JP6701834B2 - Method for producing resin particle-dispersed polyimide precursor solution, resin particle-dispersed polyimide precursor solution, resin particle-containing polyimide film, method for producing porous polyimide film, and porous polyimide film - Google Patents

Description

  The present invention relates to a method for producing a resin particle-dispersed polyimide precursor solution, a resin particle-dispersed polyimide precursor solution, a resin particle-containing polyimide film, a method for producing a porous polyimide film, and a porous polyimide film.

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

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

Further, in Patent Document 5, a positive electrode, a negative electrode, and a separator layer having an average pore diameter of 5 μm or less and including a porous polyimide film formed into a porous film by phase separation after application of a solution of polyimide or a polyimide precursor. , A non-aqueous electrolyte secondary battery having a.
In Patent Document 6, a heat-resistant resin such as polyimide, heat-extinguishing resin particles containing a polyoxyalkylene resin, and a solvent are mixed to prepare a resin composition for a film, and a resin composition for a film is manufactured. A method for producing a porous resin film, which includes a step of forming a film and a step of heating the formed resin composition for a film, is 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

  An object of the present invention is to provide a method for producing a resin particle-dispersed polyimide precursor solution in which the dispersibility of resin particles is improved as compared with the case of mixing a resin particle dispersion liquid and a polyimide precursor solution.

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

< 1 >
In a resin particle dispersion liquid in which resin particles are dispersed in an aqueous solvent, in the presence of an organic amine compound, a resin particle-dispersed polyimide precursor solution in which a tetracarboxylic dianhydride and a diamine compound are polymerized to form a polyimide precursor of production how.

< 2 >
The resin particle dispersion liquid, manufactured how the resin particles dispersed polyimide precursor solution according to a resin particle dispersion was granulated resin particles <1> in the aqueous solvent.

< 3 >
The organic amine compound is prepared how the resin particles dispersed polyimide precursor solution according to a tertiary amine compound <1> or <2>.

< 4 >
The organic amine compound is an amine compound having a heterocyclic structure containing a nitrogen <1> or manufacture how the resin particles dispersed polyimide precursor solution according to <2>.

< 5 >
<1> to <4> resin particle dispersion polyimide precursor dissolved solution obtained by the method according to any one of.

< 6 >
After coating the resin particle-dispersed polyimide precursor solution according to < 5 > to form a coating film,
Resin particles containing polyimide film beam obtained by heating a coating film.

< 7 >
The first step of applying the resin particle-dispersed polyimide precursor solution according to < 5 > to form a coating film, and then drying the coating film to form a coating film containing the polyimide precursor and the resin particles. When,
A second step of heating the coating to imidize the polyimide precursor to form a polyimide film, the second step including a treatment of removing the resin particles;
Producing how porous polyimide film having a.

< 8 >
< 7 > In the second step, a process of exposing the resin particles is performed after the process of imidizing the polyimide precursor or after the imidization and before the process of removing the resin particles. producing how the porous polyimide film.

< 9 >
The process of removing the resin particles, prepared how porous polyimide film according to a process of removing <7> or <8> by an organic solvent capable of dissolving the resin particles.

< 10 >
The process of removing the resin particles, prepared how porous polyimide film according to a process of removing <7> or <8> by heating.

< 11 >
<7> - produced by the method for producing a porous polyimide film described in any one of <10> porous polyimide film arm.

According to the invention of < 1 > or < 2 > , a method for producing a resin particle-dispersed polyimide precursor solution in which the dispersibility of resin particles is improved as compared with the case of mixing the resin particle dispersion and the polyimide precursor solution. Will be provided.

The invention according to < 3 > or < 4 > provides a method for producing a porous polyimide film having excellent film-forming properties as compared with the case where the organic amine compound is a primary amine compound.

According to the invention of < 5 > , resin particles having improved dispersibility of resin particles as compared with the case of a resin particle-dispersed polyimide precursor solution obtained by mixing a resin particle dispersion liquid and a polyimide precursor solution. A dispersed polyimide precursor solution is provided.

According to the invention of < 6 > , compared with the case of the resin particle-containing polyimide film obtained by the resin particle-dispersed polyimide precursor solution obtained by mixing the resin particle dispersion liquid and the polyimide precursor solution, Provided is a resin particle-containing polyimide film in which variation in particle distribution is suppressed.

According to the invention of < 7 > , compared with the case of the method for producing the porous polyimide film obtained by the resin particle-dispersed polyimide precursor solution obtained by mixing the resin particle dispersion and the polyimide precursor solution. Provided is a method for producing a porous polyimide film in which variation in pore size distribution is suppressed.

According to the invention of < 8 >, when the process of exposing the resin particles is not performed in the process of performing the imidization of the polyimide precursor or after the imidization and before the process of removing the resin particles. In comparison, a method for producing a porous polyimide film that provides a porous polyimide film having a high porosity is provided.

The invention according to < 9 > or < 10 > is a method for producing a porous polyimide film obtained by a resin particle-dispersed polyimide precursor solution obtained by mixing a resin particle dispersion and a polyimide precursor solution. In comparison with the case, the treatment for removing the resin particles is a treatment for removing the resin particles with an organic solvent that dissolves the resin particles, or a porous polyimide film in which the variation in the distribution of pore diameters is suppressed even if the treatment is performed by heating. A method of manufacturing the same is provided.

According to the invention of < 11 > , compared with the case where the porous polyimide film is obtained by the resin particle-dispersed polyimide precursor solution obtained by mixing the resin particle dispersion and the polyimide precursor solution, Provided is a porous polyimide film in which variation in pore size distribution is suppressed.

It is process drawing which shows an example of the manufacturing method of the porous polyimide film of this embodiment. It is an electron microscope photograph of the surface of the porous polyimide film (PIF-11) obtained in Example 11A.

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

<Resin Particle-Dispersed Polyimide Precursor Solution and Manufacturing Method Thereof>
The method for producing a resin particle-dispersed polyimide precursor solution according to the present embodiment is a resin particle dispersion liquid dispersed in an aqueous solvent, in the presence of an organic amine compound, a tetracarboxylic dianhydride and a diamine compound are polymerized. Is a method for forming a polyimide precursor.

  In addition, in this embodiment, "not dissolving" also includes that the target substance dissolves in the range of 3% by mass or less with respect to the target liquid at 25°C.

  The method for producing the resin particle-dispersed polyimide precursor solution according to the present embodiment has the above-described configuration, and the resin particle-dispersed polyimide precursor solution is compared to the case where the resin particle-dispersed liquid and the polyimide precursor solution are formed by mixing. Therefore, the dispersibility of the resin particles is improved. The reason is not clear, but it is presumed that the reason is as follows.

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

Depending on the purpose, the polyimide film may contain particles such as inorganic particles and resin particles. In this case, a polyimide precursor solution in which particles are mixed is used. For example, when inorganic particles are mixed with a polyimide precursor solution dissolved in a highly polar organic solvent to prepare a particle-dispersed polyimide precursor solution, the dispersibility of the inorganic particles in this polyimide precursor solution is low.
On the other hand, when the resin particles are mixed with the polyimide precursor solution dissolved in the high polarity organic solvent, in the case of general resin particles (for example, polystyrene resin particles etc.), the resin particles may be dissolved by the high polarity organic solvent. In this polyimide precursor solution, the dispersibility of resin particles is low. Further, for example, when the resin particles that are difficult to dissolve in a high polarity organic solvent are prepared by emulsion polymerization or the like, in order to mix with the polyimide precursor solution dissolved in a high polarity organic solvent, when replacing with a high polarity organic solvent There is. In this case, the resin particles may be taken out from the dispersion liquid of the resin particles in order to substitute the highly polar organic solvent, and the taken out resin particles may be aggregated and the dispersibility may be low.

  On the other hand, in the method for producing the resin particle-dispersed polyimide precursor solution according to this embodiment, the dispersibility of the resin particles is improved by the above configuration. This is because in the presence of an organic amine compound in a resin particle dispersion liquid in which resin particles are dispersed in advance, in order to form a polyimide precursor, in a state where the resin particles are dispersed, to form a polyimide precursor. Is considered to be. Furthermore, since the organic amine compound is present in the aqueous solvent, the formed polyimide precursor (its carboxyl group) is in a state of being amine-chlorinated by the organic amine compound. Therefore, it is considered that a part of the organic amine salt of the polyimide precursor functions as a dispersant for the resin particles, improving the dispersibility of the resin particles.

  From the above, the method for producing a resin particle-dispersed polyimide precursor solution according to the present embodiment has the above-described configuration, in which the resin particle-dispersed polyimide precursor solution is formed by mixing the resin particle dispersion and the polyimide precursor solution. It is presumed that the dispersibility of the resin particles is improved as compared with the case.

  Further, in the method for producing the resin particle-dispersed polyimide precursor solution according to the present embodiment, the polyimide precursor is formed in the resin particle dispersion liquid in which the resin particles are previously dispersed. Therefore, the resin particle-dispersed polyimide precursor solution of the present embodiment, from the production of the resin particle dispersion liquid to the production of the resin particle-dispersed polyimide precursor solution, is obtained in one system (for example, in one container), The process of producing the resin particle-dispersed polyimide precursor solution is simplified.

  The resin particle-dispersed polyimide precursor solution obtained by the method for producing a resin particle-dispersed polyimide precursor solution according to this embodiment has improved dispersibility of resin particles. Therefore, in the resin particle-containing polyimide film obtained from this polyimide precursor solution, variation in distribution of resin particles is easily suppressed.

  Further, the resin particle-dispersed polyimide precursor solution according to the present embodiment is used to form a coating film, and the first step of drying the coating film to form a coating film, and heating the coating film for imidization. And a second step of removing the resin particles in the second step, whereby the porous polyimide film of the present embodiment is obtained. In the porous polyimide film obtained by this manufacturing method, variation in the distribution of pores is easily suppressed. Further, variations in the shape of the holes, the diameter of the holes, etc. are easily suppressed. The reason for this is presumed as follows.

Since the resin particle-dispersed polyimide precursor solution of the present embodiment has improved dispersibility, it is considered that the porous polyimide film from which the resin particles have been removed is likely to suppress variations in the distribution of pores.
Further, it is considered that the use of the resin particles makes it easy to suppress variations in the shape of pores, the diameter of pores, and the like. It is considered that this is because it effectively contributes to the relaxation of residual stress in the imidization step of the polyimide precursor.
Further, since the polyimide precursor is dissolved in the aqueous solvent, the boiling point of the polyimide precursor solution is about 100°C. Therefore, as the coating containing the polyimide precursor and the resin particles is heated, the solvent is quickly volatilized, and then the imidization reaction proceeds. The resin particles in the coating lose their fluidity and become insoluble in the organic solvent before they are deformed by heat. Therefore, it is considered that the shape of the holes is easily maintained.

  Further, using the resin particle-dispersed polyimide precursor solution according to the present embodiment, to form a resin particle-containing polyimide film, the porous polyimide film of the present embodiment obtained by removing the resin particles, the occurrence of cracks It is easy to be suppressed. It is presumed that this is because, in the method for producing the porous polyimide film of the present embodiment, the use of the resin particles effectively contributes to the relaxation of the residual stress in the imidization step of the polyimide precursor.

  The porous polyimide film may be obtained, for example, by preparing a coating using a polyimide precursor solution in which silica particles are dispersed, firing the coating, and then removing the silica particles. However, according to this method, it is necessary to use a chemical such as hydrofluoric acid in the treatment for removing silica particles. Therefore, these manufacturing methods have low productivity and high cost.

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

  On the other hand, since the porous polyimide film obtained by the manufacturing method of the present embodiment does not use silica particles, the step of obtaining the porous polyimide film is simplified. Further, since hydrofluoric acid is not used for removing the resin particles, it is possible to suppress the ions from remaining as impurities.

  Hereinafter, the method for producing the resin particle-dispersed polyimide precursor solution according to the present embodiment and the resin particle-dispersed polyimide precursor solution obtained by the method will be described.

[Method for producing resin particle-dispersed polyimide precursor solution]
In the method for producing a resin particle-dispersed polyimide precursor solution of the present embodiment, first, a resin particle dispersion liquid in which resin particles are dispersed in an aqueous solvent is prepared. Then, in the resin particle dispersion liquid, a tetracarboxylic dianhydride and a diamine compound are polymerized in the presence of an organic amine compound to form a polyimide precursor.

  Specifically, a step of preparing a resin particle dispersion liquid in which resin particles are dispersed in an aqueous solvent (hereinafter, also referred to as "resin particle dispersion liquid preparation step"), an organic amine compound, tetracarboxylic Acid dianhydride, and, mixing the diamine compound, a step of polymerizing a tetracarboxylic acid dianhydride and a diamine compound to form a polyimide precursor (hereinafter, also referred to as "polyimide precursor forming step") Have.

(Resin particle dispersion liquid preparation step)
The method of preparing the resin particle dispersion liquid is not particularly limited as long as the resin particle dispersion liquid in which the resin particles are dispersed can be obtained in the aqueous solvent.
For example, there may be mentioned a method in which resin particles that are not dissolved in a polyimide precursor solution and an aqueous solvent for a resin particle dispersion are weighed, and these are mixed and stirred. The method of mixing and stirring the resin particles and the aqueous solvent is not particularly limited. For example, a method of mixing resin particles while stirring an aqueous solvent may be used. Further, in order to improve the dispersibility of the resin particles, for example, at least one of an ionic surfactant and a nonionic surfactant may be mixed.

  Further, the resin particle dispersion liquid may be a resin particle dispersion liquid obtained by granulating resin particles in the aqueous solvent. When granulating resin particles in an aqueous solvent, a resin particle dispersion liquid formed by polymerizing monomer components in an aqueous solvent may be prepared. In this case, it may be a dispersion liquid obtained by a known polymerization method. For example, when the resin particles are vinyl resin particles, known polymerization methods (radical polymerization methods such as emulsion polymerization, soap-free emulsion polymerization, suspension polymerization, miniemulsion polymerization, microemulsion polymerization) can be applied.

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

  The resin particle dispersion forming step is not limited to the above method, and a commercially available resin particle dispersion dispersed in an aqueous solvent may be prepared. When using a commercially available resin particle dispersion, an operation such as dilution with an aqueous solvent may be performed depending on the purpose. Further, the resin particle dispersion liquid dispersed in the organic solvent may be replaced with an aqueous solvent as long as the dispersibility is not affected.

(Polyimide precursor forming step)
Next, in a resin particle dispersion liquid, a tetracarboxylic dianhydride and a diamine compound are polymerized 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 an aqueous solvent is applied, the productivity is high, and the polyimide precursor solution is manufactured in one step, which is advantageous in terms of process simplification.

  Specifically, an organic amine compound, a tetracarboxylic acid dianhydride, and a diamine compound are mixed with the resin particle dispersion liquid prepared in the resin particle dispersion liquid preparation step. Then, the tetracarboxylic dianhydride and the diamine compound are polymerized in the presence of the organic amine compound to form a polyimide precursor in the resin particle dispersion liquid. The order in which the organic amine compound, the tetracarboxylic dianhydride, and the diamine compound are mixed with the resin particle dispersion liquid is not particularly limited.

  When the tetracarboxylic dianhydride and the diamine compound are polymerized in the resin particle dispersion, the aqueous solution in the resin particle dispersion may be used as it is to form the polyimide precursor. Moreover, you may mix an aqueous solvent newly as needed. When the aqueous solvent is newly mixed, the aqueous solvent may be an aqueous solvent containing a small amount of an aprotic polar solvent. Further, other additives may be mixed depending on the purpose.

  Through the above steps, a resin particle-dispersed polyimide precursor solution is obtained.

  Next, the materials constituting the resin particle-dispersed polyimide precursor solution will be described.

(Aqueous solvent)
The aqueous solvent, in the resin particle dispersion, when polymerizing the tetracarboxylic dianhydride and the diamine compound, even if the aqueous solvent in the resin particle dispersion used in the preparation of the resin particle dispersion is used as it is. Good. Further, when the tetracarboxylic dianhydride and the diamine compound are polymerized, an aqueous solvent may be prepared so as to be suitable for the polymerization.

  The aqueous solvent is an aqueous solvent containing water. Specifically, the aqueous solvent is preferably a solvent containing 50% by mass or more of water with respect to the total aqueous solvent. Examples of water include distilled water, ion-exchanged water, ultrafiltered water, 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 further preferably 80% by mass or more and 100% by mass or less with respect to the total aqueous solvent.

  The aqueous solvent used when preparing the resin particle dispersion is an aqueous solvent containing water. Specifically, the aqueous solvent for the resin particle dispersion is preferably an aqueous solvent containing 50% by mass or more of water with respect to the total aqueous solvent. Examples of water include distilled water, ion-exchanged water, ultrafiltered water, pure water and the like. When a soluble organic solvent other than water is included, for example, a water-soluble alcohol solvent may be used. The term "water-soluble" means that the target substance dissolves in water at 1% by mass or more at 25°C.

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

The above water-soluble organic solvents may be used alone or in combination of two or more.
As the water-soluble organic solvent, those which do not dissolve the resin particles described later are preferable. The reason for this is that, for example, when an aqueous solvent containing water and a water-soluble organic solvent is used, the resin particles are dissolved in the process of film formation even if the resin particles are not dissolved in the resin particle dispersion liquid. This is because there is a concern that it will happen.

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

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

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

  When an aprotic polar solvent other than water is contained as the aqueous solvent, the aprotic polar solvent used together has a boiling point of 150° C. or higher and 300° C. or lower and a dipole moment of 3.0 D or higher and 5.0 D or lower. is there. Specific examples of the aprotic polar solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), Hexamethylenephosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone (DMI), N,N′-dimethylpropyleneurea, tetramethylurea, Examples include trimethyl phosphate and triethyl phosphate.

  When a solvent other than water is contained as the aqueous solvent, the solvent used in combination preferably has a boiling point of 270°C or lower, preferably 60°C or higher and 250°C or lower, and more preferably 80°C or higher and 230°C or lower. is there. When the boiling point of the solvent used in combination is within the above range, it becomes difficult for 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 content of water and the type and amount of the organic amine compound. When the content of water is low, the polyimide precursor is easily dissolved in the region where the content of the organic amine compound is low. On the contrary, when the content of water is high, the polyimide precursor is easily dissolved in the region where the content of the organic amine compound is high. Further, when the organic amine compound has a high hydrophilicity such as having a hydroxyl group, the polyimide precursor is easily dissolved in a region where the water content is high.

(Resin particles)
The resin particles are not particularly limited as long as they do not dissolve in the polyimide precursor solution. For example, resin particles obtained by polycondensing polymerizable monomers such as polyester resin and urethane resin, resin particles obtained by radical polymerization of polymerizable monomers such as vinyl resin, olefin resin, and fluororesin. Is mentioned. Examples of the resin particles obtained by radical polymerization include resin particles of (meth)acrylic resin, (meth)acrylic acid ester resin, styrene/(meth)acrylic resin, polystyrene resin, polyethylene resin and the like.
Among these, the resin particles are preferably at least one selected from the group consisting of (meth)acrylic resin, (meth)acrylic acid ester resin, styrene/(meth)acrylic resin, and polystyrene resin.
Further, the resin particles may or may not be crosslinked. In the imidization step of the polyimide precursor, non-crosslinked resin particles are preferable because they effectively contribute to the relaxation of residual stress. Furthermore, the resin particle dispersion liquid is more preferably a vinyl resin particle dispersion liquid obtained by emulsion polymerization from the viewpoint of simplifying the step of producing a resin particle-dispersed polyimide precursor solution.

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

When the resin particles are vinyl resin particles, they are obtained by polymerizing a monomer. Examples of the vinyl resin monomer include the following monomers. For example, styrene, 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, ethyl (meth)acrylate, (meth)acrylic acid n -Propyl, n-butyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, trimethylolpropane trimethacrylate (TMPTMA) and other vinyl group-containing esters; acrylonitrile, methacrylonitrile Vinyl nitriles such as; vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone; (meth)acrylic acid, maleic acid, cinnamic acid, fumaric acid , Vinyl sulfonic acid, and other acids; ethyleneimine, vinyl pyridine, vinyl amine, and other bases; and other vinyl polymer units.
As other monomers, monofunctional monomers such as vinyl acetate, difunctional monomers such as ethylene glycol dimethacrylate, nonane diacrylate and decanediol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, etc. You may use together the polyfunctional monomer of.
Further, the vinyl resin may be a resin using these monomers alone or a resin which is a copolymer using two or more kinds of monomers.

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

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

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

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

(Polyimide precursor)
The polyimide precursor is obtained by polymerizing a tetracarboxylic dianhydride and a diamine compound. Specifically, it is a resin (polyamic acid) having a repeating unit represented by the polyimide precursor general formula (I).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

(Ratio of resin particles and polyimide precursor)
In the resin particle polyimide precursor solution, the ratio between the resin particles and the polyimide precursor is a mass ratio when the solid content of the polyimide precursor solution is 100, and the polyimide precursor solution solid content:resin particles=100:20. The range is preferably 100:600 or less. The range is preferably 100:25 or more and 100:550 or less, and more preferably 100:30 or more and 100:500 or less.

(Other additives)
In the method for producing a resin particle-dispersed polyimide precursor solution according to the present embodiment according to the present embodiment, the polyimide precursor solution contains a catalyst for promoting an imidization reaction, a leveling material for improving film-forming quality, and the like. But it's okay.
As the catalyst for promoting the imidization reaction, a dehydrating agent such as an acid anhydride, an acid catalyst such as a phenol derivative, a sulfonic acid derivative, a benzoic acid derivative, or the like may be used.

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

  Further, the polyimide precursor solution may contain inorganic particles added for improving mechanical strength depending on the purpose of use. Examples of the inorganic particles include particulate materials such as silica powder, alumina powder, barium sulfate powder, titanium oxide powder, mica and talc.

<Polyimide film containing resin particles>
The resin particle-containing polyimide film according to this embodiment is obtained by applying the resin particle-dispersed polyimide precursor solution according to this embodiment to form a coating film, and then heating the coating film.
The resin particle-containing polyimide film includes not only the resin particle-containing polyimide film that has been imidized but also a partially imidized resin particle-containing polyimide film that has not been imidized.

  Specifically, the resin particle-containing polyimide film according to the present embodiment is, for example, a step of applying a resin particle-dispersed polyimide precursor solution according to the present embodiment to form a coating film (hereinafter referred to as "coating film forming step"). ) And a step of heating the coating film to form a polyimide film (hereinafter referred to as “heating step”).

(Coating film formation process)
First, the above-mentioned resin particle-dispersed polyimide precursor solution is prepared. Next, the resin particle-dispersed polyimide precursor solution is applied onto the substrate to form a coating film.
Examples of the substrate include a resin substrate; a glass substrate; a ceramic substrate; a metal substrate; and a composite material substrate obtained by combining these materials. The substrate may include a release layer that has been subjected to a release treatment.
The method for applying the resin particle-dispersed polyimide precursor solution to the substrate is not particularly limited, and examples thereof include spray coating, spin coating, roll coating, bar coating, slit die coating, and inkjet coating. There are various methods.

  As the substrate, various substrates can be used depending on the intended use. For example, various substrates applied to liquid crystal elements; semiconductor substrates on which integrated circuits are formed, wiring substrates on which wiring is formed, printed boards on which electronic components and wiring are provided, substrates for wire coating materials, and the like. ..

(Heating process)
Next, the coating film obtained in the coating film forming step is subjected to a drying treatment. By this drying treatment, a film (a dried film before imidization) is formed.
The heating condition for the drying treatment is preferably, for example, a temperature of 80° C. or higher and 200° C. or lower for 10 minutes or longer and 60 minutes or shorter, and the heating temperature may be shorter as the temperature is higher. It is also effective to apply hot air during heating. During heating, the temperature may be raised stepwise or the rate may be raised without changing.

Next, the dried film before imidization is heated to perform imidization treatment. Thereby, the polyimide resin layer is formed.
The heating conditions for the imidization treatment are, for example, 150° C. or higher and 400° C. or lower (preferably 200° C. or higher and 300° C. or lower), and heating for 20 minutes or longer and 60 minutes or shorter causes an imidization reaction to form a polyimide film. It During the heating reaction, the temperature may be raised stepwise or gradually at a constant rate before the final heating temperature is reached.

  Through the above steps, the resin particle-containing polyimide film is formed. Then, if necessary, the resin particle-containing polyimide film is taken out from the substrate to obtain a resin particle-containing polyimide film. The resin particle-containing polyimide film may be post-processed depending on the intended use.

<Method for producing porous polyimide film>
The method for producing a porous polyimide film according to the present embodiment, after forming a coating film by coating the resin particle-dispersed polyimide precursor solution according to the present embodiment, the coating film is dried, the polyimide precursor and A first step of forming a coating film containing the resin particles, and a second step of heating the coating film to imidize the polyimide precursor to form a polyimide film, the treatment of removing the resin particles. And a second step including.

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

  Hereinafter, the manufacturing method shown in FIG. 1 (an example of the manufacturing method according to this embodiment) will be described, but the manufacturing method is not limited thereto.

(First step)
In the first step, first, the resin particle-dispersed polyimide precursor solution described above is prepared. Next, the resin particle-dispersed polyimide precursor solution is applied onto the substrate to form a coating film containing the polyimide precursor solution and the resin particles. Then, the coating film formed on the substrate is dried to form a coating film containing the polyimide precursor and the resin particles.

  Examples of the method of forming the coating film containing the polyimide precursor solution and the resin particles on the substrate in the first step include the following methods, but are not limited to this method.

  Specifically, first, a resin particle dispersion in which resin particles are dispersed in an aqueous solvent is prepared. Then, an organic amine compound, a tetracarboxylic acid dianhydride, and a diamine compound are mixed in the resin particle dispersion, and a tetracarboxylic acid dianhydride and a diamine compound are polymerized to form a polyimide precursor. Prepare body solution. Next, the resin particle-dispersed polyimide precursor solution is applied onto a substrate to form a coating film containing the polyimide precursor solution and the resin particles. The resin particles in this coating film are distributed in a state where aggregation is suppressed (see FIG. 1(A)).

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

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

  As the coating amount of the polyimide precursor solution to obtain a coating film containing a polyimide precursor solution and resin particles, the porosity of the porous polyimide film is increased, the amount of resin particles exposed from the surface of the coating film. Be good. For example, it is preferable to form a thickness at which the resin particles are exposed from the surface of the coating film (for example, a coating film in which the thickness of the coating film is smaller than the particle diameter of the resin particles).

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

  Further, the coating film may be formed in such an amount that the resin particles are embedded in the coating film. In this case, a process of exposing the resin particles may be performed in the second step described later. The porosity of the porous polyimide film is increased by the process of exposing the resin particles.

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

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

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

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

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

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

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

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

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

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

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

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

  In the second step, from the viewpoint of increasing the porosity, it is preferable to perform a process of exposing the resin particles so that the resin particles are exposed. In the second step, the process of exposing the resin particles is preferably performed in the process of imidizing the polyimide precursor, or after the process of imidizing and before the process of removing the resin particles.

  In this case, for example, when a coating film is formed on a substrate using a resin particle-dispersed polyimide precursor solution, the resin particle-dispersed polyimide precursor solution is applied on the substrate to form a coating film in which resin particles are buried (Fig. 1 (A)). Next, the coating film is dried to form a coating film containing the polyimide precursor and the resin particles. The coating film formed by this method is in a state in which the resin particles are buried. This coating is heated to expose the resin particles from the polyimide film after the process of imidizing the polyimide precursor before the removal treatment of the resin particles or after the imidization is completed (after imidization). You may give a process.

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

Further, when the imidization ratio of the polyimide precursor in the polyimide film is 10% or more (that is, it is difficult to dissolve in an organic solvent) and when the imidization is completed, the resin particles In the case of performing the treatment for exposing the resin particles, there are a method of mechanically cutting with a tool such as sandpaper to expose the resin particles, and a method of decomposing the resin particles with a laser or the like to expose the resin particles.
For example, when mechanically cutting, a part of the resin particles existing in the upper region of the resin particles embedded in the polyimide film (that is, the region on the side of the resin particles away from the substrate) is The polyimide film existing on the upper side is cut, and the cut resin particles are exposed from the surface of the polyimide film (see FIG. 1B).

  Then, the resin particles are removed from the polyimide film where the resin particles are exposed by the above-described resin particle removal treatment. Then, a porous polyimide film from which the resin particles have been removed is obtained (see FIG. 1C).

  In addition, in the above, although the manufacturing process of the porous polyimide film subjected to the treatment of exposing the resin particles in the second step has been described, the resin particles are exposed in the first step from the viewpoint of increasing the porosity. You may give a process. In this case, in the first step, the resin particles may be exposed by performing a process of exposing the resin particles in the process of forming the film by drying after obtaining the coating film. By performing the process of exposing the resin particles, the porosity of the porous polyimide film is increased.

  For example, in the process of obtaining a coating film containing a polyimide precursor solution and resin particles, and then drying the coating film to form a coating film containing the polyimide precursor and resin particles, as described above, the coating film is a polyimide precursor. The body is ready to dissolve in water. When the coating film is in this state, the resin particles can be exposed by, for example, a wiping treatment or a water immersion treatment. Specifically, the polyimide precursor solution present in a region having a thickness equal to or greater than the thickness of the resin particle layer is present in a region having a thickness equal to or greater than the thickness of the resin particle layer, for example, by performing a process of exposing the resin particle layer by wiping with water. The existing polyimide precursor solution is removed. Then, the resin particles existing in the upper region of the resin particle layer (that is, the region of the resin particle layer on the side away from the substrate) are exposed from the surface of the coating film.

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

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

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

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

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

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

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

-Measurement of imidization ratio of polyimide precursor-
-Preparation of Polyimide Precursor Sample (i) A polyimide precursor composition to be measured is applied onto a silicone wafer in a film thickness range of 1 μm to 10 μm to prepare a coating film sample.
(Ii) The coating film sample is immersed in tetrahydrofuran (THF) for 20 minutes to replace the solvent in the coating film sample with tetrahydrofuran (THF). The solvent to be immersed is not limited to THF, and can be selected from solvents that do not dissolve the polyimide precursor and that are miscible with the solvent component contained in the polyimide precursor composition. Specifically, alcohol solvents such as methanol and ethanol and ether compounds such as dioxane can be used.
(Iii) The coating film sample is taken out from THF, and N ₂ gas is blown onto the THF adhering to the surface of the coating film sample to remove it. Under a reduced pressure of 10 mmHg or less, the coating film sample is dried 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) Similar to (i) above, a polyimide precursor composition to be measured is applied onto a silicone wafer to prepare a coating film sample.
(V) The coating film sample is heated at 380° C. for 60 minutes to carry out an imidization reaction to prepare a 100% imidization standard sample.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[Preparation of resin particle dispersion]
-Preparation of resin particle dispersion liquid (1)-
770 parts by mass of styrene, 230 parts by mass of butyl acrylate, 15.7 parts by mass of dodecanethiol, 19.8 parts by mass of surfactant Dowfax2A1 (47% solution, manufactured by Dow Chemical Co.), and 576 parts by mass of deionized water were mixed. The mixture was stirred and emulsified at 1,500 rpm for 30 minutes with a dissolver to prepare a monomer emulsion. Subsequently, 1.49 parts by mass of Dowfax2A1 (47% solution, manufactured by Dow Chemical Co.) and 1270 parts by mass of ion-exchanged water were charged into the reaction vessel. After heating to 75° C. under a nitrogen stream, after adding 75 parts by mass of the monomer emulsion, a polymerization initiator solution prepared by dissolving 15 parts by mass of ammonium persulfate in 98 parts by mass of ion-exchanged water is added dropwise over 10 minutes. did. After reacting for 50 minutes after dropping, the remaining monomer emulsion was added dropwise over 220 minutes, and further reacted for 180 minutes. After cooling, a resin particle dispersion liquid (1) was obtained as a styrene/acrylic resin particle dispersion liquid whose solid content concentration was adjusted to 30% by mass. The resin particles had an average particle diameter of 0.18 μm.

-Preparation of resin particle dispersion liquid (2)-
An aqueous dispersion (FS-102E: manufactured by Nippon Paint Co., Ltd., solid content concentration: 21% by mass) of a non-crosslinked styrene/acrylic copolymer having an average particle diameter of 0.1 μm was used as a resin particle dispersion (2).

-Preparation of resin particle dispersion liquid (3)-
1000 parts by mass of styrene, 15.7 parts by mass of dodecanethiol, 15.8 parts by mass of surfactant Dowfax2A1 (47% solution, manufactured by Dow Chemical Co.), and 576 parts by mass of ion-exchanged water were mixed, and 1,500 by a dissolver. The mixture was stirred for 30 minutes with stirring to emulsify to prepare a monomer emulsion. Subsequently, 1.49 parts by mass of Dowfax2A1 (47% solution, manufactured by Dow Chemical Co.) and 1270 parts by mass of ion-exchanged water were charged into the reaction vessel. After heating to 75°C under a nitrogen stream, after adding 75 parts by mass of the monomer emulsion, a polymerization initiator solution prepared by dissolving 15 parts by mass of ammonium persulfate in 98 parts by mass of ion-exchanged water is added dropwise over 10 minutes. did. After reacting for 50 minutes after dropping, the remaining monomer emulsion was added dropwise over 220 minutes, and further reacted for 180 minutes. After cooling, a resin particle dispersion liquid (3) was obtained as a polystyrene resin particle dispersion liquid whose solid content concentration was adjusted to 30% by mass. The resin particles had an average particle diameter of 0.21 μm.

-Preparation of resin particle dispersion liquid (4)-
A resin particle dispersion liquid (4) was obtained as a polymethyl methacrylate resin particle dispersion liquid in the same manner as the resin particle dispersion liquid (3) except that methyl methacrylate was used instead of styrene. The average particle size of the resin particles was 0.23 μm.

<Example 1>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-1)]
Resin particle dispersion liquid (1): Ion-exchanged water: 350 g was added to 100 g in terms of solid content. 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 stirred at 20° C. for 10 minutes. And dispersed. 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 kept at 40°C. Then, the mixture was stirred for 24 hours for dissolution and reaction to obtain a resin particle-dispersed polyimide precursor solution (PAA-1). (Resin particles/polyimide precursor=100/100 (mass ratio), concentration of polyimide precursor: 12 mass %)

<Example 2>
[Preparation of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-2)]
A resin particle-dispersed polyimide precursor solution (PAA-2) was obtained in the same manner as in Example 1 except that the resin particle dispersion liquid (1) was changed to the resin particle dispersion liquid (2). (Resin particles/polyimide precursor=100/100 (mass ratio), concentration of polyimide precursor: 10 mass %)

<Comparative Example 1>
[Preparation of Resin Particle-Dispersed Polyimide Precursor Organic Solvent Solution (PAA-C1)]
Non-crosslinked styrene-acrylic copolymer powder having an average particle size of 0.1 μm (FS-102E: manufactured by Nippon Paint Co., Ltd.): NMP (N-methylpyrrolidone): 450 g was added to 100 g in terms of solid content. p-Phenylenediamine (molecular weight 108.14): 27.28 g (252.27 mmol) was added and dispersed by stirring at 20° C. for 10 minutes. 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 kept at 40°C. Then, the mixture was stirred for 24 hours to dissolve and react to try to prepare a resin particle-dispersed polyimide precursor organic solvent solution (PAA-C1). (Resin particles/polyimide precursor=100/100 (mass ratio), concentration of polyimide precursor: 15 mass %) By the time the polyimide precursor was obtained, all the resin particles had dissolved.

<Comparative example 2>
[Preparation of Silica Particle-Dispersed Polyimide Precursor Aqueous Solvent Solution (PAA-C2)]
Snowtex (registered trademark) ZL (aqueous dispersion of silica particles, particle size 70 nm or more and 100 nm or less, manufactured by Nissan Kagaku Co., Ltd.): To 100 g in terms of solid content, ion-exchanged water: 350 g was added. 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 stirred at 20° C. for 10 minutes. And dispersed. 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 kept at 40°C. After stirring for 24 hours to dissolve and react, a particle-dispersed polyimide precursor solution (PAA-C2) in which silica particles were dispersed was obtained. (Silica particles/polyimide precursor=100/100 (mass ratio), concentration of polyimide precursor: 12 mass %)

<Comparative example 3>
[Preparation of Silica Particle-Dispersed Polyimide Precursor Organic Solvent Solution (PAA-C3)]
30 parts by mass of monodispersed spherical silica particles (average sphere ratio: 1.0, particle size distribution index: 1.20) manufactured by Nippon Shokubai Co., Ltd. and having an average diameter of 550 nm were dispersed in 30 parts by mass of NMP.
To this silica dispersion: 100 g in terms of solid content, 350 g of NMP (N-methylpyrrolidone) was added. p-Phenylenediamine (molecular weight 108.14): 27.28 g (252.27 mmol) was added and dispersed by stirring at 20° C. for 10 minutes. 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 kept at 40°C. Then, the mixture was stirred for 24 hours for dissolution and reaction to obtain a particle-dispersed polyimide precursor solution (PAA-C3) in which silica particles were dispersed. (Silica particles/polyimide precursor=100/100 (mass ratio), concentration of polyimide precursor: 15 mass %)

<Example 3>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-3)]
A resin particle-dispersed polyimide precursor solution (PAA-3) was prepared in the same manner as in Example 1 except that ion exchange water: 290 g and isopropanol: 60 g were used instead of adding 350 g of ion exchange water. Obtained. (Resin particles/polyimide precursor=100/100 (mass ratio), concentration of polyimide precursor: 12 mass %)

<Example 4>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-4)]
A resin particle-dispersed polyimide precursor solution (PAA-4) was obtained in the same manner as in Example 3, except that 1,2-dimethylimidazole: 47.52 g was added instead of 50 g of methylmorpholine. (Resin particles/polyimide precursor=100/100 (mass ratio), concentration of polyimide precursor: 12 mass %)

<Example 5>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-5)]
In the same manner as in Example 2, except that the amount of the resin particle dispersion liquid (2) added (in terms of solid content) was changed from 100 g to 140 g, and the amount of ion-exchanged water added was changed from 350 g to 160 g. A dispersed polyimide precursor solution (PAA-5) was obtained. (Resin particles/polyimide precursor=140/100 (mass ratio), concentration of polyimide precursor: 10 mass %)

<Example 6>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-6)]
Instead of adding 350 g of ion-exchanged water in Example 1, resin particles-dispersed polyimide precursor solution (PAA-) was used in the same manner as in Example 1 except that ion-exchanged water: 290 g and N-methylpyrrolidone: 60 g were changed. 6) was obtained. (Resin particles/polyimide precursor=100/100 (mass ratio), concentration of polyimide precursor: 12 mass %)

<Example 7>
[Preparation of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-7)]
Resin particle dispersion liquid (3): Deionized water: 350 g and t-butanol: 200 g were added to 100 g in terms of solid content. 4,4′-Diaminodiphenyl ether (molecular weight 200.24): 13.66 g (68.2 mmol) and methylmorpholine (organic amine compound): 16.23 g (160.41 mmol) were added, and at 20° C. Stir for 10 minutes to disperse. Furthermore, to this solution was added 3,3′,4,4′-biphenyltetracarboxylic dianhydride (molecular weight 294.22): 19.66 g (66.84 mmol), while maintaining the reaction temperature at 40° C. Then, the mixture was stirred for 24 hours for dissolution and reaction to obtain a resin particle-dispersed polyimide precursor solution (PAA-7). (Resin particles/polyimide precursor=300/100 (mass ratio), concentration of polyimide precursor: 3.6 mass %)

<Example 8>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-8)]
Resin particle dispersion liquid (1): 200 g of deionized water and 150 g of 1-propanol were added to 100 g in terms of solid content. 4,4'-Diaminodiphenyl ether (molecular weight 200.24): 8.21 g (41.0 mmol) and methylmorpholine (organic amine compound): 9.75 g (96.43 mmol) were added, and at 20°C. Stir for 10 minutes to disperse. Further, to this solution was added 3,3′,4,4′-biphenyltetracarboxylic dianhydride (molecular weight 294.22): 11.82 g (40.17 mmol), and the reaction temperature was kept at 40° C. Then, the mixture was stirred for 24 hours for dissolution and reaction to obtain a resin particle-dispersed polyimide precursor solution (PAA-8). (Resin particles/polyimide precursor=500/100 (mass ratio), concentration of polyimide precursor: 2.8 mass %)

<Example 9>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-9)]
Same as Example 7 except that the resin particle dispersion liquid (3) was changed to the resin particle dispersion liquid (4), t-butanol was changed to 1-methoxy-2-propanol, and methylmorpholine was changed to dimethylaminoethanol. Then, a resin particle-dispersed polyimide precursor solution (PAA-9) was obtained. (Resin particles/polyimide precursor=300/100 (mass ratio), concentration of polyimide precursor: 3.6 mass %)

<Example 10>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-10)]
Resin particle dispersed polyimide in the same manner as in Example 7 except that the resin particle dispersed liquid (3) was changed to the resin particle dispersed liquid (2), 1-propanol was changed to isopropanol, and methylmorpholine was changed to diethylaminoethanol. A precursor solution (PAA-10) was obtained. (Resin particles/polyimide precursor=300/100 (mass ratio), concentration of polyimide precursor: 3.1 mass%)

<Reference example 1>
[Production of Resin Particle-Dispersed Polyimide Precursor Solution (PAA-S1)]
A flask equipped with a stirring bar, a thermometer, and a dropping funnel was filled with 900 g of ion-exchanged 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 kept at 40°C. Then, the mixture was stirred for 24 hours for dissolution and reaction to obtain a polyimide precursor “water” solution. This polyimide precursor "water" solution was diluted 10 times, and the resin particle dispersion liquid (1) was added thereto at a ratio of 10 parts of solid content to 10 parts of the polyimide precursor, and the mixture was agitated on a web-blower to obtain a resin. A particle-dispersed polyimide precursor solution (PAA-S1) was obtained.

<Evaluation 1>
[Evaluation of dispersibility]
The resin particle-dispersed polyimide precursor solutions obtained in Examples 1 to 10, Comparative Examples 1 to 3 and Reference Example 1 were evaluated for dispersibility. The specific method is as follows.
The obtained resin particle-dispersed polyimide precursor solution was allowed to stand at room temperature (25° C.) and stored under refrigeration (3° C.) and stored, and the dispersed state of the resin particles was visually evaluated (the dispersion of the resin particles was If it gets worse, layer separation of the solution and settling of particles can be observed).

-Evaluation criteria-
A: No change in solution even after more than 2 months from the start of storage B: Separation of layers or settling of particles within 1 month and more than 2 months after start of storage C: Separation of layers or settling of particles within 1 month from the start of storage To be seen

<Evaluation 2>
[Production of Porous Polyimide Film (PIF-1)]
The resin particle-dispersed polyimide precursor solution (PAA-1) was formed on a glass substrate so that the film thickness after drying was about 30 μm, and dried at 90° C. for 1 hour, and then from 90° C. to 380° C. The temperature was raised at a rate of 10° C./min, and the temperature was maintained at 380° C. for 1 hour, and then cooled to room temperature (25° C., the same applies below) to obtain a porous polyimide film (PIF-1).

[Production of Porous Polyimide Film (PIF-2)]
The resin particle-dispersed polyimide precursor solution (PAA-1) was formed on a glass substrate so that the film thickness after drying was about 30 μm, and dried at 90° C. for 1 hour. Then, it was peeled from the glass substrate and immersed in tetrahydrofuran for 1 hour. Then, the temperature was raised from 90° C. to 380° C. at a rate of 10° C./min, and the temperature was maintained at 380° C. for 1 hour, then cooled to room temperature to obtain a porous polyimide film (PIF-2).

[Preparation of Porous Polyimide Films (PIF-3) to (PIF-7), (PIF-9) to (PIF-10)]
A porous polyimide film (PIF-3) was prepared in the same manner as the porous polyimide film (PIF-2) except that the type of resin particle-dispersed polyimide precursor solution used and the solvent used for immersion were changed to those shown in Table 2. ) To (PIF-7) and (PIF-9) to (PIF-10) were obtained. However, in the case of “with exposure treatment” in Table 2, a step of exposing the resin particles with sandpaper was added after peeling from the glass substrate.

[Production of Porous Polyimide Film (PIF-8)]
Same as the porous polyimide film (PIF-1) except that the resin particle-dispersed polyimide precursor solution used is changed to (PAA-2) and a step of exposing the resin particles with sandpaper after the drying is added. Then, a porous polyimide film (PIF-8) was obtained.

[Preparation of Porous Polyimide Film (PIF-11)]
The resin particle-dispersed polyimide precursor solution (PAA-7) was formed on a glass substrate so that the film thickness after drying was about 30 μm, and dried at 80° C. for 1 hour. Then, the glass substrate was immersed in tetrahydrofuran for 20 hours. After air-drying, the temperature was raised from 80° C. to 250° C. at a rate of 1° C./min, held at 250° C. for 1 hour, cooled to room temperature, and peeled from the glass substrate to obtain a porous polyimide film (PIF- 11) was obtained.
FIG. 2 shows a photograph of the surface of the obtained porous polyimide film (PIF-11) observed with a scanning electron microscope (VE-8800 manufactured by Keyence Corporation).

[Production of Porous Polyimide Films (PIF-12) to (PIF-14)]
Porous polyimide films (PIF-12) to (PIF-14) were prepared in the same manner as the porous polyimide film (PIF-11) except that the kind of the resin particle-dispersed polyimide precursor solution used was changed to that shown in Table 2. ) Got.

[Production of Porous Polyimide Film (PIF-C1)]
A porous polyimide film (PIF-C1) was obtained in the same manner as in the production of (PIF-2) except that the liquid used was changed to (PAA-C1).

[Production of Porous Polyimide Film (PIF-C2)]
(PAA-C2) was formed on a glass substrate so that the film thickness after drying was about 30 μm, heated at 120° C. for 1 hour, and then peeled off from the glass substrate, from room temperature to 380° C. The temperature was raised at a rate of 10° C./min, and the temperature was maintained at 380° C. for 1 hour, then cooled to room temperature to obtain a silica-polyimide composite film. The silica-polyimide composite film was immersed in 10 mass% hydrogen fluoride water, the silica was dissolved and removed for 6 hours, washed sufficiently with water, and dried to obtain a porous polyimide film (PIF-C2).

[Production of Porous Polyimide Film (PIF-C3)]
A porous polyimide film (PIF-C3) was obtained in the same manner as in the production of (PIF-C2) except that the liquid used was changed to (PAA-C3).

[Evaluation of cracks]
Cracks were evaluated on the porous polyimide films prepared using the resin particle-dispersed polyimide precursor solutions obtained in Examples 1A to 14A and Comparative Examples 1A to 3A. The specific method is as follows. An area of 1 cm ² square of the polyimide film was observed with a microscope having a magnification of 500 to make 0.1 mm or more cracks, and the presence or absence was visually observed.

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

[Evaluation of pore size distribution]
Regarding the porous polyimide films produced using the resin particle-dispersed polyimide precursor solutions obtained in Examples 1A to 14A and Comparative Examples 1A to 3A, regarding the distribution of pore diameters (maximum diameter, minimum diameter, and average diameter) An evaluation was made. Specifically, the evaluation was performed by the method described above.

  It should be noted that in Comparative Example 1A, the difference between the maximum diameter and the minimum diameter (and the ratio between the maximum diameter and the minimum diameter) is larger than that in the example. It is speculated that this is because the resin particles were dissolved in N-methylpyrrolidone.

The particles of the particle dispersions in Tables 1 and 2 will be shown below.
・(1): The above-mentioned resin particle dispersion liquid (1) average particle diameter 0.18 μm
・(2): The above-mentioned resin particle dispersion liquid (2) average particle diameter 0.1 μm
-(3): The above-mentioned resin particle dispersion liquid (3) average particle diameter 0.21 μm
(4): Resin particle dispersion liquid (4) described above, average particle size 0.23 μm
Silica (1): Snowtex (registered trademark) ZL
(Particle size 70-100nm, manufactured by Nissan Chemical Co., Ltd.)
Silica (2): Monodisperse spherical silica particles having an average diameter of 550 nm
(Nippon Shokubai Co., Ltd., sphericity: 1.0, particle size distribution index: 1.20)

The details of the abbreviations in Tables 1 and 2 are shown below.
-"PDA": p-phenylenediamine-"ODA": 4,4'-diaminodiphenyl ether-"BPDA": 3,3',4,4'-biphenyltetracarboxylic dianhydride-"MMO": methylmorpholine -"DMAEt": dimethylaminoethanol-"DEAEt": diethylaminoethanol-"DMIz": 1,2-dimethylimidazole-"IPA": isopropanol-"NMP": N-methylpyrrolidone-"THF": tetrahydrofuran-"Tol" ]: Toluene-"NPA": 1-propanol-"TBA": t-butanol-"1M2PA": 1-methoxy-2-propanol-silica (1): Dispersion of silica particles used in Comparative Example 2-Silica (2): Dispersion of silica particles used in Comparative Example 3 In the particle dispersion number column of Comparative Examples 1 and 1A in Tables 1 and 2, the notation (2) indicates that Comparative Examples 1 and 1A are resins. The resin particle powder of the particle dispersion liquid (2) is used and is described as above for convenience.

1 Resin Particles, 3 Substrate, 4 Release Layer, 5 Polyimide Precursor Solution, 7 Holes, 61 Polyimide Film, 62 Porous Polyimide Film

Claims (7)

In a resin particle dispersion liquid in which resin particles are dispersed in an aqueous solvent, in the presence of an organic amine compound, a resin particle-dispersed polyimide precursor solution for polymerizing a tetracarboxylic dianhydride and a diamine compound to form a polyimide precursor after forming the coating film obtained trees fat particles dispersed polyimide precursor solution was applied by the method, the coating film was dried, first forming a film containing the polyimide precursor and the resin particles Process of
A second step of heating the coating to imidize the polyimide precursor to form a polyimide film, the second step including a treatment of removing the resin particles;
A method for producing a porous polyimide film having: The method for producing a porous polyimide film according to claim 1, wherein the resin particle dispersion liquid is a dispersion liquid in which resin particles are granulated in the aqueous solvent . The method for producing a porous polyimide film according to claim 1, wherein the organic amine compound is a tertiary amine compound . The method for producing a porous polyimide film according to claim 1, wherein the organic amine compound is an amine compound having a nitrogen-containing heterocyclic structure . In the second step, after the process or imidation perform imidization of the polyimide precursor, and, in prior treatment to remove the resin particles, according to claim 1 wherein performing a process of exposing the resin particles Item 5. A method for producing a porous polyimide film according to any one of Items 4 . The method for producing a porous polyimide film according to claim 1 , wherein the treatment for removing the resin particles is a treatment for removing the resin particles with an organic solvent that dissolves the resin particles. The method for producing a porous polyimide film according to any one of claims 1 to 5, wherein the treatment for removing the resin particles is a treatment for removing by heating.