Technical field
[0001]The present invention is a porous composite film, battery separator, battery, and to a method for producing a porous composite film that.
BACKGROUND
[0002]Lithium ion secondary batteries, as rechargeable high-capacity battery of repetition, has been enabling the high performance and long-term operation of the electronic devices such as mobile phones and notebook computers. In recent years, electric vehicles, is mounted as environment-friendly vehicles of the driving battery, such as hybrid electric vehicles, higher performance is expected.
　To performance of such a lithium ion secondary battery, high capacity of the battery capacity, input-output characteristics, life characteristics, temperature characteristics, storage characteristics, etc., are considered for the improvement of various battery characteristics is made , it is also being examined various materials constituting the battery.
　As one, the separator disposed between the positive electrode and the negative electrode also has various studies have been made so far, in particular consideration of the adhesiveness separator is advanced.
[0003]
　For example, Patent Document 1, a porous substrate, a composite film having an adhesive porous layer made of polyvinylidene fluoride resin is disclosed, tortuosity of the porous substrate, the adhesive porous layer average pore diameter, by setting the Gurley value of the porous substrate and the composite film to a specific range, adhesion to the electrode, to provide ion permeability, and a separator for a nonaqueous electrolyte battery excellent for shutdown characteristics It has been described as possible.
　Patent Document 2, a porous film made of a polyolefin resin, method for producing a battery separator obtained by laminating a modified porous layer comprising a fluorine-based resin is disclosed. This manufacturing method is contacted with fluorine-based resin coating liquid dissolved in a solvent, a step of double-sided simultaneous coating of the porous membrane, between the solidifying step, the porous membrane after coating the shake preventing device is, it is described that the conveying speed of 30 m / min. According to the manufacturing method using such a shake prevention apparatus, high productivity is obtained, it is described that it is possible to suppress the coating streaks.
[0004]
　Patent Document 3, as a manufacturing method for a nonaqueous secondary battery separator, the porous support is passed through between the two dies for supplying the dope comprising polyvinylidene fluoride or a copolymer thereof, the porous the coating film formed on both sides of the quality support and then through the air gap step, the porous substrate which is coated, conveyed into a coagulating bath containing a coagulating liquid which is installed below the die, soaked manufacturing method characterized by solidifying the coating Te is described. Such manufacturing methods are ion-permeable, adhesion to the electrode, the electrolyte solution retention is stated to be suitable as a method for producing a separator for a good nonaqueous secondary battery.
　Patent Document 4, on the polyolefin microporous membrane, a step of applying a varnish of specific fluorine resin concentration, the step of passing the polyolefin microporous membrane to a specific low-humidity zone, passing a predetermined high humidity zone a step of, immersed in a coagulation bath coating layer containing a fluorine-based resin is converted to the reforming porous layer, the battery separator reforming porous layer is laminated, including a fluorine-based resin and particles to the polyolefin microporous membrane obtaining process is described. Such battery separator obtained by the process has excellent shutdown performance and electrode adhesiveness, and has been described to be suitable for high-capacity battery having an excellent electrolyte permeability.
CITATION
Patent Document
[0005]
Patent Document 1: Japanese Japanese Patent No. 5964951
Patent Document 2: Japanese Patent 2016-38934 JP
Patent Document 3: Japanese Patent 2003-171495 JP
Patent Document 4: WO 2014/126079
Summary of the Invention
Problems that the Invention is to Solve
[0006]
　However, when using the battery separator as set forth in Patent Document 1 to 4, even when high adhesion after electrolyte injection, the film strength becomes weak, it found that not a good state cycle characteristics . Also found that the adhesion of the film strength partially missing and falling product during the manufacturing process to weak exists, defects such as short circuit had been likely to occur. In view of such problems, the objective is high while maintaining the adhesiveness also film strength is strong, the adhesion of the partial missing and falling of the manufacturing process can be suppressed, suitable porous composite to a battery separator of the present invention film, a separator using the same, is to provide a battery, and a manufacturing method of the porous composite film excellent in cycle characteristics.
[0007]
　Here, the cycle characteristics are good, the produced flat wound atmosphere of battery cells 35 ° C. for up to 4.35V charged at 1C, repeatedly charged and discharged to a discharge at 1C until 3.0 V, the capacity retention the number of cycles until the rate reaches 60% means that at least 350 times. Also, partial it and is missing and suppress the adhesion of falling off of the manufacturing process, the stress value when the tape peeling so that the porous substrate and the porous layer, cohesive failure (film strength) of 2 It says that this is .0N or more.
Means for Solving the Problems
[0008]
　The present inventors have conducted extensive studies results, the porous composite film and a porous substrate and the porous layer, also cross-sectional void area distribution and the surface pore area distribution of the porous layer, while maintaining high adhesion film the intensity strongly found that the cycle life of the battery using the porous composite film is a factor to be good.
[0009]
　That is, the present invention includes a porous substrate, a porous composite film porous layer is laminated on at least one surface of the porous substrate, the porous layer comprises a fluorine-containing resin, the following requirements ( i), it is a porous composite film satisfying (ii) and (iii).
(I) the D cross-sectional void area distribution of the porous layer 1 value of 50 is 0.06 .mu.m 2 or 0.38 .mu.m 2 or less, and wherein the porous layer of the cross-sectional void area distribution of D 1 value of 90 is 0.20μm 2 more 1.15Myuemu 2 is less than or equal to.
(Ii) the D surface pore area distribution of the porous layer 2 value of 50 0.0060Myuemu 2 more 0.0072Myuemu 2 or less, and D of the surface pore area distribution of the porous layer 2 value of 90 0 .0195Myuemu 2 more 0.0220Myuemu 2 is less than or equal to.
(Iii) The porosity of the porous layer is 50 to 70%.
　According to another aspect of the present invention, a battery separator using the above-described porous composite film is provided.
[0010]
　The present invention is a battery including a positive electrode, a negative electrode, the battery separator of the present invention disposed between the positive electrode between the negative electrode.
　The present invention provides a method of producing a porous composite film of the present invention,
　the steps of coating liquid and the fluorine-containing resin dissolved in a solvent is coated on at least one surface of a porous substrate to form a coating film ,
　the coating film was formed a porous substrate solidifying the fluorine-containing resin is immersed in a coagulation solution containing water (phase separation) to form a porous layer, porous on the porous substrate obtaining a composite film quality layer is formed,
　a step of washing the composite film,
　comprising the step of drying the composite film after rinsing, a temperature of between 10 ~ 25 ° C. of the coagulation liquid, and wherein the concentration of solvent in the coagulation liquid is less than 22 wt%, a method for producing a porous composite film.
The invention's effect
[0011]
　According to the present invention, even while having excellent adhesion and film strength, it has a porous layer which can suppress the attachment of partial missing and falling product during the manufacturing process, the separator of a battery having excellent cycle characteristics it is possible to provide a suitable porous composite film and battery using the same. Further, according to the present invention, it is possible to provide a manufacturing method of the porous composite film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012]
[1] Figure 1 is a diagram for explaining a manufacturing method of the porous composite film according to an embodiment of the present invention.
FIG 2a] Figure 2a is a (A) section of a scanning electron microscope image of a porous composite film of Example 2 (SEM image).
FIG 2b] Figure 2b is a cross-sectional SEM images of the porous composite film (B) Comparative Example 3.
[3] FIG 3 is a SEM image of the surface of the porous composite film of Examples 1, 5 and Comparative Example 3.
DESCRIPTION OF THE INVENTION
[0013]
　Porous composite film according to an embodiment of the present invention includes a porous substrate, a porous composite film porous layer is laminated on at least one surface of the porous substrate the porous layer comprises a fluorine-containing resin , it satisfies the following requirements.
(I) the D cross-sectional void area distribution of the porous layer 1 value of 50 is 0.06 .mu.m 2 or 0.38 .mu.m 2 or less, and wherein the porous layer of the cross-sectional void area distribution of D 1 value of 90 is 0.20μm 2 more 1.15Myuemu 2 is less than or equal to.
(Ii) the D surface pore area distribution of the porous layer 2 value of 50 0.0060Myuemu 2 more 0.0072Myuemu 2 or less, and D of the surface pore area distribution of the porous layer 2 value of 90 0 .0195Myuemu 2 more 0.0220Myuemu 2 is less than or equal to.
(Iii) The porosity of the porous layer is 50 to 70%.
[0014]
　The porous composite film can be suitably used as a battery separator, for example, when used as a separator for lithium ion batteries, it is preferable that the porous layer on both surfaces of the porous substrate is provided.
　Porous substrate and the porous layer of the porous composite film according to the present embodiment both have a suitable gap to the conduction of lithium ions. By holding the electrolytic solution in the gap, it is possible to conduct lithium ions.
[0015]
　(Porous layer D of the cross-section void area distribution 1 50 and D 1 90)
　the porous layer of the cross-sectional void area distribution of D 1 value of 50, 0.06 .mu.m 2 or 0.38 .mu.m 2 or less, and D 1 90 of value 0.20 [mu] m 2 or more 1.15 .mu.m 2 that it is less, the porous composite film having such a porous layer, also while include relatively small pores, having a relatively large pores. Therefore, the porous composite film also while keeping the high adhesiveness to effectively retain the electrolyte solution, it can be kept high film strength. D
　sectional void area distribution of the porous layer 1 a value of 50 0.06 .mu.m 2 or more, and D 1 0.20 [mu] m value of 90 2With more, can take the distance of each cross-section air-gap sufficiently, when the fluorine-containing resin for forming the porous layer is phase separated, it is possible fibrils are present in a bundle. Therefore, to improve the film strength of the porous layer to prevent peeling of the porous layer in the manufacturing process, the porous composite film for adhesion, an indicator of adhesion to the electrode can be improved, using the film it is possible to improve the cycle characteristics of the battery. Therefore, D sectional void area distribution of the porous layer 1 value of 50 is 0.06 .mu.m 2 or more, and D 1 value of 90 0.20 [mu] m 2 by at least the porous layer film has high strength, peel hardly, to have a good adhesion, it is possible to obtain excellent battery cycle characteristics.
[0016]
　Further, D sectional void area distribution of the porous layer 1 value of 50, 0.38 .mu.m 2 exceeds, or D 1 value of 90 1.15 .mu.m 2 exceed the, surface pore area distribution of the porous layer D 2 value of 50, 0.0060Myuemu 2 becomes less than, the porous layer outermost layer resulting in densified. Such battery using the porous composite film separator outermost surface layer has a densified porous layer, the charge and discharge time of the resistor is increased, the cycle characteristic by voltage drop occurs may be lowered. Therefore, D sectional void area distribution of the porous layer 1 value of 50 is 0.38 .mu.m 2 or less, and D 1 value of 90 1.15 .mu.m 2 by at most, a porous layer, an appropriate pore can have a surface dense layer having a result, it is possible to obtain a battery with good cycle characteristics.
[0017]
　Here, the term "porous layer outermost surface layer" refers to a surface layer region of 25 nm ~ 150 nm from the surface of the porous layer (surface opposite to the porous substrate). A porous layer outermost layer resulting in densified, for example, in the manufacturing method described later, when soaked the porous layer to become a coating liquid porous substrate coated with in the liquid of the coagulation / washing bath , the surface layer region of 25 nm ~ 150 nm is formed on the outermost surface of the porous layer, refers to the surface dense layer is formed by densification. The surface dense layer, a porous base has been coating solution coated on material (varnish) is, in earliest contact liquid interface in a non-solvent (coagulating liquid), a layer of a fluorine-containing resin to be formed during the phase separation corresponds to. When the surface dense layer is too thick, not suitable pores are formed, such a surface dense layer is used for the separator a porous composite film having a porous layer formed batteries, cycle characteristics are lowered. In the present invention "-" the above, represent the following.
[0018]
　(Porous layer D of the surface pore area distribution of 2 50 and D 2 90) D
　of the surface pore area distribution of the porous layer 2 value of 50, 0.0060Myuemu 2 more 0.0072Myuemu 2 or less, and D 2 value of 90 0.0195Myuemu 2 more 0.0220Myuemu 2 that is less than can surface dense layer has a moderate denseness and can have sufficient film strength. By using a porous composite film having such a porous layer in the separator, it is possible to obtain an excellent battery cycle characteristics. 　The porous layer D of the surface pore area distribution of 2 value of 50 0.0060Myuemu 2 below, or D 2 value of 90 0.0195Myuemu 2 is less than, the porous layer outermost layer becomes excessively dense . Battery using the porous composite film separator is such outermost surface has an excessively densified porous layer, the charge and discharge time of the resistor is increased, the cycle characteristic by voltage drop occurs decreases. Accordingly, the surface pore area distribution of the porous layer D 2
Value of 50, 0.0060Myuemu 2 or more, and D 2 value of 90 0.0195Myuemu 2 If it is more, the porous layer has a surface dense layer having a moderate pore, result, excellent cycle it can be obtained battery characteristics.
[0019]
D 　of the surface pore area distribution of the porous layer 2 value of 50 0.0072Myuemu 2 exceeds, or D 2 value of 90 0.0220Myuemu 2 exceeds sectional voids of the porous layer becomes dense. As a result, can not exist solidify the fibrils of the fluorine-containing resin to form a porous layer, since the diameter of the fibrils decreases, decreased film strength of the porous layer, the porous layer is easily peeled off in the manufacturing process . Further, since the porous composite film in which adhesion is decreased, the cycle characteristics of the battery using the film decreases. Therefore, D of the surface pore area distribution of the porous layer 2 value of 50, 0.0072Myuemu 2 or less and D 2 value of 90 0.0220Myuemu 2 by at most, the porous layer film has high strength , peeling hardly, to have a good adhesion, it is possible to obtain excellent battery cycle characteristics.
[0020]
　(Porosity of the porous layer)
　porosity of the porous layer is in the range of 50% to 70%, it may be set as appropriate depending on the intended use of the porous composite film. For example, when using a porous composite film of the present embodiment the separator of the lithium-ion battery, the porosity of the porous layer is less than 50%, low conductivity of a sufficient amount of electrolyte lithium ion can not hold will, resistance increases. Conversely, the porosity of the porous layer is greater than 70%, the film strength is lowered. Therefore, by the porosity of the porous layer is in the range of 50-70%, while sufficiently keeping the film strength of the porous layer, can hold a sufficient amount of the electrolyte, sufficient conductivity of lithium ions since obtained, it is possible to suppress an increase in resistance.
[0021]
　(Fluorine-containing resin of the porous layer)
　by the porous layer comprises a fluorine-containing resin, it is possible to adhesion to obtain a high porous layer. If the porous composite film according to the present embodiment is used in the separator of the lithium-ion battery, if the high adhesion, it is possible to increase the cycle life of the battery.
　The fluorine-containing resin, vinylidene fluoride, hexafluoropropylene, trifluoroethylene, tetrafluoroethylene, at least homopolymer or copolymerization including one polymerization unit selected from the group of polymerized units species consisting of chlorotrifluoroethylene coalescence preferably, the polymer (polyvinylidene fluoride, vinylidene fluoride copolymer) containing vinylidene fluoride unit is more preferable. In particular, in view of swelling against the electrolyte solution, preferably a vinylidene fluoride copolymer comprising vinylidene fluoride and other polymerization units, vinylidene fluoride - hexafluoropropylene copolymer, vinylidene fluoride - chlorotrifluoroethylene copolymer polymers are preferred.
[0022]
　(Porous layer ceramic)
　porous in this embodiment the composite film may comprise a ceramic on the porous layer. As the ceramic, for example, titanium dioxide, silica, alumina, silica - alumina composite oxide, zeolite, mica, boehmite, barium sulfate, magnesium oxide, magnesium hydroxide, zinc oxide.
[0023]
　(Average particle size of the ceramic)
　average particle size of the ceramic is preferably be set in a range of 0.5 [mu] m ~ 2.0 .mu.m, and more preferably in a range of from 0.5 [mu] m ~ 1.5 [mu] m. However, the average particle diameter of the ceramic is a maximum of thickness of the porous layer, it is preferable to select an average particle diameter of the ceramic.
[0024]
　(Weight ratio of the ceramic of the porous layer)
　content of the ceramic is 50% to 90% by weight relative to the total weight of the fluorine-containing resin and ceramic are preferred, more preferably 60 wt% to 80 wt%.
[0025]
　(Average area A1 of the cross section voids of the porous layer)
　porous composite film according to the present embodiment, A1 "average cross-sectional area of the air gap" in relation to the average value of the void diameter of the porous layer 0.054Myuemu 2 or more 0. 098Myuemu 2 is preferably not more than, 0.054Myuemu 2 or 0.095 m 2 and more preferably less, 0.054Myuemu 2 or 0.080 [mu] m 2 and still more preferably less. From the viewpoint of obtaining a sufficient adhesion and excellent strength of the porous layer, the average area A1 of the cross-section void in the porous layer is 0.054Myuemu 2 or more. The porous composite film of the terms to sufficiently suppress the deterioration of the cycle performance of the battery using the separator, the average area A1 of the cross gaps 0.098Myuemu 2 or less.
[0026]
　(Thickness of the porous composite film)
　total thickness of the porous composite film according to the present embodiment, preferably be set in the range of 4 [mu] m ~ 30 [mu] m, and more preferably a range of 4 [mu] m ~ 24 [mu] m. By setting the thickness in this range, while the possible film, it is possible to secure the mechanical strength insulating.
　Thickness of the porous layer of the porous composite film according to the present embodiment, preferably be set in the range of 1 ~ 5 [mu] m, more preferably in the range of 1 ~ 4μm, 1 ~ 3μm is more preferable. The thickness of the porous layer by setting such a range, a necessary minimum thickness, it is possible to obtain the formation effect and sufficient adhesion and excellent strength sufficient porous layer.
[0027]
　(Adhesive force between the electrodes of the porous layer)
　is preferably adhesion between the porous layer of the electrode of the porous composite film according to the present embodiment is not less than 5.0 N. If the adhesive force between the electrodes is less than 5.0 N, when the bubbles as a by-product by cell reaction is caused, and peeling portion having a weak adhesive strength, the cycle characteristics becomes part thereof a defect of the battery descend. On the other hand, the upper limit is not particularly defined, it is preferably 10N or less, and more preferably less 8N.
[0028]
　(Porous layer film strength cohesive failure of)
　preferably has a film strength of cohesive failure of the porous layer of the porous composite film according to the present embodiment is not less than 2.0 N, and more preferably not less than 2.4 N. If the film strength of cohesive failure is less than 2.0 N, separation of the porous layer is produced in the process, the productivity is reduced by falling material to adhere to the roll or the like. On the other hand, the upper limit is not particularly defined, it is preferable from the viewpoint of handling properties of the porous composite film (such as blocking) is 10N or less.
[0029]
　(Porous substrate)
　The porous substrate of porous composite film according to the present embodiment is preferably a polyolefin porous membrane. As the polyolefin resin, polyethylene or polypropylene are preferred. Mixtures of a single compound or two or more different polyolefin resins, may be, for example, mixtures of polyethylene and polypropylene. Further, the polyolefin may be a homopolymer and a be a copolymer, for example, polyethylene may be a homopolymer of ethylene, or a copolymer containing units of other α-olefin, polypropylene it may be a homopolymer of propylene, or a copolymer containing units of other α-olefins. The porous substrate may be a laminated film may be a single layer film composed of a plurality of layers of two or more layers.
　The polyolefin porous film, the content of the polyolefin resin in the polyolefin porous film means a porous film is 55 to 100 mass%. When the content of the polyolefin resin is less than 55 wt%, a sufficient shutdown function can not be obtained.
　The thickness of the porous substrate is preferably in the range of 3 [mu] m ~ 25 [mu] m, and more preferably a range of 3 ~ 20 [mu] m. The porosity of the porous substrate is preferably in the range of 30 to 70%, more preferably from 35 to 60%. Such a thickness, by having a porosity sufficient mechanical strength and insulating properties can be obtained and it is possible to obtain a sufficient ion conductivity.
[0030]
　(Manufacturing method of the porous composite film)
　manufacturing method of the porous composite film according to the present embodiment has the following steps (a) ~ (d), the temperature of the coagulating liquid is in a range of 10 ~ 25 ° C., and solidifying concentration of the solvent in the liquid is less than 22 wt%.
(A) a fluorine-containing resin a process by coating on at least one surface of the porous substrate a coating liquid dissolved in a solvent to form a coating film
of the porous substrate (b) a coating film is formed contains water was immersed in a coagulation liquid to coagulate the fluororesin to form a porous layer, the porous obtain a composite film porous layer is formed on a substrate process
step of washing the (c) composite film
step (d) drying the composite film after washing
[0031]
　The viscosity of the coating liquid in said step (a), is a major factor in the solvent concentration in the coagulation liquid in the process, and temperature of the coagulation liquid determines the structure of the porous layer (b).
　An example of the production method of the porous composite film according to the present embodiment will be described below with reference to FIG. In this manufacturing method, after using a head having a gap the porous substrate can pass, the coating solution on both surfaces of the porous substrate was coated (dip coating), followed by coagulation, washing, drying, porous obtaining a porous composite film porous layer is formed on both sides of the substrate.
　First, a porous substrate unwound from the unwinding roll 1, to dip the head 2, is supplied from above, it is drawn downward through the gap at the bottom of the dip head 2, followed by coagulation / washing It is supplied to the tank 3. The dip head 2 can accommodate coating solution so that it can dip coating on both surfaces of the porous substrate to pass through. On both surfaces of the drawn porous substrate is a coating film is formed, the coating thickness can be controlled by the size of the gap dip head conveyance speed.
[0032]
　The solvent of the coating liquid, capable of dissolving the fluorine-containing resin, and can be used can be good solvent (miscible at any concentration) miscible with the coagulating solution (phase separation liquid) such as water. Such a good solvent this good porous substrate coating solution was applied containing a fluorine-containing resin dissolved in a solvent, it enters the coagulation liquid during solidification / washing tank, and the resin in the coating film good solvent phase separation, the porous layer is formed the resin solidifies.
　As the good solvent, N, N- dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), phosphoric acid hexamethyltriamide (HMPA), N, N- dimethylformamide (DMF), dimethyl sulfoxide (DMSO ) and the like, can be freely selected according to the solubility of the resin. As the good solvent, N- methyl-2-pyrrolidone (NMP) are preferred.
[0033]
　The viscosity of the coating liquid can be set in the range of 600mPa · s ~ 1000mPa · s. The viscosity of the coating liquid is a viscosity measured by a B-type viscometer. By the viscosity of the coating liquid in the range of 600mPa · s ~ 1000mPa · s, it is possible to control the diffusion rate of the non-solvent during the phase separation, it is possible to form a desired porous layer.
　The concentration of the fluorine-containing resin coating liquid is preferably in the range of 2 wt% to 7 wt%, and more preferably in the range of 3% to 6% by weight.
[0034]
　Moreover, coating thickness may be set to 5 [mu] m ~ 25 [mu] m (one side). Variation 10% ± the coating thickness in the width direction (direction perpendicular to the traveling direction of the film) or less.
　Figure 1 shows a dip coating method using a dip head, a porous substrate on one surface viscosity 600 mPa · s or more 1000 mPa · s or less of the coating liquid of the can coating in coating thickness 5μm or 25μm or less , as long as it can be applied so that the thickness variation in the width direction is 10% ±, can employ various coating methods. For example, a typical dip coating, casting, spin coating, bar coating, spraying, blade coating, slit die coating, gravure coating, reverse coating, lip Thailand recto, comma coating, screen printing, mold coating, printing transfer, wet such an ink-jet mention may be made of a coating method, or the like. In particular, when coating a continuous and example coating speed 30 m / min or more, high viscosity, thin film, suitable for high-speed coating, lip direct method or a comma coating method, which is scraping method, a dip coating method is preferable . Further, from the viewpoint of capable of forming a double-sided simultaneous porous layer, dip coating method is more preferred. By adopting the dip coating method, it is possible to coating with 80 m / min or faster.
　When performing continuously coated, conveying speed, for example can be set in the range of 5 m / min ~ 100 m / min, from the viewpoint of the uniformity of productivity and coating thickness, appropriately set in accordance with the coating method be able to.
[0035]
　The coagulation liquid is preferably an aqueous solution containing water or water as a main component, the concentration of the coagulation liquid in the good solvent should be kept below 22 wt% (i.e. a water content of more than 78 wt%), 20 less than mass% (i.e., 80 or more mass% content of water) preferably be kept, it is more preferable to maintain the 16 wt% or less (i.e. an amount that the content of water exceeds 84% by mass). For example, good solvent concentration in the coagulation liquid is preferably kept within the range of 0.1% by mass to less than 22 wt%, more preferably in the range of less than 0.1% by weight to 20% by weight, more preferably 0.1 It can be set in the range of weight percent to 16 weight percent or less.
　The porous substrate having the coating film formed by dip head is immersed into a coagulating liquid of the coagulation / washing bath.
[0036]
　The temperature of the coagulation liquid is preferably set to 25 ° C., and more preferably up to 24 ° C.. When set to such a temperature range, a coating film with coagulation liquid is phase separated at a moderate rate of phase separation can form a desired porous layer, also it becomes easy to control the temperature. On the other hand, the lower limit of the temperature of the coagulating liquid is solidifying solution may be within a range capable of maintaining the liquid (temperature higher than the freezing point), from the viewpoint of the rate of temperature control and phase separation, it is necessary to be 10 ° C. or higher, 15 It is preferably at least ° C., more preferably at least 17 ° C..
[0037]
　Immersion time in the coagulation liquid of the coagulation / washing bath is preferably at least 3 seconds, more preferably not less than 5 seconds. The upper limit of the soaking time is not particularly limited, as long as immersed for 10 seconds is sufficient solidification can be achieved.
[0038]
　Coagulation / In unwound out from the coagulating liquid in the washing tank 3, the porous composite film porous layer is formed on the porous substrate can be obtained. The porous composite film is subsequently fed into water of the primary water-washing tank 4, sequentially, water in the secondary washing tank 5, are introduced into water of cubic washing tank 6, it is continuously cleaned. In Figure 1, the washing tank is three, according to the cleaning effect in the washing tank, may increase the number of water washing tanks may be reduced. It wash water of each tank can be continuously supplied, the recovered wash water may be recycled and purified.
　Next, unwound porous composite film was from the end of the third order washing tank 6, it is introduced into the drying furnace 7, deposited cleaning liquid is removed, dried porous composite film is wound around the winding roll 8.
[0039]
　(Measurement
　method) (1) D of the cross-sectional void area distribution of the porous layer 1 50, D 1 90 D
　sectional void area distribution of the porous layer 1 50, D 1 90 were determined as follows.
The base section subjected to cross out by ion milling the substrate surface and the vertical direction acceleration voltage 2.0 kV, and the substrate section and the SEM image observed randomly in the vertical direction at a magnification of 5000 times, resulting cross-sectional SEM About 50 sheets of images, a thickness direction of the respective substrates 1: 1 to cut parallel to image the plane direction of the substrate at a point which internally divides, acquires the gray value for the image, the image of the more average value thereof is large the image analysis software HALCON (Ver.13.0, manufactured MVtec Inc.) at, first to load the image data, then (sequentially in the processing of differential filter (emphasize), an edge enhancement filter (Shock_filter)) edge enhancement after, it was carried out in the procedure that binary. Incidentally, "emphasize" differential filter used for edge enhancement, "shock_filter" edge enhancement filter is an image processing filter included in HALCON. Binarization, set the lower limit of the threshold for the gray values 64, the upper limit to 255, (including that if there is a filler such as ceramic) 64 or more parts of the fluorine-containing resin such as PVdF (polyvinylidene fluoride) there is a present portion, further replace them gray value regions in which the resin component and the filler are present 255, the gray value of the other areas (sectional void portion) to 0, the consecutive pixels together with gray values 0 ligated, and extracted the area of 100 or more cross air gap from one of the images. The area of the extracted sectional void portion and cross void area, among the cross-section void area, the cross-sectional void area satisfying Formula (1), D in the distribution of the area value 1 50 and D 1 were calculated 90. Here, D 1 and 50 rearranges the sectional void area in ascending order, to the total area obtained by adding all the area, the area in which the accumulated area is 50%, D 1 90 refers to the area of the cumulative area of 90%.
[0040]
[Number 1]

[0041]
　Wherein, X is the cross-sectional void area, X max is the maximum value of each cross-section void area.
[0042]
　(2) D of the surface pore area distribution of the porous layer 2 90, D 2 50
　porous layer surface pore area distribution of D of 2 90, D 2 50 were determined as follows.
Accelerating voltage 2.0 kV, the surface SEM image 50 Like randomly is obtained by SEM image observed on the substrate surface and the vertical at a magnification of 10000 times, the image analysis software HALCON (Ver. 13.0, manufactured by MVtec Co.) Te, to load the image data first, then edge enhancement after (differential filter (emphasize), an edge enhancement filter (order in the process of shock_filter)), it was carried out in the procedure that is binarized. Binarization, the lower limit of the threshold value for the gray value 10, set 10 or more portions to the upper limit 255 and the fluorine-containing resin (if there is a filler such as ceramic including it) there are portions, such as PVdF, Furthermore, they gray values of a region in which the resin component and the filler are present 255, replacing the gray value of the other area (surface pore section) to 0, connecting the consecutive pixels together with gray value 0, a was extracted area of 100 or more surfaces pore portions from the image. The area of the extracted surface pore section and the surface pore area, among the surface pore area, the surface pore area satisfying the formula (2), D in the distribution of the area value 2 90 and D 2 were calculated 50 . Here, D 2The 90 rearranges each surface pore area in ascending order, to the total area obtained by adding all the area, the area in which the accumulated area is 90%, D 2 50 refers to the area in which cumulative area is 50% .
[0043]
[Number 2]

[0044]
　Wherein, Y is each surface pore area, Y max is the maximum value of each surface pore area.
[0045]
　(3) the porosity V of the porous layer
　porosity V of the porous layer was calculated using the following equation.
[0046]
[Number 3]

[0047]
　Wherein, W A true density, t is the thickness of the porous layer of the porous layer basis weight, D is the porous layer.
[0048]
　Basis weight W of the porous layer A was measured as follows using the following equation.
W A = the coating exposed film basis weight (W A1 ) - basis weight of the substrate (W A2 )
　basis weight W of the coating exposed film A1 basis weight W of and the substrate A2 measurements prepares a sample of 5cm square, or less It was calculated using the formula.
　W A1 = "coating pre-film 5cm angle the weight of the sample" /0.0025
　W A2 = "base 5cm angle the weight of the sample" /0.0025
[0049]
　True density D of the porous layer was calculated using the following equation.
　D = the blending ratio of the density × A material A (mass ratio) + material mixture ratio of density × B of B (mass ratio) + ...
[0050]
　The thickness t of the porous layer was measured as follows using the following equation.
　t = coating already thickness of the film (t 1 ) - thickness of the substrate (t 2 )
[0051]
　Thickness (t using contact-type film thickness meter (Mitutoyo Corporation Ltd. "Litematic" (registered trademark) Series318) 1 , t 2 was measured). Measurements using a cemented carbide spherical gauge head Fai9.5Mm, measured 20 points under the condition of a weighted 0.01 N, the average value of the measured values obtained were a thickness.
[0052]
　(4) average area A1 of the cross-section void in the porous layer
　has an average area A1 of the cross-section void in the porous layer was measured as follows.
　Substrate surface and perpendicular to the ion milling accelerate cross-section subjected to cross out voltage by 2.0 kV, the cross-sectional SEM image 50 Like the SEM image observed at random at a magnification of 5000 times, the thickness direction of the respective substrates 1: cut parallel to image the plane direction of the substrate at a point which internally divides 1, acquires the gray value for the image, the direction of the image that is larger average value, the image analysis software HALCON (Ver.13.0, MVtec at company Ltd.), to load the image data first, then edge enhancement (differential filter (emphasize), after the forward processing of the edge emphasis filter (Shock_filter), it was performed in the procedure of binarizing for .2 valued, 64 the lower limit of the threshold for the gray values, the void portions of less than an upper limit to 255 64, 64 or more parts PVd (If there are filler containing it) and a portion is present, replaces further their gray value regions in which the resin component and the filler are present 255, the gray value of the other area (air gap) to 0, gray connecting the consecutive pixels to each other with a value 0, it was extracted area of 100 or more cross air gap from one of the images. the area of the extracted sectional void portion and cross void area, among the cross-section void area, the formula ( sectional void area satisfying 1) to calculate the average area A1 of the cross-section void in equation (4).
[0053]
[Formula 4]

[0054]
　(Lithium ion secondary battery)
　porous composite film according to the present embodiment can be used as a battery separator, it can be suitably used as a separator for lithium ion secondary battery. By using the porous composite film according to the present embodiment in the separator, it is possible to provide a lithium ion secondary battery excellent in cycle characteristics.
　The battery according to the present embodiment includes a positive electrode, a negative electrode, the battery separator of the present embodiment positioned between the positive electrode and the negative electrode.
　Examples of the lithium ion secondary battery porous composite film according to the present embodiment is applied, the electrolyte solution containing an electrolyte is impregnated in the battery element the negative electrode and the positive electrode are arranged oppositely through a separator, these exterior include those having encapsulated in wood structures.
[0055]
　Examples of the negative electrode, the negative electrode active material, a negative electrode mixture comprising a conductive auxiliary agent and binder, include those formed on a current collector. As the negative electrode active material, capable of doping and dedoping materials are used lithium ions. Specifically, a carbon material such as graphite or carbon, silicon oxide, silicon alloy, tin alloy, lithium metal, and the like such lithium alloy. The conductive additive, acetylene black, carbon materials such as ketjen black is used. As the binder styrene-butadiene, polyvinylidene fluoride, polyimide is used. As the current collector copper foil, stainless steel foil, and nickel foil is used.
[0056]
　Examples of the positive electrode, the positive electrode active material, the positive electrode mixture comprising a conductive auxiliary agent, if a binder and optionally, include those formed on a current collector. As the positive electrode active material, Mn, Fe, Co, lithium composite oxide containing at least one transition metal such as Ni. Specifically, for example, lithium nickelate, lithium cobaltate, and lithium manganate. The conductive additive, acetylene black, carbon materials such as ketjen black is used. The binder such as polyvinylidene fluoride is used. Aluminum foil as a current collector, such as stainless steel foil is used.
[0057]
　As an electrolytic solution, for example, it can be used those obtained by dissolving a lithium salt in a nonaqueous solvent. The lithium salt, LiPF 6 , LiBF 4 , LiClO 4 , LiN (SO 2 CF 3 ) 2 and the like. The non-aqueous solvent, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, .gamma.-butyrolactone and the like, usually together with various additives such as vinylene carbonate, a mixture of two or more of these what was is used. Furthermore, the ionic liquid (room temperature molten salt), such as imidazolium cations systems can be employed.
　The exterior material, and metal cans or aluminum laminate pack. The shape of the battery, a coin type, cylinder type, square type, and the like laminated.
Example
[0058]
　(Measurement Method)
　For the porous composite film of the examples and comparative examples, D sectional void area distribution of the porous layer 1 50, D 1 according to the above (1) for 90, D 2 90, D 2 in accordance with 50 above for (2), in accordance with the above (3) for the porosity V of the porous layer, measuring the average area A1 of the cross section voids of the porous layer according to the above (4) It was carried out. Also, the adhesion and film strength and film thickness was measured according to the following.
[0059]
　(Film thickness)
　was measured thickness using the contact-type film thickness meter (Mitutoyo Corporation Ltd. "Litematic" (registered trademark) Series318). In this measurement, using a cemented carbide spherical gauge head Fai9.5Mm, measured 20 points under the condition of a weighted 0.01 N, the average value of the measured values obtained were a thickness.
[0060]
　(Film
　strength) of the film strength was measured by the method based on the 180 ° peel of JIS C5016-1994. Each porous composite film, laminated double-sided tape cut into approximately 20 mm × 100 mm ((Ltd.) Seiwa Sangyo transparent film double-sided tape SFR-2020), and crimped on the metal plate, the surface of the sample central portion to about 15 mm × 90 mm cut the cellophane tape (plant-based, Nanba405) attached about 80mm and the porous substrate and the porous layer and the metal plate as cellophane tape is peeled off the 180 ° direction to cohesive failure of the and set Sellotape (registered trademark) to autograph pulled at 100.0 mm / min, to measure the stress at tape peeling.
[0061]
　(Example 1)
　was prepared porous composite film according to the manufacturing process shown in FIG. 1 described above. Specifically, first, a polyolefin porous film unrolled from the roll (thickness 7 [mu] m) at a conveying speed 7m / min, passed through a gap of the dip head from above the dipping head downward, both surfaces of the polyolefin porous membrane the coating solution was applied, followed by, coating is formed on the polyolefin porous membrane by immersing into a coagulating liquid. The size (the thickness direction length) of the gap of the dip head was 45 [mu] m. As the resin of the coating liquid PVdF (polyvinylidene fluoride), the mass ratio of the resin with NMP (N-methyl-2-pyrrolidone) as a good solvent for dissolving the, PVdF and NMP is PVdF: NMP = 1: 22 and then, coating thickness (single-sided) was 12.0μm (film thickness (one side) is 1.5μm). Using alumina as the ceramic of the coating liquid, the weight ratio of PVdF and alumina PVdF: alumina = 1: 1.4.
[0062]
　Coagulating liquid of the coagulation / washing bath is using water as the phase separation liquid, holding the NMP concentration in the coagulation liquid in the 0.1 wt%, the temperature of the coagulation liquid was set at 11 ° C..
　In step drawn from coagulation liquid, the porous composite film porous layer was formed on the polyolefin porous membrane is obtained, the porous composite film, in turn, primary washing tank, a secondary washing tank, tertiary It is introduced into the water of the washing tank and washed successively.
　Subsequently, the unwound porous composite film of the last cubic washing tank, is introduced into the drying oven, to remove the adhered washings were O'by winding the dried porous composite film.
　The obtained porous composite film are shown in Table 1 for the measurement and production conditions.
[0063]
　(Examples 2-18, Comparative Examples 1-3)
　The size of the gap of the dip head as the basis weight of PVdF porous layer is equal (coating Gap,), the mass ratio of PVdF and alumina coating liquid, the coating Material viscosity, except that the NMP temperature and concentration of the coagulating liquid in the coagulating liquid was adjusted as shown in Table 1, to prepare a porous composite film in the same manner as in example 1. The measurement results are shown in Table 1.
[0064]
　(Comparative Example 4)
　in the same porous substrate as in Example 1, was applied an acrylic resin instead of the PVdF, alumina ceramics, coating solution using water as a good solvent to one side by a gravure method (coating thickness (single-sided): 12.0μm), to form a porous layer on one surface and dried. The measurement results are shown in Table 1.
[0065]
　(Lithium ion secondary battery produced and cycle characteristic evaluation)
　(Preparation of electrolyte solution)
　as an electrolytic solution, ethylene carbonate (EC): methylethyl carbonate (MEC): diethyl carbonate (DEC) = 3: 5: 2 ( volume ratio the solvent mixture in), LiPF 6 was prepared (lithium hexafluorophosphate) 1.15 M and vinylene carbonate (VC) electrolytic liquid containing 0.5 wt%.
[0066]
　(Preparation of Positive Electrode)
　Lithium cobaltate (LiCoO 2 and acetylene black graphite and polyvinylidene fluoride was added to), The slurry was uniformly applied to both sides of the positive electrode current collector aluminum foil having a thickness of 20μm to form a positive electrode layer, then compression molded by a roll press, the positive electrode except the collector density of the layer is 3.6 g / cm 3 to prepare a band-like positive electrode of.
[0067]
　(Preparation of Negative Electrode)
　carboxymethyl cellulose aqueous solution containing 1.5 parts by mass, were mixed with 96.5 parts by weight of artificial graphite, and mixed with 2 parts by mass of styrene-butadiene latex further as solid anode mixture It was formed containing slurry. The negative electrode mixture containing slurry was dried uniformly coated subjected on both sides of the negative electrode current collector having a thickness of copper foil 8μm to form a negative electrode layer, then compression molded by a roll pressing machine, collecting the density of the negative electrode layer except the conductor is 1.5 g / cm 3 to prepare a negative electrode of a strip-shaped.
[0068]
　(Preparation of Test for wound body)
　and the negative electrode prepared by the above (machine direction 161 mm × width 30 mm), overlaid a porous composite film (machine direction 160 mm × width 34 mm) of Examples or Comparative Examples, metal plate (length 300 mm, width 25 mm, thickness 1mm) winding the porous composite film and the negative electrode as a porous composite film as a core winding on the inside, to obtain a test wound body pull out the metal plate. Test wound body became a length of about 34 mm × width of about 28mm.
[0069]
　(Adhesive strength)
　laminate film of polypropylene (length 70 mm, width 65 mm, thickness 0.07 mm) overlapped two sheets, the bag-shaped laminate film to the test winding body obtained by welding three sides of the four sides brewed. The volume ratio of ethylene carbonate and ethyl methyl carbonate 3: 7 LiPF solvent obtained by mixing 6 an electrolyte solution 500μL of a dissolved at a rate of 1 mol / L is injected from the opening of the laminate film in the glove box, the test winding impregnating the body, seal the side of the opening in the vacuum sealer.
　Then, the laminate film sealed to the test for windings of the two gaskets (thickness 1 mm, 5 cm × 5 cm) sandwiched between, precise heating and pressing device (Sintokogio Co., CYPT-10) at 98 ° C., 2 minutes pressurized at 0.6 MPa, and allowed to cool at room temperature. While sealed in a laminate film, the test wound body after pressing, universal testing machine (manufactured by Shimadzu Corporation, AGS-J) were measured wet flexural strength using.
[0070]
　Two aluminum L-shaped angles (thickness 1 mm, 10 mm × 10 mm, length 5 cm) parallel to such that the top 90 ° portions, disposed aligned end, between a fulcrum 90 ° portion as a fulcrum distance is fixed so as to be 15mm. To 7.5mm point a distance between supporting points intermediate the two aluminum L-shaped angles of the combined mid-point of the width direction of the side of the test winding body (about 28mm), the length direction of the L-shaped angles so as not to protrude from the sides, was placed a test windings.
　Then, as the aluminum L-shaped angles as indenter (thickness 1 mm, 10 mm × 10 mm, length 4 cm) length direction of the side of the test wound body from the longitudinal sides (about 34 mm) does not protrude to, and in parallel, the middle point of the width direction of the side of the test wound body combined 90 ° portion of the aluminum L-shaped angles, universal testing an aluminum L-shaped angles as 90 ° portion is below It was fixed to the machine of the load cell (load cell capacity 50N). Three test wound body was measured at a load rate of 0.5 mm / min, the average value of the maximum test force, thereby providing an adhesive force.
[0071]
　(Fabrication of Battery)
　The above positive electrode, after the porous composite film of the above Examples and Comparative Examples, and the negative electrode of the stacked, flattened wound electrode assembly (height 2.2 mm × width 32 mm × depth 32 mm) It was produced. To each electrode of the flat wound electrode body, welding the sealant tabbed, and a positive electrode lead, a negative electrode lead.
　Next, the wound electrode body portion of the flat sandwiched between aluminum laminate film, and sealed leaving a part opening, which was dried for 6 hours at 80 ° C. in a vacuum oven. After drying, quickly an electrolyte solution was 0.75ml injected, and sealed with a vacuum sealer, 90 ° C., and 2 minutes pressed at 0.6 MPa.
　Subsequently, it was performed charging and discharging of the obtained battery. Discharge condition at a current of 300 mA, after constant current charging until the battery voltage 4.35V, was constant voltage charged to a 15mA in battery voltage 4.35V. After 10 minutes pause, a constant current discharge until the battery voltage 3.0V at a current of 300 mA, it was rested for 10 minutes. More charge and discharge 3 cycles performed, to prepare a secondary battery for testing the battery capacity 300 mAh (flat wound cells).
[0072]
　(Cycle costing)
　for flat winding type battery cell produced above, using a charge-discharge measuring device, under an atmosphere of 35 ° C., until 4.35V charging at 300mA, charging and discharging of the discharging at 300mA to 3.0V repetition, to determine the number of cycles until the capacity maintenance rate reaches 60%. If the number of cycles is large, indicating that the cycle characteristics are good. Charge and discharge conditions at this time, were as follows.
　Charge condition: 1C, CC-CV charging, 4.35V, 0.05 C Cut off
　rest: 10 minutes
　Discharge Conditions: 1C, CC discharge, 3V Cut off
　rest: 10 minutes.
[0073]
[Table 1]

[0074]
　As shown in Table 1, in the embodiment satisfying the requirements of the present invention, porosity sufficient composite film having a porous layer having adhesion and film strength can be obtained, battery cycle using the porous composite film separator excellent characteristics.
　Figures 2a and 2b are cross-sectional SEM images of the porous composite film of each Example 2 and Comparative Example 3, FIG. 3 is a SEM image of the surface of the porous composite film of Examples 1, 5 and Comparative Example 3 is there.
　Example 2 shown in FIG. 2a: porous composite film (NMP concentration 0.1 wt%) of Comparative Example 3 shown in Figure 2b: relative porous composite film (NMP concentration 24.8 wt%), cross the void D of the area distributions 1 50, D 1 is in a state that reflects the 90 and average area A1 of the cross gap is large. That is, the porous layer of Example 2 has a sparse structure, a porous layer of Comparative Example 3 has a dense structure.
[0075]
　Left SEM image of Example 2 in FIG. 3 (NMP concentration: 0.1 wt%), the center of the SEM image Example 5 (NMP concentration: 16.0 wt%), the right of the SEM image of Comparative Example 3 ( NMP concentration indicates the porous layer surface of the porous composite film of 24.8 wt%), lower SEM image is an enlarged image of the upper SEM image. Examples 1 and 5, with respect to Comparative Example 3, D of the distribution of surface pore area 2 50, D 2 90 is small (i.e. be a relatively dense structure), different distributions of surface pore area It is (the distribution is small difference in different but surface pore area).
　Pore distribution of the porous layer surface of the porous composite film of the thus Example 2 was relatively dense, the region of its inside (the cross-sectional area) is sparse structure, whereas, in Comparative Example 3 pore distribution of the porous layer surface of the porous composite film is relatively sparse, the region of its inside (sectional area) is a dense structure. Such a difference in structure of the porous layer is considered to have a significant impact on differences between film strength and cycle characteristics.
Industrial Applicability
[0076]
　Porous composite film according to an embodiment of the present invention, even while having excellent adhesion and film strength, has a porous layer which can suppress the attachment of partial missing and falling product during the manufacturing process, the cycle characteristics it is possible to provide a suitable porous composite film separator superior battery and battery using the same. Further, according to the present invention, it is possible to provide a manufacturing method of the porous composite film.
[0077]
　Has been described with reference to the details to the specific embodiments of the present invention, it is possible that various changes and modifications without departing from the spirit and scope of the invention will be apparent to those skilled in the art.
　The present application is based on Japanese Patent Application filed on September 29, 2017 (Japanese Patent Application No. 2017-191838), the contents of which are incorporated herein by reference.
DESCRIPTION OF SYMBOLS
[0078]
1: unwinding roll
2: Dip head
3: coagulation / washing bath
4: Primary washing tank
5: secondary washing tank
6: tertiary washing tank
7: drying oven
8: winding roll

The scope of the claims

[Requested item 1]A porous substrate, a porous composite film porous layer is laminated on at least one surface of the porous substrate, the porous layer comprises a fluorine-containing resin, the following requirements (i), (ii ) and porous composite film satisfying (iii).
(I) the D cross-sectional void area distribution of the porous layer 1 value of 50 is 0.06 .mu.m 2 or 0.38 .mu.m 2 or less, and wherein the porous layer of the cross-sectional void area distribution of D 1 value of 90 is 0.20μm 2 more 1.15Myuemu 2 is less than or equal to.
(Ii) the D surface pore area distribution of the porous layer 2 value of 50 0.0060Myuemu 2 more 0.0072Myuemu 2 or less, and D of the surface pore area distribution of the porous layer 2 value of 90 0 .0195Myuemu 2 more 0.0220Myuemu 2 is less than or equal to.
(Iii) The porosity of the porous layer is 50 to 70%.
[Requested item 2]
　The average area A1 of the cross-section void in the porous layer is 0.054Myuemu 2 more 0.098Myuemu 2 or less, the porous composite film according to claim 1.
[Requested item 3]
　Wherein the porous substrate is a polyolefin porous membrane, porous composite film according to claim 1 or 2.
[Requested item 4]
　Wherein the porous layer comprises a polymer containing vinylidene fluoride unit as the fluorine-containing resin, the porous composite film according to any one of claims 1 to 3.
[Requested item 5]
　Wherein the porous layer comprises a ceramic, porous composite film according to any one of claims 1 to 4.
[Requested item 6]
　The porous layer adhesion electrode and of is less than 10.0N or 5.0 N, the porous composite film according to any one of claims 1 to 5.
[Requested item 7]
　The film strength of the porous layer is cohesive failure is less 10.0N than 2.0 N, the porous composite film according to any one of claims 1 to 6.
[Requested item 8]
　Battery separator using the porous composite film according to any one of claims 1 to 7.
[Requested item 9]
　Battery comprising a positive electrode, a negative electrode, the battery separator according to claim 8 in which the positive electrode disposed between the negative electrode.
[Requested item 10]
　A method for producing a porous composite film according to any one of claims 1 to 7,
coating the fluorine-containing resin is coated on at least one surface of the coating liquid a porous substrate dissolved in a solvent forming a
said coating has been formed porous substrate solidifying the fluorine-containing resin is immersed in a coagulation solution comprising water to form a porous layer, the on the porous substrate a step of the porous layer to obtain a composite film formed,
a step of washing the composite film,
comprising the step of drying the composite film after washing with water,
the temperature of the coagulating liquid is in the range of 10 ~ 25 ° C. and method for producing a porous composite film characterized in that the said concentration of the solvent in the coagulation liquid is less than 22 wt%.