A bidirectional pe stretch film and its preparation method and application

Abstract

The application belongs to the technical field of polyethylene film material, and particularly relates to a biaxial PE stretch film and a preparation method and application thereof. The biaxial PE stretch film is composed of an outer layer, a middle layer and an inner layer. The outer layer is a TPU film, which comprises TPU particles, an ultraviolet absorber and an antioxidant. The middle layer is a matte PE film, which comprises low-density polyethylene, linear low-density polyethylene, metallocene polyethylene, a composite additive, polyphthalic amide, a dispersing agent and an antioxidant. The inner layer is a milky white PE film, which comprises low-density polyethylene and high-density polyethylene and titanium white powder. The biaxial PE stretch film prepared by the application effectively improves the tensile strength, elongation at break and puncture resistance of the prepared biaxial PE stretch film by improving raw materials and optimizing a process flow, and can be applied to a surface protection film of a child crawling mat, an EPE, an XPE splicing mat protection film, a yoga mat protection film and a protection film containing all floor mats.

Description

Technical Field

[0001] This invention belongs to the field of polyethylene film material technology, specifically relating to a biaxially oriented PE film, its preparation method, and its application. Background Technology

[0002] Polyethylene film (PE film) is a widely used plastic film made of polyethylene resin. It possesses excellent moisture resistance, chemical resistance, insulation, and oil resistance. Based on density, polyethylene film can be classified into several types, including low-density polyethylene (LDPE) and high-density polyethylene (HDPE), each with its unique performance characteristics. LDPE film has good transparency, is flexible, and easy to heat-seal, while HDPE film has higher mechanical strength and heat resistance. Due to its lightweight, transparency, flexibility, wear resistance, and corrosion resistance, polyethylene film has wide applications in the packaging industry. It can be used for packaging various products such as food, pharmaceuticals, cosmetics, and daily necessities, protecting them from external contamination and oxidation, and extending their shelf life. Furthermore, polyethylene film can also be used in agricultural coverings and building waterproofing.

[0003] Biaxial stretching is a widely used orientation processing method that significantly improves the mechanical, optical, heat resistance, and gas barrier properties of materials by stretching the film in both longitudinal and transverse directions. Biaxially oriented polyethylene (BOPE) film is a relatively new type of packaging material that has emerged in the film industry in recent years. Its many excellent properties have made it a major type of polyolefin film material in the flexible packaging field.

[0004] While biaxially oriented polyethylene (BOPE) film possesses many excellent properties, it also has some drawbacks, such as limitations in mechanical properties, poor abrasion and scratch resistance, insufficient barrier properties, poor heat-sealing performance, processing complexity, and poor environmental adaptability. Therefore, there is a need for a biaxially oriented PE film with superior mechanical properties such as abrasion resistance and tensile strength. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the purpose of this invention is to provide a biaxially oriented PE stretch film, its preparation method and application.

[0006] The technical solution of this invention is:

[0007] A biaxially oriented PE film, comprising an outer layer, a middle layer, and an inner layer:

[0008] The outer layer is a TPU film, comprising 70-80 parts of TPU particles, 0.2-0.4 parts of ultraviolet absorber, and 0.1-0.3 parts of antioxidant;

[0009] The middle layer is a matte PE film, comprising 40-60 parts of low-density polyethylene, 20-30 parts of linear low-density polyethylene, 10-15 parts of metallocene polyethylene, 2-6 parts of composite additives, 1-3 parts of polyphthalamide, 0.3-0.5 parts of dispersant, and 0.2-0.5 parts of antioxidant.

[0010] The inner layer is a milky white PE film, comprising 60-70 parts of low-density polyethylene, 20-25 parts of high-density polyethylene, and 1-5 parts of titanium dioxide.

[0011] Furthermore, the outer layer is a TPU film, comprising 75 parts TPU particles, 0.3 parts ultraviolet absorber, and 0.2 parts antioxidant;

[0012] The middle layer is a matte PE film, comprising 50 parts of low-density polyethylene, 25 parts of linear low-density polyethylene, 12 parts of metallocene polyethylene, 4 parts of composite additives, 2 parts of polyphthalamide, 0.4 parts of dispersant, and 0.3 parts of antioxidant.

[0013] The inner layer is a milky white PE film, comprising 65 parts of low-density polyethylene, 22 parts of high-density polyethylene, and 3 parts of titanium dioxide.

[0014] Furthermore, the composite additive in the middle matte PE film is composed of modified talc powder and polytetrafluoroethylene micro powder in a weight ratio of 2 to 4:1, preferably 3:1.

[0015] Furthermore, the preparation method of the modified talc in the intermediate matte PE film composite additive includes the following steps:

[0016] S1. Dissolve nano-talc powder in ethanol solution and stir with a magnetic stirrer to disperse it, and then prepare a nano-talc powder dispersion for later use.

[0017] S2. Dissolve the composite modifier in anhydrous ethanol by stirring, and then heat and stir in a water bath to obtain a composite modifier solution for later use.

[0018] S3. Slowly pour the composite modifier solution obtained in step S2 into the nano talc powder dispersion obtained in step S1, heat and stir to react, then wash and dry to obtain the final product.

[0019] Furthermore, the concentration of the ethanol solution in step S1 is 75%, and the mass-to-volume ratio of the added nano-talc powder to the ethanol solution is 12-15 g: 100 mL.

[0020] Further, the mass concentration of the composite modifier solution in step S2 is 1.5-2.5%; the amount of composite modifier added in step S2 is 5-8% of the weight of nano talc powder; the composite modifier is composed of sodium myristate and silane coupling agent KH-570 in a weight ratio of 2-3:1, preferably 2.5:1.

[0021] Furthermore, in step S2, the water bath heating temperature is 40-50°C, the stirring time is 20-30 min, and the stirring speed is 500-800 r / min.

[0022] Further, in step S3, the heating temperature is 60-90℃, the reaction is stirred for 2-3 hours, the stirring speed is 2000-2500 r / min, the modified talc powder is washed 2-3 times with anhydrous ethanol, and the washed modified talc powder is dried at 100℃ for 2 hours.

[0023] Furthermore, the dispersant in the intermediate matte PE film is composed of polyethylene wax and methyl stearate in a weight ratio of 1 to 3:1, preferably 2:1.

[0024] Furthermore, the ultraviolet absorber in the outer TPU film is one of ultraviolet absorber UV-326 and ultraviolet absorber UV-24.

[0025] Furthermore, the antioxidants in the outer and middle layers are one of antioxidant 168, antioxidant 1076, and antioxidant 330.

[0026] This invention also provides a method for preparing a biaxially oriented PE film, comprising the following steps:

[0027] (1) Add the raw materials of the outer layer, middle layer and inner layer to a high-speed heating mixer and mix them at high speed to obtain the outer layer, middle layer and inner layer mixture respectively;

[0028] (2) The outer layer, middle layer and inner layer mixture obtained in step (1) are extruded by a twin-screw extruder and then cooled by a cooling roller to form gel sheets. The extruder temperature is 200-220℃ and the cooling roller temperature is 30-40℃.

[0029] (3) After preheating the gel sheet obtained in step (2) in a biaxial stretching machine, it is stretched in steps, first longitudinally stretched, then transversely stretched, and after stretching is completed, it is heat-set.

[0030] (4) Next, after printing and double corona treatment, the middle matte PE film is coated with polyurethane adhesive evenly on one side of the outer and middle films using a doctor blade coating machine. Then, the three films are aligned and cured by polyurethane adhesive to obtain the final product.

[0031] Furthermore, in step (1), the temperature in the heating mixer is 80-90°C, the rotation speed is 1500-2000 r / min, and the stirring time is 20-30 min.

[0032] Furthermore, in step (2), the temperature of the extruder is 200-220°C, and the temperature of the cooling roller is 30-40°C;

[0033] Furthermore, in step (3), the preheating temperature of the biaxial stretching machine is 120-150℃, the stretching temperature of the transverse stretching and longitudinal stretching is 100-130℃, the stretching ratio is 2-4 times, the stretching speed is 60-100m / min, and after stretching, heat setting is performed at 120-140℃ for 30-60s.

[0034] Furthermore, the power density of the corona treatment in step (4) is 30 W / m². 2 The processing speed is 300m / min.

[0035] Furthermore, in step (4), the amount of polyurethane adhesive applied is 1.8–2.2 g / m³. 3 .

[0036] Further, in step (4), a doctor blade coater is used to evenly coat the polyurethane adhesive on one side of the outer and middle layers of the film. Then, the three layers are aligned and laminated using pressure rollers at a pressure of 10–30 kg / cm². 2 Then cure at a temperature of 30-40℃ for 24-48 hours to obtain the product.

[0037] Furthermore, the outer TPU film has a thickness of 2 mils, the middle matte PE film has a thickness of 3 mils, and the inner milky white PE film has a thickness of 2 mils.

[0038] This invention provides a biaxially oriented PE film, which is made from an outer TPU film, a middle layer, and an inner polyethylene film as base materials. The three-layer film is then bonded together with an adhesive. The matte PE film in the middle layer is compounded with different proportions of polyethylene materials, such as low-density polyethylene, linear low-density polyethylene, and metallocene polyethylene, which can improve the tensile strength and elongation at break of the PE film and enhance its resistance to environmental stress cracking.

[0039] The added composite additive consists of modified talc powder and polytetrafluoroethylene (PTFE) micropowder. The modified talc powder is modified using a composite modifier composed of sodium myristate and silane coupling agent KH-570, with strict control of parameters at each step. This results in modified talc powder that enhances the interfacial bonding and compatibility between talc powder and the PE matrix. The modified talc powder disperses better in the PE matrix and provides additional support points, effectively improving the mechanical properties of the PE film, including tensile strength and tear strength, as well as its barrier properties, such as improving oxygen barrier properties and reducing water vapor permeability. When the modified talc powder and PTFE micropowder are prepared in a reasonable ratio, their synergistic effect can improve the processing performance, abrasion resistance, and puncture resistance of the PE film while maintaining its good mechanical properties. Furthermore, a dispersant composed of polyethylene wax and methyl stearate is added to help other additives disperse evenly in the PE matrix during production, preventing clumping or sedimentation, thereby ensuring better performance consistency of the film.

[0040] Furthermore, by precisely controlling the conditional parameters (such as temperature and time) of the modification step, the present invention can ensure the optimization of the modification effect, thereby maximizing the effectiveness of the composite additive in the final product.

[0041] Compared with the prior art, the biaxially oriented PE film and its preparation method provided by the present invention have the following advantages:

[0042] The biaxially oriented PE stretch film prepared by this invention effectively improves the tensile strength, elongation at break, and puncture resistance of the prepared biaxially oriented PE stretch film by improving raw materials and optimizing the process flow. It also has excellent processing performance and barrier properties. It can be applied to the surface protection film of children's crawling mats, EPE and XPE splicing mats, yoga mats, and protective films for all kinds of floor mats. Detailed Implementation

[0043] The present invention will be further described below through specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0044] Unless otherwise specified, the reagents used in the following examples and comparative examples are conventional reagents, all of which can be purchased from conventional reagent manufacturers and distributors. Unless otherwise specified, the methods used are existing technologies. Information on some raw material manufacturers is as follows:

[0045] The TPU particles were purchased from Haozheng New Material Technology (Dongguan) Co., Ltd., with product number TPU521.

[0046] The CAS number for UV absorber UV-326 is 3896-11-5, and the CAS number for UV absorber UV-24 is 131-53-3.

[0047] The CAS number for antioxidant 168 is 31570-04-4; the CAS number for antioxidant 1076 is 2082-79-3; and the CAS number for antioxidant 330 is 1709-70-2.

[0048] Low-density polyethylene (LDPE), item number FB0875, brand LG Chem; linear low-density polyethylene (LLDPE), item number 41E710, brand DuPont, purchased from Dongguan Bailing New Materials Co., Ltd.

[0049] Metallocene polyethylene, DuPont Fusabond E528;

[0050] High-density polyethylene (HDPE), item number DMDA8008, brand Sinopec Fujian Refining.

[0051] The polytetrafluoroethylene micro powder, item number 05131, was purchased from Dongguan Shenghao Plastic Raw Materials Co., Ltd.

[0052] The CAS number for sodium myristate is 822-12-8; the CAS number for stearic acid is 822-16-2.

[0053] The CAS number for silane coupling agent KH-570 is 2530-85-0;

[0054] The CAS number for polyvinylidene fluoride is 24937-79-9.

[0055] Example 1

[0056] A biaxially oriented PE film, comprising an outer layer, a middle layer, and an inner layer:

[0057] The outer layer is a TPU film, comprising 70 parts TPU particles, 0.2 parts UV absorber UV-326, and 0.1 parts antioxidant 168;

[0058] The middle layer is a matte PE film, comprising 40 parts of low-density polyethylene, 20 parts of linear low-density polyethylene, 10 parts of metallocene polyethylene, 2 parts of composite additives, 1 part of polyphthalamide, 0.3 parts of dispersant, and 0.2 parts of antioxidant 330.

[0059] The dispersant in the middle matte PE film is composed of polyethylene wax and methyl stearate in a weight ratio of 1:1.

[0060] The inner layer is a milky white PE film, comprising 60 parts low-density polyethylene, 20 parts high-density polyethylene, and 1 part titanium dioxide. The composite additives in the middle matte PE film are composed of modified talc powder and polytetrafluoroethylene micro powder in a weight ratio of 2:1.

[0061] The preparation method of the modified talc in the composite additive of the intermediate matte PE film includes the following steps:

[0062] S1. Dissolve 12g of nano talc powder in 100mL of 75% ethanol solution and stir and disperse using a magnetic stirrer to obtain a nano talc powder dispersion for later use.

[0063] S2. Dissolve the composite modifier in anhydrous ethanol, heat in a water bath to 40°C, stir for 30 minutes at a stirring speed of 500 r / min to obtain a composite modifier solution with a mass concentration of 1.5%. The amount of the composite modifier added is 8% of the mass of nano talc powder. The composite modifier is composed of sodium myristate and silane coupling agent KH-570 in a weight ratio of 2:1.

[0064] S3. Slowly pour the composite modifier solution obtained in step S2 into the nano talc powder dispersion obtained in step S1, stir the reaction at 60°C for 3 hours at a stirring speed of 2000 r / min, then wash twice with anhydrous ethanol, and dry the washed modified talc powder at 100°C for 2 hours to obtain the final product.

[0065] The method for preparing the biaxially oriented PE film includes the following steps:

[0066] (1) Add the raw materials of the outer layer, middle layer and inner layer to a high-speed heating mixer respectively, and stir at a speed of 1500r / min for 30min at a temperature of 80℃ to obtain the outer layer, middle layer and inner layer mixture.

[0067] (2) The outer layer, middle layer and inner layer mixture obtained in step (1) are extruded by a twin-screw extruder and then cooled by a cooling roller to form gel sheets. The extruder temperature is 200℃ and the cooling roller temperature is 30℃.

[0068] (3) The gel sheet obtained in step (2) is preheated to 120°C in a biaxial stretching machine, and then stretched in steps, first longitudinally and then transversely. The stretching temperature of the transverse and longitudinal stretching is 100°C, the stretching ratio is 2 times, the stretching speed is 60m / min, and after stretching, each film is heat-set at 120°C for 30s to maintain its stretched shape.

[0069] (4) Next, the matte PE film obtained in step (3) is printed and then subjected to double corona treatment (corona treatment power density is 30W / m).2 The processing speed is 300 m / min. A doctor blade coater is used to evenly coat one side of the outer and middle layers of the film with polyurethane adhesive. The amount of polyurethane adhesive applied is 1.8 g / m. 3 Then, the three layers of film are aligned and laminated using pressure rollers at a pressure of 10 kg / cm². 2 Then, cure at 30℃ for 48 hours to obtain the product.

[0070] The outer TPU film has a thickness of 2 mils, the middle matte PE film has a thickness of 3 mils, and the inner milky white PE film has a thickness of 2 mils.

[0071] Example 2

[0072] A biaxially oriented PE film, comprising an outer layer, a middle layer, and an inner layer:

[0073] The outer layer is a TPU film, comprising 75 parts TPU particles, 0.3 parts UV-326 ultraviolet absorber, and 0.2 parts antioxidant 1076.

[0074] The middle layer is a matte PE film, comprising 50 parts of low-density polyethylene, 25 parts of linear low-density polyethylene, 12 parts of metallocene polyethylene, 4 parts of composite additives, 2 parts of polyphthalamide, 0.4 parts of dispersant, and 0.3 parts of antioxidant 1076.

[0075] The dispersant in the middle matte PE film is composed of polyethylene wax and methyl stearate in a weight ratio of 2.5:1.

[0076] The inner layer is a milky white PE film, comprising 65 parts of low-density polyethylene, 22 parts of high-density polyethylene, and 3 parts of titanium dioxide.

[0077] The composite additives in the middle matte PE film are composed of modified talc powder and polytetrafluoroethylene micro powder in a weight ratio of 3:1.

[0078] The preparation method of the modified talc in the composite additive of the intermediate matte PE film includes the following steps:

[0079] S1. Dissolve 13g of nano talc powder in 100mL of 75% ethanol solution and stir and disperse using a magnetic stirrer to obtain a nano talc powder dispersion for later use.

[0080] S2. Dissolve the composite modifier in anhydrous ethanol, heat in a water bath to 45°C, stir for 25 minutes at a stirring speed of 700 r / min to obtain a composite modifier solution with a mass concentration of 2.0%. The amount of the composite modifier added is 9% of the mass of nano talc powder. The composite modifier is composed of sodium myristate and silane coupling agent KH-570 in a weight ratio of 2.5:1.

[0081] S3. Slowly pour the composite modifier solution obtained in step S2 into the nano talc powder dispersion obtained in step S1, stir the reaction at 80°C for 2.5 h at a stirring speed of 2200 r / min, then wash twice with anhydrous ethanol, and dry the washed modified talc powder at 100°C for 2 h to obtain the final product.

[0082] The method for preparing the biaxially oriented PE film includes the following steps:

[0083] (1) Add the raw materials of the outer layer, middle layer and inner layer to a high-speed heating mixer, and stir at a speed of 1800 r / min for 25 min at a temperature of 85℃ to obtain the outer layer, middle layer and inner layer mixture.

[0084] (2) The outer layer, middle layer and inner layer mixture obtained in step (1) are extruded by a twin-screw extruder and then cooled by a cooling roller to form gel sheets. The extruder temperature is 210℃ and the cooling roller temperature is 35℃.

[0085] (3) The gel sheet obtained in step (2) is preheated to 130°C in a biaxial stretching machine, and then stretched in steps, first longitudinally and then transversely. The stretching temperature of the transverse and longitudinal stretching is 120°C, the stretching ratio is 3 times, the stretching speed is 80m / min, and after stretching, each film is heat-set at 135°C for 50s to maintain its stretched shape.

[0086] (4) Next, the matte PE film obtained in step (3) is printed and then subjected to double corona treatment (corona treatment power density is 30W / m). 2 The processing speed is 300 m / min. A doctor blade coater is used to evenly coat one side of the outer and middle layers of the membrane with polyurethane adhesive. The amount of polyurethane adhesive applied is 2.0 g / m. 3 Then, the three layers of film are aligned and laminated using pressure rollers at a pressure of 20 kg / cm². 2 Then cure at 35℃ for 36 hours to obtain the product.

[0087] The outer TPU film has a thickness of 2 mils, the middle matte PE film has a thickness of 3 mils, and the inner milky white PE film has a thickness of 2 mils.

[0088] Example 3

[0089] A biaxially oriented PE film, comprising an outer layer, a middle layer, and an inner layer:

[0090] The outer layer is a TPU film, comprising 80 parts TPU particles, 0.4 parts UV-24 ultraviolet absorber, and 0.3 parts antioxidant 330.

[0091] The middle layer is a matte PE film, comprising 60 parts of low-density polyethylene, 30 parts of linear low-density polyethylene, 15 parts of metallocene polyethylene, 6 parts of composite additives, 3 parts of polyphthalamide, 0.5 parts of dispersant, and 0.5 parts of antioxidant 168.

[0092] The dispersant in the middle matte PE film is composed of polyethylene wax and methyl stearate in a weight ratio of 3:1.

[0093] The inner layer is a milky white PE film, comprising 70 parts of low-density polyethylene, 25 parts of high-density polyethylene, and 5 parts of titanium dioxide.

[0094] The composite additives in the middle matte PE film are composed of modified talc powder and polytetrafluoroethylene micro powder in a weight ratio of 4:1.

[0095] The preparation method of the modified talc in the composite additive of the intermediate matte PE film includes the following steps:

[0096] S1. Dissolve 15g of nano talc powder in 100mL of 75% ethanol solution and stir and disperse using a magnetic stirrer to obtain a nano talc powder dispersion for later use.

[0097] S2. Dissolve the composite modifier in anhydrous ethanol, heat in a water bath to 50°C, stir for 20 minutes at a stirring speed of 800 r / min to obtain a composite modifier solution with a mass concentration of 2.5%. The amount of the composite modifier added is 10% of the mass of nano talc powder. The composite modifier is composed of sodium myristate and silane coupling agent KH-570 in a weight ratio of 3:1.

[0098] S3. Slowly pour the composite modifier solution obtained in step S2 into the nano talc powder dispersion obtained in step S1, stir the reaction at 90°C for 2 hours at a stirring speed of 2500 r / min, then wash it three times with anhydrous ethanol, and dry the washed modified talc powder at 100°C for 2 hours to obtain the final product.

[0099] The method for preparing the biaxially oriented PE film includes the following steps:

[0100] (1) Add the raw materials of the outer layer, middle layer and inner layer to a high-speed heating mixer respectively, and stir at a speed of 2000 r / min for 20 min at a temperature of 90℃ to obtain the outer layer, middle layer and inner layer mixture.

[0101] (2) The outer layer, middle layer and inner layer mixture obtained in step (1) are extruded by a twin-screw extruder and then cooled by a cooling roller to form gel sheets. The extruder temperature is 220°C and the cooling roller temperature is 40°C.

[0102] (3) The gel sheet obtained in step (2) is preheated to 150°C in a biaxial stretching machine, and then stretched in steps. First, longitudinal stretching is performed, and then transverse stretching is performed. The stretching temperature for the transverse stretching and longitudinal stretching is 130°C, the stretching ratio is 4 times, the stretching speed is 100m / min, and after stretching, each film is heat-set at 140°C for 60s to maintain its stretched shape.

[0103] (4) Next, the matte PE film obtained in step (3) is printed and then subjected to double corona treatment (corona treatment power density is 30W / m). 2 The processing speed is 300 m / min. A doctor blade coater is used to evenly coat one side of the outer and middle layers of the membrane with polyurethane adhesive. The amount of polyurethane adhesive applied is 2.2 g / m. 3 Then, the three layers of film are aligned and laminated using pressure rollers at a pressure of 30 kg / cm². 2 Then, cure at 40℃ for 24 hours to obtain the product.

[0104] The outer TPU film has a thickness of 2 mils, the middle matte PE film has a thickness of 3 mils, and the inner milky white PE film has a thickness of 2 mils.

[0105] Comparative Example 1

[0106] Compared with Example 2, the difference is that the metallocene polyethylene in the middle matte PE film is replaced with high-density polyethylene, while the other components and preparation methods are the same as in Example 2.

[0107] Comparative Example 2

[0108] Compared with Example 2, the difference is that in step S2 of preparing modified talc powder, sodium myristate in the composite modifier is replaced with sodium stearate. That is, the composite modifier is composed of sodium stearate and silane coupling agent KH-570 in a weight ratio of 2.5:1. The other components and preparation methods are the same as in Example 2.

[0109] Comparative Example 3

[0110] Compared with Example 2, the difference is that in step S2 of preparing modified talc, sodium myristate is not added to the composite modifier, only silane coupling agent KH-570 is added, and the other components and preparation methods are the same as in Example 2.

[0111] Comparative Example 4

[0112] Compared with Example 2, the difference is that the polytetrafluoroethylene micro powder in the composite additive of the middle matte PE film is replaced with polyvinylidene fluoride, while the other components and preparation methods are the same as in Example 2.

[0113] Test Example 1: Performance Testing

[0114] 1. Test materials: Biaxially oriented PE films prepared in Examples 1-3 and Comparative Examples 1-4.

[0115] 2. Test methods: The tensile strength (MPa), elongation at break (%), puncture resistance (N), and water vapor transmission rate (g / m³) of the biaxially oriented PE films prepared in Examples 1-3 and Comparative Examples 1-4 were measured respectively. 2 (24h).

[0116] The tensile properties were tested according to the method in GB / T1040.2-2022; the puncture resistance was tested according to the method in GB / T37841-2019; and the water vapor transmission rate was tested according to the method in GB / T 26253-2010.

[0117] The experimental results are shown in Table 1.

[0118] Table 1

[0119]

[0120] As shown in Table 1, the biaxially oriented PE films prepared in Examples 1-3 have excellent tensile strength, elongation at break, and puncture resistance. They also have excellent barrier properties and low water vapor permeability. However, when some raw materials and preparation methods in the preparation process of Comparative Examples 1-4 were changed, the properties of the biaxially oriented PE films obtained were all lower than those in Examples 1-3 of this invention.

[0121] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A biaxially oriented PE (polyethylene) stretch film, characterized in that, It consists of an outer layer, a middle layer, and an inner layer: The outer layer is a TPU film, comprising 70-80 parts of TPU particles, 0.2-0.4 parts of ultraviolet absorber, and 0.1-0.3 parts of antioxidant; The middle layer is a matte PE film, comprising 40-60 parts of low-density polyethylene, 20-30 parts of linear low-density polyethylene, 10-15 parts of metallocene polyethylene, 2-6 parts of composite additives, 1-3 parts of polyphthalamide, 0.3-0.5 parts of dispersant, and 0.2-0.5 parts of antioxidant. The inner layer is a milky white PE film, comprising 60-70 parts of low-density polyethylene, 20-25 parts of high-density polyethylene, and 1-5 parts of titanium dioxide. The composite additives in the middle matte PE film are composed of modified talc powder and polytetrafluoroethylene micro powder in a weight ratio of 2~4:1; The method for preparing the modified talc powder includes the following steps: S1. Dissolve nano-talc powder in ethanol solution and stir with a magnetic stirrer to disperse it, and then prepare a nano-talc powder dispersion for later use. S2. Dissolve the composite modifier in anhydrous ethanol by stirring, and then heat and stir in a water bath to obtain a composite modifier solution for later use. S3. Slowly pour the composite modifier solution obtained in step S2 into the nano talc powder dispersion obtained in step S1, heat and stir to react, then wash and dry to obtain the final product. The composite modifier in step S2 is composed of sodium myristate and silane coupling agent KH-570 in a weight ratio of 2~3:

1.

2. The biaxially oriented PE film according to claim 1, characterized in that, The mass concentration of the composite modifier solution in step S2 is 1.5~2.5%; the amount of composite modifier added in step S2 is 5~8% of the weight of nano talc powder.

3. The biaxially oriented PE film according to claim 1, characterized in that, The concentration of the ethanol solution in step S1 is 75%, and the mass-volume ratio of the added nano talc powder to the ethanol solution is 12~15 g:100 mL. In step S3, the heating temperature is 60~90℃, the reaction is stirred for 2~3 h, the stirring speed is 2000~2500 r / min, the modified talc powder is washed 2~3 times with anhydrous ethanol, and then dried at 100℃ for 2 h.

4. The biaxially oriented PE film according to claim 1, characterized in that, The dispersant in the middle matte PE film is composed of polyethylene wax and methyl stearate in a weight ratio of 1 to 3:

1. The ultraviolet absorber in the outer TPU film is one of ultraviolet absorber UV-326 and ultraviolet absorber UV-24; The antioxidants in the outer and middle layers are one of antioxidant 168, antioxidant 1076, and antioxidant 330.

5. A method for preparing a biaxially oriented PE film according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Add the raw materials of the outer layer, middle layer and inner layer to a high-speed heating mixer and mix them at high speed to obtain the outer layer, middle layer and inner layer mixtures respectively; (2) The outer, middle and inner layer mixtures obtained in step (1) are extruded by a twin-screw extruder and then cooled by a cooling roller to form gel sheets. The extruder temperature is 200~220℃ and the cooling roller temperature is 30~40℃. (3) After preheating the gel sheet obtained in step (2) in a biaxial stretching machine, perform step-by-step stretching, first longitudinal stretching, then transverse stretching, and after stretching, perform heat setting treatment. (4) Next, after printing and double corona treatment, the middle matte PE film is coated with polyurethane adhesive evenly on one side of the outer and middle films using a doctor blade coating machine. Then, the three films are aligned and cured by polyurethane adhesive to obtain the final product.

6. The method for preparing biaxially oriented PE film according to claim 5, characterized in that, The temperature in the heating mixer in step (1) is 80~90℃, the rotation speed is 1500~2000 r / min, and the stirring time is 20~30min.

7. The method for preparing biaxially oriented PE film according to claim 5, characterized in that, In step (3), the preheating temperature of the biaxial stretching machine is 120~150℃, the stretching temperature of the transverse stretching and longitudinal stretching is 100~130℃, the stretching ratio is 2~4 times, the stretching speed is 60~100 m / min, and after stretching, heat setting is performed at 120~140℃ for 30~60 s. The amount of polyurethane adhesive applied in step (4) is 1.8~2.2 g / m. 3 .

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