JP2006049249A - Manufacturing method of porous membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a porous membrane, capable of efficiently removing solvents and having a simple process as a manufacturing method of a porous membrane, having appropriate air permeability and vacancy rate, in particular, as a secondary battery membrane separator, and having little risk of firing explosion during a drying process, and to provide a manufacturing method of a separator for a battery. <P>SOLUTION: This manufacturing method of a porous membrane includes a process of removing, by using a cleaning solvent, a hydrocarbon-based solvent from the porous membrane containing the hydrocarbon-based solvent, after membrane formation. The manufacturing method uses a mixed solvent, containing a fluorine-based solvent and a bromide-based solvent as the cleaning solvent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a porous membrane including a step of removing a hydrocarbon solvent using a cleaning solvent from a porous membrane containing a hydrocarbon solvent after film formation, and a method for producing a battery separator, The present invention relates to a production method that is a simple production process and that can reduce the risk of a flammable explosion during the drying process.

  Porous membranes of crystalline resins are used for battery separators, electrolytic capacitor diaphragms, moisture permeable waterproof materials, various filters, and the like. Among them, battery separators are attracting attention as important components of lithium secondary batteries that can obtain light weight, high electromotive force, and high energy as a battery, and also have little self-discharge. Is also expected.

  As a method for producing a crystalline resin porous film, there are a solvent method, a dry method, and an aperture stretching method, and a solvent method is generally used. The solvent method includes a step of adding a solvent to the crystalline resin and removing the solvent after melt-kneading. The efficiency of this solvent removal step is not only the productivity of the porous membrane of the crystalline resin, but also the porous membrane. This also affects the mechanical properties of the machine.

  Conventionally, low boiling point chlorinated alkanes such as methylene chloride and low boiling point aliphatic hydrocarbon compounds such as hexane are used in the solvent removal step. Low-boiling point aliphatic hydrocarbon compounds have high detergency, but have the disadvantage of high risk of flammable explosion in the drying process.

  On the other hand, alternative solvents such as a mixed solvent of an organic solvent and water and a surfactant aqueous solution have been proposed as non-flammable solvents (see, for example, Patent Documents 1 and 2). However, it cannot be said that these semi-aqueous and aqueous solvents can sufficiently wash the solvent contained in the thermoplastic resin.

  In addition, a two- to five-stage multi-step process in which a solvent is washed with a solvent having a flash point and then washed with a fluorinated solvent having no flash point has been proposed (for example, see Patent Document 3). However, this method has a disadvantage that the process becomes complicated.

Furthermore, in the solvent removal step, a method of using a mixed solvent obtained by adding another solvent to a fluorinated solvent is also known. For example, a porous film is formed using a mixed solvent of a fluorinated solvent and an aliphatic hydrocarbon. A method for removing the remaining solvent has been proposed (see, for example, Patent Document 4). However, with this method, it has been found that the solvent is not sufficiently soluble in liquid paraffin and the solvent is difficult to remove.
JP-A-6-256559 JP-A-6-298985 JP 2000-12695 A JP 2003-103624 A

  Therefore, an object of the present invention is to produce a porous membrane having appropriate air permeability and porosity, particularly as a secondary battery membrane separator, which can efficiently remove the solvent and is simple in the process, and in the drying process. Another object of the present invention is to provide a method for producing a porous membrane and a method for producing a battery separator with a low risk of flammable explosion.

  In order to achieve the above-mentioned object, the present inventors diligently researched various cleaning solvents. By using a mixed solvent containing a fluorine-based solvent and a bromide-based solvent, the solvent can be efficiently used without taking a complicated process. It has been found that the air permeability and porosity can be improved, and the present invention has been completed.

  The method for producing a porous membrane of the present invention includes the step of removing a hydrocarbon-based solvent using a cleaning solvent from a porous membrane containing a hydrocarbon-based solvent after film formation. A mixed solvent containing a fluorine-based solvent and a bromide-based solvent is used as the cleaning solvent.

  According to the method for producing a porous membrane of the present invention, the solvent is removed with a mixed solvent containing a fluorine-based solvent and a bromide-based solvent, so that the solvent can be removed in a single stage as shown in the results of the examples. Since the speed is high, the porosity is high, and since there is no flash point, drying can proceed safely.

  In the present invention, a resin composition containing a polyolefin-based resin and a hydrocarbon-based solvent is melt-kneaded, and the obtained melt-kneaded product is cooled to obtain a sheet-like material, which is then stretched in a uniaxial direction or more. In the method for producing a porous membrane comprising a step and a step of removing the hydrocarbon solvent from the stretched product using a cleaning solvent, a mixed solvent containing a fluorine solvent and a bromide solvent is used as the cleaning solvent. It is characterized by.

  The polyolefin-based porous membrane obtained by the above series of steps contains a solvent such as liquid paraffin in the porous structure, and it is necessary to remove this, but according to the present invention, Solvent removal is performed with a mixed solvent containing bromide solvent, so solvent removal is possible in a single stage, high drying speed, high porosity, and no flash point, so drying proceeds safely. be able to.

  In the above, the cleaning solvent preferably has a KB value of 50 or more as a mixed solvent. The higher the KB value, the greater the dissolving ability. If the KB value is 50 or more, the solvent can be removed satisfactorily.

  Moreover, it is preferable that the said washing | cleaning solvent is a thing which does not have a flash point as a mixed solvent. A mixed solvent containing a fluorine-based solvent and a bromide-based solvent generally has a property that it is difficult to ignite, but when there is no cleaning solvent, the cleaning solvent drying process can be performed particularly safely.

  The battery separator manufacturing method of the present invention is characterized in that the battery separator is manufactured by any one of the above-described porous film manufacturing methods. According to the method for manufacturing a battery separator of the present invention, solvent removal is performed with a mixed solvent containing a fluorine-based solvent and a bromide-based solvent, so that the solvent can be removed in a single stage, and the porosity is high due to the high drying speed. Since it is high and has no flash point, drying can proceed safely.

  The method for producing a porous membrane of the present invention includes a step of removing a hydrocarbon-based solvent using a cleaning solvent from a porous membrane containing a hydrocarbon-based solvent after film formation, and this step is performed. In this case, a mixed solvent containing a fluorine-based solvent and a bromide-based solvent is used as the cleaning solvent.

  Examples of the porous membrane include polyolefin resin, PVDF (polyvinylidene fluoride), PSF (polysulfone), PES (polyethersulfone), PPES (polyphenylsulfone), PVA, PTFE, cellulose resin, polyamide, polyacrylonitrile, Examples thereof include polyimide.

  The film forming method is not particularly limited as long as a low molecular weight substance remains after film formation, and is a solvent method, a non-solvent induced wet phase separation method, a heat induced wet phase separation method, a dry phase separation method, Any method such as an aperture stretching method may be used.

  In the present invention, after the porous film forming step melts and kneads a resin composition containing a polyolefin resin and a hydrocarbon solvent, the obtained melt kneaded material is cooled to obtain a sheet-like material, It is effective to include a step of stretching in a uniaxial direction or more. The polyolefin-based porous membrane obtained by these series of steps contains a hydrocarbon-based solvent such as liquid paraffin in the porous structure. Hereinafter, this film forming process will be described as an example.

In the present invention, it is preferable to use a crystalline resin during film formation, and it is particularly preferable to use a polyolefin resin. As the polyolefin resin, polyolefins such as homopolymers, copolymers, and blends of olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene are preferable. Among these, it is desirable to use an ultrahigh molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, preferably 5% by weight or more. Among these, ultrahigh molecular weight polyethylene is particularly preferable as a material from the viewpoint of the mechanical strength of the obtained porous membrane.

  As the hydrocarbon-based solvent that can be used in the present invention, known solvents that are usually used can be used without limitation as long as they have excellent resin solubility and swelling property. For example, nonane, decane, undecane, dodecane, decalin, tetralin, aliphatic hydrocarbons such as liquid paraffin, and mineral oil fractions with boiling points corresponding to these, among these, liquid paraffin, etc. Nonvolatile solvents are preferred.

  The mixing ratio of polyolefin resin and solvent varies depending on the material conditions such as resin type, solubility and kneading conditions such as kneading time and kneading temperature. The composition is not particularly limited as long as it can be formed into a sheet shape when the composition is melt-kneaded. For example, the blending amount of the resin component is preferably 5% by weight or more from the viewpoint of improving the strength of the obtained porous membrane. Moreover, 30 weight% or less is preferable from a viewpoint which can fully melt | dissolve polyolefin in a solvent and knead | mix it.

  The amount of the solvent in the mixture is preferably 70 to 95% by weight, more preferably 75 to 90% by weight. The blending amount is preferably 70% by weight or more from the viewpoint of moderate kneadability and excellent characteristics, and is preferably 95% by weight or less from the viewpoint of facilitating molding with a die during extrusion.

In addition, as a purpose of providing a shutdown function (a function of blocking the current by melting the porous film by clogging the porous film in order to prevent accidents such as ignition when the temperature in the battery film rises), 5 One or more kinds of polyolefins, thermoplastic elastomers, and graft copolymers of less than × 10 ⁵ may be contained.

Examples of polyolefins having a weight average molecular weight of less than 5 × 10 ⁵ include polyolefin resins such as polyethylene and polypropylene, and modified polyolefin resins such as ethylene-acrylic monomer copolymers and ethylene-vinyl acetate copolymers. Examples of thermoplastic elastomers include thermoplastic elastomers such as polystyrene, polyolefin, polydiene, vinyl chloride, and polyester.

  Examples of the graft copolymer include graft copolymers in which the main chain is a polyolefin and the side chain is a vinyl polymer having a non-compatible group in the side chain, but polyacryls, polymethacrylates, polystyrene, polyacrylonitrile, polyoxyalkylenes. Is preferred. In addition, an incompatible group means an incompatible group with respect to polyolefin here, for example, the group derived from a vinyl polymer etc. are mentioned.

The content of these polyolefins less than 5 × 10 ⁵ , the thermoplastic elastomer, and the graft copolymer is set according to the timely required shutdown temperature, but is preferably 70% by weight or less in the raw material resin mixture of the porous membrane, 60 wt% or less is more preferable, and 50 wt% or less is still more preferable. The content is preferably 70% by weight or less from the viewpoint of sufficiently securing the crosslinking point of the high molecular weight polyolefin and obtaining sufficient heat resistance.

  Note that additives such as an antioxidant, an antistatic agent, an ultraviolet absorber, a dye, a nucleating agent, a pigment, a flame retardant, and a filler are added to the resin composition as necessary. It can add in the range which does not impair.

  The step of melt-kneading the obtained resin composition can be performed by a commonly used known method. At that time, in order to obtain sufficient entanglement of polymer chains of the high-molecular-weight polyolefin, it is preferable to carry out by applying a sufficient shearing force to the mixture. For example, the resin composition may be kneaded batch-wise using a Banbury mixer, a kneader or the like, or a continuous extruder may be used. As the continuous kneader, a multi-screw kneader such as a single-screw kneader, a twin-screw extruder, or a planetary type may be used, or a process combining a plurality of these devices may be used.

  The temperature at which the mixture is dissolved and kneaded is preferably in the range of the temperature at which the solvent starts dissolving the high molecular weight polyolefin (melting start temperature) to + 60 ° C. The temperature is preferably equal to or higher than the dissolution start temperature from the viewpoint of efficiently dispersing the high molecular weight polyolefin. In order to suppress thermal decomposition and oxidative degradation of the high molecular weight polyolefin, there is no problem even if the temperature is lowered to such an extent that the film characteristics are not deteriorated during kneading after dissolution.

  The step of forming into a sheet can be performed by a commonly used known method. It does not specifically limit as a method, For example, the method of attaching T-die etc. to the extruder tip is mentioned. Further, there is no problem even if the sheet is formed by calendar molding or press molding.

  The obtained sheet-like extrudate is preferably sandwiched between metal plates cooled to 50 ° C. or less, more preferably −10 ° C. or less, and cooled to form a sheet. Although it does not specifically limit as thickness of the sheet-like molded product obtained in this way, The thing of 2-20 mm is preferable from the ease of the process in a subsequent process.

  Next, the obtained sheet-like molded product is stretched. The method for the stretching treatment is not particularly limited, and may be a normal tenter method, a roll method, or a combination of these methods. In addition, any method such as uniaxial stretching and biaxial stretching can be applied. In the case of biaxial stretching, either longitudinal or transverse simultaneous stretching or sequential stretching may be used. preferable.

  The draw ratio can be set as appropriate depending on the desired porosity and strength, but is preferably in the range of usually 5 to 250 times the area before drawing.

  The temperature during the stretching treatment is preferably a temperature of the melting point of the high molecular weight polyolefin + 5 ° C. or less. If the temperature is too high, the structure may collapse and the strength may decrease. If the temperature is too low, the film may be severed or shrinkage after stretching may be increased during stretching.

  Next, a solvent removal process is performed from the porous film containing the hydrocarbon-based solvent after the stretching process. The solvent removal treatment is a step of forming a porous structure by removing the solvent from the stretched product. For example, there is a solvent method in which the stretched product is washed with a solvent to remove the remaining solvent.

In the present invention, a mixed solvent containing a fluorinated solvent and a bromide solvent is used as the solvent. For example, examples of the fluorine-based solvent include a chain fluorocarbon, a cyclic fluorocarbon, a perfluorocarbon, and a perfluoroether. Specific examples include pentafluorobutane, ethyl perfluorobutyl ether, C ₅ H ₃ F ₇ , and C ₅ H ₂ F ₁₀ , but are not particularly limited to these solvents.

  Examples of the bromide solvent include n-propyl bromide, n-butyl bromide, n-hexyl bromide and the like. Each of these mixed solvents may be a combination of one kind or a combination of plural kinds.

  The mixing weight ratio of the mixed solvent is preferably 70/30 to 30/70, more preferably 65/35 to 40/60 in terms of fluorine solvent / bromide solvent. If the mixing weight ratio is less than 70/30, solvent extraction tends to be insufficient.

  The KB value of the above solvent is preferably 50 or more, more preferably 55 or more. In the present specification, the “KB value” is a value used to indicate the dissolving power of the diluent in the lacquer and paint industry, and the diluent required for precipitating kauri gum from 20 g of a standard cowry butanol solution at 25 ° C. mL. The higher this value, the greater the dissolving ability. If it is 50 or more, the solvent can be removed satisfactorily.

  In addition, it is preferable to use a mixed solvent having a high flash point or no flash point, but it is particularly preferable that the mixed solvent does not have a flash point. In order not to have a flash point as a mixed solvent, a combination of solvents having no flash point or a mixing weight ratio of solvents having no flash point may be increased. In particular, it is preferable to use a fluorinated solvent having no flash point.

  The cleaning method using such a solvent is not particularly limited, and examples thereof include a method of immersing the stretched product in a solvent and extracting the solvent, and a method of showering the solvent on the stretched product from a spray nozzle or the like.

  In addition, you may perform these solvent removal processes before extending | stretching. Moreover, after performing a solvent removal process before an extending | stretching process, you may take the process of removing a residual solvent by performing a solvent removing process after an extending | stretching process again.

  In the present invention, after the stretching treatment and before and after the solvent removal treatment, a rolling treatment may be further performed for improving surface properties and characteristics. For example, the sheet-like molded product may be subjected to a stretching treatment and a solvent removal treatment (the order of stretching and solvent removal may be any first) and then subjected to a rolling treatment. The stretching process and the solvent removal process may be performed. Further, the rolling treatment may be performed both after the stretching treatment and after the solvent removal treatment.

  As a method of replacing the solvent used when the solvent is extracted and removed, extraction with another solvent that does not dissolve the resin and can dissolve the solvent is possible, but with a solvent, it is safe when the solvent is released after drying. And there is a large drying shrinkage due to the surface tension and drying speed of the solvent. In addition, since the fluorinated solvent is insufficiently washed, it is preferable to use a fluorinated mixed solvent that dissolves the solvent, has a low surface tension, has a high drying rate, and is highly safe.

  Next, it is preferable to perform a heat setting treatment for suppressing shrinkage or fixing the structure of the molded product having a porous structure obtained by the above-described steps.

  The heat setting treatment may be a one-stage heat treatment method in which heat treatment is performed at a time, a multi-stage heat treatment method in which heat treatment is first performed at a low temperature, and then heat treatment is performed at a higher temperature, or a temperature rising heat treatment in which heat treatment is performed while raising the temperature Although it may be a method, it is desirable to perform the treatment without impairing the original characteristics of the porous film such as the Gurley value.

  In the case of a one-stage heat treatment, the temperature during the heat setting treatment is preferably a temperature of the melting point of the resin of −20 ° C. or more and the melting point or less. When expressed in terms of temperature, it is preferably 40 to 140 ° C. depending on the melting point of the resin and the composition of the porous membrane.

  Further, in order to complete the heat treatment in a short time without impairing various properties, a multistage type or a temperature rising type heat treatment method is also preferable. The heat treatment time in this case depends on the resin used, but a temperature of the melting point of the resin from −20 ° C. to the melting point is preferred. When expressed in terms of temperature, it cannot be determined unconditionally depending on the melting point of the resin or the composition of the porous film, but for example, it is preferably 30 minutes or longer at 115 ° C.

  Further, if necessary, the third and subsequent heat treatments may be performed at a higher temperature and for a shorter time. Specific heat treatment methods include fixing the four corners of the porous membrane and placing it in a heat treatment furnace, winding it into a roll and placing it in the heat treatment furnace, fixing the area direction with a tenter and continuously passing it through the heat treatment furnace. A known method is used.

  The porous membrane thus obtained is safe when drying the solvent, and it can be expected to improve the porosity without having to change the molding conditions significantly.

  The thickness of the porous membrane obtained as described above is preferably 1 to 60 μm, and more preferably 5 to 60 μm. The porosity is preferably 30 to 70%, and more preferably 35 to 70%. As the permeability, for example, the air permeability according to JIS P8117 is preferably 50 to 800 seconds / 100 cc, and more preferably 100 to 500 seconds / 100 cc.

  Since the porous membrane of the present invention is excellent in permeation performance and mechanical strength as described above, it is expected to improve safety for various sizes and applications of batteries by using it as a battery separator. Moreover, the safety | security at the time of using a solvent in the manufacturing method can be improved.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. Various characteristics were measured as follows.

[Extractability]
10 μL of liquid paraffin is added to a vial bottle containing 50 ml of solvent, and it is visually observed whether it is dissolved.

[Porosity]
The porous film to be measured is cut into a 5 cm square, its volume and weight are determined, and the calculation is performed using the following formula from the obtained results.
Porosity (volume%) = 100 × (volume (cm ³ ) −weight (g) / density of membrane material (g / cm ³ )) / volume (cm ³ )
[Drying speed]
A porous membrane containing a solvent is cut into a 13 cm square, placed on a balance, and the change in weight at the time of drying is about 1/2 of the total weight until complete drying. Expressed as weight loss. The unit was [Δg / sec].

Example 1
12 parts by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 3 × 10 ⁶ , a polyolefin-based thermoplastic elastomer, Northolex, and liquid paraffin were uniformly mixed in a slurry state and kneaded at 160 ° C. with a small kneader for 60 minutes. These kneaded materials were sandwiched between 0 ° C. cooled metal plates and rapidly cooled into a sheet shape. These quenched and crystallized sheet-like resins are heat-pressed at about 120 ° C. until the thickness of the sheet becomes 0.4 to 0.6 mm, and simultaneously at a temperature of about 120 ° C., 4.5 × length × 3. Biaxial stretching was performed 8 times.

  The prepared sheet-like resin is fixed to a 9 cm × 9 cm fixing frame, and 3 baths of a fluorine-based mixed solvent (pentafluorobutane / normal propyl bromide = 50/50 (weight ratio)) are prepared and immersed in each bath for 3 minutes. Solvent removal treatment was performed. After drying, heat setting treatment was performed at 85 ° C. for 12 hours and further at 116 ° C. for 2 hours to obtain a porous film having a thickness of 20 μm and a porosity of 42%.

Example 2
A sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, and 3 baths of a fluorinated mixed solvent (pentafluorobutane / normal propyl bromide = 60/40 (weight ratio), KB value 55). Prepared and immersed in each bath for 3 minutes for solvent removal treatment. After drying, heat setting treatment was performed at 85 ° C. for 12 hours and further at 116 ° C. for 2 hours to obtain a porous film having a thickness of 20 μm and a porosity of 40%.

Example 3
A sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, and 3 baths of a fluorine-based mixed solvent (pentafluorobutane / normal propyl bromide = 70/30 (weight ratio)) were prepared. The solvent was removed by immersing in a bath for 3 minutes. After drying, heat setting treatment was performed at 85 ° C. for 12 hours and further at 116 ° C. for 2 hours to obtain a porous film having a thickness of 20 μm and a porosity of 38%.

Example 4
A sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, and three baths of a fluorine-based mixed solvent (ethyl perfluorobutyl ether / normal propyl bromide = 60/40 (weight ratio)) were prepared. Each bath was immersed for 3 minutes to remove the solvent. After drying, heat setting treatment was performed at 85 ° C. for 12 hours and further at 116 ° C. for 2 hours to obtain a porous film having a thickness of 20 μm and a porosity of 47%.

Comparative Example 1
The sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, 3 baths of decane were prepared, and each bath was immersed for 3 minutes for solvent removal treatment.

Comparative Example 2
The sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, and three baths of a fluorinated solvent (pentafluorobutane, KB value 13) were prepared, and each bath was immersed for 3 minutes to remove the solvent. Went.

Comparative Example 3
A sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, and three baths of a mixed solvent of ethyl perfluorobutyl ether / n-heptane = 95/5 (weight ratio) were prepared. Solvent removal treatment was performed by immersing for a minute.

Comparative Example 4
A sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, and three baths of a mixed solvent of ethyl perfluorobutyl ether / n-heptane = 95/5 (weight ratio) were prepared. Solvent removal treatment was performed by immersing for a minute. Further, rinsing with ethyl perfluorobutyl ether was performed.

Comparative Example 5
A sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, and 3 baths of a mixed solvent of pentafluorobutane / n-heptane = 95/5 (weight ratio) were prepared, and each bath was for 3 minutes. The solvent was removed by immersion.

Comparative Example 6
A sheet-like resin prepared in the same manner as in Example 1 was fixed to a 9 cm × 9 cm fixed frame, and 3 baths of a mixed solvent of pentafluorobutane / n-heptane = 95/5 (weight ratio) were prepared, and each bath was for 3 minutes. The solvent was removed by immersion. Further, rinsing with pentafluorobutane was performed.

  The evaluation results of the porous membrane obtained above are shown in Table 1.

表１の結果が示すように、本発明の実施例１〜４では、溶媒の抽出性が良好で、乾燥速度も速く、空孔率が十分なものが得られた。これに対して、デカンを単独で使用した比較例１では乾燥速度が遅く、空孔率が低下した。また、フッ素系溶剤の単独使用（比較例２）やフッ素系溶剤と炭化水素系溶剤との混合溶剤では（比較例３〜６）、リンス処理の有無にかかわらず、抽出が行えず、空孔率の測定が不可能であった。

As shown in the results of Table 1, in Examples 1 to 4 of the present invention, those having good solvent extractability, high drying speed, and sufficient porosity were obtained. On the other hand, in Comparative Example 1 in which decane was used alone, the drying rate was slow and the porosity was reduced. In addition, in the case of using a fluorine-based solvent alone (Comparative Example 2) or a mixed solvent of a fluorine-based solvent and a hydrocarbon-based solvent (Comparative Examples 3 to 6), extraction cannot be performed regardless of whether or not rinsing is performed. The rate could not be measured.

Claims (5)

In the method for producing a porous membrane comprising a step of removing a hydrocarbon solvent using a cleaning solvent from a porous membrane containing a hydrocarbon solvent after film formation,
A method for producing a porous film, wherein a mixed solvent containing a fluorine-based solvent and a bromide-based solvent is used as the cleaning solvent. After melt-kneading a resin composition containing a polyolefin-based resin and a hydrocarbon-based solvent, cooling the obtained melt-kneaded material to obtain a sheet-like material, and then stretching the uniaxial direction or more from the stretched product, In the method for producing a porous membrane comprising a step of removing a hydrocarbon solvent using a cleaning solvent,
A method for producing a porous film, wherein a mixed solvent containing a fluorine-based solvent and a bromide-based solvent is used as the cleaning solvent.   The method for producing a porous film according to claim 1, wherein the cleaning solvent has a KB value of 50 or more as a mixed solvent.   The method for producing a porous film according to claim 1, wherein the cleaning solvent does not have a flash point as a mixed solvent.   The manufacturing method of the separator for batteries which manufactures the separator for batteries by the manufacturing method of the porous membrane in any one of Claims 1-4.