KR101886993B1 - Ethylene based polymer and molded article - Google Patents

Abstract

Provided are an ethylene-based polymer which can give excellent oxidation resistance and shrink resistance during molding (for example, film formation such as formation of a thin film), and a molded body including the ethylene-based polymer. The ethylene-based polymer of the present invention has 18% or more of the ratio (ΔH_b/ΔH_2×100) of melting calories (ΔH_b) of a region higher than a melting point (Tm_2) with respect to melting calories (ΔH_2) of a second heating process in a differential scanning calorimeter (DSC) curved line of the second heating process which has a limiting viscosity (η) of 11 to 28 and is obtained by measuring conditions (1) to (3) using a DSC, wherein the measuring condition (1) is increasing the temperature to 180°C at the temperature increasing speed of 10°C/min after maintaining the temperature at 50°C for one minute, the measuring condition (2) is decreasing the temperature to 50°C at a temperature decreasing speed of 10°C/min after maintaining the temperature at 180°C for five minutes, and the measuring condition (3) is increasing the temperature to 180°C at a temperature increasing speed of 10°C/min after keeping warm at 50°C for five minutes.

Description

TECHNICAL FIELD [0001] The present invention relates to an ethylene polymer,

The present invention relates to an ethylene polymer and a molded article.

Background Art [0002] Polyethylene is conventionally used for various purposes such as a film, a sheet, a microporous membrane, a fiber, and a molded article. Particularly, polyethylene having a high molecular weight is used as a raw material for a microporous membrane constituting a separator for a secondary battery represented by a lead storage battery or a lithium ion battery. Examples of characteristics required for the microporous membrane for a lead-acid battery include separability between the positive electrode and the negative electrode, impregnation and diffusion properties of the electrolyte, low electric resistance, oxidation resistance and mechanical strength. Particularly in recent years, miniaturization, high capacity and high output of lead acid batteries have been studied by the spread of idling stop cars, and further thinning of microporous membranes has been demanded (see, for example, Patent Document 1). However, due to thinning of the microporous membrane, the oxidation resistance of the membrane is lowered, and the lifetime of the battery is lowered. As a method for increasing the oxidation resistance, various methods have conventionally been proposed (see, for example, Patent Documents 2 and 3).

Japanese Patent Publication No. 2013-541162 Japanese Patent No. 4583551 Japanese Patent No. 5830187

In order to make the separator for the secondary battery thinner, it is preferable to use the microporous membrane alone. On the other hand, as a general method for increasing the oxidation resistance of a film such as a microporous membrane, there can be mentioned a method of increasing the molecular weight of polyethylene used as a raw material. However, polyethylene having a high molecular weight has a high viscosity and a poor dispersibility, and may cause shrinkage, unevenness in thickness, and warpage of the film, and may cause oxidation due to contact with the electrode or the like, Is lowered. For this reason, a method of blending polyethylene having a high molecular weight and polyethylene having a low molecular weight may be considered. However, the molecular weight of the polyethylene in the entire microporous membrane is lowered, so that the strength of the microporous membrane can not be increased sufficiently and oxidation resistance is insufficient There is a problem.

Therefore, the present invention relates to an ethylene polymer capable of imparting excellent oxidation resistance and shrinkage resistance during molding (for example, film formation such as thin film molding), and a molded article (for example, a microporous film) containing the ethylene polymer The purpose is to provide.

DISCLOSURE OF THE INVENTION The inventors of the present invention have made intensive studies to solve the problems of the prior art described above and have found that the intrinsic viscosity is within a predetermined range and that a specific ratio of the heat of fusion obtained by a specific measurement condition of a differential scanning calorimeter (DSC) And that the ethylene polymer having a lower limit value or more can solve the above-described problems, thereby completing the present invention.

That is, the present invention is as follows.

[One]

The intrinsic viscosity (?) Is 11 or more and 28 or less,

The melting point Tm (Tm) of the _second heat-up process (ΔH ₂ ) in the DSC curve of the second temperature-rising process obtained by the measurement conditions of the following (1) to (3) using the differential scanning calorimeter (DSC) ₂ ) a ratio (ΔH _b / ΔH ₂ × 100) of the heat of fusion (ΔH _b ) in a higher region is 18% or more.

(DSC measurement conditions)

(1) After being maintained at 50 占 폚 for 1 minute, the temperature was raised to 180 占 폚 at a heating rate of 10 占 폚 / min.

(2) After being maintained at 180 DEG C for 5 minutes, the temperature was decreased to 50 DEG C at a rate of 10 DEG C / min.

(3) After keeping the temperature at 50 캜 for 5 minutes, the temperature was raised to 180 캜 at a temperature raising rate of 10 캜 / min.

[2]

The ethylene polymer according to the above item [1], wherein the half-width of the exothermic peak in the temperature-decreasing step of the measurement conditions using the DSC is not less than 3.0 and not more than 6.0.

[3]

The ethylene polymer according to the above [1] or [2], wherein the density of the press sheet obtained by the processing conditions of the following (1) to (3) is 910 kg / m3 or more and 940 kg / m3 or less.

(Processing conditions)

(1) Preheating for 900 seconds at 200 ° C and 0.1 MPa.

(2) Pressurization at 200 DEG C and 15 MPa for 300 seconds.

(3) Cooling for 600 seconds at 25 캜 and 10 MPa.

[4]

The ethylene polymer according to any one of items [1] to [3], wherein the titanium content is 3 ppm or less on a weight basis with respect to the total of the ethylene polymer.

[5]

The ethylene polymer as described in any one of the items [1] to [4], wherein the chlorine content is 10 ppm or less on a weight basis with respect to the total amount of the ethylene polymer.

[6]

A molded article comprising the ethylene polymer according to any one of the items [1] to [5].

[7]

The molded article according to the above item [6], which is a microporous membrane.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an ethylene polymer capable of imparting excellent oxidation resistance and shrinkage resistance at the time of molding (for example, film forming or the like), and a molded article comprising the ethylene polymer (for example, ).

Further, the ethylene polymer of the present invention can impart excellent oxidation resistance and shrinkage resistance when formed (for example, in a thin film), and therefore can be suitably used as a microporous film constituting a separator for a secondary battery have. More specifically, the microporous membrane obtained by using the ethylene polymer of the present invention can suppress the shrinkage of the membrane after the oxidation resistance test, so that the life of the battery can be further extended.

Hereinafter, a mode for carrying out the present invention (hereinafter referred to as " present embodiment ") will be described in detail. The present invention is not limited to the following description, and various modifications may be made within the scope of the present invention.

[Ethylene polymer]

The ethylene polymer of the present embodiment has an intrinsic viscosity (η) of 11 or more and 28 or less and a DSC of the second heating step obtained by the measurement conditions (1) to (3) using a differential scanning calorimeter (DSC) in the curve, it is expressed by the ratio (ΔH _b / ΔH ₂ × 100 of the melting heat of fusion (ΔH _b) a high region than (Tm ₂₎ with respect to the temperature raising heat of fusion (ΔH ₂₎ of the process for the second time. referred to as " Specific ratio of heat of fusion ") is 18% or more. The ethylene polymer of the present embodiment has an intrinsic viscosity within the above range and a specific ratio of the heat of fusion is a specific lower limit value or more so that the ethylene polymer exhibits excellent oxidation resistance and shrinkage resistance Can be given. When the intrinsic viscosity of the ethylene polymer of the present embodiment is within the above range and the specific ratio of the heat of fusion is set to a specific lower limit value or more, uniformity of the film during film formation is high, And the shrinkage unevenness tends to be small. As a result, when the film is formed using the ethylene polymer of the present embodiment, the warpage of the film is small, and there is a tendency that the winding wrinkles and the winding deviation are less likely to occur, and the quality of the film is improved.

(DSC measurement conditions)

(1) After being maintained at 50 占 폚 for 1 minute, the temperature was raised to 180 占 폚 at a heating rate of 10 占 폚 / min.

(2) After being maintained at 180 DEG C for 5 minutes, the temperature was decreased to 50 DEG C at a rate of 10 DEG C / min.

(3) After keeping the temperature at 50 캜 for 5 minutes, the temperature was raised to 180 캜 at a temperature raising rate of 10 캜 / min.

Hereinafter, the requirements of the ethylene polymer of the present embodiment will be described.

(Intrinsic viscosity)

The intrinsic viscosity (?) Of the ethylene polymer of the present embodiment is 11 or more and 28 or less, preferably 13 or more and 26 or less, and more preferably 15 or more and 25 or less. When the intrinsic viscosity (eta) is 11 or more, the minimum oxidation resistance can be imparted at the time of molding (for example, film formation by thin film forming). In addition, when formed into a thin film, good film strength can be imparted. On the other hand, if the intrinsic viscosity (eta) is 28 or less, shrinkage of the film after molding is suppressed.

The intrinsic viscosity (?) Of the ethylene polymer of the present embodiment can be controlled by appropriately adjusting the polymerization conditions and the like by using an olefin polymerization catalyst to be described later. Concretely, the intrinsic viscosity (?) Can be controlled by introducing hydrogen into the polymerization system or by changing the polymerization temperature.

The intrinsic viscosity (?) Of the ethylene polymer of the present embodiment can be specifically determined, for example, by preparing a solution obtained by dissolving an ethylene polymer in decalin at a different concentration, measuring the solution viscosity at 135 ° C of the solution , And the reduced viscosity calculated from the measured solution viscosity can be extrapolated to concentration 0. More specifically, the method described in the embodiment is used.

(Specific ratio of heat of fusion)

A specific ratio of the heat of fusion is not less than 18% (for example, not less than 18% and not more than 26%), preferably not less than 19% and not more than 25%, and more preferably not less than 20% and not more than 25%. When the specific heat of fusion is 18% or more, the amount of the polyethylene component having a large crystal size and thickness in the ethylene-based polymer is increased, and excellent oxidation resistance can be imparted when molding (for example, film formation). On the other hand, when the specific heat of fusion is 26% or less, an ethylene polymer having an even better solubility in an organic solvent (for example, liquid paraffin) can be obtained and molded (for example, It is possible to give an excellent appearance. Further, a specific ratio of the heat of fusion can be measured by the method described in the following Examples.

The specific ratio of the heat of fusion of the ethylene polymer of the present embodiment can be controlled by adjusting the viscosity average molecular weight, increasing the size of the active species of the olefin polymerization catalyst, or adding a very small amount of alcohol component to the polymerization system . As a specific method for adding a very small amount of an alcohol component to the polymerization system, for example, there is a method of adding n-butanol at an addition rate of 1 ppm / hr to a polymerization rate (polymerization rate) of 10 kg / hr in a polymerization system . Addition of a very small amount of an alcohol component to the polymerization system can inactivate an active point that generates a slight low molecular weight component that inhibits the crystal growth of the ethylene polymer and can increase the ratio of? H _b . On the other hand, by controlling the viscosity average molecular weight or by controlling the size of the active species of the olefin polymerization catalyst, the ratio of? H _b can be lowered.

(Half value width of exothermic peak of DSC)

The half width of the exothermic peak in the temperature decreasing step of the DSC measurement conditions is preferably from 3.0 to 6.0, more preferably from 3.0 to 5.5, still more preferably from 3.0 to 5.0, Is not less than 3.0 and not more than 4.3. When the half value width of the exothermic peak is 3.0 or more, it can be relatively easily formed (for example, film formation) like general polyethylene. On the other hand, when the half value width of the exothermic peak is 6.0 or less, the uniformity of the film becomes better at the time of film formation (for example, thin film formation), and thickness irregularity is further suppressed. The half width of the exothermic peak can be measured by the method described in the following Examples.

The half value width of the exothermic peak can be adjusted by adjusting the molecular weight distribution, increasing the productivity per titanium contained in the unit catalyst, or washing the ethylene polymer obtained after the polymerization reaction with methanol at a high temperature (for example, 70 DEG C or higher) Controllable. Particularly, when the ethylene polymer is washed with high-temperature methanol, impurities which are the starting point of crystallization can be removed, and the crystallization of the ethylene polymer proceeds uniformly, so that the half width of the exothermic peak can be reduced. On the other hand, by adjusting the molecular weight distribution or controlling the productivity per titanium contained in the unit catalyst, the half value width of the exothermic peak can be increased.

(Press sheet density)

The pressed sheet density of the ethylene polymer obtained under the following processing conditions (1) to (3) of the present embodiment is preferably 910 kg / m 3 or more and 940 kg / m 3 or less, and more preferably 915 kg / Or more and 935 kg / m3 or less, and more preferably 920 kg / m3 or more and 935 kg / m3 or less. When the density of the press sheet is 910 kg / m < 3 > or more, the crystallinity of the polyethylene is sufficiently high, and tends to give better oxidation resistance at the time of molding (for example, film formation). On the other hand, if the density of the press sheet is 940 kg / m < 3 > or less, the viscosity average molecular weight of the polyethylene is sufficiently high and tends to be able to impart a higher strength (e.g., film strength) .

(1) Preheating for 900 seconds at 200 ° C and 0.1 MPa.

(2) Pressurization at 200 DEG C and 15 MPa for 300 seconds.

(3) Cooling for 600 seconds at 25 캜 and 10 MPa.

The press sheet density of the ethylene polymer of the present embodiment can be controlled by adjusting the viscosity average molecular weight or introducing branches into the polyethylene chain.

(Ethylene-based polymer)

The ethylene polymer of the present embodiment is not limited to the following, but may be an ethylene homopolymer or a copolymer of ethylene and at least one other monomer (for example, a binary or ternary copolymer). The bonding type of the copolymer may be random or block. Examples of other monomers include, but are not limited to, alpha -olefins and vinyl compounds. Examples of the alpha -olefins include, but are not limited to, propylene, 1-butene, -Olefins having 3 to 20 carbon atoms such as pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-undecene, And examples of the vinyl compound include, but are not limited to, vinylcyclohexane, styrene and derivatives thereof, and the like. As other monomers, nonconjugated polyenes such as 1,5-hexadiene and 1,7-octadiene may be used as needed. These other monomers may be used singly or in combination of two or more.

The ethylene polymer of the present embodiment may contain a residual metal component derived from an olefin polymerization catalyst in some cases, and examples of the residual metal component include titanium and chlorine.

(Titanium content in ethylene polymer)

The content of titanium contained in the ethylene polymer of the present embodiment is preferably 3 ppm or less, more preferably 1 ppm or less, and even more preferably 0.5 ppm or less, on a weight basis, based on the total weight of the ethylene polymer. When the titanium content is 3 ppm or less, the crystal size of the polyethylene can be increased, and there is a tendency that excellent oxidation resistance can be imparted at the time of molding (for example, formation of a thin film or the like). The titanium content can be measured by the method described in the following Examples.

The content of titanium contained in the ethylene polymer of the present embodiment can be reduced by using a catalyst for olefin polymerization, which will be described later, or by increasing the productivity per unit catalyst.

(Chlorine content in ethylene polymer)

The chlorine content in the ethylene polymer of the present embodiment is preferably 10 ppm or less, more preferably 5 ppm or less, and even more preferably 2 ppm or less, on a weight basis, based on the whole of the ethylene polymer. When the chlorine content is 10 ppm or less, the deterioration of the ethylene polymer in the aqueous acid solution can be suppressed, and the oxidation resistance tends to be further improved when molding (for example, forming a thin film or the like). The chlorine content can be measured by the method described in the following Examples.

The content of chlorine contained in the ethylene polymer can be reduced by using a catalyst described later or by increasing the productivity per unit catalyst.

(additive)

The ethylene polymer of the present embodiment may further contain an additive such as a neutralizing agent, an antioxidant and a light stabilizer.

The neutralizing agent is used as a chlorine catcher contained in the ethylene-based polymer or as a molding processing aid. Examples of the neutralizing agent include, but are not limited to, stearates of alkaline earth metals such as calcium, magnesium and barium. The content of the neutralizing agent is not particularly limited, but is preferably 5000 ppm or less, more preferably 4000 ppm or less, further preferably 3000 ppm or less, on a weight basis, based on the total weight of the ethylene polymer.

Examples of the antioxidant include, but are not limited to, dibutylhydroxytoluene, pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and the like. The content of the antioxidant is not particularly limited, but is preferably 5,000 ppm or less, more preferably 4,000 ppm or less, further preferably 3,000 ppm or less, on a weight basis, based on the total weight of the ethylene polymer.

Examples of the light stabilizer include, but are not limited to, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- (3- Benzotriazole based light stabilizers such as 5-chlorobenzotriazole; Bis (2,2,6,6-tetramethyl-4-piperidine) sebacate, poly {[6- (1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine -2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) Imino}], and the like can be mentioned. The content of the light stabilizer is not particularly limited, but is preferably 5000 ppm or less, more preferably 4000 ppm or less, further preferably 3000 ppm or less, on a weight basis, based on the total weight of the ethylene polymer.

In the present embodiment, in addition to each component as described above, other known components useful for the production of an ethylene polymer may be included.

The ethylene polymer of the present embodiment may be composed of one kind of ethylene polymer (for example, polyethylene) or two or more different kinds of ethylene polymers (for example, two or more kinds of polyethylene). In the case of two or more kinds, an ethylene polymer (for example, polyethylene) having a different viscosity average molecular weight may be combined. As the polyethylene constituting the ethylene polymer of the present embodiment, ultrahigh molecular weight polyethylene is preferable, and the ethylene polymer may be constituted of polyethylene with ultrahigh molecular weight polyethylene alone or with ultrahigh molecular weight polyethylene and other resins. Other resins are not particularly limited, and examples thereof include other polyethylene such as low density polyethylene and linear low density polyethylene, polypropylene, and polystyrene. These other resins may be used singly or in combination of two or more.

The form of the ethylene polymer of the present embodiment is not particularly limited, but may be, for example, a powder phase (particulate) form or a pellet form, and in these forms, good handling properties can be obtained. The ethylene polymer on the powder is obtained by applying suspension polymerization or gas phase polymerization, and the ethylene polymer in the pellet is obtained by melt-kneading the ethylene polymer obtained by polymerization and then cutting the strand.

(Production method of ethylene polymer)

Hereinafter, the method for producing the ethylene polymer of the present embodiment will be described.

(Polymerization step)

The production method of the ethylene polymer of the present embodiment includes a polymerization process in which at least an monomer containing ethylene is polymerized in the presence of a catalyst for olefin polymerization to obtain an ethylene polymer (ethylene homopolymer or ethylene copolymer) .

In the polymerization step in the present embodiment, ethylene alone may be polymerized to obtain an ethylene homopolymer, or ethylene and one or more other monomers may be copolymerized to obtain an ethylene copolymer. As the above-mentioned monomers, other monomers exemplified in the section of the ethylene-based polymer can be exemplified.

As the catalyst for olefin polymerization used in the polymerization step of the present embodiment, for example, a known Ziegler Natta catalyst or metallocene catalyst may be used.

Examples of the Ziegler Natta catalyst include the olefin polymerization catalysts described in Japanese Patent Application Laid-Open No. 10-2189334, the Ziegler Natta catalysts exemplified in Japanese Patent No. 5782558 [Production Method of Polyethylene Powder] Ziegler-Natta catalyst exemplified in Japanese Patent No. 5829257 [Polymerization Process of Polyethylene] can be exemplified. More particularly, the present invention relates to a catalyst obtained by combining a solid catalyst component produced by the reaction of an organomagnesium compound with a titanium compound and an organometallic compound component (cocatalyst), or a catalyst prepared by the reaction of an organomagnesium component with a chlorinating agent , A catalyst prepared by supporting an organomagnesium compound and a titanium compound, and the like.

Examples of the metallocene catalyst include metallocene catalysts exemplified in Japanese Patent No. 5782558 [Process for the Production of Polyethylene Powder], and Catalysts for Catalysts and Catalysts exemplified in the paragraph of the method for producing the ultra high molecular weight ethylene polymer of Japanese Patent No. 4868853 And metallocene catalysts. More specifically, as a catalyst component, there is exemplified a metallocene catalyst comprising a transition metal compound having a cyclic 侶 -binding anion ligand and an activator capable of reacting with the transition metal compound to form a complex capable of exhibiting catalytic activity . As described in Japanese Patent No. 5782558, these catalyst components may be supported on a solid component (for example, silica or the like) as a supported catalyst, and as the other catalyst component, an organoaluminum compound may be further combined do. The transition metal compound, the activator, and a liquid component used as a scavenger of an impurity or an inert compound may be combined. Examples of the liquid component include liquid components described in Japanese Patent Application Laid-Open No. 2015-180716. In addition, a hydrogenating agent may be used together with the metallocene catalyst, or a compound having hydrogenation ability may be further added. Examples of the compound having a hydrogenating agent and a hydrogenating ability include a hydrogenating agent and a hydrogenating compound described in Japanese Patent No. 5782558.

The polymerization method of the present embodiment is not particularly limited, and examples thereof include a suspension polymerization method and a vapor phase polymerization method, and a suspension polymerization method is preferable from the viewpoint of efficient heat removal of polymerization heat.

In the suspension polymerization method, an inert hydrocarbon medium can be used as the medium, and the olefin itself can be further used as a solvent.

Examples of the inert hydrocarbon medium include, but are not limited to, aliphatic hydrocarbons such as propane, butane, isobutane, pentane, isopentane, hexane, heptane, octane, decane, dodecane and kerosene; Alicyclic hydrocarbons such as cyclopentane, cyclohexane and methylcyclopentane; Aromatic hydrocarbons such as benzene, toluene and xylene; Halogenated hydrocarbons such as ethyl chloride, chlorobenzene and dichloromethane, and mixtures thereof.

The polymerization temperature in the polymerization step of the present embodiment is usually 30 占 폚 or higher and 100 占 폚 or lower, more preferably 35 占 폚 or higher and 90 占 폚 or lower, and still more preferably 40 占 폚 or higher and 80 占 폚 or lower. If the polymerization temperature is 30 DEG C or higher, industrially efficient production is possible, and if the polymerization temperature is 100 DEG C or lower, stable operation can be continuously performed. On the other hand, from the viewpoint of controlling the intrinsic viscosity of the ethylene polymer, the polymerization temperature is preferably 30 占 폚 to 85 占 폚, more preferably 40 占 폚 to 80 占 폚, and still more preferably 50 占 폚 to 80 占 폚.

The polymerization pressure in the polymerization step of the present embodiment is usually atmospheric pressure to 2 MPa, more preferably 0.1 MPa to 1.5 MPa, and further preferably 0.1 MPa to 1.0 MPa. There is a tendency that an ethylene polymer having a low residual metal amount tends to be obtained at a normal pressure or higher, and the ethylene polymer tends to be able to stably produce an ethylene polymer without generating a scale of mass when the pressure is 2 MPa or less.

In the polymerization step of the present embodiment, it is preferable to add a trace amount of alcohol component in the polymerization system. Addition of a very small amount of an alcohol component can inhibit the production of a trace amount of a low molecular weight component that inhibits the growth of crystals of the obtained polyethylene and can remove a trace amount of impurities. Therefore, in the [ethylene polymer] It is possible to control a specific ratio of the heat of fusion. Examples of the alcohol component include normal butanol, methanol, ethanol, normal propanol, isopropanol, isobutanol, tert-butanol, pentanol, hexanol, heptanol and octanol. The addition rate of the alcohol component is preferably more than 0 and not more than 1 mass ppm / hr, more preferably not more than 0.8 mass ppm / hr, more preferably not more than 0.5 mass ppm / hr or less. When the addition rate is set to 1 mass ppm / hr or less, the ethylene polymer tends to be obtained while controlling the specific ratio of the heat of fusion without deteriorating the productivity.

In addition, from the standpoint of suppressing the production of a trace amount of low molecular weight component that inhibits the growth of crystals of the resulting ethylene polymer (for example, polyethylene), as another means, the polymerization catalyst is heated in an inert hydrocarbon medium And a method of bringing the polymerization catalyst into contact with an alcohol before feeding (feeding) the polymerization catalyst to the polymerization reactor. As a method of subjecting the polymerization catalyst to heat treatment in an inert hydrocarbon medium in a nitrogen atmosphere, the treatment is preferably carried out at 80 캜 or higher, more preferably 90 캜 or higher. On the other hand, if it is 100 DEG C or lower, there is a tendency that an ethylene polymer can be obtained while controlling a specific ratio of the heat of fusion without impairing the catalytic activity. As a method for bringing the polymerization catalyst into contact with the alcohol before feeding (feeding) the polymerization catalyst to the polymerization reactor, the alcohol component may be any of alcohols such as normal butanol, methanol, ethanol, normal propanol, isopropanol, isobutanol, Octanol, and the like. The amount of the alcohol component to be added is preferably more than 0 and not more than 0.1 mass ppb, more preferably not more than 0.08 mass ppb, still more preferably not more than 0.05 mass ppb with respect to the catalyst weight.

In the polymerization step of the present embodiment, hydrogen may be continuously supplied to the polymerization system from the viewpoint of controlling the intrinsic viscosity of the ethylene-based polymer.

(Separation step)

The method for producing the ethylene polymer of the present embodiment preferably includes a separation step of separating the solvent from the polymerization slurry after the polymerization step when the solvent is supplied in the polymerization step. Specific examples of the separation method include a decantation method, a centrifugation method, and a filter filtration method. From the viewpoint of high efficiency of separation of the ethylene polymer and the solvent, the centrifugation method is preferable.

(Deactivation process)

The method for producing the ethylene polymer of the present embodiment preferably includes an inactivating step of deactivating the olefin polymerization catalyst after the polymerization step. The deactivation method of the olefin polymerization catalyst used for synthesizing the ethylene polymer of the present embodiment is not particularly limited, but is preferably carried out after the separation step. Introduction of a drug for deactivating the olefin polymerization catalyst after the separation of the ethylene polymer (for example, polyethylene) and the solvent is preferable because precipitation of low molecular weight components and catalyst components contained in the solvent can be reduced . Examples of the medicament include, but are not limited to, oxygen, water, alcohols, glycols, phenols, carbon monoxide, carbon dioxide, ethers, carbonyl compounds and alkynes.

(Cleaning process)

The method for producing an ethylene polymer of the present embodiment is a method in which, after the separation step, an ethylene polymer (for example, polyethylene (hereinafter referred to as " polyethylene " ) Is preferably washed. The temperature of the methanol to be cleaned is 60 DEG C or more, and more preferably 70 DEG C or more. If the temperature of the methanol is 60 DEG C or higher, the impurity which is the starting point of crystallization can be removed, and the crystallization of the ethylene polymer proceeds uniformly, so that the half width of the exothermic peak can be controlled.

(Drying step)

The method for producing the ethylene polymer of the present embodiment preferably includes a drying step for drying the ethylene polymer after the separation step. The drying temperature in the drying step is usually 50 ° C or higher and 150 ° C or lower, more preferably 50 ° C or higher and 130 ° C or lower, and more preferably 50 ° C or higher and 100 ° C or lower. If the drying temperature is 50 ° C or higher, efficient drying is possible. On the other hand, if the drying temperature is 150 占 폚 or lower, drying can be carried out while inhibiting decomposition or crosslinking of the ethylene polymer.

(Classification process)

In the method for producing an ethylene polymer of the present embodiment, after the drying step, the ethylene polymer is classified using a sieve having a predetermined eye size (for example, 425 占 퐉) to obtain a powdery (particulate) do.

(Molded article)

The molded article of the present embodiment is characterized by containing the ethylene polymer of the present embodiment. Examples of the molded body include a drawn molded body, a microporous membrane, a high strength fiber, and a gel emulsion, and a microporous membrane is preferable. The microporous membrane of the present embodiment is suitably used as a separator for a secondary battery (for example, a separator for a lead-acid battery). These molded articles can be produced in accordance with a known method.

[Example]

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited at all by the following examples.

[Various properties used in Examples and Comparative Examples and methods for measuring physical properties]

((1) Measurement of intrinsic viscosity)

The intrinsic viscosity of the ethylene polymer prepared in Examples and Comparative Examples was determined by the following method.

First, 10 mg of an ethylene polymer was weighed into a melting tube, and the melting tube was purged with nitrogen, and 20 mL of decahydronaphthalene (1 g / L of 2,6-di-t-butyl-4-methylphenol added) And the mixture was stirred at 150 DEG C for 2 hours to dissolve the ethylene polymer. The dropping time (ts) between the marks was measured using a Ubbelode-type viscometer in a thermostatic chamber at 135 캜. Similarly, the mass of the ethylene polymer was changed to prepare a solution of three points, and the dropping time was measured. The dropping time (tb) of only decalin without the ethylene polymer was measured as a blank.

A linear expression of the concentration (C) (unit: g / dL) and the reduced viscosity (? Sp / C) of the polymer was obtained by plotting the reduced viscosity (? Sp / C) of the polymer obtained according to the following formula (1) The intrinsic viscosity (?) Extrapolated to a concentration of 0 was obtained.

(ηsp / C) = (t s / t b -1) / C ( unit: dL / g) (1)

_{((2) ΔH b / ΔH} 2 × 100 and a half-value width of the heat generating peak)

Measurement was carried out using DSC (manufactured by Perkin Elmer, product name: DSC8000). 8 to 10 mg of an ethylene polymer was filled in an aluminum pan and placed in a DSC, and measurement was carried out under the following conditions (1) to (3).

(1) After being maintained at 50 占 폚 for 1 minute, the temperature was raised to 180 占 폚 at a heating rate of 10 占 폚 / min.

(2) After being maintained at 180 DEG C for 5 minutes, the temperature was decreased to 50 DEG C at a rate of 10 DEG C / min.

(3) After keeping the temperature at 50 캜 for 5 minutes, the temperature was raised to 180 캜 at a temperature raising rate of 10 캜 / min.

Melting from the range of 60 ℃ to 150 ℃ in the heat absorption peak obtained by the temperature rising stage at the second heat measuring the heat of fusion ΔH _b of ΔH _2, the melting point Tm ₂ and ΔH _2, the melting point Tm ₂ than the high temperature side (higher domain) of the , To obtain? H _b /? H ₂占 100. Further, the half width was obtained from the exothermic peak obtained in the cooling down process.

((3) Press sheet density)

An aluminum plate having a thickness of 0.1 mm was placed on a smooth steel plate having a thickness of 5 mm and a polyethylene terephthalate film (Lamier, manufactured by Toray Industries, Inc.) having a thickness of 50 탆 and not coated with a cellophane was placed. A mold having a length of 60 mm, a width of 60 mm and a thickness of 2 mm was placed on the mold, and 8 g of the ethylene polymer was placed thereon. The above-mentioned polyethylene terephthalate film was placed thereon, More. The resultant was placed in a compression molding machine (SFA-37 manufactured by Shindo Ginzoku Kogyo Co., Ltd.) controlled to a temperature of 200 占 폚, preheated at 200 占 폚 and 0.1 MPa for 900 seconds, left for 5 seconds in air (10 MPa) 15 MPa for 300 seconds. After the completion of the pressurization, the sample was taken out. After 5 seconds from being taken out, the sample was placed in a compression molding machine (SFA-37 manufactured by Shindo Ginzoku Kogyo Co., Ltd.) temperature controlled at 25 캜 and pressurized for 15 seconds at 25 캜 and 10 MPa And cooled at a cooling rate of 2 DEG C / min. The cooling rate was controlled by inserting the mold between thick paper. After cooling, the press sheet thus taken out was annealed at 120 DEG C for 1 hour to measure the density.

((4) the titanium content in the ethylene polymer)

0.2 g of the ethylene polymer was weighed into a decomposition vessel made of Teflon (registered trademark), and high-purity nitric acid was added thereto. The mixture was subjected to pressure decomposition with a microwave demolition device ETHOS-TC manufactured by Milestone General Corporation and purified with pure water produced by Nihon Millipore Was used as the sample solution. The test solution was subjected to quantitative determination of titanium by the internal standard method using an X-ray diffraction apparatus (ICP-MS) X series 2 manufactured by Thermo Fisher Scientific Inc.

((5) Chlorine content contained in the ethylene polymer)

After the ethylene polymer was burned by an automatic sample firing apparatus (AQF-100 manufactured by Mitsubishi Chemical Co., Ltd.), it was absorbed into an absorbing solution (mixed solution of Na ₂ CO ₃ and NaHCO ₃ ), and the absorbing solution was analyzed by an ion chromatograph , ICS 1500, column (separation column: AS12A, guard column: AG12A), and the total chlorine amount was measured.

((6) shrinkage ratio after oil extraction)

A test piece of 100 mm x 100 mm was cut out from the membrane before the liquid paraffin was extracted, and the shrinkage percentage after impregnation with hexane was measured. The shrinkage percentage was calculated as (L0-L1) / L0x100 where the length of the diagonal line of the test piece before extraction was L0 and the length of the diagonal line of the test piece after extraction was L1. Based on the average value of the shrinkage ratios obtained from the two diagonal lines, The shrinkage ratio after the oil extraction was evaluated. The evaluation criteria are as follows.

⊚: shrinkage less than 2%

○: Shrinkage rate is 2% or more and less than 4%

△: Shrinkage is 4% or more and less than 5%

X: Shrinkage of not less than 5%

((7) thickness unevenness)

100 mm x 100 mm test pieces were cut out from the microporous membrane and the thickness of arbitrary 10 points was measured at room temperature 23 占 폚 using a micro thickness meter (Type KBM (registered trademark)) manufactured by TOYO SEIKI CO., LTD. The difference in thickness was evaluated, and the thickness irregularity was evaluated. The evaluation criteria are as follows.

&Amp; cir &: Difference between the thickest portion and the thinnest portion is 1 mu m or less

&Amp; cir &: The difference between the thickest portion and the thin portion exceeds 1 mu m,

?: Difference between the thickest portion and the thinnest portion exceeds 3 占 퐉, and 5 占 퐉 or less

X: Difference between the thickest portion and the thinnest portion is 5 占 퐉 or more

((8) oxidation resistance of membrane)

The dumbbell-shaped test piece was cut out from the microporous membrane and impregnated in a specific gravity of 1.5 in dilute sulfuric acid at 80 DEG C for 80 hours to measure the retention of the tensile elongation before and after impregnation according to JIS K 7127 under the following conditions to evaluate the oxidation resistance of the membrane. The evaluation criteria are as follows.

Device: A · N · D Inc. Tensilon

Sample shape: Specimen Type 5

Distance between chucks: 80 mm

Tensile speed: 300 mm / min

⊚: retention rate of tensile elongation of 90% or more

○: Retention rate of tensile elongation is 80% or more and less than 90%

DELTA: Retention rate of tensile elongation was 70% or more and less than 80%

X: Retention rate of tensile elongation was less than 70%

((9) shrinkage ratio after oxidation resistance test)

A test piece of 100 mm x 100 mm was cut out from the microporous membrane and impregnated in a specific gravity of 1.5 in dilute sulfuric acid at 80 캜 for 80 hours, and then the shrinkage ratio after the oxidation resistance test was measured in the same manner as in the method (6). The evaluation criteria are as follows.

◎: shrinkage less than 3%

○: Shrinkage rate is 3% or more and less than 5%

?: Shrinkage rate is 5% or more and less than 10%

X: Shrinkage of not less than 10%

[Catalyst synthesis example]

Hereinafter, the catalyst used in this embodiment and the comparative example will be described.

[Production of solid catalyst component [A]]

1,600 mL of hexane was added to an 8L stainless steel autoclave thoroughly purged with nitrogen. 800 mL of a 1 mol / L titanium tetrachloride hexane solution and 800 mL of an organomagnesium compound represented by the composition formula AlMg ₅ (C ₄ H ₉ ) ₁₁ (OSi (C ₂ H ₅ ) H) ₂ at 1 mol / 800 mL of the solution was simultaneously added over 2 hours. After the addition, the temperature was slowly raised, and the reaction was continued at 40 DEG C for 1 hour. After the completion of the reaction, 1600 mL of the supernatant was removed, and the solid catalyst component [A] was washed four times with 1,600 mL of hexane.

[Production of solid catalyst component [B]]

(1) Synthesis of (B-1) Carrier

As the precursor of the carrier (B-1), silica having an average particle diameter of 9.5 mu m and a specific surface area of 480 m2 / g was used.

A nitrogen-substituted 8 L autoclave was charged with 130 g of the heat-treated silica in 2500 mL of hexane to obtain a slurry. To the obtained slurry, 195 mL of a hexane solution (concentration 1M) of triethyl aluminum as a Lewis acidic compound was added at 20 占 폚 under stirring. Thereafter, the mixture was stirred for 2 hours, and triethylaluminum and the surface hydroxyl group of the silica were reacted to prepare 2695 mL of a hexane slurry of the carrier (B-1) in which triethylaluminum was adsorbed.

(Preparation of transition metal compound component [C]) [

(Hereinafter, abbreviated as " complex 1 ") is used as the transition metal compound (C-1), and [(Nt-butylamide) (tetramethyl-? 5-cyclopentadienyl) dimethylsilane] titanium- . The composition formula Mg (C ₂ H ₅ ) (C ₄ H ₉ ) (hereinafter abbreviated as "Mg 1") was used as the organomagnesium compound (C-2).

200 mmol of complex 1 was dissolved in 1000 mL of isoparaffinic hydrocarbon (Isopara E manufactured by Exxon Mobil Corp.), 40 mL of a hexane solution of Mg1 (concentration 1M) was added thereto, and further hexane was added to adjust Complex 1 concentration to 0.1M To obtain a transition metal compound component [C].

(Preparation of activator [D]) [

17.8 g of bis (hydrogenated tallowalkyl) methylammonium-tetrakis (pentafluorophenyl) borate (hereinafter abbreviated as "borate") was added to 156 mL of toluene as a borate compound (D-1) Of a 100 mmol / L toluene solution. To the toluene solution of borate was added 15.6 mL of 1 mol / L hexane solution of ethoxydiethyl aluminum as (D-2) at room temperature, and toluene was further added to adjust the borate concentration in the solution to 70 mmol / L. Thereafter, the mixture was stirred at room temperature for 1 hour to prepare an activator [D] containing borate.

(Preparation of solid catalyst [E]) [

219 mL of the activator [D] obtained by the above operation and 175 mL of the transition metal compound component [C] were quantitatively measured from another line while stirring at 265 mL of the slurry of the carrier (B-1) The solid catalyst [E] was prepared by using a pump at the same time, and the reaction was continued for an addition time of 30 minutes and then for 3 hours.

(Preparation of liquid component [F]) [

As the organomagnesium compound (F-1), a composition formula AlMg ₆ (C ₂ H ₅ ) ₃ (C ₄ H ₉ ) ₁₂ (hereinafter abbreviated as "Mg 2") was used.

40 mL of hexane and Mg2 were added to a 200 mL flask while stirring and 38.0 mmol as a total amount of Mg and Al was added with stirring to obtain a solution of methylhydrogenpolysiloxane having a viscosity of 20 centistokes at 25 캜 ) Was added with stirring, and then the temperature was raised to 80 占 폚, and the mixture was reacted under stirring for 3 hours to prepare a liquid component [F].

(Production of hydrogenation catalyst [G]) [

To a SUS autoclave having a capacity of 2.0 L in a stirrer portion substituted with nitrogen, 37.3 g of titanocene dichloride was introduced into 1 L of hexane. While stirring at 500 rpm, a mixture (9: 1) of triisobutylaluminum and diisobutylaluminum hydride (0.7 mol / L), 429 mL, was pumped over 1 hour at room temperature. After the addition, the line was washed with 71 mL of hexane. Stirring was continued for 1 hour to obtain a dark blue uniform 100 mM / L solution [G].

(Production of solid catalyst component [H]) [

<(1) Synthesis of (H-1) Carrier>

While thoroughly purged with nitrogen, a stainless steel 8L In a hexane solution 1,000mL of the silane with hydroxy trichloro of 2㏖ / L autoclave, and stirred at 65 ℃ compositional formula _{AlMg 5 (C 4 H 9)} 11 (OC 4 H 9) 2,550 mL of a hexane solution of the organomagnesium compound represented by ₂ (corresponding to 2.68 mol of magnesium) was added dropwise over 4 hours, and the reaction was continued while stirring at 65 DEG C for 1 hour.

After the completion of the reaction, the supernatant was removed and washed with 1,800 mL of hexane four times to obtain a carrier (H-1).

&Lt; (2) Production of solid catalyst component [H]

110 mL of a 1 mol / L titanium tetrachloride hexane solution and 1 mL / L of a composition formula AlMg ₅ (C ₄ H ₉ ) ₁₁ (OC ₄ (OH) ₂ ) were added to 1,970 mL of a hexane slurry containing the above- H ₉ ) ₂ was simultaneously added over a period of 1 hour.

After the addition, the reaction was continued at 65 DEG C for 1 hour.

After the completion of the reaction, 1100 mL of the supernatant was removed, and the solid catalyst component [H] was prepared by washing 4 times with 1,100 mL of hexane.

[Example 1]

(Production method of ethylene polymer)

Hexane, ethylene, hydrogen and a catalyst were continuously fed to a vessel-type 300 L polymerization reactor equipped with a stirrer under the conditions of an average residence time of 2 hours. The polymerization pressure was 0.35 MPa. The polymerization temperature was maintained at 75 占 폚 by jacket cooling. As the catalyst, a solid catalyst component [A] and triisobutyl aluminum were used as a cocatalyst. Triisobutylaluminum was added to the polymerization reactor at a rate of 10 mmol / hr. The solid catalyst component [A] was fed so that the polymerization rate (production rate) of the ethylene polymer was 10 kg / hr. Hydrogen was continuously supplied by a pump at a gas concentration of 2000 ppm. A 100 mmol / L hexane solution of n-butanol was fed so that the amount of n-butanol became 1 ppm / hr with respect to the polymerization rate (production rate) of 10 kg / hr to obtain a polymerization slurry. The obtained polymerization slurry was sent to a centrifugal separator to separate the polymer (polyethylene) from the other solvent, and then the polymer was brought into contact with stirring at 60 ° C for 1 hour. The polymerization slurry containing the polymer and methanol was sent to a centrifugal separator to separate the polymer and other solvents and the like to obtain an ethylene polymer. The separated ethylene polymer was dried at 70 DEG C while being blown with nitrogen. An ethylene polymer obtained in this way was used as a sieve having an eye size of 425 mu m to remove the non-sifted ethylene polymer, thereby obtaining a powdery (particulate) ethylene polymer.

The properties of the obtained ethylene polymer on the powder were measured by the above-mentioned method. The measurement results are shown in Table 1 below.

(Manufacturing method of microporous membrane)

3.7 g of the ethylene polymer on the powder, 26.6 g of liquid paraffin (P-350 (trade name) manufactured by Matsumura Sekiyu Co., Ltd.), 9.5 g of silica (HiSil233 made by PPG), 0.02 g of carbon black, 0.02 g of pentaerythrityl tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] was added and stirred with about a spoon to obtain a mixture Mixture).

The obtained polyethylene mixture was put into a Toyo Sekisui Seisakusho Labo Plastomill Mixer (main body type: 4C150, mixer type: R-60), and the number of revolutions was set to 50 rpm and kneaded at 200 DEG C for 10 minutes. The kneaded product was directly pressed for 300 seconds under a condition of 200 占 폚 and 10 MPa using a mold of 250 mm 占 250 mm and a thickness of 0.1 mm and cooled at 25 占 폚 and 10 MPa for 600 seconds to obtain a black film.

This black film was impregnated with hexane for 10 minutes to extract liquid paraffin and dried to obtain a microporous membrane.

The physical properties of the microporous membrane thus obtained were measured by the above-mentioned method. The measurement results are shown in Table 1 below.

[Example 2]

The solid catalyst component [E] was used in place of the solid catalyst component [A] and the triisobutyl aluminum in the polymerization process, the liquid component [F] was fed at a rate of 6 mmol / hr as the total amount of Mg and Al, Hydrogen was supplied to the feed pipe of the solid catalyst component [E] at a rate of 2 NL / hr, and a separate hydrogenation catalyst [G] was fed to the feed pipe at a concentration of 1.1 탆 ol / L , An ethylene polymer was obtained in the same manner as in Example 1. The microporous membrane was produced in the same manner as in Example 1.

[Example 3]

An ethylene polymer was obtained in the same manner as in Example 1 except that the solid catalyst component [H] was used instead of the solid catalyst component [A] in the polymerization process, the polymerization temperature was set to 73 캜, . The microporous membrane was produced in the same manner as in Example 1.

[Example 4]

An ethylene polymer was obtained in the same manner as in Example 2 except that the hydrogenation catalyst [G] was fed so as to have a concentration in the reactor of 1.6 占 퐉 ol / L in the polymerization process. The microporous membrane was produced in the same manner as in Example 1.

[Example 5]

The polymerization was carried out in the same manner as in Example 2 except that the hydrogenation catalyst [G] was fed so as to have a concentration of 1.8 탆 ol / L in the reactor, and 1-butene was fed so that the concentration of the gas phase portion became 1.0 mol% Similarly, an ethylene polymer was obtained. The microporous membrane was produced in the same manner as in Example 1.

[Example 6]

In the polymerization step, an ethylene polymer was obtained in the same manner as in Example 1 except that the polymerization temperature was 65 캜, the polymerization pressure was 0.45 MPa, no hydrogen was supplied, and no contact was made with methanol. The microporous membrane was produced in the same manner as in Example 1.

[Example 7]

An ethylene polymer was obtained in the same manner as in Example 2 except that the polymerization temperature was set at 70 캜 and that the hydrogenation catalyst [G] was fed at a concentration of 2.4 탆 ol / L in the reactor. The microporous membrane was produced in the same manner as in Example 1.

[Example 8]

Instead of using the solid catalyst component [A] as it is in the polymerization step, the solid catalyst component [A] was used in a form of stirring in hexane at 90 ° C for 1 hour under a nitrogen atmosphere. , No hydrogen was supplied, and further, a 100 mmol / L hexane solution of n-butanol was not added to the polymerization system. Thus, an ethylene polymer was obtained. The microporous membrane was produced in the same manner as in Example 1.

[Comparative Example 1]

In the polymerization step, an ethylene polymer was obtained in the same manner as in Example 1 except that the polymerization temperature was 74 占 폚, no hydrogen was supplied, and normal butanol was not added to the polymerization system. The microporous membrane was produced in the same manner as in Example 1.

[Comparative Example 2]

In the polymerization step, an ethylene polymer was obtained in the same manner as in Example 3 except that the polymerization temperature was 60 캜, the polymerization pressure was 0.8 MPa, and n-butanol was not added to the polymerization system. The microporous membrane was produced in the same manner as in Example 1.

[Comparative Example 3]

An ethylene polymer was obtained in the same manner as in Example 3 except that the polymerization temperature was changed to 75 캜 instead of 73 캜 and hydrogen was supplied to 3000 ppm. The microporous membrane was produced in the same manner as in Example 1.

[Comparative Example 4]

In the polymerization step, the polymerization temperature was changed to 60 占 폚 instead of 75 占 폚, the polymerization pressure was changed to 0.5 MPa instead of 0.35 MPa, the hydrogen was not supplied, and furthermore, a 100 mmol / L hexane solution of n-butanol was added , An ethylene polymer was obtained in the same manner as in Example 1. The microporous membrane was produced in the same manner as in Example 1.

The ethylene polymer of the present embodiment can be used for various molded articles. Examples of the molded article include high strength fibers, gel spinning and microporous membranes. In particular, the ethylene polymer is suitably used as a microporous membrane, and the microporous membrane can be used for a separator for a secondary battery, particularly a lead battery separator.

Claims (7)

The intrinsic viscosity (?) Is 11 or more and 28 or less,
The melting point Tm (Tm) of the _second heat-up process (ΔH ₂ ) in the DSC curve of the second temperature-rising process obtained by the measurement conditions of the following (1) to (3) using the differential scanning calorimeter (DSC) ₂ ) a ratio (ΔH _b / ΔH ₂ × 100) of the heat of fusion (ΔH _b ) in a higher region is 18% or more.
(DSC measurement conditions)
(1) After being maintained at 50 占 폚 for 1 minute, the temperature was raised to 180 占 폚 at a heating rate of 10 占 폚 / min.
(2) After being maintained at 180 DEG C for 5 minutes, the temperature was decreased to 50 DEG C at a rate of 10 DEG C / min.
(3) After keeping the temperature at 50 캜 for 5 minutes, the temperature was raised to 180 캜 at a temperature raising rate of 10 캜 / min. The ethylene polymer according to claim 1, wherein the half value width of the exothermic peak in the temperature decreasing step of the measurement conditions using the DSC is not less than 3.0 and not more than 6.0. The ethylene polymer as set forth in claim 1 or 2, wherein the density of the press sheet obtained by the following processing conditions (1) to (3) is 910 kg / m 3 or more and 940 kg / m 3 or less.
(Processing conditions)
(1) Preheating for 900 seconds at 200 ° C and 0.1 MPa.
(2) Pressurization at 200 DEG C and 15 MPa for 300 seconds.
(3) Cooling for 600 seconds at 25 캜 and 10 MPa. The ethylene polymer according to Claim 1 or 2, wherein the content of titanium is 3 ppm or less on a weight basis with respect to the total amount of the ethylene polymer. The ethylene polymer according to claim 1 or 2, wherein the chlorine content is 10 ppm or less on a weight basis with respect to the total of the ethylene polymer. A molded article comprising the ethylene polymer according to any one of claims 1 to 3. The molded article according to claim 6, which is a microporous membrane.