JP2016183332A - Method for producing porous polyimide film and porous polyimide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a porous polyimide film for simplifying production processes.SOLUTION: The method for producing a porous polyimide film includes: a first step of forming a coating film that comprises a polyimide precursor solution prepared by dissolving a polyimide precursor and an organic amine compound in an aqueous solvent and that contains resin particles incapable of dissolving in the polyimide precursor solution, and then drying the coating film to form a coat comprising the polyimide precursor and the resin particles; and a second step of heating the coat to imidize the polyimide precursor to form a polyimide film, including a process of removing the resin particles.SELECTED DRAWING: None

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 of monodispersed spherical inorganic particles is fired to form a sintered body of inorganic particles, and after filling a gap between the inorganic particles of the sintered body with polyamic acid, firing is performed. A method for manufacturing a separator for a lithium secondary battery is described in which the polyimide resin is formed and then immersed in a solution in which the inorganic particles are dissolved but the resin is not dissolved, and the inorganic particles are dissolved and removed.
Patent Document 2 describes an organic porous body having pores made of polyimide and an ionic conductor holding an electrolyte material containing a cation component and an anion component in the pores.
In Patent Document 3, a varnish is produced by mixing polyamic acid or polyimide, silica particles and a solvent to produce a varnish, or polymerizing polyamic acid or polyimide in a solvent in which silica particles are dispersed to produce a varnish. After the varnish produced in the production process is formed on the substrate, the imidization is completed to produce a 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 for removing silica is described.
Patent Document 4 discloses a porous silica mold produced by a porous silica mold production process for obtaining a porous silica mold after filling with silica particles and sintering, and a porous silica mold produced by the porous silica mold production process. A process for producing a porous polyimide having a polyimide filling step of filling the voids with polyimide and a silica removal step of removing the silica from a porous silica mold filled with the polyimide to obtain a porous polyimide is described.

Patent Document 5 discloses a positive electrode, a negative electrode, and a separator layer including a porous polyimide film having an average pore diameter of 5 μm or less, which is formed into a porous film by phase separation after solution application of polyimide or a polyimide precursor. , Non-aqueous electrolyte secondary batteries are described.
Patent Document 6 includes a step of preparing a resin composition for a film by mixing a heat-resistant resin such as polyimide, a heat extinguishing resin particle containing a polyoxyalkylene resin, and a solvent, and a resin composition for a film. A method for producing a porous resin film is described 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 made into a film 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 polyamic acid and make it porous. Methods for 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 not dissolved in the polyimide precursor solution, and then drying the coating film to form a coating film containing the polyimide precursor and particles. And a second step of forming a polyimide film by imidizing the polyimide precursor by heating the coating, and a second step including a process of removing particles. In a manufacturing method, it is providing the manufacturing method of the porous polyimide film by which a manufacturing process is simplified compared with the case where the solvent which melt | dissolves the polyimide precursor solution in a polyimide precursor solution is only an organic solvent.

  In order to achieve the above object, the following invention is provided.

The invention according to claim 1
In an aqueous solvent, after forming a coating film containing a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved, and resin particles not dissolved in the polyimide precursor solution, the coating film is dried, A first step of forming a 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, including a process of removing the resin particles;
It is a manufacturing method of the porous polyimide film which has this.

The invention according to claim 2
In the first step, a resin particle dispersion containing the resin particles, an organic solvent in which the resin particles are not dissolved, and a binder resin dissolved 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 manufacturing method of the porous polyimide film of Claim 1.

The invention according to claim 3
The first step applies a resin particle-dispersed polyimide precursor solution containing the polyimide precursor solution and resin particles not dissolved in the polyimide precursor solution on a substrate to form a coating film, and the coating film The method for producing a porous polyimide film according to claim 1, wherein the film is dried to form the coating film.

The invention according to claim 4
The said 1st process WHEREIN: The process which exposes the said resin particle is performed in the process in which the said coating film is dried and the said coating film is formed, The porous polyimide film as described in any one of Claims 1-3. It is a manufacturing method.

The invention according to claim 5
In the second step, a process of exposing the resin particles is performed in the process of imidizing the polyimide precursor or after the imidization and before the process of removing the resin particles. It is a manufacturing method of the porous polyimide film as described in any one of claim | item 3.

The invention according to claim 6
The method for producing a porous polyimide film according to any one of claims 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 claim 7 provides:
The process for removing the resin particles is a process for removing by heating, and the method for producing a porous polyimide film according to any one of claims 1 to 6.

The invention according to claim 8 provides:
The said organic amine compound is a tertiary amine compound, It is a manufacturing method of the porous polyimide film as described in any one of Claims 1-7.

The invention according to claim 9 is:
The said organic amine compound is an amine compound which has a heterocyclic structure containing nitrogen, It is a manufacturing method of the porous polyimide film as described in any one of Claims 1-7.

The invention according to claim 10 is:
It is a porous polyimide film manufactured by the method as described in any one of Claims 1-9.

  According to the invention which concerns on Claim 1, 2, or 3, after forming the coating film containing a polyimide precursor solution and the particle | grains which are not melt | dissolved in a polyimide precursor solution, a coating film is dried and a polyimide precursor and particle | grains A first step of forming a film including the second step, and a second step of heating the film to imidize the polyimide precursor to form a polyimide film, the second step including a process of removing particles In the method for producing a porous polyimide film having the above, the production process of the porous polyimide film 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 is provided.

  According to the invention according to claim 4 or 5, in the process of drying the coating film to form the coating film, the process of exposing the resin particles is not performed, or the process of imidizing the polyimide precursor or the imide Production of a porous polyimide film having a high porosity as compared with the case where the treatment for exposing the resin particles is not performed after the treatment and before the treatment for removing the resin particles A method is provided.

  According to the invention which concerns on Claim 6 or 7, compared with the case where the solvent which melt | dissolves the polyimide precursor solution in a polyimide precursor solution is only an organic solvent, the process which removes a resin particle melt | dissolves the said resin particle. There is provided a method for producing a porous polyimide film in which the production process is simplified even if it is a treatment to be removed by an organic solvent or a treatment to be removed by heating.

  According to the invention according to claim 8 or 9, there is provided 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. The

  According to the invention which concerns on Claim 10, after forming the coating film containing a polyimide precursor solution and the particle | grains which are not melt | dissolved in a polyimide precursor solution, the coating film is dried, The coating film containing a polyimide precursor and particle | grains 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 process of removing particles. In the porous polyimide film obtained by the method for producing a porous polyimide film, the generation of cracks is suppressed compared to the case where the solvent for dissolving the polyimide precursor solution in the polyimide precursor solution is only an organic solvent. 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. 4 is an electron micrograph of the surface of a porous polyimide film (PIF-8) obtained in Example 8. 4 is an electron micrograph of the surface of a porous polyimide film (PIF-9) obtained in Example 9. 2 is an electron micrograph of the surface of a porous polyimide film (PIF-10) obtained in Example 10.

  Embodiments that are examples of the present invention will be described below.

<Method for producing porous polyimide film>
The method for producing a porous polyimide film according to the present embodiment includes a coating containing a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved in an aqueous solvent, and resin particles not dissolved in the polyimide precursor solution. After forming the 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 and polyimide. A second step of forming a film, the second step including a process of removing the resin particles.

  In the present embodiment, “does not dissolve” means that, at 25 ° C., the target substance is substantially in the form of resin particles with respect to the target liquid, and is within the range of 3% by mass or less. Including dissolution.

  The manufacturing method of the porous polyimide film which concerns on this embodiment can simplify a manufacturing process by the said structure compared with the case where the solvent in a polyimide precursor solution is only an organic solvent.

  The polyimide film is, for example, a polyimide precursor solution (for example, N-methylpyrrolidone (hereinafter sometimes referred to as “NMP”) or N, N-dimethylacetamide (hereinafter referred to as “DMAc”) dissolved in an organic solvent. It may be obtained by applying a polyimide precursor solution in a state dissolved in a highly polar solvent, followed by thermoforming.

  Porous polyimide film is made into a film using a polyimide precursor solution dissolved in an organic solvent, and then contacted with a poor solvent such as water to deposit polyamic acid, and then to make it imidized, an organic solvent It is obtained by a method such as removing particles using a polyimide precursor solution and particles dissolved in the solution. For example, as a method for producing a porous polyimide film, a method of obtaining a porous polyimide film in which pores of a three-dimensional regular array structure (3DOM structure) are formed using a silica particle layer as a template, and a polyimide in which silica particles are dispersed Examples thereof 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 chemicals such as hydrofluoric acid in the treatment for removing the silica particles. Moreover, when producing the casting_mold | template of a silica particle layer, in order to form a silica particle layer, it is necessary to sinter by performing high heat processing at 1000 degreeC or more. In addition, when using a polyimide precursor solution in which silica particles are dispersed, the surface of the silica particles is subjected to a hydrophobic treatment to improve the dispersibility of the silica particles in the polyimide precursor solution. There is. Therefore, these manufacturing methods have low productivity and high cost.

Moreover, after forming a film from the resin composition of the polyimide precursor solution melt | dissolved in the resin particle and the organic solvent, the method of removing a resin particle and obtaining a porous polyimide film is mentioned. In this case, NMP and DMAc have a very high dissolving power, and in general resin particles (for example, polystyrene resin particles), dissolution or the like is caused by an organic solvent in which a polyimide precursor is dissolved. A polyimide film may be difficult to obtain.
On the other hand, as a resin particle, a dispersion 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 obtain a resin composition. After forming, the resin particles are removed by heating to obtain a porous polyimide film. Since these resin particles are produced by emulsion polymerization or the like, it may be necessary to provide a step of replacing with an organic solvent such as NMP in order to mix with the polyimide precursor solution.

On the other hand, in the manufacturing method of the porous polyimide film of this embodiment, the polyimide precursor is melt | dissolved in the aqueous solvent. Since dissolution of resin particles and the like are suppressed by the aqueous solvent, it is easy to produce a porous polyimide film. Further, there is no need to provide a step of replacing the dispersion medium in the aqueous dispersion of resin particles with an organic solvent.
In addition, the method for producing the porous polyimide film of this embodiment includes a method for producing a resin particle layer as a mold using resin particles, but the resin particle layer is maintained in the shape of the resin particle layer. A heating temperature (for example, 100 ° C.) for forming the resin particle layer in the finished state is sufficient. Therefore, the resin particle layer mold is produced without performing high heat treatment at 1000 ° C. or higher, which is necessary when producing a silica particle layer mold, and the manufacturing process is simplified.

  As mentioned above, it is thought that the manufacturing process of the porous polyimide film which concerns on this embodiment is simplified by the said structure compared with the case where the solvent in a polyimide precursor solution is only an organic solvent.

  In addition, the porous polyimide film obtained by the method for producing a porous polyimide film of the present embodiment is easily suppressed from cracking. This is presumed to contribute effectively to the relaxation of residual stress in the imidization step of the polyimide precursor by using resin particles in the method for producing the porous polyimide film of the present embodiment.

In the porous polyimide film obtained by the method for producing a porous polyimide film of this embodiment, variations in pore shape, pore diameter and the like are easily suppressed. The reason for this is presumed that the relaxation of residual stress contributes effectively in the imidization step of the polyimide precursor by using resin particles.
Moreover, since the porous polyimide film obtained by the manufacturing method of the porous polyimide film of this embodiment has dissolved the polyimide precursor in the aqueous solvent, the boiling point of a polyimide precursor solution will be about 100 degreeC. Therefore, as the coating containing the polyimide precursor and the resin particles is heated, the imidization reaction proceeds after the solvent is quickly volatilized. Then, before the resin particles in the coating are deformed by heat, the resin particles lose fluidity and become insoluble in the organic solvent. Therefore, it is considered that the shape of the holes is easily maintained, and variations in the shape of the holes, the hole diameter, and the like are easily suppressed. Moreover, dissolution of resin particles and the like are suppressed by the aqueous solvent. Accordingly, the pore diameter of the porous polyimide film can be controlled by the particle diameter of the resin particles.

  When silica particles are used, it is considered that cracks are likely to occur in the polyimide film after imidization because it is difficult to absorb volume shrinkage in the imidization step. In addition, when silica particles are used, it is considered that ions are likely to remain as impurities because chemicals such as hydrofluoric acid are used.

Hereinafter, the manufacturing method of the porous polyimide film which concerns on this embodiment is demonstrated.
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 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 void, and 61 is a process of imidizing the polyimide precursor. A coating (polyimide film) and 62 represent a porous polyimide film.

  The manufacturing method of the porous polyimide film which concerns on this embodiment has said 1st process and said 2nd process. Hereinafter, although the manufacturing method shown in FIG. 1 (an example of the manufacturing method according to the present embodiment) will be described, the present invention is not limited to this.

(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 including a polyimide precursor solution and resin particles not dissolved in the polyimide precursor solution is formed on the substrate. And the coating film formed on the board | substrate is dried, and the coating film containing a polyimide precursor and the said resin particle is formed.

  As a method for forming a coating film containing a polyimide precursor solution and resin particles that are not dissolved in the polyimide precursor solution on the substrate in the first step, specifically, the following method may be mentioned. It is done.

  First, a resin particle dispersion containing resin particles that do not dissolve in the polyimide precursor solution, an organic solvent that does not dissolve the resin particles, and a binder resin that dissolves in the organic solvent is prepared. Next, this resin particle dispersion is applied onto a substrate and dried to form a resin particle layer. The resin particle layer formed on the substrate exists, for example, without the resin particles adjacent to each other being dissolved, and the resin particles adjacent to each other are bound by the binder resin. And the space | gap is formed between the resin particles of a resin particle layer (refer FIG. 1 (A)).

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

  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); and composite material substrates in which these materials are combined. The substrate may be provided with a release layer by performing a release treatment with a silicone-based or fluorine-based release agent or the like, if necessary.

A method for producing the resin particle dispersion is not particularly limited. For example, the resin particles that do not dissolve in the polyimide precursor solution, the organic solvent in which the resin particles do not dissolve, and the binder resin that dissolves in the organic solvent are weighed, mixed, and stirred. As the resin particles, a dispersion of resin particles dispersed in advance may be prepared, or a commercially available product dispersed in advance may be prepared. When preparing a dispersion of resin particles dispersed in advance, for example, the dispersibility of the resin particles may be enhanced by at least one of an ionic surfactant and a nonionic surfactant.
In addition, the binder resin may be dissolved in advance in the above organic solvent, or may be mixed and dissolved with the resin particles and the organic solvent.

  The ratio (mass ratio) between the resin particles and the binder resin in the resin particle dispersion is preferably in the range of resin particles: binder resin = 100: 0.5 to 100: 50. The range is preferably from 100: 1 to 100: 30, and more preferably from 100: 2 to 100: 20. 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 adjacent resin particles are bound (primary (Including a state of so-called pseudo-adhesion). And it becomes easy to form the space | gap which becomes the state of an air layer between the resin particles of a 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 polycondensation of a polymerizable monomer such as polyester resin and urethane resin, and resin particles obtained by radical polymerization of a polymerizable monomer such as vinyl resin and olefin resin. . Examples of the resin particles obtained by radical polymerization include resin particles of (meth) acrylic resin, (meth) acrylic ester resin, styrene / (meth) acrylic resin, polystyrene resin, and polyethylene resin.
Among these, the resin particles are preferably at least one selected from the group consisting of (meth) acrylic resins, (meth) acrylic ester resins, styrene / (meth) acrylic resins, and polystyrene resins.
The resin particles may be cross-linked or may not be cross-linked. In the imidization step of the polyimide precursor, resin particles that are not cross-linked are preferable in that they contribute effectively to relaxation of residual stress.

  In the present embodiment, “(meth) acryl” means that both “acryl” and “methacryl” are included.

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

  For example, when an emulsion polymerization method is applied to the production of vinyl resin particles, monomers such as styrenes and (meth) acrylic acids are added to water in which a water-soluble polymerization initiator such as potassium persulfate and ammonium persulfate is dissolved. In addition, if necessary, a surfactant such as sodium dodecyl sulfate, diphenyl oxide disulfonates and the like is added, and polymerization is carried out by heating while stirring to obtain vinyl resin particles.

Examples of the vinyl resin monomer include styrene and alkyl-substituted styrene (for example, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4 -Ethylstyrene, etc.), halogen-substituted styrene (for example, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), styrenes having a styrene skeleton such as vinylnaphthalene; methyl (meth) acrylate, (meth) acrylic Vinyl groups such as ethyl acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate, trimethylolpropane trimethacrylate (TMPTMA) Esters with acrylonitrile, methacrylonitrile Vinyl nitriles such as vinyl methyl ether, vinyl isobutyl ether, etc .; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone; (meth) acrylic acid, maleic acid, cinnamic acid, fumaric acid And vinyl resin units obtained by polymerizing monomers such as acids such as vinyl sulfonic acid; bases such as ethylene imine, vinyl pyridine and vinyl amine;
Other monomers include monofunctional monomers such as vinyl acetate, bifunctional monomers such as ethylene glycol dimethacrylate, nonane diacrylate, decanediol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, etc. These polyfunctional monomers may be used in combination.
The vinyl resin may be a resin using these monomers alone, or may be a resin that is a copolymer using two or more monomers.

  As described above, it is preferable that the resin particles are not crosslinked. However, when the resin particles are crosslinked, when a 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 component 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 is 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, desirably 2.0 μm or less, and more desirably 1.0 μm or less. Although it does not specifically limit as a minimum, It is good that it is 0.001 micrometer or more, Desirably 0.005 micrometer or more, More desirably, it is 0.01 micrometer or more.
In addition, the average particle diameter of the resin particles is a particle size range (channel) divided by using a particle size distribution obtained by measurement with a laser diffraction particle size distribution measuring apparatus (for example, LA-700 manufactured by HORIBA, Ltd.) The cumulative distribution is drawn from the small particle diameter side with respect to the volume, and the particle diameter that becomes 50% cumulative with respect to all particles is measured as the volume average particle diameter D50v.

The resin particles may be commercially available products. Specifically, examples of the crosslinked resin particles include crosslinked polymethyl methacrylate (MBX-series, manufactured by Sekisui Plastics Co., Ltd.), crosslinked polystyrene (SBX-series, manufactured by Sekisui Plastics Co., Ltd.), methacrylic acid. Examples include methyl and styrene copolymer crosslinked resin particles (MSX-series, manufactured by Sekisui Plastics Co., Ltd.).
Examples of the resin particles that are not crosslinked include polymethyl methacrylate (MB-series, manufactured by Sekisui Plastics Co., Ltd.), (meth) acrylic acid ester / styrene copolymers (FS-series: manufactured by Nippon Paint Co., Ltd.). ) And the like.

  The binder resin is not particularly limited as long as it is soluble in an organic solvent and not soluble 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 preferred.

  Examples of the organic solvent in which the resin particles do not dissolve include 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 include esters such as ethyl acetate; nitriles such as acetonitrile. The organic solvent in which the resin particles are not dissolved may contain water.

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

  The method for applying the resin particle dispersion on the substrate is not particularly limited. Examples thereof include various methods such as spray coating, spin coating, roll coating, bar coating, slit die coating, and ink jet coating.

  The resin particle layer is obtained by drying the coating film obtained by applying the resin particle dispersion on the substrate. The drying temperature may be any temperature that maintains the shape of the resin particles and binds the resin particles (for example, 100 ° C.).

  Next, a preliminarily prepared polyimide precursor solution is impregnated between the resin particles of the resin particle layer formed as described above to form a coating film including the polyimide precursor solution and the resin particles. And a coating film is dried and the coating film containing a polyimide precursor and a resin particle is formed.

The method for impregnating the polyimide precursor solution is not particularly limited. For example, a method in which a substrate on which a resin particle layer is formed is immersed in a polyimide precursor solution, or a method in which a polyimide precursor solution is applied from above a resin particle layer formed on a substrate and impregnated between particles in the resin particle layer Etc.
Examples of the method for applying the polyimide precursor solution on 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. In addition, the polyimide precursor solution is impregnated between the resin particles on which the resin particle layer is formed, and after applying the polyimide precursor solution from above the resin particle layer, the pressure is reduced and the polyimide precursor solution is applied between the resin particles. Adopting the vacuum impregnation filling method of filling the resin is preferable because the polyimide precursor solution is efficiently impregnated into the voids between the resin particles.

In addition, as a method of forming the coating film containing a polyimide precursor solution and a resin particle, it is not restricted to said method.
For example, the following method is 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, a polyimide precursor solution in which resin particles are dispersed by mixing the polyimide precursor solution and resin particles not dissolved in the polyimide precursor solution (hereinafter also referred to as “resin particle-dispersed polyimide precursor solution”) and To do. And this resin particle dispersion polyimide precursor solution is apply | coated on a board | substrate, and the coating film containing a polyimide precursor solution and a resin particle is formed. The resin particles in the coating film are distributed in a state where aggregation is suppressed (see FIG. 3A). Then, this coating film is dried and the coating film containing a polyimide precursor and a resin particle is formed on a board | substrate.

  It does not specifically limit as a method of producing said resin particle dispersion | distribution polyimide precursor solution. For example, a method of mixing a polyimide precursor solution and dry resin particles, a method of mixing a polyimide precursor solution and a dispersion in which resin particles are previously dispersed in an aqueous solvent, and the like can be mentioned. As a dispersion in which resin particles are dispersed in an aqueous solvent in advance, a dispersion of resin particles in which resin particles are dispersed in an aqueous solvent in advance may be prepared, or commercially available in which resin particles are dispersed in an aqueous solvent in advance. A product dispersion may be prepared. When preparing a dispersion of resin particles dispersed in advance, for example, the dispersibility of the resin particles may be enhanced by 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 good in the range of 20 or more and 100: 600 or less. The range is preferably from 100: 25 to 100: 550, and more preferably from 100: 30 to 100: 500.

  The resin particle-dispersed polyimide precursor solution may contain a binder resin that does not dissolve in the polyimide precursor solution. When the resin particle-dispersed polyimide precursor solution contains the binder resin, the binder resin covers part or all of the periphery of the resin particles in the coating film, so that the pore diameter and the overlap of the pores can be easily controlled. . In addition, the binder resin is partially distributed in addition to the periphery of the resin particles, and in the process of removing the resin particles described later, a space for removing the resin particles from the film can be provided, so that 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 those exemplified as the binder resin used in the resin particle dispersion described above.

  The method for applying the resin particle-dispersed polyimide precursor solution on the substrate is not particularly limited. Examples thereof include various methods such as spray coating, spin coating, roll coating, bar coating, slit die coating, and ink jet coating.

  As the coating amount of the polyimide precursor solution for obtaining 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 amount is preferably such that the resin particles are exposed from the surface. For example, when the polyimide precursor solution is impregnated between the resin particles on which the resin particle layer is formed, the polyimide precursor solution is preferably impregnated so as to be 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 the resin particles in an amount that the resin particles are exposed from the surface of the coating film.

  And after forming the coating film containing the polyimide precursor solution and resin particle which were obtained by the above method, it dried and the coating film containing a polyimide precursor and a resin particle is formed. 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, based on the solid content of the coating film, thereby forming the coating film. This coating is in a state where the polyimide precursor can be dissolved in water.

  The coating film may be formed in such an amount that the resin particles are buried in the coating film. In this case, in the first step, after the coating film is obtained, the resin particles may be exposed by performing a process of exposing the resin particles in the process of drying to form the coating film. By performing the treatment for exposing the resin particles, the porosity of the porous polyimide film is increased.

Specific examples of the treatment for exposing the resin particles include the following method.
When the polyimide precursor solution is impregnated between the resin particles on which the resin particle layer is formed, and the coating film is formed so that the resin particle layer is buried, the polyimide precursor solution is present in a region greater than the thickness of the resin particle layer. (See FIG. 1B).

  After obtaining the coating film containing the polyimide precursor solution and the resin particles, in the process of drying the coating film and forming the coating film containing the polyimide precursor and the resin particles, as described above, the coating film is made of the polyimide precursor. It can be dissolved in water. When the coating is in this state, the resin particles can be exposed by, for example, a wiping process or a process of immersing in water. Specifically, the polyimide precursor solution present in the region having a thickness equal to or greater than the thickness of the resin particle layer is present in a region greater than the thickness of the resin particle layer by performing a process of exposing the resin particle layer by, for example, wiping with water. The polyimide precursor solution that has been removed is removed. And the resin particle which exists in the area | region (namely, area | region on the side away from the board | substrate of the resin particle layer) of the resin particle layer is exposed from the surface of a film (refer FIG.1 (C)).

  In the case where a film is formed on a substrate using the resin particle-dispersed polyimide precursor solution, even when a film in which resin particles are embedded is formed, the treatment for exposing the resin particles embedded in the film is described above. A process similar to the process of exposing the resin particles may be employed.

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

  In the second step, the step of forming the polyimide film is specifically performed by heating the film containing the polyimide precursor and resin particles obtained in the first step to advance imidization and further heating. A polyimide film is formed. In addition, as imidization proceeds and the imidization rate increases, it becomes difficult to dissolve in an organic solvent.

And the process which removes a resin particle is performed in a 2nd process. The resin particles may be removed in the process of heating the coating and imidizing 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 means that the film containing the polyimide precursor and resin particles obtained in the first step is heated to advance the imidization and the imidization is completed. The process which will be in the state before becoming a polyimide film after performing 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 is referred to as “polyimide film”). The resin particles are removed. Alternatively, the resin particles may be removed from the polyimide film after imidization is completed. And the porous polyimide film from which the resin particle was removed is obtained (refer FIG.1 (D)).

  The treatment for removing the resin particles is performed when the imidation ratio of the polyimide precursor in the polyimide film is 10% or more in the process of imidizing the polyimide precursor in terms of resin particle removability and the like. preferable. When the imidization ratio is 10% or more, it is easy to be in a state where it is 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 decomposition 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 by 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 removed by decomposing by heating for promoting imidization. In this case, there is no operation of removing the resin particles with a solvent, which is advantageous for reducing the number of processes. On the other hand, depending on the type of resin particles, decomposition gas due to heating may be generated. Due to the decomposition gas, the porous polyimide film may be broken or cracked. Therefore, in this case, it is desirable to employ a method of removing the resin particles with an organic solvent that dissolves the resin particles. It is also effective to increase the removal rate by further heating after removing the resin particles with an organic solvent that dissolves the resin particles.

  Examples of the method of removing the resin particles with the organic solvent that dissolves the resin particles include a method of contacting the resin particles with the organic solvent in which the resin particles dissolve (for example, immersing in a solvent) and dissolving and removing the resin particles. In this state, it is preferable to immerse in a solvent because the dissolution efficiency of the resin particles is increased.

  The organic solvent for dissolving the resin particles for removing the resin particles is not particularly limited as long as it is an organic solvent in which the resin particles are soluble without dissolving the polyimide film and the polyimide film that has been imidized. is not. For example, ethers such as tetrahydrofuran; aromatics such as toluene; ketones such as acetone; esters such as ethyl acetate;

  When the aqueous solvent remains when dissolving the resin particles, the aqueous solvent dissolves in the solvent that dissolves the resin particles, the polyimide precursor is precipitated, and is in a state similar to the so-called wet phase conversion method, It may be difficult to control the hole diameter. Therefore, it is preferable to dissolve and remove the resin particles with an organic solvent after the amount of the remaining aqueous solvent is reduced to 20% by mass or less, preferably 10% by mass or less, with respect to the polyimide precursor mass.

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

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

  Examples of the second stage heating condition include heating at 150 to 400 ° C. (preferably 200 to 390 ° C.) for 20 to 120 minutes. By setting the heating conditions within this range, the imidization reaction further proceeds and a polyimide film can be formed. In the heating reaction, before reaching the final temperature of heating, it is preferable to heat by gradually increasing the temperature stepwise or at a constant rate.

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

  In addition, in the case where the treatment for exposing the resin particles is not performed in the first step, the state in which the resin particles are exposed by performing the treatment for exposing the resin particles in the second step in terms of increasing the porosity. It is preferable to do. In the second step, the treatment for exposing the resin particles is preferably performed in the process of imidizing the polyimide precursor, or after the imidization and before the treatment for removing the resin particles.

  For example, in the first step, a resin particle layer is formed on the substrate (see FIG. 2A), the resin particles in the resin particle layer are impregnated with a polyimide precursor solution, 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 treatment for exposing the resin particles. The film formed by this method forms a film in which the resin particle layer is buried. Before heating the resin film and removing the resin particles, the process of imidizing the polyimide precursor, or the resin particles are exposed from the polyimide film after imidization is completed (after imidization). Process.

In the second step, the treatment for exposing the resin particles may be performed, for example, when the polyimide film is in the following state.
When the imidization ratio of the polyimide precursor in the polyimide film is less than 10% (that is, in a state where the polyimide film can be dissolved in water), when performing the treatment to expose the resin particles, the polyimide precursor is buried in the polyimide film. Examples of the treatment for exposing the resin particles to be exposed include a wiping treatment and a treatment of immersing in water.

Moreover, when the imidation ratio of the polyimide precursor in the polyimide film is 10% or more (that is, in a state in which it is difficult to dissolve in an organic solvent), and when the polyimide film has completed imidization, the resin particles In the case of performing the treatment for exposing the resin particles, a method of exposing the resin particles by mechanical cutting with a tool such as a sandpaper or a method of exposing the resin particles by decomposition with a laser or the like can be used.
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 away from the substrate of the resin particle layer) Cutting is performed together with the polyimide film present on the top of the particles, and the cut resin particles are exposed from the surface of the polyimide film (see FIG. 2C).

  Thereafter, the resin particles are removed from the polyimide film from which the resin particles are exposed by the resin particle removal process described above. And the porous polyimide film from which the resin particle was removed is obtained (refer FIG.2 (D)).

  In addition, when forming a film on a board | substrate using a resin particle dispersion | distribution polyimide precursor solution, the resin particle dispersion | distribution polyimide precursor solution is apply | coated on a board | substrate, and the coating film with which the resin particle was embedded is formed (FIG. 3 (A )reference). If a film containing a polyimide precursor and resin particles is formed without performing a process of exposing the resin particles in the process of forming the film by drying the film, a film in which the resin particles are buried is formed. And the film (polyimide film) in the process of heating and imidizing this film is in a state where the resin particle layer is buried. In order to increase the open area ratio, the same process as the process of exposing the resin particles described above can be adopted as the process of exposing the resin particles in the second step. And it cuts with the polyimide film which exists in the upper part of a resin particle, and resin particles are exposed from the surface of a polyimide film (refer to Drawing 3 (B)).

  Thereafter, the resin particles are removed from the polyimide film from which the resin particles are exposed by the resin particle removal process described above. And the porous polyimide film from which the resin particle was removed is obtained (refer FIG.3 (C)).

  In the second step, the substrate for forming the film used in the first step may be peeled off when it becomes a dry film, and the polyimide precursor in the polyimide film is an organic solvent. The film may be peeled when it is difficult to dissolve in the film, or may be peeled when the film has been imidized.

  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 imidation ratio of the polyimide precursor will be described.
The polyimide precursor partially imidized 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). A precursor is mentioned.

  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 represents 0 or an integer of 1 or more.

  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 bonds (2l + 2m + 2n) of the number of bonds (2n + m) in which the imide is ring-closed in the bond part of the polyimide precursor (reaction part of tetracarboxylic dianhydride and diamine compound). ). That is, the imidation ratio of the polyimide precursor is represented by “(2n + m) / (2l + 2m + 2n)”.

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

-Measurement of imidization rate of polyimide precursor-
-Preparation of polyimide precursor sample (i) A polyimide precursor composition to be measured is applied on 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 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.
The (iii) coating samples, taken out from in THF, blowing _{N 2} gas into THF adhering to the coating surface of the sample, removed. Under a reduced pressure of 10 mmHg or less, the film sample is dried for 12 hours or more in the range of 5 ° C. or more and 25 ° C. or less to prepare a polyimide precursor sample.

-Preparation of 100% imidized standard sample (iv) Similarly to the above (i), a polyimide precursor composition to be measured is applied on 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 produce a 100% imidized standard sample.

-Measurement and analysis (vi) Using a Fourier transform infrared spectrophotometer (FT-730, manufactured by Horiba, Ltd.), infrared absorption spectra of a 100% imidized standard sample and a polyimide precursor sample are measured. 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} )) I '(100) is obtained.
(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 ( 1780 cm ⁻¹ )) ratio I (x) is determined.

And the imidation rate of a polyimide precursor is computed based on the following formula using each measured absorption peak I '(100) and I (x).
Formula: Imidation ratio of polyimide precursor = I (x) / I ′ (100)
Formula: I ′ (100) = (Ab ′ (1780 cm ⁻¹ )) / (Ab ′ (1500 cm ⁻¹ ))
Formula: I (x) = (Ab (1780 cm ⁻¹ )) / (Ab (1500 cm ⁻¹ ))

  In addition, the measurement of the imidation rate of this polyimide precursor is applied to the measurement of the imidation rate of an aromatic polyimide precursor. When measuring the imidation ratio of the aliphatic polyimide precursor, a peak derived from a structure having no change before and after the imidation 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 the present 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 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 a 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 a diamine compound.

  The tetracarboxylic dianhydride includes both aromatic and aliphatic compounds, but is preferably an aromatic compound. That is, in the general formula (I), the tetravalent organic group represented by A is preferably an aromatic organic group.

  Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, and 3,3 ′, 4,4′-biphenyl. Sulfonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3 ′, 4,4′- Biphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4,4′-dimethyldiphenylsilane tetracarboxylic dianhydride, 3,3 ′, 4,4′-tetraphenylsilane tetracarboxylic dianhydride, 1 , 2,3,4-furantetracarboxylic dianhydride, 4,4′-bis (3,4-dicarboxyphenoxy) diphenyl sulfide dianhydride, 4,4′-bis (3,4-dicarboxyl) Noxi) diphenylsulfone dianhydride, 4,4′-bis (3,4-dicarboxyphenoxy) diphenylpropane dianhydride, 3,3 ′, 4,4′-perfluoroisopropylidenediphthalic 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′-diphenyl ether dianhydride, bis (triphenyl) Phthalic acid) -4,4'-diphenylmethane dianhydride.

  Examples of the aliphatic tetracarboxylic dianhydride include butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4. -Cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 3,5,6-tricarboxynorbonane 2-acetic acid dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic acid Aliphatic or alicyclic tetracarboxylic dianhydrides such as acid dianhydrides, bicyclo [2,2,2] -oct-7-ene-2,3,5,6-tetracarboxylic dianhydrides; , 3,3a, 4,5,9b-hexahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 1,3,3a, 4,5 9b-Hexahydro-5-methyl-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 1,3,3a, 4,5 Aliphatic tetracarboxylic acids having an aromatic ring such as 9b-hexahydro-8-methyl-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione A dianhydride etc. are mentioned.

  Among these, the tetracarboxylic dianhydride is preferably an aromatic tetracarboxylic dianhydride, specifically, for example, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyl. Tetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4 , 4′-benzophenonetetracarboxylic dianhydride is preferable, and pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4 ′ -Benzophenone tetracarboxylic dianhydride is good, especially 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride.

In addition, tetracarboxylic dianhydride may be used individually by 1 type, and may be used together in combination of 2 or more types.
In addition, when two or more types are used in combination, aromatic tetracarboxylic dianhydride or aliphatic tetracarboxylic dianhydride and aliphatic tetracarboxylic dianhydride may be used in combination. You may combine things.

  On the other hand, a diamine compound is a diamine compound having two amino groups in the molecular structure. Examples of diamine compounds include aromatic and aliphatic compounds, but aromatic compounds are preferred. 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, 4,4′-diaminodiphenyl sulfide. 4,4′-diaminodiphenylsulfone, 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, , 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] hexafluoro Propane, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) -biphenyl, 1,3′-bis (4-aminophenoxy) benzene, 9,9-bi (4-aminophenyl) fluorene, 4,4 ′-(p-phenyleneisopropylidene) bisaniline, 4,4 ′-(m-phenyleneisopropylidene) bisaniline, 2,2′-bis [4- (4-amino- Aromatic diamines such as 2-trifluoromethylphenoxy) phenyl] hexafluoropropane, 4,4′-bis [4- (4-amino-2-trifluoromethyl) phenoxy] -octafluorobiphenyl; diaminotetraphenylthiophene, etc. An aromatic diamine having two amino groups bonded to the aromatic ring and a hetero atom other than the nitrogen atom of the amino group; 1,1-metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, penta Methylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminohe Data diamine, 1,4-diaminocyclohexane, isophorone diamine, tetrahydrodicyclopentadiene cyclopentadienylide diamine, hexahydro-4,7-meth Noin mite range diamine, tricyclo [6,2,1,0 ^2.7] Examples thereof include aliphatic diamines such as undecylenedimethyl diamine and 4,4′-methylene bis (cyclohexylamine), and alicyclic diamines.

  Among these, as the diamine compound, an aromatic diamine compound is good, 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.

  In addition, a diamine compound may be used individually by 1 type, and may be used together in combination of 2 or more types. Moreover, when using together and using 2 or more types, you may use together an aromatic diamine compound or an aliphatic diamine compound, respectively, or may combine an aromatic diamine compound and an aliphatic diamine compound.

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

The number average molecular weight of the polyimide precursor is measured by a gel permeation chromatography (GPC) method under the following measurement conditions.
Column: Tosoh TSKgel α-M (7.8 mm ID × 30 cm)
Eluent: DMF (dimethylformamide) / 30 mM LiBr / 60 mM phosphoric acidFlow 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, based on the total polyimide precursor solution. Preferably they are 1 mass% or more and 20 mass% or less.

(Organic amine compound)
An organic amine compound is a compound that functions as an imidization accelerator while amine-treating a polyimide precursor (its carboxyl group) to increase its solubility in an aqueous solvent. 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 excluding a diamine compound that is a raw material for the polyimide precursor.
The organic amine compound is preferably a water-soluble compound. Water-soluble means that the target substance dissolves 1% by mass or more in water 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 the solvent is likely to be increased, and the film forming property is easily improved. Storage stability of the polyimide precursor solution is easily improved.

  Moreover, as an organic amine compound, the polyvalent amine compound more than bivalence other than a monovalent amine compound is also mentioned. When a polyvalent amine compound having two or more valences is applied, a pseudo-crosslinked structure is easily formed between the 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, and 2-ethyl-4. -Methylimidazole etc. are mentioned.

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

  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 properties, and more preferably from 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, the organic amine compound is prevented from volatilizing from the polyimide precursor solution during storage, and the solubility of the polyimide precursor in the solvent is easily suppressed.

The organic amine compound may be contained in an amount of 50 mol% to 500 mol%, preferably 80 mol% to 250 mol%, based on the carboxyl group (—COOH) of the polyimide precursor in the polyimide precursor solution. More preferably, it is contained at 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 the solvent is likely to increase, and the film forming property is easily improved. Moreover, it becomes easy to improve the storage stability of the polyimide precursor solution.

  Said organic amine compound may be used individually by 1 type, and may be used together 2 or more types.

(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 exchange water, ultrafiltration water, and pure water.

  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 still more preferably 80% by mass or more and 100% by mass or less with respect to the total aqueous solvent.

  When the aqueous solvent includes a solvent other than water, examples of the solvent other than water include a water-soluble organic solvent and an aprotic polar solvent. 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, from the viewpoint of improving various properties of the polyimide molded product such as heat resistance, electrical properties and solvent resistance in addition to transparency and mechanical strength, 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 with respect to the total aqueous solvent). Here, water-soluble means that the target substance dissolves 1% by mass or more in water at 25 ° C.

  Although the said water-soluble organic solvent may be used individually by 1 type, you may use 2 or more types together.

  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- Examples include 1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 1,2,6-hexanetriol and the like. Among these, as the water-soluble alcohol solvent, methanol, ethanol, 2-propanol, ethylene glycol, monoalkyl ether of ethylene glycol, propylene glycol, monoalkyl ether of propylene glycol, diethylene glycol, and monoalkyl ether of diethylene glycol are preferable.

  When an aprotic polar solvent other than water is contained as the aqueous solvent, the aprotic polar solvent used in combination is a solvent having a boiling point of 150 ° C. or higher and 300 ° C. or lower and a dipole moment of 3.0D or higher and 5.0D 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), dimethyl sulfoxide (DMSO), Hexamethylene phosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, N, N-dimethylimidazolidinone (DMI), N, N′-dimethylpropyleneurea, tetramethylurea, trimethyl phosphate And triethyl phosphate.

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

  Here, the range in which the polyimide precursor is dissolved in the solvent is controlled by the water content and the type and amount of the organic amine compound. In a range where the water content is low, the polyimide precursor is easily dissolved in a region where the content of the organic amine compound is low. On the contrary, in the range where the content of water is high, the polyimide precursor is easily dissolved in a region where the content of the organic amine compound is large. Further, when the organic amine compound has high hydrophilicity such as 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 a poor solvent such as water or alcohol, precipitated, and separated. It may be a precursor.

(Other additives)
In the method for producing a porous polyimide film according to the present embodiment, the polyimide precursor solution may include a catalyst for promoting imidization reaction, a leveling material for improving 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, or a benzoic acid derivative may be used.

Further, depending on the purpose of use of the porous polyimide film, for example, a conductive material (conductivity (for example, volume resistivity less than 10 ⁷ Ω · cm) or It may contain semiconductivity (for example, volume resistivity 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 or nickel); metal oxide (for example, yttrium oxide, tin oxide); ion conductive material (for example, titanium) Acid potassium, LiCl, etc.); These conductive materials may be used alone or in combination of two or more.

Moreover, the polyimide precursor solution may contain inorganic particles added for improving the 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.
It may also include the like LiCoO _2, LiMn ₂ O used as an electrode of a lithium ion battery.

(Method for producing polyimide precursor solution)
Although it does not specifically limit as a manufacturing method of the polyimide precursor solution which concerns on this embodiment, For example, the manufacturing method shown below is mentioned.
As an example, there is a method in which a tetracarboxylic dianhydride and a diamine compound are polymerized in an aqueous solvent in the presence of an organic amine compound to produce a resin (polyimide precursor) to obtain a polyimide precursor solution. .
According to this method, since the aqueous solvent is applied, the productivity is high and the polyimide precursor solution is produced in one step, which is advantageous in terms of simplification of the process.

  As another example, a resin (polyimide precursor) is obtained by polymerizing tetracarboxylic dianhydride and a diamine compound in an organic solvent such as an aprotic polar solvent (for example, N-methylpyrrolidone (NMP)). Then, it is poured into an aqueous solvent such as water or alcohol to precipitate a resin (polyimide precursor). Thereafter, a method of obtaining a polyimide precursor solution by dissolving a polyimide precursor and an organic amine compound in an aqueous solvent 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, generation of cracks is suppressed.

(Characteristics of porous polyimide film)
The porous polyimide film of the present invention is not particularly limited, but the porosity is preferably 30% or more. Moreover, it is preferable that a porosity is 40% or more, and it is more preferable that it is 50% or more. The upper limit of the porosity is not particularly limited, but is preferably in the range of 90% or less.

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

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

  In the porous polyimide film of the present embodiment, the ratio of the maximum diameter and the minimum diameter of the pores (ratio of the maximum value and the minimum value of the pore diameter) is 1 or more and 2 or less. Preferably they are 1 or more and 1.9 or less, More preferably, they are 1 or more and 1.8 or less. Of these ranges, a value closer to 1 is more preferable. By being in this range, variation in the hole diameter is suppressed. In addition, when the porous polyimide film of the present embodiment is applied to, for example, a battery separator of a lithium ion battery, turbulence in ion flow is suppressed, so that formation of lithium dendrite 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 pore diameter, the average value of the pore diameter where the pores are connected to each other, and the major and minor diameters of the pores are observed with a scanning electron microscope (SEM). And a measured value. Specifically, first, a porous polyimide film is cut out to prepare a measurement sample. Then, this measurement sample is observed and measured with image processing software provided as a standard by a VE SEM manufactured by KEYENCE. Observation and measurement are performed for each of the hole portions in the measurement sample cross section, and the average value, minimum diameter, maximum diameter, and arithmetic average diameter are obtained. When the shape of the hole is not circular, the longest part is the diameter.

  Although the film thickness of a porous polyimide film is not specifically limited, It is good that they are 15 micrometers or more and 500 micrometers or less.

(Use of porous polyimide film)
Applications for which the porous polyimide film according to this embodiment is applied include, for example, 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 materials; 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 generation of lithium dendrite is suppressed due to an action such as suppression of variations in ion flow distribution of lithium ions. . This is presumed to be because the pore shape and the pore diameter variation of the porous polyimide film of this embodiment are suppressed.
Further, for example, when applied to a battery electrode material, it is considered that the capacity of the battery increases because the chance of contact with the electrolyte increases. This is presumably because the amount of the material such as carbon black for electrodes contained in the porous polyimide film is exposed to the surface of the porous polyimide film on the pore diameter and the surface of the film.
Furthermore, for example, it is also possible to fill the pores of the porous polyimide film with, for example, an ionic gel obtained by gelling a so-called ionic liquid, and apply it as an electrolyte membrane. Since the manufacturing method of this embodiment simplifies the process, 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, “part” and “%” are all based on mass unless otherwise specified.

[Preparation of polyimide precursor “water” solution (PAA-1)]
A flask equipped with a stir bar, thermometer, and dropping funnel was charged 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, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (molecular weight 294.22): 72.72 g (247.16 mmol) was added to this solution, and the reaction temperature was maintained at 20 ° C. The solution 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 stir bar, thermometer and dropping funnel was charged with 900 g of N-methylpyrrolidone. To this, 27.28 g (252.27 mmol) of p-phenylenediamine was added and dispersed by stirring at 20 ° C. for 10 minutes. To this solution was added 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride: 72.72 g (247.16 mmol) and dissolved by stirring for 24 hours while maintaining the reaction temperature at 20 ° C. Then, a 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 while stirring to precipitate the polyimide precursor. 30 g of this polyimide precursor was added to 243 g of water and 27 g of isopropanol, and further 15 g of methylmorpholine 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 while stirring to precipitate the polyimide precursor. 30 g of this polyimide precursor is added to 243 g of water and 27 g of isopropanol, and further 15 g of 1,2-dimethylimidazole (DMIz) is added and stirred and dissolved to obtain 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 while stirring to precipitate the polyimide precursor. 30 g of this polyimide precursor is added to 243 g of water and 27 g of N-methylpyrrolidone, and further, 15 g of 1,2-dimethylimidazole is added and stirred and dissolved to obtain a polyimide precursor “water / N-methylpyrrolidone” solution. (PAA-4) was obtained.

<Example 1>
Non-crosslinked polymethyl methacrylate / styrene copolymer having an average particle size of 0.1 μm (FS-102E: manufactured by Nippon Paint): 10 parts, polyvinyl butyral resin (S-LEC SV-02: manufactured by Sekisui Chemical Co., Ltd.): One part was added to 30 parts of ethanol and stirred on a webblotter to prepare a dispersion. This was formed on a glass substrate so that the film thickness after drying was 30 μm, and dried at 90 ° C. for 1 hour to form a resin particle layer.
After diluting the polyimide precursor “water” solution (PAA-1) 10 times and applying the polyimide precursor “water” solution (PAA-1) on the resin particle layer, vacuum degassing is performed, and between resin particles Was impregnated with a polyimide precursor “water” solution (PAA-1). After drying overnight at room temperature (25 ° C., the same applies hereinafter), water was wiped so that the surface of the resin particle layer was exposed, and the excess polyimide precursor on the resin particle layer was removed. After heating this at 120 ° C. for 1 hour, it was peeled off 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, held at 380 ° C. for 1 hour, and then cooled to room temperature to obtain a porous polyimide film (PIF-1).

<Comparative Example 1>
On the resin particle layer produced in the same manner as in Example 1, the polyimide precursor “N-methylpyrrolidone” solution (RPAA-1) was diluted 10 times and applied, but the resin particles were dissolved. After heating this at 120 degreeC for 1 hour, it peeled from the board | substrate made from glass, and it immersed in toluene, and eluted resin. After drying, the temperature was raised from room temperature to 380 ° C. at a speed of 10 ° C./min, held 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 to 1.01 μm, and the distribution was wide. This is probably because the resin particles were dissolved and the form of the resin particles could not be maintained.

<Example 2>
The polyimide precursor “water / isopropanol” solution (PAA-2) was diluted 10 times and applied onto the resin particle layer prepared in the same manner as in Example 1, and the porous polyimide film (PIF) was applied 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 onto the resin particle layer prepared in the same manner as in Example 1, dried at room temperature overnight, and then the surface of the resin particle layer. Then, water was wiped so as to expose the excess polyimide precursor. This was heated at 120 ° C. for 1 hour, then peeled off from the glass substrate, heated from room temperature to 380 ° C. at a rate of 10 ° C./minute, held at 380 ° C. for 1 hour, then cooled to room temperature and porous Quality polyimide film (PIF-3) was obtained.

<Example 4>
The polyimide precursor “water / isopropanol” solution (PAA-2) was diluted 10 times, and 10 parts of the polyimide precursor was diluted with 10 parts of non-crosslinked polymethyl methacrylate / styrene having an average particle size of 0.1 μm. A copolymer (FS-102E: manufactured by Nippon Paint Co., Ltd.) was added and stirred on a webblotter to prepare a dispersion. 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./min. After holding at ° C. for 1 hour, it was cooled to room temperature to obtain a porous polyimide film (PIF-4).

<Example 5>
The polyimide precursor “water / isopropanol” solution (PAA-2) was diluted 10 times, and 10 parts of the polyimide precursor was diluted with 10 parts of non-crosslinked polymethyl methacrylate / styrene having an average particle size of 0.1 μm. A copolymer (FS-102E: manufactured by Nippon Paint Co., Ltd.) was added and stirred on a webblotter to prepare a dispersion. 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, then peeled off 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./minute, held at 380 ° C. for 1 hour, and then cooled to room temperature to form 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 and cannot be sufficiently removed by drying at room temperature, the pore diameter was larger than that of isopropanol.

<Comparative example 2>
Mono-dispersed spherical silica particles having an average diameter of 550 nm manufactured by Nippon Shokubai Co., Ltd. (true sphere ratio: 1.0, particle size distribution index: 1.20): 30 parts by mass to N-methylpyrrolidone (NMP): 30 parts by mass Distributed. A polyimide precursor “N-methylpyrrolidone” solution (RPAA-1): 100 parts by mass of silica particle dispersion: 20 parts by mass was mixed and stirred, and then applied onto a glass plate. This is heated at 120 ° C. for 1 hour, then peeled off from the glass substrate, heated from room temperature to 380 ° C. at a speed of 10 ° C./minute, held at 380 ° C. for 1 hour, then cooled to room temperature and silica -A polyimide composite membrane was obtained. The silica-polyimide composite film was immersed in 10% by mass of hydrogen fluoride water, and 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 Company), and 576 parts by mass of ion-exchanged water The mixture was stirred and emulsified with a dissolver at 1,500 rpm for 30 minutes to prepare a monomer emulsion. Subsequently, 1.49 parts by mass of Dowfax 2A1 (47% solution, manufactured by Dow Chemical Company) and 1270 parts by mass of ion-exchanged water were charged into the reaction vessel. After heating to 75 ° C. under a nitrogen stream, 75 parts by mass of the monomer emulsion is added, and then a polymerization initiator solution in which 15 parts by mass of ammonium persulfate is dissolved in 98 parts by mass of ion-exchanged water is taken for 10 minutes. It was dripped. After reacting for 50 minutes after the dropwise addition, the remaining monomer emulsion was added dropwise over 220 minutes and allowed to react for an additional 180 minutes. After cooling, a resin particle dispersion (1) was obtained as a non-crosslinked styrene / acrylic resin particle dispersion adjusted to a solid content concentration of 30% by mass. The average particle size of the resin particles in the resin particle dispersion (1) was 250 nm.
The polyimide precursor “water” solution (PAA-1) and the resin particle dispersion (1) are, in mass ratio, solid content of the polyimide precursor solution: solid content of the resin particle dispersion = 30: 70 (100: 233) to obtain a resin particle-dispersed polyimide precursor “water” solution (1). The 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-made board | substrates, and it was immersed in tetrahydrofuran (THF) for 30 minutes, and the resin particle was eluted. 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 Corporation make: VE-8800) is shown in FIG.

<Example 9>
In Example 8, the polyimide precursor “water” solution (PAA-1) and the resin particle dispersion (1) in terms of 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 so as to be 50 (100: 100) was used, and the immersion time in THF was changed to 2 hours. A 25 μm porous polyimide film (PIF-9) was obtained. Further, a photograph of the surface of the film (PIF-9) observed with 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 (1) in terms of mass ratio, solid content of the polyimide precursor solution: solid content of the resin particle dispersion = 70 : 30 (100: 43) The resin particle-dispersed polyimide precursor “water” solution (3) mixed so as to be 30 (100: 43) was used in the same manner as in Example 8 except that the immersion time in THF was 12 hours. A 25 μm porous polyimide film (PIF-10) was obtained. Further, FIG. 6 shows a photograph of the surface of the film (PIF-10) observed by a scanning electron microscope in the same manner as in Example 8.

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

[Evaluation of cracks]
The porous polyimide films obtained in Examples 1 to 10 and Comparative Examples 1 and 2 were evaluated for cracks. The specific method is as follows. The above 0.1mm area of the polyimide film 1 cm ² square by microscope magnification 500 and cracking were visually observed whether.

-Evaluation criteria-
A: No crack B: 1 or more and 3 or less C: 4 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-crosslinked polymethyl methacrylate / styrene copolymer “PBA / St”: Non-crosslinked polybutyl acrylate / styrene copolymer / “IPA” : Isopropanol / "NMP": N-methylpyrrolidone

1 resin particles, 2 binder resin, 3 substrate, 4 release layer, 5 polyimide precursor solution, 7 pores, 61 polyimide film, 62 porous polyimide film

Claims (10)

In an aqueous solvent, after forming a coating film containing a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved, and resin particles not dissolved in the polyimide precursor solution, the coating film is dried, A first step of forming a 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, including a process of removing the resin particles;
The manufacturing method of the porous polyimide film which has this.   In the first step, a resin particle dispersion containing the resin particles, an organic solvent in which the resin particles are not dissolved, and a binder resin dissolved 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 manufacturing method of the porous polyimide film of Claim 1.   The first step applies a resin particle-dispersed polyimide precursor solution containing the polyimide precursor solution and resin particles not dissolved in the polyimide precursor solution on a substrate to form a coating film, and the coating film The method for producing a porous polyimide film according to claim 1, wherein the film is dried to form the coating film.   The said 1st process WHEREIN: The process which exposes the said resin particle is performed in the process in which the said coating film is dried and the said coating film is formed, The porous polyimide film as described in any one of Claims 1-3. Manufacturing method.   In the second step, a process of exposing the resin particles is performed in the process of imidizing the polyimide precursor or after the imidization and before the process of removing the resin particles. Item 4. The method for producing a porous polyimide film according to any one of Items 3 to 4.   The method for producing a porous polyimide film according to any one of claims 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 method for producing a porous polyimide film according to any one of claims 1 to 6, wherein the treatment for removing the resin particles is a treatment for removal 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 said organic amine compound is an amine compound which has a heterocyclic structure containing nitrogen, The manufacturing method of the porous polyimide film as described in any one of Claims 1-7.   The porous polyimide film manufactured by the method as described in any one of Claims 1-9.