cm³. 3 The second metallocene polyethylene has a melt index of 1.9 g / 10 min and a density of 0.913 g / cm³. 3 ;

[0024] The middle layer comprises the following raw materials in parts by weight: 10-80 parts of third metallocene polyethylene, 10-60 parts of ethylene-vinyl acetate copolymer, 10-60 parts of elastomer, and 0.5-1 part of processing aid; the third metallocene polyethylene has a melt index of 0.5 g / 10 min and a density of 0.912 g / cm³. 3 ;

[0025] The inner layer comprises the following raw materials in parts by weight: 10-90 parts of fourth metallocene polyethylene, 20-70 parts of fifth metallocene polyethylene, 1-10 parts of opening slip agent, and 0.5-1 part of processing aid; the fourth metallocene polyethylene has a melt index of 0.8 g / 10 min and a density of 0.914 g / cm³. 3 The fifth metallocene polyethylene has a melt index of 0.85 g / 10 min and a density of 0.92 g / cm³. 3 .

[0026] Unless otherwise specified, all raw materials used in this invention are commercially available products.

[0027] The outer layer is prepared from 10-90 parts by weight of a first metallocene polyethylene, preferably 20-80 parts, and more preferably 30-60 parts; the first metallocene polyethylene has a melt index of 1 g / 10 min and a density of 0.918 g / cm³. 3 The first metallocene polyethylene was graded 1018MF and purchased from ExxonMobil.

[0028] Based on the mass percentage of the first metallocene polyethylene, the raw materials for preparing the outer layer include 30-60 parts, preferably 40-50 parts, of the second metallocene polyethylene; the melt index of the second metallocene polyethylene is 1.9 g / 10 min, and the density is 0.913 g / cm³. 3 The second metallocene polyethylene, designated SP1520H, was purchased from Mitsui Chemicals.

[0029] Based on the mass fraction of the first metallocene polyethylene, the raw materials for preparing the outer layer include 1 to 10 parts of an opening slip agent, preferably 2 to 8 parts, more preferably 3 to 6 parts; the melt index of the opening slip agent used in the outer and inner layers is preferably 1.0 to 3.0 g / 10 min, more preferably 2 g / 10 min, and the density is preferably 0.930 to 0.950 g / cm³. 3 More preferably, it is 0.94 g / cm³. 3 The preferred grade of the opening slip agent is SAB-808, manufactured by Huayi Technology Development Co., Ltd.

[0030] Based on the mass fraction of the first metallocene polyethylene, the raw materials for preparing the outer layer include 0.5 to 1 part, preferably 0.6 to 0.8 parts, of processing aids; the melt index of the processing aids is preferably 4.0 to 5.0 g / 10 min, and the density is preferably 0.910 to 0.930 g / cm³. 3 The preferred grade of the processing aid is PE103-001, manufactured by Daikin Industries, Ltd. The processing aid with grade PE103-001 has a melt index of 4.5 g / 10 min and a density of 0.92 g / cm³. 3 The processing aid is specifically a functional masterbatch prepared from fluoropolymers and polyolefin resins.

[0031] The raw materials for preparing the middle layer, by weight, include 10-80 parts of third metallocene polyethylene, preferably 20-70 parts, and more preferably 30-60 parts; the third metallocene polyethylene has a melt index of 0.5 g / 10 min and a density of 0.912 g / cm³. 3 The third metallocene polyethylene is designated XP7052 and was purchased from ExxonMobil.

[0032] Based on the mass fraction of the third metallocene polyethylene, the raw materials for preparing the middle layer include 10-60 parts of ethylene-vinyl acetate copolymer, preferably 20-50 parts, and more preferably 30-40 parts; the ethylene-vinyl acetate copolymer has a melt index of 1.5 g / 10 min and a density of 0.936 g / cm³. 3 The vinyl acetate content in the ethylene-vinyl acetate copolymer is preferably 16 wt%; the grade of the ethylene-vinyl acetate copolymer is preferably EVA630, purchased from Tosoh Corporation of Japan.

[0033] Based on the mass fraction of the third metallocene polyethylene, the raw materials for preparing the middle layer include 10-60 parts of elastomer, preferably 20-50 parts, and more preferably 30-40 parts; the elastomer has a melt index of 3 g / 10 min and a density of 0.862 g / cm³. 3 The preferred grade of the elastomer is 6102, purchased from ExxonMobil; the elastomer is specifically an propylene elastomer.

[0034] Based on the mass fraction of the third metallocene polyethylene, the raw materials for preparing the middle layer include 0.5 to 1 part of processing aids, preferably 0.6 to 0.8 parts; the processing aids used in the middle layer are the same as those used in the outer layer, and will not be described again here.

[0035] The raw materials for preparing the inner layer, by weight, include 10-90 parts of fourth metallocene polyethylene, preferably 20-80 parts, and more preferably 30-60 parts; the fourth metallocene polyethylene has a melt index of 0.8 g / 10 min and a density of 0.914 g / cm³.3 The fourth metallocene polyethylene is grade 8784MK and was purchased from ExxonMobil.

[0036] Based on the mass fraction of fourth metallocene polyethylene, the raw materials for preparing the inner layer include 20-70 parts of fifth metallocene polyethylene, preferably 30-60 parts; the fifth metallocene polyethylene has a melt index of 0.85 g / 10 min and a density of 0.92 g / cm³. 3 The fifth metallocene polyethylene is grade 5100 and was purchased from Dow Chemical.

[0037] Based on the mass fraction of the fourth metallocene polyethylene, the raw materials for preparing the inner layer include 1 to 10 parts of an opening slip agent, preferably 2 to 8 parts, and more preferably 3 to 6 parts; the opening slip agent used in the inner layer is the same as the opening slip agent used in the outer layer, and will not be described again here.

[0038] Based on the mass fraction of the fourth metallocene polyethylene, the raw materials for preparing the inner layer include 0.5 to 1 part of processing aids, preferably 0.6 to 0.8 parts; the processing aids used in the inner layer are the same as those used in the outer layer, and will not be described again here.

[0039] In this invention, taking the total mass of the outer layer, middle layer and inner layer as 100%, the mass fraction of the outer layer is preferably 20% to 25%, the mass fraction of the middle layer is preferably 50% to 60%, and the mass fraction of the inner layer is preferably 20% to 25%; the thickness of the cold jacket film is preferably 90 to 130 μm.

[0040] The present invention also provides a method for preparing the cold jacket film described in the above scheme, comprising the following steps:

[0041] The raw materials for the outer, middle, and inner layers are melted and plasticized, and then co-extruded and blown to obtain a primary film.

[0042] The primary film is sequentially subjected to upper traction rotation, corona treatment, lower traction, and winding to obtain the cold-rolled film; the upper traction rotation has an upward rotation angle of 10 to 20 degrees and a rotation speed of 5% to 20%.

[0043] This invention involves melting and plasticizing the raw materials for the outer, middle, and inner layers, followed by co-extrusion blown film production to obtain a primary film. In this invention, the extruder used for co-extrusion blown film production preferably includes an outer layer extruder, a middle layer extruder, and an inner layer extruder. The co-extrusion blown film process specifically includes: mixing the raw materials for the outer, middle, and inner layers in proportion using an automatic batching system, and then feeding them separately into the outer, middle, and inner layer extruders for melting and plasticizing; conveying the resulting adhesive solution to the die head for extrusion blown film production to obtain the primary film; preferably, each of the outer, middle, and inner layer extruders has five heating zones, designated as zones 1 to 5 according to the order in which the raw materials pass through; preferably, the die head has four heating zones, designated as zones 1 to 4 according to the order in which the raw materials pass through.

[0044] In this invention, the extrusion temperatures of the outer extruder, middle extruder, inner extruder, and each zone of the die are shown in Table 1:

[0045] Table 1. Extrusion temperatures of various zones in the outer, middle, and inner layer extruders and die.

[0046]

[0047]

[0048] In this invention, the extrusion pressure of the outer extruder is preferably 200-500 bar, more preferably 300-400 bar; the extrusion pressure of the middle extruder is preferably 200-500 bar, more preferably 300-400 bar; and the extrusion pressure of the inner extruder is preferably 200-500 bar, more preferably 300-400 bar.

[0049] After obtaining the primary film, the primary film is sequentially subjected to upper traction rotation, corona treatment, lower traction and winding to obtain the cold-rolled film. In this invention, after co-extrusion blown film, the resulting film bubble is preferably cooled by air, then flattened by a stabilizing ring and a herringbone pattern, then shaped along the side inserts, and then enters the upper traction rotation; the blowing temperature of the air cooling is preferably 10-15°C; the upper rotation angle of the upper traction rotation is 10-20 degrees, more preferably 15-20 degrees, and even more preferably 20 degrees; the rotation speed of the upper traction rotation is preferably 5%-20%, more preferably 5%-10%, and even more preferably 5%. In a specific embodiment of this invention, the parameters of the upper traction rotation can be set in the operating system of the blown film machine used for co-extrusion blown film. The rotation speed of the upper traction rotation in the co-extrusion blown film machine is expressed as a percentage, with a maximum speed of 100%. This invention sets this speed to 5%-20%. This invention uses a small angle and slow speed method for upper traction rotation, which can achieve neat winding and flat end face while ensuring the flatness of the film surface, thus solving the problem of affecting downstream use. After the upper traction rotation, the film passes through the guide rollers into the corona treatment device for corona treatment, and then passes through the lower traction clamping rollers into the winding device for winding. After the corona treatment, the corona-treated film is then sequentially printed, dried, and perforated. The device used in this invention is preferably equipped with automatic online printing and online perforation equipment. This invention does not have special requirements for the operation methods of corona treatment, printing, drying, perforation, lower traction, and winding; methods well known to those skilled in the art can be used.

[0050] 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. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0051] The raw materials used in the examples are shown in Table 2.

[0052] Table 2 shows the source of raw materials and performance parameters used in the examples.

[0053]

[0054]

[0055] The amount of raw materials used in each layer in each embodiment is shown in Table 3.

[0056] Table 3. Raw material proportions for each layer in Examples 1-3

[0057]

[0058] Example 1

[0059] The cold jacket film prepared in this embodiment has a three-layer structure. The weight percentages of the outer, middle and inner layers are as follows: outer layer 20%, middle layer 60%, inner layer 20%. The component ratios of the outer, middle and inner layers are shown in Table 3.

[0060] The preparation method is as follows:

[0061] The outer, middle, and inner layer raw materials are mixed in proportion by an automatic batching system and then fed into the outer, middle, and inner layer extruders. The raw materials are melted and plasticized and then fed into the die head for extrusion and blown film. After air cooling, the film bubble is flattened by a stabilizing ring and herringbone pattern. The film bubble is shaped along the two side inserts and rotated by upper traction (upward rotation angle of 20 degrees, speed of 5%). Then it enters the corona treatment device for corona treatment through guide rollers. After printing, drying, and perforation, it enters the front winding device through lower traction clamping rollers for winding to obtain cold-coated film. The resulting cold-coated film has a flat surface, is neatly wound, and has flat end faces.

[0062] The extruder temperature and pressure, and the die temperature are shown in Table 4.

[0063] Table 4. Temperature and pressure of the extruder and die temperature in Example 1.

[0064] outer layer 170 175 175 170 170 373 Middle layer 170 180 190 190 190 325 Inner layer 170 175 175 173 173 415 mold head 180 185 185 185

[0065] Example 2

[0066] The cold jacket film prepared in this embodiment has a three-layer structure. The weight percentages of the outer, middle and inner layers are as follows: outer layer 20%, middle layer 60%, inner layer 20%. The component ratios of the outer, middle and inner layers are shown in Table 3.

[0067] The preparation method is the same as in Example 1. The resulting cold-coated film has a smooth surface, is neatly wound, and has a flat end face.

[0068] Example 3

[0069] The cold jacket film prepared in this embodiment has a three-layer structure. The weight percentages of the outer, middle and inner layers are as follows: outer layer 20%, middle layer 60%, inner layer 20%. The component ratios of the outer, middle and inner layers are shown in Table 3.

[0070] The preparation method is the same as in Example 1. The resulting cold-coated film has a smooth surface, is neatly wound, and has a flat end face.

[0071] The tensile strength, puncture resistance, resilience and clamping force of the cold-coated films obtained in Examples 1 to 3 were tested. The test methods and test results are shown in Table 5.

[0072] Table 5. Test results of the mechanical properties of the cold-coating film obtained in Examples 1-3

[0073]

[0074] As can be seen from the data in Table 5, the cold jacket film prepared by this invention has excellent mechanical properties and can meet the requirements for use as a cold jacket film.

[0075] Comparative Example 1

[0076] The other conditions are the same as in Example 1, except that the upward rotation angle of the upper traction rotation is changed to 300 degrees and the rotation speed is changed to 60% when preparing the cold jacket film.

[0077] The results show that, compared with Example 1, although Comparative Example 1 can achieve a flat winding film surface, defects such as edge misalignment and uneven winding occur at the winding end, affecting downstream use.

[0078] Comparative Example 2

[0079] The other conditions are the same as in Example 1, except that the upper traction rotation is not turned on when preparing the cold jacket film, that is, the upper rotation angle and rotation speed are both 0.

[0080] The results show that, compared with Example 1, although Comparative Example 2 can achieve neat insertion edges and neat winding end face, the winding film surface is uneven, wavy, and the protruding parts stick together, affecting downstream use.

[0081] 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 cold-sealing film, characterized in that, The material comprises an outer layer, a middle layer, and an inner layer stacked sequentially. The outer layer comprises the following raw materials in parts by weight: 10-90 parts of first metallocene polyethylene, 30-60 parts of second metallocene polyethylene, 1-10 parts of opening slip agent, and 0.5-1 part of processing aid. The first metallocene polyethylene has a melt index of 1 g / 10 min and a density of 0.918 g / cm³. 3 The second metallocene polyethylene has a melt index of 1.9 g / 10 min and a density of 0.913 g / cm³. 3 ; The middle layer comprises the following raw materials in parts by weight: 10-80 parts of third metallocene polyethylene, 10-60 parts of ethylene-vinyl acetate copolymer, 10-60 parts of elastomer, and 0.5-1 part of processing aid; the third metallocene polyethylene has a melt index of 0.5 g / 10 min and a density of 0.912 g / cm³. 3 ; The inner layer comprises the following raw materials in parts by weight: 10-90 parts of fourth metallocene polyethylene, 20-70 parts of fifth metallocene polyethylene, 1-10 parts of opening slip agent, and 0.5-1 part of processing aid; the fourth metallocene polyethylene has a melt index of 0.8 g / 10 min and a density of 0.914 g / cm³. 3 The fifth metallocene polyethylene has a melt index of 0.85 g / 10 min and a density of 0.92 g / cm³. 3 ; The method for preparing the cold jacket film includes the following steps: The raw materials for the outer, middle, and inner layers are melted and plasticized, and then co-extruded and blown to obtain a primary film. The primary film is sequentially subjected to upper traction rotation, corona treatment, lower traction and winding to obtain the cold-rolled film; the upper traction rotation angle is 10~20 degrees, and the rotation speed is 5%~20% of the maximum upper traction rotation speed in the co-extrusion blown film machine.

2. The cold-shelter film according to claim 1, characterized in that, The first metallocene polyethylene is designated as 1018MF; the second metallocene polyethylene is designated as SP1520H; the third metallocene polyethylene is designated as XP7052; the fourth metallocene polyethylene is designated as 8784MK; and the fifth metallocene polyethylene is designated as 5100.

3. The cold-shelter film according to claim 1, characterized in that, The processing aids used in the outer, middle, and inner layers have a melt index of 4.0~5.0 g / 10 min and a density of 0.910~0.930 g / cm³. 3 The melt index of the slip agent used in the outer and inner layers is 1.0~3.0 g / 10 min, and the density is 0.930~0.950 g / cm³. 3 .

4. The cold-shelter film according to claim 1, characterized in that, The ethylene-vinyl acetate copolymer has a melt index of 1.5 g / 10 min and a density of 0.936 g / cm³. 3 The vinyl acetate content in the ethylene-vinyl acetate copolymer is 16 wt%; the melt index of the elastomer is 3 g / 10 min, and the density is 0.862 g / cm³. 3 .

5. The cold-shelter film according to claim 1 or 4, characterized in that, The grade of the ethylene-vinyl acetate copolymer is EVA630; the grade of the elastomer is 6102.

6. The cold-shelter film according to claim 1 or 3, characterized in that, The processing aids used in the outer, middle and inner layers are graded PE103-001; the slip agent used in the outer and inner layers is graded SAB-808.

7. The cold-shelter film according to claim 1, characterized in that, With the total mass of the outer layer, middle layer and inner layer as 100%, the mass fraction of the outer layer is 20% to 25%, the mass fraction of the middle layer is 50% to 60%, and the mass fraction of the inner layer is 20% to 25%.

8. The method for preparing the cold-shrink film according to any one of claims 1 to 7, characterized in that, Includes the following steps: The raw materials for the outer, middle, and inner layers are melted and plasticized, and then co-extruded and blown to obtain a primary film. The primary film is sequentially subjected to upper traction rotation, corona treatment, lower traction and winding to obtain the cold-rolled film; the upper traction rotation has an upward rotation angle of 10~20 degrees and a rotation speed of 5%~20%.

9. The preparation method according to claim 8, characterized in that, The corona treatment process also includes sequentially printing, drying, and punching the corona-treated film.

10. The preparation method according to claim 8 or 9, characterized in that, The co-extrusion blown film extruder includes an outer layer extruder, a middle layer extruder, and an inner layer extruder. Each of the outer layer extruder, middle layer extruder, and inner layer extruder is equipped with five heating zones, which are numbered 1 to 5 according to the order in which the raw materials pass through. The temperatures of zones 1 to 5 of the outer layer extruder are 165-175℃, 170-180℃, 170-180℃, 170-180℃, and 170-180℃, respectively. The temperatures of zones 1 to 5 of the middle layer extruder are 165-175℃, 180-190℃, 180-190℃, 180-190℃, and 180-190℃, respectively. The temperatures of zones 1 to 5 of the inner layer extruder are 165-175℃, 170-180℃, 170-180℃, 170-180℃, and 170-180℃, respectively.

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