KR102395346B1 - Polyethylene resin composition, method of preparing the same and product produced by the same - Google Patents

Abstract

The polyethylene resin composition of the present invention is a relatively medium-density polyethylene resin; and a relatively high-density polyethylene resin; In the polyethylene resin composition containing of High Load Melt Index (HLMI, 21.6 kg load, 190° C.) (B) is 5 to 12 g/10 min, the high load melt index ratio (B/A) is 50 to 60, and the medium density polyethylene The resin and the high-density polyethylene resin have a weight ratio of 43:57 to 47:53. The polyethylene resin composition of the present invention has excellent minimum required strength (MRS) and low-speed crack growth resistance, so it is suitable for use in pressure pipes.

Description

A polyethylene resin composition, a method for producing the same, and a molded article prepared therefrom

The present invention relates to a polyethylene resin composition suitable for use in a pressure pipe having excellent minimum required strength (MRS) and resistance to slow crack growth, a method for manufacturing the same, and a molded article manufactured therefrom.

In general, in manufacturing a pipe, a pipe, in particular, a high-pressure pipe, a technique using a high-density polyethylene resin is already known. In order for high-pressure pipes to have safety and long-term lifespan, very high resistance to external loads such as earth pressure (external pressure strength) and high stiffness combined with high resistance to slow crack growth are required.

It is known that the external pressure strength is a physical property that largely depends on the crystallinity of polyethylene. The external pressure strength can be improved by increasing the crystallinity, that is, the density of polyethylene itself. However, when the external pressure strength is increased, there is a problem that the environmental stress cracking resistance is remarkably lowered conversely. As such, the external pressure strength and environmental stress cracking resistance of the high-pressure pipe are opposite properties, and it has been a task in this field to develop a resin composition that can satisfy both properties.

Accordingly, the present invention has led to the development of a polyethylene resin composition suitable for use in a pressure pipe because it has excellent minimum required strength (MRS) and resistance to slow crack growth in order to solve the above problems.

The present invention has been proposed to solve the above problems, and a polyethylene resin composition suitable for pressure pipe use due to excellent minimum required strength (MRS) and low-speed crack growth resistance, a manufacturing method thereof, and a molded article manufactured therefrom is about

The polyethylene resin composition for a pressure tube of the present invention for solving the above problems is a relatively medium-density polyethylene resin; and a relatively high-density polyethylene resin; In the polyethylene resin composition containing of High Load Melt Index (HLMI, 21.6 kg load, 190° C.) (B) is 5 to 12 g/10 min, the high load melt index ratio (B/A) is 50 to 60, and the medium density polyethylene It is characterized in that the difference in density between the resin and the polyethylene resin composition is 0.02 to 0.03 g/cm3.

The polyethylene-based resin composition of the present invention has a minimum required strength (MRS) of 11.2 MPa or more, and has excellent low-speed crack growth resistance (800 hours or more based on ACT) suitable for a pressure pipe use, and a polyethylene resin composition prepared therefrom Molded articles can be provided.

Hereinafter, the present invention will be described in more detail. However, this is only specifically described to help the understanding of the present invention, and the scope of the present invention is interpreted based on the claims.

The polyethylene resin composition according to the present invention includes a relatively medium-density polyethylene resin and a relatively high-density polyethylene resin.

The density difference between the medium density polyethylene resin and the polyethylene resin composition is preferably 0.02 to 0.03 g/cm3. When the density difference between the resin and the resin composition is less than 0.02 g/cm ³ , the strain hardening modulus is low, and when it is greater than 0.03 g/cm ³ , the lower reliability limit may be lowered.

High Load Melt Index (HLMI, 21.6 kg load, 190 ℃) of the medium density polyethylene resin (A) is 0.1 ~ 0.2 g / 10 min, the high load melt index of the polyethylene resin composition (High Load Melt Index) , HLMI, load of 21.6kg, 190℃) (B) may be 5~12g/10min.

The high load melt index ratio (B/A) may be 50 to 60. If it is less than 50, the slow crack growth resistance cannot satisfy 450 hours or more based on ACT and the strain hardening modulus cannot satisfy all of 55 MPa or more, and if it exceeds 60, irregularity in appearance may occur during pipe processing. The medium-density polyethylene resin and the high-density polyethylene resin may have a weight ratio of 43: 57 to 47: 53.

The density of the medium-density polyethylene resin may be 0.925 to 0.935 g/cm ³ . The polyethylene resin composition may have a density of 0.950 to 0.955 g/cm ³ . The melt flow rate ratio MFRR ((HLMI (21.6 kg load, 190°C)/MI (5 kg load, 190°C)) of the polyethylene resin composition may be 33 to 38.

The polyethylene resin composition of the present invention exhibits excellent life characteristics with a lower limit of reliability (σ _LPL ) of expected hydrostatic strength at 20° C. for 50 years of 11.2 MPa or more and less than 12.5 MPa, and low-speed crack growth resistance (actually 800 hours or more, The strain hardening modulus (strain hardening modulus) of 55 MPa or more) is excellent, and may be suitable for use in a pressure pipe.

The polyethylene resin composition of the present invention may be prepared by a method of preparing a polyethylene resin composition by continuously preparing polyethylene resins having different densities in a first loop reactor and a second loop reactor connected to each other.

More specifically, preparing a relatively medium-density polyethylene resin having a high load melt index (HLMI, 21.6 kg load, 190° C.) (A) of 0.1 to 0.2 g/10 min in the first loop reactor ; And the medium-density polyethylene resin is transferred to the second loop reactor and polymerized to prepare a relatively high-density polyethylene resin; may be prepared including.

The polyethylene resin composition may be polymerized under a Ziegler-Natta catalyst. The Ziegler-Natta catalyst is a catalyst known as a conventional Ziegler-Natta catalyst and uses a transition metal compound belonging to Group IV, Group V or VI of the Periodic Table of the Elements as a main catalyst, among which the most used Ziegler-Natta catalyst is It is a halogenated complex composed of magnesium and titanium, or magnesium and vanadium.

During polymerization of the medium density polyethylene resin in the first loop reactor, a comonomer, for example, hexene-1, may be supplied in a Ziegler-Natta catalyst system at a feed ratio of 20 to 55 g/kg compared to C2. If it is less than 20g/kg, the slow crack growth resistance cannot satisfy 800 hours or more based on ACT and the strain hardening modulus cannot satisfy all of 55MPa or more. The confidence limit (σLPL) cannot satisfy 11.2 MPa or more.

During polymerization of the medium-density polyethylene resin in the first loop reactor, H2 may be supplied at a feed ratio of 4 to 8 mg/kg compared to C2.

During polymerization of the high-density polyethylene resin in the second loop reactor, H2 may be supplied at a feed ratio of 0.50 to 0.60 mol%/wt% compared to C2.

In the first loop reactor, polymerization may be performed under conditions of a pressure of 40 to 50 MPa, a polymerization temperature of 80 to 90° C., and a residence time of 40 to 70 minutes. In the second loop reactor, polymerization may be performed under conditions of a pressure of 40 to 50 MPa, a polymerization temperature of 90 to 100° C., and a residence time of 20 to 40 minutes.

The polyethylene resin composition may have a lower reliability limit (σLPL) of expected hydrostatic strength at 20°C for 50 years of 11.2 MPa or more and less than 12.5 MPa, and low-speed crack growth resistance (actually 800 hours or more based on ACT).

The polyethylene resin composition having physical properties within the above range may be suitable for use in pressure tubes and the like because it has superior strength, lifespan characteristics, and resistance to slow crack growth compared to conventional polyethylene resins.

The polyethylene resin composition according to the present invention further comprises 0.05 to 0.5 parts by weight of an antioxidant, preferably 0.1 to 0.3 parts by weight and 0.05 to 0.3 parts by weight of a neutralizing agent, preferably 0.1 to 0.2 parts by weight, based on 100 parts by weight of the polyethylene resin composition. can do. If the antioxidant content is less than 0.05 parts by weight or exceeds 0.5 parts by weight, there may be problems such as discoloration and viscosity change during processing. When the content of the neutralizing agent is less than 0.5 parts by weight, discoloration and viscosity change occur during processing, and when it exceeds 0.3 parts by weight, changes in physical properties such as color and strength may occur during long-term storage.

Representative examples of the antioxidant include 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (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)propion amido]hexane (1,6-Bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propion amido]hexane), 1,6-bis[3-(3,5-di-tert) -Butyl-4-hydroxyphenyl) propionamido] propane (1,6-Bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamido] propane), tetrakis [methylene (3, 5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane (tetrakis[methyl ene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane), bis(2,6-di- tert-Butyl-4-methylphenyl)pentaerythritol-di-phosphite (Bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphite), bis(2,4-di-tert- Butylphenyl)pentaerythritol-di-phosphite (Bis(2,4-di-tert-butylphenyl)Pentraerythritol-di-phosphite), etc. can be illustrated.

Representative examples of the neutralizing agent may include calcium stearic acid, zinc stearic acid, magnesium aluminum hydroxy carbonate, zinc oxide, magnesium hydroxy stearic acid, or a mixture thereof.

Hereinafter, the present invention will be described in more detail through the following examples, but the scope of the present invention is not limited thereto.

<Production of polyethylene resin composition>

Example 1

A main catalyst, which is a known Ziegler-Natta catalyst composed of magnesium and titanium, was prepared by a conventional method, and two reactors each having a reactor capacity of 90 liters were connected in series to conduct polymerization. The polymer in the slurry phase polymerized in the first loop reactor was transferred to the second loop reactor to continue polymerization, and the ratio of the polymerization amount in each step was 45:55. At this time, 1-hexene was supplied as a comonomer in the first loop reactor at a feed ratio of 32 g/kg compared to C2, and H2 was supplied at a feed ratio of 6 mg/kg compared to C2. During polymerization of the high-density polyethylene resin in the second loop reactor, H2 was supplied at a feed ratio of 0.59 mol%/wt% compared to C2. The polymerization reaction was carried out under the conditions that the polymerization temperature of the first loop reactor was 83° C., the reactor pressure was 45 MPa, and the residence time was 61 minutes, and the polymerization temperature of the second loop reactor was 90° C., the reactor pressure was 45 MPa, and the residence time was 34 minutes. .

After mixing 0.1 parts by weight of Irganox-1010 as an antioxidant, 0.1 parts by weight of Irgafos-168 as an antioxidant, and 0.15 parts by weight of calcium stearate as a neutralizing agent, 0.15 parts by weight of calcium stearate as a Hensel mixer to the powder-type copolymer obtained above, it was granulated in the form of pellets using a twin-screw extruder. .

Comparative Example 1

A resin composition was prepared in the same manner as in Example 1 according to the composition shown in Table 1 below.

The polymer in the slurry phase polymerized in the first loop reactor was transferred to the second loop reactor to continue polymerization, and the ratio of the polymerization amount in each step was set to 40:60. At this time, 1-hexene was supplied as a comonomer in the first loop reactor at a feed ratio of 73 g/kg compared to C2, and H2 was supplied at a feed ratio of 4 mg/kg compared to C2. During polymerization of the high-density polyethylene resin in the second loop reactor, H2 was supplied at a feed ratio of 0.59 mol%/wt% compared to C2. The polymerization reaction was carried out under the conditions that the polymerization temperature of the first loop reactor was 83° C., the residence time was 61 minutes, the polymerization temperature of the second loop reactor was 90° C., and the residence time was 34 minutes.

Comparative Example 2

A resin composition was prepared in the same manner as in Example 1 according to the composition shown in Table 1 below.

The polymer in the slurry phase polymerized in the first loop reactor was transferred to the second loop reactor to continue polymerization, and the ratio of the polymerization amount in each step was set to 50:50. At this time, 1-hexene was supplied as a comonomer in the first loop reactor at a feed ratio of 57 g/kg compared to C2, and H2 was supplied at a feed ratio of 7 mg/kg compared to C2. During polymerization of the high-density polyethylene resin in the second loop reactor, H2 was supplied at a feed ratio of 0.53 mol%/wt% compared to C2. The polymerization reaction was carried out under the conditions that the polymerization temperature of the first loop reactor was 87°C, the residence time was 59 minutes, the polymerization temperature of the second loop reactor was 93°C, and the residence time was 33 minutes.

Comparative Example 3

A resin composition was prepared in the same manner as in Example 1 according to the composition shown in Table 1 below.

The polymer in the slurry phase polymerized in the first loop reactor was transferred to the second loop reactor to continue polymerization, and the ratio of the polymerization amount in each step was set to 48:52. At this time, 1-hexene was supplied as a comonomer in the first loop reactor at a feed ratio of 11 g/kg compared to C2, and H2 was supplied at a feed ratio of 9 mg/kg compared to C2. During polymerization of the high-density polyethylene resin in the second loop reactor, H2 was supplied at a feed ratio of 0.53 mol%/wt% compared to C2. The polymerization reaction was carried out under the conditions that the polymerization temperature of the first loop reactor was 87°C, the residence time was 59 minutes, the polymerization temperature of the second loop reactor was 93°C, and the residence time was 33 minutes.

Comparative Example 4

A resin composition was prepared in the same manner as in Example 1 according to the composition shown in Table 1 below.

The polymer in the slurry phase polymerized in the first loop reactor was transferred to the second loop reactor to continue polymerization, and the ratio of the polymerization amount in each step was set to 48:52. At this time, 1-hexene was supplied as a comonomer in the first loop reactor at a feed ratio of 71 g/kg compared to C2, and H2 was supplied at a feed ratio of 6 mg/kg compared to C2. During polymerization of the high-density polyethylene resin in the second loop reactor, H2 was supplied at a feed ratio of 0.59 mol%/wt% compared to C2. The polymerization reaction was carried out under the conditions that the polymerization temperature of the first loop reactor was 83° C., the residence time was 61 minutes, the polymerization temperature of the second loop reactor was 90° C., and the residence time was 34 minutes.

Manufacturing of molded products (pressure tubes)

A pressure tube for the lower reliability limit test of the expected hydrostatic pressure strength was prepared using the polyethylene resin composition prepared in Example 1 and Comparative Examples 1-3.

An extruder of Battenfeld-Cincinnati's uniEX 35-30-C model was used, and the extruder and die temperature were set to 200 degrees and processed at a speed of 5 m/min. The diameter of the tube is 32mm, and the thickness of the tube is 3mm.

<Method for measuring physical properties of resins and molded products>

Melt Index (MI)

According to ASTM D1238, it was measured at 190°C with a load of 5 kg and 21.6 kg.

The melt flow index measured at a load of 5 kg was expressed as MI5 kg, and the melt flow index measured at a load of 21.6 kg was expressed as HLMI.

Melt Flow Ratio (MFRR)

HLMI (21.6 kg load, melt flow index at 190°C)/MI (5 kg load, melt flow index at 190°C)

density

Measured according to ASTM D1505.

strain hardening modulus

It was measured according to ISO 18488.

Accelerated FNCT test

It was tested under the conditions of ISO 16770 standard temperature 90℃, Lauramine oxide (CAS number 85408-49-7) %, 4MPa.

Lower confidence limit of expected hydrostatic strength (σLPL)

Tests were conducted at 20, 60, and 80°C according to ISO 1167-1,2, and results were derived according to ISO 9080.

Unit Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 catalyst system ZN ZN ZN ZN ZN C2 feed ratio
(Second Reactor /
first reactor) 1.25 1.6 1.05 1.18 1.18 high load
Melt index ratio (B/A) 52 57 35 40 51 first
reactor temperature ℃ 83 83 87 87 83 enter MPa 45 45 45 45 45 C2 feed kg/hr 13.3 11.5 14.6 13.7 13.7 C6 feed ratio g/kg_C2 32 73 57 11 71 H2 feed ratio mg/kg_C2 6 4 7 9 6 residence time minute 61 61 59 59 61 polymerization ratio wt% 45 40 50 48 48 HLMI (190℃) (A) g/10min 0.16 0.18 0.23 0.19 0.21 Density (C) g/cm ³ 0.930 0.922 0.927 0.935 0.924 second
reactor
temperature °C 90 90 93 93 90 enter MPa 45 45 45 45 45 C2 feed kg/hr 16.6 18.4 15.3 16.2 16.2 H2 feed ratio mol%/wt%_ C2 0.59 0.59 0.53 0.53 0.59 residence time minute 34 34 33 33 34 polymerization ratio wt% 55 60 50 52 52 MI 5kg (190℃) g/10min 0.36 0.37 0.38 0.35 0.45 density g/cm³ 0.953 0.957 0.948 0.953 0.947 profit
Properties MI 5kg (190℃) g/10min 0.24 0.34 0.28 0.24 0.33 HLMI (190℃) (B) g/10min 8 10.2 8 8 11 MFRR (HLMI/MI5kg) 35 30 28 32 32 Density (D) g/cm³ 0.952 0.953 0.948 0.953 0.947 Density difference (C-D=Δ) g/cm³ 0.022 0.031 0.021 0.018 0.024 strain hardening modulus MPa 70 50 65 48 72 ACT hr 950 410 870 370 1010 σ _LPL MPa 11.3 10.1 10.3 11.3 10.2

Referring to Table 1, in Example 1, compared to Comparative Examples 1 to 4, the slow crack growth resistance (strain hardening modulus, ACT) is 800 hr or more, and the expected hydrostatic strength (σLPL) satisfies all of the ranges of 11.2 to 12.5 MPa could confirm that

In Comparative Example 1, the density difference between the medium-density polyethylene resin and the high-density polyethylene resin was 0.031, the strain hardening modulus was as low as 50 MPa, and the slow crack growth resistance (strain hardening modulus, ACT) was 410 hr, and the expected hydrostatic strength (σLPL) ) is inferior to 10.1 MPa.

In Comparative Example 2, the high-load melt index ratio was as low as 35, the polymerization ratio of the medium-density polyethylene resin polymerized in the first reactor and the high-density polyethylene resin polymerized in the second reactor was 50:50, and the HLMI of the first reactor was 0.23 g/min. , the density is as low as 0.948 g/cm3 in the resin properties, and the MFRR is also as low as 28, so that the lower reliability limit (σLPL) of the expected hydrostatic strength at 20°C for 50 years is as low as 10.3 MPa.

Comparative Example 3 had a low high-load melt index ratio of 40, and a polymerization ratio of the medium-density polyethylene resin polymerized in the first reactor and the high-density polyethylene resin polymerized in the second reactor was 48:52, so the long-term slow crack growth resistance was inferior.

In Comparative Example 4, the polymerization ratio of the medium-density polyethylene resin polymerized in the first reactor and the high-density polyethylene resin polymerized in the second reactor was 48:52, the HLMI of the first reactor was high as 0.21 g/min, and the density was high in resin properties. As low as 0.947 g/cm3, the lower reliability limit (σLPL) of the expected hydrostatic strength at 20°C for 50 years is as low as 10.3MPa.

Claims (14)

a medium density polyethylene resin having a medium density of 0.925 to 0.935 g/cm ³ ; and
High-density polyethylene resin having a density higher than the medium density; In the polyethylene resin composition comprising a,
The high load melt index (HLMI, 21.6 kg load, 190 ℃) (A) of the medium density polyethylene resin is 0.1 ~ 0.2 g / 10 min,
High Load Melt Index (HLMI, 21.6 kg load, 190 ℃) (B) of the polyethylene resin composition is 5 to 12 g / 10 min,
The high load melt index ratio (B / A) is 50 to 60,
A polyethylene resin composition, characterized in that the density difference between the medium-density polyethylene resin and the polyethylene resin composition is 0.02 to 0.03 g/cm ³ . The polyethylene resin composition according to claim 1, wherein the medium-density polyethylene resin and the high-density polyethylene resin have a weight ratio of 43: 57 to 47: 53. According to claim 1,
The density of the polyethylene resin composition is 0.950 to 0.955 g / cm ³ Characterized in that Polyethylene resin composition. delete According to claim 1,
The melt flow rate ratio MFRR of the polyethylene resin composition ((HLMI (21.6 kg load, 190 ℃) / MI (5 kg load, 190 ℃)) is 33 to 38 polyethylene resin composition. According to claim 1,
The polyethylene resin composition, characterized in that the lower limit of reliability (σLPL) of the expected hydrostatic strength at 20°C for 50 years of the polyethylene resin composition is 11.2 MPa or more and less than 12.5 MPa. The method of claim 1,
ACT (accelerated creep test) of the polyethylene resin composition is a polyethylene resin composition, characterized in that 800 hours or more. The method of claim 1,
A strain hardening modulus of the polyethylene resin composition is 55 MPa or more. A method for producing a polyethylene resin composition by continuously producing polyethylene resins having different densities in a first loop reactor and a second loop reactor connected to each other,
In the first loop reactor, the high load melt index (HLMI, 21.6 kg load, 190° C.) (A) is 0.1 to 0.2 g/10 min and a medium density having a medium density of 0.925 to 0.935 g/cm ³ preparing a polyethylene resin; and
The medium-density polyethylene resin is transferred to a second loop reactor and polymerized to prepare a high-density polyethylene resin having a density higher than the medium density;
High Load Melt Index (HLMI, 21.6 kg load, 190 ℃) (B) of the polyethylene resin composition is 5 to 12 g / 10 min,
The high load melt index ratio (B / A) is 50 to 60,
A method for producing a polyethylene resin composition, characterized in that the density difference between the medium density polyethylene resin and the polyethylene resin composition is 0.02 to 0.030 g/cm ³ . 10. The method of claim 9,
The medium-density polyethylene resin and the high-density polyethylene resin are 43: 57 to 47: a method for producing a polyethylene resin composition, characterized in that having a weight ratio of 53. 10. The method of claim 9,
A method for producing a polyethylene resin composition, characterized in that during polymerization of the medium-density polyethylene resin in the first loop reactor, a comonomer of hexene-1 is supplied at a feed ratio of 20 to 55 g/kg compared to ethylene (C2). 10. The method of claim 9,
A method for producing a polyethylene resin composition, characterized in that during polymerization of the medium density polyethylene resin in the first loop reactor, hydrogen (H2) is supplied at a feed ratio of 4 to 8 mg/kg compared to ethylene (C2). 10. The method of claim 9,
A method for producing a polyethylene resin composition, characterized in that during polymerization of the high-density polyethylene resin in the second loop reactor, hydrogen (H2) is supplied at a feed ratio of 0.50 to 0.60 mol%/wt% compared to ethylene (C2). A molded article made of the polyethylene resin composition according to any one of claims 1 to 3 and 5 to 8.