Polyethylene resin composition for high-transparency and low-shrinkage biaxially oriented film, and biaxially oriented film comprising same

Abstract

Disclosed is a polyethylene resin composition for a biaxially oriented film, which can be molded by a biaxial stretching machine, exhibits excellent stretching properties and has excellent transparency and low-shrinkage properties. The present invention provides the polyethylene resin composition for a biaxially oriented film, comprising: (A) 1-40 wt% of a copolymer of ethylene and a C4-10 olefin, which has a density of 0.945-0.955 g / cm3; and (B) 60-99 wt% of a copolymer of ethylene and a C4-10 olefin, which has a density of 0.920-0.930 g / cm3, wherein the total calorie obtained by differential scanning calorimeter (DSC) analysis is 150-170 J / g, the molecular weight distribution (MWD, Mw / Mn) is 10-20, the crystallinity of a sheet before machine direction (MD) stretching is 45-50%, and the crystallinity after MD stretching is 80% or more.

Description

Polyethylene resin composition for high transparency and low shrinkage biaxially oriented film and biaxially oriented film comprising the same

[0001] The present invention relates to a polyethylene resin composition and a film comprising the same, and more particularly, to a polyethylene resin composition for a biaxially oriented film and a film comprising the same.

[0002] This application claims priority to and the benefit of Republic of Korea Patent Application No. 10-2023-0167230, filed November 27, 2023, which is incorporated herein by reference in its entirety.

[0003] The plastics industry is experiencing rapid market changes due to the emergence of new issues, including the issue of marine plastics. Container packaging materials, which consume a significant amount of energy, are no exception. Beyond packaging material production, the processed food / beverage and distribution sectors are also being called upon to address environmental issues such as plastic waste and greenhouse gas reduction.

[0004] In particular, packaging-related companies have recognized the need to focus on developing materials that can reduce environmental burden, and globally, the development and use of single-material products based on recycling and bioplastics that contribute to reducing carbon dioxide (CO2) emissions are becoming more active.

[0005] Globally, polyethylene (PE)-based materials are leading the trend toward single-material manufacturing. This is because, during the multilayer film design process, the sealant layer is considered first, taking into account the contents and intended use. The relatively high proportion of polyethylene used in the central sealant layer makes it easy for the surface material to also be polyethylene-based when the entire product is manufactured as a single material.

[0006] In the United States, as the recovery and recycling system for polyethylene products is being established, it is expected that the single-material flow will also become mainstream. Some companies are focusing on the single-material polyethylene system with the goal of replacing the nylon / polyethylene composition, and some companies are seeking to convert pouch materials used in films with excessive functionalities (such as dried fruit, frozen food, and pet food) from PET / PE to single-material packaging centered on PE.

[0007] Meanwhile, in the case of biaxially oriented films, replacing the layer previously used with BOPA (biaxially oriented polyamide) or BOPET (biaxially oriented polyethylene terephthalate) with BOPE (biaxially oriented polyethylene) to make it a single material may be in line with this development trend, but there is still no case presented that shows satisfactory transparency and low shrinkage characteristics along with stretching characteristics as polyethylene that can be molded with a biaxial stretching machine and used as first-grade paper (printing surface) for easy recycling.

[0008] Korean Patent No. 0746253 discloses a polyethylene-based stretched film having excellent Elmendorf tear strength and being able to be stretched uniformly. However, it is difficult to obtain satisfactory transparency and low shrinkage characteristics when biaxially stretched with the actually presented composition.

[0009] The present invention aims to provide a polyethylene resin composition for a biaxially oriented film that can be molded using a biaxial stretching machine, exhibits excellent stretching properties, and has excellent transparency and low shrinkage properties, and a biaxially oriented film comprising the same.

[0010] In order to solve the above problem, the present invention provides a polyethylene resin composition for a biaxially oriented film, comprising (A) 1 to 40 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms and having a density of 0.945 to 0.955 g / cm3; and (B) 60 to 99 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms and having a density of 0.920 to 0.930 g / cm3; wherein the polyethylene resin composition has a total calorie of 150 to 170 J / g through DSC (Differential Scanning Calorimeter) analysis, a molecular weight distribution (MWD, Mw / Mn) of 10 to 20, and a crystallinity of 45 to 50% of a sheet before MD (Machine Direction) stretching measured by the following method, and a crystallinity of 80% or more after MD stretching.

[0011] [measurement method]

[0012] For the above resin composition, a sheet is manufactured using a multilayer film molding machine under the conditions of a cooling roll temperature of 35 to 45°C, an extruder temperature of 240°C, and a line speed of 1.2 m / min, and then stretched 5 times using an MD stretching unit under the conditions of a preheating temperature of 118°C, a stretching temperature of 116°C, and a line speed of 1.2 m / min, and the crystallinity is measured for each sheet before and after MD stretching, and the crystallinity is measured according to the following mathematical formula 1 for peaks having a Full Width at Half Maximum (FWHM) of less than 1.0 generated by X-ray diffraction analysis (XRD);

[0013] <Mathematical Formula 1>

[0014] Crystallinity (%) = (Area of ​​crystalline peak / (Area of ​​crystalline peak + Area of ​​amorphous peak)) × 100.

[0015] In addition, the present invention provides a polyethylene resin composition for a biaxially oriented film, characterized in that the copolymer (A) has a melting index (190°C, 2.16 kg load) of 0.6 to 1.2 g / 10 min, and the copolymer (B) has a melting index (190°C, 2.16 kg load) of 1.2 to 2.5 g / 10 min.

[0016] In addition, the resin composition provides a polyethylene resin composition for a biaxially oriented film, characterized in that the resin composition has a melting index (190°C, 2.16 kg load) of 1 to 2 g / 10 min and a density of 0.930 to 0.940 g / cm3.

[0017] In order to solve the above-mentioned further problem, the present invention provides a biaxially oriented film comprising the resin composition.

[0018] In addition, the film provides a biaxially oriented film characterized in that the film has a shrinkage ratio in the longitudinal and transverse directions of less than 5% each in the following measurement method, a tensile strength in the longitudinal and transverse directions of 700 kgf / ㎠ or more and 1,800 kgf / ㎠ or more, respectively, and a haze of 5% or less.

[0019] [measurement method]

[0020] A biaxially stretched film was manufactured under the conditions of a film width of 8 m, a molding speed of 200 m / min, a longitudinal stretching ratio of 5 times (preheating temperature of 114 to 118°C, stretching temperature of 115°C, and annealing temperature of 110 to 115°C), and a transverse stretching ratio of 9 times (preheating temperature of 125 to 137°C, stretching temperature of 125 to 128°C, and annealing temperature of 130 to 133°C) for a film having a thickness of 30 ㎛ manufactured using the above resin composition, and a biaxially stretched film specimen (10 x 10 cm) was subjected to shrinkage rate by measuring the reduced lengths in the longitudinal and transverse directions after 5 minutes in a convection oven at 100°C using a tensile tester (model name: Instron4466) according to the regulations of ASTM D882 with a load cell of 100 N and Tensile strength was measured at a test speed of 500 mm / min, and haze was measured for the specimen using a haze meter (model name: NDH5000) according to the ASTM D1003 regulations.

[0021] According to the present invention, a polyethylene resin composition having a specific level of total heat capacity, molecular weight distribution and crystallinity, which is a copolymer of ethylene and an olefin having 4 to 10 carbon atoms and different densities within a certain range, can be provided, which is moldable by a biaxial stretching machine and has excellent stretching characteristics, as well as improved transparency and low shrinkage characteristics, and a biaxially oriented film comprising the same.

[0022] Hereinafter, the present invention will be described in detail through preferred embodiments. Prior to this, it should be noted that the terms and words used in this specification and claims should not be interpreted as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted as meanings and concepts that conform to the technical concept of the present invention. Therefore, the configuration of the embodiments described in this specification is only the most preferred embodiment of the present invention and does not represent the entire technical concept of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of filing this application.

[0023]

[0024] The inventors of the present invention have discovered that, in a situation where a composition exhibiting excellent transparency and low shrinkage characteristics along with excellent stretching characteristics has not yet been presented when replacing the layer previously used with BOPA or BOPET with BOPE to make it a single material, a polyethylene resin composition is formed by mixing a copolymer of ethylene and an olefin having 4 to 10 carbon atoms with different densities within a certain range, and having a specific level of total heat capacity, molecular weight distribution and crystallinity, and is moldable with a biaxial stretching machine, and has excellent stretching characteristics along with improved transparency and low shrinkage characteristics, leading to the invention.

[0025] Accordingly, the present invention discloses a polyethylene resin composition for a biaxially oriented film, comprising (A) 1 to 40 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.945 to 0.955 g / cm3; and (B) 60 to 99 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.920 to 0.930 g / cm3; wherein the polyethylene resin composition has a total calorie of 150 to 170 J / g as determined by DSC (Differential Scanning Calorimeter) analysis, a molecular weight distribution (MWD, Mw / Mn) of 10 to 20, and a crystallinity of 45 to 50% of a sheet before MD (Machine Direction) stretching measured by the following method, and a crystallinity of 80% or more after MD stretching.

[0026] [measurement method]

[0027] For the above resin composition, a sheet is manufactured using a multilayer film molding machine under the conditions of a cooling roll temperature of 35 to 45°C, an extruder temperature of 240°C, and a line speed of 1.2 m / min, and then stretched 5 times using an MD unit under the conditions of a preheating temperature of 118°C, a stretching temperature of 116°C, and a line speed of 1.2 m / min, and the crystallinity is measured for each sheet before and after MD stretching, and the crystallinity is measured according to the following mathematical formula 1 for peaks having a FWHM (Full Width at Half Maximum) of less than 1.0 generated by X-ray diffraction analysis (XRD);

[0028] <Mathematical Formula 1>

[0029] Crystallinity (%) = (Area of ​​crystalline peak / (Area of ​​crystalline peak + Area of ​​amorphous peak)) × 100.

[0030] In the present invention, the (A) copolymer is a high-density polyethylene having a density of 0.945 to 0.955 g / cm3, preferably 0.948 to 0.952 g / cm3. If the density is outside the above range, biaxial stretching molding is difficult.

[0031] In addition, the above (A) copolymer may be a copolymer of ethylene and an α-olefin such as propylene, 1-butene, 1-hexene, or 1-octene, and preferably a copolymer of ethylene and 1-butene may be used, and the melt index (190°C, 2.16 kg load) may be 0.6 to 1.2 g / 10 min, and preferably 0.8 to 1.2 g / 10 min. If a copolymer manufactured using an α-olefin other than 1-butene as a comonomer to be copolymerized with ethylene is applied, or if the melt index is out of the above range, there may be a limit to improving low-shrinkage characteristics, or biaxial stretching molding may be difficult. The polymerization method of the (A) copolymer is not particularly limited, and may be manufactured by any method such as a vapor phase method, a solution method, or a slurry method.

[0032] The above (A) copolymer may be included in an amount of 1 to 40 wt% of the total resin composition, and preferably 15 to 35 wt%. If the (A) copolymer content is outside the above range, transparency and low-shrinkage properties are not improved, or surface properties deteriorate during sheet molding.

[0033] In the present invention, the (B) copolymer is a low-density polyethylene having a density of 0.920 to 0.930 g / cm3, preferably 0.925 to 0.930 g / cm3. If the density is outside the above range, biaxial stretching molding is difficult.

[0034] The above (B) copolymer may be a copolymer of ethylene and an α-olefin such as propylene, 1-butene, 1-hexene, or 1-octene, and preferably a copolymer of ethylene and 1-butene or 1-octene, and may have a melt index (190°C, 2.16 kg load) of 1.2 to 2.5 g / 10 min, and preferably 1.5 to 2 g / 10 min. If a copolymer manufactured using an α-olefin other than 1-butene and 1-octene as a comonomer to be copolymerized with ethylene is applied, or if the melt index is out of the above range, there may be a limit to improving low-shrinkage characteristics, or biaxial stretching molding may be difficult. The polymerization method of the (B) copolymer is not particularly limited, and may be manufactured by any method such as a vapor phase method, a solution method, or a slurry method.

[0035] The above (B) copolymer may be included in an amount of 60 to 99 wt% of the total resin composition, and preferably 65 to 85 wt%. If the (B) copolymer content is outside the above range, transparency and low-shrinkage properties are not improved, or surface properties deteriorate during sheet molding.

[0036] According to the mixing of the (A) copolymer and (B) copolymer as described above, the melting index (190°C, 2.16 kg load) of the final resin composition may be 1 to 2 g / 10 min, preferably 1.3 to 1.7 g / 10 min, and the density may be 0.930 to 0.940 g / cm3, preferably 0.934 to 0.938 g / cm3.

[0037] In the present invention, it was confirmed that transparency and low shrinkage characteristics can be improved along with excellent stretching characteristics by controlling the thermal characteristics, molecular weight characteristics and crystallinity of the resin composition. Specifically, when the total calorie (Total Calorie) through DSC (Differential Scanning Calorimeter) analysis is 150 to 170 J / g, preferably 155 to 165 J / g, the molecular weight distribution (MWD, Mw / Mn) is 10 to 20, preferably 10 to 15, and the crystallinity of the sheet before MD (Machine Direction) stretching measured according to the following method is 45 to 50%, preferably 45 to 48%, and the crystallinity after MD stretching is controlled to 80% or more, preferably 80 to 90%, the stretching characteristics are excellent while the transparency and low shrinkage characteristics are improved.

[0038] [measurement method]

[0039] For the above resin composition, a sheet is manufactured using a multilayer film molding machine under the conditions of a cooling roll temperature of 35 to 45°C, an extruder temperature of 240°C, and a line speed of 1.2 m / min, and then stretched 5 times using an MD unit under the conditions of a preheating temperature of 118°C, a stretching temperature of 116°C, and a line speed of 1.2 m / min, and the crystallinity is measured for each sheet before and after MD stretching, and the crystallinity is measured according to the following mathematical formula 1 for peaks having a FWHM (Full Width at Half Maximum) of less than 1.0 generated by X-ray diffraction analysis (XRD);

[0040] <Mathematical Formula 1>

[0041] Crystallinity (%) = (Area of ​​crystalline peak / (Area of ​​crystalline peak + Area of ​​amorphous peak)) × 100.

[0042] At this time, considering the required molecular weight distribution of the resin composition, it is preferable that the molecular weight distributions (MWD, Mw / Mn) of the (A) copolymer and (B) copolymer to be mixed are 15 to 20 and 2 to 6, respectively.

[0043] The polyethylene resin composition for a biaxially oriented film according to the present invention may be added with general polyethylene additives for application to various purposes, and for example, an appropriate amount of an antioxidant, a heat and light stabilizer, an antistatic agent, a lubricant, an antiblocking agent, a preservative, a processing aid, a slip agent, an anti-adhesive agent, a pigment, a flame retardant, a foaming agent, etc. may be added and used.

[0044] The polyethylene resin composition for a biaxially oriented film according to the present invention can be manufactured by mixing and extruding the above components according to a conventional method known in the art. For example, the above components can be fed into a twin-screw extruder and melt-mixed to manufacture the polyethylene resin composition for a biaxially oriented film.

[0045] The polyethylene resin composition for a biaxially oriented film according to the present invention can be molded with a biaxial stretching machine and has excellent stretching properties along with improved transparency and low shrinkage properties. Specifically, the biaxially oriented film manufactured with the polyethylene resin composition for a biaxially oriented film according to the present invention has shrinkage rates in the longitudinal and transverse directions of less than 5%, preferably less than 3%, tensile strengths in the longitudinal and transverse directions of 700 kgf / cm2 or more and 1,800 kgf / cm2 or more, preferably 750 kgf / cm2 or more and 2,000 kgf / cm2 or more, and haze of 5% or less, preferably 2% or less.

[0046] [measurement method]

[0047] A biaxially stretched film having a thickness of 30 ㎛ was manufactured under the conditions of a film width of 8 m, a forming speed of 200 m / min, a longitudinal stretching ratio of 5 times (preheating temperature of 114 to 118°C, stretching temperature of 115°C, and annealing temperature of 110 to 115°C), and a transverse stretching ratio of 9 times (preheating temperature of 125 to 137°C, stretching temperature of 125 to 128°C, and annealing temperature of 130 to 133°C) for a sheet molded with the above resin composition, and the shrinkage rate was measured by measuring the reduced lengths in the longitudinal and transverse directions after 5 minutes in a convection oven at 100°C for a biaxially stretched film specimen (10 x 10 cm), and a tensile tester (model name: Instron4466) was used for the specimen according to the regulations of ASTM D882, with a load cell of 100 N and Tensile strength was measured at a test speed of 500 mm / min, and haze was measured for the specimen using a haze meter (model name: NDH5000) according to the ASTM D1003 regulations.

[0048] Hereinafter, the present invention will be described in more detail through specific examples and comparative examples.

[0049]

[0050] Examples and Comparative Examples

[0051] Copolymers having the properties shown in Table 1 below, either singly or in combination, were fed into a twin-screw extruder and melt-mixed at 180 to 220°C to produce a pellet-shaped polyethylene resin composition having the properties shown in Table 1. The measurement method for the produced polyethylene resin composition is shown below. Thereafter, the produced polyethylene resin composition was produced into a biaxially oriented film through the following steps.

[0052] Sheet forming → MD (longitudinal) stretching → TD (transverse) stretching → biaxially oriented film

[0053] The measurement method for each step until manufacturing of a biaxially oriented film was performed as follows, and the results are shown in Table 1 below.

[0054] [Method for measuring polyethylene resin composition (pellet)]

[0055] (1) Density

[0056] Measured according to ASTM D1505.

[0057] (2) Melt Index (MI)

[0058] Measured under conditions of 190℃ and 2.16 kg load according to ASTM D1238.

[0059] (3) Thermal characteristics

[0060] A 10 mg sample was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere using a differential scanning calorimeter (DSC, TA Instruments), and then the temperature was lowered to 40°C at a cooling rate of 10°C / min. The temperature was then increased at a heating rate of 10°C / min, and the peak temperature of the maximum peak of the obtained melting endotherm curve was defined as the melting point (Tm). In addition, the crystallization temperature (Tc) was measured while the sample was heated to 200°C at a heating rate of 10°C / min and then cooled to -50°C at a rate of -10°C / min. At this time, the total calories were calculated as the area of ​​the melting point peak (Tm peak) according to the temperature in the DSC curve.

[0061] (4) Molecular weight characteristics

[0062] It was measured using GPC analysis method according to ASTM D3536.

[0063] [Sheet Evaluation and Crystallinity Measurement Method]

[0064] For the above resin composition, a sheet was manufactured using a multilayer film molding machine under the conditions of a cooling roll temperature of 35 to 45°C, an extruder temperature of 240°C, and a line speed of 1.2 m / min, and the sheet was stretched 5 times using an MD stretching unit under the conditions of a preheating temperature of 118°C, a stretching temperature of 116°C, and a line speed of 1.2 m / min. At this time, the extruder pressure was measured during sheet forming, and the occurrence of unevenness and patterns was checked. In addition, the crystallinity was measured for each sheet before and after MD stretching, and the crystallinity was measured according to the following mathematical equation 1 for peaks having a full width at half maximum (FWHM) of less than 1.0 generated by X-ray diffraction analysis (XRD).

[0065] <Mathematical Formula 1>

[0066] Crystallinity (%) = (Area of ​​crystalline peak / (Area of ​​crystalline peak + Area of ​​amorphous peak)) × 100

[0067] [Method of measuring film properties]

[0068] A biaxially stretched film was manufactured under the conditions of a film width of 8 m, a forming speed of 200 m / min, a longitudinal (MD) stretching ratio of 5 times (preheating temperature of 114 to 118°C, stretching temperature of 115°C, and annealing temperature of 110 to 115°C), and a transverse (TD) stretching ratio of 9 times (preheating temperature of 125 to 137°C, stretching temperature of 125 to 128°C, and annealing temperature of 130 to 133°C) for a film having a thickness of 30 μm manufactured using the above resin composition. At this time, after longitudinal stretching, before inserting the film into the tenter frame, it was additionally checked whether a pattern was generated in the film, and after 5 minutes in a convection oven at 100°C for a biaxially stretched film specimen (10 x 10 cm), the reduced lengths in the longitudinal and transverse directions were measured to measure the shrinkage rate, and for the specimen, the shrinkage rate was measured according to ASTM D882. According to the regulations, the tensile strength was measured using a tensile tester (model name: Instron4466) under the conditions of a load cell of 100 N and a test speed of 500 mm / min, and the haze was measured for the above specimen using a haze meter (model name: NDH5000) according to the regulations of ASTM D1003.

[0069]

[0070] Classification Comparative Example 1 Comparative Example 2 Comparative Example 3 Example Comparative Example 4 Comparative Example 5 Comparative Example 6 Ingredients FB420L (Copolymer B) 100 90 80 70 60 - 70 FB420H (Copolymer A) - 10 20 30 40 100 - UF420H (Copolymer A) ------- 30 Polyethylene resin composition (Pellet) Physical properties MI (g / 10 min) 1.8 1.7 1.6 1.5 1.4 1.1 1.5 Density (g / cm) 3)0.9280.9300.9330.9360.9390.9500.937MWD(Mw / Mn)3.946.489.2712.513.717.77.89DSC Total Calories(J / g)140143152161172185162Sheet Evaluation and PropertiesExtruder Pressure(bar)164161158157155154166Sheet FormabilityGoodGoodGoodGoodGoodGoodUnevennessGoodPattern Occurrence Degree Occurred Occurred Not Occurred Not Occurred Confirmed Not OccurredXRD Crystallinity(%)45454746485047MD Physical Properties after StretchingXRD Crystallinity(%)5676768185-82Film Physical properties Haze (%) 4.9 4.0 2.3 1.5 5.0-4.5 Tensile strength (kgf / cm) 2 )MD530600650770807-700TD1,3371,7002,0002,6502,500-1,700Shrinkage rate (%)MD5.75.35.02.32.3-4.5TD2.03.83.02.54.0-5.0* Note- FB420L: MI 1.8 g / 10min / Density 0.928 / Tm 126℃, Tc 113℃, Total Calories 142 J / g / MWD 3.94- FB420H : MI 1.1 g / 10min / Density 0.950 / Tm 129℃, Tc 116℃, Total Calories 186 J / g / MWD 17.7- UF420H: MI 1.1 g / 10min / Density 0.950 / Tm 129℃, Tc 116℃, Total Calories 186 J / g / MWD 6.57

[0071]

[0072] Referring to Table 1, it can be confirmed that a biaxially stretched film manufactured from a polyethylene resin composition having a specific level of total heat capacity, molecular weight distribution and crystallinity by mixing a copolymer of ethylene and an olefin having 4 to 10 carbon atoms and having different densities within a certain range according to the present invention (Example) has excellent stretching properties while also having excellent transparency and low shrinkage properties.

[0073] In this regard, (B) when the copolymer alone or (A) when the copolymer content is below a certain level (Comparative Examples 1 to 3), the molecular weight distribution is relatively narrow, the DSC total heat capacity is low, and the crystallinity after MD stretching is low, resulting in the occurrence of patterns and also in a decrease in shrinkage characteristics.

[0074] In addition, (A) in the case of the copolymer alone (Comparative Example 5), it was found that unevenness occurred during sheet molding, which resulted in breakage due to uneven stretching during MD stretching, making stretching impossible, and (B) in the case where the copolymer content did not reach a certain level (Comparative Example 4), it was found that the DSC total heat was high, resulting in reduced transparency.

[0075] In addition, when a copolymer having a narrow molecular weight distribution is used as the (A) copolymer (Comparative Example 6), it can be seen that the molecular weight distribution of the final resin composition becomes narrow, resulting in a decrease in sheet formability, tensile strength, and shrinkage characteristics.

[0076]

[0077] The preferred embodiments of the present invention have been described in detail above. The description of the present invention is provided for illustrative purposes only, and those skilled in the art will readily appreciate that other specific modifications can be readily made without altering the technical spirit or essential features of the present invention.

[0078] Accordingly, the scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning, scope and equivalent concepts of the claims should be interpreted as being included in the scope of the present invention.

Claims

1. (A) 1 to 40 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.945 to 0.955 g / cm3; and (B) 60 to 99 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.920 to 0.930 g / cm3; Including, A polyethylene resin composition for a biaxially oriented film having a total calorie of 150 to 170 J / g as determined by DSC (Differential Scanning Calorimeter) analysis, a molecular weight distribution (MWD, Mw / Mn) of 10 to 20, a crystallinity of 45 to 50% before MD (Machine Direction) stretching as measured by the following method, and a crystallinity of 80% or more after MD stretching: [measurement method] For the above resin composition, a sheet is manufactured using a multilayer film molding machine under the conditions of a cooling roll temperature of 35 to 45°C, an extruder temperature of 240°C, and a line speed of 1.2 m / min, and the sheet is stretched 5 times using an MD stretching unit under the conditions of a preheating temperature of 118°C, a stretching temperature of 116°C, and a line speed of 1.2 m / min, and the crystallinity is measured for each sheet before and after the MD stretching, and the crystallinity is measured according to the following mathematical equation 1 for peaks having an FWHM (Full Width at Half Maximum) of less than 1.0 generated by X-ray diffraction analysis (XRD). <Mathematical formula 1> Crystallinity (%) = (Area of ​​crystalline peak / (Area of ​​crystalline peak + Area of ​​amorphous peak)) × 100.

2. In paragraph 1, A polyethylene resin composition for a biaxially oriented film, characterized in that the above (A) copolymer has a melting index (190°C, 2.16 kg load) of 0.6 to 1.2 g / 10 min, and the above (B) copolymer has a melting index (190°C, 2.16 kg load) of 1.2 to 2.5 g / 10 min.

3. In paragraph 1, A polyethylene resin composition for a biaxially oriented film, characterized in that the resin composition has a melting index (190°C, 2.16 kg load) of 1 to 2 g / 10 min and a density of 0.930 to 0.940 g / cm3.

4. A biaxially oriented film comprising a resin composition according to any one of claims 1 to 3.

5. In paragraph 4, The above film is a biaxially oriented film characterized in that the shrinkage in the longitudinal (MD) and transverse (TD) directions is each less than 5% in the following measurement method, the tensile strength in the longitudinal and transverse directions is 700 kgf / cm2 or more and 1,800 kgf / cm2 or more, respectively, and the haze is 5% or less: [measurement method] A biaxially stretched film having a thickness of 30 ㎛ was manufactured under the conditions of a film width of 8 m, a molding speed of 200 m / min, a longitudinal stretch ratio of 5 times (preheating temperature of 114 to 118°C, stretching temperature of 115°C, and annealing temperature of 110 to 115°C), a transverse stretch ratio of 9 times (preheating temperature of 125 to 137°C, stretching temperature of 125 to 128°C, and annealing temperature of 130 to 133°C) for a sheet molded with the above resin composition, and the shrinkage rate was measured by measuring the reduced lengths in the longitudinal and transverse directions after 5 minutes in a convection oven at 100°C for a biaxially stretched film specimen (10 x 10 cm). A tensile tester (model name: Instron4466) was used for the specimen according to the regulations of ASTM D882, with a load cell of 100 N and The tensile strength was measured under the condition of a test speed of 500 mm / min, and the haze was measured for the specimen using a haze meter (model name: NDH5000) according to the regulations of ASTM D1003.