JP6653581B2 - Porous membrane - Google Patents

Description

  The present invention relates to a porous membrane, a method for producing the porous membrane, and use of the porous membrane in a secondary battery or a filter.

  Conventionally, various porous membranes have been used for applications such as filters. In recent years, the application of porous membranes to separators for secondary batteries such as lithium batteries has been advanced.

  For example, as a porous film of polyimide, a varnish in which silica particles are dispersed in a solution of a polyamic acid or polyimide is applied on a substrate, and then, if necessary, the applied film is heated to obtain a polyimide film containing silica particles. Next, a porous film obtained by eluting and removing silica in a polyimide film with aqueous hydrogen fluoride is known (see Patent Document 1).

Japanese Patent No. 5605566

The porous polyimide film described above is excellent in heat resistance, and is used in various ways as a separator excellent in a function of preventing a short circuit between electrodes, and is also excellent in heat resistance, chemical resistance, solvent resistance, etc. Can be used as a filter medium in a filter device.
However, porous polyimide films used in these applications are required to be further provided with various properties.

For example, when manufacturing a secondary battery, a porous polyimide film used as a separator is housed in a case of the secondary battery in a state of being wound or curved by a mechanical device. Also, in a filter device, in order to increase a filtration area, a porous membrane as a filtering material may be housed in a case in a folded state.
At this time, if the coefficient of friction of the surface of the porous polyimide film is high, the porous polyimide film may be broken or wrinkled when the porous polyimide film is machined.
Under such circumstances, it is desired that the surface of the porous polyimide film used as a separator be reduced in friction.

  The present invention has been made in view of the above circumstances, and has a surface having reduced friction, a porous film including a porous polyimide and / or polyamideimide film, a method for producing the porous film, It is an object of the present invention to provide a use of a porous membrane in a secondary battery or a filter.

The present inventors have found that in a porous film including a porous polyimide and / or polyamideimide film, the amount of fluorine atoms present on the main surface of at least one of the two main surfaces of the porous film is determined by a fluorescent X-ray method. The above problem is solved by attaching a fluorinated organic compound so that the measured value is 0.0080 mg / cm ² or less and the Gurley air permeability of the porous film is 30 to 300 seconds. They have found that they can do this and have completed the present invention.

A first aspect of the present invention is a porous film comprising a porous polyimide and / or polyamideimide film and a fluorinated organic compound,
The fluorinated organic compound is attached to at least one of the two main surfaces of the porous film,
An abundance of fluorine atoms on the main surface to which the fluorinated organic compound is adhered, measured by a fluorescent X-ray method, is 0.0080 mg / cm ² or less;
The present invention relates to a porous membrane, wherein the Gurley air permeability of the porous membrane is 30 to 300 seconds.

A second aspect of the present invention is to deposit a liquid containing a fluorinated organic compound on at least one main surface of an untreated porous film, which contains a polyimide and / or polyamideimide film,
The present invention relates to a method for producing a porous membrane according to a first aspect, comprising: drying a liquid attached to a surface of an untreated porous membrane.

  A third aspect of the present invention relates to a secondary battery separator including the porous membrane according to the first aspect.

  A fourth aspect of the present invention relates to a secondary battery provided with the secondary battery separator according to the third aspect.

  A fifth aspect of the present invention relates to a filter including the porous membrane according to the first aspect.

  A sixth aspect of the present invention relates to a method for using the porous membrane according to the first aspect as a separator in a secondary battery.

  A seventh aspect of the present invention relates to a method of using the porous membrane according to the first aspect as a filter in filtration.

  According to the present invention, a porous film including a porous polyimide and / or polyamideimide film having a low friction surface, a method for producing the porous film, and a secondary battery or a filter using the porous film Can be provided.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the present invention. .

≫Configuration of porous membrane≫
The porous film includes a porous polyimide and / or polyamideimide film and a fluorinated organic compound.
The fluorinated organic compound is attached to at least one of the two main surfaces of the porous film.
The fluorinated organic compound is attached to the main surface of the porous film so that the abundance of fluorine atoms is 0.0080 mg / cm ² or less as measured by a fluorescent X-ray method.
The Gurley air permeability of the porous film is 30 to 300 seconds.

  Hereinafter, “polyimide and / or polyamideimide” is also referred to as PI. The “porous polyimide and / or polyamideimide film” is also referred to as a porous PI film.

The porous film may be a single-layer film containing only one porous PI film, or a laminate of a plurality of porous layers made of the porous PI film. The laminate may include one or more porous layers (PI porous layers) made of a film and a porous layer made of a material other than PI.
In the specification of the present application, when the porous film is a laminate, a layer included in the laminate is referred to as a “porous layer”. When the porous film is a laminate, the “porous PI film” and the “PI porous layer” have the same meaning.

When the porous film is a laminate, at least one of the main surfaces is preferably a porous layer made of a porous PI film, and both of the main surfaces are more preferably a porous layer made of a porous PI film. preferable. The fluorinated organic compound is preferably attached to the main surface made of the porous PI film.
This is because PI is excellent in various properties such as heat resistance, chemical resistance, and solvent resistance.

  When the porous film includes a porous layer made of a material other than PI, the material of the porous layer may be an organic material or an inorganic material, and an organic material is preferable. As the organic material, a resin is usually used.

When the porous film that is a laminate is used as a separator for a secondary battery, the laminate is made of polyvinylidene fluoride (hereinafter, also referred to as PVDF) in one of the outermost layers or inside the laminate. It preferably contains a porous layer.
For example, in the case of high-capacity batteries such as lithium-ion batteries installed in automobiles, for the purpose of ensuring safety, when the battery becomes hot, the internal conduction of the battery is cut off and the subsequent temperature rise is prevented. To be able to do so, it is required that the separator be provided with a so-called shutdown characteristic.
When the porous film that is a laminate includes a PVDF porous layer in one of the outermost layers or the inside of the laminate, the PVDF porous layer softens when the porous film that is the laminate is exposed to a high temperature, It melts, and a PVDF film is quickly formed on the surface or inside of the porous film. For this reason, by including the PVDF porous layer in one of the outermost layers or the inside of the laminate, the porous film that is a laminate easily imparts a desired shutdown characteristic to the porous film.

When the porous film is a laminate including a PVDF porous layer, a typical configuration is such that a porous layer made of PVDF (PVDF porous layer) is formed on one surface of a porous layer made of PI (PI porous layer). ) And a three-layer structure of PI porous layer / PVDF porous layer / PI porous layer. The configuration of the laminate is not limited to these configurations. The laminate may be a laminate including four or more layers. Further, another porous layer may be included between the PI porous layer and the PVDF porous layer.
As the structure of the above-mentioned laminate, a two-layer structure in which a PVDF porous layer is laminated on one surface of a PI porous layer is preferable from the viewpoint of easy production.

  Note that a porous film including a porous layer made of a fluorine-containing resin such as PVDF on both main surfaces does not correspond to the porous film according to the present invention in terms of the amount of fluorine atoms present on the main surfaces. .

  When the porous film is a laminate, the laminate can be formed according to a conventional method such as a lamination method. Further, a porous layer included in the laminate may be sequentially formed on the porous layer constituting one of the outermost layers of the laminate. After laminating a precursor layer of a porous layer by a lamination method, a coating method, or the like, the laminate of the precursor layers may be made porous to form a porous film as a laminate. Examples of the precursor layer include a layer containing fine particles that can be removed by thermal decomposition or treatment with an organic solvent, water, acid, alkali, or the like, in a matrix made of a resin.

The shape of the voids provided in the porous membrane is not particularly limited as long as the porous membrane can flow a fluid from one main surface to the other main surface.
The porous membrane preferably has a desired porosity, and preferably has a structure in which spherical holes communicate with each other (hereinafter, simply referred to as communication holes), as described later. When the porous film is a laminate, the same applies to the porous layer included in the laminate.
The spherical shape related to the shape of the hole is a concept including a true sphere, but is not necessarily limited to a true sphere. The spherical shape may be a substantially spherical shape, and a shape that can be recognized as a substantially true spherical shape when an enlarged image of the hole is visually confirmed is also included in the spherical shape.
Specifically, in a spherical hole, the surface that defines the hole is a curved surface, and the curved surface may define a true spherical or substantially spherical hole.
In the case where the porous film is a laminate, the porosity and the pore diameter of the spherical holes constituting the communication holes may be the same or different for each porous layer constituting the laminate.

For example, for a porous PI film, individual spherical holes are typically formed by removing individual fine particles present in a PI-fine particle composite film described later in a later step.
Further, the communication hole is formed by removing a plurality of fine particles present in contact with each other in the PI-fine particle composite film in a later step in a method for manufacturing a porous PI film described later. The location of the communication hole where the spherical holes communicate is derived from the location where the plurality of fine particles before removal are in contact with each other.

The diameter of the opening of the porous film is preferably 100 nm to 2000 nm, more preferably 200 nm to 1000 nm, and still more preferably 300 nm to 900 nm.
The diameter of the opening is equal to or substantially equal to the diameter of the spherical hole constituting the communication hole.
The porous membrane has a communication hole therein which penetrates the porous membrane in the thickness direction as a fluid flow path. This allows the fluid to permeate from one main surface of the porous membrane to the other main surface.
When the porous membrane is used as a filter, the fluid passes through the inside of the porous membrane while being in contact with the curved surface defining each spherical hole. The contact area of the fluid inside the porous membrane is considerably large due to the provision of the communication holes composed of spherical holes. For this reason, it is considered that, when the fluid passes through the laminate including the porous membrane, the minute substance existing in the fluid is likely to be adsorbed to the spherical holes in the porous membrane.

  The thickness of the porous film is not particularly limited. The thickness of the porous film used as the separator is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 100 μm or less, and particularly preferably 10 μm or more and 30 μm or less. The thickness of the porous membrane used as a filter is preferably from 5 μm to 500 μm, more preferably from 10 μm to 300 μm, and particularly preferably from 20 μm to 150 μm. The thickness of the porous film or, when the porous film is a laminate, the thickness of each porous layer included in the laminate, for example, measuring the thickness of a plurality of places with a micrometer or the like and averaging the thickness. Or by observing the film cross section with a scanning electron microscope (SEM) and averaging.

When the porous film is a laminate, the thickness of the PI porous layer included in the laminate and the thickness of the porous layer made of a material other than PI are appropriately determined depending on the use of the porous film.
When the laminate includes a PI porous layer, the thickness of the PI porous layer is typically preferably from 5 μm to 500 μm, more preferably from 10 μm to 100 μm, particularly preferably from 10 μm to 30 μm.
When the laminate includes a plurality of PI porous layers, the total thickness of the plurality of PI porous layers in the laminate is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 300 μm or less.

Further, when the laminate includes a PVDF porous layer, the thickness of the PVDF porous layer is preferably 0.01 to 5.0 μm, more preferably 0.1 to 4 μm, and particularly preferably 1 to 3 μm.
When the thickness of the PVDF porous layer is within the above range, when the porous film as the laminate is exposed to a high temperature, the PVDF softens and melts, and the PVDF coating covering the surface of the PI porous layer is quickly formed. Formed. For this reason, when the porous film which is a laminate includes a PVDF porous layer having a thickness within the above range, a desired degree of shutdown characteristics is easily imparted to the porous film.
When the laminate includes a plurality of PVDF porous layers, the total thickness of the plurality of PVDF porous layers in the laminate is preferably 0.05 to 15 μm, more preferably 1 to 10 μm.

As described above, in the porous film, the fluorinated organic compound is attached to at least one of the two main surfaces. The fluorinated organic compound is attached to the main surface of the porous film so that the abundance of fluorine atoms is 0.0080 mg / cm ² or less as measured by a fluorescent X-ray method. From the viewpoint of wettability of an electrolytic solution, an organic solvent, and the like, it is preferably 0.0050 mg / cm ² or less, more preferably 0.0015 mg / cm ² or less, and particularly preferably less than 0.0010 mg / cm ^2. .
The amount of fluorinated organic compound deposited on the main surface of the porous film depends on the amount of fluorine atoms present on the main surface of the porous film in view of the effect of lowering friction and reducing the internal resistance when used in batteries. but the amount is preferably 0.0001 mg / cm ² or more as a value measured by a fluorescent X-ray method, 0.0002 mg / cm ² or more is more preferable.

  If the amount of the fluorinated organic compound attached to the main surface is excessive, the fluid permeability of the porous membrane may be impaired. The amount of the fluorinated organic compound deposited on the main surface is adjusted so that the Gurley air permeability of the porous film is 30 to 300 seconds.

  Hereinafter, the porous PI film and the fluorinated organic compound which are essentially included in the porous film will be described.

«Porous PI membrane»
As described above, the porous PI film is not particularly limited as long as it is a porous film made of PI. The porous PI membrane preferably has a desired porosity, and preferably has communication holes in which spherical holes communicate with each other.
The diameter of the opening existing on the surface of the porous PI film is preferably from 100 nm to 2000 nm, more preferably from 200 to 1000 nm, and still more preferably from 300 to 900 nm.
The diameter of the opening is equal to or substantially equal to the diameter of the spherical hole constituting the communication hole.
A porous PI membrane which is a preferred porous PI membrane and has a communicating hole in which spherical holes communicate with each other is manufactured by, for example, the following method.

In particular,
An unfired PI composite film forming step of forming an unfired composite film on a substrate using the composition for producing a porous PI film,
A firing step of firing the unfired PI composite film to obtain a PI-fine particle composite film;
A fine particle removing step of removing fine particles from the PI-fine particle composite film.

  Hereinafter, with respect to the method for producing a porous PI film, a composition for producing a porous PI film (hereinafter also referred to as a varnish for PI) and a preferred method for producing the porous PI film will be described in detail.

<Composition for producing porous PI film>
The composition for producing a porous PI film (varnish for PI) contains a polyimide or a polyamideimide, or a compound capable of forming a polyimide or a polyamideimide.
Polyimide, or a compound capable of forming polyamide imide may be a polyimide, or a monomer for polyamide imide, a polyamide acid which is a precursor of polyimide, or a polymer of a monomer for polyamide imide. May be a polyamideimide precursor.
As the compound capable of forming polyimide or polyamideimide, a polyamic acid and a polyamideimide precursor which is a polymer are preferable.
As described above, the varnish for PI preferably contains at least one selected from the group consisting of polyamic acid, polyimide, polyamideimide precursor, and polyamideimide.

  Hereinafter, essential or optional components contained in the varnish for PI will be described.

[Polyamic acid]
As the polyamic acid, one obtained by polymerizing an arbitrary tetracarboxylic dianhydride and a diamine can be used without any particular limitation. The amounts of the tetracarboxylic dianhydride and the diamine are not particularly limited, but it is preferable to use 0.50 to 1.50 mol of the diamine with respect to 1 mol of the tetracarboxylic dianhydride, and 0.60 to 1.50 mol. It is more preferable to use 30 mol, and it is particularly preferable to use 0.70 to 1.20 mol.

  The tetracarboxylic dianhydride can be appropriately selected from tetracarboxylic dianhydrides conventionally used as raw materials for synthesizing polyamic acid. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride, but from the viewpoint of heat resistance of the obtained polyimide resin, aromatic tetracarboxylic dianhydride may be used. It is preferred to use carboxylic dianhydrides. As the tetracarboxylic dianhydride, one type may be used alone, or two or more types may be used in combination.

  Preferred specific examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, and bis (2,3-dicarboxy). Phenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,3 ′, 4′- Biphenyltetracarboxylic dianhydride, 2,2,6,6-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2 , 3-Dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2- Bis (2,3-dicarboxy Enyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) Ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 4,4- (p-phenylenedioxy) diphthalic Acid dianhydride, 4,4- (m-phenylenedioxy) diphthalic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride Anhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride , 2, 3 6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 9,9-bisphthalene anhydride fluorene, 3,3 ′, 4,4′-diphenyl sulfone And tetracarboxylic dianhydride. Examples of the aliphatic tetracarboxylic dianhydride include ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, cyclohexane tetracarboxylic dianhydride, 1,2,2 4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride and the like can be mentioned. Among these, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferred from the viewpoint of cost, availability and the like. These tetracarboxylic dianhydrides can be used alone or in combination of two or more.

  The diamine can be appropriately selected from diamines conventionally used as raw materials for synthesizing polyamic acid. The diamine may be an aromatic diamine or an aliphatic diamine, but is preferably an aromatic diamine from the viewpoint of the heat resistance of the obtained polyimide resin. One of these diamines may be used alone, or two or more thereof may be used in combination.

  Examples of the aromatic diamine include a diamino compound having one or about 2 to 10 phenyl groups bonded thereto. Specifically, phenylenediamine and its derivative, diaminobiphenyl compound and its derivative, diaminodiphenyl compound and its derivative, diaminotriphenyl compound and its derivative, diaminonaphthalene and its derivative, aminophenylaminoindane and its derivative, diaminotetraphenyl Compounds and derivatives thereof, diaminohexaphenyl compounds and derivatives thereof, and cardo-type fluorenediamine derivatives.

  The phenylenediamine is m-phenylenediamine, p-phenylenediamine or the like, and the phenylenediamine derivative is a diamine to which an alkyl group such as a methyl group or an ethyl group is bonded, for example, 2,4-diaminotoluene, 2,4-triphenylene Diamine and the like.

  In a diaminobiphenyl compound, two aminophenyl groups are bonded to each other. For example, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl and the like.

  A diaminodiphenyl compound is a compound in which two aminophenyl groups are bonded to each other via other groups. The bond is an ether bond, a sulfonyl bond, a thioether bond, a bond by an alkylene or a derivative thereof, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, a ureylene bond, or the like. The alkylene group has about 1 to 6 carbon atoms. The derivative group of the alkylene group is an alkylene group substituted with one or more halogen atoms.

  Examples of the diaminodiphenyl compound include 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenylsulfone, 3,4′-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylketone , 3,4'-diaminodiphenylketone, 2,2-bis (p-aminophenyl) propane, 2,2'-bis (p-aminophenyl) hexafluoropropane, 4-methyl-2,4-bis (p -Aminophenyl) -1-pentene, 4-methyl-2 4-bis (p-aminophenyl) -2-pentene, iminodianiline, 4-methyl-2,4-bis (p-aminophenyl) pentane, bis (p-aminophenyl) phosphine oxide, 4,4′- Diaminoazobenzene, 4,4′-diaminodiphenylurea, 4,4′-diaminodiphenylamide, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3 -Bis (3-aminophenoxy) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] Sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophen ) Phenyl] hexafluoropropane, and the like.

  Of these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, and 4,4'-diaminodiphenyl ether are preferred from the viewpoint of price, availability, and the like.

  A diaminotriphenyl compound is a compound in which two aminophenyl groups and one phenylene group are both bonded via another group. As other groups, the same groups as in the diaminodiphenyl compound are selected. Examples of the diaminotriphenyl compound include 1,3-bis (m-aminophenoxy) benzene, 1,3-bis (p-aminophenoxy) benzene, and 1,4-bis (p-aminophenoxy) benzene. be able to.

  Examples of diaminonaphthalene include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene.

  Examples of aminophenylaminoindane include 5 or 6-amino-1- (p-aminophenyl) -1,3,3-trimethylindane.

  Examples of the diaminotetraphenyl compound include 4,4′-bis (p-aminophenoxy) biphenyl, 2,2′-bis [p- (p′-aminophenoxy) phenyl] propane, and 2,2′-bis [ p- (p'-aminophenoxy) biphenyl] propane, 2,2'-bis [p- (m-aminophenoxy) phenyl] benzophenone, and the like.

  Examples of the cardo-type fluorenediamine derivative include 9,9-bisanilinefluorene.

  The number of carbon atoms of the aliphatic diamine is preferably, for example, about 2 to 15. Specific examples of the aliphatic diamine include pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, and the like.

  In addition, compounds in which the hydrogen atom of these diamines is substituted with at least one substituent selected from the group consisting of a halogen atom, a methyl group, a methoxy group, a cyano group, and a phenyl group may be used.

  The means for producing the polyamic acid is not particularly limited, and for example, a known method such as a method of reacting an acid and a diamine component in a solvent can be used.

  The reaction between the tetracarboxylic dianhydride and the diamine is usually performed in a solvent. The solvent used for the reaction between the tetracarboxylic dianhydride and the diamine is not particularly limited as long as it can dissolve the tetracarboxylic dianhydride and the diamine and does not react with the tetracarboxylic dianhydride and the diamine. Not done. One type of solvent may be used alone, or two or more types may be used in combination.

Examples of the solvent used for the reaction between the tetracarboxylic dianhydride and the diamine include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-dimethylformamide, Nitrogen-containing polar solvents such as N-diethylformamide, N-methylcaprolactam, N, N, N ′, N′-tetramethylurea; β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone; lactone polar solvents such as γ-caprolactone and ε-caprolactone; dimethyl sulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methylcellosolve acetate, ethylcelle Ethers such as Lube acetate; cresols include phenol-based solvents such as xylene-based solvent mixture.
One of these solvents may be used alone, or two or more thereof may be used in combination. Although there is no particular limitation on the amount of the solvent used, it is desirable that the content of the polyamic acid to be produced is 5 to 50% by mass.

  Among these solvents, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethyl Nitrogen-containing polar solvents such as formamide, N-methylcaprolactam, N, N, N ', N'-tetramethylurea are preferred.

The polymerization temperature is generally -10 to 120C, preferably 5 to 30C. The polymerization time varies depending on the raw material composition used, but is usually 3 to 24 hours (hour).
Polyamic acid may be used alone or in combination of two or more.

[Polyimide]
The polyimide is not limited in its structure or molecular weight, and a known polyimide can be used. The polyimide may have a condensable functional group such as a carboxy group or a functional group that promotes a crosslinking reaction or the like at the time of firing in the side chain. When the varnish for PI contains a solvent, a soluble polyimide soluble in the solvent used is preferable.

Use of a monomer for introducing a flexible bent structure into the main chain to obtain a polyimide soluble in a solvent, for example, ethylenediamine, hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, Aliphatic diamines such as 4,4'-diaminodicyclohexylmethane; 2-methyl-1,4-phenylenediamine, o-tolidine, m-tolidine, 3,3'-dimethoxybenzidine, 4,4'-diaminobenzanilide and the like Aromatic diamines; polyoxyalkylene diamines such as polyoxyethylene diamine, polyoxypropylene diamine, polyoxybutylene diamine; polysiloxane diamine; 2,3,3 ′, 4′-oxydiphthalic anhydride, 3,4,3 ′, 4'-oxydiphthalic anhydride, 2,2-bis (4-hydroxyphenyl R) Use of propane dibenzoate-3,3 ', 4,4'-tetracarboxylic dianhydride or the like is effective. Further, use of a monomer having a functional group for improving solubility in a solvent, for example, 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl, 2-trifluoromethyl-1,4- It is also effective to use a fluorinated diamine such as phenylenediamine. Further, in addition to the monomer for improving the solubility of the polyimide, the same monomers as those described in the section of the polyamic acid can be used in combination as long as the solubility is not impaired.
Each of the polyimide and its monomer may be used alone or in combination of two or more.

The means for producing the polyimide is not particularly limited, and for example, a known method such as a method for chemically imidizing or heating imidizing polyamic acid can be used. Examples of such polyimides include aliphatic polyimides (fully aliphatic polyimides) and aromatic polyimides, with aromatic polyimides being preferred. Examples of the aromatic polyimide include those obtained by subjecting a polyamic acid having a repeating unit represented by the formula (1) to a ring-closing reaction by heat or chemical means, or a polyimide having a repeating unit represented by the formula (2). Can be In the formula, Ar represents an aryl group. If the PI varnish contains a solvent, these polyimides may then be dissolved in the solvent used.

[Polyamide imide and polyamide imide precursor]
As the polyamideimide, a known polyamideimide can be used without being limited by its structure or molecular weight. The polyamide imide may have a condensable functional group such as a carboxy group or a functional group that promotes a cross-linking reaction or the like at the time of firing in the side chain. When the varnish for PI contains a solvent, a soluble polyamideimide that is soluble in the solvent used is preferable.

  Polyamide imide is usually obtained by reacting (i) an acid having a carboxyl group and an acid anhydride group in one molecule of trimellitic anhydride or the like with diisocyanate, (ii) trimellitic anhydride chloride or the like. Any of those obtained by imidizing a precursor polymer (polyamide imide precursor) obtained by reacting the above reactive derivative of an acid with a diamine can be used without any particular limitation.

  Examples of the acid or its reactive derivative include trimellitic anhydride halides such as trimellitic anhydride and trimellitic anhydride chloride, and trimellitic anhydride esters.

  Examples of the above-mentioned optional diamine include the same ones as exemplified in the description of the polyamic acid, and a diaminopyridine-based compound can also be used.

  The above-mentioned optional diisocyanate is not particularly limited, and examples thereof include a diisocyanate compound corresponding to the above-mentioned optional diamine, and specifically, meta-phenylene diisocyanate, p-phenylene diisocyanate, o-tolidine diisocyanate, p-phenylene Diisocyanate, m-phenylene diisocyanate, 4,4'-oxybis (phenylisocyanate), 4,4'-diisocyanatediphenylmethane, bis [4- (4-isocyanatophenoxy) phenyl] sulfone, 2,2'-bis [4- ( 4-isocyanatophenoxy) phenyl] propane, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyldiphenyl-4, '-Diisocyanate, 3,3'-diethyldiphenyl-4,4'-diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m-xylene diisocyanate, p-xylene diisocyanate, naphthalene diisocyanate and the like. Can be

  In addition to the above, compounds described as general formulas in JP-A-63-283705 and JP-A-2-198619 can be used as raw material monomers for polyamideimide. The imidation in the method (ii) may be either thermal imidation or chemical imidization. As the chemical imidization, a method of immersing a green composite film formed using a varnish for PI containing a polyamideimide precursor or the like in acetic anhydride or a mixed solvent of acetic anhydride and isoquinoline can be used. In addition, the polyamideimide precursor can also be said to be a polyimide precursor from the viewpoint of the precursor before imidization.

Examples of the polyamideimide contained in the varnish for PI include (1) a polymer obtained by reacting an acid such as trimellitic anhydride with diisocyanate, and (2) a reactive derivative of the acid such as trimellitic anhydride chloride. May be a polymer obtained by imidizing a precursor polymer obtained by a reaction of a diamine with a diamine. In the present specification and claims, the term "polyamideimide precursor" means a polymer before imidization (precursor polymer).
Each of the polyamideimide and the polyamideimide precursor may be used alone or in combination of two or more. As for the polyamideimide, each of the above-mentioned polymer, raw material monomer, and oligomer may be used alone or in combination of two or more.

[Fine particles]
The material of the fine particles is not particularly limited as long as it is insoluble in the solvent contained in the PI varnish and can be removed later from the PI-fine particle composite film, and a known material can be used. For example, as inorganic materials, metal oxides such as silica (silicon dioxide), titanium oxide, and alumina (Al ₂ O ₃ ), and as organic materials, high molecular weight olefins (polypropylene, polyethylene, etc.), polystyrene, epoxy resin, cellulose And organic polymer fine particles such as polyvinyl alcohol, polyvinyl butyral, polyester, and polyether.

  Specific examples of the fine particles include colloidal silica. Above all, it is preferable to select monodispersed spherical silica particles because uniform pores can be formed.

Further, it is preferable that the fine particles have a high sphericity and a small particle size distribution index. Fine particles satisfying these conditions have excellent dispersibility in the varnish for PI and can be used in a state where they do not aggregate with each other. The average particle size of the fine particles used is preferably, for example, 100 to 2000 nm. By satisfying these conditions, the pore size of the porous film obtained by removing the fine particles can be made uniform, so that when the laminate including the porous PI film is used as a separator, the electric field applied to the separator is uniform. This is preferable.
The fine particles may be used alone or in combination of two or more.

[solvent]
The solvent is not particularly limited as long as it can dissolve a resin composed of polyamic acid and / or polyimide and does not dissolve fine particles, and is exemplified as a solvent used for the reaction between tetracarboxylic dianhydride and diamine. What was done. The solvents may be used alone or in combination of two or more.

[Dispersant]
For the purpose of uniformly dispersing the fine particles in the PI varnish, a dispersant may be further added together with the fine particles. By adding the dispersant, the fine particles can be more uniformly mixed into the varnish for PI, and further, the fine particles can be evenly distributed in the film on which the varnish for PI is formed. As a result, a dense opening can be provided on the surface of the finally obtained porous PI film, and the front and back surfaces can be efficiently communicated, so that the air permeability of the porous film is improved. Further, by adding a dispersant, the drying property of the PI varnish is easily improved, and the peelability of the formed unfired composite film from the substrate or the like is easily improved.

  The dispersant is not particularly limited, and a known dispersant can be used. For example, palm fatty acid salt, castor sulfated oil salt, lauryl sulfate salt, polyoxyalkylene allyl phenyl ether sulfate salt, alkyl benzene sulfonic acid, alkyl benzene sulfonate, alkyl diphenyl ether disulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate Anionic surfactants such as sodium salt, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salt, polyoxyethylene allyl phenyl ether phosphate salt; oleylamine acetate, lauryl pyridinium chloride, cetyl pyridinium chloride, lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride , Behenyl trimethyl ammonium chloride, didecyl dimethyl Cationic surfactants such as ammonium chloride; amphoteric surfactants such as cocoalkyldimethylamine oxide, fatty acid amidopropyldimethylamine oxide, alkyl polyaminoethylglycine hydrochloride, amidobetaine-type activator, alanine-type activator, lauryl iminodipropionic acid Agents: polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene laurylamine, polyoxyethylene oleylamine, polyoxyethylene polystyrylphenyl ether, polyoxyalkylene polystyrylphenylether, etc. Nonionic surfactants of alkylene primary alkyl ether or polyoxyalkylene secondary alkyl ether, polyoxyethylene dilau Other polyoxyalkylene nonions such as carboxylate, polyoxyethylene laurate, polyoxyethylenated castor oil, polyoxyethylenated hardened castor oil, sorbitan laurate, polyoxyethylene sorbitan laurate, and fatty acid diethanolamide Surfactants; fatty acid alkyl esters such as octyl stearate and trimethylolpropane tridecanoate; and polyether polyols such as polyoxyalkylene butyl ether, polyoxyalkylene oleyl ether, and trimethylolpropane tris (polyoxyalkylene) ether. However, the present invention is not limited to these. Further, the above dispersants may be used as a mixture of two or more kinds.

  In the varnish for PI, the content of the dispersant is preferably, for example, 0.01 to 5% by mass, and preferably 0.05 to 1% by mass with respect to the mass of the fine particles from the viewpoint of film formability. Is more preferable, and even more preferably 0.1 to 0.5% by mass.

<Preferred manufacturing method of porous PI film>
[Unfired PI composite film forming step]
In the unbaked PI composite film formation step, for example, the above-described varnish for PI is applied on a substrate, and dried at 0 to 100 ° C., preferably 10 to 100 ° C. under normal pressure or vacuum. A fired PI composite film can be formed. Examples of the substrate include a PET film, a SUS substrate, and a glass substrate.

  In the case where the unsintered PI composite film is peeled off from the substrate, a substrate provided with a release layer in advance may be used in order to further enhance the peelability of the film. When a release layer is provided on the substrate in advance, a release agent is applied on the substrate and dried or baked before applying the varnish for PI. As the release agent used here, a known release agent such as an alkyl phosphate ammonium salt type, a fluorine type or silicone can be used without any particular limitation. When the dried unfired PI composite film is peeled off from the substrate, the release agent slightly remains on the peeled surface of the unfired PI composite film, which may cause discoloration during firing and adversely affect electrical characteristics. It is preferable to remove as much as possible. For the purpose of removing the release agent, a washing step of washing the unfired PI composite film peeled from the substrate with an organic solvent may be introduced.

  On the other hand, when the substrate is used as it is without providing a release layer for forming the unfired PI composite film, the step of forming the release layer and the cleaning step can be omitted. In the production of the unsintered composite film, an immersion step in a solvent containing water, a press step, and a drying step after the immersion step may be provided as optional steps before the sintering step described below.

[Firing step]
Post-processing (firing) by heating is performed on the unfired PI composite film to form a composite film (PI-fine particle composite film) composed of PI and fine particles. The firing temperature in the firing step varies depending on the structure of the unfired composite film and the presence or absence of a condensing agent, but is preferably from 120 to 450 ° C, and more preferably from 150 to 400 ° C. Further, when an organic material is used for the fine particles, the temperature must be set lower than the thermal decomposition temperature. In the firing step, it is preferable to complete the imidization.

  The firing conditions include, for example, a method in which the temperature is raised from room temperature to 400 ° C. in 3 hours and then maintained at 400 ° C. for 20 minutes, or the temperature is gradually raised from room temperature to 400 ° C. in steps of 50 ° C. (each step is maintained for 20 minutes). ), And a stepwise drying-thermal imidization method, such as finally holding at 400 ° C for 20 minutes, can also be used. When an unsintered PI composite film is formed on a substrate and the unsintered PI composite film is once separated from the substrate, the end of the unsintered PI composite film is fixed to a SUS frame to prevent deformation. A method can also be adopted.

[Particle removal process]
By removing the fine particles from the PI-fine particle composite film formed as described above by selecting an appropriate method, a porous PI film having a desired structure can be manufactured with good reproducibility.
When silica is used as the material of the fine particles, for example, it is possible to dissolve and remove the silica by treating the PI-fine particle composite film with a low-concentration hydrogen fluoride solution or the like.
When the fine particles are organic fine particles, the fine particles can be removed from the PI-fine particle composite film by thermally decomposing the organic fine particles.
When the fine particles are organic fine particles, a processing solution that dissolves the fine particles but does not dissolve the PI can be selected, and the treatment with the processing liquid can be performed to remove the organic fine particles. Typically, an organic solvent is used as the processing liquid. When the organic fine particles are soluble in an acid or an alkali, an acidic aqueous solution or an alkaline aqueous solution can also be used as the treatment liquid.

[Resin removal process]
Before the fine particle removing step, the resin-removing step of removing at least a part of the resin part of the PI-fine particle composite film or removing at least a part of the porous PI film after the fine particle removing step may be provided. .
By removing at least a part of the resin part of the PI-fine particle composite film before the fine particle removing step, or removing at least a part of the porous PI film after the fine particle removing step, compared with the case where the removal is not performed. In addition, it is possible to improve the porosity of the porous PI film as the final product.

  The step of removing at least a part of the resin part of the PI-particle composite film, or the step of removing at least a part of the resin part of the PI-particle composite film is performed by a usual chemical etching method, physical removal method, or It can be performed by a method combining these.

  Examples of the chemical etching method include a treatment with a chemical etching solution such as an inorganic alkali solution or an organic alkali solution. Inorganic alkaline solutions are preferred. As the inorganic alkali solution, for example, a hydrazine solution containing hydrazine hydrate and ethylenediamine, a solution of an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, an ammonia solution, a hydroxide solution An etching solution containing an alkali, hydrazine, and 1,3-dimethyl-2-imidazolidinone as main components is exemplified. Examples of the organic alkali solution include primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-butylamine; tertiary amines such as triethylamine and methyldiethylamine; dimethylethanolamine And quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; and alkaline solutions such as cyclic amines such as pyrrole and pichelidine.

  As for the solvent of each of the above solutions, pure water and alcohols can be appropriately selected. Also, a surfactant to which an appropriate amount of a surfactant has been added can be used. The alkali concentration is, for example, 0.01 to 20% by mass.

  As a physical method, for example, plasma (oxygen, argon, etc.), dry etching by corona discharge or the like, an abrasive (for example, alumina (hardness 9) or the like) is dispersed in a liquid, and this is dispersed in an aromatic polyimide film. A method of treating the film surface by irradiating the surface of the film with a speed of 30 to 100 m / s can be used.

  On the other hand, as a physical method applicable only to the resin removing step performed after the fine particle removing step, the target surface is wet-bonded to a liquid-wetted backing film (eg, a polyester film such as a PET film), without drying, or after drying. A method of peeling the laminate from the backing film can also be adopted. The porous PI film is peeled off from the backing film while only the surface layer of the porous PI film present on the surface to be treated is left on the backing film due to the surface tension or electrostatic adhesion of the liquid. Is done.

≪Fluorinated organic compounds≫
The fluorinated organic compound is not particularly limited as long as it is an organic compound containing a fluorine atom. The fluorinated organic compound may be a low molecular compound, or may be an oligomer or a polymer. Further, the fluorinated organic compound may be an aliphatic compound, an aromatic compound, or a compound containing an aliphatic portion and an aromatic portion.

  Examples of fluorinated organic compounds include fluoroalkanes, fluoroalkanols, bisfluoroalkyl ethers, fluoroalkyl alkyl ethers, fluorinated aliphatic ketones, fluorinated aliphatic carboxylic acids, fluorinated aliphatic carboxylic acid alkyl esters, fluorinated fatty acids Fluoroalkyl esters of aliphatic carboxylic acids, fluoroalkyl esters of aliphatic carboxylic acids, fluoroalkylbenzene carboxylic acids, fluoroalkylbenzene carboxylic acid salts, fluoroalkylbenzenesulfonic acids, and fluoroalkylbenzenesulfonic acid salts.

Fluorine-containing silane coupling agents are also suitably used as fluorinated organic compounds. A functional group containing an active hydrogen atom, such as a hydroxyl group, an amino group, or a carboxyl group, is often present on the surface of a porous membrane that has not been treated with a fluorinated organic compound.
The fluorine-containing silane coupling agent can react with the functional group containing an active hydrogen atom and bond. Therefore, when the fluorine-containing silane coupling agent is used as the fluorinated organic compound, a desired amount of the fluorinated organic compound is easily present on the surface of the porous film.

The fluorine-containing silane coupling agent is not particularly limited as long as it is a silane coupling agent containing a functional group containing fluorine. Examples of the fluorine-containing silane coupling agent include fluoroalkyl trialkoxysilane, difluoroalkyldialkoxysilane, and fluoroalkylalkyldialkoxysilane.
Preferred specific examples of the fluorine-containing silane coupling agent include perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, perfluorooctyltrimethoxysilane, and perfluorooctyltrimethoxysilane. Examples include fluorooctyltriethoxysilane, perfluorododecyltrimethoxysilane, perfluorododecyltriethoxysilane, perfluoropentyltriethoxysilane, and perfluoropentyltrimethoxysilane.

Fluororesins are also suitably used as fluorinated organic compounds. The type of the fluororesin is not particularly limited, and various resins containing a fluorine atom can be used.
Suitable fluororesins include, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (PFA), polyfluorinated Examples include vinylidene (PVDF) and its copolymer, polyvinyl fluoride (PVA), and ethylene / tetrafluoroethylene copolymer (ETFE). Among them, polyvinylidene fluoride (PVDF) and a copolymer thereof are preferable from the viewpoint of improving abrasion resistance. In the case of a copolymer, examples of the monomer to be copolymerized include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, and vinyl fluoride.

製造 Manufacturing method of porous membrane≫
The method for producing the porous membrane is not particularly limited. Preferably, a porous membrane is produced by the following method.
A preferred method is to apply a liquid containing a fluorinated organic compound to at least one main surface of an untreated porous film, including a polyimide and / or polyamideimide film (porous PI film);
Drying the liquid attached to the surface of the untreated porous membrane.

  According to such a method, by adjusting the amount of the liquid containing the fluorinated organic compound and the concentration of the fluorinated organic compound in the liquid containing the fluorinated organic compound, the fluorinated organic compound adhering to the main surface of the porous film is adjusted. The amount of the compound can be adjusted.

The solvent contained in the liquid containing the fluorinated organic compound is not particularly limited as long as the solvent can dissolve the fluorinated organic compound.
Preferred examples of the solvent include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylcaprolactam, , N, N ', N'-tetramethylurea and other nitrogen-containing polar solvents; lactones such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, etc. Polar solvents; lower alkyl ketones such as methyl ethyl ketone, acetone and tetrahydrofuran; and trimethyl phosphate.

The amount of the fluorinated organic compound adhering to at least one of the porous films is determined by X-ray fluorescence spectroscopy when the abundance of fluorine atoms on the main surface to which the fluorinated organic compound adheres is 0.0080 mg / cm ² or less. It is adjusted as it is.

The method for attaching a liquid containing a fluorinated organic compound to at least one main surface of the untreated porous membrane is not particularly limited. Specific methods include a method of applying a liquid to the main surface of the untreated porous film, a method of dipping the untreated porous film in the liquid, a method of spraying the liquid on the main surface of the untreated porous film, and the like. No.
Among these methods, since the fluorinated organic compound can be uniformly attached to the main surface of the porous film, a method of applying a liquid to the main surface of the untreated porous film, Is preferably immersed in a liquid.

The amount of fluorine atoms present on the main surface can be measured by the X-ray fluorescence method under the following conditions.
Measurement area shape: Concentric circle with a diameter of 3 cm Peak angle: 74.626 °
Peak measurement time: 20 seconds BG measurement time: 20 seconds Tube current: 100 mA
Tube voltage: 30 kV
Dispersion crystal: RX25

By drying the liquid adhering to the surface of the untreated porous membrane, a porous body having a predetermined amount of the fluorinated organic compound adhered on the main surface is obtained.
The drying method is not particularly limited, and includes, for example, a method in which the untreated porous membrane to which the liquid is attached is heated under atmospheric pressure or reduced pressure to a temperature according to the boiling point of the solvent contained in the liquid.

≫Applications of porous membrane≫
The use of the porous membrane described above is preferably a separator use in a secondary battery, but is not limited to a separator use. The porous membrane can be used, for example, as a separator for a secondary battery such as a lithium ion battery, a fuel cell electrolyte membrane, a gas or liquid separation membrane (filter), or a low dielectric constant material.

  The friction of the porous film described above is reduced by the action of the fluorinated organic compound attached to the main surface. For this reason, it is easy to perform bending and winding by a machine without causing wrinkles and scratches on the porous film, and it is easy to manufacture a battery and a filter device.

The porous membrane can be used as a separator for a secondary battery such as a nickel cadmium, a nickel hydride battery, and a lithium ion secondary battery, but it is particularly preferable to use the porous membrane as a porous separator for a lithium ion secondary battery. .
Hereinafter, a secondary battery including the separator including the porous membrane described above will be described.

<Secondary battery>
The secondary battery is characterized in that an electrolytic solution and a separator made of the porous film described above are arranged between a negative electrode and a positive electrode.

  The type and configuration of the secondary battery are not limited at all. A battery element in which a positive electrode, a separator, and a negative electrode are sequentially laminated is impregnated with an electrolytic solution, and if the battery element has a structure in which the battery element is sealed in an exterior, a known element such as nickel cadmium, nickel hydrogen battery, lithium ion secondary battery, or the like is used. Can be used without particular limitation.

  The negative electrode of the secondary battery can have a structure in which a negative electrode mixture including a negative electrode active material, a conductive auxiliary agent, and a binder is formed on a current collector. For example, as the negative electrode active material, cadmium hydroxide can be used for a nickel cadmium battery, and a hydrogen storage alloy can be used for a nickel hydride battery. In the case of a lithium ion secondary battery, a material capable of electrochemically doping lithium can be employed. Examples of such an active material include a carbon material, silicon, aluminum, tin, and a wood alloy.

  Examples of the conductive additive forming the negative electrode include carbon materials such as acetylene black and Ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride and carboxymethyl cellulose. As the current collector, a copper foil, a stainless steel foil, a nickel foil, or the like can be used.

In addition, the positive electrode may have a structure in which a positive electrode mixture including a positive electrode active material, a conductive auxiliary agent, and a binder is formed on a current collector. For example, as a positive electrode active material, nickel hydroxide can be used for a nickel cadmium battery, and nickel hydroxide or nickel oxyhydroxide can be used for a nickel hydrogen battery. On the other hand, in the case of a lithium ion secondary battery, examples of the positive electrode active material include lithium-containing transition metal oxides, and specifically, LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , and LiCo _{1 / 3 Ni 1/3 Mn 1/3 O 2} , LiMn 2 O 4, LiFePO 4, LiCo 0.5 Ni 0.5 O 2, LiAl 0.25 Ni 0.75 O 2 and the like. Examples of the conductive assistant include carbon materials such as acetylene black and Ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride. As the current collector, an aluminum foil, a stainless steel foil, a titanium foil, or the like can be used.

As the electrolytic solution, for example, in the case of a nickel cadmium battery or a nickel hydride battery, a potassium hydroxide aqueous solution is used. The electrolyte of the lithium ion secondary battery has a structure in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , and LiClO ₄ . Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and vinylene carbonate. These may be used alone or in combination.

  Examples of the exterior material include a metal can or an aluminum laminate pack. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, and the separator made of the porous polyimide film manufactured by the manufacturing method according to the present invention can be suitably applied to any shape.

  Hereinafter, the present invention will be described more specifically with reference to Examples, but the scope of the present invention is not limited to the following Examples.

[Examples 1 to 3 and Comparative Example 1]
In Examples and Comparative Examples, a porous polyimide film obtained by the following method was used as an untreated porous film.

[Preparation of varnish]
(1) First varnish 6.5 g of pyromellitic dianhydride and 6.7 g of 4,4'-diaminodiphenyl ether were placed in a separable flask equipped with a stirrer, a stirring blade, a reflux condenser, and a nitrogen gas inlet tube. And 30 g of N, N-dimethylacetamide. Nitrogen was introduced into the flask through a nitrogen gas inlet tube, and the inside of the flask was set to a nitrogen atmosphere. Next, while stirring the contents of the flask, pyromellitic dianhydride and 4,4′-diaminodiphenyl ether were reacted at 50 ° C. for 20 hours to obtain a polyamic acid solution. 75 g of silica having an average particle diameter of 300 nm is added to the obtained polyamic acid solution and stirred, and a first varnish having a volume ratio of polyamic acid to fine particles of 22:78 (mass ratio of 15:85) is obtained. Was prepared. The ratio of the total organic solvent in the varnish was adjusted to be 70% by mass.

(2) Second varnish In the same manner as (1), except that 53 g of silica having an average particle diameter of 700 nm was added to the obtained polyamic acid solution, the volume ratio of polyamic acid to fine particles was 28:72 (mass). A second varnish having a ratio of 20:80) was prepared.

[Formation of precursor film (polyimide-fine particle composite film)]
The first varnish was formed on a glass plate to which a release agent was applied so as to have a thickness of about 1 μm using an applicator. Subsequently, a second varnish was further formed on the film made of the first varnish using an applicator. Prebaking was performed at 70 ° C. for 5 minutes to form an unfired composite film having a thickness of 20 μm.

  After peeling the unfired composite film from the base material, the release agent was removed with ethanol, and heat treatment was performed at 350 ° C. for 15 minutes to complete imidization to obtain a precursor film (polyimide-fine particle composite film).

[Formation of porous film (porous polyimide film)]
The precursor film (polyimide-fine particle composite film) was immersed in a 10% HF solution for 10 minutes to remove fine particles contained in the film.

[Chemical etching]
A 2.38% by mass aqueous solution of tetramethylammonium hydroxide (TMAH) was diluted with a 50% by mass aqueous solution of methanol to 1.04% to prepare an alkaline etching solution. A porous polyimide film was immersed in this etching solution to remove a part of the polyimide surface. The obtained porous polyimide film was used as an untreated porous film.

In the examples, the untreated porous membrane was immersed in an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride having the concentration shown in Table 1 for 1 minute, and then baked at 100 ° C. for 5 minutes. The film was dried to obtain a porous film having polyvinylidene fluoride adhered to both main surfaces.
Further, the untreated porous membrane was used as a porous membrane of a comparative example.

Regarding the porous membranes of Examples and Comparative Examples, the amount of fluorine atoms present on the main surface (mg / cm ² ) was measured using a bottom-surface irradiation type X-ray fluorescence spectrometer (ZSXPrimsu, manufactured by Rigaku) in accordance with the aforementioned conditions. Was measured. Table 1 shows the measurement results.
For the porous membranes of the examples and comparative examples, using a pin-on-disk friction and wear tester (TRIBOMETER, manufactured by CSM Instruments), a condition of a load of 25 g, a speed of 1.0 mm / sec, and a measurement time of 5 minutes was used. A friction and wear test was performed.
Such a test is a test based on ASTM G99 and DIN 50324.
Table 1 shows the results of the friction and wear test.

The Examples and Comparative Examples show that the surface of the polyimide porous film is satisfactorily reduced in friction by attaching a very small amount of the fluorinated organic compound to the main surface of the polyimide porous film.
The Gurley air permeability of each of the porous membranes of Examples and Comparative Examples was slightly more than 50 seconds, and there was no significant difference in tensile strength and tensile elongation.

Claims (11)

A porous film comprising a porous polyimide and / or polyamideimide film and a fluorinated organic compound,
The fluorinated organic compound is attached to at least one of the two main surfaces of the polyimide and / or polyamideimide film ,
An abundance of fluorine atoms on the main surface to which the fluorinated organic compound is adhered, measured by a fluorescent X-ray method, is 0.0080 mg / cm ² or less;
A porous membrane, wherein the Gurley air permeability of the porous membrane is 30 to 300 seconds. A laminate including a porous polyimide and / or polyamideimide film, and a fluorinated organic compound, a porous film,
The fluorinated organic compound is attached to at least one of the two main surfaces of the laminate,
An abundance of fluorine atoms on the main surface to which the fluorinated organic compound is adhered, measured by a fluorescent X-ray method, is 0.0080 mg / cm ² or less;
The Gurley air permeability of the porous membrane is 30 to 300 seconds, a multi Anashitsumaku. At least one main surface of the laminate composed of the polyimide and / or polyamide-imide film, the fluorinated organic compound is attached to the main surface consisting of the polyimide and / or polyamide-imide film, according to claim 2 4. The porous membrane according to item 1.   The porous membrane according to any one of claims 1 to 3, wherein the fluorinated organic compound is a fluororesin.   The porous membrane according to claim 4, wherein the fluororesin is polyvinylidene fluoride. Including the polyimide and / or polyamide-imide film, attaching a liquid containing the fluorinated organic compound to at least one main surface of the untreated porous film;
The method for producing a porous membrane according to any one of claims 1 to 5, comprising drying the liquid attached to the surface of the untreated porous membrane.   A separator for a secondary battery, comprising the porous membrane according to claim 1.   A secondary battery comprising the secondary battery separator according to claim 7.   A filter comprising the porous membrane according to claim 1.   A method of using the porous membrane according to any one of claims 1 to 5 as a separator in a secondary battery.   A method of using the porous membrane according to claim 1 as a filter in filtration.