JP4979252B2 - Polyolefin microporous membrane - Google Patents

Description

  The present invention relates to a separation membrane for separation of substances, selective permeation, etc., and a microporous membrane widely used as a separator for electrochemical reaction devices such as alkali, lithium secondary batteries, fuel cells, capacitors, etc. The present invention relates to a polyolefin microporous membrane suitably used as a battery separator.

Polyolefin microporous membranes are widely used for separation of various substances, selective permeation separation membranes, and separators. Examples of applications include microfiltration membranes, fuel cell separators, condenser separators, or functional materials. Examples include a base material for a functional film for filling a hole and causing a new function to appear, a battery separator, and the like. In these applications, it is particularly preferably used as a separator for lithium ion batteries widely used in notebook personal computers, mobile phones, digital cameras and the like. The reason for this is that the membrane has mechanical strength and pore blocking properties.
Porosity is a performance that ensures the safety of the battery by melting and closing the hole when the battery is overheated in an overcharged state, etc., and blocking the battery reaction. The lower the temperature, the higher the safety effect.

In addition, the piercing strength and MD (machine direction) / TD (machine direction perpendicular) tensile strength of the separator have a certain level of strength when winding the separator and to prevent short circuit due to foreign matter in the battery. It is required to do.
In addition, in recent lithium-ion secondary batteries, development of alloy-based negative electrode materials, which are new materials, is being promoted in order to increase the battery output and capacity. Some of these new materials have a large expansion rate during charging and tend to increase the surface pressure on the separator. For this reason, the air permeability increases when the separator is crushed, which may adversely affect the cycle test and charge / discharge characteristics of the battery. Therefore, compression resistance to the separator is required.
Further, in recent battery oven tests and the like that become more severe, it is required to reduce the thermal contraction of the separator in order to prevent a short circuit of the electrode due to the thermal contraction of the separator.

So far, Patent Document 1 has proposed a microporous membrane in which fine particles of 1 to 10 μm are dispersed in polyolefin and cleaved around the fine particles. As a result, a certain degree of effect is expected in terms of compression resistance in the surface direction, but with such fine particles, the particles do not protrude from the front and back of the film thickness, and contribute to compression resistance. Not enough. For this reason, the pinning effect in the battery oven test is hardly exhibited. The pinning effect at this time is that when the microporous membrane is exposed to a high temperature such as in a battery oven test, the shrinkage of the microporous membrane is reduced due to the friction between the particles protruding appropriately on the surface of the microporous membrane and the electrode. It is an effect.
Furthermore, the particles present in the separator are limited to non-polyolefins, and the restoration rate against compression becomes insufficient.

Moreover, in patent document 2, the porous film containing the particle | grains whose particle diameter is 0.001-10 micrometers is proposed. However, from the viewpoint of obtaining a smooth film, the particle diameter is adjusted so that the particles do not protrude from the film surface, so that the compression resistance and the pinning effect are not sufficient.
Further, Patent Document 3 proposes a polyethylene resin porous film having a high surface roughness. Thereby, the liquid retention amount of electrolyte solution increases and the effect that the slipperiness of a film improves is anticipated. However, the polyolefin component with a Mv of 300,000 or less, which exhibits rapid pinning effect after melting, is insufficient. In addition, since it is essential that the surface roughness be 3 μm or more, in the thinning as required for batteries in recent years, the ratio of particles to the film thickness becomes too large, which may cause a decrease in strength. It was.

Furthermore, in patent document 4, the liquid retention property of electrolyte solution is improved by providing an unevenness | corrugation on the separator upper surface. However, it is not sufficient to obtain compressibility and a pinning effect only by providing such unevenness only on the upper surface.
JP 2004-149637 A Japanese Patent Laid-Open No. 2003-26847 Japanese Patent Laid-Open No. 11-60791 JP 2002-93456 A

  An object of the present invention is to provide a polyolefin microporous membrane having excellent compression resistance and low heat shrinkage without deteriorating the properties of a conventional polyolefin microporous membrane.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that polyethylene having an Mv of less than 300,000, polyethylene having an Mv of 500,000 or more, and electrochemically inert particles having a thickness greater than Is an essential component, and 0 <A / B × 100 <25 is established between the height A (μm) and the film thickness B (μm) of the portion where the particle protrudes from the film surface. It has been found that a separator having excellent properties and low heat shrinkage can be provided.

That is, the present invention is as follows.
(1) A polyolefin having a viscosity average molecular weight (Mv) of less than 300,000, a polyolefin having an Mv of 500,000 or more, and electrochemically inert particles larger than the film thickness are essential components, and the particles protrude from the film surface. A polyolefin microporous membrane characterized in that 0 <A / B × 100 <25 holds between the height A (μm) of the measured portion and the film thickness B (μm).
(2) The polyolefin microporous membrane according to (1), wherein the electrochemically inert particles are polyolefin particles.
(3) The polyolefin microporous membrane according to (2), wherein the electrochemically inert particles are polyethylene particles.
(4) The polyolefin microporous membrane according to (3), wherein the electrochemically inert particles are polyethylene particles obtained by a multistage polymerization method.
(5) The polyolefin microporous membrane according to any one of (1) to (4), wherein the electrochemically inert particles protrude through the front and back of the membrane.
(6) A non-aqueous electrolyte secondary battery using the polyolefin microporous membrane according to any one of (1) to (5).

  The polyolefin microporous membrane of the present invention has improved compression resistance and heat shrinkage compared to conventional polyolefin microporous membranes. Therefore, by using the microporous membrane of the present invention for the battery separator, it is possible to improve the characteristics of the battery using the pole material having a large expansion coefficient and the safety at high temperature.

The thickness of the polyolefin microporous membrane of the present invention is preferably 1 μm or more, more preferably 5 μm or more, and particularly preferably 10 μm or more from the viewpoint of membrane strength. Moreover, 50 micrometers or less are preferable from a permeability viewpoint, 30 micrometers or less are more preferable, and 20 micrometers or less are especially preferable.
The porosity of the polyolefin microporous membrane of the present invention is preferably 30% or more, more preferably 40% or more from the viewpoint of permeability. Further, from the viewpoint of film strength and withstand voltage, it is preferably 70% or less, more preferably 60% or less.
Although the air permeability of the polyolefin microporous membrane of the present invention is preferably as low as possible, it is preferably 1 sec or more, and more preferably 50 sec or more, from the balance between thickness and porosity. Moreover, 1000 sec or less is preferable from a viewpoint of permeability, and 500 sec or less is more preferable.

The puncture strength of the polyolefin microporous membrane of the present invention is preferably 0.15 N / μm or more, and more preferably 0.20 N / μm or more. When the puncture strength is low, when used as a battery separator, a sharp portion such as an electrode material is pierced into the microporous film, and pinholes and cracks are liable to occur. Therefore, the puncture strength is preferably high.
The tensile strength is preferably 30 MPa or more in both the MD and TD directions, and more preferably 50 MPa or more. If the tensile strength is weak, the battery winding property is deteriorated, or a short circuit is likely to occur due to a battery impact test from the outside or a foreign matter in the battery.
The smaller the heat shrinkage rate, the better. For example, at 105 ° C., both MD and TD are preferably 10% or less, and more preferably 5% or less.

Next, the method for producing the microporous membrane of the present invention will be described. If the resulting microporous membrane has the characteristics satisfying the present invention, the polymer species, solvent species, extrusion method, stretching method, extraction method, There is no limitation in the opening method, heat setting / heat treatment method, and the like.
Next, a preferred method for producing the microporous membrane of the present invention will be described.
The production method of the microporous membrane of the present invention includes melting a polymer material, a plasticizer and, if necessary, an electrochemically inert particle, or a polymer material, a plasticizer, an inorganic agent and, if necessary, an electrochemically inert particle. It is preferable to include a step of kneading and extruding; and a step of heat setting after performing stretching and plasticizer extraction, or stretching and plasticizer extraction, and inorganic agent extraction as necessary.

More specifically, the microporous membrane of the present invention is obtained by a method comprising the following steps (a) to (e).
(A) A polymer material of any of a simple substance of polyolefin, a polyolefin mixture, a polyolefin solvent mixture, and a polyolefin kneaded material is dissolved and kneaded, if necessary, with electrochemically inert particles.
(B) The melted material is extruded, formed into a sheet, and cooled and solidified. If necessary, a plasticizer and an inorganic agent are extracted.
(C) The obtained sheet is stretched in a direction of one axis or more.
(D) After stretching, a plasticizer and an inorganic agent are extracted as necessary.
(E) Next, heat setting and heat treatment are performed.

The electrochemically inert particles used in the present invention are insoluble in a non-aqueous solvent electrolyte, and are inert even under normal oxidation-reduction reactions such as those represented by lithium ion secondary batteries. It is.
Examples of the electrochemically inert particles include inorganic fillers, polyolefin particles, non-polyolefin organic fillers, and the like. These particles need not be completely melted at the time of melt-kneading, and finally have an average particle diameter equal to or larger than the film thickness, or must be adjusted so as to protrude from at least one surface of the film.
The electrochemically inert particles preferably have a certain degree of elastic modulus, and are preferably polyolefin particles, more preferably polyethylene particles, from the viewpoint of excellent restoring ability when compressed. From the viewpoint of film strength, polyethylene particles obtained by a multistage polymerization method are particularly preferred. In the separator made of polyethylene obtained by the multistage polymerization method, it is particularly preferable that the peak top of the molecular weight as measured by GPC is divided into two or more peaks because of excellent compression resistance.

When the particles are polyolefin particles, the particle size in the final separator can be easily controlled. As a method for controlling the particle size in this way, screw rotation speed of the extruder, kneading temperature, control of the particle size of the raw material and the like can be mentioned. At this time, the particle diameter in the final separator can be reduced by increasing the screw rotation, increasing the kneading temperature, or reducing the particle diameter of the raw material.
The screw rotation speed and kneading temperature conditions at this time are not limited because the behavior varies greatly depending on the capacity of the extruder, the screw shape, the extrusion amount, etc., but the screw diameter used in the examples and comparative examples of the present application is not limited, for example. In the case of a twin screw extruder of about 38 mm, the screw rotation is preferably 200 rpm or less with respect to the extrusion amount of 12 kg / h. Particularly preferably, it is 150 rpm or less. When it exceeds 200 rpm, the kneadability of the extruder increases, and the raw material polyolefin hardly remains as particles.

  In the present invention, 0 <A / B × 100 <25 is established between the height A (μm) of the portion where the electrochemically inert particles protrude from the one surface of the separator and the film thickness B (μm). Preferably less than 20, particularly preferably less than 15. The lower limit is preferably 5 <. At this time, one particle may protrude from one side of the separator, but it is more preferable that it protrudes from both sides. This is because, in a system in which pressure is applied to the separator, particles protruding from both surfaces are selectively compressed, so that it is possible to reduce the compression load on other parts having a pore structure. .

Further, when A / B × 100 is 25 or more, the proportion of particles is excessively large when the separator thickness is reduced to 20 μm or less and the strength tends to be insufficient.
The ratio of the particles to the film surface is preferably 5% or more, particularly preferably 10% or more. This occupied area can be measured by using an optical microscope utilizing the difference in transmittance between particles and other locations.

  The polyolefin used in the present invention is a homopolymer of ethylene or propylene, or a copolymer of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene or norbornene. In addition, a mixture of the above polymers may be used. From the viewpoint of the performance of the porous membrane, polyethylene and a copolymer thereof are preferable. Examples of such polyolefin polymerization catalysts include Ziegler-Natta catalysts, Phillips catalysts, metallocene catalysts, and the like.

These polyolefins preferably have a raw material particle size of 40 μm or more and 500 μm or less, and more preferably 60 μm or more and 400 μm, in that particles remain in the final product. If it is smaller than 40 μm, the particles are likely to be uniformly dispersed in the melt-kneading process, making it difficult to leave the particles in the final product, and if it is larger than 500 μm, it is difficult to knead to a desired size.
As a composition to be supplied, it is essential to blend a polyolefin having an Mv of less than 300,000, and preferably less than 200,000.
If less than 300,000 polyolefin is included, the stress relaxation of the separator occurs early in an environment that exceeds the melting point of the polyolefin, so the protruding effect that exceeds the film thickness dramatically improves the pinning effect during heat shrinkage. Can be improved. At this time, when using polyethylene obtained by the multistage polymerization method, it is not essential to blend polyolefin having Mv of less than 300,000 if Mv of the low molecular weight component is less than 300,000. May be blended together.

Further, in view of having both excellent film resistance and strength, a polyolefin having an Mv of less than 300,000 is blended with a polyolefin having an Mv of 500,000 or more, preferably 700,000 or more.
At this time, when a component on the high molecular weight side of polyethylene obtained by a multistage polymerization method is used as a polyolefin component having an Mv of 500,000 or more, entanglement with a component having an Mv of 300,000 or less occurs effectively, resulting in high strength Therefore, it is more preferable.
Polyolefins having an Mv of less than 300,000 and 500,000 or more are preferably contained in an amount of 20% or more of the whole, and more preferably 30% or more.

Furthermore, known additives such as metal soaps such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments can also be mixed and used.
Furthermore, in the present invention, inorganic agents such as alumina and titania can be added. This inorganic agent may be extracted in whole or in part in any of the steps, or may be left in the product.

The plasticizer used in the present invention is an organic compound that can form a uniform solution with polyolefin at a temperature below the boiling point, specifically decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl. Examples include alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, and paraffin oil. Of these, paraffin oil and dioctyl phthalate are preferred.
The proportion of the plasticizer is not particularly limited, but is preferably 20% by weight or more from the viewpoint of the porosity of the obtained film, and preferably 90% by weight or less from the viewpoint of viscosity. More preferably, it is 50 to 70% by weight.

  The extraction solvent used in the present invention is preferably a poor solvent for polyolefins and electrochemically inert particles and a good solvent for plasticizers and has a boiling point lower than the melting point of polyolefin. . Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane, methylene chloride, 1,1,1-trichloroethane, halogenated hydrocarbons such as fluorocarbons, alcohols such as ethanol and isopropanol, and acetone. And ketones such as 2-butanone. It selects from these and uses it individually or in mixture. These extraction solvents may be regenerated by distillation after extraction of the plasticizer and used again.

The total weight ratio of the plasticizer and the electrochemically inactive particles in the total mixture to be melt-kneaded is preferably 20 to 95 wt%, more preferably 30 to 80 wt% from the viewpoint of membrane permeability and film forming property. .
From the viewpoint of preventing thermal deterioration during melt kneading and quality deterioration due thereto, it is preferable to add an antioxidant. The concentration of the antioxidant is preferably 0.3 wt% or more, more preferably 0.5 wt% or more based on the total weight of the polyolefin. Moreover, 5.0 wt% or less is preferable and 3.0 wt% or less is more preferable.
As the antioxidant, a phenolic antioxidant which is a primary antioxidant is preferable, and 2,6-di-t-butyl-4-methylphenol, pentaerythrityl-tetrakis- [3- (3,5-di-) -t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, and the like. Secondary antioxidants can also be used in combination, such as tris (2,4-di-t-butylphenyl) phosphite, tetrakis (2,4-di-t-butylphenyl) -4,4- Examples thereof include phosphorus antioxidants such as biphenylene-diphosphonite and sulfur antioxidants such as dilauryl-thio-dipropionate.

As a method of melt kneading and extrusion, first, a part or all of raw materials are premixed by a Henschel mixer, a ribbon blender, a tumbler blender, or the like as necessary. If the amount is small, it may be stirred by hand. Next, all the raw materials are melt-kneaded by a screw extruder such as a single screw extruder or a twin screw extruder, a kneader, a mixer or the like, and extruded from a T-die or an annular die.
In the polyolefin microporous membrane of the present invention, it is preferable that the raw material polymer is mixed with an antioxidant at a predetermined concentration, and then replaced with a nitrogen atmosphere, and melt kneaded while maintaining the nitrogen atmosphere. The temperature during melt kneading is preferably 160 ° C. or higher, and more preferably 180 ° C. or higher. Moreover, less than 300 degreeC is preferable, less than 240 degreeC is more preferable, and less than 230 degreeC is further more preferable.

The melt referred to in the present application may include an unmelted inorganic agent that can be extracted in the inorganic agent extraction step.
Next, it is preferable to perform sheet forming. As a sheet forming method, a melt-kneaded and extruded melt is solidified by compression cooling. Examples of the cooling method include a method of directly contacting a cooling medium such as cold air and cooling water, a method of contacting a roll cooled by a refrigerant and a press, and a method of contacting a roll cooled by a refrigerant and a press. It is preferable in terms of excellent thickness control.
Subsequently, with regard to stretching and plasticizer extraction, or stretching, plasticizer extraction, and inorganic agent extraction, their order, method, and number of times are not particularly limited. The inorganic agent extraction may not be performed as necessary.

Examples of the stretching method used include MD uniaxial stretching with a roll stretching machine, TD uniaxial stretching with a tenter, sequential biaxial stretching with a roll stretching machine and a tenter, or a combination of a tenter and a tenter, simultaneous biaxial tenter and simultaneous bifurcation with inflation molding. Examples thereof include axial stretching. The stretching ratio is the total surface magnification, and is preferably 8 times or more, more preferably 15 times or more, and most preferably 40 times or more from the viewpoint of film thickness uniformity.
In the plasticizer extraction, the plasticizer is extracted by dipping or showering in an extraction solvent. Then, it is sufficiently dried.

As a heat setting method, a relaxation operation can be performed at a predetermined relaxation rate in a predetermined temperature atmosphere. It can be performed using a tenter or a roll stretching machine. The relaxation operation is an operation for reducing the film to MD and / or TD. The relaxation rate is a value obtained by dividing the MD dimension of the film after the relaxation operation by the MD dimension of the film before the operation, or a value obtained by dividing the TD dimension after the relaxation operation by the TD dimension of the film before the operation, or MD, TD When both are relaxed, it is a value obtained by multiplying the MD relaxation rate and the TD relaxation rate. The predetermined temperature is preferably 100 ° C. or more from the viewpoint of heat shrinkage, and is preferably less than 135 ° C. from the viewpoint of porosity and permeability. The predetermined relaxation rate is preferably 0.9 or less, and more preferably 0.8 or less, from the viewpoint of the heat shrinkage rate. Moreover, it is preferable that it is 0.6 or more from a viewpoint of wrinkle generation | occurrence | production prevention, a porosity, and permeability | transmittance. The relaxation operation may be performed in both the MD and TD directions, but it is possible to reduce the thermal contraction rate not only in the operation direction but also in the operation and vertical direction even in the relaxation operation of only MD or TD.
In addition, surface treatment such as electron beam irradiation, plasma irradiation, surfactant coating, chemical modification, and the like can be performed.

Various physical properties used in the present invention were measured based on the following test methods.
(1) Viscosity average molecular weight Mv
Based on ASTM-D4020, the intrinsic viscosity [η] at 135 ° C. in a decalin solvent is determined. Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 ⁻⁴ Mv ^0.67
(2) Film thickness (μm)
From 20 points randomly selected by the cross-sectional SEM (× 3000 times) of the microporous membrane, the film thickness B and the average height A of the particles protruding from one side of the separator surface were measured.
(3) Porosity (%)
A sample of 10 cm × 10 cm square was cut out from the microporous membrane, its volume (cm ³ ) and mass (g) were determined, and calculated from these and the film density (g / cm ³ ) using the following formula.
Porosity = (volume−mass / film density) / volume × 100
The film density was calculated at a constant 0.95.

(4) Air permeability (sec)
Based on JIS P-8117, it measured with the Gurley type air permeability meter (Toyo Seiki Co., Ltd. product, G-B2 (trademark)).
(5) Puncture strength (N / μm)
By using a KES-G5 (trademark) handy compression tester manufactured by Kato Tech, the needle tip curvature radius is 0.5 mm and the needle stick speed is 2 mm / sec. The puncture load (N) was determined.

(6) Tensile strength (MPa), tensile elongation (%)
Based on JIS K7127, it measured about MD and TD sample (shape; width 10mm x length 100mm) using the tensile tester by Shimadzu Corporation, and autograph AG-A type (trademark). Moreover, the sample used the thing which stuck the cellophane tape (the Nitto Denko Packaging System Co., Ltd. make, brand name: N.29) to the single side | surface of the both ends (each 25mm) of the sample between chuck | zippers. Furthermore, in order to prevent sample slipping during the test, 1 mm-thick fluororubber was affixed inside the chuck of the tensile tester.
The tensile elongation (%) was obtained by dividing the amount of elongation (mm) up to fracture by the distance between chucks (50 mm) and multiplying by 100.
The tensile strength (MPa) was obtained by dividing the strength at break by the sample cross-sectional area before the test. The measurement was performed at a temperature of 23 ± 2 ° C., a chuck pressure of 0.30 MPa, and a tensile speed of 200 mm / min (in the case of a sample where the distance between chucks cannot be secured 50 mm, the strain rate is 400% / min).

(7) Thermal shrinkage at 105 ° C. Cut to 100 mm in the MD direction and 100 mm in the TD direction, and leave in an oven at 105 ° C. for 1 hour. At this time, sandwich the two sheets of paper so that the warm air does not directly hit the sample. After taking out from the oven and cooling, the length (mm) is measured, and the thermal contraction rate of MD and TD is calculated by the following formula.
MD thermal shrinkage (%) = (100−MD length after heating) / 100 × 100
TD heat shrinkage rate (%) = (100−length of TD after heating) / 100 × 100
The MD / TD heat shrinkage ratio was calculated according to the following formula. (For samples for which the sample length cannot be secured, the sample is as long as possible within the range of 100 mm × 100 mm.)

(8) Air permeability change rate After cutting the sample into 50 mm x 50 mm and stacking 20 sheets, the sample was compressed with a press machine at 55 ° C for 5 seconds so as to be 80% of the initial total thickness including protruding particles, and pressed. The subsequent air permeability was measured. The air permeability change rate was calculated from the following equation. The air permeability before and after pressing was an average value of 20 sheets each.
Air permeability change rate (%) = (air permeability after pressing−initial air permeability) / initial air permeability × 100

(9) Battery evaluation Preparation of positive electrode: 92.2% by weight of lithium cobalt composite oxide LiCoO ₂ as an active material, 2.3% by weight of flake graphite and acetylene black as a conductive agent, and polyvinylidene fluoride as a binder ( A slurry was prepared by dispersing 3.2% by weight of PVDF in N-methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material coating amount of the positive electrode is 250 g / m ² and the active material bulk density is 3.00 g / cm ³ . This was cut into a width of about 40 mm to form a strip.

Production of negative electrode: 96.9% by weight of artificial graphite as active material, 1.4% by weight of ammonium salt of carboxymethyl cellulose and 1.7% by weight of styrene-butadiene copolymer latex as a binder were dispersed in purified water to prepare a slurry. did. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material application amount of the negative electrode was set to 106 g / m ² , and the active material bulk density was set to 1.35 g / cm ³ . This was cut into a width of about 40 mm to form a strip.

Preparation of non-aqueous electrolyte: Prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 mol / liter.
Battery assembly: The above-mentioned microporous membrane separator, strip-shaped positive electrode and strip-shaped negative electrode were stacked in the order of the strip-shaped negative electrode, the separator, the strip-shaped positive electrode and the separator and wound in a spiral shape to produce an electrode plate laminate. After pressing this electrode plate laminate into a flat plate, it is housed in an aluminum container, the aluminum lead led out from the positive electrode current collector is used as the container wall, and the nickel lead derived from the negative electrode current collector is used as the container lid terminal part. Connected.

The lithium ion battery thus manufactured has a size of 6.3 mm in length (thickness), 30 mm in width, and 48 mm in height. This battery was charged to a battery voltage of 4.2 V at a current value of (0.5 C) in an atmosphere of 25 ° C., and then the current value was started to be reduced so as to hold 4.2 V, thereby producing a battery for a total of 6 hours. After the first charge.
In order to perform an oven test on this battery, the battery after charging was heated from room temperature to 150 ° C. at a rate of 5 ° C./min and left at 150 ° C. for 30 minutes. Those that did not ignite were evaluated as good.

  The present invention will be described based on examples.

[Example 1]
Using a tumbler blender, 70 wt% of a homopolymer polyethylene having an Mv of 250,000 and 30 wt% of a homopolymer polyethylene having an Mv of 3 million and an average particle diameter of 150 μm were dry blended. 1 wt% of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99 wt% of the obtained pure polymer mixture, and the tumbler blender was again used. By using and dry blending, a polymer mixture was obtained. The obtained mixture of polymers and the like was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump.

The feeder and the pump were adjusted so that the liquid paraffin content ratio in the total mixture melt-kneaded and extruded was 70 wt%. The melt kneading conditions were a set temperature of 200 ° C., a screw rotation speed of 120 rpm, and a discharge rate of 12 kg / h.
Subsequently, the melt-kneaded material was extruded and cast on a cooling roll controlled at a surface temperature of 25 ° C. through a T-die, thereby obtaining a gel sheet having a thickness of 2000 μm.
Next, it led to the simultaneous biaxial tenter stretching machine, and biaxial stretching was performed. The set stretching conditions are an MD magnification of 7.0 times, a TD magnification of 6.4 times, and a set temperature of 120 ° C.

Next, the solution was introduced into a methyl ethyl ketone tank and sufficiently immersed in methyl ethyl ketone to extract and remove liquid paraffin, and then the methyl ethyl ketone was removed by drying.
Next, it was led to a TD tenter and heat fixed. The heat setting temperature was 125 ° C., and the TD relaxation rate was 0.80.
When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, all of them were good results.

[Example 2]
Using a tumbler blender, 75 wt% of an ethylene propylene copolymer (comonomer: prepylene, content ratio 0.6 mol%) having an Mv of 120,000 and 25 wt% of a homopolymer polyethylene having an Mv of 4.5 million and an average particle diameter of 180 μm Dry blended. 1 wt% of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99 wt% of the obtained pure polymer mixture, and the tumbler blender was again used. By using and dry blending, a polymer mixture was obtained. The obtained mixture of polymers and the like was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump.

The feeder and the pump were adjusted so that the liquid paraffin content ratio in the total mixture melt-kneaded and extruded was 70 wt%. The melt kneading conditions were a set temperature of 200 ° C., a screw rotation speed of 120 rpm, and a discharge rate of 12 kg / h.
Subsequently, the melt-kneaded material was extruded and cast on a cooling roll controlled at a surface temperature of 25 ° C. through a T-die, thereby obtaining a gel sheet having a thickness of 2000 μm.
Next, it led to the simultaneous biaxial tenter stretching machine, and biaxial stretching was performed. The set stretching conditions are an MD magnification of 7.0 times, a TD magnification of 6.4 times, and a set temperature of 120 ° C.
Next, the solution was introduced into a methyl ethyl ketone tank and sufficiently immersed in methyl ethyl ketone to extract and remove liquid paraffin, and then the methyl ethyl ketone was removed by drying.
Next, it was led to a TD tenter and heat fixed. The heat setting temperature was 120 ° C., and the TD relaxation rate was 0.80. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, all of them were good results.

[Example 3]
70 wt% homopolymer polyethylene with an Mv of 100,000, 20 wt% homopolymer polyethylene with an Mv of 2.5 million and an average particle size of 150 μm, and homopolymer polypropylene with an Mv of 400,000 and an average particle size of 200 μm It was produced in the same manner as in Example 1 except that 10 wt% was used.
Table 1 shows the physical properties of the obtained microporous membrane. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
As a result of battery evaluation, all of them were good results.

[Example 4]
It was produced in the same manner as in Example 3 except that the screw rotation speed was 150 rpm.
Table 1 shows the physical properties of the obtained microporous membrane. When the cross-sectional photograph of the separator was observed, a structure in which the particles protruded only from one side of the separator was confirmed.
As a result of battery evaluation, all of them were good results.

[Example 5]
Polyethylene having a Mv of 800,000, Mw / Mn of 58, a low molecular weight component of Mv of 50,000, and a weight ratio of the high molecular weight component to the low molecular weight component of 1: 1 is used, and the heat setting temperature is 123 ° C. It was produced in the same manner as in Example 1 except that. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, all of them were good results.

[Example 6]
Example 5 except that polyethylene having Mv of 800,000, Mw / Mn of 65, low molecular weight component of Mv of 30,000, and a weight ratio of high molecular weight component to low molecular weight component of 1: 1 was used. It produced similarly. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, all of them were good results.

[Example 7]
It was produced in the same manner as in Example 5 except that the screw rotation speed was 150 rpm and the thickness during casting was 1600 μm. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, all of them were good results.

[Example 8]
It was produced in the same manner as in Example 5 except that the screw rotation speed was 170 rpm and the thickness at casting was 1000 μm. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, all of them were good results.

[Example 9]
Example 1 except that 45 wt% of homopolymer polyethylene having an Mv of 250,000, 45 wt% of homopolymer polyethylene having an Mv of 700,000, and 10 wt% of polypropylene having an Mv of 400,000 and an average particle size of 200 μm were used. It produced similarly. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, all of them were good results.

[Example 10]
Example 1 except that 45 wt% of homopolymer polyethylene having an Mv of 250,000, 45 wt% of homopolymer polyethylene having an Mv of 700,000, and 10 wt% of polyetheretherketone having an average particle size adjusted to 30 μm were used. It produced similarly. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, all of them were good results.

[Comparative Example 1]
Example 1 except that 18 wt% of homopolymer polyethylene having an Mv of 500,000, 36 wt% of homopolymer polyethylene having an Mv of 1 million, and 46 wt% of calcium carbonate powder having an average particle size of 35 μm were used. went. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, good results were not obtained in oven characteristics, and the strength was weak.

[Comparative Example 2]
24 wt% of homopolymer polyethylene with an Mv of 500,000, 47 wt% of homopolymer polyethylene with an Mv of 1 million, and 29 wt% of homopolymer polyethylene with an Mv of 5.7 million and an average particle size of 150 μm, The same operation as in Example 1 was performed. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, good results were not obtained in oven characteristics, and the strength was weak.

[Comparative Example 3]
Example 1 except that 70 wt% of homopolymer polyethylene having an Mv of 350,000, 20 wt% of homopolymer polyethylene having an Mv of 2 million, and 10 wt% of polybutylene terephthalate powder having an average particle size of 4 μm were used. The same was done. When a cross-sectional photograph of the separator was observed, a structure in which the particles protruded from the front and back of the separator was not confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, good results were not obtained in terms of oven characteristics, and the rate of increase in air permeability after compression showed a high value.

[Comparative Example 4]
Other than using polyethylene with Mv of 600,000, Mw / Mn of 50, low molecular weight component of Mv of 100,000, high molecular weight component to low molecular weight component weight ratio of 1: 1, and screw rotation speed of 240 rpm Was produced in the same manner as in Example 4. When the cross-sectional photograph of the separator was observed, the physical properties of the obtained microporous film in which no particles were confirmed are shown in Table 1.
As a result of battery evaluation, good results were not obtained in terms of oven characteristics, and the rate of increase in air permeability after compression showed a high value.

[Comparative Example 5]
It was produced in the same manner as in Example 1 except that 90 wt% of polyethylene having an Mv of 250,000 and 10 wt% of the polyether ether ketone used in Example 10 were used, and the simultaneous biaxial stretching temperature was 118 ° C. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
The physical properties of the obtained microporous membrane are shown in Table 1.
As a result of battery evaluation, good results were not obtained in oven characteristics.

[Comparative Example 6]
It was produced in the same manner as in Example 7 except that the screw rotation speed was 100 rpm.
The physical properties of the obtained microporous membrane are shown in Table 1. When the cross-sectional photograph of the separator was observed, a structure in which one particle penetrated and protruded from the front and back of the separator was confirmed.
As a result of battery evaluation, good results were not obtained in oven characteristics, and the strength was weak.

  The present invention relates to a microporous membrane used for substance separation, a permselective separation membrane, a separator, and the like, and is particularly suitably used as a separator for a lithium ion battery or the like.

Claims (5)

A portion having a viscosity average molecular weight (Mv) of less than 300,000, a polyolefin having an Mv of 500,000 or more, and a polyolefin particle having an average particle diameter of a film thickness or more as essential components, and the particle protruding from the film surface A microporous membrane made of polyolefin, characterized in that 0 <A / B × 100 <25 holds between the height A (μm) and the film thickness B (μm). 2. The polyolefin microporous membrane according to claim 1, wherein the polyolefin particles are polyethylene particles. 3. The polyolefin microporous membrane according to claim 2, wherein the polyolefin particles are polyethylene particles obtained by a multistage polymerization method. The polyolefin microporous membrane according to any one of claims 1 to 3 , wherein the polyolefin particles protrude from the front and back of the membrane. Non-aqueous electrolyte secondary battery using the polyolefin microporous membrane according to any one of claims 1-4.