Polyethylene composition and oriented film comprising the same

Abstract

The present invention relates to a polyethylene composition capable of producing a stretched film having high shrink resistance, excellent film stretching processability and productivity, and an oriented film comprising the same.

Description

Technical Field

[0001] The present invention aims to provide a polyethylene composition and a stretch film comprising the polyethylene composition, the polyethylene composition being capable of producing a stretch film with high shrinkage resistance, excellent film stretching processing performance and productivity. Background Technology

[0002] Film products made of linear low-density polyethylene (LLDPE) and / or high-density polyethylene (HDPE) are widely used in the packaging industry, such as shopping bags, food and specialty packaging, and industrial liners. In these applications, a primary type of packaging film is used that maintains the shape of the item while packaging it, thus protecting it from impacts during display.

[0003] In particular, uniaxial or biaxially oriented polymer films are widely used in the packaging industry due to their excellent mechanical properties, productivity, and printability. Commercial packaging films typically use biaxially oriented polypropylene (BOPP), biaxially oriented polyethylene terephthalate (BOPET), or biaxially oriented polyamide (BOPA) as the printing layer and LLDPE film as the sealing layer. These composite materials are not recyclable, and with increasingly stringent packaging recycling regulations, the demand for single-material packaging films is growing. Therefore, research and development is underway to manufacture single-material packaging films by replacing the printed layer films with uniaxially oriented polyethylene (UPE) or biaxially oriented polyethylene (BOPE) films.

[0004] However, commercially available polyethylene (PE) resins lack sufficient tensile stability, and are prone to phenomena such as breakage and melting during stretching, making biaxial stretching difficult. To ensure tensile stability, products in the form of polyethylene compositions containing resins with low density and high melt index have been developed. However, these compositions exhibit low stiffness, high shrinkage, and poor heat resistance, making them unsuitable as polyethylene resins for uniaxial or biaxial stretch films.

[0005] In particular, stretch films, primarily used as packaging materials, are manufactured into final products through printing and coating processes. High tensile strength is required to ensure productivity and excellent film performance; and high heat resistance is also necessary because post-processing operations such as printing and coating are typically carried out at high temperatures.

[0006] Therefore, there is a need for a method to provide PE compositions for uniaxial or biaxial stretching, wherein the method selects a polyethylene resin having a molecular structure favorable to stretching and an appropriate composition, thereby exhibiting excellent tensile stability during film processing, high shrinkage resistance due to excellent heat resistance, and excellent film processing performance and productivity. Summary of the Invention

[0007] Technical issues The present invention aims to provide a polyethylene composition and a stretch film comprising the polyethylene composition, the polyethylene composition being capable of producing a stretch film with high shrinkage resistance, excellent film stretching processing performance and productivity.

[0008] Technical solution According to one embodiment of the present invention, When using the crystallization elution fraction (CEF) method to measure the relative proportions of peak areas of crystal fractions eluted at a given temperature (°C), The ratio of the peak area of ​​the low crystallinity fraction eluted above 70℃ and below 95℃ to the total peak area (CEF). ≤95℃≥70℃ The percentage is between 10% and 25%. The ratio of the peak area of ​​the highly crystalline fraction eluted above 100℃ to the total peak area (CEF) ≥100℃ The percentage is between 6% and 15%. Peak area ratio of highly crystalline fractions (CEF) ≥100℃ The ratio of peak area of ​​the low crystallinity fraction to the peak area of ​​the low crystallinity fraction (CEF) ≤95℃≥70℃ The ratio of ) to CEF ≥100℃ / CEF ≤95℃≥70℃ ) is above 0.24, and The density is 0.940 g / cm³. 3 Above and 0.970 g / cm 3 The following, and A polyethylene composition is provided.

[0009] According to another embodiment of the present invention, a stretch film comprising the polyethylene composition of the foregoing embodiments is provided.

[0010] Beneficial effects The superior effects provided by the polyethylene composition according to the present invention are that it enables the production of stretch films with high shrinkage resistance, excellent printability, good film processing performance and productivity, as well as excellent mechanical properties and tensile stability. Attached Figure Description

[0011] Figure 1 This is a crystallization elution fractionation (CEF) curve obtained from the polyethylene compositions of Example 1 and Comparative Example 1 according to one embodiment of the present invention.

[0012] Figure 2 This indicates a high crystallinity content (CEF). ≥100℃ ) and low crystallinity content (CEF) ≤95℃≥70℃The correlation distribution diagram between the high crystallinity content (CEF) and the polyethylene compositions of Examples 1 to 5 and Comparative Examples 1 to 10 according to an embodiment of the present invention is shown in the figure, with the total peak area as 100%. ≥100℃ This represents the ratio of peak area to total peak area in the temperature range above 100℃ (specifically above 100℃ and below 105℃), plotted on the Y-axis, while low crystallinity content (CEF) ≤95℃≥70℃ The peak area ratio of the crystal fractions eluted between 70°C and 95°C is represented on the X-axis. Detailed Implementation

[0013] Although ordinal numbers such as “first” and “second” may be used in this article to refer to multiple components, there is no priority order among the components.

[0014] When this document uses a particular commercially available product as a component, the nature of that component may refer to the nature described in the product’s Technical Data Sheet (TDS) or Certificate of Analysis (COA).

[0015] When the physical properties of a specific material in this article change with temperature, pressure, etc., the measurement conditions for these physical properties can be 25℃ and 101.325 kPa.

[0016] As used in this article, the numerical range "A to B" refers to "above A and below B". All numerical values ​​described in this article are rounded. For example, 1.5 is a value within the range of 1.45 to 1.54.

[0017] The terminology used herein is for describing exemplary embodiments only and is not intended to limit the invention.

[0018] Unless the context clearly indicates otherwise, the singular form contains plural references.

[0019] As used herein, the terms “comprising,” “including,” or “having” are intended to describe the presence of the said feature, quantity, step, component, or combination thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, components, or combinations thereof.

[0020] Furthermore, the degree terms such as “about” and “approximately” used throughout this specification are used to indicate that the values ​​are equal to or close to the stated values ​​when there are inherent manufacturing and material tolerances in the stated meaning. At the same time, the use of such terms is to prevent unlawful infringers from unfairly appropriating the precise or absolute values ​​marked in this application to aid understanding.

[0021] In this invention, the term "(co)polymer" encompasses both homopolymers and copolymers.

[0022] Unless otherwise defined herein, “copolymer” can mean block copolymer, random copolymer, graft copolymer or alternating copolymer, and “polymer” can mean block copolymer, random copolymer, graft copolymer or alternating copolymer.

[0023] For reference, as used herein, “parts by weight” is a relative concept, representing a ratio of the weight of one material to the weight of another material. For example, in a mixture containing 50 grams of material A, 20 grams of material B, and 30 grams of material C, based on 100 parts by weight of material A, the amounts of material B and material C are 40 parts by weight and 60 parts by weight, respectively.

[0024] Meanwhile, "wt% (weight %)" is an absolute concept, representing the percentage of one material's weight out of the total weight. In the above example of a mixture, in a total mixture weight of 100%, the contents of materials A, B, and C are 50wt%, 20wt%, and 30wt%, respectively.

[0025] This invention can be modified and taken in various forms, and specific embodiments will be described and detailed below. However, it should be understood that this invention is not limited to the specific forms disclosed, but covers all modifications, equivalents, and substitutions that fall within the spirit and scope of this invention.

[0026] The present invention will now be described in detail.

[0027] (Polyethylene composition) According to one aspect of the present invention, a polyethylene composition is provided, wherein, when the relative proportion of peak areas of crystalline fractions eluted according to temperature (°C) is measured using the crystallization elution fractionation (CEF) method, the ratio of the peak area of ​​the low crystallinity fraction eluted at temperatures above 70°C and below 95°C to the total peak area (CEF) is... ≤95℃≥70℃ The ratio of the peak area of ​​highly crystalline fractions eluted at temperatures above 100°C to the total peak area (CEF) is between 10% and 25%. ≥100℃ The percentage is between 6% and 15%.

[0028] The polyethylene composition according to one embodiment of the invention is characterized by controlling the balance between heat resistance and tensile properties by optimizing a single-peak or bi-peak slurry polymerization process in the presence of a Ziegler-Natta catalyst or a metallocene catalyst, thereby making it suitable for producing stretch films with high shrinkage resistance while maintaining productivity and tensile stability comparable to or better than conventional levels.

[0029] Specifically, by optimizing the distribution of crystalline fractions in the molecular structure within a predetermined range, a polyethylene composition according to one embodiment of the present invention can produce a film for uniaxial or biaxial stretching, which exhibits excellent tensile stability during film processing, high shrinkage resistance due to excellent heat resistance, and excellent film processing performance and productivity.

[0030] Preferably, the polyethylene composition may contain at least one ethylene-α-olefin copolymer. More preferably, the polyethylene composition may contain two ethylene-α-olefin copolymers.

[0031] The polyethylene composition according to one embodiment of the present invention is characterized in that the distribution of low-crystallinity fractions and high-crystallinity fractions eluted at a specific temperature in the molecular structure is optimized, thereby producing a stretch film with excellent tensile processing properties and heat resistance.

[0032] The polyethylene composition can simultaneously control the proportion of low crystallinity fractions eluted at temperatures above 70°C and below 95°C and the proportion of high crystallinity fractions eluted at temperatures of 100°C and above within an optimal range, thereby exhibiting high tensile properties, ensuring productivity and excellent membrane performance during membrane processing, while also possessing excellent membrane strength and shrinkage resistance, sufficient to withstand high-temperature processing in post-processing operations such as printing and coating.

[0033] Specifically, in polyethylene compositions, when the relative proportions of peak areas of crystalline fractions eluted according to temperature (°C) are measured using the crystallization elution fractionation (CEF) method, the ratio of the peak area of ​​crystalline fractions eluted above 70°C and below 95°C to the total peak area (CEF) is... ≤95℃≥70℃ That is, the peak area ratio of the low crystallinity fraction (CEF). ≤95℃≥70℃ (Low crystallinity content), ranging from 10% to 25%. In crystallization elution fractionation (CEF), the peak area ratio of crystalline fractions eluted at 70°C and above but below 95°C (CEF... ≤95℃≥70℃ That is, the low crystallinity content should be above 10% to allow the film to be stretched to a high proportion without breaking. The film is typically stretched in a semi-solid state, where the relatively low crystallinity components are mostly close to a molten state, which helps achieve high stretchability and uniform stretching. Therefore, as the content of the low crystallinity fraction increases, the stretchability can be improved. However, when the low crystallinity fraction content exceeds 25% and is too high, the film may become too soft, leading to sagging or decreased uniformity, and in severe cases, even breakage. Furthermore, its orientation may decrease, causing the film to exhibit characteristics similar to a drawn film. Moreover, because it is relatively easier to move compared to the high crystallinity components, and this movement can occur at lower temperatures, the final film shrinkage rate may also increase.

[0034] Peak area ratio of low crystallinity fraction (CE) F≤95℃≥70℃ The percentage can be 10% or higher, 10.5% or higher, 11% or higher, 11.5% or higher, 12% or higher, 12.5% ​​or higher, 13% or higher, 13.5% or higher, 14% or higher, 14.5% or higher, 15% or higher, 15.5% or higher, 16% or higher, 16.5% or higher, 17% or higher, 17.5% or higher, or 18% or higher, and can also be below 25%, below 24.8%, below 24.5%, below 24.3%, below 24%, below 23.8%, below 23.5%, below 23.3%, below 23%, below 22.8%, below 22.5%, below 22.3%, below 22%, below 21.8%, below 21.5%, or below 21%. This percentage can be within the range defined by choosing any one of the listed lower limits and any one of the listed upper limits. Preferably, this ratio can be 12% or more and 24% or less, more preferably 13% or more and 23% or less, and even more preferably 14% or more and 22% or less. This is achieved by optimizing the low crystallinity content ratio (CEF) eluted at temperatures above 70°C and below 95°C. ≤95℃≥70℃ High tensile strength during membrane processing ensures productivity and excellent membrane performance, while excellent heat resistance enhances membrane strength and shrinkage resistance.

[0035] Furthermore, in polyethylene compositions, when the relative proportions of peak areas of crystalline fractions eluted according to temperature (°C) are measured using the crystallization elution fractionation (CEF) method, the ratio of the peak area of ​​crystalline fractions eluted above 100°C to the total peak area (CEF) is... ≥100℃ That is, the proportion of peak areas of highly crystalline fractions (high crystallinity content), which can be above 6% and below 15%. For example, the high crystallinity content can be measured as the ratio of peak areas of crystalline fractions eluted above 100°C in CEF analysis; specifically, it can be the value measured above 100°C and below 120°C (CEF). ≤120℃≥100℃ More specifically, high crystallinity can be defined as a crystallinity content above 100°C and below 115°C in CEF analysis (CEF). ≤115℃≥100℃ ), above 100℃ and below 110℃ (CEF) ≤110℃≥100℃ Or above 100°C and below 105°C (CEF) ≤105℃≥100℃ The measured value.

[0036] When using crystallization elution fractionation (CEF) to measure the relative proportion of crystal-level peak areas eluted according to temperature (°C), the highly crystalline fraction eluted above 100°C has a high elution temperature relative to the total peak area and forms dense crystals. Therefore, during stretching, it acts as a framework, preventing membrane sagging or breakage and increasing orientation, thereby improving the membrane's mechanical properties and shrinkage characteristics. Thus, the content of the highly crystalline fraction should be above 6%. However, when the content of the highly crystalline fraction exceeds 15% and is excessively high, the high crystallinity reduces fluidity, adversely affecting stretchability and reducing stretchability and processing performance during membrane production.

[0037] High crystallinity fractional peak area ratio (CEF) ≥100℃ The content can be 6.5% or more, 6.8% or more, 7% or more, 7.3% or more, 7.5% or more, 7.8% or more, 8% or more, 8.3% or more, 8.5% or more, 9% or more, or 9.5% or more, and can be less than 14.5%, less than 14.3%, less than 14%, less than 13.8%, less than 13.5%, less than 13.3%, less than 13%, less than 12.8%, less than 12.5%, less than 12.3%, less than 12%, less than 11.8%, less than 11.5%, less than 11.3%, or less than 11%. This proportion can be within the range defined by any of the lower limits and any of the upper limits listed. Preferably, the proportion can be 6% or more and less than 15%, more preferably 7% or more and less than 14%, and even more preferably 8% or more and less than 13%. This is achieved by optimizing the proportion of high crystallinity content eluted at temperatures above 100°C (CEF). ≥100℃ When the stretch film is made into the final product through printing and coating processes, the film strength and shrinkage resistance can be improved through excellent heat resistance, while the high stretchability during the film processing ensures both productivity and excellent film performance.

[0038] Low crystallinity content in polyethylene compositions (CEF) ≤95℃≥70℃ ) and high crystallinity content (CEF) ≥100℃ The ratio of the two crystal fractions not only meets the above range, but by optimizing the ratio between the contents of the two crystal fractions, it is possible to produce stretch films with excellent post-stretch film quality (including heat resistance and shrinkage) and stretch processing performance.

[0039] Meanwhile, the proportion of peak areas in high crystallinity fraction (CEF) ≥100℃ ) and the ratio of low crystallinity fractional peak area (CEF) ≤95℃≥70℃ The ratio of (CEF) ≥100℃ / CEF ≤95℃≥70℃ This can be expressed as a high crystallinity content (CE). F≥100℃ ) and low crystallinity content (CEF) ≤95℃≥70℃The ratio of (CEF) ≥100℃ / CEF ≤95℃≥70℃ ).

[0040] Specifically, the ratio of the contents of the two crystal fractions mentioned above, namely, the high crystallinity content (CEF) ≥100℃ ) and low crystallinity content (CEF) ≤95℃≥70℃ The ratio of (CEF) ≥100℃ / CEF ≤95℃≥70℃ The ratio can be 0.24 or higher, or 0.24 or higher and 1.50 or lower. The lower limit of this ratio can be 0.20, 0.32, 0.44, 0.45, 0.47, 0.48, 0.59, 0.69, or 0.78, and the upper limit can be 1.47, 1.17, 0.87, 0.78, 0.69, 0.59, 0.48, 0.47, or 0.45. The ratio can fall within the range defined by any of the listed lower limits and any of the listed upper limits. Preferably, the ratio can be 0.3 or higher and 0.95 or lower, more preferably 0.35 or higher and 0.93 or lower, and even more preferably 0.4 or higher and 0.90 or lower.

[0041] In addition to the high-crystallinity and low-crystallinity fractions mentioned above, polyethylene compositions may also exhibit crystalline fractions eluted below 70°C and above 95°C but below 100°C. That is, when measuring the relative proportions of crystalline fraction areas eluted according to temperature (°C) using the crystallization elution fractionation (CEF) method, the ratio of the remaining area of ​​crystalline fractions eluted below 70°C and above 95°C but below 100°C to the total peak area (CEF... <70℃,<100℃>95℃ This can be determined by subtracting the sum of the contents of the two crystallization fractions mentioned above from 100% of the total crystallization fraction (i.e., the low crystallinity content (CEF)). ≤95℃≥70℃ ) and high crystallinity content (CEF) ≥100℃ And thus obtained.

[0042] For example, the percentage of remaining area (%) (CEF) <70℃，<100℃>95℃ The percentage can be 68.6 to 76.4, 68.8 to 76, or 69 to 75.2. Additionally, the percentage of remaining area (%) (CEF) <70℃，<100℃>95℃ The lower limit of ), i.e., the content of remaining crystal fraction (%) (CEF) <70℃，<100℃>95℃ The percentage can be 68.6, 69.1, 70.5, 71.8, 72.4, 73.0, 73.5, 74.0, 74.1, 74.1, 74.2, 74.3, or 74.7, and the upper limit can be 76.4, 75.1, 74.7, 74.3, 74.2, 74.1, 74.1, 74.0, 73.5, 73.0, 72.4, 71.8, or 70.5. This percentage can be within the range defined by any of the lower limits and any of the upper limits listed.

[0043] Peak area (CEF) of crystal fractions eluted below 70℃ <70℃ The ratio (%) can be less than 5, from 0.1 to 5, or from 0.2 to 4.9. The lower limit of the ratio can be 0.5, 0.8, 1, 1.5, 2, 2.5, or 3, and the upper limit can be 4.8, 4.6, 4.5, 4.35, 4.3, 4.25, 4.2, 4.15, 4.1, 4, 3.8, or 3.5. The ratio can be within the range defined by any of the lower limits and any of the upper limits listed.

[0044] The percentage of residual peak area (CEF) of crystalline fractions eluted above 95°C and below 100°C <100℃>95℃ The percentage (%) can be below 77, between 56 and 77, or between 57 and 76. The lower limit of this percentage can be 57, 57.5, 58, 58.5, 59, 59.5, 60, 62, 64, 64.5, or 65, and the upper limit can be 76, 74.5, 74, 73.5, 73, 72.5, 72, 71.5, 71, 70.5, 70, 69.5, 69, or 68.5. This percentage can be within the range defined by any of the lower limits and any of the upper limits listed.

[0045] In this invention, the crystallinity fraction content of the above-mentioned polyethylene composition, i.e., the low crystallinity content (CEF) ≤95℃≥70℃ ), high crystallinity content (CEF) ≥100℃ ) and the content of residual crystalline fractions (CE) F<70℃,<100℃>95℃ The value was measured by crystallization elution fractionation (CEF).

[0046] For example, the crystallinity fraction content of a polyethylene composition analyzed by CEF can be obtained using a PolymerChar Agilent Technologies 7890A instrument. For instance, the sample is dissolved in 20 mL of 1,2,4-trichlorobenzene at a concentration of 1.5 mg / mL, while the temperature is increased from 30°C to 150°C at a rate of 40°C / min. Recrystallization is then carried out while the temperature is decreased to 20°C at a rate of 0.5°C / min. Finally, the eluent volume is measured while the temperature is increased again to 140°C at a rate of 1°C / min. The weight fraction W is obtained from the elution temperature T. The integral of dW / dT over the temperature is calculated and normalized using the total integral value (from 20 to 140°C) to obtain the temperature-dependent fraction (%). The result can be represented as a CEF curve: the x-axis represents the elution temperature (°C), and the y-axis represents the fraction (%). The resulting CEF curve shows the relative proportion of the peak areas of the fractions eluted at each temperature (°C).

[0047] In such a CEF plot, with the total peak area as 100%, the proportion of the peak area in the region above 100℃ can be expressed as the high crystallinity content (CEF). ≥100℃ The proportion of peak areas in the region above 70℃ and below 95℃ can be expressed as the low crystallinity content (CEF). ≤95℃≥70℃ Specifically, the method for measuring the crystallization fraction content by CEF analysis is described in Experimental Example 1 below.

[0048] Meanwhile, the polyethylene composition according to one embodiment of the present invention may have a melt index (MI) of 0.5 to 3.0 g / 10 min, 0.51 to 2.8 g / 10 min, or 0.52 to 2.6 g / 10 min. 2.16 (190℃, 2.16 kg load). The melt index of the polyethylene resin composition affects the film properties, such as the processing properties, strength, heat resistance, and shrinkage of the film during the stretch film production process. When MI 2.16 Within the above range, the processing performance is excellent, and the heat resistance, shrinkage and film stiffness are also improved.

[0049] Melt index (MI) of polyethylene resin composition 2.16 The lower limit of the melt index (at 190℃ and a load of 2.16 kg) (g / 10 min) can be 0.45, 0.49, 0.52, 0.60, 0.67, 0.69, 0.70, 0.78, 0.85, 0.88, 0.90, 0.92, 0.93, or 1.01, and the upper limit can be 3, 2.9, 2.7, 2.5, 2.3, 2.0, 1.80, 1.50, 1.30, 1.20, 1.10, 1.09, 1.01, 0.93, 0.92, 0.90, 0.88, 0.85, 0.78, 0.70, 0.69, 0.67, or 0.60. The melt index can be within the range defined by any of the lower limits and any of the upper limits listed.

[0050] Specifically, when the melt index (MI) of the polyethylene resin composition... 2.16 When the melt index (190℃, 2.16 kg load) is too low, the extrusion pressure increases, the processing performance deteriorates, and the film appearance may be affected by melt fracture and other reasons. When the melt index is too high, bubble formation during blow molding may become difficult, or bubble instability may increase. Therefore, the melt index preferably meets the above range.

[0051] In this invention, the melt index (MI) 2.16The melt index can be measured at 190°C and 2.16 kg load according to ASTM D 1238 (Condition E, 190°C, 2.16 kg). For example, the method for measuring the melt index is described in Test Example 1 below.

[0052] The polyethylene composition can have a content of 0.940 to 0.970 g / cm³. 3 0.945 to 0.968 g / cm³ 3 Or 0.947 to 0.965 g / cm³ 3 The density of the polyethylene resin composition affects the stiffness of the stretched film. When the density is within the above range, it can prevent a decrease in the stiffness of the stretched film, as well as a decrease in the tensile properties of the film due to excessive density.

[0053] Preferably, the density (g / cm³) of the polyethylene resin composition is... 3 The lower limit can be 0.941, 0.942, 0.943, 0.944, 0.945, 0.957, 0.958, 0.959, 0.960, or 0.961, and the upper limit can be 0.968, 0.965, 0.962, 0.961, 0.960, 0.959, or 0.958. The density can be within the range defined by any of the lower limits and any of the upper limits listed.

[0054] In this invention, density (g / cm³) 3 The density can be measured according to ISO 1183-2, for example, at 23°C. For instance, the method for measuring density is described in Test Example 1 below.

[0055] Meanwhile, the polyethylene composition may have a weight-average molecular weight (Mw) of 80,000 to 160,000 g / mol, 85,000 to 140,000 g / mol, or 100,000 to 150,000 g / mol. The lower limit of the weight-average molecular weight (Mw) (g / mol) can be 123,000, 123,300, 125,900, 128,500, 128,750, 129,000, 131,000, 133,000, 133,550, 134,100, 136,450, 138,800, 141,750, 144,700 or 145,650, and the upper limit can be 153,150, 146,600, 145,650, 144,700, 141,750, 138,800, 136,450, 134,100 or 133,550. 133,000, 131,000, 129,000, 128,750, 128,500, or 125,900. The weight-average molecular weight may be within the range defined by any of the lower limits and any of the upper limits listed.

[0056] The polyethylene composition may have a number-average molecular weight (Mn) of 5,000 to 20,000 g / mol, 5,100 to 19,800 g / mol, or 5,200 to 19,500 g / mol. The lower limit for the number-average molecular weight (Mn) (g / mol) can be 5,200, 5,500, 5,800, 6,000, 6,200, 6,500, 6,800, 7,000, 8,200, 8,500, 8,800, 9,000, 9,200, 9,500, 9,800, 10,000, or 10,500, and the upper limit can be 19,500, 19,000, 18,500, 18,000, 17,500, 17,000, 16,500, 16,000, 15,500, 15,000, 14,500, 14,000, or 13,500. The number-average molecular weight can be within the range defined by any of the lower limits and any of the upper limits listed.

[0057] The polyethylene composition may have a molecular weight distribution (PDI, Mw / Mn) of 4 or more and 15 or less. The lower limit of Mw / Mn may be 5.11, 5.63, 6.14, 6.29, 6.44, 6.49, 6.53, 6.55, 6.56, 6.84, 7.12, 7.93, 8.73, 9.06, 9.39, or 9.52, and the upper limit may be 10.30, 9.98, 9.65, 9.52, 9.39, 9.06, 8.73, 7.93, 7.12, 6.84, 6.56, 6.55, 6.53, 6.49, 6.44, or 6.29. Mw / Mn may be within the range defined by any of the lower limits and any of the upper limits listed.

[0058] When the molecular weight distribution (PDI, Mw / Mn) reaches at least the lower limit, it can prevent excessive reduction of shear thinning and prevent the decline in processing performance due to increased viscosity in the high shear zone; when the molecular weight distribution reaches at most the upper limit, it can ensure uniformity of processing performance and quality.

[0059] For example, polyethylene compositions can exhibit either a unimodal or bimodal molecular weight distribution. A unimodal molecular weight distribution refers to a distribution where most polymer chains have similar molecular weights and appear as a single peak in a gel permeation chromatography (GPC) profile. This distribution provides relatively uniform polymer chains and consistent properties such as strength, durability, and processability. This ensures consistent intermolecular interactions between polymer chains, thereby improving mechanical properties such as tensile strength. A bimodal molecular weight distribution refers to a molecular weight distribution curve in a GPC profile with two peaks. If the two peaks each have independent peak shapes but are not independent, but partially overlap, and there is no minimum between their maximum values, then the shoulder peak is also considered a peak. In other words, a bimodal structure is defined when a distribution cannot be interpreted as a single peak forming a normal distribution and can be unconvoluted into two distributions.

[0060] This bimodal molecular weight distribution indicates an increased distribution of both low and high molecular weight fractions in the polyethylene resin composition. This molecular weight distribution structure can provide improved properties, particularly compared to polyethylene resin compositions exhibiting a unimodal molecular weight distribution, by enhancing the molecular structure that favors uniaxial or biaxial stretching, thereby providing superior stretchability.

[0061] Meanwhile, the polyethylene composition of the present invention is characterized by controlling the balance between mechanical properties and tensile properties by optimizing the slurry polymerization process in the presence of a Ziegler-Natta catalyst or a metallocene catalyst, for example by optimizing the total amount of introduced comonomers and their proportion introduced in each reactor, thereby producing a stretch film with high shrinkage resistance and printability, while maintaining mechanical properties, productivity and tensile stability comparable to or better than conventional levels.

[0062] In this invention, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are conversion values ​​relative to standard polystyrene and are measured using a gel permeation chromatography (GPC; manufactured by Waters). However, Mw and Mn are not limited to this and can also be measured using other methods known in the art. For example, the methods for measuring Mw and Mn are described in Test Example 1 below.

[0063] As described above, the polyethylene composition according to one embodiment of the present invention, by optimizing the low crystallinity content, high crystallinity content and their ratio, can produce a stretch film with excellent stretch film quality (including heat resistance and shrinkage) and excellent stretch processing performance.

[0064] Meanwhile, the polyethylene composition may have a crystallinity (Xc) of more than 65% and less than 95%. The lower limit of crystallinity (Xc) (%) may be 67, 68, 69, 70, 71.5, 72, 72.5, 73, 73.5, 74, 74.5, 75, 75.5, 76, 76.5, 77, 77.2, 77.4, 77.5, 77.7, 77.8, 77.9, 78, 78.1, 80.3 or 82.5, and the upper limit may be 94, 92, 90, 88, 86, 85.5, 85, 84.5, 83, 83.5, 83, 82.8, 82.6, 82.5, 80.3, 78.1, 78, 77.9, 77.8, 77.7 or 77.5. Crystallinity can be within the range defined by any of the lower limits listed and any of the upper limits listed.

[0065] The polyethylene composition may have a melt temperature (Tm) of 128°C or higher and 136°C or lower, and a crystallization temperature (Tc) of 116°C or higher and 123°C or lower. The melt temperature may be 128°C or higher, 129°C or higher, 130°C or higher, 130.5°C or higher, 131°C or higher, 131.5°C or higher, or 132°C or higher, and may be 135.8°C or lower, 135.5°C or lower, 135°C or lower, 134.5°C or lower, 134°C or lower, or 133.5°C or lower. Preferably, the crystallization temperature can be above 116.5℃, above 117℃, above 117.5℃, above 118℃, above 118.5℃, above 119℃, above 119.5℃, or above 120℃, and can be below 122.8℃, below 122.5℃, below 122.3℃, below 122℃, below 121.8℃, or below 121.5℃.

[0066] In this invention, the crystallinity Xc, melting temperature Tm, and crystallization temperature Tc can be measured using a differential scanning calorimeter (DSC; instrument: DSC Q20; manufacturer: TA Instruments). For example, the measurement methods for Tm, Tc, and Xc are described in Experimental Example 1 below.

[0067] Furthermore, the polyethylene composition according to one embodiment of the present invention may comprise at least one ethylene-α-olefin copolymer. The ethylene-α-olefin copolymer may comprise ethylene and at least one α-olefin, wherein the α-olefin is selected from 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, and mixtures thereof. Preferably, the ethylene-α-olefin copolymer may be at least one selected from ethylene / 1-hexene copolymers and ethylene / 1-butene copolymers.

[0068] When the polyethylene composition contains the above-described copolymer, the above-described properties can be achieved more easily. However, the type of polyethylene composition is not limited to this; any type known in the art can be provided as long as it can exhibit the above-described properties.

[0069] Meanwhile, the ethylene-α-olefin copolymer contained in the polyethylene composition having the above-mentioned physical properties can be produced using a Ziegler-Natta catalyst or a metallocene catalyst, preferably in the presence of a metallocene catalyst.

[0070] Specifically, ethylene-α-olefin copolymers can be produced by polymerizing olefin monomers in the presence of a hybrid supported metallocene catalyst comprising: at least one first metallocene compound selected from compounds represented by Chemical Formula 1; at least one second metallocene compound selected from compounds represented by Chemical Formula 2; and a support supporting the first metallocene compound and the second metallocene compound.

[0071] [Chemical Formula 1]

[0072] In chemical formula 1: M1 is a Group 4 transition metal; X 11 and X 12 Each is independently either substituted or unsubstituted C 1-20 Alkyl or halogen; R1 to R5 and R7 to R 12 Each is independently hydrogen, substituted or unsubstituted C. 1-20 Alkyl, substituted or unsubstituted C 6-60 Aryl or -(CH2) n1 -OR 13 ; R6 represents substituted or unsubstituted C. 1-20 Alkyl, substituted or unsubstituted C 6-60 Aryl or -(CH2) n1 -OR 13 ; R1 to R 12 At least one of them is -(CH2). n1 -OR 13 ; R 13 For substituted or unsubstituted C 1-20 Alkyl groups; and n1 is an integer from 0 to 10.

[0073] [Chemical Formula 2]

[0074] In chemical formula 2: M2 is a group 4 transition metal; X 21 and X 22 Each is a substituted or unsubstituted C independently. 1-20 Alkyl or halogen; T2 is either C (carbon) or Si (silicon); Q 21 and Q 22 Each is a substituted or unsubstituted C independently. 1-20Alkyl, substituted or unsubstituted C 6-60 Aryl or -(CH2) n2 -OR 32 , or Q 21 and Q 22 Interconnected to form substituted or unsubstituted C 3-20 cycloalkyl rings; R 20 To R 31 Each is independently a hydrogen, substituted or unsubstituted C. 1-20 Alkyl, substituted or unsubstituted C 6-60 Aryl or -(CH2) n2 -OR 32 , or R 20 To R 31 Two adjacent groups in a C14 form a substituted or unsubstituted C14. 3-20 cycloalkyl rings; R 20 To R 31 Q 21 and Q 22 At least one of them is -(CH2). n2 -OR 32 ; R 32 Is it substituted or unsubstituted C? 1-20 Alkyl groups; and n2 is an integer between 0 and 10.

[0075] The substituents in the chemical formulas will be described in detail below.

[0076] Halogens can be fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

[0077] C 1-20 Alkyl groups can be straight-chain, branched, or cyclic. Specifically, C 1-20 Alkyl groups can be C 1-20 Straight-chain alkyl; C 1-10 Straight-chain alkyl; C 1-5 Straight-chain alkyl; C 3-20 Branched or cyclic alkyl groups; C 3-15 Branched or cyclic alkyl groups; or C 3-10 Branched or cyclic alkyl groups. More specifically, C 1-20 Alkyl groups can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, cyclohexyl, etc.

[0078] C 3-20 A cycloalkylene ring can be a ring composed of carbon atoms, or it can be a C14 ring. 3-20 Hydrocarbon ring, C 3-15Hydrocarbon ring or C 3-10 Hydrocarbon ring. More specifically, C 3-20 Cycloalkyl subrings can be cyclopropenering, cyclobutene ring, cyclopentene ring, cyclohexene ring, etc.

[0079] C 2-20 The alkenyl group can be straight-chain, branched, or cyclic. Specifically, C2-20 The alkenyl group can be C 2-20 Straight-chain alkenyl, C 2-10 Straight-chain alkenyl, C 2-5 Straight-chain alkenyl, C 3-20 Branched alkenyl, C 3-15 Branched alkenyl, C 3-10 Branched alkenyl, C 5-20 Cyclic alkenyl or C 5-10 Cyclic alkenyl groups. More specifically, C 2-20 The alkenyl group can be vinyl, propenyl, butenyl, pentenyl, cyclohexenyl, etc.

[0080] C 1-20 Alkoxy groups can be straight-chain, branched, or cyclic. Specifically, C 1-20 Alkoxy groups can be C 1-20 Straight-chain alkoxy; C 1-10 Straight-chain alkoxy; C 1-5 Straight-chain alkoxy; C 3-20 Branched or cyclic alkoxy groups; C 3-15 Branched or cyclic alkoxy groups; or C 3-10 Branched or cyclic alkoxy groups. More specifically, C 1-20 Alkoxy groups can be methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, neopentoxy, cyclohexyloxy, etc.

[0081] C 2-20 The alkoxyalkyl group can be a substituent having a -Ry-O-Rz structure, wherein one or more hydrogens of the alkyl group (-Ry) are replaced by an alkoxy group (-O-Rz). Specifically, C 2-20 Alkoxyalkyl groups can be methoxymethyl, methoxyethyl, ethoxymethyl, isopropoxymethyl, isopropoxyethyl, isopropoxyhexyl, tert-butoxymethyl, tert-butoxyethyl, tert-butoxyhexyl, etc.

[0082] C 6-60 Aryl groups can refer to monocyclic, bicyclic, or tricyclic aromatic hydrocarbons. Specifically, C 6-60 Aryl groups can be phenyl, naphthyl, anthracene, etc.

[0083] C 7-20 Alkyl aryl refers to a substituent in which one or more hydrogen atoms on an aryl group are replaced by an alkyl group. Specifically, C 7-20 Alkyl aryl groups can be methylphenyl, ethylphenyl, n-propylphenyl, isopropylphenyl, n-butylphenyl, isobutylphenyl, tert-butylphenyl, cyclohexylphenyl, etc.

[0084] C 7-20 Arylalkyl refers to a substituent in which one or more hydrogen atoms on an alkyl group are replaced by an aryl group. Specifically, C 7-20 Arylalkyl groups can be benzyl, phenylpropyl, phenylhexyl, etc.

[0085] Group 4 transition metals can include titanium, zirconium, hafnium, etc.

[0086] Hybrid supported metallocene catalysts are hybrid catalysts that simultaneously contain a first metallocene compound providing high molecular weight, high crystallinity polymers and a second metallocene compound providing low molecular weight, low crystallinity polymers.

[0087] When copolymerizing using a hybrid supported metallocene catalyst in a single reactor, it is important to control the differences in polymerization characteristics among the metallocene compounds constituting the catalyst under single copolymerization conditions. Specifically, to obtain a polyethylene copolymer suitable for biaxial stretching, it is necessary to simultaneously contain a high molecular weight, high crystallinity component and a low molecular weight, low crystallinity component. Therefore, the inventors have developed a polyethylene copolymer that exhibits the aforementioned characteristics under single copolymerization conditions by utilizing a hybrid supported metallocene catalyst obtained from a combination of first and second metallocene compounds.

[0088] Because the first metallocene compound, represented by Formula 1, has a non-bridged ligand structure bonded to the central metal, it exhibits a lower polymerization rate for the comonomer and a higher polymerization rate for the ethylene monomer compared to the second metallocene compound. Therefore, under ethylene / 1-hexene copolymerization conditions, the first metallocene compound can provide high molecular weight, high crystallinity polyethylene with a small amount of short-chain branching (SCB) and a high molecular weight (Mw).

[0089] Meanwhile, because the second metallocene compound represented by Formula 2 has a bridging ligand structure bonded to the central metal, it exhibits a higher polymerization rate for the comonomer and a lower polymerization rate for the ethylene monomer compared to the first metallocene compound. Therefore, under ethylene / 1-hexene copolymerization conditions, the second metallocene compound can provide low molecular weight, low crystallinity polyethylene with high SCB and low Mw.

[0090] Preferably, the central metal M1 in Formula 1 can be a Group 4 transition metal, such as Ti, Zr or Hf, more specifically Hf or Zr.

[0091] Preferably, X 11 and X 12 Each can be methyl or chlorine independently, more preferably, X 11 and X 12 They can all be methyl or all be chlorine.

[0092] Preferably, R1 to R5 and R7 to R 12 Each can be independently hydrogen, substituted or unsubstituted C. 1-20 Alkyl, substituted or unsubstituted C 6-20 Aryl or -(CH2) n1 -OR 13 R6 can be substituted or unsubstituted C. 1-20 Alkyl, substituted or unsubstituted C 6-20 Aryl or -(CH2) n1 -OR 13 ;and R1 to R 12 One or both of them can be -(CH2) n1 -OR 13 .

[0093] Preferably, R7 or R8 is -(CH2). n1 -OR 13 The other one of R7 and R8, as well as R1 to R5 and R9 to R 12 Each can be independently hydrogen, substituted or unsubstituted C. 1-20 Alkyl, substituted or unsubstituted C 6-60 Aryl or -(CH2) n1 -OR 13 ; and R6 is substituted or unsubstituted C 1-20 Alkyl, substituted or unsubstituted C 6-60 Aryl or -(CH2) n1 -OR 13 .

[0094] Preferably, R1 to R5 can each be independently hydrogen, methyl, isopropyl, n-butyl, phenyl, or -(CH2). n1 -OR 13 More preferably, R1 to R5 can each be hydrogen, methyl, n-butyl, phenyl, or tert-butoxyhexyl.

[0095] Preferably, R6 can be unsubstituted C. 1-20 Alkyl, or C 6-10 Aryl or Si(R′)3 substituted C 1-20Alkyl, or C 6-20 aryl, where R′ is C 1-20 Alkyl or C 6-10 Aryl. More preferably, R6 can be an unsubstituted C. 1-20 Alkyl groups, or C groups substituted with phenyl, trimethylsilyl, or triphenylsilyl groups. 1-20 Alkyl, or C 6-20 Aryl group. Most preferably, R6 can be methyl, ethyl, isopropyl, benzyl, trimethylsilylmethyl, or phenyl.

[0096] Preferably, R7 or R8 can be -(CH2). n1 -OR 13 Another one from R7 and R8, and R9 through R 12 Each of them can be hydrogen. More preferably, R7 or R8 can be tert-butoxyhexyl, the other one of R7 and R8, and R9 to R 12 Each can be hydrogen.

[0097] Preferably, R 13 It can be tert-butyl.

[0098] Preferably, n1 can be an integer from 4 to 10, more preferably an integer from 4 to 7, and most preferably 6.

[0099] Preferably, the first metallocene compound represented by chemical formula 1 can be any one of the following compounds.

[0100]

[0101]

[0102] Meanwhile, there are no particular limitations on the method for preparing the first metallocene compound represented by chemical formula 1, for example, it can be carried out according to reaction scheme 1 below.

[0103] Although compounds represented by Formula 1 are difficult to synthesize due to the steric hindrance of the indene ligand, the method of reaction scheme 1 described below can produce compounds of Formula 1 in high yield and high purity.

[0104] Therefore, in one embodiment of the present invention, the compound represented by chemical formula 1 can be prepared by a method comprising the following steps: To react a compound represented by chemical formula 1-1 with a compound represented by chemical formula 1-2 to prepare a ligand represented by chemical formula 1-3; and Reaction of ligands represented by chemical formulas 1-3, compounds represented by chemical formulas 1-4, and transition metal halide salts represented by chemical formulas 1-5: [Reaction Scheme 1]

[0105] In reaction scheme 1: M1, X 11 X 12 and R1 to R 12 As defined in chemical formula 1; and Each X′ is an independent halogen.

[0106] Preferably, the central metal M2 in Formula 2 can be a Group 4 transition metal, such as Ti, Zr or Hf, and more specifically, Zr.

[0107] Preferably, X 21 and X 22 Each can be methyl or chlorine independently, more preferably, X 21 and X 22 Each can be chlorine.

[0108] Preferably, T2 can be C (carbon).

[0109] Preferably, R 20 To R 31 Q 21 and Q 22 At least one of them can be -(CH2). n2 -OR 32 More preferably, R 20 To R 25 Q 21 and Q 22 At least one of them can be -(CH2). n2 -OR 32 More preferably, R 20 To R 31 Q 21 and Q 22 One or both of them can be -(CH2) n2 -OR 32 More preferably, R 20 To R 25 Q 21 and Q 22 One or both of them can be -(CH2) n2 -OR 32 Most preferably, R 20 To R 25 Q 21 and Q 22 One or both of them can be tert-butoxyhexyl.

[0110] Preferably, Q 21 and Q 22 Each can be independently substituted or unsubstituted C. 1-20Alkyl, substituted or unsubstituted C 6-20 Aryl or -(CH2) n2 -OR 32 , or Q 21 and Q 22 They can connect to form substituted or unsubstituted C 3-20 Cycloalkylene ring. More preferably, Q 21 and Q 22 Each can be independently methyl, ethyl, isopropyl, phenyl, or -(CH2). n2 -OR 32 They can also connect to each other to form cyclopentyl subunit rings or cyclohexyl subunit rings.

[0111] Preferably, R 20 To R 23 They can be hydrogen or carbon independently. 1-20 Alkyl, C 6-20 Aryl or -(CH2) n2 -OR 32 More preferably, each of them can be hydrogen, methyl, n-butyl, phenyl, or tert-butoxyhexyl. More preferably, R 20 To R 23 One of them can be tert-butoxyhexyl or n-butyl, and the others can be hydrogen or R. 20 To R 23 Two of them can be methyl, n-butyl, or phenyl, and the rest can be hydrogen.

[0112] Preferably, R 24 To R 31 They can be hydrogen or carbon independently. 1-10 Alkyl, C 6-20 Aryl or -(CH2) n2 -OR 32 , or R 24 To R 31 Two adjacent groups can connect to each other to form substituted or unsubstituted C. 3-10 Cycloalkyl ring. More preferably, R 24 To R 31 Each can be independently hydrogen, tert-butyl, or tert-butoxyhexyl, or R 24 To R 31 Two adjacent groups can connect to each other to form a cyclohexane ring substituted with four methyl groups.

[0113] Preferably, R 32 It can be tert-butyl.

[0114] Preferably, n2 can be an integer from 4 to 10, more preferably an integer from 4 to 7, and most preferably 6.

[0115] Preferably, the metallocene compound represented by chemical formula 2 can be any one selected from the following compounds:

[0116]

[0117] Meanwhile, there are no particular limitations on the method for preparing the second metallocene compound represented by chemical formula 2; for example, it can be carried out according to reaction scheme 2 below.

[0118] Although compounds represented by Formula 2 are difficult to synthesize due to steric hindrance of the fluorene ligand, the method of reaction scheme 2 described below can produce compounds of Formula 2 in high yield and high purity.

[0119] Therefore, in one embodiment of the present invention, the compound represented by chemical formula 2 can be prepared by a method comprising the following steps: The compound represented by chemical formula 2-1 is reacted with the compound represented by chemical formula 2-2 to prepare the compound represented by chemical formula 2-3; To prepare ligands of formula 2-5 by reacting compounds represented by chemical formula 2-3 with compounds represented by chemical formula 2-4; and The ligands of formula 2-5 react with transition metal halide salts represented by formula 2-6: [Reaction Scheme 2]

[0120] In reaction scheme 2: M2, X 21 X 22 T2, Q 21 Q 22 and R 20 To R 31 As defined in chemical formula 2; and Each X″ is a halogen independently.

[0121] In the hybrid supported metallocene catalyst of the present invention, the first metallocene compound and the second metallocene compound can be supported in a molar ratio of 1:1 to 25:1, 2:1 to 25:1, 3:1 to 25:1, 3:1 to 23:1, or 3:1 to 20:1. When the molar ratio is less than 1:1, the content of high crystallinity is low, and the heat resistance of the stretched film may be insufficient; when the molar ratio is greater than 25:1, the content of low crystallinity is low, and the biaxial stretching processing performance may be insufficient.

[0122] In the hybrid supported metallocene catalyst of the present invention, a support containing hydroxyl groups on its surface can be used to support the first and second metallocene compounds. Preferably, a support with highly reactive hydroxyl, silanol, or siloxane groups on its surface can be used; for this purpose, a support that has undergone calcination surface modification or has had its surface moisture removed by drying can be used.

[0123] For example, silica prepared by calcining silica gel, high-temperature dried silica, silica-alumina, silica-magnesium oxide, etc., can be used. These materials typically contain oxide, carbonate, sulfate, and nitrate components, such as Na2O, K2CO3, BaSO4, and Mg(NO3)2.

[0124] When used as a supported catalyst, the resulting polymer exhibits excellent particle morphology and packing density, and the catalyst is suitable for conventional slurry polymerization, bulk polymerization, or gas-phase polymerization. Among various supports, silica supports are chemically bonded and support transition metal compound functional groups, thus minimizing catalyst release from the support surface during ethylene polymerization. Therefore, when producing ethylene-α-olefin copolymers via slurry or gas-phase polymerization, fouling caused by adhesion to reactor walls or polymer particle aggregation can be minimized.

[0125] The average particle size (D50) of the support can be 20 to 60 μm. At this particle size, the loading efficiency of transition metal compounds is higher, thereby improving catalytic activity. More specifically, D50 can be greater than 20 μm or greater than 25 μm, and less than 60 μm or less than 50 μm.

[0126] In this invention, the average particle size (D50) of the carrier refers to the particle size at which the cumulative distribution of particle size reaches 50%. D50 can be measured using laser diffraction. Specifically, the carrier to be tested is dispersed in a dispersion medium such as deionized water and introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). As the particles pass through the laser beam, the differences in the diffraction pattern based on particle size are measured, thereby calculating the particle size distribution. The particle size at which the cumulative distribution of particle size reaches 50% is taken as the average particle size.

[0127] When supported on a support, the loading amounts of the first and second metallocene compounds, based on 1000 g of support, can each be, for example, 1 mmol or more, 10 mmol or more, 15 mmol or more, 20 mmol or more, 25 mmol or more, or 30 mmol or more, and below 500 mmol, 400 mmol or less, 300 mmol or less, 200 mmol or less, 100 mmol or less, 80 mmol or less, 60 mmol or less, or 52.5 mmol or less. Loading within this range provides suitable supported catalyst activity and offers advantages in maintaining catalytic activity and economy.

[0128] The hybrid metallocene catalyst may also include a co-catalyst to improve its activity and process stability.

[0129] The cocatalyst is an organometallic compound containing a Group 13 metal, specifically, it may contain at least one compound represented by the following chemical formula 3.

[0130] [Chemical Formula 3] -[Al(R 41 )-O]a- In chemical formula 3: R 41 C is halogenated or unsubstituted or halogenated. 1-20 hydrocarbon group; a is an integer greater than or equal to 2.

[0131] As used herein, a hydrocarbon group refers to a monovalent functional group formed by removing a hydrogen atom from a hydrocarbon, and may include alkyl, alkenyl, alkynyl, aryl, aralkyl, aryl-alkenyl, arylynyl, alkylaryl, alkenylaryl, alkynylaryl, etc. 1-20 The hydrocarbon group can be C 1-15 Or C 1-10 Hydrocarbon group. Specifically, C 1-20 The hydrocarbon group can be a straight-chain, branched, or cyclic alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, or cyclohexyl; or an aryl group, such as phenyl, naphthyl, or anthracene.

[0132] Examples of compounds represented by Formula 3 include alkylaluminoxane compounds, such as methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, and butylaluminoxane, and any one or a mixture of two or more of them may be used.

[0133] In the above compounds, the cocatalyst can more specifically be an alkylaluminoxane cocatalyst, such as methylaluminoxane.

[0134] Alkylaluminoxane cocatalysts stabilize the first and second metallocene compounds as Lewis acids and contain a metal element that can form bonds with functional groups introduced into the bridging groups of the first and second metallocene compounds through Lewis acid-base interactions, thereby further enhancing catalytic activity.

[0135] The amount of co-catalyst can be adjusted appropriately according to the desired properties or effects of the catalyst and the polyethylene copolymer. For example, when silica is used as a support, the loading of co-catalyst can be more than 100 g, more than 1000 g, or more than 2000 g based on 1000 g of silica, and less than 6000 g, less than 5500 g, or less than 5400 g.

[0136] Hybrid metallocene catalysts having the above-described structure can be prepared by a method comprising the following steps: supporting a cocatalyst compound on a support, and supporting first and second transition metal compounds on the support. The loading order of the cocatalyst and the first and second transition metal compounds can be adjusted as needed, as can the loading order of the first and second transition metal compounds. The first and second transition metal compounds can be loaded simultaneously. Considering the role of determining the structure of the supported catalyst through the loading order, loading the cocatalyst on the support followed by the sequential loading of the first and second transition metal compounds can result in a supported catalyst exhibiting higher catalytic activity and better process stability in the production of ethylene-α-olefin copolymers.

[0137] As described above, hybrid supported metallocene catalysts can exhibit excellent catalytic activity by incorporating first and second transition metal compounds with specific structures. Therefore, such catalysts are suitable for the polymerization of ethylene and olefin monomers.

[0138] Based on the total weight of ethylene, the amount of hybrid supported metallocene catalyst added can be less than 2 wt%, or 0 to 2 wt%. Specifically, the total amount of co-catalyst (e.g., alkylaluminum compound) can be less than 1.8 wt%, less than 1.5 wt%, less than 1.2 wt%, or less than 1 wt%, and can be more than 0.001 wt%, more than 0.005 wt%, or more than 0.01 wt%.

[0139] α-Olefins can be used as olefin monomers for polymerization with ethylene. Specific examples include 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-eicosene. Two or more monomers can be mixed and copolymerized. More specifically, the olefin monomer can be at least one of 1-butene and 1-hexene.

[0140] The amount of olefin monomer used can be determined based on the desired properties of the polyethylene copolymer. Considering the properties to be achieved by the present invention, the amount of olefin monomer introduced can be less than 5 wt% or 0 to 5 wt% based on the total weight of ethylene. For example, in a bimodal slurry polymerization process, the total amount of olefin monomer introduced into the reactor can be less than 5 wt% based on the total amount of ethylene introduced into the reactor. Specifically, based on the total amount of ethylene, the total amount of olefin monomers can be less than 4.5 wt%, less than 4 wt%, less than 3.8 wt%, less than 3.5 wt%, less than 3.2 wt%, less than 3 wt%, less than 2.8 wt%, less than 2.5 wt%, less than 2.2 wt%, less than 2 wt%, less than 1.8 wt%, less than 1.5 wt%, less than 1.1 wt%, or less than 0.7 wt%, and can be more than 0.05 wt%, more than 0.1 wt%, more than 0.15 wt%, more than 0.2 wt%, more than 0.25 wt%, more than 0.4 wt%, more than 0.7 wt%, or more than 1.1 wt%.

[0141] Based on the total amount of ethylene, the total amount of olefin monomers can be 0.2 vol% or more, 0.24 vol% or more, or 0.36 vol% or more, and less than 1 vol%, less than 0.84 vol%, less than 0.61 vol%, or less than 0.37 vol%. This total amount can be within the range defined by any of the lower limits selected from the listed lower limits and any of the upper limits selected from the listed upper limits.

[0142] When the amount of comonomer olefin introduced is within the above range, the ratio of the low crystallinity fractional peak area to the total peak area (CEF) can be optimized simultaneously. ≤95℃≥70℃ The ratio of the area of ​​the high crystallinity fractional peak to the total peak area (CEF) ≥100℃ ) and the proportion of peak areas in high crystallinity fractions (CEF) ≥100℃ ) and the ratio of low crystallinity fractional peak area (CEF) ≤95℃≥70℃ The ratio of ).

[0143] Polymerization is carried out with the introduction of hydrogen.

[0144] Specifically, based on the total weight of ethylene, the amount of hydrogen introduced can be from 20 to 250 ppm. More specifically, based on the total weight of ethylene, this amount can be above 20 ppm, above 50 ppm, above 70 ppm, above 86 ppm, above 105 ppm, above 130 ppm, or above 165 ppm, and below 250 ppm, below 200 ppm, below 165 ppm, below 135 ppm, below 105 ppm, or below 85 ppm. This amount can be within the range defined by any of the lower limits and any of the upper limits listed. This amount can be calculated based on the density of liquid ethylene at 0.62 g / mL. Introducing hydrogen within this range contributes to achieving the properties of the aforementioned polyethylene copolymer.

[0145] Polymerization can be carried out using either gas-phase polymerization or slurry polymerization.

[0146] Therefore, polymerization can be carried out using a single gas-phase polymerization reactor, a continuous slurry polymerization reactor, or a loop slurry reactor.

[0147] The hybrid supported catalyst can be dissolved or diluted and introduced into aliphatic hydrocarbon solvents having 4 to 12 carbon atoms (e.g., isobutane, pentane, hexane, heptane, octane, nonane, decane, and their isomers); aromatic hydrocarbon solvents (e.g., toluene or benzene); or chlorine-substituted hydrocarbon solvents (e.g., dichloromethane or chlorobenzene). Preferably, the solvent is treated with a small amount of alkylaluminum compound to remove trace amounts of water, air, etc., which act as catalyst poisons. Additional co-catalysts may also be used.

[0148] Non-limiting examples of alkylaluminum compounds include trimethylaluminum, triethylaluminum, triisobutylaluminum, tripropylaluminum, tributylaluminum, dimethylaluminum chloride, triisopropylaluminum, trisec-butylaluminum, tricyclopentylaluminum, tripentylaluminum, triisopentylaluminum, trihexylaluminum, trioctylaluminum, ethyldimethylaluminum, methyldiethylaluminum, triphenylaluminum, tri-p-tolylaluminum, dimethylmethoxide aluminum, and dimethylethanol aluminum.

[0149] Based on the total weight of ethylene, the amount of co-catalyst such as alkylaluminum compound introduced can be less than 2 wt%, or 0 to 2 wt%. Specifically, the total amount can be less than 1.8 wt%, less than 1.5 wt%, less than 1.2 wt%, or less than 1 wt%, and can be more than 0.01 wt%, more than 0.02 wt%, or more than 0.05 wt%.

[0150] The polymerization reaction can be carried out at temperatures above 40°C, 60°C, or 80°C, and below 110°C, 100°C, or 90°C. When the pressure is further controlled, the polymerization reaction can be carried out at pressures above 5 bar, 10 bar, or 20 bar, and below 50 bar, 45 bar, or 40 bar. Conducting the polymerization reaction under these temperature and pressure conditions helps to achieve the desired properties of the ethylene-α-olefin copolymer.

[0151] An ethylene-α-olefin copolymer is produced using a catalyst in which high molecular weight and highly crystalline metallocene compounds and low molecular weight and low crystalline metallocene compounds are co-loaded. Therefore, the content of high and low crystallinity can be optimized and controlled to suitable levels when the relative proportions of peak areas of the crystalline fractions eluted according to temperature (°C) are measured by CEF analysis. Consequently, when a stretch film is produced from a polyethylene composition containing at least one such copolymer, both the heat resistance (including tensile stability and shrinkage) and the mechanical properties of the film are improved.

[0152] Therefore, the present invention provides a uniaxial or biaxial stretched film comprising a polyethylene composition containing at least one ethylene-α-olefin copolymer.

[0153] (Stretch film) According to one embodiment of the present invention, a stretch film can be formed by stretching a polyethylene composition sheet containing a polyethylene composition. The polyethylene composition having the above-described properties can stably form a uniaxial or biaxial stretch film with high shrinkage resistance and excellent printability while maintaining excellent mechanical properties, productivity, and tensile stability.

[0154] In particular, uniaxially oriented polyethylene (UPE) film exhibits high tensile strength and stiffness in the longitudinal direction (MD), along with excellent transparency and low gas and moisture permeability, thus extending shelf life. Due to its unidirectional orientation, UPE film also possesses excellent tearability, making it effective for easily cut products that have been widely used as packaging materials in recent years.

[0155] Biaxially oriented polyethylene (BOPE) film is stretched in both the longitudinal and transverse directions, thus exhibiting balanced strength, durability, and tear resistance in all directions. This type of BOPE film offers greater versatility in packaging applications requiring high puncture resistance and dimensional stability.

[0156] In addition to using the above-mentioned polyethylene composition, stretch films can also be prepared by conventional film production methods.

[0157] By incorporating the aforementioned polyethylene, the stretch film exhibits improved shrinkage resistance and superior tensile properties.

[0158] Specifically, when a polyethylene composite sheet with a width × length of 90 mm × 90 mm and a thickness of 200 μm is preheated at 126°C for 60 seconds and then uniaxially stretched at a stretching rate of 200% / s, the maximum stretch ratio of the stretched film can be 8 or more, 9 or more, or 10 or more.

[0159] When a stretched membrane undergoes a membrane shrinkage test (which involves heating the membrane to 120°C using a dynamic mechanical analyzer (DMA) at a heating rate of 5°C / min and then holding it for 1 hour), the shrinkage rate (%, [(AB) / A] × 100), expressed as a percentage of the difference between the initial membrane length (A, mm) measured before the test and the membrane length (B, mm) after the test, may be less than 4%, less than 3.8%, less than 3.6%, less than 3.5%, less than 3.4%, or less than 3.2%.

[0160] For example, when the thickness of the stretched film is 10 μm to 100 μm, it can be a uniaxial stretched film with a stretch ratio of 5 or more, or 5 to 10, in the longitudinal (MD) or transverse (TD) direction. Alternatively, the stretched film can be a biaxial stretched film with a stretch ratio of 5 or more, or 5 to 8, in the MD direction and a stretch ratio of 8 or more, or 8 to 10, in the TD direction.

[0161] The stretch ratio can be a value measured when the film thickness is 10 μm to 100 μm (e.g., 20 μm to 95 μm, 30 μm to 90 μm, or 40 μm to 85 μm).

[0162] The stretched polyethylene film according to the present invention can be prepared by preparing a polyethylene composition sheet and then subjecting it to uniaxial or biaxial stretching. A hot press can be used to prepare sheets with a thickness of 150 μm to 250 μm (e.g., 200 μm) at 190°C. Any hot press known to produce polyethylene sheets at the above temperature conditions can be used; specifically, a hot press manufactured by Collin under the product name Lab Line P300S can be used. After the sheet preparation is complete, a KARO 5.0 device can be used to perform uniaxial or biaxial stretching on the sheet with a width and length of 80 mm to 100 mm (e.g., width × length 90 mm × 90 mm) to produce a stretched polyethylene film. Specific film production methods and conditions are described in Experimental Example 2 below.

[0163] In addition to the polyethylene compositions described above, stretched polyethylene films may also contain additives known in the art. Specific examples include solvents, heat stabilizers, antioxidants, ultraviolet absorbers, light stabilizers, metal passivators, fillers, reinforcing agents, plasticizers, lubricants, emulsifiers, pigments, optical brighteners, flame retardants, antistatic agents, and foaming agents. There are no particular limitations on the types of additives; conventional additives known in the art may be used.

[0164] The stretched polyethylene film produced by the above method according to one embodiment of the present invention can improve film productivity through excellent stretching processing performance, and improve film strength and shrinkage performance through excellent heat resistance.

[0165] The performance of a stretched membrane can be measured when the membrane thickness is between 10 μm and 100 μm (e.g., 12 μm to 85 μm, 15 μm to 50 μm, 18 μm to 45 μm, or 20 μm to 35 μm). Specifically, the value can be measured for membranes stretched uniaxially in the longitudinal direction or stretched at a draw ratio of 5 × 8 (MD × TD) with a thickness of about 20 μm to about 30 μm.

[0166] In this invention, the performance of the stretch membrane can be evaluated according to the above-mentioned standards, and the specific method is described in Test Example 2 below.

[0167] In this invention, by employing a single-peak or double-peak slurry polymerization process with a Ziegler-Natta catalyst or a metallocene catalyst, the balance between mechanical properties and tensile properties is controlled, thereby obtaining excellent flowability and thus achieving excellent mechanical and tensile properties. This allows for the stable production of stretch films with high shrinkage resistance and excellent printability while maintaining excellent mechanical properties, productivity, and tensile stability.

[0168] The embodiments of the present invention will be described in more detail below with reference to the following examples. However, these examples are only for illustrating the embodiments of the present invention, and the present invention is not limited thereto.

[0169] [Example] <Preparation of Metallocene Compounds> Synthesis Example 1: Preparation of Metallocene Compound A1

[0170] (1) Synthesis of ligands: Under Ar conditions, 120 g (440 mmol) of 3-(6-tert-butoxyhexyl)-1H-indene and 1.1 L of n-hexane were added to a dry 2 L Schlenk flask. After cooling to -78 °C, 185 mL (1.05 equivalent, 462.5 mmol) of a 2.5 M n-butyllithium hexane solution was added dropwise. The reaction mixture was slowly heated to room temperature and then stirred for 8 hours. After cooling again to -78 °C, 82.8 g (1.1 equivalent, 484 mmol) of benzyl bromide was added dropwise. The mixture was slowly heated to room temperature and stirred for 24 hours, then the organic layer was separated with water and diethyl ether and dried over MgSO4 to give 137 g (377 mmol, 85.7% yield) of 3-(6-tert-butoxyhexyl)-1-benzyl-1H-indene.

[0171] 1 H NMR (500 MHz, CDCl3): 1.22 (9H, s), 1.32 (4H, m), 1.44 (2H, m), 1.57 (2H, m), 1.73 (2H, m), 2.59 (2H, m), 3.38 (2H, t), 3.75 (1H, m), 6.14 (1H, brs), 7.14-7.45 (9H, m).

[0172] (2) Synthesis of metallocene compounds: Under Ar conditions, 9.06 g (25 mmol) of the synthesized ligand and 90 mL of diethyl ether were added to a dry 250 mL Schlenk flask. After cooling to -78 °C, 11 mL (1.05 equivalent, 27.5 mmol) of a 2.5 M n-butyllithium hexane solution was added dropwise. The reaction mixture was slowly heated to room temperature and then stirred for 8 hours. After cooling again to -78 °C, 10.6 g (1.0 equivalent, 25 mmol) of (1-n-butyl-3-methylcyclopentadienyl)ZrCl3 dimethoxyethane complex and 30 mL of diethyl ether were added. The mixture was slowly heated to room temperature and stirred for 24 hours. Subsequently, the reaction mixture was dried under reduced pressure and dichloromethane was added. The resulting suspension was filtered under Ar conditions to remove LiCl, the filtrate was dried under reduced pressure, and n-hexane was added. The resulting suspension was filtered under Ar to give 8.76 g (13.3 mmol, yield 53.2%) of solid metallocene compound A1.

[0173] 1H NMR (500 MHz, CDCl3): 0.88-0.91 (3H, m), 1.22 (9H, s), 1.29-1.40(8H, m), 1.52-1.76 (4H, m), 2.06 (3H, s), 2.11-2.22 (2H, m), 2.59-2.68 (2H,m), 2.99-3.07 (2H, m), 3.34 (2H, t), 4.43 (1H, dt), 5.21 (1H, dt), 5.78 (1H,t), 6.47 (1H, brs), 7.11-7.63 (9H, m).

[0174] Synthetic Example 2: Preparation of Metallocene Compound B1

[0175] (1) Synthesis of ligands: Under Ar conditions, 5.01 g (18 mmol) of 2,7-di-tert-butylfluorene and 80 mL of tetrahydrofuran were added to a dry 250 mL Schlenk flask. After cooling to -78 °C, 8.6 mL (1.2 equivalent, 21.5 mmol) of 2.5 M n-butyllithium hexane solution was added dropwise. The reaction mixture was slowly heated to room temperature and then stirred for 8 hours. After cooling to -78 °C, 5.73 g (1.0 equivalent, 18 mmol) of 2-(6-tert-butoxyhexyl)-5-(2,4-dimethylpentan-3-ethylene)-cyclopentan-1,3-diene and 10 mL of tetrahydrofuran were added. The mixture was slowly heated to room temperature and stirred for 24 hours, then the organic layer was separated using water and diethyl ether and dried over MgSO4 to give 6.92 g (11.6 mmol, yield 64.4%) of the ligand.

[0176] 1 H NMR (500 MHz, CDCl3): 0.85 (12H, d), 1.14 (9H, s), 1.27 (18H, s), 1.31-1.60 (10H, m), 2.22 (2H, m), 2.92 (2H, m), 3.33 (2H, t), 3.76 (1H, brs), 6.11 (1H, m), 6.35 (1H, brs), 7.40 (2H, m), 7.49-7.62 (2H, m), 7.78-7.91 (2H,m).

[0177] (2) Synthesis of metallocene compounds: Under Ar conditions, 6.92 g (11.6 mmol) of the synthesized ligand, 10 mL of methyl tert-butyl ether, and 40 mL of toluene were added to a dry 250 mL Schlenk flask. After cooling to -78 °C, 10.2 mL (2.2 equivalents, 25.5 mmol) of a 2.5 M n-butyllithium hexane solution was added dropwise. The reaction mixture was slowly heated to room temperature and then stirred for 8 hours. After cooling to -78 °C, 4.38 g (1.0 equivalents, 11.6 mmol) of ZrCl4(THF)2 and 10 mL of methyl tert-butyl ether were added. The mixture was slowly heated to room temperature and stirred for 24 hours, after which the reaction mixture was dried under reduced pressure at room temperature to remove methyl tert-butyl ether. The resulting toluene suspension was filtered under Ar conditions to remove LiCl, the filtrate was dried under reduced pressure at 50 °C, and n-hexane was added. The resulting suspension was filtered under Ar to give 4.12 g (5.44 mmol, yield 46.9%) of solid metallocene compound B1.

[0178] 1 H NMR (500 MHz, C6D6): 0.90 (12H, d), 1.12 (9H, s), 1.15-1.38 (24H,m), 1.44-1.55 (6H, m), 3.21 (2H, t), 5.30-6.15 (3H, m), 7.44 (2H, dd), 7.65(2H, d), 7.91(2H, d).

[0179] <Preparation of Supported Catalysts> Catalyst Preparation Example 1: Preparation of Hybrid Supported Metallocene Catalyst 1 Silica (SP 952, manufactured by Grace Davison) was dehydrated and dried under vacuum at 200°C for 12 hours.

[0180] 800 g of dried silica was placed in a 20 L SUS reactor. 6 kg of methylaluminoxane (MAO) solution (10 wt% in toluene) was added to the toluene solution, and the reaction was carried out slowly at 70 °C with stirring for 1 hour. After the reaction, the silica was washed repeatedly with sufficient toluene until unreacted aluminum compounds were completely removed. A solution prepared by dissolving 30.1 g of metallocene compound A1 and 3.0 g of metallocene compound B1 in toluene was added sequentially to the reactor, and the reaction was carried out at 40 °C with stirring for 4 hours. The molar ratio of metallocene compound A1 to metallocene compound B1 was 12. After the reaction, the product was washed with sufficient toluene and dried under vacuum to obtain hybrid supported metallocene catalyst 1, which was a solid powder.

[0181] <Preparation of Polyethylene Compositions> Example 1 The polyethylene composition of Example 1 was subjected to slurry polymerization using a bimodal polymerization process in the presence of the hybrid supported catalyst 1 prepared in Catalyst Preparation Example 1, using two 100 L continuous stirred tank reactors (CSTRs).

[0182] Specifically, primary polymerization is carried out in a first reactor, with the amount of hydrogen and comonomer introduced controlled under the conditions shown in Table 1 below, to prepare a first polyethylene. Triethylaluminum (TEAL) at a concentration of 0.3 mM is used as a cocatalyst at a flow rate of 110 mL / h. The first polyethylene polymerized in the first reactor is transferred to a second reactor in series for secondary polymerization, with the amount of hydrogen and comonomer introduced controlled under the conditions shown in Table 1 below. All feeds shown in Table 1 are introduced continuously over the same time period.

[0183] Based on the total weight of the polymer products obtained from the secondary polymerization, 200 ppm of Irganox 1010 from BASF was added as a primary antioxidant, 400 ppm of Irgafos 168 from BASF as a secondary antioxidant, and 500 ppm of calcium stearate (Ca-St) or DHT4A as a neutralizing agent, and the mixture was prepared. The mixture was extruded using a twin-screw extruder (TEK 30 MHS, manufactured by SMPLATECH; diameter: 32 mm; L / D = 40) at an extrusion temperature of 190°C to prepare the granular polyethylene composition of Example 1.

[0184] Examples 2 to 5 The polyethylene compositions of Examples 2 to 5 were prepared in the same manner as in Example 1, except that the polyethylene compositions were subjected to slurry polymerization as described in Example 1, while primary reactor polymerization was carried out using different amounts of hydrogen and comonomers under the conditions shown in Table 1 below, and single-peak slurry polymerization was carried out without secondary reactor polymerization.

[0185] [Table 1]

[0186] Comparative Example 1 High-density polyethylene resin (manufacturer: Exxon; product name: HTA108) was prepared as Comparative Example 1.

[0187] Comparative Example 2 High-density polyethylene resin (manufacturer: DOW; product name: Elite5960G) was prepared as Comparative Example 2.

[0188] Comparative Example 3 High-density polyethylene resin (manufacturer: SK Innovation; product name: Yuzex8300) was prepared as Comparative Example 3.

[0189] Comparative Example 4 High-density polyethylene resin (manufacturer: DOW; product name: AT6900) was prepared as Comparative Example 4.

[0190] Comparative Examples 5 to 13 The polyethylene compositions of Comparative Examples 5 to 13 were prepared in the same manner as in Example 1, except that the polyethylene compositions were subjected to slurry polymerization via bimodal polymerization as described in Example 1, while the amount of hydrogen and comonomer introduced was varied and controlled according to the conditions shown in Table 2 below.

[0191] Comparative Example 14 The polyethylene composition of Comparative Example 14 was prepared in the same manner as in Example 1, except that the polyethylene composition was subjected to slurry polymerization as described in Example 1, while primary reactor polymerization was carried out using different amounts of hydrogen and comonomers under the conditions shown in Table 1 below, and single-peak slurry polymerization was carried out without secondary reactor polymerization.

[0192] [Table 2]

[0193] <Experimental Example 1: Performance Evaluation of Polyethylene Composition> The properties of the polyethylene compositions prepared in the Examples and Comparative Examples were evaluated using the following methods, and the results are shown in Table 3. (1) Melt Index According to ASTM D 1238 (Condition E, 190°C, 2.16 kg), the melt index (MI) was measured using a Gottfert MI-4 at 190°C and a load of 2.16 kg. 2.16 The weight (g) of the polyethylene composition extruded in the molten state within 10 minutes is given.

[0194] (2) Density According to ISO 1183-2, density (g / cm³) is measured at 23°C. 3 ).

[0195] (3) Number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) For the polyethylene compositions prepared in the Examples and Comparative Examples, the weight-average molecular weight (Mw, g / mol) and number-average molecular weight (Mn, g / mol) were measured using a gel permeation chromatography (GPC; manufactured by Waters) according to ASTM D 6474, and the molecular weight distribution (Mw / Mn; PDI, polydispersity index) was calculated by dividing Mw by Mn.

[0196] Specifically, a Waters PL-GPC220 instrument and a Polymer Laboratories PLgel MIX-B column (300 mm long) were used. The measurement temperature was 160 °C, 1,2,4-trichlorobenzene was used as the solvent, and the flow rate was 1 mL / min. The ethylene-α-olefin copolymer samples prepared in Examples 1 to 4 were pretreated by dissolving them in trichlorobenzene containing 0.0125% BHT at 160 °C for 3 hours using a GPC analyzer (PL-GPC220) to a concentration of 32 mg / 10 mL, which was then injected in 200 μL volumes. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) were calculated using a calibration curve established with polystyrene standards. Nine polystyrene standards with weight-average molecular weights of 2,000 g / mol, 10,000 g / mol, 30,000 g / mol, 70,000 g / mol, 200,000 g / mol, 700,000 g / mol, 2,000,000 g / mol, 4,000,000 g / mol, and 10,000,000 g / mol were used.

[0197] (4) Melting temperature (Tm), crystallization temperature (Tc) and crystallinity (%) The melting temperature (Tm), crystallization temperature (Tc), and crystallinity (Xc) of the polyethylene compositions of the examples and comparative examples were measured using a differential scanning calorimeter (DSC; instrument: DSC Q20; manufacturer: TA Instruments).

[0198] Specifically, each polyethylene composition was heated to 180°C at a rate of 10°C / min (Cycle 1), held at 180°C for 5 minutes, cooled to 0°C at a rate of 10°C / min, held at 30°C for 5 minutes, and then heated again to 180°C at a rate of 10°C / min (Cycle 2). From the resulting DSC curves, the temperature corresponding to the maximum endothermic peak was measured as the melting temperature (Tm, °C), and the temperature corresponding to the maximum exothermic peak was measured as the crystallization temperature (Tc, °C). The values ​​of Tm and Tc were taken from the measurement results of the second heating and cooling stage (Cycle 2).

[0199] In the second heating stage (cycle 2), the enthalpy of fusion ΔHm is obtained by measuring the melting peak area and then divided by the theoretical value H corresponding to 100% crystallinity. 0 m = 293.6 J / g, to calculate the crystallinity (Xc, %).

[0200] (5) High crystallinity content and low crystallinity content For the polyethylene compositions in the examples and comparative examples, the content of crystal fractions eluted at temperatures above 100°C (specifically, the content of crystal fractions eluted at temperatures above 100°C and below 105°C, i.e., high crystallinity content) and the content of crystal fractions eluted at temperatures above 70°C and below 95°C (i.e., low crystallinity content) were measured by crystallization elution fractionation (CEF).

[0201] Specifically, an Agilent Technologies 7890A instrument from PolymerChar was used. The sample was dissolved in 20 mL of 1,2,4-trichlorobenzene at a concentration of 1.5 mg / mL while the temperature was increased from 30 °C to 150 °C at a rate of 40 °C / min. Recrystallization was performed while the temperature was decreased to 20 °C at a rate of 0.5 °C / min, and the elution amount was measured while the temperature was increased again to 140 °C at a rate of 1 °C / min. The fractions (%) eluted according to temperature were obtained by normalizing the dW / dT integral value of the weight fraction W obtained according to the elution temperature T relative to the total integral value (20 to 140 °C). The results are presented as a CEF plot, with the x-axis representing the elution temperature ( °C) and the y-axis representing the fraction (%). The resulting CEF plot represents the relative proportion of the peak areas of the eluted fractions according to temperature ( °C).

[0202] In the CEF curve, the peak area ratio in the temperature range above 100℃ (specifically, above 100℃ and below 105℃) is represented by the total peak area as 100%, indicating the high crystallinity content (CEF). ≥100℃ The peak area ratio of the crystalline fraction eluted at temperatures above 70°C and below 95°C is expressed as the low crystallinity content (CEF). ≤95℃≥70℃ ).

[0203] The low crystallinity content (CEF) of the polyethylene compositions of Examples 1 to 5 and Comparative Examples 1 to 14, measured by the above method, was determined. ≤95℃≥70℃ ) and high crystallinity content (CEF) ≥100℃ The ratio of the two crystallinity contents was calculated, namely the proportion of high crystallinity / the proportion of low crystallinity (CEF). ≥100℃ / CEF≤95℃≥70℃ ).

[0204] [Table 3]

[0205] In the CEF diagrams obtained by the above method, the CEF diagrams of the polyethylene compositions of Example 1 and Comparative Example 1 are as follows: Figure 1 As shown. Figure 2 The figures show the high crystallinity content (CEF) of the polyethylene compositions of Examples 1 to 5 and Comparative Examples 1 to 10, as measured by the method described above, expressed on the y-axis and x-axis, respectively. ≥100℃ ) and low crystallinity content (CEF) ≤95℃≥70℃ A distribution diagram of the correlation between ( ). In Figure 2 In this context, Examples 1 to 5 are represented by dots 1 to 5, and Comparative Examples 1 to 10 are represented by dots 6 to 15.

[0206] according to Figure 1 The CEF plots of Example 1 and Comparative Example 1 may appear partially similar. However, as Figure 2 As shown, this indicates a high crystallinity content (CEF). ≥100℃ ) and low crystallinity content (CEF) ≤95℃≥70℃ The distribution plot of the correlation between them confirmed significant differences. In particular, such as Figure 2 As shown, compared with Comparative Examples 1 to 10, the polyethylene compositions of Examples 1 to 5 optimized the high crystallinity content (CEF). ≥100℃ ) and low crystallinity content (CEF) ≤95℃≥70℃ This is measured by the relative proportion of the peak areas of the crystal fractions eluted at temperature, thus providing excellent stretching properties with a high maximum stretch ratio during membrane production, while minimizing high-temperature shrinkage and improving heat resistance.

[0207] <Experimental Example 2: Preparation and Performance Evaluation of Stretch Membranes> Stretch films were prepared from the polyethylene compositions obtained in the Examples and Comparative Examples using the following methods, and their respective properties were measured. The results are shown in Table 4.

[0208] Preparation of stretch film - A 200μm thick polyethylene composition sheet was prepared at 190°C using a hot press (manufacturer: Collin; product name: Lab Line P300S), and then cut into sheets with a width × length of 90mm × 90mm.

[0209] - Uniaxial stretching of polyethylene composite sheets with a width × length of 90mm × 90mm was performed using a KARO 5.0 machine.

[0210] - After preheating for 60 seconds under the following conditions, uniaxial stretching was performed along the longitudinal direction (MD) (Examples 1 to 5 and Comparative Examples 1 to 14: preheating at 126°C for 60 seconds, then stretching at a stretching rate of 200% / s for 6 to 10 times; when the stretching ratio was 6, the thickness of the stretched film was about 30 μm to about 40 μm; after stretching, the film was held in an annealing chamber at 120°C for 5 seconds, then discharged and cooled).

[0211] Stretch film performance evaluation - Maximum stretch ratio: When uniaxially stretched at a stretching rate of 200% / s and stretch ratios of 6, 7.5, 9 and 10 according to the above method, the maximum stretch ratio that the film can achieve without breaking is measured.

[0212] - Shrinkage: A polyethylene composite sheet with a width × length of 90 mm × 90 mm was stretched six times uniaxially in the longitudinal (MD) direction to prepare a film. The film was cut into 6 mm wide pieces, and the film shrinkage rate was tested using a dynamic mechanical analyzer (DMA Q850; TA Instruments). The test method was as follows: the film was heated to 120°C at a heating rate of 5°C / min and held at 120°C for 1 hour, while maintaining a stress of approximately 0.06 MPa. During the test, the change in length of the film in the MD direction was measured to calculate the shrinkage rate. Specifically, based on the initial length (A, mm) of the six-fold uniaxially stretched film before heating, the shrinkage rate was calculated as the percentage difference between the initial length (A, mm) and the length (B, mm) after the film shrinkage test. That is, the shrinkage rate (%) of the stretched film = [(AB) / A] × 100.

[0213] [Table 4]

[0214] According to the results in Table 4, the polyethylene compositions of Examples 1 to 5, wherein the contents of high and low crystallinity (measured as the relative proportions of the peak areas of the crystal fractions eluted according to temperature in CEF analysis) were adjusted to appropriate levels, produced films with excellent tensile strength and heat resistance. In particular, the polyethylene compositions of Examples 1 to 5 exhibited excellent shrinkage rates of less than 4%, even at actual stretch ratios of 9 or higher. This is attributed to their high crystallinity content, which allows the film to maintain its shape without significant deformation even at high stretch ratios, thereby reducing shrinkage. Furthermore, the presence of a specific level of low crystallinity content prevented the degradation of processability caused by high crystallinity and achieved high tensile strength.

[0215] However, the polyethylene compositions of Comparative Examples 1 to 10 had film stretch ratios of only 6 or 7.5, indicating poor tensile processing properties, and the film shrinkage increased to 4.12% to 6.10%, indicating a significant decrease in heat resistance. The polyethylene compositions of Comparative Examples 11, 13, and 14 showed improved film shrinkage, but their film stretch ratios were only 6, 7.5, and 7.5, respectively, indicating a significant reduction in tensile processing properties. The polyethylene composition of Comparative Example 12 showed even worse results in terms of shrinkage.

[0216] Therefore, the polyethylene composition of the present invention can effectively produce stretch films with excellent tensile stability and heat resistance. During the formation of the stretch film, the composition maintains appropriate tension within the stretching processing area, thus being highly advantageous for commercial products such as single-material packaging films with high shrinkage resistance, printability and transparency, excellent stretching performance and productivity.

Claims

1. A polyethylene composition, wherein, When using the crystallization elution fraction (CEF) method to measure the relative proportions of peak areas of crystal fractions eluted at a given temperature (°C), The ratio of the peak area of ​​the low crystallinity fraction eluted above 70℃ and below 95℃ to the total peak area (CEF). ≤95℃≥70℃ The percentage is between 10% and 25%. The ratio of the peak area of ​​the highly crystalline fraction eluted above 100℃ to the total peak area (CEF) ≥100℃ The percentage is between 6% and 15%. Peak area ratio of highly crystalline fractions (CEF) ≥100℃ The peak area ratio of the low crystallinity fraction (CEF) ≤95℃≥70℃ The ratio of ) to CEF ≥100℃ / CEF ≤95℃≥70℃ ) is above 0.24, and The polyethylene composition has a content of 0.940 g / cm³. 3 Above and 0.970 g / cm 3 The following densities.

2. The polyethylene composition according to claim 1, in, The peak area ratio (CEF) of the highly crystalline fraction ≥100℃ The peak area ratio (CEF) of the low crystallinity fraction ≤95℃≥70℃ The ratio of ) to CEF ≥100℃ / CEF ≤95℃≥70℃ The value is above 0.24 and below 1.

50.

3. The polyethylene composition according to claim 1, in, Melt Index (MI) 2.16 (At 190℃ and 2.16 kg) the concentration is 0.5 g / 10 min or more and 3.0 g / 10 min or less.

4. The polyethylene composition according to claim 1, in, Weight-average molecular weight (Mw) of 80,000 g / mol or higher and 160,000 g / mol or lower, and The molecular weight distribution (Mw / Mn) is above 4 and below 15.

5. The polyethylene composition according to claim 1, in, The crystallinity (Xc) is above 65% and below 95%.

6. The polyethylene composition according to claim 1, in, Melting temperature (Tm) is above 128℃ and below 136℃, and The crystallization temperature (Tc) is above 116℃ and below 123℃.

7. The polyethylene composition according to claim 1, in, The polyethylene composition comprises at least one ethylene-α-olefin copolymer.

8. The polyethylene composition according to claim 7, in, The ethylene-α-olefin copolymer comprises ethylene and at least one α-olefin selected from 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, and mixtures thereof.

9. A stretch film comprising the polyethylene composition according to claim 1.

10. The stretch membrane according to claim 9, in, When a polyethylene composite sheet with a width × length of 90 mm × 90 mm and a thickness of 200 μm is preheated at 126°C for 60 seconds and then subjected to uniaxial stretching at a stretching rate of 200% / s, the maximum stretch ratio is greater than 8.

11. The stretch membrane according to claim 9, in, When the stretched membrane undergoes a membrane shrinkage test, the membrane shrinkage test includes heating the membrane to 120°C using a dynamic mechanical analyzer (DMA) at a heating rate of 5°C / min, and then holding it for 1 hour. Shrinkage rate (%, [(AB) / A]×100), expressed as the percentage difference between the initial membrane length (A, mm) measured before the membrane shrinkage test and the membrane length (B, mm) measured after the membrane shrinkage test, is less than 4%.

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