JP2016056225A - Varnish for porous film production, method for producing porous film using the same, and polyamide-imide porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a varnish for porous film production that gives an unburned composite film with less cissing, a method for producing a porous film using the same, and a polyamide-imide porous film that can be thinned.SOLUTION: A varnish for porous film production comprises at least one resin (A) selected from the group consisting of polyamide acid, polyimide, polyamide-imide precursor and polyamide-imide, fine particles (B), and a silicon atom- and/or fluorine atom-containing surfactant (C) having an alkylene oxide chain.SELECTED DRAWING: None

Description

  The present invention relates to a varnish for producing a porous membrane, a method for producing a porous membrane using the varnish, and a polyamide-imide porous membrane.

  In recent years, research has been conducted on porous polyimides as separators for lithium ion batteries, fuel cell electrolyte membranes, gas or liquid separation membranes, and low dielectric constant materials.

  For example, a method of making a porous material using a specific mixed solvent in a polyamic acid solution, a method of heat imidizing a polyamic acid containing a hydrophilic polymer, and then removing the hydrophilic polymer to make it porous, from a polyimide containing silica particles A method of removing silica and making it porous is known (see Patent Documents 1 to 3).

  Among them, the method of removing silica from a polyimide containing silica particles to make it porous is an effective means for producing a homogeneous and dense porous film. In the production method, it is necessary to first form an unfired composite film containing polyamic acid and silica particles on a substrate using a varnish for producing a porous film containing polyamic acid and silica particles. .

  As a method using silica particles, a method using a resin other than polyimide has also been proposed (see Patent Document 4). Patent Document 4 describes an example in which a porous film is obtained by spin-coating a resin solution containing silica on a substrate to form a film having a thickness of about 10 μm and then immersing in hydrofluoric acid to remove the silica. Has been.

JP 2007-2111136 A JP 2000-044719 A JP 2012-107144 A JP 2004-292537 A

  In recent years, it has been demanded that the porous film as described above be made thin while maintaining the porosity of the porous film as much as possible. However, according to the study by the present inventors, when a varnish for producing a porous film containing particles is applied thinly on a substrate, a support or the like for thinning and high porosity, repelling (pinhole) It has been found that a uniform film cannot be formed.

  The present invention has been made in view of such problems, and a varnish for producing a porous film that gives an unfired composite film that is less likely to be repelled, a method for producing a porous film using the same, and a method for reducing the thickness of the varnish It aims at providing the realized polyamide-imide porous membrane.

  In order to complete the present invention, the present inventors have found that the above-mentioned problems can be solved by including a specific surfactant in the varnish for producing a porous membrane, despite containing fine particles such as silica. It came. Specifically, the present invention provides the following.

  The first aspect of the present invention is a silicon atom having at least one resin (A) selected from the group consisting of polyamic acid, polyimide, polyamideimide precursor and polyamideimide, fine particles (B), and alkylene oxide chains. And / or a varnish for producing a porous film, which contains a fluorine atom-containing surfactant (C).

  The second aspect of the present invention includes an unfired composite film forming step of forming an unfired composite film using the porous film manufacturing varnish of the present invention, and baking the unfired composite film to form a resin-fine particle composite. It is a method for producing a porous film, which includes a baking process for obtaining a film and a fine particle removing process for removing fine particles from the resin-fine particle composite film.

  ADVANTAGE OF THE INVENTION According to this invention, the varnish for porous film manufacture which gives the unbaking composite film which cannot produce a repellency, the manufacturing method of a porous film using the same, and a polyamide-imide porous film can be provided.

5 is a diagram illustrating a photograph of a coating film of Comparative Example 1. FIG.

  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 object of the present invention. .

<Varnish for porous membrane production>
The varnish for producing a porous membrane of the present invention has at least one resin (A) selected from the group consisting of polyamic acid, polyimide, polyamideimide precursor and polyamideimide, fine particles (B), and alkylene oxide chains. A silicon atom and / or fluorine atom containing surfactant (C) is contained. As described above, the varnish for producing the porous membrane of the present invention can provide an unfired composite membrane that hardly causes repelling by containing a specific surfactant.

[Resin (A)]
The resin (A) used in the varnish for producing a porous membrane of the present invention is at least one resin selected from the group consisting of polyamic acid, polyimide, polyamideimide precursor and polyamideimide (hereinafter referred to as “polyimide resin”). There are things to do.)

[Polyamide acid]
As the polyamic acid used in the present invention, those obtained by polymerizing any tetracarboxylic dianhydride and diamine can be used without any particular limitation. Although the usage-amount of tetracarboxylic dianhydride and diamine is not specifically limited, It is preferable to use 0.50-1.50 mol of diamine with respect to 1 mol of tetracarboxylic dianhydrides, and 0.60-1. 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. From the viewpoint of the heat resistance of the resulting polyimide resin, the aromatic tetracarboxylic dianhydride may be used. Preference is given to using carboxylic dianhydrides. A tetracarboxylic dianhydride may be used individually by 1 type, and may be used in combination of 2 or more type.

  Preferable specific examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 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′-benzophenone tetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) Ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 4,4- (p-phenylenedioxy) diphthal Acid dianhydride, 4,4- (m-phenylenedioxy) diphthalic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic acid di 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-bisphthalic anhydride fluorene, 3,3 ′, 4,4′-diphenylsulfone Tetracarboxylic dianhydride etc. are mentioned. Examples of the aliphatic tetracarboxylic dianhydride include ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, cyclohexane tetracarboxylic dianhydride, 1, 2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride, and the like. Among these, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferable from the viewpoint of price and availability. Moreover, these tetracarboxylic dianhydrides can also be used individually by 1 type or in mixture of 2 or more types.

  The diamine can be appropriately selected from diamines conventionally used as a raw material for synthesizing polyamic acid. The diamine may be an aromatic diamine or an aliphatic diamine, but an aromatic diamine is preferred from the viewpoint of the heat resistance of the resulting polyimide resin. These diamines may be used alone or in combination of two or more.

  Examples of the aromatic diamine include diamino compounds in which one phenyl group or about 2 to 10 phenyl groups are bonded. Specifically, phenylenediamine and derivatives thereof, diaminobiphenyl compounds and derivatives thereof, diaminodiphenyl compounds and derivatives thereof, diaminotriphenyl compounds and derivatives thereof, diaminonaphthalene and derivatives thereof, aminophenylaminoindane and derivatives thereof, diaminotetraphenyl Compounds and derivatives thereof, diaminohexaphenyl compounds and derivatives thereof, and cardo-type fluorenediamine derivatives.

  Phenylenediamine is m-phenylenediamine, p-phenylenediamine, etc., and phenylenediamine derivatives include diamines to which alkyl groups such as methyl group and ethyl group are bonded, such as 2,4-diaminotoluene, 2,4-triphenylene. Diamines and the like.

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

  The 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 alkylene or a derivative group thereof, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, a ureylene bond, or the like. The alkylene bond has about 1 to 6 carbon atoms, and the derivative group has one or more hydrogen atoms in the alkylene group substituted with halogen atoms or the like.

  Examples of diaminodiphenyl compounds include 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl ketone 3,4′-diaminodiphenyl ketone, 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.

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

  In the diaminotriphenyl compound, two aminophenyl groups and one phenylene group are both bonded via other groups, and the other groups are the same as those of the diaminodiphenyl compound. Examples of diaminotriphenyl compounds include 1,3-bis (m-aminophenoxy) benzene, 1,3-bis (p-aminophenoxy) benzene, 1,4-bis (p-aminophenoxy) benzene, and the like. 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 diaminotetraphenyl compounds include 4,4′-bis (p-aminophenoxy) biphenyl, 2,2′-bis [p- (p′-aminophenoxy) phenyl] propane, 2,2′-bis [ p- (p′-aminophenoxy) biphenyl] propane, 2,2′-bis [p- (m-aminophenoxy) phenyl] benzophenone, and the like.

  Examples of the cardo type fluoreneamine derivative include 9,9-bisaniline fluorene.

  The aliphatic diamine has, for example, about 2 to 15 carbon atoms, and specific examples include pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

  A compound in which the hydrogen atom of these diamines is substituted with at least one substituent selected from the group such as a halogen atom, a methyl group, a methoxy group, a cyano group, and a phenyl group may be used.

  There is no restriction | limiting in particular in the means to manufacture the polyamic acid used by this invention, For example, well-known methods, such as the method of making an acid and a diamine component react in a solvent, can be used.

  Reaction of tetracarboxylic dianhydride and diamine is normally performed in a solvent. The solvent used for the reaction of tetracarboxylic dianhydride and diamine is particularly limited as long as it can dissolve tetracarboxylic dianhydride and diamine and does not react with tetracarboxylic dianhydride and diamine. Not. A solvent may be used individually by 1 type and may be used in combination of 2 or more type.

Examples of the solvent used in the reaction of tetracarboxylic dianhydride and diamine include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, 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, methyl cellosolve acetate, ethyl cell Ethers such as Lube acetate; cresols include phenol-based solvents such as xylene-based solvent mixture.
These solvents may be used alone or in combination of two or more. Although there is no restriction | limiting in particular in the usage-amount of a solvent, It is desirable that content of the polyamic acid to produce shall be 5-50 mass%.

  Among these solvents, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethyl are used because of the solubility of the resulting polyamic acid. Nitrogen-containing polar solvents such as formamide, N-methylcaprolactam, N, N, N ′, N′-tetramethylurea are preferred.

The polymerization temperature is generally -10 to 120 ° C, preferably 5 to 30 ° C. The polymerization time varies depending on the raw material composition to be used, but is usually 3 to 24 Hr (hour).
A polyamic acid may be used individually by 1 type, and may be used in combination of 2 or more type.

[Polyimide]
The polyimide used in the present invention is not limited in its structure and molecular weight, and known ones can be used. About a polyimide, you may have a functional group which accelerates | stimulates a crosslinking reaction etc. at the time of baking, or a functional group which can be condensed, such as a carboxy group. Moreover, when the varnish for producing a porous membrane of the present invention contains a solvent, a soluble polyimide that is soluble in the solvent to be used is preferable.

Use of a monomer to introduce a flexible bending structure into the main chain in order to obtain a polyimide soluble in a solvent, such as ethylenediamine, hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, 4 Aliphatic diamines such as 2,4′-diaminodicyclohexylmethane; 2-methyl-1,4-phenylenediamine, o-tolidine, m-tolidine, 3,3′-dimethoxybenzidine, 4,4′-diaminobenzanilide, etc. Aromatic diamines; polyoxyalkylene diamines such as polyoxyethylene diamine, polyoxypropylene diamine, polyoxybutylene diamine; polysiloxane diamines; 2,3,3 ′, 4′-oxydiphthalic anhydride, 3,4,3 ′, 4′-oxydiphthalic anhydride, 2,2-bis (4-hydroxypheny E) Use of propanedibenzoate-3,3 ′, 4,4′-tetracarboxylic dianhydride is effective. In addition, use of a monomer having a functional group that improves 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. Furthermore, in addition to the monomer for improving the solubility of the polyimide, the same monomers as those described in the column for the polyamic acid can be used in combination as long as the solubility is not inhibited.
A polyimide and its monomer may be used individually by 1 type, and may be used in combination of 2 or more type.

There is no restriction | limiting in particular in the means to manufacture the polyimide used by this invention, For example, well-known methods, such as the method of making a polyamic acid chemical imidation or heat imidation, can be used. Examples of such polyimide include aliphatic polyimide (total aliphatic polyimide), aromatic polyimide and the like, and aromatic polyimide is preferable. Examples of the aromatic polyimide include those obtained by thermal or chemical ring closure reaction of a polyamic acid having a repeating unit represented by the formula (1), or a polyimide having a repeating unit represented by the formula (2). In the formula, Ar represents an aryl group. When the varnish of the present invention contains a solvent, these polyimides are then preferably dissolved in the solvent used.

[Polyamideimide]
The polyamideimide used in the present invention is not limited to its structure and molecular weight, and known ones can be used. The polyamideimide may have a functional group capable of condensing such as a carboxy group in the side chain or a functional group that promotes a crosslinking reaction or the like during firing. Moreover, when the varnish for producing a porous membrane of the present invention contains a solvent, a soluble polyamideimide that is soluble in the solvent to be used is preferable.

  The polyamideimide used in the present invention is usually (i) obtained by reacting a diisocyanate with an acid having a carboxyl group and an acid anhydride group in one molecule such as trimellitic anhydride, (ii) A material obtained by imidizing a precursor polymer (polyamideimide precursor) obtained by reacting a reactive derivative of the above acid such as merit acid chloride with diamine can be used without any particular limitation.

  Examples of the acid or a reactive derivative thereof include trimellitic anhydride halides such as trimellitic anhydride and trimellitic anhydride chloride, trimellitic anhydride ester, and the like.

  As said arbitrary diamine, the thing similar to what was illustrated in description of the said polyamic acid is mentioned, Moreover, a diaminopyridine type compound can also be used.

  The arbitrary diisocyanate is not particularly limited, and examples thereof include diisocyanate compounds corresponding to the arbitrary diamines. Specifically, metaphenylene 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, Examples include '-diisocyanate, 3,3'-diethyldiphenyl-4,4'-diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m-xylene diisocyanate, p-xylene diisocyanate, and naphthalene diisocyanate. It is done.

  As the raw material monomer for polyamideimide, compounds described in general formulas in JP-A-63-283705 and JP-A-2-198619 can be used in addition to the above. The imidization in the method (ii) may be either thermal imidization or chemical imidization. For chemical imidization, a method of immersing an unfired composite film formed using a varnish for producing a porous film containing a polyamideimide precursor in acetic anhydride or a mixed solvent of acetic anhydride and isoquinoline is used. it can. The polyamideimide precursor can also be said to be a polyimide precursor in terms of a precursor before imidization.

The polyamideimide contained in the porous membrane production varnish of the present invention includes (1) a polymer obtained by reacting an acid such as trimellitic anhydride with diisocyanate, and (2) trimellitic anhydride chloride. It may be a polymer obtained by imidizing a precursor polymer obtained by the reaction of a reactive derivative of the acid and a diamine. In the present specification and claims, the “polyamideimide precursor” means a polymer (precursor polymer) before imidization.
Polyamideimide may be any of the above polymers, raw material monomers, oligomers or precursors, and may be used alone or in combination of two or more.

[Fine particles (B)]
The porous membrane manufacturing varnish of the present invention further contains fine particles (B).
The material of the fine particles (B) used in the present invention is not particularly limited as long as it can be removed from the resin-fine particle composite film later, and any known material can be used. When the varnish of the present invention contains a solvent, it may be insoluble in the solvent used.

The material of the fine particles (B) is not particularly limited, and examples of the inorganic material include metal oxides such as silica (silicon dioxide), titanium oxide, and alumina (Al ₂ O ₃ ). Include organic polymer fine particles such as high molecular weight olefin (polypropylene, polyethylene, etc.), polystyrene, epoxy resin, cellulose, polyvinyl alcohol, polyvinyl butyral, polyester, polyether, and the like. Among them, silica is preferable, and specifically, colloidal silica, in particular, monodispersed spherical silica particles are selected, which hardly causes repelling in the unfired composite film and forms uniform pores in the obtained porous film. It is preferable because it is easy.

The fine particles (B) used in the present invention preferably have a high sphericity and a small particle size distribution index. The fine particles having these conditions are excellent in dispersibility in the varnish and can be used in a state where they do not aggregate with each other.
The average particle diameter of the fine particles (B) used is preferably, for example, 100 to 2000 nm, and more preferably 100 to 1000 nm. By satisfying these conditions, the pore diameter of the porous film obtained by removing the fine particles can be made uniform, which is preferable in that the electric field applied to the separator can be made uniform.
The fine particles (B) may be used alone or in combination of two or more.

In the varnish for producing a porous membrane of the present invention, the content of the fine particles (B) is preferably 65% by volume or more based on the total of the resin (A) and the fine particles (B). Within the above range, the porosity of the obtained porous film is unlikely to decrease, and the shrinkage ratio during baking of the obtained unfired composite film is unlikely to increase.
The content of the fine particles (B) with respect to the sum of the resin (A) and the fine particles (B) is preferably 95% by volume, more preferably 90% by volume, and preferably 65% by volume as the lower limit. 70 volume% is more preferable, and 72 volume% is still more preferable. When the upper limit of the content of the fine particles is within the above range, the fine particles are less likely to aggregate, and cracks and the like are less likely to occur on the surface. Therefore, it is possible to stably form a porous film with good electrical characteristics. .
In the present specification and claims, volume% and volume ratio are values at 25 ° C. The amount of the resin (A) is the amount of the solid content of the resin (A).

  When the unfired composite film containing the resin (A) and the fine particles (B) is baked to form a resin-fine particle composite film, and the material of the fine particles (B) is an inorganic material, the fine particles for polyimide or polyamideimide It is preferable to mix the fine particles (B) with a resin composed of polyamic acid, polyimide, polyamideimide precursor and / or polyamideimide so that the ratio of (B) is 2 to 6 (mass ratio). 5 (mass ratio) is more preferable. When the material of the fine particles (B) is an organic material, the fine particles and the polyamic acid, the polyimide, and the polyamideimide precursor so that the ratio of the fine particles (B) to the polyimide or polyamideimide is 1 to 3.5 (mass ratio). And / or a resin made of polyamideimide is preferably mixed, and more preferably 1.2 to 3 (mass ratio). Also, when the resin-fine particle composite film is used, the fine particles and the polyamic acid, polyimide, polyamideimide precursor and / or polyamide so that the volume ratio of the fine particles (B) to polyimide or polyamideimide is 1.5 to 4.5. It is preferable to mix with the resin which consists of imide, and it is more preferable to set it as 1.8-3 (volume ratio). If the mass ratio or volume ratio of the fine particles (B) to the polyimide or polyamideimide is equal to or higher than the lower limit when the resin-fine particle composite film is obtained, pores having an appropriate density as a separator can be obtained, and the upper limit is equal to or lower than the upper limit. Then, it is possible to form a film stably without causing problems such as an increase in viscosity and cracks in the film.

  Moreover, in the varnish for producing a porous membrane of the present invention, the total content of the solid content of the resin (A) and the fine particles (B) is the total solid content in the varnish for producing the porous membrane described later (the solvent described later). For example, it is preferably 90% by mass or more, more preferably 95% by mass or more, and various manufacturing processes that are adjusted to substantially 99 to 100% by mass. Even more preferable in terms of stability.

[Surfactant (C)]
The varnish for producing a porous film of the present invention further contains a silicon atom and / or fluorine atom-containing surfactant (C) having an alkylene oxide chain (hereinafter sometimes simply referred to as “surfactant (C)”). Containing. Since the varnish for producing a porous membrane of the present invention contains the surfactant (C), an unfired composite membrane that hardly causes repelling can be provided.

  In the present specification and claims, the “alkylene oxide chain” means a group represented by —O—R— (R represents a linear or branched alkylene group). R is preferably a linear or branched alkylene group having 1 to 5 carbon atoms, and more preferably a linear or branched alkylene group having 1 to 3 carbon atoms.

Examples of the surfactant (C) used in the present invention include a fluorine atom-containing surfactant and a silicon atom-containing surfactant. The fluorine atom-containing surfactant is represented by the following general formula (C1-0). Fluorine-based surfactant (C1) having an alkylene oxide chain containing a group to be formed (hereinafter sometimes simply referred to as “fluorine-based surfactant (C1)”) is preferable. A polysiloxane surfactant (C2) having an alkylene oxide chain (hereinafter sometimes simply referred to as “polysiloxane surfactant (C2)”) is preferred.
The surfactant (C) used in the present invention is preferably at least one selected from the group consisting of a fluorosurfactant (C1) and a polysiloxane surfactant (C2).
[In Formula (C1-0), R ^f represents a fluorinated alkyl group having 1 to 6 carbon atoms, and R ¹¹ represents an alkylene group having 1 to 5 carbon atoms or a single bond. ]

In the above formula (C1-0), R ^f has 6 or less carbon atoms.
The fluorinated alkyl group as R ^f preferably has 1 to 3 carbon atoms, and particularly preferably has 1 or 2 carbon atoms.
The fluorination rate of the fluorinated alkyl group (ratio of fluorine atoms in the fluorinated alkyl group) is preferably 10 to 100%, more preferably 50 to 100%, and all the hydrogen atoms are replaced with fluorine atoms. Most preferred is a fluorinated alkyl group (perfluoroalkyl group).
R ¹¹ is preferably a methylene group, an ethylene group or a propylene group, and most preferably a methylene group.

The fluorine-based surfactant (C1) preferably includes a compound having a structure represented by the following general formula (C1-1).
[In Formula (C1-1), R ^f is a fluorinated alkyl group having 1 to 6 carbon atoms, and R ¹¹ and R ¹² are each independently an alkylene group having 1 to 5 carbon atoms or a single bond. , R ¹³ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, n is an integer of 1 to 50, and m is 0 or 1. ]

In the formula (C1-1), ^{R f} and ^{R 11} are respectively the same as ^{R f} and ^{R 11} in the formula (C1-0).
R ¹² is preferably a methylene group or an ethylene group, and most preferably a methylene group.
R ¹³ is preferably a hydrogen atom, a methyl group or an ethyl group, and most preferably a methyl group.
As n, 1-40 are preferable, 3-35 are more preferable, 3-9 and 15-25 are still more preferable.
As m, 1 is preferable.

  The molecular weight of the fluorosurfactant (C1) is preferably 200 as the lower limit, more preferably 1200, and preferably 7000, more preferably 6000, and still more preferably 4500 as the upper limit. When the molecular weight of the fluorosurfactant (C1) is within the above range, the unfired composite film is less likely to be repelled.

  As the compound having the structure represented by the general formula (C1-1), at least one fluorine-based surfactant selected from the following chemical formulas (C1-1-1) to (C1-1-4) is preferable. The chemical formula (C1-1-2) or the chemical formula (C1-1-3) is more preferable, and the chemical formula (C1-1-3) is most preferable because it is particularly favorable in that it is less likely to cause repelling in the unfired composite film. .

  Preferable specific examples of the fluorosurfactant (C1) include, for example, Polyfox series PF-636, PF-6320, PF-656, and PF-6520 (all trade names, manufactured by Omninova). It is done. Among these, PF-656 and PF-6320 are particularly preferable because they are less likely to cause repelling in the unfired composite film.

[Polysiloxane surfactant (C2)]
In the present specification and claims, the “polysiloxane-based surfactant” means a surfactant having a main chain composed of repeated Si—O bonds.
The polysiloxane surfactant (C2) having an alkylene oxide chain has a repeating unit represented by the following general formula (C2-11) and a repeating unit represented by the following general formula (C2-12). It preferably contains an alkylene oxide chain-containing polydialkylsiloxane surfactant (C2-1) (hereinafter sometimes simply referred to as “polydialkylsiloxane surfactant (C2-1)”).
[In Formula (C2-11), R ¹ is a linear or branched alkyl group having 1 to 3 carbon atoms, and R ² is a linear or branched chain group having 1 to 15 carbon atoms. It is an alkyl group. In formula (C2-12), R ¹ is the same as above, and R ³ is a group having an alkylene oxide chain. ]

In the above formula (C2-11), R ¹ is preferably a methyl group, an ethyl group, a propyl group, or an isopropyl group, and more preferably a methyl group.
Examples of R ² include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, pentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, Examples include decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, and eicosyl group. Among these, a linear alkyl group is preferable, and methyl A group, an ethyl group, and a decyl group are more preferable.

In the above formula (C2-12), R ¹ is the same as above.
R ³ is a group having at least one alkylene oxide chain represented by —O—R— (wherein R represents a linear or branched alkylene group as described above) as described above. It does not specifically limit, For example, when it has two or more said alkylene oxide chains, R in each alkylene oxide chain may mutually be the same, and may differ.

R ³ is preferably a group represented by the following general formula (C2-12-1).
_{^{-R 4 -O- (R 5 -O)}} p -R 6 (C2-12-1)
[In Formula (C2-12-1), R ⁴ and R ⁵ are each independently a linear or branched alkylene group having 1 to 5 carbon atoms, and R ⁶ is a straight chain having 1 to 10 carbon atoms. It is a chain or branched alkyl group, and p is an integer of 0 to 10. ]

R ⁴ is preferably a linear alkylene group having 1 to 5 carbon atoms, and more preferably a linear alkylene group having 1 to 3 carbon atoms.
R ⁵ is preferably a linear or branched alkylene group having 1 to 3 carbon atoms, and includes an ethylene group, an n-trimethylene group (—CH ₂ CH ₂ CH ₂ —), an i-trimethylene group (—CH ₂ CH (CH ₃ ) —) is more preferable, and an ethylene group and i-trimethylene group are more preferable.
R ⁶ is preferably a linear or branched alkyl group having 1 to 7 carbon atoms, more preferably a linear or branched alkyl group having 1 to 5 carbon atoms, and 1 carbon atom. More preferred are ˜3 linear alkyl groups.
As p, the integer of 0-5 is preferable and the integer of 0-3 is more preferable.

The polydialkylsiloxane surfactant (C2-1) is particularly limited as long as it has each repeating unit represented by the general formula (C2-11) and the general formula (C2-12). It may be one having the two types of repeating units and other repeating units.
However, in order to sufficiently obtain the effect of containing the polydialkylsiloxane surfactant (C2-1), it is preferable that the above two types of repeating units are the main component, and at least one of the main chains is included. It is more preferable that the terminal is represented by the following general formula (C2-10), and it is still more preferable that both terminals of the main chain are represented by the following general formula (C2-10).
Here, “main component” means that the ratio of the two kinds of repeating units is 50 mol% or more with respect to the total of all repeating units constituting the component (C2-1), preferably 70 It is at least mol%, more preferably at least 80 mol%, most preferably at least 100 mol%.

[In formula (C2-10), R ¹ is the same as above. ]

The polydialkylsiloxane surfactant (C2-1) preferably has a thermal decomposition point of 130 ° C. or higher, more preferably 170 ° C. or higher.
When the thermal decomposition point is within the above range, it is possible to maintain a state in which the unfired composite film is less likely to be repelled until the baking process described below is completed, and to obtain a porous film that minimizes repelling. it can.
The thermal decomposition point indicates a temperature (° C.) at which the mass is decreased, which is measured under a temperature rising condition of 10 ° C./min with a thermal analyzer TG / DTA6200 (product name, manufactured by Seiko Instrument).

  Specific examples of the polydialkylsiloxane-based surfactant (C2-1) include BYK-307, BYK-333, BYK-378 (all trade names, manufactured by BYK Chemie) and the like. Among these, BYK-378 is preferable in that it hardly causes repelling in an unfired composite film, and BYK-333 is preferable in terms of excellent tensile strength and elongation in the obtained porous film.

  Each of the fluorine-based surfactant (C1) and the polysiloxane-based surfactant (C2) may be used alone or in combination of two or more. Further, the fluorine-based surfactant (C1) and the polysiloxane-based surfactant (C2) may be used in combination, but in the present invention, any one of them may be used to repel the unfired composite film. It is hard to produce.

  In the varnish for producing a porous membrane of the present invention, the content of the surfactant (C) is preferably 0.001 to 5% by mass relative to the total solid content in the varnish for producing a porous membrane, for example, 0 It is more preferably 0.005 to 1% by mass, still more preferably 0.01 to 0.05% by mass, and particularly preferably 0.013 to 0.02% by mass.

[Solvent (D)]
The varnish for producing a porous membrane of the present invention may further contain a solvent (D). The solvent (D) is preferably one that can dissolve the polyimide resin and does not dissolve the fine particles. Such a solvent is not particularly limited, and examples thereof include those exemplified as the solvent used for the reaction between tetracarboxylic dianhydride and diamine.

As the solvent (D) in the varnish for producing a porous membrane of the present invention, it may be blended separately from the resin (A), or when using a commercially available varnish as the resin (A), The solvent contained in the varnish of the product may be used as it is, or the latter may be the total of the latter and the solvent added separately from the resin (A).
As the solvent (D), one type may be used alone, or two or more types may be used in combination.

  In the varnish for producing a porous membrane of the present invention, the content of the solvent (D) is 60% by mass or more based on the whole varnish for producing the porous membrane (that is, the solid in the varnish for producing the porous membrane). It is preferable that the concentration is 40% by mass or less in view of applicability. The content of the solvent is such that the upper limit of the solid content concentration in the porous membrane production varnish is more preferably 35% by mass, even more preferably 30% by mass, and the lower limit is more preferably 10% by mass, The amount is more preferably 15% by mass, particularly preferably 20% by mass. When the content (or solid content concentration) of the solvent is within the above range, the coating property is good and the resulting unfired composite film is less likely to be repelled.

[Dispersant]
In the present invention, a dispersant may be further added together with the fine particles (B) for the purpose of uniformly dispersing the fine particles (B) in the varnish. By adding the dispersant, the resin (A) and the fine particles (B) can be mixed more uniformly, and furthermore, the fine particles (B) in the unfired composite film and the like can be uniformly distributed. As a result, it is possible to provide a dense opening on the surface of the finally obtained porous membrane and to efficiently communicate the front and back surfaces, and to improve the air permeability of the porous membrane. Furthermore, by adding a dispersant, the drying property of the varnish for producing a porous membrane of the present invention is easily improved, and the peelability of the formed unfired composite membrane from the substrate or the like is easily improved.

  The dispersing agent used for this invention is not specifically limited, A well-known thing can be used. For example, palm fatty acid salt, castor sulfate oil salt, lauryl sulfate salt, polyoxyalkylene allyl phenyl ether sulfate salt, alkylbenzene sulfonic acid, alkylbenzene sulfonate, alkyl diphenyl ether disulfonate, alkylnaphthalene sulfonate, dialkyl sulfosuccinate Anionic surfactants such as nate 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 , Behenyltrimethylammonium chloride, didecyldimethyl Cationic surfactants such as ammonium chloride; amphoteric surfactants such as coconut alkyldimethylamine oxide, fatty acid amidopropyldimethylamine oxide, alkylpolyaminoethylglycine hydrochloride, amidobetaine type activator, alanine type activator, lauryliminodipropionic acid Agent: polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene lauryl amine, polyoxyethylene oleylamine, polyoxyethylene polystyryl phenyl ether, polyoxyalkylene polystyryl phenyl ether, polyoxy Nonionic surfactant of alkylene primary alkyl ether or polyoxyalkylene secondary alkyl ether, polyoxyethylene dilaur Polyoxyethylene laurate, polyoxyethylenated castor oil, polyoxyethylenated hydrogenated castor oil, sorbitan lauric acid ester, polyoxyethylene sorbitan lauric acid ester, fatty acid diethanolamide and other polyoxyalkylene nonions 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, it is not limited to these. Moreover, the said dispersing agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  In the varnish for producing a porous membrane of the present invention, the content of the dispersant is preferably 0.01 to 5% by mass with respect to the fine particles (B), for example, from the viewpoint of film-forming properties. More preferably, it is -1 mass%, and it is still more preferable that it is 0.1-0.8 mass%.

[Preparation of varnish for porous membrane production]
Preparation of the varnish for producing a porous membrane of the present invention is performed by producing a varnish containing a resin (A) and in which fine particles (B) are dispersed. Specifically, the varnish for producing a porous membrane of the present invention can be prepared, for example, by mixing a solvent (D) in which fine particles (B) are dispersed in advance and a resin (A) at an arbitrary ratio, fine particles (B ) In advance in a solvent (D) in which the resin (A) is previously dispersed. As the latter method, for example, in a solvent (D) in which fine particles (B) are dispersed in advance, tetracarboxylic dianhydride and diamine are polymerized to form polyamic acid, or further imidized to form polyimide, Examples thereof include a method of polymerizing a raw material monomer (monomer component) and / or an oligomer thereof of polyamideimide to obtain a polyamideimide precursor (precursor polymer), or further imidizing to a polyamideimide.

<Method for producing porous membrane>
The method for producing a porous membrane of the present invention comprises a step of forming an unfired composite membrane using the varnish for producing a porous membrane of the present invention, and a step of baking the unfired composite membrane to form a resin- A baking step for obtaining a fine particle composite film, and a fine particle removing step for removing fine particles from the resin-fine particle composite film.

[Manufacture of unfired composite film (unfired composite film forming step)]
Hereinafter, a method for forming an unfired composite film in the present invention will be described. In the unfired composite film forming step, the unfired composite film is formed using the varnish for producing a porous film of the present invention. At that time, the unfired composite film may be formed on a substrate, or may be formed on a support different from the unfired composite film. The unfired composite film can be formed, for example, by applying the varnish for producing the porous film of the present invention on the substrate or the support.

  Examples of substrates include glass plates; polyolefin resins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate (PET); polycarbonates, styrene resins, polytetrafluoroethylene (PTFE), and fluorine such as polyvinylidene fluoride (PVDF). Plastic sheet made of resin, vinyl chloride resin and other resin; metal plate such as stainless steel plate and aluminum plate, etc. are mentioned, PET film, SUS substrate and glass substrate are preferable, and PET film and SUS substrate are more preferable.

The unfired composite film can also be formed on a support. Examples of the support include a support made of a fiber material such as a cellulose-based resin, a nonwoven fabric (for example, a polyimide nonwoven fabric, and the fiber diameter is, for example, about 50 nm to about 3000 nm), and a polyimide film. It is done.
When forming an unfired composite film on a support, a porous film is usually formed on the support, and the support can be used as a laminated film integrated with the porous film without peeling off. it can. In the case of using a support, an unfired composite film may be formed on the support placed on the substrate (that is, on the substrate and the support), and depending on the support, it is necessary to use a base material. In some cases, an unfired composite film can be formed on the support.
In the present specification and claims, the term “support” means such that it is integrated with the porous membrane to constitute a laminated membrane, and in this respect, in principle, finally from the porous membrane. Differentiated from the substrate to be peeled off.

The unfired composite film is, for example, coated on the substrate or the support with the varnish for producing the porous film of the present invention, and at 0 to 100 ° C. (preferably 0 to 90 ° C.) under normal pressure or vacuum, preferably By drying at 10 to 100 ° C. (more preferably 10 to 90 ° C.) under normal pressure, the film can be formed with a film thickness of 1 to 10 μm (preferably 1 to 8 μm), for example.
After drying, an unfired composite film having a plurality of layers may be formed using a similar varnish for producing a porous film. In this case, the varnish used on the upper layer side may not contain the component (C).

  In the method for producing a porous film of the present invention, the baking process further includes baking the unfired composite film or the laminated film of the unfired composite film and the support to obtain a resin-fine particle composite film. When the unfired composite film or the unfired composite film and the support are formed on the substrate, they may be baked as they are, or include the unfired composite film or the unfired composite film before entering the baking step. The laminated film may be peeled from the substrate. When the support is used, it is not necessary to peel the unfired composite film from the support as described above.

In forming the laminated film,
When the composition of the porous film production varnish used for forming each unfired composite film or the component (A) in the composition is the same, the laminated film is substantially one layer (single layer). Is referred to as a laminated film.

  In the case where the unfired composite film or the laminated film containing the unfired composite film is peeled from the substrate, a substrate provided with a release layer in advance can be used in order to further improve 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 application of the varnish. As the release agent used here, known release agents such as alkyl phosphate ammonium salt, fluorine-based or silicone can be used without particular limitation. When the dried unfired composite film is peeled off from the substrate, a slight release agent remains on the peeled surface of the unfired composite film, which may cause discoloration during baking and adverse effects on electrical characteristics. It is preferable. For the purpose of removing the release agent, a cleaning step of cleaning the unfired composite film peeled from the substrate or the laminated film including the unfired composite film using 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 composite film, the step of forming the release layer and the cleaning step can be omitted.

[Production of resin-fine particle composite membrane (baking process)]
The unfired composite film is subjected to post-treatment (baking) by heating to obtain a composite film (resin-particulate composite film) composed of a polyimide resin and fine particles. When the unfired composite film is formed on the support in the unfired composite film forming step, the support is also baked together with the unfired composite film in the baking step.
Baking in this step is a concept including drying and baking, and can be performed only by drying or drying and baking depending on the type of resin (A) used. Specifically, polyimide or polyamide can be used as the resin (A). When an imide is used, firing is not particularly necessary.

The baking temperature in the baking process varies depending on the structure of the unfired composite film and the support and the presence or absence of a condensing agent, but when drying, 0 to 100 ° C. is preferable under normal pressure or vacuum, and 10 to 100 under normal pressure. ° C is more preferred.
As drying performed in a baking process, when apply | coating the varnish for porous film manufacture of this invention on a board | substrate or a support body, and forming a non-baking composite film, it is 50-100 degreeC under normal pressure or a vacuum ( Preferably, it can be dried at 60 to 95 ° C. (more preferably 65 to 90 ° C.) under normal pressure.

  As baking temperature in a baking process, although it changes also with the presence or absence of a non-baking composite film and a condensing agent, when baking, 120-375 degreeC is preferable and 150-350 degreeC is more preferable. Further, when an organic material is used for the fine particles, it is necessary to set the temperature to be lower than the thermal decomposition temperature. When polyamic acid is used as the resin (A), it is preferable to complete imidization in the baking step.

  The firing conditions are, for example, a method in which the temperature is raised from room temperature to 375 ° C. in 3 hours and then held at 375 ° C. for 20 minutes, or the temperature is gradually raised from room temperature to 375 ° C. in increments of 50 ° C. (holding 20 minutes for each step) And a stepwise drying-thermal imidization method such as a final holding at 375 ° C. for 20 minutes can also be used. When an unsintered composite film is formed on a substrate and the unsintered composite film is once peeled off from the substrate, the end of the unsintered composite film is fixed to a SUS mold or the like to prevent deformation. You can also.

  The film thickness of the completed resin-fine particle composite film can be obtained by measuring and averaging the thicknesses of a plurality of locations using, for example, a micrometer. What average film thickness is preferable depends on the use of the resin-fine particle composite film or the porous film. For example, when used for a separator or the like, it is preferably 1 to 50 μm, and preferably 5 to 30 μm. More preferably.

[Porosification of resin-particle composite membrane (particle removal step)]
By removing the fine particles (B) from the resin-fine particle composite membrane by selecting an appropriate method, the porous membrane can be produced with good reproducibility.

  When silica is employed as the material of the fine particles (B), for example, it is possible to dissolve and remove the silica by treating the resin-fine particle composite film with low-concentration hydrogen fluoride water or the like.

Moreover, an organic material can also be selected as a material of the fine particles (B). Any organic material can be used without particular limitation as long as it decomposes at a lower temperature than the polyimide resin. For example, resin fine particles made of a linear polymer or a known depolymerizable polymer can be mentioned. A normal linear polymer is a polymer in which a polymer molecular chain is randomly cleaved during thermal decomposition, and a depolymerizable polymer is a polymer in which the polymer is decomposed into monomers during thermal decomposition. Any of them disappears from the resin-fine particle composite film by decomposing into low molecular weight substances or CO ₂ . The decomposition temperature of the resin fine particles used is preferably 200 to 320 ° C, more preferably 230 to 260 ° C. When the decomposition temperature is 200 ° C. or higher, film formation can be performed even when a high boiling point solvent is used for the varnish, and the range of selection of the baking conditions for the polyimide resin is widened. If the decomposition temperature is less than 320 ° C., only the resin fine particles can be lost without causing thermal damage to the polyimide resin.

  The total film thickness of the film produced by the production method of the present invention is not particularly limited, but when polyamic acid and / or polyimide is used as the resin (A), it may be 0.5 μm or more and 500 μm or less. Preferably, it is 1 μm or more and 30 μm or less, more preferably 3 μm or more and 10 μm or less, and when a polyamideimide precursor and / or polyamideimide is used as the resin (A), the upper limit is preferably 50 μm, 30 μm is more preferable, 10 μm is further preferable, 9 μm is still more preferable, and 8 μm can be set. The lower limit is preferably 0.5 μm, and more preferably 1 μm. The film thickness can be obtained by measuring and averaging the thickness of a plurality of locations with a micrometer, for example, as in the measurement of the resin-fine particle composite film.

As described above, the varnish for producing a porous film of the present invention can form an unfired composite film that is less likely to cause repelling. Therefore, the porous film obtained using this can be made into a thin film. The polyamideimide porous membrane obtained using a polyamideimide precursor and / or polyamideimide as the resin (A) can have a thickness of, for example, 10 μm or less (preferably 8 μm or less). Moreover, since the varnish for producing a porous membrane of the present invention contains a surfactant (C), the surface smoothness of the obtained unfired composite membrane and the subsequently obtained porous membrane is dramatically improved. Can do.
In the porous membrane, the surfactant (C) may be thermally decomposed in the baking process, and therefore the surfactant (C) is not present at all or the thermal decomposition product of the surfactant (C) remains. It may be in a state of being.

[Resin removal process]
The method for producing a porous membrane of the present invention removes at least a part of a resin portion made of a polyimide-based resin of a resin-fine particle composite membrane before the fine particle removal step, or at least the porous membrane after the fine particle removal step. It has a resin removal process which removes a part. By removing at least a part of the resin part of the resin-particulate composite film before the fine particle removal process, when the fine particles are removed and pores are formed in the subsequent fine particle removal process, at least a part of the resin part is removed. It is possible to improve the open area ratio of the porous film of the final product as compared with those not removed. Further, by removing at least a part of the porous film after the fine particle removing step, the porosity of the porous film of the final product can be improved as compared with the case where at least a part of the porous film is not removed. It becomes possible.

  The step of removing at least a part of the resin part or the step of removing at least a part of the porous film may be performed by a normal chemical etching method, a physical removal method, or a combination thereof. it can.

  Examples of the chemical etching method include treatment with a chemical etching solution such as an inorganic alkali solution or an organic alkali solution. Inorganic alkaline solutions are preferred. Examples of the inorganic alkaline solution include, 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, and sodium metasilicate, an ammonia solution, and a hydroxide. Examples thereof include an etching solution mainly composed of alkali, hydrazine, and 1,3-dimethyl-2-imidazolidinone. Organic alkaline solutions 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 alcohol amines such as triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; and alkaline solutions such as cyclic amines such as pyrrole and pihelidine.

  About the solvent of said each solution, pure water and alcohol can be selected suitably. Moreover, what added a suitable amount of surfactant can also 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, etc., an abrasive (eg, alumina (hardness 9), etc.) is dispersed in a liquid, and this is used as an aromatic polyimide film. Alternatively, a method of treating the surface of the polyimide film or polyamideimide film by irradiating the surface of the aromatic polyamideimide film at a speed of 30 to 100 m / s can be used.

  The above-described method is preferable because it can be applied to any resin removal step before or after the fine particle removal step.

  On the other hand, as a physical method applicable only to the resin removal step performed after the fine particle removal step, after pressure bonding to a mount film (for example, a polyester film such as a PET film) whose target surface is wetted with a liquid, without drying or after drying, A method of peeling the porous film from the mount film can also be adopted. Due to the surface tension or electrostatic adhesion force of the liquid, the porous film is peeled off from the mount film with only the surface layer of the porous film remaining on the mount film.

<Uses of porous membrane>
The porous membrane that can be produced by the production method of the present invention can be used as a separator for a lithium ion battery, a fuel cell electrolyte membrane, a gas or liquid separation membrane, or a low dielectric constant material. The porous membrane can be used as a separator for secondary batteries such as nickel cadmium, nickel metal hydride batteries, lithium ion secondary batteries, etc., but particularly used as a porous separator for lithium ion secondary batteries. preferable. In particular, when used as a separator of a lithium ion battery, the porous film according to the present invention can form a homogeneous thin film. Therefore, when the unfired composite film is laminated in the unfired composite film forming step, the present invention also relates to the present invention. Battery performance can be improved by setting the surface formed by the varnish for producing the porous membrane to the negative electrode surface side of the lithium ion battery.

[Secondary battery]
In the secondary battery that can use the porous membrane obtained by using the varnish for producing the porous membrane of the present invention, an electrolytic solution and a separator made of the porous membrane are disposed between the negative electrode and the positive electrode. The

  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 so as to satisfy the above conditions is impregnated with an electrolytic solution, and if this is a structure enclosed in an exterior, a nickel cadmium, nickel metal hydride battery, lithium ion It can use without limitation especially for well-known secondary batteries, such as a secondary battery.

  The negative electrode of the secondary battery can have a structure in which a negative electrode mixture composed of a negative electrode active material, a conductive additive and a binder is formed on a current collector. For example, as the negative electrode active material, cadmium hydroxide can be used in the case of a nickel cadmium battery, and a hydrogen storage alloy can be used in the case of a nickel metal 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 assistant constituting 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. For the current collector, copper foil, stainless steel foil, nickel foil, or the like can be used.

The positive electrode can have a structure in which a positive electrode mixture comprising a positive electrode active material, a conductive additive and a binder is formed on a current collector. For example, as the positive electrode active material, nickel hydroxide can be used in the case of a nickel cadmium battery, and nickel hydroxide or nickel oxyhydroxide can be used in the case of 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. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , 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. For the current collector, aluminum foil, stainless steel foil, 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 metal hydride battery, an aqueous potassium hydroxide solution is used. The electrolyte solution 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 , LiClO _{4 and the} like. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, vinylene carbonate, and the like. 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, but the separator made of the porous film produced by the production method of the present invention can be suitably applied to any shape.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, the scope of the present invention is not limited to these Examples.

In the examples and comparative examples, the following were used as surfactants.
Fluorine-based surfactant having an alkylene oxide chain: Polyfox series PF-656 (Omnova)

-Polysiloxane surfactant having an alkylene oxide chain: BYK-307, BYK-333, BYK-378 (all manufactured by BYK-Chemie)

Polyester-modified polydimethylsiloxane (BYK-310; manufactured by Big Chemie)
・ High molecular weight block copolymer (BYK-167; manufactured by Big Chemie)
・ Modified urea (BYK-410; manufactured by Big Chemie)

In the examples and comparative examples, the following were used.
Polyamideimide: Polyamideimide containing trimellitic anhydride and o-tolidine diisocyanate as polymerization components (Mw: about 30,000)
Polyamic acid solution: Reaction product of tetracarboxylic dianhydride (pyromellitic dianhydride) and diamine (4,4′-diaminodiphenyl ether) (reaction solvent: N, N-dimethylacetamide)
Fine particles (1): spherical silica having an average particle size of 300 nm Fine particles (2): spherical silica having an average particle size of 700 nm Dispersant: polyoxyethylene secondary alkyl ether dispersant Organic solvent (1): N, N -Mixed solvent / organic solvent (2) of dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP): Mixed solvent of DMAc and γ-butyrolactone (GBL) The above molecular weight is determined by gel permeation chromatography (GPC). ) Measured in terms of polystyrene.

Preparation Example 1 Preparation of polyamideimide-containing varnish (varnish for producing porous membrane) Polyamideimide 6.25% by mass, fine particles (1) 18.75% by mass, fluorosurfactant (0.02% by mass based on solid content) ), A dispersant (0.5% by mass with respect to silica), and the organic solvent (1) were mixed and stirred, so that the volume ratio of polyamideimide to silica was 34:66 (mass ratio was 25:75). A polyamideimide-containing varnish having a solid content concentration of 25% by mass (the solvent composition mass ratio is DMAc: NMP = 7: 3) was prepared.

Example 1 Preparation and evaluation of polyamideimide porous membrane [Preparation of porous membrane]
An unfired composite film was formed on the above-mentioned polyamideimide-containing varnish using an applicator on a PET film (base material). After baking at 100 ° C. for 5 minutes, the unfired composite film was peeled from the substrate to obtain a resin-fine particle composite film. This resin-fine particle composite membrane was immersed in a 10% HF solution for 10 minutes to remove fine particles contained in the membrane, and then washed with water and dried to obtain a polyamideimide porous membrane having a thickness of 10 μm.
[Chemical etching]
A 2.38% by mass aqueous solution of TMAH was diluted with a 50% by mass aqueous methanol solution to 1.04% to prepare an alkaline etching solution. The polyamideimide porous membrane was immersed in this etching solution for 80 seconds to remove a portion of the polyamideimide surface.

[Evaluation]
(Air permeability)
The porous film after chemical etching was cut into a 5 cm square, and used as a sample for measuring air permeability. Using a Gurley type densometer (manufactured by Toyo Seiki Co., Ltd.), the time required for 100 ml of air to pass through the sample was measured according to JIS P 8117.
As a result, the air permeability of the polyamideimide porous membrane was 64.8 seconds.

(Tensile strength)
The porous film after chemical etching was cut into a size of 1 cm × 5 cm to obtain a strip-shaped sample. The stress (MPa) at break of this sample was evaluated using RTC-1210A TENSILON (manufactured by ORIENTEC).
As a result, the tensile strength of the polyamideimide porous membrane was 23.8 MPa.

(Tensile elongation)
From the porous film after chemical etching, a dumbbell-shaped test piece having a shape according to the IEC450 standard was punched out to obtain a test piece for measuring tensile elongation. Using the obtained test piece, the elongation at break of the porous membrane was measured with a universal material testing machine (TENSILON, manufactured by Orientec Co., Ltd.) under conditions of a distance between chucks of 20 mm and a tensile speed of 2 mm / min.
As a result, the elongation of the polyamideimide porous membrane was 18.4%.

Comparative Example 1 Preparation of Polyamideimide-Containing Varnish for Comparison and Formation and Evaluation of Coating Film A comparative polyamideimide-containing varnish was obtained in the same manner as in Preparation Example 1, except that no surfactant was used. And it apply | coated with the film thickness of 10 micrometers using the applicator on PET film (base material). As a result, as shown in the photograph in FIG. 1, the repelling occurred, and the film could not be peeled in close contact with the base material.

Preparation Example 2 Preparation of polyamic acid-containing varnish (varnish for producing porous membrane) (1) First varnish (varnish for producing porous membrane)
Mixing and stirring the fine particles (1), the polyamic acid solution (polyamic acid concentration 18.9% by mass), the surfactant described in Table 1 (0.02% by mass of solid content) and the organic solvent (2) A first varnish having a volume ratio of acid to fine particles of 22:78 (mass ratio of 15:85) and a solid content concentration of 25 mass% (solvent composition mass ratio of DMAc: GBL = 9: 1) was prepared. .
(2) Second varnish (varnish for upper layer)
The fine particle (1) is changed to the fine particle (2), the surfactant is not added, the volume ratio of the polyamic acid to the fine particle is 28:72 (mass ratio is 20:80), and the solid content concentration is 35% by mass ( A second varnish having a solvent composition mass ratio of DMAc: GBL = 9: 1) was prepared.

Examples 2 to 5 and Comparative Examples 2 to 5 Preparation and Evaluation of Polyimide Porous Membrane [Formation of Polyimide-Fine Particle Composite Film (Single Layer)]
Said 1st varnish was apply | coated using the applicator on PET film, and baked at 70 degreeC for 5 minute (s), and the unbaking composite film (single layer) with a film thickness of about 25 micrometers was formed.
After peeling off the unfired composite film from the PET film, heat treatment was performed at 320 ° C. for 15 minutes to complete imidization to obtain a polyimide-fine particle composite film (single layer).

[Film formation of polyimide-fine particle composite film (two layers)]
The first varnish was applied onto a PET film using an applicator and pre-baked at 70 ° C. for 1 minute to form an unfired composite film having a thickness of about 3 μm. Subsequently, an unfired composite film was formed on the second varnish using an applicator. By baking at 70 ° C. for 5 minutes, an unfired composite film (laminated film) having a film thickness of 25 μm was formed.
After the laminated film was peeled from the PET film, heat treatment was performed at 320 ° C. for 15 minutes to complete imidization to obtain a polyimide-fine particle composite film (two layers).

[Formation of porous polyimide film (single layer or double layer)]
The polyimide-fine particle composite film (single layer or double layer) is immersed in a 10% by mass HF solution for 10 minutes to remove the fine particles contained in the film, and the porous polyimide film (single layer or double layer) )

[Chemical etching]
A 2.38% by mass aqueous solution of TMAH was diluted with a 50% by mass aqueous methanol solution to 1.04% to prepare an alkaline etching solution. A porous polyimide film (single layer or two layers) was immersed in this etching solution for 80 seconds to remove a part of the polyimide surface.

[Evaluation]
The unfired composite film (single layer and double layer) obtained above was evaluated for the presence or absence of repelling according to the following, and for the porous polyimide film, the air permeability, tension as the film characteristics of the porous film after chemical etching Strength and tensile elongation were evaluated according to the methods described above. The single layer and the double layer had the same results. The results for the two layers are shown in Table 1.

(With or without repelling)
The surface (21 cm × 30 cm) of the obtained unfired composite film was visually observed to evaluate the presence or absence of repelling. The evaluation criteria are as follows.
○: No repelling or repelling less than several points was observed.
X: Several or more repelling was observed.

  As is clear from Table 1, in Examples using a surfactant having an alkylene oxide chain, almost no repelling in the unfired composite film was observed or even if it was observed, it remained at about 1 to 4 points. Air permeability, tensile strength, and tensile elongation were all good. On the other hand, in the comparative examples in which the surfactant having an alkylene oxide chain was not used, several or more repellings were observed in the unfired composite film.

Claims (10)

At least one resin (A) selected from the group consisting of polyamide acid, polyimide, polyamideimide precursor and polyamideimide,
Fine particles (B), and
Silicon atom and / or fluorine atom-containing surfactant having an alkylene oxide chain (C)
A varnish for producing a porous membrane, comprising Said (C) is
Fluorine-based surfactant (C1) having an alkylene oxide chain containing a group represented by the following general formula (C1-0) and polysiloxane-based surfactant (C2) having an alkylene oxide chain
Surfactant (C) which is at least one selected from the group consisting of
The varnish for producing a porous membrane according to claim 1, wherein
[In Formula (C1-0), R ^f represents a fluorinated alkyl group having 1 to 6 carbon atoms, and R ¹¹ represents an alkylene group having 1 to 5 carbon atoms or a single bond. ] The said fluorinated surfactant (C1) is a varnish for porous membrane manufacture of Claim 2 containing the compound which has a structure represented by the following general formula (C1-1).
[In Formula (C1-1), R ^f is a fluorinated alkyl group having 1 to 6 carbon atoms, and R ¹¹ and R ¹² are each independently an alkylene group having 1 to 5 carbon atoms or a single bond. , R ¹³ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, n is an integer of 1 to 50, and m is 0 or 1. ] The polysiloxane surfactant (C2) having an alkylene oxide chain has a repeating unit represented by the following general formula (C2-11) and a repeating unit represented by the following general formula (C2-12). The varnish for manufacturing a porous membrane according to claim 2 or 3, comprising an alkylene oxide chain-containing polydialkylsiloxane surfactant (C2-1).
[In Formula (C2-11), R ¹ is a linear or branched alkyl group having 1 to 3 carbon atoms, and R ² is a linear or branched chain group having 1 to 15 carbon atoms. It is an alkyl group. In formula (C2-12), R ¹ is the same as described above, and R ³ is a group having an alkylene oxide chain. ]   The varnish for producing a porous membrane according to any one of claims 1 to 4, wherein the content of the fine particles (B) is 65% by volume or more based on the total of the resin (A) and the fine particles (B). .   The varnish for producing a porous membrane according to any one of claims 1 to 5, wherein the resin (A) is polyamideimide. An unfired composite film forming step of forming an unfired composite film using the varnish for producing a porous film according to any one of claims 1 to 6,
Baking the unfired composite film to obtain a resin-fine particle composite film;
A fine particle removal step of removing fine particles from the resin-fine particle composite film;
A method for producing a porous membrane having   The method for producing a porous membrane according to claim 7, wherein the porous membrane has a thickness of 10 μm or less. The porous membrane is formed on a substrate and / or a support,
In the unfired composite film forming step, the unfired composite film is formed on the substrate and / or support.
The method for producing a porous membrane according to claim 6 or 7.   A polyamide-imide porous membrane having a thickness of 10 μm or less.