Polyethylene composition for cast film and process for the preparation thereof

Abstract

This invention belongs to the field of polyethylene technology, specifically relating to a polyethylene composition for cast film and its preparation method. It comprises the following raw materials in parts by weight: 100 parts of metallocene polyethylene resin; 0.08-0.2 parts of primary antioxidant; 0.08-0.2 parts of secondary antioxidant; 0.05-0.1 parts of stearate; and 0.05-0.2 parts of processing aids. In the metallocene polyethylene resin, the content of lamellar crystals with a thickness of 9 nm or more is 16-22 wt.%. By controlling the thickness distribution of lamellar crystals in the polyethylene resin, the content of thick lamellar crystals is increased, thereby significantly improving the mechanical properties of the material. Simultaneously, addressing the problem of thermo-oxidative aging caused by high temperatures during cast film processing, the use of a combination of high-temperature resistant antioxidants effectively prevents the thermal decomposition of antioxidants, maintaining the excellent appearance of the film product. Furthermore, the use of fluorine-free processing aids ensures good processing performance while avoiding the potential environmental hazards of fluorine-containing compounds.

Description

Technical Field

[0001] This invention belongs to the field of polyethylene technology, specifically relating to polyethylene compositions for cast films and their preparation methods. Background Technology

[0002] Polyethylene (PE) cast film, as an important packaging material, has seen rapid development and application in my country due to its advantages such as high production efficiency, good environmental adaptability, and high product quality. The main varieties of PE cast film include stretch wrap film, food preservation film, and other types of packaging films. These films play an irreplaceable role in many fields such as food packaging, logistics and transportation, and agricultural protection.

[0003] Traditional PE cast films primarily use linear low-density polyethylene (LLDPE) as raw material, and their performance is improved by introducing comonomers such as octene, hexene, and butene. However, with technological advancements and the continuous development of new products, traditional LLDPE cast films are increasingly unable to meet the market's demand for high-performance packaging materials. Particularly in terms of mechanical and optical properties, the performance of traditional LLDPE cast films still needs improvement.

[0004] In recent years, metallocene polyethylene (mPE), as a novel polyethylene material, has been widely used in the cast film field due to its unique molecular structure and performance advantages. Compared with traditional LLDPE, mPE cast films have higher strength, lower haze, and superior processing performance. These advantages have led to mPE gradually replacing ordinary LLDPE cast film resin and becoming the main raw material for cast film processing.

[0005] With the continuous advancement of packaging technology, the market demands increasingly higher comprehensive performance from cast films. In addition to basic adhesion and transparency, cast films are required to possess better mechanical, optical, and surface properties. To meet these needs, researchers are constantly improving and optimizing the raw materials and preparation processes of PE cast films. By adjusting the proportions of raw materials and preparation process parameters, they are enhancing the performance of PE cast films to satisfy the market's demand for high-performance packaging materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a polyethylene composition for cast film, wherein the cast film prepared using the composition has high mechanical strength and low haze.

[0007] Another objective of this invention is to provide a method for preparing a polyethylene composition for cast film. By controlling the thickness distribution of lamellar crystals in the polyethylene resin, the content of thick lamellar crystals is increased, thereby significantly improving the mechanical properties of the material. Simultaneously, addressing the issue of thermo-oxidative aging caused by high temperatures during cast film processing, a combination of high-temperature resistant antioxidants is selected to effectively prevent the thermal decomposition of antioxidants, maintaining the excellent appearance of the film product. Furthermore, the use of fluorine-free processing aids ensures good processing performance while avoiding the potential environmental hazards of fluorine-containing compounds.

[0008] The technical solution adopted in this invention is as follows:

[0009] The polyethylene composition for cast film comprises the following raw materials in parts by weight:

[0010] Metallocene polyethylene resin: 100 parts;

[0011] Main antioxidant: 0.08-0.2 parts;

[0012] Co-antioxidant: 0.08-0.2 parts;

[0013] Stearate: 0.05-0.1 parts;

[0014] Processing aids: 0.05-0.2 parts;

[0015] In the metallocene polyethylene resin, the content of lamellar crystals with a thickness of 9 nm or more is 16-22 wt.%, and the content of lamellar crystals with a thickness of 5 nm or less is 6-8 wt.%.

[0016] The metallocene polyethylene resin described herein is produced using ethylene as a raw material, hydrogen as a molecular weight regulator, and 1-hexene as a comonomer. It is polymerized via a gas-phase fluidized bed process using a metallocene catalyst. The polymerization temperature is 83-88℃, the polymerization pressure is 1.8-2.3 MPa, the ethylene concentration is 53-55 vol%, the hydrogen concentration is 18-300 ppm, and the 1-hexene concentration is 1.2-2.0%. Compared to titanium-based catalysts, the resin polymerized using metallocene catalysts exhibits a more uniform distribution of comonomers and possesses superior mechanical and optical properties.

[0017] The density of the metallocene polyethylene resin is 0.917-0.922 g / cm³. 3 The preferred value is 0.918 g / cm³. 3 The melt mass flow rate at a load of 2.16 kg is 3.0-4.5 g / 10 min, preferably 3.5 g / 10 min; the weight average molecular weight is 80,000-90,000, of which the relative content of the portion with a weight average molecular weight greater than 1,000,000 is 0.01-0.014%, and the molecular weight distribution is 2.5-3.0.

[0018] The content of the comonomer 1-hexene in the metallocene polyethylene resin is 3.6-4.2 mol%.

[0019] The DSC melting curve of the metallocene polyethylene resin has three melting peaks, with corresponding peak temperatures of 101-104℃, 116-119℃ and 120-123℃, respectively.

[0020] The main antioxidant is a hindered phenolic antioxidant, preferably one or more of antioxidant 1010, antioxidant 1098, antioxidant 3114 or antioxidant 330. These antioxidants have excellent high-temperature resistance properties, with a thermal weight loss rate of less than 5% at 300°C. Since the processing temperature of polyethylene cast film is usually between 250-270°C, the additives need to have good high-temperature resistance to prevent the additives from decomposing during processing, causing smoke and affecting the performance of the product.

[0021] The aforementioned auxiliary antioxidant is one of distearate thiodipropionate (DSTP), pentaerythritol tetra(3-lauryl thiopropionate), or bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphate. The main function of these antioxidants is to prevent resin damage due to thermo-oxidative degradation during high-temperature processing. Specifically, when polyethylene cast film is extruded at high temperatures, these auxiliary antioxidants can effectively protect the resin from the effects of heat and oxygen. If the auxiliary antioxidant itself is not heat-resistant and decomposes during extrusion, it cannot exert its due protective effect, leading to yellowing of the granulated resin and ultimately affecting the performance and color of the product.

[0022] The stearate mentioned is zinc stearate or calcium stearate, which has a synergistic effect with antioxidants, can reduce the yellow index of resin and improve appearance.

[0023] The processing aid is a modified polysiloxane, preferably the fluorine-free processing aid SI800, purchased from Zhejiang Jiahua Fine Chemicals Co., Ltd. It is used to improve the extrusion performance of resin processing. This processing aid does not contain fluorine and has better hygiene and safety performance compared to fluorine-containing processing aids.

[0024] The method for preparing the polyethylene composition for cast film includes the following steps: mixing metallocene polyethylene resin, primary antioxidant, secondary antioxidant, stearate and processing aid, and adding the mixture into an extruder, followed by melting, extrusion, granulation and cooling to obtain the polyethylene composition for cast film.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) By controlling the content of lamellar crystals of different thicknesses in polyethylene resin, the present invention enables polyethylene resin to have a higher melting peak, thereby increasing the relative content of thick lamellar crystals in polyethylene resin. These thick lamellar crystals correspond to polyethylene molecules with longer molecular sequence structures and lower branching degree. Therefore, the increase in this part of the content can significantly improve the mechanical properties of the material.

[0027] (2) Due to the high temperature during the casting process, polyethylene is prone to thermo-oxidative aging, which can damage the appearance of the product. This invention effectively avoids the problem of thermal decomposition of antioxidants during subsequent processing by carefully selecting primary and secondary antioxidants with excellent high-temperature resistance. This ensures that the antioxidants can continue to exert excellent anti-thermal-oxidative aging effects during extrusion, thereby maintaining the good appearance of the film products.

[0028] (3) The present invention also uses fluorine-free processing aids, which ensures that the resin has good processing performance while avoiding the adverse effects of fluorine-containing compounds on the environment. Attached Figure Description

[0029] Figure 1 The image shows the DSC melt curve of the metallocene polyethylene resin prepared in Example 1. Detailed Implementation

[0030] The present invention will be further described below with reference to the embodiments, but these embodiments do not limit the implementation of the present invention.

[0031] Unless otherwise specified, the raw materials used in the examples and comparative examples are all commercially available materials, and the process methods used in the examples and comparative examples are all conventional methods in the art.

[0032] Metallocene polyethylene resin Exceed 3518, purchased from ExxonMobil;

[0033] Linear low-density polyethylene resin DFDA7042 was prepared using a titanium-based catalyst, with 1-butene as the comonomer, purchased from China Petroleum & Chemical Corporation Qilu Branch.

[0034] Linear low-density polyethylene resin 2047G was prepared using a titanium-based catalyst, and the comonomer was 1-octene, which was purchased from Dow Chemical.

[0035] Processing aid SI800 was purchased from Zhejiang Jiahua Fine Chemicals Co., Ltd.

[0036] Metallocene catalyst TH-5 was purchased from Zibo Xinsuo Chemical Co., Ltd.

[0037] Example 1

[0038] The polyethylene composition for cast film comprises the following raw materials in parts by weight:

[0039] Metallocene polyethylene resin: 100 parts;

[0040] Antioxidant 1010: 0.12 parts;

[0041] Pentaerythritol tetra(3-lauryl thiopropionate): 0.12 parts;

[0042] Zinc stearate: 0.05 parts;

[0043] Processing aid SI800: 0.08 parts.

[0044] The metallocene polyethylene resin described herein is produced using ethylene as a raw material, hydrogen as a molecular weight regulator, and 1-hexene as a comonomer. It is polymerized via a gas-phase fluidized bed process using the metallocene catalyst TH-5. The polymerization temperature is 84℃, the polymerization pressure is 1.8 MPa, the ethylene concentration is 55%, the hydrogen concentration is 240 ppm, and the 1-hexene concentration is 1.8%. The melting peak temperature (℃) was measured using differential scanning calorimetry (DSC), and the resulting DSC curve is shown below. Figure 1 As shown, by Figure 1 It can be seen that the DSC melting curve of the prepared metallocene polyethylene resin has three melting peaks.

[0045] The method for preparing the polyethylene composition for cast film includes the following steps: mixing metallocene polyethylene resin, antioxidant 1010, pentaerythritol tetra(3-lauryl thiopropionate), zinc stearate, and processing aid SI800, and then adding the mixture to an extruder. The mixture is then melted, extruded, granulated, and cooled to obtain the polyethylene composition for cast film. The extrusion screw temperature is set at 185±25℃ from the feed end to the extrusion end.

[0046] Example 2

[0047] The polyethylene composition for cast film comprises the following raw materials in parts by weight:

[0048] Metallocene polyethylene resin: 100 parts;

[0049] Antioxidant 330: 0.1 parts;

[0050] DSTP: 0.1 copy;

[0051] Zinc stearate: 0.05 parts;

[0052] Processing aid SI800: 0.1 parts.

[0053] The metallocene polyethylene resin is produced by using ethylene as raw material, hydrogen as molecular weight regulator, and 1-hexene as comonomer. It is polymerized using metallocene catalyst TH-5 via a gas-phase fluidized bed process at a polymerization temperature of 83°C, a polymerization pressure of 2.0 MPa, an ethylene concentration of 53%, a hydrogen concentration of 260 ppm, and a 1-hexene concentration of 1.6%.

[0054] The preparation method of the polyethylene composition for cast film is the same as in Example 1.

[0055] Example 3

[0056] The polyethylene composition for cast film comprises the following raw materials in parts by weight:

[0057] Metallocene polyethylene resin: 100 parts;

[0058] Antioxidant 1010: 0.2 parts;

[0059] Bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphate: 0.2 parts;

[0060] Zinc stearate: 0.05 parts;

[0061] Processing aid SI800: 0.15 parts.

[0062] The metallocene polyethylene resin is produced by using ethylene as raw material, hydrogen as molecular weight regulator, and 1-hexene as comonomer. It is polymerized using metallocene catalyst TH-5 via a gas-phase fluidized bed process at a polymerization temperature of 85°C, a polymerization pressure of 1.9 MPa, an ethylene concentration of 53%, a hydrogen concentration of 180 ppm, and a 1-hexene concentration of 1.9%.

[0063] The preparation method of the polyethylene composition for cast film is the same as in Example 1.

[0064] Example 4

[0065] The polyethylene composition for cast film comprises the following raw materials in parts by weight:

[0066] Metallocene polyethylene resin: 100 parts;

[0067] Antioxidant 3114: 0.15 parts;

[0068] Bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphate: 0.15 parts;

[0069] Calcium stearate: 0.08 parts;

[0070] Processing aid SI800: 0.2 parts.

[0071] The metallocene polyethylene resin is produced by using ethylene as raw material, hydrogen as molecular weight regulator, and 1-hexene as comonomer. It is polymerized using metallocene catalyst TH-5 via a gas-phase fluidized bed process at a polymerization temperature of 88°C, a polymerization pressure of 1.8 MPa, an ethylene concentration of 55%, a hydrogen concentration of 250 ppm, and a 1-hexene concentration of 2.0%.

[0072] The preparation method of the polyethylene composition for cast film is the same as in Example 1.

[0073] Comparative Example 1

[0074] The polyethylene composition comprises the following raw materials in parts by weight:

[0075] Metallocene polyethylene resin: 100 parts;

[0076] Antioxidant 1010: 0.2 parts;

[0077] Antioxidant 168: 0.2 parts;

[0078] Zinc stearate: 0.05 parts;

[0079] Processing aid SI800: 0.015 parts.

[0080] The metallocene polyethylene resin is produced by using ethylene as raw material, hydrogen as molecular weight regulator, and 1-hexene as comonomer. It is polymerized using metallocene catalyst TH-5 via a gas-phase fluidized bed process at a polymerization temperature of 88°C, a polymerization pressure of 1.8 MPa, an ethylene concentration of 55%, a hydrogen concentration of 250 ppm, and a 1-hexene concentration of 2.0%.

[0081] The preparation method of the polyethylene composition is the same as in Example 1.

[0082] Comparative Example 2

[0083] The polyethylene composition comprises the following raw materials in parts by weight:

[0084] Metallocene polyethylene resin: 100 parts;

[0085] Antioxidant 1010: 0.12 parts;

[0086] Pentaerythritol tetra(3-lauryl thiopropionate): 0.05 parts;

[0087] Processing aid SI800: 0.08 parts.

[0088] The metallocene polyethylene resin is produced by using ethylene as raw material, hydrogen as molecular weight regulator, and 1-hexene as comonomer. It is polymerized using metallocene catalyst TH-5 via a gas-phase fluidized bed process at a polymerization temperature of 83°C, a polymerization pressure of 1.7 MPa, an ethylene concentration of 54%, a hydrogen concentration of 300 ppm, and a 1-hexene concentration of 2.1%.

[0089] The preparation method of the polyethylene composition is the same as in Example 1.

[0090] Comparative Example 3

[0091] The polyethylene composition comprises the following raw materials in parts by weight:

[0092] Metallocene polyethylene resin: 100 parts;

[0093] Antioxidant 1076: 0.12 parts;

[0094] Antioxidant 168: 0.12 parts;

[0095] Zinc stearate: 0.05 parts;

[0096] Processing aid SI800: 0.08 parts.

[0097] The metallocene polyethylene resin is produced by using ethylene as raw material, hydrogen as molecular weight regulator, and 1-hexene as comonomer. It is polymerized using metallocene catalyst TH-5 via a gas-phase fluidized bed process at a polymerization temperature of 86°C, a polymerization pressure of 1.9 MPa, an ethylene concentration of 52%, a hydrogen concentration of 320 ppm, and a 1-hexene concentration of 1.9%.

[0098] The preparation method of the polyethylene composition is the same as in Example 1.

[0099] Comparative Example 4

[0100] Exceed 3518, a metallocene polyethylene resin, is prepared using fluorine-containing processing aids.

[0101] Comparative Example 5

[0102] Linear low-density polyethylene resin DFDA7042, produced with titanium catalyst, copolymerized with 1-butene.

[0103] Comparative Example 6

[0104] Linear low-density polyethylene resin 2047G, produced by titanium catalyst, 1-octene copolymer.

[0105] The performance of the polyethylene resins and polyethylene compositions in Examples 1-4 and Comparative Examples 1-6 was tested respectively, and the test methods are as follows:

[0106] Density of polyethylene resin (g / cm³) 3 The test was conducted according to GB / T 1033.2-2010, using method D, and the test was performed after boiling for 30 minutes.

[0107] Melt mass flow rate (MFR, g / 10min) of polyethylene resin: tested according to GB / T 3682-2018;

[0108] Comonomer content (mol%) in polyethylene resin: First, 75 mg of sample was placed in a 5 mm sample tube, and 0.5 mL of deuterated o-dichlorobenzene solvent was added. The sample tube was kept in a constant temperature bath at 140℃ for 3.5 ± 0.5 h to ensure uniform dispersion. Then, the prepared sample tube was placed in a nuclear magnetic resonance spectrometer and stabilized at the experimental temperature of 125℃ for 30 min before scanning the sample (pulse angle 90°, pulse interval 5 s, spectral width 220 ppm, combined pulse decoupling). After scanning, the spectrum was processed, and the peaks in the range of 5-50 ppm were accurately integrated (calibrated to 30 ppm with the isolated -CH2- peak in the polymer).

[0109] Weight-average molecular weight (Mw) and molecular weight distribution (PD) of polyethylene resin: Gel permeation chromatography (GPC) was used with two columns in series. The solvent and mobile phase were both dibutoxymethane. The sample weight was 2.25±0.75 mg, the column temperature was 150℃, and the solution was dissolved for 3 h. Narrow distribution polystyrene standard was used for universal standardization.

[0110] The lamellar distribution in polyethylene resin was analyzed using the continuous self-nucleation annealing thermal classification method (SSA). A 6 mg sample was weighed, packaged in a crucible, and placed in a differential scanning calorimeter (DSC). First, the sample was heated to 165 °C at a rate of 50 °C / min and held for 5 min to eliminate thermal history. Then, the sample was cooled to 0 °C at a rate of 25 °C / min and held for 3 min. Next, the sample was heated to the set nucleation temperature at a rate of 25 °C / min and held for 5 min. Then, the sample was cooled to 25 °C at a rate of 25 °C / min, and then heated to the next nucleation temperature at a rate of 25 °C / min, and this cycle was repeated.

[0111] The melting peak temperature (°C) of polyethylene resin was measured using differential scanning calorimetry (DSC).

[0112] Yellow Index: Tested in accordance with GB / T 2409-19801;

[0113] Tensile strength (MPa) and elongation at break (%) of polyethylene composition: Tested according to GB / T 13022-1991, using type 5 specimens, with a tensile speed of 200 mm / min;

[0114] Tear resistance (N) of polyethylene composition: Tested according to GB / T 11999-1989, using rectangular specimens;

[0115] The dart impact strength (g) of the polyethylene composition was tested in accordance with GB / T 9639.1-2008.

[0116] Haze (%) of polyethylene composition: Tested according to GB / T 2410-2008;

[0117] The test results are shown in Table 1-3.

[0118] Table 1. Test results of physical properties of polyethylene resin

[0119] Item Density MFR, Melting peak corresponding temperature Yellow index Example 1 0.918 3.5 103 / 118 / 122 -0.86 Example 2 0.920 4.0 103 / 119 / 121 -0.85 Example 3 0.918 3.0 102 / 119 / 120 -0.90 Example 4 0.922 3.0 104 / 119 / 120 -0.84 Comparative Example 1 0.918 3.0 102 / 119 / 120 1.32 Comparative Example 2 0.918 3.5 102 / 118 / 121 0.96 Comparative Example 3 0.918 3.5 102 / 118 / 121 1.66 Comparative Example 4 0.918 3.5 105 / 114 0.52 Comparative Example 5 0.920 2.0 103 / 119 2.31 Comparative Example 6 0.920 2.4 122 5.21

[0120] As shown in Table 1, the polyethylene resins prepared in Examples 1-4 have three melting peaks, one of which is above 120°C, indicating a high content of thick flake crystals. Furthermore, the use of a high-temperature resistant antioxidant resulted in a low yellow index for the prepared resins. Comparative Examples 1 and 3, which did not use a high-temperature resistant antioxidant, and Comparative Example 2, which had a low amount of auxiliary antioxidant, both resulted in high yellow indices, affecting the product appearance during later processing. Comparative Examples 4 and 5 had lower melting temperatures, and Comparative Example 6 had only one melting peak and a high yellow index. The high yellow indices of all six comparative examples are mainly due to the absence of a high-temperature resistant antioxidant and the different amounts of antioxidant added.

[0121] Table 2 Results of structural analysis and testing of polyethylene resin

[0122]

[0123] As shown in Table 2, the polyethylene resins prepared in Examples 1-4 have a narrow molecular weight distribution. The polymerization processes and molecular structures of Comparative Examples 1-3 are similar to those of the Examples. Comparative Example 4 has a wider molecular weight distribution than the Examples, with lower content of thick lamellar crystals and higher content of thin lamellar crystals. Corresponding to the wider molecular weight distribution, the comonomer content is lower than that of the Examples. Comparative Examples 5 and 6 were both produced using titanium-based catalysts, resulting in a wider molecular weight distribution. However, the uniformity of the comonomer distribution is worse than that of products polymerized using metallocene catalysts, leading to a higher content of thick lamellar crystals and a lower content of thin lamellar crystals.

[0124] Table 3 Results of performance tests for cast film preparation

[0125]

[0126] As shown in Table 3, the films prepared in Examples 1-4 exhibit good mechanical and optical properties. The comparative examples, lacking a high-temperature antioxidant, showed poor optical properties during the 260°C casting process. Comparative Example 4 had a lower comonomer content and lower lamellar content, resulting in lower tensile properties compared to the examples. Comparative Example 5 had a higher content, but the comonomer was 1-butene, and its comonomer distribution uniformity was inferior to that of the metallocene catalyst polymerization product. Although it had a high lamellar content and high molecular weight, its film mechanical properties were poor. Comparative Example 6, also using a titanium-based catalyst, had poor comonomer distribution uniformity, leading to mechanical properties inferior to the metallocene catalyst polymerization product.

Claims

1. A polyethylene composition for cast film, characterized in that, The ingredients include the following parts by weight: Metallocene polyethylene resin: 100 parts; Main antioxidant: 0.08-0.2 parts; Co-antioxidant: 0.08-0.2 parts; Stearate: 0.05-0.1 parts; Processing aids: 0.05-0.2 parts; In the metallocene polyethylene resin, the content of lamellar crystals with a thickness of 9 nm or more is 16-22 wt.%, and the content of lamellar crystals with a thickness of 5 nm or less is 6-8 wt.%.

2. The polyethylene composition for cast film according to claim 1, characterized in that, The metallocene polyethylene resin is produced by using ethylene as raw material, hydrogen as molecular weight regulator, and 1-hexene as comonomer, and is polymerized using a metallocene catalyst via a gas-phase fluidized bed process. The polymerization temperature is 83-88℃, the polymerization pressure is 1.8-2.3MPa, the ethylene concentration is 53-55 vol%, the hydrogen concentration is 18-300 ppm, and the 1-hexene concentration is 1.2-2.0%.

3. The polyethylene composition for cast film according to claim 1, characterized in that, The density of the metallocene polyethylene resin is 0.917-0.922 g / cm³. 3 The melt mass flow rate at a load of 2.16 kg is 3.0-4.5 g / 10 min, the weight average molecular weight is 80,000-90,000, the relative content of the portion with a weight average molecular weight greater than 1,000,000 is 0.01-0.014%, and the molecular weight distribution is 2.5-3.

0.

4. The polyethylene composition for cast film according to claim 1, characterized in that, The content of the comonomer 1-hexene in the metallocene polyethylene resin is 3.6-4.2 mol%.

5. The polyethylene composition for cast film according to claim 1, characterized in that, The DSC melting curve of the metallocene polyethylene resin has three melting peaks, with corresponding peak temperatures of 101-104℃, 116-119℃ and 120-123℃, respectively.

6. The polyethylene composition for cast film according to claim 1, characterized in that, The primary antioxidant is a hindered phenolic antioxidant.

7. The polyethylene composition for cast film according to claim 1, characterized in that, The co-antioxidant is one of distearate, pentaerythritol tetra(3-lauryl thiopropionate), or bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphate.

8. The polyethylene composition for cast film according to claim 1, characterized in that, The stearate is zinc stearate or calcium stearate.

9. The polyethylene composition for cast film according to claim 1, characterized in that, The processing aid is a modified polysiloxane.

10. A method for preparing a polyethylene composition for cast film according to any one of claims 1-9, characterized in that, The process includes the following steps: mixing metallocene polyethylene resin, primary antioxidant, secondary antioxidant, stearate and processing aid, and adding the mixture to an extruder, followed by melting, extrusion, granulation and cooling to obtain a polyethylene composition for cast film.

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