High-density polyethylene resin composition for biaxially oriented film

Abstract

Disclosed is a polyethylene resin composition for a biaxially oriented film, which can be molded by a biaxial stretching machine and exhibits excellent stretching properties. The present invention provides a polyethylene resin composition for a biaxially oriented film, comprising: (A) 60 to 95 wt% of a copolymer of ethylene and olefin of 4 to 10 carbon atoms, having a density of 0.950 to 0.970 g / ㎤; and (B) 5 to 40 wt% of a copolymer of ethylene and olefin of 4 to 10 carbon atoms, having a density of 0.870 to 0.920 g / ㎤, wherein the resin composition has a melt index (190℃, 2.16-kg load) of 0.5 to 3 g / 10 min and a density of 0.925 to 0.955 g / ㎤.

Description

High-density polyethylene resin composition for biaxially oriented films

[0001] The present invention relates to a polyethylene resin composition, and more particularly, to a high-density polyethylene resin composition for a biaxially oriented film.

[0002] This application claims priority to and the benefit of Republic of Korea Patent Application No. 10-2023-0162633, filed November 21, 2023, which is incorporated herein by reference in its entirety.

[0003] Environmental issues arising from plastic use are by no means a new phenomenon and require ongoing attention and resolution. The environmental issues, which have become even more prominent since the COVID-19 pandemic due to the indiscriminate use of packaging, have raised awareness not only among companies but also among consumers. The plastics manufacturing industry is responding sensitively to the emerging market environment, including the issue of marine plastics. Container and packaging materials, which account for a significant portion of the market, are no exception, and the need to address environmental issues beyond mere production, including plastic waste and greenhouse gas reduction, is growing. Recognizing this need, plastics manufacturing companies are developing materials that can reduce environmental burden. Globally, there is a growing movement to develop recyclable, single-material products and bioplastics that contribute to carbon dioxide (CO2) reduction.

[0004] The 3R movement is a representative global response to plastic environmental issues. These 3Rs consist of reducing usage (Reduce), using alternatives (Replace), and recycling and reuse (Recycle, Reuse). BOPE (bi-oriented polyethylene) can address plastic environmental issues related to single materials within the 3Rs, particularly within the recycling and reuse categories. Because BOPE is biaxially stretched in the machine direction (MD) and transverse direction (TD), it offers superior transparency compared to standard PE film. Furthermore, its orientation enhances the film's mechanical strength and impact resistance. Furthermore, biaxial stretching reduces thickness, which can help reduce the use of plastic products. 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 conform to this development trend, but there is no case yet presented that shows satisfactory stretching characteristics as polyethylene that can be molded with a biaxial stretching machine and used as first-grade paper (printing surface) for easy recycling.

[0005] 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 stretching characteristics during biaxial stretching with the actually presented composition.

[0006] The present invention aims to provide a polyethylene resin composition for a biaxially oriented film that can be molded using a biaxial stretching machine and exhibits excellent stretching properties.

[0007] In order to solve the above problem, the present invention provides a polyethylene resin composition for a biaxially oriented film, comprising (A) 60 to 95 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.950 to 0.970 g / cm3; and (B) 5 to 40 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.870 to 0.920 g / cm3; wherein the resin composition has a melt index (190°C, 2.16 kg load) of 0.5 to 3 g / 10 min and a density of 0.925 to 0.955 g / cm3.

[0008] In addition, the resin composition provides a polyethylene resin composition for a biaxially oriented film, characterized in that the longitudinal and transverse tensile strengths measured by the following method are 700 kgf / ㎠ or more and 1,500 kgf / ㎠ or more, respectively, the heat shrinkage rate is 5% or less, and the modulus of elasticity is 300 MPa or more and 600 MPa or more, respectively.

[0009] [measurement method]

[0010] A biaxially stretched film having a thickness of 30 ㎛ was manufactured under the conditions of a longitudinal stretch ratio of 5 to 6.5 times (preheating temperature 114 to 118°C, stretching temperature 105 to 116°C, and annealing temperature 110°C) and a transverse stretch ratio of 9 times (preheating temperature 134 to 156°C, stretching temperature 116 to 130°C, and annealing temperature 120 to 125°C) for a sheet molded with the above resin composition, and a biaxially stretched film specimen (10 x 10 cm) was heat treated in a convection oven at 100°C for 1 minute, and the reduced lengths in the longitudinal and transverse directions were measured to measure the shrinkage rate, 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 a test speed of 500 mm / min. The tensile strength was measured as a condition, and the value corresponding to the tangent slope within the initial linear region was extracted from the stress-strain curve obtained through the above measurement method, and this was quantified as the elastic modulus.

[0011] According to the present invention, a polyethylene resin composition having a specific level of melting index and density, 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 a polyethylene resin composition for a biaxially oriented film that can be molded using a biaxial stretching machine and has excellent stretching properties.

[0012] 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.

[0013]

[0014] The inventors of the present invention have discovered that a polyethylene resin composition having a specific melting index and density while mixing a copolymer of ethylene and an olefin having 4 to 10 carbon atoms with different densities within a certain range can be molded with a biaxial stretching machine and exhibits excellent stretching properties in a situation where a composition exhibiting excellent stretching properties has not yet been presented in replacing the layer previously used with BOPA or BOPET with BOPE and forming a single material, and this has led to the invention.

[0015] Accordingly, the present invention discloses a polyethylene resin composition for a biaxially oriented film, comprising (A) 60 to 95 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.950 to 0.970 g / cm3; and (B) 5 to 40 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.870 to 0.920 g / cm3; wherein the resin composition has a melt index (190°C, 2.16 kg load) of 0.5 to 3 g / 10 min and a density of 0.925 to 0.955 g / cm3.

[0016] In the present invention, the (A) copolymer is a high-density polyethylene having a density of 0.950 to 0.970 g / cm3, preferably 0.955 to 0.960 g / cm3. If the density is outside the above range, biaxial stretching molding is difficult.

[0017] 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 0.5 to 3 g / 10 min, and preferably 0.6 to 1.5 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 the 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.

[0018] The above (A) copolymer may be included in an amount of 60 to 95 wt%, and preferably 70 to 90 wt%, of the entire resin composition. If the (A) copolymer content is outside the above range, the elongation properties may not be improved.

[0019] In the present invention, the (B) copolymer is a low-density polyethylene having a density of 0.870 to 0.920 g / cm3, preferably 0.880 to 0.910 g / cm3. If the density is outside the above range, biaxial stretching molding is difficult.

[0020] 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 3 to 30 g / 10 min, and preferably 4 to 20 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 the stretching properties, 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.

[0021] The above (B) copolymer may be included in an amount of 5 to 40 wt% of the total resin composition, and preferably 10 to 30 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.

[0022] 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 1.3 g / 10 min, and the density may be 0.925 to 0.955 g / cm3, preferably 0.950 to 0.955 g / cm3.

[0023] In the present invention, it was confirmed that the elongation characteristics can be improved by mixing a copolymer of ethylene and an olefin having 4 to 10 carbon atoms with different densities within a certain range and controlling the melt index and density of the final resin composition, and specifically, a polyethylene resin composition for a biaxially oriented film can be provided, wherein the longitudinal and transverse tensile strengths measured by the following method are 700 kgf / cm2 or more and 1,500 kgf / cm2 or more, preferably 1,000 kgf / cm2 or more and 2,000 kgf / cm2 or more, respectively, the heat shrinkage rate is 5% or less and preferably 3% or less, and the modulus of elasticity is 300 MPa or more and 600 MPa or more, preferably 800 MPa or more and 1,000 MPa or more, respectively.

[0024] [measurement method]

[0025] A biaxially stretched film having a thickness of 30 ㎛ was manufactured under the conditions of a longitudinal stretch ratio of 5 to 6.5 times (preheating temperature 114 to 118°C, stretching temperature 105 to 116°C, and annealing temperature 110°C) and a transverse stretch ratio of 9 times (preheating temperature 134 to 156°C, stretching temperature 116 to 130°C, and annealing temperature 120 to 125°C) for a sheet molded with the above resin composition, and a biaxially stretched film specimen (10 x 10 cm) was heat treated in a convection oven at 100°C for 1 minute, and the reduced lengths in the longitudinal and transverse directions were measured to measure the shrinkage rate, 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 a test speed of 500 mm / min. The tensile strength was measured as a condition, and the value corresponding to the tangent slope within the initial linear region was extracted from the stress-strain curve obtained through the above measurement method, and this was quantified as the elastic modulus.

[0026] 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.

[0027] 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.

[0028] Hereinafter, the present invention will be described in more detail through specific examples and comparative examples. In the examples and comparative examples, density and melt index were measured according to the following methods.

[0029] [measurement method]

[0030] (1) Density

[0031] Measured according to ASTM D1505.

[0032] (2) Melt Index (MI)

[0033] Measured under conditions of 190℃ and 2.16 kg load according to ASTM D1238.

[0034]

[0035] Examples and Comparative Examples

[0036] The copolymers shown in Table 1 below were mixed and fed into a twin-screw extruder, melt-mixed at 180 to 220°C, and a pellet-shaped polyethylene resin composition having the properties shown in Table 1 was prepared. For comparative examples, commercial products were prepared.

[0037]

[0038] Exam example

[0039] For the polyethylene resin composition manufactured or prepared above, a stretched film was manufactured and its properties were measured by the following method, and the results are shown in Table 1 below.

[0040] [Film properties]

[0041] After forming a sheet using the above resin composition using an extruder set to a maximum of 260°C, a biaxially stretched film having a thickness of 30 μm was manufactured under the conditions of a longitudinal stretching ratio of 5 to 6.5 times (preheating temperature 114 to 118°C, stretching temperature 105 to 116°C and annealing temperature 110°C) and a transverse stretching ratio of 9 times (preheating temperature 134 to 156°C, stretching temperature 116 to 130°C and annealing temperature 120 to 125°C), and the maximum stretching ratio of the film was confirmed by adjusting the Stretching Ratio in the biaxial stretcher, and the shrinkage rate was measured by measuring the reduced lengths in the longitudinal and transverse directions after heat treatment for 1 minute in a convection oven at 100°C for a biaxially stretched film specimen (10 x 10 cm), and the specimen was measured according to the regulations of ASTM D882. 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 value corresponding to the tangent slope within the initial linear region was extracted from the stress-strain curve obtained through the above measurement method and quantified as the elastic modulus.

[0042]

[0043]

[0044]

[0045] Referring to Table 1, in the case of a biaxially oriented film manufactured from a polyethylene resin composition having a specific level of melting index and density by mixing a copolymer of ethylene and an olefin having 4 to 10 carbon atoms and having different densities in a certain range according to the present invention (Examples 1 to 6), the film has excellent stretching properties with a maximum stretching ratio of 5 to 6.5 times in the MD direction and 9 times in the TD direction, while also having excellent mechanical properties and heat shrinkage resistance, and in particular, has a density of 0.950 to 0.955 g / cm 3 It can be confirmed that the balance of mechanical properties and heat shrinkage resistance is dramatically improved under ideal conditions (Examples 5 and 6) where the melting index is within the range of 1 to 1.3.

[0046] In this regard, in the case of commercial products according to the comparative example, although the specific composition is unknown, the density is somewhat low and the melting index is somewhat high, and although the tensile strength is excellent, the elastic modulus is low and the heat shrinkage rate is high, so it can be seen that it has inferior characteristics in the printing process.

[0047]

[0048] 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.

[0049] 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) 60 to 95 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.950 to 0.970 g / cm3; and (B) 5 to 40 wt% of a copolymer of ethylene and an olefin having 4 to 10 carbon atoms, having a density of 0.870 to 0.920 g / cm3; A polyethylene resin composition for a biaxially oriented film comprising: 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 0.925 to 0.955 g / cm3.

2. In paragraph 1, The above resin composition is a polyethylene resin composition for a biaxially oriented film, characterized in that the longitudinal and transverse tensile strengths measured by the following methods are 700 kgf / ㎠ or more and 1,500 kgf / ㎠ or more, respectively, the heat shrinkage rate is 5% or less, and the modulus of elasticity is 300 MPa or more and 600 MPa or more, respectively: [measurement method] A biaxially stretched film having a thickness of 30 ㎛ was manufactured under the conditions of a longitudinal stretch ratio of 5 to 6.5 times (preheating temperature of 114 to 118°C, stretching temperature of 105 to 116°C, and annealing temperature of 110°C) and a transverse stretch ratio of 9 times (preheating temperature of 134 to 156°C, stretching temperature of 116 to 130°C, and annealing temperature of 120 to 125°C) for a sheet molded with the above resin composition, and a biaxially stretched film specimen (10 x 10 cm) was heat treated in a convection oven at 100°C for 1 minute, and the reduced lengths in the longitudinal and transverse directions were measured to measure the shrinkage rate, and the specimen was tested using a tensile tester (model name: Instron4466) according to the regulations of ASTM D882 at a load cell of 100 N and a test speed of 500 mm / min. The tensile strength was measured as a condition, and the value corresponding to the tangent slope within the initial linear region was extracted from the stress-strain curve obtained through the above measurement method, and this was quantified as the elastic modulus.

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