JP6383479B1 - Ethylene polymer and molded body - Google Patents

Abstract

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 body including the ethylene polymer are provided.
[Solution]
The intrinsic viscosity (η) is 11 or more and 28 or less,
In the DSC curve of the second temperature raising process obtained by the following measurement conditions (1) to (3) using a differential scanning calorimeter (DSC), with respect to the heat of fusion (ΔH ₂ ) of the _second temperature raising process An ethylene polymer having a ratio (ΔH _b / ΔH ₂ × 100) of heat of fusion (ΔH _b ) in a region higher than the melting point (Tm ₂ ) of 18% or more.

(DSC measurement conditions)
(1) After holding at 50 ° C. for 1 minute, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.
(2) After holding at 180 ° C. for 5 minutes, the temperature is decreased to 50 ° C. at a temperature decreasing rate of 10 ° C./min.
(3) After holding at 50 ° C. for 5 minutes, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.

[Selection figure] None

Description

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

  Polyethylene has been conventionally used for various applications such as films, sheets, microporous membranes, fibers, and molded articles. In particular, polyethylene having a high molecular weight is used as a raw material for a microporous film constituting a separator for a secondary battery represented by a lead storage battery or a lithium ion battery. The characteristics required for the microporous membrane for a lead-acid battery include isolation between the positive electrode and the negative electrode, electrolyte impregnation and diffusibility, low electrical resistance, oxidation resistance, mechanical strength, and the like. Particularly in recent years, lead-acid batteries are being reduced in size, increased in capacity, and increased in output due to the widespread use of idling stop vehicles, and further reduction in the thickness of microporous membranes is required (for example, Patent Document 1). reference). However, the oxidation resistance of the film is lowered due to the thinning of the microporous film, and the life of the battery is reduced. For this reason, various methods have been conventionally proposed as methods for improving the oxidation resistance (see, for example, Patent Documents 2 and 3).

Special table 2013-541162 gazette Japanese Patent No. 4583551 Japanese Patent No. 5830187

  In order to reduce the thickness of the separator for a secondary battery, it is preferable to use a microporous film alone. On the other hand, generally, as a method for increasing the oxidation resistance of a film such as a microporous film, a method for increasing the molecular weight of polyethylene used as a raw material can be mentioned. However, polyethylene with a high molecular weight not only has high viscosity and poor dispersibility, but also may cause film shrinkage, uneven thickness, and deflection, and induces local oxidation by contact with the electrode. As a result, there is a problem that the oxidation resistance is lowered. For this reason, a method of blending polyethylene having a high molecular weight and polyethylene having a low molecular weight can be considered, but the molecular weight of polyethylene in the entire microporous membrane is lowered, and the strength of the microporous membrane cannot be sufficiently increased. There is a problem that the oxidation resistance is insufficient.

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

  As a result of intensive studies to solve the above-described problems of the prior art, the inventors of the present invention have an intrinsic viscosity within a predetermined range, and the heat of fusion obtained under specific measurement conditions of a differential scanning calorimeter (DSC). It has been found that an ethylene polymer having a specific ratio of not less than a specific lower limit can solve the above-mentioned problems, and has completed the present invention.

That is, the present invention is as follows.
[1]
The intrinsic viscosity (η) is 11 or more and 28 or less,
In the DSC curve of the second temperature raising process obtained by the following measurement conditions (1) to (3) using a differential scanning calorimeter (DSC), with respect to the heat of fusion (ΔH ₂ ) of the _second temperature raising process An ethylene polymer having a ratio (ΔH _b / ΔH ₂ × 100) of heat of fusion (ΔH _b ) in a region higher than the melting point (Tm ₂ ) of 18% or more.

(DSC measurement conditions)
(1) After holding at 50 ° C. for 1 minute, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.
(2) After holding at 180 ° C. for 5 minutes, the temperature is decreased to 50 ° C. at a temperature decreasing rate of 10 ° C./min.
(3) After holding at 50 ° C. for 5 minutes, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.

[2]
The ethylene polymer according to [1], wherein the half-value width of the exothermic peak is 3.0 or more and 6.0 or less in the temperature lowering process under the measurement conditions using the DSC.
[3]
The ethylene polymer according to [1] or [2] above, wherein a press sheet density obtained under the following processing conditions (1) to (3) is from 910 kg / m ^{3 to} 940 kg / m ³ .

(Processing conditions)
(1) Preheating for 900 seconds under the conditions of 200 ° C. and 0.1 MPa.
(2) Pressurization for 300 seconds under conditions of 200 ° C. and 15 MPa.
(3) Cooling for 600 seconds under conditions of 25 ° C. and 10 MPa.

[4]
The ethylene polymer according to any one of [1] to [3], wherein the titanium content is 3 ppm or less in terms of weight with respect to the whole ethylene polymer.
[5]
The ethylene polymer according to any one of [1] to [4] above, wherein the chlorine content is 10 ppm or less in terms of weight with respect to the entire ethylene polymer.
[6]
A molded article comprising the ethylene polymer according to any one of [1] to [5].
[7]
The molded product according to [6] above, which is a microporous membrane.

According to the present invention, 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 body containing the ethylene polymer (for example, , A microporous membrane) can be provided.
Furthermore, since the ethylene-based polymer of the present invention can provide excellent oxidation resistance and shrinkage resistance during film formation (for example, thin film molding), for example, the microporous material constituting a separator for a secondary battery. It can be suitably used as a film. More specifically, the microporous film obtained by using the ethylene polymer of the present invention can further extend the battery life because shrinkage of the film after the oxidation resistance test is suppressed.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following description, It can implement by changing variously within the range of the summary.

[Ethylene polymer]
The ethylene polymer of the present embodiment has an intrinsic viscosity (η) of 11 or more and 28 or less, and is obtained for the second time obtained under the following measurement conditions (1) to (3) using a differential scanning calorimeter (DSC). In the DSC curve of the temperature raising process, the ratio of the heat of fusion (ΔH _b ) in the region higher than the melting point (Tm ₂ ) to the heat of fusion (ΔH ₂ ) of the _second temperature raising process (ΔH _b / ΔH ₂ × 100 Hereinafter, it is also referred to as “specific ratio of heat of fusion”)) of 18% or more. The ethylene-based 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 it can be molded (for example, film formation such as thin film molding). In addition, excellent oxidation resistance and shrinkage resistance can be imparted. In addition, 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 not less than a specific lower limit value. It has a high property, and there is a tendency that the residual oil unevenness and shrinkage unevenness during oil extraction are small. For this reason, when the film is formed using the ethylene-based polymer of the present embodiment, the film is less likely to be bent and less likely to be wound or misaligned, thereby improving the quality of the film.

(DSC measurement conditions)
(1) After holding at 50 ° C. for 1 minute, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.
(2) After holding at 180 ° C. for 5 minutes, the temperature is decreased to 50 ° C. at a temperature decreasing rate of 10 ° C./min.
(3) After holding at 50 ° C. for 5 minutes, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.

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

(Intrinsic viscosity)
The intrinsic viscosity (η) 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 (η) is 11 or more, a minimum oxidation resistance can be imparted during molding (for example, film formation such as thin film molding). Moreover, when shape | molded into a thin film, favorable film | membrane strength can be provided. On the other hand, when the intrinsic viscosity (η) is 28 or less, shrinkage of the film after molding is suppressed.

  The intrinsic viscosity (η) of the ethylene polymer of the present embodiment can be controlled by appropriately adjusting the polymerization conditions and the like using an olefin polymerization catalyst described later. Specifically, the intrinsic viscosity (η) can be controlled by allowing hydrogen to be present in the polymerization system or changing the polymerization temperature.

  Specifically, the intrinsic viscosity (η) of the ethylene polymer of this embodiment is prepared by, for example, preparing solutions in which ethylene polymer is dissolved in decalin at different concentrations, and determining the solution viscosity at 135 ° C. of the solution. It can be determined by extrapolating the reduced viscosity calculated from the measured solution viscosity to a concentration of zero. More specifically, the method described in the examples is used.

(Specific ratio of heat of fusion)
The specific ratio of the heat of fusion is 18% or more (for example, 18% or more and 26% or less), preferably 19% or more and 25 or less, more preferably 20% or more and 25% or less. When the specific ratio of the heat of fusion is 18% or more, the polyethylene component having a large crystal size and thickness in the ethylene-based polymer increases, and has excellent acid resistance when molding (for example, film formation such as thin film molding). Can be imparted. On the other hand, when the specific ratio of the heat of fusion is 26% or less, an ethylene polymer having better solubility in an organic solvent (for example, liquid paraffin) can be obtained, and molding (for example, thin film molding) When forming a film, an excellent appearance can be imparted. In addition, the specific ratio of heat of fusion can be measured by the method described in Examples described later.

The specific ratio of the heat of fusion of the ethylene polymer of the present embodiment adjusts the viscosity average molecular weight, increases the size of the active species of the olefin polymerization catalyst, or adds a very small amount of alcohol component to the polymerization system. It can be controlled by doing. As a specific method of adding a very small amount of alcohol component to the polymerization system, for example, a method of adding normal butanol at an addition rate of 1 ppm / hr to a polymerization rate (polymerization rate) of 10 kg / hr in the polymerization system. Is mentioned. The addition of only alcohol component traces to the polymerization system, it is possible to deactivate the active sites to produce a slight low molecular weight components such as to inhibit the growth of crystals of the ethylene polymer, to increase the ratio of [Delta] H _b Can do. On the other hand, the ratio of ΔH _b can be lowered by adjusting the viscosity average molecular weight or controlling the size of the active species of the olefin polymerization catalyst.

(Half width of DSC exothermic peak)
The half-value width of the exothermic peak in the temperature lowering process under the DSC measurement conditions is preferably 3.0 or more and 6.0 or less, more preferably 3.0 or more and 5.5 or less, and further preferably 3.0 or more and 5 or less. 0.0 or less, particularly preferably 3.0 or more and 4.3 or less. When the half-value width of the exothermic peak is 3.0 or more, it can be molded (for example, film formation) relatively easily as in the case of 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 is further improved during film formation (for example, thin film forming), and thickness unevenness is further suppressed. In addition, the half value width of the said exothermic peak can be measured by the method as described in the Example mentioned later.

  The half-value width of the exothermic peak adjusts the molecular weight distribution, increases the productivity per titanium contained in the unit catalyst, or converts the ethylene polymer obtained after the polymerization reaction to methanol at a high temperature (eg, 70 ° C. or higher). It can be controlled by washing with. In particular, when an ethylene polymer is washed with high-temperature methanol, impurities that can be the starting point of crystallization can be removed, and the crystallization of the ethylene polymer proceeds uniformly, so that the half-value width of the exothermic peak can be reduced. it can. On the other hand, the half width of the exothermic peak can be increased by adjusting the molecular weight distribution or controlling the productivity per titanium contained in the unit catalyst.

(Press sheet density)
The press sheet density of the ethylene polymer obtained by 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, more preferably 915 kg / m ^3. It is 935 kg / m ³ or less, more preferably 920 kg / m ³ or more and 935 kg / m ³ or less. When the press sheet density is 910 kg / m ³ or more, the crystallinity of polyethylene is sufficiently high, and there is a tendency that even better oxidation resistance can be imparted during molding (for example, film formation such as thin film molding). . On the other hand, when the press sheet density is 940 kg / m ³ or less, the viscosity-average molecular weight of polyethylene is sufficiently high, and it tends to be able to impart more excellent strength (for example, film strength) during molding (for example, film formation). is there.

(1) Preheating for 900 seconds under the conditions of 200 ° C. and 0.1 MPa.
(2) Pressurization for 300 seconds under conditions of 200 ° C. and 15 MPa.
(3) Cooling for 600 seconds under conditions of 25 ° C. and 10 MPa.

  The press sheet density of the ethylene-based polymer of this embodiment can be controlled by adjusting the viscosity average molecular weight or introducing a branch in the polyethylene chain.

(Ethylene polymer)
The ethylene polymer of the present embodiment is not limited to the following, but is an ethylene homopolymer or a copolymer of ethylene and one or more other monomers (for example, a binary or ternary copolymer). Is mentioned. The bond type of the copolymer may be random or block. Examples of other monomers include, but are not limited to, α-olefins and vinyl compounds. Examples of the α-olefin include, but are not limited to, propylene, 1-butene, 4-methyl-1 -Α-olefins having 3 to 20 carbon atoms such as pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, etc. Examples of the vinyl compound include, but are not limited to, vinylcyclohexane, styrene, and derivatives thereof. If necessary, non-conjugated polyenes such as 1,5-hexadiene and 1,7-octadiene can be used as other monomers. These other monomers can be used individually by 1 type or in combination of 2 or more types.

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

(Titanium content in ethylene polymer)
The titanium content 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, in terms of weight with respect to the entire ethylene polymer. It is. When the titanium content is 3 ppm or less, the polyethylene crystal size can be increased, and excellent oxidation resistance tends to be imparted during molding (for example, film formation such as a thin film). In addition, titanium content can be measured by the method as described in the Example mentioned later.

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

(Chlorine content in ethylene polymer)
The chlorine content contained in the ethylene polymer of the present embodiment is preferably 10 ppm or less, more preferably 5 ppm or less, and further preferably 2 ppm or less in terms of weight with respect to the entire ethylene polymer. . When the chlorine content is 10 ppm or less, deterioration of the ethylene-based polymer in the acid aqueous solution can be suppressed, and more excellent oxidation resistance tends to be imparted during molding (for example, film formation such as a thin film). . In addition, chlorine content can be measured by the method as described in the Example mentioned later.

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

(Additive)
Furthermore, the ethylene-based polymer of the present embodiment may contain additives such as a neutralizing agent, an antioxidant, and a light stabilizer.

  The neutralizing agent is used as a chlorine catcher or a molding processing aid contained in the ethylene polymer. 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, and still more preferably 3000 ppm or less in terms of weight with respect to the entire ethylene polymer.

  Examples of the antioxidant include, but are not limited to, dibutylhydroxytoluene, pentaerythryl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- ( And phenolic antioxidants such as 3,5-di-t-butyl-4-hydroxyphenyl) propionate. The content of the antioxidant is not particularly limited, but is preferably 5,000 ppm or less, more preferably 4,000 ppm or less, and still more preferably 3,000 ppm or less in terms of weight with respect to the whole ethylene polymer. is there.

  Examples of the light-resistant stabilizer include, but are not limited to, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- (3-t-butyl-5-methyl-2-hydroxyphenyl) -5 Benzotriazole light stabilizers such as 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 Hindered amine light-resistant stabilizers such as -piperidyl) imino}]. Although content of a light-resistant stabilizer is not specifically limited, Preferably it is 5000 ppm or less in weight conversion with respect to the whole ethylene polymer, More preferably, it is 4000 ppm or less, More preferably, it is 3000 ppm or less.

  In the present embodiment, in addition to the above-described components, other known components useful for the production of an ethylene polymer can be included.

  The ethylene polymer of this embodiment may be composed of one type of ethylene polymer (for example, polyethylene), or may be composed of two or more different types of ethylene polymers (for example, two or more types of polyethylene). May be. In the case of two or more types, for example, ethylene polymers (for example, polyethylene) having different viscosity average molecular weights may be combined. In addition, as the polyethylene constituting the ethylene polymer of the present embodiment, ultrahigh molecular weight polyethylene is preferable, and the ethylene polymer may be composed of ultrahigh molecular weight polyethylene alone as polyethylene, You may combine with other resin. Other resins are not particularly limited, and examples include other polyethylenes such as low density polyethylene and linear low density polyethylene, polypropylene, and polystyrene. These other resins may be used alone or in combination of two or more.

  Although it does not specifically limit as a form of the ethylene-type polymer of this embodiment, For example, a powder form (particulate form) and a pellet form may be sufficient, and if it is these forms, favorable handleability Is obtained. The powdery ethylene polymer is obtained by applying a suspension polymerization method or a gas phase polymerization method, and the pellet-like ethylene polymer is obtained by melting and kneading the ethylene polymer obtained by polymerization, and then stranding. Is obtained by cutting.

(Method for producing ethylene polymer)
Hereinafter, the manufacturing method of the ethylene polymer of this embodiment is demonstrated.

(Polymerization process)
The method for producing an ethylene polymer of the present embodiment includes, for example, polymerizing a monomer containing at least ethylene in the presence of an olefin polymerization catalyst to produce an ethylene polymer (ethylene homopolymer or ethylene copolymer). A resulting polymerization step.

  In the polymerization step in the present embodiment, ethylene may be polymerized alone to obtain an ethylene homopolymer, or ethylene may be copolymerized with one or more other monomers to obtain an ethylene copolymer. Good. As said monomer, the other monomer illustrated by the term of the ethylene-type polymer can be illustrated.

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

  As the Ziegler-Natta catalyst, for example, an olefin polymerization catalyst described in JP-A-10-2189334, a Ziegler-Natta catalyst exemplified in the section of [Method for producing polyethylene powder] of Japanese Patent No. 578558, Patent No. Examples include the Ziegler-Natta catalyst exemplified in [Polymerization polymerization method] of No. 5829257. More specifically, a catalyst obtained by combining a solid catalyst component produced by a reaction between an organomagnesium compound and a titanium compound and an organometallic compound component (co-catalyst), or a reaction between the organomagnesium component and a chlorinating agent. Examples thereof include a catalyst produced by supporting an organomagnesium compound and a titanium compound on the prepared carrier.

  As the metallocene catalyst, for example, the metallocene catalyst exemplified in the section of [Method of producing polyethylene powder] of Japanese Patent No. 5582558, and the method of producing an ultrahigh molecular weight ethylene polymer of Japanese Patent No. 4868853 are exemplified. Examples thereof include metallocene catalysts. More specifically, as a catalyst component, a metallocene in which a transition metal compound having a cyclic η-bonding anion ligand and an activator capable of forming a complex that reacts with the transition metal compound and exhibits catalytic activity are combined. A system catalyst can be illustrated. As described in Japanese Patent No. 5784558, these catalyst components may be supported on a solid component (for example, silica) and used as a supported catalyst, and an organoaluminum compound may be used as another catalyst component. You may combine. Moreover, you may combine the said transition metal compound, the said activator, and the liquid component used as a scavenger of an impurity or an inactive compound. Examples of the liquid component include liquid components described in JP-A-2015-180716. Further, a hydrogenating agent may be used together with the metallocene catalyst, and a compound having hydrogenation ability may be added. Examples of the hydrogenating agent and the compound having hydrogenation ability include the hydrogenating agent and the compound having hydrogenation ability described in Japanese Patent No. 5784558.

  Although it does not specifically limit as a polymerization method of this embodiment, Suspension polymerization method and a gas phase polymerization method are mentioned, Suspension polymerization method is preferable from a viewpoint which can remove heat of polymerization efficiently.

  In the suspension polymerization method, an inert hydrocarbon medium can be used as a medium, and the olefin itself can also be 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; cyclopentane, cyclohexane, Examples thereof include alicyclic hydrocarbons such as methylcyclopentane; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as ethyl chloride, chlorobenzene and dichloromethane, or mixtures thereof.

  The polymerization temperature in the polymerization step of the present embodiment is usually preferably from 30 ° C. to 100 ° C., more preferably from 35 ° C. to 90 ° C., and further preferably from 40 ° C. to 80 ° C. If the polymerization temperature is 30 ° C. or higher, industrially efficient production is possible, and if the polymerization temperature is 100 ° C. or lower, continuous stable operation is possible. On the other hand, from the viewpoint of controlling the intrinsic viscosity of the ethylene polymer, the polymerization temperature is preferably 30 ° C. or higher and 85 ° C. or lower, more preferably 40 ° C. or higher and 80 ° C. or lower, and 50 ° C. or higher and 80 ° C. or lower. More preferably.

  The polymerization pressure in the polymerization step of the present embodiment is usually preferably from normal pressure to 2 MPa, more preferably from 0.1 MPa to 1.5 MPa, and even more preferably from 0.1 MPa to 1.0 MPa. When the pressure is normal pressure or more, an ethylene polymer having a low residual metal amount tends to be obtained. When the pressure is 2 MPa or less, an ethylene polymer can be stably produced without generating a lump scale. There is a tendency.

  In the polymerization step of this embodiment, it is preferable to add a very small amount of alcohol component in the polymerization system. The addition of a very small amount of an alcohol component can suppress the formation of a very small amount of low molecular weight component that inhibits the growth of the resulting polyethylene crystal and can remove a very small amount of impurities. The specific ratio of the heat of fusion described above can be controlled. Examples of the alcohol component include normal butanol, methanol, ethanol, normal propanol, isopropanol, isobutanol, tertiary butanol, pentanol, hexanol, heptanol, octanol and the like. The addition rate of the alcohol component is preferably more than 0 and 1 mass ppm / hr or less, more preferably 0.8 mass ppm / hr or less, and even more preferably 0.5 mass with respect to a polymerization rate of 10 kg / hr. It is below ppm / hr. When the addition rate is 1 mass ppm / hr or less, the ethylene polymer tends to be obtained while controlling a specific ratio of the heat of fusion without impairing productivity.

  In addition, from the viewpoint that it is possible to suppress the production of a very small amount of low molecular weight components that inhibit crystal growth of the resulting ethylene polymer (for example, polyethylene), as another means, a polymerization catalyst is used in a nitrogen atmosphere. Examples thereof include a method of heat treatment in an inert hydrocarbon medium and a method of bringing a polymerization catalyst into contact with alcohol before feeding (feeding) the polymerization catalyst to the polymerization vessel. As a method of heat-treating the polymerization catalyst in an inert hydrocarbon medium in a nitrogen atmosphere, the treatment is preferably performed at 80 ° C. or higher, more preferably 90 ° C. or higher. Moreover, if it is 100 degrees C or less, it exists in the tendency which can obtain an ethylene-type polymer, controlling the specific ratio of heat of fusion, without impairing catalyst activity. As a method of bringing the polymerization catalyst into contact with the alcohol before feeding (feeding) the polymerization catalyst, the alcohol component includes normal butanol, methanol, ethanol, normal propanol, isopropanol, isobutanol, tertiary butanol, pentanol, hexanol, heptanol. And octanol. The addition amount of the alcohol component is preferably more than 0 and 0.1 mass ppb or less, more preferably 0.08 mass ppb or less, and still more preferably 0.05 mass ppb or less 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 polymer.

(Separation process)
The method for producing an ethylene-based 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 centrifugal separation method, a filter filtration method, and the like. From the viewpoint of high separation efficiency between the ethylene polymer and the solvent, the centrifugal separation method is preferable.

(Deactivation process)
It is preferable that the manufacturing method of the ethylene-type polymer of this embodiment includes the deactivation process which deactivates the said catalyst for olefin polymerization after a superposition | polymerization process. The method for deactivating the olefin polymerization catalyst used for synthesizing the ethylene-based polymer of the present embodiment is not particularly limited, but is preferably performed after the separation step. It is preferable to introduce an agent for deactivating the olefin polymerization catalyst after separating the ethylene polymer (for example, polyethylene) and the solvent because precipitation of low molecular weight components and catalyst components contained in the solvent can be reduced. . Examples of the drug include, but are not limited to, oxygen, water, alcohols, glycols, phenols, carbon monoxide, carbon dioxide, ethers, carbonyl compounds, alkynes, and the like.

(Washing process)
From the viewpoint of controlling the half-value width of the exothermic peak described above in the section [Ethylene polymer], the ethylene polymer production method of the present embodiment is an ethylene polymer (for example, with high-temperature methanol after the separation step). , Polyethylene) is preferably washed. The temperature of the methanol to be washed is 60 ° C. or higher, more preferably 70 ° C. or higher. When the temperature of methanol is 60 ° C. or higher, impurities that can be a starting point for crystallization can be removed, and the crystallization of the ethylene-based polymer proceeds uniformly, so that the half-value width of the exothermic peak can be controlled.

(Drying process)
It is preferable that the manufacturing method of the ethylene polymer of this embodiment includes the drying process which dries an ethylene polymer after a isolation | separation process. The drying temperature in the drying step is usually preferably 50 ° C or higher and 150 ° C or lower, more preferably 50 ° C or higher and 130 ° C or lower, and further preferably 50 ° C or higher and 100 ° C or lower. When the drying temperature is 50 ° C. or higher, efficient drying is possible. On the other hand, when the drying temperature is 150 ° C. or lower, drying can be performed in a state where decomposition and crosslinking of the ethylene-based polymer are suppressed.

(Classification process)
In the method for producing an ethylene polymer according to the present embodiment, after the drying step, the ethylene polymer is classified using a sieve having a predetermined mesh size (for example, 425 μm) to form a powder (particulate) form. Also good.

(Molded body)
The molded body of the present embodiment is characterized by including the ethylene polymer of the present embodiment. Examples of the molded body include stretched molded bodies, microporous membranes, high-strength fibers, gel spinning, and the like, and microporous membranes are preferred. The microporous membrane of this embodiment is suitably used as a secondary battery separator (for example, a lead storage battery separator). In addition, these molded objects can be manufactured according to a well-known method.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example and a comparative example, this invention is not limited at all by the following examples.

[Methods for measuring various properties and physical properties used in Examples and Comparative Examples]
((1) Measurement of intrinsic viscosity)
The intrinsic viscosity of the ethylene polymers produced in the examples and comparative examples was determined by the method shown below.
First, 10 mg of ethylene polymer was weighed in a dissolution tube, and the dissolution tube was purged with nitrogen, and then 20 mL of decahydronaphthalene (with 1 g / L of 2,6-di-t-butyl-4-methylphenol added). In addition, the mixture was stirred at 150 ° C. for 2 hours to dissolve the ethylene polymer. The dropping time (ts) between the marked lines was measured for the solution in a thermostatic bath at 135 ° C. using an Ubbelohde type viscometer. Similarly, three-point solutions were prepared by changing the mass of the ethylene polymer, and the drop time was measured. The fall time (tb) of only decalin not containing an ethylene polymer as a blank was measured.
By plotting the reduced viscosity (ηsp / C) of the polymer determined according to the following formula (1), respectively, a linear expression of the concentration (C) (unit: g / dL) and the reduced viscosity (ηsp / C) of the polymer was derived. The intrinsic viscosity (η) extrapolated to a concentration of 0 was determined.

(Ηsp / C) = (t _s / t _b −1) / C (unit: dL / g) (1)

((2) ΔH _b / ΔH ₂ × 100 and half-value width of exothermic peak)
Measurement was performed using DSC (trade name: DSC8000, manufactured by Perkin Elmer). 8-10 mg of ethylene polymer was inserted into an aluminum pan and placed on the DSC, and then measured under the following measurement conditions (1) to (3).

(1) After holding at 50 ° C. for 1 minute, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.
(2) After holding at 180 ° C. for 5 minutes, the temperature is decreased to 50 ° C. at a temperature decreasing rate of 10 ° C./min.
(3) After holding at 50 ° C. for 5 minutes, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.

Heat of fusion [Delta] H _b of the second heat of fusion [Delta] H ₂ from the range of 60 ° C. of 0.99 ° C. in an endothermic peak obtained in the temperature raising process, the melting point Tm _2, and the high temperature side than the melting point Tm ₂ in [Delta] H ₂ (high region) Was measured to obtain ΔH _b / ΔH ₂ × 100. Moreover, the half width was calculated | required from the exothermic peak obtained in the temperature fall process.

((3) Press sheet density)
An aluminum plate having a thickness of 0.1 mm was placed on a smooth iron plate having a thickness of 5 mm, and a polyethylene terephthalate film having a thickness of 50 μm that was not coated with cellophane (Lumirror manufactured by Toray Industries, Inc.) was placed thereon. A 60 mm long, 60 mm wide, 2 mm thick mold is placed thereon, 8 g of ethylene polymer is placed thereon, the above polyethylene terephthalate film is placed thereon, the above aluminum plate is further placed thereon, and the above iron plate is further placed. I put. This was put into a compression molding machine (SFA-37 manufactured by Shindo Metal Industry Co., Ltd.) whose temperature was adjusted to 200 ° C., preheated at 200 ° C. and 0.1 MPa for 900 seconds, and then vented for 5 seconds (10 MPa). Pressurization was performed at 15 ° C. for 300 seconds. After completion of pressurization, the sample is taken out, and after 5 seconds from taking out, it is put into a compression molding machine (SFA-37 manufactured by Shindo Metal Industries Co., Ltd.) whose temperature is adjusted to 25 ° C., and pressurizing at 25 ° C. and 10 MPa for 600 seconds. Cooling was performed at a cooling rate of 15 ± 2 ° C./min. The cooling rate was adjusted by sandwiching the mold with cardboard. After cooling, the removed press sheet was annealed at 120 ° C. for 1 hour, and the density was measured.

((4) Titanium content contained in ethylene polymer)
0.2 g of ethylene polymer was weighed in a Teflon (registered trademark) decomposition vessel, high-purity nitric acid was added, and after pressure decomposition with Milestone General's microwave decomposition apparatus ETHOS-TC, ultrapure manufactured by Nihon Millipore Pure water purified with a water production apparatus with a total volume of 50 mL was used as a test solution. Using the inductively coupled plasma mass spectrometer (ICP-MS) X series 2 manufactured by Thermo Fisher Scientific, titanium was quantified by the internal standard method for the above test solution.

((5) Chlorine content in ethylene polymer)
The ethylene polymer is burned with an automatic sample combustion device (AQF-100 manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and then absorbed into an absorption liquid (mixed solution of Na ₂ CO ₃ and NaHCO ₃ ), and the absorption liquid is ion chromatographed. The total chlorine amount was measured by injection into a ICS1500, manufactured by Dionex Corporation (column (separation column: AS12A, guard column: AG12A) suppressor ASRS300).

((6) Shrinkage after oil extraction)
A test piece of 100 mm × 100 mm was cut out from the membrane before extracting liquid paraffin, and the shrinkage rate after impregnation with hexane was measured. The shrinkage rate is calculated as (L0−L1) / L0 × 100, where L0 is the diagonal length of the test specimen before extraction and L1 is the diagonal length of the test specimen after extraction. The shrinkage rate after oil extraction was evaluated by the average value of the shrinkage rate obtained from the above. The evaluation criteria are as follows.

◎: Shrinkage rate is less than 2% ○: Shrinkage rate is 2% or more and less than 4% △: Shrinkage rate is 4% or more and less than 5% ×: Shrinkage rate is 5% or more

((7) thickness unevenness)
A test piece of 100 mm × 100 mm was cut out from the microporous membrane, and the thickness of any 10 points was measured at room temperature 23 ° C. using a micro-thickness meter (type KBM (registered trademark)) manufactured by Toyo Seiki. The difference in the thin portion was determined and the thickness unevenness was evaluated. The evaluation criteria are as follows.

◎: The difference between the thickest part and the thin part is 1 μm or less ○: The difference between the thickest part and the thin part exceeds 1 μm and 3 μm or less △: The difference between the thickest part and the thin part exceeds 3 μm and 5 μm or less X: The difference between the thickest part and the thinnest part is 5 μm or more

((8) Oxidation resistance of film)
A dumbbell-shaped test piece was cut out from the microporous membrane, impregnated in dilute sulfuric acid having a specific gravity of 1.5 at 80 ° C. for 80 hours, and the tensile elongation retention before and after the impregnation was measured according to JIS K 7127 under the following conditions. The oxidation resistance was evaluated. The evaluation criteria are as follows.

Apparatus: Tensilon sample made by A & D, Inc. Sample shape: Specimen type 5
Distance between chucks: 80mm
Tensile speed: 300 mm / min

◎: Retention rate of tensile elongation is 90% or more ○: Retention rate of tensile elongation is 80% or more and less than 90% △: Retention rate of tensile elongation is 70% or more and less than 80% ×: Retention rate of tensile elongation is less than 70%

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

◎: Shrinkage rate is less than 3% ○: Shrinkage rate is 3% or more and less than 5% Δ: Shrinkage rate is 5% or more and less than 10% ×: Shrinkage rate is 10% or more

[Example of catalyst synthesis]
The catalysts used in the examples and comparative examples are described below.

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

[Preparation of solid catalyst component [B]]
(1) (B-1) Synthesis of Support As a precursor of the support (B-1), silica having an average particle size of 9.5 μm and a specific surface area of 480 m ² / g was used.
Silica (130 g) after heat treatment was dispersed in 2500 mL of hexane in a nitrogen-substituted 8 L autoclave to obtain a slurry. To the obtained slurry, 195 mL of a hexane solution (concentration 1 M) of triethylaluminum, which is a Lewis acidic compound, was added at 20 ° C. with stirring. Thereafter, the mixture was stirred for 2 hours to react triethylaluminum with the surface hydroxyl group of silica to prepare 2695 mL of hexane slurry of (B-1) carrier on which triethylaluminum was adsorbed.

(Preparation of transition metal compound component [C])
As the transition metal compound (C-1), [(Nt-butylamide) (tetramethyl-η5-cyclopentadienyl) dimethylsilane] titanium-1,3-pentadiene (hereinafter abbreviated as “complex 1”) It was used. Further, as the organomagnesium compound (C-2), a composition formula Mg (C ₂ H ₅ ) (C ₄ H ₉ ) (hereinafter abbreviated as “Mg 1”) was used.
200 mmol of Complex 1 is dissolved in 1000 mL of isoparaffin hydrocarbon (Isopar E manufactured by ExxonMobil), 40 mL of hexane solution of Mg1 (concentration 1M) is added thereto, and further hexane is added to adjust the concentration of complex 1 to 0.1M. As a result, a transition metal compound component [C] was obtained.

(Preparation of activator [D])
As a borate compound (D-1), 17.8 g of bis (hydrogenated tallow alkyl) methylammonium-tetrakis (pentafluorophenyl) borate (hereinafter abbreviated as “borate”) was added to 156 mL of toluene and dissolved, and borate Of 100 mmol / L in toluene was obtained. To this toluene solution of borate, 15.6 mL of a 1 mol / L hexane solution of ethoxydiethylaluminum was added as (D-2) at room temperature, and further toluene was added to adjust the borate concentration in the solution to 70 mmol / L. Then, it stirred at room temperature for 1 hour and prepared activator [D] containing a borate.

(Preparation of solid catalyst [E])
While stirring 2500 mL of the carrier (B-1) obtained by the above operation at 500 rpm at 5 ° C., 219 mL of the activator [D] obtained by the above operation and 175 mL of the transition metal compound component [C] Were added at the same time from a separate line using a metering pump, and the reaction was continued for 30 minutes and then for 3 hours to prepare a solid catalyst [E].

(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.
To a 200 mL flask, 40 mL of hexane and Mg2 and 38.0 mmol of Mg and Al as a total amount were added with stirring. At 20 ° C., methylhydropolysiloxane (viscosity at 25 ° C., 20 centistokes; hereinafter referred to as “siloxane compound”) (Abbreviated) Liquid component [F] was prepared by adding 40 mL of hexane containing 2.27 g (37.8 mmol) with stirring, then raising the temperature to 80 ° C. and reacting with stirring for 3 hours. .

(Preparation of hydrogenation catalyst [G])
37.3 g of titanocene dichloride was introduced in 1 L of hexane into a 2.0 L SUS autoclave equipped with a stirrer substituted with nitrogen. While stirring at 500 rpm, a 0.7 mol / L, 429 mL mixture of triisobutylaluminum and diisobutylaluminum hydride (9: 1) was added at room temperature over 1 hour. 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].

(Preparation of solid catalyst component [H])
<(1) Synthesis of (H-1) Support>
Into an 8 L stainless steel autoclave thoroughly purged with nitrogen, 1,000 mL of a 2 mol / L hydroxytrichlorosilane hexane solution was charged, and stirred at 65 ° C., compositional formula AlMg ₅ (C ₄ H ₉ ) ₁₁ (OC ₄ H ₉ ) 2,550 mL of an organic magnesium compound represented by ₂ (corresponding to 2.68 mol of magnesium) was added dropwise over 4 hours, and the reaction was continued with stirring at 65 ° C. for 1 hour.
After completion of the reaction, the supernatant was removed and washed 4 times with 1,800 mL of hexane to obtain (H-1) carrier.
<(2) Preparation of solid catalyst component [H]>
While stirring at 65 ° C. in 1,970 mL of hexane slurry containing 110 g of the above (H-1) carrier, 110 mL of 1 mol / L titanium tetrachloride hexane solution and 1 mol / L composition formula AlMg ₅ (C ₄ H ₉ ) ₁₁ ( 110 mL of a hexane solution of an organomagnesium compound represented by OC ₄ H ₉ ) ₂ was simultaneously added over 1 hour.
After the addition, the reaction was continued at 65 ° C. for 1 hour.
After 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]
(Method for producing ethylene polymer)
Hexane, ethylene, hydrogen, and catalyst were continuously fed to a vessel type 300 L polymerization reactor equipped with a stirrer under conditions of an average residence time of 2 hours. The polymerization pressure was 0.35 MPa. The polymerization temperature was kept at 75 ° C. by jacket cooling. As the catalyst, a solid catalyst component [A] and triisobutylaluminum as a cocatalyst were used. Triisobutylaluminum was added to the polymerization vessel at a rate of 10 mmol / hr. The solid catalyst component [A] was supplied so that the polymerization rate (production rate) of the ethylene polymer was 10 kg / hr. Hydrogen was continuously supplied by a pump so that the gas phase concentration was 2000 ppm. A 100 mmol / L hexane solution of normal butanol was supplied so that the amount of normal butanol was 1 ppm / hr with respect to a polymerization rate (production rate) of 10 kg / hr to obtain a polymerization slurry. The obtained polymerization slurry was sent to a centrifuge to separate the polymer (polyethylene) from other solvents and the like, and then the polymer was brought into contact with methanol at 60 ° C. with stirring for 1 hour. The polymerization slurry containing the polymer and methanol was sent to a centrifuge, and the polymer and other solvents were separated to obtain an ethylene polymer. The separated ethylene polymer was dried while blowing nitrogen at 70 ° C. A powdery (particulate) ethylene polymer was obtained by removing the ethylene polymer obtained by using a sieve having an opening of 425 μm and removing the ethylene polymer that did not pass through the sieve.
The characteristics of the obtained powdery ethylene polymer were measured by the method described above. The measurement results are shown in Table 1 below.

(Method for producing microporous membrane)
In a 100 mL polycup, 3.7 g of powdery ethylene polymer, 26.6 g of liquid paraffin (P-350 (trademark) manufactured by Matsumura Oil Co., Ltd.), 9.5 g of silica (HiSil 233 manufactured by PPG), 0.02 g of carbon black, An ethylene polymer is contained by adding 0.02 g of pentaerythrityl-tetrakis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as an antioxidant and stirring with a spoon. A mixture (polyethylene mixture) was obtained.

  The obtained polyethylene mixture was charged into a lab plast mill mixer (main body model: 4C150, mixer type: R-60) manufactured by Toyo Seiki Seisakusho, and the number of revolutions was set to 50 rpm and kneaded at 200 ° C. for 10 minutes. The kneaded material was immediately pressurized for 300 seconds at 200 ° C. and 10 MPa using a 250 mm × 250 mm, 0.1 mm thick mold, and cooled for 600 seconds at 25 ° C. and 10 MPa, thereby obtaining a black film.

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

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

[Example 2]
In the polymerization process, instead of the solid catalyst component [A] and triisobutylaluminum, the solid catalyst component [E] was used, the liquid component [F] was supplied at a total amount of Mg and Al of 6 mmol / hr, The pressure was set to 0.8 MPaG. Hydrogen was supplied to the solid catalyst component [E] feed pipe at 2 NL / hr, and the hydrogenated catalyst [G] was separately supplied to the feed pipe at a concentration of 1.1 μmol / L. An ethylene polymer was obtained in the same manner as in Example 1 except that it was supplied so that The microporous membrane was produced in the same manner as in Example 1.

Example 3
In the polymerization step, ethylene was used in the same manner as in Example 1 except that the solid catalyst component [H] was used instead of the solid catalyst component [A], the polymerization temperature was 73 ° C., and no hydrogen was supplied. A polymer was obtained. The microporous membrane was produced in the same manner as in Example 1.

Example 4
In the polymerization step, an ethylene polymer was obtained in the same manner as in Example 2 except that the hydrogenation catalyst [G] was supplied so that the concentration in the reactor was 1.6 μmol / L. The microporous membrane was produced in the same manner as in Example 1.

Example 5
In the polymerization step, the hydrogenation catalyst [G] was supplied so that the concentration in the reactor was 1.8 μmol / L, and 1-butene was supplied so that the concentration in the gas phase was 1.0 mol%. Except for the above, an ethylene polymer was obtained in the same manner as in Example 2. 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 ° C., the polymerization pressure was 0.45 MPa, hydrogen was not supplied, and no contact was made with methanol. It was. The microporous membrane was produced in the same manner as in Example 1.

Example 7
In the polymerization step, ethylene heavy was obtained in the same manner as in Example 2, except that the polymerization temperature was 70 ° C. and the hydrogenation catalyst [G] was supplied so that the concentration in the reactor was 2.4 μmol / L. Coalescence was obtained. The microporous membrane was produced in the same manner as in Example 1.

Example 8
In the polymerization step, instead of using the solid catalyst component [A] as it is, the solid catalyst component [A] was used in a form of being stirred in hexane at 90 ° C. for 1 hour in a nitrogen atmosphere, and the polymerization temperature was changed. Instead of 75 ° C., the temperature was set to 70 ° C., hydrogen was not supplied, and a 100 mmol / L hexane solution of normal butanol was not added into the polymerization system. 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 set to 74 ° C., hydrogen was not 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 ° C., the polymerization pressure was 0.8 MPa, and no normal butanol was added in the polymerization system. . The microporous membrane was produced in the same manner as in Example 1.

[Comparative Example 3]
In the polymerization step, an ethylene polymer was obtained in the same manner as in Example 3 except that the polymerization temperature was changed to 73 ° C. and 75 ° C., and 3000 ppm of hydrogen was supplied. 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 75 ° C., 60 ° C., the polymerization pressure was changed to 0.35 MPa, 0.5 MPa, hydrogen was not supplied, and An ethylene polymer was obtained in the same manner as in Example 1 except that a 100 mmol / L hexane solution of normal butanol was not added. The microporous membrane was produced in the same manner as in Example 1.

  The ethylene polymer of this embodiment can be used for various molded products, and examples of the molded product include high-strength fibers, gel spinning, and microporous membranes. In particular, an ethylene-based polymer is suitably used as a microporous membrane, and this microporous membrane can be used for a secondary battery separator, particularly a lead storage battery separator.

Claims (7)

The intrinsic viscosity (η) is 11 dL / g or more and 28 dL / g or less,
In the DSC curve of the second temperature raising process obtained by the following measurement conditions (1) to (3) using a differential scanning calorimeter (DSC), with respect to the heat of fusion (ΔH ₂ ) of the _second temperature raising process An ethylene polymer having a ratio (ΔH _b / ΔH ₂ × 100) of heat of fusion (ΔH _b ) in a region higher than the melting point (Tm ₂ ) of 18% or more.

(DSC measurement conditions)
(1) After holding at 50 ° C. for 1 minute, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.
(2) After holding at 180 ° C. for 5 minutes, the temperature is decreased to 50 ° C. at a temperature decreasing rate of 10 ° C./min.
(3) After holding at 50 ° C. for 5 minutes, the temperature is raised to 180 ° C. at a temperature rising rate of 10 ° C./min.
2. The ethylene-based polymer according to claim 1, wherein a half-value width of an exothermic peak is 3.0 ° C. or more and 6.0 ° C. or less in a temperature lowering process under the measurement conditions using the DSC. The ethylene polymer according to claim 1 or 2, wherein a press sheet density obtained under 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 under the conditions of 200 ° C. and 0.1 MPa.
(2) Pressurization for 300 seconds under conditions of 200 ° C. and 15 MPa.
(3) Cooling for 600 seconds under conditions of 25 ° C. and 10 MPa.
  The ethylene polymer according to any one of claims 1 to 3, wherein the titanium content is 3 ppm or less in terms of weight with respect to the entire ethylene polymer.   The ethylene polymer according to any one of claims 1 to 4, wherein the chlorine content is 10 ppm or less in terms of weight with respect to the whole ethylene polymer.   The molded object containing the ethylene-type polymer as described in any one of Claim 1 to 5.   The molded article according to claim 6, which is a microporous film.