High density polyethylene film and flexible packaging film containing same

Abstract

Disclosed is a high-density polyethylene film comprising an intermediate layer containing a first high-density polyethylene resin, and a first surface layer and a second surface layer provided on both surfaces of the intermediate layer, respectively, the first surface layer and the second surface layer containing a second high-density polyethylene resin, wherein the density of the first high-density polyethylene resin is higher than the density of the second high-density polyethylene resin, and the concentration of the polymer dissolved in a polymer solution at a temperature of 100 DEG C is less than the concentration of the polymer dissolved in the polymer solution based on the crystallization analysis fractionation result of the polymer solution of the second high-density polyethylene resin dissolved in a solvent. The concentration of the polymer dissolved in the polymer solution at a temperature of 80-90 DEG C is reduced by 30-75%.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority and benefit of Korean Patent Application No. 10 - 2023 - 0170987, filed with the Korean Intellectual Property Office on November 30, 2023, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] Embodiments of the present invention relate to a high - density polyethylene film and a flexible packaging film containing the same. Background art

[0004] Recently, regulations on recycling have been continuously strengthened worldwide. With the change in social responsibility awareness of inherent sustainability and solutions to widespread environmental problems, companies are also striving to design flexible packaging materials that are easy to collect, classify, and recycle.

[0005] The most effective method is to use packaging materials produced from a single material instead of conventional packaging produced from a mixture of multiple materials. In particular, packaging materials produced from a single material such as polyethylene (PE) or polypropylene (PP) are easily recyclable and contribute to improving the quality of recycled products.

[0006] For this purpose, biaxially oriented polyethylene (BOPE) films are required. Generally, when using the tenterframe process as the process for preparing biaxially oriented polyethylene films and stretching the films in the machine direction (MD) and the transverse direction (TD), the polyethylene chains and crystal structures are highly oriented, thereby providing improved mechanical strength, especially improved impact strength, and significantly improved optical properties such as transparency and film appearance.

[0007] However, during film processing, the tenterframe process is greatly affected by the molecular structure of the raw materials, and the stretching process conditions are very strict. Generally, polyethylene (PE) has a narrow stretching temperature range and a very low stretching rate due to its high crystallization rate and excellent crystallinity, and polyethylene films will break when wrinkled during the stretching process or have uneven thickness during the stretching process. In particular, BOPE films produced from high - density polyethylene (HDPE) exhibit high heat resistance and significantly improved modulus, but, disadvantageously, they are difficult to stretch and have low transparency compared to BOPE films produced from linear low - density polyethylene (LLDPE).

[0008] Therefore, there is a need for a high - density polyethylene film applicable to recyclable single - material flexible packaging films, which has excellent mechanical properties, especially high modulus and excellent transparency, and is easily biaxially stretchable by the tenterframe process.

[0009] The information disclosed in this section is only for enhancing the understanding of the background of the present invention, and thus may include information that does not constitute the prior art.

[0010] [Prior Art]

[0011] [Patent Document]

[0012] Korean Patent Publication No. 10-2016-0114603 Summary of the Invention

[0013] Embodiments of the present invention provide a high-density polyethylene film that is easily biaxially stretchable, has excellent thickness uniformity during stretching, and has excellent mechanical properties, especially excellent modulus and transparency.

[0014] It should be noted that the objectives of the present invention are not limited to those mentioned above, and those skilled in the art will clearly understand other objectives not mentioned in the present invention according to the following description.

[0015] The high-density polyethylene film according to an embodiment of the present invention includes an intermediate layer containing a first high-density polyethylene resin, and a first surface layer and a second surface layer respectively disposed on two surfaces of the intermediate layer, wherein the first surface layer and the second surface layer contain a second high-density polyethylene resin. The density of the first high-density polyethylene resin is higher than the density of the second high-density polyethylene resin, and based on the crystallization analysis fractionation result of the polymer solution of the second high-density polyethylene resin dissolved in a solvent, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature of 80 - 90 °C can be 30 - 75%.

[0016] Each of the intermediate layer, the first surface layer, and the second surface layer may have a single-layer structure or a multi-layer structure including 2 - 5 layers.

[0017] The density of the first high-density polyethylene resin may be 0.945 - 0.970 g / cm 3 .

[0018] In the first high-density polyethylene resin, based on the integral value of the total area of the total molecular weight distribution graph of the first high-density polyethylene resin, the integral value ratio of the graph area corresponding to the polymer with a molecular weight of 10 5 -10 6 g / mol may be 18 - 28%, and the number of short chain branches of the polymer may be 5 - 15 per thousand carbons.

[0019] In the first high-density polyethylene resin, based on the integral value of the total area of the molecular weight distribution graph of the first high-density polyethylene resin, the integral value ratio of the graph area corresponding to the polymer with a molecular weight of 10 3 -10 4 g / mol can be 20-30%, and the number of short side chains of the polymer can be 1-8 per thousand carbons.

[0020] At least one of the first high-density polyethylene resin or the second high-density polyethylene resin may have short side chains, and the short side chains have a broad orthogonal comonomer distribution (BOCD) structure.

[0021] Based on the results of crystallization analysis fractionation of the polymer solution of the first high-density polyethylene resin dissolved in a solvent, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature of 70-80 °C can be 10-20%.

[0022] Based on the results of crystallization analysis fractionation of the polymer solution of the first high-density polyethylene resin dissolved in a solvent, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature of 80-90 °C can be 50-70%.

[0023] The melt index (MI2 (2.16 kg load, 190 °C)) of the first high-density polyethylene resin can be 0.40-3.0 g / 10 min.

[0024] The melt flow rate ratio (MI21.6 (21.6 kg load, 190 °C) / MI2 (2.16 kg load, 190 °C), MFRR) of the first high-density polyethylene resin can be 70 or more.

[0025] Based on the results of crystallization analysis fractionation of the polymer solution of the second high-density polyethylene resin dissolved in a solvent, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature higher than 30 °C and not higher than 50 °C can be 10-20%.

[0026] Based on the crystallization analysis fractionation results of the polymer solution of the second high-density polyethylene resin dissolved in the solvent, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100°C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature higher than 30°C and not higher than 60°C can be 15-25%.

[0027] In the second high-density polyethylene resin, based on the integral value of the total area of the total molecular weight distribution diagram of the second high-density polyethylene resin, the integral value ratio of the graphic area corresponding to the polymer with a molecular weight of 10 3 -10 4 g / mol can be 18-30%, and the number of short chain branches of the polymer can be 0.1-8 per thousand carbons.

[0028] The density of the second high-density polyethylene resin can be 0.940-0.965 g / cm 3 。

[0029] The melt index (MI2 (2.16 kg load, 190°C)) of the second high-density polyethylene resin can be 0.50-5.0 g / 10 min.

[0030] The melt flow rate ratio (MI21.6 (21.6 kg load, 190°C) / MI2 (2.16 kg load, 190°C), MFRR) of the second high-density polyethylene resin can be 60 or more.

[0031] The high-density polyethylene film can be a film biaxially stretched by a tenter frame process at a draw ratio of 4-7 times in the longitudinal direction (MD) and 8-10 times in the transverse direction (TD) in sequence.

[0032] The thickness of the high-density polyethylene film can be 15-70 μm, and based on the total amount of the high-density polyethylene film, the amount of the intermediate layer can be 70-98% by weight.

[0033] The flexible packaging film according to another embodiment of the present invention contains the high-density polyethylene film. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings incorporated herein illustrate the preferred embodiments and are used to further illustrate the technical idea of the present invention in combination with the following detailed description of the exemplary embodiments, and the present invention should not be construed as limited to the content shown in these drawings. In the drawings:

[0035] Figure 1 is a schematic diagram illustrating a high-density polyethylene film according to an embodiment;

[0036] Figure 2It is a schematic diagram illustrating a high-density polyethylene film according to an embodiment;

[0037] Figure 3 It is a graph showing the total molecular weight distribution and the number of short chain branches per thousand carbons of the first high-density polyethylene resin according to Preparation Examples 1-1 and 1-2 as determined by gel permeation chromatography-infrared (GPC-IR);

[0038] Figure 4 It is a graph showing the crystallization analysis fractionation (CRYSTAF) of the first high-density polyethylene resin according to Preparation Examples 1-1 and 1-2; and

[0039] Figure 5 It is a graph showing the crystallization analysis fractionation (CRYSTAF) of the second high-density polyethylene resin according to Preparation Examples 2-1 and 2-2. Detailed Description

[0040] The above objects and other objects, features, and advantages can be clearly understood through the following preferred embodiments with reference to the accompanying drawings. However, the present invention is not limited to these embodiments and can be implemented in different forms. The proposed embodiments are only for providing a comprehensive and complete understanding of the disclosed content and enabling those skilled in the art to fully understand the technical concept of the present invention. The present invention is only defined by the scope of the claims.

[0041] The terms used herein are only for describing exemplary embodiments and should not be construed as limiting the scope of the present invention. Unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. It should also be understood that the terms "comprising" and / or "containing" used herein do not exclude the presence or addition of one or more other components in addition to the components mentioned. Throughout the description of the drawings, the same reference numerals represent the same elements. The term "and / or" used herein includes any one of the listed items and any combination of one or more of them. It should be understood that although the terms "first", "second", etc. may be used herein to describe various elements, these elements should not be construed as being limited by these terms. These terms are only used to distinguish one element from another. For example, within the scope defined by the present invention, the first element may be referred to as the second element.

[0042] Unless otherwise defined, all terms (including technical or scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. In addition, terms that are the same as those defined in commonly used dictionaries should be construed as having the same meaning as the context of the related art, and unless clearly defined in the present invention, they are not construed as having an ideal or overly formal meaning.

[0043] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0044] Before the description, the meanings of the terms used herein will be briefly described. However, the explanations of the terms are provided for better understanding of the present invention, and these terms should not be construed as limiting the technical idea of the present invention unless the context clearly indicates that the terms are used to limit the scope of the present invention.

[0045] The high-density polyethylene film according to an embodiment of the present invention includes an intermediate layer containing a first high-density polyethylene resin, and a first surface layer and a second surface layer respectively provided on two surfaces of the intermediate layer, and the first surface layer and the second surface layer contain a second high-density polyethylene resin.

[0046] Figure 1 is a schematic diagram illustrating a high-density polyethylene film according to an embodiment. Referring to Figure 1 , the high-density polyethylene film 100 includes an intermediate layer 10 and surface layers 20 formed on each of two surfaces of the intermediate layer 10. More specifically, a first surface layer 21 and a second surface layer 22 are provided on two surfaces of the intermediate layer 10.

[0047] In one embodiment, each of the intermediate layer, the first surface layer, and the second surface layer of the high-density polyethylene film may have a single-layer structure or a multi-layer structure including 2 to 5 layers. For example, the first surface layer and the second surface layer may have a single-layer structure, and the intermediate layer may have a multi-layer structure including 2 to 4 layers. Such a high-density polyethylene film having a multi-layer structure can select high-density polyethylene suitable for its functional requirements, diversify the change of physical properties according to the composition of its layers, and provide excellent thickness distribution uniformity of each layer.

[0048] Figure 2 is a schematic diagram illustrating a high-density polyethylene film according to an embodiment. Referring to Figure 2 , the high-density polyethylene film 100 has the following structure: the first surface layer 21 and the second surface layer 22 have a single-layer structure, and the intermediate layer 10 has a multi-layer structure including a first intermediate layer 11, a second intermediate layer 10, and a third intermediate layer 12.

[0049] The high-density polyethylene film may be a film that is biaxially stretched by a tenter frame process at a longitudinal (MD) draw ratio of 4 to 7 times and a transverse (TD) draw ratio of 8 to 10 times in sequence. By adjusting the draw ratios in the longitudinal (MD) and transverse (TD) directions within this range, the desired effect of improving physical properties is obtained due to the sufficient orientation of crystals, but it is difficult to ensure a draw ratio higher than a predetermined draw ratio due to equipment limitations.

[0050] The thickness of the high-density polyethylene film may be 15 - 70 μm or 20 - 50 μm. When the thickness of the high-density polyethylene film is controlled within the above range, excellent mechanical properties can be obtained without causing problems such as difficulty in obtaining a thin final film due to excessive film thickness.

[0051] Based on the total amount of the high-density polyethylene film, the amount of the intermediate layer may be 70 - 98 wt%, 80 - 95 wt%, or 85 - 95 wt%. Additionally, based on the total amount of the high-density polyethylene film, the total amount of the first surface layer and the second surface layer may be 2 - 30 wt%, 5 - 20 wt%, or 5 - 15 wt%. By adjusting the thicknesses of the intermediate layer, the first surface layer, and the second surface layer to the above ranges, the thickness uniformity of the high-density polyethylene film can be further improved, mechanical properties can be ensured, and transparency can be enhanced.

[0052] In one embodiment, the first high-density polyethylene resin may be used alone as the resin for forming the intermediate layer of the high-density polyethylene film.

[0053] The density of the first high-density polyethylene resin may be higher than the density of the second high-density polyethylene resin. The density of the first high-density polyethylene resin may be, for example, 0.945 - 0.970 g / cm 3 or 0.945 - 0.965 g / cm 3 . When the density of the first high-density polyethylene resin falls within the above range, the final high-density polyethylene film has excellent thermal stability, low thermal shrinkage rate, and the modulus can be improved.

[0054] In the first high-density polyethylene resin, based on the integral value of the total area of the total molecular weight distribution graph of the first high-density polyethylene resin, the integral value ratio of the graph area corresponding to the polymer with a molecular weight of 10 5 -10 6 g / mol may be 18 - 28%, and the number of short-chain branches of the polymer may be 5 - 15 per thousand carbons. For example, in the first high-density polyethylene resin, based on the integral value of the total area of the total molecular weight distribution graph of the first high-density polyethylene resin, the integral value ratio of the graph area corresponding to the polymer with a molecular weight of 10 5 -10 6 g / mol may be 20 - 23%, and the number of short-chain branches of the polymer may be 6 - 12 per thousand carbons. When the ratio of the polymer with a molecular weight of 10 5 -10 6 g / mol and the number of short-chain branches fall within the above ranges, the film can be stably biaxially stretched sequentially in the longitudinal and transverse directions, and the final physical properties of the film can be significantly improved. In the present invention, the molecular weight distribution graph can be measured by infrared gel permeation chromatography.

[0055] In the first high-density polyethylene resin, based on the integral value of the total area of the molecular weight distribution graph of the first high-density polyethylene resin, the integral value ratio of the graph area corresponding to the polymer with a molecular weight of 10 3 -10 4 g / mol can be 20-30%, and the number of short side chains of the polymer can be 1-8 per thousand carbons. For example, in the first high-density polyethylene resin, based on the integral value of the total area of the molecular weight distribution graph of the first high-density polyethylene resin, the integral value ratio of the graph area corresponding to the polymer with a molecular weight of 10 3 -10 4 g / mol can be 22-26%, and the number of short side chains of the polymer can be 1.5-6 per thousand carbons. When the molecular weight is 10 3 -10 4 g / mol and the number of short side chains of the polymer fall within the above ranges, the longitudinal and transverse stretching ratios can be increased, and the thickness uniformity of the film can be ensured.

[0056] The first high-density polyethylene may have short side chains, and the short side chains may have a BOCD (broad orthogonal comonomer distribution) structure. The BOCD structure contains a large amount of monomers, has a broad molecular weight distribution, and the short side chains increase with the increase in molecular weight. When the molecular weight and the number of short side chains of the polymer used to form the first high-density polyethylene resin fall within the above ranges and the short side chains have a BOCD profile, when the polyethylene film prepared from the first high-density polyethylene resin is successively biaxially stretched by a tenter frame process, the film can be stably biaxially stretched successively in the longitudinal and transverse directions to ensure a uniform thickness, increase the stretching ratio, and significantly improve the mechanical strength, especially the modulus, of the stretched film.

[0057] Based on the results of crystallization analysis fractionation of the polymer solution of the first high-density polyethylene resin dissolved in a solvent, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature of 70-80 °C can be 10-20%, 12-18%, or 14-17%. Within the above ranges, during the successive biaxial stretching of the final high-density polyethylene film using a tenter frame process, the stretching in the longitudinal and transverse directions can be increased, and the modulus can be improved. In crystallization analysis fractionation, as the temperature decreases, the polymer is eluted from the polymer solution, thereby reducing the concentration of the polymer dissolved in the polymer solution. Therefore, the reduction ratio of the concentration of the polymer dissolved in the polymer solution can represent the fraction in which the polymer is eluted.

[0058] In the present invention, with respect to measuring the reduction ratio of the polymer concentration from the results of crystallization analysis fractionation, the polymer refers to the first high-density polyethylene resin or the second high-density polyethylene resin dissolved in a solvent. The physical properties of polyethylene are greatly affected not only by the content of the comonomer, but also by the distribution of the comonomer in the polyethylene main chain. Here, crystallization analysis fractionation is a method for measuring the comonomer distribution between polyethylene molecules.

[0059] Based on the results of crystallization analysis fractionation of a polymer solution of the first high-density polyethylene resin dissolved in a solvent, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature of 80 - 90 °C is 50 - 70%, 55 - 68%, or 60 - 65%. Within the above ranges, during the sequential biaxial stretching of the final high-density polyethylene film using a tenter frame process, the stretching in the longitudinal and transverse directions can be increased, and the modulus can be improved.

[0060] The melt index (MI2 (2.16 kg load, 190 °C)) of the first high-density polyethylene resin can be 0.40 - 3.0 g / 10 min or 0.45 - 1.5 g / 10 min. When the melt index of the first high-density polyethylene resin falls within the above ranges, excellent extrusion processing performance can be obtained and the deterioration of physical properties due to low molecular weight can be prevented.

[0061] The melt flow rate ratio (MI21.6 (21.6 kg load, 190 °C) / MI2 (2.16 kg load, 190 °C), MFRR) of the first high-density polyethylene resin can be 70 or more, 80 or more, or 80 - 90. When the melt flow rate ratio of the first high-density polyethylene resin falls within the above ranges, excellent final extrusion processing performance can be obtained, the film can be stably biaxially stretched in the longitudinal (MD) and transverse (TD) directions, and the film can be stretched to a uniform thickness.

[0062] The melting temperature Tm of the first high-density polyethylene resin can be 120 - 145 °C, 125 - 144 °C, or 128 - 135 °C. When the melting temperature of the first high-density polyethylene resin falls within this range, excellent heat resistance and high modulus can be imparted to the final high-density polyethylene film.

[0063] The crystallization temperature Tc of the first high-density polyethylene resin can be 105 - 130 °C, 110 - 130 °C, or 115 - 125 °C. When the crystallization temperature of the first high-density polyethylene resin falls within this range, the temperature range in which the final high-density polyethylene film can be stretched can be broadened.

[0064] The first high-density polyethylene resin can be obtained by polymerizing ethylene monomers, comonomers, and hydrogen in the presence of a catalyst. The first high-density polyethylene resin can be formed by polymerization using a two-stage reactor including a first reactor and a second reactor connected to each other. Specifically, ethylene monomers are polymerized in the first reactor to form a polyethylene resin as a primary intermediate polymer, and the polyethylene resin is transferred to the second reactor and then further polymerized therein to obtain the first high-density polyethylene resin as the final polymer. The first reactor and the second reactor can be based on a slurry process.

[0065] The polymerization in the first reactor and the second reactor can be carried out in the presence of a Ziegler-Natta (Zn) catalyst. The Ziegler-Natta (Zn) catalyst is a well-known conventional Ziegler-Natta catalyst, and a compound of a transition metal belonging to Group IV, V, or VI of the periodic table is used as the main catalyst. The most commonly used Ziegler-Natta (Zn) catalyst is a halogenated complex containing magnesium and titanium, or magnesium and vanadium.

[0066] In addition, during the polymerization in one or more of the first reactor and the second reactor, in addition to ethylene monomers, comonomers can be fed thereto. The comonomer can be an α-olefin of C3-C20, such as an α-olefin of C4-C8, or C6-C8. As a specific example, the comonomer can include at least one of 1-butene, 1-hexene, or 1-octene.

[0067] In the first reactor, the ratio of ethylene monomers to comonomers can be 50-90 g / kg, 60-80 g / kg, or 65-80 g / kg. When the comonomer is fed to the first reactor at a feed ratio within this range, clogging and fouling of the reactor can be prevented, the draw ratio in the machine direction (MD) and the transverse direction (TD) during the biaxial stretching process of the final film can be increased, and a polymer polyethylene film with high mechanical strength can be obtained.

[0068] In the first reactor, the ratio of ethylene monomers to hydrogen can be 20-70 mg / kg, 25-55 mg / kg, or 35-50 mg / kg. When hydrogen is fed to the first reactor at a feed ratio within this range, clogging and fouling of the reactor can be prevented, the draw ratio in the machine direction (MD) and the transverse direction (TD) during the biaxial stretching process of the final film can be increased, and a polymer polyethylene film with high mechanical strength can be obtained.

[0069] The comonomer can not be fed into the second reactor. Since the comonomer is not fed into the second reactor, excellent production stability can be obtained.

[0070] In the second reactor, the ratio of ethylene monomer to hydrogen can be 0.1 - 2 g / kg, 0.1 - 1.5 g / kg, or 0.5 - 0.8 g / kg. When hydrogen is fed to the second reactor at a feed ratio within this range, clogging and fouling of the reactor can be prevented, the draw ratios in the machine direction (MD) and the transverse direction (TD) during the biaxial stretching process of the final film can be increased, and a polymer polyethylene film with high mechanical strength can be obtained.

[0071] In one embodiment, the second high-density polyethylene resin can be used alone as the resin for forming the first and second surface layers of the high-density polyethylene film.

[0072] The second high-density polyethylene resin for forming the first and second surface layers can be prepared by mixing the prepared first high-density polyethylene with 5 - 25 wt% or 10 - 15 wt% of a commercially available polyolefin elastomer (POE).

[0073] The results of the fractional crystallization analysis of the polymer solution of the second high-density polyethylene resin dissolved in a solvent show that, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature higher than 30 °C and not higher than 50 °C can be 10 - 20%, 12 - 18%, or 15 - 17%. When the reduction ratio of the concentration of the second high-density polyethylene resin falls within this range, the biaxial stretching of the final film using the tenter frame process increases the draw ratios in the machine direction (MD) and the transverse direction (TD), and imparts excellent transparency, thus imparting low haze and high clarity to the final film.

[0074] The results of the fractional crystallization analysis of the polymer solution of the second high-density polyethylene resin dissolved in a solvent show that, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature higher than 30 °C and not higher than 60 °C can be 15 - 25% or 18 - 25%. When the reduction ratio of the concentration of the second high-density polyethylene resin falls within this range, the biaxial stretching of the final film using the tenter frame process increases the draw ratios in the machine direction (MD) and the transverse direction (TD), and imparts excellent transparency, thus imparting low haze and high clarity to the final film.

[0075] The results of the fractional crystallization analysis of the polymer solution of the second high-density polyethylene resin dissolved in the solvent show that, compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100 °C, the reduction ratio of the concentration of the polymer dissolved in the polymer solution at a temperature of 80 - 90 °C can be 30 - 75%, 40 - 70%, or 50 - 60%. When the reduction ratio of the concentration of the second high-density polyethylene resin falls within this range, the biaxial stretching of the final film using the tenter frame process increases the stretching rate in the machine direction (MD) and the transverse direction (TD), and imparts excellent transparency, thus imparting low haze and high clarity to the final film.

[0076] In the second high-density polyethylene resin, based on the integral value of the total area of the total molecular weight distribution diagram of the second high-density polyethylene resin, the integral value ratio of the graphic area corresponding to the polymer with a molecular weight of 10 3 - 10 4 g / mol can be 18 - 30%, and the number of short side chains of the polymer can be 0.1 - 8 per thousand carbons.

[0077] For example, in the second high-density polyethylene resin, based on the integral value of the total area of the total molecular weight distribution diagram of the second high-density polyethylene resin, the molecular weight is 10 3 - 10 4 g / mol, the integral value ratio of the graphic area corresponding to the polymer can be 20 - 25%, and the number of short side chains of the polymer can be 0.5 - 5 per thousand carbons. When the molecular weight is 10 3 - 10 4 g / mol, the ratio of the polymer and the number of short side chains fall within the above ranges, the stretching ratio in the longitudinal and transverse directions can be increased, and the thickness uniformity of the film can be ensured.

[0078] In the second high-density polyethylene resin, based on the integral value of the total area of the total molecular weight distribution diagram of the second high-density polyethylene resin, the molecular weight is 10 5 - 10 6 g / mol, the integral value ratio of the graphic area corresponding to the polymer can be 20 - 26%, and the number of short side chains of the polymer can be 1 - 12 per thousand carbons.

[0079] For example, in the second high-density polyethylene resin, based on the integral value of the total area of the total molecular weight distribution diagram of the second high-density polyethylene resin, the molecular weight is 10 5 - 10 6 g / mol, the integral value ratio of the graphic area corresponding to the polymer can be 21 - 24%, and the number of short side chains of the polymer can be 1.5 - 10 per thousand carbons. When the molecular weight is 10 5 - 106 When the proportion of the polymer in g / mol and the number of short chain branches fall within the above ranges, the film can be stably biaxially stretched successively in the longitudinal and transverse directions, and the final physical properties of the film can be significantly improved.

[0080] The density of the second high-density polyethylene resin can be lower than that of the first high-density polyethylene resin. The density of the second high-density polyethylene resin can be, for example, 0.940 - 0.965 g / cm 3 or 0.942 - 0.960 g / cm 3 . When the density of the second high-density polyethylene resin falls within this range, the transparency of the final high-density polyethylene film can be improved.

[0081] The melt index of the second high-density polyethylene resin (MI2 (2.16 kg load, 190 °C)) can be 0.50 - 5.0 g / 10 min or 1.0 - 3.0 g / 10 min. When the melt index of the second high-density polyethylene resin falls within the above range, the extrusion processability is excellent, the roughness of the film surface can be reduced, and the transparency of the film can be improved.

[0082] The melt flow rate ratio of the second high-density polyethylene resin (MI21.6 (21.6 kg load, 190 °C) / MI2 (2.16 kg load, 190 °C), MFRR) can be 60 or more, 70 or more, or 70 - 80. When the melt flow rate ratio of the second high-density polyethylene resin falls within the above range, the final extrusion processability is excellent, the film can be stably biaxially stretched in the longitudinal direction (MD) and the transverse direction (TD), and the film can be stretched to a uniform thickness.

[0083] According to one embodiment of the high-density polyethylene resin, that is, each of the first high-density polyethylene resin and the second high-density polyethylene, can be mixed with additives including antioxidants, neutralizers, or combinations thereof to form a composition.

[0084] Based on 100 parts by weight of the high-density polyethylene resin, the amount of the additive can be 0.005 - 0.5 parts by weight.

[0085] The antioxidant may include at least one selected from the group consisting of phenolic compounds and phosphorus-based compounds. The phenolic compounds include pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), octadecyl (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), tris(3,4-di-tert-butyl-4-hydroxybenzyl) isocyanate, triethylene glycol-bis(3-(tert-butyl-4-hydroxy-5-methylphenyl)propionate), etc., and the phosphorus-based compounds include tris(2,4-di-tert-butylphenyl) phosphite, tetra(2,4-di-tert-butylphenyl)-4,4'-biphenyldiphosphite, distearyl pentaerythritol diphosphite, 2,4-dinonylphenyl bis(4-monononylphenyl) phosphite, etc.

[0086] Based on 100 parts by weight of the high-density polyethylene resin, the amount of the antioxidant may be 0.01 - 0.5 parts by weight, for example, 0.1 - 0.3 parts by weight. When the amount of the antioxidant is within the above range, excellent processing performance can be obtained without causing discoloration or viscosity change.

[0087] The neutralizer may include calcium stearate, zinc stearate, magnesium aluminum hydroxycarbonate, zinc oxide, magnesium hydroxystearate, etc.

[0088] Based on 100 parts by weight of the high-density polyethylene resin, the amount of the neutralizer may be 0.005 - 0.3 parts by weight, for example, 0.02 - 0.1 parts by weight. When the amount of the neutralizer is within the above range, excellent processing performance can be obtained without causing discoloration or viscosity change.

[0089] According to one embodiment, a flexible packaging film containing the high-density polyethylene film is provided.

[0090] Recently, regulations on recycling have been continuously strengthened worldwide. Along with the change in the social responsibility awareness of inherent sustainability and the solutions to a wide range of environmental problems, companies are also making efforts to design flexible packaging materials that are easy to collect, classify, and recycle.

[0091] The most effective way to easily collect, classify, and recycle flexible packaging materials is to use packaging materials produced from a single material, rather than conventional packaging produced from a mixture of multiple materials.

[0092] For this purpose, biaxially oriented polyethylene (BOPE) film is required. Generally, when using the tenter frame process as the process for preparing the biaxially oriented polyethylene film and stretching the film in the machine direction (MD) and the transverse direction (TD), the polyethylene chains and crystal structures are highly oriented, thereby improving the mechanical strength, especially the impact strength, and significantly improving the optical properties such as transparency and the film appearance.

[0093] However, during film processing, the tentering machine process is greatly affected by the molecular structure of the raw material, and the stretching process conditions are very strict. Generally, polyethylene (PE) has a narrow stretching temperature range and a very low stretching rate due to its high crystallization rate and excellent crystallinity, and the polyethylene film will break when wrinkling during the stretching process, or has uneven thickness during the stretching process. In particular, the BOPE film produced from high-density polyethylene (HDPE) exhibits high heat resistance and significantly improved modulus, but is difficult to stretch and has a problem of reduced transparency compared to the BOPE film produced from linear low-density polyethylene (LLDPE).

[0094] Therefore, there is a need for a high-density polyethylene film applicable to recyclable single-material flexible packaging films, which has excellent mechanical properties, especially high modulus and excellent transparency, and is easily biaxially stretchable by the tentering machine process.

[0095] Hereinafter, specific embodiments of the present invention will be described. These embodiments are only used to illustrate or elaborate the present invention in detail and should not be construed as limiting the scope of the present invention. In addition, other details that can be fully conceived by those skilled in the art technically will not be described.

[0096] [Preparation of High-Density Polyethylene Resin]

[0097] Preparation Examples 1-1 and 1-2: Preparation of the First High-Density Polyethylene Resin Composition

[0098] 1. Preparation of the First High-Density Polyethylene Resin

[0099] The first high-density polyethylene resin was prepared under the conditions of Table 1 below.

[0100] Two 90L reactors were connected in series, and ethylene polymerization was carried out with ethylene monomer and comonomer in the presence of Ziegler-Natta catalyst. The Ziegler-Natta catalyst used herein is a known catalyst containing magnesium and titanium and is prepared by a conventional method.

[0101] Specifically, ethylene polymerization was carried out in the first reactor with ethylene monomer (C 2 ), 1-hexene (C 6 ) as comonomer, and hydrogen (H 2 ). The polymerization ratio in the first reactor, the feed ratio of C 2 to C 6 , and the ratio of C 2 to H 2The feed ratio, polymerization temperature, and polymerization pressure are shown in Table 1 below, and the residence time is 61 minutes. The intermediate polymer in the slurry phase polymerized in the first reactor is transferred to the second reactor and then further polymerized to obtain the final polymer in the slurry phase. Then, a powdered high-density polyethylene resin is prepared from the final polymer in the slurry phase. In the second reactor, ethylene polymerization is carried out using ethylene monomer (C 2 ) and hydrogen (H 2 ), and no comonomer (C 6 ) is used. The polymerization ratio in the second reactor, the feed ratio of C 2 to C 6 , the feed ratio of C 2 to H 2 , the polymerization temperature, and the polymerization pressure are shown in Table 1 below, and the residence time is 34 minutes.

[0102] Table 1

[0103]

[0104] 2. Preparation of the First High-Density Polyethylene Resin Composition

[0105] Using a Henschel mixer, 100 parts by weight of each first high-density polyethylene resin is mixed with 0.1 part by weight of antioxidant Irganox-3114, 0.1 part by weight of antioxidant Irgafos-168, and 0.025 part by weight of neutralizing agent basic magnesium aluminum carbonate (DHT-4A), and then using a twin-screw extruder, a first high-density polyethylene resin composition in pellet form is prepared.

[0106] Preparation Examples 2-1 and 2-2: Preparation of the Second High-Density Polyethylene Resin Composition

[0107] The second high-density polyethylene resin composition is prepared under the conditions shown in Table 2 below.

[0108] Using a Henschel mixer, 100 parts by weight of the first high-density polyethylene resin prepared in Preparation Example 1-1 or 1-2 and a mixture of commercially available POE Supreme 004 or Supreme 883 produced by SK Geocentric is mixed with 0.1 part by weight of antioxidant Irganox-3114, 0.1 part by weight of antioxidant Irgafos-168, and 0.025 part by weight of neutralizing agent basic magnesium aluminum carbonate (DHT-4A), and then using a twin-screw extruder, a second high-density polyethylene resin composition in pellet form is prepared.

[0109] Table 2

[0110] Preparation Example 2-1 Preparation Example 2-2 Preparation Example 1-1 (wt%) 85 - Preparation Example 1-2 (wt%) - 90 SK Supreme 004 (wt%) 15 - SK Supreme 883 (wt%) - 10

[0111] Comparative Preparation Example 1-3: Preparation of the Second High-Density Polyethylene Resin Composition

[0112] 1. Preparation of the Second High-Density Polyethylene Resin

[0113] The second high-density polyethylene resin of Comparative Preparation Example 1 is the C330A product produced by Hanwa Solutions Co., Ltd. through a slurry process, and 1-butene is used as a copolymer. The density of the C330A product is 0.958 g / cm 3 , the melt index (MI2) is 1.0 g / 10 min, and the melt flow rate ratio is 150. The term "melt flow rate ratio" used herein refers to the ratio of the melt index (MI21.6) measured according to ASTM D1238 at 190 °C under a load of 21.6 kg to the melt index (MI2) measured according to ASTM D1238 at 190 °C under a load of 2.16 kg.

[0114] The second high-density polyethylene resin of Comparative Preparation Example 2 is the C910C product produced by Hanwa Solutions Co., Ltd. through a gas-phase process using a gas-phase reactor (GPR), and 1-butene is used as a copolymer. The density of the C910C product is 0.950 g / cm 3 , the melt index (MI2) is 2.2 g / 10 min, and the melt flow rate ratio is 30.

[0115] The second high-density polyethylene resin of Comparative Preparation Example 3 is the R904U product produced by Hanwa Solutions Co., Ltd. through a gas-phase process using a gas-phase reactor (GPR), and 1-hexene is used as a copolymer. The density of the R904U product is 0.940 g / cm 3 , the melt index (MI2) is 4.0 g / 10 min, and the melt flow rate ratio is 25.

[0116] 2. Preparation of the Second High-Density Polyethylene Resin Composition

[0117] Using a Henschel mixer, 100 parts by weight of each second high-density polyethylene resin is mixed with 0.1 part by weight of antioxidant Irganox-3114, 0.1 part by weight of antioxidant Irgafos-168, and 0.025 part by weight of neutralizing agent basic magnesium aluminum carbonate (DHT-4A), and then using a twin-screw extruder, a second high-density polyethylene resin composition in the form of pellets is prepared.

[0118] [Production of High-Density Polyethylene Film]

[0119] Examples 1-4 and Comparative Examples 1-7

[0120] Using the high-density polyethylene resin compositions prepared in Preparation Examples 1-1, 1-2, 2-1, 2-2 and Comparative Preparation Example 1-3, a biaxially oriented polyethylene (BOPE) film having a multilayer structure was produced. At this time, the types of the high-density polyethylene resin compositions constituting each layer and the ratios (%) of the thicknesses of the respective layers to the total thickness of the film are shown in Table 3 below.

[0121] Specifically, a biaxially oriented polyethylene film having a multilayer structure was biaxially stretched on a Bruckner production line (hybrid BOPE / BOPP production line, 5 layers, 6.6 m wide). The film was applied in 5 layers, and at an extrusion speed of 190 m / min and a die temperature of 230 - 240 °C, and finally stretched 5.2 times in the machine direction (MD) and 9 times in the transverse direction (TD). The extrusion conditions of the biaxially stretched film and the film processing conditions are specifically shown in Table 4 below.

[0122] Table 3

[0123] First Surface Layer (A1) Intermediate Layer (B) Second Surface Layer (A2) A1 / B / B / B / A2 (wt%) Example 1 Preparation Example 2-1 Preparation Example 1-1 Preparation Example 2-1 5 / 10 / 70 / 10 / 5 Example 2 Preparation Example 2-2 Preparation Example 1-1 Preparation Example 2-2 5 / 10 / 70 / 10 / 5 Example 3 Preparation Example 2-1 Preparation Example 1-2 Preparation Example 2-1 5 / 10 / 70 / 10 / 5 Example 4 Preparation Example 2-2 Preparation Example 1-2 Preparation Example 2-2 5 / 10 / 70 / 10 / 5 Comparative Example 1 Preparation Example 1-1 Preparation Example 1-1 Preparation Example 1-1 5 / 10 / 70 / 10 / 5 Comparative Example 2 Preparation Example 1-2 Preparation Example 1-2 Preparation Example 1-2 5 / 10 / 70 / 10 / 5 Comparative Example 3 Preparation Example 2-1 Preparation Example 2-1 Preparation Example 2-1 5 / 10 / 70 / 10 / 5 Comparative Example 4 Preparation Example 2-2 Preparation Example 2-2 Preparation Example 2-2 5 / 10 / 70 / 10 / 5 Comparative Example 5 Comparative Preparation Example 1 Preparation Example 1-1 Comparative Preparation Example 1 5 / 10 / 70 / 10 / 5 Comparative Example 6 Comparative Preparation Example 2 Preparation Example 1-2 Comparative Preparation Example 2 5 / 10 / 70 / 10 / 5 Comparative Example 7 Comparative Preparation Example 3 Preparation Example 1-2 Comparative Preparation Example 3 5 / 10 / 70 / 10 / 5

[0124] Table 4

[0125]

[0126] [Physical Property Evaluation of High-Density Polyethylene Resin Composition]

[0127] The physical properties of the first high-density polyethylene resin compositions of Preparation Examples 1-1 and 1-2 were evaluated, and the results are shown in Table 5 below. The physical properties of the second high-density polyethylene resin compositions of Preparation Examples 2-1 and 2-2 and Comparative Preparation Example 1-3 were evaluated, and the results are shown in Table 6 below. The evaluation methods are as follows.

[0128] Density

[0129] Measurement was carried out according to ASTM D1505.

[0130] Melt Index (MI)

[0131] The melt index (MI2) was measured according to ASTM D1238 at 190 °C under a load of 2.16 kg.

[0132] The melt index (MI21.6) was measured according to ASTM D1238 at 190 °C under a load of 21.6 kg.

[0133] Melt Flow Rate Ratio (MFRR)

[0134] The melt flow rate ratio (MFRR) refers to the ratio of the melt index (MI21.6) measured according to ASTM D1238 at 190 °C under a load of 21.6 kg to the melt index (MI2) measured according to ASTM D1238 at 190 °C under a load of 2.16 kg.

[0135] Melting Temperature (Tm) and Crystallization Temperature (Tc)

[0136] Determination is carried out using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / min according to ASTM D 3418.

[0137] Infrared Gel Permeation Chromatography (GPC-IR)

[0138] Using the equipment of Polymer Char. Add 12 mg of the sample to 8 mL of 1,2,4-trichlorobenzene (containing 125 ppm BHT) and dissolve at 160 °C for 2 hours. The eluent used is 1,2,4-trichlorobenzene (containing 125 ppm BHT), and the columns used are one PLgel Olexis Guard and three PLgel Olexis. Analyze 200 μL. Use polystyrene standard materials for column calibration in molecular weight calculation, and calculate the molecular weight of polyethylene using the Mark-Houwink constants (K = 44.6, a = 0.725).

[0139] The number of short chain branches (SCB) in the sample refers to the number of short chain branches present per thousand carbons and is calibrated using a known standard (1-octene copolymer of Polymer Char). The number of short chain branches (SCB) refers to the average value of the number of methyl groups (-CH 3 ) present per thousand carbons in the sample excluding the methyl groups at the chain ends, and is the value calculated by end-chain correction from the number of methyl groups (CH 3 / 1000TC) present per thousand carbons in the sample. The end-chain correction is determined by Equation 1 below.

[0140] [Equation 1]

[0141] The number of chain ends per thousand carbons (number of chain ends / 1000TC) = (A × 14000) / M

[0142] where A represents the number of end groups. For example, for linear polyethylene (linear PE), A is 2, and for long chain branch (LCB) polymers, A is greater than 2. In addition, M refers to the given molecular weight.

[0143] When the chain end groups are capped with vinyl (-CH=CH 2 ), a value of 0 is used for end-chain correction.

[0144] The followingFigure 3 is a graph showing the total molecular weight distribution and the number of short chain branches per thousand carbons of the first high density polyethylene resins of Preparation Example 1-1 and Preparation Example 1-2 measured by infrared gel permeation chromatography (GPC-IR). As can be seen from Figure 3 in the total molecular weight distribution graph of the first high density polyethylene, the integral values in the regions where logM is 3-4 and 5-6 respectively correspond to the proportion of polymers with a molecular weight (M) of 10 5 -10 6 g / mol and the proportion of polymers with a molecular weight (M) of 10 3 -10 4 g / mol in the high density polyethylene resin according to one embodiment.

[0145] Based on this, the proportion of polymers with a molecular weight of 10 5 -10 6 g / mol (10 5 -10 6 ), the proportion of polymers with a molecular weight of 10 3 -10 4 g / mol (10 3 -10 4 ), the number of short chain branches of polymers with a molecular weight of 10 5 -10 6 g / mol (10 5 to -10 6 ) and the number of short chain branches of polymers with a molecular weight of 10 3 -10 4 g / mol (10 3 -10 4 ) were measured.

[0146] Crystallization Analysis Fractionation (CRYSTAF)

[0147] Measurement was carried out using the CRYSTAF device of Polymer Char. 20 mg of the sample was dissolved in 20 mL of 1,2,4-trichlorobenzene at 160 °C for 60 minutes with stirring to prepare a polymer solution. The polymer solution was injected into the device and stabilized at 100 °C for 45 minutes, and then the temperature was lowered to 35 °C at a constant rate of 0.2 °C / min. At this time, the formed crystals were filtered through a filter, and the concentration of the polymer dissolved in the solution was measured. The cumulative curve shows the ratio (%) of the concentration of the polymer dissolved in the polymer solution as the temperature decreases with respect to the concentration at the initial set temperature of 100 °C (which is 100%). Based on the cumulative curve, the ratio (%) of the decrease in the concentration of the polymer dissolved in the polymer solution at each temperature was measured. The crystallization analysis fractionation diagrams of the first high density polyethylene resins of Preparation Example 1-1 and 1-2 are as Figure 4As shown, the crystallization analysis fractionation diagrams of the second high-density polyethylene resins according to Preparation Examples 2-1 and 2-2 are as Figure 5 shown.

[0148] Table 5

[0149]

[0150] Table 6

[0151]

[0152]

[0153] [Evaluation of Physical Properties of High-Density Polyethylene Films]

[0154] The physical properties of the high-density polyethylene films of Examples 1-4 and Comparative Examples 1-7 were evaluated according to the following methods, and the results are shown in Table 7 below.

[0155] Tensile Strength and Modulus

[0156] According to ASTM D 882, the tensile strength (MPa) and modulus (MPa) of each film were measured in the machine direction (MD) and the transverse direction (TD).

[0157] Haze and Clarity

[0158] The haze (%) and clarity (%) were measured according to ASTM D 1003.

[0159] Film Thickness and Standard Deviation (2σ)

[0160] Using a non-contact thickness gauge, the thickness of each film was measured about 50 times at 20 mm intervals in the machine direction (MD) and the transverse direction (TD), the average value was calculated, 2σ was calculated, and it was expressed as the standard deviation (%).

[0161] Table 7

[0162]

[0163]

[0164] As can be seen from Table 7, the biaxially stretched films of Examples 1-4 of the present invention using a film including an intermediate layer (B) formed of a composition containing a first high-density polyethylene resin and a film including a first surface layer (A1) and a second surface layer (A2) formed of a composition containing a second high-density polyethylene resin have excellent properties, namely, a high modulus, especially an MD modulus of 1300 MPa or more, a haze of less than 6%, a clarity of 97% or more, and high thickness uniformity.

[0165] On the other hand, the haze or modulus of Comparative Examples 1-4 in which the intermediate layer, the first surface layer, and the second surface layer all use the first high-density polyethylene resin or the second high-density polyethylene resin are low. In addition, Comparative Examples 5-7 in which the intermediate layer uses the first high-density polyethylene resin according to the present invention, but the first surface layer and the second surface layer do not use the second high-density polyethylene resin according to the present invention have low haze and modulus.

[0166] From the above description, it is obvious that, compared with the films including the respective layers formed by using a combination of various polyethylene resins, the high-density polyethylene film according to the present invention can be uniformly stretched, thereby ensuring thickness uniformity, and exhibits excellent mechanical properties and optical properties. In addition, the high-density polyethylene film according to the present invention can be applied to a flexible packaging film formed of a single and recyclable material.

[0167] The effects of the present invention are not limited to the above, and according to the above description of the exemplary embodiments, other technical effects not mentioned are obvious to those skilled in the art.

[0168] Although the embodiments of the present invention have been disclosed with reference to the accompanying drawings, those skilled in the art can understand that various modifications, additions, and substitutions can be made without departing from the scope and spirit of the present invention. Therefore, it is obvious that the above exemplary embodiments are illustrative in all aspects and do not limit the present invention.

Claims

1. A high-density polyethylene film, wherein The high-density polyethylene film comprises: an intermediate layer comprising a first high-density polyethylene resin; and A first surface layer and a second surface layer are respectively arranged on both surfaces of the intermediate layer, and the first surface layer and the second surface layer contain a second high-density polyethylene resin, wherein the density of the first high-density polyethylene resin is higher than the density of the second high-density polyethylene resin, Based on the crystallization analysis classification results of the polymer solution of the second high-density polyethylene resin dissolved in a solvent, the concentration of the polymer dissolved in the polymer solution at a temperature of 80-90°C is reduced by 30-75% compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100°C.

2. The high-density polyethylene film according to claim 1, wherein Each of the intermediate layer, the first surface layer, and the second surface layer has a single-layer structure or a multi-layer structure including 2 to 5 layers.

3. The high-density polyethylene film according to claim 1, wherein The density of the first high-density polyethylene resin is 0.945-0.970 g / cm 3 .

4. The high-density polyethylene film according to claim 1, wherein In the first high-density polyethylene resin, the molecular weight is 10 5 -10 6 The integral value ratio of the graph area corresponding to the polymer of g / mol is 18-28%, and the number of short chain branches of the polymer is 5-15 per thousand carbon atoms.

5. The high-density polyethylene film according to claim 1, wherein In the first high-density polyethylene resin, the molecular weight is 10 3 -10 4 The integral value ratio of the graph area corresponding to the polymer of g / mol is 20-30%, and the number of short chain branches of the polymer is 1-8 per thousand carbon atoms.

6. The high-density polyethylene film according to claim 1, wherein At least one of the first high-density polyethylene resin or the second high-density polyethylene resin has short chain branches, and the short chain branches have a broad orthogonal comonomer distribution (BOCD) structure.

7. The high-density polyethylene film according to claim 1, wherein Based on the results of crystallization analysis classification of the polymer solution of the first high-density polyethylene resin dissolved in a solvent, the concentration of the polymer dissolved in the polymer solution at a temperature of 70-80°C is reduced by 10-20% compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100°C.

8. The high-density polyethylene film according to claim 1, wherein Based on the results of crystallization analysis classification of the polymer solution of the first high-density polyethylene resin dissolved in a solvent, the concentration of the polymer dissolved in the polymer solution at a temperature of 80-90°C is reduced by 50-70% compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100°C.

9. The high-density polyethylene film according to claim 1, wherein The first high-density polyethylene resin has a melt index (MI2 (2.16 kg load, 190° C.)) of 0.40-3.0 g / 10 min.

10. The high-density polyethylene film according to claim 1, wherein The first high-density polyethylene resin has a melt flow rate ratio (MI21.6 (21.6 kg load, 190° C.) / MI2 (2.16 kg load, 190° C.), MFRR) of 70 or more.

11. The high-density polyethylene film according to claim 1, wherein Based on the results of crystallization analysis classification of a polymer solution of the second high-density polyethylene resin dissolved in a solvent, the concentration of the polymer dissolved in the polymer solution at a temperature higher than 30°C and not higher than 50°C is reduced by 10-20% compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100°C.

12. The high-density polyethylene film according to claim 1, wherein Based on the results of crystallization analysis classification of the polymer solution of the second high-density polyethylene resin dissolved in a solvent, the concentration of the polymer dissolved in the polymer solution at a temperature higher than 30°C and not higher than 60°C is reduced by 15-25% compared with the concentration of the polymer dissolved in the polymer solution at a temperature of 100°C.

13. The high-density polyethylene film according to claim 1, wherein In the second high-density polyethylene resin, the molecular weight is 10 3 -10 4 The integral value ratio of the graph area corresponding to the g / mol polymer is 18-30%, and the number of short chain branches of the polymer is 0.1-8 per thousand carbon atoms.

14. The high-density polyethylene film according to claim 1, wherein The density of the second high-density polyethylene resin is 0.940-0.965 g / cm 3 .

15. The high-density polyethylene film according to claim 1, wherein The melt index (MI2 (2.16 kg load, 190° C.) of the second high-density polyethylene resin is 0.50-5.0 g / 10 min.

16. The high density polyethylene film according to claim 1, wherein The melt flow rate ratio (MI21.6 (21.6 kg load, 190° C.) / MI2 (2.16 kg load, 190° C.), MFRR) of the second high-density polyethylene resin is 60 or more.

17. The high-density polyethylene film according to claim 1, wherein The high-density polyethylene film is biaxially stretched by a tenter process in a longitudinal direction (MD) at a stretching ratio of 4 to 7 times and in a transverse direction (TD) at a stretching ratio of 8 to 10 times.

18. The high-density polyethylene film according to claim 1, wherein The thickness of the high-density polyethylene film is 15-70 μm, and the amount of the intermediate layer is 70-98 wt % based on the total amount of the high-density polyethylene film.

19. A flexible packaging film, wherein: The flexible packaging film comprises the high-density polyethylene film according to any one of claims 1 to 18.

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