Polyethylene powder and moldings

Abstract

A polyethylene powder is a polyethylene powder for which the component proportion R and relaxation time T for each component satisfy < condition (1) > and < condition (2) > when the free induction decay curve yielded by the Carr-Purcell-Meiboom-Gill method in pulsed NMR is subjected to three component approximation. < condition (1) > The entanglement index at 180°C given by (formula I) is 12-25 ms. (formula I): (entanglement index) = Tα x Rα / (Rα + Rβ) + Tβ x Rβ / (Rα + Rβ). In the formula I, Tα represents relaxation time for low-mobility component α (ms), Ra represents proportion for low-mobility component α (%), Tβ represents relaxation time for intermediate component β (ms), and Rβ represents proportion for intermediate component β (%). < condition (2) > The intermediate component proportion at 180°C given by (formula II) is 0.25-0.5. (formula II): (intermediate component proportion) = Rβ / (Rα + Rβ)

Description

[Technical field]

[0001] The present invention relates to a polyethylene powder and a molded article. [Background technology]

[0002] Ultra-high molecular weight polyethylene powder is molded by various molding methods such as melt drawing, injection molding, extrusion molding, and compression molding, and is used in a wide variety of applications such as films, sheets, microporous membranes, fibers, foams, and pipes. In recent years, the demand for polyethylene powder has been growing for use in microporous membranes and fibers, and in particular, the demand for it as a raw material for separators, which are important components in lithium-ion batteries, lead-acid batteries, and the like, has been rapidly expanding.

[0003] Since ultra-high molecular weight polyethylene powder has a high viscosity when melted and is poor in moldability, wet extrusion processing is generally used to produce microporous membranes and high-strength fibers by dissolving the powder in a specific solvent and extruding it. If the dispersibility of the polyethylene powder in the solvent during wet extrusion processing is poor, the high molecular weight component is localized in the molded product, causing dimensional unevenness in width and thickness, etc., and generating unmelted material, which leads to deterioration of the physical properties and appearance of the molded product. Therefore, there is a demand for improving the dispersibility of the polyethylene powder in the solvent.

[0004] Furthermore, when a microporous membrane made using the polyethylene powder is used as a battery separator, it is required that the membrane have a function of isolating the positive and negative electrodes to prevent short circuits while allowing only ions to pass through, a shutdown function for preventing runaway battery reactions by melting the pores when a large current flows, thereby blocking ion permeation, i.e., a function for closing the pores at a temperature lower than the temperature at which thermal runaway occurs, i.e., a so-called fuse effect, and high mechanical strength.

[0005] In recent years, the demand for higher capacity and higher output has been rapidly increasing, especially for in-vehicle batteries, and accordingly, separators for batteries are required to have further improved mechanical strength and dimensional stability. Furthermore, as the capacity of electrodes increases, the electrodes expand and contract significantly during charging and discharging, so creep resistance that can withstand long-term stress is becoming more important for battery separators.

[0006] Patent Document 1 discloses a technology for obtaining a film and a microporous membrane having high permeability, small heat shrinkage rate, and excellent mechanical strength and heat resistance by using a polyolefin resin containing an ultra-high molecular weight ethylene polymer having a specific intrinsic viscosity and melting point.

[0007] In addition, Patent Document 2 discloses a technique for obtaining a microporous film having excellent moldability, high air permeability, and excellent mechanical strength by using a polyethylene resin composition made of an ethylene homopolymer having a specific melt flow rate, a specific molecular weight distribution, and a specific elution amount measured by cross fractionation chromatography. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2018-090744 A [Patent Document 2] Patent No. 5840743 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the technology disclosed in Patent Document 1, although the resulting microporous membrane has excellent mechanical strength and dimensional stability, no consideration has been given to improving moldability or creep resistance, and there is a possibility that the mechanical strength may be uneven and that the membrane may not be able to withstand long-term stress caused by expansion and contraction of the electrodes during charge and discharge. In addition, although the technology disclosed in Patent Document 2 achieves both moldability and mechanical strength, there is a problem in that no consideration is given to improving dimensional stability and creep resistance.

[0010] Therefore, an object of the present invention is to provide a polyethylene powder which can achieve both excellent moldability and high mechanical strength and can give a microporous film excellent in dimensional stability and creep resistance. [Means for solving the problem]

[0011] As a result of intensive research by the present inventors to solve the above-mentioned problems, it was found that a polyethylene powder in which the relaxation time T and the component ratio R of each component satisfy a predetermined relationship when a free induction decay curve obtained by the Carr Purcell Meiboom Gill method in pulsed NMR is approximated by three components can solve the above-mentioned problems of the conventional technology, and thus the present invention was completed. That is, the present invention is as follows.

[0012] [1] In pulsed NMR, when a free induction decay curve obtained by the Carr Purcell Meiboom Gill method is approximated as a three-component curve, the relaxation time T of each component and the abundance ratio R of each component satisfy the following <requirement (1)> and <requirement (2)>. Polyethylene powder. <Requirement (1)> At 180°C, the entanglement index calculated by the following formula (I) is: Between 12 ms and 25 ms. (Entanglement Index)=T α ×R α / (R α +R β )+T β ×R β / (R α +R β ) (Formula I) T α : Relaxation time of low-mobility component α (ms) R α: Proportion of low-mobility component α (%) T β : Relaxation time of intermediate component β (ms) R β : Presence ratio of intermediate component β (%) <Requirement (2)> At 180°C, the intermediate component ratio calculated by the following formula (II) is: Between 0.25 and 0.5 inclusive. (Intermediate component ratio) = R β / (R α +R β )...(Formula II) [2] In pulsed NMR, the abundance ratio R of the components obtained by approximating the free induction decay curve obtained by the Carr Purcell Meiboom Gill method using three components is as follows: The polyethylene powder according to [1] above, wherein a rate of change in the abundance ratio of low mobility components at 180°C is -5% or more and 10% or less. [3] In pulsed NMR, the abundance ratio R of the components obtained by approximating the free induction decay curve obtained by the Carr Purcell Meiboom Gill method using three components is as follows: The polyethylene powder according to [1] or [2] above, wherein the rate of change in the proportion of highly mobile components at 180°C is 50% or less. [4] The polyethylene powder according to any one of [1] to [3] above, having an isothermal crystallization time of 5 minutes or less at 125°C. [5] The polyethylene powder according to any one of [1] to [4] above, having a viscosity average molecular weight of 200,000 or more and 10,000,000 or less. [6] The polyethylene powder according to any one of [1] to [5] above, having a median diameter of 50 μm or more and 250 μm or less. [7] The polyethylene powder according to any one of [1] to [6] above, which is for use in a battery separator. [8] A molded body of the polyethylene powder according to any one of [1] to [7] above. [9] The molded article according to [8] above, which is a microporous membrane.

[10] The molded article according to [8] above, which is a fiber.

[11] The molded article according to [8] above, which is a battery separator. Effect of the Invention

[0013] According to the present invention, there is provided a polyethylene powder which can achieve both excellent moldability and high mechanical strength and can give a microporous film having excellent dimensional stability and creep resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention (hereinafter also referred to as "the present embodiment") will be described in detail. It should be noted that the following embodiment is merely an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be implemented in various modifications within the scope of the gist thereof.

[0015] [Polyethylene powder] The polyethylene powder of the present embodiment is characterized in that, when a free induction decay curve obtained by the Carr Purcell Meiboom Gill method in pulse NMR is approximated for three components, the relaxation time T of each component and the abundance ratio R of each component satisfy the following <requirement (1)> and <requirement (2)>. The abundance ratio R (%) is calculated assuming the total of the three components to be 100%. <Requirement (1)> At 180° C., the entanglement index calculated by the following formula I is 12 ms or more and 25 ms or less. (Entanglement Index)=T α ×R α / (R α +R β )+T β ×R β / (Rα +R β ) (Formula I) T α : Relaxation time of low-mobility component α (ms) R α : Proportion of low-mobility component α (%) T β : Relaxation time of intermediate component β (ms) R β : Presence ratio of intermediate component β (%) <Requirement (2)> At 180° C., the ratio of the intermediate component calculated by the following (formula II) is 0.25 or more and 0.5 or less. (Intermediate component ratio) = R β / (R α +R β )...Formula (II) The polyethylene powder of the present embodiment has the above-mentioned configuration, and thus has the effect of enabling both excellent moldability and high mechanical strength to be achieved, and enabling the production of a microporous film having excellent dimensional stability and creep resistance.

[0016] The configuration of the polyethylene powder of this embodiment will be described below. The polyethylene powder of this embodiment (hereinafter, may be simply referred to as "powder") is composed of an ethylene polymer. Ethylene-based polymers include ethylene homopolymers and copolymers (eg, copolymers or terpolymers) of ethylene and other comonomers copolymerizable with ethylene. The bonding form of the copolymer may be random or block. The other comonomer is not particularly limited, but examples thereof include α-olefins, vinyl compounds, etc. The other comonomers may be used alone or in combination of two or more. The α-olefin is not particularly limited, but examples thereof include α-olefins having 3 to 20 carbon atoms, specifically, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, etc. Among these, the other comonomer is preferably propylene and / or 1-butene, from the viewpoint of further improving the heat resistance and strength of the microporous membrane. The vinyl compound is not particularly limited, but examples thereof include vinylcyclohexane, styrene, and derivatives thereof. As other comonomers, non-conjugated polyenes such as 1,5-hexadiene and 1,7-octadiene may be used as necessary.

[0017] (Intertwining index and intermediate component ratio at 180℃) A known index for estimating the entanglement of molecular chains in polyethylene powder is the evaluation of dynamic viscoelasticity. In the evaluation of dynamic viscoelasticity, the degree of entanglement of molecular chains is evaluated from the response when stress is applied to the resin, so it is possible to obtain the average degree of entanglement of molecular chains in the entire resin. However, when multiple physical properties such as mechanical properties and moldability are controlled simultaneously, it is preferable to handle multiple entangled components present in the resin separately, so the average degree of entanglement of molecular chains alone is insufficient as an index. In order to identify a raw material suitable for moldings with well-controlled physical properties such as mechanical properties and moldability, the present inventors accurately evaluated the degree of entanglement of polyethylene powder by using an entanglement index calculated from pulse NMR measurements at 180°C in combination with the proportion of intermediate components, as indicators that can separately evaluate the entanglement components of multiple molecular chains present in a resin. For the pulsed NMR measurements, the Carr Purcell Meiboom Gill method was used, which is a measurement method suitable for evaluating the mobility of polymers with active molecular chain motion, such as polymers in a rubbery state. As a result, it was found that when a free induction decay curve obtained by the Carr Purcell Meiboom Gill method in pulse NMR was approximated with three components, a polyethylene powder in which the relaxation time T and component ratio R of each component simultaneously satisfy the following <requirement (1)> and <requirement (2)> is surprisingly suitable as a raw material for a microporous membrane from the standpoints of mechanical properties and moldability.

[0018] <Requirement (1)> At 180° C., the entanglement index calculated by the following formula I is 12 ms or more and 25 ms or less. (Entanglement Index)=T α ×R α / (R α +R β )+T β ×R β / (R α +R β ) (Formula I) T α : Relaxation time of low-mobility component α (ms) R α : Proportion of low-mobility component α (%) T β : Relaxation time of intermediate component β (ms) R β : Presence ratio of intermediate component β (%) <Requirement (2)> At 180° C., the ratio of the intermediate component calculated by the following formula II is 0.25 or more and 0.5 or less. (Intermediate component ratio) = R β / (R α +R β )...(Formula II)

[0019] The polyethylene powder of this embodiment has an entanglement index at 180° C. calculated by the above formula I in the range of 12 ms or more and 25 ms or less, preferably 13 ms or more and 22 ms or less, and more preferably 14 ms or more and 20 ms or less. When the free induction decay curve of the polyethylene powder of this embodiment obtained by the Carr Purcell Meiboom Gill method in pulse NMR is approximated as a three-component curve, the low mobility component α corresponds to a portion of the polyethylene powder in which the molecular chains are strongly entangled, and is considered to be a component that is likely to remain in the microporous film without being unraveled during the molding process. On the other hand, the intermediate component β in the polyethylene powder of this embodiment corresponds to a portion in which the molecular chains are more weakly entangled than the low mobility component α, and is considered to be a component that is likely to be unraveled during the molding process. Furthermore, the stronger the degree of entanglement of each component, the smaller the value of the relaxation time T.

[0020] When the entanglement index determined by the formula (I) at 180°C is 12 ms or more, the stress remaining after molding is reduced, tending to provide a microporous membrane with excellent dimensional stability. On the other hand, when the entanglement index calculated by formula (I) at 180°C is 25 ms or less, the degree of entanglement of molecular chains in the polyethylene powder is strong, and the microporous film obtained by molding tends to have high mechanical strength and excellent creep resistance.

[0021] In the polyethylene powder of this embodiment, when a free induction decay curve obtained by the Carr Purcell Meiboom Gill method in pulse NMR is approximated with three components, the intermediate component ratio at 180°C calculated by the above (Formula II) is 0.25 or more and 0.5 or less, preferably 0.25 or more and 0.45 or less, and more preferably 0.3 or more and 0.4 or less. When the intermediate component ratio at 180° C. calculated by the above (formula II) is 0.25 or more, the molding processability of the polyethylene powder is improved, and a microporous film with excellent appearance tends to be obtained. On the other hand, when the intermediate component ratio at 180°C is 0.5 or less, an appropriate amount of entanglement points of molecular chains remain in the microporous membrane obtained by molding, which tends to facilitate stress propagation and provide excellent creep resistance.

[0022] Generally, when the degree of entanglement of polymer molecular chains is high, the mechanical strength of the resulting microporous membrane is improved, but the dispersibility of the polymer molecular chains is low, which deteriorates moldability and causes unevenness in thickness, etc. When a microporous membrane has uneven thickness, etc., it has weak mechanical strength in some areas and is likely to become a starting point for deterioration. On the other hand, if the degree of entanglement of the polymer molecular chains is weak, the moldability is good but the mechanical strength is low. In the polyethylene powder of this embodiment, the strength of entanglement of polymer molecular chains is well controlled, and therefore, when a microporous membrane is produced from the powder, it is possible to improve both the mechanical strength and moldability. Furthermore, when a microporous membrane has many entanglement points of polymer molecular chains, it has high mechanical strength and is easy to transmit stress, resulting in excellent creep resistance, but it also has a tendency to have poor dimensional stability due to large residual stress, which can lead to short circuits and degradation when the microporous membrane is used as a battery separator. On the other hand, when the number of entanglement points of polymer molecular chains is small, the dimensional stability is excellent, but sufficient mechanical strength tends not to be exhibited. In addition, since stress is difficult to propagate, localized loads are likely to be applied. Therefore, when the microporous membrane is used as a battery separator, it tends not to be able to withstand the volume change of the electrode due to charging and discharging. In the polyethylene powder of this embodiment, the number of entanglement points of the polymer molecular chains is well controlled, and therefore it is possible for the powder to have excellent dimensional stability, sufficient mechanical strength and creep resistance.

[0023] In order for the entanglement index at 180°C calculated by the above formula (I) and the intermediate component ratio calculated by the above formula (II) to exhibit values ​​within the above-mentioned specified ranges, it is necessary that the degree of entanglement of strongly entangled molecular chains in the polyethylene powder has a certain strength, and that the ratio of weakly entangled molecular chains is high. The polyethylene powder that satisfies these requirements is characterized by including a plurality of polymer components that are entangled in different states. Methods for controlling the entanglement index at 180°C calculated by (Formula I) above and the proportion of the intermediate component calculated by (Formula II) above include changing the state of the catalyst during polyethylene polymerization and mixing a plurality of catalyst components having significantly different polymerization behaviors. Specifically, examples of the method include using a polymerization catalyst containing a carrier having large pores and easily cracked, polymerizing under high pressure conditions in the first half of the polymerization, and then setting the slurry concentration in the polymerization vessel to 40 mass% or more, prepolymerizing a polymerization catalyst containing a carrier having large pores and easily cracked, and then setting the stirring speed in the polymerization vessel to 300 rpm or more, and using a mixture of multiple catalysts having significantly different distributions of active species on the carrier surface.

[0024] By using a carrier having large pores in the synthesis of a polymerization catalyst used in the polymerization reaction of polyethylene, the amount of active species supported in the pores increases, and the polymerization of polyethylene in the pores can be promoted in the polymerization reaction of polyethylene. Furthermore, in the space within the narrow pores, molecular chains of growing polyethylene are likely to cross each other, so it is possible to polymerize components with a high degree of entanglement of molecular chains. On the other hand, if the carrier used in the polymerization catalyst has a fragile structure, the catalyst becomes fragile during polyethylene polymerization due to the increase in pressure within the pores that accompanies the growth of the polyethylene molecular chains. Furthermore, when the catalyst is broken by increasing the stirring strength, the molecular chains of the growing polyethylene are less likely to intertwine, making it possible to polymerize components with weakly entangled molecular chains. Furthermore, by adding a thickener after synthesis of the support and adjusting the pressure difference between the source and destination of the catalyst during transport to be small, it is possible to prevent the catalyst support from cracking before the polymerization step, and multiple polyethylene components with different degrees of entanglement of molecular chains can be produced during polymerization.

[0025] Specifically, the pulse NMR measurement applied to the measurement of the polyethylene powder of this embodiment is carried out by the following method. First, a sample tube filled with polyethylene powder to a height of 1 cm from the bottom is placed in a Bruker TD-NMR device (model: minispec mq20) set so that the internal temperature of the sample tube is 30°C, and the sample tube is heated according to the <heating conditions> shown below. The temperatures shown in the <Heating Conditions> below are values ​​obtained by measuring the internal temperature of the sample with a thermocouple. <Heating conditions> (1) Set the temperature to 30°C and leave it for 5 minutes. (2) Raise the temperature to 180°C at a rate of 5°C / min. (3) Heat to 180°C and leave to stand for 25 minutes. After the temperature rise is completed using the above procedure, the spin-spin relaxation time (T 2 , sometimes simply referred to as "relaxation time T" in this specification, is measured. After the measurement is completed, the same measurement is repeated three times for a total of four measurements. <Measurement conditions> Magnetic field strength: 0.47T Measured nuclides: 1 H(20MHz) Measurement method: Carr Purcell Meiboom Gill method Number of times accumulated: 256 Repeat time: 3 seconds Interval between the first 90° pulse and the 180° pulse (τ): 0.04 ms Total number of echo signals: 6400

[0026] Of the total four measurements described above, the free induction decay (FID) obtained in the fourth measurement is subjected to curve fitting using the analysis program TD-NMR-A manufactured by Bruker. For fitting, the function shown in the following Equation 1 is used. <Expression 1> f(t)=R α exp(-t / T α )+R β exp(-t / T β )+R γ exp(-t / T γ ) (However, R α +R β +R γ = 100) t: variable (time elapsed since pulse irradiation) T α : Relaxation time of low-mobility component α (ms) R α : Proportion of low-mobility component α (%) T β : Relaxation time of intermediate component β (ms) R β : Presence ratio of intermediate component β (%) T γ : Relaxation time of the high-mobility component gamma (ms) R γ : Proportion of highly mobile component γ (%)

[0027] Finally, the entanglement index and the intermediate component ratio are calculated from the relaxation time T and the abundance ratio R obtained by curve fitting of the free induction decay, using the following (Equation I) and (Equation II). (Entanglement Index)=T α ×R α / (R α +R β )+T β ×R β / (R α +R β ) (Formula I) (Intermediate component ratio) = R β / (R α +R β ) (Formula II)

[0028] In general, for polymers in a rubbery state where the molecular chains are actively moving, the free induction decay obtained by pulsed NMR measurement can be expressed by an exponential function. Therefore, in this measurement, the free induction decay obtained can be fitted as the sum of three different components expressed by exponential functions, as shown in the above <Equation 1>. The decay rate of free induction decay is 1 It is known that the higher the mobility of H, i.e., the higher the mobility of the molecular chain, the slower the rate. The relaxation time T in each exponential function is T α <Tβ <T γ Based on this relationship, the component with the lowest mobility was designated α, the component with intermediate mobility β, and the component with the highest mobility γ. Furthermore, component α corresponds to a portion of the polyethylene powder in which the molecular chains are strongly entangled, component β corresponds to a portion in which the molecular chains are weakly entangled, and component γ corresponds to a portion in which the molecular chains are not entangled. More specifically, the entanglement index and the intermediate component ratio at 180° C. in this embodiment can be measured by the method described in the Examples.

[0029] (Change in the proportion of low-mobility components at 180°C) In the polyethylene powder of this embodiment, the range of the rate of change in the abundance ratio of the low mobility component α at 180°C with respect to the abundance ratio R of components calculated by three-component approximation of a free induction decay curve obtained by the Carr Purcell Meiboom Gill method in pulse NMR is preferably −5% or more and 10% or less, more preferably −2% or more and 8% or less, and even more preferably 0% or more and 6% or less.

[0030] The rate of change in the abundance ratio of low mobility components at 180° C. in the polyethylene powder of this embodiment is determined by the following method. When determining the above (entanglement index and intermediate component ratio at 180°C), curve fitting is performed using the analysis program TD-NMR-A manufactured by Bruker Corp. for the free induction decay (FID) obtained from the first and fourth measurements among the pulse NMR measurements specifically shown above. The function shown in the above <Formula 1> is used for fitting. From the abundance ratio R obtained by fitting, the rate of change (%) of the abundance ratio of low mobility components is calculated according to the following (Equation III). (Rate of change in the proportion of low-mobility components) = ((R α4 -R α1 ) / R α1 )×100...(Formula III) R α1: The proportion of low-mobility component α in the first measurement R α4 : The proportion of low-mobility component α in the fourth measurement

[0031] This rate of change exhibits a negative value when the molecular chains of a component having strong entanglements are disentangled under heating conditions, and exhibits a positive value when the molecular chains of a component having weak entanglements become strongly entangled. By setting the rate of change in the abundance ratio of the low mobility components to -5% or more, strongly entangled components are more likely to remain even after molding, and a microporous membrane with better mechanical strength and creep resistance can be obtained. On the other hand, by setting the rate of change in the abundance ratio of the low mobility components to 10% or less, the proportion of weakly entangled molecular chains and non-entangled molecular chains can be maintained at a certain level or higher, and molding processability tends to be excellent. The rate of change in the abundance ratio of low mobility components in the polyethylene powder of this embodiment at 180° C. can be specifically measured by the method described in the Examples. The rate of change in the proportion of low mobility components in the polyethylene powder of this embodiment at 180°C can be controlled within the above numerical range by adjusting the concentration and temperature during synthesis of the catalyst support to a certain value or higher.

[0032] (Change in the proportion of highly mobile components at 180℃) In the polyethylene powder of this embodiment, the range of the rate of change of the abundance ratio of highly mobile components at 180° C. in terms of the abundance ratio R of components calculated by three-component approximation of a free induction decay curve obtained by the Carr Purcell Meiboom Gill method in pulse NMR is preferably 50% or less, more preferably 10% or less, and even more preferably 5% or less. The lower limit is not particularly limited, and is usually 0% or more.

[0033] The rate of change in the abundance ratio of the highly mobile component in the polyethylene powder of the present embodiment is determined by the following method. When determining the above-mentioned (entanglement index and intermediate component ratio at 180°C), curve fitting is performed using the analysis program TD-NMR-A manufactured by Bruker Corporation for the free induction decay (FID) obtained from the first and fourth measurements among the pulse NMR measurements specifically shown above. The fitting uses the function shown in Equation 1 above. From the abundance ratio R obtained by fitting, the rate of change (%) of the highly mobile component is calculated as shown in the following (Formula IV). (Rate of change in the proportion of highly mobile components) = ((R γ4 -R γ1 ) / R γ1 )×100...(Formula IV) R γ1 : The proportion of highly mobile components γ in the first measurement R γ4 : The proportion of high-mobility component γ in the fourth measurement This rate of change becomes larger as the molecular chains become more entangled under heating conditions. By keeping the rate of change in the proportion of the above-mentioned highly mobile components to 50% or less, components having entangled molecular chains are more likely to remain even after molding, making it possible to obtain a microporous membrane with superior mechanical strength and creep resistance. The rate of change in the abundance ratio of highly mobile components in the polyethylene powder of this embodiment at 180° C. can be specifically measured by the method described in the Examples. The rate of change in the proportion of highly mobile components in the polyethylene powder of this embodiment at 180° C. can be controlled within the above numerical range by, for example, adjusting the slurry concentration and stirring speed during polymerization within appropriate ranges.

[0034] (Isothermal crystallization time at 125°C) The polyethylene powder of the present embodiment has an isothermal crystallization time of preferably 5 minutes or less, more preferably 4.5 minutes or less, and even more preferably 4 minutes or less. The lower limit of the isothermal crystallization time is not particularly limited, and is usually 0 minute or more.

[0035] The isothermal crystallization time at 125° C. of the polyethylene powder of this embodiment is determined by the following method using a differential scanning calorimeter (DSC). First, place the aluminum pan containing the polyethylene powder in a heating furnace and heat it according to the <temperature increase and decrease conditions> shown below. Note that the heating operation must be carried out in a nitrogen atmosphere. <Temperature rise and fall conditions> (1) Hold at 50°C for 1 minute. (2) Raise the temperature to 180°C at a rate of 200°C / min. (3) Hold at 180°C for 5 minutes. (4) The temperature is decreased to 125°C at a rate of 80°C / min. The time when the temperature reached 125°C was taken as the starting point (0 min), and the time when the top of the exothermic peak due to crystallization was obtained was taken as the isothermal crystallization time at 125°C. By setting the above-mentioned isothermal crystallization time at 125°C to 5 minutes or less, components having entangled molecular chains tend to be uniformly present in the molded body, which facilitates stress propagation and allows for the production of a microporous membrane with superior creep resistance.

[0036] Methods for controlling the isothermal crystallization time at 125°C of the polyethylene powder of this embodiment include a method in which active sites are uniformly supported on a catalyst support used in the polymerization step of the polyethylene powder, and a method in which the temperature in a polymerization reactor is uniformly adjusted. The isothermal crystallization time at 125° C. of the polyethylene powder of this embodiment can be measured specifically by the method described in the Examples.

[0037] (Viscosity average molecular weight (Mv)) The viscosity average molecular weight (Mv) of the polyethylene powder of this embodiment is preferably 200,000 or more and 10,000,000 or less, more preferably 250,000 or more and 3,000,000 or less, and even more preferably 300,000 or more and 2,000,000 or less. The viscosity average molecular weight (Mv) of the polyethylene powder can be controlled within the above numerical range by appropriately adjusting the polymerization conditions, which will be described later. Specifically, the viscosity average molecular weight (Mv) can be controlled within the above numerical range by making hydrogen present as a chain transfer agent in the polymerization system or by changing the polymerization temperature.

[0038] The polyethylene powder of this embodiment has a viscosity average molecular weight (Mv) of 200,000 or more, and therefore the microporous film containing the polyethylene powder of this embodiment has sufficient mechanical strength. On the other hand, since the viscosity average molecular weight (Mv) is 10,000,000 or less, the polyethylene powder of this embodiment tends to have excellent moldability, such as dispersibility in a solvent and extensibility, and therefore a microporous film formed using the polyethylene powder of this embodiment has less unevenness in thickness and less unmelted material, is less susceptible to deterioration, and has an excellent appearance. The viscosity average molecular weight (Mv) of the polyethylene powder of this embodiment can be calculated from the intrinsic viscosity [η] (dL / g) determined in accordance with ISO1628-3 (2010) by the following formula. More specifically, it can be measured by the method described in the Examples. Mv = (5.34 × 10 4 )×[η] 1.49

[0039] (Median diameter) The polyethylene powder of the present embodiment has a median diameter in the range of preferably 50 μm or more and 250 μm or less, more preferably 60 μm or more and 200 μm or less, and even more preferably 70 μm or more and 150 μm or less. The median diameter of the polyethylene powder of this embodiment is the particle diameter (D50) at which the cumulative mass is 50%. When the above-mentioned median diameter is 50 μm or more, the polyethylene powder becomes easier to handle (improved fluidity, suppression of dust, etc.) in the manufacturing process and the extrusion processing process. On the other hand, by having a median diameter of 250 μm or less, the plasticizer can be easily impregnated into the polyethylene powder, and molding processability tends to improve. Methods for controlling the median diameter of the polyethylene powder of the present embodiment within the above-mentioned numerical range include, for example, a method for controlling the particle diameter of the polymerization catalyst and a method for adjusting the polymerization conditions described below so as to suppress the rapid progress of the polymerization reaction (hereinafter, sometimes referred to as rapid polymerization). Specifically, the median diameter of the polyethylene powder of the present embodiment can be measured by the method described in the examples described below.

[0040] [Method for producing polyethylene powder] The method for producing the polyethylene powder of this embodiment will be described below. (Catalyst Component) The catalyst component used in the production of the ethylene polymer constituting the polyethylene powder of the present embodiment is not particularly limited, and a Ziegler-Natta catalyst or a metallocene catalyst produced by the method described in Japanese Patent No. 5782558 or Japanese Patent Laid-Open No. 2019-19265 can be used. In particular, it is preferable to use a Ziegler-Natta catalyst.

[0041] The Ziegler-Natta catalyst used in the production of the polyethylene powder of this embodiment is, for example, preferably an olefin polymerization catalyst comprising a solid catalyst component [A] and an organometallic compound component [B], the solid catalyst component [A] being produced by supporting an organomagnesium compound (A-4) soluble in an inert hydrocarbon solvent represented by the following formula (iii) and a titanium compound (A-5) represented by the following formula (iv) on a support (A-3) prepared by reacting an organomagnesium compound (A-1) soluble in an inert hydrocarbon solvent represented by the following formula (i) with a chlorinating agent (A-2) represented by the following formula (ii).

[0042] (A-1):(M 1 ) γ (Mg) δ (R 1 ) e (R2 ) f (OR 3 ) g (Eq. i) (In formula i, M 1 is a metal atom selected from the group consisting of Groups 12, 13, and 14 of the periodic table; R 1 , R 2 and R 3 are hydrocarbon groups having 2 to 20 carbon atoms, and γ, δ, e, f, and g are real numbers satisfying the following relationship: 0≦γ, 0<δ, 0≦e, 0≦f, 0≦g, 0 <e+f、0≦g / (γ+δ)≦2、kγ+2δ=e+f+g(ここで、kはM 1 Represents the valence of .

[0043] (A-2):H h SiCl i R 4 (4-(h+i)) ...(Formula ii) (In formula ii, R 4 is a hydrocarbon group having 1 to 12 carbon atoms, and h and i are real numbers that satisfy the following relationship: 0 <h、0<i、0<h+i≦4)

[0044] (A-4):(M 2 ) α (Mg) β (R 4 ) a (R 5 ) b Y 1 c ...(Formula iii) (In formula iii, M 2 is a metal atom selected from the group consisting of Groups 12, 13, and 14 of the periodic table; R 4 and R 5 is a hydrocarbon group having 2 to 20 carbon atoms, and Y 1 is alkoxy, siloxy, aryloxy, amino, amido, -N=CR 6 , R 7 , -SR 8 (where R 6 , R 7 and R 8represents a hydrocarbon group having 1 to 20 carbon atoms. When c is 2, Y 1 may be different from each other.) and a β-keto acid residue, and α, β, a, b, and c are real numbers that satisfy the following relationship: 0≦α, 0<β, 0≦a, 0≦b, 0≦c, 0 <a+b、0≦c / (α+β)≦2、nα+2β=a+b+c(ここで、nはM 2 Represents the valence of .

[0045] (A-5): Ti(OR 9 ) d X 1 (4-d) ...(Formula iv) (In formula iv, d is a real number between 0 and 4, and R 9 is a hydrocarbon group having 1 to 20 carbon atoms, and X 1 is a halogen atom.)

[0046] First, the organomagnesium compound (A-1) will be described. The organomagnesium compound (A-1) is shown in the form of an organomagnesium complex compound soluble in an inert hydrocarbon solvent, but includes all dihydrocarbylmagnesium compounds and complexes of these compounds with other metal compounds. The above-mentioned relational formula kγ+2δ=e+f+g of the symbols γ, δ, e, f and g in the above formula (i) indicates the stoichiometry of the valence of the metal atom and the substituent.

[0047] In the above formula (i), R 1 , R 2 The hydrocarbon group represented by the formula (I) is not particularly limited, but for example, each independently represents an alkyl group, a cycloalkyl group, or an aryl group, and examples thereof include methyl, ethyl, propyl, butyl, propyl, hexyl, octyl, decyl, cyclohexyl, and phenyl groups. Among these, R 1 and R 2 is preferably an alkyl group. When γ>0, the metal atom M 1As the metal atom, any of the metal atoms belonging to the group consisting of Groups 12, 13, and 14 of the periodic table can be used, and examples thereof include zinc, boron, aluminum, etc. Aluminum and zinc are particularly preferred.

[0048] metal atom M 1 The ratio δ / γ of magnesium to γ ​​is not particularly limited, but is preferably 0.1 or more and 30 or less, and more preferably 0.5 or more and 10 or less. In addition, when a specific organomagnesium compound with γ=0 is used as (A-1), for example, R 1 When the group is a 1-methylpropyl group, the compound is soluble in an inert hydrocarbon solvent, and such a compound also gives favorable results in the production of the polyethylene powder of this embodiment. In the above formula (i), the hydrocarbon group R 1 , R 2 is preferably any one of the following three groups: (1), (2), and (3).

[0049] Group (1): R 1 , R 2 At least one of R is a secondary or tertiary alkyl group having 4 to 6 carbon atoms. 1 , R 2 each of which has 4 to 6 carbon atoms, and at least one of which is a secondary or tertiary alkyl group.

[0050] Group (2): R 1 and R 2 and R are alkyl groups having different carbon numbers. 1 is an alkyl group having 2 or 3 carbon atoms, and R 2 is an alkyl group having 4 or more carbon atoms.

[0051] Group (3): R 1 , R 2 At least one of R is a hydrocarbon group having 6 or more carbon atoms. 1 , R 2It is an alkyl group whose total number of carbon atoms is 12 or more.

[0052] Hereinafter, in the above formula (i), the hydrocarbon group R 1 , R 2 The following is a concrete example. In group (1), examples of the secondary or tertiary alkyl group having 4 to 6 carbon atoms include 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, 2-methylbutyl, 2-ethylpropyl, 2,2-dimethylpropyl, 2-methylpentyl, 2-ethylbutyl, 2,2-dimethylbutyl, 2-methyl-2-ethylpropyl, etc. In particular, the 1-methylpropyl group is preferred.

[0053] In addition, examples of the alkyl group having 2 or 3 carbon atoms in group (2) include ethyl, 1-methylethyl, and propyl groups. An ethyl group is particularly preferred. The alkyl group having 4 or more carbon atoms is not particularly limited, but examples thereof include butyl, pentyl, hexyl, heptyl, and octyl groups. In particular, butyl and hexyl groups are preferred.

[0054] Furthermore, in group (3), the hydrocarbon group having 6 or more carbon atoms is not particularly limited, but examples thereof include hexyl, heptyl, octyl, nonyl, decyl, phenyl, 2-naphthyl groups, etc. Among the hydrocarbon groups, alkyl groups are preferred, and among the alkyl groups, hexyl and octyl groups are more preferred.

[0055] In general, as the number of carbon atoms contained in the alkyl group increases, the compound tends to be more soluble in an inert hydrocarbon solvent, and the viscosity of the solution tends to increase. 1 , R 2For ease of handling, it is preferable to use an alkyl group having a suitable length as the alkyl group. The organomagnesium compound (A-1) is used as an inert hydrocarbon solution, and it is acceptable for the solution to contain or remain a trace amount of Lewis base compounds such as ethers, esters, and amines.

[0056] Next, the alkoxy group (OR 3 ) will be explained. R 3 The hydrocarbon group represented by the formula (I) is preferably an alkyl group or aryl group having 1 to 12 carbon atoms, and more preferably an alkyl group or aryl group having 3 to 10 carbon atoms. R 3 Examples of the aryl group include, but are not limited to, methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 1,1-dimethylethyl, pentyl, hexyl, 2-methylpentyl, 2-ethylbutyl, 2-ethylpentyl, 2-ethylhexyl, 2-ethyl-4-methylpentyl, 2-propylheptyl, 2-ethyl-5-methyloctyl, octyl, nonyl, decyl, phenyl, and naphthyl groups. In particular, butyl, 1-methylpropyl, 2-methylpentyl, and 2-ethylhexyl groups are more preferred.

[0057] The method for synthesizing the organomagnesium compound (A-1) is not particularly limited. For example, the organomagnesium compound (A-1) represented by the formula: 1 MgX 1 and the formula: R 1 2 Mg(R 1 is as mentioned above, and X 1 is a halogen atom.) and an organomagnesium compound of the formula: M 1 R 2 k and formula: M 1 R 2 (k-1) H(M 1 , R 2and k are as defined above.) in an inert hydrocarbon solvent at a temperature of 25° C. to 150° C., and if necessary, subsequently R 2 (R 2 is as described above.) R soluble in an alcohol having a hydrocarbon group represented by 2 and / or an alkoxyaluminum compound having a hydrocarbon group represented by the following formula (I):

[0058] Among the above-mentioned methods, when an organomagnesium compound soluble in an inert hydrocarbon solvent is reacted with an alcohol, there is no particular restriction on the order of the reaction, and any of the following methods can be used: a method in which the alcohol is added to the organomagnesium compound, a method in which the organomagnesium compound is added to the alcohol, or a method in which both are added simultaneously. The reaction ratio of an organomagnesium compound soluble in an inert hydrocarbon solvent and an alcohol is not particularly limited, but the molar composition ratio of alkoxy groups to all metal atoms in the alkoxy group-containing organomagnesium compound obtained as a result of the reaction: g / (γ+δ) is 0≦g / (γ+δ)≦2, and preferably 0≦g / (γ+δ)<1.

[0059] Next, the chlorinating agent (A-2) will be described. The chlorinating agent (A-2) is a silicon chloride compound having at least one Si-H bond, represented by formula (ii). (A-2):H h SiCl i R 4 (4-(h+i)) ...(Formula ii) (In formula ii, R 4 is a hydrocarbon group having 1 to 12 carbon atoms, and h and i are real numbers that satisfy the following relationship: 0 <h、0<i、0<h+i≦4)

[0060] In the above formula (ii), R 4The hydrocarbon group represented by the formula (I) is not particularly limited, but examples thereof include aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups, and specific examples thereof include methyl, ethyl, propyl, 1-methylethyl, butyl, pentyl, hexyl, octyl, decyl, cyclohexyl, and phenyl groups. In particular, alkyl groups having 1 to 10 carbon atoms are preferred, and alkyl groups having 1 to 3 carbon atoms such as methyl, ethyl, propyl, and 1-methylethyl are more preferred. Furthermore, h and i are numbers greater than 0 that satisfy the relationship h+i≦4, and it is preferred that i is 2 or more and 3 or less.

[0061] The chlorinating agent (A-2) is not particularly limited, but may be, for example, HSiCl 3 , HSiCl 2 CH 3 , HSiCl 2 C 2 H 5 , HSiCl 2 (C 3 H 7 ), HSiCl 2 (2-C 3 H 7 ), HSiCl 2 (C 4 H 9 ), HSiCl 2 (C 6 H 5 ), HSiCl 2 (4-Cl-C 6 H 4 ), HSiCl 2 (CH=CH 2 ), HSiCl 2 (CH 2 C 6 H 5 ), HSiCl 2 (1-C 10 H 7 ), HSiCl 2 (CH 2 CH=CH 2 ), H 2 SiCl(CH 3 ), H 2 SiCl(C 2 H 5 ), HSiCl(CH 3) 2 , HSiCl(C 2 H 5 ) 2 , HSiCl(CH 3 )(2-C 3 H 7 ), HSiCl(CH 3 )(C 6 H 5 ), HSiCl(C 6 H 5 ) 2 etc. As the chlorinating agent (A-2), silicon chloride compounds consisting of these compounds or mixtures of two or more kinds selected from these compounds are used. In particular, HSiCl 3 , HSiCl 2 CH 3 , HSiCl(CH 3 ) 2 , HSiCl 2 (C 3 H 7 ) is preferred, and HSiCl 3 , HSiCl 2 CH 3 is more preferred.

[0062] Next, the reaction between the organomagnesium compound (A-1) and the chlorinating agent (A-2) will be described. In the reaction, it is preferable to dilute the chlorinating agent (A-2) in advance with an inert hydrocarbon solvent, chlorinated hydrocarbons such as 1,2-dichloroethane, o-dichlorobenzene, dichloromethane, etc., ether solvents such as diethyl ether, tetrahydrofuran, etc., or a mixture of these solvents. Among these, it is more preferable to use an inert hydrocarbon solvent in terms of catalyst performance. The reaction ratio of the organomagnesium compound (A-1) and the chlorinating agent (A-2) is not particularly limited, but the number of moles of silicon atoms contained in (A-2) per mole of magnesium atoms contained in (A-1) is preferably 0.01 mol or more and 100 mol or less, and more preferably 0.1 mol or more and 10 mol or less.

[0063] There is no particular limitation on the method for reacting the organomagnesium compound (A-1) with the chlorinating agent (A-2), and any of the following methods can be used: a simultaneous addition method in which (A-1) and (A-2) are simultaneously introduced into a reactor and reacted; a method in which (A-2) is previously charged into a reactor and then (A-1) is introduced into the reactor; or a method in which (A-1) is previously charged into a reactor and then (A-2) is introduced into the reactor. In particular, a method in which (A-2) is charged in advance into a reactor and then (A-1) is introduced into the reactor is preferred.

[0064] The carrier (A-3) obtained by the above reaction is preferably separated by filtration or decantation, and then thoroughly washed with an inert hydrocarbon solvent to remove unreacted materials or by-products.

[0065] The reaction temperature between the organomagnesium compound (A-1) and the chlorinating agent (A-2) is not particularly limited, but from the viewpoint of enlarging the pores of the support (A-3) and making it easier to crack, it is preferably from 75°C to 150°C, more preferably from 80°C to 120°C, and even more preferably from 80°C to 100°C. In the simultaneous addition method in which (A-1) and (A-2) are simultaneously introduced into a reactor and reacted, it is preferable to adjust the temperature of the reactor to a predetermined temperature in advance and to adjust the temperature inside the reactor to the predetermined temperature while performing the simultaneous addition. In the method of previously charging (A-2) into a reactor and then introducing (A-1) into the reactor, it is preferable to adjust the temperature of the reactor charged with the chlorinating agent (A-2) to a predetermined temperature, and to adjust the temperature inside the reactor to the predetermined temperature while introducing the organomagnesium compound (A-1) into the reactor. In the method of previously charging (A-1) into a reactor and then introducing (A-2) into the reactor, it is preferable to adjust the temperature of the reactor into which (A-1) has been charged to a predetermined temperature, and to adjust the temperature inside the reactor to the predetermined temperature while introducing (A-2) into the reactor.

[0066] The concentration of (A-1) (magnesium concentration) in the reaction system of the organomagnesium compound (A-1) and the chlorinating agent (A-2) is not particularly limited, but from the viewpoint of enlarging the pores of the support (A-3) and making it easier to break, it is preferably 0.8 mol / L or more and 2.5 mol / L or less, and more preferably 1.0 mol / L or more and 2.0 mol / L or less.

[0067] Next, the organomagnesium compound (A-4) will be described. As (A-4), the one represented by the above formula (iii) is preferable. (A-4):(M 2 ) α (Mg) β (R 4 ) a (R 5 ) b Y 1 c ...(Formula iii) (In formula iii, M 2 is a metal atom selected from the group consisting of Groups 12, 13, and 14 of the periodic table; R 4 and R 5 is a hydrocarbon group having 2 to 20 carbon atoms, and Y 1 is alkoxy, siloxy, aryloxy, amino, amido, -N=CR 6 ,R 7 , -SR 8 (where R 6 , R 7 and R 8 represents a hydrocarbon group having 1 to 20 carbon atoms. When c is 2, Y 1 may be different from each other.) and a β-keto acid residue, and α, β, a, b, and c are real numbers that satisfy the following relationship: 0≦α, 0<β, 0≦a, 0≦b, 0≦c, 0 <a+b、0≦c / (α+β)≦2、nα+2β=a+b+c(ここで、nはM 2 Represents the valence of .

[0068] The amount of the organomagnesium compound (A-4) used is preferably such that the molar ratio of magnesium atoms contained in the organomagnesium compound (A-4) to titanium atoms contained in the titanium compound (A-5), Mg / Ti, is 0.1 or more and 10 or less, more preferably 0.5 or more and 5 or less. The temperature for the reaction of the organomagnesium compound (A-4) with the titanium compound (A-5) is not particularly limited, but is preferably from -80°C to 150°C, more preferably from -40°C to 100°C. The concentration of the organomagnesium compound (A-4) when used is not particularly limited, but is preferably 0.1 mol / L or more and 2 mol / L or less, more preferably 0.5 mol / L or more and 1.5 mol / L or less, based on the magnesium atoms contained in the organomagnesium compound (A-4). It is preferable to use an inert hydrocarbon solvent to dilute the organomagnesium compound (A-4).

[0069] Next, the titanium compound (A-5) will be described. As described above, the titanium compound (A-5) is a titanium compound represented by the following formula iv. (A-5): Ti(OR 9 ) d X 1 (4-d) ...(Formula iv) (In formula iv, d is a real number between 0 and 4, and R 9 is a hydrocarbon group having 1 to 20 carbon atoms, and X 1 is a halogen atom.)

[0070] In the above formula (iv), d is preferably 0 or more and 1 or less, and d is more preferably 0. In formula (iv), R 9The hydrocarbon group represented by the formula (I) is not particularly limited, but examples thereof include aliphatic hydrocarbon groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, 2-ethylhexyl, heptyl, octyl, decyl, and allyl groups; alicyclic hydrocarbon groups such as cyclohexyl, 2-methylcyclohexyl, and cyclopentyl groups; and aromatic hydrocarbon groups such as phenyl and naphthyl groups. Aliphatic hydrocarbon groups are particularly preferred. X 1 The halogen represented by the formula (I) is not particularly limited, but examples thereof include chlorine, bromine, and iodine. Chlorine is particularly preferred. The titanium compound (A-5) may be used alone or in combination of two or more kinds.

[0071] The amount of the titanium compound (A-5) used is not particularly limited, but from the viewpoint of increasing the amount supported in the pores of the support, the molar ratio of titanium to magnesium atoms (Ti / Mg) contained in the support (A-3) is preferably 0.15 or more and 20 or less, more preferably 0.2 or more and 10 or less. The reaction temperature of the titanium compound (A-5) is not particularly limited, but is preferably from -80°C to 150°C, and more preferably from -40°C to 100°C.

[0072] The method of supporting the titanium compound (A-5) on the carrier (A-3) is not particularly limited, and may be a method of reacting an excess of the titanium compound (A-5) with the carrier (A-3), or a method of efficiently supporting the titanium compound (A-5) by using a third component. In particular, the method of supporting the titanium compound (A-5) on the carrier (A-3) by reacting the titanium compound (A-5) with an organomagnesium compound (A-4) is preferred. There is no particular restriction on the order of addition of the organomagnesium compound (A-4) and the titanium compound (A-5) to the support (A-3). Any of the following methods may be used: adding the organomagnesium compound (A-4) followed by the titanium compound (A-5), adding the titanium compound (A-5) followed by the organomagnesium compound (A-4), or adding the organomagnesium compound (A-4) and the titanium compound (A-5) simultaneously. In particular, the method of adding the organomagnesium compound (A-4) and the titanium compound (A-5) simultaneously is preferred. The reaction between the organomagnesium compound (A-4) and the titanium compound (A-5) is carried out in an inert hydrocarbon solvent, preferably an aliphatic hydrocarbon solvent such as hexane or heptane. The catalyst obtained as described above is used as a slurry solution using an inert hydrocarbon solvent. When transferring the slurry solution, it is preferable to add a thickener or control the pressure difference between the source and destination to be small, from the viewpoint of preventing the obtained catalyst from cracking before the polymerization step. The thickener is not particularly limited, but from the viewpoint of maintaining the performance of the catalyst, saturated hydrocarbons are preferred, and specific examples thereof include liquid paraffin and polyolefin wax. The pressure difference between the source and destination is not particularly limited, but is preferably 0.1 MPa or more and 0.5 MPa or less, and more preferably 0.1 MPa or more and 0.3 MPa or less.

[0073] Next, the organometallic compound component [B] used as a catalyst component in the polymerization of the polyethylene powder of this embodiment will be described. The catalyst used in the polymerization of the polyethylene powder of this embodiment becomes a highly active solid catalyst for polymerization by combining the above-mentioned solid catalyst component [A] and organometallic compound component [B]. The organometallic compound component [B] is sometimes called the "cocatalyst." The organometallic compound component [B] is preferably a compound containing any metal belonging to the group consisting of Groups 1, 2, 12 and 13 of the periodic table, and is particularly preferably an organoaluminum compound and / or an organomagnesium compound. As the organoaluminum compound, it is preferable to use a compound represented by the following formula (v) alone or in combination. AlR 10 j Z 1 (3-j) ...(formula v) (In formula v, R 10 is a hydrocarbon group having 1 to 20 carbon atoms, Z 1 is any group belonging to the group consisting of hydrogen, halogen, alkoxy, aryloxy, and siloxy groups, and j is a number between 2 and 3.

[0074] In the above formula (v), R 10 The hydrocarbon group having 1 to 20 carbon atoms represented by the formula (I) is not particularly limited, but examples thereof include aliphatic hydrocarbons, aromatic hydrocarbons, and alicyclic hydrocarbons. Specific examples thereof preferably include trialkylaluminum such as trimethylaluminum, triethylaluminum, tripropylaluminum, tributylaluminum, tri(2-methylpropyl)aluminum (or triisobutylaluminum), tripentylaluminum, tri(3-methylbutyl)aluminum, trihexylaluminum, trioctylaluminum, and tridecylaluminum; halogenated aluminum compounds such as diethylaluminum chloride, ethylaluminum dichloride, bis(2-methylpropyl)aluminum chloride, ethylaluminum sesquichloride, and diethylaluminum bromide; alkoxyaluminum compounds such as diethylaluminum ethoxide and bis(2-methylpropyl)aluminum butoxide; siloxyaluminum compounds such as dimethylhydrosiloxyaluminum dimethyl, ethylmethylhydrosiloxyaluminum diethyl, and ethyldimethylsiloxyaluminum diethyl; and mixtures thereof. In particular, trialkylaluminum compounds are more preferred.

[0075] The organomagnesium compound is preferably an organomagnesium compound soluble in an inert hydrocarbon solvent, as represented by the above formula (i). In the formula (i), γ, δ, e, f, g, and M 1 , R 1 , R 2 , OR 3As already mentioned above, it is preferable that the organomagnesium compound has high solubility in an inert hydrocarbon solvent, so that β / α is preferably in the range of 0.5 to 10. 1 More preferred are compounds in which is aluminum.

[0076] There is no particular limitation on the method for adding the solid catalyst component [A] and the organometallic compound component [B] to a polymerization system under polymerization conditions. They may be added separately to the polymerization system, or they may be reacted in advance and then added to the polymerization system. The ratio of the two to be combined is not particularly limited, but it is preferable that the organometallic compound component [B] is 1 mmol or more and 3000 mmol or less per 1 g of the solid catalyst component [A].

[0077] (Polymerization method for ethylene-based polymer) Examples of a polymerization method for the ethylene polymer constituting the polyethylene powder of the present embodiment include a method in which ethylene is polymerized or ethylene is copolymerized with a comonomer by a suspension polymerization method or a gas phase polymerization method. Among these, the suspension polymerization method is preferred because it is capable of efficiently removing the heat of polymerization. In the suspension polymerization process, an inert hydrocarbon medium can be used as the solvent, and further, the olefin itself can be used as the solvent. The inert hydrocarbon medium is not particularly limited, but examples thereof include 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.

[0078] In the polymerization of an ethylene polymer in the production method for polyethylene powder of the present embodiment, the method of adding the above-mentioned [catalyst component] into a polymerization reactor is not particularly limited, but from the viewpoint of polymerizing a component whose molecular chains are tightly entangled in the catalyst pores and from the viewpoint of making the catalyst more likely to crack in the polymerization system, it is preferable to add a [catalyst component] that has been pre-polymerized in advance.

[0079] In the method for producing the polyethylene powder of the present embodiment, the polymerization temperature of the ethylene polymer is preferably 40°C or more and 100°C or less, more preferably 45°C or more and 95°C or less, and even more preferably 50°C or more and 90°C or less. A polymerization temperature of 40°C or higher enables industrially efficient production, while a polymerization temperature of 100°C or lower can suppress the formation of lumpy scale caused by partial melting of the polymer, enabling continuous and stable production without clogging of pipes.

[0080] In the method for producing the polyethylene powder of this embodiment, the polymerization pressure for the ethylene polymer is preferably from normal pressure to 2 MPaG, more preferably from 0.2 MPaG to 1.5 MPaG, and even more preferably from 0.3 MPaG to 0.9 MPaG. A polymerization pressure of normal pressure or higher allows for industrially efficient production, whereas a polymerization pressure of 2 MPaG or lower tends to enable stable production without the generation of clumpy scale due to rapid polymerization in the polymerization reactor.

[0081] In general, when polymerizing an ethylene-based polymer, an antistatic agent such as Stadis or STATSAFE manufactured by Innospec (distributor: Maruwa Bussan) can be used to suppress static adhesion of the polymer to a polymerization reactor. Antistatic agents such as Stadis and STATSAFE can be diluted in an inert hydrocarbon medium and added to a polymerization reactor by a pump, etc. The antistatic agent can be added by a method of adding it to a solid catalyst in advance or by a method of adding it to a polymerization reactor, and the amount added is preferably 1 ppm or more and 500 ppm or less, more preferably 10 ppm or more and 100 ppm or less, based on the amount of ethylene polymer produced per unit time.

[0082] The molecular weight of the ethylene polymer can be adjusted by making hydrogen present in the polymerization system or by changing the polymerization temperature, as described in German Patent Application Publication No. 3,127,133. Specifically, the molecular weight of the ethylene polymer can be controlled within an appropriate range by adding hydrogen as a chain transfer agent to the polymerization system. When hydrogen is added to the polymerization system, the range of the molar fraction of hydrogen is preferably 0 mol% or more and 30 mol% or less, more preferably 0 mol% or more and 25 mol% or less. Alternatively, hydrogen can be brought into contact with the catalyst beforehand and then added to the polymerization system through the catalyst introduction line. Immediately after the catalyst is introduced into the polymerization system, the catalyst concentration near the outlet of the introduction line becomes high, causing rapid polymerization, increasing the possibility of localized high temperature conditions. On the other hand, by bringing hydrogen into contact with the catalyst before being introduced into the polymerization system, the initial activity of the catalyst can be suppressed, and the generation of clumpy scale due to rapid polymerization and the deactivation of the catalyst at high temperatures can be suppressed.

[0083] The concentration of the polymerization slurry in the method for producing the ethylene-based polymer constituting the polyethylene powder of the present embodiment is preferably in the range of 30% by mass or more and 60% by mass or less, and more preferably 40% by mass or more and 50% by mass or less, from the viewpoint of making the catalyst more susceptible to cracking in the polymerization system.

[0084] The range of the stirring speed in the production method for the ethylene polymer constituting the polyethylene powder of this embodiment is preferably 300 rpm or more and 600 rpm or less, and more preferably 400 rpm or more and 500 rpm or less, from the viewpoint that the catalyst is easily cracked in the polymerization system.

[0085] The polymerization reaction may be carried out in any of a batch system, a semi-continuous system, and a continuous system, and is preferably carried out in a continuous system. By continuously supplying ethylene gas, a solvent, a catalyst, etc. into the polymerization system and continuously discharging them together with the produced ethylene polymer, it is possible to suppress a partial high temperature state caused by a sudden reaction of ethylene, and the polymerization system becomes more stable. If ethylene reacts in a homogeneous state in the system, the generation of branches, double bonds, etc. in the polymer chain is suppressed, or the generation of low molecular weight components or ultrahigh molecular weight substances due to decomposition or crosslinking of the ethylene polymer is suppressed, and crystalline components of the ethylene polymer are easily produced. As a result, in a film, a microporous membrane, etc. using the polyethylene powder of this embodiment, a crystalline component necessary and sufficient for strength is easily obtained.

[0086] The polymerization reaction may be a single-stage polymerization method using one polymerization reactor, or a multi-stage polymerization method in which polymerization is carried out continuously in sequence in two or more polymerization reactors connected in series. The production of an ethylene polymer using a multi-stage polymerization method is specifically carried out by the following method. First, an ethylene polymer X is produced in a first-stage polymerization reactor under the above-mentioned production conditions, and the ethylene polymer X discharged from the first-stage polymerization reactor is transferred to an intermediate flash tank, where unreacted ethylene, hydrogen, and comonomer (only when copolymerization is performed in the first-stage polymerization reactor) are separated. Then, a suspension containing the ethylene polymer X is transferred to a second-stage polymerization reactor, where an ethylene polymer Y is produced under the above-mentioned production conditions. The range of the polymerization pressure in the first-stage polymerization reactor is preferably 0.6 MPaG or more and 2.0 MPaG or less, more preferably 0.7 MPaG or more and 1.5 MPaG or less, and even more preferably 0.8 MPaG or more and 1.0 MPaG or less, from the viewpoint of polymerizing components whose molecular chains are highly entangled in the pores of the catalyst. The concentration of the polymerization slurry in the first-stage polymerization reactor is preferably in the range of 10% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 20% by mass or less, from the viewpoint of controlling the catalyst in the first-stage polymerization reactor so as not to crack. The range of the stirring speed in the first-stage polymerization reactor is preferably 100 rpm or more and 300 rpm or less, more preferably 150 rpm or more and 250 rpm or less, from the viewpoint of controlling the stirring speed so as not to crack the catalyst in the first-stage polymerization reactor. The concentration of the polymerization slurry in the second-stage polymerization reactor is preferably in the range of 30 mol% to 60 mol%, more preferably 40 mol% to 50 mol%, from the viewpoint of making the catalyst more likely to crack in the polymerization system. The stirring speed in the second-stage polymerization reactor is preferably in the range of 300 rpm or more and 600 rpm or less, more preferably 400 rpm or more and 500 rpm or less, from the viewpoint of making the catalyst easily cracked in the polymerization system.

[0087] The proportion of the ethylene polymer X contained in the polyethylene powder produced by the above-mentioned multistage polymerization method, i.e., the range of the production amount in the first-stage polymerization reactor, is preferably from 10% by mass to 50% by mass, more preferably from 15% by mass to 45% by mass, and even more preferably from 20% by mass to 40% by mass, from the viewpoint of controlling the catalyst to crack in the second-stage polymerization reactor.

[0088] As each physical property value of the ethylene polymer Y, the viscosity average molecular weight and density can be determined based on additivity from the production amount in each polymerization reactor after measuring the physical property values ​​of the ethylene polymer X extracted from the first-stage polymerization reactor and the finally produced polyethylene powder.

[0089] The suspension containing the ethylene-based polymer constituting the polyethylene powder of the present embodiment is quantitatively extracted from the polymerization reactor and transferred to a flash tank, where unreacted ethylene, hydrogen, and comonomer (only in the case where copolymerization is performed in a reactor) are separated. As a method for separating the solvent in the polymerization step of the polyethylene powder of this embodiment, any of a decantation method, a centrifugation method, a filter filtration method, etc. can be used, but a centrifugation method that has a good efficiency in separating the ethylene polymer and the solvent is more preferable.

[0090] The method for deactivating the catalyst used in the polymerization step of the ethylene-based polymer constituting the polyethylene powder of the present embodiment is not particularly limited, but the catalyst is preferably deactivated after the ethylene-based polymer is separated from the solvent. By introducing an agent for deactivating the catalyst after separating the polyethylene powder from the solvent, it is possible to suppress precipitation of low-molecular-weight components, catalyst components, and the like contained in the solvent in the ethylene polymer. Agents for deactivating the catalyst include oxygen, water, alcohols, glycols, phenols, carbon monoxide, carbon dioxide, ethers, carbonyl compounds, alkynes, and the like.

[0091] In the method for producing the polyethylene powder of the present embodiment, it is preferable to carry out a drying step after separating the ethylene polymer from the solvent. In the drying step, it is preferable to use a rotary kiln method, a paddle method, a fluidized dryer, or the like. The drying temperature is preferably 50°C or more and 150°C or less, more preferably 70°C or more and 110°C or less. It is also effective to introduce an inert gas such as nitrogen into the dryer to accelerate drying. In this case, it is even more effective to use steam or the like as a catalyst deactivating agent.

[0092] After drying the ethylene polymer constituting the polyethylene powder of the present embodiment, it may be sieved to remove coarse particles.

[0093] The polyethylene powder of the present embodiment may be a mixture of multiple polyethylene powders containing ethylene polymers obtained by the above-mentioned production method. If necessary, the toner may be used in combination with known additives such as slip agents, neutralizing agents, antioxidants, light resistance stabilizers, antistatic agents, and pigments. The slip agent or neutralizing agent is not particularly limited, but examples thereof include aliphatic hydrocarbons, higher fatty acids, higher fatty acid metal salts, fatty acid esters of alcohols, waxes, higher fatty acid amides, silicone oils, rosins, etc. Specifically, stearates such as calcium stearate, magnesium stearate, and zinc stearate can be cited as suitable additives. The antioxidant is not particularly limited, but for example, a phenol-based compound or a phenol-phosphate-based compound is preferable. Specific examples of the antioxidant include phenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol (dibutylhydroxytoluene), n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate, and tetrakis(methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate))methane; phenol-phosphorus-based antioxidants such as 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepine; and phosphorus-based antioxidants such as tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene-diphosphonite, tris(2,4-di-t-butylphenyl)phosphite, and cyclic neopentanetetraylbis(2,4-t-butylphenylphosphite). The light resistance stabilizer is not particularly limited, but examples thereof include benzotriazole-based light resistance stabilizers such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole and 2-(3-t-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole; and hindered amine-based light resistance stabilizers such as bis(2,2,6,6-tetramethyl-4-piperidine)sebacate and 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}]. The antistatic agent is not particularly limited, but examples thereof include aluminosilicates, kaolin, clay, natural silica, synthetic silica, silicates, talc, diatomaceous earth, and glycerin fatty acid esters.

[0094] [Application] The polyethylene powder of the present embodiment can be used as a raw material for various molded articles such as microporous films, fibers, particularly high-strength fibers, sintered bodies, press molded articles, and ram-pressed molded articles. It is particularly suitable as a raw material for microporous membranes for battery separators.

[0095] [Molded body] The molded article of this embodiment is a molded article of the polyethylene powder of this embodiment described above. Examples of the molded article include microporous membranes, particularly microporous membranes used as battery separators, fibers, particularly high-strength fibers, sintered bodies, press molded articles, and ram-pressed molded articles. The method for producing the molded body includes a molding method that includes steps of extruding a resin using a wet extrusion method, stretching, extracting, and drying. Examples of the battery separator include a lithium ion secondary battery separator and a lead acid battery separator. EXAMPLES

[0096] The present embodiment will be described in more detail below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples and comparative examples. First, the method for evaluating the physical properties of the polyethylene powder will be described.

[0097] [Physical properties of polyethylene powder] (Intertwining index and intermediate component ratio at 180℃) First, a sample tube filled with polyethylene powder to a height of 1 cm from the bottom was placed in a Bruker TD-NMR device (model: minispec mq20) set to an internal temperature of the sample tube of 30°C, and the sample tube was heated according to the heating conditions shown below. The temperatures shown in the following <Heating Conditions> are values ​​obtained by measuring the internal temperature of the sample with a thermocouple. <Heating conditions> (1) Set the temperature to 30°C and leave it for 5 minutes. (2) Raise the temperature to 180°C at a rate of 5°C / min. (3) Heat to 180°C and leave to stand for 25 minutes. After the temperature rise is completed using the above procedure, the spin-spin relaxation time (T 2 , sometimes simply referred to as "relaxation time" in this specification, was measured. After the measurement was completed, the same measurement was repeated three times, for a total of four measurements. <Measurement conditions> Magnetic field strength: 0.47T Measured nuclides: 1 H(20MHz) Measurement method: Carr Purcell Meiboom Gill method Number of times accumulated: 256 Repeat time: 3 seconds Interval between the first 90° pulse and the 180° pulse (τ): 0.04 ms Total number of echo signals: 6400

[0098] Of the four measurements described above, the free induction decay (FID) obtained in the fourth measurement was subjected to curve fitting using the analysis program TD-NMR-A manufactured by Bruker. For fitting, the function shown in the following Equation 1 was used. <Expression 1> f(t)=R α exp(-t / T α )+R β exp(-t / T β )+R γ exp(-t / T γ ) (However, R α +R β +R γ = 100) t: variable (time elapsed since pulse irradiation) T α : Relaxation time of low-mobility component α (ms) R α : Proportion of low-mobility component α (%) T β : Relaxation time of intermediate component β (ms) R β : Presence ratio of intermediate component β (%) T γ : Relaxation time of the high-mobility component gamma (ms) R γ : Proportion of highly mobile component γ (%)

[0099] Finally, the entanglement index (ms) and the intermediate component ratio were calculated from the relaxation time T and the abundance ratio R obtained by curve fitting of the free induction decay, using the following (Equation I) and (Equation II). (Entanglement Index)=T α ×R α / (R α +R β )+T β ×R β / (R α +R β ) (Formula I) (Intermediate component ratio) = R β / (R α +R β )...(Formula II)

[0100] (Change in the proportion of low-mobility components at 180°C) Of the pulse NMR measurements performed to determine the above-mentioned (entanglement index and intermediate component ratio at 180°C), curve fitting was performed using the analysis program TD-NMR-A manufactured by Bruker Corporation for the free induction decay (FID) obtained from the first and fourth measurements. For fitting, the function shown in Equation 1 above was used. From the abundance ratio R obtained by fitting, the rate of change (%) of the abundance ratio of low mobility components was calculated using the following (Equation III). (Rate of change in the proportion of low-mobility components) = ((R α4 -R α1 ) / R α1 )×100...(Formula III) R α1 : The proportion of low-mobility component α in the first measurement (%) R α4 : The proportion of low-mobility component α in the fourth measurement (%)

[0101] (Change in the proportion of highly mobile components at 180℃) Of the pulse NMR measurements performed to determine the above-mentioned (entanglement index and intermediate component ratio at 180°C), curve fitting was performed using the analysis program TD-NMR-A manufactured by Bruker Corporation for the free induction decay (FID) obtained from the first and fourth measurements. The function shown in Equation 1 above was used for fitting. From the abundance ratio R obtained by fitting, the rate of change (%) of the abundance ratio of the highly mobile component was calculated using the following (Equation IV). (Rate of change in the proportion of highly mobile components) = ((R γ4 -R γ1 ) / R γ1 )×100...(Formula IV) R γ1 : The proportion of highly mobile components γ in the first measurement (%) R γ4: The proportion of highly mobile components γ in the fourth measurement (%)

[0102] [Isothermal crystallization time] The isothermal crystallization time of the polyethylene powder at 125° C. was determined by the following method using a differential scanning calorimeter (manufactured by PerkinElmer, product name: DSC8000). First, an aluminum pan containing 8.5 mg of polyethylene powder was placed in a heating furnace in the DSC device, and a heating operation was carried out according to the following <temperature increase and decrease conditions>. However, all heating operations were carried out under a nitrogen atmosphere. <Temperature rise and fall conditions> (1) Hold at 50°C for 1 minute. (2) Raise the temperature to 180°C at a rate of 200°C / min. (3) Hold at 180°C for 5 minutes. (4) The temperature is decreased to 125°C at a rate of 80°C / min. The time when the temperature reached 125° C. was defined as the starting point (0 min), and the time when the top of the exothermic peak due to crystallization was obtained was defined as the isothermal crystallization time (min) at 125° C.

[0103] (Viscosity average molecular weight (Mv)) The viscosity average molecular weight of the polyethylene powder was measured by the following method in accordance with ISO1628-3 (2010). First, polyethylene powder was weighed in the range of 4.0 to 4.5 mg into a dissolution tube. The weighed mass is represented as "m (unit: mg)" in the following formula. Next, the air inside the dissolution tube was degassed with a vacuum pump and replaced with nitrogen, and then 20 mL of decahydronaphthalene (containing 1 g / L of 2,6-di-t-butyl-4-methylphenol, hereinafter referred to as decalin) that had been degassed with a vacuum pump and replaced with nitrogen was added, and the polyethylene powder was dissolved by stirring at 150°C for 90 minutes to obtain a decalin solution. Thereafter, the decalin solution was placed in a Cannon-Fenske viscometer (manufactured by Shibata Scientific Instruments Co., Ltd. / viscometer number: 100) in a constant temperature liquid bath at 135° C., and the fall time (ts) between the marked lines was measured. Furthermore, as a blank, the drop time (tb) of decalin alone without adding polyethylene powder was measured, and the specific viscosity (ηsp) was calculated according to the following (Formula A). ηsp=(ts / tb)-1 (Formula A) The intrinsic viscosity IV was calculated from the specific viscosity (ηsp) and the concentration (C) (unit: g / dL) using the following (Formula B) and (Formula C). Concentration C = m / (20 × γ) / 10 (unit: g / dL) (Formula B) γ = (density of decalin at 20°C) / (density of decalin at 135°C) =0.888 / 0.802=1.107 Intrinsic viscosity IV = (ηsp / C) / (1 + 0.27 × ηsp) (Formula C) The intrinsic viscosity IV was substituted into the following (Equation D) to determine the viscosity average molecular weight (Mv). Viscosity average molecular weight (Mv)=(5.34×10 4 )×[η] 1.49 (Formula D)

[0104] (Median diameter) The median diameter of the polyethylene powder was determined by the following method. The polyethylene powder was classified using a sieve conforming to the JIS Z8801 standard. Sieves with openings of 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, and 53 μm were used, and the mass of the polyethylene powder recovered for each fraction was measured. Then, the fraction (mass%) of each fraction relative to the total mass of the polyethylene powder before classification was calculated, and the cumulative undersize fraction (mass%) was obtained. A cumulative undersize distribution graph, i.e., a particle size distribution cumulative curve (cumulative curve from small particles), was drawn with the value of the opening on the horizontal axis and the cumulative undersize fraction on the vertical axis, and the particle diameter (D50 (μm)) at which the cumulative undersize fraction was 50% was taken as the median diameter.

[0105] [Method for producing microporous membrane] To 25 to 50 parts by mass of the polyethylene powder of each of the Examples and Comparative Examples described below, 1 part by mass of pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant, and the mixture was dry-blended using a tumbler blender to obtain a powder mixture. The obtained powder mixture was subjected to nitrogen replacement and then fed into a twin-screw extruder through a feeder under a nitrogen atmosphere. Furthermore, liquid paraffin (P-350P (trademark) manufactured by MORESCO Co., Ltd.) was weighed so that the total amount with the polyethylene powder was 100 parts by mass, and was injected into the twin-screw extruder by side feed, kneaded under 200°C conditions, extruded from a T-die installed at the tip of the extruder, and immediately cooled and solidified by a cast roll cooled to 25°C, and molded into a gel-like sheet with a thickness of 1200 μm. This gel-like sheet was stretched 7×7 times at 115 to 125°C using a simultaneous biaxial stretching machine to obtain a stretched film. Thereafter, this stretched film was immersed in methyl ethyl ketone for 30 minutes, and the liquid paraffin was extracted and removed, and then dried. Further, it was heat-set at 115°C to 125°C for 3 minutes to obtain a microporous membrane. The stretching temperature and heat setting temperature were appropriately adjusted for each microporous membrane within the specified temperature range.

[0106] [Evaluation of Microporous Membrane] (Evaluation of the formability of microporous membranes) As an evaluation index of moldability, the uniformity of the thickness of the microporous membrane was evaluated. Specifically, eight sheets of 100 mm x 50 mm were punched out from a 250 mm x 250 mm microporous membrane obtained by the above-mentioned "Method for producing a microporous membrane," and the thickness of each membrane was measured at 23°C using a micro thickness gauge (model: KBM) manufactured by Toyo Seiki Seisakusho, Ltd. The film thickness was measured at three points on each punched film. The standard deviation of the measured values ​​at a total of 24 points was calculated, and the moldability was evaluated according to the following evaluation criteria. (Evaluation Criteria) ◎(Good): Less than 0.5μm ○(Normal): 0.5μm or more and less than 1μm × (bad): 1 μm or more

[0107] (Evaluation of mechanical strength of microporous membrane) As an evaluation index for mechanical strength, the puncture strength of the microporous membrane was evaluated. Specifically, eight 100 mm × 50 mm membranes were punched out from 250 mm × 250 mm of the microporous membrane obtained by the above-mentioned [Microporous membrane manufacturing method], and the puncture strength of each membrane was measured using a compression tester (model: KES-G5) manufactured by Kato Tech Co., Ltd. under conditions of a needle tip curvature radius of 0.5 mm, a puncture speed of 2 mm / s, and 23° C. Measurements were performed at three points per punched membrane. In addition, the mass of each cut film was measured and the basis weight (1 m 2 The film mass [g] per unit area was then calculated and the puncture strength converted into basis weight was calculated using the following formula. The measured values ​​at a total of 24 points were averaged, and the mechanical strength was evaluated according to the following evaluation criteria. (Puncture strength converted into basis weight) = (Puncture strength [N]) / (Basis weight [g / m 2 ]) (Evaluation Criteria) ◎(Good): 0.85N / (g / m 2 ) End ○(normal):0.7N / (g / m 2 ) or more 0.85N / (g / m 2 )less than ×(bad): 0.7N / (g / m 2 )less than

[0108] (Evaluation of dimensional stability of microporous membrane) As an evaluation index for dimensional stability, the heat shrinkage rate of the microporous membrane was evaluated. Specifically, eight sheets of 100 mm x 50 mm were punched out from the microporous membrane obtained by the above-mentioned "Method for producing a microporous membrane" of 250 mm x 250 mm, and placed in an oven set to 120°C for 60 minutes. After being heated and left to stand, the film was cooled at room temperature for 15 minutes, and the dimensions of the microporous film were measured, and the heat shrinkage rate (%) was calculated according to the following formula. The measured values ​​at a total of eight points were averaged, and the dimensional stability was evaluated according to the following evaluation criteria. (Heat shrinkage rate) = (Heat shrinkage rate in MD direction) + (Heat shrinkage rate in TD direction) (MD heat shrinkage)=(1-D MD120 / D MD23 ) x 100 (Thermal shrinkage in TD direction)=(1-D TD120 / D TD23 ) x 100 D MD120 : Dimension in MD direction at 120℃ [mm] D MD23 : Dimension in MD direction at 23℃ [mm] D TD120 : Dimension in TD direction at 120℃ [mm] D TD23 : Dimension in TD direction at 23℃ [mm] (Evaluation Criteria) ◎ (Good): Less than 15% ○(Normal): 15% to less than 25% × (bad): 25% or more

[0109] (Evaluation of creep resistance of microporous membrane) A sample with a width of 20 mm and a length of 100 mm was cut out from the microporous membrane obtained by the above-mentioned [Microporous membrane manufacturing method] and attached to a Tensilon with a chuck distance of 50 mm manufactured by A&D Co., Ltd. After holding for 12 hours under conditions of a temperature of 23°C and a load of 10 N, the length of the microporous membrane was measured and the tensile elongation (%) was calculated from the following formula. The creep resistance was evaluated according to the following criteria. (Tensile elongation) = {(L 12h / 100)-1}×100 L 12h : Length of microporous membrane after 12 hours [mm] (Evaluation Criteria) ◎(Good): Less than 5% ○(Normal): 5% to less than 10% × (bad): 10% or more

[0110] [Preparation of Ziegler-Natta catalyst] (Preparation of Ziegler-Natta catalyst (A)) <(1) Synthesis of raw material (a-1)> In an 8L stainless steel autoclave that had been thoroughly substituted with nitrogen, add 2.5 mol / L Mg 6 (C 4 H 9 ) 12 AL(C 2 H 5 ) 3 800mL of hexane solution (equivalent to 2000mmol of magnesium and aluminum) was charged, and 146mL of 5.47mol / L n-butanol hexane solution was dropped over 3 hours while stirring at 50℃. After completion, the line was washed with 200mL of hexane. Stirring was continued for another 2 hours at 50℃ to carry out the reaction. After the reaction was completed, the mixture was cooled to room temperature and used as raw material (a-1). Raw material (a-1) had a magnesium concentration of 1.5 mol / L. <(2) Synthesis of raw material (a-2)> In an 8L stainless steel autoclave that had been thoroughly substituted with nitrogen, add 1mol / L of Mg 6 (C 4 H 9 ) 12 AL(C 2 H 5 ) 3 While stirring at 80°C, 240 mL of a hexane solution of 8.33 mol / L methylhydrogenpolysiloxane (manufactured by Shin-Etsu Chemical Co., Ltd.) was pumped in, and stirring was continued at 80°C for a further 2 hours. After the reaction was completed, the mixture was cooled to room temperature and used as raw material (a-2). The total concentration of magnesium and aluminum in the raw material (a-2) was 0.786 mol / L. <(3) Synthesis of Support (a-3)> An 8 L stainless steel autoclave that had been thoroughly purged with nitrogen was charged with 333 mL of a 3 mol / L hexane solution of hydroxytrichlorosilane, and 629 mL of a hexane solution of the organomagnesium compound (a-1), which was the raw material, was added dropwise over a period of 3 hours at 80°C (corresponding to 943 mmol of magnesium). The reaction was then continued for an additional 1 hour at 80°C with stirring. After the reaction was completed, the supernatant was removed and the residue was washed four times with 1,800 mL of hexane to obtain a carrier (a-3). Analysis of this support revealed that it contained 7.5 mmol of magnesium per gram of solid. <(4) Preparation of Ziegler-Natta catalyst (A)> In an 8 L stainless steel autoclave that had been thoroughly purged with nitrogen, 1,970 mL of a hexane slurry containing 110 g of the carrier (a-3) was stirred at 10° C., and 103 mL of a 1 mol / L hexane solution of titanium tetrachloride and 131 mL of the raw material (a-2) were added simultaneously over a period of 3 hours. After the addition, the reaction was continued for 1 hour at 10°C. After the reaction was completed, the supernatant was removed and the unreacted raw material components were removed by washing four times with hexane, and then 10 vol% (volume ratio: liquid paraffin / (liquid paraffin + hexane)) of liquid paraffin (P-350P (trademark) manufactured by MORESCO Corporation) was added as a thickener to prepare Ziegler-Natta catalyst (A). When transferring this Ziegler-Natta catalyst (A), the differential pressure between the source and destination was set to 0.3 MPa.

[0111] (Preparation of Ziegler-Natta catalyst (B)) A 1.6L autoclave was used to carry out prepolymerization of 20g of the above Ziegler-Natta catalyst (A). 800mL of normal hexane was used as the solvent, 0.4mmol of triisobutylaluminum and diisobutylaluminum hydride (9:1 mixture) was used as the cocatalyst component, and hydrogen was supplied at 20mol% (molar ratio: hydrogen / (ethylene + hydrogen)). The polymerization temperature was set at 20℃, and ethylene was supplied so that 5g of polyethylene was polymerized per 1g of Ziegler-Natta catalyst (A). After the polymerization was completed, the supernatant was removed and the unreacted raw material components were removed by washing with hexane four times to prepare Ziegler-Natta catalyst (B). When this Ziegler-Natta catalyst (B) was transferred, the differential pressure between the transfer source and the transfer destination was set at 0.8MPa.

[0112] (Preparation of Ziegler-Natta catalyst (C)) <(5) Synthesis of carrier (c-3)> A support (c-3) was obtained by carrying out the same operation as in the synthesis of the support (a-3) except that the reaction temperature was set to 65° C. The support (c-3) was analyzed, and the magnesium content per gram of solid was found to be 7.5 mmol. <(6) Preparation of Ziegler-Natta catalyst (C)> The Ziegler-Natta catalyst (C) was prepared in the same manner as in the preparation of the Ziegler-Natta catalyst (A), except that the carrier (c-3) was used instead of the carrier (a-3) and liquid paraffin was not added. When transferring this Ziegler-Natta catalyst (C), the differential pressure between the transfer source and the transfer destination was set to 0.3 MPa.

[0113] (Preparation of Ziegler-Natta catalyst (D)) <(7) Synthesis of raw material (d-1)> 1 mol / L Mg 6 (C 4 H 9 ) 12 AL(C 2 H 5 ) 3The raw material (d-1) was obtained by the same procedure as in the synthesis of the raw material (a-1), except that 2,000 mL of the hexane solution was used and the amount of normal hexane used for washing the line was 300 mL. The magnesium concentration of the raw material (d-1) was 0.7 mol / L. <(8) Synthesis of Support (d-3)> A carrier (d-3) was obtained by carrying out the same operation as in the synthesis of the carrier (a-3) except that 1340 mL of the raw material (d-1) was used instead of 629 mL of the raw material (a-1) and the reaction temperature was 65° C. The carrier (d-3) was analyzed and found to contain 7.5 mmol of magnesium per gram of solid. <(9) Preparation of Ziegler-Natta catalyst (D)> The Ziegler-Natta catalyst (D) was prepared in the same manner as in the preparation of the Ziegler-Natta catalyst (A), except that the carrier (d-3) was used instead of the carrier (a-3) and liquid paraffin was not added. When transferring this Ziegler-Natta catalyst (D), the differential pressure between the transfer source and the transfer destination was set to 0.8 MPa.

[0114] (Preparation of Ziegler-Natta catalyst (E)) The Ziegler-Natta catalyst (E) was prepared by carrying out the same polymerization procedure as for the preparation of the Ziegler-Natta catalyst (B), except that the Ziegler-Natta catalyst (D) was used instead of the Ziegler-Natta catalyst (A). When transferring this Ziegler-Natta catalyst (E), the differential pressure between the source and destination was set to 0.3 MPa.

[0115] (Preparation of Ziegler-Natta catalyst (F)) In an 8 L stainless steel autoclave that had been thoroughly purged with nitrogen, 1600 mL of hexane was stirred at 5° C., and 786 mL of a 1 mol / L hexane solution of titanium tetrachloride and 1000 mL of the raw material (a-2) were added simultaneously over a period of 4 hours. After the addition, the temperature was slowly raised and the reaction was continued at 10° C. for 1 hour. After the reaction was completed, the supernatant was removed and the unreacted raw materials were removed by washing with hexane four times to prepare the Ziegler-Natta catalyst (F). When transferring this Ziegler-Natta catalyst (F), the differential pressure between the source and destination was set to 0.8 MPa.

[0116] (Preparation of Ziegler-Natta catalyst (G)) To the Ziegler-Natta catalyst (F), 10 vol% (volume ratio: liquid paraffin / (liquid paraffin+hexane)) of liquid paraffin (P-350P (trademark) manufactured by MORESCO Corp.) was added as a thickener to prepare Ziegler-Natta catalyst (G). When transferring this Ziegler-Natta catalyst (G), the differential pressure between the source and destination was set to 0.8 MPa.

[0117] [Production of polyethylene powder and microporous film] Example 1 As shown below, an ethylene polymer (X A ) is polymerized in the second polymerization reactor to produce an ethylene polymer (Y A ) was polymerized to obtain polyethylene powder (A). The polyethylene powder (A) had a viscosity average molecular weight of 300,000 and a median diameter of 101 μm. The polyethylene powder (A) and the microporous film of the polyethylene powder (A) produced by the above-mentioned "Method for producing a microporous film" were subjected to the various evaluations described above, and the results are shown in Table 1. <(1) Ethylene-based polymer (X A Polymerization of Polymerization of ethylene-based polymer was carried out using a vessel-type 300L polymerization reactor equipped with three swept-back impellers and three baffles. Normal hexane was supplied as a solvent at a flow rate of 40L / hour, the total liquid volume was adjusted so that the slurry concentration was 16% by mass, and the stirring speed was 200rpm. Ziegler-Natta catalyst (A) was used as the polymerization catalyst, and it was supplied so that the production rate of ethylene-based polymer was 9.0kg / hour. STATSAFE3000 (90g / L) diluted with normal hexane was added as the polymerization catalyst in an amount of 20 massppm relative to the production rate of ethylene-based polymer. Triisobutylaluminum and diisobutylaluminum hydride (9:1 mixture) were used as the cocatalyst component, and were supplied at 10mmol / hour. Hydrogen was supplied at 26mol% (molar ratio: hydrogen / (ethylene+hydrogen)). The polymerization temperature was 60°C, the polymerization pressure was 0.7MPaG, and the average residence time was 3.3 hours. The thus obtained ethylene polymer (X A The viscosity average molecular weight of the copolymer was 300,000. The polymerization activity in the first-stage polymerization reactor was 12,000 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was led to an intermediate flash tank at a pressure of 0.05 MPaG and a temperature of 70° C. so that the level in the polymerization reactor was kept constant, and unreacted ethylene and hydrogen were separated in this intermediate flash tank. <(2) Ethylene-based polymer (Y A Polymerization of From the intermediate flash tank, an ethylene polymer (X) was fed into a vessel-type 300 L polymerization reactor equipped with three swept-back impellers and three baffles. A The polymerization slurry containing the ethylene polymer (Y A ) was polymerized. The total liquid volume was adjusted so that the slurry concentration was 40% by mass, the stirring speed was 450 rpm, and triisobutylaluminum and diisobutylaluminum hydride (9:1 mixture) were supplied as cocatalyst components at 10 mmol / hour. Hydrogen was supplied at 10 mol% (molar ratio: hydrogen / (ethylene+hydrogen)). The polymerization temperature was 78°C, the polymerization pressure was 0.75 MPaG so that the production rate was 11.1 kg / hour, and the average residence time was 0.75 hours. The thus obtained ethylene polymer (Y A The viscosity average molecular weight of the copolymer was 300,000. The polymerization activity in the second-stage polymerization reactor was 14,700 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was led to a final flash tank at a pressure of 0.05 MPaG and a temperature of 70°C so that the level in the polymerization reactor was kept constant, and unreacted ethylene and hydrogen were separated in this final flash tank. Next, the polymerization slurry was continuously sent from the flash tank to a centrifuge by a pump, and after the polymer and the solvent were separated in this centrifuge, the separated polyethylene powder was sent to a rotary kiln type dryer controlled at 90°C and dried while blowing nitrogen, to obtain polyethylene powder (A). In this drying process, steam was sprayed onto the polyethylene powder to deactivate the catalyst and co-catalyst.

[0118] Example 2 As shown below, an ethylene polymer (X B ) is polymerized in the second polymerization reactor to produce an ethylene polymer (Y B ) was polymerized to obtain polyethylene powder (B). The polyethylene powder (B) had a viscosity average molecular weight of 900,000 and a median diameter of 99 μm. The polyethylene powder (B) and the microporous film of the polyethylene powder (B) produced by the above-mentioned "Microporous film production method" were subjected to the above-mentioned various evaluations, and the results are shown in Table 1. <(3) Ethylene-based polymer (X B Polymerization of The same procedure as in Example 1 was repeated except that the amount of hydrogen supplied was 16 mol%. A ) was polymerized in the same manner as above to obtain an ethylene polymer (X B The resulting ethylene polymer (X B The viscosity average molecular weight of the copolymer was 900,000. The polymerization activity in the first-stage polymerization reactor was 13,000 g per 1 g of catalyst. <(4) Ethylene-based polymer (Y B Polymerization of The same procedure as in Example 1 was repeated except that the stirring speed was 550 rpm and the hydrogen supply amount was 2 mol%. A ) was polymerized in the same manner as in Example 1 to obtain an ethylene polymer (Y B ) was obtained. The obtained ethylene polymer (Y B The viscosity average molecular weight of the copolymer was 900,000. The polymerization activity in the second-stage polymerization reactor was 15,900 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was subjected to the same separation and drying procedures as in Example 1 above, to obtain a polyethylene powder (B).

[0119] Example 3 <(5) Polymerization of Polyethylene Powder (C)> Polymerization of polyethylene powder was carried out using a vessel-type 300L polymerization reactor equipped with three swept-back impellers and three baffles. Normal hexane was supplied as a solvent at a flow rate of 40L / h, the total liquid volume was adjusted so that the slurry concentration was 40% by mass, and the stirring speed was 550rpm. Ziegler-Natta catalyst (B) was used as the polymerization catalyst, and it was supplied so that the production rate of polyethylene powder was 13kg / h. STATSAFE3000 (90g / L) diluted with normal hexane was added as the polymerization catalyst in an amount of 20 mass ppm relative to the production rate of polyethylene powder. Triisobutylaluminum and diisobutylaluminum hydride (9:1 mixture) were used as the cocatalyst components, and were supplied at 10mmol / h. Hydrogen was supplied at 2.9mol% (molar ratio: hydrogen / (ethylene + hydrogen)). The polymerization temperature was 78°C, the polymerization pressure was 0.3MPaG, and the average residence time was 3.0 hours. The polymerization slurry in the polymerization reactor was led to a flash tank at a pressure of 0.05 MPaG and a temperature of 70°C so that the level in the polymerization reactor was kept constant, and unreacted ethylene and hydrogen were separated in the flash tank. Next, the polymerization slurry was continuously sent from the flash tank to a centrifuge by a pump to separate the polymer and the solvent, and the separated polyethylene powder was sent to a rotary kiln-type dryer controlled at 90°C and dried while blowing nitrogen. In this drying process, steam was sprayed onto the polyethylene powder to deactivate the catalyst and co-catalyst. The thus obtained polyethylene powder (C) had a viscosity average molecular weight of 900,000 and a median diameter of 110 μm, and the polymerization activity in the polymerization reactor was 20,000 g per 1 g of catalyst. The polyethylene powder (C) and the microporous film of the polyethylene powder (C) produced by the above-mentioned "Microporous film production method" were subjected to the above-mentioned various evaluations, and the results are shown in Table 1.

[0120] Example 4 As shown below, an ethylene polymer (X D ) is polymerized in the second polymerization reactor to produce an ethylene polymer (Y D) was polymerized to obtain polyethylene powder (D). The viscosity average molecular weight of the polyethylene powder (D) was 300,000 and the median diameter was 105 μm. The polyethylene powder (D) and the microporous film of the polyethylene powder (D) produced by the above-mentioned "Microporous film production method" were subjected to the above-mentioned various evaluations, and the results are shown in Table 1. <(6) Ethylene-based polymer (X D Polymerization of The same procedure as in Example 1 was repeated except that the polymerization catalyst was a Ziegler-Natta catalyst (C). A ) was polymerized in the same manner as above to obtain an ethylene polymer (X D The resulting ethylene polymer (X D The viscosity average molecular weight of the copolymer was 300,000. The polymerization activity in the first-stage polymerization reactor was 11,500 g per 1 g of catalyst. <(7) Ethylene-based polymer (Y D Polymerization of (Y A ) was polymerized in the same manner as in Example 1 to obtain an ethylene polymer (Y D The resulting ethylene polymer (Y D The viscosity average molecular weight of the copolymer was 300,000. The polymerization activity in the second-stage polymerization reactor was 14,000 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was subjected to the same separation and drying procedures as in Example 1 above, to obtain a polyethylene powder (D).

[0121] Example 5 <(8) Polymerization of polyethylene powder (E)> Polymerization was carried out in the same manner as in the above (Example 3) except that the flow rate of normal hexane was 80 L / hour, the production rate was 10 kg / hour, the slurry concentration was 16 mass%, and the average residence time was 1.75 hours, to obtain a polyethylene powder (E). The viscosity average molecular weight of the polyethylene powder (E) thus obtained was 900,000, the median diameter was 108 μm, and the polymerization activity in the polymerization reactor was 19,000 g per 1 g of catalyst. The polyethylene powder (E) and the microporous film of the polyethylene powder (E) produced by the above-mentioned "Microporous film production method" were subjected to the above-mentioned various evaluations, and the results are shown in Table 1.

[0122] Example 6 As shown below, an ethylene polymer (X F ) is polymerized in the second polymerization reactor to produce an ethylene polymer (Y F ) was polymerized to obtain polyethylene powder (F). The polyethylene powder (F) had a viscosity average molecular weight of 300,000 and a median diameter of 95 μm. The polyethylene powder (F) and the microporous membrane of the polyethylene powder (F) produced by the above-mentioned "Microporous membrane production method" were subjected to the above-mentioned various evaluations, and the results are shown in Table 1. <(9) Ethylene-based polymer (X F Polymerization of (X A ) was polymerized in the same manner as above to obtain an ethylene polymer (X F The resulting ethylene polymer (X F The viscosity average molecular weight of the copolymer was 300,000. The polymerization activity in the first-stage polymerization reactor was 12,000 g per 1 g of catalyst. <(10) Ethylene-based polymer (Y F Polymerization of The same procedure as in Example 1 was repeated except that the slurry concentration was 30% by mass and the stirring speed was 230 rpm. A ) was polymerized in the same manner as in Example 1 to obtain an ethylene polymer (Y F The resulting ethylene polymer (Y F The viscosity average molecular weight of the copolymer was 300,000. The polymerization activity in the second-stage polymerization reactor was 14,500 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was subjected to the same separation and drying procedures as in Example 1 above, to obtain a polyethylene powder (F).

[0123] Example 7 <(11) Polymerization of Polyethylene Powder (G)> Polymerization was carried out in the same manner as in the above (Example 3) except that the production rate was 9 kg / hour, the slurry concentration was 30 mass %, and the hydrogen supply amount was 1 mol %, to obtain a polyethylene powder (G). The viscosity average molecular weight of the polyethylene powder (G) thus obtained was 2,000,000 and the median diameter was 103 μm. The polymerization activity in the polymerization reactor was 18,000 g per 1 g of catalyst. The polyethylene powder (G) and the microporous membrane of the polyethylene powder (G) produced by the above-mentioned "Microporous membrane production method" were subjected to the various evaluations described above, and the results are shown in Table 1.

[0124] Example 8 As shown below, an ethylene polymer (X H ) is polymerized in the second polymerization reactor to produce an ethylene polymer (Y H ) was polymerized to obtain polyethylene powder (H). The viscosity average molecular weight of polyethylene powder (H) was 900,000 and the median diameter was 99 μm. The polyethylene powder (H) and the microporous film of polyethylene powder (H) produced by the above-mentioned [Production method of microporous film] were subjected to the above-mentioned various evaluations, and the results are shown in Table 1. <(12) Ethylene-based polymer (X H Polymerization of The same procedure as in Example 2 was repeated except that the stirring speed was 300 rpm and the slurry concentration was 30 mass%. B ) was polymerized in the same manner as above to obtain an ethylene polymer (X H The resulting ethylene polymer (X H The viscosity average molecular weight of the copolymer was 900,000. The polymerization activity in the first-stage polymerization reactor was 13,000 g per 1 g of catalyst. <(13) Ethylene-based polymer (Y H Polymerization of The same procedure as in Example 2 was repeated except that the stirring speed was 450 rpm. B ) was polymerized in the same manner as in Example 1 to obtain an ethylene polymer (Y HThe resulting ethylene polymer (Y H The viscosity average molecular weight of the copolymer was 900,000. The polymerization activity in the second-stage polymerization reactor was 15,900 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was subjected to the same separation and drying procedures as in Example 1 above, to obtain a polyethylene powder (H).

[0125] Comparative Example 1 <(14) Polymerization of Polyethylene Powder (I)> Polymerization was carried out in the same manner as in Example 5, except that the stirring speed was 230 rpm and the polymerization catalyst was a Ziegler-Natta catalyst (E), to obtain a polyethylene powder (I). The thus obtained polyethylene powder (I) had a viscosity average molecular weight of 900,000 and a median diameter of 111 μm. The polymerization activity in the polymerization reactor was 18,000 g per 1 g of catalyst. The polyethylene powder (I) and the microporous film of the polyethylene powder (I) produced by the above-mentioned "Microporous film production method" were subjected to the above-mentioned various evaluations, and the results are shown in Table 2.

[0126] Comparative Example 2 <(15) Polymerization of Polyethylene Powder (J)> Polymerization was carried out in the same manner as in Example 3 except that the polymerization catalyst was a Ziegler-Natta catalyst (D), to obtain a polyethylene powder (J). The viscosity average molecular weight of the polyethylene powder (J) thus obtained was 900,000, the median diameter was 113 μm, and the polymerization activity in the polymerization reactor was 18,500 g per 1 g of catalyst. The polyethylene powder (J) and the microporous film of the polyethylene powder (J) produced by the above-mentioned "Microporous film production method" were subjected to the various evaluations described above, and the results are shown in Table 2.

[0127] Comparative Example 3 As shown below, an ethylene polymer (XK ) is polymerized in the second polymerization reactor to produce an ethylene polymer (Y K ) was polymerized to obtain polyethylene powder (K). The polyethylene powder (K) had a viscosity average molecular weight of 900,000 and a median diameter of 94 μm. The polyethylene powder (K) and the microporous membrane of the polyethylene powder (K) produced by the above-mentioned "Microporous membrane production method" were subjected to the various evaluations described above, and the results are shown in Table 2. <(16) Ethylene-based polymer (X K Polymerization of The same procedure as in Example 2 was repeated except that the stirring speed was 450 rpm and the slurry concentration was 30% by mass. B ) was polymerized in the same manner as above to obtain an ethylene polymer (X K ) was obtained. The obtained ethylene polymer (X K The viscosity average molecular weight of the copolymer was 900,000. The polymerization activity in the first-stage polymerization reactor was 12,500 g per 1 g of catalyst. <(17) Ethylene-based polymer (Y K Polymerization of The same procedure as in Example 2 was repeated except that the stirring speed was 230 rpm and the slurry concentration was 20 mass%. B ) was polymerized in the same manner as in Example 1 to obtain an ethylene polymer (Y K The resulting ethylene polymer (Y K The viscosity average molecular weight of the copolymer was 900,000. The polymerization activity in the second-stage polymerization reactor was 15,400 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was subjected to the same separation and drying procedures as in Example 1 above, to obtain a polyethylene powder (K).

[0128] Comparative Example 4 <(18) Polymerization of polyethylene powder (L)> Polymerization was carried out in the same manner as in Example 5 except that the stirring speed was 230 rpm and the polymerization catalyst was a Ziegler-Natta catalyst (D), to obtain a polyethylene powder (L). The viscosity average molecular weight of the polyethylene powder (L) thus obtained was 900,000, the median diameter was 99 μm, and the polymerization activity in the polymerization reactor was 19,000 g per 1 g of catalyst. The polyethylene powder (L) and the microporous film of the polyethylene powder (L) produced by the above-mentioned "Microporous film production method" were subjected to the above-mentioned various evaluations, and the results are shown in Table 2.

[0129] Comparative Example 5 As shown below, an ethylene polymer (X M ) is polymerized in the second polymerization reactor to produce an ethylene polymer (Y M ) was polymerized to obtain polyethylene powder (M). The polyethylene powder (M) had a viscosity average molecular weight of 600,000 and a median diameter of 87 μm. The polyethylene powder (M) and the microporous membrane of the polyethylene powder (M) produced by the above-mentioned "Microporous membrane production method" were subjected to the above-mentioned various evaluations, and the results are shown in Table 2. <(16) Ethylene-based polymer (X M Polymerization of The same procedure as in Example 2 was repeated except that the flow rate of normal hexane was 20 L / hour, the slurry concentration was 40 mass%, the polymerization catalyst was a Ziegler-Natta catalyst (F), the production rate was 13 kg / hour, the amount of hydrogen supplied was 6 mol%, the polymerization temperature was 80° C., and the polymerization pressure was 0.5 MPaG. B ) was polymerized in the same manner as above to obtain an ethylene polymer (X M ) was obtained. The obtained ethylene polymer (X M The viscosity average molecular weight of the copolymer was 800,000. The polymerization activity in the first-stage polymerization reactor was 70,000 g per 1 g of catalyst. <(17) Ethylene-based polymer (Y M Polymerization of The same procedure as in Example 2 was repeated except that the stirring speed was 230 rpm, the production rate was 7 kg / hour, the hydrogen supply amount was 25 mol%, the polymerization temperature was 80° C., and the polymerization pressure was 0.5 MPaG. B) was polymerized in the same manner as in Example 1 to obtain an ethylene polymer (Y M The resulting ethylene polymer (Y M The viscosity average molecular weight of the copolymer was 150,000. The polymerization activity in the second-stage polymerization reactor was 38,000 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was subjected to the same separation and drying procedures as in Example 1 above, to obtain a polyethylene powder (M).

[0130] Comparative Example 6 As shown below, an ethylene polymer (X N ) is polymerized in the second polymerization reactor to produce an ethylene polymer (Y N ) was polymerized to obtain polyethylene powder (N). The polyethylene powder (N) had a viscosity average molecular weight of 600,000 and a median diameter of 89 μm. The polyethylene powder (N) and the microporous membrane of the polyethylene powder (N) produced by the above-mentioned "Microporous membrane production method" were subjected to the various evaluations described above, and the results are shown in Table 2. <(16) Ethylene-based polymer (X N Polymerization of The same procedure as in Comparative Example 5 was repeated except that the polymerization catalyst was a Ziegler-Natta catalyst (G). M ) was polymerized in the same manner as above to obtain an ethylene polymer (X N ) was obtained. The obtained ethylene polymer (X N The viscosity average molecular weight of the copolymer was 800,000. The polymerization activity in the first-stage polymerization reactor was 70,000 g per 1 g of catalyst. <(17) Ethylene-based polymer (Y N Polymerization of (Y M ) was polymerized in the same manner as in Example 1 to obtain an ethylene polymer (Y N The resulting ethylene polymer (Y N The viscosity average molecular weight of the copolymer was 150,000. The polymerization activity in the second-stage polymerization reactor was 38,000 g per 1 g of catalyst. The polymerization slurry in the polymerization reactor was subjected to the same separation and drying procedures as in Example 1 above, to obtain a polyethylene powder (N).

[0131] [Table 1]

[0132] [Table 2]

[0133] This application is based on a Japanese patent application (Patent Application No. 2020-196103) filed with the Japan Patent Office on November 26, 2020, the contents of which are incorporated herein by reference. [Industrial Applicability]

[0134] The polyethylene powder of the present invention has industrial applicability as a raw material for various molded articles, microporous membranes, battery separators, and fibers.

Claims

1. A polyethylene powder having a median diameter of 50 μm or more and 250 μm or less, in which the relaxation time T of each component and the abundance ratio R of each component when a free induction decay curve obtained by the Carr Purcell Meiboom Gill method in pulse NMR is approximated for three components satisfy the following <requirement (1)> and <requirement (2)>. <Requirement (1)> At 180° C., the entanglement index calculated by the following formula I is: Between 12 ms and 25 ms. (Entanglement index) = T α ×R α / (R α +R β ) + T β ×R β / (R α +R β ) (Formula I) T α : Relaxation time of low-mobility component α (ms) R α : Presence ratio of low-mobility component α (%) T β : Relaxation time of intermediate component β (ms) R β : Abundance ratio of intermediate component β (%) <Requirement (2)> At 180° C., the intermediate component ratio calculated by the following (Equation II) is: It is equal to or greater than 0.25 and equal to or less than 0.

5. (Intermediate component ratio) = R β / (R α +R β )...(Formula II)

2. The polyethylene powder according to claim 1, wherein in pulse NMR, with respect to a abundance ratio R of components calculated by three-component approximation of a free induction decay curve obtained by the Carr Purcell Meiboom Gill method, a rate of change in the abundance ratio of low mobility components at 180°C calculated by the following (Formula III) is from -5% to 10%: (Rate of change in the proportion of low-mobility components) = (R α４ -R α１ ) / R α１ )×100...(Formula III) R α１ : The proportion of low-mobility component α in the first measurement R α４ : Proportion of low-mobility component α in the fourth measurement

3. 3. The polyethylene powder according to claim 1 or 2, wherein in pulse NMR, with respect to a abundance ratio R of components calculated by three-component approximation of a free induction decay curve obtained by the Carr Purcell Meiboom Gill method, a rate of change in the abundance ratio of highly mobile components at 180° C. calculated by the following (Formula IV) is 50% or less: (Rate of change in the proportion of highly mobile components) = (R γ４ -R γ１ ) / R γ１ )×100...(Formula IV) R γ１ : The proportion of highly mobile components γ in the first measurement R γ４ : Proportion of high-mobility component γ in the fourth measurement

4. The isothermal crystallization time at 125°C is 5 minutes or less. The polyethylene powder according to any one of claims 1 to 3.

5. The viscosity average molecular weight calculated by the following (Formula D) using the intrinsic viscosity [η] measured according to ISO 1628-3 (2010) is 200,000 or more and 10,000,000 or less. The polyethylene powder according to any one of claims 1 to 4. Viscosity average molecular weight (Mv) = (5.34 x 104) x [η] 1.49... (Formula D)

6. The polyethylene powder according to any one of claims 1 to 5, which is used for a battery separator.

7. A molded article of the polyethylene powder according to any one of claims 1 to 5.

8. The molded article according to claim 7, which is a microporous membrane.

9. The molded article according to claim 7, which is a fiber.

10. The molded article according to claim 7, which is a battery separator.

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