Ethylenic polymer

Abstract

To provide an ethylenic polymer which can improve tensile characteristics of a molding without impairing moldability, and achieves thinning of the molding and long life of the molding.SOLUTION: An ethylenic polymer satisfies the following characteristics (1) to (3). (1): A melt flow rate (HLMFR) according to JIS K 6922-2:1997 is 0.01 to 50 g / 10 min, (2) An elution curve measured by GPC has two peaks, when the elution curve is subjected to peak resolution into two normal distributions, the elution curve satisfies the following (2-1) to (2-3). (2-1): Mw by a peak on a high molecular weight side is 900,000 to 5,000,000, and Mw / Mn is 2.0 to 5.0. (2-2): Mw by a peak on a low molecular weight side is 10,000 to 500,000, and Mw / Mn is more than 5.0 and 10.0 or less. (2-3): A weight ratio (wt.%) of the peak on the high molecular weight side / a weight ratio (wt.%) of the peak on the low molecular weight side is more than 5 / 95 and less than 80 / 20. (3): Tm1 measured using DSC has a single peak.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a specific ethylene-based polymer, and more specifically to an ethylene-based polymer which contains a specific ultra-high molecular weight component and a low molecular weight component having a broader molecular weight distribution, and is therefore expected to improve the tensile properties of a molded article without impairing moldability, thereby enabling the molded article to be made thinner. [Background technology]

[0002] Polyethylene is a resin used in a wide range of applications, and in order to tailor it to each application, various techniques have been proposed to control the molecular weight distribution and composition by combining two or more resin components, thereby improving various physical properties and appearance. For example, increasing the amount of higher molecular weight components improves mechanical strength but decreases moldability, while increasing the amount of lower molecular weight components decreases mechanical strength but improves moldability.

[0003] Proposed methods for combining two or more polyethylene components include a method in which each component is polymerized and then blended by melt kneading or dry blending, a method in which multistage polymerization is carried out continuously, a method in which two or more polyethylene components are simultaneously produced by adding multiple transition metal catalysts to a polymerization system, and a combination of these methods. Furthermore, a resin modifier has also been proposed (see, for example, Patent Document 1), which is blended with a target material to modify the physical properties, appearance, etc. of the target material.

[0004] In the blow molding, injection molding, inflation molding, and extrusion molding of polyethylene, materials with good moldability and physical properties are generally required. In recent years, there has been a demand for lighter weight and thinner walls to reduce costs, but at the same time, excellent mechanical strength is also required.

[0005] Ultra-high molecular weight polyethylene, which has attracted attention in recent years (see, for example, Patent Documents 2 and 3), has an extremely high molecular weight equivalent to a viscosity average molecular weight (hereinafter sometimes referred to as Mv) of 1 million or more, and therefore has excellent impact resistance, self-lubrication, abrasion resistance, weather resistance, chemical resistance, dimensional stability, etc., and has high physical properties comparable to those of engineering plastics. For this reason, attempts have been made to apply it to uses such as lining materials, food industry line parts, machine parts, artificial joints, sporting goods, microporous membranes, and separators using various molding methods.

[0006] However, due to its high molecular weight, ultra-high molecular weight polyethylene has extremely low fluidity when melted, making it difficult to mold by kneading and extrusion, as is the case with ordinary polyethylene, which has a molecular weight in the range of several tens of thousands to approximately 300,000.Therefore, ultra-high molecular weight polyethylene is molded by various methods, such as direct sintering of polymer powder obtained by polymerization, compression molding, molding using a ram extruder in which extrusion molding is performed while intermittently compressing, and extrusion molding in a state where it is dispersed in a solvent or the like, followed by removal of the solvent.

[0007] In order to improve the moldability of ultra-high molecular weight polyethylene and its kneadability with other resins, a method of adding low molecular weight polyethylene has been proposed (see, for example, Patent Documents 4 and 5), and an ultra-high molecular weight polyethylene exhibiting a specific melting behavior has also been proposed (see, for example, Patent Document 6). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2017-179304 [Patent Document 2] Patent No. 4868853 [Patent Document 3] Patent No. 6405888 [Patent Document 4] Patent No. 4173444 [Patent Document 5] Patent No. 7071966 [Patent Document 6] Patent Publication No. 2021-172716 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the proposal in Patent Document 1 relates to a modifier that is effective in improving processability to a certain extent. Patent Documents 2 and 3 merely propose ultra-high molecular weight polyethylene, leaving room for improvement in molding processability. Furthermore, the proposals in Patent Documents 4 to 6 only improve the processability of ultra-high molecular weight polyethylene, leaving room for improvement in processability as polyethylene.

[0010] Therefore, there has been a desire for the emergence of an ethylene-based polymer that can improve the mechanical properties without impairing the processability of the ethylene-based polymer. [Means for solving the problem]

[0011] Means for Solving the Problems The present inventors have conducted extensive studies to solve the above problems and have found that an ethylene polymer containing specific components in specific ratios can improve tensile properties without impairing processability, thereby completing the present invention.

[0012] That is, the present invention relates to an ethylene polymer that satisfies the following properties (1) to (3) and a method for producing the same. (1) The melt flow rate (hereinafter sometimes referred to as HLMFR) at a temperature of 190° C. under a load of 21.6 kg conforming to JIS K 6922-2:1997 is 0.01 to 50 g / 10 min. (2) The elution curve measured by gel permeation chromatography (hereinafter sometimes referred to as GPC) is bimodal, and when the elution curve is expressed as a differential molecular weight distribution (x-axis: Log [M], y-axis: differential distribution value), and the peak is divided into two normal distributions according to the following formula (i), the following (2-1) to (2-3) are satisfied: y=a×(1 / (2π(σ 2 ))(1 / 2) ) exp(-((x-μ) 2 ) / (2(σ 2 ))) Formula (i) (Here, a is the peak intensity, σ is the standard deviation, x is the variable, and μ is x at the peak top.) (2-1): The weight average molecular weight (hereinafter sometimes referred to as Mw) calculated as linear polyethylene based on the peak on the high molecular weight side is 900,000 to 5,000,000, and the molecular weight distribution expressed as Mw / number average molecular weight (hereinafter sometimes referred to as Mn) is 2.0 to 5.0.

[0013] (2-2): The Mw of the low molecular weight peak calculated as linear polyethylene is 10,000 to 200,000, and the Mw / Mn is more than 5.0 and 10.0 or less.

[0014] (2-3): The weight ratio of the high molecular weight peak to the weight ratio of the low molecular weight peak (wt %) is greater than 5 / 95 and smaller than 80 / 20. (3) Using a differential scanning calorimeter (hereinafter sometimes referred to as DSC), the sample is heated from 0°C to 230°C at a rate of 10°C / min (hereinafter sometimes referred to as the first scan). The crystal melting peak (hereinafter sometimes referred to as Tm1) in the first scan is unimodal.

[0015] The present invention will be described in detail below.

[0016] The ethylene polymer of the present invention may be a bimodal ethylene polymer having a specific ultra-high molecular weight polyethylene component and a specific low molecular weight polyethylene component and exhibiting a bimodal molecular weight distribution, and examples thereof include ethylene homopolymers and ethylene-α-olefin copolymers. In this case, examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene. Ethylene homopolymers are preferred because they have a particularly excellent effect of modifying resins, particularly ethylene resins.

[0017] The ethylene polymer (1) has a melt fluidity of 0.01 to 50 g / 10 min at a temperature of 190°C under a load of 21.6 kg according to JIS K 6922-2:1997. If the melt fluidity is less than 0.01 g / 10 min, the processability and the modifying effect will be poor. On the other hand, if the melt fluidity is more than 50 g / 10 min, the mechanical properties will be poor and the modifying effect will be poor.

[0018] The ethylene polymer is an ethylene polymer containing a specific ultra-high molecular weight polyethylene component and a specific low-molecular weight polyethylene component having a broader molecular weight distribution as specific components, and has a bimodal molecular weight distribution. The bimodal molecular weight distribution is defined as a bimodal elution curve measured by GPC, which is expressed as a differential molecular weight distribution (x-axis: Log [M], y-axis: differential distribution value) and divided into two normal distributions (ultra-high molecular weight polyethylene component normal distribution and polyethylene component normal distribution) according to the above formula (i), where (2-1) the ultra-high molecular weight polyethylene component (hereinafter sometimes referred to as component (A)) represented as the high-molecular weight peak component has an Mw of 900,000 to 5,000,000 and a molecular weight distribution expressed as Mw / Mn of 2.0 to 5.0, and (2-2) the polyethylene component (hereinafter sometimes referred to as component (B)) represented as the low-molecular weight peak component has an Mw of 10,000 to 500,000 and a Mw / Mn of more than 5.0 but not more than 10.0. In addition, (2-3) the component (A) / component (B) (weight %) is greater than 5 / 95 and less than 80 / 20, and since this provides a good balance between the molding processability and the effect of improving the mechanical properties, it is preferable that the component (A) / component (B) (weight %) is 10 / 90 to 50 / 50.

[0019] Here, if the Mw / Mn ratio of component (ii) is 5.0 or less, good molding processability cannot be obtained, and it becomes difficult to exhibit the original mechanical properties. On the other hand, if it exceeds 10.0, the mechanical strength will be poor. If component (i) is 5 wt% or less, the effect of improving the mechanical properties will be low. On the other hand, if it is 80 wt% or more, the processability will be poor.

[0020] The ethylene polymer of the present invention contains component (A), an ultra-high molecular weight component, and component (B), a low molecular weight component, in a specific ratio, which allows component (A) to be highly dispersed, thereby enabling improved mechanical strength when molded without impairing processability or appearance, and resulting in a particularly excellent balance between mechanical properties and processability. (3) Since Tm1, which is the crystalline melting peak in the first scan measured using DSC, shows a single peak, it is desirable that if Tm1 is not a single peak, component (A) and component (B) will be dispersed independently, like a simple blend, resulting in poor mechanical properties and processability.

[0021] Furthermore, since the ethylene polymer of the present invention has a particularly excellent balance between mechanical properties and processability, (4) the Mw / Mn, calculated as standard polyethylene as measured by GPC, is preferably 4.0 or more and less than 50, and particularly preferably 4.0 or more and 30 or less.

[0022] Furthermore, since the ethylene polymer of the present invention has component (A) highly dispersed in component (B), after the first scan, the sample is allowed to stand for 5 minutes, cooled to −20° C. at a rate of 10° C. / min, allowed to stand for 5 minutes, and then heated again from −20° C. to 230° C. at a rate of 10° C. / min (hereinafter also referred to as the second scan). The melting point (hereinafter also referred to as Tm2) in the second scan is measured, and the difference between Tm1 and Tm2 (ΔTm=Tm1−Tm2) is −1° C. or more and less than 15° C., and the ratio (ΔH2 / ΔH1) of the heat of fusion in the first scan (hereinafter also referred to as ΔH1) to the heat of fusion in the second scan (hereinafter also referred to as ΔH2) is preferably 0.94 or more.

[0023] The ethylene polymer of the present invention may be any polymer that satisfies the above-mentioned properties, and there is no limitation on the method for producing it. Among them, those produced using a metallocene catalyst are preferred, since it is particularly easy to control the molecular weight and molecular weight distribution and to produce (ultra)high molecular weight components. Examples of methods for producing an ethylene polymer having both component (a) and component (b) include a method using a co-supported catalyst in which two or more metallocene complexes are supported on a carrier, and a method using two or more multi-stage polymerization.

[0024] Examples of polymerization methods for the ethylene polymer include solution polymerization, bulk polymerization, gas-phase polymerization, and slurry polymerization. Among these, slurry polymerization is preferred because it enables the production of ethylene polymers having a uniform particle shape and enables the efficient and stable production of ethylene polymers that are excellent in improved mechanical strength while maintaining processability. The solvent used in the slurry polymerization may be any commonly used organic solvent, such as benzene, toluene, xylene, pentane, hexane, and heptane. Liquefied gases such as isobutane and propane, and olefins such as 1-butene and 1-hexene can also be used as the solvent.

[0025] The catalyst used to produce the ethylene polymer may be a metallocene catalyst. For example, in multi-stage polymerization, the metallocene catalyst may be obtained from at least a transition metal compound (A-1), an organically modified clay (B) modified with an aliphatic salt, and an organoaluminum compound (C). For example, in the co-supported catalyst method, the metallocene catalyst may be obtained from at least a transition metal compound (A-1), a transition metal compound (A-2), an organically modified clay (B) modified with an aliphatic salt, and an organoaluminum compound (C).

[0026] Examples of the transition metal compound (A-1) include transition metal compounds having a (substituted) cyclopentadienyl group and a (substituted) fluorenyl group, transition metal compounds having a (substituted) cyclopentadienyl group and a (substituted) indenyl group, and transition metal compounds having a (substituted) indenyl group and a (substituted) fluorenyl group. In this case, examples of the transition metal include zirconium and hafnium. Among these, zirconium compounds having a (substituted) cyclopentadienyl group and an amino group-substituted fluorenyl group and hafnium compounds having a (substituted) cyclopentadienyl group and an amino group-substituted fluorenyl group are preferred, as they enable efficient production of ethylene polymers suitable as resin modifiers.

[0027] More specifically, for example, diphenylmethylene(1-indenyl)(9-fluorenyl)zirconium dichloride, diphenylmethylene(1-indenyl)(2,7-di-t-butyl-9-fluorenyl)zirconium dichloride, diphenylmethylene(4-phenyl-1-indenyl)(2,7-di-t-butyl-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(2-(dimethylamino)-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl) )(2-(diethylamino)-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(2-(dibenzylamino)-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(2,7-bis(dimethylamino)-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(2,7-bis(diethylamino)-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(2,7-bis (Dibenzylamino)-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(4-(dimethylamino)-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(4-(diethylamino)-9-fluorenyl)zirconium dichloride, diphenylsilanediyl(cyclopentadienyl)(4-(dibenzylamino)-9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(dimethylamino)-9-fluorenyl) diphenylmethylene(cyclopentadienyl)(2-(diethylamino)-9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(diisopropylamino)-9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(dibenzylamino)-9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(diethylamino)-7-ethyl-9-fluorenyl)zirconium dichloride,Diphenylmethylene(cyclopentadienyl)(2-(diisopropylamino)-7-ethyl-9-fluorenyl)zirconium dichloride, Diphenylmethylene(cyclopentadienyl)(2-(dibenzylamino)-7-ethyl-9-fluorenyl)zirconium dichloride, Diphenylmethylene(cyclopentadienyl)(2-(dimethylamino)-7-n-propyl-9-fluorenyl)zirconium dichloride, Diphenylmethylene(cyclopentadienyl)(2-(diethylamino)-7-n-propyl-9-fluorenyl)zirconium dichloride diphenylmethylene(cyclopentadienyl)(2-(diisopropylamino)-7-n-propyl-9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(dibenzylamino)-7-n-propyl-9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(dibenzylamino)-7-n-propyl-9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(dimethylamino)-7-isopropyl-9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2-(di Diphenylmethylene(cyclopentadienyl)(2-(diisopropylamino)-7-isopropyl-9-fluorenyl)zirconium dichloride, Diphenylmethylene(cyclopentadienyl)(2-(dibenzylamino)-7-isopropyl-9-fluorenyl)zirconium dichloride, Diphenylmethylene(cyclopentadienyl)(2-(dimethylamino)-7-n-butyl-9-fluorenyl)zirconium dichloride, Diphenyl Examples include zirconium compounds such as methylene(cyclopentadienyl)(2-(diisopropylamino)-7-t-butyl-9-fluorenyl)zirconium dichloride and diphenylmethylene(cyclopentadienyl)(2-(dibenzylamino)-7-t-butyl-9-fluorenyl)zirconium dichloride; zirconium compounds in which the dichloro form of these compounds is replaced with a dimethyl form, a diethyl form, a dihydro form, a diphenyl form, or a dibenzyl form; and hafnium compounds in which the zirconium in these compounds is replaced with hafnium.

[0028] Examples of the transition metal compound (A-2) include a transition metal compound having a (substituted) cyclopentadienyl group and a (substituted) fluorenyl group, a transition metal compound having a (substituted) cyclopentadienyl group and a (substituted) indenyl group, and a transition metal compound having a (substituted) indenyl group and a (substituted) indenyl group.

[0029] More specifically, dimethylsilanediylbis(cyclopentadienyl)zirconium dichloride, diethylsilanediylbis(cyclopentadienyl)zirconium dichloride, dicyclohexylsilanediylbis(cyclopentadienyl)zirconium dichloride, diphenylsilanediylbis(cyclopentadienyl)zirconium dichloride, dimethylsilanediylbis(methylcyclopentadienyl)zirconium dichloride, diethylsilanediylbis(methylcyclopentadienyl)zirconium dichloride, dicyclohexylsilanediylbis(cyclopentadienyl)zirconium dichloride, Silsilanediylbis(methylcyclopentadienyl)zirconium dichloride, diphenylsilanediylbis(methylcyclopentadienyl)zirconium dichloride, dimethylsilanediylbis(2,4-dimethylcyclopentadienyl)zirconium dichloride, diethylsilanediylbis(2,4-dimethylcyclopentadienyl)zirconium dichloride, dicyclohexylsilanediylbis(2,4-dimethylcyclopentadienyl)zirconium dichloride, diphenylsilanediylbis(2,4-dimethylcyclopentadienyl) Dimethylsilanediyl[(cyclopentadienyl)(indenyl)]zirconium dichloride, Dimethylsilanediyl[(cyclopentadienyl)(indenyl)]zirconium dichloride, Diethylsilanediyl[(cyclopentadienyl)(indenyl)]zirconium dichloride, Dicyclohexylsilanediyl[(cyclopentadienyl)(indenyl)]zirconium dichloride, Diphenylsilanediyl[(cyclopentadienyl)(indenyl)]zirconium dichloride, Dimethylsilanediyl[(cyclopentadienyl)(4,7-dimethylindenyl)]zirconium dichloride silanediyl[(cyclopentadienyl)(4,7-dimethylindenyl)]zirconium dichloride, dicyclohexylsilanediyl[(cyclopentadienyl)(4,7-dimethylindenyl)]zirconium dichloride, diphenylsilanediyl[(cyclopentadienyl)(4,7-dimethylindenyl)]zirconium dichloride, dimethylsilanediyl[(cyclopentadienyl)(2,4,7-trimethylindenyl)]zirconium dichloride, diethylsilanediyl[(cyclopentadienyl)(2,4,7-trimethylindenyl)]zirconium dichloride, dicyclohexylsilanediyl[(cyclopentadienyl)(2,4,7-trimethylindenyl)]zirconium dichloride, diphenylsilanediyl[(cyclopentadienyl)(2,4,7-trimethylindenyl)]zirconium dichloride, bis(indenyl)zirconium dichloride, isopropylidenebis(indenyl)zirconium dichloride, (methyl)(phenyl)methylenebis(indenyl)zirconium dichloride, di Phenylmethylenebis(indenyl)zirconium dichloride, ethylenebis(indenyl)zirconium dichloride, isopropylidenebis(2-methylindenyl)zirconium dichloride, (methyl)(phenyl)methylenebis(2-methylindenyl)zirconium dichloride, diphenylmethylenebis(2-methylindenyl)zirconium dichloride, ethylenebis(2-methylindenyl)zirconium dichloride, isopropylidenebis(tetrahydroindenyl)zirconium dichloride Iodide, (methyl)(phenyl)methylenebis(tetrahydroindenyl)zirconium dichloride, diphenylmethylenebis(tetrahydroindenyl)zirconium dichloride, ethylenebis(tetrahydroindenyl)zirconium dichloride, isopropylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride, (methyl)(phenyl)methylene(cyclopentadienyl)(fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(fluorenyl) Zirconium dichloride, ethylene(cyclopentadienyl)(fluorenyl)zirconium dichloride, isopropylidene(cyclopentadienyl)(2,7-di-t-butyl-fluorenyl)zirconium dichloride, (methyl)(phenyl)methylene(cyclopentadienyl)(2,7-di-t-butyl-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(2,7-di-t-butyl-fluorenyl)zirconium dichloride, ethylene(cyclopentadienyl)(2,Examples include zirconium compounds such as 7-di-t-butyl-fluorenyl)zirconium dichloride; zirconium compounds in which the dichloro form of these compounds is replaced with a dimethyl form, a diethyl form, a dihydro form, a diphenyl form, or a dibenzyl form, and hafnium compounds in which the zirconium in these compounds is replaced with hafnium.

[0030] Examples of the organically modified clay (B) modified with an aliphatic salt include N,N-dimethyl-behenylamine hydrochloride, N-methyl-N-ethyl-behenylamine hydrochloride, N-methyl-Nn-propyl-behenylamine hydrochloride, N,N-dioleyl-methylamine hydrochloride, N,N-dimethyl-behenylamine hydrofluoride, N-methyl-N-ethyl-behenylamine hydrofluoride, N-methyl-Nn-propyl-behenylamine hydrofluoride, N,N-dioleyl-methylamine hydrofluoride, N,N-dimethyl-behenylamine N-methyl-N-ethyl-behenylamine hydrobromide, N-methyl-Nn-propyl-behenylamine hydrobromide, N,N-dioleyl-methylamine hydrobromide, N,N-dimethyl-behenylamine hydroiodide, N-methyl-N-ethyl-behenylamine hydroiodide, N-methyl-Nn-propyl-behenylamine hydroiodide, N,N-dioleyl-methylamine hydroiodide, N,N-dimethyl-behenylamine sulfate, N-methyl-N-ethyl-behenylamine sulfate aliphatic amine salts such as N-methyl-Nn-propyl-behenylamine sulfate, N,N-dioleyl-methylamine sulfate; P,P-dimethyl-behenylphosphine hydrochloride, P,P-diethyl-behenylphosphine hydrochloride, P,P-dipropyl-behenylphosphine hydrochloride, P,P-dimethyl-behenylphosphine hydrofluoride, P,P-diethyl-behenylphosphine hydrofluoride, P,P-dipropyl-behenylphosphine hydrofluoride, P,P-dimethyl-behenylphosphine hydrobromide, P,P- Examples of clays modified with aliphatic salts include aliphatic phosphonium salts such as diethyl-behenylphosphine hydrobromide, P,P-dipropyl-behenylphosphine hydrobromide, P,P-dimethyl-behenylphosphine hydroiodide, P,P-diethyl-behenylphosphine hydroiodide, P,P-dipropyl-behenylphosphine hydroiodide, P,P-dimethyl-behenylphosphine sulfate, P,P-diethyl-behenylphosphine sulfate, and P,P-dipropyl-behenylphosphine sulfate.

[0031] The clay compound constituting the organically modified clay (B) may be any compound as long as it belongs to the category of clay compounds. In general, the organically modified clay (B) is formed by stacking many layers called silicate layers, which are composed of a tetrahedral sheet of silica tetrahedra connected in two dimensions and an octahedral sheet of alumina octahedrons or magnesia octahedrons connected in two dimensions in a 1:1 or 2:1 ratio. The Si in some of the silica tetrahedra is replaced by Al, the Al in the alumina octahedron by Mg, and the Mg in the magnesia octahedron by Li, etc., resulting in a lack of positive charge within the layer, and the layer as a whole is negatively charged. To compensate for this negative charge, Na is introduced between the layers. + Ya Ca 2+ The clay compounds are known to contain cations such as kaolinite, talc, smectite, vermiculite, mica, brittle mica, and mercury, both natural and synthetic, and these can be used, with smectite being preferred because of its ease of availability and ease of organic modification, and hectorite or montmorillonite being even more preferred among smectites.

[0032] The organically modified clay (B) can be obtained by introducing the aliphatic salt between the layers of the clay compound to form an ionic complex. When preparing the organically modified clay (B), it is preferable to select conditions for a clay compound concentration of 0.1 to 30% by weight and a treatment temperature of 0 to 150°C. The aliphatic salt may be prepared as a solid and dissolved in a solvent for use, or a solution of the aliphatic salt may be prepared by chemical reaction in a solvent and used as is. Regarding the reaction ratio of the clay compound to the aliphatic salt, it is preferable to use an equivalent or greater amount of aliphatic salt relative to the exchangeable cations of the clay compound. Examples of suitable treatment solvents include aliphatic hydrocarbons such as pentane, hexane, and heptane; aromatic hydrocarbons such as benzene and toluene; alcohols such as ethyl alcohol and methyl alcohol; ethers such as ethyl ether and n-butyl ether; halogenated hydrocarbons such as methylene chloride and chloroform; acetone; 1,4-dioxane; tetrahydrofuran; and water. Preferably, alcohols or water are used alone or as one of the solvent components.

[0033] Furthermore, there is no limitation on the particle size of the organo-modified clay (B) constituting the catalyst for polyethylene production, but a particle size of 1 to 100 μm is preferred because this results in excellent efficiency during catalyst preparation and polyethylene production. The method for adjusting the particle size is also not limited; large particles may be pulverized to an appropriate particle size, small particles may be granulated to an appropriate particle size, or pulverization and granulation may be combined. Furthermore, particle size adjustment may be performed on the clay before organo-modification or on the organo-modified clay after modification.

[0034] As the organoaluminum compound (C), any compound that falls into the category of organoaluminum compounds can be used, including, for example, alkylaluminums such as trimethylaluminum, triethylaluminum, and triisobutylaluminum.

[0035] The transition metal compounds (A-1) and (A-2) (hereinafter, the transition metal compounds (A-1) and (A-2) are sometimes collectively referred to as component (A)), the organically modified clay (B) (hereinafter, sometimes referred to as component (B)), and the organoaluminum compound (C) (hereinafter, sometimes referred to as component (C)) that constitute the catalyst for polyethylene production are not subject to any particular restrictions as long as they can be used as a catalyst for polyethylene production. In particular, in order to obtain a catalyst for polyethylene production that is capable of efficiently producing an ethylene-based polymer, the molar ratio per metal atom of component (A) to component (C) is preferably component (A):component (C) = 100:1 to 1:100,000, and particularly preferably 1:1 to 1:10,000. The weight ratio of component (A) to component (B) is preferably component (A):component (B)=10:1 to 1:10000, and more preferably 3:1 to 1:1000.

[0036] The catalyst for polyethylene production may be prepared by any method that allows for the preparation of a catalyst for polyethylene production containing the component (A), the component (B), and the component (C). For example, components (A), (B), and (C) may be mixed in a solvent that is inert to them, or using the monomer to be polymerized as the solvent. There are no limitations on the order in which these components are reacted, nor on the temperature or time at which this treatment is carried out. It is also possible to prepare a catalyst for polyethylene production using two or more types of each of the component (A), component (B), and component (C).

[0037] The polymerization conditions, such as polymerization temperature, polymerization time, and polymerization pressure, used in producing the ethylene polymer can be selected arbitrarily. Among these, it is preferable to carry out the polymerization at a temperature of 0 to 100°C, for a polymerization time of 10 seconds to 20 hours, and at a polymerization pressure in the range of normal pressure to 100 MPa. It is also possible to adjust the molecular weight using hydrogen or the like during the polymerization. The polymerization can be carried out by any of batch, semi-continuous, and continuous methods, and can also be carried out in two or more stages by changing the polymerization conditions. The polymer particles obtained after the polymerization are separated and recovered from the polymerization solvent by a conventionally known method, and then dried.

[0038] Among these, two-stage polymerization is preferred because different polymerization conditions for component (A) and component (B) enable efficient production of the ethylene polymer of the present invention having different molecular weight distributions for component (A) and component (B). Two-stage batch polymerization is particularly preferred because it allows easier control of the polymerization conditions. In this case, polymerization termination mechanisms in polymerization, particularly coordination polymerization, include a β-hydrogen elimination reaction in which hydrogen bonded to the carbon at the β-position from the growing end is eliminated to produce an alkene and a metal hydride, and a chain transfer reaction to the monomer, hydrogen, and organoaluminum compound in the polymerization system. Lower monomer pressure conditions enable lower molecular weight and broader molecular weight distribution, so it is preferred to relatively lower the monomer pressure during polymerization of component (B). For example, by setting the ethylene pressure during polymerization of component (B) to 0.35 MPa or less, particularly 0.25 MPa or less, component (B) having Mw = 10,000 to 500,000 and Mw / Mn exceeding 5.0 but not exceeding 10.0 can be efficiently produced. The ethylene pressure during polymerization of component (A) can be selected to exceed 0.35 MPa if it is possible to produce component (B) having an Mw of 900,000 to 5,000,000 and an Mw / Mn of 2.0 to 5.0, and to polymerize an ethylene polymer more efficiently, it is preferable to set each ethylene pressure to 0.35 MPa or less, or even 0.25 MPa or less. Furthermore, when polymerization is carried out by the co-supported catalyst method, polymerization can be easily carried out by setting the ethylene pressure to 0.35 MPa or less, or even 0.25 MPa or less.

[0039] The form of the ethylene polymer of the present invention is not limited, and for example, the polymer obtained by the above-mentioned production method may be used as it is, or may be formed into pellets using an extruder, etc. Furthermore, additives such as antioxidants may be added to the resin modifier.

[0040] The ethylene polymer of the present invention has an excellent balance between mechanical properties and processability, and can be used not only as sheets and films but also as various structural materials. [Effects of the Invention]

[0041] The ethylene polymer contains a specific ultra-high molecular weight component and a low molecular weight component having a broader molecular weight distribution, and thus provides an ethylene polymer having improved tensile properties of a molded product without impairing molding processability. This enables the molded product to be made thinner by improving the tensile properties, while still using conventional molding methods. [Example]

[0042] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples as long as they do not depart from the gist of the invention.

[0043] Unless otherwise specified, the reagents used were commercially available products or those synthesized according to known methods.

[0044] The organically modified clay was pulverized using a jet mill (Seishin Enterprise Co., Ltd., product name CO-JET SYSTEM α MARK III), and the particle size after pulverization was measured using a Microtrac particle size distribution analyzer (Nikkiso Co., Ltd., product name MT3000) using ethanol as a dispersant.

[0045] The production of the catalyst for polyethylene production, the preparation of the ethylene polymer, and the solvent purification were all carried out under an inert gas atmosphere. The hexane solution (20 wt%) of triisobutylaluminum manufactured by Tosoh Finechem Co., Ltd. was used.

[0046] Furthermore, various physical properties of the ethylene polymer were measured by the following methods.

[0047] ~Measurement of intrinsic viscosity ([η])~ The measurement was carried out using an Ubbelohde viscometer at 135° C. with decahydronaphthalene as a solvent and an ethylene polymer concentration of 0.005 wt %.

[0048] ~Measurement of Mw and Mn~ Measurements were performed using an ultra-high temperature gel permeation chromatography (Senshu Scientific, SSC-7110) equipped with a column (Tosoh, TSKgel GMHHR-H(S)HT) using 1-chloronaphthalene as the eluent, at a column temperature of 210°C, a sample concentration of 0.5 mg / ml, and an injection volume of 0.2 ml. The molecular weight calibration curve was calibrated using standard polystyrene samples, and Mw and Mn were converted to linear polyethylene.

[0049] ~MFR~ The melt flow rate was measured at a temperature of 190°C under a load of 2.16 kg in accordance with JIS K 6922-2:1997.

[0050] ~HLMFR~ The melt flow rate was measured at a temperature of 190°C under a load of 21.6 kg in accordance with JIS K 6922-2:1997.

[0051] ~Measurement of thermal melting~ Using a differential scanning calorimeter (DSC) (DSC6220, manufactured by SII NanoTechnology Inc.), the sample was heated from 0°C to 230°C at a heating rate of 10°C / min (first scan), and the crystalline melting peak (Tm1) and heat of fusion (ΔH1) of the first scan were measured. After leaving the sample for 5 minutes, the sample was cooled to -20°C at a heating rate of 10°C / min, and after leaving the sample for 5 minutes, the sample was again heated from -20°C to 230°C at a heating rate of 10°C / min (second scan), and the crystalline melting peak (Tm2) and heat of fusion (ΔH2) of the second scan were measured. The sample weight of the ethylene polymer was 6 mg.

[0052] ~Tensile properties~ The nominal breaking strain of a dumbbell piece (ATMS-1822) was measured at 25°C and 50 mm / min using an RTG-1210 (trade name, manufactured by Orientec Co., Ltd.).

[0053] ~Mixability evaluation~ The kneadability was evaluated by the number of particles with a diameter of 0.05 mm or more observed on the surface per 10.0 cm of a strand obtained by HLMFR measurement.

[0054] Manufacturing Example 1 (1) Manufacturing of organically modified clay A 1-liter flask was charged with 300 ml of industrial alcohol (Equinene F-3, manufactured by Japan Alcohol Sales Co., Ltd.) and 300 ml of distilled water. 15.0 g of concentrated hydrochloric acid and 42.4 g (120 mmol) of dimethylbehenylamine (Lipomin DM22D, manufactured by Lion Specialty Chemicals Co., Ltd.) were added, and the mixture was heated to 45°C to disperse 100 g of synthetic hectorite (Laponite RDS, manufactured by BYK Additives Limited). The mixture was then heated to 60°C and stirred for 1 hour while maintaining the temperature. The resulting slurry was filtered, washed twice with 600 ml of hot water at 60°C, and dried in a dryer at 85°C for 12 hours to obtain 125 g of organically modified clay. This organically modified clay was then jet-milled to a median diameter of 10 μm.

[0055] (2) Production of suspensions of catalysts for polyethylene production After replacing the air in a 5-liter flask equipped with a thermometer and reflux condenser with nitrogen, 450 g of the organically modified clay obtained in (1) and 1,000 ml of hexane were added, followed by the addition of 11.30 g of diphenylmethylene(cyclopentadienyl)(2-dimethylamino-9-fluorenyl)dichloride and 1,280 ml of a 20 wt % hexane solution of triisobutylaluminum, and stirring for 3 hours at 60°C. After cooling to 45°C, the supernatant was removed and washed twice with 3,735 ml of hexane, and 3,735 ml of hexane was added to obtain a suspension of a catalyst for polyethylene production (solids content: 12.5 wt %).

[0056] Manufacturing Example 2 (1) Manufacturing of organically modified clay The same procedure as in Production Example 1 was carried out.

[0057] (2) Production of suspensions of catalysts for polyethylene production A 5-liter flask equipped with a thermometer and reflux condenser was purged with nitrogen, and then 450 g of the organically modified clay obtained in (1) and 1,000 ml of hexane were added, followed by 12.87 g of diphenylmethylene(cyclopentadienyl)(2-diethylamino-9-fluorenyl)hafnium dichloride and 1,280 ml of a 20 wt % hexane solution of triisobutylaluminum, and the mixture was stirred for 3 hours at 60°C. After cooling to 45°C, the supernatant was removed and washed twice with 3,735 ml of hexane, and 3,735 ml of hexane was added to obtain a suspension of a catalyst for polyethylene production (solids content: 12.5 wt %).

[0058] Manufacturing Example 3 (1) Manufacturing of organically modified clay A 1-liter flask was charged with 300 ml of industrial alcohol (Equinene F-3, manufactured by Japan Alcohol Sales Co., Ltd.) and 300 ml of distilled water. 15.0 g of concentrated hydrochloric acid and 63.7 g (120 mmol) of dioleylmethylamine ((C18H35)2(CH3)N, manufactured by Lion Specialty Chemicals Co., Ltd., product name Lipomin MO) were added, heated to 45°C, and 100 g of synthetic hectorite (Laponite RD, manufactured by BYK) was dispersed in the flask. The mixture was then heated to 60°C and stirred for 1 hour while maintaining the temperature. The resulting slurry was filtered, washed twice with 600 ml of water at 60°C, and dried in a dryer at 85°C for 12 hours to obtain 130 g of organically modified clay. This organically modified clay was then jet-milled to a median diameter of 15 μm.

[0059] (2) Production of suspensions of catalysts for polyethylene production After replacing the air in a 300 ml flask equipped with a thermometer and reflux condenser with nitrogen, 25.0 g of the organically modified clay obtained in (1) and 108 ml of hexane were added, followed by the addition of 0.392 g (1 mmol) of bis(indenyl)zirconium dichloride and 142 ml of 20% triisobutylaluminum, and stirring for 3 hours at 60°C. After cooling to room temperature, the supernatant was removed and washed twice with 220 ml of hexane, and then 220 ml of hexane was added to obtain a catalyst suspension (solid weight content: 12.0 wt%).

[0060] Example 1 A bimodal polyethylene ethylene polymer (III-1) was prepared by two-stage polymerization in which component (III-1) was polymerized followed by component (III-1) as follows: The ethylene polymer (III-1) had an HLMFR of 2.4 g / 10 min and an [η] of 4.6.

[0061] Preparation of component (A-1) 1m 3 A reactor was charged with 600 L of hexane, 1.8 kg of a 20 wt % triisobutylaluminum hexane solution, and 1.62 kg (equivalent to 196 g of solids) of the suspension of the polyethylene production catalyst obtained in Production Example 1. The temperature was then raised to 60°C. Ethylene was continuously supplied to maintain the ethylene pressure at 0.24 MPa, and hydrogen was intermittently added to maintain the hydrogen concentration in the gas phase of the reactor at 430 ppm, thereby carrying out slurry polymerization. During the polymerization, 15 kg of ethylene was consumed in terms of polyethylene, and the polymerization time was 38 minutes. The [η] of component (A-1), calculated in relation to the hydrogen concentration in the system during the polymerization reaction, was 10.1.

[0062] Preparation of component (B-1) and ethylene polymer (C-1) After polymerization of component (A-1), ethylene was continuously supplied to maintain the ethylene pressure at 0.24 MPa at 60°C. Hydrogen was intermittently added to maintain the hydrogen concentration in the gas phase of the reactor at 34,200 ppm. Slurry polymerization was then performed to polymerize component (B-1), producing ethylene polymer (H-1), an ethylene homopolymer. 61 kg of ethylene was consumed in polyethylene equivalent, and the polymerization time was 190 minutes. The [η] of component (B-1), calculated in relation to the hydrogen concentration in the system during the polymerization reaction, was 2.0.

[0063] Using peak separation software, the peaks of the ethylene polymer (III-1) were separated according to a Gaussian distribution, and the calculated Mw of component (III-1) was 1 million, with an Mw / Mn of 3.5. Similarly, the Mw of component (III-1) was calculated to be 100,000, with an Mw / Mn of 6.1. Furthermore, component (III-1) / component (III-1) was 20 / 80 (wt%). DSC measurement revealed a single peak at Tm1 = 136.6°C. The measurement results are shown in Table 1.

[0064] The obtained polyethylene polymer (H-1) was melt-kneaded and pelletized using a twin-screw extruder (manufactured by Toyo Seiki Seisakusho, trade name: Labo Plastomill parallel twin-screw extruder 2D25S) at 160°C, 30 rpm, and a discharge rate of 0.8 kg / h. At this time, the discharge of strands was stable, and no stick-slip phenomenon was observed, confirming that the polymer had excellent fluidity and processability.

[0065] Example 2 A bimodal polyethylene ethylene polymer (H-2) was prepared by two-stage polymerization in which component (A-2) was polymerized followed by component (B-2) as follows: The ethylene polymer (H-2) had an HLMFR of 1.50 g / 10 min and an [η] of 7.3.

[0066] Preparation of component (A-2) 1m 3A reactor was charged with 600 L of hexane, 1.8 kg of a hexane solution of 20 wt % triisobutylaluminum, and 1.87 kg (equivalent to 230 g of solids) of the suspension of the polyethylene production catalyst obtained in Production Example 2. The temperature was then raised to 60°C. Ethylene was continuously supplied to maintain the ethylene pressure at 0.24 MPa, and hydrogen was intermittently added to maintain the hydrogen concentration in the gas phase of the reactor at 390 ppm, thereby conducting slurry polymerization. During the polymerization, 13 kg of ethylene was consumed in terms of polyethylene, and the polymerization time was 40 minutes. The [η] of component (A-3), calculated in relation to the hydrogen concentration in the system during the polymerization reaction, was 21.0.

[0067] Preparation of component (B-2) and ethylene polymer (H-2) After polymerization of component (A-2), ethylene was continuously supplied to maintain the ethylene pressure at 0.24 MPa at 60°C. Hydrogen was intermittently added to maintain the hydrogen concentration in the gas phase of the reactor at 65,600 ppm. Slurry polymerization was then performed to polymerize component (B-2), producing ethylene polymer (H-2), an ethylene homopolymer. 47 kg of ethylene was consumed in polyethylene equivalent, and the polymerization time was 300 minutes. The [η] of component (B-2), calculated in relation to the hydrogen concentration in the system during the polymerization reaction, was 2.0.

[0068] Using peak separation software, the peaks of the ethylene polymer (H-2) were separated according to a Gaussian distribution, and the calculated Mw of component (A-2) was 3 million, with an Mw / Mn of 3.3. Similarly, the Mw of component (B-2) was calculated to be 100,000, with an Mw / Mn of 6.1. Similarly, the ratio of component (A-2) / component (B-2) was calculated to be 20 / 80 (wt%). DSC measurement showed a single peak at Tm1 = 137.1°C. The measurement results are shown in Table 1.

[0069] The obtained polyethylene polymer (H-2) was melt-kneaded and pelletized using a twin-screw extruder (manufactured by Toyo Seiki Seisakusho, trade name: Labo Plastomill parallel twin-screw extruder 2D25S) at 160°C, 30 rpm, and a discharge rate of 0.8 kg / h. At this time, the discharge of strands was stable, and no stick-slip phenomenon was observed, confirming that the polymer had excellent fluidity and processability.

[0070] Comparative Example 1 A bimodal polyethylene ethylene polymer (III-3) was prepared by two-stage polymerization in which component (III-3) was polymerized followed by component (III-3) as follows: The ethylene polymer (III-3) had an HLMFR of 2.74 g / 10 min and an [η] of 3.2.

[0071] Preparation of component (A-3) A 10-liter autoclave was charged with 6 liters of hexane, 5.5 ml of a 20 wt % triisobutylaluminum hexane solution, and 2.50 g (equivalent to 310 mg of solids) of the suspension of the polyethylene production catalyst obtained in Production Example 1. The temperature was then raised to 60°C. Ethylene was continuously supplied to maintain the ethylene pressure at 0.87 MPa, and hydrogen was intermittently added to maintain a hydrogen concentration of 1000 ppm in the gas phase of the autoclave. Slurry polymerization was carried out. During the polymerization, 200 g of ethylene was consumed in polyethylene equivalent terms, and the polymerization time was 1 hour. The [η] of component (A-3), calculated in relation to the hydrogen concentration in the system during the polymerization reaction, was 10.1.

[0072] Preparation of component (B-3) and ethylene polymer (C-3) After polymerization of component (A-3), ethylene was continuously supplied to maintain the ethylene pressure at 0.87 MPa at 60°C. Hydrogen was intermittently added to maintain the hydrogen concentration in the gas phase of the autoclave at 30,000 ppm. Slurry polymerization was then performed to polymerize component (B-3), producing ethylene polymer (C-3), an ethylene homopolymer. Ethylene was consumed in an amount equivalent to 800 g of polyethylene, and the polymerization time was 4.5 hours. The [η] of component (B-3), calculated in relation to the hydrogen concentration in the system during the polymerization reaction, was 2.0.

[0073] Using peak separation software, the peaks of the ethylene polymer (III-3) were separated according to a Gaussian distribution, and the calculated Mw of component (III-3) was 1 million, with an Mw / Mn of 3.2. Similarly, the Mw of component (III-3) was calculated to be 100,000, with an Mw / Mn of 4.1. Furthermore, component (III-3) / component (III-3) ratio was 20 / 80 (wt%), and DSC measurement showed a single peak at Tm1 = 138.5°C. The measurement results are shown in Table 1.

[0074] The obtained polyethylene polymer (H-3) was melt-kneaded and pelletized using a twin-screw extruder (manufactured by Toyo Seiki Seisakusho, trade name: Labo Plastomill parallel twin-screw extruder 2D25S) at 160°C, 30 rpm, and a discharge rate of 0.8 kg / h. During this process, the discharge of strands was unstable, and stick-slip phenomenon occurred, resulting in poor fluidity and processability.

[0075] Comparative Example 2 Bimodal polyethylene ethylene polymer (III-4) was prepared by two-stage polymerization in which component (III-4) was polymerized in succession after component (III-4) was polymerized as follows: The ethylene polymer (III-4) had an HLMFR of 0.01 g / 10 min, but was meltable, and its [η] was 16.9.

[0076] Preparation of component (A-4) A 10-liter autoclave was charged with 6.0 liters of hexane, 5.5 ml of a 20 wt % hexane solution of triisobutylaluminum, and 2.50 g (corresponding to 310 mg of solids) of the suspension of the catalyst for polyethylene production obtained in Production Example 1, and the temperature was raised to 60°C. Ethylene was continuously supplied so that the ethylene pressure could be maintained at 0.80 MPa, and hydrogen was added intermittently so that the hydrogen concentration in the gas phase of the autoclave became 300 ppm, thereby carrying out slurry polymerization. 200 g of ethylene, calculated as polyethylene, was consumed in the reaction, and the [η] of component (A-4) calculated from the relationship with the hydrogen concentration in the system during the polymerization reaction was 22.

[0077] Preparation of component (B-4) and ethylene polymer (C-4) After polymerization of component (A-4), ethylene was continuously supplied to maintain the ethylene pressure at 0.80 MPa at 60°C, and hydrogen was intermittently added to maintain the hydrogen concentration in the gas phase of the autoclave at 30,000 ppm. Slurry polymerization was then carried out to polymerize component (B-4), producing ethylene polymer (C-4), an ethylene homopolymer. 800 g of ethylene was consumed in terms of polyethylene, and the [η] of component (B-4), calculated in relation to the hydrogen concentration in the system during the polymerization reaction, was 2.

[0078] Using peak separation software, the peaks of the ethylene polymer (III-4) were separated according to a Gaussian distribution, and the calculated Mw of component (III-4) was 3 million, with an Mw / Mn of 2.8. Similarly, the Mw of component (III-4) was calculated to be 100,000, with an Mw / Mn of 4.5. Furthermore, component (III-4) / component (III-4) ratio was 30 / 70 (wt%), and DSC measurement showed a single peak at Tm1 = 138.9°C. The measurement results are shown in Table 1.

[0079] The obtained polyethylene polymer (H-3) was melt-kneaded and pelletized using a twin-screw extruder (manufactured by Toyo Seiki Seisakusho, trade name: Labo Plastomill parallel twin-screw extruder 2D25S) at 160°C, 30 rpm, and a discharge rate of 0.8 kg / h. During this process, the discharge of strands was unstable, and stick-slip phenomenon occurred, resulting in poor fluidity and processability.

[0080] [Table 1] [Industrial Applicability]

[0081] The ethylene polymer of the present invention contains a specific ultra-high molecular weight component and a low molecular weight component having a broader molecular weight distribution, and therefore can improve the tensile properties of a molded article without impairing molding processability, and can reduce the wall thickness of a molded article by improving the tensile properties without using a conventional molding method.

Claims

1. An ethylene polymer characterized by satisfying the following properties (1) to (3): (1): The melt flow rate (HLMFR) conforming to JIS K 6922-2:1997 at a temperature of 190°C and a load of 21.6 kg is 0.01 to 50 g / 10 min. (2) The elution curve measured by gel permeation chromatography (GPC) is bimodal, and when the elution curve is expressed as a differential molecular weight distribution (x-axis: Log [M], y-axis: differential distribution value), and the peak is divided into two normal distributions according to the following formula (i), the following (2-1) to (2-3) are satisfied: y=a×(1 / (2π(σ ２ )) （１／２） ) x ２ ) / (2(s ２ ))) formula (i) (Here, a is the peak intensity, σ is the standard deviation, x is the variable, and μ is x at the peak top.) (2-1): The weight average molecular weight, calculated as linear polyethylene, based on the peak on the high molecular weight side is 900,000 to 5,000,000, and the molecular weight distribution, expressed as weight average molecular weight / number average molecular weight, is 2.0 to 5.

0. (2-2): The weight average molecular weight, calculated as linear polyethylene, based on the peak on the low molecular weight side is 10,000 to 500,000, and the molecular weight distribution is more than 5.0 and 10.0 or less. (2-3): The weight ratio of the high molecular weight peak to the weight ratio of the low molecular weight peak (wt %) is greater than 5 / 95 and smaller than 80 / 20. (3) The crystal melting peak (Tm1) in the first scan measured using a differential scanning calorimeter (DSC) by raising the temperature from 0°C to 230°C at a heating rate of 10°C / min is single-peaked.

2. 2. The ethylene polymer according to claim 1, which further satisfies the following property (4): (4) The molecular weight distribution (Mw / Mn) of the polyethylene-equivalent polymer measured by GPC is 4.0 or more and less than 50.

3. 3. The ethylene polymer according to claim 1, further satisfying the following property (5): (5) Using DSC, after the first scan, the sample is left for 5 minutes, cooled to -20°C at a rate of 10°C / min, left for 5 minutes, and then heated again from -20°C to 230°C at a rate of 10°C / min (second scan). The melting point (Tm2) of the second scan is measured, and the difference between Tm1 and Tm2 (ΔTm=Tm1-Tm2) is -1°C or more and less than 15°C, and the ratio (ΔH2 / ΔH1) of the heat of fusion of the first scan (ΔH1) to the heat of fusion of the second scan (ΔH2) is 0.94 or more.

4. 3. The ethylene-based polymer according to claim 1, which is an ethylene homopolymer.

5. A method for producing an ethylene polymer, comprising: polymerizing at least ethylene in the presence of a metallocene catalyst for ethylene production to produce an ethylene polymer having a bimodal molecular weight; and controlling the ethylene pressure to 0.35 MPa or less when producing at least a low-molecular-weight ethylene polymer.

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