JPWO2007116672A1 - Polyolefin microporous membrane - Google Patents

Abstract

The present invention is a polyolefin microporous membrane which is a laminate of three or more layers including two surface layers and at least one intermediate layer, wherein the intrinsic viscosity [η] of the intermediate layer is 3.0 dl / g or more. And the intrinsic viscosity [η] of the surface layer is smaller than the intrinsic viscosity [η] 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. It is a polyolefin microporous film characterized by being.

Description

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

  Polyolefin microporous membranes are widely used as separation of various substances, selective permeation separation membranes, and separators. Specific applications include microfiltration membranes, separators for lithium secondary batteries and fuel cells, separators for capacitors, and various functional materials filled in the holes to make new functions appear. Examples include a base material for a functional membrane. 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.

Pore plugging means that when the inside of a battery is overheated due to overcharging, etc., the polymer constituting the film melts and closes the hole, thereby blocking the reaction inside the battery and increasing the electric resistance of the film. It is the performance to ensure safety. The lower the temperature at which hole clogging occurs, the higher the safety effect.
Further, 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. For this reason, it is desirable that the short circuit temperature is high.
In recent years, with the increase in battery capacity, it has been required to reduce the thickness of the separator and increase the porosity. However, there is a concern that a short circuit or the like may occur due to a decrease in the puncture strength associated with a thin film and a high porosity. Therefore, it is desired to reduce the thickness of the separator 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 puncture strength of the separator and the tensile strength in the machine direction (MD direction) and the machine direction (TD direction). Needs to have a certain strength or more. Furthermore, it is also necessary that the thermal shrinkage rate at a high temperature is low (low heat shrinkability) such as a battery drying process, a high temperature storage test, a high temperature cycle test, and an oven test.
Generally, it is said that the lower the thermal shrinkage rate of the separator, the better. This is because when the battery is in a high temperature state, the separator shrinks, and the isolation function between the electrodes is lost. However, there is generally a contradictory relationship between increasing strength and thermal shrinkage.

  Patent Document 1 proposes a film in which a microporous film formed by blending ultrahigh molecular weight polyethylene and polypropylene and a polyethylene microporous film are laminated. However, in this method, the difference in pore closing temperature between the layer obtained by blending ultra-high molecular weight polyethylene and polypropylene and the layer containing only polyethylene is large, and the amount of heat that can be applied to the film in the heat setting step is limited. As a result, it is difficult to achieve both a high tensile strength and a low thermal shrinkage sufficiently, and the types of physical properties that can be imparted are also limited. Moreover, since the difference of the hole blockage temperature between layers is large, a problem also remains 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.

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 1000 kg / cm 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. Further, the difference in the hole closing temperature between the layers is large, and the hole closing temperature in the entire film is increased.

  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 component having a low melting point 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.

Patent Document 4 proposes improvement of hole closing property by laminating films having different porosity. However, there is no description regarding strength and heat shrinkability. Therefore, heat shrinkage is expected to be high.
JP 2002-321323 A JP-A-8-99382 Japanese Patent Laid-Open No. 2002-367587 JP 2002-319386 A

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

As a result of intensive studies to achieve the above object, the present inventors have obtained a polyolefin microporous film composed of a laminate of three or more layers, and the intrinsic viscosity of both surface layers and intermediate layers, and both surface layers and intermediate layers. By paying attention to the relationship of the layers, it has been found that the above-mentioned problems can be solved even with a polyolefin microporous membrane that maintains porosity and strength. That is, the present invention is as follows.

(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 [η] of the intermediate layer is 3.0 dl / g or more And the limiting viscosity [η] of the surface layer is smaller than the limiting viscosity [η] of the intermediate layer, and the absolute value of the difference between the hole closing temperature of the surface layer and the hole closing temperature of the intermediate layer is less than 10 ° C. A polyolefin microporous membrane characterized by the above.
(2) The polyolefin microporous membrane as described in (1) above, wherein both surface layers are composed only of polyethylene.
(3) The polyolefin microporous membrane as described in (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 polyolefin microporous membrane according to any one of (1) to (4) above, 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 the above (1) to (5), which is produced using a composition containing a polyolefin and a plasticizer.
(7) The method includes melt-kneading a polymer material and a plasticizer, forming a sheet laminated by coextrusion, performing biaxial stretching, extracting the plasticizer, and then heat-setting ( The manufacturing method of the polyolefin microporous film in any one of 1)-(6).
(8) A polyolefin microporous film obtained by melt-kneading a polymer material and a plasticizer to form a laminated sheet by coextrusion, biaxial stretching to extract the plasticizer, and heat setting .
(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).

  The polyolefin microporous membrane of the present invention is high in strength but has a small heat shrinkage ratio when overheated compared to the conventional polyolefin microporous membrane. Further, when the membrane is adhered 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.

  The polyolefin microporous membrane of the present invention needs to be composed of three or more layers including two surface layers and at least one intermediate layer in order to maintain different types of physical properties. The surface layer here refers to the outermost two layers of the film laminated in three or more layers, and the intermediate layer refers to the other layers. The intermediate layer may be one layer or a plurality of layers, but the intermediate layer is preferably one layer from the viewpoint of productivity.

  A surface layer consists of 1 type, or 2 or more types of polyolefin. 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, a homopolymer of polyethylene or polypropylene, or these homopolymers and ethylene, propylene and 1-butene, 4-methyl-1-pentene, 1 -A copolymer of hexene, 1-octene, norbornene, etc., which may be a mixture of the above polymers. From the viewpoint of the performance of the porous membrane, polyethylene and a copolymer thereof are preferable. Examples of polymerization catalysts for these polyolefins include Ziegler-Natta catalysts, Phillips catalysts, metallocene catalysts, and the like. The polyolefin may be obtained by a one-stage polymerization method or may be obtained by a multi-stage polymerization method.

  Further, the polyolefin microporous membrane of the present invention is mixed with known additives such as metal soaps such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. Can be used.

  In the polyolefin microporous membrane of the present invention, the intrinsic viscosity [η] of the intermediate layer is 3.0 dl / g or more, and the intrinsic viscosity [η] of the surface layer needs to be smaller than the intrinsic viscosity [η] of the intermediate layer. By maintaining the intrinsic viscosity of the surface layer and the intermediate layer within this range, not only the strength as the film can be maintained, but also the effect of sticking the film surface layer can be exhibited when the film is heated. From the viewpoint of the balance between the film sticking effect and the puncture strength, the intrinsic viscosity of the intermediate layer is preferably 2.0 dl / g or more, more preferably 5.0 dl / g or less than the intrinsic viscosity of the surface layer. .

When the intrinsic viscosity of the intermediate layer is less than 3.0 dl / g, the mechanical strength of the entire film such as piercing strength and tensile strength is lowered. 3.5 dl / g or more is preferable, 4.0 dl / g or more is more preferable, and 5.0 dl / g or more is further more preferable. Moreover, it is preferable that it is 7.0 dl / g or less from a small heat shrinkage rate.
The intrinsic viscosity [η] of the surface layer is preferably less than 3.0 dl / g from the viewpoint that the effect of sticking to the electrode due to stress relaxation at high temperature appears more remarkably. Moreover, it is preferable that it is less than 2.5 dl / g from the point of having a low fuse characteristic and a high short characteristic further, and less than 2.0 dl / g is more preferable. Further, from the viewpoint of strength, it is preferably larger than 1.0 dl / g.
The intrinsic viscosity [η] of the layer depends on the intrinsic viscosity [η] of the polyolefin component contained in the layer and its ratio. Therefore, by adjusting the polymer composition of each layer and its ratio, the range of the intrinsic viscosity specified in the present invention can be obtained. The intrinsic viscosity [η] is the intrinsic viscosity [η] at 135 ° C. in a decalin solvent based on ASTM-D4020.

  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 all layers at substantially the same temperature, so that the pores can be clogged throughout the 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, by selecting a polymer composition having a desired melting point, the pore closing temperature of the surface layer and the intermediate layer can be set.

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 ° C./min, and an alternating current of 1 kHz was applied. The temperature and electrical resistance value 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.
Further, 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 film is overheated, and can maintain the isolation between the electrodes, and the battery It is preferable that the outermost layer is composed of the same components in order to stabilize the running performance during winding.

Moreover, it is preferable that it is comprised only from polyethylene since the hole closing temperature becomes low, More preferably, both surface layers are comprised only from polyethylene.
The tensile strength in the MD direction is preferably 100 MPa or more because the battery is resistant to an external collision test and hardly causes a short circuit due to foreign matter in the battery. More preferably, it is 110 MPa or more.

  The tensile strength in the TD direction is preferably 30 MPa or more, more preferably 60 MPa or more, and more preferably 90 MPa or more, since resistance to an external collision test in the battery and resistance to a short circuit due to foreign matter in the battery are less likely to occur. preferable.

  The thickness of the entire film is preferably 5 μm or more in order to maintain mechanical strength and to completely insulate the electrodes. Moreover, when incorporating in the separator of a small battery, 40 micrometers or less are preferable, More preferably, it is 10-20 micrometers. The thickness of the surface layer is preferably 0.1 μm or more from the viewpoint of easily achieving the sticking effect during overheating, preferably 10 μm or less, and more preferably 1 to 5 μm from the viewpoint of the strength of the entire film.

  When used as a battery separator, the porosity is preferably 20% or more from the viewpoint of preventing an increase in resistance inside the battery, 70% or less from the viewpoint of mechanical strength, and more preferably 30 to 50%. The air permeability is preferably 10 sec / cc or more from the viewpoint of mechanical strength, 1000 sec / cc or less from the viewpoint of transmission performance, more preferably 30 to 700 sec / 100 cc, and further preferably 50 to 500 sec / cc.

  The puncture strength is preferably 3.0 N / 25 μm or more, more preferably 4.0 N / 25 μm or more, and further preferably 5.5 N / 25 μm or more, from the viewpoint of preventing film breakage by the electrode active material.

  The lower the heat shrinkage rate when the microporous membrane is measured without being constrained at 130 ° C., the better. Specifically, the thermal shrinkage rate in the MD direction is preferably less than 30%. The thermal contraction rate in the TD direction is preferably 30% or less, more preferably less than 20%, and still more preferably 15%.

  The above TD tensile strength, overall film thickness, porosity, pin puncture strength, and crystallinity are appropriately changed in the composition ratio of polyolefin components contained in the layer, extrusion conditions, stretching conditions, plasticizer extraction conditions, and heat setting conditions. Adjustment is possible.

  Since the polyolefin microporous membrane of the present invention is particularly effective when used as a battery separator, the case of using it in this application has been mainly described. However, the microporous membrane of the present invention is a microfiltration membrane. Membranes, separators for condensers, and various functional materials can also be used as a base material for functional membranes for filling the holes with new functions. In that case, it has the advantage that the stability of the separation membrane and the base material can be improved by having the effect of uniformly closing the pores in a short time during overheating and having the effect of sticking the surface of the membrane. .

  Next, the manufacturing method of the microporous film of this invention is demonstrated.

As the method for producing the microporous membrane of the present invention, the polymer species, the solvent species, and the extrusion method are selected as long as the polymer materials of both the surface layer and the intermediate layer are selected so that the obtained microporous membrane has the characteristics satisfying the present invention. The stretching method, the extraction method, the hole opening method, the heat setting / heat treatment method and the like are not limited at all. 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 characteristics of the polyolefin microporous membrane of the present invention, the following composition is preferred.

  A surface layer and an intermediate | middle layer consist of 1 type, or 2 or more types of polyolefin. In order to produce the microporous membrane defined in the present invention, the intrinsic viscosity [η] of the surface layer polymer is preferably less than 3.0 dl / g, and a polyolefin having an intrinsic viscosity [η] of 1.5 dl / g or less is preferably used. It is more preferable that it is contained at 50 wt% or more. On the other hand, the polymer of the intermediate layer is also composed of one or more polyolefins. It is necessary that the intrinsic viscosity [η] of the polymer of the intermediate layer is 3.0 dl / g or more. When two or more kinds of polyolefins are used, the polyolefin having the intrinsic viscosity [η] of 4.5 dl / g or more is used. It is preferably composed of 30 w% or more, more preferably 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 must be selected to be less than 10 ° C. is there. 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.

Furthermore, known additives such as metal soaps such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments can be added to the polymer material. These additives can be added to the raw material, or can be added at the time of melt kneading of the polymer or after the stretching treatment, but are not particularly limited as long as the effect of the additive is exhibited.
The microporous membrane of the present invention can be obtained by melt kneading and extruding a polymer material, stretching it, heat setting and heat treatment. More specifically, it is obtained by a method comprising the following steps (a) to (e).

(A) Melt-kneading First, raw materials such as polymers for the surface layer and the intermediate layer are melt-kneaded, respectively. 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 premixed with a Henschel mixer, a ribbon blender, a tumbler blender, or the like, if necessary. If the amount is small, it may be stirred by hand. The temperature during melt kneading is preferably 160 ° C. or higher, and more preferably 180 ° C. or higher. Moreover, less than 300 degreeC is preferable, less than 240 degreeC is more preferable, and less than 230 degreeC is further more preferable.
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 may be added at any time as long as it is before the extrusion process, such as before melt kneading or during melt kneading.

(B) Extrusion / Cooling The obtained melt-kneaded product is extruded and formed into a sheet to form a gel sheet, which is cooled and solidified. Extrusion molding includes a method of cooling from a sheet die such as a slit die or a T die with an extrusion cast roll or the like, and a method of cooling after performing an inflation method. The lamination of the surface layer and the intermediate layer can be performed by either integrating the gel sheets obtained from the respective extruders and co-extruding them with a single die, or extruding each of the gel sheets and overlaying them to heat-seal. Can be made. The coextrusion method is more productive. Further, the obtained film is more preferable because it easily obtains high interlayer adhesion strength and easily forms a communication hole between the layers, so that the permeability of the film is easily maintained.

(C) Stretching The obtained sheet is stretched in a uniaxial or biaxial direction. It is preferable to stretch biaxially or more from the viewpoint of easily ensuring the strength of the resulting film, and it is preferable to simultaneously stretch in the biaxial direction from the viewpoint of fewer stretching steps. There are no particular limitations on the stretching method and the number of stretching, but for example, MD uniaxial stretching with a roll stretching machine, TD uniaxial stretching with a tenter, sequential biaxial stretching with a combination of a roll stretching machine and a tenter, or a tenter and a tenter, Examples thereof include simultaneous biaxial stretching by axial tenter and inflation molding. From the viewpoint of film thickness productivity, the draw ratio is preferably 8 times or more, more preferably 26 times or more, and most preferably 40 times or more. Further, from the viewpoint of film uniformity, the upper limit is preferably 100 times or less, more preferably 65 times or less.

(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 or showering the stretched sheet in an extraction solvent. Then, it is sufficiently dried.

(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 is an operation for reducing the stretched sheet in the MD direction and / or the TD direction. The relaxation rate is a value obtained by dividing the MD dimension of the film after the relaxation operation by the MD dimension of the film before the operation, or a value obtained by dividing the TD dimension after the relaxation operation by the TD dimension of the film before the operation, or MD, When both TDs are relaxed, it is a value obtained by multiplying the MD relaxation rate and the TD relaxation rate. As a specific method, a method using a tenter or a roll stretching machine can be mentioned. The predetermined temperature is preferably 100 ° C. or higher in order to reduce the heat shrinkage rate, and is preferably less than 135 ° C. in order to bring the porosity and permeability into the above-described preferable ranges. 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. Moreover, in order to prevent generation | occurrence | production of a wrinkle and to make a porosity and permeability | transmittance into the said preferable range, it is preferable that it is 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, the thermal contraction rate can be reduced not only in the operation direction but also in the direction perpendicular to the operation direction.

Further, surface treatment such as electron beam irradiation, plasma irradiation, surfactant coating, chemical modification and the like can be performed on the surface of the heat-set stretched sheet.
Furthermore, it is preferable that the master roll after the heat setting is aged at a predetermined temperature and then the master roll is rewound. By this step, the residual stress of the polyolefin in the master roll is released. The heat treatment temperature of the master roll is preferably 35 ° C. or higher, more preferably 45 ° C. or higher, and particularly preferably 60 ° C. or higher. Moreover, 120 degrees C or less is preferable from a viewpoint of hold | maintaining the permeability | transmittance of a film | membrane.

  Examples of the plasticizer that can be used in the present invention include organic compounds that can form a uniform solution with polyolefin at temperatures below the boiling point, specifically decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol. Decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, paraffin oil and the like. Of these, paraffin oil and dioctyl phthalate are preferred.

  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 raw material input amount of each layer in order to make the porosity of the obtained film in an appropriate range, and the viscosity is set appropriately. In order to make the range, it is preferable that it is 90% by weight or less in all layers. More preferably, it is 50 to 70% by weight.

  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 that 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, and fluorocarbons, alcohols such as ethanol and isopropanol, and acetone. And ketones such as 2-butanone. It selects from these suitably, and is used individually or in mixture. These extraction solvents may be regenerated by distillation after extraction of the plasticizer and used again.

  From the viewpoint of preventing thermal deterioration during melt kneading and quality deterioration due thereto, an antioxidant is preferably added in the step (a). In particular, it is preferable that the resin is added before heating because of the characteristics of the material. 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. Moreover, 5.0 wt% or less is preferable and 3.0 wt% or less is more preferable.

  As the antioxidant, a phenolic antioxidant which is a primary antioxidant is preferable, and 2,6-di-t-butyl-4-methylphenol, pentaerythrityl-tetrakis- [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, and the like. Secondary antioxidants can also be used in combination, such as tris (2,4-di-t-butylphenyl) phosphite, tetrakis (2,4-di-t-butylphenyl) -4,4- Examples thereof include phosphorus-based antioxidants such as biphenylene-diphosphonite and sulfur-based antioxidants such as dilauryl-thio-dipropionate.

  Furthermore, it is preferable to mix the antioxidant in the raw material polymer at a predetermined concentration as described above, and then replace the inside of the mixer or the extruder with a nitrogen atmosphere, and perform melt-kneading while maintaining the nitrogen atmosphere.

  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.

  First, the microporous membrane is formed into a vertically long shape having a width of 10 mm to 100 mm and a length of 200 mm to 2000 mm. The separator is 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 housed in a battery can and an electrolyte is injected.

  Although the kind of battery in this invention is not specifically limited, From a viewpoint of the affinity of a polyolefin microporous membrane and electrolyte solution, it is preferable that it is a non-aqueous electrolyte battery. Moreover, it is more preferable that it is a lithium ion battery from a viewpoint that the outstanding safety | security can be provided when the microporous film of this invention is used as a separator.

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.
Note that (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.

  A sample was cut into an arbitrary size, and a curing cross tape manufactured by Sliontec Co., Ltd. was attached to the entire surface of one surface. Sliontec Co., Ltd. Curing Cloth Cross Tape Affixed to the entire surface and a part of the surface layer opposite to the surface layer, the Slion Tech Co., Ltd. Curing Cloth Cross Tape is applied and pulled, and the intermediate layer and Slion Tech Co., Ltd. Curing Cloth The surface layer on the side where the 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 side. The layer was peeled off.

(1) Intrinsic viscosity [η] and viscosity average molecular weight (Mv)
Based on ASTM-D4020, the intrinsic viscosity [η] at 135 ° C. in a decalin solvent was determined. Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 ⁻⁴ Mv ^0.67
For polypropylene, Mv was calculated by the following formula.
[Η] = 1.10 × 10 ⁻⁴ Mv ^0.80
The Mv of the layer was calculated from the polyethylene equation.
(2) Film thickness (μm)
The measurement was performed at a room temperature of 23 ± 2 ° C. using a fine thickness measuring instrument KBM (trademark) manufactured by Toyo Seiki Seisakusho.

(3) Porosity (%)
A sample of 10 cm × 10 cm square was cut out from the microporous membrane, its volume (cm ³ ) and mass (g) were determined, and calculated from these and the film density (g / cm ³ ) using the following formula.
Porosity = (volume−mass / film density) / volume × 100
The film density was calculated at a constant 0.95.
(4) Air permeability (sec)
Based on JIS P-8117, it measured with the Gurley type air permeability meter (the Toyo Seiki Seisakusho Co., Ltd. product, G-B2 (trademark)).
(5) Puncture strength (g), (N / 25 μm)
By using a KES-G5 (trademark) handy compression tester manufactured by Kato Tech, the needle tip curvature radius is 0.5 mm and the needle stick speed is 2 mm / sec. The puncture strength (N / 25 μm) obtained by multiplying the puncture load (N) by / 25 (μm) was calculated.

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

(7) Melting point It measured using Seiko Electronics Industry Co., Ltd. DSC-220C. 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 having a diameter of 5 mm, a crimping cover was placed, and the sample was sealed 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 ° C./min, and the temperature at which the melting endotherm curve was maximized was taken as the melting point.
(8) Terminal Vinyl Group Concentration The polyolefin microporous membrane was measured with an infrared spectrophotometer (FTS60A / 896 / UMA300 manufactured by Varian Technologies Japan Limited) after making the thickness of the polyolefin microporous film about 1 mm using a heating press. From the absorbance at 910 cm ^−1, the density of the polyolefin microporous membrane (g / cm 3) and the thickness of the sample (mm), POLYMER LETTERS
VOL. 2, PP. With reference to the formula described in 339-341, the concentration of terminal vinyl groups, that is, the number of terminal vinyl groups per 10,000 carbon atoms in polyethylene (hereinafter, this unit is expressed in units / 10,000 C) is as follows. It was calculated from the following formula. In addition, it rounded down and calculated.
Terminal vinyl group concentration (pieces / 10,000 C) = 11.4 × absorbance / (density / thickness)
The unit of density is g / cm ³ and the unit of thickness is mm.

(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 pieces of paper so that the sample was not directly exposed to the warm air. After taking out from the oven and cooling, the length (mm) was measured, and the thermal contraction rate of MD and TD was calculated by the following formula.
MD thermal shrinkage (%) = (100−MD length after heating) / 100 × 100
TD heat shrinkage rate (%) = (100−length of TD after heating) / 100 × 100
(10) Hole Clogging Temperature FIG. 1 (A) shows a schematic diagram of a device for measuring the hole clogging temperature. 1 is a microporous film, 2A and 2B are 10-micrometer-thick nickel foils, and 3A and 3B are glass plates. 4 is an electric resistance measuring device (LCR meter “AG-4411” (trademark) manufactured by Ando Electric Co., Ltd.), which is connected to the nickel foils 2A and 2B. A thermocouple 5 is connected to the thermometer 6. A data collector 7 is connected to the electrical resistance measuring device 4 and the thermometer 6. 8 is an oven, and the microporous film was heated here.

  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 a 1 mol / liter lithium borofluoride solution (solvent: propylene carbonate / ethylene carbonate / γ-butyllactone = 1/1/2) as an electrolytic solution. As shown in FIG. 1 (C), “Teflon” (registered trademark) tape (shaded portion in the figure) is pasted on the nickel foil 2B, and masking is performed by leaving a window portion of 15 mm × 10 mm at the center of the foil 2B. did.

The nickel foil 2A and the nickel foil 2B were overlapped with each other so as to sandwich the microporous film 1, and two nickel foils were sandwiched by the glass plates 3A and 3B from both sides thereof. At this time, it arrange | positioned so that the part of the window of foil 2B and the porous film 1 may come to the position which opposes.
Moreover, the two glass plates were fixed by pinching with a commercially available double clip. The thermocouple 5 was fixed to a glass plate with “Teflon” (registered trademark) tape.
Temperature and electric resistance were continuously measured with such an apparatus. When the temperature was raised from 25 ° C. to 200 ° C. at a rate of 2 ° C./min and measured at an alternating current of 1 kHz, the temperature at which the electrical resistance value of the microporous membrane reached 10 ³ Ω was defined as the pore closing temperature.

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

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

Preparation of non-aqueous electrolyte: Prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 mol / liter.

Battery assembly: The above-mentioned microporous membrane separator, strip-shaped positive electrode and strip-shaped negative electrode were stacked in the order of the strip-shaped negative electrode, separator, strip-shaped positive electrode, and separator and wound in a spiral shape to produce an electrode plate laminate. After pressing this electrode plate laminate into a flat plate, it is housed in an aluminum container, the aluminum lead led out from the positive electrode current collector is used as the container wall, and the nickel lead derived from the negative electrode current collector is used as the container lid terminal part. Connected.
Then, after drying at 65 ° C. for 8 hours under vacuum, the above-described non-aqueous electrolyte was poured into the container and sealed.
The lithium ion battery thus produced was 6.3 mm in length (thickness), 30 mm in width, and 48 mm in height. This battery is charged to a battery voltage of 4.2 V at a current value of (0.5 C) in an atmosphere of 25 ° C., and then the current value is started to be reduced so as to hold 4.2 V, thereby producing a battery for a total of 6 hours. After the first charge.

(A) In order to perform an oven test on this battery, the battery after charging was heated from room temperature to 150 ° C. at a rate of 5 ° C./min and left at 150 ° C. for 1 hour.
As a result, those that ignited in 10 minutes or less were marked with ×, those that did not ignite until 30 minutes were marked with ○, and those that did not ignite for 1 hour were marked with ◎.

  (B) In order to perform a collision test of the battery, the battery was dropped 10 times from a height of 1.9 m onto a concrete floor. Thereafter, the battery was disassembled, and the state of the separator was observed. Those that did not cause a short circuit due to the deformation of the separator were evaluated as good.

[Example 1]
A microporous membrane composed of two surface layers and intermediate layers having the same composition was prepared using two extruders. The composition of the surface layer is [η] of 1.2 dl / g, Mv of 70,000, homopolymer polyethylene 45 wt% with a melting point of 133 ° C., [η] of 2.8 dl / g, Mv of 250,000, melting point The polymer was 45 wt% of a homopolymer having a temperature of 136 ° C., 5 wt% of a homopolymer having a [η] of 4.9 dl / g and a Mv of 400,000. The composition of the intermediate layer was [η] of 5.6 dl / g, Mv of 700,000, 46.5 wt% of homopolymer polyethylene having a melting point of 135 ° C., and [η] of 2.8 dl / g, Mv. Was 26.5 wt% of homopolymer polyethylene at 250,000 and 136 ° C., and 7 wt% of homopolymer polypropylene with [η] of 4.9 dl / g and Mv 400,000. Each of these compositions was blended. As an antioxidant, 0.3 wt% of tetrakis- (methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propinate) methane was mixed with respect to the total polymer in each layer. Each composition was charged into a twin screw extruder having a diameter of 25 mm and L / D = 48 via a feeder. Furthermore, liquid paraffin (kinematic viscosity at 37.78 ° C. 75.90 cSt) 50 wt% is injected into each extruder from the side feed with respect to 50 wt% polymer in each layer, and kneaded at 200 ° C. and 200 rpm. Extruded from a co-extrudable T-die installed at the tip. Thereafter, the sheet 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 liquid paraffin was extracted and dried, followed by heat treatment at 120 ° C. to obtain a microporous film. 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 [η] of 1.2 dl / g, Mv of 70,000 and melting point of 133 ° C., [η] of 2.8 dl / g and Mv of 250,000. A microporous membrane was prepared in the same manner as in Example 1 except that the homopolymer polyethylene having a melting point of 136 ° C. was changed to 50 wt%. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
[Example 3]
Using three extruders, a microporous film composed of two surface layers and intermediate layers having different compositions was prepared. The composition of the surface layer on one side is as follows: [η] is 1.2 dl / g, Mv is 70,000, 50 wt% of homopolymer polyethylene having a melting point of 133 ° C., [η] is 2.8 dl / g, and Mv is 25 The homopolymer polyethylene having a melting point of 136 ° C. is 50 wt%, and 50 wt% of liquid paraffin (kinematic viscosity at 37.78 ° C.) is injected into each extruder from the side feed with respect to 50 wt% of the polyethylene. did. On the other hand, the composition of the surface layer on the opposite side is as follows: [η] is 1.2 dl / g, Mv is 70,000, 50 wt% of a homopolymer polyethylene having a melting point of 133 ° C., [η] is 2.8 dl / g, Mv 30 wt% of a homopolymer having a melting point of 250,000 and a melting point of 136 ° C., and 20 wt% of a homopolymer having an [η] of 5.6 dl / g, an Mv of 700,000 and a melting point of 135 ° C. A microporous membrane was prepared in the same manner as in Example 1 except that 65 wt% of liquid paraffin (kinematic viscosity at 37.78 ° C. 75.90 cSt) was injected into the surface layer extruder from the side feed. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.

[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. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
[Example 5]
The composition of the surface layer is as follows: [η] is 1.7 dl / g, Mv is 120,000, the copolymer is 50 wt% polyethylene having a melting point of 127 ° C., [η] is 2.8 dl / g, Mv is 250,000, melting point A microporous membrane was prepared in the same manner as in Example 3 except that the homopolymer polyethylene was 50 wt% at 136 ° C. and the heat treatment temperature was 117 ° C. The physical properties of the produced 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 prepared are shown in Tables 1 and 2.

[Example 7]
The composition of the surface is 75 wt% of homopolymer polyethylene with [η] of 1.2 dl / g, Mv of 70,000 and melting point of 133 ° C., [η] of 2.8 dl / g, Mv of 250,000, melting point A microporous membrane was prepared in the same manner as in Example 5 except that 25 wt% of a homopolymer polyethylene having a temperature of 136 ° C. was used. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
[Example 8]
The composition of the surface layer is as follows: [η] is 1.2 dl / g, Mv is 70,000, 50 wt% of homopolymer polyethylene having a melting point of 133 ° C., [η] is 2.8 dl / g, Mv is 250,000, 30 wt% of homopolymer polyethylene having a melting point of 136 ° C. and 20 wt% of homopolymer having [η] of 5.6 dl / g, Mv of 700,000 and melting point of 135 ° C. A microporous membrane was prepared in the same manner as in Example 5 except that 65 wt% of liquid paraffin (kinematic viscosity at 37.78 ° C., 75.90 cSt) was injected from the side feed into the surface layer extruder. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
[Example 9]
The composition of the surface layer is such that [η] is 3.2 dl / g, Mv 300,000, melting point is 136 ° C., homopolymer polyethylene 50 wt% with a terminal vinyl group concentration of 10 / 10,000 C, and [η] is 2. A microporous membrane was prepared in the same manner as in Example 5 except that 50 wt% of homopolymer polyethylene having a 0 dl / g, Mv of 150,000, and a melting point of 133 ° C. was used. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.

[Example 10]
The composition of the intermediate layer is such that [η] is 11.3 dl / g, Mv is 2 million, homopolymer polyethylene having a melting point of 135 ° C. is 30 wt%, [η] is 2.8 dl / g, and Mv is 250,000. 70 wt. Of homopolymer polyethylene having a melting point of 136 ° C., and 65 wt.% Of liquid paraffin (kinematic viscosity at 37.78 ° C. of 75.90 cSt) from the side feed for the intermediate layer of 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. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
[Example 11]
The composition of the intermediate layer is [η] is 13.1 dl / g, Mv is 2.5 million, 20 wt% of homopolymer polyethylene having a melting point of 135 ° C., [η] is 5.6 dl / g, Mv is 700,000, 15 wt% of homopolymer polyethylene having a melting point of 135 ° C., [η] of 2.8 dl / g, Mv of 250,000, 30 wt% of homopolymer polyethylene having a melting point of 136 ° C., and [η] of 1 0.7 dl / g, Mv 120,000, ethylene propylene copolymer having a melting point of 131 ° C. (comonomer: propylene; content ratio 0.6 mol%) is 30 wt%, and liquid paraffin (37.78 is added to 35 wt% of the polymer in the intermediate layer. Example 5 except that 65 wt% of kinematic viscosity at 75 ° C. was injected into the extruder for the intermediate layer from the side feed and the heat treatment temperature was set to 118 ° C. A microporous membrane was prepared. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.

[Example 12]
The composition of the intermediate layer is 15 wt% in a molecular weight of 10,000 or less, Mw / Mn is 43, [η] is 5.6 dl / g, Mv is 700,000, and the homopolymer polyethylene having a melting point of 137 ° C. is 80 wt. % And [η] were 4.9 dl / g, and a microporous membrane was prepared in the same manner as in Example 5 except that the homopolymer polypropylene of Mv 400,000 was changed to 20 wt%. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
[Example 13]
The composition of the intermediate layer is [η] of 13.1 dl / g, Mv of 2.5 million, 25 wt% of homopolymer polyethylene having a melting point of 132 ° C., [η] of 1.7 dl / g, Mv of 120,000, melting point The ethylene propylene copolymer (comonomer: prepylene, content ratio 0.6 mol%) having a temperature of 131 ° C. is 75 wt%, and the liquid paraffin (kinematic viscosity at 37.78 ° C. 75.90 cSt) is 65 wt% with respect to 35 wt% of the polymer. A microporous film was produced in the same manner as in Example 5 except that the heat treatment temperature was set to 118 ° C. from the side feed into the intermediate layer extruder. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
For all the microporous membranes shown in Examples obtained in Examples 1 to 13, batteries were prepared and left in an oven at 150 ° C. for 1 hour. As a result, nothing ignited at least within 30 minutes. It did not ignite in a test of repeatedly dropping 10 times from a height of 1.9 m onto a concrete floor. When the battery after the test was disassembled and the shrinkage of the separator was confirmed, no short circuit of the electrode due to the shrinkage of the separator was observed. Moreover, although the test which repeatedly drops to a concrete floor 10 times from the height of 1.9 m was done, the short circuit by deformation | transformation of a separator was not observed.
Moreover, when the crystallinity degree was measured using DSC (differential scanning calorimeter) for all the films, the crystallinity degree of all the layers exceeded 70%.

[Comparative Example 1]
The composition of the surface layer is [η] of 1.2 dl / g, Mv of 70,000, homopolymer polyethylene 45 wt% with a melting point of 133 ° C., [η] of 2.8 dl / g, Mv of 250,000, The intermediate layer has a composition of [η] of 2.5 dl / g, with a homopolymer polyethylene of 45 wt% having a melting point of 136 ° C. and an [η] of 4.9 dl / g and a homopolymer polypropylene of 5 wt% of Mv 400,000. Example 5 except that the homopolymer polyethylene having an Mv of 210,000 and a melting point of 136 ° C. is 95 wt%, and the [η] is 4.9 dl / g and the homopolymer polypropylene of Mv 400,000 is 5 wt%. Similarly, a microporous membrane was produced. The physical properties of the produced 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 collision test.

[Comparative Example 2]
The composition of the surface is 75 wt% of homopolymer polyethylene with [η] of 1.2 dl / g, Mv of 70,000 and melting point of 133 ° C., [η] of 2.8 dl / g, Mv of 250,000 and melting point A microporous membrane was prepared in the same manner as in Comparative Example 1, except that the homopolymer polyethylene was 25 wt% at 136 ° C. and the sheet thickness was 2.0 mm. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
As a result of battery evaluation, good results were not obtained in the oven test.
[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 produced 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 collision test.

[Comparative Example 4]
The composition of the surface layer is 100 wt% of a homopolymer having [η] of 5.6 dl / g, Mv of 700,000 and a melting point of 135 ° C., and liquid paraffin (at 37.78 ° C. with respect to 30 wt% of the polyethylene). A microporous membrane was prepared in the same manner as in Example 5 except that 70 wt% of the kinematic viscosity 75.90 cSt) was injected into the surface layer extruder by side feed. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
As a result of battery evaluation, good results were not obtained in the oven test.
[Comparative Example 5]
The composition of the surface layer is 50 wt% of copolymer polyethylene with [η] of 1.7 dl / g, Mv of 120,000 and melting point of 125 ° C., [η] of 2.8 dl / g and Mv of 250,000. A microporous membrane was prepared in the same manner as in Example 5 except that the homopolymer polyethylene was 50 wt% at 136 ° C., the temperature of the biaxial stretching machine was 121 ° C., and the heat treatment temperature was 115 ° C. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
As a result of battery evaluation, good results were not obtained in the oven test.

[Comparative Example 6]
46.5 wt% of homopolymer polyethylene having [η] of 5.6 dl / g, Mv of 700,000 and a melting point of 135 ° C., [η] of 2.5 dl / g, Mv of 250,000 and a melting point of 136 The same as in Example 5, except that the homopolymer polyethylene at 4 ° C. is a single layer film of 46.5 wt% and [η] is 4.9 dl / g and the homopolymer polypropylene of Mv 400,000 is 7 wt%. A porous membrane was produced. Table 1 shows the physical properties of the obtained microporous membrane. The physical properties of the produced microporous membrane are shown in Tables 1 and 2.
As a result of battery evaluation, good results were not obtained in the oven test.

[Comparative Example 7]
It carried out similarly using the commercially available dry-type film | membrane with which both surface layers consisted of polypropylene and the intermediate | middle layer was 3 layers which are polyethylene.
As a result of battery evaluation, good results were not obtained in the collision test.

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

The schematic of the measuring apparatus of the hole obstruction | occlusion temperature of the microporous film of this invention is shown.

Explanation of symbols

1: Microporous film 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 (10)

  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 [η] of the intermediate layer is 3.0 dl / g or more, and The intrinsic viscosity [η] of the surface layer is smaller than the intrinsic viscosity [η] 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. 2. The polyolefin microporous membrane according to claim 1, wherein both surface layers are composed only of polyethylene. Both the surface layers are comprised by the same composition, The polyolefin microporous film of Claim 1 or 2 characterized by the above-mentioned.   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 claim 1, 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.   The polyolefin microporous membrane according to any one of claims 1 to 5, which is produced using a composition containing a polyolefin and a plasticizer. A method comprising melt-kneading a polymer material and a plasticizer to form a laminated sheet by coextrusion, biaxial stretching and extracting the plasticizer, followed by heat setting. The method for producing a polyolefin microporous membrane according to claim 6.   Any one of claims 1 to 5 obtained by melt-kneading a polymer material and a plasticizer to form a laminated sheet by coextrusion, biaxial stretching to extract the plasticizer, and then heat setting. The polyolefin microporous membrane according to claim 1.   The separator for non-aqueous electrolyte batteries using the polyolefin microporous film as described in any one of Claims 1-6 and 8.   A non-aqueous electrolyte battery using the separator according to claim 9.

Images