Polyethylene resin composition for pipes, its manufacturing method and molded article manufactured therefrom

Abstract

To provide a polyethylene resin composition for pipe, which is all superior in resistance to sagging of pipe, resistance to slow crack growth, and an odor level.SOLUTION: There are provided a polyethylene resin composition for pipe which has a melt index (under a load of 5 kg, at 190°C) of 0.16 g / 10 min to 0.24 g / 10 min, and is prepared by passing through a two stage reactor, passing through an extruder, and adding a peroxide, wherein a rate of change in the melt index (MI) by the extruder is 60% to 90% according to Equation 1 below, and a rate of change in the melt index (MI) by the peroxide is 10% to 40% according to Equation 2 below, a method of preparing the same, and a molded article including the same. {(MI after passing through the two stage reactor-MI after passing through the extruder) / (MI after passing through the two stage reactor-final MI)}×100....(1) {(MI after passing through the extruder-MI after adding peroxide) / (MI after passing through the two stage reactor-final MI)}×100....(2)SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a polyethylene resin composition for pipes, a method for producing the same, and molded articles produced therefrom. [Background technology]

[0002] Polyethylene pipes are used for water pipes, sewer pipes, industrial pipes, etc., and because of their excellent resistance to sagging and slow crack growth, their use in large diameter pipes is increasing and their applications are gradually diversifying.

[0003] When processing large diameter pipes, resistance to sagging due to the weight of the pipe itself must be ensured, and this can be improved by reducing the melt index of the polyethylene resin.

[0004] The melt flow index can be reduced by changing the physical properties of the polyethylene resin itself, by changing the extrusion conditions in a post-treatment method, or by adding peroxide during extrusion.

[0005] When the melt flow index is decreased by adding peroxide, the resistance to sagging is greatly increased, but the resistance to slow crack growth is decreased and the odor level tends to increase. On the other hand, there is a limit to the effect of increasing the resistance to sagging by changing the physical properties of the polyethylene resin itself or decreasing the melt flow index only by the extrusion conditions. Summary of the Invention [Problem to be solved by the invention]

[0006] In one embodiment, a polyethylene resin composition for pipes is provided that has excellent resistance to pipe sagging, resistance to slow crack growth, and odor levels.

[0007] In another embodiment, there is provided a method for producing the polyethylene resin composition for pipes.

[0008] In yet another embodiment, a molded article made from the polyethylene resin composition for pipes is provided. [Means for solving the problem]

[0009] In one embodiment, there is provided a polyethylene resin composition for pipes having a melt flow index (5 kg load, 190°C) of 0.16 g / 10 min to 0.24 g / 10 min, and produced by passing through a two-stage reactor, passing through an extruder and adding a peroxide, wherein the rate of change in melt flow index (MI) (5 kg load, 190°C) due to the extruder is 60% to 90% according to the following formula (1), and the rate of change in melt flow index (MI) (5 kg load, 190°C) due to the peroxide is 10% to 40% according to the following formula (2).

[0010] {(MI after passing through the second reactor - MI after passing through the extruder) / (MI after passing through the second reactor - final MI)} x 100 ... (1)

[0011] {(MI after passing through the extruder - MI after adding peroxide) / (MI after passing through the second reactor - final MI)} x 100 ... (2)

[0012] The polyethylene resin composition may have a zero shear viscosity (η0) of 8,000,000 to 20,000,000 poise.

[0013] The polyethylene resin composition may have a melt strength of 200 mN to 300 mN.

[0014] The drop time when sagging occurs during extrusion of the polyethylene resin composition may be reduced by 0% to 17% relative to the drop time when no sagging occurs, and the drop time may be measured using a single-screw extruder.

[0015] The polyethylene resin composition may have a strain hardening modulus of 53 MPa to 80 MPa.

[0016] In another embodiment, there is provided a method for producing a polyethylene resin composition for pipes, comprising the steps of obtaining a polyethylene resin by passing through a two-stage reactor, adding a peroxide to the polyethylene resin, and passing the mixture through an extruder to obtain a polyethylene resin composition, wherein the extruder is operated at a temperature of 230° C. to 250° C. and at a speed of 1,050 rpm to 1,150 rpm.

[0017] The peroxide may be added in an amount of 0.001 to 0.01 parts by weight based on 100 parts by weight of the polyethylene resin.

[0018] The melt flow index (5 kg load, 190° C.) of the polyethylene resin after passing through the two-stage reactor may be 0.32 g / 10 min to 0.44 g / 10 min.

[0019] The polyethylene resin composition after passing through the extruder before the addition of the peroxide may have a melt flow index (5 kg load, 190° C.) of 0.24 g / 10 min to 0.32 g / 10 min.

[0020] The polyethylene resin composition after the peroxide is added and passed through the extruder may have a melt flow index (5 kg load, 190° C.) of 0.16 g / 10 min to 0.24 g / 10 min.

[0021] In yet another embodiment, there is provided a molded article made from the polyethylene resin composition for pipes. Effect of the Invention

[0022] The polyethylene resin composition for pipes according to an embodiment has excellent resistance to pipe sagging, resistance to slow crack growth, and odor level, and can therefore be usefully used for pipes, particularly large diameter pipes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Although the present invention will be described in detail below so that those skilled in the art can easily implement the present invention, the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0024] The polyethylene resin composition for pipes according to an embodiment may have a melt flow index (5 kg load, 190°C) of 0.16 g / 10 min to 0.24 g / 10 min, for example, 0.18 g / 10 min to 0.22 g / 10 min. When the melt flow index of the polyethylene resin composition is within the above range, the processing load during pipe processing and the surface roughness of the product may be reduced, and the resistance to pipe sagging and strain hardening modulus may be increased. As a result, a polyethylene resin composition having excellent resistance to pipe sagging and the opposing property of resistance to slow crack growth may be obtained.

[0025] The melt flow index of the polyethylene resin composition may change step by step during the manufacturing process before obtaining the final melt flow index. According to an embodiment, a polyethylene resin may be obtained by polymerizing ethylene while passing through a two-stage reactor, and then the polyethylene resin may be passed through an extruder together with the addition of peroxide to manufacture a polyethylene resin composition. In this case, the melt flow index (MI1) of the polyethylene resin immediately after passing through the two-stage reactor, the melt flow index (MI2) of the polyethylene resin composition immediately after passing through the extruder before the addition of the peroxide, and the melt flow index of the final polyethylene resin composition, i.e., the melt flow index MI3 after passing through the extruder together with the addition of the peroxide, may be different at each step. In other words, the melt flow index immediately after passing through the two-stage reactor may change its value after passing through an extruder having a predetermined operating condition (change from MI1 to MI2), and the melt flow index after passing through an extruder without the addition of the peroxide may change its value after passing through an extruder having a predetermined operating condition and further adding peroxide (change from MI2 to MI3).

[0026] According to one embodiment, the change rate from MI1 to MI2, i.e., the change rate of the melt flow index (MI) (5 kg load, 190°C) by the extruder, may be 60% to 90%, for example, 70% to 80%, according to the following formula (1):

[0027] {(MI after passing through the second reactor - MI after passing through the extruder) / (MI after passing through the second reactor - final MI)} x 100 ... (1)

[0028] In addition, the rate of change from MI2 to MI3, i.e., the rate of change of the melt flow index (MI) (5 kg load, 190°C) due to the peroxide, may be 10% to 40% according to the following formula (2), and may be, for example, 20% to 30%.

[0029] {(MI after passing through the extruder - MI after adding peroxide) / (MI after passing through the second reactor - final MI)} x 100 ... (2)

[0030] When the rate of change in melt flow index by the extruder and the rate of change in melt flow index by the peroxide are each within the above ranges, a polyethylene resin composition having excellent resistance to pipe sagging and the opposing property of resistance to slow crack growth, as well as an excellent odor level, can be obtained.

[0031] The polyethylene resin composition may have a zero shear viscosity (η0) of 8,000,000 poise to 20,000,000 poise, for example, 8,000,000 poise to 12,000,000 poise. The zero shear viscosity can be obtained by measuring a storage modulus and a loss modulus according to a shear rate (unit: rad / sec). When the polyethylene resin composition has a zero shear viscosity within the above range, it may have excellent resistance to sagging during processing of a pipe, specifically, during processing of a large-diameter pipe, and thus the polyethylene resin composition may be usefully used for a large-diameter pipe.

[0032] The melt strength of the polyethylene resin composition may be 200 mN to 300 mN, for example, 200 mN to 250 mN. The melt strength can be obtained by measuring the stabilizing force by increasing the speed at which the resin is pulled at a resin temperature of 200° C. and a chamber temperature of 180° C. When the melt strength of the polyethylene resin composition is within the above range, it may have excellent resistance to sagging during pipe processing, specifically during large-diameter pipe processing, and therefore the polyethylene resin composition may be usefully used for large-diameter pipes.

[0033] The drop time of the polyethylene resin composition when sagging occurs may be 0% to 17%, for example, 10% to 17%, relative to the drop time when sagging does not occur during extrusion. The drop time may be measured using a single-screw extruder. Specifically, the polyethylene resin composition is measured and the drop rate is calculated based on the conditions of a temperature of 200° C., an extrusion rate of 38.1 g / min, and an initial linear velocity of the extruded resin of 0.546 cm / sec, a height to the ground of 90.5 cm, and a ground arrival time of 165.7 seconds when no sagging occurs. When the drop time reduction rate is within the above range, the polyethylene resin composition may have excellent resistance to sagging during pipe processing, specifically during large-diameter pipe processing, and thus the polyethylene resin composition may be usefully used for large-diameter pipes.

[0034] The strain hardening modulus of the polyethylene resin composition may be 53 MPa to 80 MPa, for example, 53 MPa to 70 MPa. When the strain hardening modulus of the polyethylene resin composition is within the above range, the resistance to slow crack growth is excellent, so that the pipe can be used for a long period of time, and a large-diameter pipe having excellent durability can be provided.

[0035] Hereinafter, a method for preparing the polyethylene resin composition for pipes will be described in accordance with another embodiment.

[0036] The polyethylene resin composition may be produced through a step of obtaining a polyethylene resin by passing through a two-stage reactor, and a step of adding a peroxide to the polyethylene resin and passing the mixture through an extruder. At this time, the extruder may be operated at a temperature of 230° C. to 250° C., for example, at a temperature of 240° C. to 250° C., and at a speed of 1,050 rpm to 1,150 rpm, for example, at a speed of 1,080 rpm to 1,140 rpm.

[0037] When the polyethylene resin composition is produced by passing it through an extruder operated within the above temperature and speed ranges, the rate of change in melt flow index (MI) (5 kg load, 190°C) of the polyethylene resin composition through the extruder can be obtained within the range of 60% to 90%, thereby ensuring a polyethylene resin composition that is excellent in both resistance to pipe sagging and the opposing property of resistance to slow crack growth, as well as in odor level. The rate of change in melt flow index through the extruder can be obtained by the above formula (1) as described above.

[0038] Specifically, the melt flow index (5 kg load, 190° C.) of the polyethylene resin after passing through the two-stage reactor may be 0.32 g / 10 min to 0.44 g / 10 min, for example, 0.35 g / 10 min to 0.42 g / 10 min. Also, the melt flow index (5 kg load, 190° C.) of the polyethylene resin composition after passing through the extruder before the addition of the peroxide may be 0.24 g / 10 min to 0.32 g / 10 min, for example, 0.24 g / 10 min to 0.28 g / 10 min.

[0039] In addition, when the polyethylene resin composition is produced by passing it through an extruder together with the addition of the peroxide, the change rate of the melt flow index (MI) (5 kg load, 190°C) of the polyethylene resin composition due to the peroxide can be obtained within a range of 10% to 40%, thereby ensuring a polyethylene resin composition that is excellent in all of resistance to pipe sagging, resistance to slow crack growth, which is the opposing property, and odor level.

[0040] Specifically, the melt flow index (5 kg load, 190° C.) of the polyethylene resin composition after passing through the extruder before the addition of the peroxide, and the melt flow index of the polyethylene resin composition after passing through the extruder together with the addition of the peroxide, i.e., the melt flow index of the final polyethylene resin composition, are as exemplified above.

[0041] The peroxide may be added in an amount of 0.001 to 0.01 parts by weight, for example, 0.001 to 0.005 parts by weight, or 0.001 to 0.003 parts by weight, based on 100 parts by weight of the polyethylene resin. When the peroxide is added in an amount within the above range, a polyethylene resin composition having excellent resistance to pipe sagging, resistance to slow crack growth, and odor level can be obtained.

[0042] In the step of obtaining the polyethylene resin composition, an additive including an antioxidant, a neutralizing agent, or a combination thereof may be further included. The additive may be included in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the polyethylene resin composition.

[0043] The antioxidant may include 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, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol-di-phosphite, or combinations thereof.

[0044] The antioxidant may be included in an amount of 0.01 to 0.5 parts by weight, for example, 0.2 to 0.4 parts by weight, based on 100 parts by weight of the polyethylene resin composition. When the antioxidant is included within the above content range, a polyethylene resin composition having excellent resistance to pipe sagging, resistance to slow crack growth, and odor level can be obtained.

[0045] The neutralizing agent may include calcium stearate, zinc stearate, magnesium aluminum hydroxycarbonate, zinc oxide, magnesium hydroxystearate, or combinations thereof.

[0046] The neutralizing agent may be included in an amount of 0.01 to 0.3 parts by weight, for example, 0.1 to 0.2 parts by weight, based on 100 parts by weight of the polyethylene resin composition. When the neutralizing agent is included within the above content range, a polyethylene resin composition having excellent resistance to pipe sagging, resistance to slow crack growth, and odor level can be obtained.

[0047] According to yet another embodiment, there is provided a molded article made from the polyethylene resin composition.

[0048] The molded product may be a pipe used for water pipes, sewer pipes, industrial pipes, etc., and specifically may be a large-diameter pipe having a large diameter.

[0049] The polyethylene resin composition described above has excellent resistance to pipe sagging, resistance to slow crack growth, and odor levels, and may therefore be usefully used in large diameter pipes. EXAMPLES

[0050] Specific examples of the present invention will be presented below. However, the examples described below are merely for the purpose of specifically illustrating or explaining the present invention, and are not intended to limit the present invention. In addition, since the contents not described here can be sufficiently inferred by those skilled in the art, the description thereof will be omitted.

[0051] <Production of polyethylene resin composition> [Example 1] Ethylene polymerization was carried out using a Ziegler-Natta catalyst and 1-hexene comonomer in a series polymerization system in which two reactors were connected in series.

[0052] The melt flow index (5 kg load, 190° C.) of the powder-type polyethylene resin obtained after the second-stage reactor was 0.40 g / 10 min.

[0053] 100 parts by weight of the powder-type polyethylene resin obtained above was mixed with 0.15 parts by weight of Irganox 1010 and 0.15 parts by weight of Irgafos-168 as antioxidants, 0.15 parts by weight of calcium stearate as a neutralizing agent, and 0.001 parts by weight of Trigonox 101 as a peroxide in a Henschel mixer, and then a pellet-shaped polyethylene resin composition was produced using a twin screw extruder. At this time, the twin screw extruder had a screw with a diameter of 608 mm and an L / D (screw length / diameter) of 8, and was operated at a temperature of 240° C. and a speed of 1,090 rpm.

[0054] The melt flow index (5 kg load, 190°C) of the pelletized polyethylene resin composition produced from this was 0.25 g / 10 min before the peroxide was added and 0.21 g / 10 min after the peroxide was added, as shown in Table 1 below.

[0055] [Example 2] Ethylene polymerization was carried out using a Ziegler-Natta catalyst and 1-hexene co-monomer in a series polymerization system in which two reactors were connected in series.

[0056] The melt flow index (5 kg load, 190° C.) of the powder-type polyethylene resin obtained after the second-stage reactor was 0.40 g / 10 min.

[0057] 100 parts by weight of the powder-type polyethylene resin obtained above was mixed with 0.15 parts by weight of Irganox 1010 and 0.15 parts by weight of Irgafos-168 as antioxidants, 0.15 parts by weight of calcium stearate as a neutralizer, and 0.002 parts by weight of Trigonox 101 as a peroxide in a Henschel mixer, and then a pellet-shaped polyethylene resin composition was produced using a twin screw extruder. At this time, the twin screw extruder had a screw with a diameter of 608 mm and an L / D (screw length / diameter) of 8, and was operated at a temperature of 240° C. and a speed of 1,090 rpm.

[0058] The melt flow index (5 kg load, 190°C) of the pelletized polyethylene resin composition produced from this was 0.25 g / 10 min before the peroxide was added and 0.19 g / 10 min after the peroxide was added, as shown in Table 1 below.

[0059] [Comparative Example 1] A polyethylene resin composition was produced in the same manner as in Example 1, except that no peroxide was added.

[0060] The melt flow index (5 kg load, 190° C.) of a pelletized polyethylene resin composition produced from this was 0.25 g / 10 min.

[0061] [Comparative Example 2] A polyethylene resin composition was produced in the same manner as in Example 1, except that the melt flow index (5 kg load, 190°C) of the powder-type polyethylene resin obtained after the second-stage reactor was 0.35 g / 10 min instead of 0.40 g / 10 min, and no peroxide was added.

[0062] The melt flow index (5 kg load, 190° C.) of a pelletized polyethylene resin composition produced from this was 0.21 g / 10 min.

[0063] [Comparative Example 3] A polyethylene resin composition was produced in the same manner as in Example 1, except that no peroxide was added and the twin-screw extruder was operated at a temperature of 252° C. and a speed of 1,140 rpm.

[0064] The melt flow index (5 kg load, 190° C.) of a pelletized polyethylene resin composition produced from this was 0.21 g / 10 min.

[0065] [Comparative Example 4] Ethylene polymerization was carried out using a Ziegler-Natta catalyst and 1-hexene comonomer in a series polymerization system in which two reactors were connected in series.

[0066] The melt flow index (5 kg load, 190° C.) of the powder-type polyethylene resin obtained after the second reactor was 0.41 g / 10 min.

[0067] 100 parts by weight of the powder-type polyethylene resin obtained above was mixed with 0.15 parts by weight of Irganox 1010 and 0.15 parts by weight of Irgafos-168 as antioxidants, 0.15 parts by weight of calcium stearate as a neutralizing agent, and 0.02 parts by weight of Trigonox 101 as a peroxide in a Henschel mixer, and then a pellet-shaped polyethylene resin composition was produced using a single screw extruder. At this time, the single screw extruder used a screw with a diameter of 40 mm and an L / D (screw length / diameter) of 33, and was operated at a temperature of 200° C. and a speed of 90 rpm.

[0068] The melt flow index (5 kg load, 190°C) of the pelletized polyethylene resin composition produced from this was 0.36 g / 10 min before the peroxide was added and 0.20 g / 10 min after the peroxide was added, as shown in Table 1 below.

[0069] <Evaluation: Measurement of physical properties of polyethylene resin composition> The polyethylene resin compositions prepared in Examples 1 and 2 and Comparative Examples 1 to 4 were measured for the following physical properties, and the results are shown in Tables 1 and 2 below.

[0070] [Melt index (MI)] Measured at 190°C with a 5 kg load according to ASTM D1238.

[0071] [Change in Melt Flow Index (MI)] The rate of change in melt flow index due to the extruder was obtained by the following formula (1), and the rate of change in melt flow index due to the peroxide was obtained by the following formula (2).

[0072] {(MI after passing through the second reactor - MI after passing through the extruder) / (MI after passing through the second reactor - final MI)} x 100 ... (1)

[0073] {(MI after passing through the extruder - MI after adding peroxide) / (MI after passing through the second reactor - final MI)} x 100 ... (2)

[0074] [Zero shear viscosity (η0)] The storage modulus (G', storage modulus) and loss modulus (G'', loss modulus) were measured as a function of shear rate (unit: rad / sec) using ARES (advanced rheometer expansion system, 190°C), and the zero shear viscosity (η0) was calculated by applying the Carreau model.

[0075] [Melt strength] The stabilizing force was measured by increasing the speed at which the resin was pulled at a resin temperature of 200°C and a chamber temperature of 180°C.

[0076] [Drop time reduction rate] A HAAKE™ Reomex OS single screw extruder was used, and a bar-shaped die with a diameter of 12 mm was used. The temperature was 200°C, the extrusion rate was maintained at 38.1 g / min, and the initial linear velocity of the extruded resin was 0.546 cm / sec. The height to the ground was 90.5 cm, and the ground arrival time was 165.7 seconds when no sagging of the extruded resin occurred. The ground arrival time of each polyethylene resin composition was measured, and the reduction rate was calculated relative to the case when no sagging occurred.

[0077] [Strain hardening modulus (SHM)] Measured according to ISO 18488.

[0078] [Odor] 100 g of the polyethylene resin composition and 5 mL of water were placed in a sealed container, and the container was left in an oven at 80° C. for 3 hours, and then left at room temperature for 1 hour, after which the odor level was evaluated. The worse the odor level, the higher the score was given, and the evaluation was performed on a scale of 1 to 5.

[0079] [Impact strength] The Charpy impact test was performed at -30°C according to ISO 179-1.

[0080] [Oxidation induction time (OIT)] Measured according to ISO 11357-6 at 210°C.

[0081] [Table 1]

[0082] [Table 2]

[0083] As shown in Table 1, the polyethylene resin compositions according to Examples 1 and 2 satisfy the predetermined ranges according to an embodiment in terms of the final melt flow index, the rate of change in melt flow index due to the extruder, and the rate of change in melt flow index due to the peroxide. It can be seen that the polyethylene resin compositions according to Examples 1 and 2 are superior to Comparative Examples 1 to 4 in terms of resistance to pipe sagging, resistance to slow crack growth, and odor level.

[0084] On the other hand, in Comparative Example 1 where no peroxide was added, the final melt flow index was outside the range of an embodiment, and in this case, the resistance to slow crack growth and odor level were slightly better, but the zero shear viscosity and melt strength were significantly reduced, and the drop time reduction rate was significantly increased, which indicates that the resistance to pipe sagging was reduced.In addition, in Comparative Example 2, the resistance to slow crack growth was increased, but since no peroxide was added, the resistance to pipe sagging was reduced.

[0085] In Comparative Example 3, no peroxide was added and the extruder was run under conditions of temperature and speed that were not specified. Although the resistance to sagging of the pipe was slightly increased, the odor level increased due to high shear stress and the oxidation induction time decreased.

[0086] The polyethylene resin composition of Comparative Example 4 was extruded under low shear stress conditions using a single screw extruder, reducing the rate of change in melt flow index due to the extruder to 24%, and adding an excessive amount of peroxide significantly increased the rate of change in melt flow index due to the peroxide to 76%. As a result, resistance to pipe sagging was significantly increased, but the addition of a high content of peroxide significantly reduced resistance to slow crack growth and oxidation induction time, and significantly increased odor levels.

[0087] Although the above describes a preferred embodiment of the present invention, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, which of course also fall within the scope of the present invention.

Claims

1. passing through a two-stage reactor to obtain a polyethylene resin; and adding a peroxide to the polyethylene resin and passing the mixture through an extruder to obtain a polyethylene resin composition; The extruder is operated at a temperature of 230° C. to 250° C. and a speed of 1,050 rpm to 1,150 rpm; The polyethylene resin composition has a melt flow index (5 kg load, 190° C.) of 0.16 g / 10 min to 0.24 g / 10 min, In a polyethylene resin composition produced by adding a peroxide when passing through an extruder after passing through a two-stage reactor, a rate of change in melt flow index (MI) (5 kg load, 190°C) due to the extruder is 60% to 90% according to the following formula (1), and a rate of change in melt flow index (MI) (5 kg load, 190°C) due to the peroxide is 10% to 40% according to the following formula (2): The polyethylene resin composition has a zero shear viscosity (η0) of 8,000,000 poise to 12,000,000 poise, the drop time when sagging occurs during extrusion of the polyethylene resin composition is reduced by 10% to 17% relative to the drop time when sagging does not occur, and the drop time is measured using a single screw extruder; The strain hardening modulus of the polyethylene resin composition is 53 MPa to 80 MPa. {(MI after passing through the second reactor−MI after passing through the extruder without adding peroxide) / (MI after passing through the second reactor−final MI)}×100 (1) {(MI after passing through an extruder without adding peroxide−MI after passing through an extruder under peroxide-addition conditions) / (MI after passing through a second-stage reactor−final MI)}×100 (2)

2. The method for producing a polyethylene resin composition for pipes according to claim 1, wherein the peroxide is added in an amount of 0.001 to 0.01 parts by weight per 100 parts by weight of the polyethylene resin.

3. 2. The method for producing a polyethylene resin composition for pipes according to claim 1, wherein the polyethylene resin after passing through the two-stage reactor has a melt flow index (5 kg load, 190° C.) of 0.32 g / 10 min to 0.44 g / 10 min.

4. 2. The method for producing a polyethylene resin composition for pipes according to claim 1, wherein the melt flow index (5 kg load, 190° C.) of the polyethylene resin composition after passing through the extruder before the addition of the peroxide is 0.24 g / 10 min to 0.32 g / 10 min.

5. 2. The method for producing a polyethylene resin composition for pipes according to claim 1, wherein the polyethylene resin composition has a melt flow index (5 kg load, 190° C.) of 0.16 g / 10 min to 0.24 g / 10 min after the addition of the peroxide and passing through the extruder.

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