JP6701833B2 - Method for producing porous polyimide film, and porous polyimide film - Google Patents

Description

  The present invention relates to a method for producing a porous polyimide film and a porous polyimide film.

  Polyimide resin is a material having excellent properties such as mechanical strength, chemical stability, and heat resistance, and a porous polyimide film having these properties has attracted attention.

For example, in Patent Document 1, a close-packed deposit body of monodisperse spherical inorganic particles is fired to form a sintered body of inorganic particles, and polyamic acid is filled in the inorganic particle gaps of the sintered body, and then fired. A method for producing a lithium secondary battery separator is described, in which the inorganic resin is formed by immersing it in a solution in which the inorganic particles are dissolved but the resin is not.
Patent Document 2 describes an organic porous body having holes made of polyimide and an ionic conductor having an electrolyte material containing a cation component and an anion component held in the holes.
Patent Document 3 discloses a varnish manufacturing process for manufacturing a varnish by mixing a polyamic acid or a polyimide, silica particles and a solvent to manufacture a varnish, or polymerizing a polyamic acid or a polyimide in a solvent in which silica particles are dispersed to manufacture a varnish. After the varnish produced in the production process is formed into a film on the substrate, the imidization is completed to produce a polyimide-silica composite film, and a composite film production process of producing the polyimide-silica composite film, and the polyimide-silica composite film produced in the composite film production process. A method for producing a porous polyimide film having a silica removing step of removing silica is described.
In Patent Document 4, after the silica particles are filled, sintering is performed to obtain a porous silica mold, a porous silica mold manufacturing process, and a porous silica mold obtained in the porous silica mold manufacturing process. There is described a method for producing a porous polyimide having a polyimide filling step of filling the voids with polyimide and a silica removing step of removing silica from the porous silica mold filled with polyimide to obtain a porous polyimide.

In Patent Document 5, a positive electrode, a negative electrode, and a separator layer having an average pore size of 5 μm or less and including a porous polyimide film formed into a porous film by phase separation after application of a solution of polyimide or a polyimide precursor. , A non-aqueous electrolyte secondary battery is described.
In Patent Document 6, a heat-resistant resin such as polyimide, heat-extinguishing resin particles containing a polyoxyalkylene resin, and a solvent are mixed to prepare a resin composition for a film, and a resin composition for a film is manufactured. It describes a method for producing a porous resin film, which includes a step of forming a film and a step of heating the formed resin composition for a film.
In Patent Document 7, a polyimide precursor solution is formed into a film by using a solution in which a resin such as water-soluble polyethylene glycol is dissolved, and then contacted with a poor solvent such as water to precipitate a polyamic acid and to make it porous. Methods of promoting and imidizing are described.

Japanese Patent No. 5331627 JP, 2008-034212, A JP, 2012-107144, A JP, 2011-111470, A JP, 10-302749, A JP, 2010-024385, A JP, 2014-240189, A

  An object of the present invention is to form a coating film containing a polyimide precursor solution and particles that are insoluble in the polyimide precursor solution, and then dry the coating film to form a coating film containing the polyimide precursor and particles. And a second step of heating the coating to imidize the polyimide precursor to form a polyimide film, the second step including a treatment for removing particles. In the manufacturing method, it is an object of the invention to provide a method for manufacturing a porous polyimide film in which the manufacturing process is simplified as compared with the case where the solvent for dissolving the polyimide precursor solution in the polyimide precursor solution is only an organic solvent.

  In order to achieve the above object, the following inventions are provided.

The invention according to < 1 > is
In an aqueous solvent, a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved, and after forming a coating film containing resin particles not soluble in the polyimide precursor solution, the coating film is dried, A first step of forming a coating containing the polyimide precursor and the resin particles,
A second step of heating the coating to imidize the polyimide precursor to form a polyimide film, the second step including a treatment of removing the resin particles;
A method for producing a porous polyimide film having

The invention according to < 2 > is
In the first step, a resin particle dispersion liquid containing the resin particles, an organic solvent in which the resin particles are insoluble, and a binder resin soluble in the organic solvent is applied onto a substrate and dried to form a resin particle layer. After the formation, the polyimide precursor solution is impregnated between the resin particles of the resin particle layer to form a coating film containing the resin particles, and the coating film is dried to form the coating film. It is a method for producing a porous polyimide film according to < 1 > .

The invention according to < 3 > is
In the first step, the polyimide precursor solution and a resin particle-dispersed polyimide precursor solution containing resin particles that are not soluble in the polyimide precursor solution are applied onto a substrate to form a coating film, and the coating film is formed. The method for producing a porous polyimide film according to < 1 > , which is a step of forming a coating film by drying.

The invention according to < 4 > is
The porous polyimide film according to any one of < 1 > to < 3 > , wherein in the first step, a process of exposing the resin particles is performed in a process of drying the coating film to form the coating film. Is a manufacturing method.

The invention according to < 5 > is
In the second step, a process of exposing the resin particles is performed after the process of performing the imidization of the polyimide precursor or after the imidization and before the process of removing the resin particles < 1 > to < >. < 3 > The method for producing a porous polyimide film according to any one of < 3 > .

The invention according to < 6 > is
The method for producing a porous polyimide film according to any one of < 1 > to < 5 > , wherein the treatment for removing the resin particles is a treatment for removing the resin particles with an organic solvent that dissolves the resin particles.

The invention according to < 7 > is
The method for producing a porous polyimide film according to any one of < 1 > to < 6 > , wherein the treatment for removing the resin particles is a treatment for removing by heating.

The invention according to < 8 > is
The said organic amine compound is a manufacturing method of the porous polyimide film as described in any one of < 1 > - < 7 > which is a tertiary amine compound.

The invention according to < 9 > is
The method for producing a porous polyimide film according to any one of < 1 > to < 7 > , wherein the organic amine compound is an amine compound having a nitrogen-containing heterocyclic structure.

The invention according to < 10 > is
It is a porous polyimide film manufactured by the method described in any one of < 1 > to < 9 > .

According to the invention of < 1 > , < 2 >, or < 3 > , after forming a coating film containing a polyimide precursor solution and particles that are not dissolved in the polyimide precursor solution, the coating film is dried to obtain a polyimide. A first step of forming a coating film containing a precursor and particles, and a second step of heating the coating film to imidize the polyimide precursor to form a polyimide film, which includes a treatment of removing particles. In the method for producing a porous polyimide film having the step 2), a porous material in which the production step is simplified as compared with the case where the solvent for dissolving the polyimide precursor solution in the polyimide precursor solution is only an organic solvent. A method for manufacturing a polyimide film is provided.

According to the invention of < 4 > or < 5 > , in the process of drying the coating film to form the coating film, when the process of exposing the resin particles is not performed, or the process of imidizing the polyimide precursor Or after imidization, and prior to the treatment for removing the resin particles, compared to the case where the treatment for exposing the resin particles is not performed, a porous polyimide film having a high porosity is obtained. A method of manufacturing the same is provided.

According to the invention of < 6 > or < 7 > , the treatment for removing the resin particles is performed by removing the resin particles as compared with the case where the solvent for dissolving the polyimide precursor solution in the polyimide precursor solution is only the organic solvent. There is provided a method for producing a porous polyimide film, in which the production process is simplified even if it is a treatment for removing it by an organic solvent that dissolves it, or a treatment for removing it by heating.

According to the invention of < 8 > or < 9 > , a method for producing a porous polyimide film having excellent film-forming properties and high strength as compared with the case where the organic amine compound is a primary or secondary amine compound is provided. Provided.

According to the invention of < 10 > , after forming a coating film containing a polyimide precursor solution and particles that are not dissolved in the polyimide precursor solution, the coating film is dried to form a coating film containing the polyimide precursor and particles. Pores having a first step of forming and a second step of heating the coating to imidize the polyimide precursor to form a polyimide film, the second step including a treatment for removing particles. In the porous polyimide film obtained by the method for producing a high quality polyimide film, as compared with the case where the solvent that dissolves the polyimide precursor solution in the polyimide precursor solution is only an organic solvent, the occurrence of cracks is controlled to be porous. A polyimide film is provided.

It is process drawing which shows an example of the manufacturing method of the porous polyimide film of this embodiment. It is process drawing which shows another example of the manufacturing method of the porous polyimide film of this embodiment. It is process drawing which shows another example of the manufacturing method of the porous polyimide film of this embodiment. 9 is an electron micrograph of the surface of the porous polyimide film (PIF-8) obtained in Example 8. 9 is an electron micrograph of the surface of the porous polyimide film (PIF-9) obtained in Example 9. 3 is an electron micrograph of the surface of the porous polyimide film (PIF-10) obtained in Example 10.

  Hereinafter, an embodiment that is an example of the present invention will be described.

<Method for producing porous polyimide film>
The method for producing a porous polyimide film according to the present embodiment, an aqueous solvent, a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved, and a coating containing resin particles insoluble in the polyimide precursor solution. After forming a film, the coating film is dried to form a coating film containing the polyimide precursor and the resin particles, and the coating film is heated to imidize the polyimide precursor to form a polyimide. A second step of forming a film, the second step including a treatment of removing the resin particles.

  In the present embodiment, “not dissolved” means that the target substance substantially maintains the form of resin particles in the target liquid at 25° C., and is within a range of 3% by mass or less. Including dissolving in.

  In the method for producing a porous polyimide film according to the present embodiment, the above configuration simplifies the production process as compared with the case where the solvent in the polyimide precursor solution is only the organic solvent.

  The polyimide film is, for example, a polyimide precursor solution dissolved in an organic solvent (for example, N-methylpyrrolidone (hereinafter sometimes referred to as “NMP”) or N,N-dimethylacetamide (hereinafter, referred to as “DMAc”). It may be obtained by applying a polyimide precursor solution in a state of being dissolved in a highly polar solvent such as (in some cases) and then heat-molding.

  The porous polyimide film is formed into a film by using a polyimide precursor solution dissolved in an organic solvent, and then contacted with a poor solvent such as water, polyamic acid is precipitated, and after porosification, a method of imidizing, an organic solvent. It is obtained by a method such as removing particles by using the polyimide precursor solution and particles which are dissolved in. For example, as a method for producing a porous polyimide film, using a silica particle layer as a template, a method for obtaining a porous polyimide film having pores of a three-dimensional ordered array structure (3DOM structure), and a polyimide in which silica particles are dispersed are used. Examples include a method of preparing a coating film using a precursor solution, firing the coating film, and then removing silica particles to obtain a porous polyimide film. However, according to these methods, it is necessary to use a chemical such as hydrofluoric acid in the treatment for removing silica particles. Further, when a template for the silica particle layer is produced, it is necessary to perform high heat treatment at 1000° C. or higher to sinter in order to form the silica particle layer. When using a polyimide precursor solution in which silica particles are dispersed, when the surface of the silica particles is subjected to a hydrophobizing treatment and a treatment for improving the dispersibility of the silica particles in the polyimide precursor solution is performed. There is. Therefore, these manufacturing methods have low productivity and high cost.

Further, there is a method of forming a film from a resin composition of resin particles and a polyimide precursor solution dissolved in an organic solvent, and then removing the resin particles to obtain a porous polyimide film. In this case, NMP and DMAc have a very high dissolving power, and in general resin particles (for example, polystyrene resin particles, etc.), the organic solvent in which the polyimide precursor is dissolved causes the dissolution and the like. It may be difficult to obtain a polyimide film.
On the other hand, as resin particles, a dispersion liquid of a polyoxyalkylene resin that is difficult to dissolve in an organic solvent such as NMP is prepared, and mixed with a polyimide precursor solution dissolved in an organic solvent to prepare a resin composition, and a film is formed from this resin composition. After the formation, the resin particles are removed by heating to obtain a porous polyimide film. Since the resin particles are produced by emulsion polymerization or the like, it may be necessary to provide a step of substituting an organic solvent such as NMP for mixing with the polyimide precursor solution.

On the other hand, in the method for producing the porous polyimide film of this embodiment, the polyimide precursor is dissolved in the aqueous solvent. Since the dissolution of the resin particles and the like are suppressed by the aqueous solvent, it is easy to manufacture the porous polyimide film. Further, the step of substituting the organic solvent for the dispersion medium of the resin particles in the aqueous dispersion may be omitted.
Further, the method for producing the porous polyimide film of the present embodiment includes a method for producing a resin particle layer serving as a template using resin particles, but in producing the resin particle layer, the shape of the resin particles is maintained. The heating temperature (for example, 100° C.) for forming the resin particle layer in this state is sufficient. Therefore, the mold for the resin particle layer is manufactured without performing the high heat treatment at 1000° C. or higher required for manufacturing the mold for the silica particle layer, and the manufacturing process is simplified.

  From the above, it is considered that the manufacturing method of the porous polyimide film according to the present embodiment is simplified by the above-mentioned configuration as compared with the case where the solvent in the polyimide precursor solution is only the organic solvent.

  In addition, the porous polyimide film obtained by the method for producing a porous polyimide film of the present embodiment is likely to suppress the occurrence of cracks. It is presumed that this is because, in the method for producing the porous polyimide film of the present embodiment, the use of the resin particles effectively contributes to the relaxation of the residual stress in the imidization step of the polyimide precursor.

The porous polyimide film obtained by the method for producing a porous polyimide film of the present embodiment is likely to suppress variations in the shape of pores, the diameter of pores, and the like. The reason for this is presumed that the use of the resin particles effectively contributes to the relaxation of the residual stress in the imidization step of the polyimide precursor.
Further, the porous polyimide film obtained by the method for producing a porous polyimide film of the present embodiment has a polyimide precursor solution dissolved in an aqueous solvent, so that the boiling point of the polyimide precursor solution is about 100°C. Therefore, as the coating containing the polyimide precursor and the resin particles is heated, the solvent is quickly volatilized, and then the imidization reaction proceeds. The resin particles in the coating lose their fluidity and become insoluble in the organic solvent before they are deformed by heat. Therefore, it is considered that the shape of the holes is easily maintained and variation in the shape of the holes, the diameter of the holes, and the like is easily suppressed. Further, the aqueous solvent suppresses dissolution of the resin particles and the like. Therefore, the pore size of the porous polyimide film can be controlled by the particle size of the resin particles.

  When silica particles are used, it is difficult to absorb the volume shrinkage in the imidization process, and thus it is considered that the polyimide film after imidization is likely to be cracked. Further, when silica particles are used, it is considered that ions are likely to remain as impurities because a chemical such as hydrofluoric acid is used.

Hereinafter, a method for manufacturing the porous polyimide film according to this embodiment will be described.
In the description of the manufacturing method, the same reference numerals are given to the same components in the drawings to be referred to. In the reference numerals of each figure, 1 is a resin particle, 2 is a binder resin, 3 is a substrate, 4 is a release layer, 5 is a polyimide precursor solution, 7 is a hole, and 61 is a process of imidizing the polyimide precursor. The coating (polyimide film) and 62 represent a porous polyimide film.

  The method for producing a porous polyimide film according to the present embodiment has the above first step and the above second step. Hereinafter, the manufacturing method shown in FIG. 1 (an example of the manufacturing method according to this embodiment) will be described, but the manufacturing method is not limited thereto.

(First step)
In the first step, first, a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved in an aqueous solvent is prepared. Next, a coating film containing a polyimide precursor solution and resin particles that are insoluble in the polyimide precursor solution is formed on the substrate. Then, the coating film formed on the substrate is dried to form a coating film containing the polyimide precursor and the resin particles.

  In the first step, as a method of forming a coating film containing a polyimide precursor solution and resin particles that are not soluble in the polyimide precursor solution on a substrate, specifically, the following method may be mentioned. Be done.

  First, a resin particle dispersion liquid containing resin particles insoluble in the polyimide precursor solution, an organic solvent in which the resin particles are insoluble, and a binder resin soluble in the organic solvent is prepared. Next, this resin particle dispersion liquid is applied onto a substrate and dried to form a resin particle layer. In the resin particle layer formed on the substrate, for example, the resin particles adjacent to each other exist without being dissolved, and the resin particles adjacent to each other are bound by the binder resin. Then, voids are formed between the resin particles in the resin particle layer (see FIG. 1A).

On the other hand, a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved is prepared in advance in an aqueous solvent.
Then, the polyimide precursor solution prepared in advance is impregnated between the resin particles of the resin particle layer formed on the substrate. The polyimide precursor solution is filled in the voids formed between the resin particles of the resin particle layer by impregnating the resin particles of the resin particle layer with the polyimide precursor solution. In order to accelerate the filling, it is also preferable to reduce the pressure in the state where the polyimide precursor solution and the resin particles are in contact with each other to remove the gas component between the voids. After that, this coating film is dried to form a coating film containing a polyimide precursor and resin particles on the substrate (see FIG. 1B).

  The substrate on which the coating containing the polyimide precursor and the resin particles is formed is not particularly limited. Examples thereof include resin substrates such as polystyrene and polyethylene terephthalate; glass substrates; ceramic substrates; metal substrates such as iron and stainless steel (SUS); composite material substrates obtained by combining these materials. In addition, the substrate may be provided with a release layer, if necessary, by performing a release treatment with a silicone-based or fluorine-based release agent or the like.

The method for producing the resin particle dispersion is not particularly limited. For example, there may be mentioned a method in which resin particles which are not dissolved in a polyimide precursor solution, an organic solvent in which resin particles are not dissolved, and a binder resin which is dissolved in this organic solvent are weighed, and these are mixed and stirred. As the resin particles, a dispersion liquid of resin particles dispersed in advance may be prepared, or a commercially available product which has been dispersed in advance may be prepared. When preparing a dispersion liquid of resin particles dispersed in advance, the dispersibility of the resin particles may be enhanced by, for example, at least one of an ionic surfactant and a nonionic surfactant.
The binder resin may be dissolved in the above organic solvent in advance, or may be mixed with the resin particles and the organic solvent and dissolved.

  The ratio (mass ratio) of the resin particles to the binder resin in the resin particle dispersion is preferably in the range of resin particles:binder resin=100:0.5 or more and 100:50 or less. It is preferably in the range of 100:1 or more and 100:30 or less, and more preferably in the range of 100:2 or more and 100:20 or less. Within this range, in the resin particle layer formed by the resin particle dispersion, the binder resin covers a part or all of the surface of each resin particle, and a state in which adjacent resin particles are bound (primary To be adhered to: including a so-called pseudo-adhesion state) is easily formed. Then, voids that are in the state of an air layer are easily formed between the resin particles of the resin particle layer.

The resin particles are not particularly limited as long as they do not dissolve in the polyimide precursor solution. Examples thereof include resin particles obtained by polycondensing polymerizable monomers such as polyester resins and urethane resins, and resin particles obtained by radical polymerization of polymerizable monomers such as vinyl resins and olefin resins. . Examples of the resin particles obtained by radical polymerization include resin particles of (meth)acrylic resin, (meth)acrylic acid ester resin, styrene/(meth)acrylic resin, polystyrene resin, polyethylene resin and the like.
Among these, the resin particles are preferably at least one selected from the group consisting of (meth)acrylic resin, (meth)acrylic acid ester resin, styrene/(meth)acrylic resin, and polystyrene resin.
Further, the resin particles may be crosslinked or may not be crosslinked. In the imidization step of the polyimide precursor, non-crosslinked resin particles are preferable because they effectively contribute to the relaxation of residual stress.

  In addition, in this embodiment, "(meth)acryl" means including both "acryl" and "methacryl."

  Further, when the resin particles are, for example, vinyl resin particles, the synthetic method is not particularly limited, and known polymerization methods (emulsion polymerization, soap-free emulsion polymerization, suspension polymerization, miniemulsion polymerization, microemulsion) are used. Radical polymerization methods such as polymerization) can be applied.

  For example, when the emulsion polymerization method is applied to the production of vinyl resin particles, styrenes, monomers such as (meth)acrylic acid are added to water in which a water-soluble polymerization initiator such as potassium persulfate or ammonium persulfate is dissolved. In addition, if necessary, a surfactant such as sodium dodecylsulfate or diphenyl oxide disulfonate is added, and the mixture is heated with stirring to carry out polymerization to obtain vinyl resin particles.

Examples of the vinyl resin monomer include styrene, alkyl-substituted styrene (eg, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4 -Ethyl styrene, etc.), halogen-substituted styrene (for example, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), styrenes having a styrene skeleton such as vinylnaphthalene; Vinyl groups such as ethyl acidate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and trimethylolpropane trimethacrylate (TMPTMA). Esters having: Vinyl nitriles such as acrylonitrile and methacrylonitrile; Vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and vinyl isopropenyl ketone; (meth)acrylic acid, Examples thereof include vinyl resin units obtained by polymerizing monomers such as acids such as maleic acid, cinnamic acid, fumaric acid and vinyl sulfonic acid; bases such as ethyleneimine, vinylpyridine and vinylamine.
As other monomers, monofunctional monomers such as vinyl acetate, difunctional monomers such as ethylene glycol dimethacrylate, nonane diacrylate and decanediol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, etc. You may use together the polyfunctional monomer of.
Further, the vinyl resin may be a resin using these monomers alone or a resin which is a copolymer using two or more kinds of monomers.

  As described above, it is preferable that the resin particles are not crosslinked, but when the resin particles are crosslinked, when the crosslinking agent is used as at least a part of the monomer component, The proportion is preferably 0% by mass or more and 20% by mass or less, more preferably 0% by mass or more and 5% by mass or less, and particularly preferably 0% by mass.

  When the monomer used for the resin constituting the vinyl resin particles contains styrene, the proportion of styrene in the total monomer components is preferably 20% by mass or more and 100% by mass or less, and 40% by mass or more and 100% by mass. The following are more preferable.

The average particle size of the resin particles is not particularly limited. For example, the thickness is preferably 2.5 μm or less, preferably 2.0 μm or less, and more preferably 1.0 μm or less. The lower limit is not particularly limited, but it is preferably 0.001 μm or more, preferably 0.005 μm or more, and more preferably 0.01 μm or more.
The average particle size of the resin particles is the particle size distribution obtained by measurement with a laser diffraction particle size distribution measuring device (for example, LA-700 manufactured by Horiba Ltd.), and for the divided particle size range (channel), The cumulative distribution of the volume is subtracted from the small particle size side, and the particle size at which cumulative 50% of all particles is obtained is measured as the volume average particle size D50v.

The resin particles may be commercially available products. Specifically, as the crosslinked resin particles, for example, crosslinked polymethylmethacrylate (MBX-series, manufactured by Sekisui Plastics Co., Ltd.), crosslinked polystyrene (SBX-series, manufactured by Sekisui Plastics Co., Ltd.), methacrylic acid. Examples include copolymerized crosslinked resin particles of methyl and styrene (MSX-series, manufactured by Sekisui Plastics Co., Ltd.).
Examples of non-crosslinked resin particles include polymethylmethacrylate (MB-series, manufactured by Sekisui Plastics Co., Ltd.), (meth)acrylic acid ester/styrene copolymer (FS-series: manufactured by Nippon Paint Co., Ltd.). ) And the like.

  The binder resin is not particularly limited as long as it dissolves in an organic solvent and does not dissolve in a polyimide precursor solution. For example, acetal resin such as polyvinyl butyral resin; polyamide resin such as nylon; polyester resin such as polyethylene terephthalate and polyethylene naphthalate; polyolefin resin such as polyethylene and polypropylene; vinyl such as acrylic resin, polyvinyl chloride resin and polyvinylidene chloride resin. Resin; polyurethane resin; polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and the like. Polyvinyl acetal resin and aliphatic polyamide resin are preferable.

  As the organic solvent in which the resin particles are insoluble, alcohols such as methanol, ethanol and ethylene glycol; cellosolves such as ethylene glycol monomethyl ether; hydrocarbons such as hexane; ketones such as acetone; aromatics such as toluene; Examples thereof include esters such as ethyl acetate; nitriles such as acetonitrile. The organic solvent in which the resin particles are insoluble may contain water.

  Among these, alcohols and cellosolves are preferable from the viewpoint of the shape retention of the resin particles, and as the binder resin, resins soluble in alcohols and cellosolves (for example, acetal resin and polyamide resin) are preferable.

  The method of applying the resin particle dispersion liquid on the substrate is not particularly limited. For example, various methods such as a spray coating method, a spin coating method, a roll coating method, a bar coating method, a slit die coating method and an inkjet coating method can be mentioned.

  A resin particle layer is obtained by drying the coating film obtained by applying the resin particle dispersion liquid on the substrate. The drying temperature may be a temperature at which the shape of the resin particles is maintained and the resin particles are bound to each other (for example, 100° C.).

  Next, a polyimide precursor solution prepared in advance is impregnated between the resin particles of the resin particle layer formed above to form a coating film containing the polyimide precursor solution and the resin particles. Then, the coating film is dried to form a coating film containing the polyimide precursor and the resin particles.

The method of impregnating with the polyimide precursor solution is not particularly limited. For example, a method of immersing the substrate on which the resin particle layer is formed in a polyimide precursor solution, or a method of applying the polyimide precursor solution from above the resin particle layer formed on the substrate and impregnating the resin particle layer between particles. Etc.
Examples of the method for applying the polyimide precursor solution from the resin particle layer formed on the substrate include spray coating, spin coating, roll coating, bar coating, slit die coating, and inkjet coating. There are various methods. Further, between the resin particles forming the resin particle layer, in that the polyimide precursor solution is impregnated, after applying the polyimide precursor solution from the resin particle layer, the pressure is reduced, the polyimide precursor solution between the resin particles. It is preferable to use a vacuum impregnation filling method in which the polyimide precursor solution is efficiently impregnated into the voids between the resin particles.

The method of forming the coating film containing the polyimide precursor solution and the resin particles is not limited to the above method.
For example, the following method may be specifically mentioned. First, a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved in an aqueous solvent is prepared. Next, by mixing the polyimide precursor solution and resin particles that are not dissolved in the polyimide precursor solution, a polyimide precursor solution in which resin particles are dispersed (hereinafter, also referred to as "resin particle-dispersed polyimide precursor solution") and To do. Then, the resin particle-dispersed polyimide precursor solution is applied onto a substrate to form a coating film containing the polyimide precursor solution and the resin particles. The resin particles in this coating film are distributed in a state where aggregation is suppressed (see FIG. 3(A)). Then, the coating film is dried to form a coating film containing the polyimide precursor and the resin particles on the substrate.

  The method for producing the resin particle-dispersed polyimide precursor solution is not particularly limited. For example, a method of mixing a polyimide precursor solution and resin particles in a dry state, a method of mixing a polyimide precursor solution and a dispersion liquid in which resin particles are previously dispersed in an aqueous solvent, and the like can be mentioned. As the dispersion liquid in which the resin particles are previously dispersed in the aqueous solvent, a dispersion liquid of the resin particles in which the resin particles are previously dispersed in the aqueous solvent may be prepared, and the resin particles are preliminarily dispersed in the aqueous solvent. A dispersion of the product may be prepared. When preparing a dispersion liquid of resin particles dispersed in advance, the dispersibility of the resin particles may be enhanced by, for example, at least one of an ionic surfactant and a nonionic surfactant.

  In the polyimide precursor solution in which the resin particles are dispersed, the ratio of the resin particles is a mass ratio when the solid content of the polyimide precursor solution is 100, and the polyimide precursor solution solid content: resin particles = 100: It is preferable that the range is 20 or more and 100:600 or less. The range is preferably 100:25 or more and 100:550 or less, and more preferably 100:30 or more and 100:500 or less.

  The resin particle-dispersed polyimide precursor solution may include a binder resin that is not dissolved in the polyimide precursor solution. When the resin particle-dispersed polyimide precursor solution contains a binder resin, the binder resin covers a part or all of the periphery of the resin particles in the coating film, so that it becomes easier to control the pore diameter and the overlap between the pores. .. In addition, the binder resin is partially distributed in areas other than the periphery of the resin particles, and in the process of removing the resin particles described later, it is possible to provide a space for removing the resin particles out of the film, and thus the particles can be easily removed.

  Examples of the binder resin used in the resin particle-dispersed polyimide precursor solution include the same resins as the resins exemplified as the binder resin used in the resin particle dispersion liquid described above.

  The method of applying the resin particle-dispersed polyimide precursor solution on the substrate is not particularly limited. For example, various methods such as a spray coating method, a spin coating method, a roll coating method, a bar coating method, a slit die coating method and an inkjet coating method can be mentioned.

  As the coating amount of the polyimide precursor solution to obtain a coating film containing the polyimide precursor solution and resin particles obtained by the above method, the porosity of the porous polyimide film is increased, the coating film It is preferable that the resin particles are exposed from the surface. For example, when the polyimide precursor solution is impregnated between the resin particles forming the resin particle layer, the polyimide precursor solution may be impregnated so that the thickness is less than the thickness of the resin particle layer.

  When the resin particle-dispersed polyimide precursor solution is formed on the substrate, it is preferable to add resin particles in an amount such that the resin particles are exposed from the surface of the coating film.

  Then, after forming a coating film containing the polyimide precursor solution obtained by the above method and the resin particles, it is dried to form a coating film containing the polyimide precursor and the resin particles. Specifically, the coating film containing the polyimide precursor solution and the resin particles is dried by a method such as heat drying, natural drying, or vacuum drying to form a coating film. More specifically, the coating film is dried so that the solvent remaining in the coating film is 50% or less, preferably 30% or less with respect to the solid content of the coating film to form the coating film. This coating is in a state in which the polyimide precursor can be dissolved in water.

  Further, the coating film may be formed in such an amount that the resin particles are embedded in the coating film. In this case, in the first step, the resin particles may be exposed by performing a process of exposing the resin particles in the process of forming the film by drying after obtaining the coating film. By performing the process of exposing the resin particles, the porosity of the porous polyimide film is increased.

Specific examples of the process of exposing the resin particles include the following methods.
When the polyimide precursor solution is impregnated between the resin particles forming the resin particle layer and a coating film is formed so that the resin particle layer is buried, the polyimide precursor solution is present in the region of the thickness of the resin particle layer or more. (See FIG. 1B).

  After obtaining a coating containing a polyimide precursor solution and resin particles, the coating is dried, in the process of forming a coating containing a polyimide precursor and resin particles, as described above, the coating, the polyimide precursor It is in a state that it can be dissolved in water. When the coating film is in this state, the resin particles can be exposed by, for example, a wiping treatment or a water immersion treatment. Specifically, the polyimide precursor solution present in a region having a thickness equal to or greater than the thickness of the resin particle layer is present in a region having a thickness equal to or greater than the thickness of the resin particle layer, for example, by performing a process of exposing the resin particle layer by wiping with water. The existing polyimide precursor solution is removed. Then, the resin particles existing in the upper region of the resin particle layer (that is, the region of the resin particle layer on the side away from the substrate) is exposed from the surface of the coating (see FIG. 1C).

  Incidentally, in the case of forming a coating film on a substrate using a resin particle-dispersed polyimide precursor solution, even when a coating film in which resin particles are buried is formed, as a treatment for exposing the resin particles buried in the coating film, The same treatment as the treatment for exposing the resin particles can be adopted.

(Second step)
The second step is a step of heating the coating containing the polyimide precursor and the resin particles obtained in the first step to imidize the polyimide precursor to form a polyimide film. And a 2nd process contains the process which removes a resin particle. A porous polyimide film is obtained through the treatment for removing the resin particles.

  In the second step, in the step of forming the polyimide film, specifically, the coating containing the polyimide precursor and the resin particles obtained in the first step is heated to promote imidization and further heated. , A polyimide film is formed. Note that as imidization proceeds and the imidization ratio increases, it becomes difficult to dissolve in an organic solvent.

Then, in the second step, a process of removing the resin particles is performed. The resin particles may be removed in the process of heating the coating to imidize the polyimide precursor, or may be removed from the polyimide film after imidization is completed (after imidization).
In the present embodiment, the process of imidizing the polyimide precursor is to heat the coating containing the polyimide precursor and the resin particles obtained in the first step to promote imidization and complete imidization. The process of becoming a state before becoming a polyimide film after the above is shown.

  Specifically, the coating film in which the resin particles obtained in the first step are exposed is heated to imidize the polyimide precursor (hereinafter, the coating film in this state may be referred to as a “polyimide film”). A)), the resin particles are removed. Alternatively, the resin particles may be removed from the polyimide film after the imidization is completed. Then, a porous polyimide film from which the resin particles have been removed is obtained (see FIG. 1D).

  The process of removing the resin particles may be performed when the imidization ratio of the polyimide precursor in the polyimide film is 10% or more in the process of imidizing the polyimide precursor in terms of the removability of the resin particles. preferable. When the imidization ratio is 10% or more, it tends to be difficult to dissolve in an organic solvent and the form is easily maintained.

  Examples of the treatment for removing the resin particles include a method of removing the resin particles by heating, a method of removing the resin particles with an organic solvent that dissolves the resin particles, and a method of removing the resin particles by decomposing with a laser or the like. Among these, a method of removing the resin particles by heating and a method of removing the resin particles with an organic solvent that dissolves the resin particles are preferable.

  As a method of removing by heating, for example, in the process of imidizing the polyimide precursor, the resin particles may be decomposed and removed by heating for promoting imidization. In this case, there is no operation for removing the resin particles with a solvent, which is advantageous in reducing the number of steps. On the other hand, depending on the type of resin particles, decomposition gas may be generated by heating. Then, due to the decomposed gas, breakage or cracks may occur in the porous polyimide film. Therefore, in this case, it is preferable to adopt a method of removing the resin particles with an organic solvent that dissolves the resin particles. It is also effective to further heat the resin particles after removing them with an organic solvent that dissolves them to increase the removal rate.

  Examples of the method of removing the resin particles with an organic solvent that dissolves the resin particles include a method of bringing the resin particles into contact with an organic solvent that dissolves the resin particles (for example, immersing the resin particles in the solvent) to dissolve and remove the resin particles. In this state, immersion in a solvent is preferable because the dissolution efficiency of the resin particles can be increased.

  The organic solvent that dissolves the resin particles for removing the resin particles is not particularly limited as long as it is an organic solvent in which the polyimide film and the polyimide film that has completed imidization are not dissolved and the resin particles are soluble. is not. For example, ethers such as tetrahydrofuran; aromatics such as toluene; ketones such as acetone; esters such as ethyl acetate;

  If the aqueous solvent remains when dissolving the resin particles, the aqueous solvent is dissolved in a solvent that dissolves the resin particles, the polyimide precursor is deposited, a state similar to the so-called wet phase conversion method, It may be difficult to control the pore size. Therefore, it is preferable to dissolve and remove the resin particles with an organic solvent after reducing the amount of the remaining aqueous solvent to 20% by mass or less, preferably 10% by mass or less based on the mass of the polyimide precursor.

  In the second step, the heating method for heating the coating film obtained in the first step to promote imidization to obtain a polyimide film is not particularly limited. For example, there is a method of heating in two steps. When heating in two steps, the following heating conditions are specifically mentioned.

  The heating condition for the first stage is preferably a temperature at which the shape of the resin particles is maintained. Specifically, for example, the range of 50° C. or higher and 150° C. or lower is preferable, and the range of 60° C. or higher and 140° C. or lower is preferable. The heating time is preferably 10 minutes or more and 60 minutes or less. The higher the heating temperature, the shorter the heating time may be.

  The heating conditions in the second stage include, for example, heating at 150° C. or higher and 400° C. or lower (preferably 200° C. or higher and 390° C. or lower) for 20 minutes or longer and 120 minutes or shorter. By setting the heating conditions in this range, the imidization reaction can further proceed and a polyimide film can be formed. During the heating reaction, the temperature may be raised stepwise or gradually at a constant rate before the final heating temperature is reached.

  The heating conditions are not limited to the above two-step heating method, and for example, a one-step heating method may be adopted. In the case of the method of heating in one stage, for example, the imidization may be completed only by the heating conditions shown in the above second stage.

  In addition, in the first step, when the process of exposing the resin particles is not performed, in order to increase the porosity, in the second step, the process of exposing the resin particles is performed to expose the resin particles. Preferably. In the second step, the process of exposing the resin particles is preferably performed in the process of imidizing the polyimide precursor, or after the process of imidizing and before the process of removing the resin particles.

  For example, in the first step, a resin particle layer is formed on the substrate (see FIG. 2A), the polyimide precursor solution is impregnated between the resin particles of the resin particle layer, and the resin particles are buried. A coating film is formed (see FIG. 2B). Next, in the process of drying the coating film to form the coating film, the coating film containing the polyimide precursor and the resin particles is formed without performing the process of exposing the resin particles. The film formed by this method is a film in which the resin particle layer is buried. This coating is heated to expose the resin particles from the polyimide film after the process of imidizing the polyimide precursor before the removal treatment of the resin particles or after the imidization is completed (after imidization). Perform processing.

In the second step, the process of exposing the resin particles can be performed, for example, when the polyimide film is in the following state.
When the imidation ratio of the polyimide precursor in the polyimide film is less than 10% (that is, when the polyimide film can be dissolved in water), when the resin particles are exposed, they are buried in the polyimide film. Examples of the treatment for exposing the existing resin particles include a wiping treatment and a water immersion treatment.

Further, when the imidization ratio of the polyimide precursor in the polyimide film is 10% or more (that is, it is difficult to dissolve in an organic solvent) and when the imidization is completed, the resin particles In the case of performing the treatment for exposing the resin particles, there are a method of mechanically cutting with a tool such as sandpaper to expose the resin particles, and a method of decomposing the resin particles with a laser or the like to expose the resin particles.
For example, when mechanically cutting, a part of the resin particles existing in the upper region of the resin particle layer embedded in the polyimide film (that is, the region on the side of the resin particle layer away from the substrate) is The polyimide film existing above the particles is cut, and the cut resin particles are exposed from the surface of the polyimide film (see FIG. 2C).

  Then, the resin particles are removed from the polyimide film where the resin particles are exposed by the above-described resin particle removal treatment. Then, a porous polyimide film from which the resin particles have been removed is obtained (see FIG. 2D).

  When a coating film is formed on a substrate by using a resin particle-dispersed polyimide precursor solution, the resin particle-dispersed polyimide precursor solution is applied on the substrate to form a coating film in which resin particles are embedded (FIG. )reference). In the process of drying the coating film to form the coating film, if the coating film containing the polyimide precursor and the resin particles is formed without performing the process of exposing the resin particles, the coating film in which the resin particles are buried is formed. Then, the resin particle layer is buried in the film (polyimide film) in the process of heating and imidizing the film. As the treatment for exposing the resin particles performed in the second step in order to increase the porosity, the same treatment as the treatment for exposing the resin particles described above can be adopted. Then, the resin particles are cut together with the polyimide film existing above the resin particles, and the resin particles are exposed from the surface of the polyimide film (see FIG. 3B).

  Then, the resin particles are removed from the polyimide film where the resin particles are exposed by the above-described resin particle removal treatment. Then, a porous polyimide film from which the resin particles have been removed is obtained (see FIG. 3C).

  In the second step, the substrate for forming the coating film used in the first step may be peeled off when it becomes a dried coating film, and the polyimide precursor in the polyimide film is an organic solvent. It may be peeled when it becomes difficult to dissolve in, and may be peeled when it is in the state of a film in which imidization is completed.

  A porous polyimide film is obtained through the above steps. The porous polyimide film may be post-processed depending on the purpose of use.

Here, the imidization ratio of the polyimide precursor will be described.
The partially imidized polyimide precursor has, for example, a structure having a repeating unit represented by the following general formula (I-1), the following general formula (I-2), and the following general formula (I-3). Examples include precursors.

  In general formula (I-1), general formula (I-2), and general formula (I-3), A represents a tetravalent organic group, and B represents a divalent organic group. l represents an integer of 1 or more, and m and n each independently represent 0 or an integer of 1 or more.

  In addition, A and B have the same meanings as A and B in the general formula (I) described later.

  The imidization ratio of the polyimide precursor is the total number of bond parts (2l+2m+2n) of the bond parts (2n+m) that are imide ring-closed in the bond part of the polyimide precursor (reaction part of tetracarboxylic dianhydride and diamine compound). ) Represents the ratio. That is, the imidization ratio of the polyimide precursor is represented by “(2n+m)/(2l+2m+2n)”.

  The imidation ratio (value of “(2n+m)/(2l+2m+2n)”) of the polyimide precursor is measured by the following method.

-Measurement of imidization ratio of polyimide precursor-
-Preparation of Polyimide Precursor Sample (i) A polyimide precursor composition to be measured is applied onto a silicone wafer in a film thickness range of 1 μm to 10 μm to prepare a coating film sample.
(Ii) The coating film sample is immersed in tetrahydrofuran (THF) for 20 minutes to replace the solvent in the coating film sample with tetrahydrofuran (THF). The solvent to be immersed is not limited to THF, and can be selected from solvents that do not dissolve the polyimide precursor and that are miscible with the solvent component contained in the polyimide precursor composition. Specifically, alcohol solvents such as methanol and ethanol and ether compounds such as dioxane can be used.
(Iii) The coating film sample is taken out from THF, and N ₂ gas is blown onto the THF adhering to the surface of the coating film sample to remove it. Under a reduced pressure of 10 mmHg or less, the coating film sample is dried at 5° C. or more and 25° C. or less for 12 hours or more, and the polyimide precursor sample is prepared.

-Preparation of 100% imidized standard sample (iv) Similar to (i) above, a polyimide precursor composition to be measured is applied onto a silicone wafer to prepare a coating film sample.
(V) The coating film sample is heated at 380° C. for 60 minutes to carry out an imidization reaction to prepare a 100% imidization standard sample.

-Measurement and analysis (vi) The infrared absorption spectra of 100% imidized standard sample and polyimide precursor sample are measured using a Fourier transform infrared spectrophotometer (FT-730, manufactured by Horiba Ltd.). Aromatic ring-derived absorption peak near 1500 cm ^-1 and 100% imidization standard sample (Ab ratio 'for (1500cm ^-1)), absorption peaks derived from an imide bond in the vicinity of ^{1780cm -1 (Ab' (1780cm -1} )) Find I'(100).
(Vii) In the same manner, was measured on the polyimide precursor sample, relative to the aromatic ring derived absorption peak near ^{1500cm -1 (Ab (1500cm -1)} ), absorption peaks derived from imide bond near 1780 cm ^-1 (Ab ( The ratio I(x) of 1780 cm ⁻¹ )) is obtained.

Then, the measured absorption peaks I′(100) and I(x) are used to calculate the imidization ratio of the polyimide precursor based on the following formula.
Formula: Imidization ratio of polyimide precursor=I(x)/I′(100)
· Formula: I '(100) = ( Ab' (1780cm -1)) / (Ab '(1500cm -1))
- ^{Formula: I (x) = (Ab} (1780cm -1)) / (Ab (1500cm -1))

  The measurement of the imidization ratio of the polyimide precursor is applied to the measurement of the imidization ratio of the aromatic polyimide precursor. When measuring the imidization ratio of the aliphatic polyimide precursor, a peak derived from a structure that does not change before and after the imidization reaction is used as an internal standard peak instead of the absorption peak of the aromatic ring.

[Polyimide precursor solution]
Hereinafter, each component of the polyimide precursor solution according to this embodiment will be described.

(Polyimide precursor)
The polyimide precursor is a resin (polyamic acid) having a repeating unit represented by the following general formula (I).

(In the general formula (I), A represents a tetravalent organic group, and B represents a divalent organic group.)

Here, in the general formula (I), the tetravalent organic group represented by A is a residue obtained by removing four carboxyl groups from tetracarboxylic dianhydride as a raw material.
On the other hand, the divalent organic group represented by B is a residue obtained by removing two amino groups from a diamine compound as a raw material.

  That is, the polyimide precursor having the repeating unit represented by the general formula (I) is a polymer of tetracarboxylic dianhydride and diamine compound.

  Examples of the tetracarboxylic dianhydride include aromatic compounds and aliphatic compounds, but aromatic compounds are preferable. That is, in the general formula (I), the tetravalent organic group represented by A is preferably an aromatic organic group.

  Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, 3,3′,4,4′-biphenyl Sulfone tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 3,3',4,4'- Biphenyl ether tetracarboxylic acid dianhydride, 3,3′,4,4′-dimethyldiphenylsilane tetracarboxylic acid dianhydride, 3,3′,4,4′-tetraphenylsilane tetracarboxylic acid dianhydride, 1 ,2,3,4-furantetracarboxylic acid dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfide dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy) ) Diphenylsulfone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylpropane dianhydride, 3,3',4,4'-perfluoroisopropylidene diphthalic acid dianhydride, 3 ,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, bis(phthalic acid)phenylphosphine oxide dianhydride, p-phenylene -Bis(triphenylphthalic acid) dianhydride, m-phenylene-bis(triphenylphthalic acid) dianhydride, bis(triphenylphthalic acid)-4,4'-diphenylether dianhydride, bis(triphenylphthalic acid) Acid)-4,4′-diphenylmethane dianhydride and the like.

  Examples of the aliphatic tetracarboxylic dianhydride include butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and 1,3-dimethyl-1,2,3,4. -Cyclobutane tetracarboxylic acid dianhydride, 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride, 2,3,5-tricarboxycyclopentyl acetic acid dianhydride, 3,5,6-tricarboxy norbonane -2-Acetic acid dianhydride, 2,3,4,5-tetrahydrofuran tetracarboxylic acid dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid Aliphatic or alicyclic tetracarboxylic acid dianhydrides such as acid dianhydride and bicyclo[2,2,2]-oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride; 1 , 3,3a,4,5,9b-Hexahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,5 9b-Hexahydro-5-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,5 Aliphatic tetracarboxylic acid having aromatic ring such as 9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione Examples thereof include dianhydride.

  Among these, aromatic tetracarboxylic dianhydrides are preferable as the tetracarboxylic dianhydride, and specific examples thereof include pyromellitic dianhydride and 3,3′,4,4′-biphenyl. Tetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-biphenyl ether tetracarboxylic acid dianhydride, 3,3',4 , 4'-benzophenone tetracarboxylic dianhydride is preferable, and further pyromellitic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4' Benzophenone tetracarboxylic acid dianhydride is preferable, and 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride is particularly preferable.

In addition, tetracarboxylic dianhydride may be used individually by 1 type, and may be used in combination of 2 or more type.
When two or more kinds are used in combination, the aromatic tetracarboxylic acid dianhydride and the aliphatic tetracarboxylic acid dianhydride are combined with the aromatic tetracarboxylic acid dianhydride and the aliphatic tetracarboxylic acid dianhydride. You may combine things.

  On the other hand, the diamine compound is a diamine compound having two amino groups in its molecular structure. Examples of the diamine compound include aromatic compounds and aliphatic compounds, but aromatic compounds are preferable. That is, in the general formula (I), the divalent organic group represented by B is preferably an aromatic organic group.

Examples of the diamine compound include p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylethane, 4,4′-diaminodiphenyl ether and 4,4′-diaminodiphenyl sulfide. , 4,4'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, 3,3-dimethyl-4,4'-diaminobiphenyl, 5-amino-1-(4'-aminophenyl)-1,3,3 -Trimethylindane, 6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 4,4'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethylbenzanilide , 3,5-diamino-4'-trifluoromethylbenzanilide, 3,4'-diaminodiphenyl ether, 2,7-diaminofluorene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4' -Methylene-bis(2-chloroaniline), 2,2',5,5'-tetrachloro-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5,5' -Dimethoxybiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2-bis[4-(4- Aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene, 4,4′-bis(4-amino Phenoxy)-biphenyl, 1,3'-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, 4,4'-(p-phenyleneisopropylidene)bisaniline, 4,4' -(M-phenylene isopropylidene)bisaniline, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, 4,4'-bis[4-(4-amino Aromatic diamines such as 2-trifluoromethyl)phenoxy]-octafluorobiphenyl; aromatics having two amino groups bonded to an aromatic ring such as diaminotetraphenylthiophene and a hetero atom other than the nitrogen atom of the amino group. Group diamines: 1,1-metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, no Namethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadienylenediamine, hexahydro-4,7-methanoindanylene dimethylenediamine, tricyclo[6. 2,1,0 ^2.7 ]-undecylenedimethyldiamine, and aliphatic diamines such as 4,4′-methylenebis(cyclohexylamine) and alicyclic diamines.

  Among these, the diamine compound is preferably an aromatic diamine compound, and specifically, for example, p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide and 4,4'-diaminodiphenyl sulfone are preferable, and 4,4'-diaminodiphenyl ether and p-phenylenediamine are particularly preferable.

  The diamine compounds may be used alone or in combination of two or more. When two or more kinds are used in combination, the aromatic diamine compound or the aliphatic diamine compound may be used in combination, or the aromatic diamine compound and the aliphatic diamine compound may be combined.

The number average molecular weight of the polyimide precursor is preferably 1,000 or more and 150,000 or less, more preferably 5,000 or more and 130,000 or less, and further preferably 10,000 or more and 100,000 or less.
When the number average molecular weight of the polyimide precursor is within the above range, the decrease in the solubility of the polyimide precursor in a solvent is suppressed, and the film forming property is easily secured.

The number average molecular weight of the polyimide precursor is measured by the gel permeation chromatography (GPC) method under the following measurement conditions.
・Column: Tosoh TSK gel α-M (7.8 mm ID×30 cm)
Eluent: DMF (dimethylformamide)/30 mM LiBr/60 mM phosphoric acid Flow rate: 0.6 mL/min
・Injection volume: 60 μL
・Detector: RI (differential refractive index detector)

  The content (concentration) of the polyimide precursor may be 0.1% by mass or more and 40% by mass or less, preferably 0.5% by mass or more and 25% by mass or less, with respect to the total polyimide precursor solution. It is preferably 1% by mass or more and 20% by mass or less.

(Organic amine compound)
The organic amine compound is a compound that amine-chlorides a polyimide precursor (its carboxyl group) to enhance its solubility in an aqueous solvent and also functions as an imidization accelerator. Specifically, the organic amine compound is preferably an amine compound having a molecular weight of 170 or less. The organic amine compound may be a compound other than the diamine compound that is the raw material of the polyimide precursor.
The organic amine compound is preferably a water-soluble compound. Water-soluble means that the target substance dissolves in water at 1% by mass or more at 25°C.

Examples of organic amine compounds include primary amine compounds, secondary amine compounds, and tertiary amine compounds.
Among these, as the organic amine compound, at least one selected from a secondary amine compound and a tertiary amine compound (particularly, a tertiary amine compound) is preferable. When a tertiary amine compound or a secondary amine compound is applied as the organic amine compound (particularly, a tertiary amine compound), the solubility of the polyimide precursor in a solvent is likely to be increased, and the film-forming property is easily improved. The storage stability of the polyimide precursor solution is easily improved.

  Further, as the organic amine compound, in addition to the monovalent amine compound, a divalent or higher polyvalent amine compound may be mentioned. When a polyvalent amine compound having two or more valences is applied, a pseudo-crosslinked structure is easily formed between molecules of the polyimide precursor, and the storage stability of the polyimide precursor solution is easily improved.

Examples of the primary amine compound include methylamine, ethylamine, n-propylamine, isopropylamine, 2-ethanolamine, 2-amino-2-methyl-1-propanol, and the like.
Examples of the secondary amine compound include dimethylamine, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, morpholine and the like.
Examples of the tertiary amine compound include 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, methylmorpholine, ethylmorpholine, 1,2-dimethylimidazole, 2-ethyl-4. -Methylimidazole and the like.

  Here, as the organic amine compound, an amine compound having a nitrogen-containing heterocyclic structure (particularly, a tertiary amine compound) is also preferable from the viewpoint of film-forming property. Examples of the amine compound having a nitrogen-containing heterocyclic structure (hereinafter referred to as “nitrogen-containing heterocyclic amine compound”) include, for example, isoquinolines (amine compounds having an isoquinoline skeleton), pyridines (amine compounds having a pyridine skeleton). ), pyrimidines (amine compounds having a pyrimidine skeleton), pyrazines (amine compounds having a pyrazine skeleton), piperazines (amine compounds having a piperazine skeleton), triazines (amine compounds having a triazine skeleton), imidazoles (imidazole) Examples thereof include amine compounds having a skeleton), morpholines (amine compounds having a morpholine skeleton), polyaniline, polypyridine, and polyamine.

  The nitrogen-containing heterocyclic amine compound is preferably at least one selected from the group consisting of morpholines, pyridines, and imidazoles from the viewpoint of film-forming property, and more preferably N-methylmorpholine, pyridine, and picoline. More preferably, it is at least one selected from the group consisting of

  Among these, the organic amine compound is preferably a compound having a boiling point of 60°C or higher (preferably 60°C or higher and 200°C or lower, more preferably 70°C or higher and 150°C or lower). When the boiling point of the organic amine compound is 60° C. or higher, evaporation of the organic amine compound from the polyimide precursor solution is suppressed during storage, and the decrease in solubility of the polyimide precursor in the solvent is easily suppressed.

The organic amine compound may be contained in an amount of 50 mol% or more and 500 mol% or less, preferably 80 mol% or more and 250 mol% or less, with respect to the carboxyl group (-COOH) of the polyimide precursor in the polyimide precursor solution. , And more preferably 90 mol% or more and 200 mol% or less.
When the content of the organic amine compound is in the above range, the solubility of the polyimide precursor in a solvent is likely to increase, and the film forming property is likely to improve. In addition, the storage stability of the polyimide precursor solution also tends to be improved.

  The above organic amine compounds may be used alone or in combination of two or more.

(Aqueous solvent)
The aqueous solvent is an aqueous solvent containing water. Specifically, the aqueous solvent is preferably a solvent containing 50% by mass or more of water with respect to the total aqueous solvent. Examples of water include distilled water, ion-exchanged water, ultrafiltered water, pure water and the like.

  The content of water is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and further preferably 80% by mass or more and 100% by mass or less with respect to the total aqueous solvent.

  When the aqueous solvent contains a solvent other than water, examples of the solvent other than water include water-soluble organic solvents and aprotic polar solvents. As the solvent other than water, a water-soluble organic solvent is preferable from the viewpoints of transparency and mechanical strength of the polyimide molded body. In particular, in addition to transparency and mechanical strength, heat resistance, electrical characteristics, from the viewpoint of improving various properties of the polyimide molded article such as solvent resistance, the aqueous solvent does not contain an aprotic polar solvent, or contains a small amount. (For example, 40% by mass or less, preferably 30% by mass or less, based on the total aqueous solvent). Here, the term “water-soluble” means that the target substance dissolves in water at 1% by mass or more at 25° C.

  The above water-soluble organic solvents may be used alone or in combination of two or more.

  The water-soluble ether solvent is a water-soluble solvent having an ether bond in one molecule. Examples of the water-soluble ether solvent include tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether and the like. Among these, tetrahydrofuran and dioxane are preferable as the water-soluble ether solvent.

  The water-soluble ketone solvent is a water-soluble solvent having a ketone group in one molecule. Examples of the water-soluble ketone solvent include acetone, methyl ethyl ketone, and cyclohexanone. Among these, acetone is preferable as the water-soluble ketone solvent.

  The water-soluble alcohol solvent is a water-soluble solvent having an alcoholic hydroxyl group in one molecule. Examples of the water-soluble alcohol solvent include methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, ethylene glycol monoalkyl ether, propylene glycol, propylene glycol monoalkyl ether, diethylene glycol and diethylene glycol. Monoalkyl ether, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-butene- 1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 1,2,6-hexanetriol and the like can be mentioned. Among these, the water-soluble alcohol solvent is preferably methanol, ethanol, 2-propanol, ethylene glycol, ethylene glycol monoalkyl ether, propylene glycol, propylene glycol monoalkyl ether, diethylene glycol or diethylene glycol monoalkyl ether.

  When an aprotic polar solvent other than water is contained as the aqueous solvent, the aprotic polar solvent used together has a boiling point of 150° C. or higher and 300° C. or lower and a dipole moment of 3.0 D or higher and 5.0 D or lower. is there. Specific examples of the aprotic polar solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), Hexamethylenephosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, N,N-dimethylimidazolidinone (DMI), N,N'-dimethylpropyleneurea, tetramethylurea, trimethyl phosphate , Triethyl phosphate and the like.

  When a solvent other than water is contained as the aqueous solvent, the solvent used in combination preferably has a boiling point of 270°C or lower, preferably 60°C or higher and 250°C or lower, and more preferably 80°C or higher and 230°C or lower. is there. When the boiling point of the solvent used in combination is within the above range, it becomes difficult for the solvent other than water to remain in the polyimide molded body, and a polyimide molded body having high mechanical strength can be easily obtained.

  Here, the range in which the polyimide precursor is dissolved in the solvent is controlled by the content of water and the type and amount of the organic amine compound. When the content of water is low, the polyimide precursor is easily dissolved in the region where the content of the organic amine compound is low. On the contrary, when the content of water is high, the polyimide precursor is easily dissolved in the region where the content of the organic amine compound is high. Further, when the organic amine compound has a high hydrophilicity such as having a hydroxyl group, the polyimide precursor is easily dissolved in a region where the water content is high.

  In addition, a polyimide precursor synthesized with an organic solvent such as an aprotic polar solvent (for example, N-methylpyrrolidone (NMP)) is added to water or a poor solvent such as alcohol, precipitated, and separated to obtain polyimide. It may be a precursor.

(Other additives)
In the method for producing a porous polyimide film according to this embodiment, the polyimide precursor solution may include a catalyst for promoting the imidization reaction, a leveling material for improving the film-forming quality, and the like.
As the catalyst for promoting the imidization reaction, a dehydrating agent such as an acid anhydride, an acid catalyst such as a phenol derivative, a sulfonic acid derivative, a benzoic acid derivative, or the like may be used.

In addition, the polyimide precursor solution may include, for example, a conductive material (conductivity (eg, volume resistivity of less than 10 ⁷ Ω·cm)) or a conductive material added for imparting conductivity depending on the purpose of use of the porous polyimide film. It may contain semiconductivity (for example, volume resistivity of 10 ⁷ Ω·cm or more and 10 ¹³ Ω·cm or less).
Examples of the conductive agent include carbon black (for example, acidic carbon black having a pH of 5.0 or less); metal (for example, aluminum and nickel); metal oxide (for example, yttrium oxide and tin oxide); ion conductive substance (for example, titanium) Acid potassium, LiCl, etc.); and the like. These conductive materials may be used alone or in combination of two or more.

Further, the polyimide precursor solution may contain inorganic particles added for improving mechanical strength depending on the purpose of use of the porous polyimide film. Examples of the inorganic particles include particulate materials such as silica powder, alumina powder, barium sulfate powder, titanium oxide powder, mica and talc.
Further, it may contain LiCoO ₂ , LiMn ₂ O or the like used as an electrode of a lithium ion battery.

(Method for producing polyimide precursor solution)
The method for producing the polyimide precursor solution according to this embodiment is not particularly limited, but examples thereof include the following production methods.
As an example, a method of obtaining a polyimide precursor solution by polymerizing a tetracarboxylic dianhydride and a diamine compound in an aqueous solvent in the presence of an organic amine compound to produce a resin (polyimide precursor) can be mentioned. ..
According to this method, since an aqueous solvent is applied, the productivity is high, and the polyimide precursor solution is advantageous in that the process is simplified because it is produced in one step.

  As another example, a resin (polyimide precursor) is obtained by polymerizing a tetracarboxylic dianhydride and a diamine compound in an organic solvent such as an aprotic polar solvent (eg, N-methylpyrrolidone (NMP)). After being generated, the resin (polyimide precursor) is precipitated by adding it to water or an aqueous solvent such as alcohol. Then, a method of dissolving a polyimide precursor and an organic amine compound in an aqueous solvent to obtain a polyimide precursor solution can be mentioned.

<Porous polyimide film>
Hereinafter, the porous polyimide film of this embodiment will be described.

  In the porous polyimide film obtained by the method for producing a porous polyimide film according to this embodiment, the occurrence of cracks is suppressed.

(Characteristics of porous polyimide film)
The porous polyimide film of the present invention is not particularly limited, but preferably has a porosity of 30% or more. The porosity is preferably 40% or more, more preferably 50% or more. The upper limit of the porosity is not particularly limited, but is preferably 90% or less.

  The shape of the holes is preferably spherical or nearly spherical. Further, it is preferable that the holes have a shape in which the holes are connected to each other to be continuous (see FIGS. 1D, 2D, and 3C). The pore diameter of the portion where the pores are connected to each other is, for example, preferably 1/100 or more and 1/2 or less of the maximum diameter of the pores, and preferably 1/50 or more and 1/3 or less. , 1/20 or more and 1/4 or less is more preferable. Specifically, it is preferable that the average value of the pore diameters of the portion where the pores are connected and continuous to each other is 5 nm or more and 1500 nm or less.

  The average value of pore diameters is not particularly limited, but is preferably in the range of 0.01 μm or more and 2.5 μm or less, more preferably in the range of 0.05 μm or more and 2.0 μm or less, and 0.1 μm or more and 1.5 μm or less. The following range is preferable, and a range of 0.15 μm or more and 1.0 μm or less is more preferable.

  In the porous polyimide film of the present embodiment, the ratio between the maximum diameter and the minimum diameter of the pores (the ratio between the maximum value and the minimum value of the pore diameter) is 1 or more and 2 or less. It is preferably 1 or more and 1.9 or less, more preferably 1 or more and 1.8 or less. Within this range, one closer to 1 is more preferable. Within this range, variation in pore diameter is suppressed. Further, when the porous polyimide film of the present embodiment is applied to, for example, a battery separator of a lithium-ion battery, it is possible to prevent the ion flow from being disturbed, so that the formation of lithium dendrites is easily suppressed. The "ratio between the maximum diameter and the minimum diameter of the holes" is a ratio represented by a value obtained by dividing the maximum diameter of the holes by the minimum diameter (that is, the maximum value/minimum value of the hole diameter).

  The maximum value, minimum value, average value of the hole diameters, average value of the hole diameters of the portions where the holes are connected to each other, and the long and short diameters of the holes are observed with a scanning electron microscope (SEM). And the measured value. Specifically, first, a porous polyimide film is cut out and a measurement sample is prepared. Then, the measurement sample is observed and measured by the VE SEM manufactured by KEYENCE Co., Ltd. with the image processing software provided as standard. The observation and measurement are performed 100 times for each of the pores in the measurement sample cross section, and the average value and the minimum diameter, the maximum diameter, and the arithmetic mean diameter of each are obtained. When the shape of the holes is not circular, the longest part is the diameter.

  The thickness of the porous polyimide film is not particularly limited, but is preferably 15 μm or more and 500 μm or less.

(Uses of porous polyimide film)
Examples of applications to which the porous polyimide film according to the present embodiment is applied include battery separators such as lithium batteries; separators for electrolytic capacitors; electrolyte membranes such as fuel cells; battery electrode materials; gas or liquid separation membranes; Low dielectric constant material; and the like.

When the porous polyimide film according to the present embodiment is applied to, for example, a battery separator, it is considered that the production of lithium dendrite is suppressed by the action of suppressing the variation of the ion flow distribution of lithium ions. .. It is presumed that this is because the porous polyimide film of the present embodiment suppresses variations in the shape of the holes and the diameter of the holes.
Further, for example, when it is applied to a battery electrode material, it is considered that the capacity of the battery increases because the chances of coming into contact with the electrolytic solution increase. It is presumed that this is because the amount of the material such as carbon black for the electrode contained in the porous polyimide film exposed on the surface of the pore diameter of the porous polyimide film or the surface of the film increases.
Furthermore, for example, it is possible to fill the pores of the porous polyimide film with, for example, an ionic gel obtained by gelling a so-called ionic liquid or the like, and apply it as an electrolyte membrane. Since the manufacturing method of the present embodiment simplifies the steps, it is considered that a lower cost electrolyte membrane can be obtained.

  Examples will be described below, but the present invention is not limited to these examples. In the following description, all “parts” and “%” are based on mass unless otherwise specified.

[Preparation of Polyimide Precursor "Water" Solution (PAA-1)]
A flask equipped with a stir bar, a thermometer, and a dropping funnel was filled with 900 g of water. To this, p-phenylenediamine (molecular weight 108.14): 27.28 g (252.27 mmol) and methylmorpholine (organic amine compound): 50.00 g (494.32 mmol) were added, and at 20°C. Stir for 10 minutes to disperse. Further, to this solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (molecular weight 294.22): 72.72 g (247.16 mmol) was added, and the reaction temperature was kept at 20°C. Then, the mixture was stirred for 24 hours for dissolution and reaction to obtain a polyimide precursor “water” solution (PAA-1).

[Preparation of Polyimide Precursor "N-Methylpyrrolidone" Solution (RPAA-1)]
A flask equipped with a stirring bar, a thermometer, and a dropping funnel was charged with 900 g of N-methylpyrrolidone. To this, p-phenylenediamine: 27.28 g (252.27 mmol) was added and dispersed by stirring at 20° C. for 10 minutes. To this solution, 3,3′,4,4′-biphenyltetracarboxylic dianhydride: 72.72 g (247.16 mmol) was added, and the mixture was stirred for 24 hours while dissolving at 20° C. to dissolve. , And the reaction was performed to obtain a polyimide precursor “N-methylpyrrolidone” solution (RPAA-1).

[Preparation of Polyimide Precursor "Water/Isopropanol" Solution (PAA-2)]
500 g of the polyimide precursor "N-methylpyrrolidone" solution (RPAA-1) was added dropwise to 3000 g of water with stirring to precipitate the polyimide precursor. This polyimide precursor (30 g) was added to water (243 g) and isopropanol (27 g), and methylmorpholine (15 g) was added and stirred and dissolved to obtain a polyimide precursor "water/isopropanol" solution (PAA-2).

[Preparation of Polyimide Precursor "Water/Isopropanol" Solution (PAA-3)]
500 g of the polyimide precursor "N-methylpyrrolidone" solution (RPAA-1) was added dropwise to 3000 g of water with stirring to precipitate the polyimide precursor. This polyimide precursor: 30 g was added to water: 243 g and isopropanol: 27 g, and further 1,2-dimethylimidazole (DMIz): 15 g was added, and the mixture was stirred and dissolved to prepare a polyimide precursor "water/isopropanol" solution (PAA- 3) was obtained.

[Preparation of Polyimide Precursor "Water/N-Methylpyrrolidone" Solution (PAA-4)]
500 g of the polyimide precursor "N-methylpyrrolidone" solution (RPAA-1) was added dropwise to 3000 g of water with stirring to precipitate the polyimide precursor. This polyimide precursor: 30 g was added to water: 243 g and N-methylpyrrolidone: 27 g, 1,2-dimethylimidazole: 15 g, and the mixture was stirred and dissolved to prepare a polyimide precursor "water/N-methylpyrrolidone" solution. (PAA-4) was obtained.

<Example 1>
Non-crosslinked polymethylmethacrylate/styrene copolymer having an average particle diameter of 0.1 μm (FS-102E: manufactured by Nippon Paint Co., Ltd.): 10 parts, polyvinyl butyral resin (S-LEC SV-02: manufactured by Sekisui Chemical Co., Ltd.): 1 part was added to 30 parts of ethanol, and the mixture was stirred on a web browser to prepare a dispersion liquid. This was formed on a glass substrate so that the film thickness after drying would be 30 μm, and dried at 90° C. for 1 hour to form a resin particle layer.
After the polyimide precursor "water" solution (PAA-1) was diluted 10 times and the polyimide precursor "water" solution (PAA-1) was applied on the resin particle layer, defoaming under reduced pressure was performed to remove resin particles. The polyimide precursor “water” solution (PAA-1) was impregnated into the voids of FIG. After drying overnight at room temperature (25° C., the same applies below), water wiping was performed so that the surface of the resin particle layer was exposed, and excess polyimide precursor on the resin particle layer was removed. This was heated at 120° C. for 1 hour, then peeled from the glass substrate and immersed in toluene to elute the resin particles. After drying, the temperature was raised from room temperature to 380° C. at a rate of 10° C./min, the temperature was maintained at 380° C. for 1 hour, and then cooled to room temperature to obtain a porous polyimide film (PIF-1).

<Comparative Example 1>
A polyimide precursor "N-methylpyrrolidone" solution (RPAA-1) was diluted 10 times on the resin particle layer prepared in the same manner as in Example 1 and applied, but the resin particles dissolved. This was heated at 120° C. for 1 hour, then peeled from the glass substrate and immersed in toluene to elute the resin. After drying, the temperature was raised from room temperature to 380° C. at a rate of 10° C./min, the temperature was maintained at 380° C. for 1 hour, and then cooled to room temperature to obtain a porous polyimide film (RPIF-1). However, the pore diameter was in the range of 0.05 μm or more and 1.01 μm or less, and the distribution was wide. It is considered that this is because the resin particles were dissolved and the morphology of the resin particles could not be maintained.

<Example 2>
A polyimide precursor “water/isopropanol” solution (PAA-2) was diluted 10-fold and applied on a resin particle layer prepared in the same manner as in Example 1, and the porous polyimide film (PIF) was prepared in the same manner as in Example 1. -2) was obtained.

<Example 3>
The polyimide precursor “water/isopropanol” solution (PAA-2) was diluted 10 times, applied on the resin particle layer prepared in the same manner as in Example 1, and dried overnight at room temperature, and then the surface of the resin particle layer. Was wiped with water so that the film was exposed to remove excess polyimide precursor. After heating this at 120° C. for 1 hour, it was peeled from the glass substrate, heated from room temperature to 380° C. at a rate of 10° C./min, kept at 380° C. for 1 hour, and then cooled to room temperature to make it porous. A high quality polyimide film (PIF-3) was obtained.

<Example 4>
A polyimide precursor “water/isopropanol” solution (PAA-2) was diluted 10-fold, and 10 parts of this polyimide precursor were mixed with 10 parts of non-crosslinked poly(methyl methacrylate/styrene) having an average particle diameter of 0.1 μm. A copolymer (FS-102E: manufactured by Nippon Paint Co., Ltd.) was added, and the mixture was stirred on a web rotor to prepare a dispersion liquid. This was formed on a glass substrate so that the film thickness after drying was about 30 μm, dried at 90° C. for 1 hour, and then heated from 90° C. to 380° C. at a rate of 10° C./minute to 380° C. After holding at ℃ for 1 hour, it was cooled to room temperature to obtain a porous polyimide film (PIF-4).

<Example 5>
A polyimide precursor “water/isopropanol” solution (PAA-2) was diluted 10-fold, and 10 parts of this polyimide precursor were mixed with 10 parts of non-crosslinked poly(methyl methacrylate/styrene) having an average particle diameter of 0.1 μm. A copolymer (FS-102E: manufactured by Nippon Paint Co., Ltd.) was added, and the mixture was stirred on a web rotor to prepare a dispersion liquid. This was formed on a glass substrate so that the film thickness after drying was about 30 μm, dried at room temperature for 1 hour, peeled from the glass substrate and immersed in tetrahydrofuran to dissolve the resin particles. After drying at 90° C. for 1 hour, the temperature was raised from 90° C. to 380° C. at a rate of 10° C./min, held at 380° C. for 1 hour, and then cooled to room temperature to give a porous polyimide film (PIF-5). Obtained.

<Example 6>
A porous polyimide film (PIF-6) was obtained in the same manner as in Example 2 except that the polyimide precursor "water/isopropanol" solution (PAA-3) was used.

<Example 7>
A porous polyimide film (PIF-7) was obtained in the same manner as in Example 5 except that the polyimide precursor “water/N-methylpyrrolidone” solution (PAA-4) was used. Since N-methylpyrrolidone has a high boiling point, it cannot be sufficiently removed by drying at room temperature, so that the pore diameter is larger than that in the case of isopropanol.

<Comparative example 2>
Made by Nippon Shokubai Co., Ltd., monodispersed spherical silica particles having an average diameter of 550 nm (sphericity: 1.0, particle size distribution index: 1.20): 30 parts by mass to N-methylpyrrolidone (NMP): 30 parts by mass Dispersed. Polyimide precursor "N-methylpyrrolidone" solution (RPAA-1): 100 parts by mass of silica particle dispersion: 20 parts by mass were mixed and stirred, and then applied onto a glass plate. After heating this at 120° C. for 1 hour, it was peeled from the glass substrate, heated from room temperature to 380° C. at a speed of 10° C./min, kept at 380° C. for 1 hour, and then cooled to room temperature to obtain silica. -A polyimide composite film was obtained. The silica-polyimide composite film was immersed in 10 mass% hydrogen fluoride water, the silica was dissolved and removed over 6 hours, washed thoroughly with water, and dried to obtain a porous polyimide film (RPIF-2).

<Example 8>
900 parts by mass of styrene, 100 parts by mass of butyl acrylate, 15.7 parts by mass of dodecanethiol, 15.8 parts by mass of surfactant Dowfax2A1 (47% solution, manufactured by Dow Chemical Co.), and 576 parts by mass of deionized water are mixed. The mixture was stirred and emulsified at 1,500 rpm for 30 minutes with a dissolver to prepare a monomer emulsion. Subsequently, 1.49 parts by mass of Dowfax2A1 (47% solution, manufactured by Dow Chemical Co.) and 1270 parts by mass of ion-exchanged water were charged into the reaction vessel. After heating to 75° C. under a nitrogen stream, after adding 75 parts by mass of the monomer emulsion, a polymerization initiator solution prepared by dissolving 15 parts by mass of ammonium persulfate in 98 parts by mass of ion-exchanged water is taken over 10 minutes. Dropped. After reacting for 50 minutes after dropping, the remaining monomer emulsion was added dropwise over 220 minutes, and further reacted for 180 minutes. After cooling, a resin particle dispersion liquid (1) was obtained as a non-crosslinked styrene-acrylic resin particle dispersion liquid having a solid content concentration adjusted to 30% by mass. The average particle diameter of the resin particles in the resin particle dispersion liquid (1) was 250 nm.
The polyimide precursor "water" solution (PAA-1) and the resin particle dispersion liquid (1) are in a mass ratio, solid content of the polyimide precursor solution: solid content of the resin particle dispersion = 30:70 (100: 233) to prepare a resin particle-dispersed polyimide precursor “water” solution (1). This solution (1) was applied on a glass substrate and then dried at room temperature (25° C.) for 5 hours. Then, after heating at 120 degreeC for 1 hour, it peeled from the glass substrate and was immersed in tetrahydrofuran (THF) for 30 minutes to elute the resin particles. After drying, the temperature was raised from room temperature to 250° C. at a rate of 10° C./min, held at 250° C. for 1 hour, and then cooled to room temperature to obtain a porous polyimide film (PIF-8) having a film thickness of 25 μm. .. Moreover, the photograph which observed the surface of the film (PIF-8) with the scanning electron microscope (Keyence company make: VE-8800) is shown in FIG.

<Example 9>
In Example 8, the polyimide precursor “water” solution (PAA-1) and the resin particle dispersion liquid (1) were mass ratio, solid content of the polyimide precursor solution: solid content of the resin particle dispersion=50. The film thickness was the same as in Example 8 except that the resin particle-dispersed polyimide precursor “water” solution (2) mixed to give a mixing ratio of 50:100 (100:100) was used and the immersion time in THF was 2 hours. A 25 μm porous polyimide film (PIF-9) was obtained. A photograph of the surface of the film (PIF-9) observed by a scanning electron microscope in the same manner as in Example 8 is shown in FIG.

<Example 10>
In Example 8, the polyimide precursor “water” solution (PAA-1) and the resin particle dispersion liquid (1) were mass ratio, solid content of the polyimide precursor solution: solid content of the resin particle dispersion=70. The film thickness was the same as in Example 8 except that the resin particle-dispersed polyimide precursor “water” solution (3) mixed so as to be :30 (100:43) was used and the immersion time in THF was 12 hours. A 25 μm porous polyimide film (PIF-10) was obtained. A photograph of the surface of the film (PIF-10) observed by a scanning electron microscope in the same manner as in Example 8 is shown in FIG.

[Evaluation of pore size distribution]
The porous polyimide films obtained in Examples 1 to 10 and Comparative Examples 1 and 2 were evaluated for the distribution of pore diameters (maximum diameter, minimum diameter, and average diameter). Specifically, the evaluation was performed by the method described above.

[Evaluation of cracks]
The cracks were evaluated for the porous polyimide films obtained in Examples 1 to 10 and Comparative Examples 1 and 2. The specific method is as follows. An area of 1 cm ² square of the polyimide film was observed with a microscope having a magnification of 500 to make 0.1 mm or more cracks, and the presence or absence was visually observed.

-Evaluation criteria-
A: No crack B: 1 place or more and 3 places or less C: 4 places or more

The details of the abbreviations in Table 1 are shown below.
-"PDA": p-phenylenediamine-"BPDA": 3,3',4,4'-biphenyltetracarboxylic dianhydride-"MMO": methylmorpholine-"DMIz": 1,2-dimethylimidazole- "THF": Tetrahydrofuran "Tol": Toluene "PMMA/St": Non-cross-linked polymethylmethacrylate-styrene copolymer-"PBA/St": Non-cross-linked polybutyl acrylate-styrene copolymer-"IPA ": Isopropanol/"NMP": N-methylpyrrolidone

DESCRIPTION OF SYMBOLS 1 Resin particle, 2 Binder resin, 3 Substrate, 4 Release layer, 5 Polyimide precursor solution, 7 Hole, 61 Polyimide film, 62 Porous polyimide film

Claims (9)

After forming a coating film containing a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved in an aqueous solvent containing 50% by mass or more of water, and resin particles that are not dissolved in the polyimide precursor solution, A first step of drying the coating film to form a coating film containing the polyimide precursor and the resin particles,
A second step of heating the coating to imidize the polyimide precursor to form a polyimide film, the second step including a treatment of removing the resin particles;
A method for producing a porous polyimide film having:   In the first step, a resin particle dispersion liquid containing the resin particles, an organic solvent in which the resin particles are insoluble, and a binder resin soluble in the organic solvent is applied onto a substrate and dried to form a resin particle layer. After the formation, the polyimide precursor solution is impregnated between the resin particles of the resin particle layer to form a coating film containing the resin particles, and the coating film is dried to form the coating film. The method for producing a porous polyimide film according to claim 1.   In the first step, the polyimide precursor solution and a resin particle-dispersed polyimide precursor solution containing resin particles that are not soluble in the polyimide precursor solution are applied onto a substrate to form a coating film, and the coating film is formed. The method for producing a porous polyimide film according to claim 1, which is a step of forming a coating film by drying the film.   The porous polyimide film according to any one of claims 1 to 3, wherein in the first step, a process of exposing the resin particles is performed in a process of drying the coating film to form the coating film. Manufacturing method.   In the second step, a process of exposing the resin particles is performed after the process of imidizing the polyimide precursor or after the imidization and before the process of removing the resin particles. Item 4. A method for producing a porous polyimide film according to any one of Items 3.   The method for producing a porous polyimide film according to claim 1, wherein the treatment for removing the resin particles is a treatment for removing the resin particles with an organic solvent that dissolves the resin particles.   The method for producing a porous polyimide film according to claim 1, wherein the treatment for removing the resin particles is a treatment for removing by heating.   The said organic amine compound is a tertiary amine compound, The manufacturing method of the porous polyimide film as described in any one of Claims 1-7. The method for producing a porous polyimide film according to any one of claims 1 to 7, wherein the organic amine compound is an amine compound having a nitrogen-containing heterocyclic structure.