Polyethylene resin compositions, methods of making the same and articles

Abstract

Disclosed are a polyethylene resin composition, a method of preparing the same, and an article produced therefrom, the polyethylene resin composition comprising 4.5% to 55% by weight of an ethylene copolymer based on the total weight of the polyethylene resin composition wherein the ethylene copolymer has a melt flow index MI21.6 (21.6 kg load, 190 DEG C) of 0.26 g / 10 min to 0.50 g / 10 min, a density of 0.919 g / cm < 3 > to 0.924 g / cm < 3 >, and a weight average molecular weight (Mw) of 450,000 g / mol to 650,000 g / mol.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0050605, filed on April 16, 2024, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. TECHNICAL FIELD

[0003] The present disclosure relates to a polyethylene resin composition having excellent pressure resistance and slow crack growth resistance, a method for preparing the same, and an article produced therefrom. BACKGROUND

[0004] Pipes produced from polyethylene have been used as water pipes, gas pipes, industrial pipes, etc. Recently, in order to introduce non-traditional installation techniques (e.g., trenchless and sandless bed techniques) that can reduce installation costs and time of traditional installation techniques, there is a demand for conventional polyethylene materials for pipes to have excellent slow crack growth resistance.

[0005] Slow crack growth resistance is generally evaluated using a strain hardening modulus (SHM), a full notched creep test (FNCT), and a notched pipe test (NPT). Recently, four new slow crack growth test items, i.e., SHM, aFNCT (accelerated full notched creep test), aNPT (accelerated notched pipe test), and CRB (crack round bar), have been established according to the EN1555-1:2021 standard. The aFNCT and the aNPT are accelerated test methods that increase the test temperature or replace a more reactive surfactant as a medium in the conventional method. A new CRB test method is a fatigue test that includes applying a sinusoidal load to a cylindrical bar specimen and evaluating the number of failure cycles at a failure point due to stress. The CRB test is known to be a method for evaluating slow crack growth resistance in a relatively short time at a test temperature of room temperature (23°C).

[0006] In general, in order to improve slow crack growth resistance, polyethylene materials need to have a molecular structure that is highly entangled between connecting molecules. For this purpose, a comonomer having a high molecular weight or a large number of carbon atoms is used. However, the slow crack growth resistance of polyethylene materials is directly related to the crystallinity, i.e., the density. As the density increases, the pressure resistance of the pipe improves, but there is a problem in that the slow crack growth resistance significantly decreases. Therefore, there is a trade-off between the pressure resistance and the slow crack growth resistance of the pipe. Thus, there is a need to develop a polyethylene resin composition that can satisfy both of these properties at the same time.

[0007]

Prior Art Documents

[0008]

Patent Documents

[0009] Korean Patent Publication No. 10-2020-0101872 SUMMARY

[0010] Embodiments of the present disclosure provide a polyethylene resin composition having excellent pressure resistance and slow crack growth resistance.

[0011] Embodiments of the present disclosure provide a method of producing a polyethylene resin composition.

[0012] Embodiments of the present disclosure provide an article produced from the polyethylene resin composition.

[0013] The objects to be achieved by the present disclosure are not limited to the above-mentioned aspects, and other objects not mentioned herein will be clearly understood by those skilled in the art from the following description.

[0014] To achieve the above object, the polyethylene resin composition according to the embodiments of the present disclosure can include an ethylene copolymer in an amount of 45 wt% to 55 wt% based on the total weight of the polyethylene resin composition, wherein the ethylene copolymer has a melt flow index MI21.6 (21.6 kg load, 190°C) of 0.26 g / 10 min to 0.50 g / 10 min, a density of 0.919 g / cm 3 to 0.924 g / cm 3 , and a weight average molecular weight (Mw) of 450,000 g / mol to 650,000 g / mol.

[0015] The comonomer contained in the ethylene copolymer can include at least one of 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, or 1-eicosene.

[0016] The polyethylene resin composition can have a melt flow index MI5 (5 kg load, 190°C) of 0.16 g / 10 min to 0.30 g / 10 min.

[0017] The polyethylene resin composition can have a melt flow rate ratio (MFRR, MI21.6 / MI5) of 30 to 40.

[0018] The polyethylene resin composition can have a density of 0.956 g / cm 3 to 0.960 g / cm 3 .

[0019] The polyethylene resin composition can have a zero shear viscosity (η0) of 5,000,000 poise to 25,000,000 poise.

[0020] To achieve the above object, according to another embodiment of the present disclosure, a method of preparing a polyethylene resin composition can include preparing an ethylene copolymer using an ethylene monomer and a comonomer in the presence of a catalyst in a plurality of slurry polymerization reactors including a first reactor and a second reactor connected to each other, wherein the ethylene copolymer prepared in the first reactor has a melt flow index MI21.6 (21.6 kg load, 190°C) of 0.26 g / 10 min to 0.50 g / 10 min, a density of 0.919 g / cm 3 to 0.924 g / cm 3 , a weight average molecular weight (Mw) of 450,000 g / mol to 650,000 g / mol, and a polymerization rate of 45 wt% to 55 wt% in the first reactor.

[0021] The catalyst can be a Ziegler-Natta catalyst.

[0022] To achieve the above object, according to another embodiment of the present disclosure, an article can be produced from the polyethylene resin composition.

[0023] The article can have a crack round bar (CRB, 12.5 MPa) property of 1,500,000 cycles or more.

[0024] The article can have a strain hardening modulus of 70 MPa to 90 MPa.

[0025] The article can have a pipe hydrostatic pressure test (20°C, 12.0 MPa) property of 100 hours or more.

[0026] The article can have a Charpy impact strength (-30°C) of 10 kJ / m 2 to 15 kJ / m 2 .

[0027] The article can be a pipe. DETAILED DESCRIPTION

[0028] Advantages and features of the present disclosure and a method of achieving the same will be clearly understood from the following detailed description of the embodiments taken in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments and can be implemented in various forms. The embodiments are merely provided to give a complete and thorough understanding of the technical concept of the present disclosure to one of ordinary skill in the art, and the present disclosure is limited only by the scope of the claims.

[0029] Before proceeding with the description, a brief description of the meanings of the terms used herein will be given. However, the explanation of the terms is for better understanding of the present disclosure, and the terms should not be interpreted as limiting the technical idea of the present disclosure, unless the context clearly indicates that the terms are used to limit the scope of the present disclosure.

[0030] The terminology used herein is for the purpose of describing illustrative embodiments only and is not intended to be limiting of the scope of the present disclosure. As used herein, singular forms are intended to include the plural forms as well unless the context clearly indicates otherwise. It will be further understood that the terms "includes" and / or "including," when used herein, specify the presence of

[0031] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is

[0032] Embodiments of the present disclosure will be described in detail below.

[0033] According to one embodiment, the present disclosure provides a polyethylene resin composition. The polyethylene resin composition can include 45 to 55 wt% of an ethylene copolymer based on the total weight of the polyethylene resin composition, the ethylene copolymer can have a melt flow index MI21.6 (21.6 kg load, 190℃) of 0.26 to 0.50 g / 10 min, a density of 0.919 to 0.924 g / cm3, and a weight average molecular weight (Mw) of 450,000 to 650,000 g / mol. 3 to 0.924 g / cm3 3 , a weight average molecular weight (Mw) of 450,000 to 650,000 g / mol.

[0034] In one embodiment, the polyethylene resin composition can include 45 to 55 wt%, 47 to 53 wt%, or 50 to 53 wt% of the ethylene copolymer based on the total weight of the polyethylene resin composition. The polyethylene resin composition including the ethylene copolymer in the above range can have excellent pressure resistance and slow crack growth resistance.

[0035] In one embodiment, the melt flow index MI21.6 (21.6 kg load, 190°C) of the ethylene copolymer can be 0.26 g / 10 min to 0.50 g / 10 min, 0.30 g / 10 min to 0.45 g / 10 min, or 0.30 g / 10 min to 0.35 g / 10 min. The melt flow index MI21.6 of the ethylene copolymer is measured at 190°C with a 21.6 kg load using an orifice having an inner diameter of 2.75 mm. When the ethylene copolymer comprising a melt flow index MI21.6 within the above range is included, pressure resistance and slow crack growth resistance can be excellent, and in addition, appearance can be improved.

[0036] The density of the ethylene copolymer can be 0.919 g / cm 3 to 0.924 g / cm 3 , 0.919 g / cm 3 to 0.922 g / cm 3 , or 0.919 g / cm 3 to 0.921 g / cm 3 . The density of the ethylene copolymer can be within the above range, thereby allowing the pipe to have excellent pressure resistance and slow crack growth resistance.

[0037] The weight average molecular weight (Mw) of the ethylene copolymer can be 450,000 g / mol to 650,000 g / mol, 500,000 g / mol to 650,000 g / mol, or 550,000 g / mol to 600,000 g / mol. The weight average molecular weight of the ethylene copolymer is measured by gel permeation chromatography (GPC). When the ethylene copolymer comprises an ethylene copolymer having a density within the above range, slow crack growth resistance can be excellent.

[0038] The comonomer included in the ethylene copolymer can include at least one of 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, or 1-eicosene, and as a specific example, the comonomer can be 1-hexene.

[0039] In one embodiment, the polyethylene resin composition can have a melt flow index MI5 (5 kg load, 190°C) of 0.16 g / 10 min to 0.30 g / 10 min, 0.16 g / 10 min to 0.26 g / 10 min, or 0.20 g / 10 min to 0.26 g / 10 min. The melt flow index MI5 of the polyethylene resin composition is measured at 190°C under a load of 5 kg using an orifice having an inner diameter of 2.095 mm. The melt flow index MI5 of the polyethylene resin composition can be in the above range, thereby preventing deterioration of pressure resistance of a pipe due to a decrease in density, further improving pressure resistance and slow crack growth resistance, and further preventing processability problems such as poor appearance in a pipe forming process.

[0040] In one embodiment, the polyethylene resin composition can have a MFRR (melt flow rate ratio, MI21.6 / MI5) of 30 to 40, 32 to 38, or 34 to 36, the MFRR being a ratio of melt flow indices (MI21.6 / MI5) each measured at 190°C under a load of 21.6 kg and 5 kg using an orifice having an inner diameter of 2.095 mm. The polyethylene resin composition has the MFRR in the above range, thereby preventing processability problems such as poor appearance in a pipe forming process due to a decrease in melt flow index.

[0041] In one embodiment, the polyethylene resin composition can have a density of 0.950 g / cm 3 to 0.966 g / cm 3 , 0.953 g / cm 3 to 0.962 g / cm 3 , or 0.955 g / cm 3 to 0.960 g / cm 3 . The polyethylene resin composition can have the density in the above range, thereby simultaneously exhibiting excellent pressure resistance and slow crack growth resistance of a pipe.

[0042] The polyethylene resin composition can have a zero shear viscosity (η0) of 5,000,000 poise to 25,000,000 poise, or 10,000,000 poise to 25,000,000 poise. The zero shear viscosity can be obtained by measuring changes in storage modulus and loss modulus with respect to shear rate (unit: rad / sec). When the zero shear viscosity of the polyethylene resin composition is in the above range, a sagging problem due to thickness imbalance when the polyethylene resin composition flows in a gravitational direction before being cooled in a pipe extrusion process can be solved.

[0043] In one embodiment, the present disclosure provides a method of preparing a polyethylene resin composition. The method of preparing a polyethylene resin composition includes preparing a polyethylene resin composition comprising an ethylene copolymer using ethylene monomers and comonomers in the presence of a catalyst in a plurality of slurry polymerization reactors including a first reactor and a second reactor connected to each other, wherein the ethylene copolymer prepared in the first reactor has a melt flow index MI21.6 (21.6 kg load, 190°C) of 0.26 g / 10 min to 0.50 g / 10 min, a density of 0.919 g / cm3to 0.924 g / cm3, a weight average molecular weight (Mw) of 450,000 g / mol to 650,000 g / mol, and a polymerization rate in the first reactor of 45 wt% to 55 wt%. 3 to 0.924 g / cm3 3 , a weight average molecular weight (Mw) of 450,000 g / mol to 650,000 g / mol, and a polymerization rate in the first reactor of 45 wt% to 55 wt%.

[0044] In one embodiment, the catalyst can be a Ziegler-Natta catalyst. The slurry polymerization reaction can be performed in the presence of the Ziegler-Natta catalyst. Specifically, the polyethylene resin composition can be prepared by performing slurry polymerization in a two-stage polymerization manner by feeding ethylene monomers and comonomers in the presence of the Ziegler-Natta catalyst using the first reactor and the second reactor connected in series.

[0045] The Ziegler-Natta catalyst is a known conventional Ziegler-Natta catalyst, and a transition metal compound belonging to Group IV, Group V, or Group VI of the periodic table of elements can be used as a main catalyst. Among them, the most commonly used Ziegler-Natta catalyst is a halogenated complex containing magnesium and titanium, or a halogenated complex containing magnesium and vanadium.

[0046] In one embodiment, the comonomer contained in the ethylene copolymer can include at least one of 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, or 1-eicosene. As a specific example, the comonomer can be 1-hexene.

[0047] In one embodiment, the melt flow index MI21.6 (21.6 kg load, 190°C) of the ethylene copolymer prepared in the first reactor can be 0.26 g / 10 min to 0.50 g / 10 min, 0.30 g / 10 min to 0.45 g / 10 min, or 0.30 g / 10 min to 0.35 g / 10 min. When the ethylene copolymer having a melt flow index MI21.6 in the above range is prepared in the first reactor, the pressure resistance and slow crack growth resistance of the polyethylene resin composition can be excellent, and the appearance can be improved.

[0048] The density of the ethylene copolymer can be 0.919 g / cm 3 to 0.924 g / cm 3 , 0.919 g / cm 3 to 0.922 g / cm 3 , or 0.919 g / cm 3 to 0.921 g / cm 3 . Since the density of the ethylene copolymer is within the above range, the pipe has both excellent pressure resistance and excellent slow crack growth resistance.

[0049] The weight average molecular weight (Mw) of the ethylene copolymer can be 450,000 g / mol to 650,000 g / mol, 500,000 g / mol to 650,000 g / mol, or 550,000 g / mol to 600,000 g / mol. The weight average molecular weight of the ethylene copolymer is measured by gel permeation chromatography (GPC). When the density of the ethylene copolymer is within the above range, the slow crack growth resistance can be excellent.

[0050] The polymerization rate in the first reactor can be 45 wt% to 55 wt%, 47 wt% to 53 wt%, or 50 wt% to 53 wt%. The polyethylene resin composition comprising the ethylene copolymer, the polymerization rate of which is within the above range, can exhibit excellent pressure resistance and slow crack growth resistance when it is produced in the first reactor.

[0051] The melt flow index MI21.6 (21.6 kg load, 190°C) of the ethylene copolymer can be 0.26 g / 10 min to 0.50 g / 10 min, 0.30 g / 10 min to 0.45 g / 10 min, or 0.30 g / 10 min to 0.35 g / 10 min. The melt flow index MI21.6 of the ethylene copolymer is measured at 190°C under a 21.6 kg load using an orifice having an inner diameter of 2.75 mm. When the ethylene copolymer comprising the melt flow index MI21.6 within the above range, the pressure resistance and the slow crack growth resistance can be excellent, and the appearance can also be improved.

[0052] In one embodiment, the melt flow index MI5 (5 kg load, 190°C) of the ethylene comonomer prepared in the second reactor can be 0.16 g / 10 min to 0.30 g / 10 min, 0.16 g / 10 min to 0.26 g / 10 min, or 0.20 g / 10 min to 0.26 g / 10 min. The melt flow index MI5 of the ethylene copolymer is measured at 190°C under a load of 5 kg using an orifice having an inner diameter of 2.095 mm. The ethylene copolymer has a melt flow index MI5 within the above range, thereby avoiding a decrease in pipe pressure resistance due to a decrease in density, further improving pressure resistance and slow crack growth resistance, and further preventing processability problems such as poor appearance during pipe forming.

[0053] In one embodiment, the MFRR (melt flow rate ratio) of the polyethylene resin composition refers to the ratio of the melt flow indices measured at 190°C under a load of 21.6 kg and 5 kg using an orifice having an inner diameter of 2.095 mm (MI21.6 / MI5), and the MFRR of the polyethylene resin composition can be 30 to 40, 32 to 38, or 34 to 36. The polyethylene resin composition can have an MFRR within the above range, thereby preventing processability problems such as poor appearance during pipe forming due to a decrease in melt flow index.

[0054] The density of the polyethylene resin composition can be 0.950 g / cm 3 to 0.966 g / cm 3 , 0.953 g / cm 3 to 0.962 g / cm 3 , or 0.955 g / cm 3 to 0.960 g / cm 3 . The polyethylene resin composition has a density within the above range, thereby allowing the pipe to have excellent pressure resistance and slow crack growth resistance.

[0055] The zero shear viscosity (η0) of the polyethylene resin composition can be 5,000,000 poise to 25,000,000 poise, or 10,000,000 poise to 25,000,000 poise. When the zero shear viscosity of the polyethylene resin composition is within the above range, a "sag" problem caused by thickness imbalance when the polyethylene resin composition flows in the direction of gravity before cooling during pipe extrusion can be solved.

[0056] In one embodiment, in the step of preparing the polyethylene resin composition, an additive including at least one of an antioxidant or a neutralizing agent can also be added, and the content of the additive can be 0.1 to 5 parts by weight based on 100 parts by weight of the polyethylene resin composition.

[0057] The type of antioxidant is not particularly limited, and the antioxidant can include at least one selected from the group consisting of, for example, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 1,6-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamido]hexane, 1,6-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamido]propane, tetrakis[methylene-(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane, and bis(2,4-di-tert-butylphenyl)pentaerythrityl diphosphite.

[0058] The content of the antioxidant can be 0.1 to 5 parts by weight, or 0.2 to 0.4 parts by weight, based on 100 parts by weight of the polyethylene resin composition. When the content of the antioxidant is within the above range, corrosion and discoloration due to oxidation of the pipe can be prevented.

[0059] The type of neutralizing agent is not particularly limited, and for example, can include at least one selected from the group consisting of calcium stearate, zinc stearate, basic magnesium aluminum carbonate, zinc oxide, and basic magnesium stearate.

[0060] The content of the neutralizing agent can be 0.01 to 0.3 parts by weight, or 0.1 to 0.2 parts by weight, based on 100 parts by weight of the polyethylene resin composition. When the content of the neutralizing agent is within the above range, the sag resistance, slow crack growth resistance, and odor of the pipe can be improved.

[0061] According to one embodiment, the present disclosure provides an article produced from the polyethylene resin composition. The method of producing the article from the polyethylene resin composition is not particularly limited. For example, the method of producing the article from the polyethylene resin composition can include passing the polyethylene resin composition through an extruder. At this time, the extruder can be operated at a temperature of 230°C to 250°C, such as 240°C to 250°C, and a speed of 1050 rpm to 1150 rpm, such as 1080 rpm to 1140 rpm.

[0062] Due to the excellent pressure resistance and slow crack growth resistance, the polyethylene resin composition can be used for pipes, and more particularly, for producing pipes that are introduced using a non-conventional installation method.

[0063] The article can be a pipe for applications such as water pipes, gas pipes, and industrial pipes, and in particular, can be a pipe that is introduced by a non-conventional installation method, which requires excellent slow crack growth resistance.

[0064] The CRB (Crack Round Bar, 12.5 MPa) performance of the article can be 1,500,000 cycles or more cycles, 1,500,000 cycles to 3,500,000 cycles, 1,800,000 cycles to 3,000,000 cycles, or 1,900,000 cycles to 2,500,000 cycles, measured according to ISO 18489. When the CRB performance is within the above range, the resistance to slow crack growth can be very excellent, and thus a pipe using a very unconventional installation method can be easily produced.

[0065] The article can have a strain hardening modulus of 70 MPa to 90 MPa, 75 MPa to 90 MPa, or 75 MPa to 85 MPa, measured according to ISO 18488. When the article has a strain hardening modulus within the above range, a pipe having excellent long-term stability can be provided due to improved resistance to slow crack growth.

[0066] The pipe pressure resistance (measured by hydrostatic pressure test) performance of the article (condition 20℃, 12.0 MPa) is 100 hours or more, or 150 hours or more. The pipe pressure resistance is measured according to ISO 1167. Specifically, a pipe having a dn of 32 mm (SDR11) is molded using the polyethylene resin composition, and the breaking time is measured under a hoop stress condition of 20℃ and 12.0 MPa. When the breaking time is less than 100 hours, the pipe can not satisfy the minimum strength required for a PE100 material, and can not be suitable for a gas pipe, a water pipe, etc.

[0067] The Charpy impact strength (-30℃) of the article can be 10 kJ / m 2 to 15 kJ / m 2 , or 12 kJ / m 2 to 15 kJ / m 2 , measured according to ISO 1872-2. When the Charpy impact strength of the article is within the above range, a pipe having excellent impact strength can be obtained.

[0068] Hereinafter, specific embodiments of the present disclosure will be described. However, the embodiments described hereinafter are for the purpose of exemplifying or explaining the present disclosure in detail, and should not be construed as limiting the scope of the present disclosure. In addition, other details that can be sufficiently conceived by those skilled in the art will not be described.

[0069] (Preparation of the polyethylene resin composition)

[0070] Example 1

[0071] Two-stage polymerization was performed by continuous slurry polymerization using a first reactor and a second reactor connected in series, with a Ziegler-Natta catalyst as a catalyst, and 1-hexene as a comonomer.

[0072] The melt flow index MI21.6 of the ethylene copolymer obtained in the first reactor was 0.30 g / 10 min, the density was 0.919 g / cm 3 , the weight average molecular weight was 565000 g / mol, and the polymerization rate in the first reactor was 52 wt%.

[0073] The reaction product obtained in the first reactor was supplied to the second reactor to participate in the reaction, and a polyethylene resin composition in the form of a pellet was produced from the reaction product of the second reactor, the melt flow index MI5 of the polyethylene resin composition was 0.20 g / 10 min, the MFRR was 36, and the density was 0.956 g / cm 3 .

[0074] Example 2

[0075] A two-stage polymerization was performed by continuous slurry polymerization using a first reactor and a second reactor connected in series, with a Ziegler-Natta catalyst as a catalyst, and 1-hexene as a comonomer.

[0076] The melt flow index MI21.6 of the ethylene copolymer obtained in the first reactor was 0.35 g / 10 min, the density was 0.920 g / cm 3 , the weight average molecular weight was 560000 g / mol, and the polymerization rate in the first reactor was 51 wt%.

[0077] The reaction product obtained in the first reactor was supplied to the second reactor to participate in the reaction, and a polyethylene resin composition in the form of a pellet was produced from the reaction product of the second reactor, the melt flow index MI5 of the polyethylene resin composition was 0.21 g / 10 min, the MFRR was 36, and the density was 0.957 g / cm 3 .

[0078] Comparative Example 1

[0079] A polyethylene resin composition was produced in the same manner as in Embodiment 1, except that the composition and the conditions shown in Table 1 below were used.

[0080] In comparison with Example 1, by adjusting the polymerization rate of the ethylene copolymer in the first reactor to 49 wt%, the melt flow index MI21.6 of the ethylene copolymer obtained was 0.51 g / 10 min, the density was 0.925 g / cm 3 , and the weight average molecular weight was 445000 g / mol. The melt flow index MI5 of the pellet-like polyethylene resin composition thus produced was 0.22 g / 10 min, the MFRR was 41, and the density was 0.958 g / cm 3 .

[0081] Comparative Example 2

[0082] A polyethylene resin composition was prepared in the same manner as in Embodiment 1, except according to the composition and conditions shown in Table 1 below.

[0083] Compared with Example 1, by adjusting the polymerization rate of the ethylene copolymer in the first reactor to 50% by weight, the melt flow index MI21.6 of the obtained ethylene copolymer is 0.25 g / 10 min and the density is 0.917 g / cm 3 , a weight average molecular weight of 655000 g / mol; the melt flow index MI5 of the granular polyethylene resin composition prepared thereby is 0.15 g / 10 min, MFRR is 29, and the density is 0.954 g / cm 3 .

[0084] Comparative Example 3

[0085] A polyethylene resin composition was prepared in the same manner as in Example 1, except according to the composition and conditions shown in Table 1 below.

[0086] Compared with Example 1, by adjusting the polymerization rate of the ethylene copolymer in the first reactor to 49 wt %, the melt flow index MI21.6 of the obtained ethylene copolymer is 0.42 g / 10 min and the density is 0.926 g / cm 3 , a weight average molecular weight of 540,000 g / mol; the melt flow index MI5 of the granular polyethylene resin composition prepared thereby is 0.22 g / 10 min, MFRR is 34, and the density is 0.959 g / cm 3 .

[0087] Comparative Example 4

[0088] A polyethylene resin composition was prepared in the same manner as in Example 1, except according to the composition and conditions shown in Table 1 below.

[0089] Compared with Example 1, by adjusting the polymerization rate of the ethylene copolymer in the first reactor to 49 wt %, the melt flow index MI21.6 of the obtained ethylene copolymer is 0.42 g / 10 min and the density is 0.918 g / cm 3 , a weight average molecular weight of 540,000 g / mol; the melt flow index MI5 of the granular polyethylene resin composition prepared thereby is 0.24 g / 10 min, MFRR is 34, and the density is 0.954 g / cm 3 .

[0090] Comparative Example 5

[0091] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 1 below were used.

[0092] Compared to Example 1, by adjusting the polymerization rate of the ethylene copolymer in the first reactor to 47 wt%, the melt flow index MI21.6 of the obtained ethylene copolymer was 0.48 g / 10 min, the density was 0.924 g / cm3, and the weight average molecular weight was 460000 g / mol; the melt flow index MI5 of the granular polyethylene resin composition thus prepared was 0.31 g / 10 min, the MFRR was 42, and the density was 0.960 g / cm3. 3 3 .

[0093] Comparative Example 6

[0094] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 1 below were used.

[0095] Compared to Example 1, by adjusting the polymerization rate of the ethylene copolymer in the first reactor to 54 wt%, the melt flow index MI21.6 of the obtained ethylene copolymer was 0.48 g / 10 min, the density was 0.919 g / cm3, and the weight average molecular weight was 460000 g / mol; the melt flow index MI5 of the granular polyethylene resin composition thus prepared was 0.19 g / 10 min, the MFRR was 33, and the density was 0.956 g / cm3. 3 3 .

[0096] Table 1

[0097]

[0098] Test 1 : Measurement of physical properties of polyethylene resin compositions

[0099] The following physical properties of the polyethylene resin compositions prepared in Examples 1 and 2 and Comparative Examples 1 to 6 were measured, and the results are shown in Table 2.

[0100] Melt flow index (MI)

[0101] The melt flow index MI21.6 was measured according to ASTM D1238 at 190℃ under a load of 21.6 kg (orifice inner diameter 2.75 mm).

[0102] The melt flow index MI5 was measured according to ASTM D1238 at 190℃ under a load of 5 kg (orifice inner diameter 2.095 mm).

[0103] Melt flow rate ratio (MFRR) ​​

[0104] The ratio of melt flow index measured at 190 °C and 21.6 kg load to melt flow index measured at 5 kg load (orifice inner diameter of 2.095 mm) was calculated according to ASTM D1238.

[0105] Density

[0106] Measured according to ASTM D1505.

[0107] Weight average molecular weight (Mw)

[0108] Measured by gel permeation chromatography (GPC).

[0109] Zero shear viscosity (η0)

[0110] The storage modulus (G’) and loss modulus (G”) were measured as a function of shear rate (in rad / sec) using ARES (Advanced Rheometric Expansion System, 190 °C) and the zero shear viscosity (η0) was calculated by applying the resulting values to the Carreau model.

[0111] Test 2: Measurement of pipe properties

[0112] The following properties of the pipes produced using the polyethylene resin compositions prepared in Examples 1 and 2 and Comparative Examples 1 to 6 were measured, and the results are shown in Table 2.

[0113] Fatigue test (crack round bar test, CRB)

[0114] The fatigue test was performed according to ISO 18489, with a target stress range of 11.5 ~ 13.5 MPa, and the number of cycles at an extrapolated stress of 12.5 MPa.

[0115] Strain hardening modulus (SHM)

[0116] Measured according to ISO 18488.

[0117] Charpy impact strength

[0118] Measured according to ISO 179 / 1 Ea at -30 °C using samples satisfying the requirements of ISO 1872-2.

[0119] Hydrostatic pressure test

[0120] A pipe having a dn of 32 mm, a size of SDR 11 was produced using the polyethylene resin composition, and the breaking time was measured according to ISO 1167 under a hoop stress condition of 20 °C and 12.0 MPa.

[0121] Appearance

[0122] Pipes with a dn of 32 mm (SDR11) or dn of 110 mm (SDR11) were produced from the polyethylene resin composition using a pipe extrusion device (uniEX 35-30C) from Battenfeld-Cincinnati GmbH. The outer and inner surfaces of the produced pipes were visually observed and evaluated for appearance according to the following criteria.

[0123] [Test standard]

[0124] ○: The surface is smooth and normal

[0125] ×: The surface is rough and has uneven surfaces.

[0126] [Table 2]

[0127]

[0128]

[0129] As can be seen from Table 2 above, the melt flow index MI21.6 of Comparative Example 1 is 0.51 g / 10 min and the density is 0.925 g / cm 3 , the weight average molecular weight is 445000 g / mol, which exceeds the range of the polyethylene resin composition for pipes according to one embodiment. At this time, the CRB is 120×10 4 cycles, which means that its resistance to slow crack growth is significantly reduced compared with Example 1.

[0130] The melt flow index MI21.6 of Comparative Example 2 is 0.25 g / 10 min and the density is 0.917 g / cm 3 The weight-average molecular weight was 655,000 g / mol, exceeding the range of the polyethylene resin composition for pipes according to one embodiment. The hydrostatic pressure test had a rupture time of 60 hours, significantly reducing the pressure resistance of the pipe and causing appearance problems.

[0131] The density of the ethylene copolymer of Comparative Example 3 is 0.926 g / cm 3 , which exceeds the range of the polyethylene resin composition for pipes according to one embodiment, in which case the CRB is 140×10 4 This means that compared with Examples 1 and 2, its resistance to slow crack growth is significantly reduced.

[0132] The density of the ethylene copolymer of Comparative Example 4 is 0.918 g / cm 3, the breaking time in the hydrostatic pressure test was 80 hours, which means that the pressure resistance of the pipe was significantly reduced.

[0133] The ethylene copolymer polymerization rate in the first reactor of Comparative Example 5 was 44 wt%, and the melt flow index MI5 of the granular polyethylene resin composition thus produced was 0.31 g / 10 min, which was outside the range of the polyethylene resin composition for pipes according to one embodiment. At this time, the CRB was 110 x 10 4 times of the slow crack growth resistance and the impact strength was also reduced compared to Examples 1 and 2.

[0134] The ethylene copolymer polymerization rate of Comparative Example 6 was 56 wt%, which was outside the range of the polyethylene resin composition for pipes according to one embodiment. At this time, the breaking time in the hydrostatic pressure test was 70 hours, which means that the pressure resistance of the pipe was significantly reduced.

[0135] As can be seen from the above Table 1, Examples 1 and 2 using the polyethylene resin composition according to one embodiment exhibited excellent slow crack growth resistance and satisfied the pressure resistance requirement of pipes, thereby satisfying the conventional PE100 requirement, compared to Comparative Examples 1 to 6.

[0136] As is apparent from the above, the polyethylene resin composition according to the present disclosure can be used to produce pipes using a non-conventional installation method due to its excellent pressure resistance and slow crack growth resistance.

[0137] The effects of the present disclosure are not limited to the above-mentioned effects, and other technical effects not mentioned will be apparent to those skilled in the art from the above description of the exemplary embodiments.

[0138] Although embodiments of the present disclosure have been disclosed, those skilled in the art will understand that various modifications, additions and substitutions can be made without departing from the scope and spirit of the present disclosure. Therefore, it is apparent that the above exemplary embodiments are illustrative in all aspects and do not limit the present disclosure.

Claims

1. A polyethylene resin composition comprising: 45 to 55 wt% of an ethylene copolymer, based on the total weight of the polyethylene resin composition, wherein The ethylene copolymer has a melt flow index MI21 6 (21.6 kg load, 190 °C) of 0.26 g / 10 min to 0.50 g / 10 min, a density of 0.919 g / cm 3 to 0.924 g / cm 3 and a weight average molecular weight (Mw) of 450 000 g / mol to 650 000 g / mol.

2. The polyethylene resin composition according to claim 1, wherein, the comonomer contained in the ethylene copolymer includes at least one of 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, or 1-eicosene.

3. The polyethylene resin composition of claim 1, wherein, The polyethylene resin composition has a melt flow index MI5 (5 kg load, 190℃) of 0.16 to 0.30 g / 10 min.

4. The polyethylene resin composition according to claim 1, wherein The polyethylene resin composition has a melt flow rate ratio (MFRR, MI21.6 / MI5) of 30 to 40.

5. The polyethylene resin composition of claim 1, wherein, The polyethylene resin composition has a density of 0.956 g / cm 3 to 0.960 g / cm 3 .

6. The polyethylene resin composition of claim 1, wherein, The polyethylene resin composition has a zero shear viscosity (η0) of 5000000 to 25000000 poise.

7. The polyethylene resin composition of claim 1, wherein, The polyethylene resin composition is used for producing a pipe. 8.A method of producing a polyethylene resin composition comprising an ethylene copolymer using an ethylene monomer and a comonomer in the presence of a catalyst in a plurality of slurry polymerization reactors, the plurality of slurry polymerization reactors including a first reactor and a second reactor connected to each other, wherein The melt flow index MI21 6 (21.6 kg load, 190°C) of the ethylene copolymer produced in the first reactor is 0.26 g / 10 min to 0.50 g / 10 min, the density is 0.919 g / cm3to 0.924 g / cm3 3 to 0.924 g / cm3 3 , the weight average molecular weight (Mw) is 450 000 g / mol to 650 000 g / mol, and the molecular weight distribution (Mw / Mn) is 2.0 to 3.

5. a polymerization rate in the first reactor is 45 to 55 wt%.

9. The method of claim 8, wherein, The catalyst is a Ziegler-Natta catalyst. 10.An article produced from the polyethylene resin composition according to any one of claims 1 to 7.

11. The article of claim 10, wherein, The article has a crack round bar (CRB, 12.5 MPa) performance of 1500000 cycles or more.

12. The article of claim 10, wherein, The article has a strain hardening modulus of 70 to 90 MPa.

13. The article of claim 10, wherein, The article has a pipe hydrostatic pressure test (20℃, 12.0 MPa) performance of 100 hours or more.

14. The article of claim 10, wherein, The article has a Charpy impact strength (-30°C) of 10 to 15 kJ / m 2 2 .​ 15. The article of claim 10, wherein, The article is a pipe.

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