High-density polyethylene film and flexible packaging film containing the same

Abstract

To provide a high-density polyethylene film that is excellent in mechanical properties, especially the modulus and transparency, and easy to biaxially stretch, and realizes excellent thickness uniformity of the stretched film.SOLUTION: A high-density polyethylene film includes: an intermediate layer containing a first high-density polyethylene resin; and a first skin layer and a second skin layer that are respectively disposed on opposite surfaces of the intermediate layer and 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. Based on a result of crystallization analysis fractionation of a polymer solution of the second high-density polyethylene resin dissolved in a solvent, the concentration of a polymer dissolved in the polymer solution at a temperature of 80°C to 90°C is decreased by 30% to 75%, compared to the concentration of the polymer dissolved in the polymer solution at 100°C. A flexible packaging film comprising the high-density polyethylene film is also provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a high-density polyethylene film and a flexible packaging film containing the same. [Background technology]

[0002] In recent years, regulations on recycling have been strengthened worldwide, and companies are also making efforts to design flexible packaging materials that are easy to collect, sort, and recycle, driven by a growing awareness of their own social responsibility for sustainability and a broader focus on addressing environmental issues.

[0003] The most effective approach is to use packaging materials made from a single material instead of existing packaging materials that use a mixture of various materials. In particular, using packaging materials made from a single material such as polyethylene (PE) or polypropylene (PP) makes recycling easier and can contribute to improving the quality of recycled products.

[0004] To achieve this, the application of biaxially oriented polyethylene (BOPE) film is required. Generally, the tenter frame process is applied as a manufacturing process for biaxially oriented polyethylene (BOPE) film. When the film is stretched in the machine direction (MD) and transverse direction (TD), the polyethylene chains and crystalline structure are highly oriented, resulting in improved mechanical strength, especially impact strength, and a revolutionary improvement in optical properties such as transparency and film appearance.

[0005] However, the tenter frame process is greatly affected by the molecular structure of the raw material during film processing, and the stretching process conditions are very complex. General polyethylene (PE) has a high crystallization rate and high crystallinity, so the temperature range that can be stretched is narrow, the stretching ratio is very low, and if wrinkles form or the thickness is not uniform during stretching, ultimately, the phenomenon of film tearing occurs during stretching. In particular, in the BOPE film applying high density polyethylene (HDPE), compared with the BOPE film applying linear low density polyethylene (LLDPE), it has excellent heat resistance and the modulus of the film is significantly improved, but there are problems such as being difficult to stretch and a decrease in transparency.

[0006] Therefore, in order to apply to recyclable single-material flexible packaging films, there is a need to develop a high density polyethylene film that has high mechanical properties, especially high modulus values, excellent transparency, and is easily biaxially stretched by the tenter frame process.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention for solving the above-mentioned problems provides a high density polyethylene film that is easily biaxially stretched, has excellent thickness uniformity of the stretched film, and has excellent mechanical properties, especially modulus values and transparency.

[0009] The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0010] A high-density polyethylene film according to one embodiment of the present invention for solving the above-mentioned problems comprises an intermediate layer containing a first high-density polyethylene resin composition, and a first skin layer and a second skin layer disposed on both sides of the intermediate layer, respectively, and containing a second high-density polyethylene resin composition, wherein the density of the first high-density polyethylene resin composition is higher than the density of the second high-density polyethylene resin composition. The second high-density polyethylene resin composition is obtained by melt-mixing a polyolefin elastomer with the first high-density polyethylene resin composition in an amount of 5% to 25% by weight relative to the total amount of the second high-density polyethylene resin composition. In the results of crystallization fractionation analysis of the polymer solution obtained by dissolving the second high-density polyethylene resin composition in a solvent, the decrease ratio of the polymer concentration dissolved in the polymer solution at temperatures of 80°C to 90°C compared to the polymer concentration at 100°C is 30% to 75%.

[0011] Each of the aforementioned intermediate layer, the first skin layer, and the second skin layer may be a single layer or a multilayer structure consisting of two to five layers.

[0012] The first high-density polyethylene resin composition The density is 0.945 g / cm³. 3 ~0.970g / cm 3 That's fine.

[0013] The first high-density polyethylene resin composition The first high-density polyethylene resin composition For the integral of the total area of ​​the overall molecular weight distribution graph, the molecular weight is 10 5 g / mol~10 6 The ratio of integral values ​​in the graph region corresponding to a polymer with a concentration of g / mol is 18% to 28%, and the number of single-chain branches in the polymer may be 5 to 15 per 1000 carbon atoms.

[0014] The first high-density polyethylene resin composition The first high-density polyethylene resin composition For the integral of the total area of ​​the overall molecular weight distribution graph, the molecular weight is 10 3g / mol~10 4 The ratio of integral values ​​in the graph region corresponding to a polymer with a concentration of g / mol is 20% to 30%, and the number of single-chain branches in the polymer may be 1 to 8 per 1000 carbon atoms.

[0015] At least one of the first high-density polyethylene and the second high-density polyethylene is single-chain branched, and the single-chain branching may have a BOCD (broad orthogonal comonomer distribution) structure.

[0016] The first high-density polyethylene resin composition In the results of crystallization fractionation analysis of a polymer solution obtained by dissolving in a solvent, the decrease ratio of the polymer concentration dissolved in the polymer solution at a temperature of 70°C to 80°C compared to the polymer concentration dissolved in the polymer solution at 100°C may be 10% to 20%.

[0017] The first high-density polyethylene resin composition In the results of crystallization fractionation analysis of a polymer solution obtained by dissolving in a solvent, the decrease ratio of the polymer concentration dissolved in the polymer solution at a temperature of 80°C to 90°C compared to the polymer concentration dissolved in the polymer solution at 100°C may be 50% to 70%.

[0018] The first high-density polyethylene resin composition The melt flow index (MI2 (2.16 kg load, 190°C)) may be between 0.40 g / 10 min and 3.0 g / 10 min.

[0019] The first high-density polyethylene resin composition The melt flow ratio (MI21.6 (21.6 kg load, 190°C) / MI2 (2.16 kg load, 190°C), MFRR) may be 70 or greater.

[0020] The second high-density polyethylene resin compositionIn the results of crystallization fractionation analysis of a polymer solution dissolved in a solvent, the decrease ratio of the polymer concentration dissolved in the polymer solution at a temperature exceeding 30°C and not exceeding 50°C may be 10% to 20% with respect to the polymer concentration dissolved in the polymer solution at 100°C.

[0021] The second high-density polyethylene resin composition In the results of crystallization fractionation analysis of a polymer solution dissolved in a solvent, the decrease ratio of the polymer concentration dissolved in the polymer solution at a temperature exceeding 30°C and not exceeding 60°C is 15% to 25% with respect to the polymer concentration dissolved in the polymer solution at 100°C.

[0022] The second high-density polyethylene resin composition is the second high-density polyethylene resin composition With respect to the integral value of the total area of the overall molecular weight distribution graph of the second high-density polyethylene resin, the ratio of the integral value of the graph region corresponding to polymers with a molecular weight of 10 3 g / mol to 10 4 g / mol is 18% to 30%, and the number of single-chain branches of the polymer may be 0.1 to 8 per 1000 carbon atoms.

[0023] The second high-density polyethylene resin composition The density of the second high-density polyethylene resin is 0.940 g / cm 3 to 0.965 g / cm 3 and may be such.

[0024] The second high-density polyethylene resin composition The melt flow index (MI2 (2.16 kg load, 190°C)) of the second high-density polyethylene resin may be 0. fifty g / 10 min to 5.0 g / 10 min.

[0025] The second high-density polyethylene resin composition The melt flow ratio (MI21.6 (21.6 kg load, 190°C) / MI2 (2.16 kg load, 190°C), MFRR) of the second high-density polyethylene resin may be 60 or more.

[0026] The high-density polyethylene film may be a film that has been successively biaxially stretched by a tenter frame process to a longitudinal (MD) stretch ratio of 4 to 7 times and a transverse (TD) stretch ratio of 8 to 10 times.

[0027] The thickness of the high-density polyethylene film is in the range of 15 μm to 70 μm, and the intermediate layer may be formed in an amount of 70% to 98% by weight relative to the total amount of the high-density polyethylene film.

[0028] Furthermore, one embodiment of the present invention for solving the above-mentioned problems is to provide a flexible packaging film containing the high-density polyethylene film. [Effects of the Invention]

[0029] The high-density polyethylene film according to the present invention exhibits superior mechanical properties and optical properties compared to films in which various polyethylene resins are mixed and applied to each layer. This allows for uniform stretching, ensures uniform thickness, and provides excellent mechanical properties. Furthermore, the high-density polyethylene film according to the present invention is applicable to recyclable single-material flexible packaging films.

[0030] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned above will be clearly understood by an ordinary person from the following description. [Brief explanation of the drawing]

[0031] [Figure 1] This is a schematic diagram showing a high-density polyethylene film relating to one example. [Figure 2] This is a schematic diagram showing a high-density polyethylene film relating to one example. [Figure 3] This graph shows the overall molecular weight distribution and the number of single-chain branches per 1000 carbon atoms of the first high-density polyethylene resin according to Production Example 1-1 and Production Example 1-2, as measured by infrared gel permeation chromatography-infrared (GPC-IR). [Figure 4] This is a graph of the crystallization analysis fractionation (CRYSTAF) of the first high-density polyethylene resin related to manufacturing examples 1-1 and 1-2. [Figure 5] This is a graph of the crystallization analysis fractionation (CRYSTAF) of the second high-density polyethylene resin related to manufacturing examples 2-1 and 2-2. [Modes for carrying out the invention]

[0032] The advantages and features of the present invention, as well as methods for achieving them, will become clear from the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be embodied in a variety of different forms, and these embodiments are provided merely to complete the disclosure of the present invention and to fully inform a person of the ordinary skill in the art to which the present invention belongs of the scope of the invention, and therefore the present invention is defined only by the scope of the claims.

[0033] The terms used herein are for illustrative purposes only and are not intended to limit the invention. In this specification, the singular form includes the plural form unless otherwise specified. The terms “comprises” and / or “comprising” as used in this specification do not exclude the existence or addition of one or more other components in addition to the components mentioned. Throughout this specification, the same reference numerals indicate the same component, and “and / or” includes each of the components mentioned and any combination of one or more of them. Terms such as “first,” “second,” etc., are used to describe various components, but these components are not limited by such terms. The terms are used only to distinguish one component from another. Therefore, the first component mentioned below may, of course, be the second component within the technical concept of the invention.

[0034] Unless otherwise specified, all terms used herein (including technical and scientific terms) will be used in the sense that would ordinarily be understood by a person of ordinary skill in the art to which this invention pertains. Furthermore, terms defined in commonly used dictionaries will not be interpreted ideally or excessively unless explicitly defined otherwise.

[0035] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0036] In explaining this specification, the meanings of the terms used herein will be briefly stated. However, these explanations are intended to aid in understanding this specification. Therefore, please note that unless explicitly stated as limitations of the invention, the terms are not used to limit the technical concept of the invention.

[0037] A high-density polyethylene film according to one embodiment of the present invention includes an intermediate layer containing a first high-density polyethylene resin, and a first skin layer and a second skin layer, respectively, disposed on both sides of the intermediate layer and containing a second high-density polyethylene resin.

[0038] Figure 1 is a schematic diagram showing a high-density polyethylene film according to one embodiment. Referring to Figure 1, the high-density polyethylene film 100 includes an intermediate layer 10 and skin layers 20 formed on both sides of the intermediate layer 10, and more specifically, it may have a structure in which a first skin layer 21 and a second skin layer 22 are arranged on both sides of the intermediate layer 10, respectively.

[0039] In one embodiment, the high-density polyethylene film may have a single layer or a multilayer structure of 2 to 5 layers, each of which may be a single layer or a multilayer structure of 2 to 5 layers. For example, the first and second skin layers may be single layers, and the intermediate layer may be a multilayer structure of 2 to 4 layers. When a high-density polyethylene film is formed with such a multilayer structure, it is possible to select the high-density polyethylene required for the functional requirements of the film, the changes in physical properties can be diversified by the layer composition of the film, and a film with excellent uniformity in the thickness distribution of each layer can be secured.

[0040] Figure 2 is a schematic diagram showing a high-density polyethylene film according to one embodiment. Referring to Figure 2, the high-density polyethylene film 100 may have a multilayer structure in which the first skin layer 21 and the second skin layer 22 are single-layer structures, and the intermediate layer 10 is a three-layer structure including a first intermediate layer 11, a second intermediate layer 12, and a third intermediate layer 13.

[0041] The high-density polyethylene film may be a film that has been successively biaxially stretched by a tenter frame process to a longitudinal (MD) stretch ratio of 4 to 7 times and a transverse (TD) stretch ratio of 8 to 10 times. By adjusting the stretch ratios in the longitudinal and transverse directions within the above ranges, sufficient crystal orientation can be achieved, ensuring the expected improvement in physical properties, and it is difficult to achieve stretch ratios higher than the above due to equipment limitations.

[0042] The thickness of the high-density polyethylene film may be 15 μm to 70 μm or 20 μm to 50 μm. When the thickness of the high-density polyethylene film is controlled within this range, it can have excellent mechanical properties without the problem of the film being too thick, making it difficult to thin the final film.

[0043] The intermediate layer may be formed in an amount of 70% to 98% by weight, 80% to 95% by weight, or 85% to 95% by weight relative to the total amount of the high-density polyethylene film. The total content of the first and second skin layers may be 2% to 30% by weight, 5% to 20% by weight, or 5% to 15% by weight relative to the total amount of the high-density polyethylene film. By adjusting the thickness of the intermediate layer, the first skin layer, and the second skin layer within the above ranges, the thickness of the high-density polyethylene film can be made more uniform, ensuring mechanical properties and improving transparency.

[0044] In one embodiment, the first high-density polyethylene resin can be used alone as the resin for forming the intermediate layer of the high-density polyethylene film.

[0045] The density of the first high-density polyethylene resin may be higher than that of the second high-density polyethylene resin. For example, the density of the first high-density polyethylene resin may be 0.945 g / cm³. 3 ~0.970g / cm 3 , or 0.945 g / cm³ 3 ~0.965g / cm 3 This may be the case. If the density of the first high-density polyethylene resin is within the above range, the final high-density polyethylene film may have excellent thermal stability, low thermal shrinkage, and improved modulus.

[0046] The first high-density polyethylene resin has a molecular weight of 10 relative to the integral of the total area of ​​the overall molecular weight distribution graph of the first high-density polyethylene resin. 5 g / mol~10 6 The ratio of the integral values ​​of the graph region corresponding to polymers with a molecular weight of g / mol is 18% to 28%, and the number of single-chain branches in the polymer may be 5 to 15 per 1000 carbon atoms. For example, the first high-density polyethylene resin has a molecular weight of 10 5 g / mol~10 6 The ratio of integral values ​​in the graph region corresponding to a polymer with a molecular weight of g / mol is 20% to 23%, and the number of single-chain branches in the polymer may be 6 to 12 per 1000 carbon atoms. 5 g / mol~10 6 If the polymer ratio in g / mol and the number of single-chain branches are within the aforementioned range, stable sequential biaxial stretching in both the longitudinal and transverse directions of the film is possible, and the final physical properties of the film can be significantly improved. In this invention, the molecular weight distribution graph may be measured by infrared gel permeation chromatography.

[0047] The first high-density polyethylene resin has a molecular weight of 10 relative to the integral of the total area of ​​the overall molecular weight distribution graph of the first high-density polyethylene resin. 3 g / mol~10 4The ratio of the integral values ​​of the graph region corresponding to polymers with a molecular weight of g / mol is 20% to 30%, and the number of single-chain branches in the polymer may be 1 to 8 per 1000 carbon atoms. For example, the first high-density polyethylene resin has a molecular weight of 10 3 g / mol~10 4 The ratio of integral values ​​in the graph region corresponding to polymers with a molecular weight of g / mol is 22% to 26%, and the number of single-chain branches in the polymer may be 1.5 to 6 per 1000 carbon atoms. 3 g / mol~10 4 If the polymer ratio (in g / mol) and the number of single-chain branches are within the aforementioned range, the stretching ratio can be improved in both the longitudinal and transverse directions of the film, and the uniformity of the film's thickness can be ensured.

[0048] The first high-density polyethylene may have single-chain branches, and the single-chain branches may have a BOCD (broad orthogonal commonomer distribution) structure. The BOCD structure contains many monomers and has a broad molecular weight distribution, and the number of single-chain branches may increase as the molecular weight increases. If the molecular weight of the polymer making up the resin of the first high-density polyethylene and the number of single-chain branches are within the above range, and the single-chain branches have a BOCD profile, then when the final high-density polyethylene film produced from the first high-density polyethylene resin is sequentially biaxially stretched in the tenter frame process, stable sequential biaxial stretching is possible in both the longitudinal (MD) and transverse (TD) directions. Therefore, a uniform thickness can be ensured, the stretching ratio can be improved, and the mechanical strength of the stretched film, especially the modulus, can be significantly improved.

[0049] In the results of the crystallization fractionation analysis of the polymer solution obtained by dissolving the first high-density polyethylene resin in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 70°C to 80°C compared to the polymer concentration dissolved in the polymer solution at 100°C may be 10% to 20%, 12% to 18%, or 14% to 17%. Within this range, the longitudinal and transverse stretching rates can be increased in the sequential biaxial stretching process of the final high-density polyethylene film using the tenter frame process, thereby improving the modulus. The lower the temperature during the crystallization fractionation analysis, the more polymer is eluted from the polymer solution, which reduces the polymer concentration dissolved in the polymer solution. Therefore, the reduction ratio of the polymer concentration dissolved in the polymer solution can represent the fraction from which the polymer is eluted.

[0050] In this invention, when measuring the polymer concentration reduction ratio from the results of crystallization fractionation analysis, the polymer refers to the first high-density polyethylene resin or the second high-density polyethylene resin dissolved in the solvent. The physical properties of polyethylene are greatly influenced not only by the comonomer content but also by how the comonomers are distributed in the polyethylene main chain. Here, crystallization fractionation analysis is one method for measuring the intermolecular comonomer distribution of polyethylene.

[0051] In the results of crystallization fractionation analysis of the polymer solution obtained by dissolving the first high-density polyethylene resin in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 80°C to 90°C compared to the polymer concentration dissolved in the polymer solution at 100°C may be 50% to 70%, 55% to 68%, or 60% to 65%, and within this range, the longitudinal and transverse elongation rates can be increased in the sequential biaxial stretching process of the final high-density polyethylene film using the tenter frame process, thereby improving the modulus.

[0052] The melt flow index (MI2 (2.16 kg load, 190°C)) of the first high-density polyethylene resin may be 0.40 g / 10 min to 3.0 g / 10 min, or 0.45 g / 10 min to 1.5 g / 10 min. If the melt flow index of the first high-density polyethylene resin is within the above range, it exhibits excellent extrusion processability and prevents deterioration of physical properties due to low molecular weight.

[0053] The melt flow ratio (MI21.6 (21.6 kg load, 190°C) / MI2 (2.16 kg load, 190°C), MFRR) of the first high-density polyethylene resin may be 70 or more, 80 or more, or 80 to 90. If the melt flow ratio of the first high-density polyethylene resin is within the above range, the final extrusion processability is excellent, the film can be stably and sequentially biaxially stretched in the longitudinal and transverse directions, and it can be stretched to a uniform film thickness.

[0054] The melting temperature (Tm) of the first high-density polyethylene resin may be 120°C to 145°C, 125°C to 140°C, or 128°C to 135°C. If the melting temperature of the first high-density polyethylene resin is within the above range, the final high-density polyethylene film will have excellent heat resistance and an improved modulus value.

[0055] The crystallization temperature (Tc) of the first high-density polyethylene resin may be 105°C to 130°C, 110°C to 130°C, or 115°C to 125°C. If the crystallization temperature of the first high-density polyethylene resin is within the above range, the stretchable temperature range of the final high-density polyethylene film may be widened.

[0056] The first high-density polyethylene resin may be polymerized using ethylene monomers, comonomers, and hydrogen in the presence of a catalyst. The first high-density polyethylene resin may be formed by polymerization using a two-stage reactor consisting of a first reactor and a second reactor connected to each other. Specifically, polymerization is carried out in the first reactor to form a polyethylene resin as an intermediate polymer in the first stage, and the polyethylene resin obtained at this time is transferred to the second reactor where polymerization continues, thereby obtaining the first high-density polyethylene resin as the final polymer. The first and second reactors may be slurry processes.

[0057] Polymerization in the first and second reactors may be carried out in the presence of a Ziegler-Natta (Zn) catalyst. The Ziegler-Natta catalyst is a catalyst known as a typical Ziegler-Natta catalyst, and uses a transition metal compound belonging to Group IV, V, or VI of the periodic table as the main catalyst. Among these, the most commonly used Ziegler-Natta catalyst is a halogen complex composed of magnesium and titanium, or magnesium and vanadium.

[0058] Furthermore, when polymerization is carried out in at least one of the first and second reactors, a comonomer may be added in addition to the ethylene monomer. The comonomer can be C3-C20, for example, C4-C8, C6-C8 α-olefins. Specifically, the comonomer may be one or more of 1-butene, 1-hexene, and 1-octene.

[0059] In the first reactor, the supply ratio of comonomers to ethylene monomers may be 50 g / kg to 90 g / kg, 60 g / kg to 80 g / kg, or 65 g / kg to 80 g / kg. When comonomers are supplied to the first reactor in a supply ratio within the above range, plugging and fouling of the reactor are prevented, the elongation in the longitudinal and transverse directions is increased in the biaxial stretching process of the final film, and a high-mechanical-strength polymer polyethylene film can be obtained.

[0060] In the first reactor, the hydrogen supply ratio to the ethylene monomer supply may be 20 mg / kg to 70 mg / kg, 25 mg / kg to 55 mg / kg, or 35 mg / kg to 50 mg / kg. When hydrogen is supplied to the first reactor at a supply ratio within the above range, it prevents the formation of plugging and fouling in the reactor, increases the elongation in the longitudinal and transverse directions in the biaxial stretching process of the final film, and makes it possible to obtain a high-molecular-weight polyethylene film with high mechanical strength.

[0061] In the second reactor, the comonomer does not need to be supplied. By not supplying the comonomer in the second reactor, excellent production stability can be ensured.

[0062] In the second reactor, the hydrogen supply ratio to the ethylene monomer supply may be 0.1 g / kg to 2 g / kg, 0.1 g / kg to 1.5 g / kg, or 0.5 g / kg to 0.8 g / kg. When hydrogen is supplied to the second reactor at a supply ratio within the above range, it prevents the formation of plugging and fouling in the reactor, increases the elongation in the longitudinal and transverse directions during the biaxial stretching process of the final polymer polyethylene film, and allows for the production of a polymer polyethylene film with high mechanical strength.

[0063] In one embodiment, a second high-density polyethylene resin can be used alone as the resin for forming the first and second skin layers of the high-density polyethylene film.

[0064] The second high-density polyethylene resin used to form the first and second skin layers can be manufactured by melt-mixing a commercial polyolefin elastomer (POE) in an amount of 5% to 25% or 10% to 15% by weight with the first high-density polyethylene manufactured earlier.

[0065] In the results of crystallization fractionation analysis of the polymer solution obtained by dissolving the second high-density polyethylene resin in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at temperatures above 30°C and below 50°C compared to the polymer concentration at 100°C may be 10% to 20%, 12% to 18%, or 15% to 17%. If the reduction ratio of the concentration of the second high-density polyethylene resin is within the above range, the stretching ratio in the longitudinal and transverse directions can be increased in the sequential biaxial stretching process of the final film using the tenter frame process, resulting in excellent transparency of the film, and thus a final film with low turbidity and high clarity can be obtained.

[0066] In the results of crystallization fractionation analysis of the polymer solution obtained by dissolving the second high-density polyethylene resin in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at temperatures above 30°C and below 60°C compared to the polymer concentration at 100°C may be 15% to 25% or 18% to 25%. If the reduction ratio of the concentration of the second high-density polyethylene resin is within the above range, the stretching ratio in the longitudinal and transverse directions can be increased in the sequential biaxial stretching process of the final film using the tenter frame process, resulting in excellent transparency of the film, and thus a final film with low turbidity and high clarity can be obtained.

[0067] In the results of crystallization fractionation analysis of the polymer solution obtained by dissolving the second high-density polyethylene resin in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 80°C to 90°C compared to the polymer concentration dissolved in the polymer solution at 100°C may be 30% to 75%, 40% to 70%, or 50% to 60%. If the reduction ratio of the concentration of the second high-density polyethylene resin is within the above range, the stretching ratio in the longitudinal and transverse directions can be increased in the sequential biaxial stretching process of the final film using the tenter frame process, resulting in excellent transparency of the film, and thus a final film with low turbidity and high clarity can be obtained.

[0068] The second high-density polyethylene resin has a molecular weight of 10 relative to the integral of the total area of ​​the overall molecular weight distribution graph of the second high-density polyethylene resin.3 g / mol~10 4 The ratio of the integral values ​​in the graph region corresponding to a polymer with a value of g / mol may be 18% to 30%, and the number of single-chain branches in the polymer may be 0.1 to 8 per 1000 carbon atoms.

[0069] For example, the second high-density polyethylene resin has a molecular weight of 10 relative to the integral value of the total area of ​​the overall molecular weight distribution graph of the second high-density polyethylene resin. 3 g / mol~10 4 The ratio of integral values ​​in the graph region corresponding to polymers with a molecular weight of g / mol is 20% to 25%, and the number of single-chain branches in the polymer may be 0.5 to 5 per 1000 carbon atoms. 3 g / mol~10 4 If the polymer ratio (in g / mol) and the number of single-chain branches are within the aforementioned range, the stretching ratio can be improved in both the longitudinal and transverse directions of the film, and the uniformity of the film's thickness can be ensured.

[0070] The second high-density polyethylene resin has a molecular weight of 10 relative to the integral of the total area of ​​the overall molecular weight distribution graph of the second high-density polyethylene resin. 5 g / mol~10 6 The ratio of integral values ​​in the graph region corresponding to a polymer with a concentration of g / mol may be 20% to 26%, and the number of single-chain branches in the polymer may be 1 to 12 per 1000 carbon atoms.

[0071] For example, the second high-density polyethylene resin has a molecular weight of 10 relative to the integral value of the total area of ​​the overall molecular weight distribution graph of the second high-density polyethylene resin. 5 g / mol~10 6 The ratio of integral values ​​in the graph region corresponding to polymers with a molecular weight of g / mol is 21% to 24%, and the number of single-chain branches in the polymer may be 1.5 to 10 per 1000 carbon atoms. 5 g / mol~10 6If the polymer ratio (g / mol) and the number of single-chain branches are within the aforementioned range, stable sequential biaxial stretching is possible in both the longitudinal and transverse directions of the film, and the final physical properties of the film can be significantly improved.

[0072] The density of the second high-density polyethylene resin may be lower than the density of the first high-density polyethylene resin. For example, the density of the second high-density polyethylene resin may be 0.940 g / cm³. 3 ~0.965g / cm 3 , or 0.942 g / cm³ 3 ~0.960g / cm 3 This may be the case. If the density of the second high-density polyethylene resin is within the above range, the transparency of the final high-density polyethylene film may be improved.

[0073] The melt flow index (MI2 (2.16 kg load, 190°C)) of the second high-density polyethylene resin may be 0.50 g / 10 min to 5.0 g / 10 min or 1.0 g / 10 min to 3.0 g / 10 min. If the melt flow index of the second high-density polyethylene resin is within the above range, it is possible to achieve excellent extrusion processability and reduce the roughness of the film surface, thereby improving the transparency of the film.

[0074] The melt flow ratio (MI21.6 (21.6 kg load, 190°C) / MI2 (2.16 kg load, 190°C), MFRR) of the second high-density polyethylene resin may be 60 or more, 70 or more, or 70 to 80. If the melt flow ratio of the second high-density polyethylene resin is within the above range, the final extrusion processability is excellent, the film can be stably and sequentially biaxially stretched in the longitudinal and transverse directions, and the film can be stretched to a uniform thickness.

[0075] In one embodiment, the high-density polyethylene resin, namely the first high-density polyethylene resin and the second high-density polyethylene, can be mixed with an additive containing an antioxidant, a neutralizing agent, or a combination thereof to form a composition.

[0076] The additive may be included in an amount of 0.005 to 0.5 parts by weight per 100 parts by weight of the high-density polyethylene resin.

[0077] The antioxidant may contain one or more compounds selected from the group consisting of phenolic compounds and phosphorus compounds. Examples of the phenolic compounds include pentaerythritol tetrakis(3-(3,5-ditetrabutyl-4-hydroxyphenyl)propionate), octadecyl(3-(3,5-ditetrabutyl-4-hydroxyphenyl)propionate), tris(3,4-ditetrabutyl-4-hydroxylbenzyl)isocyanate, and triethylene glycol-bis(3-(tetrabutyl-4-hydroxy-5-methylphenyl)propionate). Examples of the phosphorus compounds include tris(2,4-ditetrabutylphenyl)phosphite, tetrakis(2,4-diter-butylphenyl)-4,4-diphenyl diphosphonate, distearyl pentaerythritol diphosphite, and 2,4-dinonylphenyl di(4-mononylphenyl)phosphite.

[0078] The antioxidant may be present in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the high-density polyethylene resin, for example, in an amount of 0.1 to 0.3 parts by weight. When the antioxidant is present within the above content range, excellent processability can be obtained without discoloration or change in viscosity.

[0079] Examples of the neutralizing agent include calcium stearate, zinc stearate, magnesium aluminum hydroxycarbonate, zinc oxide, and magnesium hydroxystearate.

[0080] The neutralizing agent may be included in an amount of 0.005 to 0.3 parts by weight per 100 parts by weight of the high-density polyethylene resin, for example, in an amount of 0.02 to 0.1 parts by weight. When the neutralizing agent is included within the above content range, excellent processability can be obtained without discoloration or change in viscosity.

[0081] According to one example, a flexible packaging film containing the high-density polyethylene film is provided.

[0082] In recent years, regulations on recycling have been strengthened worldwide, and companies are also making efforts to design flexible packaging materials that are easy to collect, sort, and recycle, driven by a growing awareness of their own social responsibility for sustainability and a broader focus on addressing environmental issues.

[0083] In the collection, classification, and recycling of flexible packaging materials, the most effective approach is to use packaging materials made from a single material, such as polyethylene (PE) or polypropylene (PP), instead of existing packaging materials that use a mixture of various materials.

[0084] To achieve this, the application of biaxially oriented polyethylene (BOPE) film is required. Generally, the tenter frame process is applied as a manufacturing process for biaxially oriented polyethylene (BOPE) film. When the film is stretched in the machine direction (MD) and transverse direction (TD), the polyethylene chains and crystalline structure are highly oriented, resulting in improved mechanical strength, especially impact strength, and a revolutionary improvement in optical properties such as transparency and film appearance.

[0085] However, in the tenter frame process, the film processing is greatly influenced by the molecular structure of the raw material, making the stretching process conditions very complex. General polyethylene (PE) has a fast crystallization rate and high crystallinity, resulting in a narrow stretchable temperature range and a very low stretch ratio. Furthermore, if wrinkles form or the thickness is not uniform during stretching, the film will eventually tear. In particular, BOPE films using high-density polyethylene (HDPE) have superior heat resistance and dramatically improved film modulus compared to BOPE films using linear low-density polyethylene (LLDPE), but they are difficult to stretch and suffer from reduced transparency.

[0086] In contrast, the flexible packaging film containing the high-density polyethylene film according to the present invention is made of a single polyethylene material, is easy to recycle, has high mechanical properties, particularly a high modulus value, excellent transparency, and is easily biaxially stretched by a tenter frame process.

[0087] The following describes specific embodiments of the present invention. However, these embodiments are merely for illustrative purposes and to illustrate the present invention, and the invention should not be limited thereto. Furthermore, matters not described herein can be sufficiently inferred by technical analogy to those skilled in the art, and their explanations are omitted.

[0088] [Manufacturing of high-density polyethylene resin] Manufacturing Examples 1-1 and 1-2: Production of the first high-density polyethylene resin composition 1. Manufacturing of the first high-density polyethylene resin First high-density polyethylene resin was manufactured according to the conditions shown in Table 1 below. Two 90L reactors were connected in series, and ethylene polymerization was carried out using ethylene monomers and comonomers in the presence of a Ziegler-Natta catalyst. The Ziegler-Natta catalyst used was a known catalyst composed of magnesium and titanium, manufactured by conventional methods.

[0089] Specifically, ethylene polymerization was carried out in the first reactor by supplying ethylene monomer (C2), 1-hexene (C6) as a comonmer, and hydrogen (H2). The polymerization ratio, the ratio of C6 supply to C2 supply, the ratio of H2 supply to C2 supply, the polymerization temperature, and the polymerization pressure in the first reactor are shown in Table 1 below, and the process was carried out with a residence time of 61 minutes. The slurry-like intermediate polymer polymerized in the first reactor was transferred to the second reactor to continue polymerization, and a slurry-like final polymer was obtained. Subsequently, a powder-like high-density polyethylene resin was produced from the slurry-like final polymer. In the second reactor, ethylene polymerization was carried out by supplying ethylene monomer (C2) and hydrogen (H2), but no comonmer (C6) was supplied. The polymerization ratio, the ratio of H2 supply to C2 supply, the polymerization temperature, and the polymerization pressure in the second reactor are shown in Table 1 below, and the process was carried out with a residence time of 34 minutes.

[0090] [Table 1]

[0091] 2. Production of the first high-density polyethylene resin composition To each of the first high-density polyethylene resins (100 parts by weight), 0.1 parts by weight of Irganox-3114 and 0.1 parts by weight of Irgafos-168 were added as antioxidants, and 0.025 parts by weight of magnesium aluminum hydroxycarbonate (DHT-4A) was added as a neutralizing agent. These were mixed in a Henschel mixer, and then the first high-density polyethylene resin composition was produced in pellet form using a twin-screw extruder.

[0092] Manufacturing Examples 2-1 and 2-2: Production of the second high-density polyethylene resin composition A second high-density polyethylene resin composition was prepared according to the conditions shown in Table 2 below. The second high-density polyethylene resin composition was prepared by mixing the first high-density polyethylene resin of Production Example 1-1 or Production Example 1-2, which had been previously produced, with commercial POE Supreme 004 or Supreme 883 manufactured by SK Geocentric. 100 parts by weight of the mixture of the first high-density polyethylene resin of Production Example 1-1 or Production Example 1-2 and the commercial POE was mixed with 0.1 parts by weight of Irganox-3114 and 0.1 parts by weight of Irgafos-168 as antioxidants, and 0.025 parts by weight of magnesium aluminum hydroxycarbonate (DHT-4A) as a neutralizing agent in a Henschel mixer, and then the second high-density polyethylene resin composition in pellet form was produced using a twin-screw extruder.

[0093] [Table 2]

[0094] Comparative Manufacturing Examples 1-3: Production of the second high-density polyethylene resin composition 1. Manufacturing of the second high-density polyethylene resin The second high-density polyethylene resin in Comparative Production Example 1 is the C330A product produced in our slurry process, using 1-butene as the copolymer, and has a density of 0.958 g / cm³. 3 The product has a melt flow index (MI2) of 1.0 g / 10 min and a melt flow ratio of 150. In this invention, the melt flow ratio refers to the ratio of the melt flow index (MI21.6) measured at 190°C with a load of 21.6 kg according to ASTM D1238 to the melt flow index (MI2) measured at 190°C with a load of 2.16 kg according to ASTM D1238.

[0095] The second high-density polyethylene resin in comparative manufacturing example 2 is a C910C product produced in a gas-phase process using our Gas Phase Reactor (GPR), with 1-butene used as the copolymer and a density of 0.950 g / cm³. 3The product has a melt flow index (MI2) of 2.2 g / 10 min and a melt flow ratio of 30.

[0096] The second high-density polyethylene resin in comparative manufacturing example 3 is the R904U product produced in our gas-phase process, using 1-hexene as the copolymer, and has a density of 0.940 g / cm³. 3 The product has a melt flow index (MI2) of 4.0 g / 10 min and a melt flow ratio of 25.

[0097] 2. Production of the second high-density polyethylene resin composition To each of the 100 parts by weight of the second high-density polyethylene resin, 0.1 parts by weight of Irganox-3114 and 0.1 parts by weight of Irgafos-168 were added as antioxidants, and 0.025 parts by weight of magnesium aluminum hydroxycarbonate (DHT-4A) was added as a neutralizing agent. These were mixed in a Henschel mixer, and then the second high-density polyethylene resin composition was produced in pellet form using a twin-screw extruder.

[0098] [Manufacturing of high-density polyethylene film] Examples 1-4 and Comparative Examples 1-7 Multilayer biaxially oriented polyethylene (BOPE) films were manufactured using the high-density polyethylene resin compositions produced in Production Examples 1-1, 1-2, 2-1, 2-2, and Comparative Production Examples 1-3. The types of high-density polyethylene resin compositions used to constitute each layer and the thickness ratio (%) of each layer to the total thickness of the film are shown in Table 3 below.

[0099] Specifically, the multilayer biaxially oriented polyethylene film was biaxially stretched on a dedicated Bruckner mass production line (hybrid BOPE / BOPP line, 5-layer, 6.6m width). The film was applied in a 5-layer configuration, and at an extrusion speed of 190m / min and a die temperature of 230-240°C, a film ultimately stretched 5.2 times in the longitudinal (MD) direction and 9 times in the transverse (TD) direction was successfully produced. The extrusion conditions and film processing conditions for the biaxially oriented film are specifically shown in Table 4 below.

[0100] [Table 3]

[0101] [Table 4]

[0102] [Evaluation of physical properties of high-density polyethylene resin compositions] The physical properties of the first high-density polyethylene resin composition according to Production Examples 1-1 and 1-2 were evaluated and are shown in Table 5 below. The physical properties of the second high-density polyethylene resin composition according to Production Examples 2-1, 2-2, and Comparative Production Examples 1-3 were evaluated and are shown in Table 6 below. The evaluation method is as follows.

[0103] density: Measurements were taken in accordance with ASTM D1505.

[0104] Melt flow index (MI): The melt flow index (MI2) was measured at 190°C with a load of 2.16 kg in accordance with ASTM D1238. The melt flow index (MI21.6) was measured at 190°C with a load of 21.6 kg in accordance with ASTM D1238.

[0105] Molten flow ratio (MFRR): This refers to the ratio of the melt flow index (MI21.6) measured at 190°C with a 21.6 kg load to the melt flow index (MI2) measured at 190°C with a 2.16 kg load according to ASTM D1238.

[0106] Melting temperature (Tm) and crystallization temperature (Tc): The measurements were taken using a differential scanning calorimetry (DSC) at a heating rate of 10°C / min in accordance with ASTM D3418.

[0107] Infrared gel permeation chromatography (GPC-IR): Polymer Char GPC-IR (registered trademark) equipment was used. 12 mg of the sample was placed in 8 ml of 1,2,4-trichlorobenzene (containing 125 ppm BHT) and dissolved at 160°C for 2 hours to prepare the sample. 1,2,4-trichlorobenzene (containing 125 ppm BHT) was used as the eluent, and a column consisting of one Orexis Guard and three Orexis columns (Column: PLgel Olexis guard X1 + PLgel Olexis X3) was used. 200 μl was injected and analyzed. For column calibration for molecular weight calculation, polystyrene standards were used, and the molecular weight of polyethylene was calculated using the Mark-Houwink constant (K=44.6, a=0.725).

[0108] The number of single-chain branches (SCBs) in the sample represents the number of single-chain branches per 1000 carbon atoms and was calibrated using a standard whose value was already known (1-octene copolymer provided by Polymer Char). It represents the average number of methyl groups (-CH3) per 1000 carbon atoms in the sample, excluding the methyl groups at the chain ends. This value is calculated from the number of methyl groups (CH3 / 1000TC) per 1000 carbon atoms in the sample using end-chain correction. The end-chain correction is determined by the following equation 1.

[0109] Number of chain ends per 1000 carbon atoms (No. of Chain ends / 1000TC) = (A × 14,000) / M ... (Equation 1)

[0110] In Equation 1, A represents the number of end groups. For example, linear polyethylene (linear PE) has 2 end groups, while long-chain branched (LCB) polymers have more than 2. M represents the given molecular mass.

[0111] When the chain end group terminates with a vinyl group (-CH=CH2), the end chain correction value was set to 0.

[0112] Figure 3 is a graph showing the overall molecular weight distribution and the number of single-chain branches per 1000 carbon atoms of the first high-density polyethylene resins of Production Example 1-1 and Production Example 1-2, as measured by infrared gel permeation chromatography (GPC-IR). Referring to Figure 3, the integral values ​​in the regions where the logM values ​​are 3-4 and 5-6 in the overall molecular weight distribution graph of the first high-density polyethylene are such that the molecular weight (M) of the high-density polyethylene resin in one embodiment is 10 5 g / mol~10 6 The ratio of polymers in g / mol and the molecular weight (M) are 10 3 g / mol~10 4 It can be seen that this corresponds to the ratio of polymers in g / mol.

[0113] As a result, molecular weight 10 5 g / mol~10 6 The polymer ratio is g / mol (10 5 ~10 6 ), molecular weight is 10 3 g / mol~10 4 The polymer ratio is g / mol (10 3 ~10 4 ), molecular weight is 10 5 g / mol~10 6 Number of single-chain branches of polymer in g / mol (10 5 ~10 6 ), and a molecular weight of 10 3 g / mol~10 4Number of single-chain branches of polymer in g / mol (10 3 ~10 4 The following values ​​were measured:

[0114] Crystallization Analysis Fractionation (CRYSTAF): The measurement was performed using CRYSTAF, which is equipped with a polymer char. 20 mg of the sample was placed in 20 ml of 1,2,4-trichlorobenzene and dissolved with stirring at 160°C for 60 minutes to prepare a polymer solution. After injecting the polymer solution into the equipment, it was stabilized at 100°C for 45 minutes, and then the crystallized portion was filtered off while the temperature was lowered to 35°C at a constant rate of 0.2°C / min, and the concentration of polymer dissolved in the solution was measured. The cumulative curve shows the percentage decrease in polymer concentration dissolved in the polymer solution with temperature, with the concentration at the initial temperature of 100°C set to 100%, and the percentage decrease in polymer concentration dissolved in the polymer solution at each temperature condition was measured. The crystallization fractionation analysis graphs for the first high-density polyethylene resin related to manufacturing examples 1-1 and 1-2 can be seen in Figure 4, and the crystallization fractionation analysis graphs for the second high-density polyethylene resin related to manufacturing examples 2-1 and 2-2 can be seen in Figure 5.

[0115] [Table 5]

[0116] [Table 6]

[0117] [Evaluation of physical properties of high-density polyethylene film] The physical properties of the high-density polyethylene films of Examples 1-4 and Comparative Examples 1-7 were evaluated using the following method and are shown in Table 7 below.

[0118] Tensile strength, modulus: The tensile strength (MPa) and modulus (MPa) of each film in the longitudinal (MD) and transverse (TD) directions were measured in accordance with ASTM D882.

[0119] Turbidity (haze), clarity (Clarity): Turbidity (%) and clarity (%) were measured in accordance with ASTM D1003.

[0120] Film thickness and standard deviation (2σ): Using a non-contact thickness measuring device, the thickness of each film was measured approximately 50 times at 20 mm intervals in both the longitudinal (width direction, MD) and transverse (travel direction, TD) directions. The average value was calculated, and the standard deviation (%) was shown by calculating 2 sigma (2σ).

[0121] [Table 7]

[0122] From Table 7 above, it was confirmed that the biaxially oriented films of Examples 1 to 4 according to the present invention, which were manufactured by applying a film formed from a composition containing a first high-density polyethylene resin to the intermediate layer (B) and films formed from a composition containing a second high-density polyethylene resin to the first skin layer (A1) and second skin layer (A2), had a high modulus value, particularly an MD modulus value of 1,300 MPa or higher, excellent turbidity of less than 6%, and clarity of 97% or higher, and that the film thickness was very uniform.

[0123] In contrast, in Comparative Examples 1 to 4, where the first high-density polyethylene resin or the second high-density polyethylene resin was used for all of the intermediate layer, first skin layer, and second skin layer, a decrease in turbidity and modulus was confirmed. Furthermore, in Comparative Examples 5 to 7, where the first high-density polyethylene resin according to the present invention was used as the intermediate layer, but materials other than the second high-density polyethylene resin according to the present invention were used for the first and second skin layers, a decrease in turbidity and modulus was confirmed.

[0124] While embodiments of the present invention have been described above with reference to the attached drawings, a person of ordinary skill in the art to which the present invention belongs will understand that the present invention can be implemented in other specific forms without changing its technical idea or essential features. Therefore, the embodiments described above should be understood to be illustrative and non-limiting in any respect. [Explanation of symbols]

[0125] 10 Middle Class 11. First Meso-Place 12. Second Meso-Marginal Layer 13. Third Meso-Collateral Layer 20 skin layers 21. First Skin Layer 22. Second Skin Layer 100 High-density polyethylene film

Claims

1. An intermediate layer comprising a first high-density polyethylene resin composition, The intermediate layer comprises a first skin layer and a second skin layer, each disposed on both sides of the intermediate layer and containing a second high-density polyethylene resin composition, The density of the first high-density polyethylene resin composition is higher than the density of the second high-density polyethylene resin composition. The second high-density polyethylene resin composition is obtained by melt-mixing a polyolefin elastomer with the first high-density polyethylene resin composition in an amount of 5% to 25% by weight relative to the total amount of the second high-density polyethylene resin composition. A high-density polyethylene film in which, as a result of crystallization fractionation analysis of a polymer solution obtained by dissolving the second high-density polyethylene resin composition in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 80°C to 90°C compared to the polymer concentration at 100°C is 30% to 75%.

2. The high-density polyethylene film according to claim 1, wherein each of the intermediate layer, the first skin layer, and the second skin layer has a single-layer or two- to five-layer multilayer structure.

3. The density of the first high-density polyethylene resin composition is 0.945 g / cm³. ３ ~0.970g / cm ３ The high-density polyethylene film according to claim 1.

4. The first high-density polyethylene resin composition has a molecular weight of 10 relative to the integral of the total area of ​​the overall molecular weight distribution graph of the first high-density polyethylene resin composition. ５ g / mol ~ 10 ６ The high-density polyethylene film according to claim 1, wherein the ratio of integral values ​​in the graph region corresponding to a polymer of g / mol is 18% to 28%, and the number of single-chain branches in the polymer is 5 to 15 per 1000 carbon atoms.

5. The first high-density polyethylene resin composition has a molecular weight of 10 relative to the integral of the total area of ​​the overall molecular weight distribution graph of the first high-density polyethylene resin composition. ３ g / mol ~ 10 ４ The high-density polyethylene film according to claim 1, wherein the ratio of integral values ​​in the graph region corresponding to a polymer of g / mol is 20% to 30%, and the number of single-chain branches in the polymer is 1 to 8 per 1000 carbon atoms.

6. The high-density polyethylene film according to claim 1, wherein at least one of the first high-density polyethylene resin composition and the second high-density polyethylene resin composition is single-chain branched, and the single-chain branching has a BOCD (broad orthogonal commoner distribution) structure.

7. The high-density polyethylene film according to claim 1, wherein, as a result of crystallization fractionation analysis of a polymer solution obtained by dissolving the first high-density polyethylene resin composition in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 70°C to 80°C compared to the polymer concentration dissolved in the polymer solution at 100°C is 10% to 20%.

8. The high-density polyethylene film according to claim 1, wherein, as a result of crystallization fractionation analysis of a polymer solution obtained by dissolving the first high-density polyethylene resin composition in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 80°C to 90°C compared to the polymer concentration dissolved in the polymer solution at 100°C is 50% to 70%.

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

10. The high-density polyethylene film according to claim 1, wherein the melt flow ratio (MI2 1.6 (21.6 kg load, 190°C) / MI2 (2.16 kg load, 190°C), MFRR) of the first high-density polyethylene resin composition is 70 or more.

11. The high-density polyethylene film according to claim 1, wherein, as a result of crystallization fractionation analysis of a polymer solution obtained by dissolving the second high-density polyethylene resin composition in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 30°C to 50°C or less compared to the polymer concentration dissolved in the polymer solution at 100°C is 10% to 20%.

12. The high-density polyethylene film according to claim 1, wherein, as a result of crystallization fractionation analysis of a polymer solution obtained by dissolving the second high-density polyethylene resin composition in a solvent, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 30°C to 60°C or less compared to the polymer concentration dissolved in the polymer solution at 100°C is 15% to 25%.

13. The second high-density polyethylene resin composition has a molecular weight of 10 relative to the integral value of the total area of ​​the overall molecular weight distribution graph of the second high-density polyethylene resin composition. ３ g / mol ~ 10 ４ The high-density polyethylene film according to claim 1, wherein the ratio of integral values ​​in the graph region corresponding to a polymer of g / mol is 18% to 30%, and the number of single-chain branches in the polymer is 0.1 to 8 per 1000 carbon atoms.

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

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

16. The high-density polyethylene film according to claim 1, wherein the melt flow ratio (MI2 1.6 (21.6 kg load, 190°C) / MI2 (2.16 kg load, 190°C), MFRR) of the second high-density polyethylene resin composition is 60 or more.

17. The high-density polyethylene film according to claim 1, wherein the high-density polyethylene film is a film that has been successively biaxially stretched by a tenter frame process to a longitudinal (MD) stretch ratio of 4 to 7 times and a transverse (TD) stretch 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 in the range of 15 μm to 70 μm, and the intermediate layer is formed in an amount of 70% to 98% by weight relative to the total amount of the high-density polyethylene film.

19. A flexible packaging film comprising a high-density polyethylene film according to any one of claims 1 to 18.

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