High-pressure resistant polyethylene and cross-linked polyethylene pipes containing the polyethylene

Abstract

This disclosure relates to polyethylene with high pressure resistance and cross-linked polyethylene pipes containing the same. The polyethylene of this disclosure has a high melt index and density, and exhibits sufficient cross-linking, thereby exhibiting excellent strength and pressure resistance properties.

Description

[0001] This application is a divisional application. The original application's international application number is PCT / KR2020 / 002467, the international application date is February 20, 2020, the Chinese national application number is 202080006546.1, the entry date into the Chinese national phase is May 28, 2021, and the invention title is "Polyethylene with high pressure resistance and cross-linked polyethylene pipe containing the polyethylene".

[0002] Cross-references to related applications

[0003] This application claims the benefit of Korean Patent Application No. 10-2019-0020026, filed on February 20, 2019, and Korean Patent Application No. 10-2020-0020643, filed on February 19, 2020, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0004] This disclosure relates to polyethylene with high pressure resistance and cross-linked polyethylene pipes containing the polyethylene. Background Technology

[0005] Cross-linked polyethylene was developed by a wire company in 1960 to improve the temperature characteristics caused by the heating of wires, and Thomas Engel of Germany used this polyethylene to produce pipes with excellent durability in 1967.

[0006] Cross-linked polyethylene is a polyethylene that has been modified by cross-linking high-density polyethylene (HDPE) with a linear molecular structure into a polyethylene with a three-dimensional network structure, and has excellent properties such as heat resistance, durability, chemical resistance and flexibility.

[0007] On the other hand, as methods for crosslinking polyethylene in this manner, crosslinking methods using organic peroxides (peroxide crosslinking), crosslinking methods using silane compounds (silane crosslinking), and crosslinking methods using electron beam irradiation (radiation crosslinking) can be mentioned.

[0008] Generally, polyethylene cross-linked with organic peroxides is called PE-Xa, polyethylene cross-linked with silane compounds is called PE-Xb, and polyethylene cross-linked with electron beam irradiation is called PE-Xc.

[0009] Because cross-linked polyethylene pipes (especially PE-Xa pipes) require uniform high pressure during extrusion molding, they are typically manufactured by extruding a mixture of polyethylene resin, cross-linking agent, and antioxidant using a RAM-type extruder.

[0010] In the case of PE-Xa, it has superior physical properties compared to PE-Xb and PE-Xc, and has the advantage of being able to manufacture flexible pipe products.

[0011] On the other hand, to meet the pressure resistance requirements of pipe products, polyethylene needs to have a high density; however, for this purpose, polyethylene with a high melt index is suitable. This is because as the melt index increases, chain mobility increases, and the density becomes higher. However, polyethylene with a high melt index has the disadvantage of producing a large number of low molecular weight polyethylenes, thus reducing the degree of crosslinking.

[0012] Therefore, there is a need to develop cross-linked polyethylene pipes that have both high melt index and high density, as well as excellent cross-linking degree. Summary of the Invention

[0013] Technical issues

[0014] Therefore, the present invention was made in view of the above problems, and the object of the present invention is to provide a polyethylene and a cross-linked polyethylene pipe containing the polyethylene, which not only has a high melt index and density and thus improves pressure resistance, but also exhibits excellent cross-linking degree, and therefore has excellent physical properties as a pipe material.

[0015] Technical solutions

[0016] To achieve the above objectives, according to one embodiment of the present invention, a polyethylene is provided that satisfies the following:

[0017] According to ASTM D792, the density is 0.940 g / cm³. 3 Above and 0.960 g / cm 3 the following;

[0018] The number average molecular weight (Mn) is above 20,000 g / mol and below 70,000 g / mol;

[0019] The weight average molecular weight (Mw) is above 100,000 g / mol and below 250,000 g / mol;

[0020] The polydispersity index (PDI, Mw / Mn) is above 2.5 and below 3.7; and

[0021] According to ASTM D1238, the melt flow index (MI) was determined at 190°C under a load of 21.6 kg. 21.6 The concentration is 1g / 10min or more and 20g / 10min or less.

[0022] According to another embodiment of this disclosure, a cross-linked polyethylene pipe comprising the polyethylene is provided.

[0023] Beneficial effects

[0024] The polyethylene disclosed herein has high density and exhibits sufficient crosslinking, thereby demonstrating excellent strength and pressure resistance properties.

[0025] Therefore, it can be used to produce cross-linked polyethylene pipes, especially PE-Xa pipes. Detailed Implementation

[0026] As used herein, terms such as first and second can be used to describe various components, and the term is used only to distinguish one component from another.

[0027] Furthermore, the terminology used herein is for describing exemplary embodiments only and is not intended to limit this disclosure. Singular expressions include plural expressions unless they have a clearly express opposite meaning in the context. It should be understood that the terms “comprising,” “including,” and “having” as used herein are intended to indicate the presence of the stated features, steps, constituent elements, or combinations thereof. However, it should be understood that they do not preclude the possibility of the presence or addition of one or more other features, steps, constituent elements, or combinations thereof.

[0028] Because this disclosure can be modified in various forms and can have several implementations, specific implementations will be shown and described in detail below. However, it will be understood that this disclosure is not limited to the specific implementations, but rather that the invention includes all modifications, equivalents, and alternatives falling within the scope and spirit of this disclosure.

[0029] The polyethylene of this disclosure and the cross-linked polyethylene pipe comprising the polyethylene will be described in more detail below.

[0030] One embodiment of the polyethylene disclosed herein is characterized in that its density, measured according to ASTM D792, is 0.940 g / cm³. 3 Above and 0.960 g / cm 3 The following are acceptable molecular weights: Number average molecular weight (Mn) ≥ 20,000 g / mol and ≤ 70,000 g / mol; Weight average molecular weight (Mw) ≥ 100,000 g / mol and ≤ 250,000 g / mol; Polydispersity index (PDI, Mw / Mn) ≥ 2.5 and ≤ 3.7; Melt index (MI) measured according to ASTM D1238 at 190°C under a load of 21.6 kg. 21.6 The concentration is 1g / 10min or more and 20g / 10min or less.

[0031] Cross-linked polyethylene is a polyethylene that has been modified by cross-linking high-density polyethylene (HDPE) with a linear molecular structure into a polyethylene with a three-dimensional network structure, and has excellent properties such as heat resistance, durability, chemical resistance and flexibility.

[0032] Pipes made from this type of cross-linked polyethylene are typically produced by mixing polyethylene with a cross-linking agent and an antioxidant, and then extruding the mixture using a RAM-type extruder.

[0033] In pipes made of cross-linked polyethylene in this manner, PE-Xa exhibits superior cross-linking physical properties compared to PE-Xb and PE-Xc, and has the advantage of being able to manufacture flexible pipe products.

[0034] On the other hand, in order to meet the pressure resistance requirements of pipe products, polyethylene needs to have high density. However, polyethylene with a high melt index has the disadvantage of producing a large number of low molecular weight products and reducing the degree of crosslinking.

[0035] Therefore, this disclosure is designed to further improve the pressure resistance of PE-Xa. The inventors have developed a polyethylene resin suitable for PE-Xa pipes in which the molecular weight distribution of polyethylene is improved, and the melt index (MI) and density are increased compared to before. Thus, while exhibiting improved pressure resistance, the degree of crosslinking is not reduced, but is maintained at more than 70%, thereby completing this disclosure.

[0036] Specifically, in one embodiment of this disclosure, the polyethylene may be high-density polyethylene (HDPE), such as polyethylene with a density of 0.940 g / cm³ as measured according to ASTM D792. 3 Above and 0.960 g / cm 3 the following.

[0037] More specifically, according to one embodiment, the density of the polyethylene disclosed herein can be 0.940 g / cm³. 3 Above, or 0.945 g / cm 3 Above, or 0.949 g / cm 3 Above, or 0.950 g / cm 3 Above, and 0.960 g / cm 3 Below, or 0.958 g / cm 3 Below, or 0.956 g / cm 3 Below, or 0.955 g / cm 3 The following describes how the polyethylene disclosed herein achieves excellent compressive strength properties by having a density within the aforementioned range.

[0038] Furthermore, in one embodiment of this disclosure, the number average molecular weight (Mn) of the polyethylene is 20,000 to 70,000 g / mol. More specifically, the number average molecular weight may be 20,000 g / mol or more, or 25,000 g / mol or more, or 30,000 g / mol or more, or 33,000 g / mol or more, and 70,000 g / mol or less, or 65,000 g / mol or less, or 60,000 g / mol or less, or 57,000 g / mol or less, or 55,000 g / mol or less.

[0039] Furthermore, in one embodiment of this disclosure, the polyethylene has a weight-average molecular weight (Mw) of 100,000 to 250,000 g / mol. More specifically, the weight-average molecular weight can be 100,000 g / mol or more, 120,000 g / mol or more, or 125,000 g / mol or more, or 130,000 g / mol or more, and 250,000 g / mol or less, 230,000 g / mol or less, or 220,000 g / mol or less, or 210,000 g / mol or less, or 200,000 g / mol or less.

[0040] Furthermore, in one embodiment of this disclosure, the molecular weight distribution (MWD, Mw / Mn) of the polyethylene is 2.5 to 3.7. More specifically, the molecular weight distribution may be 2.5 or more, or 2.6 or more, or 2.7 or more, or 2.8 or more, and 3.7 or less, or 3.6 or less, or 3.5 or less, or 3.4 or less.

[0041] With the molecular weight distribution described above, the polyethylene disclosed herein satisfies the requirement of high crosslinking properties.

[0042] In this disclosure, the number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution are measured, wherein the weight average molecular weight (Mw) and number average molecular weight (Mn) of polyethylene are measured using gel permeation chromatography (GPC), and the ratio of weight average molecular weight to number average molecular weight (Mw / Mn) is calculated as a polydispersity index.

[0043] Specifically, polyethylene samples were evaluated using a Waters PL-GPC220 instrument with a 300 mm PLgel Mixed-B column from Polymer Laboratories. The evaluation temperature was set at 160 °C, 1,2,4-trichlorobenzene was used as the solvent, and the flow rate was set at 1 mL / min. Samples were prepared at a concentration of 10 mg / 10 mL and then supplied in 200 μL increments. Calibration curves using polystyrene standards were used to determine Mw and Mn values. The polystyrene standards used had molecular weights of 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000.

[0044] Furthermore, the melt flow index (MI) of polyethylene according to one embodiment of this disclosure is measured at 190°C under a load of 21.6 kg, as determined by ASTM D1238. 21.6 The melt flow rate is 1 g / 10 min to 20 g / 10 min. More specifically, the melt flow index (MI) is... 21.6 The dosage can be 3g / 10min or more, or 4g / 10min or more, or 5g / 10min or more, or 6g / 10min or more, and less than 18g / 10min, or less than 16g / 10min, or less than 15g / 10min, or less than 14g / 10min.

[0045] By using a melt index (MI) within the above range 21.6 The polyethylene disclosed herein has excellent pressure resistance properties.

[0046] Furthermore, in the GPC curve plot with log Mw on the x-axis and dw / dlog Mw on the y-axis, the integral value of polyethylene in one embodiment of this disclosure in the region where the log Mw value is below 4.5 is less than 25% of the total integral value. The GPC curve plot means that the logarithmic molecular weight and mass fraction of polyethylene are measured by GPC and plotted on the x and y axes. Also, in the above, Mw represents the weight-average molecular weight.

[0047] More specifically, according to one embodiment, the integral value in the region where the log Mw value of the polyethylene of this disclosure is less than 4.5 is 25% or less, 24% or less, 23% or less, 22% or less, or 21% or less, and more than 15% or more, or more than 16% or more, or more than 17% or more, or more than 18% or more, relative to the total integral value.

[0048] As described above, relative to the total integral value, the integral value of the polyethylene of this disclosure in the region where the log Mw value is below 4.5 can be below 25%. Compared with conventional products with similar low molecular weight content, the polyethylene has a higher melt index, excellent crosslinking degree, and compressive strength. Therefore, due to these characteristics, it can meet the requirements for high crosslinking properties.

[0049] On the other hand, polyethylene of one embodiment of the present disclosure having the above-mentioned physical properties can be prepared by a preparation method including the following process: polymerizing ethylene monomer in the presence of a specific metallocene compound as a catalytically active component.

[0050] More specifically, the polyethylene disclosed herein includes, but is not limited to, a first metallocene compound represented by the following chemical formula 1; and a second metallocene compound represented by the following chemical formula 3, and can be prepared by polymerizing ethylene monomer in the presence of a hybrid metallocene catalyst in which the molar ratio between the first metallocene compound and the second metallocene compound is 1:5 to 1:20.

[0051] [Chemical Formula 1]

[0052]

[0053] In chemical formula 1,

[0054] Q1 and Q2 may be the same or different from each other, and each independently represents hydrogen, halogen, C1 to C20 alkyl, C2 to C20 alkenyl, C2 to C20 alkoxyalkyl, C6 to C20 aryl, C7 to C20 alkylaryl or C7 to C20 arylalkyl;

[0055] B is carbon, silicon, or germanium;

[0056] M1 is a group 4 transition metal;

[0057] X1 and X2 may be the same or different from each other, and each independently represents halogen, C1 to C20 alkyl, C2 to C10 alkenyl, C6 to C20 aryl, C7 to C20 alkylaryl or C7 to C20 arylalkyl;

[0058] One of C1 and C2 is represented by the following chemical formula 2a or chemical formula 2b, and the other of C1 and C2 is represented by the following chemical formula 2c;

[0059] [Chemical Formula 2a]

[0060]

[0061] [Chemical Formula 2b]

[0062]

[0063] [Chemical formula 2c]

[0064]

[0065] In chemical formulas 2a, 2b, and 2c,

[0066] R1 to R 21 and R1' to R 13 'Identical or different from each other, each independently representing hydrogen, halogen, C1 to C20 alkyl, C1 to C20 haloalkyl, C2 to C20 alkenyl, C1 to C20 alkylsilyl, C1 to C20 silylalkyl, C1 to C20 alkoxysilyl, C1 to C20 alkoxy, C6 to C20 aryl, C7 to C20 alkylaryl or C7 to C20 arylalkyl, provided that R9 to R 13 and R9' to R 13 At least one of them is a C1 to C20 haloalkyl group.

[0067] [Chemical Formula 3]

[0068]

[0069] In chemical formula 3,

[0070] M2 is a group 4 transition metal;

[0071] C p1 and C p2 The same or different from each other, each independently representing any cyclic group selected from the group consisting of cyclopentadienyl, indenyl, 4,5,6,7-tetrahydro-1-indenyl and fluorenyl, wherein one or more hydrogens of the cyclic group may be independently substituted by any substituent selected from C1 to C20 alkyl, C1 to C20 alkoxy, C2 to C20 alkoxyalkyl, C6 to C20 aryl, C7 to C20 alkylaryl or C7 to C20 arylalkyl; and

[0072] X3 and X4 may be the same or different from each other, each independently representing halogen, C1 to C20 alkyl, C2 to C10 alkenyl, C6 to C20 aryl, C7 to C20 alkylaryl or C7 to C20 arylalkyl.

[0073] The substituents of chemical formulas 1 and 2 will be described in more detail below.

[0074] C1 to C20 alkyl groups include straight-chain or branched alkyl groups, specifically including, but not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, pentyl, hexyl, heptyl, and octyl.

[0075] C2 to C20 alkenyl groups include straight-chain or branched alkenyl groups, specifically allyl, vinyl, propenyl, butenyl, and pentenyl, but not limited to these.

[0076] C6 to C20 aryl groups include monocyclic or fused-ring aryl groups, specifically phenyl, biphenyl, naphthyl, phenanthryl and fluorenyl, etc., but are not limited to these.

[0077] C1 to C20 alkoxy groups may include, but are not limited to, methoxy, ethoxy, phenoxy, and cyclohexyloxy groups.

[0078] C2 to C20 alkoxyalkyl groups are functional groups in which at least one hydrogen atom of the aforementioned alkyl group is substituted by an alkoxy group. Specifically, alkoxyalkyl groups such as methoxymethyl, methoxyethyl, ethoxymethyl, isopropoxymethyl, isopropoxyethyl, isopropoxyhexyl, tert-butoxymethyl, tert-butoxyethyl, and tert-butoxyhexyl may be mentioned, but are not limited thereto.

[0079] C1 to C20 alkylsilyl or C1 to C20 alkoxysilyl are functional groups in which one to three hydrogens of -SiH3 are substituted by one to three alkyl or alkoxy groups as described above. Specifically, alkylsilyl such as methylsilyl, dimethylsilyl, trimethylsilyl, dimethylethylsilyl, dimethylmethylsilyl or dimethylpropylsilyl may be mentioned; alkoxysilyl such as methoxysilyl, dimethoxysilyl, trimethoxysilyl or dimethoxyethoxysilyl; alkoxyalkylsilyl such as methoxydimethylsilyl, diethoxymethylsilyl or dimethoxypropylsilyl, but not limited thereto.

[0080] C1 to C20 silyl alkyl refers to a functional group in which at least one hydrogen atom of the alkyl group described above is replaced by a silyl group, specifically -CH2-SiH3, methylsilylmethyl or dimethylethoxysilylpropyl, but not limited thereto.

[0081] Halogens can be fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

[0082] The aforementioned substituents may optionally replace one or more substituents selected from the group consisting of: hydroxyl; halogen; alkyl or alkenyl, aryl, alkoxy; alkyl or alkenyl, aryl, or alkoxy containing at least one heteroatom selected from groups 14 to 16; silyl; alkylsilyl or alkoxysilyl; phosphin; phosphoro; sulfonate group; and sulfonyl, within the range exhibiting the same or similar effects as desired.

[0083] Group 4 transition metals may include, but are not limited to, titanium (Ti), zirconium (Zr) and hafnium (Hf).

[0084] According to one embodiment of this disclosure, R1 to R2 in chemical formulas 2a, 2b and 2c 21 and R1' to R 13 Each of the following can be independently hydrogen, halogen, C1 to C20 alkyl, or C1 to C20 haloalkyl, and R9 to R 13 and R9' to R 13 At least one of them can be a C1 to C20 haloalkyl group.

[0085] More specifically, R1 to R 21 and R1' to R 13 Each of the following can be independently hydrogen, methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, or fluoroalkyl, and R9 to R 13 and R9' to R 13 At least one of the components can be a fluoroalkyl group, but is not limited thereto.

[0086] According to one embodiment of this disclosure, Q1 and Q2 in Formula 1 may each be independently hydrogen, halogen, C1 to C20 alkyl or C2 to C20 alkoxyalkyl.

[0087] More specifically, Q1 and Q2 may each be hydrogen, methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, methoxymethyl, tert-butoxymethyl, tert-butoxyhexyl, 1-ethoxyethyl, 1-methyl-1-methoxyethyl, tetrahydropyranyl or tetrahydrofuranyl, but are not limited thereto.

[0088] According to one embodiment of this disclosure, B in chemical formula 1 is preferably silicon, but is not limited thereto.

[0089] According to one embodiment of this disclosure, X1 and X2 in Formula 1 may each be independently a halogen or a C1 to C20 alkyl group.

[0090] The first metallocene compound of Formula 1 forms a structure in which an indendoindole derivative and a cyclopentadiene derivative are asymmetrically crosslinked via bridging, and is loaded onto a Lewis acid-like surface of a support by means of non-shared electron pairs in the ligand structure capable of functioning as Lewis bases, exhibiting high polymerization activity even when loaded. Furthermore, by incorporating electron-rich indendoindole and cyclopentadiene groups, it exhibits high activity and maintains excellent copolymerization properties and high activity due to appropriate steric hindrance and the electronic effects of the ligands. Moreover, the β-hydrogen of the polymer chain in which the nitrogen atom of the indendoindole derivative grows can be stabilized by hydrogen bonding, thereby inhibiting β-hydrogen elimination and enabling the polymerization of ultra-high molecular weight polyolefins.

[0091] Specifically, R9 to R1 in the transition metal compounds of formula 113 and R9' to R 13 One or more of the ' ' include C1-C20 haloalkyl groups. Furthermore, while haloalkyl groups containing halogen elements other than fluorine can also interact with β-hydrogen, hydrogen forms hydrogen bonds with highly electronegative atoms such as nitrogen, oxygen, and fluorine. Not all haloalkyl groups form hydrogen bonds with β-hydrogen. The effect of forming hydrogen bonds with β-H is not due to the inclusion of a haloalkyl group, but rather the introduction of a fluorine substituent. For example, fluorinated alkyl groups, such as CF3, can be mentioned. Its function is similar to that of the nitrogen atom in indole derivatives, stabilizing the β-hydrogen in the growing polymer chain through hydrogen bonding, further inhibiting β-hydrogen elimination, and enabling more efficient polymerization of ultra-high molecular weight polyolefins. In other words, it maintains the basic framework of the catalyst, where indole derivatives and cyclopentadiene derivatives are asymmetrically crosslinked through bridging, and enhances the inhibition of β-hydrogen elimination by stabilizing β-hydrogen through hydrogen bonding by introducing substituents (such as the stronger hydrogen bond acceptor CF3), thereby enabling the polymerization of ultra-high molecular weight polyolefins.

[0092] According to one embodiment of this disclosure, specific examples of compounds represented by chemical formula 2a may include compounds represented by the following structural formulas, but this disclosure is not limited thereto.

[0093]

[0094] According to one embodiment of this disclosure, specific examples of compounds represented by chemical formula 2b may include compounds represented by the following structural formulas, but this disclosure is not limited thereto.

[0095]

[0096] According to one embodiment of this disclosure, specific examples of compounds represented by chemical formula 2c may include compounds represented by the following structural formulas, but this disclosure is not limited thereto.

[0097]

[0098] According to one embodiment of the present disclosure, specific examples of the first metallocene compound represented by chemical formula 1 may include compounds represented by chemical formula 1-1, but the present disclosure is not limited thereto.

[0099] [Structure 1-1]

[0100]

[0101] First metallocene compounds can be synthesized using known reactions; for more detailed synthesis methods, please refer to the examples.

[0102] According to one embodiment of this disclosure, Cp1 and Cp2 in Formula 3 may each be independently cyclopentadienyl or indene, and at least one hydrogen atom of the cyclopentadienyl or indene may each be independently substituted by any one of the substituents selected from C1 to C20 alkyl or C2 to C20 alkoxyalkyl.

[0103] According to one embodiment of this disclosure, M2 in chemical formula 3 is preferably zirconium (Zr), but this disclosure is not limited thereto.

[0104] According to one embodiment of this disclosure, X3 and X4 in Formula 3 may each be independently halogenated or C1 to C20 alkyl.

[0105] The second metallocene compound represented by chemical formula 3 may be, for example, a compound represented by one of the following structural formulas, but this disclosure is not limited thereto.

[0106]

[0107]

[0108] Furthermore, the second metallocene compound represented by chemical formula 3 can be more preferably represented by the following formula 3-1:

[0109] [Chemical Formula 3-1]

[0110]

[0111] The second metallocene compound represented by chemical formula 3 can be synthesized by applying known reactions, and more detailed synthetic methods can be found in the examples.

[0112] In a hybrid metallocene catalyst according to one embodiment of this disclosure, the first metallocene compound represented by Formula 1 can primarily contribute to the expression of high molecular weight polyethylene, and the second metallocene compound represented by Formula 3 can primarily contribute to the expression of low molecular weight polyethylene with a narrow molecular weight distribution.

[0113] Since the hybrid metallocene catalyst of one embodiment of the present disclosure uses both a low molecular weight metallocene compound with a narrow polydispersity index and a high molecular weight metallocene compound as a hybrid metallocene catalyst, it is advantageous for polymerizing the polyethylene of the present disclosure as described above.

[0114] In the hybrid metallocene catalyst of this disclosure, the molar ratio between the first metallocene compound represented by Formula 1 and the second metallocene compound represented by Formula 3 can be 1:5 to 1:20, or 1:7 to 1:18, or 1:8 to 1:15. In this case, when the molar ratio of the first and second metallocene compounds exceeds 1:20 and the content of the second metallocene compound is too high, the expression rate of low molecular weight compounds becomes too high, thus potentially worsening the crosslinking properties. When the molar ratio is less than 1:5 and the content of the second metallocene compound is too low, chain mobility decreases, and the polyethylene density decreases, which may lead to poorer compressive strength. Therefore, from this perspective, the molar ratio of the first and second metallocene compounds is preferably within the above-mentioned ranges.

[0115] In the hybrid metallocene catalysts used in this disclosure, one or more of the first metallocene compound represented by Formula 1 and one or more of the second metallocene compound represented by Formula 3 may be supported together with a co-catalyst compound on their respective supports.

[0116] In the hybrid metallocene catalysts disclosed herein, the co-catalyst supported together on the support to activate the first and second metallocene compounds is an organometallic compound containing a Group 13 metal. There are no specific limitations on the co-catalyst, as long as it can be used to polymerize olefins under the action of a conventional metallocene catalyst.

[0117] Specifically, the cocatalyst compound may include at least one of an aluminum-containing first cocatalyst selected from the following chemical formula 4 and a borate-based second cocatalyst selected from the following chemical formula 5.

[0118] [Chemical Formula 4]

[0119] -[Al(R a )-O-] k -

[0120] In chemical formula 4, each R a A hydrocarbon group containing 1 to 20 carbon atoms that is independently halogenated, halogenated-substituted, or unsubstituent, where k is an integer greater than 2.

[0121] [Chemical Formula 5]

[0122] T + [BG4] -

[0123] In chemical formula 5, T + It is a polyatomic ion with a charge of +1, B is boron in the oxidation state of +3, and each G is independently selected from the group consisting of hydride group, dialkylamide group, halide group, alkoxide group, aryloxy group, hydrocarbon group, haloalkyl group and halogen-substituted hydrocarbon group, wherein G has 20 or fewer carbon atoms, provided that G is a halide in one or more positions.

[0124] The polymerization activity can be further enhanced by using the first and second cocatalysts as described above.

[0125] The first cocatalyst of Formula 4 can be an alkylaluminoxane compound, wherein the repeating units are arranged in a linear, cyclic, or network form. Specific examples of the first cocatalyst include methylaluminoxane (MAO), ethylaluminoxane, isobutylaluminoxane, and butylaluminoxane.

[0126] Furthermore, the second cocatalyst of Formula 5 can be a trisubstituted ammonium salt, a dialkylammonium salt, or a trisubstituted phosphate-type borate compound. Specific examples of the second cocatalyst include borate compounds in the form of trisubstituted ammonium salts, such as trimethylammonium tetraphenylborate, methyl dioctadecylammonium tetraphenylborate, triethylammonium tetraphenylborate, tripropylammonium tetraphenylborate, tri(n-butyl)ammonium tetraphenylborate, methyl tetradecyloctadecylammonium tetraphenylborate, N,N-dimethylphenylammonium tetraphenylborate, N,N-diethylphenylammonium tetraphenylborate, N,N-dimethyl(2,4,6-trimethylphenylammonium tetraphenylborate), and trimethyl(pentafluorophenyl)borate. Methyl bis(tetradecyl)ammonium tetra(pentaphenyl)borate, methyl bis(octadecyl)ammonium tetra(pentafluorophenyl)borate, triethylammonium tetra(pentafluorophenyl)borate, tripropylammonium tetra(pentafluorophenyl)borate, tri(n-butyl)ammonium tetra(pentafluorophenyl)borate, tri(sec-butyl)ammonium tetra(pentafluorophenyl)borate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate, N,N-diethylphenylammonium tetra(pentafluorophenyl)borate, N,N-dimethyl(2,4,6-trimethylphenylammonium tetra(pentafluorophenyl)borate, N,N-dimethyl(2,4,6-trimethylphenylammonium tetra(pentafluorophenyl)borate, tetra(2,3) Trimethylammonium tetra(2,3,4,6-tetrafluorophenyl)borate, triethylammonium tetra(2,3,4,6-tetrafluorophenyl)borate, tripropylammonium tetra(2,3,4,6-tetrafluorophenyl)borate, tri(n-butyl)ammonium tetra(2,3,4,6-tetrafluorophenyl)borate, dimethyl(n-butyl)ammonium tetra(2,3,4,6-tetrafluorophenyl)borate, N,N-dimethylphenylammonium tetra(2,3,4,6-tetrafluorophenyl)borate, N,N-diethylphenylammonium tetra(2,3,4,6-tetrafluorophenyl)borate, or tetra-(2,3,4,6-tetrafluorophenyl)borate 4,6-Tetrafluorophenyl)boronic acid-N,N-dimethyl-(2,4,6-trimethylphenylammonium), etc.; borate compounds in the form of dialkylammonium salts, such as bis(octadecylammonium)tetra(pentafluorophenyl)boronic acid, bis(tetradecylammonium)tetra(pentafluorophenyl)boronic acid, or dicyclohexylamine tetra(pentafluorophenyl)boronic acid; or borate compounds in the form of trisubstituted phosphonium salts, such as triphenylphosphonium tetra(pentafluorophenyl)boronic acid, methylbis(octadecyl)phosphonium tetra(pentafluorophenyl)boronic acid, or tri(2,6-dimethylphenyl)phosphonium tetra(pentafluorophenyl)boronic acid.

[0127] In the metallocene catalysts disclosed herein, the total weight ratio of the transition metals contained in the first and second metallocene compounds to the support can be from 1:10 to 1:1,000. Optimal configuration is provided when the support and metallocene compounds are contained in mass ratios within the aforementioned range. Furthermore, the mass ratio of the co-catalyst compound to the support can be from 1:1 to 1:100.

[0128] In the metallocene catalysts disclosed herein, a support containing hydroxyl groups on its surface can be used as the support, and preferably a support having highly reactive hydroxyl and siloxane groups whose surface has been dried and moisture removed can be used.

[0129] For example, silicon dioxide, silicon dioxide-alumina, or silicon dioxide-magnesium oxide dried at high temperatures can be used, and they can typically contain oxides, carbonates, sulfates, and nitrates, such as Na2O, K2CO3, BaSO4, and Mg(NO3)2.

[0130] The drying temperature of the support is preferably 200 to 800°C, more preferably 300 to 600°C, and most preferably 300 to 400°C. If the drying temperature of the support is below 200°C, it retains too much moisture, causing the moisture on the surface to react with the cocatalyst. If the drying temperature is above 800°C, the pores on the support surface combine with each other, reducing the surface area, and many hydroxyl groups are lost on the surface, leaving only siloxane groups. Therefore, it is not preferred due to the reduction in reaction sites with the cocatalyst.

[0131] The amount of hydroxyl groups on the carrier surface is preferably 0.1 to 10 mmol / g, more preferably 0.5 to 5 mmol / g. The amount of hydroxyl groups on the carrier surface can be controlled according to the preparation method and the conditions of the carrier, or drying conditions such as temperature, time, vacuum degree and spray drying.

[0132] If the amount of hydroxyl groups is less than 0.1 mmol / g, the reaction sites with the co-catalyst are reduced. If the amount of hydroxyl groups exceeds 10 mmol / g, it is unsuitable because this may be caused by moisture in addition to the hydroxyl groups present on the surface of the support particles.

[0133] Meanwhile, the polyethylene of the present invention can be prepared by polymerizing ethylene monomer in the presence of the above-mentioned hybrid metallocene catalyst.

[0134] Alternatively, according to one embodiment of this disclosure, it can be prepared by copolymerizing an ethylene monomer with another olefinic comonomer.

[0135] Specific examples of olefinic monomers may include 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-eicosene, which can be copolymerized by mixing two or more of them.

[0136] When the olefin polymer is an ethylene / α-olefin copolymer, there is no specific limit to the content of the α-olefin as a comonomer, and it can be appropriately selected according to the use or purpose of the olefin polymer.

[0137] Continuous slurry polymerization reactors, loop slurry reactors, gas-phase reactors, or solution reactors can be used to carry out polymerization reactions by polymerizing monomers.

[0138] Furthermore, the polymerization temperature can be from about 25 to about 500°C, preferably from about 25 to about 200°C, and more preferably from about 50 to about 150°C. In addition, the polymerization pressure can be from about 1 to about 100 kgf / cm². 2 Preferably about 1 to about 50 kgf / cm 2 More preferably about 5 to about 30 kgf / cm 2 .

[0139] Metallocene catalysts can be injected after being dissolved or diluted in aliphatic hydrocarbon solvents (e.g., pentane, hexane, heptane, nonane, decane and their isomers), aromatic hydrocarbon solvents (e.g., toluene and benzene), or hydrocarbon solvents substituted with chlorine atoms (e.g., dichloromethane and chlorobenzene). The solvent is preferably used after removing trace amounts of water or air, which act as catalyst poisons, by treating with a small amount of aluminum. This can also be achieved by further using a co-catalyst.

[0140] According to another embodiment of this disclosure, a cross-linked polyethylene pipe comprising polyethylene is provided.

[0141] The cross-linked polyethylene pipe disclosed herein can be manufactured by RAM extrusion molding of the aforementioned polyethylene. RAM extrusion molding is used in extrusion molding fields requiring uniform high pressure, and compared with screw extrusion molding, it has the effect of processing high molecular weight polyethylene resin during the manufacturing process of cross-linked polyethylene pipe.

[0142] RAM extrusion molding can be carried out using methods used to manufacture conventional cross-linked polyethylene pipes, and there are no specific limitations.

[0143] Furthermore, in the manufacture of cross-linked polyethylene pipes, conventional cross-linking agents and antioxidants can be mixed with the polyethylene disclosed herein for extrusion.

[0144] Organic peroxide crosslinking agents can be used as crosslinking agents. Specific examples of organic peroxide crosslinking agents may include di-tert-butyl peroxide (DTBP), dicumyl peroxide, di-tert-pentyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, but this disclosure is not limited thereto. Furthermore, there is no specific limitation on the content of the crosslinking agent, but based on 100 parts by weight of polyethylene, the content may be from 0.4 to 1 part by weight.

[0145] Phenolic antioxidants can be used as antioxidants. Specific examples of phenolic antioxidants may include IRGANOX 1076, IRGANOX 1010, BHT, and songnox 1076, but this disclosure is not limited thereto. Furthermore, there is no specific limitation on the content of the antioxidant, but based on 100 parts by weight of polyethylene, the content may be from 0.1 to 0.6 parts by weight.

[0146] In addition, the cross-linked pipe can be a PE-Xa pipe.

[0147] Furthermore, as measured according to KS M ISO 10147, the degree of crosslinking of the crosslinked polyethylene pipe of the embodiments of this disclosure can be 70% or more.

[0148] More specifically, according to one embodiment, as measured according to KS M ISO 10147, the degree of crosslinking of the crosslinked polyethylene pipe of this disclosure is 70% or more, or 75% or more, or 77% or more, or 80% or more, or 81% or more, or 82% or more, or 83% or more, and 99% or less, or 96% or less, or 93% or less.

[0149] With a high degree of crosslinking of over 70%, the crosslinked polyethylene pipe of this disclosure can have excellent mechanical strength.

[0150] Furthermore, as measured according to ISO 1167-1, the circumferential stress of the cross-linked polyethylene pipe of the present disclosure embodiment can be 18.5 MPa or higher.

[0151] More specifically, according to one embodiment, the circumferential stress of the cross-linked polyethylene pipe of this disclosure may be 18.5 MPa or more, or 18.7 MPa or more, and 25 MPa or less, 24 MPa or less, or 22 MPa or less.

[0152] As described above, the cross-linked polyethylene pipe of this disclosure has excellent pressure resistance.

[0153] Preferred embodiments are presented below to aid in understanding this disclosure. However, the following embodiments are provided to better understand this disclosure, and the scope of this disclosure is not limited thereto.

[0154] <Example>

[0155] <Examples of Synthesis of Metallocene Compounds>

[0156] Synthesis Example 1: Synthesis of the First Metallocene Compound

[0157]

[0158] 1-1 Preparation of ligand compounds

[0159] 2.9 g (7.4 mmol) of 8-methyl-5-(2-(trifluoromethyl)benzyl)-5,10-dihydroindeno[1,2-b]indole was dissolved in 100 mL of hexane and 2 mL (16.8 mmol) of MTBE (methyl tert-butyl ether), and 3.2 mL (8.1 mmol) of 2.5 M n-BuLi hexane solution was added dropwise in a dry ice / acetone bath. The mixture was then stirred overnight at room temperature. In another 250 mL Schlenk flask, 2 g (7.4 mmol) of (6-tert-butoxyhexyl)dichloro(methyl)silane was dissolved in 50 mL of hexane, and then added dropwise in a dry ice / acetone bath. A lithiumized slurry of 8-methyl-5-(2-(trifluoromethyl)benzyl)-5,10-dihydroindeno[1,2-b]indole was added dropwise through a sleeve. After the injection was completed, the mixture was slowly brought to room temperature and then stirred overnight at room temperature. Meanwhile, 1.2 g (7.4 mmol) of fluorene was dissolved in 100 mL of THF, and 3.2 mL (8.1 mmol) of 2.5 M n-BuLi hexane solution was added dropwise in a dry ice / acetone bath. The mixture was then stirred overnight at room temperature.

[0160] The reaction solution (Si solution) of 8-methyl-5-(2-(trifluoromethyl)benzyl)-5,10-dihydroindo[1,2-b]indole and (6-(tert-butoxy)hexyl)dichloro(methyl)silane was sampled by NMR to confirm the completion of the reaction.

[0161] 1 H NMR(500MHz, CDCl3):7.74-6.49(11H,m),5.87(2H,s),4.05(1H,d),3.32(2 H,m),3.49(3H,s),1.50-1.25(8H,m),1.15(9H,s),0.50(2H,m),0.17(3H,d)

[0162] After confirming the synthesis, the lithiation solution of fluorene was slowly added dropwise to a Si solution in a dry ice / acetone bath, and the mixture was then stirred overnight at room temperature. Following the reaction, extraction with diethyl ether / water was performed, and residual water in the organic layer was removed with MgSO4. The solvent was then removed under vacuum and reduced pressure to obtain 5.5 g (7.4 mmol) of an oily ligand compound, which can be obtained by… 1H-NMR confirmed.

[0163] 1 H NMR(500MHz, CDCl3):7.89-6.53(19H,m),5.82(2H,s),4.26(1H,d),4.14-4.10(1H,m),3 .19(3H,s),2.40(3H,m),1.35-1.21(6H,m),1.14(9H,s),0.97-0.9(4H,m),-0.34(3H,t).

[0164] Preparation of 1-2 metallocene compounds

[0165] 5.4 g (Mw 742.00, 7.4 mmol) of the ligand compound synthesized in step 1-1 was dissolved in 80 mL of toluene and 3 mL (25.2 mmol) of MTBE. 7.1 mL (17.8 mmol) of a 2.5 M n-BuLi hexane solution was added dropwise to a dry ice / acetone bath, and the mixture was stirred overnight at room temperature. 3.0 g (8.0 mmol) of ZrCl4(THF)2 was added to 80 mL of toluene to prepare a slurry. The 80 mL of ZrCl4(THF)2, which served as the toluene slurry, was transferred to the ligand-Li solution in a dry ice / acetone bath, and the mixture was stirred overnight at room temperature.

[0166] The reaction mixture was filtered to remove LiCl, and the filtrate was dried under vacuum to remove toluene. Then, 100 mL of hexane was added, and the mixture was sonicated for 1 hour. The mixture was then filtered to give 3.5 g of a purple metallocene compound as a solid (yield: 52 mol%).

[0167] 1 H NMR (500MHz, CDCl3): 7.90-6.69(9H,m),5.67(2H,s),3.37(2H,m),2.56(3H,s),2.13-1.51(11H,m),1.17(9H,s).

[0168] Synthesis Example 2. Synthesis of the Second Metallocene Compound

[0169] Preparation of [tBu-O-(CH2)6-C5H4]2ZrCl2

[0170] tert-butyl-O-(CH2)6-Cl was prepared using the method suggested in the literature [Tetrahedron Lett. 2951 (1988)] using 6-chlorohexanol, and reacted with NaCp to give tert-butyl-O-(CH2)6-C5H5 (yield: 60%, bp 80℃ / 0.1mmHg).

[0171] Furthermore, tert-butyl-O-(CH2)6-C5H5 was dissolved in THF at -78°C, and n-butyllithium (n-BuLi) was slowly added to it. The reaction temperature was then raised to room temperature, and the mixture was allowed to react for 8 hours. The solution was reacted again, wherein the synthesized lithium salt solution was slowly added to a suspension of ZrCl4(THF)2 (1.70 g, 4.50 mmol) / THF (30 ml) at -78°C, and the reaction was further carried out at room temperature for 6 hours.

[0172] All volatile substances were dried under vacuum, and hexane solvent was added to the resulting oily liquid. The mixture was then filtered off. The filtered solution was dried under vacuum, and hexane was added to induce precipitation at low temperature (-20°C). The precipitate was filtered off at low temperature to give the compound [tBu-O-(CH2)6-C5H4]2ZrCl2 as a white solid (yield: 92%).

[0173] 1 H NMR (300MHz, CDCl3): 6.28 (t, J = 2.6 Hz, 2H), 6.19 (t, J = 2.6 Hz, 2H), 3.31 (t, 6.6 Hz, 2H), 2.62 (t, J = 8 Hz), 1.7-1.3 (m, 8H), 1.17 (s, 9H).

[0174] 13 C NMR(CDCl3):135.09,116.66,112.28,72.42,61.52,30.66,30.61,30.14,29.18,27.58,26.00.

[0175] <Preparation Examples of Hybrid Supported Catalysts>

[0176] Preparation Example 1

[0177] 5.0 kg of toluene solution was added to a 20 L autoclave, and the reactor temperature was maintained at 40 °C. 1000 g of silica (manufactured by Grace Davison, SP 948) was dehydrated by applying a vacuum at 600 °C for 12 hours, and then added to the reactor to fully disperse the silica. Then, 55 g of the first metallocene compound from Synthesis Example 1 was dissolved in toluene and added to the reactor. The mixture was reacted at 40 °C for 2 hours while stirring at 200 rpm. Stirring was then stopped, the reaction solution was allowed to stand for 30 minutes, and then decanted.

[0178] 2.5 kg of toluene was added to the reactor, followed by 9.4 kg of a 10% by weight methylaluminoxane (MAO) / toluene solution. The mixture was stirred at 200 rpm for 12 hours at 40°C. After the reaction, stirring was stopped, the reaction solution was allowed to stand for 30 minutes, and then decanted. 3.0 kg of toluene was added and stirred for 10 minutes, then stirring was stopped, the reaction solution was allowed to stand for 30 minutes, and then decanted.

[0179] 3.0 kg of toluene was added to the reactor. 142.3 g of the second metallocene compound from Synthesis Example 2 was dissolved in 1 L of toluene solution and added to the reactor. The reaction was carried out at 40 °C for 2 hours while stirring at 200 rpm. After the reactor temperature was lowered to room temperature, stirring was stopped, the reaction solution was allowed to stand for 30 minutes, and then decanted.

[0180] Add 2.0 kg of toluene to the reactor and stir for 10 minutes. Then, stop stirring, let the reaction solution stand for 30 minutes, and then decant.

[0181] 3.0 kg of hexane was added to the reactor, and the hexane slurry was transferred to a filter dryer and filtered to obtain a hexane solution. The filtrate was dried under reduced pressure at 40 °C for 4 hours to prepare 1 kg of SiO2 hybrid supported catalyst (molar ratio between the first metallocene compound and the second metallocene compound was 1:10).

[0182] Polyethylene Polymerization

[0183] Example 1

[0184] The supported catalyst prepared in Preparation Example 1 was added to a single slurry polymerization process to prepare high-density polyethylene.

[0185] First, inject the following substances into a volume of 100m³ at the following flow rates. 3 In the reactor: 25 ton / hr hexane, 10 ton / hr ethylene, 35 ppm (relative to ethylene) hydrogen, and 10 kg / hr triethylaluminum (TEAL). Additionally, the hybrid supported metallocene catalyst of Example 1 was injected at 0.5 kg / hr. Then, the reaction was carried out at a reaction temperature of 82 °C and 7.0 kg / cm³. 2 Up to 7.5 kg / cm 2 Ethylene is continuously reacted in the form of hexane slurry under pressure, followed by solvent removal and drying processes to prepare high-density polyethylene in powder form.

[0186] Example 2

[0187] High-density polyethylene in powder form was prepared in the same manner as in Example 1, except that the hydrogen content was 25 ppm relative to ethylene.

[0188] Comparative Example 1

[0189] Polyethylene prepared using the Ziegler-Natta catalyst (LG Chem's XL1800 product) was used as Comparative Example 1.

[0190] Comparative Example 2

[0191] Polyethylene prepared using the Ziegler-Natta catalyst (Lotte Chemical's 8100GX product) was used as Comparative Example 2.

[0192] <Preparation of Cross-linked Polyethylene Pipes>

[0193] Example 3

[0194] 100g of polyethylene from Example 1 was mixed with 0.3g of octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate (product name: Irganox 1076, manufactured by BASF) as an antioxidant and 0.6g of di-tert-butyl peroxide (product name: Trigonox B, manufactured by Akzo Nobel) as a crosslinking agent and dispersed using a Henschel mixer (RPM 400, mixing time 15 min, mixing temperature <40°C).

[0195] Subsequently, to prepare cross-linked polyethylene pipes, extrusion was performed using a Ram-type extruder. At this time, the extruder's pipe diameter was set to 20 mm, the thickness to 1.9 mm, and the temperature conditions were set to 130°C for the main body, 180°C for the adapter, and -240°C for the die. Furthermore, the linear speed during extrusion was set to 1.8 m / min.

[0196] Example 4

[0197] Cross-linked polyethylene pipes were prepared in the same manner as in Example 3, except that the polyethylene of Example 2 was used instead of the polyethylene of Example 1.

[0198] Example 5

[0199] Cross-linked polyethylene pipes were prepared in the same manner as in Example 3, except that the polyethylene of Example 2 was used instead of the polyethylene of Example 1, and 0.5 g of di-tert-butyl peroxide (product name: Trigonox B, manufactured by AkzoNobel) was used as the cross-linking agent.

[0200] Comparative Example 3

[0201] Cross-linked polyethylene pipes were prepared in the same manner as in Example 3, except that the polyethylene of Comparative Example 1 was used instead of the polyethylene of Example 1.

[0202] Comparative Example 4

[0203] Crosslinked polyethylene pipes were prepared in the same manner as in Example 3, except that polyethylene from Comparative Example 1 was used instead of polyethylene from Example 1, and 0.5 g of di-tert-butyl peroxide (product name: Trigonox B, manufactured by AkzoNobel) was used as a crosslinking agent.

[0204] Comparative Example 5

[0205] Cross-linked polyethylene pipes were prepared in the same manner as in Example 3, except that polyethylene from Comparative Example 2 was used instead of polyethylene from Example 1.

[0206] <Experimental Example>

[0207] Evaluation of physical properties

[0208] The physical properties of the polyethylene and cross-linked polyethylene pipes prepared in the Examples and Comparative Examples were evaluated using the following methods.

[0209] (1) Weight-average molecular weight (Mw) and molecular weight distribution (MWD, polydispersity index), GPC curve:

[0210] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polymer were measured using gel permeation chromatography (GPC; manufactured by Waters Corp.), and the polydispersity index (PDI) was calculated by dividing the weight-average molecular weight by the number-average molecular weight.

[0211] Specifically, polyethylene samples were evaluated using a Waters PL-GPC220 instrument with a 300 mm PLgel Mixed-B column from Polymer Laboratories. The evaluation temperature was set at 160 °C, 1,2,4-trichlorobenzene was used as the solvent, and the flow rate was set at 1 mL / min. Samples were prepared at a concentration of 10 mg / 10 mL and then supplied in 200 μL increments. Calibration curves using polystyrene standards were used to determine Mw and Mn values. The polystyrene standards used had molecular weights of 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000.

[0212] (2) Melt Index (MI) 21.6 ):

[0213] Measured according to ASTM D1238 standard (condition E, 190°C, 21.6 kg load).

[0214] (3) Density: Measured according to ASTM D792 standard.

[0215] (4) Log Mw (≤4.5): Calculated by the ratio of the integral value in the region with a Log Mw value below 4.5 to the total area (integral value) of the entire GPC curve obtained from (1) above.

[0216] (5) Crosslinking degree: Measured according to KS M ISO 10147.

[0217] (6) Circumferential stress

[0218] Pressure is increased at room temperature (25°C), and the pressure at which ductile fracture occurs within 5 minutes is measured and calculated as the circumferential stress. Then, the compressive strength test method is performed according to ISO 1167-1 to determine the circumferential stress at which ductile fracture occurs.

[0219] Table 1

[0220]

[0221] * In a GPC curve plot where the x-axis is log Mw and the y-axis is dw / dlog Mw, the ratio of the integral value to the total integral value in the region where the log Mw value is below 4.5.

[0222] Referring to Table 1, the polyethylene of Examples 1 and 2 of this disclosure has a melt flow index (MI) of... 21.6 It exhibits higher properties than the comparative example in terms of both density and other properties.

[0223] Therefore, while the cross-linked polyethylene of Examples 3 to 5 exhibits high circumferential stress and improved pressure resistance, the degree of cross-linking also shows a level comparable to that of the comparative examples.

Claims

1. A polyethylene that satisfies: According to ASTM D792, the density is 0.950 g / cm³. 3 Above and 0.955 g / cm 3 the following; The number average molecular weight (Mn) is above 33,000 g / mol and below 55,000 g / mol; The weight average molecular weight (Mw) is above 130,000 g / mol and below 200,000 g / mol; The polydispersity index (PDI, Mw / Mn) is above 2.8 and below 3.4; and According to ASTM D1238, the melt flow index (MI) was determined at 190°C under a load of 21.6 kg. 21.6 The concentration of g / 10 min is greater than 6 g / 10 min and less than 14 g / 10 min. in, In a GPC curve plot where the x-axis is log Mw and the y-axis is dw / dlog Mw, the integral value in the region where the log Mw value is below 4.5 is less than 25% of the total integral value.

2. The polyethylene as described in claim 1, wherein, In a GPC curve plot where the x-axis is log Mw and the y-axis is dw / dlog Mw, the integral value in the region where the log Mw value is below 4.5 is between 15% and 22% of the total integral value.

3. A cross-linked polyethylene pipe, which is prepared by cross-linking reaction of polyethylene and cross-linking agent as described in claim 1.

4. The cross-linked polyethylene pipe as described in claim 3, wherein, The crosslinking agent includes at least one selected from the group consisting of di-tert-butyl peroxide (DTBP), dicumyl peroxide, di-tert-pentyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane.

5. The cross-linked polyethylene pipe as described in claim 3, wherein, According to KS M ISO 10147, the degree of crosslinking is above 70%.

6. The cross-linked polyethylene pipe as described in claim 3, wherein, The pipe is a PE-Xa pipe.

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