JP2001072788A - Polyolefin microporous membrane and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microporous polyolefin membrane having a low shutdown temperature, a high meltdown temperature, a small average through-hole diameter, a high strength and a low heat shrinkage. SOLUTION: (A) a composition comprising ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more or ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more and polyethylene having a weight average molecular weight of 10,000 to less than 500,000; 95 melting point
A polyolefin microporous membrane comprising a substantially linear ethylene-α-olefin copolymer and (C) polypropylene produced by using a single-site catalyst at １２５125 ° C., and a method for producing the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microporous polyolefin membrane, and more particularly, to a polyolefin microporous membrane used for a battery separator or the like and having a function of suppressing thermal runaway during overcharge and heat retention tests. It relates to a porous membrane.

[0002]

2. Description of the Related Art Microporous polyolefin membranes are used for various separation membranes, separators for batteries, separators for electrolytic capacitors, and the like. In particular, lithium batteries are being widely used as separators which are insoluble in organic solvents and stable to electrolytes and electrode active materials. As the microporous polyolefin membrane, a high-strength and high-elasticity microporous membrane using an ultra-high-molecular-weight polyolefin is used. For example, an ultra-high-molecular-weight polyolefin having a weight average molecular weight of 7 × 10 ⁵ or more is heated and dissolved in a solvent. A gel-like sheet is formed from the solution thus obtained, the amount of the solvent in the gel-like sheet is adjusted by a desolvation treatment, and after stretching by heating, a microporous membrane is obtained by removing the residual solvent (Japanese Patent Laid-Open No. 60-24235). And the like, and a microporous membrane (JP-A-3-64334) from a high-concentration solution of a polyolefin composition containing an ultrahigh molecular weight polyolefin having a specific molecular weight distribution has been proposed.

[0003] By the way, recent lithium ion battery separators have been demanded to have higher capacity, improved battery characteristics, safety and productivity. That is,
To increase capacity and improve battery characteristics, improve air permeability and liquid retention of the microporous membrane, increase capacity, improve low-temperature rate characteristics and cycle characteristics, and improve safety by short-circuiting electrodes. In order to prevent accidents such as fire when the temperature inside the battery rises, a function to shut down the current that melts and clogs the holes before lithium fires, and further raises the temperature after shutdown The separator itself melts and breaks down (melt down) when it is fired, and has the function of suppressing ignition and explosion of the battery. It also suppresses thermal runaway during overcharge and heat storage tests. It is required to have high strength and the like in order to suppress a minute short circuit due to separator compression due to mixed fine particles.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a low shutdown temperature, high meltdown temperature, small average through-hole diameter,
An object of the present invention is to provide a microporous polyolefin membrane having high strength and low heat shrinkage.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a substantially linear ethylene-α-polymer prepared by using a single-site catalyst on ultra-high molecular weight polyethylene or a composition thereof. By adding an olefin copolymer and polypropylene, it has been found that a microporous membrane having excellent permeation performance and mechanical strength, a low shutdown temperature, a high meltdown temperature, and a low heat shrinkage can be obtained. I arrived. That is, the present invention provides (A) a composition comprising an ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more or an ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more and a polyethylene having a weight average molecular weight of 10,000 to less than 500,000; B) a microporous polyolefin membrane comprising a substantially linear ethylene-α-olefin copolymer and (C) polypropylene, produced using a single-site catalyst having a melting point of 95 to 125 ° C; A) a composition comprising ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more, or ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more and polyethylene having a weight average molecular weight of 10,000 to less than 1,000,000; (B) a melting point of 95 to 125 ° C. Linear ethylene-α-olefin copolymer and (C) polyp produced using a single-site catalyst A solution comprising 10 to 50% by weight of a polyolefin composition comprising propylene and a solvent of 50 to 90% by weight is prepared, and the solution is extruded from a die and cooled to form a gel-like composition. In the method for producing a microporous polyolefin membrane, the stretching of the gel composition is performed at a temperature equal to or lower than the melting point of the polyolefin composition + 10 ° C., and the remaining solvent is removed. while,
Alternatively, it is a method for producing a microporous polyolefin membrane, which is performed before stretching.

Preferred embodiments of the present invention are described below. (A) The polyolefin composition is an ultra-high-molecular-weight polyethylene, a high-density polyethylene, and a substantially linear ethylene-α-olefin copolymer produced using a single-site catalyst having a melting point of 95 to 125 ° C. And the polyolefin microporous membrane comprising polypropylene. (B) (A) a composition comprising ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more, or ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more and polyethylene having a weight average molecular weight of 10,000 to less than 500,000; Is 95-125
(C) a substantially linear ethylene-α-olefin copolymer produced using a single-site catalyst at 10 ° C.
When the total amount of polypropylene is 100% by weight,
(A) is 20 to 90% by weight, (B) is 5 to 35% by weight,
(C) 5 to 35% by weight of the microporous polyolefin membrane. (C) the ultrahigh molecular weight polyethylene has a weight average molecular weight of 1
The said microporous polyolefin membrane which is from 500,000 to 5,000,000. (D) substantially linear ethylene-α- produced using a single-site catalyst having a melting point of 95 to 125 ° C;
Olefin copolymer is an ethylene-octene copolymer,
The said microporous polyolefin membrane which is at least 1 type or more selected from ethylene-heptene copolymer and ethylene-hexene copolymer. (E) The α-olefin copolymerization amount of the substantially linear ethylene-α-olefin copolymer produced using a single-site catalyst at 95 to 125 ° C. is 0.1 to 0.1
The said microporous polyolefin membrane which is 15 mol%. (F) The weight average molecular weight of the polypropylene is 300,000 or more
The said microporous polyolefin membrane which is 1,000,000. (G) The polyolefin microporous membrane having an average through-hole diameter of 0.01 to 0.05 μm. (H) The polyolefin microporous membrane having a porosity of 30 to 95%. (I) The microporous polyolefin membrane having a tensile strength at break of 800 kg / cm ² or more. (V) The microporous polyolefin membrane having an air permeability of 900 sec / 100 cc or less. (I) The microporous polyolefin membrane having a bubble point of 10 kg / cm ² or more. (Iii) The microporous polyolefin membrane having a heat shrinkage of 8% or less. (C) The microporous polyolefin membrane having a shutdown temperature of 90 to 140 ° C, a meltdown temperature of 160 ° C or higher, and a difference between the shutdown temperature and the meltdown temperature of 60 to 80 ° C. (F) The microporous hydrophilized polyolefin membrane, wherein the microporous membrane is hydrophilized with a nonionic surfactant. (V) The method for producing a microporous polyolefin membrane according to the above method for producing a microporous polyolefin membrane, wherein the step of extracting the solvent is performed after stretching.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The components, physical properties and production method of the microporous polyolefin membrane of the present invention will be described in detail below. 1. Polyolefin (A) Ultra-high molecular weight polyethylene component The ultra-high molecular weight polyethylene component (A) used in the microporous polyolefin membrane of the present invention has a weight-average molecular weight of 500,000 or more, preferably 1,000,000 to 5,000,000. Polyethylene or ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more, preferably 1,000,000 to 5,000,000, and polyethylene having a weight average molecular weight of 10,000 to less than 500,000, preferably high molecular weight of 10,000 to less than 500,000. It is a composition comprising high density polyethylene. Ultra high molecular weight polyethylene having a weight average molecular weight of 50
If it is less than 10,000, the strength of the film is undesirably reduced.
On the other hand, the upper limit is not particularly limited, but those having more than 5,000,000 are inferior in moldability in forming a gel-like molded product at the time of producing a microporous membrane. When used as a composition, the ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more preferably contains 20% by weight or more, preferably 30% by weight or more. When the content of the ultrahigh molecular weight polyethylene is less than 20% by weight, a high strength microporous membrane cannot be obtained.
If the weight-average molecular weight of polyethylene, preferably high-density polyethylene, is less than 10,000, the resulting microporous membrane tends to break, and the desired microporous membrane cannot be obtained.

The molecular weight distribution (weight average molecular weight / number average molecular weight) of the ultrahigh molecular weight polyethylene or the ultrahigh molecular weight polyethylene and the polyethylene composition having a weight average molecular weight of 10,000 or more and less than 500,000 is preferably 300 or less, particularly preferably 5 or less. ~
Preferably it is 50. If the molecular weight distribution exceeds 300, breakage due to low molecular weight components occurs, and the strength of the entire film is reduced, which is not preferable. When a polyethylene composition is used, an appropriate amount of ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more and polyethylene having a weight average molecular weight of 10,000 or more and less than 500,000 are mixed so that the molecular weight distribution falls within the above range. This polyethylene composition can be obtained by multi-stage polymerization or a composition of two or more polyethylenes, as long as the polyethylene composition has the above-mentioned weight average molecular weight and molecular weight distribution. Good. The blending ratio of the composition comprising the ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more or the ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more and the polyethylene having a weight average molecular weight of 10,000 or more and less than 500,000 is the total of the polyolefin composition. It is preferably from 20 to 90% by weight, especially from 20 to 80% by weight.
% By weight is preferred. If it is less than 20% by weight, it is difficult to increase the strength, and if it exceeds 90% by weight, the effect of improving the shutdown and meltdown characteristics is not exhibited.

(B) Linear Ethylene-α-Olefin Copolymer As the (B) linear ethylene-α-olefin copolymer used in the present invention, a polyolefin microporous membrane was used as a separator for a lithium battery or the like. It is a polymer that can provide a low-temperature shutdown function in some cases. The linear ethylene-α-olefin copolymer is a linear ethylene-α-olefin copolymer polymerized using a single-site catalyst such as a metallocene catalyst, and is, for example, ethylene-butene-1 copolymer. Examples thereof include a polymer, an ethylene-hexene-1 copolymer, and an ethylene-octene-1 copolymer. The melting point (DSC peak temperature) of the ethylene-α-olefin copolymer is 95 to 125 ° C, preferably 100 to 120 ° C. If the temperature is lower than 95 ° C., the battery characteristics under high temperature conditions are significantly deteriorated. If the temperature exceeds 125 ° C., the shutdown function is not exhibited at a preferable temperature, which is not preferable. The copolymerization amount of the α-olefin of the ethylene-α-olefin copolymer is 0.1 to 15 m
ol%. If it is less than 0.1 mol%, the shutdown characteristics are not improved, and if it exceeds 15 mol%, the strength is greatly reduced, which is not preferable. Weight average molecular weight Mw and number average molecular weight Mn of the ethylene / α-olefin copolymer
Is desirably 1.5 to 3.0, preferably 1.5 to 2.5. By adding this substantially linear ethylene-α-olefin copolymer to ultra-high molecular weight polyethylene or a composition thereof,
By using a microporous polyolefin membrane as a separator for a lithium battery or the like, when the electrodes are short-circuited and the temperature inside the battery rises, a function of shutting down at a low temperature can be provided. Further, the temperature dependency of the film resistance at the time of shutdown is improved, and the shutdown temperature can be freely controlled.
The mixing ratio of the ethylene-α-olefin copolymer is preferably from 5 to 35% by weight of the entire polyolefin composition,
Particularly, 15 to 30% by weight is preferable. If it is less than 5% by weight, the effect of lowering the shutdown temperature is small.

(C) Polypropylene The polypropylene used in the present invention is a homopolypropylene having a weight average molecular weight of 300,000 or more, preferably 300,000 to 1,000,000, or an ethylene propylene random copolymer having an ethylene content of 1.0% by weight or less. An ethylene propylene block copolymer or the like can be used. If the weight average molecular weight is less than 300,000, it becomes difficult to open the resulting microporous polyolefin membrane, and the ethylene content becomes 1.0.
If it exceeds 0% by weight, the crystallinity of the polyolefin will be low, and it will be difficult to open the microporous polyolefin membrane.

By adding polypropylene to ultra high molecular weight polyethylene or its composition, a microporous polyolefin membrane is used as a separator for lithium batteries and the like,
When the temperature inside the battery rises due to short-circuiting of the electrodes, the meltdown temperature increases, and a highly safe battery is obtained. Further, the polypropylene used in the present invention, when using a polyolefin microporous membrane as a battery separator,
There is an effect that microscopic unevenness is generated on the surface of the microporous film, and the retention of the electrolyte is improved. The amount of polypropylene used in the present invention is 5 to 35% of the total polyolefin.
%, Preferably 15 to 30% by weight. If it is less than 5% by weight, the effect of increasing the meltdown temperature is not seen,
If the content exceeds 35% by weight, the strength of the microporous polyolefin membrane is remarkably reduced, and if the content is further increased, polyethylene and polypropylene are phase-separated during sheet molding, and molding is difficult.

(D) Other Ingredients The above-mentioned polyolefin composition may further contain, as necessary, a low density polyethylene, a low molecular weight polyethylene, an antioxidant, an ultraviolet absorber, an antiblocking agent, a pigment, a dye, Various additives such as inorganic fillers can be added within a range that does not impair the purpose of the present invention.

2. Polyolefin microporous membrane The polyolefin microporous membrane of the present invention has the following physical properties. (1) Average Through-pore Diameter The average through-pore diameter of the polyolefin microporous membrane of the present invention is preferably 0.01 to 0.05 μm. If the average through-hole diameter is less than 0.01 μm, the permeability is too low,
When the thickness exceeds 0.05 μm, when used as a battery separator, a short circuit due to dendrite growth is likely to occur, and a defect such as a voltage drop is likely to occur.

(2) Porosity The porosity of the microporous polyolefin membrane of the present invention is 30 to 9
5%, preferably 400 to 80%. Porosity of 30
%, The ionic conductivity is poor when the microporous polyolefin membrane is used as a battery separator, and the battery characteristics such as battery capacity and cycle characteristics at low temperatures are particularly poor. On the other hand, if it exceeds 95%, the strength itself of the film becomes too low, which is not preferable.

(3) Air permeability The air permeability of the microporous polyolefin membrane of the present invention is 900 s.
ec / 100 cc or less, more preferably 50 ec / 100 cc or less.
７００700 sec / 100 cc. 900 s air permeability
When the polyolefin microporous membrane is used as a battery separator, the ion permeation ability is improved by setting the ec / 100 cc or less, so that a low-temperature rate characteristic and a high capacity can be achieved.

(4) Puncture Strength The puncture strength of the microporous polyolefin membrane of the present invention is 400
g / 25 μm or more, more preferably 450 g
/ 25 μm or more. Piercing strength 400g / 25μm
If it is less than 30, when a microporous polyolefin membrane is used as a battery separator, a failure due to a minute short circuit is likely to occur.

(5) Tensile breaking strength The tensile breaking strength of the microporous polyolefin membrane of the present invention is M
It is preferably 800 kg / cm ² or more in both the D and TD directions. When the tensile breaking strength is 800 kg / cm ² or more, when a polyolefin microporous film is used as a battery separator, there is no fear of film breakage, which is preferable.

(6) Bubble point The bubble point of the microporous polyolefin membrane of the present invention is:
It is at least 10 kg / cm ² , preferably at least 15 kg / cm ² , most preferably at least 150 kg / cm ² . When the bubble point is less than 10 kg / cm ² , when the microporous polyolefin membrane is used as a battery separator,
The pores become too large, and the dendrite growth is not preferable because defects such as voltage drop and self-discharge occur.

(7) Heat Shrinkage The heat shrinkage of the microporous polyolefin membrane of the present invention is 8% or less, preferably 5% or less. When the heat shrinkage ratio exceeds 8%, when the microporous polyolefin membrane is used as a battery separator, a phenomenon in which the electrodes are exposed at the time of abnormal battery temperature rise tends to occur, which is not preferable.

(8) Shutdown Temperature and Meltdown Temperature The microporous polyolefin membrane of the present invention has a shutdown temperature of 90 to 140 ° C., preferably 90 to 130 ° C. If the shutdown temperature is lower than 90 ° C., the thermal stability is too low, and if the temperature is higher than 140 ° C., the battery temperature rise cannot be suppressed when a large current flows due to an external short circuit when used as a separator. Absent. The meltdown temperature is 160 ° C. or higher, preferably 170 ° C. or higher. Melt down temperature is 16
If the temperature is lower than 0 ° C., the electrodes are in direct contact with each other during thermal runaway of the battery, which is not preferable. Further, the difference between the shutdown temperature and the meltdown temperature is preferably 60 to 80C.

Since the polyolefin microporous membrane of the present invention has the above-mentioned physical properties, it has a low shutdown temperature,
It is a highly safe microporous membrane as a separator with a high meltdown temperature. In addition, it can be used as a highly productive separator with excellent strength, and despite its high bubble point value, it has a high porosity and is characterized by having high permeability. It can be suitably used as a liquid filter or the like.

3. Production of Microporous Polyolefin Membrane The microporous polyolefin membrane of the present invention is obtained by mixing an organic liquid or a solid with the above polyolefin composition, melt-kneading, extruding, extracting and stretching. Also, there is no problem even if inorganic fine powder is added to the mixture of the resin component and the organic liquid or solid. As a preferable method for obtaining the polyolefin microporous membrane of the present invention, a solution of the polyolefin composition is prepared by supplying a good solvent for the polyolefin to the polyolefin composition, and after extruding this solution into a sheet from a die of an extruder, The gel composition is formed by cooling, and the gel composition is stretched and the residual solvent is removed to produce a microporous polyolefin membrane.

In the present invention, a solution of the polyolefin composition as a raw material is prepared by heating and dissolving the above-mentioned polyolefin composition in a solvent. The solvent is not particularly limited as long as it can sufficiently dissolve the polyolefin. For example, nonane, decane, undecane, dodecane, aliphatic or cyclic hydrocarbons such as liquid paraffin, or a mineral oil fraction having a boiling point corresponding thereto, and the like. To obtain, a non-volatile solvent such as liquid paraffin is preferred. The heating dissolution is performed by stirring at a temperature at which the polyolefin composition is completely dissolved or by a method of uniformly mixing and dissolving in an extruder. The temperature varies depending on the polymer and the solvent used in the case of dissolving while stirring in a solvent in an extruder, but it is preferably in the range of, for example, 140 to 250 ° C. When producing a microporous membrane from a high-concentration solution of the polyolefin composition, it is preferable to dissolve it in an extruder.

When dissolving in an extruder, first, the above-mentioned polyolefin composition is supplied to the extruder and melted. The melting temperature depends on the type of the polyolefin used, but is preferably the melting point of the polyolefin plus 20 to 100 ° C. Here, the melting point is based on JIS K7121.
This is a value measured by DSC (the same applies hereinafter). For example,
160-230 ° C for polyethylene, especially 170-230 ° C
The temperature is preferably 200 ° C, and in the case of polypropylene, it is preferably 190 to 270 ° C, particularly preferably 190 to 250 ° C. Therefore, since the polyolefin composition used in the present invention contains polypropylene as an essential component,
It is preferably from 0 to 270 ° C, particularly preferably from 190 to 250 ° C. Next, a liquid solvent is supplied to the molten polyolefin composition in the middle of the extruder.

The mixing ratio of the polyolefin composition and the solvent is such that the total of the polyolefin composition and the solvent is 100% by weight.
The polyolefin composition is 10 to 50% by weight, preferably 10 to 40% by weight, and the solvent is 90 to 50% by weight, preferably 90 to 60% by weight. When the polyolefin composition is less than 10% by weight (when the solvent exceeds 90% by weight), when forming into a sheet, at the die exit,
The swell and neck-in are large, making the sheet formability and self-supporting difficult. On the other hand, when the polyolefin composition is 50
If the content exceeds 50% by weight (the content of the solvent is less than 50% by weight), the shrinkage in the thickness direction increases, and the moldability decreases. By changing the concentration in this range, the permeability of the membrane can be controlled. In addition, at the time of heating and dissolving, it is preferable to add an antioxidant to prevent oxidation of the polyolefin.

Next, the heated solution of the polyolefin composition melt-kneaded in this manner is directly or further through another extruder, and the thickness of the final product is 5 to 5 mm from a die or the like.
It is extruded and molded to have a thickness of 100 μm. As the die, a sheet die having a rectangular base shape is usually used, but a double cylindrical inflation die or the like can also be used. When a sheet die is used, the die gap is usually 0.1 to 5 mm, and the extrusion temperature is 140 to 250 ° C. At this time, the extrusion speed is
Usually, it is 20 to 30 cm / min to 10 m / min.

The solution thus extruded from the die is formed into a gel composition by cooling.
Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature or less. Generally, when the cooling rate is slow,
The higher order structure of the obtained gel composition becomes coarser, and the pseudo cell units forming the same become larger, but when the cooling rate is high, the cell units become denser. If the cooling rate is less than 50 ° C./min, the degree of crystallinity increases, and it is difficult to obtain a gel composition suitable for stretching. As a cooling method, a method of directly contacting with cold air, cooling water, or another cooling medium, a method of contacting with a roll cooled by a refrigerant, or the like can be used. The solution extruded from the die may be taken up at a take-up ratio of preferably 1 to 10, more preferably 1 to 5, before or during cooling. When the take-up ratio is 10 or more, neck-in becomes large, and breakage tends to occur during stretching, which is not preferable.

Next, this gel-like molded product is stretched. The stretching is performed by heating the gel-like molded product and at a predetermined magnification by a usual tenter method, a roll method, an inflation method, a rolling method or a combination of these methods. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, either vertical or horizontal simultaneous stretching or sequential stretching may be used. The stretching temperature is equal to or lower than the melting point of the polyolefin composition + 10 ° C. The stretching ratio varies depending on the thickness of the raw material, but in biaxial stretching, the area ratio is preferably 9 times or more, more preferably 16 to 400 times. If the area ratio is less than 9 times, stretching is insufficient, and a highly elastic and high-strength microporous film cannot be obtained. On the other hand, if the area magnification exceeds 400 times, restrictions are imposed on the stretching operation and the like.

Next, the stretched molded product is washed with a solvent to remove the residual solvent to obtain a polyolefin microporous membrane. The removal of the residual solvent is performed before and during the stretching step. Any after the stretching step,
It is preferably performed after the stretching step. As a cleaning solvent,
Easily volatile substances such as hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as ethane trifluoride, and ethers such as diethyl ether and dioxane Can be used. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin composition, and used alone or as a mixture. The washing method is a method of immersing and extracting in a solvent,
It can be carried out by a method of showering a solvent, a method of a combination thereof, or the like.

The washing as described above is performed until the residual solvent in the stretch molded product becomes less than 1% by weight. Thereafter, the washing solvent is dried, and the washing solvent can be dried by a method such as heat drying or air drying. It is desirable that the dried stretch molded product is further heat-set.

The heat setting is performed at a relatively high temperature if necessary.
It is performed under a stress that prevents the resulting shrinkage in at least one direction. The heat setting temperature is set in the range of the crystal melting point of the polyolefin composition + 30 ° C or lower. For example, in a composition containing ultrahigh molecular weight polyethylene, 100 to 1
At 40 ° C, more preferably 110 to 130 ° C. When the temperature exceeds the crystal melting point + 30 ° C., the strength of the microporous film is extremely reduced, and the microporous film is dissolved, so that it is difficult to maintain the shape. The time for heat setting is not particularly limited, but may be 0.1.
It is preferable that the time is not less than seconds and not more than 100 hours. If the time is less than 0.1 second, the effect of heat setting is hardly obtained, and the air permeability does not improve much. If the time exceeds 100 hours, not only the productivity is lowered but also the deterioration of the resin becomes severe, which is not preferable.

4. Hydrophilization treatment of polyolefin microporous membrane The polyolefin microporous membrane of the present invention can be subjected to a surface modification such as a hydrophilization treatment by a surfactant treatment, if necessary. As a surfactant used for treating the polyolefin microporous membrane, a polyether-type nonionic surfactant, a sulfone-type ionic surfactant, or the like can be used in the ESCR (environmental stress crack) of the polyolefin microporous membrane. From the viewpoint of deterioration in strength of polyether, non-ionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl allyl ether, fatty acid monoglyceride, and sorbitan fatty acid ester are preferred. In particular, the weight average molecular weight is 1500 to 50,000,
Polyether-type nonionic surfactants having a molecular weight distribution Mw / Mn of 10 or less and a melting point of 30 ° C. or more are preferred.

The surfactant is preferably used as a solution dissolved in a solvent. As the solvent, any type can be used as long as it can dissolve the surfactant.
Solvents selected from at least one or more alcohols from 10 to 10 are preferable, and methyl alcohol, ethyl alcohol
Propyl alcohol, a mixed solvent of water and methyl alcohol, and a mixed solvent of water and ethyl alcohol are preferred. The concentration of the surfactant solution relative to the solvent is 0.01 to
5% by weight is preferred, more preferably 0.1-5% by weight
It is. If the concentration of the surfactant is less than 0.01% by weight,
Insufficient lyophilicity, when used as a separator for batteries / capacitors, causes electrolyte to dry out, causing long-term capacity degradation, and when used as a water treatment filter, lacks long-term permeability, making handling difficult . If the content exceeds 5% by weight, the pores of the polyolefin membrane will be blocked by the treating agent, so that the transfer of ions is hindered when used as a battery / capacitor separator, and air permeability and liquid transfer when used as a filter for water treatment. It is not preferable because the property is hindered.

A solution in which a surfactant is dissolved in the polyolefin microporous film is treated by a roll coater, spray, gravure coat, dipping, doctor blade, or the like. The lyophilic treatment temperature and time are not particularly limited, but are preferably 5 to 60 ° C. and 0.1 to 300 seconds. By this lyophilic treatment, a surfactant of 0.2 to 10% by weight, preferably 0.5 to 2.5% by weight is adhered and coated in the pores of the microporous polyolefin membrane and on the membrane surface. The solvent is removed from the microporous polyolefin membrane to which the surfactant solution obtained above has adhered, followed by drying or heat treatment to obtain the lyophilic microporous membrane of the present invention. For the drying treatment, a hot roll drying method, a hot air drying method, a suction drying method, a dry room drying method or a combination thereof can be used.
The drying temperature is 40 to 130 ° C, and the drying time is 0.5 to 3
A method performed in 00 seconds is preferable.

[0035]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not particularly limited to the examples. In addition, the test method in an Example is as follows. (1) Film thickness: The cross section was measured by a scanning electron microscope. (2) Air permeability: Measured according to JIS P8117. (3) Average through-hole diameter: Measured with a Coulter porometer (manufactured by Coulter). (4) Porosity: measured by a gravimetric method. (5) Puncture strength: 25 μm thick microporous membrane 1 mm in diameter
A (0.5 mmR) needle was pierced at 2 mm / sec, and the load at break was measured. (6) Tensile breaking strength: The breaking strength of a 10 mm-wide strip test piece was measured in accordance with ASTM D822. (7) Bubble point: Measured in ethanol according to ASTM E-128-61. If the measured value exceeds the measurement limit value, it is set to “none” and 150 kg / c
m ² or more. (8) Thermal shrinkage: The film was left in an atmosphere at 105 ° C. for 8 hours, and was determined from changes in the lengths in the MD and TD directions. (9) Shutdown temperature: Measured as a temperature at which the air permeability becomes 100,000 sec / 100 cc or more by heating to a predetermined temperature. (10) Meltdown temperature: Measured as the temperature at which the film melts and breaks when heated to a predetermined temperature.

EXAMPLE 1 30% by weight of ultra-high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000, 40% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000, and ethylene-octene produced with a metallocene catalyst. Polymer (Af
polyolefin composition obtained by adding 0.375 parts by weight of an antioxidant to 100 parts by weight of a composition consisting of 10% by weight of fnityPOPPL1880, melting point of 100 ° C., octene content of 12.0 mol%) and 20% by weight of polypropylene having a weight average molecular weight of 530,000. Was obtained (melting point: 165 ° C.). 30 parts by weight of this polyolefin composition was added to a twin screw extruder (58 mm
φ, L / D = 42, strong kneading type). Also, liquid paraffin 7 is supplied from the side feeder of this twin screw extruder.
0 parts by weight were supplied and melt-kneaded at 200 rpm to prepare a polyolefin solution in an extruder. Subsequently, the extruder was extruded at 190 ° C. from a T-die installed at the tip of the extruder, and a gel-like sheet was formed while being taken up by a cooling roll. Subsequently, the gel-like sheet was simultaneously biaxially stretched 5 × 5 times at 116 ° C. to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove remaining liquid paraffin, and then dried and heat-set at 120 ° C. to obtain a microporous polyolefin membrane. Table 1 shows the composition and production conditions of the microporous polyolefin membrane, and Table 2 shows the results of the physical property evaluation.

Example 2 The procedure of Example 1 was repeated, except that the ethylene-octene copolymer produced with a metallocene catalyst having a melting point of 100 ° C. was replaced with a melting point of 10
A microporous polyolefin membrane was obtained in the same manner as in Example 1, except that an ethylene-octene copolymer (AffnityPOP FM1570, octene content: 7.5 mol%) produced using a metallocene catalyst at 8 ° C was used. Table 1 shows the composition and production conditions of the microporous polyolefin membrane, and Table 2 shows the results of the physical property evaluation. The melting point of the composition is 1
65 ° C.

Example 3 50% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000, 30% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000, and ethylene-octene produced with a metallocene catalyst. Polymer (Af
polyolefin composition obtained by adding 0.375 parts by weight of an antioxidant to 100 parts by weight of a composition consisting of 15 parts by weight and a weight average molecular weight of 530,000 polypropylene 20% by weight (Melting point: 165 ° C.). Twenty parts by weight of this polyolefin composition was added to a twin-screw extruder (58 mm
φ, L / D = 42, strong kneading type). Liquid paraffin 8 is supplied from the side feeder of this twin-screw extruder.
0 parts by weight were supplied and melt-kneaded at 200 rpm to prepare a polyolefin solution in an extruder. Subsequently, the extruder was extruded at 190 ° C. from a T-die installed at the tip of the extruder, and a gel-like sheet was formed while being taken up by a cooling roll. Subsequently, the gel-like sheet was simultaneously biaxially stretched at 115 ° C. 5 × 5 times to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove remaining liquid paraffin, and then dried and heat-set at 120 ° C. to obtain a microporous polyolefin membrane. Table 1 shows the composition and production conditions of the microporous polyolefin membrane, and Table 2 shows the results of the physical property evaluation.

Example 4 The procedure of Example 3 was repeated, except that the ethylene-octene copolymer produced with a metallocene catalyst having a melting point of 100 ° C. was replaced with a melting point of 10
A microporous polyolefin membrane was obtained in the same manner as in Example 3, except that an ethylene-octene copolymer (AffnityPOP FM1570, octene content: 7.5 mol%) produced using a metallocene catalyst at 8 ° C was used. Table 1 shows the composition and production conditions of the microporous polyolefin membrane, and Table 2 shows the results of the physical property evaluation. The melting point of the composition is 1
65 ° C.

Comparative Example 1 An antioxidant was added to 100 parts by weight of a composition comprising 20% by weight of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000 and 80% by weight of 350,000 high density polyethylene (HDPE). A polyolefin composition (melting point: 165 ° C.) to which .375 parts by weight was added was obtained. 30 parts by weight of this polyolefin composition was added to a twin screw extruder (58 mm
φ, L / D = 42, strong kneading type). Also, liquid paraffin 7 is supplied from the side feeder of this twin-screw extruder.
0 parts by weight were supplied and melt-kneaded at 200 rpm to prepare a polyolefin solution in an extruder. Subsequently, the extruder was extruded at 190 ° C. from a T-die installed at the tip of the extruder, and a gel-like sheet was formed while being taken up by a cooling roll. Subsequently, the gel-like sheet was simultaneously biaxially stretched at 115 ° C. 5 × 5 times to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, and then dried and heat-set at 122 ° C. to obtain a polyolefin microporous membrane. Table 1 shows the composition and production conditions of the microporous polyolefin membrane, and Table 2 shows the results of the physical property evaluation.

Comparative Example 2 20% by weight of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000, 60% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000 and polypropylene (PP) 20 having a weight average molecular weight of 530,000 A polyolefin composition (melting point: 165 ° C.) was obtained by adding 0.375 parts by weight of an antioxidant to 100 parts by weight of a composition consisting of 100% by weight. 30 parts by weight of this polyolefin composition was charged into a twin-screw extruder (58 mmφ, L / D = 42, strong kneading type). Also, 70 parts by weight of liquid paraffin was supplied from a side feeder of the twin-screw extruder, and melt-kneaded at 200 rpm to prepare a polyolefin solution in the extruder. Subsequently, 190 D from the T-die installed at the tip of this extruder.
The mixture was extruded at a temperature of ° C. and taken up by a cooling roll to form a gel-like sheet. Subsequently, this gel-like sheet was heated at 115 ° C. for 5 minutes.
Simultaneous biaxial stretching was performed by a factor of 5 to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, and then dried and heat-set at 122 ° C. to obtain a polyolefin microporous membrane. Table 1 shows the composition and production conditions of the microporous polyolefin membrane, and Table 2 shows the results of the physical property evaluation.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

The microporous polyolefin membrane of the present invention is a polyolefin microporous membrane having a high strength, a small average through-hole diameter, a low shutdown temperature and a high meltdown temperature, and was used as a battery separator. In this case, battery characteristics, safety, and productivity can be improved, and in particular, the battery has a function of preventing or reducing thermal runaway during overcharge and heat retention tests. In addition, since it has high film strength, short-circuiting is small even if the electrode packing density is increased,
Since a short circuit due to compression during charge and discharge hardly occurs, when used as a separator for a lithium battery, it is highly reliable in terms of safety and can be suitably used as a filter.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shigeaki Kobayashi 3-27-1-342, Baba, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Koichi Kono 3-29-10-404 F-term, Mihara, Asaka-shi, Saitama (Reference) 4F074 AA17 AA18 AA24 AA98 AB01 AB03 CA03 CA07 CB34 CC02Y CC02Z CC27Y CC27Z CC28Z CC29Y CC29Z CC32Y CC32Z CD14 CD17 DA49

Claims (6)

[Claims] 1. A composition comprising (A) an ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more or an ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more and a polyethylene having a weight average molecular weight of 10,000 to less than 500,000, ) Melting point 95
A polyolefin microporous membrane comprising a substantially linear ethylene-α-olefin copolymer and (C) polypropylene produced using a single-site catalyst at 〜125 ° C. 2. (A) Ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more or ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more and a weight average molecular weight of 10,000 or more and 100
A composition comprising less than 10,000 polyethylene, (B) a melting point of 9
10 to 50% by weight of a polyolefin composition comprising a substantially linear ethylene-α-olefin copolymer and (C) polypropylene produced using a single-site catalyst at 5 to 125 ° C; A solution comprising 90% by weight is prepared, and the solution is extruded from a die, cooled to form a gel composition, and thereafter stretched and a residual solvent is removed, thereby producing a microporous polyolefin membrane. In the method, the stretching of the gel composition is performed at a temperature equal to or lower than the melting point of the polyolefin composition + 10 ° C, and the removal of the residual solvent is performed after the stretching, during the stretching step, or before the stretching. A method for producing a microporous polyolefin membrane. 3. A hydrophilized polyolefin microporous membrane obtained by hydrophilizing the polyolefin microporous membrane according to claim 1. 4. A battery separator using the polyolefin microporous membrane according to claim 1. 5. A battery using the microporous polyolefin membrane according to claim 1 as a battery separator. 6. A filter using the microporous polyolefin membrane according to claim 1 or 3.