WO2007116672A1

WO2007116672A1 - Polyolefin microporous film

Info

Publication number: WO2007116672A1
Application number: PCT/JP2007/056170
Authority: WO
Inventors: Daisuke Inagaki; Yosuke Inoue
Original assignee: Asahi Kasei Chemicals Corporation
Priority date: 2006-03-30
Filing date: 2007-03-26
Publication date: 2007-10-18
Also published as: KR101060380B1; KR20080102255A; JPWO2007116672A1; CN101384429B; TWI348969B; CN101384429A; TW200808547A; JP4931911B2

Abstract

A polyolefin microporous film being a laminate of three or more layers including two surface layers and at least one interlayer, characterized in that the limiting viscosity [η] of the interlayer is 3.0 dl/g or higher, and that the limiting viscosity [η] of the surface layers is smaller than the limiting viscosity [η] of the interlayer, and that the absolute value of the difference between the pore closing temperature of the surface layers and the pore closing temperature of the interlayer is less than 10°C.

Description

Specification

Polyolefin microporous membrane

Technical field

[0001] The present invention is widely used as a separation membrane used for separation of substances, selective permeation, and the like, and as a separator for electrochemical reaction devices such as alkali, lithium secondary batteries, fuel cells, capacitors, etc. The present invention relates to a microporous membrane. In particular, the present invention relates to a polyolefin microporous membrane suitably used as a separator for non-aqueous electrolyte batteries such as lithium ion batteries. Background art

[0002] Polyolefin microporous membranes are widely used as separation of various substances, selective permeation separation membranes, separators and the like. Specific examples of applications include microfiltration membranes, separators for lithium secondary batteries and fuel cells, separators for capacitors, and various functional materials filled in the holes to create new functions. Examples include base materials for functional membranes. Among these uses, it is particularly suitably 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 polyolefin microporous membrane is excellent in mechanical strength of the membrane and has good pore blocking properties.

[0003] Pore occluding property means that when the battery is overheated in an overcharged state, the polymer constituting the membrane melts and closes the pores, blocking the reaction inside the cell and blocking the electric resistance of the membrane. This is a performance that enhances battery safety and ensures battery safety. The lower the temperature at which pore clogging occurs, the higher the safety effect.

Furthermore, as a function of the separator, it is necessary to maintain the film shape even after the hole is closed and to maintain insulation between the electrodes. Therefore, the short temperature is high! Would you like it?

In recent years, as the capacity of batteries has increased, separator thin films and high porosity have been demanded. However, there is a concern that short-circuiting may occur due to a decrease in puncture strength associated with thinning and high porosity. Therefore, it is desirable to reduce the film thickness while maintaining the strength of the separator. In addition to this, in order to prevent the short circuit due to foreign matter in the battery when winding the separator, the piercing strength, machine direction (MD direction) and machine of the separator The tensile strength in the machine direction and the perpendicular direction (TD direction) must have a certain level of strength. In addition, it is necessary to have a low heat shrinkage (low heat shrinkage) at high temperatures, such as battery drying processes, high-temperature storage tests, high-temperature cycle tests, and oven tests.

In general, a separator has a low heat shrinkage rate. This is because when the battery is at a high temperature, the separator shrinks and the isolation function between the electrodes is lost. However, there is generally a contradictory relationship between increasing the strength and the heat shrinkage rate.

[0004] Patent Document 1 proposes a film in which a microporous film obtained by blending ultrahigh molecular weight polyethylene and polypropylene and a polyethylene microporous film are laminated. However, this method limits the amount of heat that can be imparted to the membrane in the heat setting step where the difference in pore clogging temperature between the layer of blended ultra-high molecular weight polyethylene and polypropylene and the layer of polyethylene alone is large. As a result, it is difficult to achieve both high tensile strength and low thermal shrinkage sufficiently, and the physical properties that can be imparted are limited. In addition, since the difference in the hole closing temperature between the layers is large, there remains a problem in safety. Furthermore, since heat fixation is performed according to the melting point of the low melting point component, low heat shrinkability is also insufficient.

[0005] Patent Document 2 proposes a film having a high tensile strength by bonding a surface layer made of a high molecular weight polyolefin having a tensile strength of lOOOKgZcm ² or more and an intermediate layer made of an ethylene-based copolymer. However, there is a concern that these methods increase the heat shrinkage rate. In addition, the hole closing temperature in the entire membrane with a large difference in the hole closing temperature between layers increases.

[0006] Patent Document 3 proposes a laminated film containing a low melting point component on the positive electrode side. In this method, the hole closing property is improved, but the low melting point component is contained only on the positive electrode side, so that the electrode sticking effect is insufficient. In addition, since the melting point difference between the surface layer and the intermediate layer is large, the heat setting temperature has to be lowered, and the low heat shrinkability is insufficient.

[0007] Patent Document 4 proposes improvement of hole closing properties by laminating films having different porosity. However, there is no description regarding strength and heat shrinkability. Therefore, heat shrinkage is expected to be high.

Patent Document 1: Japanese Patent Laid-Open No. 2002-321323

Patent Document 2: JP-A-8-99382 Patent Document 3: Japanese Patent Laid-Open No. 2002-367587

Patent Document 4: Japanese Patent Application Laid-Open No. 2002-319386

Disclosure of the invention

Problems to be solved by the invention

[0008] An object of the present invention is to provide a polyolefin microporous membrane that maintains safety even when overheated and satisfies mechanical strength.

Means for solving the problem

[0009] As a result of intensive studies to achieve the above object, the inventors of the present invention have obtained the intrinsic viscosity of both the surface layer and the intermediate layer in order to obtain a polyolefin microporous membrane having a layered body strength of three or more layers, and By paying attention to the relationship between both surface layers and the intermediate layer, it has been found that the above problems can be solved even with a porous microporous membrane that maintains its porosity and strength. That is, the present invention is as follows.

[0010] (1) A polyolefin microporous membrane that is a laminate of three or more layers including two surface layers and at least one intermediate layer, wherein the intrinsic viscosity [r?] Of the intermediate layer is 3. OdlZg In addition, the intrinsic viscosity [r?] Of the surface layer is smaller than the intrinsic viscosity [r?] Of the intermediate layer, and the absolute value of the difference between the pore closing temperature of the surface layer and the pore closing temperature of the intermediate layer Polyolefin microporous membrane characterized by a temperature of less than 10 ° C.

(2) The polyolefin microporous membrane as described in (1) above, wherein both surface layers are composed only of polyethylene.

(3) The polyolefin microporous membrane according to (1) or (2) above, wherein both surface layers have the same composition.

(4) The polyolefin microporous membrane according to any one of (1) to (3) above, wherein the tensile strength in the direction perpendicular to the machine (TD direction) of the membrane is 30 MPa or more.

(5) The absolute value of the difference between the pore closing temperature of the surface layer and the pore closing temperature of the intermediate layer is 5 ° C. or less, wherein the polyolefin fine particles according to any one of (1) to (4) above are characterized. Porous membrane.

(6) The polyolefin microporous membrane according to any one of (1) to (5) above, which is produced using a composition containing polyolefin and a plasticizer.

(7) A polymer material and a plasticizer are melted and kneaded to form a laminated sheet by coextrusion, The method for producing a polyolefin microporous membrane according to any one of (1) to (6), comprising a step of heat setting after biaxial stretching and extraction of a plasticizer.

(8) Polyolefin microporous material obtained by melting and kneading polymer material and plasticizer to form a laminated sheet by coextrusion, biaxial stretching and extracting the plasticizer, followed by heat setting film.

(9) A separator for a non-aqueous electrolyte battery using the polyolefin microporous membrane according to any one of (1) to (6) and (8) above.

(10) A non-aqueous electrolyte battery using the separator according to (9) above.

The invention's effect

[0011] The polyolefin microporous membrane of the present invention is high in strength, but has a smaller heat shrinkage ratio when heated than a conventional polyolefin microporous membrane. In addition, when the membrane is stuck to an electrode or the like during overheating (hereinafter referred to as a sticking effect), the membrane separation effect can be reliably maintained. Therefore, when the microporous membrane of the present invention is used particularly for a battery separator, it is possible to ensure the safety of the battery.

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] The polyolefin microporous membrane of the present invention needs to have a force of three or more layers including two surface layers and at least one intermediate layer in order to maintain different kinds of physical properties. As used herein, the surface layer refers to the two outermost layers of the film laminated in three or more layers, and the intermediate layer refers to the other layers. The intermediate layer may be a single layer or a plurality of layers, but the intermediate layer is preferably a single layer from the viewpoint of productivity.

[0013] The surface layer is composed of one or more polyolefins. On the other hand, the intermediate layer is also composed of one or more polyolefins.

Here, the polyolefin used as the polymer material in the present invention is, for example, polyethylene, a homopolymer of polypropylene, or these homopolymers and ethylene, propylene and 1-butene, 4-methyl-1 pentene, 1 A copolymer of 1-hexene, 1-octene, norbornene and the like, and a mixture of the above-mentioned polymers may be used. From the viewpoint of the performance of the porous membrane, polyethylene and its copolymer are preferred. The polymerization catalysts for these polyolefins include Ziegler Natta catalysts, Phillips catalysts, A catalyst etc. are mentioned. Polyolefin may be obtained by a single-stage polymerization method or may be obtained by a multi-stage polymerization method.

Further, the polyolefin microporous membrane of the present invention may be added with known additives such as metal stalagmites such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. Agents can also be mixed and used.

[0016] In the polyolefin microporous membrane of the present invention, the intrinsic viscosity [r?] Of the intermediate layer is 3. OdlZg or more, and the intrinsic viscosity [7?] Of the surface layer is smaller than the intrinsic viscosity [7?] Of the intermediate layer. There is a need. By maintaining the intrinsic viscosity of the surface layer and the intermediate layer within this range, it is possible to exert the effect of adhering the film surface layer when heat is applied to the film as long as the strength of the film can be maintained. From the viewpoint of the balance between the film sticking effect and the puncture strength, the intrinsic viscosity of the intermediate layer is preferably 2. OdlZg or more, more preferably 5. OdlZg or less than the intrinsic viscosity of the surface layer.

[0017] If the intrinsic viscosity of the intermediate layer is less than 3. OdlZg, the mechanical strength of the entire film such as piercing strength and tensile strength is lowered. 3. 5dlZg or more is preferred 4. OdlZg or more is more preferred 5. OdlZg or more is more preferred. Further, since the heat shrinkage rate is small, 7. Odl / g or less is preferable.

The intrinsic viscosity [τ?] Of the surface layer is preferably less than 3. OdlZg, and the point force at which the effect of sticking to the electrode due to stress relaxation at high temperature appears more remarkably is also preferable. Moreover, it is preferable that it is less than 2.5 dlZg in that it has both low fuse characteristics and high short-circuit characteristics. 2. It is more preferable that it is less than OdlZg. Furthermore, from the viewpoint of strength, it is preferably greater than 1. Odl / g. The intrinsic viscosity [r?] Of the layer depends on the intrinsic viscosity [r?] Of the polyolefin component contained in the layer and its ratio. Therefore, by adjusting the polymer composition of each layer and the ratio thereof, the range of the intrinsic viscosity specified in the present invention can be achieved. The intrinsic viscosity [7?] Is the intrinsic viscosity [η] at 135 ° C in a decalin solvent based on ASTM-D4020.

[0018] In the polyolefin microporous membrane of the present invention, the difference between the pore closing temperature of the surface layer and the pore closing temperature of the intermediate layer needs to be less than 10 ° C. As a result, pore clogging occurs in almost all layers at substantially the same temperature, so that the pores can be clogged in the entire membrane. This temperature difference is preferably 5 ° C or less, more preferably 3 ° C or less. . The pore closing temperature depends on the lowest melting point of the polyolefin component contained in the layer. Therefore, the pore closing temperature of the surface layer and the intermediate layer can be set by selecting a polymer yarn having a desired melting point.

[0019] The hole closing temperature was measured by the following method. That is, a microporous membrane was set in the apparatus shown in FIG. 1 (A), the temperature was raised from 25 ° C to 200 ° C at a rate of 2 ° CZmin, and an alternating current of 1kHz was applied. The temperature and electrical resistance at this time were measured continuously, and the temperature at which the electrical resistance value of the microporous membrane reached 10 ³ Ω was defined as the pore closing temperature.

In addition, the surface layer of the polyolefin microporous membrane of the present invention can exhibit the same sticking effect on the positive electrode and the negative electrode in the battery when the membrane is overheated, and can maintain the isolation between the electrodes.

For the sake of running stability when the battery is wound, the outermost layer is preferably composed of the same component.

[0020] In addition, since the pore closing temperature is lowered, it is preferable that it is composed only of polyethylene, and more preferably, both surface layers are composed only of polyethylene!

The tensile strength in the MD direction is preferably lOOMPa or more because it is resistant to external impact tests on the battery and is less likely to cause a short circuit due to foreign matter in the battery. More preferably, it is l lOMPa or more.

[0021] The tensile strength in the TD direction is preferably 30 MPa or more, more preferably 60 MPa or more, because the battery is resistant to external impact tests on the battery and causes a short circuit due to foreign matter in the battery. More preferably 90 MPa or more.

[0022] The thickness of the entire film is preferably 5 m or more in order to maintain mechanical strength and to completely insulate the electrodes. In addition, when incorporated in a separator of a small battery, it is preferably 40 m or less, more preferably 10 to 20 m. The thickness of the surface layer is preferably 0.1 μm or more in order to easily achieve the sticking effect during overheating, and the strength of the entire film is preferably 10 μm or less, more preferably 1 to 5 μm. .

[0023] When used as a battery separator, the porosity is preferably 20% or more from the viewpoint of preventing an increase in the internal resistance of the battery, and the mechanical strength is preferably 70% or less, and more preferably 30 to 30%. 50%. The air permeability is preferably lOsecZcc or more from the viewpoint of mechanical strength and 1000 sec / cc or less from the viewpoint of permeation performance, more preferably from 30 to 700 secZlOOcc force. I prefer ~ 500secZcc! / ヽ.

[0024] The puncture strength is 3. ON / 25 μm or more from the viewpoint of preventing film breakage by the electrode active material. S is preferable, 4. ONZ25 m or more is more preferable 5.5 NZ25 m or more That force S is more preferable.

[0025] The heat shrinkage rate when measured in a state where the microporous membrane is not restrained at 130 ° C is preferably as low as possible. Specifically, the thermal shrinkage rate in the MD direction is preferably less than 30%. The thermal shrinkage in the TD direction is preferably 30% or less, more preferably less than 20%, and even more preferably 15%.

[0026] The above TD tensile strength, overall film thickness, porosity, puncture strength, and crystallinity are determined by the composition ratio of the polyolefin component contained in the layer, extrusion conditions, stretching conditions, plasticizer extraction conditions, and heat setting conditions. Adjustments can be made by appropriate changes.

[0027] Since the polyolefin microporous membrane of the present invention is particularly effective when used as a battery separator, the force mainly described for use in this application is the microporous membrane of the present invention. It can also be used as a base material for microfiltration membranes, condenser separators, and functional membranes for filling various functional materials into the holes to bring out new functions. In that case, the membrane has the advantage of being able to increase the stability of the separation membrane and the base material by having the effect that the entire membrane is uniformly clogged in a short time during overheating and the surface of the membrane sticks. .

[0028] Next, a method for producing a microporous membrane of the present invention will be described.

[0029] As a method for producing the microporous membrane of the present invention, as long as the polymer material of both the surface layer and the intermediate layer is selected so that the obtained microporous membrane has characteristics satisfying the present invention, the polymer species and the solvent species are selected. In the extrusion method, stretching method, extraction method, hole opening method, heat setting, heat treatment method and the like, there is no limitation. Moreover, an inorganic substance can also be mixed in a raw material. In this case, the inorganic substance may be extracted during the production process or may be contained as it is.

In order to obtain the properties of the polyolefin microporous membrane of the present invention, the following composition is preferred.

[0030] The surface layer and the intermediate layer may be one or more kinds of polyolefin ink. In order to produce a microporous membrane as defined in the present invention, the intrinsic viscosity [r?] Of the surface polymer should be less than 3. OdlZg. More preferably, the polyolefin having an intrinsic viscosity [r?] Of 1.5 dlZg or less is contained in an amount of 50 wt% or more. On the other hand, the polymer of the intermediate layer also has one or more polyolefin forces. The intrinsic viscosity [τ?] Of the polymer in the intermediate layer must be 3. OdlZg or more, and when two or more types of polyolefine are used, the polyolefin having an intrinsic viscosity [r?] Of 4.5 dlZg or more. It is more preferable that it is composed of 30 wt% or more, and it is more preferable that it is composed of 50 wt% or more. In addition, the absolute value of the difference between the melting point of the component having the lowest melting point contained in the surface polymer and the melting point of the component having the lowest melting point contained in the intermediate layer polymer is selected to be less than 10 ° C. There is a need to. The absolute value of the difference between the melting points of the components having the lowest melting point contained in the polymer of the surface layer and the intermediate layer is preferably 5 ° C or less, more preferably 3 ° C or less.

[0031] Furthermore, known additives such as metal stones such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments are added to the polymer material. I can do it. These additives are not particularly limited as long as the effect of a force additive that can be added to a raw material, melted and kneaded of a polymer, or after stretching is expressed.

The microporous membrane of the present invention can be obtained by melt-kneading a polymer material, extruding it, stretching it, heat setting and heat treatment. More specifically, it can be obtained by a method comprising the following steps (a) to (e).

[0032] (a) Melt kneading

First, raw materials such as surface layer and intermediate layer polymers are melt-kneaded. The melt-kneading can be performed by a screw extruder such as a single screw extruder or a twin screw extruder, a kneader, a mixer or the like. Some or all of the raw materials may be pre-mixed with a Henschel mixer, a ribbon blender, a tumbler blender, etc. as necessary. If the amount is small, it may be stirred by hand. The temperature at the time of melt kneading is preferably 160 ° C or higher, more preferably 180 ° C or higher. Further, less than 300 ° C is preferable, and less than 240 ° C is more preferable, and less than 230 ° C is more preferable.

Further, a plasticizer may be used in order to facilitate the work in the melt-kneading process and the subsequent extrusion process and to facilitate the production of the microporous membrane of the present invention. The plasticizer is added before melting and kneading. As long as it is before the extrusion process, such as during melt kneading.

[0033] (b) Extrusion 'cooling

The obtained melt-kneaded product is extruded, formed into a sheet shape to obtain a gel sheet, and this is cooled and solidified. Extrusion molding includes a method of cooling the sheet die force such as a slit die and a T die with an extrusion cast tool, and a method of cooling after an inflation method. For the lamination of the surface layer and the intermediate layer, either the method of co-extrusion with a single die by integrating the gel sheets obtained with the respective extruder force, or the method of extruding each of the gel sheets and superimposing them to heat-seal them Can be made. The coextrusion method is more productive. In addition, the obtained film is more preferable because it easily obtains high interlayer adhesion strength and easily forms communication holes between the layers, so that the permeability of the film is easily maintained.

[0034] (c) Stretching

The obtained sheet is stretched in a uniaxial or biaxial or more direction. It is preferable to stretch biaxially or more because it is easy to ensure the strength of the resulting film, and it is preferable to stretch in the biaxial direction at the same time because there are fewer stretching steps. There are no particular restrictions on the stretching method and the number of stretching operations. For example, MD-axial stretching with a roll stretching machine, TD-axial stretching with a tenter, roll stretching machine and tenter, or a combination of tenter and tenter. Examples include secondary biaxial stretching, simultaneous biaxial tenter and simultaneous biaxial stretching by inflation molding. From the viewpoint of film thickness productivity, the draw ratio is preferably a total surface magnification of 8 times or more, more preferably 26 times or more, and most preferably a force of 40 times or more. The upper limit of the uniformity of the film is preferably 100 times or less, more preferably 65 times or less.

[0035] (d) Plasticizer extraction

When a plasticizer is added to the polymer material in (a), the plasticizer is extracted as necessary. There are no particular restrictions on the timing, method, and number of plasticizer extractions. For example, the plasticizer is extracted using an extraction solvent after stretching. In this case, the plasticizer is extracted by immersing the stretched sheet in an extraction solvent or showering. Then, it is sufficiently dried.

[0036] (e) Heat setting and heat treatment

The obtained stretched sheet is subjected to heat setting and heat treatment. As a heat setting method, a relaxation operation is performed so that a predetermined relaxation rate is obtained in a predetermined temperature atmosphere. The relaxation operation means that the stretched sheet is M It is an operation to reduce in the D direction and Z or TD direction. The relaxation rate is the 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 the value obtained by dividing the TD dimension after the relaxation operation by the TD dimension of the film before the operation, or When both MD and TD are relaxed, the value is the product of the MD relaxation rate and the TD relaxation rate. Specific methods include a method using a tenter or a roll drawing machine. The predetermined temperature is preferably less than 135 ° C. in order to make the porosity and permeability preferable above 100 ° C. in order to lower the heat shrinkage rate and in the above-mentioned preferable range. The predetermined relaxation rate is preferably 0.9 or less, and more preferably 0.8 or less, in order to reduce the heat shrinkage rate. Further, in order to prevent the generation of wrinkles and to make the porosity and permeability within the above-mentioned preferable ranges, it is preferably 0.6 or more. The relaxation operation may be performed in both the MD direction and the TD direction, but may be performed only in one direction in the MD direction or the TD direction. Even when the relaxation operation is performed in one direction, it is possible to reduce the heat shrinkage rate not only in the operation direction but also in the direction perpendicular to the operation direction.

[0037] Further, surface treatment such as electron beam irradiation, plasma irradiation, surfactant coating, chemical modification, etc. can be applied to the surface of the heat-set stretched sheet.

Further, it is preferable that the master roll after the heat setting is aged at a predetermined temperature, and then the master roll is rewound. This step releases the residual stress of the polyolefin in the master roll. The heat treatment temperature of the master roll is preferably 35 ° C or higher, more preferably 45 ° C or higher, particularly preferably 60 ° C or higher. Further, 120 ° C. or less is preferable from the viewpoint of maintaining the permeability of the membrane.

[0038] Plasticizers that can be used in the present invention include organic compounds that can form a homogeneous solution with polyolefin at temperatures below the boiling point, and specifically include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl. Examples include alcohol, oleyl alcohol, decyl alcohol, normal alcohol, diphenyl ether, _n -decane, _n -dodecane, and paraffin oil. Of these, paraffin oil and dioctyl phthalate are preferable.

[0039] The proportion of the plasticizer is not particularly limited, but it is preferable to add 20% by weight or more in all layers with respect to the amount of raw material input in each layer in order to keep the porosity of the obtained film in an appropriate range. In order to make the viscosity within an appropriate range, it is preferable that the content is 90% by weight or less in all layers. More preferably, it is 50 to 70% by weight.

[0040] The extraction solvent that can be used in the present invention is preferably a poor solvent for polyolefin, a good solvent for plasticizer, and a boiling point lower than the melting point of polyolefin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane, halogenated hydrocarbons such as methylene chloride, 1,1,1 trichloroethane, fluorocarbon, ethanol and isopropanol. And alcohols such as acetone and ketones such as acetone and 2-butanone. Select from among these, and use alone or in combination. These extraction solvents may be regenerated by distillation after extraction of the plasticizer and used again.

[0041] From the viewpoint of preventing thermal deterioration during melt kneading and quality deterioration due thereto, it is preferable to add an anti-oxidation agent in the step (a). In particular, from the standpoint of the material properties, it is preferable that the resin is calcined before heating. The concentration of the antioxidant is preferably 0.3 wt% or more, more preferably 0.5 wt% or more, based on the weight of the total polyolefin material. Further, 5.0% or less is preferable, and 3.0% or less is more preferable.

[0042] Phenol-based acid-detergents, which are primary acid-detergents, are preferred as acid-detergents. 2,6-Di-tert-butyl-4-methylphenol, pentaerythrityl-tetrakis [3 — (3,5-di-tert-butyl 4-hydroxyphenol) propionate], octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenol) propionate, and the like. Secondary anti-oxidation agents can also be used in combination with tris (2,4 di-t-butylphenol) phosphite, tetrakis (2,4-di-t-butylphenol), 1,4,4 Examples thereof include phosphoric acid inhibitors such as biphenylene phosphonite and thio acid inhibitors such as dilauric dithiopropionate.

[0043] Further, as described above, after mixing the raw material polymer with the anti-oxidation agent at a predetermined concentration, the inside of the mixer or the extruder is replaced with a nitrogen atmosphere, and the mixture is melted while maintaining the nitrogen atmosphere. It is preferable to perform kneading.

[0044] When the microporous membrane of the present invention is used as a battery separator, for example, a battery may be prepared by the following method.

[0045] First, the microporous membrane is formed into a vertically long shape having a width of 10 mm to: LOO mm and a length of 200 mm to 2000 mm. To do. The separators are stacked in the order of positive electrode separator, negative electrode separator, or negative electrode separator positive electrode separator, and wound into a circular or flat spiral shape. Further, the wound body is accommodated in a battery can and an electrolyte is injected.

[0046] The type of the battery in the present invention is not particularly limited, but it is preferably a non-aqueous electrolyte battery from the viewpoint of the affinity between the polyolefin microporous membrane and the electrolyte. In addition, a lithium ion battery is more preferable from the viewpoint of providing excellent safety when the microporous membrane of the present invention is used as a separator.

Example

[0047] The present invention will be described based on examples.

Various physical properties used in the present invention were measured based on the following test methods.

The (1) intrinsic viscosity and (11) pore closing temperature were measured for each layer by separating the surface layer and the intermediate layer from the laminated film. The peeling method is described below.

[0048] A sample was cut into an arbitrary size, and a curing cloth tape manufactured by Sliontec Co., Ltd. was attached to the entire surface of one surface. Attach and pull the crossing tape made of Sliontec Co., Ltd. on a part of the surface layer opposite to the layer on which the crossing tape made by Sliontec Co., Ltd. is applied. The surface layer on the side where the cross tape was not applied to the entire surface was peeled off. Paste Sliontec Co., Ltd.'s curing cloth tape on the entire surface of one side of the peeled laminate. Paste Sliontec Co., Ltd.'s curing cloth tape on a part of the opposite layer. Any layer was peeled off.

[0049] (1) Intrinsic viscosity [7?] And viscosity average molecular weight (Mv)

Based on ASTM-D4020, the intrinsic viscosity [] at 135 ° C in decalin solvent was determined. The Mv of polyethylene was calculated by the following formula.

[τ?] = 6. 77 Χ 10 " ⁴ Μν ° · ⁶⁷

For polypropylene, Mv was calculated according to the following formula.

[r?] = l. 10 Χ 10- ⁴ Μν ° · ⁸⁰

The Mv of the layer was calculated from the polyethylene equation.

(2) Film thickness m)

Measured at room temperature 23 people at 2 ° C using KBM (trademark), a micro thickness gauge from Toyo Seiki Seisakusho Co., Ltd. It was.

[0050] (3) Porosity (%)

A sample of lOcm × 10 cm square was cut from a microporous membrane, and its volume (cm ³ ) and mass (g) were determined. From these and the film density (gZcm ³ ), the following equation was used.

Porosity = (volume mass Z film density) Z volume X 100

The film density was calculated at a constant 0.95.

(4) Air permeability (sec)

Based on JIS P-8117, it was measured with a Gurley type air permeability meter (G-B2 (trademark), manufactured by Toyo Seiki Seisakusho Co., Ltd.).

(5) Puncture strength (g), (NZ25 m)

Using a KES-G5 (trademark) handy compression tester manufactured by Kato Tech, the maximum piercing is performed by performing a piercing test in a 23 ± 2 ° C atmosphere with a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mmZsec. The puncture strength (NZ25 μm) obtained by multiplying the load (N) by Z25 (μm) was calculated.

[0051] (6) Tensile strength (MPa), Tensile elongation (%)

In accordance with JIS K7127, measurement was performed using a tensile tester manufactured by Shimadzu Corporation, Autograph AG-A type (trademark). This sample (shape: width 10 mm x length 100 mm) was cut in the MD and TD directions. The sample used was a sample with a chuck spacing of 50 mm and cellophane tape (Nitto Denko Packaging System Co., Ltd., trade name: N. 29) on one side of each end of the sample (25 mm each). Furthermore, in order to prevent sample slip during the test, lmm-thick fluororubber was affixed inside the chuck of the tensile tester.

The tensile elongation (%) was obtained by dividing the amount of elongation (mm) until the sample broke by the distance between chucks (5 Omm) and multiplying by 100.

The tensile strength (MPa) was obtained by dividing the strength at break of the sample by the cross-sectional area of the sample before the test. Also, by summing the MD direction value and the TD direction value, the total (%) of MD tensile elongation and TD tensile elongation was obtained. The measurement was performed at a temperature of 23 ± 2 ° C, a chuck pressure of 0.30 MPa, and a tensile speed of 200 mmZ (for a sample where the distance between chucks cannot be secured to 50 mm, the strain rate is 400% Z). [0052] (7) Melting point

Measurement was performed using DSC-220C manufactured by Seiko Ichi Kogyo Co., Ltd. The sample was punched into a circle with a diameter of 5 mm, and several sheets were stacked to make 3 mg. This was spread on an aluminum open sample pan with a diameter of 5 mm, a crimping cover was put on, and it was fixed in the aluminum pan with a sample sealer. The temperature from 30 ° C to 180 ° C was measured at a rate of temperature increase of 10 ° CZmin, and the temperature at which the melting endotherm curve was maximized was taken as the melting point.

(8) Terminal vinyl group concentration

After making the polyolefin microporous film into a thickness of about 1 mm using a heating press, it was measured with an infrared spectrophotometer (FTS60AZ896ZU MA300 manufactured by Varian Technologies Japan Limited). Absorbance at 910 cm ^_1, the density of the polyolefin microporous film (g / cm3) and the thickness of the sample from (mm), POLYMER LETTERS

VOL. 2, PP. 339-341 Referring to the concentration of terminal bur groups, that is, the number of terminal bur groups per 10,000 carbon atoms in polyethylene (hereinafter this unit is expressed in units of Zio, 000C). (Expressed) was calculated from the following equation. The calculation was performed by rounding down the decimals.

Terminal vinyl group concentration (pieces ZIO, 000C) = 11. 4 X absorbance Z (density'thickness)

The unit of density is gZcm ³ and the unit of thickness is mm.

[0053] (9) 130 ° C heat shrinkage

A sample cut to 100 mm in the MD direction and 100 mm in the TD direction was left in an oven at 130 ° C for 1 hour. At this time, it was sandwiched between two sheets of paper so that the sample was not directly exposed to the hot air. After removing from the oven and cooling, the length (mm) was measured, and the thermal shrinkage of MD and TD was calculated by the following formula.

MD heat shrinkage rate (%) = (100—MD length after heating) Z100 X 100 TD heat shrinkage rate (%) = (100—TD length after heating) Z100 X 100 (10) Hole closure temperature

Fig. 1 (A) shows a schematic diagram of a device for measuring the hole closing temperature. 1 is a microporous film, 2A and 2B are 10 m thick nickel foil, and 3A and 3B are glass plates. 4 is an electric resistance measuring device (LCR meter “AG-4311” (trademark) manufactured by Ando Electric Co., Ltd.), which is in contact with nickel foils 2A and 2B. It has been continued. 5 is a thermocouple connected to a thermometer 6. A data collector 7 is connected to the electrical resistance measuring device 4 and the thermometer 6. 8 is an oven in which the microporous membrane was heated.

Further, a measurement method using this apparatus will be described in detail with reference to FIGS.

As shown in FIG. 1 (B), the microporous membrane 1 was superposed on the nickel foil 2A, and this was fixed to the nickel foil 2A with “Teflon” (registered trademark) tape (shaded portion in the figure) in the vertical direction. The microporous membrane 1 was impregnated with an ImolZ liter lithium borofluoride solution (solvent: propylene carbonate Z ethylene carbonate Ύ butyl rataton = 1 Ζ 1 Ζ 2) as the electrolyte. As shown in Fig. 1 (C), "Teflon" (registered trademark) tape (shaded area in the figure) is pasted onto nickel foil 2mm, leaving a 15mm x 10mm window part in the center of foil 2mm. Masked.

[0055] Nickel foil 2A and nickel foil 2B were superposed so as to sandwich microporous film 1, and two nickel foils were sandwiched between glass plates 3A and 3B. At this time, it was arranged so that the window portion of the foil 2B and the porous membrane 1 were at opposite positions.

The two glass plates were fixed by sandwiching with a commercially available double clip. The thermocouple 5 was fixed to the glass plate with “Teflon” (registered trademark) tape.

Temperature and electric resistance were continuously measured with such an apparatus. When the temperature was increased from 25 ° C to 200 ° C at a rate of 2 ° CZ min and measured at an alternating current of 1 kHz, the temperature at which the electrical resistance of the microporous membrane reached ^ 10 ³ Ω was defined as the pore closure temperature. Defined.

[0056] (11) Battery evaluation

Fabrication of positive electrode: 92.2% by weight of lithium cobalt composite oxide LiCoO as the active material

2

Each 2.3% by weight of scaly graphite and acetylene black as a conductive agent, polyvinylidene as a binder one mold - isopropylidene (PVDF) 3. dispersed therein 2 wt ^_0/0 in N-methylpyrrolidone (NMP) and the slurry Was prepared. This slurry was applied to one side of a 20 / zm 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 amount of active material applied to the positive electrode was 250 gZm ² and the bulk density of the active material was 3.OOgZcm ³ . This was cut to a width of about 40 mm to form a strip.

[0057] Preparation of negative electrode: artificial graphite 96.9% by weight as an active material, ammonium of carboxymethyl sheet methylcellulose as binders - © beam salt 1.4 wt ^_0/0 and styrene-butadiene copolymer La Tex 1. A slurry was prepared by dispersing 7% by weight in purified water. This slurry was applied to one side of a 12 m 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 coating amount of the negative electrode was set to 106 gZm ² , and the active material bulk density was set to 1.35 gZcm ³ . This was cut to a width of about 40 mm to form a strip.

[0058] 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. OmolZ liter.

Battery assembly: The above microporous membrane separator, strip-shaped positive electrode, and strip-shaped negative electrode were stacked in the order of the strip-shaped negative electrode, separator, strip-shaped positive electrode, and separator, and wound in a spiral shape to produce an electrode plate laminate. This electrode plate laminate is pressed into a flat plate shape and then housed in an aluminum container. The aluminum lead derived from the positive electrode current collector force is placed on the container wall, and the nickel lead derived from the negative electrode current collector is placed on the container lid terminal. Connected to the department.

Thereafter, after drying at 65 ° C. for 8 hours under vacuum, the above-mentioned non-aqueous electrolyte was poured into the container and sealed.

The lithium-ion battery thus fabricated was 6.3 mm in length (thickness), 30 mm in width, and 48 mm in height. The battery voltage at a current value of (0.5C) in an atmosphere of 25 ° C 4.2

The battery was charged to V, and then the current value was started to be reduced so as to hold 4.2 V. The first charge after the battery was made for a total of 6 hours was performed.

[0060] (a) In order to perform an oven test on this battery, the battery after charging was charged from room temperature.

The temperature was raised to 0 ° C at a rate of 5 ° CZ and left at 150 ° C for 1 hour.

As a result, X was fired in less than 10 minutes, ○ was fired until 30 minutes, and ◎ was fired for 1 hour.

[0061] (b) In order to perform a collision test of this battery, 1. 9m high force Repeated on the concrete floor 1

Dropped 0 times. Thereafter, the battery was disassembled, and the state of the separator was observed. A separator that did not cause a short circuit due to a single deformation was evaluated as good.

[Example 1]

Using two extruders, a microporous membrane consisting of two surface and intermediate layers with the same composition was made. Made. The composition of the surface layer is as follows: [7?] Is 1.2 dlZg, Mv is 70,000, 45% by weight of homopolymer polyethylene with a melting point of 133 ° C, [7?] Is 2.8 dlZg, Mv is 250,000, and the melting point is The homopolymer polyethylene was 45 wt% at 136 ° C, [7?] ^ 4.9 dlZg, and the homopolymer polypropylene was 5 wt% with Mv 400,000. The intermediate layer has a [7?] Force of 6dlZg, Mv of 700,000 and a homopolymer polyethylene with a melting point of 135 ° C of 46.5 wt%, [7?] 2.8dlZg, Mv Power 250,000, 136. The homopolymer polyethylene of C was 46.5 wt%, [7?] 4.9 dl / g, and the homopolymer polypropylene of Mv 400,000 was 7 wt%. Each of these yarns was blended. As an antioxidant, 0.3 wt% tetrakis (methylene 3- (3,5,1-di-tert-butyl 4'-hydroxyphenol) propylene) methane was mixed with the total polymer in each layer. did. Each composition was introduced into a twin screw extruder having a diameter of 25 mm and LZD = 48 via a feeder. Furthermore, 50 wt% of flow paraffin (37.78 ° C kinematic viscosity 75.90cSt) is injected into each extruder from the side feed with respect to 50wt% of polymer in each layer, and kneaded under the conditions of 200 ° C and 200rpm. The T-die force that can be co-extruded installed at the tip of the extruder was also extruded. After that, it was immediately cooled and solidified with a cast roll cooled to 25 ° C. to form a sheet having a thickness of 1.1 mm. This sheet was stretched 7 × 4 times with a simultaneous biaxial stretching machine at 124 ° C. Thereafter, this stretched sheet was immersed in methylene chloride, and the fluid paraffin was extracted and dried, followed by heat treatment at 120 ° C. to obtain a microporous membrane. The physical properties of the obtained microporous membrane are shown in Tables 1 and 2.

[Example 2]

The composition of the surface layer is 50 wt% of homopolymer polyethylene with [7?] Of 1.2 dlZg, Mv of 70,000 and melting point of 133 ° C, and [7?] Force of .8dlZg, Mv of 250,000 and melting point. A microporous membrane was prepared in the same manner as in Example 1 except that the homopolymer polyethylene at 136 ° C. was changed to 50 wt%. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2.

[Example 3]

Using three extruders, a microporous membrane consisting of two surface and intermediate layers with different compositions was produced. The composition of the surface layer on one side is: [r?] Is 1.2 dlZg, Mv is 70,000, homopolymer polyethylene 50wt% with a melting point of 133 ° C, [7?] Is 2.8dlZg, Mv is 25 Homopolymer with a melting point of 136 ° C is 50 wt% of polyethylene. Liquid paraffin (37.78 ° C kinematic viscosity 75.90cSt) 50wt% was injected into each extruder from the side feed. On the other hand, the composition of the surface layer on the opposite side is as follows: [r?] Is 1.2 dl / g, Mv is 70,000, 50 wt% of homopolymer polyethylene with a melting point of 133 ° C, [] force. 8 dl / g, Each surface layer is 30 wt% of a homopolymer with an Mv of 250,000 and a melting point of 136 ° C, and a homopolymer of 20 wt% with an [r?] Of 5.6 dlZg, an Mv of 700,000 and a melting point of 135 ° C. A microporous membrane was formed in the same manner as in Example 1 except that 65 wt% of liquid paraffin (37.78 ° C kinematic viscosity 75.90 cSt) was injected into the surface layer extruder from the side feed with respect to 35 wt% of the polymer. Produced. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2.

[0064] [Example 4]

A microporous membrane was prepared in the same manner as in Example 2 except that the thickness of the sheet was 0.7 mm. Tables 1 and 2 show the physical properties of the prepared microporous membrane.

[Example 5]

The composition of the surface layer is as follows: [7?] Is 1.7 dlZg, Mv is 120,000, the copolymer is 50 wt% of polyethylene with a melting point of 127 ° C, [7?] Is 2.8 dlZg, Mv is 250,000, and the melting point is A microporous membrane was prepared in the same manner as in Example 3 except that 50 wt% of the homopolymer polyethylene at 136 ° C. was used and the heat treatment temperature was 117 ° C. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2.

[Example 6]

A microporous membrane was prepared in the same manner as in Example 2 except that the thickness of the sheet was 1.3 mm and the sheet was stretched 7 × 7 times with a simultaneous biaxial stretching machine. The physical properties produced are shown in Tables 1 and 2.

[0065] [Example 7]

The composition of the surface is 75 dl% of homopolymer polyethylene with [7?] 1.2 dlZg, Mv 70,000 and melting point 133 ° C, [7?] 2.8 dlZg, Mv 250,000, melting point A microporous membrane was prepared in the same manner as in Example 5 except that homopolymer polyethylene at 136 ° C. was changed to 25 wt%. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2.

[Example 8]

The surface layer is composed of yarn, [7?] Is 1.2dlZg, Mv is 70,000, homopolymer polyethylene 50wt% with melting point 133 ° C, [7?] Is 2.8dlZg, Mv is 250,000 30 wt% homopolymer polyethylene with a melting point of 136 ° C, [7?] Is 5.6dlZg, Mv is 700,000, and the melting point is 135 ° C. Except for injecting 65 wt% liquid paraffin (37.78 cC kinematic viscosity 75.90 cSt) into the surface layer extruder from the side layer feed with 20 wt% homopolymer 20 wt%. A microporous membrane was prepared as in 5. Tables 1 and 2 show the properties of the prepared microporous membrane.

[Example 9]

The composition of the surface layer is as follows: [r?] Is 3.2 dlZg, Mv 300,000, melting point is 136 ° C, terminal bur group concentration is 10 ZlO, OOOC 50 wt% homopolymer polyethylene, [7?] 2 A microporous membrane was prepared in the same manner as in Example 5, except that 50 wt% of homopolymer polyethylene having an Odl / g, Mvl of 50,000, and a melting point of 133 ° C. was used. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2.

[Example 10]

The composition of the intermediate layer is [7?] 11.3 dlZg, Mv 2 million, 30 wt% of homopolymer polyethylene with melting point 135 ° C, [7?] Force 2. 8 dlZg, Mv 250,000, 70 wt% homopolymer polyethylene with a melting point of 136 ° C, and 65 wt% liquid paraffin (kinematic viscosity at 37.78 ° C 75.90 cSt) from the side feed to the intermediate layer 35 wt% A microporous membrane was prepared in the same manner as in Example 5 except that the microporous membrane was injected into the extruder. Tables 1 and 2 show the physical properties of the fabricated microporous membrane.

[Example 11]

The composition of the intermediate layer is [7?] 13. ldl / g, Mv 2.5 million, 20 wt% homopolymer polyethylene with melting point 135 ° C, [7?] 5.6 dlZg, Mv 700,000 15 wt% of homopolymer polyethylene with a melting point of 135 ° C, 30 wt% of homopolymer polyethylene with a melting point of 136 ℃, 2.8 dlZg, Mv of 250,000 ] Is 1.7 dlZg, Mvl 20,000, melting point 131 ° C, ethylene propylene copolymer (comonomer: prepylene, content ratio 0.6 mol%) is 30 wt%, and liquid paraffin is used for 35% of the intermediate layer polymer. (37.7 Kinematic viscosity at 8 ° C 75.90cSt) Microporous membrane as in Example 5, except that 65wt% was injected from the side feed into the intermediate layer extruder and the heat treatment temperature was set to 118 ° C. Was made. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2.

[0067] [Example 12] The intermediate layer is composed of 15 wt% of a molecular weight of 10,000 or less, MwZMn is 43, [] is 5.6 dlZg, Mv is 700,000, and a homopolymer polyethylene having a melting point of 137 ° C is 80 wt%. A microporous membrane was prepared in the same manner as in Example 5 except that the homopolymer polypropylene of Μν400,000 and [] was 4.9 dlZg and 20 wt%. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2.

[Example 13]

[7?] Is 13. ldl / g, Mv is 2.5 million, homopolymer polyethylene of melting point 132 ° C is 25wt% 7?] Is 1.7dlZg, Mv is 120,000, 75% by weight of ethylene propylene copolymer (comonomer: prepylene, content ratio 0.6 mol%) having a melting point of 131 ° C was used for liquid paraffin (37.78 ° C dynamic viscosity 75%) relative to 35% by weight of the above polymer. .9 OcSt) A microporous membrane was prepared in the same manner as in Example 5 except that 65 wt% was injected from the side feed into the intermediate layer extruder and the heat treatment temperature was set to 118 ° C. Tables 1 and 2 show the physical properties of the prepared microporous membrane.

All the microporous membranes shown in the examples obtained in Examples 1 to 13 were made into batteries and then left in an oven at 150 ° C. for 1 hour. As a result, nothing ignited within at least 30 minutes. 1. A 9m high force was applied to the concrete floor 10 times, and it did not ignite. When the battery after the test was disassembled and the separator contraction was confirmed, no short circuit of the electrode due to the contraction of the separator was observed. In addition, a short circuit due to deformation of the force separator, which was tested to repeatedly drop 10 times from the height of L 9m onto the concrete floor, was not observed.

In addition, when all the films were measured for crystallinity using DSC (Differential Scanning Calorimetry), the crystallinity of all layers exceeded 70%.

[Comparative Example 1]

The composition of the surface layer is as follows: [7?] Is 1.2dlZg, Mv is 70,000, homopolymer polyethylene 45wt% with melting point 133 ° C, [7?] Is 2.8dlZg, Mv is 250,000, melting point The intermediate layer is 45 wt% of homopolymer with a temperature of 136 ° C and [7?] 4.9 dlZg, and the Mv400,000 homopolymer polypropylene is 5 wt%. Example 5 and Example 5 except that the homopolymer polyethylene with an Mv of 210,000 and a melting point of 136 ° C is 95 wt%, and [7?] 9 dlZg and the homopolymer polypropylene with an Mv of 400,000 is 5 wt%. Similarly, make a microporous membrane Made. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2.

As a result of battery evaluation, good results were not obtained in oven test and crash test

[0069] [Comparative Example 2]

The composition of the surface is 75 dl% of homopolymer polyethylene with [7?] 1.2 dlZg, Mv 70,000 and melting point 133 ° C, and [7?] Force. 8dlZg, Mv 250,000 with melting point 136 A microporous membrane was prepared in the same manner as in Comparative Example 1 except that the polyethylene was 25 wt% of the homopolymer at ° C and the sheet thickness was 2. Omm. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2. As a result of the battery evaluation, the oven test proved to be satisfactory.

[Comparative Example 3]

A microporous membrane was prepared in the same manner as in Comparative Example 2, except that the thickness of the sheet was 0.7 mm and the sheet was stretched 7 × 4 times with a simultaneous biaxial stretching machine. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2. As a result of battery evaluation, good results were not obtained in the oven test and the crash test.

[0070] [Comparative Example 4]

The composition of the surface layer is [7?] 5.6 dlZg, Mv is 700,000 and the melting point is 135 ° C. The homopolymer polyethylene is 100 wt%, and liquid paraffin (37.78 ° C A microporous membrane was prepared in the same manner as in Example 5 except that 70 wt% was injected into the surface layer extruder by side feed. Tables 1 and 2 show the physical properties of the fabricated microporous membrane.

As a result of the battery evaluation, the oven test proved to be satisfactory.

[Comparative Example 5]

The composition of the surface layer is [7?] 1.7 dlZg, Mv is 120,000, and the copolymer has a melting point of 125 ° C, 50 wt% of polyethylene, [7?] Force. 8 dlZg, Mv is 250,000, and the melting point is 136. A microporous membrane was prepared in the same manner as in Example 5 except that 50% by weight of the homopolymer polyethylene at ° C, the temperature of the biaxial stretching machine was 121 ° C, and the heat treatment temperature was 115 ° C. Tables 1 and 2 show the physical properties of the fabricated microporous membrane.

As a result of the battery evaluation, the oven test proved to be satisfactory. [0071] [Comparative Example 6]

[r?] Force. 46.5 wt% of homopolymer polyethylene with 6dl / g, Mv 700,000 and melting point 135 ° C, [7?] Force. 5dlZg, Mv 250,000 and melting point 136 ° The same as Example 5 except that the homopolymer polyethylene of C is 46.5 wt% and [7?] 4.9 dlZg and the homopolymer polypropylene of Mv 400,000 is 7 wt% monolayer film. A porous membrane was produced. Table 1 shows the physical properties of the obtained microporous membrane. The physical properties of the prepared microporous membrane are shown in Tables 1 and 2. As a result of battery evaluation, the oven test showed that good results could not be obtained.

[0072] [Comparative Example 7]

It carried out similarly using the commercially available dry-type film | membrane by which three surface layers which both layers consist of polypropylene and an intermediate layer is polyethylene are bonded together.

As a result of the battery evaluation, in the collision test, good results were not obtained.

[0073] [Table 1]

Intermediate layer Intermediate layer temperature [7)] Pore plugging temperature

(dl / g) (.C) '(dl / g)

' ⁽ . ^C) Example 1 2.2 135.' 4.3 140 Example 2 2.1 135 '4.3 140 Example 3 2.1 / 2.8 135 4.3 140 Example 4 2.1 135 4.3 140 Example 5 2.3 131 4,3 140 Example 6 2.1 135 4.3 140 Example 7 1.7 135 4.3 '140 Example 8 2.8 136 4.3 140 Example 9 2.3 135 4.3 140 .Example 10 2.1 135 6.0 139 Example 11 2.1 135 5.9 136 Example 12 2.1 135 5.3 138 Example 13 2.1 135 5.7 134 Comparative Example 1 2.2 135, 2.5 139 Comparative Example 2 1.7 134 2.5 139 Comparative Example 3 1.7 '134 2.5 139

Ji Comparative Example 4 5.6 139 4.3 140 I Comparative Example 5 2.3 129 4.3.140 Comparative Example 6 ― ――. 4.3 ■ 140 Comparative Example 7 ― 165 ― 133

Corrected form (Rule 91)

Industrial applicability

The present invention relates to a microporous membrane used for separation of substances, a selective permeation separation membrane, a separator, and the like, and is particularly suitably used as a separator for lithium ion batteries and the like.

Corrected form (Rule 91) Brief Description of Drawings

[0076] [Fig. 1] Fig. 1 shows a schematic diagram of an apparatus for measuring the pore closing temperature of a microporous membrane of the present invention.

Explanation of symbols

[0077] 1: Microporous membrane

2A: Nickel foil

2B: Nickel foil

3A: Glass plate

3B: Glass plate

4: Electrical resistance measuring device

5: Thermocouple

6: Thermometer

7: Data collector

8: Oven

Claims

The scope of the claims

[1] A polyolefin microporous membrane that is a laminate of three or more layers including two surface layers and at least one intermediate layer, and the intrinsic viscosity [r?] Of the intermediate layer is 3. OdlZg or more, In addition, the intrinsic viscosity [r?] Of the surface layer is smaller than the intrinsic viscosity [r?] Of the intermediate layer, and the absolute value of the difference between the pore closing temperature of the surface layer and the pore closing temperature of the intermediate layer is less than 10 ° C. A polyolefin microporous membrane characterized by

[2] The polyolefin microporous membrane according to [1], wherein both surface layers are composed only of polyethylene.

[3] The polyolefin microporous membrane according to claim 1 or 2, wherein both surface layers are composed of the same composition.

[4] The polyolefin microporous membrane according to any one of claims 1 to 3, wherein the tensile strength in the direction perpendicular to the machine direction (TD direction) of the entire membrane is 30 MPa or more.

[5] The polyolefin microporous membrane according to any one of claims 1 to 4, wherein the absolute value of the difference between the pore closing temperature of the surface layer and the pore closing temperature of the intermediate layer is 5 ° C or less. .

[6] The polyolefin microporous membrane according to any one of claims 1 to 5, which is produced using a composition containing polyolefin and a plasticizer.

[7] The method includes the steps of melt-mixing the polymer material and the plasticizer to form a laminated sheet by coextrusion, biaxial stretching, extracting the plasticizer, and then heat-setting. Term 1

The manufacturing method of the polyolefin microporous film as described in any one of -6.

[8] The polymer material and the plasticizer are melt-kneaded to form a laminated sheet by coextrusion, the biaxial stretching is performed, the plasticizer is extracted, and then heat-fixed to obtain the sheet. 5. The polyolefin microporous membrane according to any one of 5!

[9] A separator for a non-aqueous electrolyte battery using the polyolefin microporous membrane according to any one of claims 1 to 6 and 8.

[10] A non-aqueous electrolyte battery using the separator according to claim 9.