High-density polyethylene films and flexible packaging film comprising 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] The present invention relates to a high-density polyethylene film and a flexible packaging film containing the same.

Background Art

[0002] In recent years, regulations on recycling have been strengthened globally. Due to the social responsibility of enterprises for their own sustainability and the change in awareness towards solving a wide range of environmental problems, efforts have been made to design flexible packaging materials to facilitate collection, classification, and recycling.

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

[0004] For this purpose, the application of a biaxially oriented polyethylene (BOPE) film is required. Generally, as a manufacturing process of the biaxially oriented polyethylene (BOPE) film, a tenter frame process is applied. When the film is stretched in the machine direction (MD) and the transverse direction (TD), by highly orienting the polyethylene chains and the crystal structure, better mechanical strength, especially impact strength, is improved, and optical properties such as transparency and film appearance are remarkably improved.

[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 stretchable temperature range is narrow, the stretch ratio is very low, and if wrinkles form or the thickness is not uniform during stretching, ultimately, the film will tear 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 improved epoch-makingly, but there are problems that it is difficult to stretch and the transparency decreases.

[0006] Therefore, in order to apply to a recyclable single-material flexible packaging film, there is a demand for the development of a high density polyethylene film with high mechanical properties, especially high modulus value, excellent transparency, and easy biaxial stretching 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 easy to biaxially stretch, has excellent thickness uniformity of the stretched film, and is excellent in mechanical properties, especially modulus value 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 of ordinary skill in the art from the following description.

Means for Solving the Problem

[0010] The high-density polyethylene film according to an embodiment of the present invention for solving the above problems includes an intermediate layer containing a first high-density polyethylene resin, and 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. The density of the first high-density polyethylene resin is higher than the density of the second high-density polyethylene resin. In the result of crystallization fractionation analysis on a polymer solution obtained by dissolving the second high-density polyethylene resin in a solvent, with respect to the polymer concentration dissolved in the polymer solution at 100 °C, the reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature of 80 °C to 90 °C is 30% to 75%.

[0011] Each of the intermediate layer, the first skin layer, and the second skin layer may be a single layer or a multilayer structure of 2 to 5 layers.

[0012] The density of the first high-density polyethylene resin is 0.945 g / cm 3 ~0.970 g / cm 3 and may be.

[0013] The first high-density polyethylene resin has a ratio of the integrated value of the graph region corresponding to a polymer having a molecular weight of 10 5 g / mol to 10 6 g / mol with respect to the integrated value of the total area of the entire molecular weight distribution graph of the first high-density polyethylene resin of 18% to 28%, and the number of single-chain branches of the polymer may be 5 to 15 per 1000 carbon atoms.

[0014] The first high-density polyethylene resin has a ratio of the integrated value of the graph region corresponding to a polymer having a molecular weight of 10 3 g / mol to 10 4 g / mol with respect to the integrated value of the total area of the entire molecular weight distribution graph of the first high-density polyethylene resin of 20% to 30%, and the number of single-chain branches of 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 a single-chain branch, and the single-chain branch may have a BOCD (broad orthogonal comonomer distribution) structure.

[0016] In the result of the crystallization fractionation analysis of the polymer solution in which the first high-density polyethylene resin is dissolved in a solvent, the decrease ratio of the polymer concentration dissolved in the polymer solution at a temperature of 70 °C to 80 °C may be 10% to 20% with respect to the polymer concentration dissolved in the polymer solution at 100 °C.

[0017] In the result of the crystallization fractionation analysis of the polymer solution in which the first high-density polyethylene resin is dissolved in a solvent, the decrease ratio of the polymer concentration dissolved in the polymer solution at a temperature of 80 °C to 90 °C may be 50% to 70% with respect to the polymer concentration dissolved in the polymer solution at 100 °C.

[0018] 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.

[0019] 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.

[0020] In the result of the crystallization fractionation analysis of the polymer solution in which the second high-density polyethylene resin is 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] In the results of the 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 exceeding 30°C and not exceeding 60°C with respect to the polymer concentration dissolved in the polymer solution at 100°C is 15% to 25%.

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

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

[0024] 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.

[0025] 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 is sequentially biaxially stretched by a tenter frame process to a longitudinal (MD) elongation ratio of 4 to 7 times and a transverse (TD) elongation 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 at 70% to 98% by weight based on the total amount of the high-density polyethylene film.

[0028] ​In addition, one embodiment of the present invention for solving the above-described problems provides a flexible packaging film including the high-density polyethylene film.

Advantages of the Invention

[0029] The high-density polyethylene film according to the present invention is uniformly stretched, can ensure thickness uniformity, exhibits excellent mechanical properties, and is very excellent in optical properties as compared with a film in which various polyethylene resins are mixed and applied to each layer. In addition, the high-density polyethylene film according to the present invention can be applied to a flexible packaging film made of a recyclable single material.

[0030] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0032] The advantages and features of the present invention, and the method for achieving them, will become clear from the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various different forms. These embodiments are merely provided to make the disclosure of the present invention complete and to fully inform those of ordinary skill in the art to which the present invention pertains of the scope of the present invention. Therefore, the present invention is defined only by the scope of the claims.

[0033] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless otherwise specifically stated for the terms. The terms "comprises" and / or "comprising" used in the specification do not exclude the existence or addition of one or more other components in addition to the recited components. Throughout the specification, the same reference numerals indicate the same components, and "and / or" includes each and every combination of the recited components. Terms such as "first", "second", etc. are used to describe various components, but of course these components are not limited by these terms. These terms are only used to distinguish one component from another. Therefore, it goes without saying that the first component mentioned below may be the second component within the technical idea of the present invention.

[0034] Unless otherwise specified, all terms (including technical and scientific terms) used in this specification will be used in the meaning commonly understood by those of ordinary skill in the art to which the present invention pertains. Also, terms defined in commonly used dictionaries will not be interpreted ideally or excessively unless clearly defined.

[0035] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0036] In the description, the meanings of the terms used in this specification will be briefly described. However, the description of the terms is for the purpose of assisting in the understanding of this specification. Therefore, it should be noted that unless explicitly described as a matter limiting the present invention, it is not used in a sense limiting the technical idea of the present invention.

[0037] A 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 skin layer and a second skin layer each disposed on both surfaces of the intermediate layer and containing a second high-density polyethylene resin.

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

[0039] In one embodiment, in the high-density polyethylene film, each of the intermediate layer, the first skin layer, and the second skin layer may be a single layer or a multilayer structure of 2 to 5 layers. For example, the first skin layer and the second skin layer may be a single layer structure, 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 each high-density polyethylene required for the functional requirements of the film, diversify the physical properties according to the layer composition of the film, and ensure a film with excellent uniformity in the thickness distribution of each layer.

[0040] FIG. 2 is a schematic view showing a high-density polyethylene film according to an embodiment. Referring to FIG. 2, the high-density polyethylene film 100 may have a multilayer structure such that the first skin layer 21 and the second skin layer 22 are single layer structures, and the intermediate layer 10 includes 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 is sequentially biaxially stretched by a tenter frame process to a longitudinal direction (MD) stretch ratio of 4 to 7 times and a transverse direction (TD) stretch ratio of 8 to 10 times. By adjusting the stretch ratios in the longitudinal and transverse directions within the above ranges, the orientation of the crystals becomes sufficient, the expected improvement effect of physical properties can be ensured, and it is difficult to ensure a stretch ratio higher than the above magnification due to the limitations of the equipment.

[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 the above range, there is no problem that the film is too thick and it is difficult to thin the final film, and it can have excellent mechanical physical properties.

[0043] The intermediate layer may be formed at 70% to 98% by weight, 80% to 95% by weight, or 85% to 95% by weight based on the total amount of the high-density polyethylene film. Also, the total content of the first skin layer and the second skin layer may be 2% to 30% by weight, 5% to 20% by weight, or 5% to 15% by weight based on the total amount of the high-density polyethylene film. By adjusting the thicknesses 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 adjusted more uniformly, mechanical physical properties can be ensured, and transparency can be improved.

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

[0045] The density of the first high-density polyethylene resin may be higher than that of the second high-density polyethylene resin. The density of the first high-density polyethylene resin is, for example, 0.945 g / cm 3 ~0.970 g / cm 3 、or 0.945 g / cm 3 ~0.965 g / cm 3It may be. If the density of the first high-density polyethylene resin is within the above range, the final high-density polyethylene film has excellent thermal stability, a low thermal shrinkage rate, and the modulus can be improved.

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

[0047] The ratio of the integrated value of the graph region corresponding to the polymer having a molecular weight of 10 3 g / mol to 10 4 g / mol in the first high-density polyethylene resin is 20% - 30% of the integrated value of the total area of the overall molecular weight distribution graph of the first high-density polyethylene resin, and the number of single-chain branches of the polymer may be 1 - 8 per 1000 carbon atoms. For example, the ratio of the integrated value of the graph region corresponding to the polymer having a molecular weight of 10 3 g / mol to 10 4The ratio of the integrated value of the graph region corresponding to the polymer having a molecular weight of g / mol is 22% to 26%, and the number of single-chain branches of the polymer may be 1.5 to 6 per 1000 carbons. When the molecular weight is 10 3 g / mol to 10 4 g / mol and the number of single-chain branches is within the above range, the stretching ratios in the longitudinal and transverse directions of the film can be improved, and the thickness uniformity of the film 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 comonomer distribution) structure. The BOCD structure contains a large amount of monomers and has a wide molecular weight distribution. The single-chain branches may have a BOCD structure that increases as the molecular weight increases. When the molecular weight and the number of single-chain branches of the polymer forming the first high-density polyethylene resin are within the above ranges and the single-chain branches have a BOCD profile, when the final high-density polyethylene film made of the first high-density polyethylene resin is successively biaxially stretched in a tenter frame process, stable successive biaxial stretching in the longitudinal direction (MD) and the transverse direction (TD) is possible. Therefore, a uniform thickness can be ensured, the stretching ratio can be improved, and the mechanical strength, particularly the modulus, of the stretched film 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 may be 10% to 20%, 12% to 18%, or 14% to 17% with respect to the polymer concentration dissolved in the polymer solution at 100°C. Within the above range, in the sequential biaxial stretching process of the final high-density polyethylene film using a tenter frame process, the stretching ratios in the longitudinal and transverse directions can be increased, and the modulus can be improved. As the temperature is lowered during the crystallization fractionation analysis, the polymer is eluted from the polymer solution, thereby reducing the polymer concentration dissolved in the polymer solution. Therefore, the reduction ratio of the polymer concentration dissolved in the polymer solution can mean the fraction from which the polymer is eluted.

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

[0051] 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 80°C to 90°C may be 50% to 70%, 55% to 68%, or 60% to 65% with respect to the polymer concentration dissolved in the polymer solution at 100°C. Within the above range, in the sequential biaxial stretching process of the final high-density polyethylene film using a tenter frame process, the stretching ratios in the longitudinal and transverse directions can be increased, and the modulus can be improved.

[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, the extrusion processability is excellent, and it is possible to prevent the 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, and the film can be stably and sequentially biaxially stretched in the longitudinal and transverse directions and 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 heat resistance of the final high-density polyethylene film is excellent, and the modulus value can be improved.

[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 temperature range in which the final high-density polyethylene film can be stretched can be widened.

[0056] The first high-density polyethylene resin may be polymerized from an ethylene monomer, a comonomer, and hydrogen in the presence of a catalyst. The first high-density polyethylene resin may be formed by polymerization using a two-stage reactor composed of a first reactor and a second reactor connected to each other. Specifically, polymerization is carried out in the first reactor to primarily form a polyethylene resin as an intermediate polymer. The polyethylene resin obtained at this time is transferred to the second reactor and polymerization continues, whereby a first high-density polyethylene resin can be obtained as the final polymer. The first reactor and the second reactor may be a slurry process.

[0057] The polymerization in the first reactor and the second reactor may be carried out in the presence of a Ziegler-Natta (ZN) catalyst. The Ziegler-Natta catalyst is a catalyst known as a normal Ziegler-Natta catalyst, and uses a transition metal compound belonging to Group IV, V, or VI of the periodic table of elements as the main catalyst. Among them, the most commonly used Ziegler-Natta catalyst is a halogenated complex composed of magnesium and titanium, or magnesium and vanadium.

[0058] Also, when polymerizing in at least one of the first reactor and the second reactor, a comonomer may be introduced in addition to the ethylene monomer. As the comonomer, α-olefins having 3 to 20 carbon atoms, for example, 4 to 8 carbon atoms or 6 to 8 carbon atoms can be used. As a specific example, the comonomer may be any one or more of 1-butene, 1-hexene, and 1-octene.

[0059] The supply ratio of the comonomer to the ethylene monomer supply amount in the first reactor 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 the comonomer is supplied to the first reactor at a supply ratio within the above range, plugging of the reactor and formation of fouling are prevented, the draw ratios in the longitudinal and transverse directions are increased in the biaxial stretching process of the final film, and a high-molecular polyethylene film with high mechanical strength can be obtained.

[0060] In the first reactor, the hydrogen supply ratio to the ethylene monomer supply amount 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, plugging and fouling formation in the reactor can be prevented, the draw ratios in the longitudinal and transverse directions can be increased in the biaxial stretching process of the final film, and a high-molecular-weight polyethylene film with high mechanical strength can be obtained.

[0061] In the second reactor, a comonomer may not be supplied. By not supplying a 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 amount 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, plugging and fouling formation in the reactor can be prevented, the draw ratios in the longitudinal and transverse directions can be increased in the biaxial stretching process of the final high-molecular-weight polyethylene film, and a high-molecular-weight polyethylene film with high mechanical strength can be obtained.

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

[0064] The second high-density polyethylene resin used to form the first skin layer and the second skin layer can be produced by melt-mixing 5 wt% to 25 wt% or 10 wt% to 15 wt% of a commercial polyolefin elastomer (POE) with the previously produced first high-density polyethylene.

[0065] In the results of the crystallization fractionation analysis of the polymer solution obtained by dissolving the second high-density polyethylene resin 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%, 12% to 18%, or 15% to 17% with respect to the polymer concentration dissolved in the polymer solution at 100°C. If the decrease ratio of the concentration of the second high-density polyethylene resin is within the above range, the draw ratios in the longitudinal and transverse directions can be increased in the sequential biaxial stretching process of the final film using the tenter frame process, and the transparency of the film is excellent. Therefore, a final film with low turbidity and high clarity can be obtained.

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

[0067] In the results of the crystallization fractionation analysis of the polymer solution obtained by dissolving the second high-density polyethylene resin in a solvent, the decrease ratio of the polymer concentration dissolved in the polymer solution at a temperature of 80°C to 90°C may be 30% to 75%, 40% to 70%, or 50% to 60% with respect to the polymer concentration dissolved in the polymer solution at 100°C. If the decrease ratio of the concentration of the second high-density polyethylene resin is within the above range, the draw ratios in the longitudinal and transverse directions can be increased in the sequential biaxial stretching process of the final film using the tenter frame process, and the transparency of the film is excellent. Therefore, 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 with respect 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 to 10 4 The ratio of the integrated value of the graph region corresponding to the polymer having a molecular weight of 10 g / mol to 10 g / mol may be 18% to 30%, and the number of single-chain branches of 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 3 g / mol to 10 4 g / mol. The ratio of the integrated value of the graph region corresponding to the polymer is 20% to 25%, and the number of single-chain branches of the polymer may be 0.5 to 5 per 1000 carbon atoms. The molecular weight is 10 3 g / mol to 10 4 g / mol. If the polymer ratio and the number of single-chain branches are within the above ranges, the stretching ratios in the longitudinal and transverse directions of the film can be improved, and the thickness uniformity of the film can be ensured.

[0070] The second high-density polyethylene resin has a molecular weight of 10 5 g / mol to 10 6 g / mol. The ratio of the integrated value of the graph region corresponding to the polymer may be 20% to 26%, and the number of single-chain branches of 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 5 g / mol to 10 6 g / mol. The ratio of the integrated value of the graph region corresponding to the polymer is 21% to 24%, and the number of single-chain branches of the polymer may be 1.5 to 10 per 1000 carbon atoms. The molecular weight is 10 5 g / mol to 10 6If the polymer ratio is g / mol and the number of single-chain branches is within the above range, stable sequential biaxial stretching can be performed in 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. The density of the second high-density polyethylene resin is, for example, 0.940 g / cm 3 ~0.965 g / cm 3 or 0.942 g / cm 3 ~0.960 g / cm 3 It may be. If the density of the second high-density polyethylene resin is within the above range, the transparency of the final high-density polyethylene film can 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 has excellent extrusion processability and can reduce the roughness of the film surface to improve 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, it has excellent final extrusion processability, the film can be stably sequentially biaxially stretched in the longitudinal and transverse directions, and the film can be stretched with a uniform thickness.

[0075] The high-density polyethylene resin according to one embodiment, that is, each of the first high-density polyethylene resin and the second high-density polyethylene, can be mixed with additives including an antioxidant, a neutralizing agent, or a combination thereof to form a composition.

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

[0077] The antioxidant may include one or more selected from the group consisting of phenolic compounds and phosphorus compounds. Examples of the phenolic compound include pentaerythritol tetrakis(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-hydroxylbenzyl) isocyanate, triethylene glycol-bis(3-(tert-butyl-4-hydroxy-5-methylphenyl)propionate), etc. Examples of the phosphorus compound include tris(2,4-di-tert-butylphenyl) phosphite, tetrakis(2,4-di-tert-butylphenyl)-4,4-diphenyldiphosphonate, distearyl pentaerythritol diphosphite, 2,4-dinonylphenyl bis(4-mono-nonylphenyl) phosphite, etc.

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

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

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

[0082] In recent years, regulations on recycling have been strengthened globally. Due to the change in awareness of the social responsibility for the company's own sustainability and the solution of a wide range of environmental problems, efforts have been made to design flexible packaging materials so that collection, classification, and recycling are facilitated.

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

[0084] For this purpose, the application of a biaxially oriented polyethylene (BOPE) film is required. Generally, as a manufacturing process of the biaxially oriented polyethylene (BOPE) film, a tenter frame process is applied. When the film is stretched in the machine direction (MD) and the transverse direction (TD), by highly orienting the polyethylene chains and the crystal structure, better mechanical strength, especially impact strength, is improved, and optical properties such as transparency and film appearance are epoch-making improved.

[0085] However, in the tenter frame process, it 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 stretchable temperature range is narrow, the stretch ratio is very low, and if wrinkles form or the thickness is not uniform during stretching, ultimately, the film will tear during stretching. In particular, the BOPE film applying high density polyethylene (HDPE) has excellent heat resistance compared to the BOPE film applying linear low density polyethylene (LLDPE), and the modulus of the film is improved epoch-makingly, but there are problems that it is difficult to stretch and the transparency decreases.

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

[0087] Hereinafter, specific embodiments of the present invention will be presented. However, the following embodiments are merely for specifically exemplifying or explaining the present invention, and the present invention should not be limited thereto. In addition, the content not described herein can be sufficiently technically analogized by those skilled in the art of this technology, and the description thereof is omitted.

[0088] [Manufacture of High Density Polyethylene Resin] Production Example 1-1 and Production Example 1-2: Manufacture of the First High Density Polyethylene Resin Composition 1. Manufacture of the First High Density Polyethylene Resin The first high density polyethylene resin was manufactured according to the conditions in Table 1 below. Two reactors with a capacity of 90 L were connected in series, and ethylene polymerization was carried out using an ethylene monomer and a comonomer in the presence of a Ziegler-Natta catalyst. The Ziegler-Natta catalyst is a known catalyst composed of magnesium and titanium, and one produced by a conventional method was used.

[0089] Specifically, in the first reactor, ethylene monomer (C2), 1-hexene (C6) as a comonomer, and hydrogen (H 2 ) were supplied, and ethylene polymerization was carried out. The polymerization ratio in the first reactor, the C6 supply ratio with respect to the C2 supply amount, the H 2 supply ratio with respect to the C2 supply amount, the polymerization temperature, and the polymerization pressure are shown in Table 1 below, and the reaction 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. Thereafter, a powdery high-density polyethylene resin was produced from the slurry-like final polymer. In the second reactor, ethylene monomer (C2) and hydrogen (H 2 ) were supplied to carry out ethylene polymerization, and no comonomer (C6) was supplied. The polymerization ratio in the second reactor, the H 2 supply ratio with respect to the C2 supply amount, the polymerization temperature, and the polymerization pressure are shown in Table 1 below, and the reaction was carried out under the condition of a residence time of 34 minutes.

[0090]

Table 1

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

[0092] Production Examples 2-1 and 2-2: Production of the Second High-Density Polyethylene Resin Composition The second high-density polyethylene resin composition was produced according to the conditions shown in Table 2 below. The second high-density polyethylene resin composition was prepared by mixing the previously produced first high-density polyethylene resin of Production Example 1-1 or Production Example 1-2 with a commercial POE, Supreme 004 or Supreme 883 manufactured by SK Geocentrics. To 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, 0.1 part by weight of Irganox-3114 and 0.1 part by weight of Irgafos-168 as antioxidants, and 0.025 part by weight of magnesium aluminum hydroxy carbonate (DHT-4A) as a neutralizing agent were mixed using a Henschel mixer, and then a second high-density polyethylene resin composition in pellet form was produced using a twin-screw extruder.

[0093]

Table 2

[0094] Comparative Production Examples 1 to 3: Production of the Second High-Density Polyethylene Resin Composition 1. Production of the Second High-Density Polyethylene Resin The second high-density polyethylene resin of Comparative Production Example 1 is the C330A product produced in our slurry process, using 1-butene as a comonomer, with a density of 0.958 g / cm 3 , a melt flow index (MI2) of 1.0 g / 10 min, and a melt flow ratio of 150. In the present invention, the melt flow ratio means the ratio of the melt flow index (MI21.6) measured at a load of 21.6 kg at 190°C in accordance with ASTM D1238 to the melt flow index (MI2) measured at a load of 2.16 kg at 190°C in accordance with ASTM D1238.

[0095] The second high-density polyethylene resin of Comparative Production Example 2 is the C910C product produced in the gas phase process using our Gas Phase Reactor (GPR), using 1-butene as a comonomer, with a density of 0.950 g / cm3 The 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 of Comparative Production Example 3 is the R904U product produced in our company's gas-phase process. 1-Hexene is used as a copolymer, and the density is 0.940 g / cm 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 100 parts by weight of each second high-density polyethylene resin, 0.1 part by weight of Irganox-3114 and 0.1 part by weight of Irgafos-168 as antioxidants, and 0.025 part by weight of magnesium aluminum hydroxycarbonate (DHT-4A) as a neutralizing agent were mixed with a Henschel mixer, and then a second high-density polyethylene resin composition in pellet form was produced using a twin-screw extruder.

[0098] [Production of High-Density Polyethylene Film] Examples 1 to 4 and Comparative Examples 1 to 7 Using the high-density polyethylene resin compositions produced in Production Examples 1-1, 1-2, 2-1, 2-2 and Comparative Production Examples 1 to 3 respectively, a biaxially oriented polyethylene (BOPE) film with a multilayer structure was produced. At this time, the types of high-density polyethylene resin compositions used to form 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 biaxially oriented polyethylene film with a multilayer structure was biaxially stretched on a dedicated mass production line of Bruckner (Hybrid BOPE / BOPP line, 5-layer, 6.6 m width). The film was applied in 5 layers, and a film finally stretched 5.2 times in the machine direction (MD) × 9 times in the transverse direction (TD) was successfully produced at an extrusion speed of 190 m / min and a die temperature of 230 to 240 °C. Here, the extrusion conditions of the biaxially stretched film and the film processing conditions are specifically shown in Table 4 below.

[0100]

Table 3

[0101]

Table 4

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

[0103] Density: Measured in accordance with ASTM D1505.

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

[0105] Melt flow ratio (MFRR): It means the ratio of the melt flow index (MI21.6) measured at 190 °C with a load of 21.6 kg to the melt flow index (MI2) measured at 190 °C with a load of 2.16 kg in accordance with ASTM D1238.

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

[0107] Gel permeation chromatography-infrared (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 of BHT), and dissolved at 160 °C for 2 hours for preparation. The eluent used was 1,2,4-trichlorobenzene (containing 125 ppm of BHT). The columns used were one Olexis guard column and three Olexis columns (Column; PLgel Olexis guard X1 + PLgel Olexis X3) connected in series. 200 μl was injected for analysis. For column calibration for molecular weight calculation, polystyrene standards were used, and for the molecular weight calculation of polyethylene, the Mark-Houwink constants (K = 44.6, a = 0.725) were applied.

[0108] The number of single-chain branches (SCB) in the sample represents the number of single-chain branches per 1000 carbons and was calibrated using a standard substance (1-octene copolymer provided by Polymer Char) whose value was already known. The number of methyl groups (-CH 3 ) per 1000 carbons in the sample is the average value obtained by excluding the methyl groups at the chain ends from the number of methyl groups, and represents the value calculated by end chain correction from the number of methyl groups (CH 3 / 1000TC) per 1000 carbons in the sample. The end chain correction is determined by Equation 1 below.

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

[0110] In Formula 1, A represents the number of end groups. For example, in linear polyethylene (linear PE), it is 2, and in long chain branch (LCB) polymers, it is more than 2. Also, M represents the given molar mass.

[0111] When the chain end group is terminated with a vinyl group (-CH=CH 2 ), 0 was applied as its value for end chain correction.

[0112] Figure 3 is a graph showing the overall molecular weight distribution of the first high-density polyethylene resins of Production Example 1-1 and Production Example 1-2 measured by gel permeation chromatography-infrared (GPC-IR) and the number of single chain branches per 1000 carbons. Referring to Figure 3, in the overall molecular weight distribution graph of the first high-density polyethylene, the integral values in the regions where the logM values are 3 to 4 and 5 to 6 respectively correspond to the ratios of polymers with a molecular weight (M) of 10 5 g / mol to 10 6 g / mol and the ratios of polymers with a molecular weight (M) of 10 3 g / mol to 10 4 g / mol according to one embodiment.

[0113] Thus, the polymer ratio with a molecular weight of 10 5 g / mol to 10 6 g / mol (10 5 to 10 6 ), the polymer ratio with a molecular weight of 10 3 g / mol to 10 4 g / mol (10 3 to 10 4 ), the number of single chain branches of polymers with a molecular weight of 10 5 g / mol to 10 6 g / mol (10 5 to 10 6 ), and the polymer with a molecular weight of 10 3 g / mol to 10 4The number of single-chain branches of the polymer (10 3 ~10 4 ) was measured respectively.

[0114] Crystallization Analysis Fractionation (CRYSTAF): It was measured using CRYSTAF, which is equipment of Polymer Char. 20 mg of the sample was put into 20 ml of 1,2,4-Trichlorobenzene and dissolved while stirring at 160 °C for 60 minutes to produce a polymer solution. After injecting the polymer solution into the equipment, it was stabilized at 100 °C for 45 minutes, and then, while lowering the temperature to 35 °C at a constant rate of 0.2 °C / min, the crystallized part was filtered off with a filter, and the concentration of the polymer dissolved in the solution was measured. The cumulative curve sets the concentration at the initial set temperature of 100 °C to 100% and shows the reduction ratio (%) of the polymer concentration dissolved in the polymer solution depending on the temperature. Thus, the reduction ratio (%) of the polymer concentration dissolved in the polymer solution under each temperature condition was measured. The crystallization fractionation analysis graphs of the first high-density polyethylene resins according to Production Example 1-1 and Production Example 1-2 can be confirmed from Figure 4, and the crystallization fractionation analysis graphs of the second high-density polyethylene resins according to Production Example 2-1 and Production Example 2-2 can be confirmed from Figure 5.

[0115]

Table 5

[0116]

Table 6

[0117] [Physical Property Evaluation of High-Density Polyethylene Film] For the high-density polyethylene films of Examples 1 to 4 and Comparative Examples 1 to 7 above, the physical properties were evaluated by the following method and shown in Table 7 below.

[0118] Tensile strength, modulus: The respective tensile strengths (MPa) and moduli (MPa) in the machine direction (MD) and transverse direction (TD) of each film were measured in accordance with ASTM D882, respectively.

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

[0120] Film thickness and standard deviation (2σ): Using a non-contact thickness measuring machine, the thickness of each film was measured approximately 50 times at 20 mm intervals in the machine direction (width direction, MD) and transverse direction (running direction, TD), and the average value was calculated. 2 sigma (2σ) was calculated to show the standard deviation (%).

[0121]

Table 7

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

[0123] On the other hand, 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, the first skin layer, and the second skin layer, it was confirmed that the turbidity and modulus decreased. Further, 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 as the first skin layer and the second skin layer, it was confirmed that the turbidity and modulus decreased.

[0124] As described above, the embodiments of the present invention have been described with reference to the accompanying drawings. However, those of ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing its technical idea and essential features. Therefore, the embodiments described above should be understood as illustrative in any aspect and not restrictive.

Explanation of Reference Numerals

[0125] 10 Intermediate layer 11 First intermediate layer 12 Second intermediate layer 13 Third intermediate layer 20 Skin layer 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; a first skin layer and a second skin layer disposed on either side of the intermediate layer, the first skin layer and the second skin layer comprising 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; A high-density polyethylene film, wherein, as a result of a crystallization fractionation analysis of a polymer solution obtained by dissolving the second high-density polyethylene resin in a solvent, a reduction ratio of a polymer concentration dissolved in the polymer solution at a temperature of 80°C to 90°C is 30% to 75% relative to the polymer concentration dissolved in the polymer solution at 100°C.

2. 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 structure or a multilayer structure of 2 to 5 layers.

3. The density of the first high density polyethylene resin is 0.945 g / cm ３ ~0.970g / cm ３ 2. The high density polyethylene film of claim 1 ,

4. The first high density polyethylene resin has a molecular weight of 10 with respect to an integral value of a total area of ​​a molecular weight distribution graph of the first high density polyethylene resin. ５ g / mol to 10 ６ 2. The high-density polyethylene film according to claim 1, wherein a ratio of an integral value of a graph region corresponding to a polymer having a molecular weight of 1000 g / mol is 18% to 28%, and the number of short chain branches of the polymer is 5 to 15 per 1000 carbon atoms.

5. The first high density polyethylene resin has a molecular weight of 10 with respect to an integral value of a total area of ​​a molecular weight distribution graph of the first high density polyethylene resin. ３ g / mol to 10 ４ 2. The high-density polyethylene film of claim 1, wherein a ratio of an integral value of a graph region corresponding to a polymer having a molecular weight of 1000 g / mol is 20% to 30%, and the number of short chain branches of the polymer is 1 to 8 per 1,000 carbons.

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

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

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

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 is 0.40 g / 10 min to 3.0 g / 10 min.

10. 2. The high-density polyethylene film according to claim 1, wherein 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 is 70 or more.

11. 2. The high-density polyethylene film according to claim 1, wherein, in a crystallization fractionation analysis of a polymer solution obtained by dissolving the second high-density polyethylene resin in a solvent, a reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature exceeding 30° C. and not exceeding 50° C. to the polymer concentration dissolved in the polymer solution at 100° C. is 10% to 20%.

12. 2. The high-density polyethylene film according to claim 1, wherein, in a crystallization fractionation analysis of a polymer solution obtained by dissolving the second high-density polyethylene resin in a solvent, a reduction ratio of the polymer concentration dissolved in the polymer solution at a temperature exceeding 30° C. and not exceeding 60° C. to the polymer concentration dissolved in the polymer solution at 100° C. is 15% to 25%.

13. The second high density polyethylene resin has a molecular weight of 10 to 10 with respect to the integral value of the total area of ​​the entire molecular weight distribution graph of the second high density polyethylene resin. ３ g / mol to 10 ４ 2. The high-density polyethylene film of claim 1, wherein a ratio of an integral value of a graph region corresponding to a polymer having a molecular weight of 1000 g / mol is 18% to 30%, and the number of short chain branches of the polymer is 0.1 to 8 per 1000 carbon atoms.

14. The density of the second high density polyethylene resin is 0.940 g / cm ３ ~0.965g / cm ３ 2. The high density polyethylene film of claim 1 ,

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 is 0.50 g / 10 min to 5.0 g / 10 min.

16. 2. The high-density polyethylene film according to claim 1, wherein 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 is 60 or more.

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

18. 2. 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% by weight to 98% by weight based on the total amount of the high density polyethylene film.

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

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