JP2011216376A - Compound porous film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound porous film and a method for manufacturing the same, having both a shutdown function and a heat-resistant shape holding function, and without jeopardizing film usage characteristics of ventilation, quality of a film material of film stability and surface smoothness or the like, charge and discharge characteristics, and durability or the like.SOLUTION: The compound porous film includes a polyimide layer and a porous film with ventilation, with a thickness of the film of 4 to 300 μm, a ventilation resistance in Gurley values of 10 to 1,000 sec/100 cc. The polyimide layer itself does not have ventilation, and two-dimensionally covers at least one of the surfaces of the porous film, and is formed in a two-dimensional pattern having a number of openings making the porous film exposed on the surface.

Description

  The present invention relates to a method for producing a porous film used as a diaphragm for isolating positive and negative electrodes in a battery and selectively permeating an electrolyte or specific ions in an electrolytic solution, the porous film, and the porous film The present invention relates to battery separators and electrolytic capacitor diaphragms.

  Utilizing features such as small size, light weight, and high energy density, secondary batteries are expected to be widely deployed in mobile electronic devices, hybrid vehicles, and electric vehicles. The lithium secondary battery having the highest energy density among the secondary batteries includes a positive electrode made of a composite oxide with a transition metal containing Li ions, a negative electrode made of a carbon-based material that adsorbs and desorbs Li ions, It consists of a separator that separates the positive and negative electrodes from an electrolytic solution composed of a Li ion electrolyte and an organic solvent.

Here, the characteristics required for the battery separator are:
(1) Isolate so that the positive and negative electrodes are not in direct contact (2) Shield (shut down) the battery circuit at the time of overcurrent that occurs when a partial short circuit occurs in the circuit (3) Good in the state of holding the electrolyte (4) having chemical / electrical / mechanical stability, etc.

  In particular, the shutdown function is important for preventing the battery circuit from running out of control and for improving safety when using the battery. Polyolefin microporous membrane used mainly as a separator material induces a melting phenomenon due to a rise in heat temperature that occurs when an electrical circuit is short-circuited, and as a result, the microporous is blocked, thereby achieving a shutdown mechanism. .

  Furthermore, it is important to maintain the shape of the separator after shutdown. This is to prevent inducing the risk of short-circuiting of the electrode because the shape of the entire separator is lost (meltdown) when melting proceeds even after the micropores are closed.

  In order to solve this problem, several composite materials of a high-melting-point material and a low-melting-point material that share a shutdown function and a shape-holding function have been proposed as secondary battery separator materials.

  For example, Patent Document 1 discloses a composite sheet obtained by thermocompression bonding to a laminate composed of a non-woven fabric derived from polyacrylate fibers and a polyethylene film. Is a low-melting-point material rich in flexibility, the porosity of the substrate is often lost by heating and pressure bonding, and the air permeability is often deteriorated.

  Patent Document 2 discloses a composite porous membrane obtained by applying a slurry made of inorganic fine particles, a binder, and a solution onto a polyolefin and drying the slurry. However, uniform application is difficult due to the cohesiveness of the inorganic fine particles in the slurry. It is.

  In addition, the composite material has a problem that low durability due to surface contact between the high melting point material and the low melting point material and a further increase in interface resistance may occur, and all these problems have not been solved.

  Patent Document 3 discloses a composite porous film obtained by applying a polyimide resin solution by a screen or gravure roll printing method, and then dipping and drying in a poor solvent for the resin. Since the resin film is a porous film, there is room for improvement in terms of mechanical strength. In addition, since the porous structure of the polyimide resin porous layer, such as air permeability, changes sensitively depending on the process conditions for making it porous, advanced process control is required for industrially stable production. This is a big issue.

JP 2009-248357 A JP 2000-30686 A JP 2006-155914 A

  The present invention is a composite porous material that has both a shutdown function and a heat-resistant shape maintaining function, and does not impair the film material such as air permeability, film stability and surface smoothness, and film use characteristics such as charge / discharge characteristics and durability. It is an object to provide a method for producing a film and a composite porous film easily and more stably.

1. A composite porous film having a polyimide layer and a breathable porous membrane,
The film thickness of the film is 4 to 300 μm, the ventilation resistance is 10 to 1000 seconds / 100 cc in terms of Gurley value,
The polyimide layer itself is not air permeable, two-dimensionally covers at least one surface of the porous membrane two-dimensionally, and has a plurality of openings that expose the porous membrane to the surface. A composite porous film characterized by being formed into a shape.

  2. 2. The film according to claim 1, wherein the plurality of openings of the polyimide layer are present as a continuous pattern that is regularly and two-dimensionally repeated.

  3. 3. The film according to 1 or 2 above, wherein the polyimide layer has a thickness of 0.5 to 50 μm.

  4). 4. The film as described in any one of 1 to 3 above, wherein the ratio (coverage) of the area where the polyimide layer is present on the same surface of the porous film is 10% or more and 70% or less.

  5. 5. The film as described in any one of 1 to 4 above, wherein the porous film is a single layer film or a multilayer film formed of a layer selected from a polyolefin porous film and a nonwoven fabric.

6). It is a manufacturing method of the composite porous film in any one of said 1-5,
(Step a) Applying the polyimide solution in a two-dimensional pattern having a plurality of openings covering at least one surface of the porous membrane two-dimensionally and exposing the porous membrane to the surface; ,
(Step b) A method for producing a composite porous film, comprising the step of immersing the porous membrane coated with the polyimide solution obtained in Step a in a poor solvent bath of polyimide.

  7). 7. The method according to 6 above, wherein in the step a, the polyimide solution is applied in a pattern so that the large number of openings form a continuous pattern that is regularly and two-dimensionally repeated.

  8). 8. The method according to 6 or 7, wherein in the step a, the polyimide solution is applied by a gravure coating method or a screen printing method.

  9. 9. The method according to any one of 6 to 8 above, wherein the poor solvent bath of polyimide is an aqueous solution having a water component of 40% by weight or more.

  10. 10. The method according to any one of 6 to 9 above, wherein the porous membrane used in step a has a thickness of 3 to 300 [mu] m and a ventilation resistance of 10 to 1000 seconds / 100 cc in terms of Gurley value.

  11. A battery separator using the composite porous film according to any one of 6 to 10 above.

  12 12. The battery separator as described in 11 above, wherein the membrane breaking temperature is 200 ° C. or higher.

  According to the present invention, a composite porous film having good air permeability can be easily obtained. The obtained composite porous film can be used as a separator for a storage battery, and by having a polyimide layer, it exhibits higher heat resistance than a separator made of only polyolefin, so that the safety of the storage battery can be improved. Moreover, since the affinity with respect to liquids, such as electrolyte solution, increases, when using for a separator, the electrolyte solution injection property in the assembly process of a battery improves.

An example of the composite porous film of this invention is shown typically. An example of the composite porous film of this invention is shown typically. An example of the composite porous film of this invention is shown typically. It is the apparatus figure used in the measurement of the electrical resistance value of a composite porous film. It is a figure which shows the temperature characteristic of the thermal obstruction | occlusion of the composite porous film of Example 1. It is the figure which observed the surface of the composite porous film of Example 1 with the optical microscope. It is the figure which observed the surface of the composite porous film of Example 1 by SEM. Example 1 It is the figure which observed the boundary of the polyimide application part of the surface of a composite porous film, and an unapplication part by SEM (the left side is an unapplication part). 1 is a view of a cross section of a composite porous film observed with an SEM. FIG. It is the figure which observed the surface of the composite porous film of Example 2 with the optical microscope. It is the figure which observed the surface of the composite porous film of Example 2 by SEM. It is the figure which observed the surface of the composite porous film of Example 3 with the optical microscope. It is the figure which observed the surface of the composite porous film of Example 3 by SEM. The top view of the printing plate used in Example 4, and the schematic diagram of a cross section are shown. It is the figure which observed the surface of the composite porous film of Example 4 with the optical microscope. It is the figure which observed the surface of the composite porous film of Example 4 by SEM. The top view of the printing plate used in Example 5, and the schematic diagram of a cross section are shown. It is the figure which observed the surface of the composite porous film of Example 5 with the optical microscope. It is the figure which observed the surface of the composite porous film of Example 6 with the optical microscope. In the composite porous film of Example 7, it is the figure which observed the surface which apply | coated the polyimide layer previously with the optical microscope. In the composite porous film of Example 7, it is the figure which observed the surface which apply | coated the polyimide layer later with the optical microscope. It is the figure which observed the surface of the composite porous film of the comparative example 2 with the optical microscope. It is the figure which observed the surface of the composite porous film of the comparative example 2 by SEM. It is the figure which observed the surface of the composite porous film of the comparative example 2 by SEM.

  Hereinafter, the present invention will be described in detail.

<Composite porous film>
The composite porous film of the present invention has a breathable porous membrane and a polyimide layer laminated on at least one surface of the porous membrane, and the polyimide layer is a polyimide layer on the same surface of the porous membrane. And a region where no polyimide layer is present. That is, the polyimide layer is formed in a two-dimensional pattern having a plurality of openings that two-dimensionally covers at least one surface of the porous film and exposes the porous film to the surface.

  The polyimide layer may be formed on one side of the porous film, but may have a structure in which a polyimide layer is formed on both sides of the porous film depending on the application.

  In the present invention, the portion where the polyimide layer is formed on the region where the polyimide layer is present is non-porous having no through holes, that is, the polyimide layer itself is not air permeable. That is, when the entire surface of a porous film having air permeability is covered with a polyimide layer without forming an opening, it means that there is no air permeability. Due to this non-porous feature, the mechanical strength of the composite porous film is increased, and the function as a storage battery separator can be exhibited with a thinner layer than when the polyimide layer itself is porous and air permeable.

  On the other hand, since the composite porous film of the present invention needs to have an appropriate air permeability from the viewpoint of the ion permeability of the battery, etc., a region where the polyimide layer does not exist on the porous membrane (hereinafter referred to as an opening portion). Called).

  In the composite porous film of the present invention, the ratio (coverage) of the area where the polyimide layer is present on the porous film is 10% to 70%, preferably 18% to 45%, depending on the film thickness. More preferably, it is 23% to 35%. If the coverage is too high, the air permeability of the composite porous film is impaired, and if the coverage is too low, the effect of the polyimide layer that prevents meltdown is not exhibited.

  The region where the polyimide layer is present is preferably formed so as to continuously exist two-dimensionally on the same surface of the porous membrane. This is because when the composite porous film of the present invention is used as a battery separator, the polyimide layer serves to prevent meltdown and maintain the shape of the entire separator.

  FIG. 1 schematically shows an example of the composite porous film of the present invention. As shown in FIG.1 (b) (XX sectional drawing of Fig.1 (a)), the composite porous film 20 has the porous film 21 and the polyimide layer 22 formed in the surface. Further, as shown in the plan view of FIG. 1A, the polyimide layer 22 is present on the porous film 21 so as to spread two-dimensionally continuously and is not separated. A large number of openings 23 are provided in the polyimide layer 22, and the porous film 21 is exposed to the surface from the openings 23. Thereby, the composite porous film 20 has air permeability as a whole.

  The size and shape of each opening are determined so that the meltdown of the porous film can be prevented, but any point on the surface of the porous film exposed to the opening exceeds 100 μm from the polyimide layer. It is preferable not to leave. This means that the point on the surface of the porous film is within a distance of 100 μm or less from the polyimide layer around the opening (this distance is hereinafter referred to as “maximum proximity distance”). This maximum proximity distance is more preferably 50 μm or less. The maximum proximity distance is usually preferably 0.1 μm or more, and more preferably 0.2 μm or more.

  The maximum proximity distance is ½ of the length of one side if the opening is a square as shown in FIG. 1, the radius if the opening is a circle, and ½ of the short side if the opening is a rectangle. In the case of an ellipse, it corresponds to half the short axis, and in the case of a triangle, it corresponds to the radius distance of the inscribed circle.

  In addition, if the polyimide layer existing between the openings is too thin, it also affects the strength of the polyimide layer, so the line width between the openings is preferably 0.5 μm or more, more preferably It is 5 μm or more, usually 150 μm or less, more preferably 80 μm or less.

  Therefore, the polyimide layer has a large number of openings so that the maximum proximity distance satisfies the above range, the line width between the openings satisfies the above range, and the coverage satisfies the above range. It is preferable. Furthermore, from the viewpoint of the strength of the polyimide layer, the opening is a continuous pattern that is regularly repeated. As a result, a large number of openings are uniformly distributed as a repeating pattern throughout the polyimide layer, and the polyimide layer exists in a balanced manner. It is preferable.

  Opening shapes include squares, rectangles, triangles, pentagons, hexagons, larger polygons, circles, ellipses, and other shapes surrounded by curves, but squares, rectangles, triangles, hexagons, and circles. In particular, a pattern in which a square, a rectangle (long side / short side is preferably 4 or less, more preferably 3 or less), a regular triangle, or a regular hexagon is repeated in a close-packed manner at a predetermined interval is preferable. As a specific pattern of the close-packing mode, for example, the square is the pattern shown in FIG. 1, the regular triangle is, for example, FIG. 2, and the regular hexagon is, for example, the pattern shown in FIG.

  Although the film thickness of the composite porous film of this invention is not specifically limited, It is 4-300 micrometers, Preferably it is 10-100 micrometers, More preferably, it is 10-50 micrometers. If the film thickness is too thin, the effect of preventing meltdown will be insufficient, and if the film thickness is too thick, when used as a battery separator, the amount of electrolyte injected will increase, contributing to an increase in battery manufacturing costs.

  Moreover, in the composite porous film of this invention, although it does not specifically limit, The thickness of a polyimide layer becomes like this. Preferably it is 0.5 micrometer-50 micrometers, More preferably, they are 1 micrometer-10 micrometers, More preferably, they are 1 micrometer-5 micrometers. If the polyimide layer is too thin, the effect of preventing meltdown will be insufficient, and if it is too thick, the amount of electrolyte injected will increase, contributing to an increase in battery manufacturing costs.

  The Gurley value of the composite porous film of the present invention is not particularly limited, but is 10 to 1000 seconds / 100 cc, preferably 10 to 800 seconds / 100 cc, and more preferably 30 to 600 seconds / 100 cc. If the Gurley value is too high, the function when used as a battery separator is not sufficient, and if the Gurley value is too low, there is a risk of increasing the non-uniformity of the reaction inside the battery.

  In the composite porous film of the present invention, in order to ensure the function as a battery separator, the thermal clogging temperature described later is preferably 120 ° C. to 140 ° C., and the membrane breaking temperature described later is 200 ° C. or higher. The heat resistant time at 200 ° C. is preferably 10 minutes or more, and more preferably 30 minutes or more.

  Next, the polyimide and porous membrane used for the composite porous film will be described in detail.

<Polyimide>
The polyimide used in the present invention preferably has a melting point of 210 ° C. or higher from the viewpoint of ensuring safety when an internal short circuit occurs in the battery. Furthermore, in the production of the composite porous film of the present invention, the polyimide used is preferably soluble in a solvent because it includes a step of applying a polyimide solution to the surface of the porous membrane as described later.

The polyimide used for this invention can be manufactured by a well-known method. In particular,
(1) A method of heating and dehydrating an acid component and a diamine component in a solvent, or
(2) A polyimide precursor can be produced from an acid component and a diamine component, and the polyimide precursor can be imidized using a dehydrating agent, or the polyimide precursor can be further heated to imidize.

  Known acid components and diamine components can be used.

As an acid component,
Pyromellitic dianhydride, 2,3 ′, 3,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (s- BPDA), 2,3 ′, 2,3′-biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, diphenylsulfone-3,4,3 ′, 4′-tetracarboxylic dianhydride, bis (3 , 4-Dicarboxyphenyl) sulfide dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3 ′ , 4,4'-benzophenonetetracarboxylic dianhydride (BTDA), bis (3,4-dicarboxyphenyl) methane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride , P-phenylenebis ( Trimellitic acid monoester anhydride), p-biphenylenebis (trimellitic acid monoester anhydride), m-terphenyl-3,4,3 ′, 4′-tetracarboxylic dianhydride, p-ter Phenyl-3,4,3 ′, 4′-tetracarboxylic dianhydride, 1,3-bis (3,4-dicarboxyphenoxy) benzene dianhydride, 1,4-bis (3,4-dicarboxy) Phenoxy) benzene dianhydride, 1,4-bis (3,4-dicarboxyphenoxy) biphenyl dianhydride, 2,2-bis [(3,4-dicarboxyphenoxy) phenyl] propane dianhydride, 2, Examples include 3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and the like. These can be used alone or in combination of two or more.

  In particular, as an acid component, 2,3 ′, 3,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA) is preferably included. More preferably, it contains s-BPDA, and if necessary, contains a-BPDA, BTDA, pyromellitic dianhydride and the like.

As a diamine component,
p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene (TDA), 3,3′-dichlorobenzidine, 3,3′-dimethylbenzidine, 2,2′-dimethylbenzidine, 3 , 3'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4 , 4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 3,3'-diamino- 4,4'-dichlorobenzophenone, 3,3'-diamino-4 4'-dimethoxybenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 2,2-bis (3-aminophenyl) propane, 2,2-bis (4 -Aminophenyl) propane, 2,2-bis (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-bis (4-aminophenyl) -1,1, 1,3,3,3-hexafluoropropane, 3,3′-diaminodiphenyl sulfoxide, 3,4′-diaminodiphenyl sulfoxide, 4,4′-diaminodiphenyl sulfoxide, 1,3-bis (3-aminophenyl) Benzene, 1,3-bis (4-aminophenyl) benzene, 1,4-bis (3-aminophenyl) benzene, 1,4-bis (4-a Nophenyl) benzene, 1,3-bis (4-aminophenoxy) benzene (TPE-R), 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 1, 3-bis (3-aminophenoxy) -4-trifluoromethylbenzene, 3,3′-diamino-4- (4-phenyl) phenoxybenzophenone, 3,3′-diamino-4, 4′-di (4- Phenylphenoxy) benzophenone, 1,3-bis (3-aminophenyl sulfide) benzene, 1,3-bis (4-aminophenyl sulfide) benzene, 1,4-bis (4-aminophenyl sulfide) benzene, 1,3 -Bis (3-aminophenylsulfone) benzene, 1,3-bis (4-aminophenylsulfone) benzene, 1,4-bis (4-a Minophenylsulfone) benzene, 1,3-bis [2- (4-aminophenyl) isopropyl] benzene, 1,4-bis [2- (3-aminophenyl) isopropyl] benzene, 1,4-bis [2- (4-Aminophenyl) isopropyl] benzene, 3,3′-bis (3-aminophenoxy) biphenyl, 3,3′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) Biphenyl, 4,4′-bis (4-aminophenoxy) biphenyl, bis [3- (3-aminophenoxy) phenyl] ether, bis [3- (4-aminophenoxy) phenyl] ether, bis [4- (3 -Aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, bis [3- (3-aminophenoxy) ) Phenyl] ketone, bis [3- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [3 -(3-aminophenoxy) phenyl] sulfide, bis [3- (4-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl ] Sulfide, bis [3- (3-aminophenoxy) phenyl] sulfone, bis [3- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- ( 4-aminophenoxy) phenyl] sulfone, bis [3- (3-aminophenoxy) phenyl] methane Bis [3- (4-aminophenoxy) phenyl] methane, bis [4- (3-aminophenoxy) phenyl] methane, bis [4- (4-aminophenoxy) phenyl] methane, 2,2-bis [3- (3-aminophenoxy) phenyl] propane, 2,2-bis [3- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2- Bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2 -Bis [3- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1 1,1,3,3,3
-Aromatic diamines such as hexafluoropropane and 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane. These can be used alone or in combination of two or more.

  As the diamine component, in addition to the aromatic diamine, diamines such as aliphatic, alicyclic, and silicon-containing diamines can be used as long as the characteristics of the present invention are not impaired.

  Furthermore, it is also possible to use a diisocyanate compound derived from the diamine compound instead of or together with the diamine. In the following description, these diisocyanate compounds are also described as being included in the diamine component.

  Examples of the diisocyanate compound include various aliphatic or aromatic diisocyanates, and the following are easily available. Specific examples of the aliphatic diisocyanate include 1,3-trimethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,2,4-trimethyl-1,6-hexamethylene. Alkane diisocyanates such as diisocyanate, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,9-nonamethylene diisocyanate, 1,10-decamethylene diisocyanate,

  Cycloalkane diisocyanates such as 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hydrogenated xylylene diisocyanate,

  2,2′-diethyl ether diisocyanate, 2,2′-diethyl sulfide diisocyanate, hexamethylene diisocyanate-biuret, 2-isocyanoethylthio-1,3-isocyanopropane, isophorone diisocyanate, 1,4-dithian-2 , 5-diisocyanate, and cycloalkane diisocyanate having a hetero atom such as tetrahydrothiophene-2,5-diisocyanate.

  Specific examples of the aromatic diisocyanate include p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, toluene diisocyanate (TDI), xylylene diisocyanate (XDI), 4,4. '-Methylenebis (phenylisocyanate) (MDI), 3,3'-methyleneditolylene-4,4'-diisocyanate, tolylene diisocyanate trimethylolpropane adduct, 4,4'-diphenylether diisocyanate, tetrachlorophenylene diisocyanate, 3, Examples include 3′-dichloro-4,4′-diphenylmethane diisocyanate.

  Among the diamine components, toluene diisocyanate (TDI), 4,4′-methylenebis (phenylisocyanate) (MDI), 1,3-bis (4-aminophenoxy) benzene (TPE-R), 2,4- It is preferable to use diaminotoluene (TDA).

  As an example of a preferable combination of an acid component and a diamine component, a mixture of a-BPDA and TPE-R, a-BPDA / s-BPDA and TDI, BTDA and TDI, and the like can be given.

  The polyimide solution is prepared by adding an acid component and a diamine component in an organic polar solvent at a predetermined composition ratio, and performing a polymerization reaction at a low temperature of about room temperature to produce a polyamic acid, followed by heating to heat imidization or pyridine. Or the like, or a chemical imidization at a high temperature of about 100 to 250 ° C., preferably about 130 to 200 ° C. by adding an acid component and a diamine component in an organic polar solvent at a predetermined composition ratio. This is preferably carried out by a one-stage method of reacting. When the imidization reaction is carried out by heating, it is preferred to carry out while removing water or alcohol that is eliminated. The amount of the acid component and diamine component used in the organic polar solvent is such that the concentration of polyimide in the solvent is about 5 to 40% by weight, preferably 5 to 20% by weight.

  Examples of the organic solvent for preparing the polyimide include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide and the like. These organic solvents may be used alone or in combination of two or more.

  If necessary, an imidization catalyst, an organic phosphorus-containing compound, fine particles such as inorganic fine particles and organic fine particles, and the like may be added to the polyimide adjustment solution.

  Examples of the imidization catalyst include a substituted or unsubstituted nitrogen-containing heterocyclic compound, an N-oxide compound of the nitrogen-containing heterocyclic compound, a substituted or unsubstituted amino acid compound, an aromatic hydrocarbon compound having a hydroxyl group, or an aromatic heterocyclic compound. Cyclic compounds such as 1,2-dimethylimidazole (2MZ), N-methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 5-methylbenzimidazole. Lower alkyl imidazole, benzimidazole such as N-benzyl-2-methylimidazole, isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, 4 -Substituted pyridines such as n-propylpyridine It can be suitably used and the like. The amount of imidation catalyst used is preferably about 0.01 to 2 times equivalent, particularly about 0.02 to 1 times equivalent to the number of amino groups of the diamine component (isocyanate group in the case of a diisocyanate compound). By using an imidization catalyst, properties of the resulting polyimide film, particularly elongation and end resistance, may be improved.

  When chemical imidization is intended, a chemical imidizing agent combining a dehydrating ring-closing agent and an organic amine is usually contained in the polyimide precursor solution. Examples of the dehydrating ring-closing agent include dicyclohexylcarbodiimide, and acid anhydrides such as oxalic anhydride, acetic anhydride, propionic anhydride, valeric anhydride, benzoic anhydride, and trifluoroacetic acid dianhydride. , Picoline, quinoline, isoquinoline, pyridine and the like, but are not limited thereto.

  As a solvent which melt | dissolves the polyimide used for this invention, the solvent which can melt | dissolve a polyimide 20-20 mass%, More preferably, 30-56 mass%, More preferably, 36-50 mass% is preferable. Specifically, for example, phenol, cresol, xylenol, catechol having two hydroxyl groups in the benzene ring, catechols such as resorcin, 3-chlorophenol, 4-chlorophenol , Halogenated phenols such as 3-bromophenol, 4-bromophenol, 2-chloro-5-hydroxytoluene, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N- It can be appropriately selected from amides such as diethylformamide, N, N-dimethylacetamide and N, N-diethylacetamide, ketones such as sulfolane and γ-butyrolactone, ethers such as diglyme and triglyme. These organic solvents are simple and preferable to use alone, but two or more of them may be used in combination if necessary.

<Porous membrane>
The porous membrane used in the present invention is not particularly limited, but when the composite porous film of the present invention is used as a battery separator, it is difficult to ensure safety when an internal short circuit occurs if the separator's thermal blockage temperature is too high. If it is too low, it may become non-porous in the temperature range of the normal use range, which impairs the convenience of the battery. For this reason, although it sets according to the characteristic and use environment of a battery, it is preferable to set so that heat obstruction | occlusion temperature may be 130-140 degreeC in a specific use. In addition, the membrane breaking temperature of the separator using the composite porous film of the present invention exceeds the temperature of a separator consisting only of a conventional porous membrane, but in order to maintain non-porous up to a high temperature, the porous membrane alone However, it is preferable to have a non-porous maintenance temperature of 170 ° C. or higher.

  In order to satisfy such characteristics, the porous membrane of the present invention has a thermoplastic polymer layer having a melting point of 150 ° C. or higher, preferably a laminated porous membrane, and preferably has a melting point of 150 ° C. or higher. And a thermoplastic polymer layer having a melting point in the range of 120 ° C to 140 ° C.

  The porous membrane is preferably composed of a polyolefin-based material. The thermoplastic polymer layer having a melting point of 150 ° C. or higher may be formed of polypropylene (PP), and the thermoplastic polymer layer having a melting point in the range of 120 ° C. to 140 ° C. may be formed of polyethylene (PE). preferable. Most preferably, it is a porous film laminated in the order of PP / PE / PP. The porous membrane may be a nonwoven fabric on which the polyolefin material is laminated.

  The film thickness of the porous film is 3 to 300 μm, preferably 10 to 100 μm, more preferably 10 to 50 μm, although it depends on the type of battery used.

  Further, the porous membrane needs to have an appropriate air permeability (gas permeation rate) although it varies somewhat depending on the production conditions, and the Gurley value is preferably 10 to 1000 seconds / 100 cc, and preferably 10 to 800. It is more preferable that it is second / 100 cc, and it is still more preferable that it is 30-600 second / 100 cc. If the Gurley value is too high, the function when used as a battery separator is not sufficient, and there is a risk of increasing the non-uniformity of the reaction inside the battery. .

  In the case where the porous membrane is used as a battery separator, a resin additive typified by a colorant, a plasticizer, a lubricant, a flame retardant, an antioxidant, an antioxidant, etc., as long as the performance as a battery separator is not impaired. An adhesive and a reinforcing agent made of an inorganic material may be included.

  The method for producing the porous membrane used in the present invention is not particularly limited, but in the case of a polyolefin laminated porous membrane, it is particularly preferably produced by a dry stretching method, and specifically, JP-A-7-307146 or It can be produced by a known method such as JP-A-4-181651.

<Method for producing composite porous film>
The composite porous film of the present invention can be obtained by applying the polyimide solution to at least one surface of the porous membrane and then immersing it in a poor solvent bath of polyimide. As the polyimide, a solution obtained by polymerization may be used as it is, or a polyimide powder obtained by precipitating polyimide from a polymerization solution may be used by dissolving in a solvent.

  Since the application pattern of the polyimide solution and the pattern of the obtained polyimide layer match, the application method of the polyimide solution is not particularly limited as long as the polyimide solution can be applied in the pattern of the polyimide layer described above. As described above, since a two-dimensionally continuous pattern is preferable on the porous film, a gravure coating method, a screen printing method, a spraying method, and the like can be given. Industrially, a method that can be continuously applied by a roll-to-roll method is preferable. In particular, the gravure coating method is more preferable because a pattern continuous on the porous film can be uniformly and easily produced by a roll-to-roll method by using a printing roll.

  In the case of using a gravure coat, the design of the gravure plate is the main factor determining the pattern of the polyimide layer, but the gravure plate pattern does not necessarily have to be transferred as it is. In other words, even if a general gravure engraving plate is used, the polyimide layer is continuously connected by two-dimensionally linking the solution when it is transferred, the solution flowing after transfer, the flow during precipitation in the coagulation bath, etc. A layer may be formed.

  Also note that the final polyimide layer coverage cannot simply be estimated from the gravure design, because volume shrinkage occurs when the solution is transferred to the porous membrane and then solvent extracted in the coagulation bath. It is necessary to design the plate.

  Furthermore, the degree of penetration of the polyimide solution into the gravure plate recess varies depending on the solution viscosity and the application conditions of the solution. By using this phenomenon, the degree of penetration of the solution into the gravure plate recess is combined to reduce the coating. If necessary, it is possible to suppress the coverage of the polyimide layer to be lower than the coverage estimated from the dimensions of the gravure design.

  The porous film coated with the polyimide solution is immersed in a coagulation bath containing a polyimide poor solvent as a main component, whereby the solvent in the solution is extracted, and the polyimide is solidified and deposited on the porous film, and then dried. The poor solvent for polyimide is preferably compatible with the solvent used when applying polyimide. For example, water, alcohol (monovalent alcohol having 3 to 8 carbon atoms, or ethylene glycol is preferable). ), Acetone and the like, and when an aqueous solution is used, the water component is preferably 40% by weight or more.

Generally, when a polyimide solution is immersed in a poor solvent, a porous structure is formed when the polyimide solidifies and precipitates. As a method of avoiding this porosity,
(1) Water is used as a coagulation bath component.
(2) A polyimide solution is applied, and after a sufficient time, it is immersed in a coagulation bath.
(3) Heat drying with a suitable amount of residual solvent remaining in the polyimide by shortening the coagulation bath immersion time.
Porous formation can be suppressed by combining these methods in a timely manner.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

<Measurement of viscosity of polyimide solution>
In the reference examples described later, the viscosity of the polyimide solution was measured with an E-type rotational viscometer. The measurement procedure is shown below.
(I) The polyimide solution prepared in the reference example was put in a sealed container and held in a thermostatic bath at 30 ° C. for 10 hours.
(Ii) Using an E-type viscometer (manufactured by Tokyo Keiki Co., Ltd., high-viscosity (EHD type) conical plate type rotary type, cone rotor: 1 ° 34 ′), using the polyamic acid solution prepared in (i) as a measurement solution, The measurement was performed at a temperature of 30 ± 0.1 ° C. Three measurements were taken and the average value was adopted. When there was a variation of 5% or more at the measurement points, the measurement was further performed twice and the average value of the five points was adopted.

<Reference Example 1>: Preparation of polyimide solution In a reaction vessel equipped with a stirrer, 12.59 g of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 80 g of N-methylpyrrolidone (NMP), 0.77 g of water and 0.08 g of 1,2-dimethylimidazole (2MZ) were added and stirred at 120 ° C. for 1 hour. Next, 5.44 g (0.8 mol parts) of toluene diisocyanate (TDI) and 1.96 g (0.2 mol parts) of 4,4′-methylenebis (phenyl isocyanate) (MDI) were added dropwise at 120 ° C. Stir for hours. Thereafter, 20 g of toluene was added, and the mixture was stirred at 180 ° C. for 6 hours while removing water out of the system by azeotropy with toluene to prepare a viscous polyimide solution.

  An equal weight of NMP was added to 10 g of the prepared polyimide solution, and stirred and diluted to prepare a polyimide solution for coating. The solution viscosity was 260 poise.

<Reference Example 2>
In a reaction vessel equipped with a stirrer, 2.512 g 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride (a-BPDA), 10.05 g 3,3 ′, 4,4′- Biphenyltetracarboxylic dianhydride (s-BPDA), 80 g of NMP, 0.77 g of water and 0.08 g of 2MZ were added and stirred at 120 ° C. for 1 hour. Next, 7.44 g of TDI was added dropwise and stirred at 120 ° C. for 1 hour. Thereafter, 20 g of toluene was added, and the mixture was stirred at 180 ° C. for 6 hours while removing water out of the system by azeotropy with toluene to prepare a viscous polyimide solution.

  An equal weight of NMP was added to 10 g of the prepared polyimide solution, and a polyimide solution for coating was prepared by stirring and diluting. The solution viscosity was 300 poise.

<Reference Example 3>
In a reaction vessel equipped with a stirrer, 10.03 g of a-BPDA, 9.969 g of 1,3-bis (4-aminophenoxy) benzene (TPE-R), and 80 g of NMP were added. Stir for 5 hours. Thereafter, 20 g of toluene was added and stirred at 180 ° C. for 8 hours while removing water out of the system by azeotropy with toluene to prepare a viscous polyimide solution. The solution viscosity was 240 poise.

  An equivalent amount of NMP was added to 10 g of the prepared polyimide solution, and stirred and diluted to prepare a polyimide solution for coating.

<Reference Example 4>: Preparation of polyimide solution In a reaction vessel equipped with a stirrer, 12.59 g of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 80 g of N-methylpyrrolidone (NMP), 0.77 g of water and 0.08 g of 1,2-dimethylimidazole (2MZ) were added and stirred at 120 ° C. for 1 hour. Then 5.406 g (0.795 mol parts) of toluene diisocyanate (TDI), 1.96 g (0.2 mol parts) of 4,4′-methylenebis (phenylisocyanate) (MDI) were added dropwise, Stir for hours. Thereafter, 20 g of toluene was added, and the mixture was stirred at 180 ° C. for 6 hours while removing water out of the system by azeotropy with toluene to prepare a viscous polyimide solution. The solution viscosity was 550 poise.
<Reference Example 5>
A polyimide solution for coating was prepared by adding 1.5 times the weight of NMP to 10 g of the prepared polyimide solution, followed by stirring and dilution. The solution viscosity was 25 poise.

<Performance evaluation of composite porous film>
In the following examples, the film thickness, Gurley value, resistance value before heating, thermal clogging temperature, and film breaking temperature of the obtained composite porous film were evaluated by the following methods.

(1) Film thickness It measured with the contact-type thickness meter (made by Peacock).

(2) Gurley value Measured according to JIS P8117. A B-type Gurley Densometer (manufactured by Toyo Seiki Co., Ltd.) was used as a measuring device. The sample piece is clamped in a circular hole having a diameter of 28.6 mm and an area of 645 mm ² . With the inner cylinder weight of 567 g, the air in the cylinder is allowed to pass out of the cylinder from the test circular hole. The air permeability (Gurley value) was measured by measuring the time for 100 cc of air to pass.

(3) Resistance value before heating, thermal clogging temperature, membrane breakage temperature Using a self-made cell for measuring electrical resistance (FIG. 4), the resistance value before heating, the thermal clogging temperature, and the membrane breaking temperature were measured. The sample was degassed by immersing it in a non-aqueous electrolyte prepared by dissolving lithium perchlorate in a 1: 1 (vol / vol) (hereinafter, DEC / PC) mixed solution of dimethoxyethane / propylene carbonate to 1 M / L. The nonaqueous electrolytic solution was contained in the microporous material. This sample was sandwiched between nickel electrodes 3 and 4 and set in a measuring cell, and the resistance value before heating was measured. Next, the temperature was raised in the oven at a rate of 10 ° C./min. The electrical resistance between the electrodes was measured using 3520 LCR HiTESTER manufactured by Hioki Electric Co., Ltd. The measurement was performed from room temperature, and the temperature at which the resistance value reached 1000Ω or higher was defined as the thermal clogging temperature, the temperature exceeding the thermal clogging temperature, and the temperature at which the resistance value was again lower than 100 KΩ by 2 times.

(4) Water contact angle (degrees)
Measurement was performed using a contact angle measuring device (manufactured by KRUSS). A 3 μL water droplet was dropped on the sample surface, and the angle formed by the sample surface and the droplet was measured every 10 seconds for 1 minute from the dropping, and the average was defined as the water contact angle.

(5) Propylene carbonate (PC) contact angle (degrees)
Measurement was performed using a contact angle measuring device (manufactured by KRUSS). 3 μL of PC droplet was dropped on the sample surface, and the angle formed between the sample surface and the droplet at that time was measured every 10 seconds for 1 minute from the dropping, and the average was taken as the PC contact angle.

(6) 200 ° C heat resistant time (minutes)
A sample heating cell (manufactured by LinKAM, HFS-91) was mounted on the stage of an optical microscope (manufactured by Keyence, VH-Z75) to obtain a hot stage microscope. Fix with a heat-resistant adhesive tape (Sumitomo 3M, polyimide tape 5413) so as to overlap in the order of a 22 mm diameter circular cover glass, a Teflon (registered trademark) sheet with a 5 mm diameter hole, and a sample sample cut into TD2 mm × MD8 mm A heat resistance test sample was prepared. At that time, both ends 5 mm of the sample sample in the MD direction were fixed so that the center of the sample sample was on the hole center. The heat resistance test sample was placed in the center of the sample heating cell and heated from 25 ° C. to 200 ° C. at 100 ° C./min. After reaching 200 ° C., the temperature was kept for 30 minutes. The change with time of the sample sample was observed so that both ends of the sample sample were in the observation field. At that time, the time from the start of the 200 ° C. temperature keep until the defect was confirmed in the observation visual field was defined as the 200 ° C. heat resistance time.

(7) Observation The surface of the obtained film was observed with an optical microscope and a scanning electron microscope (SEM) to confirm the pattern of the polyimide layer and non-porous / porous. Moreover, the SEM observation of the film cross section was also performed as needed.

(8) Ratio of area where polyimide layer is present (coverage)
It measured by image-processing the optical microscope photograph of the surface image | photographed by (7).

  Tables 1 and 2 show the performance evaluation of the films produced in the following examples and comparative examples.

<Example 1>
A polypropylene / polyethylene / polypropylene three-layer separator (manufactured by Ube Industries, Inc., film thickness 16 μm, Gurley value 290 seconds / 100 ml) is attached to a polyimide film (manufactured by Ube Industries, Ltd., film thickness 75 μm), and the laminate to be printed Was made. The laminate was set on a roll part of a gravure coater. The polyimide solution prepared in Reference Example 1 was dropped in the immediate vicinity of a 10 ml doctor blade, and a polyimide solution was applied using a 175 line / inch engraving plate (both manufactured by RK Print Coat Instruments Ltd.).

  The laminate was immersed in a water bath containing 3 wt% NMP for 15 seconds and then in a water bath containing 1 wt% NMP for 30 seconds. Thereafter, drying was performed for 3 minutes in a thermostatic bath set at 80 ° C. After drying, the polyimide film was removed from the laminate to obtain a polyolefin-polyimide composite film.

  FIG. 5 shows the behavior of the temperature characteristics of thermal blockage of the produced composite porous film. The observation result by the optical microscope and SEM of the surface coat | covered with the polyimide layer of the composite porous film is shown to FIG. 6A and FIG. 6B. Furthermore, it was confirmed by SEM observation that the surface of the polyimide layer covering the polyolefin porous membrane had no pores with a diameter of 0.1 μm or more (FIG. 6C). Moreover, it confirmed that PI layer and the polyolefin layer were closely_contact | adhering by SEM observation of the manufactured composite porous film cross section (FIG. 6D).

<Example 2>
A polyolefin-polyimide composite film was obtained in the same manner as in Example 1 except that the polyimide solution used was the polyimide solution prepared in Reference Example 2. The observation result by the optical microscope and SEM of the surface coat | covered with the polyimide layer of the manufactured composite porous film is shown to FIG. 7A and FIG. 7B. Furthermore, it was confirmed by SEM observation that the surface of the coated polyimide layer had no holes having a diameter of 0.1 μm or more.

<Example 3>
A polyolefin-polyimide composite film was obtained in the same manner as in Example 1 except that the polyimide solution used was the polyimide solution prepared in Reference Example 3. The observation result by the optical microscope and SEM of the surface coat | covered with the polyimide layer of the manufactured composite porous film is shown to FIG. 8A and FIG. 8B. Furthermore, it was confirmed by SEM observation that the surface of the coated polyimide layer had no holes having a diameter of 0.1 μm or more.

<Example 4>
A polyolefin-polyimide composite film was obtained in the same manner as in Example 1 except that the printing plate used was a self-made printing plate having a pattern in which convex portions of 100 μm × 100 μm were arranged at equal intervals (50 μm). FIG. 9 shows a plan view and a cross-sectional schematic view of the printing plate. The observation result by the optical microscope and SEM of the surface coat | covered with the polyimide layer of the manufactured composite porous film is shown to FIG. 10A and FIG. 10B. Furthermore, it was confirmed by SEM observation that the surface of the coated polyimide layer had no holes having a diameter of 0.1 μm or more.

<Example 5>
A polyolefin-polyimide composite film was obtained in the same manner as in Example 1 except that the printing plate used was a self-made printing plate having a pattern in which circular convex portions having a diameter of 260 μm were arranged at equal intervals. FIG. 11 shows a plan view and a cross-sectional schematic view of the printing plate. The observation result by the optical microscope of the surface coat | covered with the polyimide layer of the manufactured composite porous film is shown in FIG.

<Example 6>
A polyolefin-polyimide composite film was obtained in the same manner as in Example 5 except that the solution used in Reference Example 4 was used. The observation result by the optical microscope of the surface coat | covered with the polyimide layer of the manufactured composite porous film is shown in FIG.

<Example 7>
The same operation as in Example 6 was performed on the non-coated surface of the polyolefin porous membrane of the polyolefin-polyimide composite film obtained in the same manner as in Example 6 to obtain a polyolefin-polyimide composite film. FIG. 14A and FIG. 14B show the observation results of the surface of the composite porous film that was previously coated with the polyimide layer and the other surface that was subsequently coated with an optical microscope, respectively. Later, it was confirmed by SEM observation that the surface of the coated polyimide layer had no holes having a diameter of 0.1 μm or more.

<Comparative Example 1>
The same performance evaluation as in Example 1 was performed on a polypropylene / polyethylene / polypropylene three-layer separator (manufactured by Ube Industries, Ltd., film thickness 16 μm, Gurley value 290 seconds / 100 ml).

<Comparative example 2>
A multilayer film was obtained in the same manner as in Example 1 except that the solution used in Reference Example 5 was used. By observation with an optical microscope, it was confirmed that the macro pattern of the polyimide layer had a heterogeneous structure that was probably due to the flow of the polyimide solution (FIG. 15A). In addition, the surface of the polyimide layer coated by SEM observation was found to have a heterogeneous structure in which a portion having a hole having a diameter of 0.1 μm or more and a portion having no hole were mixed (FIGS. 15B and 15C).

  The separator of the present invention is high in safety and has an improved liquid absorption rate. For this reason, it is advantageously used as a separator for a battery, for example, a lithium ion secondary battery.

1 Top case (aluminum)
2 Top current collector (stainless steel)
3 Top electrode (Nickel)
4 Bottom electrode (made of nickel)
5 Bottom current collector (stainless steel)
6 Bottom case (Teflon)
7 Spacer (Teflon)
8 Separator (sample)
9 Hexagon socket head cap screw 10 Wing nut 11 Color (brass)
12 Spring (SUS)
20 Composite porous film 21 Porous membrane 22 Polyimide layer 23 Opening

Claims (12)

A composite porous film having a polyimide layer and a breathable porous membrane,
The film thickness of the film is 4 to 300 μm, the ventilation resistance is 10 to 1000 seconds / 100 cc in terms of Gurley value,
The polyimide layer itself is not air permeable, two-dimensionally covers at least one surface of the porous membrane two-dimensionally, and has a plurality of openings that expose the porous membrane to the surface. A composite porous film characterized by being formed into a shape.   The film according to claim 1, wherein the plurality of openings of the polyimide layer exist as a continuous pattern that is regularly and two-dimensionally repeated.   The film according to claim 1 or 2, wherein the polyimide layer has a thickness of 0.5 to 50 µm.   The ratio (coverage) of the area | region where a polyimide layer exists on the same surface of the said porous film is 10% or more and 70% or less, The any one of Claims 1-3 characterized by the above-mentioned. the film.   The film according to any one of claims 1 to 4, wherein the porous film is a single layer film or a multilayer film formed of a layer selected from a polyolefin porous film and a nonwoven fabric. A method for producing a composite porous film according to any one of claims 1 to 5,
(Step a) Applying the polyimide solution in a two-dimensional pattern having a plurality of openings covering at least one surface of the porous membrane two-dimensionally and exposing the porous membrane to the surface; ,
(Step b) A method for producing a composite porous film, comprising the step of immersing the porous membrane coated with the polyimide solution obtained in Step a in a poor solvent bath of polyimide.   7. The method according to claim 6, wherein in the step a, the polyimide solution is applied in a pattern so that the large number of openings form a continuous pattern that is regularly and two-dimensionally repeated.   The method according to claim 6 or 7, wherein in the step (a), the polyimide solution is applied by a gravure coating method or a screen printing method.   The method according to any one of claims 6 to 8, wherein the poor solvent bath of polyimide is an aqueous solution having a water component of 40% by weight or more.   10. The method according to claim 6, wherein the porous film used in step a has a thickness of 3 to 300 μm and a ventilation resistance of 10 to 1000 seconds / 100 cc in terms of Gurley value.   The battery separator using the composite porous film of any one of Claims 6-10.   The battery separator according to claim 11, wherein the membrane breaking temperature is 200 ° C or higher.