Polyethylene resin composition for biaxially oriented film and biaxially oriented film comprising same

Abstract

A polyethylene resin composition for a biaxially oriented film, which can be molded by a biaxial stretching machine in a wide stretching temperature range and has improved mechanical properties and transparency as well as excellent stretching properties, is disclosed. The present invention provides the polyethylene composition for biaxially oriented film, comprising (A) 10-50 wt% of a copolymer of ethylene and C4-C10 olefin, the copolymer having a density of 0.880-0.910 g / cm3; (B) 50-90 wt% of a copolymer of ethylene and C4-C10 olefin, the copolymer having a density of 0.935-0.955 g / cm3, wherein, according to cross-fractionation chromatography (CFC) analysis, a fraction eluted at a temperature of 50℃ or less is 16-40 wt%, a fraction eluted at a temperature of 91℃ or more is 30-60 wt%, and a molecular weight distribution (MWD, Mw / Mn) is 8-20.

Description

Polyethylene resin composition for biaxially oriented film and biaxially oriented film comprising the same

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

[0002] This application claims priority to and the benefit of Republic of Korea Patent Application No. 10-2023-0166030, filed November 24, 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] In the EU, a packaging consultative body (CEPLEX, A Circular Economy for Flexible Packaging) has been formed by resin makers, film producers, converters, and food / product brand owners who produce polyethylene film raw materials. This is shifting the technological trend from the existing multilayer film-centered packaging using different materials to single-material packaging using a single polyolefin series and some barrier materials. This is aimed at ensuring recyclability for packaging applications and fostering an industry transition toward a circular economy and energy efficiency. The EU is enacting and implementing transnational regulations. If these efforts become tangible regulations, most packaging industries will require recyclability and energy circulation as essential properties, in addition to the current packaging trend reflecting diverse characteristics for each application.

[0006] In addition, high-density biaxially oriented polyethylene resin compositions are being researched and developed to enhance heat resistance for the purpose, but to date, no case has been presented for a film composition with satisfactory stretching characteristics and mechanical properties.

[0007] In addition, in the case of North America, as the recovery and recycling system for polyethylene products is being improved and established, the single-material flow is expected to become mainstream. Some companies are focusing on single-material polyethylene 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.

[0008] 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 form a single material may be in line with this development trend, but there has not yet been a case presented that shows satisfactory stretching characteristics as polyethylene that can be molded with a biaxial stretching machine.

[0009] 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 strength characteristics when biaxially stretched with the composition actually presented.

[0010] Japanese Patent No. 4498913 discloses a biaxially oriented ethylene polymer multilayer film that is easily torn in either the longitudinal or transverse directions, has excellent transparency and shrinkage properties, and has excellent heat sealing and bending resistance. However, it does not mention a method for improving mechanical properties while widening the processing range.

[0011] The present invention aims to provide a polyethylene resin composition for a biaxially oriented film having improved mechanical properties and transparency, as well as excellent stretching properties, which can be formed by a biaxial stretching machine in a wide stretching temperature range, and a biaxially oriented film comprising the same.

[0012] In order to solve the above problem, the present invention provides a polyethylene resin composition for a biaxially oriented film, comprising (A) 10 to 50 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms and having a density of 0.880 to 0.910 g / cm3; and (B) 50 to 90 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms and having a density of 0.935 to 0.960 g / cm3; wherein, through CFC (Cross-Fractionation Chromatography) analysis, a fraction eluted at a temperature of 50°C or lower is 16 to 40 wt%, a fraction eluted at a temperature of 91°C or higher is 30 to 60 wt%, and a molecular weight distribution (MWD, Mw / Mn) is 8 to 20.

[0013] 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 4 to 25 g / 10 min, and the copolymer (B) has a melting index (190°C, 2.16 kg load) of 0.2 to 1.5 g / 10 min.

[0014] In addition, the above (B) copolymer provides a polyethylene resin composition for a biaxially oriented film, characterized in that the weight average molecular weight (Mw) is 180,000 to 250,000 g / mol and the molecular weight distribution (MWD, Mw / Mn) is 10 to 30.

[0015] 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 0.5 to 3 g / 10 min and a density of 0.920 to 0.955 g / cm3.

[0016] In order to solve the above-mentioned further problem, the present invention provides a biaxially oriented film comprising a resin composition.

[0017] In addition, the film provides a biaxially oriented film characterized in that the film has a longitudinal and transverse tensile strength of 800 kgf / ㎠ or more, a haze of 10% or less, and a shrinkage rate of 5% or less, measured under the following conditions.

[0018] [measurement method]

[0019] Using the above resin composition, a biaxially stretched film having a thickness of 30 ㎛ and a width of 1 m was manufactured under the conditions of a molding speed of 100 m / min, a longitudinal (MD) stretch ratio of 5 times and a stretch temperature of 105 to 120°C, a transverse (TD) stretch ratio of 9 times and a stretch temperature of 120 to 130°C, and the tensile strength of the biaxially stretched film specimen was measured using a tensile tester (model name: Instron, 4466) according to the provisions of ASTM D882 under the conditions of a load cell of 100 N and a test speed of 500 mm / min, and the haze of the specimen was measured using a Haze meter (model name: Nippon Denshoku, NDH5000) according to the provisions of ASTM D1003, and the biaxially stretched film was cut and sampled in a square shape of 50 mm × 50 mm and subjected to a cycle at 100°C. After placing in a convection oven for 5 minutes, the length dimension is measured, and the longitudinal (MD) and transverse (TD) shrinkage ratios are calculated according to the following mathematical formula 1;

[0020] [Mathematical Formula 1]

[0021] .

[0022] According to the present invention, a polyethylene resin composition having a molecular weight distribution at a specific level and a fractional characteristic according to a specific CFC analysis, which is a mixture of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms and having different densities within a certain range, can be provided, which is moldable by a biaxial stretching machine in a wide stretching temperature range and has excellent stretching characteristics as well as improved mechanical properties and transparency for a biaxially oriented film, and a biaxially oriented film comprising the same.

[0023] Figure 1 is a graph showing the results of measuring the preheating temperature and time range that enable stretching 5 times MD and 9 times TD without fracture in Experimental Example 1.

[0024] 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.

[0025]

[0026] The present inventors have discovered that, in a situation where a composition that can be molded in a biaxial stretching machine over a wide temperature range and exhibits satisfactory stretching characteristics when replacing the layer previously used with BOPA or BOPET with BOPE to make it a single material has not yet been presented, a copolymer of ethylene and an olefin having 4 to 10 carbon atoms with different densities within a certain range is mixed, and a polyethylene resin composition having a fractionation characteristic according to a specific CFC (Cross-Fractionation Chromatography) analysis and a molecular weight distribution at a specific level can be molded in a biaxial stretching machine over a wide temperature range, and excellent stretching characteristics are achieved along with improved mechanical properties and transparency, leading to the present invention.

[0027] Accordingly, the present invention discloses a polyethylene resin composition for a biaxially oriented film, comprising (A) 10 to 50 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.880 to 0.910 g / cm3; and (B) 50 to 90 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.935 to 0.960 g / cm3; wherein, as determined by CFC (Cross-Fractionation Chromatography) analysis, a fraction eluted at a temperature of 50°C or lower is 16 to 40 wt%, a fraction eluted at a temperature of 91°C or higher is 30 to 60 wt%, and a molecular weight distribution (MWD, Mw / Mn) is 8 to 20.

[0028] In the present invention, the (A) copolymer is an ultra-low density polyethylene, and has a density of 0.880 to 0.910 g / cm3, preferably 0.890 to 0.900 g / cm3. If the density is outside the above range, biaxial stretching molding is difficult.

[0029] 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 4 to 25 g / 10 min, and preferably 10 to 20 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 expanding the temperature range for stretching processing, 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.

[0030] The above (A) copolymer may be included in an amount of 10 to 50 wt%, and preferably 20 to 40 wt%, of the entire resin composition. If the (A) copolymer content is outside the above range, biaxial stretching molding is also difficult.

[0031] In the present invention, the (B) copolymer is a linear low-density polyethylene, and has a density of 0.935 to 0.960 g / cm3, preferably 0.940 to 0.960 g / cm3. If the density is outside the above range, biaxial stretching molding is difficult.

[0032] 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, and may have a melt index (190°C, 2.16 kg load) of 0.2 to 1.5 g / 10 min, and preferably 0.5 to 1.0 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 expanding the temperature range for stretching processing, 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.

[0033] The above (B) copolymer may be included in an amount of 50 to 90 wt%, and preferably 60 to 80 wt%, of the entire resin composition. If the (B) copolymer content is outside the above range, biaxial stretching molding is also difficult.

[0034] 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 0.5 to 3 g / 10 min, preferably 1 to 2 g / 10 min, and the density may be 0.920 to 0.955 g / cm3, preferably 0.930 to 0.955 g / cm3.

[0035] In the present invention, it was confirmed that the stretching characteristics and stretching processing temperature characteristics can be improved by controlling the molecular weight characteristics of the resin composition, and specifically, when the (B) copolymer has a weight average molecular weight (Mw) of 180,000 to 250,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 10 to 30, preferably a weight average molecular weight (Mw) of 200,000 to 230,000 g / mol, and a molecular weight distribution (MWD, Mw / Mn) of 15 to 20, and the molecular weight distribution (MWD, Mw / Mn) of the polyethylene resin composition is controlled to 8 to 20, preferably 9 to 15, the composition can be molded with a biaxial stretching machine in a wide stretching temperature range, and excellent stretching characteristics can be achieved along with improved mechanical properties and transparency.

[0036] In addition, in the present invention, it was confirmed that when the polyethylene resin composition of the above composition has a fraction characteristic according to a certain CFC analysis when molded into a biaxially oriented film, it exhibits smooth moldability and implements satisfactory strength characteristics, and the low-temperature stretching characteristics are improved, thereby further expanding the stretching processing temperature range. Specifically, the resin composition according to the present invention has a fraction eluted at a temperature of 50°C or lower through CFC analysis of 16 to 40 wt%, and a fraction eluted at a temperature of 91°C or higher of 30 to 60 wt%, and preferably, a fraction eluted at a temperature of 50°C or lower of 25 to 40 wt%, and a fraction eluted at a temperature of 91°C or higher of 30 to 50 wt%.

[0037] 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.

[0038] 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.

[0039] The polyethylene resin composition for a biaxially oriented film according to the present invention can be subjected to biaxial stretching molding in a wide stretching temperature range, and has excellent stretching characteristics along with improved mechanical properties and transparency. Specifically, the biaxially oriented film manufactured from the polyethylene resin composition for a biaxially oriented film according to the present invention may have a tensile strength in the longitudinal and transverse directions of 800 kgf / cm2 or more, preferably 1,200 kgf / cm2 or more, measured under the following conditions, a haze of 10% or less, preferably 2% or less, and a shrinkage of 5% or less.

[0040] [measurement method]

[0041] Using the above resin composition, a biaxially stretched film having a thickness of 30 ㎛ and a width of 1 m was manufactured under the conditions of a molding speed of 100 m / min, a longitudinal (MD) stretch ratio of 5 times and a stretch temperature of 105 to 120°C, a transverse (TD) stretch ratio of 9 times and a stretch temperature of 120 to 130°C, and the tensile strength of the biaxially stretched film specimen was measured using a tensile tester (model name: Instron, 4466) according to the provisions of ASTM D882 under the conditions of a load cell of 100 N and a test speed of 500 mm / min, and the haze of the specimen was measured using a Haze meter (model name: Nippon Denshoku, NDH5000) according to the provisions of ASTM D1003, and the biaxially stretched film was cut and sampled in a square shape of 50 mm × 50 mm and subjected to a cycle at 100°C. After placing in a convection oven for 5 minutes, the length dimension is measured, and the longitudinal (MD) and transverse (TD) shrinkage ratios are calculated according to the following mathematical formula 1;

[0042] [Mathematical Formula 1]

[0043] .

[0044] Hereinafter, the present invention will be described in more detail through specific examples and comparative examples. In the examples and comparative examples, density, melt index, thermal properties, molecular weight properties, and CFC analysis were measured according to the following methods.

[0045] [measurement method]

[0046] (1) Density

[0047] Measured according to ASTM D1505.

[0048] (2) Melt Index (MI)

[0049] Measured under conditions of 190℃ and 2.16 kg load according to ASTM D1238.

[0050] (3) Thermal characteristics

[0051] 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 by heating the sample to 200°C at a heating rate of 10°C / min and then cooling it to -50°C at -10°C / min.

[0052] (4) Molecular weight characteristics

[0053] It was measured using GPC analysis method according to ASTM D3536.

[0054] (5) CFC (Cross-Fractionation Chromatography) analysis

[0055] CFC analyses were performed on a CFC instrument from Polymer Char, Valencia, Spain. The instrument included a TREF column in the first dimension, a GPC column set in the second dimension, and an infrared detector (IR4 from Polymer Char) downstream of the GPC column. The sample to be analyzed was dissolved in 1,2,3-trichlorobenzene at a concentration of approximately 2.5 mg / mL by stirring at 150°C for 80 minutes. The solution was loaded onto the center of the TREF column, stabilized at 100°C for 45 minutes, and then slowly cooled (0.5°C / min) to 35°C to crystallize the polymer. After a 10-minute cryostat, the soluble fraction was injected onto the GPC column. All GPC analyses were performed using 1,2,4-trichlorobenzene as the solvent, at a flow rate of 1 mL / min, a column temperature of up to 140°C, and in "nested GPC injection" mode.

[0056]

[0057] Examples and Comparative Examples

[0058] In the case of Examples, Comparative Examples 2 and 3, two copolymers having the properties shown in Table 1 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. In the case of Comparative Example 1, a commercially available polyethylene resin composition (Dow Chemical, INNATE TF80) was prepared separately.

[0059]

[0060] Measurement items Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Final melting index (190℃, 2.16 kg) 1.7 1.8 0.8 1.4 Final density (g / cm 3 )0.9280.9280.9330.930DSCmelting point(Tm)125.3125.1125.6125.5Crystallization temperature(Tc)113.3113.0113.1112.9GPCMw115,800107,700184,400166,700Mz335,100318,700816.500689,700MWD(Mw / Mn)4.173.9411.789.71Comonomer typeC8C4 / C8C4 / C8C4a-TREFWeight fraction(%)<50℃16.414.615.234.5> 91 ℃52.847.340.136.6Copolymer-ACBCBDComonomer typeC4C8C4C8C4C4Melt index(190℃, 2.16 kg)-1.54.00.84.00.818.0Density(g / cm 3 )-0.9380.9050.9450.9050.9450.890Weight average molecular weight (Mw)113,80094,400219,50094,400219,50054,000Molecular weight distribution (MWD, Mw / Mn)-3.884.1215.94.1215.92.14Composition ratio (weight %)-703070307030* Note- Copolymer A and B: Linear low density polyethylene- Copolymer C and D: Ultra low density polyethylene

[0061]

[0062] Experimental Example 1

[0063] In this experiment, the possibility of 5×9 stretching at each temperature was confirmed using a laboratory stretching machine. To this end, compression molding was performed on each pellet manufactured above using a 190℃ press machine, and sheet samples with a thickness of 1.3 mm, width of 10 cm, and length of 10 cm were manufactured. After that, preheating was performed under specific temperature and time conditions using a laboratory stretching machine, and after mechanical stretching 5 times in the MD (longitudinal direction) and 9 times in the TD (transverse direction) mechanical stretching (sequential stretching) was performed. The preheating temperature and time range where the stretched film could be stretched 5 times in the MD and 9 times in the TD without fracture were measured, and the results are shown in Fig. 1.

[0064] Referring to FIG. 1, when the molecular weight distribution of the resin composition is narrow, such as 5 or less (Comparative Example 2), the processing temperature condition is very narrow, such as less than 3°C, due to reduced extensibility, whereas when the molecular weight distribution is wide, such as 9 or more (Example), the preheating temperature condition is widened to about 7°C, and it can be confirmed that the preheating temperature condition is improved by 1°C compared to the existing C8-based commercial product (Comparative Example 1).

[0065] Meanwhile, when comparing the characteristics of each manufactured resin, the melting point and crystallization temperature based on DSC are not significantly different, but when comparing Comparative Examples 2 and 3, it can be confirmed that when a copolymer having a wide molecular weight characteristic of a weight average molecular weight (Mw) of 200,000 or more and a molecular weight distribution of 15 or more is applied under the same weight ratio conditions, it is more advantageous in stretchability.

[0066] In addition, when comparing Comparative Example 3 and the Examples, although the copolymers having the above-mentioned molecular weight characteristics are applied, when a copolymer that increases the elution weight fraction below 50°C based on the CFC analysis standard is applied (Example), it can be seen that the low-temperature elongation characteristics are improved, and the elongation in the low-temperature range is improved by about 2°C or more compared to Comparative Example 3. Through this, it can be concluded that when a resin composition having the elution weight fraction below 50°C based on the CFC analysis standard is applied at a certain level or higher and having a wide molecular weight distribution is applied, the elongation characteristics are further improved, and a wider range of elongation processing temperature characteristics can be implemented.

[0067]

[0068] Experimental Example 2

[0069] This experiment was conducted on the evaluation of a tenter-frame biaxial stretching line, and, as in the evaluation using the above-mentioned laboratory stretching machine, sequential stretching (stretching in the MD direction followed by stretching in the TD direction (TDO)) was used. Stretching in the MD direction (MDO) is performed by attaching the sheet extruded through the T-die to rolls set to a temperature below the melting point of the resin to perform preheating necessary for stretching, and then performing mechanical stretching and resin orientation within the gap between rolls with different rotation speeds after a certain number of preheating rolls. Through this, stretching was performed 5 times in the MD direction, as in the laboratory stretching machine evaluation. Thereafter, the edges of the stretched film were inserted into a heating chamber with appropriate clips biting them, preheating was performed for a certain distance, and then stretching was performed approximately 9 times in the TD direction. In TDO stretching, compared to MDO stretching, which utilizes a roll-bonding method with relatively high thermal energy exchange efficiency, heated air is blown onto the film to be stretched, supplying the thermal energy required for stretching. This process occurs at a temperature higher than the MDO stretching temperature. While the stretching temperature is typically set above the melting point of the resin, the film residence time is very short, so the temperature is set above the melting point. The conditions for the detailed biaxial stretching line process are shown in Table 2 below.

[0070]

[0071] Processing temperature in the extruder 230~250℃ Extrusion cooling roll temperature 30~60℃ Extrusion cooling roll speed 10~40 m / min MDO stretching roll temperature 105~120℃ MDO stretching ratio 3:1~5:1 TDO stretching zone temperature 120~125℃ TDO stretching ratio 9:1

[0072]

[0073] Under the above conditions, the resin composition according to each comparative example and example was extruded to manufacture a film under the processing conditions shown in Table 3 below using a tenter frame BOPE line, and the physical properties of the manufactured film were measured by the following method, and the results are shown in Table 4 below.

[0074] [measurement method]

[0075] (1) Tensile strength

[0076] Using the above resin composition, a biaxially oriented film having a thickness of 30 ㎛ and a width of 1 m was manufactured under the conditions of a molding speed of 100 m / min, a longitudinal (MD) stretching ratio of 5 times, and a stretching temperature of 105 to 120°C, a transverse (TD) stretching ratio of 9 times, and a stretching temperature of 120 to 130°C. The tensile strength of the biaxially oriented film specimen was measured using a tensile tester (model name: Instron, 4466) according to the regulations of ASTM D882 under the conditions of a load cell of 100 N and a test speed of 500 mm / min.

[0077] (2) Haze

[0078] For the above specimen, the haze was measured using a haze meter (model name: Nippon Denshoku, NDH5000) according to the ASTM D1003 regulations.

[0079] (3) Heat shrinkage rate

[0080] A biaxially stretched film was manufactured in the same manner as in the above tensile strength measurement, and a 50 mm × 50 mm square shape was cut and sampled from the biaxially stretched film, placed in a 100°C convection oven for 5 minutes, and then the length dimension was measured. The longitudinal (MD) and transverse (TD) shrinkage ratios were calculated according to the following mathematical equation 1.

[0081] [Mathematical Formula 1]

[0082]

[0083] (4) Modulus of Elasticity

[0084] A biaxially oriented film was manufactured using the same method as the above tensile strength measurement, and the tensile strength and elongation of the biaxially oriented film specimen were measured using a tensile tester (model name: Instron, 4466) according to the ASTM D882 regulations under the conditions of a load cell of 100 N and a test speed of 500 mm / min. In the stress-strain curve obtained through the above measurement method, a value corresponding to the tangent slope within the initial linear region was extracted and digitized as the elastic modulus.

[0085]

[0086] Processing Conditions MI (g / 10min) Density (g / cm3) MDO (℃_) TDO (℃_) Preheating Elongation Annealing Preheating Elongation Annealing InOutInOutInOutInOutComparative Example 11.70.928110106105105108132132122120130Comparative Example 21.80.928 Low MD Elongation Ratio Early BreakageComparative Example 30.80.933110107106106108134134123121132Example 1.40.930110105104104108131131120120128

[0087] Evaluation items MI (g / 10min) Density (g / cm3) Haze (%) Heat shrinkage (%) (100℃_ / 5min) Tensile strength (kgf / cm2) Elastic modulus (MPa) MDT DMDT DMDT D Comparative example 11.7 0.92 8 2.35 5 1, 1722, 007 346 5 11 Comparative example 21.8 0.92 8 Maximum elongation ratio: MD 3.6 Х TD 9 (breakage when MD elongation ratio increases) Comparative example 30.8 0.93 34.75 5 1, 304 2, 093 5 2 390 4 Example 1.4 0.93 0 1.45 5 1, 3142, 107 5 158 98

[0088]

[0089] Referring to Tables 3 and 4, first, when the molecular weight distribution of the resin composition was narrow to 5 or less (Comparative Example 2), the target stretching ratio of 5 times MD and 9 times TD was not achieved even with many temperature adjustments, and film breakage occurred in the TDO stretching zone at a stretching ratio of 3.6 times MD or more.

[0090] Next, when comparing the lowest elongation processing temperature conditions that can achieve MD 5 times and TD 9 times, it can be seen that when using a polyethylene resin composition having fraction characteristics according to a specific CFC analysis and having a specific level of molecular weight distribution according to the present invention (Example), it is possible to manufacture BOPE films at lower MDO and TDO temperature conditions than Comparative Examples 1 and 3, which is a result that proves that the processing temperature range is wide.

[0091] Here, due to the characteristic of widening the processing temperature range, there is an advantage in that transparency can be improved among the characteristics of the biaxially stretched polyethylene film. For example, when a film is manufactured under low stretching / annealing temperature conditions, the effect of improving film transparency can be obtained due to the small crystal size characteristic through a rapid crystallization time in the crystal structure within the film. In the case of a film manufactured using a resin composition according to an embodiment capable of stretching under low temperature conditions, it can be confirmed that it has lower haze compared to Comparative Examples 1 and 3. In addition, it can be confirmed that the tensile strength, heat shrinkage rate, and elastic modulus characteristics have properties equivalent to or higher than those of a commercial product (Comparative Example 1).

[0092]

[0093] 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.

[0094] 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) 10 to 50 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.880 to 0.910 g / cm3; and (B) 50 to 90 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.935 to 0.960 g / cm3; Including, A polyethylene resin composition for a biaxially oriented film, wherein a fraction eluted at a temperature of 50°C or lower is 16 to 40 wt% as determined by CFC (Cross-Fractionation Chromatography), a fraction eluted at a temperature of 91°C or higher is 30 to 60 wt%, and a molecular weight distribution (MWD, Mw / Mn) is 8 to 20.

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 4 to 25 g / 10 min, and the above (B) copolymer has a melting index (190°C, 2.16 kg load) of 0.2 to 1.5 g / 10 min.

3. In paragraph 1, A polyethylene resin composition for a biaxially oriented film, characterized in that the above (B) copolymer has a weight average molecular weight (Mw) of 180,000 to 250,000 g / mol and a molecular weight distribution (MWD, Mw / Mn) of 10 to 30.

4. 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 0.5 to 3 g / 10 min and a density of 0.920 to 0.955 g / cm3.

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

6. In paragraph 5, The above film is a biaxially oriented film characterized in that the longitudinal and transverse tensile strengths measured under the following conditions are each 800 kgf / ㎠ or more, the haze is 10% or less, and the shrinkage is 5% or less: [measurement method] Using the above resin composition, a biaxially stretched film having a thickness of 30 ㎛ and a width of 1 m was manufactured under the conditions of a molding speed of 100 m / min, a longitudinal (MD) stretch ratio of 5 times and a stretch temperature of 105 to 120°C, a transverse (TD) stretch ratio of 9 times and a stretch temperature of 120 to 130°C, and the tensile strength of a biaxially stretched film specimen was measured using a tensile tester (model name: Instron, 4466) in accordance with the provisions of ASTM D882 under the conditions of a load cell of 100 N and a test speed of 500 mm / min, and the haze of the specimen was measured using a haze meter (model name: Nippon Denshoku, NDH5000) in accordance with the provisions of ASTM D1003, and the biaxially stretched film was cut into a square shape of 50 mm × 50 mm and sampled and subjected to a cyclic test at 100°C. After being placed in a convection oven for 5 minutes, the length dimensions were measured and the longitudinal (MD) and transverse (TD) shrinkage ratios were calculated according to the following mathematical formula 1; [Mathematical Formula 1] .

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